Hydrogenation Reaction Pathways in the Systems Li₃N–H₂, Li₃N–Mg–H₂, and Li₃N–MgH₂–H₂ by in Situ X-ray Diffraction, in Situ Neutron Diffraction, and in Situ Thermal Analysis

Abstract

The phase diagram Li−Mg−N−H offers ample opportunities for potential hydrogen storage systems. Three systems based on lithium nitride, Li 3 N, were investigated by time-resolved in situ methods (thermal analysis, Xray and neutron diffraction) at temperatures up to 703 K and hydrogen gas pressures up to 9.4 MPa. Pure lithium nitride reacts in a one-step reaction to lithium amide according to Li 3 N + 2H 2 → LiNH 2 + 2LiH at 1.0 MPa hydrogen pressure. Equimolar mixtures of lithium nitride with magnesium hydride, both at 1.5 and 9.4 MPa hydrogen gas pressure, react in the same way up to 543 K, i.e., magnesium hydride does not participate in the reaction. At higher temperatures, lithium magnesium nitride is formed according to the endothermic reaction LiNH 2 + MgH 2 → LiMgN + 2H 2 at moderate (≤1.5 MPa) and via the exothermic reaction Li 3 N + MgH 2 → LiMgN + 2LiH at higher hydrogen gas pressures (5.0 MPa). Mixed imide Li 2 Mg(NH) 2 is formed when an excess of Li 3 N is used in the reaction. The hydrogenation of mixtures of lithium nitride with magnesium starts with the formation Li 2 NH and Li 4 NH, followed by the mixed imide Li 2 Mg(NH) 2 at higher temperatures and finally the formation of Mg 3 N 2 and LiH. Deuterides react accordingly.

Mechanochemistry of Metal Hydrides: Recent Advances

“…This “quasi-imide” Li 4 NH phase has however been detected by in-situ neutron diffraction at the early stage of hydrogenation during thermally driven reaction at 250 °C [143] Second, the hydrogenation path by mechanochemistry at P H2 = 9 MPa follows a two-step reaction (Reactions (20) and (21)), whereas, for the thermally-driven reaction (~200–250 °C), a single step is observed also using elevated pressures ( P H2 ≈ 1 MPa). The latter result has been evidenced in several in-situ neutron diffraction studies [144,145].…”

Superior Dehydrogenation Performance of α‐AlH3 Catalyzed by Li3N: Realizing 8.0 wt.% Capacity at 100 °C

“…Interestingly, Gereon et al explored and described the hydrogen transport process of magnesium hydride in the Li-N-H system, indicating that the possible transmission path of hydrogen can be changed by reaction between light metal hydrides and metal nitrides so as to accelerate the release process of hydrogen. [35] Inspired by those works, we introduced Li 3 N into aluminum hydride as the catalyst to concurrently decrease hydrogenreleased temperature and accelerate hydrogen-released kinetics. As a result, enhanced dehydrogenation performance and satisfactory capacity can be obtained at a lower temperature.…”

“…explored and described the hydrogen transport process of magnesium hydride in the Li–N–H system, indicating that the possible transmission path of hydrogen can be changed by reaction between light metal hydrides and metal nitrides so as to accelerate the release process of hydrogen. [ 35 ]…”

Lanthanide Ions as Local Probes in Ionic Hydrides: A Pulsed Electron Nuclear Double Resonance and Thermoluminescence Study of Eu2+-Doped Hydride Perovskites

“…Hydrides and partially hydride substituted materials are currently attracting a lot of attention. − The former show a rich chemistry with different possible bonding situations, − and the applications range from hydrogen storage − to electrochemical storage and ion conduction. ,,, Introducing hydride into materials or (partially) substituting anions by hydride can lead to significant changes in the structural, chemical, and physical properties. − ,, Even though diffraction methods are a powerful tool for the study of these compounds, − it may still be desirable to obtain additional local information in order to gain a deeper understanding of the materials. Two excellent possibilities to do so are the use of optical and paramagnetic resonance spectroscopy.…”