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 Ni3+ or even Ni4+ species under mild conditions. Herein, a one‐step synthesis of high‐valence nickel‐doped CeO2−x covered with FeOOH nanosheets in the presence of Ni2+/Fe3+ 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 Fe3+, which induces substitutional doping of Ni2+ ions into the etched sites and their further oxidation to the high‐valance Ni3+/Ni4+ by coupling to the Ce4+/Ce3+ pair in the oxygen‐vacancy‐rich CeO2−x. Concomitantly, Fe3+ is deposited on the surface of ceria as FeOOH nanosheets. The dispersed high‐valent Ni3+/Ni4+ coupled with the decorated FeOOH nanosheets on CeO2−x leads to efficient OER electrocatalysis with a low overp…