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

• Aprotic ionic liquid embedded sulphonated silica based anhydrous conducting PEM.
• Anhydrous conducting PEM with high bound water content.
• Trade-off behavior between conductivity and sulphonated silica/aprotic IL content.
• Improved conductivity by H+ exchange between highly acidic matrix and IL cations.

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 0–10 wt% sulphonated silica and 20 wt% 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 (1.57 mS cm−1) was increased with incorporation of sulphonated-SiO2 (10 wt%) in the membrane matrix (BFC/Si-10) (3.56 mS cm−1), may be due to formation of interconnected network or channels in the membrane matrix. After embedding of aprotic IL (20 wt%; ~80 µS/cm conductivity) in highly acidic polymer (BFC/Si-10), conductivity of BFC/Si-10/IL composite PEM was about 8.79 mS cm−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.

Incorporation of sulphonated-SiO2 in bi-functionalized matrix improved the anhydrous conductivity due to formation of network or interconnected channels. Conductivity was further improved by embedding of aprotic IL in highly acidic polymer, may be due to exchange of protons from highly acidic membrane matrix by IL cation.Figure optionsDownload high-quality image (341 K)Download as PowerPoint slide