Construction of thermal, chemical and mechanically stable ion exchange membranes with improved ion selectivity for vanadium redox flow batteries applications

As an alternative to expensive Nafion membrane, SPEEK (Sulfonated Poly Ether Ether Ketone) membrane reinforced with hydroxylated boron nitride is investigated as a potential proton exchange membrane for vanadium redox flow battery (VRFB). SPEEK based hybrid membranes are characterized for their thermal, mechanical and chemical stability along with proton conductivity and vanadium permeability. The results reveal that the hydroxylated boron nitride enhances the physicochemical properties of SPEEK and shown to improve selectivity of ions (52.629 *103. S.cm  3.min) with better stability. The improved properties are attributed to hydrogen bond formation between hydroxyl moieties of born nitride and sulfonic acid group in SPEEK. Among the hybrid membrane, SPEEK reinforced with 0.05 wt % of hydroxylated boron nitride exhibits a higher coulombic efficiency of 93.6 % (91.8 % for Nafion), higher self-discharge time of 14.21 h (11.36 h for Nafion) in VRFB single cell performance study. Cyclic performance study in VRFB with hybrid membrane shows stable characteristics during 50 cycles and it reaffirms the structural, thermal and chemical stability of hybrid membranes. Thus, this study provides insight into replacing commercial Nafion with hydroxylated boron nitride reinforced SPEEK hybrid membrane for vanadium redox flow battery.