Unique Cd 0.5 Zn 0.5 S/WO 3- x direct Z -scheme heterojunction with S, O vacancies and twinning superlattices for efficient photocatalytic water-splitting.

Photocatalytic water-splitting employing the Z -scheme semiconductor systems mimicking natural photosynthesis is regarded as a promising way to achieve efficient soalr-to-H 2 conversion. Nevertheless, it still remains a big challenge to design high-performance direct Z -scheme photocatalysts without the use of noble metals as electron mediators. Herein, a unique Cd 0.5 Zn 0.5 S/WO 3- x direct Z -scheme heterojunction was constructed for the first time, which consisted of smaller O-vacancy-decorated WO 3- x nanocrystals anchoring on Cd 0.5 Zn 0.5 S nanocrystals with S vacancies and zinc blende/wurtzite (ZB/WZ) twinning superlattices. Under visible-light ( λ > 420 nm) irradiation, the Cd 0.5 Zn 0.5 S/WO 3- x composites exhibited an outstanding H 2 evolution reaction (HER) activity of 20.50 mmol h -1 g -1 (corresponding to the apparent quantum efficiency of 18.0% at 420 nm), which is much superior to that of WO 3- x , Cd 0.5 Zn 0.5 S, and Cd 0.5 Zn 0.5 S loaded with Pt. Interestingly, the introduced O and S vacancies contributed to improving the HER activity of Cd 0.5 Zn 0.5 S/WO 3- x significantly. Moreover, the cycling and long-term HER measurements confirmed the robust photocatalytic stability of Cd 0.5 Zn 0.5 S/WO 3- x for H 2 production. The excellent light harvesting and efficient spatial charge separation induced by the ZB/WZ twinning homojunctions and defect-promoted direct Z -scheme charge-transfer pathway are responsible for the exceptional HER capability. Our study could enlighten the rational engineering and optimization of semiconductor nanostructures for energy and environmental applications.