Electrocatalytic performance investigation of NiCo2O4 nanostructures prepared by hydrothermal method and thermal post-annealing treatment

Nickel-cobalt oxide (NiCo2O4), also known as nickel–cobalt ore, is a spinel-structured mixed oxide. It is more environmentally friendly, abundant in nature, has better electrical conductivity, and has higher electrochemical activity than two single-component oxides, nickel oxide and cobalt oxide. Here, NiCo2O4 is synthesized using a simple hydrothermal method and then annealed in the air for 3 h at 300, 350, 400 and 450 °C. The resulting materials were characterized using X-ray diffraction (XRD), Fourier-Transform-Infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectroscopy and electrochemical techniques. A single-phase face-centered cubic spinel structure with a nanorod-like morphology is obtained at 350 °C, and samples above this temperature show mixed phases consisting of nanowires and nanorods.. The sample annealed at 350 °C demonstrated excellent electrochemical performance for hydrogen evolution reaction (HER), with an overpotential of 435 mV at a current density of 10 mA/cm2, a pseudo-capacitance of 0.287 mF/cm2, a Tafel slope of 71 mV/dec, an exchange current density of 3.5 × 10-3 mA/cm2, and a minimum charge transfer resistance of 98 O. The study thus demonstrated the efficacy of the hydrothermal method and thermal post-annealing treatment in producing NiCo2O4 nanostructures with excellent electrocatalytic performance for energy conversion and storage applications.