Corrosion behavior of coated steels and Mn- and Co-alloyed steels for separator materials on the cathode side in molten carbonate fuel cells

The corrosion behavior and the electrical resistivity of the oxide scale th at forms on alternative materials for bipolar plates in molten carbonate fu el cells (MCFCs) were investigated. Commercial stainless steels (SS) contai ning cobalt (Haynes 556) and manganese (Nitronic 30, Nitronic 50, and Nitro nic 60) were tested under cathodic MCFC conditions Additionally, 316L SS co ated with cobalt by thermal spraying was studied. Oxide-scale resistivity m easurements were coupled with observations of microstructural/compositional changes over time. All tested materials formed multilayered oxide scales. The composition of t hese phases was the key factor in determining the interfacial electrical re sistivity. The high cobalt content of Haynes 556 (18 wt%) did not decrease its electrical resistivity or improve its corrosion resistance. Thus, Go-co ntaining stainless steels, such as Haynes 556, do not appear to be candidat e bipolar plate materials for MCFCs. In contrast, the cobalt coating on 316 L SS did lead to improved corrosion resistance. The Nitronic alloys formed Mn-containing oxide scales, which appear to have a beneficial effect on low ering the resistivity of the oxide scale. The corrosion resistance of these Mn-containing stainless steels was greater than that of 316LSS, the presen t bipolar plate material.