Effects of adding different morphological carbon nanomaterials on supercapacitive performance of sol-gel manganese oxide films

In this study, the supercapacitive performances of manganese oxide films were investigated by adding different carbon nanomaterials, including carbon nanocapsules (CNC), multiwalled carbon nanotubes (MWCNTs) and multi-layered graphene. The manganese oxide films were prepared with manganese acetate precursor by sol-gel method, and the post-treatment effects were also examined. With a heat-treatment above 300 °C, the as-prepared amorphous films transformed to a compound of Mn₃O₄ and Mn₂O₃ phases, and the smooth surface became rough as well. Cyclic voltammogram (CV) tests showed that the manganese oxide film, which was mixed with 0.05 wt% MWCNTs and annealed at 350 °C for 1 h, exhibited the optimized specific capacitance, 339.1 F/g. During 1000CV cycles, the specific capacitances of original manganese oxide film decreased gradually from 198.7 to 149.1 (75%) F/g. After same number of cycle tests, the modified films containing 0.025 wt% CNC, 0.05 wt% MWCNTs and 0.1 wt% graphene retained 201.8 (64.2%), 267.4 (78.9%) and 193.1 (57.4%) F/g respectively. The results indicates that the supercapacitive performance of manganese oxide films were significantly modified by carbon nanomaterials; in addition, the MWCNTs additive could also reduce the decay rate.