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

Abstract

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.

Anode Process on Platinum in Low Temperature KF-AlF3-Al2O3 Based Melts: An Update

“…Thus, at the initial time after replacing the atmosphere in the retort with oxygen, the measured potential difference (0.75-0.78 V) is close to the thermodynamic value. The increase in the potential difference during further purging of the quartz retort with oxygen can be explained by the adsorption of oxygen atoms on Pt 35,36 and the formation of stable Pt x O oxides at the measurement temperature. 36,37 As a result, oxygen supersaturation or a change in the function of oxygen electrode may occur.…”