Reversible hydrogen storage in titanium-catalyzed LiAlH₄-LiBH₄ system

We have investigated the hydrogen storage properties of the LiAlH₄-LiBH₄ system, both un-doped and doped with titanium based catalysts. It was found that TiF₃ exhibited the superior catalytic effects in terms of enhancing the hydriding/dehydriding kinetics and reducing the dehydrogenation temperature of the LiAlH₄-LiBH₄ system. Compared to the un-doped LiAlH₄-LiBH₄ system, the onset temperatures of the 5 mol% TiF₃-doped sample for the first and second dehydrogenation steps were decreased by 64 and 150 °C, respectively. X-ray diffraction patterns of the dehydrogenated samples revealed that the produced Al from LiAlH₄ could react with B from the decomposition of LiBH₄ to form AlB₂ and LiAl compounds. Pressure-composition-temperature (PCT) and van't Hoff plots made it clear that the decomposition enthalpy of LiBH₄ in the TiF₃-doped LiAlH₄-LiBH₄ system is decreased from 74 kJ/(mol of H₂) for the pure LiBH₄ to 60.4 kJ/(mol of H₂). The dehydrogenation products of the TiF₃-doped LiAlH₄-LiBH₄ sample can absorb 3.76 and 4.78 wt.% of hydrogen in 1 h and 14 h, respectively, at 600 °C and under 4 MPa of hydrogen. The formation of LiBH₄ was detected by X-ray diffraction in the rehydrogenated sample. © 2009.