Hydrogen Desorption Properties of LiBH₄/xLiAlH₄ (x = 0.5, 1, 2) Composites

A detailed analysis of the dehydrogenation mechanism of LiBH₄/xLiAlH₄ (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 LiBH₄/xLiAlH₄ had a four-step character. The experimental dehydrogenation amount did not reach the theoretical expectations, because the products such as AlB₂ 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 LiAlH₄ 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 LiBH₄/xLiAlH₄ composites.