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 (OHad) coverage and oxygen vacancy (OV) 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 OHad and OV 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.