Investigation of microstructure characteristics, kinetics, and thermodynamics of Mg-Ni-RE (RE = Y and RE = Ce) hydrogen storage alloys

The alloys' phase composition and microstructure, along with the reaction paths, which are analyzed by using Xray diffraction, scanning electron microscope, transmission electron microscope, high-resolution transmission electron microscopy, and selective region electron diffraction technologies. Mg96NiY3 and Mg96NiCe3 alloys absorb hydrogen, yielding catalytically efficient YH3 and CeH2.53 hydrides in situ, respectively. Mg96NiCe3 demonstrates superior dehydrogenation kinetics compared to Mg96NiY3, as evidenced by the fact that at the same temperature of 553 K, both alloys release the same mass fraction of hydrogen, Mg96NiCe3 achieves this in only 600 s, whereas Mg96NiY3 requires 1680 s. This is not only since the corresponding hydrides of Mg96NiCe3 alloy are more stable, but it is also well known that the addition of Ce to Mg alloys are more brittle and are more prone to fragmentation during hydrogen uptake and discharge cycles, thus providing more channels for hydrogen diffusion. The dehydrogenation activation energies for Mg96NiY3 and Mg96NiCe3 are 89.77 kJ/mol and 71.89 kJ/ mol, respectively. It is a pity that the thermodynamic properties of Mg96NiCe3 and Mg96NiY3 did not show significant improvement.