Oxidation-etching preparation of MnO ₂ tubular nanostructures for high-performance supercapacitors

1D hierarchical tubular MnO ₂ nanostructures have been prepared through a facile hydrothermal method using carbon nanofibres (CNFs) as sacrificial template. The morphology of MnO ₂ nanostructures can be adjusted by changing the reaction time or annealing process. Polycrystalline MnO ₂ nanotubes are formed with a short reaction time (e.g., 10 min) while hierarchical tubular MnO ₂ nanostructures composed of assembled nanosheets are obtained at longer reaction times (>45 min). The polycrystalline MnO ₂ nanotubes can be further converted to porous nanobelts and sponge-like nanowires by annealing in air. Among all the types of MnO ₂ nanostructures prepared, tubular MnO ₂ 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.