NiFe-based electrocatalysts have attracted great interests due to the low price and high activity in oxygen evolution reaction (OER). However, the complex reaction mechanism of NiFe-catalyzed OER has not been fully explored yet. Detection of intermediate species can bridge the gap between OER performances and catalyst component/structure properties. Here, we performed label-free surface-enhanced Raman spectroscopic (SERS) monitoring of interfacial OER process on Ni₃ FeOx nanoparticles (NPs) in alkaline medium. By using bifunctional Au@Ni₃ FeOx core-satellite superstructures as Raman signal enhancer, we found direct spectroscopic evidence of intermediate O-O⁻ species. According to the SERS results, Fe atoms are the catalytic sites for the initial OH⁻ to O-O⁻ oxidation. The O-O⁻ species adsorbed across neighboring Fe and Ni sites experiences further oxidation caused by electron transfer to NiIII and eventually forms O₂ product.
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Hu et al. (2021) studied this question.