Bi-functionalized copolymer-sulphonated SiO2 embedded with aprotic ionic liquid based anhydrous proton conducting membrane for high temperature application

Abstract

We prepared highly charged bi-functionalized copolymer (BFC) and sulphonated mesoporous silica embedded with aprotic ionic liquid (IL) (1-ethyl-3-methylimidazolium ethyl sulfate) based anhydrous conducting cross-linked polymer electrolyte membrane (PEM) by sol–gel. Composite PEMs with 0–10wt% sulphonated silica and 20wt% IL content (BFC/Si-x/IL) were characterized by their morphology, stability, IEC, water retention ability and temperature dependent anhydrous conductivity. Conductivity of pristine BFC membrane (1.57mScm−1) was increased with incorporation of sulphonated-SiO2 (10wt%) in the membrane matrix (BFC/Si-10) (3.56mScm−1), may be due to formation of interconnected network or channels in the membrane matrix. After embedding of aprotic IL (20wt%; ~80µS/cm conductivity) in highly acidic polymer (BFC/Si-10), conductivity of BFC/Si-10/IL composite PEM was about 8.79mScm−1 at 30°C. High anhydrous conductivity for BFC/Si-10/IL PEM was attributed to the exchanged protons from highly acidic membrane matrix by IL cation, and accordingly a mechanism was proposed. Further, enhanced bound water content and thus slow dehydration of BFC/Si-x/IL composite PEMs, make them a promising candidate for fuel cell application under low humidification.