Electrocrystallization Of Silver Research Articles

Silver Electrodeposition on Nanocrystalline Graphite: Galvanostatic Control As a Tool in the Study Electrodes with High Resistance

Carbon based materials, such as glassy carbon or highly oriented pyrolytic carbon (HOPG), have been used extensively as working electrodes for electrodeposition. Due to their chemical inertness and electrochemical stability they are commonly used as substrates for electrodeposition studies. HOPG in particular has attracted great deal of attention due to its close relation to carbon nanotubes and graphene [1]. Miranda-Hernández et al. [2] investigated silver electrodeposition on HOPG, mechanically polished glassy carbon and fractured glassy carbon. Their results showed that the surface conditions, including morphology of the carbon substrate, have an effect on the overpotential required to start a 3D silver electrocrystallization. Additionally, their results led to the conclusion that the active sites do not depend on physical features on the electrode's surface and thus their nature must be electronic. In carbon materials, the shape and magnitude of the density of electronic states (DOS) distribution vary according to their structure [3]. Since the rate of heterogeneous electron transfer depends on the electrode’s DOS [4], it is expected that different carbon materials would exhibit different electrodeposition behaviors. Furthermore, simple electrodeposition systems could be used to characterize the properties of novel carbon materials. Recently, Cholula-Díaz et al. [5] used aerosol assisted chemical vapor deposition to synthesize nanocrystalline graphite (NCG) thin films. The low nanoscale roughness of this material may lead to some insight into the electrodeposition process. Additionally, their complex electronic behavior may lead to the observation of new phenomena. These samples were used as working electrodes for silver electrodeposition. A single compartment electrochemical cell was used, with Hg|HgSO4 and a Pt wire as reference and counter electrodes, respectively. The composition of the platting bath was: 10 mM AgNO3, 1 M KNO3 and 1.6 M NH4OH [2]. Cyclic voltammetry experiments resulted in tilted voltammograms, which are typical of a high ohmic resistance. Since the platting bath had a high ionic concentration, this behavior is adscribed to the resistance of the NCG sample. The cell voltage U is equal to the sum of the double-layer potential φDL and the ohmnic drop. U= φDL + iR Hence, under potentistatic control, current changes result in variations of the ohmic term, to which the system responds by adjusting the double-layer potential to comply with the applied voltage value. This feedback loop between the double-layer potential and the current makes it difficult to establish a clear relationship between the experimental conditions and the characteristics of the deposited material. In contrast, galvanostatic control offers a far simpler scenario; since the current is fixed in the experiment, it is easier to determine the double-layer potential. Figure 1a shows the time evolution of the double-layer potential during controlled current experiments. The time scale on which the potential stabilizes is larger for the one observed for similar experiments on glassy carbon. This shows the importance of galvanostatic control as means to study electrodeposition samples with high resistivity. Figure 1b shows an SEM image in which submicrometric silver particles can be identified. We explore the dependence between the current pulses applied and the resulting particle size distributions. References R. Unwin, Faraday Discuss., 172, 521 (2014)Miranda-Hernández, I. González, and N. Batina, J. Phys. Chem. B, 105, 4214 (2001).Richard L. McCreery, Chem. Rev., 108, 2646 (2008)J. Royea, T. W. Hamann, B. S. Brunschwig, N. S. J. Lewis, Phys. Chem. B, 110, 19433 (2006).L. Cholula-Díaz, J. Barzola-Quiquia, H. Krautscheid, U. Teschner, P. Esquinazi, Carbon, 67, 10 (2014). Figure 1. a) Time dependence of nanocrystalline graphite electrode potential after applying cathodic current pulses from −50 to −325 µA in 10 mM AgNO3 + 1 M KNO3 + 1.6 M NH4OH electrolyte. b) SEM image (BS detector) of the surface of the nanocrystalline graphite showing particles of silver deposit. Figure 1

Role of the doping ions for the electrocrystallization of silver on poly(3,4-ethylenedyoxythiophene)-modified electrodes

