Single pit on iron generated by SECM: An electrochemical impedance spectroscopy investigation

The analysis of a single pit behavior on iron in various media (sulfuric acid, borate buffer, and potassium hydroxide solutions) is reported. The use of SECM technique to generate a single pit has allowed usual electrochemical techniques to be applied. Electrochemical impedance spectroscopy was used to characterize the pit propagation. In acidic solution, the pit returned to its passive state quickly whereas for the same amount for chloride ions generated locally, the pits remained active for long time in KOH solution. An intermediate behavior was evidenced in borate buffer for which a slow repassivation ascribed to the accumulation of insoluble corrosion products inside the pit was observed. The Raman analysis also evidenced the strong influence of the thin-layer-cell configuration on the nature of corrosion products in borate buffer.