Comparative studies of the decomposition of alanates followed by in situ XRD and DSC methods

Mamatha, M.; Weidenthaler, Claudia; Pommerin, A.; Felderhoff, Michael; Schüth, Ferdi

doi:10.1016/j.jallcom.2005.09.004

Cited by 84 publications

(81 citation statements)

References 20 publications

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“…[11][12][13] On the other hand, M 00 (AlH 4 ) 2 (M 00 : alkaline-earth metals) has been reported to decompose into the intermediate phase, M 00 AlH 5 , as follows: 10,11,[14][15][16] …”

Section: Introductionmentioning

confidence: 99%

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Direct Dry Syntheses and Thermal Analyses of a Series of Aluminum Complex Hydrides

Sato

Ikeda

et al. 2009

Mater. Trans.

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Synthesis of a series of aluminum complex hydrides, namely, LiAlH 4 , Li 3 AlH 6 , NaAlH 4 , Na 3 AlH 6 , Mg(AlH 4 ) 2 , MgAlH 5 , Ca(AlH 4 ) 2 , and CaAlH 5 , was attempted by the mechanochemical milling of AlH 3 and the other elemental hydrides. Aluminum complex hydrides, except MgAlH 5 , were synthesized, and their dehydriding (decomposition) properties were systematically investigated by thermogravimetry. The dehydridng temperatures possibly showed a correlation with the geometrical distances in space between M 0 (M 00 ) and H in the crystal structures of the aluminum complex hydrides.

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“…[11][12][13] On the other hand, M 00 (AlH 4 ) 2 (M 00 : alkaline-earth metals) has been reported to decompose into the intermediate phase, M 00 AlH 5 , as follows: 10,11,[14][15][16] …”

Section: Introductionmentioning

confidence: 99%

“…14,15) Corner-shared AlH 6 -units are probably a characteristic of aluminum complex hydrides containing alkaline-earth metals (Ex. BaAl-H 5 17) ), although the structure of MgAlH 5 is still unclear.…”

Section: Introductionmentioning

confidence: 99%

Direct Dry Syntheses and Thermal Analyses of a Series of Aluminum Complex Hydrides

Sato

Ikeda

et al. 2009

Mater. Trans.

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“…It decomposes to CaH 2 in a two-step process with the formation of a CaAlH 5 intermediate in the first step, as indicated in reactions ͑1͒ and ͑2͒. [3][4][5] Overall the decomposition can be described as reaction ͑3͒. The intermediate CaAlH 5 phase has been identified only recently.…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5] Overall the decomposition can be described as reaction ͑3͒. The intermediate CaAlH 5 phase has been identified only recently. Thus many researchers have neglected the two step mechanism, considering only reaction ͑3͒;…”

Section: Introductionmentioning

confidence: 99%

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Ca ( Al H 4 ) 2 , CaAlH5, and CaH2+6LiBH4: Calculated dehydrogenation enthalpy, including zero point energy, and the structure of the phonon spectra

Marashdeh

Frankcombe

2008

The Journal of Chemical Physics

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The dehydrogenation enthalpies of Ca͑AlH 4 ͒ 2 , CaAlH 5 , and CaH 2 + 6LiBH 4 have been calculated using density functional theory calculations at the generalized gradient approximation level. Harmonic phonon zero point energy ͑ZPE͒ corrections have been included using Parlinski's direct method. The dehydrogenation of Ca͑AlH 4 ͒ 2 is exothermic, indicating a metastable hydride. Calculations for CaAlH 5 including ZPE effects indicate that it is not stable enough for a hydrogen storage system operating near ambient conditions. The destabilized combination of LiBH 4 with CaH 2 is a promising system after ZPE-corrected enthalpy calculations. The calculations confirm that including ZPE effects in the harmonic approximation for the dehydrogenation of Ca͑AlH 4 ͒ 2 , CaAlH 5 , and CaH 2 + 6LiBH 4 has a significant effect on the calculated reaction enthalpy. The contribution of ZPE to the dehydrogenation enthalpies of Ca͑AlH 4 ͒ 2 and CaAlH 5 calculated by the direct method phonon analysis was compared to that calculated by the frozen-phonon method. The crystal structure of CaAlH 5 is presented in the more useful standard setting of P2 1 / c symmetry and the phonon density of states of CaAlH 5 , significantly different to other common complex metal hydrides, is rationalized.

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Complex Hydrides

and

Felderhoff

2010

Handbook of Hydrogen Storage

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Complex hydrides are salt-like materials in which hydrogen is covalently bound to the central atoms, in this way a crystal structure consisting of so-called complex anions is formed. In general, complex hydrides have the chemical formula A x Me y H z . Compounds where position A is preferentially occupied by elements of the first and second groups of the periodic table and Me is occupied either by boron or aluminum are well known and have been intensively investigated. However, another possibility is that complex hydrides are built by transition metal cations. Complex metal hydrides have been known for more than 50 years, but for many years they were not considered for reversible hydrogen storage due to the high kinetic barriers of the decomposition requiring high temperatures. The situation changed in 1997 when Bogdanovi c and Schwickardi discovered that the kinetic barrier of the decomposition of the complex metal hydride, NaAlH 4 , can be lowered by the addition of Ti catalysts and that the material becomes reversible close to acceptable technical conditions [1]. They further showed not only that catalysts can enhance the kinetics of dehydrogenation but also that rehydrogenation under moderate conditions becomes feasible. This breakthrough induced the publication of a tremendous number of papers focusing on the synthesis and the properties of complex hydrides. The major goal is to understand the basic steps of dehydrogenation and rehydrogenation and the role of catalysts. Many complex metal hydrides have high hydrogen gravimetric storage capacities and some of them are commercially available. Some complex hydride systems, such as Mg 2 FeH 6 and Al(BH 4 ) 3 , have an extremely high volumetric hydrogen density of up to 150 kg m À3 . Compared to liquid hydrogen with a volumetric density of 70 kg m À3 , the amount of hydrogen in such metal hydrides is much higher. This makes complex transition metal hydrides interesting as potential storage materials.Handbook of Hydrogen Storage. Edited by Michael Hirscher

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Comparative studies of the decomposition of alanates followed by in situ XRD and DSC methods

Cited by 84 publications

References 20 publications

Direct Dry Syntheses and Thermal Analyses of a Series of Aluminum Complex Hydrides

Direct Dry Syntheses and Thermal Analyses of a Series of Aluminum Complex Hydrides

Ca ( Al H 4 ) 2 , CaAlH5, and CaH2+6LiBH4: Calculated dehydrogenation enthalpy, including zero point energy, and the structure of the phonon spectra

Complex Hydrides

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