Probing the Buried Metal-Organic Coating Interfacial Reaction Kinetic Mechanisms by a Hydrogen Permeation Based Potentiometric Approach

Abstract

Corrosion driven delamination of coatings is crucially determined by the rate of the cathodic oxygen reduction reaction at the buried metal-organic coating interface. Quantitative measurement of this rate at such interfaces by conventional techniques is impeded due to the blocking of ion transport by the coating. A new approach where hydrogen permeation is used as a tool to measure the oxygen reduction rate underneath coatings has been recently introduced. This permeation based potentiometry approach measures the rate of the oxygen reduction reaction by correlating the open circuit potential established as a consequence of the dynamic electrochemical equilibrium between hydrogen oxidation and oxygen reduction reactions on the coated exit side with the hydrogen uptake rate on the entry side. In this work, the interfacial reaction kinetics of the oxygen reduction reaction causing delamination of the coating are investigated by this hydrogen permeation based potentiometric approach. Moreover, thus performed prolonged cathodic polarizations of the palladium/coating interface have been found to destroy the interface, just like it is the case in the cathodic delamination process. Initial results obtained on ultra-thin films of iron on palladium are also presented, showing that the technique is applicable also on technically more relevant metal surfaces. Corrosion driven degradation of the buried metal/organic coating interface is of utmost interest in the contemporary space of coatings science. Earlier studies have shown conclusively that the oxygen reduction reaction (ORR) plays a fundamental role in the destruction of this buried metal/organic coating interface. The role of the interface between organic coating and metal has been object of intense research over last decades. Leidheiser et al.1 pointed out the key role of the cathodic ORR for the degradation process and also showed that diffusion processes such as water and oxygen transport through the coating can influence this delamination rate. Stratmann and co-workers 2-4 proposed a detailed delamination mechanism for a basic polymer coating on steel where galvanic coupling between the defect site of metal dissolution (local anode) and delamination site of electrochemical oxygen reduction (local cathode) supported by cation migration along the polymer/metal interface lead to the progressive deadhesion of the polymer from the underlying metal based on comprehensive analysis of the local electrode potential at the metal/polymer interface using primarily the Scanning Kelvin Probe (SKP) technique along with complementary Auger electron spectroscopy and mechanical deadhesion tests. Fürbeth and Stratmann 5-7 extended their studies to coated zinc (or galvanized steel), which also involves anodic processes at the interface. Also other works by Brewis et al. 8 and Dickie et al. 9 show the importance of interfacial electrochemical reactions on metal/polymer adhesion. Up to now our knowledge about the reactions and how they are determined by the interface itself is too rest...

An in situ spectro-electrochemical monitoring of aqueous effects on polymer/metal oxide interfaces

“…Therefore, Vijayshankar et al used a hydrogen permeation based potentiometric approach to quantitatively determine the interfacial reaction kinetics of the oxygen reduction. [19] A Devanathan-Stachurski permeation technique, where hydrogen can permeate from one side of an iron-on-palladium membrane, is used to quantify the ORR rate at a buried polymer/metal oxide interface on the other side. However, the question is posed on how the electrochemical reactivity of such metal/polymer coated systems is determined by the interfacial chemistry of the metal oxide/coating interface.…”

Cyclodextrins as Carriers for Organic Corrosion Inhibitors in Organic Coatings

“…18,19 A critical point is the bonding between the metal and the polymer, which can significantly reduce the delamination rate. 12,20,21 An approach for further suppression of cathodic delamination is the addition of active components into the organic coating. 22,23 The most effective inhibitors are based on Cr VI .…”

Limiting Current Density of Oxygen Reduction under Ultrathin Electrolyte Layers: From the Micrometer Range to Monolayers

“…In our previous work, [26,27] we developed a hydrogen permeation based potentiometric approach that was successfully used to indirectly measure the ORR current in bulk solution using a conventional reference system. Namely, the current‐potential relationship curve of oxygen reduction reaction on an electrode surface can be constructed by measuring the potential resulting from dynamic equilibrium of oxygen reduction and hydrogen oxidation and the corresponding hydrogen charging current density at its backside.…”