The hydrogenation and dehydrogenation behaviours of Mg 20− xLa xNi 10( x = 0–6) alloys prepared by casting and rapid quenching

Abstract

In order to improve the hydrogenation and dehydrogenation performances of the Mg 2Ni-type alloys, Mg in the alloy was partially substituted by element La, and rapid quenching technology was used for the preparation of the Mg 20− x La x Ni 10 ( x = 0, 2, 4, 6) hydrogen storage alloys. The structures and morphologies of the as-cast and quenched alloys were studied by XRD and high-resolution transmission electronic microscope (HRTEM). Thermal stability of the as-quenched alloys was researched by differential scanning calorimetry (DSC). The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The results show that no amorphous phase forms in the as-quenched La-free alloy, but the as-quenched alloys containing La hold a major amorphous phase, which is attributed to the fact that the substitution of La for Mg significantly heightens the glass forming ability of the Mg 2Ni-type alloy. The quenching rate induced a light influence on the crystallization temperature of the amorphous phase, but it significantly improved the hydrogenation and dehydrogenation capacities and the kinetics of the alloys. When the quenching rate increases from 0 (as-cast was defined as quenching rate of 0 m/s) to 30 m/s, the hydrogen capacity of the alloys ( x = 0) at 200 °C and 1.5 MPa in 10 min rises from 1.21 to 3.10 wt.%, and from 1.26 to 2.60 wt.% for the alloy ( x = 2). The hydrogen desorption capacity of the alloy ( x = 0) in 10 min increases from 0.23 to 0.99 wt.%, and from 1.48 to 2.46 wt.% for the alloy ( x = 2), respectively.