Portal de Periódicos da CAPES

Ternary Mg-Nb-H polyhydrides under high pressure

2021; American Physical Society; Volume: 104; Issue: 22 Linguagem: Inglês

10.1103/physrevb.104.224510

2469-9977

Xilong Dou, Xiao‐Yu Kuang, Weiguo Sun, Gang Jiang, Cheng Lü, Andreas Hermann,

Ammonia Synthesis and Nitrogen Reduction

Magnesium based alloys are promising solid materials for hydrogen storage. However, it is a real challenge to synthesise hydrogen storage materials with high hydrogen storage capacity and low dehydrogenation temperature. Here, we have performed extensively structural searches for ternary magnesium-based hydrogen storage compounds of ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{n}$ with n ranging from 16 to 25 by calypso method and first-principles calculations. We readily identified the experimentally observed ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{16}$ hydride and uncovered a stable stoichiometry of ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{19}$ with high hydrogen storage capacity of 6.7 wt% and low dehydrogenation temperature of 273 K. The remarkable decrease of the hydrogen release temperature is attributed to the atomic rearrangements in ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{19}$, which forms H-H pairs and has weakened metal-hydrogen chemical bonds compared to the stable ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{16}$ and $\mathrm{Mg}{\mathrm{H}}_{2}$ compounds. Our calculations show that ${\mathrm{Mg}}_{7}\mathrm{Nb}{\mathrm{H}}_{16}$ undergoes a structural phase transition from its $P\overline{4}2m$ phase to a $Fm\overline{3}m$ phase at 75 GPa, and the $Fm\overline{3}m$ phase is a potential polyhydride superconductor. The present findings offer insights for understanding the hydrogen storage and release of Mg-Nb-H ternary magnesium-based hydrogen storage compounds, which open avenues for the design and synthesis of magnesium-based hydrogen storage material.