The dehydrogenation performance and reaction mechanisms of Li₃AlH₆ with TiF₃ additive

For Li₃AlH₆ prepared by mechanical milling method, the dissociation reaction enthalpy and activation energy are calculated to be 22.1 kJ mol^-1 H₂ and 133.7 ± 2.7 kJ mol^-1, respectively. The dehydrogenation performance of Li₃AlH₆ is greatly enhanced by TiF₃ additive, especially in the kinetic behaviors. For the Li₃AlH₆ + 10 mol% TiF₃ sample, the starting temperature of dehydrogenation is obviously decreased by 60 °C from that of pure Li₃AlH₆ (190 °C), and 3.0 wt.% H₂ may be released within 1000 s at 120 °C under an initial vacuum. With the amount of TiF₃ increasing, the starting temperature decreases and the kinetics improves due to the decrease in the activation energy. The X-ray diffraction (XRD) together with thermogravimetric analysis (TGA) results show that there are three mechanochemical reactions involved during milling: i) Li₃AlH₆ + TiF₃ → 3 LiF + Al + Ti + 3H₂, ii) Ti + H₂ → TiH₂, iii) 3 Al + Ti → Al₃Ti. The in-situ formed Ti species (TiH₂ and Al₃Ti) co-catalyze the thermal dehydrogenation of Li₃AlH₆.