Novel complexing additives to reduce the immiscible phase formed in the hybrid ZnBr2 flow battery

Declan Bryans, Brian McMillan, Mark Spicer, Alastair Wark, Leonard Berlouis

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37 Citations (Scopus)
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The zinc-bromine redox flow battery (RFB) is one of a very few commercially viable RFB energy storage system capable of integration with intermittent renewable energy sources to deliver improved energy management. However, due to the volatility of the electrogenerated bromine and potential for its crossover from positive to negative electrolytes, this system requires the use of quaternary ammonium complexes (N-methyl-N-ethylpyrrolidinium, (MEP)) to capture this bromine. This produces an immiscible phase with the Br2 which requires a complex network of pipes, pumps and automated controls to ensure access to the electroactive material during discharge. In this work, the use of novel quaternary ammonium complexes to capture the electrogenerated bromine but to keep it in the aqueous phase is examined. Three compounds, 1-(carboxymethyl) pyridine-1-ium, 1-(2-carboxymethyl)-1-methylmorpholin-1-ium and 1-(2-carboxymethyl)-1-methylpyrrolidin-1-ium, were found to successfully reduce the volume of the immiscible phase formed on complexing with the polybromide (Brx-) whilst displaying similar enthalpy of vaporisation values as that of MEP. Electrochemical analysis also revealed that these compounds did not impact on the electrode kinetics of the Br-/Brx- reaction indicating that the resulting surface film formed with these compounds behaved as a chemically modified electrode, in contrast to the surface film formed with MEP.
Original languageEnglish
Number of pages7
JournalJournal of the Electrochemical Society
Issue number13
Publication statusPublished - 2 Nov 2017
Event231st Meeting of the Electrochemical Society - New Orleans, United States
Duration: 28 May 20171 Jun 2017


  • zinc bromine
  • complexing agents
  • redox flow battery


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