Determination of bidirectional permeability of proton exchange membranes using a 1H nuclear magnetic resonance technique

Bidirectional permeability of proton exchange membranes was measured using a 1H nuclear magnetic resonance (NMR) technique based on the assignment of characteristic peaks and derivation of a relationship between the peak areas and the concentrations of methanol, water and D2O. The concentration variations of the liquids determined with NMR spectra showed that both methanol and the water transports were affected by the thickness and the chemical structure of membranes. Molar ratios of methanol to water diffused through membranes elucidated that chemical structures of membranes had a strong influence on the methanol transport, compared to thickness. Reverse-direction diffusion behaviors of membranes, back-diffusions, were also appraised with the D2O amounts. The amounts of back-diffusions were much less than those of the water transported from the opposite direction, which is the first report on the direct measurements of back-diffusions. The results suggest that 1H NMR technique can evaluate bidirectional transports of proton exchange membranes.