Anisotropic diffusion of water in perfluorosulfonic acid membrane and hydrocarbon membranes

Polymer electrolyte membranes that are applied for polymer electrolyte fuel cell (PEFC) retain water in their three-dimensional network structure. Diffusion behavior of water in the membranes was analyzed by pulsed field gradient (PFG)-NMR method to estimate diffusion coefficient of proton species as water or hydronium ion. The membrane samples were put in a sample tube vertically or horizontally toward to the field gradient axis under determined temperature and humidity conditions. As the results, anisotropic diffusion behavior of water in the membranes was indicated. Anisotropic properties depended on the sample type, preparation conditions of the wet membranes, and measurement conditions. A perfluorosulfonic acid membrane tended to have smaller anisotropy while hydrocarbon membranes showed greater anisotropy.