Microwave Hydrothermal Synthesis of NiCo Bimetallic Oxides and Their Electrocatalytic Oxygen Evolution Performance

In this work, a series of Ni–Co bimetallic oxide materials were synthesized via a microwave-assisted hydrothermal method. Their phase structure, morphology, valence states, and defect features were systematically analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The results reveal that the Ni–Co bimetallic synergy effectively regulates the formation of oxygen vacancies (O_v). Notably, when the molar ratio of Ni to Co is 1:3, the obtained NiCo₃Oₓ exhibits the optimal OER performance, delivering an overpotential of only 393 mV at 50 mA·cm⁻², along with a low Tafel slope (172.3 mV·dec⁻¹) and robust stability over 24 h. This superior activity originates from the synergistic redox transitions of Co²⁺/Co³⁺ and Ni²⁺/Ni³⁺, which were further validated by in situ Raman spectroscopy through the enhanced adsorption of the *OOH intermediate and the O_v-mediated fast electron transfer mechanism. Density functional theory (DFT) calculations confirmed that electronic coupling at the Ni–Co bimetallic interface improved the material’s conductivity. This study provides a new strategy for designing efficient OER catalysts via oxygen-vacancy regulation.