First-Principles Assessment of H2S and H2O Reaction Mechanisms and the Subsequent Hydrogen Absorption on the CeO2(111) Surface

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• 作者：Dario Marrocchelli ; Bilge Yildiz
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：January 26, 2012
• 年：2012
• 卷：116
• 期：3
• 页码：2411-2424
• 全文大小：782K
• 年卷期：v.116,no.3(January 26, 2012)
• ISSN：1932-7455

文摘

The main goal of this study is to assess the resistance of ceria against hydrogen penetration into its bulk, in the context of its application as a protective surface coating against hydrogen embrittlement in metals. We evaluate the reaction mechanisms between the H₂S and H₂O molecules and the CeO₂(111) surface and their kinetic descriptors, using first principles based calculations in the density functional theory framework. Our approach is validated by performing an extensive comparison with the available experimental data. We predict that hydrogen penetration into CeO₂(111) is a surface-absorption-limited process with a high-energy barrier (1.67 eV) and endothermicity (1.50 eV), followed by a significantly lower bulk dissolution energy and diffusion barrier (0.67 and 0.52 eV, respectively). We find that the presence of surface vacancies and higher coverages affects significantly the energetics of H₂S/H₂O adsorption, dissociation, and hydrogen subsurface absorption, facilitating most of these processes and degrading the protectiveness of ceria against hydrogen penetration. The reasons behind these effects are discussed. Overall we expect ceria to hinder the hydrogen incorporation significantly due to the effectively large energy barrier against subsurface absorption, provided vacancy formation is suppressed.