Tuning the Crystal Phases of SnIn ₄ S ₈ for Precise Regulation of C ₁ /C ₂ Products Selectivity in Photocatalytic CO ₂ Reduction

The photocatalytic CO 2 reduction system yields a complex and diverse range of products, and the precise regulation of product selectivity remains one of the core challenges in this field. This work focuses on the crystal phase engineering of bimetallic sulfides, systematically investigating their regulatory effect on the selectivity of CO 2 photoreduction products. The cubic-phase SnIn 4 S 8 (SIS-C) and tetragonal-phase SnIn 4 S 8 (SIS-T) photocatalysts were successfully prepared by adjusting the solvent type under a high-pressure synthetic route. Although SIS-C exhibits stronger light absorption, its highly symmetric crystal structure shows three-dimensional isotropy, leading to a lack of directional driving force for photogenerated electron–hole separation. Additionally, the uniform atomic coordination environment of SIS-C hinders the formation of asymmetric charges, resulting in a specific selectivity toward C 1 products (mainly CO). In contrast, SIS-T possesses stronger electron reducibility due to its more negative conduction band potential, providing sufficient thermodynamic driving force. The low symmetry of its tetragonal phase induces an asymmetric electron density distribution at metal sites, facilitating asymmetric coupling and creating favorable conditions for C–C coupling and C 2 products (mainly C 2 H 6 ) generation. This work clarifies the critical influence of crystal phase regulation on the behavior of photogenerated carriers and the C–C coupling process, offering an important theoretical basis for the design of highly selective photocatalysts for C 2 products formation.