CdS/CdSe co-sensitized brookite H:TiO2 nanostructures: Charge carrier dynamics and photoelectrochemical hydrogen generation

In this study, we have synthesized CdS/CdSe co-sensitized brookite TiO2 nanostructures with hydrogen doping (H:TiO2/CdS/CdSe) in a facile solution reaction and studied their PEC performances. Compared to undoped brookite TiO2, the H:TiO2/CdS/CdSe composites exhibit much enhanced photocurrent generation, which originates from the improved charge transfer kinetics endowed by hydrogen doping and sensitization. Time-resolved photoluminescence (PL) and electrochemical impendence spectroscopy (EIS) are employed to explore the charge transfer dynamics between sensitizers and TiO2 and charge carrier kinetics at the semiconductor/electrolyte interface. According to the analytical results, sensitizations of TiO2 are found to enhance the charge separation efficiency. Besides, the hydrogen doping into TiO2 generates oxygen vacancy states, providing additional charge transfer pathway and prohibiting charge recombination, beneficial for enhancing the PEC performances as well. Based on the charge dynamics data, we further develop charge transfer models for TiO2/CdS/CdSe and H:TiO2/CdS/CdSe. The findings from this work can help understanding the charge transfer dynamics in brookite TiO(2)based composite systems as well as designing versatile photoelectrodes for solar energy conversion.