Oxidation-Etching Preparation of MnO2 Tubular Nanostructures for High-Performance Supercapacitors

1D hierarchical tubular MnO2 nanostructures have been prepared through a facile hydrothermal method using carbon nanofibres (CNFs) as sacrificial template. The morphology of MnO2 nanostructures can be adjusted by changing the reaction time or annealing process. Polycrystalline MnO2 nanotubes are formed with a short reaction time (e.g., 10 min) while hierarchical tubular MnO2 nanostructures composed of assembled nanosheets are obtained at longer reaction times (>45 min). The polycrystalline MnO2 nanotubes can be further converted to porous nanobelts and sponge-like nanowires by annealing in air. Among all the types of MnO2 nanostructures prepared, tubular MnO2 nanostructures composed of assembled nanosheets show optimized charge storage performance when tested as supercapacitor electrodes, for example, delivering an power density of 13.33 kW.kg(-1) and a energy density of 21.1 Wh.kg(-1) with a long cycling life over 3000 cycles, which is mainly related to their features of large specific surface area and optimized charge transfer pathway.