Theoretical Analysis of the Electrochemical Promotion of Infiltrations in MIEC Based Electrodes for IT-SOFCs

Abstract

We consider mixed ionic-electronic conducting (MIEC) electrodes for intermediate temperature-solid oxide fuel cells (IT-SOFCs). Focusing on the mechanism of charge conduction along the MIEC, we consider that it features two separated charge conduction paths, one for electrons and one for oxygen-ions. Infiltrated nano- sized dopant particles, adherent to the MIEC fibers, create contact points between the ionic and the electronic conductive paths, among which, otherwise, the charge transfer reaction would be negligible.
Based on this picture of the doped MIEC electrode, a model is developed. The model includes the evaluation of i) charge transfer reaction occurring at the dopant particles and, possibly, at the electrode/electrolyte interface; ii) electron and oxygen-ion conduction along the MIEC fiber, and iii) additional charge conduction along the dopant nano-particles, if percolating throughout the electrode structure. The model is applied to Sm_0.5Sr_0.5CoO_3-d (SSC) infiltrated La_1-xSr_xCo_1-yFe_yO_3-d (LSCF) cathodes, and also to Gd-doped CeO₂ (GDC) infiltrated La-doped SrTiO₃ (LST) anodes. At 1023 K, an overall reciprocal electrode resistance in the order of 1/R_p ˜?1x10⁶ S m^-2 is calculated for the SSC-LSCF cathodes, and 1/R_p ˜?8x10³ S m^-2 for the GDC-LST anodes. Simulation results are compared to literature experimental data, demonstrating good agreement.