Efficient\nElectroreduction of CO<sub>2</sub> to Formate\nvia Simultaneous Tuning of Hydroxyl Group Coverage and Oxygen Vacancy\nAmount of In<sub>2</sub>O<sub>3</sub>

Electrochemical CO<sub>2</sub> reduction (ECR) to high\nvalue-added\nfeedstocks is a sustainable way to address energy and environmental\nissues. However, there still exists a bottleneck in comprehending\nthe structure–activity relationship of catalysts for ECR. Herein,\nwe demonstrated that the simultaneous tuning of surface-adsorbed hydroxyl\ngroup (OH<sub>ad</sub>) coverage and oxygen vacancy (O<sub>V</sub>) amount on the In<sub>2</sub>O<sub>3</sub> surface was an effective\napproach to derive an excellent formate Faradaic efficiency (FE) of\nabove 80% at a wide potential range from −1.0 to −1.5\nV versus the reversible hydrogen electrode (vs RHE) with promising\ndurability. Electrochemical experiments and theoretical analyses revealed\nthat the synergistic effect of OH<sub>ad</sub> and O<sub>V</sub> could\nsmartly optimize the adsorption sites, accelerate the electron transfer,\nand stabilize *CO<sub>2</sub><sup>•–</sup> and *OCHO\nintermediates, and thus facilitate ECR activity. This result will\ncontribute to the understanding of the critical role of these surface\noxygen species in ECR, which can offer valuable insights into the\nrational catalyst design for comprehensive utilization of CO<sub>2</sub> with high energy efficiency.