Reversible Storage of Hydrogen in Destabilized LiBH4

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.