Journal of Power Sources 184 (2008) 172–179 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour MnCo 1.9 Fe 0.1 O 4 spinel protection layer on commercial ferritic steels for interconnect applications in solid oxide fuel cells X. Montero a,b,∗ , F. Tietz b , D. Sebold b , H.P. Buchkremer b , A. Ringuede c , M. Cassir c , A. Laresgoiti a , I. Villarreal a a Ikerlan-Energia, Parque Tecnologico de Alava, Juan de La Cierva 1, 01501 Mi˜ nano, Spain b Jülich Forschungszentrum, Institute for Materials and Processes in Energy Systems, 52428 Jülich, Germany c LECA UMR7575, ENSCP, 11 rue Pierre et Marie Curie, 75231 Paris cedex 05, France article info Article history: Received 15 April 2008 Received in revised form 15 May 2008 Accepted 24 May 2008 Available online 8 June 2008 Keywords: Solid oxide fuel cell Interconnect Oxidation Coating Resistivity abstract In solid oxide fuel cells (SOFC) for operating temperatures of 800 ◦ C or below, the interconnection plates can be made from stainless steel. This is a big economic advantage, but energy losses can be caused by undesirable reactions between the alloys and other SOFC components. The use of coatings on interconnect stainless steels can reduce this degradation. A MnCo 1.9 Fe 0.1 O 4 (MCF) spinel not only significantly decreases the contact resistance between a La 0.8 Sr 0.2 FeO 3 cathode and a stainless steel interconnect, but also acts as a diffusion barrier to prevent Cr outward migration through the coating. The level of improvement in electrical performance depends on the ferritic substrate composition. For Crofer22APU and F18TNb, with a Mn concentration of 0.4 and 0.12wt%, respectively, the reduction in contact resistance is significant. In comparison, limited improvement is achieved by application of MCF on IT-11 and E-Brite containing no Mn. No influence of the minor additions of Si or Al is observed on contact resistance. The MCF protection layer bonds well to the stainless steel substrates under thermal cycling, but the thermal expansion difference is too large between the La 0.8 Sr 0.2 Co 0.75 Fe 0.25 O 3 contact layer used and Crofer22APU and IT-11. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The SOFC designed by Ikerlan for an operating temperature of 600–800 ◦ C is a metal-supported tubular fuel cell [1,2], developed to be used for electricity and heat generation in domestic systems. This electrochemical device will operate at temperatures below 800 ◦ C, allowing the ceramic components to be replaced, i.e. LaCrO 3 , by metallic materials as current collectors [3–5]. Several earlier publications were dedicated to cathode current collectors [3,4,6]. The characteristics of these current collectors are the following: 1- Compatibility of the thermal expansion coefficient with that of the ceramic components, i.e. electrolyte material (yttria- stabilised zirconia YSZ, 10.5 × 10 -6 K -1 between 20 and 1000 ◦ C [3,4]) and cathode material (strontium-substituted lanthanum ferrite, La 0.8 Sr 0.2 FeO 3 , 13.3 × 10 -6 K -1 [7]). 2- High electronic conductivity in cathode atmosphere. In the case of oxides with low conductivity, the oxide scale should be mod- ified or should have a slow growth rate [8,9]. ∗ Corresponding author at: Ikerlan-Energia, Parque Tecnologico de Alava, Juan de La Cierva 1, 01501 Mi˜ nano, Spain. Tel.: +34 945297032; fax: +34 945296926. E-mail address: xmontero@ikerlan.es (X. Montero). 3- Very low chemical reactivity with the cathode material and no chromium evaporation at the operating temperature. 4- The interconnect should be easy to manufacture, which is a key point in determining the feasibility of large-scale manufactur- ing. 5- The cost of raw materials as well as manufacturing processes for the interconnect also need to be as low as possible so that they will not present major obstacles to commercialization. A reduc- tion in the cost of the interconnect especially is of particular significance for the metal-supported tubular SOFC. Ferritic steels with more than 16% of chromium content are the most desirable materials combining most of these properties [3]. A disadvantage of the metallic interconnects is the formation of oxide scales leading to significant ohmic losses. The oxidation of steels can be improved, and many studies reported on the effect of small amounts of alloyed elements in oxidation, demonstrating that the oxidation of steels does not only depend on the Cr content. The most commonly used reactive elements (RE), which are added in concentrations of a few hundreds or tenths of a percent, are Y, La, Ce and Nd as metallic or oxide particles. Apart from improved oxide scale adhesion, the RE addition leads to a substantial decrease in oxide growth rate [10,11] and in the case of low Cr alloys they pro- mote the selective oxidation of chromium [12]. If the RE is added 0378-7753/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2008.05.081