Mechanochemical Synthesis and Crystal Structure of α‘-AlD<sub>3</sub> and α-AlD<sub>3</sub>

Brinks, H.W.; Istad-Lem, and Andreas; Hauback, Bjørn C.

doi:10.1021/jp0630774

Cited by 91 publications

(140 citation statements)

References 24 publications

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“…A similar exothermic peak was observed during decomposition of α -AlH 3 [80]. These peaks are due [21] 10.1 90…”

Section: Thermodynamics and Decomposition Pathwayssupporting

confidence: 61%

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Metastable Metal Hydrides for Hydrogen Storage

Graetz

2012

ISRN Materials Science

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The possibility of using hydrogen as a reliable energy carrier for both stationary and mobile applications has gained renewed interest in recent years due to improvements in high temperature fuel cells and a reduction in hydrogen production costs. However, a number of challenges remain and new media are needed that are capable of safely storing hydrogen with high gravimetric and volumetric densities. Metal hydrides and complex metal hydrides offer some hope of overcoming these challenges; however, many of the high capacity "reversible" hydrides exhibit a large endothermic decomposition enthalpy making it difficult to release the hydrogen at low temperatures. On the other hand, the metastable hydrides are characterized by a low reaction enthalpy and a decomposition reaction that is thermodynamically favorable under ambient conditions. The rapid, low temperature hydrogen evolution rates that can be achieved with these materials offer much promise for mobile PEM fuel cell applications. However, a critical challenge exists to develop new methods to regenerate these hydrides directly from the reactants and hydrogen gas. This spotlight paper presents an overview of some of the metastable metal hydrides for hydrogen storage and a few new approaches being investigated to address the key challenges associated with these materials.

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“…A similar exothermic peak was observed during decomposition of α -AlH 3 [80]. These peaks are due [21] 10.1 90…”

Section: Thermodynamics and Decomposition Pathwayssupporting

confidence: 61%

“…[18][19][20][21][22][23][24][25][26][27][28]. The crystal structure of α-AlH 3 is trigonal (R3c space group) and consists of corner connected AlH 6 octahedra with each H bridging two octahedra as shown in Figure 2 (left).…”

Section: Crystal Structuresmentioning

confidence: 99%

Metastable Metal Hydrides for Hydrogen Storage

Graetz

2012

ISRN Materials Science

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“…10,13) After desorption, -(þ-)AlH 3 , -AlH 3 , andAlH 3 are present but aluminum etherate, aluminum oxide, and aluminum hydroxide are not identified. [8][9][10][14][15][16][17] We can also confirm the existence of single-phase -AlD 3 after desorption at 383 K for AlD 3 -etherate. The corresponding Raman spectra of samples before and after thermal desorption of solvated ether are shown in Fig.…”

Section: Resultssupporting

confidence: 65%

“…13) For comparison with the obtained spectra, we calculated spectral modes for -, -, -AlH 3 , and -AlD 3 (Table 1); calculations were performed by CASTEP density functional code 18) using the crystallographic parameters in the literature. [14][15][16] The obtained spectra thus confirm the presence of -(þ-, -)AlH 3 at 323 K, -AlH 3 at 343 K, and -AlH 3 19) at 363 K but neither aluminum hydroxide (3:3{3:7 Â 10 5 m À1 ) 20,21) nor oxide (0:3{0:8 Â 10 5 m À1 ) 22) are observed. We infer that -AlH 3 partly transformed into -AlH 3 and -AlH 3 by laser irradiation of Raman spectroscopy because -phase is thermodynamically unstable.…”

Section: Resultssupporting

confidence: 60%

Structural and Hydrogen Desorption Properties of Aluminum Hydride

Ikeda¹,

Ohshita²,

Kaneko³

et al. 2011

Mater. Trans.

