The evolution from typical type-I CdS/ZnS to type-II and Z-scheme hybrid structure for efficient and stable hydrogen production under visible light

An incompletely covered CdS/ZnS core/shell is synthesized via a simple hydrothermal method. Due to the defect energy levels introduced by zinc vacancies, the typical type-I heterojunction of CdS/ZnS evolves to a type-II heterojunction and Z-scheme hybrid structure so that the ZnS shell can timely transfer and capture the photogenerated holes from the CdS core. The surface photovoltage (SPV) distribution caused by photogenerated charges on the surface of catalyst is visually presented by Kelvin probe force microscopy with synchronous illumination (microscope SPV). It intuitively proves the effective spatial separation of photogenerated holes from the CdS core to the ZnS shell, for the first time. Under optimal conditions, the highest hydrogen production rate of CdS/ZnS reached 24.1 mmol g–1 h–1 under visible light illumination. The average apparent quantum yield of 9.3% can be achieved for 9 h of illumination (λ = 420 ± 5 nm). It exhibits highly efficient photocatalytic H2 evolution with well stability.