Tracking element-specific dissolution during pitting corrosion: an operando ICP-AES–electrochemical study of the CoCrFeMnNi Cantor alloy

Abstract In this work, a flow-through electrochemical–ICP-AES platform for operando monitoring of pitting corrosion on the CoCrFeMnNi high-entropy alloy is introduced. This setup combines localized chloride injection, potentiostatic control, and online, element-resolved dissolution analysis, thereby addressing a long-standing gap in mechanistic studies of early pit initiation and repassivation. Experiments in 0.5 M H 2 SO 4 with Cl - injection enabled the continuous transfer of dissolved species from the electrode surface to the ICP-AES detector, achieving sub-ppb sensitivity and allowing quantification of Co, Cr, Fe, Mn, and Ni dissolution rates during the pitting process. The results reveal four characteristic stages, namely, incubation, initiation, propagation, and repassivation, with subtle but systematic differences between alloying elements. Co and Fe contribute slightly more during initiation, while Cr plays a dominant role during repassivation, reflecting its critical involvement in passive film regeneration. Charge analysis demonstrates that repassivation consumes a quantity of charge far greater than expected for compact passive films, pointing instead to a slow, iterative re-formation and partial dissolution of hydrated oxides. This methodology provides new mechanistic insight into the dynamic sequence of film breakdown, localized dissolution, and film repair in multicomponent alloys, and establishes a versatile framework for studying localized corrosion processes with element-specific resolution.