The electrochemical characteristics of porous Pt and La0.8Sr0.2CoO3-delta (LSC) electrodes has been found to depend strongly on polishing of the underlying Ce0.8Sm0.2O2-delta (SDC) electrolyte using SiC and/or diamond prior to cell fabrication. The effect of surface treatment on the microstructure and composition of SDC was investigated using scanning electron microscopy and electron spectroscopy for chemical analysis. After high-temperature sintering, the surface of SDC is Sm-enriched and has granular morphology; grinding or polishing removes this grained layer and leads to a decrease in Sm concentration. Refiring of the polished electrolyte at 1450-1650 degrees C results in restoration of the grain structure and Sm composition on the surface. It was found using electrochemical impedance spectroscopy that the surface treatment most strongly influences the high-frequency component of the impedance, suggesting the changes are associated primarily with an interfacial resistance. (c) 2005 The Electrochemical Society.