Nafion absorption properties

The effect of NaOH concentration on the ion transport and rheological properties of the Nafion ion exchange membranes may be attributable to some variation in the ionic domain structure in the presence of NaOH. Therefore, it is extremely Important to understand the ionic domain structure under these conditions. The anomalous behavior of Na" " ion transport as a function of NaOH concentration is seen more frequently in bilayer Nafion membranes in which one layer is treated with diamine and also in perfluorinated carboxylic ion exchange membranes. Several mechanisms have been proposed to explain their ion transport results including water absorption, transport of hydroxide ion tunneling, ion pairing mechanisms, etc. (54-56). As the ion transport properties are beyond the scope of this review, no detailed discussion will be presented. 

In fuel cells, temperature (X) and water activity (Ow) change in response to the current. These changes in T and can alter the transport properties of the Nafion membrane, which can in turn alter the fuel cell operation. Decreases in water activity cause the proton conductivity to decrease, which reduces the current and further reduces the water activity this feedback mechanism can result in steady-state multiplicity in PEM fuel cells [15,16]. Water absorption and desorption from Nafion causes it to swell and shrink, which can cause mechanical failure of the membrane and alter the interfacial contact between the membrane and the electrode [17, 18]. Choosing and controlling the operating conditions of PEM fuel cells require knowledge of the mechanical and transport properties of Nafion. 

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