Search Results (295)

Tea waste contains various substances with phenolic hydroxyl groups, including lignin, tannins, tea polyphenols, etc., which are rarely utilized. In this study, tea waste was directly dispersed with graphene oxide to prepare tea waste/reduced graphene oxide (TW/rGO) hydrogel through a one-step hydrothermal method. The prepared hydrogel presented a continuous three-dimensional porous structure and exhibited good mechanical properties with a compressive strength of 53.4 ± 4.0 kPa. It also showed excellent electrochemical performance as an electrode material. Its specific capacitance reached 434.7 F g⁻¹ at a current density of 1 A g⁻¹, and its capacitance retention was 55.8% when the current density was increased to 100 A g⁻¹. In addition, an TW/rGO assembled all-solid-state supercapacitor demonstrated a superior specific capacitance of 372.8 F g⁻¹ and a competitive energy density of 12.9 Wh kg⁻¹ at 1 A g⁻¹. Full article

Flexible supercapacitors (SCs), as promising energy storage devices, have shown great potential for both next-generation wearable electronics and addressing the global energy crisis. Conductive hydrogels (CHs) are suitable electrode materials for flexible SCs on account of their intrinsic characteristics and functional advantages, such as a unique 3D porous structure, remarkable conductivity, tunable chemical and physical properties, and outstanding mechanical properties. Herein, an overview of the fabrication strategies for CHs as electrode materials in flexible SCs, as well as their advantages and disadvantages, and perspectives on CH-based SCs is provided. First, the fabrication strategies for CHs are systematically introduced. Second, various multifunctional CH-based SCs are presented and discussed. Finally, this review concludes with insights into the challenges and opportunities related to CHs or CH-based SCs, indicating future research prospects and application orientations in this field. Full article

Needle-like CoO nanowires have been successfully synthesized by a facile hydrothermal process on an electrospun carbon nanofibers substrate. The as-prepared sample mesoporous CoO nanowires aligned vertically on the surface of carbon nanofibers and cross-linked with each other, producing loosely porous nanostructures. These hybrid composite electrodes exhibit a high specific capacitance of 1068.3 F g⁻¹ at a scan rate of 5 mV s⁻¹ and a good rate capability of 613.7 F g⁻¹ at a scan rate of 60 mV s⁻¹ in a three-electrode cell. The CoO NWs@CNF//CNT@CNF asymmetric device exhibits remarkable cycling stability and delivers a capacitance of 79.3 F/g with a capacitance retention of 92.1 % after 10,000 cycles. The asymmetric device delivers a high energy density of 37 Wh kg⁻¹ with a power density of 0.8 kW kg⁻¹ and a high power density of 16 kW kg⁻¹ with an energy density of 23 Wh kg⁻¹. This study demonstrated a promising strategy to enhance the electrochemical performance of flexible supercapacitors. Full article

The continuously growing penetration of renewable energy sources (RESs) in electrical networks provides increasing challenges and critical situations to be managed by worldwide system operators. Due to their features and variability, non-programmable RES power plants, whose increasing penetration reduces the inertia level of the power system, may determine the instability effects on the grids, especially from the frequency and voltage regulation standpoints. The present study focuses on the support that advanced FACTS (Flexible Alternating Current Transmission System) devices, such as STATCOMs (Static Synchronous Compensators), can provide to the power system operation in terms of system inertia improvement, frequency stability, and voltage stability. In particular, a review of the scientific literature and practice is performed, with the aim of benchmarking the ongoing evolution of these technologies, also comparing them with different options based on synchronous condensers, synchronous condensers integrated with flywheels, and STATCOMs with supercapacitors. The outcome of the analysis consists of an updated evaluation of the state-of-the-art technological development in the field and of a comparison between different FACTSs with the purpose of identifying the most suitable solutions for different practical situations, also taking account of synergies across various options. This study includes an updated overview regarding the status of STATCOM installation in the Italian power grid. Full article

