P. Tsiakaras

The effect of oxygen and water vapor partial pressures on the total conductivity of BaCe0.7Zr0.1Y0.2O3–δ

The effect of oxygen and water vapor partial pressure on the total conductivity of the proton-conducting BaCe0.7Zr0.1Y0.2O3–δ material is investigated in the present work. Single-phase and dense ceramic materials have been successfully obtained using the citrate–nitrate synthesis method. The contributions of partial conductivities (hole, oxygen-ionic, protonic) are evaluated based on electrical and emf measurements. At 900xa0°C in air atmosphere, ionic and hole conductivities almost equivalently contribute to the total conductivity, while in reducing temperatures, the transport of the studied material becomes ionic; the predominant protonic transport (tHxa0≈xa01) realizes under wet hydrogen atmospheres at temperatures below 700xa0°C. Based on the measurements of total conductivity as a function of water vapor partial pressure, it is found that the increase of conductivity in reducing atmospheres is associated with the growth of proton conductivity. A non-monotonic change of total conductivity in oxidizing atmospheres is caused by the competing effects, namely decreasing the hole conductivity and increasing the protonic one.

Charge transfer in mixed proton, oxygen ion and electron solid oxide conductor

Analysis of the equivalent scheme of the mixed proton-oxygen ion-electron conductor (MPOEC) allowed to obtain relationships between parameters of the membrane (total conductivity and transfer numbers) and parameters of the charge and mass transfer through the membrane (partial ion and electron currents, the specific flux of hydrogen at the cathode membrane surface) under regime of electrochemical reforming. It was stated that presence of proton conductivity in addition to oxygen ion conductivity led to increase of total flux of produced hydrogen. However, under conditions typical for the electrochemical reforming of methane into hydrogen, the specific hydrogen flux is about four times lower in the case when the membrane has proton-electron conductivity than in the case when the membrane has oxygen ion-electron conductivity.