Effect of LiCl presence on the hydrogen storage performance of the Mg(NH sub(2)) sub(2)-2LiH composite

• Published in: RSC advances Vol. 5; no. 84; pp. 68542 - 68550
• Main Authors: Gamba, N S, Arneodo Larochette, P, Gennari, F C
• Format: Journal Article
• Language: English
• Published: 01.08.2015
• Subjects: Cycles; Dehydrogenation; Deterioration; Formations; Hydrogen storage; Hydrogen storage materials; Nanostructure; Reaction kinetics
• ISSN: 2046-2069
• DOI: 10.1039/c5ra12241d

The Mg(NH sub(2)) sub(2)-2LiH composite is a promising hydrogen storage material due to its favourable thermodynamics and hydrogen storage reversibility. However, its application is restricted owing to the presence of severe kinetic barriers. In the present work, the Mg(NH sub(2)) sub(2)-2LiH was synthesized by metathesis reaction of LiNH sub(2) plus MgCl sub(2) and posterior milling with LiH. LiCl is a co-product that operates as a separation phase favouring the nanostructure of the composite. The synthesized material exhibits good dehydrogenation rate and approximately the theoretical hydrogen storage capacity at 200 degree C. However, the formation of Li sub(4)(NH sub(2)) sub(3)Cl and the incomplete rehydrogenation of Li sub(2)Mg sub(2)(NH sub(2 )) sub(3) are progressively favoured during successive hydrogen cycling, deteriorating the storage properties. Two competitive reactions can simultaneously occur involving LiNH sub(2) as an intermediate phase: the formation of Li sub(4)(NH sub(2)) sub(3)Cl using the co-product LiCl and the complete dehydrogenation of Li sub(2)Mg sub(2)(NH sub(2 )) sub(3) leading to the Li sub(2)Mg(NH) sub(2) formation. The worst effect of Li sub(4)(NH sub(2)) sub(3)Cl formation was simultaneously demonstrated by kinetics and PCI measurements. The amide-chloride phase was actually the active species for the deterioration of dehydrogenation kinetics and hydrogen storage capacity of the Li-Mg-N-H-Cl system.