Available online at www.sciencedirect.com Journal of Power Sources 177 (2008) 376–385 DC electrodeposition of Mn–Co alloys on stainless steels for SOFC interconnect application Junwei Wu a , Yinglu Jiang a , Christopher Johnson b , Xingbo Liu a,∗ a Mechanical and Aerospace Engineering Department, West Virginia University, Morgantown, WV 26506, USA b National Energy Technology Laboratory, Department of Energy, Morgantown, WV 26507, USA Received 1 November 2007; received in revised form 14 November 2007; accepted 15 November 2007 Available online 9 January 2008 Abstract High conductivity coatings that resist oxide scale growth and reduce chromium evaporation are needed to make stainless steel interconnect materials viable for long-term stable operation of solid oxide fuel cells (SOFC). Mn 1.5 Co 1.5 O 4 spinel is one of the most promising coatings for interconnect application because of its high conductivity, good chromium retention capability, as well as good CTE match to ferritic stainless steels. Mn–Co electrodeposition followed by oxidization is potentially a low cost method for fabrication of (Mn,Co) 3 O 4 spinel coatings. This work looks at the co-deposition of Mn–Co alloys for this application. As a guide to optimize the deposition process, characterizations of the cathodic reactions and reaction potentials are done using polarization curves. It was found that as cobalt concentration was varied that the alloy composition became richer in cobalt, indicating that the deposition is regular co-deposition process. It was also found that at 0.05 M Co concentration in excess gluconate the Mn–Co alloys composition could be tuned by varying the current density. Coatings with Mn–Co around 1:1 could be obtained at a current density of 250 mA/cm 2 . However, the higher potential increased hydrogen production making the films more porous. Oxidation of the alloy coatings showed that much of the porosities could be eliminated during oxidation. It was found in a number of samples that fully dense coatings where obtained. The composition of the oxidized coating was found to become enriched in Mn, possibly due to the Mn fast diffusion from the substrate. © 2007 Elsevier B.V. All rights reserved. Keywords: Interconnect; Manganese; Cobalt; SOFC; Electrodeposition 1. Introduction The solid oxide fuel cells (SOFCs) are promising candidates for future energy conversion systems because they have higher energy conversion efficiency than conventional heat engine sys- tems and other types of fuel cells. Interconnects are in contact with both electrodes and act as electrical connection in a SOFC stacks, and thus there are a number of requirements they must meet. They must exhibit long-term stability in both oxidizing (air side) and reducing (fuel side) environment, good conduc- tivity, and good CTE match with other ceramic components [1]. Decreasing the operation temperature of SOFC to between 600 and 800 ◦ C enables the use of cheap metallic interconnects mate- rials such as stainless steel or other chromia-forming alloys [2,3]. ∗ Corresponding author. E-mail address: xingbo.liu@mail.wvu.edu (X. Liu). However, bare metal does not remain stable after long time operation at high temperature [4] because of continued scale growth and high volatility of Cr(VI), which can contaminate electrolyte and cathode, and cause degradation of SOFC perfor- mance. Even newly developed Fe–Cr–Mn [5] alloys, Crofer 22 APU (ThyssenKrupp VDM) and ZMG232 (Hitachi Metals), that form (Mn,Cr) 3 O 4 spinel as the top scale layer do not eliminate Cr volatility completely [1]. One of the most effective approaches to improve the inter- connect properties is to apply surface coatings to provide better conductivity, reduced scale growth and Cr volatility. Recently, cobalt and containing spinels, such as MOCVD deposited Co 3 O 4 [6], MnCo 2 O 4 by slurry coating and electroplating fol- lowed by oxidation [7,8], electroplating and PVD coatings of pure cobalt [9,10], have shown promising results for SOFC applications due to good conductivity and improved chromium retention capabilities, nevertheless, Mn 1.5 Co 1.5 O 4 spinel is the most promising, because of its high conductivity (60 S/cm at 0378-7753/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2007.11.075