Hydrogen Desorption Properties of LiBH(4)/xLiAlH(4) (x = 0.5, 1, 2) Composites

A detailed analysis of the dehydrogenation mechanism of LiBH(4)/xLiAlH(4) (x = 0.5, 1, 2) composites was performed by thermogravimetry (TG), differential scanning calorimetry (DSC), mass spectral analysis (MS), powder X-ray diffraction (XRD) and scanning electronic microscopy (SEM), along with kinetic investigations using a Sievert-type apparatus. The results show that the dehydrogenation pathway of LiBH(4)/xLiAlH(4) had a four-step character. The experimental dehydrogenation amount did not reach the theoretical expectations, because the products such as AlB(2) and LiAl formed a passivation layer on the surface of Al and the dehydrogenation reactions associated with Al could not be sufficiently carried out. Kinetic investigations discovered a nonlinear relationship between the activation energy (E(a)) of dehydrogenation reactions associated with Al and the ratio x, indicating that the E(a) was determined both by the concentration of Al produced by the decomposition of LiAlH(4) and the amount of free surface of it. Therefore, the amount of effective contact surface of Al is the rate-determining factor for the overall dehydrogenation of the LiBH(4)/xLiAlH(4) composites.