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

Abstract

TiH2 was introduced into the 4MgH2-NaAlH4 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 4MgH2-NaAlH4-TiH2 is at around 100 °C, which is lower by 50 °C than that of 4MgH2-NaAlH4. The investigation by Kissinger's method indicates that 4MgH2-NaAlH4-TiH2 possesses much lower activation energy (68 kJ mol−1) than 4MgH2-NaAlH4 (159 kJ mol−1), indicating an enhanced dehydrogenation kinetics due to the additional TiH2. TiH2 catalyzes the decomposition of MgH2 and NaAlH4, respectively, and also the reaction between their products during the dehydrogenation process below 375 °C. At temperatures above 375 °C, TiH2 will react with Mg17Al12 to form Al3Ti and liberate contained hydrogen. TiH2 also improved the isothermal hydrogenation kinetics of 4MgH2-NaAlH4 desorbed system. The activation energy of re-hydrogenation for 4MgH2-NaAlH4-TiH2 system was greatly reduced from 161.62 kJ mol−1 H2 to 125.80 kJ mol−1 H2 of 4MgH2-NaAlH4. The kinetics enhancement of hydrogen absorption is probably due to the intermediate phase Al3Ti, which is beneficial to the recombination of MgH2.