Novel SrSc 0.2 Co 0.8 O 3d as a cathode material for low temperature solid-oxide fuel cell Wei Zhou, Zongping Shao * , Ran Ran, Rui Cai State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology, No. 5 Xin Mofan Road, Nanjing 210009, PR China article info Article history: Received 31 July 2008 Received in revised form 6 August 2008 Accepted 14 August 2008 Available online 23 August 2008 Keywords: Solid-oxide fuel cells Cathode Perovskite Thermal expansion SrSc 0.2 Co 0.8 O 3d abstract The SrSc 0.2 Co 0.8 O 3d (SSC) perovskite was investigated as a cathode material for low temperature solid- oxide fuel cell. The material showed an almost linear thermal expansion from room temperature to 1000 °C in air with the average thermal expansion coefficient of only 16.9  10 6 K 1 . The Sc-doping made the absence of Co 4+ in SSC, which resulted in not only dramatically reduced thermal expansion coefficient but also extremely high oxygen vacancies concentrations in the lattice at low temperature. The area specific polarization resistance was 0.206 X cm 2 for SSC at 550 °C, which is about 52% lower than the value of a Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3d -based cathode. A peak power density as high as 564 mW cm 2 was obtained at 500 °C based on a 20 lm thick Sm 0.2 Ce 0.8 O 1.9 electrolyte by adopting SSC cathode. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Recent solid-oxide fuel cell (SOFC) development has focused on low temperature operation (400–600 °C) primarily to facilitate the use of low-cost metallic interconnects, to decrease materials de- mands for seals and balance-of-plant components, and to improve long-term cell stability [1]. A major concern with reduced operat- ing temperatures is the deterioration of electrochemical activity of the cathode for oxygen reduction, and hence reduced cell perfor- mance. It is generally accepted that an ideal SOFC cathode should possess high electronic and ionic conductivity in addition to high catalytic activity for oxygen reduction at the desired operating temperatures. Several perovskite compounds with cobalt as the predominant B-site cation satisfy these requirements [2–4]. How- ever, cobalt-rich compositions have high thermal expansion coeffi- cients (TECs), and there is concern with respect to delamination of the cathode from the electrolyte on thermal cycling [5]. Some co- balt-free alternatives have been developed as the cathodes, such as (La,Sr)FeO 3d and La(Ni,Fe)O 3d , which have closer TEC to the electrolyte, but they suffer from unfavorable electrocatalysis on oxygen reduction reaction at the reduced operating temperatures [6,7]. Some researches showed that the partial substitution of co- balt could reduce the TECs of the cobalt-containing materials to some extent by depressing the oxidation of cobalt ion from Co 3+ to Co 4+ [8,9]. However, further reducing the TECs of the materials by decreasing the cobalt content led to a steady increase in catho- dic resistance to oxygen reduction reaction. Therefore, a key issue is to exploit a cobalt-containing material with low TEC but maintaining high electrocatalysis at low operat- ing temperatures. Among the cobalt-containing materials, the fam- ily of Sr–Co–O system oxides has both the high oxygen ionic and electronic conductivity when they are in cubic crystal structure. Zeng et al. reported that Sc-doping in cobalt position in SrCoO 3d oxides stabilized the cubic structure in a wide range of tempera- tures [10]. In addition, it was reported that the introduction of small amount of Sc 3+ likely led to the stabilization the cobalt ion at the lower valence state and/or the high spin state. Therefore, it is reasonable to believe that the TEC of the materials can be re- duced by the Sc-doping. In this preliminary work, the thermal expansion and electrochemical properties of SrSc 0.2 Co 0.8 O 3d (SSC) cathode are studied based on a Sm 0.2 Ce 0.8 O 1.9 (SDC) electro- lyte. Excellent cathode performance at reduced temperatures was reported. 2. Experimental 2.1. Powder synthesis and cell fabrication SSC and SDC powders were synthesized by a combined EDTA- citrate complexing sol–gel process according to Ref. [10]. The SSC cathode powder was dispersed in a premixed solution of glycerol, ethylene glycol, and isopropyl alcohol, and a colloidal suspension was formed via high-energy ball milling (Fritsch, Pulverisettle 6) 1388-2481/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2008.08.033 * Corresponding author. Tel.: +86 25 83587722; fax: +86 25 83365813. E-mail address: shaozp@njut.edu.cn (Z. Shao). Electrochemistry Communications 10 (2008) 1647–1651 Contents lists available at ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom