3D Graphene, Fundamentals, Synthesis, and Emerging Applications (2023) - Ram K. Gupta

Carbon Nanostructures
Ram K. Gupta Editor
3D
Graphene
Fundamentals, Synthesis, and Emerging
Applications
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Ram K. Gupta
Editor
3D Graphene
Fundamentals, Synthesis, and Emerging
Applications
Editor
Ram K. Gupta
Department of Chemistry
Pittsburg State University
Pittsburg, PA, USA
ISSN 2191-3005 ISSN 2191-3013 (electronic)

ISBN 978-3-031-36248-4 ISBN 978-3-031-36249-1 (eBook)
https://doi.org/10.1007/978-3-031-36249-1
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Contents
Introduction to 3D Graphene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chuanyin Xiong, Tianxu Wang, Yongkang Zhang, and Qing Xiong
Synthesis and Printing of 3D Graphene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Arash Ghazitabar and Malek Naderi
Synthesis and Characteristics of 3D Graphene . . . . . . . . . . . . . . . . . . . . . . . 43
Hiran Chathuranga, Ishara Wijesinghe, Ifra Marriam, and Cheng Yan
Architectural and Chemical Aspects of 3D Graphene for Emerging
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Juan Bai and Jun Mei
Recent Advancements in 3D Graphene for Electrochemical Sensors . . . . 75
Hamide Ehtesabi and Seyed-Omid Kalji
3D Graphene-Based Biosensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Mert Akin Insel, Sena Nur Karabekiroglu, and Selcan Karakuş
3D Graphene-Based Optical Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Amrit Kumar, V. Manjuladevi, and Raj Kumar Gupta
3D Graphene for Flexible Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Ahmad Hussain, Adeela Naz, Nawishta Jabeen, and Jazib Ali
Graphene-Based Materials for the Remediation of Hydrogen
Sulfide Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Nishesh Kumar Gupta, Kaptan Rajput, and Herlys Viltres
3D Graphene for Removal of Inorganic Pollutants . . . . . . . . . . . . . . . . . . . . 169
Iqra Fareed, Muhammad Danish Khan, Danish Rehman,
Masood ul Hassan Farooq, and Faheem K. Butt
vii
viii Contents
3D Graphene Structures for the Removal of Pharmaceutical

Residues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
Wan Ting Tee, Nicholas Yung Li Loh, Billie Yan Zhang Hiew,
and Lai Yee Lee
3D Graphene for Metal-Ion Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
Jin Kwei Koh and Chin Wei Lai
3D Graphene for Metal–Air Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
Runwei Mo and Yuan An
3D Graphene for Flexible Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
Demet Ozer
Recent Development in 3D Graphene for Wearable and Flexible
Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
Wei Ni and Ling-Ying Shi
3D Graphene for High-Performance Supercapacitors . . . . . . . . . . . . . . . . . 285
K. A. U. Madhushani and Ram K. Gupta
3D Graphene for Photovoltaics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305
Alka Pareek and Sreekanth Mandati
3D Graphene for Fuel Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
Norazuwana Shaari, Nik Farah Hanis Nik Zaiman,
Siti Hasanah Osman, and Ajaz Ahmad Wani
3D Graphene as Electrocatalysts for Water Splitting . . . . . . . . . . . . . . . . . . 341
Farkhondeh Khodabandeh and Mohammad Reza Golobostanfard
3D Graphene as a Photocatalyst for Water Splitting . . . . . . . . . . . . . . . . . . 359
Rozan Mohamad Yunus, Nurul Nabila Rosman,
and Nur Rabiatul Adawiyah Mohd Shah
3D Graphene for Flexible Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
Arpana Agrawal
3D Graphene for Capacitive De-ionization of Water . . . . . . . . . . . . . . . . . . 389
Sara Madani and Cavus Falamaki
The Evolution of 3D Graphene and Its Derivatives for Theranostic
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
Aditya Srivastava, Akshit Rajukumar Prajapati, Sunil Venkanna Pogu,
and Aravind Kumar Rengan
Toxicity, Stability, Recycling, and Risk Assessments . . . . . . . . . . . . . . . . . . . 427
Raunak K. Tamrakar, Kanchan Upadhyay, Judith Gomes,
and Sunil Kumar
Introduction to 3D Graphene
Chuanyin Xiong, Tianxu Wang, Yongkang Zhang, and Qing Xiong
Abstract The 3D graphene-based materials fabricated by various methods not only

effectively prevent mutual re-stacking between the graphene layers to make full
use of its specific surface area, but also obtain excellent functional characteristics via
introducing other functional materials. This part briefly summarizes the types, prepa-
ration methods, application fields, existing problems, and development trends of 3D
graphene-based materials with different structures and components. The purpose is
to provide methods and theoretical references for the research and efficient utilization
of 3D graphene-based materials.
Keywords 3D graphene · Classification · Preparation · Application
1 Classification of Graphene
Graphene is a 2D carbon material with a hexagonal honeycomb lattice structure

hybridized by carbon atoms connected by sp2 [1] and is the basic building block
of fullerene, carbon nanotubes, and 3D graphene. Andre Geim and Konstantin
Novoselov successfully prepared 2D graphene sheets by mechanical stripping for
the first time in 2004. Because of its excellent conductivity (electron mobility of
150,000 cm2 V−1 s−1 ) [2], ultra-high theoretical specific surface area (2630 m2 g−1 )
[3], high mechanical strength (Young’s modulus 1.1 Tpa, tensile strength 125 GPa)
[4], and good thermal conductivity (thermal conductivity of 5300 W m−1 K−1 ) [5],
it has attracted wide attention of researchers around the world.
Although the 2D graphene nanosheets with a single thickness of about 0.35 nm
have excellent performance, in practical applications, due to the van der Waals force
and π–π bond between the graphene layers [6], it is very easy to often stack between
the graphene layers to form graphite powder. This seriously affects the surface utiliza-
tion of 2D graphene nanosheets and reduces their inherent excellent performance. For
C. Xiong (B) · T. Wang · Y. Zhang · Q. Xiong

College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science and
Technology, Xi’an, China
e-mail: xiongchuanyin@126.com; xiongchuanyin@sust.edu.cn
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 1

R. K. Gupta (ed.), 3D Graphene, Carbon Nanostructures,
https://doi.org/10.1007/978-3-031-36249-1_1
2 C. Xiong et al.
example, when graphene is used as an energy storage material, the stacking between
the layers will lead to a decrease in the electrochemical reaction site and a decrease
in the efficiency of electrolyte ion conduction inside the electrode material, which
seriously affects the energy storage performance of the device [7]. In view of the
above problems, the construction of graphene matrix composites with 3D structure
by certain methods is an effective solution. Figure 1a summarizes the relationship
between 3D graphene and 2D graphene [8].
As shown in Fig. 1b, according to the currently reported work, the types of 3D
graphene can be divided into 3D graphene nanoribbons, 3D graphene powder, 3D
graphene spheres, 3D graphene fibers, 3D graphene with a layered structure, 3D
graphene foam, 3D graphene aerogels, etc.
1.1 3D Graphene Nanoribbons
Graphene nanoribbons refer to graphene nanomaterials with a width of less than

50 nm, which can be prepared to form 3D graphene nanoribbons through the inter-
action between carbon-containing molecules. As shown in Fig. 2a, Kawai et al. [9]
synthesized 3D graphene nanoribbons using surface chemical reactions of organic
molecules. The 3D graphene nanoribbon is a periodic out-of-plane substructure by
controlling the addition reaction of a single molecule on the adsorption surface of
the local probe at low temperatures. This work has a certain reference value for the
precise synthesis of 3D graphene nanoribbons.
1.2 3D Graphene Powder
3D graphene powder appears macroscopically in a powder state, but microscopi-

cally has a 3D structure. Cao et al. [10] used CH4 as a carbon source to prepare
3D graphene powder with different particle sizes by combining CVD and physical
crushing. As shown in Fig. 2b, thanks to the excellent microporous structure of
3D graphene powder and the embedding of Pt atoms. The prepared 3D graphene
powder is beneficial to the transport of oxygen and lithium ions when applied to
Li–O2 batteries, thereby reducing the decomposition barrier of Li2 O2 .
1.3 3D Graphene Spheres
3D graphene spheres can be prepared by a template method and self-assembly. Zhang

et al. [11] converted benzene rings into high-purity 3D few-layer graphene micro-
spheres by sulfur-assisted methods. The structure of this 3D graphene microsphere
is shown in Fig. 2c, and it can be clearly seen that the 3D graphene microsphere
Introduction to 3D Graphene 3
Fig. 1 a Schematic diagram of the relationship between graphite, graphene, and 3D graphene.
Adapted with permission [8], Copyright (2020), American Chemical Society. b Classification
diagram of 3D graphene
shows a distinct spherical fluffy state due to the interconnection between several
layers of graphene. This provides an excellent energy storage structure for its appli-
cation in high-performance potassium–ion batteries. In addition, Hirani et al. [12]
prepared nitrogen-doped 3D graphene particles (Fig. 2d) by self-assembly, and the
microspheres showed excellent wastewater treatment performance.
4 C. Xiong et al.
Fig. 2 a Schematic representation of the structure of 3D graphene nanoribbons. Adapted with

permission [9], Copyright (2020), American Association for the Advancement of Science.
b Schematic diagram of the preparation process of 3D graphene powder and its properties as a
battery cathode material. Adapted with permission [10], Copyright (2022), American Chemical
Society. c Microscopic image of 3D few-layer graphene microspheres. Adapted with permission
[11], Copyright (2021), Royal Society of Chemistry. d Fabrication process of 3D nitrogen-doped
graphene particles. Adapted with permission [12], Copyright (2022), Elsevier. e Preparation of 3D
graphene fibers and their SEM images. Adapted with permission [13], Copyright (2018), Wiley–
VCH. f Preparation process of 3D graphene with hierarchical structure and its corresponding SEM
microscopic image. Adapted with permission [14], Copyright (2022), Royal Society of Chemistry.
g Schematic diagram of the preparation process of MWCNTs enhanced 3D graphene foam and its
structure. Adapted with permission [15], Copyright (2020), American Chemical Society. (H) SEM
image of Ni-doped 3D-Fe3 O4 @C/rGO aerogel. Adapted with permission [16], Copyright (2022),
Springer Nature
1.4 3D Graphene Fibers
3D graphene fibers can be prepared by electrospinning, wet spinning, electrophoresis,

and fiber surface coating. Zeng et al. [13] prepared tightly arranged 3D graphene
fibers by electrospinning, NH3 etching, and CVD combination. The preparation

process is shown in Fig. 2e, which mainly includes electrospinning PAN nanofibers,
etching under NH3 conditions, and CH4 and H2 mixtures to grow 3D graphene by
CVD. It is worth mentioning that the etching of NH3 makes a great number of fringed
structures on the surface of carbonized fibers, which provides rich sites for the growth
of 3D graphene.
1.5 3D Graphene with a Hierarchical Structure
The preparation of 3D graphene with layered structure by separating 2D graphene

nanosheets by introducing the second component is also a relatively simple and
efficient method to solve the stacking phenomenon between 2D graphene nanosheets.
Lei et al. [14] used polyaniline-coated selenium nanowires as a separating agent
to improve the stacking between 2D graphene sheets. The preparation process is
shown in Fig. 2f, first polyaniline is coated on the surface of Se nanowires by in situ
polymerization to obtain a Se@PANI composite with core–shell structure, and then
graphene and Se@PANI nanowires are uniformly dispersed to obtain 3D graphene-
based composites. Thanks to the layered structure of the material, the power of
the electrochemical reaction is accelerated, so that the material has excellent cycle
stability and energy storage characteristics when used as an aluminum–selenium
battery.
1.6 3D Graphene Foam
3D graphene foam has the advantages of 3D network structure, high porosity, and
ultra-low density, and has been widely used in energy storage, electromagnetic
shielding, and wave absorption. As shown in Fig. 2g, Shu et al. [15] prepared
an N-doped 3D RGO/multi-walled carbon nanotube (MWCNTs) composite foam
by hydrothermal and high-temperature carbonization methods. Thanks to the 3D
network structure formed between the RGOs in this material, the material has
excellent absorption properties.
1.7 3D Graphene Aerogel
3D graphene aerogels have attracted more and more attention from material scientists
due to their good properties. According to existing reports, the preparation methods
of 3D graphene aerogels are diverse, mainly including hydrothermal methods,
chemical reduction, chemical crosslinking, 3D printing, and self-assembly. Huang
et al. [16] prepared Ni-doped 3D-Fe3 O4 @C/rGO aerogels with excellent absorption
6 C. Xiong et al.
performance by the hydrothermal method. Figure 2h is a schematic diagram of the

microstructure of a 3D graphene composite aerogel. It can be seen that 3D graphene
aerogels have rich porous structures and can provide rich loading sites for active
materials to prepare high-performance composites.
2 Preparation of Graphene
This section systematically summarizes and classifies the preparation methods of 3D

graphene, as shown in Fig. 3. The preparation methods of 3D graphene are mainly
divided into CVD growth, self-assembly, 3D printing, 3D laser induction, pyrolysis
of organic precursors, and other methods [7]. Templates are also used to assist in
the preparation process as required. At present, CVD and self-assembly are used in
most studies.
2.1 CVD Growth of 3D Graphene
2.1.1 CVD Growth Based on a Metal Template
Metal templates can be used as catalysts to accelerate the decomposition of hydro-

carbons and the nucleation of graphene, making the lattice arrangement of graphene
more perfect [8]. Chen et al. [17] first used template-based CVD to synthesize 3D
Fig. 3 Preparation method of 3D graphene

porous graphene structure on nickel foam and used methane as carbon precursor
nickel foam as a metal template to grow graphene. Graphene was coated on the
surface of nickel foam in a tubular furnace at 1000 °C, then etched the nickel foam
with FeCl3 /HCl solution, and added acetone to remove the PMMA support layer.
Finally, 3D porous graphene flexible network structure with the original nickel foam
structure was formed. Lin et al. [18] designed a kind of 3D nanoporous graphene
based on 12 component ultra-high entropy nanoporous alloy (Fig. 4a), and synthe-
sized a self-contained 3D nanoporous graphene with high N-doping by CVD growth.
However, there are some defects in the selection of metal templates, and the etching
of the metal template cannot be completely removed, resulting in the preparation of
3D porous graphene being greatly limited in the use process.
2.1.2 CVD Growth Based on a Non-metal Template
Compared with the metal template, the non-metal template has more diversity in
morphology, high melting point, and low cost [6]. As shown in Fig. 4b, Shi et al.
[19] first calcined the shell (calcium carbonate (CaO)) to porous CaO at 1050 °C,
then CVD graphene on porous CaO as a non-metal template, and finally prepared 3D
porous graphene structure by removing CaO with hydrochloric acid. In the process
of calcining calcium carbonate at high temperatures, the release of CO2 can form
an interconnected porous structure in the shell, which provides favorable conditions
for the growth of porous graphene. At the same time, porous CaO as a support
structure provides a template for the CVD growth of graphene. The 3D graphene
prepared by this method completely retained the porous structure of CaO template,
showing ultra-low density and ultra-high porosity. As mentioned in the above section,
Zeng et al. [13] used carbon material as a template, carbonized PAN nanofibers by
electrospinning under NH3 etching conditions, and CVD-grown vertically aligned
3D graphene fibers with CH4 as a carbon source.
2.1.3 Growth of 3D Graphene by PECVD
Through PECVD, hydrocarbons can be pyrolyzed at relatively low temperatures, and

3D graphene can be grown without metal catalysts or even templates. According to the
plasma energy source, PECVD can be divided into DC-PECVD, MW-PECVD, and
RF-PECVD. No matter which discharge method is used, the formation mechanism
of 3D graphene is similar. Yin et al. [20] as shown in Fig. 4c used Si3 N4 nanowire
film as a template to obtain 3D graphene microtubules (3DGMTs) by PECVD and
subsequent heat treatment.
8
Fig. 4 a Schematic diagram of CVD process using NP-12 and NP-Ni as templates. Adapted with permission [18], Copyright (2022), American Chemical
Society. b Schematic diagram of graphene foam formation. Adapted with permission [19], Copyright (2016), American Chemical Society. c Schematic diagram
of manufacturing 3D GMTs and CMTs films. Adapted with permission [20], Copyright (2020), Elsevier. d A schematic illustration of the fabrication of a TAGAH
using granulate hydrogel (GH) self-assembled with graphene-coated agarose microbeads (GAMs). Adapted with permission [21], Copyright (2022), Elsevier.
e Schematic diagram of the structure of NRGO/hollow CoFe2 O4 composite aerogel. Adapted with permission [22], Copyright (2023), Elsevier. f Schematic
diagram of the manufacturing route of NS-G fiber. Adapted with permission [23], Copyright (2020), Royal Society of Chemistry. g 3G rGO@Cuf/Schematic
diagram of overall design and process flow of step-by-step manufacturing of copper supercapacitors. Adapted with permission [25], Copyright (2018), Springer
Nature. h Schematic diagram of SF-3D GA preparation. Adapted with permission [26], Copyright (2020), Wiley–VCH. i Schematic diagram and SEM image
of 3D RGO aerogel prepared by DLP method. Adapted with permission [27], Copyright (2022), Wiley–VCH. j Process of graphene formation on PI by electron
C. Xiong et al.
beam bombardment. Adapted with permission [28], Copyright (2021), Elsevier. k SEM image of 3D vertical graphene prepared at different temperatures.
Adapted with permission [30], Copyright (2021), Elsevier
2.2 Preparation of 3D Graphene by Self-Assembly Method
Self-assembly is a method of self-assembly of 2D graphene materials into 3D

graphene structures through a bottom-up strategy.
2.2.1 Thermal Reduction
Thermal reduction, the elimination of oxygen-containing functional groups on GO by

thermal annealing, is the most conventional, direct, and effective method. As shown in
Fig. 4d, Park et al. [21] used GO-coated agarose beads as precursors to self-assemble
into the granular hydrogel and then reduced GO to rGO by thermal annealing to form
a thermal annealing graphene channel agarose (TAGAH) hydrogel composed of 3D
conductive rGO network. TAGAH has high conductivity, low impedance, and good
biocompatibility, and has great potential in soft bioelectrode, pressure sensors, strain
sensors, and conductive tissue scaffolds.
2.2.2 Hydro/Solvothermal Reduction
The initial purpose of hydrothermal reduction is to reduce GO to rGO tablets. With

the development of research, it has gradually become a method to self-assemble
3D rGO hydrogels while reducing GO. These reactions usually need to be carried
out at medium–high temperatures in the high-pressure reactor. During these reac-
tions, the thermally induced solvent acts as a reductant, most carboxyl groups are
removed, and rGO sheets are assembled into a 3D rGO framework. Xu et al. [22]
prepared nitrogen-doped reduced GO/hollow cobalt ferrite composite aerogels with
3D network structures through simple solvothermal and hydrothermal self-assembly
processes. Figure 4e shows the preparation process of composite aerogel.
2.2.3 Chemical Reduction Induction
The chemical reduction was first used to reduce GO to rGO using a strong reductant
represented by hydrazine. Then, it was used in the synthesis of 3D graphene hydrogel,
and the reductant used was also milder. Compared with hydrothermal reduction,
chemical reduction has mild conditions, a higher reduction degree, and easier doping
of heteroatoms into 3D rGO. As shown in Fig. 4f, Ma et al. [23] showed a scalable
and low-cost microgel spinning method for preparing nitrogen sulfur co-doped 3D
porous graphene fibers. Firstly, nitrogen sulfur co-doped GO (NS-GO) microgels
with the 3D structure were prepared by chemical reduction-induced self-assembly
method. Then, NS-GO fibers were prepared by wet spinning using microgel as a
spinning stock solution. Finally, NS-GO fibers were reduced to NS-GF by the thermal
reduction method. Jha et al. [24] used copper chloride (I) (CuCl) to reduce GO, and
10 C. Xiong et al.
then removed copper ions through HCl to obtain 3D mesoporous rGO, which has
significant supercapacitor performance in the field of all-solid-state supercapacitors.
2.2.4 Electrochemical Reduction
GO sheets will be electrochemically reduced near the cathode and deposited on

the cathode. The layers support each other to form an interconnected 3D graphene
network. As shown in Fig. 4g, Purkait et al. [25] first prepared foamed copper by
constant current electrodeposition and then electrodeposited GO with GO suspension
containing 1 M phosphoric acid solution as electrolyte. The GO sheet was reduced
to a conductive 3D porous rGO network structure at a constant potential. The 3D
porous rGO can be directly used to prepare solid-state supercapacitors.
2.3 3D Printing
3D printing is an efficient method to directly construct large-volume objects. First,

the target product is designed by using relevant software, and then 3D structural
materials are prepared by heating and deposition layer by layer under the control
of the computer. The combination of nanotechnology and 3D printing can produce
3D large volumes of materials with unique properties and versatility. Yao et al.
[26] prepared a new surface functionalized 3D-printed graphene aerogel electrode
material. In Fig. 4h, the GO ink prepared by mixing a single-layer GO sheet with
hydroxypropyl methylcellulose is sprayed through a nozzle, heated, and deposited
layer by layer, and then freeze-dried to obtain 3D GO aerogel. Finally, the 3D GO
aerogel is transformed into a 3D graphene aerogel by thermal annealing at 1050 °C.
In addition, 3D graphene aerogels were prepared by the template-assisted method.
The ideal shape was designed by software. The hollow templates were arranged into
interconnected 3D structures by 3D printing. GO or chemically modified graphene
was injected into the hollow template, and the 3D graphene structure was obtained by
subsequent processing. As shown in Fig. 4i, Zhou et al. [27] designed and prepared
3D graphene aerogel inheriting a high-resolution polyacrylate resin template by
combining digital light processing technology and 3D printing.
2.4 3D Laser-Induced Graphene (3D LIG)
3D LIG is a kind of 3D graphene formed by laser irradiation of polymer precursors

to induce photochemical and thermal conversion. It naturally presents a 3D porous
structure, which is usually called 3D LIG or 3D laser-scribed graphene (LSG). The
quality of LIG is slightly inferior to that of 3D graphene prepared by other methods,
but low cost and relatively simple are the advantages of laser-induced graphene.
Han et al. [28] directly synthesized 3D graphene on polymer-based polyimide by a

high-energy electron beam. The preparation process is shown in Fig. 4j. The final 3D
graphene film has a thickness of 0.66 mm and a specific surface area of 363 m2 g−1 . At
present, most studies use macromolecular synthetic resins or natural polymers as laser
irradiation precursors, but this largely limits the geometry and size of 3D graphene. Yu
et al. [29] used 10.6 μm CO2 laser to irradiate liquid precursors to prepare 3D laser-
induced graphene materials and synthesized non-polymer precursors by introducing
aromatic units conducive to high carbonization and oxazine rings with high flame
retardancy. Then it is directly converted into graphene by laser irradiation.
2.5 Pyrolytic Organic Precursors
Pyrolysis of organic precursors is a method of direct pyrolysis of organic molecules

to obtain 3D graphene materials. Generally speaking, some organic molecules will
be mixed through the sol–gel process to form organic polymer carbon precursors
before pyrolysis, but organic molecules can also be directly pyrolyzed without sol–
gel treatment. Li et al. [30] prepared disordered molecular chain foam as a precursor
by thermally induced phase separation and then pyrolyzed it at 900–1200 °C. With
the increase of carbonization temperature, the surface roughness of carbon increases,
and 3D vertical graphene gradually forms. SEM at different temperatures is shown
in Fig. 4k.
3 Application of 3D Graphene
3.1 Energy Conversion
3.1.1 Solar-Thermal Conversion
The best way to collect solar energy is to convert photons into heat directly through
the solar heat absorber. It can achieve higher conversion efficiency because it uses
a wider bandwidth in the solar spectrum, and is environmentally friendly. Lin et al.
demonstrated structured graphene metamaterials (SGM), as shown in Fig. 5a [31].
The structured graphene metamaterials exploit the wavelength selectivity of the base-
grooved metal structures. Moreover, the ultra-thin graphene metamaterial membrane
has the characteristics of broadband optical dispersion-free and excellent thermal
conductivity. The photothermal conversion efficiency is up to 90.1%, the total effi-
ciency is 68.9%, the water evaporation rate is 1.5 kgm−2 h−1 , and the solar-steam
efficiency is up to 96.2%, to realize the high-efficiency solar photothermal conversion
at large angles.
12
Fig. 5 a SGM solar selective absorber. Adapted with permission [31], Copyright (2020), Nature. (B) (a) Schematic diagram of the synthetic route for preparing
the SnS2@GA heterostructure. b SEM image of SnO2@GA. SEM image of the final product vulcanized at c 300 1C, d 350 1C, e 400 1C. Adapted with
permission [34], Copyright (2022), Chinese Chemical Society and Royal Society of Chemistry. (C) Genetically modified enhanced solar cells. Adapted with
permission [35], Copyright (2022), American Chemical Society. (D) The structural models and preparation routes of Zn (MAA) 2 and ZG HS are described.
C. Xiong et al.
3.1.2 Photocatalysis
Graphene photocatalytic composites have developed rapidly in recent years and have
great application value in solving energy and environmental problems. On the basis
of achieving uniform dispersion of photocatalyst, the construction of 3D graphene
has many new advantages: the internal porous structure increases the adsorption of
materials on reactants; good mechanical strength makes the material easy to recover
after catalytic reaction, which is particularly important in the field of sewage purifi-
cation. These characteristics make graphene composite photocatalyst materials with
a 3D structure more prominent and practical. Wang et al. designed a new method to
modify UIO-66-NH2 metal–organic framework material for efficient photocatalytic
reduction of CO2 by building a 3D graphene framework [32]. Through theoret-
ical calculation and experimental research, it is confirmed that the rearrangement
of charge carriers has occurred at the interface of different materials. During the
photocatalysis process, the charge transfer and separation can be effectively carried
out, which effectively promotes the photocatalytic reduction of the CO2 conversion
process. It provides a promising way to explore the application of nano-composite
materials based on MOFs in environmental governance and other related fields.
3.2 Energy Storage
3.2.1 Batteries
Li–ion batteries (LIBs)

In recent years, lithium batteries have developed rapidly to meet the application
of rechargeable batteries in various fields (such as portable electronic devices and
electric vehicles). As the core of LIB, electrode active materials generally require
high capacity and energy density, long-term cycle stability, and safety. Mo and
others showed a 3D hierarchical metal hydride/graphene composite (LiNa2 AlH6 /
3DG) [33]. And LiNa2 AlH6 /3DG have significantly better lithium storage perfor-
mance in solid-state batteries than previously reported aluminate negative elec-
trodes. LiNa2 AlH6 nanoparticles are uniformly anchored on graphene nanosheets.
The graphene nanosheets self-assemble to form a 3D flower hierarchical structure,
which shows excellent cycle stability when LiBH4 is used as a solid electrolyte. At
the current density of 5 Ag−1 , its capacity reaches 861 mA h g−1 , its cycle life reaches
500 times, and its capacity retention rate reaches 97%.
Sodium–ion battery (SIBs)
Sodium–ion battery (SIBs) has shown great potential application value in the field of
energy storage and power transportation due to their advantages of rich resources, low
cost, and environmental friendliness. As shown in Fig. 5b, Guo and others show a 2D
heterostructure, in which dense SnS2 nanosheets are uniformly and vertically fixed
14 C. Xiong et al.
on graphene aerogel(SnS2 @GA) for high-performance sodium–ion batteries [34].

The composite exhibits enhanced electrochemical reaction kinetics and enhanced
structural stability based on the charge storage mechanism dominated by pseudo-
capacitance. SnS2 @GA The negative electrode provides a high reversible capacity
of 690 mAhg−1 at 0.2 Ag−1 , excellent rate performance, and long cycle life, and the
capacity retention rate reaches 83% after 1000 cycles.
Other Batteries
The emergence of silicon solar cells provides feasible and effective solutions to
challenges such as energy and environmental crisis. The high reflection and surface
recombination loss caused by the silicon interface and its nanometer processing
technology are the main obstacles to achieving high energy conversion efficiency.
Jia et al. proposed a 3D conformal coating concept for graphene metamaterials [35],
as shown in Fig. 5c. Among them, 2D graphene can perfectly adapt to 3D silicon
structural surfaces, reducing optical reflection by 20%, and improving surface passi-
vation performance by 60%. Subsequently, the graphene metamaterial 3D conformal
coating concept was then further applied to standard silicon solar cells, resulting in an
overall 23% increase in solar energy conversion efficiency. Moreover, the concept of
3D conformal coating can be easily extended to a variety of optoelectronic and semi-
conductor devices with excellent performance, opening a practical and promising
way to achieve efficient energy acquisition and storage.
3.2.2 Supercapacitor
Supercapacitors have become one of the most promising energy storage devices
due to their high-power density and long cycle life. Due to the advantages of 3D
Graphene such as high surface area, high conductivity, high carrier mobility and rich
pore structure, many researchers have begun to explore the electrochemical prop-
erties of 3D graphene materials in the application of supercapacitors. As shown in
Fig. 5d, Ma et al. investigated a novel and efficient molecular self-assembly strategy to
prepare 3D flower-like ZG microstructures by calcination of self-assembled precur-
sors (directly deriving three-dimensional amphiphilic Zn(MAA)2 precursors with
well-layered structure into three-dimensional graphene mixtures to produce high-
quality three-dimensional graphene microstructures with uniform metal oxide (ZnO)
nanoparticles) [36]. ZnO NP generated from carboxylic acid groups of Zn (MAA)2
molecules permeates into graphene. The resulting ZG-500 HS as a supercapacitor
electrode has a specific capacitance of 272.1 Fg−1 at 1 Ag−1 . In addition, an asym-
metric supercapacitor based on ZG-500 HS and activated carbon provides an energy
density of 13.4 Whkg−1 at a power density of 387.5 Wkg−1 . This opens up a green
route for the preparation of high-quality 3D graphene composite supercapacitors.
3.3 Environment
With the rapid development of global industrialization and urbanization, environ-

mental problems have become one of the most worldwide threats. 3D graphene has a
large specific surface area, suitable pore size, controllable hydrophilicity and conduc-
tivity, and 3D interconnection structure, which shows great potential in environmental
treatment such as water purification, seawater desalination, and gas purification.
3.3.1 Water Decontamination
Nowadays, domestic sewage, industrial and agricultural wastewater, and other prob-
lems have led to serious water pollution, economic and efficient removal of various
pollutants in water needs to be solved immediately.
As one of the widely used water treatment methods, 3D graphene has the advan-
tages of a large specific surface area, good chemical stability, and can easy realize
solid–liquid separation. It can also be used as a catalyst carrier to catalyze the degra-
dation of pollutants in water [37]. It is a good new type of economic and efficient
adsorption material. 3D graphene composite can be used for water treatment through
permeability, π–π interaction, electrostatic interaction, and surface complexation,
and becomes a potential adsorbent for treating oil, organic solvents, dyes, metal
ions, and other pollutants. It is reported that the adsorption capacity of 3D graphene
is tens to hundreds of times that of traditional adsorption materials. 3D graphene has
broad application prospects in water environmental pollution treatment.
3.3.2 Gas Adsorption
With the deepening of human industrialization, the problem of natural environ-

mental pollution has gradually emerged. Volatile organic compounds (VOCs) are
harmful pollutants and are released from various experimental sources, including
the petroleum industry, oil refineries, and the cleaning process of silicon chips. Even
at very low concentrations, long-term exposure can cause serious health problems.
The adsorption method is considered to be the most reasonable and effective method
to control air pollution. The adsorption of gas molecules onto the graphene surface
mainly depends on electrostatic adsorption, dispersion interaction, van der Waals
force, and charge transfer.
3.4 Catalyst
The traditional catalysts are generally noble metal-based materials, such as Pt, Ru,
and alloy. Although they are often used as catalysts in oxygen reduction reactions,
16 C. Xiong et al.
their high cost, sensitivity, and poor stability have largely prevented their large-scale
commercialization. Doped graphene can be a metal-free, anti-toxic, and durable
electrocatalyst to reduce costs [38]. Xie et al. successfully prepared nitrogen-doped
graphene aerogel (NGA) by a simple one-pot hydrothermal method. Selecting small-
size graphene oxide as a precursor, dopamine as a nitrogen source and the crosslinking
agent is conducive to the formation of micropores [39]. When NGA was used as an
electrocatalyst in an oxygen reduction reaction, NGA showed higher electrocatalytic
performance than Pt/C catalyst. It is due to the high active N atom doping amount
and abundant microporous structure.
3.5 Sensor
With the progress of the Internet of Things technology, sensors are becoming increas-
ingly important in life in the information age. They are widely used in industrial
manufacture, space exploration, ocean exploration, and other fields of our life.
Currently, scientists are working on developing 3D graphene sensors with a wide
strain sensing range, high sensitivity, and high cyclic stability. Common types of
graphene sensors include gas, strain, optical, magnetic field, mechanical sensor, etc.
3.5.1 Gas Sensor
After graphene adsorbs the target gas, its conductivity changes. By determining the
relationship between the conductivity change and the target surface gas concentra-
tion, the concentration of the target gas can be measured by measuring the conduc-
tivity change of graphene. The detection of graphene material gas is mainly based
on the adsorption of the sensing material and its conductivity change. For example,
as shown in Fig. 6a, Bag and others studied the effect of the concentration of meso-
porous ZnFe2 O4 particles on the gas sensing performance [40]. Due to the defect site
of mesoporous particles being relatively high density, the introduction of ZnFe2 O4
in graphene oxide (rGO)-based chemical resistance sensors shows a rapid detec-
tion performance of nitrogen dioxide (NO2 ) in a wide range from 50 to 4000 ppb.
Compared with the original rGO sensor, the sensitivity is higher and the lower detec-
tion limit is lower. RGO-ZnFe2 O4 -based gas sensor shows good reproducibility and
stable dynamic response under static and dynamic tension.
3.5.2 Strain Sensor
Graphene can be used appropriately as a strain and pressure sensor. In graphene

strain and pressure sensors, the perception of physical signals (including strain and
pressure) is carried out using graphene as an active material. Because of its high
electrical conductivity, graphene materials are often used as conductive layers or
Introduction to 3D Graphene
Fig. 6 a An extendable, body-attached NO2 gas sensor based on rGO and ZnFe2 O4 hollow octahedra. Adapted with permission [40], Copyright (2021),
Elsevier. b The G/CB/Ni-2 strain sensor is used to monitor human movement in real time. Adapted with permission [41], Copyright (2020), Royal Society of
Chemistry. c Schematic diagram of high-performance photoelectric sensor based on 3D graphene field-effect tube. Adapted with permission [42], Copyright
(2019), American Chemical Society. d Demonstration of 3D bi-continuous nanoporous graphene. Adapted with permission [43], Copyright (2019), Cell Press
17
18 C. Xiong et al.
electrodes for graphene-based strain and pressure sensors. As shown in Fig. 6b, Sun
et al. integrated graphene (G), carbon black (CB), and polydimethylsiloxane (PDMS)
into a 3D frame of a commercial nickel sponge using a simple, cost-effective, and
scalable drip coating method [41]. The G/CB/Ni strain sensor shows good flexibility,
high sensitivity (strain coefficient 138 at 16% strain), and long-term stability. The G/
CB/Ni sensor can not only accurately monitor the pulse, blink, swallow, and other
subtle human movements, but also has broad application prospects in muscle strength
detection.
3.5.3 Other Sensors
Due to graphene’s excellent electronic and optical properties, it has become an ideal
material for high-performance photodetectors. As shown in Fig. 6c, Deng et al.
showed a method of using a silicon nitride stress layer to drive 2D graphene field-
effect tube to self-curl into a microtubule 3D graphene field-effect tube (3D GFET)
structure, and first manufactured the number of curl layers (1–5) and radius (30–
65 μm) Precise and controllable 3D GFET device array [42]. The 3D GFET photode-
tector can detect ultraviolet, visible, mid-infrared, and Hertz (THz) regions at room
temperature. The light response of ultraviolet and visible light exceeds 1 AW −1 ,
and the light response at 3.11 THz is 0.232 AW −1 . It realizes ultra-high sensitivity
and ultra-fast detection of ultraviolet light, visible light, medium infrared light, and
terahertz waves.
3.6 Electromagnetic Interference (EMI)
With the wide use of advanced electronic and communication equipment, electro-
magnetic radiation seriously affects the precision and sensitivity of precision elec-
trical equipment and causes serious environmental pollution. It is urgent to solve
the problem of electromagnetic interference and pollution. Graphene has attracted
wide attention because of its excellent electrical and thermal conductivity as well
as mechanical properties. The electromagnetic interference (EMI) shielding perfor-
mance of 3D graphene materials relies strongly on the porous structure. The ideal
3D structure would avoid damaging graphene’s electrical conductivity. As shown in
Fig. 6d, Kashani’s group demonstrated highly conductive bi-continuous nanoporous
graphene with excellent EMI shielding performance of 50.9 dB and 83 dB at film
thicknesses of 150 mm and 300 mm, respectively [43]. This high shielding effi-
ciency value from light and flexible nanoporous membranes gives the superhigh
EMI shielding performance of up to 75,407 and 61630 dB cm2 g−1 with superior
shielding efficiency due to the abundant absorbing interface at a minimum thickness
in the bi-continuous porous 3D nanostructures and the high conductivity from the
interconnected graphene networks.
References
1. Cui, H.J., Guo, Y.B., Zhou, Z.: 3D graphene-based macrostructures for electrocatalysis. Small
17, 2005255 (2021)
2. Choi, M.S., Nipane, A., Kim, B.S.Y., Ziffer, M.E., Datta, I., Borah, A., Jung, Y.H., Kim,
B., Rhodes, D., Jindal, A., Lamport, Z.A., Lee, M., Zangiabadi, A., Nair, M.N., Taniguchi,
T., Watanabe, K., Kymissis, I., Pasupathy, A.N., Lipson, M., Zhu, X.Y., Yoo, W.J., Hone,
J., Teherani, J.T.: High carrier mobility in graphene doped using a monolayer of tungsten
oxyselenide. Nat. Electron. 4, 731–739 (2021)
3. Zhi, D.D., Li, T., Li, J.Z., Ren, H.S., Meng, F.B.: A review of 3D graphene-based aero-
gels: synthesis, structure and application for microwave absorption. Compos. Part B-Eng.
211,108642 (2021)
4. Xiao, W., Li, B., Yan, J., Wang, L., Huang, X.W., Gao, J.F.: Three dimensional graphene
composites: preparation, morphology and their multi-functional applications. Compos. Part
A-Appl. Sci. Manuf. 165, 107335 (2023)
5. Zhao, H.Y., Yu, M.Y., Liu, J., Li, X.F., Min, P., Yu, Z.Z.: Efficient preconstruction of 3D
graphene networks for thermally conductive polymer composites. Nano-Micro Lett. 14, 129
(2022)
6. Chen, K., Shi, L.R., Zhang, Y.F., Liu, Z.F.: Scalable chemical-vapour-deposition growth of
3D graphene materials towards energy-related applications. Chem. Soc. Rev. 47, 3018–3036
(2018)
7. Qiu, B.C., Xing, M.Y., Zhang, J.L.: Recent advances in 3D graphene based materials for
catalysis applications. Chem. Soc. Rev. 47, 2165–2216 (2018)
8. Sun, Z.X., Fang, S.Y., Hu, Y.H.: 3D graphene materials: from understanding to design and
synthesis control. Chem. Rev. 120, 10336–10453 (2020)
9. Kawai, S., Krejci, O., Nishiuchi, T., Sahara, K., Kodama, T., Pawlak, R., Meyer, E., Kubo, T.,
Foster, A.S.: 3D graphene nanoribbons as a framework for molecular assembly and local probe
chemistry. Sci. Adv. 6, eaay8913 (2020)
10. Cao, D., Hao, Y.Z., Wang, Y.H., Bai, Y., Li, Y., Wang, X.R., Chen, J.H., Wu, C.: Platinum
nanocrystals embedded in 3D graphene for high-performance Li–O2 batteries. ACS Appl.
Mater. Interfaces. 14, 40921–40929 (2022)
11. Zhang, Q.F., Cheng, X.L., Wang, C.X., Rao, A.M., Lu, B.G.: Sulfur-assisted large-scale
synthesis of graphene microspheres for superior potassium-ion batteries. Energy Environ. Sci.
14, 965–974 (2021)
12. Hirani, R.A.K., Asif, A.H., Rafique, N., Wu, H., Shi, L., Zhang, S., Duan, X.G., Wang, S.B.,
Saunders, M., Sun, H.Q.: 3D nitrogen-doped graphene oxide beads for catalytic degradation
of aqueous pollutants. Chem. Eng. J. 446, 137042 (2022)
13. Zeng, J., Ji, X.X., Ma, Y.H., Zhang, Z.X., Wang, S.G., Ren, Z.H., Zhi, C.Y., Yu, J.: 3D graphene
fibers grown by thermal chemical vapor deposition. Adv. Mater. 30, 1705380 (2018)
14. Lei, H.P., Tu, J.G., Li, S.Q., Huang, Z., Luo, Y.W., Yu, Z.J., Jiao, S.Q.: Graphene-
encapsulated selenium@polyaniline nanowires with 3D hierarchical architecture for high-
capacity aluminum-selenium batteries. J. Mater. Chem. A 10, 15146–15154 (2022)
15. Shu, R.W., Wan, Z.L., Zhang, J.B., Wu, Y., Liu, Y., Shi, J.J., Zheng, M.D.: Facile design of
3D nitrogen-doped reduced graphene oxide/multi-walled carbon nanotube composite foams
as lightweight and highly efficient microwave absorbers. ACS Appl. Mater. Interfaces. 12,
4689–4698 (2020)
16. Huang, X.G., Wei, J.W., Zhang, Y.K., Qian, B.B., Jia, Q., Liu, J., Zhao, X.J., Shao, G.F.:
Ultralight magnetic and dielectric aerogels achieved by metal-organic framework initiated
gelation of graphene oxide for enhanced microwave absorption. Nano-Micro Lett. 14, 107
(2022)
17. Chen, Z.P., Ren, W.C., Gao, L.B., Liu, B.L., Pei, S.F., Cheng, H.M.: 3D flexible and conductive
interconnected graphene networks grown by chemical vapour deposition. Nat. Mater. 10, 424–
428 (2011)
20 C. Xiong et al.
18. Lin, X.R., Hu, Y.X., Hu, K.L., Lin, X., Xie, G.Q., Liu, X.J., Reddy, K.M., Qiu, H.J.: Inhibited
surface diffusion of high-entropy nano-alloys for the preparation of 3D nanoporous graphene
with high amounts of single atom dopants. ACS Mater. Lett. 4, 978–986 (2022)
19. Shi, L.R., Chen, K., Du, R., Bachmatiuk, A., Rümmeli, M.H., Xie, K.W., Huang, Y.Y., Zhang,
Y.F., Liu, Z.F.: Scalable seashell-based chemical vapor deposition growth of 3D graphene
foams for oil–water separation. J. Am. Chem. Soc. 138, 6360–6363 (2016)
20. Yin, X.M., Li, H.J., Han, L.Y., Meng, J.C., Lu, J.H., Zhang, L.L., Li, W., Fu, Q.G., Li, K.Z.,
Song, Q.: Lightweight and flexible 3D graphene microtubes membrane for high-efficiency
electromagnetic-interference shielding. Chem. Eng. J. 387, 124025 (2020)
21. Park, J., Jeon, N., Lee, S., Choe, G., Lee, E., Lee, J.Y.: Conductive hydrogel constructs with
3Dly connected graphene networks for biomedical applications. Chem. Eng. J., 137344 (2022)
22. Xu, J., Shu, R., Wan, Z., Shi, J.J.: Construction of 3D hierarchical porous nitrogen-doped
reduced graphene oxide/hollow cobalt ferrite composite aerogels toward highly efficient
electromagnetic wave absorption. J. Mater. Sci. Technol. 132, 193–200 (2023)
23. Ma, W.J., Li, W.F., Li, M., Mao, Q.H., Pan, Z.H., Zhu, M.F., Zhang, Y.G.: Scalable microgel
spinning of a 3D porous graphene fiber for high-performance flexible supercapacitors. J. Mater.
Chem. A 8, 25355–25362 (2020)
24. Jha, P.K., Gupta, K., Debnath, A.K., Rana, S., Sharma, R., Ballav, N.: 3D mesoporous reduced
graphene oxide with remarkable supercapacitive performance. Carbon 148, 354–360 (2019)
25. Purkait, T., Singh, G., Kumar, D., Singh, M., Dey, R.S.: High-performance flexible superca-
pacitors based on electrochemically tailored 3D reduced graphene oxide networks. Sci. Rep.
8, 1–13 (2018)
26. Yao, B., Chandrasekaran, S., Zhang, H.Z., Ma, A., Kang, J.Z., Zhang, L., Lu, X.H., Qian, F.,
Zhu, C., Duoss, E.B., Spadaccini, C.M., Worsley, M.A., Li, Y.: 3D-printed structure boosts
the kinetics and intrinsic capacitance of pseudocapacitive graphene aerogels. Adv. Mater. 32,
1906652 (2020)
27. Zhou, J.Z., Wu, X., Chen, Y., Yang, C., Yang, R., Tan, J.Y., Liu, Y.L., Qiu, L., Cheng, H.M.:
3D printed template-directed assembly of multiscale graphene structures. Adv. Func. Mater.
32, 2105879 (2022)
28. Han, S., Li, N., Song, Y.P., Chen, L.Q., Liu, C., Xi, M., Yu, X.L., Qin, Y., Xu, T.T., Ma, C.,
Zhang, S.D.: E-beam direct synthesis of macroscopic thick 3D porous graphene films. Carbon
182, 393–403 (2021)
29. Yu, W.J., Zhao, W.W., Wang, S.P., Chen, Q., Liu. X.Q.: Direct conversion of liquid organic
precursor into 3D laser-induced graphene materials. Adv. Mater. (2022)
30. Li, G.Z., Wang, S.S., Zeng, J., Yu, J.: In-situ formation of 3D vertical graphene by carbonizing
organic precursor in ammonia. Carbon 171, 111–118 (2021)
31. Lin, K.T., Lin, H., Yang, T.S., Jia, B.H.: Structured graphene metamaterial selective absorbers
for high efficiency and omnidirectional solar thermal energy conversion. Nat. Commun. 11,
1389 (2020)
32. Wang, X.J., Liu, Y.P., Chai, G.D., Yang, G.R., Wang, C.Y., Yan, W.: Interfacial charge modula-
tion via in situ fabrication of 3D conductive platform with MOF nanoparticles for photocatalytic
reduction of CO2 . Chem. Europ. J. 28, e202200583 (2022)
33. Mo, F.J., Chi, X.W., Yang, S.P., Wu, F.L., Song, Y., Sun, D.L., Yao, Y., Fang, F.: Stable three-
dimensional metal hydride anodes for solid-state lithium storage. Energy Storage Mater. 18,
423–428 (2019)
34. Guo, X., Wang, S., Yu, L.P., Guo, C.Y., Yan, P.G., Gao, H., Liu, H.: Dense SnS2 nanoplates
vertically anchored on a graphene aerogel for pseudocapacitive sodium storage. Mater. Chem.
Front. 6, 325–332 (2022)
35. Yang, Y.Y., Zhang, Y.N., Zhang, J., Zheng, X.R., Gan, Z.X., Lin, H., Hong, M.H., Jia, B.H.:
Graphene metamaterial 3D conformal coating for enhanced light harvesting. ACS Nano (2022)
36. Ma, Q.H., Liu, M.F., Cui, F., Zhang, J.J., Cui, T.Y.: Fabrication of 3D graphene microstruc-
tures with uniform metal oxide nanoparticles via molecular self-assembly strategy and their
supercapacitor performance. Carbon 204, 336–345 (2023)
37. Wang, H.T., Mi, X.Y., Li, Y., Zhan, S.H.: 3D graphene-based macrostructures for water
treatment. Adv. Mater. 32, 1806843 (2019)
38. Shi, C.J., Maimaitiyiming, X.: FeNi-functionalized 3D N, P doped graphene foam as a noble
metal- free bifunctional electrocatalyst for direct methanol fuel cells. J. Alloy. Compd. 867,
158732 (2021)
39. Xie, B.B., Zhang, Y., Zhang, R.J.: Pure nitrogen-doped graphene aerogel with rich micropores
yields high ORR performance. Mater. Sci. Eng. B 242, 1–5 (2019)
40. Bag, A., Kumar, M., Moon, D.B., Hanif, A., Sultan, M.J., Yoon, D.H., Lee, N.E.: A room-
temperature operable and stretchable NO2 gas sensor composed of reduced graphene oxide
anchored with MOF-derived ZnFe2 O4 hollow octahedron. Sens. Actuat. B Chem. 346, 130463
(2021)
41. Sun, S.B., Liu, Y.Q., Chang, X.T., Jiang, Y.C., Wang, D.S., Tang, C.J., He, S.Y., Wang, M.W.,
Guo, L., Gao, Y.: Wearable, waterproof, and highly sensitive strain sensor based on three-
dimensional graphene/carbon black/Ni sponge for wirelessly monitoring human motions. J.
Mater. Chem. C 6, 2074–2085 (2020)
42. Deng, T., Zhang, Z.H., Liu, Y.X., Wang, Y.X., Su, F., Li, S.S., Zhang, Y., Li, H., Chen, H.J., Zhao,
Z.R., Li, Y., Liu, Z.W.: Three-dimensional graphene field-effect transistors as high-performance
photodetectors. Nano Lett. 19, 14940–21503 (2019)
43. Kashani, H., Giroux, M., Johnson, I., Han, J.H., Wang, C., Chen, M.W.: Unprecedented electro-
magnetic interference shielding from three-dimensional bi-continuous Nanoporous graphene.
Matter 1, 1077–1087 (2019)
Synthesis and Printing of 3D Graphene
Arash Ghazitabar and Malek Naderi
Abstract In this chapter, we discuss the various synthesis routes of 3D graphene,

also known as Graphene Aerogel (GA). This material, owing to its special structure,
provides unique features such as ultra-low density and high surface area. These
features meet the requirements, which are fundamental for different applications
including supercapacitors, sensors, batteries, and sorbents. This chapter describes the
main synthesis methods of hydrothermal, direct self-assembly, chemical reduction,
cross-linking agents, template-based, and 3D printing. Graphene oxide (GO), in most
of these methods, is almost the main precursor to produce 3D Graphene Hydrogel
(GH), which is followed by the GA structure fabrication process achieved through
the application of special drying methods like supercritical drying or freeze-drying.
In some cases, the post-treatments such as heat treatment are employed to improve
the physiochemical properties of GA. Nevertheless, the target application and desired
properties are the critical factors in guiding the researchers to choose the most proper
synthesis method.
Keywords Freeze-drying · Graphene aerogel · Hydrogel · Hydrothermal · 3D

printing
A. Ghazitabar · M. Naderi (B)

Department of Materials and Metallurgical Engineering, Amirkabir University of Technology,
No. 350, Hafez Ave., Tehran, Iran
e-mail: mnaderi@aut.ac.ir
Graphene and Advanced Materials Laboratory (GAMLab), Amirkabir University of Technology,
No. 7, Balavar Alley, Tehran, Iran
A. Ghazitabar
e-mail: Arash_Ghazitabar@aut.ac.ir
A. Ghazitabar
Department of Inorganic Pigments and Glazes, Institute for Color Science and Technology
(ICST), No. 55, Vafamanesh St., Tehran, Iran

https://doi.org/10.1007/978-3-031-36249-1_2
24 A. Ghazitabar and M. Naderi
1 Introduction
Aerogels are structurally amazing porous synthetic materials, which provide ultra-
low density as well as very high specific surface area. Graphene is, also, a miraculous
material that has created a tremendous revolution in the field of engineering mate-
rials. Considering these definitions, it is obvious that scientists and researchers were
looking to produce and synthesize a novel material that combines with the above-
mentioned material, i.e., Graphene Aerogel (GA). The graphene-based aerogels have
provided an effective way to engineer graphene or Graphene Oxide (GO) into the
three-dimensional networks, which provides a high specific surface area with no obli-
gation to restack the graphene sheets. The resulting structure is mostly expected to
provide distinguished features including ultra-low density, very high specific surface
area, and good mechanical stability. In fact, Wang et al. were the pioneers to produce
GA using a conventional hydrothermal synthesis method. First of all, GO is added
to a Teflon-lined autoclave reactor vessel, and then the temperature is increased to
200 °C to form the graphene hydrogel (GH). After drying the GH, the GA is formed
with a 3D porous interconnected structure [1]. This unique resulting material consists
of 2–5% solid materials (i.e., carbon atoms) as well as more than 95% air entrapped
in the pores. A theoretical density of 16 g/m3 is expected.
The drying process is regarded as one of the main steps when producing GA.
While drying graphene hydrogel conventionally, the graphene network collapses due
to the high capillary force imposed by solvent evaporation. This is why an alternative
method of drying should be sought. Supercritical drying and freeze-drying are the
most promising proposed methods, which greatly prevent such collapse in the GA
structure. Due to π–π interaction, graphene sheets in GA are prone to slip during the
supercritical drying process. This results in high shrinkage, and consequently, the
reduction in density is not obtained as low as expected in GA. Freeze-drying is the
most appropriate method for graphene hydrogel production. It is an effective process
to eliminate capillary forces, which are generated during drying. In this method,
first, the solvent is replaced with water in the wet gel. Second, the hydrogel is frozen
applying low temperatures (i.e., ~60 °C), and finally ice is sublimated into vapor
by implying a vacuum. Due to the generation of several micropores in graphene
hydrogels, the scaffold of GA remains unchanged, almost no shrinkage occurs, and
the density is achieved in the range of expected limits. However, freeze-drying is
proposed as the most suitable method, but it is not cost- and energy-effective when it
comes to scaling up the GA production, due to the need for applying the high vacuum
and very low operating temperature, along with being time-consuming process [2].
The researchers have focused on developing the GA synthesis methods due to
the outstanding properties of GA, and their composite materials. In majority of
these methods, the GO is the most preferred precursor to begin with because of
its functional structure. The main synthesis methods are
. Hydrothermal.
. Direct self-assembly.
. Chemical reduction.
Synthesis and Printing of 3D Graphene 25
. Cross-linking agents.
. Template-based.
. 3D printing.
All the synthesis methods are briefly discussed in the following sections.
2 Hydrothermal Method
Hydrothermal method was the first process employed to synthesize the graphene
aerogel. In this method, the GO suspension is used as a main starting material, which
can be mixed with other components such as polymers (cross-linking agents), metal
salts (nickel nitrate and cobalt acetate), and reducing agents (ascorbic acid and sodium
bisulfite) to fabricate the various types of graphene aerogel. Herein, the most effective
parameters that should be considered are including concentration of GO suspension,
time and temperature of reaction, and the ratio of free volume (or occupied volume)
to total volume of autoclave. The application of hydrothermal method is preferred
by researchers since it is a simple one-step process that can be used to produce wide
range of composites with high repeatability. However, someone may believe not only
it is time-consuming, but also specific equipment is required, and there is a limitation
to minimum GO concentration (that should be higher than 2 mg.mL−1 ) [3–5].
Xu et al. employed hydrothermal method to produce one of the earliest graphene
aerogels. They used graphene oxide (2 mg.mL−1 ) as starting material in a sealed
Teflon-lined autoclave at 180 °C for 12 h to make the 3D hydrogel structure [6]. The
resulting hydrogel showed high mechanical strength, which could bear the load of
100 g with the lowest deformation. This excellent mechanical stability was due to
π–π stacking interactions between graphene sheets. Three main factors that affected
the final structure of produced graphene aerogel were initial GO concentration,
processing time, and temperature [7].
3 Direct Self-Assembly of GO
Gelation process of GO is the simplest route to produce graphene oxide aerogel.

However, it occurs at higher concentration of GO suspension (higher than
10 mg.mL−1 ). It requires a simple and cost-effective equipment compared to other
GA synthesis routes. Furthermore, the more oxygen functional groups could be main-
tained in the final 3D graphene structure (without any reduction), which is the main
advantage of this method especially when the purpose is to produce an adsorbent/
absorbent material in sorption of heavy metals ions or dyes. Qin et al. produced
a 3D graphene oxide using self-assembly method to be applied as an organic dye
rhodamine B adsorbent. A dispersion of 20–50 mg of dried GO was prepared in 1 mL
of deionized water, which was followed by 1 min ultrasonication to generate the 3D
graphene oxide hydrogel (GOH). The GOH was either freeze- or vacuum-dried while
producing graphene oxide aerogels [8].
In the early research, scientists proposed a novel self-assembly method of 2D
GO structure to form the 3D graphene by stimuli-responsive polymers, which
could be categorized as a smart material fabrication. These 3D objects can offer
reversible, visible, and tangible reactions in response to external stimuli such as
mechanical stress, heat, light, gas, electricity, and pH. Zhao et al. used poly (N-
isopropylacrylamide) (PNIPAM) and poly (propylene oxide) (PPO) as stimuli-
responsive polymers to convert the GO and RGO to 3D graphene structure in order
to be used as flexible/foldable supercapacitor electrode [9]. In this work, GO and
PNIPAM or PPO polymers were mixed and kept at temperature of 3 °C. Then, the
temperature was raised to 50 °C to fabricate 3D hydrogel. The obtained hydrogel was
reduced to RGO hydrogel by immersing the hydrogel in sodium ascorbate solution
at 80 °C. Freeze-dried hydrogel was used as flexible/foldable electrode for superca-
pacitor. The electrode exhibited good photo/thermal reversibility thanks to the low
critical solution temperature (LCST) of the cross-linking polymers which were used
as smart polymers [10].
4 Chemical Reduction Method
Hydrothermal method has some limitations such as high temperature and high
amount of residual oxygen-containing groups, which cause reduction in hydropho-
bicity and conductivity of final graphene aerogel. Moreover, high-pressure autoclave
equipment is necessary for hydrothermal process to make the graphene aerogels.
Researchers have proposed the chemical reduction method as a highly controllable
process to overcome these limitations while fabricating an engineered GA structure.
In this method, reducing agents are used to make the 3D graphene hydrogel. The main
reducing agents are including L-Ascorbic Acid (LAA) [11], oxalic acid–NaI [12],
sodium bisulphite (NaHSO3 ) [13], sodium sulfide (Na2 S) [14], LAA + NaHSO3
[15], and L-cysteine [16] that can do both chemical self-assembly and reduction of
GO at low temperature and under atmospheric pressure.
For instance, Chen et al. investigated the time needed for graphene hydrogel
formation, which was affected by the type of applied reducing agents. Vitamin C
and Na2 S needed only 10 min to form graphene hydrogel while for NaHSO3 this
time was about 30 min. The higher degree of reduction for graphene aerogel was
obtained by HI (80%, v/v in acetic acid), which provided high electrical conductivity
of 110 S.m−1 [14]. Ghazitabar et al. showed that chemical reduction method using L-
Ascorbic Acid (L-AA) as reducing agent can form the graphene aerogel/cobalt oxide
composites with high specific surface area (215 m2 .g−1 ) along with an amazing load-
bearing performance (compression load), which was higher than 2000 times of its
own weight [17]. Some researchers claimed that the highest electrical conductivity
and lowest density of graphene aerogels may be gained by using simultaneously the
mixture of two or more reducing agents in chemical reduction method. A mixture of
hypophosphorous acid and iodine is used in dilute GO suspension to form an ultra-

low-density graphene aerogel with superior electrical conductivity of 500 S.m−1
[18]. Shadkam et al. introduced a high electrochemical performance of graphene
aerogel, which was reduced by using the combined reducing agents of L-Ascorbic
Acid (L-AA) and NaHSO3 . The aerogel exhibited high specific capacitance with
superb retention of 91% after 1000 charge/discharge cycles [19]. Their proposed
mechanisms of reduction are presented in Fig. 1.
One of the important challenges to make ultra-low-density graphene aerogel
applying chemical reduction method is its limitation in using lower concentration
of GO (below 0.5 mg.mL−1 ). Zhang et al. [12] could design a new reducing agent
mixture to form a stable 3D graphene aerogel. In their research, oxalic acid and
NaI were used as reducing agents. The formation of hydrogen bonding between GO
(0.1–4.5 mg.mL−1 ) and carboxylic acid groups on oxalic acid was the main reason
to result in making a stable 3D structure [12]. In most cases, the functional groups
of reducing agents act as cross-linkers between graphene sheets to form graphene
aerogel. Ghazitabar et al. reported the cross-linking capability of L-Ascorbic Acid
(LAA) when it was used as reducing agent. By-products of LAA oxidation in GO
suspension form hydrogen bonding with edge of graphene sheets to form the 3D
structure of graphene aerogel [20].
5 Cross-Linking Agents
As said, self-assembly of graphene sheets employing cross-linking agents (for

instance, some functional groups on reducing agents as discussed in Sect. 3) is one
of the mechanisms to form graphene aerogel structure. These methods are divided
to three sub-categories based on the type of the used cross-linking agents.
5.1 Hydrogen Bonding
GO suspension is the stable form of colloid dispersion in water since it contains

hydrophilic functional groups on its sheets. In the acidic form, the protonation of
carboxyl groups causes reduction in electrostatic repulsion of graphene sheets, and
enhances the hydrogen bonding to make an unstable graphene suspension in water.
Ghazitabar et al. investigated the effect of the pH of GO suspension on formation
of graphene hydrogel in presence of LAA as reducing agent. They selected three
different pH values (3, 7, and 10), and concluded that the acidic suspension (with
pH value of 3) was the best to form high-strength 3D graphene hydrogel when using
chemical reduction method (Fig. 2a), resulting in a porous structure (Fig. 2b) [17].
On the contrary, some studies reported that the alkaline suspension was the proper
condition for GA formation. Hu et al. investigated the susceptible mechanisms
engaged in formation of 3D graphene hydrogel in both acidic and alkaline media
Fig. 1 a The mechanism of NaHSO3 in reduction process; ring-opening reaction and b Schematic
of the reduction reaction and cross-linking effect [19]. Adapted with permission [19], Copyright
(2023), Elsevier
Fig. 2 a Hydrogel
formation at pH of 3, 7, and
10, b SEM image of 3D
porous structure of GA
which was prepared at pH of
3 [17]. Adapted with
permission [17], Copyright
(2023), Elsevier
(with pH values of 3 and 10). They reported that the CO2 bubbles evolved from
acidic media of hydrogel led to the formation of macroscopic voids in hydrogel.
While in alkaline media, no formation of macroscopic voids was observed due to
the conversion of CO2 into ionic species, which generated a compressible graphene
hydrogel that was a good candidate for applications such as supercapacitor and
battery electrodes [21]. Therefore, the condition of media (to be acidic or alkaline
suspension) relies on the target applications (such as energy storage or adsorption)
and the expected features (such as conductivity and mechanical properties) to obtain
the proper structure. This, also, is applicable to both hydrothermal and chemical
reduction methods.
In general, two factors are the most effective to produce high-quality 3D graphene
aerogels: first, enhancing the bonding forces, and second, decreasing the repulsion
forces between graphene sheets. Researchers also proposed some polymeric organic
materials, which can act as cross-linking agents to form the graphene aerogels, such
as PVA, PEI, and EDA. These materials possess functional groups, which are bonded
to graphene sheets through hydrogen bonding to facilitate the formation of a high
mechanical strength 3D graphene hydrogel [22–24].
5.2 Multivalent Metal Ions
Inducing the metal ions into the GO structure is one of the novel methods in graphene
aerogel production. Divalent (Ca2+ , Mg2+ , and Cu2+ ) and trivalent ions (Cr3+ , Fe3+ )
provide better interaction with GO to encourage self-assembly of graphene sheets to
make 3D graphene hydrogel. X. Jiang et al. showed that Ca2+ , Ni2+ , and Co2+ act as
linker resulting in formation of stable 3D graphene hydrogel. The authors optimized
the mass ratio of metal ions to GO, and concluded that the mass ratio of 0.1 was the
best to form 3D graphene hydrogel due to the cross-linking effect of divalent ions
[25].
The effect of using two different types of divalent metal ions on formation and
properties of graphene aerogels was studied by Ghazitabar et al. In this research, Zn2+
and Co2+ were introduced to 3D graphene structure to make the interconnected meso-
porous structure, which was the best choice for electrochemical energy storage appli-
cation. In graphene aerogel structure, the high surface area along with high meso-
porous volume was obtained in the presence of both Zn2+ and Co2+ . In this proposed
model, zinc and cobalt ions were converted to oxide forms without forming any
clusters or agglomerates. This structure had specific and separated sites on graphene
sheets because of adsorption of metal ions on oxygen functional groups on GO sheets
[20]. The proposed mechanism of composite formation is shown in Fig. 3a The TEM
and FESEM images of final composite are illustrated in Fig. 3b, c, respectively. Due
to available separated and monodispersed nanoparticles on graphene sheets, it is
highly recommended to use this method for sensing and catalytic applications such
as electrochemical hydrogen evolution.
5.3 Biomacromolecules
Some of organic materials can interact with graphene oxide sheets to form 3D porous
interconnected structure of graphene hydrogel through hydrogen bonding (in some
cases, covalent or non-covalent interactions), such as polysaccharide [26], polyvinyl
alcohol (PVA) [27], protein [28], and chitosan [29]. The GA, which was synthe-
sized by this route, represented good mechanical stability and compressibility with
less aggregated graphene sheets, becoming suitable for use as sorbent to absorb the
organic and inorganic pollutants. The mechanical stability provided by this method
can facilitate the sorption process in large-scale operations.
Chitosan, as a natural biopolymer, acts as a cross-linking agent through hydrogen
bonding with functional groups on GO sheets to make the 3D graphene aerogel,
providing good potential for organic and inorganic adsorption applications [30].
Cellulose fibers are another potential biomaterials, which have been used as building
blocks in graphene aerogel composites applicable in various applications such as
heavy metal ions adsorption and flexible supercapacitors. Cellulose has numerous
hydroxyl groups, which can form hydrogen bonding to functional groups on graphene
Fig. 3 a Mechanism of composite formation, b TEM image of composite aerogel, and c FESEM
image of composite aerogel [20]. Adapted with permission [20], Copyright (2023), Elsevier
sheets in order to enhance the formation of 3D interconnected porous structure in

graphene aerogel, as given in Fig. 4a. Researchers used the cellulose fibers and
magnetite nanoparticles in graphene aerogel structure to make the specific Au adsor-
bent from cyanide solution. Cellulose fibers increased the compression strength (at
the 50% strain) of graphene aerogel more than 27% (Fig. 4b). The authors reported
that the adsorption capacity of this adsorbent was 112 mg Au per 1 g of graphene
aerogel composite, which was higher than the results reported in previous studies
due to cross-linking role of cellulose fibers [31].
Fig. 4 a SEM image of cellulose/Fe3 O4 nanoparticle/graphene aerogel composite (GCM) and

b compression test of Fe3 O4 nanoparticle/graphene aerogel (GM) and GCM composites [31].
In the recent work, researchers evaluated different types of cellulose fibers to be

used as cross-linking agent for 3D graphene structure. Microfiber and nanofiber of
cellulose were dispersed separately in GO solution, and chemically were reduced by
reducing agents to form graphene aerogel composites to use as sorbent for organic
pollutants removal (Fig. 5a, b). In the microfiber cellulose-bearing composite, the
reduced graphene sheets were folded around the cellulose fibers, (Fig. 5c), which
resulted in increasing the hydrophobicity of final structure. However, in the case
of cellulose nanofibers, graphene sheets were converted to 3D porous structure with
well-dispersed nanofibers between the sheets to make a hydrophilic sorbent (Fig. 5d)
[15].
6 Template-Based Method
The porous structure of graphene aerogels, which was mentioned in previous sections,
had an irregular shape and randomly arrangements. The template-based method is
introduced to obtain the specific shape and size of pores in graphene aerogel structure.
In this method, the resulting macropores are uniform as a replica of the template.
Indeed, the template and its porous morphology structure can predict the shape and
size of pores in 3D graphene aerogel. Three sub-categories for this method are briefly
introduced in the following.
Fig. 5 a Sorption process of toluene stained with Sudan red by GA with cellulose microfibers (top)
and b cellulose nanofibers (bottom), SEM images of c GA with cellulose microfibers and (d) GA
with cellulose nanofibers [15]. Adapted with permission [15], Copyright (2023), Elsevier
6.1 Chemical Vapor Deposition (CVD)
In this method, a foam, such as nickel foam, is used as template to grow the 3D
graphene by means of chemical deposition of carbon in gas phase followed by etching
the metallic foam in acidic solution to obtain the 3D structure of graphene [32]. The
porous structure obtained in final 3D graphene is related to the initial design of the
template. The porous metallic frameworks (nickel foam), oxides (silica nanospheres
and MgO nanoparticles), crystalline aluminosilicate minerals (zeolites), biomorphic
templates (seashells), and dielectric substrate (Al2 O3 ) are the common sacrificed
templates, which are used in 3D graphene fabrication by CVD process.
Banciu et al. synthesized a 3D graphene structure for energy-related applica-

tions by means of CVD process on a nickel foam template. Carbon sources for
this purpose were chosen from gaseous (methane, ethylene, and acetylene), liquid
(ethanol, benzene, styrene, and petroleum asphalt), and solid (polyvinyl alcohol and
camphor) phase. CVD process was carried out at 1000 °C under a hydrogen and argon
atmosphere. The nickel foam was etched by 3 M HCl, after completing the graphene
growth process, in order to prepare a 3D graphene applicable in supercapacitor as
electrode material [33]. In another study, porous MgO was used as sacrificed template
to fabricate 3D graphene structure. In this study, methane was selected as a carbon
precursor to make the graphene nanomesh with large surface area (1654 m2 .g−1 )
in order to use as electrode material for supercapacitor [34]. The similar research
was performed by Shi et al. to fabricate 3D N-doped graphene in order to find use
in catalytic applications due to its extraordinary large surface area (1531 m2 .g−1 ) as
well as being dominant pyrrolic type for nitrogen doping (1.3 wt% N content). In this
research, a mixture of pyridine (C5 H5 N) and methane (CH4 ) was used as nitrogen
and carbon sources, respectively, for CVD process at 900 °C to grow the N-doped
graphene on MgO template [35].
6.2 Template-Directed Self-Assembly
The directional-freezing route is one of the proposed methods to fabricate a highly

compressible graphene aerogel due to providing an anisotropic porous structure.
Liu et al. proposed directional-freezing of graphene hydrogel, followed by freeze-
drying, to obtain a graphene aerogel with a high compressive strength, which made
it a promising highly recyclable material for oil absorption applications [36]. A
progressive method was introduced by Oh et al. They used the directional-freezing
to fill the polyurethane foam with graphene oxide aerogel to use as sound absorber.
This 3D aerogel composite had high resilient properties under cyclic loads, and
presented full sound absorption with thickness of 45 mm at 2000 Hz frequency [37].
The anisotropic structure of graphene aerogel, which is synthesized by directional-
freezing or ice-templated method is a good candidate for Electromagnetic Inter-
ference (EMI) shielding application due to highly arranged tubular pores formed
in its microstructure. Anisotropic polyimide (PI)/graphene composite aerogel was
fabricated by unidirectional freezing of the mixture of GO, poly (amic acid) (PAA)
ammonium salt, and trimethylamine followed by freeze-drying and thermal imidiza-
tion process. The obtained density of the aerogel was 76 mg.cm−3 with EMI shielding
effectiveness (SE) of 26.1–28.8 dB when 13 wt% of the final aerogel was graphene
[38].
Some researchers synthesized a graphene aerogel composite to improve its elas-
ticity and conductivity, applying porous template. Mohsenpour et al. proposed a novel
synthesis route for graphene aerogel composite. They used cellulose and carbon
aerogel (Fig. 6a, b) as a template to fabricate the carbon/graphene aerogel composite
by immersion of monolithic carbon aerogel in GO suspension followed by chemical
reduction and freeze-drying. The synthesized monolithic carbon/graphene aerogel

presented a great electrochemical performance thanks to its high-strength binder-free
electrodes, as shown in Fig. 6c [11].
Fig. 6 The photograph and SEM images of a Cellulose aerogel, b Carbon aerogel, and c Graphene/
carbon aerogel [11]. Adapted with permission [11], Copyright (2023), Elsevier
6.3 Bubble-Based Method
The latest template-based method is using the bubbles as a template to form manage-
able porous structure of GA. The bubbles can be made by fabricating an organic/
inorganic emulsion or purging air bubbles at high shear rate. The earliest attempt
for this method was proposed by Zhang et al. who made a GO/cyclohexane emul-
sion under ultrasonication to fabricate oil phase droplets. They also used NaHSO3
in that mixture, and kept the mixture at 70 °C for 12 h to reduce GO. The GO was
reduced to RGO that led to decrease in hydrophilicity, and gathered around the oil
phase droplets to form a honeycomb network. The time and power of ultrasonication
operation, and the volume ratio of GO:Cyclohexane were the additional parameters
to tailor the porous structure of GA along with other usual synthesis parameters
including time and temperature of the GO mixture as well as the type and amount of
reducing agent. After freeze-drying the obtained hydrogel, the produced GA had an
ultra-light weight (<3 mg.cm−3 ), and exhibited a high mechanical strength in order
to function as a reusable oil absorbent material [39].
In recent works, Zhang et al. proposed the synthesis of ultra-light and superelastic
GA by means of air bubble-templated method. In this process, at first the emulsified
foam of GO/sodium dodecyl sulfonate (SDS)/LAA mixture was created at the high
speed of 2040 rpm. SDS was added to stabilize the bubbles to make a pupil-like rings
structure wherein the graphene sheets were located on the bubbles’ outer layer. After
partially reduction at 75 ºC, the aerogel was obtained by drying at atmospheric pres-
sure. The final aerogel was heat-treated at 500 ºC for further reduction. The uniform
honeycomb-like porous structure was templated by the closely packed air bubbles.
The regular arrangement graphene cell walls provided supercompression resilience
property at compressive strain of 99% at high compressive stress of 87.5 kPa [40]. In
summary, bubble-templated method is one of the major methods to fabricate supere-
lastic ultra-low-density GA in order to make materials such as absorbents widely
applicable for oil removal, soft robot, and flexible devices.
7 3D Printing
Recently, some of the research groups have introduced 3D printing method for
graphene aerogel fabrication. In 3D printing, the parts are built up layer by layer
as depositing materials according to digital 3D design data. This procedure has
several advantages such as proper flexibility, good durability, and high feasibility for
complex designs. Three different sub-categories of 3D printing technique proposed
to fabricate the 3D graphene aerogels are Direct Ink Writing (DIW), Inkjet printing,
and Stereolithography (SLA).
7.1 Direct Ink Writing (DIW)
This method is one of the extrusion-based 3D printing techniques that has been used
to fabricate the lightweight structure. In this technique, extruding the ink through a
micronozzle is done continuously in a three-axis motion stage to make the 3D struc-
ture. The main challenge for this method is to form a proper gel-based viscoelastic
ink, possessing shear-thinning behavior to facilitate the flow under pressure, and a
rapid pseudoplastic characteristic to recover after printing. Therefore, the resulting
graphene aerogel, which is fabricated by this technique, is highly dependent on the
ink formulation and its properties. Graphene oxide (GO) is the main precursor for
ink preparation. Printable GO ink is fabricated by engineering its composition and
rheology to get it applicable for nozzle of DIW technique. As reported in some
studies, the minimum concentration of 5 mg.mL−1 of GO was needed to generate
the required rheological behavior for a 3D printable ink [41]. There are many reports
in which the concentrated alkaline GO suspension, more than 10 mg.mL−1 using
ammonia as pH-adjusting agent, was used as printable ink due to the good gelation
of GO under this condition [3].
Some of the researchers proposed application of cross-linking organic mate-
rials such as resorcinol–formaldehyde (R–F) solution in order to induce the gela-
tion to high concentrated GO suspensions. A few studies indicated that addition
of hydrophilic fumed silica or alumina powders to the GO suspensions caused
an increase in viscosity, and provided non-Newtonian fluid with a shear-thinning
behavior, applicable as a printable ink [42]. As discussed in Sect. 4–2, Ca2+ as a diva-
lent ion can enhance the graphene aerogel formation by increasing the GO suspension
viscosity, and enhancing the gelation of GO suspension. This method was used for ink
preparation by Jiang et al. [43]. Guo et al. fabricated highly recoverable elastic porous
material in 3D form by means of ink-printing solution of GO and multi-walled carbon
nanotubes (MWNTs). In this study, a post-treatment, such as reduction process, was
implemented to accomplish more desired mechanical properties in final 3D-printed
material [44].
Partially reduced GO suspension is another favorite material for being used as
printable ink to fabricate the 3D graphene aerogel. Ultra-light, with the density of
8.5 mg.cm−3 , and elastic 3D graphene aerogel was printed by Peng et al. They
used partially reduced GO inks, prepared by mixing ascorbic acid aqueous solution
and GO suspensions at various mass ratios [45]. In most studies that used DIW
technique, investigating the viscoelasticity of the printed graphene aerogels was the
main research subject. However, some challenges have remained unanswered so far.
One of the challenges is how to print properly a complex and miniature design. In this
case, a small syringe nozzle hole size is needed, meaning that we must incorporate
nanoparticles into the ink. Gue et al. investigated 3D printing of graphene aerogel
using DIW technique in order to function in energy storage devices, and to address
the challenge faced in printing the nano-size graphene ink [46].
7.2 Inkjet Printing
Zhang et al. introduced a novel technique to assemble graphene sheets into macro-
scopic 3D structure by combining inkjet printing and directional-freezing methods
followed by freeze-drying process. The desired printable ink of graphene oxide was
charged into the inkjet printer syringe, and then ejected onto the cold plate (heat
sink) to complete the first layer of designed path. Printing the second layer initiated
when the freezing of first layer was completed at −20 °C to ensure the layer-by-layer
formation of 3D structure. The resulting 3D graphene structure was then emerged
into a liquid nitrogen followed by freeze-drying for 48 h to produce the 3D graphene
aerogel. Heat-treatment process was conducted at 1000 °C, under argon atmosphere,
to increase the conductivity and lightweight of printed graphene aerogel [47]. Such
assemblies have been designed and developed in Graphene and Advanced Materials
Laboratory (GAMLab) in Amirkabir University of Technology to fabricate graphene
hydrogel and aerogel by means of LaserJet and inkjet technologies, respectively
(Fig. 7a, b). The cold base is frozen up to −30 °C to make the frozen graphene in
order to add later layers to form the 3D structure of graphene hydrogel (Fig. 7c).
The fabricated frozen hydrogel is then transferred to the Freeze-dryer (FD-10 V
freeze-dryer, Tajhizat Sazan Pishtaz Co., Iran) to produce the final GA (Fig. 7d).
Fig. 7 Photograph images of a LaserJet and b inkjet technologies of GA formation, c the frozen
3D graphene hydrogel is freeze-dried to make d the ultra-light 3D GA
7.3 Stereolithography (SLA)
In this method, the 3D structure of graphene is made layer by layer employing laser
light that exposes a photocrosslinkable resin to cure it, and to make the 3D graphene.
Herein, the right selection of photocrosslinkable resin materials, to form GO in 3D
structure, is the critical point. Korhonen et al. used GO and the commercial PIC100
as precursors for graphene and photocrosslinkable resin, respectively, to print the 3D
graphene by SLA method. At the first step, GO and PIC100 were stirred in different
mass ratios to make the printable suspension. 3D model was prepared by CAD
software, and the printing was performed by self-made projection stereolithography
(PSLA) system, which used the light intensity of 3900 μW.cm−2 along with various
curing times. The thermal reduction of 3D-printed graphene/polymer was carried
out under nitrogen atmosphere to gain higher electrical conductivity required for
electrical applications [48].
Markandan et al. suggested the SLA method to print a 3D graphene lattice by
graphene at lower concentration, which was reported as disadvantage in previous
similar works. The objective of this work was to achieve the mechanical properties
suitable for various applications including aerospace, automotive, and sports equip-
ment, while fabricating the 3D graphene structure. Graphene platelets were dispersed
in a gray resin, used as photosensitive agent, to make the printable mixture. The 3D
SLA printing was done by 405 nm laser to cure the liquid polymer resin followed by
a thermal reduction process. The authors indicated that SLA technique encouraged
the incorporation of aligned graphene platelets to make 3D graphene structure with
higher mechanical properties [49].
8 Summary
In this chapter, the main 3D graphene synthesis methods were briefly introduced.
Herein, researcher finds the preliminary knowledge and the most probable findings
related to synthesize GA, while using different methods as discussed. However, the
selection of the most proper synthesis method mainly relies on the target application
as well as the available facilities. Of course, the related cost and mass production
feasibilities are the matter of concerns as well. To simplify the decision-making,
and to contribute to the better understanding of all discussed 3D graphene synthesis
methods, the main synthesis parameters along with the properties of the GA produced
employing different synthesis methods are summarized in Table 1.
Table 1 Summary of different GA synthesis methods

Synthesis Main synthesis Main features of GA Application
methods parameters areas
Hydrothermal Temperature, time, and Partially reduced GO without Adsorption
GO concentration any macroscopic voids and good and wearable
mechanical stability devices
Direct GO concentration Highest functional groups and Adsorption
self-assembly of hydrophilic structure
GO
Chemical Temperature, type, and Highly reduced graphene, good Electrodes
reduction concentration of reducing conductivity, lowest oxygen for energy
agent, and GO functional groups, and storage
concentration hydrophobic structure devices
Cross-linking Type and concentration Extraordinary mechanical Adsorption,
agents of cross-linking agent stability and compressive wearable
strength devices and
soft robots
Template-based Precursor composition Highest conductivity, uniform Adsorption,
and type of template porous structure, and high wearable
elasticity devices and
soft robots
3D printing Type of printing method Desirable and complex shape Electronic
and graphene-based and size sensing
charging material
References
1. Wang, J., Ellsworth, M.W.: Graphene aerogels. ECS Trans. 19(5), 241–247 (2009)
2. Ding, M., Li, C.: Recent advances in simple preparation of 3D graphene aerogels based on 2D
graphene materials 10, 1–9 (2022)
3. Kondratowicz, I., Żelechowska, K., Nadolska, M., Jażdżewska, A., Gazda, M.: Comprehensive
study on graphene hydrogels and aerogels synthesis and their ability of gold nanoparticles
adsorption. Colloids Surfaces A Physicochem. Eng. Asp. 528, 65–73 (2017)
4. Huang, Y., Li, C., Lin, Z.: EDTA-induced self-assembly of 3D graphene and its superior
adsorption ability for paraquat using a teabag. ACS Appl. Mater. Interfaces 6(22), 19766–19773
(2014)
5. Liu, H., Qiu, H.: Recent advances of 3D graphene-based adsorbents for sample preparation of
water pollutants: a review. Chem. Eng. J. 393, 124691 (2020)
6. Yuxi Xu, G.S., Sheng, K., Li, C.: Self-assembled graphene hydrogel via a one-step hydrothermal
process. ACS Nano 4(7), 4324–4330 (2010)
7. Nguyen, S.T., Nguyen, H.T., Rinaldi, A., Nguyen, N.P.V., Fan, Z., Duong, H.M.: Morphology
control and thermal stability of binderless-graphene aerogels from graphite for energy storage
applications. Colloids Surfaces A Physicochem. Eng. Asp. 414, 352–358 (2012)
8. Qin, S., Liu, X., Zhuo, R., Zhang, X.: Microstructure-controllable graphene oxide hydrogel
film based on a pH-responsive graphene oxide hydrogel, 1–8
9. Zhao, Z., Wang, X., Qiu, J., Lin, J., Xu, D.: Three-dimensional graphene-based hydrogel/
aerogel materials. Rev. Adv. Mater. Sci 36(2), 137–151 (2014)
10. Li, K., Xu, Y., Angeles, L.: Reversible 3D self-assembly of graphene oxide and stimuli-
responsive polymers and its enabled high-performance graphene-based supercapacitors (2017)
11. Mohsenpour, M., Naderi, M., Ghazitabar, A., Aghabararpour, M., Haghshenas, D.F.: Fabri-
cation of paper based carbon/graphene/ZnO aerogel composite decorated by polyaniline
nanostructure: investigation of electrochemical properties. Ceram. Int. (2021)
12. Zhang, L., Chen, G., Hedhili, M.N., Zhang, H., Wang, P.: Three-dimensional assemblies of
graphene prepared by a novel chemical reduction-induced self-assembly method. Nanoscale
4(22), 7038 (2012)
13. Du, A., Zhou, B., Zhang, Z., Shen, J.: A special material or a new state of matter: a review and
reconsideration of the aerogel, 941–968 (2013)
14. Chen, W., Yan, L.: In situ self-assembly of mild chemical reduction graphene for three-
dimensional architectures. Nanoscale 3(8), 3132 (2011)
15. Hoviatdoost, A., Naderi, M., Ghazitabar, A., Gholami, F.: Fabrication of high-performance
ultralight and reusable graphene aerogel/cellulose fibers nanocomposite to remove organic
pollutants. Mater. Today Commun. 34, 105077 (2023)
16. Qiao, Y., Wen, G.-Y., Wu, X.-S., Zou, L.: l—Cysteine tailored porous graphene aerogel for
enhanced power generation in microbial fuel cells. RSC Adv. 5(72), 58921–58927 (2015)
17. Ghazitabar, A., Naderi, M., Fatmehsari Haghshenas, D.: A facile chemical route for synthesis
of nitrogen-doped graphene aerogel decorated by Co3O4 nanoparticles. Ceram. Int. 44(18),
23162–23171 (2018)
18. Pham, H.D., Pham, V.H., Cuong, T.V.: ChemComm Synthesis of the chemically converted
graphene xerogel with superior electrical conductivity w, c, 9672–9674 (2011)
19. Shadkam, R., Naderi, M., Ghazitabar, A., Asghari-Alamdari, A., Shateri, S.: Enhanced elec-
trochemical performance of graphene aerogels by using combined reducing agents based on
mild chemical reduction method. Ceram. Int. 46(14), 22197–22207 (2020)
20. Ghazitabar, A., Naderi, M., Haghshenas, D.F., Rezaei, M.: Synthesis of N-doped graphene
aerogel/Co 3 O 4/ZnO ternary nanocomposite via mild reduction method with an emphasis on
its electrochemical characteristics. J. Alloys Compd. 794, 625–633 (2019)
21. Hu, K., Xie, X., Szkopek, T., Cerruti, M.: Understanding Hydrothermally Reduced Graphene
Oxide Hydrogels: From Reaction Products to Hydrogel Properties (2016)
22. Wang, X., Nie, S., Zhang, P., Song, L., Hu, Y.: Superhydrophobic and superoleophilic graphene
aerogel for ultrafast removal of hazardous organics from water. J. Mater. Res. Technol., 1–8
(2019)
23. Simón-Herrero, C., Peco, N., Romero, A., Valverde, J.L., Sánchez-Silva, L.: PVA/nanoclay/
graphene oxide aerogels with enhanced sound absorption properties. Appl. Acoust. 156, 40–45
(2019)
24. Sui, Z.Y., Cui, Y., Zhu, J.H., Han, B.H.: Preparation of Three-dimensional graphene oxide-
polyethylenimine porous materials as dye and gas adsorbents. ACS Appl. Mater. Interfaces
5(18), 9172–9179 (2013)
25. Jiang, X., Ma, Y., Li, J., Fan, Q., Huang, W.: Self-assembly of reduced graphene oxide into
three-dimensional architecture by divalent ion linkage. J. Phys. Chem. C 114(51), 22462–22465
(2010)
26. Guastaferro, M., Reverchon, E., Baldino, L.: Polysaccharide-based aerogel production for
biomedical applications: a comparative review. Materials (Basel) 14(7) (2021)
27. Rapisarda, M., Malfense Fierro, G.P., Meo, M.: Ultralight graphene oxide/polyvinyl alcohol
aerogel for broadband and tuneable acoustic properties. Sci. Rep. 11(1), 1–10 (2021)
28. Zhuang, Y., Yu, F., Ma, J., Chen, J.: Facile synthesis of three-dimensional graphene–soy protein
aerogel composites for tetracycline adsorption. Desalin. Water Treat. 57(20), 9510–9519 (2016)
29. Pinelli, F., Nespoli, T., Rossi, F.: Graphene oxide-chitosan aerogels: Synthesis, characterization,
and use as adsorbent material for water contaminants. Gels 7(4), (2021)
30. Luo, J., Fan, C., Xiao, Z., Sun, T., Zhou, X.: Novel graphene oxide/carboxymethyl chitosan
aerogels via vacuum-assisted self-assembly for heavy metal adsorption capacity. Colloids
Surfaces A 578, 123584 (2019)
31. Ghazitabar, A., Naderi, M., Haghshenas, D.F., Ashna, D.A.: Graphene aerogel/cellulose fi bers/
magnetite nanoparticles (GCM) composite as an effective Au adsorbent from cyanide solution
with favorable electrochemical property. J. Mol. Liq. 314, 113792 (2020)
32. Jiang, W., Xin, H., Li, W.: Microcellular 3D graphene foam via chemical vapor deposition of
electroless plated nickel foam templates. Mater. Lett. 162, 105–109 (2016)
33. Banciu, C.A., Florin Nastase, L.M.V.: Anca-Ionela Istrate, “3D graphene foam by chemical
vapor deposition: synthesis, properties, and energy-related applications. Molecules 27, 3634
(2022)
34. Ning, G., Fan, Z., Wang, G., Gao, J., Qian, W., Wei, F.: Gram-scale synthesis of nanomesh
graphene with high surface area and its application in supercapacitor electrodes. Chem.
Commun. 47(21), 5976–5978 (2011)
35. Le Shi, J., Tang, C., Huang, J.Q., Zhu, W., Zhang, Q.: Effective exposure of nitrogen heteroatoms
in 3D porous graphene framework for oxygen reduction reaction and lithium–sulfur batteries.
J. Energy Chem. 27(1), 167–175 (2018)
36. Liu, T., Huang, M., Li, X., Wang, C., Gui, C., Yu, Z.: Beijing Key Laboratory on Preparation
and Processing of Novel Polymer Materials, Beijing,” Carbon N. Y., (2016)
37. Oh, J.H., Kim, J., Lee, H., Kang, Y., Oh, I.K.: Directionally antagonistic graphene oxide-
polyurethane hybrid aerogel as a sound absorber. ACS Appl. Mater. Interfaces 10(26), 22650–
22660 (2018)
38. Yu, Z., Dai, T., Yuan, S., Zou, H., Liu, P.: Electromagnetic interference shielding performance
of anisotropic polyimide/graphene composite aerogels. ACS Appl. Mater. Interfaces 12(27),
30990–31001 (2020)
39. Zhang, B. et al.: Cellular graphene aerogel combines ultralow weight and high mechanical
strength: a highly efficient reactor for catalytic hydrogenation. Sci. Rep. 6, 25830 (2016)
40. Xiaofang Zhang, J.Z., Zhang, T., Wang, Z., Ren, Z., Yan, S., Duan, Y.: Ultralight , superelastic
and fatigue resistant graphene aerogel templated by graphene oxide liquid crystal stabilized air
bubbles. Appl. mat (2018)
41. Palaganas, J.O., Palaganas, N.B., Ramos, L.J.I., David, C.P.C.: 3D printing of covalent func-
tionalized graphene oxide nanocomposite via stereolithography. ACS Appl. Mater. Interfaces
11(49), 46034–46043 (2019)
42. Zhu, C., et al.: Highly compressible 3D periodic graphene aerogel microlattices. Nat. Commun.
6, 1–8 (2015)
43. Jiang, Y., et al.: Direct 3D printing of ultralight graphene oxide aerogel microlattices. Adv.
Funct. Mater. 28(16), 1–8 (2018)
44. Guo, F., et al.: Highly stretchable carbon aerogels. Nat. Commun. 9(1), 1–9 (2018)
45. Peng, M., et al.: 3D printing of ultralight biomimetic hierarchical graphene materials with
exceptional stiffness and resilience. Adv. Mater. 31(35), 1–9 (2019)
46. Guo, B., Liang, G., Yu, S., Wang, Y., Zhi, C., Bai, J.: 3D printing of reduced graphene oxide
aerogels for energy storage devices: a paradigm from materials and technologies to applications.
Energy Storage Mater. 39, 146–165 (2021)
47. Zhang, F., Yang, F., Lin, D., Zhou, C.: Parameter study on 3D-printing graphene oxidize based
on directional freezing. ASME 2016 11th Int. Manuf. Sci. Eng. Conf. MSEC 2016, vol. 3,
pp. 1–11 (2016)
48. Korhonen, H., et al.: Fabrication of graphene-based 3D structures by stereolithography. Phys.
Status Solidi Appl. Mater. Sci. 213(4), 982–985 (2016)
49. Markandan, K., Lai, C.Q.: Enhanced mechanical properties of 3D printed graphene-polymer
composite lattices at very low graphene concentrations. Compos. Part A 129, 105726 (2020)
Synthesis and Characteristics of 3D
Graphene
Hiran Chathuranga, Ishara Wijesinghe, Ifra Marriam, and Cheng Yan
Abstract Three-dimensional (3D) graphene structures have high electrical conduc-

tivity, excellent mechanical properties, high porosity, and large surface area,
demonstrating great potential for broad applications, including sensors, absorbents
, solar cells, flexible batteries, supercapacitors, and fuel cells. Their physical and
chemical properties are mainly determined by the synthesis methods. Numerous
fabrication methods have been successfully developed to tailor the structures and
properties of 3D graphene structures. In general, the synthesis approaches can be
categorized as template-assisted methods (e.g., chemical vapor deposition, template-
assisted graphene oxide (GO) reduction, soft template techniques, and ice templating)
and template-free methods (e.g., GO crosslinking, assembly of GO by reduction,
3D printing, and sugar blowing). In addition, 3D graphene structures can be also
produced using other techniques like roll-to-roll (R2R) manufacturing and 3D
laser-induced manufacturing. Therefore, in this chapter, the recent advances in the
synthesis and characteristics of 3D graphene structures are discussed.
Keywords 3D graphene · 3D graphene synthesis · Methods · Template-assisted

synthesis · Template-free synthesis
1 Introduction
Graphene, a two-dimensional material (2D) containing sp2 -hybridized carbon

atoms arranged into a honeycomb-like structure, has attracted unprecedented
research interest in recent years owing to its remarkable properties, including
high electron mobility (250,000 cm2 V−1 ), excellent thermal conductivity
(2000–5000 Wm−1 K−1 ), and strong mechanical strength (Young’s modulus of
~1 TPa) [1, 2]. Despite these extraordinary properties, the use of graphene in prac-
tical applications has been hindered due to the challenges like high contact resistance
H. Chathuranga · I. Wijesinghe · I. Marriam · C. Yan (B)

School of Mechanical, Medical and Process Engineering, Faculty of Engineering, Queensland
University of Technology, 2 George St, Brisbane, QLD 4000, Australia
e-mail: c2.yan@qut.edu.au

https://doi.org/10.1007/978-3-031-36249-1_3
44 H. Chathuranga et al.
Fig. 1 Synthesis methods of 3D graphene structures
between individual graphene sheets and agglomeration of graphene due to strong van
der Waals interactions. Many efforts have been made to address these issues, and the
assembly of graphene into 3D structures has been identified as one of the promising
solutions [3–6].
In recent years, extensive efforts have been devoted to fabricating 3D graphene
structures with outstanding physical and chemical properties. In general, the fabri-
cation of 3D graphene structures can be divided into two main categories: template-
assisted methods and template-free methods (Fig. 1) [7, 8]. In template-assisted
methods, a template is used to assemble the 3D graphene network. The commonly
used template-assisted methods are chemical vapor deposition, template-assisted
GO reduction, soft template techniques, and ice templating. On the other hand, 3D
graphene structures can also be synthesized without using a template. Here, GO
or its derivatives are directly assembled into 3D structures using physical and/or
chemical methods such as GO crosslinking, assembly of GO by reduction, and 3D
printing [9–13]. Furthermore, manufacturing techniques like R2R manufacturing and
3D laser-induced manufacturing can be used to synthesize 3D graphene structures in
large quantities. Thus, the fabrication of 3D graphene structures using these methods
is discussed in this chapter.
2 Synthesis of 3D Graphene
2.1 Template-Assisted Synthesis Methods
2.1.1 Chemical Vapor Deposition
Chemical vapor deposition (CVD) is a process that involves decomposing a carbon

precursor onto a metal substrate to form single- or multilayer graphene sheets.
3D graphene structures can be synthesized by CVD using prefabricated 3D metal
Synthesis and Characteristics of 3D Graphene 45
templates as the substrate [3]. The commonly applied metal substrates to grow 3D
graphene are copper (Cu) and nickel (Ni), and the growth mechanisms of graphene
on these two substrates are different. Graphene growth on the Cu substrate is mainly
governed by surface growth, resulting in the formation of single-layer graphene
sheets. As a result of the weak connectivity of single-layer graphene sheets, forming
3D graphene networks using Cu substrate is difficult, and these 3D graphene struc-
tures break down easily during handling. Graphene has two growth mechanisms
when grown on Ni substrate: surface growth and carbon dissolution–precipitation.
Thus, multiple layers of graphene can be grown on the Ni substrate, improving the
strength and stability of the 3D graphene structure [4, 14].
Synthesis of 3D graphene using Ni substrate is first demonstrated by Chen and co-
workers in 2011 [15]. In their pioneering work, commercial Ni foam was used as the
3D substrate and graphene was grown on this substrate by introducing methane gas
(CH4 ) at 1000 °C under atmospheric pressure. Next, the surface of the 3D structure
was coated with a thin layer of poly (methyl methacrylate) (PMMA) to prevent the
graphene structure from collapsing during Ni etching. Subsequently, Ni was etched
using hot hydrochloric acid (HCl) or ferric chloride (FeCl3 ), and a free-standing 3D
graphene structure was obtained after removing PMMA using acetone (Fig. 2a). The
as-prepared 3D graphene structure demonstrated high porosity (99.7%), excellent
specific surface area (850 m2 g−1 ), and low density (5 mg cm−3 ). However, these 3D
graphene structures often suffer from drawbacks like large pore size (200–500 μm),
structural properties determined by the commercial Ni foam, and porous structure
collapsing during handling.
Meanwhile, Ito et al. developed a nano-porous 3D graphene structure using a nano-
porous Ni substrate [16]. The nano-porous Ni substrate was produced by leaching Mn
from the Ni30 Mn70 alloy. Graphene was grown on this nano-porous substrate using
benzene, argon (Ar), and hydrogen (H2 ) precursors at 900 °C, and nano-porous 3D
graphene was obtained by etching Ni substrate using HCl (Fig. 2b, c). In comparison
to commercial Ni foam-based 3D graphene, nano-porous Ni substrate-based 3D
graphene has a homogeneous porosity, and the pore size of nano-porous 3D graphene
structure can be tailored by altering the temperature and graphene growing time of the
CVD process. For instance, the average pore sizes of the nano-porous 3D graphene
structures grown at 800 °C for 5 min and 1000 °C for 10 min were ~250 nm and
~3 μm, respectively [17, 18]. Moreover, these 3D graphene structures have better
structural and mechanical stabilities owing to the bi-continuous architecture.
In addition to Ni and Cu templates, several other oxides have also been employed
as porous substrates for the CVD synthesis of 3D graphene, including SiO2 [19],
CaO [20], Al2 O3 [21], and MgO [22]. For example, Nishihara et al. employed Al2 O3
nanoparticles for the CVD growth of 3D graphene [21]. The resulting graphene
structure demonstrated a large surface area (1940 m2 g−1 ), high electrical conduc-
tivity (~8 S cm−3 ), and low density (0.4 g cm−3 ). In this process, first, graphene was
grown on the Al2 O3 nanoparticles using CH4 gas at 900 °C. Afterward, 3D graphene
or graphene mesosponge (GMS) was obtained by removing Al2 O3 using NaOH.
Finally, the 3D structure was annealed at 1800 °C for 2 h to improve the crystallinity
(Fig. 2d). The Al2 O3 substrate-based 3D graphene has fine mesopores (~5.8 nm).
Fig. 2 Schematic illustration of the fabrication process of 3D graphene using a commercial Ni foam
substrate. Adapted with permission [14]. Copyright (2021) © The Authors, some rights reserved;
exclusive licensee John Wiley and Sons. Distributed under a Creative Commons Attribution License
4.0 (CC BY) and b nano-porous Ni substrate. Adapted with permission [4]. Copyright (2022) John
Wiley and Sons. c SEM image of the nano-porous 3D graphene. Adapted with permission [16].
Copyright (2014) John Wiley and Sons. d Schematic demonstration of the synthesis steps of 3D
graphene using Al2 O3 substrate. Adapted with permission [21]. Copyright (2016) John Wiley and
Sons
However, these mesopores have a spherical shape, and the interconnectivity of these
pores is poor.
2.1.2 Template-Assisted GO Reduction Process
In this synthesis method, first, the templates were soaked in GO solution. Next,
these templates were chemically or physically treated to convert GO into reduced
graphene oxide (rGO). Finally, the 3D graphene structure was obtained by removing
the template skeleton using chemical etching (for metallic templates) or thermal
decomposition (for polymeric templates). Su et al. used this technique to synthesize
a 3D graphene structure for the non-invasive detection of tumor cells [23]. The 3D
graphene structure was fabricated by immersing a Ni foam in an aqueous GO solution,
converting GO into rGO with hydrazine (N2 H4 .H2 O), followed by the removal of
Ni foam using HCl (Fig. 3a). In another study, Yang and co-workers immersed a
polyurethane (PU) sponge in a GO dispersion and annealed it at 900 °C for 2 h
in an inert environment to achieve a sponge-shaped 3D graphene structure with
a high specific surface area (305 m2 g−1 ), good pore size distribution (>3.5 nm),
and excellent electrosorptive capacity (4.95 mg g−1 ) (Fig. 3b) [24]. Although the
synthesis of 3D graphene using this technique is straightforward, the resulting 3D
graphene structures are associated with issues like poor quality owing to the stacking
of GO sheets and difficulty in controlling the pore size.
2.1.3 Freeze-Casting or Ice Templating
In freeze-casting, first, an aqueous slurry of GO is subjected to freezing, which causes

ice crystals to form on the freezing side of the slurry and advance along the temper-
ature gradient. Once the freezing has ended, the solid structure is freeze-dried to
remove the ice crystal, and the resulting samples will have pores similar to subli-
mated crystals. Finally, the 3d structure is thermally treated to enhance physical
properties [25, 26]. The freeze-casting method has numerous benefits, including a
simple operating procedure, low cost, and the ability to adjust the pore structure.
For example, Zhang and colleagues utilized the freeze-casting technique to develop
a vertically aligned graphene membrane as a solar thermal converter to produce
clean water (Fig. 3c) [27]. This converter exhibited maximum solar thermal conver-
sion efficiency of 94.2%. In another study, Wu et al. fabricated a 3D graphene/
polyaniline composite for supercapacitor electrodes [28]. The 3D graphene struc-
ture was designed using the freeze-casting method. After freeze-drying and reducing
GO, polyaniline was introduced into the 3D structure by in situ polymerization. The
graphene/polyaniline electrode demonstrated improved specific capacitance (538 F
g−1 at 1.0 A g−1 ) and cycle stability (74% specific capacitance after 1000 cycles).
Fig. 3 Schematic diagrams of the preparation process of the a Ni-Foam (adapted with permission
[23]. Copyright (2021) Elsevier) and b PU sponge (adapted with permission [24]. Copyright (2014)
John Wiley and Sons)-assisted 3D graphene structure. c 3D graphene synthesis using freeze-casting
method. Adapted with permission [27]. Copyright (2017) American Chemical Society
2.1.4 Soft Template Techniques
Soft templates like emulsions or gases can also be employed to develop 3D graphene
structures. When compared with hard template methods, soft template approaches
have numerous advantages like low cost, facile manufacturing steps, and the ability
to alter the pore diameter of 3D graphene structure from nano-scale to micro-scale
[29, 30]. For instance, Yeo et al. developed a rhombic dodecahedral honeycomb 3D
graphene structure using a hierarchical design strategy [31]. First, GO was func-
tionalized with alkylating agents. The alkylated GO sheets were micro-fluidically
treated to generate micro-scale spherical solid-shelled bubbles. Subsequently, these
homogeneous bubbles were assembled into a 3D structure through post-treatment.
Finally, the thermal reduction process was used to obtain the 3D graphene frame-
work (Fig. 4a, b). The as-prepared 3D graphene structure demonstrated a rhombic
dodecahedral honeycomb structure (Fig. 4c). Furthermore, it exhibited high Young’s
modulus (300 kPa), low density (7.7 mg cm−3 ), and excellent compressive strain
(87%). Meanwhile, Barg et al. also fabricated a 3D graphene structure by combing
Fig. 4 a Soft template-assisted multiscale design of 3D graphene. b Photograph and c SEM image
of the rhombic dodecahedral honeycomb 3D graphene. Adapted with permission [31]. Copyright
(2018) John Wiley and Sons. d Assembly strategy of the 3D graphene structure using combined
soft templating and ice templating techniques. Adapted with permission [32]. Copyright (2014) ©
The Authors, some rights reserved; exclusive licensee Springer Nature. Distributed under a Creative
Commons Attribution License 4.0 (CC BY)
soft templating with ice templating, and the resulting graphene structure illustrated
outstanding morphological properties (Fig. 4d) [32].
2.2 Template-Free Synthesis Methods
2.2.1 Crosslinking
3D graphene structures can be synthesized by crosslinking GO sheets using numerous

gelling agents. GO hydrogels are formed during the crosslinking of GO sheets,
and after reduction and freeze-drying, the 3D graphene structure can be obtained.
Polyvinyl alcohol (PVA), polyaniline, poly (N-isopropyl acrylamide), sodium algi-

nate, cyclodextrin, metal ions (Mg2+ , Fe3+ , and Ni2+ ), and chitosan-like crosslinkers
have been widely used to make 3D graphene structures [12, 33, 34]. PVA is the
first crosslinker used in 3D graphene synthesis [35]. The hydrogen bonds formed
between PVA and functional groups (hydroxyl, epoxy, and carboxyl) of GO sheets
cause gelation during hydrogel formation. Remarkably, this crosslinked hydrogel
formation is pH dependent, as at high pH levels the hydrogel remains in aqueous
form while at acidic pH levels, it gels. Moreover, the hydrogels formed with acidic
conditions are strong because of π–π stacking between graphene sheets.
It is reported that the crosslinking mechanisms depend on the type of crosslinkers
used in the hydrogel formations. For example, it is a nucleophilic addition mechanism
when GO is reduced with chitosan, where epoxy groups in GO react with the amino
groups of chitosan [36]. Another benefit of this 3D graphene synthesis method is its
flexibility, which enables the fabrication of flexible structures such as beads. These
beads are formed by injecting GO drops and crosslinkers into a gelling agent followed
by washing and removing excess chemicals [37]. Further, additional properties like
magnetic properties can be included in these materials by adding Fe+3 ions.
2.2.2 Assembly of GO by Reduction
GO is an amphiphilic 2D material. Hence, preparing GO dispersions using solvents

like water is relatively easy due to the formation of H-bonds between water molecules
and functional groups of GO sheets. However, when these interactions are unstabi-
lized via GO reduction techniques, GO sheets coagulate and form hydrogels, after
freeze-drying these hydrogels, free-standing 3D graphene structures can be obtained.
Acids, hydrazine, metals, metal oxides, and reducing salts have been used as reducing
agents [38]. The nature of the reducing agent affects the 3D graphene’s properties (to
produce uniform structures of 3D graphene mild reducing agents have been used).
Furthermore, during GO reduction, the mixture should not be stirred, as it disturbs
the stacking of graphene into 3D structures. In addition, plant derivatives such as
extracts of tea leaves, roselle flowers, and spinach leaves have also been found as
effective reducing agents [39–41].
Hydrothermal reduction of GO sheets has also been identified as a template-
free approach to synthesizing 3D graphene. Here, a GO solution in a Teflon-
lined hydrothermal reactor is heated under pressure to enable the construction of
3D graphene hydrogels. Zhuang and co-workers designed a reduced GO nanofil-
tration membrane using the hydrothermal method [42]. The resultant membrane
exhibited excellent water purification performance, rejecting ~100% organic dye
at 53 L m−2 h−1 water flux (Fig. 5a). In another study, Wasalathilake et al. fabricated
3D graphene structures with various pore sizes using a pH-assisted hydrothermal
process [43]. They found that the 3D graphene structures with small pores and thick
walls exhibit the best mechanical properties. Besides, 3D graphene structure with
small pores has the highest electrical conductivity owing to the highly interconnected
structure. Meanwhile, the hydrothermal process can be converted into a solvothermal
process by changing the dispersion medium of water with a solvent [44]. Moreover,
the ability of these hydrothermal and solvothermal techniques to surface functionalize
3D graphene structures with diverse end groups is an added benefit.
Fig. 5 a Synthesis of 3D graphene using hydrothermal method. Adapted with permission [42].
Copyright (2021) © The Authors, some rights reserved; exclusive licensee American Chemical
Society. Distributed under a Creative Commons Attribution License 4.0 (CC BY) b 3D printing of
graphene structures using silica/GO ink. c Photograph and d SEM image of the 3D-printed graphene
structure. Adapted with permission [47]. Copyright (2015) © The Authors, some rights reserved;
exclusive licensee Springer Nature. Distributed under a Creative Commons Attribution License 4.0
(CC BY) e 3D printing of graphene structures using GO/Ca+2 ink. Adapted with permission [48].
Copyright (2018) John Wiley and Sons
2.2.3 3D Printing
3D printing is a manufacturing technique that constructs 3D objects using computer-

aided designed (CAD) models. Numerous materials, including polymers, metals, and
ceramics, can be used as precursors in 3D printing. Recently, manufacturing of 3D
graphene structures using the 3D printing method has attracted a lot of attention owing
to the advantages like low cost, short design-manufacturing cycle, scalability, and the
possibility to design complex 3D objects in large quantities [45, 46]. For instance,
Zhu et al. fabricated a lightweight and highly conductive graphene aerogel using a 3D
printing method called direct ink writing [47]. Here, the 3D printing ink was synthe-
sized by mixing silica powder with a GO solution, which improved the viscosity of
the ink. After printing, the 3D structure was freeze-dried and carbonized. Finally,
the silica filler was etched to produce the 3D graphene framework (Fig. 5b). The
3D-printed graphene structure demonstrated 90% compressive strain, high surface
area (~1000 m2 g−1 ), and large mesopores (3 cm3 g−1 ) (Fig. 5c, d). In a similar
study, Jiang et al. 3D-printed a graphene structure using GO/Ca+2 ink [48]. After
printing, the free-standing 3D graphene structure was obtained via freeze-drying
and hydroiodic acid (HI) reduction (Fig. 5e). To demonstrate the potential appli-
cations, this 3D graphene structure was employed as supercapacitor electrodes and
exhibited outstanding gravimetric capacitance (213 F g−1 ) and cyclic performance
(50 000 cycles).
2.2.4 Sugar Blowing Technique
Sugar-blown 3D graphene foams can be developed using a glucose and ammo-

nium chloride mixture followed by heating at 1350 °C [12, 49]. Here, a mixture of
glucose with ammonium chloride at a 1:1 ratio was heated for 3 h at a heating rate of
4 °C min−1 under Ar atmosphere in a tube furnace (Fig. 6a). In principle, the molten
glucose syrup was formed by the decomposition products of the ammonium mixture
to produce graphene, while the subsequent heating forms the 3D graphene structure.
The 3D graphene produced with this method was a pack of polyhedral bubbles with
an average diameter of 186 μm.
2.3 Scalable Production of 3D Graphene
Despite extensive research into various 3D graphene production techniques, scaling

up the processes to produce high-quality 3D graphene structures has proven to be a
persistent obstacle. The goal of 3D graphene synthesis on a large scale is to provide
3D graphene for real-world applications. The requirement to accomplish this goal is a
low production cost. Generally, the prices of 3D graphene structures produced using
Ni foams are very high (~$100–600/1 cm3 ) when compared with similar commercial
products. To reduce the production cost of 3D graphene, the development of simple
Fig. 6 a Growth of 3D graphene using sugar-blown technique. Adapted with permission [49].
Copyright (2013) Springer Nature. b R2R manufacturing of 2D graphene. Adapted with permission
[50]. Copyright (2015) © The Authors, some rights reserved; exclusive licensee Springer Nature.
Distributed under a Creative Commons Attribution License 4.0 (CC BY) c R2R manufacturing
of laser-induced 3D graphene films. Adapted with permission [51]. Copyright (2018) American
Chemical Society
and large-scale processes is critically important. Therefore, in this section, recent

advances in the mass production of 3D graphene structures are discussed.
It is possible to scale up the CVD synthesis of 2D graphene using Cu or Ni metal
foils as templates. This novel technique is called R2R manufacturing of 2D graphene
[50]. As illustrated in Fig. 6b, this process contains a concentric tube reactor which
continuously deposits graphene on a metal foil. In this system, a ribbon of metal foil
is fed through from one end of the reactor and graphene sheets are grown on this
foil using C2 H4 and H2 gases. Subsequently, graphene-deposited metal foil exists
from the reactor and is rolled up for further processing. Here, the R2R manufacturing
technique has only been used for the large-scale synthesis of 2D graphene. However,
this technique can be applied to the mass production of 3D graphene by substituting
the metal foils with thin and flexible metal foams.
Meanwhile, 3D graphene films can be produced by utilizing the laser-induced
on-site polymerization method. This technique has many advantages such as low
manufacturing time, availability of many substrates, and mild reaction conditions.
Furthermore, these 3D graphene films can be directly applied as electrode materials
for energy storage, sensors, flexible wearable devices, adsorbents, etc. As shown in
Fig. 6c, Ye et al. reported the R2R manufacturing of 3D laser-induced 3D graphene
films [51]. In this manufacturing process, the laser source is fixed, and the laser beam
is focused on a line to maximize efficiency. Then, the polymer substrate (polyimide)
is constantly fed into the laser chamber and subjected to the laser to form 3D graphene
films. Afterward, this film is immersed in a catalyst bath to obtain hybrid structures.
Finally, the film is dried and collected by a roller.
2.4 Conclusion and Outlook
Graphene with sp2 -hybridized carbon atoms arranged into a 2D honeycomb-like

structure has attracted a lot of research interest owing to its outstanding electrical,
thermal, and mechanical properties. However, restacking and high contact resis-
tance of graphene sheets have hindered its practical applications, especially at a
large scale. These challenges can be largely overcome by assembling graphene or
its derivatives into 3D structures. Typically, 3D graphene structures can be synthe-
sized using two techniques: template-assisted synthesis and template-free synthesis.
For the template-assisted approach, a template is used to assemble the 3D graphene
structure. Then, the template can be removed via chemical etching or thermal decom-
position. With the template-free method, graphene or its derivatives are assembled
into 3D graphene structures by altering their interfacial properties. Despite recent
advances, numerous challenges remain in the development of 3D graphene structures
with unique properties, which include
• Each 3D graphene structure exhibits distinctive features based on its unique struc-
ture. Therefore, to establish a structure–property relationship in 3D graphene
structures, comprehensive and standardized characterization methodologies need
to be developed.
• Less focus is given to analyzing the effects of internal and external defects in
3D graphene structures. Hence, understanding the role of defects in the overall
performance of 3D graphene structures is required.
• Only a few studies have focused on the industry-scale fabrication of 3D graphene.
So, more attention should be given to upgrading the lab-scale processes to
industry-scale technologies. Also, optimizing the process window against cost,

property, and environmental considerations should be prioritized.
• Future research can be focused on multifunctional 3D graphene structures by
coupling graphene with other functional materials like CNTs, MXenes, TMDs,
and functional polymers.
References
1. Novoselov, K.S., Fal' ko, V.I., Colombo, L., Gellert, P.R., Schwab, M.G., Kim, K.: A roadmap
for graphene. Nature 490, 192–200 (2012)
2. Lee, C., Wei, X., Kysar, J.W., Hone, J.: Measurement of the elastic properties and intrinsic
strength of monolayer graphene. Science 321(80), 385–388 (2008)
3. Sun, Z., Fang, S., Hu, Y.H.: 3D graphene materials: from understanding to design and synthesis
control. Chem. Rev. 120, 10336–10453 (2020)
4. Han, J., Johnson, I., Chen, M.: 3D continuously porous graphene for energy applications. Adv.
Mater. 34, e2108750 (2022)
5. Yun, Q., Ge, Y., Chen, B., Li, L., Wa, Q., Long, H., Zhang, H.: Hybridization of 2D nanomate-
rials with 3D graphene architectures for electrochemical energy storage and conversion. Adv.
Funct. Mater., 32 (2022)
6. Zhao, H.Y., Yu, M.Y., Liu, J., Li, X., Min, P., Yu, Z.Z.: Efficient Preconstruction of Three-
Dimensional Graphene Networks for Thermally Conductive Polymer Composites. Springer
Nature Singapore (2022)
7. Zhi, D., Li, T., Li, J., Ren, H., Meng, F.: A review of three-dimensional graphene-based aero-
gels: synthesis, structure and application for microwave absorption. Compos. Part B Eng. 211,
108642 (2021)
8. Xiao, W., Li, B., Yan, J., Wang, L., Huang, X., Gao, J.: Three dimensional graphene composites:
preparation, morphology and their multi-functional applications. Compos. Part A Appl. Sci.
Manuf. 165, 107335 (2023)
9. Sun, H., Lin, Y., Takeshi, H., Wang, X., Wu, D., Tian, Y.: Synthesis of 3D graphene-based
materials and their applications for removing dyes and heavy metals. Environ. Sci. Pollut. Res.
28, 52625–52650 (2021)
10. Shi, Q., Cha, Y., Song, Y., Lee, J.I., Zhu, C., Li, X., Song, M.K., Du, D., Lin, Y.: 3D graphene-
based hybrid materials: Synthesis and applications in energy storage and conversion. Nanoscale
8, 15414–15447 (2016)
11. Bano, Z., Mazari, S.A., Saeed, R.M.Y., Majeed, M.A., Xia, M., Memon, A.Q., Abro, R., Wang,
F.: Water decontamination by 3D graphene based materials: a review. J. Water Process Eng.
36, 101404 (2020)
12. Hiew, B.Y.Z., Lee, L.Y., Lee, X.J., Thangalazhy-Gopakumar, S., Gan, S., Lim, S.S., Pan, G.T.,
Yang, T.C.K., Chiu, W.S., Khiew, P.S.: Review on synthesis of 3D graphene-based configura-
tions and their adsorption performance for hazardous water pollutants. Process Saf. Environ.
Prot. 116, 262–286 (2018)
13. Fang, Q., Shen, Y., Chen, B.: Synthesis, decoration and properties of three-dimensional
graphene-based macrostructures: a review. Chem. Eng. J. 264, 753–771 (2015)
14. Zeng, J., Xu, C., Gao, T., Jiang, X., Bin Wang, X.: Porous monoliths of 3D graphene for electric
double-layer supercapacitors. Carbon Energy 3, 193–224 (2021)
15. Chen, Z., Ren, W., Gao, L., Liu, B., Pei, S., Cheng, H.M.: Three-dimensional flexible and
conductive interconnected graphene networks grown by chemical vapour deposition. Nat.
Mater. 10, 424–428 (2011)
16. Ito, Y., Tanabe, Y., Qiu, H.-J., Sugawara, K., Heguri, S., Tu, N.H., Huynh, K.K., Fujita, T.,
Takahashi, T., Tanigaki, K., Chen, M.: High-quality three-dimensional nanoporous graphene.
Angew. Chemie Int. Ed. 53, 4822–4826 (2014)
17. Han, J., Guo, X., Ito, Y., Liu, P., Hojo, D., Aida, T., Hirata, A., Fujita, T., Adschiri, T., Zhou,
H., Chen, M.: Effect of chemical doping on cathodic performance of bicontinuous nanoporous
graphene for Li-O2 batteries. Adv. Energy Mater. 6, 1–9 (2016)
18. Kashani, H., Ito, Y., Han, J., Liu, P., Chen, M.: Extraordinary tensile strength and ductility of
scalable nanoporous graphene. Sci. Adv. 5, 1–7 (2019)
19. Chen, K., Li, C., Shi, L., Gao, T., Song, X., Bachmatiuk, A., Zou, Z., Deng, B., Ji, Q., Ma,
D., Peng, H., Du, Z., Rümmeli, M.H., Zhang, Y., Liu, Z.: Growing three-dimensional biomor-
phic graphene powders using naturally abundant diatomite templates towards high solution
processability. Nat. Commun. 7, 13440 (2016)
20. Han, G.F., Chen, Z.W., Jeon, J.P., Kim, S.J., Noh, H.J., Shi, X.M., Li, F., Jiang, Q., Baek, J.B.:
Low-temperature conversion of alcohols into bulky nanoporous graphene and pure hydrogen
with robust selectivity on CaO. Adv. Mater. 31, 1–7 (2019)
21. Nishihara, H., Simura, T., Kobayashi, S., Nomura, K., Berenguer, R., Ito, M., Uchimura, M.,
Iden, H., Arihara, K., Ohma, A., Hayasaka, Y., Kyotani, T.: Oxidation-resistant and elastic
mesoporous carbon with single-layer graphene walls. Adv. Funct. Mater. 26, 6418–6427 (2016)
22. Sunahiro, S., Nomura, K., Goto, S., Kanamaru, K., Tang, R., Yamamoto, M., Yoshii, T., Kondo,
J.N., Zhao, Q., Ghulam Nabi, A., Crespo-Otero, R., Di Tommaso, D., Kyotani, T., Nishihara,
H.: Synthesis of graphene mesosponge via catalytic methane decomposition on magnesium
oxide. J. Mater. Chem. A 9, 14296–14308 (2021)
23. Su, H., Yin, S., Yang, J., Wu, Y., Shi, C., Sun, H., Wang, G.: In situ monitoring of circulating
tumor cell adhered on three-dimensional graphene/ZnO macroporous structure by resistance
change and electrochemical impedance spectroscopy. Electrochim. Acta. 393, 139093 (2021)
24. Yang, Z.-Y., Jin, L.-J., Lu, G.-Q., Xiao, Q.-Q., Zhang, Y.-X., Jing, L., Zhang, X.-X., Yan, Y.-
M., Sun, K.-N.: Sponge-templated preparation of high surface area graphene with ultrahigh
capacitive deionization performance. Adv. Funct. Mater. 24, 3917–3925 (2014)
25. Shao, G., Hanaor, D.A.H., Shen, X., Gurlo, A.: Freeze casting: from low-dimensional building
blocks to aligned porous structures—a review of novel materials. Methods Appl. Adv. Mater.,
32 (2020)
26. Shahbazi, M.A., Ghalkhani, M., Maleki, H.: directional freeze-casting: a bioinspired method
to assemble multifunctional aligned porous structures for advanced applications. Adv. Eng.
Mater., 22 (2020)
27. Zhang, P., Li, J., Lv, L., Zhao, Y., Qu, L.: Vertically aligned graphene sheets membrane for
highly efficient solar thermal generation of clean water. ACS Nano 11, 5087–5093 (2017)
28. Wu, X., Tang, L., Zheng, S., Huang, Y., Yang, J., Liu, Z., Yang, W., Yang, M.: Hierarchical
unidirectional graphene aerogel/polyaniline composite for high performance supercapacitors.
J. Power Sources 397, 189–195 (2018)
29. Zhang, R., Hu, R., Li, X., Zhen, Z., Xu, Z., Li, N., He, L., Zhu, H.: A bubble-derived strategy
to prepare multiple graphene-based porous materials. Adv. Funct. Mater., 28 (2018)
30. Huang, X., Sun, B., Su, D., Zhao, D., Wang, G.: Soft-template synthesis of 3D porous graphene
foams with tunable architectures for lithium-O2 batteries and oil adsorption applications. J.
Mater. Chem. A. 2, 7973–7979 (2014)
31. Yeo, S.J., Oh, M.J., Jun, H.M., Lee, M., Bae, J.G., Kim, Y., Park, K.J., Lee, S., Lee, D., Weon,
B.M., Lee, W.B., Kwon, S.J., Yoo, P.J.: A Plesiohedral cellular network of graphene bubbles
for ultralight, strong, and superelastic materials. Adv. Mater. 30, 1–7 (2018)
32. Barg, S., Perez, F.M., Ni, N., Do Vale Pereira, P., Maher, R.C., Garcia-Tuñon, E., Eslava, S.,
Agnoli, S., Mattevi, C., Saiz, E.: Mesoscale assembly of chemically modified graphene into
complex cellular networks. Nat. Commun., 5 (2014)
33. Venkateshalu, S., Grace, A.N.: Review—Heterogeneous 3D graphene derivatives for superca-
pacitors. J. Electrochem. Soc. 167, 050509 (2020)
34. Moussa, M., Zhao, Z., El-, M.F., Liu, H., Michelmore, A., Kawashima, N., Majewski, P., Ma, J.:
Free-standing composite hydrogel films for superior volumetric capacitance. J. Mater. Chem.
A. 3, 15668–15674 (2015)
35. Bai, H., Li, C., Wang, X., Shi, G.: A pH-sensitive graphene oxide composite hydrogel. Chem.
Commun. 46, 2376 (2010)
36. Shao, L., Chang, X., Zhang, Y., Huang, Y., Yao, Y., Guo, Z.: Graphene oxide cross-linked
chitosan nanocomposite membrane. Appl. Surf. Sci. 280, 989–992 (2013)
37. Rasoulzadeh, M., Namazi, H.: Carboxymethyl cellulose/graphene oxide bio-nanocomposite
hydrogel beads as anticancer drug carrier agent. Carbohydr. Polym. 168, 320–326 (2017)
38. Ma, Y., Chen, Y.: Three-dimensional graphene networks: synthesis, properties and applications.
Natl. Sci. Rev. 2, 40–53 (2015)
39. De Silva, K.K.H., Huang, H.H., Joshi, R.K., Yoshimura, M.: Chemical reduction of graphene
oxide using green reductants. Carbon N. Y. 119, 190–199 (2017)
40. Chu, H.J., Lee, C.Y., Tai, N.H.: Green reduction of graphene oxide by Hibiscus sabdariffa L.
to fabricate flexible graphene electrode. Carbon N. Y. 80, 725–733 (2014)
41. Wang, J., Salihi, E.C., Šiller, L.: Green reduction of graphene oxide using alanine. Mater. Sci.
Eng. C. 72, 1–6 (2017)
42. Zhuang, P., Guo, Z., Wang, S., Zhang, Q., Zhang, M., Fu, L., Min, H., Li, B., Zhang, K.: Inter-
facial hydrothermal assembly of three-dimensional lamellar reduced graphene oxide aerogel
membranes for water self-purification. ACS Omega 6, 30656–30665 (2021)
43. Wasalathilake, K.C., Galpaya, D.G.D., Ayoko, G.A., Yan, C.: Understanding the structure-
property relationships in hydrothermally reduced graphene oxide hydrogels. Carbon N. Y. 137,
282–290 (2018)
44. Liu, X., Shen, L., Hu, Y.: Preparation of TiO2 -graphene composite by a two-step solvothermal
method and its adsorption-photocatalysis property. Water, Air, Soil Pollut. 227, 141 (2016)
45. Wu, X., Mu, F., Lin, Z.: Three-dimensional printing of graphene-based materials and the
application in energy storage. Mater. Today Adv., 11 (2021)
46. Yao, B., Chandrasekaran, S., Zhang, H., Ma, A., Kang, J., Zhang, L., Lu, X., Qian, F., Zhu, C.,
Duoss, E.B., Spadaccini, C.M., Worsley, M.A., Li, Y.: 3D-printed structure boosts the kinetics
and intrinsic capacitance of pseudocapacitive graphene aerogels. Adv. Mater., 32 (2020)
47. Zhu, C., Han, T.Y.J., Duoss, E.B., Golobic, A.M., Kuntz, J.D., Spadaccini, C.M., Worsley,
M.A.: Highly compressible 3D periodic graphene aerogel microlattices. Nat. Commun. 6, 1–8
(2015)
48. Jiang, Y., Xu, Z., Huang, T., Liu, Y., Guo, F., Xi, J., Gao, W., Gao, C.: Direct 3D printing of
ultralight graphene oxide aerogel microlattices. Adv. Funct. Mater., 28 (2018)
49. Wang, X., Zhang, Y., Zhi, C., Wang, X., Tang, D., Xu, Y., Weng, Q., Jiang, X., Mitome, M.,
Golberg, D., Bando, Y.:Three-dimensional strutted graphene grown by substrate-free sugar
blowing for high-power-density supercapacitors. Nat. Commun., 4 (2013)
50. Polsen, E.S., McNerny, D.Q., Viswanath, B.: Pattinson, S.W., John Hart, A.: High-speed roll-
to-roll manufacturing of graphene using a concentric tube CVD reactor. Sci. Rep., 5, 1–12
(2015)
51. Ye, R., James, D.K., Tour, J.M.: Laser-induced graphene. Acc. Chem. Res. 51, 1609–1620
(2018)
Architectural and Chemical Aspects
of 3D Graphene for Emerging
Applications
Juan Bai and Jun Mei
Abstract As one of the versatile and intensively studied functional materials, three-
dimensional (3D) graphene has shown great potential in a wide range of emerging
applications, particularly in energy and environment fields. To well meet practical
requirements, different 3D graphene nano architectures, such as gels, sponges, and
membranes, with various structural features have been designed and synthesized,
aiming to improve physical, chemical, mechanical, thermal, and biological proper-
ties. In this chapter, the design principles of different architectures of 3D graphene
are first summarized. Subsequently, some chemical aspects associated with surfaces,
interfaces, defects, pores, and functional groups are well analyzed to explore the
cost-effective goal for a specific application. Finally, a brief summary of the current
challenges is concluded to provide some useful insights on the future design of 3D
graphene for emerging applications.
Keywords Graphene · Three-dimensional · Surface chemistry · Environmental ·

Energy
1 Introduction
Since the successful exfoliation of graphene from layered graphite, two-dimensional

(2D) graphene has received unprecedented attention [1]. It is a honeycomb-like planar
structure that is arranged by sp2 hybridized carbon atoms. Due to the ultra-thin
and long-range π−π conjugated links, 2D graphene possesses fascinating chemical
and physical properties in terms of surface area, carrier mobility, thermal conduc-
tivity, chemical stability, mechanical properties, and so on [2]. However, until now,
achieving large-scale production of single-layer and defect-free high-quality 2D
J. Bai · J. Mei (B)

