Alexander Milchev

Electrolytic nucleation of silver on a glassy carbon electrode: Part I. Mechanism of critical nucleus formation

Abstract The initial stage of electrodeposition of silver on a glassy carbon electrode is investigated using a double-pulse potentiostatic method. Data are obtained for the concentration dependence of the steady-state nucleation rate I and conclusions are drawn for the probable mechanism of critical nucleus formation.

Electrochemical phase formation on a foreign substrate—basic theoretical concepts and some experimental results

Abstract Electrochemical phase formation is a typical example of a first-order phase transition. The precursor of the overall phase change is nucleation—the appearance of small clusters of atoms or molecules carrying the basic properties of the new phase. Why and how the nuclei form on a foreign substrate are the fundamental questions addressed by this article.

Classical and atomistic models of electrolytic nucleation: Comparison with experimental data

Abstract Some recent experimental results on the steady state nucleation rate have been analyzed in detail. It has been established that the qualitative agreement between the experimental data and either the classical or the atomistic model cannot be considered as a reliable criterion for the validity of either of the two theoretical concepts. The quantitative treatment of the experimental data indicates the use of the atomistic model of nucleation to be more correct in the cases under consideration. Nevertheless the classical theory equations appear to be applicable, at least formally, to an interpretation of the experimental results.

On some probabilistic aspects of the nucleation process

Abstract Nucleation is a random phenomenon. The analysis of the expressions giving the time-dependence of the probability of formation of at least one (P⩾1), two (P⩾2), etc, nuclei makes it possible to assess the role of transient effects in nucleation kinetics as well as to evaluate the parameters of the process. Experiments on the electrolytic nucleation of mercury and cadmium on platinum are carried out by means of the double pulse potentiostatic technique ensuring reproducible working conditions and a precise control of the factors governing the deposition process. It is shown that the distribution of the number of the deposited nuclei as well as the P⩾m(t) plots (t = time) obtained are in good agreement with formal probabilistic considerations. The P⩾1(t) functions are S-shaped over the whole interval of variation of the overvoltage (equivalent to the supersaturation) which is an important indication of the non-steady state character of the process of electrolytic nucleation within the studied time intervals. A semianalytical procedure is developed to calculate stationary nucleation rates and induction times (in the sense of Zeldovich) from the experimental results. The outlined probabilistic approach may prove very useful in situations in which the time-dependence of the mean number of the nuclei formed at constant supersaturation is not available experimentally.

Electroless deposition of Pt on Ti : catalytic activity for the hydrogen evolution reaction

Abstract The deposition of platinum on titanium at open-circuit potential from an aqueous 0.1 M HClO 4 solution containing K 2 PtCl 6 was studied. On freshly polished titanium, spontaneous deposition of platinum takes place through a displacement reaction between Ti(0) and dissolved Pt(IV). At very short times of deposition, fine dispersions of platinum crystals were formed on titanium. At longer deposition times, the size of the platinum crystals increases whereas their number decreases due to coalescence and agglomeration processes. On titanium covered by a thin oxide film, the rate of deposition is very low and photocatalytic deposition of Pt on the TiO 2 surface occurs simultaneously with the displacement reaction. The hydrogen evolution reaction (her) was used as a probe reaction for testing both the catalytic activity and deposition conditions. There is evidence that the catalytic activity of the Pt crystals for the her increases with decreasing crystal size.

Electrochemical formation and stability of polyaniline films

Abstract A pulse potentiostatic method (PPM) is used for the electrochemical formation of polyaniline films. Under given parameters of the potentiostatic pulses an enhanced mode of growth of the polymer films is observed. Polyaniline films obtained by PPM and by the conventional potential-scan and potential-hold methods are compared with respect to their stability at two different electrochemical treatments.

Electrochemical nucleation and growth of rhodium on gold substrates

Abstract The mechanism of rhodium adlayer formation on the (100) face of a gold single crystal and on a polycrystalline gold electrode has been studied using cyclic voltammetry and chronoamperometry. The voltammogram shows the presence of two peaks associated with the deposition of rhodium from the Na 3 RhCl 6 salt in 0.1 M HClO 4 . The results obtained on the (100) face of a gold single crystal indicate that the two monolayers of rhodium can be deposited before the nucleation and growth of the three-dimensional (3D) rhodium clusters. The experimental results described in this paper show that the bulk rhodium electrodeposition on a gold electrode includes a nucleation process combined with a diffusion-controlled growth of the stable rhodium crystals. The nucleation kinetics is compared for the 3D electrodeposition on the 〈100〉 face of a single crystal gold electrode and on a polycrystalline gold electrode.

Electrolytic nucleation of silver on a glassy carbon electrode: Part II. Steady-state nucleation rate

Abstract The dependence of the number of nuclei on time is investigated in a wide overvoltage interval using different glassy carbon electrodes. The data for the steady-state nucleation rate are interpreted on the basis of both classical and atomistic theoretical concepts. Conclusions are drawn for the applicability of the two models of nucleation.

Electrochemical nucleation on active sites—what do we measure in reality? Part I.

This paper considers the process of electrochemical nucleation in the general case when active sites may appear and disappear from the electrode surface simultaneously with the nuclei of the new phase. In this case it is impossible to distinguish between the actual nucleation rate and the rate of appearance and disappearance of active sites, especially if the nucleation experiments are carried out by means of the standard pulse potentiostatic technique. To surmount this difficulty we propose a modified potential step method which allows one to fix the energetic state of the electrode surface.

Electrocrystallization: Nucleation and growth of nano-clusters on solid surfaces

Electrocrystallization phenomena are considered and basic thermodynamic and kinetic concepts related to the electrochemical nucleation and growth are defined and discussed in details. Theoretical and experimental findings related to the stationary and non-stationary nucleation kinetics, growth of single two-and three-dimensional crystals as well as underpotential deposition phenomena and spatial distribution of clusters are reviewed and the reader is referred to suitable sources of reliable information on the most important subjects concerned.