Effects of Stoichiometry on the H$_{2}$-Storage Properties of Mg(NH$_{2}$)$_{2}$-LiH-LiBH$_{4}$ Tri-Component Systems

The hydrogen desorption pathways and storage properties of 2 Mg(NH$_2$)$_2$–3 LiH–xLiBH$_4$ samples (x=0, 1, 2, and 4) were investigated systematically by a combination of pressure composition isotherm (PCI), differential scanning calorimetric (DSC), and volumetric release methods. Experimental results showed that the desorption peak temperatures of 2 Mg(NH$_2$)$_2$–3 LiH–xLiBH$_4$ samples were approximately 10–15 °C lower than that of 2 Mg(NH$_2$)$_2$–3 LiH. The 2 Mg(NH$_2$)$_2$–3 LiH–4 LiBH$_4$ composite in particular began to release hydrogen at 90 °C, thereby exhibiting superior dehydrogenation performance. All of the LiBH$_4$-doped samples could be fully dehydrogenated and re-hydrogenated at a temperature of 143 °C. The high hydrogen pressure region (above 50 bar) of PCI curves for the LiBH$_4$-doped samples rose as the amount of LiBH4 increased. LiBH$_4$ changed the desorption pathway of the 2 Mg(NH$_2$)$_2$–3 LiH sample under a hydrogen pressure of 50 bar, thereby resulting in the formation of MgNH and molten [LiNH2–2 LiBH4]. That is different from the dehydrogenation pathway of 2 Mg(NH$_2$)$_2$–3 LiH sample without LiBH4, which formed Li$_2$Mg$_2$N$_3$H$_3$ and LiNH$_2$, as reported previously. In addition, the results of DSC analyses showed that the doped samples exhibited two independent endothermic events, which might be related to two different desorption pathways