Microscopic Study on Hydrogenation Mechanism of MgH₂ Catalyzed by Nb₂O₅

Abstract

We propose the microstructural change model of magnesium hydride catalyzed by Nb₂O₅ during hydrogenation. The ball-milled composites, MgH₂ and 1 mol% Nb₂O₅, were dehydrogenated and then rehydrogenated for varied time at room temperature under 0.1 MPa H₂ atmosphere. The crystallite size of Mg and MgH₂ was evaluated by powder X-ray diffraction (XRD) measurement and confirmed by transmission electron microscopy (TEM) observation. The crystallite size of generated MgH₂ was smaller than that of Mg and did not change significantly with increasing time of hydrogenation. It is suggested that the number density of MgH₂ crystallites increases during the hydrogenation process.