Twins in Cd_1-xZn_xS solid solution: Highly efficient photocatalyst for hydrogen generation from water

Cd_1-xZn_xS solid solution with nano-twin structures are synthesized and exhibit superior photocatalytic activities for H₂ evolution from water under visible light irradiation (λ ≥ 430 nm) without noble metal co-catalysts. Such Cd_0.5Zn_0.5S nanocrystals show the highest activity for hydrogen evolution with an extremely high apparent quantum yield (AQY = 43%) at 425 nm, achieving a hydrogen evolution rate of 1.79 mmol h^-1 without noble metals. The hydrogen evolution rate of 1.70 mmol h^-1 was achieved under simulated sunlight conditions (without infrared light). The "back to back" potential formed by parallel nano-twins in the Cd_1-xZn_xS crystals can significantly improve the separation of the photo-generated electrons/holes (preventing their recombination) thus enhancing the photocatalytic activity. Photodeposition experiments of noble metals strongly support such a mechanism. It is found that noble metals were selectively photo-deposited at central regions between the twin boundaries. The concentration of free electrons at the central region of twins was markedly higher and the twins can effectively separate the H₂ evolution sites (electrons) from oxidation reaction sites (holes).