In the field of contemporary epidermal bioelectronics, there is a demand for energy supplies that are safe, lightweight, flexible and robust. In this work, double-network polymer hydrogels were synthesized by polymerization of 3,4-ethylenedioxythiophene (EDOT) into a poly(vinyl alcohol)/poly(ethylene glycol diacrylate) (PVA/PEGDA) double-network hydrogel matrix. The PEDOT-PVA/PEGDA double-network hydrogel shows both excellent mechanical and electrochemical performance, having a strain up to 498%, electrical conductivity as high as 5 S m⁻¹ and specific capacitance of 84.1 ± 3.6 mF cm⁻². After assembling two PEDOT-PVA/PEGDA double-network hydrogel electrodes with the free-standing boron cross-linked PVA/KCl hydrogel electrolyte, the formed supercapacitor device exhibits a specific capacitance of 54.5 mF cm⁻² at 10 mV s⁻¹, with an energy density of 4.7 μWh cm⁻². The device exhibits excellent electrochemical stability with 97.6% capacitance retention after 3000 charging–discharging cycles. In addition, the hydrogel also exhibits great sensitivity to strains and excellent antifouling properties. It was also found that the abovementioned hydrogel can achieve stable signals under both small and large deformations as a flexible sensor. The flexible and antifouling PEDOT-PVA/PEGDA double-network hydrogel-based supercapacitor is a promising power storage device with potential applications in wearable electronics. Full article

It is difficult for carbonaceous materials to combine a large specific surface area with flexibility. Here, a flexible all-carbon nanoarchitecture based on the in situ growth of nanoporous graphene within “skeletal-capillary” carbon nanotube (CNT) networks has been achieved by a chemical vapor deposition (CVD) process. Multi-path long-range conductivity is established, and the porous graphene provides a large specific surface area for charge storage. The flexibility of the films allows them to be directly used as binder-free electrodes for supercapacitors. Since the polymeric binders are saved, the supercapacitors exhibit a higher overall storage density. Full article

In recent years, the demand for solid, thin, and flexible energy storage devices has surged in modern consumer electronics, which require autonomy and long duration. In this context, hybrid supercapacitors have become strategic, and significant efforts are being made to develop cells with higher energy densities while preserving the power density of conventional supercapacitors. Motivated by these requirements, we report the development of a new high-performance dual-redox-mediator supercapacitor. In this study, cells were constructed using fully moldable buckypapers (BPs), composed of carbon nanotubes and cellulose nanofibers, as electrodes. We evaluated the compatibility of BPs with hydrogel polymer electrolytes, based on 1 mol L⁻¹ H₂SO₄ and polyvinyl alcohol (PVA), supplemented with different redox species: methylene blue, indigo carmine, and hydroquinone. Solid cells were constructed containing two active redox species to maximize the specific capacity of each electrode. Considering the main results, the dual-redox-mediator supercapacitor exhibits high energy density of 32.0 Wh kg⁻¹ (at 0.8 kW kg⁻¹) and is capable of delivering 25.9 Wh kg⁻¹ at high power demand (4.0 kW kg⁻¹). Stability studies conducted over 10,000 galvanostatic cycles revealed that the PVA polymer matrix benefits the system by inhibiting the crossover of redox species within the cell. Full article

The decline in fossil fuels on the earth has become a primary global concern which has urged mankind to explore other viable alternatives. The exorbitant use of fuels by an ever-increasing global population demands a huge production of energy from renewable sources. Renewable energy sources like the sun, wind, and tides have been established as promising substitutes for fossil fuels. However, the availability of these renewable energy sources is dependent on weather and climatic conditions. Thus, this goal can only be achieved if the rate of energy production from renewable sources is enhanced under favorable weather conditions and can be stored using high energy storing devices for future utilization. The energy from renewable sources is principally stored in hydropower plants, superconducting magnetic energy storage systems, and batteries. Full article

