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

Abstract

Abstract Stepwise solid‐state reaction between LiNH 2 and LiAlH 4 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 LiNH 2 –LiAlH 4 (2:1) after mechanical ball milling. The transformation of tetrahedral [AlH 4 ] – in LiAlH 4 to the octahedral [AlH 6 ] 3– in Li 3 AlH 6 is observed after ball milling LiAlH 4 with LiNH 2 . Al–N bonding is identified by using solid‐state 27 Al 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 Li 3 AlN 2 H 4 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 Li 3 AlN 2 . More than 5 wt % hydrogen can be reversibly stored by Li 3 AlN 2 . The hydrogenated sample contains LiNH 2 , LiH, and AlN. The role of AlN in the reversible hydrogen storage over Li–Al–N–H is discussed.