Hydrogen Release and Structural Transformations in LiNH2-MgH2 Systems

Reactive hydride composites are good candidates for solid hydrogen storage due to their high gravimetric capacity, cyclability, and suitable thermodynamic properties. The LiNH2- MgH2 system is promising as changes in stoichiometry and milling conditions may result in tailoring of these properties. In this work, LiNH2-MgH2 with different ratios (Li2:Mg, Li:Mg) and ball milling conditions (100, 600 rpm) were investigated. Thermal desorption profiles shows hydrogen release starting at 125 °C for Li2:Mg 600 sample and at 225 °C for Li:Mg 600 sample, while for Li:Mg 100 sample simultaneous hydrogen and ammonia release at 175 °C is observed. In-situ synchrotron X-ray diffraction shows the related structural transformations, such as formation of Mg(NH2)2 and allotropic transformation of a into ß-Li2Mg(NH)2 for Li2:Mg 600 sample at 350 °C or direct formation of ß- Li2Mg(NH)2 for Li:Mg 100 sample at 370 °C. Different polymorphs of the LiMgN phase were also observed during cooling for these two samples. For the Li:Mg 600 sample, transformation occurs in a unique reaction from an unknown phase into ß-Li2Mg(NH)2 at 290 °C. The unknown phase is indexed as a Fm-3m cubic similar to the high temperature gamma-Li2Mg(NH)2.

POTTMAIER Daphiny;  DOLCI Francesco;  ORLOVA Maria;  VAUGHAN Gavin;  FICHTNER Maximilan;  LOHSTROH Wiebke;  BARICCO Marcello; 

2011-11-30

ELSEVIER SCIENCE SA

JRC61200

0925-8388,   

http://www.sciencedirect.com/science/article/pii/S0925838810026964,    https://publications.jrc.ec.europa.eu/repository/handle/JRC61200,   

10.1016/j.jallcom.2010.10.166,