Scavenger-Dependent Hole Removal Dynamics in Pt-Tipped CdSe/CdS Dot-in-Rod Nanohybrids

Combining the light-absorbing properties of semiconductors with the catalytic activity of noble metals, Pt-tipped CdSe/CdS dot-in-rods are perfectly suited for photocatalytic applications including light-driven hydrogen generation in water.^[1-3]<br/>We conducted a systematic study, investigating the influence of the choice of hole (h⁺) scavenger and pH value on the quantum yield of the hydrogen evolution reaction and combined this with investigations on the charge carrier dynamics, using time-resolved transient absorption (TA) spectroscopy from the femtosecond- to the microsecond-time scale. While the fs-TA spectroscopy enabled us to investigate the charge carrier movement within the semiconductor domain and onto the metal tip, in the μs-TA measurements the h⁺ transfer onto the h⁺ scavengers was observable. Contrary to expectations, the charge carrier dynamics did not follow the observed trend of the scavenger-dependent performance in hydrogen production. Instead, it was possible to distinguish exclusively between “surface-active” and “diffusion-controlled” scavengers, based on the charge carrier dynamics. These results reveal that it is not the h⁺ transfer onto the scavenger, that is the efficiency-limiting step of the photocatalytic process and therefore represent an important insight on the way towards optimizing this nanoscopic photocatalytic system.<br/><br/>[1] Carbone, L. et al. Nano Lett., 7, 2942–2950 (2007).<br/>[2] Habas, S. E. et al. J. Am. Chem. Soc., 130, 3294–3295 (2008).<br/>[3] Amirav, L. et al. J. Phys. Chem. Lett., 1, 1051–1054 (2010).