Hydrogen desorption processes in Li–Mg–N–H systems Original Research Article

Li–Mg–N–H systems composed of Mg(NH2)2 and LiH with various ratios can reversibly store a large amount of hydrogen under the temperature condition above 150 °C. These composites with 3:6, 3:8 and 3:12 ratio of Mg(NH2)2 and LiH have been independently reported by four groups as promising candidates of high performance hydrogen storage materials possessing the reversibility and the high capacity. In any cases, an interaction between NH3 and LiH plays an important role for the progress of hydrogen desorbing and absorbing reactions. For the hydrogen desorption process, the NH3 molecule generated from Mg(NH2)2 reacts with LiH, forming LiNH2 and H2. Especially, under an equilibrium condition, in situ diffraction results indicated that the single phase of LiNH2·MgNH (LiMgN2H3) could be generated other than the separated two phases. As a next step, the NH3 molecule generated from LiNH2 reacts with LiH, desorbing H2. As a result, the dehydrogenated phase was evaluated to be Li2NH·MgNH (Li2MgN2H2) or separated two phases, in which the final phase should depend on the experimental conditions. Thus, if the amount of LiH is enough to react with NH3, the hydrogen desorption processes are described by the NH3 generation from the corresponding amides and the imide.