Identifying the O(2) Diffusion and Reduction Mechanisms on CeO(2) Electrolyte in Solid Oxide Fuel Cells: A DFT plus U Study

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题名:	Identifying the O(2) Diffusion and Reduction Mechanisms on CeO(2) Electrolyte in Solid Oxide Fuel Cells: A DFT plus U Study
作者:	Chen, HL (Chen, Hui-Lung) Chen, HT (Chen, Hsin-Tsung) Chang, JG (Chang, Jee-Gong) Ju, SP (Ju, Shin-Pon)
贡献者:	化學系
关键词:	density functional theory CeO(2) SOFC oxygen reduction oxygen diffusion
日期:	2009
上传时间:	2011-11-28 15:27:28 (UTC+8)
摘要:	The interactions and reduction mechanisms of O(2) molecule on the fully oxidized and reduced CeO(2) surface were studied using periodic density functional theory calculations implementing on-site Coulomb interactions (DFT + U) consideration. The adsorbed O(2) species on the oxidized CeO(2) surface were characterized by physisorption. Their adsorption energies and vibrational frequencies are within -0.05 to 0.02 eV and 1530-1552 cm(-1) respectively. For the reduced CeO(2) surface, the adsorption of O(2) on Ce(4+), one-electron defects (Ce(3+) on the CeO(2) surface) and two-electron defects (neutral oxygen vacancy) can alter geometrical parameters and results in the formation of surface physisorbed O(2), O(2)(a-) (0 < a < 1), superoxide (O(2)(-)), and peroxide (O(2)(2-)) species. Their corresponding adsorption energies are -0.01 to -0.09, -0.20 to -0.37, -1.34 and -1.86 eV, respectively. The predicted vibrational frequencies of the peroxide, superoxide, O(2)(a-) (0 < a < 1) and physisorbed species are 897, 1234, 1323-1389, and 1462-1545 cm(-1), respectively, which are in good agreement with experimental data. Potential energy profiles for the O(2) reduction on the oxidized and reduced CeO(2) (111) surface were constructed using the nudged elastic band method. Our calculations show that the reduced surface is energetically more favorable than the unreduced surface for oxygen reduction. In addition, we have studied the oxygen ion diffusion process on the surface and in bulk ceria. The small barrier for the oxygen ion diffusion through the subsurface and bulk implies that ceria-based oxides are high ionic conductivity at relatively low temperatures which can be suitable for IT-SOFC electrolyte materials. (C) 2009 Wiley Periodicals, Inc. J Comput Chem 30: 2433-2442, 2009
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