Electron transfer kinetics in CdS/Pt heterojunction photocatalyst during water splitting

Abstract

Noble metal cocatalysts have shown great potential in boosting the performance of CdS in photocatalytic water splitting. However, the mechanism and kinetics of electron transfer in noble-metal-decorated CdS during practical hydrogen evolution is not clearly elucidated. Herein, Pt-nanoparticle-decorated CdS nanorods (CdS/Pt) are utilized as the model system to analyze the electron transfer kinetics in CdS/Pt heterojunction. Through femtosecond transient absorption spectroscopy, three dominating exciton quenching pathways are observed and assigned to the trapping of photogenerated electrons at shallow states, recombination of free electrons and trapped holes, and radiative recombination of locally photogenerated electron-hole pairs. The introduction of Pt cocatalyst can release the electrons trapped at the shallow states and construct an ultrafast electron transfer tunnel at the CdS/Pt interface. When CdS/Pt is dispersed in acetonitrile, the lifetime and rate for interfacial electron transfer are respectively calculated to be ~5.5 ps and ~3.5 × 1010 s−1. The CdS/Pt is again dispersed in water to simulate photocatalytic water splitting. The lifetime of the interfacial electron transfer decreases to ~5.1 ps and the electron transfer rate increases to ~4.9 × 1010 s−1, confirming that Pt nanoparticles serve as the main active sites of hydrogen evolution. This work reveals the role of Pt cocatalysts in enhancing the photocatalytic performance of CdS from the perspective of electron transfer kinetics.