Тhe aim of the present study is to reveal the role of organic anions-induced characteristics of poly(3,4-ethylenedioxythiophene) (PEDOT) for metal electrocrystallization. PEDOT layers are obtained in the presence of perchlorate ions and one of the two organic anions, polystyrene sulfonate (PSS) or dodecyl sulfate (DDS). Potentiostatic current transients of silver electrodeposition are measured in the course of several consecutive deposition/dissolution experiments on both PEDOT/PSS- and PEDOT/DDS-coated electrodes. It is found that the metal nucleation and growth is markedly influenced by the type of organic ions used, with PEDOT/DDS providing conditions for more intense metal electrodeposition in comparison to PEDOT/PSS. The latter type of layers shows also an effect of deactivation in the course of several consecutive measurements. Experimental current transients obtained in the PEDOT/PSS case are interpreted by means of Scharifker model for multiple nucleation and growth. The seeming deactivation of the PEDOT/PSS layers is considered to occur at the expense of decrease in both number of active sites for nucleation and nucleation rate per active site. These results are commented in terms of the appearance of concentration gradient in the polymer bulk of the more hydrophilic PEDOT/PSS resulting in a lower effective overpotential for electrochemical nucleation and growth than the formally calculated one.

Nucleation kinetics and contact angles of silver clusters electrodeposited on indium tin oxide surfaces

The nucleation rate and the number density of nucleation sites, as well as the contact angle of silver clusters growing under diffusion control, have been determined with single-step potentiostatic experiments, from the electrical current and optical transmittance during electrocrystallization of silver on optically transparent indium tin oxide electrodes. It was found that silver grows at overpotentials as crystallites with an aspect corresponding to an effective contact angle with the indium tin oxide surface of ca. 13°. Comparison with results obtained from ex situ atomic force microscopy analysis suggests that electrodeposited nuclei undergo conformational relaxation at open circuit, leading to significantly higher equilibrium contact angles. The results obtained indicate that while the contact angles measured during growth at overpotentials have no bearing on the values of nucleation rates determined from the electrical and optical responses to potential steps, they lead to lower number densities of sites, in relation to values corresponding to the growth of hemispherical centers. Implications of the results obtained for the clustering of silver atoms leading to the electrocrystallization process are also discussed.

Silver and silver–copper electrodeposition from a pyridinium-based ionic liquid

Silver(I) was extracted from aqueous solutions in the absence and presence of copper(II) with the ionic liquid (IL) 3-butylpyridinium bis(trifluoromethanesulfonyl)imide, [3-BuPyr][NTf2]. After extraction, silver and silver–copper were electrodeposited on glassy carbon at room temperature from the ionic liquid phase. The mechanism of silver electrodeposition has been studied using electrochemical techniques such as cyclic voltammetry (CV) and chronoamperometry (CA). At suitably overpotentials silver electrocrystallization proceeds via a diffusion controlled mechanism and was analyzed using the Scharifker and Hills model for potentiostatic growth. The growth-nucleation mechanism of silver from the extracted phase is more progressive in character at low overpotentials, while at elevated overpotentials an instantaneous nucleation behavior was determined. In contrast, the silver nucleation closely followed the response predicted for instantaneous nucleation in neat [3-BuPyr][NTf2]. The electrochemical co-deposit of Ag–Cu was studied by linear sweep stripping voltammetry (LSSV). The resultant electrodeposits were characterized by scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis.

Polynuclear crystal growth in electrocrystallization of silver: Determining the nucleus size via the nucleation theorem

We employ the nucleation theorem for a model-independent determination of the size of the two-dimensional (2D) Ag nucleus with the aid of experimental data for nucleation-mediated electrochemical crystal growth. The growth is investigated of a screw dislocation-free Ag(100) single crystal face in aqueous solution of AgNO3 at 318 K. The data are for the stationary values of the overpotential during galvanostatic pulses with sufficiently high amplitudes to ensure polynuclear growth mechanism. It is found that the Gibbs-Thomson equation of the classical theory of 2D nucleation describes very well the experimentally obtained overpotential dependence of the size of the 2D Ag nucleus.

The electroreduction kinetics of silver sulfite complexes

The electroreduction kinetics of silver sulfite complexes was investigated by rotation disk electrode (RDE) voltammetry, chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). The stability constants of the silver sulfite complexes, pβ 2 = 7.9 and pβ 3 = 8.53 were determined. For the series of isopotential solutions investigated, a reaction order of 0.67 was obtained, the diffusion coefficient of the silver complexes varies in the range of 3.36 × 10 −6 to 5.54 × 10 −6 cm 2 s −1 and the silver degree of complexation (2.31–2.67) were found. The analysis of the RDE, CP data and EIS spectra indicate the existence of a slow stage of the silver electrocrystallization in the region of the equilibrium potential and at stronger polarization of the electrode at initial time moments.

