Electrochemical Performances of ZnO–NiO–CuO Mixed Metal Oxides as Smart Electrode Material for Solid-State Asymmetric Device Fabrication

Mixed transition-metal oxides are emerging electrode materials, because of their higher electrochemical performances. In the present work, single-metal oxides, binary-metal oxides, and ternary mixed-metal oxides (MMOs) of zinc oxide (ZnO), nickel oxide (NiO), and copper oxide (CuO) are successfully prepared by simple gel-combustion process. The structure and properties of MMOs are of great interest, because of the opportunity to tune their properties for better multifunctional performance than single and binary metal oxides. The crystal structure, functional group, surface morphology, and binding energy of all of the single, binary, and ternary MMOs are studied through X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron microscopy (XPS), respectively. The entire electrochemical studies are also performed using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS). From the electrochemical study, the ZnO–NiO–CuO MMOs electrode was found to possess pseudocapacitor-type features and shows an outstanding specific capacitance of 1831 F g–1 at a current density of 1 A g–1, which is higher than that of single and binary metal oxides. The fabricated asymmetric (ASC) device [ZnO–NiO–CuO MMOs || r-GO] exhibits maximum specific capacitance of 118 F g–1 at the current density of 1 A g–1. Hence, it leads to the supercapacitance property of maximum storage response; the ASC device possessed the excellent retentivity of (89.97%) up to 10 000 repeated cycles. The ASC device reveals a maximum specific power of 5672 W h kg–1 with a specific energy of 15.7 W h kg–1 with a high current density of 10 A g–1. This finding shows that the ZnO–NiO–CuO MMOs can be used as potential electrode material and might have promising applications in high-performance energy storage devices.