Highly efficient visible-light-assisted photocatalytic hydrogen generation from water splitting catalyzed by Zn0.5Cd0.5S/Ni2P heterostructures

Abstract Development of heterostructured photocatalysts which can facilitate spatial separation of photo-generated charge carriers is crucial for achieving improved photocatalytic H 2 production. Consequently, herein, we report the synthesis of Zn 0.5 Cd 0.5 S/Ni 2 P heterojunction photocatalysts with varying amount of Ni 2 P, 0.5 ( S1 ), 1 ( S2 ), 3 ( S3 ), 5 ( S4 ) and 10wt% ( S5 ) for the efficient visible-light-assisted H 2 generation by water splitting. The heterostructures were characterized thoroughly by PXRD, FE-SEM, EDS, HR-TEM and XPS studies. FE-SEM and HR-TEM analyses of the samples unveiled the presence of Zn 0.5 Cd 0.5 S microspheres composed of smaller nanocrystals with the surface of the microspheres covered with Ni 2 P nanosheets and the intimate contact between the Zn 0.5 Cd 0.5 S and the Ni 2 P. Further, visible-light-assisted photocatalytic investigation of the samples showed excellent water splitting activity of the heterostructure, Zn 0.5 Cd 0.5 S/1wt%Ni 2 P ( S2 ) with very high H 2 generation rate of 21.19 mmol h −1 g −1 and the AQY of 21.16% at 450 nm with turnover number (TON) and turnover frequency (TOF) of 251,516 and 62,879 h −1 respectively. Interestingly, H 2 generation activity of S2 was found to be about four times higher than that of pure Zn 0.5 Cd 0.5 S (5.0 mmol h −1 g −1 ) and about 240 times higher than that of CdS/1wt%Ni 2 P. The enhanced H 2 generation activity of S2 has been attributed to efficient spatial separation of photogenerated charge carriers and the presence of highly reactive Ni 2 P sites on the surface of Zn 0.5 Cd 0.5 S microspheres. A possible mechanism for the enhanced photocatalytic H 2 generation activity of Zn 0.5 Cd 0.5 S/1wt%Ni 2 P ( S2 ) has been proposed and is further supported by photoluminescence and photocurrent measurements. Furthermore, the catalyst, S2 can be recycled for several cycles without significant loss of catalytic activity and photostability. Remarkably, the H 2 generation activity of S2 was found to be even higher than the reported examples of Zn x Cd 1-x S doped with noble metal cocatalysts. Hence, the present study highlights the importance of Zn 0.5 Cd 0.5 S/Ni 2 P heterostructures based on non-noble metal co-catalyst for efficient visible-light-driven H 2 production from water splitting.