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 Mg_88.5Ni_xLa_y (x+y=11.5, y/x=0, frac(1, 16), frac(1, 4), frac(1, 2) and frac(2, 1)) composites prepared by hydriding combustion synthesis followed by mechanical milling was investigated. It was found that Mg_88.5Ni_xLa_y (y / x = frac(1, 16)) 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, Mg_88.5Ni_xLa_y (y / x = frac(1, 16)) 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, Mg₂NiH_0.3, Mg₂NiH₄ and LaH₂. From the analysis of pressure-concentration isotherms, the existence of LaH₂ resulted in the increased hydrogen storage capacity in Mg_88.5Ni_xLa_y (y / x = frac(1, 16)) composite. It was demonstrated that the excellent hydrogen storage properties of Mg_88.5Ni_xLa_y (y / x = frac(1, 16)) were attributed to the effective synergetic catalysis of LaH₂ and Mg₂Ni.