Visualization of oxygen reduction sites at Pt electrodes on YSZ by means of 18O tracer incorporation: the width of the electrochemically active zone.

In this study the electrochemically active region of oxygen incorporation into yttria stabilized zirconia (YSZ) was visualized by means of (18)O tracer incorporation experiments on dense Pt thin film microelectrodes combined with ToF-SIMS analysis. The localization and the shape of the incorporation zone were found to strongly depend on the polarization of the electrode. In case of lower overpotentials the active zone next to the three phase boundary (TPB) was frame-shaped and located beneath the Pt electrode. Increases in polarization led to an extension of the incorporation zone along the free YSZ surface. Owing to the low temperature of 300-330 °C a profile-broadening caused by diffusion in YSZ could be minimized and quantitatively separated from the measured profiles. The TPB-width (i.e. the decay length of electrochemical activity) was determined to be approximately 1.0-1.3 μm at these temperatures.