Dehydrogenation properties of Mg₂₂Y₂Ni₁₀Cu₂ hydrogen storage alloy

Abstract

The Mg2Ni-type hydrogen storage alloy with the addition of a little Y and Cu was prepared by medium frequency induction melting. The phase composition and microstructure were characterized by X-ray diffractometer, scanning electron microscope, energy dispersive spectrum analyzer and transmission electron microscope. Hydrogen desorption performances of the alloy were measured by hydrogen absorption/desorption equipment based on the Sieverts method and high pressure differential scanning calorimeter. The activation energy and corresponding mechanism of dehydrogenation under isothermal and continuous heating conditions were investigated. The results show that the as-cast alloy presents lamellar-shaped structures which are composed of Mg2Ni and YMgNi4 as the main phase and small amount of Mg. The alloy exhibits good activation properties in which the time taken to reach 90% of the maximum dehydrogenation content is 446, 418, 360, 354, 342 s and 336 s in the first six isothermal hydrogen desorption cycles respectively. The fitting results of the hydrogen desorption kinetics indicate that the dehydrogenation is governed by random nucleation and subsequent growth mechanism. The activation energy of the isothermal hydrogen desorption of the alloy is Ea=67.6 kJ/mol. Comparatively, the activation energy of hydrogen evolution at continuous heating is Ea=69.5 kJ/mol. At the same time, it is found that crystal transitions of Mg2NiH4 are identified to be triggered at 505 K and 512 K. Furthermore, dehydrogenation of Mg2NiH4 starts more easily than that of MgH2.

Keywords

• mg₂₂y₂ni₁₀cu₂ hydrogen storage alloy
• hydrogen desorption performance
• activation ene-rgy
• random nucleation
• subsequent growth