Transport phenomena in polymer electrolyte membranes - II. Binary friction membrane model

The insight gained from the analysis conducted in Part I (see the preceding article) is used in the development of a general transport model for water and protons in perfluorosulfonic acid membranes based on the binary friction model. As a tool for investigating the unknown parameters in the general membrane transport model, a simplified conductivity model is derived to represent conditions found in alternating current (ac) impedance conductivity measurements. This binary friction conductivity model (BFCM) is applied to 1100 equivalent weight (EW) Nafion, and compared to other established membrane models. It is shown to provide a more consistent fit to the data over the entire range of water contents and at different temperatures. The subset of transport coefficients in the BFCM is the same as in the general binary friction membrane model (BFM2), and thus with additional data on water transport, the BFM2 model and all its required parameters can be fully specified. The paper discusses possible experimental investigations and fundamental simulations to determine the model parameters required to apply the general BFM2 to predict coupled proton and water transport in PEM fuel cells. (c) 2005 The Electrochemical Society.