Electrode properties of Co-doped Ca 2Fe 2O 5 as new cathode materials for intermediate-temperature SOFCs

Abstract

Brownmillerite oxide Ca 2Fe 2− x Co x O 5 ( x = 0.2, 0.4, 0.6) was characterized by XRD, SEM and electrochemical impedance spectrum (EIS), respectively. Ca 2Fe 2− x Co x O 5 has no reaction with Sm 0.2Ce 0.8O 1.9 (SDC) electrolyte at 1100 °C for 10 h in air. The thermal expansion coefficient (TEC) of Ca 2Fe 2− x Co x O 5 increased with increasing Co content, and the TEC value was compatible with SDC. The electrode properties of Ca 2Fe 2− x Co x O 5 were studied under various temperatures and oxygen partial pressures. The polarization resistance ( R p) of Ca 2Fe 2− x Co x O 5 with x = 0.2, 0.4 and 0.6 are 0.23, 0.48 and 1.05 Ω cm 2 at 700 °C in air, respectively. The rate-limiting step for oxygen reduction reaction was the charge transfer process. Ca 2Fe 1.8Co 0.2O 5 cathode exhibits the lowest overpotential of about 50 mV at a current density of 70 mA cm −2 at 700 °C in air.