Electroless versus electrodriven deposition of silver crystals in polyaniline: Role of silver anion complexes

Electrocrystallization of silver is studied at polyaniline-coated electrodes using silver cations and two silver anion complexes (silver thiosulfate and silver–EDTA) as reducing species. Use of the silver thiosulfate complex results in a significant shift of the silver deposition potential window in the negative direction and highly impeded metal crystallization. The silver cation and silver–EDTA plating solutions allow to perform both electrodriven and electroless metal deposition. Number and size of silver crystals obtained by the two deposition methods in the different plating solutions are compared. Electroless precipitation in the silver–EDTA solution results in the highest number (∼10 8 cm −2) of small-sized crystals. This result is discussed in terms of the special role of the EDTA anions for the redox state of the polyaniline layers. It is demonstrated that factors such as polyaniline redox charge, concentration of reducing ions and dipping time allow effective control over the amount of electroless deposited metal.

Effect of Potential on the Early Stages of Nucleation and Growth during Silver Electrocrystallization in Ammonium Medium on Vitreous Carbon

In this work, a systemic study of silver electrocrystallization process was performed on a vitreous carbon (VC) electrode in a medium of at pH 11. The analysis of current transients, using different theoretical models, shows that the systematic evolution of electrocrystallization process is observable through the gradual modification of energetic conditions of the interface by either changing the concentration of electroactive species to or the potential imposed to the electrode. At low concentrations of electroactive species and not so negative potentials, 2D-2D growth of silver may be observed forming deposits less than the monolayer coverage. At more negative potentials 2D-3D growths are obtained. In this type of transition, two kinds of silver growth sites are identifiable, first on the VC and afterward, on the recently deposited silver. At concentrations and less negative potentials, 3D growth of nuclei can be seen, forming deposits far beyond a monolayer. Their growth is influenced by either diffusion of or the incorporation of silver adatoms into the substrate lattice, depending on the conditions of imposed potential. At concentrations and very negative potentials, where the deposited silver was much greater than a monolayer, 2D growths were found associated with the growth of Ag° on the previously deposited silver. It is worth noting that this is the first time, that in the same chemical system, the systematic evolution of electrocrystallization of 2D and 3D stages of nuclei growth on heterogeneous VC surfaces can be observed, through the gradual modification of energetic conditions at the interface by either changing the concentration of electroactive species or the potential imposed to the electrode. © 2004 The Electrochemical Society. All rights reserved.

Magnetohydrodynamic Analysis of Silver Electrocrystallization from a Nitric and Tartaric Solution

The magnetic field effects on silver electrocrystallization from nitric solutions containing small amounts of tartaric acid have been investigated either by stationary methods (steady-state current/potential curves) or by dynamic techniques such as the classical electrochemical impedance spectroscopy (EIS) method and the magneto-hydro-dynamical (MHD) transfer function analysis. In the stationary regime, a classical behavior, typical of a mass-transport controlled system, has been characterized. The EIS measurements revealed three characteristic responses, illustrating the unexpected complexity of the reaction mechanism. The MHD transfer function analysis shows a high frequency response that is regularly modified according to the polarization and the magnetic induction values. © 2004 The Electrochemical Society. All rights reserved.

Silver electrocrystallization at polyaniline-coated electrodes

The initial stage of silver electrocrystallization is studied at polyaniline (PANI)-coated platinum electrodes by means of potentiostatic current transients and electron microscopic observations. Data for the nucleation frequency and the number of active sites for nucleation are obtained by interpreting of current transients according to the theory for nucleation and 3D growth under diffusion limitations. It is found that depending on the PANI layers thickness, d, two different regimes for silver nucleation and growth exist. For thin PANI coatings ( d<0.3 μm), the crystallization occurs with high nucleation frequency at active sites located at the polymer layer/metal electrode interface, the number of active sites decreasing sharply with increasing PANI coverage. For thick PANI layers ( d>0.3 μm), silver nucleation occurs with a two orders of magnitude lower nucleation frequency at active sites located most probably at the polymer surface, their number remaining constant for thicknesses up to 1.4 μm. It is established that reduction of the PANI layer occurring in parallel with the silver electrodeposition does not influence the number of active sites for nucleation. The results obtained by interpretation of current transients are in good agreement with results for the number of crystals obtained by microscopic observation.

