Achieving Almost 100% Selectivity in Photocatalytic CO2 Reduction to Methane via In‐Situ Atmosphere Regulation Strategy

Artificial photosynthesis, harnessing solar energy to convert CO2 into hydrocarbons, presents a promising solution for climate change and energy scarcity. However, photocatalytic CO2 reduction often terminates at the CO stage due to limited electron transfer capacity, hindering the formation of higher‐energy hydrocarbons such as CH4. 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 CO2‐to‐CH4 conversion. Specifically, the single‐atom Cu catalyst (Cu‐SA‐CO) is prepared by anchoring single‐atom Cu onto defective TiO2 substrates (Cu‐SA‐CO) under a CO reduction atmosphere. Under illumination, the catalyst exhibited outstanding CH4 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 *CHxO) 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 CO2 reduction selectivity, providing a novel avenue for designing efficient photocatalysts. The strategy of molecular imprinting by dynamically reacting molecules is proposed and applied to precisely tailor surface sites on catalysts for the first time. The single‐atomic Cu catalyst (Cu‐SA‐CO) is prepared and achieved almost 100% selectivity in photocatalytic CO2 reduction to methane, due to enhanced *CO adsorption and hydrogenation by the synergistic interaction between Cu atoms and oxygen defects.