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Crystals 2012, 2(2), 159-175; doi:10.3390/cryst2020159
Article

Mechanical and Thermal Dehydrogenation of Lithium Alanate (LiAlH4) and Lithium Amide (LiNH2) Hydride Composites

1,*  and 2
Received: 13 January 2012 / Revised: 21 February 2012 / Accepted: 22 March 2012 / Published: 2 April 2012
(This article belongs to the Special Issue Hydrogen Storage Alloys)
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Abstract

Hydrogen storage properties of the (nLiAlH4 + LiNH2) hydride composite where n = 1, 3, 11.5 and 30, synthesized by high energy ball milling have been investigated. The composite with the molar ratio n = 1 releases large quantities of H2 (up to ~5 wt.%) during ball milling up to 100–150 min. The quantity of released H2 rapidly decreases for the molar ratio n = 3 and is not observed for n = 11.5 and 30. The XRD studies indicate that the H2 release is a result of a solid state decomposition of LiAlH4 into (1/3)Li3AlH6 + (2/3)Al + H2 and subsequently decomposition of (1/3)Li3AlH6 into LiH + (1/3)Al + 0.5H2. Apparently, LiAlH4 is profoundly destabilized during ball milling by the presence of a large quantity of LiNH2 (37.7 wt.%) in the n = 1 composite. The rate of dehydrogenation at 100–170 °C (at 1 bar H2) is adversely affected by insufficient microstructural refinement, as observed for the n = 1 composite, which was milled for only 2 min to avoid H2 discharge during milling. XRD studies show that isothermal dehydrogenation of (nLiAlH4 + LiNH2) occurs by the same LiAlH4 decomposition reactions as those found during ball milling. The ball milled n = 1 composite stored under Ar at 80 °C slowly discharges large quantities of H2 approaching 3.5 wt.% after 8 days of storage.
Keywords: solid state hydrogen storage; lithium alanate; lithium amide; ball milling; mechanical and thermal dehydrogenation solid state hydrogen storage; lithium alanate; lithium amide; ball milling; mechanical and thermal dehydrogenation
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Varin, R.A.; Zbroniec, L. Mechanical and Thermal Dehydrogenation of Lithium Alanate (LiAlH4) and Lithium Amide (LiNH2) Hydride Composites. Crystals 2012, 2, 159-175.

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