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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.

Mg2Ni-Ni-5%RExOy(CeO2, Nd2O3, Tb4O7) composites were synthesized via ball milling method. The microstructure and hydrogen storage properties of the materials were analyzed systematically by XRD, SEM, EDS, the electrochemical and kinetic measurements. The results show that the crystallinities of the composites with rare earth oxides decrease, and the distribution of the rare earth oxide catalysts on the surface of alloys is uniform. The maximum discharge capacities of the composites with rare earth oxides rise evidently,the discharge capacity of the sample containing Tb4O7 reaches to 871mAh·g-1 at room temperature, and the composites can also keep higher cycling stability. The CeO2 and Tb4O7 catalysts can enhance the abilities of charge transfer on the surface of alloys, and improve the transmission rate of H atoms in the bulk of Mg2Ni alloy obviously. The rare earth oxides catalysts can also increase the gaseous hydrogen absorption capacity. The hydrogen storage capacity of the sample with Tb4O7 reaches to 2.02%(mass fraction) at 250℃, which is the maximum hydrogen absorption capacity among these samples, but the hydriding rate is relatively slow at lower temperature. The catalytic effect of the rare earth oxides is mainly related to the changeable valences of the rare earth ions, that is, the more likely of the valences change of the ions, the better the catalytic activities exhibit. The catalytic activities in descending order are Tb4O7, CeO2 and Nd2O3.

Nanosized CuO particles were synthesized via precipitation method, and the crystalline sizes were controlled by adjusting different calcinations temperature. XRD result shows that the obtained samples exhibit CuO single phase structure, the crystalline sizes are 7.5, 14.4nm and 23.4nm respectively. Then Mg2Ni-Ni-5%CuO composites were obtained through ball milling technique, the electrochemical hydrogen storage properties, kinetic performances and the activation energies of hydrogen desorption were tested and analyzed. The results show that the maximum discharge capacities and the electrocatalytic activity on the surface and the diffusivities of H in the bulk of the Mg-based composites electrodes are improved by adding the nanosized CuO catalysts. DSC measurement shows that the nanosized CuO catalyst leads to decrease in hydrogen desorption temperature by about 50K than that of composites without CuO. The activation energies of the composites of Mg2Ni-Ni and Mg2Ni-Ni -5% CuO600,which are calculated by Kissinger formula, are 86.9kJ/mol and 89.3kJ/mol respectively.

The Ni-5%RExOy (CeO2, La2O3, Eu2O3) as composite additives, Mg2Ni-Ni-5%RExOy composites were prepared by the ball milling method. The effects of different additives on the structure, morphology, electrochemistry and kinetic properties of Mg2Ni alloy were studied systematically. The results show that composite additives can improve the proportion of amorphous and nanocrystalline structure of Mg2Ni alloy. The particle size is homogeneous but the agglomeration is observed in the sample with Ni-5%CeO2 additives. The composites with additives show higher maximum discharge capacity and better cycle stabilities. All of these three kinds of composite additives can improve the kinetic properties of the composites effectively, including optimizing the charge-transfer ability, the reversibility of the electrochemical reaction on the alloy surface, and enhancing the diffusion coefficients of H atoms in the bulk of alloy. Among these three kinds of additives, Ni-5%CeO2 additive shows the best catalysis effect on promoting the kinetic properties of the composites.