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The structural and hydrogen/deuterium desorption properties of AlH 3 /AlD 3 were investigated by Raman spectroscopy, high-intensity X-ray/neutron diffraction, and thermogravimetric analysis. The latter revealed that more than 9.6 mass% of hydrogen/18.1 mass% of deuterium desorbs from AlH 3 /AlD 3 , respectively. The presence of -Al 2 O 3 on the surface may prevent the hydrogen/deuterium desorption reaction of AlH 3 /AlD 3 to Al at room temperature.

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“…[1] The major challenge that prevents its widespread application is lack of efficient, low-cost processes for the preparation of alane on a large scale. Chemical [2][3][4][5] and mechanochemical [6][7] methods to synthesize alane from other metal hydrides have been demonstrated, but direct synthesis from the elements at moderate hydrogen pressure remains elusive. Pure Al does not react with hydrogen to form alane at room temperature unless subjected to impractically high hydrogen pressures exceeding 7 kbar [1,8] .…”

Section: Introductionmentioning

confidence: 99%

Towards Direct Synthesis of Alane: A Predicted Defect‐Mediated Pathway Confirmed Experimentally

et al. 2016

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Alane (AlH3) is a unique energetic material that has not found a broad practical use for over 70 years because it is difficult to synthesize directly from its elements. Using density functional theory, we examine the defectmediated formation of alane monomers on Al(111) in a two-step process: (1) dissociative adsorption of H2 and (2) alane formation, which are both endothermic on a clean surface. Only with Ti dopant to facilitate H2 dissociation and vacancies to provide Al adatoms, both processes become exothermic. In agreement, in situ scanning tunneling microscopy showed that during H2 exposure, alane monomers and clusters form primarily in the vicinity of Al vacancies and Ti atoms. Moreover, ball milling of the Al samples with Ti (providing necessary defects) showed a 10 % conversion of Al into AlH3 or closely related species at 344 bar H2, indicating that the predicted pathway may lead to the direct synthesis of alane from elements at pressures much lower than the 104 bar expected from bulk thermodynamics. [d,f] S. Gupta, [a] and V. K. Pecharsky* [a,c] Abstract: Alane (AlH3) is a unique energetic material that has not found broad practical use for over 70 years due to difficulties of its direct synthesis from elements. Using density functional theory we examine the defect-mediated formation of alane monomers on Al(111) in a two-step process: (1) dissociative adsorption of H2 and (2) alane formation; both are endothermic on clean surface. Only with Ti-dopant to facilitate H2 dissociation and vacancy to provide Al adatoms, both processes become exothermic. In agreement, in situ scanning tunnelling microscopy showed that during H2 exposure alane monomers and clusters form primarily in the vicinity of Al vacancies and Ti atoms. Moreover, ball-milling samples of Al with Ti (providing necessary defects) showed a 10% conversion of Al into AlH3 or closely related species at 344 bar H2, indicating that the predicted pathway may lead to direct synthesis of alane from elements at pressures much lower than the 10 4 bar expected from bulk thermodynamics.

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Mechanochemical Synthesis and Crystal Structure of α‘-AlD₃ and α-AlD₃

Cited by 91 publications

References 24 publications

Metastable Metal Hydrides for Hydrogen Storage

Metastable Metal Hydrides for Hydrogen Storage

Structural and Hydrogen Desorption Properties of Aluminum Hydride

Towards Direct Synthesis of Alane: A Predicted Defect‐Mediated Pathway Confirmed Experimentally

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Mechanochemical Synthesis and Crystal Structure of α‘-AlD3 and α-AlD3

Cited by 91 publications

References 24 publications

Metastable Metal Hydrides for Hydrogen Storage

Metastable Metal Hydrides for Hydrogen Storage

Structural and Hydrogen Desorption Properties of Aluminum Hydride

Towards Direct Synthesis of Alane: A Predicted Defect‐Mediated Pathway Confirmed Experimentally

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Product

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Mechanochemical Synthesis and Crystal Structure of α‘-AlD₃ and α-AlD₃