Impact of oxygen content in pure Ni electrode on the oxygen evolution reaction in alkaline water electrolysis

In alkaline water electrolysis, the oxygen evolution reaction (OER) is the rate-determining step, and extensive research has been conducted to improve its efficiency. However, limited attention has been paid to the influence of the oxygen content in catalytic electrodes on their microstructure and electrochemical reactions. In this study, changes in the microstructure and OER characteristics of the catalytic electrodes were investigated by varying their oxygen content. Pure Ni asymmetric electrodes were fabricated through a powder metallurgy method and subsequently subjected to a hydrogen reduction heat treatment to control their oxygen content. Thermodynamic calculations and microstructural analysis revealed that, due to the low solubility of oxygen in the Ni matrix, NiO precipitates with sizes of several tens of nanometers precipitated in the electrodes. As the heat treatment time increased, the oxygen content decreased, which was attributed to the reduction of NiO. Linear sweep voltammetry curves demonstrated that a decrease in the oxygen content resulted in an increase in the reaction current density and a reduction in the overpotential. Moreover, Nyquist plots confirmed that the charge transfer resistance of the electrodes was reduced with decreasing oxygen content. These results confirm that the hydrogen reduction heat treatment reduced the amount of NiO in the Ni electrodes, thereby lowering the charge transfer resistance and enhancing the OER performance.