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  • Hydrogen absorption kinetics and structural features of NaAlH4 enhanced with transition-metal and Ti-based nanoparticles

    Author(s)
    Pitt, MP
    Vullum, PE
    Sorby, MH
    Emerich, H
    Paskevicius, M
    Webb, CJ
    Gray, E MacA
    Buckley, CE
    Walmsley, JC
    Holmestad, R
    Hauback, BC
    Griffith University Author(s)
    Webb, Jim J.
    Gray, Evan M.
    Year published
    2012
    Metadata
    Show full item record
    Abstract
    The hydrogen cycled (H) planetary milled (PM) NaAlH4 + xM (x < 0.1) system (M = 30 nm Ag, 80 nm Al, 2-3 nm C, 30 nm Cr, 25 nm Fe, 30 nm Ni, 25 nm Pd, 65 nm Ti) has been studied by high resolution synchrotron powder X-ray diffraction. Isothermal absorption kinetic isotherms have been measured over the first two H cycles. The PM NaAlH4 + 0.1Ti system has also been studied by high resolution transmission electron microscopy (TEM). 80 nm Al and 2-3 nm C were inactive, and would not allow hydrogen (H) desorption from NaAlH4. 30 nm Cr, 25 nm Fe, 30 nm Ni, and 25 nm Pd showed activity, but with weak kinetics of only ca. 1 wt.% ...
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    The hydrogen cycled (H) planetary milled (PM) NaAlH4 + xM (x < 0.1) system (M = 30 nm Ag, 80 nm Al, 2-3 nm C, 30 nm Cr, 25 nm Fe, 30 nm Ni, 25 nm Pd, 65 nm Ti) has been studied by high resolution synchrotron powder X-ray diffraction. Isothermal absorption kinetic isotherms have been measured over the first two H cycles. The PM NaAlH4 + 0.1Ti system has also been studied by high resolution transmission electron microscopy (TEM). 80 nm Al and 2-3 nm C were inactive, and would not allow hydrogen (H) desorption from NaAlH4. 30 nm Cr, 25 nm Fe, 30 nm Ni, and 25 nm Pd showed activity, but with weak kinetics of only ca. 1 wt.% H/hour. The NaAlH4 + 0.1Ti system displays absorption kinetics of ca. 7 wt.% H/hour, comparable to TiCl3 enhanced NaAlH4 after five H cycles. After H cycling the PM NaAlH4 + 0.1Ti system, we observe a body centred tetragonal (bct) ?-TiH2 phase, which displays intense anisotropic peak broadening. The broadening is evident as a massive dislocation density of ca. 1.20 נ1017/m2 in high resolution TEM images of the ?-TiH2 phase. All originally added Ti can be accounted for in the bct ?-TiH2 phase by quantitative phase analysis (QPA) after five H cycles. The PM NaH + Al + 0.02 (Ti-nano-alloy) system shows absorption kinetic rates in the order TiO2 > TiN > TiC > Ti, with rapid hydrogenation kinetics of ca. 23 wt.% H/hour for TiO2 enhanced NaAlH4, equivalent to TiCl3 enhanced NaAlH4. The TiN and TiC are partially reduced by ca. 7 and 22% respectively, and the TiO2 is completely reduced. The location of the reduced Ti cannot be discerned by X-ray diffraction at these minor proportions.
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    Journal Title
    International Journal of Hydrogen Energy
    Volume
    37
    Issue
    20
    DOI
    https://doi.org/10.1016/j.ijhydene.2012.08.014
    Subject
    Surfaces and Structural Properties of Condensed Matter
    Chemical Sciences
    Engineering
    Publication URI
    http://hdl.handle.net/10072/50036
    Collection
    • Journal articles

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