Perovskite Conversion Coatings as Novel and Simple Approach for Improving Functional Performance of Ferritic Stainless Steel SOFC Interconnects

Abstract

A novel type of iron conversion process has been recently developed to produce dense and adherent LaFeO3 perovskite coatings onto ferritic stainless steel surfaces by reaction with La2O3 dissolved in specially‐formulated alkali molten carbonate baths. The major application of LaFeO3 perovskite coatings is for use as electrically conductive and Cr barrier layers for enhancing the functional performance of solid oxide fuel cell (SOFC) stainless steel interconnects. An overview of the molten salt bath conversion process including the effect of chemical accelerants on structure and morphology of the deposited perovskite coatings is illustrated in this work. Latest results on SOFC coating functional properties obtained in recent European Union (EU) funded projects are also briefly mentioned. In particular, the tight correlation between coating thickness and electrical functional properties in terms of area specific resistance is highlighted here. Although thickness dependency may indicate a mediocre electrical conductivity of LaFeO3 coatings produced by the conversion process, nonetheless very promising ASR results could be obtained in SOFC cathode environments at 700 °C with optimized coating structures and appropriate low coating thickness, thus suggesting a high potential of the conversion process for SOFC interconnect applications.

Protective Coatings for Ferritic Stainless Steel Interconnect Materials in High Temperature Solid Oxide Electrolyser Atmospheres

“…Interesting results have been recently obtained also with chemical LaFeO3 (LFO) perovskite coatings produced by molten salt surface modification treatments [37][38][39]. These treatments have been carried out at around 600 • C in La 2 O 3 -containing molten carbonate reaction baths.…”

“…Cr presence in the outer perovskite layer is minimized because Cr dissolves in the reaction bath as soluble chromate during the iron conversion process, which represents a further advantage. Perovskite LFO coatings with variable structures and thicknesses ranging from the sub-micron level to several microns can be obtained by properly tuning reaction conditions and bath chemical composition [37]. Functional properties and oxidation resistance, including the influence of coating thickness, were studied thoroughly on K41 and Crofer 22H steel grades under SOFC conditions, namely at 700 • C in humid air (3% relative humidity).…”