Comparative study for microstructure and hydrogen storage capabilities of Mg₉₅Zn₂R₃ (R[dbnd]Y, La) alloys

For the sake of enhancing the hydrogen storage kinetics of Mg-based alloys, the functions of Y and La on microstructure evolution and de/hydrogenation behavior of Mg–Zn alloy are examined and discussed. The thermodynamic calculations reveal that the kind of rare-earth element affect solidification paths of the alloys. La introduction enables the eutectoid transformation. The hydrogenation kinetics of Mg₉₅Zn₂Y₃ and Mg₉₅Zn₂La₃ is dominated by hydrogen diffusion. The fine α-Mg grains and alternating structured eutectoid phase in Mg₉₅Zn₂La₃ provide abundant phase boundary for hydrogen diffusion. Besides, the residual Mg content in hydrogenated Mg₉₅Zn₂La₃ is far lower than that in Mg₉₅Zn₂Y₃, which is ascribed to the weakened effect of nucleation-growth-impingement caused by growing MgH₂. The hydrogen desorption kinetics of Mg₉₅Zn₂Y₃ and Mg₉₅Zn₂La₃ is determined by the nucleation and growth of Mg/MgH₂. The fine La₈H_18.4 nanophases and Mg grains provide plenty of nucleation sites for Mg on MgH₂. Additionally, La₈H_18.4 nanophase exhibits more positive role than YH₂/YH₃ phase in promoting hydrogen desorption.