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

Abstract

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 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 -axis of the ac impedance spectrum) matches that measured from a dc current–voltage sweep (the tangent of a dc 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.