Hydrogen absorption properties of scandium and aluminium based compounds

Abstract: In a time of global environmental problems due to overuse of fossil fuels, and a subsequent depletion of the supplies, hydrogen is considered as one of the most important renewable future fuels for use in clean energy systems with zero greenhouse-gas emission. Hydrogen storage is the main issue that needs to be solved before the technology can be implemented into key areas such as transport. The high energy density, good stability and reversibility of metal hydrides make them appealing as hydrogen storage materials. In this thesis research on synthesis and hydrogen absorption properties for intermetallic compounds based on scandium and aluminium is reported. The compounds were synthesized by arc melting or induction melting and exposed to hydrogen in a high pressure furnace. Desorption investigations were performed by thermal desorption spectroscopy. The samples were analyzed by x-ray powder diffraction and electron microscopy. ScAlNi, crystallizing in the MgZn2-type structure (space group: P63/mmc; a = 5.1434(1) Å, c = 8.1820(2) Å), was found to absorb hydrogen by two different mechanisms at different temperature regions. At ~120 °C hydrogen was absorbed by solid solution formation with estimated compositions up to ScAlNiH0.5. At ~500 °C hydrogen was absorbed by disproportionation of ScAlNi into ScH2 and AlNi. The reaction was found to be fully reversible due to destabilization effects which lowered the decomposition temperature of ScH2 by ~460 °C.