Corrosion Behavior and Interfacial Resistivity of Bipolar Plate Materials under Molten Carbonate Fuel Cell Cathode Conditions

Abstract

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.

Fuel Cells: Principles, Types, Fuels, and Applications

“…Chromium-containing SS forms a LiCrO 2 inner layer under operating conditions, which is a barrier against Fe 3 diffusion, thus decreasing the corrosion. [124,125] Cost reduction is still a major factor in the fabrication of fuel cell components. An overview on molten carbonate fuel cell materials has been published.…”

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

“…Figure 2 shows the weight loss results of specimens after immersion in the carbonate melt at 650 o C. A. C. Schoeler et al (4) have shown the corrosion resistance of stainless steels under MCFC conditions is mainly influenced by the Cr content of the base metal. In Figure 2, the weight loss result shows 316L contained low Cr content has the highest weight loss among the specimens.…”

The role of temperature on the corrosion and passivation of type 310S stainless steel in eutectic (Li+K) carbonate melt

“…In detail, type 310S steel exhibits a much slower oxide growth rate, although 316L steel is sometimes preferred as its oxide scale has a higher electrical conductivity [1]. The corrosion resistance of these steels basically relies on the rapid formation of a protective passive oxide scale that is able to suppress the outward diffusion of base-metal cations (mainly, iron) into the molten electrolyte.…”

“…After long test periods, the two-layered structure of the passive scale consists of an external LiFeO 2 layer and an inner Cr-rich oxide layer. The passivity of stainless steels depends on the stability of this inner layer [1,2]. In the case of the high-Cr type 310S steel (ca.…”

“…Conversely, the 316L steel forms higher inner conductive spinel layer mainly consisting of LiFe 5 O 8 and FeCrO 4 phases. The spinel layer is less effective in retarding the outer iron diffusion, thus leading to a faster growth of the external LiFeO 2 layer and to an overall higher thickness of the scale [1,3].…”