Free energy profiles governing electron transfer from a reactant to an electrode surface in water are investigated, based on the reference interaction site model (RISM) theory. Three models of a redox pair for charge separation reactions are examined: a pair of atomic solutes, and systems consisting of an atom and a surface with a localized or a delocalized electron. The profile becomes highly asymmetrical, when an electron in the electrode is delocalized. The behaviors are essentially due to the asymmetrical response of water polarization to positive and negative charges of solute. The results are related to models of ion-hydration.
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