Effect of AlCl3 additive on Li-N-H hydrogen storage properties

L. FERNÁNDEZ ALBANESI; S. GARRONI; F. C. GENNARI; S. ENZO; P. NOLIS; M. D. BARÓ

Roma

Conferencia; ISMANAM 2018, 25th International Symposium on Metastable, amorphous and nanostructured Materials; 2018

ISMANAM 2018, 25TH INTERNATIONAL SYMPOSIUM ON METASTABLE, AMORPHOUS AND NANOSTRUCTURED MATERIALS

Combination of light metal amides with hydrides represents one of the most valid approach for generating promising systems for solid-state hydrogen storage with favorable thermodynamic stability and hydrogen storage reversibility. Among them, the LiNH2 -LiH system is one of the most attractive lightweight composites for hydrogen storage thanks to their high gravimetric capacity of 6.5 wt%. However, the temperature required for its re-hydrogenation is still too high for any real application as storage material. For these reasons, different efforts have been addressed on incorporating additives to destabilize the Li-N-H system. Significant improvement of the hydrogen sorption properties of the LiNH2 -LiH system, has been achieved, for example, by introducing AlCl3 in the initial mixture by ball milling [1-2]. The new substituted amide displays improved hydrogen storage properties with respect to the pristine Li-N-H system. Additionally, the concurrent incorporation of AlCl3 and the presence of LiH are effective for mitigating the ammonia release, which is responsible for the loss of the hydrogen storage capacity. In the light of the above-mentioned facts and considering that AlCl3 is a well-known Lewis acid and both LiNH2 and LiH are Lewis bases, it is plausible to expect a competitive and free-activated reaction for the couple LiNH2 -AlCl3 and LiH-AlCl3 in the ternary system LiNH2 ?LiH?AlCl3 . Therefore, understanding of the reactivity involved at the beginning of these reactions results a crucial step for gain relevant information on the mechanism formation of the new Al-based halide amide phases and their precursors. In this work a detailed study on the structural modification and phase evolution in the hand-milled samples, is reported for the system LiNH2 ?1.6LiH?xAlCl3 . The samples have been systematically investigated by X-ray powder diffraction, FTIR and NMR measurements. It is demonstrated that the reaction between LiNH2 -LiH and AlCl3 takes place at room temperature in the ternary system without ball milling and thermochemical activation. Furthermore, a competitive reaction between LiNH2 -AlCl3 and LiH-AlCl3 is also confirmed. From these reactions, LiAlCl4 and NH4 Cl are detected and their formation achieved under unexpected conditions.