Effects of Temperature and Solvent Activity on the Viscoelastic Response of

ii This thesis will investigate the mechanical properties of Nafion®, specifically with respect to viscoelastic creep and membrane swelling, under a range of temperatures and solvent activities. Studies have shown that the mechanical properties of the membrane are extremely important to the performance and longevity of the fuel cell. This paper will focus on a relatively new Polymer Electrolyte Membrane fuel cell (PEM) fuel cell technology, the Direct Methanol Fuel Cell (DMFC). Nafion®, a perfluorinated ionomer, is the most commonly used membrane in these fuel cells. Nafion ® is a viscoelastic material, which means that it responds to stress in a time-dependant manner. The membrane of a fuel cell is subject to various stresses, including those due to solvent mass uptake and clamping between flow plates, which causes Nafion to creep. Creep can result in membrane thinning and pinhole formation, which increase the incidence of methanol crossover, the leading failure mechanism in DMFC’s. Temperature and solvent activity strongly affect the viscoelastic response of Nafion. Thus, an accurat