Behavior of Water Molecules in PEFCs as Studied by 1H NMR Spectroscopy

Abstract

Water molecules confined in perfluorinated ionomer membranes which are extensively used for polymer electrolyte fuel cells, presented characteristic 1H NMR spectra reflecting the difference in the morphology. For the hydrated membrane the water molecules at the distinct segments of the polymer undergo rapid exchange to give an apparent single signal. The signal shifts to the higher field with increasing the water content due to the increase of the fraction of the bulk water molecules. On shortage of bulk water the morphological conversion takes place. The membrane of such morphology exhibits a spectrum with separated regions at room temperature regardless of the water content, since the morphology prohibit the rapid exchange among the water molecules localized at the distinct segments. The characteristic spectral changes of water molecules associated with the chemical exchange among the water molecules in the different water domains and the change of the polymer morphology were demonstrated