Molten salt synthesis of perovskite conversion coatings: A novel approach for corrosion protection of stainless steels in molten carbonate fuel cells

A novel conversion coating process has been developed to meet the stability requirements of stainless steel hardware in the demanding MCFC fuel cell environments. The process applies a perovskite-based coating by exploiting spontaneous oxidizing reactions of the metallic surface with La2O3 in eutectic alkali carbonate mixtures. By using well controlled synthesis procedures, conversion coating layers covering the entire metallic surface with a uniform and compact structure could be obtained. The as-formed coatings with a surface morphology of agglomerated crystallite particles consisted of a thin (<5 μm) LaFeO3 perovskite layer grown over a thicker (>5 μm) LiFeO2-rich layer. Test coupons of 316L stainless steel with the perovskite conversion coating were analyzed for corrosion protection and interfacial resistivity properties. It was found that the conversion coating is highly conductive while showing excellent long-term corrosion stability in simulated MCFC environments. These results suggested that perovskite coatings formed by molten salt conversion reactions could be particularly attractive to confer optimal protection and electrical continuity to MCFC current collectors.

► Perovskite coatings were obtained by thermochemical conversion reactions in a molten carbonate bath.
► Potential method for corrosion protection of stainless steels against oxidation and hot corrosion.
► The conductive nature of the perovskite coatings is also promising for high temperature electrical applications.
► High quality dual-layer coating structure was obtained consisting of LaFeO3 layer grown over a LiFeO2 innermost layer.
► Molten carbonate corrosion of a 316L stainless steel was drastically decreased after the perovskite conversion treatment.