School of Chemistry and Physics, Queensland University of Technology, 2 George Street,
Brisbane, QLD 4000, Australia
e-mail: j2.mei@qut.edu.au
Centre for Materials Science, Queensland University of Technology, 2 George Street, Brisbane,
QLD 4000, Australia

https://doi.org/10.1007/978-3-031-36249-1_4
60 J. Bai and J. Mei
graphene is still challenging, which is limited by high-cost manufacturing tech-

nology and high-demanding conditions for long-term storage. Another major issue
for graphene is the serious restack of 2D nanosheets at the post-processing stage, such
as drying and modifications, leading to performance decay in practical applications
[3].
To well address these issues, one of the effective solutions is to explore
2D graphene unit-based three-dimensional (3D) structures. The assembly of 2D
graphene into a well-organized and interconnected 3D structure can not only retain
the primary characteristics of 2D nanosheets, but also maintain the interconnected
porous structures, endowing 3D graphene with abundant exposed surfaces, high-rate
diffusion channels, and active chemical reactivity [4]. There are many types of 3D
graphene that have been successfully synthesized, including hydrogel, aerogel, foam,
sponge, and membrane, and some other 3D networks with a flower-like, coral-like,
or honeycomb-like framework [5]. With aspect to synthetic methods of 3D graphene,
the assembly step and the reduction process are generally involved in a separate or
simultaneous way. For example, one of the simple and commonly used approaches
is the hydrothermal reaction conducted in aqueous solutions at elevated tempera-
tures by using graphene oxide (GO) as the starting material. Compared to relatively
unstable 2D structure, the massive production and storage of 3D graphene, and the
quality control are readily achieved, resulting in much wider applications, partic-
ularly in batteries, supercapacitors, electrocatalysis, sensors, solar-thermal devices,
and environmental adsorption field [6, 7].
In this chapter, the design principles on different architectures of 3D graphene,
such as gels, sponges, and membranes, are briefly reviewed, and then some chemical
aspects associated with surfaces, interfaces, defects, pores, and functional groups are
well analyzed. Subsequently, a summary on the emerging energy and environment-
related applications by using 3D graphene is given. Finally, the current challenges
and the possible solutions are critically analyzed, which provides some insights and
ideas on future studies.
2 Typical Architectures of 3D Graphene
2.1 3D Graphene Gels
As a typical 3D structure, graphene hydrogel is composed of loose and porous

network with multi-dimensional molecular, ion, or electron transport and diffusion
properties, so it is widely used in electrochemical materials, catalysis, sensors, and
industrial wastewater treatment fields. Generally, the preparation methods of 3D
graphene hydrogel include self-assembly, mixed solution, and in situ polymeriza-
tion. In 2010, Xu et al. prepared the self-assembled 3D graphene hydrogels with the
assistance of a facile hydrothermal method, in which the resultant graphene hydrogel
was composed of ~2.6% graphene and ~97.4% water, and a typical interconnected
Architectural and Chemical Aspects of 3D Graphene for Emerging … 61
3D porous framework was identified after freeze drying (Fig. 1a, b, c, d). More-
over, the 3D graphene hydrogel delivered a measured conductivity of 5 × 10–3 S
cm−1 and good thermal stability in the temperature between 25 and 100 °C [8].
If some functionalized molecules are introduced during reduction processes, the
functionalized 3D graphene hydrogels can be obtained for specific applications. For
example, the chemical reduction conducted at 100° C for 12 h of GO in the pres-
ence of hydroquinone as the reducing and functionalizing molecule could produce
3D functionalized graphene hydrogels, which could be used as binder-free superca-
pacitor electrodes with a specific capacitance of 441 F g−1 at a rate of 1.0 A g−1 in the
acidic electrolyte, much higher than that of the unfunctionalized graphene hydrogels
(211 F g−1 ) [10].
In contrast to 2D unit-based uniform films, 3D aerogel frameworks are assembled
based on interconnected micro-/nano-size sheets and hierarchical pores at a wide
scale ranging from micropore, mesopore, to macropore. The unique porous structure
and the 2D morphology of individual graphene units contribute to high-percentage
exposed surfaces of 3D aerogels. More importantly, 3D graphene aerogels possess
quite low density and excellent flexibility, leading to superior mechanical stability
and high bending strength. Compared to the dispersed graphene sheets, 3D graphene
aerogels exhibit much higher conductivity. Besides, 3D graphene aerogels are light,
even lighter than air in some cases, which is proposed as an alternative candidate to
Fig. 1 a Photographs of a GO aqueous dispersion before and after hydrothermal reduction and b the
resultant self-assembled graphene hydrogel (SGH), and c, d SEM images of SGH. Adapted with
permission [8]. Copyright (2010) American Chemical Society. e, f Photographs of e knotted holey-
graphene aerogel fibers (HGAFs) and f flexible HGAF-derived textiles. Adapted with permission
[9]. Copyright (2022) Copyright The Authors, some rights reserved; exclusive licensee Springer
Nature. Distributed under a Creative Commons Attribution License 4.0 (CC BY)
the relatively rare helium gas [11]. 3D graphene aerogels are generally synthesized
from molecular precursors via sol–gel methods, in which the solvent is removed
by freezing or supercritical drying and replaced by air. Some reported preparation
methods include chemical reduction, hydrothermal reduction, and 3D printing [4].
Due to the high porosity, the low refractive index, and the high conductivity, 3D
graphene aerogels have been widely used in capacitors, catalysis, photo-thermal
processes, and electronic devices.
3D graphene aerogels with superhydrophobic surfaces exhibit sensitive responses
to some external stimuli, such as electric, light, and thermal fields, and can be used
as porous hosts to incorporate the second responsive phase. Hou et al. fabricated
hygroscopic porous graphene aerogel fibers (LiCl@HGAFs) and explored their mois-
ture capture, heat distribution, and microwave absorption properties [9]. Based on
the synthetic design, the holey GO was first prepared by etching GO in H2 O2 at
100 °C, and the LiCl@HGAFs were fabricated by wet-spinning, reducing, supercrit-
ical drying, and then LiCl-filling. Morphological characterization results indicated
that the holey-graphene sheets were assembled in a long-range order and subse-
quently the uniform deposition of the hygroscopic LiCl was achieved with the assis-
tance of a liquid impregnation strategy. Also, the obtained HGAFs manifested a
hierarchical structure and could be knotted or woven into a textile, demonstrating
excellent flexibility (Fig. 1e, f).
2.2 3D Graphene Foams/Sponges
Graphene foams are composed of a 3D macroscopic graphene and a contin-

uous network of interconnected graphene sheets with pore sizes ranging from
submicron to several microns. 3D graphene foams are advantageous in terms of
high specific surface area and pore volume, good structural integrity, integrated
conductive network, and superior adsorption capacity, which is suitable for energy
storage, biomedicine, electronics, and environment remediations. With respect to
the synthetic approaches of 3D graphene foam, the commonly used ones mainly
include templates, metal ion-induced self-assembly, (electro)chemical reduction,
chemical vapor deposition (CVD), and 3D printing. Chen et al. developed an effective
strategy for the synthesis of 3D graphene foams by using template-directed CVD [12].
Figure 2a demonstrates a large piece of free-standing graphene foam with an area of
170 × 220 mm2 that is produced by using a CVD furnace coupled with a 71-mm-
in-diameter quartz tube. Unlike the structures formed from chemically derivatized
small graphene sheets, the graphene foams produced by this method are integral to
a 3D network (Fig. 2b), which could facilitate the fast transport of charge carriers
for achieving high conductivity. Even with a low loading of ~0:5 wt% graphene
foam, the resultant graphene/poly(dimethyl siloxane) composites manifested a high
electrical conductivity of approximately 10 S cm−1 [12].
Fig. 2 a Photograph of a free-standing graphene foam and b SEM image. Adapted with permission
from [12]. Copyright (2011) Springer Nature. c Photograph of 3D graphene network and d SEM
images. Adapted with permission from [13]. Copyright (2015) Wiley
Graphene sponges, as expressed in their names, possess 3D sponge-like struc-

tures and similar functional characteristics, such as efficient and recyclable absorp-
tion properties. Li et al. developed a template-induced fabrication of 3D graphene
sponges, in which GO nanosheets were first hydrothermally distributed on the
skeleton of a commercialized sponge, followed by a heat reduction process under
argon atmosphere [13]. The obtained 3D graphene sponges delivered ultra-thin
graphene walls and a low density of 1.6 mg L−1 (Fig. 2c, d). Furthermore, to generate
3D graphene foam–silicon networks, a silica layer was grown onto the skeleton of
GO sponges, which were subsequently reduced into silicon and graphene with the
assistance of a magnesium thermal reaction. When employed as an anode material
for Li-ion batteries, the optimal graphene–silicon networks presented a high capacity
over 2050 mAh g−1 after 200 cycles [13].
2.3 3D Graphene Membranes
Graphene membranes are another important family of 3D graphene networks, which

can be fabricated through spray coating, layer-by-layer assembly, and filter-based
assembly. Shao et al. developed an integrated approach for synthesizing 3D porous

graphene films by using freeze-casting and filtration assembly [14]. Figure 3a shows
a typical cross-section SEM image of a 3D porous graphene film (Fig. 3b), delivering
a continuous open and porous framework. Due to the presence of ice crystals during
freeze, the honeycomb-like structures were finally formed, in which a wide pore size
distribution ranging from nanoscales to several micrometers was identified (Fig. 3c,
d). This scalable synthetic approach could be applied for the synthesis of various
3D porous films by assembling the corresponding 2D units. Recently, inspired by
multilevel natural bamboo-membrane (Fig. 3e) with the unique function for rapid
water and electrolyte transport, Mei et al. synthesized a multilevel graphene-based
membrane consisting of 2D graphene and 2D cobalt oxide nanosheets and the resul-
tant membrane manifested a multilevel interlayer spacing distribution and a gradient
interlayer channel, which could facilitate ultrafast Li-ion transport [15]. Specifically,
the inner layers are closely packed with sub-nanosized spacing for confined ion
transport, and the outer layers are loosely stacked with micro-sized open channels
for rapid wetting of liquid electrolytes, which is much favorable to significantly
increasing volumetric capacity as free-standing electrodes for rechargeable Li-ions
batteries.
3 Surface Chemistry of 3D Graphene
As known, the pristine graphene possesses a zero-bandgap, and it is also a chem-

ically inert 2D material. To open its intrinsic bandgap and expand its application
fields, a series of effective strategies, such as doping (e.g. N, P, B, and S), defects
(e.g. point defects, topological defects, vacancy defects, and edge defects), pores
(e.g. micropores, mesopores and macropores) and functionalization (e.g. functional
groups and crosslinking), have been applied to modulate surface chemistry of 3D
graphene networks.
3.1 Doping Chemistry
Doping 3D graphene with heteroatoms (Fig. 4a), such as N, B, S, and P, can signif-
icantly change the intrinsically inertness of graphene and thus induce excellent
catalytic and chemical properties of 3D graphene [16]. This is mainly caused by
the differences on the electronegativity and the atomic size between these introduced
heteroatoms and carbon in graphene, which can break the electroneutrality and mean-
while introduce strain/stress on the graphene planes [17]. Furthermore, the integration
of different heteroatoms into 3D graphene can result in desirable charge polarization
and spin density, endowing 3D graphene with new physicochemical properties. For
the synthesis of doped graphene, the heteroatom-containing precursors are generally
required, and the doping reactions are often proceeded via a wet-chemical reaction
Fig. 3 a Cross-section SEM image of a 3D porous reduced GO film; b photograph of a 3D folded

film, and c, d the corresponding SEM images. Adapted with permission [14]. Copyright (2016)
Wiley. e SEM image of the natural bamboo membrane, and f schematic illustration of graphene-
based multilevel membranes for ion transport in batteries. Adapted with permission [15]. Copyright
(2021) Wiley
or a thermal impregnation technique. However, the high-concentration doping is

still challenging. Mei et al. proposed a self-sacrificing strategy to achieve ultrahigh-
level P-doped 3D graphene hydrogels by using 2D black phosphorus nanosheets as
the precursor. As a result, the P-doping concentration in the obtained 3D graphene
hydrogel reached 4.84 at%, accompanied by the formation of adjustable pore sizes
in the range of 1.7−17.5 nm. Through reaction kinetic analysis on electrochemical
Li-ions storage, the P-doped 3D graphene hydrogel presented a favorable capacitive-
controlled characteristic, as evidenced by a high specific Li-ions storage capacity of
1,000 mA h g−1 after 1,700 discharging/charging cycles, outperforming the undoped
3D graphene hydrogel [19].
Fig. 4 a Schematical illustration of various doping configurations on graphene. Adapted with

permission [16]. Copyright (2019) Wiley. b Schematical illustration of various defects on graphene.
Adapted with permission [17]. Copyright (2019) Elsevier. c Schematical illustration of various
functionalization reactions on graphene. Adapted with permission [18]. Copyright (2020) Royal
Society of Chemistry
3.2 Defect Chemistry
Defective 3D graphene networks have been intensively studied for energy conver-
sion and storage applications, which is primarily due to their active reactivities at
defective sites and the optimal electronic structures. There are various levels of
defects in nanomaterials, including point-level, line-level, plane-level, and volume-
level defects. Based on specific locations and compositions, point-level defects can
be further classified into heteroatom dopants, vacancies, interstitial atoms, and impu-
rities [20]. The inherent defects of 3D graphene networks mainly include edge and
lattice/topological defects (Fig. 4b), which usually originates from the assembly
and/or the reduction process of 3D graphene. If the reduction of GO networks is
employed to produce 3D graphene networks, the defect levels are largely asso-
ciated with the GO precursors and the reducing agents. Generally, more oxygen-
containing groups in the GO precursors may induce more defects in the reduced 3D
graphene networks. It should be noteworthy that defects are not always static, which
may further migrate upon reduction. At present, different effective methods have
been developed for generating various defects on the surfaces of graphene, mainly
including thermal annealing, particle irradiation, and chemical treatment, and these
defects act as crucial roles in some applications such as catalysis [21]. For example,
it was concluded that electrocatalytic performance is highly related to the edge sites
of 3D graphene networks. 3D graphene with high-density edge sites could efficiently
catalyze H2 evolution, as verified by a low onset potential of ~18 mV and a Tafel

slope of ~64 mV dec−1 [22].
3.3 Pore Chemistry
As mentioned above, one obvious feature of 3D graphene networks is porosity, so

the modulation on the pore chemistry is significant for adapting the practical appli-
cations. For example, 3D hierarchical and macro-porous graphene foam assembled
from graphene mesh with in-plane nanopores presented a hierarchical pore arrange-
ment, which is much more favorable for mass transport and edge exposure for devel-
oping functional materials for energy applications [23]. After further doping with
N, the resultant 3D graphene delivered a uniform pore size of 2–50 nm, a specific
surface area of 362 m2 g−1 , a high nanohole density of ~5.0 × 109 holes per cm2 , a
high porosity of ~99.79%, and an interpore distance up to ~100 nm [23]. Choi et al.
prepared a 3D macro-porous graphene structure with the assistance of polystyrene
colloidal particles as the sacrificial template [24]. This porous 3D graphene with a
surface area of 194.20 m2 g−1 and an electrical conductivity of 1204 S m−1 could
facilitate rapid ion transport for energy storage devices and it could be a suitable candi-
date as for hosting metal oxides that are active for electrochemical reactions, such as
the widely used MnO2 in supercapacitors, to enhance electrochemical performance
[24].
3.4 Functionalization
Generally, the functionalization strategy of graphene can be achieved through a

covalent or noncovalent bonding reaction. Due to the stronger chemical bonding
capability for robust interfaces, covalent modification on graphene is a widely used
approach. The covalent functionalization motivations of graphene are largely depen-
dent on the existing chemistry, particularly at these defect or edge sites (Fig. 4c). In
the synthesis of 3D graphene networks, GO is often used as the starting material.
GO surfaces contain many oxygen-containing groups, such as hydroxyl, carboxyl,
carbonyl, and epoxy, leading to a serious conductivity decay. Hence, the reduction
is highly required for partial or complete removal of oxygen species on graphene
surfaces. Currently, the reduction methods used during the synthesis of 3d graphene
mainly include high-temperature treatment, chemical reduction, electrochemical
reduction, hydrothermal or solvothermal reduction, and photon-induced reduction.
In most cases, after reduction under thermal or (electro)chemical treatment, most of
the unstable oxygen species are removed, leaving a small amount of O−H, C−O, and
C=O on the surfaces. This existing oxygen chemistry environment is crucial for the
further covalent functionalization of 3D graphene and offers many new possibilities
for structural modifications. Besides, if highly reactive species are introduced with
the assistance of plasmas (e.g. H, F, and Cl), the π-bonded network on the basal
plane of graphene will be directly destroyed and meanwhile the functionalization of
reactive species on graphene is achieved [18].
Another intensively studied and versatile functionalization approach for 3D
graphene is to design graphene-based composites. Depending on the synergistic
effects in graphene-based composites, the functionalization of 3D graphene by the
combination with other counterpart materials is a powerful approach. Specifically,
this strategy can make use of the advantages of graphene and overcome the intrinsic
weakness of graphene by coupling with these materials with complementary struc-
tures and/or functions [25]. Moreover, the rational integration of graphene and other
functional materials could bring about some new physicochemical properties, such
as increasing catalytic sites and improving reaction kinetics for electrocatalysis via
the functionalization of 3D graphene with the incorporation of highly reactive metal
sites. For example, the advantages of the combination of 3D graphene and noble-
metal nanoparticles for catalysis can be summarized as follows: (i) an integrated
conductive framework can be formed; (ii) the serious agglomeration of nano-sized
graphene sheets can be overcome; (iii) the dispersion degree of metal nanoparticles
can be increased as exposed active sites; (iv) the strong metal–carbon coupling may
exist for robust interfaces; (v) the consumption of expensive noble metals can be
reduced; (vi) the structural stability and durability can be improved to accommodate
the practical conditions; (vii) the reaction mechanisms may be rationally modulated
for favorable kinetics and increased activities; (viii) the operation process and the
manufacture technology is promising for large-scale applications.
4 3D Graphene for Emerging Applications
3D graphene networks have been widely applied in various fields across physics,
chemistry, biology, nanotechnology, and engineering [26, 27]. In this part, as summa-
rized in Fig. 5, we mainly focus on the emerging energy and environment-associated
applications of 3D graphene, such as batteries, capacitors, solar cells, electrocatalysis,
sensors, and environmental adsorption.
4.1 Energy Storage
Owing to the ever-increasing demands for portable electronics and electric vehi-
cles in our daily life, the innovation of energy storage devices with high power
density and high energy density, such as batteries and capacitors, is becoming
urgent. Currently, one major concern for achieving performance enhancement is
highly associated with electrode materials. For example, as one of the important
energy storage devices, supercapacitors possess high capacity, high rate, and long
cycle life, however, the cost-effective electrode materials are still lacking. Graphene
Fig. 5 Summary of emerging energy and environment-related applications of 3D graphene.

a Adapted with permission [28]. Copyright (2017) American Association for the Advancement
of Science. b Adapted with permission [29]. Copyright (2016) Copyright The Authors, some rights
reserved; exclusive licensee Springer Nature. Distributed under a Creative Commons Attribution
License 4.0 (CC BY). c Adapted with permission [30]. Copyright (2017) Wiley. d Adapted with
permission [31]. Copyright (2018) Wiley
has been regarded as one of the potential electrode materials for supercapacitors,
and 3D graphene networks could maximize the exposed active area and accelerate
electrons/ions transfer, resulting in superior electrochemical performance [24]. To
date. different types of 3D graphene networks have been designed and synthesized
for high-performance energy storage devices. Wang et al. proposed a 3D graphene
bubble network, which was fabricated by using a sugar-blowing approach, and this
network was composed of continuous graphitic membranes tightly scaffolded by
graphitic struts. Such intimate topological configuration is beneficial to increasing
power and energy densities for electrochemical capacitors [32].
Besides, 3D graphene networks and their derived composite electrodes have been
intensively used in rechargeable batteries, such as anodes in Li/Na/K-ion batteries and
cathodes in metal-air/sulfur batteries [33, 34]. In 2017, a 3D holey-graphene/niobia
(Nb2 O5 ) composite was reported for high-rate energy storage at a mass loading above
10 mg cm−2 . Within the designed composite electrode, the interconnected graphene
network facilitates electron transport while the hierarchical porous framework favors
ion transport. As a result, the optimal electrode presented a capacity of 139 mAh g−1
with a high loading of 11 mg cm−2 , and a stable cycle life with 90% capacity retention
after 10,000 cycles at a rate of 10C [28].
4.2 Energy Conversion
As one of the essential reactions for energy conversion, electrocatalysis aims to

converting renewable resources (e.g. CO2 or biomass), to valuable chemicals, fuels,
and electrical energy with the assistance of highly active catalyst materials [35]. An
ideal electrocatalyst should possess high conductivity, abundant active sites, good
mass transfer capability, suitable structural stability and durability, and earth abun-
dant. Except for the structural merits of 3D graphene associated with surface area and
porous framework, the modulation of surface chemistry is crucial for electrocatalysis.
To increase the reactivity of graphene units, doping, defects, and functionalization
are often adopted for 3D graphene for tuning electronic structures and optimizing
reaction pathways, and thus improving catalytic activities. 3D graphene networks
have been explored for various electrocatalytic reactions, such as oxygen evolu-
tion reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction
(HER), and carbon dioxide reduction reaction (CO2 RR) [36]. For example, Yang
et al. synthesized N-doped graphene nanoribbons with interconnected 3D architec-
tures, exhibiting excellent electrocatalytic activity for both ORR and OER. It was
revealed that the ORR activity originated from the electron-donating quaternary N
sites and the OER activity was determined by the electron-withdrawing pyridinic N
moieties. When used as rechargeable Zn-air batteries in a two-electrode configura-
tion, an open-circuit voltage of 1.46 V, a specific capacity of 873 mAh g−1 , and a
peak power density of 65 mW cm−2 , and a stable cycle over 150 cycles at a rate of
2 mA cm−2 [29].
Graphene materials are also used as a promising substitution for noble-metal elec-
trodes in fuel cells. For ORR occurred at cathodes in fuel cells, the dominant catalysts
are Pt-based metals, however, the limited reservation and high price of Pt metal inhib-
ited their practical applications. Perfect graphene is chemically inert toward ORR,
so structural modifications are required for graphene materials. Heteroatom-doped
3D graphene has been evidenced as one of the promising metal-free catalysts with
high electrochemical activities. Foreign atoms, such as N, P, B, and S, can change the
distribution states of local electrons within graphene lattices and enhance reaction
kinetics. Among them, N-doped graphene catalysts are commonly studied for ORR,
which is largely due to the favorable charge redistribution and the decreased energy
barrier for ORR [37].
4.3 Solar Energy Utilization
3D graphene networks deliver a wide range of light absorption properties and tune-
able thermal conductivity, endowing them promising for photovoltaic solar cells
and solar-thermal energy conversion systems. Solar-thermal energy conversion is a
continuous process for solar energy harvest by collecting the steam generated by the
heat of localized sunlight. 3D graphene has good light absorption effect, low thermal
conductivity and excellent wettability, and efficient light-to-heat conversion rate [30,
38]. It should be noteworthy that the hierarchical pores in 3D graphene networks are
significant for steam generation. Specifically, the small pores can promote the high
light absorption while the micropores can induce the capillary effect of water [5]. Ren
et al. reported a hierarchical porous graphene foam, in which graphene arrays were
grown on 3D foam skeleton by using plasma-enhanced chemical vapor deposition,
manifested attractive broadband and omnidirectional absorption capability, resulting
in a solar-thermal energy conversion efficiency of ~93.4% when utilized as a heating
material [30].
4.4 Environmental Sensors and Remediation
Sensors are a large family of functional devices that demonstrate the immediate
response to environmental varieties, such as temperature, humidity, pressure, and
chemicals, which can be easily found in industrials and residential communities.
3D graphene materials have been widely used in various sensors, including strain
sensors, gas sensors, and (electro)chemical sensors [31, 39]. Particularly, gas sensors
are mainly used to detect low-concentration gases (e.g. O2 , COx , NOx , Cl2 , SO2 , H2 S,
NH3 , and CH4 ) and volatile organic compounds (e.g. acetone, alcohol, aromatics, and
hydrazine) [40]. Based on the adsorption mechanism, the target gas can be adsorbed
onto 3D graphene skeletons with the assistance of interaction drivers such as van
der Waals force or covalent bonding, and then the gas concentration can be reflected
by the conductance changes of 3D graphene. For example, Wu et al. designed a
NO2 gas sensor based on 3D graphene flowers grown on a Ni foam skeleton, which
presented a high sensitivity of 133.2 ppm−1 , a high response of 1411% to 10 ppm,
a low theoretical detection limit of 785 ppt, and an ultrafast signal recovery of 2 s
[41].
3D porous graphene networks can be also employed in environment remedia-
tion fields in terms of pollutant control and toxicant adsorption. 3D graphene mate-
rials have been investigated for the effective adsorption of various pollutants, such
as harmful gas (e.g. SO2 , H2 S, and CO2 ) and impurities in solutions (e.g. dyes,
oils, organic solvents, and heavy metals) [42–44]. Generally, the adsorption capa-
bility of 3D graphene networks for environmental purification is closely associated
with surface area, pore size and distribution density, and surface chemistry. A high
surface area with high porosity is essential for achieving efficient adsorption of 3D
graphene for most adsorbates, however, the adsorbed types depend on surface chem-
istry. A hydrophobic surface facilitates the adsorption of organic compounds, and
the adsorption in aqueous solutions depends on the interaction between adsorbates
and adsorbents, including electrostatic force, hydrogen bonding, and π−π bonding.
5 Summary
In this chapter, some typical architectures of 3D graphene networks, such as gels,

foams, sponges, and membranes, are briefly discussed. However, one of the major
challenges is the large-scale production of 3D graphene materials. There are many
factors, including concentrations, temperatures, reaction time, reactors, and costs,
which require to be considered. Also, there is a large gap between laboratory
synthesis and industrial massive production, in which the accurately control on
the interconnected porous structures at a large scale is more difficult. Therefore,
it is still essential to design and develop new synthetic methods for 3D graphene
networks. Surface chemistry acts as a crucial role for structural modifications on 3D
graphene. By adjusting surface chemistry, 3D graphene networks have been widely
used in the emerging energy storage and conversion and environmental remedia-
tion fields. Further understanding and modulating surface chemistry on 3D graphene
networks can bring about some customed properties to well meet the practical require-
ments and can intrigue more new applications. The regulation on the macroscopic
morphology, the specific surface area, the pore distribution, the surface wettability
state, the electronic structures, the thermal conductivity, the mechanical flexibility,
and the electrical conductivity, have been investigated for 3D graphene networks.
To further improve the performance of 3D graphene and to widen the application
scope, a variety of 3D graphene-based composites have been fabricated by coupling
with the structure- or function-complementary counterparts. It is expected that these
research outputs on the synthesis and the optimization strategies of 3D graphene by
controlling surface chemistry can offer some scientific evidence for constructing 3D
graphene-based devices for addressing the current energy and environmental issues.
References
1. Hernandez, Y., Nicolosi, V., Lotya, M., Blighe, F.M., Sun, Z., De, S., McGovern, I.T., Holland,
B., Byrne, M., Gun’Ko, Y.K.: High-yield production of graphene by liquid-phase exfoliation
of graphite. Nat. Nanotechnol. 3(9), 563–568 (2008)
2. Lee, C., Wei, X., Kysar, J.W., Hone, J.: Measurement of the elastic properties and intrinsic
strength of monolayer graphene. Science 321(5887), 385–388 (2008)
3. Li, D., Müller, M.B., Gilje, S., Kaner, R.B., Wallace, G.G.: Processable aqueous dispersions
of graphene nanosheets. Nat. Nanotechnol. 3(2), 101–105 (2008)
4. Zhu, C., Han, T., Duoss, E.B., Golobic, A.M., Kuntz, J.D., Spadaccini, C.M., Worsley, M.A.:
Highly compressible 3D periodic graphene aerogel microlattices. Nat. Commun. 6, 6962 (2015)
control. Chem. Rev. 120(18), 10336–10453 (2020)
6. Yousefi, N., Lu, X., Elimelech, M., Tufenkji, N.: Environmental performance of graphene-based
3D macrostructures. Nat. Nanotechnol. 14(2), 107–119 (2019)
7. Xu, X., Zhang, Q., Yu, Y., Chen, W., Hu, H., Li, H.: Naturally dried graphene aerogels with
superelasticity and tunable Poisson’s ratio. Adv. Mater. 28(41), 9223–9230 (2016)
8. Xu, Y., Sheng, K., Li, C., Shi, G.: Self-assembled graphene hydrogel via a one-step
hydrothermal process. ACS Nano 4(7), 4324–4330 (2010)
9. Hou, Y., Sheng, Z., Fu, C., Kong, J., Zhang, X.: Hygroscopic holey graphene aerogel fibers
enable highly efficient moisture capture, heat allocation and microwave absorption. Nat.
Commun. 13, 1227 (2022)
10. Xu, Y., Lin, Z., Huang, X., Wang, Y., Huang, Y., Duan, X.: Functionalized graphene hydrogel-
based high-performance supercapacitors. Adv. Mater. 25(40), 5779–5784 (2013)
11. Gorgolis, G., Galiotis, C.: Graphene aerogels: a review. 2D Materials 4(3), 032001 (2017)
12. Chen, Z., Ren, W., Gao, L., Liu, B., Pei, S., Cheng, H.-M.: Three-dimensional flexible and
Mater. 10(6), 424–428 (2011)
13. Li, B., Yang, S., Li, S., Wang, B., Liu, J.: From commercial sponge toward 3D graphene–silicon
networks for superior lithium storage. Adv. Energy Mater. 5(15), 1500289 (2015)
14. Shao, Y., El-, M.F., Lin, C.W., Zhu, G., Marsh, K.L., Hwang, J.Y., Zhang, Q., Li, Y., Wang,
H., Kaner, R.B.: 3D freeze-casting of cellular graphene films for ultrahigh-power-density
supercapacitors. Adv. Mater. 28(31), 6719–6726 (2016)
15. Mei, J., Peng, X., Zhang, Q., Zhang, X., Liao, T., Mitic, V., Sun, Z.: Bamboo-membrane inspired
multilevel ultrafast interlayer ion transport for superior volumetric energy storage. Adv. Func.
Mater. 31(31), 2100299 (2021)
16. Ullah, S., Hasan, M., Ta, H.Q., Zhao, L., Shi, Q., Fu, L., Choi, J., Yang, R., Liu, Z., Rümmeli,
M.H.: Synthesis of doped porous 3D graphene structures by chemical vapor deposition and its
applications. Adv. Func. Mater. 29(48), 1904457 (2019)
17. Sun, T., Zhang, G., Xu, D., Lian, X., Li, H., Chen, W., Su, C.: Defect chemistry in 2D materials
for electrocatalysis. Materials Today Energy 12, 215–238 (2019)
18. Clancy, A.J., Au, H., Rubio, N., Coulter, G.O., Shaffer, M.S.: Understanding and controlling
the covalent functionalisation of graphene. Dalton Trans. 49(30), 10308–10318 (2020)
19. Mei, J., He, T., Zhang, Q., Liao, T., Du, A., Ayoko, G.A., Sun, Z.: Carbon–phosphorus bonds-
enriched 3D graphene by self-sacrificing black phosphorus nanosheets for elevating capacitive
lithium storage. ACS Appl. Mater. Interfaces. 12(19), 21720–21729 (2020)
20. Yan, D., Li, Y., Huo, J., Chen, R., Dai, L., Wang, S.: Defect chemistry of nonprecious-metal
electrocatalysts for oxygen reactions. Adv. Mater. 29(48), 1606459 (2017)
21. Liu, L., Qing, M., Wang, Y., Chen, S.: Defects in graphene: generation, healing, and their
effects on the properties of graphene: a review. J. Mater. Sci. Technol. 31(6), 599–606 (2015)
22. Wang, H., Li, X.B., Gao, L., Wu, H.L., Yang, J., Cai, L., Ma, T.B., Tung, C.H., Wu, L.Z.,
Yu, G.: Three-dimensional graphene networks with abundant sharp edge sites for efficient
electrocatalytic hydrogen evolution. Angew. Chem. 130(1), 198–203 (2018)
23. Zhao, Y., Hu, C., Song, L., Wang, L., Shi, G., Dai, L., Qu, L.: Functional graphene nanomesh
foam. Energy Environ. Sci. 7(6), 1913–1918 (2014)
24. Choi, B.G., Yang, M., Hong, W.H., Choi, J.W., Huh, Y.S.: 3D macroporous graphene frame-
works for supercapacitors with high energy and power densities. ACS Nano 6(5), 4020–4028
(2012)
25. Wang, M., Duan, X., Xu, Y., Duan, X.: Functional three-dimensional graphene/polymer
composites. ACS Nano 10(8), 7231–7247 (2016)
26. El-, M.F., Shao, Y., Kaner, R.B.: Graphene for batteries, supercapacitors and beyond. Nat. Rev.
Mater. 1(7), 1–14 (2016)
27. Bonaccorso, F., Colombo, L., Yu, G., Stoller, M., Tozzini, V., Ferrari, A.C., Ruoff, R.S., Pelle-
grini, V.: Graphene, related two-dimensional crystals, and hybrid systems for energy conversion
and storage. Science 347(6217), 1246501 (2015)
28. Sun, H., Mei, L., Liang, J., Zhao, Z., Lee, C., Fei, H., Ding, M., Lau, J., Li, M., Wang, C.:
Three-dimensional holey-graphene/niobia composite architectures for ultrahigh-rate energy
storage. Science 356(6338), 599–604 (2017)
29. Yang, H.B., Miao, J., Hung, S.-F., Chen, J., Tao, H.B., Wang, X., Zhang, L., Chen, R.,
Gao, J., Chen, H.M.: Identification of catalytic sites for oxygen reduction and oxygen evolu-
tion in N-doped graphene materials: Development of highly efficient metal-free bifunctional
electrocatalyst. Sci. Adv. 2(4), e1501122 (2016)
30. Ren, H., Tang, M., Guan, B., Wang, K., Yang, J., Wang, F., Wang, M., Shan, J., Chen, Z., Wei,
D.: Hierarchical graphene foam for efficient omnidirectional solar–thermal energy conversion.
Adv. Mater. 29(38), 1702590 (2017)
31. Pan, F., Chen, S.M., Li, Y., Tao, Z., Ye, J., Ni, K., Yu, H., Xiang, B., Ren, Y., Qin, F.: 3D
graphene films enable simultaneously high sensitivity and large stretchability for strain sensors.
Adv. Func. Mater. 28(40), 1803221 (2018)
32. Wang, X., Zhang, Y., Zhi, C., Wang, X., Tang, D., Xu, Y., Weng, Q., Jiang, X., Mitome, M.,
Golberg, D.: Three-dimensional strutted graphene grown by substrate-free sugar blowing for
high-power-density supercapacitors. Nat. Commun. 4, 2905 (2013)
33. Wang, Z., Gao, H., Zhang, Q., Liu, Y., Chen, J., Guo, Z.: Recent advances in 3D graphene
architectures and their composites for energy storage applications. Small 15(3), 1803858 (2019)
34. Mei, J., Zhang, Y., Liao, T., Peng, X., Ayoko, G.A., Sun, Z.: Black phosphorus nanosheets
promoted 2D-TiO2 -2D heterostructured anode for high-performance lithium storage. Energy
Storage Materials 19, 424–431 (2019)
35. Mistry, H., Varela, A.S., Kühl, S., Strasser, P., Cuenya, B.R.: Nanostructured electrocatalysts
with tunable activity and selectivity. Nat. Rev. Mater. 1, 16009 (2016)
36. Cui, H., Guo, Y., Zhou, Z.: Three-dimensional graphene-based macrostructures for electro-
catalysis. Small 17(22), 2005255 (2021)
37. Wu, Z.-S., Yang, S., Sun, Y., Parvez, K., Feng, X., Müllen, K.: 3D nitrogen-doped graphene
aerogel-supported Fe3 O4 nanoparticles as efficient electrocatalysts for the oxygen reduction
reaction. J. Am. Chem. Soc. 134(22), 9082–9085 (2012)
38. Ito, Y., Tanabe, Y., Han, J., Fujita, T., Tanigaki, K., Chen, M.: Multifunctional porous graphene
for high-efficiency steam generation by heat localization. Adv. Mater. 27(29), 4302–4307
(2015)
39. Wu, S., He, Q., Tan, C., Wang, Y., Zhang, H.: Graphene-based electrochemical sensors. Small
9(8), 1160–1172 (2013)
40. Wang, T., Huang, D., Yang, Z., Xu, S., He, G., Li, X., Hu, N., Yin, G., He, D., Zhang, L.: A
review on graphene-based gas/vapor sensors with unique properties and potential applications.
Nano-Micro Letters 8(2), 95–119 (2016)
41. Wu, J., Feng, S., Wei, X., Shen, J., Lu, W., Shi, H., Tao, K., Lu, S., Sun, T., Yu, L.: Facile
synthesis of 3D graphene flowers for ultrasensitive and highly reversible gas sensing. Adv.
Func. Mater. 26(41), 7462–7469 (2016)
42. Wu, Y., Yi, N., Huang, L., Zhang, T., Fang, S., Chang, H., Li, N., Oh, J., Lee, J.A., Kozlov, M.:
Three-dimensionally bonded spongy graphene material with super compressive elasticity and
near-zero Poisson’s ratio. Nat. Commun. 6, 6141 (2015)
43. He, K., Chen, G., Zeng, G., Chen, A., Huang, Z., Shi, J., Huang, T., Peng, M., Hu, L.: Three-
dimensional graphene supported catalysts for organic dyes degradation. Appl. Catal. B 228,
19–28 (2018)
44. Shi, L., Chen, K., Du, R., Bachmatiuk, A., Rümmeli, M.H., Xie, K., Huang, Y., Zhang, Y., Liu,
Z.: Scalable seashell-based chemical vapor deposition growth of three-dimensional graphene
foams for oil–water separation. J. Am. Chem. Soc. 138(20), 6360–6363 (2016)
Recent Advancements in 3D Graphene
for Electrochemical Sensors
Hamide Ehtesabi and Seyed-Omid Kalji
Abstract Graphene, a new class of carbon nanostructures, has recently garnered

much attention and is a quickly growing field. It exhibits a wide range of features,
including thermal conductivity, charge carrier mobility, electrical and mechanical
characteristics, magnetism, and more. These characteristics, along with a large
surface area, are essential in electrochemical, optoelectronic, and medicinal applica-
tions. However, some features have restricted its applicability, including poor light
absorption, low capacitance, ease of stacking and agglomeration in a solvent, and
its zero-gap semi-metal nature. In response to these limitations, there has been a
rising effort to alter the graphene surface and create three-dimensional (3D) graphene
arrangements to broaden its applicability in various industries. Due to their high effi-
ciency, simple operation, as well as modularity in chemical, physical, and biological
features, electrochemical sensors have developed over time. With outstanding quali-
ties, such as a high surface area, abundant pores, and free binder, 3D graphene with a
porous structure is a suitable electrode for electrochemical sensors. The most current
developments in 3D graphene-based electrochemical sensing for various analytes
are covered in this chapter.
Keywords Graphene Oxide · Three-dimensional · Electrode · Sensing ·

Detection · Nanoparticle
1 Introduction
Graphene is a two-dimensional (2D) layer of carbon atoms with a lattice of hexag-

onal structures. Owing to its high surface area, remarkable electrical conductivity, and
appropriate charge carrier mobility, graphene is widely used in various applications,
H. Ehtesabi (B)
Faculty of Life Sciences and Biotechnology, Shahid Beheshti University, Tehran, Iran
e-mail: h_ehtesabi@sbu.ac.ir
S.-O. Kalji
Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran

https://doi.org/10.1007/978-3-031-36249-1_5
76 H. Ehtesabi and S.-O. Kalji
including sensors, supercapacitors, catalysis, bio-fuel cells, and chromatography

analysis [1–3]. Despite high structural stability, via the π–π interactions and strong
Van der Waals forces, the 2D plane of graphene sheets can stack together irreversibly
and create graphitic form. Graphene loses its particular properties after these stacking
interactions. Preparing a 3D graphene structure prevents the stacking and agglomera-
tion of 2D nanosheets. Currently, 3D graphene constructions come in various forms,
including hydrogel, aerogel, foam, sponge, and others [4, 5]. These 3D materials have
an ordered and interconnected framework, and they have the distinct advantages of
a greater surface area, abundant pores, and a free binder. Therefore, 3D graphene
could be promising material in various problematic applications [6, 7]. Because of its
advanced surface area and electron transport capacity, 3D graphene shows a specific
ability as an electrode material. Its porous structure is also applicable as a supporting
substrate for various materials, catalysts, and enzymes for the designation and fabri-
cation of desired systems such as electrochemical sensors [8]. However, these new
3D graphene-based sensors suffer from low selectivity, sensitivity, repeatability,
and a slow dynamic response against the analyte changes. Accordingly, searching
for a novel approach to achieving proportional 3D graphene-based nanocompos-
ites and hybrids is required to overcome the sensing and detection limitations of
electrochemical sensors and improve their robustness and reusability [1].
Herein, we review the latest advancements in 3D graphene-based electrochemical
sensors. First, a basic explanation of 3D graphene and the processes used for its fabri-
cation is given. The electrochemical sensing of numerous analytes, including heavy
metals, pesticides, phenolic compounds, drugs, chiral materials, dopamine, glucose,
free radicals, ions, and hydrogen peroxide (H2 O2 ), is then presented using 3D
graphene. The chapter concludes with a consideration of current issues and prospects.
2 Definition of 3D Graphene Materials
3D graphene materials currently do not have a clear definition. The goal of devel-
oping 3D graphene frameworks is to achieve a stable graphene material with high
performance through a 3D organization of layers instead of graphite-like ordering,
which dramatically reduces the surface area and other unique features of graphene.
Because of this, it is obvious that non-graphite 3D structured graphene materials are
named 3D graphene materials. Fewer than ten layers of graphene should form the
walls of a 3D graphene material while maintaining the fundamental properties of
graphene materials. Figure 1 illustrates the connections of graphite, graphene, 2D
and 3D graphene materials [9].
Recent Advancements in 3D Graphene for Electrochemical Sensors 77
Fig. 1 Diagram showing the connections between graphite, 2D and 3D graphene, and graphene
materials. Adapted with permission [9]. Copyright (2020) Copyright The Authors, some rights
reserved; exclusive licensee American Chemical Society. Distributed under a Creative Commons
Attribution License 4.0 (CC BY)
3 Synthesis Methods of 3D Graphene
In recent years, numerous techniques for creating 3D graphene have been done
in order to give it different morphologies, structures, and characteristics. The
key methods that have been developed are the hydro/solvothermal approach,
chemical vapor deposition (CVD), template-assisted assembly, chemical reduction
self-assembly, 3D printing, etc., [10–13]. These techniques can generally be split
into template free and template-based methods (Fig. 2). While the template-based
approach can precisely regulate the production of a desired pore size, shape, and
density, the template free approach offers the benefits of self-assembly but cannot
manage the pore structure. The dependent (hydrogel, aerogel) and independent
(foam, sponge) 3D graphene on the substrate can be produced using a single
preparation process or a mixture of several procedures to fulfill various needs [1].
4 Electrochemical Sensing of Different Analytes
Because different compounds can be oxidized or reduced at various potentials,

electrochemical detection is very sensitive to electroactive compounds and enables
detection selectivity. Because of their high surface renewable potential, low residual
current, and broad potential window, carbon materials (such as graphene, graphite,
Fig. 2 Synthesis methods of 3D graphene materials. Adapted with permission [1]. Copyright (2020)
Elsevier
carbon nanotube (CNT), and fullerene) are frequently utilized in electrochemistry.

Electron transfer from multiple active sites to biospecies is provided by the overpo-
tential for O2 reduction and H2 density of the edge-plane defect site on them [14,
15]. The use of 2D and 3D graphene and their composites as sensing materials for
the electrochemical monitoring of various analytes is widespread. In contrast to a flat
graphene film, 2D porous graphene has a higher surface area and additional exposed
active sites because of its distinctive structural design. Due to the extra channels,
it has improved electrochemical performance in terms of ion and mass transport
(e.g., sensing, energy storage, catalytic ability, etc.). A 3D graphene has a similar
distinctive structure of constantly interconnected networks, with a sizable accessible
surface area and a significant pore volume. Additionally, it improves mechanical
strength, flexibility, and stability [16]. In this section, a few illustrative examples of
3D graphene-based electrochemical sensing are presented.
4.1 Heavy Metal
It is crucial to create rapid, sensitive, and precise methods for identifying toxic
heavy metal ions because they pose a serious threat to human life and the environ-
ment. Owing to its great sensitivity, outstanding selectivity, simplicity, low-cost, and
good portability, electrochemical detection has become one of the most popular tech-
niques. In one study, pyrrole (Py) was added to 3D graphene aerogels to control their
structures and properties. These aerogels were then used as electrode materials to
study the unique function of Py for sensing metal ions. Py can act as a reductant and a
regulator to change the composition and structure of graphene aerogels, significantly
affecting their electrochemical performance for sensing cadmium (Cd2+ ). Py also
functions as a nitrogen source to provide active metal ion binding sites. The effec-
tiveness of Py is greatly influenced by the reaction ratio between Py and graphene
oxide (GO). The 3D-GO-Py modified electrode can successfully determine Cd2+ in
aqueous solutions using the square wave anodic stripping voltammetry method [17].
4.2 Pesticide
Many crops and vegetables are protected against pests by applying organophos-
phate pesticides (OPs) [18]. OPs, however, have several detrimental consequences
on humans and animals due to their excessive use. Therefore, it is critical to make
a rapid, precise, sensitive, and trustworthy analytical approach for OPs detection
[19]. Due to their straightforward preparation processes, high sensitivity, and excel-
lent selectivity, acetylcholinesterase (AChE)-based electrochemical biosensors have
recently become recognized as viable alternatives to traditional approaches for pesti-
cide residues. Enzymatic-based biosensors, however, have certain drawbacks that
limit their uses, including high price, poor stability, and low repeatability. Nonenzy-
matic sensors appear to be a promising solution in this situation. 3D graphene was
used to prepare a copper oxide nanoparticle (CuO-NPs/3DG) electrocatalyst that
was used as a nonenzymatic sensing platform for malathion detection (Fig. 3a).
A 3D graphene framework offered a great surface area for excellent dispersion
of CuO-NPs. Given that the resulting CuO-NPs/3DG nanocomposite has a high
affinity for malathion, CuO’s redox reaction may be constrained. Under ideal circum-
stances, measurements of the suppressed signal allowed the CuO-NPs/3DG modi-
fied electrode to detect malathion at concentrations as low as 0.01 nmol/L. The 3D
graphene has a high surface area to anchor CuO-NPs and promote electron transfer,
contributing to the high sensitivity. The sensor also revealed good recovery, stability,
and selectivity for recognizing malathion in real samples [20].
4.3 Phenolic Compound
Applications for electrochemical sensors in the monitoring of dangerous compounds

may benefit from graphene’s special electrical characteristics. A significant and often
utilized chemical feedstock, 4-nitrophenol (4-NP), is typically found in wastewater.
Unfortunately, it is a stable compound with a high level of carcinogenicity and is listed
as one of the most important pollutants [21]. Therefore, it is crucial to detect 4-NP
effectively in the environment. In a study, it was suggested to manufacture nitrogen-
doped 3D graphene with manganese-doped Fe3 O4 -NPs loaded on the surface (Mn–
Fe3 O4 /3DG) using a straightforward urushiol templated solvothermal technique
(Fig. 3b) accompanied with calcination. The as-prepared Mn-Fe3 O4 /3DG sensor
demonstrated great activity in detecting 4-NP, which is much better than the control
unmodified samples due to the wide active surface area, porous channel, and high
Fig. 3 a Diagram showing the creation of CuO-NPs/3DGR/glassy carbon electrode (GCE) and
the electrochemical sensing of malathion. Adapted with permission [20]. Copyright (2018) Copy-
right The Authors, some rights reserved; exclusive licensee Elsevier. Distributed under a Creative
Commons Attribution License 4.0 (CC BY) b Diagram showing how electrode materials are made
for 4-NP detection. Adapted with permission [22]. Copyright (2021) Copyright The Authors, some
rights reserved; exclusive licensee Elsevier. Distributed under a Creative Commons Attribution
License 4.0 (CC BY)
loading ratio of Mn–Fe3 O4 –NPs. The Mn-Fe3 O4 /3DG electrode may be used in prac-
tical applications due to its broad linear range (5–100 μmol/L), low LOD (19 nmol/
L), and acceptable recovery of 4-NP in a variety of water samples [22].
4.4 Biomarker Detection
4.4.1 Cancer
For the recognition of tumor markers, electrochemical aptasensors using an aptamer

as a probe have obtained a lot of consideration because of their exceptional qualities,
which include good selectivity, cost-effectiveness, high stability, a widespread
target range, and the simplicity of synthesizing and modifying methods. A study
creates an electrochemical aptasensor for the simultaneous measurement of carci-
noembryonic antigen (CEA) and cancer antigen 15–3 (CA 15–3), which are two
critical biomarkers of breast cancer. The biosensing substrate was a nanocomposite
made of 3D graphene hydrogel with gold NPs (Au-NPs/3DGH). Aptamers of CEA
and CA 15–3 were connected to graphene nanocomposite-redox probe-Au-NPs
as biosensing probes. Hemin (the redox agent of CEA) and ferrocene (the redox
agent of CA 15–3) provided electrochemical signals to detect dual biomarkers. The
aptamers CEA and CA 15–3 were immobilized on Au-NPs/3DGH. The current and
potential of peaks in the differential pulse voltammograms provided information
about the nature and concentration of the biomarkers (Fig. 4a). The LOD for CEA
and CA 15–3 were 11.2 pg/mL and 11.2 × 10–2 U/mL, respectively. The analysis
of clinical serum samples was also done with the duplexed aptasensor. The results
showed good compliance with the enzyme-linked immunosorbent assay (ELISA)
method, proving the aptasensor’s high validity [23].
Circulating tumor DNA (ct-DNA) is a reliable biomarker for predicting treat-
ment effects and is critical for the early detection of many cancers. One of the best
advantages of the ct-DNA detection method is its non-invasive nature, but the low
abundance in peripheral blood and the large background of wild-type DNA hamper
the exact and specific detection of ct-DNA. For the efficient detection of ct-DNA,
a team created a 3D graphene/Au-platinum-palladium nanoflower sensing platform
(3DGR/Au-Pt–Pd) based on the CRISPR/Cas9 cleavage-triggered entropy-driven
strand displacement reaction (ESDR). This technique allows for the detection of
low quantities of ct-DNA. Their approach produced excellent specificity for distin-
guishing single nucleotide mismatches by the rapid amplification of ESDR and the
site-specific cleavage of Cas9/sgRNA. The 3DGR/Au-Pt–Pd biosensor in human
serum tests showed high specificity and acceptable performance [24].
4.4.2 Osteoblast Activity
An important biomarker for osteoblast activity and skeletal growth is alkaline phos-
phatase (ALP). Methods for effective ALP detection are crucial for clinical diagnosis
and medication development. An electrochemical sensor based on in situ generated
3D graphene networks (3DGN) was designed to measure ALP activity. The sensor
uses ALP to convert a non-electroactive substrate into a product with electroactivity;
finally, the activity of ALP is shown as an electrochemical signal (Fig. 4b). The
Fig. 4 a Schematic illustrating the simultaneous detection of the biomarkers CEA and CA 15–
3. Adapted with permission [23]. Copyright (2021) Copyright The Authors, some rights reserved;
exclusive licensee Elsevier. Distributed under a Creative Commons Attribution License 4.0 (CC BY).
b Using a 3DGNs modified sensor, the ALP activity of adhering osteocyte cells is detected. Adapted
with permission [25]. Copyright (2022) Copyright The Authors, some rights reserved; exclusive
licensee Multidisciplinary Digital Publishing Institute. Distributed under a Creative Commons
Attribution License 3.0 (CC BY)
sensor detects ALP activity in a wide range (10–10,000 U/L) and a LOD of 5.70
U/L with 5μL sample volume and a 2 min incubation time when 3DGN catalyzes
the process and amplifies the signal. This sensor shows good performance in various
biological systems and serum samples. It offers a rapid response, economical, and
nondestructive technique for tracking living adherent osteoblast cell activity [25].
4.4.3 Acute Kidney Injury
Compared to conventional biomarkers such as creatinine, neutrophil genatase-

associated lipocalin (NGAL) responds significantly faster to acute kidney injury
(AKI). For the detection of NGAL, a 3D graphene nickel (Ni) foam (GF) electrochem-
ical sensor covered with Au-NPs was created. It achieved a low LOD (42 pg/mL) and
a linear range of 0.05–210 ng/mL. In order to facilitate antibody binding on Au-NPs,
self-assembled monolayers, and 11-mercaptoundecanoic acid were used. Utilizing
cyclic voltammetry and chronoamperometry on ferri/ferrocyanide redox measure-
ments, NGAL was electrochemically determined. The ability to detect NGAL in the
presence of uric acid (UA) and creatinine was examined. Large surface areas of GF
and Au-NPs, and the role of the graphene/Ni/Au electric dipole in the enhanced elec-
tron transport from the analyte may be responsible for the achieved performances
[26].
4.5 Drug
Drug monitoring is very important in the field of drug safety. By electropolymeriza-

tion imprinting on 3D Au–Pd–NPs-ionic liquid (IL) functionalized graphene-CNTs
nanocomposite (Au–Pd/GN-CNTs-IL) modified GCE, a novel paracetamol (PCM)
sensor was created. In addition to promoting the construction of Au–Pd alloy NPs, IL
(1-hydroxyethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) imide) served
as a “spacer” to avoid the π–π stacking and aggregation of graphene sheets and
CNTs during the preparation of the GN-CNTs that supported Au–Pd alloy NPs.
The resultant composite has significant electrocatalysis and a large surface area. The
imprinted position of PCM on poly(carbazole)-co-Poly(Py) demonstrated good PCM
detection and showed excellent stability. Using 3D Au–Pd/GN-CNTs-IL nanocom-
posite and PCM imprinted position on copolymer, an electrochemical sensor was
developed. Having a LOD of 50 nmol/L, it displayed an excellent linear range of
0.10–10 μmol/L. The sensor’s recoveries are adequate for PCM detection in biolog-
ical samples. Additionally, it successfully monitored the level of PCM in a patient’s
urine with a fever cold [27]. A straightforward approach for anchoring silver NPs
(Ag-NPs) onto 3D reduced GO (3D-rGO) has been described in another work for the
detection of rifampicin (Ag-NPs/3D-rGO). Due to its substantial electrochemically
active surface area and superior electron transport capabilities, the modified elec-
trode demonstrated effective electrical activity to measure rifampicin. With a LOD
of 0.810 nmol/L, the sensor showed an excellent linear range (0.01 nmol/L–45 μmol/
L). Notably, the created sensor was used to evaluate rifampicin in samples of human
blood, drugs, and aquatic products [28].
4.6 Chiral Material
In biochemical analysis, enantioselective recognition is crucial. Therefore, sepa-

rating amino acid enantiomers using diverse methods is critical for biochemistry,
pharmaceutical science, and medical systems. The creation of practical and effec-
tive methods for chiral discrimination is still regarded as a difficult problem. Due to
their straightforward equipment, low-cost, fast, and effective detection, chiral elec-
trochemical sensors have generated a great deal of attention. A group described how
to recognize L and D tryptophan (Trp) using a chiral sensor. The sensor consists of
self-assembly between Cu2+ /β-cyclodextrin with carboxymethyl cellulose (CD-Cu-
CMC) as a chiral selector, N-doped rGO as substrate, and differential pulse voltam-
metry for enantiomer recognition. rGO and Py were used as the initial components to
create the 3D N-rGO. The carboxy groups of CMC and Cu2+ in Cu-CD interact elec-
trostatically. The CD-Cu-CMC was able to be immobilized owing to the 3D N-rGO,
which also enhances the active regions. N-rGO/CD-Cu-CMC was used to modify
a GCE, which then demonstrated a larger electrochemical signal for L than for the
D isomer, typically at a working potential of about 0.78 V. It was demonstrated by
UV–visible spectroscopy that CD-Cu-CMC has a stronger affinity for the D isomer.
D-Trp has a 4.72 enantioselectivity over L-Trp. The modified electrode had a linear
detection range of 0.01–5 mmol/L and a LOD of 0.063 and 0.003 μmol/L for L and D
isomers, respectively. Trp (D or L) was found using the sensor in samples of human
serum protein and spiked real human urine [29].
4.7 Dopamine
The cardiovascular, central neurological, renal, and hormonal systems all depend on
the neurotransmitter dopamine (DA). Regular assessment of DA levels in patients’
bodies is necessary because excess or insufficient concentrations of DA in neuro-
logical systems can cause schizophrenia, Parkinson’s disease, hyperactivity disorder,
and other conditions. As a result, it is particularly important for developing a sensitive
and reliable test for DA molecule detection in the medical and biological fields. To
monitor the electrochemical behavior of DA, a 3D-rGO with CD-modified GCE was
created (Fig. 5a). The CD was effectively modified on 3D porous graphene. By
using cyclic voltammetry and electrochemical impedance spectroscopy to examine
the electrochemical characteristics of various modified electrodes, it was determined
that the 3D-rGO/CD-modified electrode had the highest electron transfer rate. Scan
rate, pH, enrichment time, and layer thickness were among the experimental param-
eters that were optimized. A wide linear range of 0.5–100 μmol/L and the LOD of
0.013 μmol/L were achieved by differential pulse voltammetry by 3D-rGO/CD/
GCE under the best experimental conditions for DA detection [30]. A rapid and
easy method for creating 3D graphene nanomesh (3D-GNM) with electrocatalytic
property has been demonstrated. The initial electrode is made of monolithic and
macroporous 3D graphene foam (Fig. 5b). Simple electrochemical polarization of
3D graphene, which involves oxidation of the anode and subsequent reduction of the
cathode, makes it simple to create 3D-GNM. The entire process takes only 10 min.
The peaks of DA, UA, and ascorbic acid (AA) in 3D-GNM are clearly distinct. Selec-
tive detection of DA, UA, and AA in triplex mixtures or serum samples is accom-
plished with the LOD of 0.26 μmol/L, 6.0 nmol/L, and 3.1 μmol/L, respectively [31].
4.8 Glucose
Due to their remarkable advantages of simplicity and ease of use, electrochem-

ical sensors are greatly desired for the detection of glucose in diabetes prevention,
diagnosis, and treatment. Creating a 3D sensing interface with an immobilized elec-
trochemical probe and nonenzymatic recognition groups is still difficult. By adding
functional nanostructure to 3D graphene, a new nonenzymatic electrochemical sensor
was created for glucose. The electrode scaffold was a 3D graphene foam created by
CVD. 3D graphene was first electrodeposited with Prussian blue (PB) and Au-NPs
(3DG/PB-Au-NPs) as an immobilized signal indicator and electron conductor. A
simple self-polymerization of DA was used to add a layer of polydopamine (PDA)
to 3DG/PB-Au-NPs for stabilizing of internal PB probe and providing chemical
reducibility. After that, in situ formation of a second layer of Au-NPs was done
for recognition ligand placement, i.e., mercaptobenzoboric acid. The nonenzymatic
sensor could detect glucose without reagent with good selectivity, a wide linear range
(5–65 μmol/L), and a low LOD (1.5 μmol/L) because of the PB stability and good
affinity between mercaptobenzoboric acid and glucose. Additionally, the sensor has
been used to measure glucose in human serum samples [32].
4.9 Free Radicals
The measurement of nitric oxide released by living cells helps to understand the
pathological and physiological processes of the human body and related disorders
[33]. In a research, a new sensor called COF-366-Fe/GA was developed by growing
COF-366-Fe electrocatalyst on 3D porous graphene aerogel (GA) for nitric oxide
detection (Fig. 6a). The constructed biosensor exhibits a sensitive response in the
wide range of 0.18–400 μmol/L with a LOD of 30 nmol/L. Furthermore, after the
release of nitric oxide by HUVEC cells (human umbilical vein endothelial cells), the
Fig. 5 a Electrochemical detection of DA by prepared 3D-rGO/CD. Adapted with permission [30].

Copyright (2021) Copyright The Authors, some rights reserved; exclusive licensee Royal Society
of Chemistry. Distributed under a Creative Commons Attribution License 3.0 (CC BY) h. b The
preparation of 3D-GNM for detecting DA, UA, and AA. Adapted with permission [31]. Copyright
(2022) Copyright The Authors, some rights reserved; exclusive licensee [Elsevier]. Distributed
under a Creative Commons Attribution License 3.0 (CC BY)
constructed device was able to capture the molecular signals rapidly. According to
these findings, this biosensor solves the problem of random organization of active
sites for nitrogen-coordinated electrocatalysts because its active sites are adjustable
and also have the 3D porous structure of graphene [34].
Fig. 6 a Nitric oxide detection using COF-366-Fe/GA. Adapted with permission [34]. Copyright
(2021) Copyright The Authors, some rights reserved; exclusive licensee Elsevier. Distributed under
a Creative Commons Attribution License 4.0 (CC BY), b Fabrication of an Ag@rGOF-NH2 /GCE
sensor for Cl− detection. Adapted with permission [35]. Copyright (2021) Copyright The Authors,
some rights reserved; exclusive licensee Elsevier. Distributed under a Creative Commons Attribution
License 4.0 (CC BY)
4.10 Ion
Cl− is extensively dispersed in nature, and specific concentration ranges are needed
for agricultural production, concrete engineering, and the medical and health indus-
tries. Therefore, quick detection of Cl− concentrations in the environment has signif-
icant applicability. A study showed the direct usage of multilayer GO to synthesize
mesoporous 3D-rGO framework (rGOF) (Fig. 6b). This work used a KOH activa-
tion procedure that relies on the adsorption and fixation of the proper amount of K+
by utilizing the interlayer space of multilayer GO and freeze-drying crystallization
technology. Additionally, they found that the structure of rGOF is consistent with
the usual 3D structure. Moreover, rGOF has a unique 3D structure and rGO char-
acteristics, making it an excellent platform for functionalized modifications. The
prepared Ag@rGOF-NH2 /GCE sensor detects Cl− over a broad linear range of 5–
10 μmol/L, with a LOD of 0.1 μmol/L. This study demonstrates the effectiveness
of rGOF as a platform with modification by amine and loading of Ag-NPs [35].
4.11 H2 O2
H2 O2 is a crucial component of biological, medical, food, and environmental activi-

ties and is a signaling molecule involved in cell growth, cell death, and intracellular
signaling transduction. Studies show that improper management of H2 O2 in cells
leads to some diseases, from cancer to neurological diseases [36]. Therefore, H2 O2
must be detected accurately and reliably. Hydrothermal reduction, freeze-drying, and
high-temperature annealing were proposed as synthesis methods for graphene foam
that was functionalized with taurine (a-NSGF). The increased temperature during
annealing made it possible for taurine’s N/S atoms to reach the graphene lattice,
considerably enhancing its electrocatalytic activity. The 3D layers of graphene modi-
fied with taurine make up the a-NSGF that quickly responds to H2 O2. Owing to the
stable 3D structure and superior electrical conductivity of a-NSGF, the modified
electrode with a-NSGF exhibits excellent sensitivity and stability to the concentra-
tion change of H2 O2 . From 1.5–300 μmol/L, there is a linear relationship between
the H2 O2 concentration and the electrochemical signal, with a R2 = 0.99. The modi-
fied electrode was used to measure H2 O2 in rain samples, and the outcomes were
compared to those obtained using the standard method. The recoveries vary between
94.6 and 106.7% [37].
5 Conclusion, Challenges, and Future Perspective
This chapter highlights recent advancements and successes in 3D graphene for elec-
trochemical sensing. 3D graphene is an amazing electrode substance, and there are
many prospects to study its application in electrochemical sensors. Its properties
make it incredibly competitive in comparison to traditional electrodes. High electro-
chemical activity, simplicity of surface functionalization, and outstanding electron
transport capabilities are just a few of the exceptional properties of 3D graphene
that have made it possible to employ it to detect analytes with better sensitivity and
selectivity. We concentrated on using 3D graphene related materials as sensors for
detecting dopamine, glucose, free radicals, ions, pesticides, phenolic compounds,
biomarkers of disease, drugs, and H2 O2 .
While 3D graphene production, functionalization, and applications have come a
long way, there are still plenty of obstacles to overcome. For instance, new methods
for 3D graphene synthesis need to be developed. These procedures must have the
benefits of speed, economy, simplicity, and a high potential for 3D graphene mass
production. Additionally, 3D graphene’s exceptional properties depend solely on
the material’s successful creation. The material’s porosity has not been accurately
regulated up to this moment, and the distribution of pore sizes is between nm and
μm. In addition, many architectural defects are created during preparation, negatively
affecting how well they work in electrochemical sensing. The mechanical stability
still needs to be improved to make the 3D network of graphene a useful sensing
instrument. Additionally, there is a need to pay more attention to identifying material
defects during construction and figuring out how to fix them. This will benefit the 3D
graphene electrodes’ mechanical stability and electrochemical activity. To get the best
synergistic impact for selective and sensitive sensing of the analytes, more theoretical
and experimental investigation of 3D graphene with other nanocomposites is needed.
In conclusion, to create sensitive and affordable sensors for electrochemical sensing,
3D graphene has great potential.
References
1. Hou, X., Xu, H., Zhen, T., Wu, W.: Recent developments in three-dimensional graphene-based
electrochemical sensors for food analysis. Trends Food Sci. Technol. 105, 76–92 (2020)
2. Kalji, O., Sefidbakht, Y., Nesterenko, A.M., Uskoković, V., Ranaei-Siadat, S.-O.: Colloidal
graphene oxide enhances the activity of a lipase and protects it from oxidative damage: Insights
from physicochemical and molecular dynamics investigations. J. Colloid Interface Sci. 567,
285–299 (2020)
3. Ehtesabi, H., Gupta, R.K.: Flexible and Wearable Sensors, Flexible and Wearable Sensors for
Biomedical Applications. CRC Press (2023)
4. Haque, E., Yamauchi, Y., Malgras, V., Reddy, K.R., Yi, J.W., Hossain, M.S.A., Kim, J.:
Nanoarchitectured graphene-organic frameworks (GOFs): synthetic strategies, properties, and
applications. Chem. Asian J. 13, 3561–3574 (2018)
5. Idowu, A., Boesl, B., Agarwal, A.: 3D graphene foam-reinforced polymer composites–a review.
Carbon 135, 52–71 (2018)
6. Wu, Y., Zhu, J., Huang, L.: A review of three-dimensional graphene-based materials: synthesis
and applications to energy conversion/storage and environment. Carbon 143, 610–640 (2019)
7. Yousefi, N., Lu, X., Elimelech, M., Tufenkji, N.: Environmental performance of graphene-based
3D macrostructures. Nat. Nanotechnol. 14, 107–119 (2019)
8. Owusu-, S., Tripp, C.P.: Controlled growth of layer-by-layer assembled polyelectrolyte
multilayer films under high electric fields. J. Colloid Interface Sci. 541, 322–328 (2019)
control. Chem. Rev. 120, 10336–10453 (2020)
10. Dong, S., Xia, L., Guo, T., Zhang, F., Cui, L., Su, X., Wang, D., Guo, W., Sun, J.: Controlled
synthesis of flexible graphene aerogels macroscopic monolith as versatile agents for wastewater
treatment. Appl. Surf. Sci. 445, 30–38 (2018)
11. Lai, K.C., Lee, L.Y., Hiew, B.Y.Z., Thangalazhy-Gopakumar, S., Gan, S.: Environmental appli-
cation of three-dimensional graphene materials as adsorbents for dyes and heavy metals: Review
on ice-templating method and adsorption mechanisms. J. Environ. Sci. 79, 174–199 (2019)
12. Tang, X., Zhou, H., Cai, Z., Cheng, D., He, P., Xie, P., Zhang, D., Fan, T.: Generalized 3D
printing of graphene-based mixed-dimensional hybrid aerogels. ACS Nano 12, 3502–3511
(2018)
13. Li, F., Yu, Z., Han, X., Lai, R.Y.: Electrochemical aptamer-based sensors for food and water
analysis: A review. Anal. Chim. Acta 1051, 1–23 (2019)
14. Shao, Y., Wang, J., Wu, H., Liu, J., Aksay, I.A., Lin, Y.: Graphene based electrochemical sensors
and biosensors: a review. Electroanal. Int. J. Devoted Fund. Practical Aspects Electroanal. 22,
1027–1036 (2010)
15. Lawal, A.T.: Synthesis and utilisation of graphene for fabrication of electrochemical sensors.
Talanta 131, 424–443 (2015)
16. Zhang, Y., Wan, Q., Yang, N.: Recent advances of porous graphene: synthesis, functionalization,
and electrochemical applications. Small 15, 1903780 (2019)
17. Guo, X., Cui, R., Huang, H., Li, Y., Liu, B., Wang, J., Zhao, D., Dong, J., Sun, B.: Insights into
the role of pyrrole doped in three-dimensional graphene aerogels for electrochemical sensing
Cd (II). J. Electroanal. Chem. 871, 114323 (2020)
18. Derbalah, A., Ismail, A., Shaheen, S.: Monitoring of organophosphorus pesticides and remedi-
ation technologies of the frequently detected compound (chlorpyrifos) in drinking water. Polish
J. Chem. Technol. 15, 25–34 (2013)
19. Zheng, Q., Chen, Y., Fan, K., Wu, J., Ying, Y.: Exploring pralidoxime chloride as a universal
electrochemical probe for organophosphorus pesticides detection. Anal. Chim. Acta 982, 78–83
(2017)
20. Xie, Y., Yu, Y., Lu, L., Ma, X., Gong, L., Huang, X., Liu, G., Yu, Y.: CuO nanoparticles
decorated 3D graphene nanocomposite as non-enzymatic electrochemical sensing platform for
malathion detection. J. Electroanal. Chem. 812, 82–89 (2018)
21. Hu, L., Peng, F., Xia, D., He, H., He, C., Fang, Z., Yang, J., Tian, S., Sharma, V.K., Shu, D.:
Carbohydrates-derived nitrogen-doped hierarchical porous carbon for ultrasensitive detection
of 4-nitrophenol. ACS Sustain. Chem. Eng. 6, 17391–17401 (2018)
22. Su, Y., Zheng, X., Cheng, H., Rao, M., Chen, K., Xia, J., Lin, L., Zhu, H.: Mn-Fe3O4 nanopar-
ticles anchored on the urushiol functionalized 3D-graphene for the electrochemical detection
of 4-nitrophenol. J. Hazard. Mater. 409, 124926 (2021)
23. Shekari, Z., Zare, H.R., Falahati, A.: Dual assaying of breast cancer biomarkers by using a sand-
wich–type electrochemical aptasensor based on a gold nanoparticles–3D graphene hydrogel
nanocomposite and redox probes labeled aptamers. Sens. Actuators, B Chem. 332, 129515
(2021)
24. Chen, M., Wu, D., Tu, S., Yang, C., Chen, D., Xu, Y.: CRISPR/Cas9 cleavage triggered ESDR
for circulating tumor DNA detection based on a 3D graphene/AuPtPd nanoflower biosensor.
Biosens. Bioelectron. 173, 112821 (2021)
25. Zhao, N., Shi, J., Li, M., Xu, P., Wang, X., Li, X.: Alkaline phosphatase electrochemical micro-
sensor based on 3D graphene networks for the monitoring of osteoblast activity. Biosensors
12, 406 (2022)
26. Danvirutai, P., Ekpanyapong, M., Tuantranont, A., Bohez, E., Anutrakulchai, S., Wisitsoraat,
A., Srichan, C.: Ultra-sensitive and label-free neutrophil gelatinase-associated lipocalin elec-
trochemical sensor using gold nanoparticles decorated 3D Graphene foam towards acute kidney
injury detection. Sens. Bio-Sens. Res. 30, 100380 (2020)
27. Yang, L., Zhang, B., Xu, B., Zhao, F., Zeng, B.: Ionic liquid functionalized 3D graphene-
carbon nanotubes-AuPd nanoparticles-molecularly imprinted copolymer based paracetamol
electrochemical sensor: Preparation, characterization and application. Talanta 224, 121845
(2021)
28. Zhang, Q., Ma, S., Zhuo, X., Wang, C., Wang, H., Xing, Y., Xue, Q., Zhang, K.: An ultrasensitive
electrochemical sensing platform based on silver nanoparticle-anchored 3D reduced graphene
oxide for rifampicin detection. Analyst 147, 2156–2163 (2022)
29. Niu, X., Yang, X., Mo, Z., Liu, N., Guo, R., Pan, Z., Liu, Z.: Electrochemical chiral sensing
of tryptophan enantiomers by using 3D nitrogen-doped reduced graphene oxide and self-
assembled polysaccharides. Microchim. Acta 186, 1–12 (2019)
30. Chen, X., Li, N., Rong, Y., Hou, Y., Huang, Y., Liang, W.: β-Cyclodextrin functionalized 3D
reduced graphene oxide composite-based electrochemical sensor for the sensitive detection of
dopamine. RSC Adv. 11, 28052–28060 (2021)
31. Gong, J., Tang, H., Wang, M., Lin, X., Wang, K., Liu, J.: Novel three-dimensional graphene
nanomesh prepared by facile electro-etching for improved electroanalytical performance for
small biomolecules. Mater. Des. 215, 110506 (2022)
32. Liu, Q., Zhong, H., Chen, M., Zhao, C., Liu, Y., Xi, F., Luo, T.: Functional nanostructure-loaded
three-dimensional graphene foam as a non-enzymatic electrochemical sensor for reagentless
glucose detection. RSC Adv. 10, 33739–33746 (2020)
33. Privett, B.J., Shin, J.H., Schoenfisch, M.H.: Electrochemical nitric oxide sensors for physio-
logical measurements. Chem. Soc. Rev. 39, 1925–1935 (2010)
34. Zhu, P., Li, S., Zhou, S., Ren, N., Ge, S., Zhang, Y., Wang, Y., Yu, J.: In situ grown COFs on
3D strutted graphene aerogel for electrochemical detection of NO released from living cells.
Chem. Eng. J. 420, 127559 (2021)
35. Dai, J., Meng, L., Rong, S., Gao, H., Zhang, Z., Zhang, Y., Qiu, R., Wang, Y., Chang, D.,
Ding, P.: Facile preparation of 3D graphene frameworks as functional modification platform
for sensitive electrochemical detection of chloride ions. J. Electroanal. Chem. 887, 115155
(2021)
36. Zhao, Y., Hu, Y., Hou, J., Jia, Z., Zhong, D., Zhou, S., Huo, D., Yang, M., Hou, C.: Elec-
trochemical biointerface based on electrodeposition AuNPs on 3D graphene aerogel: direct
electron transfer of Cytochrome c and hydrogen peroxide sensing. J. Electroanal. Chem. 842,
16–23 (2019)
37. Guo, Z.-Y., Feng, Y.-F., Chen, Y.-Y., Yao, Q.-H., Luo, H.-Z., Chen, X.: A taurine-functionalized
3D graphene-based foam for electrochemical determination of hydrogen peroxide. Talanta 208,
120356 (2020)
3D Graphene-Based Biosensors
Mert Akin Insel, Sena Nur Karabekiroglu, and Selcan Karakuş
Abstract In the last 30 years, there have been increasingly developments in the
fabrication, properties, and applications of graphene-based three-dimensional (3D)
materials with their excellent performances of high mechanical strength, excellent
surface area, high electrical conductivity, and thermal stability. Over the last century,
the number of various applications of 3D graphene has increased dramatically in areas
such as sensors, batteries, separation, aerospace, catalysis, and thermal management.
In this chapter, all aspects of fabrication strategies, characterization, and biosensing
mechanisms of 3D graphene-based biosensors are reviewed. In addition, there is
a great deal of interest in a variety of 3D graphene-based sensor systems, such
as gas sensors, health monitoring, wearable temperature sensors, electrochemical
food sensors, and environmental pollutant sensors. Consequently, a comprehensive
understanding of the unique performance, current limitations, and outlook of 3D
graphene-based biosensors was highlighted.
Keywords 3D graphene · Sensing systems · Biosensors · Fabrication strategy
1 3D Material-Based Sensing Systems
Detection systems detect physical quantities such as temperature, light, sound, or

motion, make the desired measurements, and convert the data into electrical signals
that a device can read and interpret. The design and stability of the sensor are critical,
as they affect measurement performance and the quality of system performance [1].
The single layer of graphite termed “graphene,” which has 2D arrays of sp2
hybrid carbon atoms, is an excellent structure with exceptional qualities, including
M. A. Insel · S. N. Karabekiroglu
Faculty of Chemical-Metallurgical Engineering, Department of Chemical Engineering, Yıldız
Technical University, Istanbul, 34210, Turkey
S. Karakuş (B)
Faculty of Engineering, Department of Chemistry, Istanbul University-Cerrahpaşa, 34320
Istanbul, Turkey
e-mail: selcan@iuc.edu.tr

https://doi.org/10.1007/978-3-031-36249-1_6
94 M. A. Insel et al.
high chemical resistance, high surface area, and high conductivity. Graphene mate-
rials have unique properties such as a high optical transmittance of 98%, charge-
carrier mobility of 2 × 105 cm2 /(Vs), high mechanical strength of 125 GPa, high
surface area of 2600 m2 /g, and excellent thermal conductivity of 5000 W/(mK) [2].
It enables significant new advancements in a variety of sectors, including chemical
sensors, biosensors, field-effect transistors, conversion technology, energy storage
systems, etc. Although typically found as powders, graphene is not flexible enough.
Many studies have focused on developing porous, three-dimensional (3D)-structured
graphene materials with superior mechanical strength, outstanding photothermal
conversion, electrochemical properties, and high electrical conductivity to solve
this problem. There have been reports of graphene-derived sponges, graphene-based
foams, graphene-based hydrogels, and graphene-based aerogels. These 3D graphene-
based structures have been manufactured using a variety of techniques, including
direct fabrication techniques as a solution-based method and chemical vapor depo-
sition, hydrothermal methods, solvothermal treatments, and freeze-drying methods.
Different components, such as inorganic materials, activated carbon, conducting
polymers, sulfur compounds, are combined into 3D graphene to form nanosized
composites, further increasing their performance and broadening their application
areas. 3D graphene-based nanomaterials show promising possibilities in the sectors
of sensors, energy, water treatment, medicine, etc. 3D graphene-based nanomaterials
offer promising therapeutic applications in the areas of biosensing, physical sensors,
drug delivery systems, gene delivery systems, bone tissue engineering, etc. by taking
advantage of intriguing features such as high specific surface area, nanoscale size,
excellent morphology, high antibacterial activity, high antifungal activity, high anti-
cancer activity, and excellent photoluminescence. There are several types of 3D
materials that can be used in sensing systems, including metals, semiconductors,
polymers, and ceramics. Some of the most common examples of 3D materials used
in sensing systems with superior properties are gold nanoparticles (GNP), zinc oxide
(ZnO) nanowires, polymer nanofibers, and graphene.
1.1 Gold Nanoparticles
Gold nanostructures are small particles of gold that have dimensions on the nanoscale.
Gold has a very stable structure and is preferred because it has biologically inert and
plasmonic properties. The surface of GNP reacts spontaneously with amine, sulfur,
and carboxyl groups. Therefore, it is known that GNPs are conjugated with target
molecules such as nucleic acids, carbohydrates, enzymes, DNA, RNA, and peptides,
which are important building blocks in all living systems and play an important
role in biosensing and bioactive nanomaterials. One of the key properties of gold
nanostructures that makes them useful for sensing applications is their ability to
exhibit surface-enhanced Raman scattering (SERS) [3]. SERS is a phenomenon in
which the Raman scattering signal of a molecule is significantly enhanced when the
molecule is adsorbed onto the surface of a metal nanoparticle with high plasmonic
3D Graphene-Based Biosensors 95
properties [4, 5]. In addition, the functional groups play an important role in the
determination of the target molecule. Composite materials containing metals/metal
oxides are used to further increase the sensitivity, selectivity, and accuracy of the
sensor. Graphene-based nanostructures containing metal NPs show great potential
for high-performance electrochemical sensors as they conduct electrons very well.
This enhancement can be used to detect specific biomolecules, such as proteins
and DNA, with high sensitivity and selectivity [6, 7]. GNPs have been used to detect
different structures, including target biomolecules, harmful gases, and environmental
pollutants. In addition, they have a wide range of uses in the field of health, such
as the detection of cancer biomarkers in blood samples, the detection of oxygen
saturation, the assessment of cardiovascular activity, and the detection of heart rate.
Overall, gold nanoparticles are a promising material for use in sensing systems (espe-
cially calorimetric sensors) due to their excellent optical, chemical, and electronic
properties and their ability to exhibit SERS [6, 7].
1.2 Zinc Oxide Nanowires
ZnO nanowires are thin zinc oxide wires with a high surface-to-volume ratio and
nanoscale dimensions [8]. ZnO nanowires have many advantages, such as optical
transparency, biocompatibility, good chemical stability, ease of fabrication, the ability
to be converted into 3D structures, and a well-known synthesis method (Lupan et al.
2017). In addition, the detection of gases (such as CO2 , NO2 , and so on), proteins,
biological molecules such as DNA, and the development of sensors for environmental
monitoring and medical diagnosis is in high demand [8, 9].
1.3 Polymer Nanofibers
Polymer nanofibers are nanoscale polymer material fibers with larger surface areas
per unit mass. Polymer nanofibers are utilized as filters, tissue engineering scaffolds,
protective clothing, reinforcements, and sensors in composite materials. In general,
polymer nanofibers are widely used in sensing systems due to their unique properties,
good chemical stability that makes them resistant to degradation, and their ability to
be converted into a wide variety of 3D structures [10]. They can be produced into a
wide variety of 3D structures, such as mats, films, bars, aerogels, and coatings [11].
1.4 Graphene
Graphene is a form of carbon that exists as a two-dimensional (2D), atomic-scale

lattice. Because of its extremely thin and flat structure, it is considered a 2D mate-
rial. It is known as a nanomaterial with superior properties consisting of a perfect
arrangement of carbon molecules linked by covalent bonds with a hexagonal struc-
ture [12, 13]. Although graphene is typically synthesized as a 2D material, 3D struc-
tures can be created using layering, folding, wrapping, or 3D printing methods [14].
The differences among graphene, graphite, 2D graphene-based formulations, 3D
graphene-based nanomaterials, are illustrated in Fig. 1.
The trend in the latest literature is toward sensitive and accurate detection of
traditional food contaminants, predominately bacteria, agrochemicals, and toxic
metabolites with nanotechnological solutions. In truth, really novel graphene-based
biosensor solutions are lacking, and the latest published advances are frequently
based on tried-and-true methods with the application of graphene nanostructures or
nanosized blends to produce highly sensitive detectors. Due to its numerous special
qualities, graphene has the potential to be useful in a variety of applications. The
most prevalent superior characteristics of graphene are listed below [13];
. high surface area
. superior thermal conductivity
. excellent electron mobility
. stronger than steel, more durable than a diamond
Fig. 1 American Chemical Society. The differences among graphene, graphite, 2D graphene-based
formulations, 3D graphene-based nanomaterials. Adapted with permission [12]. Copyright (2020),
American Chemical Society.
. flexibility up to 20%
. high thermal conductivity
. high current carrying capacity >102
. very high intrinsic mobility provides outstanding electronic characteristics.
. very high critical properties.
Thanks to these superior properties, graphene is used in many application areas.
These include transparent electrodes, biosensors, field-effect transistors, clean energy
storage systems, nanostructures, and organic photovoltaic platforms. It is also used as
a conductive material in a number of sensitive electronic/optoelectronic systems, such
as thin-film photovoltaic touch screens, light-emitting diodes (LEDs), and transparent
electrodes [15]. Recent studies also focus on enabling the fabrication of graphene in
numerous applications, including supercapacitors, batteries, and fuel [12].
2 Fabrication of 3D Graphene-Based Biosensors
Graphene can be fabricated using various methods such as micromechanical sepa-

ration of graphite layers (exfoliation), chemical vapor deposition (CVD), electrode-
position, 3D graphene-based printing, and the folded graphene method [12].
. 3D printing systems: Utilization of a 3D printer to create the sensor structure by
depositing layers of graphene in the desired shape.
. Exfoliation: The process of obtaining a single or few layers of material from
a bulk sample. This process is used to obtain a single layer or a few layers of
graphene from bulk graphite.
. Chemical vapor deposition (CVD): Growing of graphene on a material using the
chemical process and then etching away the substrate to create a free-standing
graphene structure.
. Electrodeposition: Deposition of layers of graphene onto a substrate using an
electric current.
. Folded graphene: Folding of a sheet of graphene into a 3D structure that can be
used as a sensor.
. Directed Assembly: The self-assembly of graphene layers into 3D morpholo-
gies using various techniques such as capillary forces, mechanical folding, and
electrostatic interactions.
After the 3D graphene structure is developed, functionalization of biomolecules
for biosensor fabrication may be possible. Numerous methods, such as covalent
bonding, physical adsorption, and chemical modification, can be used for this purpose
[12]. The identification and recognition of specific biomolecules form the basis for
the modifications of 3D graphene-based biosensors. With this purpose, a functional-
ized 3D structure can be fabricated using various fabrication techniques. One of the
most widely used processes for creating 3D graphene structures is electrospinning.
According to this method, a polymer solution or a graphene-containing melt is spun
to produce highly porous and conductive 3D graphene fibers. Other methods include
3D printing, self-assembly, and template creation. These methods are ideal for fabri-
cating high-precision and complex 3D graphene structures for difficult-to-control
systems [13, 15].
2.1 3D Printing
One of the most promising applications for developing micro or nanomaterials with
specific multifunctional characteristics and design flexibility is 3D printing, which
aims to address the growing demand for such materials. This process, which also
plays an active role in the production of graphene or its derivatives, is preferred in
most cases for the fabrication of complex 3D structures, as it offers significantly
better properties, shorter processing time, and lower printing costs [16].
2.2 Exfoliation
Graphite is a form of packaged graphene sheet bonded together by van der Wall ties.
For this reason, graphene can be obtained from the graphite raw material by breaking
the weak bonds (a repeated peeling process) using high-purity graphite [15].
Mechanical exfoliation: In this technique, tiny layers of graphene are peeled off from
a bulk sample of graphite using adhesive tape or a sharp object (such as pencil lead).
This process works well for manufacturing tiny quantities of high-quality graphene,
but it is unsuitable for fabrication on a large scale. Although this approach is more
scalable and less complicated than others, it enables the creation of graphene of
inferior quality.
Electrochemical exfoliation: This method involves suspending graphite flakes in a
liquid electrolyte and applying an electric current to exfoliate the flakes into indi-
vidual graphene layers. This method is relatively simple and scalable, but it allows
the production of lower-quality graphene compared to other methods.
Novoselov et al. investigated the ability of highly oriented pyrolytic graphite and
adhesive tape to block monocrystalline graphite films between the tape [17]. The
resulting structure was metallic, only a few atoms thick, and of extremely high quality.
It was also stable under ambient settings. In this work, they produced graphene as
thin as a few atoms by repeatedly manipulating the separated blocks. This method has
proven useful for producing small quantities of high-quality graphene; however, due
to its labor-intensive and time-consuming structure, it is not suitable for large-scale
productions [12].
2.3 Chemical Vapor Deposition
CVS is a technique for depositing material from the vapor phase onto a substrate
to form thin films and coats [18]. CVD is known as an inexpensive, efficient, high
quality, and reproducible production method [15]. In the context of graphene produc-
tion, CVD involves heating a substrate (such as copper or silicon) to a high temper-
ature (typically around 1000–1500 °C) and introducing a hydrocarbon gas (such as
methane or ethylene) into the chamber. The hydrocarbon gas decomposes on the
substrate and the carbon atoms rearrange themselves into a monolayer graphene
sheet. Graphene grows layer by layer on the substrate, and the thickness of the
graphene can be controlled by adjusting the growth time [12]. Transition metals
such as nickel, palladium, iridium, and copper are used as catalysts in this effective
method [18, 19].
The basic principle of electrochemical biosensors is based on the change in some
parameters (impedance, current, or potential) when a reaction occurs on an electrode
surface. Following this approach, graphene-based biosensors are primarily preferred
as they are effective in DNA and miRNA bioassays with their unique properties such
as ultra-high sensitivity, high selectivity, and the lowest limit of detection (LOD)
values [19].
In producing 3D graphene biosensors, the CVD method offers many advantages,
including:
. The capacity to develop graphene on a number of different substrates,
generate high-quality graphene films with few problems, and manufacture
reproducible and scalable graphene are all advantages of the CVD approach.
. It promotes the growth of high-quality graphene films with good coverage and
few defects. This property is important for biosensors that rely on graphene’s
electrical conductivity and stability to function properly.
. It allows graphene to grow on various surfaces (silicon and glass) in biosensor
devices.
. It can be used to grow graphene in a controlled and uniform manner, which is
important for producing reproducible biosensor devices.
. It can be used to deposit graphene over large areas, making it suitable for the
fabrication of scalable biosensor devices [15, 19, 20].
2.4 Electrodeposition
Electrodeposition is a process in which reduced metal ions are used to form a solid
metal residue on a substrate. The process typically involves the use of an ionic solution
containing metal ions and an electric current to drive the reduction reaction. The elec-
trodeposition method is widely used to prepare high-quality and low-cost graphene
films and is an advanced technique for the production of large-scale graphene [20].
In the electrodeposition method, an ultrathin layer of graphene is deposited on the
surface by applying an electric current in a precursor solution containing carbon

ions. The substrate is typically used as the cathode in the electrodeposition process.
Excellent properties of 3D graphene can be controlled by changing the electrode-
position conditions, such as the applied voltage and the precursor solution [20, 21].
Electrodeposition is the process of the electrochemical interaction of a thin layer
of conductive material (metals or conductive polymers) with the target analyte on
the surface of biosensors using an electric current from a solution. An increase in
contact area is given by the change of metal nanostructures in the cathode, which are
most typically formed from gold. For enzymes, this typically encourages electron
transfer directly between the surface of the metal and the active catalytic site. The
functionalized biosensor can be used in various fields, such as medical diagnostics,
oxygen saturation level, glucose monitoring, pulse rate, daily physical activity, food
safety, food quality, environmental analysis, and many other fields. This method has
been used since 1980 to improve the properties of sensors and biosensors. The three
most important reasons for choosing this method are (i) precision, (ii) selectivity,
and (iii) consistency [12, 21].
2.5 Folded Graphene
Folded graphene is a term used to describe a sheet of graphene that has been folded
or bent into a specific shape. The double fold can form a tri-layer region with highly
curved fold edges embedded in the endless single layer [22]. It was showed using
potential density functional theory calculations that bi-folding alters the electronic
band structure of 3D graphene and that localized electronic states can form in the
folded regions. This can be achieved by various methods such as mechanical folding,
electrostatic folding, or chemical folding [15, 22]. Folded graphene has gained atten-
tion in recent years as it has excellent electronic, chemical, mechanical, and thermal
properties that can be used for various applications such as energy storage devices,
sensors, and electronics. It has been shown that folded graphene can exhibit unique
electronic properties compared to plain graphene. For example, it has been found
that folded graphene can exhibit a bandgap not found in plain graphene [23].
Folded graphene-based material is preferred in sensor applications due to its
unique electronic and mechanical properties. Particularly, folded graphene can be
used as a conductive layer in a field-effect transistor (FET) sensor and mechan-
ical sensing elements. The greatest bindings in scientific knowledge are the two-
dimensional, carbon/carbon bindings found in monolayer graphene. These connec-
tions give graphene-based biosensors with its extraordinary mechanical strength,
flexibility, and toughness. Folded graphene can also be used in biosensor appli-
cations by functionalizing the graphene with biological recognition elements such
as enzymes, DNA, RNA, proteins, and antibodies that can bind to specific target
molecules [13, 23].
2.6 Directed Assembly
In the innovation of 3D graphene-based materials with hierarchical morphologies,

oriented assembly uses the remarkable and adaptable building blocks of 3D struc-
ture graphene and its functionalized derivatives. Due to the combination of the
3D graphene structure and the extraordinary fundamental characteristics of the
layered structure, 3D formulations show 3D graphene’s large specific surface areas,
small sizes, unique electron transport, shape, and high mechanical properties. 3D
architectures produced by this method exhibit graphene materials with small dimen-
sions, large specific surface areas, unique shapes, and high mechanical properties due
to the interaction of the 3D graphene structure and the extraordinary fundamental
properties of the layered structure. Here are a few methods that can be used for the
directed assembly of 3D graphene-based systems:
Self-assembly: This method involves using chemical or physical interactions between
graphene building blocks to drive the assembly process. For example, the researchers
used self-assembly to create 3D graphene structures by stacking graphene sheets
together using Van der Waals interactions [24].
Template creation: This method involves using a template, such as formwork or
scaffolding, to guide the assembly of the graphene building blocks. For example, the
researchers used templating to create 3D graphene structures by growing graphene
on a stencil patterned with a specific 3D shape. Directed assembly by using external
fields, and directed assembly by using DNA or proteins as scaffolds are also less
common methods.
3 Application and Characterization of 3D Graphene-Based

Biosensors
3D graphene-based biosensors are widely preferred in the field of health. Examples

of these are COVID-19 detection, advanced health technology applications, and indi-
vidualized medical applications. 3D graphene-based nanomaterial-based biosensors
are typically needed in the medical field, which is still in its infancy. The development,
extraordinary capabilities, and applications of next-generation 3D graphene-based
biosensors with smart and in situ modules are in high demand. The structural charac-
teristics of 3D graphene can be correlated with the crystal structure and the number
of layers of graphene in the 3D graphene. The crystal structure of graphene can be
either hexagonal (also known as “few-layer graphene”) or turbostratic (also known
as “disordered graphene”). Hexagonal graphene has a regular arrangement of carbon
atoms while turbostratic graphene has a disordered arrangement of carbon atoms. The
number of layers of graphene in a 3D structure may also vary, with some structures
having single layers of graphene and others having multiple layers [13, 14]. In fact,
the unique morphological and structural features of 3D graphene can have an impor-
tant effect on the development of the material and support its potential applications.
For example, structures with small, uniform particles may have better mechanical
properties and be more suitable for use in energy storage applications while struc-
tures with large particles may be more suitable for use in filtration and separation
applications. Similarly, structures with a high number of layers may show better
electrical performances and be more suitable for use in electronic applications while
structures with a low number of layers could be more suitable for use in biomedical
applications [12]. 3D graphene, a carbon molecule with layers of single carbon atoms
arranged in a hexagonal shape, has the function to detect bioactive molecules and their
composites. The 3D graphene layer’s special physical and chemical features, such
as superior thermal and electrical conductivity, optical transmittance, highly chem-
ically sensitive surface area, biocompatibility, and increased mechanical resistance,
make it an ideal solution for cancer biomarker detection. Graphene is able to achieve
the experimental goal of any biosensing, which is to generate more portable and
compact point-of-care equipment for early cancer diagnosis, pH, and temperature.
Graphene-based biosensors may detect a broad range of illnesses, their metabolites,
and infections in addition to detecting cancers. The effectiveness of nanoparticles in
detecting the majority of biochemical markers has been demonstrated by numerous
impressive recent studies [23, 25, 26].
Biosensors can be prepared of 3D graphene-based materials that appeal to a variety
of applications due to their distinctive features. The following are some of the crucial
traits of 3D graphene-based biosensors [15, 22]:
. High sensitivity: 3D graphene-based biosensors have an ultra-high sensitivity,
allowing for the detection of low concentrations of biomolecules.
. High selectivity: 3D graphene-based biosensors have a high selectivity, allowing
them to distinguish between different types of biomolecules.
. Fast response time: 3D graphene-based biosensors have a fast response time,
allowing for rapid detection of biomolecules.
. High stability: 3D graphene-based biosensors have a high stability, allowing them
to maintain their performance over a long period of time.
. Biocompatibility: Graphene is considered biocompatible, and 3D graphene-
based biosensors can also be biocompatible. It makes them suitable for use in
biomedical applications such as drug efficacy monitoring, disease diagnosis, and
environmental pollutant detection.
. Easy to fabricate: 3D graphene-based biosensors can be fabricated by growing
graphene on a substrate or assembling graphene nanoparticles into a 3D structure,
making them easy to produce and scale up.
. Low cost: 3D graphene-based biosensors can be made at low cost by using a
simple fabrication process, and the material is relatively inexpensive.
. High conductivity: Due to the high conductivity and transparency of 3D graphene-
based materials, CVD-graphene is an excellent choice for manufacturing flexible
electrodes used in optoelectronic applications [28].
In point-of-care (POC) systems, 3D graphene-based biosensors are frequently

low cost and simple to operate. Point-of-care systems could result from virtual and
real-time mobile medical screening using sensor technologies. Due to their potential
to identify patterns of indicator organisms and provide experimental data on their
existence in biological fluids, which enables correct assessment, 3D graphene-based
biosensors have been the center of significant research in recent years. Future point-
of-care 3D graphene-based biosensors will be limited in the types of biosensors
they can use because of requirements like rapid label-free detection, small sensor
size, and mobility with artificial intelligence approaches. It’s worth mentioning that
the properties of 3D graphene-based biosensors can vary depending on the specific
design and fabrication method. Therefore, to understand the properties and potential
sensor applications of biosensors, it is important to comprehensively characterize
them[12]. Some of the application areas of 3D graphene biosensors are [25]:
Medical Diagnostics
Because of its outstanding qualities in nano additive manufacturing, 3D graphene
as a filler has recently attracted a lot of study attention. 3D graphene biosensors can
be used to detect biomolecules such as proteins, DNA, and enzymes in the blood,
urine, and other body fluids. This type of early diagnosis is of great importance in the
prevention of diseases. The integration of all the applied studies into a single frame
and their relationship to global applications are two limitations that this research
is currently subject to. These 3D graphene-based biosensors, however, represent the
next generation of portable, adaptable, small, energy-efficient, and reasonably priced
medical technology that has the potential to reach even the most distant regions
of the globe. Additionally, making education and healthcare services available to
everyone, will contribute to the sustainable performance targets of human health and
well-being. As a result, hospital-in-chip biosensors have the ability to turn the current
health insurance system into a small-scale method of reducing future fatalities and
the severity of infectious and potentially lethal diseases. With this approach, Chen
et al. [28] prepared a novel 3D graphene-silver nanoparticle-based DNA biosensor for
the detection of the CYFRA21-1 DNA lung cancer biomarker. Experimental results
presented that the prepared DNA biosensor had good sensitivity (1.0 × 10−14 M)
in the range of 1.0 × 10−14 M–1.0 × 10−7 M. According to their research, this 3D
graphene-silver nanoparticle-based DNA biosensor has the ability to play a role in
the early detection of lung cancer.
Environmental applications
To present, a number of hybrid adsorbents based on graphene, GO, and rGO have been
studied for the excellent removal of inorganic and organic contaminants from water,
including chemicals that affect health. The preservation of water quality has been one
of the most urgent issues in the modern world. Recent years have seen an increase in
the number of dangerous pollutants in the environment, including, explosive mate-
rials, heavy metals, organophosphate pesticides, hydrocarbons, phenolic acids, and
other pollutants. This is due to the quick advancements in market and agriculture
as well as the widespread use of pharmaceutical chemicals in the ordinary routine.
A very minimal percentage of these carcinogenic compounds is dangerous, directly

enter the ecosystem, and can be extremely harmful to both the ecosystem and public
health. Thus, it is vital to develop acute, economic sensors that can quickly and
accurately identify these important chemicals. While GO has a variety of oxygen-
containing functional molecules on its surface, it has low binding interactions for ions
with negative charges and molecules due to strong electrostatic interactions between
them. Moreover, additional pollutants are produced by the problem of desorbing and
removing 3D graphene and its derivatives from tap wastewater following adsorp-
tion. The modification of graphene, GO, and rGO with other chemicals through
covalent or ionic bonding has been carried out to produce composite materials
having the extraordinary features of all the adsorbates. It was done to overcome
these shortcomings.
Alves et al. [29] developed a novel reduced graphene oxide (rGO)-modified glassy
carbon sensor for the amperometric sensing of diuron (DIU) herbicide in real water
and food samples. According to the experimental results, they found that the sensor
had a low detection limit of 0.36 µmol L−1 in the range of 5 µmol L−1 –50 µmol
L−1 and a high recovery of 81%–106%. In this regard, the proposed methodology
demonstrates that it can be used as an experimental platform for use in the examina-
tion of food and environmental real samples. In another study, Srivastava et al. [30]
prepared a graphene-based sensor for sensing different heavy metals such as cadmium
(Cd), arsenic (As), mercury (Hg), chromium (Cr), and lead (Pb). Experimental data;
confirmed that graphene, As, and Cr exhibited chemisorption interaction, while Pb
exhibited physisorption interaction. In addition, graphene has proven to have a high
detection capacity against heavy metals in threshold voltage.
Food applications
Food pollutants have received attention because they can appear at any step of food
manufacturing. Due to its detrimental impact on human health, a quick, selective,
flexible, sensitive, and robust method is required to analyze the unwanted substances
in food. Several scientists are currently taking a greater interest in the electrochemical
sensor technology utilized in food analysis. Jiang et al. [31] prepared a novel elec-
trochemical 3D graphene foam-based sensor for the determination of uric acid and
dopamine. They showed that the sensor had high sensitivities to uric acid (1.27 µM)
and dopamine (0.21 µM) in real samples. In this study, the electrochemical perfor-
mance of 3D graphene is confirmed to be high due to its outstanding physical and
chemical properties, such as its interesting electronic conductivity and large specific
surface area. The success of highly sensitive and precise uric acid and dopamine eval-
uation in real samples was demonstrated in relation to 3D graphene’s large specific
surface areas.
4 Comparative Sensing Performance of 3D

Graphene-Based Biosensors
Graphene is a two-dimensional substance comprised of carbon atoms arranged in a

hexagonal shape. One type of biosensor that uses graphene is called a 3D graphene-
based biosensor. They are compared with other reported biosensors in terms of their
sensitivity, specificity, cost, electrical conductivity, biocompatibility, stability, and
potential applications [27, 32]. These structures can include things like microfabri-
cated scaffolds, hydrogels, and other materials that can be used to develop a 3D envi-
ronment for the biological components of the biosensor [14]. There are many different
types of biosensors, each with its own unique characteristics and various applications
such as antibody-based biosensors, enzyme-based biosensors, cell-based biosensors,
optical sensors, and electrochemical sensors [32, 33].
Graphene has been used in transparent electrodes, field-effect transistors (FETs),
energy harvesting and storage, and many electronic applications with its superior
electronic and chemical properties. Furthermore, the small thickness of graphene
allows all carbon atoms to interact directly with the analyte. It means that it gives more
sensitive results in sensor applications compared to one-dimensional Si nanowires
(1D SiNWs) and carbon nanotubes [27, 34].
“Optical biosensors” are a type of sensor that uses light to detect changes in the
biological components of the sensor and has highly sensitive and specific proper-
ties. Optical biosensors have been used in various sensor applications, such as the
detection of biological components, enzymes, nucleic acids, proteins, and cells, and
can be used in various types of samples such as urine, blood, and saliva samples. 3D
graphene-based biosensors detect minor changes in biological components compared
to optical biosensors; they are preferred due to their high sensitivity, high specificity,
high surface area, and low cost [35]. He et al. investigated a 3D graphene foam
with several layers of graphene grown by the CVD method that can detect NO2 gas
at much lower concentrations compared to the commercially produced polypyrrole
sensor [27]. 3D graphene-based biosensors are biocompatible, meaning they can be
used without damaging living cells if they come into contact with them. They also
have a very stable structure and are highly resistant to harsh environments. In this
way, they are preferred in biosensors that need to be used in harsh conditions [32].
5 Future Outlook of 3D Graphene-Based Biosensors
3D graphene-based materials have garnered a lot of attention in recent years due

to their exceptional qualities, including strong electrical conductivity, a very high
surface area, stability and flexibility. The preparation of 3D graphene with a special
porosity structure is given a lot of attention because of the issues it encounters,
like its ease of aggregation. Nanomaterials are frequently created by combining
nanosized materials with 3D graphene to enhance their overall performance and

their applications.
One of the most promising applications of nanomaterials and 3D graphene-based
material is in energy storage fields. Graphene-based materials have a high elec-
trical conductivity and a high surface area, making them ideal for use in batteries
applications and supercapacitors studies. Researchers continue to explore the use
of graphene in lithium-ion batteries, where it can be used as a conductive mate-
rial to improve the performance of electrodes. The fabrication of graphene-based
supercapacitors, which have the potential to charge and discharge much faster than
conventional batteries and have a longer life, is also one of the promising applica-
tions. These energy storage systems will have an important place in electric vehicles,
in the production of portable electronics, and in many other areas of the renewable
energy system [36].
Graphene’s superior properties, such as its large surface area, high conductivity,
biocompatibility, make it highly suitable for general consumer applications and
multi-purpose use when making measurements such as strain, pressure, or magnetic
field using a single sensor. The large surface area, low pollution levels, and easy
functionalization make graphene suitable for further use in biosensing applications.
However, more work is needed to select a reliable, robust, environmentally sound,
and financially viable production method for such applications. In addition, excellent
properties of graphene make it a potential candidate for detecting and monitoring
cardiovascular and neurodegenerative diseases For example, previous studies showed
that graphene can be used to scavenge amyloid monomers, which are associated with
the development of neurodegenerative diseases such as Alzheimer’s.
Due to their unique morphology, 3D graphene-based materials have recently been
investigated for gas sensing applications since they provide a larger area of contact
and holes large enough in gas diffusion than their 2D materials. The 3D graphene-
system increases the sensor devices’ robustness and stability in addition to their sensi-
tivity and repeatability to gas molecules. According to numerous experts, graphene-
based sensors also offer effective H2 detection sensing capabilities. There have been
a few previous study of ultrasensitive H2 gas sensors composed of 3D graphenes, but
their use has been limiting due to their slow response and recovery times. In compar-
ison to traditional 2D graphene sensors, the findings on 3D graphene-based sensors
showed tremendous potential for its usage in a successful comprehension in sensing
performance. In comparison to pure graphene, the addition of functional groups
provides the 3D graphene surface more sensitive to target molecules. The degree of
control of the binding sites may significantly improve the improved electrochemical
and optical performance of 3D graphene-based sensors and enable ongoing research
in gas sensing systems. The modification of graphene-based materials, synthesis
method, control of the functional groups, and development of composite materials are
some effective techniques to enhance 3D graphene-based sensor’s sensing capacity.
New types of molecular-scale bioelectronic systems based on graphene contribute
to the development of engineered tissues with biosensors closely integrated into
natural tissues, in addition to the improvement of in vitro formulations for nanoma-
terials’ close association with cells and tissues, fundamental research or biomedical
applications. Such laboratory-on-a-chip systems enable, for example, the testing of

candidate bio-therapeutic molecules. In addition, graphene-based biosensors have
begun to be produced for the early detection and continuous monitoring of the
progression of some common cancer diseases [37]. Unfortunately, these studies are
very limited. Many studies need to be expanded to be used more effectively for the
production of biosensors in the health field. While research in this area is still in its
infancy, the potential for graphene to impact the medical field in such a significant
way is certainly worth further exploration. The use of 3D graphene-based biosensors
in point-of-care diagnostics and personalized medicine is also seen as a promising
area of research [38, 39].
In the future studies, 3D graphene-based biosensors are expected to have improved
sensitivity, selectivity, and affordability in the field of sensors. Wide-ranging fields,
particularly in catalysis, energy, and smart drug systems, could benefit from the
improved electrochemical property of 3D graphene mixed with polymers, inorganic
compounds, and other biomaterials. The exploration of wearable, flexible, portable,
and economical electrochemical sensors based on 3D graphene nanomaterials will
undoubtedly receive increasing attention. Finally, the use of 3D graphene-based
biosensors in point-of-care diagnostics and personalized medicine is also seen as a
promising area of research [13, 39].
References
1. Pallas-Areny, R., Webster, J.G.: kupdf.net_pallas-areny-r-jg-webster-sensors-and-signal-

conditioning-wiley-1991 (1991)
2. Ikram, M., Bari, M.A., Bilal, M., Jamal, F., Nabgan, W., Haider, J., et al.: Innovations in the
synthesis of graphene nanostructures for bio and gas sensors. Biomater. Adv. 145, 213234
(2023)
3. Hegde, M., Pai, P., Gangadhar Shetty, M., Sundara Babitha, K.: Gold nanoparticle based biosen-
sors for rapid pathogen detection: a review. Environ. Nanotechnol. Monitoring Manag., 100756
(2022)
4. Liu, C., Xu, D., Dong, X., Huang, Q.: A review: research progress of SERS-based sensors for
agricultural applications. Trends Food Sci. Technol. 128, 90–101 (2022)
5. Gupta, Y., Ghrera, A.S.: Recent advances in gold nanoparticle-based lateral flow immunoassay
for the detection of bacterial infection. Arch. Microbiol. 203(7), 3767–3784 (2021)
6. Sadsri, V., Trakulsujaritchok, T., Tangwattanachuleeporn, M., Hoven, V.P., Na, P.: Simple
colorimetric assay for vibrio parahaemolyticus detection using aptamer-functionalized
nanoparticles. ACS Omega 5(34), 21437–21442 (2020)
7. Ahmadi, S., Kamaladini, H., Haddadi, F., Sharifmoghadam, M.R.: Thiol-capped gold nanopar-
ticle biosensors for rapid and sensitive visual colorimetric detection of Klebsiella pneumoniae.
J. Fluoresc. 28(4), 987–998 (2018)
8. Tonezzer, M., Lacerda, R.G.: Zinc oxide nanowires on carbon microfiber as flexible gas sensor.
Physica E 44(6), 1098–1102 (2012)
9. Lupan, O., Schütt, F., Postica, V., Smazna, D., Mishra, Y.K., Adelung, R.: Sensing performances
of pure and hybridized carbon nanotubes-ZnO nanowire networks: a detailed study. Scientific
Reports 7(1) (2017)
10. Vasita, R., Katti, D.S.: Nanofibers and their applications in tissue engineering. Int. J. Nanomed.
1(1), 15–30 (2006)
11. Cheng, Y., Xiong, Y., Pan, M., Li, L., Dong, L.: A flexible, sensitive and stable humidity sensor
based on an all-polymer nanofiber film. Mater. Lett. 330 (2023)
12. Sun, Z., Fang, S., Hu, Y.H.: 3D Graphene materials: from understanding to design and synthesis
control. Chem. Rev. 120(18), 10336–10453 (2020)
13. Moldovan, O., Iñiguez, B., Deen, M.J., Marsal, L.F.: Graphene electronic sensors—review of
recent developments and future challenges. IET Circuits Dev. Syst. 9(6), 446–453 (2015)
14. Bianco, A., Cheng, H.-M., Enoki, T., Gogotsi, Y., Hurt, R.H., Koratkar, N., et al.: All in the
graphene family-a recommended nomenclature for two-dimensional carbon materials (2013)
15. Bedeloğlu, A., Taş, M.: Graphene and its production methods. Afyon Kocatepe Univ. J. Sci
Eng. 16(3), 544–554 (2016)
16. Ponnamma, D., Yin, Y., Salim, N., Parameswaranpillai, J., Thomas, S., Hameed, N.: Recent
progress and multifunctional applications of 3D printed graphene nanocomposites. Compos.
Part B: Eng., 204 (2021)
17. Novoselov, K.S., Geim, A.K., Morozov, S.V., Jiang, D., Zhang, Y., Dubonos, S.V. et al.: Electric
Field Effect in Atomically Thin Carbon Films (n.d.)
18. Bahri, M., Gebre, S.H., Elaguech, M.A., Dajan, F.T., Sendeku, M.G., Tlili, C. et al.: Recent
advances in chemical vapour deposition techniques for graphene-based nanoarchitectures: from
synthesis to contemporary applications. Coordination Chem. Rev., 475 (2023)
19. Mattevi, C., Kim, H., Chhowalla, M.: A review of chemical vapour deposition of graphene on
copper. J. Mater. Chem. 21(10), 3324–3334 (2011)
20. Biswal, H.J., Vundavilli, P.R., Gupta, A.: Perspective—electrodeposition of graphene rein-
forced metal matrix composites for enhanced mechanical and physical properties: a review. J.
Electrochem. Soc. 167(14), 146501 (2020)
21. Stine, K.J.: Biosensor applications of electrodeposited nanostructures. Appl. Sci. (Switzerland)
9(4) (2019)
22. Kim, K., Lee, Z., Malone, B.D., Chan, K.T., Alemán, B., Regan, W. et al.: Multiply folded
graphene. Phys. Rev. B Condensed Matter Mater. Phys., 83 (24) (2011)
23. Zhang, C., Li, Z., Jiang, S.Z., Li, C.H., Xu, S.C., Yu, J., et al.: U-bent fiber optic SPR sensor
based on graphene/AgNPs. Sens. Actuators B Chem. 251, 127–133 (2017)
24. Cao, X., Yin, Z., Zhang, H.: Three-dimensional graphene materials: preparation, structures and
application in supercapacitors. Energy Environ. Sci. 7(6), 1850–1865 (2014)
25. Lei, H., Mi, L., Zhou, X., Chen, J., Hu, J., Guo, S., et al.: Adsorption of double-stranded DNA
to graphene oxide preventing enzymatic digestion. Nanoscale 3(9), 3888–3892 (2011)
26. Schedin1, F., Geim1, A.K., Morozov2, S.V., Hill1, E.W., Blake1, P., Katsnelson3, M.I. et al.:
Detection of Individual Gas Molecules Adsorbed on Graphene (n.d.)
27. He, Q., Wu, S., Yin, Z., Zhang, H.: Graphene-based electronic sensors. Chem. Sci. 3(6), 1764–
1772 (2012)
28. Chen, M., Wang, Y., Su, H., Mao, L., Jiang, X., Zhang, T., et al.: Three-dimensional electro-
chemical DNA biosensor based on 3D graphene-Ag nanoparticles for sensitive detection of
CYFRA21-1 in non-small cell lung cancer. Sens. Actuators B Chem. 255, 2910–2918 (2018)
29. Alves, G.F., de Faria, L.V., Lisboa, T.P., Matos, M.A.C., Muñoz, R.A.A., Matos, R.C.: Simple
and fast batch injection analysis method for monitoring diuron herbicide residues in juice and
tap water samples using reduced graphene oxide sensor. J. Food Compos. Anal. 106, 104284
(2022)
30. Srivastava, M., Srivastava, A., Pandey, S.K.: Suitability of graphene monolayer as sensor for
carcinogenic heavy metals in water: a DFT investigation. Appl. Surf. Sci. 517, 146021 (2020)
31. Jiang, J., Wang, J., Wang, P., Lin, X., Diao, G.: Three-dimensional graphene foams with two
hierarchical pore structures for metal-free electrochemical assays of dopamine and uric acid
from high concentration of ascorbic acid. J. Electroanal. Chem. 928, 117056 (2023)
32. Liu, Y., Dong, X., Chen, P.: Biological and chemical sensors based on graphene materials.
Chem. Soc. Rev. 41(6), 2283–2307 (2012)
33. Xie, Y., Xie, G., Yuan, J., Zhang, J., Yang, Y., Yao, Y., et al.: A novel fluorescence biosensor
based on double-stranded DNA branch migration-induced HCR and DNAzyme feedback circuit
for sensitive detection of Pseudomonas aeruginosa (clean version). Analytica Chimica Acta,
1232 (2022)
34. Wang, F., Liu, L., Li, W.J.: Graphene-based glucose sensors: a brief review. İn: IEEE Trans
Nanobioscience, Institute of Electrical and Electronics Engineers Inc., pp. 818–834 (2015)
35. Cao, X., Shi, Y., Shi, W., Lu, G., Huang, X., Yan, Q., et al.: Preparation of novel 3D graphene
networks for supercapacitor applications. Small 7(22), 3163–3168 (2011)
36. Gao, X., Li, J., Xie, Y., Guan, D., Yuan, C.: A multilayered silicon-reduced graphene oxide
electrode for high performance lithium-ion batteries. ACS Appl. Mater. Interfaces. 7(15), 7855–
7862 (2015)
37. Goenka, S., Sant, V., Sant, S.: Graphene-based nanomaterials for drug delivery and tissue
engineering. J. Control. Release 173(1), 75–88 (2014)
38. Cohen-, T., Langer, R., Kohane, D.S.: The smartest materials: the future of nanoelectronics in
medicine. ACS Nano 6(8), 6541–6545 (2012)
39. Celik, N., Balachandran, W., Manivannan, N.: Graphene-based biosensors: methods, analysis
and future perspectives. IET Circuits Dev. Syst. 9(6), 434–445 (2015)
3D Graphene-Based Optical Sensors
Amrit Kumar, V. Manjuladevi, and Raj Kumar Gupta
Abstract 3D graphene (3DG) has been utilized as a functional material for the
development of gas and chemical sensors. The sensor based on optical phenomena
such as surface plasmon resonance (SPR) offers label-free measurements at a very
high resolution and sensitivity. It is essential for any sensor to exhibit a very high
analyte adsorption capability and good perceptibility to measure changes in elec-
trical and optical properties due to such adsorption. Although SPR is extremely
sensitive, 3DG is one of the potential functional materials which can exhibit a high
analyte adsorption capability. Therefore, the use of 3DG as a functional layer in
SPR devices can ensure a next-generation sensor. The Kretschmann configuration in
angular interrogation-based SPR sensors may offer a sensitivity of the order of 10–8
RIU. In the SPR sensor, the extent of the plasmonic field over the metallic surface
is limited to a few hundred nanometres. The excellent adsorption capability of 3D
graphene can be employed for bio-sensing applications. However, due to the bulk
nature of 3DG, the plasmonic field during SPR-based sensing decays rapidly into the
porous structure of the 3DG, and therefore, the measurement becomes unresponsive
even after the efficient adsorption of the analytes. Therefore, the layer of 3D graphene
can be grown over the gold surface by some bottom-up deposition mechanism with
control over the thickness. The bottom-up deposition mechanism may yield mono-
layer, bilayer, and twisted bilayer graphene which also exhibit excellent bio-sensing
merits.
Keywords 3D graphene · Surface plasmon resonance · Biosensing · Monolayer ·

Bilayer graphene · Twisted bilayer graphene
A. Kumar · V. Manjuladevi · R. K. Gupta (B)

Department of Physics, Birla Institute of Technology and Science Pilani, (BITS Pilani),
Pilani 333031, Rajasthan, India
e-mail: raj@pilani.bits-pilani.ac.in
https://doi.org/10.1007/978-3-031-36249-1_7
112 A. Kumar et al.
1 Introduction
Since its discovery in 2004, graphene has been considered one of the most widely used
nanomaterials in diverse applications. This 2D hexagonal crystalline arrangement of
carbon atoms has inducted a great deal of interest in the fields of sensors, biomedi-
cals, composite materials, and microelectronics. Graphene has sp2 hybridized carbon
atoms arranged in a honeycomb-like network on a single plane. It is the thinnest
material with an unusually large specific surface area. Graphene has many unique
properties due to its long-range π–π conjugation including high chemical stability,
excellent mechanical strength, enormous electron mobility, and outstanding thermal
conductivity at room temperature. It also demonstrates excellent optical properties
including wideband optical absorption in the near-infrared and visible range. The
nonlinear optical feature such as saturation absorption is also observed for graphene
and its derivatives. Moreover, graphene systems have a unique band structure. The
Fermi surface is located at the junction of the completely filled valence band and
the empty conduction band, and in the middle of the band formed by p-orbitals [1].
The electrons in the valence band of graphene have very high mobility and are also
known as massless Dirac Fermions. Due to the linear distribution of the Dirac elec-
trons, a single layer of graphene absorbs 2.3% of the incident light from the visible
to the terahertz band [2]. Thus, even though single-layer graphene has a thickness
of 3.35 Å, its absorbance is predominately very high. These fast Dirac Fermions
have a linear energy–momentum dispersion ratio around the Dirac point, allowing
for an ultra-wide frequency range resonant optical response to input photons. Thus,
due to its unique optical and electrical characteristics, graphene has been employed
in various optical devices such as polarizers, modulators, ultrafast lasers, sensors,
photodetectors, and light-emitting diodes. The excellent physicochemical properties
of graphene play a vital role in various sensing applications. These sensors are based
on the electrical, electrochemical, or optical properties of graphene.
Despite of many promising applications of 3D graphene, the drawbacks in the
scalable production of high-quality graphene with minimal defects have prevented its
prevalent use in physical devices. This, on the other hand, has propelled the growth of
graphene-based chemistry research, where many novel ways to synthesize graphene
materials with different functionality and w application of graphene materials have
been projected.
2 3D Graphene
One way to overcome the drawbacks is to build 3D structures of the 2D interconnected

graphene layers. These 3D structures can maintain the extraordinary qualities of 2D
graphene materials while also being easily used without the issue of restacking. The
interconnected graphene sheets form a highly 3D conductive network with ultrahigh
porosity, extremely low density, high surface area, and exceptional electrical, optical,
3D Graphene-Based Optical Sensors 113
and mechanical properties. Thus, the capabilities and potential uses of graphene are
significantly increased through the assembly and integration of the 2D graphene
sheets into 3D form. 3DG materials are explicitly characterized as nongraphite 3D
structured graphene materials. 3DG walls may have less than ten graphene layers
which retain the typical features of graphene materials.
In general, 3D graphene structures can be divided into two groups: (1) micro-
scopic 3D graphene materials which are less than 100 μm along all dimensions,
and (2) macroscale 3D graphene materials, which are greater than 100 μm in one or
more dimensions. These 3D graphene structures are widely regarded as 3D graphene
monoliths (foams/sponges/aerogels), films, fibers, and milli spheres.
Recently, substantial progress has been achieved in the production of 3D graphene
(3DG) with ultralow density and customizable optical properties, which may open
the way for graphene to be used as an ultralight, wideband, and wide-angle tera-
hertz absorber [3]. In comparison to conventional 2D graphene and functionalized
graphene networks, 3DG with an extremely porous structure has higher absorption
intensity, a wider qualifying bandwidth, and a significantly lower density. The porous
structure and long-range conductive network of 3DG are responsible for its excellent
optical efficiency and broadband absorption performance. The effective dielectric
constants of 3DG may match the dielectric constants of air. Thus, the design of a
highly porous structure becomes critical in reducing surface reflection in comparison
to other graphene systems [4]. Because of their finite (micrometer) thickness, 3DG
samples have virtually constant minimal transmittance, corresponding to 99% extinc-
tion of incident light in the near-infrared and visible spectrum [5]. It shows excellent
absorption of the electromagnetic (EM) wave in the frequency range from 0.1 to 1.2
THz due to low surface reflection and high internal absorption. The absorbance can be
modified by changing the physical parameters such as pore size, annealing temper-
ature, and the angle of incidence of the external electromagnetic field [4]. It also
exhibits high-frequency pass-filter behavior with a sharp rise in transmittance from
THz to mid-Infrared. The transmittance achieves a saturation value of about 13% in
this range. For the lower frequency (below 1THz), the transmittance converges to a
minimum value [6]. The observed broadband transmittance behavior implies that due
to their nano and micro spatial morphology light-matter interaction is dominated by
scattering processes. This exhibits that the optical properties of 3D graphene samples
are directed by scattering, rather than the usual intrinsic absorption that occurs in the
graphene layers. This is further supported by the absence of absorptive characteris-
tics in the UV spectral region, which predicts the interband electronic transitions in
graphene. The absence of such absorptive characteristics is due to the higher intrinsic
roughness (>100 nm) related to interconnected graphene layers which are similar in
nanoporous metal frameworks [7]. The 3DG architectures are effective absorbers
in the microwave frequency range (i.e., 2 GHz–110 GHz). The frequency range is
engaged for many critical applications, including radar-centered detections, satellite
communications, and remote sensing [3]. It’s interesting to note that 3DG structures
with a nonporous structure display exceptional photosensitivity for increased light
absorption and photo carrier transfer. Ito et al. [8] have reported that optimized 3DG
exhibits a ~40-times higher light absorption than monolayer graphene materials. The
114 A. Kumar et al.
photodetector based on 3D graphene validates extraordinary photo response of 3.10

× 104 A/W at room temperature and retains an excellent external quantum efficiency
of 1.04 × 107 %, which is higher than that of commercial silicon photodetector (~6.5
× 105 %).
To improve the physicochemical properties of 3D graphene-based materials,
nanocomposites of 3D graphene with technologically important materials can be
developed. The 3D nanocomposite structures of graphene can offer objective-driven
physicochemical properties. It can also exhibit high porosity, a large surface-to-
volume ratio, and excellent electron and mass transfer materials during device oper-
ation. Polymers, metal, and metal oxides can easily be incorporated during the fabri-
cation of the nanostructure of 3D graphene [9]. These nanocomposites promise wider
applications such as energy storage, sensors, water treatment, catalysts, and electro-
magnetic interference (EMI) shielding. The EMI shielding materials are essential to
address the EM pollution in our daily life. The shielding materials protects not only
the electrical devices, but also the health of human being due to prolonged exposure
to non-avoidable EM radiations. EM shielding is required for defense-related equip-
ment seeking stealth technology. In general, EM shielding can be obtained using a
conductor such as metal. The present state of the art requires the EM shielding mate-
rial not only to be good in thermal and electrical conduction, but also flexible and
lightweight. The research in this field employs composites of epoxy resin as EMI
shielding materials as it offers good flexibility, thermal and electrical properties,
easy processibility, and low cost. However, the shielding effectiveness (SE) needs
tremendous improvement due to advancements in technology causing EM pollution
and defense threat with rapid development. The shielding material can be improvised
by adding nanofillers in epoxy resin. There are several works where the nanocompos-
ites of epoxy resin with carbon nanotubes and graphene have been utilized. However,
the improvement in SE was found to be minuscule. 3D graphene can be a suitable
material due to its excellent electrical and thermal behavior, porous structure, and
easy dispersibility in solvents. The 3D graphene can act as a template for devel-
oping polymer nanocomposite for EMI shielding applications. Wan et al. [10] have
developed a 3 mm thick graphene aerogel-epoxy composite layer for an EMI shield.
They reported the best SE to be around 30 dB. The low performance is due to poor
conducting networks in such composites. In an interesting article by Liang et al. [11],
a template method was reported for the fabrication of 3D graphene nanoplatelets/
reduced graphene oxide foam/epoxy (GNPs/rGO/EP). The 3D framework enhances
the EMI shielding remarkably with an SE value ~51 dB. The porous 3D structures
exhibited excellent electrical conductivity (Fig. 1) and can entrap the EM waves by
absorption and internal scattering in the nanocomposites. This ensures a very high
degree of EMI shielding performance by the 3D graphene nanocomposites.
Fig. 1 Schematic of 3D graphene nanocomposites for electromagnetic shielding application.

