Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells I. Cross Validation of Polarization Measurements by Impedance Spectroscopy and Current-Potential Sweep

The aim of this paper is to address three issues in solid oxide fuel cells (SOFC): (i) cross-validation of the polarization of a single cell measured using both dc and ac approaches, (ii) the precise determination of the total area specific resistance (ASR), and (iii) understanding cathode polarization with (La0.60Sr0.40)(Co0.20Fe0.80)O-3 cathodes. The ASR of an SOFC is a dynamic property, meaning it changes with current density. The ASR measured using impedance spectroscopy (low frequency interception with the real Z(')-axis of the ac impedance spectrum) matches that measured from a dc current-voltage (i-E) sweep (the tangent of a dc i-E curve). Due to the dynamic nature of ASR, we found that an impedance spectrum measured under open-circuit voltage or on a half-cell may not represent the cathode performance under real operating conditions, particularly at a high current density. In this work, the electrode polarization was governed by the cathode activation polarization; the anode contribution was negligible.