An efficient improvement for photocatalytic hydrogen peroxide production: Sulfur vacancies in CaIn₂S₄

Visible-light-driven hydrogen peroxide (H₂O₂) synthesis is a sustainable and economically viable strategy for green production. However, most metal sulfide semiconductors exhibit insufficient band potentials, limiting selectivity and quantum yield. Here, we introduce sulfur vacancies into CaIn₂S₄ to modify its band structure, enhancing the conduction band's reduction capability and shifting oxygen reduction from a single direct 2e^- pathway to a dual-pathway mechanism. This adjustment improves electron utilization efficiency. Theoretical calculations reveal that sulfur vacancies act as electron traps, promoting charge separation and suppressing recombination. Structural and electronic characterizations confirm these effects, and as a result, sulfur-vacancy-rich CaIn₂S₄ (CaIS SV) achieves a photocatalytic H₂O₂ production rate 9-fold than that of pristine CaIn₂S₄.