A-site Ba-deficiency layered perovskite EuBa1−xCo2O6−δ cathodes for intermediate-temperature solid oxide fuel cells: Electrochemical properties and oxygen reduction reaction kinetics

Abstract

A-site Ba-deficiency layered perovskite oxides, EuBa1−xCo2O6−δ (EB1−xCO, x = 0.02 and 0.04), have been synthesized by a citric acid-ethylene diamine tetraacetic acid complexation sol-gel method, and evaluated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Room temperature powder X-ray diffraction patterns indicate that the EB1−xCO oxides crystallize in an orthorhombic symmetry with space group Pmmm. Among all of components, EB0.98CO exhibits a good chemical compatibility with Ce0.9Gd0.1O1.95 (CGO) electrolyte, as evidenced by phase analysis of mixed EB0.98CO-CGO after calcining at 950 °C for 12 h in air. Thermal expansion analysis gives an average thermal expansion coefficient of 16.7 × 10−6 K−1 for EB0.98CO. Thermogravimetric measurement confirms the high oxygen nonstoichiometric characteristic of EB0.98CO at elevated temperatures. The electrical conductivity values of EB0.98CO exceed 300 S cm−1 in the temperature range of 100–750 °C. When tested as cathode in IT-SOFCs, the polarization resistance of 0.107 Ω cm2 and the overpotential of 10 mV at current density of 77 mA cm−2 are achieved in the EB0.98CO cathode at 700 °C in air. The EB0.98CO cathode-based anode-supported single cell delivers the maximum power density of 505 mW cm−2 at 700 °C. Finally the rate-limiting steps for oxygen reduction reaction at the EB0.98CO cathode interface are determined to be the charge transfer reaction and gas-phase diffusion process.