Adapted with permission [11], Copyright (2019), Royal Society of Chemistry
3 3D Graphene-Based Sensors
Due to its interesting physical properties, 3DG may offer a variety of sensing applica-
tions. It offers high electroactive surface area, good inner and outer surface contact
with the analyte, ease of loading with (bio)catalysts, and strong electrochemical
sensitivity. The 3D linked network provides many electron routes, allowing for quick
and sensitive analyte detection. The interconnected open porosity of the 3D graphene
may facilitate the kinetic diffusion and mass transfer of macromolecules. The porous
network allows efficient absorption of small biomolecules as well as micromolecules.
The high surface-to-volume ratio and the porous structure of the 3D graphene network
amplify the interaction between gas molecules and the 3D network of sp2 hybridized
carbon atoms. Xing et al. [12] enhanced the sensitivity of a graphene-based optical
fiber humidity sensor by employing a 3D graphene network as a cladding mate-
rial. They observed enhancement in the response time and sensitivity compared to
the conventional graphene cladding optical fiber-based humidity sensor. At present,
3D graphene is predominantly studied for gas sensing, biofuel cells, energy storage
supercapacitors, electrochemical sensing, and battery applications [13]. It is a poten-
tial material for the electrochemical sensing of toxic heavy metals [14]. In terms of
gases, 3D graphene is very sensitive to gases such as NO2 and NH3 . The adsorption
and desorption of the analyte gases on 3D graphene need to be accelerated to reduce
the response and recovery times of the sensor [15]. Figure 2 shows the normal-
ized change in electrical resistance (/\R/R) during the sensing of NH3 and NO2 at
different concentrations. The recovery of the sensor is completely achieved by the
Joule heating ~400 K [16].
Compared to the different graphene-based biosensors, 3D graphene exhibits the
highest affinity for redox species mass transfer. 3D graphene has a larger surface
area than its 2D equivalents. Thus, more enzymatic, and catalytic activities can take
place at the surface of the materials. As a result, it is an excellent option for photo-
electrochemical sensors for various bio-analytes and enzymes. Wang et al. [17] have
116 A. Kumar et al.
Fig. 2 a Normalized change

in electrical resistance (/\R/
R) as a function of time for
three cycles at a
concentration of 1000 ppm
of NH3 . b, c Sensing cycles
for NH3 and NO2 ,
respectively. Adapted with
(2011), Nature
developed a photo-electrochemical biosensor for studying the enzymatic activity of

lipase. The immobilization of glycerol dehydrogenase on the photoelectrode was
found to be easier due to the huge specific surface area of 3D graphene. The sensor
showed outstanding optoelectronic characteristics and clear signal amplification. The
photoelectric response of the sensor in the presence of glycerol was activated by a
redox interaction between the enzyme and the substrate that results in an electron
transfer under the influence of light. The photocurrent was linearly associated with
the lipase activity throughout the 0.1–6 U/mL range of enzyme activity, proving the
utility of the biosensor with a detection limit as low as 0.069 U/mL. The above result
indicates that the 3D graphene is highly responsive toward the external incident light.
Therefore, the application of 3D graphene structures for optical and optoelectronic
sensing is clearly foreseen.
The 3D nanoarchitecture of graphene is also being efficiently employed for
Surface Enhanced Raman Spectroscopy (SERS). In 3D graphene, high-intensity
hot spots magnify the SERS signals remarkably. These high-intensity hot spots
are formed due to broad plasmonic peaks from 550–850 nm. The plasmonic peak
broadening signifies the aggregation of nanomaterials; these aggregations are very
conducive to the formation of amplified Raman signals. Thus, the 3D graphene nano
architectures have the potential to be employed in the SERS of different bio conju-
gates and analytes in future research. Fan et al. [18] developed a chemically modified
3D plasmonic graphene architecture to employ as a selective sensor for rotavirus
using SERS. They observed that extremely selective and sensitive virus detection
is conceivable due to the presence of broad plasmonic peaks and high-intensity hot
spots in the magneto-plasmonic 3D graphene configuration system.
The SERS substrate should be stimulated at its localized surface plasmon reso-
nance (LSPR) peak for the most effective surface-enhanced Raman scattering. In
the conventional SERS platforms, metal nanoparticles are employed for the sensi-
tive detection of analytes. In recent years, it has been observed that the practice
of graphene/metal hybrid structure gives a much higher field enhancement. This
enhancement ascends due to the strong coupling between the metallic nanoparti-
cles and the graphene layer. The 3D graphene structures, due to their large specific
surface area and improved optical scattering, are being employed for SERS-based
chemical sensing. The dispersed light from many metallic nanoparticles located on
multi-layer graphene sheets in 3D graphene is incorporated cumulatively, leading to
a greater Raman enhancement factor. Srichan et al. [19] studied the field enhance-
ment in silver/3D graphene foam composite SERS platform and compared the results
with the conventional silver/graphene and silver/silicon substrates. They observed
approximately 104 times Raman signal enhancement compared to the other SERS
substrate. They further employed the fabricated substrate for low-level detection of
methylene blue. For sensing studies, the sensitivity of the silver/3D graphene foam
composite offered the highest sensitivity and best lower-level detection.
Due to the absence of a bandgap in graphene, fluorescence has not yet been seen
in pristine two-dimensional (2D) or three-dimensional (3D) graphene. However,
creating fluorescent-labeled graphene by noncovalent or covalent alteration is one
of the best techniques to adjust the optical characteristics of graphene. It has been
observed, most organic compounds have a limited lifespan, and more significantly,
when adsorbed on graphene sheets, their fluorescence is quickly satiated because
of photoinduced electron transfer or energy transfer to graphene. Therefore, to
encourage fluorescence, 2D graphene is doped with some rare earth elements. Rare
118 A. Kumar et al.
earth elements such as lanthanides ion compounds have been one of the finest fami-
lies of inorganic luminous metals. They attracted attention due to their high quantum
yields, extended luminescence durations, considerable stokes shifts, and outstanding
chemical stabilities. Therefore, to study the photoluminescence of 3D graphene,
Wang et al. [20] have presented a one-step hydrothermal method for preparing triva-
lent Europium (Eu)-complexed graphene in a 3D self-assembled architecture. In
addition to altering the inherent structure of 3D self-assembled graphene and adding
active emission sites, complexing it with Eu-ions results in unique phenomena and
abilities. The outcomes show that doping Eu-ion is a feasible method to enhance
graphene’s photoluminescence performance. Its potential use in optoelectronics and
bio-sensing is indicated by its dual optical activities, such as self-luminescence and
quenching of organic dye fluorescence.
The existence of intrinsic 2D Dirac plasmons in 3D graphene shows strong and
tuneable plasmonic absorption from terahertz to mid-infrared through appropriate
doping and pore size control. Thus, the nonporous 3D graphene can be used to develop
plasmonic-based sensors. Plasmonic sensing is based on the interaction of light with
free electrons in the graphene lattice. Because of its large surface area, 3D graphene
is the potential candidate to be engaged as a substrate for plasmonic sensing [5]. This
can improve the interaction between light and the graphene surface. The plasmonic
behaviors of graphene are similar to those generated at the metal–dielectric inter-
face. Additionally, the plasmonic waves on graphene exhibit low losses in a range of
frequencies and better mechanical flexibility. Graphene shows a better light–matter
interaction. These attributes make graphene suitable for nanophotonic and waveg-
uide applications. Several 3D graphene structures have been proposed with the possi-
bility of better waveguide applications. In an interesting article [21], a 3D graphene
structure has been reported to generate transverse electric and transverse magnetic
graphene plasmon polaritons. The proposed structure can be used for the detection of
electromagnetic wave detection. The plasmon polaritons are found to be stable under
temperature variation. Such structure can be used for photonic devices operating in
extreme environments. The excellent optical properties of 3DG in addition to the
superior analyte adsorption capabilities can ensure that it is a wonderful functional
material for sensing applications through the efficient SPR optical phenomenon. The
Kretschmann configuration in an angular interrogation-based SPR sensor consists
of a functional layer deposited over the gold surface. The selectivity and sensitivity
of the sensor depend on the nature of the functional layer. At the resonance, the
plasmonic field generated in the gold film gets perturbed due to the interaction of the
analytes with that of the functional layer. Such interaction may change the refractive
index which can be measured at a very high resolution using the SPR phenomenon.
The extent of the plasmonic field in the sensing medium decays rapidly, and there-
fore, the thickness of the functional layer should be optimal for perception by the
SPR sensing instrument. Although 3DG can be an ideal functional layer for analyte
adsorption capability and exceptional electrical and optical properties, the bulk nature
of the 3DG can reduce the SPR perception even due to the adsorption of the analytes.
It is, therefore, essential to deposit the 3DG over the gold film through a bottom-up
mechanism that ensures good control over the thickness. Some of the bottom-up
deposition techniques are Langmuir–Blodgett and chemical vapor deposition mech-

anisms. Using the bottom-up deposition techniques often a functionalized film of the
monolayer, bilayer, and twisted bilayer graphene is obtained. These films of graphene
can be considered as a 2D layer that exhibits physicochemical properties similar to
2D graphene. It is, therefore, essential to understand the bio-sensing performance of
the graphene in its fundamental geometrical states, i.e., 2D graphene in monolayer
and bilayer graphene (MLG) states. Additionally, the electrical and optical properties
of the BLG system are found to be dependent on the in-plane twist angle between
the individual layers. The understanding of such a graphene system may enable us to
develop the next-generation SPR biosensors using 3GD as the functional materials.
Hence, further discussion follows some preliminary studies on bio-sensing using 2D
graphene as the functional material.
2D Graphene: The superior optical properties of graphene are due to its unique two-
dimensional band structure. Its exceptional optical features such as tuneable broad-
band absorption, saturation absorption, polarization-dependent effects, and fluores-
cence have drawn scientific attention. It shows a resonant optical response to photons
at any frequency in the broadband spectrum [22]. The linear optical characterization
shows that it has high absorbance in the incident visible light [23]. The reflectance
and absorption of graphene monolayer depend on Drude–Boltzmann conductivity
for infrared incidence and interband absorption for lower wavelength. The absorp-
tion spectra for the monolayer graphene show three major peaks as shown in Fig. 3.
The low energy peaks (2.62 eV and 4.45 eV) are attributed to the π–π ∗ transition
and the high energy peak (14 eV) is attributed to σ–σ ∗ interband transitions. The
corresponding variation in the real (n) and imaginary (γ ) parts of the refractive index
is consistent with Lorentz’s electron model of the origin of the refractive index (RI).
The broadened spectra of n shown in Fig. 3 are caused by an empty conduction
band and a completely filled valence band in monolayer graphene, which generates
free electron–hole pairs that are ready to be stimulated by incoming photons. The
optical characteristics of graphene are also dependent on its structure. It varies with
the number of graphene layers due to stacking. The bilayer graphene has different
optical properties based on the type of stacking. For instance, AA-type stacking
exhibits nearly monolayer type of behavior whereas AB-stacked bilayer has different
behavior as compared to that of monolayer graphene. This variation in properties
is due to the difference in the band structure of AA and AB stacking of the bilayer
graphene. In AA stacking, the band structure shows two identical copies of monolayer
bands that are vertically offset from each other, with Dirac cones located at the
edge of the Brillouin zone. On the other hand, the band structure in AB stacking
appears as a pair of intersecting parabolic bands, with additional parabolic bands
located further away from these intersecting bands. Further, the band structure gets
more complex if the bilayer system contains an additional relative in-plane twist
between the layers. The optical properties are also altered due to such twists. The
development of the Moiré pattern because of the application of relative in-plane
twist in the bilayer graphene suggests that the optical and electrical characteristics
can be altered as a function of the twist angle. If a relative in-plane twist is applied
120 A. Kumar et al.
Fig. 3 Real index of

refraction (n) and absorption
spectra (γ) of monolayer
graphene, where the
refractive index
(r = n + iγ ). Adapted with
(2022), IOP
in the AA-type of stacked bilayer graphene, it shows a dominant dielectric material

type behavior for a wide range of incident wavelengths, whereas in AB, it has semi-
metallic and metallic behavior depending on the twist angle [24]. Thus, depending
on the relative in-plane twist angle, twisted bilayer graphene exhibits either a semi-
metallic, dielectric, metallic, or semiconducting behavior, over a range of incident
energy photons. Such flexibility in bilayer graphene promises a range of innovative
applications including waveguides, sensors, and modulators.
Monolayer and bilayer graphene-based optical sensors: Optical sensors based
on graphene exploit its excellent optical properties which are generally designed
to analyze the energy transfer mechanism between the source and the material.
Graphene has ultrahigh luminescence quenching efficacy, a large planar surface
that permits simultaneous adsorption of multiple analytes to achieve detection in
the same solution. Graphene possesses excellent capabilities for the adsorption of
biomolecules due to the π–π stacking and hydrophobic interactions. The three
primary types of graphene-based optical sensors available are surface plasmon reso-
nance (SPR) sensors [25], graphene-based photoluminescence sensors [26], and
graphene-based spatial light sensors [27]. The SPR sensor is highly sensitive, label-
free, and capable of real-time measurement. SPR sensors can be used for real-time
monitoring, rapid detection, high sensitivity, tracking and observing ligand stability,
maintaining reaction equilibrium, and a variety of other applications. In a conven-
tional SPR system, a metallic layer (preferably Au or Ag) of optimal thickness is
coupled with a high-index glass prism. Surface plasmon (SP) waves are generated
at the metal–dielectric interface due to the incident EM radiation. These SP waves

are due to the collective oscillations of free charges at the metallic surface. When the
wavevector of the incident radiation and the SP waves exhibit a matching condition, a
resonance is established. At resonance, the maximum energy is transferred from the
incident wave to the SP wave, leading to the extinction of the unique incident electro-
magnetic wave from the spectrum. The conventional Kretschmann configuration of
SPR involves using a p-polarized monochromatic electromagnetic wave to probe the
metal–dielectric interface via a coupling medium, with angular interrogation being
the typical approach. The SPR effect is determined by changing the angle of incidence
and measuring the reflected light intensity. The reflected intensity reduces to zero
at the point of resonance, which is recorded as the resonance angle (RA). The reso-
nance angle is unique to the individual metal-dielectric interaction. During sensing,
analyte adsorption on the metal surface causes a change in the dielectric property. A
change in the dielectric property is observed as a result of the analyte adsorption on
the metal surface during sensing. Such changes can shift the resonance angle (RA)
accordingly. The change in RA is used to compute the change in RI due to the adsorp-
tion of the analyte using Fresnel’s equations [28]. Therefore, a RI vs concentration
of the analyte calibration curve can be obtained. The interaction of the analyte at the
interface plays an important role in the sensing performance of SPR instruments. In
the conventional metal and dielectric-based SPR, gold is most recurrently preferred
as the plasmonic material for the generation of SP waves. It has several advantages
over other materials, such as chemical inertness, ease of functionalization, and high
stability in aqueous media. However, gold possesses a very low affinity toward many
analytes. Thus, to increase the analyte affinity, the gold surface can be functionalized
with a suitable layer. Recently, it has been studied that graphene may be employed as
a biomolecular recognition element (BRE) to functionalize the metal film. Graphene
has a high surface-to-volume ratio and a rich π electron conjugation. It enhances the
binding affinity of bio-analytes through π-π interaction. Thus, graphene is largely
employed as a functionalized layer over the metal film for sensitivity enhancement.
There are many advantages of using graphene-functionalized gold surfaces during
sensing measurements, they are:
1. In contrast to gold, graphene has a very high surface-to-volume ratio, which is
anticipated to be advantageous for the effective adsorption of biomolecules.
2. The carbon-based ring structures in organic and biomolecules might enable
efficient π stacking interaction with hexagonal graphene.
3. The control over the number of graphene layers transferred to the metal interface
enables control of the SPR response and its sensitivity.
Thus, the employment of graphene as the functionalized layers seem to be appro-
priate for SPR sensing applications [25, 29]. In 2010, Wu et al. [30] investigated the
effect of graphene layers on sensitivity enhancement in the gold-prism-based SPR.
They presented that graphene monolayer-coated over gold surface-based bio-sensing
chip had a larger SPR angle shift than traditional gold chips for the same refractive
index variation (n = 0.005). The calculation also shows that the graphene on gold
SPR biosensors exhibits (1 + 0.025 L) × t times more sensitivity than standard gold
122 A. Kumar et al.
SPR biosensors (where t > 1, L-number of graphene layer). He et al. [29] proposed
a point-of-care device employing graphene-coated SPR chips to detect folic acid
protein (FAP). By utilizing the exceptional properties of graphene, a highly selective
and sensitive SPR device was observed for the detection of serum folate biomarkers.
The interaction due to π-stacking on the graphene-coated SPR chip and analyte in
serum allowed femtomolar (fM) detection of albumin mixtures. Thus, the detec-
tion of very low concentrations is also possible using graphene-functionalized gold
chips. It is rational to presume that increasing the number of graphene layers might
increase the sensitivity. However, the SPR curve broadens as we increase the number
of graphene layers which makes it difficult to measure the resonant angle/wavelength.
Also, one of the most important parameters in SP generations is the strength of the
evanescent waves at the metal–dielectric interface and the decay length of these
evanescent waves in the sensing medium. If the decay length is small, the detection
in the RI change due to the adsorption of the analyte will not be observable. If the
decay length is smaller than the thickness of the functionalized layer, the evanescent
waves will not be perturbed by the adsorption of the analyte. Therefore, if the sensing
layer has a large thickness even in the case of stacked graphene, the sensitivity of
the SPR sensor would tend to decrease. Therefore, stacking a few layers of graphene
may boost sensitivity, however, using bulk or macroscopic structures will reduce the
effectiveness of the sensor. The bulk behavior of 3DG would limit the perception of
the interaction of evanescent waves with the analytes at the interface. Therefore, there
will be minuscule responses that cannot be measured even with SPR technology.
Although, graphene-coated gold chips can enhance the adsorption affinity of the
analytes. However, sensitivity and figure-of-merit (FOM) decrease in the aqueous
medium when graphene is coupled with a gold chip [31, 32]. Therefore, for the
fabrication of a highly sensitive device, if the plasmonic field can be itself generated
in the graphene layer system, it can operate both as a plasmonic material and BRE
through π-π interaction.
Plasmons generation in graphene
Due to the two-dimensional (2D) character of graphene, surface plasmons excited in
graphene are much more strongly confined than those in traditional noble metals
because of the collective excitations. The plasmons generated in graphene are
confined to a volume million times smaller than the diffraction limit. This strong
confinement facilitates efficient light–matter interaction and offers minimal losses
and effective wave localization up to mid-infrared frequencies [33]. Since the carrier
densities in graphene can also be adjusted by electrical gating and doping, the
tunability of surface plasmons would be the most significant benefit of graphene
[34]. Inspired by these findings, a few research groups [35–37] have performed
SPR-based sensing using graphene as the plasmonic material. Maleki et al. [35]
have deposited a double-layer graphene nanograting on a dielectric substrate as the
basis of the gas sensor. They were able to monitor the sensitivity of 430 nm/RIU
over incident radiation of 1–2 μm. Wu et al. [36] have proposed an SPR sensor that
uses an array of graphene nanoribbons over a SiO2 substrate operating in the infrared
range. They recorded a sensitivity of 4720 nm/RIU and a FOM of 5.43. Kumar et al.
Fig. 4 A schematic diagram showing the SPR sensor where ZnSe is employed as the coupling
prism. Graphene as both plasmonic and biorecognition element, incident electromagnetic infrared
source, detector, and flow cell. Inset shows the geometry, viz. XY as the plane of incidence, and
YZ as the surface plane of the graphene layer. The analytes are dispersed through the flow cell.
Adapted with permission [37], Copyright (2022), Springer
[37] have proposed a novel and highly sensitive graphene-ZnSe-based SPR sensor
for biomolecule detection (Fig. 4). They measured the sensitivity of 20,000 nm/RIU
for monolayer graphene, which is the highest in the class of graphene-based SPR
sensors available in the literature. They observed the FOM of 15 for the wavelength
interrogation Kretschmann configuration of the SPR device operating in an aqueous
medium.
Figure 5 shows the observed spectrum for the proposed graphene-based SPR
configuration [37]. The resonant wavelength is observed at 13.7 μm. The two-
dimensional surface field profile at resonance also shows anisotropic behavior which
is consistent with the conventional gold-based SPR system [38].
Therefore, the graphene monolayer itself over a semiconducting substrate can
be employed for plasmon generation. Additionally, the BRE features for attracting
bio-analytes have made it a more suitable functional material for bio-sensing using
the SPR technology. This may not only reduce device size, but also the fabrication
complexity. The number of layers can be increased optimally to enhance the sensing
performance. The bilayer graphene (BLG) and twisted–BLG (TBLG) exhibit inter-
esting physicochemical properties which can be altered as a function of in-plane twist
angle. Such a BLG system can lead to the development of next-generation sensors.
Kumar et al. [37] have proposed a bilayer graphene-based SPR sensor. They observed
that bilayer graphene does not show any drastic change in the sensitivity irrespective
of the type of stacking (Bernal or non-Bernal). Thus, to alter the sensing character-
istics, a relative in-plane twist can be added between the two graphene layers of the
124 A. Kumar et al.
Fig. 5 a SPR spectrum for the proposed graphene-based SPR configuration and b two-dimensional
surface EM field profile over the graphene monolayer surface measured at resonance. Reprinted
with permission [37], Copyright (2022), Springer
BLG system. In the case of non-Bernal stacking, the optical property of the graphene
system does not change drastically due to the relative in-plane twist. However, in the
case of Bernal stacking, the in-plane twist plays a major role in altering its optical
properties. A phase diagram depicting the different optical characteristics of both
stacking with varied relative in-plane twists (θ) is shown in Fig. 6 [24].
From Fig. 6, it is evident that for non-Bernal stacking, the BLG system exhibits
mostly dielectric behavior, irrespective of in-plane twist and incident photon energy.
But, in Bernal stacking, the material property varies. It showed semi-metallic
behavior between 13–14 μm of incident wavelength. This range of incident photon
energy also corresponds to the SPR wavelength for the monolayer and BLG system.
Thus, it will be interesting to probe the system in this range for studying SPR sensing.
Thus, for different in-plane twists, Kumar et al. [37] studied the sensitivity of SPR-
based sensors where the twisted graphene system was employed both as BRE and
plasmonic material. They proposed that for Bernal stacked twisted bilayer graphene,
the sensitivity near the magic angle (1°) is maximum. They observed a sensitivity
of 29,120 nm/RIU sensitivity with 23.5 FOM which is much higher than the mono-
layer/bilayer graphene system. The collective oscillations of plasmons near the magic
angle is maximum. Also, near the magic angle, the time-periodic electric field causes
electrons to vibrate around their equilibrium positions, resulting in an interband tran-
sition. So, the oscillating electrons create a strong electric field at resonance, allowing
the oscillation to continue for a longer period. This resonant action produces collec-
tive modes known as interband plasmons [39]. Therefore, the interaction with the
adjacent dielectric is amplified due to this strong collective mode oscillation. A
comparative data for the sensitivity for various twists (θ) is shown in Fig. 7. It is
observed that the sensitivity for smaller in-plane twists is comparatively higher than
the sensitivity for larger in-plane twists.
The decrease in sensitivity for larger in-plane twists is due to the decrease in the
oscillation of the collective mode and the dominant metallic behavior as shown in
Fig. 6.
(a) Non-Bernal (AA) stacking with small in (b) Non-Bernal (AA) stacking with large in-
plane twist plane twist
(c) Bernal (AB) stacking with small in-plane (d) Bernal (AB) stacking with large in-plane
twist twist
Fig. 6 A phase diagram representation of diverse material properties observed for different in-plane
twists (θ) in Bernal and non-Bernal stacking. (D = Dielectric, M = Metallic, SC = Semiconducting,
and SM = Semi-metallic). Here E is the energy of the incident photons. Adapted with permission
[24], Copyright (2022), IOP
Fig. 7 Sensitivity of various

graphene-based SPR
systems. Corresponding
values of sensitivity are as
mentioned. The numeric
value with the symbol AB
represents the twist angle (θ)
in degrees. Adapted with
(2022), Springer
126 A. Kumar et al.
Future Scope and Challenges: 3DG can be considered a remarkable material that
can find numerous novel applications. The unique morphology, very high porosity,
and excellent electrical, thermal, and optical properties of 3DG have ranked the mate-
rial among the top for device fabrication. However, the vast surface area and high
porosity of 3DG may enhance the possibility of non-specific binding of analytes,
resulting in misleading positive or negative findings in sensing applications. There-
fore, careful data analysis is required for isolating the signals for specific and non-
specific interactions. Surface functionalization is frequently necessary to increase the
sensitivity and selectivity of sensors. Still, the complex surface structure of 3DG may
make it more challenging to get functionalized like any other material. Development
of 3DG using the existing protocols can yield material with different porosity and
the network which may alter the physical properties beyond the tolerance. 3DG is
a relatively new and specialized material, which may make it more expensive than
other materials typically used for SPR-based sensing applications. Therefore, the
fabrication of 3GD from the bottom-up approach can provide a good level of confi-
dence. 3DG can be fabricated through layer-by-layer assembly of graphene. Most of
the reported studies on monolayer and BLG systems are based on theoretical calcula-
tions. The fabrication of devices based on monolayer, BLG, and TBLG is challenging
and a good number of efforts are being invested in this direction. The monolayer and
bilayer state of graphene can be controlled experimentally by a few advanced thin
film fabrication techniques such as Langmuir–Blodgett (LB) deposition [40] and
chemical vapor deposition [41, 42]. In-plane twisting of the graphene layers in BLG
is another challenge in this field. The twists can be applied by the advanced LB or
CVD technique. The SPR sensors employing the monolayer, BLG, or TBLG still
require the immobilization of suitable ligands to make the sensing selective, rapid,
and sensitive. A suitable protocol can be developed for the immobilization and stable
sensing measurement using the SPR technology.
The fundamental studies on monolayer, BLG, and TBLG yield better scenarios
for the development of the next-generation sensor. Although the 3DG is a random
network of 2D graphene sheets, it will be very interesting to study 3D graphene with
twisted bilayers at a magic angle. Such a state of graphene will be important not only
for fundamental studies, but also for the development of efficient biosensors.
Acknowledgments The authors are thankful to the Physics Department, BITS Pilani, for
supporting Lumerical software. AK is thankful to SERB for the fellowship (CRG/2018/000755).
References
1. Cao, M.-S., Wang, X.-X., Cao, W.-Q., Yuan, J.: Ultrathin graphene: electrical properties and
highly efficient electromagnetic interference shielding. J. Mater Chem. C 3, 6589 (2015). https:/
/doi.org/10.1039/c5tc01354b
2. Mak, K.F., Ju, L., Wang, F., Heinz, T.F.: Optical spectroscopy of graphene: From the far infrared
to the ultraviolet. Solid State Commun. 152, 1341–1349 (2012). https://doi.org/10.1016/j.ssc.
2012.04.064
3. Zhang, Y., Huang, Y., Zhang, T., et al.: Broadband and tunable high-performance microwave
absorption of an ultralight and highly compressible graphene foam. Adv. Mater. 27, 2049–2053
(2015). https://doi.org/10.1002/ADMA.201405788
4. Huang, Z., Chen, H., Huang, Y., et al.: Ultra-broadband wide-angle terahertz absorption prop-
erties of 3D graphene foam. Adv. Funct. Mater. 28, 1–8 (2018). https://doi.org/10.1002/adfm.
201704363
5. D’Apuzzo, F., Piacenti, A.R., Giorgianni, F., et al.: Terahertz and mid-infrared plasmons in
three-dimensional nanoporous graphene. Nat Commun 8, 1–7 (2017). https://doi.org/10.1038/
ncomms14885
6. Tomarchio, L., Macis, S., D’Arco, A. et al.: Disordered photonics behavior from terahertz to
ultraviolet of a three-dimensional graphene network. NPG Asia Mater., 13 (2021). https://doi.
org/10.1038/s41427-021-00341-9
7. Ron, R., Haleva, E., Salomon, A.: Nanoporous metallic networks: fabrication, optical
properties, and applications. Adv. Mater., 30 (2018). https://doi.org/10.1002/ADMA.201
706755
8. Ito, Y., Zhang, W., Li, J., et al.: 3D Bicontinuous Nanoporous Reduced Graphene Oxide for
Highly Sensitive Photodetectors (2015). https://doi.org/10.1002/adfm.201504146
9. Xiao, W., Li, B., Yan, J., et al.: Three dimensional graphene composites: preparation,
morphology and their multi-functional applications. Compos. Part A Appl. Sci. Manuf. 165,
107335 (2023). https://doi.org/10.1016/J.COMPOSITESA.2022.107335
10. Wan, Y.J., Yu, S.H., Yang, W.H., et al.: Tuneable cellular-structured 3D graphene aerogel and
its effect on electromagnetic interference shielding performance and mechanical properties of
epoxy composites. RSC Adv. 6, 56589–56598 (2016). https://doi.org/10.1039/C6RA09459G
11. Liang, C., Qiu, H., Han, Y., et al.: Superior electromagnetic interference shielding 3D
graphene nanoplatelets/reduced graphene oxide foam/epoxy nanocomposites with high thermal
conductivity. J. Mater Chem. C Mater 7, 2725–2733 (2019). https://doi.org/10.1039/C8TC05
955A
12. Xing, Z., Zheng, Y., Yan, Z., et al.: High-sensitivity humidity sensing of microfiber coated with
three-dimensional graphene network. Sens Actuators B Chem. 281, 953–959 (2019). https://
doi.org/10.1016/J.SNB.2018.11.057
13. Baig, N., Saleh, T.A.: Electrodes modified with 3D graphene composites: a review on methods
for preparation, properties and sensing applications. Microchim. Acta, 185 (2018).https://doi.
org/10.1007/s00604-018-2809-3
14. Yang, Y., Kang, M., Fang, S., et al.: Electrochemical biosensor based on three-dimensional
reduced graphene oxide and polyaniline nanocomposite for selective detection of mercury
ions. Sens Actuators B Chem. 214, 63–69 (2015). https://doi.org/10.1016/j.snb.2015.02.127
15. Dong, Q., Xiao, M., Chu, Z. et al.: Recent progress of toxic gas sensors based on 3d graphene
frameworks. Sensors, 21 (2021). https://doi.org/10.3390/s21103386
16. Yavari, F., Chen, Z., Thomas, A.V. et al.: High sensitivity gas detection using a macroscopic
three-dimensional graphene foam network. Scientific Reports 1:1 1:1–5 (2011). https://doi.org/
10.1038/srep00166
17. Wang, L., Zhang, H., Li, Z., et al.: Development of a three-dimensional graphene-based photo-
electrochemical biosensor and its use for monitoring lipase activity. LWT 170, 114076 (2022).
https://doi.org/10.1016/J.LWT.2022.114076
18. Fan, Z., Yust, B., Nellore, B.P.V., et al.: Accurate identification and selective removal of rotavirus
using a plasmonic-magnetic 3D graphene oxide architecture. J. Phys. Chem. Lett. 5, 3216–3221
(2014). https://doi.org/10.1021/JZ501402B/SUPPL_FILE/JZ501402B_SI_001.PDF
19. Srichan, C., Ekpanyapong, M., Horprathum, M. et al.: Highly-sensitive surface-enhanced
Raman spectroscopy (SERS)-based chemical sensor using 3d graphene foam decorated with
silver nanoparticles as SERS substrate. Scientific Reports 6:1 6:1–9 (2016). https://doi.org/10.
1038/srep23733
20. Wang, D., Gao, H., Roze, E., et al.: Synthesis and photoluminescence of three-dimensional
europium-complexed graphene macroassembly. J. Mater Chem. C Mater 1, 5772–5778 (2013).
https://doi.org/10.1039/C3TC30732H
128 A. Kumar et al.
21. Zhang, L., Wang, L., Liu, D. et al.: Plasmon polaritons in 3D graphene periodic structure 42,
210–225 (2022). https://doi.org/10.1080/02726343.2022.2082099
22. Wang, F., Zhang, Y., Tian, C., et al.: (2008) Gate-variable optical transitions in graphene.
Science 320, 206–209 (1979). https://doi.org/10.1126/SCIENCE.1152793/SUPPL_FILE/
WANG_SOM.PDF
23. Kumar, V.: Linear and nonlinear optical properties of graphene: a review. J. Electron. Mater
50, 3773–3799 (2021). https://doi.org/10.1007/s11664-021-08904-w
24. Kumar, A., Manjuladevi, V., Gupta, R.K.: Refractive index of graphene AA and AB stacked
bilayers under the influence of relative planar twisting. J. Phys. Condens. Matter 34, 15302
(2022). https://doi.org/10.1088/1361-648X/ac2d5f
25. Szunerits, S., Maalouli, N., Wijaya, E., et al.: Recent advances in the development of graphene-
based surface plasmon resonance (SPR) interfaces. Anal. Bioanal. Chem. 405, 1435–1443
(2013). https://doi.org/10.1007/s00216-012-6624-0
26. Li, Z., He, M., Xu, D., Liu, Z.: Graphene materials-based energy acceptor systems and sensors.
J. Photochem. Photobiol. C 18, 1–17 (2014). https://doi.org/10.1016/J.JPHOTOCHEMREV.
2013.10.002
27. de Sanctis de, A., Mehew, J.D., Craciun, M.F., Russo, S.: (2018) Graphene-based light sensing:
fabrication, characterisation, physical properties and performance. Materials 11, 1762 11 1762
(2018). https://doi.org/10.3390/MA11091762
28. Devanarayanan, V.P., Manjuladevi, V., Gupta, R.K.: Surface plasmon resonance sensor based
on a new opto-mechanical scanning mechanism. Sens. Actuat. B Chem. 227, 643–648 (2016).
https://doi.org/10.1016/J.SNB.2016.01.027
29. He, L., Pagneux, Q., Larroulet, I., et al.: Label-free femtomolar cancer biomarker detection in
human serum using graphene-coated surface plasmon resonance chips. Biosens. Bioelectron.
89, 606–611 (2017). https://doi.org/10.1016/j.bios.2016.01.076
30. Wu, L., Chu, H.S., Koh, W.S. et al.: Highly sensitive graphene biosensors based on surface
plasmon resonance. Opt. Express 18(14), 14395–14400 (2010). https://doi.org/10.1364/OE.
18.014395
31. Saeed, W., Abbasi, Z., Majeed, S., et al.: An insight into the binding behavior of graphene oxide
and noble metal nanoparticles. J. Appl. Phys. 129, 125302 (2021). https://doi.org/10.1063/5.
0041894
32. Vanin, M., Mortensen, J.J., Kelkkanen, A.K., et al.: Graphene on metals: A Van Der Waals
density functional study. Phys. Rev. B Condens. Matter Mater Phys. 81, 1–4 (2010). https://
doi.org/10.1103/PhysRevB.81.081408
33. Jablan, M., Buljan, H., Soljačić, M.: Plasmonics in graphene at infrared frequencies. Phys. Rev.
B Condens. Matter Mater Phys. 80, 245435 (2009). https://doi.org/10.1103/PHYSREVB.80.
245435/FIGURES/5/MEDIUM
34. Koppens, F.H.L., Chang, D.E., García De Abajo, F.J.: Graphene plasmonics: a platform for
strong light-matter interactions. Nano Lett. 11, 3370–3377 (2011). https://doi.org/10.1021/NL2
01771H/SUPPL_FILE/NL201771H_SI_001.PDF
35. Mokhtari, A., Mehran, M., Maleki, M.: Design of a near-infrared plasmonic gas sensor based on
graphene nanogratings. JOSA B 37(11), 3478–3486 (2020). https://doi.org/10.1364/JOSAB.
401589
36. Wu, J., Zhou, C., Yu, J., et al.: Design of infrared surface plasmon resonance sensors based on
graphene ribbon arrays. Opt. Laser Technol. 59, 99–103 (2014). https://doi.org/10.1016/J.OPT
LASTEC.2013.12.019
37. Kumar, A., Gupta, V.M.: The effect of relative in-plane twisting in graphene bilayer on sensing
using surface plasmon resonance Plasmonics 1, 1–12 (2022).https://doi.org/10.1007/S11468-
022-01760-2/TABLES/2
38. Kumar, A., Gupta, R.K., Manjuladevi, V., Joshi, A.: Surface plasmon resonance for in-plane
birefringence measurement of anisotropic thin organic film. Plasmonics 16, 1023–1028 (2021).
https://doi.org/10.1007/s11468-021-01373-1
39. Stauber, T., Kohler, H.: Quasi-flat Plasmonic bands in twisted bilayer graphene. Nano Lett 16,
6844–6849 (2016). https://doi.org/10.1021/acs.nanolett.6b02587
40. Poonia, M., Manjuladevi, V., Gupta, R.K.: Ultrathin film of carboxylated graphene at air-water
and air-solid interfaces. Surfaces Interfaces 13, 37–45 (2018). https://doi.org/10.1016/J.SUR
FIN.2018.07.007
41. Fu, Y., Hansson, J., Liu, Y. et al.: Graphene-based biosensors. 2d Mater 7, 040401. https://doi.
org/10.1088/2053-1583/ABA3BF
42. Kuila, T., Bose, S., Khanra, P., et al.: Recent advances in graphene-based biosensors. Biosens.
Bioelectron. 26, 4637–4648 (2011). https://doi.org/10.1016/j.bios.2011.05.039
3D Graphene for Flexible Sensors
Ahmad Hussain, Adeela Naz, Nawishta Jabeen, and Jazib Ali
Abstract Recently, the importance of research for graphene-based materials and

their applications has risen especially for flexible and wearable sensors. There exist
several features which make it a promising material for devices including lightweight,
cost-effective fabrication, heat resistance, and flexibility. Graphene in the form of
three-dimensional (3D) composites or hybrid materials is investigated as a useful
material to be utilized in different types of sensors including flexible humidity, biolog-
ical, piezoelectric, electronic, piezoresistive, and pressure sensors. But the fabrication
of flexible, super-elastic, and stable 3D graphene-based designs is challenging to date
owing to structural distortion or substantial plastic bending and deformation. Integra-
tion of various morphologies, modifications in the synthesis techniques, and dopants/
additives are employed to surmount the fundamental effects of high deformation in
graphene-based materials for the utilization of wearable and flexible sensors. In this
chapter, the focus will lie to discuss the till date achievements and methodologies
of 3D graphene-based flexible sensors, their synthesis, and their performances for
various applications.
Keywords Graphene · Flexible · Piezoresistive · Strain · Humidity · Sensors
A. Hussain · A. Naz
Department of Physics, The University of Lahore, Sargodha Campus, Sargodha 40100, Pakistan
N. Jabeen
Department of Physics, Fatima Jinnah Women University Rawalpindi, Rawalpindi 46000,
Pakistan
J. Ali (B)
Center for Hybrid and Organic Solar Energy (CHOSE), University of Rome Tor Vergata, 00133
Rome, Italy
e-mail: jazibali028@gmail.com
https://doi.org/10.1007/978-3-031-36249-1_8
132 A. Hussain et al.
1 Introduction
3D functional systems like sensors and actuators have attained rapid development in
the past few decades because of their excessive utilization in robotics [1, 2], memory
and logic devices, portable technology [3, 4], flexible medical equipment [5, 6],
tissues manufacturing [7, 8], and energy storage/harvesting devices [9, 10]. Complex
3D structures are essential as the main building blocks of functioning systems or
devices due to the advantages provided by their geometrical shapes. In line with
this development, Andre and Konstantin at the University of Manchester focused
their research on such materials and described the significance of graphene-based
materials in 2004 [11]. Graphene has remained the subject of scientific speculation
since the early twentieth century. The most recent discovery in carbon nanostructures
is the graphene-based material as an allotropic form of carbon that takes the shape
of a two-dimensional (2D) hexagon with one atom at each vertex. Graphene-based
materials are renowned for their flexibility, strength, lightweight, and conductivity.
Combining graphene with already-existing materials is one of the most efficient
strategies to acquire the promising properties of this material. Graphene and its
composite materials have shown magnificent characteristics in various applications,
which have not only caused improvement in their performance, but also expanded
the versatility in new generation applications.
There exist various synthesis techniques for graphene-based materials, including
chemical vapor deposition (CVD) and wet-chemical techniques. No technique has
been able to fabricate 2D graphene larger than a microscopic scale yet [12]. In many
studies and publications, graphene has been fabricated as a 3D porous structure.
The graphene structure may increase its surface area while retaining its exceptional
mechanical characteristics and strong electrical conductivity. Figure 1 depicts the
unit cell structural overview of graphene.
3D porous systems made on 2D graphene architectures have intrigued the sensing-
related properties, which are capable to perform in sensing devices. There are many
features present in 3D graphene-based structures, including a significant outer and
inner surface area to contact with the analyte, a suitable electro-active surface area,
the ability to easily load (bio)catalysts, and flexibility. It is even feasible to employ
3D freely standing graphene-based morphologies as an electrode for energy storage
devices. An extensive section on fabrication techniques for 3D graphene is followed
including the hydrothermal process, CVD, chemical deposition, electrochemical
deposition method, and lithography. Figure 2 presents the specific reasons why 3D
graphene-based morphologies are preferred for flexible sensors depending upon their
unique characteristics. 3D graphene-based composites comprising carbon nanotubes
decorated 3D graphene, organic polymers, and 3D graphene-based morphologies are
significantly explored as electrode materials for energy storage applications. Eval-
uation of such potential materials as device-based applications is made possible by
analyzing the potential directions and recent challenges [13].
3D Graphene for Flexible Sensors 133
Fig. 1 The unit cell structure of 3D graphene
Fig. 2 Potential and best

merits of 3D graphene-based
composites for sensing
devices [13]
2 Sensors
Science and technology are always being improved by humanity, and they are always
searching for new methods to raise standards of living. Humans created the computer
and the internet as advanced technology, changing how people transmit information.
Humans are now developing sensors to broaden their field of perception, and various
sensors are used often in daily life and the workplace.
A sensor is a gadget that can gauge a certain quantity, such as pressure, temper-
ature, and humidity, and then relay the data to other gadgets for processing. The
measurement of an ideal sensor has two characteristics: first, it is unaffected by
the measuring factor; and second, it does not alter the measuring factor. As sensors
can compromise the information required to understand the instantaneous surround-
ings, they henceforward upkeep the decision-making ability. Nowadays, sensors have
become an essential part of all sorts of vehicles [14]. This chapter describes each
of these sensors’ functions, benefits, and drawbacks, as well as how sensor fusion
techniques might be applied to build a more ideal.
Flexible sensors possess basic construction, which is inexpensive in nature and can
be utilized in wearable devices. Furthermore, flexible sensors need to be very sensitive
and stretchable for various possible applications, including monitoring human health,
robotics, wearable electronics, and artificial intelligence [15]. This study presents a
summary of the most recent progress for flexible sensors. Moreover, the current status
of flexible sensors, including the materials used, sensing mechanisms, manufacturing
processes, and the most recent advancements in 3D graphene-based flexible sensors
for utilization in soft robotics and healthiness nursing. Additionally, this chapter
offers viewpoints on the difficulties facing this sector and the potential of flexible
sensors.
3 3D Graphen-Based Flexible Sensors
The use of graphene in several electrical gadgets has increased in recent years.
As a flexible material for piezoresistive, electrical, pressure, and humidity sensors,
graphene has gained popularity. 3D graphene-based structures offer the potential to
be utilized in gas sensors, oil absorption sensors, electrode material the s for superca-
pacitors and piezoresistive sensors owing to their electrical conductivity, mechanical
toughness, and high porosity [16]. For sensors, graphene is the perfect material,
as it can detect changes in its surroundings. The main purpose to idealize chem-
ical sensors is to detect injurious materials. Graphene-based materials and compos-
ites have been developed to construct tiny sensors with molecular-level sensitivity.
Figure 3 is representing the utilization of 3D graphene-based materials for various
kinds of sensors.
With the era of advanced technology, crop monitoring graphene-based sensors
have been developed, and moreover, improvement in efficiency is occurring in the
Fig. 3 3D graphene-based materials utilization for various flexible sensors
agricultural sector. With such developments, farmers will be able to explore and
highlight the existence of any hazardous gases which might distress crop growth and
they will be able to take appropriate actions on time without any significant damage.
With the existence of the sensitivity property of graphene-based sensors, it is possible
to locate the positions to cultivate specific crops based on environmental conditions.
3.1 Flexible Humidity Sensors
Porous 3D graphene-based structures have received notable consideration in the

field of humidity sensing owing to their several reaction sites, and improved sensing
properties [17]. The performance of the humidity sensor is totally dependent on the
sensitivity of the employed material, which can be described as (Eq. (1))
Iwet − Idr y
S= × 100 (1)
Idr y R H
Recently, Yu et al. reported the 3D Graphene foam humidity sensor. Implemen-

tation of such materials with strong characteristics, such as humidity sensors, have
enabled electrical devices to transform the amount of water present in the environ-
ment into electronic signals. 3D graphene foam is synthesized by the CVD process
on 3D metallic foam. Graphene-based foam can be utilized in humidity sensors, as
this material is strongly conductive. Yu et al. demonstrated that 3D graphene foam
with exceptional permeability for water allows the humidity sensors to display a
wider relative humidity range (0%–85.9%), along with a quick reaction response of
89 ms and rapid recovery time of 189 ms. Moreover, the 3D graphene foam model
was overstated with water molecules to compute the structural energy. The authors
employed the software Materials Studio to explain the physical mechanism of elec-
trical contribution due to chemically adsorbed water into a 3D graphene foam surface.
Additionally, this gadget offered a user interface with unmatched performance for
humidity-sensitive materials [18].
One of the lightest materials in the world is 3D graphene aerogel spheres (GASs),
which possess the promising character to be utilized in high-performance thermal
flexible sensors. Mao et al. fabricated the 3D graphene aerogel spheres through a
unique spinning process, the material was capable to sense pressure, temperature,
and material elasticity. Fabricated sensors demonstrated a temperature coefficient
of resistance of 2.2% C−1 , five times greater compared to conventional resistance
thermometers. The fabricated thermal humid sensor also demonstrated exceptional
temperature-detecting capabilities. The 3D design of the graphene aerogel spheres
allows the sensor to sense forces coming from all directions (360°). Because of
the unique 3D special structures of graphene aerogel spheres, it exhibited improved
sensitivity (0.15 kPa−1 ) and rapid response and relaxation durations (~100 ms). Even
after significant distortion, extraordinary cycle stability and lengthy operating life
were observed for the sensor [19].
In comparison to the two sensors, the thermal humidity sensor is extremely unique.
This sensor is frequently used to detect absolute humidity (AH). It consists of two
thermistors, one of which is in touch with dry nitrogen, and the other is enclosed
in the ambient air. Two thermistors’ resistances can be measured. Humidity-sensing
devices have been made using a variety of nanomaterials, including multi-wall carbon
nanotubes. The shape and excellent electrical conductivity of 3D porous graphene
make it a suitable material for a humidity sensor. The material’s 3D structure and
porous nature increase its surface area and improve its hygroscopicity, and its strong
electrical conductivity might contribute to its high sensitivity to humidity [20].
3.2 Flexible Electronic Sensors
2D graphene-based structures are governing interest of researchers because of their

exceptional features regarding electronic devices. The thickness of the graphene sheet
makes it the best contender to be utilized in field effect transistors for electronic
sensors since it is very sensitive to the changes in the surrounding environment.
Here various types of graphene-based electronic sensors will be discussed, which
are capable to detect numerous substances and biological materials. Firstly, the focus
will lie on the types of graphene-based materials and then their utilization in electronic
sensors, and finally in what way those materials impact the sensitivity of the resulting
devices [21].
For the emerging field of flexible intelligent electronic stretchable sensors, flex-
ibility and sensitivity play crucial roles. The sensitivity and stretchability of 3D
graphene-based foams can be improved by modifying the specific surface area and
mechanical strength. Yang et al. reported the stretchable electronic sensor appli-
cations by 3D graphene-based nickel particles peasecod foams. These foams were
fabricated by stamp transfer and CVD techniques [22]. The nickel particles were
proven to be beneficial for the construction of 3D nanostructures and remained
isolated from one another to facilitate stretchy applications since they are coated
by graphene layers. Such 3D graphene-based nickel particle foams were capable to
show 80% stretchability. There exists a low limit of detection of <1%, as well as
strong linearity (R2 ) of ~0.997. Manjakkal reported the fabrication of a flexible 3D
porous graphene-based foam supercapacitor to work as a chemo-resistive pH sensor.
The 3D porous graphene-based foam supercapacitor demonstrated exceptional elec-
trochemical and supercapacitive performance owing to its innovative layer structure
of conductive nature. The 3D porous graphene-based foam supercapacitor exhib-
ited better character for the areal capacitance of ~38 mFcm2 which was around 3
times greater than reported flexible carbon-based supercapacitors at 0.67 mA cm2
current density. The measured power and energy densities are 0.27 mWcm2 and
3.4 Whcm2 , respectively. These values are higher than those reported carbon-based
supercapacitors. The 3D porous graphene-based foam supercapacitor also demon-
strated better cycling stability with capacitance retention of 68% even after 25,000
charge/discharge cycling examined under flexible circumstances [23].
Wearable electronics which are very sensitive and stretchable have become a
promising topic of research for scientists with several applications, including e-
skin and human motion sensing. Li et al. reported the 3D graphene-based structures
for high-performance strain. In this study, the authors described a revolutionary 3D
graphene-based structure as a flexible electronic sensor, which can self-heal. Furfuryl
amine was employed as a reducing and modifying agent. The fabricated composite
demonstrated high stretchability of ~200% and intrinsic conductivity with a little
combination of graphene (~2 wt%), making it a suitable candidate for utilization in
stretchable electronics for human motion detection [24].
Boxing et al. reported the successful fabrication of graphene aerogel endows
with 3D deformation morphology and good flexibility to be utilized in wearable
electronics as an electrical sensor. Printing of graphene patterns demonstrated high
conductivity, and the 3D nano-structured graphene aerogel subsidizes multidimen-
sional deformation responses, making them ideal for multi-recognition stretch-
able electric sensors. Moreover, fabricated electrical sensor devices with movement
perception showed the ability to perform astonishingly well with gesture language
analysis for a deaf-mute [25].
Zahed et al. fabricated the poly aziridine-encapsulated phosphorene-inserted flex-
ible 3D porous graphene (PEP-3DPG) electrode via laser writing and drop-casting
techniques. Due to the very stable PEP’s superior electrochemical properties and
surface functionality, the fabricated PEP/3DPG was considered a possible electrode
in micro/nano supercapacitors, electrocardiogram recording, and immunosensing.
The fabricated PEP/3DPG carcinoembryonic immune sensor demonstrated better
linear ranges (0.1–700 pg mL−1 and 1–100 ng mL−1 ) with a detection limit of
0.34 pg mL−1 operating under optimum circumstances. Moreover, signal to noise
ratio of the constructed sensor was 13.5 dB equivalent to that of traditional electrodes
Ag/AgCl, because the finger touch-based ECG sensor exhibits comparatively steady
and low impedance at the skin–electrode interface. Additionally, the prepared micro
supercapacitor exhibited an areal capacitance of 16.94 mF cm2 , six times more than
a non-doped 3DPG-based micro supercapacitor. These findings show the potential
of fabricated PEP/3DPG systems for multimodal applications [26].
Watthanawisuth et al. fabricated the 3D graphene foam sensors which were
stretchable and wearable sensors employed for Internet of Things (IoT) technology.
Herein, authors used the Wi-Fi to transfer the data from a sensor to the cloud by using
of web-socket powered by Node.js. The authors fabricated the armband muscle to
measure muscle expansion and stretch in real-time by utilizing 3D graphene foam
sensors based on an IoT device. The data displayed the muscle’s expansion on the
website. These wearable flexible sensors are made up of 2–5 cm long strips of 3D
graphene foam that were joined by conductive epoxy. The silver paste was applied
to the sensor edge to achieve conductivity for better accuracy. As Intel Edison was
used in the main CPU, connecting the sensor to the internet was made simpler.
ADXL335 was selected along with the fabricated sensor as a three-axis accelerom-
eter for monitoring gesticulations and fitness tracking applications. Intel Edison’s
main CPU board’s lower side was equipped with an accelerometer, a battery, and an
analog-to-digital conversion circuit [27].
3.3 Flexible Biological Sensors
Devices called biosensors combine biological and physical–chemical elements to

detect analytes by creating a signal that can be measured. In many different domains,
including the diagnosis of diseases and the bio-monitoring of contaminants, biosen-
sors have a wide range of uses. Blood glucose biosensors are widely utilized devices
in medical sciences. Antibodies, DNA probes, and cell receptors that interrelate with
analytes can all be used as biological sensing materials. The transducer converts
biological signals into optical and electrical impulses using materials that are optical,
physicochemical, or piezoelectric [28].
It has been observed that H2 O2 and glucose sensors are mostly used enzyme-
based electrodes which possesses several drawbacks. Si et al. proposed a unique
hierarchical composite-type material made of Mn3 O4 that was fabricated at the
top of 3D graphene foam (Mn3 O4 /3D GF). This fabricated composite-type mate-
rial was flexible and free-standing biosensor, capable to detect nonenzymatic H2 O2
and glucose for the applications of the medical industry and health care. Mn3 O4 /
3D GF biosensor demonstrated a better sensitivity of 360 µA mM cm−2 , detec-
tion limit of 10 µM, and linear range of 0.1–8 mM. Synergistic effects among
Mn3 O4 /3D GF-based biosensors exhibited the high electrocatalytic performance of
the nano-structured Mn3 O4 system with better conductance and improved surface
area of 3D GF. Real-time detection of H2 O2 and glucose in food and blood trials
by the enzyme-less biosensor also showed good performance [29]. Xiao et al. fabri-
cated the flexible electrochemical sensor by adding the high-density Pt nanoparti-
cles on free-standing graphene oxide paper along with nanowires of MnO2 . This
triple constituent system detected H2 O2 from an alive cell with <5% amperometric
response after 100 bending conditions [30]. Wang et al. fabricated the graphene with
a conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), by galvanos-
tatic electro-polymerization to achieve a G/PEDOT hybrid anode for biological fuel
cell sensor. The fabricated device demonstrated the maximum 873 mW m−2 power
output, presenting a 15-fold variation as compared to carbon paper bioanodes [31].
There are several applications of biosensors including environmental monitoring,
illness diagnosis, drug development, food safety, biological research, etc. Collabora-
tion of bio-molecular analytes with detecting constituents, device manufacturing and
scheme, microfluidics, microchip technology, sample selection methods, etc., are just
a few of the extremely particular properties that these devices rely on. An upcoming
advanced generation of sensing technologies/science can be developed by incorpo-
rating nanoparticles into biosensors. On the other hand, nanoparticle-based biosen-
sors have promising future applications in food analysis, process control, clinical
diagnostics, and environmental monitoring.
3.4 Flexible Piezoresistive Sensors
For wearable piezoresistive sensors, 3D graphene-based materials are regarded as

auspicious stretchable sensors because of their easy fabrication, straightforward
understanding procedure, short power need, and simple gesture collection. In the
last two decades, piezoresistive sensors are recognized as outstanding potential
contenders in the field of human expression sensing, healthcare detecting, etc., that are
now considered as being crucial in developing next-generation artificial intelligence
classifications [32].
Graphene-based aerogels with their better porosity, high conductance, and good
flexibility have become the ideal materials to be utilized in piezoresistive applications/
sensors. But, achieving a successful synthesis along with excellent sensing abilities,
electric, piezoelectric, and mechanical characteristics at the same time is a chal-
lenge. Following the above-mentioned fact, Cao et al. fabricated unique nanofiber-
reinforced graphene-based aerogel that possessed a hierarchical 3D inter-connected
micro-structure. This designed morphological structure demonstrated significant
43.50 kPa compressive stress and high 28.62 kPa−1 piezoresistive sensitivity along
with a linear sensitivity range of 0–14 kPa. The piezoresistive sensor exhibited better
resilience of compression at 3 Pa, fast response time (37 ms) and stability of the
structure along with sensing ability remained significant even after 2600 cycles. At
20% compressive strain, assembled sensors exhibited a 91.57% value of the current
signal of the initial value. Such stable, durable, and persistent current signal values
correspond to the excellent features of assembled piezoresistive biosensor to monitor
wrist pulse, real-time movement of the throat, knee joints, and finger impressions
[33].
There are several excellent techniques to fabricate extremely well-ordered 3D
porous graphene sponges (PGSs), and where emulsion process is one of them. Wang
et al. demonstrated a well-organized ordered 3D PGSs-based wearable pressure
sensor with great sensitivity and flexibility. High-performance piezoresistive sensors
fabricated on 3D PGSs have evolved rapidly due to their effective performances, yet
issues including low sensitivity, high cost, and restricted flexibility still exist. After
the successful fabrication of well-organized ordered 3D PGSs by emulsion approach,
a wearable pressure sensor at the device level was put together with an Au electrode
and polydimethylsiloxane for dependable packaging. To achieve a stable emulsion,
the pH values were carefully regulated. The ordered 3D PGSs demonstrated lower
density, better conductance, and better porosity, proving a 0.79–1.46 gauge factor
with a compression strain of 50% and excellent durability even after 500 cycles.
The designed pressure sensor demonstrated improved sensing ability to distinguish
hominoid activities such as human finger, wrist, palm, and elbow movements. There-
fore, pressure sensors showed tremendous promise in the areas of human–computer
interaction, e-skin, biomechanical systems, etc. [34].
Recently, Ma et al. fabricated 3D graphene-based flexible piezoresistive sensors
with excellent stability and sensing abilities. Here, a unique surface-filled conduc-
tive layer of graphene nanosheets was created using fused deposition molding; 3D
printing was performed to create a stable, highly sensitive 3D graphene-based flex-
ible piezoresistive sensor. The device exhibited better flexibility of strain 1960%,
175.57 kPa−1 sensitivity at <300 Pa applied pressure, high 18.95–66.29 gauge
factor (0–100% strain), exceptional stability even after >2000 compression/relaxing
cycles, the 105 ms mechanical response time and 66 ms recovery time owing to the
surface-filled graphene conductive layer. Such features of the device make it an ideal
candidate to be utilized in practical applications to detect human behaviors [35].
Nowadays, researchers are focusing to adjust the high content of conductive
nanocomposites into graphene to improve the detecting ability of flexible piezore-
sistive sensors. Ma et al. have utilized two carbon black (CB)/graphene nanosheet
(GN) composite structures, which were employed to fabricate flexible piezoresistive
3D sensors. Three different styles of CB and GNs were adjusted to fabricate flexible
piezoresistive sensors with nanocomposites and so much difference in their gauge
factor and sensitivity was observed. The sensor with the composite construction was
first coated with GNs and then filled with CB in a substrate. The sensor demonstrated
the maximum 197.56 kPa−1 sensitivity below 300 Pa and 47.60 gauge factor. More-
over, it demonstrated better stability >2000 compression and relaxation cycles, with
a quick response of 120 ms and rapid recovery of 63 ms. The sensor also showed the
potential for speech and gesture monitoring. This study offers a method for making
conductive nanocomposites into a highly sensitive piezoresistive sensor [36].
Sengupta et al. presented the 3D squeezable piezoresistive graphene poly-
dimethylsiloxane foam sensor fabricated by incorporating multi-layered graphene
nanoparticles in porous polydimethylsiloxane foam supported by a sugar scaffold.
A 3D printing method was used to create cellular graphene/PDMS composites
with controlled topologies. Under diverse loading scenarios, the resulting composite
exhibited outstanding stretchability, toughness, and exceptionally stable temperature
sensitivity. The resultant piezoresistive foam sensors underwent strain testing with
two response areas and linearity of 2.87–8.77 gauge factor range throughout the 0–
50% strain range. To measure the dynamic pressure, the dynamic-stimulus–response
experiment also demonstrated the ability of sensors’ capacity to accurately measure
dynamic pressure up to a frequency of ~70 Hz. A high level of stability was also
shown by the sensor during 36,000 compressing/relaxing cycles and 100 cycles of a
whole human stride. By using simulated gait models and real-time gait classification
trials, both have identified precise human gait monitoring by 3D sensing foams. The
sensors’ capacity to detect a variety of fundamental joint bending responses further
demonstrated their applicability for individualized health-caring devices/applications
[37].
Chen et al. have demonstrated a detailed description of the fabrication, impor-
tance, and utilization of graphene-based flexible piezoresistive sensors. One of the
key elements of intelligent tactile skin, the piezoresistive sensor, is a widely used flex-
ible pressure sensor with outstanding performance. Such sensors can be categorized
methodically into different formations, such as 1D, 2D, and 3D foamed geometry,
and can be utilized in various real-world devices, such as multifunctional sensing,
health monitoring, system integration, and human motion sensing [38].
3.5 Flexible Pressure Sensor
Flexible pressure sensors possessing improved sensing abilities and extensive prac-
tical implementation range are widely used in wearable technology and biomimetic
technology. In particular, the skin of the human fingertip may be a useful model to
follow for very sensitive sensors since it has many epidermal ridges that enhance
external stimulations. Xia et al. developed the flexible pressure sensing membrane
(3D graphene films) via CVD and it displayed extraordinary 110 (kPa)−1 sensitivity
at 0–0.2 kPa and up to 75 kPa an extensive workable pressure range. The pressure
sensors’ enhanced performance is also a result of the usage of hierarchically struc-
tured supporting elastic films (polydimethylsiloxane). This pressure sensor demon-
strated stability for more than 10,000 compressing/relaxing cycles, with a 0.2 Pa low
detection limit and 30 ms swift reaction time. The authors illustrated the potential
uses of sensors for sensing small stuffs, human physical gestures, and sound [39].
Xu et al. fabricated the flexible force sensor with flexible polydimethylsiloxane
and 3D graphene foam (GF/PDMS). The 3D GF/PDMS sensor demonstrated the
ability to sense frequency response via a piezoelectric transducer and tuning fork
tests. The sensor has clearly shown the audio frequency linear response with an
ultrasound frequency range of up to 141 kHz, since the sensor’s work on the prin-
ciple of alteration in the electronic band structure. Such sensors are desirable for
collaborative wearable sensor technology or simulated prostheses that can sense
ultrasonic waves, seismic waves, transient pressures, and shock waves due to their
Fig. 4 a SEM micrographs

of graphene foam (GF)
illustration of morphology
b High resolution SEM
micrographs of GF to show
its porous 3D structure,
c Picture of the 3D GF/
PDMS sensor shows bending
ability, and d 3D GF/PDMS
sensor’s cross-sectional
optical image e Raman
spectra of GF [40]
excellent response and broad bandwidth [40]. SEM images, flexibility, and Raman
spectra of the 3D graphene foam (GF/PDMS) sensor are presented in Fig. 4.
There are many ways to prepare graphene where intricate steps are involved
in creating multilayer 3D graphene structures. Depending on the variation in the
resistance offered by electrical signals of 3D graphene by the influence of sonic
waves, the flexible acoustic pressure sensor has been created by Xu et al. The detector
was synthesized by flexible 3D graphene foam and PDMS. Such sensors showed the
ability in real time to delicately sense the distortion and the acoustic pressure; studies
used human physiological data and a tuning fork. These findings are important for
the creation of graphene-based applications/devices in the areas of transient pressure
measurement, in-vitro-diagnostics, and improved therapeutics [41].
Zhu et al. employed the neoteric method to fabricate a 3D structure graphene-
based pressure and strain sensor [42]. Ultrahigh sensitivity and significant hysteresis
were exhibited by the 3D bubble-derived graphene-based porous sensor. Fang et al.
followed the confined self-assembly methodology to fabricate a novel 3D porous
network with the aligned graphene-based wall, that was treated with holey-reduced
graphene oxide/lignin sulfonate (HrGO/Lig) composites and were oriented on the
framework of the Lig/single-wall carbon nanotube (Lig/SWCNT) hydrogel by
vacuum-assisted filtration. Achieved ultra-light Lig/SWCNT/HrGOal aerogel was
employed as pressure sensor which demonstrated 2.28 kPa–1 high sensitivity and
0.27–14.1 kPa wide detection range. Moreover, the fabricated aerogel film showed
the ability to perform in the symmetric supercapacitor and exhibited better energy
storage performance even after 5000 fatigue bending cycles [43].
Baolin et al. discussed that bionic skin is a kind of scheme that has the ability
to perform many simulations and also demonstrate several identifications of human
skin. The authors fabricated the flexible graphene piezoresistive tactile sensor, which
showed the ability to disclose the use of graphene’s piezoresistive capabilities. The
innovative tactile-pressure sensor was combined with a 2D graphene-based film

tactile sensor along with a 3D graphene foam pressure sensor to concurrently quantify
highly precise and extended range measurements simultaneously. The test findings
demonstrated that this sensor’s measuring range was split into two ranges: 0–2 N
and 2–40 N. The 472.2 y(kPa)−1 sensitivity, the 0.01 N force resolution, and less
than 40 ms reaction time were observed for the 0–2 N measurement range. While
5.05 ky(kPa)−1 sensitivity, the 1 N force resolution, and less than 20 ms reaction
time were the observations for the 2–40 N measurement range. This sensor provided
utilization for numerous applications like in biomedical devices and prosthetic limbs
and also can be employed for highly precise and broad range force implemented
calculations [44].
Flexible sensors are in great demand for research in many intelligence-based
systems such as the Internet-of-Things (IoT). Wei et al. provided the easiest and most
environmentally facile process for producing pressure sensors which were based on
an aerogel composite made of bacterium cellulose and caffeic acid-reduced graphene
oxide. The fabricated 3D graphene-based sensor showed a porosity of 98.9% and
demonstrated the 13.89 kPa−1 high sensitivity, 47.2 Pa ultra-low detection limit, and
120 ms fast response time, clearly detecting subtle strain and monitoring human
physical motions. Moreover, the aerogel demonstrated remarkable durability even
after 1000 compressing/relaxing cycles, depicting the suitable performance of the
material to be utilized in the area of flexible electronics [45].
3.6 Flexible Strain Sensors
Regarding flexible and stretchy strain sensors, various scholarly findings have
recently been presented [46]. Pan et al. have discussed the ability to increase the
stretchability of graphene-based materials by transforming the 2D membranes into
3D macroscopic structures. The authors used the porous copper foil as a template
for atmospheric pressure to fabricate the 3D graphene films. Later, 3D graphene
film (3D GF) was transferred to the PDMS membrane by treating the 3D GF at
1000 °C (3D GF-1000/PDMS). 3D GF-1000/PDMS hybrid film exhibited good flex-
ibility, as evidenced by relatively low resistance changes (R/R0 ), 2.67 and 0.36, under
employing 50% tensile strain and 1.6 mm bending radius. Conversely, 3D GF-900/
PDMS hybrid film demonstrates exceptional strain sensing capability with 187%
practical strain range and 1500 gauge factor. Additionally, the 3D GF-900/PDMS
exhibited astonishing strength in its resistance to repeatedly stretching-relaxing
cycles of 5000. Kinetic investigations demonstrated that resistance changes depen-
dence on strain was relying on graphitization, while the conductivity of 3D GF was
sensitive to the temperature of the CVD process [47]. The core elements of smart and
flexible electronics are pressure and strain sensors, which are a hot topic of research
[48]. Flexible graphene-based pressure sensors possessing PbTiO3 nanowires are
renowned for their piezoelectric performance, reported by Xu et al. The material was
employed to monitor healthcare and human gesture detection. The sensor exhibited
0 to 1400 Pa good linearity and 9.4 × 10−3 kPa−1 ultrahigh sensitivity [49].
Li et al. demonstrated the importance of graphene-based strain sensors as wearable
strain sensors which can be utilized in biomechanical systems, human motion detec-
tion, and other applications. There are several examples where high-performance
strain sensors have achieved the unique morphology of 3D graphene foam, although
there are still issues with preparation costs, sensitivity, and stretchability. Li et al.
presented a composite fabricated by 3D graphene foam and PDMS that showed
extremely flexible behavior and showed a response to strain. The graphene foam was
fabricated from graphene oxide using a simple technique and it demonstrated better
mechanical properties which make it easier to incorporate PDMS into the graphene
system. The fabricated sensor showed a gauge factor of 98.66 under applied strain
5%, and it may be extended up to 30% of its original length. Additionally, the strain
sensor exhibited excellent durability after 200 stretching–relaxing cycles. When the
elbow and finger bending monitoring device was used, it produced repeatability and
a variety of reactions due to resistance variation [50].
Xiang et al. fabricated the strain sensor composed of the printed nanocomposite of
carbon nanotube and thermoplastic polyurethane (CNT/TPU) via fused deposition
modeling (FDM), and later 1-pyrenecarboxylic acid (PCA) was added non-covalently
to alter the CNT and amplify polymer-nanofiller collaborations. The sensor exhibited
the 117,213 gauge factor at 250% strain, high detectable 0–250% strain range, and
better durability up to 10,000 loading–unloading cycles [51]. Xu et al. described that
by incorporating PDMS into 3D graphene foam (GF), fabricated by CVD employing
Ni foam as a template, a 3D GF-PDMS composite was investigated. In order to
increase the sensitivity of the 3D GF-PDMS composite, a thin layer of poly(ethylene
terephthalate) (PET) was added to work as substrate and designed the double-layer
3D GF-PDMS/PET composite. According to calculations made for resistance, there
was variation in the composite’s resistance after bending the edge side of PET, but
it started to decrease when bent from the side of GF. In both instances, bending
curvature increased the relative change in electrical resistance. More crucially, at the
same bending curvature, the relative change in electrical resistance for double-layer
3D GF-PDMS/PET composite can be up to six times greater. Additionally, the 3D
GF-PDMS/PET composite has demonstrated greater stability and flexibility [52].
Highly-flexible strain sensors with good multifunctional properties are required
for significant developments in the field of flexible electronics. Xu et al. proposed a
novel strain sensor based on Eco-flex rubbers, 3D graphene foams (GF), and altered
silicone rubber in a straightforward and affordable production technique (MSR).
Highly stretchable with tolerable 100% strain including pressure sensing, strain
meditation, and strain-dependent heating, are all features of the device. The strain
sensor demonstrated the broad sensing range of 100% strain and 66 kPa stress, high
sensitivity with gauge factor 584.2 for strain range 80% to 100%, and sensitivity of
0.183 kPa−1 in 5–10 kPa. The sensor exhibited excellent durability life even above
10,000 compressing/relaxing cycles. The GF showed splendid electrical properties,
and the MSR exhibited ideal mechanical properties. Under 5 V, the device’s temper-
ature may be raised by 35 °C in 5 min. As a result, the thermochromic MSR’s color
change rendered the deformation visible to the naked eye. The reversible and soft
strain sensor has the potential to be utilized in the intelligent visual-touch panel and
real-time detection of electrophysiological stimuli [53].
3.7 Flexible Temperature Sensor
Temperature sensors must be periodically calibrated to ensure accurate readings

while in continuous operation. Wu et al. reported a self-calibrating thermistor,
which was regarded as practical, economical, and quick self-calibration employing
embedded microheaters to operate as a self-heating platform. Based on the n micro-
heater platform, authors illustrated the sensing abilities of 3D reduced graphene
oxide hydrogel (RGOH), for the first time. They reported the 3D sulfonated RGOH
(S-RGOH) based thermistor, which demonstrated exceptional resolution (0.2 °C),
high sensitivity 2.04% K−1 , and a wide detection range of 26–101 °C. By compar-
ison, it was found that S-RGOH showed improved thermal sensitivity as compared to
RGOH, which is dependent upon the chemical modification during varying temper-
ature sensing. The microheaters were also employed for in situ thermal annealing
of S-RGOH and assessed temperature-dependent characteristics in addition to self-
calibration. Future wearable electronics will be able to use the flexible S-RGOH
thermistor since it is mechanically flexible and has a variety of useful applications
[54]. Figure 5 is not only representing the schematic illustration of 3D S-RGOH, but
also demonstrates the SEM images, Raman, and FTIR spectra as well.
4 Conclusion
In this chapter, a comprehensive review of the 3D graphene-based flexible sensors

has been presented. It is noticed that structural destruction or considerable plastic
distortion are the causes of restrictions for developing flexible 3D graphene-based,
super-elastic structures. Flexible sensors’ specific uses are determined by perfor-
mance factors including sensitivity, linearity, and stability. A detailed literature
review regarding various types of 3D graphene-based flexible sensors is demon-
strated. Understanding sensing processes and researching novel sensing mechanisms
are equally elaborated. Future research on 3D graphene-based flexible sensors should
focus on computational and machine learning techniques, as well as the chemistry,
preparation, and characterization of polymer nanocomposites. Presented summarized
work will be helpful for researchers to better understand the relationship between flex-
ible sensors’ process structure and performance to improve their structural designs in
accordance with the applications. We can conclude that 3D graphene-based wearable/
flexible sensors illustrate the magnificent potential for multifunctional applications/
devices which should be further scrutinized.
Fig. 5 a Schematic diagram for the 3D S-RGOH synthesis by one-pot self-assembly process and
application for constructing a self-calibrated thermistor. b Picture of GO aqueous solution and
resultant S-RGOH. c SEM micrographs of 3D porous S-RGOH. d Raman spectra of GO and S-
RGOH. e FTIR spectra of GO and S-RGOH. f SEM micrograph of Au IEs patterned porous and
flexible LCP substrate with 3D S-RGOH [54]
References
1. Guo, Y., Liu, L., Liu, Y., Leng, J.: Review of dielectric elastomer actuators and their applications
in soft robots. Adv. Intell. Syst. 3(10), 2000282 (2021)
2. Guan, Q., Sun, J., Liu, Y., Wereley, N.M., Leng, J.: Novel bending and helical extensile/
contractile pneumatic artificial muscles inspired by elephant trunk. Soft Rob. 7(5), 597–614
(2020)
3. Huang, Zhenlong, Hao, Y., Li, Y., Hu, H., Li1, W., Lei, Y., Kim, N., Wang, C., Zhang, L.,
Ward, J.W., Maralani, A., Li, X., Durstock, M.F., Pisano, A., Lin, Y., Xu, S.: Three-dimensional
integrated stretchable electronics. Nat. Electron., 473–480 (2018)
4. Xue, Zhaoguo, Xu, M., Li, X., Wang, J., Jiang, X., Wei, X., Yu, L., Xu, J., Shi, Y., Chen, K.,
Cabarrocas, P.R.I.: Adv. Funct. Mater 26, 5352–5359 (2016)
5. Lü, Chaofeng, Li, M., Xiao, J., Jung, I., Wu, J., Huang, Y., Hwang, K-C., Rogers, J.A.:
Mechanics of tunable hemispherical electronic eye camera systems that combine rigid device
elements with soft elastomers. J. Appl. Mech. 80(6) (2013)
6. Yi, N., Gao, Y., Jr, A.L.V., Zhu, J., Erdely, D., Xue, C., Lavelle, R., Cheng, H.: Fabricating
functional circuits on 3D freeform surfaces via intense pulsed light-induced zinc mass transfer.
Mater. Today 50, 24–34 (2021)
7. Zhao, W., Huang, Z., Liu, L., Wang, W., Leng, J., Liu, Y.: Porous bone tissue scaffold concept
based on shape memory PLA/Fe3 O4 . Compos. Sci. Technol. 203, 108563 (2021)
8. Lu, Haiqing, Zou, Z., Wu, X., Shi, C., Xiao, J.: Fabrication and characterization of highly
deformable artificial muscle fibers based on liquid crystal elastomers. J. Appl. Mech. 88(4)
(2021)
9. Lan, Xin, Liu, L., Pan, C., Li, F., Liu, Z., Hou, G., Sun, J., et al.: Smart solar array consisting of
shape-memory releasing mechanisms and deployable hinges. Aiaa J. 59(6), 2200–2213 (2021)
10. Gao, H., Li, J., Liu, Y., Leng, J.: Shape memory polymer solar cells with active deformation.
Adv. Compos. Hybrid Mater. 4(4), 957–965 (2021)
11. Lin, Jian, Peng, Z., Liu, Y., Ruiz-Zepeda, F., Ye, R., Samuel, E.L.G., Yacaman, M.J., Yakobson,
B.I., Tour, J.M.: Laser-induced porous graphene films from commercial polymers. Nature
Commun. 5(1), 1–8 (2014)
12. Wang, C., Vinodgopal, K., Dai, G.-P.: Large-area synthesis and growth mechanism of graphene
by chemical vapor deposition. Chem. Vap. Depos. Nanotechnol 5, 97–113 (2018)
for preparation, properties and sensing applications. Microchim. Acta 185(6), 1–21 (2018)
14. Campbell, Sean, O’Mahony, N., Krpalcova, L., Riordan, D., Walsh, J., Murphy, A., Ryan, C.:
Sensor technology in autonomous vehicles: a review. In: 2018 29th Irish Signals and Systems
Conference (ISSC), pp. 1–4. IEEE (2018)
15. Zazoum, Bouchaib, Mujasam Batoo, K., Azhar Ali Khan, M.: Recent advances in flexible
sensors and their applications. Sensors 22(12), 4653 (2022)
16. Xu, Xiang, Hui, L., Zhang Q., Han, H., Zhao, Z., Li, J., Jingye, L., Qiao, Yu., Gogotsi, Y.:
Self-sensing, ultralight, and conductive 3D graphene/iron oxide aerogel elastomer deformable
in a magnetic field. ACS Nano 9(4), 3969–3977 (2015)
17. Ding, Haojun, Wei Wei, Y., Wu, Z., Tao, K., Ding, M., Xi, X., Wu, J.: Recent advances in gas
and humidity sensors based on 3D structured and porous graphene and its derivatives. ACS
Mater. Lett. 2(11), 1381–1411 (2020)
18. Yu, Yu, Zhang, Y., Jin, L., Chen, Z., Li, Y., Li, Q., Cao, M., Che, Y., Yang, J., Yao, J.: A fast
response−recovery 3D graphene foam humidity sensor for user interaction. Sensors 18(12),
4337 (2018)
19. Mao, Renwei, Yao, W., Qadir, A., Chen, W., Gao, W., Xu, Y., Hu, H.: 3-D graphene aerogel
sphere-based flexible sensors for healthcare applications. Sens. Actuators A 312, 112144 (2020)
20. Chen, W.-P., Zhao, Z.-G., Liu, X.-W., Zhang, Z.-X., Suo, C.-G.: A capacitive humidity sensor
based on multi-wall carbon nanotubes (MWCNTs). Sensors 9(9), 7431–7444 (2009)
21. He, Qiyuan, Wu, S., Yin, Z., Zhang, H.: Graphene-based electronic sensors. Chem. Sci. 3(6),
1764–1772 (2012)
22. Yang, Cheng, Xu,Y., Man, P., Zhang, H., Huo, Y., Yang, C., Li, Z., Jiang, S., Man, B.: Formation
of large-area stretchable 3D graphene–nickel particle foams and their sensor applications RSC.
Adv. 7(56), 35016–35026 (2017)
23. Manjakkal, Libu, Núñez, C.G., Dang, W., Dahiya, R.: Flexible self-charging supercapacitor
based on graphene-Ag-3D graphene foam electrodes. Nano Energy 51, 604–612 (2018)
24. Li, Jinhui, Liu, Q., Ho, D., Zhao, S., Wu, S., Ling, L., Han, F. et al.: Three-dimensional
graphene structure for healable flexible electronics based on diels–alder chemistry. ACS Appl.
Mater Interfaces 10(11), 9727–9735 (2018)
25. An, Boxing, Ma, Y., Li, W., Su, M., Li, F., Song, Y.: Three-dimensional multi-recognition
flexible wearable sensor via graphene aerogel printing. Chem. Commun. 52(73), 10948–10951
(2016)
26. Zahed, Abu, Md., Barman, S.C., Sharifuzzaman, Md., Zhang, S., Yoon, H., Park, C., Yoon, S.H.,
Park, J.Y.,: Polyaziridine-encapsulated phosphorene-incorporated flexible 3D porous graphene
for multimodal sensing and energy storage applications. Adv. Funct. Mater. 31(25), 2009018
(2021)
27. Watthanawisuth, N., Maturos, T., Sappat, A., Tuantranont, A.: The IoT wearable stretch sensor
using 3D-Graphene foam. In: 2015 IEEE SENSORS, pp. 1–4. IEEE (2015)
28. Nguyen, Hiep, H., Lee, S.H., Lee, U.J., Fermin, C.D., Kim, M.: Immobilized enzymes in
biosensor applications. Materials 12(1), 121 (2019)
29. Si, P., Dong, X.-C., Chen, P., Kim, D.-H.: A hierarchically structured composite of Mn 3 O
4/3D graphene foam for flexible nonenzymatic biosensors. J. Mater. Chem. B 1(1), 110–115
(2013)
30. Xiao, Fei, Li, Y., Zan, X., Liao, K., Rong, X., Duan, H.: Growth of metal–metal oxide nanos-
tructures on freestanding graphene paper for flexible biosensors. Adv. Func. Mater. 22(12),
2487–2494 (2012)
31. Wang, Ying, Zhao, C.-E., Sun, D., Zhang, J.-R., Zhu, J.-J.: A graphene/poly (3, 4-
ethylenedioxythiophene) hybrid as an anode for high-performance microbial fuel cells.
ChemPlusChem 78(8), 823–829 (2013)
32. Cao, Minghui, Su, J., Fan, S., Qiu, H., Dongliang, S., Li, L.: Wearable piezoresistive pressure
sensors based on 3D graphene. Chem. Eng. J. 406, 126777 (2021)
33. Cao, Xueyuan, Zhang, J., Chen, S., Varley, R.J., Pan, K.: 1D/2D nanomaterials synergistic,
compressible, and response rapidly 3D graphene aerogel for piezoresistive sensor. Adv. Funct.
Mater. 30(35), 2003618 (2020)
34. Wang, Tao, Li, J., Zhang, Y., Liu, F., Zhang, B., Wang, Y., Jiang, R., Zhang, G., Sun, R., Wong,
C.-P.: Highly ordered 3D porous graphene sponge for wearable piezoresistive pressure sensor
applications. Chem. Europ. J. 25(25), 6378–6384 (2019)
35. Ma, L., Lei, X., Li, S., Guo, S., Yuan, J., Li, X., Cheng, G.J., Liu, F.: A 3D flexible piezoresistive
sensor based on surface-filled graphene nanosheets conductive layer. Sens. Actuators A 332,
113144 (2021)
36. Ma, Lijun, Lei, X., Guo, X., Wang, L., Li, S., Shu, T., Cheng, G.J., Liu, F.: Carbon black/
graphene nanosheet composites for three-dimensional flexible piezoresistive sensors. ACS
Appl. Nano Mater. (2022)
37. Sengupta, D., Pei, Y., Kottapalli, A.G.P.: Ultralightweight and 3D squeezable graphene-
polydimethylsiloxane composite foams as piezoresistive sensors. ACS Appl. Mater. Interfaces.
11(38), 35201–35211 (2019)
38. Chen, Kai-Yue, Xu, Y.-T., Zhao, Y., Li, J.-K., Wang, X.-P., Qu, L.-T. Recent progress in
graphene-based wearable piezoresistive sensors: From 1D to 3D device geometries. Nano
Mater. Sci. (2022)
39. Xia, Kailun, Wang, C., Jian, M., Wang, Q., Zhang, Y.: CVD growth of fingerprint-like patterned
3D graphene film for an ultrasensitive pressure sensor. Nano Res. 11(2), 1124–1134 (2018)
40. Xu, R., Zhang, H., Cai, Y., Ruan, J., Qu, K., Liu, E., Ni, X., Lu, M., Dong, X.: Flexible and
wearable 3D graphene sensor with 141 KHz frequency signal response capability. Appl. Phys.
Lett. 111(10), 103501 (2017)
41. Xu, Rongqing, Wang, D., Zhang, H., Xie, N., Shan, L., Ke, Q.: Simultaneous detection of static
and dynamic signals by a flexible sensor based on 3D graphene. Sensors 17(5), 1069 (2017)
42. Zhang, Rujing, Hu, R., Li, X., Zhen, Z., Xu, Z., Na, L., He, L., Zhu, H.: A bubble-derived
strategy to prepare multiple graphene-based porous materials. Adv. Func. Mater. 28(23),
1705879 (2018)
43. Peng, Zhiyuan, Yu, C., Zhong, W.: Facile preparation of a 3D porous aligned graphene-based
wall network architecture by confined self-assembly with shape memory for artificial muscle,
pressure sensor, and flexible supercapacitor. ACS Appl. Mater. Interfaces. 14(15), 17739–17753
(2022)
44. Sha, Baolin, Lü, X., Jiang, L.: High sensitivity and wide range biomimetic tactile-pressure
sensor based on 2D graphene film and 3D graphene foam. Micromachines 13(7), 1150 (2022)
45. Wei, S., Qiu, X., An, J., Chen, Z., Zhang, X.: Highly sensitive, flexible, green synthesized
graphene/biomass aerogels for pressure sensing application. Compos. Sci. Technol. 207,
108730 (2021)
46. Yan, T., Wang, Z., Pan, Z.-J.: Flexible strain sensors fabricated using carbon-based nanomate-
rials: a review. Curr. Opin. Solid State Mater. Sci. 22(6), 213–228 (2018)
47. Pan, Fei, Chen, S.-M., Li, Y., Tao, Z., Ye, J., Ni, k., Yu, H. et al.: 3D graphene films enable
simultaneously high sensitivity and large stretchability for strain sensors. Adv. Funct. Mater.
28(40), 1803221 (2018)
48. Luo, Zewei, Hu, X., Tian, X., Luo, C., Xu, H., Li, Q., Li, Q. et al.: Structure-property rela-
tionships in graphene-based strain and pressure sensors for potential artificial intelligence
applications. Sensors 19(5), 1250 (2019)
49. Chen, Zefeng, Wang, Z., Li, X., Lin, Y., Luo, N., Long, M., Zhao, N., Xu., J.-B.: Flexible
piezoelectric-induced pressure sensors for static measurements based on nanowires/graphene
heterostructures. ACS Nano 11(5), 4507–4513 (2017)
50. Li, J., Zhao, S., Zeng, X., Huang, W., Gong, Z., Zhang, G., Sun, R., Wong, C.-P.: Highly
stretchable and sensitive strain sensor based on facilely prepared three-dimensional graphene
foam composite. ACS Appl. Mater. Interfaces. 8(29), 18954–18961 (2016)
51. Xiang, D., Zhang, X., Li, Y., Harkin-Jones, E., Zheng, Y., Wang, L., Zhao, C., Wang,
P.: Enhanced performance of 3D printed highly elastic strain sensors of carbon nanotube/
thermoplastic polyurethane nanocomposites via non-covalent interactions. Compos. B Eng.
176, 107250 (2019)
52. Xu, Rongqing, Lu, Y., Jiang, C., Chen, J., Mao, P., Gao, G., Zhang, L., Wu, S.: Facile fabrication
of three-dimensional graphene foam/poly (dimethylsiloxane) composites and their potential
application as strain sensor. ACS Appl. Mater. Interfaces. 6(16), 13455–13460 (2014)
53. Xu, M., Li, F., Zhang, Z., Shen, T., Zhang, Q., Qi, J.: Stretchable and multifunctional strain
sensors based on 3D graphene foams for active and adaptive tactile imaging. Sci. China Mater.
62(4), 555–565 (2019)
54. Wu, Jin, Huang, W., Liang, Y., Wu., Z., Zhong, B., Zhou, Z., Ye, J., Tao, K., Zhou, Y., Xie, X.:
Self-calibrated, sensitive, and flexible temperature sensor based on 3D chemically modified
graphene hydrogel. Adv. Electron. Mater. 7(4), 2001084 (2021)
Graphene-Based Materials
for the Remediation of Hydrogen Sulfide
Gas
Nishesh Kumar Gupta, Kaptan Rajput, and Herlys Viltres
Abstract In the family of carbon allotropes, graphene oxide (GO) has shown
tremendous potential in energy and the environment. Besides being developed for
the remediation of water pollutants, these carbon nanostructures are highly effective
for air purification applications. Air pollutants like hydrogen sulfide (H2 S) could
lead to the acidification of ecosystems and a high human mortality rate. GO-based
adsorbents with suitable structural and functional modifications have shown unprece-
dented performance for the capture and mineralization of H2 S in relevant experi-
mental conditions. This chapter is focused on highlighting the potential of GO-based
adsorbents in removing H2 S gas in ambient conditions. The chapter aims to present
an in-depth explanation of the trend and mechanism, which is the driving force for
future research.
Keywords Adsorption · Graphene oxide · Hydrogen sulfide · Mechanism
N. K. Gupta (B)
Department of Environmental Research, University of Science
and Technology (UST), 217 Gajeong-Ro, Daejeon 34113, Republic of Korea
e-mail: guptan@kict.re.kr
Department of Environmental Research, Korea Institute of Civil Engineering and Building
Technology (KICT), 283 Goyang-Daero 10223, Goyang-si, Republic of Korea
K. Rajput
Materials and Biophysics Group, Department of Applied Physics, Sardar Vallabhbhai National
Institute of Technology, Ichchhanath Surat-Dumas, Surat 395007, India
School of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST),
291 Daehak-Ro, Daejeon 34141, Republic of Korea
H. Viltres
School of Engineering Practice and Technology, McMaster University, 1280 Main Street,
West Hamilton, ON L8S 4L8, Canada
https://doi.org/10.1007/978-3-031-36249-1_9
152 N. K. Gupta et al.
1 Introduction
While graphene nanosheets have found numerous applications in energy and the
environment, this sp2 hybridized, covalently bonded chain of polycyclic aromatic
hydrocarbons needs further modification for their compatibility in gas treatment
applications. More often, graphene oxide (GO) or reduced graphene oxide (RGO)
materials are explored for treating acidic gases in conjugation with an active adsorbent
due to the poor acidic gas adsorption behavior of GO/RGO. Since RGO/GO is highly
porous, they are used as a support for anchoring gas-binding functionalities and
catalysts/adsorbents. Section 2 of this chapter has discussed some strategies adopted
for developing novel GO-based materials.
Among numerous acidic gaseous pollutants, hydrogen sulfide (H2 S) stands out
due to its ubiquitous presence in different ecosystems. Naturally, H2 S is released from
the hydrolysis of volcanic rocks and the anaerobic respiration of sulfate-reducing
bacteria. However, a large proportion of H2 S in the atmosphere is released from oil
refineries and coal gasification units. Even the wastewater treatment facilities in our
areas are a common source of H2 S gas. H2 S is a colorless, pungent-smelling, and
flammable gas which tends to settle in poorly ventilated areas [1]. While inhaling a
low concentration (1–5 ppm) of H2 S can irritate the eyes and throat, exposure to high
concentrations (500–1000 ppm) could be fatal to humans [2]. Thus, it is necessary
to develop techniques to eliminate H2 S gas from different sources.
RGO/GO-based materials could act as adsorbents/catalysts in eliminating a broad
concentration of H2 S gas in different experimental conditions. As such, Sect. 3 of
this chapter is focused on the performance of RGO/GO-based adsorbents for elim-
inating H2 S gas in ambient conditions. The section further aims to explore the role
of GO and experimental conditions that affect uptake performance. The H2 S capture
process over GO-based adsorbents is associated with H2 S dissociation, followed by
its oxidation to sulfur byproducts like sulfur, sulfite, and sulfate. Understanding H2 S
removal mechanisms are necessary to develop superior materials for their industrial
applications. Section 4 has presented a detailed discussion of the H2 S removal mech-
anism with a particular interest in spectroscopic findings and theoretical calculations.
This chapter provides brief and concise information on GO-based adsorbents for the
remediation of H2 S gas from different contamination sources. Moreover, Sect. 5
provides the limitations and possible developments that could make these materials
suitable for industrial purposes.
2 Synthesis of RGO/GO-Based Adsorbents
Since many of the chapters in this book have discussed the synthesis of graphene and
GO in detail, this section provides a brief description of the conventional synthesis
route adopted for graphene, GO, and RGO. The two-dimensional (2D) graphene
describes a single layer of sp2 hybridized aromatic carbon structure peeled off from
Graphene-Based Materials for the Remediation of Hydrogen Sulfide Gas 153
a three-dimensional (3D) graphite block. The poor dispersion behavior of graphene

sheets due to π–π interactions between the sheets limits their possible application
in environmental decontamination. However, anchoring oxygen-rich functionalities
like hydroxyl groups, epoxides, and carboxylic acid on the graphene sheets, termed
GO, could improve its dispersion behavior without compromising the intrinsic prop-
erties of graphene. GO was produced in large quantities through the chemical exfoli-
ation of graphite in a strong acidic oxidizing medium (Hummers’ method). However,
the method has seen numerous modifications in the last six decades to improve the
physicochemical properties, yield, greenness, and affordability [3]. The thermal or
chemical reduction of GO sheets yields RGO with graphene domains, defects, and
residual O-functionalities on the surface of the sheets. Though RGO has a lower
mechanical strength and conductivity than graphene sheets, these oxidation–reduc-
tion strategies have been employed for the large-scale synthesis of graphene-like
materials [4].
For H2 S gas removal, RGO/GO is covalently modified with functional groups
or integrated with metal oxides or other active adsorbents to form RGO/GO-based
nanocomposites. Covalent modification of RGO/GO is a straightforward strategy
as the O-functionalities could be used for supporting other functional groups [6].
Rahighi and coworkers reported a simple covalent modification of GO nanosheets
with piperazine by refluxing in ethanol for 24 h at 100 ºC (Fig. 1a) [5]. The same
group modified the RGO surface with amide functionality by amidation of acyl-
chlorinated RGO in a multi-step approach [7]. Even waste ammonia gas could be
used for the covalent functionalization of GO through high-temperature annealing
in an inert atmosphere after ammonia gas adsorption [8].
Since GO-based nanocomposites are better-suited adsorbents for H2 S removal,
the synthetic strategies adopted for their fabrication have been discussed here. The
most common method adopted for synthesizing GO-based nanocomposites relies
on the in situ growth of active adsorbent with the GO. For this, pre-synthesized
GO is dispersed in the reactant medium before subjecting it to the regular route
of active adsorbent synthesis. The in situ growth allows uniform distribution of
active adsorbents over the GO surface on a nanoscale. In some cases, thermal
annealing in an inert atmosphere to form active adsorbents could reduce the GO
into RGO [9, 10]. When discussed in the context of MOF-GO composites, GO is
dispersed in the metal-linker reactant solution before subjecting it to hydrothermal/
solvothermal synthesis (Fig. 1b) [11]. However, some researchers have added addi-
tional functionalities to the composite by pre-modifying the GO surface. Karanikolos
et al. have reported polyethyleneimine-GO/HKUST-1 composite for H2 S removal,
where primary amine functionality was grafted on the GO surface before forming
a composite with HKUST-1 [12]. Bandosz and coworkers have reported the pre-
functionalization of GO with sulfanilic acid or 4-ammonium polystyrene sulfonate
before composite formation with Cu-BTC [13]. Some researchers have reported the
benefits of ternary composites with two active adsorbents distributed on the GO
Fig. 1 a Covalent modification of GO with piperazine [5]; b in situ growth of HKUST-1

nanocrystals over GO surface
surface. In such a case, one active component is pre-synthesized and dispersed in

the reaction medium like GO. For Au–Zn(OH)2 –GO composite, pre-synthesized Au
nanoparticles were dispersed in ZnCl2 solution along with GO to form the composite
[14].
3 H2 S Removal Application
GO has limited H2 S uptake capacity (3 mg g−1 ) [9], which makes it less relevant to
the purpose in the raw form. However, anchoring suitable functional groups over the
GO surface makes it an efficient adsorbent for H2 S gas removal. GO surface function-
alization with amine-bearing or similar basic functional groups is an ideal strategy to
improve the H2 S capture performance of GO-based materials. Though some studies
have reported improvement in H2 S gas uptake after the surface modification with N-
donor groups (amido and piperazine), the method adopted for functionalization is a
multi-step approach, which severely limits the scale-up of materials [5, 7]. However,
using a waste gas like NH3 for GO surface modification with N-groups and subse-
quent utilization for H2 S capture could reduce the overall cost and improve the
efficiency of GO materials. GO with a high NH3 capacity of 90 mg g−1 was ther-
mally treated in N2 gas after NH3 capture and used for H2 S adsorption (capacity
~30.5 mg g−1 ) [8]. Unlike GO surface functionalization, GO-based composites
are well-researched materials in the literature, where GO acts as a porous support
for metal oxides, metal hydroxides, and metal–organic frameworks (MOFs). The
subsequent section is dedicated to the discussion involving GO-based composites.
The main reason behind the use of GO-based composite is to improve the distri-
bution of active adsorbent over a porous surface, which provides a better adsorbate–
adsorbent (gas-active site) interaction. Moreover, GO in the nanocomposite opposed
to graphene, provides a higher H2 S uptake capacity both in dry and moist conditions
[18]. However, the implications of this approach on the surface and pore properties
are highly related to the kind of active adsorbent, i.e., metal oxide, metal oxyhy-
droxide, or MOFs. For metal oxides like ZnO, GO acts as a highly porous support
irrespective of the ZnO: GO composition ratio ZnO has a much lower surface area
than GO (Fig. 2a). Though the increasing proportion of ZnO in the composite could
lower the surface area and clog the pores, the H2 S adsorption capacity increased
due to abundant ZnO active sites [9]. For some porous metal oxyhydroxides, the
composite fabrication with GO could either lower the surface area, like in the case
of CoOOH-GO (Fig. 2b) [15], or improve slightly with the increasing GO propor-
tion, like in the case of FeOOH-GO (Fig. 2c) [16]. In such a case, the adsorption
capacity is improved slightly or decreases to an extent, which makes the overall
process of incorporating GO inconsequential. In the case of highly porous materials
like MOFs, GO incorporation is beneficial as it improves the surface area and H2 S
uptake capacity to a greater extent [17, 19, 20]. However, only a small fraction of
GO could be incorporated into the MOF-GO composite. Beyond an optimum GO
loading, both surface area and uptake capacity drop drastically due to the interference
of GO in the MOF crystallization [19] or loss of microporosity and pore blocking
[20]. For HKUST-1-GO nanocomposite, only a fraction of GO (~5%) was sufficient
to double the H2 S adsorption capacity, and beyond, it declined rapidly and reached
below HKUST-1’s adsorption capacity (Fig. 2d). Thus, it is essential to understand
the nature of active adsorbent before fabricating GO-adsorbent composites, and an
optimum GO loading is required to have promising H2 S removal performance.
The synthesis method affects the composite physicochemical properties, and thus
its H2 S adsorption capacity. In one such study involving the fabrication of ZnO-RGO
through reflux and microwave methods, the ZnO-RGO synthesized by microwave
heating had a superior H2 S removal capacity (120.6 mg g−1 ) than the one synthesized
by reflux method (50.2 mg g−1 ). Besides being a faster synthetic route, the microwave
method created smaller-size ZnO nanoparticles distributed uniformly over the RGO
surface [10]. Other than the surface area of a composite, the synergy between the
constituents [21] or the surface heterogeneity [13] could improve its H2 S adsorption
Fig. 2 Relationship between GO loading, surface area, and H2 S adsorption capacity of a ZnO-GO
[9]; b CoOOH-GO [15]; c FeOOH-GO [16]; d HKUST-1-GO [17] nanocomposites
capacity. The increasing surface heterogeneity improves the H2 S removal perfor-

mance, which was observed for a ternary Au–ZnO–GO composite. The ternary
composite showed a higher H2 S uptake than the binary composites, even with a
minor increment in its surface area. Au and GO in the nanocomposite provided a
pathway for rapid electron transport, which benefitted the H2 S oxidation process. The
surface heterogeneity could be further improved by introducing functional groups
and active adsorbents over the GO layers as in Cu-BTC-sulfanilic acid-modified GO
[13]. The functionalized MOF-GO composite has a higher H2 S adsorption capacity
(241 mg g−1 ) than the MOF-GO composite (130 mg g−1 ), highlighting the importance
of increasing surface heterogeneity.
In practice, these adsorbents are always tested for breakthrough studies in column
configuration where experimental parameters like gas flow rate, adsorbent mass
(bed height), gas concentration, and humidity play an important role in deciding
the adsorption performance. However, the moisture content in the adsorbent has
a striking effect on the H2 S adsorption capacity. The experimental and theoretical
calculations predict a preferential interaction of H2 O with the carbonyl groups on
the GO surface, which blocks the potential active sites for H2 S decomposition [22].
However, for metal oxides like ZnO, water molecules chemisorbed over the ZnO
surface improve the hydroxyl density and provide an alternative reaction pathway
for H2 S dissociation with lower activation energy [23]. Thus, the amount of water
pre-adsorbed on the composite surface improves its H2 S adsorption capacity if GO
loading is much lower than the active adsorbent.
The effect of moisture has been studied in detail in numerous reported studies.
For many GO-based composites, there is a linear relationship between the amount of
water pre-adsorbed and their H2 S adsorption capacity (Fig. 3a). Pre-adsorbed water
on the composite surface creates a thin film, which dissolute and dissociates an H2 S
molecule into 2H+ and S2− ions. This proton release during the dissociation reaction
is the reason behind an increase in the surface acidity of the composite, which rises
further with the increasing amount of pre-adsorbed water [17]. The easy dissociation
of H2 S molecules improves the adsorption capacity, and for this reason, a positive
linear relationship has been witnessed for GO-based composites, even though H2 O
and H2 S compete for the binding sites over the GO surface. The linear relationship
could also be associated with the amount of GO in the composites. Since GO is
a hydrophobic material, a higher proportion of it in the composite could lower the
hydrophilicity of the composite, which reduces the amount of pre-adsorbed water and
H2 S uptake capacity [17, 26]. Thus, the proportion of GO in the composite decides its
adsorption capacity in dry and humid conditions. Unlike humidity, the effect of other
experimental factors like gas flow rate, gas concentration, and adsorbent loading has
been reported the least in these studies, which should be the focus of future studies
to understand the column design parameters. Long et al. studied the effect of space
velocity on H2 S adsorption capacity with MgO/RGO as the catalyst/adsorbent. The
adsorption capacity decreased with the increasing space velocity due to the drop in
gas retention time, which disfavored the interaction of H2 S molecules with the MgO/
RGO surface [28].
Some studies have probed the role of visible light on the H2 S removal capaci-
ties of GO-based composites [18, 25, 27]. The sp2 hybridized aromatic structure of
GO provides a photoactive surface for electron–hole pair formation during radiation
exposure and works as a conductive surface for a fast electron transfer. Besides, transi-
tion metal-containing active adsorbents are excellent absorbers of ultraviolet–visible
radiation and generate electron–hole pairs. Thus, the GO-based adsorbents could also
serve as photocatalysts for H2 S removal. The effect of ambient light exposure on the
H2 S adsorption capacity of Cd(OH)2 -GO nanocomposite was reported in both the dry
and moist conditions (Fig. 3b) [25]. For Cd(OH)2 -GO nanocomposite, the effect of
visible light is more pronounced in dry conditions. In moist conditions, the favorable
splitting of surface water molecules could lower the sensitivity of H2 S molecules.
This negative effect of moisture on the gas uptake behavior of composite has been
reported for Zn(OH)2 -GO, where the adsorption capacity of 155 mg g−1 in the dark
condition dropped to 115 mg g−1 under ambient light [27]. In the dry condition, the
increasing GO loading in the composite negatively impacted the composite’s gas
uptake behavior. However, this behavior reversed during the visible light exposure,
as more GO in the composite provided efficient photoelectrons mobility, extended
their lifetime, and restricted the electron–hole pair recombination process [25].
Fig. 3 a A linear relationship between the amount of water pre-adsorbed in the composites and their
H2 S adsorption capacity [16, 17, 24]; b The H2 S adsorption capacity of Cd(OH)2 -GO nanocom-
posite in the absence and presence of ambient light in dry and moist conditions [25]; c The H2 S
adsorption capacity of different GO composites with metal oxides, hydroxides, (oxy)hydroxides,
and MOFs as active adsorbents [9, 15–20, 25–27]
GO-based composites for fuel and flue-gas desulfurization need to be non-toxic,

high performing, and regenerable. Considering the high toxicity of cadmium, Cd-
based materials for desulfurization application should be replaced with other tran-
sition metals like Zn, Fe, and Co [25]. Based on the adsorption performance of
GO composites with Zn-based active adsorbents, ZnO, Zn(OH)2 , and ZnOOH are
better choices than Zn-terephthalate MOF (MOF-5). Since MOF-5 fabrication needs
toxic chemicals like N,N-dimethylformamide (DMF), chloroform, and an expensive
terephthalic acid linker ($85 kg−1 , Sigma Aldrich) [19, 29], the overall benefits of
using MOF-5-GO composites are minimal. The only cost-cutting and environmen-
tally benign solution is the use of polyethylene terephthalate (PET) bottle waste to
fabricate MOF-5 [30]. Among MOFs, UiO-66 (Zr-terephthalate MOF) is a suitable
candidate for GO composite formation due to its excellent H2 S uptake behavior and
regenerability after heating in N2 gas [20]. But considering the cost of Zr salts and
organic linkers and the toxicity of organic solvents used in the MOF fabrication,
the most suitable adsorbents are transition metal (oxy)hydroxides, which are porous
materials with high hydroxyl density and H2 S removal capacity (Fig. 3c).
4 Removal Mechanism
Based on theoretical calculations, H2 S adsorption over pure graphene and hydro-

genated graphene (graphane) nanosheets are governed by physical interaction,
reflected by a lower adsorption energy and charge transfer in the range of −0.02–
0.05 eV and 0.002–0.007e, respectively. However, when 3d transition metals like
Fe, Co, and Cu are doped in the graphene nanosheets, it exhibits significantly higher
adsorption energy of −0.93, −1.50, and −0.88 eV and charge transfer of 0.058,
0.170, and 0.302 e, respectively, which eventually leads to chemisorption [31]. Inter-
actions with the graphene surface could be improved by modifying the surface with
O-functionalities like epoxy and hydroxyl groups which enhanced the adsorption
energy and charge transfer. The maximum change in these parameters is noticed for
zigzag graphene nanoribbons as −0.0252 eV and −0.097e, respectively [32]. More
detailed experimental and theoretical analyses have confirmed that H2 S molecules
react with the carbonyl functional groups on the GO surface, which was also reflected
in the population analysis of H2 S, where the functional group coverage increase from
10 to 30% led to an increment in the number of chemisorbed H2 S molecules. The
population analysis spectra confirmed that water molecules could block these reac-
tive sites and restrict the decomposition of H2 S molecules [22]. The introduction of
transition metal (Cu) or metal oxide (CuO) in GO nanostructures could substantially
improve the H2 S binding energy in the range of −1.33–−1.93 eV for Cu atom and
−2.36–−2.95 eV for CuO at the top, hollow, and bridge binding sites compared to
the pristine GO nanostructure [33]. Water over the surface of transition metal oxides
could improve their H2 S removal capacity by lowering the energy barrier from 63.3
to 53.3 kJ mol−1 for newly formed hydroxyl groups, further confirmed for ZnO
through spectroscopy and density functional theory calculations [23]. Thus, theo-
retical calculations have demonstrated that GO nanosheets decorated with transition
metal oxides are highly effective in H2 S mineralization, which we have critically
discussed here.
In dry conditions, the H2 S adsorption mechanism over a metal oxide such as ZnO
is initiated with the dissociation of H2 S molecules to H+ and HS− ions, followed by
diffusion of HS− ions in the oxide lattice and migration of oxide and formed water
molecules to the surface. Thus, the conversion of ZnO to ZnS is facilitated by protons
transfers from H2 S to the surface-bound hydroxyl groups. Due to this direct acid–base
reaction, ZnS as a byproduct could be traced in the X-ray diffraction pattern of spent
ZnO samples [10, 34]. However, this is not the case with other studies dealing with
H2 S adsorption due to the sulfidation of two to three oxide surface monolayers after
H2 S saturation, and sophisticated techniques are required to deduce the mechanism
[35, 36]. Since sulfide formation is a common occurrence in the H2 S adsorption
process over transition metal oxide, X-ray photoelectron spectroscopy (XPS) is a
standard analytical technique to conclude the adsorption mechanism. Due to the
replacement of lattice O2− with S2− ions, there is a change in the electron density
around transition metal ions, which causes a shift in the binding energy of metal
ions [37]. Moreover, the sulfide ions could be detected in the high-resolution S2p
spectrum, where a 2p3/2 -2p1/2 doublet is witnessed at 161–162 eV [38]. Other than
sulfide, even sulfate ions could form in dry conditions. This acidic high-valent sulfur
species could be identified in the S 2p spectrum as a 2p3/2 -2p1/2 doublet between
168–170 eV. The sulfate species generates through the oxidation of S2− or HS− by
loosely bound oxygen species or adsorbed molecular oxygen [34].
In moist conditions, the H2 S adsorption mechanism has more complexities due to
the involvement of chemically adsorbed water on the GO-based composite surface.
As discussed earlier, moisture certainly restricts the interaction of H2 S with the GO
surface due to the competitive nature of H2 O for the H2 S binding sites. However,
chemisorbed H2 O plays a positive role in H2 S adsorption over the transition metal
oxide surface. The chemisorbed water could dissociate on the transition metal oxide
surface with alkaline nature to form additional hydroxyl groups, which promotes the
reactive dissociation of H2 S by providing a low activation energy pathway [23, 28].
Thus, the role of water toward H2 S adsorption over RGO/GO-based composites is
highly related to the active adsorbent of the composite. The H2 S adsorption-oxidation
over metal oxide composite forms sulfide, sulfur, and sulfate species, which are
distinguishable in the S 2p spectrum of the exhausted samples (Fig. 4a). The elemental
sulfur formation is associated with the redox chemistry of transition metal ions, where
high-valent cation reduces to a lower oxidation state by accepting electrons from the
sulfide ions, which changes the sulfide into elemental sulfur.
A more recent investigation by Long et al. has provided better insight into the reac-
tion byproducts of the H2 S adsorption-oxidation process. Three RGO/metal oxide
composites with MgO, ZnO, and Fe2 O3 were investigated for H2 S adsorption in
humid conditions at room temperature. While sulfide, sulfur, and sulfate species were
confirmed over ZnO/RGO and Fe2 O3 /RGO, sulfide formation was absent in MgO/
RGO when experiments were performed with 1% O2 in the carrier gas (Fig. 4a). Theo-
retical calculations and electron paramagnetic spectroscopy confirmed the formation
of O2 ·− radicals in the O2 flow, which were absent in the N2 flow. These O2 ·− radi-
cals were generated by the single-electron transfer from the RGO matrix, which
catalytically oxidized S2− and HS− species to elemental sulfur. This radical-based
oxidation (/\G = −0.174 eV) is preferred over acid–base neutralization of sulfides
(/\G = 0.853 eV) in MgO/RGO, which resulted in a large proportion of elemental
sulfur. However, for Fe2 O3 /RGO and ZnO/RGO, the calculations suggested that HS−
prefers reacting with ZnO (/\G = −0.365 eV) and Fe2 O3 (/\G = −0.771 eV) to
form ZnS and Fe2 S3 , respectively, rather than being oxidized by O2 ·− radicals. For
this reason, a large proportion of formed sulfide remained metal-bound, and a small
fraction oxidized to elemental sulfur and sulfate species (Fig. 4b, c) [28].
Even the physicochemical properties of active adsorbents play an important role
in the adsorption mechanism and are responsible for the H2 S uptake capacity. Unlike
metal oxides, where the role of hydroxyl groups in H2 S dissociation is limited due
to the low hydroxyl group density, metal (oxy)hydroxides have a high hydroxyl
group density. These hydroxyl groups are responsible for a high H2 S uptake capacity
compared to metal oxides or hydroxides. For instance, CoOOH-GO with Co3+ ions
has a higher oxidation ability than Co(OH)2 -GO with Co2+ ions, which makes
CoOOH-GO a superior material for H2 S mineralization [15, 24]. In dry conditions,
Graphene-Based Materials for the Remediation of Hydrogen Sulfide Gas
Fig. 4 A High-resolution S 2p spectra of MgO/rGO-S, ZnO/rGO-S, and Fe2 O3 /rGO-S; b The calculated free-energy changes of the H2 S catalytic oxidation
reaction on the MgO (200), ZnO (100), and Fe2 O3 (311); c Schematic illustrations of room-temperature H2 S removal over MgO/rGO, ZnO/rGO, or Fe2 O3 /
rGO. Adapted with permission [28], Copyright (2022), The Royal Society of Chemistry
161
the high oxidation activity of CoOOH results in the minor evolution of SO2 gas, which
could be suppressed in moist conditions. The H2 S reaction chemistry over moist
CoOOH involves multiple reaction pathways, forming several sulfurous byprod-
ucts, including metal sulfides and sulfates [15]. The same is true for other metal
(oxy)hydroxides like FeOOH, where both the lattice oxygen and hydroxyl groups
are crucial for H2 S oxidation (Fig. 5). The H2 S molecules dissociate in the water
film to generate HS− ions which replace the surface hydroxyl groups to form iron
sulfide. The formed sulfide is oxidized to elemental sulfur by molecular oxygen and
water to replenish the consumed hydroxyl groups. In another reaction pathway, H2 S
molecules react with the lattice oxygen to form SO2 molecules and reduced Fe2+
species. SO2 could oxidize to SO3 by molecular oxygen and form surface-bound
SO4 2− species by reacting with water. Furthermore, this molecular oxygen could
oxidize Fe2+ to Fe3+ ions [16].
For MOFs-GO composite, the adsorption mechanism involves the reactive inter-
action of H2 S molecules with the open metal sites in the MOF framework. The open
metal sites are highly active and accommodate the incoming H2 S molecules [17,
19]. However, this reactive dissociation of H2 S is accompanied by the release of H+
ions, which dissociate the metal–carboxylate bonding and lowers the overall struc-
tural stability of the MOF (Fig. 6). Thus, despite having a large adsorption capacity,
Fig. 5 Reactive adsorption mechanism of H2 S on the surface of FeOOH-GO composite. Adapted

with permission [16], Copyright (2022), American Chemical Society
Fig. 6 H2 S adsorption mechanism over MOF-5-GO or HKUST-1-GO composites [17, 19]
MOF-GO composites of 3d transition metals like Cu and Zn are hard to regenerate

with conventional regeneration techniques.
5 Challenges and Strategies
Though the research on the room-temperature desulfurization process has made

significant progress toward developing outstanding GO-based adsorbents and under-
standing the mechanism driving the H2 S removal processes, these studies do not
shed light on the regeneration capabilities of the composites. Regeneration is
vital from economic and environmental perspectives as single-use adsorbents are
misfit for achieving sustainable development goals. The researchers should focus
on developing affordable and green regeneration strategies for commercialization
with minimal labor and energy requirements [39]. Another major drawback of these
studies is the lack of research data on operational parameters like gas concentration,
flow rate, and adsorbent loading (bed height). These operation parameters should
be systematically investigated in future studies for testing composite materials on
an industrial scale. Besides optimizing the experimental parameters, the researchers
should keenly seek pilot-scale studies and provide practical solutions for real-world
problems like the desulfurization of biogas, fuel gas, and industrial flue gases.
As discussed earlier, the researchers have devoted efforts to developing GO-based
composites using numerous active adsorbents, including metal oxides, hydroxides,
oxyhydroxides, and MOFs. These materials have been judged for desulfurization
applications solely based on their H2 S capture performance without considering the
cost-to-performance ratio and the environmental impact of the overall gas cleaning
process. Firstly, the researchers should look for green alternatives for the precursors
and synthetic processes required for composite development. Instead of using the
conventional Hummer’s method for GO synthesis, which uses toxic oxidants and
generates a large volume of wastewater, the researchers should follow water elec-
trolytic oxidation of graphite that is safe, fast, and green and provides better control
over the thickness and oxidation degree of GO [40]. Secondly, instead of using
graphene as precursors for GO synthesis, the current focus should be on agro-waste
for GO/RGO production [41, 42].
The choice of active adsorbent in the GO composite is hectic as there are numerous
possibilities, and any of these adsorbents could be integrated with GO. However,
the choice should not be merely influenced by the performance, but also by the
non-toxicity and greenness of the overall synthesis process. Like in the case of
MOFs, non-toxic and green solvents like water/ethanol should be adopted over
DMF. HKUST-1, widely used in GO composite for H2 S adsorption [11–13, 17,
21], could be synthesized at room temperature in water on a commercial scale
[43]. The alternative method over high-temperature solvothermal synthesis could
reduce the environmental cost. Moreover, reliance on solvothermal synthesis could
be ignored by adopting solvent-free synthesis routes, which are less expensive ($13–
36 kg−1 ) than solvothermal synthesis ($35–71 kg−1 ) [44]. As such, even commercial
organic linkers like terephthalic acid used in the synthesis of UiO-66(Zr) and MOF-5
could be replaced by extracting these linkers from PET bottle waste through mid-
temperature acidic/alkaline hydrolysis [45] or directly using the crushed PET bottles
[46]. This approach can further reduce the plastic burden on the planet and convert
PET waste into value-added products, providing a win-win strategy required in the
current research scenario.
6 Conclusion
In this chapter, we have highlighted the application of various RGO/GO-based

composites for the room-temperature removal of H2 S gas. GO has been integrated
with transition metal oxides, hydroxides, (oxy)hydroxides, and MOFs to construct
porous nanocomposites with uniform distribution of active sites over the GO surface.
In general, these composites have shown high H2 S adsorption capacity in moist condi-
tions due to the dissociation and reactive dissolution of H2 S in surface water films.
Moreover, the performances of these composites were primarily controlled by the
nature of the active adsorbent, GO loading, and synthesis methods. Besides providing
a large surface area, GO imparted heterogeneity to the surface, which was crucial in
the reactive adsorption of H2 S. Some studies highlighted the role of visible light in
improving the H2 S uptake performance in dry conditions by creating electron–hole
pairs required during the oxidation of dissociated H2 S byproducts (like sulfide). The
adsorption mechanism over these adsorbents involved the dissociation and oxidation
of H2 S into sulfide, sulfur, and sulfates. In some cases, the reactive adsorbent oxidized
H2 S into SO2 gas in dry conditions. Though the literature has been saturated with
numerous studies on GO/RGO-based composites for H2 S removal, their practical
application is limited due to improper investigation of operational parameters and
utilization of GO-adsorbent composites as aerogels and fabrics, which could be used

directly in real-world applications.
References
1. Shah, M.S., Tsapatsis, M., Siepmann, J.I.: Hydrogen sulfide capture: from absorption in polar
liquids to oxide, zeolite, and metal–organic framework adsorbents and membranes. Chem. Rev.
117, 9755–9803 (2017)
2. Yalamanchili, C., Smith, M.D.: Acute hydrogen sulfide toxicity due to sewer gas exposure.
Am. J. Emerg. Med. 26(518), e5-518.e7 (2008)
3. Marcano, D.C., Kosynkin, D.V., Berlin, J.M., Sinitskii, A., Sun, Z., Slesarev, A., Alemany,
L.B., Lu, W., Tour, J.M.: Improved synthesis of graphene oxide. ACS Nano 4, 4806–4814
(2010)
4. Compton, O.C., Nguyen, S.T.: Graphene oxide, highly reduced graphene oxide, and graphene:
versatile building blocks for carbon-based materials. Small 6, 711–723 (2010)
5. Khaleghi Abbasabadi, M., Khodabakhshi, S., Esmaili Zand, H.R., Rashidi, A., Gholami, P.,
Sherafati, Z.: Covalent modification of reduced graphene oxide with piperazine as a novel
nanoadsorbent for removal of H2 S gas. Res. Chem. Intermed. 46, 4447–4463 (2020)
6. Georgakilas, V., Otyepka, M., Bourlinos, A.B., Chandra, V., Kim, N., Kemp, K.C., Hobza, P.,
Zboril, R., Kim, K.S.: Functionalization of graphene: Covalent and non-covalent approaches,
derivatives and applications. Chem. Rev. 112, 6156–6214 (2012)
7. Khaleghi Abbasabadi, M., Rashidi, A., Safaei-Ghomi, J., Khodabakhshi, S., Rahighi, R.: A
new strategy for hydrogen sulfide removal by amido-functionalized reduced graphene oxide
as a novel metal-free and highly efficient nanoadsorbent. J. Sulfur Chem. 36, 660–671 (2016)
8. Seredych, M., Bandosz, T.J.: Adsorption of hydrogen sulfide on graphite derived materials
modified by incorporation of nitrogen. Mater. Chem. Phys. 113, 946–952 (2009)
9. Lonkar, S.P., Pillai, V., Abdala, A., Mittal, V.: In situ formed graphene/ZnO nanostructured
composites for low temperature hydrogen sulfide removal from natural gas. RSC Adv. 6,
81142–81150 (2016)
10. Song, H.S., Park, M.G., Kwon, S.J., Yi, K.B., Croiset, E., Chen, Z., Nam, S.C.: Hydrogen sulfide
adsorption on nano-sized zinc oxide/reduced graphite oxide composite at ambient condition.
Appl. Surf. Sci. 276, 646–652 (2013)
11. Petit, C., Bandosz, T.J.: Exploring the coordination chemistry of MOF–graphite oxide
composites and their applications as adsorbents. Dalton Trans. 41, 4027–4035 (2012)
12. Bhoria, N., Basina, G., Pokhrel, J., Kumar Reddy, K.S., Anastasiou, S., Balasubramanian, V.V.,
AlWahedi, Y.F., Karanikolos, G.N.: Functionalization effects on HKUST-1 and HKUST-1/
graphene oxide hybrid adsorbents for hydrogen sulfide removal. J. Hazard. Mater. 394, 122565
(2020)
13. Ebrahim, A.M., Jagiello, J., Bandosz, T.J.: Enhanced reactive adsorption of H2 S on Cu–BTC/
S- and N-doped GO composites. J. Mater. Chem. A 3, 8194–8204 (2015)
14. Giannakoudakis, D.A., Bandosz, T.J.: Zinc (hydr)oxide/graphite oxide/AuNPs composites: role
of surface features in H2 S reactive adsorption. J. Colloid Interface Sci. 436, 296–305 (2014)
15. Florent, M., Bandosz, T.J.: Effects of surface heterogeneity of cobalt oxyhydroxide/graphite
oxide composites on reactive adsorption of hydrogen sulfide. Microporous Mesoporous Mater.
204, 8–14 (2015)
16. Arcibar, J.A., Wallace, R., Mitchell, J.K., Bandosz, T.J.: Role of surface chemistry and
morphology in the reactive adsorption of H2 S on iron (hydr)oxide/graphite oxide composites.
Langmuir 31, 2730–2742 (2015)
17. Petit, C., Mendoza, B., Bandosz, T.J.: Hydrogen sulfide adsorption on MOFs and MOF/graphite
oxide composites. ChemPhysChem 11, 3678–3684 (2010)
18. Seredych, M., Mabayoje, O., Bandosz, T.J.: Visible-light-enhanced interactions of hydrogen
sulfide with composites of zinc (oxy)hydroxide with graphite oxide and graphene. Langmuir
28, 1337–1346 (2012)
19. Huang, Z.-H., Liu, G., Kang, F.: Glucose-promoted Zn-based metal–organic framework/
graphene oxide composites for hydrogen sulfide removal. ACS Appl. Mater. Interfaces 4,
4942–4947 (2012)
20. Daraee, M., Ghasemy, E., Rashidi, A.: Synthesis of novel and engineered UiO-66/graphene
oxide nanocomposite with enhanced H2 S adsorption capacity. J. Environ. Chem. Eng. 8, 104351
(2020)
21. Petit, C., Levasseur, B., Mendoza, B., Bandosz, T.J.: Reactive adsorption of acidic gases on
MOF/graphite oxide composites. Microporous Mesoporous Mater. 154, 107–112 (2012)
22. Huang, L., Seredych, M., Bandosz, T.J., van Duin, A.C.T., Lu, X., Gubbins, K.E.: Controllable
atomistic graphene oxide model and its application in hydrogen sulfide removal. J. Chem. Phys.
139, 194707 (2013)
23. Zhao, Y., Zhang, Z., Yang, C., Fan, H., Wang, J., Tian, Z., Zhang, H.: Critical role of water on the
surface of ZnO in H2 S removal at room temperature. Ind. Eng. Chem. Res. 57, 15366–15374
(2018)
24. Mabayoje, O., Seredych, M., Bandosz, T.J.: Cobalt (hydr)oxide/graphite oxide composites:
Importance of surface chemical heterogeneity for reactive adsorption of hydrogen sulfide. J.
Colloid Interface Sci. 378, 1–9 (2012)
25. Florent, M., Wallace, R., Bandosz, T.J.: Removal of hydrogen sulfide at ambient conditions on
cadmium/GO-based composite adsorbents. J. Colloid Interface Sci. 448, 573–581 (2015)
26. Seredych, M., Bandosz, T.J.: Reactive adsorption of hydrogen sulfide on graphite oxide/
Zr(OH)4 composites. Chem. Eng. J. 166, 1032–1038 (2011)
27. Mabayoje, O., Seredych, M., Bandosz, T.J.: Reactive adsorption of hydrogen sulfide on visible
light photoactive zinc (hydr)oxide/graphite oxide and zinc (hydr)oxychloride/graphite oxide
composites. Appl. Catal. B, 132–133, 321–331 (2013)
28. Xu, H., Pan, Y., Hu, F., Niu, B., Zhang, Y., Long, D.: Anti-corrosion MgO nanoparticle-equipped
graphene oxide nanosheet for efficient room-temperature H2 S removal. J. Mater. Chem. A 10,
18308–18321 (2022)
29. Kim, T.H., Kim, S.G.: Clinical outcomes of occupational exposure to N, N-dimethylformamide:
Perspectives from experimental toxicology. Saf. Health Work 2, 97–104 (2011)
30. Villarroel, D., Bernini, M.C., Arroyo-Gómez, J.J., Villarroel, J., Sapag, K.: Synthesis of MOF-5
using terephthalic acid as a ligand obtained from polyethylene terephthalate (PET) waste and
its test in CO2 adsorption. Braz. J. Chem. Eng. 39, 949–959 (2022)
31. Zhou, Q., Su, X., Ju, W., Yong, Y., Li, X., Fu, Z., Wang, C.: Adsorption of H2 S on graphane
decorated with Fe. Co and Cu: a DFT Study RSC Adv. 7, 31457–31465 (2017)
32. Salih, E., Ayesh, A.I.: DFT investigation of H2 S adsorption on graphene nanosheets and
nanoribbons: Comparative study. Superlattices Microstruct. 146, 106650 (2020)
33. Jyoti, R., Deji, Choudhary, B.C., Sharma, R.K.: Graphene oxide nanoribbons decorated with
Cu and CuO as H2 S gas sensor optimized with DFT. AIP Conf. Proc. 2369, 020130 (2021)
34. Song, H.S., Park, M.G., Ahn, W., Lim, S.N., Yi, K.B., Croiset, E., Chen, Z., Nam, S.C.:
Enhanced adsorption of hydrogen sulfide and regeneration ability on the composites of zinc
oxide with reduced graphite oxide. Chem. Eng. J. 253, 264–273 (2014)
35. Balsamo, M., Cimino, S., de Falco, G., Erto, A., Lisi, L.: ZnO-CuO supported on activated
carbon for H2 S removal at room temperature. Chem. Eng. J. 304, 399–407 (2016)
36. Galtayries, A., Bonnelle, J.-P.: XPS and ISS studies on the interaction of H2 S with
polycrystalline Cu, Cu2 O and CuO surfaces. Surf. Interface Anal. 23, 171–179 (1995)
37. Lee, S., Kim, D.: Enhanced adsorptive removal of hydrogen sulfide from gas stream with
zinc-iron hydroxide at room temperature. Chem. Eng. J. 363, 43–48 (2019)
38. Gupta, N.K., Bae, J., Kim, K.S.: Metal organic framework derived NaCox Oy for room
temperature hydrogen sulfide removal. Sci Rep. 11, 14740 (2021)
39. Gupta, N.K., Vikrant, K., Kim, K.S., Kim, K.-H., Giannakoudakis, D.A.: Regeneration strate-
gies for metal–organic frameworks post acidic gas capture. Coord. Chem. Rev. 467, 214629
(2022)
40. Pei, S., Wei, Q., Huang, K., Cheng, H.-M., Ren, W.: Green synthesis of graphene oxide by
seconds timescale water electrolytic oxidation. Nat. Commun. 9, 145 (2018)
41. Tamilselvi, R., Ramesh, M., Lekshmi, G.S., Bazaka, O., Levchenko, I., Bazaka, K., Mand-
hakini, M.: Graphene oxide–based supercapacitors from agricultural wastes: a step to mass
production of highly efficient electrodes for electrical transportation systems. Renew. Energy
151, 731–739 (2020)
42. Debbarma, J., Naik, M.J.P., Saha, M.: From agrowaste to graphene nanosheets: chemistry and
synthesis. Fullerenes, Nanotubes, Carbon Nanostruct. 27, 482–485 (2019)
43. Huo, J., Brightwell, M., El Hankari, S., Garai, A., Bradshaw, D.: A versatile, industrially
relevant, aqueous room temperature synthesis of HKUST-1 with high space-time yield. J.
Mater. Chem. A 1, 15220 (2013)
44. DeSantis, D., Mason, J.A., James, B.D., Houchins, C., Long, J.R., Veenstra, M.: Techno-
economic analysis of metal–organic frameworks for hydrogen and natural gas storage. Energy
Fuels 31, 2024–2032 (2017)
45. Kaur, R., Marwaha, A., Chhabra, V.A., Kaushal, K., Kim, K.-H., Tripathi, S.K.: Facile synthesis
of a Cu-based metal-organic framework from plastic waste and its application as a sensor for
acetone. J. Cleaner Prod. 263, 121492 (2020)
46. Deleu, W.P.R., Stassen, I., Jonckheere, D., Ameloot, R., De Vos, D.E.: Waste PET (bottles) as
a resource or substrate for MOF synthesis. J. Mater. Chem. A 4, 9519–9525 (2016)
3D Graphene for Removal of Inorganic
Pollutants
Iqra Fareed, Muhammad Danish Khan, Danish Rehman,

Masood ul Hassan Farooq, and Faheem K. Butt
Abstract 3D Graphene (3DG) has attracted a lot of attention in recent years because
of its unique features. The advancement in 3DG structures fundamentally makes it
easier to use the material in practical applications while maintaining its beneficial
features such as low density, large surface area, high porosity, outstanding mechanical
properties, and rapid transport for mass and electron. 3DG has been investigated to
remove inorganic pollutants, such as heavy metal ions (lead, arsenic, chromium,
mercury), fluorides, nitrides, chlorides, phosphates, antimony, and radium, that
mainly come from industrial litter, pharmaceutical waste, agricultural discharge,
oil refineries, improper radioactive disposal, and natural seepage which seriously
threaten the human health as well as aquatic flora and fauna. Environmental reme-
diation using 3DG is still being explored. The progress that has been made thus far
in this respect is summarized in the current chapter. Further research is required to
focus on its development for real-world applications.
Keywords 3D Graphene · Adsorption · Heterostructures · Synergy · Inorganic

pollutant
I. Fareed · M. D. Khan
Department of Physics, University of Engineering and Technology, G.T. Road, Lahore 54890,
Pakistan
D. Rehman · F. K. Butt (B)
Department of Physics, Division of Science and Technology, University of Education Lahore,
Township, Lahore 54770, Pakistan
e-mail: faheemk.butt@ue.edu.pk
M. ul Hassan Farooq
Department of Natural Sciences and Humanities, University of Engineering and Technology
(UET), New Campus (KSK), Lahore 54890, Pakistan
https://doi.org/10.1007/978-3-031-36249-1_10
170 I. Fareed et al.
1 Introduction
Pollutants are known to have adverse effects on surrounding and are found as gases,
aerosols, liquids, or solids that are either naturally occurring or produced by human
activity [11]. Pollutants with non-biodegradable nature have a harmful impact on
health even in minute quantities. These pollutants are generally caused by man-made
activities including industrialization, urbanization, uncontrolled sewerage discharge,
and so on in addition to naturally occurring activities [22]. They hail from chemi-
cals that are being dumped out by industries and factories working in the field of
engineering, papermaking, fine chemicals, dyes, paints, pharmaceuticals, and textiles
[21]. They include trace elements, mineral acids, inorganic salts, metals that have
formed complexes with organic compounds, sulfates, and cyanides, contaminating
waters. These inorganic contaminants are persistent in the environment and are not
biodegradable. Human health as well as flora and fauna are all negatively impacted by
this inorganic pollution [43]. Drinking water that has inorganic pollutants dissolved in
them has diverse effects on the human body because these materials are carcinogenic,
teratogenic, and mutagenic with accumulative amplification effects [21].
The world health organization (WHO) has set standards for several inorganic
pollutants, acceptable in drinking water. Many countries around the world have
constructed models and adopted guidelines to reduce the number of inorganic pollu-
tants in heavy water which is in support of WHO standards. The following Table 1
summarizes the limit of inorganic pollutants that are acceptable in drinking water
and the diseases that may be caused in case of access amount.
Due to the cumulative long-term impacts on health, inorganic contamination in
the environment is a serious health hazard all around the globe, even at low concen-
trations. Ingesting these hazardous substances through consumables not only affects
Table 1 Acceptable limit of

Heavy metals WHO standards (mg/mL)
inorganic pollutants. Adapted
with permission [19], Cadmium (Cd) 0.003
Copyright (2018), Elsevier Lead (Pb) 0.010
Chromium (Cr-III) 0.050
(Cr-VI) 0.010
Arsenic (As) 0.010
Nickel (Ni) 0.070
Manganese (Mn) 0.400
Zinc (Zn) 3.000
Tin (Sn) –
Mercury (Hg) 0.006
Copper (Cu) 2.000
Iron (Fe) 0.300
Silver (Ag) –
3D Graphene for Removal of Inorganic Pollutants 171
organs and body function, but also diminishes body immunity and causes growth
retardation, poor mental development, bad psycho-social attitude, and a number of
disorders in people. Radioactive elements such as Uranium (U), Radium (Ra), and
others, if they are present in drinking water, can cause genetic damage and infertility
and are carcinogenic which in low traces can cause changes in bone structure and
nephritis [31]. Water pollution is bad for the environment and human health. Statistics
showed that each year, 1 billion people are directly harmed by toxic pollutants in the
water, and therefore, diseases and other health problems erupt. Inorganic pollutants
can cause gastrointestinal distress, cirrhosis, necrosis, low blood pressure, hyperten-
sion, headaches, stomachaches, diarrhea, and vomiting [43]. Inorganic contaminants
that accumulate in the food chain and harm human health are polluting the environ-
ment at a devastating rate. It has been discovered that both organic and inorganic
substances can increase the generation of free radicals [30].
Rapid industrialization results in the discharge of significant inorganic pollutants
that impact water and soil. Heavy metals, which are hazardous or deadly even at
low concentrations, make up many inorganic contaminants [34]. Pesticides can be
detrimental to human health when used carelessly and without discrimination. The
sensitivity and toxicity of these pollutants to the organisms define their scope and
adverse effects. But no inferences regarding the amounts of heavy metals could be
made based only on an extensive evaluation of human impacts [30].
1.1 Categorizing Inorganic Pollutants
There are many inorganic pollutants that exist, but we mainly categorize them into
metallic pollutants, sulfides, and fertilizers as illustrated in Fig. 1.
Fig. 1 Inorganic pollutants divided into three main categories

Aluminum (Al), Copper (Cu), Iron (Fe), Lead (Pb), and Zinc (Zn) are all present
in drinking water. However, the naturally occurring materials that are the major
cause of inorganic pollution include compounds of Boron (B), Arsenic (As), and
Fluorides (F− ). These naturally occurring inorganic minerals typically contaminate
surface water and groundwater as well as canals, ponds, lakes, distribution pipelines
systems, and primarily, tap water. Other than that, heavy metals like Mercury (Hg),
Cadmium (Cd), Chromium (Cr), Cyanides (−CN), etc. are also categorized as inor-
ganic industrial waste. They can create health problems by entering the body through
consumables [18]. The phylogenetic sources that are connected to the soil and plants
discharge heavy metals, which have a negative influence on the environment. The
resultant food insecurity causing health risks leads to a troubling situation with
undeniable environmental distress [1].
From the deepest strata of the earth, heavy metals are excavated and released
into the environment. On the other hand, mines, smelters, thermal power plants,
metallurgical industries, electronics, textiles, phosphatic fertilizers, and municipal
solid waste are also a few of the businesses and sources that give off heavy metals
into the surroundings. The largest contributors to Cr, Hg, Nickel (Ni), Vanadium (V),
and Selenium (Se) emissions were from stationary sources such as coal-fired power
plants, while Pb emissions come from transportation, Cu production causing As, Cd,
and Cu emissions, while Zn manufacturing leads to Zn emission. Trace metals after
being released into the atmosphere are transported within air masses. A significant
portion of these metals is deposited on the land mass, sometimes even covering
national or continental boundaries [31].
Salt (primarily sodium chloride, NaCl) is majorly used in industries, particularly
those related to the manufacturing of soap and detergent, glass, textiles, rubber,
leather tanning, metal processing, and oil/gas drilling. Industrial effluents contain
salt ions that are highly mobile in the soil and can seep through the soil profile,
contaminating groundwater reservoirs when released into the environment. Agricul-
tural land soils can become salinized (have access of NaCl) or sodic (have a large
amount of sodium) when such salt-laden groundwater and surface water are utilized
to irrigate crops. Na damages typical plant growth at greater concentrations and this
damage is relative to high chloride and salt levels. As a result, harm brought on by
excess Na and salinity occurs simultaneously. Reduced water availability rather than
a specific harmful effect is typically blamed for growth inhibition brought on by high
Na and salinity concentrations [31].
Obsolete inorganic-based pesticides have accumulated over the last few decades
in practically every developing nation or emerging market. Given that many of the
products are quite old and usually lack documentation, it is challenging to determine
the precise number of obsolete pesticides. Insecticides containing organochlorines
were initially used to manage parasites. Persistent and non-biodegradable pesticides
have contaminated numerous elements of the soil, water, and air ecosystems. A
number of factors, such as gene mutation, altered population growth rates, and an
increase in population size in terms of generations, could be a consequence of the
pest’s adaptation to the new environment [30]. Heavy metals are poisonous to soil
microorganisms; they have an impact on a number of important microbial-mediated
soil processes in agriculture. Toxicity mostly manifests as inhibition of growth,

morphology, and activity of various microorganisms, including symbiotic N2 fixers.
Nutrient cycling in soil involves biochemical, chemical, and physico-chemical reac-
tions, with microorganisms primarily mediating biochemical processes. As the quan-
tity of heavy metals in the soil grew, it was discovered that the activities of soil
dehydrogenases, proteases, lipases, and esterases considerably decreased. Pb did not
significantly alter the activity of acid phosphatases, while only Ni and Cr consider-
ably reduced the activity of arylsulfatases [31]. Some of the most commonly reported
inorganic pollutants in water are listed below:
Ammonia: Industrial, agricultural, and food processing waste are its main sources
in water channels. Its overuse makes the body poisonous. The toxic gaseous content
is produced when mixed with bleach [43].
Arsenic: Glass, pigments, and textiles are a few examples of industrial waste sources
that contain As. As is found in materials like preservatives, paper, and metal adhe-
sives. In the past, it was utilized in feed additives, medicines, and pesticides. It is a
group-I carcinogen according to Organization for International Cancer Research [43].
If As becomes part of the body, it can cause gastronomical symptoms, melanosis,
hepatomegaly, and in severe cases death [19].
Barium: Barium has the same adverse effects as As. It can result in heart abnormal-
ities, tremors, weakness, shortness of breath, and paralysis if ingested in excess. It
comes from the scrap metal industry [43].
Chloride: Manure, sewage effluent, salt storage waste, industrial waste, and drilling
waste all contain chlorides. The widespread usage of water contaminated with
chloride can result in toxicity above the allowable level of 250 mg/L [43].
Chrome: Cr waste is released by the dye, paints, and tanning of leather in industries.
Total Cr in drinking water is permitted up to 0.1 mg/L. There are two oxidation
states of Cr+3 , among them Cr+6 is notorious for having cancer-causing properties
[43]. This also brews up diseases like genotoxic and alopecia [19].
Copper: Cu is released into water resources from the corrosion of water pipes. While
0.3 mg/L per day is required for metabolic processes, excessive ingestion can result
in stomach pain and intestinal conditions [43], liver and kidney disease, cancer, and
stomach irritation [19].
Mercury: Hg is an extremely hazardous inorganic element at ultra-trace concentra-
tions. It enters aquatic bodies because of a number of activities, such as small-scale
gold mining, the production of non-ferrous metals, and the burning of fossil fuels
[43]. Symptoms of Hg poisoning include kidney disease, muscle impairment, and
gum inflammation, and if left untreated can cause death [19].
Uranium: Uranium is discovered in water-polluting sources because of the extrac-
tion, processing, and disposal of radioactive waste. It might be detrimental to the
heart, brain, kidney, liver, and other organ systems [43].
Zinc: In addition to other items, Zn is frequently used in dry-cell batteries, paints,

dyes, plastics, wood preservatives, rubber, cosmetics, and coatings that resist corro-
sion. Rubber tires, waste incineration, metal manufacturing, and industrial coal
combustion are further sources of Zn-contaminated waste [43]. Zn poisoning often
causes dizziness [19].
Cadmium: Cd seeping in the water cycle also has adverse effects on human health.
If unfiltered water is consumed by humans, this can irritate the eyes which can lead
to retinal failure. It can also harmfully affect pregnant women and brew up birth
defects. Other than that, this can cause anemia and is a carcinogen [19].
Lead: Excess consumption of Pb can lead to problems related to blood filtration and
can cause kidney failure. This can also affect the motor nerves of the body leading
to a lack of response in muscles [19].
Silver: Ag is considered a precious metal and is used in many industries, but it is not
harmless. Indigestion of this element can cause argyria and argyrias, and if inhaled
can cause respiratory damage [19].
Tin: Sn can cause metabolic disruption and its excess amount is carcinogenic [19].
Iron: Fe lies at the heart of the industrial revolution and is used in almost every
household product. In places like steel mills, the concentration of Fe is too high and
causes unrequired disruption in health. Indigestion of Fe can cause swear kidney
damage and blood creatinine [19].
Nickel: Ni poisoning is caused when drinking water has an excess amount of Ni
than the limit introduced by WHO, i.e., 0.070 mg/mL. In this case, diseases like
anaphylaxis, lung cancer, loss of red blood cells, and nephrotoxic nature take place
[19].
Manganese: Mn is an important part of the chemical industry. Production of goods
leads to contamination of surface water. If the amount of this element exceeds
0.400 mg/mL, it can cause sleep dysfunction and is neurotoxic [19].
2 Conventional Remediation Techniques
There are several conventional methods to remove inorganic pollutants which can
be classified into biological, chemical, and physical processes, as shown in Fig. 2.
2.1 Biological Processes
The reaction between microorganisms and pollutants is carried out for the decontam-
ination of the environment. This cost-effective bioremediation extracts the pollutants
Fig. 2 Conventional methods to remove inorganic pollutants
with the help of microorganisms like algae, fungi, and bacteria using sunlight. But
the process is quite slow and unable to remove all the contaminants. Enzymes being
biological catalysts trigger biological oxidation in the aquatic environment. Neverthe-
less, bio-oxidation processes strongly depend on temperature and pH. In suspended
growth, contaminants surround the free-floating microorganisms, forming biolog-
ical flocs (larger size particles), providing low-concentration pollutant removal. But
it suffers from the disadvantage of microorganism removal with the variable water
flow. The attached growth is another resilient process in which bacteria are attached to
immersed media (called a biofilm) for high-concentration pollutants treatment. The
odor problem and inefficiency in cold weather conditions are causes of its limited use.
The reverse osmosis procedure provides contaminant removal under high pressure
using a semi-permeable membrane. However, it requires pre-treatment to avoid unde-
sired depositions on the membrane surface or inside the membrane pores, resulting
in a decrease in permeation flux and a reduced process efficiency [3, 23, 28].
2.2 Chemical Processes
In this process, certain chemicals are added to facilitate the separation of pollutants.
Precipitation is performed by the deliberate addition of appropriate flocculants to
remove dissolved pollutants. Nevertheless, it is specific to some pollutants, resulting
in sludge with a large quantity of toxic compounds. Advance oxidation processes
(AOPs) remove the inorganic pollutants by in situ formation of hydroxyl radicals via
redox reactions. The fast reaction kinetics is involved at room temperature and atmo-
spheric pressure with no footprints and sludge formation. Sometimes AOPs involve
ultraviolet exposure on a catalyst, leading to high operating costs and inefficient use
of reactive species. Ozonation, another AOP, removes inorganic contaminants by
generating highly reactive free radicals during the reaction of ozone with water. The
short life of ozone necessitates its on-site production, which raises the cost of treat-
ment. Fenton’s reagent, i.e., hydrogen peroxide and ferrous ion, provides the most
efficient oxidation of pollutants. However, it produces acidic conditions that must be
neutralized. Zeolites being aluminosilicate crystals with oxygen bridging provide the
removal of pollutants with high sorption capacity through ion exchange. Nonethe-
less, zeolites require suspended matter and turbidity-free fluid to avoid clogging
[32, 38, 41].
2.3 Physical Processes
The suspended or floating inorganic contaminants can be removed by settling

and skimming from the top of the surface. Coagulation is a process that converts
suspended, emulsified, unsettled, dissolved contaminants or slow-settling fine-sized
particles into larger sizes by the addition of a coagulant in an aqueous medium.
The larger size particles (flocs) are de-stabilized, weekly bound with water, and
can be removed through filtration. Post-coagulation results in sludge that requires
additional sedimentations for further filtration purposes. The ion-exchange process
provides water treatment without the formation of sludge; nevertheless, it is specific
to certain pollutants, resulting in salty water, chlorine, and/or bacterial contamina-
tion, as well as a high cost required for the replacement of the ion-exchanged resin
over time. Membrane filtration is another simple and efficient separation technology
used to remove contaminants with no secondary pollutant generation. However, its
use is limited by the cause of severe fouling and high engineering costs. In another
process, the solution with adsorbable solute is brought into contact with a porous
structure called adsorbent (may be natural or synthetic). The intermolecular forces
are responsible for the adsorption/deposition of impurities onto the adsorbent, which
is retained at the adsorbent surface; the accumulation of targeted particles onto the
adsorbent surface is known as adsorption. This is an effective method, employed for
a long time to remove pollutants by absorbing the contaminants [2, 5, 40].
3 3DG Architecture
Since the discovery of graphene, it has been a material of interest because it exhibits
sp2 hybridization. The sp2 hybridization of graphene is responsible for a honeycomb-
like structure, and to date, it is the thinnest material known to man. Many defects can
be created in graphene due to its pi-pi junction. Because of its fascinating properties,
graphene can be found in zero-dimensional quantum dots, one-dimensional carbon
nanotubes (CNT), two-dimensional graphene nanosheets, and 3D graphene-based
macro and microstructures. 3DG owing to its outstanding characteristics, as exhib-

ited in Fig. 3 is a very attractive material for researchers and is used in a variety
of applications. However, there is one problem with graphene, i.e., restacking of
layers during the performance that accompanies less yield as compared to theoretical
calculations [36].
The study of graphene architecture in 3D structures has been greatly investigated
after 2009. 3DG has a high specific area and does not restack itself when in use. If
the structure of graphene has a size of 10 nm or greater, it is referred to as 3DG archi-
tecture. The 3D architecture of graphene includes macroscopic hydrogels, graphene
forms, macroscopic graphene flowers, and porous graphene framework. The porosity
of the 3DG-based materials depends upon the bending, wrinkling, and carving of
graphene nanosheets. This induces a high specific area in the graphene architecture,
and the average surface area of graphene ranges from 500 m2 /g to 1000 m2 /g [36].
The properties of graphene and the 3D architecture of graphene are highly depen-
dent upon the synthesis process. The minor changes in the experimental conditions
give unique and diverse graphene structures. The perfect graphene is a semicon-
ductor with zero bandgaps. The bandgap is introduced to the material by producing
topological defects, edge defects, disordered graphene, the substitution of functional
groups, and doping of heterogeneous atoms [36].
Fig. 3 Characteristics of
3DG
4 3DG for Removal of Inorganic Pollutants
Graphene has been studied a lot for the elimination of inorganic pollutants because of
its efficient light absorption properties, superior charge transfer capabilities, thermal
conductivity, and multidimensional electron transport channels. 3DG architecture
exhibits high absorption, profound stability, high specific area, enhanced active
sites, availability of oxygen, carboxyl, and hydroxyl functional groups and acts
as a charge carrier mediator [48]. 3DG bestows excellent steadiness under acidic
and salty conditions. Other than that, 3DG architectures are also stable in organic
solvents such as dimethylformamide and cyclohexane [33]. 3DG architecture has
been employed and reported for inorganic pollutant removal through the adsorption
method, photocatalysis, and their synergistic outcomes [48].
4.1 3DG Adsorption Technology
The adsorption properties of graphene depend on the following factors.
4.1.1 Adsorption Sites
Graphene usually has three possible adsorption sites.

