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

The present work reports the fabrication of MgRE (RE = Pr, Sm, Nd) alloys by a vacuum induction furnace. The phase analysis, structure characterization and microstructure observation of MgRE 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 MgRE (RE = Pr, Nd, Sm) alloys from the comprehensive analysis made from XRD and SEM, which are containing the major phase (REMg) and several secondary phases (REMg and REMg). The detections of XRD and TEM reveal that these experimental alloys turn into a MgH nanocrystalline composite with equably distributed RE hydride nanoparticles after hydriding and this MgH 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 (de) of MgPr, MgNd, MgSm are 140.595, 139.191, 135.280 kJ mol H, respectively. Specially, the hydrogen storage capacity (wt%) of MgSm alloy that added Sm element can reached 5 wt%. The improvement of the hydrogen storage performance of MgRE alloys can be principally ascribed to the RE hydride nanoparticles facilitating the hydriding and dehydriding reactions.