Intermediate species and kinetics of lithium imide decomposition

The decomposition of lithium imide (Li2NH) is an important step for hydrogen storage in Li3N. In this paper, the decomposition of Li2NH was investigated by using temperature-programmed decomposition (TPD) and X-ray diffraction (XRD) techniques. It was found that the decomposition of Li2NH produced Li, N2 and H2 via two steps: Li2NH into an intermediate species—Li4NH and then into Li. The kinetic analysis of Li2NH decomposition showed that the activation energies are 533.6 kJ/mol for the first step and 754.2 kJ/mol for the second step. Furthermore, XRD demonstrated that the Li4NH, which was generated in the decomposition of Li2NH, formed a solid solution with Li2NH. In the solid solution, Li4NH possesses a similar cubic structure as Li2NH. The lattice parameter of the cubic Li4NH is 0.5033 nm.

► Decomposition of Li2NH produced Li, N2 and H2 via intermediate species—Li4NH.
► Li2NH to Li4NH is 2nd-order decomposition with activation energy of 533.6 kJ/mol.
► Li4NH generated in Li2NH decomposition could form a solid solution with Li2NH.
►  In Li2NH/Li4NH solid solution, Li4NH possesses a similar cubic structure as Li2NH.