Effect of Alloy Elements on the Corrosion Resistance and Electrical Conductivity of Austenitic Stainless Steel for MCFC

Bipolar plate and current collector are important stainless steel components of the molten carbonate fuel cell (MCFC) because they supply the pathway of the electron flow between each unit cell. However, these stainless steel components are prone to corrosion in the hot corrosion environment and corrosion products forming on the surface increase the ohmic resistance. In addition, hot corrosion reduces the mechanical strength of the current collector, accelerates electrolyte loss, and finally leads to degradation in cell performance. Therefore, corrosion of stainless steel components is one of the main problems in MCFC systems. To solve these problems, various methods have been studied, such as addition of alloy elements, surface coatings and replacement with higher grade materials. Corrosion resistance of stainless steels is evaluated by potentiodynamic polarization test and weight loss measurements. Electrical conductivity of specimens is measured in molten carbonate at 650 ^oC. Results from electrochemical tests show that high Cr content causes the formation of a dense and thin oxide layer, subsequently improving the corrosion resistance. However, high Cr content gives rise to inner oxide penetration. Mn enrichment occurs in the oxide layer and may lead to an increase in electrical conductivity. In addition, minor elements such as Si, Nb and N may contribute to the improvement of corrosion resistance and electrical conductivity.