Kinetics and Thermodynamics of H2O Dissociation on Reduced CeO2(111)

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• 作者：Heine A. Hansen ; Christopher Wolverton
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：November 26, 2014
• 年：2014
• 卷：118
• 期：47
• 页码：27402-27414
• 全文大小：685K
• ISSN：1932-7455

文摘

We use density functional theory to investigate the reaction between reduced CeO_2鈥?i>x(111) and water. H₂O dissociation to hydroxyl is facile on surface vacancies and lattice oxygen, while subsequent decomposition of hydroxyl into H₂ has a high barrier, which results in reversible adsorption of H₂O under ultra-high-vacuum conditions. The barrier to H₂ formation through hydroxyl decomposition decreases by 0.2 eV, while H₂O formation becomes more difficult at high hydroxyl coverage. However, on isolated oxygen vacancies on a hydroxyl covered surface, H₂ may be produced through a CeH intermediate with a 1.14 eV barrier. Oxygen vacancies are found to be more stable in the subsurface than in the surface layer at all vacancy coverages and for hydroxyl coverages less than 25鈥?0%. The competition of H₂O desorption and vacancy diffusion from the subsurface to the surface may prevent formation of hydroxyl from H₂O dosing at low temperature, while the highly stable hydroxyl phase may provide a thermodynamic driving force for further surface reduction in the presence of water. On the basis of our calculations we suggest substitutional doping with a cation that binds H stronger than Ce may improve the decomposition of hydroxyls into hydrogen.