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-delta, Ba0.5Sr0.5Co0.8Fe0.2O3-delta and Sm0.5Sr0.5CoO3-delta as electrode materials. Owing to the simple geometry of the circular microclectrodes direct comparison of electrochemical material parameters is possible and reveals that the Fe/Co ratio in La0.6Sr0.4Co1-xFexO3-delta has only little effect on the resistance associated with the surface oxygen exchange. Ba0.5Sr0.5Co0.8Fe0.2O3-delta in films exhibit very low surface-related polarization resistances. Strongly decreased resistances can also be observed in Co-rich La0.6Sr0.4Co1-xFexO3-delta electrodes after a cathodic voltage pulse treatment of several tens of seconds. Area-related surface resistances below 0.1 Omega cm(2) at 700 degrees C can be achieved by such activation. Further phenomena associated with this voltage activation are discussed. (c) 2008 Elsevier B.V. All rights reserved.