Improved performance of vanadium redox flow battery with tuneable alkyl spacer based cross-linked anion exchange membranes

We synthesize cross-linked aliphatic polymer with side chain grafted imidazole based anion exchange membranes (AEMs) using alkyl chain spacer. Prepared AEMs exhibit excellent stabilities, ionic conductivity, and vanadium ion impervious nature. These AEMs with rigid polymer matrix show low swelling ratio in spite of high molality of exchangeable functional groups. Cross-linked methylmethacrylate-co-vinyl imidazole copolymer (CMVI) with C3 spacer (CMVI-C3) possess 1.21 meq/g ion exchange capacity, and 8.1 x 10(-2) S/cm conductivity. Well optimized CMVI-C3 AEM shows extremely low VO2+ permeability (1.96 x 10(-9) cm(2) s(-1)) in comparison to Nafion 117 (16.34 x 10(-9) cm(2) s(-1)), due to blocking property of CMVI AEMs for VO2+. At 120.0 mA cm(-2), relatively high Coulombic (98.8%), energy (78.2%), and voltage (80.5%) efficiencies of CMVI-C3 AEM in comparison with Nafion 117 membrane, has been attributed to synergetic balance between hydrophobic and hydrophilic segments. The CMVI-C3 AEM maintains the high performance and good integrity during in-situ VRFB cycle performance assessment up to 200 cycles. Simple method for the preparation, good stabilities, and high performance are attractive features of CMVI-C3 AEM for vanadium redox flow battery.

Automated summary

The study synthesizes cross-linked aliphatic polymer with side chain grafted imidazole based anion exchange membranes (AEMs) and obtains AEMs with excellent stability and high conductivity. These AEMs show low swelling ratio despite the high molality of exchangeable functional groups and exhibit blocking property for VO2+.