Concentration dependent structure evolution and electrical properties of MnO2 nanostructures

•Nanostructured MnO2 were synthesized by a template-free hydrothermal route.•The transition from MnO2 nanospheres to MnO2 nanowires was observed.•The specific capacitance of MnO2 nanowires is 1.8 times that of MnO2 nanospheres.

MnO2 with various nanostructures was prepared by a facile hydrothermal method. X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) together recorded the composition and structure evolution during the entire produce process by adjusting the amount-of-substance concentration of precursors. It was found that the wormlike MnO2 nanospheres evolved toward nanowires along with the increasing of the concentration. Such MnO2 nanowire showed a high specific capacitance of 405 F g−1 at 2 mV s−1 and an attractive cycling stability of 99.0% retention after 1000 cycles. The method presented in this paper also gives us new inspires to improve the electrochemical properties of other nanostructured materials.