Effect of palladium oxidation state on the kinetics and mechanism of the charge transfer reaction taking place at the Pd/YSZ interface

Electrode polarization and conductivity measurements were carried out at the Pd/YSZ interface and at conditions close to the Pd-PdO thermodynamic equilibrium. The steady-state current-overpotential characteristics were analyzed with a Butler-Volmer type of equation. Both, apparent exchange current density, Io, and anodic/cathodic charge transfer coefficients (αa/αc), were calculated. Based on the experimental results, it was concluded that the charge transfer at the electrode is rate-determining in the case of PdO during anodic operation and Pd during cathodic operation, while in the other case mass transport of adsorbed oxygen species along the electrode/solid electrolyte interface is in competition with the charge transfer process.