A kinetic model to simulate charge flow through an electrochemical half cell

Abstract

A kinetic model of the electron transfer at the electrode / electrolyte solution interface is developed, implemented in a Monte Carlo framework, and applied to simulate this process in idealised systems consisting of the primitive model of electrolyte solutions limited by an impenetrable conducting surface. In the present implementation, a charged, spherical interface surrounding an equally spherical sample of electrolyte solution is introduced to model a single-electrode system, providing the computational analog to the conceptual half-cell picture that is widely used in electrochemistry. The electron transfer itself is described as a simple surface hopping process underlying a first order reaction corresponding to one of the coupled M/M$^+$ and X$^-$/X half reactions. Then, the electron transfer at the interface is combined with the self-diffusion of ions in the electrolyte solutions whose role is to supply reagents and disperse products, allowing the system to settle in a stationary non-equilibrium state. Simulations for the primitive model of electrolyte in contact with a charged impenetrable surface show that, after a brief transient, the samples sustain a steady current through the electrolyte solution. The results quantify the dependence of the current on: the overall charge of the electrode, the electrolyte concentration, the solvent viscosity and the kinetic parameter $k_e$ that represents the rate of the electron transfer for each ion in contact with the electrode. Since the simulated interface is very idealised, strategies to overcome the limitations of the present model are outlined and briefly discussed.