Membrane properties and behaviour in the Generation 2 Vanadium Bromide Redox Flow batteries

In this study, a number of membranes were evaluated for possible application in the Generation 2 Vanadium Bromide Redox Flow Cell (G2 V/Br). Both anion and cation exchange membranes were evaluated in small test cells under constant current charge discharge conditions and the selectivity and resistivity of each material was assessed from the measured coulombic and voltage efficiencies. Pre-treatments were used to improve the performance of selected membranes in the V/Br cell and Fourier Transform Infrared spectroscopy was employed to determine any surface chemical changes produced. Of the membrane tested, the non-selective polyethylene separator was found to exhibit poor selectivity leading to low coulombic efficiencies in the V/Br, while the polysulphone anion exchange membrane also gave low coulombic efficiencies due to the transfer of the polybromide anions from the positive half-cell into the negative half-cell electrolyte, leading to self-discharge. The pre-treated perfluorinated membrane VF02 was found to possess the required characteristics for application in the V/Br including good chemical stability in acidic vanadium bromide electrolyte, good resistance to the highly oxidising polyhalide ions in the charged positive half-cell electrolyte, low electrical resistance and good mechanical properties. © Institute of Materials Engineering Australasia Ltd.