Boosting Visible-Light Photocatalytic Syngas Production via Spatially Adjacent Dual Sites of Co Metal and Sulfur Vacancy in ZnIn ₂ S ₄

Solar-driven conversion of CO2 to syngas (CO/H2) represents a promising approach for carbon-neutral fuel synthesis. However, achieving efficient and selective photocatalytic CO2 reduction remains challenging due to competition from the hydrogen evolution reaction (HER) and inadequate spatial control over active site distribution. Herein, we introduce a Co-doped ZnIn2S4 (CoZIS) photocatalyst, where Co doping induces the formation of adjacent Co metal sites and sulfur vacancies (Vs), establishing spatially coordinated dual active sites. This architecture enables selective CO2 adsorption and activation at Co sites via d-p orbital hybridization coupled with proton reduction at neighboring Vs, thereby promoting proton-coupled electron transfer (PCET) and facilitating *COOH intermediate formation. The optimized CoZIS delivers a syngas production rate of 1314.8 μmol g–1 h–1 under visible-light irradiation, surpassing reported yields for many analogous sulfide-based photocatalysts. In-situ spectroscopic studies, kinetic isotope effect (KIE) experiments, and density functional theory (DFT) calculations demonstrate that the proximity of Co and Vs sites reduces the *COOH formation energy barrier while improving the charge separation efficiency. This work advances a versatile dopant-defect engineering strategy for creating synergistic dual sites that orchestrate CO2 and proton reduction, offering broad implications for syngas production and carbon recycling technologies.