Nitrogen-stimulated superior catalytic activity of niobium oxide for fast full hydrogenation of magnesium at ambient temperature

Magnesium hydride (MgH₂) is one of the most promising high-capacity hydrogen storage materials. However, limited progress has been made in storing hydrogen in Mg under ambient conditions. Here, we demonstrate for the first time that the dehydrogenated MgH₂ is fully hydrogenated below 100 °C with the presence of N-containing Nb₂O₅ (N-Nb₂O₅). MgH₂ composites doped with N-Nb₂O₅ (10 wt%) releases hydrogen from 170 °C, which is lowered by 130 °C compared with pristine MgH₂, while still having 6.3 wt% hydrogen capacity available. Most importantly, full hydrogenation can be achieved by the dehydrogenated N-Nb₂O₅-containing sample at temperature as low as 70 °C under 50 atm of hydrogen, which is superior to other known catalyst-doped MgH₂ systems. The in-situ formed NbN_0.9O_0.1 plays the critical catalyst role due to the joint action of N and Nb as elucidated by density functional theory (DFT) calculations. This finding remarkably facilitates the future design and exploration of much higher-performance catalysts for room-temperature hydrogen storage in metal hydrides.