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.