Sensing electrochemical activity in polymer coated metals during the early stages of coating degradation–Effect of the polarization of the substrate

This study explores the limitations of scanning electrochemical microscopy (SECM) in monitoring electrochemical activity near defects in polymer coatings used to protect metals from corrosive environments. It addresses potential chemical interferences during corrosion reactions that could affect the faradaic signals recorded at the SECM tip. The experiment involved applying both positive and negative polarization to the substrate relative to its corrosion potential in an aqueous solution to distinguish the contributions of half-cell processes. The analysis of signals detected at the SECM tip allowed for the monitoring of local concentrations of Fe(II) ions, hydrogen peroxide, and oxygen. Notably, the observed oxygen reduction reaction at cathodic sites on the corroding steel surface produced hydrogen peroxide as an intermediate, which complicates the accurate detection of dissolved metal ions at the tip. These findings highlight the importance of considering the dynamics between different electrochemical species during the investigation of coating performance under corrosion conditions.