Sulfonated Poly(Fluorenyl Ether Ketone) Membranes with Suppressed Semi-Interpenetrating Crossover and Enhanced Proton Selectivity for Vanadium Redox Flow Batteries

Abstract

A series of hybrid membranes with special microstructure, based on sulfonated poly (fluorenyl ether ketone) ionomer (SPFEK, IEC=1.74 mequiv.g-1) and secondary amine group containing SiO2 (SiO2–NH–NH2), has been successfully designed and prepared for vanadium redox flow battery (VRB) application. The hybrid membranes are prepared by simply adding KH792 into the SPFEK solution in N,N’-dimethylacetamide (DMAc), followed by dispersion, co-condensation and solvent casting. The water uptake, mechanical property, proton conductivity, (VO)2+ permeability and single cell performance are investigated in order to understand the relationship between morphology and property of the membranes. The hybrid membranes show dramatically improved proton selectivity when compared with SPFEK. The vanadium ion (VO)2+ permeability through the hybrid membrane is about 10 times lower than that of virgin SPFEK. The columbic efficiency and energy efficiency of the single cell of the hybrid membrane are higher than the SPFEK membrane. The results inidicate that hybrid membranes of this type are promising for VRBs.