Boosted CO₂ Photoreduction Performance by CdSe Nanoplatelets via Se Vacancy Engineering

2D metal-chalcogenide nanoplatelets (NPLs) exhibit promising photocatalysis properties due to their ultrathin morphology, high surface-to-volume ratio, and enhanced in-plane electron transport mobility. However, NPLs, especially cadmium chalcogenides, encounter challenges in CO₂ photoreduction due to insufficient solar energy utilization and fast recombination of photogenerated charge carriers. Defect engineering offers a potential solution but often encounters difficulties maintaining structural integrity, mechanical stability, and electrical conductivity. Herein, by taking two monolayers (2ML) CdSe NPLs as a model system, selenium (Se) vacancies confined in atomic layers can enhance charge separation and conductivity. A straightforward approach to create Se vacancies in various monolayers CdSe NPLs (2, 4, and 5ML) has been developed, enabling efficient CO₂ photoreduction with a 4-fold increase in CO generation compared to their defect-free counterparts. Significantly, accounting for higher charge density and efficient carrier transport due to Se vacancies, defective 2ML CdSe NPLs (V_Se-2ML CdSe) exhibit CO evolution performance up to 2557.5 µmol g^-¹ h^-¹ with no significant decay over 5 h, which is an order of magnitude higher than that of common semiconductor catalysts. This study establishes a practical way to design advanced 2D semiconductor photocatalysts to achieve efficient CO₂ photoreduction via defect engineering.