Surface Kinetics and Mechanism of Oxygen Incorporation Into Ba1-xSrxCoyFe1-yO3-delta SOFC Microelectrodes

The understanding of the oxygen incorporation mechanism at the cathode is crucial for the improvement of solid oxide fuel cell performance. To elucidate the reaction mechanism on the prototype cathode material Ba1-xSrxCoyFe1-yO3-delta (BSCF), the reaction kinetics is studied on geometrically well-defined dense thin film microelectrodes by impedance spectroscopy. This avoids interference from the electrode morphology and allows a quantitative comparison of the oxygen incorporation rate for BSCF with different cation compositions. The correlation between the effective surface exchange rate constant k extracted from the impedance spectra and various bulk properties is studied. With oxygen diffusion coefficients reliably measured by oxygen isotope exchange and secondary ion mass spectrometry (SIMS), a correlation between k and the concentration and mobility of oxygen vacancies is confirmed. Together with the temperature and oxygen partial pressure dependence of k, an oxygen incorporation mechanism on BSCF is proposed with a rate-determining step involving the migration of oxygen vacancies. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3494224] All rights reserved.