Charge-Transfer Dynamics Promoted by Hole Trap States in CdSe Quantum Dots–Ni²⁺ Photocatalytic System

Manipulation of the photoinduced hole dynamics is a key strategy to improve the H 2 evolution efficiency in quantum dots (QDs)-based photocatalytic systems. The ultrafast hole trapping by surface states of the QDs is beneficial to electron transfer but retards the trapped hole transfer. Whether ultrafast hole trapping is beneficial to the photocatalytic H 2 evolution activity deserves to be investigated. We employed two types of CdSe QDs, QDs-1 and QDs-2, with tuned surface hole trap states to investigate the effect of ultrafast hole trapping on charge-transfer dynamics in the photocatalytic system. QDs-1 possesses higher density of surface hole trap states than QDs-2. Compared with QDs-2, the transfer dynamics of free electrons in QDs-1 to the proton reduction catalyst, Ni 2+, is more promoted by hole trapping, characterized by the transient absorption spectroscopy and photoluminescence techniques. Interestingly, the free hole transfer from QDs-1 to the sacrificial reagent, ascorbic acid (AA), was also improved more. Moreover, the surface defects of the QDs serve as binding sites for Ni 2+ and AA, further promoting the electron transfer and hole removal dynamics, respectively. Our results illustrate that the ultrafast hole trapping increases the H 2 production activity in the actual CdSe QDs–Ni 2+ photocatalytic system.