Molecular dynamics calculations of the electrochemical properties of electrolyte systems between charged electrodes

Abstract

We investigate the interfacial electrochemical properties of an aqueous electrolyte solution with discrete water molecules in slab geometry between charged atomistic electrodes. Long-range intermolecular Coulombic interactions are calculated using the particle–particle–particle–mesh method with a modification to account for the slab geometry. Density distribution profiles and potential drops across the double layer are given for 0, 0.25, and 1 M aqueous electrolyte solutions each at 0, ±0.1, ±0.2, and ±0.3 C/m2 electrode surface charges. Results are compared qualitatively with experimental x-ray scattering findings, other computer simulation results, and traditional electrochemistry theory. The interfacial fluid structure characteristics are generally in good qualitative agreement with the conclusions obtained in some integral equation theories and in the experimental x-ray study. The potential in the simulations shows an oscillatory behavior near the electrode, which theories that do not include the molecular nature of water cannot reproduce for the given conditions. Surprisingly, the results also show that the water structure near the electrode is dominated by the charge on the electrode and is fairly insensitive to the ion concentrations. Except at large electrode charge, the potential drop across the double layer does not depend significantly upon the concentration of the ions.