Abstract
PFSA-based reinforced membranes are used today as the benchmark material for the electrolyte in PEMFCs. Although greatly improved relatively to their unreinforced version, they still suffer from aging and degradation during fuel cell (FC) operation. In this study we first performed proton NMR to characterize the different water populations in the pristine Nafion XL reinforced membrane. Then we used proton and fluorine NMR, FTIR and sorption measurements in order to qualitatively observe the differences induced in the membrane's chemical structure and properties by long term FC operation. Proton NMR is seen to be an adapted tool to quickly measure a signature that is correlated to the degradation state while FTIR can serve as a local probe of the chemical structure.
Highlights
The degradation of the proton exchange membrane (PEM) is one of the main factors limiting the proton exchange membrane fuel cell (PEMFC) stability and performance [1, 2]
The chemical shift of the most intense component at 4.69 ppm corresponds approximately to that observed in nonreinforced hydrated perfluorosulfonic acid (PFSA) membranes at equivalent temperature and water content: Nafion
The fluorine NMR and FTIR spectroscopies provide experimental clues for a chemical degradation of the PFSA ionomer by side chain scission. This results in a partial loss of the ionic sulfonic groups and a decrease of the maximum water uptake as observed on the sorption isotherm and through the intensity ratio of the two resonance lines in the proton NMR spectrum
Summary
The degradation of the proton exchange membrane (PEM) is one of the main factors limiting the proton exchange membrane fuel cell (PEMFC) stability and performance [1, 2]. The decomposition of the membrane is induced by several factors among which mechanical stress and chemical degradation prevail. The resulting reduction of the polymer mechanical strength can lead to the formation of cracks and to the final failure of the membrane electrode assembly (MEA) [3,4,5]. The electrochemical reactions of these gases cause the formation of free radicals and the attack of the polymer chemical structure, which results in scissions in the main chain and in the side chain and to the thinning of the membrane [6, 7]
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