Modulating eg 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.