A Dynamic Mechanistic Model of an Electrochemical Interface

Abstract

We propose a dynamic mechanistic model, based on nonequilibrium thermodynamics and electrodynamics, describing the transient response to current perturbations of an electrochemical double layer at the metal/electrolyte interface in the presence of electrochemical reactions. As an example of application, we have simulated the hydrogen oxidation reaction taking place in a polymer electrolyte fuel cell anode. The model is composed of (i) a 0-D inner layer submodel describing the composition of the metallic phase surface where water and reactant can be adsorbed, and the generated electric potential difference between the metal and the electrolyte phases; and (ii) a 1-D diffuse layer submodel in the electrolyte constituted by spatially moving ions and counterions, describing the ionic transport by migration - diffusion, based on the coupling of a Nernst - Planck's equation with a Poisson's equation. At the interface, the reaction kinetics depending on the potential difference is coupled with the inner-layer model through the charge conservation law. The numerical model allows dynamic simulation of the evolution of the local electric potentials (ionic and electronic) and concentrations inside the interface, and the influence of the working conditions on the impedance spectra characteristics. (C) 2006 The Electrochemical Society.