PNNL

Abstract

Molecular dynamics simulations of the electrical double layer at AgCl/aqueous electrolyte (KCl) interfaces are presented, accompanied by a new force field and properties of bulk AgCl computed using planewave density functional theory. Long dynamics simulations were performed to estimate ion adsorption free energies at the AgCl surface. The simulations demonstrate formation of a bilayer hydration sheet composed of two sublayers of water molecules interconnected by hydrogen bonds. Potassium ions prefer to form an inner-sphere complex, whereas chloride ions prefer outer-sphere complexes. The adsorbed ions/water layers form a relatively rigid structure within the range of ionic strength considered, which confirms the applicability of the Helmholtz model in a high concentration regime. Profiles of the charge density, electric field and electrostatic potential across the simulation cell revealed that oscillations of water molecules govern these quantities. The electrostatic potential generated only by the electrolyte ions was used to study the quasi-Nernstian response of the silver chloride surface to the variation in the ionic strength.