Adsorption Isotherms for Intermediates Formed in Charge Transfer Processes

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Abstract
The adsorption of phenol in the form of phenoxy radicals on the surface of a bright Pt electrode is discussed. Two main features of the adsorption isotherm are brought out. The fractional coverage Θ changes suddenly at a characteristic potential, in a manner reminiscent of two dimensional phase formation. This is attributed to the existence of an isotherm with strong lateral attraction interaction forces. The corresponding two‐dimensional equation of state resembles qualitatively the Van der Waals equation of state at temperatures below the critical temperature. For the potential dependence of adsorption a new type of isotherm is used which combines the effects of potential on charge‐transfer equilibrium and on the solvent‐solute replacement equilibrium on the surface of the electrode. The resulting function, describing the variation of Θ with E fits the observed inhibition effects of phenol on the rate of oxidation of Γ, and should also be taken into consideration in deriving Tafel slopes for different mechanisms.

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