Microstructure and hydrogen storage kinetics of Mg89RE11 (RE = Pr, Nd, Sm) binary alloys.

Abstract

The present work reports the fabrication of Mg89RE11 (RE = Pr, Sm, Nd) alloys by a vacuum induction furnace. The phase analysis, structure characterization and microstructure observation of Mg89RE11 alloys were carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). There exhibits a multiphase microstructure in the as-cast Mg89RE11 (RE = Pr, Nd, Sm) alloys from the comprehensive analysis made from XRD and SEM, which are containing the major phase (RE5Mg41) and several secondary phases (REMg3 and REMg12). The detections of XRD and TEM reveal that these experimental alloys turn into a MgH2 nanocrystalline composite with equably distributed RE hydride nanoparticles after hydriding and this MgH2 major phase turns into a Mg nanocrystalline after dehydriding. The determination results of the hydrogen storage kinetics show that adding the rare earth element (Pr, Sm and Nd) ameliorates the hydriding and dehydriding kinetics of the Mg-based alloys dramatically. The hydrogen desorption activation energy Ea(de) of Mg89Pr11, Mg89Nd11, Mg89Sm11 are 140.595, 139.191, 135.280 kJ mol−1 H2, respectively. Specially, the hydrogen storage capacity (wt%) of Mg89Sm11 alloy that added Sm element can reached 5 wt%. The improvement of the hydrogen storage performance of Mg89RE11 alloys can be principally ascribed to the RE hydride nanoparticles facilitating the hydriding and dehydriding reactions.