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A novel organic/inorganic composite membrane synthesized with sulfonated multiwalled carbon nanotubes (s-MWNTs) and sulfonated polyetherimide (s-PEI) is prepared for use in a direct methanol fuel cell (DMFC). A solution casting method was used to prepare s-MWNT/s-PEI membranes (SPEI membranes) with various s-MWNT contents. This composite membrane showed not only low methanol crossover and water swelling but also enhanced mechanical properties. The IEC and proton conductivity of SPEI membranes were increased by incrementing their s-MWNT content. This is because the number of sulfonic acid groups (SO 3 À ) increases as s-MWNTs are added. The water uptake of SPEI membranes increased as s-MWNT content was increased due to the hydrogen bonded interaction between sulfonic groups and carboxylic groups in s-MWNTs and water molecules. However, the water uptake of SPEI membranes is remarkably low, compared with Nafion membranes. The methanol permeability of the SPEI membranes (8.8 Â 10 À8 cm 2 s À1 ) in this study was also lower than that of the Nafion membrane. Therefore, SPEI membranes were expected to have potential applications in DMFCs. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 126: E467-E477, 2012

An organic/inorganic composite membrane was prepared based on sulfonated poly(ether sulfone) (s-PES) embedded with sulfonated multiwalled carbon nanotubes (s-MWNTs). The ion exchange capacity (IEC), proton conductivity, and water uptake of the SPES membranes increased with increasing s-MWNTs content. The increased water uptake was attributed to hydrogen bond formation between the carbonyl group of the s-MWNTs and a water molecule. The composite membranes exhib-ited proton conductivities ranging from 3.9281 Â 10 À4 to 7.0788 Â 10 À3 S/cm at 80 C, as well as low methanol permeability ranging from 4.4405 Â 10 À10 to 9.1008 Â 10 À10 cm 2 s À1 at 25 C. V C 2012 Wiley Periodicals, Inc. J Appl Polym Sci 126: E513-E521, 2012