Effect of sintering additive and low temperature on the electrode polarization of CGO

Ceria-based materials were prepared by freeze-drying precursor route and calcined at low temperature to obtain nanometric powders. Sintered pellets were prepared after calcining cylindrical discs at 1400–1600 °C. The addition of small amounts of cobalt to the starting powders allowed us to obtain dense samples at temperatures as low as 1000 °C. The effect of temperature in cobalt-doped samples was also analyzed after sintering at 1150 and 1500 °C. Symmetrical Pt-electrodes were placed on both surfaces of the samples and impedance spectroscopy was used to study the electrode polarization in the temperature range of 500–1000 °C. Estimation of p-type electronic contribution was provided by the ion-blocking/Hebb-Wagner technique under oxidizing conditions. The results revealed that the addition of cobalt produce an important decrease in the electrode polarization, probably due to the onset of significant p-type electronic conductivity, thus extending the effective location of electrode reaction from triple metal–ceramic–gas contacts to larger interfaces. Other results showed certain correlations between the grain boundary behaviour and electrode polarization for samples with and without the sintering aid. The increase of the sintering temperature spoils the positive effects of the sintering additive on grain boundary conductivity and causes higher electrode polarization. Furthermore, the decrease of the lanthanide additive content also harms the ionic grain boundary conduction and the electrode polarization.