SDC-carbonate composite electrolytes for low-temperature Solid Oxide Fuel Cells (LTSOFC) have been synthesized by an improved freeze drying method based on the formation of lanthanide citrate complex solution/gel. This method can not only maintain small particle sizes in composite, but also control the carbonate composition precisely. To optimize the electrochemical performance of the composite electrolytes, SDC-carbonate samples with different carbonate contents were prepared and investigated. SEM, EDS, MPD and XRD analyses were applied to characterize the morphology and carbonate content and EIS was used to determine the ionic conductivity of the electrolyte. The highest conductivity achieved was 400 mS/cm at 600 degrees C. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.