Catalytic mechanism of Nb2O5 and NbF5 on the dehydriding property of Mg95Ni5 prepared by hydriding combustion synthesis and mechanical milling

The catalytic mechanism of Nb2O5 and NbF5 on the dehydriding property of Mg95Ni5 prepared by hydriding combustion synthesis and mechanical milling (HCS+MM) was studied. It was shown that NbF5 was more efficient than Nb2O5 in improving the dehydriding property. In particular, the dehydriding temperature onset decreases from 460 K for Mg95Ni5 to 450 K for Mg95Ni5 with 2.0 at.% Nb2O5, whereas it decreases to 410 K for that with 2.0 at.% NbF5. By means of X-ray diffraction and X-ray photcelectron spectroscopy, it was confirmed that the interaction between the Nb ions and the H atoms and that between the anions (O2- or F-) and Mg2+ existed in Mg95Ni5 doped with Nb2O5 or NbF5. Further, the pressure-concentration-isotherms analysis clarified that these interactions destabilized the Mg-H bonding, and that NbF5 had a better effect on the destabilization of the Mg-H bonding than Nb2O5 contributing to the better dehydriding property Of (Mg95Ni5)2.0-NbF5. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.