Electrochemical Properties of Ion-Exchange Membranes Based on Sulfonated EPDM-Polypropylene Blends

The preparation of cation-exchange membranes by compression molding of sulfonated EPDM-polypropylene blends is described. Concentration potentials measured in a two-compartmental cell with configuration Ag/AgCI HC1 solution (CO/membrane/ HC1 solution (C2) AgCl/Ag., are a linear function of log a2 (= C21/2, where C2 and 'y2 are, respectively, the concentration and activity coefficient of the solution in compartment 2 keeping constant the concentration in compartment 1, C1. The values of the proton transport numbers, t+, decrease from 0.99 to 0.94 when the ratio C2/Ci increases from 0.1 to 5, nearly the same decrease reported for Nafion 117 in the same variation of concentration ratios. Proton conductivities at 25 deg C are 9.84 X 10-4 and 7.25 X 10-4 S /cm, respectively, for water-saturated membranes containing 20 and 10% of polypropylene, more than one decade below the value reported in the literature for the conductivity of Nafion membranes at the same temperature. These conductivities at 90 deg C amount to 8.35 x 10-2 and 1.03 x 10-2 S/cm, respectively.