Tailoring Electrochemical Property of Layered Perovskite Cathode by Cu- doping for Proton-Conducting IT-SOFCs Y. Ling 1,2 *, L. Zhao 3 , X. Liu 1 , B. Lin 4 * 1 CAS Key Laboratory of Materials for Energy Conversion, Department of Materials Science and Engineering, University of Science and Technology of China (USTC), Hefei, Anhui 230026, PR China 2 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577, Japan 3 Department of Material Science and Chemistry, China University of Geoscience, Wuhan 430074, PR China 4 Anhui Key Laboratory of low temperature Co-fired Materials, Department of Chemistry and Engineering, Huainan Normal University (HNNU), Huainan 232001, PR China Received September 15, 2014; accepted February 02, 2015; published online ¢¢¢ Abstract Layered perovskite oxide YBaCuCoO 5+x (YBCC) was synthe- sized by an EDTA-citrate complexation process and was inves- tigated as a novel cathode for proton-conducting intermediate temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion coefficient (TEC) of YBCC was 15.3 · 10 –6 K –1 and the electrical conductivity presented a semiconductor-like behavior with the maximum value of 93.03 Scm –1 at 800 °C. Based on the defect chemistry analysis, the electrical conduc- tivity gradually decreases by the introduction of Cu into Co sites of YBaCo 2 O 5+x and the conductor mechanism can trans- form from the metallic-like behavior to the semiconductor-like behavior. Thin proton-conducting (BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3–d ) BZCYYb electrolyte and NiO–BZCYYb anode functional layer were prepared over porous anode substrates composed of NiO–BZCYYb by a one-step dry-pressing/co-firing process. Laboratory-sized quad-layer cells of NiO-BZCYYb / NiO- BZCYYb / BZCYYb / YBCC with a 20 mm-thick BZCYYb elec- trolyte membrane exhibited the maximum power density as high as 435 mW cm –2 with an open-circuit potential (OCV) of 0.99 V and a low interfacial polarization resistance of 0.151 Wcm 2 at 700 °C. The experimental results have indicated that the layered perovskite oxide YBCC can be a cathode candidate for utilization as proton-conducting IT-SOFCs. Keywords: Defect Chemistry Analysis, Intermediate Tem- perature Solid Oxide Fuel Cells, Layered Perovskite Oxide, Polarization Resistance 1 Introduction Proton-conducting intermediate temperature solid oxide fuel cells (IT-SOFCs) have attracted increasing attention because of some advantages over those cells with oxygen-ion conducting solid oxide fuel cells such as water formed at the cathode side, simpler fuel-recycling instruments and a lower active energy of proton transport [1, 2]. Unfortunately, reduc- ing the operating temperature must result in the overall elec- trochemical performance reduction due to the increased the electrolyte’s ohmic losses and the electrode polarization losses. BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3–d (BZCYYb) showed the highest ionic conductivity below 750 °C among the several proton-conduct- ing oxides and can effectively decrease the electrolyte’s ohmic losses [3–5]. However, the development of alternative cathode materials with low cathode interface polarization for proton- conducting IT-SOFCs remains a challenge. Efforts have been devoted to lowering the cathode polarization resistance for proton-conducting IT-SOFCs by introducing novel cathode materials to meet the demand for commercialization [6–10]. Compared to conventional cathode material La 1–x Sr x MnO 3–d (LSM), layered perovskites LnBaCo 2 O 5+x (Ln=Pr, La, Nd, Sm, Gd and Y) with mixed ionic and electrical conductivity have exhibited excellent electrochemical performance as potential cathode materials for IT-SOFCs [11–20]. Kim et al. [13] reported that the YBaCo 2 O 5+x oxide exhibited a lowest ther- mal expansion coefficient with decreasing size of the Ln 3+ ions from Ln = La to Y. However, Co occupying the whole of B-sites often suffers some problems such as poor chemical sta- bility in CO 2 and high thermal expansion coefficients in practi- cal long-term applications [21, 22]. As known, the thermal expansion contains thermal induced expansion and chemical – [ * ] Corresponding author, lyhyy@mail.ustc.edu.cn FUEL CELLS 00, 0000, No. 0, 1–6 ª 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 ORIGINAL RESEARCH PAPER DOI: 10.1002/fuce.201400141