Kinetics of Silver Electrocrystallization in Nonaqueous Solutions

The effect of the solvent nature on the silver electroreduction and electrooxidation, including the initial electrocrystallization stage, is studied. Basic kinetic parameters of the process are determined. With increasing donor number of the solvent, which defines its capability for solvating cations, the rate constant of the electrochemical reaction decreases and the silver nucleation overvoltage increases. With increasing dipole moment of the solvent, which defines its adsorption properties, the surface energy of the silver nucleation decreases. The effect of the solvent on the silver electroreduction reveals itself through its solvation and adsorption properties.

Size distributions of silver and copper crystals as a function of electrocrystallization conditions on glassy carbon

Specific features and regularities of size distributions of crystalline nuclei are studied using the electrocrystallization of copper and silver on glassy carbon as an example. For a potentiostatic nucleation mode, with increasing overvoltage, a nonuniform size distribution approaches a uniform one. For a galvanostatic nucleation mode, the most probable nuclei size decreases with increasing current density and decreasing concentration of copper ions in solution, and the nuclei size distribution becomes more nonuniform due to a more pronounced non-steady-state nature of galvanostatic nucleation.

Silver Electrocrystallization onto Carbon Electrodes with Different Surface Morphology: Active Sites vs Surface Features

The influence of the electrode surface quality and surface morphology on the silver electrocrystallization process onto a carbon substrate from 10-2 M Ag(NH3)2+/1.6 M NH3, 1 M KNO3 (pH = 11) electrolyte solution was studied. Three substrates with different types of surface morphology and surface roughness were used: highly oriented pyrolitic graphite (HOPG), mechanically polished vitreous carbon (MPVC), and fractured vitreous carbon (FVC). Before the silver deposition process, the electrode surface was examined and characterized by means of Atomic Force Microscopy (AFM) analysis. Evaluation of the kinetic parameters of the silver nucleation and the growth behavior, as well as other characteristics of the silver electrocrystallization process onto carbon substrates, were based on cyclic voltammetry and chronoamperometric measurements. Cyclic voltammetry data also show that silver deposition efficiency is proportional to the increase of electrode surface roughness (from HOPG, via MPVC to FVC). The silver bulk deposition process on all three carbon substrates was characterized as 3D nucleation and diffusion-controlled growth. However, this process proceeds with different overpotentials on different substrates: the lowest for HOPG and the highest for MPVC electrode surface. The major electrocrystallization parameters, such as nucleation rate, number of active sites, and number of formed silver nuclei, strictly related to the electrode surface conditions, seem to not follow the same trends as the cyclic voltammetry data. It is clearly indicated in the nonlinear relationship between number of active sites and the surface features (recognized in AFM images). As pointed out in the discussion, it opens new questions regarding the nature of the active sites for deposition on the electrode surface and their identification by microscopic techniques.

Electrocrystallization and electrodeposition of silver on titanium nitride

The electrocrystallization and electrodeposition of silver on TiN substrates in AgNO3 + KSCN solutions were studied by electrochemical methods and scanning electron microscopy. The description of Ag electrocrystallization is given in terms of instantaneous, progressive or mixed nucleation models. The parameters of electrocrystallization were determined and the fractional area covered by silver was estimated. A two-step procedure was used for forming a continuous silver film on a TiN substrate. During the first step, a seed layer was deposited on TiN by applying either high negative potential or cathodic current density in 0.011 M AgNO3 + 2.5 M KSCN solution. The applied cathodic current density was higher than the limiting diffusion current in the solution. During the second step, a bulk silver film was deposited galvanostatically from a 0.22 M AgNO3 + 2.5 M KSCN solution at a cathodic current density lower than the limiting current density.

