H-2 nuclear magnetic resonance study of deuterated water dynamics in perfluorosulfonic acid ionomer Nafion

Abstract

We have employed deuteron nuclear magnetic resonance (NMR) spectroscopy in order to study the dynamics of the deuterated water (D2O) molecules introduced into a perfluorosulfonic acid ionomer Nafion (NR-211) film. According to the H-2 NMR spectral analysis, the deuterated water molecules at low temperatures occupied either relatively rigid or mobile sites up to the temperature T-M=240 K where all the deuterated water molecules became mobile. The temperature-dependent NMR linewidths sensitively reflected the motional narrowing of the rigid and mobile sites, and the NMR chemical shift reflected significant changes in the hydrogen bonds of the deuterated water. While a slow-to fast-limit motional transition was manifested at T-M in the laboratory-frame NMR spin-lattice relaxation, the rotating-frame spin-lattice relaxation indicated no bulk liquid water state down to 200 K. (C) 2016 Elsevier Ltd. All rights reserved.