Corrosion and Passive Layers of 316L Stainless Steel in the Context of PEMFC Application

Aiming at a better understanding of the corrosion resistance of stainless steel within the frame of its use for bipolar plates in proton exchange membrane fuel cell applications, model electrochemical investigations were conducted in well-defined experimental conditions on 316L grade steel. Passive films were grown electrochemically at various potentials in an aqueous electrolyte at pH 3, and semi-conducting characteristics and thicknesses were determined via electrochemical impedance spectroscopy methods. A restructuring of the passive film formed under polarization takes place after a rest at open circuit potential, and the resulting corrosion current densities were measured with the polarization resistance technique, providing non-invasive quantification, pathing the way to establish direct interrelationships to characteristics of passive films grown electrochemically. For the first time, corrosion current densities were found to scale exponentially with the apparent acceptor charge carrier density ( N A ) associated with defects in the Cr-oxide layer demonstrating N A ’s pivotal role for electrochemically grown passive film on stainless steels. The characteristics of the native oxide layer of the pristine sample were systematically found out of the trends established for the electrochemically grown passive film, highlighting the environmental gap existing with electrochemical experimental conditions for the passive film formation on 316L SS.