Liquid-Phase Exfoliation

The present thesis work concerns the synthesis and processing of nanostructured materials for supercapacitor applications. Various nanostructured materials were synthesized and subsequently processed into thin film electrodes at a laboratory and/or semi-industrial scale which were then investigated for their potential application as supercapacitor electrodes.

In the first part of the work, a spray deposition technique for the manufacture of 1,500 cm2 area electrodes with thickness from 10-25 nm to typically 1-2 micrometers was developed, optimized and validated. First films of multi-walled carbon nanotubes with demonstrated uniformity of thickness, microstructure, and electrochemical properties across the 1,500 cm2 area were manufactured.

Next, molybdenum trioxide was investigated for its potential application
as supercapacitor electrode. alpha-MoO3 nanobelts were synthesized using a hydrothermal method and spray deposited electrodes were tested in various electrolytes. Cyclic voltammetry of alpha-MoO3 nanobelt electrodes in aqueous electrolytes showed the greatest charge storage in 1 M H2SO4 with a complex redox activity in a 0 to 1 V (vs Ag/AgCl) electrochemical window. The oxido-reduction processes were then investigated by a combination of X-ray photoelectron spectroscopy and electrochemical characterization methods. The charge storage properties of alpha-MoO3/SWNTs (75 %/ 25 % w/w) (MOSC) electrodes were investigated in LiClO4/propylene carbonate in a 1.5 to 3.5 V vs Li/Li+ (half cell). Cyclic voltammetry was performed at scan rates from 0.1 mV/s to 50 mV/s and the separate contributions to charge storage of capacitive and diffusion-controlled 3D ion intercalation processes were estimated.

Graphene electrodes were manufactured by a surfactant-water based exfoliation method followed by spray-deposition. Cyclic voltammetry and galvanostatic charge-discharge experiments revealed a combination of electric double layer and pseudocapacitive behavior that was maintained to unusually high scan rates of 10,000  mV/s.

Finally, the high power density of graphene and high energy density of
single-walled carbon nanotubes were combined in a hybrid electrode manufactured following a layer by layer approach (LBL).

Solution processing and biofunctionalization of two-dimensional crystals are pivotal for their (biomedical) applications. Here we interface ultrathin layers of MoS 2 with the surface active and self-assembling fungal proteins named Vmh2, which belong to the hydrophobin family. We produce few-layered biofunctionalized MoS 2 (bio-MoS 2) nanosheets via liquid phase exfoliation in a green solvent, and controlled centrifugation; a low-cost and eco-friendly process. The dispersions are investigated by electrophoretic mobility, atomic force microscopy (AFM), UV-Vis, Raman and photoluminescence (PL) spectroscopy. The nanosheets present a defect-free vibrational spectrum, tunable zeta-potential and their photoluminescence is preserved after non-covalent biofunctionalization making them well suited for various biomedical applications.