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

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