Modulating e_g Occupancy by A‐Site Vacancy to Boost Photocatalytic CO₂ Reduction on Perovskite Oxides

Abstract For photocatalytic CO₂ reduction, traditional ABO₃ perovskite oxides have suffered from the natural surface covered by the passivated AO layer, resulting in low photocatalytic activity. Herein, the double perovskite Sr₂TiFeO₆ is used as a precursor and citric acid is employed to selectively dissolve the A‐site cation, obtaining Sr_v‐Sr₂TiFeO₆ with abundant A‐site vacancies. Without using any co‐catalysts or sacrificial agents, the Sr_v‐Sr₂TiFeO₆ achieves efficient photoreduction of CO₂ to CH₄ with 91% selectivity and 43.17 µmol g⁻¹ h⁻¹ yield, which is almost five times that of the original Sr₂TiFeO₆. The results indicate that selectively removing A‐site can increase the concentration of oxygen vacancies and significantly reduce the exciton binding energy from 0.61 to 0.32 eV, thereby enhancing the charge transfer efficiency. Furthermore, the A‐site vacancies can adjust the surface electronic structure, leading to a decrease of e_g electrons occupancy on the active B‐site. This results in a shift of the reaction intermediates from strong adsorption to moderate adsorption. Specifically, the energy barrier of the water oxidation reaction, the rate‐determining step for the overall CO₂ reduction, is greatly reduced. This work provides a vivid case for modulating the electronic structure of perovskite oxide through introducing A‐site defects for efficient photoreduction of CO₂.