Synthesis and decomposition of Li3Na(NH2)(4) and investigations of Li-Na-N-H based systems for hydrogen storage

摘要

Previous studies have shown modified thermodynamics of amide-hydride composites by cation substitution, while this work systematically investigates lithium-sodium-amide, Li-Na-N-H, based systems. Li3Na(NH2)(4) has been synthesized by combined ball milling and annealing of 3LiNH(2)-NaNH2 with LiNa2(NH2)(3) as a minor by-product. Li3+xNa1-x(NH2)(4) releases NaNH2 and forms non-stoichiometric Li3+xNa1-x(NH2)(4) before it melts at 234 degrees C, as observed by in situ powder X-ray diffraction. Above 234 degrees C, Li3+xNa1-x(NH2)(4) releases a mixture of NH3, N-2 and H-2 while a bi-metallic lithium sodium imide is not observed during decomposition. Hydrogen storage performances have been investigated for the composites Li3Na(NH2)(4)-4LiH, LiNH2-NaH and NaNH2-LiH. Li3Na(NH2)(4)-4LiH converts into 4LiNH(2)-NaH-3LiH during mechanochemical treatment and releases 4.2 wt% of H-2 in multiple steps between 25 and 340 degrees C as revealed by Sievert's measurements. All three investigated composites have a lower peak temperature for H-2 release as compared to LiNH2-LiH, possibly owing to modified kinetics and thermodynamics, due to the formation of Li3Na(NH2)(4) and LiNa2(NH2)(3).