Sm0.5Sr0.5CoO3 (SSC)-Sm0.2Ce0.8O1.9 (SDC) core-shell composite cathodes are synthesized via a polymerizable complex method, and the durability of a cell incorporating the cathodes is examined. Nanocrystalline SSC powders have been coated onto the surfaces of SDC cores to enable the formation of a rigid backbone structure, over which the catalyst phase is effectively dispersed. A symmetrical SSC-SDC vertical bar SDC vertical bar SSC-SDC half-cell exhibits a polarization resistance of 0.098 Omega cm(2) at 650 degrees C. The durability and microstructure of the cathode are investigated by electrochemical impedance spectroscopy and thermo-cycle tests at temperatures in the range of 100 degrees C-650 degrees C. After 30 cycles, the polarization resistance is found to increase by 9.04 x 10(-2) Omega cm(2), a 3.56% rise wit a respect to the initial resistance. Coarsening of the SSC catalyst phase has been prevented with the use of core-shell type powders, as confirmed by a nearly constant low frequency polarization resistance and a microstructural analysis. The performance of a unit cell comprised of the core-shell type cathode exhibits 1.07 W cm(-2) at 600 degrees C and 0.62 W cm(-2) at 550 degrees C. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.