Performance and stability of five cermet-supported button-type solid oxide fuel cells featuring a bilayered electrolyte (SSZ/SDC). an SSC cathode, and a Ni-SSZ anode, were analyzed using polarization curves, impedance spectroscopy, and post-mortem SEM observation. The cell performance degradation at 650 degrees C in H-2/air both with and without DC bias conditions was manifested primarily as an increase in polarization resistance, approximately at a rate of 2.3 m Omega cm(2) h(-1) at OCV, suggesting a decrease in electrochemical kinetics as the main phenomenon responsible for the performance decay. In addition, the initial series resistance was about ten times higher than the calculated resistance corresponding to the electrolyte, reflecting a possible inter-reaction between the electrolyte layers that occurred during the sintering stage. In situ and ex situ sintered cathodes showed no obvious difference in cell performance or decay rate. The stability of the cells with and without electrical load was also investigated and no significant influence of DC bias was recorded. Based on the experimental results presented, we preliminarily attribute the performance degradation to electrochemical and microstructural degradation of the cathode. Crown Copyright (c) 2008 Published by Elsevier B.V. All rights reserved.