Hewett, David R. (2012)
Ph.D. thesis, University of Birmingham.
Metal hydride materials have attracted much interest for their potential use as hydrogen storage materials. Complex hydrides are amongst the most promising due to their high gravimetric storage capacities and favourable de/rehydrogenation conditions. Here, mixed anion complex hydrides are investigated both through halide doping of LiNH\(_2\) and Li\(_2\)NH, and though a mixed LiNH\(_2\)-LiBH\(_4\) system.
The reaction of LiNH\(_2\) and Li\(_2\)NH with lithium or magnesium chloride, bromide and iodide has been shown to form a series of amide- and imide-halide phases. The structures of these phases were investigated through powder diffraction methods as well as Raman spectroscopy. The hydrogen releasing properties of these materials were investigated through reaction with LiH and MgH\(_2\); while the equivalent hydrogenation reactions were also tested. In both cases these materials performed more favourably than the pure LiNH\(_2\)-LiH system. The lithium ion conductivity of these materials was also investigated; it was shown that the most conducting materials were also the quickest to release and uptake hydrogen.
The LiNH\(_2\)-LiBH\(_4\) system was studied, with particular focus on the decomposition product, Li\(_3\)BN\(_2\). All three known polymorphs of this compound were shown to be able to form by the reaction of \(_2\)LiNH\(_2\) + LiBH\(_4\) by carefully changing the reaction conditions. Further stages of this system were investigated through reaction of Li\(_2\)NH and Li\(_3\)N with LiBH\(_4\). Here the products from these reactions were studied along with the thermal desorption properties of the systems.
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