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  4. Improvement of safe bromine electrolytes and their cell performance in H2/Br2 flow batteries caused by tuning the bromine complexation equilibrium
 
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2022
Journal Article
Title

Improvement of safe bromine electrolytes and their cell performance in H2/Br2 flow batteries caused by tuning the bromine complexation equilibrium

Abstract
Hydrogen bromine redox flow batteries utilize bromine electrolytes in their positive half cell, offering capacities larger than 100 Ah L−1. Addition of quaternary ammonium compounds, so-called bromine complexing agents (BCA), may increase safety as they reduce the vapour pressure of bromine in the posolyte. However, they have not been applied so far. They (a) interact with perfluorosulfonic acid membranes leading to significant reduction of membrane conductivity and (b) they form a low conductive ionic liquid with polybromides, leading to high overvoltage if the formation happens at the electrode. In this work a solution to this problem is proposed by an excess addition of Br2 to these electrolytes. The excess bromine leads to a permanent bromine fused salt phase in the tank. Bromine formed in the cell stays in the aqueous phase and bromine transfer between the two phases happens in the tank. Transfer of Br2 without the transfer of [BCA]+ cations exists between the phases, while [C2Py]+ cations remain in the fused salt and do not influence cell performance. For the first time a posolyte capacity of 179.6 Ah L−1 based on 7.7 M hydrobromic acid with BCA is achieved compared to previous investigations with e.g. 53.9 Ah L−1.
Author(s)
Küttinger, Michael
Fraunhofer-Institut für Chemische Technologie ICT  
Riasse, Raphaël
Fraunhofer-Institut für Chemische Technologie ICT  
Wlodarczyk, Jakub K.
Zurich University of Applied Sciences (ZHAW)
Fischer, Peter  
Fraunhofer-Institut für Chemische Technologie ICT  
Tübke, Jens  
Fraunhofer-Institut für Chemische Technologie ICT  
Journal
Journal of power sources  
Open Access
File(s)
Download (14.99 MB)
Rights
CC BY 4.0: Creative Commons Attribution
DOI
10.24406/publica-r-271139
10.1016/j.jpowsour.2021.230804
Language
English
Fraunhofer-Institut für Chemische Technologie ICT  
Keyword(s)
  • redox flow battery

  • bromine posolytes

  • bromine complexing agent

  • complexation reaction

  • storage capacity

  • cycling performance

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