Spatial Configurations of Ti- and Ni- Species Catalyzing Complex Metal Hydrides: X-Ray Absorption Studies and First-Principles DFT and MD Calculations

Journal Article · Fri Feb 02 00:00:00 EST 2007 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2644617· OSTI ID:21054704

Ignatov, A Yu ^[1]; Graetz, J ^[2]; Chaudhuri, S ^[3]; Salguero, T T; Vajo, J J ^[4]; Meyer, M S; Pinkerton, F E ^[5]; Tyson, T A ^[6]

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1. Center for Biophysics at the NSLS, Case Western Reserve Univ., Brookhaven Natl. Lab, Upton, NY 11973 (United States)
2. Department of Energy, Science, and Technology, Brookhaven Natl. Lab, Upton, NY 11973 (United States)
3. Department of Chemistry, Brookhaven Natl. Lab, Upton, NY 11973 (United States)
4. HRL Laboratories, LLC, Malibu, CA 90265 (United States)
5. Materials and Processes Lab, General Motors Research and Development Center, Warren, MI 48090 (United States)
6. Department of Physics, New Jersey Inst. of Tech., Newark, NJ 07102 (United States)

We have performed Ti K-edge EXAFS and XANES measurements on 4 and 3 wt% TiCl3-activated NaAlH4 and (LiBH4+0.5MgH2) and Ni K-edge measurements on 3 and 11 wt% NiCl2-activated (LiBH4+0.5MgH2) and (Li3BN2H8) - prospective hydrogen storage materials. The valence of Ti and Ni is close to zero and invariant during hydrogen cycling. None of the metals enter substitutionally or interstitially into the crystalline lattice of the initial or final products. For the Ti- activated NaAlH4 and (LiBH4+0.5MgH2), amorphous TiAl3 and TiB2 alloys are formed, which are almost invariant during cycling. The Ni doped (LiBH4+0.5MgH2) initially forms amorphous Ni3B, which is partly converted to amorphous Mg2NiHy upon hydrogen loading. Local structure around Ti(Ni) atoms is expressed in terms of a cluster expansion and the interatomic distances, coordination numbers and Debye-Waller factors are determined for competitive structural models. For Ti-activated NaAlH4 the models are elaborated by Ti K-edge XANES, which are interpreted in terms of single-electron multiple scattering calculations. Structural properties and phase stability of hypothetical hydrogenated TiAl3 as well as several products of the decomposition reaction are determined from density functional theory calculation. First-principles molecular dynamics simulations of surface diffusion and chemical reactivity imply that the formation of a few monolayers of TiAl3 on the surface may be responsible for the significant increase in the reaction rate.

• OSTI ID: 21054704
• Journal Information: AIP Conference Proceedings, Vol. 882, Issue 1; Conference: XAFS13: 13. international conference on X-ray absorption fine structure, Stanford, CA (United States), 9-14 Jul 2006; Other Information: DOI: 10.1063/1.2644617; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION SPECTROSCOPY
CLUSTER EXPANSION
DEBYE-WALLER FACTOR
DENSITY FUNCTIONAL METHOD
DIFFUSION
DOPED MATERIALS
ELECTRONS
FINE STRUCTURE
HYDRIDES
HYDROGEN
HYDROGEN STORAGE
INTERATOMIC DISTANCES
MOLECULAR DYNAMICS METHOD
MULTIPLE SCATTERING
NICKEL ALLOYS
PHASE STABILITY
STRUCTURAL MODELS
TITANIUM ALLOYS
TITANIUM BORIDES
X-RAY SPECTROSCOPY