Reversible Storage of Hydrogen in Destabilized LiBH4

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Abstract
Destabilization of LiBH4 for reversible hydrogen storage has been studied using MgH2 as a destabilizing additive. Mechanically milled mixtures of LiBH4 + 1/2MgH2 or LiH + 1/2MgB2 including 2−3 mol % TiCl3 are shown to reversibly store 8−10 wt % hydrogen. Variation of the equilibrium pressure obtained from isotherms measured at 315−400 °C indicate that addition of MgH2 lowers the hydrogenation/dehydrogenation enthalpy by 25 kJ/(mol of H2) compared with pure LiBH4. Formation of MgB2 upon dehydrogenation stabilizes the dehydrogenated state and, thereby, destabilizes the LiBH4. Extrapolation of the isotherm data yields a predicted equilibrium pressure of 1 bar at approximately 225 °C. However, the kinetics were too slow for direct measurements at these temperatures.