Structural Basis for Hydrogen Interaction in Selected Metal Hydrides

Sammanfattning: Metal hydrides have existing and potential uses in many applications such as in batteries, for hydrogen storage and for heat storage. New metal hydrides and a better understanding of the behaviour of known metal hydrides may prove crucial in the realisation or further development of these applications. The aims of the work described in this thesis have been to characterise new metal hydrides, investigate how the properties of known metal hydrides can be improved and understand how their structure influences these properties. Metal hydrides, in most cases synthesised via high-temperature techniques, were structurally characterised using X-ray powder diffraction, X-ray single crystal diffraction and neutron powder diffraction and their thermodynamic and kinetic properties by in-situ X-ray powder diffraction, thermal desorption spectroscopy and pressure-composition-temperature measurements.The investigations showed that: the storage capacity of the hexagonal Laves phase Sc(Al1-xNix)2 decreases with increasing Al content. There is a significant decrease in the stability of the hydrides and faster reaction kinetics when Zr content is increased in the cubic Laves phase Sc1-xZrx(Co1-xNix)2. Nb4M0.9Si1.1 (M=Co, Ni) form very stable interstitial hydrides which have very slow sorption kinetics. MgH2 mixed with 10 mol% ScH2 reaches full activation after only one cycle at 673 K while it takes at least four cycles at 593 K. LnGa (Ln=Nd, Gd) absorb hydrogen in two steps, it is very likely that the first step is interstitial solution of hydride ions into Ln4 tetrahedra and the second step places hydrogen atoms in Ln3Ga tetrahedra. The nature of the Ga-H bond is still unclear.