J.R.P. Jayakody

Studies of Water in Nafion Membranes Using Deuteron and Oxygen‐17 Nuclear Magnetic Resonance, and Dielectric Relaxation Techniques

Deuteron and oxygen-17 nuclear magnetic resonance measurements and dielectric relaxation studies of Nafion-117 membranes with variable water content (approximately 5-18% by weight) have been carried out. Glassy behavior of the water domains at low temperature, below ca. 200 K, is evidenced by the specific nature of the 1 H NMR line shapes. Activation energies extracted from 1 H spin-lattice relaxation data on the high temperature side of the T 1 minimum exhibit a steady increase with increasing water content. In spite of a high degree of molecular mobility, angular-dependent spectra in both as-received and stretched samples reflect considerable anisotropy of the host polymer

Ormosil/Sulfonated Polyetheretherketone-Based Hybrid Composite Proton Conducting Membranes

A modified silane bearing a sulfonic acid function (sulfonated diphenylsilanediole, SDPSD) was prepared and characterized. The resulting ormosil was mixed with sulfonated polyetheretherketone (SPEEK) with high degree of sulfonation (0.9) leading to homogeneous composite membranes. The formation of the composite substantially modified the properties of SPEEK in terms of water uptake and solubility. The structural and electrochemical performance of the components and of the composite were investigated with thermogravimetric analysis, field emission scanning electron microscopy, H-1 and Si-29 nuclear magnetic resonance, both in solution and in the solid state, and electrochemical impedance spectroscopy. Both conductivity values, as high as 0.1 S cm(-1), and H-1 diffusion coefficients of the composite SPEEK/SDPSD demonstrated that it possesses good proton transport characteristics up to 120 S C, and it is then suitable for application as an electrolyte in polymer electrolyte fuel cells operating at intermediate temperature

High pressure studies of hydrated NAFION membranes: Dielectric relaxation and deuteron NMR

Abstract Audio frequency electrical conductivity/dielectric relaxation and nuclear magnetic resonance studies of NAFION-117 have been carried out at pressures up to 0.3 GPa (3 kbar). For some samples, the electrical conductivity exhibits dispersion typical of hopping conductivity in an amorphous material, σ = σ 0 ω m . The values of m are sample dependent and vary from about 0.55 to 0.75. In addition, the values of m are not strongly pressure sensitive. At a given frequency, the electrical conductivity tends to decrease as pressure increases and yield activation volumes on the order of 5 to 10 cm 3 /mol. The activation volume determined from the NMR spin-lattice relaxation time measurements are also sample dependent. The data shown correspond to an activation volume of about 8.6 cm 3 /mol. The results of the high pressure electrical conductivity studies also yield activation volumes on the order of that determined via NMR.

Deuteron and Oxygen-17 NMR Studies of Molecular Motion in Methanol- Saturated Nafion Membranes

Abstract : Deuteron and oxygen-17 NMR linewidth and spin-lattice relaxation measurements in Nafion-117 films containing methanol at -75% and -100% saturation are reported. Molecular motion probed by room temperature measurements in stretched films and low T measurements in unstretched films is found to be quite rapid compared to previous results obtained for Nafion-117 containing water.

Investigation of Dynamics in BMIM TFSA Ionic Liquid through Variable Temperature and Pressure NMR Relaxometry and Diffusometry

A comprehensive variable temperature, pressure and frequency multinuclear (1H, 2H, and 19F) magnetic resonance study was undertaken on selectively deuterated 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) ionic liquid isotopologues. This study builds on our earlier investigation of the effects of increasing alkyl chain length on diffusion and dynamics in imidazolium-based TFSA ionic liquids. Fast field cycling 1H T1 data revealed multiple modes of motion. Through calculation of diffusion coefficient (D) values and activation energies, the low- and high-field regimes were assigned to the translational and reorientation dynamics respectively. Variable-pressure 2H T1 measurements reveal site-dependent interactions in the cation with strengths in the order MD3 > CD3 > CD2, indicating dissimilarities in the electric field gradients along the alkyl chain, with the CD2 sites having the largest gradient. Additionally, the α saturation effect in T1 vs. P was observed for all three sites, suggesting significant reduction of the short-range rapid reorientational dynamics. This reduction was also deduced from the variable pressure 1H T1 data, which showed an approach to saturation for both the methyl and butyl group terminal methyl sites. Pressure-dependent D measurements show independent motions for both cations and anions, with the cations having greater D values over the entire pressure range.