Electrochemical performance of Ba0.5Sr0.5CoxFe1-xO3-δ (x=0.2-0.8) cathode on a ScSZ electrolyte for intermediate temperature SOFCs

Intermediate temperature solid oxide fuel cell cathode materials (Ba, Sr)CoxFe1-xO3-delta [x=0.2-0.8] (BSCF), were synthesized by a glycine-nitrate process (GNP) using Ba(NO3)(2), Sr(NO3)(2), Co(NO3)(2).6H(2)O, and Fe(NO3)(3).9H(2)O as starting materials and glycine as an oxidizer and fuel. Electrolyte-supported symmetric BSCF/GDC/ScSZ/GDC/BSCF cells consisting of porous BSCF electrodes, a GDC buffer layer, and a ScSZ electrolyte were fabricated by a screen printing technique, and the electrochemical performance of the BSCF cathode was investigated at intermediate temperatures (500-700 degrees C) using AC impedance spectroscopy. Crystallization behavior was found to depend on the pH value of the precursor solution. A highly acidic precursor solution increased the single phase perovskite formation temperature. In the case of using a precursor solution with pH 2, a single perovskite phase was obtained at 1000 degrees C. The thermal expansion coefficient of BSCF was gradually increased from 24 x 10(-6) K-1 for BSCF (x = 0.2) to 31 x 10(-6) K-1 (400-1000 degrees C for BSCF (x = 0.8), which resulted in peeling-off of the cathode from the GDC/ScSZ electrolyte. Only the BSCF (x = 0.2) cathode showed good adhesion to the GDC/ScSZ electrolyte and low polarization resistance. The area specific resistance (ASR) of the BSCF (x = 0.2) cathode was 0. 183 Omega cm(2) at 600 degrees C. The ASR of other BSCF (x = 0.4, 0.6, and 0.8) cathodes, however, was much higher than that of B S CF (x = 0. 2). (C) 2007 Elsevier B.V All rights reserved.