Effects of Bi-doping on structure and properties of YBaCo2O5+ layered perovskite cathode for intermediate-temperature solid oxide fuel cells

Layered perovskite oxides, Y _1–xBi _xBaCo ₂O _5+δ (YBBC x, x = 0.0–0.2) were investigated as cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results indicate the YBBC x could be indexed to a tetragonal phase with trace of 3 × 3 × 1 superstructure configuration. No significant change in thermal expansion coefficients (TECs) was detected with the Bi-doping, and the TECs were 15.7–16.8 × 10 ⁻⁶ K ⁻¹ at 100–935 °C in air. Although the Bi-doping results in a decrease in conductivity of the YBBC x, the x = 0.2 sample still shows higher conductivity than that of a standard SOFC cathode (∼100 S cm ⁻¹). Additionally, the Bi-doping leads to an enhancement in the electrochemical performance mainly due to improved ion and electron charge transfers. Among the YBBC x compositions, the YBBC _0.2 cathode shows the lowest polarization resistance ( R _p) of 0.034 Ω cm ² at 700 °C. For a single cell with 300 µm thick La _0.9Sr _0.1Ga _0.8Mg _0.2O _3–δ (LSGM) and YBBC _0.2 cathode, a peak power density ( P _max) of 537 mW cm ⁻² at 700 °C was achieved with no significant deterioration in performance after a 100–h testing.