Synthesis of Mg (NH2)2 and Hydrogen Storage Properties of Mg (NH2)2–LiH System
Mg(NH2)2 was synthesized by first high energy milling MgH2 powder in a 99.995% NH3 atmosphere and then heat treating at 300oC, and hydrogen storage properties of prepared Mg(NH2)2+2.2LiH (molar ratio) had been studied in the temperature range of 150-240oC. It was found that mechanical milling of Mg (NH2)2 and LiH with molar ratio 1:2.2 followed by heat treatment under static hydrogen pressure and dehydrogenating at 208.5oC yields the desired reversible hydrogen storage phase: Li2Mg(NH)2. Desorption kinetics reveal a rapid reaction for the system and the maximum hydrogen capacity can reach 4.6 wt. % at 208.5oC. The system starts to dehydrogenate at 150oC and the Arrhenius activation energy Ea of desorption reaction can be determined to be 25.8 kJ/mol H2 based on the data of kinetics. Additionally, the desorption reaction enthalpy (H) and entropy (S) are calculated to be 42.8 kJ/mol H2 and 149.2 J. K-1/ mol H2 respectively from PCI measurements.
Weiguo Pan, Jianxing Ren and Yongguang Li
K. Zhang et al., "Synthesis of Mg (NH2)2 and Hydrogen Storage Properties of Mg (NH2)2–LiH System", Advanced Materials Research, Vols. 347-353, pp. 3609-3615, 2012