Gas Permeation through Nafion. Part 1: Measurements

This study focuses on the characterization of gas permeation through Nafion, the most commonly used polymer electrolyte membrane (PEMs) for low-temperature fuel cells and water electrolyzers. In the first part of this study, novel modifications of the electrochemical monitoring technique to precisely measure the hydrogen and oxygen permeabilities of Nafion are presented. With these techniques, the gas permeabilities of Nafion were observed to be independent of pressures, which was ascribed to a solely diffusive process. Moreover, the temperature dependence of the hydrogen and oxygen permeabilities through Nafion in the fully hydrated state (where the water content is independent of the temperature) were measured in order to determine the activation energies of the permeation mechanisms. On the basis of the measured influence of temperature and relative humidity on the gas permeabilities of Nafion, the pathways for gas permeation through its aqueous and solid phase are qualitatively discussed. The second part of this study presents a resistor network model to quantitatively correlate the microscopic structure of Nafion and its gas permeabilities.