Efficient Electroreduction of CO2 to Formate via Simultaneous Tuning of Hydroxyl Group Coverage and Oxygen Vacancy Amount of In2O3

Electrochemical CO₂ reduction (ECR) to high value-added feedstocks is a sustainable way to address energy and environmental issues. However, there still exists a bottleneck in comprehending the structure–activity relationship of catalysts for ECR. Herein, we demonstrated that the simultaneous tuning of surface-adsorbed hydroxyl group (OH_ad) coverage and oxygen vacancy (O_V) amount on the In₂O₃ surface was an effective approach to derive an excellent formate Faradaic efficiency (FE) of above 80% at a wide potential range from −1.0 to −1.5 V versus the reversible hydrogen electrode (vs RHE) with promising durability. Electrochemical experiments and theoretical analyses revealed that the synergistic effect of OH_ad and O_V could smartly optimize the adsorption sites, accelerate the electron transfer, and stabilize *CO₂^•– and *OCHO intermediates, and thus facilitate ECR activity. This result will contribute to the understanding of the critical role of these surface oxygen species in ECR, which can offer valuable insights into the rational catalyst design for comprehensive utilization of CO₂ with high energy efficiency.