Polymer electrolyte membrane in fuel cell modeling

POLYMER ELECTROLYTE MEMBRANE IN FUEL CELL MODELING 

The water content is the state variable of PEMs. Water uptake from a vapor or liquid water reservoir results in a characteristic vapor sorption isotherm. This isotherm can be described theoretically under a premise that the mechanism of water uptake is sufficiently understood. The main assumption is a distinction between surface water and bulk water. The former is chemisorbed at pore walls and it strongly interacts with sulfonate anions. Weakly bound bulk-like water equilibrates with the nanoporous PEM through the interplay of capillary, osmotic, and elastic forces, as discussed in the section Water Sorption and Swelling of PEMs in Chapter 2. Given the amounts and random distribution of water, effective transport properties of the PEM can be calculated. Applicable approaches in theory and simulation are rooted in the theory of random heterogeneous media. They involve, for instance, effective medium theory, percolation theory, or random network simulations. 

From a practical perspective, it is important to understand the response of water distribution and fluxes in PEMs to variations in external conditions. Such variations can be applied in a controlled fashion in ex situ studies to isolate and extract effective transport parameters, or they could occur spontaneously in fuel cell operation under varying load requirements. 

In view of their application in PEFCs, PEMs are assessed by the following criteria  

Ability to be fabricated by robust high-volume and low-cost processes. 

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See also in sourсe #XX -- [ ]

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