Hierarchical Nickel Cobaltate/Manganese Dioxide Core-Shell Nanowire Arrays on Graphene-Decorated Nickel Foam for High-Performance Supercapacitors

Hierarchical NiCo2O4@MnO2 core-shell nanowire arrays have been synthesized on graphene-nickel foam as binder-free electrodes. The thickness of MnO2 nanosheets can be controlled by different hydrothermal reaction times, and a whole array of unique NiCo2O4@MnO2 nanostructures have been synthesized and investigated successfully for supercapacitor applications. The graphene deposited on nickel foam can enhance the electrical conductivity of electrode materials and strengthen corrosion resistance of the current collector. As a result, NiCo2O4@MnO2 core-shell arrays electrode exhibits an ultra-high specific capacitance of 2125 Fg(-1) at a current density of 1 Ag-1, outstanding cycling stability (93.4% of its initial value after 5000 cycles) and good rate performance. In addition, an asymmetric supercapacitor based on NiCo2O4@MnO2 as the positive electrode and activated graphene (AG) as the negative electrode achieves an energy density of 27.8 Whkg(-1) at a power density of 400.3 WKg(-1). These notable findings suggest that the unique NiCo2O4@MnO2 core-shell nanostructure on graphene-nickel foam is a potential candidate for application as a high-performance supercapacitor electrode.