Identifying the Active Site of WaterOxidation Catalyst Based onDefective Fe-Doped Ni Oxyhydroxide

Electrochemical water splitting plays a crucial role instoring sustainable energy into H2as an ideal fuel, inwhich the anodic oxygen evolution reaction (OER) isthe bottleneck. Currently, Fe-doped NiOOH (Ni1-xFexOOH) is a promising OER catalyst under alkalineconditions. However, the specific active sites respon-sible for their good performances remain debatable.Here, we identify a nickel-oxygen radical (Ni-O center dot) andan iron-oxo (Fe=O) group as two essential states foradsorbed oxygen. Meanwhile, both thermochemicalO-O coupling and electrochemical OER elementarysteps are considered on the Ni1-xFexOOH catalysts.Sophisticated mechanistic studies with a combineddensity functional theory simulation and experimen-tal analysis unravel that both the Ni and Fe centerscan act as the active sites for the defective Ni1-xFexOOH to catalyze OER, depending on the natureof the defect. The presence of Fe can benefitthestabilization of the defective surface and influencethe electronic property of the nearby Ni site. Thiswork not only identifies the intrinsic active sites ofNi1-xFexOOH, but also illustrates the essential roles ofdefects in catalysis, which sheds light on the design ofmore efficient OER catalysts in the future.