In-situ X-ray diffraction study of the decomposition of NaAlH4

Gross, Karl; Guthrie, S.E.; Takara, Satoshi; Thomas, George J.

doi:10.1016/s0925-8388(99)00598-8

Cited by 232 publications

(290 citation statements)

References 17 publications

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“…The cell parameters at 10 K and room temperature are consistent with those reported in previous work [11,14,[24][25][26][27][28]. However, they show small but significant differences among the samples (up to 30 e.s.d.…”

Section: Structuresupporting

confidence: 81%

Effects of milling, doping and cycling of NaAlH4 studied by vibrational spectroscopy and X-ray diffraction

Gomes

Renaudin

Hagemann

et al. 2005

Journal of Alloys and Compounds

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The effects of milling and doping NaAlH 4 with TiCl 3 , TiF 3 and Ti(OBu n ) 4 , and of cycling doped NaAlH 4 have been investigated by infrared (IR) and Raman spectroscopy and X-ray powder diffraction. Milling and doping produce similar effects. Both decrease the crystal domain size (∼900Å for milled and ∼700Å for doped, as compared to ∼1600Å for unmilled and undoped NaAlH 4 ) and increase anisotropic strain (by a factor >2.5, mainly along c). They also influence structure parameters such as the axial ratio c/a, cell volume and atomic displacement amplitudes. They show IR line shifts by ∼15 cm −1 to higher frequencies for the Al-H asymmetric stretching mode ν 3 , and by ∼20 cm −1 to lower frequencies for one part of the H-Al-H asymmetric bending mode ν 4 , thus suggesting structural changes in the local environment of the [AlH 4 ] − units. The broad ν 3 bands become sharpened which suggests a more homogeneous local environment of the [AlH 4 ] − units, and there appears a new vibration at 710 cm −1 . The Raman data show no such effects. Cycling leads to an increase in domain size (1200-1600Å), IR line shifts similar to doped samples (except for TiF 3 : downward shift by ∼10 cm −1 ) and a general broadening of the ν 3 mode that depend on the nature of the dopants. These observations support the idea that some Ti diffusion and substitution into the alanate lattice does occur, in particular during cycling, and that this provides the mechanism through which Ti-doping enhances kinetics during re-crystallisation.

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Section: Structuresupporting

confidence: 81%

Effects of milling, doping and cycling of NaAlH4 studied by vibrational spectroscopy and X-ray diffraction

Gomes

Renaudin

Hagemann

et al. 2005

Journal of Alloys and Compounds

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“…Dehydrogenation via two discrete pathways was also observed for Ti-enhanced NaAlH 4 , despite the dramatic lowering of the activation energy for both of the dehydrogenation reactions. 3,7 This stepwise pathway has been confirmed for Ti-enhanced NaAlH 4 by a number of in situ XRD, 8,9 TEM 10 and NMR studies 11 of the dehydrogenation reaction. It has long been assumed that the rehydrogenation of NaH and Ti-enhanced Al (Al*) proceeds through the microscopic reverse of the-two step dehydrogenation process (eqn (1) and (2)), entailing the complete conversion of NaH to Na 3 AlH 6 before there is any significant formation of NaAlH 4 .…”

Section: Q4mentioning

confidence: 83%

“…8,17 Hwang et al have reported chemical shifts of 5.8, 21.5, and 10.9/36.0 ppm for a-, b-, and g-AlH 3 respectively. 18 Our study is not able to explore this possibility, as the broad resonance at 59 ppm associated with the alumina of the NMR cell will likely Fig.…”

Section: Q4mentioning

confidence: 99%

In situ high pressure NMR study of the direct synthesis of NaAlH4

Humphries

Birkmire

Hauback

et al. 2013

Phys. Chem. Chem. Phys.

