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The processes of lead and zinc electrodeposition from the very dilute electrolytes were compared by the analysis of polarization characteristics and by the scanning electron microscopic (SEM) analysis of the morphology of the deposits obtained in the galvanostatic regime of electrolysis. The exchange current densities for lead and zinc were estimated by comparison of experimentally obtained polarization curves with the simulated ones obtained for the different the exchange current density to the limiting diffusion current density ratios. Using this way for the estimation of the exchange current density, it is shown that the exchange current density for Pb was more than 1300 times higher than the one for Zn. In this way, it is confirmed that the Pb electrodeposition processes are considerably faster than the Zn electrodeposition processes. The difference in the rate of electrochemical processes was confirmed by a comparison of morphologies of lead and zinc deposits obtained at current densities which corresponded to 0.25 and 0.50 values of the limiting diffusion current densities. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172046]

The processes of lead electrodeposition from electrolytes of various concentrations of sodium nitrate as the supporting electrolyte have been examined by chronoamperometry and by the scanning electron microscopic (SEM) analysis of deposits obtained in the potentiostatic regime of electrolysis. The good agreement between the diffusion coefficents determined by Cottrell equation and non-linear fitting method was observed. For the first time, the transition from the mixed ohmic-diffusion to the full diffusion control was defined from the analysis of Cottrell equation. The parameters, such as the number density of active sites and the nucleation rate constant, obtained by non-linear fitting method were discussed in accordance with the fact that lead belongs to the group of metals characterized by the high values of the exchange current density. The data obtained by the chronoamperometric analysis were succesfully correlated with morphologies of electrodeposited lead obtained in the different types of electrodeposition control. [Projekat Ministarstva nauke Republike Srbije, br. 172046]

Lead electrodeposition processes from the basic (nitrate) and complex (acetate) electrolytes were mutually compared by the scanning electron microscopic and the X-ray diffraction analysis of the produced powder particles. The shape of dendritic particles strongly depended on the type of electrolyte. The dendrites composed of stalk and weakly developed primary branches (the primary type) were predominantly formed from the basic electrolyte. The ramified dendrites composed of stalk and of both primary and secondary branches (the secondary type) were mainly formed from the complex electrolyte. In the both type of powder particles Pb crystallites were predominantly oriented in the (111) plane. Formation of powder particles of the different shape with the strong (111) preferred orientation was discussed and explained by the consideration of the general characteristics of the growth of a crystal in the electrocrystallization processes. [Projekat Ministarstva nauke Republike Srbije, br. 172046: Electrochemical synthesis and characterization of nanostructured functional materials for application in new technologies]

The formation of tin dendritic nanostructures by electrolysis from the alkaline electrolyte has been investigated. Morphology and structure of Sn dendrites produced applying both potentiostatic and galvanostatic regimes of the electrolysis are characterized by SEM and XRD, respectively. Depending on the applied cathodic potentials, three types of Sn dendrites were obtained: (a) needle-like and spear-like, (b) fern-like, and (c) stem-like dendrites. The very branchy dendrites with branches of the prismatic shape obtained by the galvanostatic regime of electrolysis represented a novel type of Sn dendrites, not previously reported in the literature. To explain the formation of various dendritic forms, correlation with the polarization characteristics for this electrodeposition system is considered. The needle-like and the spear-like dendrites represented monocrystals of (200),(400) preferred orientation, the fern-like dendrites exhibited the predominant (220),(440) preferred orientation, while in the stem-like particles Sn crystallites were oriented to a greater extent in the (440) crystal plane than in other planes. The galvanostatically synthesized Sn particles possessed the strong (200),(400) preferred orientation. The strong influence of parameters and regimes of electrodeposition on structural characteristics of Sn dendrites is explained by the fundamental laws of electrocrystallization taking into consideration the concept of slow-growing and fast-growing crystal planes. [ABSTRACT FROM AUTHOR]

