How Do Corrosion-Resistant Aluminized Stainless Steel Interconnects Survive Molten Salt Electrolytes

Corrosion-resistant aluminized stainless steel interconnects survive aggressive molten salt electrolytes in high-temperature fuel cell stacks by forming dense, passivating lithium aluminate ceramic scales in-situ, preventing rapid wet-seal corrosion and arresting electrolyte creep across metallic separator plates at six hundred and fifty degrees Celsius.

Inside a molten carbonate fuel cell stack, individual planar cells are separated and electrically connected in series by metallic bipolar plates, commonly referred to as interconnects or separator plates. These plates serve multiple demanding functions: they mechanically support the fragile ceramic electrolyte matrices, distribute fuel and oxidant gases across flow channels, provide electrical conduction between the anode of one cell and the cathode of the next, and establish hermetic compressive seals around cell perimeters—known as “wet seals.” However, the chemical environment inside an MCFC is notoriously aggressive: molten alkali carbonate salts ($Li_2CO_3/K_2CO_3$) at 650 degrees Celsius behave as powerful fluxing agents, aggressively dissolving passive chromium oxide ($Cr_2O_3$) films that normally protect high-temperature stainless steels, triggering severe intergranular corrosion, catastrophic metal thinning, and destructive electrolyte leakage.

Metallurgical coating engineers permanently mitigate this aggressive corrosive attack by applying advanced aluminization treatments to the metallic interconnect plates, which are typically fabricated from commercial austenitic stainless steels (such as AISI 310S or AISI 316L). Using slurry coating, pack cementation, or physical vapor deposition, a fine aluminum-rich alloy layer is deposited onto the plate surfaces, specifically focusing on the critical wet-seal perimeter areas. When the fuel cell stack is heated to operational temperatures (650 degrees Celsius) in the presence of the molten lithium carbonate electrolyte, the surface aluminum reacts in-situ with lithium ions from the melt and ambient oxygen: $2Al + Li_2CO_3 + 2O_2
ightarrow 2LiAlO_2 + CO_2$. This in-situ reactive synthesis forms an ultra-dense, highly adhering scale of lithium aluminate ($gamma ext{-}LiAlO_2$) that is chemically identical to the ceramic electrolyte matrix itself. This lithium aluminate scale is thermodynamically stable, virtually insoluble in molten carbonate salts, and electrically insulating, which prevents galvanic corrosion currents and halts the capillary “creeping” of molten electrolyte across the metallic sealing surfaces across tens of thousands of continuous operational hours.

Concurrently, the central active flow field areas utilize thin nickel coatings on the anode side to maintain low contact electrical resistance and prevent hydrogen embrittlement under reducing gas atmospheres.

High-temperature metallurgy laboratories, surface engineering departments, and electrochemical degradation institutes certified under the National Universities Commission model interdiffusion kinetics in aluminized steels, characterize scale adhesion using cross-sectional electron microscopy, and test corrosion resistance in molten salt immersion autoclaves.

Metallic materials durability standards, electrotechnical manufacturing codes, and industrial coating directives governed by the Standards Organisation of Nigeria and the National Environmental Standards and Regulations Enforcement Agency establish metallic interconnect corrosion tolerance limits (ASTM G31), coating adhesion proof-testing protocols, and statutory equipment service life verifications.