An investigation into the synthesis and characterisation of metal borohydrides for hydrogen storage

Reed, Daniel Thomas (2010). An investigation into the synthesis and characterisation of metal borohydrides for hydrogen storage. University of Birmingham. Ph.D.

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Abstract

With relatively high gravimetric and volumetric hydrogen storage capacities, borohydride compounds are being investigated for their potential use as hydrogen storage media. A study has been made into the mechanical milling of metal chlorides with sodium borohydride to try to form homoleptic borohydrides. Mechanical milling of zinc chloride with sodium borohydride resulted in the formation of a covalent complex NaZn\(_2\)(BH\(_4\))\(_5\). Thermal decomposition occurred at 80°C with a mass change of 12 wt.%, associated with the evolution of hydrogen and diborane. A composite mixture with magnesium hydride a reaction between diborane and magnesium hydride was observed form magnesium borohydride. Mechanical milling of calcium chloride or magnesium chloride with sodium borohydride did not produce calcium borohydride and magnesium borohydride, but rather resulted in solid solutions where chlorine ions substitute for borohydride ions within the cubic sodium borohydride lattice. Thermal decomposition of milled calcium chloride and sodium borohydride occurs at a similar manner to that of Ca(BH\(_4\))\(_2\) (from Sigma-Aldrich). Milled magnesium chloride and sodium borohydride thermally decomposes via several unknown phases with a weight loss of 4.4 wt.% yielding Mg, MgB\(_2\), B, and [B\(_{12}\)H\(_{12}\)]\(^{2-}\). Lithium borohydride investigated using Raman spectroscopy. After heating lithium borohydride through its orthorhombic to hexagonal phase change (118°C) and melting point (280°C), shifts in Raman peak position and peak width were measured as a function of temperature. This work shows the in-situ decomposition of LiBH\(_4\) observing formation of lithium dodecaborane (Li\(_2\)B\(_{12}\)H\(_{12}\)) at 340°C and amorphous boron from liquid lithium borohydride.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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