Improved kinetics of the Mg(NH2)2–2LiH system by addition of lithium halides

Abstract

The Mg(NH₂)₂–2LiH composite is a promising on-board hydrogen storage material due to its high reversible hydrogen capacity and suitable thermodynamic properties. However, the severe kinetic barrier inhibits its low temperature operation. In the present work, the additive effects of lithium halides on the Mg(NH₂)₂–2LiH system were studied systematically. Experimental results showed that, among all those lithium halides, the LiBr doped Mg(NH₂)₂–2LiH composite exhibited the best dehydrogenation performance. The hydrogen sorption and desorption rates of the Mg(NH₂)₂–2LiH–0.2LiBr sample are ∼3 and 2 times, respectively, faster than that of the pristine sample at 140 °C. At the same time, enhanced kinetics for hydrogen desorption was observed from an activation energy (E_a) of ca. 92 ± 9 kJ mol⁻¹ which was significantly decreased by 35 kJ mol⁻¹ compared with the pristine sample. Subsequently, a plausible mechanism for the modified dehydrogenation/re-hydrogenation process was proposed.