Effects of Temperature and Concentration on the Structure and Specific Capacitance of Manganese Oxide Deposited in Manganese Acetate Solution

The deposition of manganese oxide on a carbon substrate in manganese acetate solution by anodic deposition was investigated. The effects of electrolyte concentration (0.05–1 m) and temperature (0–50 °C) on the characteristics of the oxide prepared were explored. The surface morphology of the oxide deposited was examined by scanning electron microscopy (SEM). Oxide whiskers were found on the deposited film surface, and they became coarser and longer when deposited at a high temperature. X-ray photoelectron spectroscopy (XPS) was carried out to examine the composition of the deposit. The results indicated that the oxides deposited at 0 and 25 °C contained trivalent and tetravalent manganese oxide. However, the mixture of bivalent and trivalent oxide was found when the deposition temperature was raised to 50 °C. Moreover, the amount of anhydrous Mn oxide (i.e., Mn–O–Mn) and water content in the deposit gradually decreased with increasing deposition temperature. The concentration of manganese acetate could affect the oxidation state of manganese ions as well as the morphology of the oxide deposited. Cyclic voltammetry (CV) was used to evaluate the electrochemical performance of the oxide deposited. The results showed that the specific capacitance of the manganese oxide increased with decreasing deposition temperature. Moreover, an optimum value of specific capacitance was found for the oxide deposited in 0.5 m manganese acetate solution.