SPPO/PEI-based acid-base blend membranes for direct methanol fuel cells

New acid-base polymer blends based on sulfonated poly(phenylene oxide) (SPPO) as the proton-conducting component and poly(ether imide) (PEI) as the basic component were considered for use as proton-exchange membranes (PEM). The obtained blend membranes had a higher thermal stability and a higher glass transition temperature (T _g) than the pure SPPO, as revealed by TGA and DSC. The morphology of blend membranes indicated that PEI was highly compatible with SPPO polymers because of the formation of hydrogen bonds between the sulfonated acid and PEI. Although the blend membranes exhibited a lower water uptake and lower proton conductivity than the pure SPPO membrane, the PEI component improved the dimensional stability, mechanic properties, and especially inhibited methanol permeation. The methanol permeability coefficient of the blend membrane with 30 wt.% PEI content was 9.68×10 ^-8 cm ²/s, which is lower than that of the pure SPPO and just one tenth of that of Nafion® 112. This considerable reduction in methanol crossover revealed the feasibility of the blend membranes as promising electrolytes for direct methanol fuel cells.