New amide–chloride phases in the Li–Al–N–H–Cl system: formation and hydrogen storage behaviour

Abstract

New amide–chloride phases were successfully synthesized by mechanical milling of the LiNH₂–AlCl₃ mixture at a molar ratio of 1 : 0.11 and further heating at 150 °C under argon (0.1 MPa) or under hydrogen pressure (0.7 MPa). Powder X-ray diffraction measurements as a function of milling time increase revealed that the milling of the LiNH₂–0.11AlCl₃ mixture results in the formation of a FCC solid solution with an excess of LiNH₂. Subsequent heating of the LiNH₂–0.11AlCl₃ sample ball milled for 5 hours at 150 °C under argon or under hydrogen induces the appearance of an amide–chloride phase isostructural with cubic Li₄(NH₂)₃Cl. This Li–Al–N–H–Cl phase transforms progressively into the trigonal phase after prolonged heating at 300 °C under hydrogen pressure. The thermal behaviour of the amide–chloride without and with LiH addition displays dissimilar decomposition pathways. The decomposition of amide–chloride alone involves the formation of ammonia and hydrogen from 120 to 300 °C. Conversely, the amide–chloride material in the presence of LiH only releases hydrogen avoiding the emission of ammonia. The resultant material is able to be rehydrogenated under moderate conditions (300 °C, 0.7 MPa H₂), providing a new reversible hydrogen storage system.