The dehydrogenation process of amorphous (Mg60Ni25)92La8 alloy

The dehydrogenation of the amorphous (Mg60Ni25)92La8 alloy was investigated by both galvanostatic and non-isothermal methods. The non-isothermal dehydrogenation process of the alloy was analyzed in detail by differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray diffraction (XRD). Experimental results showed a maximum discharge capacity of 558 mAh/g at room temperature and 4.5 wt.% of released hydrogen at a heating rate of 5 °C/min. The non-isothermal dehydrogenation process was divided in two steps. In the first step, the alloy released 2 wt.% H, which corresponded to the amorphous phase dehydrogenation and the growth of Mg2NiH4. In the second step, the alloy released 2.5 wt.% H, corresponding to the dehydrogenation of Mg2NiH4 accompanied by the formation of LaH2. During the charging process, the amorphous phase partially crystallized into a Mg2NiH4 phase. It was found that the hydrogen storage capacity of the amorphous phase was larger than that of Mg2NiH4. The solute H atoms dissolved in the amorphous phase could be easily released at room temperature, which suggested that restraining the amorphous phase crystallization during charging could be useful to improve the discharge capacity.