Roles of Interface Polaron in the Z-Scheme Photocatalytic Mechanism for Water Splitting: A Multiscale Simulation Study

Using multiscale simulations, the effect of the polaron formation on the Z-scheme charge separation in g-C3N4/TiO2 heterojunction was systematically studied in this work. It was confirmed that the presence of a polaron at the interface of the g-C3N4/TiO2 heterojunction enhances the interface dipole moment, thereby strengthening the driving force of the charge separation and accelerating the interface recombination of an electron from the anatase TiO2 conduction band and hole from the valence band of g-C3N4. The enhancement in Z-scheme charge transport was further demonstrated through the comparison of nonadiabatic molecular dynamics (NAMD) calculation and the classical Shockley–Read–Hall (SRH) recombination model, which gave very similar theoretical recombination rate changes, 3.7 and 3.5 times greater than the polaron-free model, respectively. This theoretical study reveals the origins of the strong Z-scheme, which mostly occurs in the heterojunction photocatalysts composed of semiconductor phases having polarons. In addition, our study suggests that the polaron formation level and concentration can be the factors of degree of the Z-scheme recombination of a semiconductor heterostructure.