Electro-Osmotic Flow of Water-Methanol Mixtures Through Nafion Membranes Revisited: Composition and Temperature Dependence

The electro-osmotic drag coefficient of water and methanol mixtures through Nafion 117 membranes was measured as a function of the composition at several temperatures between 25 and 60 degrees C using a two-compartment capillary cell with Ag/AgCl electrodes. The electro-osmotic water drag in HCl aqueous solutions is higher than that reported in measurements where the membrane is in contact with pure water; hence, all the reported results were performed at the same acid concentration. It was found that the drag coefficient for pure methanol is about 40% higher than that for water at all the temperatures studied as a consequence of the expanded nanostructure of Nafion in methanol. The drag coefficients of the water-methanol mixtures exhibit a high non-linearity, which can be explained by considering the Nafion sorption in the binary solvent. The electro-osmotic flow in pure methanol is similar to that of 5 M methanol aqueous solutions, which opens the opportunity to use pure methanol in DMFCs. The methanol crossover due to permeability can be minimized. Controversial results with previous studies are also addressed.

Automated summary

The electro-osmotic drag coefficient of water-methanol mixtures through Nafion 117 membranes was measured at different temperatures using a capillary cell. The drag coefficient for pure methanol was found to be 40% higher than that of water, and the drag coefficients of the mixtures showed non-linear behavior. Using pure methanol instead of methanol aqueous solutions can minimize methanol crossover in DMFCs.