Given the pressing climate and sustainability challenges, shifting industrial processes towards environmentally friendly practices is imperative. Among various strategies, the generation of green, flexible materials combined with efficient reutilization of biomass stands out. This review provides a comprehensive analysis of the hydrothermal carbonization (HTC) process as a sustainable approach for developing carbonaceous materials from biomass. Key parameters influencing hydrochar preparation are examined, along with the mechanisms governing hydrochar formation and pore development. Then, this review explores the application of hydrochars in supercapacitors, offering a novel comparative analysis of the electrochemical performance of various biomass-based electrodes, considering parameters such as capacitance, stability, and textural properties. Biomass-based hydrochars emerge as a promising alternative to traditional carbonaceous materials, with potential for further enhancement through the incorporation of extrinsic nanoparticles like graphene, carbon nanotubes, nanodiamonds and metal oxides. Of particular interest is the relatively unexplored use of transition metal dichalcogenides (TMDCs), with preliminary findings demonstrating highly competitive capacitances of up to 360 F/g when combined with hydrochars. This exceptional electrochemical performance, coupled with unique material properties, positions these biomass-based hydrochars interesting candidates to advance the energy industry towards a greener and more sustainable future. Full article

The global transportation sector is rapidly shifting towards electrification, aiming to create more sustainable environments. As a result, there is a significant focus on optimizing performance and increasing the lifespan of batteries in electric vehicles (EVs). To achieve this, the battery pack must operate with constant current charging and discharging modes of operation. Further, in an EV powertrain, maintaining a constant DC link voltage at the input stage of the inverter is crucial for driving the motor load. To satisfy these two conditions simultaneously during the energy transfer, a hybrid energy storage system (HESS) consisting of a lithium–ion battery and a supercapacitor (SC) connected to the semi-active topology of the bidirectional DC–DC converter (SAT-BDC) in this research work. However, generating the duty cycle for the switches to regulate the operation of SAT-BDC is complex due to the simultaneous interaction of the two mentioned constraints: regulating the DC link voltage by tracking the reference and maintaining the battery current at a constant value. Therefore, this research aims to efficiently resolve the issue by incorporating a highly flexible nonlinear model predictive control (NMPC) to control the switches of SAT-BDC. Furthermore, the converter system design is tested for operational performance using MATLAB 2022B with the battery current and the DC link voltage with different priorities. In the NMPC approach, these constraints are carefully evaluated with varying prioritizations, representing a crucial trade-off in optimizing EV powertrain operation. The results demonstrate that battery current prioritization yields better performance than DC link voltage prioritization, extending the lifespan and efficiency of batteries. Thus, this research work further aligns with the conceptual realization of the sustainability goals by minimizing the environmental impact associated with battery production and disposal. Full article

We review recent results on textile triboelectric nanogenerators (T-TENGs), which function both as harvesters of mechanical energy and self-powered motion sensors. T-TENGs can be flexible, breathable, and lightweight. With a combination of traditional and novel manufacturing methods, including nanofibers, T-TENGs can deliver promising power output. We review the evolution of T-TENG device structures based on various textile material configurations and fabrication methods, along with demonstrations of self-powered systems. We also provide a detailed analysis of different textile materials and approaches used to enhance output. Additionally, we discuss integration capabilities with supercapacitors and potential applications across various fields such as health monitoring, human activity monitoring, human–machine interaction applications, etc. This review concludes by addressing the challenges and key research questions that remain for developing viable T-TENG technology. Full article

Composite track-etched membranes (CTeMs) emerged as a versatile and high-performance class of materials, combining the precise pore structures of traditional track-etched membranes (TeMs) with the enhanced functionalities of integrated nanomaterials. This review provides a comprehensive overview of the synthesis, functionalization, and applications of CTeMs. By incorporating functional phases such as metal nanoparticles and conductive nanostructures, CTeMs exhibit improved performance in various domains. In environmental remediation, CTeMs effectively capture and decompose pollutants, offering both separation and detoxification. In sensor technology, they have the potential to provide high sensitivity and selectivity, essential for accurate detection in medical and environmental applications. For energy storage, CTeMs may be promising in enhancing ion transport, flexibility, and mechanical stability, addressing key issues in battery and supercapacitor performance. Biomedical applications may benefit from the versality of CTeMs, potentially supporting advanced drug delivery systems and tissue engineering scaffolds. Despite their numerous advantages, challenges remain in the fabrication and scalability of CTeMs, requiring sophisticated techniques and meticulous optimization. Future research directions include the development of cost-effective production methods and the exploration of new materials to further enhance the capabilities of CTeMs. This review underscores the transformative potential of CTeMs across various applications and highlights the need for continued innovation to fully realize their benefits. Full article

