Facile Construction of Cu ₃₁ S ₁₆ /CdS p–n Heterojunctions for Enhanced Photocatalytic H ₂ Production via Efficient Charge Separation

To meet the urgent global demand for hydrogen (H 2 ) energy, the development of highly efficient, stable, and noble‐metal‐free photocatalysts has become a crucial research direction. While CdS possesses broad light absorption and a suitable band structure, its practical application is severely limited by rapid charge carrier recombination, insufficient active sites, and particle agglomeration. Integrating semiconductors to construct heterojunctions effectively mitigates these issues by providing abundant active sites and accelerating charge separation. Herein, a facile in situ solvothermal synthesis strategy was employed to construct a Cu 31 S 16 /CdS heterojunction photocatalyst. The optimized composite (0.2‐Cu 31 S 16 /CdS) exhibited a remarkable H 2 production rate of 5369 μmol g −1 h −1 , representing 20.4 times enhancement over pure CdS. Furthermore, the heterojunction maintained robust H 2 production performance without noticeable activity decay over five consecutive cycles. Photoelectrochemical measurements and density functional theory (DFT) revealed that introducing Cu 31 S 16 generates a stable built‐in electric field and induces interfacial band bending. This formed p–n heterojunction provides a strong driving force for spatial charge separation, significantly reducing charge transfer resistance, prolonging carrier lifetime, and enhancing the H 2 production performance. This work provides valuable guidelines for the rational design of robust metal sulfide heterojunctions, paving the way for sustainable solar‐to‐H 2 conversion.