Alloy design of cyclic hydro and dehydrogenation tolerant hydrogen storage materials

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The objective of this study is to understand the effect of metallurgical factors on hydrogen absorbing properties and to indicate the appropriate alloys design of hydrogen storage materials with advanced cyclic properties. The results obtained are summarized as followsEffects of microstructure and composition on hydrogen absorbing properties in binary TiMn_2 based alloy: The hydrogen absorbing properties of binary TiMn_2 based alloys have been investigated as function of composition in the range between Ti-59.4 and -66.8 at.% Mn. The volume of fraction of TiMn_2 phase increases with increasing Mn content. The Mn content of TiMn_2 phase is almost constant atcompositions between Ti-56.4 and -59.4 at.% Mn, while is increases with increasing Mn content at compositions between Ti-59.4 nod -66.8 at.% Mn. Ti-59.4 at.% Mn containing TiMn_2 phase with 60 at.% Mn exhibits the superior hydrogen absorbing capacity and she least degradation of capacity during repeated hydrogen absorption and desorp … More tion. It is concluded that both hydrogen absorbing capacity and cyclic property in binary TiMn_2 based alloy are improved by increasing the volume fraction of TiMn_2 phase with keeping Mn content as low as possible.TiMn_2 based alloys: Degradation of the hydrogen absorbing capacity in cyclically hydrogenated TiMn_2 (Ti-60 at.% Mn) with Laves structure was studied by measurement of pressure-composition-isotherm (PCT) curves, X-ray diffraction and microstructure observation. Characteristic changes with cyclic hydrogenation are observed as follows. The hydrogen absorbing capacity remarkably decreases, the lattice constant increases, the amount of hydrogen retained in TiMn_2 increases and it approaches almost zero by dehydrogenation as 673 K in vacuum. Nano-sized regions with Mere patterns are produced in TiMn_2 with hydrogenation and Debye rings corresponding to titanium hydride δ-TiH appear in the diffraction pattern. Based on these observations it is concluded that the degradation of hydrogen absorbing capacity after cyclic hydrogenation is attributable to the introduction of retained hydrogen, heterogeneous strain and/or nano-regions. Less