Core-shell structured ZnCo₂O₄@ZnWO₄ nanowire arrays on nickel foam for advanced asymmetric supercapacitors

One of the most effective tactics to promote the electrochemical performance of supercapacitors is to design and synthesize hybrid binder-free electrodes with core-shell structures. In this work, hierarchical ZnCo₂O₄@ZnWO₄ core-shell nanowire arrays grown on nickel foam are successfully fabricated via a facile two-step hydrothermal route and subsequent thermal treatment. The ZnCo₂O₄ nanowire arrays supported on nickel foam serve as the backbone for anchoring ZnWO₄ nanosheets. When tested as binder-free electrodes for supercapacitors, the as-prepared ZnCo₂O₄@ZnWO₄ hybrid electrode exhibits an ultrahigh specific areal capacitance of 13.4 F cm^-2 at a current density of 4 mA cm^-2 and superb cycling stability (98.5% retention after 5000 continuous cycles at a current density of 100 mA cm^-2). Furthermore, an asymmetric supercapacitor based on ZnCo₂O₄@ZnWO₄//active carbon is successfully designed. The as-designed asymmetric supercapacitor can achieve a maximum energy density of 24 Wh kg^-1 at a power density of 400 W kg^-1. Moreover, two as-prepared asymmetric supercapacitor devices in a series connection are able to light up a white light-emitting diode over 30 min. The outstanding electrochemical properties of the hybrid electrode demonstrate that it holds great potential for next generation energy storage applications.