HYDROGEN DIFFUSION, SOLUBILITY, AND WATER-UPTAKE IN DOWS SHORT-SIDE-CHAIN PERFLUOROCARBON MEMBRANES

Hydrogen gas diffusion coefficients and solubilities as well as water uptake values are reported for Dow's short-side-chain perfluoro-sulfonic and -carboxylic membranes of different equivalent weight (EW). The diffusion coefficients and solubilities were determined with an electrochemical test cell. Hydrogen solubility decreases with increasing EW in the lower EW range and tends to level off at higher EWs for both types of membranes. Both hydrogen solubility and diffusion coefficients of a sulfonic membrane with EW higher than 800 are higher than the corresponding values of a carboxylic membrane of similar EW. An unusual maximum is observed in the diffusion coefficient-EW plot of sulfonic membranes. Water uptake decreases with increasing EW for both types of membranes. Various trends in the hydrogen diffusion coefficients and solubilities are discussed in terms of a number of physical and morphological properties, such as the percent of crystallinity, intrusion of one phase into another phase, extent of ion-pair formation, and pore sizes of membranes.