ИСТИНА

Voltammetry is widely used to study the electrode reaction mechanisms that involve homogeneous chemical processes coupled to electron transfer [1]. The theory of сyclic voltammetry of homogeneous redox catalysis of electrochemical reactions is well developed and enables one to describe adequately the cyclic voltammetric responses as functions of two dimensionless parameters: a kinetic parameter, and an excess factor [2]. Homogeneous autocatalysis (so-called CE mechanism) [3], when an amount of the catalyst increases in the course of the process, is a specific, but very important case of electrocatalysis. The mechanism of homogeneous autocatalysis can be presented by the following simplifies scheme (k>1): This mechanism is realized in the electrochemical reduction of iodine (which is present in the solution in a very small concentration) with the formation of iodide, and subsequent reduction of iodate by iodide (known as the Dushman reaction) [4]. In [5], it was shown that the catalytic reduction of iodate at a rotating platinum disk electrode can be employed to study the kinetics of the reaction between iodate and iodide and, using several simplifications, a closed form solution for the catalytic current was obtained. This work is devoted to the theoretic study of transfer processes in the homogeneous autocatalytic reduction of iodate on a rotating disk electrode (RDE). The non-steady-state equations of ionic transfer, which take into account the diffusion, migration, convection, homogeneous chemical reactions, and the electroneutrality condition, are used as the mathematical model. The Butler-Volmer equations are used to take into account the kinetics of electrochemical reaction. The numerical solution is realized by the finite element method on a deformable grid, which provides a high efficiency and the required accuracy of numerical solution. As a result of numerical simulation, the dependences of the shape and parameters of the voltammograms on the concentration of solution, potential scan rate, and RDE rotation rate are obtained. It is found that, at sufficiently high potential scan rates, the peak current of oxidation is significantly higher than that of reduction. This is explained by the fact that, at high potential scan rates, during the direct scan, a sufficient amount of iodide has no time to form.