Defect‐Driven Enhancement of Electrochemical Oxygen Evolution on Co‐Fe‐Al Ternary Hydroxides

: 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 Fe3 Co2 Al2 -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. Fe3 Co2 Al2 -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 Fe3 Co2 Al2 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 Fe3 Co2 Al2 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.