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(NH2 )2 -3 LiH-xLiBH4 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(NH2 )2 -3 LiH-xLiBH4 samples were approximately 10-15 °C lower than that of 2 Mg(NH2 )2 -3 LiH. The 2 Mg(NH2 )2 -3 LiH-4 LiBH4 composite in particular began to release hydrogen at 90 °C, thereby exhibiting superior dehydrogenation performance. All of the LiBH4 -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 LiBH4 -doped samples rose as the amount of LiBH4 increased. LiBH4 changed the desorption pathway of the 2 Mg(NH2 )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(NH2 )2 -3 LiH sample without LiBH4 , which formed Li2 Mg2 N3 H3 and LiNH2 , 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.