Nb2O5 "pathway effect" on hydrogen sorption in Mg

In the present work we investigate the hydrogen sorption mechanism in a MgH2/Nb2O5 composite and analyze why Nb2O5 could strongly improve hydrogen sorption kinetics in magnesium. Hereby we make use of the fact that Nb2O5 nanoparticles are able to reduce the milling time significantly with the achievement of excellent sorption kinetics, and can so exclude effects occurring at long-term milling that make difficult the study of the mechanism. On the basis of extensive chemical, crystalline, and microstructural characterization of the MgH2/Nb2O5 nanopowder system, a "pathway model" is proposed, which explains the kinetic hydrogen sorption improvement by a formation of pathways of niobium oxide species with lower oxidation state that facilitate the hydrogen transport into the sample. This mechanism is shown to be supported by additional oxidation experiments, which indicate increased oxygen diffusion through these pathways.