Investigation of Oxygen Transport Paths in Geometrically Defined Thick-Film Composite Pt Electrodes on YSZ

Thick-film platinum (Pt) model electrodes with defined geometry screen-printed on yttria stabilized zirconia (YSZ) substrate were investigated to identify oxygen reactions and transport pathways in the Pt|YSZ electrode system. A 3D reconstruction of the electrode based on Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) data was made to confirm that no percolating pores exist. Electrochemical impedance spectroscopy (EIS) was performed at 800°C and oxygen partial pressures (pO2) between 10−4 and 1 bar. The experimental data was interpreted using a Randles equivalent circuit. By variation of electrode area and three phase boundaries as well as electrode thickness, two oxygen transport pathways were found: an electrode surface path which contributes to the conductivity mostly at low pO2 and an electrode bulk path that represents the dominating path at high pO2. An advanced electrode layout enabled the separation of the transport pathways and confirmed that the two paths are parallel.