Studies of a high temperature proton exchange membrane based on incorporating an ionic liquid cation 1-butyl-3-methylimidazolium into a Nafion matrix

High temperature proton exchange membranes based on Nafion were prepared by incorporating the polymer with ionic liquid cation 1-butyl-3-methylimidazolium (BMIm) and doping with phosphoric acid (PA). We found that using the hydroxide form rather than the chloride form of BMIm incorporated more readily the BMIm cation into Nafion film. A mole ratio of about 2 of BMIm cation to Nafion repeat unit, i.e., λBMIm/Nafion, was reached with the hydroxide form BMIm. The incorporated BMIm cation enhanced the doping of phosphoric acid into Nafion. A proton conductivity of 10.9 mS cm−1 and a tensile stress at break of 5.3 MPa were achieved, respectively, with a composite membrane of Nafion/2.3BMIm/5.2PA in molar ratio at 160 °C without humidification.

► High temperature proton exchange membranes of Nafion/BMIm/PA.
► BMImOH results in easy incorporation of ionic liquid cations in Nafion membranes.
► Low methanol permeability of Nafion/BMIm membranes.
► The incorporated ionic cation BMIm enhances the PA doping in Nafion.