Effect of Ni content on microstructural evolution and hydrogen storage properties of Mg-xNi-3La (x = 5, 10, 15, 20 at.%) alloys

The effect of Ni content on microstructural evolution and hydrogen storage properties of Mg-xNi-3La (x = 5, 10, 15, 20 at.%) ternary alloys prepared by vacuum induction melting has been investigated. The as-cast Mg-xNi-3La (x = 5, 10, 15, 20 at.%) alloys consist of Mg, Mg2Ni, LaMg12 and La2Mg17 phases. An increase of Ni content results in an amount increase of the Mg2Ni phase and coarsening of the Mg2Ni microstructure in the alloys. The P-C-isotherms of the Mg-based alloys show that the hydrogen storage capacity decreases in the order “Mg-5Ni-3La (5.50 wt%) > Mg-10Ni-3La (5.16 wt%) > Mg-15Ni-3La (4.60 wt%) > Mg-20Ni-3La (4.51 wt%)”. But the change of Ni content does not alter the thermodynamic properties of Mg-H2 system and Mg2Ni-H2 system in Mg-xNi-3La (x = 5, 10, 15, 20 at.%) alloys. All of the four alloys show excellent desorption kinetics. The desorption kinetics of the alloys first increases, and then decreases with the increase of Ni content. The Mg-15Ni-3La alloy shows the highest dehydriding rate and the lowest apparent activation energy value of 80.36 kJ/mol, which is the optimum kinetics of hydrogen desorption among the alloys. This is attributed to the most appropriate amount of the Mg2Ni phase and eutectic microstructures in the alloy.