In this study, mechanism of electrodeposition of zinc from the alkaline electrolytes has been investigated using the general theory of disperse deposits formation. The exchange current densities in the range 18.4–88 mA cm − 2 were determined using new method based on comparison of experimental and simulated polarization curves, and the excellent agreement with the values found in the literature has been attained. Correlation between the polarization characteristics and morphologies of zinc deposits characterized by the scanning electron microscopic (SEM) technique was established. The spongy-like particles constructed from nanofilaments and the large grains or boulders were formed in the zone of the fast increase of the current density with the overpotential before the plateau of the limiting diffusion current density was reached. The shape of dendrites, formed inside the plateau of the limiting diffusion current density and at the higher ones, strongly depended on overpotential of the electrodeposition. Mechanism of formation of all obtained forms was discussed by the consideration of the different rates of growth of surface protrusions in a function of the overpotential of electrodeposition through the analysis of the change of the ratio between the height and the radius of the protrusions. In order to confirm of the proposed mechanism, comparison with polarization and morphological characteristics of the other metals characterized by the different exchange current density values was made and discussed. Although zinc is classified in the group of the normal metals characterized by the high values of the exchange current density, it was found that the polarization and morphological characteristics of zinc show certain and strong similarities with those of copper, classifying zinc just at boundary between the normal and intermediate metals, that is confirmed by the estimation of the exchange current density value for zinc. [ABSTRACT FROM AUTHOR]

The polarization and morphological characteristics of powder forms of the group of the intermediate metals were examined by the analysis of silver and copper electrodeposition processes at high over potentials. The pine-like dendrites constructed from the corncob-like forms, which are very similar to each other, were obtained by electrodeposition of these metals at the overpotential belonging to the plateaus of the limiting diffusion current density. A completely different situation was observed by the electrodeposition of silver and copper at the overpotential outside the plateaus of the limiting diffusion current density in the zone with the fast increase in current density with the overpotential. Silver dendrites, which were very similar to silver and copper dendrites obtained inside the plateaus of the limiting diffusion current density, were obtained at the overpotential outside the plateau. Due to the lower overpotential for hydro-gen evolution for copper, hydrogen produced during the copper electrodeposition process strongly affected the surface morphology of copper. The same shape polarization curves with completely different surface morphologies of Cu and Ag electrodeposited at over potentials after the inflection point clearly indicate the importance of morphological analysis in the investigation of polarization characteristics of the electrodeposition systems. The role of hydrogen as a crucial parameter in the continuous change of cop-per surface morphology from dendrites to honeycomb-like structures was investigated in detail. On the basis of this analysis, the transitional character of the intermediate metals between the normal and inert metals was considered. The typical powder forms characterising electrodeposition of the intermediate metals were also defined and systematized. [ABSTRACT FROM AUTHOR]

A series of bimetallic Sn-Pd catalysts were prepared by a template-free two step electrodeposition method. According to this method, Sn was electrodeposited firstly in potentiostatic or galvanostatic regime on Cu electrodes in the form of dendrites, then Pd was galvanostatically electrodeposited in the second step on the electrode with the electrodeposited Sn dendrites. The produced Sn-Pd electrocatalysts were compared with an electrocatalyst obtained by Pd electrodeposition on a bare Cu electrode. The morphological and elemental analysis of Sn-Pd and Pd electrocatalysts was performed by means of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) techniques. The dendrites of various shapes and degree of branching were obtained by Sn deposition depending on electrodeposition regime, while Pd was electrodeposited in a form of compact Pd islands on both Sn dendrites and the Cu electrode. Cyclic voltammetry (CV) was applied for the electrochemical examination of Sn-Pd and Pd catalysts towards the ethanol oxidation reaction (EOR) in the alkaline solution. The electrocatalyst Sn0.6-Pd0.4 with an atomic ratio of 60 at.% Sn-40 at.% Pd showed higher oxidation efficiency and better tolerance towards intermediate species in EOR than the other examined electrocatalysts. It was shown that the lower fraction of Pd, relative to Sn, was crucial to achieving optimal synergy of Sn with Pd thus contributing to enhanced electrochemical behavior regarding EOR. [ABSTRACT FROM AUTHOR]

