| Abstract
| - The hydrogen storage reaction ScH2 + 2LiBH4 → ScB2 + 2LiH + 4H2 (8.91 wt %), based on the thermodynamic destabilization of LiBH4, is predicted to have a reaction enthalpy of ΔH300K = 34.1 kJ/mol H2. The isothermal kinetic desorption behavior in this system was measured. At temperatures up to 450 °C, less than 5 wt % H2 is released, which is only half of the theoretical capacity. Powder X-ray diffraction data indicate that LiBH4 has decomposed into LiH in the final desorption product, but the data provide no evidence that ScH2 has participated in the reaction. Magic angle spinning NMR (MAS NMR) results do not show that the expected ScB2 equilibrium product phase has formed during desorption. While the addition of 2 mol % TiCl3 catalyst does improve desorption kinetics at 280 °C, it does not otherwise assist the destabilization reaction. The calculated reaction enthalpy suggests that this system should be of interest at moderate temperatures, but the large heats of formation of the reactant phases in this system appear to play a critical role in determining overall kinetics. Furthermore, the formation of a Li2B12H12 intermediate phase was determined by MAS NMR, which is an undesirable stable product if reaction reversibility is to be accomplished.
|
