Molten salt construction of core-shell structured S-scheme CuInS2@CoS2 heterojunction to boost charge transfer for efficient photocatalytic CO2 reduction

Weak redox ability and severe charge recombination pose significant obstacles to the advancement of CO₂ photoreduction. To tackle this challenge and enhance the CO₂ photoconversion efficiency, fabricating well-matched S-scheme heterostructure and establishing a robust built-in electric field emerge as pivotal strategies. In pursuit of this goal, a core-shell structured CuInS₂@CoS₂ S-scheme heterojunction was meticulously engineered through a two-step molten salt method. This approach over the CuInS₂-based composites produced an internal electric field owing to the disparity between the Fermi levels of CoS₂ and CuInS₂ at their interface. Consequently, the electric field facilitated the directed migration of charges and the proficient separation of photoinduced carriers. The resulting CuInS₂@CoS₂ heterostructure exhibited remarkable CO₂ photoreduction performance, which was 21.7 and 26.5 times that of pure CuInS₂ and CoS₂, respectively. The S-scheme heterojunction photogenerated charge transfer mechanism was validated through a series of rigorous analyses, including in situ irradiation X-ray photoelectron spectroscopy, work function calculations, and differential charge density examinations. Furthermore, in situ infrared spectroscopy and density functional theory calculations corroborated the fact that the CuInS₂@CoS₂ heterojunction substantially lowered the formation energy of *COOH and *CO. This study demonstrates the application potential of S-scheme heterojunctions fabricated via the molten salt method in the realm of addressing carbon-related environmental issues.