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

Abstract The catalytic mechanism of Nb 2 O 5 and NbF 5 on the dehydriding property of Mg 95 Ni 5 prepared by hydriding combustion synthesis and mechanical milling (HCS + MM) was studied. It was shown that NbF 5 was more efficient than Nb 2 O 5 in improving the dehydriding property. In particular, the dehydriding temperature onset decreases from 460 K for Mg 95 Ni 5 to 450 K for Mg 95 Ni 5 with 2.0 at.% Nb 2 O 5 , whereas it decreases to 410 K for that with 2.0 at.% NbF 5 . By means of X-ray diffraction and X-ray photoelectron spectroscopy, it was confirmed that the interaction between the Nb ions and the H atoms and that between the anions (O 2− or F − ) and Mg 2+ existed in Mg 95 Ni 5 doped with Nb 2 O 5 or NbF 5. Further, the pressure–concentration-isotherms analysis clarified that these interactions destabilized the Mg–H bonding, and that NbF 5 had a better effect on the destabilization of the Mg–H bonding than Nb 2 O 5 contributing to the better dehydriding property of (Mg 95 Ni 5 )2.0−NbF 5 .