Development of MnCoO coating with new aluminizing process for planar SOFC stacks Jung Pyung Choi*, K. Scott Weil, Y. Matt Chou, Jeffry W. Stevenson, Z. Gary Yang Pacific Northwest National Laboratory, PO Box 999 Richland, WA 99352, USA article info Article history: Received 21 December 2009 Received in revised form 18 March 2010 Accepted 18 April 2010 Keywords: SOFC High temperature MnCo Aluminizing Cr volatility abstract Chromia-forming ferritic stainless steels find widespread use as interconnect materials in SOFCs at operating temperatures below 800  C, because of their thermal expansion match and low cost. However, volatile Cr-containing species originating from this scale can poison the cathode material in the cells and subsequently cause power degradation in the devices. To prevent this, a conductive manganese cobaltite spinel coating has been developed, but unfortunately; this coating is not compatible with glass-based seals between the interconnect or cell frame components and the ceramic cell due to reactions between the coating and the glass. Thus, a new aluminizing process has been developed to improve the stability of the sealing regions of these components, as well as for other metallic stack and balance-of-plant components. Copyright ª 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Solid oxide fuel cells (SOFCs) are solid-state energy conversion devices that produce electricity by electrochemical reaction of fuel and air across an ionic conducting electrolyte membrane. The operating temperature range of anode-supported SOFCs is between 600w800  C, making it possible to consider cost- effective high temperature oxidation-resistant alloys as replacements for conventional lanthanum chromate ceramics for construction of interconnects in SOFC stacks [1e3]. The chromia-forming ferritic stainless steels are considered among the most promising candidate materials for interconnect applications due to their electrically conducting oxide scale, appropriate thermal expansion behavior, and low cost [1e6]. For satisfactory long-term performance, however, there remain several issues, which may include chromia-scale evaporation [7,8] and subsequent cell poisoning [9e11], surface instability (including oxidation and reactions with neighboring components such as sealing glasses) [12,13], and increasing electrical resistance due to scale growth on the metallic inter- connects surface and potential spallation [14,15]. Newly developed alloys, such as Crofer22 APU (manufactured by ThyssenKrupp, Germany), are protected at elevated tempera- tures via formation of a unique scale comprised of a (Mn, Cr) 3 O 4 spinel top layer and a chromia or chromia-rich sub-layer [14,16,17]. This spinel offers lower volatility of Cr than chromia. However, this reduction is less than an order of magnitude. Therefore, it appears that further improvement in long-term scale stability is needed, particularly for SOFC stacks with an operating temperature over 700  C. For this purpose, protective interconnect coatings are being developed which, when applied to the cathode side, can help reduce Cr volatility, as the oxide scale growth occurs between the coating and the steel substrate. These coatings can also minimize the decrease in electrical conductivity caused by oxide scale growth by reducing the oxidation kinetics of the steel. Sr doped * Corresponding author. Tel.: þ1 509 376 3380; fax: þ1 509 376 2248. E-mail address: jungpyung.choi@pnl.gov (J.P. Choi). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 36 (2011) 4549 e4556 0360-3199/$ e see front matter Copyright ª 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2010.04.110