Mixed protonic/electronic conductor cathodes for intermediate temperature SOFCs based on proton conducting electrolytes

The electrical properties of doped SrCe O₃ and BaCe O ₃ were studied as a function of temperature, and oxygen and water vapor partial pressure using electrochemical impedance spectroscopy. Rare-earth elements, such as Yb, Eu, and Sm, were used as cation dopants because of their multivalent oxidation state, low third ionization potential, and comparable ionic radius with cerium. Higher conductivity values were recorded doping SrCe O₃ and BaCe O₃ oxides with Yb. Partial conductivities and transport numbers were calculated from the conductivity measurements at different oxygen partial pressures using an established defect model. In an oxidizing condition, electron-hole conduction was dominant at high temperatures and decreased with decreasing the temperature and increasing the water vapor content in the gas atmosphere. Ba Ce0.9 Yb0.1 O3-δ presented the highest conductivity among the tested samples both in dry and wet oxygen atmospheres. Moreover, Ba Ce0.9 Yb0.1 O3-δ showed a mixed conduction of ions and holes at temperatures above 600°C, suggesting that this perovskite-type oxide could be a possible cathode material in a solid oxide fuel cell (SOFC) based on a proton conductor electrolyte.