Journal of Power Sources 195 (2010) 4695–4699 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Short communication Samarium doped ceria–(Li/Na) 2 CO 3 composite electrolyte and its electrochemical properties in low temperature solid oxide fuel cell Jing Di a , Mingming Chen a,∗ , Chengyang Wang a , Jiaming Zheng a , Liangdong Fan a , Bin Zhu b a Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering and Technology, Tianjin University, Weijin Road 92#, Nankai District, Tianjin 300072, PR China b Department of Energy Technology, Royal Institute of Technology, Stockholm S-100 44, Sweden article info Article history: Received 6 January 2010 Received in revised form 22 February 2010 Accepted 23 February 2010 Available online 1 March 2010 Keywords: Low temperature solid oxide fuel cell Samarium doped ceria Composite electrolyte abstract A composite of samarium doped ceria (SDC) and a binary carbonate eutectic (52 mol% Li 2 CO 3 /48 mol% Na 2 CO 3 ) is investigated with respect to its morphology, conductivity and fuel cell performances. The mor- phology study shows the composition could prevent SDC particles from agglomeration. The conductivity is measured under air, argon and hydrogen, respectively. A sharp increase in conductivity occurs under all the atmospheres, which relates to the superionic phase transition in the interface phases between SDC and carbonates. Single cells with the composite electrolyte are fabricated by a uniaxial die-press method using NiO/electrolyte as anode and lithiated NiO/electrolyte as cathode. The cell shows a maxi- mum power density of 590 mW cm -2 at 600 ◦ C, using hydrogen as the fuel and air as the oxidant. Unlike that of cells based on pure oxygen ionic conductor or pure protonic conductor, the open circuit voltage of the SDC–carbonate based fuel cell decreases with an increase in water content of either anodic or cathodic inlet gas, indicating the electrolyte is a co-ionic (H + /O 2- ) conductor. The results also exhibit that oxygen ionic conductivity contributes to the major part of the whole conductivity under fuel cell circumstances. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Solid oxide fuel cells (SOFCs) have received much attention in terms of environment friendliness, fuel flexibility and high energy efficiency. Conventional SOFCs use typical yttria-stabilized zirconia (YSZ) electrolytes at operational temperatures of about 1000 ◦ C. At such high temperatures, the conductivity of YSZ is improved up to more than 0.1 S cm -1 , which is indispensable for high performance SOFCs [1]. However, high running temperature is accompanied by some negative effects such as thermal expansion mismatch, seal- ing problem and even instability of fuel cells. Extensive studies have been developed to reduce the operating temperature to rela- tively lower temperatures by decreasing the electrolyte thickness or introducing alternative materials with higher ionic conductiv- ity [2,3]. Doped ceria has been studied as a potential electrolyte for low temperature solid oxide fuel cells (LTSOFCs) in view of its high ionic conductivity [4]. However, doped ceria exhibits mixed ionic and electronic conductivity in reducing atmospheres due to the partial reduction of Ce 4+ to Ce 3+ . The electronic conduc- tion leads to a loss of open circuit voltage (OCV) and a drop of power output of the cell. Furthermore, it may also cause lattice ∗ Corresponding author. Tel.: +86 22 27890481; fax: +86 22 27890481. E-mail address: chmm@tju.edu.cn (M. Chen). expansion of the electrolyte, resulting in mechanical instability of cells. Recently, novel ceria–salt composite materials are regarded as a kind of promising electrolytes for LTSOFCs [5–10]. The composition materials, composed of doped ceria and salts (carbonate, chloride, hydrate or sulphate), demonstrate conductivity of 0.01–1 S cm -1 in 400–600 ◦ C region and suppress the electronic conductivity effectively [6]. The composite electrolyte was considered to be con- ductors for both oxygen ion and proton under air/H 2 atmosphere, evidenced by the facts that water was generated at both sides of the electrodes [9,10]. However, little information about transfer process has been involved in the former studies during fuel cell operation. At the present time, there is still a lack of detailed mech- anism uncovered for the oxygen ionic and protonic conductions in these materials. Among the composite materials, samarium doped ceria (SDC)–carbonate composites were widely used as electrolytes for LTSOFCs with excellent power densities between 400 and 600 ◦ C [11–13]. In this study, the conduction behavior of the SDC–carbonate composite was studied under air, argon and hydrogen, respectively. The single cells based on the composite electrolyte were fabricated and studied by evaluating the power output. The dependence of OCV on the water content of either anode or cathode gas was also investigated to demonstrate the O 2- /H + transfer process under fuel cell environment. 0378-7753/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2010.02.066