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CO₂-tolerant (Y,Tb)Ba(Co,Ga)₄O₇ cathodes with low thermal expansion for solid oxide fuel cells

Lai, Ke-Yu, Manthiram, Arumugam
Journal of materials chemistry A 2019 v.7 no.14 pp. 8540-8549
air, barium, barium carbonate, carbon dioxide, catalysts, catalytic activity, cathodes, electrochemistry, fuel cells, oxygen, strontium, strontium carbonate, thermal expansion
Oxide catalysts with alkaline earth metal dopants, such as Sr²⁺ and Ba²⁺, are widely applied as cathode materials in intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, one of the irreversible performance degradation mechanisms is the formation of BaCO₃ and SrCO₃ on the cathode surface when CO₂ in air reacts with the cathode. This study presents a series of CO₂-tolerant swedenborgite oxides (Y,Tb)Ba(Co,Ga)₄O₇₊δ with high catalytic activity and relatively low thermal expansion coefficients (TECs, 9.2–10.2 × 10⁻⁶ K⁻¹). The doping effect of Tb and Ga on the phase stability in air and CO₂-containing air is comprehensively investigated. Unlike the >500% increase in area-specific resistance (ASR) of Co-containing perovskite oxides exposed to 5% CO₂ in air in the literature, the ASRs of (Y,Tb)Ba(Co,Ga)₄O₇₊δ–Gd-doped ceria (GDC) composite cathodes only increase by ∼120% at 600 °C. In addition, the ASRs recover to their initial values after switching the gas back to pure air within 1 h, indicating good CO₂ tolerance and recovery capability. The low number of oxygen vacancies in (Y,Tb)Ba(Co,Ga)₄O₇₊δ might explain the high CO₂ tolerance compared to Co-containing perovskite materials. Furthermore, a high electrochemical performance of 1.17 W cm⁻² at 700 °C is demonstrated with an anode-supported single cell and Y₀.₅Tb₀.₅BaCo₃.₂Ga₀.₈O₇₊δ–GDC composite cathode.