Asymmetric Triple‐Atom Sites Combined with Oxygen Vacancy for Selective Photocatalytic Conversion of CO 2 to Propionic Acid

Photocatalytic CO₂ reduction to multicarbon products is an emerging approach for achieving carbon neutrality; however, the design of active sites that effectively promote multistep C-C coupling remains a challenge. Here, we propose a straightforward defect engineering approach to construct asymmetric triple-atom sites (Cu-Cu^δ+-W^δ+) on CuWO₄ with oxygen vacancies (OVs) (named CWO-OVs). The optimized CWO-OVs achieve a photochemical synthesis rate of propionic acid (C₃H₆O₂, PA) of 86.46±2.92 μmol g^-1 h^-1, with an electron-based selectivity of 89.27 %, which exhibits a remarkable advantage in the field of photocatalytic CO₂ reduction to C₂₊ products. Experimental results and density functional theory calculations corroborate the prominent role of OVs in inducing the triple-atom sites: (1) the asymmetric Cu-Cu^δ+ triggers the first step of C₁-C₁ coupling to form *CH₂CH₃; (2) Cu^δ+-W^δ+ facilitates subsequent C₂-C₁ bonding, ultimately leading to PA production. This charge-asymmetric cascade reaction system offers new insights into the design of efficient photocatalysts for the synthesis of multi-carbon products.