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Anion exchange membranes provide the basis for potentially more cost-effective fuel cells, electrochemical energy conversion, and energy storage. The membranes consist of a polymer domain with tethered cationic side groups and a pervading aqueous domain that conducts water and anions. Water diffusion is investigated through temperature-dependent quasielastic neutron scattering (QENS) at application relevant water contents, employing the BASIS spectrometer at ORNL. The spectrometer resolves two distinct quasielastic components corresponding to localized water diffusion (on length scales lower than the water domain thickness) and to extended water diffusion (on length scales approaching the water domain thickness). Water diffusion coefficients in membranes are time and length scale dependent and water exchanges between diffusion on a localized and extended volume increment. An exchange model for QENS is developed to describe the exchange of water between the two volume increments. The populations and lifetimes of water in each volume are discussed in terms of their connection to long-range water transport and membrane nanomorphology.

Perovskite-type oxyhydrides, BaTiO3–xHx, have been recently shown to exhibit hydride-ion (H–) conductivity at elevated temperatures, but the underlying mechanism of hydride-ion conduction and how it depends on temperature and oxygen vacancy concentration remains unclear. Here, we investigate, through the use of quasielastic neutron scattering techniques, the nature of the hydride-ion dynamics in three metal hydride-reduced BaTiO3samples that are characterized by the simultaneous presence of hydride ions and oxygen vacancies. Measurements of elastic fixed window scans upon heating reveal the presence of quasielastic scattering due to hydride-ion dynamics for temperatures above ca. 200 K. Analyses of quasielastic spectra measured at low (225 and 250 K) and high (400–700 K) temperature show that the dynamics can be adequately described by established models of jump diffusion. At low temperature, ≤250 K, all of the models feature a characteristic jump distance of about 2.8 Å, thus of the order of the distance between neighboring oxygen atoms or oxygen vacancies of the perovskite lattice and a mean residence time between successive jumps of the order of 0.1 ns. At higher temperatures, >400 K, the jump distance increases to about 4 Å, thus of the order of the distance between next-nearest neighboring oxygen atoms or oxygen vacancies, with a mean residence time of the order of picoseconds. A diffusion constant Dwas computed from the data measured at low and high temperatures, respectively, and takes on values of about 0.4 × 10–6cm–2s–1at the lowest applied temperature of 225 K and between ca. 20 × 10–6and 100 × 10–6cm–2s–1at temperatures between 400 and 700 K. Activation energies Eawere derived from the measurements at high temperatures and take on values of about 0.1 eV and show a slight increase with increasing oxygen vacancy concentration.

Molecular motion of hydrocarbons under confinement exhibits several peculiarities and has important implications in industries like gas recovery. A quasielastic neutron scattering (QENS) study of the dynamics of propane in nanoporous silica aerogel was carried out to quantify its molecular mobility. The dynamical properties of propane were studied as a function of temperature, pressure and presence of CO2. The effects of pressure, i.e., fluid density and composition, are found to be more pronounced than the effects of temperature. At low pressures of propane, many propane molecules are adsorbed onto the pore surfaces and are thus immobile. As the pressure of propane loading is increased, more molecules become available to take part in the diffusional dynamics and thus enhance the diffusivity. At low pressure the propane molecules take part in a continuous diffusion, while at higher pressures, the diffusion of propane molecules within the aerogel occurs via the mechanism of jumps. Presence of CO2enhances the jump rate of propane molecules, thereby increasing the diffusion coefficient. This study aims to aid in understanding the complex processes involved in hydrocarbon migration in porous quartz-rich rocks and enhanced hydrocarbon recovery.

We have investigated the diffusion dynamics of protons in hydrated 4.2% Ca-doped LaPO4, a candidate electrolyte for proton-conducting intermediate temperature fuel cells. The macroscopic and microscopic dynamics have been studied using electrochemical impedance spectroscopy (EIS) and quasi-elastic neutron scattering (QENS), respectively. The conductivity of the bulk hydrated sample was determined in the temperature range of 500–850 °C by EIS and showed a clear signature of proton conductivity with an activation energy of about 1.0 eV. The QENS experiment revealed a fast dynamical process below 500 °C that was not observed by EIS. The activation energy of the fast proton diffusion is 0.09 eV in the temperature range from 150 °C to 500 °C.

Polyoligosilsesquioxanes (POSS) are a large family of Si–O cage molecules that have diameters of 1–2 nm and can be viewed as perfectly monodisperse silica nanoparticles. POSS can be synthesized with a wide variety of functional ligands attached to their surfaces. Here we report the results of a comprehensive study of the crystal structure and ligand dynamics of one of the simplest POSS nanoparticles, octamethyl-POSS or Si8O12(CH3)8, where the central Si8O12cage is surrounded by eight methyl ligands. Neutron powder diffraction data highlight the presence of strongly temperature-dependent methyl group rotational dynamics. Vibrational spectra were measured using Raman and inelastic neutron scattering techniques, and the results of the measurements were compared with the predictions of density functional theory calculations. In particular, the inelastic neutron scattering spectra show the fundamental and first overtone transitions of the methyl torsional vibrations; these transitions are forbidden in both Raman and infrared spectroscopy for the molecule with its ideal octahedral symmetry. The energies of these transitions are used to determine the height of the torsional energy barrier. Direct measurements of the methyl group dynamics using quasielastic incoherent neutron scattering provide the hydrogen atom jump distance and the activation energy for rotation of the methyl groups. Together these results provide a detailed picture of the structure and ligand dynamics of this POSS molecule.

Sr6Ta2O11presents an interesting model system of a highly defective and disordered complex perovskite, exhibiting oxide ion conductivity at high temperatures as well as proton conductivity when hydrated by presence of water vapor. In this paper, we present a comprehensive structural study of Sr6Ta2O11in its dry and hydrated state, based on DFT calculations and NPD measurements. At low temperatures, dry Sr6Ta2O11has a tetragonal symmetry with ordered oxygen vacancies. The oxygen vacancy induces perturbations to its near surroundings, disturbing particularly the A site cations. As a consequence, the elaborate structural picture collapses at higher temperatures. The high-temperature structure has a cubic symmetry with fractionally occupied structural oxygen sites and disorder on the oxygen and strontium sublattices. The structure of the fully hydrated compound Sr6Ta2O10(OH)2was determined as monoclinic with significant distortions of the anion and metal cation sites.

The bulk conductivity of polycrystalline 1 mol-% Fe-doped rutile TiO2has been measured as a function of pH2Oand temperature under oxidizing and reducing conditions. From the pH2O-dependency of the conductivity, it is concluded that protons are significant positive defects and, furthermore, that mixed p-type electronic and protonic, and n-type electronic conduction dominate under oxidizing and reducing conditions, respectively. H2O/D2O isotope exchange confirmed that protons are significant charge carriers under wet oxidizing conditions below approximately 600 °C. Thermodynamic parameters for the hydration reaction were obtained by modeling the experimental pH2Oand temperature dependencies, assuming that the acceptor dopant (Fe3+) is charge compensated by protons and oxygen vacancies, and from ab initio density functional theory (DFT) calculations. The experimental data yield standard enthalpy changes of hydration of −130 ± 16 kJ/mol, whereas the calculated values are somewhat more negative; −155 to −162 kJ/mol. Based on such favorable thermodynamics of hydration, it is concluded that protons will be the dominating positive defect in TiO2under most conditions of practical interest.