Fluorine-Free Polynorbornene Membranes Based on a Sterically Hindered Pyridine for Vanadium Redox Flow Batteries

A 2,6-di-tert-butylpyridine-containing norbornene was synthesized by a one-step synthesis and copolymerized with an aromatic norbornene to obtain a membrane with a proton conductivity of 56 mS cm–1 in 2 M H2SO4. Decreased vanadium(IV) permeability was reached compared to the fluorine-containing reference membrane FAPQ330. A vanadium(V) stability test for 55 days [1.6 M V(V)/2 M H2SO4] showed no degradation of functional groups but a loss of molecular weight. Vanadium redox flow battery single-cell tests resulted in a performance comparable to that of FAPQ330, and an in situ self-discharge test lasted more than 3 times longer for the cell equipped with pNorb-Pyr61.