Manganese oxide film electrodes prepared by electrostatic spray deposition for electrochemical capacitors

Porous manganese oxide thin film electrodes were prepared for use in electrochemical capacitors by electrostatic spray deposition. The as-prepared manganese oxide film showed ideal capacitive behavior after potential cycling within the range of -0.1 to 0.9 V (vs saturated calomel electrode) in a 0.1 M Na₂SO₄ electrolyte. Analysis of the X-ray diffraction, X-ray absorption spectroscopy, and Raman scattering data during the cycling showed that the as-prepared crystalline Mn₃O₄ film was electrochemically oxidized to pseudocapacitive amorphous MnO₂ film by the potential cycling. The effects of the film thickness and heat treatment temperature of the as-prepared manganese oxide films on the electrochemical properties were also investigated. The specific capacitance of the electrochemically oxidized amorphous MnO₂ films was dependent on the film thickness, rather than on the heat treatment of the as-prepared oxide films. The specific capacitance decreased from 330 to 150 F/g as the mass (i.e., thickness) of the oxide was increased from 18 to 116 μg/cm².