Effects of La doping on electrical conductivity, thermal expansion and electrochemical performance in LaxSr1-xCo0.9Sb0.1O3-δ cathodes for IT-SOFCs

Perovskite oxides LaxSr1-xCo0.9Sb0.1O3-δ (LSCSbx, x=0.0-0.8) are investigated as IT-SOFC cathodes supported with La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) electrolyte. All LSCSbx oxides have a tetragonal distorted perovskite structure with s.g. P4/mmm, while a La2Co2O5 impurity phase was observed within La doping levels at x=0.6-0.8. The LSCSb0.4 has a good chemical compatibility with LSGM electrolyte for temperatures up to 1050 °C. XPS examinations indicate the existence of Co3+/Co4+ mixed valence states in LSCSbx. The conductivity increases with La doping and the LSCSbx with x=0.4 exhibits the highest electrical conductivity (e.g., 673-1637 S cm−1 at 300-850 °C). The thermal expansion coefficient (TEC) decreases from 25.89×10-6 K-1 for x=0.0 to 18.5×10-6 K-1 for x=0.6 at 30-900 °C. Among the LSCSbx compositions, the LSCSb0.2 exhibits the lowest polarization resistance (Rp), which is merely 0.069 Ω cm2 at 700 °C. The maximum power density of the cell with LSCSb0.2 cathode on 300 µm thick LSGM electrolyte attains 564 mW cm-2 at 850 °C, which is higher than that of SrCo0.9Sb0.1O3-δ (SCSb) cathode. All of the results indicate that LSCSb0.2 is a promising material for application in IT-SOFCs cathodes.