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

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-0.5Cd0.5S/Ni2P heterojunction photocatalysts with varying amount of Ni2P, 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-0.5Cd0.5S microspheres composed of smaller nanocrystals with the surface of the microspheres covered with Ni2P nanosheets and the intimate contact between the Zn-0.5Cd0.5S and the Ni2P. Further, visiblelight-assisted photocatalytic investigation of the samples showed excellent water splitting activity of the heterostructure, Zn-0.5Cd0.5S/1wt%Ni2P (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-0.5Cd0.5S (5.0 mmolh(-1)g(-1)) and about 240 times higher than that of CdS/1wt%Ni2P. The enhanced H-2 generation activity of S-2 has been attributed to efficient spatial separation of photogenerated charge carriers and the presence of highly reactive Ni2P sites on the surface of Zn-0.5Cd0.5S microspheres. A possible mechanism for the enhanced photocatalytic H-2 generation activity of Zn-0.5Cd0.5S/1wt%Ni2P (S2) has been proposed and is further supported by photoluminescence and photocurrent measurements. Furthermore, the catalyst, S-2 can be recycled for several cycles without significant loss of catalytic activity and photostability. Remarkably, the H-2 generation activity of S-2 was found to be even higher than the reported examples of ZnxCd1-xS doped with noble metal cocatalysts. Hence, the present study highlights the importance of Zn-0.5Cd0.5S/Ni2P heterostructures based on non-noble metal co-catalyst for efficient visible-light-driven H-2 production from water splitting. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.