Selectively Etching Vanadium Oxide to Modulate Surface Vacancies of Unary Metal–Based Electrocatalysts for High‐Performance Water Oxidation

Electrocatalytic water splitting for hydrogen generation is hindered by the sluggish kinetics of water oxidation, and highly efficient electrocatalysts for the oxygen evolution reaction (OER) are urgently required. Numerous bi‐ and multimetal‐based, low‐cost, high‐performance OER electrocatalysts have been developed. However, unary metal–based high‐performance electrocatalysts are seldom reported. In the present study, Co2(OH)3Cl/vanadium oxide (VOy) composites are synthesized, from which VOy is completely etched out by a simple cyclic voltammetry treatment, which simultaneously transforms Co2(OH)3Cl in situ to ultrafine CoOOH. The selective removal of VOy modulates the nature of the surface in the obtained CoOOH by creating surface oxygen vacancies (Vo), along with disordered grain boundaries. The best‐performing CoOOH with optimum Vo is found to be associated with a low overpotential of 282 mV at 10 mA cm−2 catalytic current density on a simple glassy carbon electrode for OER. This facile protocol of selectively etching VOy to modulate the nature of the surface is successfully applied to synthesize another Fe‐based electrocatalyst with high OER performance, thus establishing its utility for unary metal–based electrocatalyst synthesis. Using an in situ transformation, the selective removal of VOy from hybrid materials modulates the nature of catalyst surfaces by creating surface oxygen vacancies. This is a promising synthetic approach that can be used to prepare low‐cost, unary metal–based electrocatalysts with excellent water oxidation performance.