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Improved Characterization of Hydrogen Fuel Cell Membranes

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I characterized the morphology of a hydrogen fuel cell membrane commercially known as Nafion. First generation Nafion (N112/N115) was compared with the second generation (N211) at various temperatures and humidities to examine their structural differences. The membranes were analyzed in a new humidity- and temperature-controlled chamber (Xenocs) using small angle X-ray scattering (SAXS) at temperatures ranging from 30-80C and relative humidities (RH) between 30-90%. The Kapton chamber windows were characterized to allow for proper background subtraction of Kapton intensity profiles, and folded and not folded membrane samples were compared to determine an easier method for mounting. Equilibration time for changes in the Nafion structure after an RH change of 30 and 40% were observed to be of the order of 30 minutes. The membrane profiles at different RH were fit to a multi-peak pseudo-Voigt function with a constant offset and negative power law at low Q (reciprocal space) values, with a clear ionomer peak (0.2 A^-1) appearing above 40% RH for N115 and 30% RH for N112 and N211. The membranes were also analyzed using dynamic vapour sorption (DVS) at 80C; N211 showed a significantly higher increase in water uptake than N112/N115.
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