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

Abstract 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 *CH_xO) 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.