TiF4-doped Mg(AlH4)2 with significantly improved dehydrogenation properties

• TiF4-doped Mg(AlH4)2 exhibits improved dehydrogenation properties.
• TiF4 participates in the dehydrogenation reaction upon heating.
• TiF4 changes the type of nucleation and growth of dehydrogenation products.
• The presence of Ti species is also beneficial for hydrogen uptake.

A significant decrease in the dehydrogenation temperature of Mg(AlH4)2 was achieved by low-energy ball milling with TiF4. Approximately 8.0 wt% of hydrogen was released from the Mg(AlH4)2-0.025TiF4 sample with an on-set temperature of 40 °C, which represents a decrease of 75 °C relative to pristine Mg(AlH4)2. In contrast to the three-step reaction for pristine Mg(AlH4)2, hydrogen desorption from the TiF4-doped sample involves a two-step process because the Ti-based species participates in the dehydrogenation reaction. The presence of TiF4 alters the nucleation and growth of the dehydrogenation product, significantly decreasing the activation energy barrier of the first step in the dehydrogenation of Mg(AlH4)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 TiF4-doped sample, compared with 130 °C for the additive-free sample.