Nano-scale oxide formation inside electrochemically-formed Pt blisters at a solid electrolyte interface

Abstract We report on platinum oxide formation during electrochemical anodic polarization of a platinum film on yttria-stabilized zirconia (YSZ) under electrochemical oxygen potential control. The electrochemical potential drives oxygen through the YSZ electrolyte towards a nominally 175 nm thin Pt film, which we found to locally delaminate from 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 single bubbles of a few micrometers in diameter reveal them to be hollow and enclosed by a Pt outer and a few tens of nanometers thick PtO x inner shell. The oxide shell presumably formed due to the increase of local oxygen chemical activity under the applied process conditions (723 K, 500 mbar O 2 , bias voltage +100 mV). Interface X-ray diffraction indicates that the solid electrolyte surface morphology is largely unaffected by the process suggesting that 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 oxide-scale thicknesses of the order of 1 nm. Our results however indicate that many of the kinetic barriers for oxidation during the nano-confined blistering process are lowered. This may have implications in general for the mechanism how oxygen is stored in an electrode at such an internal metal - oxide/metal - gas interface, which is important for the functionality of many solid-state electrochemical and memresistive devices.