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

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.