Surface‐Enhanced Raman Spectroscopic Evidence of Key Intermediate Species and Role of NiFe Dual‐Catalytic Center in Water Oxidation

Abstract 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 Ni 3 FeO x nanoparticles (NPs) in alkaline medium. By using bifunctional Au@Ni 3 FeO x 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 Ni III and eventually forms O 2 product.