The effect of Mm content on microstructure and hydrogen storage properties of the as-cast Mg-10Ni-xMm (x = 1, 2, 3 at.%) alloys

The effect of Mm content on microstructure and hydrogen storage properties of the as-cast Mg-10Ni-xMm (x = 1, 2, 3 at.%) alloys prepared by a simple one-step method of induction melting is studied. Increasing the content of Mm, the diffraction peaks of Mg and MmMg12 are drastically weakened and broadened, indicating a reduction of the grain size. The interface between MmMg12 and Mg2Ni is semi-coherent, with an ordered repetition of the consistent atomic arrangements. It is found that an increase in the amount of Mm leads to good hydriding and dehydriding rate meanwhile resulting in an increase in hydrogen absorption/desorption capacity. The as-cast Mg-10Ni-3Mm alloy exhibits the best hydrogen storage properties among the alloys. The amount of hydrogen absorption reaches 5.26 wt.% within 350 s at 573 K and hydrogen desorption amount is 4.72 wt.% within only 300 s at the same temperature. The dehydrogenation activation energy of MgH2 in this system is decreased to 88.6 kJ/mol H2. The pressure-composition isotherms (PCI) of the Mg-10Ni-3Mm were performed, and the reversible hydrogen capacity of reaches as high as 5.79 wt.%. The values of ΔH of the hydrogenation and dehydrogenation of Mg2Ni are −57.62 kJ mol−1 H2 and +56.75 kJ mol−1 H2, respectively. In addition, a hydrogen storage synergetic mechanism including microstrain-induced effect and heterogeneous nucleation effect is proposed, being correlated by the local introduction of Mm content into the alloy.