(a) Oxygen functional groups.
(b) π-electrons of carbon.
(c) Decorated nanoparticles.
Metal ions have a higher affinity toward oxygen atoms that are present in
the graphene structure. The adsorption is performed by two types of interactions
involving electrostatic interactions and coordination of oxygen and metal ions, espe-
cially in the carboxyl group. Heat treatment of the material can cause a decrease in
oxygen functional groups, but the number of carboxyl group increases [4]. 3DG archi-
tecture has delocalized π-electrons which can react with inorganic impurity obeying
the Lewis acid and base. In 3DG and metal ion interaction, 3DG act as Lewis’s
base while metal ion behaves like Lewis’s acid, and upon interaction, complexes are
formed [17]. Decorating the outer surface of 3DG architecture with different types
of nanoparticles such as MnO2 , TiO2 , and ZnO increases the number of active sites
of graphene, thus leading to enhanced adsorption [4].
4.1.2 Pore Structure
The adsorption capacity of graphene-based architecture depends upon the number

of available pores and pore size. Ultrapure graphene has an immense specific area
and zero porosity. To increase the porosity of 3DG, it is combined with other porous
materials [4].
3DG when synthesized with natural acids, self-assembled themselves through
π-π interaction. This material shows superhydrophobicity, high porosity, and low
density, which proved itself efficient for fast adsorption [4]. CNT-Aerogel shows an
adsorption rate of 230–451 μmol g−1 for Pb, which is better than pristine CNTs. The
extent of adsorption depends upon the particle diffusion which is the rate-controlling
step. The particle diffusion further depends upon the complexes in the medium and
the ion exchange [33].
4.1.3 pH of the Solution
The pH of the polluted solution is of great importance and majorly affects the adsorp-
tion properties of 3DG. The pH of the solution provides a surface charge to the
absorbing material and gives an ionization impact to the pollutants. In the case of
3DG, the effect of pH on adsorption is discussed by evaluating the pH at the point of
zero charges pHPZC . If pH < pHPZC , 3DG is positively charged and attract negatively
charged (anionic) inorganic pollutant. Conversely, for pH > pHPZC , cationic inorganic
pollutants are attracted by the negatively charged surface of 3DG architecture [4].
The ion-exchange method was much preferred for the adsorption of pollutants, but
in 2012 electrostatic adsorption was introduced. 3DG macrostructures display good
results in increasing pH values so that metal ions (cations) from the aqueous phase
attracts negatively charged 3DG macrostructures. The temperature changes and co-
existing ions can affect this phenomenon. Adsorption is an endothermic reaction so
having a high temperature helps, and with electrostatic attraction, the removal of
inorganic pollutants can be achieved with high efficiency [33].
4.1.4 Contact Time
The absorption properties of graphene are mainly influenced by the contact time
between adsorbent and adsorbate. In case of graphene, the adsorption occurs on its
planar surface, which then diffuses into the material through pores to get captured
by carbon atoms [45]. By keeping the adsorption properties of 3DG in view, the
pollutants are divided into anionic pollutants and cationic pollutants.
Anionic Pollutants:
Fluoride (F− ) is one of the main anionic inorganic species that pollutes the water.
The toxicity of heavy metal-polluted water greatly depends upon the valence state of
dissolved metal ions [48]. For example, As is found as arsenate (As-V) and arsenite
(As-III). Surface water contains As-V in large quantities, while As-III is present in
groundwater. Ar-III as a negative ion is H2 AsO3 − but As-V changes its anionic state
based on pH, i.e., H3 AsO4 at pH < 2.2, H2 AsO4 − at pH 2.2 to 6.98, HAsO4 2− at
pH 6.98 to 11.5, and AsO4 3− at pH > 11.5. Similarly, Cr originates in two oxidation
states, Cr(III) and Cr(VI). At lower values of pH, Cr(VI) is found as HCrO4 − but as
the increment in pH takes place, Cr changes its form to Cr2 O7 2− or CrO4 2− . For the
removal of anionic inorganic pollutants, low pH solutions are preferred because they
give graphene a positive charge and promote electrostatic attraction [4].
Cationic Pollutants:
Wastewater contains many cationic pollutants; the most common are Pb+2 , Hg+2 ,
Cd+2 , Cu+2 , Ni+2 , Co+2 , and Zn+2 . For the adsorption of these cationic pollutants,
three main adsorption mechanisms, electrostatic interactions, ion-exchange method,
and complex formations are used. 3DG enriched with oxygen-containing functional
groups have anchoring sites that secure the metal ions, either by electrostatic inter-
action, ion-exchange, or coordination method. A solution having a high pH also
facilitates the adsorption process. This is because higher pH poses a negative charge
on the surface of 3D graphene, which helps in attracting the metal ions, and adsorption
efficiency increases as the consequence [4].
3DG macrostructures having many oxygen functional groups perform adsorption
by π-cation interactions and form strong complexes with heavy metals, resulting in
the successful removal of pollutants. The absorption rate of 3DG macrostructures
is 434 mg/g for Cd2+ , 882 mg/g for Pb2+ ,1683 mg/g for Ni2+ , and 3820 mg/g for
Cu2+ . The adsorption ability of graphene-based hydrogel is 139.2 mg/g for Cr(VI),
373.8 mg/g of Pb, and 15.6 mg/g for γ-iron oxide [33]. Other methods of adsorption
of inorganic pollutants contain physio-sorption and hydrogen bonding interactions.
Chromates (Cr2 O7 )−2 adsorption by graphene hydrogel has been reported through
physiochemical adsorption and hydrogen bonding, at the rate of 140 mg/g [33].
4.2 3DG with Synergistic Effects of Adsorption

and Photocatalysis
The high porosity of the graphene material, the catalytic functional groups that are
present in the 3DG architecture, the presence of micropores and mesopores that
increase surface area, and the availability of active sites all contribute toward the
increased synergistic effects of 3DG when combined with different photocatalysts.
On the other hand, 3DG shows fantastic recyclability and can be used for several
rounds. Owing to such fascinating properties, 3DG macrostructures have been used
in multiple systems for the removal of Pb, Hg, Cd, cobalt (Co), and As [33]. 3DG
architecture and 3DG-based microstructures provide a good number of binding sites
which are favorable for the fabrication of heterojunctions. During the fabrication
of different types of heterojunctions, the material can stick with graphene due to
electrostatic interactions, hydrogen bonding, π -π interactions, and chelation [12].
3DG and its heterojunctions with different materials have been reported for the
removal of inorganic pollutants via the adsorption method, photocatalysis, or the
synergistic effect of both, as displayed in Table 2.
Table 2 3DG structures for inorganic pollutant removal

Adsorbate Adsorbent Adsorption Method References
Rate (mg/g)
Graphene Aerogel (GA) Pb(II) 80 Adsorption [14]
GA Cu(II) 68.2 Adsorption [29]
GA Cd(II) 149.25 Adsorption [37]
GA U(VI) 238.67 Adsorption [49]
3DG macroscopic gel modified with As(III) 172 Adsorption [13]
polydopamine and Fe3 O4 As(V) 217
nanoparticles
3DG Foam/MnO2 Sr(II) 47 Adsorption [20]
3DGA /TiO2 U(VI) 441 Adsorption [47]
Graphene Foam As(V) 177 Adsorption [6]
Pb(II) 399 Adsorption
Cyclodextrin functionalized 3D Cr(VI) 107 Adsorption [42]
Graphene (CDGF)
Tetraethylenepentamine modified Pb(II) 305 Adsorption [15]
Graphene Foam (TEPA-GF)
N,N,N’,N’-Tetraoctyldiglycolamide Th(IV) 67 Adsorption [7]
impregnated GA ( GA-TODGA)
GA /Fe3 O4 As(V) 40.048 Adsorption [46]
Graphene Sb(III) 7.463 Adsorption [24]
Amine functionalized GA Cr(VI) 170 Adsorption [35]
GA Cr(VI) Almost 100% Photocatalysis [9]
removal in 5 h
g-C3 N5 /reduced Graphene Oxide U(VI) 94.9% Photocatalysis [44]
Aerogel removal
3D RGO/TiO2 Aerogel U(VI) 99% removal Photocatalysis [10]
within
140–270 min
under visible
light
3D MXene-derived U(VI) 95.7% Photocatalysis [8]
TiO2 (M)@reduced Graphene Oxide removal
Aerogel within 60 min
under visible
light
g-C3 N4 integrated Cellulose/ Cr(VI) 98% removal Photocatalysis [16]
Graphene Oxide Foams within 3 h
under visible
light
(continued)
Table 2 (continued)
Adsorbate Adsorbent Adsorption Method References
Rate (mg/g)
TiO2 -Graphene Hydrogel Cr(VI) 100% removal Synergy of [25]
in 30 min adsorption and
under UV photocatalysis
irradiation
TiO2 /Znx Cd1-x S/ GA Cr(VI) 100% removal Synergy of [26]
in 30 min adsorption and
under visible photocatalysis
irradiation
Bi2 S3 /BiVO4 / GA Cr(VI) 100% removal Synergy of [27]
Bisphenol after adsorption and
A adsorption for photocatalysis
40 min and
photocatalysis
for 120 min
under visible
light
g-C3 N4 /Graphene Hydrogel Cr(VI) 80% Synergy of [39]
absorption in adsorption and
30 min and photocatalysis
100% removal
in 120 min
under visible
light
The presence of micropores in 3DG offers accessibility to the adsorption of pollu-

tants. The increased surface area and many active sites provide the profound photo-
catalytic ability to 3DG macrostructures. Adsorption and photocatalysis can work
together to remove inorganic pollutants more effectively. 3DG macrostructures and
microstructures are used with different photocatalysts to take advantage of their
synergistic effects. Based on this aspect, the removal of many metals such as anti-
mony (Sb) and Cr(VI) has been reported [48]. 3DG has also been employed with
different materials by fabricating binary and ternary heterojunctions to improve the
removal efficiency because of synergism. The construction of heterojunction is also
advantageous for graphene as it reduces the agglomeration of the particles, provides
the material with a hydrophilic nature, and reduces the number of oxygen groups
[12].
Li et al. [25] reported the 3D TiO2 /GA structure exhibiting 100% Cr(VI) removal
from aqueous solution within 30 min upon UV light exposure, as illustrated in Fig. 4b.
π–π interaction of graphene caused enhanced adsorption while TiO2 nanospheres
facilitated the charge formation, transport, and separation. The removal efficacy of
Cr(VI) is attributed to synergistic performance. Liang et al. [26] combined TiO2 with
Znx Cd1-x S and GA to take the advantage of the synergistic effect of adsorption and
photocatalysis to remove Cr(VI) from an aqueous environment. The graphene acted
as a mediator to accelerate the electron transfer, Cr(VI) adsorbent and 100% removal
of Cr(VI) occurred in 30 min of visible light irradiation, as shown in Fig. 4e. The
toxic Cr(VI) removal was also tested by D. Hou et al. [16] using g-C3 N4 integrated
cellulose/graphene oxide foams as photocatalysts. The carboxylic group of cellulose/
graphene oxide foams and amino group present in g-C3 N4 made a strong contact at the
interface and enhanced conductivity. 98% of Cr(VI) removal was demonstrated with
excellent recyclability, as displayed in Fig. 4i. Liang et al. [27] constructed Z-scheme
heterojunction Bi2 S3 /BiVO4 /GA to study Cr(VI) removal efficacy. Graphene signif-
icantly enhanced the removal efficiency by facilitating electron transport. 40 min of
adsorption and 120 min of photocatalysis collectively provided the 100% removal
of Cr(VI) from the aqueous environment, exhibited in Fig. 4k. X. Wang et al. [39]
carried out g-C3 N4 /graphene hydrogel to explore the synergistic effect of adsorption
and photocatalysis on Cr(VI) removal. The graphene sheets provided fast surface
adsorption of Cr(VI) and promoted charge transfer. As a consequence, 100% Cr(VI)
degradation was obtained in 120 min of visible light irradiation, which can be seen
in Fig. 4n.
5 Conclusion
Different materials and methods in the past have been used to eliminate toxic inor-
ganic pollutants that arise from various sources and pose the danger to living entities.
But the advantageous traits of 3DG structures have attracted a lot of interest in recent
years. 3DG owing to its outstanding characteristics such as large specific surface
area, low density, increased porosity, small aggregation, more active sites, and high
light adsorption capability has been widely investigated for the removal of inorganic
pollutants. The mesoporous structure of 3DG favors the adsorption of inorganic
pollutants while photocatalytic reaction degrades the harmful pollutants. The syner-
gistic effect of adsorption and photocatalytic reaction provides efficient removal
as compared to conventional methods. The excellent charge separation and migra-
tion ability of graphene enhance the rate of photocatalytic reaction. Furthermore,
3DG and its composites exhibit exceptional recyclability, allowing its repeated use.
This chapter covers the current development made in removing hazardous inorganic
pollutants from the environment.
Fig. 4 a Transmission electron microscopy (TEM) micrograph of TiO2 -rGH highlighting enhanced
porosity, b Cr(VI) removal by 3D TiO2 -rGH in 30 min, c TiO2 -rGH displaying exceptional cyclic
stability over the course of 5 cycles. Adapted with permission [25], Copyright (2016), Elsevier.
d SEM image of TiO2 -Znx Cd1-x S graphene hydrogel heterojunction. e TiO2 -Znx Cd1-x S graphene
hydrogel shows enhanced results for the removal of Cr(VI) due to synergism. f Cyclic stability
of TiO2 -Znx Cd1-x S graphene hydrogel. Adapted with permission [26], Copyright (2023), Elsevier.
g SEM micrograph of CNF foam. (h) Cr(VI) removal using CG-3 photocatalyst. i Cyclic stability
test of CG-3 and g-C3 N4. Adapted with permission [16], Copyright (2022), Elsevier. j SEM image of
Bi2 S3 -BiVO4 GA. k Cr(VI) removal tested for Bi2 S3 , BiVO4 , GA, Bi2 S3 /GA and BiVO4 /GA and
Bi2 S3 -BiVO4 . l Cyclic stability test of Bi2 S3 -BiVO4 -GA. Adapted with permission [27], Copyright
(2020), Elsevier. m SEM micrograph of g-C3 N4 /rGH. n Corresponding Cr(VI) removal ability and
o cyclic stability. Adapted with permission [39], Copyright (2017), Elsevier
References
1. Akram, R., Turan, V., Hammad, H., Ahmad, S., Hussain, S., Hasnain, A., Maqbool, M.,
Rehmani, M., Rasool, A., Masood, N., Mahmood, F., Mubeen, M., Sultana, S., Fahad, S.,
Amanet, K., Saleem, M., Abbas, Y., Akhtar, H., Hussain, S., Waseem, F., Murtaza, R., Amin,
A., Zahoor, S., Sami ul Din, M., Nasim, W.: Fate of organic and inorganic pollutants in paddy
soils, 197–214 (2018)
2. Ambaye, T.G., Vaccari, M., van Hullebusch, E.D., Amrane, A., Rtimi, S.: Mechanisms and
adsorption capacities of biochar for the removal of organic and inorganic pollutants from
industrial wastewater. Int. J. Environ. Sci. Technol. 18:10, 18, 10, 3273–3294 (2020)
3. Anna, I., Bartkowska, I., Biedka, P.: Treatment of young and stabilized landfill leachate
by integrated sequencing batch reactor (SBR) and reverse osmosis (RO) process. Environ.
Nanotechnol. Monitoring Manag. 16, 100502 (2021)
4. Cao, Y., Li, X.: Adsorption of graphene for the removal of inorganic pollutants in water
purification: a review. Adsorption 20(5–6), 713–727 (2014)
5. Chadha, U., Selvaraj, S.K., Vishak Thanu, S., Cholapadath, V., Abraham, A.M., Zaiyan, M.M.,
Manoharan, M., Paramsivam, V.: A review of the function of using carbon nanomaterials
in membrane filtration for contaminant removal from wastewater. Mater. Res. Express 9(1),
012003 (2022)
6. Chen, G., Liu, Y., Liu, F., Zhang, X.: Fabrication of three-dimensional graphene foam with high
electrical conductivity and large adsorption capability. Appl. Surf. Sci. 311, 808–815 (2014)
7. Chen, M., Li, Z., Geng, Y., Zhao, H., He, S., Li, Q., Zhang, L.: Adsorption behavior of thorium
on N, N, N' , N' -tetraoctyldiglycolamide (TODGA) impregnated graphene aerogel. Talanta 181,
311–317 (2018)
8. Chen, T., He, P., Liu, T., Zhou, L., Li, M., Yu, K., Meng, Q., Lian, J., Zhu, W.: MXene-derived 3D
defect-Rich TiO2 @reduced graphene oxide aerogel with ultrafast carrier separation for photo-
assisted uranium extraction: a combined batch, X-ray absorption spectroscopy, and density
functional theory calculations. Inorg. Chem. 61(32), 12759–12771 (2022)
9. Dong, S., Xia, L., Guo, T., Zhang, F., Cui, L., Su, X., Wang, D., Guo, W., Sun, J.: Controlled
synthesis of flexible graphene aerogels macroscopic monolith as versatile agents for wastewater
treatment. Appl. Surf. Sci. 445, 30–38 (2018)
10. Dong, Z., Zhang, Z., Li, Z., Feng, Y., Dong, W., Wang, T., Cheng, Z., Wang, Y., Dai, Y., Cao,
X., Liu, Y., Liu, Y.: 3D structure aerogels constructed by reduced graphene oxide and hollow
TiO2 spheres for efficient visible-light-driven photoreduction of U( vi ) in air-equilibrated
wastewater. Environ. Sci. Nano 8(8), 2372–2385 (2021)
11. Fuller, R., Landrigan, P.J., Balakrishnan, K., Bathan, G., Bose-O’Reilly, S., Brauer, M., Cara-
vanos, J., Chiles, T., Cohen, A., Corra, L., Cropper, M., Ferraro, G., Hanna, J., Hanrahan, D.
et al.: Pollution and health: a progress update. Lancet Planetary Health 6(6), e535–e547 (2022)
12. G.G., Sathish, A, Kumar, P.S., Nithya, K., Rangasamy, G.: A review on current progress
of graphene-based ternary nanocomposites in the removal of anionic and cationic inorganic
pollutants. Chemosphere 309, 136617 (2022)
13. Guo, L., Ye, P., Wang, J., Fu, F., Wu, Z.: Three-dimensional Fe3 O4 -graphene macroscopic
composites for arsenic and arsenate removal. J. Hazard. Mater. 298, 28–35 (2015)
14. Han, Z., Tang, Z., Shen, S., Zhao, B., Zheng, G., Yang, J.: Strengthening of graphene aerogels
with tunable density and high adsorption capacity towards Pb2+. Sci. Rep. 4(1), 5025 (2014)
15. Han, Z., Tang, Z., Sun, Y., Yang, J., Zhi, L.: Controllable synthesis of tetraethylenepentamine
modified graphene foam (TEPA-GF) for the removal of lead ions. Sci. Rep. 5(1), 16730 (2015)
16. Hao, D., Liu, J., Sun, H., Fu, B., Liu, J., Zhou, J.: Integration of g-C3N4 into cellulose/graphene
oxide foams for efficient photocatalytic Cr(VI) reduction. J. Phys. Chem. Solids 169, 110813
(2022)
17. Hao, L., Song, H., Zhang, L., Wan, X., Tang, Y., Lv, Y.: SiO2/graphene composite for highly
selective adsorption of Pb(II) ion. J. Colloid Interface Sci. 369(1), 381–387 (2012)
18. Hayet, S., Sujan, K.M., Mustari, A., Miah, M.A.: Hemato-biochemical profile of turkey birds
selected from Sherpur district of Bangladesh. Int. J. Adv. Res. Biol. Sci 8(6), 1–5 (2021)
Prot. 116, 262–286 (2018)
20. Kasap, S., Nostar, E., Öztürk, İ: Investigation of MnO2 nanoparticles-anchored 3D-graphene
foam composites (3DGF-MnO2) as an adsorbent for strontium using the central composite
design (CCD) method. New J. Chem. 43(7), 2981–2989 (2019)
21. Kong, Q., Shi, X., Ma, W., Zhang, F., Yu, T., Zhao, F., Zhao, D., Wei, C.: Strategies to improve
the adsorption properties of graphene-based adsorbent towards heavy metal ions and their
compound pollutants: A review. J. Hazard. Mater. 415, 125690 (2021)
22. Kumar, M., Borah, P., Devi, P.: Priority and emerging pollutants in water. Inorganic Pollut.
Water, 33–49 (2020)
23. Lee, J., Ahn, W.Y., Lee, C.H.: Comparison of the filtration characteristics between attached
and suspended growth microorganisms in submerged membrane bioreactor. Water Res. 35(10),
2435–2445 (2001)
24. Leng, Y., Guo, W., Su, S., Yi, C., Xing, L.: Removal of antimony(III) from aqueous solution
by graphene as an adsorbent. Chem. Eng. J. 211–212, 406–411 (2012)
25. Li, Y., Cui, W., Liu, L., Zong, R., Yao, W., Liang, Y., Zhu, Y.: Removal of Cr(VI) by 3D
TiO2 -graphene hydrogel via adsorption enriched with photocatalytic reduction. Appl. Catal. B
199, 412–423 (2016)
26. Liang, Q., Chen, X., Liu, R., Xu, K., Luo, H.: Efficient removal of Cr(VI) by a 3D Z-scheme
TiO2-Zn Cd1-S graphene aerogel via synergy of adsorption and photocatalysis under visible
light. J. Environ. Sci. 124, 360–370 (2023)
27. Liang, Q., Ploychompoo, S., Chen, J., Zhou, T., Luo, H.: Simultaneous Cr(VI) reduction and
bisphenol A degradation by a 3D Z-scheme Bi2S3-BiVO4 graphene aerogel under visible light.
Chem. Eng. J. 384, 123256 (2020)
28. Mohammadi, S.A., Najafi, H., Zolgharnian, S., Sharifian, S., Asasian-Kolur, N.: Biological
oxidation methods for the removal of organic and inorganic contaminants from wastewater: a
comprehensive review. Sci. Total Environ. 843, 157026 (2022)
29. Pan, M., Shan, C., Zhang, X., Zhang, Y., Zhu, C., Gao, G., Pan, B.: Environmentally friendly
in situ regeneration of graphene aerogel as a model conductive adsorbent. Environ. Sci. Technol.
52(2), 739–746 (2018)
30. Radwan, E.H., Saber, M.A.K., Saber, M.E.K., Fahmy, G.H.: The impact of some organic and
inorganic pollutants on fresh water (Rashid, River Nile). Egypt. J. Adv. Biol. 10(2), 2133–2145
(2017)
31. Saha, J.K., Selladurai, R., Coumar, M.V., Dotaniya, M.L., Kundu, S., Patra, A.K.: Major
inorganic pollutants affecting soil and crop quality, 75–104 (2017)
32. Saleh, I.A., Zouari, N., Al-, M.A.: Removal of pesticides from water and wastewater: chemical,
physical and biological treatment approaches. Environ. Technol. Innov. 19, 101026 (2020)
33. Shen, Y., Fang, Q., Chen, B.: Environmental applications of three-dimensional graphene-based
macrostructures: adsorption, transformation, and detection. Environ. Sci. Technol. 49(1), 67–84
(2015)
34. Sidana, N., Kaur, H., Devi, P.: Organic linkers for colorimetric detection of inorganic water
pollutants. Inorganic Pollut. Water, 135–152 (2020)
35. Singh, D.K., Kumar, V., Mohan, S., Hasan, S.H.: Polylysine functionalized graphene aerogel
for the enhanced removal of Cr(VI) through adsorption: kinetic, isotherm, and thermodynamic
modeling of the process. J. Chem. Eng. Data 62(5), 1732–1742 (2017)
control. Chem. Rev. 120(18), 10336–10453 (2020)
37. Trinh, T.T.P.N.X., Quang, D.T., Tu, T.H., Dat, N.M., Linh, V.N.P., van Cuong, L., Nghia, L.T.T.,
Loan, T.T., Hang, P.T., Phuong, N.T.L., Phong, M.T., Nam, H.M., Hieu, N.H.: Fabrication,
characterization, and adsorption capacity for cadmium ions of graphene aerogels. Synthetic
Metals 247, 116–123 (2019)
38. Vishnu, D., Dhandapani, B., Kannappan Panchamoorthy, G., Vo, D.V.N., Ramakrishnan, S.R.:
Comparison of surface-engineered superparamagnetic nanosorbents with low-cost adsorbents
of cellulose, zeolites and biochar for the removal of organic and inorganic pollutants: a review.
Environ. Chem. Lett. 19(4), 3181–3208 (2021)
39. Wang, X., Liang, Y., An, W., Hu, J., Zhu, Y., Cui, W.: Removal of chromium (VI) by a self-
regenerating and metal free g-C3N4/graphene hydrogel system via the synergy of adsorption
and photo-catalysis under visible light. Appl. Catal. B 219, 53–62 (2017)
40. Wang, X., Xu, J., Xu, M., Zhou, B., Liang, J., Zhou, L.: High-efficient removal of arsenite by
coagulation with titanium xerogel coagulant. Sep. Purif. Technol. 258, 118047 (2021)
41. Wang, Y., Kuntke, P., Saakes, M., van der Weijden, R.D., Buisman, C.J.N., Lei, Y.: Electro-
chemically mediated precipitation of phosphate minerals for phosphorus removal and recovery:
progress and perspective. Water Res. 209, 117891 (2022)
42. Wang, Z., Lin, F., Huang, L., Chang, Z., Yang, B., Liu, S., Zheng, M., Lu, Y., Chen, J.:
Cyclodextrin functionalized 3D-graphene for the removal of Cr(VI) with the easy and rapid
separation strategy. Environ. Pollut., 254 (2019)
43. Wasewar, K.L., Singh, S., Kansal, S.K.: Process intensification of treatment of inorganic water
pollutants. Inorganic Pollut. Water, 245–271 (2020)
44. Wu, L., Yang, X., Chen, T., Li, Y., Meng, Q., Zhu, L., Zhu, W., He, R., Duan, T.: Three-
dimensional C3N5/RGO aerogels with enhanced visible-light response and electron-hole
separation efficiency for photocatalytic uranium reduction. Chem. Eng. J. 427, 131773 (2022)
45. Yagub, M.T., Sen, T.K., Afroze, S., Ang, H.M.: Dye and its removal from aqueous solution by
adsorption: a review. Adv. Coll. Interface. Sci. 209, 172–184 (2014)
46. Ye, Y., Yin, D., Wang, B., Zhang, Q.: Synthesis of three-dimensional Fe3O4/graphene aerogels
for the removal of arsenic ions from water. J. Nanomater. 2015, 1–6 (2015)
47. Yu, S., Wei, D., Shi, L., Ai, Y., Zhang, P., Wang, X.: Three-dimensional graphene/titanium
dioxide composite for enhanced U(VI) capture: Insights from batch experiments, XPS
spectroscopy and DFT calculation. Environ. Pollut. 251, 975–983 (2019)
48. Zhang, F., Li, Y.H., Li, J.Y., Tang, Z.R., Xu, Y.J.: 3D graphene-based gel photocatalysts for
environmental pollutants degradation. Environ. Pollut. 253, 365–376 (2019)
49. Zhao, D., Wang, Y., Zhao, S., Wakeel, M., Wang, Z., Shaikh, R.S., Hayat, T., Chen, C.: A simple
method for preparing ultra-light graphene aerogel for rapid removal of U(VI) from aqueous
solution. Environ. Pollut. 251, 547–554 (2019)
3D Graphene Structures for the Removal
of Pharmaceutical Residues
Wan Ting Tee, Nicholas Yung Li Loh, Billie Yan Zhang Hiew,
and Lai Yee Lee
Abstract Graphene nanomaterials have great potential applications in treating

wastewater containing pharmaceutical residues due to their extraordinary physic-
ochemical and adsorption properties. Despite being present in minute amounts in
the aquatic environment, pharmaceutical residues can cause various health and envi-
ronmental risks owing to their non-biodegradability, bioaccumulative and toxicity
features. Hence, it is extremely vital to control the concentration of pharmaceutical
residues in water resources. Notably, three-dimensional (3D) graphene structures
have emerged as innovative adsorbents with fortified adsorption properties such
as super-large theoretical surface area, abundant functional groups, and the capa-
bility to preserve the intrinsic properties of nanomaterials at a macroscopic level.
In this chapter, the classification and main sources of pharmaceutical pollution are
discussed. Thereafter, the principles and advantages of adsorption for pharmaceu-
tical removal are covered. This chapter further evaluates the performance of primary
3D graphene structures, namely graphene aerogel, hydrogel, and beads, in relation
to pharmaceutical adsorption. The synthesis methods and adsorption mechanisms of
pharmaceutical residues by 3D graphene structures are assayed. Lastly, the challenges
and outlook of 3D graphene structures in pharmaceutical adsorption are presented.
Keywords Graphene · 3D graphene structures · Pharmaceutical residues ·

Adsorption · Wastewater treatment
W. T. Tee · N. Y. L. Loh · L. Y. Lee (B)

Department of Chemical and Environmental Engineering, University of Nottingham Malaysia,
Jalan Broga, 43500 Semenyih, Selangor, Malaysia
e-mail: Lai-Yee.Lee@nottingham.edu.my
N. Y. L. Loh
Department of Chemical and Environmental Engineering, University of Nottingham Ningbo
China, Ningbo 315100, China
B. Y. Z. Hiew
School of Engineering and Physical Sciences, Heriot-Watt University Malaysia, 62200 Putrajaya,
Wilayah Persekutuan Putrajaya, Malaysia
https://doi.org/10.1007/978-3-031-36249-1_11
190 W. T. Tee et al.
1 Introduction
The detection of pharmaceutical residues in the aquatic environment is an emerging

environmental issue owing to their high toxicity and detrimental effects on all
lifeforms and the environment. Pharmaceuticals can be considered as chemical
compounds produced to cure and control diseases to achieve desired therapeutic
effects via biological activity. The market sales of global pharmaceutical indus-
tries reached USD 1.27 trillion in 2020, signifying an escalating demand for phar-
maceutical products [1]. Nonetheless, the growing production and consumption of
medicinal products are accompanied by the release of such compounds into the
environment. In general, pharmaceutical residues are micropollutants as they are
detected in very low concentrations, ranging from ng/dm3 to μg/dm3 [1]. Further-
more, the presence of pharmaceutical residues in the water body can lead to adverse
effects, including anti-microbial resistance, endocrine disruption, and toxic metabo-
lites discharge [2]. As such, it is crucial that these drug components are removed
from the affected water effluent prior to release into the environment.
Conventional remediation technologies which include coagulation, flocculation,
and biological treatment are ineffective in removing pharmaceutical-based pollutants
and are also associated with other issues such as non-selectivity, low performance
at trace concentrations, and generation of undesired by-products upon treatment [3].
Among the available technologies, adsorption offers a promising treatment solution
for pharmaceutical residues. The performance of adsorption is highly influenced by
the selection of adsorbing material. Ideally, adsorbents with high selectivity, effi-
ciency, and renewability are favourable for use in wastewater treatment [4]. Despite
their wide availability, commercial adsorbents such as activated carbon and zeolites
are ineffective against pharmaceutical residues. They also pose potential sustain-
ability problems, hindering their applications in pharmaceuticals removal. Hence,
there is an urgent need to devise new and effective adsorbents capable of fully
removing the pharmaceutical pollutants.
Recently, three-dimensional (3D) graphene structures have surfaced as the next
generation of adsorbing materials for wastewater treatment. Notably, the unique
characteristics of 3D graphene such as ultralight density, ease of functionaliza-
tion, and high porosity have supported their role in remediating polluted aqueous
systems. The porous framework of 3D graphene is one of the prominent features
that can promote high selective affinity towards a wide range of pharmaceutical
pollutants [5]. In comparison to nanometer-scale adsorbing particles, 3D graphene
adsorbents offer merits in terms of reusability and regenerability, increasing their
feasibility in industrial wastewater treatment [6]. From the current literature, various
3D graphene configurations with relatively high adsorption performance for different
pharmaceutical residues have been constructed. For instance, a three-dimensional
manganese dioxide-engrafted reduced graphene oxide (3D MnO2 /rGO) hybrid
aerogel was reported to adsorb a higher amount of acetaminophen (252.87 mg/g)
[7] as compared to spent tea leaves activated carbon (59.2 mg/g) [8]. In a sepa-
rate study, Tee et al. [9] investigated the adsorptive removal of amitriptyline using
3D Graphene Structures for the Removal of Pharmaceutical Residues 191
a 3D boron-doped graphene oxide (3D-BGO) aerogel. The adsorbent achieved an

amitriptyline adsorption capacity of 737.4 mg/g which was at least 4 times higher
than commercial granular activated carbon [9]. A relatively high removal efficiency
(89.31%) was achieved at 50 ppm amitriptyline solution concentration and 30 °C
using 10 mg of the adsorbent, while the adsorption process reached equilibrium
within 60 min across solution concentrations ranging from 10 to 300 ppm. These
results suggested that the 3D-BGO aerogel was a superior adsorbent for amitripty-
line removal [9]. The findings indicated the high potential utilization of 3D graphene
structures for pharmaceuticals adsorption.
This chapter focuses on the application of 3D graphene structures for eliminating
pharmaceutical residues from aqueous media. The background of pharmaceuticals
and types of 3D graphene structures along with their respective adsorption perfor-
mance are discussed. The challenges and possible improvements of 3D graphene
structures for enhanced removal of pharmaceuticals are also addressed.
2 Pharmaceutical Pollution
More than 10,000 different types of pharmaceutical products have been produced for
human and veterinary medications [10], resulting in the detection of numerous phar-
maceutical residues in the aquatic ecology. It is essential to understand the properties
of pharmaceuticals in order to devise appropriate treatment strategies for minimizing
their adverse effects on the environment.
3 Classification and Harmful Effects of Pharmaceuticals
Generally, pharmaceuticals can be classified based on their therapeutic effects.

Table 1 summarizes the key classes of medicinal products with their corresponding
therapeutic effects and examples.
Despite having disease healing and control effects, the active ingredients of phar-
maceuticals usually cannot be metabolized completely by consumers and the metabo-
lite residuals can reach the environment, causing toxicity accumulation [11]. It was
reported that the concentrations of pharmaceuticals exceeding 1–500 ng/L could
harm the aquatic organisms [12]. Moreover, a prolong exposure to the medicinal
pollutants can lead to different negative responses, highly influenced by the species’
vulnerability and pharmaceutical type [13]. For instance, diclofenac drug caused
mortality in pigeon and chicken at dosages of 0.25 and 2.5 mg/kg, respectively [14].
A post-mortem study detected the buildup of triclosan, triclocarban, and other drug
residues in human tissues [15]. Hence, these revelations indicated that the uncon-
trolled discharge of medicinal products into the water body can impose significant
impacts on the ecological systems.
Table 1 Classifications and examples of pharmaceuticals

Pharmaceutical class Therapeutic effect Examples
Antibiotics Eliminate bacteria Sulfamethoxazole
Ofloxacin
Tetracycline
Ciprofloxacin
Trimethoprim
Antifungal Treat and prevent fungal infections Triclosan
Anticonvulsants Mood stabilizer, anti-seizure, and treat mood Carbamazepine
disorder Primidone
Mephobarbital
Antidepressants Treat major depression-related symptoms and Diazepam
relieve long term neuropathic pain Doxepin
Amitriptyline
Beta blockers Hormone/adrenaline/neurotransmitter Acebutolol
inhibitor Atenolol
Satolol
Hormones Regulate the metabolism rate, control sexual Estrone
development, and maintain homeostasis Estradiol
Testosterone
Lipid regulators Regulate triglycerides and cholesterol in Clorfibric acid
blood stream Gemfibrozil
Non-steroidal Pain reliever and reduce inflammation Diclofenac
anti-inflammatory drugs Ibuprofen
Acetaminophen
Naproxen
4 Occurrence and Sources of Pharmaceuticals
Terrestrial and aquatic systems are the major sinks for pharmaceutical residues in
the environment. The occurrence and major sources of pharmaceutical residue are
illustrated in Fig. 1.
Both commercial (pharmaceutical manufacturers and wastewater treatment
plants) and domestic (organisms’ excreta and landfill) activities are the primary
contributors of pharmaceutical residues in the environment. The effluent and solid
disposals from clinical facilities such as hospitals and veterinary centers also
contribute significantly to pharmaceutical water pollution [17]. Typically, the microp-
ollutants enter the surface water through direct effluent discharge from identified
sources. Thereafter, the pharmaceuticals infiltrate to the groundwater, eventually
ending up in the wastewater treatment plants. Due to low efficiency of current treat-
ment systems, the treatment effluent contains a variety of pharmaceutical residues.
Some of the pharmaceutical residues may undergo rapid metabolism upon interac-
tion with the biological treatment system and the unmetabolized active ingredients
may cause toxicity accumulation [16]. In view of their harmful effects, it is desired
Fig. 1 Potential sources and pathway of pharmaceutical residues in the environment. Adapted with
permission [16]. Copyright (2023) Elsevier
to develop alternative treatment systems to regulate the pharmaceutical levels in the

environment.
5 Adsorption of Pharmaceuticals
Table 2 compiles the principal terminologies associated with adsorption technology.

Generally, the term ‘adsorption’ is the enrichment of one or more components in the
region between two bulk phases (interfacial layer or adsorption space). In the context
of aqueous pharmaceutical adsorption, one of these phases is a solid while the other
is a liquid.
Adsorption can be utilized for treating various pharmaceutical pollutants, whereby
the pharmaceutical molecules or ions are removed from the aqueous media by
attaching onto the solid surface of the adsorbent. Owing to its relatively low operating
cost and simple operation, adsorption is a widely acceptable technique for treating
pharmaceutical contaminated water [19]. Another highlight of this approach is the
Table 2 Terminology used in adsorption [18]

Term Definition
Adsorption Enrichment of one or more components in the vicinity of an interface
Adsorbate Substance in the adsorbed state
Adsorptive Adsorbable substance in fluid phase
Adsorbent Solid material on which adsorption occurs
Chemisorption Adsorption involving chemical bonding
Physisorption Adsorption without chemical bonding
Monolayer Either chemisorbed amount required to occupy all surface sites or physisorbed
capacity amount required to cover the surface
Surface Ratio of amount of adsorbed substance to monolayer capacity
coverage
ability to perform regeneration on the adsorbent, specifically through manipulation

of the aqueous phase conditions (temperature, pH, and concentration), which can
prolong its lifespan for extended adsorption–desorption operations as well as reduce
operating cost [20].
A vital adsorption parameter, namely the equilibrium adsorption capacity (qe ),
is applied for gauging the adsorption efficiency or adsorbent performance. It is
represented by Eq. (1):
(Co − Ce )V
qe = (1)
m
where C o is the initial adsorbate concentration (mg/L), C e is the equilibrium adsor-
bate concentration (mg/L), V is the volume of solution (L), and m is the mass of
adsorbent (g). Typically, an adsorbent should possess features such as high adsorp-
tion capacity, adaptability to remove a wide range of pollutants, and high reusability,
as well as low production cost [21]. The effectiveness of the adsorption process
is influenced by various parameters such as adsorbent surface area, porosity, and
surface chemistry [1]. Apart from that, the adsorbent should also be able to adsorb
the pharmaceuticals rapidly and can be regenerated completely for reutilization [22].
Pharmaceutical adsorption can be influenced by various adsorption mechanisms.
As depicted in Fig. 2, interactive mechanisms such as hydrophobic, hydrogen
bonding, electron donor-acceptance, electrostatic, covalent bonding, and oxidative
reactions are the dominant adsorption mechanisms for pharmaceuticals removal [2].
As indicated by the various literature, the characteristics of adsorbent and adsorbate
could initiate different adsorption mechanisms to facilitate the sequestration of phar-
maceuticals [7, 23]. Hence, a suitably designed adsorbent is crucial for the successful
removal of pharmaceuticals from wastewater.
3D Graphene Structures for the Removal of Pharmaceutical Residues
Fig. 2 An overview of adsorption mechanisms for pharmaceutical residues. Adapted with permission [2]. Copyright (2022) Elsevier
195
6 3D Graphene Structures for Pharmaceutical Adsorption
The assembly of nano-sized two-dimensional (2D) graphene into 3D graphene struc-

tures has been extensively explored in recent years. Synthesis of 3D graphene
structures can be categorized into two main routes, namely direct synthesis and
solution-based synthesis [24]. The construction of 3D graphene structures via inter-
connecting graphene nano-layers can form a highly porous network, favouring the
mass transfer of pharmaceuticals in the water body. Several configurations of 3D
graphene have been devised for removing the pharmaceuticals, and these include
graphene aerogel [20], hydrogel [25], beads [26], and fibre [27]. Each configuration
is further elaborated in the following section, together with the respective synthesis
step and pharmaceutical removal performance.
7 Graphene Aerogel
Graphene aerogel is a 3D self-supporting solid network that resembles interconnected

graphene sheets forming various pore structures. It is mostly filled with air (> 90%)
while maintaining its nanoscale properties within the macroscale structure [28]. This
structure presents attractive properties such as low apparent density, large specific
surface area, and abundant pores, making it a potential adsorbent for pharmaceutical
adsorption. Graphene aerogel has relatively high colloidal and chemical stabilities,
as well as ease of modification compared to conventional adsorbents, hence making
it the most assayed configuration of 3D graphene for wastewater treatment. Various
synthesis methods for graphene aerogels have been reported in the literature and
Fig. 3 depicts the schematics of different graphene aerogels preparation.
Among the reported methods, self-assembly coupled with freeze drying is the
most widely investigated method in graphene aerogels preparation. This method is
also known as solution-based synthesis, whereby graphene oxide (GO) is used as
the precursor material. It involves the initial formation of graphene hydrogel through
hydrothermal reduction of GO under the influence of a reducing agent. At this stage,
the electrostatic repulsion among the GO sheets is reduced by the elimination of
oxygen-rich functional groups, hence triggering the bridging of reduced GO sheets
to form the 3D graphene hydrogel. The hydrogel is subsequently transformed into
aerogel via freeze drying or supercritical fluid drying. The main benefit of this route
is that functionalization and process scale-up are possible without the requirement
of further processing steps [29].
The template assembly method is an alternative approach for the synthesis of
graphene aerogel. This method is flexible, whereby a template is applied as the
scaffold for shaping the 3D graphene. Furthermore, organic or inorganic polymers
can be incorporated into the GO to construct the 3D structure through van der Waals
force, hydrogen, and/or ionic bonding [29]. However, the aerogel constructed may
experience stacking of GO sheets leading to the inconsistent internal structure of the
Fig. 3 Schematic diagram for graphene aerogels preparation. Adapted with permission [29].
Copyright (2023) Elsevier
aerogel. In contrast, chemical vapour deposition (CVD) can produce high-quality

graphene aerogels. The CVD method requires a porous catalyst framework to initiate
the growth of graphene layers from a gaseous carbon precursor. The graphene aerogel
can be retrieved by etching the sacrificial template out from the graphene framework.
Furthermore, this method enables tuning of pore size of the graphene aerogel through
size adjustment of the catalytic template.
Graphene aerogel has been applied in the adsorption of various pharmaceutical
residues. For instance, a novel graphene aerogel fabricated by integrating cellulose
nanocrystalline with polyvinylamine and reduced GO (CNC-PVAm/rGO) exhibited
a high adsorption capacity of 605.87 mg/g towards diclofenac [30]. One interesting
finding from the study is the incorporation of PVAm and rGO had increased the
adsorption capacity by 53 times as compared to bare CNC aerogel, which might be
due to the presence of rGO in the aerogel [30]. According to X-ray photoelectron
spectroscopy (XPS) analysis, the π–π groups of graphene were detected at a binding
energy of 291.50 eV (C1s spectra) and the percentage of π–π groups decreased from
3.92 to 0.86%, confirming that π–π interaction was one of the adsorption mechanisms
[30].
In addition, a graphene-boron nitride composite aerogel (GNP/BNA) was
prepared via one-pot foam-gelcasting/nitridation route for ciprofloxacin removal
[31]. The developed GNP/BNA possessed low density (28–34 mg/cm3 ) as well as
high porosity (~99%), compressive strength (40–52 kPa), and ciprofloxacin removal
(99%) [31]. Furthermore, the main adsorption mechanism of ciprofloxacin by the

GNP/BNA aerogel was determined as synergistic interaction between graphene
and boron nitride functional groups that resulted in the remarkable adsorption of
185 mg/g [31]. An impressive adsorption of tetracycline (1776.26 mg/g) was also
achieved using the zeolitic-imidazolate framework-8@reduced graphene oxide (ZIF-
8@rGO) aerogel [32]. The ZIF-8@rGO aerogel demonstrated interesting character-
istics, where the ZIF-8 nanoparticles grown on the rGO aerogel acted like tentacles
to attract tetracycline, while the rGO aerogel served as the storage sites to accom-
modate the pharmaceutical [32]. The adsorption mechanisms involved were largely
linked to hydrogen bonding, π–π interaction, and electrostatic attraction [32].
8 Graphene Hydrogel
Graphene hydrogel is another 3D form developed for the adsorption of pharma-

ceutical residues in wastewater. In general, hydrogel is a polymeric material with
capabilities to swell and retain large portions of water within its structure without
collapsing when contacted with aqueous media [33]. Furthermore, the hydrogel has a
strong hydrophilicity imparted by the hydrophilic functional groups (e.g., hydroxyl,
carboxyl, and carbonyl) of graphene derivatives and polymer additives [34]. As such,
the hydrogel can facilitate access and diffusion of aqueous pollutants through its
porous channels.
Graphene hydrogels can be synthesized via facile hydrothermal reaction and
graft polymerization technique. Nonetheless, the mechanical strength of hydrogel is
comparatively poor as the internal structure tends to suffer from irreversible damage
once it is broken under a high strain [35]. Therefore, many strategies have been
used to strengthen the mechanical properties of hydrogel with crosslinking being
the widely accepted approach. Crosslinkers can be incorporated into the graphene
precursor to improve interactions between the precursor constituents and promote
self-assembly. Crosslinkers such as metal ions, biomolecules, organic molecules,
and polymer have been studied in the construction of 3D graphene hydrogels [36].
A yttrium-immobilized GO-alginate hydrogel (Y-GO-SA) with a high specific
surface area (147 m2 /g) was developed for the adsorption of tetracycline [6]. The
adsorbent contained -COO, -CH2 , and C–O–C groups as the key chemical functional
groups [6]. It was reported that the tetracycline adsorption capacity was 477.9 mg/
g and the prevailing adsorption mechanisms were hydrogen bonding, π–π interac-
tion, and cation-bonding bridge effects [37]. Interestingly, the potential of Y-GO-SA
hydrogel in arsenic adsorption was also investigated. According to the study, the
arsenic removal by Y-GO-SA hydrogel was initiated with the formation of hydrogen
bonding and ionic exchange mechanisms, resulting in the arsenic adsorption capacity
of 273.4 mg/g [37]. In the binary adsorption study, the presence of tetracycline has
competed with arsenic for the sorption sites, leading to a lower arsenic adsorp-
tion capacity. However, the presence of arsenic has a negligible effect on tetra-
cycline adsorption due to the balance contributions from anion–π interaction and
competitions from Y-ions [37].
An organic-crosslinked graphene hydrogel, namely β-cyclodextrin-immobilized
rGO composite (β-CD/rGO), was constructed for the adsorption of naproxen [38].
The hydrogel exhibited a relatively large adsorption of naproxen (361.85 mg/
g) through distinctive adsorption mechanisms including host–guest interaction,
hydrogen bonding, and π–π interaction [38]. In this study, the 3D structure was
constructed by crosslinking reaction through acetalization between the aldehyde
groups of glutaraldehyde (crosslinker) and the hydroxyl groups of β-CD, and the
rGO [38]. In addition, the saturated β-CD/rGO hydrogel was regenerated using
ethanol. The adsorption capacity remained as 286.95 mg/g at minimum efficiency
[38]. Hence, this finding recommended the graphene hydrogel as an effective and
regenerable adsorbent for the pharmaceutical residue.
A continuous removal of chloroquine by an agar-GO hydrogel which was packed
in a borosilicate glass column was investigated [39]. The pharmaceutical solution
was pumped in an up-flow manner through the column. The breakthrough times for
chloroquine at flowrates of 2 and 4 mL/min were 91 and 21 min, respectively [39].
The results showed a decreasing trend of breakthrough time with flowrate, proposing
pore diffusion as the limiting step in the pharmaceutical adsorption [39].
9 Graphene Beads
Graphene beads are spherically shaped 3D graphene structures which have attracted
much attention owing to their relatively small macro-size with a shorter diffu-
sional pathway for micropollutants to reach the sorption sites [40]. Graphene beads
can be synthesized through crosslinking between the GO/polymer matrix and the
crosslinking agent (calcium chloride, glutaraldehyde, sodium hydroxide, etc.) with
the assistance of freeze drying or supercritical fluid drying [40].
The adsorption of bilirubin onto macro-mesoporous reduced GO aerogel beads
was investigated by Li et al. [41]. The graphene beads were synthesized via self-
assembly of GO in the presence of a crosslinking agent (calcium ions) and reducing
chemical (ascorbic acid), followed by freeze drying [41]. The graphene beads shown
in Fig. 4 possessed a spherical shape and a specific surface area of 287.5 m2 /g. It was
reported that the size of the graphene beads could be customized by adjusting the
needle size during the synthesis stage, and the beads structure became more regular
at higher GO concentrations [41].
From the results of scanning electron microscopy (SEM), the graphene beads had
a 3D interconnected porous network with randomly distributed pore sizes from 1 to
10 μm, and these might have served as the binding sites for bilirubin. Furthermore,
π–π interaction between the graphene sheets provided a high mechanical strength for
the beads, where they could support a mass of 202 g, which was 101,000 times more
Fig. 4 Optical photograph of rGOn beads (a: rGO8 , b: rGO12 , c: rGO16 ). The SEM morphologies
of rGOn beads (a1: rGO8 , b1: rGO12 , c1: rGO16 ) and internal structure of rGOn beads (a2: rGO8 ,
b2: rGO12 , c2: rGO16 ). Adapted with permission [41]. Copyright (2020) Elsevier
than the original weight of the beads [41]. Such attractive features have resulted
in a remarkable bilirubin adsorption capacity of 649 mg/g, further supporting the
application of 3D graphene beads in wastewater treatment.
In a separate study, Yang et al. [42] have successfully synthesized GO modi-
fied κ-carrageenan/sodium alginate (GO-κ-car/SA) double network hydrogel beads
for the removal of different antibiotics (ciprofloxacin and ofloxacin). An interesting
highlight from this study is the double network strategy to enhance the mechanical
strength of the beads. In this work, sodium alginate (with high content of carboxyl
group) and carrageenan (with high content of hydroxyl group) were bonded via
hydrogen bonding and ionic interactions [42]. The crosslinked network not only
retained the shape of the beads, but also decreased the intermolecular spacing between
the sodium alginate and the carrageenan, thereby creating more compact graphene
beads. Notably, the addition of GO further enhanced the elastic modulus of the
beads from 2.1 MPa (without GO) to 4.5 MPa [42]. Hydrogen bonding and electro-
static interaction were the primary adsorption mechanisms for ciprofloxacin removal
(272 mg/g) [42]. Additionally, the continuous removal of ofloxacin by GO-κ-car/
SA double network graphene beads was investigated in a fixed-bed operation. The
study revealed that the developed adsorbent was reliable for practical applications
as supported by the extended breakthrough time of 4 h and bed sorption capacity

of 84.43 mg/g [41]. Notably, the GO-κ-car/SA double network beads demonstrated
excellent mechanical properties and could withstand high-pressure operation as they
did not show any sign of deformation and breakage during the fixed-bed operation.
10 Other Structures
Owing to the ease of modification of graphene materials, there are other config-
urations of 3D graphene that can be synthesized for pharmaceutical adsorption.
Contrarily to aerogel, graphene xerogel can be formed through the sol–gel technique.
However, the developed xerogel may experience shrinkage due to capillary collapse
of liquid inside the pores of the hydrogel network during the drying stage [43]. As a
result, graphene xerogel tends to be denser than aerogels and has a smaller surface
area and a lower porosity. A carbon xerogel/graphene hybrid adsorbent was devel-
oped to adsorb metronidazole antibiotic. The addition of GO increased the specific
surface area of the adsorbent from 648 to 816 m2 /g as the GO content was increased
from 0.62 to 1.87 g [44]. Furthermore, the metronidazole adsorption capacity was
also increased from 116.86 to 172.59 mg/g as the GO content was increased [44]. The
addition of GO was reported to promote π–π interactions between the adsorbent and
metronidazole species along with other mechanisms such as electrostatic attraction
and hydrogen bonding [44].
Fibrous structure is also another configuration of 3D graphene adsorbent. The
3D graphene fibre can be prepared through electrospinning, crosslinking, and wet
coating. A work was conducted to study the adsorption of trimethoprim by GO-
carboxymethylcellulose film coated on polyethylene terephthalate (PET) support
[45]. The addition of GO film content demonstrated an increase in trimethoprim
adsorption capacity from 2.15 to 39.43 mg/g when the GO film was increased by 20
%(w/w) [45]. This was due to the increase in active sites availability at higher GO
film content. However, the adsorption capacity was not significantly increase when
the GO film content exceeded 20 % due probably to the aggregation of GO has led
to a reduction in surface area and active sites for adsorption [45].
The fibrous structure can be applied in membrane operation to adsorb pharmaceu-
tical residues. For instance, a GO-polysulfone hollow fibre membrane (PSU-GO HFs)
was developed to synergize ultrafiltration and adsorption mechanisms for enhanced
ciprofloxacin removal [46]. The effect of GO loading on the development of PSU-GO
HFs was investigated (Fig. 5) [46].
It was revealed that the optimum removal of ciprofloxacin was achieved at a
loading of 3.5% GO, but loadings above 3.5% did not show any significant improve-
ments. This observation was due to the reduction in surface area caused by GO
aggregation at higher GO loading [46]. Another highlight of this study is the pilot-
test investigation using 100 L tap water with 1 mg/L ciprofloxacin concentration. The
initial ciprofloxacin removal was around 65% and decreased to 30% after treating 40
Fig. 5 a PSU HFs and

b filtration modules, with
different amounts of GO (w/
w). From left to right:
pristine PSU; PSU-GO 1%;
PSU-GO 2.5%; PSU-GO
3%; PSU-GO 3.5%;
PSU-GO 5%. Adapted with
permission [46]. Copyright
(2022) Elsevier
L of ciprofloxacin-spiked tap water and the adsorption capacity was approximately

110 mg/g [46].
11 Conclusion and Outlook
3D graphene structures development for environmental pollution control has attracted

great interest lately. The 3D hierarchical network of graphene has showcased supe-
rior adsorption capacities towards numerous pharmaceuticals. The construction of
3D graphene has introduced additional adsorption functionalities from the chem-
ical additives while maintaining the intrinsic properties of the nanomaterial in the
bulk structure, thus making it a favourable adsorbent. Presently, the most devel-
oped 3D graphene structures are aerogel, hydrogel, and spherical beads as they offer
practical structures to remove pharmaceutical residues. The primary binding mech-
anisms involved in the adsorption of pharmaceuticals are π–π interaction, hydrogen
bonding, and electrostatic interaction.
The application of 3D graphene structure for industrial-scale removal of pharma-
ceutical has not been realized yet. The graphene structures previously discussed were
mostly prepared at a laboratory scale and may not be sufficiently robust to withstand
the harsh flow conditions of industrial wastewater treatment. To improve the mechan-
ical strength of 3D graphene, it is crucial to optimize the formulation of the graphene
from the aspects of crosslinker choice, chemical functionalities, crosslinking condi-
tions, and post-treatment processes. Additionally, most of the studied pharmaceutical
residues were under the classes of antibiotic and non-steroidal anti-inflammatory
drugs, but studies on other classes of medicines such as antidepressant, hormones,
and beta-blocker remain scarce. Therefore, comprehensive research on these drugs
is necessary to understand the adsorption affinity of 3D graphene structures towards
the persistent pharmaceutical pollutants.
Moreover, the simultaneous adsorption of multi-pollutants, continuous adsorption
via fixed-bed column, and pilot-scale adsorber design are still lacking in the litera-
ture. Hence, it is highly recommended to conduct such studies to increase the feasi-
bility of commercialization of 3D graphene structures for pharmaceutical wastewater
treatment. In addition, most research works mainly focussed on the development
and assessment of the 3D graphene structures in pharmaceuticals removal, but the
sustainability of using these structures is unclear. As such, life cycle analysis, techno-
economic analysis, and density functional theory should be applied to determine the
viability of 3D graphene structures in large-scale wastewater remediation.
Acknowledgements The authors gratefully acknowledge the financial support provided by

the Ministry of Higher Education (MOHE), Malaysia, under the Fundamental Research Grant
Scheme, FRGS/1/2020/STG05/UNIM/02/2.
References
1. Kujawska, A., Kiełkowska, U., Atisha, A., Yanful, E., Kujawski, W.: Comparative analysis
of separation methods used for the elimination of pharmaceuticals and personal care products
(PPCPs) from water—a critical review. Sep. Purif. Technol. 290, 120797 (2022)
2. Shearer, L., Pap, S., Gibb, S.W.: Removal of pharmaceuticals from wastewater: a review of
adsorptive approaches, modelling and mechanisms for metformin and macrolides. J. Environ.
Chem. Eng. 10(4), 108106 (2022)
3. Alnajjar, M., Hethnawi, A., Nafie, G., Hassan, A., Vitale, G., Nassar, N.N.: Silica-alumina
composite as an effective adsorbent for the removal of metformin from water. J. Environ.
Chem. Eng. 7(3), 102994 (2019)
4. Quesada, H.B., Baptista, A.T.A., Cusioli, L.F., Seibert, D., de Oliveira Bezerra, C., Bergamasco,
R.: Surface water pollution by pharmaceuticals and an alternative of removal by low-cost
adsorbents: a review. Chemosphere 222, 766–780 (2019)
5. Liu, Y.-P., Lv, Y.-T., Guan, J.-F., Khoso, F.M., Jiang, X.-Y., Chen, J., Li, W.-J., Yu, J.-G.:
Rational design of three-dimensional graphene/graphene oxide-based architectures for the
efficient adsorption of contaminants from aqueous solutions. J. Mol. Liq. 343, 117709 (2021)
6. He, J., Cui, A., Ni, F., Deng, S., Shen, F., Yang, G.: A novel 3D yttrium based-graphene oxide-
sodium alginate hydrogel for remarkable adsorption of fluoride from water. J. Colloid Interface
Sci. 531, 37–46 (2018)
7. Hiew, B.Y.Z., Tee, W.T., Loh, N.Y.L., Lai, K.C., Hanson, S., Gan, S., Thangalazhy-Gopakumar,
S., Lee, L.Y.: Synthesis of a highly recoverable 3D MnO2/rGO hybrid aerogel for efficient
adsorptive separation of pharmaceutical residue. J. Environ. Sci. 118, 194–203 (2022)
8. Wong, S., Lim, Y., Ngadi, N., Mat, R., Hassan, O., Inuwa, I.M., Mohamed, N.B., Low, J.H.:
Removal of acetaminophen by activated carbon synthesized from spent tea leaves: equilibrium,
kinetics and thermodynamics studies. Powder Technol. 338, 878–886 (2018)
9. Tee, W.T., Loh, N.Y.L., Hiew, B.Y.Z., Show, P.L., Hanson, S., Gan, S., Lee, L.Y.: Evaluation
of adsorption performance and mechanisms of a highly effective 3D boron-doped graphene
composite for amitriptyline pharmaceutical removal. J. Environ. Manage. 344, 118363 (2023)
10. Iqbal, J., Shah, N.S., Khan, Z.U.H., Rizwan, M., Murtaza, B., Jamil, F., Shah, A., Ullah, A.,
Nazzal, Y., Howari, F.: Visible light driven doped CeO2 for the treatment of pharmaceuticals
in wastewater: a review. J. Water Process Eng. 49, 103130 (2022)
11. Al Falahi, O.A., Abdullah, S.R.S., Hasan, H.A., Othman, A.R., Ewadh, H.M., Kurniawan, S.B.,
Imron, M.F.: Occurrence of pharmaceuticals and personal care products in domestic wastewater,
available treatment technologies, and potential treatment using constructed wetland: a review.
Process Saf. Environ. Protect. 168, 1067–1088 (2022)
12. Mackuľak, T., Černanský, S., Fehér, M., Birošová, L., Gál, M.: Pharmaceuticals, drugs, and
resistant microorganisms—environmental impact on population health. Curr. Opin. Environ.
Sci. Health 9, 40–48 (2019)
13. Ramírez-Durán, N., Moreno-Pérez, P.A., Sandoval-Trujillo, A.H.: Bacterial treatment of
pharmaceutical industry effluents. Ecopharmacovigilance 175–187 (2017)
14. Hussain, I., Khan, M.Z., Khan, A., Javed, I., Saleemi, M.K.: Toxicological effects of diclofenac
in four avian species. Avian Pathol. 37(3), 315–321 (2008)
15. Van der Meer, T.P., Artacho-Cordón, F., Swaab, D.F., Struik, D., Makris, K.C., Wolffenbuttel,
B.H.R., Frederiksen, H., Van Vliet-Ostaptchouk, J.V.: Distribution of non-persistent endocrine
disruptors in two different regions of the human brain. Int. J. Environ. Res. Public Health (2017)
16. Kumar, M., Sridharan, S., Sawarkar, A.D., Shakeel, A., Anerao, P., Mannina, G., Sharma, P.,
Pandey, A.: Current research trends on emerging contaminants pharmaceutical and personal
care products (PPCPs): a comprehensive review. Sci. Total Environ. 859, 160031 (2023)
17. Madikizela, L.M., Ncube, S., Chimuka, L.: Uptake of pharmaceuticals by plants grown under
hydroponic conditions and natural occurring plant species: a review. Sci. Total Environ. 636,
477–486 (2018)
18. Rouquerol, F., Rouquerol, J., Sing, K.S.W., Maurin, G., Llewellyn, P.: 1 - Introduction. In:
Rouquerol, F., Rouquerol, J., Sing, K.S.W., Llewellyn, P., Maurin, G. (eds.) Adsorption by
Powders and Porous Solids (Second Edition), pp. 1–24. Academic Press, Oxford (2014)
19. Chen, M., Yan, Z., Luan, J., Sun, X., Liu, W., Ke, X.: π-π electron-donor-acceptor (EDA)
interaction enhancing adsorption of tetracycline on 3D PPY/CMC aerogels. Chem. Eng. J.
454, 140300 (2023)
20. Pinelli, F., Piras, C., Rossi, F.: A perspective on graphene based aerogels and their environmental
applications. FlatChem 36, 100449 (2022)
21. Gang, D., Uddin Ahmad, Z., Lian, Q., Yao, L., Zappi, M.E.: A review of adsorptive remediation
of environmental pollutants from aqueous phase by ordered mesoporous carbon. Chem. Eng.
J. 403, 126286 (2021)
22. Ateia, M., Helbling, D.E., Dichtel, W.R.: Best practices for evaluating new materials as
adsorbents for water treatment. ACS Mater. Lett. 2(11), 1532–1544 (2020)
23. Liu, H., Qiu, H.: Recent advances of 3D graphene-based adsorbents for sample preparation of
water pollutants: a review. Chem. Eng. J. 393, 124691 (2020)
24. Hiew, B.Y.Z., Lee, L.Y., Lee, X.J., Thangalazhy-Gopakumar, S., Gan, S., Lim, S.S., Pan,
G.-T., Yang, T.C.-K., Chiu, W.S., Khiew, P.S.: Review on synthesis of 3D graphene-based
configurations and their adsorption performance for hazardous water pollutants. Process Saf.
Environ. Prot. 116, 262–286 (2018)
25. Zhuang, Y., Yu, F., Ma, J., Chen, J.: Enhanced adsorption removal of antibiotics from aqueous
solutions by modified alginate/graphene double network porous hydrogel. J. Colloid Interface
Sci. 507, 250–259 (2017)
26. Ma, J., Jiang, Z., Cao, J., Yu, F.: Enhanced adsorption for the removal of antibiotics by
carbon nanotubes/graphene oxide/sodium alginate triple-network nanocomposite hydrogels
in aqueous solutions. Chemosphere 242, 125188 (2020)
27. Zhang, P., Yin, L., Yang, X., Wang, J., Chi, M., Qiu, J.: Cotton-derived 3D carbon fiber aerogel
to in situ support Bi2O3 nanoparticles as a separation-free photocatalyst for antibiotic removal.
Carbon 201, 110–119 (2023)
28. Jiang, X., Du, R., Hübner, R., Hu, Y., Eychmüller, A.: A roadmap for 3D metal aerogels:
materials design and application attempts. Matter 4(1), 54–94 (2021)
29. Wu, W., Du, M., Shi, H., Zheng, Q., Bai, Z.: Application of graphene aerogels in oil spill
recovery: a review. Sci. Total Environ. 856, 159107 (2023)
30. Lv, Y., Liang, Z., Li, Y., Chen, Y., Liu, K., Yang, G., Liu, Y., Lin, C., Ye, X., Shi, Y., Liu, M.:
Efficient adsorption of diclofenac sodium in water by a novel functionalized cellulose aerogel.
Environ. Res. 194, 110652 (2021)
31. Han, L., Khalil, A.M.E., Wang, J., Chen, Y., Li, F., Chang, H., Zhang, H., Liu, X., Li, G.,
Jia, Q., Zhang, S.: Graphene-boron nitride composite aerogel: a high efficiency adsorbent for
ciprofloxacin removal from water. Sep. Purif. Technol. 278, 119605 (2021)
32. Liu, Y., Fu, J., He, J., Wang, B., He, Y., Luo, L., Wang, L., Chen, C., Shen, F., Zhang, Y.:
Synthesis of a superhydrophilic coral-like reduced graphene oxide aerogel and its application
to pollutant capture in wastewater treatment. Chem. Eng. Sci. 260, 117860 (2022)
33. Yu, F., Yang, P., Yang, Z., Zhang, X., Ma, J.: Double-network hydrogel adsorbents for
environmental applications. Chem. Eng. J. 426, 131900 (2021)
34. Guo, Y., Bae, J., Fang, Z., Li, P., Zhao, F., Yu, G.: Hydrogels and hydrogel-derived materials
for energy and water sustainability. Chem. Rev. 120(15), 7642–7707 (2020)
35. Wang, X.-H., Song, F., Qian, D., He, Y.-D., Nie, W.-C., Wang, X.-L., Wang, Y.-Z.: Strong and
tough fully physically crosslinked double network hydrogels with tunable mechanics and high
self-healing performance. Chem. Eng. J. 349, 588–594 (2018)
36. Wu, Y., Zhu, J., Huang, L.: A review of three-dimensional graphene-based materials: synthesis
and applications to energy conversion/storage and environment. Carbon 143, 610–640 (2019)
37. He, J., Ni, F., Cui, A., Chen, X., Deng, S., Shen, F., Huang, C., Yang, G., Song, C., Zhang,
J., Tian, D., Long, L., Zhu, Y., Luo, L.: New insight into adsorption and co-adsorption of
arsenic and tetracycline using a Y-immobilized graphene oxide-alginate hydrogel: adsorption
behaviours and mechanisms. Sci. Total Environ. 701, 134363 (2020)
38. Feng, X., Qiu, B., Dang, Y., Sun, D.: Enhanced adsorption of naproxen from aquatic envi-
ronments by β-cyclodextrin-immobilized reduced graphene oxide. Chem. Eng. J. 412, 128710
(2021)
39. Bezerra de Araujo, C.M., Wernke, G., Ghislandi, M.G., Diório, A., Vieira, M.F., Bergamasco,
R., Alves da Motta Sobrinho, M., Rodrigues, A.E.: Continuous removal of pharmaceutical
drug chloroquine and Safranin-O dye from water using agar-graphene oxide hydrogel: selective
adsorption in batch and fixed-bed experiments. Environ. Res. 216, 114425 (2023)
40. Liu, H., Tian, X., Xiang, X., Chen, S.: Preparation of carboxymethyl cellulose/graphene
composite aerogel beads and their adsorption for methylene blue. Int. J. Biol. Macromol.
202, 632–643 (2022)
41. Li, Z., Huang, X., Wu, K., Jiao, Y., Zhou, C.: Fabrication of regular macro-mesoporous reduced
graphene aerogel beads with ultra-high mechanical property for efficient bilirubin adsorption.
Mater. Sci. Eng., C 106, 110282 (2020)
42. Yang, P., Yu, F., Yang, Z., Zhang, X., Ma, J.: Graphene oxide modified κ-carrageenan/sodium
alginate double-network hydrogel for effective adsorption of antibiotics in a batch and fixed-bed
column system. Sci. Total Environ. 837, 155662 (2022)
43. Bratovcic, A., Petrinic, I.: Carbon based aerogels and xerogels for removing of toxic organic
compounds. In: International Conference “New Technologies, Development and Applications”,
Springer, pp. 743–749 (2020)
44. Segovia-Sandoval, S.J., Pastrana-Martínez, L.M., Ocampo-Pérez, R., Morales-Torres, S.,
Berber-Mendoza, M.S., Carrasco-Marín, F.: Synthesis and characterization of carbon xerogel/
graphene hybrids as adsorbents for metronidazole pharmaceutical removal: effect of operating
parameters. Sep. Purif. Technol. 237, 116341 (2020)
45. Juengchareonpoon, K., Wanichpongpan, P., Boonamnuayvitaya, V.: Trimethoprim adsorption

using graphene oxide-carboxymethylcellulose film coated on polyethylene terephthalate as a
supporter. Chem. Eng. Process.—Process Intensification 169, 108641 (2021)
46. Zambianchi, M., Khaliha, S., Bianchi, A., Tunioli, F., Kovtun, A., Navacchia, M.L., Salatino,
A., Xia, Z., Briñas, E., Vázquez, E., Paci, D., Palermo, V., Bocchi, L., Casentini, B., Melucci,
M.: Graphene oxide-polysulfone hollow fibers membranes with synergic ultrafiltration and
adsorption for enhanced drinking water treatment. J. Membr. Sci. 658, 120707 (2022)
3D Graphene for Metal-Ion Batteries
Jin Kwei Koh and Chin Wei Lai
Abstract A metal-ion battery is a rechargeable secondary battery. Lithium-ion was

the first metal-ion battery introduced in the 1980s. Various metal-ion batteries have
then emerged in the last few decades. However, each has limitations in terms of cost
and availability. Several recent inventions employ three-dimensional (3D) graphene
oxide to advance the electrochemical performance of metal-ion batteries. This chapter
discusses the type of metal-ion batteries, followed by an overview of 3D graphene,
including its fabrication method and structure. Various structures of 3D graphene
material in metal-ion batteries are discussed, including foam, aerogels, microsphere,
ball, vertical sheet, and others. Each structure of modified 3D graphene has been
outlined with its detailed fabrication process. Additionally, the recent development
regarding 3D graphene in metal-ion batteries is also discussed detailed. This review
concludes that most studies exhibited good electrochemical performance using modi-
fied 3D graphene materials in a metal-ion battery. In the future, there is a need to seek
alternatives for metal ions or graphene resources as they suffer from a few limitations,
such as the depletion of metal ions and the cost and fabrication of graphene.
Keywords 3D graphene · Metal-ion battery system · Electrochemical ·

Fabrication methods
1 Introduction
A metal-ion battery is a rechargeable battery with two electrodes (cathode and

anode), a separator membrane, an electrolyte, and an external electronic circuit.
There is various type of metal-ion batteries. The lithium-ion battery is the most
common electrochemical technology and is convenient in numerous industries, such
as communications, transportation, and others. The primary functioning mechanism
of all metal-ion batteries is the discharge and charge process (Fig. 1). Energy is
J. K. Koh · C. W. Lai (B)

Nanotechnology and Catalysis Research Centre (NANOCAT), Institute for Advanced Studies,
Universiti Malaya, Level 3, Block A, 50603 Kuala Lumpur, Malaysia
e-mail: cwlai@um.edu.my
https://doi.org/10.1007/978-3-031-36249-1_12
208 J. K. Koh and C. W. Lai
Fig. 1 Schematic of
metal-ion battery structure
generally stored in the form of electrons in the lithium ions within the anode for the
discharge process. The anode initiates an oxidation process, which causes lithium
ions to exit the anode and move to the cathode. The electrons that have been stored are
released to produce the electric current. The charging mechanism can be explained
as the electrons from the power source charging the battery attaching with the lithium
ions in the cathode during the charging phase, during which the ions pass through
the electrolyte and the separator to the anode [1, 2].
The concept of the lithium-ion battery was introduced in the late 1970s. Armand
proposed a lithium-ion battery, using two different intercalation materials for anodes
and cathodes. Meanwhile, the lithium-ion battery was named a “rocking-chair
battery” because its charge–discharge mechanism shuttles the ions from one electrode
to another. Subsequently, Lazzari and Scrosati demonstrated the concept of lithium-
ion batteries in 1980. The sodium-ion battery also was introduced in the 1980s.
Over that decade, the research and development of metal-ion batteries were mainly
focused on lithium-ion batteries. The lithium-ion battery was also commercialised by
Sony in 1991, while sodium-ion batteries received less attention in the market. Due
to the cost-efficiency of materials, other types of metal-ion batteries have emerged,
such as aluminium and potassium-ion batteries [1–3]. Due to concerns about the effi-
ciency of battery technology, the charging and discharging capacity with the cycling
performance are the main criteria to improve the metal-ion batteries. There have
been many advancements in all metal-ion batteries, including existing lithium and
sodium-ion batteries. The advancement of all metal-ion batteries is focused on modi-
fying electrodes using nanomaterial. Currently, 3D graphene has garnered attention
in the electrochemical battery industry as its nanostructure contributes to the higher
theoretical capacity, large surface area contact for charging and discharging process,
and others. This chapter summarises the recent development of 3D graphene in the
metal-ion battery and their achievement of electrochemical properties. This chapter
then outlines the future challenges and opportunities of this 3D graphene in metal-ion
batteries.
3D Graphene for Metal-Ion Batteries 209
2 Overview of the Types of Metal-Ion Battery
Metal-ion battery is mainly made up of four basic functional components, which

are the anode, cathode, electrolyte, and current collector. There are various types of
metal-ion batteries, such as lithium-ion, magnesium-ion, aluminium-ion, sodium-
ion, potassium-ion, and others. The type of metal in the metal-ion battery can be
classified based on the inclusion of alkaline metal, alkaline earth metal, or other
transition metal.
2.1 Alkaline Metal-Ion Battery
According to the periodic table, lithium and sodium are the most frequently studied in
the metal-ion battery systems. The lithium-ion battery is one of the most successful
commercialised in the electrochemistry and power field. This is due to the high
energy and power density supply in that system. It has been utilised in electric
vehicles since the 1990s. Normally, lithium-ion acts as a cathode, while the anode is
made of lithium metal. The lithium-ion battery has been used in various applications,
such as electronic communications gadgets, transportation, and others in this era of
technology. However, it has a short lifespan and there are safety concerns in the
practical application of lithium-ion batteries [3–6].
Due to these concerns, abundant resources on Earth, such as sodium and potas-
sium, are emerging in battery systems, since they are alkali metals with similar
physicochemical properties to lithium. Further, both are inexpensive and can be
utilised in large-scale electric storage. However, both have large radii, which can
influence metal-ion batteries’ discharge and charge capacity [7, 8].
2.2 Alkali Earth Metal
Due to the high cost of lithium-based batteries, safety concerns, and the scarcity of
lithium elements in nature, there is an urgent need to develop alternatives in the battery
system. Hence, alkali earth metals also have been giving rise to battery research, such
as magnesium and aluminium. For instance, magnesium ions in battery systems can
be more economical and eco-friendly in electric vehicles. Magnesium can act as
both an anode and cathode for the intercalation or deintercalation of magnesium
ions. Hence, it is a potential candidate in the metal-ion battery system.
An aluminium ion is another metal earth metal that can flow from anode to cathode
in an electro-battery system. It can exchange three electrons for every ion and has
three times the energy density of a lithium-ion battery system. It is a low-cost and
high-abundance material, but it has operation issues at high temperatures [9].
3 Overview of 3D Graphene Material with Its Fabrication

Method and Structure in the Current Metal-Ion Battery
Technology
Graphene is known as a two-dimensional (2D) and was discovered in 2000. Normally,

this material is called “graphene” and is rarely specifically named “2D graphene”.
Graphene garners attention with the remarkable improvement of advanced science
and technology to date. This is due to its unique structural configuration, which
consists of a single layer of honeycomb configuration with sp2 hybridised carbon
atoms. Its intrinsic features have been broadened in various research fields, providing
insights into cutting-edge nanomaterials. 3D graphene materials are considered an
advanced technology because the 3D features of graphene oxide are conducive to
various applications. Theoretically, 3D graphene material is formed from unstacked
2D graphene. Graphene material is conventionally synthesised via two distinct
approaches, namely bottom-up and top-down approaches. Chemical vapour deposi-
tion (CVD), pyrolysis, and epitaxial growth are examples of bottom-up approaches,
whereas chemical synthesis, chemical exfoliation, and mechanical exfoliation are
examples of top-down approaches.
CVD, synthesis of carbon, and other bottom-up approaches are unfavourable in
the massive production of graphene due to several concerns, including cost, product
purity, scalability, and yield. For instance, Table 1 shows CVD having low crys-
tallinity with controlled layers and sizes, which is convenient in graphene synthesis
and boosts graphene-based energy devices’ performance. However, it is costly and
available on a limited scale [10, 11]. However, liquid phase exfoliation and reduction
of graphene oxide are favourable in the massive production of graphene, because of
their cost-effectiveness and high scalability for bulk production [10, 12]. Technically,
pristine graphite is used as starting material to undergo pre-treatment, such as thermal
treatment, mechanical milling, or Hummers’ oxidation, followed by exfoliation by
ultra-sonification. Besides, the pristine graphite also can undergo direct exfoliation in
the liquid phase. After exfoliation, the treated and exfoliated sources are converted to
reduced graphene oxide or graphene oxide-based compounds by chemical, thermal,
and electrochemical reactions.
Although 2D graphene has outstanding performance with its extraordinary proper-
ties, the agglomeration effects of 2D graphene-based materials are the main problem
of dispersive behaviour, which is caused by its morphology structure. Hence, 3D
graphene materials have been advocated for nanotechnology emerging in the past
few years. Although the fabrication of 3D graphene materials is almost similar to
the fabrication of the graphene materials that is aforementioned, there is a difference
in terms of crystallinity, purity, cost, and scalability between 2 and 3D graphene
materials, as shown in Table 1 [13]. As electrical battery technology is sensitive to
conductivity, the powder form is more favourable than bulk materials. Therefore,
there are challenges faced in 3D graphene material synthesis. This is attributed to the
high crystallinity in most approaches, such as micromechanical exfoliation, reduction
of graphene oxide, and liquid phase exfoliation, which contribute to bulk material
Table 1 The comparison of 2D graphene and 3D graphene in terms of crystallinity, purity, layer
number controllability, cost aspect, and scalability for each process. Adapted with permission [13],
copyright (2018), chemical society reviews
Graphene Method of Crystallinity Purity Layer number Cost Scalability
types fabrication controllability aspect
2D Chemical vapour Low High High High Medium
deposition
Micromechanical High High Medium Low Low
exfoliation
3D Chemical vapour Medium High High Medium High
deposition
Reduction of High Low Low Low High
graphene oxide
Liquid phase High Medium Low Low High
exfoliation
production. The fabrication of 3D graphene materials in powder form is thus more

attractive in battery design [14].
3D graphene can be prepared using several methods with different morphology
structures. In battery technology, the typical structural design of 3D graphene
composite can be encapsulated in a ball, mixed, anchored, and layered form,
according to Chang et al. [12]. In the following, the previous studies regarding the
fabrication of 3D graphene material on the electrochemical battery are discussed in
terms of the process, structure, precursors, template, and temperature required, as
summarised in Table 2.
3.1 Cvd
In 2006, CVD was launched. This is fabricated with a planar few-layer graphene
structure. Up to now, there have been various studies on the fabrication of graphene
via CVD. This process requires the precursor for the fabrication of the graphene
material, which can be applied in various forms. Methane gas is the most common
carbon source for the production of graphene materials [14–19]. For the growth
of graphene, nickel is usually used as the template. The operation temperature is
in the range of 790–1050 °C. The samples are always treated in a hydrogen or
Argon atmosphere. Certain researchers have utilised CVD process initially for the
synthesis of 2D graphene material and then further with other processes such as
hydrothermal, calcination, annealing, and others. However, CVD also can be used to
produce 3D graphene materials further. For instance, Guo et al. [15] and Son et al.
[16] synthesised graphene foam and graphene balls using methane gas as a carbon
source via CVD process. They also utilised 3D graphene material fabricated from
CVD process, further hybridising with the functionalised materials in their metal
Table 2 Previous studies of metal-ion batteries with their process details
212
Method of Product structure Precursor Template Operating condition Author

fabrication
CVD, etching Graphene hollow structure Methane (CVD), Nitric acid Nickel foam 790 Pa and 1000 °C Guo et al.
(hybrid with ZnO and Mg(OH)2 (etching) (CVD) [15]
intermediate nanostructure layer)
CVD Graphene ball: hybrid silica with Methane, hydrogen Silica Atm pressure and Son et al.
graphene in popcorn structure 900–1050 °C [16]
CVD, plasma Graphene-nanoribbon on the Methane, hydrogen, Argon nickel (CVD) Ambient pressure and Yu et al.
etching, annealing surface of highly porous 3D (CVD) 1000 °C (CVD), 110 °C [19]
graphene Ar+ ion (plasma etching) (plasma etching), 650
Argon and hydrogen (annealing) (Annealing)
CVD, hydrothermal Multilayer 3D graphene foam: Methane, soybean oil (CVD) Nickel foam (CVD) 800 °C (CVD), 155 °C Choi et al.
hybrid with sulphur-based Carbon Sulphide (hydrothermal) (hydrothermal) [23]
material
D graphene foam: hybrid with Hydrogen, argon, methane nickel foam (CVD) 1000 °C (CVD), 155 °C He et al.
sulphur-based material 3 (CVD) (hydrothermal) [18]
Sulphur, argon (hydrothermal)
CVD, hydrothermal Graphene foam: hybrid with Methane (CVD) Nickel 1000 °C (CVD, 200 °C Ren et al.
carbon nanotube and MoS2 Argon (hydrothermal) (hydrothermal) [17]
nanoparticles
Thermal CVD Vertical graphene sheets on Methane, hydrogen NA Ar atmosphere and Ji et al. [14]
carbon black 1100 °C
Modified Hummer’s Crystal Microstructure of GO powder and potassium NA 180 °C (hydrothermal), Li et al. [22]
method, antimony/graphene composite antimony tartrate (hydrothermal) −56 °C (freeze-drying),
Hydrothermal and Argon (calcination) 850 °C (calcination)
freeze-drying and
calcination
(continued)
J. K. Koh and C. W. Lai
Table 2 (continued)
fabrication
Mesoporous amorphous FePO4 Graphene nanosheet, CTAB, n-hexane, 180 °C (hydrothermal), Mo et al.
nanoparticles cross-linked with (NH4 )2 Fe(SO4 )2 and NH4 H2 PO4 n-butanol 400 (calcination) [24]
3D holey graphene framework
Modified Hummer’s Hybrids of 3D graphene with Graphene oxide, ferric citrate NA 180 °C (hydrothermal), Liu et al.
method, Fe3 O (hydrothermal), nitrogen 500 °C (annealing) [25]
hydrothermal, (annealing)
freeze-drying and
annealing
SnO2 -GA 3D porous aerogels SnO2 , graphene oxide NA 75 °C (hydrothermal), Chen et al.
600 (annealing) [27]
Modified Hummer’s, 3D graphene-encapsulated nearly FeSO4 .7H2 O, lysine Graphene oxide 180 °C (hydrothermal), Li et al. [21]
hydrothermal and monodisperse Fe3 O4 (3D (hydrothermal) argon 600 °C (calcination)
calcination Fe3 O4 @rGO) composite (calcination)
Hummer’s method, Nano FeSb2 S4 in CNT/graphene SbCl2 , FeCl2 , S (hydrothermal) NA 180 °C (Reflux), Zeng et al.
Reflux, annealing 3D porous network argon (annealing) 450 °C (annealing), − [28]
and freeze-drying carbon nanotubes (mixed before 50 °C
freeze-drying) (freeze-drying)
Hydrothermal Microsphere: crystal carbon Sucrose (hydrothermal process), Aluminium nitrate 200 °C (hydrothermal), Liu et al.
process and roasting shell-coated graphene sheets argon (roasting process) nonahydrate 2000 °C (roasting [26]
process process)
Solvothermal and Oxygen-rich graphene is Graphene oxide, alcohol Melamine 180 °C (solvothermal), Ma et al.
2-step annealing vertically grown on 3D N-doped (solvothermal) (solvothermal) 800 °C (1st calcination), [30]
carbon foam composite argon (annealing) and 325 °C (2nd
calcination)
(continued)
213
Table 2 (continued)
214

fabrication
Facile spray drying, 3D graphene decorated Fe(NO3 )3 ·9H2 O, NA 500 °C (spray drying), Yuan et al.,
ball milling, iron-based mixed-polyanion NaH2 PO4 ·2H2 O and 900 °C (calcination) [29]
calcination compound Na4 Fe3 (PO4 )2 (P2 O7 ) C6 H8 O7 ·H2 O, GO (spray drying)
microspheres argon (calcination)
Modified Hummer’s, Ultrathin MoS2 nanosheet/ Ammonium tetrathiomolybdate, Carbon fibre paper 800 °C Yuan et al.
Freeze-drying and graphene hybrid aerogels graphene oxide (freeze-drying) [8]
thermal reduction argon and hydrogen (for thermal
use)
Pyrolysis Porous monolith of graphene Glucose Zinc 1000 °C Wang et al.
(also known as zinc-guided 3D [7]
graphene)
Modified Hummer’s, 3D wrinkled N, S co-doped Thiourea, SiOx NA 800 °C Shi et al.
pyrolysis multilayer graphene sheets [31]
embedding with SiOx
microparticles
battery studies, as explained in Table 2. This indicates the broader use of graphene-
based composite, promoting the integration of 3D graphene materials with other
functionalised materials. A CVD-based process that is applied at high temperatures
for the reduction and decomposition of atoms in the synthesis of nanomaterial is
known as a thermal CVD. Ji et al. [14] produced a novel 3D graphene powder via
thermal CVD. This study revealed that the specific surface area of powder substrate
led to higher yield production. Therefore, the carbon black utilised in this study was
34 nm, contributing to a kilogram yield of 3D graphene powder through thermal
CVD.
3.2 Hummer’s Method and Modified Hummer’s Method
Hummer’s method is an older method that is a form of oxidative exfoliation. This

method has been replaced by Brodie’s method, as it offers several advantages, such
as safety concerns in Brodie’s method in the past. However, there is an environmental
problem related to toxic waste removal associated with Nitrogen dioxide (NO2 ) and
Dinitrogen tetroxide (N2 O4 ) during the fabrication of graphite material via Hummer’s
method. Therefore, several researchers have modified this method in various ways,
such as the exclusion of the consumption of sodium nitrate (NaNO3 ), an incline
of the potassium permanganate (KMnO4 ) usage, and others [20]. For instance, Li
et al. [21] worked with the modified method by excluding NaNO3 . However, Li
et al. [22] reported the fabrication of graphene using a KMnO4 : NaNO3 ratio of
6:1 for modified Hummer’s method. Concerning 3D graphene-based battery tech-
nology, several studies have also reported on this modified method in the fabrication
of graphene oxide. Therefore, the precursors of reduced graphene material and 3D
graphene-based materials are initiated by this modified method before further under-
going other processes (hydrothermal, calcination, annealing, etc.) in the fabrication
of 3D graphene-based materials. Related studies are shown in Table 2.
3.3 Hydrothermal
Hydrothermal process is generally utilised for the thermal reduction of graphene

oxide which has been synthesised from the modified Hummer’s method or any initial
pre-treatment. It emerged in the late nineteenth century. Several studies have been
performed with this step for the reduction of graphene oxide in metal-ion battery
technology. For instance, Choi et al. [23] and He et al. [18] performed a hydrothermal
process at 155 °C for 12 h after CVD process, which involvedsulphur-based material
in the hydrothermal process. Their finalised product is graphene foam hybridising
with sulphur-based material.
Further, several researchers have reported on the operation temperature of the
hydrothermal process at 180 °C with various precursors with graphene material. The
precursors depend on hybridised organic or inorganic material in the battery studies.

For instance, Li et al. [22] fabricated a crystal antimony/graphene composite for a
metal-ion battery. The hydrothermal process involved graphene oxide with potassium
antimony tartrate at 180 °C for 24 h. Mo et al. [24] developed a holey 3D graphene
cross-linked with mesoporous amorphous Iron (III) Phosphate (FePO4 ) nanoparti-
cles using graphene nanosheet, Ammonium Iron (II) Sulphate ((NH4 )2 Fe(SO4 )2 ),
Ammonium dihydrogen Phosphate (NH4 H2 PO4 ), Centrimonium Bromide (CTAB),
n-hexane, and n-butanol at 180 °C for 10 h. Additionally, Li et al. [21] fabricated a 3D
graphene-encapsulated nearly monodisperse Iron (II, III) Oxide (Fe3 O4 ) composite
using lysine and Iron(II) Sulphate Heptahydrate (FeSO4 .7H2 O) in the thermostatic
oven at 180 °C for 12 h. Similarly, Liu et al. [25] also performed 12 h of hydrothermal
process at 180 °C to fabricate 3D graphene hybridising with the ferric citrate. Liu
et al. [26] synthesised a 3D graphene microsphere using the hydrothermal process
at 200 °C for 12 h. Hence, the typical hydrothermal process is 180 °C or more than
180 °C, according to Chen et al. [27]. Apparently, the period of the hydrothermal
process is 10–24 h. However, Chen et al. [27] reported that the hydrothermal process
for the fabrication of 3D graphene aerogels was at 75 °C for 4 h. They proposed this
operating parameter to save on industrial production cost.
3.4 Freeze-Drying
Freeze-drying is a process of freezing a sample under a vacuum at a low temper-

ature for dehydration. The pore structure on the sample can be observed when the
sublimation of the ice developed itself during vacuum freeze-drying, which was
studied by Zeng et al. [28]. The result revealed that a macrospore structure was
formed after freeze-drying at −50 °C. This method can maintain the integral struc-
ture for battery assembly, and the macropore can facilitate the mass transfer of the
electrolyte channel. Li et al. [22] also performed a freeze-drying process at −50 °C
for 72 h for the precipitated sample from the hydrothermal process, which obtained
an antimony/graphene composite after further calcination. Mo et al. [24] performed
a similar method for 48 h to synthesise mesoporous amorphous FePO4 nanoparti-
cles cross-linked with a 3D holey graphene framework. Similarly, Chen et al. [27]
utilised this method to maintain the shape and size of graphene aerogels. Apparently,
this method is always performed after the hydrothermal process and before further
calcination. However, Liu et al. [25] performed this method before further annealing
treatment for the synthesis of 3D graphene-Fe3 O4 . In short, freeze-drying is a step
that maintains the structure and size of a sample.
3.5 Calcination
Calcination is a high-temperature process that happens normally in an inert atmo-

sphere. This method is used for the removal of the volatile component, oxidation of
the organic or inorganic precursor, and crystallisation of the final product. Hence, it is
always considered the last step in the synthesis of the crystal structure of nanomate-
rials; sometimes, it can be considered a purification process. In the fabrication of 3D
graphene-based material for battery technology, several researchers have reported
this step as the last step after undergoing several processes, including Hummer’s
method, hydrothermal, freeze-drying, and others. For instance, Li et al. [22] prepared
an Sb/graphene composite using potassium antimony tartrate and graphene oxide via
the hydrothermal method, followed by high-temperature calcination at 850 °C for
8 h. The operations are performed in an argon atmosphere. However, Mo et al. [24]
spent 1 day in the calcination process at 400 °C to fabricate 3D holey graphene frame-
works cross-linked with encapsulated mesoporous amorphous FePO4 nanoparticles.
Further, Li et al. [21] used a shorter calcination period of 2 h to fabricate 3D graphene-
encapsulated nearly monodisperse Fe3 O4 , performed at 600 °C. An oxidation process
is involved in the calcination process, which can be observed in the study of Yuan
et al. [29]. This study revealed that the oxidation of Ferum (III) ion into Ferum (II)
and the transformation of pyrophosphate ion from phosphate ion, which cause the
formation of reduced graphene oxide (rGO) confined iron-based mixed-polyanion
compound Na4 Fe3 (PO4 )2 (P2 O7 ). Its calcination process was performed at 900 °C for
6 h in an air atmosphere. Apparently, the operation temperature is interrelated with
the operation period. A higher calcination temperature requires a shorter period.
3.6 Annealing
Annealing is a process of sample heating at a high temperature and cooling down

naturally. It is similar to calcination in heat treatment, but does not involve phase
or chemical changes, such as oxidation and decomposition. This process minimises
crystal defects, which can alter microstructure properties, such as hardness, ductility,
and strength. Yu et al. [19] studied a graphene nanoribbon on the surface of 3D
graphene. The last step of the product preparation process in this study is annealing
in argon/hydrogen (80 sccm) at 600 °C for 2 h. Similarly, Liu et al. [25] experimen-
tally determined the finalised powder (hybrids of 3D Graphene with Iron (II, III)
oxide, Fe3 O4 ) obtained from hydrothermal with a freeze-drying process was heated
at 500 °C for 2 h in the nitrogen atmosphere. Further, Chen et al. [27] also performed
the annealing process as the last step for fabricating Tin Oxide-3D graphene aerogels
(SnO2 -GA). This study showed the formation of Sn–C–O bonds between Tin Oxide
(SnO2 ) and reduced graphene sheets after annealing at 600 °C for 30 min under the
nitrogen atmosphere. In short, annealing conditions are usually in the range of 500
to 600 °C under an ambient atmosphere.
3.7 Solvothermal
The solvothermal process is a process similar to the hydrothermal process in terms

of operation parameters, but its precursor is usually a non-aqueous solvent such as
alcohol. For instance, Ma et al. [30] utilised alcohol suspension mixed with dilute
alcohol and exfoliated graphene oxide suspension for soaking cleaned melamine
foam, which was subsequently heated at 180 °C for 10 h.
3.8 Pyrolysis
Pyrolysis is a process that produces carbon components. Normally, this method

requires heat energy to decompose the organic compounds. A few researchers have
reported that the process of fabrication on 3D graphene material can be initiated
by pyrolysis. For instance, Wang et al. [7] use sugar to produce porous monolithic
graphene as the sugar consists of glucose, which is a carbon source for fabricating
graphene materials. They used zinc as a template for pyrolysis in the tubular furnace
at 1000 °C for 2 h in the atmosphere of ammonia/nitrogen. Additionally, Shi et al.
[31] utilised thiourea and SiOx as a precursor in the pyrolysis process at 800 °C
for 2 h for the fabrication of 3D wrinkled N,S co-doped multilayer graphene sheets
embedded with SiOx microparticles.
3.9 Facile Spray Drying
Spray drying is a technique that is widely used in the food and chemical industry,
owing to the simple setup and scale-up with low cost for massive production. In
spray drying, the particle size can achieve nano or microstructure of bulk particles.
For instance, one study showed that the reduced graphene oxide confined iron-based
mixed-polyanion compound was obtained in 60 nm of particle size [29].
3.9.1 Ball Milling
Ball milling is a liquid phase exfoliation of bulk materials into powder form. Yuan
et al. [29] utilised this method at 300 rpm for 3 h in a planetary mill to obtain
powder from bulk particles. The bulk particles are from reduced graphene oxide
confined iron-based mixed-polyanion compound, which is obtained from spray
drying. The ball mill method in this study involved the bulk particles, Sodium
Carbonate (Na2 CO3 ), Nickel (II) Oxide (NiO), and Manganese (III) Oxide (Mn2 O3 ).
3.9.2 Etching
The etching step is the process that removes the intermediate substance by using acid
or solvent. Guo et al. [15] designed a 3D graphene hollow structure using an etching
step to remove the intermediate Magnesium oxide (MgO) and Zinc oxide (ZnO) that
developed from CVD of graphene foam. Similarly, Yu et al. [19] induced the defect
on the graphene foam into nanoribbon via plasma etching, using a power of 40 W
for 5 to 20 min.
4 Recent Research Regarding 3D Graphene in Metal-Ion

Batteries—in Terms of Performance
3D graphene material is considered a potential energy conservation material in

various metal-ion battery systems. The previous section describes the process
involved in the fabrication of 3D graphene materials in metal-ion batteries. Subse-
quently, this section further discusses the achievement of the recent research
regarding 3D graphene material in the metal-ion battery system according to the
type of battery, as summarised in Table 3.
4.1 Lithium-Ion Batteries
Several researchers have investigated the improvement of a lithium-ion battery

system by using graphene materials because it has high conductivity, chemical
stability, low lithium reaction, and volume change during lithium intercalation.
However, there are a few limitations of simple graphene applied in the lithium-ion
battery system, such as the weak capacity of graphene in lithium adsorption and the
interaction of lithium in the surface unit area. Therefore, Guo et al. [15] fabricated
3D graphene materials by developing an enhanced defect derivative graphene and
incorporating zinc oxide and magnesium hydroxide as the intermediate nanostruc-
ture layer. The result revealed an improvement in the electrochemical performance
of graphene hollow structure from ∼382 mAh g−1 to ∼2204 mAh g−1 at 0.5 A g−1 .
Further, the initial electrochemical capacity in this study achieved 10,009 mAh g−1
with 83% of retention at 4A g-1 for 500 cycles. The high-rate characterisation at a
rate of 20 A g−1 was ∼330 mAh g−1 .
Cyclability and fast charging function are concerns in this study. Several
researchers have modified the design of cathode and anode with various inventions.
For instance, Son et al. [16] developed a graphene ball in popcorn structure (Fig. 2)
applied as anode and coating on the cathode, demonstrating a high specific capacity
of anode material (716.2 mAh g−1 ), and an incline of capacity at 0.33 Cycle by
27.6% from 49.67 to 63.40 Ah. The commercial cell settling reached 800Wh L−1 in
Table 3 Previous studies with their achievements
220
Method of Product structure Battery Achievement Author

fabrication
CVD Graphene hollow Lithium – Improvement of electrochemical performance from ∼382 mAh g−1 to ∼2204 mAh g−1 Guo et al.
structure (hybrid with at 0.5 A g−1 [15]
ZnO and Mg(OH)2 – Improvement of electrochemical initial capacity at 4A g−1 :10,009 mAh g−1 with 83%
intermediate of retention after 500 cycles
nanostructure layer) – Improvement of high-rate characterisation at the rate of 20 A g−1 : ∼330 mAh g−1
Graphene ball: Hybrid Lithium – High specific capacity of anode material: 716.2 mAh g−1 Son et al.
silica with graphene in – Incline of capacity at 0.33 Cycle: 27.6% from 49.67 to 63.40 Ah, which is potentially [16]
popcorn structure reaching 800Wh L−1 in a commercial cell setting
– High cyclability of capacity retention after 500 cycles: 78.6% at 5 Cycle and 60 °C
CVD, plasma Graphene-nanoribbon Aluminium – Improvement in low charge voltage Yu et al.
etching, on surface of highly – High capacity of freestanding and flexible hybridised graphene foam-based pouch cell: [19]
annealing porous 3D graphene 123 mA hg−1 at 5000 mA g−1
– Excellent cycling ability after 10 000 cycles, which contribute the fast charging (80 s)
and slow discharged (more than 3100 s)
CVD, Multilayer 3D graphene lithium-sulphur – Initial discharge capacity with the cycling performance of lithium/sulphur with 3D Choi et al.
hydrothermal foam: hybrid with graphene oxide after 200 cycles: ~1300 mAh/g at 0.8 A/g with approximately ~80% [23]
sulphur-based material capacity retention
and coated with the – Improvement on the initial capacity with the cycling performance of Lithium/Sulphur
tungsten oxide with the coating of tungsten oxide on the 3D graphene oxide after 500 cycles: 1425 mAh/
g with approximately 95% capacity retention
3D graphene foam: Lithium-Sulphur – Improvement of areal capacity (10.9 mAhr/cm2 ) when applied over sulphur loading He et al.
hybrid with (10.4 mg/cm2 ) and its content (86.9 wt%) [18]
sulphur-based material
(continued)
Table 3 (continued)
fabrication
Graphene foam: hybrid Lithium-sulphur – High specific capacity of MoS2 as outer layer of electrode, high conductivity of carbon Ren et al.
with carbon nanotube nanotubes as middle layer of electrode, and large electrode/electrolyte contact with short [17]
and MoS2 diffusion distance of lithium ions
nanoparticles – Achieved a specific capacity of 935 mAh g−1 at a current density of 0.1 A g−1 , high
reversible capacity of 606 mAh g−1 after 200 cycles at 0.2 A g−1 in the modified 3D
graphene foam electrode
Thermal CVD Vertical graphene Lithium – High specific capacity of LiFePO4 electrode with 3D graphene material at 1C: 150 mAh Ji et al.
sheets on carbon black g−1 with an 88.9% retention even after 1000 cycles [14]
– Achieved 542.8 mAh with 93.3% retention after 400 cycles at 0.2 C by using 1.3 wt % of
modified 3D graphene material assembled with the LiFePO4 electrode and graphite
electrode
Modified Crystal microstructure Potassium – High charge capacity (601.4 mAh g−1 at 100 mA g−1 ), better cycle performance (345.3 Li et al.
Hummer’s of antimony/graphene mAh g−1 at 100 mA g−1 after 100 cycles), and rate capability (255.9 mAh g−1 at [22]
method, composite 800 mA g−1 )
hydrothermal Mesoporous amorphous Lithium – Achieved a high-mass-loading electrodes with high reversible capacity (156 mA h g−1 Mo et al.
and FePO4 nanoparticles under 0.5C), ultra-high-rate capability (76 mA h g−1 under 50C), and outstanding cycle [24]
freeze-drying cross-linked with 3D stability (>95% reversible capacity retention over 500 cycles)
and calcination holey graphene
framework
Modified Hybrids of 3D Sodium – Achieved ultra-high sodium storage capacity (525 mAh g−1 at 30 mA g−1 ), outstanding Liu et al.
Hummer’s graphene with Fe3 O4 cycling stability (312 mAh g−1 after 200 cycles at 50 mA g−1 ), and superior rate [25]
method, performance (56 mAh g−1 at 10 A g−1 )
hydrothermal, SnO2 -GA 3D porous Lithium – A synergistic effect between flexible graphene layers and nano-sized SnO2 improves the Chen et al.
freeze-drying aerogels capacity and cyclic stability [27]
and annealing
(continued)
221
Table 3 (continued)
222

fabrication
Modified 3D Lithium – Discharge-specific capacity and capacity retention of 3D graphene composite at a current Li et al.
Hummer’s, graphene-encapsulated density of 400 mA g−1 : 1139mAh g−1 and 85% capacity retention after 100 cycles [21]
hydrothermal nearly monodisperse – A good cycling stability and high capacity of 3D graphene composite on electrode even
and calcination Fe3 O4 at 1000 mA g−1 : 665 mA h g−1 after 200 cycles
Hummer’s Disc shape: nano Sodium – Achieved a mass capacity of 391.7 mAh g–1 under 0.1 A g–1 , corresponding to 3.11 Zeng et al.
method, reflux, FeSb2 S4 in CNT/ mAh cm–2 of area-capacity and 57.64 mAh cm–3 of volume-capacity [28]
annealing and graphene 3D porous
freeze-drying network
Hydrothermal Microsphere: crystal Potassium and – Achievement of Potassium-ion battery electrode in a half-cell: Liu et al.
process and carbon shell-coated aluminium – Initial capacity with coulumbic efficiency: 297.89 mAh g−1 , 99% after 1250 cycles [26]
roasting Graphene sheets – Achievement of the cathode for an aluminium battery
process – Reversible specific capacity at 1000 mA g−1 : 99.1 mAh g−1
– Retention capacity at 4000 mA g−1 : ~100% after 10 000 cycles
Solvothermal Oxygen-rich graphene sodium – Reversible capability at 0.1 A g−1 : 508.6 mAh g−1 Ma et al.
and 2-step vertically grown on 3D – Superior rate performance at 5.0 A g−1 : 113.3 mAh g−1 remarkable cycle stability at 1.0 [30]
annealing N-doped carbon foam A g−1 : 329.3 mAh g−1 over 1000 cycles
composite
(continued)
Table 3 (continued)
fabrication
Facile spray 3D graphene decorated sodium – Reversible capacity at 0.1 C: 128 mAh g−1 Yuan et al.
drying, ball iron-based – Superior rate capability at 200 C: 35 mAh g−1 [29]
milling, mixed-polyanion – Long cycling life at 10 C: 62.3% capacity retention over 6000 cycles
calcination compound
Na4 Fe3 (PO4 )2(P2 O7 )
microspheres
Modified Ultrathin MoS2 Lithium and – Specific capacities and superior cyclic stability Yuan et al.
Hummer’s, nanosheet/graphene sodium – Lithium at 0.2 A g−1 : 1526 mAh g−1 after 100 cycles [8]
freeze-drying hybrid aerogels
– Sodium at 0.1 A g−1 : 850 mAh g−1 after 100 cycles

and thermal
– Notable rate performance at 1 A g−1
reduction
– Lithium: 865 mAh g−1 ; Sodium: 462 mAh g−1
Pyrolysis Porous monolith of Potassium – Capacity at a current density of 10 A g−1 : 180 mAh g−1 Wang
graphene (also known – Cycling capability at 1 A g−1 : 4000 cycles et al. [7]
as zinc-guided 3D
graphene)
Modified 3D wrinkled N, S Lithium – Reversible capacity: 1150 mA h g−1 after 500 cycles Shi et al.
Hummer’s, co-doped multilayer – high reversible capacity and superior energy density: 151 mA h g−1 and 501 W h kg−1 [31]
pyrolysis graphene sheets after 330 cycles
embedding with SiOx
microparticles
223
Fig. 2 Graphene ball in popcorn structure developed by Son et al. [16] in lithium-ion battery.
Adapted from [16]. Copyright The Authors, some rights reserved; exclusive licensee springer nature
limited. distributed under a creative commons attribution license 3.0 (CCB BY)
this study. That study achieved 78.6% of high cyclability of capacity retention after
500 cycles at 5 Columb (C) and 60 °C.
Similarly, a vertical graphene sheet growth on carbon black in a lithium-
ion battery was studied by Ji et al. [14], who demonstrated a specific capacity
of 150 mAh g−1 with an 88.9% retention at 1C even after 1000 cycles in a lithium iron
phosphate (LiFePO4 ) electrode. Further, there is an achievement in 542.8 mAh with
93.3% retention after 400 cycles at 0.2 C when the soft pack full cell was designed
with 1.3 wt % of modified 3D graphene material assembled with an LiFePO4 and
graphite electrode. Mo et al. [24] achieved a high-mass-loading electrode with high
reversible capacity in a lithium-ion battery, at 156 mA h g−1 under 0.5 C using a
3D holey graphene frameworks cross-linked with encapsulated mesoporous amor-
phous FePO4 nanoparticles. Further, this result also achieved ultra-high-rate capa-
bility (76 mA h g−1 under 50 C) and outstanding cycle stability (>95% reversible
capacity retention over 500 cycles).
A 3D graphene aerogel was modified with the nano-sized Tin Oxide (SnO2 )
to enhance the capacity and cyclic stability, which exhibited the synergistic effect
between the flexible layer of graphene and nano SnO2 particles involved in the
lithium-ion battery [27]. Similarly, Yuan et al. [8] developed an anchor 3D few-
layered molybdenum sulphide (MoS2 ) hybridised with graphene aerogels in the
lithium-ion battery, which achieved 1526 mAh g−1 of specific capacities after 100
cycles. This study revealed the notable electrochemical performance of 865 mAh g−1
at 1 A g−1 . Another researcher reported that 3D graphene could be encapsulated with
monodisperse Fe3 O4 nanoparticles for lithium-ion battery systems, which achieved
1139 mAh g−1 of discharge capacity and 85% capacity retention at 400 mA g−1
after 100 cycles. Further, this study also achieved good cycling and high capacity
(665 mA h g−1 ) at 1000 mA g−1 after 200 cycles when a 3D graphene composite was
applied to the electrode [21]. Additionally, Shi et al. [31] fabricated a novel silicon
oxides (SiOx ) hybridised into 3D wrinkled multilayer graphene sheets, contributing
1150 mA h g−1 of reversible capacity after 500 cycles, along with high reversible
capacity (151 mA h g−1 ) and superior energy density (501 W h kg−1 ) after 330
cycles.
4.2 Lithium Ion-Sulphur
Although lithium-ion batteries have been improved for cathode

materials, there is a limitation in the theoretical capacity of transition metal
oxides cathode (150–170 mAh/g2 ) in commercial lithium-ion batteries. To improve
the theoretical capacity of the cathode, sulphur has been introduced as a commercial
cathode material. However, a few difficulties are related to the use of sulphur as
commercial cathode material, such as polysulphide dissolution in the electrolyte,
the poor electrical and ionic conductivity properties of sulphur, and the changes
of charging with discharging volume. For instance, the polysulphide dissolution
phenomenon is significantly found in 3D graphene materials involved in lithium-
sulphur battery, as investigated by Choi et al. [23]. Owing to the amelioration of
tungsten oxide on the polysulphide and shuttling effect, this study also further
investigated the coating of tungsten oxide on 3D graphene oxide. An improvement
of the initial capacity with the cycling performance of Lithium/Sulphur has been
demonstrated with the coating of tungsten oxide on 3D graphene after 500 cycles
(1425 mAh/g with approximately 95% capacity retention) when compared to the
initial discharge capacity with the cycling performance of lithium/sulphur with
3D graphene after 200 cycles (~1300 mAh/g at 0.8 A/g with approximately ~80%
capacity retention).
Further, He et al. [18] developed a 3D graphene foam material with the hybridisa-
tion of cobalt sulphide and sulphur (Fig. 3) as a cathode in lithium-sulphur batteries,
which achieved a higher areal capacity (10.9 mAhr/cm2 ) when applied over sulphur
loading (10.4 mg/cm2 ) and sulphur content (86.9 wt%). Additionally, the strong
chemical entrapment of sulphur in lithium-ion batteries system is promoted by the
synergistic effect of 3D graphene materials and cobalt sulphide.
Similarly, Ren et al. [17] fabricated a 3D graphene foam hybridised with carbon
nanotube as the middle layer and MoS2 as the outer layer in an electrode for the
3D Cobalt
Graphene sulphide and
foam sulphur
Fig. 3 3D graphene foam hybridised with cobalt sulphide in lithium ion-sulphur battery. Adapted
with permission [18], copyright (2018), elsevier
Carbon nanotubes Molybdenum

