Synthesis And Hydrogen Storage Properties Of Mg-In-M(M=Y, Ni) Ternary Solid Solution Alloys

Pure Mg has many advantages such as high hydrogen storage capacity （7.6wt.%）,good reversibility, rich resource, low-cost and so on. It has become one of the mostpromising hydrogen storage materials. However, its sluggish hydrogen sorption kinetics andhigh thermodynamic stability hinder its application. Among the methods to improve itsthermodynamics, a Mg（In） solid solution can reduce the hydrogen desorption enthalpychange （Δ-）, but poor kinetics and still high hydrogen desorption temperature. There is anecessary to introduce the other components into Mg（In） solid solution to further improveits hydrogen storage properties. In this paper, Mg₉₀In₅Y₅, Mg₉₀In₅Ni₅, Mg_81.8In_4.6Ni_13.6alloys were synthesized via two-step method, namely sintering the elemental powders andsubsequent milling. The structures of samples were characterized by XRD, DSC, SEManalysis methods. Their hydrogen storage properties were tested using Sivert method. Herewe clarified the hydrogen sorption mechanism of Mg（In, Y） ternary solid solution, and theinfluence of Ni addition on the structure transformation and hydrogen storage properties ofMg（In） solid solution.The Mg（In, Y） ternary solid solution was successfully synthesized by ball-milling asthe solubility of Y in Mg had been expend via ball-milling and the existence of In. Themiddle-phases, β and In₃Y, formed when Mg（In, Y） solid solution was hydrogenated, whichturned back to solid solution state after dehydrogenation. At the same time, YH₃formedfrom Mg（In, Y） solid solution when hydrogenated, and the transformation of YH₂YH₃during hydrding/dehydriding played a role of catalysis. The formation of β and In₃Ypromoted the decomposition of MgH₂, and the reversible transformation reduced thehydrogen desorption enthalpy change of Mg（In, Y） solid solution alloy to62.9kJ/mol. DSCresults indicated that the dehydrogenation temperature had lowered84K and60Kcompared with pure MgH₂and Mg（In） binary solid solution, respectively. Mg₉₀In₅Ni₅alloyhad great hydrogen sorption kinetics. The active energies of hydrogenation for Mg₉₀In₅Y₅alloy is58kJ/mol, and145.6kJ/mol for dehydrogenation.There is no any reaction between Ni and Mg（In） solid solution during ball-milling.When hydrogenated, Mg₉₀In₅Ni₅alloy turned to MgH₂, Mg₂NiH₄and the unknown phaseX1consisting In. Mg₂NiH₄reacted with X1to form Mg₃In, InNi₂and unknown phase X2,and MgH₂decomposed directly instead of returning back to solid solution. Thehydrogenation process of Mg_81.8In_4.6Ni_13.6alloy was very similar with Mg₉₀In₅Ni₅alloy, butInMg phase else and more Mg₂NiH₄. When dehydrogenated, the products of Mg₂NiH₄ decomposition consisted not only InNi₂and unknown phase X2, but also Mg₂Ni. MgH₂reacted with InMg to form Mg（In） solid solution, thus partial In returned back solid solution.The hydrogen desorption enthalpy change of Mg-In-Ni system hadn’t changed, but thedehydrogenation temperature had reduced. Mg₉₀In₅Ni₅alloy had very excellent hydrogensorption kinetics. It could absorbed hydrogen completely with5min at453K and couldrelease hydrogen completely with30min at553K. The active energies of hydrogenationand dehydrogenation for Mg₉₀In₅Ni₅alloy is33.8kJ/mol, and58kJ/mol, respectively.