Physicochemical characterization of ion-exchange membranes in water–methanol mixtures

A complete physicochemical characterization of two ion-exchange membranes—CM2 and Nafion®117—used in electrodialysis and in direct methanol fuel cells (DMFC) has been carried out. For each membrane, in different methanol–water mixtures—0%, 20%, 40%, 60%, 80% and 100%—and at different temperatures (25.0; 40.0 et 55.0 °C), we have measured the variations of the geometrical dimensions, the proton electrical conductivity, the swelling rate and the amount of methanol in the membrane. The FTIR analysis of Nafion®117 was performed at different methanol contents of the external solution. The results show that the CM2 membrane presents the best geometrical stability, and the lowest conductivity at any methanol content. At high methanol contents, Nafion®117 is 10 times more conductive than the CM2 membrane. It was found that the methanol is absorbed more by Nafion®117, and its effect is more noticeable on the microstructure of this membrane, under standard conditions. The high methanol permeability of these membranes, particularly of the Nafion®117, induces bad cell efficiencies and lifetimes.