Carbon nanotubes
(a) (b) (c)
Fig. 4 a 3D graphene foam, b 3D graphene foam hybridised with carbon nanotube, and c 3D
graphene foam hybridised with carbon nanotube and molybdenum sulphide. Adapted with
permission [17], copyright (2018), elsevier
improvement of lithium-ion battery, as shown in Fig. 4. Due to the high specific

capacity of MoS2 , high conductivity of carbon nanotubes, and large electrode/
electrolyte contact with short diffusion distance of lithium ions, the electrochem-
ical performance of this study achieved a specific capacity of 935 mAh g−1 at a
current density of 0.1 A g−1 , a high reversible capacity of 606 mAh g−1 after 200
cycles at 0.2 A g−1 in the modified 3D graphene foam electrode.
4.3 Aluminium Batteries
Aluminium-ion batteries conventionally offer low discharge voltage and short cycle
life. In order to achieve cutting edge of batteries performance with high power and
energy density, safety, and long cycle life, Yu et al. [19] investigated the plasma
etching of graphene nanoribbons on porous 3D graphene as a cathode in aluminium-
ion batteries. The study revealed that the low charge voltage was improved with a
high capacity of freestanding and flexible hybridised graphene foam-based pouch
cell: 123 mA hg−1 at 5000 mA g−1 . It also demonstrated excellent cycling ability
after 10 000 cycles, contributing to 80 s of fast charging and more than 3100 s of slow
discharge rate in the aluminium-ion battery system. Liu et al. [26] also improved the
aluminium-ion battery using a microsphere which is armoured graphene wrapped
by a crystal carbon shell as illustrated in Fig. 5, which obtained a 99.1 mAh g−1
of reversible specific capacity at 1000 mA g−1 and ~ 100% retention capacity at
4000 mA g−1 after 10 000 cycles.
4.4 Potassium Batteries
Due to the abundance of potassium elements and low electrode potential of

potassium-ion/potassium atom (K+ /K) couple, the electrochemical industry recently
garnered attention on potassium-ion batteries. Although potassium-ion battery is
Fig. 5 Microsphere of 3D
graphene, showing graphene Graphene microsphere
wrapped by a crystal carbon
shell. Adapted with
permission [26], copyright
(2019), American chemical Carbon shell
society
Armour
inexpensive and has high energy density, its ionic radius is larger, which is unfea-
sible in its rapid transport and degradation of potassium storage. To mitigate this
issue, a graphene material, with 279mAhg−1 of theoretical capacity, can be used as
anode material for potassium-ion batteries because it has a larger surface of the inter-
layer, notable electron mobility, and mechanical properties. For the advancement of
graphene materials, antimony can be used to incorporate graphene materials as its
theoretical capacity is 660 mAh g−1 . This can enhance the electrochemical properties
of potassium-ion battery. For instance, a study revealed that the antimony/graphene
with a crystal microstructure exhibited a high charge capacity (601.4 mAh g−1 at
100 mA g−1 ), better cycle performance (345.3 mAh g−1 at 100 mA g−1 after 100
cycles), and rate capability (255.9 mAh g−1 at 800 mA g−1 ) [22].
Further, Liu et al. [26] synthesised a microsphere of crystal carbon shell wrapped
with a graphene sheet, which obtained an initial capacity with a Coulombic effi-
ciency (297.89 mAh g−1 , 99%) after 1250 cycles. Wang et al. [32] fabricated a
porous monolith of graphene as the binder-free anode, which contributed a 180
mAh g−1 of capacity at a current density of 10 A g−1 and 4000 cycles of cycling
capability at 1 A g−1 .
4.5 Sodium-Ion Battery
Sodium-ion batteries have garnered attention in the electrochemical industry because

their theoretical interlinkage and technical inheritance are similar to the lithium-ion
battery, such as inert materials used in the electrode (graphite anodes). However,
Silicon (Si) anode in sodium-ion battery demonstrated lower electrochemical perfor-
mance than Si anode in the lithium-ion battery. Hence, the anode in sodium-ion
battery can be replaced by various materials such as Sodium Chromite (NaCrO2 ),
Sodium Vanadium Phosphate (Na3 V2 (PO4 )3 ), and Maricite (NaFePO4 ). Metal
sulphides are alternatives to anode materials that may offer better electrochemical
properties than monometallic sulphide. In the electrochemical industry, 3D graphene
material is usually incorporated with the novel binary metal sulphide, which can
demonstrate high mass capacity and remarkable cyclability. For instance, Zeng et al.
Fig. 6 Disc shape of anode 3D porous

that consists of carbon
nanotubes/graphene 3D network
porous network hybridised hybridised with
with binary metal sulphide binary metal
(FeSb2 S4 ). Adapted with sulphide
permission [28], copyright
(2021), elsevier
Disc shape
[28] developed a disc shape material that consists of high theoretical binary metal
sulphide (Berthierite, FeSb2 S4 ) hybridised in 3D graphene as an anode (Fig. 6),
which achieved a mass capacity of 391.7 mAh g–1 under 0.1 A g–1 , corresponding
to 3.11 mAh cm–2 of area-capacity and 57.64 mAh cm–3 of volume-capacity.
In addition, 3D graphene was introduced in carbon foam for an
electrode in sodium-ion battery, reaching a reversible capability
at 0.1 A g−1 (508.6 mAh g−1 ), superior rate performance at 5.0 A g−1 (113.3
mAh g−1 ), and remarkable cycle stability at 1.0 A g−1 (329.3 mAh g−1 over
1000 cycles), according to Ma et al. [30]. Yuan et al. [29] fabricated 3D graphene
microsphere hybridised with Na4 Fe3 (PO4 )2 (P2 O7 ) in sodium-ion batteries, which
contributed reversible capacity (128 mAh g−1 ) at 0.1 C, superior rate capability
(35 mAh g−1 ) at 200 C, and long cycling life (62.3% capacity retention over 6000
cycles) at 10 C. Similarly, Yuan et al. [8] developed an anchor 3D few-layered
MoS2 hybridised with graphene aerogels in the sodium-ion battery, which achieved
850 mAh g−1 of specific capacities after 100 cycles. This study revealed notable
electrochemical performance of 462 mAh g−1 at 1 A g−1 .
5 Conclusion, Challenges, and Future Prospects
This chapter discussed the modified 3D graphene in the electrode for each metal-ion
battery. Owing to the superior characteristic of graphene, several research studies
have reported 3D graphene material applied in the metal-ion batteries by hybridising
with additives such as metal oxide, carbon nanotube, sulphur-based materials, and
others involved in metal-ion batteries. Various fabrication processes in graphene
material and its 3D graphene material incorporation method are discussed in this
chapter. After being incorporated with the modified 3D graphene oxide in metal-ion
batteries, most studies reported good electrochemical properties in terms of capacity,
discharge and charging capacity, cycling rate, and reversible capacity. Although 3D
graphene material is a promising dopant in various applications, there are a few
challenges in terms of economics. The main challenge in this study is the produc-
tion of 3D graphene, including the several processes involved in the synthesis of
3D graphene. Subsequently, the cost of production increases. Further, the cost of
graphene also depends on the purity and crystallinity of graphene. For 3D graphene
material involved in metal-ion batteries, the other concerns include product cost and
portability, and the battery design’s size since it is still not commercialised in the
market.
Although most metal-ion batteries performed good electrochemical properties
using modified 3D graphene material for sustainable energy, the metal-ion resources
could be depleted, especially lithium-ion. Further, there are the difficulties afore-
mentioned regarding the graphene material in the market. Owing to this issue, there
are a few suggestions required to implement in the future as follows:
(a) Recycle metal ions if possible.
(b) Seek for alternatives of metal ion for the design of a dischargeable battery.
(c) Continue investigation on alternatives for graphene material as it is costly.
(d) Investigate sustainable resources for metal-ion batteries.
In short, this review has provided the overview of types of metal-ion batteries,
the fabrication of 3D graphene material, and the recent development of 3D graphene
material involved in metal-ion batteries.
References
1. Liu, Y., Holze, R.: Metal-ion batteries. Encyclopedia 2(3), 1611–1623 (2022)
2. Hou, D., Xia, D., Gabriel, E., Russell, J.A., Graff, K., Ren, Y., Sun, C.J., Lin, F., Liu, Y., Xiong,
H.: Spatial and temporal analysis of sodium-ion batteries. ACS Energy Lett. 6(11), 4023–4054
(2021)
3. Li, Y., Lu, Y., Adelhelm, P., Titirici, M.M., Hu, Y.S.: Intercalation chemistry of graphite: alkali
metal ions and beyond. Chem. Soc. Rev. 48(17), 4655–4687 (2019)
4. Zhan, C., Wu, T., Lu, J., Amine, K.: Dissolution, migration, and deposition of transition metal
ions in Li-ion batteries exemplified by Mn-based cathodes-a critical review. Energy Environ.
Sci. 11(2), 243–257 (2018)
5. Zhang, X.Q., Wang, X.M., Li, B.Q., Shi, P., Huang, J.Q., Chen, A., Zhang, Q.: Crosstalk
shielding of transition metal ions for long cycling lithium-metal batteries. J. Mater. Chem. A
8(8), 4283–4289 (2020)
6. Husmann, S., Zarbin, A.J.G.: Cation effect on the structure and properties of
hexacyanometallates-based nanocomposites: improving cathode performance in aqueous
metal-ions batteries. Electrochim. Acta 283(2018), 1339–1350 (2018)
7. Wang, Q., Wang, Y., Zeng, J., Zhang, C., Liu, P., Hao, T., Ding, R., Jiang, X., Zhang, Y., Da, B.,
Liu, J., Hong, G., Xu, W., Meng, Z., Wang, X.B.: Zinc-guided 3D graphene bulk materials for
high-performance binder-free anodes of potassium-ion batteries. J. Power Sources 540(2022),
231613 (2022)
8. Yuan, J., Zhu, J., Wang, R., Deng, Y., Zhang, S., Yao, C., Li, Y., Li, X., Xu, C.: 3D few-
layered MoS2 /graphene hybrid aerogels on carbon fiber papers: a free-standing electrode for
high-performance lithium/sodium-ion batteries. Chem. Eng. J. 398(2020), 125592 (2020)
9. Verma, J., Kumar, D.: Metal-ion batteries for electric vehicles: current state of the technology,
issues and future perspectives. Nanoscale Adv. 3(12), 3384–3394 (2021)
10. Ali, A., Liang, F., Zhu, J., Shen, P.K.: The role of graphene in rechargeable lithium batteries:
synthesis, functionalisation, and perspectives. Nano Mater. Sci. 2022, 2–19 (2022)
11. Ma, J., Yang, C., Ma, X., Liu, S., Yang, J., Xu, L., Gao, J., Quhe, R., Sun, X., Yang, J., Pan,
F., Yang, X., Lu, J.: Improvement of alkali metal ion batteries: via interlayer engineering of
anodes: from graphite to graphene. Nanoscale 13(29), 12521–12533 (2021)
12. Chang, H.-H., Ho, T.-H., Su, Y.-S.: Graphene-enhanced battery components in rechargeable
lithium-ion and lithium metal batteries. J. Carbon Res. 7(65), 1–28 (2021)
13. Chen, K., Shi, L., Zhang, Y., Liu, Z.: Scalable chemical-vapour-deposition growth of three-
dimensional graphene materials towards energy-related applications. Chem. Soc. Rev. 47(9),
3018–3036 (2018)
14. Ji, X., Mu, Y., Liang, J., Jiang, T., Zeng, J., Lin, Z., Lin, Y., Yu, J.: High yield production of
3D graphene powders by thermal chemical vapor deposition and application as highly efficient
conductive additive of lithium ion battery electrodes. Carbon 176(2021), 21–30 (2021)
15. Guo, H., Long, D., Zheng, Z., Chen, X., Ng, A.M.C., Lu, M.: Defect-enhanced performance
of a 3D graphene anode in a lithium-ion battery. Nanotechnology 28(2017), 505402 (2017)
16. Son, I.H., Park, J.H., Park, S., Park, K., Han, S., Shin, J., Doo, S.G., Hwang, Y., Chang, H., Choi,
J.W.: Graphene balls for lithium rechargeable batteries with fast charging and high volumetric
energy densities. Nat. Commun. 8(1561), 1–10 (2017)
17. Ren, J., Ren, R.P., Lv, Y.K.: A flexible 3D graphene@CNT@MoS2 hybrid foam anode for
high-performance lithium-ion battery. Chem. Eng. J. 353(2018), 419–424 (2018)
18. He, J., Chen, Y., Manthiram, A.: MOF-derived cobalt sulfide grown on 3D graphene foam as
an efficient sulfur host for long-life lithium-sulfur batteries. IScience 4, 36–43 (2018)
19. Yu, X., Wang, B., Gong, D., Xu, Z., Lu, B.: Graphene nanoribbons on highly porous 3D
graphene for high-capacity and ultrastable Al-Ion batteries. Adv. Mater. 29(4), 1604118 (2017)
20. Paramasivan, T., Sivarajasekar, N., Muthusaravanan, S., Subashini, R., Prakashmaran, J., Siva-
mani, S., Koya, P.A.: Chapter 13: gaphene family materials for the removal of peticides from
water. In: Naushad, M. (ed.) A New Generation Material Graphene: Applications in Water
Technology. Springer International Publishing, Switzerland (2018)
21. Li, L., Wang, H., Xie, Z., An, C., Jiang, G., Wang, Y.: 3D graphene-encapsulated nearly
monodisperse Fe3 O4 nanoparticles as high-performance lithium-ion battery anodes. J. Alloy.
Compd. 815(2020), 152337 (2020)
22. Li, W., Gao, N., Li, H., Sun, R., Wu, J., Chen, Q.: A novel method to prepare Sb/graphene
composite with high capacity for potassium-ion batteries. Mater. Lett. 319(2022), 132259
(2022)
23. Choi, S., Seo, D.H., Kaiser, M.R., Zhang, C., Van Der Laan, T., Han, Z.J., Bendavid, A., Guo,
X., Yick, S., Murdock, A.T., Su, D., Lee, B.R., Du, A., Dou, S.X., Wang, G.: WO3 nanolayer
coated 3D-graphene/sulfur composites for high performance lithium/sulfur batteries. J. Mater.
Chem. A 7(9), 4596–4603 (2019)
24. Mo, R., Rooney, D., Sun, K., Wang, J.N.: 3D holey-graphene frameworks cross-linked
with encapsulated mesoporous amorphous FePO4 nanoparticles for high-power lithium-ion
batteries. Chem. Eng. J. 417(2021), 128475 (2021)
25. Liu, H., Jia, M., Zhu, Q., Cao, B., Chen, R., Wang, Y., Wu, F., Xu, B.: 3D–0D graphene-Fe3 O4
quantum dot hybrids as high-performance anode materials for sodium-ion batteries. ACS Appl.
Mater. Interfaces 8(40), 26878–26885 (2016)
26. Liu, Z., Wang, J., Jia, X., Li, W., Zhang, Q., Fan, L., Ding, H., Yang, H., Yu, X., Li, X., Lu,
B.: Graphene armored with a crystal carbon shell for ultrahigh-performance potassium ion
batteries and aluminum batteries. ACS Nano 13(9), 10631–10642 (2019)
27. Chen, Z., Li, H., Tian, R., Duan, H., Guo, Y., Chen, Y., Zhou, J., Zhang, C., Dugnani, R.,
Liu, H.: Three dimensional Graphene aerogels as binder-less, freestanding, elastic and high-
performance electrodes for lithium-ion batteries. Sci. Rep. 6(2016), 27365 (2016)
28. Zeng, T., Li, Z., Feng, D., Zhu, Y.: Confining nano FeSb2 S4 in carbon nanotube/oxide graphene
3D porous networks for high-capacity sodium ion battery anode. J. Alloy. Compd. 884(2021),
161116 (2021)
29. Yuan, T., Wang, Y., Zhang, J., Pu, X., Ai, X., Chen, Z., Yang, H., Cao, Y.: 3D graphene decorated
Na4Fe3(PO4)2(P2O7) microspheres as low-cost and high-performance cathode materials for
sodium-ion batteries. Nano Energy 56(2018), 160–168 (2019)
30. Ma, X., Ji, C., Liu, Y., Yu, X., Xiong, X.: Oxygen-rich graphene vertically grown on 3D N-
doped carbon foam for high-performance sodium ion batteries. J. Power Sources 530(2021),
231292 (2022)
31. Shi, L., Li, Y., Xing, Y., Lin, R., Cheng, G., Ding, J., Lam, K.H.: SiOx microparticles embedded
into 3D wrinkled N, S co-doped multilayer graphene sheets as a high-performance anode for
long-life full lithium-ion batteries. Electrochim. Acta 390(2021), 138841 (2021)
3D Graphene for Metal–Air Batteries
Runwei Mo and Yuan An
Abstract In recent years, metal–air batteries have attracted extensive research owing
to their extremely high theoretical energy density. However, the bottleneck problem
of current metal–air batteries is the slow kinetics of oxygen reduction reaction cata-
lysts. Recently, graphene has been widely used in metal–air batteries owing to its
many active sites, excellent electrical conductivity, and large specific surface area.
To meet the requirements of practical applications, three-dimensional (3D) graphene
structures are prepared from two-dimensional graphene nanosheets through various
assembly methods, which can tune their mechanical stability, electrochemical proper-
ties, and catalytic performance. 3D graphene can act as a catalyst carrier in metal–air
batteries, which can not only improve its long-term stability and catalytic activity
but also reduce the amount of active components. It is worth noting that the proper-
ties of 3D graphene can be further optimized by functionally modifying the surface
of graphene. In this chapter, we describe the synthesis techniques of 3D graphene
and summarize the properties and functional modifications of 3D graphene. Then
we focus on the latest research progress and status of 3D graphene in metal–air
batteries. Finally, future directions for enhancing the electrochemical properties of
3D graphene-based metal–air batteries prospect.
Keywords Graphene · Metal–air battery · Structural design · Oxygen reduction

reaction · Catalyst
1 Introduction
With the rapid development of society, the sustainable development of energy has
an increasingly important impact on the survival and development of human beings.
Due to the non-renewable nature of the traditional energy structure dominated by
fossil fuels, it is necessary to urgently develop new energy conversion and storage
R. Mo (B) · Y. An
School of Mechanical and Power Engineering, East China University of Science and Technology,
Shanghai, China
e-mail: rwmo@ecust.edu.cn
https://doi.org/10.1007/978-3-031-36249-1_13
234 R. Mo and Y. An
systems with sustainable development. As a representative energy storage device

in the field of new energy, secondary batteries are more and more widely used in
mobile electronic equipment, electric vehicles, and other fields. Among them, metal–
air batteries (MABs) have attracted extensive attention owing to their ultra-high
theoretical energy density, which makes them promising candidates for vehicle power
sources or large-scale energy storage stations [1–3].
As one of the representatives of high energy density energy storage and conversion
systems, MABs use metals with negative electrode potential, such as zinc, iron,
magnesium, aluminum, and mercury, and the gas in the air is used as the active
material of the positive electrode. Generally speaking, the main components of MABs
are divided into air cathode, metal anode, current collector, electrolyte with separator,
and gas diffusion layer. Different from the fully closed system of metal–ion batteries,
the cathode reactant in MABs is the gas component in the air, which leads to the
characteristics of the semi-open system of the battery [4, 5]. It is worth noting that
the current cathodes of MABs containing alkali metals are usually studied in the
environment of pure O2 , which is mainly attributed to the fact that various components
in the air can easily make the reaction mechanism difficult to distinguish, and even
some components can cause undesirable side reactions [6, 7].
MABs are classified in a number of different ways. According to the different types
of electrolytes, MABs can be classified into four types: non-aqueous, aqueous, solid-
state, and mixed-mode. In addition, according to the different types of anode metals,
MABs can also be divided into the following types: zinc––air batteries, lithium–air
batteries, magnesium or aluminum–air batteries, sodium or potassium–air batteries,
etc. It is worth noting that different kinds of MABs have their own unique advan-
tages. Compared with aqueous MABs, non-aqueous MABs tend to have the advan-
tages of higher discharge platforms, wider electrochemical windows, and higher
energy densities. Compared with non-aqueous MABs, aqueous MABs generally
have the advantages of lower fabrication costs, more environmental protection, and
faster mass transfer rates. Furthermore, solid MABs tend to have a more pronounced
advantage in preventing fire risks and liquid leakage compared to liquid electrolytes.
Different kinds of MABs have similar problems, which are mainly attributed to their
similar working principles and electrode reaction pairs. The main factors hindering
the improvement of the electrochemical properties of MABs are the slow kinetics
of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In
order to solve the above problems, the development of cathode materials with large
specific surface area, high electronic conductivity, sufficient active sites, and hier-
archical pore structure is an effective way to further enhance the electrochemical
properties of MABs [8–10].
Recently, graphene has been widely used in MABs due to its many active sites,
excellent electrical conductivity, and large specific surface area. As we all know,
graphene was successfully prepared for the first time in 2004 and has attracted exten-
sive research interest in many fields owing to its outstanding chemical and physical
properties [11–13]. More importantly, the electrochemical properties, mechanical
stability, and catalytic performance can be regulated by functional modification of
the graphene surface, such as porous structure design, heteroatom doping, and defect
3D Graphene for Metal–Air Batteries 235
fabrication [14–20]. On the one hand, more active sites can be provided by the design
of porous structures. On the other hand, the kinetics of ORR and OER can be enhanced
by heteroatom doping and defect fabrication. In order to meet the requirements of
practical applications, three-dimensional (3D) graphene structures are prepared from
two-dimensional (2D) graphene nanosheets through various assembly methods. It
is worth noting here that 3D graphene is considered an ideal cathode material for
MABs due to its abundant defects, hierarchical pore structure, and selective doping
of atoms. Equally important, 3D graphene has a unique three-dimensional connected
conductive network structure, which can provide an efficient transport path for metal
ions and gas molecules, low charge transfer resistance, and can be used for the storage
space of solid discharge products on the air electrode side. In this chapter, the latest
research results of 3D graphene as a key material in the field of MABs are summa-
rized. Based on an in-depth understanding of the reaction mechanism of ORR and
OER, the synthesis strategies of 3D graphene are mainly introduced, and the prop-
erties and functional modifications of 3D graphene are summarized. In addition, the
latest research results of 3D graphene as cathode materials in the field of MABs are
summarized. Finally, future directions for enhancing the electrochemical properties
of 3D graphene-based MABs prospect.
2 Synthesis of 3D Graphene
2.1 Chemical Reduction Self-Assembly Method
Chemical reductive self-assembly is a common method for preparing 3D graphene-

based materials. The basic principle is that the raw graphene oxide (GO) is first
reduced to reduced graphene oxide (rGO) by using a reducing agent (such as
NaHSO3 , sodium ascorbate, vitamin C, Na2 S, etc.) under low-temperature heating
conditions, and then its self-assembly is controlled to form a 3D graphene. Sheng et al.
successfully prepared 3D graphene hydrogels by chemical reduction self-assembly
method [21]. The specific steps are to use sodium ascorbate as the reducing agent
and GO as the precursor. The homogeneous suspension was obtained by ultrasonic
treatment first, and then the self-assembly process was carried out at a certain reaction
temperature. The results showed that the optimum concentration of GO suspension
was 2.0 mg·mL−1 , and the optimum reaction temperature and time were 90 °C and
1.5 h, respectively. The chemical reduction treatment reduces the oxygen-containing
functional groups of GO and restores the conjugated structure. On the one hand, it
leads to a large number of π–π bonding sites and strong mutual adsorption force on
the rGO surface, and on the other hand, it enhances the hydrophobicity of the rGO
sheet. The synergistic effect of the above two aspects promotes the self-assembly of
rGO sheets to form 3D graphene hydrogels. The chemical reduction self-assembly
method to prepare 3D graphene-based materials has the advantages of a simple
process and no harsh preparation conditions such as high temperature and high
236 R. Mo and Y. An
pressure. The self-assembly process and morphology of the product rGO can be
precisely regulated by controlling the concentration of the raw GO suspension, the
amount of the reducing agent, the reaction time, and other process conditions. The
three-dimensional graphene-based material prepared by this method has outstanding
mechanical properties and electrical conductivity, but its surface oxygen-containing
functional groups are difficult to be completely removed, resulting in its electrical
conductivity failing to reach the theoretical value.
2.2 Hydrothermal Reduction Self-Assembly Method
The hydrothermal reduction self-assembly method is mainly used to prepare 3D

graphene materials with a three-dimensional network structure. The preparation
principle of this method is to first place a suspension of GO or rGO in a sealed
autoclave. Then, by controlling the pressure, temperature, time, and concentration of
reactants in the hydrothermal process, GO or rGO was self-assembled to form a three-
dimensional graphene material. Xu et al. successfully prepared three-dimensional
graphene by hydrothermal reduction self-assembly method [22]. Specifically, the
GO suspensions with concentrations of 0.5, 1.0, and 2.0 mg·mL−1 were heated to
180 °C in the reactor and kept for 1 to 12 h. In this process, the hydrothermal reduc-
tion conditions, on the one hand, are the introduction of interlayer conjugated struc-
tures and high-density bonding (π-stacking) sites into the graphene sheets, thereby
improving the π–π bonding force between graphene sheets and the structural stability
of the product. On the other hand, the oxygen-containing functional groups on the
GO sheets were reduced to exhibit hydrophobic properties. Under the synergistic
effect of hydrophobicity and π–π bonds, the GO nanosheets self-assembled to form
a 3D graphene hydrogel with a cross-linked structure. Its strength and conductivity
increased with the increase of the concentration of the raw GO suspension and the
reaction time. It is worth noting that the storage modulus of the material is as high
as 490 kPa, and the corresponding conductivity is as high as 0.5 S·m−1 . Overall, the
process of preparing 3D graphene materials by hydrothermal reduction self-assembly
is relatively simple. However, this method requires harsh preparation conditions such
as high pressure, high temperature, and long incubation time and requires the concen-
tration of GO suspension to be higher than 2.0 mg·mL−1 . More importantly, the
self-assembly process of this method is realized by physical binding force, which is
often prone to the problem of poor structural stability.
2.3 Freeze-Drying Self-Assembly Method
The basic principle of the freeze-drying self-assembly method is to freeze the GO

suspension or rGO after self-assembly to promote the formation of solid organic
molecules or the growth of ice crystals. Then, the ice or solid organic molecules
are sublimated and escaped by vacuum drying, thereby obtaining three-dimensional

graphene with a porous structure. Jung et al. successfully prepared 3D graphene mate-
rials with hierarchical pore structures by freeze-drying self-assembly method [23].
Specifically, a suspension of sheet-like graphene was first prepared by an electro-
chemical exfoliation method and then self-assembled to form a 3D graphene hydrogel
by a sol–gel method. Finally, 3D graphene can be obtained by freeze-drying. The
results show that the pore structure and size distribution of the product 3D graphene
can be effectively controlled by adjusting the aspect ratio of the exfoliated graphene
sheets and the temperature of the freeze-drying treatment. The three-dimensional
graphene aerogel prepared by this method has the advantages of high porosity,
low density, large specific surface area, and high electrical conductivity, which is
beneficial to the high-speed diffusion of electrolyte ions and the rapid transport of
electrons.
In addition, this method can also be used to prepare 3D graphene-based compos-
ites. Xie et al. successfully prepared platinum or platinum–carbon-supported 3D
graphene composites by freeze-drying self-assembly method [24]. Specifically, GO,
carbon black, potassium tetrachloroplatinate, and ascorbic acid were used as raw
materials, which were sequentially subjected to heat treatment at 90 °C for 3 h and
rapid freeze-drying treatment to finally obtain 3D graphene-based composites. In
the above-mentioned platinum–carbon/3D graphene composite formation process,
the presence of carbon black effectively separates the clusters formed by graphene
and platinum nanoparticles, thereby helping to improve platinum atom utilization
and catalytic graphitization effect. In addition, the wrinkled graphene structure in
the platinum–carbon/3D graphene composite increases the specific surface area and
the density of active sites, which is beneficial to improve the electrocatalytic activity
of platinum for reactions such as methanol oxidation. Although the freeze-drying
self-assembly method has certain requirements in the vacuum environment, the 3D
graphene-based materials prepared by this method generally have the characteristics
of high porosity, high specific surface area, tunable pore size distribution, and high
electrical conductivity.
2.4 Template Self-Assembly Method
Template self-assembly is an effective method to prepare 3D graphene materials with

regular pore structures. For example, polystyrene colloid or silica colloid is used as
the sacrificial template, and potassium hydroxide, hydrofluoric acid, or tetrahydro-
furan are used as the corresponding template etchant, respectively [25–28]. Huang
et al. successfully synthesized 3D graphene foams with porous nanostructures using
a template self-assembly method [25]. Specifically, silica nanoparticles with methyl
groups were used as templates, which were sequentially soaked in GO suspension
and heat-treated at 900 °C for 5 h under an argon atmosphere. Then, the 3D graphene
material was collected by hydrofluoric acid etching treatment. Among them, silica
nanoparticles modified by methyl groups with hydrophobic properties can not only
238 R. Mo and Y. An
serve as templates for the preparation of graphene foams but also interact with
hydrophobic GO nanosheets. Therefore, the modified silica nanoparticles can inhibit
the agglomeration of GO nanosheets and promote the formation of porous nanostruc-
tures. The research results show that the pore size range of the 3D graphene foams
prepared by this method is 30–90 nm, and the pore density and specific surface area
are as high as 4.3 cm3 ·g−1 and 851 m2 ·g−1 , respectively.
In addition, Kim et al. also successfully prepared 3D graphene foams using a
similar method [27]. Specifically, GO-coated silica nanomaterials with a core–shell
structure were prepared by utilizing the interaction between the amphiphilicity of
GO and the hydrophobicity of methyl groups on the template surface. Then, the
3D graphene foams with porous nanostructures were obtained by successive treat-
ments such as centrifugal collection, condensation, and hydrofluoric acid etching.
The process of preparing 3D graphene materials using silica as a sacrificial template
is relatively simple. It is worth noting that the pore structure, pore order, and pore size
of the product can be effectively regulated by controlling the size of the template.
However, the main disadvantage of this method is that the sacrificial template is
difficult to be completely removed, and the prepared 3D graphene is prone to plastic
cracking.
2.5 3D Printing Method
3D printing is an additive manufacturing method that prints raw materials into

materials with specific shapes and sizes based on three-dimensional digital models
[29]. Zhu et al. successfully synthesized 3D graphene-based composites through 3D
printing. [30] Specifically, a mixed solution of 12.5 wt.% graphene nanosheets (GN),
3.3 wt.% GO, 4.2 wt.% SiO2 , and resorcinol–formaldehyde (R-F) were used as the
printing ink, which was successively formed by direct writing, gelation, supercrit-
ical drying, carbonization, and etching to obtain GO/GN composite aerogels. It is
worth noting that pre-soaking the printing ink in isooctane solution helps the ink to
remain wet during the gelation and printing process, which avoids the deformation or
cracking of the printing material during the freeze-drying process. The results show
that the addition of SiO2 and GN can synergistically improve the yield strength and
storage modulus of printing ink. The electrical resistance of the GO/GN composite
aerogel prepared by this method is only 0.96 Ω·sq−1 and the specific surface area is
as high as 418 m2 ·g−1 . The results show that the material has the characteristics of
a large specific surface area, low density, and high electrical conductivity and has
application prospects in many fields. The direct writing molding method has the char-
acteristics of a wide selection of raw materials, low cost, high preparation efficiency,
and good shape controllability of the product. However, there are problems such as
strict requirements on the rheological properties of the ink and subsequent heat treat-
ment of the printing materials. The quality of printing ink (including core evaluation
indicators such as rheological properties and solid content) is the key to determining
the performance of direct-write molding products. By increasing the solid content
of the ink, that is, the concentration of the GO suspension, not only the rheolog-
ical properties of the ink can be enhanced, but also the volume and shape changes
of the printed material during post-processing can be effectively reduced. The 3D
graphene-based composites prepared by direct writing generally have outstanding
mechanical properties and electrical conductivity.
3 Properties of 3D Graphene
The 3D graphene prepared by the above various self-assembly methods exhibits

excellent properties, including large surface area and pore volume, high electrical
conductivity, low density, and good mechanical properties. Compared with 3D
graphene assembled by physical bonding, 3D graphene assembled by chemical
bonding exhibits better properties, such as higher electrical conductivity, lower
contact resistance, and better mechanical stability. The analytical reason is that cross-
linking easily occurs between the functional groups on the edge and the GO surface
during the self-assembly process through chemical bonding. In addition, the process
of preparing 3D graphene by the self-assembly method is very versatile, and the
microstructure and macrostructure can be regulated by changing the experimental
conditions [31]. For example, the porosity and pore size of 3D graphene can be tuned
by changing the size of the template. The number of graphene layers and the solu-
tion concentration also have a great influence on the density of 3D graphene. Higher
graphene solution concentrations lead to an increase in the density of 3D graphene,
which results in larger changes in the density, mechanical strength, and electrical
conductivity of 3D graphene.
The microstructure and properties of 3D graphene can be optimized by changing
the preparation conditions. For example, in the process of preparing 3D graphene
by freeze-drying self-assembly, the freezing temperature plays an important role
in the microstructure and properties of 3D graphene [32]. The results show that
when the freezing temperature is decreased from −10 to −170 °C, the pore wall
thickness and pore diameter decrease by 4000 times and 80 times, respectively. The
water absorption properties of 3D graphene largely depend on its average pore size.
Generally, the water absorption property of 3D graphene requires its pore size to be
less than 150 μm, while the waterproof property of 3D graphene requires its pore
size to be larger than 300 μm. To achieve water absorption in the central region of
3D graphene and water resistance in the edge region of 3D graphene, it is necessary
to control the pore size between 150 and 300 μm. The regulation of the water-
absorbing and waterproof properties of 3D graphene can expand the application
of graphene materials in other fields. Furthermore, the pore morphology is also
greatly altered, enabling a transition from an anisotropic layered architecture to a
homogeneous cellular architecture. By manipulating the 3D graphene microstructure,
Young’s modulus was increased from 13.7 kPa to 204.4 kPa. In a word, the properties
of 3D graphene can be adjusted in various ways, which can meet the requirements
of graphene materials in different application fields.
240 R. Mo and Y. An
4 Functional Modifications
It is well known that graphene generally exhibits poor catalytic activity, which
is mainly attributed to its intrinsic structure. To effectively improve its catalytic
activity, it is necessary to optimize the surface chemistry and atomic composition of
graphene through functional modification. The electron density polarization at this
carbon-heteroatom bond can be constructed by heteroatom doping of the graphene
honeycomb lattice. More importantly, the sp2 bond state can be effectively recon-
structed by heteroatom doping treatment and the intrinsic electronic structure can be
optimized, which is beneficial to provide more active sites [33]. On the one hand,
functional modification of graphene can tune its interface and surface behavior. On
the other hand, new functions can also be induced through the synergistic effect
between multiple species. Therefore, functional modification plays an important
role in optimizing the properties and functions of 3D graphene.
4.1 Heteroatom Doping
The electronic structure and properties of graphene can be optimized by doping its
crystal structure with heteroatoms, which can effectively improve its electrochem-
ical activity. In recent years, researchers have carried out a series of research work
on the heteroatom doping of 3D graphene, such as N, B, S, P, and other element
doping [34–36]. In order to perform heteroatom doping in 3D graphene, the corre-
sponding precursors are usually introduced during the preparation of 3D graphene.
For example, Mei et al. successfully prepared ultra-high-level P-doped 3D graphene
materials. [34] The principle of this doping method is to sacrifice the heterostruc-
tured 2D black phosphorus on graphene to achieve P doping with a P content of
4.84%. The whole preparation process is mainly divided into three parts, the first
part is the liquid exfoliation of GO and black phosphorus bulk. The second part is
the construction of 2D-2D BPN/GO heterostructures. The third part is the formation
of ultra-high-level P-doped 3D graphene materials by sacrificing BPNs to GO under
hydrothermal reaction conditions. It is worth noting that the reason for the prepa-
ration of high-level P-doped 3D graphene materials is the stable and abundant C-P
bonds.
In addition, to achieve the purpose of co-doping, it is necessary to introduce
precursors containing a variety of different heteroatoms during the preparation of
3D graphene [37]. The results show that the co-doping treatment of 3D graphene
significantly improves its electrochemical performance, which is mainly attributed to
the synergistic effect between different heteroatoms. Recently, Yu et al. successfully
synthesized P and S co-doped 3D graphene using thioglycolic acid and phytic acid
as heteroatom precursors [38]. Specifically, the researchers used HI chemical reduc-
tion to synthesize modified 3D graphene under hydrothermal reaction and freeze-
drying conditions. Then, co-doping of S and P was achieved in 3D graphene under
thermal treatment conditions. In addition to the above metal-free heteroatom co-

doping, researchers also successfully synthesized non-metal and metal co-doped 3D
graphene using corresponding precursors [39]. Qiu et al. successfully achieved Ni
and N co-doping in graphene [39]. The results showed that the loading of Ni was as
high as 23 wt%, which was mainly attributed to the promotion of Ni doping by the
pre-doping of N.
4.2 Single Dispersion of Metal Atoms
In order to achieve maximum atom utilization efficiency, single-atom catalysts in

which metal atoms are dispersed on a substrate have attracted extensive attention in
recent years [40]. 3D graphene is an ideal substrate for the synthesis of single-atom
catalysts due to its unique three-dimensional continuous network structure. On the
one hand, 3D graphene as a substrate can provide a large specific surface area to
expose more active metal sites. On the other hand, 3D graphene as a substrate can
provide heteroatom centers to anchor metal atoms. Mou et al. successfully synthe-
sized Ni-based single-atom catalysts on N-doped 3D graphene substrates using an
impregnation-pyrolysis strategy [41]. In this synthetic strategy, 3D graphene was
prepared using 3D porous melamine foam as a template. During the pyrolysis process,
highly dispersed Ni single atoms were successfully loaded on N-doped 3D graphene
substrates through the combined action of nitrogen anchoring and atomic trapping.
Hu et al. also successfully loaded a single iron atom into 3D N,S co-doped graphene
through a similar strategy [42]. Notably, the as-prepared 3D graphene-based single-
atom catalysts were used as electrode materials for Li-CO2 batteries, which exhibited
excellent electrochemical performance. The results show that the potential gap of this
electrode material is only 1.17 V under a current density of 100 mA g−1 . More impor-
tantly, when the current density is increased to 1 A g−1 , the charge–discharge cycles
of the electrode material can still reach 200 times. The electrode material exhibits
excellent electrochemical properties, which is mainly attributed to the synergistic
effect between the presence of “Fe-N4” moieties in the 3D graphene substrate and
the spin and charge redistribution generated by N,S co-doping.
4.3 Compositing with Other Active Species
Besides the two strategies mentioned above, constructing 3D graphene-based

composites by combining the advantages of multiple components is another effective
strategy to significantly enhance their performance. The 3D graphene has a hierar-
chical pore structure and good electrical conductivity, which makes it a support mate-
rial that can significantly improve electron mobility and ion diffusion rates. In recent
years, researchers have carried out a lot of work on 3D graphene-based composites,
242 R. Mo and Y. An
such as polymers, metals, and their compounds, and MXenes [43–47]. Sun et al. inno-
vatively designed a two-step process to successfully synthesize 3D graphene/niobium
pentoxide composites [43]. The research results show that the composite material
exhibits excellent fast-charging characteristics. The reason for the analysis is that the
hierarchical porous structure and 3D graphene network structure in this composite
provide fast ion diffusion channels and electron transport channels, respectively.
Zhong et al. innovatively designed a hydrazine hydrate vapor reduction strategy
to successfully synthesize polyurethane/rGO composite foam [44]. The composite
material exhibits the function of a micro switch, which realizes the regulation of
the number and contact area of its equivalent circuit. An in-depth analysis of the
reason for this revealed that the composite had a unique wrinkle and burr structure.
The composite exhibits excellent performance as a flexible piezoresistive sensor,
such as high sensitivity, fast response, wide sensitive pressure range, and excel-
lent durability. Chen et al. innovatively proposed a GO-assisted self-convergence
method to successfully prepare the composite structure of Ti3 C2 Tx /3D graphene
[45]. During the self-assembly process, GO was partially reduced by Ti3 C2 Tx , which
facilitated the self-assembly of 2D graphene nanosheets to form a 3D connected
network architecture. Furthermore, the interfacial interaction occurred between GO
and Ti3 C2 Tx during the self-assembly process, which also facilitated the uniform
loading of Ti3 C2 Tx in the 3D graphene structure. To further improve its perfor-
mance, 3D graphene can also be treated with heteroatom doping, which can exploit
the synergistic effect between active species and heteroatoms. Recently, Zhou et al.
successfully supported Pt nanoparticles on 3D nitrogen-doped graphene by electro-
chemical deposition. The composite exhibits excellent electrochemical performance,
which is mainly attributed to the synergistic effect between Pt nanoparticles and
nitrogen atoms [46].
5 Recent Developments in Metal–Air Batteries
MABs play an important role in next-generation energy conversion and storage

systems owing to their ultra-high theoretical energy density. For example, when
lithium metal is used as the metal electrode, the energy density of the battery is even
comparable to that of petroleum, and its theoretical energy density can be as high
as 11,680 W h kg−1 . The electrochemical properties of the air battery system with
lithium metal as the metal electrode is largely dependent on the cathode material.
After many charge–discharge cycles in this battery system, the cathode material is
prone to the problem of accumulation of a large number of discharge by-products.
This not only reduces the gas transport efficiency of the cathode material but also
causes passivation of the electrode, which greatly reduces the electrochemical prop-
erties of the battery. In order to solve the above problems, it is urgent to develop suit-
able cathode materials, which are of great significance for the development of high-
performance lithium–air batteries. 3D graphene has the characteristics of hierarchical
pore architecture, high electrical conductivity, large specific surface area, and inter-
connected network structure, which make it an ideal catalyst substrate for lithium–air
batteries. In recent years, Wu et al. innovatively designed a 3D graphene-based N-
doped carbon nitride composite and tested it as a cathode material for lithium–air
batteries. [48] The results show that the composite material exhibits excellent elec-
trochemical performance. In particular, the overpotential and reversible capacities of
the composite are 430 mV and 8892 mA h g−1 , respectively, under the test conditions
of a current density of 1000 mA g−1 . An in-depth analysis of the reasons found that
there are mainly two factors. On the one hand, the introduction of N atoms in the
composite increases the number of active sites, which is beneficial to promote the
kinetic rate of the electrochemical reaction. On the other hand, the 3D graphene in
the composite has a unique connected network structure, which provides sufficient
reaction space for active substances.
In addition to MABs based on organic electrolyte systems, MABs based on
aqueous electrolyte systems have attracted widespread attention in recent years owing
to their high safety and low cost. Among them, the air battery system based on the
aqueous electrolyte with zinc metal as the metal electrode has the characteristics of
high safety, high theoretical energy density (1086 W h kg−1 ), and low cost, which
makes it a research hotspot in the field of MABs. After years of research, zinc–
air battery technology has been greatly developed. However, Zinc–air batteries still
have some key problems that need to be solved. For example, cathode materials still
have disadvantages such as poor cycle stability and low catalytic activity. Designing
single-atom catalysts in cathode materials through surface/interface engineering prin-
ciples is an effective strategy to solve the above problems. It is worth noting that 3D
graphene can be used as an efficient support for single-atom catalysts owing to its
large surface area and unique network structure. Fu et al. successfully fabricated
a Ni–MnO/3D rGO composite using a hydrogel strategy and tested it as a cathode
material in a zinc–air battery [49]. In this composite, Ni–MnO is uniformly dispersed
in 3D rGO. The results show that the composite material exhibits outstanding elec-
trochemical performance. It is even close to commercial Pt/C in some metrics, such
as the half-wave unit and onset of this composite are 0.78 V and 0.94 V, respectively.
Through the innovative design of the composite structure, the composite material
exhibits excellent electrochemical performance, which is mainly attributed to the
good electrical conductivity, connected network structure, and stable active sites of
the composite material. It is worth noting that other types of MABs have similar prob-
lems. Therefore, this strategy provides an efficient way to realize high-performance
MABs.
6 Conclusions and Perspectives
As a new energy storage technology, MABs show high energy density and good
application prospects. However, to realize the power of MABs, there are still a lot
of scientific and technological problems that need to be solved urgently. Among
244 R. Mo and Y. An
them, the development of cost-effective oxygen reduction catalysts is particularly

critical. In recent years, with the development of graphene application research, it
has been found that 3D graphene can be used as an excellent oxygen reduction
catalyst support. The doped graphene can be directly applied as an oxygen reduction
catalyst and shows excellent catalytic activity for oxygen reduction. Therefore, 3D
graphene-based oxygen reduction catalysts have become a research hotspot in this
field and have received more and more attention from researchers. According to the
research and development progress and status quo in 3D graphene-based oxygen
reduction catalysts, this chapter divides them into three categories. The first category
is the application of graphene as an oxygen reduction catalyst support. The second
category is the direct application of doped graphene as an oxygen reduction catalyst.
The third category is the formation of composite oxygen reduction catalysts by doped
graphene and other types of catalysts. The following conclusions can be drawn from
this chapter.
(i) Due to the special pore structure, ultra-high specific surface area, and corrosion
resistance of 3D graphene, it is applied as a support for noble metal catalysts
or transition metal oxide catalysts. On the one hand, 3D graphene can improve
its catalytic activity for oxygen reduction. On the other hand, it can effectively
inhibit the agglomeration and dissolution of catalyst active substances and
greatly improve their long-term stability.
(ii) The heteroatom-doped graphene provides many “active centers” for the oxygen
reduction catalytic reaction, thereby exhibiting good oxygen reduction catalytic
activity and long-term stability. However, the catalytic mechanism of oxygen
reduction in heteroatom-doped 3D graphene is still controversial and needs
further research.
(iii) Combining heteroatom-doped graphene with other catalysts can obtain oxygen
reduction catalysts with better performance. The catalytic activity of this
composite catalyst is much higher than that of its single component, which
is attributed to the strong interaction between heteroatom-doped graphene and
other types of catalysts.
In recent years, a lot of research work has been carried out on the application of 3D
graphene in MABs, and it has shown good prospects. However, research in this field
is still at an early stage, and extensive and in-depth scientific work is still needed to
realize the successful application of 3D graphene-based oxygen reduction catalysts
in MABs. The author believes that the focus of future work can be summarized as
the following aspects.
(i) Mechanism research and exploration
In order to design high-performance catalysts more rationally, it is necessary to
further study and explore the catalytic mechanism of oxygen reduction of heteroatom-
doped graphene and the interaction mechanism of heteroatom-co-doped graphene
and other types of oxygen reduction catalysts. More importantly, it will also help to
deeply understand the catalytic behavior of oxygen reduction of the catalysts in this
system.
(ii) Material design and preparation

In order to better construct the relationship between 3D graphene microstructure and
electrochemical performance, it is necessary to control and optimize the structure,
morphology, composition, and preparation process of 3D graphene-based oxygen
reduction catalyst in detail. In addition, it is also beneficial to obtain more cost-
effective 3D graphene-based oxygen reduction catalysts.
(iii) Scale production technology
At present, the research on 3D graphene-based oxygen reduction catalysts is still
in the laboratory stage. To ensure the repeatability and stability of the process and
performance in the large-scale and batch preparation stages, a lot of work still needs
to be done to develop the technology and process.
References
1. Cheng, F., Chen, J.: Metal–air batteries: from oxygen reduction electrochemistry to cathode
catalysts. Chem. Soc. Rev. 41, 2172–2192 (2012)
2. Zhang, T., Tao, Z., Chen, J.: Magnesium–air batteries: from principle to application. Mater.
Horizons. 1, 196–206 (2014)
3. Lee, J.S., Kim, S.T., Cao, R., Choi, N.S., Liu, M., Lee, K.T., Cho, J.: Metal–air batteries with
high energy density: Li–air versus Zn–air. Adv. Energy Mater. 1, 34–50 (2011)
4. Tan, P., Chen, B., Xu, H., Zhang, H., Cai, W., Ni, M., Liu, M., Shao, Z.: Flexible Zn– and
Li–air batteries: recent advances, challenges, and future perspectives. Energy Environ. Sci. 10,
2056–2080 (2017)
5. Feng Lu, X., Lin Zhang, S., Shangguan, E., Zhang, P., Gao, S., Lou, X.W.: Nitrogen-doped
cobalt pyrite yolk–shell hollow spheres for long-life rechargeable Zn–air batteries. Adv. Sci.
7, 2001178 (2020)
6. Chen, K., Huang, G., Ma, J.L., Wang, J., Yang, D.Y., Yang, X.Y., Yu, Y., Zhang, X.B.: The
stabilization effect of CO2 in lithium–oxygen/CO2 batteries. Angew. Chem. Int. Ed. 59, 16661–
16667 (2020)
7. Zhang, Z., Zhang, Q., Anan Chen, Y., Bao, J., Zhou, X., Xie, Z., Wei, J., Zhou, Z.: The
first introduction of graphene to rechargeable Li–CO2 batteries. Angew. Chem. Int. Ed. 127,
6650–6653 (2015)
8. Wang, P., Wan, L., Lin, Y., Wang, B.: Construction of mass-transfer channel in air electrode
with bifunctional catalyst for rechargeable zinc-air battery. Electrochim. Acta. 320, 134564
(2019)
9. Han, X., Li, X., White, J., Zhong, C., Deng, Y., Hu, W., Ma, T.: Metal–air batteries: from static
to flow system. Adv. Energy Mater. 8, 1801396 (2018)
10. Gao, Y., Xiao, Z., Kong, D., Iqbal, R., Yang, Q.H., Zhi, L.: N, P co-doped hollow
carbon nanofiber membranes with superior mass transfer property for trifunctional metal-free
electrocatalysis. Nano Energy 64, 103879 (2019)
11. Novoselov, K.S., Geim, A.K., Morozov, S.V., Jiang, D., Zhang, Y., Dubonos, S.V., Grigorieva,
I.V., Firsov, A.A.: Electric field in atomically thin carbon films. Science 306, 666–669 (2004)
12. Novoselov, K.S., Geim, A.K., Morozov, S.V., Jiang, D., Katsnelson, M.I., Grigorieva, I.V.,
Dubonos, S.V., Firsov, A.A.: Two-dimensional gas of massless Dirac fermions in graphene.
Nature 438, 197–200 (2005)
13. Kucinskis, G., Bajars, G., Kleperis, J.: Graphene in lithium ion battery cathode materials: a
review. J. Power Sources 240, 66–79 (2013)
246 R. Mo and Y. An
14. Cui, H., Guo, Y., Zhou, Z., Cui, H.J., Guo, Y.B., Zhou, Z.: Three-dimensional graphene-based
macrostructures for electrocatalysis. Small 17, 2005255 (2021)
15. Hou, S., Kluge, R.M., Haid, R.W., Gubanova, E.L., Watzele, S.A., Bandarenka, A.S., Garlyyev,
B.: A review on experimental identification of active sites in model bifunctional electrocatalytic
systems for oxygen reduction and evolution reactions. ChemElectroChem 8, 3433–3456 (2021)
16. Quílez-Bermejo, J., Morallón, E., Cazorla-Amorós, D.: Metal-free heteroatom-doped carbon-
based catalysts for ORR: a critical assessment about the role of heteroatoms. Carbon 165,
434–454 (2020)
17. Fu, J., Liang, R., Liu, G., Yu, A., Bai, Z., Yang, L., Chen, Z.: Recent progress in electrically
rechargeable zinc–air batteries. Adv. Mater. 31, 1805230 (2019)
18. Zhu, J., Yang, D., Yin, Z., Yan, Q., Zhang, H.: Graphene and graphene-based materials for
energy storage applications. Small 10, 3480–3498 (2014)
19. Arafat, Y., Azhar, M.R., Zhong, Y., Tadé, M.O., Shao, Z.: Metal-free carbon based air electrodes
for Zn-air batteries: recent advances and perspective. Mater. Res. Bull. 140, 111315 (2021)
20. Liu, Q., Pan, Z., Wang, E., An, L., Sun, G.: Aqueous metal-air batteries: fundamentals and
applications. Energy Storage Mater. 27, 478–505 (2020)
21. Sheng, K.X., Xu, Y.X., Li, C., Shi, G.Q.: High-performance self-assembled graphene hydrogels
prepared by chemical reduction of graphene oxide. New Carbon Mater. 26, 9–15 (2011)
hydrothermal process. ACS Nano 4, 4324–4330 (2010)
23. Jung, S.M., Mafra, D.L., Te Lin, C., Jung, H.Y., Kong, J.: Controlled porous structures of
graphene aerogels and their effect on supercapacitor performance. Nanoscale 7, 4386–4393
(2015)
24. Xie, Y., Li, Z., Wang, Y., Xu, S., Lin, S.: Freezing synthesis of Pt/3D GNs (C) composites as
efficient electrocatalysts for methanol oxidation. J. Appl. Electrochem. 48, 355–364 (2018)
25. Huang, X., Qian, K., Yang, J., Zhang, J., Li, L., Yu, C., Zhao, D.: Functional nanoporous
graphene foams with controlled pore sizes. Adv. Mater. 24, 4419–4423 (2012)
26. Yu, P., Zhao, X., Li, Y., Zhang, Q.: Controllable growth of polyaniline nanowire arrays on
hierarchical macro/mesoporous graphene foams for high-performance flexible supercapacitors.
Appl. Surf. Sci. 393, 37–45 (2017)
27. Kim, F., Luo, J., Cruz-Silva, R., Cote, L.J., Sohn, K., Huang, J.: Self-propagating domino-like
reactions in oxidized graphite. Adv. Funct. Mater. 20, 2867–2873 (2010)
28. Choi, B.G., Yang, M., Hong, W.H., Choi, J.W., Huh, Y.S.: 3D macroporous graphene frame-
works for supercapacitors with high energy and power densities. ACS Nano 6, 4020–4028
(2012)
29. Lee, J.Y., An, J., Chua, C.K.: Fundamentals and applications of 3D printing for novel materials.
Appl. Mater. Today 7, 120–133 (2017)
30. Zhu, C., Liu, T., Qian, F., Han, T.Y.J., Duoss, E.B., Kuntz, J.D., Spadaccini, C.M., Worsley,
M.A., Li, Y.: Supercapacitors based on three-dimensional hierarchical graphene aerogels with
periodic macropores. Nano Lett. 16, 3448–3456 (2016)
Mater. 10, 424–428 (2011)
32. Xie, X., Zhou, Y., Bi, H., Yin, K., Wan, S., Sun, L.: Large-range control of the microstructures
and properties of three-dimensional porous graphene. Sci. Rep. 3, 2117 (2013)
33. Cheng, H., Huang, Y., Shi, G., Jiang, L., Qu, L.: Graphene-based functional architectures: sheets
regulation and macrostructure construction toward actuators and power generators. Acc. Chem.
Res. 50, 1663–1671 (2017)
34. Mei, J., He, T., Zhang, Q., Liao, T., Du, A., Ayoko, G.A., Sun, Z.: Carbon-phosphorus bonds-
lithium storage. ACS Appl. Mater. Interfaces 12, 21720–21729 (2020)
35. Qi, Y., Cao, Y., Meng, X., Cao, J., Li, X., Hao, Q., Lei, W., Li, Q., Li, J., Si, W.: Facile
synthesis of 3D sulfur/nitrogen co-doped graphene derived from graphene oxide hydrogel and
the simultaneous determination of hydroquinone and catechol. Sens. Actuators B Chem. 279,
170–176 (2019)
36. Ge, L., Wang, D., Yang, P., Xu, H., Xiao, L., Zhang, G.X., Lu, X., Duan, Z., Meng, F., Zhang,
J., An, M.: Graphite N-C–P dominated three-dimensional nitrogen and phosphorus co-doped
holey graphene foams as high-efficiency electrocatalysts for Zn–air batteries. Nanoscale 11,
17010–17017 (2019)
37. Cheng, H., Yi, F., Gao, A., Liang, H., Shu, D., Zhou, X., He, C., Zhu, Z.: Supermolecule self-
assembly promoted porous N, P Co-doped reduced graphene oxide for high energy density
supercapacitors. ACS Appl. Energy Mater. 2, 4084–4091 (2019)
38. Yu, X., Kang, Y., Park, H.S.: Sulfur and phosphorus co-doping of hierarchically porous
graphene aerogels for enhancing supercapacitor performance. Carbon 101, 49–56 (2016)
39. Qiu, H.-J., Du, P., Hu, K., Gao, J., Li, H., Liu, P., Ina, T., Ohara, K., Ito, Y., Chen, M.: Metal
and nonmetal codoped 3D nanoporous graphene for efficient bifunctional electrocatalysis and
rechargeable Zn–air batteries. Adv. Mater. 31, 1900843 (2019)
40. Peng, Y., Lu, B., Chen, S., Peng, Y., Lu, B.Z., Chen, S.W.: Carbon-supported single atom
catalysts for electrochemical energy conversion and storage. Adv. Mater. 30, 1801995 (2018)
41. Mou, K., Chen, Z., Zhang, X., Jiao, M., Zhang, X., Ge, X., Zhang, W., Liu, L.: Highly efficient
electroreduction of CO2 on nickel single-atom catalysts: atom trapping and nitrogen anchoring.
Small 15, 1903668 (2019)
42. Hu, C., Gong, L., Xiao, Y., Yuan, Y., Bedford, N.M., Xia, Z., Ma, L., Wu, T., Lin, Y., Connell,
J.W., Shahbazian-Yassar, R., Lu, J., Amine, K., Dai, L.: High-performance, long-life, recharge-
able Li–CO2 batteries based on a 3D holey graphene cathode implanted with single iron atoms.
Adv. Mater. 32, 1907436 (2020)
43. Sun, H., Mei, L., Liang, J., Zhao, Z., Lee, C., Fei, H., Ding, M., Lau, J., Li, M., Wang, C.,
Xu, X., Hao, G., Papandrea, B., Shakir, I., Dunn, B., Huang, Y., Duan, X.: Three-dimensional
holey-graphene/niobia composite architectures for ultrahigh-rate energy storage. Science 356,
599–604 (2017)
44. Zhong, W., Ding, X., Li, W., Shen, C., Yadav, A., Chen, Y., Bao, M., Jiang, H., Wang, D.:
Facile fabrication of conductive graphene/polyurethane foam composite and its application on
flexible piezo-resistive sensors. Polymers 11, 1289 (2019)
45. Chen, Y., Xie, X., Xin, X., Tang, Z.R., Xu, Y.J.: Ti3 C2 Tx -based three-dimensional hydrogel by
a graphene oxide-assisted self-convergence process for enhanced photoredox catalysis. ACS
Nano 13, 295–304 (2019)
46. Zhou, Y., Zhang, G., Yu, M., Wang, X., Lv, J., Yang, F.: Free-standing 3D porous N-doped
graphene aerogel supported platinum nanocluster for efficient hydrogen production from
ammonia electrolysis. ACS Sustain. Chem. Eng. 6, 8437–8446 (2018)
47. Hu, X., Huang, T., Tang, Y., Fu, G., Lee, J.M.: Three-dimensional graphene-supported Ni3 Fe/
Co9 S8 composites: rational design and active for oxygen reversible electrocatalysis. ACS Appl.
Mater. Interfaces 11, 4028–4036 (2019)
48. Wu, A., Shen, S., Yan, X., Xia, G., Zhang, Y., Zhu, F., Zhang, J.: Cx Ny particles@N-doped
porous graphene: a novel cathode catalyst with a remarkable cyclability for Li–O2 batteries.
Nanoscale 10, 12763–12770 (2018)
49. Fu, G., Yan, X., Chen, Y., Xu, L., Sun, D., Lee, J.-M., Tang, Y.: Boosting bifunctional
oxygen electrocatalysis with 3D graphene aerogel-supported Ni/MnO particles. Adv. Mater.
30, 1704609 (2018)
3D Graphene for Flexible Batteries
Demet Ozer
Abstract The rapid advancement and widespread usage of flexible electronic

devices need the development of flexible batteries, which depend on the use of flexible
electrodes. The special electrical conductivity, mechanical stability, and switchable
surface characteristics of graphene make it a great choice. Flexible batteries have
recently seen a dramatic increase in the use of electrodes made of graphene. This
chapter examines the usage of 3D graphene electrodes (based on hydrogels, aero-
gels, sponges, and foams) in flexible lithium-ion, metal-air, and metal-ion batteries.
It appears to have unique qualities like a three-dimensional structure, a large surface
area, and high porosity that increase active sites, allow for the doping of active
substances, increase the mobility and effectiveness of electrolytes, and boost effi-
ciency in both applications and devices. The challenges and expectations for the use
and advancement of flexible batteries are addressed in the final stage.
Keywords 3D graphene · Battery · Graphene composites · Flexible electrodes
1 Introduction
The necessity of “green” energy conversion/storage systems is increasing continu-

ously because of global warming, the rapid depletion of fossil fuels, and the rise in
carbon dioxide emissions. In addition to its benefits, the rapidly changing and devel-
oping technology and the Internet of Things (IoT) creates the need for research and
development about new generation energy systems. Flexible energy storage mate-
rials must be developed to accommodate flexible electronic devices such as wear-
able computers, touch screens, robotics, and portable medical equipment. Secondary
batteries possess a high energy density and a long cycle life, making them appealing
technologies. Since Sony first made lithium-ion batteries available for purchase in
1991, they have dominated the market for portable gadgets like laptops, tablets, and
smartphones. Personal clothes, tents, packaging, and other items can all be powered
D. Ozer (B)
Department of Chemistry, Hacettepe University, Beytepe, Ankara 06800, Turkey
e-mail: demetbaykan@hacettepe.edu.tr
https://doi.org/10.1007/978-3-031-36249-1_14
250 D. Ozer
by flexible batteries with good deformability and impact resistance. Flexibility, great
speed capability, better stability under deformations, and the ability to be customized
to operating circumstances are all benefits of flexible batteries. The same parts found
in conventional rigid batteries, such as cathode/anode electrodes and electrolytes,
are also present in flexible batteries. To take advantage of high-performance flexible
batteries, flexible electrode materials need to be developed and made commercially
available. The electrodes specify the capacity, energy, and power density of batteries
because they supply ions and electrons and conduct electricity. High mechanical
flexibility, great electrical conductivity, and structural strength to endure repeated
deformations are all qualities that a flexible battery electrode should possess [1].
Conducting polymers, carbon cloth (CC), carbon fibers, and nanomaterials (carbon
nanotubes, graphenes, and MXenes) are the most often employed materials as an
electrode for flexible batteries.
The graphene-based materials are great alternatives choices for energy storage
applications due to their high energy density, quick charging, and long-lasting perfor-
mance. Large surface area and high porosity are two distinguishing features of the
3D structure, which enhance the active sites, improve the doping of active chemi-
cals, and promote accessibility and mobility of electrolytes as well as efficiency. This
section examines the preparation of 3D graphene electrodes and their uses as flexible
electrodes for a variety of flexible batteries, including metal-ion, lithium-sulfide, and
metal-air batteries. The difficulties with flexible batteries are also discussed, along
with a preview of upcoming research.
2 Preparation of 3D Graphene Electrodes
The use of graphene in electrochemical applications has become widespread because

of its exceptional electrical conductivity, mechanical toughness, and lightweight.
Graphene and derivatives (graphene oxide and reduced graphene oxide) outperform
other electrodes in terms of weight, cost, and energy density without the use of
extra parts like conductive carbons and binders, as well as external heavy metal
current collectors. Electron transport can be facilitated by conductive graphene struc-
tures by altering the kinetics of electrochemical reactions. Graphene has a large
surface area, making it perfect for active agent doping and active agent dispersion.
This reduces the van der Waals forces between layers, prevents the formation of
graphene clumps, and gives graphene sheets structural stability with open channels
for surface and ion migration and charge. Elastic graphene layers might lessen active
material volume fluctuations during alloying or transformation events, improving
the electrodes’ integrity. The growing demand for flexible and portable electronic
devices presents an incredible advantage for flexible graphene because of its strong
mechanical resilience and conductivity [2].
Graphene is produced from graphite. It can be prepared as one-dimensional
fibers and nanotubes, two-dimensional films and nanosheets, and three-dimensional
networks as effective electrode material. The 1D graphene fibers can adapt to severe
3D Graphene for Flexible Batteries 251
deformations in the length direction. The 2D films have excellent flexibility under
different bending states without structural damage. The 3D offers special qualities
including a wide surface area and high porosity that enhance the active sites, improve
the doping of active chemicals, increase the accessibility and mobility of electrolytes,
and improve the effectiveness of different applications and production tools. Agglom-
eration and subsequent deposition of graphene can be avoided by converting a 2D
structure into a 3D one. The advantages of employing 3D graphene-based materials
for energy storage purposes include: (1) Since the majority of the electrons in the
honeycomb pattern are sp2 hybrid electrons, the remaining electrons in the p-orbit
are well suited for forming strong bonds that are flexible enough to support electron
transmission. (2) A 3D cross-linking channel for ion/molecule diffusion is created
by sequential pores. (3) The enhanced adsorption/desorption capability encourages
mass transfer. (4) It is more suitable for usage in energy storage systems because
of its amazing versatility in terms of structural traits, hydrophilicity, and electrical
conductivity. (5) Excellent mechanical and chemical stability may be found in very
stable energy storage systems [3].
The two main categories of 3D graphene materials are shown in Fig. 1 as follows:
(1) macroscopic materials (>100 m in one or more dimensions), such as macro 3D
graphene monoliths (foams/sponges/aerogels), films, fibers, and spheres; and (2)
microscopic materials (100 m in all dimensions). Depending on the applied synthesis
technique, the type of 3D graphene can be altered. In general, self-assembly tech-
niques including reduction, cross-linking, sol–gel, and hydrothermal procedures,
template techniques like template-directed chemical vapor deposition and assembly
synthesis, laser casting, 3D printing, and electrothermal expansion have been used
[4]. The 3D graphene hydrogel was prepared through the hydrothermal method using
a Teflon autoclave at 180 °C for 12 h [5]. The obtained graphene hydrogel has high
electrical conductivity (5 × 10–3 S/cm), strong mechanical strength, high thermal
stability, high specific capacity (175 F/g at 10 mV/s scan rate), and is biocompatible.
These characteristics make it useful in biotechnology and electrochemistry applica-
tions such as supercapacitors, tissue engineering, drug delivery, and biomaterials. The
three-step sol–gel process was used to create the 3D aerogel graphene. In the first step,
monolithic solids are prepared from single-layered graphene oxide suspensions, in
the second step the obtained gels are dried in a supercritical environment, and finally,
graphene aerogels are formed by thermal reduction. These graphene aerogels have
two times higher electrical conductivity (87 S/m) compared to graphene with phys-
ical crosslinks alone. Graphene aerogels can be used effectively in energy storage,
catalysis, and sensing applications due to their large surface areas (584 m2 /g), pore
volumes (2.96 cm3 /g), and ultra-low densities (10 mg/cm3 ) [6]. Three-dimensional
(3D) graphene foam (GF) was created by chemical vapor deposition (CVD) using
nickel foam as a template. Poly-(dimethylsiloxane) (PDMS) was then infused into the
3D GF. Investigation of the GF/PDMS composite’s electrical characteristics under
bending stress revealed that the resistance of the material increased with the curvature
of the bend. It is more adaptable and environmentally stable, and it may be used as
a strain sensor with high sensitivity for crucial real-time monitoring applications for
buildings like bridges, dams, and high-speed railroads [7]. By using the ice template
252 D. Ozer
Fig. 1 The types of 3D graphenes. Reprinted with permission [4], copyright (2020) American
chemical society
approach, which is often employed to create hierarchical microstructure for nanopar-

ticles, the flexible macroporous 3D graphene sponge was created. A macroporous
graphene sponge was created after freeze-drying the as-formed ice crystals, which
rebuilt the inner walls of the graphene hydrogel into a hierarch macroporous structure
at a gradual cooling rate. A microbial fuel cell made with a graphene sponge as the
anode material had a power density of 427.0 W.m−3 , which was higher than an MFC
made with carbon felt as the anode material [8].
3 Design of Flexible Batteries
The development of flexible electronics, which can fit complex curved surfaces with
superior fatigue resistance and safety, has gradually advanced the requirement for
flexibility. Flexible batteries consist of three main components: substrates, elec-
trolytes, and electrodes (anode and cathode), along with a current collector and
battery shell (Fig. 2a, b). Active materials are supported as they are utilized to create
batteries by current collectors, which also serve as substrates for the collection
and transit of electrons from active materials and external circuits. Because of their
Fig. 2 a The representation of a flexible battery cell. Reproduced from [11], copyright 2016,
springer nature, b schematic illustration of batteries
outstanding electrochemical durability against oxidation and reduction, low price,

and exceptional electrical conductivity, Al and Cu are used as the cathode and anode
current collectors in industrial Li-ion batteries, respectively. Additionally, enhanced
current collector and electrode material adhesion as well as mechanical stability under
deformation are required for flexible batteries. Battery performance degradation and
thermal runaway are caused by the constant stretching of operational batteries, which
leads to the failure of current collectors and active components. Flexible Cu and Al
current collectors need to be made with a thickness that allows the tensile stress to be
much lower than the yield stress and tensile breaking stress, or the metal foils need
to be porous to lessen the stress. Flexibility improves with an increase in structural
porosity. However, the current collectors’ electrical conductivity is harmed by the
porous structure. Flexible current collectors based on Cu and Al foils must there-
fore appropriately consider mechanical stress, thickness, porosity, and conductivity
to build superior flexible batteries [9]. The electrolyte, which functions as both an
ionic conductor and an electronic insulator, is an essential component to maintain
simple ion movement and little self-discharge. A suitable electrolyte is required to
produce functional batteries. Liquid electrolytes are frequently used for flexible Li-
ion batteries because of their straightforward percolation, quick ion mobility, robust
wetting ability, and stable solid electrolyte interphase features. Among the issues
that need fixing are the safety issues with liquid electrolytes as well as the short-
ening of battery life brought on by the growth of lithium dendrites and electrolyte
leaks. Alternative solid-state electrolytes to liquid electrolytes have recently shown
promise as charge carriers when combined with lithium metal anodes to create flex-
ible batteries that are both safe and highly energetic. Inert components to facilitate
high voltage cathode requests, low electrolyte leakage to prevent cell failure or fire, a
large electrochemical window, strong Young’s modulus to prevent lithium dendrites,
and straightforward cell modeling to reduce production costs have all benefited solid
electrolytes. Separators are placed between the cathode and the anode and assist in
the transport of ions. It also prevents electrons from migrating into internal circuits.
The performance, dependability, and safety of batteries are primarily affected by
the mesh structure, material structure, and processing technique of the separators.
254 D. Ozer
Typically, separators made of 20–40 µm thick mixes of polyethylene, polypropylene

(PP), and other microporous polyolefin membranes are utilized. However, poly-
olefin membranes are notorious for having poor electrolyte wettability and low heat
stability. Therefore, it’s critical to use separator materials in flexible batteries that
have improved thermal stability, wettability, and fire resistance.
The other crucial part of flexible batteries is the electrodes (anodes and cathodes).
It is substantial to enhance the properties of electrode materials like high specific
capacity, better cycle life, mechanical stability, and rapid ion diffusion. Electrons are
released during chemical processes between the anode and the cathode. The inter-
calation and deintercalation of the metal-ion take place between the anode and the
cathode. Cell architecture is as important factor as electrode materials for developing
a fully flexible battery. To increase the flexibility of the battery, each component must
be portable, bendable, twistable, stretchable, ultrathin, and wearable [10]. The 3D
graphene-based electrodes have successfully applied as both anode and cathode for
various types of batteries like lithium-ion, sodium-ion, other ions, lithium-sulfide,
and metal-air batteries.
4 3D Graphene Electrodes for Flexible Metal-Ion Batteries
Metal-ion batteries are applied as a reliable form of energy storage due to their
high energy density, extended cycle life, and high energy conversion efficiency. The
development of flexible rechargeable batteries is highlighted by the rising demand for
flexible electronics of the future, including wearable electronics, portable electronics,
and implanted biomedical technologies. The anode and cathode materials for 3D
graphene-based electrodes have been effectively used in a majority of lithium-ion,
sodium-ion, and other ion batteries.
4.1 3D Graphene Electrodes for Flexible Lithium-Ion

Batteries
In mobile electronic devices like electric cars, laptop computers, and phones, lithium-
ion batteries are among the metal-ion batteries that work well. Due to its high energy
density and operating voltage, the lithium-ion battery (LIB) is evolving into a crucial
energy storage technology. Lithium-ion batteries are sold in solid squares or cylinders
that are brittle when deformed. Active materials and collectors have poor adherence
when metallic aluminum and copper foils are utilized as current stabilizers. The active
components tend to slip out of the current collectors when the electrodes are repeat-
edly deformed, which causes irreversible reductions in the device’s energy density
and cycle life. A good solution to these issues is flexible lithium-ion batteries with
flexible electrodes. For instance, the hydrothermal approach was used after chemical
vapor deposition to generate the 3D nitrogen-doped graphene foam containing encap-

sulated germanium quantum dots. The resultant electrode is extremely flexible and
may be twisted in any direction without suffering any damage. The porous graphene
foam facilitated the access of the electrolyte while suppressing the volume change of
the germanium. It showed that flexible lithium-ion batteries could have a high specific
capacity (1220 mAh g−1 at 1C), ultra-high speed performance (800 mAh g−1 at 40C),
and a long life cycle (1000 cycles) [12]. Three-dimensional (3D) graphene foams
(GF) were produced via chemical vapor deposition on nickel foam. After that, GF
was covered in MoS2 nanosheets that resembled flowers thanks to a microwave-
assisted hydrothermal process. Due to its highly conductive network and linked
channel, the flexible MoS2 @GF electrode demonstrates exceptional electrochemical
performance for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). At a
current rate of 100 mA g−1 , MoS2 @GF’s specific capacity for LIBs can reach up to
1400 mAh g−1 , and after 100 cycles, the high specific capacity (1127 mAh g−1 ) can
be attained at a rate of 250 mA g−1 . Additionally, at a rate of 100 mA g, the obtained
specific capacity for SIBs after 50 cycles is 290 mAh g−1 . Fast electron transport,
more effective electrolyte penetration, and shorter ion diffusion time for high conduc-
tivity, stable 3D structures are all credited with the flexible MoS2 @GF electrode’s
good performance [13]. Using ferrous sulfate as the iron supply and lysine as the
precipitator, simple hydrothermal synthesis has been used to produce 3D graphene-
encapsulated, essentially monodisperse Fe3 O4 composites. The 3D Fe3 O4 @rGO
composite has consistent Fe3 O4 particle size, according to SEM and TEM character-
izations. In addition to reducing volume changes and enhancing electric connection,
the unique 3D graphene-encapsulated Fe3 O4 structure can also prevent the aggre-
gation of Fe3 O4 NPs during repeated charge/discharge cycles. The 3D Fe3 O4 @rGO
exhibits good electrochemical characteristics when used as an anode in LIBs. Elec-
trochemical experiments show that the as-synthesized Fe3 O4 @rGO has an excellent
rate capability and an improved discharge capacity (1139 mAh g−1 at 400 mA g−1
after 100 charge/discharge cycles) [14]. By calcining a 3D graphene/metal–organic
framework in one step with selenium powder under an Ar/H2 flow for two hours
at 600 °C, Xu and colleagues created Fe7 Se8 @C core–shell nanoparticles enclosed
within a 3D graphene aerogel composite as a flexible anode. In tests between 0.01
and 3.00 V, the 3DG/Fe7 Se8 @C composite showed exceptional rate performance
and a high reversible capacity of 884.1 mAh g−1 at 0.1 A g−1 after 120 cycles and
815.2 mAh g−1 at 1 A g−1 after 250 cycles [15].
4.2 3D Graphene Electrodes for Flexible Sodium-Ion

Batteries
The need for alternatives has arisen as a result of the challenges that lithium-
ion batteries confront, particularly their inadequate energy/power density, safety
256 D. Ozer
concerns, durability, and particularly their limited supply, and expensive raw ingre-
dients (cobalt and lithium). Due to the extensive accessibility of natural sodium
sources including Na2 CO3 , Na2 SO4 , and NaCl as well as their affordability, sodium-
ion batteries are of interest. The battery performance is influenced by low ion–solvent
interaction energy and high Na+ diffusion rate. Additionally, as cobalt is not neces-
sary for the production of SIB cathodes, increasing the market share of SIB can lower
the risk of cobalt supply for LIB [2].
A host must have lots of active sites for adsorption/chemisorption, large interlayer
spacing, and long-range organized graphitic sheets for electron transport to store Na+ .
These elements combine to create a host that has a large capacity, rapid charging, and
stable cycling. Graphite shows limited capacity, low-velocity capacity, and a short
life cycle due to its inability to adapt to sodium addition. Besides, the large atomic
radius of sodium ions causes low conductivity and structural instability in sodiation
and desodiation. While graphene oxide with adjustable d-spacing and flaws perform
better, pure graphene is not the best material for holding sodium. As efficient anode
materials for SIBs, metal oxides, which have the benefit of large theoretical capacity,
are of great interest. When SIBs are charged or discharged, their low conductivity and
significant volumetric shift cause these materials to typically have low cycle stability
and capacitance ratios. The use of graphene to support metal oxides is effective in
SIBs. A novel flexible electrode for sodium-ion batteries has been created by Chen
et al. utilizing hydrothermal and CVD techniques. It is composed of 2D arrays of
ultrathin SnO nanoflakes supporting a 3D substrate made of graphene foam and
carbon nanotubes as the anode (Fig. 3a–c). In contrast, the large surface area 3D GF/
CNTs@SnO electrode, high porosity, and strong permeability have improved the
Na+ diffusion and charge transfer kinetics due to their ultra-fine shape (Fig. 3d–f)
of well-separated SnO nanoflakes (Fig. 3g). Figure 3h, i, j, and l demonstrate how
the final 3D GF/CNTs@SnO electrode outperformed the competition in terms of
high-rate capability and cycle stability in SIBs. It is possible to see a decrease in
the GF/CNTs@SnO electrode’s specific capacity from 584 to 390 mAh g−1 and an
increment in the current density from 0.1 to 1 A g−1 . It’s impressive that the higher
speeds were able to achieve higher high-speed capabilities, providing 302 mAh g−1
at 2 A g−1 and 170 mAh g−1 at 10 A g−1 , respectively. After 600 charge/discharge
cycles at 0.1 A g−1 , the initial capacity of 584 mAh g−1 was reduced to 540 mAh g−1
with only 91% retention. Two additional charge storage mechanisms in the 3D GF/
CNTs@SnO electrode include diffusion-controlled faradaic doping from the alloying
reaction and capacitive additive from charge transfer with surface/subsurface atoms.
A qualitative analysis of the capacitance effect against diffusion behavior is possible.
The results demonstrate that the capacitive contribution makes up roughly 46% of
the overall sodium load, as shown by the relationship between current I and scan
rate (v) as determined by the CV curves (Fig. 3k). According to the Nyquist plots,
the GF/CNTs/SnO electrode has a lower overall ohmic resistance of the solution
and electrodes than the GF@SnO electrode (Fig. 3m). Furthermore, there is less
charge transfer resistance. The good conductivity of CNTs arrays as a component
of electron and ion transportation networks, which results in faster reaction kinetics
and greater capacity, is primarily responsible for the fast charge transfer and low
Fig. 3 Schematic representation of composite preparation a graphene foam; b GF/CNTs; c GF/

CNTs@SnO; d–f SEM images of composite; g Schematic illustration of the GF/CNTs@SnO
electrode; h Charge/discharge curves at various current densities; ı Rate capability; j, l Low and
high-rate cycle life; k at 3 mV s−1 ; m Nyquist plots of GF@SnO and GF/CNTs@SnO. Adapted
with permission [16] copyright (2017) john wiley & sons
258 D. Ozer
resistance in GF/CNTs/SnO. Quantitative analysis showed that the ultrathin GF/

CNTs@SnO electrode’s extraordinarily quick Na+ kinetics considerably increased
the surfactant sites. The high surface area, porosity, and superior permeability of GF/
CNT foam enable a 3D porous design for Na+ diffusion and transport. CNTs with an
entangled 3D conductive structure are crucial for the dispersion of SnO nanoflakes
[16].
Sun and colleagues developed the hydrothermal and freeze-drying method to
prepare the 3D nitrogen-doped graphene (3DNG) frameworks doped Bi2 S3 nanorods,
which will serve as the anode material for a flexible sodium-ion battery. With
a high reversible capacity (649 mAh g−1 at 62.5 mA g−1 ), and excellent dura-
bility, the Bi2 S3 /3DNG composites displayed remarkable Na storing behavior (307
and 200 mAh g–1 after 100 cycles at 125 and 312.5 mA g–1 , respectively) [17].
Na3 V2 O2 (PO4 )2 F (NVOPF), with its high operating voltage and theoretical capacity,
is a potential cathode material for sodium-ion batteries (SIBs). Its weak intrinsic
electrical conductivity significantly impairs its electrochemical performance. To get
around this, NVOPF is combined with very flexible graphene sheets using the spray
drying technique. The highly electrically conductive graphene framework contains
uniformly dispersed NVOPF nanocrystal particles. The durable NVOPF/rGO micro-
sphere composite performs admirably as a cathode for SIBs thanks to its high specific
capacity (127.2 mAh g−1 ), long-term cycle stability (83.4% capacity retention at
30 °C after 2000 cycles), and exceptional high-speed performance (70.3 mAh g−1 at
100 °C). For enhanced energy storage applications, the electrochemical character-
istics of electrode materials seem to be improved by the graphene skeleton, which
also functions as a high-throughput electronic conduction matrix [18].
4.3 3D Graphene Electrodes for Flexible Other Metal-Ion

Batteries
Similar to how there is an abundance of Na (2.3 wt%), there is also a plenty of K

(1.5 wt%) in the Earth’s crust, and K raw materials like K2 CO3 are widely available,
which helps keep potassium-ion battery prices stable. Creating a 3D porous frame-
work is a successful way to improve surface adsorption/desorption of potassium-ion
saving. The one-pot hydrothermal synthesis of N/P dual-doped 3D graphene aerogels
with hierarchical pores increased interlayer distance and high doping level results
in materials with exceptional potassium-ion battery electrochemical performance.
The products that were produced with the help of potassium bis(fluoro sulfonyl)imide
(KFSI) in an EC/DEC electrolyte showed good rate capability (185 mAh g−1 at 5
A g−1 ) and high reversible capacity (507 mAh g−1 at 100 mA g−1 after 100 cycles)
[19].
Multivalent metal ions technologies, like those utilizing Mg2+ , Zn2+ , Ca2+ , and
3+
Al , are being researched more and more as low-cost alternatives to lithium-ion
batteries in recent years. Zinc-ion batteries have drawn a lot of interest because of their
advantages in two-electron redox, high level of security, and simplicity in scaling.

Additionally, because of the sluggish diffusion of divalent cations at the cathode, the
speed performance of the majority of ZIBs is still insufficient. To produce high-rate
ZIBs, Fan et al. produced a flexible graphene-based ZIB. On flexible graphene foam, a
fresh layer of zinc orthovanadate was created and employed as a cathode. The Zn array
anode was also supported by porous graphene foam. Since no active material peeled
off the graphene substrate after periodic bending, it was found that both the graphene-
based cathode and anode had exceptional mechanical stability and flexibility. An
ultra-high-rate performance of 50C (discharge in 60 s) was demonstrated by the
resulting flexible Zn-ion battery [20]. The cost-benefit of aluminum ion batteries
outweighs the benefit of aluminum’s inherent abundance. Aluminum metal has a
large volumetric and gravimetric capacity (2980 mAh g−1 and 8034 mAh mL−1 ).
Aluminum is stable in air and may be used without the use of inert gases because of its
outer oxide film. This improves the aluminum battery’s safety throughout production
and use. As an illustration, the 3D graphene mesh network was successfully designed
and built using the folded Ni mesh-aided CVD technique. Ni was electroplated onto
the surface of the Ni mesh before it was folded and attached. With a capacity retention
rate of 96.5% after 200 cycles, this 3D graphene mesh network offers a high capacity
of 57 mAh g−1 in an Al-ion battery at an extremely high rate of 40C. The cathode of
an ultrafast Al-ion battery that has a similar gravimetric capacity but a substantially
higher volumetric capacity can be made using this high-density 3D graphene mesh
network [21].
5 3D Graphene Electrodes for Flexible Lithium-Sulfur

Batteries
One of the best lithium-ion battery substitutes is lithium-sulfur technology. The most
significant advantages include high theoretical specific capacities (1672 mAh g−1 ),
high energy densities (2600 Wh kg−1 ), natural abundance of the sulfur cathode, low
cost, and non-toxicity. In addition to the advantages, some disadvantages are still
seeking solutions. One of these is sulfur’s low electrical conductivity. Another is that
the reaction’s discharge products (Li2 S or Li2 S2 ) are essentially insulating, which
can significantly raise the cell’s internal resistance. Volume expansion is another
drawback. Li2 S and sulfur have different densities, and when sulfur is changed into
Li2 S, the volume of the electrode rises by around 80%. When the electrode’s volume
increases, the structural degradation of the electrode causes the capacity to drop off
quickly, creating a risk for injury. The shuttle effect, which occurs when polysulfide
generated during charge and discharge dissolves in the electrolyte, is the final draw-
back. The polysulfide formed at the cathode dissolves in the electrolyte, advances
to the lithium anode with the help of the separator comes into direct contact with
lithium, and results in irreversible side reactions that cause loss of active substance
from the cell. Low active material consumption has negative effects on coulomb
260 D. Ozer
efficiency and cycle performance. The flexibility of the electrodes and leakage of
electrolyte place further limitations on the design of flexible lithium-sulfur batteries.
If the electrode cannot withstand mechanical deformation under bending and folding,
the electrode surface may crack and break, creating a safety hazard. Novel materials
for Li anodes, functionalized solid-state electrolytes, functionalized separators, and
sulfur cathodes could be developed to address these shortcomings [22].
Flexible sulfur cathodes differ from conventional cathodes in that a portion of
the cathode becomes independent, the amount of sulfur in the electrode’s total mass
increases, increasing the battery’s energy density in turn, the cathode is resistant
to volume widening during charging, and discharging, and the amount of sulfur
is improved by using 3D structures. The 3D graphene-based materials have been
obtained and successfully applied as cathode material for flexible lithium-sulfide
batteries. The 3D graphene sponge with sulfur nanoparticles was prepared through the
facile reduction method and freeze-drying. The resulting composite was applied as a
cathode material and provided fast Li+ conduction, superior absorption, and effective
electrochemical redox effects of sulfur with continuous conductivity, superior struc-
tural integrity, and flexibility. It has a high reversible capacity of 580 mA h g−1 over
500 cycles with a high-capacity retention of 78.4% and a low decay rate of 0.043% per
cycle [23]. Zhou and coworkers prepared 3D graphene foam which provides a highly
electrically conductive network, robust mechanical support, and sufficient space for a
high sulfur loading as a sulfur cathode host. Figure 4a depicts a schematic representa-
tion of the cathode’s synthesis. The process involved chemically depositing graphene
on nickel (Ni) foam, coating the foam with poly(dimethylsiloxane), and then etching
away the nickel and infiltrating it with a thoroughly mixed sulfur slurry. The PDMS/
GF is very flexible and may be bent in any direction without breaking (Fig. 4b, c).
Even after being loaded with a significant amount of sulfur, the flexible S-PDMS/GF
electrode maintains its flexibility while the linked graphene network is kept intact
during electrode construction (Fig. 4d, e). The sulfur loading was improved by the
graphene foam’s rich porosity, which allowed for significant amounts of sulfur to
be accommodated. The structural variations between the flexible electrode based on
GF and the electrode incorporating sulfur coating on an Al foil current collector
are shown in Fig. 4g, h. The active components are principally supported by the
current collector, which also offers a continuous conductive path. The foam struc-
ture produced interconnected conductive networks that aided in the rapid transport of
ions and electrons. The flexible cathode’s mechanical stability was improved by the
thin PDMS covering, which also reinforced the topology of the conducting network.
A 20% elastic strain flexible cathode that was created kept its conductivity through
22,000 bending tests. The electrodes exhibited no evidence of cracking after being
bent. This demonstrates that the electrode is strong and flexible even when bent. After
1000 cycles with a constant cycling mechanism and a deterioration rate of 0.07%,
this flexible cathode showed a reversible capacity of 450 mAh/g at 3.5C (Fig. 4f–i)
[24].
Fig. 4 a The schematic illustration of the synthesis of the cathode; b, c Photographs of a PDMS/
GF; d, e Photographs of S-PDMS/GF electrode with sulfur; f Rate performance of S-PDMS/GF
electrodes with various sulfur loadings and the electrode with sulfur deposited on an Al foil; g,
h Comparison of a flexible electrode based on GF and an electrode design with sulfur coated on an
Al foil; i Cycling performance and Coulombic efficiency of the S-PDMS/GF electrode. Adapted
with permission of [24], copyright (2015) Elsevier
262 D. Ozer
6 3D Graphene Electrodes for Flexible Metal-Air Batteries
For the future generation of EVs, metal-air batteries including lithium, zinc, magne-
sium, and aluminum show promise. They reduce the weight of the battery and increase
the amount of space available for energy storage by using oxygen from the air as one
of the battery’s primary reactants. The lithium-air battery exhibits the highest poten-
tial energy density among all these metal-air batteries. Despite this, the practical
energy density of commercial lithium-air batteries is still insufficient for high-power
applications, and they have short lives. Including other metal-air batteries like zinc-
air, aluminum-air, and magnesium-air batteries, the present lithium-air battery is
not resistant to atmospheric moisture. Compared to magnesium-air, aluminum-air,
and zinc-air batteries, it is more expensive to produce. While aluminum-air batteries
cannot be recharged, lithium-air batteries have superior reversibility than zinc-air
and magnesium-air batteries [25].
Electrodes made of graphene have recently been used as effective electrodes for
metal-air batteries. To produce a moisture-resistant cathode for high-performance Li-
air batteries, Duan et al. developed a three-dimensional (3D) hydrophobic graphene
membrane without the need for a binder. The 3D graphene membranes have a
porous nature for effective oxygen and electrolyte ion diffusion, an interconnected
graphene network for efficient charge transfer, a large specific surface area for high-
capacity storage of the insulating discharge product, and hydrophobic channels for
O2 /H2 O selectivity. It promotes O2 ingress, delays moisture diffusion, and offers
outstanding charge/discharge cycle stability under ambient settings. It has a maximal
cathode capacity of over 5,700 mAh/g and great recharge cycle behavior (> 2,000
cycles at 140 mAh/g and >100 cycles at 1,400 mAh/g), making it a strong Li-air
membrane with exceptional performance. can make the batteries work. Unlike a
standard lithium-ion battery cathode, the graphene membrane air cathode has a life-
time capacity of 100,000–300,000 mAh/g. Future mobile power supply might find the
stable operation of Li-air batteries to be a desirable high energy density storage alter-
native thanks to their greatly improved single-charge capacities and lifetime capac-
ities comparable to Li-ion batteries. These batteries can offer much lower charging
frequency and much longer battery life [26]. CeO2 microsphere doped 3D graphene
foam was prepared by the hydrothermal method as a flexible cathode material for
the lithium-air battery. The obtained cathode exhibits a high discharge capacity of
roughly 3250 mAhg−1 at a current density of 200 mAg−1 with high flexibility and
good reversibility due to the synergetic effect of hollow graphene foam and ceria
microsphere [27]. For zinc-air batteries, Qiu and colleagues used chemical vapor
deposition and chemical etching to create 3D nanoporous graphene with nitrogen
and nickel. To build the battery, co-doped graphene is employed as a flexible and
free-standing air–cathode, PVA gel serves as the electrolyte, and Zn foil serves as the
anode. Due to the high bifunctional activities, electrical conductivity, and improved
mass movement, the produced battery demonstrated 83.8 mW cm−2 power density
after a 48-h testing period. It can continue to work reliably for a long time and even in
a variety of bending situations [28]. In another study, the ultrathin Co3 O4 nanosheet
clusters embedded onto nitrogen-doped carbon nanotubes/3D graphene (NCNTs/3D

graphene) composite on top of a nickel foam substrate were made using chemical
vapor deposition (CVD) and heat treatments. When the obtained composite is applied
as the cathode in an aluminum-air battery, it exhibits higher open circuit voltages,
specific capacities, and maximum power densities than Co3 O4 /3D graphene and Pt/
C. It has a specific capacity of 482.80 mAh g−1 at a discharge current density of
1.0 mA cm−2 and a maximum power density of 4.88 mW cm−2 [29].
7 Challenges and Perspectives for Future Research
The environmental crisis is made worse by the increasing consumption of fossil fuels
as a result of rising energy demand. Due to intense pressure from the energy and
environmental sectors, researchers are looking for effective and renewable energy
storage and transformation solutions. Flexible batteries as energy storage devices
have a wide range of potential applications since they provide flexible displays, flex-
ible sensors, and other components a consistent and dependable power source. The
flexible electrode plays a crucial role in flexible batteries by carrying out a variety
of functions such as facilitating electron transport, providing interfaces for elec-
trode reactions, supporting battery architectures, and implementing flexible features.
The flexible electrode material has a considerable impact on the energy density,
rate performance, and flexibility of the battery. The development of flexible struc-
tures is essential for enhancing the mechanical characteristics of flexible batteries
and broadening their scope of use. The advancement of flexible electronics and the
expansion of its useful application fields will be aided by research on flexible battery
electrodes.
The flexible electrodes made of carbon-based materials have special benefits when
they used in flexible batteries. (1) Carbon materials with pores and a large amount
of surface area provide a strong and conductive cross-linked framework for strong
adhesion of active materials. The carbon structure enhances electrochemical kinetics
by allowing both ion and electron transport and can tolerate repetitive deformation.
(2) The positive traits of carbon materials, such as their lightweight nature, low
interface resistance, and abundance of active sites, tend to boost FLIBs’ energy
density. (3) The excellent electrochemical stability of carbon materials enhances
the electrodes for FLIBs’ speed capability and favorable cyclic reversibility. The
excellent conductivity and electrochemical activity of the graphene-based electrodes
have allowed them to be successfully used as anodes and cathodes. Aside from these
benefits, 3D graphene also has a large theoretical specific surface area (approximately
2630 m2 /g), outstanding mechanical flexibility, strong electrical conductivity, high
thermal conductivity, superb chemical stability, and minimal installation cost. As
a conductive additive to enhance kinetics and as a buffer to support the structural
integrity of electrodes, graphene is utilized actively in electrochemical reactions.
Due to the low theoretical capacity, enormous initial irreversible capacity, and rapid
264 D. Ozer
capacity loss during the cycling of graphene-based anodes, the incorporation of high-
capacitance inorganic active materials atop the flexible graphene matrix is necessary.
Given the advancements in structure design technology and materials synthesis
engineering, FLIBs, which combine exceptional mechanical flexibility and electro-
chemical performance, will help to significantly advance energy storage technology
in the future. Additionally, the development and commercialization of portable and
flexible electronics will spread quickly.
References
1. Dai, C., Sun, G., Hu, L., Xiao, Y., Zhang, Z., Qu, L.: Recent progress in graphene-based
electrodes for flexible batteries. InfoMat 2(3), 509–526 (2020)
2. Xu, H., Chen, H., Gao, C.: Advanced graphene materials for sodium/potassium/aluminum-ion
batteries. ACS Mater. Lett. 3(8), 1221–1237 (2021)
3. Ma, Y., Chen, J., Hu, Y., Zhang, Y., Zhang, Z., Zhan, J., Chen, A., Peng, Q.: Synthesis of three-
dimensional graphene-based materials for applications in energy storage. Jom 72, 2445–2459
(2020)
control. Chem. Rev. 120(18), 10336–10453 (2020)
hydrothermal process. ACS Nano 4(7), 4324–4330 (2010)
6. Worsley, M.A., Pauzauskie, P.J., Olson, T.Y., Biener, J., Satcher, J.H., Jr., Baumann, T.F.:
Synthesis of graphene aerogel with high electrical conductivity. J. Am. Chem. Soc. 132(40),
14067–14069 (2010)
7. Xu, R., Lu, Y., Jiang, C., Chen, J., Mao, P., Gao, G., Zhang, L., Wu, S.: Facile fabrication
of three-dimensional graphene foam/poly (dimethylsiloxane) composites and their potential
application as strain sensor. ACS Appl. Mater. Interfaces 6(16), 13455–13460 (2014)
8. Chen, W., Huang, Y.-X., Li, D.-B., Yu, H.-Q., Yan, L.: Preparation of a macroporous flexible
three dimensional graphene sponge using an ice-template as the anode material for microbial
fuel cells. RSC Adv. 4(41), 21619–21624 (2014)
9. Kong, L., Tang, C., Peng, H.J., Huang, J.Q., Zhang, Q.: Advanced energy materials for flexible
batteries in energy storage: a review. SmartMat 1(1) (2020)
10. Ozer, D., Ertekin, Z.: Nanocomposites of 2D materials for flexible Li-ion batteries. In: Energy
Applications of 2D Nanomaterials, pp. 301–318. CRC Press (2022)
11. Lukatskaya, M.R., Dunn, B., Gogotsi, Y.: Multidimensional materials and device architectures
for future hybrid energy storage. Nat. Commun. 7(1), 1–13 (2016)
12. Mo, R., Rooney, D., Sun, K., Yang, H.Y.: 3D nitrogen-doped graphene foam with encapsu-
lated germanium/nitrogen-doped graphene yolk-shell nanoarchitecture for high-performance
flexible Li-ion battery. Nat. Commun. 8(1), 13949 (2017)
13. Xiang, J., Dong, D., Wen, F., Zhao, J., Zhang, X., Wang, L., Liu, Z.: Microwave synthesized
self-standing electrode of MoS2 nanosheets assembled on graphene foam for high-performance
Li-Ion and Na-Ion batteries. J. Alloy. Compd. 660, 11–16 (2016)
14. Li, L., Wang, H., Xie, Z., An, C., Jiang, G., Wang, Y.: 3D graphene-encapsulated nearly
monodisperse Fe3O4 nanoparticles as high-performance lithium-ion battery anodes. J. Alloy.
Compd. 815, 152337 (2020)
15. Jiang, T., Bu, F., Liu, B., Hao, G., Xu, Y.: Fe 7 Se 8@ C core–shell nanoparticles encapsu-
lated within a three-dimensional graphene composite as a high-performance flexible anode for
lithium-ion batteries. New J. Chem. 41(12), 5121–5124 (2017)
16. Chen, M., Chao, D., Liu, J., Yan, J., Zhang, B., Huang, Y., Lin, J., Shen, Z.X.: Rapid pseudo-
capacitive sodium-ion response induced by 2D ultrathin tin monoxide nanoarrays. Adv. Func.
Mater. 27(12), 1606232 (2017)
17. Lu, C., Li, Z., Yu, L., Zhang, L., Xia, Z., Jiang, T., Yin, W., Dou, S., Liu, Z., Sun, J.: Nanostruc-
tured Bi 2 S 3 encapsulated within three-dimensional N-doped graphene as active and flexible
anodes for sodium-ion batteries. Nano Res. 11, 4614–4626 (2018)
18. Yin, Y., Xiong, F., Pei, C., Xu, Y., An, Q., Tan, S., Zhuang, Z., Sheng, J., Li, Q., Mai, L.:
Robust three-dimensional graphene skeleton encapsulated Na3V2O2 (PO4) 2F nanoparticles
as a high-rate and long-life cathode of sodium-ion batteries. Nano Energy 41, 452–459 (2017)
19. Gao, X., Dong, X., Xing, Z., Nie, C., Zheng, G., Ju, Z.: Electrolyte salt chemistry enables 3D
nitrogen and phosphorus dual-doped graphene aerogels for high-performance potassium-ion
batteries. Adv. Mater. Technol. 6(8), 2100207 (2021)
20. Chao, D., Zhu, C., Song, M., Liang, P., Zhang, X., Tiep, N.H., Zhao, H., Wang, J., Wang, R.,
Zhang, H.: A high-rate and stable quasi-solid-state zinc-ion battery with novel 2D layered zinc
orthovanadate array. Adv. Mater. 30(32), 1803181 (2018)
21. Yang, G., Chen, L., Jiang, P., Guo, Z., Wang, W., Liu, Z.: Fabrication of tunable 3D graphene
mesh network with enhanced electrical and thermal properties for high-rate aluminum-ion
battery application. RSC Adv. 6(53), 47655–47660 (2016)
22. He, Y., Bi, S., Jiang, C., Song, J.: Recent progress of sulfur cathodes and other components for
flexible lithium-sulfur batteries. Mater. Today Sustain. 100181 (2022)
23. Lin, C., Niu, C., Xu, X., Li, K., Cai, Z., Zhang, Y., Wang, X., Qu, L., Xu, Y., Mai, L.: A
facile synthesis of three dimensional graphene sponge composited with sulfur nanoparticles
for flexible Li–S cathodes. Phys. Chem. Chem. Phys. 18(32), 22146–22153 (2016)
24. Zhou, G., Li, L., Ma, C., Wang, S., Shi, Y., Koratkar, N., Ren, W., Li, F., Cheng, H.-M.: A
graphene foam electrode with high sulfur loading for flexible and high energy Li-S batteries.
Nano Energy 11, 356–365 (2015)
25. Rahman, M.A., Wang, X., Wen, C.: High energy density metal-air batteries: a review. J.
Electrochem. Soc. 160(10), A1759 (2013)
26. Zhong, X., Papandrea, B., Xu, Y., Lin, Z., Zhang, H., Liu, Y., Huang, Y., Duan, X.: Three-
dimensional graphene membrane cathode for high energy density rechargeable lithium-air
batteries in ambient conditions. Nano Res. 10, 472–482 (2017)
27. Jiang, Y., Cheng, J., Zou, L., Li, X., Huang, Y., Jia, L., Chi, B., Pu, J., Li, J.: Graphene
foam decorated with ceria microspheres as a flexible cathode for foldable lithium-air batteries.
ChemCatChem 9(22), 4231–4237 (2017)
28. Qiu, H.J., Du, P., Hu, K., Gao, J., Li, H., Liu, P., Ina, T., Ohara, K., Ito, Y., Chen, M.: Metal
rechargeable Zn–air batteries. Adv. Mater. 31(19), 1900843 (2019)
29. Liu, Y., Yang, L., Xie, B., Zhao, N., Yang, L., Zhan, F., Pan, Q., Han, J., Wang, X., Liu, J.: Ultra-
thin Co3O4 nanosheet clusters anchored on nitrogen doped carbon nanotubes/3D graphene as
binder-free cathodes for Al-air battery. Chem. Eng. J. 381, 122681 (2020)
Recent Development in 3D Graphene
for Wearable and Flexible Batteries
Wei Ni and Ling-Ying Shi
Abstract 3D graphene-based flexible materials have attracted ever-increasing atten-

tion due to the fantastic intrinsic merits of graphene and its assemblies with high
surface area, lightweight, superior electronic conductivity, and outstanding mechan-
ical properties. Thus, 3D graphene-based wearable and flexible materials have
been extensively investigated for various promising applications including advanced
energy storage and conversion. In this chapter, we conducted a focused review of
the recent progress in the design, synthesis, and engineering of 3D graphene mate-
rials/architectures as well as their specific applications for advanced wearable and
flexible batteries. The major challenges, strategies, and prospects are also discussed
for further development of 3D graphene materials for wearable and flexible batteries
toward ultimate practical application.
Keywords 3D graphene · Batteries · Flexible · Wearable
1 Introduction
Flexible and wearable electrochemical energy storage devices (EESDs) have

attracted tremendous attention as promising adaptive power sources for the fast-
growing flexible and wearable smart electronic products market [1–3]. Carbon-based
nanomaterials, especially graphene and its derivatives, have aroused intense interest
as a vital component for flexible batteries for wearable electronics [4–7]. As a new
generation of a special member of the graphene family, 3D graphene materials have
been receiving considerable attention over the past decade [8]. Graphene-based 3D
W. Ni (B)
State Key Laboratory of Vanadium and Titanium Resources Comprehensive Utilization,
ANSTEEL Research Institute of Vanadium and Titanium (Iron and Steel), Chengdu 610031,
China
e-mail: niwei@iccas.ac.cn; max.ni@hotmail.com
L.-Y. Shi
College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China
https://doi.org/10.1007/978-3-031-36249-1_15
268 W. Ni and L.-Y. Shi
materials have exceptional conductivity, superior surface area, lightweight, favor-

able mechanical strength, and flexibility, as well as interconnected structures for
high mass loading and superior charge transfer, thus for advanced flexible/wearable
batteries with both high energy and power densities. 3D graphene materials have
recently been exploited for potential applications including but not limited to flex-
ible and wearable IoT stretch sensors (e.g., for real-time armband muscle measure-
ment), (all-solid-state) electrochemical capacitors, alkali-metal–ion batteries, Li–S
batteries, Zn–ion and Zn–air batteries, as well as other batteries (e.g., Ni–Fe batteries,
Ni–Bi batteries).
2 Structures, Properties, and Methods
3D graphene may be classified into two distinct categories, i.e., macroscopic 3D

graphene architecture and microscopic 3D graphene structure; although different
from the appearance (e.g., adsorbent materials emphasizing more on macroscopic
structure, compared to granular graphene materials emphasizing on microscopic 3D
graphene structure to eliminate property changes), they are closely relative and are
aiming at avoiding the restacking of 2D graphene layers in practical application
[8]. 3D graphene materials inherit the astonishingly synergistic merits of 3D porous
structures and exceptional intrinsic characteristics of graphene, thus endowing them
with high specific surface area, large pore volume, enhanced mechanical strength, fast
electron/ion transfer as ideal candidates for emerging wearable and flexible energy
storage and conversion devices.
Graphene plays a vital role of framework, substrate, or modifier in the classic
composite/hybrid structures as electrodes for energy storage and conversion [9].
For 3D graphene, the framework structures are usually fabricated by hydrothermal/
chemical/electrochemical reduction, freeze drying [10, 11], 3D printing (or direct
ink writing, DIW) [12–15], assembly, wet-spinning, (vacuum) filtration [16, 17],
template-assisted chemical vapor deposition (CVD), or integrated techniques
[18–20]. The as-prepared typical 3D graphene-based electrode materials for wear-
able or flexible batteries by these techniques include fiber-shaped rGO compos-
ites (rGO: reduced graphene oxide) [21], rGO/MnO2 -rGO-CNT nanocomposite
membrane (CNT: carbon nanotube) [16], rGO-wrapped CNT/rGO@MnO2 porous
film [10], 3D porous MXene/rGO hybrid film [22], sandwich-structured graphene/
NASICON/graphene hybrid film [23], rGO/2D materials (e.g., MoS2 ) flexible free-
standing porous film [18], rGO/TMOs hybrid paper or film (e.g., NiO microflowers)
[17], graphene-regulated carbon cloth [24], graphene-modified SiOC ceramic cloth
[11], and graphene aerogel-based composite (e.g., with ultrasmall Co3 O4 , Bi2 S3
nanorods, MXene/Zn) [19, 20, 25].
It should be noted that some other carbonaceous materials including carbon
nanotubes are often incorporated into graphene systems for microstructure adjust-
ment and performance improvement thereof [10, 26]. Some other carbon-based
3D hierarchical electrodes such as carbon nanofiber/Na3 V2 (PO4 )3 freestanding
Recent Development in 3D Graphene for Wearable and Flexible Batteries 269
composite, polymer foam/sponge (e.g., melamine foam, MF)-derived flexible free-

standing graphene-like carbon foam/paper and its composites [27, 28], or 3D
graphene-like porous carbon nanosheets pyrolyzed from hydrocarbons [29] are not
mentioned in this specific chapter.
3 Applications
3D graphene can endow the electrodes with high electric/ionic conductivity, flex-
ible merits, and avoid using additional metal current collectors in the conventional
battery design; also the lightweight 3D porous graphene framework with intercon-
nected channels lowers the percolation threshold compared to other conductive adhe-
sives (e.g., carbon black particles, 1D carbon nanotubes/nanofibers). In the following
paragraphs, we highlighted the most promising rechargeable batteries based on
3D graphene including alkali-metal–ion batteries (Li–ion, Na–ion batteries), Li–S
batteries, Zn–ion batteries, Zn–air batteries, and other batteries.
3.1 Li–Ion Batteries
Li–ion batteries (LIBs) hold substantial promise for current and next-generation
power devices; 3D graphene provides promising pathways for the development of
high power/energy density LIBs via improving the ion/electron transfer, accommo-
dating the volume change and eliminating the conventional nonactive but heavy
metal current collectors. For example, a flexible freestanding rGO-wrapped CNT/
rGO@MnO2 porous (GCMP) film with 3D multilevel conductive architecture as
anode for LIBs demonstrates an increasing capacity of up to 1344 mAh g−1 at a
constant current density of 2 A g−1 after 630 repeated cycles, as well as a supe-
rior rate performance and a prolonged cycling life (609 mAh g−1 at 7.5 A g−1
after 1000 cycles) [10]. Compared to traditional vacuum filtration method [16], the
as-prepared composite film electrode showed enhanced long-term cycling perfor-
mances; however, the relatively high average potential plateau (e.g., delithiation
potential) as well as the lower initial capacity followed by gradual increase with acti-
vation may somewhat deteriorate the potential for practical application as advanced
anode of high-performance LIBs. Cong et al. designed a soft-packed flexible LIBs
by using ultrasmall Co3 O4 /ionic liquid-modified N-doped graphene aerogel (Co3 O4 -
GA-IL) [19]. The flexible freestanding 3D porous electrode material could deliver a
superior capacity of 1304 mAh g−1 at a rate of 0.5C, with an outstanding capacity
retention of 98.4% after long-term cycle (500 cycles, 0.003% capacity loss per cycle),
as well as an enhanced rate capability of 715 mAh g−1 at 5C. The 3D graphene frame-
work with high conductivity and ultrasmall Co3 O4 with shortened ion diffusion length
synergistically improved the overall performance.
MoS2 is a kind of classic 2D or layered material with significantly higher theoret-

ical capacity (670 mAh g−1 ) compared with commercial graphite, which simultane-
ously allows higher rate performance [18, 30]. For example, neuron-like few-layered
MoS2 could be incorporated into the N-doped graphene foam (derived from a GO-
modified melamine sponge) to form a freestanding and binder-free anode for high-
performance LIBs [30]. The polymer sponge/graphene composite precursor-derived
graphene foam showed enhanced mechanical performances and improved charge
transfer properties, and thus are showing advantages as freestanding electrodes for
flexible soft-package batteries (SPB). For the as-assembled SPB, the freestanding
composite electrode demonstrated an excellent specific capacity of 713 mAh g−1
at 0.5 A g−1 after 200 cycles with an average coulombic efficiency (CE) of 99.5%.
It should also be mentioned that MoS2 usually has a relatively high lithium extrac-
tion potential (i.e., delithiation potential) compared with commercial graphite, thus
resulting in a lower voltage output for a full cell, although the lithium dendrites are
avoided and high-power LIBs can be achieved.
Si-based materials possess much lower potential plateaus compared to conven-
tional transition-metal oxides (TMOs) and thus more suitable for application as anode
materials for high-energy-density LIBs. Cai et al. fabricated a nano-Si encapsulated
rGO hybrid film as binder-free anode for flexible high-energy-density LIBs [31]. The
silicon nanoparticles are confined in multilayered rGO film via zinc-induced redox
layer-by-layer assembly followed by freeze drying. With commercial LiCoO2 as
cathode, the flexible full cell could deliver a high average voltage of 3.9 V (discharge)
along with an initial coulombic efficiency (ICE) of 87.8% and around 97–100% after-
ward. The high reversible capacity of anode (667 mAh g−1 at 0.287 A g−1 and 713
mAh g−1 at 0.2 A g−1 , respectively, after 200 cycles) and low cut-off voltage (0–
1.2 V) enhanced the energy density of flexible LIBs. Sang et al. fabricated a graphene-
modified SiOC ceramic fiber cloth (3D-GNS/SiOCf ) for high-performance flexible
LIBs [11]. The incorporation of graphene into the electrospun SiOC fibers enhances
the electron transfer and assures the robust lithium storage. As a freestanding anode
for LIBs, it demonstrated a high capacity of 924 mAh g−1 at 0.1 A g−1 , a good
rate capacity of 330 mAh g−1 at 2 A g−1 , and an impressive cycle stability with
stable capacity of 686 mAh g−1 at 0.5 A g−1 over 500 cycles. When configured with
LiFePO4 cathode for full-cell test the 3D-GNS/SiOCf anode exhibited a good elec-
trochemical performance (with a high capacity of 703 mAh g−1 at 0.1 A g−1 after
100 cycles, and acceptable rate capacities) along with favorable flexible features,
which could shed light on the design and engineering of general electrospun flexible
devices. However, for these flexible electrodes, the simultaneous realization of high
strength, high active material loading, and high cycling stability is still a challenge
for competitive real-world application.
Mo et al. designed a 3D N-doped graphene composite foam comprised of
Ge/graphene yolk–shell nanostructures (Ge-QD@NG/NGF) for high-performance
flexible LIBs [32]. The N-doped graphene foam framework was first fabricated
by a classic CVD method using a commercial porous nickel foam template and
the common N,C-containing precursors (e.g., pyridine), followed by incorporating
Ge quantum dots into the framework and removing the template. The interspace
between yolks (quantum dots) and shell (N-doped graphene) could be tuned by the
mediation of an etchable electroplating deposition layer (Fig. 1 a–e). As a highly
conductive 3D interconnected porous N-doped graphene composite anode for LIBs,
it demonstrated a superior specific capacity of 1220 mAh g−1 at 1C (here 1C =
1600 mAh g−1 ), long-term cycle stability (with capacity retention of >96% from
2 to 1000 cycle, and an average CE of ~99.7%), excellent rate performance (1001
and 801 mAh g−1 at 10 and 40 C, respectively), and negligible overpotential and
capacity loss (<2%) under bend state (Fig. 1f–h). The nickel foam-derived flexible
3D graphene anode with incorporated alloying materials (e.g., Si, Ge, Sn) paves a
way for the development of flexible high-specific-capacity electrode systems, espe-
cially for those active materials with huge volume expansion. However, it should be
noted that these Ni or Cu foam-derived lightweight 3D graphene frameworks may
show uncompetitive volumetric capacity due to their lower tap density.
For the 3D printable LIBs, the graphene nanoplatelets may serve as conductive
components for the preparation of printable electrode filaments as primary mate-
rials of 3D-printed electrodes, i.e., the classic and low-cost fused filament fabrica-
tion (FFF) or DIW [12, 15]. However, the content of active materials is low in the
polymer-based filaments and higher energy densities are required for competitive
applications. Active conductive fillers such as functional graphene may be a new
class of promising alternative nanomaterials for 3D-printed electrodes and the full
cells thereof. Furthermore, the 3D printing technique may be exploited for advanced
batteries in arbitrary geometry to fulfill a customized product design with integrated
batteries, which could simultaneously serve as a structural component in the wearable
electronic devices.
3.2 Na-Ion Batteries
The most significant advantage of Na–ion batteries (SIBs) comes from the abun-
dance of sodium in the Earth’s crust as well as the low cost compared to lithium.
SIBs are emerging as one kind of the most cost-effective rechargeable batteries and
are getting more competitive and poised for rapid growth as an alternative to LIBs.
To date, most flexible SIBs are based on graphene and carbon nanotubes, some
electrospun carbon nanofibers are also referred to. Fiber battery is another kind of
the most promising wearable devices, featured by their flexibility and knittability/
weavability. However, the sluggish ion transport kinetics, owing to the limited inter-
facial intimacy and lowered conductivity of solid/gel-type electrolytes, have hindered
their practical application. 3D graphene frameworks with interconnected tunnel could
provide exclusive fast ion transport along with intrinsic electron conductivity. Wang
et al. fabricated a wet-spun fibrous, 3D porous cathode comprised of 2D tungstate
nanosheets and graphene nanosheets both with rigid and open lattice structures as well
as molecular/atomic thickness and large lateral size (Fig. 2a–f) [21]. When configured
with sodium or lithium metal fiber anode, the as-assembled fiber-shaped SIB and LIB
Fig. 1 a Schematic illustration of the preparation process of 3D N-doped graphene foam with
encapsulated Ge-quantum-dot@N-doped graphene yolk–shell (denoted as Ge-QD@NG/NGF/
PDMS) nanoarchitectures. PDMS: polydimethylsiloxane. b Photograph of the as-prepared flex-
ible Ge-QD@NG/NGF electrode (size of 7 × 4 cm), and c–e the corresponding SEM and TEM
images. f Galvanostatic charge–discharge (GCD) profiles in the potential window of 0.01–1.5 V
(vs. Li/Li+ ) at 1C rate, and g the cycling performance and CE of the Ge-QD@NG/NGF/PDMS
electrode, compared to Ge/NGF/PDMS and Ge/Cu electrodes (1C, 1000 cycles). h Schematic
illustration showing the advantages of the NGF-based flexible electrode structure. Adapted from
reference [32]. Copyright The Authors, some rights reserved; exclusive licensee Springer Nature.
Distributed under a Creative Commons Attribution License 4.0 (CC BY) https://creativecommons.
org/licenses/by/4.0/
showed superior capacities (178 mAh g−1 for SIB and 206 mAh g−1 for LIB, respec-
tively), outstanding rate performance, long-term cycle stability (up to 1000 cycles),
and excellent flexibility (up to 200 bending cycles). Besides the structural advan-
tages, the high-proportion pseudocapacitive charge storage contributes greatly to the
enhanced capacities (Fig. 2g–i). The 3D graphene fiber-based electrodes provide
new insight into the elegant engineering of fiber electrodes and the resultant fiber
energy storage devices including fiber batteries; however, the strength of the fiber
electrodes and the batteries thereof as well as the safety of the alkali-metal-based
batteries needs to be further enhanced for actual wearable applications.
NASICON-type materials such as NaTi2 (PO4 )3 with open 3D framework as
well as the high thermal stability and superior Na+ conductivity are another
kind of promising anode materials for SIBs [33, 34]. NaTi2 (PO4 )3 can be
combined with graphene to form flexible freestanding electrode, e.g., sandwich-like
GN/NaTi2 (PO4 )3 /GN film [23]. It can deliver a high specific capacity of
137 mAh g−1 at a current density of 0.1 A g−1 and a high rate capacity of 93 mAh
g−1 at 1 A g−1 , as well as an excellent cycle stability with 92% capacity retention
at 0.5 A g−1 after 1000 cycles. When configured with a typical cathode material,
Na0.44 MnO2 , the full cell (voltage window of 4–2 V) demonstrated a high initial
Fig. 2 a and b Schematic illustration of the preparation procedure of fiber electrode from 2D
tungstate nanosheets, and the ion transport inside the fiber electrode. c–e SEM images of the
tungstate/rGO fiber at different magnifications, and f the corresponding cross-sectional HRTEM
image (HRTEM: high-resolution transmission electron microscopy). g rate performance of the
fiber battery at different current densities (0.052–0.520 mA), and h the cycle performance and
corresponding CE at 0.520 mA. i contribution ratio of capacitive-controlled (red color) and diffusion-
controlled (black color) capacities at various scan rates. Adapted with permission [21], copyright
(2020), the royal society of chemistry
capacity of 114 mAh g−1 (discharge at 0.1 mA g−1 , based on anode mass) and a
high ICE of 82.3%. However, it should be noted that these NASICON-type high
potential negative electrode materials somewhat deteriorate the voltage output and
energy density of the full cell compared to Na metal anode, although theoretically
and ideally the Na metal and its hybrids/composites are most eagerly anticipated for
flexible SIBs.
Some other transition-metal chalcogenides (TMCs) were also applied as flexible
anode materials for SIBs, e.g., graphene paper hybrids with CuS nanoflowers (flower-
like microspheres) [35] and SnSe nanosheets [36] fabricated by a facile vacuum filtra-
tion approach. However, for transition-metal sulfides (TMSs) the low ICE should be
paid particular attention for appropriate solutions. Compared to sulfides, the selenides
possess lower Na–ion insertion/extraction potential and enhanced conductivity [37],
thus for a battery with higher output voltage and enhanced rate performance. The
annealing and presodiation of GO or rGO are effective strategies to improve the ICE.
3.3 Li–S Batteries
Due to the high mechanical flexibility and superior charge transfer merits, 3D
graphene with multiscale structures holds great promise for energy storage; by
incorporation of lithium–sulfur batteries (LSBs) featured by high theoretical energy
density (2600 Wh kg−1 ) and low cost, the 3D graphene-based flexible lithium–sulfur
batteries (FLSBs) may demonstrate synergistic effects to overcome some of the crit-
ical obstacles faced by traditional LSBs and realize the simultaneous achievement
of good flexibility, high energy density, and long cycle life [9, 38]. For example,
Ni et al. designed a honeycomb-like graphene/sulfur composite film with multi-
scale sulfur particles confined in the ultrathin but robust freestanding electrode via a
facile vacuum filtration method (Fig. 3a–c) [39]. The as-prepared flexible composite
cathode of Li–S batteries shows an enhanced specific capacity of 823 mAh g−1
at 0.5C after 100 cycles. The adoption of biosurfactant tuned the dimensions of
the sulfur particles and increased the interfacial adhesion, thus for an enhance-
ment of the flexibility and strength of the thin freestanding electrode in addition to
the increased utilization of sulfur. These freestanding/flexible graphene/sulfur cath-
odes can be further incorporated with specific multifunctional separators/interlayers
(e.g., polysulfone-functionalized separators, boron nitride–graphene interlayers) or
advanced Li-metal-hosting anodes (e.g., 3D nanostructured lithium cloth or other
carbon-based lithium hosts [40] with the adoption of Li metal anode but suppressed
formation of Li dendrites) for high-performance flexible Li–S batteries with high
energy density, long cycle life, and enhanced safety (Fig. 3d) [41, 42].
Fig. 3 a Schematic illustration of the synthesis procedure for the honeycomb-like S@rGO ultra-
thin nanocomposite membrane, and b and c the corresponding digital photo and SEM image of the
upper surface of nanocomposite membrane. Adapted with permission [39], copyright (2016), the
royal society of chemistry. d schematic illustration of a typical flexible soft-packed Li–S full cell,
configured by lithium cloth anode, PSU-Celgard separator, and FBN/G interlayer protected free-
standing graphene/sulfur cathode. PSU: polysulfone; FBN: functionalized boron nitride nanosheets.
Adapted with permission [41], copyright (2020), American chemical society
The addition of graphene to other 3D matrices (e.g., MXene, cellulose nanofiber)

can also improve the conductivity and enhance the immobilization/conversion of
polysulfides. The incorporation of nanofillers such as cellulose nanocrystalline/
nanofiber could improve the mechanical properties [43]. For more information
on graphene/sulfur nanocomposites as cathode/anode materials and separators/
interlayers for Li–S batteries, one may refer to some recent critical reviews [9, 42].
3.4 Zn-Ion and Zn–Air Batteries
Aqueous rechargeable Zn–ion batteries (ZIBs) with intrinsic safety and low cost have
been revived due to the growing popular demand for wearable and portable elec-
tronics; however, the dendrite and low flexibility of zinc metal anode are hampering
their practical application. 3D carbon frameworks, especially 3D graphene, are ideal
materials for the construction of flexible freestanding anode as well as cathode [44].
Cao et al. fabricated a robust and dendrite-free electrodeposited Zn anode by in situ
growth of 3D N-doped vertical graphene nanosheets on the carbon cloth (N-VG@CC,
PECVD method) for uniform Zn nucleation (Fig. 4a–c) [24]. The N-containing
groups (zincophilic) in the framework lowered the Zn nucleation overpotential due
to the enhanced interaction between Zn2+ and N-VG, thus for uniform distribution
of Zn nuclei; together with the synergistic effect of 3D graphene with homogenized
electric distribution for optimized Zn deposition process, it suppressed the dendrite
growth and significantly improved the Zn plating/stripping process (more reversible
and higher CE) (Fig. 4d). When configured with elaborately fabricated cathode,
MnO2 @N-VG@CC (similar structure with anode), the flexible ZIBs (quasi-solid-
state) showed superior cycling performance with a high capacity retention of 80%
over 300 cycles as well as excellent mechanical flexibility (Fig. 4e–g). The robust 3D
graphene@CC framework could be a promising candidate for ultimate application
of portable/wearable electronics [24, 45]. Some graphene-based aerogel hybrid with
encapsulated Zn for foldable ZIB are also explored, these hybrid aerogels featured by
abundant zincophilic micropores are showing even higher performances; however,
additional current collector (e.g., Ti foil) is used, and further critical investigation is
needed for real-world application as wearable/flexible batteries [25].
Rechargeable Zn–air batteries (ZABs) are another kind of promising energy
storage device for flexible and wearable electronics, due to the high theoretical
energy density (1086 Wh kg−1 ), cost-effectiveness, inherent safety, and environ-
mental friendliness [46]. 3D graphene with favorable honeycomb nanostructures
(i.e., macroporous channels) could also be applied as efficient frameworks/skeletons
of cathode in flexible/wearable rechargeable ZABs owing to the enhanced air/
electrolyte permeability and efficient air diffusion compared to carbon membrane
or carbon cloth. For example, Wu et al. fabricated an iron-decorated carbon
aerogel (FeP/Fe2 O3 @N,P-doped rGO/CNF, abbr. FeP/Fe2 O3 @NPCA; CNF: cellu-
lose nanofibril) with high ORR and OER catalysis activities (ORR, oxygen reduction
reaction; OER, oxygen evolution reaction) via freeze-drying and pyrolysis (Fig. 5a–
d) [46]. The as-obtained freestanding FeP/Fe2 O3 @NPCA air cathode for flexible
solid-state ZAB (with classic alkaline PVA gel electrolyte) showed high mechanical
stability (especially compressibility), an excellent specific capacity of 676 mAh g−1
and energy density of 517 Wh kg−1 (at 20 mA cm−2 ), as well as small overpoten-
tial, distinct flexibility, and good cycling stability (Fig. 5e–g). It offers an alternative
strategy for the design and preparation of competitive bifunctional air cathodes of
ZABs. Some similar works by adhering/pressing the functional graphene (e.g., via
CVD) to glassy carbon or carbon cloth also showed comparable performances [47].
Fig. 4 SEM images of a and b the intermediate N-VG@CC at different magnifications and c the
resultant Zn@N-VG@CC anode. d schematic illustration of Zn plating on CC and N-VG@CC elec-
trodes, showing the effect of N-VG on Zn deposition. e schematic illustration of the construction
of the flexible quasi-solid-state ZIB. f GCD curves of the as-designed ZIB at various current densi-
ties, and g the corresponding Ragone plot, compared with other reported energy storage devices.
Adapted with permission [24], Copyright (2021) Wiley–VCH GmbH
Some researches also referred to rGO/MXene-coated nickel foam as air cathodes for
flexible ZABs.
3.5 Other Batteries
Some other kinds of flexible or compressible quasi-solid-state batteries such as Ni–

Fe batteries (QSS-NFB), Ni–Bi batteries have also been fabricated for flexible or
compression-tolerant electronics. However, for these nickel-based aqueous batteries,
self-discharge rate and power/energy density should be further improved. Kong
et al. 3D-printed a series of freestanding electrodes with diverse structural config-
urations for Ni–Fe batteries [48]. The hierarchically porous rGO/CNTs composite
electrodes were fabricated by the classic extrusion-based 3D printing technology,
with embedded ultrathin Ni(OH)2 nanosheet array serving as cathode, and with holey
Fig. 5 a Schematic illustration of the fabrication of FeP/Fe2 O3 @NPCA air cathode of Zn–air
battery (ZAB). b–d SEM images of FeP/Fe2 O3 @NPCA at different magnifications. e and f Rate
performance (discharge) of FeP/Fe2 O3 @NPCA-based ZAB and the corresponding discharge curves
(galvanostatic) at varied current densities (with specific capacity normalized by consumed Zn mass).
g Schematic illustration of the solid-state ZAB with FeP/Fe2 O3 @NPCA working as freestanding
air cathode. Adapted with permission [46], Copyright (2020), WILEY–VCH Verlag GmbH & Co.
KGaA, Weinheim
Fe2 O3 nanorod array serving as anode, respectively (Fig. 6a). When configured as
a full cell, the QSS-NFB showed an outstanding long-term cycling stability (with a
capacity retention of 91.3% over 10,000 cycles), a superior energy density of 28.1
mWh cm−3 (at a power density of 10.6 mW cm−3 ), as well as a high loading of
active materials of over 130 mg cm−3 and favorable compressibility (up to 60%)
(Fig. 6b–d). Wang et al. fabricated a fiber-shaped Ni–Bi battery via coaxial coating
of CNT fibers with electrodeposited 3D honeycomb-like rGO. For the fibrous hier-
archical electrodes, NiO/Ni-containing electrode is working as cathode and the Bi
metal-containing electrode as anode [49]. The fiber-shaped Ni–Bi battery (rGO/Ni/
NiO/CNT//rGO/Bi/CNT) could deliver a high capacity of 164 mAh g−1 at 5 A g−1 ,
enhanced by the incorporation of graphene, i.e., 187% increase compared to orig-
inal Bi/CNT anode, as well as 115% increase by introducing rGO/NiO/Ni. Also it
showed a high energy density of 43.4 Wh kg−1 (or 26.0 mWh cm−3 ) and a high power
Fig. 6 a Schematic illustration of the preparation of rGO/CNTs@Ni(OH)2 cathode and rGO/

CNTs@α-Fe2 O3 anode by 3D printing, and the corresponding configuration and compressibility of
the as-prepared quasi-solid-state Ni–Fe battery (QSS-NFB). b cycle performance of the QSS-NFB
at varied compression states at a constant current density of 200 mA cm−2 , and c the corresponding
capacity retention of the QSS-NFB as a function of compression cycle number (inset: variation
of electrical resistance with repeated compression up to 60% strain). d long-term cycling perfor-
mance of the 3D-printed QSS-NFB (10,000 cycles at 300 mA cm−2 ; insets: GCD curves for the
initial 5 cycles and the last 5 cycles, respectively). Adapted with permission [48], copyright (2020)
American chemical society
density of 6.6 kW kg−1 (or 4.0 W cm−3 ), as well as an ultrahigh capacity retention
of 96% after 10,000 cycles. Although the output voltage of Ni–Bi batteries is lower
than that of Ni–Fe batteries, their high-rate performance demonstrates promising
high-power applications. Some similar solid-state flexible/wearable batteries based
on fiber-shaped electrodes are assembled to extend their practical application [50].
These abovementioned nickel-based batteries are beneficial addition to the family
of flexible/wearable quasi-solid-state aqueous rechargeable batteries beyond alkali-
metal–ion batteries and multivalent metal–ion batteries, and are showing great
promise for safe, low-cost, and even large-scale electrochemical energy storage
systems. Moreover, some novel batteries such as flexible H2 O2 microfluidic fuel
cell and dye-sensitized solar cell are also of research interest.
4 Challenges and Perspectives
3D graphene with specific structures possesses great advantages of integral conduc-

tivity of the electrodes, and the inherently soft framework with high surface area
ensures the overall structural stability, high active material loading, and compati-
bility for advanced flexible/wearable rechargeable batteries. However, the simulta-
neous combination of electrochemical, mechanical properties, and cost performance
index (CPI or price–performance ratio) is challenging, which may eventually deter-
mine its practical application and industrialization in wearable and flexible energy
storage field.
(1) The microstructure control (e.g., for ordered structure) to rationally reduce
the undesired defects could enhance the mechanical flexibility; some favor-
able defects may improve the electrochemical performances, thus, the physical/
chemical defects should be weighed in the balance and an optimized synergy is
favored.
(2) Carbon/graphite fibers and carbon cloth, as well as carbon nanotube foam, are
versatile platforms for the fabrication of various robust flexible and wearable
batteries, including rechargeable alkali-metal–ion batteries, Zn-ion and Zn–
air batteries, Ni–Fe batteries, all-solid-state hybrid capacitors, etc. Some metal
wires (such as stainless steel, copper) are often used as conductive backbone
for flexible energy storage devices; however, these matrices/substrates may be
relatively heavier and the reduced energy density limits its wide application.
(3) For some composite electrodes, suspending or thickening agents such as
nanofibrillated cellulose (NFC) may be introduced to assist the preparation and/
or performance of 3D graphene materials with enhanced structural uniformity
and stability.
(4) The incorporation of high-energy-density materials and functional materials
with 3D graphene such as sulfur for flexible Li–S batteries and electrocatalysts
for metal–air or metal–CO2 batteries is of great promise. Besides the promising
cathode materials, 3D graphene can also serve as efficient anode materials or

