Ion adsorption at a metallic electrode: an ab initio based simulation study

Abstract

A method for parametrizing, from first principles density functional theory calculations, amodel of the interactions between the ions in an ionic liquid and a metallic (electrode)surface is described. The interaction model includes the induction of dipoles on the ions ofthe liquid by their mutual interaction and the interaction with the electrode surface aswell as the polarization of the metal by the ionic charges and dipoles (‘image’interactions). The method is used to obtain a suitable interaction model for asystem consisting of a LiCl liquid electrolyte and a solid aluminium electrode. Themodel is then used in simulations of this system for various values of the electricalpotential applied to the electrode. The evolution of the liquid structure at theelectrochemical interface with applied potential is followed and the capacitance ofthe electrochemical interface is measured. The electrolyte is found to exhibita potential-driven phase transition which involves the commensurate orderingof the electrolyte ions with the electrode surface; this leads to a maximum inthe differential capacitance as a function of applied potential. Away from thephase transition the capacitance was found to be independent of the appliedpotential.