Abstract: The processes of lead electrodeposition from the basic (nitrate) and complex (acetate) electrolytes were mutually compared by the analysis of their polarization characteristics and by the scanning electron microscopic (SEM) analysis of the morphology of formed deposits. Although the polarization characteristics of lead recorded from these two electrolytes were relatively similar to each other, the shape of formed dendrites strongly depended on the type of electrolyte. The dendrites composed of stalk and weak developed primary branches (the primary (P) type) were predominantly formed from the basic electrolyte. On the other hand, the very branchy dendrites composed of stalk and of both primary and secondary branches (the secondary (S) type) were mainly electrodeposited from the complex electrolyte. Considering the fact that the application of lead powder in many technologies is closely related with its surface morphology, the special attention was given to the analysis of the type of electrolytes on formation of the different dendritic forms. It was shown that formation of more branchy dendrites from the acetate electrolyte can be ascribed to the lower exchange current density (or to the lower rate of electrochemical process) for this electrolyte than for the nitrate one due to the process of complex formation. [Copyright &y& Elsevier]

Abstract: A new insight into the mechanism of lead electrodeposition from nitrate solutions is presented by analysis of the polarization characteristics and by scanning electron microscopic (SEM) analysis of the surface morphology of the lead deposits obtained in the potentiostatic regime of electrolysis. In dependence on the concentration of Pb(II) ions, the electrodeposition process is either mixed ohmic-diffusion or completely ohmic controlled. The ratio of the ohmic control to the total control of the electrodeposition process increased with increasing concentration of Pb(II) ions and at the higher concentrations of Pb(II) ions, the electrodeposition process became completely ohmic controlled. The polarization characteristics were well correlated with the morphologies of the obtained lead deposits. The formation of regular crystals was a characteristic of ohmic control of the electrodeposition process, while needle-like and fern-like dendrites were the predominant morphological forms obtained under diffusion control. The critical overpotentials for both dendritic growth initiation and instantaneous dendritic growth were analyzed and a mechanism of lead electrodeposition based on this analysis is presented. It was shown that the values of these critical overpotentials decreased and approached one another with increasing concentration of Pb(II) ions and finally became the same when full ohmic control was attained. The presented results were in good agreement with the predications of the general theory for the formation of disperse metal electrodeposits. [Copyright &y& Elsevier]

Electrodeposition of lead from the concentrated nitrate electrolyte in the potentiostatic regime of electrolysis has been investigated by the analysis of the potentiostatic current transients and scanning electron microscope (SEM). It was found that the process of Pb nucleation from the concentrated electrolyte follows Scharifker model based on the 3D (three-dimensional) instantaneous nucleation with diffusion-controlled growth. The deviations of the obtained dependencies from the theoretical prediction for this model have been also discussed. Needle-like and fern-like dendrites, as well as crystals of irregular shape (precursors of dendrites) were formed in the diffusion controlled electrodeposition. The SEM analysis of these dendritic forms revealed their 2D (two-dimensional) growth. The size of needle-like dendrites was considerably larger than the size of both the fern-like dendrites and the irregular crystals. Although the electrodeposition process occurred inside the linear diffusion layer of the macroelectrode, the shape and size of dendrites were determined by the effect of local diffusion fields formed around tips (spherical diffusion) and top edges (cylindrical diffusion) of protrusions formed in the initial stage of the electrodeposition. The growth rates under the conditions of spherical and cylindrical diffusion control were mutually compared and a faster growth under the conditions of the spherical, in relation to the cylindrical diffusion, was proved. The effect of the current density distribution on formation of the final forms of Pb dendrites was also discussed. [ABSTRACT FROM AUTHOR]