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

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 E _a(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.