Study of CO2 stability and electrochemical oxygen activation of mixed conductors with low thermal expansion coefficient based on the TbBaCo3ZnO7+δ system

The influence of different application-oriented factors on the electrochemical activity and stability of TbBaCo3ZnO7+δ when used as a solid oxide fuel cell cathode has been studied. Calcination at temperatures above 900 °C (e.g. 1000 °C) leads to a significant increase in the electrode polarization resistance. The effect of the sintering temperature of the TbBaCo3ZnO7+δ cathode seems to be more important than the effect produced by the Tb substitution as observed when compared with 900 °C-sintered YBaCo3ZnO7+δ; and ErBaCo3ZnO7+δ electrode performances. The presence of CO2 in the air flow leads to an increase of roughly 10% in the polarization resistance for the whole studied temperature range (500–850 °C) while this effect is reversible. Analysis of the impedance spectroscopy measurements shows that the exchange rate constant (kG from Gerischer element) is significantly affected by CO2 at temperatures below 700 °C, while the diffusion coefficient related parameter is slightly influenced at low temperatures. Electrode degrades with a low constant rate of 1 mΩ cm2 h−1 after 60 h. This cathode material exhibits high CO2 tolerance, as shown by temperature programmed treatment under a continuous gas flow of air with 5% CO2, and a relatively low thermal expansion coefficient.