| Abstract
| - By in situ energy-dispersive X-ray absorption spectroscopy (EDXAS) and X-ray diffraction (XRD), we analyzedthe evolution of niobium in a MgH2/Nb2O5 system based on high-energy ball milling during hydrogen cycling.The high time resolution of the EDXAS method allowed us to monitor fast sample changes during this process.Thereby, we demonstrated that the Nb2O5 is already partially reduced during the milling process with theMgH2. Further reduction occurs during the heating and cycling processes, in which a lower limit of oxidationstate is reached. Hereby, a reaction between the niobium oxide and the Mg/MgH2 leads to a decrease ofcrystalline Nb2O5 and the formation of a ternary oxide phase MgxNbyO. During the cycling processes a repetitiveNb oxidation−reduction process was observed, which may indicate hydrogen diffusion along the ternaryoxide by the formation of metastable niobium hydrides. This points to a mechanism of kinetic sorptionimprovement by diffusion of hydrogen through pathways of ternary Mg−Nb oxides, which may also reducethe activation energy of the Mg−MgH2 transition.
|
