Ultrafast Hole Transfer from CdS Quantum Dots to a Water Oxidation Catalyst

作者：Pearce Orion M; Duncan Jeremiah S; Damrauer Niels H^*; Dukovic Gordana^*

来源：Journal of Physical Chemistry C, 2018, 122(30): 17559-17565.

DOI：10.1021/acs.jpcc.8b06237

The first step in light-driven multielectron redox catalysis driven by semiconductor nanocrystals is the transfer of a photoexcited carrier to the catalyst. The efficiency of that step defines the upper limit on the efficiency of catalysis. Although progress has been made in transferring electrons from nanocrystals to catalysts for multielectron reduction reactions, there has been little success in moving photoexcited holes to water oxidation catalysts (WOCs). Here, we describe the kinetics of hole transfer from a photoexcited CdS quantum dot to a ruthenium polypyridine molecular WOC. Ultrafast transient absorption and photoluminescence (PL) upconversion experiments reveal that this hole transfer is surprisingly fast, occurring on a picosecond time scale. To determine the rate constant for hole transfer, we develop a model for PL quenching as a function of catalyst loading that takes into account both the catalyst binding equilibrium and the finite quenching efficiency. The rate constant for hole transfer is found to be 1.3 X 10(11) s(-1) per adsorbed catalyst, which is comparable to the fastest reported hole transfer from CdS nanocrystals to a noncatalyst hole acceptor. The catalyst binds strongly to the surface with an equilibrium constant of 7 X 10(5) M-1 and can remove up to 37% of the photoexcited holes. Our results suggest that valence band hole harvesting from CdS quantum dots for water oxidation can in principle be an efficient process. However, fast competing hole trapping limits this efficiency in the current system. We propose strategies for mitigating this limitation.

• 出版日期2018-8-2