Mechanism of mediated alkali peroxide oxidation and triplet versus singlet oxygen formation

Yann K. Petit, Eléonore Mourad, Christian Prehal, Christian Leypold, Andreas Windischbacher, Daniel Mijailovic, Christian Slugovc, Sergey M. Borisov, Egbert Zojer, Sergio Brutti, Olivier Fontaine, Stefan A. Freunberger

Research output: Contribution to journalArticle

Abstract

Aprotic alkali metal–O 2 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 ( 1O 2). Redox mediators are recognized to be key for improving rechargeability. However, it is unclear how they affect 1O 2 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 1O 2 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 1O 2 evolution from superoxide oxidation, while disproportionation always generates some 1O 2. We find that 1O 2 suppression requires oxidation to be faster than the generation of 1O 2 from disproportionation. Oxidation rates decrease with growing driving force following Marcus inverted-region behaviour, establishing a region of maximum rate. [Figure not available: see fulltext.]

Original languageEnglish
Pages (from-to)465-471
Number of pages7
JournalNature Chemistry
Volume13
Issue number5
DOIs
Publication statusPublished - 15 May 2021

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Chemistry(all)

Fields of Expertise

  • Advanced Materials Science

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