Aprotic alkali metal–O2 batteries face two major obstacles to their chemistry occurring efficiently, the insulating nature of the formed alkali superoxides/peroxides and parasitic reactions that are caused by the highly reactive singlet oxygen (1O2). Redox mediators are recognized to be key for improving rechargeability. However, it is unclear how they affect 1O2 formation, which hinders strategies for their improvement. Here we clarify the mechanism of mediated peroxide and superoxide oxidation and thus explain how redox mediators either enhance or suppress 1O2 formation. We show that charging commences with peroxide oxidation to a superoxide intermediate and that redox potentials above ~3.5 V versus Li/Li+ drive 1O2 evolution from superoxide oxidation, while disproportionation always generates some 1O2. We find that 1O2 suppression requires oxidation to be faster than the generation of 1O2 from disproportionation. Oxidation rates decrease with growing driving force following Marcus inverted-region behaviour, establishing a region of maximum rate.
S.A.F. is indebted to the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 636069) as well as IST Austria. O.F thanks the French National Research Agency (STORE-EX Labex Project ANR-10-LABX-76-01). We thank EL-Cell GmbH (Hamburg, Germany) for the pressure test cell. We thank R. Saf for help with the mass spectrometry, J. Schlegl for manufacturing instrumentation, M. Winkler of Acib GmbH, G. Strohmeier and R. Fürst for HPLC measurements and S. Mondal and S. Stadlbauer for kinetic measurements.
Petit YK, Mourad E, Prehal C, et al. Mechanism of mediated alkali peroxide oxidation and triplet versus singlet oxygen formation. Nature Chemistry. 2021. doi:10.1038/s41557-021-00643-z
Petit, Y. K., Mourad, E., Prehal, C., Leypold, C., Windischbacher, A., Mijailovic, D., … Freunberger, S. A. (2021). Mechanism of mediated alkali peroxide oxidation and triplet versus singlet oxygen formation. Nature Chemistry. Springer Nature. https://doi.org/10.1038/s41557-021-00643-z
Petit, Yann K., Eléonore Mourad, Christian Prehal, Christian Leypold, Andreas Windischbacher, Daniel Mijailovic, Christian Slugovc, et al. “Mechanism of Mediated Alkali Peroxide Oxidation and Triplet versus Singlet Oxygen Formation.” Nature Chemistry. Springer Nature, 2021. https://doi.org/10.1038/s41557-021-00643-z.
Y. K. Petit et al., “Mechanism of mediated alkali peroxide oxidation and triplet versus singlet oxygen formation,” Nature Chemistry. Springer Nature, 2021.
Petit YK, Mourad E, Prehal C, Leypold C, Windischbacher A, Mijailovic D, Slugovc C, Borisov SM, Zojer E, Brutti S, Fontaine O, Freunberger SA. 2021. Mechanism of mediated alkali peroxide oxidation and triplet versus singlet oxygen formation. Nature Chemistry.
Petit, Yann K., et al. “Mechanism of Mediated Alkali Peroxide Oxidation and Triplet versus Singlet Oxygen Formation.” Nature Chemistry, Springer Nature, 2021, doi:10.1038/s41557-021-00643-z.
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