Metal oxides as electrode materials for electrochemical capacitors

Electrochemical capacitors are becoming attractive energy storage devices and fill the gap between batteries and conventional capacitors because they have higher energy density than conventional dielectric capacitors and have higher power density and a longer cycling life than batteries. In this study, transition metal oxides, such as Co3O4, NiO, V2O5 and MnO2, have been successfully synthesized by different chemical-based solution methods. Their physical properties were characterized by X-ray diffraction, SEM, and BET analysis. The as-prepared Co3O4, NiO, V2O5 and MnO2 were investigated as electrode materials for electrochemical capacitors and demonstrated very high specific capacitances, which were 168 F/g, 203 F/g, 262 F/g, and 406 F/g, respectively. This may be due to their large surface areas (Co3O4 (82 m2/g), NiO (90 m2/g), V2O5 (41 m2/g) and MnO2 (269 m2/g)) and pseudocapacitive behaviour. Compared with expensive RuO2, which has been used extensively as electrode material for electrochemical capacitors, the as-prepared Co3O4, NiO, V2O5, and MnO2 are much cheaper. This makes them very promising candidates as electrode materials for electrochemical capacitors.