Identification of O2 reduction processes at yttria stabilized zirconiadoped lanthanum manganite interface

Oxygen reduction processes at a yttria stabilized zirconiadoped lanthanum manganite (LSMYSZ) interface are investigated by ac impedance spectroscopy. Three semi-arcs are clearly observed at an oxygen partial pressure (pO2) of 0.001 atm. The constant-phase element of frequency arc and the pO2-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 LSMYSZ 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 pO2-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 LSMYSZ interface.