The polarization resistance of mixed conducting SOFC cathodes: A comparative study using thin film model electrodes

The oxygen reduction reaction on YSZ solid electrolytes is investigated by means of thin film microelectrodes employing perovskite-type mixed conductors such as La0.6Sr0.4Co0.8Fe0.2O3 − δ, Ba0.5Sr0.5Co0.8Fe0.2O3 − δ and Sm0.5Sr0.5CoO3 − δ as electrode materials. Owing to the simple geometry of the circular microelectrodes direct comparison of electrochemical material parameters is possible and reveals that the Fe/Co ratio in La0.6Sr0.4Co1 − xFexO3 − δ has only little effect on the resistance associated with the surface oxygen exchange. Ba0.5Sr0.5Co0.8Fe0.2O3 − δ thin films exhibit very low surface-related polarization resistances. Strongly decreased resistances can also be observed in Co-rich La0.6Sr0.4Co1 − xFexO3 − δ electrodes after a cathodic voltage pulse treatment of several tens of seconds. Area-related surface resistances below 0.1 Ωcm2 at 700 °C can be achieved by such activation. Further phenomena associated with this voltage activation are discussed.