Enhanced Supercapacitor Performance Using a Co 3 O 4 @Co 3 S 4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes

To avoid an enormous energy crisis in the not‐too‐distant future, it be emergent to establish high‐performance energy storage devices such as supercapacitors. For this purpose, a three‐dimensional (3D) heterostructure of Co 3 O 4 and Co 3 S 4 on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro‐deposited on rGO/Ni foam by applying cyclic‐voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co 3 O 4 @Co 3 S 4 nanocomposite, the nanostructure of Co 3 S 4 was fabricated from Co 3 O 4 nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm −2 (5651.24 F g −1 ) at a current density of 6 mA cm −2 compared to the Co 3 O 4 /rGO/NF electrode with a capacitance of 3.06 F cm −2 (1230.77 F g −1 ) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg −1 , specific power density of 6048.03 W kg −1 and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s −1 ). Finally, by using Co 3 O 4 @Co 3 S 4 /rGO/NF and the activated carbon‐based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm −2 at the applied current density of 1 mA cm −2 , and delivered an energy density of 0.143 Wh kg −1 at the power density of 5.42 W kg −1 .