Formation of FeOOH Nanosheets Induces Substitutional Doping of CeO2−x with High‐Valence Ni for Efficient Water Oxidation

Abstract Transition metal elements such as Ni in high oxidation states can promote oxygen evolution reaction (OER) activity, but it is difficult to prepare dispersed Ni 3+ or even Ni 4+ species under mild conditions. Herein, a one‐step synthesis of high‐valence nickel‐doped CeO 2− x covered with FeOOH nanosheets in the presence of Ni 2+ /Fe 3+ is reported. A series of ex situ and in situ experiments reveal the etching effect on ceria of the H + species from the hydrolysis of Fe 3+ , which induces substitutional doping of Ni 2+ ions into the etched sites and their further oxidation to the high‐valance Ni 3+ /Ni 4+ by coupling to the Ce 4+ /Ce 3+ pair in the oxygen‐vacancy‐rich CeO 2− x . Concomitantly, Fe 3+ is deposited on the surface of ceria as FeOOH nanosheets. The dispersed high‐valent Ni 3+ /Ni 4+ coupled with the decorated FeOOH nanosheets on CeO 2− x leads to efficient OER electrocatalysis with a low overpotential of 195 mV cm −2 at a current density of 10 mA cm −2 and a high turnover frequency (TOF) of 0.99 s −1 , which, to the best of the authors’ knowledge represents the best Ce‐containing OER catalyst reported to date, and comparable to other top OER catalysts. This work opens an avenue for engineering high‐valence metal ions in an oxide matrix for the OER or other oxidation reactions.