Pseudocapacitive characteristics of manganese oxide anodized from manganese coating electrodeposited from aqueous solution

A metallic manganese coating was successfully electrodeposited from an aqueous solution containing manganese sulfate and ammonium sulfate at low temperature, and then converted to manganese oxide by anodic oxidation at room temperature. The morphology and pseudocapacitive performance of the obtained oxide were evaluated by SEM, cyclic voltammetry and electrochemical impedance spectroscope. The results show that the manganese oxide is amorphous and porous, which exhibits a near-rectangular CV curve with broad quasi-reversible redox peaks, and a specific capacitance of 214 F g−1 at a CV scan rate of 5 mV s−1. After heat-treatment, the oxide shows a much more symmetrical and rectangular CV curve, better high-rate capability but a lower specific capacitance. Electrochemical impedance spectroscopy reveals that heat-treatment on this material can lead to a lower reaction resistance but a higher diffusion resistance and diffusion time constant.