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.

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This work investigates the reactions occurring in K 2 CO 3 − H 2 O−CO 2 under ambient CO 2 pressures in temperature and vapor pressure ranges applicable for domestic thermochemical heat storage. The investigation shows that depending on reaction conditions, the primary product of a reaction isis preferred far above the equilibrium conditions for the hydration reaction. On the other hand, the formation of double salt is preferred at conditions where hydration reaction is inhibited or impossible, as the thermogravimetric measurements identified a new phase transition line below the hydration equilibrium line. The combined X-ray diffraction, thermogravimetric analysis, and Fourier-transform infrared spectroscopy study indicates that this transition line corresponds to the formation of K 2 CO 3 •2KHCO 3 , which was not observed in any earlier study. In view of thermochemical heat storage, the formation of K 2 CO 3 •2KHCO 3 •(1.5H 2 O) increases the minimum charging temperature by approximately 40 °C. Nevertheless, the energy density and cyclability of the storage material can be preserved if the double salt is decomposed after each cycle.

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