In Situ Energy-Dispersive XAS and XRD Study of the Superior Hydrogen Storage System MgH2/Nb2O5

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• 作者：Oliver Friedrichs ; Diego Martí ; nez-Martí ; nez ; Gemma Guilera ; Juan Carlos Sá ; nchez L&oacute ; pez ; Asunci&oacute ; n Ferná ; ndez
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：July 19, 2007
• 年：2007
• 卷：111
• 期：28
• 页码：10700 - 10706
• 全文大小：377K
• 年卷期：v.111,no.28(July 19, 2007)
• ISSN：1932-7455

文摘

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 Mg_xNb_yO. 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.