Significantly improved hydrogen storage properties of Mg90Al10 catalyzed by TiF3

Abstract

Magnesium hydride (MgH 2 ) 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, Mg 90 Al 10 was prepared by hydriding combustion synthesis (HCS), and then various Ti-based compounds (Ti, TiH 2 , TiO 2 and TiF 3 ) were introduced into Mg 90 Al 10 by ball milling. Mg 90 Al 10 + 10 wt% TiF 3 displays the most excellent dehydrogenation property compared with those doped with other Ti-based compounds. For instance, due to the addition of 10 wt% TiF 3 , 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 Mg 90 Al 10 (364 °C and 155.95 kJ/mol). In addition, the catalytic effect of TiF 3 on the hydrogen storage properties of Mg 90 Al 10 has been investigated in detail. Except for the unreacted TiF 3 , Al 3 Ti and MgF 2 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 Mg 90 Al 10 + 10 wt% TiF 3 can be attributed to the catalytic effect of TiF 3 , in-situ formed Al 3 Ti and MgF 2 . Our result is very significant to emphasize the practical application of the Mg-Al hydrogen storage alloys. • The hydrogen storage property of Mg 90 Al 10 doped with TiF 3 is remarkably improved. • The onset dehydrogenation temperature is reduced to 175 °C after TiF 3 addition. • The Mg 90 Al 10 -TiF 3 shows superior hydrogenation/dehydrogenation cycling stability. • TiF 3 , the in-situ formed Al 3 Ti and MgF 2 exhibit excellent catalytic effect.