Transport properties of proton- and hydroxide-exchange membranes for fuel cells

The electro-osmotic drag coefficients (xi) of water-vapor equilibrated Nafion (R) 117, a proton conductor, and Tokuyama (R) A201, a hydroxide conductor were determined from the steady-state voltage of a water concentration cell. The xi values are reported, along with water uptake, ion-exchange capacity, ionic conductivity, and methanol permeability of these membranes. The room-temperature of Nafion (R) 117 and Tokuyama (R) A201 is 0.99 (+/- 0.07) and 0.61 (+/- 0.12), respectively, and is relatively independent of water content over the relative humidity range of 14-96%. The time to steady potential in the water concentration cell was longer for the Tokuyama (R) A201 membrane than the Nafion (R) 117 membrane. which is tentatively attributed to the lower mobility of hydrated hydroxide (or carbonate from absorption of adventitious carbon dioxide) in comparison to hydronium ion. Published by Elsevier Ltd.