Design of NiCo2O4@NiMoO4 core–shell nanoarrays on nickel foam to explore the application in both energy storage and electrocatalysis

Abstract

NiCo₂O₄@NiMoO₄ core–shell nanowires (NCNMW) and nanosheets (NCNMS) with high electrochemical capabilities were synthesized using a simple two-step hydrothermal reaction, together with a calcination process. As active electrode materials, all of the prepared electrodes were tested in a three-electrode system. Among all the electrodes, NCNMS-2 exhibited a large specific capacity (1770.95 C g⁻¹ at a current density of 3 mA cm⁻²), a high-rate capability (1334.18 C g⁻¹ at 40 mA cm⁻²), and superior cycling stability (102.78% capability retention after 5000 cycles at 10 mA cm⁻²). The NCNMS-2//activated carbon battery–supercapacitor hybrid device yielded a high energy density of 30.57 W h kg⁻¹ at a power density of 676.06 W kg⁻¹ and excellent stability with a capacitance retention of 92.71% after 5000 continuous cycles at a current density of 10 mA cm⁻². In addition, as an electrocatalyst for the oxygen evolution reaction (OER), the NCNMS-2 exhibited a small Tafel slope of 59 mV Dec⁻¹, and a low overpotential of 175 mV at a current density of 10 mA cm⁻². The excellent electrochemical performance of the hierarchical NiCo₂O₄@NiMoO₄ structure was attributed to its porosity and the characteristics of the 3D nanostructure subunits that possess many active reaction sites, rapid electron/ion transport, and high stability. Based on the excellent electrochemical properties, it will serve well for energy storage and conversion.