Hydrogen absorption properties of Li-Mg-N-H system

Isothermal hydrogen absorption properties of the ball milled mixture of 3Mg(NH2)2 and 8LiH after dehydrogenation at 200 °C under high vacuum were investigated at two different temperatures of 150 and 200 °C. The pressure-composition isotherm (PCT) curve at 200 °C revealed a two-plateaus-like behavior, while the PCT curve at 150 °C showed a single-plateau-like behavior. The hydrogenated phases were composed of LiH and Mg(NH2)2 under 9 MPa at 200 °C, while those were observed as mixed phases of LiH and LiNH2 at 150 °C without any trace of Mg(NH2)2 in XRD measurements. These results indicate that there are two-step hydrogenation processes corresponding to high and low pressures at 200 °C, but the kinetics at 150 °C is too slow to proceed with the second hydrogenating step at high pressure region.