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PEM Fuel Cells by Ken S. Chen, Yun Wang

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4.3 WATER TRANSPORT IN POLYMER ELECTROLYTE MEMBRANES

Water plays an important role in membrane properties, as seen in the previous section. Weber and Newman [17] proposed a physical model as depicted in Figure 4-8, to study the effect of water content on the membrane microstructure. As illustrated inFig. 4-8, a dry membrane initially absorbs water to solvate its sulfonic acid groups, which builds strong bonds of water-acid groups. The addition of extra water loosens the bonds, leading to the micelles formation in the polymer matrix (Fig. 4-8 b). As more water is absorbed, the clusters become larger, eventually interconnecting with each other. The cluster-channel network forms a transport pathway. The percolation threshold occurs around ⋋ = 2.0. ...

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