Characterization of polymer electrolyte Nafion membranes: Influence of temperature, heat treatment and drying protocol on sorption and transport properties

We carried out systematic sorption, proton conductivity and water diffusion measurements in commercial Nafion N115 and Nafion NRE212 membranes. Because of the high dispersion of data in the literature, our primary objective was to gather a comprehensive set of experimental measurements and compare them with published results. Our simple, reproducible, experimental protocol allowed us to measure these important membrane properties over a wide range of experimental conditions. The membrane samples were heat-treated at different temperatures and the effect of thermal history on water sorption capacity and transport properties was investigated. We show that water uptake, proton conductivity and water self-diffusion coefficient decrease with increasing drying temperature. As a consequence, these variations must systematically be taken into account when comparing literature values to each other. The effect of temperature on sorption has also been investigated. The measurements show that the water sorption capacity of heat-treated (60 °C during 24 h) N115 and NRE212 membranes measured in vapor phase decreases with temperature while it increases in liquid phase. In membranes that were not heat-treated, however, the sorption in liquid water is independent of temperature.