Unraveling the Influence of Oxygen Vacancy Concentration on Electrocatalytic CO₂ Reduction to Formate over Indium Oxide Catalysts

Rational engineering of oxygen vacancies in a metal oxide-based catalyst represents an effective strategy to regulate catalytic performances by influencing both their electrochemical active surface areas and the microelectronic structure. However, the precise control and modulation of the concentration and uniformity of oxygen vacancies on the catalyst surface still remains inadequately explored and poorly elucidated. Herein, we develop a facile and effective method to prepare a series of In2O3 nanorods with varying oxygen vacancy concentrations for efficient electrolytic CO2 reduction to formate. Experimental results and theoretical calculations reveal that the abundant oxygen vacancies in the In2O3 catalyst significantly improve CO2 activation and promote the production of *HCOO intermediates, achieving a maximum formate Faradaic efficiency of 91.2% at −1.27 V vs a reversible hydrogen electrode (RHE) with high partial current density and, meanwhile, superior stability. The underlying relationship between the oxygen vacancy concentration and CO2 reduction reaction (CO2RR) performance was further established. This work offers a feasible strategy to finely tune the oxygen vacancy concentration in p-block metal oxide-based catalysts for highly efficient electrolytic CO2RR.