Estimation of Water Contents of Polymer Electrolytes from 1H NMR Peak of Confined Water

Abstract

Water molecules confined in perfluorinated ionomer membranes which are widely used for polymer electrolyte fuel cells, presented apparently a single 1H NMR peak in hydrated states because of the rapid exchange among the water molecules at the distinct segments of the polymer. The peak shifts to the lower field with decreasing the water content due to the decrease of the fraction of the bulk water molecules which present a peak at higher field. The chemical shifts were found to be well correlated with the peak area. The water peak for MEA (Membrane Electrode Assembly) showed also similar behaviors to the membranes. From the relationship between the chemical shift and the peak area of the confined water peak we demonstrated the potential that the chemical shift could be utilized to estimate the water content in the hydrated membranes and MEA.