Influence of Electrode Potential on Oxygen Mobility Probed by Polarized Isotopic Exchange in Solid Oxide Electrolyser Cells: Insights for Electro-Assisted Oxidation Reactions

Oxygen mobility was studied by oxygen isotopic exchange on three electrodes used in Solid Oxide Electrolyser Cells under polarization (La0.8Sr0.2MnO3 (LSM), La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) and La2NiO4+delta (LNO)). The rate of the surface and the bulk mechanisms for oxygen mobility is depending on the type of conductivity (electronic conduction or mixed ionic and electronic conductivity). It is shown that a one oxygen atom exchange is dominant for the surface path whereas a two oxygen atoms mechanism dominates for the bulk path. The rate constant for the bulk path is much higher than the one for the surface path by two orders of magnitude. Additionally, polarized oxygen isotopic exchange revealed that electrode overvoltage increases significantly the rate constant for the surface path, whereas its impact on the bulk path is negligible. The multi-step process for oxygen mobility in solid oxide electrolyser cells including dissociation and incorporation in the electrolyte is investigated with polarized oxygen isotopic exchange. The fastest way is O2- incorporation in the electrode catalyst if it shows mixed ionic and electronic properties, whereas the much slower surface path can be activated by the electrode overpotential (eta). image