Analysis of Nafion Fuel Cell Membrane Chemical Durability Using Broadband Dielectric Spectroscopy

Abstract

Changes in macromolecular dynamics associated with the Tg -related β relaxation of Nafion®, with chemical degradation, were investigated using broadband dielectric spectroscopy. Loss permittivity vs. frequency spectra showed peak splitting reflecting microstructural heterogeneity. Spectra were analyzed using the conductivity-modified Havriliak-Negami equation and the Kramers-Krönig integral transform, both of which showed broadening and peak splitting for degraded samples. Peak broadening and bi and tri-modal character of the spectra of degraded samples was also manifest in distributions of relaxation times which reflected a broadening of molecular weight distribution and related microstructural heterogeneity induced by chemical degradation.

Modeling and simulation of the water gradient within a Nafion membrane

“…This result agrees well with the obtained values from dielectric relaxation spectroscopy (DRS) measurements. 62,68,74 Increasing the permittivity coefficient by increasing the temperature exhibits the weakening of the confinement effect of water molecules and increasing the saturation level of the membrane. In an ion-exchange membrane with a gradient of water molecules across its thickness, the total permittivity is controlled with the minimum value.…”

Nafion β-Relaxation Dependence on Temperature and Relative Humidity Studied by Dielectric Spectroscopy

“…Such a complex arrangement results in entangled dynamical properties of Nafion membranes that have been studied by dielectric spectroscopy (DS) and dynamic mechanical analysis (DMA) as a function of both temperature and membrane water content. [12][13][14][15] Nafion in the Na + form was probed by DMA and four distinct relaxation processes, namely γ, β , β , and α, were identified with increasing temperature. 16 The γ-relaxation occurring at T γ ∼ −100 • C was attributed to the motion of backbone TFE segments.…”