Integral equation theory for the electrode - electrolyte interface with the central force water model . Results for an aqueous solution of sodium chloride

The structure of an aqueous solution of sodium chloride at a planar electrode is investigated by integral equation techniques. With the central force water model the aqueous electrolyte is modelled as a mixture of sodium and chloride ions and partially charged hydrogen and oxygen atoms interacting via effective spherically symmetric pair potentials. The correlation functions obtained from the Ornstein-Zernike equation with Reference-Hypernetted-Chain closure gives a good description of the bulk structure (e.g. hydrogen bonded water network, solvation shell). With the bulk information and the Wertheim-Lovett-Mou-Buff equation we have calculated the density profiles at the uncharged and charged electrode. The rather rigid ice-like water structure found previously at the neutral surface strongly repels the ions. Steric interactions between the differently sized ions and the ice-like water structure dominates the ionic distribution near the electrode. This model electrolyte also responds differently to opposite charges on the electrode. We found the asymmetry in the differential capacitance curve entirely determined by the response of the interfacial water structure.