Twins in Cd1−xZnxS solid solution: Highly efficient photocatalyst for hydrogen generation from water

Cd1−xZnxS 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 Cd0.5Zn0.5S 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 Cd1−xZnxS 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).