An investigation on the hydrogen storage characteristics of the melt-spun nanocrystalline and amorphous Mg 20− xLa xNi 10 ( x = 0, 2) hydrogen storage alloys

Abstract

Mg 2Ni-type hydrogen storage alloys Mg 20− x La x Ni 10 ( x = 0, 2) were prepared by casting and rapid quenching. The structures and morphologies of the as-cast and quenched alloys were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron 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, and their electrochemical properties were measured by a tri-electrode open cell. The results showed that the no amorphous phase formed in the as-quenched La-free alloy, but the as-quenched alloys containing La held a major amorphous phase. The quenching rate induced a light influence on the crystallization temperature of the amorphous phase, and it significantly improved the initial hydrogenation rate and the hydrogen absorption capacity of the alloys. The discharge capacity and the cycle stability of the alloys grew with the increase of the quenching rate. When the quenching rate increased from 0 (as-cast was defined at a quenching rate of 0 m s −1) to 30 m s −1, the hydrogen absorption capacity of the alloys for x = 0 and 2 at 200 °C and 1.5 MPa in 10 min changed from 1.21 to 3.10 wt.% and from 1.26 to 2.60 wt.%, the maximum discharge capacity from 30.26 to 135.51 mAh g −1 and from 197.23 to 406.51 mAh g −1 at a current density of 20 mA g −1, and the capacity retaining rate at 20th cycle from 36.71 to 27.06% and from 37.26 to 78.33%, respectively.