Effect of Bromine Complexing Agents on Membrane Performance in Hydrogen Bromine Flow Batteries

Abstract

The addition of bromine complexing agent (BCA) to bromine electrolyte is an accepted method to reduce bromine vapor pressure making bromine-based flow batteries inherently safer. It is well-known that the amine functional group of the BCAs interact with Nafion membranes. The novelty of the current work is that it investigates how this interaction of BCA with the four different membrane chemistries impacts the membrane characteristics and performance of hydrogen bromine flow batteries (HBFBs). The impact of BCA 13 on the system performance is determined by the membrane chemistry. Exposure of Nafion membranes to BCA leads to 60% higher cell resistance, and 55% lower cell power density at 0.5 V at 50% state-of-charge (SOC). This decrease is caused by the strong interaction between the negatively charged sulfonic acid groups in the membrane and the positively charged BCA. Lower SOC, lower bromine concentration and a higher free BCA concentration is detrimental in the cell operation. The use of LC PFSA membranes in the presence of BCA ions should be avoided. while BCA in combination with grafted sulfonated polyvinylidene fluoride (SPVDF) or grafted sulfonated polyethylene (SPE) membranes promising HBFB results are obtained.

High energy density electrolytes for H2/Br2redox flow batteries, their polybromide composition and influence on battery cycling limits

“…7 High peak power densities of 1.4 W cm À2 and a voltage efficiency of 91% at 400 mW cm À2 were achieved in the past. 8 Main research activities are the investigation of performant separators allowing for the limitation of hydrobromic acid (HBr), bromine (Br 2 ) and polybromides crossover [8][9][10][11][12] as well as the development of resistant catalyst materials. [13][14][15] The H 2 /Br 2 -RFB storage technology is thereby progressing from prototype testing to commercialisation.…”

“…20 An application of the known equilibria and their constants for the range of application of a bromine electrolyte up to c(HBr) ¼ 7.7 M and c(Br 2 ) ¼ 3.35 M has not been investigated so far and seems to be doubtful, however, these are oen adopted in studies on H 2 /Br 2 -RFB or Zn/Br 2 -RFB. 6,10,15,36,[38][39][40] Polybromides show Raman peaks in the range of the Raman shi [41][42][43] between ṽ ¼ 125 cm À1 and 325 cm À1 . Raman peaks of symmetric and antisymmetric stretching vibrations of Br 3 À and Br 5 À as well as the symmetric stretching vibration of heptabromide (Br 7 À ) at known Raman shis 32,[41][42][43] can be considered and related to Br 2 distribution and polybromide concentration.…”

“…5: 1.7 M HBr and 3 M Br 2. For higher concentrations of bromine and lower concentrations of bromide, a second phase is present in the electrolyte mixture and the bromine concentration in the aqueous phase is dened according to eqn (10).…”

“…Based on the denition of the SOC range the total concentrations of bromine c(Br 2 ) T and HBr c(HBr) T are calculated following eqn (11) and (12) and considering the solubility limitation according to eqn (10). Including polybromide equilibria for Br 3 À and Br 5…”

Hydrogen‐Bromine Redox‐Flow Battery Cycling with Bromine Complexing Agent: on the Benefits of Nanoporous Separator Versus Proton Exchange Membrane

“…This last point has been confirmed through the investigation of the ionic exchange capacity (IEC) of perfluorosulfonic acid (PFSA) membranes in the presence of 1‐butyl 3‐methylpyridinum bromide. [ 20 ] The decrease in IEC has been correlated with the acidity of the sulfonic group and the ionic pathway on different polymeric backbones. In long‐side‐chain perfluorosulfonic acid (LSC‐PFSA), the phase ordering between the hydrophobic and hydrophilic domains, together with the high acidity, triggers the BCA fouling in the channels.…”