Transport Phenomena in Polymer Electrolyte Membranes

Abstract

The insight gained from the analysis conducted in Part I ͑see the preceding article͒ 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 ͑ac͒ impedance conductivity measurements. This binary friction conductivity model ͑BFCM͒ is applied to 1100 equivalent weight ͑EW͒ 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 ͑BFM2͒, 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.

Accelerated Membrane Durability Testing of Heavy Duty Fuel Cells

“…The ratio of the membrane resistivity measured during the wet and dry cycle was used to estimate the RH during the dry cycle, based on the corresponding conductivity and water content levels known for 100% RH. 54,55 Idling and changes in humidity naturally occur in close proximity during driving. Therefore the baseline AMDT uses chemical and mechanical stressors simultaneously, simulating the real bus operating conditions.…”

Modeling Water Management in Polymer-Electrolyte Fuel Cells

“…As discussed by Fimrite et al 59,61 and Carnes and Djilali, 60 this treatment is similar to that of the dusty fluid model applied to the membrane, 62,63 but accounts for the bulk movement of water in a more consistent manner using a different reference frame. The binary friction model assumes that hydronium ions and water act as separate species within the membrane microstructure.…”

Macroscopic Modeling of Polymer-Electrolyte Membranes

“…Doing the above substitution into equation (14) where the m denotes the interaction with the membrane and e denotes an effective property of the membrane. As discussed by Fimrite et al [3,86], this treatment is similar to that of the dusty-fluid model applied to the membrane [87][88][89], but accounts for the bulk movement of water in a more consistent manner using a different reference frame. This analysis is akin to the analysis of gas movement in porous media presented by Weber and Newman [90].…”

“…A problem with the fit is that it does not take into account the observed lower uptake at higher temperatures (see for example references [146][147][148]), although this can be done with other curve fits or by extrapolating the curve if some data points are known at higher temperatures [149]. Finally, there are some models that use the same approach except use a fourth-order polynomial [86,133]. Equation 33 has a maximum water content of λ = 16.8 for essentially a liquid-equilibrated membrane.…”