A significant decrease in the dehydrogenation temperature of Mg(AlH 4 ) 2 was achieved by low-energy ball milling with TiF 4 . Approximately 8.0 wt% of hydrogen was released from the Mg(AlH 4 ) 2 -0.025TiF 4 sample with an on-set temperature of 40 °C, which represents a decrease of 75 °C relative to pristine Mg(AlH 4 ) 2 . In contrast to the three-step reaction for pristine Mg(AlH 4 ) 2 , hydrogen desorption from the TiF 4 -doped sample involves a two-step process because the Ti-based species participates in the dehydrogenation reaction. The presence of TiF 4 alters the nucleation and growth of the dehydrogenation product, significantly decreasing the activation energy barrier of the first step in the dehydrogenation of Mg(AlH 4 ) 2 . Further hydrogenation measurements revealed that the presence of the Ti-based species was also advantageous for hydrogen uptake, as the on-set hydrogenation temperature was only 100 °C for the dehydrogenated TiF 4 -doped sample, compared with 130 °C for the additive-free sample.