Infrared Reflectance Absorption Spectroscopy (IRRAS) has been used to study the thermal stability of Nafion (du Pont, equivalent weight=1100) and a similar perfluorinated sulphonic acid ionomer (PFSI) made by the Dow Chemical Company (equivalent weight=560). Purified aqueous PFSI electrolytes solutions were prepared, PFSI films (0.5-5 μm) were cast from these aqueous PFSI solutions onto Pt foil substrates for spectral study after heating at various temperatures. Spectra were recorded at room temperature in a vacuum after a film on Pt had been heated at a particular temperature in the presence of air. The temperature range was 22-300°C. Spectral changes for a PFSI film on Pt were not significant when heated at up to 200°C in an air atmosphere; however, when heated at 300°C there was a significant decrease in intensity for S-O related bands indicating substantial loss of the sulphonic acid groups from these ionomers.
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