Delayed photoelectron transfer in Pt-decorated CdS nanorods under hydrogen generation conditions

Noble-metal-decorated colloidal semiconductor nanocrystals are currently receiving significant attention for photocatalytic hydrogen generation. A detailed knowledge of the charge-carrier dynamics in these hybrid systems under hydrogen generation conditions is crucial for improving their performance. Here, a transient absorption spectroscopy study is conducted on colloidal, Pt-decorated CdS nanorods addressing this issue. Surprisingly, under hydrogen generation conditions (i.e., in the presence of the hole-scavenger sodium sulfite), photoelectron transfer to the catalytically active Pt is slower than without the hole scavenger, where no significant hydrogen generation occurs. This unexpected behavior can be explained by different degrees of localization of the electron wavefunction in the presence and absence of holes on the nanorods, which modify the electron transfer rates to the Pt. The results show that solely optimizing charge transfer rates in photocatalytic nanosystems is no guarantee of improved performance. Instead, the collective Coulomb interaction-mediated electron-hole dynamics need to be considered. Photoelectron transfer to catalytically active Pt clusters on CdS nanorods is slower under hydrogen generation conditions (i.e., in the presence of hole scavengers) than in situations without significant hydrogen production (without hole scavengers). This surprising result is explained by different degrees of delocalization of the electronic wavefunction in the presence and absence of holes on the nanorod due to electron-hole Coulomb interactions. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.