Photogenerated charge dynamics of CdS nanorods with spatially distributed MoS2 for photocatalytic hydrogen generation

Abstract A series of MoS2-loaded CdS nanorods (NRs) have been successfully fabricated with the MoS2 spatially distributed only on the tips or on the tips and walls of the CdS NRs, which impacted on photocatalytic H2 evolution activity. MoS2-tipped CdS NRs were found to exhibit a better H2 evolution performance (31.46 mmol h−1 g−1) than MoS2-coated CdS NRs (7.32 mmol h−1 g−1) and bare CdS NRs (2.96 mmol h−1 g−1). Kelvin probe force microscopy (KPFM) was used to identify the presence of a spatial electric field between the CdS NR and MoS2 tip, with the electric field strongly inducing photogenerated electron-hole separation along the long axis of the CdS NRs and electron transfer to MoS2 tips. The effect of longitudinal transfer of photogenerated electrons was confirmed by Pt photodeposition where it was found that Pt particles were photodeposited on the MoS2 tips, whereas, in the case of pure CdS NRs and MoS2-coated CdS NRs, Pt particles were photodeposited on the walls and tips of the NRs, indicating a lack of spatially directional charge transfer. Time-resolved photoluminescence (TRPL) spectroscopy using band pass and long pass filters was employed to demonstrate that MoS2 located on the tips of CdS NR can better separate photogenerated electron-hole pairs and suppress charge recombination. Consequently, slow charge recombination and spatially separated redox sites, deriving from MoS2 tip engendered long distance of electron separation and transfer within the CdS NRs, give rise to the superior photoactivity by the MoS2-tipped CdS NRs. This study reveals the relationship between the MoS2 distribution and photogenerated charge dynamics, and also provides greater insight into the performance of CdS-MoS2 composites for photocatalytic H2 evolution.