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), Ln(1 - x)Sr(x)Co(1 - y)Fe(y)O(3 - delta) (LSCF) (Ln = Pr, Nd, Gd; x = 0.2, 0.3; 0 less than or equal to y less than or equal to 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 greater than or equal to 0.8) compositions demonstrate above 200 S/cm at 800 degreesC. The adjustment of thermal expansion rate to electrolyte, which is one of the main problems of Ln(1-x)Sr(x)CoO(3 - delta), 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 degreesC and exhibit no significant dependence on the kind of lanthanide elements. These electrode behaviors are analogous to widely used La1 - xSrxCo1 - yFeyO3 - delta, Ln(1 - x)Sr(x)Co(1 - y)Fe(y) O3 - delta (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 Ln(2)Zr(2)O(7) and SrZrO3 are both suppressed when sintered at 1000 degreesC for 100 h. LSCF also yield no reaction product with CGO when sintered at 1200 T for 36 h. (C) 2002 Elsevier Science B.V. All rights reserved.