In-situ Raman spectroscopy reveals the reconstructions of NiMoO 4 for neutral water oxidation: Insights from activation processes

Albeit surface reconstruction of precatalysts for alkaline oxygen evolution reaction (OER) is extensively studied, the dynamic structure evolution and true active phase in neutral media remain largely unexplored. Here, the activation behaviors in neutral and alkaline media are comparatively studied using NiMoO₄ as a model precatalyst. Our results reveal that, when electrochemically activated in harsh alkaline conditions, NiMoO₄ undergoes rapid and complete reconstruction with the formation of a considerable NiOOH active phase. On the other hand, direct activation in neutral media only results in weak reconstruction with a thin NiOOH layer on NiMoO₄ surface. Accordingly, the electrode oxidized in basic electrolyte yields a superior OER performance compared to that directly treated mild pH condition. Our study deepens the understanding of the neutral water oxidation reaction, which provides insightful guidelines for further development of efficient electrocatalysts for neutral water electrolysis with self-reconstruction.