Hot corrosion study of coated separator plates of molten carbonate fuel cells by slurry aluminides

The corrosion behavior of Al coated AISI 310S stainless steel by slurry and ion vapor deposition (IVD) was investigated as an electrolyte seal material in a mounted carbonate fuel cell (MCFC) at 650 °C. The results were compared with uncoated AISI 310S stainless steel and TA6V alloy. The characterization of the samples after exposure to the eutectic 62 mol.% Li2CO3–38 mol.% K2CO3 mixture at 650 °C up to 1000 h has shown the presence of LiAlO2 (coated samples), LiFeO2 and LiCrO2 (stainless steels), and Li2TiO3 (TA6V) oxides at the scale–melt interface. The electrochemical impedance spectroscopy (EIS) technique has shown high values of polarization resistances for TA6V and lower values for coated steels. The uncoated AISI 310S stainless steel have shown the lowest polarization resistance. A mechanism for the corrosion of Al-coated stainless steels in molten carbonate is proposed taking into account thermodynamic simulations, X-ray diffraction (XRD), scanning electron microscopy (SEM) characterizations, and EIS results. This proposed mechanism confirms that a slurry aluminide coating is able to improve the stainless steel behavior in molten carbonate. However, the TA6V titanium alloy is the most resistant material in molten carbonate but the Al-coated stainless steels appear as the best lifetime-cost compromise.