An asymmetric supercapacitor based on a NiO/Co₃O₄@NiCo cathode and an activated carbon anode

Pseudocapacitive metal oxide active materials are promising for use in high performance supercapacitors. However, their poor electrical conductivity greatly hinders their practical application. We formed NiO and Co₃O₄ active materials on the surface of a highly conductive NiCo nanowire membrane current collector by a simple air oxidation method to fabricate a self-supported flexible NiO/Co₃O₄@NiCo electrode. This significantly improves electron transport at the interface between the current collector and the active NiO/Co₃O₄. Furthermore, the reticular nanowire network facilitates ion transportation and releases strain caused during charge and discharge. Due to this unique structural characteristic, the NiO/Co₃O₄@NiCo electrode delivers a high specific capacitance of 1.36 F cm^-2 at a current density of 5 mA cm^-2, and excellent cycling stability with a capacitance retention of 96.95% after 10 000 cycles. An asymmetric supercapacitor was assembled using the NiO/Co₃O₄@NiCo as the cathode and an activated carbon electrode as the anode, which delivered an energy density of 0.32 mWh cm^-2 at a power density of 8 mW cm^-2. Even at a high power density of 40 mW cm^-2, an energy density of 0.17 mWh cm^-2 was achieved, suggesting its promising use as an efficient electrode for high performance supercapacitors.