Proton-conducting membrane with spatially heterogeneous structure based on polymer-silica nanocomposites

Abstract

An original approach for the preparation of ternary proton-conducting membranes consisting of high density polyethylene (PE), silicon dioxide, and phosphoric acid for the intermediate temperature (140- 180 oC) fuel cell is presented. The base of this method is a template synthesis of silica phase using hyperbranched polyethoxysiloxane as a precursor by hydrolytic condensation reaction within the volume of the nanoporous polymer matrix with pore’s diameter of about 10 nm obtained via the mechanism of delocalized solvent-crazing. The received polymer-silica nanocomposites containing up to 40 wt.% of SiO2 were characterized by a structure of two interpenetrating networks, and silicon dioxide formed a rigid three- dimensional framework. Loading of composites by phosphoric acid was carried out by their heating in an environment of H3PO4 at 160 oC that was above the melting point of PE. In this case, the polyethylene melt migrated from inner volume to surfaces of the composite while emerged pores were filled with acid. The amount of introduced acid increased linearly with a growth of silica phase in the composite and maximum content of H3PO4 equaled to 50 wt.%. The proton-conducting membranes obtained are characterized by conductivity of 0.03 S/cm and the best performance of 0.4 V at current densities of 0.4 A/cm2 at 160 oC.