title: Synthesis and decomposition of Li3Na(NH2)4 and investigations of Li-Na-N-H based systems for hydrogen storage.
abstract: 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 3LiNH2-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 °C, as observed by in situ powder X-ray diffraction. Above 234 °C, Li3+xNa1-x(NH2)4 releases a mixture of NH3, N2 and H2 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 4LiNH2-NaH-3LiH during mechanochemical treatment and releases 4.2 wt% of H2 in multiple steps between 25 and 340 °C as revealed by Sievert's measurements. All three investigated composites have a lower peak temperature for H2 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.
authors.affiliation: Center for Materials Crystallography, Interdisciplinary Nanoscience Center and Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark. trj@chem.au.dk.
authors.forename: Lars H
authors.initials: LH
authors.lastname: Jepsen
authors.forename: Peikun
authors.initials: P
authors.lastname: Wang
authors.forename: Guotao
authors.initials: G
authors.lastname: Wu
authors.forename: Zhitao
authors.initials: Z
authors.lastname: Xiong
authors.forename: Flemming
authors.initials: F
authors.lastname: Besenbacher
authors.forename: Ping
authors.initials: P
authors.lastname: Chen
authors.forename: Torben R
authors.initials: TR
authors.lastname: Jensen