Long-Term Stability of SOFC Composite Cathode Activated by Electrocatalyst Infiltration

Changes in cell performance with operation time were investigated for commercial cells possessing a composite cathode modified by nanostructured La0.6Sr0.4CoO3-delta (LSCo). The electrocatalyst was introduced into a porous scaffold composed of Sm2O3-doped CeO2 (SDC) and La1-xSrxCoyFe1-yO3-delta (LSCF) by solution infiltration, which decreased polarization resistance (R-p) of baseline cells by 20-35%. R-p of both a baseline cell and an infiltrated cell increased as the operation progressed for 1,500 h, while obeying a parabolic power law and showing 65% of total increase in the initial 150 hours. The degradation rate of the infiltrated cell was statistically indistinguishable from that of the baseline cell, implying that there was no measurable negative effect of infiltrated electrocatalysts on the cells' time-dependent performance for the systems studied here. The stability of the infiltrated cathode was affirmed by multiple samples tested for 200 hours. AC impedance spectra analysis demonstrated that degradation of cathode activity would be the critical mechanism affecting long-term stable performance for both baseline cells and infiltrated cells. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.067207jes] All rights reserved.