Oxygen reduction at thin dense La0.52Sr0.48Co0.18Fe0.82O3-δ electrodes.: Part I:: Reaction model and faradaic impedance

The faradaic impedance of oxygen reduction has been simulated for thin dense two-dimensional La0.52Sr0.48Co0.18Fe0.82O3-delta electrodes in air at 600 degrees C. The reaction model accounts for the defect chemistry of the ceramic films and includes bulk and surface pathways. It was demonstrated that the contribution of the surface pathway to the reaction was negligible due to the small length of triple phase boundary gas/electrode/electrolyte. The diffusion of oxygen in the bulk of La0.52Sr0.48Co0.18Fe0.82O3-delta (LSCF) can be evidenced by measuring the polarization resistance as a function of the electrode thickness that ranged between 10 and 800 nm. When recorded as a function of the electrode potential and thickness, the frequency response exhibited features that were specific to the rate-determining steps of the reaction. The oxygen reduction mechanism and kinetics can therefore be identified by means of impedance spectroscopy. The faradaic impedances calculated for realistic values of the rate constants exhibited a noteworthy large faradaic capacitance.