Slow morphological change of perfluorinated ionomer as deduced from 1H NMR spectra of confined water

The behaviour of water molecules confined in the perfluorinated ionomer membrane, which is widely used for polymer electrolyte fuel cells, was investigated by 1H NMR spectroscopy. The 1H NMR spectra of water molecules confined in the membrane presented characteristic features depending on temperature and hydrated conditions. On the basis of the observations of the variations in the 1H NMR signals, it was deduced that the polymer underwent very slow conversions among distinct morphologies depending on temperatures and humidified conditions below 348 K. A plausible scheme of the local conversion of the states of the water molecules associated with the morphological changes of the polymer was proposed.