engleski

Contribution to the Studies of Eelectrocrystallization

The early stages of a new-phase formation (electrochemical metal deposition, oxide nucleation and reduction) are usually associated with 2D or 3D nucleation processes, the rate of which and hence the number of formed nuclei, being strong dependent on the overpotential. It is therefore important to establish the exact relationship between the overpotential and the kinetic of nucleation, either by direct observations of electrode, or by indirect procedure of relating the current to the area of electroactive surface and hence to the total number of nuclei. The aim of this work was to study the kinetic of the surface phase transformations on Bi-electrode during the processes of an oxide formation and reduction, in borate buffer solution pH 9.2 using cyclic voltammetry, chronoamperometry and impedance spectroscopy, by considering the general case of joint ohmic and diffusion limitations. The chronoamperometry method was a valuable tool in these investigations (Figure 1). General models applicable to the electrochemical nucleation of a bismuth oxide on the bare Bi-metal surface and to the electrocrystallization of bismuth metal in the oxide matrix were analyzed and the relevant current-time transients for the initial stages of new-phase formation were derived. From the reduced variable plots of current-time data it is evident that the nucleation in both cases follows closely the response predicted for 3D nucleation and growth mechanism under diffusion control Initial stages of nucleation were governed by localized hemispherical diffusion which at long times turns into linear diffusion due to the overlapping of diffusion zones of neightbouring centers.

electrocrystalization; 3D diffusion control; bismuth oxide; chronopotentiometry; impedance spectroscopy; cyclic voltammetry

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