Structures and properties of Mg-La-Ni ternary hydrogen storage alloys by microwave-assisted activation synthesis

It is a challenge to prepare a material meeting two conflicting criteria - absorbing hydrogen strongly enough to reach a stable thermodynamic state and desorbing hydrogen at moderate temperature with a fast reaction rate. With the guide of the Mg-La-Ni phase diagram, microwave sintering (MS) was successfully applied to preparing Mg-La-Ni ternary hydrogen storage alloys from the powder mixture of Mg, La and Ni. Their phase structures, morphologies and hydrogen absorption and desorption (A/D) properties have been studied by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), pressure-composition-isotherm (PCI) and differential scanning calorimetry (DSC). The metal hydride of 70 Mg-9.72 La-20.28 Ni (wt pct) has the best comprehensive hydriding and dehydriding (H/D) properties, which can absorb 4.1 wt.% H2 in 600 s and desorb 3.9 wt.% H2 in 1500 s at 573 K. The DSC results reveal its onset temperatures of hydrogen A/D are the lowest among all the samples, which are 671.4 and 600.9 K. Its activation energy of dehydriding reaction is 113.5 kJ/mol H2, which is the smallest among all the samples. Also, Chou model was used to analyze the reaction kinetic mechanism.