Influence of melt spinning and annealing treatment on structures and hydrogen storage thermodynamic properties of La_0.8Pr_0.2MgNi_3.6Co_0.4 alloy

La_0.8Pr_0.2MgNi_3.6Co_0.4 alloys were prepared by induction melting, annealing and melt spinning techniques. The influences of annealing treatment and melt spinning on phase structure and hydrogen storage properties were systematically investigated. The results of X-ray diffraction determine that the as-cast and as-spun La_0.8Pr_0.2MgNi_3.6Co_0.4 alloys consist of LaMgNi₄ and LaNi₅ phases, while only LaMgNi₄ phase is present in the as-annealed alloy. The scanning electron microscope images illustrate that the grain of the alloy is significantly refined by melt spinning technology. The gaseous hydrogen storage kinetic and thermodynamic properties were measured by using a Sievert’s apparatus at different temperatures. The maximum hydrogen storage capacity of the as-cast, as-spun and as-annealed La_0.8Pr_0.2MgNi_3.6Co_0.4 alloy is 1.699, 1.637 and 1.535 wt.% at 373 K and 3 MPa, respectively. The annealed alloy has flatter and wider pressure plateaus compared with the as-cast and as-spun alloys, which correspond to the hydrogen absorption and desorption process of LaMgNi₄ and corresponding hydride. Furthermore, the enthalpy and entropy changes of LaMgNi₄ during hydrogenation at different temperatures were calculated using Van’t Hoff methods.