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

Abstract

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.