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  4. Exploring the thermodynamics of the bromine electrode in concentrated solutions for improved parametrisation of hydrogen-bromine flow battery models
 
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2021
Journal Article
Title

Exploring the thermodynamics of the bromine electrode in concentrated solutions for improved parametrisation of hydrogen-bromine flow battery models

Abstract
Thermodynamic properties of the bromine electrode in an exemplary hydrogen-bromine flow battery (HBFB) are investigated in detail. Open-circuit potential (OCP) measurements of HBRB electrolytes in a liquid junction-free setup and electrolyte Raman spectra are employed to estimate polybromides speciation. An improved mathematical description of the bromine electrode OCP versus state of charge is provided. This paper addresses the phenomenon of polybromides formation at concentrations up to 7.7 mol L-1 HBr and 3.85 mol L-1 Br2 and their significant impact on the OCP. The model takes into account tri-, penta- and heptabromides formation, precisely modelled electrolyte activity coefficients (up to 11-molal HBr), electrolyte density, and temperature. It is elucidated that the polybromide formation constants found in literature treating dilute electrolytes are substantially too low. Newly determined equilibrium constants, applicable over a wider concentration range are provided for 25 and 43 °C together with their standard enthalpy changes. The model is successfully validated in an independent experiment using a real, pilot-scale HBFB. It is concluded that the usage of a simple Nernst-like equation to calculate the OCP of flow battery electrodes containing concentrated electrolytes leads to erroneous results.
Author(s)
Wlodarczyk, Jakub K.
Zürcher Hochschule Winterthur
Küttinger, Michael
Fraunhofer-Institut für Chemische Technologie ICT  
Friedrich, Andreas K.
Deutsches Zentrum fur Luft- Und Raumfahrt
Schumacher, Jürgen O.
Zürcher Hochschule Winterthur
Journal
Journal of power sources  
Open Access
DOI
10.1016/j.jpowsour.2021.230202
Additional full text version
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Language
English
Fraunhofer-Institut für Chemische Technologie ICT  
Keyword(s)
  • activity coefficient

  • bromine electrode

  • hydrogen-bromine redox flow battery

  • modelling and simulation

  • open circuit potential

  • thermodynamics

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