Significantly improved hydrogen storage properties of Mg₉₀Al₁₀ catalyzed by TiF₃

Magnesium hydride (MgH₂) is one of the most promising materials for solid state hydrogen storage, but overly stable thermodynamics and sluggish kinetics of hydrogenation and dehydrogenation hinders its application. In this study, Mg₉₀Al₁₀ was prepared by hydriding combustion synthesis (HCS), and then various Ti-based compounds (Ti, TiH₂, TiO₂ and TiF₃) were introduced into Mg₉₀Al₁₀ by ball milling. Mg₉₀Al₁₀ + 10 wt% TiF₃ displays the most excellent dehydrogenation property compared with those doped with other Ti-based compounds. For instance, due to the addition of 10 wt% TiF₃, the peak dehydrogenation temperature and the apparent dehydrogenation activation energy of the composite are 86 °C and 77.1 kJ/mol lower than those of Mg₉₀Al₁₀ (364 °C and 155.95 kJ/mol). In addition, the catalytic effect of TiF₃ on the hydrogen storage properties of Mg₉₀Al₁₀ has been investigated in detail. Except for the unreacted TiF₃, Al₃Ti and MgF₂ can be found during the first dehydrogenation process and remain stable in the subsequent de/hydrogenation cycles, which can act as the active sites to accelerate the hydrogen dissociation and recombination. Therefore, the excellent hydrogen storage properties of Mg₉₀Al₁₀ + 10 wt% TiF₃ can be attributed to the catalytic effect of TiF₃, in-situ formed Al₃Ti and MgF₂. Our result is very significant to emphasize the practical application of the Mg-Al hydrogen storage alloys.