Corrosion Product Formation Monitored Using the Feedback Mode of Scanning Electrochemical Microscopy with Carbon Microelectrodes

When studying magnesium alloy corrosion, the quantitative analysis of probe approach curves acquired in the feedback mode of scanning electrochemical microscopy is particularly challenging. The oxidation current of the ferrocenemethanol mediator recorded at conventional Pt microelectrodes is systematically plagued by parasitic faradaic contribution from the oxidation hydrogen. Herein we demonstrate the use of carbon microelectrodes to remove this unwanted faradaic contribution, allowing for in situ time lapse monitoring of the corrosion product layer growth. Applying a one-dimensional diffusion approximation, the extracted rate constants obtained by scanning electrochemical microscopy probe approach curves could be correlated to the corrosion product film thickness and porosity obtained by transmission electron microscopy.