Molecular Description of the Persulfate Ion Reduction on a Mercury Electrode

The polarization curves for the S₂O₈^2- electroreduction on a mercury electrode at high overvoltages and various concentrations of a surface-inactive supporting electrolyte are modeled within modern theory of charge transfer in polar media and quantum-chemical approaches. Based on an analysis of the reactant adsorption in terms of a cluster model, the conclusion is drawn that the persulfate ion is localized in the diffuse part of EDL. When calculated the current, it was assumed that the transfer of the first electron, accompanied by the bond cleavage, is the limiting stage of the total two-electron process. The integration if performed over the entire electron spectrum of the metallic electrode and an attempt is made to account for electrostatic and solvation effects on a molecular level. It is shown that the experimentally-studied overvoltage interval corresponds to the occurrence of the process near the activationless region. The increase in the current at high negative charges of the surface is due to an increase in the reaction layer thickness. This effect arises from a change in the ratio between contributions made by the reactants at the distance of closest approach and the species farther away.