SOME SPECIFIC FEATURES OF THE EFFECT OF MULTICHARGED CATIONS ON THE ELECTROREDUCTION OF ANIONS

According to the slow discharge theory, small additions of multicharged cations accelerate the charge-transfer step during the electroreduction of anions of K3(Fe(CN)6), K2S2O8 and Na2S4O6 salts. However, this effect decreases as the negative charge on the mercury electrode increases, which contradicts the predictions of the slow discharge theory in combination with the Gouy-Chapman-Grahame model of the electric double layer. It is shown that the observed results can be explained within the framework of the diffuse-layer model, according to which singly charged cations of a salt in which the anion is being reduced approach the metal surface more closely than the hydrated multicharged cations because of their smaller Stokes radius.