The electrochemical polarization resistance of the oxygen exchange reaction on yttria stabilized zirconia (YSZ) was investigated by means of geometrically well-defined dense platinum microelectrodes. The polarization resistance was found to be strongly affected by two different phenomena changing the electrode kinetics. One process is only observable in oxidizing atmosphere and was almost reversible (i.e. causes degradation as well as regeneration of the electrode performance). It is attributed to the formation/decomposition of a PtOx “phase”. The second process leads to continuous degradation and is discussed to be related to impurities accumulating at the three phase boundary (TPB). The effects of both time dependent phenomena on the electrochemical oxygen exchange at the TPB and at the Pt|YSZ interface are analyzed by means of equivalent circuits. It can be shown that the PtOx related degradation/regeneration affects both the TPB process as well as the electrochemical process at the Pt|YSZ interface. The impurity related degradation, however, is demonstrated to only influence the TPB kinetics.