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The sections in this article are Phase Formation on Electrodes Thermodynamics of Electrochemical Phase Formation Electrochemical Nucleation Kinetics The Classical Nucleation Model Nucleation on Electrode Surfaces Microscopic Approach to Phase Formation: The Atomistic Model Experimental Studies of Electrochemical Phase Formation Three‐dimensional Nucleation Two‐dimensional Electrocrystallization Spatial Distribution of Nuclei Experimental Examples

Several available theoretical descriptions of the potentiostatic current transient that allow the determination of the rates of the nucleation process, A, and the number densities of sites for nucleation, N0 , with three‐dimensional, diffusion‐controlled growth of clusters are critically examined and compared with experimental and computer‐simulated data. All these obtain the overall current from the material flux to free, noninteracting growing centers, considering the overlap of circular diffusion zones expanding around them. It is shown that even though when compared to experimental data the diverse theories appear almost indistinguishable, essential differences among them arise from their distinct calculation of the growth rate of diffusion zones, yielding significantly different values for A and N0 . Computer simulations of the process for which the values of A and N0 are accurately known allowed meaningful comparisons between theories and an assessment of the relative accuracy with which the different available formulations yield estimates of the kinetic parameters. © 1999 The Electrochemical Society. All rights reserved.

The thermodynamics of the so-called perfectly polarized electrode was employed to analyze the total charge densities for stepped Pt(hkl) electrodes in solutions of H2SO4 with an excess of an inert electrolyte (0.1 M HClO4). Three Pt single-crystal electrodesPt(10,10,9) = 20(111)×(111), Pt(7,7,6) = 14(111)×(111), and Pt(5,5,4) = 10(111)×(111)vicinal to the Pt(111) surface were employed in these studies. A complete thermodynamic analysis using the electrode potential and the charge as independent variables has been performed. The Gibbs excess, Gibbs energy of adsorption, electrosorption valency, and Esin−Markov coefficients for (bi)sulfate adsorption at these surfaces have been determined. The thermodynamic data display a dependence on the crystallographic structure of the Pt electrode surface. Both the Gibbs excess and the Gibbs energy of adsorption decrease with increasing step density or decreasing terrace length. This result indicates that adsorption of (bi)sulfate is stronger at larger (111) terraces.

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