Microstructural evolution and hydrogen storage proprieties of melt-spun eutectic Mg76.87Ni12.78Y10.35 alloy with low hydrides formation/decomposition enthalpy.

Ternary eutectic Mg 76.87 Ni 12.78 Y 10.35 (at. %) ribbons with mixed amorphous and nanocrystalline phases were prepared by melt spinning. The microstructures of the melt-spun, hydrogenated and dehydrogenated samples were examined and compared by X-ray diffraction and transmission electron microscopy. The amorphous structure transforms into a thermally stable nanocrystalline structure with a grain size of about 5 nm during hydrogen ab/desorption cycles. The Mg, Mg 2 Ni and phases with Y in the melt-spun state transform into MgH 2 , Mg 2 NiH 4 , Mg 2 NiH 0.3 , YH 2 and YH 3 after hydrogenation, and transform back to Mg, Mg 2 Ni and YH 2 upon subsequent dehydrogenation. The reaction enthalpy (ΔH) and entropy (ΔS) of the higher plateau pressure corresponding to Mg 2 Ni hydride formation are −53.25 kJ mol−1 and −107.74 J K−1 mol−1, respectively. The amorphous/nanocrystalline structure effectively reduces the enthalpy and entropy of Mg 2 Ni hydride formation, but has little effect on Mg. The activation energy for dehydrogenation of the hydrogenated ribbons is 69 kJ mol−1. This suggests that Mg–Ni–Y with ternary eutectic composition can form an amorphous/nanocrystalline structure by melt spinning, and this nanostructure efficiently improves the thermodynamics and kinetics for hydrogen storage. • Ternary eutectic Mg–Ni–Y and melt spinning are used to maximize the amorphous. • Amorphous Mg–Ni–Y becomes nanocrystalline structure with a grain size of only 5 nm. • Nanocrystalline structure is stable in hydrogenation and dehydrogenation processes. • Low enthalpy and activation energy are achieved in this nanostructured alloy. [ABSTRACT FROM AUTHOR]