Asymmetric supercapacitor is constructed using hierarchical porous electrode materials of nickel oxide and carbon with the aim to facilitate ion transport. Hierarchical porous nickel oxide and carbon are prepared by template-directed synthesis. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charging-discharging are used to test the asymmetric supercapacitor and investigate the electrode processes at different supercapacitor voltages. The capacitance, energy density and power density of the asymmetric supercapacitor can be improved by elevating the supercapacitor voltage, and its cycling stability decays at high voltage, but the columbic efficiency stays close to 100%. (C) 2008 Elsevier B.V. All rights reserved.