Achieving Higher Activityof Acidic Oxygen EvolutionReaction Using an Atomically Thin Layer of IrO_<i>x</i> over Co₃O₄

The development of electrocatalysts with reduced iridium (Ir) loading for the oxygen evolution reaction (OER) is essential to produce low-cost green hydrogen from water electrolysis under acidic conditions. Herein, an atomically thin layer of iridium oxide (IrO_<i>x</i>) has been uniformly dispersed onto cobalt oxide (Co₃O₄) nanocrystals to improve the efficient use of Ir for acidic OER. In situ characterization and theoretical calculations reveal that compared to the conventional IrO_<i>x</i> cluster, the atomically thin layer of IrO_<i>x</i> shows stronger interaction with the Co₃O₄ and consequently higher OER activity due to the Ir–O–Co bond formation at the interface. Equally important, the facile synthetic method and the promising activity in the proton exchange membrane water electrolyzer, reaching 1 A cm^–2 at 1.7 V with remarkable durability, enable potential scale-up applications. These findings provide a mechanistic understanding for designing active, stable and lower-cost electrocatalysts with well-defined structures for acidic OER.