In our previous study copper oxide additions were used to accelerate the formation of perovskite LaFeO 3 conversion coatings on stainless steels from molten carbonate baths. Incorporation of copper particles into the growing coating was an additional effect resulting in the formation of a composite Cu-LaFeO 3 structure. In continuation to our previous study, the aim of this work is to report the effect of copper additions on long-term stability and performance of perovskite conversion coatings under IT-SOFC interconnect conditions. To this end, a Cu-LaFeO 3 coated K41 18Cr ferritic stainless steel was examined in air at 700 • C up to 1000 h. In order to simulate properly the situation of a real IT-SOFC cell, Area Specific Resistance (ASR) and Cr-barrier properties of the coated steel were evaluated simultaneously with a special coating characterization setup. Studies were conducted by comparison with single-phase LaFeO 3 coatings obtained in a molten carbonate bath similar to that used for the formation of the composite Cu-LaFeO 3 coatings but without the addition of copper oxide. Copper addition did not change the general morphology of the perovskite coating, which remains a multi-layer coating, being composed of an outer LaFeO 3 crystalline layer, a middle Fe-rich oxide and two inner Fe-Cr rich oxide layers. However, copper was beneficial in promoting a thinner and more stable coating structure along with finer perovskite grain size. These structural improvements were further confirmed by the results obtained with electrical measurements that showed a better ASR behavior of the Cu-LaFeO 3 coatings. On the other hand, no relevant copper effects could be detected on the coating oxidation stability and on the Cr-barrier properties of the perovskite conversion coatings. Both LaFeO 3 and Cu-LaFeO 3 coatings showed similarly high coating stability and excellent Cr-barrier capability in experiments conducted at 700 • C up to 1000 h. In definitive, dual-phase Cu-LaFeO 3 seem more promising systems for IT-SOFC interconnects than single-phase LaFeO 3 conversion coatings, although further improvements in ASR electrical properties are needed. Conventional 18Cr ferritic stainless steels are promising candidates for Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC) interconnects as they provide an optimal combination of cost, structural and chemical composition properties.1-3 However, the use of 18Cr ferritic stainless steels is not without its cost. Issues are related to formation of insulating chromia layers with high tendency to evaporate during their exposure to the IT-SOFC operating conditions. Hence, coating with a ceramic layer made of electro-conductive and corrosion-resistant spinel 4 or perovskite 5 oxides is usually considered a necessary addition for ensuring a stable and low Area Specific Resistance (ASR), which is a common way to express interfacial ohmic resistance in electrochemical devices. In particular, (Co-Mn) or (CuMn)-based spinel oxides as well as (La-Cr), (La-Co) or (La-Mn) perovskite oxides h...
Chromium poisoning is a widely recognized degradation process in solid oxide fuel cells (SOFC). Stainless steel interconnect plates, in direct contact with the cathode, have been identified as the major chromium source, raising a need for electrically conducting protective coatings for the interconnects. This work evaluates four different manganese-cobalt protective coatings manufactured on thin steel foils, made by three commercial companies and a research centre. Area specific resistance, coating microstructure, and chromium retention are compared. Measurements were done in a humid atmosphere over 1000 hours at 700 °C. An innovative measurement setup was used, in which the coated steel samples are stacked adjacent to thin palladium foils with a screen-printed lanthanum strontium cobalt layer, replicating an SOFC cathode. As a conclusion, TeerCoating Ltd’s and Turbocoating S.p.A’s coatings performed similar to the Sandvik Material Technology’s cerium-cobalt reference coating, and could be employed as such in SOFC applications.
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