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

Layered perovskite oxides, Y1-xBixBaCo2O5+delta (YBBCx, x = 0.0-0.2) were investigated as cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results indicate the YBBCx could be indexed to a tetragonal phase with trace of 3 x 3 x 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 x 10(-6) K-1 at 100-935 degrees C in air. Although the Bi-doping results in a decrease in conductivity of the YBBCx, the x = 0.2 sample still shows higher conductivity than that of a standard SOFC cathode (similar to 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 YBBCx compositions, the YBBC0.2 cathode shows the lowest polarization resistance (R-p) of 0.034 Omega cm(2) at 700. C. For a single cell with 300 mu m thick La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM) and YBBC0.2 cathode, a peak power density (P-max) of 537 mW cm(-2) at 700 degrees C was achieved with no significant deterioration in performance after a 100-h testing.