Dynamic Octahedral Breathing in Oxygen-Deficient Ba0.9Co0.7Fe0.2Nb0.1O3-δ Perovskite Performing as a Cathode in Intermediate-Temperature SOFC
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- 作者：Yudong Gong ; Chunwen Sun ; Qiu-an Huang ; Jose Antonio Alonso ; Maria Teresa Fernández-Díaz ; Liquan Chen
- 刊名：Inorganic Chemistry
- 出版年：2016
- 出版时间：March 21, 2016
- 年：2016
- 卷：55
- 期：6
- 页码：3091-3097
- 全文大小：444K
- ISSN：1520-510X
文摘
Ba0.9Co0.7Fe0.2Nb0.1O3-δ outperforms as a cathode in solid-oxide fuel cells (SOFC), at temperatures as low as 700–750 °C. The microscopical reason for this performance was investigated by temperature-dependent neutron powder diffraction (NPD) experiments. In the temperature range of 25–800 °C, Ba0.9Co0.7Fe0.2Nb0.1O3-δ shows a perfectly cubic structure (a = a0), with a significant oxygen deficiency in a single oxygen site, that substantially increases at the working temperatures of a SOFC. The anisotropic thermal motion of oxygen atoms considerably rises with T, reaching Beq ≈ 5 Å2 at 800 °C, with prolate cigar-shaped, anisotropic vibration ellipsoids that suggest a dynamic breathing of the octahedra as oxygen ions diffuse across the structure by a vacancies mechanism, thus implying a significant ionic mobility that could be described as a molten oxygen sublattice. The test cell with a La0.8Sr0.2Ga0.83Mg0.17O3-δ electrolyte (∼300 μm in thickness)-supported configuration yields a peak power density of 0.20 and 0.40 W cm–2 at temperatures of 700 and 750 °C, respectively, with pure H2 as fuel and ambient air as oxidant. The electrochemical impedance spectra (EIS) evolution with time of the symmetric cathode fuel cell measured at 750 °C shows that the Ba0.9Co0.7Fe0.2Nb0.1O3-δ cathode possesses a superior ORR catalytic activity and long-term stability. The mixed electronic–ionic conduction properties of Ba0.9Co0.7Fe0.2Nb0.1O3-δ account for its good performance as an oxygen-reduction catalyst.