SrCo1-xSbxO3-δ perovskite oxides as cathode materials in solid oxide fuel cells

The SrCo(1-x)Sb(x)O(3-delta) (x = 0.05, 0.1, 0.15 and 0.2) system was tested as possible cathode for solid oxide fuel cells (SOFCs). X-ray diffraction results show the stabilization of a tetragonal P4/mmm structure with Sb contents between x = 0.05 and x = 0.15. At x = 0.2 a phase transition takes place and the material is defined in the cubic Pm-3m space group. In comparison with the undoped hexagonal SrCoO(3) phase, the obtained compounds present high thermal stability without abrupt changes in the expansion coefficient. In addition, a great enhancement of the electrical conductivity was observed at low and intermediate temperatures (T <= 800 degrees C). The sample with x = 0.05 displays the highest conductivity value that reaches 5005 cm(-1) at 400 degrees C and is over 160 S cm(-1) in the usual working conditions of a cathode in SOFC (650-900 degrees C). Moreover, the impedance spectra of the SrCo(1-x)Sb(x)O(3-delta)/Ce(0.8)Nd(0.2)O(2-delta)/SrCo(1-x)Sb(x)O(3-delta) (x >= 0.05) symmetrical cells reveal polarization resistances below 0.09 Omega cm(2) at 750 degrees C which are much smaller than that displayed by the pristine SrCoO(3-delta) sample. The composition with x = 0.05 shows the lowest ASR values ranging from 0.009 to 0.23 Omega cm(2) in the 900-600 degrees C temperature interval with an activation energy of 0.82 eV. (C) 2009 Elsevier B.V. All rights reserved.