Hierarchically structured MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors.

We report a hierarchical Ni@MnO2 structure consisting of MnO2 nanowires supported on hollow Ni dendrites for high-performance supercapacitors. The Ni@MnO2 structure, which was prepared via a facile electrodeposition method, is highly porous and appears like a forest of pine trees grown vertically on a substrate. At a MnO2 mass loading of 0.35 mg cm(-2), the Ni@MnO2 electrode demonstrated a specific capacitance of 1125 F g(-1) that is close to the theoretical value. In addition, a remarkable high-rate performance (766 F g(-1) at a discharge current density of 100 A g(-1)) was achieved. Electrochemical tests in a two-electrode configuration for the Ni@MnO2 structure with a high MnO2 loading of 3.6 mg cm(-2) showed a low equivalent series resistance (ESR) of 1 Ω and a high specific power of 72 kW kg(-1). This superior performance can be attributed to the highly porous and hierarchical structure of Ni@MnO2 that favors rapid diffusion of an electrolyte, highly conductive pathway for electron transport, and efficient material utilization.