Impedance spectroscopy of single chamber SOFC P. Jasinski * , T. Suzuki, F. Dogan, H.U. Anderson Electronic Materials Applied Research Center, University of Missouri-Rolla, 303 MRC, Rolla, 65401 Missouri, USA Abstract The mechanism of operation of a single chamber solid oxide fuel cell (SOFC), where a mixture of fuel and oxidant is utilized, is not completely understood. In this study, electrolyte supported single chamber SOFCs consisting of lanthanum strontium cobalt ferrite cathode, yttria stabilized zirconia (YSZ) electrolyte and nickel cermet anode have been fabricated and investigated in the intermediate temperature range (500–700 8C) using propane–air mixtures as fuel. An attempt has been made to separate the cathode and anode overpotentials on the fuel cell performance using impedance spectroscopy and utilizing different anode compositions. Low and high frequency relaxations of impedance data were attributed to the anode and cathode overpotentials, respectively. D 2004 Elsevier B.V. All rights reserved. PACS: 84.60.D; 66.30.H Keywords: Impedance spectroscopy; Single chamber fuel cell; Solid oxide fuel cell; Propane fuel 1. Introduction In contrast to conventional solid oxide fuel cell (SOFC), single chamber fuel cells operate in a mixture of fuel and oxidant gas, and therefore, cell structure can be significantly simplified [1,2]. Recently, relatively high current and power densities were obtained in single chamber SOFCs at moderate operating temperatures (300–600 8C) [3,4]. How- ever, little information is available on the mechanism of power generation in single chamber SOFCs. This knowl- edge may help in optimizing the cell structure and improving the cell performance. Although the SOFC configuration is significantly simplified in a single chamber cell, the reactions between the SOFC materials and gas mixtures become more complex. The oxygen partial pressures at the anode and cathode sides are not fixed and do depend on the catalytic activity of the electrodes, temperature, fuel and oxidant ratio and its flow rate. Ideally, the fuel reaction should take place only at the anode. For the fuel used in current investigation (mixture of 10% propane and 90% air), the most favorable reaction can be described by Eq. (1): C 3 H 8 þ 2O 2 Y2CO þ CO 2 þ 4H 2 ð1Þ Reaction (1) leads to a decrease of oxygen partial pressure in the vicinity of the anode and consequently to an increase of the voltage according to the Nernst relation. Once the load is connected to the cell, the current starts to flow due to reactions (2) and (3) occurring at the anode and (4) cathode: H 2 þ O 2 YH 2 O þ 2e  ð2Þ CO þ O 2 YCO 2 þ 2e  ð3Þ 1=2O 2 þ 2e  YO 2 ð4Þ As a consequence of the reaction (2) the following reaction (5) may also occur: C 3 H 8 þ 3H 2 OY3CO þ 7H 2 ð5Þ Since reaction (1) is exothermic (DG=903 kJ at 600 8C) and reaction (5) is endothermic (DG=4 kJ at 600 8C), the cell temperature is influenced by reaction kinetics. The reactions become even more complex when the cathode becomes catalytically active as well. In this case, cathode 0167-2738/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2004.09.041 * Corresponding author. On Post Doctoral Fellowship from Gdansk University of Technology, Poland. Tel:. +1 573 3414858; fax: +1 573 3416151. E-mail address: piotrj@umr.edu (P. Jasinski). Solid State Ionics 175 (2004) 35 – 38 www.elsevier.com/locate/ssi