Subnanometric Bismuth Clusters Confined in Pyrochlore‐Bi2Sn2O7 Enable Remarkable CO2 Photoreduction

The development of highly efficient photocatalysts for conversion of carbon dioxide (CO₂ ) with water (H₂ O) into chemical fuels is of great importance for energy sustainability and carbon resource utilization. Herein, we demonstrated a facile hydrothermal method for in situ construction of subnanometric Bi metallic clusters in pyrochlore-Bi₂ Sn₂ O₇ frameworks, leading to the remarkable improvements of photocatalytic performances for CO₂ reduction into CO in the absence of sacrificial reagent. More specifically, an outstanding CO evolution activity of 114.1 μmol g^-1 h^-1 has been achieved, more than 20-fold improvement compared with the pristine Bi₂ Sn₂ O₇ (5.7 μmol g^-1 h^-1 ). Detailed experiments together with in situ characterizations reveal that the spatially confined Bi clusters could significantly promote charge-separation/electron-enrichment and adsorption/activation of CO₂ molecules, which provides highly efficient reaction channels to facilitate the generation of *COOH intermediate as well as the subsequent desorption of *CO towards CO formation. These demonstrations provide an important knowledge for precise design and fabrication of highly efficient photocatalysts for CO₂ conversion into solar fuels.