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Publication type: Article in scientific journal
Type of review: Peer review (publication)
Title: High energy density electrolytes for H2/Br2 redox flow batteries, their polybromide composition and influence on battery cycling limits
Authors: Küttinger, Michael
Wlodarczyk, Jakub K.
Daubner, Daniela
Fischer, Peter
Tübke, Jens
et. al: No
DOI: 10.1039/D0RA10721B
Published in: RSC Advances
Volume(Issue): 11
Issue: 9
Pages: 5218
Pages to: 5229
Issue Date: 2021
Publisher / Ed. Institution: Royal Society of Chemistry
ISSN: 2046-2069
Language: English
Subjects: Flow battery; Bromine; Energy storage; Renewable energy; Hydrogen; Redox flow battery
Subject (DDC): 621.3: Electrical, communications, control engineering
Abstract: Hydrogen–bromine redox flow batteries (H2/Br2-RFB) are a promising stationary energy storage solution, offering energy storage densities up to 200 W h L−1. In this study, high energy density electrolytes of concentrated hydrobromic acid of up to 7.7 M are investigated. Particular polybromide ion (Br2n+1−; n = 1–3) concentrations in the electrolyte at different states of charge, their effect on the electrolytic conductivity and cell operation limits are investigated for the first time. The concentrations of individual polybromides in the electrolytes are determined by Raman spectroscopy. Tribromide (Br3−) and pentabromide (Br5−) are predominantly present in equal concentrations over the entire concentration range. Besides Br3− and Br5−, heptabromide (Br7−) exists in the electrolyte solution at higher bromine concentrations. It is shown that polybromide equilibria and their constants of Br3− and Br5− from literature are not applicable for highly concentrated solutions. The conductivity of the electrolytes depends primarily on the high proton concentration. The presence of higher polybromides leads to lower conductivities. The solubility of bromine increases disproportionately with increasing bromide concentration, since higher polybromides such as Br7− or Br5− are preferably formed with increasing bromide concentration. Cycling experiments on electrolyte in a single cell are performed and combined with limitations due to electrolyte conductivity and bromine solubility. Based on these results concentrations of the electrolyte are defined for potential operation in a H2/Br2-RFB in the range 1.0 M < c(HBr) < 7.7 M and c(Br2) < 3.35 M, leading to a theoretical energy density of 196 W h L−1.
Fulltext version: Published version
License (according to publishing contract): CC BY 3.0: Attribution 3.0 Unported
Departement: School of Engineering
Organisational Unit: Institute of Computational Physics (ICP)
Appears in collections:Publikationen School of Engineering

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