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The direct synthesis of NaAlH 4 has been studied, for the first time, by in situ 27 Al and 23 Na wide-line NMR spectroscopy using high pressure NMR apparatus. Na 3 AlH 6 formation is observed within two minutes of hydrogenation addition, while NaAlH 4 is detected after a total of four minutes. This indicates the formation of the hexahydride does not proceed to completion before the formation of the tetrahydride ensues.The practical utilization of hydrogen as an energy carrier awaits the development of high-capacity, hydrogen storage materials that can be recharged under moderate conditions. A viable on-board hydrogen carrier must have high gravimetric and volumetric hydrogen capacities; thermodynamic properties that fall within rather stringent limits; and dehydrogenation and rehydrogenation kinetics that allow hydrogen cycling at moderate temperatures and pressures. 1,2 One of the most important breakthroughs in the development of hydrogen storage materials in the past 20 years was provided by Q4Bogdanović and Schwickardi, whose pioneering studies demonstrated that addition of selected titanium compounds to NaAlH 4 results in enhanced kinetics and reversibility under moderate conditions in the solid state. 3 These studies were prompted by earlier reports from Wiberg et al., who observed that titanium compounds catalyze the dehydrogenation of complex aluminum hydrides in solution. 4 The enigmatic extension of this catalytic effect to the solid state has been the inspiration for over 260 publications on Ti-enhanced NaAlH 4 alone, and it is safe to estimate that it prompted an equal number of studies of the effect of Ti additives on the dehydrogenation kinetics of other complex hydrides. 5

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“…In contrast, for non supported Ti(OBu) 4 catalyzed NaAlH 4 , an in situ diffraction study by Gross et al indicated that Na 3 AlH 6 crystallized in co-presence of NaAlH 4 . 31 The simultaneous presence of Na 3 AlH 6 and NaAlH 4 during decomposition was also reported in an in situ XRD study of TiCl 3 -catalyzed bulk NaAlH 4 . 32 Thus, the decomposition mechanism of nanoNaAlH 4 differs noticeably from that of bulk-NaAlH 4 .…”

mentioning

confidence: 60%

Towards a structure-performance relationship for hydrogen storage in Ti-doped NaAlH₄nanoparticles

et al. 2011

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Hydrogen storage properties of Ti-doped nanosized (B20 nm) NaAlH 4 supported on carbon nanofibers were affected by the stage at which Ti was introduced. When Ti was deposited first followed by NaAlH 4, sorption properties were superior to the case where NaAlH 4 was deposited first followed by NaAlH 4 . This was the result of both a smaller NaAlH 4 particle size and the more extensive catalytic action of Ti in the former material.Sodium alanate has become a show-case for research on lightweight complex metal hydrides for hydrogen storage. 1 Nevertheless, hydrogen release rates and absorption rates are often impeded in metal hydrides and need to be improved. 2 Most effective in improving the performance of metal hydrides are reducing the particle size to the nm range (typically below 30 nm) 3-13 or adding one or more promoters/catalysts to bulk materials. [14][15][16][17][18][19][20][21][22][23][24][25]

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In-situ X-ray diffraction study of the decomposition of NaAlH4

Cited by 232 publications

References 17 publications

Effects of milling, doping and cycling of NaAlH4 studied by vibrational spectroscopy and X-ray diffraction

Effects of milling, doping and cycling of NaAlH4 studied by vibrational spectroscopy and X-ray diffraction

In situ high pressure NMR study of the direct synthesis of NaAlH4

Towards a structure-performance relationship for hydrogen storage in Ti-doped NaAlH₄nanoparticles

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In-situ X-ray diffraction study of the decomposition of NaAlH4

Cited by 232 publications

References 17 publications

Effects of milling, doping and cycling of NaAlH4 studied by vibrational spectroscopy and X-ray diffraction

Effects of milling, doping and cycling of NaAlH4 studied by vibrational spectroscopy and X-ray diffraction

In situ high pressure NMR study of the direct synthesis of NaAlH4

Towards a structure-performance relationship for hydrogen storage in Ti-doped NaAlH4nanoparticles

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Towards a structure-performance relationship for hydrogen storage in Ti-doped NaAlH₄nanoparticles