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

Abstract

• A series of MoS 2 -loaded CdS NRs were prepared to study the photogenerated charge dynamics. • MoS 2 -tipped CdS NRs exhibited an excellent photocatalytic H 2 evolution activity. • MoS 2 deposited on the tips of CdS NRs gave a slow charge recombination. • Spatially longitudinal charge separation and transfer intensified by the MoS 2 tip was verified as a crucial factor. A series of MoS 2 -loaded CdS nanorods (NRs) have been successfully fabricated with the MoS 2 spatially distributed only on the tips or on the tips and walls of the CdS NRs, which impacted on photocatalytic H 2 evolution activity. MoS 2 -tipped CdS NRs were found to exhibit a better H 2 evolution performance (31.46 mmol h −1 g −1 ) than MoS 2 -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 MoS 2 tip, with the electric field strongly inducing photogenerated electron-hole separation along the long axis of the CdS NRs and electron transfer to MoS 2 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 MoS 2 tips, whereas, in the case of pure CdS NRs and MoS 2 -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 MoS 2 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 MoS 2 tip engendered long distance of electron separation and transfer within the CdS NRs, give rise to the superior photoactivity by the MoS 2 -tipped CdS NRs. This study reveals the relationship between the MoS 2 distribution and photogenerated charge dynamics, and also provides greater insight into the performance of CdS-MoS 2 composites for photocatalytic H 2 evolution.