Hydrogen activation and storage properties of laves phase Ti1-xScxMn1.6V0.4 alloys

Abstract Hydrogen activation, storage properties and associated crystal structures of Ti1-xScxMn1.6V0.4 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.25) alloys are investigated by hydrogenation and XRD. The unit-cells of alloys and hydrides expand with Sc content and hydrogen concentration. Minor addition of Sc significantly improves hydrogen activation and storage properties. The plateau pressure decreases, whereas the sloping factor and relative partial molar enthalpy for hydrogenation increase with Sc content. The activation properties strongly depend on the particle sizes. The bulk samples can easily be activated by implementing a hydrogen-induced cracking mechanism, which avoids removal of protective oxide films and compensates the lack of metallic B-metal in catalysis of hydrogen dissociation. Samples with smaller particle sizes are difficult to activate. The unusual particle size effect is interpreted by activation kinetics, and attributed to the high oxygen binding ability of B-metals and their contribution to the surface oxide films.