Effects of trivalent dopants on phase stability and catalytic activity of YBaCo4O7-based cathodes in solid oxide fuel cells

In order to understand the doping and co-doping effects of trivalent cations (Al3+, Ga3+, and Fe3+) in the swedenborgite oxide YBaCo4O7 as a cathode in intermediate-temperature solid oxide fuel cells (IT-SOFCs), four series of YBaCo4O7-based materials, including YBaCo4−xAlxO7+δ, YBaCo4−x−yGaxAlyO7+δ...

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Bibliographic Details
Published in:Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2018, Vol.6 (34), p.16412-16420
Main Authors: Ke-Yu, Lai, Arumugam Manthiram
Format: Article
Language:English
Subjects:
Aluminum
Catalysis
Catalytic activity
Cathodes
Cations
Chemical reduction
Dopants
Doping
Electrode materials
Electrolytic cells
Fuel cells
Fuel technology
High temperature
Iron
Oxygen reduction reactions
Phase stability
Solid oxide fuel cells
Stability analysis
Substitution reactions
Thermal expansion
Thermal stress
X-ray diffraction
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Summary:In order to understand the doping and co-doping effects of trivalent cations (Al3+, Ga3+, and Fe3+) in the swedenborgite oxide YBaCo4O7 as a cathode in intermediate-temperature solid oxide fuel cells (IT-SOFCs), four series of YBaCo4O7-based materials, including YBaCo4−xAlxO7+δ, YBaCo4−x−yGaxAlyO7+δ, YBaCo3.2Ga0.8−xFexO7+δ, and YBaCo3.5−xAl0.5FexO7+δ, have been synthesized and investigated. The long-term phase stability has been evaluated by X-ray diffraction after the samples were annealed at 600–800 °C under ambient air for 120 h. Although Al has been suggested to have better phase stabilization capability than Ga in the literature, severe decomposition above 700 °C occurs in all the YBaCo4−xAlxO7+δ samples. Fe has much weaker phase stabilization capability than Al and Ga, but excellent phase stability is still maintained with a small substitution of Fe for Ga. All the materials with a stable phase at high temperatures exhibit well-matched thermal expansion coefficients (8.0–9.5 × 10−6 K−1) with common electrolyte materials, which alleviates the thermal stress during the SOFC operation. In comparison to YBaCo3.2Ga0.8O7+δ, a partial substitution of Ga by Fe enhances the catalytic activity for the oxygen reduction reaction. In addition, the performance of the anode-supported single cell with the YBaCo3.2Ga0.7Fe0.1O7–Ce0.8Gd0.2O1.9 composite cathode reached 1.0 W cm−2 with H2 fuel at 700 °C. Thus, this work provides a guideline on trivalent dopants for developing swedenborgite-based cathode materials with a high phase stability and catalytic activity in IT-SOFCs.
ISSN:2050-7488
2050-7496
DOI:10.1039/c8ta01230j