Understanding the Decomposition Mechanisms of LiNH2, Mg(NH2)2 and NaNH2: A Joint Experimental and Theoretical Study

Metal amides are promising candidates for hydrogen storage, hydrogen production, NH3 synthesis and cracking etc. However, the decomposition behaviors and mechanisms of metal amides remain unclear. In this study, the decomposition properties of three metal amides, including LiNH2, Mg(NH2)2 and NaNH2, are studied by thermogravimetry, mass spectroscope and in-situ X-ray diffraction techniques combining with density functional theory calculations. It is found that Mg(NH2)2, LiNH2 and NaNH2 exhibit very different metal-N and N-H bond strengths, which precipitates various formations energies of different kinds of vacancies. As a result, LiNH2 releases a major amount of NH3, with a small amount of N2 at a temperature as high as 350 oC. Mg(NH2)2 releases NH3 and N2 synchronously at a temperature range of 300-400 oC without emission of H2. NaNH2 synchronously releases H2, NH3, and a small amount of N2, at a narrow temperature range of 275-290 oC. Using density functional theory calculations, the decomposition beha...