Abstract

Studying the mechanism of electrochemical reactions benefits from implementation of steady state and transient techniques such as electrochemical impedance spectroscopy (EIS). To develop an understanding of experimental results and how they relate to corrosion mechanisms requires their comparison with a mechanistic model. In this study, a physico-chemical model was used to simulate both the steady state potentiodynamic sweep, and the EIS response of cathodic reduction of H+ in an acidic environment. The modeled steady state potentiodynamic sweep, Nyquist plot and Bode plot were validated by comparison with experimental data.

Introduction

EIS is one of the techniques which is frequently used for studying electrochemical reactions on a metal surface in an aqueous environment. However, one of the main challenges in using EIS is the interpretation of results. Various interpretation methods and their associated uncertainties lead to ambiguous outcomes and often end up with a biased analysis One of the methods frequently used is the so-called "equivalent electrical circuit" method which models the response of and electrochemical system by matching it to that of a combination of "analogous" electrical circuit components, such as resistors, inductors, capacitors, etc.1,2 However, it is often seen that several different equivalent electrical circuits match the impedance response of an electrochemical system and therefore, the analysis of the results using this approach can be misguided and ambiguous1. Furthermore, it is not always easy to assign physical meaning to all the various electrical components of an equivalent circuit that seems to match the electrochemical data best.

Therefore, the main motivation of the present work is to directly model the impedance response of an electrochemical system by directly building a model involving electrochemical reactions and other associated processes such as mass transfer, chemical reactions, etc.3,4

Consequently, the simulated impedance response using this type of model can be directly used to analyze the experimental results and evaluate mechanisms of electrochemical reactions in a complex system. In this work, the transient electrochemical/physico-chemical models behind the mechanistic corrosion prediction package MULTICORPTM, have been used as a base for building a new module, LABCORP-ACTM, focused modeling the current response to an imposed alternating potential perturbation in an electrochemical system3. The physico-chemical, mathematical, and numerical aspects of this model are explained in detail in a previous paper 5. The model describes the main reactions and processes in an electrochemical system such as electrochemical and chemical reactions at the steel surface, transport of species between the steel surface and the bulk solution, and formation/growth of corrosion product layers. All these mechanistic features make this particular model a suitable tool for simulating the impedance response of electrochemical reactions associated with the corrosion of mild steel.

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