(multi)functional components in advanced flexible/wearable batteries.
(5) More novel and compatible configuration designs of electrodes, electrolytes,
and the energy storage devices should be explored for portable and wearable/
flexible electronics. And general and consistent standards should be established
for the evaluation of these unconventional energy storage devices regarding to
their mechanical and electrochemical properties.
References
1. Fu, K.K., Cheng, J., Li, T., Hu, L.: Flexible batteries: from mechanics to devices. ACS Energy
Lett. 1, 1065–1079 (2016)
2. Xiang, F., Cheng, F., Sun, Y., Yang, X., Lu, W., Amal, R., Dai, L.: Recent advances in flexible
batteries: from materials to applications. Nano Res. 16, 4821–4854 (2023)
3. Nasreldin, M., de Mulatier, S., Delattre, R., Ramuz, M., Djenizian, T.: Flexible and stretchable
microbatteries for wearable technologies. Adv. Mater. Technol. 5, 2000412 (2020)
4. Wu, Z., Wang, Y., Liu, X., Lv, C., Li, Y., Wei, D., Liu, Z.: Carbon-nanomaterial-based flexible
batteries for wearable electronics. Adv. Mater. 31, 1800716 (2019)
5. Chen, K., Wang, Q., Niu, Z., Chen, J.: Graphene-based materials for flexible energy storage
devices. J. Energy Chem. 27, 12–24 (2018)
6. Kim, S.D., Sarkar, A., Ahn, J.-H.: Graphene-based nanomaterials for flexible and stretchable
batteries. Small 17, 2006262 (2021)
7. Dai, C., Sun, G., Hu, L., Xiao, Y., Zhang, Z., Qu, L.: Recent progress in graphene-based
electrodes for flexible batteries. InfoMat 2, 509–526 (2020)
control. Chem. Rev. 120, 10336–10453 (2020)
9. Yang, T., Xia, J., Piao, Z., Yang, L., Zhang, S., Xing, Y., Zhou, G.: Graphene-based materials
for flexible lithium–sulfur batteries. ACS Nano 15, 13901–13923 (2021)
10. Li, S., Zhao, Y., Liu, Z., Yang, L., Zhang, J., Wang, M., Che, R.: Flexible graphene-wrapped
carbon nanotube/graphene@MnO2 3D multilevel porous film for high-performance lithium-ion
batteries. Small 14, 1801007 (2018)
11. Sang, Z., Yan, X., Wen, L., Su, D., Zhao, Z., Liu, Y., Ji, H., Liang, J., Dou, S.X.: A graphene-
modified flexible SiOC ceramic cloth for high-performance lithium storage. Energy Storage
Mater. 25, 876–884 (2020)
12. Reyes, C., Somogyi, R., Niu, S., Cruz, M.A., Yang, F., Catenacci, M.J., Rhodes, C.P.,
Wiley, B.J.: Three-dimensional printing of a complete lithium ion battery with fused filament
fabrication. ACS Appl. Energy Mater. 1, 5268–5279 (2018)
13. Zhang, Y., Shi, G., Qin, J., Lowe, S.E., Zhang, S., Zhao, H., Zhong, Y.L.: Recent progress
of direct ink writing of electronic components for advanced wearable devices. ACS Appl.
Electron. Mater. 1, 1718–1734 (2019)
14. Zhang, S., Liu, Y.Q., Hao, J.N., Wallace, G.G., Beirne, S., Chen, J.: 3D-printed wearable
electrochemical energy devices. Adv. Funct. Mater. 32, 2103092 (2022)
15. Jiang, Y., Guo, F., Liu, Y., Xu, Z., Gao, C.: Three-dimensional printing of graphene-based
materials for energy storage and conversion. SusMat 1, 304–323 (2021)
16. Li, Y., Ye, D., Shi, B., Liu, W., Guo, R., Pei, H., Xie, J.: Free-standing reduced graphene
oxide/MnO2 –reduced graphene oxide–carbon nanotube nanocomposite flexible membrane as
an anode for improving lithium-ion batteries. Phys. Chem. Chem. Phys. 19, 7498–7505 (2017)
17. Fu, J., Kang, W., Guo, X., Wen, H., Zeng, T., Yuan, R., Zhang, C.: 3D hierarchically porous
NiO/Graphene hybrid paper anode for long-life and high rate cycling flexible Li-ion batteries.
J. Energy Chem. 47, 172–179 (2020)
18. Chao, Y., Jalili, R., Ge, Y., Wang, C., Zheng, T., Shu, K., Wallace, G.G.: Self-assembly of
flexible free-standing 3D porous MoS2 -reduced graphene oxide structure for high-performance
lithium-ion batteries. Adv. Funct. Mater. 27, 1700234 (2017)
19. Cong, L., Zhang, S., Zhu, H., Chen, W., Huang, X., Xing, Y., Xia, J., Yang, P., Lu, X.: Structure-
design and theoretical-calculation for ultrasmall Co3 O4 anchored into ionic liquid modified
graphene as anode of flexible lithium-ion batteries. Nano Res. 15, 2104–2111 (2022)
20. Lu, C., Li, Z., Yu, L., Zhang, L., Xia, Z., Jiang, T., Yin, W., Dou, S., Liu, Z., Sun, J.: Nanostruc-
tured Bi2 S3 encapsulated within three-dimensional N-doped graphene as active and flexible
anodes for sodium-ion batteries. Nano Res. 11, 4614–4626 (2018)
21. Wang, Y., Zheng, Y., Zhao, J., Li, Y.: Flexible fiber-shaped lithium and sodium-ion batteries
with exclusive ion transport channels and superior pseudocapacitive charge storage. J. Mater.
Chem. A 8, 11155–11164 (2020)
22. Ma, Z., Zhou, X., Deng, W., Lei, D., Liu, Z.: 3D porous MXene (Ti3 C2 )/reduced graphene
oxide hybrid films for advanced lithium storage. ACS Appl. Mater. Interfaces 10, 3634–3643
(2018)
23. Guo, D., Qin, J., Zhang, C., Cao, M.: Constructing flexible and binder-free NaTi2 (PO4 )3 film
electrode with a sandwich structure by a two-step graphene hybridizing strategy as an ultrastable
anode for long-life sodium-ion batteries. Cryst. Growth Des. 18, 3291–3301 (2018)
24. Cao, Q.H., Gao, H., Gao, Y., Yang, J., Li, C., Pu, J., Du, J.J., Yang, J.Y., Cai, D.M., Pan, Z.H.,
Guan, C., Huang, W.: Regulating dendrite-free zinc deposition by 3D zincopilic nitrogen-
doped vertical graphene for high-performance flexible Zn-ion batteries. Adv. Funct. Mater. 31,
2103922 (2021)
25. Zhou, J., Xie, M., Wu, F., Mei, Y., Hao, Y., Li, L., Chen, R.: Encapsulation of metallic Zn
in a hybrid MXene/graphene aerogel as a stable Zn anode for foldable Zn-ion batteries. Adv.
Mater. 34, 2106897 (2022)
26. Ni, W., Shi, L.: Layer-structured carbonaceous materials for advanced Li-ion and Na-ion
batteries: beyond graphene. J. Vac. Sci. Technol. A 37, 040803 (2019)
27. Wang, B., Yuan, W., Zhang, X., Xiang, M., Zhang, Y., Liu, H., Wu, H.: Sandwiching defect-
rich TiO2 −δ nanocrystals into a three-dimensional flexible conformal carbon hybrid matrix
for long-cycling and high-rate Li/Na-ion batteries. Inorg. Chem. 58, 8841–8853 (2019)
28. Wang, Y., Kong, D., Huang, S., Shi, Y., Ding, M., Von Lim, Y., Xu, T., Chen, F., Li, X.,
Yang, H.Y.: 3D carbon foam-supported WS2 nanosheets for cable-shaped flexible sodium ion
batteries. J. Mater. Chem. A 6, 10813–10824 (2018)
29. Wang, Y.S., Yang, J., Liu, S.Y., Che, X.G., He, S.J., Liu, Z.B., Wang, M., Wang, X.T., Qiu,
J.S.: 3D graphene-like oxygen and sulfur-doped porous carbon nanosheets with multilevel ion
channels for high-performance aqueous Zn-ion storage. Carbon 201, 624–632 (2023)
30. Chen, F., Yuan, J., Zhou, M., Gui, H., Xiang, Y., Yang, J., Li, X., Xu, C., Wang, R.: Compressible
neuron-like 3D few-layered MoS2 /N-doped graphene foam as freestanding and binder-free
electrodes for high-performance lithium-ion batteries. ACS Appl. Energy Mater. 5, 7249–7259
(2022)
31. Cai, X., Liu, W., Zhao, Z., Li, S., Yang, S., Zhang, S., Gao, Q., Yu, X., Wang, H., Fang, Y.:
Simultaneous encapsulation of nano-Si in redox assembled rGO film as binder-free anode for
flexible/bendable lithium-ion batteries. ACS Appl. Mater. Interfaces 11, 3897–3908 (2019)
flexible Li-ion battery. Nat. Commun. 8, 13949 (2017)
33. Wu, M., Ni, W., Hu, J., Ma, J.: NASICON-structured NaTi2 (PO4 )3 for sustainable energy
storage. Nano-Micro Lett. 11, 44 (2019)
34. Ni, W., Shi, L.: 2D and Layered Ti-based materials for supercapacitors and rechargeable
batteries: synthesis, properties, and applications. Curr. Appl. Mater. 1, e200521193451 (2022)
35. Liu, W., Shi, B., Wang, Y., Li, Y., Pei, H., Guo, R., Hou, X., Zhu, K., Xie, J.: A flexible,
binder-free graphene oxide/copper sulfides film for high-performance sodium ion batteries.
ChemistrySelect 3, 5608–5613 (2018)
36. Kong, P., Zhu, L., Li, F., Xu, G.: Self-supporting electrode composed of SnSe nanosheets,
thermally treated protein, and reduced graphene oxide with enhanced pseudocapacitance for
advanced sodium-ion batteries. ChemElectroChem 6, 5642–5650 (2019)
37. Wei, Z., Wang, L., Zhuo, M., Ni, W., Wang, H., Ma, J.: Layered tin sulfide and selenide anode
materials for Li- and Na-ion batteries. J. Mater. Chem. A 6, 12185–12214 (2018)
38. Zhang, Y., Gao, Z., Song, N., He, J., Li, X.: Graphene and its derivatives in lithium–sulfur
batteries. Mater. Today Energy 9, 319–335 (2018)
39. Ni, W., Cheng, J., Li, X., Guan, Q., Qu, G., Wang, Z., Wang, B.: Multiscale sulfur particles
confined in honeycomb-like graphene with the assistance of bio-based adhesive for ultrathin
and robust free-standing electrode of Li–S batteries with improved performance. RSC Adv. 6,
9320–9327 (2016)
40. Chen, S., Chen, S., Han, D., Bielawski, C.W., Geng, J.: Carbon-based materials as lithium hosts
for lithium batteries. Chem. Eur. J. 28, e202201580 (2022)
41. Yu, B., Fan, Y., Mateti, S., Kim, D., Zhao, C., Lu, S., Liu, X., Rong, Q., Tao, T., Tanwar, K.K.,
Tan, X., Smith, S.C., Chen, Y.I.: An ultra-long-life flexible lithium–sulfur battery with lithium
cloth anode and polysulfone-functionalized separator. ACS Nano 15, 1358–1369 (2021)
42. Ni, W., Shi, L.-Y.: 14 - Graphene–sulfur nanocomposites as cathode materials and separators
for lithium–sulfur batteries. In: Gupta, R.K., Nguyen, T.A., Song, H., Yasin, G. (eds.) Lithium-
Sulfur Batteries, pp. 289–314. Elsevier (2022)
43. Luo, Y., Wan, Y., Huang, J., Li, B.: Nanofiber enhanced graphene–elastomer with unique
biomimetic hierarchical structure for energy storage and pressure sensing. Mater. Des. 203,
109612 (2021)
44. Wu, L.-S., Zhang, M.-H., Xu, W., Dong, Y.-F.: Recent advances in carbon materials for flexible
zinc ion batteries. New Carbon Mater. 37, 827–851 (2022)
45. Chen, J., Liang, J., Zhou, Y., Sha, Z., Lim, S., Huang, F., Han, Z., Brown, S.A., Cao, L., Wang,
D.-W., Wang, C.H.: A vertical graphene enhanced Zn–MnO2 flexible battery towards wearable
electronic devices. J. Mater. Chem. A 9, 575–584 (2021)
46. Wu, K., Zhang, L., Yuan, Y., Zhong, L., Chen, Z., Chi, X., Lu, H., Chen, Z., Zou, R., Li, T.,
Jiang, C., Chen, Y., Peng, X., Lu, J.: An iron-decorated carbon aerogel for rechargeable flow
and flexible Zn–air batteries. Adv. Mater. 32, 2002292 (2020)
47. Qiu, H.-J., Du, P., Hu, K., Gao, J., Li, H., Liu, P., Ina, T., Ohara, K., Ito, Y., Chen, M.: Metal
rechargeable Zn–air batteries. Adv. Mater. 31, 1900843 (2019)
48. Kong, D.Z., Wang, Y., Huang, S.Z., Zhang, B., Lim, Y.V., Sim, G.J., Alvarado, P.V.Y., Ge,
Q., Yang, H.Y.: 3D printed compressible quasi-solid-state nickel-iron battery. ACS Nano 14,
9675–9686 (2020)
49. Wang, M., Xie, S., Tang, C., Zhao, Y., Liao, M., Ye, L., Wang, B., Peng, H.: Making fiber-
shaped Ni//Bi battery simultaneously with high energy density, power density, and safety. Adv.
Funct. Mater. 30, 1905971 (2020)
50. Li, X., Gao, T., Liu, Q., Xu, Y., Li, J., Xiao, D.: Designing a high-performance anode composed
of carbon nanotubes and Fe–Fe3 C nanoparticles for quasi-solid-state fibrous Ni/Fe batteries.
Mater. Chem. Front. 5, 3636–3645 (2021)
3D Graphene for High-Performance
Supercapacitors
K. A. U. Madhushani and Ram K. Gupta
Abstract Over the past decades, the supercapacitor (SC) has received great attention
as a developing energy storage device due to its unique characteristic features of high-
power density and relatively high energy density. It is known that the properties of SC
can be modified by tuning the electrode materials. Among those materials, graphene
(GN) has great potential to transfer a higher amount of charge at a fast rate and
store more energy in electrical double-layer capacitor-based supercapacitors. The
properties of GN such as large specific area, porosity, higher specific capacitance,
and higher electrical conductivity have led to novel routes for the modification of
alternative materials. Although 2D structured GN was discovered earlier, it limited
the performance of the devices due to the assembling of the sheets. As a result of the
tremendous effort of many past studies, 3D-GN synthesized from the 2D-GN was able
to overcome those limitations and become an effective electrode material compared
to others. Some reports recorded that the strongness of 3D-GN is ten times greater
than steel. Along with the changes in the morphological changes of the structure,
some heterogeneous configurations of 3D-GN such as aerogel, sponge, film, fibers,
foam, monolith, and spheres have been found for various purposes. This nanomaterial
has already expanded in different fields including supercapacitors, batteries, fuel
cells, sensors, flexible electronic devices, solar steam generation devices, catalysts ,
and absorbents. Although this material applies to various applications, this chapter
focuses only on the contribution of 3D-GN to energy storage in SCs. Under this
topic, various types of synthesis methods of 3D-GN with examples, the fundamental
characteristics of three different SCs and the energy storage mechanism of each SC,
and the electrochemical performances of both 3D-GN-based SCs and flexible SCs
are discussed in detail.
Keywords 3D Graphene · Graphene synthesis · Energy storage devices ·

Supercapacitors · Flexible-supercapacitors
K. A. U. Madhushani · R. K. Gupta (B)

Department of Chemistry, Pittsburg State University, Pittsburg, KS 66762, USA
e-mail: ramguptamsu@gmail.com
National Institute for Materials Advancement, Pittsburg, KS 66762, USA
https://doi.org/10.1007/978-3-031-36249-1_16
286 K. A. U. Madhushani and R. K. Gupta
1 Introduction
With the development of cutting-edge technology, the burning of fossil fuels as

the main source of energy is increasing at an unprecedented rate. However, it has
been recorded so many problems such as ozone layer depletion resulting in global
warming, water, and air pollution because of the industrial revolution and global-
ization. Therefore, a leading solution should be essential to reduce these kinds of
threats. Though renewable energy sources such as solar, wind tidal, and water can
be used as eco-friendly energy sources, some problems such as their availability
being limited to a certain region, time, and climate are being recorded. So, an effi-
cient solution is essential to overcome these problems. Therefore, electrochemical
energy storage devices (EESDs) are being invented to generate and store energy for
future purposes. Depending on the utility, properties, processing costs, and long-
term usage, these devices can be in a wide range. Some examples of EESDs are
supercapacitors (SCs), fossil fuels, capacitors, and batteries. Among those, SCs are
considered promising candidates due to their unique properties such as higher super
capacitance, high-power density, fast charge–discharge rate, and excellent stability.
The main issue with that is lower energy density. Therefore, a lot of research is being
done to improve energy density.
The electrochemical performances of the devices mainly depend on two factors;
electrode materials and the electrolyte, which are used for fabrication. Therefore,
there should be much attention when selecting electrode materials that can be used for
both energy transfer and storage. Among electrode materials, carbons have a greater
potential in energy applications due to their surface characteristics. With the changes
in the degrees of sp2 hybridization, different types of carbon nanomaterials resulted.
Based on the arrangement of the layers and coordination number, those carbon nanos-
tructures can be classified as 0D (carbon dots), 1D (carbon nanotubes-CNT), 2D
(graphene), and 3D (graphite) (Fig. 1). Zero-D materials, C60 , are composed of 60
carbon atoms with 12 pentagonal and 20 hexagonal rings. Two types of 1D carbons,
single-walled and multi-walled carbon nanotubes (CNTs), were prepared by concen-
trically rolling one or more graphene (GN) sheets, respectively [1]. Some examples
of each electrode material which are used for fabrication SCs are mentioned in Fig. 2.
Fig. 1 Type of carbonaceous material based on layer arrangement. Adapted with permission [1],
Copyright (2015), Springer Nature
3D Graphene for High-Performance Supercapacitors 287
Fig. 2 Classification of nanostructured electrode materials used for fabrication of SCs
GN, the first synthesized 2D material in the world was discovered by Andre Geim
and Konstantin Novoselov in 2004 [2]. This was a brilliant innovation that led to
the award of the Nobel Prize in 2010. Due to the arrangement of the sp2 carbon
atoms, GN has the lowest thickness with a high surface area of ~2630 m2 /g. When
considering the morphological features of 2D graphene, it has remarkable properties
of carrier mobility (over 200,000 cm2 /V.s), high mechanical strength (Young modulus
of ~1 TPa which is 300 times that of steel), excellent biocompatibility, high thermal
conductivity (~5000 W/m.K), and magnetic properties. Although GN can act as an
ideal electrode material for SCs, the material has some drawbacks. In that sense, due
to the strong interlayer Van der Waals forces, GN sheets tend to assemble. Because of
restacking, some properties such as lightness, porosity, and specific surface area are
reduced, and this will end up in many defects. The problems arising in the synthesis
of 2D-GN, and its structural limitations lead to an innovative new tunable structure
with high properties. Thus, synthesizing a controllable design of 3D-GN from the
2D-GN would be an excellent approach to avoid the aggregation of GN sheets [3].
With the advance of 3D-GN in 2009, the demand for the GN has increased in
the fabrication of different devices like sensors, catalysts, SCs, and batteries. Due
to its unique characteristics and high porosity, this material shows better functional
performance. To modify this material, the geometry of the GN is changed by applying
mechanical strains, chemical functionalization, complex treatments for GN folding,
etc. Typically, due to the multilayered structure or the morphology of the substrate,
the folded GN has a high thickness. This can be controlled by changing the shapes
like capsules, flowers, boxes, rings, etc. (Fig. 3). Experimentally, those configurations
can be obtained with the changes in the temperature. Some research has confirmed
that geometry is a considerable factor that decides the properties of the 3D-GN.
This has two different structures, graphene foam and vertically aligned graphene
(VAGN). Among them, VAGN is the most functioning electrode material due to its
higher mass-transfer capability and fast rate of reaction [4].
3D-GNs possess a high surface area due to the presence of uniformly distributed,
active porous sites. By combining this material with other effective functional groups,
the volume change of this material can be reduced. And functionalization with
different atoms gives an ultrathin, graded structure. Through these alternations, the
properties of GN such as flexibility and mechanical strength can be enhanced. Further,
the long-range π–π conjugation and hybridization allow transferring more electrons
and ions rapidly resulting in high conductivity. In addition to the porosity and design,
some aspects including the techniques used to produce nanocomposites, the relation-
ship between GN and embedded atoms, and the arrangements of the sites within the
material mainly affect the improvement of the electrochemical performances [5].
Fig. 3 Configuration of different 3D Graphene. Adapted with permission [3], Copyright (2020),
American Chemical Society
2 3D Graphene: Synthesis and Functionalization
2.1 Synthesis of 3D Graphene
Over recent times, the demand for the 3D-GN has increased due to its unique elec-
trochemical properties. Although the experimental higher values of specific capaci-
tance, energy density, and conductivity bring good performance to the electrocatal-
ysis processes, this material shows the contribution to energy storage applications.
This issue can be recovered by composing 3D-GN with relevant materials such
as metal oxides, and inorganic or organic materials. Over time, several methods
such as hydrothermal methods, chemical vapor deposition (CVD), 3D printing, and
self-assembly have been discovered for the fabrication of 3D-GN.
As a hydrothermal method, Li et al. produced 3D-GN monoliths from aqueous
graphene oxide (GO) and hexane droplets [6]. In that sense, reduced GO was formed
with the reduction of GO sheets, and they were bound around hexane droplets to
produce 3D-GN which is called microporous graphene monolith (MGM). As a first
step, an aqueous solution of GO and hexane were shaken to form MGMs. Then it
was dipped in 80 °C de-ionized water to remove hexane. On the other hand, water
was added to this to maintain the porosity of MGMs. Consequently, resulted from the
product was freeze-dried and annealed at 40 °C under 100% moisture condition via
the air-drying method (Fig. 4). The resulting 3D-GN is combined with the properties
of pressure sensing, excellent electrical conductivity, low density, and high elasticity.
Fig. 4 Schematic illustration of 3D Graphene synthesized via hydrothermal method. Adapted with
permission [6], Copyright (2014), John Wiley and Sons
In the synthesis of 3D-GN, the CVD process is the most popular technique that
can be classified under a bottom-up method. The principle behind CVD is the trans-
formation of gaseous carbon precursors into thin layers via chemical reactions under
heating conditions. The product obtained through this has better properties like higher
specific area, good quality, and uniform and thin layer structure. Generally, a high
temperature of 500 to 1000 °C was applied for CVD, and the other significant factor
is the carbon precursor that determines the structure of the GN formed afterward.
Among those, methane which has robustness and high stability is considered a good
precursor which can form uniform layers of GN. Although methane works at temper-
atures above 900 °C, some high carbon-contained materials can be operated at lower
temperatures. The CVD process occurs inside a tube furnace, and it happens by
completing five steps. As a first step, the carbon precursor is transferred into the
CVD chamber. Then, a vapor-based product is obtained after several chemical reac-
tions of gaseous carbon precursor. Later, the remaining carbon precursor with resulted
carbon product is moved to the substrate via the process of surface adsorption. This is
relatively the same as the latter after the decomposition and growth of the active sites
are complete. Finally, the active material is formed with some physical actions of
diffusion and collision. The most significant step in this CVD is to control the defects
and the thickness of the obtained 3D-GN. Overall, a carbon precursor, a chamber, a
substrate, and a heating system are needed to complete this process [5].
As a novel strategy, Zhu and his team produced graphene aerogels (GNA) through
direct ink writing which is considered an extrusion-based 3D printing technique
[7]. This 3D printed GN shows a high surface area, high compressibility, excellent
conductivity, and lightweight. Herein, they faced two challenges in designing a print-
able GN-based ink and keeping the same intrinsic features of GN in the synthesized
products. GO ink was prepared by applying both methods of addition of resorcinol
and formaldehyde (R-F solution) with sodium carbonate as catalyst (sol–gel) and
gelation to the highly concentrated GO suspension. Further, the viscosity of the
ink can be increased with the concentration of GO solution resulting in good print-
ability. Finally, hydrophilic fumed silica powder was added to the GO to enhance
the viscosity with the increment of the yield stress and elastic modulus of the ink.
This gives a highly viscous, homogenous ink. In 3D printing, this ink is loaded into
the syringe barrel, and the 3D patterned GN structure is printed layer-by-layer with
the extrusion of ink from the nozzle. As Fig. 5a, a simple cubic structured 3D-GN
was designed via this method. During the process of converting aerogels from 3D
printed GO structure, supercritical or freeze-drying steps are applied to remove the
GO gel to maintain the porosity of the final product. Moreover, they analyzed the
properties by comparing sol–gel and gelation separately. It is stated that the sol–gel
method gives a less crosslinked more open network compared with gelation (without
treating the R-F solution) Fig. 5b.
Most studies significantly stated that self-assembly via GO is very applicable in the
large-scale preparation of 3D-GNs. Herein, 2D-GO sheets are gathered by dissolving
GO in a solvent. These are bounded uniformly with the balanced interaction of Van
der Waals and electrostatic repulsions. After adding cross-linking agent, the gelation
process starts with the changes in the pH in the solution and its effects on the breakage
Fig. 5 a Steps in the 3D printing process of 3D-GNA. b Microstructure of 3D printed GNA (i)
Optical image. SEM images of (ii) 3D-GNA and (iii) GNA without treating R-F. (iv) GNA after
treating R-F. (v) GNAs at various thickness levels, (vi) honeycomb type 3D-GNA. Adapted with
permission [7], Copyright (2015), Macmillan Publishers Limited. This is an open-access article
distributed under the terms of the Creative Commons CC BY license
of the bonds. As a result of the chemical or physical assembling reactions, a 3D-GN

network is formed, followed by the drying process which contributes to removing the
excess water in this structure. For that, different types of drying methods, for instance,
supercritical drying, freeze-drying, vacuum drying, and air-drying methods are used.
In that process, the drying step is considered a significant factor that mainly affects
the synthesis of porous materials [8, 9].
2.2 Functionalization of 3D Graphene
To improve some features of the 3D-GN in different applications, some issues arise,
including variation in pore structure, high cost, and difficulty in controlling the struc-
ture while synthesizing only 3D-GN materials. Hence, it is necessary to develop this
material by composing it with various functional groups/elements to enhance its func-
tionality and manage the other expenses in large-scale production. Hetero atoms like
nitrogen, boron, sulfur, and phosphorus doping can promote both interaction between
inter-atoms, and the number of active sites and change the spreading pattern of the
electron. After doping, this breaks the symmetrical structure of 3D-GN material and
ended in a modified chemical design with improved conductivity properties.
With the changes in the valence electron numbers, the insertion of the hetero
atoms into the lattice affects the changes in the position of carbon atoms. When
considering the effectiveness of the atoms, nitrogen is the most popular dopant
element compared with others. This is because its atomic diameter is very similar to
that of the carbon atom, and the higher negativity of nitrogen compared to carbon
can persuade the polarizability of carbon within the web and change the electronic
configuration. The most important point is this has been able to improve the elec-
tronic properties without disturbing the structure of the carbon. Most research has
been conducted related to N doping in 3D graphene lattices. For instance, Qiao and
his team produced N-doped 3D bubble-like porous GN using melamine (as an N
source) and polystyrene (as a skeleton) for the energy storage application [10]. Typi-
cally, porous GN can transfer ions/electrons rapidly resulting in fast charge/discharge
cycles. Herein, melamine can influence the n-doing level, and this might contribute
to greater electrochemical performances. In contrast, Wang et al.found that N-doped
graphene can promote the catalytic properties of noble metal particles [11]. Further,
they concluded that N-doped 3D-GN is an excellent catalytic carrier that can enhance
the rate of the reaction. Due to the inability to recycle those materials, the N-dopped
metal nanocomposites are rarely used as catalysts. In another recent study carried out
by Yang et al., 3D nitrogen-doped graphene aerogel from the combination of graphitic
carbon nitride (as N source) and graphene oxide (as template) with a higher surface
area (536 m2 /g) and high photocatalytic performance was synthesized [12].
Apart from nitrogen, the atomic size and valency of boron are quite similar to that
of carbon. When boron is incorporated with GN, it is considered a p-type dopant.
Doping of this element can enhance the functionality of the 3D-GN. It has been
proven by several recent pieces of research applied to various uses. For instance,
boron-doped graphene aerogels via a simple hydrothermal method for the fabrication
of electrodes in EESDs were synthesized by Li and his team [13]. Comparatively,
boron can transfer more electrons than carbon, leading to high conductivity. Through
this process, the capacitance of the devices can be improved instead of using a single
3D-GN.
Sulfur (S) and phosphorous (P) are also used as dopants with 3D-GN. Mostly,
S-doped 3D-GN was used as both cathode and anode material for energy storage
devices like metal-ion batteries, hybrid capacitors, etc. Due to the strong behavior of
S in the GN structure, it is affected by the changes in carbon density while increasing
the width of the band gap over N-doped GN. Li and co-workers discovered an S-doped
3D-GN with S composites as cathode material for Li–S batteries [14]. The design
of the porous 3D-GN tends to incorporate hetero atoms doping due to having an
open structure. Only S-doped carbonaceous material does not have high conductivity.
Therefore, S-contained composites like polysulfide are combined with this to enhance
properties. Compared with highly demanding N and S dopants, the large-sized P
can modify the structure of 3D-GN very easily. P-doping can be showed higher
electrochemical performances due to the presence of active P=O bonds. As a recent
innovation, Mei et al. synthesized P-doped 3D-GN material as an anode material for
Li-based devices [15]. They concluded that high P-doping to GN can be achieved to
meet the requirements of industrial-scale production of EESDs.
Recently, doping of combined elements has become a very effective approach to

achieve better performances of the EESDs. Xing-Quan et al. successfully designed a
Co9 S8 - composed N, S, and P tertiary-doped 3D-GN electrode which has a catalytic
property [16]. The composition of all the elements accelerates to the form of more
sites and speeds up the reaction. Here, is just one example of the combination of
the doping process discussed, many studies tend to explore it. Overall, the electro-
chemical and electronic performances of GN are increased through the technique
of n-(electron) and p-(hole) doping into 3D-GN. This might be applicable in large-
scale manufacturing processes. With the type of integrated element, the activity of
the functional groups in the GN lattice might be changed. So, the behavior of the
groups, either electron donating or withdrawing should be paid attention to while
selecting dopants for GN [17].
3 Fundamentals of Supercapacitors
With the arising necessity for energy storage, different types of devices are invented
based on their applications. Among those devices, SCs which are known as elec-
trochemical capacitors, ultracapacitors have attracted attention due to their unique
properties. When compared to other devices like batteries, capacitors, and fuel cells,
this exhibited intermediate electrochemical performances. Most of the research has
significantly proven that SCs have high-power density, fast charge–discharge density,
superior specific capacitance, long cyclic stability, etc. Comparatively, batteries have
high energy density while capacitors show low energy density. The variation in energy
density and power density in different EESDs are shown in the Ragone plot. This
provides a clear comparison of those two properties (Fig. 6). By putting all the
properties together, SCs are lightweight, safe, portable, and flexible devices [18].
In general, SC consists of two electrodes, an electrolyte, and a separator that is
permeable to ions. On the hand, the electrode is a decisive factor in electrochem-
ical performance. Typically, a material that has high porosity and a high surface
should be selected as an electrode. In SCs, energy storage occurs according to the
charge–discharge (CD) principle at the interface of electrode and electrolyte. The CD
process in SCs is relatively higher in speed. Based on the energy storage mechanism,
there are three types of SCs such as electrical double-layer capacitors (EDLCs),
pseudocapacitors (PCs), and hybrid capacitors (HCs) (Fig. 7).
3.1 Electrical Double-Layer Capacitors
As mentioned earlier, EDLCs, which is called an electrostatic capacitor, is one type

of SCs. The surface of the electrode contributes to both the generation and storage
of energy. Electrochemically inactive carbon-derived materials such as carbon,
graphene, carbon aerogels, carbon nanotube, etc., are used for the fabrication of
Fig. 6 Ragone plot which describes the power-energy density variation. Adapted with permission
[18], Copyright (2020) by authors. Licensee MDPI, Basel, Switzerland. This article is an open-
access article distributed under the terms and conditions of the Creative Commons Attribution (CC
BY) license
Fig. 7 Classification of three different SCs like EDLC, PC, and HC. Adapted with permission [19],
Copyright (2019), The Royal Society of Chemistry. This article is an open-access article distributed
under the terms and conditions of the Creative Commons Attribution (CC BY) license
electrodes of EDLCs. These materials do not involve any chemical reactions for
energy storage and physical charge gathering contributes to this. It happens due
to the ion adsorption from the electrolyte and the surface dissociation. The charge
stores with the formation of the double layer. This originates on the external surface
of the electrode due to the electroneutrality created from excess or deficit charges
loaded on the electrode and the oppositely charged ion in the electrolytes. Here, this
Fig. 8 Schematic illustration of charge–discharge mechanism in EDLC. Adapted with permission

[19], Copyright (2019), The Royal Society of Chemistry. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license
scenario occurs within the CD period. During the charging process, the electrons
in the negative electrode move to the positive electrode via the exterior circuit after
supplying current. With that, anions and cations in the electrolyte start to migrate to
negative and positive charged electrodes, respectively. After that, the reverse process
is continued as discharging (Fig. 8). Shortage or excess electrons move through the
external load. There is no ion/charge exchange between electrodes and electrolytes.
Because of this circumstance, this kept a constant ion concentration within the CD
process. The accumulated ions in the double-layer interface decide the amount of
capacitance of EDLCs. When considering this mechanism, the surface character-
istics of the electrode material are mainly affected by the electrochemical perfor-
mance of EDLCs. Although carbons have excellent properties, their high availability
and low cost lead to the development of novel innovations through modifications
[19, 20].
3.2 Pseudocapacitors
PC, which is commonly known as redox or faradic capacitor, is also very popular
as other SCs. The main difference between PCs compared to EDLC is that rapid,
reversible redox reactions involve energy storage. Like EDLCs, energy stores with
the formation of a double layer at the surface of the electrodes due to the CD process.
Electrochemically active materials, which can provide redox reactions, for instance,
transitional metal oxides/hydrides (TMOs/TMHs) and conducting polymers, are used
for the fabrication of PCs. Herein, these materials exhibit three types of oxida-
tion–reduction reactions such as the faradaic reaction of TMOs/TMHs, reversible
adsorption, and electrochemical doping-de-doping reactions in CPs. Through these
reactions, both energy density and specific capacitance can be enhanced. Because
the rate of faradaic reaction is slower than that of non-faradaic ones, PCs show lower
power density and reduced cyclic stability compared to EDLCs [21].
3.3 Hybrid Capacitors
With the modification of the electrode materials, each EDLC and PC show excellent
unique electrochemical properties. As the best option to overcome the limitations
related to each device, HC is made up of combining both devices. This illustrates
an asymmetrical configuration because one electrode is made up of carbonaceous
material, while the other one is composed of electrochemically active material. Based
on the type of electrode materials, there are three categories of HC. The first group is
based on composites of capacitive and pseudocapacitive materials. The other two are
made with asymmetrical designs. One of them consists of an EDLC electrode and
the other a PC electrode/battery-type electrode. The third one uses electrodes from
PCs and rechargeable batteries. Here, non-faradaic electrodes provide high density
and superior cyclic stability, while pseudocapacitive or battery-type ones have large
energy densities. Therefore, it exhibits an improved electrochemical performance
compared to the other SCs [22].
4 3D Graphene-Based Supercapacitors
It is significantly discovered that the features of the electrode material play a decisive
role in the electrochemical performances of the SCs. Some factors like functional
groups, surface, structural, and morphological characteristics are mainly affected by
the changes in the properties of the electrode materials. Therefore, most research
tends to innovate novel strategies to modify the features of the electrode materials.
It is known that electrode material that has high porosity, high surface area, good
mass-transfer efficiency, and an effective pathway for ion diffusion leads to good
conductivity resulting in excellent behaviors in SCs. Although GN is richer in some
properties compared to others, this can be improved through several modifications
at the structural level. For example, 2D-GN, which has a less porous structure with
limited surface area, was improved through the synthesis of 3D-GN from it to achieve
better performance.
Mostly, GN-based carbon materials are used to fabricate the electrodes for EDLCs.
In that sense, this shows the higher surface area in the range of 2630–3290 m2 /g and
high specific capacitance of 135–205 F/g in aqueous electrolyte compared to other
electrode materials (CNT, active carbon) applied for EDLCs. Zang and his team
synthesized 3D-GN hydrogel via the one-step hydrothermal method (GN-H) which
contributes to reaching the optimum properties of EDLC [23]. In this work, this
device exhibited a high capacitance of 200 F/g at a low current density (0.3 A/g). At
a high discharge rate, its capacitance is reduced due to a large amount of remaining
oxygenated groups in the hydrogel, and its relatively low conductivity. Therefore,
they treated this material with hydrazine (Hz)/HI to increase the capacitance by
removing the residue and improving the conductivity. Compared to HI-reduced GN-
H, Hz-reduced one shows better capacitive performances. This is because some
nitrogen atoms were doped into GN-H while reducing with HZ and it enhances the
wettability of the electrode that leads to excellent features. However, this showed
higher stability, indicating capacitance retention of 92% over the 2000 cycles. These
results were obtained because of the 3D microporous structures of GN-H. Overall,
they observed that the power density and rate capability of this device are relatively
higher than that of chemically treated GNs reported in previous research.
Most research considerably reported that doping heteroatoms into the GN lattice
was a great strategy to improve the properties of the SCs. This is because these
elements can impact the functional group of the GN surface. As discussed in Sect. 2,
B or N is the best element that has similar characteristics to carbon for the fabrication
of electrodes for SCs [13] For energy storage purposes, more benefits can be achieved
through heteroatom-doping. Some of them are, that the spaces between the layers
and the surface structure accelerate the rapid ion exchange, the number of active sites
on the surface increases with defects, and the stability between the electrode and the
electrolyte is enhanced by heteroatoms [15].
For instance, Wu et al. synthesized solid-state SCs using 3D-GN and boron co-
doped monolithic GN aerogels (BN-GAs) [24]. As in Fig. 9, GO and ammonia
boron trifluoride (NH3 BF3 ) were used as precursors to synthesize BN-GAs through
the combined processes of hydrothermal and freeze-drying. Here, GN behaves as
the binder-free electrode, and polyvinyl alcohol (PVA)/H2 SO4 was used as a gel
electrolyte for the fabrication of SCs. Further, they produced nitrogen and boron-
doped graphene aerogel (N-GAs and B-GAs) using dicyandiamide and boric acid as
nitrogen and boron source, respectively. This is done to distinguish the electrochem-
ical performance of the N-GAs, B-GAs, and BN-GAs. The size and shape of the
GN aerogel monoliths can be adjusted with the changes in some factors including
the concentration of GO, treated temperature, and time of the hydrothermal. They
have experimentally found that BN-GAs showed higher specific capacitance, power
density, and improved energy density with respect to N-GAs, and B-GAs.
Moreover, the preparation of nanomaterial by composting different elements gives
better electrochemical performance rather than using a single type of electrode mate-
rial. As an example, for this strategy, Sahoo et al. developed an effective multi-
functional 3D-GN/Ag nanocomposite via the freeze-drying method for the fields of
energy, catalysis, and medicine [25]. The main challenge in 3D-GN-based composite
with noble metal elements processing is to improve its properties without harming the
environment and keeping it cost-effective. Here, they synthesized the composite with
different percentages (10, 20, and 40 wt. %) of Ag and in the presence of 0.625, 1.25,
and 2.5 mg of AgNO3 , respectively. Among those, the 3D-GN/Ag (40%) nanocom-
posite exhibited the highest electrochemical performance due to the presence of a
high amount of Ag particles. For example, this has more active sites, surface area,
fast faradaic rate, and excellent conductivity resulting in the highest specific capaci-
tance of 876 F/g at 1 A/g. And also, this showed great stability by giving capacitance
Fig. 9 The fabrication process of BN co-doped GN-based solid-state supercapacitor, Adapted with
permission [24], Copyright (2012), John Wiley and Sons
retention of 97% after 1000 cycles. Further, they observed that Ag nanoparticles with
an average particle size of 36 nm were uniformly arranged on the surface of the GN
sheets without any collision. Even with a higher weight percentage of Ag molecules
(40%), they are strongly bound together, proving that there is no separation even
upon sonication for 10 min.
Recently, Kaner et al. used 3D-GN with covalently grafted aniline tetramer (TANI)
material for the fabrication of a supercapacitor [26]. Here, they made this PANI/
TANI-GN composite material using TANI which is the fundamental construction
block of PANI onto 3D-GN through the single-step hydrothermal self-assembly
process. Initially, GO and 4-azido-tetrafluoro benzoyl tetra-aniline (ATFB-TANI)
were used for the formation of 3D-GN and after the one-step process, ATFB-TANI
grafted 3D-GN (ATgGN) was obtained as electrode material for SCs. Herein, the
symmetric SC was prepared using two similar ATgGN electrodes divided by an
ion-permeable separator and PVA/H2 SO4 /HQ gel electrolyte (Fig. 10a). In this 3D
porous structure, both TANI and HQ are contributing to the faradaic processes leading
to high super capacitance. The 3D porous ATgGN electrode materials used both
mechanisms of ion adsorption–desorption (EDLC) and redox reaction to store more
energy within this system. As demonstrated in Fig. 10b, c, this composite in HQ
contained electrolyte shows excellent electrochemical performance compared to the
regular electrolyte. According to Fig. 10d, the capacitance retention in PVA/H2 SO4
electrolyte exhibits a higher value (87%) compared to that of HQ-contained solution.
This is because of the incompletion of HQ redox reactions. However, specific and
areal the capacitance of HQ contained device illustrated a high rate of 94 mF/cm2
at 0.5 mA/cm2 (Fig. 10e). The main challenge with PANI-based SC is poor cycling
stability throughout the life cycle. But this synthesized composite material retained
more than 85% of capacity after 30,000 charge–discharge cycles from this GN-TANI-
based SC. Further, this value was maintained at about 82% even after 100,000 cycles
using a redox-active electrolyte for this device.
Fig. 10 a Schematic illustration of ATgGN symmetric supercapacitor, Characterization of HQ

containing electrolyte and non-contained electrolyte (PVA/ H2 SO4 ) b CV analysis at different scan
rates, c GCD analysis at different densities, Comparison of (d) Stability and e capacitance with the
presence of HQ in the electrolyte, Adapted with permission [26], Copyright (2021), John Wiley
and Sons
5 3D Graphene-Based Flexible Supercapacitors
With the differentiation of the applications, the synthesis of the electrode material
is changed according to their purposes of usage. fabricating 3D graphene having
both high surface area and porosity brings significant value in practical applica-
tions, especially for energy storage purposes. It can be found that most wearable
electronic devices are made up of electrode materials having flexible, stretchable,
and folding properties. Based on past reports, only single material cannot achieve
high flexibility for reaching its desired application. Therefore, most of them are
synthesized by composing chemically treated materials together. In that sense, it can
be seen that most electrodes in flexible SCs are coming from chemically derives
3D-GN-based composite materials. On the other hand, most current research has
targeted the synthesis of 3D hybrid electrode materials for the fabrication of flex-
ible devices using transitional metals (TMs) and carbon-based materials. But their
electrochemical performance is comparatively very low. This happened because of
their low conductivity and faults in reversible reactions. Some techniques including
composing TMs on carbon materials, doping TMs with conductive polymers, etc., are
used to avoid these errors. Therefore, it is an important task in the selection of doping
material to synthesize a composite electrode that shows excellent electrochemical
performance with flexibility. Here, some practices for the novel innovations of those
are briefly discussed in this section.
As an example, Chen et al. developed a foam-typed macro-structured 3D-GN
(GF) via the template-based CVD technique for the use of SCs [27]. Here, they
followed the procedure where carbon was initiated into the nickel foam (NiF) through
the decomposition of CH4 at high temperature and ambient pressure and then GN
films were dropped on the NiF. By changing the type of nickel foam, the macro/
microstructure of GF can be adjusted and variations in the concentration of the CH4
affect the surface area, density, and several layers of GF. The most significant fact is
that this GF is composed of an internally connected flexible web of GN that acts as a
carrier for the fast ion charge mobility resulting in high conductivity. As the final step,
this GF was composed of poly (dimethyl siloxane) (PDMS) to gain high flexibility,
twisting, and bending without breaking. The features of stretching and bending were
tested using a homemade two-point bending device and a high-precision mechanical
instrument. The structure of GF was not disturbed by incorporating PDMS and this
was not affected by changes in the conductivity of GF. Because of the mechanical
and electrical properties of this composite, this composite has great potential for
application as a flexible conductor in EESDs. Even though conventional conductors
like metallic foils provide better conductivity, those cannot apply for stretchable
purposes. But this composite is the best combination for fabricating SCs with both
high electrochemical performances and flexibility.
In another instance, Yu et al. invented a laser-induced 3D-GN (LIG)-based flexible
solid-state micro-supercapacitor having ultra-thickness of 320 μm [28]. Herein, they
have been discovered that porous 3D-GN can be synthesized with the conversion of
commercial polyimide (PI) by the IR laser method in CO2 air condition (Fig. 11a).
The pores structure of this material proved a fast route for ion transportation. In
electrochemical testing, LIG achieved a higher specific capacitance of 132.2 mF/cm2
at 0.5 mA/cm2 which is comparatively higher than that of GN electrodes. Further,
they were able to improve the specific capacitance of this electrode material up to
2412.2 mF/cm2 at 0.5 mA/cm2 by composing it with pseudocapacitive polypyrrole
(Ppy). This LIG/Ppy composite was prepared by the electrodeposition of Ppy on the
porous 3D-LIG. The increased porosity of LIG allows more access to deposit more
Ppy, leading to a higher loaded mass resulting in optimal properties (Fig. 11b). This
composite, which achieved 325 μW/cm2 of power density and 134.4 μWh/cm2 of
energy density, gives this device not only superior electrochemical performances,
but also high flexibility.
Fig. 11 a Preparation process of LIG/PPy electrode for the flexible solid-state supercapacitor
b Pore structure of LIG, Adapted with permission [28], Copyright (2020), Elsevier
Recently, Chen et al. developed a lightweight flexible solid-state SC using the

composite of GN, Fe, and MnCo2 O4 targeting wearable applications [29]. Here,
Fe was doped into MnCo2 O4 to obtain the metallic properties of the compounds by
maintaining electron density in the electrodes. After doping, the electron transfer rate
and processing speed of MnCo2 O4 enhanced resulting in good cyclic performance.
In that case, 3DGN-PPy with a high surface area was used as a substrate to build
the composite of FeMnCo2 O4 nanowires while avoiding the production of adhesives
and additional current collectors. This combination provides both low-weight and
stretch characteristics for conductors. As experimental details, they prepared the 3D-
GN on Ni foam via the CVD method. Then electrodeposition technique was used to
deposit PPy on 3D-GN to synthesize the G-PPy composite. Later, through the process
of the hydrothermal method, they made MnCo2 O4 nanowire arrays. After doping
Fe into that composite, it was grown on the substrate via a one-step hydrothermal
method to finish the synthesis of the composite (Fig. 12). After all, symmetrical
solid-state SC was fabricated by assembling 3DGN-PPy@MnCo2 O4 electrodes. In
this device, filter paper and PVA/KOH were used as a separator and gel electrolyte,
respectively. However, 3D G-PPy@Fe- MnCo2 O4 -based SC exhibited 5136 mF/
cm2 at 2 mA/cm2 of specific capacitance with long-term durability. The stability
of this device was shown to be about 94.7% of capacitance retention after 7000
cycles. This study demonstrates that the 3D-GN can be applied to the production of
wearable electronic devices by improving flexibility by changing the composition of
the electrode materials.
Fig. 12 Fabrication process of 3D G-PPy@Fe- MnCo2 O4 electrode material for the flexible solid-
state supercapacitor. Adapted with permission [29], Copyright (2022), American Chemical Society
The demand for the usage of 3D-GN is increased because it can prevent the aggrega-
tion of GN sheets. Hydrogels, aerogels, foams, and monoliths which are the different
formations of 3D-GN are widely used materials in recent studies. Depending on the
application and material formation, the synthesis methods of 3D-Gn are varied.
Some examples of strategies can be summarized as CVD, hydrothermal method,
3D printing, and self-assembly. Here, each method is briefly discussed with several
examples in the above sections. Until today, there have been many findings on 3D-
GN-based SCs because of their chemical, morphological, and electrochemical perfor-
mances. The inherent features of 3D-GN including high surface area and porous
structure that facilitate improved capacitance through fast ion transportation led to
novel innovations. Considering all the properties, GN has become desired material
for various applications not only for supercapacitors, but also in sensors, catalysts,
adsorption of dyes and heavy metals, etc. Especially, the need for flexible GN-based
SCs is enhanced in wearable electronic systems. In this review, the recent effort for
the development of novel electrode materials by composing 3D-GN materials that
are used for flexible SCs is discussed. It is noted that only 3D-GN does not have
flexible properties, the composition of materials which has flexible, stretching, and
bending properties can promote flexibility in 3D-GN.
When considering the industrial and practical applications, several challenges
need to be developed in large-scale production. One of these is that most experiments
regarding these 3D-GN materials are done on the laboratory scale, and because of
its fragility, it is difficult to manipulate this material in a friendly manner. However,
this can be overcome by combining different highly flexible materials to improve
mechanical properties. But it should be more careful while integrating additives into
3D-GNs. Although some materials can improve the properties of 3D-GN, on the other
hand, they can cause side effects to the primary materials. Therefore, it is necessary
to study the characteristic features of each element before incorporating them into
3D-GN materials. An added solution for that issue is to adjust the cross-linking status.
Another problem regarding 3D-GN production is that the size of this material cannot
be controlled as much as desired. This should be done after a thorough analysis
of structural characteristics. For future innovations, various structured 3D-GNs like
scrolls, honeycombs, corals, and nano sacks are still to be studied for supercapacitor
application.
References
1. Bergmann, C.P., Machado, F.M.: Carbon Nanomaterials as Adsorbents for Environmental and
Biological Applications (2015). https://doi.org/10.1007/978-3-319-18875-1
I.V., Firsov, A.A.: Electric field effect in atomically thin carbon films. Science 306(2004),
666–669 (1979)
control. Chem Rev. 120, 10336–10453 (2020). https://doi.org/10.1021/acs.chemrev.0c00083
4. Song, J., Xia, X., Chen, J., Xia, D., Xue, Q., Li, Q., Dong, M.: Folding 2D Graphene Nanorib-
bons into 3D Nanocages Induced by Platinum Nanoclusters (2020). https://doi.org/10.1021/
acs.jpcc.0c00463
5. Zaka, A., Hayat, K., Mittal, V.: Recent trends in the use of three-dimensional graphene structures
for supercapacitors. ACS Appl. Electron. Mater. 3, 574–596 (2021). https://doi.org/10.1021/
acsaelm.0c00953
6. Li, Y., Chen, J., Huang, L., Li, C., Hong, J.D., Shi, G.: Highly compressible macroporous
graphene monoliths via an improved hydrothermal process. Adv. Mater. 26, 4789–4793 (2014).
https://doi.org/10.1002/adma.201400657
7. Zhu, C., Han, T.Y.J., Duoss, E.B., Golobic, A.M., Kuntz, J.D., Spadaccini, C.M., Worsley,
M.A.: Highly compressible 3D periodic graphene aerogel microlattices. Nat Commun. 6, 1–8
(2015). https://doi.org/10.1038/ncomms7962
8. Ding, M., Li, C.: Recent advances in simple preparation of 3D graphene aerogels based on 2D
graphene materials. Front Chem. 10, 1–9 (2022). https://doi.org/10.3389/fchem.2022.815463
9. Lu, H., Li, C., Zhang, B., Qiao, X., Liu, C.Y.: Toward highly compressible graphene aerogels
of enhanced mechanical performance with polymer. RSC Adv. 6, 43007–43015 (2016). https:/
/doi.org/10.1039/c6ra04995h
10. Qiao, Y., Cheng, X., Liu, Y., Han, R., Ma, M., Li, Q., Dong, H., Li, X., Yang, S.: Architecture
design of nitrogen-doped 3D bubble-like porous graphene for high performance sodium ion
batteries. Inorg Chem. Front. 4, 2017–2023 (2017). https://doi.org/10.1039/c7qi00574a
11. Wei, Q., Liu, T., Wang, Y., Dai, L.: Three-dimensional N-doped graphene aerogel-supported
Pd nanoparticles as efficient catalysts for solvent-free oxidation of benzyl alcohol. RSC Adv.
9, 9620–9628 (2019). https://doi.org/10.1039/C9RA00230H
12. Maouche, C., Zhou, Y., Peng, J., Wang, S., Sun, X., Rahman, N., Yongphet, P., Liu, Q., Yang,
J.: A 3D nitrogen-doped graphene aerogel for enhanced visible-light photocatalytic pollutant
degradation and hydrogen evolution. RSC Adv. 10, 12423–12431 (2020). https://doi.org/10.
1039/d0ra01630f
13. Li, J., Li, X., Xiong, D., Wang, L., Li, D.: Enhanced capacitance of boron-doped graphene
aerogels for aqueous symmetric supercapacitors. Appl. Surf. Sci. (2018). https://doi.org/10.
1016/j.apsusc.2018.12.152
14. Li, N., Gan, F., Wang, P., Chen, K., Chen, S., He, X.: In situ synthesis of 3D sulfur-doped
graphene/sulfur as a cathode material for lithium-sulfur batteries. J. Alloys Compd. 754, 64–71
(2018). https://doi.org/10.1016/j.jallcom.2018.04.018
15. Mei, J., He, T., Zhang, Q., Liao, T., Du, A., Ayoko, G.A., Sun, Z.: Carbon-phosphorus bonds-
lithium storage. ACS Appl. Mater Interfaces 12, 21720–21729 (2020). https://doi.org/10.1021/
acsami.0c03583
16. Ma, X.X., Dai, X.H., He, X.Q.: Co9S8-modified N, S, and P ternary-doped 3D graphene
aerogels as a high-performance electrocatalyst for both the oxygen reduction reaction and
oxygen evolution reaction. ACS Sustain. Chem. Eng. 5, 9848–9857 (2017). https://doi.org/10.
1021/acssuschemeng.7b01820
17. Pumera, M.: Heteroatom modified graphenes: electronic and electrochemical applications. J.
Mater Chem. C Mater. 2, 6454–6461 (2014). https://doi.org/10.1039/c4tc00336e
18. Forouzandeh, P., Kumaravel, V., Pillai, S.C.: Electrode materials for supercapacitors: a review
of recent advances. Catalysts 10, 1–73 (2020). https://doi.org/10.3390/catal10090969
19. Pal, B., Yang, S., Ramesh, S., Thangadurai, V., Jose, R.: Electrolyte selection for supercapacitive
devices: a critical review. Nanoscale Adv. 1, 3807–3835 (2019). https://doi.org/10.1039/c9n
a00374f
20. Soc, C., Wang, G., Zhang, J.: Chem. Soc. Rev. Critical Review A review of electrode materials
for electrochemical supercapacitors, 797–828 (2012). https://doi.org/10.1039/c1cs15060j
21. Guan, M., Wang, Q., Zhang, X., Bao, J., Gong, X., Liu, Y.: Two-dimensional transition metal
oxide and hydroxide-based hierarchical architectures for advanced supercapacitor materials.
Front. Chem. 8, 1–14 (2020). https://doi.org/10.3389/fchem.2020.00390
22. Zhong, C., Deng, Y., Hu, W., Qiao, J., Zhang, L., Zhang, J.: A review of electrolyte materials
and compositions for electrochemical supercapacitors. Chem. Soc. Rev. 44, 7484–7539 (2015).
https://doi.org/10.1039/c5cs00303b
23. Zhang, L., Shi, G.: Preparation of highly conductive graphene hydrogels for fabricating super-
capacitors with high rate capability. J. Phys. Chem. C 115, 17206–17212 (2011). https://doi.
org/10.1021/jp204036a
24. Wu, Z.S., Winter, A., Chen, L., Sun, Y., Turchanin, A., Feng, X., Müllen, K.: Three-dimensional
nitrogen and boron co-doped graphene for high-performance all-solid-state supercapacitors.
Adv. Mater. 24, 5130–5135 (2012). https://doi.org/10.1002/adma.201201948
25. Sahoo, P.K., Kumar, N., Thiyagarajan, S., Thakur, D., Panda, H.S.: Freeze-casting of multifunc-
tional cellular 3D-graphene/Ag nanocomposites: synergistically affect supercapacitor. Catalyt.
Antibacterial Properties ACS Sustain. Chem. Eng. 6, 7475–7487 (2018). https://doi.org/10.
1021/acssuschemeng.8b00158
26. Chang, X., El-Kady, M.F., Huang, A., Lin, C.W., Aguilar, S., Anderson, M., Zhu, J.Z.J.,
Kaner, R.B.: 3D graphene network with covalently grafted aniline tetramer for ultralong-life
supercapacitors. Adv. Funct. Mater., 31 (2021). https://doi.org/10.1002/adfm.202102397
conductive interconnected graphene networks grown by chemical vapour deposition. Nat Mater.
10, 424–428 (2011). https://doi.org/10.1038/nmat3001
28. Yu, X., Li, N., Zhang, S., Liu, C., Chen, L., Han, S., Song, Y., Han, M., Wang, Z.:
Ultra-thick 3D graphene frameworks with hierarchical pores for high-performance flexible
micro-supercapacitors. J. Power Sources, 478 (2020). https://doi.org/10.1016/j.jpowsour.2020.
229075
29. Chen, Z., Zu, X., Chen, L., Qi, Y., Jian, W., Wu, Y., Zhang, W., Lin, X., Yi, G., Liu, Q., Tang,
Z., Wu, J., Dong, H., Qin, Y.: Flexible self-supporting 3D electrode based on 3D graphene-
PPy@Fe-MnCo2O4Nanostructure arrays toward high-performance wearable supercapacitors.
ACS Appl. Energy Mater (2012). https://doi.org/10.1021/acsaem.2c00311
3D Graphene for Photovoltaics
Alka Pareek and Sreekanth Mandati
Abstract Three-dimensional graphene (3D-G) is among the most interesting and

emerging materials of the carbon clan due to its exemplary properties like high
surface area, remarkable electrical properties, and exceptional mechanical charac-
teristics that urged profound interest in various applications. Graphene sheets assem-
bled into an ordered and internally connected three-dimensional network are a great
solution to the problem of aggregation or overlaying that limits the active surface
area and distinct characteristics of sheets. Furthermore, these structures possess inter-
connected porosity, larger specific surface area, and more integrality providing short
ion diffusion length and additional active sites. 3D-G structures are widely used in
various applications like supercapacitors, batteries, fuel cells, gas storage, biosensors,
solar cells, and so on. In photovoltaics (PVs), the graphene-based materials appear
very promising for (1) making cost-effective, lightweight, and flexible devices, (2)
obtaining a wide range absorption window from UV to far IR regions, (3) improving
charge transfer kinetics, and (4) high catalytic activities. Moreover, the optoelec-
tronic and electrocatalytic activity of 3D-G structures can be altered through different
ways of surface functionalization that expand the application in multiple PV devices
like dye-sensitized, quantum dot-sensitized, and perovskite solar cells. This chapter
highlights the recent research advancement and contribution of 3D-G structures and
composites in PV applications while also discussing the limitations in achieving
higher performance and directions for future development.
Keywords 3D graphene · Photovoltaics · Dye-sensitized solar cells · Quantum

dot-sensitized solar cells · Perovskite solar cells
A. Pareek (B) · S. Mandati

Laboratory of Thin Film Chemical Technologies, Department of Materials and Environmental
Technology, School of Engineering, Tallinn University of Technology, Ehitajate Tee 5, 19086
Tallinn, Estonia
e-mail: alkapareek7@gmail.com
https://doi.org/10.1007/978-3-031-36249-1_17
306 A. Pareek and S. Mandati
1 Introduction
Solar PV technologies that deal with the conversion of sunlight directly into electricity
are sustainable, clean, and zero-emission energy production processes. In 1954, the
first Si solar cell in crystalline form was invented in Bell Labs, after which PV research
has seen a rapid increase in the next few decades with extensive studies dedicated
to developing various absorber materials [1]. A variety of device configurations and
architectures with different solar cell layers have been studied and several of them
have seen industrial production. Solar cells are broadly divided into three categories
according to the type of material and configuration: (1) The first generation solar cells
are referred to as monocrystalline and polycrystalline silicon-based cells. Presently,
Si solar cell technology covers 90% of the PV market and is considered the most
mature PV technology. They have witnessed the best commercial success among
all PV technologies on account of their higher output efficiencies and longer panel
lifetime [2]. However, Si technology is still limited to meeting the global energy
demand owing to the sophisticated and high-cost fabrication processes. (2) Solar
cells based on thin film technologies are second generation wherein the absorbers
are CdTe, copper-based chalcopyrite like CIGS, and GaAs. These absorbers possess
direct bandgap and are advantageous for effective absorption of light even with very
few microns thickness as compared to the indirect bandgap Si. (3) Third generation
solar cells are constructed with recent structures and devices that can decrease the
overall cost of devices. They include dye- and quantum dot- sensitized solar cells
(DSSC and QDSC), and organic and perovskite solar cells (OSC and PSC). Low
cost, abundance, flexibility, and simple production methods have paved the path for
fast development and a rapid rise in interest in these devices. The performance of
these devices is largely dependent on material aspects like the composition of the
absorber layer, efficient charge transport layers, counter electrode, contact layer, and
passivation layer. Extensive efforts are being dedicated to improving each of these
areas to unveil a highly efficient and stable PV device that could meet the global
energy demand.
Carbon-based materials and their numerous allotropes are among the most
explored and indispensable parts of the current materials and energy industry.
There are diverse nanostructures of carbon like zero-dimensional fullerenes, one-
dimensional carbon nanotubes, and two-dimensional graphene materials, that have
gathered huge interest and possess fascinating electrical, mechanical, and optical
properties [3]. Among them, graphene is one of the most studied and appreciated
thinnest materials with an exceptionally large specific surface area of 2630 m2 /g,
electron mobility of 200 000 cm2 /Vs, high strength (Young’s modulus of ~1 TPa),
and thermal conductivity of 5000 W/mK. These properties make graphene apt for
numerous applications like supercapacitors, batteries, fuel cells, gas storage, biosen-
sors, and solar cells [4]. Although, graphene in its conventional two-dimensional
form has significantly contributed to the performance enhancement of various PV and
battery devices, it tends to agglomerate quickly countering its outstanding properties.
3D Graphene for Photovoltaics 307
To combat this shortcoming, various strategies are employed to architect 2D layers

into a 3D-G. The 3D-G architectures preserve most of the unique characteristics of
individual layers without the issue of stacking. These architectures are basically non-
graphitic 3D structured graphene material constituting not more than ten layers. The
relationship between different graphene structures and transformation from one struc-
ture to another can easily be visualized as shown in Fig. 1a. Based on the morphology
and dimensions, 3D-G structures are broadly classified into two categories as depicted
in Fig. 1b [5]: (1) macrostructures or monoliths, such structures possess dimensions
greater than 100 µm, for example, 3D-G foams, aerogels, sponges, films, fibres, and
milli-spheres; (2) microscopic materials having dimensions smaller than 100 µm like
micro-sized or nano-sized powdered 3D structures. Although dimensions are impor-
tant in these structures, the type of connection between these graphene sheets is also
crucial for the characteristics of 3D structures. Based on the type of connectivity, there
are two types of structures: (1) Joint 3D structures in which individual graphene sheets
are interlinked by weak Van der Waals forces; (2) Integrated graphene structures that
possess strong chemical bonds among graphene sheets. Due to the strong chemical
bonds, integrated structures display better electrical and mechanical properties. The
precursor and synthesis methods of these structures are very essential in controlling
the properties of these materials. For example, 3D-G architecture obtained from the
hydrothermal method has depicted a very low conductivity of 0.5 S/m [6]. These
structures are primarily produced using three types of precursors that include [3]: (1)
direct assembly from rGO (reduced graphene oxide) sheets, (2) use of hydrocarbons,
and (3) from inorganic chemicals such as CO, CS2 , and CO2 .
The exceptional properties of 3D-G like remarkably high transparency, high
mobility, and superior electrical and thermal conductivity, have made it a great choice
to be applied as counter electrodes, transparent electrodes, passivation/protective
layer, and electron transport layer (ETL) or hole transport layer (HTL) in solar cells
[7, 8]. Basically, these architectures are employed as conducting units to improve
the charge transfer process in the solar cell and are required to possess long-term
stability against moisture and air. It is pertinent to note that the conductivity of 3D-G
plays an essential part in the successful establishment of these materials for power
generation devices. The overall electrical conductivity is controlled by the quality of
composing graphene sheets and the connection between them, which directly affects
the charge transfer of electrons [9]. According to recent reports, conductivity of 3D-
G varies between 100 000 to 1 S/m [10, 3]. The conductivity is generally measured
by four-probe or two-probe methods, but the values may differ based on the position
of detecting electrodes owing to the anisotropy of macro-monoliths of 3D-G [11].
The conductivity is also dependent on the mass density of the material, for example,
a material having high density generally exhibits higher overall conductivity, and
therefore, materials like 3D-G sponges with low mass density exhibit poor conduc-
tivities (0.7–110 S/m) [10, 11]. In addition to the mass density, as discussed earlier,
the synthesis methods or reduction of graphene also impact the conductivity of this
material. For instance, 3D-G produced by the hydrothermal reduction method with
an exceptional density of 1600 mg/cm3 has displayed limited conductivity (760 S/
m) [12].
Fig. 1 Schematic diagram showing a different types of graphene-related materials and their forma-
tion b variety of microscopic 3D-G (<100 µm dimension) and macroscopic 3D-G materials
(>100 µm dimension). Adapted with permission [3], Copyright (2020), American Chemical Society
While we are discussing the potential of 3D-G electrodes in PVs, it may be noted
that the optical properties also play a vital role along with conductivity. Despite
being just an atomic-layer thick, the graphene monolayers show absorption from the
visible to infrared range [13]. Moreover, absorption of these structures can be further
improved by mechanical compression or the introduction of surface defects and
chemical functional groups on the surface of rGO [14]. Structural modification can
also alter absorption phenomena like bi-continuous or nanoporous structures have
displayed enhanced light absorption for visible light [15]. With further optimiza-
tion of reduction degree, the 3D structure-based photodetector has shown 40 fold
enhanced photon absorption than the single graphene layer that resulted in external
quantum efficiency of 1.04 × 107 % as compared to Si (6.5 × 105 %) [15]. The
preceding discussion emphasizes the scope of 3D-G structures in PV technologies.
The output of PV devices is basically dependent on the open circuit potential and fill
factor, which is correlated to the quasi-Fermi level splitting of the absorber. 3D-G
with enhanced electrical and optical properties improves these two parameters, and
hence boosts the overall performance of devices. In PV, 3D-G-based architectures
are very appealing for making economic, lightweight, and flexible devices to obtain
a wide range of absorption windows from UV to far IR region, to improve charge
separation kinetics, and for high catalytic activity purposes. The optoelectronic and
electrocatalytic characteristics of 3D-G could be suitably altered by surface func-
tionalization. Based on these aspects, the use of 3D-G in different types of solar
cells is discussed while focusing on the limitations in improving the performance
and further directions for enhancement.
2 3D-G in DSSC
DSSC is among the promising alternative PV systems that offer reasonably high
conversion efficiency, ease of fabrication, and integration into surfaces, while being
a low-cost and environmentally friendly technology [16]. Typical construction of
DSSC consists of a dye-adsorbed metal-oxide electrode, counter electrode, and an
iodide electrolyte as shown in Fig. 2a [17]. Each component performs a signifi-
cant part in improving the output performance of DSSC. Different types of dyes
are explored such as black dye (N749), indoline, porphyrin, and phthalocyanine to
enhance the optical properties of DSSC in the visible solar spectrum [18]. There
have been numerous efforts to devise new photoanode to enhance the efficiency
of existing metal-oxides like TiO2 and ZnO [19]. While improving the properties
of the photoanode is the widely studied aspect, the potential of the counter elec-
trode to reduce the triiodide to iodide is also important for DSSC’s performance.
Pt is so far the most explored material as a counter electrode as a result of its high
conductivity, remarkable stability, and exceptional electrocatalytic properties for the
reduction of triiodide, but its high cost hinders the commercialization of the devices
[20]. Carbon-based materials with robust catalytic activity, high conductivity, and
superior chemical stability are considered a convincing substitute for Pt. There is a
wide range of carbon materials like graphite, graphene, CNTs, and 3D-G that are
studied in DSSC as both an efficient photoanode as well as the counter electrode.
3D-G is the emerging and the most promising material owing to its very porous,
conductive, and flexible interconnected framework that provides an interconnected
highway system for electron transfer. It also possesses defects and more enriched
edges that act as catalytic active sites [21]. Moreover, due to its remarkably high
electrical conductivity, desirable optoelectronic properties, and exceptionally large
Fig. 2 a Schematic diagram showing the working principle of DSSC b Fabrication of N-doped
graphene foam counter electrode (N-GF), c DSSC cell constituting N-GF as the counter electrode,
and d electrolyte reduction on the counter electrode. Adapted with permission [17] and [31], respec-
tively. Copyright (2012), WILEY–VCH Verlag GmbH & Co. KGaA, Weinheim. Copyright (2010),
specific surface area, it is regarded as a convincing alternative for DSSC’s working

and counter electrodes [22]. Wang et al. have synthesized honeycomb structured
3D-G nanosheets that have exhibited a PCE of 7.8% which is equivalent to the
DSSC with expensive platinum electrodes [23]. Tang et al. have adopted a chem-
ical vapour deposition process to synthesize 3D-G with the nickel foam rod as a
template which is then used as a photoanode. The electrode has demonstrated an
efficiency enhancement of 32.7% as compared to pure P25 which could be attributed
to the reduced contact resistance between the junction of graphene sheets forming
the efficient channel for carrier transport [24]. Flexible DSSCs fabricated on plastic
substrates often experience losses due to poor electron diffusion rates that could
be correlated to the implausible situation of high-temperature sintering. Hence, the
output efficiency of such devices is reported to be below 6%. Zhi et al. have fabricated
flexible DSSCs on plastic substrates with improved performance by constructing a
3D-G decorated nanocrystalline TiO2 electrode. The impact of the efficient charge
transfer process and large surface area in 3D-G-based DSSC has assisted in exhibiting
output efficiency of 6.41% (56% greater than DSSC without 3D-G). Yang et al. have
synthesized Pt-free counter electrode by attaching Fe2 O3 nanoparticles onto 3D-G
frameworks, wherein Fe2 O3 acts as a highly active site, and the 3D-G provides an
internally connected electron transfer mechanism. The resulting system has demon-
strated an improved PCE of 7.45% as compared to platinum electrodes (7.29%) [21].
He et al. have studied the effect of ZIF-8 and three-dimensional graphene network
co-deposited TiO2 electrode as photoanode in DSSC that has demonstrated superior
PCE of 8.77% with 5 wt.% ZIF-8 loading. The combination of the large BET surface
area of ZIF-8 and fast charge transport of 3D-G enhances the amount of dye loading
and produces a high output current [25]. In a similar kind of study, Tang et al. have
demonstrated RGO and 3D-G network co-deposited structures, wherein the 3D-G
provides a fast charge transport network for electrons, while RGO nanosheets further
accelerate the carrier transport at the interface between the graphene basal plane and
TiO2 [26]. Sun et al. have fabricated RGO and 3D-G-based two-layer constructed
electrodes that have depicted a PCE of 8.87% as compared to the pristine P25-based
DSSCs [27].
Chang et al. have fabricated a unique architecture of graphene nanosheets deco-
rated with graphene foam that has shown a PCE of 7.70%. In this study, the group
has explored the effect of big size graphene nanosheets and smaller size graphene
quantum dots, produced by the reduction of GO using heat and laser, respectively.
They have found that the quantum dots with a size of 100 nm or less provide a
greater number of electroactive sites and edges and offer low charge transfer resis-
tance. These novel structures utilize a fast electron transfer system using a graphene
framework and smooth charge injection between the graphene nanosheets and the
substrate [28]. In the quest for developing hierarchical structures, Yu et al. have
contributed to synthesizing N-doped rGO to form a three-dimensional N-doped holey
rGO framework (NHGF). The NHGF in the form of compressed paper possesses
sufficient mechanical strength to be installed as free-standing counter electrodes and
rGO nanosheets in 3D framework are interconnected and interlocked together to
avoid restacking [29]. Zhu et al. have synthesized CuS nanocrystals modified 3D-G
frameworks by in situ hydrothermal process and reported PCE of 7.07%. Figure 2b
shows the complete process of electrode formation in DSSC using different methods.
The 3D-G electrode in DSSC and a schematic diagram illustrating the reduction of
triiodide electrolyte are shown in Fig. 2c, d. To further explore composite structures
of 3D-G, Sun et al. have constructed 3D porous rGO/CoS containing spherical hier-
archical (CSHPS-G) architectures as an effective counter electrode in DSSC by a
simple hydrothermal method [30].
The porous structure of nanostructured electrode ensures a proficient electrolyte
diffusion system and provides plenty of electrocatalytic sites. Consequently, CSHPS-
G-based DSSC shows a remarkable PCE of 5.41% which is better than platinum-
based DSSC. Roh et al. have fabricated 3D crumpled graphene (3D CGR)/GR sheets-
based DSSC that has demonstrated a PCE of 7.2%, which is 56% greater than the
conventional DSSC [32]. Lee et al. have studied 3D nano-foam graphene (3D-NFG)
synthesized by CVD, where pyrolyzed carbonized-C and the nickel nano-frame are
employed as carbon sources [33]. The study proves that the benefits of high surface
area and electrical conductivity of 3D-NFG can be utilized to substitute expensive
platinum as a counter electrode in DSSC. The 3D-NFG-based DSSC has exhibited a
PCE of 5.2%. In one of the creative works, Wei et al. have reported 3D cauliflower-
fungus-like graphene (3D CFG) from CO2 and have employed it as an electrode in
DSSC [34]. 3D-CFG-based DSSC has manifested maximum conversion efficiency
of 8.1%, which is tenfold higher than the regular graphene counter electrode prepared
through the graphite chemical exfoliation process (0.7%). The same group has also
reported 3D crape myrtle flower-like graphene counter electrodes synthesized by the
reaction of carbon dioxide and Na, and have obtained a high PCE of 10.1% [35].
Most of the studies discussed herein focus on the modification of working elec-
trodes (generally TiO2 ) with 3D-G where the dye adsorption capacity, charge transfer,
and separation mechanisms depend on the properties of the working electrode.

Loeblein et al. have utilized 3D-G as an independent working electrode by modi-
fying it as an oxidized 3D-G (o-3D). By functionalizing oxygen groups over 3D-
G, a bandgap of 0.2 eV is induced and a desirable electronic band structure is
formed that could facilitate the interactions between p-p electron donors and accep-
tors, and induce the attraction between positive dye ions and negative adsorbents.
[22]. Figure 3a shows the construction of DSSC with p-doped 3D-G nano-networks
(3D-GN) as an electrode [36]. A comparative study is carried out between 3D-GN
and platinum counter electrodes using photocurrent–voltage curves as depicted in
Fig. 3b. The electrochemical impedance spectroscopy (EIS) and IPCE measurements
are demonstrated in Fig. 3c and d, respectively. The 3D-GN nanostructure electrodes
have exhibited a PCE of 8.46% as compared to Pt-based DSSC (6.01%) which is
also evident from the IV and IPCE measurements. This detailed discussion on the
reports constituting numerous studies clearly projects excellent performance of 3D-
G-related materials as electrodes due to their large surface area and efficient charge
transfer process.
Fig. 3 a Schematic diagram showing DSSC with 3D-G electrode, PV performance of DSSC
including b J–V, c EIS curves and d IPCE spectra using 3D graphene and platinum counter elec-
trodes under the illumination of AM 1.5. Adapted with permission [36], Copyright (2014), The
Royal Society of Chemistry
3 3D-G in QDSCs
QDSCs are the emerging third generation solar cells that are studied extensively
owing to unique characteristics of quantum dots like easy tunability of band gap by
altering size or composition, considerably high molar attenuation coefficient, large
intrinsic dipole moments, and stability against photons, heat, and water as opposed
to dye molecules and lead halide perovskite [37]. Moreover, the concept of multiple
exciton generation provides the insights that QDSCs could break the Shockley–
Quessier efficiency limit of 32.9% established for mono-junction solar cells. The
concept of QDSC is like DSSC where a wide bandgap semiconductor is sensitized
with a low bandgap material to harvest the light and produce charge carriers, though in
QDSC, dye is replaced by quantum dots. Generally, QDSC consists of a quantum dot
sensitized photoanode and counter electrode immersed in the electrolyte as displayed
in Fig. 4a. The light absorption, charge carrier generation, and transfer processes are
stepwise explained in Fig. 4b. When light is incident on the photoanode, quantum
dots absorb it and produce electron in conduction band and hole in the valence band,
respectively. Due to the favourable band edge alignment, the electrons from quantum
dots are transferred to the conduction band of metal oxide (1) and then to counter
electrode (2) via an external circuit, whereas holes travel from the valence band of
quantum dots to electrolyte (3) where reduction of sulphides takes place (4). This
leads to the efficient separation of charge carriers avoiding the charge recombination
losses ((5) and (6)). The most employed metal-oxides in QDSC include TiO2 , ZnO,
SnO2 , etc., while the most explored sensitizing quantum dots are Cd, Pb or multi-
layer chalcogenides. The performance of QDSC is limited by the losses due to the
characteristic nature of electron transport throughout the quantum dots network [38].
The electron transfer in the network of quantum dots is through the hopping of elec-
trons between orbitals of adjacent quantum dots, which is defined as a random walk.
This process affects the electron collection at the photoanode as the electron must
complete multiple hopping steps to reach the current-collecting substrate without
unwanted processes like recombination or trapped-state termination. Not only the
electron transfer kinetics is hindered, but also with an increase in quantum dots thick-
ness or layering, quantum dots near metal oxide lack access to electrolytes, and hence
regeneration of quantum dots is hindered. Utilizing graphene-related compounds
improves this charge transfer phenomenon between different layers and provides
efficient interface engineering by acting like an electron funnel.
In some reports, it has been established that incorporating graphene in quantum
dots improved the collection and transport of photogenerated charge carriers. 3D-G
possesses the potential to further improve the efficiency of these working electrodes
by offering an efficient electron transfer mechanism through an interconnected elec-
tron transfer highway system, the presence of enriched edges and defects acting as
electroactive sites, and a large surface area for electrolyte diffusion. Lightcap et al.
constructed a unique structure of 3D QD-sensitized graphene photoelectrodes that
provide a substantial solution to overcome the problem associated with a random walk
and limited conductivity of quantum dot sensitizers [38]. In addition, the photocurrent
Fig. 4 Schematic diagram showing a typical construction of QDSSC b charge transfer processes
in a QDSSC. Adapted with permission [39], Copyright (2016), Elsevier Ltd
response is improved by 150% as compared to QDSC without graphene. Tavakoli

et al. have studied 3D-G networks (3DGNs)-based transparent electrodes to improve
the output of lead sulphide-based QDSC [40]. The study has demonstrated that 3DGN
electrodes improve the electron transfer process which leads to a 30% improvement
in efficiency in comparison to the conventional DSSC. There are few reports where
3D-G is utilized as an efficient counter electrode owing to its extraordinary conduc-
tivity and large surface area. Zhu et al. have synthesized CuS nanocrystals loaded
with 3D-G framework (GF) as a counter electrode in QDSC [41]. It is demon-
strated that QDSC with GF counter electrode displays a PCE of 5.04% as compared
to those of the traditional counter electrodes like platinum (3.18%), CuS (3.75%),
and 2D graphene–CuS electrode (4.17%). The electron transport in 2D and 3D GF
are explained in Fig. 5a, b. The GF–CuS electrode possessing an interconnected
3D conductive network structure facilitates the electron transfer via. “multi-channel
transport pathways” and uniformly distributed copper sulphide nanoparticles provide
numerous electrocatalytic sites, enhancing the electrical and catalytic properties of
the composite electrode, as depicted in Fig. 5b. Superior performance of 3D-G-CuS-
based counter electrodes as compared to platinum is quite evident by I-V plots in
Fig. 5c. However, despite possessing the excellent potential to contribute to the signif-
icant improvement in the efficiency of QDSCs, as discussed already, the studies are
yet limited and thus paves the way for researchers to explore this excellent material
extensively to further enhance the performance of QDSCs.
3D-G in other solar cells
Research on perovskite solar cells (PSCs) is growing enormously and garnering atten-
tion due to their outstanding performance and cost-effective easy solution process-
ability. PSCs have achieved higher performance in terms of conversion efficiency
above 25% on par with monocrystalline, heterojunction Si [5], and higher than
CIGS and CdTe solar cells (26.1, 26.7, 23.4, and 22.1%, respectively) in a quick
Fig. 5 Schematic diagram showing transfer of the electrons in a 2D graphene sheets, b 3D-G-CuS
counter electrode for electrolyte reduction in QDSSC, and c I-V plots comparing the performance
of various counter electrodes. Adapted with permission [41], Copyright (2016), Elsevier Ltd
time [42]. A typical PSC consists of three major layers classified based on their
specific roles that control the performance and stability of devices like perovskite
absorbers, ETLs, and HTLs. The hurdles in the commercialization of PSCs include
instability of absorber and HTLs and the use of costly noble metal-based counter
electrodes. It is reported that metal-free counter electrodes could contribute to the
stability of PSCs [43]. Moreover, cost-effective counter electrodes also support in
realization of achieving the ideal levelized cost of energy (LCOE) of PSC less than
5 US cents kWh−1 [5]. Carbon-based electrodes are a viable option to replace these
costly metal-based counter electrodes as they are cheap, abundant, possess high
chemical/electrochemical stability, large surface area, better electrical conductivity,
and are eco-friendly. Recently, 3D-G is gaining attention as an efficient electrode
material in PSC owing to its high surface area, remarkable electrical conductivity,
and stability.
Wei et al. have studied the synthesis of a 3D honeycomb resembling graphene
(3DHG) by a simple reaction of K and CO2 . They have utilized 3DHG as a counter
electrode in PSC without any hole transport material (HTM) and have recorded a
PCE of 10.06%. This study has embarked on a novel journey of material synthesis
using chemistry related to potassium to produce electricity from solar light [44].
Similarly, Pandey et al. have fabricated 3D-G nanosheets (GNs) using plastic and
have employed them in PSC without HTL. They have used a two-step pyrolysis
technique in which a mesh of nickel (99.99%) is used as the template to synthesize
3D GNs without using any kind of acid in reaction. Figure 6a shows the cyclic
voltammetry curves of 3D-GN which is used to determine the HOMO–LUMO of 3D-
GN and compare with pristine graphene material (Fig. 6b). The device has resulted in
a PCE of 12.40% as compared to the conventional device (11.04%) due to improved
conductivity and lowered recombination process [5]. The reduced recombination is
achieved owing to the fast charge transfer process as shown by bang edge positions
in Fig. 6c where a desirable HOMO position of the 3D-GN can easily promote faster
transfer of holes. Saheed et al. fabricated 3D-G foams that have improved the charge
transport in ZnO ETL in PSCs. The 3D/ZnO architecture has not only improved PCE
to 10.9% with respect to ZnO (4.2%), but has even enhanced the open circuit potential
Fig. 6 A CV plots of 3DG nanosheets derived from waste, b HOMO–LUMO levels of 3DGNs
and conventional graphene, and c band edge positions of 3DGN employed PSC. Adapted from
reference [5]. Copyright The Authors, some rights reserved; exclusive licensee [The Royal Society
of Chemistry 2021]. Distributed under a Creative Commons Attribution License 3.0 (CC BY) https:/
/creativecommons.org/licenses/by/3.0/
of the device by two-fold. The improvement in the performance is attributed to the

electron transporting highway system that leads to effective charge separation within
the 3D-G framework [45]. 3D-G electrodes are also studied in other PV devices like
CdTe solar cells. Bi et al. have carried out large-scale fabrication of 3D-G upon
nickel foams using ambient pressure chemical vapour deposition (APCVD). The
highly conductive films with a sheet resistance of ≈0.45 Ω/▢ and a conductivity of
ca 600 S/cm are explored in CdTe-based devices that have dramatically enhanced the
PCE to 9.1% [46]. The above discussion clearly validates the fact that there are very
few reports exploring 3D-G electrodes in PSC and other solar cells, and additional
research efforts are required in order to utilize and realize the full potential of 3DG
electrodes in PSC, CdTe, Si, organic, and other emerging solar cells.
4 Conclusions
The present chapter discusses the latest developments in the application of 3DG
and its functional composites in PVs. These materials boost the PV performance
of devices owing to their unique physical and chemical characteristics and remark-
able properties like high carrier mobility, low resistivity, transmittance, and two-
dimensional networks. There are pathbreaking evolutions happening in the field of
3DG synthesis, formation of composites, and its employment in various constituents
of next generation solar cells. 3DG is being used as electrode material in liquid
junction cells like DSSC and QDSC as well as solid junctions like organic PVs and
PSCs, because of its minimal mass density, high specific surface area, remarkable
electrocatalytic activity, stability, and excellent mechanical properties coupled with
outstanding electrical and optical properties. Presently, most of the 3DG electrodes
are used in conjunction with other semiconducting electrodes due to the absence
of bandgap in these materials. Therefore, it is highly desirable to induce a bandgap
in 3DG materials by implying some chemical modifications. Efforts should also
be concentrated on developing 3DG-based functional and composite materials that
could improve the interfacial charge transfer process across the electrode and elec-
trolyte. This can be a significant step in replacing platinum as counter electrodes in
QDSC since platinum causes a poisoning effect with polysulphide electrode. Defects
in 3DG are favourable for catalytic properties but in some devices, controlled defects
or high purity could be very beneficial. Achieving such purity depends on the method
of reduction of GO explored in order to form 3DG structures. Utilizing CVD-based
3DG looks more promising for maintaining purity, innate 3D charge transport system,
and superior electrical conductivity. Owing to these advantages, more studies should
be concentrated on improving the CVD-3DG synthesis technique and making it
industrially viable.
Moreover, attempts could be targeted to modify synthesis techniques in order to
achieve precise control of surface properties like pore size and thickness. 3DG with
a large pore size in the range from one hundred to several hundred micrometres
decreases its mechanical properties, therefore, meso- or microporous features are
highly desirable. In addition, there are only a few reports on the application of 3DG
electrodes in PSC and other solid junction solar cells. There is wide scope to test this
material and check its feasibility as a working or counter electrode, ETL or HTL,
and passivation layers to enhance the performance and stability. Further, efforts are
required in the field of interfacial engineering as it is very beneficial to control inter-
facial voltage drop and leakage current which plays an important part in enhancing
the efficiency of PV devices. There is still huge scope to discover novel 3DG-based
architectures that can be incorporated into numerous devices like multijunction or
tandem solar cells to improve the output performance of these devices.
Acknowledgements The authors would like to acknowledge the project titled “Development of
NiOx Thin Films as Electrode Material for Semi-transparent Solar Cells” (SJD78) from the Estonian
Research Council (ERC) granted to the Department of Materials and Environmental Technology,
Tallinn University of Technology, Estonia. The authors wish to thank Prof. Ilona Oja Acik, Head of
the Laboratory of Thin Film Chemical Technologies, Department of Materials and Environmental
Technology, Tallinn University of Technology for her continuous support.
References
1. Chapin, D.M., Fuller, C.S., Pearson, G.L.: A new silicon p-n junction photocell for converting
solar radiation into electrical power. J. Appl. Phys. 25, 676 (1954)
2. Branker, K., Pathak, M.J.M., Pearce, J.M.: A review of solar photovoltaic levelized cost of
electricity. Renew. Sustain. Energy Rev. 15, 4470–4482 (2011)
control. Chem. Rev. 120, 10336–10453 (2020)
4. Novoselov, K.S., Fal, V.I., Colombo, L., Gellert, P.R., Schwab, M.G., Kim, K., Ko, V.I.F.,
Colombo, L., Gellert, P.R., Schwab, M.G., Kim, K.: A roadmap for graphene. Nature 490,
192–200 (2012)
5. Pandey, S., Kumar, A., Karakoti, M., Garg, K.K., Rana, A., Tatrari, G., Bohra, B.S., Yadav,
P., Singh, R.K., Sahoo, N.G.: 3D graphene nanosheets from plastic waste for highly efficient
HTM free perovskite solar cells. Nanoscale Adv. 3, 4726–4738 (2021)
hydrothermal process. ACS Nano 4, 4324–4330 (2010)
7. Yang, P., Hu, Z., Zhao, X., Chen, D., Lin, H., Lai, X., Yang, L.: Cesium-containing perovskite
solar cell based on graphene/TiO2 electron transport layer. ChemistrySelect 2, 9433–9437
(2017)
8. Yan, K., Wei, Z., Li, J., Chen, H., Yi, Y., Zheng, X., Long, X., Wang, Z., Wang, J., Xu, J., Yang, S.:
High-performance graphene-based hole conductor-free perovskite solar cells: schottky junction
enhanced hole extraction and electron blocking. Small 11, 2269–2274 (2015)
9. Pei, S., Cheng, H.: The reduction of graphene oxide. Carbon N. Y. 50, 3210–3228 (2011)
10. García-TOn, E., Barg, S., Franco, J., Bell, R., Eslava, S., D’Elia, E., Maher, R.C., Guitian, F.,
Saiz, E.: Printing in three dimensions with Graphene. Adv. Mater. 27, 1688–1693 (2015)
11. Qiu, L., Liu, J.Z., Chang, S.L.Y., Wu, Y., Li, D.: Biomimetic superelastic graphene-based
cellular monoliths. Nat. Commun. 3, 1–7 (2012)
12. Bi, H., Yin, K., Xie, X., Zhou, Y., Wan, N., Xu, F., Banhart, F., Sun, L., Ruoff, R.S.: Low
temperature casting of graphene with high compressive strength. Adv. Mater. 24, 5124–5129
(2012)
13. Nair, R.R., Blake, P., Grigorenko, A.N., Novoselov, K.S., Booth, T.J., Stauber, T., Peres, N.M.R.,
Geim, A.K.: Fine structure constant defines visual transparency of graphene. Science 320, 1308
(2008)
14. Gao, H.L., Zhu, Y.B., Mao, L.B., Wang, F.C., Luo, X.S., Liu, Y.Y., Lu, Y., Pan, Z., Ge, J., Shen,
W., Zheng, Y.R., Xu, L., Wang, L.J., Xu, W.H., Wu, H.A., Yu, S.H.: Super-elastic and fatigue
resistant carbon material with lamellar multi-arch microstructure. Nat. Commun. 7, 1–8 (2016)
15. Ito, Y., Zhang, W., Li, J., Chang, H., Liu, P., Fujita, T., Tan, Y., Yan, F., Chen, M.: 3D bicon-
tinuous nanoporous reduced graphene oxide for highly sensitive photodetectors. Adv. Funct.
Mater. 26, 1271–1277 (2016)
16. Cells, P.D.S., Meyer, G.J.: The 2010 millennium technology grand, 4337–4343 (2010)
17. Hagfeldt, A., Boschloo, G., Sun, L., Kloo, L., Pettersson, H.: Dye-sensitized solar cells. Chem.
Rev. 110, 6595–6663 (2010)
18. Nazeeruddin, M.K., Péchy, P., Grätzel, M.: Efficient panchromatic sensitization of nanocrys-
talline TiO2 films by a black dye based on a trithiocyanato-ruthenium complex. Chem.
Commun., 1705–1706 (1997)
19. Grätzel*, M.: Solar energy conversion by dye-sensitized photovoltaic cells. Inorganic Chem.
44, 6841–6851 (2005)
20. Yen, M.Y., Teng, C.C., Hsiao, M.C., Liu, P.I., Chuang, W.P., Ma, C.C.M., Hsieh, C.K., Tsai,
M.C., Tsai, C.H.: Platinum nanoparticles/graphene composite catalyst as a novel composite
counter electrode for high performance dye-sensitized solar cells. J. Mater. Chem. 21, 12880–
12888 (2011)
21. Yang, W., Xu, X., Li, Z., Yang, F., Zhang, L., Li, Y., Wang, A., Chen, S.: Construction of
efficient counter electrodes for dye-sensitized solar cells: Fe2O3 nanoparticles anchored onto
graphene frameworks. Carbon 96, 947–954 (2016)
22. Loeblein, M., Bruno, A., Loh, G.C., Bolker, A., Saguy, C., Antila, L., Tsang, S.H., Teo, E.H.T.:
Investigation of electronic band structure and charge transfer mechanism of oxidized three-
dimensional graphene as metal-free anodes material for dye sensitized solar cell application.
Chem. Phys. Lett. 685, 442–450 (2017)
23. Wang, H., Sun, K., Tao, F., Stacchiola, D.J., Hu, Y.H.: 3D honeycomb-like structured graphene
and its high efficiency as a counter-electrode catalyst for dye-sensitized solar cells. Angew.
Chemie - Int. Ed. 52, 9210–9214 (2013)
24. Tang, B., Hu, G., Gao, H., Shi, Z.: Three-dimensional graphene network assisted high
performance dye sensitized solar cells. J. Power Sources. 234, 60–68 (2013)
25. He, Y., Wang, W.: ZIF-8 and three-dimensional graphene network assisted DSSCs with high
performances. J. Solid State Chem. 296, 121992 (2021)
26. Tang, B., Ji, G., Wang, Z., Chen, H., Li, X., Yu, H., Li, S., Liu, H.: Three-dimensional graphene
networks and reduced graphene oxide nanosheets co-modified dye-sensitized solar cells. RSC
Adv. 7, 45280–45286 (2017)
27. Sun, Y., Cao, Y., Huang, W., Zhu, Y., Heng, L., Tang, B.: High-performance photoanode for
dye sensitized solar cells with graphene modified two-layer construction. Mater. Lett. 165,
178–180 (2016)
28. Chang, Q., Huang, L., Wang, J., Ma, Z., Li, P., Yan, Y., Zhu, J., Xu, S., Shen, L., Chen, Q.,
Yu, Q., Shi, W.: Nanoarchitecture of variable sized graphene nanosheets incorporated into
three-dimensional graphene network for dye sensitized solar cells. Carbon 85, 185–193 (2015)
29. Yu, M., Zhang, J., Li, S., Meng, Y., Liu, J.: Three-dimensional nitrogen doped holey
reduced graphene oxide framework as metal-free counter electrodes for high performance
dye-sensitized solar cells. J. Power Sources. 308, 44–51 (2016)
30. Sun, L., Lu, L., Bai, Y., Sun, K.: Three-dimensional porous reduced graphene oxide/sphere-like
CoS hierarchical architecture composite as efficient counter electrodes for dye-sensitized solar
cells. J. Alloys Compd. 654, 196–201 (2016)
31. Xue, Y., Liu, J., Chen, H., Wang, R., Li, D., Qu, J., Dai, L.: Nitrogen-doped graphene foams as
metal-free counter electrodes in high-performance dye-sensitized solar cells. Angew. Chemie
Int. Ed. 51, 12124–12127 (2012)
32. Roh, K.M., Kim, S.K., Choi, J.H., Jo, E.H., Chang, H., Jang, H.D.: Synergetic effect of graphene
sheet and three-dimensional crumpled graphene on the performance of dye-sensitized solar
cells. AIChE J. 62, 574–579 (2016)
33. Lee, J.S., Ahn, H.J., Yoon, J.C., Jang, J.H.: Three-dimensional nano-foam of few-layer graphene
grown by CVD for DSSC. Phys. Chem. Chem. Phys. 14, 7938–7943 (2012)
34. Wei, W., Sun, K., Hu, Y.H.: Synthesis of 3D cauliflower-fungus-like graphene from CO2 as a
highly efficient counter electrode material for dye-sensitized solar cells. J. Mater. Chem. A. 2,
16842–16846 (2014)
35. Wei, W., Sun, K., Hu, Y.H.: Direct conversion of CO2 to 3D graphene and its excellent perfor-
mance for dye-sensitized solar cells with 10% efficiency. J. Mater. Chem. A. 4, 12054–12057
(2016)
36. Ahn, H.J., Kim, I.H., Yoon, J.C., Kim, S.I., Jang, J.H.: p-Doped three-dimensional graphene
nano-networks superior to platinum as a counter electrode for dye-sensitized solar cells. Chem.
Commun. 50, 2412–2415 (2014)
37. Pan, Z., Rao, H., Mora-Seró, I., Bisquert, J., Zhong, X.: Quantum dot-sensitized solar cells.
Chem. Soc. Rev. 47, 7659–7702 (2018)
38. Lightcap, I.V., Kamat, p.V.: Fortification of CdSe quantum dots with graphene oxide. Excited
state interactions and light energy conversion. J. Am. Chem. Soc. 134, 7109–7116 (2012)
39. Sun, J.K., Jiang, Y., Zhong, X., Hu, J.S., Wan, L.J.: Three-dimensional nanostructured
electrodes for efficient quantum-dot-sensitized solar cells. Nano Energy 32, 130–156 (2017)
40. Tavakoli, M.M., Simchi, A., Fan, Z., Aashuri, H.: Chemical processing of three-dimensional
graphene networks on transparent conducting electrodes for depleted-heterojunction quantum
dot solar cells. Chem. Commun. 52, 323–326 (2016)
41. Zhu, Y., Cui, H., Jia, S., Zheng, J., Yang, P., Wang, Z., Zhu, Z.: 3D graphene frameworks with
uniformly dispersed cus as an efficient catalytic electrode for quantum dot-sensitized solar
cells. Electrochim. Acta. 208, 288–295 (2016)
42. Muchuweni, E., Martincigh, B.S., Nyamori, V.O.: Perovskite solar cells: current trends in
graphene-based materials for transparent conductive electrodes, active layers, charge transport
layers, and encapsulation layers. Adv. Energy Sustain. Res. 2, 2100050 (2021)
43. Mariani, P., Najafi, L., Bianca, G., Zappia, M.I., Gabatel, L., Agresti, A., Pescetelli, S., Di
Carlo, A., Bellani, S., Bonaccorso, F.: Low-temperature graphene-based paste for large-area
carbon perovskite solar cells. ACS Appl. Mater. Interfaces. 13, 22368–22380 (2021)
44. Wei, W., Hu, B., Jin, F., Jing, Z., Li, Y., García Blanco, A.A., Stacchiola, D.J., Hu, Y.H.:
Potassium-chemical synthesis of 3D graphene from CO2 and its excellent performance in
HTM-free perovskite solar cells. J. Mater. Chem. A 5, 7749–7752 (2017)
45. Mohamed Saheed, M.S., Mohamed, N.M., Mahinder Singh, B.S., Wali, Q., Saheed, M.S.M.,
Jose, R.: Foam-like 3D graphene as a charge transport modifier in zinc oxide electron transport
material in perovskite solar cells. Photochem 1, 523–536 (2021)
46. Bi, H., Huang, F., Liang, J., Tang, Y., Lü, X., Xie, X., Jiang, M.: Large-scale preparation of
highly conductive three dimensional graphene and its applications in CdTe solar cells. J. Mater.
Chem. 21, 17366–17370 (2011)
3D Graphene for Fuel Cells
Norazuwana Shaari, Nik Farah Hanis Nik Zaiman, Siti Hasanah Osman,
and Ajaz Ahmad Wani
Abstract Materials science technology and research are advancing all the time
which has a direct impact on the large contribution of carbon-based materials. Carbon
can be present in various allotropes including zero-dimensional Carbon-60 (0D C60)
and one-dimensional (1D) carbon nanotubes, two-dimensional (2D) graphene mate-
rials, and many more with unique and excellent properties. However, the function
of 2D graphene still needs to be improved to meet the needs of various applica-
tions such as electrochemical catalysis, environmental remediation, energy storage,
and conversion. Modifications on 2D graphene have been done at various levels to
obtain a material with more efficient properties, which is in the allotrope of three-
dimensional (3D) graphene. This chapter focuses on the application of 3D graphene
materials in fuel cell applications starting with the introduction of fuel cells, classifi-
cation, and synthesis methods for 3D graphene. Then, the current study on aerogel,
hydrogel, and foam-based graphene material for fuel cell application is discussed.
Next, the challenge and future perspective as well as the conclusion are given to be
a reference for the reader.
Keywords 3D Graphene · Aerogel · Hydrogel · Foam · Fuel cell
1 Introduction
A device called a fuel cell transforms the chemical energy from a fuel into electrical
energy by engaging in a chemical reaction with an oxidizing agent. It operates simi-
larly to a battery but requires a continuous source of fuel and air to sustain the reaction
and produce electricity [1]. Fuel cells are highly efficient and emit very little pollu-
tion, making them a promising technology for use in clean energy systems, including
N. Shaari (B) · N. F. H. N. Zaiman · S. H. Osman · A. A. Wani

Fuel Cell Institute, National University of Malaysia, 43650 Bangi, Selangor, Malaysia
e-mail: norazuwanashaari@ukm.edu.my
A. A. Wani
Department of Chemistry, Aligarh Muslim University, Aligarh, India
https://doi.org/10.1007/978-3-031-36249-1_18
322 N. Shaari et al.
transportation and power generation [2]. Fuel cells have been a significant aspect of
research due to their crucial role in various fields such as portable, stationary, trans-
portation, engineering tissue, and medical. Despite rapid growth, some challenges
need to be addressed to keep fuel cells making a positive impact, such as reducing
costs and improving component durability. The most crucial component in a fuel
cell in Fig. 1 illustrates a membrane electrode assembly (MEA), which includes a
membrane and an electrocatalyst. The anode and cathode are key parts in determining
the chemical reaction, and catalyst poisoning can occur due to ineffective oxidation.
The reaction is also influenced by various factors like fuel concentration and process
conditions [3].
The conventional catalyst commonly used in fuel cells is platinum supported
by carbon black, known as Vulcan XC-72. This type of catalyst requires a large
quantity of platinum which can lead to increased costs and stability problems, such
as poisoning and sintering. There is a need for research to develop more affordable
and efficient catalysts [4]. In order to attain optimal electrochemical performance,
the catalyst layer should be manufactured. High reaction rates are achieved through
a good catalyst’s facilitation of electron, proton, and reactant transfers. It is vital
for this to happen that the catalyst layer’s structure and composition are optimized.
Despite these promising characteristics and enhanced functionality, carbon-based
nanostructured materials have been gaining favor as electrocatalysts [5].
Fig. 1 Schematic of fuel cell component. Adapted with permission [14], copyright (2017), Elsevier
3D Graphene for Fuel Cells 323
Paraknowitsch et al. [6] have conducted research on the use of advanced doped
carbon-based catalysts in energy applications, including fuel cells. Examples of these
materials include carbon and graphene in the structure of aerogels, xerogels, cryogels,
hydrogels, and foam. The first carbon aerogels were created in the 1930s using the
supercritical drying technique introduced by Kistler [7]. Additionally, the sol–gel
polycondensation process of organic monomers such as resorcinol and formalde-
hyde can produce organic gels that can be transformed into carbon aerogels through
carbonization, as demonstrated by the Pakalas method.
3D graphene-based materials have become highly popular for their various appli-
cations, such as in electrochemistry, fuel cells, photocatalysis, microelectronics,
supercapacitors, oil clean-up sorbents, and lithium-ion batteries [8]. This is due to
its unique properties, such as its high porosity, low thermal conductivity, large active
surface area, and controlled pore size. It can be formed into different shapes, such
as monoliths, thin films, and pellets. The structure of 3D graphene-based materials
such as aerogel is composed of interconnected nano-sized particles, and it can be
made with different textures like micropore, mesopore, and macropore [9]. As seen
in Fig. 2, aerogel exists in a state between liquid and gas, and its texture can be
fine-tuned to produce optimal catalyst support for fuel cell applications.
Recent research has shown that the gel made of 3D graphene can lower the mass
transfer rate in the catalyst layer due to its distinctive pore structure. The surface
chemistry of the 3D graphene-based materials gel can be altered through various
methods, such as modifying the precursor used in the organic gel production stage
or applying gas or liquid treatments during the final stages of gel production. These
methods allow for the introduction of functional groups on the 3D graphene-based
Fig. 2 The figure of “density” versus “enthalpy of the system” shows the distribution and transition
of various states of matter. Adapted with permission [15], Copyright (2013) by the authors; licensee
MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and
conditions of the Creative Commons Attribution License
materials support surface, which is crucial in preparing metal-supported catalysts

and determining the loading, dispersion, oxidation conditions, and stability of the
metal phase [8].
In the modern chemical industry, solid catalysts have gained prominence and 3D
graphene-based materials structures have emerged as promising materials for hetero-
geneous catalysis and catalyst support. Kistler was the first researcher to explore
the potential of aerogel as a catalyst, followed by further studies by researchers
such as Baiker, Pajonk, Teichner, and other groups [10–13]. The development of 3D
graphene-based materials for fuel cell applications, such as aerogel, hydrogel, and
foam, is the main topic of this chapter. It also discusses the synthesis of catalysts
and catalyst supports, as well as the materials’ potential in fuel cells in terms of
electrochemistry and power density. This chapter also nalyses how the design and
operational parameters of fuel cells affect activity.
2 3D Graphene Based Aerogel Application in Fuel Cell
Nowadays, the use of nanomaterials produced by aerogel is of great importance in

decreasing the reliance of fuel cells on pricey noble metals such as platinum and
palladium that are used in the anode and cathode catalyst layers. The ultimate aim is
to decrease the overall cost of the fuel cell system and boost its commercialization
in the markets of both China and the United States. Aerogels’ special qualities have
the potential to increase fuel cells’ effectiveness. The Proton Exchange Membrane
Fuel Cell (PEMFC) stack is a widely utilized technology in various fields such as
automotive, domestic, military, and small-scale applications. In order to function
optimally, the PEMFC stack requires a certain amount of platinum, with a minimum
requirement of 0.2 g per kilowatt, and a cell voltage of 0.65 V.
Despite this, the current PEMFC system needs to use a lot of platinum catalysts
in order to achieve the desired power density of 1 kilowatt, ranging from 0.85 to
1.2 g per kilowatt. As a result, reaching the minimum level of platinum usage, which
is five times less than what is currently being used, will be difficult for large-scale
applications [4]. An intriguing fact is that graphene-based aerogel has the ability to
stabilize on a leaf, and this material is noted for being exceptionally lightweight.
Due to its appealing qualities like electrical conductivity, high mechanical strength,
adsorption capacity, and thermal resistance, graphene aerogel has been reserved for a
variety of applications as a special material. It also licenses names and shows to boost
the characteristics and performance of catalysts in fuel cell applications. Recently,
Guan and his co-worker [16] fabricated a new membrane electrode assembly (MEA),
which involves placing a layer of graphene aerogel (GA) between the carbon powder
microporous layer and the catalytic layer, has been developed to improve the output
of direct methanol fuel cell (DMFC) at high methanol concentrations. This approach
has been found to enhance the performance of DMFC significantly.
The maximal power density of the new MEA, which is 234% greater than that of
the standard electrode, is reported in this study to be 27.4 mWcm−2 in an environment
of 8 M methanol. According to the electrochemical impedance spectroscopy (EIS)

test results, the novel MEA’s internal resistance is not increased by the addition of GA,
and the mass transfer resistance is noticeably lower at high concentrations. Çögenli
et al. [17] work on graphene with carbon black heteroatoms Platinum nanoparticles
supported by an aerogel hybrid served as Pt nanoparticles supported by three different
hybrid carbons (50:50)—Pt/GA-C (Platinum/carbon black and graphene aerogel),
Pt/NGA-C (Platinum/carbon black and nitrogen-doped graphene aerogel), and Pt/
BGA-C (Platinum/carbon black and boron-doped graphene aerogel)—were used as
electrocatalysts for the oxidation of methanol and formic acid that were made using
the modified Hummers technique, hydrothermal procedure of the support materials,
and microwave irradiation. In terms of methanol and formic acid oxidation, the Pt/
BGA-C catalyst had the maximum catalytic activity.
Other than that, Guo and his colleague [18] performed the electrocatalyst support
for methanol oxidation using nitrogen-doped graphene aerogel microspheres. This
supported catalyst was produced by freeze-drying, thermal annealing, and elec-
trospraying pyrrole and an oxidizing agent into a graphene oxide dispersion. The
reported results show that Pt/N-doped graphene aerogel bulk (Pt/rGNAB), and Pt/N-
doped graphene aerogel millimeter spheres (Pt/rGNAS) show that anode electrocata-
lysts achieve higher mass activity performance compared to Pt/C of 840.11 mA mg−1
for the electrooxidation of methanol. The Pt/rGNAMs additionally exhibit enhanced
long-term electrocatalytic stability. Additionally, Sahoo et al. [19] consider 3D
graphene supported by Palladium (Pd) as a possible electrocatalyst for alkaline direct
methanol fuel cells. This study describes a straightforward, inexpensive, and envi-
ronmentally friendly Pd supported on 3D graphene aerogel (Pd/GA) using a single
freeze-casting process. According to this research, the Pd/GA catalyst outperforms
standard Pd/carbon black (Vulcan XC-72R) with the same loading (20%) of Pd in
electrocatalysis and exhibits abnormally high toxin tolerance and stability.
Interestingly in 2018, Selim Çögenli et al. [20] research on platinum nanoparticles
for formic acid electrooxidation supported by graphene aerogel. Different support
materials, such as commercial carbon black (C), produced graphene aerogel (GA),
and their hybrids (GA/C), were used in this investigation. According to the research,
commercially produced carbon-supported catalysts for the oxidation of formic acid
did not perform as well as synthetic GA-supported catalysts did. Direct pathway
dominated the electrooxidation of formic acid, and Pt/GA and Pt/GA/C(2) catalysts
demonstrated improved tolerance against the CO poisoning effect. Since the study
by Kwok and his team [21], graphene and carbon nanotube composites were used as
catalyst supports for Ru at Pt catalyst to produce a high porosity anode for a flow-
through direct methanol microfluidic fuel cell (MFC) application. The porosity size
of the electrode and the size of the nanoparticles synthesized were in the range of
5 nm and 10 m, respectively. The conductivity had been enhanced due to the well-
connected nature of the graphene sheets owing to the existence of carbon nanotubes
(CNT).
In the presence of 1 M methanol and 1 M KOH, a catalyst with a maximum specific
power of 13.1 mWmg−1 attained its highest performance in comparison to earlier
research. Tsang et al. [22] studied a nickel foam plate covered with a bimetallic Pd/
Pt loaded GA that is free of a binder. The Pd/Pt/GA/NFP electrode is then put to

the test in alkaline direct ethanol fuel cell (DEFC) applications, with the highest
maximum power density achieved being 3.6 mWcm−2 at room temperature and a
Pd/Pt ratio of 1:1. Besides, Zhou et al. [23], polyvinyl alcohol (PVA), which serves
as an organic binder to be employed as an ultrafine Pt nanoparticle catalytic support,
was used in the freeze-drying procedure to create 3D graphene/carbon nanotube
(GRCNTs) aerogels. The good ant poisoning capability, high activity, and exceptional
durability of this manufactured catalyst were indisputable great qualities. In addition,
Kwok et al. [24] have successfully anchored the platinum nanoparticles on GA with
a diameter of 1.5 nm for use in a direct methanol microfluidic fuel cell. Pt/GO
aerogel has some reimbursements over commercial Pt/C electrodes, including a 358%
increase in specific power, greater catalytic activity, and electroactive surface area.
In applications involving direct glucose fuel cells (DGFC), Tsang and his team [22]
search for alternate ways to generate binder-free electrocatalytic electrodes. Then,
various Pd/Pt ratios on nickel foam plates without a binder were achieved by utilizing
GA as catalyst support (1:2.32, 1:1.62, and 1:0.98). This innovative PdPt/GO/nickel
form plate (NFP) composite was created using an environmentally friendly one-step
mild reduction technique. The best performance was 1.25 mWcm−2 of maximal
power density under ideal conditions (0.5 M glucose/3 M KOH as the anodic fuel
and Pd1Pt0.98/GA/NFP as the catalyst).
Krittayavathananon and Sawangphruk [25] have successfully improved the perfor-
mance of the Pd catalyst due to the high porosity of the graphene oxide aerogel paper
support. They also conducted another study as a control and comparison, namely Pd
coated on 3 other types of carbon materials including bare carbon fiber (CFP), and
CFP modified with either 2D graphene oxide (GO) and 2D rGO nanosheets. It turns
out that Pd supported RGO aerogel has higher performance than others. Based on
the high porosity of 3D rGO support, the direct ethylene glycol fuel cell performs
best when the catalyst is Pd/3D rGO aerogel. This Pd/3D rGO aerogel was capable
of delivering a high anodic current density of 267.8 mAcm−2 at 3000 rpm. The
distribution of pores and the shape of aerogel and aerogel composite are shown in
Fig. 3.
Zhao et al. [26] used three straightforward combination techniques, including
template removal process thermal treatment, and hydrothermal self-assembly to
create 3D porous nitrogen-doped GA (3D NGA). The current-produced catalyst
performs much better than Pt/G and Pt/3D-GA catalysts, especially when it comes
to the electrooxidation of methanol. It has a high electrochemical active surface area
(ECSA) of 90.7 m2 g−1 , good stability, and greater catalytic activity. This exceptional
performance was due to the well-connected 3D porous structure, high N doping level,
and uniform Pt NP dispersion. Instead of that, Öztuna and his team [27] studied a
supercritical deposition technique to create extremely tiny, thin, pyramidal meso-
porous graphene aerogel (GA) supported Pt nanoparticles (scCO2 ). The conversion
temperature (400 °C to 800 °C) and the typical particle size were the variables exam-
ined in this study (1.2 to 2.9 nm). The supercritical deposition (SCD) technique
allows for the preservation of the original textural characteristics of GA even after
the deposition of Pt nanoparticles. According to Fig. 4, the Pt/GA produced has a
Fig. 3 SEM images at varying magnifications show the 3D rGO aerogel coated on CFP a, c and
the Pd electrodeposition on the top layer of the 3D rGO/CFP b, d. Additionally, N2 adsorption/
desorption isotherms of the 3D rGO aerogel and 2D rGO sheets restacked (e), as well as the pore
size distribution of these materials (f), are also presented. Adapted with permission [25], Copyright
(2016), Elsevier
maximum mass activity of 30.6 mAmg−1 Pt, which is significant when compared to
the mass activity of the Pt/GA electrocatalyst produced using the traditional method.
This makes the conversion temperature of 600 °C the most suitable. Furthermore,
Huang and his collaborator [28] were employing 3D-GA as the support for the Pt
catalyst, and Pt was subsequently added to 3D-GA using a straightforward process
called the one-step co-reduction approach. The electrocatalyst of Pt/GA performed
Fig. 4 Pt/GA, graphene aerogel morphology and electrochemistry behavior. Adapted with permis-
sion [27], Copyright (2017), Elsevier
well in terms of durability and electrocatalytic activity due to GA’s unique 3D archi-
tecture structure, effective Pt deployment in GA spaces, and efficient interactions
between Pt nanoparticles and GA.
Zhao et al. [29] used the quick and environmentally friendly hydrothermal
technique in order to create a platinum, carbon, and graphene aerogel (Pt/C/GA)
combined to form a highly stable hybrid electrocatalyst. The unusual 3D graphene
framework structure of this electrocatalyst played a major role in its ability to accom-
plish substantial methanol electrooxidation without losing electrocatalytic activity.
The Pt/C/GA is also more stable than Pt/C, whose mass activity remained relatively
stable after 200 cycles of testing. Methanol electrooxidation’s performance needs to
be increased. Duan and team [30] synthesized graphene oxide aerogel (GOA) as a
substitute for platinum as a catalyst. Pt/GOA has a large active surface area, which
contributes to its excellent mass transfer process efficiency. In this research, a number
of parameters that affected GA structures were found. One of them is the process
used to make aerogel. The second is the temperature and time for drying the aerogel.
The size of the pore, pore dispersion, and the networking established are all observed
to be influenced by all of these factors and last is the usage of precursor materials.
3 3D Graphene-Based Hydrogel Application in Fuel Cell
Recently, Moradian and his team [31] studied the anode for effective microbial fuel
cells powered by xylose using yeast-induced production of graphene hydrogels, as
illustrated in Fig. 5. Yeast-based MFCs were developed employing an autonomously
self-modified 3D reduced graphene oxide (rGO) hydrogel anode, which has a two-
fold improvement in bioelectricity and biohydrogen production from xylose. Addi-
tional investigation revealed that the underlying reason for the enhancement of MFC
performance was the 3D rGO hydrogel’s ability to draw in more yeast cells and
minimize the interfacial charge transfer resistance.
Additionally, Chen and his colleague [32] introduced an anode for microbial
fuel cells that were constructed using a suggested 3D composite hydrogel made of
reduced graphene oxide and polyacrylamide (rGO/PAM) and connected to a current
collector graphite brush (GB). The in situ polymerization of acrylamide in a graphene
oxide dispersion was used to create the rGO/PAM, which was then reduced with
ascorbic acid. The resulting macro-porous scaffold had a high surface area and was
biocompatible, which facilitated mass diffusion of the culture medium, microbial
colonization, and electron mediators. The findings of this work show that at the
stable stage of power generation, the maximal power density, and volumetric power
density of the GB/rGO/PAM anode are impressively high 758 mWm−2 and 53 Wm−3 ,
respectively. The orientated rGO/PAM (O-rGO/PAM) with higher conductivity can
significantly increase the greatest power density of MFCs and reach 782 mWm−2 .
Apparently, Kumar and his team [33] are emphasizing research on Carbona-
ceous nanocomposite hydrogels in their approach to the suspension polymerization
Method used in anodes in microbial fuel cells (MFCs). In comparison to the empty
hydrogel, (Poly N-Isopropylacrylamide) (PNIPAM) hydrogels loaded with electri-
cally conductive carbonaceous nanoparticles have much greater MFC efficiency.
Carbon nanotubes (CNTs) and graphene oxide (GO) are evenly dispersed throughout
the PNIPAM matrix, as seen in the obtained morphological images. Remarkably, this
work discovered that the synthesized PNIPAM-GO-CNT composite showed supe-
rior MFC performances with a durability of more than 300 h thanks to the combined
efforts of high electrical conductivity and strong active carbon support. Hydrogel
based structure material has several advantages that can potentially be used in MFC
applications including low cost, a simple technique of manufacture, environmental
friendliness, and outstanding electrocatalytic activity.
4 3D Graphene-Based Foam in Fuel Cell
In energy conversion and storage devices like fuel cells, oxygen evolution and reduc-
tion reactions (OER, ORR) are two vital electrochemical processes. Due to the slow
nature of OER and ORR, commercial ruthenium and platinum-fabricated electrocat-
alysts as electrode materials are commonly employed to accelerate the reaction rates.
However, the practical feasibility of these electrochemical applications is hampered
by high noble metal cost, unavailability, and inadequate durability. Hence, signif-
icant efforts are being made to develop economic and sustainable electrocatalysts
that replace costly noble metals in renewable energy technologies. Two-dimensional
nanomaterials, specifically 2D graphene, are most commonly used in fuel cells owing
to their remarkable electrical, optical, and mechanical properties. Strong interactions
Fig. 5 a photograph of a bare CF electrode, while b, c CF electrodes with GO adsorption and

yeast-induced bio-rGO/CF hydrogel, respectively. SEM images of d, e show the bare CF electrode,
and f, g bio-rGO/CF electrode after discharge in MFC, with yeast cells indicated by red arrows
and rGO nanosheets indicated by blue arrows which different magnifications used in the SEM
images and h performance of yeast-induced formation of graphene hydrogels in MFC. Adapted
with permission [31], Copyright (2022), Elsevier
between graphene sheets, aggregation, and stacking lower graphene nanosheets’

conductivity and specific surface area.
One of the most efficient approaches to solving these drawbacks is to develop
three-dimensional (3D) nanostructures. Graphene foam (GF) with a 3D structure,
interconnected macropores, and high surface area has been effectively designed using
different approaches [34]. These superior qualities make 3D graphene foam a poten-
tially useful catalyst in fuel cells. Heteroatoms (like S, P, and N) and transition metals
(like Ni, Co, and Fe) supported on 3D graphene foam appropriately are better alter-
natives to Ru/Pt-based electrocatalysts owing to their availability, cheap cost, and
high stability. Highly efficient electrocatalysts, such as those that catalyze both the
ORR and OER, hold great promise as a potential replacement for fossil fuels in the
generation of usable energy in the future. The expensive noble metal electrocatalysts
are consistently replaced by developing economic nanohybrid materials.
In Jeong et al. [35] studies, CoFe nanoparticles, and an N-doped carbon shell
were integrated on three-dimensional (3D) mesoporous N-doped graphene foam
(CoFe@N–C/MNGF). This CoFe@N–C/MNGF nanohybrid has shown excellent
electron transfer efficiency with better OER activity in alkaline electrolytes and a
lower overpotential of 330 mV. Due to high ORR activity (stability, electron transfer,
catalytic activity, etc.), it may be a good replacement for noble-metal-based ORR
materials in alkaline fuel cells as the cathode electrode. In an alkaline electrolyte,
the nanohybrid displays a potential of 0.87 V and a low Tafel plot of 71.7 mV dec-1
at 5 mA cm−2 , with an estimated electron transfer number (n) of 2.1–3.61 at 0.15
to 0.35 V. The findings of this research provide novel perspectives on developing a
low-cost, bi-functional electrocatalyst that does not require expensive noble metal
catalysts. In Li et al. [36] study, 3D reduced graphene oxide (rGO) was synthesized
and fabricated with Co nanosheets and Au nanoparticles for the electrooxidation of
sodium borohydride (NaBH4) in an alkaline medium. The as-prepared 3D rGO foam
shows a good current collector, and the composite material CoAu/rGO foam is used in
a direct borohydride-hydrogen peroxide fuel cell (DBHPFC), as the anode electrode.
The structural features of 3D rGO foam provide low electrochemical impedance,
large electrochemical surface area (390 m2 g−1 ), and high efficiency for NaBH4
oxidation. The electrode kinetics of CoAu/rGO foam suggests 6.9 electron transfer
and first-order kinetics for the oxidation of NaBH4 .
Optimizing the efficiency of polymer electrolyte membrane fuel cells requires
combining a gas diffusion layer with a flow field. This is accomplished by combining
the gas diffusion layer with the flow field to reduce the thickness of the membrane
electrode assembly (MEA) and reactant pathway, hence decreasing electron-mass
transport resistance. In Park et al’s. [37] study, graphene foam serves as a flow field
as well as a gas diffusion layer as part of a unified MEA. A reduction in thick-
ness of 82% allows for an increase in the projected volume power density. When
compared to a conventional MEA, the unified membrane electrode performs better in
the area of high current density due to a larger pressure drop, which is also confirmed
by structural and design simulation data analysis. As a three-dimensional material
consisting of interconnecting macropores, graphene foam combines the benefits of
graphene with the morphological features of metal foam. The enhanced porosity
of metal foams has led to their development as a flow field since it can be used to
disperse reactants evenly over a large surface area and drain off any water that is
generated during the process. However, these metal foams are highly susceptible to
the corrosion process, which limits their practical applications during the working of
polymer-electrolyte-membrane fuel cells. 3D graphene foam has been employed as
a flow field to analyze its characteristic features toward the mass transfer of substrate
and products [38]. The efficiency of 3D graphene foam has been enhanced at high
current densities owing to its improved mass transfer properties in a single-cell test.
The detailed electrochemical analysis, including the simulation, oxygen gain, and
electrochemical impedance results, reveals that the 3D graphene foam-based elec-
trode assembly offers lower mass transport resistance than conventional electrode
assembly. These improved results displayed by 3D graphene foam are assumed due
to the 3D graphene foam and interconnected macropores.
During the electrooxidation of NaBH4, the catalytic efficiency and the use of
NaBH4 are of paramount importance. Ultra-thin CoNi nanosheets fabricated with
innovative 3D reduced graphene oxide foam are developed as an effective anode
catalyst to enhance the efficiency of NaBH4 oxidation in Li et al.’s [39] study. The
electrooxidation of NaBH4 has been studied by developing ultrathin transition metal
nanosheets on a 3D rGO anode catalyst (CoNi-NS/rGO foam). CoNi-NS fabricated
on 3D rGO foam has been employed in a three-electrode system to determine its
potential in an alkaline medium toward the oxidation of NaBH4. The as-prepared
CoNi-NS/rGO foam exhibits low electrochemical impedance, high electrochemical
surface area, and low activation energy (8.29 kJ·mol−1 ). The oxidation of NaBH4
on the fabricated electrode follows first-order kinetics, as confirmed by LSV studies.
The as-prepared catalyst has been used in DBHPFC, and the results suggest excellent
efficiency toward NaBH4 oxidation. Zhou et al. have synthesized transition metal-
fabricated hierarchical porous N-doped graphene foams (HPGFs) that are supported
by silica nanoparticles [40]. The transition metal and silica NPs provide excess
surface active sites and high surface area (918.7 m2 g−1 ). The ORR catalytic activity
of HPGFs is tuned by employing different nitrogen precursors (urea, melamine, and
cyanamide). HPGF displays better ORR activity than commercial Pt/C electrode
materials. Furthermore, HPGF shows enhanced electrochemical performance in an
acidic medium when compared to an alkaline medium. HPGF exhibits long-term
stability (5000 cycles) and high resistance to methanol in both acidic and alkaline
solutions. The HPGF-1 electrocatalyst has been integrated into the zinc-air battery
for electrochemical energy conversion systems.
Platinum ruthenium (PtRu) NPs were successfully deposited on 3D graphene foam
(PtRu/3D GF) to develop a hierarchical novel composite material in Kung et al. [41].
This PtRu/3D GF has been used as a nanocatalyst for methanol and ethanol oxida-
tion. PtRu/3D GF has displayed better electrochemical efficiency toward oxidation of
methanol and ethanol, along with high resistance to CO poisoning than PtRu, PtRu/
C, and PtRu/graphene (commercial graphene). The methanol and ethanol oxidation
is nearly doubled by PtRu/3D GF than PtRu/graphene, which is assumed due to
the reduced crystal size of PtRu (3.5 nm) and enhanced surface area (186.2 m2 g−1 )
provided by 3D graphene foam. A facile, economic, and single-step pyrolysis method
is used in Shi et al. [42] study to prepare 3D FeNi-functionalized N, P doped graphene

foam (FeNi@NP-GF) electrocatalyst for DMFCs. The FeNi@NP-GF exhibits high
limiting current density and positive half-wave potential as compared to its precur-
sors, which is due to the combined interaction of Fe/Ni-Nx with Fe/Ni and N groups
and high surface active sites of 3D graphene foam. It also exhibits significant resis-
tance in an alkaline medium for methanol crossover and a four-electron transfer mech-
anism. In addition, FeNi@NP-GF served as a reliable platform for Pt nanoparticles
(NPs). The as-synthesized electrocatalyst showed excellent activity, for methanol
electrooxidation in an acid medium.
The superior features of metal oxide nanostructures make them a competitive
material for energy storage, conversion, and other green energy applications. In
Kumar et al. [43] work, an asymmetric supercapacitor with a cathode electrode
made of ZnO@stainless steel (SS) nano cauliflower and an anode electrode made
of reduced graphene oxide (rGO) on nickel (Ni) has been successfully developed
(rGO@Ni/ZnO@SS). ZnO thin film electrode is produced by reactive DC magnetron
sputtering, and the rGO electrode by electrodeposition. In addition, the kinetics of
thin film electrodes were studied in an alkaline electrolyte solution and the capaci-
tance performance of this unique supercapacitor, rGO@Ni/ZnO@SS, exceeds that
of conventional nanostructured metal oxides. The as-prepared ASCs show enhanced
capacitance values (0–1.4 V), excellent electrochemical efficiency, and extended
stability (89.5% after 5000 cycles). The ASC performs better than the previously
reported ASCs, with an energy density of 23 Whkg−1 and an optimal power density
of 156 Wkg−1 in alkaline aqueous electrolyte solutions. Because of their high perfor-
mance, there is tremendous potential for using nanostructured rGO@Ni/ZnO@SS
in portable electronic devices.
The hydrogen evolution process (HER) in alkaline electrolytes has seen the
development of several catalysts, although its conversion efficiency has remained
poor. Niobium disulfide (NbS2) heterostructures and graphene foam were grown
on nickel foam to develop a mixed-dimensional structure (NbS2-Gr-NF) success-
fully synthesized by Aslam et al. [44] as shown in Fig. 6. The strong syner-
gistic interaction between NbS2-Gr and NF activates the NbS2 surface active sites,
enhances the surface area, and improves conductivity. As a consequence, NbS2-
Gr-NF heterostructures result in a high current density of 500 mA cm−2 at a low
overpotential of 306 mV in 1 M KOH solution, and the current density is further
increased upto 914 mA cm−2 by an insignificant increase in overpotential (32 mV).
Fast reaction kinetics, where the Volmer step is primarily responsible for controlling
the reaction, have been confirmed by a Tafel value of 72 mV dec-1 for the prepared
heterostructure. NbS2-Gr-NF is promising for water-splitting, particularly in alka-
line electrolytes, because of their ability to achieve high current density at a rapid
pace while maintaining high stability.
Fig. 6 SEM pictures of a NF, b NbS2 deposited on NF, c graphene foam deposited on NF, d NbS2-
Gr-NF, and e a schematic showing the growth of graphene foam on nickel foam and the movement
of carbon atoms within nickel. Adapted with permission [44], copyright (2021), Elsevier
5 Challenges and Future Perspectives
The use of 3D graphene-based materials such as aerogel structures has expanded into
a variety of applications due to their unique chemical properties and their ability to
form wet gels. The high pore volume and high surface area contribute to its versatility,
making it one of the lightest and most adaptable materials. While thermal insulation
remains the most widely used application, 3Dgraphene-based materials have also
been utilized in fields such as electrochemistry (supercapacitors, fuel cells), as a
carrier of catalysts and active agents, as filling materials, and in tissue engineering.
In the fuel cell industry, 3D graphene-based materials have shown great potential as
a catalyst or as part of a catalyst due to their high pore volume, high surface area,
well-connected structure, and flexibility, performing better than commercial catalyst
support like Pt/C. There are still many aspects that can be explored for the properties
of 3D graphene-based materials to increase their potential and development in various
applications including:
1. Flexibility in design. The flexibility of 3D graphene-based materials design such
as aerogel is another advantage in its development. The 3D graphene-based
aerogel structure can be easily modified and optimized to meet the desired
specifications. For example, the surface area and pore size can be adjusted to
meet the needs of the application. In fuel cell applications, the properties of 3D
graphene-based materials structures can be tailored to maximize electrocatalytic
performance.
2. Cost-effectiveness. Despite being a relatively new material, 3D graphene-based
materials structures are cost-effective compared to traditional materials. For
example, the cost of producing 3D-graphene-based materials structures for fuel
cell applications is relatively low compared to other materials such as platinum.
This makes 3D graphene-based materials a potential alternative to traditional
catalysts, making them more accessible for commercial use.
3. Green synthesis. 3D graphene-based materials structures can be synthesized
using environmentally friendly methods, which is an important factor in the
development of sustainable technology. For example, the 3D graphene-based
materials aerogel can be synthesized using a sol–gel process using natural mate-
rials such as resorcinol and formaldehyde. This green synthesis method makes
aerogel an attractive option for environmentally conscious consumers.
4. Additionally, the low cost of these raw materials compared to other materials used
in the catalyst industry makes 3D graphene-based materials a more attractive
option for catalyst support. The availability of raw materials also allows for
the large-scale production of 3D graphene-based materials, making them more
accessible for various applications.
The 3D graphene-based materials structure still faces a few obstacles that limit
its application possibilities and delay commercialization, including the following:
i. Cost and high production time. The production time of 3D graphene-based
materials is still long and the cost is still high compared to other materials.
This is because the production process is still not efficient and requires high
energy consumption. To achieve commercial success, it is important to find
more efficient and cost-effective production methods.
ii. Handling and storage. Handling and storage of 3D graphene-based materials
such as aerogel is also a challenge due to its lightweight and brittle nature. This
requires special handling and storage facilities, which can increase the cost of
aerogel use.
iii. Commercialization. Finally, the commercialization of 3D graphene-based mate-
rials is still limited due to limited applications and a lack of understanding of the
properties and capabilities of 3D graphene-based materials among industries.
This requires further research and development to explore the full potential of
3D graphene-based materials and to increase their commercialization in various
fields.
In summary, further steps need to be taken to fully realize the potential of 3D
graphene-based materials and their commercialization. This includes exploring alter-
native raw materials for 3D graphene-based materials production, innovating produc-
tion methods to increase efficiency and scale, and standardizing 3D graphene-based
materials characterization techniques. By addressing these challenges, the potential
for 3D graphene-based materials in various applications can be further realized.
6 Conclusions
In conclusion, 3D graphene-based materials have a lot of potential to be used in

various applications due to their high pore volume, high surface area, and lightweight
properties. However, there are still challenges that need to be addressed such as
the production process, regulation in characterization methods, and transforma-
tion from lab-scale to industrial-scale production. Further studies are needed to
explore the diverse raw materials for 3D graphene-based materials fabrication, hybrid
composite potentials, and regulations for comparison and standardization. With
more research and development, 3D graphene-based materials have the potential
to continue to penetrate new application areas in the future, particularly in the fields
of environmental and electrochemistry.
Acknowledgments The authors would like to express their gratitude to Universiti Kebangsaan
Malaysia (UKM) and the Ministry of Higher Education for providing financial assistance through
a Fundamental Research Grant Scheme FRGS/1/2021/STG05/UKM/02/10.
References
1. Yusoff, Y.N., Shaari, N.: An overview on the development of nanofiber-based polymer elec-
trolyte membrane and electrocatalyst in fuel cell application. Int. J. Energy Res. 45(13),
18441–18472 (2021)
2. Shaari, N., Zakaria, Z., Kamarudin, S.K.: The optimization performance of cross-linked sodium
alginate polymer electrolyte bio-membranes in passive direct methanol/ethanol fuel cells. Int.
J. Energy Res. 43(14), 8275–8285 (2019)
3. Sajid, A., Pervaiz, E., Ali, H., Noor, T., Baig, M.M.: A perspective on development of fuel cell
materials: electrodes and electrolyte. Int. J. Energy Res. 46(6), 6953–6988 (2022)
4. Ramli, Z.A.C., Shaari, N., Saharuddin, T.S.T.: Progress and major BARRIERS of nanocatalyst
development in direct methanol fuel cell: a review. Int. J. Hydrogen Energy (2022)
5. Zaman, S., Wang, M., Liu, H., Sun, F., Yu, Y., Shui, J., ... & Wang, H.: Carbon-based catalyst
supports for oxygen reduction in proton-exchange membrane fuel cells. Trends Chem. (2022)
6. Paraknowitsch, J.P., Thomas, A.: Doping carbons beyond nitrogen: an overview of advanced
heteroatom doped carbons with boron, sulphur and phosphorus for energy applications. Energy
Environ. Sci. 6(10), 2839–2855 (2013)
7. Kistler, S.S.: Coherent expanded-aerogels. J. Phys. Chem. 36(1), 52–64 (2002)
control. Chem. Rev. 120(18), 10336–10453 (2020)
9. Yu, X., Wang, B., Gong, D., Xu, Z., Lu, B.: Graphene nanoribbons on highly porous 3D
graphene for high-capacity and ultrastable Al-ion batteries. Adv. Mater. 29(4), 1604118 (2017)
10. Ng, S., Jelle, B.P., Sandberg, L.I.C., Gao, T., Wallevik, Ó.H.: Experimental investigations
of aerogel-incorporated ultra-high performance concrete. Constr. Build. Mater. 77, 307–316
(2015)
11. Moreno-Castilla, C., Maldonado-, F.: Carbon aerogels for catalysis applications: an overview.
Carbon 43(3), 455–465 (2005)
12. Tleimat-Manzalji, R., Manzalji, T., Pajonk, G.: Aerogels and xerogels for catalytic applications.
J. Non-Cryst. Solids 147, 744–747 (1992)
13. Schneider, M., Baiker, A.: Aerogels in catalysis. Catalysis Rev. 37(4), 515–556 (1995)
14. Sutharssan, T., Montalvao, D., Chen, Y.K., Wang, W.C., Pisac, C., Elemara, H.: A review on
prognostics and health monitoring of proton exchange membrane fuel cell. Renew. Sustain.
Energy Rev. 75, 440–450 (2017)
15. Du, A., Zhou, B., Zhang, Z., Shen, J.: A special material or a new state of matter: a review and
reconsideration of the aerogel. Materials 6(3), 941–968 (2013)
16. Guan, L., Balakrishnan, P., Liu, H., Zhang, W., Deng, Y., Su, H., Xing, L., Penga, Ž, Xu, Q.: A
tortuosity engineered dual-microporous layer electrode including graphene aerogel enabling
largely improved direct methanol fuel cell performance with high-concentration fuel. Energies
15(24), 9388 (2022)
17. Çögenli, M.S., Bayrakçeken Yurtcan, A.: Carbon black-heteroatom-doped graphene aerogel
hybrid supported platinum nanoparticles as electrocatalysts for oxidation of methanol and
formic acid. Int. J. Energy Res. 46(15), 24130–24147 (2022)
18. Guo, Q., Lu, X., Fei, G., Wang, Z., Xia, H.: Nitrogen-doped graphene aerogel microspheres
used as electrocatalyst supports for methanol oxidation. Ind. Eng. Chem. Res. 61(3), 1398–1407
(2022)
19. Sahoo, B.B., Biswal, K., Jena, A., Naik, B., Nayak, N.C., Dash, B.P., Mahanto, B.S., Soam,
A., Sahoo, P.K.: Pd supported on 3D graphene aerogel as potential electrocatalyst for alkaline
direct methanol fuel cells. Mater. Today Proc. 41, 150–155 (2021)
20. Çögenli, M.S., Ayşe, B.Y.: Graphene aerogel supported platinum nanoparticles for formic acid
electro-oxidation. Mater. Res. Express 5(7), 075513 (2018)
21. Kwok, Y.H., Wang, Y.F., Tsang, A.C., Leung, D.Y.: Graphene-carbon nanotube composite
aerogel with Ru@ Pt nanoparticle as a porous electrode for direct methanol microfluidic fuel
cell. Appl. Energy 217, 258–265 (2018)
22. Tsang, C.H.A., Leung, D.: Use of Pd-Pt loaded graphene aerogel on nickel foam in direct
ethanol fuel cell. Solid State Sci. 75, 21–26 (2018)
23. Zhou, Y., Hu, X., Guo, S., Yu, C., Zhong, S., Liu, X.: Multi-functional graphene/carbon
nanotube aerogels for its applications in supercapacitor and direct methanol fuel cell.
Electrochim. Acta 264, 12–19 (2018)
24. Kwok, Y.H., Tsang, A.C., Wang, Y., Leung, D.Y.: Ultra-fine Pt nanoparticles on graphene
aerogel as a porous electrode with high stability for microfluidic methanol fuel cell. J. Power
Sources 349, 75–83 (2017)
25. Krittayavathananon, A., Sawangphruk, M.: Electrocatalytic oxidation of ethylene glycol on
palladium coated on 3D reduced graphene oxide aerogel paper in alkali media: effects of
carbon supports and hydrodynamic diffusion. Electrochim. Acta 212, 237–246 (2016)
26. Zhao, L., Sui, X.L., Li, J.L., Zhang, J.J., Zhang, L.M., Wang, Z.B.: Ultra-fine Pt nanoparticles
supported on 3D porous N-doped graphene aerogel as a promising electro-catalyst for methanol
electrooxidation. Catal. Commun. 86, 46–50 (2016)
27. Oztuna, F.E.S., Barim, S.B., Bozbag, S.E., Yu, H., Aindow, M., Unal, U., Erkey, C.: Graphene
aerogel supported Pt electrocatalysts for oxygen reduction reaction by supercritical deposition.
28. Huang, Q., Tao, F., Zou, L., Yuan, T., Zou, Z., Zhang, H., Zhang, X., Yang, H.: One-step
synthesis of Pt nanoparticles highly loaded on graphene aerogel as durable oxygen reduction
electrocatalyst. Electrochim. Acta 152, 140–145 (2015)
29. Zhao, L., Wang, Z.B., Li, J.L., Zhang, J.J., Sui, X.L., Zhang, L.M.: Hybrid of carbon-supported
Pt nanoparticles and three dimensional graphene aerogel as high stable electrocatalyst for
methanol electrooxidation. Electrochim. Acta 189, 175–183 (2016)
30. Duan, J., Zhang, X., Yuan, W., Chen, H., Jiang, S., Liu, X., Zhang, Y., Chang, L., Sun, Z.,
Du, J.: Graphene oxide aerogel-supported Pt electrocatalysts for methanol oxidation. J. Power
Sources 285, 76–79 (2015)
31. Moradian, J.M., Mi, J.L., Dai, X., Sun, G.F., Du, J., Ye, X.M., Yong, Y.C.: Yeast-induced forma-
tion of graphene hydrogels anode for efficient xylose-fueled microbial fuel cells. Chemosphere
291, 132963 (2022)
32. Chen, J.Y., Xie, P., Zhang, Z.P.: Reduced graphene oxide/polyacrylamide composite hydrogel
scaffold as biocompatible anode for microbial fuel cell. Chem. Eng. J. 361, 615–624 (2019)
33. Kumar, G.G., Hashmi, S., Karthikeyan, C., GhavamiNejad, A., Vatankhah-Varnoosfaderani,
M., Stadler, F.J.: Graphene oxide/carbon nanotube composite hydrogels—versatile materials
for microbial fuel cell applications. Macromol. Rapid Commun. 35(21), 1861–1865 (2014)
34. Liu, Z., Shen, D., Yu, J., Dai, W., Li, C., Du, S., Jiang, N., Li, H., Lin, C.T.: Exceptionally
high thermal and electrical conductivity of three-dimensional graphene-foam-based polymer
composites. RSC Adv. 6(27), 22364–22369 (2016)
35. Jeong, D.I., Choi, H.W., Woo, S., Yoo, J.H., Kumar, M., Song, Y.H., Lim, B., Koo, B.K.,
Kang, B.K., Yoon, D.H.: Complementary performance improved crystalline N-doped carbon
encapsulated CoFe/mesoporous N-doped graphene foam as bifunctional catalyst. Appl. Surf.
Sci. 559, 149077 (2021)
36. Li, B., Song, C., Zhang, D., Ye, K., Cheng, K., Zhu, K., Yan, J., Cao, D., Wang, G.: Novel
self-supported reduced graphene oxide foam-based CoAu electrode: an original anode catalyst
for electrooxidation of borohydride in borohydride fuel cell. Carbon 152, 77–88 (2019)
37. Park, J.E., Lim, J., Lim, M.S., Kim, S., Kim, O.H., Lee, D.W., Lee, J.H., Cho, Y.H., Sung,
Y.E.: Gas diffusion layer/flow-field unified membrane-electrode assembly in fuel cell using
graphene foam. Electrochim. Acta 323, 134808 (2019)
38. Park, J.E., Lim, J., Kim, S., Choi, I., Ahn, C.Y., Hwang, W., Lim, M.S., Cho, Y.H., Sung, Y.E.:
Enhancement of mass transport in fuel cells using three-dimensional graphene foam as flow
field. Electrochim. Acta 265, 488–496 (2018)
39. Li, B., Yan, Q., Song, C., Yan, P., Ye, K., Cheng, K., Zhu, K., Yan, J., Cao, D., Wang, G.:
Reduced graphene oxide foam supported CoNi nanosheets as an efficient anode catalyst for
direct borohydride hydrogen peroxide fuel cell. Appl. Surf. Sci. 491, 659–669 (2019)
40. Zhou, X., Tang, S., Yin, Y., Sun, S., Qiao, J.: Hierarchical porous N-doped graphene foams
with superior oxygen reduction reactivity for polymer electrolyte membrane fuel cells. Appl.
Energy 175, 459–467 (2016)
41. Kung, C.C., Lin, P.Y., Xue, Y., Akolkar, R., Dai, L., Yu, X., Liu, C.C.: Three dimensional
graphene foam supported platinum–ruthenium bimetallic nanocatalysts for direct methanol
and direct ethanol fuel cell applications. J. Power Sources 256, 329–335 (2014)
42. Shi, C., Maimaitiyiming, X.: FeNi-functionalized 3D N, P doped graphene foam as a noble
metal-free bifunctional electrocatalyst for direct methanol fuel cells. J. Alloy. Compd. 867,
158732 (2021)
43. Kumar, A., Adalati, R., Sharma, M., Choudhary, N., Kumar, K.S., Hurtado, L., Jung, Y.,
Kumar, Y., Thomas, J. and Chandra, R.: Self-assembled zinc oxide nanocauliflower and
reduced graphene oxide nickle-foam based Noval asymmetric supercapacitor for energy storage
applications. Materials Today Commun., 105362 (2023)
44. Aslam, S., Sagar, R.U.R., Ali, R., Gbadamasi, S., Khan, K., Butt, S., Xian, J., Mahmood, N.,
Qiu, Y.: Mixed-dimensional niobium disulfide-graphene foam heterostructures as an efficient
catalyst for hydrogen production. Int. J. Hydrogen Energy 46(68), 33679–33688 (2021)
3D Graphene as Electrocatalysts
for Water Splitting
Farkhondeh Khodabandeh and Mohammad Reza Golobostanfard
Abstract Considering the rapidly growing Earth pollution and energy crisis in the
last several decades, the development of renewable energy sources has been at the
forefront of research trends. Hydrogen production and storage through electrochem-
ical water splitting holds great promise for the future green energy system. From the
commercial side of the spectrum, higher reaction kinetics is required for these devices
to meet industry demands. Graphene with a 3D hierarchical network has represented
a great progress in water electrolysis both as an electrocatalyst and a support for
other active materials owing to its distinctive properties such as large surface area,
chemical robustness, and exceptional conductivity. This chapter provides a compre-
hensive review of the latest advances in 3D graphene-based electrocatalysts for water
splitting techniques. In this regard, the electrocatalytic activity and performance of
pristine graphene are discussed in the first place followed by the introduction of
some design strategies to improve its efficiency. Then, various hybrid structures are
profiled highlighting the role of 3D graphene as a great support. Finally, the future
outlook and main challenges of this emerging field are discussed in the last section
to offer an approach for further investigations.
Keywords 3D graphene · Hydrogen production · Water splitting · Renewable

energy sources · Electrocatalyst
F. Khodabandeh
School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran,
North Kargar, 1417614411 Tehran, Iran
M. R. Golobostanfard (B)
Ecole Polytechnique Fédérale de Lausanne (EPFL), Institute of Microengineering (IMT),
Photovoltaics and Thin-Film Electronics Laboratory (PV-Lab), Rue de La Maladiere, 2000
Neuchâtel, Switzerland
e-mail: mohammadreza.golobostanfard@epfl.ch
https://doi.org/10.1007/978-3-031-36249-1_19
342 F. Khodabandeh and M. R. Golobostanfard
1 Introduction
Due to the limited resources and environmental issues associated with fossil fuels,
enormous efforts have been devoted to developing a renewable alternative. Molec-
ular hydrogen (H2 ), with its higher gravimetric energy capacities and pollution-free
nature, is deemed to be an attractive candidate to fulfill modern society’s demands.
However, for a complete replacement of traditional fuels, economical and scalable
hydrogen production is highly crucial. In stark contrast, industrial hydrogens evolu-
tion methods like steam reforming and coal gasification produce gigantic amounts
of greenhouse gases contributing to global warming and air pollution [1].
Among various possible green approaches for hydrogen production, electrochem-
ical water splitting is regarded to be a promising option since it only needs water
as raw material, which is totally abundant and renewable and leaves no hazardous
by-product. This method basically relies on a series of electrochemical reactions [2]:
oxygen and hydrogen evolution reactions (HER and OER). Despite all the intriguing
features of this method, the sluggish kinetics of the reactions hinders its widespread
application. In this manner, the implementation of a high efficiency electrocatalyst is
of significant importance. Precious Pt-group metals (PGM) have always represented
great electrocatalytic behavior. Nevertheless, the scarcity and high cost of noble
metals bound their practical usage for mass H2 production. In recent years, massive
research is going on in the development of cost-effective and more abundant elec-
trocatalysts such as carbon-based nanostructures and transition metal compounds to
replace PGMs.
The glamorous and charismatic properties of graphene such as its large specific
surface area, high intrinsic conductivity, and great durability in an aqueous envi-
ronment have paved the way for efficient and economical hydrogen production [3].
Graphene has a multifunctional structure and not only can be utilized as an elec-
trocatalyst, but it can provide a proper support for other active materials. However,
the considerable van der Waals force between its layers leads to the aggregation of
graphene sheets. This phenomenon extremely reduces the accessibility of active sites
and blocks electron transfer and gas diffusion to a high extent [4]. Therefore, it is
necessary to overcome this challenge to realize the commercialization of graphene-
based electrocatalysts. The construction of a three-dimensional (3D) network out of
graphene sheets is a facile and novel solution to this problem. 3D graphene inherits
the outstanding features of graphene and its hierarchical network and porous structure
even make it a more reliable catalyst and support. The various interconnected pores in
this framework expose more active sites to the reactants and simultaneously promote
the diffusion of gas products. By precisely taking advantage of the aforementioned
merits, 3D graphene-based materials can further optimize the electrocatalytic water
splitting technique [5].
3D Graphene as Electrocatalysts for Water Splitting 343
Regardless of all opportunities that 3D graphene provides, bare graphene has

poor catalytic activity due to its zero-bandgap property and falls short of scalable fuel
production [6]. In this regard, multitudes of strategies have been introduced to address
this inferior performance. Chemical heteroatom doping of its lattice structure can
highly improve its catalytic capability by manipulating the electronic structure. From
another point of view, 3D graphene can be a fantastic support, and the hybridization
of graphene sheets with other earth-abundant catalysts is a more practical and feasible
route.
This chapter reviews recent progress made by 3D graphene as an electrocata-
lyst for water splitting process. First, the electrochemical water splitting mecha-
nism and the functional properties of 3D graphene for the electrolysis reactions are
explained. Then, the mostly utilized strategies to improve the catalytic activity of
graphene are discussed including heteroatom doping of graphene and fabrication of
various hybrid structures. Although substantial progress has been made inspired by
the mentioned benefits, such investigations are still in their infancy and 3D graphene
hybrids cannot yet compete with their Pt-based counterparts. Accordingly, chal-
lenges for the commercialization of 3D graphene-based electrocatalysts and future
perspectives for their widespread applications are summarized in the last section.
2 Electrochemical Water Splitting Mechanism
Electrochemical water splitting is an eco-friendly and facile approach to store elec-

trical energy as a chemical fuel. This conversion process involves a couple of elec-
trochemical redox reactions. These reactions take place in an electrochemical cell
consisting of (1) working electrodes, (2) electrolyte, and (3) external power supply as
illustrated in Fig. 1a [7]. After the application of an external voltage to the electrodes,
water molecules split into gaseous H2 and O2 on cathode and anode, respectively.
The reaction mechanisms on each electrode in different media are as follows [8]:
Overall water splitting reaction:
H2 O → H2 + 0.52
In acidic medium:
2H+ + 2e− → H2 (cathode)
H2 O → 2H+ + 0.5O2 + 2e− (anode)
In neutral and alkaline medium:
H2 O + 2e− → 2OH− (cathode)

