Vaporization-exchange model for dynamic water sorption in Nafion: Transient solution

Abstract

A recently proposed vaporization exchange model for Nafion-type polymer electrolyte membranes was applied to transient water flux data. The original model has been modified to include bulk transport coefficients that depend on local membrane water content. Numerical calculations are compared with transient sorption experiments to isolate and extract the transport coefficients of water at low and high water contents as well as the interfacial vaporization exchange rate constant. The transition from slow to rapid bulk water transport upon increasing water content suggests that hydraulic permeation prevails over chemical diffusion above a critical water content. The value of the critical water content agrees with the percolation threshold obtained from independent data on structure and transport in Nafion.