We report on platinum oxide formation during electrochemical anodic polarization of a platinum film on yttriastabilizedzirconia (YSZ) under electrochemical oxygen potential control. The electrochemical potential drivesoxygen through the YSZ electrolyte towards a nominally 175 nm thin Pt film, which we found to locally delaminatefrom the substrate by forming nano-scale blisters. High resolution scanning electron microscopy (SEM)and energy dispersive spectroscopy (EDX) mapping of focused-ion beam (FIB)-prepared cross-sections of singlebubbles of a few micrometers in diameter reveal them to be hollow and enclosed by a Pt outer and a few tens ofnanometers thick PtOx inner shell. The oxide shell presumably formed due to the increase of local oxygenchemical activity under the applied process conditions (723 K, 500 mbar O2, bias voltage +100 mV). Interface Xraydiffraction indicates that the solid electrolyte surface morphology is largely unaffected by the process suggestingthat the YSZ surface is stable on the atomic scale under application relevant oxygen transport conditions.Platinum is known to be rather stable towards oxidation, even at elevated oxygen pressure, leading to oxidescalethicknesses of the order of 1 nm. Our results however indicate that many of the kinetic barriers for oxidationduring the nano-confined blistering process are lowered. This may have implications in general for themechanism how oxygen is stored in an electrode at such an internal metal - oxide/metal - gas interface, which isimportant for the functionality of many solid-state electrochemical and memresistive devices.