Light energy storage in TiO2/MnO2 composite electrode for photoelectrochemical capacitor

Composite electrodes comprising TiO2 and MnO2 particles were prepared as hotoelectrochemical capacitor electrodes that enable both photoelectric conversion and energy storage. A MnO2 electrode was also prepared for characterization of MnO2 alone, and its electrochemical capacitor property was evaluated. The MnO2 electrode showed higher specific capacitance than a RuO2 electrode. Results of the photoelectrochemical measurements demonstrated that the discharge capacity of the TiO2/MnO2 composite electrode was slightly inferior to that of the TiO2 and RuO2 electrodes using. By reducing MnO2 particle size, the composite electrode exhibited increased surface roughness and enhanced capacity. We consider that the smaller MnO2 particles can efficiently store Na+ ions even at a low photo-charge voltage of TiO2.