Synthesis of LiNH2 + LiH by reactive milling of Li3N

The hydrogen sorption properties of Li3N under reactive milling conditions have been investigated in- and ex-situ as a function of polytype structure (alpha vs. beta), 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 situ Raman spectroscopy. In situ Raman 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.