Electrostatic Interaction in the Double Layer

Abstract

The fundamental difference between the electrostatic potential of a unit charge and its average electrostatic energy content, in a medium containing a number of similar, statistically equivalent, charges, is clarified. The expression , where is the valence, the electronic charge, and the electrostatic potential at its location, does not represent the average electrostatic energy content of a charged particle ; proper consideration of the mutual electrostatic interaction terms leads to the introduction of a factor of 1/2 into this expression. The summation over all the energy terms involved when the particles are transferred individually from infinity into the considered system is shown to be equivalent to the charging procedure used by Debye or Guntelberg, leading to the factor of ½. The factor of ½ enters the expression for the activation energy of electrochemical reactions and is identified as the dominant part of the “transfer coefficient α.” The dependence of the structure of the double layer on potential is shown to be related to the deviations of α from the constant value of ½. As examples, the hydrogen and oxygen evolution reactions are discussed in the light of this treatment.