Dataset Information

A Computational Study on Halogen/Halide Redox Mediators and Their Role in ¹O₂ Release in Aprotic Li-O₂ Batteries.

ABSTRACT: We present a computational study on the redox reactions of small clusters of Li superoxide and peroxide in the presence of halogen/halide redox mediators. The study is based on DFT calculations with a double hybrid functional and an implicit solvent model. It shows that iodine is less effective than bromine in the oxidation of Li₂O₂ to oxygen. On the basis of our thermodynamic data, in solvents with a low dielectric constant, iodine does not spontaneously promote either the oxidation of Li₂O₂ or the release of singlet oxygen, while bromine could spontaneously trigger both events. When a solvent with a large dielectric constant is used, both halogens appear to be able, at least on the basis of thermodynamics, to react spontaneously with the oxides, and the ensuing reaction sequence turned out to be strongly exoergic, thereby providing a route for the release of significant amounts of singlet oxygen. The role of spin-orbit coupling in providing a mechanism for singlet-triplet intersystem crossing has also been assessed.

SUBMITTER: Pierini A

PROVIDER: S-EPMC10641837 | biostudies-literature | 2023 Nov

REPOSITORIES: biostudies-literature

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A Computational Study on Halogen/Halide Redox Mediators and Their Role in 1O2 Release in Aprotic Li-O2 Batteries.

Pierini Adriano A Petrongari Angelica A Piacentini Vanessa V Brutti Sergio S Bodo Enrico E

The journal of physical chemistry. A 20231027 44

We present a computational study on the redox reactions of small clusters of Li superoxide and peroxide in the presence of halogen/halide redox mediators. The study is based on DFT calculations with a double hybrid functional and an implicit solvent model. It shows that iodine is less effective than bromine in the oxidation of Li2O2 to oxygen. On the basis of our thermodynamic data, in solvents with a low dielectric constant, iodine does not spontaneously promote either the ...[more]

PMID: 37885210

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Project description:A theoretical framework to explain how interactions between redox mediators (RMs) and electrolyte components impact electron transfer kinetics, thermodynamics, and catalytic efficiency is presented. Specifically focusing on ionic association, 2,5-di-tert-butyl-1,4-benzoquinone (DBBQ) is used as a case study to demonstrate these effects. Our analytical equations reveal how the observed redox couple's potential and electron transfer rate constants evolve with Li+ concentration, resulting from different redox activity mechanisms. Experimental validation by cyclic voltammetry measurements shows that DBBQ binds to three Li+ ions in its reduced state and one Li+ ion in its neutral form, leading to a maximum in the electron transfer kinetic constant at around 0.25 M. The framework is extended to account for other phenomena that can play an important role in the redox reaction mechanisms of RMs. The effect of Li+ ion solvation and its association with the supporting salt counteranion on the redox processes is considered, and the role of "free Li+" concentration in determining the electrochemical behaviour is emphasized. The impact of Li+ concentration on oxygen reduction reaction (ORR) catalysis was then explored, again using DBBQ and modelling the effects of the Li+ concentration on electron transfer and catalytic kinetics. We show that even though the observed catalytic rate constant increases with Li+ concentration, the overall catalysis can become more sluggish depending on the electron transfer pathway. Cyclic voltammograms are presented as illustrative examples. The strength of the proposed theoretical framework lies in its adaptability to a wider range of redox mediators and their interactions with the various electrolyte components and redox active molecules such as oxygen. By understanding these effects, we open up new avenues to tune electron transfer and catalytic kinetics and thus improve the energy efficiency and rate capability of Li-O2 batteries. Although exact results may not transfer to different solvents, the predictions of our model will provide a starting point for future studies of similar systems, and the model itself is easily extensible to new chemistries.

Dataset Information

A Computational Study on Halogen/Halide Redox Mediators and Their Role in ¹O₂ Release in Aprotic Li-O₂ Batteries.

Publications

A Computational Study on Halogen/Halide Redox Mediators and Their Role in <sup>1</sup>O<sub>2</sub> Release in Aprotic Li-O<sub>2</sub> Batteries.

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