Kinetics and hydrogen storage performance of Li-Mg-N-H systems doped with Al and AlCl3

Abstract

Recent investigations showed the formation of new amide-chloride phases between LiNH 2 and AlCl 3 after milling and/or heating under hydrogen pressure. These phases exhibited a key role in the improvement of the hydrogen storage properties of the LiNH 2-LiH composite. In the present work, we studied the effects of Al and AlCl 3 additives on the hydrogen storage behavior of the Li-Mg-N-H system. The dehydrogenation kinetics and the reaction pathway of Al and AlCl 3 modified LiNH 2-MgH 2 composite were investigated through a combination of kinetic measurements and structural analyses. During the first cycle, the addition of Al catalytically accelerates the hydrogen release at 200°C. In the subsequent cycles, the formation of a new phase of unknown nature is probably responsible for both increased equilibrium hydrogen pressure and decreased dehydrogenation rate. In contrast, AlCl 3 additive reacts with LiNH 2-MgH 2 through the milling and continues during heating under hydrogen pressure. Addition of AlCl 3 leads to the formation of two cubic structures identified in the Li-Al-N-H-Cl system, which improves dehydrogenation rate by modifying the thermodynamic stability of the material. This study evidences positive effect of cation and/or anion substitution on hydrogen storage properties of the Li-Mg-N-H system.

A Review of High Density Solid Hydrogen Storage Materials by Pyrolysis for Promising Mobile Applications

“…The dehydrogenation performance and reaction pathway of LiNH 2 –MgH 2 composites were found to be enhanced by the addition of Al or AlCl 3 additives. The dehydrogenation rate of LiNH 2 –MgH 2 composites was measured to be about two or three times faster at 200 °C under 6.0 MPa hydrogen pressure with the addition of Al or AlCl 3 , respectively . The (MgNH)­(LiNH 2 ) 5 nanoclusters have been demonstrated to be a kind of promising hydrogen-storage materials by the investigation of (LiNH 2 ) 6 -LiH nanoclusters and metal (Na, K, or Mg)-cation substituted nanoclusters.…”

“…The dehydrogenation rate of LiNH 2 −MgH 2 composites was measured to be about two or three times faster at 200 °C under 6.0 MPa hydrogen pressure with the addition of Al or AlCl 3 , respectively. 313 The (MgNH)(LiNH 2 ) 5 nanoclusters have been demonstrated to be a kind of promising hydrogen-storage materials by the investigation of (LiNH 2 ) 6 -LiH nanoclusters and metal (Na, K, or Mg)-cation substituted nanoclusters. It was found that all NH 2 groups in the nanocluster were affected by Mg-cation substitution, which weakened the N−H covalent bonding and enhanced the ionic interactions between Li and the −NH 2 group.…”