Laves type intermetallic compounds as hydrogen storage materials: A review

Abstract

Laves type AB 2 intermetallics belong to the most abundant group of intermetallic compounds containing over 1000 compounds. A large variety of the chemical nature of A (Mg, Ca, Ti, Zr, Rare Earth Metals) and B (V, Cr, Mn, Fe, Co, Ni, Al) metals together with the existence of the extended solid solutions formed by mixing various selected components on both A and B sites dramatically extends the list the known binary and ternary individual compounds. A vast majority of the Laves type intermetallics crystallises with C15 / FCC MgCu 2 and C14 / hexagonal MgZn 2 types of structures, both formed for a large range of ratios between the atomic radii of the A and B components outside the ideal ratio r A / r B = 1.225. Their hydrogenation performance is defined by the chemical composition and structure of the alloys and proceeds according to the following alternative / parallel mechanisms: (a) Formation of the insertion type interstitial hydrides containing up to 6–7 at. H/f.u.AB 2 ; (b) Amorphisation of the alloys on hydrogenation; (c) Disproportionation with the formation of a binary hydride of the A metal and depleted by A metal B-components based alloys/hydrides. Equilibrium pressures of hydrogen desorption from the AB 2 -type hydrides span a huge range of ten orders of magnitude and thus Laves type-based intermetallics satisfy the requirements for various applications including getters of hydrogen gas, volume- and mass-efficient hydrogen storage materials operating at ambient conditions, materials for the efficient thermally driven compression of hydrogen gas with an output pressure of several hundred bar and high capacity and high rate anode materials for the metal hydride batteries operating in a challenging temperature range - at subzero temperatures and also above 60 °C. The paper contains references to 245 publications and will guide the future work in the areas of fundamental research and also in advancing the applications of the hydrides of the Laves type intermetallics. • Laves type AB 2 intermetallics are the most abundant group of alloys. • Hydrogenation performance is defined by the chemical composition and structure. • Mechanisms of hydrogenation: interstitial hydrides / amorphization / disproportionation. • Structure-properties relationships are described. • Important applications are reviewed: H stores/MH compression/MH batteries/H getters.