Study On Corrosion Behavior And Mechanism Of316L Stainless Steel Bipolar Plate With Chromium Carbide Coating

Thin stainless steel, with the advantage of low cost, easy processing and high mechanical strength, is one of the most competitive materials as bipolar plates in proton exchange membrane fuel cell (PEMFC). But it must be modified to obtain good resistance in PEMFC’s applications.Chromium carbide coating, which not only has excellent conductive properties but also shows relatively good anti-corrosion properties, is the most likely stainless steel bipolar plate modification technology to be used in commercialization of PEMFC.In-depth study of modified stainless steel with chromium carbide’s electrochemical performance in PEMFC environment is not only beneficial to understand its corrosion process, but also guide its preparation. Thereby it will improve the coating’s performance and accelerate its application.In this paper, traditional electrochemical test methods such as potentiostatic polarization, potentiodynamic polarization, EIS and scanning electrochemical microscopy were used to study the electrochemical properties of stainless steel bipolar plate having chromium carbide coating in simulated PEMFC environment. The results showed that the polarization curve of316L stainless steel with chromium carbide presented all characteristics of the anode polarization curves and the pitting corrosion resistance of the coated316L stainless steel was improved. The EIS results indicated the coated steel’s reaction resistance increased and electric double layer capacitors declined. It suggested that chromium carbide coating had high resistance and low capacitance, and acted as a barrier layer, which inhibited the corrosive ion from corroding the substrate.Pitting corrosion occurred on the surface of316L stainless steel with chromium carbide in simulated cathodic environment at80℃. The corrosion kinetics equations was i0=7.6341t-0.5. The result manifested the speed of pitting corrosion was controlled by surface coating’s dissolution in our test conditions.The surface of316L stainless steel with chromium carbide was in uneven dissolution in local area no matter when it was at open circuit potential or in simulated operation environment. In simulated operation conditions, the corrosion of316L stainless steel with chromium carbide was obviously accelerated in local area.The corrosion current increased first, and then slightly decreased with immersion time prolonging. The defects of coating led to uneven corrosion in local area.