Exploring the Kinetics of Oxygen Reduction Reaction in Relation to Pitting Corrosion Resistance in Fe-Cr Alloys

Abstract

Pitting corrosion, a major concern in materials science and engineering, threatens critical metallic structures and components. Its implications reach across daily life and industries such as energy, transportation, and infrastructure, potentially causing environmental harm, economic losses, and even loss of life. This complex process is influenced by factors including material composition, local environment, and mechanical stresses.1 Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film.2 In Fe-Cr alloys, the ORR occurs on this film, undergoing a mixed diffusion and kinetic-controlled process. The number of electrons involved and the corrosion rate are determined by the thermodynamically stable state of the passive film.This research studies the ORR kinetics on FeCr alloys fabricated by arc-melting, using both computational and experimental methods. The rotating disc electrode technique was employed across various Fe:Cr alloys in alkaline and neutral electrolytes. The Koutecky-Levich analysis showed a dominant four-electron ORR pathway in all tested Fe-Cr alloys, with the ORR significantly inhibited by higher proportions of Cr2O3 in the film, suggesting a correlation with high chromium content. Experimental ORR overpotentials, when combined with theoretical potential-pH (Pourbaix) diagrams, helped discern the likely characteristics of the passive films on the alloys. It was deduced that the catalytic properties of potential passive films increased in the order Cr2O3 < Fe3O4 < Fe2O3 < FeCr2O4. These findings, excellently aligned with density functional theory (DFT) modelling, underscore the role of increased chromium levels in slowing pitting progression by suppressing the ORR.In summary, this research offers distinctive insights into the correlation between the kinetics of the ORR and the resistance to localized corrosion in Fe-Cr alloys, which enhances our understanding of the underlying mechanisms of pitting corrosion. Keywords FeCr alloy, pitting corrosion, ORR, rotating disc electrode, DFT Reference [1] B. Zhang, J. Wang, B. Wu, X. W. Guo, Y. J. Wang, D. Chen, Y. C. Zhang, K. Du, E. E. Oguzie, and X. L. Ma, Nat. Commun. (2018) 9, 2559.[2] G. T. Burstein, P. C. Pistorius, and S. P. Mattin, Corros. Sci. (1993) 35, 57.