Substitutional effect of Ti-based AB2 hydrogen storage alloys: A density functional theory study

Stability of AB₂ alloy in Laves phases C14 and C15 were studied by first-principle density functional theory simulations. A range of different combinations of B and C elements in the Ti_1?xC_xB₂ alloys were considered. The formation energies of these alloys generally increase with the unit cell volumes of alloys. The volume also affects the stability of the corresponding metal hydride. We find that the formation energies and the hydrogenation enthalpies of AB₂ alloys are likely to be determined by at least three factors: electronegativity, atomic radius and covalent radius. The enthalpies of AB₂ hydrides increase with increasing compositionally-averaged electronegativity and volume change upon hydrogenation. However, the enthalpies of AB₂ hydrides decrease with increasing compositionally-averaged atomic and covalent radii. This study provides useful insights for future exploration of AB₂-type alloys for hydrogen storage applications.