Reversible hydrogen storage in AlH ₃ −LiNH ₂ system

Abstract As a hydrogen storage material, both AlH 3 and LiNH 2 possess a high hydrogen capacity. However, the dehydrogenated AlH 3 can hardly absorb hydrogen under normal conditions, while LiNH 2 will generate NH 3 rather than H 2 upon decomposition. In this work, we report that the combination of AlH 3 and LiNH 2 through simple ball milling leads to partial reversibility of the AlH 3 −LiNH 2 system and the suppression of NH 3 liberation. The negatively charged H δ − in AlH 3 will react with the positively charged H δ + in LiNH 2 through a redox reaction to form Li 2 NH, AlN, and H 2 at 120−170 °C. After dehydrogenation at above 270 °C, Li 3 AlN 2 is generated, which is crucial for the reversibility of this system. The more the Li 3 AlN 2 generated, the better the reversibility of this system. The dehydrogenation capacity of AlH 3 + 2LiNH 2 at the third cycle (3.0 wt%) is higher than that of AlH 3 + LiNH 2 (1.2 wt%) due to the generation of more Li 3 AlN 2 . The role of AlH 3 /Al in the AlH 3 −LiNH 2 system is to fix the nitrogen into the form of AlN and Li 3 AlN 2 and thus suppress the liberation of NH 3 . Therefore, the synergy of AlH 3 and LiNH 2 leads to the reversibility of the Li–Al–N–H system and the suppression of NH 3 .