AbstractA deep cathodic polarization has been applied to a Platinum/Polycrystalline Yttria Stabilized Zirconia interface under low oxygen pressure. In the temperature range 973–1273 K the Electromotive Force recorded after the current cut off did not show any rest potential at a level corresponding to nucleation of a zirconium metal phase, likely because such process is kinetically unfavoured with respect to that of formation of intermetallic phases, whose stability introduces a limitation of the local oxygen chemical potential depression.Two rest potentials were found at less negative potentials which levels correspond to intermetallic phases which very high stability can be accounted for d–d orbitals bonding, as described by the Engel‐Brewer correlation.In some EMF decays it was observed the occurrence of a third rest potential, located at ∼ −450 mV (reference pure oxygen) that could be attributed to a transitory presence of a Pt–Zr–O phase.