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Naji, M. |
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Motta, Antonella |
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Aletan, Dirar |
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Mohamed, Tarek |
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Ertürk, Emre |
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Taccardi, Nicola |
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Kononenko, Denys |
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Petrov, R. H. | Madrid |
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Alshaaer, Mazen | Brussels |
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Bih, L. |
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Casati, R. |
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Muller, Hermance |
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Kočí, Jan | Prague |
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Šuljagić, Marija |
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Kalteremidou, Kalliopi-Artemi | Brussels |
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Azam, Siraj |
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Ospanova, Alyiya |
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Blanpain, Bart |
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Ali, M. A. |
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Popa, V. |
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Rančić, M. |
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Ollier, Nadège |
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Azevedo, Nuno Monteiro |
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Landes, Michael |
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Rignanese, Gian-Marco |
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Grundlach, Carsten
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article
A novel intermediate in the LiAlH4–LiNH2 hydrogen storage system
Abstract
<p>The decomposition pathways for the composite LiAlH<sub>4</sub>-LiNH<sub>2</sub> in different ratios of (1:1), (1:1.5), (1:2) and (1:2.5) have been systematically studied using in situ synchrotron radiation powder X-ray diffraction (SR-PXD) as well as simultaneous thermogravimetric analysis and differential scanning calorimetry coupled with mass spectroscopy. The study reveals that LiAlH<sub>4</sub> decomposes in two steps to LiH, Al and H<sub>2</sub> and, subsequently, the produced LiH reacts with LiNH<sub>2</sub> forming Li<sub>2</sub>NH and H<sub>2</sub>. A new intermediate, Li<sub>4-x</sub>Al<sub>x</sub>(NH)<sub>2-2x</sub>N<sub>2x</sub>, is observed during the decomposition of LiAlH<sub>4</sub>-LiNH<sub>2</sub> (1:1.5), (1:2) and (1:2.5), formed from Li<sub>2</sub>NH and Al prior to the formation of Li<sub>3</sub>AlN<sub>2</sub>. Li<sub>4-x</sub>Al<sub>x</sub>(NH)<sub>2-2x</sub>N<sub>2x</sub> is characterized by Rietveld refinement of SR-PXD data and solid-state<sup>27</sup>Al MAS NMR spectroscopy (chemical shift, δ(Al) = 125 ppm) and both techniques reveal a maximum value for x of ∼0.10, i.e., Li<sub>3.90</sub>Al<sub>0.10</sub>(NH)<sub>1.80</sub>N<sub>0.20</sub>. The solid solution Li<sub>4-x</sub>Al<sub>x</sub>(NH)<sub>2-2x</sub>N<sub>2x</sub> crystallizes in a cubic unit cell, a = 4.9854(7) Å with space group Fm3m, similar to the crystal structure for Li<sub>2</sub>NH and is a rare type with both cation and anion disorder. For LiAlH<sub>4</sub>-LiNH<sub>2</sub> (1:1) 8.7 wt% of H<sub>2</sub> is released during heating from RT to 500°C, while for LiAlH<sub>4</sub>-LiNH<sub>2</sub> composites with molar ratios of LiNH<sub>2</sub> higher than 0.5 the release of both H<sub>2</sub> and NH<sub>3</sub> is observed.</p>