Controlled synthesis of a hierarchical CuNi2O4@SnS nanocauliflower-like structure on rGO as a positive electrode material for an asymmetric supercapacitor

Abstract

In this paper, a hierarchical CuNi₂O₄@SnS@rGO nanocauliflower-like structure was grown on Ni foam for the first time via a novel two-step synthesis. Through a hydrothermal method, SnS@rGO was prepared and after this a facile and commendable electrodeposition process was used for fabricating CuNi₂O₄ on it. The hierarchical CuNi₂O₄@SnS@rGO/NF is a promising electrode material for building up an impressive supercapacitor. The morphology and structure of the prepared samples were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption, energy dispersive spectroscopy (EDS), elemental mapping analysis, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). N₂ adsorption tests showed that the specific surface area of CuNi₂O₄@SnS@rGO/NF (295.82 m² g⁻¹) is much higher than that of SnS@rGO/NF (168.53 m² g⁻¹). The electrochemical properties of the modified electrodes have been studied in detail at various scan rates using cyclic voltammetry, galvanostatic charge–discharge (GCD) analysis, and electrochemical impedance spectroscopy (ESI). As a result, the nanocauliflower-like structure of CuNi₂O₄@SnS@rGO/NF exhibits a high specific capacitance of 1061 F g⁻¹ and the specific capacity of 177 A h g⁻¹ at a current density of 1 A g⁻¹. The specific capacitance of CuNi₂O₄@SnS@rGO/NF is more than the capacitance of the individual modified electrodes and shows good stability during long-term cycling with perfect cycling stability up to 3000 cycles and a high energy density of 688 W h kg⁻¹ at a power density of 3892 W kg⁻¹ in a KOH (3 mol L⁻¹) electrolyte. Also, a CuNi₂O₄@SnS@rGO/NF//AC asymmetric supercapacitor was assembled, which displayed excellent electrocapacitive performance. The flexible asymmetric supercapacitor exhibits high energy density (589 W h kg⁻¹), and long cycle life (86.7% of capacitance retention after 3000 cycles).