Microstructure characteristics, hydrogen storage thermodynamic and kinetic properties of Mg–Ni–Y based hydrogen storage alloys

In this paper, the Mg 95-X -Ni x -Y 5 (x = 5, 10, 15) alloy were prepared by vacuum induction melting. The X-ray diffraction was used to analytical phase composition in different states, and the Scanning Electron Microscope and Transmission Electron Microscope were used to characterize the microstructure and crystalline state. Meanwhile, the kinetic properties of isothermal hydrogen adsorption and desorption at different temperatures also were tested by the Sievert isometric volume method. The results indicate that the hydrogenated Mg–Ni–Y samples is a nanocrystalline structure consists of MgH 2 , Mg 2 NiH 4 , and YH 3 phases. And, the in-situ formed YH 3 phase not decompose in the process of dehydrogenation and evenly dispersed in the mother alloy, which plays a paly a positive the catalytic role for the reversible cyclic reaction of Mg and Mg 2 Ni phases. In addition, the Ni elements are effectively to improve the thermodynamic properties of the Mg-based hydrogen storage alloy, the desorption enthalpy of the Ni 5 , Ni 10 , and Ni 15 samples successively decrease to 84.5, 69.1, and 63.5 kJ/mol H 2 . The hydrogen absorption and desorption kinetics of the Mg–Ni–Y alloy are improved obviously with the increase of Ni content, especially for Mg 80 Ni 15 Y 5 alloy, which the optimal hydrogenated temperature is reduced to 200 °C, and the 90% of the maximum hydrogen storage capacity can be absorbed within 1 min, about 5.4 wt % H 2 . Besides, the dehydrogenated activation energy of the Mg 80 Ni 15 Y 5 alloy also is reduced to 67.0 kJ/mol, and it can completely release hydrogen at 320 °C within 5 min, which is almost reached the hydrogen desorption capability of Ni 5 alloy at 360 °C. This means that Ni element is a very positive element to reduce the hydrogen desorption temperature. • The hydrogenated Y–Mg–Ni based sample has a nanocrystalline structure. • The optimal hydrogenated temperature is reduced to 200 °C by the Ni elements. • The dehydrogenated enthalpy evaluated to be to be 63.5 kJ/mol. • The dehydrogenation activation energy is evaluated to be 65.8 kJ/mol. • The Ni 15 sample only takes 5 min to release hydrogen completely at 320 °C.