Evaluation of A-site deficient Sr 1 À x Sc 0.175 Nb 0.025 Co 0.8 O 3 À δ (x ¼ 0, 0.02, 0.05 and 0.1) perovskite cathodes for intermediate-temperature solid oxide fuel cells Guihua Chen a,1 , Jaka Sunarso b,1 , Yong Wang a,c,n , Changhua Ge a , Jianguo Yang a , Fengli Liang d,nn a School of Pharmaceutical and Chemical Engineering, Taizhou University, Jiaojiang 318000, PR China b Faculty of Engineering, Computing and Science, Swinburne University of Technology, Jalan Simpang Tiga, 93350 Kuching, Sarawak, Malaysia c Jiangsu Key Laboratory for Environment Functional Materials, Suzhou University of Science and Technology, Suzhou 215009, PR China d College of Energy & Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, PR China article info Article history: Received 11 April 2016 Received in revised form 6 May 2016 Accepted 9 May 2016 Available online 10 May 2016 Keywords: A. Powders: solid state reaction E. Fuel cells E. Electrodes abstract This work strives to improve the performance of SrSc 0.175 Nb 0.025 Co 0.8 O 3Àδ (SSNC) cathode by introducing A-site cation deficiency up to 10 mol%. Three different Sr-deficient compositions, i.e., Sr 1Àx Sc 0.175 Nb 0.025 Co 0.8 O 3 Àδ (S 1Àx SNC, x ¼0.02, 0.05 and 0.1) including the non-deficient analogue, SSNC are prepared. Powder X-ray diffraction patterns indicate that the original cubic perovskite structure is retained. The thermal expansion coefficient between 50 °C and 900 °C increases progressively with in- creasing Sr deficiency, consistent with the “β-oxygen” release profiles trend. The electrical conductivities for SSNC, S 0.98 SNC, S 0.95 SNC and S 0.9 SNC show a maximum-type profile against increasing temperature, i.e., semiconducting behavior followed by metallic behavior. Despite the consistent increase in the oxygen non-stoichiometry with increasing Sr deficiency, the oxygen reduction reaction performance increases in the order of SSNC, S 0.9 SNC, S 0.98 SNC and S 0.95 SNC. That the highest oxygen reduction reaction (ORR) performance is demonstrated by S 0.95 SNC indicates the trade-off between the increase in the concentration of oxygen vacancies and the formation of the phase impurities. At 650 °C, S 0.95 SNC shows an area specific resistance of 0.017 Ω cm 2 (from symmetric cell test) and a peak power density of 1263 mW cm À2 (from single fuel cell test on a Ni-Sm 0.2 Ce 0.8 O 1.9 (SDC) anode supported SDC electrolyte). & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved. 1. Introduction Solid oxide fuel cells (SOFCs), due to their high chemical to electrical energy conversion efficiency, low emission and fuel flexibility, have been recognized as attractive energy conversion devices particularly during the past decade [1–4]. The conven- tional SOFCs generally operate beyond 800 °C, which are suffi- ciently high to induce issues such as the incidental post-sintering of the electrode, the high reactivity between the cell components and the limited options on the interconnecting materials. These become the major hurdle towards their large scale application to produce electrical energy. Intensive research efforts have been undertaken to develop new class of SOFCs capable to operate at intermediate-temperature range (500–800 °C) [5–9]. Despite the anticipated advantages such lowering in temperature provides, i.e., wider materials selection, decreased corrosion rate and lower operation cost [10–13], finding cathode which provides high oxy- gen reduction reaction (ORR) activity at such temperatures still remains a challenge given the exponential temperature depen- dence of ORR activity in most cathodes [14]. Mixed ionic-electronic conducting (MIEC) perovskite cathode is a better choice than a conventional electronic conducting per- ovskite since the former can extend the active sites for ORR which is limited to the cathode-electrolyte-air triple phase boundaries (TPBs) (in the latter) to the bulk phase and the entire cathode surface [15]; therefore substantially enhancing cathode activity at lower temperatures. Several well-known examples are Ba 1 Àx Sr x Co 1 Ày Fe y O 3 Àδ [16–19], La 1 Àx Sr x Co 1 Ày Fe y O 3 Àδ [20,21], Sm 1 Àx Sr x CoO 3 Àδ [22,23] and LnBaCo 2 O 5 þ δ [24,25]. Superior ORR activity is attained only on several MIEC cathodes and is generally characterized by the high oxygen surface exchange kinetics in addition to high oxygen bulk-diffusion rate. SrNb 0.1 Fe 0.9 O 3 Àδ (SNF), for example, showed higher ORR activity of 0.031 Ω cm 2 at Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ceramint Ceramics International http://dx.doi.org/10.1016/j.ceramint.2016.05.057 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved. n Corresponding author at: School of Pharmaceutical and Chemical Engineering, Taizhou University, Jiaojiang 318000, PR China. nn Corresponding author. E-mail addresses: wang_yong932@hotmail.com (Y. Wang), fengli0912@nuaa.edu.cn (F. Liang). 1 These authors contributed equally to this work. Ceramics International 42 (2016) 12894–12900