Characterizing Through-Plane and In-Plane Ionic Conductivity of Polymer Electrolyte Membranes

Ionic transport resistance is a key performance property of polymer electrolyte membranes (PEMs) and can be determined for transport within the plane of material (in-plane, longitudinal or transverse directions) and through the thickness of the membrane (through-plane). The conductivity of extruded Nafion® 112, dispersion-cast Nafion® NR-212 and two Gore-Select® membranes that contain a non-conductive support were characterized as a function of orientation, temperature and relative humidity. The conductivity of extruded Nafion 112 was highest in the extrusion direction and lowest in the through-plane orientation. In contrast, the conductivity of dispersion-cast NR-212 was isotropic. The effective conductivity of Gore-Select material was higher in-plane vs. through-plane, consistent with the analytical treatment of a membrane composed of layers of unequal intrinsic ion transport resistivity. The results highlight the need to make measurements in the relevant orientation.