Achieving Almost 100% Selectivity in Photocatalytic CO 2 Reduction to Methane via In-Situ Atmosphere Regulation Strategy.

Artificial photosynthesis, harnessing solar energy to convert CO 2 into hydrocarbons, presents a promising solution for climate change and energy scarcity. However, photocatalytic CO 2 reduction often terminates at the CO stage due to limited electron transfer capacity, hindering the formation of higher-energy hydrocarbons such as CH 4 . This study introduces, for the first time, an in-situ atmosphere regulation strategy, refined from molecular imprinting methodologies, using dynamically reacting molecules to precisely engineer photocatalytic surface sites for selective *CO adsorption and hydrogenation in CO 2 -to-CH 4 conversion. Specifically, the single-atom Cu catalyst (Cu-SA-CO) is prepared by anchoring single-atom Cu onto defective TiO 2 substrates (Cu-SA-CO) under a CO reduction atmosphere. Under illumination, the catalyst exhibited outstanding CH 4 selectivity (almost 100%) and productivity (58.5 µmol g -1  h -1 ). Mechanistic investigations reveal that the coordination environment of the Cu single atoms is significantly affected by dynamically reacting molecules (CO and *CH x O) during synthesis, leading to a Ti-Cu-O structure. The structure, with the synergistic interaction between Cu single atoms and oxygen defects, significantly enhances *CO adsorption and hydrogenation, thereby promoting the formation of methane. This work pioneers the use of dynamically reactive molecules as imprinted templates to tune photocatalytic CO 2 reduction selectivity, providing a novel avenue for designing efficient photocatalysts.