A process for synthesizing the Li–Mg–N–H hydrogen storage system from Mg and LiNH2

We successfully established a method to synthesize the Li–Mg–N–H hydrogen storage system composed of Mg(NH2)2 and LiH from Mg and LiNH2 as starting materials. First of all, Mg and Li2NH were homogeneously mixed by ball-milling for 2 h under 1 MPa argon atmosphere. After that, the mixture was heat-treated at 250 °C for 16 h under vacuum condition to be transformed into Mg3N2 and Li2NH. Target materials, Mg(NH2)2 and LiH, were synthesized by a further heat-treatment for Mg3N2 and Li2NH at 200 °C under 10 MPa hydrogen atmosphere for 12 h. The phases in the sample at each processing stage were examined by X-ray diffraction (XRD) and Fourier transformation infrared absorption measurements and confirmed to be the expected ones. From experimental results of a thermal desorption mass spectroscopy, the final hydrogenated sample indicated that ∼7 mass% hydrogen was desorbed starting from about 150 °C and peaked around 230 °C under helium flow condition at 5 °C/min heating rate without ammonia emission in our experimental accuracy.