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Xu – Electron Transfer and Proton-Coupled Electron Transfer Kinetics and Reorganization Energies at a Conductive Metal Oxide Interface

 

Electron Transfer and Proton-Coupled Electron Transfer Kinetics and Reorganization Energies at a Conductive Metal Oxide Interface (2023)

Undergraduate: Jeremiah Xu


Faculty Advisor: Gerald Meyer
Department: Chemistry

Artificial photosynthesis, the process of generating usable fuels with solar power via photocatalysis, is a promising and bountiful source of energy that offers a potential solution to the current energy crisis. However, the efficiency of artificial photosynthetic systems is kinetically limited by photocatalytic water oxidation which provides the protons and electrons necessary for fuel production. This kinetic bottleneck arises from the recombination of separated charges at electrode interfaces that occurs in competition with the desired reactions necessary for water oxidation. The mechanism of these recombination reactions is often dependent on the experimental conditions with both electron transfer (ET) and proton-coupled electron transfer (PCET) pathways accessible. Using Marcus-Gerischer theory, the kinetics behind these ET and PCET reactions were studied, and the associated reorganization energy, lambda, was obtained. It was found that the maximum rate constant for the recombination reaction, k_{max}, decreased under more alkaline conditions, and that lambda increased from approximately 0.6 eV for an ET reaction to 1.07 eV for a PCET reaction. These results suggest a significant kinetic barrier to charge recombination when water oxidation is performed under alkaline conditions where the PCET mechanism is operative. A greater understanding of these recombination reaction kinetics will aid in the design of future artificial photosynthetic systems where competitive recombination pathways are inhibited under alkaline conditions.

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