Nano- and Mesoscale Conduction, Diffusion and Electrokinetics in Perfluorosulfonic-Acid Membranes*

Perflurosulfonic-acid (PFSA) membrane properties result from transport in a tortuous (mesoscale) network of interconnected, heterogenous, nanoscale hydrophilic domains. Consequently, optimization of membrane performance relies on understanding the emergent phenomena of this multiscale system. Continuum and network modeling elucidate how macroscopic conductivity, water diffusivity, and electrokinetics arise from meso- and nanoscale phenomena of PFSAs.

We predict transport properties of nanoscale hydrophilic domains as a function of water content using concentrated solution theory. A Voronoi resistor network upscales the pore-level description to macroscopic dimensions. Ion-pair formation is accounted for at the nanoscale and network swelling and heterogeneities are included at the mesoscale. This work shows clearly how transport modes couple across length scales and identifies how nonlinearities govern macroscale transport.