Electrochemical capacitance of Co3O4 nanowire arrays supported on nickel foam

Co3O4 nanowire arrays freely standing on nickel foam are prepared via template-free growth followed by thermal treatment at 300 °C in air. Their morphology is examined by scanning and transmission electron microscopy. The electrochemical capacitance behavior of the self-supported binderless nanowire array electrode is investigated by cyclic voltammetry, galvanostatic charge–discharge test and electrochemical impedance spectroscopy. The results show that nanowires are formed by nanoplatelets packed roughly layer by layer. They densely cover the nickel foam substrate and have diameters around 250 nm and the lengths up to around 15 μm. The Co3O4 nanowires display a specific capacitance of 746 F g−1 at a current density of 5 mA cm−2. The capacitance loss is less than 15% after 500 charge–discharge cycles. The columbic efficiency is higher than 93%.