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.