Electrochemically growth-controlled honeycomb-like NiMoO4 nanoporous network on nickel foam and its applications in all-solid-state asymmetric supercapacitors

Abstract

A honeycomb-like NiMoO₄ nanoporous network electrode was synthesized on nickel foam using an electrodeposition method and used for the fabrication of asymmetric supercapacitors (ASCs). The growth process of the NiMoO₄ nanostructure was controlled by varying the number of electrochemical cycles. The evolution of the NiMoO₄ nanoflakes with the electrochemical cycles was confirmed by field emission scanning electron microscopy. The supercapacitive properties of NiMoO₄ nanostructure were measured by cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy. The well-grown NiMoO₄ nanoporous network exhibited a highest specific capacitance of 1475 F g⁻¹ at a current density of 1 A g⁻¹ in an aqueous KOH electrolyte with a good rate capability of 72.8% when the current density was increased 20 fold. The nanoporous network also exhibited a capacitive retention of 87.9% after 5000 charge–discharge cycles at a fixed current density of 20 A g⁻¹. A NiMoO₄//reduced graphene oxide (rGO)-based solid state ASC was fabricated using a poly(vinyl alcohol)–KOH gel electrolyte. The NiMoO₄//rGO ASC delivered a maximum energy density of 45 W h kg⁻¹ and a power density of 14.5 kW kg⁻¹ as well as an electrochemical stability of 84% after 5000 cycles, highlighting the potential of NiMoO₄//rGO ASCs for portable electronic applications.