Photodriven Charge Separation Dynamics in CdSe/ZnS Core/Shell Quantum Dot/Cobaloxime Hybrid for Efficient Hydrogen Production

Abstract

Photodriven charge-transfer dynamics and catalytic properties have been investigated for a hybrid system containing CdSe/ZnS core/shell quantum dots (QDs) and surface-bound molecular cobaloxime catalysts. The electron transfer from light-excited QDs to cobaloxime, revealed by optical transient absorption spectroscopy, takes place with an average time constant of 105 ps, followed a much slower charge recombination process with a time constant of ≫3 ns. More interestingly, we also observed photocatalytic hydrogen generation by this QD/cobaloxime hybrid system, with >10,000 turnovers of H(2) per QD in 10 h, using triethanolamine as a sacrificial electron donor. These results suggest that QD/cobaloxime hybrids succeed in coupling single-photon events with multielectron redox catalytic reactions, and such systems could have potential applications in long-lived artificial photosynthetic devices for fuel generation from sunlight.

Recent Progress in Energy‐Driven Water Splitting

“…The results emphasized the dependency of charge transfer kinetics on thermodynamic driving force of the reaction, as predicted by theory, and the possibility of fine‐tuning photocatalytic activity through particle sizing. Huang et al reported the core‐shell CdSe/ZnS quantum dots functionalized with cobaloxime for efficient hydrogen production under visible light irradiation in the presence of a proton source and a sacrificial electron donor 111. It was demonstrated that the quantum dots have the ability to store and donate multiple electrons to the adsorbed cobaloxime catalysts, playing a key role in improving the photocatalytic efficiency.…”

Efficient and Limiting Reactions in Aqueous Light-Induced Hydrogen Evolution Systems using Molecular Catalysts and Quantum Dots

“…This TOF Co,max value is one of the highest reported using quantum dots as photosensitizers and a molecular catalyst in water that has not been generated in situ, together with two recent reports that use CdSe QDs and diiron or nickel catalysts. 9,10 Other related systems with high catalytic activity are active only in organic solvents 19 or they use inorganic salts as precursors of the catalyst. 3,8 Blank experiments were performed in the absence of catalyst Co(III)-1 and in the dark and we did not observe the formation of significant amount of hydrogen.…”

“…In this context, a deeper knowledge of the kinetics of both charge transfer and bond formation-breaking are the keys to understand the limitations of photo-driven hydrogen evolving systems based on molecular approaches. [19][20][21] Herein, we take advantage of a highly active system composed of quantum dots and a cobalt molecular catalyst to study the kinetics involved in the overall photoinduced catalytic process. We selected the components based on the following requirements: (1) a light harvesting unit that absorbs in the visible light region, (2) a molecular water reduction catalyst with a well-defined structure, (3) the whole system has to work in purely aqueous conditions.…”

Hybrid Artificial Photosynthetic Systems Comprising Semiconductors as Light Harvesters and Biomimetic Complexes as Molecular Cocatalysts

“…The fast photodriven electron transfer from semiconductor to cobaloxime was confirmed by Huang et al very recently. 51 Results show that the photoexcited electron transfer from CdSe/ZnS core/shell quantum dot (QD) to cobaloxime takes place with an average time of 105 ps, which is much faster than that for the charge recombination.…”