The Synthesis of NiCo₂O₄-MnO₂ Core-Shell Nanowires by Electrodeposition and Its Supercapacitive Properties

Hierarchical composite films grown on current collectors are popularly reported to be directly used as electrodes for supercapacitors. Highly dense and conductive NiCo₂O₄ nanowires are ideal backbones to support guest materials. In this work, low crystalline MnO₂ nanoflakes are electrodeposited onto the surface of NiCo₂O₄ nanowire films pre-coated on nickel foam. Each building block in the composite films is a NiCo₂O₄-MnO₂ core-shell nanowire on conductive nickel foam. Due to the co-presence of MnO₂ and NiCo₂O₄, the MnO₂@NiCo₂O₄@Ni electrode exhibits higher specific capacitance and larger working voltage than the NiCo₂O₄@Ni electrode. It can have a high specific capacitance of 1186 F·g^-1 at 1 A·g^-1. When the core-shell NiCo₂O₄-MnO₂ composite and activated carbon are assembled as a hybrid capacitor, it has the highest energy density of 29.6 Wh·kg^-1 at a power density of 425 W·kg^-1 with an operating voltage of 1.7 V. This work shows readers an easy method to synthesize composite films for energy storage.