Abstract
Scanning electrochemical microscopy (SECM) provides spatially resolved insights into localized electrochemical activity on corroding materials, making it a promising technique for identifying corrosion sites associated with microstructural heterogeneity. Reducing probe size, in principle, can enable investigation of submicron features such as grain boundaries, inclusions, and heterogeneities within surface oxide films. In this work, feedback (FB) mode SECM was applied to investigate the localized electrochemical behaviour of cold-sprayed (CS) Cu coatings intended for use as a corrosion barrier in nuclear waste containers. These coatings exhibit a complex microstructure characterized by deformed grains, pores, and oxide inclusions at particle-particle boundaries that act as preferential corrosion initiation sites in aggressive environments. Macro electrochemical measurements confirmed that CS Cu coatings exhibit higher corrosion activity than wrought oxygen-free Cu, with localized damage observed near oxide inclusions at particle boundaries. To probe these submicron features electrochemically, SECM measurements were performed in diluted chloride solutions using ultramicroelectrodes (UMEs) and nanoelectrodes (NEs) with different redox mediators (RMs). While stable and reproducible FB responses were obtained employing UMEs, nanoelectrode-based SECM mapping was limited by rapid probe fouling and current drift, even under conditions designed to minimize Cu oxidation, such that prolonged nanoscale SECM imaging resulted in irreversible degradation of NE performance. These results demonstrate that, for actively corroding Cu surfaces, probe stability rather than instrumental resolution is the primary factor limiting the practical application of nanoscale SECM, underscoring probe stability as the key challenge for achieving reliable, localized nanoscale corrosion analysis. This work, therefore, defines both the capabilities and the current practical limits of FB mode SECM for studying localized electrochemical activity in CS Cu coatings.