Lithium amide halides for hydrogen storage

Davies, Rosalind (2016). Lithium amide halides for hydrogen storage. University of Birmingham. Ph.D.

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Abstract

The lithium amide halides are a promising series of materials for hydrogen storage as they release hydrogen at a lower temperature than lithium amide on reaction with lithium hydride. The amide chloride system has been studied in detail, and two phases with reduced chloride content, Li\(_7\)(NH\(_2\))\(_6\)Cl and Li\(_6\)Mg\(_1\)\(_/\)\(_2\)(NH\(_2\))\(_6\)Cl, have been identified by powder X-ray diffraction and Raman spectroscopy. Both were seen to release hydrogen on reaction with LiH at a lower temperature than lithium amide, and ammonia release was suppressed. Rehydrogenation of the imide products of reaction of both new phases occurred more readily under the conditions used than for the known phase Li\(_4\)(NH\(_2\))\(_3\)Cl.

The hydrogen cycling properties of Li\(_7\)(NH\(_2\))\(_6\)Cl were investigated alongside Li\(_7\)(NH\(_2\))\(_6\)Br and Li\(_3\)(NH\(_2\))\(_2\)I. The systems successfully cycled hydrogen, and the reversible structural changes that happened during cycling were studied. All three materials, however, showed a capacity loss on cycling under dynamic vacuum.

The conductivity of the amide and imide halides was studied using A.C. impedance and found to be higher than for LiNH\(_2\) and Li\(_2\)NH, respectively. This supports kinetic analyses that indicate ion diffusion is not rate-limiting for the hydrogen cycling of these systems.

Type of Work:

Thesis (Doctorates > Ph.D.)

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Doctorates > Ph.D.

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