Mechanochemical transformations in Li(Na)AlH4–Li(Na)NH2 systems

Mechanical and Thermal Dehydrogenation of Lithium Alanate (LiAlH4) and Lithium Amide (LiNH2) Hydride Composites

“…Furthermore, it seems that the entire quantity of H 2 desorbed during ball milling for the n = 1 composite (Figure 1b) can be easily provided by reactions (1) and (2) without invoking other reactions as claimed by Dolotko et al [10]. The fact that the diffraction peaks of LiNH 2 in the n = 1 composite persist throughout a long period of milling (Figure 2a, b) indicates that LiNH 2 does not react/decompose but most likely becomes heavily nanostructured or even partially amorphized, and in this capacity destabilizes LiAlH 4 during ball milling and enhances its decomposition according to reactions (1) and (2) without involvement of any other reactions.…”

“…However, the observed alterations in the intensities of peaks assigned to Al after 3 h milling could also, at least to some extent, be induced by severe nanostructuring/amorphization of the ball-milled composite powders. Still, the maximum desorbed quantity of 5 wt.% H 2 , reproducibly observed after 3 h of milling (Figure 1b), does not support the reaction path involving the formation of AlN which requires 6.6 wt.% H 2 as claimed by Dolotko et al [10]. The XRD patterns for the (3LiAlH 4 + LiNH 2 ) (n = 3) composite after ball milling for 2 and 15 min (Figure 2c) still indicate the presence of both LiAlH 4 , LiNH 2 and Al, the latter being a pre-existing impurity for the composite milled for 2 min.…”

“…However, in their second paper [8] on the ball milling of (0.5LiAlH 4 + LiNH 2 )(molar ratio n = 0.5) they reported that no Al peaks were detected during the milling process. In contrast, Dolotko et al [10] reported that no Al was detected in the (1LiAlH 4 + LiNH 2 ) composite during ball milling but instead they concluded that the amorphous AlN compound was formed during ball milling. On that basis, they proposed that a solid state reaction between LiAlH 4 and LiNH 2 occurred during ball milling which resulted in the formation of AlN, 2LiH and 2H 2 .…”

“…The synthesis of composite requires more energetic ball milling in order to induce an alloying of the phases within particles, an intimate contact between constituent particles and a simultaneous reduction of the particle size and the size of crystallites (grains) within the particles [2]. Xiong et al [7,8], Nakamori et al [9] and Dolotko et al [10] were the first to report decomposition of the composites (1LiAlH 4 + LiNH 2 ) (molar ratio 1:1) and (0.5LiAlH 4 giving a total capacity of 9.5 wt.% H 2 . None of these references reported systematic studies of the effect of molar ratio LiAlH 4 to LiNH 2 on behavior during ball milling and ball milling conditions on subsequent mechanical and thermal dehydrogenation.…”

Recent Progress and New Perspectives on Metal Amide and Imide Systems for Solid-State Hydrogen Storage

“…Finally, different studies have also been focused on the opportunity to improve the hydrogen storage properties of NaNH 2 by combining it with LiAlH 4 as effectively occurred for LiNH 2 [164][165][166][167]. In this context, Xiong et al proved that during ball milling a solid-state interaction between NaNH 2 and LiAlH 4 took place, leading to the formation of the tetramide Li 3 Na(NH 2 ) 4 which seems to favor the desorption at lower temperatures [166].…”