Microstructure and pseudocapacitive performance of anodically deposited manganese oxide with various heat-treatments

Amorphous, hydrous manganese oxide was prepared by anodic deposition in manganese acetate solution. The effect of heat-treatments (up to 600°C) on the material characteristics of the oxides was investigated. The results indicated that the as-deposited oxide, which was fully amorphous, was transformed into a fibrous shape with nanocrystallinity after annealing at 200°C for 2 h. Mn ₃O ₄ and Mn ₂O ₃ were formed within the nanocrystalline oxide when heating at 400°C. Furthermore, by increasing the temperature over 500°C, the spherical Mn ₂O ₃ particles became the only phase present. In addition, atomic force microscopy was also carried out to explore the surface morphology of the oxide electrodes. This characterization method recognized condensation, rearrangement, reconstruction, and growth of the deposited manganese oxide as a function of temperature. The corresponding electrochemical performances of the oxides were evaluated by chronopotentiometry. The pseudocapacitive characteristics, reversibility, and cyclic stability of the deposited manganese oxide were improved by introducing the proper heat-treatment. However, high-temperature (>200°C) heat-treatment promoted the formation of crystalline Mn ₃O ₄ and Mn ₂O ₃ and consequently resulted in the loss of the pseudocapacitive property of the oxides.