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 NbN0.9O0.1 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.