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Roles of Oxygen Vacancies and Excess Electron Localization on Ceria Surfaces: First Principles Study |
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PP: 217-224 |
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doi:10.18576/ijtfst/120307
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Author(s) |
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Nabil Al Aqtash,
Anas Y. Al-Reyahi,
Said M. Al Azar,
Ahmad Mufleh,
Saber S. Essaoud,
Khadidja Berarma,
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Abstract |
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| In this study, we investigate the (111), (110) and (100) surfaces of reduced ceria (CeO2) using density functional theory (DFT) within DFT+U. We examine the process by which oxygen vacancy sites form on CeO2 (111), (110), and (100) surfaces as well as the stability of these sites close to the ceria surface regions. Our calculations demonstrate that electron localizations of the reduced CeO2 on each of these three surface terminations are caused by oxygen vacancies, both surface and subsurface, which results in the emergence of Ce3+ sites. The oxygen vacancy at the surface and subsurface of CeO2 (111) surfaces results in the formation of Ce3+ at the vacancys next-closest neighbor. Ce3+ is formed at the sites closest to the oxygen vacancy sites on CeO2 (100) and CeO2 (110) surfaces. The calculated total density of states (TDOS) of the reduced surfaces displays that the Ce 4 f states are partially occupied and appeared in a new state near the band gap compared to that for the unreduced ceria surfaces. The existence of these new states was found to have a large effect on the nature of ceria. In (111) ceria surface, the material remains semiconductor with a smaller band gap. However, (110) and (100) ceria surfaces become semi-metallic due to the crossing of a new state of the fermi level that converts ceria to become semi- metallic material. Therefore, the conductivity and chemical properties of ceria are expected to be modified by the creation of oxygen vacancy. The reduced ceria expects to catalyze the dissociation of molecules on its surface. The dissociation is assisted by the oxidation of Ce3+ that is generated on reduced ceria surfaces.
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