An improved synthesis method of ceria-carbonate based composite electrolytes for low-temperature SOFC fuel cells Yifu Jing a , Janne Patakangas a , Peter D. Lund a, *, Bin Zhu b a Aalto University, School of Science, P.O. Box 14100, FI-00076 Espoo-Aalto, Finland b Royal Institute of Technology, Department of Energy Technology, SE-10044 Stockholm, Sweden article info Article history: Received 3 January 2013 Received in revised form 12 May 2013 Accepted 24 May 2013 Available online 1 July 2013 Keywords: Electrolyte Fuel cell LT-SOFC Freeze drying Complex ions Citric acid abstract 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 ach- ieved was 400 mS/cm at 600  C. Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Fuel cells are potentially clean energy converters. The solid oxide fuel cell (SOFC) is a promising fuel cell technology, but has drawbacks due to high operating temperature (>750  C) which limits e.g. the materials that can be used. A traditional SOFC employs an yttria stabilized zirconia (YSZ) electrolyte which requires a high temperature for adequate ionic conductivity. Operating temperatures could be decreased by using thinner electrolyte layers or employing low-temperature solid ion conducting materials. In partic- ular doped ceria electrolytes have drawn attention as they have higher conductivity than YSZ at temperatures around 300e600  C. However, beyond ca. 600  C and in a reducing atmosphere, they suffer from partial reduction of Ce 4þ into Ce 3þ becoming mixed electron/ion conductors. Carbonate/doped ceria composites show enhanced prop- erties compared to pure doped ceria, such as improved sta- bility [1], higher ionic conductivity and low electron conductivity at low or intermediate temperatures 400e600  C. A state-of-the-art composite electrolyte has achieved a power density of 900 mW/cm 2 at 550  C with hydrogen and air as fuel and oxidant, respectively, and a conductivity of 500 mS/cm at 600  C in air [2]. A record power density of 1700 mW/cm 2 at 650  C has been reported with hydrogen as fuel and air CO 2 as oxidants [3]. * Corresponding author. Tel.: þ358 405150144. E-mail addresses: peter.lund@aalto.fi, peter.lund@tkk.fi (P.D. Lund). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 38 (2013) 16532 e16538 0360-3199/$ e see front matter Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2013.05.136