Crosslinked sulfonated poly(phenylene sulfide sulfone) membranes for vanadium redox flow batteries

In this work, crosslinked hydrocarbon-based cation exchange membranes have been developed for vanadium redox flow battery applications. By Friedel-Crafts alkylation of sulfonated poly(phenylene sulfide sulfone) (sPSS), membranes with various degrees of crosslinking have been prepared in one step. Among those, the membrane containing 9% of crosslinker (sPSScl9) represents the best solution. Owing to a much higher selectivity, battery self-discharge and capacity fading (tested over 100 charge/discharge cycles at 120 mA cm−2) of sPSScl9 outperform benchmark Nafion of comparable thickness (N212). Furthermore, the crosslinking strategy permits to obtain stable membranes even in highly oxidizing environments, due to a combination of crosslinking, that holds together the polymer chains, and oxidation of sulfides to sulfones that increases the rigidity of the backbone. As a result, sPSScl9 incubated in the presence of V(V) shows unchanged ion exchange capacity and proton conductivity, and a 10× reduction of vanadium permeability with respect to untreated membranes.