Hierarchical zinc cobalt sulfide flowers grown on nickel foam as binder-free electrodes for high-performance asymmetric supercapacitors

Enhanced Supercapacitor Performance Using a Co3 O4 @Co3 S4 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 Co₃ O₄ and Co₃ S₄ 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 Co₃ O₄ @Co₃ S₄ nanocomposite, the nanostructure of Co₃ S₄ was fabricated from Co₃ O₄ 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 Co₃ O₄ /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 Co₃ O₄ @Co₃ S₄ /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 .

Construction of hierarchical sea urchin-like manganese substituted nickel cobaltite@tricobalt tetraoxide core-shell microspheres on nickel foam as binder-free electrodes for high performance supercapacitors

Construction of binder-free electrodes with hierarchical core-shell nanostructures is considered to be an effective route to promote the electrochemical performance of supercapacitors. In this work, the porous Ni_0.5Mn_0.5Co₂O₄ nanoflowers anchored on nickel foam are utilized as framework for further growing Co₃O₄ nanowires, resulting in the hierarchical sea urchin-like Ni_0.5Mn_0.5Co₂O₄@Co₃O₄ core-shell microspheres on nickel foam. Owing to the advantages brought by unique porous architecture and synergistic effect of the multi-component composites, the as-prepared electrode exhibits a high specific capacitance (931 F/g at 1 A/g), excellent rate performance (77% capacitance retention at 20 A/g) and outstanding cycle stability (92% retention over 5000 cycles at 5 A/g). Additionally, the assembled Ni_0.5Mn_0.5Co₂O₄@Co₃O₄//AC (activated carbon) asymmetric supercapacitor achieves a high energy density (50 Wh/kg at 750 W/kg) and long durability (88% retention after 5000 cycles).

Rational design of flower-like cobalt–manganese-sulfide nanosheets for high performance supercapacitor electrode materials

The design and development of composite materials with novel structures is one of the effective ways to enhance the electrochemical properties of supercapacitors.