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

Abstract

The corrosion behavior and the electrical resistivity of the oxide scale that forms on alternative materials for bipolar plates in molten carbonate fuel cells (MCFCs) were investigated. Commercial stainless steels (SS) containing cobalt (Haynes 556) and manganese (Nitronic 30, Nitronic 50, and Nitronic 60) were tested under cathodic MCFC conditions Additionally, 316L SS coated with cobalt by thermal spraying was studied. Oxide‐scale resistivity measurements were coupled with observations of microstructural/compositional changes over time. All tested materials formed multilayered oxide scales. The composition of these phases was the key factor in determining the interfacial electrical resistivity. The high cobalt content of Haynes 556 (18 wt%) did not decrease its electrical resistivity or improve its corrosion resistance. Thus, Co‐containing stainless steels, such as Haynes 556, do not appear to be candidate bipolar plate materials for MCFCs. In contrast, the cobalt coating on 316L SS did lead to improved corrosion resistance. The Nitronic alloys formed Mn‐containing oxide scales, which appear to have a beneficial effect on lowering the resistivity of the oxide scale. The corrosion resistance of these Mn‐containing stainless steels was greater than that of 316L SS, the present bipolar plate material.

Oxidation of stainless steel 316 and Nitronic 50 in supercritical and ultrasupercritical water

“…This oxide structure is formed by the diffusion of alloying elements; with an inner layer consisting of attributed to its higher Mn content. It has been observed that N50, and other steels with high Mn content, form Mn incorporated spinel compounds [37,38]. It has also been shown that the inclusion of larger amounts of Mn improves the oxidation resistance of chromium and iron by stabilizing the surface film formed on the alloy [39][40][41][42].…”

Corrosion Properties of Boron- and Manganese-Alloyed Stainless Steels as a Material for the Bipolar Plates of PEM Fuel Cells

“…This phenomenon was also observed for the steels tested, with 316L steel achieving better contact resistance values compared to 2205 steel with a higher Cr content. Although a higher manganese content was expected to result in the improved conductivity of the passive layer [ 80 ], the LDX steel showed higher values of contact resistance than the 2205 steel.…”