Effect of La/Ni ratio on hydrogen storage properties of Mg–Ni–La system prepared by hydriding combustion synthesis followed by mechanical milling

The effect of La/Ni ratio on hydrogen storage properties of Mg88.5NixLay (x+y=11.5, y/x  =0, 116, 14, 12 and 21) composites prepared by hydriding combustion synthesis followed by mechanical milling was investigated. It was found that Mg88.5NixLay   (y/x=116) composite showed the largest hydrogen absorption capacity of 4.45 wt% in 30 s at 373 K among the composites. Compared with the other composites, Mg88.5NixLay   (y/x=116) had the rapid dehydriding rate during heating though the initial dehydriding temperatures of all the composites were almost the same and approximately 460 K. XRD analysis indicated that Mg–Ni–La composites contained Mg, MgH2, Mg2NiH0.3, Mg2NiH4 and LaH2. From the analysis of pressure–concentration isotherms, the existence of LaH2 resulted in the increased hydrogen storage capacity in Mg88.5NixLay   (y/x=116) composite. It was demonstrated that the excellent hydrogen storage properties of Mg88.5NixLay   (y/x=116) were attributed to the effective synergetic catalysis of LaH2 and Mg2Ni.