Direct Z-Scheme Photocatalytic System: Insights into the Formative Factors of Photogenerated Carriers Transfer Channel from Ultrafast Dynamics

The direct Z-scheme photocatalytic heterojunction, possessing type II band alignments but simultaneously realizing the spatial separation of photogenerated electrons and holes (PEHs) and the well-preserved strong redox ability, is a promising strategy for solving energy and environmental issues. However, the conventional method of solely relying on the direction of interfacial electric field (IEF) to determine the Z-scheme is often different with experiments. Properly evaluating and constructing the direct Z-scheme remain limited. Herein, combining hybrid density functional theory and excited state ultrafast dynamics simulation, we find that the formative factor of the Z-scheme path comes from two aspects by systematically exploring a series of prototypical heterojunctions taking X2Y3 ferroelectrics (X: Al, Ga, In. Y: S, Se, Te) and BCN semiconductors. On the one hand, the interlayer recombination of PEHs with weak redox ability can be significantly promoted by the IEF. On the other hand, for PEHs with strong redox ability, the weak nonadiabatic coupling of interface transfer channel plays a key role in preserving the high activity of PEHs, which can extend the reacting time of PEHs from femtosecond to hundreds of nanosecond scale. This study deepens the understanding of Z-scheme formation and can accelerate the design of direct Z-scheme photocatalysts.