Preparation and characterizations of direct methanol fuel cell membrane from sulfonated polystyrene/poly(vinylidene fluoride) blend compatibilized with poly(styrene)-b-poly(methyl methacrytlate) block copolymer

This work concerned a development of sulfonated polystyrene (SPS)/poly(vinylidene fluoride) (PVDF) blend membrane for use as an electrolyte in a direct methanol fuel cell. The aim of this work was to investigate effects of the blend ratio on properties of the blend membranes. The partially SPS with various degrees of substitution were prepared by using propionyl sulfate as a sulfonating agent. After that, the optimum SPS was selected for further blending with PVDF, at various blend ratios. Poly(styrene)-poly(methyl methacrytlate) block copolymer (PS-b-PMMA), used as a compatibilizer, was synthesized via a controlled radical polymerization through the use of an iniferter. Thermal behaviors, water uptake, proton conductivity, and methanol permeability of various blend membranes were determine by using TGA, gravimetry, impedance analyzer, and gas chromatography, respectively. From the results, it was found that, water uptake and methanol permeability of the blend membranes tended to increase with the weight ratio of SPS. It was also found that the blend membranes were incompatible, especially those containing more than 40 wt % of the SPS. However, by adding 5 wt % of the block copolymer, the blend became more compatible. Mechanical strength, proton conductivity, and resistance to methanol crossover of the blend membrane remarkably increased after the compatibilization. (C) 2007 Wiley Periodicals, Inc.