Transient Metal Centers at the Covalent Heterointerface Favor Photocatalytic Hydrogen Evolution

Semiconductor heterostructures effectively promote the transfer and separation of interfacial photoinduced charges for the photocatalytic process. Herein, we constructed a direct Z-scheme SnSe₂/CdS heterojunction photocatalyst. N-type SnSe₂ semiconductors are suitable candidate materials for oxidation half-reactions in Z-scheme heterojunctions. The intimate atomic-level interfacial contact through Cd-Se bonds provides a better interfacial charge transport channel for the photoinduced charges. Moreover, the transient Sn⁴⁺/Sn⁰ centers caused by the photoredox process boost the interfacial charge transport/separation at the interface. Besides, the presence of S vacancies acting as electron enrichment centers further enhances the redox ability for hydrogen production. Therefore, the SnSe₂/CdS heterostructure showed a superior visible-light photocatalytic H₂-production activity of 13.6 mmol·g^-1·h^-1 using ascorbic acid as a sacrificial agent, which is 9.7 times higher than that of pristine CdS. The apparent quantum yield reaches 10.5% at λ = 420 nm. This work provides a useful way to improve charge transfer in the Z-scheme heterojunction photocatalyst for hydrogen production.