Computational Characterization of Single-Electron Transfer Steps in Water Oxidation

Adiran de Aguirre,Ignacio Funes-Ardoiz,Feliu Maseras

doi:10.3390/inorganics7030032

Abstract

The presence of single-electron transfer (SET) steps in water oxidation processes catalyzed by first-row transition metal complexes has been recently recognized, but the computational characterization of this type of process is not trivial. We report a systematic theoretical study based on density functional theory (DFT) calculations on the reactivity of a specific copper complex active in water oxidation that reacts through two consecutive single-electron transfers. Both inner-sphere (through transition state location) and outer-sphere (through Marcus theory) mechanisms are analyzed. The first electron transfer is found to operate through outer-sphere, and the second one through inner-sphere. The current work proposes a scheme for the systematic study of single-electron transfer in water oxidation catalysis and beyond.

Highlights

One of the most promising reactions to replace the undesirable use of fossil fuels in energy production is the water splitting process triggered by sunlight, which generates oxygen and hydrogen from water
In 2015, we reported a step-by-step variant of the water nucleophilic attack (WNA) mechanism, where the classical two-electron concerted reaction was divided in two sequential single-electron transfer (SET) steps that we called SET–WNA [41,42]
Inner-sphere electron transfer is characterized by a transition state, which yields anSET

Summary

Introduction

One of the most promising reactions to replace the undesirable use of fossil fuels in energy production is the water splitting process triggered by sunlight, which generates oxygen and hydrogen from water. The resulting water can be used to reinitiate the overall process in a clean and green scheme This hydrogen can be used to reduce CO2 to produce more complex and convenient fuels [3]. From a mechanistic point of view, involves the breaking of four H–O bonds, the release of 4 protons and 4 electrons, together with the formation of an O–O bond. This is associated with a high kinetic barrier, usually translated into the need of a very high overpotential [8]

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Conclusion