Corrosion behavior and interfacial resistivity of bipolar plate materials under molten carbonate fuel cell cathode conditions

A material is needed for bipolar plate materials in molten carbonate fuel cells (MCFCs) that combines the low oxide resistivity of 316L stainless steel (SS) with the low corrosion rate of the type 310 SS. We tested a group of materials that included Nitronic 50 SS and a newly developed high-temperature nickel-rich alloy, having chromium contents ranging from 16 to 31 wt %. Our results indicate that chromium content is the primary determinant of oxide scale composition and resistivity. In the MCFC cathode compartment, all tested alloys formed a duplex structure with an inner Cr-rich layer and an outer Fe-rich one. The composition of the inner Cr-rich layer was determined by the chromium content of the base alloy and has a controlling effect on scale resistivity. Oxide scale resistivity was measured for three electrolyte compositions: Li/K, Li/Na, and newly developed (Li, Na, Ca, Ba) carbonates. Changes in the physical/mechanical properties (spallation/cracking) in the oxide scale of 316L SS provided an understanding of its resistivity fluctuations over time.