Bifunctional Cross-Linking Agents Enhance Anion Exchange Membrane Efficacy for Vanadium Redox Flow Batteries

A series of cross-linked fluorinated poly(aryl ether oxadiazole) membranes (FPAEOM) derivatized with imidazolium groups were prepared. Poly(N-vinylimidazole) (PVI) was used as the bifunctional cross-linking agent to (a) lower vanadium permeability, (b) enhance dimensional stability, and (c) concomitantly provide added ion exchange capacity in the resultant anion exchange membranes. At a molar ratio of PVI to FPAEOM of 1.5, the resultant membrane (FPAEOM-1.5 PVI) had an ion exchange capacity of 2.2 mequiv g-1, a vanadium permeability of 6.8 x 10-7 cm2 min-1, a water uptake of 68 wt %, and an ionic conductivity of 22.0 mS cm-1, all at 25 degrees C. The FPAEOM-1.5 PVI membrane showed high chemical stability in highly acidic and oxidizing vanadium solution. Single cells prepared with the FPAEOM-1.5 PVI membrane exhibited a higher Coulombic efficiency (>92%) and energy efficiency (>86%) after 40 test cycles in vanadium redox flow battery.

Automated summary

A series of cross-linked fluorinated poly(aryl ether oxadiazole) membranes derivatized with imidazolium groups were prepared using poly(N-vinylimidazole) (PVI) as the bifunctional cross-linking agent. The resulting membrane showed high ion exchange capacity, low vanadium permeability, and good dimensional stability. It also exhibited high chemical stability in acidic and oxidizing environments, and demonstrated superior electrochemical performance in vanadium redox flow battery testing.