Abstract: A NiCo₂O₄ spinel composite oxide was obtained by co-precipitation. A Ni/NiCo₂O₄ composite coating was prepared by composite electrodeposition in a Ni plating solution by mixing with NiCo₂O₄ powder. The best plating conditions for the composite electrodeposition were investigated by changing factors such as the plating bath pH and the cathode current density j_k. The surface morphology, the NiCo₂O₄ content, and the structure of the Ni/NiCo₂O₄ composite coating were characterized by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). As a result, the NiCo₂O₄ content in the Ni/NiCo₂O₄ composite coating was found to be the highest (30.6%, w) for a bath pH of 6.2 and a cathodic current density j_k of 100 mA·cm^-2. In 5 mol·L^-1 KOH solution the electrocatalytic properties toward the oxygen evolution reaction (OER) of the Ni/NiCo₂O₄ composite electrode was studied using cyclic voltammetry, electrochemical steady-state polarization, and electrochemical impendence spectroscopy (EIS). Compared with the Ni electrode, the electrocatalytic properties for the OER of the Ni/NiCo₂O₄ composite electrode improved greatly and the apparent activation energy was reduced to 53.2 kJ·mol^-1. The apparent exchange current density of the Ni/NiCo₂O₄ composite electrode toward the OER was 7 times as high as that of a nickel electrode. An electrochemical impendence spectroscopy analysis indicated that the oxygen evolution reaction of the Ni/NiCo₂O₄ composite electrode was co-controlled by an electrochemical step and a diffusion step. Constant potential electrolysis over extended periods for the OER shows that the stability of the Ni/NiCo₂O₄ composite electrode is good.

Key words: Ni/NiCo₂O₄, Spinel, Composite electrodeposition, Oxygen evolution electrode, Stability