Performance degradation of impregnated La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 DY 2 O 3 stabilized ZrO 2 composite cathodes of intermediate temperature solid oxide fuel cells Yihui Liu, Bo Chi*, Jian Pu, Jian Li School of Materials Science and Engineering, State Key Laboratory of Material Processing and Die & Mould Technology, Huazhong University of Science and Technology, 1037 Luoyu Rd, Wuhan, Hubei 430074, PR China article info Article history: Received 10 November 2011 Received in revised form 28 November 2011 Accepted 30 November 2011 Available online 22 December 2011 Keywords: La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 Y 2 O 3 stabilized ZrO 2 Impregnated cathode Polarization resistance Performance degradation abstract Composite cathodes of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) and Y 2 O 3 stabilized ZrO 2 (YSZ) are fabricated by impregnating the porous YSZ scaffold pre-formed on YSZ electrolyte substrate with a solution containing La, Sr, Co and Fe in desired composition. The performance stability of the cathodes is evaluated in air at 750  C for up to 120 h by elec- trochemical impedance spectroscopy under the condition of open circuit. An insignificant small amount of resistive phase SrZrO 3 is formed at 800  C during cathode preparation; however, its volume is not further increased at 750  C for 120 h, as indicated by the XRD results. The cathode polarization resistance (R p ) increases from 0.17 to 0.30 Ucm 2 after the 120 h test mainly due to the increase of the low frequency polarization resistance (R p2 ), which characterizes the low frequency processes in the reaction of oxygen reduction. The morphology change of the well connected LSCF particles to dispersive and flattened configuration accounts for the increase of the R p2 and in turn the degradation of cathode performance. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction (La, Sr)(Co, Fe)O 3 (LSCF) perovskite oxides are widely accepted as the cathode material for solid oxide fuel cells (SOFCs) that operate in the intermediate temperature between 600 and 800  C [1e3] due to their high electronic and ionic conductiv- ities. Unfortunately, the electrochemical performance of LSCF cathodes is not stable with time [4e7]; and the performance degradation becomes one of the most important issues that limit LSCF applications in SOFCs. It has been suggested that there are two possible mechanisms for the degradation of LSCF cathodes, that is, the instability of LSCF materials and the change of LSCF microstructure. The former leads to either forming resistive SrZrO 3 by reaction with Y 2 O 3 stabilized ZrO 2 (YSZ) electrolyte or Sr releasing from the LSCF to form prob- ably SrO at interfaces and reducing Sr content in the LSCF; and the later increases both ohmic and activation polarizations due to reduction in the connection between LSCF particles and the active surface area [6]. Developing a dense buffer layer in between YSZ electrolyte and LSCF cathode with Gd-doped CeO 2 (GDC) [8] or Sm-doped CeO 2 (SDC) [9] seems to improve electrochemical performance of the cell by suppressing Sr 2þ migration to form SrZrO 3 with YSZ; however, the cell with a GDC-LSCF composite cathode on YSZ electrolyte shows only increase in cathode polarization resistance R p at 800  C with time, rather than the ohmic resistance R o , which implies that * Corresponding author. Tel./fax: þ86 27 87558142. E-mail addresses: chibo@hust.edu.cn, chibo@tsinghua.org.cn (B. Chi). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 4388 e4393 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.11.151