The enhanced de/re-hydrogenation performance of 4MgH2-NaAlH4 composite by doping with TiH2

TiH 2 was introduced into the 4MgH 2 -NaAlH 4 composite by ball milling to improve the dehydrogenation and re-dehydrogenation performance of the composite. The non-isothermal dehydrogenation curve shows that the onset temperature of hydrogen release from 4MgH 2 -NaAlH 4 -TiH 2 is at around 100 °C, which is lower by 50 °C than that of 4MgH 2 -NaAlH 4 . The investigation by Kissinger's method indicates that 4MgH 2 -NaAlH 4 -TiH 2 possesses much lower activation energy (68 kJ mol −1 ) than 4MgH 2 -NaAlH 4 (159 kJ mol −1 ), indicating an enhanced dehydrogenation kinetics due to the additional TiH 2 . TiH 2 catalyzes the decomposition of MgH 2 and NaAlH 4 , respectively, and also the reaction between their products during the dehydrogenation process below 375 °C. At temperatures above 375 °C, TiH 2 will react with Mg 17 Al 12 to form Al 3 Ti and liberate contained hydrogen. TiH 2 also improved the isothermal hydrogenation kinetics of 4MgH 2 -NaAlH 4 desorbed system. The activation energy of re-hydrogenation for 4MgH 2 -NaAlH 4 -TiH 2 system was greatly reduced from 161.62 kJ mol −1 H 2 to 125.80 kJ mol −1 H 2 of 4MgH 2 -NaAlH 4 . The kinetics enhancement of hydrogen absorption is probably due to the intermediate phase Al 3 Ti, which is beneficial to the recombination of MgH 2 .