Article révisé par les pairs
Résumé : A study of the Ni(II)-o-phenylenediamine prewave has shown that a pronounced double-layer effect is observed when measurements are made of polarographs obtained with various types and concentrations of supporting electrolytes. The effect on the prewave is qualitatively consistent with theoretical predictions when the concentration of the electrolyte is not so high as to invalidate the assumptions employed in the theoretical treatment. The results of this investigation support the existence of a surface-controlled chemical reaction involving an adsorbed ligand and the nickel ion diffusing to the electrode. The conclusion by Tur'yan and Malyavinskaya that the chemical rate-limiting reaction involves the formation of an electroactive Ni(II)-o-phenylenediamine complex in the bulk of the solution well beyond the influence of the electrode double layer is therefore incorrect. A quantitative analysis of the relationship between the height of the prewave and the potential of the outer Helmholtz plane indicates that the charge on the electroactive species in the rate-determining step is +1 rather than +2 as expected from the charge of the hexaaquonickel ion. The reason for this disagreement may lie in the adsorption behavior of the ligand.