Effect of gas back pressure on hydrogen storage properties and crystal structures of Li2Mg(NH)2

•The crystal structure of Li2Mg(NH)2 is associated with the gas back pressure.•Hydrogen storage properties of Mg(NH2)2–2LiH depend on the gas back pressure.•Mechanism of hydrogen storage property depended on gas back pressure is discussed.

The ternary imide Li2Mg(NH)2 is considered to be one of the most promising on-board hydrogen storage materials due to its high reversible hydrogen capacity of 5.86 wt%, favorable thermodynamic properties and good cycling stability. In this work, Li2Mg(NH)2 was synthesized by dynamically dehydrogenating a mixture of Mg(NH2)2–2LiH up to 280 °C under different gas (Ar and H2) and pressures (0–9.0 bar). The crystal structure of Li2Mg(NH)2 was found to depend on the gas back pressure in the dehydrogenation process. The crystal structure of Li2Mg(NH)2 and the dehydrogenation/rehydrogenation properties of the Mg(NH2)2–2LiH system strongly depend on the gas back pressure in the dehydrogenation process due to the effect of the pressure on the dehydrogenation kinetics. This study provides a new approach for improving the hydrogen storage properties of the amide–hydride systems.