Synergistic dual-vacancy engineering in a Cl-doped Cu2O/Cu3SnS4 S-scheme heterojunction for selective photocatalytic CO2-to-C2H4 conversion

Photocatalytic conversion of CO 2 into valuable multicarbon products is often limited by inefficient charge separation and insufficient catalytic sites in conventional monovacancy catalysts. In this work, we address these challenges by constructing an S-scheme heterojunction of Cl-doped Cu 2 O/Cu 3 SnS 4 (COCS) with deliberately engineered dual oxygen and sulfur vacancies via an in situ growth strategy. The synergistic interaction between the two types of vacancies significantly promotes charge transfer and reduces the energy barrier for C–C coupling. Under visible-light irradiation in pure water without sacrificial agents, the optimized COCS-2 catalyst exhibits a C 2 H 4 production rate of 15.99 μmol·g −1 ·h −1 with 37.3% selectivity, along with an apparent quantum yield of 3.46% at 400 nm. Combined experimental characterization and theoretical calculations elucidate that the dual vacancies not only enhance spatial charge separation but also stabilize key reaction intermediates. This study provides a rational design principle for vacancy-engineered heterojunctions and advances the development of selective CO 2 -to-C 2 H 4 photocatalysts.