•Mg2NiH4 and AB5 alloy combined system was investigated firstly for Ni-MH battery.•Discharge capacity of Mg2NiH4-40 wt.% AB5 composite reaches 848 mAh/g (Mg2NiH4).•A schematic representation of discharge mechanism of the electrode is proposed.•An in-depth exploration of the electrode kinetics is reported.The structure, kinetics and electrochemical characteristics of Mg2NiH4-x wt.% MmNi3.8Co0.75Mn0.4Al0.2 (x = 5, 10, 20, 40) composites prepared by mechanical milling have been investigated in this paper. XRD results indicate that the as-milled Mg2NiH4 shows nanocrystalline or amorphous-like structure, and it does not react with MmNi3.8Co0.75Mn0.4Al0.2 during mechanical milling. As the amount of MmNi3.8Co0.75Mn0.4Al0.2 increases, the maximum discharge capacity decreases initially from 508 mAh/g (x = 5) to 440 mAh/g (x = 10) and then increases to 509 mAh/g (x = 40). Meanwhile, the capacity retention (R10) increases from 12.8% (x = 5) to 23.4% (x = 40), and the corrosion potential of electrode (Ecorr) increases from −0.930 V to −0.884 V (vs. Hg/HgO). Especially, the more MmNi3.8Co0.75Mn0.4Al0.2 content the composite contains, the higher high rate dischargeability (HRD) the electrode exhibits, which could be attributed to the catalytic reaction and reduction of the Mg2NiH4 grain size brought by MmNi3.8Co0.75Mn0.4Al0.2. The improvement in electrode kinetics has been depicted from the bulk hydrogen diffusion coefficient (D), the exchange current density (I0) and the charge transfer resistance (Rct) on the alloy surface.

Mg2−xAlxNi (x = 0, 0.3, 0.5, 0.7) hydrogen storage alloys used as the negative electrode in a nickel–metal hydride (Ni–MH) battery were successfully prepared by means of hydriding combustion synthesis (HCS) and the selected alloy Mg1.5Al0.5Ni was further modified by mechanical milling (MM). The structural and electrochemical hydrogen storage properties of Mg2−xAlxNi alloys have been investigated in detail. XRD results show that a new phase Mg3AlNi2 that possesses an excellent cycling stability is observed with the substitution of Al for Mg. A short-time mechanical milling has a significant effect on improving the discharge capacity of the HCS product of Mg1.5Al0.5Ni. The maximum discharge capacity of Mg1.5Al0.5Ni ascends with increasing mechanical milling time and reaches the maximum 245.5 mAh/g when milled for 10 h. The alloy milled for 5 h shows the best electrochemical kinetics, which is due to its smaller mean particle size and uniform distribution of the particles. Further increasing in mechanical milling time could not bring about better electrochemical kinetics, which might be attributed to the agglomeration of the alloy particles and thus the charge-transfer reaction and hydrogen diffusion are restrained. It is suggested that the novel method of HCS + MM is promising to prepare ternary Mg-based intermetallic compound for electrochemical hydrogen storage.Highlights► A ternary Mg3AlNi2 alloy was synthesized for the first time by HCS. ► Mg3AlNi2 alloy possesses an excellent cycling stability. ► A short time milling increases notably the discharge capacity of the alloy. ► The alloy milled for 5 h shows the best electrochemical kinetics property.

In this paper, Al was partially substituted by Ni in the Zintl phase alloy SrAl2 and the structural and hydrogenation characteristics of the SrAl2−xNix (0 ≤ x ≤ 0.4) alloys were studied by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and hydrogenation measurements. The alloy consisted of a single Zintl phase of SrAl2 when x = 0. However, partial substitution of Al by Ni resulted in multiphase structure of the alloys. When x = 0.1, the alloy was composed of SrAl2, Sr5Al9, SrAl and AlNi phases. With the increase of x, the amount of SrAl2 and Sr5Al9 phases decreased, while the amount of SrAl and AlNi phases increased. Hydrogenation measurements were made at 473 K under 3 MPa hydrogen pressure. It was interesting to find that the hydriding kinetics of the alloy was improved greatly after Ni substitution, which could be attributed to the catalysis of AlNi phase.