Electrode processes involving multi-charge reagents: Allowing for the outer-sphere ionic association

The feasibility of applying the Frumkin-Petrii equation for the determinati on of the reagent charge in the case where a random number of ionic associa tes (anion-cation pairs) of different charge is present in solution is disc ussed. II is shown that a quantity, which is determined from the j vs. c de pendence (where j is the current density and c is the supporting-electrolyt e concentration), is equal to an average charge of electrochemically active species in the bulk solution z only at negative charges of the electrode ( sigma < 0) if the electrochemically active species is an anion, or only at sigma > 0 if the initial reagent is a cation. Conversely, if the electrode conversions of an anion that is bound in an associate occur at sigma > 0 an d, correspondingly, a cation at sigma < 0, a nonlinear run is predicted for the (log j)(sigma) vs. log c dependence, while for the magnitude of the re levant derivative-the dependence not only on the bulk properties of the sys tem (concentration, charges of species, stage stability constants) but also on the localization of reagents at the interface and partial rate constant s of all forms of associates. The modeling of the outer-sphere association is performed using a simplified version of the Fuoss equation, as well as t he modeling of the (partial derivative log j/partial derivative log c)(sigm a) vs. c dependences for reagents of different size and charge, including t he case where the effective localization is varied. It is found that, under the conditions of ionic association, the corrected Tafel dependences are n onlinear in the general case and do not coincide for different c.