Effect of Li₃N additive on the hydrogen storage properties of Li-Mg-N-H system

The effect of Li₃N additive on the Li-Mg-N-H system was examined with respect to the reversible dehydrogenation performance. Screening study with varying Li₃N additions (5, 10, 20, and 30 mol%) demonstrates that all are effective for improving the hydrogen desorption capacity. Optimally, incorporation of 10 mol% Li₃N improves the practical capacity from 3.9 wt% to approximately 4.7 wt% hydrogen at 200 °C, which drives the dehydrogenation reaction toward completion. Moreover, the capacity enhancement persists well over 10 de-/rehydrogenation cycles. Systematic x-ray diffraction examinations indicate that Li₃N additive transforms into LiNH₂ and LiH phases and remains during hydrogen cycling. Combined structure/property investigations suggest that the LiNH₂ “seeding” should be responsible for the capacity enhancement, which reduces the kinetic barrier associated with the nucleation of intermediate LiNH₂. In addition, the concurrent incorporation of LiH is effective for mitigating the ammonia release.