Abstract:

Converting CO₂ into multi-carbon hydrocarbons through artificial photosynthesis remains challenging due to sluggish C–C coupling dynamics and complex multi-electron processes. In this study, ultrathin In_2.77S₄/CuInS₂ heterojunctions with abundant sulfur vacancies (S_V) were synthesized via a one-step hydrothermal method. The S-scheme charge-transfer mechanism, driven by the built-in electric field, was confirmed through in situ X-ray photoelectron spectroscopy (XPS), femtosecond transient absorption spectroscopy (fs-TAS) and photoelectrochemical characterization. This S-scheme heterojunction not only enhanced the separation efficiency of photogenerated charge carriers but also maintained excellent reduction capability, enabling CO₂ photoreduction to C₂ hydrocarbons. Furthermore, experimental results and density functional theory (DFT) calculations demonstrated that S_V shortened the Cu-In active site distance, optimized the local charge density and lowered the energy barrier for critical dimer formation (*CHOCO), thereby accelerating the C–C coupling kinetics. Finally, the In_2.77S₄/CuInS₂-4 catalyst exhibited excellent yield (47.2 μmol g⁻¹ h⁻¹) and selectivity (99.1%) of C₂H₄, which attributed to the synergistic effect of efficient carrier rectification by the S scheme heterojunction and optimized C–C coupling dynamics facilitated by S_V. Furthermore, isotope labeling confirmed CO₂ as the sole carbon source for the reaction. Overall, this "sulfur vacancy-heterojunction" strategy for CO₂ photoreduction to C₂H₄ with superior electron selectivity offers valuable insights into CO₂ utilization.

Key words: S-scheme, Photocatalysts, C₂H₄, CO₂ reduction, In_2.77S₄/CuInS₂