Mechanism of hydrogenation reaction in the Li-Mg-N-H system

The Li-Mg-N-H system composed of 3 Mg(NH2)2 and 8 LiH reversibly desorbs/absorbs approximately 7 wt % of H2 at 120-200 degrees C and transforms into 4 Li2NH and Mg3N2 after dehydrogenation. In this work, the mechanism of the hydrogenation reaction from 4 Li2NH and Mg3N2 to 8 LiH and 3 Mg(NH2)2 was investigated in detail. Experimental results indicate that 4 Li2NH is first hydrogenated into 4 LiH and 4 LiNH2. At the next step, 4 LiNH2 decomposes into 2 Li2NH and 2 NH3, and the emitted 2 NH3 reacts with (1/2) Mg3N2 and produces the (3/2) Mg(NH2)2 phase, while the produced 2 Li2NH is hydrogenated into 2 LiH and 2 LiNH2 again. Such successive steps continue until all 4 Li2NH and Mg3N2 completely transform into 8 LiH and 3 Mg(NH2)2 by hydrogenation.