Synthesis and decomposition reactions of metal amides in metal–N–H hydrogen storage system

The synthesis and decomposition properties of some metal amides M(NH2)x such as LiNH2, NaNH2, Mg(NH2)2 and Ca(NH2)2 were investigated, which play important roles for designing a new family of metal–N–H hydrogen storage systems. Both the gas chromatographic examination and X-ray diffraction measurement indicated that the reaction between alkali or alkaline earth metal hydride MHx (such as LiH, NaH, MgH2 and CaH2) and gaseous NH3 could quickly proceed at room temperature by ball milling and the corresponding metal amides were easily synthesized in high quality. The kinetics of these kind of reactions is faster in the order of NaH > LiH > CaH2 > MgH2, which is consistent with the inverse order of electronegativity of those metals, i.e. Na < Li = Ca < Mg. The thermal decomposition properties indicated that both Mg(NH2)2 and Ca(NH2)2 decomposed and emitted NH3 at lower temperature than LiNH2.