Ln1−xSrxCo1−yFeyO3−δ (Ln=Pr, Nd, Gd; x=0.2, 0.3) for the electrodes of solid oxide fuel cells

Promising candidates of intermediate temperature electrodes for solid oxide fuel cells (SOFCs), Ln1−xSrxCo1−yFeyO3−δ (LSCF) (Ln=Pr, Nd, Gd; x=0.2, 0.3; 0≦y≦1) were studied for their electrical conductivity, thermal expansion rate, cathodic polarization, and reactivity with gadolinia-doped ceria (Ce0.9Gd0.1O1.95, CGO) or yttria-stabilized zirconia (YSZ). Superiorly electrical conductivity has been demonstrated for LSCF electrodes and all samples except Ln=Gd (y≧0.8) compositions demonstrate above 200 S/cm at 800 °C. The adjustment of thermal expansion rate to electrolyte, which is one of the main problems of Ln1−xSrxCoO3−δ, can be achieved to lower thermal expansion coefficient (TEC) values with more Fe substitution. Using CGO electrolytes, LSCF electrodes over the composition range of y=0.0–0.8 show high cathodic activity for oxygen reduction operating at temperatures from 700 to 900 °C and exhibit no significant dependence on the kind of lanthanide elements. These electrode behaviors are analogous to widely used La1−xSrxCo1−yFeyO3−δ, Ln1−xSrxCo1−yFeyO3−δ (Ln=Pr, Nd, Gd) systems, however, have potential advantages in reactivity with YSZ. In Ln=Pr, Nd (y=0.8) compositions, for example, the by-products of Ln2Zr2O7 and SrZrO3 are both suppressed when sintered at 1000 °C for 100 h. LSCF also yield no reaction product with CGO when sintered at 1200 °C for 36 h.