Image-charge effects on ion adsorption near aqueous interfaces

Significance Understanding electrostatic interactions across interfaces is of critical importance in energy storage devices and biological science. We study the adsorption of salt ions on aqueous interfaces using molecular dynamics simulations, applying an efficient algorithm that enables us to systematically control the effect of surface, solvent, and solute polarization. In the absence of applied potential difference, the image-charge attraction of the ions predicted by continuum electrostatics is shown to be screened out by the solvating water molecules, resulting in no appreciable difference in the ion profiles near a metal surface vs. a nonpolarizable surface. However, the metal surfaces promote significantly enhanced fluctuation in, and magnitude of, the charge separation across the confined electrolyte, leading to greater capacitance under applied electric field.