Electrochemical Insight into the Role of H₂O₂ in Galvanostatic Passivation of AISI 316L Austenitic Stainless Steel in Citric Acid Electrolyte

In this study, AISI 316L stainless steel was passivated under galvanostatic conditions in citric acid solutions in the absence and presence of hydrogen peroxide (H₂O₂). The electronic-semiconducting properties of the resulting passive layers were assessed using Mott–Schottky (MS) analysis. Moreover, the corrosion resistance of the passivated alloy produced under different experimental conditions was examined using cyclic potentiodynamic polarization and electrochemical impedance spectroscopy test methods. The passive films were also characterized using grazing incidence X-ray diffraction. The MS results revealed that higher passivating current densities foster film formation, leading to lower concentration of charge carriers, which beneficially influences the corrosion performance of the alloy. Besides, the addition of H₂O₂ to the passivating electrolyte was accompanied by deterioration of passive film properties and inferior corrosion resistance. The DC and AC corrosion test results were also consistent with those of the MS approach. Last, but not least, the samples that were surface treated in H₂O₂-containing baths, especially those passivated at higher current densities, were more prone to localized attack compared to their counterparts produced in H₂O₂-free electrolyte.