Effects of doped ceria conductivity on the performance of La0.6Sr0.4Co0.2Fe0.8O3−δ cathode for solid oxide fuel cell

Abstract

Electrochemical reaction at the cathodes of solid oxide fuel cells has typically been proposed to include a series of elementary steps occurring in the electrode, especially on the electrode surface. However, the electrode performance depends critically on the properties of both the electrode and electrolyte materials. This work assumes oxygen vacancy/ion transport cross the electrode–electrolyte interface as an elementary step to demonstrate the electrolyte effect on electrode performance. With this assumption, the electrode interfacial polarization resistance, Rp, can be theoretically related to the electrolyte conductivity, σ, with a general formula, Rp∝σlPO2n, where PO2 is the oxygen partial pressure at the cathode, l and n are the controlling parameters corresponding to various elementary steps occurred at the electrode–electrolyte interface as well as on the electrode. The assumed elementary step is experimentally confirmed by analyzing the electrochemical impedance spectra of symmetric cells of porous La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) electrodes on samaria-doped ceria (SDC) electrolytes with different conductivities as a result of various dopant contents. The high frequency resistance, which can be fitted to a Warburg-type element, increases linearly with the electrolyte resistivity, clearly demonstrating that this process corresponds to the transport of oxygen vacancy at the electrode–electrolyte interface, from the electrolyte to the electrode.