Synthesis of LiNH2 + LiH by reactive milling of Li3N

Abstract

The hydrogen sorption properties of Li₃N under reactive milling conditions have been investigated in- and ex-situ as a function of polytype structure (α vs. β), focusing on the influence of the micro-structure and/or the crystal structure upon hydrogen uptake. LiNH₂ and LiH were synthesized by reactive milling of Li₃N at 20 bar hydrogen pressure for 4 h. Reactive milling represents a quick and effective technique to produce LiNH₂ by hydrogenation of Li₃N at low hydrogen pressure and without any need for heating. As to our knowledge, we present a full hydrogenation of Li₃N under the aforementioned conditions for the first time. The (de)hydrogenation and rehydrogenation behaviour of milled amides was evaluated using a combination of powder X-ray diffraction, differential scanning calorimetry, thermogravimetry and in situRaman spectroscopy. In situRaman spectroscopy showed a shift in the lithium amide stretching modes upon hydrogenation supporting a non-stoichiometric storage mechanism consistent with the literature. The microstructure and polytype composition of the Li₃N dehydrogenated materials had no effect on the hydrogenation products and only minor effects on the hydrogen uptake profile during milling.