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

Abstract Perovskite oxides La x Sr 1–x Co 0.9 Sb 0.1 O 3– δ (LSCSbx, x=0.0–0.8) are investigated as IT–SOFC cathodes supported with La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3– δ (LSGM) electrolyte. All LSCSbx oxides have a tetragonal distorted perovskite structure with s.g. P4/mmm , while a La 2 Co 2 O 5 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 Co 3+ /Co 4+ 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 ( R p ), which is merely 0.069 Ω cm 2 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 SrCo 0.9 Sb 0.1 O 3– δ (SCSb) cathode. All of the results indicate that LSCSb0.2 is a promising material for application in IT–SOFCs cathodes.