EFFECT OF MULTICHARGED CATIONS ON THE ELECTROREDUCTION OF ANIONS

According to the slow discharge theory, small additions of multicharged cations (Ca2+, La3+, Th4+, etc.) accelerate the charge-transfer step during the electroreduction of anions of K3Fe(CN)6, K2S2O8, and Na2S4O6 salts. However, the acceleration effect decreases at high cathodic potentials of a mercury electrode, and this contradicts the conclusions of this theory in combination with the Gouy-Chapman-Grahame model of the double layer. It was shown that the observed results can be explained within the framework of the slow discharge theory and in combination with the diffuse-layer model. According to this model, because of their smaller Stokes radius, single-charged cations K+ or Na+ of the salt, in which the anion is being reduced, approach die metal surface more closely than the hydrated multicharged cations.