Influence of strong bromine binding complexing agent in electrolytes on the performance of hydrogen/bromine redox flow batteries

Michael Küttinger, Kobby Saadi, Théo Faverge, Nagaprasad Reddy Samala, Ilya Grinberg, David Zitoun, Peter Fischer

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Abstract

1-n-Hexylpyridin-1-ium bromide [C6Py]Br is investigated in this work as bromine complexing agent (BCA) in aqueous bromine electrolytes on its influence on hydrogen bromine redox flow battery (H2/Br2-RFB) performance. [C6Py]+-cations bind bromine of aqueous polybromide solutions safely in an additional fused salt phase limiting the vapor pressure of Br2. Dissolved in aqueous electrolyte solutions, however, [BCA]+ cations drastically lower PFSA membranes' conductivity in the H2/Br2-RFB. In this work the combination of the very strong bromine-binding [C6Py]+cation and an excess of bromine in the electrolyte lead to an almost complete absorption of 99.6 mol% [C6Py]+ into the fused salt within the electrolyte's operation range. In comparison to similar application of short side chain 1-ethylpyridinium bromide, adverse effects are stronger compensated by use of [C6Py]Br. Increases in membrane resistance of the membrane in contact with [C6Py]+ cations are reversible in contrast for contact with [C2Py]+ cations. Electrolytes are cycled for at least 12 cycles and offer a stable useable capacity of 176.7 Ah L−1 and reach and stable discharge energy densities of 138.91 Wh L−1. Strong bromine binding properties between [C6Py]+ cations and polybromides are confirmed by DFT studies. In contrast to [C2Py]+ electrolytes, the long-chain [C6Py]+ cation in electrolytes has a higher cycling stability or a low decrease in capacity and energy density.

Original languageEnglish
Article number107890
JournalJournal of Energy Storage
Volume70
DOIs
StatePublished - 15 Oct 2023

Bibliographical note

Publisher Copyright:
© 2023 The Authors

Funding

Authors are grateful to the Federal Ministry of Education and Research Germany (BMBF) and the Israel Ministry of Science and Technology (MOST) for financial support of the project through the German-Israeli Battery and Electrochemistry Research Program. We would also like to thank Grenoble-INP/France for a scholarship for the internship period of Théo Faverge.

FundersFunder number
Ministry of Science, Technology and Space
Bundesministerium für Bildung und Forschung
Ministry of science and technology, Israel

    Keywords

    • Battery performance
    • Bromine
    • Bromine complexing agent
    • Ionic liquid
    • Redox flow battery

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