INTEGRAL-EQUATION THEORY FOR THE ELECTRODE-ELECTROLYTE INTERFACE WITHTHE CENTRAL FORCE WATER MODEL - RESULTS FOR AN AQUEOUS-SOLUTION OF SODIUM-CHLORIDE

The structure of an aqueous solution of sodium chloride at a planar su rface is investigated by integral equation techniques. With the centra l force water model the aqueous electrolyte is modelled as a mixture o f 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 give a good description of t he bulk structure (e.g., hydrogen bonded water network, solvation shel l). With the bulk information and the Wertheim-Lovett-Mou-Buff equatio n we have calculated the density profiles at the uncharged and charged surfaces. The rather rigid ice-like water structure found previously at the neutral surface strongly repels the ions. Steric interactions b etween the ions of different sizes and the ice-like water structure do minate the ionic distribution near the surface. This model electrolyte also responds differently to opposite charges on the surface. We foun d the asymmetry in the differential capacitance curve determined entir ely by the response of the interfacial water structure.