Fig. 1 a Schematic representation of an electrochemical water splitting cell. Adapted with permis-
sion [16]. Copyright (2018) American Chemical Society. b OER mechanism (Blue and red lines
represent acidic and alkaline media, respectively). Adapted with permission [17]. Copyright (2017)
Royal Society of Chemistry
2OH− → H2 O + 0.5O2 + 2e− (anode)
In acidic medium, a proton obtains an electron to produce a Hads in the Volmer

step (X + H+ → X-Hads , X is an active site), and after that, there are two possible
reactions for HER resulting in two different mechanisms. The second step can be
either Heyrovsky (X-Hads + H+ +e− → X + H2 ) or Tafel (X–H2 + X–H2 → 2X +
H2 ) reaction depending on the coverage of Hads . However, in alkaline conditions, the
aforementioned reactions will be X + H2 O + e− → X-Hads + OH− , X-Hads + H2 O
+ e− → X + H2 + OH− , and X–Hads + X–Hads → 2X + H2 , respectively [9]. In
comparison, HER is quite faster in acidic medium and consumes less energy since
there is no need for water molecules dissociation. In contrast to hydrogen production,
the OER mechanism in both acidic and alkaline media is so complicated and involves
many factors. Many research groups have investigated OER mechanism in different
media and the most widely accepted one is shown in Fig. 1b; however, the precise
OER mechanism is still an ongoing issue.
The Gibbs free energy of the overall water splitting reaction is ~237 kJ/mol [10].
Therefore, the minimum required voltage for a continuous water electrolysis under
standard conditions (25 °C and 1 atm) is ~1.23 V. Practically, greater applied poten-
tials are needed to overcome ohmic potential drop and other overpotentials associated
with this process to produce hydrogen with an acceptable rate. Consequently, it is
essential to coat electrodes with stable and active electrocatalysts to lower the overpo-
tentials and accelerate the slow kinetics of both decomposition reactions. Although
accelerating the HER on cathode is the major goal of water electrolysis, it is so
important to develop efficient electrocatalysts for OER as it is the rate controlling
reaction in most cases. The slow kinetics of OER arises from its multi-step proce-
dure, which highly degrades the total performance of the cell. To date, IrO2 [11] and
RuO2 [12] are known to be the two most efficient and stable catalysts to lower the
high overpotential for oxygen evolution.
To promote an energy-saving and affordable water splitting process, electrocat-

alysts should possess certain characteristics regardless of the electrolyte medium.
Factors including free energy of hydrogen adsorption (ΔGH ), Tafel slope, Faradic
efficiency, turnover frequency (TOF), and overpotential are some of the functional
criteria for material selection. ΔGH of an electrocatalyst is its most decisive prop-
erty indicating whether an electrocatalyst is qualified or not [13]. While a high
binding energy between H atoms and catalyst surface is critical for the adsorption
step (Volmer), a weak bonding is more favorable for electrochemical (Heyrovsky)
and chemical (Tafel) desorption reactions. Taking this trade-off into account, a near-
zero ΔGH is considered to be the most ideal and this is the reason why Pt is the best
electrocatalyst for HER under acidic circumstances [14]. Furthermore, the exchange
current density is also another important property of electrocatalysts, and the rela-
tion between these two parameters is determined by the famous volcano diagram
represented in Fig. 2, which is a great tool for estimating the catalytic performance
of different materials. In addition to all these thermodynamic and kinetic factors, an
electrocatalyst should also have a high mass transport ability, conductivity, number
of active sites with suitable electron density, abundance, and stability in electrolyte
to serve as a promising candidate.
It is well established that PGM-based electrocatalysts have always been the front
runners for water splitting catalysis. However, these materials also have some prob-
lems, i.e., heavy anodic potential oxidizes RuO2 to RuO4 and reduces its active sites
[15]. More importantly, their limited natural reserve and high cost hamper their prac-
tical and commercial applications. Therefore, it is urgent to develop earth-abundant
and cost-effective substitutions with performance comparable to that of PGMs. In
Fig. 2 Volcano diagram for HER exhibiting the relation between exchange current density and ΔGH
at U = 0 V. The solid line is a prediction depicted by a kinetic model and the dashed line represents
the metals which usually form oxides at U = 0 V. The open circles are for (111) surface data and
the filled circles are polycrystalline. Adapted with permission [18]. Copyright (2010) American
Chemical Society
this regard, transition metal compounds such as chalcogenides, nitrides, carbides,

and phosphides as well as carbon-based materials have been introduced, though
their efficiency still lags behind that of noble metals.
3 Properties of 3D Graphene for Electrocatalytic Water

Splitting
Outstanding physicochemical properties and conductivity of carbon materials have

made them great candidates for PGM replacement [19]. Compared with transition
metal compounds, carbon-based electrocatalysts introduce less pollution to the envi-
ronment and are indeed less expensive making them superior options for mass produc-
tion. The 2D member of this large family, graphene, has drawn much more researcher
interests due to its extraordinary characteristics [3]. Theoretically, the specific surface
area of graphene is incredibly high (2630 m2 /g), which facilitates the diffusion of
electrolytes to the active sites and the release of reaction products. In addition, being a
zero-bandgap semimetal endows graphene with a high electrical conductivity, which
extremely increases reactions kinetics. Moreover, graphene is chemically stable and
preserves its integrity even under harsh media. Finally, high thermal and mechanical
stability of graphene can also be some interesting features for industrial applications.
Despite all these distinctive merits, ideal graphene is electrochemically inert and
exhibits low catalytic performance [6]. The poor catalytic activity of a high-quality
graphene originates from its special electronic structure and lack of any dangling
bonds on its surface. Inspired by this limitation, diverse modification methods have
been implemented to regulate the electronic structure and increase its chemical
activity. Chemical doping by different elements and the introduction of defects to
graphene lattice can effectively improve its performance since they can serve as active
sites. On top of that, graphene can also be a fantastic support for the dispersion of
other active materials.
In addition to inherent poor catalytic activity, graphene-based electrocatalysts
cannot overcome the van der Waals forces between adjacent layers and tend to restack
[20]. As a consequence, the number of active sites remarkably drops and all of the
intriguing properties of graphene vanish, simultaneously. The development of a 3D
framework out of graphene nanosheets can be a brilliant solution to alleviate this
obstacle as it surpasses the reaggregation of graphene sheets and provides a suitable
platform for the growth of other active materials. Another attractive feature of 3D
graphene is that the interconnected pores in this structure surprisingly increase the
surface area and available active sites compared with its 2D counterpart resulting
in a much faster diffusion and HER rate. Additionally, this hierarchical network
offers more pathways for electron transfer and lowers the overpotential for gas
evolution reactions [4]. Coexistence of the advantages that this 3D scaffold brings
along with functional inherent properties of graphene makes 3D graphene a reliable
electrocatalyst for water electrolysis process.
4 3D Graphene as an Electrocatalyst for Water Splitting
In the past few years, numerous research have been focused on developing a novel
method to trigger the intrinsic electrocatalytic capability of graphene. Chemical
doping with heteroatoms, surface engineering, defect’s introduction, and function-
alization are some of the most feasible approaches to tailor the electronic properties
of graphene sheets. However, heteroatom doping by non-metals has gained more
attention in the case of 3D graphene.
4.1 Heteroatom Doping by Non-metals
Among all recommended techniques for boosting the weak catalytic activity of pris-
tine graphene, heteroatom doping by non-metals is realized to be more practical
[21]. The introduction of dopants to the graphene lattice furnishes abundant active
sites to this structure and activates adjacent C atoms. In more detail, the foreign
atoms effectively modulate the local electronic structure and contribute to charge
redistribution in this hierarchical network, thus, promoting electrocatalytic perfor-
mance. Electronegativity difference with carbon is the reason behind this activity
improvement, and accordingly, elements including N, S, P, B, O, and Cl have been
studied more frequently [4, 6, 22–24]. A schematic representation of various doping
configurations of some common elements is demonstrated in Fig. 3.
When N is added to graphene planes, its lone electron pairs highly distort the
planner structure by the formation of sp2 and sp3 hybridization. Additionally, high
electronegativity of nitrogen leads to a noticeable polarization effect. Shen et al.
Fig. 3 A schematic representation of various doping configurations; from top and left: pyrrolic N,
pyridinic N, graphitic N, B-2C-O, B-3C, B-C-2O, P-3C(-O), P-2C(-2O), th-S, S-2O, py-O, C–O–C,
C–OH, C=O, g-C, z–C, and a-C. (C: Green/Gray, N: Blue, B: Pink, P: Purple, S: Gold, O: Red, and
H: White). Adapted with permission [27]. Copyright (2016) Nature Publishing Group
[25] synthesized a 3D Ti3 C2 Tx /N-doped graphene (NG) hydrogel through a co-

assembly approach using NH3 .H2 O as a nitrogen source for graphene doping. A
complex N 1 s spectrum in X-ray photoelectron spectroscopy results confirmed the
presence of pyridinic, pyrrolic, and graphitic nitrogen in graphene sheets, and the
catalytic activity of the first two provided so many active sites for HER. The sample
containing 35% of MXene phase exhibited the lowest onset potential of 354 mV
and overpotential of 474 mV to produce 10 mA/cm2 in comparison with undoped
graphene, bare samples, and the ones with different Ti3 C2 Tx contents. The poor
performance of blank 3D graphene and bare Ti3 C2 Tx was ascribed to the inadequacy
of active sites, while the introduction of nitrogen solved this issue. In the case of
phosphorous, electronegativity is not the key factor, and the larger size of P atoms
as well as its extra orbitals can impose distortion to the lattice and lead to a higher
catalytic activity. However, boron and carbon have almost similar electronegativity
and size and a modest change in bond length is responsible for catalytic performance
enhancement.
Compared with other dopants, nitrogen has drawn much more attention for both
HER and OER, though it is not still comparable with noble and transition metals. This
inferior performance is mostly attributed to a nonideal ΔGH and weak binding energy
between hydrogen atoms and the catalyst surface. An elaborate strategy to further
optimize ΔGH of 3D graphene is dual or even multiatom doping. In such a case,
a synergistic effect is induced in the procedure, which greatly improves the overall
efficiency. Ito et al. [26] fabricated a nitrogen and sulfur codoped 3D nanoporous
graphene catalyst through chemical vapor deposition method based on Ni template
using pyridine and thiophene as N and S sources, respectively. Undoped, single-
doped, and dual-doped samples were all synthesized under various temperatures
for comparison and their HER polarization curves are illustrated in Fig. 4a. From
samples prepared at 800 °C, it can easily be comprehended that HER activity has
drastically increased after doping and a gradual decrease in onset potential is evident
from undoped, N-doped, S-doped to N and S-doped graphene. Thus, doped samples
exhibited a better electrocatalytic activity and the codoped catalyst had a superior
performance, hence, showed the lowest Tafel slope of 105 mV/dec. In all, the best
HER activity belonged to the codoped sample prepared in 500 °C with a Tafel slope
of 80.5 mV.dec−1 and overpotential of 0.28 V at 10 mA/cm2 comparable to that of
chalcogenide catalysts. Furthermore, the electrochemical impedance spectroscopy
(EIS) results indicated that the resistance of samples decreased after doping and it
reached a minimum after doping with both N and S. As a result, the enhanced catalytic
activity of doped samples could be attributed to this phenomenon. Reaction pathway
of different samples achieved by density functional theory (DFT) calculations is
shown in Fig. 4b. These results disclosed that ΔGH of undoped graphene is positive,
which means that adsorption of Hads on its surface is not very favorable, while it
is negative in the case of single-doped samples making it difficult for hydrogen
desorption. However, N and S-doped graphene had the smallest value (0.12 eV) near
to that of Pt. Therefore, the combination of positive and negative active sites created
by N and S dopants, respectively, guaranteed fast electron transfer for HER.
Fig. 4 a Cyclic voltammetry (CV) curves of the undoped and doped samples prepared at different
temperatures, b Reaction pathways of undoped and doped samples achieved by DFT calculations.
The inset shows a codoped graphene structure with a sulfur (yellow), nitrogen (blue), and hydrogen
atom (white). Adapted with permission [26]. Copyright (2015) Wiley–VCH
In a nutshell, heteroatom doping of 3D graphene has undeniably opened a new

door toward efficient metal-free catalysts for water electrolysis. Engineering the
electronic structure of graphene to improve its catalytic activity and ΔGH by non-
metallic dopants has become an accepted method in recent decades. However, it is
worth noting that although distortion of the ideal structure of graphene and tailoring
its intrinsic characteristics are beneficial for catalytic activity, other exceptional prop-
erties of graphene, especially conductivity, degrade in exchange. Subsequently, an
optimum dopant concentration should be employed for water splitting purpose.
5 3D Graphene as Electrocatalysts Support
Contrary to all the progress made by chemical doping in 3D graphene-based catalysts,

they are not still among commercial candidates due to their unsatisfactory perfor-
mance and high cost of the doping process. However, as it is already mentioned,
graphene has got great potentials to be a support for other active materials. In this case,
the high conductivity of graphene can contribute to the hybrid structure to dramati-
cally increase the electron transfer kinetics. Meanwhile, the synergistic interaction of
introduced materials with graphene modulates the electronic structure of active sites
increasing their catalytic activity. Furthermore, graphene highly increases the number
of exposed active sites by complete dispersion and controlling the morphology of
the active material. Interestingly enough, these hybrid structures are greatly more
durable in comparison with bare ones since graphene hinders their aggregation and
bleaching after immersion in the electrolyte.
5.1 3D Graphene/Metals
It is well established that metal-based catalysts have always been the front runner
for water electrolysis and their limited resources are the major bottleneck for their
commercialization. A promising strategy to lower the metal consumption is to inte-
grate them into a suitable support like 3D graphene [4]. A uniform dispersion of
metal nanoparticles on the porous structure of graphene increases their exposed
active sites and they definitely outperform due to the fascinating properties of 3D
graphene mentioned in Sect. 2. From the stability point of view, graphene encapsu-
lates dispersed nanoparticles and hinders their direct contact with electrolyte resulting
in a more durable catalyst. Finally, metal particles regulate the electron density of
graphene and make graphene itself catalytically more active. In the context, two
bifunctional electrocatalysts based on Co-CoO/3D hierarchical porous graphene (Co-
CoO/3DHPG) and Ni-NiO/3DHPG were investigated for HER and OER using cobalt
nitrate and nickel acetate as Co and Ni sources, respectively [28]. The onset poten-
tial of Co-CoO/3DHPG, Ni-NiO/3DHPG, and 3DHPG electrodes obtained from the
linear sweep voltammetry (LSV) plots were −0.26, −0.18, and -0.33 VRHE , respec-
tively, and the order of electrocatalytic activity was calculated to be Ni-NiO/3DHPG
> Co-CoO/3DHPG > 3DHPG. Expectedly, overpotentials of samples at 10 mA/cm2
for Co-CoO/3DHPG, Ni-NiO/3DHPG, and 3DHPG were −0.402, −0.31, and −
0.45 VRHE , respectively, and Tafel slopes were 65, 85, and 225 mV. Obviously, the
presence of metal nanoparticles enhanced the catalytic performance of 3D graphene
and Ni element was a better option for HER, while Co particles were more preferred
for OER. It is worth noting that high electron density at the metal/oxide and graphene
interface was advantageous for water splitting.
Hybrid structures of multiple metals alloys anchored on 3D graphene substrates
have also been investigated for further improvements compared with single metals. In
this respect, Zhong et al. [29] investigated the coupling of Pt3 Ni alloy nanoparticles
with 3D N-doped graphene (Pt3 Ni/3DNG) for HER in alkaline media (1 M KOH).
The transmission electron microscopy (TEM) image of Pt3 Ni/3DNG structure is
illustrated in Fig. 5a. LSV curves in Figure 5b indicated that the Pt3 Ni/3DNG elec-
trode produced the highest current density compared with Pt/3DG, Pt3 Ni/3DG, and
even benchmark 40 wt.% Pt/C electrocatalysts. Importantly, Pt3 Ni/3DNG sample
exhibited a very limited HER performance loss after 10,000 cycles in the alka-
line electrolyte. This significant difference between catalytic performance of Pt3 Ni/
3DNG and its non-alloy Pt/3DNG counterpart and other catalysts was attributed to
the generation of a tensile strain and a ligand effect on active sites, which promoted the
dissociation of water molecules and adsorption of Hads species, respectively. Note-
worthily, doping graphene before the introduction of single metal atoms or alloys
can significantly improve the coordination of these catalysts and it was completely
proved in the mentioned investigation.
Fig. 5 a TEM image of Pt3 Ni/3DNG structure, b LSV polarization curves of Pt3 Ni/3DNG, Pt3 Ni/
3DG, Pt/3DG, and commercial JM 40%Pt/C (with IR compensation). Adapted with permission
[29]. Copyright (2022) Elsevier
5.2 3D Graphene/Dichalcogenides
Among countless electrocatalysts suggested for noble metals substitution, transi-

tion metal dichalcogenides (TMDCs) are the most likely candidates [30]. Their high
catalytic activity and stability along with the economical synthesis process have
attracted much attention in energy conversion and storage applications. In this regard,
transition metal oxides, sulfides, and selenides have been studied more recently due
to their high active sites and defects. Their inferior performance to that of PGMs
arises from their low electrical conductivity, morphology transformation during catal-
ysis, and high aggregation tendency [31]. Implementing a suitable support like 3D
graphene for TMDCs increases not only their durability, but also electrocatalytic
activity. It has been reported that graphene significantly prevents TMDCs from disso-
lution and aggregation while its high conductivity compensates that of TMDCs to
some extent. The extremely high active sites and strong synergistic effect inherent in
3D graphene/TMDCs hybrid structures ensure a stable and efficient water electrolysis
[4].
Among different kinds of TMDCs, sulfides, especially MoS2 , have represented
adequate exciting breakthroughs. The binding energy between S atoms on the active
edge sites and H+ is so strong, providing a high HER rate. Furthermore, heteroatom
doping is usually employed to improve catalytic activity of graphene; as a result, it
can be a great way to develop a better support as well. Taking this approach, MoS2 /
3D N-doped reduced graphene oxide (N-rGO) hydrogels were prepared as HER
electrocatalysts by vertical integration of MoS2 sheets to graphene planes [32]. N
atoms in the graphene lattice served as nucleation sites for the vertical growth of
MoS2 sheets. A schematic representation of this process is shown in Fig. 6.
Figure 6 MoS2 /N-rGO had the lowest onset potential of 119 mV while N-rGO
electrode exhibited negligible HER activity. Overpotential of this hybrid structure
was 188 mV to approach 10 mA/cm2 , while it was a lot higher for pure MoS2
Fig. 6 Schematic representation of the synthesis process of MoS2 /N-rGO electrocatalyst. Adapted
with permission [32]. Copyright (2017) Elsevier
(270 mV), confirming the superior performance of MoS2 /N-rGO to the non-hybrid
electrodes. The incorporation of N atoms was also useful for the stability of elec-
trodes and increased it for 1000 cycles (comparing MoS2 /N-rGO and MoS2 /rGO).
In addition to MoS2 , other transition metal sulfides like WS2 [33, 34] and CoS2 [35]
have also been supported on 3D graphene substrate and represented promoted elec-
trocatalytic activities. Unlike sulfides, selenide and oxide compounds have rarely
been studied.
Noticeably, hybrid structures based on two chalcogenides composed of two
different metal elements can increase the number of active sites and accelerate the
electron transfer rate. Recently, Kuang et al. [36] investigated interactions between
MoS2 -NiS2 nanoparticles and 3D N-doped graphene foam (NGF) and the perfor-
mance of the electrode based on them toward water splitting reactions. The over-
potential (172 mV) of this structure to obtain 10 mA/cm2 was a lot lower than
those of MoS2 /NGF, NiS2 /NGF, and bare NGF electrodes which was attributed to
the synergistic effect between graphene and the bimetallic sulfides and the resultant
abundant active sites. Moreover, the EIS results demonstrated a reduced semicircle in
low frequency for MoS2 -NiS2 /NGF/nickel foam indicating the accelerated interfa-
cial reaction and charge-transfer kinetics. Luckily, MoS2 -NiS2 /NGF hybrid structure
exhibited acceptable OER activity in alkaline medium as well making it a bifunc-
tional electrocatalyst for complete water electrolysis reactions. A two-electrode cell
employing MoS2 -NiS2 /NGF as both electrodes needed 1.64 V to deliver 10 mA/cm2
current density which is quite comparable to that of commercial noble metals and it
was highly stable.
5.3 3D Graphene/Phosphides
Hydrogenase-like catalytic mechanism of transition metal phosphides is consider-

ably advantageous for water splitting reactions. However, challenges like their low
stability in electrolyte and poor electron transfer hamper further applications. In this
vein, 3D graphene as a support can enhance their electron transfer capability while
providing a large specific surface area to disperse them. Phosphides including Co2 P
[37], FeP [38], and Ni2 P/Ni5 P4 [39] have extensively been studied for this purpose.
5.4 Others
Although great progress has been made toward the electrocatalytic performance of
compounds discussed in the above sections, developing robust and efficient novel
catalysts for water splitting reactions is still an urgent demand. A plethora of different
compounds, especially nitrides [40], carbides [41], layered double hydroxides [42],
etc. have represented great potentials when integrated with 3D graphene. In addition
to metallic compounds, polymeric catalysts have also received enormous attentions
in recent years. However, low conductivity and poor stability of these materials
are thoroughly detrimental to electrocatalytic operations. Coupling active polymers
with highly conductive and stable 3D graphene has paved the way for their practical
use. Graphitic carbon nitride (g-C3 N4 ) is a relatively stable polymer and its low-
cost synthesis process along with tunable chemical structure make it a fascinating
option in this field. Electrochemical performance of Cu2 P/g-C3 N4 nanocomposite
merged with 3D graphene was assessed in 1 M H2 SO4 [43]. This electrode disclosed
a very low onset potential of 5 mV in comparison with bare graphene. Investigations
revealed that the nitrogen functionalities of g-C3 N4 served as active sites and the
protonated phosphate groups of Cu3 P contributed to electron transfer between g-
C3 N4 and the support. Pure Cu3 P or g-C3 N4 -based electrocatalysts delivered poor
cathodic current densities confirming the role of the graphene network for electron
and mass transfer.
6 Self-Supported 3D Graphene Electrodes
Although the implementation of 3D graphene instead of 2D sheets extremely

increased surface area and number of active sites, deposition of this structure on 2D
substrates like F-doped tin oxide and glassy carbon electrode greatly restricts this
advantage. From another respect, if a polymeric binder is used for better adhesion of
graphene powder to substrate, diffusion of gas products is blocked and conductivity
reduces significantly. Replacing 2D substrates with 3D frameworks such as carbon
cloth (CC) and metal foams leads to the formation of self-supported free-standing
electrodes with superior performance. Zhang et al. [44] integrated MoS2 nanosheets
with vertical graphene-coated CC (MDNS/VG/CC) and assessed its HER perfor-
mance in comparison with CC, VG/CC, and MDNS/CC. The fabrication process
of MDNS/VG/CC sample and its final microstructure is demonstrated in Fig. 7a–
d. The MDNS/VG/CC electrode possessed the lowest onset potential (50 mV) and
overpotential (78 mV). Furthermore, it produced 95 mA/cm2 at 300 mV, which was
4 and 2 times higher than that of VG/CC and MDNS/CC electrodes, respectively. In
addition, EIS results indicated a significant decrease in charge-transfer resistance of
MDNS/VG/CC to 5.0 Ω from 85, 50, and 130 Ω for VG/CC, MDNS/CC, and CC,
respectively. This improvement in HER activity for MDNS/VG/CC was attributed
to the high conductivity of graphene, hence, faster electron transfer kinetics between
MoS2 edges and the support. Ni foam has always been regarded as a great support for
other active materials and graphene sheets due to its high surface area and conduc-
tivity. Riyajuddin et al. [45] supported superhydrophilic Ni2 P − CuP2 on Ni foam-
graphene-carbon nanotubes heterostructure (NGCNC) through an electrochemical
process shown in Fig. 7e. Impressively, NGCNC showed outstanding HER perfor-
mance with an ultralow overpotential of 12 mV at 10 mA/cm2 comparable with Ni
− Pt/C (10 mV). Chronopotentiometry measurement at 100, 200, and 500 mA/cm2
for 10 days disclosed a negligible (3%) fluctuation in potential, which indicates the
superstability of NGCNC in acidic media. TOF values of NGCNC reached 1, 2,
and 3 s−1 at low overpotentials of 100, 141, and 174 mV, respectively, illustrating
its exceptional electrochemical HER activity. The superior performance of NGCNC
electrode was attributed to the in-situ growth of graphene and bimetallic phosphides
on Ni foam which prevented the use of any binder and formation of multiphases
minimizing the series resistance.
The development of an active, robust, and earth-abundant electrocatalyst for

hydrogen fuel production is still known to be the most critical challenge for the
industrialization of water electrolysis technique. Benefiting from its unique physical
and chemical features, 3D graphene has been regarded as a promising candidate to
address this issue. In this chapter, the inherent catalytic activity of graphene was
estimated with emphasis on some practical modifications like heteroatom doping
of the structure. As pristine graphene suffers poor catalytic activity and chemical
doping results are not yet desirable, performances of several heterostructures were
also reviewed in brief in which 3D graphene is mainly utilized as a support. However,
there are still numerous issues to be dealt with in the way of practical applications
and mass production and some of them are as follows.
Current methods employed for 3D graphene synthesis, either template-based or
not, are not at all capable of large-scale applications. The exploitation of economical
and less complicated strategies with more controllable synthesis conditions is consid-
ered essential to achieve products with desired properties, porosity, and morphology.
Fig. 7 a Schematic representation of the fabrication process of MDNS/VG/CC electrode, Low and
high magnification SEM images of b VG/CC, c, d MDNS/VG/CC. Adapted with permission [44].
Copyright (2015) Elsevier. (e) Schematic illustration of the synthesis steps of NGCNC electrode.
Adapted with permission [45]. Copyright (2021) American Chemical Society
Furthermore, doping is an efficient route to increase catalytic activity and stability of

graphene even for hybrid structures, but it is too difficult to control the dopant content
and existing methods are mostly expensive. Therefore, it is of great importance to
attempt various methods to realize a controllable doping process.
Stability of the hybrid structures in harsh media is another long-standing obstacle
for the scientific community. Although graphene plays a crucial role in increasing
the durability of the whole structure, they still cannot compete with commercial elec-
trocatalysts. Designing more stable composites applicable in less harsh electrolytes
is considered necessary. On top of these, new research direction and enhancement
strategies are needed rather than doping and compositing to regulate the electronic
structure of graphene while maintaining its own properties to improve catalytic
performance.
One of the most important reasons behind the poor performance of 3D graphene-
based electrocatalysts is definitely the lack of information about the catalysis mecha-
nism and active sites on the atomic scale and the blind design of catalysts. Moreover,
DFT calculations are so simple and limited to the three steps mentioned in Sect. 2,
which cannot provide sufficient information of more complex reaction intermediates
formed on reaction sites. Development of more precise theoretical models toward the
water spitting system and in-situ detecting technologies for characterization of the
real reaction environment can provide a deep understanding of the whole process.
Consequently, a more rational design of graphene-based electrocatalysts with faster
reaction kinetics and higher stabilities becomes possible.
Acidic media accelerate HER kinetics while an alkaline environment is more
favorable for OER; thus, bifunctional electrocatalysts which can be utilized for both
reactions are more preferred options for future applications. In this regard, searching
for electrodes that can catalyze the water splitting reactions in neutral pH values
is a more preferred solution due to the stability issues. However, graphene-based
bifunctional electrocatalysts are not yet efficient enough for widespread hydrogen
production and require much more optimizations.
In total, bearing in mind all the fascinating opportunities that 3D graphene provides
along with the challenges discussed above, one can make sure that this structure is
an ideal choice for renewable electrochemical energy conversion and is worth much
more investigations to march forward. In this connection, massive theoretical studies
and experimental works should be devoted to the existing and future problems. In
this unstoppable trend for the construction of the most efficient electrocatalyst for
commercial water splitting, 3D graphene is undeniably a realistic candidate.
References
1. Chu, S., Majumdar, A.: Opportunities and challenges for a sustainable energy future. Nature
488, 294–303 (2012)
2. Ibrahim, H., Ilinca, A., Perron, J.: Energy storage systems—characteristics and comparisons.
Renew. Sustain. Energy Rev. 12, 1221–1250 (2008)
3. Geim, A.K., Novoselov, K.S.: The rise of graphene. Nat. Mater. 6, 183–191 (2007)
4. Kuang, P., Sayed, M., Fan, J., Cheng, B., Yu, J.: 3D graphene-based H2-production
photocatalyst and electrocatalyst. Adv. Energy Mater. 10, 1903802 (2020)
catalysis. Small 17, 2005255 (2021)
6. Zhang, X., Gao, J., Xiao, Y., Wang, J., Sun, G., Zhao, Y., Qu, L.: Regulation of 2D graphene
materials for electrocatalysis. Chem. Asian J. 15, 2271–2281 (2020)
7. Bard, A.J., Faulkner, L.R., White, H.S.: Electrochemical Methods: Fundamentals and Appli-
cations. Wiley (2022)
8. Schalenbach, M., Zeradjanin, A.R., Kasian, O., Cherevko, S., Mayrhofer, K.J.J.: A perspective
on low-temperature water electrolysis–challenges in alkaline and acidic technology. Int. J.
Electrochem. Sci. 13, 1173–1226 (2018)
9. de Chialvo, M.R.G., Chialvo, A.C.: The resolution of the volmer-heyrovsky-tafel mechanism
with a normal distribution of the standard gibbs energy of adsorption. J. Braz. Chem. Soc. 5,
137–143 (1994)
10. Godula-Jopek, A.: Hydrogen Production: by Electrolysis. Wiley (2015)
11. Fierro, S., Nagel, T., Baltruschat, H., Comninellis, C.: Investigation of the oxygen evolu-
tion reaction on Ti/IrO2 electrodes using isotope labelling and on-line mass spectrometry.
Electrochem. Commun. 9, 1969–1974 (2007)
12. Audichon, T., Napporn, T.W., Canaff, C., Morais, C., Comminges, C., Kokoh, K.B.: IrO2
coated on RuO2 as efficient and stable electroactive nanocatalysts for electrochemical water
splitting. J. Phys. Chem. C. 120, 2562–2573 (2016)
13. Nørskov, J.K., Bligaard, T., Logadottir, A., Kitchin, J.R., Chen, J.G., Pandelov, S., Stimming,
U.: Trends in the exchange current for hydrogen evolution. J. Electrochem. Soc. 152, J23 (2005)
14. Trasatti, S.: Work function, electronegativity, and electrochemical behaviour of metals:
III. Electrolytic hydrogen evolution in acid solutions. J. Electroanal. Chem. Interfacial
Electrochem. 39, 163–184 (1972)
15. Kötz, R., Lewerenz, H.J., Stucki, S.: XPS studies of oxygen evolution on Ru and RuO2 anodes.
J. Electrochem. Soc. 130, 825 (1983)
16. You, B., Sun, Y.: Innovative strategies for electrocatalytic water splitting. Acc. Chem. Res. 51,
1571–1580 (2018)
17. Suen, N.-T., Hung, S.-F., Quan, Q., Zhang, N., Xu, Y.-J., Chen, H.M.: Electrocatalysis for the
oxygen evolution reaction: recent development and future perspectives. Chem. Soc. Rev. 46,
337–365 (2017)
18. Skúlason, E., Tripkovic, V., Björketun, M.E., Gudmundsdóttir, S., Karlberg, G., Rossmeisl,
J., Bligaard, T., Jónsson, H., Nørskov, J.K.: Modeling the electrochemical hydrogen oxidation
and evolution reactions on the basis of density functional theory calculations. J. Phys. Chem.
C. 114, 18182–18197 (2010)
19. Serp, P., Figueiredo, J.L.: Carbon Materials for Catalysis. Wiley (2009)
20. Qiu, B., Xing, M., Zhang, J.: Recent advances in three-dimensional graphene based materials
for catalysis applications. Chem. Soc. Rev. 47, 2165–2216 (2018)
21. Duan, J., Chen, S., Jaroniec, M., Qiao, S.Z.: Heteroatom-doped graphene-based materials for
energy-relevant electrocatalytic processes. Acs Catal. 5, 5207–5234 (2015)
22. Li, J., Zhao, Z., Ma, Y., Qu, Y.: Graphene and their hybrid electrocatalysts for water splitting.
ChemCatChem 9, 1554–1568 (2017)
23. Nemiwal, M., Zhang, T.C., Kumar, D.: Graphene-based electrocatalysts: Hydrogen evolution
reactions and overall water splitting. Int. J. Hydrogen Energy. 46, 21401–21418 (2021)
24. Kumar, R., Sahoo, S., Joanni, E., Singh, R.K., Maegawa, K., Tan, W.K., Kawamura, G., Kar,
K.K., Matsuda, A.: Heteroatom doped graphene engineering for energy storage and conversion.
Mater. Today. 39, 47–65 (2020)
25. Shen, B., Huang, H., Liu, H., Jiang, Q., He, H.: Bottom-up construction of three-dimensional
porous MXene/nitrogen-doped graphene architectures as efficient hydrogen evolution electro-
catalysts. Int. J. Hydrogen Energy. 46, 29984–29993 (2021)
26. Ito, Y., Cong, W., Fujita, T., Tang, Z., Chen, M.: High catalytic activity of nitrogen and sulfur
co-doped nanoporous graphene in the hydrogen evolution reaction. Angew. Chemie. 127, 2159–
2164 (2015)
27. Jiao, Y., Zheng, Y., Davey, K., Qiao, S.-Z.: Activity origin and catalyst design principles for
electrocatalytic hydrogen evolution on heteroatom-doped graphene. Nat. Energy. 1, 1–9 (2016)
28. Ullah, N., Zhao, W., Lu, X., Oluigbo, C.J., Shah, S.A., Zhang, M., Xie, J., Xu, Y.: In situ growth
of M-MO (M=Ni, Co) in 3D graphene as a competent bifunctional electrocatalyst for OER and
HER. Electrochim. Acta. 298, 163–171 (2019)
29. Zhong, H., Luo, X., Chen, H., Huang, S., Chen, Y.: Pt3Ni alloy catalyst coupled with
three-dimensional nitrogen-doped graphene for enhancing the alkaline hydrogen evolution.
Electrochim. Acta. 429, 141030 (2022)
30. Peng, X., Pi, C., Zhang, X., Li, S., Huo, K., Chu, P.K.: Recent progress of transition metal
nitrides for efficient electrocatalytic water splitting, Sustain. Energy Fuels. 3, 366–381 (2019)
31. Xia, B., Yan, Y., Wang, X., Lou, X.W.D.: Recent progress on graphene-based hybrid
electrocatalysts. Mater. Horizons. 1, 379–399 (2014)
32. Zhao, L., Hong, C., Lin, L., Wu, H., Su, Y., Zhang, X., Liu, A.: Controllable nanoscale engi-
neering of vertically aligned MoS2 ultrathin nanosheets by nitrogen doping of 3D graphene
hydrogel for improved electrocatalytic hydrogen evolution. Carbon N. Y. 116, 223–231 (2017)
33. Qi, F., Li, P., Chen, Y., Zheng, B., Liu, J., Zhou, J., He, J., Hao, X., Zhang, W.: Three-dimensional
structure of WS2/graphene/Ni as a binder-free electrocatalytic electrode for highly effective
and stable hydrogen evolution reaction. Int. J. Hydrogen Energy. 42, 7811–7819 (2017)
34. Duan, J., Chen, S., Chambers, B.A., Andersson, G.G., Qiao, S.Z.: 3D WS2 nanolayers@
heteroatom-doped graphene films as hydrogen evolution catalyst electrodes. Adv. Mater. 27,
4234–4241 (2015)
35. Pawar, R.C., Kang, S., Khan, H., Han, H., Lee, C.S.: Study of multi-faceted CoS2 introduced
graphene aerogel hybrids via chemical approach for an effective electrocatalytic water splitting.
Curr. Appl. Phys. 32, 78–85 (2021)
36. Kuang, P., He, M., Zou, H., Yu, J., Fan, K.: 0D/3D MoS2-NiS2/N-doped graphene foam
composite for efficient overall water splitting. Appl. Catal. B Environ. 254, 15–25 (2019)
37. Li, G., Yu, J., Jia, J., Yang, L., Zhao, L., Zhou, W., Liu, H.: Cobalt-Cobalt phosphide nanoparti-
cles@ nitrogen-phosphorus doped carbon/graphene derived from cobalt ions adsorbed saccha-
romycete yeasts as an efficient, stable, and large-current-density electrode for hydrogen
evolution reactions. Adv. Funct. Mater. 28, 1801332 (2018)
38. Venugopal, N.K.A., Yin, S., Li, Y., Xue, H., Xu, Y., Li, X., Wang, H., Wang, L.: Prussian blue-
derived iron phosphide nanoparticles in a porous graphene aerogel as efficient electrocatalyst
for hydrogen evolution reaction. Chem. Asian J. 13, 679–685 (2018)
39. Ding, G., Zhang, Y., Dong, J., Xu, L.: Fabrication of Ni2P/Ni5P4 nanoparticles embedded in
three-dimensional N-doped graphene for acidic hydrogen evolution reaction. Mater. Lett. 299,
130071 (2021)
40. Song, G., Luo, S., Zhou, Q., Zou, J., Lin, Y., Wang, L., Li, G., Meng, A., Li, Z.: Doping and
heterojunction strategies for constructing V-doped Ni 3 FeN/Ni anchored on N-doped graphene
tubes as an efficient overall water splitting electrocatalyst. J. Mater. Chem. A. 10, 18877–18888
(2022)
41. Wang, J., Xia, H., Peng, Z., Lv, C., Jin, L., Zhao, Y., Huang, Z., Zhang, C.: Graphene porous
foam loaded with molybdenum carbide nanoparticulate electrocatalyst for effective hydrogen
generation. Chemsuschem 9, 855–862 (2016)
42. Shen, B., Huang, H., Jiang, Y., Xue, Y., He, H.: 3D interweaving MXene–graphene network–
confined Ni–Fe layered double hydroxide nanosheets for enhanced hydrogen evolution.
Electrochim. Acta. 407, 139913 (2022)
43. Riyajuddin, S., Tarik Aziz, S.K., Kumar, S., Nessim, G.D., Ghosh, K.: 3D-graphene decorated
with g-C3N4/Cu3P composite: a noble metal-free bifunctional electrocatalyst for overall water
splitting. ChemCatChem. 12, 1394–1402 (2020)
44. Zhang, Z., Li, W., Yuen, M.F., Ng, T.-W., Tang, Y., Lee, C.-S., Chen, X., Zhang, W.: Hierarchical
composite structure of few-layers MoS2 nanosheets supported by vertical graphene on carbon
cloth for high-performance hydrogen evolution reaction. Nano Energy 18, 196–204 (2015)
45. Riyajuddin, S., Azmi, K., Pahuja, M., Kumar, S., Maruyama, T., Bera, C., Ghosh, K.: Super-
hydrophilic hierarchical Ni-foam-graphene-carbon nanotubes-Ni2P–CuP2 nano-architecture
as efficient electrocatalyst for overall water splitting. ACS Nano 15, 5586–5599 (2021)
3D Graphene as a Photocatalyst
for Water Splitting
Rozan Mohamad Yunus, Nurul Nabila Rosman,

and Nur Rabiatul Adawiyah Mohd Shah
Abstract Hydrogen production by photoelectrochemical (PEC) water splitting has

attracted considerable interest because it is a promising clean source of energy for
improving the earth’s climate in the future. Owing to the excellent properties of
graphene, the use of graphene in photocatalysis for green hydrogen production has
attracted remarkable interest. 3D graphene, which can act as a co-catalyst and transfer
agent to enhance photocatalytic hydrogen production, is a potential component for
PEC electrodes due to its substantial surface area, fast electron transfer, high electron
conductivity, low mass density, mechanical stability, interconnected and hierarchical
structure. The use of 3D-graphene-based photocatalysts in PEC water-splitting appli-
cations is highlighted and discussed in this chapter. Various strategies and approaches
for the synthesis of 3D graphene are also presented. Efforts have been made in the
incorporation of 3D graphene with metal oxides, transition-metal dichalcogenides
(TMDCs), or other semiconductor materials wherein the synergistic effect between
these materials can suppress the recombination of photogenerated electron–hole pairs
to enhance PEC water-splitting performance considerably. This chapter presents an
inclusive review of the photocatalytic characteristics and current development of 3D
graphene-based photocatalysts for water-splitting applications.
Keywords 3D graphene · Photocatalysts · Photoelectrochemical water splitting ·

Hydrogen production
1 Introduction
Graphene, the thinnest material, is an independent carbon material. It has a highly

crystalline structure that is composed of a monolayer of carbon atoms packed tightly
into a two-dimensional (2D) honeycomb lattice via sp2 -hybridized carbon–carbon
bonds in a hexagonal arrangement, thus forming a strong and unique long-range
π-conjugation structure. Graphene has extraordinary physicochemical properties
R. M. Yunus (B) · N. N. Rosman · N. R. A. M. Shah

Fuel Cell Institute, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia
e-mail: rozanyunus@ukm.edu.my
https://doi.org/10.1007/978-3-031-36249-1_20
360 R. M. Yunus et al.
that include high theoretical specific surface area (2630 m2 /g), ultrahigh intrinsic
carrier mobility (≈200 000 cm2 /V/s), high mechanical strength (breaking strength
of 42 N/m), outstanding high Young’s modulus (≈1 TPa), good thermal conductivity
(3000–5000 W/m/K), excellent optical transparency (≈97.7%), and strong chemical
stability, all of which assist in attenuating the effect of wide band gaps and the
recombination of electron–hole pairs in photocatalysts [1–4].
Graphene has highly attractive physical properties. Many studies on 2D materials
have been conducted because of graphene’s excellent properties. In 2004, Novoselov
and Geim discovered the first 2D graphene sheets, which are the building blocks of
graphite [5]. In the last decade, numerous 2D structures of π-conjugated carbon-
based materials, such as graphene, graphene oxide (GO), reduced GO (rGO), and
graphene/carbon quantum dots, have been introduced as efficient, attractive, and valu-
able substrates/templates/supports for catalysts and semiconducting nanomaterials.
Additionally, many studies have reported that graphene can enhance the photocat-
alytic efficiency of photoelectrochemical (PEC) water splitting due to its unique 2D
conjugated structure and electronic properties. However, producing high-quality 2D
graphene, especially single-layer and free-defect graphene, on a large scale is diffi-
cult because it tends to aggregate and restack, thus decreasing its specific surface
area, causing the loss of its distinct properties, and consequently resulting in poor
photocatalytic performance [1, 2, 4, 6].
One effective solution to overcome these problems is the assembly of 2D layers
of graphene into three-dimensional (3D) structures known as 3D graphene. Inter-
estingly, interconnected 3D graphene structures retain the outstanding properties of
2D graphene and are free from aggregation or restacking. Therefore, their photocat-
alytic properties can be enhanced by increasing light adsorption, providing additional
accessible active sites, and improving charge transport [1, 2, 4]. 3D graphene is also
known as foams, sponges, aerogels, or hydrogels. Surface area, electrical conduc-
tivity, thermal properties, and mechanical stability are determined by synthesis
methods, which include the hydrothermal, chemical vapor deposition (CVD), and
self-assembly methods (Fig. 1). Understanding the important factors that influence
the properties and nucleation and growth mechanism of 3D structures is required
particularly when tuning the functionalization of 3D graphene structures [2].
3D graphene is suitable for application in PEC water hydrogen production due
to its main properties, such as its porous structure, large surface area, outstanding
mechanical properties, and rapid electron transport. The incorporation of 3D
graphene with metal oxides, transition-metal dichalcogenides (TMDCs), and other
semiconductor materials has been explored to improve photocatalytic properties for
water splitting. Photocatalysts/photoelectrodes that can employ a wide solar spec-
trum, suppress the recombination of photogenerated electron–hole pairs, and improve
system stability are expected to be obtained through these combinations. Thus, recent
advancements in this effort are addressed in the last part of this book chapter.
3D Graphene as a Photocatalyst for Water Splitting 361
Fig. 1 Structures, properties, and synthesis methods related to 3D graphene
2 Properties of 3D Graphene
3D graphene structures can be classified into two types: (1) microscopic structures
(less than 100 μm in all dimensions), which are typically in the form of macroscopi-
cally sized powders with 3D structures on the micrometer or nanometer scale and (2)
macroscopic or macrostructures (more than 100 μm in all dimensions), such as macro
3D graphene monoliths, film, fibers, and millispheres [1, 2]. Graphene walls should
be composed of not more than 10 layers of graphene and must preserve the basic prop-
erties of graphene. 3D graphene structures can be divided into two types depending
on the form of connections: (1) joint 3D graphene, wherein several single-layer
graphene sheets/cells are interknitted primarily through van der Waal’s forces, and
(2) integrated 3D graphene, in which chemical bonds continuously connect carbon
atoms. Between these two structures, integrated 3D graphene structures exhibit excel-
lent conductivity and mechanical robustness [2]. 3D graphene structures provide a
solution to the challenge posed by graphene sheet aggregation and restacking. Such
a solution is important for ion transfer in water splitting. 3D graphene not only has
the intrinsic properties of graphene sheets, but it also has a variety of advantages,
including very small mass density, high specific surface area and porosity, an inter-
connected and hierarchical structure, and excellent mechanical stability that allows
for increased access to active sites by providing additional pathways for rapid mass
and electron transport kinetics in photocatalysis. Given its ability to create new func-
tionalities through cross-interactions, 3D graphene has been referred to as a bridge
connecting the nano- and macroworlds. Considering its above distinguishing proper-
ties, 3D graphene has great potential for photocatalytic water-splitting applications
[1, 4].
2.1 Surface Area
The number of nanosized (typically 1–100 nm) pores and the thickness of
the graphene wall [2, 7] are important factors determining the surface area
of 3D graphene. Several parameters, such as reaction time, temperature, and inlet gas
flow rate, can be controlled to adjust the wall thickness and specific surface area of
graphene [4, 7–13]. The template, substrate, scaffold, or catalyst used also influences
the properties of 3D graphene [4, 14]. Generally, 3D graphene has a density of less
than 0.1 g/cm, a surface area of 500–1000 m2 /g, and pore sizes ranging from several
micrometers to several nanometers [2]. Min et al. prepared 3D graphene by using
a conventional nickel foam template with a specific surface area of approximately
145 m2 /g and a density of 0.073 g/cm3 [7]. Even after annealing at 1500 °C, the
specific surface area of 3D graphene increased from 336.5 m2 /g to 440.8 m2 /g. A
high proportion of mesopores were found in a narrow range of 3 nm to 5 nm with
a peak pore diameter of approximately 3.8 nm (Fig. 2a, b) [11]. Meanwhile, the
hierarchical interconnected structure of 3D graphene prepared by a 3D printed silica
sacrificial template has obtained a higher BET surface area (994.2 m2 /g) as shown in
Fig. 2c) [9]. Following template etching, 3D graphene maintained a porous structure
with a large area. Freeze–drying is crucial for maintaining the structure of 3D porous
graphene without considerable aggregation [7, 12, 13]. Shen et al. discovered that
from a theoretical perspective, the graphene sheet size determines the microstructure
and density of 3D graphene. Reducing the graphene sheet size to 2 nm facilitated
the stacking and action as building blocks of 3D graphene with a density and pore
value of 1.49 g/cm3 and 5–10 nm, respectively. The graphene sheet became stag-
gered and bent as its size increased, resulting in its low density [15]. Consequently,
protecting the structure of 3D graphene photocatalysts from restacking, aggregation,
staggering, or bending is essential to acquire a high surface area that increases the
exposure of active sites for water-splitting reactions. However, obtaining graphene
sheets with a uniform thickness remains challenging.
2.2 Electrical Conductivity
3D graphene has excellent electrical conductivity due to its porous interconnected

structure and high-quality graphene walls. The electrical conductivity of 3D graphene
can be measured by using a two-or four-probe method and generally ranges from
2 S/cm to 1600 S/cm [2, 9, 11, 16–18]. 3D graphene has an electrical conduc-
tivity of approximately 2.39 S/cm due to its highly continuous structure that
comprises few- and multilayered graphene [9]. Figure 3a shows that even when
synthesized from powder templates, 3D graphene has a good electrical conductivity
of 13.84 S/cm [18]. Furthermore, a conductivity of 17.5 S/cm was obtained with more
than five layers of graphene with wrinkled and folded morphologies [7]. The bulk
electrical conductivities of 3D graphene increased from 14.4 S/m to 53.7 S/m with
Fig. 2 FESEM image of 3D graphene (aerogel) a before and b after annealing. Adapted with
permission [11], Copyright (2017), Scientific Reports. c Comparison of the BET surface areas
of the silica template and 3D graphene (foam). Adapted with permission [9], Copyright (2020),
the increase in bulk density and increased to 53.5–157.3 S/m after annealing (Fig. 3b)
[11]. Xia et al. applied 3D microporous copper as a catalyst to grow graphene. The
resulting 3D graphene had a high density and strong structure without any support,
allowing for a high conductivity of approximately 1600 S/cm with a resistance
of ~2.6 Ω (Fig. 3c) [16]. However, cross-linking agents with the function of strength-
ening the porous structure must be carefully selected to maintain the electrical
conductivity of 3D graphene [1].
Fig. 3 a Current–voltage curve of 3D graphene (foam). Adapted with permission from [18], copy-
right (2016), American Chemical Society. b Electrical conductivities of 3D graphene (aerogel)
before and after annealing. Adapted with permission [11], Copyright (2017), Scientific Reports.
c Current–voltage measurement of 3D graphene. Adapted with permission [16], Copyright (2017),
Journal of Physical Chemistry C
Fig. 4 a Thermal conductivities of 3D graphene (aerogel) before and after annealing. Adapted
with permission [11], Copyright (2017), Scientific Reports. b Density and thermal conductivity
measurements of 3D graphene (foam) (as 3D-C). Adapted with permission [20], Copyright (2017),
2.3 Thermal Properties
Effective thermal conductivity is (κ) is calculated as κ = K sample × L/A, where

L is the sample length, and A is the sample cross-sectional area. It is mainly
influenced by two morphological factors: (1) primary structure, namely, building
blocks, and (2) secondary structure, namely, assembled building blocks [19]. As
shown in Fig. 4a, Cheng et al. discovered that 3D graphene had a thermal conduc-
tivity of 0.0281–0.0390 W/m/K after losing approximately 15% of its weight, and
its thermal conductivity slightly increased to 0.0363–0.0667 W/m/K after being
annealed at high temperatures (1500 °C) [11]. Moreover, 3D graphene with a density
of 5 mg/cm3 had a thermal conductivity of 1.2 W/m/K. As its density increased,
its thermal conductivity increased to 86 ± 10 W/m/K (Fig. 4b) [20]. This finding
demonstrated that in 3D graphene, thermal conductivity is directly proportional to
mass density and could be improved without increasing graphene wall thickness
[21]. Another approach for increasing mass density is to compress 3D graphene
materials, which also can enhance the intrinsic thermal properties of 3D graphene
as a photocatalyst [19]. In addition, the etchant solution used in substrate/template/
support removal and the reaction temperature could affect the thermal conductivity
of 3D graphene by reducing defects and defect-induced phonon scattering [2]. Never-
theless, 3D graphene exhibits hydrophobic properties, particularly after being etched
away from the substrate/template/support.
2.4 Mechanical Stability
3D graphene photocatalysts can be obtained after the optimization of processing

parameters that affect microscopic geometry and mass density. Interestingly, 3D
graphene retains its freestanding structure after being etched from its template or
supported substrate (regardless of thickness) due to the superior mechanical strength

of graphene [2, 4]. A theoretical study by Li et al. demonstrated that triangle-like 3D
graphene structures (only sp2 –sp2 carbon bond, armchair, and zigzag) are strongly
dependent on structural size. The in-plane Young’s moduli (x and y directions) of the
sp2 –sp2 carbon bond, armchair, and zigzag can reach 505.20–578.51, 504–583.46,
and 640.22–744.32 GPa, respectively [22]. 3D graphene is likely stable because
multilayered graphene is highly crystallized and carbon shells are connected by a
2D graphene layer structure. 3D graphene with a density of 18 mg/cm3 had Young’s
modulus of approximately 239.7 kPa, and its stress remained nearly constant at
55% compression strain for different loops, reflecting its flexibility and elasticity
[9]. Moreover, Young’s modulus and yield strength of 3D graphene rose to 1.02–
17.29 and 0.08–1.05 MPa, respectively, after annealing [11]. Sha et al. reported
that 3D graphene had remarkably similar morphologies before and after loading
with weights, emphasizing its structural resiliency (Fig. 5) [18]. Hence, the porous
structure of 3D graphene as a photocatalyst is crucial in providing intimate structural
interconnectivities, a pathway for electron/phonon transport, high surface area, and
strong mechanical properties.
Fig. 5 Digital photos of 3D graphene (foam) before and after weight loading. Adapted with
permission [18], Copyright (2016), American Chemical Society
2.5 Other Properties
Given its zero-band gap and strong Dirac fermion interactions with electromagnetic
radiation, graphene has superior optical properties and thus can absorb photons from
the visible to infrared spectrum. Xu et al. reported that 3D graphene has no response
in the visible spectrum [23]. Its optical properties vary depending on the growth
reaction temperature [24]. Furthermore, its in-plane pores provide numerous edge
defects, resulting in additional active sites and efficient transport pathways. The
substrate/template/support used, the hydrocarbon precursor, and the annealing and
growth duration all have an effect on the in-plane properties of 3D graphene.
3 Methods for 3D Graphene Synthesis
Functionalized 3D graphene-based materials can be successfully self-assembled by

using graphene and its functionalized derivatives and typical 2D structures as the
building blocks. The usefulness of graphene in technologies is anticipated to increase
as 3D graphene frameworks are developed [25]. 3D graphene foams (GFs) provide a
number of benefits, including an expansive surface area, improved catalytic perfor-
mance, reduced thermal conductivity, and moderate electronic conductivity [26].
A variety of terms, including “sponge”, “foam”, “aerogel”, “hydrogel”, “network”,
“bead”, and “monolith”, have been used to define 3D graphene-based structures. The
manufacture of 3D graphene utilizes a variety of templates, including polystyrene
spheres, nickel foam, and copper foam [27]. Direct synthesis from carbon sources
and solution-based synthesis methods, such as CVD and hydrothermal synthesis,
can be used to create 3D porous graphene [27]. The direct fabrication method can
provide the appropriate quality for the development of pore density, size, and distribu-
tion in 3D structures. Nevertheless, it has high production costs. The solution-based
manufacturing process offers some advantages, including elemental functionaliza-
tion, possible scalability, improved production efficiency, and cheap manufacturing
costs, despite resulting in the dispersion of pore structure [28]. The template-based
synthesis of the 3D porous network typically involves three processes: (1) precursors
of the reaction are incorporated into the template, (2) the solid form is continuously
grown in and on the surface of the template, and (3) a 3D porous structure is created
by removing the template in a variety of ways [27]. Both synthesis methods are
discussed in subsequent sections.
3.1 Hydrothermal Method
An aqueous solution that is being utilized as a reaction system is heated and pres-
surized in a particular closed reaction vessel to create a high-temperature and high-
pressure reaction environment. In this process, a chemical that is weakly soluble
or insoluble under normal conditions is dissolved and then recrystallized [29]. For
example, Men et al. used the hydrothermal method to fabricate free-standing rGO
foam for photocurrent generation and photocatalytic activity. Morphologically, the
produced rGO/nickel foam had a porous structure. After the template was removed,
the rGO foam demonstrated an interpenetrating 3D porous structure. The pore
size of the rGO foam was in the order of approximately hundreds of microme-
ters, which was comparable with that of nickel foam (Fig. 6a, b) [13]. Zhou et al.
synthesized a covalent 3D graphene network via the hydrothermal method by using
an aromatic diamine, such as 2,2, -dimethyl-4,4, -biphenyldiamine (DMPDA), 4,4, -
diaminodiphenylmethane (MDA), and benzidine, as a cross-linker to functionalize
GO at ambient temperature. The treatment of stiff benzidine molecules with 2D
GO flakes prevented face-to-face stacking because the surface of GO-benzidine was
rougher and more porous than that of GO. GO-benzidine had a smaller surface area
than GO-DMPDA and GO-MDA but 5.4 times higher photocatalytic activity than
noncovalent 3D graphene. This finding showed that the particular surface area of
3D graphene did not have a significant effect on the production of hydrogen in the
form of H2 during photocatalysis [4, 30]. Meanwhile, GO hydrogels were fabri-
cated by using a hydrothermal technique with exfoliated GO, which can be obtained
through a modified Hummer method [31]. Graphene hydrogels can be turned into
graphene aerogels by eliminating water through freeze–drying [32, 33]. The 3D
porous network structure of graphene aerogel was clearly defined and connected by
many micrometers of interconnected pores. A 3D graphene-based geometric frame-
work with embedded nanoparticles had been shown to improve interface contact,
reduce nanoparticle aggregation and dissolution, and increase stability and PEC
performance [33].
Fig. 6 SEM images a rGO/nickel foam and b free-standing rGO foam. Adapted with permission
[13], Copyright (2016), Elsevier
3.2 CVD
CVD is the process of depositing nanomaterial in the form of a thin film from vapor
species onto substrates through chemical reactions [34]. CVD has been widely used
and is the current method for the molecular synthesis of graphene because it can
produce graphene with high surface areas. In the CVD method, a thin metal substrate
is placed into a furnace and heated to high temperatures (900 °C–1000 °C) under
a low vacuum. Hydrogen gas and carbon from methane gas must flow through the
chamber to ignite a reaction between methane and the surface of the metal film, such
as copper, nickel, or cobalt film [35]. Chen et al. synthesized 3D GF on a nickel
foam substrate by using the CVD method at 1000 ◦ C under ambient pressure. Then,
the nickel foam was etched away by using 3 M hydrochloric acid to produce free-
standing GF. Ripples and wrinkles develop on the graphene films as a result of the
differing thermal expansion coefficients of nickel and graphene. The wrinkling and
ripples in composite materials produced when a GF is combined with a polymer
are expected to promote mechanical interlocking between polymer chains, which
improves adhesion. This effect is similar to the effect of the wrinkles in chemically
produced graphene sheets. However, the building blocks of monolayer GF tend to
collapse and break when copper foams are used as a template due to their inability to
withstand the liquid capillary force exerted by acetone evaporation [36]. Meanwhile,
Cai et al. synthesized a 3D GF to enhance the photocatalytic activity of ZnO. The
morphological structure of 3D GF showed that additional ZnO nanorod nucleation
sites were provided by the oxygen-containing functional groups of 3D graphene; thus
ZnO nanorods were dispersed randomly and were well-separated from one another
on 3D GF [37]. Flower-like 3D porous graphene (FG) can also be synthesized by
using transformer-coupled plasma-enhanced CVD in a chamber wherein methane
and argon had been introduced as precursors. The graphene framework features a
densely packed and consistently dispersed flower-like structure as shown in Fig. 7a,
b. The fold width was typically 200 nm. FG displays porous structures that might
make it an ideal photocatalyst support material. The photocurrent performance of
ZnS was approximately 4.4 times higher than that of bare ZnS after the addition
of FG. Thus, FG can perform as an electron acceptor that can enhance separation
and reduce the recombination of the photogenerated charge carriers of the ZnS/FG
composite, permitting additional charge carriers to generate reactive species [38].
3.3 Self-Assembly Method
Self-assembly is one of the natural methods for building complex living structures in
the nano-, micro-, and macro dimensions. Self-assembly has been widely acknowl-
edged as a “bottom-up” nanotechnology approach. This method generates exten-
sive molecular structures from molecules sustainably. The top-down chemical and
mechanical exfoliation processes of natural graphite are used to create nano- and
Fig. 7 FESEM images a FG b enlarged image of FG. Adapted with permission [38], Copyright
(2017), Elsevier
microscale graphene sheets that can be employed as building blocks in self-assembly

[39]. 3D structures of graphene can be self-assembled through π −π interactions with
ecofriendly phenolic acids. The hydrogels derived from assembling graphene into 3D
frameworks were approximately 20 mm in height and 15 mm in diameter. After water
removal through freeze–drying, the ultralight aerogels revealed consistently intercon-
nected micrometer pores. This 3D graphene material has a variety of uses due to its
unique mix of superhydrophobicity, high porosity, outstanding electrical conduc-
tivity, and exceptional mechanical properties [40]. L-cysteine also can be utilized as
a template and reducing agent in the self-assembly of 3D graphene materials [41].
Graphene aerogel has a hierarchical pore structure with pore sizes ranging from a few
hundred nanometers to micrometers. Thin graphene nanosheets serve as the building
blocks for pore walls, and their overlapping helps create 3D porous networks. Interest-
ingly, 3D graphene generated through self-assembly exhibits exceptional mechanical
strength and thermal stability despite its low density.
4 Current Progress in Water-Splitting Applications
The incorporation of 3D graphene with metal oxides, transition-metal dichalco-

genides (TMDCs), and other semiconductor materials is certainly an efficient
approach for increasing utilization effectiveness and photocatalytic hydrogen evolu-
tion reaction (HER) performance because it enhances 3D graphene’s ability as a
co-catalyst to absorb incident light and provide numerous channels for gas diffu-
sion, ion transfer, and electron transport. Yoon et al. used the hydrothermal method
to synthesize 3D graphene inverse opal (GIO) nanostructures with α-Fe2 O3 . GIO
was directly grown on a glass surface under low-temperature conditions, yielding
3D conducting networks for electron movement and photon-trapping effects. The
activity of α-Fe2 O3 /GIO was 1.4 times higher than that of bare α-Fe2 O3 , indicating
that the close proximity of the conducting electrode to the active components in the α-
Fe2 O3 /GIO composite materials reduced electron–hole recombination and promoted
quick electron transport [42].
Recently, Men et al. prepared free-standing ZnO/3D GF to study its photocat-
alytic performance in the energy field. ZnO nanorods acted as the active material
that can most effectively optimize dimensions and interfaces. Meanwhile, the 3D
self-supporting and hierarchical porous graphene structure served as the conductive
substrate that would allow the solution to travel through itself. The photocurrent
performance of ZnO/rGO foam was higher than that of rGO itself due to the simul-
taneous enhancement in light harvesting and charge transfer of ZnO/rGO foam [13].
Lu et al. fabricated TiO2 nanoparticles on 3D graphene by using a hot electron
mechanism. The H2 generation efficiencies of TiO2 /3DG were 4.46 and 17.72 times
greater than those of pure 3DG and TiO2 , respectively, due to the high synergetic
effects between TiO2 and 3DG [43].
3D graphene also can be incorporated with dual photoactive nanomaterials to
further improve its photocatalytic HER performance. For example, Han et al. synthe-
sized 3D-like ternary TiO2 /MoS2 /graphene aerogel via the hydrothermal reaction
to enhance photocatalytic activities. The photocurrent activity of the TiO2 /MoS2 /
graphene aerogel was 6 times higher than that of the pure TiO2 , implying that the good
synergetic effect between the three composite materials and 3D graphene aerogel/
MoS2 nanosheets played a key role in enhancing active adsorption sites and photocat-
alytic reaction centers [44]. Shah et al. reported that the photocurrent density of 3D
graphene on Ni foam incorporated with ZnO through the combination of CVD and
the hydrothermal method was approximately 8.06 higher than that of the photocata-
lyst without graphene on Ni foam. This significant increase was due to the important
role of 3D graphene as a co-catalyst for electron and hole transport in ZnO [45].
Various types of 3D graphene materials synthesized through different methods with
their corresponding photocatalytic activities in PEC water splitting are summarized
in Table 1.
Numerous studies have reported that pure metal oxide photocatalysts have poor
PEC performances due to their rapid photogenerated electron–hole pair recombi-
nation. Loading graphene as a co-catalyst is an efficient approach for reducing the
recombination of electron–hole pairs, which corresponds to the increased efficiency
of PEC water splitting. The current trend in designing novel materials for photo-
catalysis is the incorporation of 3D graphene with materials, such as metal oxides
and TMDCs and other semiconductor materials. Catalysts on 3D self-supported
photoelectrodes have improved diffusion kinetics and a larger contact area with
the electrolyte, resulting in their significantly superior performance compared with
their planar counterparts and conventional 2D photoelectrodes. The combination
of TMDCs with graphene enhances the features of the materials, such as stability,
charge separation, and transport capabilities, which can improve the total photocat-
alytic PEC hydrogen generation. Additionally, the performance of the photocatalytic
process can be improved by simplifying charge transfer between materials by using
3D porous graphene structures. Although several synthetic techniques can be applied,
the physicochemical characteristics of the produced graphene materials differ greatly.
Table 1 Fabrication methods and photocatalytic activities of several 3D graphene-based composite

materials
Type of 3D Composite Fabrication Photocurrent Hydrogen References
graphene materials method density (mA/cm2 ) production rate
(mmol/g/h)
GIO α-Fe2 O3 Hydrothermal 1.62 at 1.5 V – [42]
versus RHE
Graphene TiO2 /MoS2 Hydrothermal 37.45 at + 0.6 V – [44]
aerogel
3D Silicon CVD 37.6 at + 0.16 V – [46]
graphene
3D ZnO CVD and 108.2 at 0–1.0 V – [45]
graphene Hydrothermal versus Ag/AgCl
GF ZnO Hydrothermal 0.041 at 0 V – [13]
versus Ag/AgCl
GF TiO2 Hot/free – 1.205 [43]
electron
mechanism
Graphene N-doped Hydrothermal – 0.013 [47]
aerogel
Graphene Cu Gas exfoliation – 4.87 [48]
aerogel
The highest photocurrent density and hydrogen production rate of 3D graphene for
pyramid-like graphene/p-Si Schottky junctions were approximately 37.6 mA/cm2
and 11.60 mmol/g/h, respectively, at + 0.16 V. [45] Consequently, graphene-based
3D materials not only act as supports to increase the photoelectrocatalytic perfor-
mance of composite materials, but also build a small skeleton framework that results
in an increased surface area and hence a superior photoelectrocatalytic performance.
5 Summary
Graphene is an attractive material for photocatalysis applications. It is particularly

attractive as a co-catalyst and transfer agent that can assist in reducing the effect of the
wide band gaps of semiconducting materials and the recombination of electron–hole
pairs in photocatalysts owing to its excellent intrinsic properties. Interconnected 3D
graphene structures are a promising solution to the restacking or aggregation issues
of 2D graphene in photocatalysis applications while still preserving the outstanding
properties of 2D graphene. 3D graphene can exist in the form of foams, sponges,
aerogels, or hydrogels. The current research trend in designing novel materials for
photocatalysis is the incorporation of 3D graphene with metal oxides, TMDCs, and
other semiconductor materials. The use of 3D graphene-based materials as a co-

catalyst and catalyst support to enhance the performance of PEC water splitting can be
ascribed to their large surface areas, porosity, effective transport, and improved reac-
tion site accessibility. Many efforts have been made to synthesize 3D graphene-based
photocatalysts for PEC water-splitting applications, and the number of researchers
involved in this area has considerably increased. The properties, synthesis methods,
and current progress in the water-splitting applications of 3D graphene-based photo-
catalysts reported to date were discussed thoroughly in this chapter. Nevertheless, the
performance and stability of the photocatalyst still need further exploration. Thus,
the design of 3D graphene-based photocatalysts with high photoelectrochemical effi-
ciency and good stability is needed to realize the use of 3D graphene in practical
PEC water-splitting applications.
Acknowledgments The authors would like to acknowledge the financial support given for this book
chapter by FRGS/1/2019/STG07/UKM/02/2 from the Ministry of Higher Education, Malaysia.
References
1. Kuang, P., Sayed, M., Fan, J., Cheng, B., Yu, J.: 3D graphene-based H2-production
photocatalyst and electrocatalyst. Adv. Energy Mater. 10, 1–53 (2020)
control. Chem. Rev. 120, 10336–10453 (2020)
catalysis. Small 17, 1–19 (2021)
4. Mohd, N.R.A., Mohamad, R., Rosman, N.N., Wong, W.Y., Arifin, K., Jeffery, L.: Current
progress on 3D graphene-based photocatalysts: from synthesis to photocatalytic hydrogen
production. Int. J. Hydrogen Energy 46, 9324–9340 (2021)
I.V., Firsov, A.A.: Electric field effect in atomically thin carbon films. Nat. Mater 6, 666–669
(2004)
6. Bramhaiah, K., Bhattacharyya, S.: Challenges and future prospects of graphene-based hybrids
for solar fuel generation: moving towards next generation photocatalysts. Mater Adv 3, 142–172
(2022)
7. Min, B.H., Kim, D.W., Kim, K.H., Choi, H.O., Jang, S.W., Jung, H.-T.: Bulk scale growth of
CVD graphene on Ni nanowire foams for a highly dense and elastic 3D conducting electrode.
Carbon N Y 80, 446–452 (2014)
8. Kamedulski, P., Skorupska, M., Binkowski, P., Arendarska, W., Ilnicka, A., Lukaszewicz, J.P.:
High surface area micro-mesoporous graphene for electrochemical applications. Sci. Rep. 11,
1–12 (2021)
9. Xu, X., Guan, C., Xu, L., Tan, Y.H., Zhang, D., Wang, Y., Zhang, H., Blackwood, D.J., Wang,
J., Li, M., Ding, J.: Three dimensionally free-formable graphene foam with designed structures
for energy and environmental applications. ACS Nano 14, 937–947 (2020)
10. Tsai, H.C., Vedhanarayanan, B., Lin, T.W.: Freestanding and hierarchically structured Au-
dendrites/3D-graphene scaffold supports highly active and stable Ni3S2 electrocatalyst toward
overall water splitting. ACS Appl. Energy Mater 2, 3708–3716 (2019)
11. Cheng, Y., Zhou, S., Hu, P., Zhao, G., Li, Y., Zhang, X., Han, W.: Enhanced mechanical,
thermal, and electric properties of graphene aerogels via supercritical ethanol drying and high-
Temperature thermal reduction. Sci. Rep. 7, 1–11 (2017)
12. Cui, C., Li, S., Qiu, Y., Hu, H., Li, X., Li, C., Gao, J., Tang, W.: Fast assembly of Ag3PO4
nanoparticles within three-dimensional graphene aerogels for efficient photocatalytic oxygen
evolution from water splitting under visible light. Appl. Catal B Environ. 200, 666–672 (2017)
13. Men, X., Chen, H., Chang, K., Fang, X., Wu, C., Qin, W., Yin, S.: Three-dimensional
free-standing ZnO/graphene composite foam for photocurrent generation and photocatalytic
activity. Appl. Catal B Environ. 187, 367–374 (2016)
14. Banciu, C.A., Nastase, F., Istrate, A.I., Veca, L.M.: 3D Graphene foam by chemical vapor
deposition: synthesis, properties, and energy-related applications. Molecules, 27 (2022)
15. Shen, Z., Ye, H., Zhou, C., Kröger, M., Li, Y.: Size of graphene sheets determines the structural
and mechanical properties of 3D graphene foams. Nanotechnology 29, 1–13 (2018)
16. Xia, D., Yi, K., Zheng, B., Li, M., Qi, G., Cai, Z., Cao, M., Liu, D., Peng, L., Wei, D., Wang,
Z., Yang, L., Wei, D.: Solvent-free process to produce three dimensional graphene network
with high electrochemical stability. J. Phys. Chem. C 121, 3062–3069 (2017)
17. Drieschner, S., Weber, M., Wohlketzetter, J., Vieten, J., Makrygiannis, E., Blaschke, B.M.,
Morandi, V., Colombo, L., Bonaccorso, F., Garrido, J.A.: High surface area graphene foams
by chemical vapor deposition. 2D Mater 3, 1–10 (2016)
18. Sha, J., Gao, C., Lee, S.K., Li, Y., Zhao, N., Tour, J.M.: Preparation of three-dimensional
graphene foams using powder metallurgy templates. ACS Nano 10, 1411–1416 (2016)
19. O’Neill, C., Johnson, M.B., DeArmond, D., Zhang, L., Alvarez, N., Shanov, V.N., White, M.A.:
Thermal conductivity of 3-dimensional graphene papers. Carbon Trends 4, 100041 (2021)
20. Loeblein, M., Tsang, S.H., Pawlik, M., Phua, E.J.R., Yong, H., Zhang, X.W., Gan, C.L., Teo,
E.H.T.: High-density 3D-boron nitride and 3D-graphene for high-performance nano-thermal
interface material. ACS Nano 11, 2033–2044 (2017)
21. Pettes, M.T., Ji, H., Ruoff, R.S., Shi, L.: Thermal transport in three-dimensional foam
architectures of few-layer graphene and ultrathin graphite. Nano Lett. 12, 2959–2964 (2012)
22. Li, X.L., Guo, J.G., Zhou, L.J.: The Young’s modulus of triangle-like three-dimensional
graphene under uniaxial tension: Finite element method and theoretical model. J. Phys. Chem.
Solids 161, 110473 (2022)
23. Xu, Z., Jiang, J., Zhang, Q., Chen, G., Zhou, L., Li, L.: 3D graphene aerogel composite of 1D–
2D Nb2O5-g-C3N4 heterojunction with excellent adsorption and visible-light photocatalytic
performance. J. Colloid Interface Sci. 563, 131–138 (2020)
24. Bayram, O.: A study on 3D graphene synthesized directly on Glass/FTO substrates: Its Raman
mapping and optical properties. Ceram Int 45, 16829–16835 (2019)
25. Zeng, M., Wang, W.L., Bai, X.D.: Preparing three-dimensional graphene architectures: review
of recent developments. Chinese Phys. B 22 (2013)
26. Thiyagarajan, P.: A review on three-dimensional graphene: synthesis, electronic and biotech-
nology applications-the unknown riddles. IET Nanobiotechnol. 15, 348–357 (2021)
for preparation, properties and sensing applications. Microchim Acta 185 (2018)
Prot. 116, 262–286 (2018)
29. Yang, G., Park, S.J.: Conventional and microwave hydrothermal synthesis and application of
functional materials: a review. Materials (Basel) 12, 1177 (2019)
30. Zhou, X., Cui, S.C., Liu, J.G.: Three-dimensional graphene oxide cross-linked by benzidine
as an efficient metal-free photocatalyst for hydrogen evolution. RSC Adv. 10, 14725–14732
(2020)
31. Ding, Y., Zhou, Y., Nie, W., Chen, P.: MoS2 -GO nanocomposites synthesized via a
hydrothermal hydrogel method for solar light photocatalytic degradation of methylene blue.
Appl. Surf. Sci. 357, 1606–1612 (2015)
32. Cao, X., Guo, W., Li, A., Du, J., Du, L., Zhang, G., Liu, H.: Facile synthesis of reduced graphene
oxide/CdS nanowire composite aerogel with enhanced visible-light photocatalytic activity. J.
Nanoparticle Res. 22, 81 (2020)
33. Han, W., Ren, L., Gong, L., Qi, X., Liu, Y., Yang, L., Wei, X., Zhong, J.: Self-assembled three-
dimensional graphene-based aerogel with embedded multifarious functional nanoparticles and
its excellent photoelectrochemical activities. ACS Sustain. Chem. Eng. 2, 741–748 (2014)
34. Saeed, M., Alshammari, Y., Majeed, S.A., Al-Nasrallah, E.: Chemical vapour deposition of
graphene-synthesis, characterisation, and applications: a review. Molecules 25, 3856 (2020)
35. Bhaviripudi, S., Jia, X., Dresselhaus, M.S., Kong, J.: Role of kinetic factors in chemical vapor
deposition synthesis of uniform large area graphene using copper catalyst. Nano Lett. 10,
4128–4133 (2010)
Mater 10, 424–428 (2011)
37. Cai, R., Wu, J.G., Sun, L., Liu, Y.J., Fang, T., Zhu, S., Li, S.Y., Wang, Y., Guo, L.F., Zhao,
C.E., Wei, A.: 3D graphene/ZnO composite with enhanced photocatalytic activity. Mater Des.
90, 839–844 (2016)
38. Chang, C.J., Wei, Y.H., Huang, K.P.: Photocatalytic hydrogen production by flower-like
graphene supported ZnS composite photocatalysts. Int. J. Hydrogen Energy 42, 23578–23586
(2017)
39. Nine, M.J., Tung, T.T., Losic, D.: Self-assembly of graphene derivatives: methods, structures,
and applications. Compr. Supramol. Chem. II 9, 47–74 (2017)
40. Wang, J., Shi, Z., Fan, J., Ge, Y., Yin, J., Hu, G.: Self-assembly of graphene into three-
dimensional structures promoted by natural phenolic acids. J. Mater. Chem. 22, 22459–22466
(2012)
41. Zhang, X., Liu, D., Yang, L., Zhou, L., You, T.: Self-assembled three-dimensional graphene-
based materials for dye adsorption and catalysis. J. Mater. Chem. A 3, 10031–10037 (2015)
42. Yoon, K.Y., Lee, J.S., Kim, K., Bak, C.H., Kim, S.I., Kim, J.B., Jang, J.H.: Hematite-based
photoelectrochemical water splitting supported by inverse opal structures of graphene. ACS
Appl. Mater. Interfaces 6, 22634–22639 (2014)
43. Lu, Y., Ma, B., Yang, Y., Huang, E., Ge, Z., Zhang, T., Zhang, S., Li, L., Guan, N., Ma, Y., Chen,
Y.: High activity of hot electrons from bulk 3D graphene materials for efficient photocatalytic
hydrogen production. Nano Res. 10, 1662–1672 (2017)
44. Han, W., Zang, C., Huang, Z., Zhang, H., Ren, L., Qi, X., Zhong, J.: Enhanced photocatalytic
activities of three-dimensional graphene-based aerogel embedding TiO2 nanoparticles and
loading MoS2 nanosheets as Co-catalyst. Int. J. Hydrogen Energy 39, 19502–19512 (2014)
45. Mohd, N.R.A., Yunus, R.M., Rosman, N.N., Wong, W.Y., Arifin, K., Minggu, L.J.: Synthesis
of ZnO on 3D Graphene/Nickel Foam for Photoelectrochemical Water Splitting. Malaysian J.
Anal. Sci. 26, 546–553 (2022)
46. Ku, C.K., Wu, P.H., Chung, C.C., Chen, C.C., Tsai, K.J., Chen, H.M., Chang, Y.C., Chuang,
C.H., Wei, C.Y., Wen, C.Y., Lin, T.Y., Chen, H.L., Wang, Y.S., Lee, Z.Y., Chang, J.R., Luo, C.W.,
Wang, D.Y., Hwang, B.J., Chen, C.W.: Creation of 3D textured Graphene/Si Schottky junction
photocathode for enhanced photo-electrochemical efficiency and stability. Adv. Energy Mater
9, 1–9 (2019)
47. Qiao, H., Huang, Z., Liu, S., Tao, Y., Zhou, H., Li, M., Qi, X.: Novel mixed-dimensional
photocatalysts based on 3D graphene aerogel embedded with TiO2/MoS2 hybrid. J. Phys.
Chem. C 123, 10949–10955 (2019)
48. Wang, Y., Song, T., Zhang, P., Huang, T., Wang, T., Wang, T., Zeng, H.: Gas-exfoliation
assisted fabrication of porous graphene nanosheets derived from plumeria rubra for highly
efficient photocatalytic hydrogen evolution. ACS Sustain. Chem. Eng. 6, 11536–11546 (2018)
3D Graphene for Flexible Electronics
Arpana Agrawal
Abstract Three-dimensional graphene structures are nowadays grabbing enormous

research interest due to their porous structures exhibiting high conductivity, high
specific surface area, and low density, hence making them excellent materials for
flexible electronic applications including flexible wearable sensors, flexible elec-
trodes for metal–ion batteries, supercapacitors, human body compatible e-skins, etc.
Accordingly, the present chapter provides an overview of various three-dimensional
graphene architectures (foams, hydrogels, aerogels, sponges, and films). A brief
discussion of the various preparation methods has also been presented. A few exam-
ples of the applications of three-dimensional graphene structures for flexible elec-
tronics, particularly for flexible sensor-based applications (strain/pressure sensors,
electronic skins, etc.) and flexible energy storage device applications (flexible super-
capacitors, metal-based batteries such as lithium–ion, lithium–sulfur, etc.) have been
highlighted critically. Finally, the concluding remarks and perspectives are presented.
Keywords 3D graphene structures · Porous structures · Flexible electronics ·

Supercapacitors · Sensors
1 Introduction
2D graphene is an exceptional material because of its several fascinating properties

and is a planar sheet (one-atom-thick) where carbon atoms with sp2 hybridization
are bounded with each other in a honeycomb lattice. Apart from 2D graphene layers,
3D graphene structures are nowadays attracting immense research interest. Such
structures can be termed as sponges/foams/aerogels and exhibit excellent porosity,
encouraging conductivity, high specific surface area and hence are considered as
promising materials for various electronic device applications. Owing to the highly
A. Agrawal (B)
Department of Physics, Shri Neelkantheshwar Government Post-Graduate College,
Khandwa 450001, India
e-mail: agrawal.arpana01@gmail.com
https://doi.org/10.1007/978-3-031-36249-1_21
376 A. Agrawal
Fig. 1 Various 3D graphene

structures along with their
flexible electronic
applications
porous structure of 3D graphene structures with excellent conductivity and encour-

aging compatibility with various polymeric materials possessing high elasticity, they
are one of the potential candidates, particularly for flexible electronics including flex-
ible electrodes, conductors, metal–ion batteries, metal–air batteries, wearable and
flexible sensors, etc. Figure 1 pictorially shows the various 3D graphene structures
along with their flexible electronic applications.
So far, various 3D graphene architectures have been reported including graphene
spheres, graphene networks (foams, hydrogels, aerogels, sponges) and films, etc., and
can be fabricated via a number of techniques such as self-assembly method, template-
assisted method, electro-spinning/spraying, chemical vapor deposition (CVD), etc.
In the spray assembly method, 3D graphene structures were prepared via gela-
tion of graphene oxide dispersion which then undergo a reduction process to form
reduced graphene oxide, whereas, in the template-assisted method, 3D templates of
polystyrene or SiO2 were utilized which can be easily removed from the 3D graphene
structure. Electro-spinning/spraying facilitates the formation of 3D graphene struc-
tures in the form of fibers, spheres, or beads with diameters ranging from a few
micrometers to nanometers and CVD allows straightforward deposition of 3D
graphene architectures. Chen et al. [1] reported the growth of highly flexible and
conducting 3D graphene networks employing CVD approach. Shehzad et al. [2]
presented a critical review of various 3D macrostructures of 2D nanomaterials. An
extensive review of the CVD growth of 3D graphene foam was also presented by
Banciu et al. [3], along with their fascinating properties and various energy appli-
cations. Another review in this area deals with the preparation and morphological
studies of various 3D graphene composites along with their numerous applications
[4]. Li and Shi [5] also described various 3D graphene structures. Wu et al. [6] also
reported a highly compressive 3D graphene sponge possessing near-zero Poisson’s
ratio. Hu et al. [7] discussed the growth of highly compressible and lightweight
3D Graphene for Flexible Electronics 377
graphene aerogels. Li et al. [8] discussed the preparation method of a compressible

3D graphene sponge. Han et al. [9] reported a method to strengthen 3D graphene
sponges using an ammonia solution.
It is worth mentioning here that in contrast to 2D graphene materials which exhibit
outstanding mechanical strength, 3D graphene structures are usually reported to
possess poor mechanical properties and hence are unfit for flexible device applica-
tions in as it is formed. The performance of flexible electronic devices fabricated from
these structures in pristine form would get deteriorated after various deformable situ-
ations. However, to utilize 3D graphene structures for flexible electronics, they are
combined with several polymeric materials. The very first report on flexible conduc-
tors based on template-assisted chemical vapor-deposited 3D graphene foam is with
polydimethylsiloxane (PDMS). Wang et al. [10] have also reported the preparation of
a 3D graphene-polymer-based composite. The preparation of 3D graphene/polymer
composite not only provides flexibility and stretchability but also helps in improving
their conductivity, and hence there is a utility for flexible electronics. Another fasci-
nating property of 3D graphene structures is their ability to prepare composites via
doping with other materials which adds further dimensions to the utility.
Accordingly, the present chapter provides an overview of various 3D graphene
architectures (foams, hydrogels, aerogels, sponges, films) along with a few exam-
ples of their applications for flexible electronics, particularly for flexible sensor-
based applications (strain/pressure sensors, electronic skins, etc.) and flexible energy
storage device applications (flexible supercapacitors, metal–ion batteries such as
lithium–ion battery, lithium–sulfur battery, sodium–ion battery, etc.).
2 3D Graphene for Flexible Electronic Applications
Several researchers have discussed the applications of 3D graphene structures

including foams, sponges, aerogels, nanowalls, etc. for flexible electronics, partic-
ularly for sensor applications (flexible pressure/strain sensors/electronic skin) of
energy storage applications (flexible capacitor/supercapacitors/fuel cells/metal–ion
batteries), etc. This section will focus on a few applications of 3D graphene-based
structures, particularly for sensor applications and energy storage applications.
2.1 3D Graphene for Sensor Applications
3D graphene-based structures have extensively been employed for sensor applica-

tions. Samad et al. [11] reported sensor applications of graphene foam composite
having to regulate the sensitivity. 3D interconnecting structures of reduced graphene/
polyimide nanocomposite-based flexible strain sensor applications with excellent
elasticity, flexibility, and mechanical strength were reported by Qin et al. [12]. An
et al. [13] fabricated a flexible wearable sensor utilizing graphene aerogel which was
378 A. Agrawal
prepared via micro-extrusion printing technology using an ink obtained by dissolving

graphene oxide in water. The prepared ink was loaded in a syringe and then patterned
on the PET substrate which then undergoes a vacuum freeze-drying process to obtain
GO aerogel followed by chemical reduction to produce reduced graphene oxide
aerogel. Finally, to prepare a graphene aerogel-based wearable sensor, the aerogel
allows electrodes to be glued to it and is packaged with PDMS. It should be noted
here that the morphology of graphene aerogels strongly depends on the concentration
of the graphene oxide inks and the fabricated sensor facilitates 3D multi-recognition
and multi-deformation responses with excellent performances.
Fabrication of wearable and flexible pressure and strain sensors utilizing graphene
porous structures is also reported by Pang et al. [14]. Highly compressible composite
of graphene/thermoplastic polyurethane foam possessing high conductivity is also
reported to be useful for piezoresistive sensing applications [15]. Facilely grown
3D graphene foam composite was employed to fabricate strain sensors [16]. Flex-
ible sensors with self-healing properties were also reported to be fabricated using
composite material composed of 3D graphene and polyborosiloxane (PBS) polymer
where PBS acts as the self-healing material [17]. This sensor has an excellent capacity
of sensing pressure and flexion angle and can automatically heal for 6–8 cycles.
However, the fabricated sensor is unsuitable under harsh environmental conditions
because of the poor mechanical strength of PBS polymer. Li et al. [18] have also
reported the applications of reduced graphene oxide/polyurethane composite for
healable flexible electronics.
An efficient lightweight, wearable, sensitive, and squeezable piezoresistive sensor
was fabricated by Sengupta et al. [19], employing graphene-PDMS composite foam.
To prepare this sensor, initially, the PDMS foam was prepared as a base material then
the graphene nanoflakes were loaded in it. For this, a conductive graphene suspen-
sion was prepared by suspending graphene nanoflakes in N, N-dimethylformamide
(DMF) solution which undergoes sonication followed by dipping of porous PDMS
sponges in it for 1 h. This leads to the formation of graphene-coated PDMS sponges
which then dried in oven at 60 °C for 1 h. The same steps continue for six cycles
to prepare porous graphene-PDMS composite foam. Figure 2a shows the overall
fabrication process of graphene-PDMS composite foam. Finally, to fabricate the
sensor with all the electrical connections, conductive silver epoxy was coated on the
sides of the prepared composite foam (Fig. 2b). The squeezability and lightweight
of the developed sensor were demonstrated in Fig. 2c and d, respectively. Figure 2e
and f shows the scanning electron microscopy images of the PDMS foam before
loading and after loading of graphene nanoflakes, respectively, which clearly shows
the penetration of graphene nanoflakes within the PDMS foam.
In order to examine the applicability of the developed graphene-PDMS-based
sensor for flexible and wearable device applications, they have examined the
developed sensor under several strain-loading circumstances. In their experimental
setup as shown in Fig. 3a, the squeezable graphene-PDMS foam-based sensor was
compressed using pistons doubling as electrodes which are connected to a Wheat-
stone bridge and hence the data is acquainted. The response of the sensor was obtained
at different compressive stain loadings varying from 10 to 50% and the change in
Fig. 2 a Schematic illustration of the overall fabrication process of graphene-PDMS composite

foam. b Electrical connections to fabricate the sensor for signal acquisition. c, d Demonstration of
squeezability (c) and lightweight (d) of the developed sensor. e, f SEM images of the PDMS foam
before loading (e) and after loading (f) of graphene nanoflakes. Adapted with permission [19]. Copy-
right (2019) Copyright The Authors, some rights reserved; exclusive licensee ACS Publications.
Distributed under a Creative Commons Non-Commercial No Derivative Works (CC-BY-NC-ND)
Attribution License
380 A. Agrawal
the normalized resistance as a function of time is obtained as represented in Fig. 3b.

They have further examined the applications of the developed sensor for real-time
human foot pressure monitoring where the developed sensor was attached to the shoe
sole at intense and low-pressure points of the foot mainly the toe ball, heels, and foot
arch, respectively, as illustrated in Fig. 3c. The real-time response of the sensor while
walking is then recorded as shown in Fig. 3d. The response of the sensor during the
movements of the index finger and wrist was also examined (Fig. 3e, f), which clearly
shows the feasibility of the developed sensor for flexible wearable health monitoring
devices.
The same group has also designed piezoelectric 3D graphene-PDMS foam-based
pressure sensors for smart gloves applications for Internet of things-enabled wear-
able pressure monitoring devices [20]. The photographs of the developed pressure
sensor attached to a nitrile glove are represented in Fig. 4a where four identical 3D
graphene-PDMS foam-based pressure sensors were attached to the thumb, index
finger, middle finger, and ring finger. To cover and protect the attached sensors from
foreign elements, another nitrile layer was employed (Fig. 4a). Finally, these gloves
were used to hold a paper cup and the response in terms of resistance change was
recorded. However, to convert this resistance change into voltage signals, a voltage
divider is also connected to the sensor. Figure 4b depicts the sensor response obtained
while holding a paper cup in terms of the voltage signal, suggesting its utility for
wearable smart gloves as pressure-sensing devices.
Yang et al. [21] reported the fabrication of extremely flexible, stretchable, skin-
compatible, and highly sensitive electronic nose utilizing 3D graphene microstruc-
tured nanowalls and PDMS substrate. Graphene nanowalls were grown onto a silicon
substrate employing a plasma-enhanced CVD method using methane and hydrogen
gases. Finally, the grown nanowall structures were loaded with PDMS polymer
followed by solidification in a vacuum oven. Thereafter, the graphene nanowalls were
transferred to PDMS substrate via a peeling off approach. Finally, to prepare elec-
trodes for graphene nanowalls-PDMS-based e-skin, silver paste was polished on the
edges of the grown structure. They have also examined the applications of the devel-
oped e-skin in the bending motion of joints of the human body including knee joints,
elbow, fingers, eye movements, and voice sensations. It was found that the devel-
oped graphene nanowalls-PDMS-based e-skin shows excellent sensitivity toward
stretching and bending motions with a gauge factor ~65.9 under 100% stretching
conditions.
2.2 3D Graphene for Energy Storage Applications
In addition to sensor applications, 3D graphene structures are widely employed for

energy storage applications. Several energy storage devices including supercapac-
itors, fuel cells, or metal–ion batteries particularly lithium–ion batteries have been
reported to be fabricated from 3D graphene structures. Electrodes prepared from
Fig. 3 a Schematic depiction of the experimental setup for performing the piezoresistivity measure-
ments. b The response of the sensor in terms of change in the normalized resistance as a function of
time at different compressive stain loadings varying from 10 to 50%. c Attachment of the developed
sensor on the shoe sole at intense and low-pressure points of the foot, mainly toe ball, heels, and foot
arch. d The real-time response of the sensor while walking for the demonstration of real-time human
foot pressure monitoring. Response of the developed sensor in terms of voltage signals during the
movements of the index finger (e) and wrist (f). Adapted with permission [19]. Copyright (2019)
Copyright The Authors, some rights reserved; exclusive licensee ACS Publications. Distributed
under a Creative Commons Non-Commercial No Derivative Works (CC-BY-NC-ND) Attribution
License
382 A. Agrawal
Fig. 4 a The photographs of four identical pressure sensors attached on a nitrile glove at fingertip
regions with another nitrile layer to shield the attached sensors from foreign elements. b Sensor
response obtained while holding a paper cup in terms of voltage signal. Adapted with permis-
sion [20]. Copyright (2022) Copyright The Authors, some rights reserved; exclusive licensee IOP
Publishing. Distributed under a Creative Commons Attribution License 4.0
3D graphene were reported to be employed for fabricating high-performance pseu-

docapacitors and supercapacitors. Wang et al. [22] utilized electrodes made up of
3D graphene nickel oxide nanoflakes for pseudocapacitors while Dong et al. [23]
employed electrodes of 3D graphene cobalt oxide for supercapacitors. Xu et al.
[24] have reported the fabrication of highly flexible solid-state supercapacitors.
Herein, the electrolyte was a mixture of polyvinyl alcohol (PVA) and sulfuric acid
(H2 SO4 ) and the electrode was made up of graphene hydrogel film having a thick-
ness of 120 µm. The fabricated supercapacitor exhibits excellent performance with
gravimetric capacitance ~186 Fg−1 at 1 Ag−1 . Flexible supercapacitors were also
fabricated by Zheng et al. [25], employing hybrid aerogels composed of cellulose
nanofibril, reduced graphene oxide, and carbon nanotubes. Highly flexible and effi-
cient solid-state supercapacitors are also reported to be fabricated from nanoporous
graphene films [26]. Fabrication of high-rate capability electrodes for supercapac-
itors made up of a composite material comprising of nanostructured 3D graphene
and Ni3 S2 was also demonstrated [27]. He et al. [28] also demonstrated flexible and
ultralight supercapacitor electrodes obtained from graphene/MnO2 composite.
Apart from supercapacitors, 3D graphene structures-based composites serving as
either anodes or cathodes are extremely utilized for metal-based batteries (lithium–
ion batteries or lithium–sulfur batteries, sodium–ion batteries, etc.). Generally silicon
(Si)-based anodes were employed for lithium–ion batteries. However, one of the
major drawbacks of using Si anodes is their extended volume variations while
lithiation. To circumvent this drawback, Phadatare et al. [29] have prepared a Si-
nanographite aerogel anode where an aerogel fabrication approach was employed to
grow Si nanoparticles on nanographite flakes. The prepared electrode exhibits excel-
lent cycle stability with a specific capacity of 455 mAhg−1 at 100 mAg−1 . Ji et al.
[30] have also employed 3D conductive networks serving as an anode for fabricating
lithium–ion batteries which comprises a Si/graphene composite grown on ultrathin
graphene foam. A critical review was presented by Zhang et al. [31], demonstrating
the potentiality of 3D nanoarchitecture as anode materials for various lithium or

sodium storage applications. TiO2 /graphene composite was also reported to exhibit
high photocatalysis activity with excellent stability and capability [32]. Herein, to
prepare the composite, TiO2 nanocrystals were hydrothermally grown on graphene
aerogels (001). Wei et al. [33] have also examined the utility of Fe3 O4 nanospheres
encapsulated in 3D graphene foam for encouraging lithium storage applications.
Mo et al. [34] have reported the fabrication of a highly flexible, sensitive, and
efficient lithium–ion battery with long cycling capacity for flexible electronic appli-
cations using a 3D porous structured nitrogen-incorporated graphene foam (NGF)
encapsulated with germanium quantum dots (QD)/nitrogen-incorporated graphene
(NG) yolk–shell nanostructure (Ge-QD@ NG/NGF). This porous structure facilitates
the large volumetric expansion of germanium due to the presence of internal void
spaces and easy access to electrolytes because of the open channels. The template-
assisted technique was employed to prepare the desired 3D graphene composite struc-
ture. Figure 5a schematically illustrates the overall growth process of Ge-QD@NG/
NGF/PDMS yolk–shell nanoarchitecture. Here, 3D interconnected porous Ni foam
was used as the template to grow N-doped graphene via the CVD method which then
undergoes a hydrothermal process in presence of GeCl4 to prepare GeO2 -decorated
N-doped graphene on Ni foam. The obtained product was then undergoing electro-
less Ni deposition to form N-doped graphene with GeO2 @Ni on Ni foam which
again undergoes a CVD process followed by Ar/H2 annealing. This process leads to
the preparation of N-doped graphene with Ge quantum dot@Ni@N-doped graphene
on Ni foam. Thereafter, Ni etching was done to prepare yolk–shell nanoarchitecture
and finally coated with PDMS to prepare the end product mainly Ge-QD@NG/NGF/
PDMS yolk–shell electrode.
The electrochemical performances of the fabricated lithium–ion battery
employing Ge-QD@NG/NGF/PDMS were examined by obtaining the galvanos-
tatic charging–discharging and cycling response of the battery. Figure 5b depicts the
galvanostatic charging–discharging behavior of the battery containing Ge-QD@NG/
NGF yolk–shell nanoarchitecture for several cycles at 1 C which clearly shows a
discharge and charge capacity of 1,597 mAhg−1 and 1,220 mAhg−1 , respectively,
for the first cycle. Figure 5c shows the cycling response of Ge/Cu electrode, Ge/NGF/
PDMS electrode, and prepared Ge-QD@NG/NGF/PDMS yolk–shell electrode for
1000 cycles at 1 C. In pristine Ge/Cu electrode, fast capacity fading was observed
which is mainly attributed to the greater size of the Ge nanoparticles resulting in
pitiable strain relaxation, while in the case of Ge/NGF/PDMS electrode, added space
was available to load the electrode material resulting in the formation of the intercon-
nected conductive network. However, in contrast to both these electrodes, encour-
aging cycle stability was observed in the prepared Ge-QD@NG/NGF/PDMS yolk–
shell electrode. Figure 5d schematically represents the assembled electrochemical
cell comprising of lithium foil, Ge-QD@NG/NGF/PDMS yolk–shell nanoarchitec-
ture as electrodes, and the experimental setup for in situ Raman measurements. In situ
Raman experiment was performed using laser light (operating wavelength = 532 nm)
for the working electrochemical cell before and during the lithiation process and the
obtained results were shown in Fig. 5e. It was found that the first-order Raman band
384 A. Agrawal
Fig. 5 a Pictorial demonstration of the overall growth process of Ge-QD@NG/NGF/PDMS yolk–

shell-based nanoarchitecture. b Galvanostatic charging–discharging behavior of the fabricated
battery containing Ge-QD@NG/NGF yolk–shell nanoarchitecture electrode for several cycles at 1
C. c Cycling response of Ge/Cu electrode, Ge/NGF/PDMS electrode and prepared Ge-QD@NG/
NGF/PDMS yolk–shell electrode for 1000 cycles at 1 C. d Schematic representation of the assem-
bled electrochemical cell comprising of lithium foil, Ge-QD@NG/NGF/PDMS yolk–shell nanoar-
chitecture as electrodes and separator along with the experimental setup for in situ Raman measure-
ments. e In situ Raman spectra obtained using 532 nm laser light for the working electrochemical
cell before and during lithiation process. Design of the traditional electrode (Ge/Cu) (f) and the flex-
ible 3D N-doped graphene-based electrode (g). Adapted with permission [34]. Copyright (2017)
Copyright The Authors, some rights reserved; exclusive licensee Nature Publishing. Distributed
under a Creative Commons Attribution License 4.0 (CC BY)
appeared at 296 cm−1 for the fabricated battery before the start of lithiation along with
a few other Raman peaks appearing due to the electrolyte or the packaging material.
The difference between the design of the traditional electrode and the flexible 3D
N-doped graphene-based electrode is also shown in Fig. 5f, g.
The same group has also reported the construction of lithium–ion batteries using
Ge nanoparticles encapsulated in a 3D double-walled ultrathin graphite tube serving
as a potential anode [35]. The superior electrochemical performance was observed
with cycle stability up to 1000 cycles, a specific capacity of 1338 mAhg−1 , and
a rate performance of 752 mAhg−1 at 40 C. It should be noted that other than
PDMS, polyaniline (PANI) polymer was also reported to be a compatible polymer
for 3D graphene structures. Zhang et al. [36] discussed the fabrication of lithium–
ion batteries using electrodes comprising of SnO2 @PANI core–shell nanorod arrays
grown on graphite foam. For this, initially, the SnO2 nanorod arrays were grown
on graphite foam which was then uniformly coated with a PANI layer to prepare
SnO2 @PANI core–shell structure and hence the electrode. This prepared electrode
shows enhanced electrochemical responses.
Cathode prepared from sulfur/3D network-structured graphene foam was also
reported to be employed for the fabrication of lithium–sulfur batteries [37]. This
cathode was synthesized by sulfur solution infiltration approach where sulfur was
loaded on a 3D graphene structure. Herein, initially, the 3D network graphene
structure was prepared via the CVD method employing template-assisted approach
without using any binder. Ni foam was used as the sacrificial template and can be
easily etched away after growth. The fabricated lithium–sulfur battery containing
sulfur/3D network-structured graphene foam as cathode exhibits excellent electro-
chemical stability. Ji et al. [38] have reported the use of lithium iron phosphate-loaded
3D network of ultrathin graphite foam as a potential, economic, and compatible
cathode material for fabricating lithium–ion batteries. This battery possesses high
current density and a specific capacity of 1280 mAg−1 and 70 mAhg−1 , respectively.
Lithium–sulfur batteries exhibiting excellent electrochemical properties were also
fabricated using 3D Li2 S/graphene serving as a potential cathode [39]. Chang et al.
[40] demonstrated the utility of 3D graphene-based N-incorporated carbon compos-
ites as efficient anode materials for sodium–ion batteries. Another report on the
utility of composite electrodes made up of N-incorporated graphene on graphite foam
serving as anode material for lithium–ion batteries was presented where an encour-
aging specific capacity of 1687 mAhg−1 was observed [41]. 3D N-incorporated
graphene foam was also reported to be synthesized by the green synthesis method
and can be employed for electrochemical applications [42].
3D graphene structures are also employed for the purpose of detection devices
mainly photodetectors. Li et al. [43] reported the utility of 3D graphene foam for
fabricating photodetectors working from ultraviolet to microwave region. Highly
sensitive photodetectors constructed from flexible 3D graphene/organic-based hybrid
material were also reported for photodetection purposes in the visible to mid-infrared
regime [45]. For the fabrication of an ultraviolet photodetector, Boruah et al. [44]
have demonstrated the applications of ZnO nanowires grown on 3D graphene foam.
Overall, 3D graphene structures are one of the important classes of materials for
flexible device applications owing to their various fascinating characteristics such
as ultrathin, lightweight compatibility with various polymers that help in enhancing
their flexibility, and ability to combine with other materials to synthesize compos-
ites. All these properties suggests their potential as electrode materials for energy
storage applications including batteries, supercapacitors, lightweight sensors, and
photodetectors.
386 A. Agrawal
3 Conclusion
In conclusion, an overview of various 3D graphene architectures mainly foams,

hydrogels, aerogels, sponges, and films are provided. Various growth techniques
employed to prepare these 3D graphene structures are also briefly discussed. Various
flexible devices fabricated by utilizing such 3D graphene structures are critically
highlighted with a particular focus on flexible sensor-based applications and flex-
ible energy storage device applications including flexible supercapacitors, metal–ion
batteries such as lithium–ion battery, etc. However, further work is still required to
apprehend the commercialization of such flexible devices obtained from 3D struc-
tures because of the lack of standardization of the growth technique and/or fabrication
technique. Constant efforts along with scientific innovations in this field will certainly
lead to the fabrication of highly efficient flexible electronic devices.
References
1. Chen, Z.P., Ren, W., Gao, L., Liu, B., Pei, S., Cheng, H.-M.: Three-dimensional flexible
and conductive interconnected graphene networks grown by chemical vapour deposition. Nat.
Mater. 10, 424–428 (2011)
2. Shehzad, K., Xu, Y., Gao, C., Duan, X.: Three-dimensional macro-structures of two-
dimensional nanomaterials. Chem. Soc. Rev. 45, 5541–5588 (2016)
3. Banciu, C.A., Nastase, F., Istrate, A.I., Veca, L.M.: 3D graphene foam by chemical vapor
deposition: synthesis, properties, and energy-related applications. Molecules 27, 3634 (2022)
4. Xiao, W., Li, B., Yan, J., Wang, L., Huang, X., Gao, J.: Three dimensional graphene composites:
preparation, morphology and their multi-functional applications. Compos. Part A: Appl. Sci.
Manuf. 154, 107335 (2022)
5. Li, C., Shi, G.: Three-dimensional graphene architectures. Nanoscale 4, 5549–5563 (2012)
6. Wu, Y., Yi, N., Huang, L., Zhang, T., Fang, S., Chang, H., Li, N., Oh, J., Lee, J.A., Kozlov, M.:
Three-dimensionally bonded spongy graphene material with super compressive elasticity and
near-zero poisson’s ratio. Nat. Commun. 6, 6141 (2015)
7. Hu, H., Zhao, Z., Wan, W., Gogotsi, Y., Qiu, J.: Ultralight and highly compressible graphene
aerogels. Adv. Mater. 25, 2219–2223 (2013)
8. Li, J., Zhao, S., Zhang, G., Gao, Y., Deng, L., Sun, R., Wong, C.-P.: A facile method to
prepare highly compressible three-dimensional graphene-only sponge. J. Mater. Chem. A 3,
15482–15488 (2015)
9. Han, Z., Tang, Z., Li, P., Yang, G., Zheng, Q., Yang, J.: Ammonia solution strengthened three-
dimensional macro-porous graphene aerogel. Nanoscale 5, 5462–5467 (2013)
10. Wang, M., Duan, X., Xu, Y., Duan, X.: Functional three-dimensional graphene/polymer
composites. ACS Nano 10, 7231–7247 (2016)
11. Samad, Y.A., Li, Y., Alhassan, S.M., Liao, K.: Novel graphene foam composite with adjustable
sensitivity for sensor applications. ACS Appl. Mater. Interfaces 7, 9195–9202 (2015)
12. Qin, Y., Peng, Q., Ding, Y., Lin, Z., Wang, C., Li, Y., Xu, F., Li, J., Yuan, Y., He, X.: Lightweight,
superelastic, and mechanically flexible graphene/polyimide nanocomposite foam for strain
sensor application. ACS Nano 9, 8933–8941 (2015)
13. An, B., Ma, Y., Li, W., Su, M., Li, F., Song, Y.: Three-dimensional multi-recognition flexible
wearable sensor via graphene aerogel printing. Chem. Commun. 52, 10948–10951 (2016)
14. Pang, Y., Tian, H., Tao, L., Li, Y., Wang, X., Deng, N., Yang, Y., Ren, T.-L.: Flexible, highly
sensitive, and wearable pressure and strain sensors with graphene porous network structure.
ACS Appl. Mater. Interfaces 8, 26458–26462 (2016)
15. Liu, H., Dong, M., Huang, W., Gao, J., Dai, K., Guo, J., Zheng, G., Liu, C., Shen, C.,
Guo, Z.: Lightweight conductive graphene/thermoplastic polyurethane foams with ultrahigh
compressibility for piezoresistive sensing. J. Mater. Chem. C 5, 73–83 (2017)
16. Li, J., Zhao, S., Zeng, X., Huang, W., Gong, Z., Zhang, G., Sun, R., Wong, C.-P.: Highly
stretchable and sensitive strain sensor based on facilely prepared three-dimensional graphene
foam composite. ACS Appl. Mater. Interfaces 8, 18954–18961 (2016)
17. D’Elia, E., Barg, S., Ni, N., Rocha, V.G., Saiz, E.: Self-healing graphene-based composites
with sensing capabilities. Adv Mater. 27, 4788–4794 (2015)
18. Li, J., Zhang, G., Sun, R., Wong, C.-P.: A covalently cross-linked reduced functionalized
graphene oxide/polyurethane composite based on diels–alder chemistry and its potential
application in healable flexible electronics. J. Mater. Chem. C 5, 220–228 (2017)
19. Sengupta, D., Pei, Y., Kottapalli, A.G.P.: Ultralightweight and 3D squeezable graphene poly-
dimethylsiloxane composite foams as piezoresistive sensors. ACS Appl. Mater. Interfaces 11,
35201–35211 (2019)
20. Sengupta, D., Kamat, A.M., Smit, Q., Jayawardhana, B., Kottapalli, A.G.P.: Piezoresistive 3D
graphene–PDMS spongy pressure sensors for IoT enabled wearables and smart products. Flex.
Print. Electron. 7, 015004 (2022)
21. Yang, J., Ran, Q., Wei, D., Sun, T., Yu, L., Song, X., Pu, L., Shi, H., Du, C.: Three-
dimensional conformal graphene microstructure for flexible and highly sensitive electronic
skin. Nanotechnol. 28, 115501 (2017)
22. Wang, C.D., Xu, J., Yuen, M.-F., Zhang, J., Li, Y., Chen, X., Zhang, W.: Hierarchical composite
electrodes of nickel oxide nanoflake 3D graphene for high-performance pseudocapacitors. Adv.
Funct. Mater. 24, 6372–6380 (2014)
23. Dong, X.C., Xu, H., Wang, X.-W., Huang, Y.-X., Chan-Park, M.B., Zhang, H., Wang, L.-H.,
Huang, W., Chen, P.: 3D graphene cobalt oxide electrode for high-performance supercapacitor
and enzymeless glucose detection. ACS Nano 6, 3206–3213 (2012)
24. Xu, Y., Lin, Z., Huang, X., Liu, Y., Huang, Y., Duan, X.: Flexible solid-state supercapacitors
based on three-dimensional graphene hydrogel films. ACS Nano 7, 4042–4049 (2013)
25. Zheng, Q., Cai, Z., Ma, Z., Gong, S.: Cellulose Nanofibril/reduced graphene oxide/carbon
nanotube hybrid aerogels for highly flexible and all-solid-state supercapacitors. ACS Appl.
Mater. Interfaces 7, 3263–3271 (2015)
26. Qin, K., Kang, J., Li, J., Liu, E., Shi, C., Zhang, Z., Zhang, X., Zhao, N.: Continuously
hierarchical nanoporous graphene film for flexible solid-state supercapacitors with excellent
performance. Nano Energy 24, 158–164 (2016)
27. Wang, M., Wang, Y., Dou, H., Wei, G., Wang, X.: Enhanced rate capability of nanostructured
three-dimensional graphene/Ni3 S2 composite for supercapacitor electrode. Ceram. Int. 42,
9858–9865 (2016)
28. He, Y., Chen, W., Li, X., Zhang, Z., Fu, J., Zhao, C., Xie, E.: Freestanding three-dimensional
graphene/MnO2 composite networks as ultralight and flexible supercapacitor electrodes. ACS
Nano 7, 174–182 (2013)
29. Phadatare, M., Patil, R., Blomquist, N., Forsberg, S., Örtegren, J., Hummelgård, M., Meshram,
J., Hernández, G., Brandell, D., Leifer, K., Sathyanath, S.K.M., Olin, H.: Silicon-nanographite
aerogel-based anodes for high performance lithium ion batteries. Sci. Rep. 9, 14621 (2019)
30. Ji, J.Y., Ji, H., Zhang, L.L., Zhao, X., Bai, X., Fan, X., Zhang, F., Ruoff, R.S.: Graphene-
encapsulated Si on ultrathin-graphite foam as anode for high capacity lithium-ion batteries.
Adv. Mater. 25, 4673–4677 (2013)
31. Zhang, Z., Chen, Y., Sun, S., Sun, K., Sun, H., Li, H., Yang, Y., Zhang, M., Li, W., Chou, S.,
Liu, H., Jiang, Y.: Recent progress on three-dimensional nanoarchitecture anode materials for
lithium/sodium storage. J. Mater. Sci. Technol. 119, 167–181 (2022)
32. Qiu, B.C., Xing, M.Y., Zhang, J.L.: Mesoporous TiO2 nanocrystals grown in situ on graphene
aerogels for high photocatalysis and lithium-ion batteries. J. Am. Chem. Soc. 136, 5852–5855
(2014)
33. Wei, W., Yang, S., Zhou, H., Lieberwirth, I., Feng, X., Müllen, K.: 3D graphene foams cross-
linked with pre-encapsulated Fe3 O4 nanospheres for enhanced lithium storage. Adv. Mater.
25, 2909–2914 (2013)
388 A. Agrawal
flexible Li-ion battery. Nat. Commun. 8, 13949 (2017)
35. Mo, R., Lei, Z., Rooney, D., Sun, K.: Three-dimensional double-walled ultrathin graphite tube
conductive scaffold with encapsulated germanium nanoparticles as a high-areal-capacity and
cycle-stable anode for lithium-ion batteries. ACS Nano 13, 7536–7544 (2019)
36. Zhang, F., Yang, C., Gao, X., Chen, S., Hu, Y., Guan, H., Ma, Y., Zhang, J., Zhou, H., Qi, L.:
SnO2 @PANI core-shell nanorod arrays on 3d graphite foam: a high-performance integrated
electrode for lithium-ion batteries. ACS Appl. Mater. Interfaces 22, 9620–9629 (2017)
37. Xi, K., Kidambi, P.R., Chen, R., Gao, C., Peng, X., Ducati, C., Hofmann, S., Kumar, R.V.:
Binder free three-dimensional sulphur/few-layer graphene foam cathode with enhanced high-
rate capability for rechargeable lithium sulphur batteries. Nanoscale 6, 5746–5753 (2014)
38. Ji, H., Zhang, L., Pettes, M.T., Li, H., Chen, S., Shi, L., Piner, R., Ruoff, R.S.: Ultrathin graphite
foam: a three-dimensional conductive network for battery electrodes. Nano Lett. 12, 2446–2451
(2012)
39. He, J., Chen, Y., Lv, W., Wen, K., Li, P., Qi, F., Wang, Z., Zhang, W., Li, Y., Qin, W., He,
W.: Highly-flexible 3D Li2 S/graphene cathode for high-performance lithium sulfur batteries.
J. Power Sources 327, 474–480 (2016)
40. Chang, B., Chen, J., Zhou, M., Zhang, X., Wei, W., Dai, B., Han, S., Huang, Y.: Three-
dimensional graphene-based n-doped carbon composites as high-performance anode materials
for sodium-ion batteries. Chem Asian J. 13, 3859–3864 (2018)
41. Ji, J., Liu, J., Lai, L., Zhao, X., Zhen, Y., Lin, J., Zhu, Y., Ji, H., Zhang, L.L., Ruoff, R.S.: In situ
activation of nitrogen-doped graphene anchored on graphite foam for a high-capacity anode 9,
8609–16 (2015)
42. Yu, H., Ye, D., Butburee, T., Wang, L., Dargusch, M.: Green synthesis of porous three-
dimensional nitrogen-doped graphene foam for electrochemical applications. ACS Appl. Mater.
Interfaces 8, 2505–2510 (2016)
43. Li, Y., Zhang, Y., Yu, Y., Chen, Z., Li, Q., Li, T., Li, J., Zhao, H., Sheng, Q., Yan, F., Ge, Z.,
Ren, Y., Chen, Y., Yao, J.: Ultraviolet-to-microwave room-temperature photodetectors based
on three-dimensional graphene foams. Photonics Res. 8, 368–374 (2020)
44. Ge, Z., Xu, N., Zhu, Y., Zhao, K., Ma, Y., Li, G., Chen, Y.: Visible to Mid-Infrared photodetec-
tion based on flexible 3D graphene/organic hybrid photodetector with ultrahigh responsivity
at ambient conditions. ACS Photonics 9, 59–67 (2022)
45. Boruah, B.D., Mukherjee, A., Sridhar, S., Misra, A.: Highly dense ZnO nanowires grown on
graphene foam for UV photodetection. ACS Appl. Mater. Interfaces 7, 10606–10611 (2015)
3D Graphene for Capacitive
De-ionization of Water
Sara Madani and Cavus Falamaki
Abstract Herein we consider the use of 3D graphene structures in the so-called

capacitive de-ionization (CDI) process of water. The topic is hot and the need for such
structures is explained by presenting a brief description of CDI technology including
the latest configurations and discussing the most important and recent steps taken so
far to use 3D graphene as an electrode material. The advantages and disadvantages
of using 3D structures as electrode materials to be implemented in the CDI process
of water are discussed. The state of art related to 3D graphene-only electrodes, 3D
graphene composites with carbonaceous materials, and 3D graphene composites
with non-carbonaceous materials are discussed in detail. The future perspective is
briefly addressed and considers the use of 3D printing, pseudocapacitive layered
materials and introduces 3D graphene/3D non-graphene structures. The use of new
3D graphene materials in the field of CDI is constantly increasing. Accordingly, this
chapter can serve as a motivational tool to encourage researchers to focus on the
development of new 3D graphene-based materials for CDI electrodes to combat the
increasing scarcity of drinking water worldwide.
Keywords 3D graphene · Capacitive de-ionization · Water desalination ·

