A Model of Irreversible Electro-Oxidation Inhibited by Either Adsorption or Surface Complexation of the Product

Theoretical models of irreversible electro-oxidation of dissolved reactant giving dissolved product on the stationary planar electrode are developed for the conditions of staircase cyclic voltammetry. In the first model it is assumed that the product is adsorbed on the electrode surface and that the adsorbate prevents the transfer of electrons. In the second model it is assumed that the electrode surface is reversibly covered by the oxide monolayer and that the product of electro-oxidation forms the inhibiting complex with the oxide. The calculations were performed by the transformation of transport defining differential equations into integral equations and by the numerical solution of the latter. The described mechanisms are investigated in order to analyse the relationship between the second anodic peak in cyclic voltammetry and the type of inhibition. It is shown that anomalous responses appear only if the electro-oxidation is inhibited by the surface complex of its product and the electrode oxide. The condition is that the electrode oxidation is reversible and that the complex disappears when the oxide is reduced.