Engineering hydrogenated manganese dioxide nanostructures for high-performance supercapacitors.

Improving the rate capability of transition metal oxides is of great important for the development of high-performance electrodes for supercapacitors. Here, a novel strategy of hydrogenation to enhance the electron transfer rate of manganese dioxide (MnO2 ) is proposed. Detailed preparative parameters (i.e. hydrogenation temperature and time) are systematically investigated. The hydrogenated MnO2 (H-MnOx ) exhibits modified crystal phase/surface structures and increased electrical conductivity. The prepared H-MnOx exhibits high specific capacitance (640 mF cm-2 at current density of 1 mA cm-2 ), good rate capability (89.6% of capacitance retained from 1 to 10 mA cm-2 ), and good cycling stability (84.6% retention after 1000 cycles). The high specific capacitance is ascribed to the unique interconnected ultrathin nanosheets structure, which could not only provide porous channels for electrolyte infiltration to offer sufficient electrode/electrolyte interface, but also shorten the ions diffusion distance inside the active material. The good rate capability could be attributed to the good conductivity of the H-MnOx nanosheets, which was confirmed by the DFT calculation. These results highlight the importance of hydrogenation as a facile yet effective strategy to improve the rate capability of transition metal oxides for supercapacitors.