Hierarchical pore structure · Graphene-based electrode
1 Why CDI?
Water scarcity is becoming a crucial problem for humanity in recent decades [1].
Therefore, desalination technologies have been intensively developed as desirable
solutions in recent years. Currently, thermal desalination technologies including
multi-stage flash distillation (MSF), multi-effect distillation (MED), mechanical
vapor compression (MVC), and multi-effect solar stills (MESS), and membrane-
based technologies such as reverse osmosis (RO) and electrodialysis (ED) have been
S. Madani (B) · C. Falamaki

Chemical Engineering Department, Amirkabir University of Technology (Tehran Polytechnic),
Tehran, Iran
e-mail: sm.saramadani@gmail.com
https://doi.org/10.1007/978-3-031-36249-1_22
390 S. Madani and C. Falamaki
widely developed. However, these established techniques suffer from high costs, poor
efficiency, and pollution, and require large amounts of energy in the form of thermal
and/or electrical energy [2]. To reduce energy consumption, several new technolo-
gies such as forward osmosis (FO) [3], membrane distillation (MD) [4], reverse
electrodialysis (RED) [5], and capacitive de-ionization (CDI) [6] have evolved and
may soon approach full commercialization. CDI is known as an environmentally
friendly desalination technology with lower energy consumption and lower capital
costs compared to traditional desalination methods. The use of high-pressure pumps
and membranes is not required, and no secondary waste is generated during the
process in these systems. In addition, a wide range of applications from water soft-
ening and water desalination to selective ion removal has been established for CDI
systems [6].
2 CDI Technology in Brief
In 1960, Blair and Murphy first explored the idea of electrochemical desalination of
water [7]. The pioneering work of CDI was continued by Murphy and Caudle [8] in
the mid-1960s. In 1971, the theory of ion transport in porous carbon electrodes in
CDI and ion storage based on the capacitor mechanism was introduced [9]. In 1996,
Farmer et al. improved the performance of a carbon aerogel electrode CDI device
[10]. After introduction of this first 3D carbonaceous structure as electrode material,
CDI process development underwent an unprecedented accelerated rapid growth.
Basically, the term capacitive de-ionization denotes two main functions: The term
capacitive is used to indicate that charged ions are adsorbed by water and stored on
the inner surface of porous electrodes, while de-ionization causes the removal of
cations and anions from the water. In fact, CDI is an electrochemically controlled
technique for removing salt from salt water. In a basic design (Fig. 1), salt water
flows between a pair of large surface area electrodes and simultaneously a small
potential difference (<2 V) is applied across them. The potential window should not
exceed the water splitting potential point [11]. Charged ions are pulled toward the
electrode with contrary polarity during a charge cycle, while they are expelled to
the secondary stream during a discharge cycle when application of voltage to the
electrodes is discontinued or reversed.
Two important types of CDI have been studied extensively: symmetric and asym-
metric. The most common CDI configuration is flow-through CDI (Fig. 2a), first
proposed by Blair et al. [7]. Later, this configuration was widely used in a variety of
research and works. In another configuration, referred to as osmotic CDI, the feed
current flows directly through the osmotic electrodes. This configuration was first
reported in 1970 by Johnson et al. (Fig. 2b) [12]. This type of CDI was used to
study key performance parameters and showed more rapid cell charging compared
to flow-through CDI. In 2012, two battery electrodes for desalination in a desalina-
tion battery were presented as a novel CDI design (Fig. 2c). Although a desalination
battery is a desirable configuration for high salinity water desalination, this type of
3D Graphene for Capacitive De-ionization of Water 391
Fig. 1 Schematic diagram

of a traditional CDI system
CDI suffers from instability due to Faraday reactions. A novel CDI design is the flow
electrode CDI (Fig. 2d), which may offer compact, low-resistance systems using
slurry or flow electrodes [13]. Carbon suspensions were used as a novel suspension
electrode in the CDI system (Fig. 2e) for desalination of brackish and sea water [14].
Asymmetric CDI has been subject of emerging research in recent years due to its
better performance compared to symmetric CDI.
Materials with different potential of zero charge (PZC), surface functional
groups, surface charges [12, 15, 16], electrode thicknesses [17], and even different
ion removal mechanisms [18] can increase desalination performance and system
capacity. One of the most popular asymmetric configurations is membrane-
assisted capacitive de-ionization (MCDI), which is a combination of ion-exchange
membranes with classic forms of CDI (flow-by, flow-through) configurations [19].
Anion and cation exchange membranes were applied to the anode and cathode elec-
trodes, respectively. Covalently attached groups allow easy access of the ions to the
counter-electrode while repelling co-ions. Ion-exchange membranes can be installed
free-standing [19] or ion-selective groups can be grafted directly onto porous elec-
trodes [20]. When the co-ions are expelled from the electrodes, they must not move
toward the spacer channel. Thus, co-ions remain on the electrode side and accu-
mulate in higher concentrations in the macropores. Charge neutrality in macropores
D Flow-electrode CDI
A Flow-through CDI
B Osmosis CDI E Suspension-electrode CDI
I Hybrid CDI
C Desalination battery
Fig. 2 a Various CDI configurations (A to E). b Various CDI configurations (F to K). c Legend
also requires the accumulation of counter-ions. This eventually improves the charging
efficiency.
The remarkably fast recovery of the electrodes due to the application of a reverse
voltage in the regeneration cycle is another advantage of MCDI over CDI. Finally,
membranes prevent the electrode from disintegrating in the long term [21]. Inverted-
CDI (i-CDI) as another modified CDI guarantees the desalination stability and effi-
ciency of the CDI over time. Unlike traditional CDI, ion adsorption and desorption
F Flow-through MCDI J Flow-electrode MCDI
G Ion-selective flow-through CDI K Asymmetric flow-electrode CDI
H Inverted CDI
Fig. 2 (continued)
occur during the discharge and charge time of i-CDI, respectively [15]. A combi-
nation of faradic and capacitive electrodes in a CDI structure is called hybrid-CDI
(HCDI) [18]. Hybrid systems exhibit a higher sorption capacity for ion removal than
a typical CDI system. Flowing suspension carbon was used as the electrode material
in a membrane CDI to desalinate water with high salinity. In another similar configu-
ration, activated carbon suspension is used in combination with metal oxide to create
an asymmetric structure to increase the voltage window. Consequently, SAC with
this configuration is much higher than that of a typical flow electrode CDI.
capacitive electrode
cation exchange membrane
anion exchange membrane
surface modified electrode
ion selective electrode
surface modified electrode
faradic electrode
separator
flow electrode (AC particles)
current collector
Fig. 2 (continued)
2.1 Electrode Material: A Key Component
Electrode material is a key component in CDI configuration, and affects ion sorption
capacity, de-ionization rate, and system reliability. An ideal CDI electrode material
possesses high electrical conductivity and surface area, and proper wettability that
benefits from continuous electron transfer pathways, rich active sites, and fast ion
transport pathways to form an efficient electrochemical double layer [23, 24].
Therefore, abundant accessible surface areas and hierarchical pore morphology
are key properties for the electrode materials. In addition, good electrode candi-
dates are inexpensive, scalable, and easy-to-process materials [25]. Members of the
carbon family of materials as ideal CDI electrode materials are conductive with
easily tunable properties that exhibit excellent chemical/electrochemical stability and
diverse morphology. So far, activated carbon, ordered mesoporous carbon, carbon
nanotubes, carbon nanofibers, carbon aerogels, carbon nanospheres, and graphene
and their composites have been widely used as electrode material in CDI systems
[26–28]. Graphene as the newest class of carbon material with exceptional character-
istics such as high theoretical surface area of 2630 m2 g−1 , high carrier mobility up to
10 000 m2 V−1 s−1 , substantially high conductivity (7200 S m−1 ), high electron and
thermal mobility, tunable surface properties and morphology, and excellent physical
and chemical properties has attracted the attention of researchers for large-scale CDI
applications [22, 29].
Graphene is the two-dimensional layer of carbon atoms with hexagonal crystalline
arrangement, which has created promising perspectives in a variety of applications
due to its unique physicochemical properties. The history of using graphene in CDI
systems dates back to 2009 when Li et al. used reduced graphene oxide as the elec-
trode material in a CDI for the first time [30]. They hypothesized that corrugated
sheets of reduced graphene oxide (RGO) create a porous structure to facilitate ion
storage. Although the obtained electrosorption capacity superseded that of activated
carbon (AC) in the similar experimental conditions, the salt adsorption capacity
(SAC) value for reduced graphene oxide was not satisfactory. The low specific
surface area (14.2 m2 g−1 ) due to the aggregation of the graphene nanosheets was
the main cause resulting in low electrosorption capacity. The same group performed
another study and increased the specific surface area of RGO nanoflakes from 222 to
254 m2 g−1 , while the achieved NaCl removal capacity remained at about 1.35 mg g–1
under the same experimental conditions [31].
One of the possible solutions to increase the electrosorption capacity was to
propose a novel reduction method such as solar irradiation and/or thermal shock
reduction. For example, in the solar irradiance reduction method, the sunlight focused
on graphene oxide (GO) causes a sudden temperature rise that decomposes GO into
RGO, CO2 , and marginal H2 O. The pressurized CO2 promoted exfoliation of the
graphene, resulting in a structural transition from a dense structure to a fluffy/fuzzy
structure. The folded and crumpled structure of the obtained RGO creates a large
surface area that can generate up to a high SAC of 22.4 mg g−1 in a 5844 mg L−1
NaCl solution at 1 V [32]. The SAC growth of RGO electrodes has been mainly
attributed to microstructure modification such as in-plane porous structures or curve
morphology and surface functional groups like oxygenates. However, creation of 3D
porous graphene structure and surface modification of graphene are considered as
more promising solutions, which are discussed in the following section.
3 3D Structures in Water Treatment: Advantages

and Challenges
In general, low-dimensional nanomaterials show enormous potential for water treat-

ment; however, these material agglomerates not only cause a loss of activity in water,
but their recovery is difficult and expensive. In addition, nanomaterials potentially
remaining in drinking water cause many health concerns. 3D macrostructures made
from low-dimensional nanomaterials inherit the special properties of their corre-
sponding nanoscale building blocks. Unlike nanomaterials themselves, 3D structures
can be easily recovered and recycled without using membrane separation techniques.
Thus, these material classes improve the application of low-dimensional nanomate-
rials and make the treatment process more economical to carry out. The likelihood of
release (leaching) of nanomaterials in the water treatment process decreases signif-
icantly, eliminating health concerns related to treated water consumption. Instead
of using expensive and environmentally harmful processes such as thermal treat-
ment or chemical washing, environmentally friendly regeneration techniques can be
used. It also gives the treatment system a good opportunity to design the flow units
in a continuous mode of operation. Last but not least, a 3D structure of graphene
resembles a scaffold, and other functional groups or nanomaterials can be grafted
onto these unique structures to build macro-sized multifunctional nanocomposites
to simultaneously separate different contaminants. Therefore, making a 3D structure
from low-dimensional material is very important. These multifunctional nanocom-
posites can be synthesized by mixing other nanomaterial with the precursor or by
accommodating it on graphene’s 3D structural surface. While the fabrication of low-
dimensional material is a tedious, time-consuming process that makes its large-scale
application problematic, the fabrication of 3D graphene-based macrostructures (3D
GBMs) is simple and inexpensive.
The cause of graphene sheet aggregation and restacking lies in interplanar van
der Waals forces and strong π–π interactions of the basal planes of graphene sheets.
In a CDI system, the physisorption process is responsible for NaCl electrosorp-
tion on graphene electrodes. Two key strategies can be considered to prevent graph
restacking; as already mentioned, the first and main solution is to fabricate a 3D
porous structure to promote accessibility to separate graphene layers and increase
the surface area in the system meaningfully, and the second way is to apply spacer
material such as carbon nanotube (CNT) and mesoporous carbon between layers of
graphene, which is not our focus.
3.1 3D Graphene-Based Electrodes
Till now, different methods have been adopted to manufacture 3D structures of

graphene as a CDI electrode, such as aerogels, hydrogels, foams, scaffolds, and
sponges. Depending on the GO synthesis method and 3D structure, GO concentra-
tion, pH of the GO suspension, reduction method, pre-treatments or post-treatments,
chemicals used in the production stages, treatment time, and temperature, the struc-
tures produced differ in specific surface area and pore size distribution, porosity,
internal structure, wettability, and electrical and mechanical properties. Hence, we
will observe different reported results for the application of different 3D structures
of graphene in CDI systems under the same test conditions.
Graphene hydrogel as one of these 3D structures is a jelly-like macroporous mate-
rial. Water is trapped within the pores of graphene hydrogels (GHs) and they have
hydrophilic nature. GO as a starting material is used to produce GH using chemical
reduction or cross-linking processes. Graphene aerogels (GAs) have been produced
through controlled dehydration of GHs without appreciable volume shrinkage or by
chemical vapor deposition on 3D porous scaffolds. GAs and GHs fulfill ideal CDI
electrode properties such as high specific surface area and conductivity, appropriate
hydrophilicity, and connected porous structure. GAs and GHs benefit from a hierar-
chical pore structure which can play different key roles in the electrosorption process.
They can be easily adapted to the required electrode architecture based on synthesis
methods and their parameters. Macropores/mesopores are mainly responsible for
providing efficient pathways to transport ions, while mesopores resemble storage
reservoirs for adsorbed ions. Furthermore, micropores in this structure provide high
surface area ions for EDL formation. Wang and co-workers used GAs as the elec-
trode material in a CDI and achieved a SAC of 5.39 mg g−1 at 2.0 V and an initial
NaCl concentration of 105 μS cm−1 [33].
Graphene oxide layers undergo self-assembly provided their concentration is
higher than a critical value that leads to the formation of liquid crystals as a result of
nematic phase separation [34]. Therefore, the GO concentration is crucial to deter-
mine the morphology of the hydrogel. Drying the hydrogel in direct contact with
air disintegrates the 3D structure due to capillary forces. Drying methods such as
freeze-drying or supercritical drying are commonly used to remove water from the
hydrogel, and the aerogel produced does not show any significant reduction in volume
or collapse of the internal structure. As ice crystals grow, RGO layers are pushed to
align along the moving freezing front, creating a well-organized cellular structure
through the freezing process. Interconnected layers of GA create a highly compress-
ible/elastic structure (in one or all directions) called sponges or graphene foams.
Polyurethane-templated technique was used to fabricate a spongy graphene with a
specific surface area of 305 m2 g−1 in 2014, whose SAC was 4.95 mg g−1 in 1 mL
of aqueous NaCl at 1.5 V [35].
In another study, a graphene sponge was fabricated by directly freeze-drying the
GO suspension and then annealing it in a nitrogen atmosphere [36]. The reported
SAC for this electrode material was about 14.9 mg g−1 at 1.2 V in 500 mg L−1
NaCl solution, ca. 3.2 times the capacity of pristine graphene (4.64 mg g−1 ). Such a
high capacitance value is obtained not only for a relatively large specific surface area
(356.0 m2 g−1 ), but also because of the accessible 3D cross-linked porous structure
(pore volume of 1.51 cm3 g−1 versus 0.83 cm3 g−1 for pristine graphene) and low
charge transfer resistance. Because the EDLs are formed at the electrode surface, a
higher quantity of charges is adsorbed eventually leading to a superb capacitance.
Therefore, effectively increasing the surface area has been known as one of the
solutions to improve the CDI operation.
KOH activation is considered a traditional method to increase the surface area of
activated carbon (AC), CNT, and carbon nanofibers. Zhuo et al. applied the KOH-
activated graphene electrode with a 3D porous structure in a CDI system, which
possess an unusual specific surface area of 3513 m2 g−1 and an electrical conductivity
of 104 S m−1 [37]. The thermal shock in the first step of the fabrication process leads
to the decomposition of most of the oxygenate groups, generating pressurized gas
in a very short time that promotes exfoliation of the graphene sheets (Fig. 3). This
process was followed by a KOH treatment to etch the graphene layers and form
in-plane micropores. The ion removal capacity of this electrode was 11.86 mg g−1 at
2 V in 70 mg L−1 NaCl solution, which is much better than that of activated carbon,
CNT- and RGO-based electrodes under the same experimental conditions until then
(2015). In addition, the de-ionization rate for activated graphene is much higher than
for RGO. The de-ionization process with the KOH-activated graphene is completed
in less than 20 min, while the same process for RGO takes almost 50 min.
On the other hand, the etching process creates a lot of surface (or edge) carbon,
which has a much larger specific capacity than that of the graphene basal plane,
resulting in a significant increase in the overall electrosorption capacity. The inter-
connected structure forms a conductive percolated network that guarantees rapid
electrosorption and good mechanical robustness. In 2015, another research group
constructed a 3D graphene architecture with nanopores using an H2 O2 -induced
chemical etching process of the graphene ground plane [38]. Graphene carbon
atoms were etched and then enlarged into nanopores with H2 O2 . The 3D holey
graphene hydrogel was a connected highly porous 3D architecture of huge surface
area due to numerous in-plane pores (NP-3DG). This electrode showed a large SAC
of 17.1 mg g−1 at 1.6 V in 500 mg L−1 NaCl solution. NP-3DG showed a much
higher salt removal capacity (15 mg g−1 ) than that of 3D graphene (3DG) struc-
ture (8.3 mg g−1 ) under the same experimental conditions (1.4 V and 500 mg L−1 ).
3D holey graphene contained in-plane macropores and nanopores, which provided
ions with larger available surface area (3DG structure having a specific surface area
of 247 m2 g−1 ) and efficient pathways for ion transport. In fact, the interconnected
macropores of the graphene matrix improve demineralization process by storing ions
to decrease the diffusion paths from the outer electrolyte to the inner surface.
Increasing the voltage increases the driving force on ions, causing more micro-
pores to participate in improving the SAC of the electrode. For this reason, some
studies report high SAC values, however, when actually evaluating and comparing
the results of different studies, voltage and other experimental parameters such as
initial concentration should be taken into account. The voltage should not be too
Fig. 3 SEM images of a, b KOH-activated graphene and c, d reduced graphene oxide. Adapted
with permission from [37]. Copyright (2023) Elsevier
high to exceed the hydrolysis voltage. In a study, a high-hole graphene framework

(HGF) was successfully applied as the CDI electrode material using lyophilization
and heat treatment at 200 °C [39]. The reported SACs of HGF were 8.0, 16.9, and
even 29.6 mg g−1 in different NaCl concentrations of 80, 270, and 572 mg L−1 ,
respectively. Such values are substantially larger than those reported for other carbon-
based materials at 2.0 V. A higher NaCl concentration increased the ions transporta-
tion rate within the pores and decreased overlaying phenomena of EDL, therefore
the cell SAC improved with increasing NaCl concentration under the same experi-
mental conditions (constant applied voltage). However, in another study, scientists
obtained the high NaCl level of 9.13 mg g−1 at 2.0 V in an ultra-low salt concen-
tration of 50 mg L−1 NaCl solution using surface microporous graphene (SMG)
[40]. This shows that structural manipulation of the graphene surface without using
heteroatoms or pseudocapacitive material can be an essential tool to increase the
system performance even in very low concentration. The excellent CDI performance
at such a low salt concentration is due to the rich active sites with short ion transport
distance in the surface micropore structure.
The existence of an original 3D structure incorporated in a hierarchical hole
system in HGF is a major factor enhancing CDI performance. The 3D graphene
with hierarchical porous structure (3DHGR) has been fabricated as an effective CDI
electrode material [41]. These electrodes were fabricated using a template-controlled
process in combination with the in situ defect etching process (oxometalate etching).
3DHGR consists of 3D graphene entities containing many micro-mesopores over
the associated macroporous walls. 3DHGR has been reported to have a large SAC of
14.7 mg g−1 in 500 ppm NaCl solution at 1.2 V and good regeneration performance in
repeated charge–discharge cycles and a speedier salt adsorption rate compared to 3D
graphene under the same conditions. Although macropores in 3DHGR impose a short
diffusion path by screening ions, micro- and mesopores play the key role in providing
accessible surfaces and adsorption sites and facilitating ion transport in macroporous
3D graphene. The charge efficiency (Λ) is one of the main parameters for determining
the proportion of salt take up to charge transfer. The calculated charging efficiency
of 3DHGR is 0.63. This is significantly larger compared to 3DGR (0.28).
In 2018, Ma et al. compared the performance of RGO hydrogel and graphene
aerogel in the CDI system, achieving exceptional electrosorption capacities of 49.34
and 45.88 mg g−1 (at an initial concentration of 500 mg L−1 and a voltage of 2.0 V)
for GH and GA, respectively [42]. The specific surface area of GH and its average
pore size are higher than that of GA. The hydrophilicity and electrical conductivity of
GH are higher than that of GA, however, the function of water is a cornerstone of the
performance dissimilarities. The SAC of GH is 49.34 mg g−1 , larger than that of GA
(45.88 mg g−1 ) at 2.0 V with an initial NaCl concentration of 500 mg L−1 . Water has
the function of supporting and transferring: water can reduce graphene rearrangement
(supports) and facilitate ion transport from the inner pores to the outside. Many of
the techniques mentioned above involve templating processes, which are somewhat
complex and time-consuming. In addition, the desalination performance needs to be
improved to be economical and practical.
One of the simple ways to fabricate a 3D hierarchically porous graphene is a
merging of H2 O2 -assisted hydrothermal and microwave processes [43]. An ultrahigh
CDI capacitance of 21.58 mg g−1 in a 500 ppm NaCl solution at 1.4 V was obtained
with this unique hierarchically porous 3D graphene (GO-Mw-Hyd). The charging
efficiency of the system is 0.73, which is excellent compared to GO (Λ = 0.41) and
AC (Λ = 0.37).
3.2 3D Graphene Composite with Carbonaceous Material
Researchers have constructed various carbonaceous composites using 3D graphene

macrostructures in association with other carbon family members such as AC, carbon
nanotubes (CNT), and carbon spheres to create the large specific surface area with
porous structure and improve demineralization operation. CNTs are used to play
the role of spacer material when used with GO to prevent the agglomeration of
GR layers. Several successful studies have been conducted with GR and CNT. One
of them was an analogy between the CDI operation of 3D graphene hydrogel in
combination with single-walled CNT (SWCNT) and multi-walled CNT (MWCNT)
as electrode materials [44]. This research showed that SWCNTs/RGO hydrogel had
a larger specific surface area of 308.37 m2 g−1 (lower internal resistance) and a larger
SAC of 48.73 mg g−1 compared to MWCNTs/RGO with a capacity of 39.53 mg g−1

at 2 V in a 300 mg L−1 NaCl solution.
In 2020, microwave-irradiated graphene oxide (mwGO) 3D-CDI electrode mate-
rials with CNT deposited on RVC by the dip-coating method were constructed and
evaluated [45]. The optimized composition (9-CNT/mwGO/RVC) showed 100%
cycling stability and the amount of water produced per day for this electrode rose
by a factor of 1.67 in comparison with CNT/RVC in a full desalination process.
The maximum electrosorption capacity in 500 mg L−1 NaCl feed concentration
was 10.84 mg g−1 for this optimal electrode, while this value is 65% of the theoret-
ically calculated highest value (16.59 mg g−1 ) of this composition. In another case
study, a 3D graphene network embellished with microporous carbon spheres (3DGF-
MCS) showed a maximum SAC of 19.8 mg g−1 at 1.2 V in a NaCl concentration
of 100 mg L−1 [46]. Hybrid aerogel electrodes composed of graphene and nitrogen-
doped multi-walled carbon nanotubes (Gr-MWCNT) (N-Gr-MWCNT) were fabri-
cated using a facile hydrothermal synthesis method [47]. The large SAC of 20.1–
22.5 mg g−1 at 1.8 V in 0.5 g L−1 NaCl solution was attributed to an interconnected
network of graphene sheets with hierarchical porosity, uniform structure, outstanding
electrical conductivity, large specific surface area, and high wettability.
Graphene composite carbon aerogels (GCCAs) have been synthesized under
ambient pressure drying methods as electrode material for a CDI system [48].
Rational design of pore structure and highly conductive network resulted in a high
SAC of 26.9 mg g−1 and 18.9 mg g−1 in NaCl solutions with concentrations of
500 mg L−1 and 250 mg L−1 , respectively.
3.3 3D Graphene Composites with Non-carbonaceous

Material
In CDI, ion storage occurs by two main phenomena: capacitive ion storage and pseu-
docapacitive ion storage. Based on these mechanisms, the electrode material should
be developed to achieve a proper de-ionization performance. Although carbonaceous
electrodes have shown a gradual improvement in adsorption capacity, they are still
not completely amenable to commercialization. Redox and faradic active interca-
lation materials have emerged as the latest class of proposed materials to search
for better electrode materials capable of surpassing the electrosorption capacity
of EDL-powered electrodes with fast electrosorption/desorption properties. So far,
many pseudocapacitive materials from metal oxides and conducting polymers to
heteroatoms such as nitrogen and phosphorus have been extensively used in combi-
nation with graphene in the 3D structures to significantly increase the performance
of CDI due to their synergistic effects. Metal oxide nanoparticles such as TiO2 ,
MnO2 , ZnO2 , Fe3 O4 , and Co3 O4 can inhibit the association of RGO sheets, and their
proper physicochemical characteristics like high hydrophilicity enhance electrode
wettability.
In 2013, Tang et al. applied a flexible technique to construct 3D graphene aerogel/

metal oxide using various metal oxide nanoparticles (TiO2 , CeO2 , Fe2 O3 , and
Mn3 O4 ) [49]. The properties of low toxicity, good stability, low cost, easy anchoring
in the carbon structure, and large dielectric constant for containing a higher amount
of electric charges make TiO2 a desirable candidate for the graphene/metal oxide
nanocomposite. They could achieve the high capacity of 15.1 mg g−1 at 1.2 V
(500 ml g−1 NaCl solution) for graphene aerogel/TiO2 , which is 1.5 and 12.6 times
the capacity of GA and AC, respectively. For a NaCl concentration of 6000 mg L−1 ,
the CDI adsorption was 24.2 mg g−1 for the same electrode, representing the 1.6-
and 7.3-fold that of GA (15.4 mg g−1 ) and AC (3.3 mg g−1 ). Among the transition
metal oxides, MnO2 has a high theoretical specific capacity (1,400 F g−1 ), natural
occurrence, and environmental friendliness, making it a potential candidate for modi-
fication of carbon-based composite electrodes. Conductive polymers are known as
another important class of CDI electrode materials that improve CDI performance.
Polyaniline (PANI), polypyrrole (PPy), and polyvinyl alcohol (PVA) are widely
utilized in graphene composites because of their high electrical conductivity and
acceptable chemical stability, ease of synthesis process, and being economical. On
the other hand, the incorporation of polymers can reduce restacking of graphene
sheets. In a research study, a three-dimensional electrode with a hierarchically porous
structure was fabricated using RGOs, polypyrrole, and MnO2 (RGO-PPy-Mn) [27].
This electrode exhibited a large specific surface area and specific capacity, which
was the result of inserting two active materials (PPy and MnO2 ) into the graphene
network. The RGO-PPy-Mn hydrogels have a distinct porous network that opti-
mizes ion diffusion in the electrode network. The high electrosorption capacity of
18.4 mg g−1 for RGO-PPy-Mn can be attributed to the synergistic effect of these
components’ capacitive properties and improved ion transport. Increased electro-
chemical capacity and excellent SAC show that the RGO-PPy-Mn electrode is fully
suitable for CDI embracing both high performance and low energy consumption.
In another research, carbonization of GO-MF composites leads to 3D-RGO-
melamine–formaldehyde (3D-RGO-MF) composites synthesized via electrostatic
attraction between GO and MF nanoparticles [50]. Hierarchical porous structure
of this composite (specific surface area of 352 m2 g−1 ) with high nitrogen doping
level of 10.86% gives an extraordinarily high value of the electrosorption capacity
of 21.93 mg g−1 at a potential of 2.0 V in NaCl solution. Low internal resistance and
high reversibility prove that the 3D-RGO-MF electrodes can be a proper contender
for high-performance CDI. In addition, a study showed that GO/PPy on a copper–
nickel foam (CNF) could remove Rhodamine B (RhB) with a unique capacity of
270.3 mg g−1 and a rate of 3.762 mg g−1 min−1 .
Ensuring high electrical conductivity and hydrophilicity at the same time is a
challenge that needs to be considered to achieve high-performance CDI. On the one
hand, the surface functional groups of GO sheets should be removed as much as
possible during a reduction process to preserve the conjugated structure of graphene
sheets and increase conductivity. On the other hand, the elimination of the oxygenate
groups leads to a decrease in hydrophilicity, which is essential in the capacitive de-
ionization of salt water. Doping heteroatoms such as nitrogen into graphitic networks
is considered to be one of the most effective methods to address the problem and
fabricate n-type conductive materials of enhanced conductivity. In this way, the ions
can straightforwardly be adsorbed by the electrode materials, and the salt uptake rate
is accelerated. Nitrogen-doped graphene is usually produced by thermal conversion
of various nitrogen precursors, plasma and flame, and hydrothermal treatment.
In 2015, a simple and economical strategy to produce nitrogen-doped sponge
graphene (NGS) on a large scale was proposed [51]. GO was simply freeze-dried
and annealed in an NH3 atmosphere instead of the template method or hydrothermal
technique. The prepared NGS showed an ultrahigh SAC of 21.0 mg g−1 at 1.5 V in a
NaCl solution of about 500 mg L−1 , which is about 1.4 and 4.6 times that of graphene
sponge (GS) (14.6 mg g−1 ) and PG (4.5 mg g−1 ), respectively. An increased specific
surface area (526.7 m2 g−1 ) and increased pore volume (3.13 cm3 g−1 ) provide
short ion diffusion paths and more accessible spaces for receiving and storing ions.
In addition, pseudocapacitance is increased by doping with nitrogen. Doping also
increases the electrical conductivity of graphene, and increases the wettability of
the electrode–electrolyte interface. This can reduce the internal resistance of the
electrodes and lead to promoting the electrosorption performance of NGS.
An easy and inexpensive method has been used to first synthesize 3D interca-
lated graphene sheet-sphere nanocomposite architectures (Fig. 4) [52]. Since 3D
graphene nanospheres between graphene layers prevent stacking of graphene layers,
this structure guarantees a high specific surface area, a well-defined/favorable pore
size distribution, and high conductivity. An outstanding electrosorption capacity of
22.09 mg g−1 is obtained in a 500 mg L−1 NaCl solution at 1.2 V using graphene
oxide and [Ni2 (EDTA)] as precursors in a rational assembly of a 3D structure. The salt
removal percentage was about 90% and the electrodes show excellent de-ionization
stability and regeneration performance. This unique structure was fabricated using
a two-step process of direct thermal conversion of GO and the Ni+2 coordination
complex and acid etching without using additional templates, catalysts, or CVD
processes. This work presents a promising scalable method to fabricate efficient CDI
electrode materials for brackish and seawater desalination.
4 Future Perspective
3D graphene is establishing itself as a fundamental pillar in the architecture of CDI

systems. Development of advanced 3D structures embracing all the desired char-
acteristics like high SAC, low energy consumption, and high charging efficiency at
the same time remains a tricky challenge. Some new researches are oriented toward
the use of 3D printing [53], doping with heteroatoms [54], using pseudocapacitive
layered transition metal sulfides (like MoS2 ) [54] and nitrides (MXenes) [55], and
combining 3D graphene structures with other non-graphene 3D structures (like 3D
Prussian Blue) [56].
Fig. 4 Schematic of fabrication process of 3D multi-layered mesoporous GR sheet-sphere-like

microstructure. Adapted with permission from [52]. Copyright (2023) Royal Society of Chemistry
References
1. Woo, Y.C., Kim, S.H., Shon, H.K., Tijing, L.D.: Introduction: membrane desalination today,
past, and future (2018)
2. Kokabian, B., Gude, V.G.: Microbial desalination systems for energy and resource recovery.
In: Microbial Electrochemical Technology, pp. 999–1020. Elsevier (2019)
3. Phuntsho, S., Lotfi, F., Hong, S., Shaffer, D.L., Elimelech, M., Shon, H.K.: Membrane scaling
and flux decline during fertiliser-drawn forward osmosis desalination of brackish groundwater.
Water Res. 57, 172–182 (2014)
4. Kebria, M.R.S., Rahimpour, A.: Membrane distillation: basics, advances, and applications. In:
Advances in Membrane Technologies (2020)
5. Tian, H., Wang, Y., Pei, Y., Crittenden, J.C.: Unique applications and improvements of reverse
electrodialysis: a review and outlook. Appl. Energy 262, 114482 (2020)
6. Gupta, S.S., Islam, M.R., Pradeep, T.: Capacitive Deionization (CDI): An Alternative Cost-
Efficient Desalination Technique, pp. 165–202. Advances in Water Purification Techniques.
Elsevier (2019)
7. Blair, J.W., Murphy, G.W.: Electrochemical Demineralization of Water with Porous Electrodes
of Large Surface Area. ACS Publications (1960)
8. Murphy, G., Caudle, D.: Mathematical theory of electrochemical demineralization in flowing
systems. Electrochim. Acta 12(12), 1655–1664 (1967)
9. Johnson, A.M., Newman, J.: Desalting by means of porous carbon electrodes. J. Electrochem.
Soc. 118(3), 510 (1971)
10. Farmer, J.C., Fix, D.V., Mack, G.V., Pekala, R.W., Poco, J.F.: Capacitive deionization of NaCl
and NaNO3 solutions with carbon aerogel electrodes. J. Electrochem. Soc. 143(1), 159 (1996)
11. Tong, Y., Zhou, S., Zhou, J., Zhang, G., Li, X., Zhao, C., Liu, P.: Advances in efficient desalina-
tion technology of capacitive deionization for water recycling. J. Water Reuse Desalin. 11(2),
189–200 (2021)
12. Johnson, A., Venolia, A., Newman, J., Wilbourne, R., Wong, C., Gillam, W., Johnson, S.,
Horowitz, R.: Electrosorb process for desalting water, Office of Saline Water Research and
Development Progress Report No. 516, US Dept, Interior Pub 200(056) 31 (1970)
13. Jeon, S.-I., Yeo, J.-G., Yang, S., Choi, J., Kim, D.K.: Ion storage and energy recovery of a
flow-electrode capacitive deionization process. J. Mater. Chem. A 2(18), 6378–6383 (2014)
14. Hatzell, K.B., Iwama, E., Ferris, A., Daffos, B., Urita, K., Tzedakis, T., Chauvet, F., Taberna,
P.-L., Gogotsi, Y., Simon, P.: Capacitive deionization concept based on suspension electrodes
without ion exchange membranes. Electrochem. Commun. 43, 18–21 (2014)
15. Gao, X., Omosebi, A., Landon, J., Liu, K.: Surface charge enhanced carbon electrodes for stable
and efficient capacitive deionization using inverted adsorption–desorption behavior. Energy
Environ. Sci. 8(3), 897–909 (2015)
16. Han, L., Karthikeyan, K., Anderson, M., Wouters, J., Gregory, K.B.: Mechanistic insights
into the use of oxide nanoparticles coated asymmetric electrodes for capacitive deionization.
17. Porada, S., Bryjak, M., Van Der Wal, A., Biesheuvel, P.: Effect of electrode thickness variation
on operation of capacitive deionization. Electrochim. Acta 75, 148–156 (2012)
18. Lee, J., Kim, S., Kim, C., Yoon, J.: Hybrid capacitive deionization to enhance the desalination
performance of capacitive techniques. Energy Environ. Sci. 7(11), 3683–3689 (2014)
19. Biesheuvel, P., Zhao, R., Porada, S., Van der Wal, A.: Theory of membrane capacitive deioniza-
tion including the effect of the electrode pore space. J. Colloid Interface Sci. 360(1), 239–248
(2011)
20. Kim, Y.-J., Choi, J.-H.: Improvement of desalination efficiency in capacitive deionization using
a carbon electrode coated with an ion-exchange polymer. Water Res. 44(3), 990–996 (2010)
21. Porada, S., Zhao, R., van der Wal, A., Presser, V., Biesheuvel, P.M.: Review on the science and
technology of water desalination by capacitive deionization. Prog. Mater. Sci. 58(8), 1388–1442
(2013)
22. Liu, P., Yan, T., Shi, L., Park, H.S., Chen, X., Zhao, Z., Zhang, D.: Graphene-based materials
for capacitive deionization. J. Mater. Chem. A 5(27), 13907–13943 (2017)
23. Sun, M.-H., Huang, S.-Z., Chen, L.-H., Li, Y., Yang, X.-Y., Yuan, Z.-Y., Su, B.-L.: Applications
of hierarchically structured porous materials from energy storage and conversion, catalysis,
photocatalysis, adsorption, separation, and sensing to biomedicine. Chem. Soc. Rev. 45(12),
3479–3563 (2016)
24. Wu, Z.-S., Sun, Y., Tan, Y.-Z., Yang, S., Feng, X., Müllen, K.: Three-dimensional graphene-
based macro-and mesoporous frameworks for high-performance electrochemical capacitive
energy storage. J. Am. Chem. Soc. 134(48), 19532–19535 (2012)
25. Porada, S., Borchardt, L., Oschatz, M., Bryjak, M., Atchison, J.S., Keesman, K.J., Kaskel,
S., Biesheuvel, P.M., Presser, V.: Direct prediction of the desalination performance of porous
carbon electrodes for capacitive deionization. Energy Environ. Sci. 6(12), 3700–3712 (2013)
26. Madani, S., Falamaki, C., Kazemzadeh, M., Rahmanifard, A., Aboutalebi, S.H.: Conceptual
circuit model for the prediction of electrochemical performance of carbonaceous electrodes
containing reduced ultra large graphene oxide. J. Electrochem. Soc. 169(4), 040554 (2022)
27. Gu, X., Yang, Y., Hu, Y., Hu, M., Huang, J., Wang, C.: Facile fabrication of graphene–polypyr-
role–Mn composites as high-performance electrodes for capacitive deionization. J. Mater.
Chem. A 3(11), 5866–5874 (2015)
28. Huang, Z.-H., Yang, Z., Kang, F., Inagaki, M.: Carbon electrodes for capacitive deionization.
J. Mater. Chem. A 5(2), 470–496 (2017)
29. Rao, C.N.R., Sood, A.K., Subrahmanyam, K.S., Govindaraj, A.: Graphene: the new two-
dimensional nanomaterial. Angewandte Chemie Int. Edn. 48(42), 7752–7777 (2009)
30. Li, H., Lu, T., Pan, L., Zhang, Y., Sun, Z.: Electrosorption behavior of graphene in NaCl
solutions. J. Mater. Chem. 19(37), 6773–6779 (2009)
31. Li, H., Zou, L., Pan, L., Sun, Z.: Novel graphene-like electrodes for capacitive deionization.
Environ. Sci. Technol. 44(22), 8692–8697 (2010)
32. Mohanapriya, K., Ghosh, G., Jha, N.: Solar light reduced graphene as high energy density
supercapacitor and capacitive deionization electrode. Electrochim. Acta 209, 719–729 (2016)
33. Wang, H., Zhang, D., Yan, T., Wen, X., Zhang, J., Shi, L., Zhong, Q.: Three-dimensional macro-
porous graphene architectures as high performance electrodes for capacitive deionization. J.
Mater. Chem. A 1(38), 11778–11789 (2013)
34. Madani, S., Falamaki, C., Alimadadi, H., Aboutalebi, S.H.: Binder-free reduced graphene
oxide 3D structures based on ultra large graphene oxide sheets: high performance green micro-
supercapacitor using NaCl electrolyte. J. Energy Storage 21, 310–320 (2019)
35. Yang, Z.Y., Jin, L.J., Lu, G.Q., Xiao, Q.Q., Zhang, Y.X., Jing, L., Zhang, X.X., Yan, Y.M., Sun,
K.N.: Sponge-templated preparation of high surface area graphene with ultrahigh capacitive
deionization performance. Adv. Func. Mater. 24(25), 3917–3925 (2014)
36. Xu, X., Pan, L., Liu, Y., Lu, T., Sun, Z., Chua, D.H.: Facile synthesis of novel graphene sponge
for high performance capacitive deionization. Sci. Rep. 5(1), 1–9 (2015)
37. Li, Z., Song, B., Wu, Z., Lin, Z., Yao, Y., Moon, K.-S., Wong, C.: 3D porous graphene with
ultrahigh surface area for microscale capacitive deionization. Nano Energy 11, 711–718 (2015)
38. Kong, W., Duan, X., Ge, Y., Liu, H., Hu, J., Duan, X.: Holey graphene hydrogel with in-plane
pores for high-performance capacitive desalination. Nano Res. 9, 2458–2466 (2016)
39. Li, J., Ji, B., Jiang, R., Zhang, P., Chen, N., Zhang, G., Qu, L.: Hierarchical hole-enhanced 3D
graphene assembly for highly efficient capacitive deionization. Carbon 129, 95–103 (2018)
40. Chang, L., Hu, Y.H.: Surface-microporous graphene for high-performance capacitive deion-
ization under ultralow saline concentration. J. Phys. Chem. Solids 125, 135–140 (2019)
41. Wang, H., Yan, T., Liu, P., Chen, G., Shi, L., Zhang, J., Zhong, Q., Zhang, D.: In situ
creating interconnected pores across 3D graphene architectures and their application as high
performance electrodes for flow-through deionization capacitors. J. Mater. Chem. A 4(13),
4908–4919 (2016)
42. Ma, J., Wang, L., Yu, F.: Water-enhanced performance in capacitive deionization for
desalination based on graphene gel as electrode material. Electrochim. Acta 263, 40–46 (2018)
43. Dianbudiyanto, W., Liu, S.-H.: Outstanding performance of capacitive deionization by a
hierarchically porous 3D architectural graphene. Desalination 468, 114069 (2019)
44. Cao, J., Wang, Y., Chen, C., Yu, F., Ma, J.: A comparison of graphene hydrogels modified with
single-walled/multi-walled carbon nanotubes as electrode materials for capacitive deionization.
J. Colloid Interface Sci. 518, 69–75 (2018)
45. Aldalbahi, A., Rahaman, M., Almoiqli, M., Meriey, A.Y., Periyasami, G.: Efficiency improve-
ment of a capacitive deionization (CDI) system by modifying 3D SWCNT/RVC electrodes
using microwave-irradiated graphene oxide (mwGO) for effective desalination. J. Nanomater.
2020, 1–14 (2020)
46. Xu, X., Liu, Y., Wang, M., Zhu, C., Lu, T., Zhao, R., Pan, L.: Hierarchical hybrids with
microporous carbon spheres decorated three-dimensional graphene frameworks for capacitive
applications in supercapacitor and deionization. Electrochim. Acta 193, 88–95 (2016)
47. Gupta, S., Henson, A., Evans, B., Meek, R.: Graphene-based aerogels with carbon nanotubes as
ultrahigh-performing mesoporous capacitive deionization electrodes for brackish and seawater
desalination. Water Desal. Treat. 162, 97–111 (2019)
48. Zhang, C., Wang, X., Wang, H., Wu, X., Shen, J.: Ambient pressure-dried graphene–composite
carbon aerogel for capacitive deionization. Processes 7(1), 29 (2019)
49. Yin, H., Zhao, S., Wan, J., Tang, H., Chang, L., He, L., Zhao, H., Gao, Y., Tang, Z.:
Three-dimensional graphene/metal oxide nanoparticle hybrids for high-performance capacitive
deionization of saline water. Adv. Mater. 25(43), 6270–6276 (2013)
50. Gu, X., Yang, Y., Hu, Y., Hu, M., Huang, J., Wang, C.: Nitrogen-doped graphene composites
as efficient electrodes with enhanced capacitive deionization performance. RSC Adv. 4(108),
63189–63199 (2014)
51. Xu, X., Sun, Z., Chua, D.H., Pan, L.: Novel nitrogen doped graphene sponge with ultrahigh
capacitive deionization performance. Sci. Rep. 5(1), 11225 (2015)
52. Khan, Z.U., Yan, T., Shi, L., Zhang, D.: Improved capacitive deionization by using 3D interca-
lated graphene sheet–sphere nanocomposite architectures. Environ. Sci. Nano 5(4), 980–991
(2018)
53. Vafakhah, S., Sim, G.J., Saeedikhani, M., Li, X., y Alvarado, P.V., Yang, H.Y.: 3D printed
electrodes for efficient membrane capacitive deionization. Nanoscale Adv. 1(12), 4804–4811
(2019)
54. Han, B., Cheng, G., Wang, Y., Wang, X.: Structure and functionality design of novel carbon
and faradaic electrode materials for high-performance capacitive deionization. Chem. Eng. J.
360, 364–384 (2019)
55. Bo, Z., Huang, Z., Xu, C., Chen, Y., Wu, E., Yan, J., Cen, K., Yang, H., Ostrikov, K.K.:
Anion-kinetics-selective graphene anode and cation-energy-selective MXene cathode for high-
performance capacitive deionization. Energy Storage Mater. 50, 395–406 (2022)
56. Vafakhah, S., Guo, L., Sriramulu, D., Huang, S., Saeedikhani, M., Yang, H.Y.: Efficient
sodium-ion intercalation into the freestanding Prussian blue/graphene aerogel anode in a hybrid
capacitive deionization system. ACS Appl. Mater. Interfaces. 11(6), 5989–5998 (2019)
The Evolution of 3D Graphene and Its
Derivatives for Theranostic Applications
Aditya Srivastava, Akshit Rajukumar Prajapati, Sunil Venkanna Pogu,

and Aravind Kumar Rengan
Abstract Beginning with the humble pencil, graphene has evolved to play a vital
role in nanomedicine, particularly in the early detection of abnormalities and effec-
tive treatments thereof. Graphene and its derivatives have recently attracted much
interest in various fields, including biomedicine, due to their exceptional physical
and electrochemical properties. Owing to the high customizability, tuneability, and
potential to functionalize using multiple biomolecules, the prospect of graphene to
realize theranostic applications holds great promise for the advancement of modern
healthcare. Theranostic applications like biosensing, drug delivery, “hybrid theranos-
tics”, etc., benefit significantly from the said functionalization. This is because they
enhance graphene’s solubility, stability, and loading capacity, among other properties.
Recent applications also include multi-modal imaging and imaging-guided therapy,
particularly in the case of Cancer. In this chapter, various aspects of 3D graphene-
based theranostic modules, including fabrication and functionalization techniques,
have been discussed, along with multiple applications and advantages. The recent
advancements and challenges faced therein have also been elaborated upon.
Keywords 3D graphene · Graphene · Theranostics · Bioimaging · Graphene

oxide · Reduced graphene oxide · Quantum dots · Drug delivery · Photothermal
therapy · Photodynamic therapy
1 Introduction
In the case of materials sciences, almost all innovations and advances are the culmi-
nation of the merger between pre-existing technologies. The same is true for ther-
anostics, a field that extensively applies both materials science and biomedicine.
Despite the inherent complexity, theranostics is now one of the foremost strategies
for multifunctional nano-engineered systems, more so because of the incessant need
A. Srivastava · A. R. Prajapati · S. V. Pogu · A. K. Rengan (B)

Department of Biomedical Engineering, Indian Institute of Technology Hyderabad,
Telangana 502285, India
e-mail: aravind@bme.iith.ac.in
https://doi.org/10.1007/978-3-031-36249-1_23
410 A. Srivastava et al.
for novel theranostic modalities to facilitate fast and accurate diagnosis of complex
diseases. Theranostic modalities are rapid, cost-effective, and minimally invasive,
hence advantageous over traditional diagnosis strategies that are slow, tedious, and
costly. The said theranostic modalities must be not only extremely sensitive but also
highly specific to distinguish between diseases exhibiting similar biomarkers and
pathophysiology. These may also prove pivotal to the success of surgical interventions
by enabling accurate pre-surgical guidance imaging and post-surgical confirmation
of the absence of cancers.
Ever since the discovery of graphene in 2002 and the subsequent Nobel Prize
awarded for the same in 2010, various attempts have been made to determine the full
extent of the potential of graphene and derivatives thereof (alone or modified with
nanoparticles) in various advanced fields like quantum physics; nanoelectronics; and,
obviously, biomedicine [1]. Due to the versatility of its structure, it has rightfully been
called the “mother of all carbon materials”, as it is the prime component of numerous
carbon allotropes [2], and complex structures like carbon nanotubes (both single-
layered and multi-layered), graphene oxide (GO), reduced graphene oxide (rGO),
etc., and more carbon-based materials like “nanoribbons” [3] can be synthesized
from it. An added advantage is the ease of fabrication and cost-effectiveness of
these materials. Furthermore, a plethora of inorganic nanostructures can be cultivated
from nanographene due to its remarkable surface properties, giving rise to various
functional nanocomposites with equally impressive unique properties. Hence, it can
be said that graphene has the potential to be the precursor for multiple theranostic
modalities, some of which can also be multifunctional. In addition, various cargoes
like drugs, nucleic acids, biomolecules, chromophores, fluorescent probes, etc. can
be easily loaded onto graphene and its derivatives.
1.1 Strengths of Graphene
Graphene can be defined as a 2D monolayered, honeycomb-latticed nano-sheet of

sp2 hybridized carbons, having high intrinsic mobility. This unique arrangement
confers some supreme properties to graphene, making it a novel, promising thera-
nostic modality. Graphene nanostructures can be detected rapidly even at very low
sensitization, and the sensing is highly specific and precise [4]. Recently, graphene
nanostructures have even been employed in the diagnosis of COVID-19 [1]. Some
of the most prominent features of graphene have been enumerated as follows:
1. Ultra-high Surface Area: Single-layered graphene sheets have an extremely
high surface area because of the exposure of each atom, thereby providing
free bonds for efficacious molecular loading and biological conjugation. This
also opens graphene to functionalization, allowing the modifications to improve
biocompatibility, enabling biosensing and cargo delivery.
2. High Aromaticity: Graphene has an abundance of delocalized π electrons, which
significantly increase its aromaticity while also enabling functionalization and, in
The Evolution of 3D Graphene and Its Derivatives for Theranostic … 411
turn, loading of various cargoes like drugs, genes, biomolecules, and even thera-
peutic cells. Higher aromaticity in rGOs makes them better at photosensitization
than GOs.
3. Oxygen-containing Functional Groups: Most GOs and rGOs have an abun-
dance of defects and functional groups enriched with oxygen. This improves the
overall stability in a physiological sense and improves biological functionaliza-
tion. Oxygen-rich functional groups also have an enhancing effect on the solu-
bility of GOs. Graphene derivatives can easily be functionalized using polymeric
agents like PEG, chitosan, and even biomolecules like peptides and antibodies.
4. NIR and Fluorescent Optical Properties: Graphene and its derivatives show
impeccable inherent optical properties, both as fluorescent activity and NIR
range excitation. This makes them highly suited for biosensing, bioimaging,
and photothermal and photodynamic applications at both in vitro and in vivo
levels [5]. The excitation and emission characteristics can also be tailored during
synthesis [6]. The most common agents that can find use in fluorescence imaging
are carbon nanotubes and quantum dots.
5. Biocompatibility and Toxicity: Graphene (and derivatives thereof) shows high
biocompatibility and low toxicity but only after surface and size modifications,
as seen in a few in vivo studies [7], wherein the ADME characteristics of
nanographene were studied.
Apart from these properties, graphene also shows many intrinsic properties like
high conductivity; high sensitivity; selectiveness; intrinsic mobility [1]; and other
structural, optical, and electromagnetic properties surpassing other carbon and plas-
monic nanomaterials. Some structures have also been known to show photoacoustic
properties, enabling their usage in ultrasound-based therapies. Several attempts have
been made to enhance the passivation, solubility, and biocompatibility of graphene.
2 Classification and Fabrication of Common

Graphene-Based Theranostic Modalities
Several nanomaterials can be incorporated with graphene to create various nanosys-

tems, which can find use in a plethora of biomedical applications, and there are
numerous ways to obtain them. Classic examples of synthetic techniques include
exfoliation (both chemical and mechanical), GO reduction, chemical vapor deposi-
tion (CVD), and organic synthesis. Despite the persistent lack of consensus when it
comes to the classification of graphene-based theranostic modalities, some attempts
have been made by a few. A broad classification of the said modalities has been
shown in Fig. 1.
The synthesis of some common graphene-derivative theranostic materials has
been discussed as follows.
Fig.1 Overview of the classification of graphene-based theranostic modalities
2.1 Graphene-Based Metallic Nanocomposites
Metal nanoparticles are incorporated into graphene during synthesis to create inno-
vative nanocomposites and other hybrid materials. This enables the possibility of
nano-structuring remarkable nanoscale building blocks for new materials based on
graphene derivatives. While there are many ways to manufacture graphene, most of
them pose many stacking-related issues, which emerge from the consecutive layers
having intermediate Van der Waals interactions, resulting in a loss of many valu-
able properties, and decreased utility. This problem can easily be rectified by func-
tionalizing or modifying surface characteristics. These “stacking interactions” can
efficiently be culled using metal or metal oxide nanosystems [8].
A vast variety of fabrication techniques are applicable in the synthesis of graphene-

based metal nanocomposites, including bonding interactions (covalent or otherwise),
growth methods (hydrothermal or solvothermal), reduction, microwave irradiation,
and electrochemical deposition. It goes unsaid that each of these methods has its
own set of advantages and disadvantages, and the choice of fabrication method can
crucially affect the quality of the product obtained.
2.2 Graphene-Based Quantum Dots
“Graphene quantum dots”, or GQDs, are fundamentally composed of triangular, zero-

dimension (less than 10nm) forms of graphene. Drug delivery and theranostics benefit
from GQDs because of their robust quantum confinement and edge effects. If their
diameter is smaller than 30 nm, graphene balls produced from tens of graphene layers
can also be considered GQDs. GQDs are an attractive replacement for semiconductor
QDs, which are based on heavy metals. Compared to heavy metals, GQDs have been
proven to be far more stable, easy to prepare, and benign to the environment. It is
also possible to tailor GQDs for specific uses.
Carbon and hydrogen make up the bulk of the molecules in GQDs. GQDs can take
on a variety of shapes, including spherical, oval, hexagonal, and even pyramidal ones.
Carbonyl, carboxyl, hydroxyl, and epoxy groups, as well as the essential elements
(C, O, and H) found in graphene, can be introduced to the surface of GQDs. To create
GQDs having desired shapes, sizes, and homogeneity, attempts are being made to
develop various simple and environment-friendly methods.
2.2.1 Top-Down Approaches
In these methods, GQDs are formed by partitioning larger GO sheets into smaller
ones and rearrangement. Typical examples of such methods are chemical ablation
and exfoliation, electron beam lithography, acidic and hydrothermal exfoliation,
oxidation, laser ablation, etc.
2.2.2 Bottom-Up Approaches
In bottom-up methods, GQDs are built from organic molecular building blocks.
Examples of such strategies are carbonization of organic precursors, solution chem-
istry, comprehensive utilization strategy, solvothermal synthesis, ultrasonic method,
irradiation method, etc.
2.3 Graphene-Based Polymeric Nanocomposites
Nanomedicine has advanced leaps and bounds with the advent of novel modal-
ities like polymeric nanocomposites, graphene included. A multiphase solid
polymer nanocomposite has one phase with dimensions less than 100 nm. Poly-
meric nanocomposites contain therapeutic components in a polymer matrix. These
nanocomposites can be made from cellulose and derivatives thereof, PET, polyamides
and imides, polyethylene, and polycarbonates. In certain plastics, graphene can also
be employed as a nanofiller [9]. Polymeric nanocomposites’ physicochemical qual-
ities depend on the polymer graphene layer distribution in the polymer matrix, and
the interfacial connectivity. In its purest state, graphene does not produce composites
with complete consistency. Chitosan coating on GO reduced hemolysis and increased
erythrocyte compatibility [10].
The molecular weight, polarity, and hydrophobicity of the component mate-
rial may affect the preparation procedure. Numerous technologies have produced
polymer/graphite composites. Polymers are combined with graphite and intercalated
between graphite layers.
Standard methods to synthesize polymeric nanocomposites of graphene include
the non-covalent dispersion method, intercalation (solution-based or melting-based),
in situ polymerization, in situ emulsion polymerization, and compounding.
2.4 Graphene-Based Liposomal Nanocomposites
To emulate the fluid mosaic structure and cell membrane features, liposomes have
emerged as bio-inspired nano-platforms. Phospholipid-GO hybrids have only been
described in a small number of investigations, including some that reported GO func-
tionalized with a phospholipid monolayer, and studied its interactions with negatively
charged, positively charged, and neutral liposomes. When compared to neutral or
cationic liposomes, it was discovered that negatively charged liposomes were more
stable in an aqueous solution [11].
Sonicating graphite in a liposomal suspension is one of the simplest methods used
to create graphene-based liposomes. This is achieved due to the resultant nanoscale
sheets of graphene being produced by sonication, which are then sandwiched between
alkyl chains of phospholipids.
2.5 Graphene-Based Carbon Nanotubes (CNTs)

and CNT-Hybrids
1D carbon nanotubes (CNTs), like 2D graphene, have inspired theoretical and prac-
tical research due to their large surface area and biological versatility. CNTs are
certainly bigger in size and are structurally durable, but structural disruptions often
tend to reduce their electric conductivity. Graphene-carbon nanotube hybrid films
overcome this limitation, as graphene inhibits CNTs from clumping while carbon
nanotubes prevent graphene sheets from restacking, making the hybrid stable. Among
carbon nanostructures, graphene-CNT has the maximum edge density per unit area.
Single-walled or multi-walled CNT hybrids have a certain number of carbon layers
based on their diameter and catalyst size. Single-walled CNTs are usually cylin-
drical and 2–5 nm wide, whereas multi-walled CNTs are cylinders made of several
graphene layers with a diameter between 2 and 100 nm [12].
Numerous methods like ultrasonication, chemical vapor deposition (CVD),
layering-based assembly, or even self-assembly can be used to create graphene-CNT
hybrid nanomaterials.
2.6 Graphene Nanocrystal Hybrids
The term “nanocrystal” refers to any substance composed of a crystalline lattice while
being in the nanoscale range in at least one dimension. Graphene or its derivatives
can be conjugated, integrated physically, or bonded chemically to form nanocrystal
hybrids having the best of both worlds, i.e., the favorable characteristics of both parent
substances. Nanocrystals (NCs) adorn a core made of graphene, creating a hybrid
material with remarkable properties. Semiconducting nanocrystals can be made by
using materials having singular or multi-crystalline arrangements of atoms. This
particular arrangement confers various properties like broadened absorption bands,
and efficacy in signal transduction and conversion, which result in enhanced photo-
physical, photochemical, and biological properties. Graphene-nanocrystal hybrids
are now being studied for their potential in theranostics and targeted delivery.
Methods such as a direct method, oxidation method, in situ method, assembly
method, and solution phase synthesis can be used to synthesize nanocrystals.
2.7 Graphene-Based Biosensors
Graphene and its derivative materials are especially advantageous as biosensors,

owing to the transduction of various optical, thermal, and electrochemical signals
enabled by them. Thus, many graphene-based biosensors can be fabricated based on
the desired applicability and method of detection, with electrochemical biosensors
being used more frequently than optical biosensors [1]. Apart from cancer thera-
nostics, graphene-based biosensors are also being explored for other diseases like
Diabetes mellitus [13].
Direct coating is the most frequent method for making biosensors because it
is simple, cost-effective, and requires no special equipment [1]. In this method,
electrodes can be directly coated, as the name suggests, using a graphene-rich gel
or solution. Methods like blade coating, drip coating, spin coating, or drop-casting
can be chosen for this purpose, based on the desired effects. Other parameters like
surface area, film thickness, and homogeneity also play a key role in defining the
properties of the product. Despite being highly convenient, some have pointed toward
the wastefulness and time-consuming nature of this method [14].
Of late, 3D printers have introduced printing-based fabrication technologies.
Printing techniques are desirable because of large-scale fabrication, cost-savings,
and low processing temperature requirements, among other favorable factors, which
facilitate the convenient incorporation of materials such as graphene. Various 3D
printing methods like ink-jet or nozzle-jet printing, laser scribing, or screen printing
can be employed.
Growing nanoparticles on electrodes is another biosensor fabrication process.
This approach gained popularity due to adjustable manufacturing factors, which
include time-related, thermal, pH, barometric, and concentration-based parameters.
This method uses thermal, hydrothermal, and chemical degradation and anodization
to accelerate nanomaterial development on electrode surfaces [1]. Due to restricted
direct growth to the electrode surface, these approaches are given limited attention
for fabricating graphene-based biosensors.
3 Novel Graphene-Based Nanocomposites
Recent years have seen the rise of many hybrid modalities, wherein the most advan-
tageous properties of two or more systems (one of them being graphene based) have
been combined to obtain superior properties. The utility of these systems is certainly
not limited to theranostic applications but also tissue engineering and other such
fields.
Hydrogels are desirable due to their properties like high moldability and water
content. Add to that the structural reinforcement and other properties of graphene,
and we get superior hybrid hydrogels that compensate for the lack of biocompatibility
of graphene. These hybrid gels can act as scaffolds, model ECMs, with applicability
in wound healing purposes, and even as drug delivery models, among various other
applications [15].
Nowadays, a novel concept called “Organic dots” or “O-dots” has started gaining
momentum. O-dots are basically graphene and other carbon derivatives that are
dependent on other moieties like oxygen, hydrogen, and nitrogen for their optical
properties [6]. Owing to their minuscule sizes, O-dots have been known to be highly
photostable even after extended exposure to radiation. A variety of O-dots-based
hybrid nanosystems find use in cancer theranostics.
The shortcomings of traditional magnetic nanoparticles (MNPs) manifesting as a
lack of biocompatibility and overall low biofunctionalization can also be corrected
using graphene-based nanosystems. Carbon-based magnetic nanosystems have been
widely explored recently owing to their various interesting properties and potential
for synergistic and image-guided therapy. Hybrid graphene-MNPs combine the best
properties of both graphene and magnetic nanosystems, enabling utility in various

domains like biosensing, MRI, hyperthermia, etc. Other novel materials like graphene
nano-diamonds are also being explored [16].
4 Biocompatibility
The composition of graphene is mainly the carbon element, which is also a major
component of body biomolecules that reduces the chances of tissue toxicity and
its related complications. Multiple literature have reported the biocompatibility of
graphene materials using various in vitro and in vivo analyses. For example, Jian-
feng Li et al. bioprinted gelatine-supported alginate 3D scaffold coated with ascorbic
acid-reduced graphene oxide to evaluate its adhesion property and cytocompatibility
toward human adipose stem cells (ADSCs). It was found that reduced graphene oxide
displayed superior cytocompatibility and supported the proliferation and differen-
tiation of ADSCs (Fig. 2), which can be useful in autologous implant generation
[17]. Similarly, Lee et al. reported the biocompatibility of graphene quantum dots
(GQDs) against hepatocytes using a cell viability assay. It was found that GQDs-
treated hepatocytes displayed no variation in cell viability for 48 h of treatment,
and the extracellular aminotransferase, lactate dehydrogenase, and intracellular reac-
tive oxygen species concentration also remained similar to the untreated cells [18].
In another study, graphene-coated polyimide electrodes were fabricated and their
biocompatibility as a retinal implant was evaluated, and it was found that graphene-
coated electrodes were more biocompatible as compared to uncoated electrodes.
Through the histopathological studies, it was observed that graphene-coated elec-
trodes attracted or activated less number of microglial cells compared to uncoated
polyimide electrodes [19]. Another recent study has shown the enhanced biocom-
patibility of composite scaffolds with GOs, besides improvement in mechanical
properties for the development of bone scaffolds [20].
5 Theranostic Applications of 3D Graphene
Graphene and its derivatives have recently garnered much attention in the scien-
tific community due to its unique physical and chemical properties, including high
mechanical strength, thermal stability, and electrical conductivity. These proper-
ties make graphene a promising material for various applications in electronics,
energy, and biomedical fields. In recent years, 3D graphene-based nanostructures
have emerged as a new class of materials that combine the advantages of graphene
with those of 3D structures, making them ideal for use in theranostics. Theranostics,
a rapidly growing field, refers to the development of multifunctional materials that
can be used for both diagnosis and therapy of diseases, particularly cancer. Most of
these applications can broadly be classified as follows.
Fig. 2 Cell viability and adhesion on the 3D RGO/Alg scaffolds. Fluorescence microscope images
of live/dead ADSC staining on 3D RGO/Alg scaffolds from a rear view, b top view, and c cross-
sectional view following 7-day culture. Adapted with permission [17], Frontiers in Bioengineering
and Biotechnology
5.1 Imaging-Based Theranostics
There are various imaging modalities that stand to benefit from the inclusion of
graphene-based imaging agents. This is because of the excellent optical properties
of graphene, which make it highly suitable for imaging in vivo. MRI contrast imaging
is a widely used modality for cancer diagnosis and uses contrast agents to enhance the
visibility of tumors. Multiple studies have shown the potency of nanographene enti-
ties in MRI imaging, and even in synergy with photodynamic activity [21]. Photoa-
coustic imaging (PAI) is a newer imaging modality that combines light and sound
to generate images of biological tissues. Graphene-based nanostructures show high
photoacoustic activity, thereby facilitating efficient imaging. A recent study shows the
use of gallium-modified graphene nanobodies for photoacoustic and photothermal
activities [22]. The proposed nanosystem could convert more than 42% of the incident
light into heat.
Fluorescence imaging is a powerful tool for in vivo imaging, and can be used to
visualize biological tissues and cells. Graphene-based modalities have the potential
to further the progress of fluorescence imaging in cancer theranostics owing to the
enhanced binding of fluorescent probes, as demonstrated in recent attempts [23].
Safe and efficiently targeted imaging of tumors has also been demonstrated recently
using GO-based QDs [24].
X-ray CT imaging is a widely used diagnostic tool that uses X-rays to generate
images of internal tissues and organs. 3D graphene-based nanostructures have the
potential to act as contrast agents for X-ray CT imaging due to their high X-ray
absorption properties, as shown in recent research [25]. Anjusha et al. showed the
efficacy of amino acid-conjugated graphene nanosystems in simultaneous X-ray
CT imaging and PDT [26]. Certain multi-modal imaging platforms involving other
techniques like Positron Emission Tomography imaging have also been developed.
5.2 Therapy-Enabling Applications
In recent years, various therapeutic applications of 3D graphene-based nanostruc-

tures have been investigated, including photothermal therapy, photodynamic therapy,
hyperthermia therapy, chemotherapy, radiation therapy, immunotherapy, and gene
therapy. Photothermal therapy is a method in which 3D graphene-based nanostruc-
tures are utilized as photothermal converters to convert light energy into heat, thereby
destroying cancer cells. Quite literally, a vast number of graphene-based PTT agents
have been shown to have a high therapeutic index in cancer therapy. Examples of such
systems include both particulate and hydrogel-based PTT modalities [27, 28]. On
the other hand, photodynamic therapy is a method in which a photosensitizer is acti-
vated by light to produce reactive oxygen species that can destroy cancer cells. The
potential of graphene nanostructures to facilitate the same has been verified experi-
mentally [29]. Along similar lines, hyperthermia therapy is a method in which heat
is used to destroy cancer cells, which can also be enabled by various graphene-based
nanosystems.
Chemotherapy is a method in which drugs are used to destroy cancer cells. 3D
graphene-based nanostructures can be used to improve the efficacy of chemotherapy
drugs by increasing drug accumulation in cancer cells. This also coincides with
drug-delivery-related applications.
Radiation therapy is a method in which high-energy radiation is used to destroy
cancer cells. A recent study shows the implementation of the same in facilitating
terahertz wave ablation using a graphene-based antennary nanosystem [30].
Immunotherapy is a method in which the immune system is activated to fight
cancer cells. Graphene-based nanostructures can be used to improve immunotherapy
efficacy by enhancing antigen presentation and T-cell activation [31]. On the other
hand, gene therapy is a method in which genes are introduced into cells to treat
cancer. 3D graphene-based nanostructures can be used as gene delivery vehicles to
improve gene transfection efficiency and therapeutic efficacy [32].
5.3 Application in Drug Delivery
The surface characteristics of graphene enable high tunability and surface engi-
neering, which can be harnessed to facilitate the delivery of drugs and other active
agents. Targeted drug delivery refers to the delivery of drugs specifically to the site of
disease, such as a tumor, with the aim of maximizing therapeutic efficacy and mini-
mizing side effects. 3D graphene-based nanostructures have been functionalized with
targeting ligands such as antibodies, peptides, and small molecules to enhance their
specificity for cancer cells. For example, a recent study utilized a 3D graphene-
based nanostructure functionalized with folic acid to target and deliver doxoru-
bicin to cancer cells [33]. The nanostructure showed improved therapeutic efficacy
and reduced systemic toxicity compared to free doxorubicin while simultaneously
enabling imaging as well.
Similarly, imaging-guided drug delivery involves the use of imaging techniques
to monitor the distribution and efficacy of the therapeutic agents in real time. 3D
graphene-based nanostructures can be conjugated with imaging agents such as fluo-
rescent dyes, radionuclides, and near-infrared dyes to enable non-invasive imaging.
Such nanosystems can be used as highly efficient delivery systems, while also
providing the advantages of imaging.
Graphene-based nanomaterials are also highly applicable in developing various
diagnosing point-of-care devices as graphene itself is a good electrical signal
conductor. Concerning this, Tutku Beduk et al. developed a rapid point-of-care device
based on the laser-scribed graphene technique. This device detects the change in elec-
trical signal on the binding of the virus on antibody-coated gold nanostructures [34].
Similarly, Zahra et al. fabricated an aptamer-based biosensor using 3D graphene
hydrogel and gold nanoparticles composites for diagnosing breast cancer markers’
carcinoembryonic antigen (CEA) and cancer antigen 15–3 [35].
The excellent biocompatibility property of graphene-based material makes it suit-
able for disease diagnosis, drug delivery, and as a coating material for implants and
3D scaffolds (Fig. 3). In a study reported by Maria Romero et al., graphene oxide
nanocomposites coated with PEG-folic acid, Indocyanine green, and Rhodamine
B were synthesized. These nanocomposites were preferentially accumulated at tumor
region visualized using in vivo imaging techniques, and under NIR light irradiation,
nanocomposites displayed significant rise in temperature which aided in reducing the
tumor size [36]. Graphene oxide displays an antimicrobial property and coating these
on implants or surgical instruments can reduce the chances of microbial infection
occurring during the post-surgical period. Similar to these contexts, Sofia Melo et al.
fabricated poly caprolactone 3D scaffold with or without incorporating graphene
oxide. 3D scaffold with graphene oxide displayed more bactericidal effect against S.
epidermidis and E. coli and allowed adhesion of human cells [37]. Similarly, another
study reported that incorporating graphene oxide in polylactic acid-based scaffolds
had increased its cytocompatibility and mechanical properties [38].
6 Challenges and Shortcomings
According to recent market trends, 3D graphene theranostic systems have high

commercialization potential, with immense growth rates by 2023. However, their
commercialization certainly warrants the resolution of challenges that hinder their
full use [1]. Scaling and mass-producing graphene-based theranostic systems are
tedious and demand dedicated and skilled personnel for any significant pharmaco-
logical enterprise, which seems to be the prime cause for the lack of a clinically
Fig. 3 Theranostic applications of 3D graphene
significant product. The synthesis parameters, although minimalistic and thoroughly

explored, have a lot of anomalies and non-standardized protocols which in turn
lead to batch inconsistency [39]. Most recent research studies lack significant data
about various parameters like the size and stability of various systems. There are
various parameters that affect the biocompatibility, including timing of intervention,
release profiles, and even concentrations [40]. Size-toxicity relations are still not
fully understood, worsening the situation even further. Thus, a crucial optimization
of the said parameters needs to be done to establish and standardize protocols, only
after which the up-scaling and industrialization of therapeutic modalities are possible
[41]. This is not limited to synthesis alone—surface engineering and functionaliza-
tion approaches are still daunting for many [6]. This is further problematic because
the surface properties have a significant role in culling magnetic interactions and
preventing aggregation of nanosystems.
Perhaps the most challenging aspect of most graphene-based systems seems to
be that of toxicity and biocompatibility. Many of the recently published articles
have shown the potential of these systems in vitro, but fall short of results on
actual histological or in vivo levels [39]. Furthermore, such systems are also known
to frequently elicit inflammatory responses [16]. Many experts in this field have
reported weak fluorescence and photon yield [3] and false positives due to errant
or unintended surface characteristics [1], worsened by other disadvantages like low
solubility [42]. Magnetic nanoparticles have also been known to give false results,
especially in viability tests like the MTT assay [41]. Recently, significant questions
have been raised about the bioresponsiveness and rapid clearance of these systems
and the effect of exposure routes on immune response and toxicity [43]. Some studies
go even further, showing that these systems may be teratogenic or even foeticidal [44].
Incidences of disruption of membranes have also been reported in some cases [45].
Traditional in vivo approaches to screen for toxicity and other issues are limited by
financial and time-related confinements [46]. All these issues necessitate resolution
before these modalities can be put to clinical use without endangering the well-being
of the patient. Approaches like biomicrofluidics and stealth functionalization [47] can
be used as possible ways to achieve adequate biosafety. A recent study has shown the
amelioration of graphene toxicity using Ginsenoside Rg3 in a therapeutic approach
against liver and breast cancer cell lines [48]. Furthermore, in silico algorithms with
good predictability are also being developed, which can provide another layer of
validation for the development of new theranostic modalities [46].
7 Conclusion and Future Prospects
In recent years, graphene and its derivatives have been used as prime components to
develop multiple theranostic modalities [49]. Various methods have been discov-
ered for synthesizing the said systems, including both top-down and bottom-up
approaches. The many remarkable properties of these modalities make them rather
versatile and applicable in a diverse array of applications ranging from sensing and
diagnosis, to drug delivery and photosensitization-based therapies [50]. Various novel
systems like radio-labeled graphene and graphene nanoribbons have been proposed,
with great therapeutic potential. Other modalities like sonodynamic therapy [43]
and photoacoustic imaging [3] have also emerged as novel non-invasive theranostic
strategies. Graphene-based theranostic systems are superior because of the inherent
superior properties which enable tuneability and customization.
Despite the remarkable advantages and versatility associated with graphene-
derived systems, there are various drawbacks that hinder their full usage potential
and bench-to-bedside translation. Most of these hindrances are due to batch incon-
sistencies, dicey biocompatibility, and an overall inadequacy of clinically significant
research in this direction. However, this is being rectified by the numerous research
groups who are working on developing novel modalities and improving the existing
ones. Upconversion [42, 43], 3D-bioprinting, and green synthesis are only a few of
the new avenues being explored, apart from existing areas like synergistic therapy,
radiotherapy, and even photoacoustic and sonodynamic therapy. As most market
trends reveal, redressal of the drawbacks is well underway, and the day is not far
when graphene-based theranostic modalities will emerge with commercial success.
References
1. Alhazmi, H.A., Ahsan, W., Mangla, B., Javed, S., Hassan, M.Z., Asmari, M., Al Bratty, M.,
Najmi, A.: Graphene-based biosensors for disease theranostics: development, applications, and
recent advancements. Nanotechnol Rev. 11, 96–116 (2021)
2. Sharma, J., Sharma, S., Ajay, K., Sharma, L.K.: Role of graphene in biomedical applications.
Mater. Today Proc. 63, 542–546 (2022)
3. Lee, S.Y., Kwon. M., Raja. I.S., Molkenova. A., Han. D.W., Kim. K.S.: Graphene-based
nanomaterials for biomedical imaging, pp. 125–148 (2022)
4. Peña-Bahamonde, J., Nguyen, H.N., Fanourakis, S.K., Rodrigues, D.F.: Recent advances in
graphene-based biosensor technology with applications in life sciences. J Nanobiotechnol. 16,
75 (2018)
5. Cheung, F.: Engineering of new graphene-based materials as potential materials to assist near-
infrared photothermal therapy cancer treatment. Heliyon 6, e04131 (2020)
6. Shiralizadeh Dezfuli, A., Kohan, E., Tehrani Fateh, S., Alimirzaei, N., Arzaghi, H., Hamblin,
M.R.: Organic dots (O-dots) for theranostic applications: preparation and surface engineering.
RSC Adv. 11, 2253–2291 (2021)
7. Yang, K., Feng, L., Shi, X., Liu, Z.: Nano-graphene in biomedicine: theranostic applications.
Chem. Soc. Rev. 42, 530–547 (2013)
8. Manolata Devi, M., Sahu, S.R., Mukherjee, P., Sen, P., Biswas, K.: Graphene-metal nanoparticle
hybrids: electronic interaction between graphene and nanoparticles. Trans. Indian Inst. Met.
69, 839–844 (2016)
9. Das, T.K., Prusty, S.: Graphene-based polymer composites and their applications. Polym. Plast.
Technol. Eng. 52, 319–331 (2013)
10. Miculescu, M., Thakur, V.K., Miculescu, F., Voicu, S.I.: Graphene-based polymer nanocom-
posite membranes: a review. Polym. Adv. Technol. 27, 844–859 (2016)
11. Shim, G., Kim, M.-G., Park, J.Y., Oh, Y.-K.: Graphene-based nanosheets for delivery of
chemotherapeutics and biological drugs. Adv. Drug Deliv. Rev. 105, 205–227 (2016)
12. Shahriary, L., Ghourchian, H., Athawale, A.A.: Graphene-multiwalled carbon nanotube hybrids
synthesized by gamma radiations: application as a glucose sensor. J. Nanotechnol. 2014, 1–10
(2014)
13. Wang, C., Raza, S.A., Adebayo, T.S., Yi, S., Shah, M.I.: The roles of hydro, nuclear and biomass
energy towards carbon neutrality target in China: a policy-based analysis. Energy 262, 125303
(2023)
14. Sun, C.-L., Lai, S.-Y., Tsai, K.-J., Wang, J., Zhou, J., Chen, H.-Y.: Application of nanoporous
core–shell structured multi-walled carbon nanotube–graphene oxide nanoribbons in electro-
chemical biosensors. Microchem. J. 179, 107586 (2022)
15. Sangam, S., Garg, P., Sanyal, T., Pahari, S., Khurana, S.M.P., Mukherjee, M.: Graphene
quantum dots and their hybrid hydrogels: a multifaceted platform for theranostic applications.
In: Synthesis and Applications of Nanoparticles, pp. 417–453. Springer Nature Singapore,
Singapore (2022)
16. Jiang, H., Xia, C., Lin, J., Garalleh, H.A.L., Alalawi, A., Pugazhendhi, A.: Carbon nanomate-
rials: a growing tool for the diagnosis and treatment of diabetes mellitus. Environ. Res. 221,
115250 (2023)
17. Li, J., Liu, X., Crook, J.M., Wallace, G.G.: 3D printing of cytocompatible graphene/alginate
scaffolds for mimetic tissue constructs. Front. Bioeng. Biotechnol. 8, 1–11 (2020)
18. Lee, N.E., Jeong, J.M., Lim, H.S., Lee, S.Y., Cho, S.O.: Ultraviolet/blue light emitting high-
quality graphene quantum dots and their biocompatibility. Carbon NY 170, 213–219 (2020)
19. Nguyen, D., Valet, M., Dégardin, J., Boucherit, L., Illa, X., de la Cruz, J., del Corro, E., Bous-
quet, J., Garrido, J.A., Hébert, C., Picaud, S.: Novel graphene electrode for retinal implants:
an in vivo biocompatibility study. Front. Neurosci. 15, 1–10 (2021)
20. Sahafnejad-Mohammadi, I., Rahmati, S., Najmoddin, N., Bodaghi, M.: Biomimetic
polycaprolactone-graphene oxide composites for 3D printing bone scaffolds. Macromol. Mater.
Eng. 2200558 (2023)
21. Hassani, S., Gharehaghaji, N., Divband, B.: Chitosan-coated iron oxide/graphene quantum
dots as a potential multifunctional nanohybrid for bimodal magnetic resonance/fluorescence
imaging and 5-fluorouracil delivery. Mater. Today Commun. 31, 103589 (2022)
22. Zhang, Y., Guo, Z., Zhu, H., Xing, W., Tao, P., Shang, W., Fu, B., Song, C., Hong, Y., Dickey,
M.D., Deng, T.: Synthesis of liquid gallium@reduced graphene oxide core-shell nanoparticles
with enhanced photoacoustic and photothermal performance. J. Am. Chem. Soc. 144, 6779–
6790 (2022)
23. Chen, C.Y., Chiu, H.Y., Chang, S.J., Yeh, N.L., Chan, C.H., Shih, C.C., Chen, S.L., Yang,
J.W., Huang, C.Y., Chen, G.Y.: Enhanced probe bonding and fluorescence properties through
annealed graphene oxide nanosheets. ACS Biomater. Sci. Eng. (2022) acsbiomaterials 1c01044
24. Ouyang, A., Zhao, D., Wang, X., Zhang, W., Jiang, T., Li, A., Liu, W.: Covalent RGD–
graphene–phthalocyanine nanocomposite for fluorescence imaging-guided dual active/passive
tumor-targeted combinatorial phototherapy. J. Mater. Chem. B 10, 306–320 (2022)
25. Mirrahimi, M., Alamzadeh, Z., Beik, J., Sarikhani, A., Mousavi, M., Irajirad, R., Khani, T.,
Davani, E.S., Farashahi, A., Ardakani, T.S., Bulte, J.W.M., Ghaznavi, H., Shakeri-Zadeh,
A.: A 2D nanotheranostic platform based on graphene oxide and phase-change materials for
bimodal CT/MR imaging, NIR-activated drug release, and synergistic thermo-chemotherapy.
Nanotheranostics 6, 350–364 (2022)
26. Anjusha, A.J., Thirunavukkarasu, S., Resmi, A.N., Jayasree, R.S., Dhanapandian, S., Krish-
nakumar, N.: Multifunctional amino functionalized graphene quantum dots wrapped upconver-
sion nanoparticles for photodynamic therapy and X-ray CT imaging. Inorg. Chem. Commun.
149, 110428 (2023)
27. Costa, F.J.P., Nave, M., Lima-Sousa, R., Alves, C.G., Melo, B.L., Correia, I.J., de Melo-Diogo,
D.: Development of Thiol-Maleimide hydrogels incorporating graphene-based nanomaterials
for cancer chemo-photothermal therapy. Int. J. Pharm. 635, 122713 (2023)
28. Lei, Z., Fan, J., Li, X., Chen, Y., Shi, D., Xie, H., Liu, B.: Biomimetic graphene oxide quantum
dots nanoparticles targeted photothermal-chemotherapy for gastric cancer. J. Drug Target. 31,
320–333 (2023)
29. Vinothini, K., Dhilip Kumar, S.S., Abrahamse, H., Rajan, M.: Synergistic effect of polymer
functionalized graphene oxide system for breast cancer treatment. Int. J. Pharm. 632, 122556
(2023)
30. Geyikoglu, M.D., Koc, H., Çavusoglu, B., Ertugrul, M., Abbasian, K.: Designing graphene-
based antenna for terahertz wave ablation (TWA) system. Erzincan Üniversitesi Fen Bilimleri
Enstitüsü Dergisi 15, 507–514 (2022)
31. Shi, C., Fu, W., Zhang, X., Zhang, Q., Zeng, F., Nijiati, S., Du, C., Liu, X., Wang, M., Yao, Y.,
Huang, H., Zheng, N., Chen, X., Wu, B., Zhou, Z.: Boosting the immunoactivity of T cells by
resonant thermal radiation from electric graphene films for improved cancer immunotherapy.
Adv. Ther. (Weinh) 2200163 (2022)
32. Demirel, E., Yuksel Durmaz, Y.: PEGylated reduced graphene oxide as nanoplatform for
targeted gene and drug delivery. Eur. Polym. J. 186, 111841 (2023)
33. Kang, H., Wang, T., Liu, W., Tian, D.: Folic acid modified graphene quantum dots from konjac
glucomannan for cell imaging and targeted drug delivery. ChemistrySelect 7 (2022)
34. Beduk, T., Beduk, D., de Oliveira Filho, J.I., Zihnioglu, F., Cicek, C., Sertoz, R., Arda, B.,
Goksel, T., Turhan, K., Salama, K.N., Timur, S.: Rapid point-of-care covid-19 diagnosis with a
gold-nanoarchitecture-assisted laser-scribed graphene biosensor. Anal. Chem. 93, 8585–8594
(2021)
35. Shekari, Z., Zare, H.R., Falahati, A.: Dual assaying of breast cancer biomarkers by using a sand-
wich–type electrochemical aptasensor based on a gold nanoparticles–3D graphene hydrogel
nanocomposite and redox probes labeled aptamers. Sens. Actuators B Chem. 332, 129515
(2021)
36. Romero, M.P., Buzza, H.H., Stringasci, M.D., Estevão, B.M., Silva, C.C.C., Pereira-Da-
silva, M.A., Inada, N.M.: Bagnato versus graphene oxide theranostic effect: conjugation of
photothermal and photodynamic therapies based on an in vivo demonstration. Int. J. Nanomed.
16, 1601–1616 (2021)
37. Melo, S.F., Neves, S.C., Pereira, A.T., Borges, I., Granja, P.L., Magalhães, F.D., Gonçalves,
I.C.: Incorporation of graphene oxide into poly(E-caprolactone) 3D printed fibrous scaffolds
improves their antimicrobial properties. Mater. Sci. Eng. C 109 (2020)
38. Belaid, H., Nagarajan, S., Teyssier, C., Barou, C., Barés, J., Balme, S., Garay, H., Huon,
V., Cornu, D., Cavaillès, V., Bechelany, M.: Development of new biocompatible 3D printed
graphene oxide-based scaffolds. Mater. Sci. Eng. C 110, 110595 (2020)
39. Roy, S., Jaiswal, A.: Graphene-based nanomaterials for theranostic applications. Rep. Adv.
Phys. Sci. 01, 1750011 (2017)
40. Huang, S., Zhong, Y., Fu, Y., Zheng, X., Feng, Z., Mo, A.: Graphene and its derivatives: “one
stone, three birds” strategy for orthopedic implant-associated infections. Biomater. Sci. 11,
380–399 (2023)
41. Lage, T., Rodrigues, R.O., Catarino, S., Gallo, J., Bañobre- López, M., Minas, G.: Graphene-
based magnetic nanoparticles for theranostics: an overview for their potential in clinical
application. Nanomaterials 11, 1073 (2021)
42. Kansara, V., Tiwari, S., Patel, M.: Graphene quantum dots: a review on the effect of synthesis
parameters and theranostic applications. Colloids Surf B Biointerfaces 217, 112605 (2022)
43. Geetha Bai, R., Ninan, N., Muthoosamy, K., Manickam, S.: Graphene: a versatile platform for
nanotheranostics and tissue engineering. Prog Mater Sci 91, 24–69 (2018)
44. Xu, S., Zhang, Z., Chu, M.: Long-term toxicity of reduced graphene oxide nanosheets: effects
on female mouse reproductive ability and offspring development. Biomaterials 54, 188–200
(2015)
45. Liao, C., Li, Y., Tjong, S.: Graphene nanomaterials: synthesis, biocompatibility, and cytotoxi-
city. Int. J. Mol. Sci. 19, 3564 (2018)
46. Wang, T., Russo, D.P., Bitounis, D., Demokritou, P., Jia, X., Huang, H., Zhu, H.: Integrating
structure annotation and machine learning approaches to develop graphene toxicity models.
Carbon NY 204, 484–494 (2023)
47. Belling, J.N., Jackman, J.A., Yorulmaz Avsar, S., Park, J.H., Wang, Y., Potroz, M.G., Ferhan,
A.R., Weiss, P.S., Cho, N.-J.: Stealth immune properties of graphene oxide enabled by surface-
bound complement factor H. ACS Nano 10, 10161–10172 (2016)
48. Rahimi, S., van Leeuwen, D., Roshanzamir, F., Pandit, S., Shi, L., Sasanian, N., Nielsen, J.,
Esbjörner, E.K., Mijakovic, I.: Ginsenoside Rg3 reduces the toxicity of graphene oxide used
for pH-responsive delivery of doxorubicin to liver and breast cancer cells. Pharmaceutics 15,
391 (2023)
49. Zhang, L., Dong, Q., Zhang, H., Xu, J., Wang, S., Zhang, L., Tang, W., Li, Z., Xia, X., Cai,
X., Li, S., Peng, R., Deng, Z., Donovan, M.J., Chen, L., Chen, Z., Tan, W.: A magnetocat-
alytic propelled cobalt–platinum@graphene navigator for enhanced tumor penetration and
theranostics. CCS Chem. 4, 2382–2395 (2022)
50. Atiyah, N.A., Albayati, T.M., Atiya, M.A.: Functionalization of mesoporous MCM-41 for the
delivery of curcumin as an anti-inflammatory therapy. Adv. Powder Technol. (2022)
Toxicity, Stability, Recycling, and Risk
Assessments
Raunak K. Tamrakar, Kanchan Upadhyay, Judith Gomes, and Sunil Kumar
Abstract As the production of graphene has increased and its range of uses has
expanded, worries about the possible harmful effects that its derivative nanoparticles
and materials may have on human health have come to the fore. Numerous studies
have demonstrated that graphene, in whatever shape it takes, affects a wide range of
living things. Prokaryotic bacteria, viruses, plants, micro- and macro-invertebrates,
mammalian and human cells, and whole creatures in vivo are some of these organ-
isms. However, there is frequently a great deal of disagreement, if not outright
controversy, regarding the results of the studies that have been carried out. As a
result, we present in this paper a critical analysis of the most recent reports that have
been gathered in the area of the biocompatibility and toxicology of materials related
to graphene. Our objective is to provide information on the most current develop-
ments, new trends, and potential career opportunities in this area. Graphene exposure
scenarios like inhalation through the respiratory system, ingestion through the diges-
tive tract, administration via the parenteral route, and topical exposure through the
skin are examined in the context of the experiment results using a variety of in vitro
and in vivo model systems.
Keywords Graphene · Graphene derivatives · Health · Environment · Cytotoxicity
1 Introduction
Carbonaceous nanomaterials are being used in an increasing number of applications,

thoroughly evaluating the risks associated with them and identifying strategies to
reduce those risks of the utmost importance from the standpoint of human health and
safety. Since the announcement of the Nobel Prize in this field in 2010, graphene
has been at the forefront of 2D representatives and as such deserves a special level
of merit and scrutiny. In many publications, graphene toxicity has been explored in
R. K. Tamrakar (B) · K. Upadhyay · J. Gomes · S. Kumar

Bhilai Institute of Technology (Seth Balkrishan Memorial), Near Bhilai Power House, Durg,
Chhattisgarh, India
e-mail: rounak.tamrakar@bitdurg.ac.in; raunak.ruby@gmail.com
https://doi.org/10.1007/978-3-031-36249-1_24
428 R. K. Tamrakar et al.
terms of various issues including synthesis method, environmental exposure, tissue

engineering, biological applications, its physiochemical behavior, a new system for
nano-drug delivery, and its use in the advanced treatment or as a theranostic tool [1].
The toxicity study of the 3D graphene material has not been studied in detail;
however, new experimental evidence shows that our current understanding of the
biocompatibility, toxicity, and potential applications of graphene-based nanomate-
rials is still lacking clarity and, at times, even controversy. This is due in large part to
the wide variety of graphene forms currently on hand, but it is also attributable
to differences in experimental setups and approaches between research centers.
Graphene is a 2D carbon nanomaterial consisting of a single layer, and it is char-
acterized by the formation of strong covalent bonds between its constituent carbon
atoms in sp2 hexagonal networks [2]. These hexagonal networks are the building
blocks of 3D graphite, while 2D carbon nanotubes are created by rolling up sheets.
Graphene materials have different dimensions and are interconnected with each other
as described in Fig. 1. When comparing the edge effects and surface chemistries of
these materials, we will find that they are vastly distinct. It is the edges and defects
in graphene that facilitate bio-interactions, but the hydrophilic surface of graphene
oxide makes it a stable dispersion in water [3]. We have attempted to provide a more
thorough overview of the most recent developments in this field here in order to
cast light on the cutting-edge trends and future prospects in the field of graphene-
related biocompatibility and toxicology. Graphene and its derivatives are being used
more frequently in advanced structures and technologies for applications in elec-
tronics, catalysis, computing, and health care. In this situation, one must consider
the potentially harmful effects of graphene materials on the environment and human
health when released from the devices at the end of their useful lives, with a focus
primarily on the assessment of potential risks connected to the individual components
and implemented materials of the devices themselves. The idea behind a number of
novel drug delivery methods is that the drug will come into direct touch with human
cells either after topical application or after systemic administration. The identifica-
tion and characterization of the potential hazards are anticipated to make use of the
maximum physicochemical characterization of the questioned nanomaterial, which
includes physicochemical factors.
However, there are numerous safety concerns surrounding graphene materials.
Although the potential toxicity of GBMs has been brought to light, there are only a
small number of toxicity studies available, and the threat they pose to human health
is largely unexplored. Workplace exposure to GBMs appears to pose the greatest
threat to human health at this time, while their uses are still in the testing phase.
Humans are most likely to be exposed to GBMs during industrial or small-scale
production and waste discharge through inhalation, cutaneous, and ocular routes due
to the proximity of the respiratory tract, skin, and eyes to the work environment. It
is also possible to ingest GBMs through secondary inhalation and accidental oral
ingestion.
A thorough description and classification for 3D graphene architectures have
not yet been established, despite the rapid development of 3D graphene materials
over the past 10 years and the exploration of many new synthesis techniques and
Toxicity, Stability, Recycling, and Risk Assessments 429
Fig. 1 Relationships among graphene, 2D graphene materials, 3D graphene materials, and graphite.
Reproduced with permission [1], Copyright 2020, American Chemical Society
application fields. It’s true despite the fact that both of those things have been tried.
Furthermore, there were clear differences in the features of 3D graphene materials
made with various methods, leading to a wide range of performances when applied
to various contexts. The formation mechanism for each 3D graphene family and the
key steps that influence the properties of the 3D architectures must all be thoroughly
understood in order to fine-tune the functionalization of a 3D graphene structure
and maximize its performance for specific applications. Several excellent reviews of
methods for producing large, three-dimensional graphene monoliths were published
in the early years of the field (one type of 3D graphene materials). The most recent,
relevant studies have primarily focused on 3D graphene-based composite materials
for a variety of applications. Further research into the 3D graphene family is still
needed [4].
The safe and effective management of nanoparticles is a topic that must be revis-
ited frequently to ensure that any risks to respiratory health are mitigated or elimi-
nated. As graphene nanomaterials continue to gain in popularity, it’s important that
information about potential risks and how to mitigate them is regularly updated and
made accessible. And this is even though studies are being run on the topic. In this
chapter, we assess the potential for mitigating the risks associated with graphene-
based materials, and we look at ways to do so, such as by making use of graphene’s
physicochemical properties, surface modifications, and potential catabolic degra-
dation pathways. Finally, we offer an in-depth evaluation of recent developments
in health care, diagnostics, and novel therapeutic approaches that are enabled by
graphene.
2 Toxicity and Exposure Route of Graphene-Based

Nanoparticles
Different exposure methods or routes of administration allow GFNs to enter the

body or cells, where they can cause toxicity both in vivo and in vitro (Fig. 2). The
degree of GFN toxicity may depend on factors such as the administration route, the
route of entry, the tissue distribution and excretion, and the pattern of cell uptake [4].
Therefore, it may be useful to clarify them in order to better comprehend the rules
governing the emergence and evolution of GFNs’ toxicity.
For the most comprehensive toxicological information, bio-persistence and accu-
mulation patterns of nanomaterials as well as the effects of acute and chronic long-
term exposure need to be fully investigated. In light of the aforementioned factors,
we assess the most current information on the toxicity of graphene.
2.1 Respiratory Exposure
One of the most probable exposure routes is through the respiratory system (inhala-
tion), with potential applications in both industrial manufacturing settings and in the
event that graphene is unintentionally exposed to people through the environment.
Han et al. [5] investigated the effects of a single 6-h nasal inhalation method at doses
of 0.46 and 3.76 mg/m3 on the lungs of Sprague–Dawley rats. Following graphene
exposure, there were no appreciable changes in body weight, food intake, or organ
weight during the 2-week recovery interval. The findings of the study demonstrate
Fig. 2 Exposure route of graphene materials. Adapted from [4]. Copyright © 2021 Asmaa
Rhazouani et al. This is an open-access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided
the original work is properly cited
that even at concentrations that are relatively high in comparison to the possible real-
istic environmental equivalent, graphene oxide’s pulmonary toxicity is low following
either a single dose or a series of doses over an extended period of time.
In order to investigate the potential pro-inflammatory effects of graphene
nanoplatelets and their accumulation in the mediastinal lymph nodes of rats, a
different intratracheal instillation paradigm and the context of variable surface func-
tionalization of nanomaterials by carboxylic acid groups were used. Even though it
was discovered that all particle types had dose-dependent, unidirectional impacts,
only the positively charged graphene nanoplatelets significantly increased neutrophil
counts after 24 h. In other words, the acute pro-inflammatory effect that was noticed
was not sustained, and cell counts had already returned to normal by the end of the
first week. No matter how the surface charge was modified, nanomaterial eventually
built up in the local lymph nodes [6]. It is clear that there is an urgent need for
researchers in the field to agree on a long-awaited unified approach to dose-exposure
calculations in nanotoxicology studies, including those involving animals. This is
because different authors in the aforementioned studies estimated exposure dose in
different ways.
2.2 Oral Exposure
In Sprague–Dawley rats, the effects of oral graphene oxide doses varying from 10 to
40 mg/kg have been studied [7]. The findings demonstrated that superoxide dismu-
tase, catalase, and glutathione peroxidase activities increased in the kidneys of rats
in a dose-dependent manner and that the accumulation of hydrogen peroxide and
lipid hydroperoxide was also substantially elevated. All in all, these results provide
strong evidence for oxidative stress’s role in inducing nephrotoxicity in experimental
animals, calling for more thorough research into the topic. The authors suggest that
reduced graphene oxide exposure may have an influence on the activity of serum
superoxide dismutase, which may explain the transient changes in the animals’
behavior observed after ingestion of the compound. In contrast, there is hardly any
evidence that a person’s explorer, anxious, learner, or memory behaviors alter [8].
However, it is difficult to extrapolate from these reports the conceivable exposure
doses for humans in the workplace or through consumer products.
This is the first major study to determine the effects of administering multi-
layered pristine graphene intragastrically to mice on a daily basis for 4 weeks. It
was surprising to learn, in light of the review’s discussion of graphene’s antibacterial
properties, that exposure to the material increased the diversity of gut microbiota and
shifted the microbial community in favor of G-bacteria. This may be due to the fact
that different microorganisms are more or less sensitive to oxidative stress and have
varying degrees of membrane stability after coming into contact with graphene.
Antibiotic-resistant genes in the gut microbiota of mice were found to be signifi-
cantly more numerous and diverse after exposure to graphene. The results of this
study should be considered in the development of new graphene-based drugs for oral
administration, and similar groundbreaking discoveries are likely to be made in the

near future.
2.3 Cutaneous Exposure
The literature is growing in favor of the utilization of graphene nanomaterials in

cutting-edge applications for various skin-related issues which include wearable
skin sensors, diagnostic devices, and transdermal patches for medicine delivery,
tissue engineering, and regenerative systems [9]. While it is common knowledge that
carbonaceous nanomaterials are associated with an elevated risk of skin illnesses.
Surprisingly little research has been done into the impacts of graphene on dermal toxi-
city and the functional state of its cellular components in vivo. Out of all the studies
only one has reported that the antibacterial cotton textiles infused with graphene oxide
were found to be over 90% effective against bacteria even after being washed 100
times without causing irritation to rabbit skin [10]. The impacts of graphene and its
derivatives, such as PEGylated graphene oxide/polypropylene fumarate nanocom-
posites, on dermal fibroblasts, an important cellular component of the skin, have
only been studied in vitro so far. In both studies, graphene was determined to be safe
for fibroblasts. However, Wang et al. [11] discovered that graphene oxide actually
inhibits the adhesion, cytotoxicity, and apoptosis of human fibroblasts at concentra-
tions higher than 50 g/mL. More research is required because this exposure scenario
is still largely unexplored, particularly in light of the conflicting experimental data
that are presently available.
2.4 Intravenous Exposure
Graphene oxide’s acute and chronic dose-dependent toxicity in mice following

systemic intravenous administration was previously reported by Wang et al. In animal
studies, no acute or chronic toxicity was observed at doses up to 0.25 mg/animal. At a
higher dose of 0.4 mg/animal graphene accumulated inside the organs due to insuffi-
cient clearance, causing chronic toxicity manifestations like lung granuloma forma-
tion [11]. There was no accumulation of unmodified, pristine few-layered graphene
in the brain, heart, or testes after 3 months of monitoring in a study using similar high
doses (20 mg/kg). Regardless of the surface chemistry, the accumulation of graphene
materials in the organs caused significant cellular and organ damage, as evidenced by
the development of necrotic and fibrotic foci and dysfunction in glomerular filtration.
Recently, comparable outcomes were seen after injecting graphene oxide func-
tionalized with poly sodium 4-styrene sulfonate into the veins. This injected graphene
material shows persistent accumulation for 6 months inside the internal organs liver,
lungs, etc. and results in chronic specific organ inflammation. By using a novel
administration method, intraperitoneal parenteral, Kurantowicz et al. investigated
the biodistribution of several carbonaceous nanomaterials. The connective tissue of

the epidermis, muscles, and peritoneum of the abdominal cavity, as well as the injec-
tion location, all contained significant aggregates of the nanomaterials [12]. Despite
the significance of these findings from a mechanistic and experimental standpoint,
this route of administration is unlikely to be used in humans.
3 Biological Fate of Graphene Materials
A number of variables, including administration methods, physicochemical charac-

teristics, particle agglomeration, and surface coating, have a major influence on
the biological fate including biodistribution, biotransformation, and excretion of
graphene materials. The effect of graphene materials on different organs has been
shown in Fig. 3. After giving mice GO intravenously, Zhang et al. [13] found that
the substance was securely retained in a number of organs, including the lungs, liver,
spleen, and bone marrow. GO caused pulmonary edema in rodents when administered
intravenously at a dose of 10 mg/kg body weight [13]. Due to its increased chem-
ical reactivity, GO can be biotransformed to significantly alter its physicochemical
properties [14]. Qi and coworkers demonstrated that GO could undergo a substantial
physicochemical transformation in Gamble’s solution and artificial lysosomal fluid,
both of which mimic human lung fluids (ALF). The carbonyl and epoxy groups in
GO were converted to phenolic groups after being treated with lung fluids, resulting
in a smaller molecule. This alteration got rid of macrophages, which slowed down
the endocytosis of GO. In addition, the changes occurring in Gamble’s solution
lessened GO’s interaction with cells and allowed for its precipitation. But modifi-
cations to the ALF improved the adhesion of large sheet-like GO aggregates to the
plasma membrane in the absence of cell uptake [15]. Biotransformation of GO in
blood plasma has been shown to affect toxicity, according to other studies. Analyses
of metabolic pathways revealed that biotransformation mitigated oxidative stress
caused by GO by primarily modifying fatty acid metabolism and decreasing galac-
tose metabolism. New research has shown that the interaction of GO particles with
the digestive fluids and the acidic pH of the stomach causes them to aggregate.
Oral absorption of GO does not result in biotransformation, as no structural changes
or degradation have been observed [16]. In different organs, GO is eliminated in
different ways. Difficult to clear from the lungs, GO triggers inflammation, cell infil-
tration, granuloma formation, and pulmonary edema. Following the bile duct from
the duodenum, GO nanoparticles are excreted from the body via the hepatobiliary
pathway in the liver [17]. The functional derivatives of GO polyethylene glycol tend
to build up in the liver, while the spleen can be eliminated gradually, most likely via
the kidneys and fecal excretion. Although the precise mechanisms by which GO is
excreted in vivo remain unclear, it appears that the kidneys and the intestines play a
significant role in its elimination. There have been a number of conflicting findings
about where and how much of this nanomaterial is excreted so far.
Fig. 3 Toxic effect of graphene oxide in different organs. Adapted from [4]. Copyright © 2021
Asmaa Rhazouani et al. This is an open-access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited
Sasidharan et al. prepared FLG and two of its derivatives (carboxylated FLG-
COOH and PEGylated FLG-PEG) to investigate the biodistribution of these
compounds over a 24-h period (lateral dimension: 100,200 nm, thickness: 0.8 nm)
[18]. FLG-COOH accumulated more in the lungs than FLG-PEG did anywhere else
over the period of 24 h, whereas FLG-PEG accumulated in the lungs first and then
moved on to the liver and spleen. To assess their biodistribution in both small and
large GO sheets, researchers in another study intravenously injected mice with 125I-
labeled GO sheets for 180 min. It was discovered that small GO had a longer blood
circulation period than large GO. While only a trace amount of small GO sheets were
identified in the lungs and spleen, they accumulated mainly in the liver (with a peak
at 5 min and a gradual decline through 180 min) rapidly disappearing from these
organs [19].
All told, these studies have helped researchers better understand the fate of
different GBMs after being administered in different ways. Several different GBMs
have been shown to overcome normal physiological barriers and spread to distant
secondary organs. However, it is still too soon to draw definitive conclusions with
respect to relationships between physicochemical features and the biodistribution
patterns of GBMs due to the paucity of published data and the lack of systematic
investigations. What happens to GBMs over time at the site where they tend to
accumulate is also crucial. To generate such information, however, is not simple; it
necessitates labeled materials that can be followed and measured quantitatively over
extended periods of time, even as GBMs undergo biotransformation or degradation

within the body.
4 Toxicity Mechanism
One of the key elements significantly affecting the biocompatibility of nanomate-

rials, independent of their ex-synthesis composition, is biocorona formation upon
contact with the biological milieu, which contains a broad range of biomolecules,
including a profusion of proteins. Since the word was first coined nearly 10 years ago,
numerous reports have established the significance of the phrase “protein corona”
for the functional behavior of nanoparticles and their ensuing effects at the cellular
and organismal levels [20].
However, a nanoparticle core containing a coat of surface functionalized
substances can also significantly affect the biocorona’s dynamic makeup. It was
discovered that one instance of a surface change that improves biocompatibility
in vitro and in vivo involves the functionalization of GO with PAA (poly acrylic
acid). When compared to the pristine or PEGylated graphene oxide nanomaterials,
this surface modification significantly decreased the cytotoxicity and other significant
biological and pathological changes in the internal organs of mice that are typically
induced by graphene oxides. According to the authors’ hypotheses, differences in
the amount of platelet depletion in blood, the formation of thrombi during short-term
exposure, and the known pro-inflammatory effects following long-term exposure are
caused by the different protein corona compositions, particularly immunoglobulin
G, which form on the surface of nanoparticles and regulate their interactions with
cell membranes and cellular uptake [21]. These findings are in line with research
suggesting that covering graphene oxide with a protein like BSA can lessen the cyto-
toxicity of the material by preventing it from penetrating cell membranes. Due to
a reduction in accessible surface area and unfavorable steric effects, the interaction
between the graphene surface and the phospholipids in the cell membrane is reduced
in order to achieve this [22]. Similar to this, it was discovered using a simulation-
based molecular dynamics method that graphene oxide strongly binds to proteins
via pi-pi stacking interactions with aromatic protein residues. This raised the theo-
retical possibility of reduced cytotoxicity of reduced graphene oxide nanosheets and
graphene oxide after coating with major high abundance blood proteins, a finding
that has since been experimentally verified [23].
However, it is still debatable and uncertain exactly how the biocorona’s compo-
sition affects the toxicity of graphene. In light of this, the possibility of reducing the
toxicity of these biological secretions was complexed with graphene, which resulted
in modified nanoplatelets.
4.1 Risk Assessment Methods
Risks and uncertainties related to the commercialization of graphene-enabled prod-

ucts (GEP) need to be evaluated thoroughly on a macro-, micro-, and nano-scale
basis. In particular, it is essential to reduce risks associated with development costs,
regulatory requirements, and environmental concerns before introducing novel mate-
rials and products to the market (i.e., health and safety aspects). Since graphene is an
advanced material with many potential uses, it can be difficult to determine whether
or not the material poses any significant risks to consumers, workers, or the envi-
ronment. The aforementioned discussion also shows that GEP can vary widely in its
physicochemical properties depending on the application to which it is ultimately
put. As a result, GEP risk assessment can be very time-consuming and resource-
intensive if dedicated separately to each product. Due to this, the scientific, indus-
trial, and regulatory communities have been working very hard over the past 10
years to develop the necessary characterization cascades, quality assurance tools, and
frameworks for risk assessments, management, and monitoring of emerging products
containing advanced materials. Most of the time, the improvement is linked to some
characteristic of the materials being used that operates at the nano-scale [24].
The incorporation of a tiered safe-by-design method [25] can be used as a de-
risking strategy to identify uncertainties and risks during the early stages of GEP
development. Standardization of graphene characterization is necessary for improved
customer trust, reproducibility, and quality assurance. In addition, the risk assessment
procedure can be prioritized with the help of newly introduced safety thresholds for
each GEP component. Those who pose the greatest health risks are screened first, as
this is where the bulk of the data is gathered and analyzed. Dekkers et al. developed
a non sepcific risk assesment strategy [26] and put into practice for the benefit of
consumers and, in the case of medical goods, patients.
4.2 Optimal Physical and Chemical Properties
The best way to reduce the dangers brought on by graphene exposure depends
on a number of important considerations. By utilizing basic physical properties,
graphene’s toxicity is influenced by how much of it has been oxidized; less oxidized
graphene has been shown to produce more reactive oxygen species, cytotoxicity,
and apoptosis, which can have a big impact. One of the most recent and intriguing
findings is the possibility of making use of the chiral characteristics of graphene
quantum dots.
4.3 Surface Functionalization
It has been demonstrated that coating with chitosan is one of the earliest documented
simple methods to reduce the harmful impact of graphene oxide on red blood cells
and is a nearly 100% effective method of eliminating this type of toxicity [27]. Recent
research suggests that the hydrophilicity and weak inductive nature of a novel hydrox-
ylated graphene derivative promote cell adhesion and growth of stromal cells derived
from rat adipose tissue. Because of the ease of this method, industrial quantities of
this graphene derivative can be produced in the kilogram range [28]. It has been
demonstrated that amine-modified graphene oxide is a much safer functionalized
material than its unmodified graphene oxide or reduced graphene oxide counterparts
in terms of its possible thrombogenic and hemolytic effects in mice in vivo [29].
4.4 Modified Degradation
GO nanoparticles tweaked with PEG and branched PEE when introduced in biolog-
ical systems as nano-drug carriers join plasmid DNA through electrostatic interac-
tion to create a stable nano-complex. After being absorbed by cells, the complex can
quickly leave endosomes by photothermally converting graphene oxide after being
exposed to near-infrared light and causing endosome disruption. The reduced intra-
cellular environment enables polymer dissociation and rapid gene release, increasing
transfection efficacy and lowering toxicity when compared to non-reducible amide-
functionalized graphene nanocarriers. Additionally, the exposed disulfide bonds in
the de-PEGylated graphene oxide nanocarriers boost phagocyte engulfment and facil-
itate macrophage degradation [30]. In order to create biocompatible and seemingly
biodegradable structures with the potential to act as sensitive T2 contrast agents,
Zan et al. have created a novel technique for creating water-dispersible nanocom-
posites with iron oxide nanoparticles attached to graphene. These composites are
non-toxic, according to the writers, because the body’s metabolic processes excrete
them [31]. As the biodegradation process, in this case, was only related to the iron
oxide component of the complex, this study emphasizes the importance of imple-
menting the aforementioned safe-by-design approach [25], which must be strictly
adhered to from the very early stages of the development of new nanomedicines in
relation to all the constituent components. It ensures that cutting-edge diagnostic and
therapeutic preparations are risk-free, successful in healing their intended cells, and
have the least possible impact on unrelated cells.
5 Stability and Sustainability of 3D Graphene
Graphene is an extraordinary substance; it has been hailed as a wonder substance

with the potential to revolutionize the entire industry. The potential to revolutionize
entire sectors and our built environment lies in a one-atom-thick layer of carbon that
is 200 times stronger than steel, transparent, flexible, and extremely thermally and
electrically conductive. Thus, we can say graphene carries the property of higher
conductivity, higher mechanical strength than steel, and a dense packing structure
along with the flexibility of modifying them in the form of other nanotubes. This
makes a tremendous impact in every field, whether it is a medical, chemical, or any
other industrial application. Graphene has been praised as one of the most important
material advancements since the plastics revolution more than a century ago since
its discovery in 2004. Early predictions suggested that the kinds of goods and tech-
nologies are seen in science fiction movies would almost instantly be made possible
by graphene. After more than 15 years, that has yet to take place [32].
Graphene is a form of carbon that could bring us bulletproof armor and space
elevators, improve medicine, cell phone batteries, headphones, and even bridges
and make the Internet run faster. In 15 years of the journey of graphene and its
applicability, consumers have been hearing about this wonder material and all the
ways it could change everything. Graphene opened a new window in materials science
in 3D materials and has enormous properties and has the potential to use in electronics
in aerospace industries. The main constraint is its mass production and production
cost [33]. The main reason why manufacturing doesn’t produce the desired products
is that growth frequently only produces thin flakes of various sizes. There are a lot
of tiny flakes, but we need big sheets so that we can use them for electronics. But
that’s really challenging. The flash technique only produces flakes, as do the items
shown, which is useful if you need just flakes for some reason. The biggest advance,
however, will come from the production of huge sheets of pure single-layer graphene.
Although many people are working on it, nobody has had much luck with it [34].
From solar cells to computer chips, graphene is set to disrupt many industries.
This is because the biggest hurdle to overcome is not science but mass production.
There are several companies working on graphene materials to be used in a vast array
of markets. These companies are on the cutting edge and getting closer by the day to
unlocking the key to mass-producing graphene. Sustainability is now a priority, and
we should concentrate on graphene applications that already separate waste from
other waste streams, applications that can increase the operational lifetime, and inte-
gration with materials from which graphene can be recovered most easily [34]. As
a sustainable material, graphene has enormous potential. This includes sustainable
methods of producing graphene from either natural or waste sources, as well as using
graphene to reduce material usage (and reducing the carbon footprint of these mate-
rials in the process). Many people talk about graphene in high-tech applications,
but it is in these fundamental applications where graphene can be used as an addi-
tive that the graphene market will be propelled forward. 3D graphene is expected
to be a sustainable, autonomous wearable devices that could be biodegradable or
compostable and would rely on Graphene Flagship developments in the electronic

components, powering of the device, and also the sensors which are integrated into
that device in years to come. Future graphene research anticipates new directions as
the demand for environmental protection and sustainable alternatives grows. So, we
know graphene hasn’t changed the world yet but is truly on the verge of skyrocketing
the changes by revolutionizing the world. The future of graphene appears bright, but
we must ensure that the world we live in is taken into account when making decisions
about graphene applications.
6 Conclusion and Future Prospects
Graphene is a wonder material with properties like a diamond, 200 times stronger
than steel, has high elasticity, is lighter than aluminum, and is a pure substance that
has a very large surface area and carries some semi-conductor properties and can be
stretched 20 to 25% of its original length. Graphene with such quality can be mixed
with other materials to make extraordinary composites. Graphene has a very high
thermal conductivity ratio which is even better than that of silver and copper and
even has good electrical conductivity. Due to its flat hexagonal lattice structure, it
has low resistance and hence has electrical conductivity 13 times higher than that
of copper and very near to that of superconductors. Graphene has higher electron
mobility as compared to semi-conductors like silicon and thus is very useful in the
electronic industry on a large scale and it will revolutionize the electronic industry
and technology as a whole. Graphene is super thin and almost completely transparent
and can transmit 97 to 99% of light and hence has super optical properties, thus in the
future it can be used in the optical industry and even can be used as a perfect material
for solar panels, LCDs, touch screens, etc. Graphene is already started being used in
new forms of energy storage devices like supercapacitors and water filters and can
reduce pressure on the planet by helping us turn ocean water into safe drinking water.
With constraints of mass production for commercial purposes, it is expected that
bottom-up and top-down graphene production methods will solve the commercial
production of graphene in coming years with the different types of graphene, and
very soon in coming years, we can expect to see the different types of graphene in
products.
References
control. Chem. Rev. 120, 10336–10453 (2020)
2. Malard, L.M., Pimenta, M.A., Dresselhaus, G., Dresselhaus, M.S.: Raman spectroscopy in
graphene. Phys. Rep. 473, 51–87 (2009)
3. Russier, J., Treossi, E., Scarsi, A., Perrozzi, F., Dumortier, H., Ottaviano, L., Meneghetti, M.,
Palermo, V., Bianco, A.: Evidencing the mask effect of graphene oxide: a comparative study
on primary human and murine phagocytic cells. Nanoscale 5, 11234–11247 (2013)
4. Asmaa, R., Halima, G., Mounir, E.A., Khalid, A., Lhoucine, G., Md Sahab, U., Faissal, A.:
Synthesis and toxicity of graphene oxide nanoparticles: a literature review of in vitro and in vivo
studies. BioMed Res. Int. 2021 (2021), Article ID 5518999
5. Han, S.G., Kim, J.K., Shin, J.H., Hwang, J.H., Lee, J.S., Kim, T.G., Lee, J.H., Lee, G.H., Kim,
K.S., Lee, H.S., Song, N.W., Ahn, K., Yu, I.J.: Pulmonary responses of sprague-dawley rats in
single inhalation exposure to graphene oxide nanomaterials. Biomed. Res. Int. 2015, 376756
(2015)
6. Lee, J.K., Jeong, A.Y., Bae, J., Seok, J.H., Yang, J.Y., Roh, H.S., Jeong, J., Han, Y., Jeong,
J., Cho, W.S.: The role of surface functionalization on the pulmonary inflammogenicity and
translocation into mediastinal lymph nodes of graphene nanoplatelets in rats. Arch. Toxicol.
91(2), 667–676 (2016)
7. Patlolla, A.K., Randolph, J., Kumari, S.A., Tchounwou, P.B.: Toxicity evaluation of graphene
oxide in kidneys of sprague-dawley rats. Int. J. Environ. Res. Public Health 13, 380–388 (2016)
8. Zhang, D., Zhang, Z., Liu, Y., Chu, M., Yang, C., Li, W., Shao, Y., Yue, Y., Xu, R.: The short-
and long-term effects of orally administered high-dose reduced graphene oxide nanosheets on
mouse behaviors. Biomaterials 68, 100–113 (2015)
9. Ding, X., Liu, H., Fan, Y.: Graphene-based materials in regenerative medicine. Adv. Healthc.
Mater. 4, 1451–1468 (2015)
10. Zhao, J., Deng, B., Lv, M., Li, J., Zhang, Y., Jiang, H., Peng, C., Li, J., Shi, J., Huang, Q., Fan,
C.: Graphene oxide-based antibacterial cotton fabrics. Adv. Healthc. Mater. 2(9), 1259–66
(2013)
11. Wang, K., Ruan, J., Song, H., Zhang, J., Wo, Y., Guo, S., Cui, D.: Biocompatibility of graphene
oxide. Nanoscale Res. Lett. 6, 8 (2011)
12. Kurantowicz, N., Strojny, B., Sawosz, E., Jaworski, S., Kutwin, M., Grodzik, M., Wierzbicki,
M., Lipinska, L., Mitura, K., Chwalibog, A.: Biodistribution of a high dose of diamond graphite,
and graphene oxide nanoparticles after multiple intraperitoneal injections in rats. Nanoscale
Res. Lett. 10, 398 (2015)
13. Zhang, X., Yin, J., Peng, C., Hu, W., Zhu, Z., Li, W., Fan, C., Huang, Q.: Distribution and
biocompatibility studies of graphene oxide in mice after intravenous administration. Carbon
49, 986–995 (2011)
14. Raslan, A., Burgo, L.S.D., Ciriza, J., Pedraz, J.L.: Graphene oxide and reduced graphene
oxide-based scaffolds in regenerative medicine. Int. J. Pharm. 580, 119226 (2020)
15. Qi, Y., Liu, Y., Xia, T., Xu, A., Liu, S., Chen, W.: The biotransformation of graphene oxide
in lung fluids significantly alters its inherent properties and bioactivities toward immune cells.
NPG Asia Mater. 10(5), 5385–5396 (2018)
16. Guarnieri, D., Sánchez-Moreno, P., Del Rio Castillo, A.E., Bonaccorso, F., Gatto, F., Bardi,
G., Martín, C., Vázquez, E., Catelani, T., Sabella, S., Pompa, P.P.: Small 14, 1800227 (2018)
17. Hirn, S., Semmler-Behnke, M., Schleh, C., Wenk, A., Lipka, J., Schäffler, M., Takenaka, S.,
Möller, W., Schmid, G., Simon, U., Kreyling, W.G.: Particle size dependent and surface charge-
dependent biodistribution of gold nanoparticles after intravenous administration. Eur. J. Pharm.
Biopharm. 77(3), 407–416 (2011)
18. Sasidharan, A., Swaroop, S., Koduri, C.K., Girish, C.M., Chandran, P., Panchakarla, L.S.,
Somasundaram, V.H., Gowd, G.S., Nair, S., Koyakutty, M.: Comparative in vivo toxicity,
organ biodistribution and immune response of pristine, carboxylated and PEGylated few-layer
graphene sheets in swiss albino mice: a three month study. Carbon 95, 511–524 (2015)
19. Liu, J.-H., Yang, S.-T., Wang, H., Chang, Y., Cao, A., Liu, Y.: Effect of size and dose on the
biodistribution of graphene oxide in mice. Nanomedicine 7, 1801–1812 (2012)
20. Volkov, Y.: Quantum dots in nanomedicine: recent trends, advances and unresolved issues.
Biochem. Biophys. Res. Commun. 468, 419–27 (2015)
21. Xu, M., Zhu, J., Wang, F., Xiong, Y., Wu, Y., Wang, Q., Weng, J., Zhang, Z., Chen, W.,
Liu, S.: Improved in vitro and in vivo biocompatibility of graphene oxide through surface
modification: poly(acrylic acid)-functionalization is superior to PEGylation. ACS Nano 10,
3267–3281 (2016)
22. Duan, G., Kang, S.G., Tian, X., Garate, J.A., Zhao, L., Ge, C., Zhou, R.: Protein corona mitigates
the cytotoxicity of graphene oxide by reducing its physical interaction with cell membrane.
Nanoscale 7, 15214–15224 (2015)
23. Chong, Y., Ge, C., Yang, Z., Garate, J.A., Gu, Z., Weber, J.K., Liu, J., Zhou, R.: Reduced
cytotoxicity of graphene nanosheets mediated by blood-protein coating. ACS Nano 9, 5713–
5724 (2015)
24. Mu, L., Gao, Y., Hu, X.: Characterization of biological secretions binding to graphene oxide
in water and the specific toxicological mechanisms. Environ. Sci. Technol. 50(16), 8530–8537
(2016)
25. Movia, D., Gerard, V., Maguire, C.M., Jain, N., Bell, A.P., Nicolosi, V., O’Neill, T., Scholz,
D., Gun’ko, Y., Volkov, Y., Prina-Mello, A.: A safe-by-design approach to the development of
gold nanoboxes as carriers for internalization into cancer cells. Biomaterials 35, 2543–2557
(2014)
26. Dekkers, S., Oomen, A.G., Bleeker, E.A., Vandebriel, R.J., Micheletti, C., Cabellos, J., Janer,
G., Fuentes, N., Vazquez-Campos, S., Borges, T., Silva, M.J., Prina-Mello, A., Movia, D.,
Nesslany, F., Ribeiro, A.R., Leite, P.E., Groenewold, M., Cassee, F.R., Sips, A.J., Dijkzeul, A.,
van Teunenbroek, T., Wijnhoven, S.W.: Towards a nanospecific approach for risk assessment.
Regul. Toxicol. Pharmacol. 80, 46–59 (2016)
27. Liao, K.H., Lin, Y.S., Macosko, C.W., Haynes, C.L.: Cytotoxicity of graphene oxide and
graphene in human erythrocytes and skin fibroblasts. ACS Appl. Mater. Interfaces 3, 2607–2615
(2011)
28. Sun, J., Deng, Y., Li, J., Wang, G., He, P., Tian, S., Bu, X., Di, Z., Yang, S., Ding, G., Xie,
X.: A new graphene derivative: hydroxylated graphene with excellent biocompatibility. ACS
Appl. Mater. Interfaces 8, 10226–10233 (2016)
29. Singh, S.K., Singh, M.K., Kulkarni, P.P., Sonkar, V.K., Gracio, J.J., Dash, D.: Amine-modified
graphene: thrombo-protective safer alternative to graphene oxide for biomedical applications.
ACS Nano 6, 2731–2740 (2012)
30. Kim, H., Kim, J., Lee, M., Choi, H.C., Kim, W.J.: Stimuli-regulated enzymatically degrad-
able smart graphene-oxide-polymer nanocarrier facilitating photothermal gene delivery. Adv.
Healthc. Mater. 5, 1918–1930 (2016)
31. Zan, P., Yang, C., Sun, H., Zhao, L., Lv, Z., He, Y.: One-pot fabricating Fe3 O4 /graphene
nanocomposite with excellent biocompatibility and non-toxicity as a negative MR contrast
agent. Colloids Surf. B Biointerfaces 145, 208–16 (2016)
32. Barbhuiya, N.H., Kumar, A., Singh, A., Chandel, M.K., Arnusch, C.J., Tour, J.M., Singh, S.P.:
The future of flash graphene for the sustainable management of solid waste. ACS Nano 15(10),
15461–15470 (2021)
33. Shukla, S., Khan, I., Bajpai, V.K., Lee, H., Kim, T., Upadhyay, A., Tripathi, K.M.: Sustainable
graphene aerogel as an ecofriendly cell growth promoter and highly efficient adsorbent for
histamine from red wine. ACS Appl. Mater. Interfaces 11, 18165−18177 (2019)
34. Zhang, X., Wang, L., Lu, Q., Kaplan, D.L.: Mass production of biocompatible graphene using
silk nanofibers. ACS Appl. Mater. Interfaces 10, 22924–22931 (2018)

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Carbon Nanostructures

ISSN 2191-3005 ISSN 2191-3013 (electronic)

3D Graphene Structures for the Removal of Pharmaceutical

Chuanyin Xiong, Tianxu Wang, Yongkang Zhang, and Qing Xiong

Abstract The 3D graphene-based materials fabricated by various methods not only

Keywords 3D graphene · Classification · Preparation · Application

Graphene is a 2D carbon material with a hexagonal honeycomb lattice structure

C. Xiong (B) · T. Wang · Y. Zhang · Q. Xiong

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 1

1.1 3D Graphene Nanoribbons

Graphene nanoribbons refer to graphene nanomaterials with a width of less than

1.2 3D Graphene Powder

3D graphene powder appears macroscopically in a powder state, but microscopi-

1.3 3D Graphene Spheres

3D graphene spheres can be prepared by a template method and self-assembly. Zhang

Fig. 2 a Schematic representation of the structure of 3D graphene nanoribbons. Adapted with

1.4 3D Graphene Fibers

3D graphene fibers can be prepared by electrospinning, wet spinning, electrophoresis,

fibers by electrospinning, NH3 etching, and CVD combination. The preparation

1.5 3D Graphene with a Hierarchical Structure

The preparation of 3D graphene with layered structure by separating 2D graphene

1.6 3D Graphene Foam

1.7 3D Graphene Aerogel

performance by the hydrothermal method. Figure 2h is a schematic diagram of the

This section systematically summarizes and classifies the preparation methods of 3D

2.1 CVD Growth of 3D Graphene

2.1.1 CVD Growth Based on a Metal Template

Metal templates can be used as catalysts to accelerate the decomposition of hydro-

Fig. 3 Preparation method of 3D graphene

2.1.2 CVD Growth Based on a Non-metal Template

2.1.3 Growth of 3D Graphene by PECVD

Through PECVD, hydrocarbons can be pyrolyzed at relatively low temperatures, and

2.2 Preparation of 3D Graphene by Self-Assembly Method

Self-assembly is a method of self-assembly of 2D graphene materials into 3D

2.2.1 Thermal Reduction

Thermal reduction, the elimination of oxygen-containing functional groups on GO by

2.2.2 Hydro/Solvothermal Reduction

The initial purpose of hydrothermal reduction is to reduce GO to rGO tablets. With

2.2.3 Chemical Reduction Induction

2.2.4 Electrochemical Reduction

GO sheets will be electrochemically reduced near the cathode and deposited on

3D printing is an efficient method to directly construct large-volume objects. First,

2.4 3D Laser-Induced Graphene (3D LIG)

3D LIG is a kind of 3D graphene formed by laser irradiation of polymer precursors

Han et al. [28] directly synthesized 3D graphene on polymer-based polyimide by a

2.5 Pyrolytic Organic Precursors

Pyrolysis of organic precursors is a method of direct pyrolysis of organic molecules

3.1 Energy Conversion

3.1.1 Solar-Thermal Conversion

3.2 Energy Storage

Li–ion batteries (LIBs)

on graphene aerogel(SnS2 @GA) for high-performance sodium–ion batteries [34].

With the rapid development of global industrialization and urbanization, environ-

3.3.1 Water Decontamination

3.3.2 Gas Adsorption

With the deepening of human industrialization, the problem of natural environ-

3.5.1 Gas Sensor

3.5.2 Strain Sensor

Graphene can be used appropriately as a strain and pressure sensor. In graphene

3.5.3 Other Sensors