Abstract

Efficient, abundant and low‐cost catalysts for the oxygen evolution reaction (OER) are required for energy conversion and storage. In this study, a doping–etching route has been developed to access defect rich Fe–Co–Al (Fe–Co–Al‐AE) ternary hydroxide nanosheets for superior electrochemical oxygen evolution. After partial etching of Al, ultrathin Fe₃Co₂Al₂‐AE electrocatalysts with a rich pore structure are obtained with a shift of the cobalt valence state towards higher valence (Co²⁺→Co³⁺), along with a substantial improvement in the catalytic performance. Fe₃Co₂Al₂‐AE shows a notably lower overpotential of only 284 mV at a current density of 10 mA cm⁻² and double the OER mass activity of the etching‐free Fe₃Co₂Al₂ with an overpotential of 350 mV. Density functional theory shows the leaching of Al changes the rate‐determining step of the OER from conversion of *OOH into O₂ on Fe₃Co₂Al₂ to formation of OOH from *O on the Al‐defective catalysts. This work demonstrates an effective route to design and synthesize transition metal electrocatalysts and provides a promising alternative for the further development of oxygen evolution catalysts.