Catalytic properties on the hydrogen desorption process of metallic additives dispersed in the MgH2 matrix

Composite transition metal (TM)-doped magnesium samples (TM = Nb, Fe and Zr) were produced by r.f. magnetron sputtering. The hydrogen desorption kinetics of the TM-doped MgH2 samples was studied by Sievert analysis and its thermal stability by thermal desorption spectroscopy (TDS). Energy dispersive spectroscopy (EDS) analysis indicates that the additive is contained in the magnesium bulk at 10(-2) atomic concentration. The microstructural characterization of the sample was carried out by X-rays diffraction spectroscopy (XRD) and the obtained spectra indicate that, in the activated MgH2 samples, the TM additive is contained in form of nanosized clusters. TDS spectra and isothermal H-2 desorption curves indicate that the TM nanoclusters dispersed in the MgH2 matrix reduce its thermal stability and accelerate the H-2 desorption kinetics as compared to the pure MgH2 samples. The improved H-2 desorption properties can be explained by the presence of extended interfaces between MgH2 and TM nanoclusters acting as heterogeneous nucleation sites, with reduced activation energy, for the h-Mg phase and fast diffusion channels for H migrating atoms. (C) 2006 Elsevier B.V. All rights reserved.