Kinetic and Mechanistic Insights into the All-Solid-State Z-Schematic System

An all-solid-state Z-schematic system, CdS/Au/TiO1.96C0.04, has been reported for the efficient H2 generation from water under visible-light irradiation. However, a kinetic and mechanistic study of the directional charge transfer at the interfaces has not been done. In this study, electron pathways were constructed on the basis of steady-state photoluminescence (PL) spectral data, and the rate constants for charge transfer were calculated from time-resolved PL spectra. The PL results revealed that Au core played an important role in capturing the photoexcited electrons in the conduction band (CB) of TiO1.96C0.04 and accelerating the electron transfer to the valence band (VB) of CdS, leading to an efficient quenching of the holes left in the VB of CdS shell. The minimum energy pathways for H2 production on the surfaces of TiO1.C-96(0.04)(101) and CdS(101) were elucidated through first-principles calculations, indicating that the CdS shell has a lower energy barrier (2.81 eV) for the surface reaction than that (3.34 eV) of TiO1.96C0.04. Consequently, CdS/Au/TiO1.96C0.04 showed a vectorial electron transfer of TiO1.96C0.04 -> Au -> CdS in the form of the letter Z, which allowed the photoexcited electrons to be shuttled to a higher energy level, thereby producing a substantial level of H-2 on the CdS(101) surface.