(607a) Novel Polyether-Based Amphoteric Ion Exchange Membrane for Electrochemical Systems

Vanadium Redox Flow Batteries (VRFBs) are considered promising candidates for energy storage due to their high energy efficiency. Nafion ion exchange membranes have been used in VRFB applications owing to their good ionic conductivity and excellent chemical and mechanical stability, but Nafion’s high cost, excessive swelling and low ion selectivity limits its use for commercialization. Amphoteric ion-exchange membranes have potential for preventing vanadium ion penetration thus increasing ion selectivity. In our current work, we have synthesized an economical crosslinked network to make amphoteric ion exchange membranes. Membranes were synthesized by grafting of epichlorohydrin and propargyl glycidyl ether-based charged copolymer (S-PPGE-ECH) to the PVDF-co-HFP membrane matrix. We varied the copolymer composition in the matrix to study its effect on ionic conductivity. All membranes were characterized using NMR and FTIR spectroscopy to confirm the presence of sulfonate and ammonium charged groups. Gradual increase of copolymer content decreases the contact angle from 85.6° (1% of S-PPGE-ECH) to 67.6° (10% of S-PPGE-ECH) indicating improvement in the hydrophilicity of membrane surfaces with addition of the copolymer. This increase in hydrophilicity resulted in a commensurate increase in swelling ratio from 17.5% to 27.0%, comparable to Nafion. We further saw a commensurate increase in ionic conductivity with an increase in copolymer content up to 0.64 mS/cm. Cation exchange capacity also increased steadily with increasing copolymer content while anion exchange capacity increased only slightly. The increase in exchange capacity was attributed to the presence of -NR₃ and-SO₃H groups in the membranes. In this work, we demonstrated control over ionic conductivities by tuning copolymer content without compromising thermal and mechanical stability of the membrane.