Reversible Hydrogen Storage by a Li–Al–N–H Complex

Abstract

Stepwise solid‐state reaction between LiNH2 and LiAlH4 at a molar ratio of 2:1 is investigated in this paper. It is observed that approximately four H atoms are evolved from a mixture of LiNH2–LiAlH4 (2:1) after mechanical ball milling. The transformation of tetrahedral [AlH4]– in LiAlH4 to the octahedral [AlH6]3– in Li3AlH6 is observed after ball milling LiAlH4 with LiNH2. Al–N bonding is identified by using solid‐state 27Al nuclear magnetic resonance (NMR) measurements. The NMR data, together with the results of X‐ray diffraction and Fourier transform IR measurements, indicate that a Li–Al–N–H intermediate with the chemical composition of Li3AlN2H4 forms after ball milling. Heating the post‐milled sample to 500 °C results in the liberation of an additional four H atoms and the formation of Li3AlN2. More than 5 wt % hydrogen can be reversibly stored by Li3AlN2. The hydrogenated sample contains LiNH2, LiH, and AlN. The role of AlN in the reversible hydrogen storage over Li–Al–N–H is discussed.

Role of aluminum chloride on the reversible hydrogen storage properties of the Li–N–H system

“…Indeed, these wave numbers are still high (above 3200 cm À1 ) to account for an imide formation. Similar bands were previously reported by Xiong et al [28] due to the formation of an intermediate with the proposed Li 3 AlN 2 H 4 chemical composition during dehydrogenation of 2LiNH 2 eLiAlH 4 . Additionally, analogous bands were observed after 48 h of milling of the LiAl(NH 2 ) 4 :4LiH mixture [29] and after 24 h of milling of the Li 2 AlH 6 eLiNH 2 mixture [10].…”

Large Amount of Hydrogen Desorption from the Mixture of Mg(NH2)2 and LiAlH4

“…XRD measurement shows the formation of Li 3 AlN 2 and Mg 3 N 2 . However, AlN was difficult to distinguish probably due to the poor crystallization as previously reported. , By summarizing the characterization results the overall reaction of Mg(NH 2 ) 2 −LiAlH 4 (1:1) can be expressed as follows: which is in good agreement with the number of hydrogen atoms (ca. 7.9) desorbed from the starting mixture and the structures identified by NMR, XRD, and FTIR.…”

Ambient temperature hydrogen desorption from LiAlH4–LiNH2 mediated by HMPA

“…The ball-to-sample weight ratio was about 30 : 1. Same as the previously reported, 16,23 no phase transformation was observed on either LiAlH 4 or LiNH 2 at the end of mechanical milling. To prevent oxygen and moisture contaminations, all the sample handlings were conducted in a MBRUM glovebox filled with purified argon.…”