Oxygen ionization and diffusion at SOFC cathode/electrolyte interface under cathodic polarization

Oxygen ionization and diffusion were visualized at cathode/interlayer/electrolyte interfaces by isotopic oxygen labeling (16O/18O exchange) in real flatten tube solid oxide fuel cells. Three-flatten tube cell‐stacks were exposed to 18O2 under fuel cell operation conditions at different current densities (J = 0, 0.10, and 0.25 A/cm2 at a temperature of 650 °C), and the distribution of 18O was observed at the quenched samples by secondary ion mass spectrometry (SIMS). An increase of 18O concentration at LaFeO3 based cathode and a peak 18O concentration formation around the CeO2-based interlayer were observed. The increase of 18O concentration at the LaFeO3 based cathode is attributed to an increase of oxygen surface exchange rates under polarization. The peak 18O concentration increased with current densities through the interlayer/electrolyte interfaces. The formation of 18O peak can be related to the formation of a slow 18O-diffusion layer at the interlayer/electrolyte interfaces. Possible mechanism for formation of the 18O peak around the interlayer/electrolyte interfaces was considered.