Oxygen reduction and transport on the La1-xSrxCo1-yFeyO3-δ cathode in solid oxide fuel cells: a first-principles study
Oxygen reduction and transport on the La1-xSrxCo1-yFeyO3-δ cathode in solid oxide fuel cells: a first-principles study
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DOI：
10.1039/c3ta11554b
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发表时间：
2013-01-01
影响因子：
11.9
通讯作者：
Lu, Yalin
中科院分区：
文献类型：
--
作者：
Wang, Zhenbin;Peng, Ranran;Lu, Yalin
氧还原和阴极上的连续迁移是固体氧化物燃料电池的关键步骤。在这项工作中，我们基于密度泛函理论计算，系统地研究了氧物质在La1-xSrxCo1-yFeyO3（LSCF）阴极上的吸附、解离、掺入和连续扩散。我们发现O-2分子更喜欢吸附在B位（Fe或Co）的过渡金属原子上而不是A位（La或Sr）的过渡金属原子上。氧分子在表面过渡金属原子上形成超氧化物(O-2(-))或过氧化物(O-2(2-))物质，它们之间的异构化能垒能小于0.14 eV。 SrCo封端表面具有最小的氧空位形成能，表面氧空位的存在促进了B位原子上的氧解离，且没有能垒。相反，如果没有表面氧空位，Co 位点上的氧解离需要克服 0.30 eV 的能垒，而 Fe 位点上的氧离解约为 0.14 eV。计算的最小能量路径表明，氧在表面迁移的能垒远高于含有氧空位的本体中的能垒。此外，提高Co浓度将有效促进氧空位的形成，大大增强氧的整体传输。我们的研究全面了解了 LSCF 阴极上氧还原和迁移的机制。
Oxygen reduction and successive migration on a cathode are key steps in solid oxide fuel cells. In this work, we have systematically studied the adsorption, dissociation, incorporation, and successive diffusion of oxygen species on the La1-xSrxCo1-yFeyO3 (LSCF) cathode on the basis of density-functional theory calculation. We found that the O-2 molecule prefers to be adsorbed on the transition metal atoms at the B site (Fe or Co) than those at the A site (La or Sr). The oxygen molecule forms either superoxide (O-2(-)) or peroxide (O-2(2-)) species on the surface transition metal atoms, and the isomerisation energy barrier energies between them are less than 0.14 eV. The SrCo-terminated surface has the smallest oxygen vacancy formation energy, and the existence of surface oxygen vacancy promotes the oxygen dissociation on the B-site atom without an energy barrier. Instead, without the surface oxygen vacancy, the oxygen dissociation on the Co site needs to overcome an energy barrier of 0.30 eV, while that on the Fe site is about 0.14 eV. The calculated minimum energy pathways indicate that the energy barrier of oxygen migration on the surface is much higher than that in the bulk which contains the oxygen vacancy. Moreover, increasing the concentration of Co will effectively facilitate the formation of oxygen vacancy, greatly enhancing the oxygen bulk transport. Our study presents a comprehensive understanding of the mechanism of oxygen reduction and migration on the LSCF cathode.