skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Abstract

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 ofmore » TiAl3 on the surface may be responsible for the significant increase in the reaction rate.« less

Authors:
 [1];  [2];  [3];  [4]; ;  [5]; ;  [6];  [7]
  1. Center for Biophysics at the NSLS, Case Western Reserve Univ., Brookhaven Natl. Lab, Upton, NY 11973 (United States)
  2. (United States)
  3. Department of Energy, Science, and Technology, Brookhaven Natl. Lab, Upton, NY 11973 (United States)
  4. Department of Chemistry, Brookhaven Natl. Lab, Upton, NY 11973 (United States)
  5. HRL Laboratories, LLC, Malibu, CA 90265 (United States)
  6. Materials and Processes Lab, General Motors Research and Development Center, Warren, MI 48090 (United States)
  7. Department of Physics, New Jersey Inst. of Tech., Newark, NJ 07102 (United States)
Publication Date:
OSTI Identifier:
21054704
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 882; Journal 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)
Country of Publication:
United States
Language:
English
Subject:
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

Citation Formats

Ignatov, A. Yu., Department of Physics, New Jersey Inst. of Tech., Newark, NJ 07102, Graetz, J., Chaudhuri, S., Salguero, T. T., Vajo, J. J., Meyer, M. S., Pinkerton, F. E., and Tyson, T. A.. Spatial Configurations of Ti- and Ni- Species Catalyzing Complex Metal Hydrides: X-Ray Absorption Studies and First-Principles DFT and MD Calculations. United States: N. p., 2007. Web. doi:10.1063/1.2644617.
Ignatov, A. Yu., Department of Physics, New Jersey Inst. of Tech., Newark, NJ 07102, Graetz, J., Chaudhuri, S., Salguero, T. T., Vajo, J. J., Meyer, M. S., Pinkerton, F. E., & Tyson, T. A.. Spatial Configurations of Ti- and Ni- Species Catalyzing Complex Metal Hydrides: X-Ray Absorption Studies and First-Principles DFT and MD Calculations. United States. doi:10.1063/1.2644617.
Ignatov, A. Yu., Department of Physics, New Jersey Inst. of Tech., Newark, NJ 07102, Graetz, J., Chaudhuri, S., Salguero, T. T., Vajo, J. J., Meyer, M. S., Pinkerton, F. E., and Tyson, T. A.. Fri . "Spatial Configurations of Ti- and Ni- Species Catalyzing Complex Metal Hydrides: X-Ray Absorption Studies and First-Principles DFT and MD Calculations". United States. doi:10.1063/1.2644617.
@article{osti_21054704,
title = {Spatial Configurations of Ti- and Ni- Species Catalyzing Complex Metal Hydrides: X-Ray Absorption Studies and First-Principles DFT and MD Calculations},
author = {Ignatov, A. Yu. and Department of Physics, New Jersey Inst. of Tech., Newark, NJ 07102 and Graetz, J. and Chaudhuri, S. and Salguero, T. T. and Vajo, J. J. and Meyer, M. S. and Pinkerton, F. E. and Tyson, T. A.},
abstractNote = {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.},
doi = {10.1063/1.2644617},
journal = {AIP Conference Proceedings},
number = 1,
volume = 882,
place = {United States},
year = {Fri Feb 02 00:00:00 EST 2007},
month = {Fri Feb 02 00:00:00 EST 2007}
}
  • It has been previously hypothesized that the enhanced rate capability of Li-Ni-PO{sub 4}-treated xLi{sub 2}MnO{sub 3} {center_dot} (1-x)LiMO{sub 2} positive electrodes (M = Mn, Ni, Co) in Li-ion batteries might be associated with a defect Ni-doped Li{sub 3}PO{sub 4} surface structure [i.e., Li{sub 3-2y}Ni{sub y}PO{sub 4} (0 < y < 1)], thereby promoting fast Li{sup +}-ion conduction at the xLi{sub 2}MnO{sub 3} {center_dot} (1-x)LiMO{sub 2} particle surface. In this paper, the solubility of divalent metals (Fe, Mn, Ni, Mg) in {gamma}-Li{sub 3}PO{sub 4} is predicted with the first-principles GGA+U method in an effort to understand the enhanced rate capability. Themore » predicted solubility (x) is extremely small; this finding is consistent with experimental evidence: 1) X-ray diffraction data obtained from Li-Ni-PO{sub 4}-treated xLi{sub 2}MnO{sub 3} {center_dot} (1-x)LiMO{sub 2} electrodes that show that, after annealing at 550 C, a Li{sub 3}PO{sub 4}-like structure forms as a second phase at the electrode particle surface, and 2) X-ray absorption spectroscopy, which indicate that the nickel ions are accommodated in the transition metal layers of the Li{sub 2}MnO{sub 3} component during the annealing process. However, electrochemical studies of Li{sub 3-2y}Ni{sub y}PO{sub 4}-treated xLi{sub 2}MnO{sub 3} {center_dot} (1-x)LiMO{sub 2} electrodes indicate that their rate capability increases as a function of y over the range y = 0 (Li{sub 3}PO{sub 4}) to y = 1 (LiNiPO{sub 4}), strongly suggesting that, at some level, the nickel ions play a role in reducing electrochemical impedance and increasing electrode stability at the electrode particle surface.« less
  • We report a combined experimental and theoretical study of CaCu{sub 3}Ti{sub 4}O{sub 12}. Based on our experimental observations of nanoscale regions of Ca-Cu antisite defects in part of the structure, we carried out density-functional theory (DFT) calculations that suggest a possible electronic mechanism to explain the gigantic dielectric response in this material. The defects are evident in atomically resolved transmission electron microscopy measurements, with supporting evidence from a quantitative analysis of the electron diffraction and DFT which suggests that such defects are reasonable on energetic grounds. To establish the extent of the defects, bulk average measurements of the local structuremore » were carried out: extended x-ray absorption fine structure (EXAFS), atomic pair-distribution function analysis of neutron powder-diffraction data, and single-crystal x-ray crystallography. The EXAFS data are consistent with the presence of the nanoclustered defects with an estimate of less than 10% of the sample being disordered while the neutron powder-diffraction experiments place an upper of -5% on the proportion of the sample in the defective state. Because of the difficulty of quantifying nanoscale defects at such low levels, further work will be required to establish that this mechanism is operative in CaCu{sub 3}Ti{sub 4}O{sub 12} but it presents a nontraditional plausible avenue for understanding colossal dielectric behavior.« less
  • Favorable thermodynamics are a prerequisite for practical H2 storage materials for vehicular applications. Destabilization of metal hydrides is a versatile route to finding materials that reversibly store large quantities of H2. First principles calculations have proven to be a useful tool for screening large numbers of potential destabilization reactions when tabulated thermodynamic data are unavailable. We have used first principles calculations to screen potential destabilization schemes that involve Sc-containing compounds. Our calculations use a two-stage strategy in which reactions are initially assessed based on their reaction enthalpy alone, followed by more detailed free energy calculations for promising reactions. Our calculationsmore » indicate that mixtures of ScH2 + 2LiBH4, which will release 8.9 wt.% H2 at completion and will have an equilibrium pressure of 1 bar at around 330 K, making this compound a promising target for experimental study. Along with thermodynamics, favorable kinetics are also of enormous importance for practical usage of these materials. Experiments would help identify possible kinetic barriers and modify them by developing suitable catalysts.« less