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-Cuδ+-Wδ+) 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-Cuδ+ triggers the first step of C1-C1 coupling to form *CH2CH3
(2) Cuδ+-Wδ+ 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.