Reindarstellung und Kristallstruktur von Lithiumnitridhydrid, Li4NH, Li4ND

Compositional flexibility in Li-N-H materials: implications for ammonia catalysis and hydrogen storage

Li–N–H materials, particularly lithium amide and lithium imide, have been explored for use in a variety of energy storage applications in recent years. Compositional variation within the parent lithium imide, anti-fluorite crystal structure has been related to both its facile storage of hydrogen and impressive catalytic performance for the decomposition of ammonia. Here, we explore the controlled solid-state synthesis of Li–N–H solid-solution anti-fluorite structures ranging from amide-dominated (Li_4/3(NH₂)_2/3(NH)_1/3 or Li_1.333NH_1.667) through lithium imide to majority incorporation of lithium nitride–hydride (Li_3.167(NH)_0.416N_0.584H_0.584 or Li_3.167NH). Formation of these solid solutions is demonstrated to cause significant changes to the thermal stability and ammonia reactivity of the samples, highlighting the potential use of compositional variation to control the properties of the material in gas storage and catalytic applications.

A wide solid solution based on the lithium imide anti-fluorite structure is demonstrated and related to its energy storage functions.

Isotopic studies of the ammonia decomposition reaction using lithium imide catalyst

¹⁵N-Labelled ammonia decomposition experiments over lithium imide catalyst reveal a bulk-surface mechanism via a lithium-rich phase.

Rapid Microwave Synthesis, Characterization and Reactivity of Lithium Nitride Hydride, Li₄NH

Lithium nitride hydride, Li₄NH, was synthesised from lithium nitride and lithium hydride over minute timescales, using microwave synthesis methods in the solid state for the first time. The structure of the microwave-synthesised powders was confirmed by powder X-ray diffraction [tetragonal space group I4₁/a; a = 4.8864(1) Å, c = 9.9183(2) Å] and the nitride hydride reacts with moist air under ambient conditions to produce lithium hydroxide and subsequently lithium carbonate. Li₄NH undergoes no dehydrogenation or decomposition [under Ar_(g)] below 773 K. A tetragonal-cubic phase transition, however, occurs for the compound at ca. 770 K. The new high temperature (HT) phase adopts an anti-fluorite structure (space group Fm 3̅ m; a = 4.9462(3) Å) with N^3- and H^- ions disordered on the 4a sites. Thermal treatment of Li₄NH under nitrogen yields a stoichiometric mixture of lithium nitride and lithium imide (Li₃N and Li₂NH respectively).

In situ powder neutron diffraction study of non-stoichiometric phase formation during the hydrogenation of Li3N

The hydrogenation of Li3N at low chemical potential has been studied in situ by time-of-flight powder neutron diffraction and the formation of a non-stoichiometric Li4-2xNH phase and Li4NH observed. The results are interpreted in terms of a model for the reaction pathway involving the production of Li4NH and Li2NH, which subsequently react together to form Li4-2xNH. Possible mechanisms for the production of Li4NH from the hydrogenation of Li3N are discussed.