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 LiBH 4 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 [LiNH 2 –2 LiBH 4 ]. That is different from the dehydrogenation pathway of 2 Mg(NH 2 ) 2 –3 LiH sample without LiBH 4 , 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.