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

Abstract

Hydrogen storage properties of the (nLiAlH 4 + LiNH 2 ) hydride composite where n = 1, 3, 11.5 and 30, synthesized by high energy ball milling have been investigated. The composite with the molar ratio n = 1 releases large quantities of H 2 (up to ~5 wt.%) during ball milling up to 100-150 min. The quantity of released H 2 rapidly decreases for the molar ratio n = 3 and is not observed for n = 11.5 and 30. The XRD studies indicate that the H 2 release is a result of a solid state decomposition of LiAlH 4 into (1/3)Li 3 AlH 6 + (2/3)Al + H 2 and subsequently decomposition of (1/3)Li 3 AlH 6 into LiH + (1/3)Al + 0.5H 2 . Apparently, LiAlH 4 is profoundly destabilized during ball milling by the presence of a large quantity of LiNH 2 (37.7 wt.%) in the n = 1 composite. The rate of dehydrogenation at 100-170 °C (at 1 bar H 2 ) is adversely affected by insufficient microstructural refinement, as observed for the n = 1 composite, which was milled for only 2 min to avoid H 2 discharge during milling. XRD studies show that isothermal dehydrogenation of (nLiAlH 4 + LiNH 2 ) occurs by the same LiAlH 4 decomposition reactions as those found during ball milling. The ball milled n = 1 composite stored under Ar at 80 °C slowly discharges large quantities of H 2 approaching 3.5 wt.% after 8 days of storage.

Mechano-chemical synthesis of manganese borohydride (Mn(BH4)2) and inverse cubic spinel (Li2MnCl4) in the (nLiBH4 + MnCl2) (n = 1, 2, 3, 5, 9 and 23) mixtures and their dehydrogenation behavior

“…Recently, it has been reported for the first time by Varin et al that a few ball milled LiAlH 4 -based mixtures combined with nanometric-size metal catalysts [18,24], complex hydride LiNH 2 [25] and a MnCl 2 catalytic precursor [33] continuously self-discharge H 2 when stored for a prolonged time in glass vials at a temperature range from room temperature (RT) to 80 C under slight overpressure of high purity argon. In order to find out if the same phenomenon occurs for the present (nLiBH 4 þ MnCl 2 ) mixtures, first of all, a ball milled (2LiBH 4 þ MnCl 2 ) mixture, which according to reaction (6) and Fig.…”

Mechanochemical modification of LiAlH4 with Fe2O3 - A combined DFT and experimental study

“…LiAlH4 is a focus of research in the last decade, due to its outstanding properties: high gravimetric and volumetric density and easy synthesis [1]. Its theoretical capacity is 10.6 wt% H2 [2] and 7.9 wt% H2, for the first and the second decomposition stage [3].…”

Mechanical and Thermal Dehydrogenation of the Mechano-Chemically Synthesized Calcium Alanate (Ca(AlH4)2) and Lithium Chloride (LiCl) Composite

“…It is to be pointed out that the mechano-chemical synthesis was carried out in the present work using a Fritsch Pulverisette 7 planetary mill. The milling energy generated by this type of mill is relatively modest by comparison with the magneto-mill Uni-Ball Mill 5 used for inducing a profound mechanical dehydrogenation reported in [ 3 , 4 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ]. In addition, the milling time up to 5 h used in the present work might have been too short to provide a sufficient milling energy input per gram of powder (kJ/g) to induce more pronounced mechanical dehydrogenation in a Fritsch Pulverisette 7 planetary mill.…”

“…In the past years, novel hydride systems that are capable of rapid generation of H 2 at the ambient and low temperatures have been synthesized. So far, we found, that the hydride/hydride [ 6 , 7 , 8 , 9 ] and hydride/halide [ 6 , 7 , 8 , 9 ] mixtures were capable of mechanical dehydrogenation of about 4 wt % H 2 after injecting a quite low ball milling energy at the ambient temperature. A few other hydrides also released the quantity of 4 wt % H 2 although at lower mechanical dehydrogenation rates [ 6 , 10 , 11 , 12 ].…”