Simulated and measured response of oxygen SECM-measurements in presence of a corrosion process

Scanning electrochemical microscopy (SECM) with its high spatial resolution and chemical selectivity is a powerful technique for studying a wide range of corrosion processes. A common procedure to detect qualitatively a corrosion activity on a metal substrate consists of measuring the local oxygen concentration. The aim of this work is to clarify the local impact of the O2 measurement and the undesired effect on the corrosion process. By means of numerical simulation the variations of the anodic and cathodic currents on the aluminum substrate, as well as concentration profiles, are obtained. The multi-ion transport and reaction model (MITReM) is used considering the homogeneous reactions taking place in the solution, transport of species dominating the corrosion process and the electrochemical reactions. The model case study in this work is corrosion of pure aluminum in chloride solution. We concluded that amperometric O2 SECM measurements lead to a local increase of the solution pH and decrease of partial current densities for O2 reduction on the metal. This influence becomes significant when the distance to the substrate and when the size of the active surface is comparable with the size of the SECM probe.