Water Sorption and Transport Properties of Polymer Electrolyte Membranes: New Insights from Theory

Pertinent polymer electrolyte membranes (PEM) channel protons through random networks of water-filled pores. Their operation hinges on sufficient amounts of water for proton conduction. This requirement affects structure and properties on > 6 scales. Theoretical research on PEM employs a hierarchy of physical models to address these multiscale challenges. The first part of this contribution focuses on recent progress in ab initio calculations of structural correlations and proton dynamics at dense interfacial arrays of protogenic surface groups. These results have vital implications for the design of PEM that could attain high proton conductivity at minimal hydration. The second part explores the realms of equilibrium and dynamic water sorption and swelling of PEM. The outlined approaches in modeling provide capabilities to predict the membrane response to changing external conditions and to extract parameters of bulk water transport in PEM and vaporization exchange at the membrane surfaces from measured water fluxes through the membrane.