Symmetric solid oxide cells with Gd doped ceria (GDC) electrolytes and La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF)-infiltrated-GDC cathodes were maintained in air with no current at temperatures from 650 to 850 degrees C. Comparison of SEM images before and after aging showed inhomogeneous coarsening of LSCF nano-particles in the cathodes. The polarization resistance, measured periodically at 600 degrees C using electrochemical impedance spectroscopy, increased at a higher rate with increasing aging temperature. The resistance variation was fit using a model that relates resistance to time-dependent LSCF surface area, based on surface diffusion limited coarsening. Good agreement with the experimental data is obtained for a limited range of fitting parameters. The model predicts that the cathode resistance should increase from similar to 0.2 to 0.28-0.35 Omega cm(2), if maintained at the operating temperature of 600 degrees C for 40,000 h. (C) 2011 Elsevier B.V. All rights reserved.