The dependence of the oxygen-metal distance for water adsorbed at a metal electrode

Abstract

It has been observed in SEXAFS studies that the oxygen-metal distance for water or an electrolyte adsorbed at an electrode, formed by a monolayer of lead deposited on silver, becomes increasingly dilated as the electrode becomes more negative, whereas this distance is unchanged when the electrode is formed by a monolayer of silver deposited on gold. It is suggested that this difference may be due to the fact that the potential is positive of the point of zero charge in the latter case. As a result, the oxygen-metal distance is determined by the hard core repulsion of the metal ions on the electrode surface which we approximate as a hard wall. In contrast, the potential is negative in the former case, and the conduction electrons in the metal penetrate into the electrolyte and push the water away from the metal. The distance the oxygen atoms are pushed from the metal surface increases as the potential becomes more negative. A simple calculation based on the jellium model of a metal leads to reasonable agreement with experiment. © 1993.