Effects of trivalent dopants on phase stability and catalytic activity of YBaCo 4 O 7 -based cathodes in solid oxide fuel cells

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 6; no. 34; pp. 16412 - 16420
• Main Authors: Lai, Ke-Yu, Manthiram, Arumugam
• Format: Journal Article
• Language: English
• Published: 2018
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/C8TA01230J

In order to understand the doping and co-doping effects of trivalent cations (Al 3+ , Ga 3+ , and Fe 3+ ) in the swedenborgite oxide YBaCo 4 O 7 as a cathode in intermediate-temperature solid oxide fuel cells (IT-SOFCs), four series of YBaCo 4 O 7 -based materials, including YBaCo 4−x Al x O 7+δ , YBaCo 4−x−y Ga x Al y O 7+δ , YBaCo 3.2 Ga 0.8−x Fe x O 7+δ , and YBaCo 3.5−x Al 0.5 Fe x O 7+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 YBaCo 4−x Al x O 7+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 YBaCo 3.2 Ga 0.8 O 7+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 YBaCo 3.2 Ga 0.7 Fe 0.1 O 7 –Ce 0.8 Gd 0.2 O 1.9 composite cathode reached 1.0 W cm −2 with H 2 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.