Self-diffusion micromechanism in Nafion studied by 2H NMR relaxation dispersion

Field Cycling (FC) H-2 nuclear magnetic resonance (NMR) relaxometry was applied to study dynamics in Nafion NR 212 in the temperature range from 300 K to 190 K and water content of lambda = 8.2. The sensitive time window of FC was extended up to eight decades using the temperature-frequency superposition principle and master curve. The rotational correlation times obtained from H-2 FC NMR coincide with translational correlation times gained from static field H-2 NMR diffusometry in the temperature range applied. This fact means that a long-range mass transport in Nafion is coupled to molecular rotations. It is assumed that confined water in Nafion has more ordered oxygen sublattices as compared with bulk water, on a short range is similar to ice. We discuss the possible role of D and L defects, typical for the ordered ice structure and using this concept to describe the processes of self-diffusion of confined water in Nafion, as well as the similarity of temperature and humidity dependence of self-diffusion and proton conductivity.

Automated summary

Field Cycling H-2 nuclear magnetic resonance relaxometry was utilized to study dynamics in Nafion NR 212, revealing a coupling between long-range mass transport and molecular rotations. Confined water in Nafion is believed to have more ordered oxygen sublattices compared to bulk water, similar to ice in the short range.