The performance degradation of a solid oxide fuel cell (SOFC) single cell caused by delamination of the cathode is investigated. When the TEC difference between the cathode and the electrolyte is large, detachment of the interface occurs. This is confirmed by SEM images and impedance analysis during long-term operation. As delamination occurs, the active area naturally decreases, and the oxygen reduction reaction concentrates into the intact area. This leads to an increase in polarization and ohmic losses so that the performance of the single cell degrades by approximately 7.7% during 1000 h of operation. Assuming that the drop of power density was due only to delamination, the area change is approximately 10% when the TEC difference is 7 x 10(-6) K(-1). Crown Copyright (C) 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.