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Decomposition Reactions and Reversibility of Ca(BH4)2 Composite

초록/요약

LiBH4 is one of the promising candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen capacity. However, its high dehydrogenation temperature and limited reversibility has been a hurdle for its use in real applications. In an effort to overcome this barrier and to adjust the thermal stability, we make a composite system LiBH4-Ca(BH4)2. In order to fully characterize this composite system we study xLiBH4 + (1-x)Ca(BH4)2 for several x values between 0 and 1, using DSC, in situ XRD, TG-Mass. Interestingly, this composite undergoes a eutectic melting at ca. 200℃ in a wide composition range, and the eutectic composition lies between x=0.6 and 0.8. The decomposition characteristics and the hydrogen capacity of this composite vary with x, and the decomposition temperature is lower than both the pure LiBH4 and Ca(BH4)2 at intermediate compositions, for example, for x≒0.4, decomposition is finished below 400℃ releasing about 10 wt % of hydrogen. Partial reversibility of this system was also confirmed for the first time for the case of a mixed borohydride composite.

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초록/요약

Some transition metal Floride or Chlorid catalyst decrease decomposition temperature. Each anion (F- or Cl-) is solid solution with H- or BH4- ion. It show dopped LiBH4 with F or Cl anion may generate F or Cl lattice substitution in both the hydrogenated (LiBH4) and dehydrogenated (LiH) states of the hydride, and accordingly result in a favorable thermodynamics modification, even to a level suitable for on board H-storage application. Experimentally evidencing these theoretical predictions may pave a new way to pursue improved hydrogen storage properties of LiBH4 and other related complex borohydrides which like Ca(BH4)2. Along this line, we have studied Anion substitution effect of Ca(BH4)2.

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