Unveiling the direct-to-indirect bandgap transition mechanism in the photocatalytic hydrogen evolution of ZnxCd1−xS solid solution

Solid solution strategy could improve the photocatalytic performance thermodynamically, yet the study focusing on the carrier dynamics of the solid solution catalysts was equally important. Herein, a series of Zn_xCd_1−xS solid solutions were successfully synthesized based on band structure regulation, and the carrier dynamics were investigated by femtosecond transient absorption spectroscopy (TAS) and DFT, which unveiled a variation of the mixed direct-to-indirect bandgap transition mechanism in Zn_xCd_1−xS solid solution. The indirect bandgap exhibited a lower photocarrier recombination rate and, more importantly, could also serve as a trapping center for photocarrier, thus promoting the efficiency of charge separation. Consequently, Zn_xCd_1−xS solid solutions achieved an approximately eleven-fold enhancement in the hydrogen evolution rate (1426.66 μmol h⁻¹) relative to that of bare CdS (129.83 μmol h⁻¹) under visible light (>420 nm). This work proposed that the enhanced photocatalytic performance could originate from both thermodynamic and kinetic aspects simultaneously, and that the alteration of the photocarrier transition mechanism is one of the main factors affecting the kinetics.