A comparison study of hydrogen storage performances of as-cast La10-xRExMg80Ni10 (x=0 or 3; RE = Sm or Ce) alloys

Nano-rare earth hydrides generated in situ were believed to catalyze the reversible reaction of magnesium-based alloys and hydrogen. In this paper, La in La2Mg16Ni2 was partially substituted by Ce or Sm. The related impacts of element substitution by Sm or Ce on the structure and hydrogen storage properties of the La10-xRExMg80Ni10 (x = 0 or 3; RE = Sm or Ce) alloys were investigated in detail. XRD, SEM and TEM were used to characterize the microstructure of the alloys. The thermodynamics and kinetics of hydrogen storage reaction at specific temperatures were measured by an automatic Sievert apparatus. The non-isothermal dehydrogenation performance of the alloys was investigated by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at different heating rates. It is revealed that the major phase of alloys is La2Mg17 and the secondary phases are Mg2Ni and La2Ni3, respectively. There is no new phase appearing with the addition of Ce or Sm as the elements Ce and Sm exist in the solid solution of the alloy. The addition of Ce or Sm makes the grain of the as-cast alloy obviously refined. The related reaction kinetics is ameliorated obviously by the method of replacing La with Ce or Sm. Moreover, the operation makes the stability of the hydride visibly declined and reduces the initial temperature of dehydrogenation and the hydrogenation reaction enthalpy (Delta H). Furthermore, the operation results in the dehydrogenation activation energy of the alloys distinctly reduced. A comparison of the total results reveals that the favorable impact dedicated by the operation of substitution with Ce to the comprehensive properties of hydrogen storage alloys is more significant than the Sm substitution. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Nano-rare earth hydrides catalyze the reversible reaction of magnesium-based alloys and hydrogen. Ce or Sm substitution for La in La-Mg-Ni alloys improves the reaction kinetics and refining the grain structure, with Ce showing more significant benefits than Sm.