Advanced NiCo₂O₄ /ZnO-CuO/NF composite for high-performance asymmetric supercapacitor and efficient oxygen evolution reaction applications

It is imperative that composite systems with high performance, low-cost, enhanced simplicity, and scalability be developed in order to convert and store energy. This, however, has been a challenging endeavor throughout the years. In this study, we present a cost-effective, efficient, scale-up-friendly, and environmentally friendly method of producing in situ sandwich layers of ZnO-CuO composite between NiCo₂O₄ nanostructures and nickel foam using lemon peel extract (LPE) during hydrothermal processes. NiCo₂O₄/ZnO-CuO/nickel foam was analyzed using powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). According to XRD and HRTEM studies of NiCo₂O₄/ZnO-CuO/nickel foam, NiCo₂O₄, ZnO, and CuO exhibit cubic, hexagonal, and monoclinic phases, respectively. With NiCo₂O₄/ZnO-CuO/nickel foam as the active anode electrode, an asymmetric supercapacitor has been developed in an alkaline solution of 3 M KOH. At a low current density of 2 Ag⁻¹, the asymmetric supercapacitor exhibited a high specific capacitance of 3614.8 F g⁻¹, a power density of 1549.2 W kg⁻¹, and an energy density of 75.3 Wh kg⁻¹. Upon repeatable 40,000 galvanic charge–discharge cycles, the asymmetric device demonstrated a high specific capacitance retention percentage of approximately 100 to 95 and a columbic efficiency of 98%. Moreover, NiCo₂O₄/ZnO-CuO/nickel foam composite had a low overpotential of 210 mV at 40 mA cm⁻² and a Tafel slope of 70 mV dec⁻¹ for OER in 1 M KOH. During continuous OER measurements over a period of 40 h, NiCo₂O₄/ZnO-CuO/nickel foam composites demonstrated high durability and stability. NiCo₂O₄/ZnO-CuO/nickel foam exhibits good electrochemical performance as a result of its synergetic effects, its high conductivity, its abundant exposed catalytic sites, its oxygen vacancies, and its high durability.