Hydrogen absorption–desorption mechanisms for the ball-milled Li3N–MgH2 (1:1) mixture

• LiMgN/2LiH is directly synthesized by a reaction of Li3N + MgH2 → LiMgN + 2LiH.
• Higher pressure results in full hydrogenation of the LiMgN/2LiH system.
• H-absorption/desorption reaction mechanisms are explained by the phase constitutes.

The Li–Mg–N–H system is a very promising hydrogen storage material due to its high capacity, reversibility and moderate operating conditions. In this work, the LiMgN/2LiH was directly synthesized by ball-milling the mixture of Li3N–MgH2 at 1:1 molar ratio by a reaction of Li3N + MgH2 → LiMgN + 2LiH. The hydrogenation/dehydrogenation properties of the as-prepared LiMgN/2LiH were investigated by a Sieverts'-type apparatus. The mixture of LiMgN/2LiH started to absorb hydrogen at 130 °C, and 2.2 wt%, 3.2 wt% hydrogen were absorbed under a pressure of 5 MPa and 10 MPa, respectively. Powder X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectrometer measurements were used to identify the phase characterizations of the products during the hydrogen absorption–desorption process. The reaction mechanism during the hydrogenation/dehydrogenation process for the Li3N–MgH2 system is discussed.