Probing passivity of corroding metals using scanning electrochemical probe microscopy

Abstract

Passive films are essential for the longevity of metals and alloys in corrosive environments. A great deal of research has been devoted to understanding and characterizing passive films, including their chemical composition, thickness, uniformity, thickness, porosity, and conductivity. Many characterization techniques are conducted under vacuum, which do not portray the true in‐service environments passive films will endure. Scanning electrochemical probe microscopy (SEPM) techniques have emerged as necessary tools to complement research on characterizing passive films to enable the in situ extraction of passive film parameters and monitoring of local breakdown events of compromised films. Herein, we review the current research efforts using scanning electrochemical microscopy, scanning electrochemical cell microscopy (or droplet cell measurements), and local electrochemical impedance spectroscopy techniques to advance the knowledge of local properties of passivated metals. The future use of SEPM for quantitative extraction of local film characteristics within in‐service environments (i.e., with varying pH, solution composition, and applied potential) is promising, which can be correlated to nanostructural and microstructural features of the passive film and underlying metal using complementary microscopy and spectroscopy methods. The outlook on this topic is highlighted, including exciting avenues and challenges of these methods in characterizing advanced alloy systems and protective surface films.

Effect of Redox Mediators on Corrosion Behavior and Scanning Electrochemical Microscopy Response

“…The UME can be used amperometrically or potentiometrically while scanned close to the substrate’s surface to collect local current or potential maps of the metal studied. There are different operating modes of SECM that have been used to study corroding metals, including feedback mode, , generation-collection mode, , redox competition mode, , AC mode, , and potentiometric mode. , The use of SECM in corrosion science has been reviewed by many authors over the past decade. − …”