Influence of Melt Spinning on Gaseous and Electrochemical Hydrogen Storage Kinetics of Mg2Ni-type Alloys

The Mg2Ni-type Mg2-xLaxNi (x=0, 0.2, 0.4, 0.6) hydrogen storage alloys were synthesized by casting and direct melt quenching technique. The microstructures of the as-cast and spun alloys were investigated by XRD, SEM and HRTEM. The gaseous hydrogen storage kinetics of the alloys was measured using an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the alloys was tested by constant current to charge and discharge the electrode. The results show that the substitution of La for Mg visibly alters the phase composition of the alloys. For x <= 0.2, the substitution leads to formation of a small amount of secondary phases LaMg3 and La2Mg17 without changing major phase Mg2Ni. But the major phase of the alloys are changed to the (La, Mg)Ni-3+LaMg3 phases by increasing La content to x >= 0.4. The as-spun alloys substituted by La hold an evident amorphous structure, meaning the substitution of La for Mg facilitates the glass formation of the Mg2Ni-type alloy. The gaseous and electrochemical hydrogen storage kinetics of the alloys are sensitive to both the amount of La substitution and the melt spinning technology. The appropriate melt spinning process can significantly ameliorate the gaseous and electrochemical hydrogen storage kinetics of the alloys, whereas the melt spinning technology, by which the optimal hydrogen storage kinetics of the alloy can be yielded, is associated with the chemical composition of the alloy.