Efficient spatial charge separation in unique 2D tandem heterojunction CdxZn1-xIn2S4-CdS-MoS2 rendering highly-promoted visible-light-induced H2 generation

Two-dimensional (2D) semiconductor nanostructures have exhibited great prospect as an efficient photocatalyst for solar-to-fuel application. In this work, a unique 2D tandem heterojunction consisting of ultrathin CdxZn1-xIn2S4 nanosheets coupled with rectangular CdS flakes and defect-rich MoS2 few-layered nanosheets was constructed for the first time. Remarkably, the efficient electron transfer channels present in the CdS/CdxZn1-xIn2S4 and CdxZn1-xIn2S4/MoS2 2D tandem heterojunctions facilitate the spatial separation and directional migration of photo-induced charge carriers effectively. Moreover, such 2D tandem heterojunction CdxZn1-xIn2S4-CdS-MoS2 is provided with excellent light harvesting capacity and abundant HER active sites from the defective MoS2 co-catalyst. These distinct advantages endow the optimized C(0.15)ZIS-5C-3M hybrid (5 wt% CdS, 3 wt% MoS2) with an exceptional photocatalytic H-2 evolution reaction (HER) activity of 27.14 mmol h(-1) g(-1), approximately 47 times that of pure ZnIn2S4 and it is much superior to that of Pt-decorated C(0.15)ZIS-5C and most ZnIn2S4-based composites reported previously. A high HER apparent quantum yield (AQY) of 19.97% is achieved at lambda = 400 nm. In addition, both the cycling and long-term HER measurements evidence the prominent stability of C(0.15)ZIS-5C-3M for H-2 production. The results indicated here could pave the way for the exploitation of new 2D heterostructures toward highly-efficient solar conversion and utilization.