| Nanoparticulate manganese dioxide thin films have been prepared by the sol-gel process to study their potential applications as novel electrode materials for electrochemical capacitors. Manganese dioxide is specially chosen for these purposes as it fulfills all of the material requirement criteria for exhibiting a high specific capacitance, cheap and environmentally benign, and can be prepared easily using the sol-gel process.; Both electrochemical and material characterizations conducted on sol-gel-derived manganese dioxide thin films on nickel substrates showed very promising electrochemical properties with high capacitance values and good cycling behaviors in unbuffered Na2SO4 solutions. Sol-gel-derived manganese dioxide thin films are largely amorphous, nanoparticulate and highly porous in nature. While the high specific surface area of these films yield sizeable double-layer capacitance, the redox processes associated with the homogeneous reduction of MnO2 to MnOOH yields pseudocapacitance.; The capacitive and cycling behaviors of sol-gel-derived films have been shown to be superior to those of electrodeposited films. Cyclic voltammetry experiments on ultra-thin films showed a specific capacitance of about 700 F/g, which is comparable to that of ruthenium dioxide, currently the best ultracapacitor material in terms of specific energy storage. These films exhibit good cycling behaviors, remain both structurally and chemically intact, and not losing much more than 10% of charge-storage capacity after 1,500 cycles. Electrochemical impedance studies of sol-gel-derived films showed a distinctive impedance response depending upon the range of frequencies: an almost purely capacitive behavior at low frequencies, a diffusion controlled behavior at intermediate frequencies, and a purely resistive behavior at high frequencies. These frequency responses are independent of the applied dc polarization potentials within the range of 0.0V to 0.9V versus SCE. Both the ionic composition and ionic strength of supporting electrolytes are shown to have substantial effects on the charge capacity and cycling performance of sol-gel-derived MnO 2 thin films.; Further enhancement in the specific capacitance and electrical response is envisaged through optimizing the microstructure and thickness of these sol-gel films. Future studies are recommended to address the effect of microstructural parameters such as grain size, specific surface area, porosity, pore size distribution, film thickness and uniformity. |
