Concentration Polarization and Mass Transfer Influence on the Kinetics of Two Stepwise-Proceeding Electrode Reactions under Galvanostatic Conditions

Abstract

The previous system of equations derived for the kinetics of two stepwise‐proceeding electrode reactions under galvanostatic conditions is extended for the case when both concentration polarization and mass transfer of the intermediate and final ion are taken into account.

Multistep Electrochemical Reactions Involving Transport of Intermediates between the Near-electrode Layer and the Bulk Solution: The Kinetics of Two-Step Processes in Conditions of Non-steady-state Diffusion

“…Specifically, all other conditions being equal, an increase in π 2 leads to an increase in Y 2 (and a corresponding increase in lnY 2 ). As follows from the data we obtained, at sufficiently positive values of π 2 and at a value of π 1 that is not too large (in fact, in the same conditions that correspond to the occurrence of the process in a quasi-steady-state regime), practically immediately after the beginning of electrolysis, the condition Y 2 1 is fulfilled. This situation means that the currents of the first and second steps of discharge are equal to one another.…”

“…To this end we will make use of the procedure of reduction of differential equations, which was described in detail in [4][5][6]. 3 From equations (2), for example, one can form two complexes, specifically, 2 That the time dependences of i 2 exhibit a maximum, we confirmed for the multistep electrochemical reaction Cr(III)…”

“…In [1], for example, it was mentioned that, for multistep reactions in non-steady-state conditions, in some cases one should expect the accumulation of intermediate species, and the currents that correspond to each of successive steps will be different. In [2], Fick's equations for nonsteady-state diffusion were solved for a galvanostatic regime of the occurrence of a two-step electrode reaction and dependences of overvoltage and concentration of intermediates on time were obtained. The authors of [3] performed numerical simulation of cyclic voltamograms for a two-step reaction of electrodeposition of a metal with allowance made for the possibility of diffusion and adsorption of intermediates and compared the calculation results with experimental data on the multistep discharge of Cr(III) in chloride melts.…”

“…Let us assume that equations of non-steady-state linear diffusion (2) describe the mass transfer of species A and P between the surface layer and the bulk of electrolyte. In the above equations, c A and c P are concentrations of species A and P, respectively; D A and D P refer to the diffusion coefficients for species A and P, respectively; x denotes the distance from the electrode surface; and τ is the time.…”

“…It passes through a maximum and then starts fading. 2 The position of the maximum in a time dependence of i 2 (τ) probably corresponds to the time instant when a maximum value of the concentration of the intermediate is reached at x = 0.…”