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

Abstract

Isothermal hydrogen absorption properties of the ball milled mixture of 3Mg(NH 2 ) 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(NH 2 ) 2 under 9 MPa at 200 • C, while those were observed as mixed phases of LiH and LiNH 2 at 150 • C without any trace of Mg(NH 2 ) 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.

Evaluation of the enthalpy change due to hydrogen desorption for M–N–H (M = Li, Mg, Ca) systems by differential scanning calorimetry

“…This result is shown as a slope in the PCI curve after a well-defined plateau area [27,34], and the products can be termed as 3Li 1þx MgN 2 H 3ex (x: 0 / 1.7) [35] during this process. A similar non-stoichiometric variation was found in the LieNeH system as well [36].…”

“…This method is useful for conventional metal-hydrogen systems (M þ (x/2)H 2 4 MH x ) with moderate reaction kinetics. However, the accurate and precise evaluation of DH values for complex hydrogen storage materials composed of light elements is difficult [21,27] because these systems often reveal complicated reaction processes such as phase separation. Moreover, a long time, which sometimes extends to a couple of weeks, is necessary to reach an equilibrium state due to the slow kinetics.…”

Preparation and hydrogen storage properties of an Li-Mg-N-H system

“…Unfortunately, its enthalpy change is too large for practical application. Since then, many related studies on similar hydrogen storage systems such as Li-Mg-N-H [8,9] , Li-Na-N-H [10] , Li-Ca-N-H [11] , and Mg-Na-N-H [12] have been performed in an effort to improve the dehydrogenation/rehydrogenation behavior of the Li-N-H system. Of these systems, Li-Mg-N-H is regarded as one of the most promising, due to its high hydrogen storage capability, appropriate enthalpy of dehydrogenation/ rehydrogenation and good reversibility.…”

Improved hydrogen storage performance of Li–Mg–N–H materials by optimizing composition and adding single-walled carbon nanotubes

“…Correspondingly, the enthalpy change of the dehydrogenation reaction was decreased from about 60 kJ/mol for LiNH 2 /LiH to 40 kJ/mol for Mg(NH 2 ) 2 /LiH [2,3]. Therefore, the Li-Mg-N-H system rapidly attracts intensive interests as a promising hydrogen storage medium [4][5][6][7][8][9][10].…”