Preparation of SERS-active silver film electrodes via electrocrystallization of silver

The electrodeposition of a sufficiently large amount of silver on silver films at high over potentials leads to excellent substrates for surface-enhanced Raman scattering (SERS) spectroscopy. The surfaces roughened in this manner show great uniformity across the active area and exhibit SERS enhancement factors which are superior to those of silver surfaces roughened by conventional oxidation–reduction cycles. Since they are excellently reproduced from one sample to another, the prospects for application of this substrate for analytical purposes are very promising. Copyright © 2000 John Wiley & Sons, Ltd.

Silver Electrocrystallization on Vitreous Carbon from Ammonium Hydroxide Solutions

The early stages of the electrolytic deposition of silver onto vitreous carbon electrodes from ammonium hydroxide solutions have been investigated by the potential step technique. The analysis of the experimental current transients according to existing theories indicates that this process occurs by multiple three‐dimensional nucleation, followed by diffusion controlled growth of nuclei. It is shown that treatments that involve classifying the process as either instantaneous or progressive nucleation are not always adequate for the quantitative analysis of electrochemical nucleation phenomena. The nucleation kinetics parameters A (nucleation rate constant per site) and No (number density of active sites on the substrate surface) were estimated separately from the current transient maxima by two different approaches. Both quantities were found to vary with the potential and with the concentration of silver ions, except at very high overpotentials for silver deposition. The potential dependence of the nucleation rate A was interpreted according to the atomistic theory and in all cases it was found that the number of atoms in the critical nucleus (nk) was one over the entire potential range analyzed.

Silver electrocrystallization from a nonpolluting aqueous leaching solution containing ammonia and chloride

Silver electrocrystallization from aqueous solutions at pH 11, pC10 and pNH3 - 0.2, where Ag(NH3) + is the dominant Ag(i) species, has been studied. In spite of the complexities of this medium, the experimental results can be satisfactorily described in terms of multiple nucleation and diffusioncontrolled growth of hemispherical nuclei. Nucleation rates, A, and number densities of active sites on the electrode surface, No, were determined from potentiostatic current transients as a function of overpotential. Saturation number densities of silver nuclei on the electrode surface obtained from the A and No values were found to be in excellent agreement with those obtained from the direct, microscopic observation of the electrode surface. Spatial distributions of nuclei were also analysed for silver electrodeposited at different potentials. It was found that nuclei were uniformly distributed when electrodeposited at low overpotentiats, whereas inhibition of nucleation close to already established nuclei occurred at higher overpotentials. From the change of the true nucleation rate with overpotential, it was found that the critical nucleus is formed by a single atom within the - 100 to -300 mV overpotential range.

Two-dimensional silver electrocrystallization under monolayers spread on aqueous silver nitrate

Two-dimensional silver electrocrystallization under monolayers spread on aqueous silver nitrate

Elementary growth kinetics of silver electrocrystallization

The elementary processes of electrochemical growth of cubic faces of silver single crystals were investigated after the so-called capillary method by means of in situ laser Michelson interferometry. Data were obtained about the motion of dislocation generated steps during electrocrystallization from a stagnant solution. It was proved that step motion proceeds after the direct incorporation mechanism, with bulk diffusion field overlap, leading to deviation from linearity in the step velocity/overvoltage dependence at higher hillock slopes. The true value of the step kinetic coefficient for the studied face was determined: β = 1.2 cm/s. In acidified solutions β is much smaller: β = 0.17 cm/s. Interferometric measurements of hillock slope versus overvoltage dependencies allowed us to determine the Burgers vectors of the leading growth dislocation sources. The free surface energy of the step riser was determined without any additional suppositions: for pH ≅ 5 it was 130 erg/cm 2 and for pH ≅ 1 it was 110 erg/cm 2.

Rate of crystal growth by 2D nucleation in the case of electrocrystallization of silver. II

The studies of the growth kinetics of a screw-dislocation-free (100) face of a silver single crystal have been extended over a broader overpotential range. The growth rate of screw-dislocation-free (100) faces at constant potential has been measured and the 2D nucleation rate has been determined therefrom. It is established that the values of the 2D nucleation rate obtained follow the classical Volmer dependence in the range of higher overpotentials. At lower overpotentials, deviations from the Volmer dependence are observed. These deviations may eventually be attributed to the presence of active sites for nucleation at the face surface.