String-like core-shell ZnCo2O4@NiWO4 nanowire/nanosheet arrays on Ni foam for binder-free supercapacitor electrodes

We report the synthesis of 3D, string-like, core-shell, heterostructured ZnCo2O4@NiWO4 nanowire/nanosheet arrays on nickel foam using a simple two-step hydrothermal method followed by an annealing process, without the needs of conventional electrode preparation. The direct growth of ZnCo2O4 nanowires serves both as core and mains active materials for charge storage with high mechanical stability, while the higher conductive NiWO4 nanosheets act as the shell, which could provide enough voids for electrolyte accommodation and facilitate charge transfer and storage. When working as a binder-free electrode, the as-synthesized ZnCo2O4@NiWO4 nanowire/nanosheet arrays electrode delivers a specific capacitance as high as 1782 F g(-1) (2.14 F cm(-2)) at a current density of 1 mA cm(-2) and retains 95.4% of original capacitance after 5000 cycles at 5 A cm(-2), compared with single ZnCo2O4 nanowires electrode with 1300 F g(-1) (1.04 F cm(-2)) and 90.9%. The excellent capacitance performance demonstrates that constructing 3D, heterostructured, core-shell, nanowire/nanosheet arrays with two different binary transition metal oxides holds great potential for high-performance supercapacitors due to the synergic effects and large specific surface area.