Activation to Deactivation Dynamics of Cu‐Embedded TiO ₂ for Solar CH ₄ Generation

Photocatalytic CO 2 reduction is known to accelerate on surfaces with defects such as oxygen vacancies (Vo), undercoordinated metal atoms, and hydroxyl groups (). This is further boosted while these defects, Vo‐coupled undercoordinated metal atoms, and proximal , act synergistically. However, it is challenging to make atomic‐level patterns of such structural arrangements and monitor their activation anddeactivation pathways. Herein, we report single‐atom hydroxylated‐Cu in the vicinity of Ti atom that triggers Vo generation owing to specific structural arrangements. It finally activates CO 2 by coordinative activation and eventually transforms CO 2 to CH 4 through Cu–*CHO intermediate. Alongside the activation, deactivation of photocatalyst also proceeds, accompanied by the change in the binding environment of the Cu, generation of the oxidizing hydroxyl radicals, and photocatalytically inactive carbonaceous species. This work outlines the efficacious role of Cu in CO 2 reduction to CH 4 and provides valuable insights into the activation and deactivation mechanisms.