Morphological control of metal-organic frameworks (MOFs) at the micro/nanoscopic scale is critical for optimizing the electrochemical properties of them and their derivatives. In this study, manganese organic phosphate (Mn-MOP) with three distinct two-dimensional (2D) morphologies was synthesized by varying the molar ratio of Mn²⁺ to phenyl phosphonic acid, and one of the morphologies is a unique palm leaf shape. In addition, a series of 2D Mn-MOP derivatives were obtained by calcination in air at different temperatures. Electrochemical studies showed that 2D Mn-MOP derivative calcined at 550 °C and exhibited a superior specific capacitance of 230.9 F g⁻¹ at 0.5 A g⁻¹ in 3 M KOH electrolyte. The aqueous asymmetric supercapacitor and the constructed flexible solid-state device demonstrated excellent rate performance. This performance reveals the promising application of 2D Mn-MOP materials for energy storage. Full article

The development of photo-/electro-chemical and flexible electronics has stimulated research in catalysis, informatics, biomedicine, energy conversion, and storage applications. Gels (e.g., aerogel, hydrogel) comprise a range of polymers with three-dimensional (3D) network structures, where hydrophilic polyacrylamide, polyvinyl alcohol, copolymers, and hydroxides are the most widely studied for hydrogels, whereas 3D graphene, carbon, organic, and inorganic networks are widely studied for aerogels. Encapsulation of functional species with hydrogel building blocks can modify the optoelectronic, physicochemical, and mechanical properties. In addition, aerogels are a set of nanoporous or microporous 3D networks that bridge the macro- and nano-world. Different architectures modulate properties and have been adopted as a backbone substrate, enriching active sites and surface areas for photo-/electro-chemical energy conversion and storage applications. Fabrication via sol–gel processes, module assembly, and template routes have responded to professionalized features and enhanced performance. This review presents the most studied hydrogel materials, the classification of aerogel materials, and their applications in flexible sensors, batteries, supercapacitors, catalysis, biomedical, thermal insulation, etc. Full article

Simple and scalable production of micro-supercapacitors (MSCs) is crucial to address the energy requirements of miniature electronics. Although significant advancements have been achieved in fabricating MSCs through solution-based printing techniques, the realization of high-performance MSCs remains a challenge. In this paper, graphene-based MSCs with a high power density were prepared through screen printing of aqueous conductive inks with appropriate rheological properties. High electrical conductivity (2.04 × 10⁴ S∙m⁻¹) and low equivalent series resistance (46.7 Ω) benefiting from the dense conductive network consisting of the mesoporous structure formed by graphene with carbon black dispersed as linkers, as well as the narrow finger width and interspace (200 µm) originating from the excellent printability, prompted the fully printed MSCs to deliver high capacitance (9.15 mF∙cm⁻²), energy density (1.30 µWh∙cm⁻²) and ultrahigh power density (89.9 mW∙cm⁻²). Notably, the resulting MSCs can effectively operate at scan rates up to 200 V∙s⁻¹, which surpasses conventional supercapacitors by two orders of magnitude. In addition, the MSCs demonstrate excellent cycling stability (91.6% capacity retention and ~100% Coulombic efficiency after 10,000 cycles) and extraordinary mechanical properties (92.2% capacity retention after 5000 bending cycles), indicating their broad application prospects in flexible wearable/portable electronic systems. Full article