Destabilized LiBH4/MgH2 for reversible hydrogen storage

DOE and FreedomCAR technical targets of 6.0 and 9.0 wt.% are set forth capacities to realize a “holy grail” for hydrogen storage systems for 2010 and 2015 respectively. Alkali metal complex hydrides with high theoretical hydrogen capacity, for example: LiBH4 (18 wt.%), are being investigated for their properties to store large quantities of hydrogen. The catalytic doping of SiO2, seems to enhance the performance of LiBH4. However, the poor cyclic reversibility due to thermodynamic barrier limits their wide usage. Recently, a destabilization mechanism was adopted in order to improve the cycling capacity of LiBH4 by the addition of MgH2. We have successfully synthesized the complex hydride mixtures LiBH4 + 1⁄2MgH2 + Xmol% ZnCl2 catalyst (X=2, 4, 6, 8 and 10) by an inexpensive mechano-chemical process. The structural characterization by X-ray powder diffraction profiles exhibit the presence of LiCl, MgH2 and LiBH4 as majority and minority phases. Besides, the LiCl peaks relative intensity increases with increase of ZnCl2 concentration. The thermal decomposition (gravimetric weight loss) and heat flow measurements have been performed by simultaneous DSC and TGA techniques. An earlier decomposition temperature of 270° C has been observed for the 10mol% ZnCl2 doped LiBH4/MgH2 in comparison to the pristine LiBH4 compound. The pressure-composition-temperature isotherms of the destabilized LiBH4 show an extended plateau pressure around 4-5 bars at 350° C with a good cyclic stability.