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 Mg₉₅Ni₅with 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 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 Mg²⁺ existed in Mg₉₅Ni₅ doped with Nb₂O₅ or NbF_5. 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.