Compositional flexibility in Li–N–H materials: implications for ammonia catalysis and hydrogen storage

Abstract

Li-N-H materials, particularly lithium amide and lithium imide, have been explored for use in a variety of energy storage applications in recent years. Compositional variation within the parent lithium imide,...

Lithium–nitrogen–hydrogen systems for ammonia synthesis: exploring a more efficient pathway using lithium nitride–hydride

“…S3, ESI†). This corresponds to the observed upper limit of nitride–hydride incorporation into the solid solution; 20 further formation of stoichiometric Li 4 NH appears to result in rapid hydrogenation to LiH (Fig. S3, ESI†), which reduces the ammonia productivity in subsequent cycles.…”

“…This builds on our recent work where we highlighted the implications of compositional variation in the Li-N-H system for hydrogen storage and ammonia catalysis. 20 More precisely, we revealed the formation of a solid solution with a highly disordered anti-fluorite structure for mixed lithium amide-imide (Li 2Àx NH 1+x , 0 o x o 1) and lithium imide-nitride-hydride (Li 2+x NH, 0 o x o 2) phases. 20 While the former is more extensively studied from a hydrogen storage and release standpoint, 21 the latter solid solution with nitridehydride character is of interest to this study, considering the reported involvement of hydridic hydrogen in electron and hydrogen transfer during ammonia synthesis.…”

“…20 More precisely, we revealed the formation of a solid solution with a highly disordered anti-fluorite structure for mixed lithium amide-imide (Li 2Àx NH 1+x , 0 o x o 1) and lithium imide-nitride-hydride (Li 2+x NH, 0 o x o 2) phases. 20 While the former is more extensively studied from a hydrogen storage and release standpoint, 21 the latter solid solution with nitridehydride character is of interest to this study, considering the reported involvement of hydridic hydrogen in electron and hydrogen transfer during ammonia synthesis. 16 Lithium nitride-hydride (Li 4 NH) was synthesized by heating a ball-milled mixture of lithium nitride (Li 3 N) and LiH in a microwave reactor (Experimental section, ESI †) 22 and subsequently subject to a chemical looping ammonia synthesis process.…”

“…23–25 Instead, a phase with an Fm 3̄ m structure and a varying lattice parameter value in the range of 4.93 to 5.03 Å is emblematic of a lithium imide–nitride–hydride solid solution, with a lattice parameter towards the higher end indicating an imide-rich solution. 20 A small amount of the Fm 3̄ m phase is present in the as-synthesized Li 4 NH sample, but with a much lower lattice parameter of 4.9339(6) Å, representing very slightly off-stoichiometry lithium nitride–hydride. 20 These assignments are corroborated by Raman spectroscopy.…”

“…20 A small amount of the Fm 3̄ m phase is present in the as-synthesized Li 4 NH sample, but with a much lower lattice parameter of 4.9339(6) Å, representing very slightly off-stoichiometry lithium nitride–hydride. 20 These assignments are corroborated by Raman spectroscopy. While the spectrum of the parent Li 4 NH has sharp features at low wavenumbers corresponding to phonon modes of the nitride–hydride phase, the same features are much broader and less well-defined for the sample after reaction under nitrogen (Fig.…”