Water and methanol uptake in proton conducting Nafion® membranes

Methanol uptake from methanol-water mixtures has been measured at ambient temperature in Nafion®117 membranes initially saturated with water. After equilibration for 18 h the membranes were dried at 70°C in vacuum with a cold trap cooled with liquid nitrogen and the total amount of absorbent was determined from the weight loss. The methanol-water ratio was determined by ¹H NMR. A plot of the mole fraction of methanol in the membrane vs. the mole fraction in the water-methanol mixture was linear in the whole range from pure water to pure methanol. The slope indicated that Nafion® does not preferentially take up either water or methanol. The number of solvent molecules was found to be 23 per sulphonic group for both methanol and water.