Fuel cell membranes based on blends of PPO with poly(styrene-b-vinylbenzylphosphonic acid) copolymers

Well defined ion containing block copolymers of poly(styrene-b-vinylbenzylphosphonic acid) (PS-b-PVBPA) were blended with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) to obtain polymer electrolyte membranes (PEM) for higher temperature applications, and their properties were studied. Phase morphologies of the membranes were also studied by small angle X-ray scattering (SAXS) and atomic force microscopy (AFM). The blend membranes showed glass transition temperatures (Tg) higher than 160 °C, and thermal stability up to 350 °C. For the blend membranes, the water uptake, ion exchange capacity (IEC), proton conductivity, and methanol permeability increased with the block copolymer content, and the trends of changes of proton conductivities and methanol permeabilities were very similar. Water uptake was quite low and was less than 16 wt%. Highest proton conductivity at 25 °C was 1.48 × 10−3 S/cm (RH = 100%) and increased to 2.85 × 10−2 S/cm at 140 °C. The ratio of proton conductivity to methanol permeability was quite comparable to that of Nafion 117.