Manganese oxide films prepared by sol-gel process for supercapacitor application

In this study, manganese oxide electrodes with promising pseudo-capacitive behavior were prepared by sol-gel process using manganese acetate as the precursor. Effects of post-heat treatment on material characteristics and electrochemical properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal analysis, synchrotron X-ray absorption spectroscopy (XAS), and cycling voltammetry (CV). Experimental results showed that manganese oxide films prepared by sol-gel technique exhibited Mn₂O₃ and Mn₃O₄ phases after heat treating at a temperature higher than 300 °C. Meanwhile, a porous manganese oxide coating was observed due to the burnout of organics. The specific capacitance of the manganese oxide electrodes was 53.2, 230.5, 185.6, and 189.9 F/g after heat treating at 250, 300, 350, and 400 °C, respectively. After three hundred charging-discharging cycles, the specific capacitance of the manganese oxide electrodes heat treated at 300 °C decreased to 78.6% of its maximum. Synchrotron XAS examination revealed that manganese oxide electrodes exhibited the same trend where the trivalent manganese was transited into tetravalent manganese after cyclic voltammetry tests.