Superior catalysis of NbN nanoparticles with intrinsic multiple valence on reversible hydrogen storage properties of magnesium hydride

Magnesium hydride, as a potential solid state hydrogen carrier has attracted great attention around the world especially in the energy storage domain due to the high hydrogen storage capacity and the good cycling stability. But kinetic and thermodynamic barriers also impede the practical application and development of MgH2. Nanoscale catalysts are deemed to be the most effective measure to overcome the kinetic barrier and lower the temperature required for hydrogen release in MgH2. NbN nanoparticles (similar to 20 nm) with intrinsic Nb3+ -N and Nb5+ -N were prepared using the molten salt method and used as catalysts in the MgH2 system. It is found that the NbN nanoparticles exhibit a superior catalytic effect on de/rehydrogenation kinetics for the MgH2/Mg system. About 6.0 wt% hydrogen can be liberated for the MgH2+5NbN sample within 5 min at 300 degrees C, and it takes 12 min to desorb the same amount of hydrogen at 275 degrees C. Meanwhile, the MgH2+5NbN sample can absorb 6.0 wt% hydrogen within 16 min at 150 degrees C, and absorb 5.0 wt% hydrogen within 24 min even at 100 degrees C. Particularly, the catalyzed samples exhibit excellent hydrogen absorption/desorption kinetic stability. After multiple cycles, there is no kinetic attenuation and the hydrogen capacity remains at about 6.0 wt%. It is demonstrated that the NbN nanoparticles with intrinsic multiple valence can be the critical effect in improving the hydrogen storage kinetics of MgH2. The stability of Nb4N3 phase and Nb-3+ -N and Nb5+ -N valence states can ensure a stable catalytic effect in the system. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.