Electrochemical performance of Ba_(o.5)Sr_(o.5)Co_xFe_(1-x)O_(3-δ) (x = 0.2-0.8) cathode on a ScSZ electrolyte for intermediate temperature SOFCs

摘要

Intermediate temperature solid oxide fuel cell cathode materials (Ba, Sr)Co_zFet_(1-χ)O_(3_δ) [z = 0.2-0.8] (BSCF), were synthesized by a glycine-nitrate process (GNP) using Ba(NO_3)_2, Sr(NO_3)_2, Co(NO_3)_2·6H_2O, and Fe(NO_3)_3·9H_2O 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 ℃) 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 ℃. The thermal expansion coefficient of BSCF was gradually increased from 24 × 10~(-6)K~(-1) for BSCF (x=0.2) to 31 x 10~(-6)K~(-1) (400-1000℃) 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 ft cm~2 at 600 ℃. The ASR of other BSCF (x = 0.4, 0.6, and 0.8) cathodes, however, was much higher than that of BSCF (x = 0.2).