Effect of equivalent weight on electrochemical mass transport properties of oxygen in proton exchange membranes based on sulfonated α,β,β-trifluorostyrene (BAM®) and sulfonated styrene-(ethylene-butylene)-styrene triblock (DAIS-analytical) copolymers

Mass transport parameters and limiting current densities are determined for a series of sulfonated alpha,beta,beta -trifluorostyrene-co-substituted-alpha,beta,beta -trifluorostyrene (BAM (R)) (EW 407-735 g mol(-1)) and sulfonated styrene-(ethylene-butylene)-styrene copolymers (DAIS-Analytical) (EW 555-1062 g mol(-1)) proton exchange membranes using microelectrode techniques. These materials were investigated in an environment that mimics proton exchange membrane fuel cells. The oxygen diffusion coefficient increases with temperature, while its solubility decreases. AII membranes exhibit a Henry's Law dependence for the limiting current of the oxygen reduction reaction with increasing oxygen pressure. The limiting current and the oxygen diffusion coefficient decreases with increasing equivalent weight, while the solubility of oxygen decreases due to the corresponding change in water content. These data are discussed in the context of previously published data on Nafion 117 and ethylenetetrafluoroethylene-g-polystyrene sulfonic acid membranes. (C) 2001 Elsevier Science B.V. All rights reserved.