Neutron Probes for the Hydrogen Economy

1. J=5 J=4 J=3 J=2 J=1 J=0 (Neutron energy loss) • Hydrogen-Storage Systems • Metal Hydrides • Alkali-Metal Hydrides • Alkali Borohydrides • Nanoporous Materials 500 seconds Real time imaging of water dynamics in a fuel cell • location of H, OH, H2O • in materials • hydrogen vibrations • H bonding states • diffusion of H, H2O • in materials • nanostructure • e.g., H clustering • quantitative H analysis • in materials • H/H2O imaging • in storage vessels/fuel-cells • H in thin films • e.g. H density profile, • membrane structures • diffractionsensitivity> 2 % H (D) • vibrational spectroscopy • sensitivity: > 0.1% H (D) • quasielastic scattering • sensitivity: > 0.1% H (D), 10-8-10-12 s • small-angle scattering • sensitivity: > .01%, 10-10,000 Å • prompt- activation analysis • sensitivity: ~ 3g H • neutron imaging • sensitivity: ~100 m, 1 g H • reflectometry • sensitivity: > 2 %, ~ 5–1000 Å Average water distribution 1 mm water 2000 seconds 0 mm water Quantification of water content From the images the water content can be determined at the 1 mg level. Large areas can be summed to quantify the water mass during any frame. How it works Comparison of the relative size of the x-ray and thermal neutron scattering cross section s for various elements. x-ray cross section Sample t H D C O Al Si Fe neutron cross section SrZr0.95Y0.05H0.02O2.985 E. H. Majzoub, et al. T. J. Udovic, et al. B. Fultz, et al. Neutron Probes for the Hydrogen Economy David Jacobson,Terry Udovic, and Jack Rush, Muhammad Arif, National Institute of Standards & Technology (NIST) Materials of Interest for Neutron Measurements and Theory Neutron Methods: Special Characteristics NIST Center for Neutron Research (NCNR) • Fuel-Cell Materials • High-Temperature Protonic Conductors • Inorganic Superprotonic Conductors • Polymeric Membranes • Very large H cross section: • - “see” H better than other atoms - H/D contrast, high sensitivity • Covers unique range: • - time (10-7-10-15s) • - distance (0.5-10,000 Å) • State-of-the art instrumentation available at NIST • Cover many phenomena at the atomic • and nanoscale • Especially powerful for H in materials Website: www.ncnr.nist.gov NR SANS QENS SANS NI NPD QENS Neutron Imaging Facility(NIF) NVS QENS PGAA For more information, contact: Jack Rush (jack.rush@nist.gov) Terry Udovic (udovic@nist.gov) David Jacobson (jacobson@nist.gov) Muhammad Arif (arif@nist.gov) SANS Neutron Vibrational Spectroscopy (NVS) Quasielastic Neutron Scattering (QENS) Phenomena Probed in Hydrogenous Materials Combining NVS with a first principles computational approach can yield detailed information about H-storage materials and their limits for the hydrogen kinetics and uptakes. QENS simultaneously provides atomic-scale temporal and spatial information on the localized and diffusive motions of hydrogen in a host lattice. Diffusion mechanisms and pathways are keys to understanding performance of hydrogen-storage materials and fuel cells. Hydrogen in Carbon Nanotubes Computation indicates 3 wt% at best. T. Yildirim, et al. A.V. Skripov, et al. E. Majzoub / C. Jensen, et al. The broad quasielastic component for the cubic Laves-phase ZrMo2H0.92 below reflects fast localized H motion within the hexagons formed by interstitial g (Zr2Mo2) sites. • N – numerical density of sample atoms per cm3 • I0 - incident neutrons per second per cm2 •  - neutron cross section in ~ 10-24 cm2 • t - sample thickness Alkali Alanates Neutron vibrational spectrum of NaAlH4 compared with ab initio calculations that include one- and two-phonon processes Small-Angle Neutron Scattering (SANS) Prompt- Activation Analysis (PGAA) Neutron Powder Diffraction (NPD) Neutron Time and Space Domain NPD is invaluable for determining the positions of light elements such as hydrogen in a crystal lattice. For example, it is essential for an accurate determination of the structures of the alkali alanates. PGAA is a nondestructive technique for in situ quantitative analysis of hydrogen and many other elements based on the measured intensity of element-specific prompt gamma rays emitted upon nuclear capture of a neutron. In the present example, the small hydrogen concentration is accurately measured in a solid-oxide protonic conductor material. Using SANS, hydrogen distributions and internal strains that accompany hydriding of LaNi5 are compared to those in the ternary alloy LaNi4.75Sn0.25. Porod plots of the excess SANS intensity of LaNi5Dx compared to LaNi4.75Sn0.25Dx for partial D loadings (x=2,4) indicate a more homogeneous distribution of D in the latter alloy, at least on a scale of 4-15 nm. Increased homogeneity may suppress strain gradients that cause hydride decrepitation. Neutron methods at the NIST Center for Neutron Research (NCNR) encompass an enormous range of time and length scales.