S-scheme Co3(PO4)2/Twinned-Cd0.5Zn0.5S homo-heterojunction for enhanced photocatalytic H2 evolution

Abstract

Heterojunction photocatalysts have been demonstrated to be effective for the interfacial charge transfer and utilization, if the charge transfer in bulk phase can be promoted, more photoinduced charges can be utilized to achieve a higher efficiency of light energy conversion. Herein, twinned-Cd0.5Zn0.5S (T-CZS) homojunction formed by zinc blende Cd0.5Zn0.5S (ZB-CZS) and wurtzite Cd0.5Zn0.5S (WZ-CZS) is obtained via a facile hydrothermal method, and then Co3(PO4)2 is introduced to the surface of T-CZS to form homo-heterojunction using a solvent evaporation strategy. The photocatalytic H2 evolution tests show that the activity of T-CZS is obviously higher than ZB-CZS or WZ-CZS, and Co3(PO4)2 can increase the H2 releasing rate of T-CZS from 13.0 mmol·h−1·g−1 to 64.8 mmol·h−1·g−1 over 5.7 wt% Co3(PO4)2/T-CZS. The apparent quantum efficiency (AQE) can reach 6.4% under 400 nm light irradiation. Under 800 nm near-infrared light (NIR), the H2 releasing rate can reach 0.23 mmol·h−1·g−1. The investigation shows that the carrier transfer between T-CZS and Co3(PO4)2 follows the S-scheme transfer path according to the electron paramagnetic resonance spectroscopy analysis and calculation by density flooding theory (DFT) The enhanced activity of Co3(PO4)2/T-CZS can be mainly attributed to the homo-heterojunction synergistic effect between ZB-CZS/WZ-CZS homojunction in T-CZS and the S-scheme heterojunction between T-CZS and Co3(PO4)2, which well avoids the rapid recombination of bulk and surface electron-hole pairs by accelerating charge transfer. Meanwhile, the improved light-harvesting ability, more active sites and lower H2 production overpotential induced by Co3(PO4)2, jointly contribute to a quick kinetics of H2 evolution. In addition, other metal phosphates MPO4 (M = Ba, Bi, Ag and Zn) are also employed to enhance the activity of T-CZS, they are all effective candidates for construction homo-heterojunction with T-CZS.