Abstract
The Li-Mg-N-H system composed of Mg(NH2)2 and LiH,which was eagerly expected as one of the promising hydrogen media, was investigated. First, we examined hydrogen desorption properties and ammonia desorption properties for 3 different Mg:Li molar ratio mixtures (Mg:Li=1:2, 3:8, 1:4). As a result of examination, it was clarified that the amount of hydrogen desorption was decreasing as the Li/Mg molar ratio was increasing, and that the amount of ammonia release was much less at the operation temperature 200℃. The effect of additives on hydrogen desorption temperature in the Li-Mg-N-H system was examined in this work as well. The result indicated that vanadium chloride was the most effective additive for reduction of hydrogen desorption temperature. On the other hand, iron chloride was the worst additive. Moreover, chemical bonding state of catalytic V in the VCl2-doped Li-Mg-N-H system was examined by X-ray absorption fine structure (XAFS) measurements at SPring-8 in Japan. The V K-edge in the X-ray absorption near edge structure (XANES) profile had such a specific feature that the pre-edge existed near the Fermi energy and the valence of V was located between the 3+ and 4+ states. Similar behavior was observed in the XAFS of the Li-N-H system doped with Ti as well.
