Photoswitchable Chlorine Vacancies in Ultrathin Bi₄O₅Cl₂ for Selective CO₂ Photoreduction

CO₂ photoreduction currently faces two challenges: low photoreduction efficiency and poor product selectivity. Ultrathin two-dimensional bismuth oxyhalide, with a large number of surface vacancies (active sites), is an ideal material for regulating CO₂ photoconversion. However, surface vacancies in this catalyst are easily deactivated during the reaction. CO₂ photoreduction relies on sufficient active sites; hence, we synthesized ultrathin Bi₄O₅Cl₂ nanoplates via a water-assisted self-assembly process with sufficient photoswitchable surface Cl vacancies for solar-driven CO₂-to-CO reduction. The surface Cl vacancies were generated under light irradiation and filled again with migrated Cl^– under an O₂ atmosphere after turning off the irradiation. These photoswitchable vacancies enabled Bi₄O₅Cl₂ to produce 58.49 μmol g^–1 CO after 4 h of irradiation with high stability and lowered the energy barriers of the rate-determining (CO₂-to-COOH^–) and selectivity-determining steps (COOH^–-to-CO), enabling 100% product selectivity. The reversible, photoswitchable Cl vacancies have a higher potential as active sites for CO₂ photoreduction than synthetically introduced static surface vacancies, which could provide a feasible strategy for the creation of highly dynamic, active-defective catalysts for solar-energy conversion.