Identification of O₂ reduction processes at yttria stabilized zirconia|doped lanthanum manganite interface

Oxygen reduction processes at a yttria stabilized zirconia|doped lanthanum manganite (LSM|YSZ) interface are investigated by ac impedance spectroscopy. Three semi-arcs are clearly observed at an oxygen partial pressure (pO₂) of 0.001atm. The constant-phase element of frequency arc and the p_O2-dependence of 1/R (R: resistance) are correlated to interpret the reaction processes associated with the frequency arcs. It is found that at least five elementary steps are involved in oxygen reduction at the LSM|YSZ interface. Three of these steps are identified as the rate-determining steps, namely: (i) gas diffusion through the porous LSM electrode from the bulk to the reaction sites; (ii) surface diffusion of oxygen intermediate species along the LSM surface; (iii) incorporation of oxygen ions from the three phase boundary into the YSZ electrolyte lattice. The p_O2-dependent exchange current density of the rate-determining step predicted by model is consistent with the experimental data, which further confirms the validity of the proposed oxygen reduction processes at the LSM|YSZ interface.