Proton conducting electrolyte membranes based on the pendant-sulfonated poly(arylene ether ketone)/polyorganosiloxane interpenetrating polymer networks

An organosiloxane polymer network (OSPN) was pre-synthesized from 3-glycidyloxypropyltrimethoxysilane and 1-hydroxyethane-1,1-diphosphonic acid, and a pendant-sulfonated poly(arylene ether ketone) (PSPAEK) from the intermediate containing carboxylic acid. Proton-conducting polymer electrolyte membranes were prepared in semi-interpenetrating polymer network (semi-IPN) form from PSPAEK and OSPN. The prepared membranes exhibited superior proton conductivity but similar methanol permeability to the pristine PSPAEK. The water uptake increased only to 64% as the OSPN content was increased to 50%, even at 80 °C. The single direct methanol fuel cell (DMFC) performance based on the semi-IPN membrane possessing 50 wt% OSPN showed an excellent power density of 70 mW cm−2. The chemical and morphological structures of the synthesized membranes were characterized using Fourier transform infrared (FTIR) spectroscopy and small angle X-ray scattering (SAXS) and their results were correlated with the essential membrane properties such as water uptake, proton conductivity, and methanol permeability. The thermal and mechanical stabilities were also investigated using thermogravimetric analysis (TGA) and a universal tensile machine (UTM).