Metathesis of MgFeH and LiNH leading to hydrogen production at low temperatures

Mg 2 FeH 6 with a purity of up to 94.5 wt% was synthesized and its interaction with LiNH 2 was investigated in this study. It was found that Li 4 FeH 6 , normally synthesized by hydriding a mixture of LiH and Fe at 700 °C and 5.5 GPa H 2 pressure, can be formed via ball-milling Mg 2 FeH 6 and LiNH 2 under ambient conditions following the reaction of Mg 2 FeH 6 + 4LiNH 2 → Li 4 FeH 6 + 2Mg(NH 2 ) 2 , Δ H = −92.8 kJ mol −1 . The formation of Li 4 FeH 6 was confirmed by XRD, FTIR and Mössbauer spectroscopic characterization. Li 4 FeH 6 further reacts with 2Mg(NH 2 ) 2 releasing ca. 4.8 wt% H 2 at 225 °C and reabsorbing 3.7 wt% H 2 at 200 °C and 50 bar H 2 pressure. Mg(NH 2 ) 2 , LiH and Fe are the hydrogenated products. The metathesis reaction between Mg 2 FeH 6 and LiNH 2 produces Li 4 FeH 6 , which provides an alternative route for synthesizing Li 4 FeH 6 under mild conditions.