Electrochemical properties of GdBaCo 2/3 Fe 2/3 Cu 2/3 O 5+d –CGO composite cathodes for solid oxide fuel cell Seung Jun Lee, Dong Seok Kim, Seung Hwan Jo, P. Muralidharan, Do Kyung Kim * Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 335 Gwahak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea Available online 25 May 2011 Abstract The composite cathodes of double-perovskite structure of xwt.% Ce 0.9 Gd 0.1 O 1.95 (CGO)–(100  x)wt.% GdBaCo 2/3 Fe 2/3 Cu 2/3 O 5+d (FC- GBCO), where x = 0, 10, 20, 40 and 50, were synthesized via a citrate combustion method followed by an organic precipitant method. The thermal- expansion coefficient (TEC) and electrochemical performance of the oxides were investigated as potential cathode materials for intermediate- temperature solid oxide fuel cells (IT-SOFCs). The TEC exhibited by composite cathode made of 40 wt.% CGO–60 wt.% FC-GBCO (CG40) up to 900 8C is 13.7  10 6 8C 1 , which is lower value than FC-GBCO (16.3  10 6 8C 1 ). The composite cathode of CG40 coated on Ce 0.9 Gd 0.1 O 1.95 electrolyte showed the lowest area specific resistance (ASR) i.e., 0.041 V cm 2 at 750 8C. An electrolyte supported (300 mm thick) single-cell configuration of CG40/CGO/Ni-CGO attained a maximum power density of 800 mW cm 2 at 800 8C. The unique composite composition of CG40 exhibited enhanced electrochemical performance, reduced TEC and good chemical compatibility with CGO electrolyte compared with their FC- GBCO cathode for IT-SOFCs. # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Composites; D. Perovskites; E. Electrodes; E. Fuel cells 1. Introduction Recently, solid oxide fuel cells (SOFCs) have attracted as one of the most promising electrochemical energy conversion device because of high power efficiency, low pollutant emission and fuel flexibility [1–3]. Lowering operation temperature to intermediate temperature (600–800 8C) is one of the main goals in the SOFC field [4,5]. A reduced operating temperature can extend the choice of materials, enhance the thermal stability of SOFC by minimizing thermal stresses experienced by the components during temperature cycling. However, the electro- chemical activity of the cathode dramatically decreases with decreasing temperature and thus cathode becomes the limiting factor in determining the overall cell performance [4–6]. Therefore, the development of new electrodes with high electro-catalytic activity for the oxygen-reduction reaction is significant for intermediate-temperature solid-oxide fuel. Recently, the mixed ionic-electronic conductors (MIECs) GdBaCo 2 O 5+d have been developing to be attractive potential cathode materials for IT-SOFCs [6–8]. This material exhibits high ionic conductivity due to the oxygen vacancies and high electronic conductivity [6–9]. Although very promising results were reported, double-perovskite oxides have high TEC that are not compatible with electrolyte materials [6,8,9]. The thermal expansion mismatch can cause thermal stress at interface of electrolyte and cathode and thus results in its long-term stability performance. More recently, our group have reported that Co site doped GBCO exhibits lower TEC and enhancement of electrochemical performance [8]. However, a further investiga- tion on the optimization of TEC and electrochemical performance is necessary for the double-perovskite oxides to be used as potential cathodes in IT-SOFCs. In order to improve cathode performance, the composite cathodes are of great interest that includes mixtures of cathode and ionic conducting materials [3,5,10–12]. The second phase, doped ceria in the cathode can expand the triple-phase boundaries (TPB) at which the oxygen reduction reaction occur from the two-dimensional interface between the electrolyte and the cathode to the entire zone of the cathode www.elsevier.com/locate/ceramint Available online at www.sciencedirect.com Ceramics International 38S (2012) S493–S496 * Corresponding author. Tel.: +82 42 350 4118; fax: +82 42 350 3310. E-mail address: dkkim@kaist.ac.kr (D.K. Kim). 0272-8842/$36.00 # 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2011.05.061