Visible-light-driven CO2 reduction to ethylene on CdS: Enabled by structural relaxation-induced intermediate dimerization and enhanced by ZIF-8 coating

• Photocatalytic CO 2 reduction to C 2 H 4 was first achieved on CdS with S vacancies. • S v -CdS@ZIF-8 heterojunction promotes efficiency and selectivity of C 2 H 4 production. • Sulfur vacancies lead to reduced Cd-Cd distance and charge enrichment on Cd atoms. • Structural relaxation endows successful *CHO dimerization and ethylene generation. Visible-light-driven CO 2 reduction yielding commodity chemicals such as ethylene holds tremendous potentials for achieving a carbon-neutral circular economy in the energy and chemical industry. Despite the success of electrochemical CO 2 reduction, efficient and selective ethylene generation has not been achieved by photocatalytic means because the intermediate dimerization fails to occur on existing photocatalysts. Here, we first demonstrate that the presence of sulfur vacancies in CdS (S v -CdS) lead to reduced Cd-Cd distance and charge enrichment on Cd atoms. This structural relaxation and associated electronic structure tuning endow successful *CHO dimerization and hence ethylene generation. The photocatalyst can be optimized by coating S v -CdS with ZIF-8 to form a core-shell structure, which presents further lowered energy barrier for both *CO hydrogenation and *CHO dimerization. With these combined intermediate manipulation strategies, the optimized photocatalyst exhibits a record-high ethylene selectivity of 12.8 % at a production rate of 0.8 μmol g −1 h −1 .