Ammonia-Mediated Model for Hydrogen Desorption

Usually, it is very difficult to understand the appearance ofthe first order solid-solid reaction [14], because the reaction rate can be controlled by the diffusion process of elements between the solid phases and/or the growth of the nuclei of the Li2NH 

Using this NH3-mediated model, the reaction between LiH and Mg(NH2)2 can also be explained, with the Li+ cation being supplied from LiH after the reaction between LiH and NH3. Here, we discuss the transformation of the phases during the dehydrogenating reaction processes in the Li-Mg-N-H systems. Rijssenbeek et al. [81], for the case of Li/Mg = 6/3 , determined three new imide crystal structures by high-resolution X-ray and neutron diffraction, identifying a new family of imides with formula LLt 2xMgx(NH)2 (up to 6 mass% of H2, at 220°C). 

Luo et al. [25] studied the case of Li/Mg = 6/3 and characterized the products at several points on the PC isotherm and proposed the reactions as follo-ws  

For the case of Li/Mg = 8/3 , Nakamura et al. determined the phase of Li2.6MgN2Di 4 as a dehydrogenated state (in vacuum conditions, at 200 °C) by using synchrotron radiation (SR)-X-ray and neutron diffraction [109]. For Li/Mg = 6/3, 8/3, 12/3 systems, Aoki et al. performed PC-isotherm measurements only for the dehydrogenation at 250 °C and observed the complex imide Li2Mg(NH)2 as a dehydrogented state by SR-XRD [110]. Considering all these experimental results, the reaction steps of the Li-Mg-N-H system can be stated as below, 

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