CeO2-supported In2O3 for enhanced CO2 electroreduction to formate: the role of support defects.

Simultaneous activation of CO2 and H2O remains a key challenge in the electrochemical carbon dioxide reduction reaction (CO2RR) to formate. Beyond providing structural support, the catalyst support can serve as a secondary active component that facilitates reactant adsorption and activation. Herein, an In2O3/CeO2 catalyst was constructed by tuning the oxygen vacancy (OV) concentration in the CeO2 support. The kinetic analysis, in situ spectroscopic studies, and density functional theory calculations collectively confirm that the abundant OV-associated Lewis acid sites facilitate the adsorption and dissociation of H2O, thereby supplying reactive hydrogen species for CO2-derived intermediates. This process enhances the hydrogenation steps in CO2RR and selectively promotes the formation of formate. In addition, defective support simultaneously stabilizes highly dispersed In2O3 species with enhanced interfacial electron transfer, promoting the adsorption of the *OCHO intermediate. Remarkably, the optimal catalyst (20%In2O3/CeO2-OVR) delivers a high current density of 238.0 mA cm-2 and a high Faradaic efficiency for formate (FEformate%) of 96.0% at -1.37 V vs. RHE, while maintaining FEformate% above 90% over a broad potential range (-0.77 to -1.37 V vs. RHE). Furthermore, it demonstrates high stability with no significant activity decay over 50 h of operation. This study highlights support-defect engineering as a strategy for promoting efficient and selective CO2 electroreduction to formate.