Analysis Of Potentiostatic Current Transients Research Articles

Influence of supporting electrolyte on electrochemical formation of copper nanoparticles and their electrocatalytic properties

Comparative analysis of copper nanoparticles (CuNPs) obtained by electrodeposition on highly oriented pyrolytic graphite (HOPG) substrates from different supporting electrolytes containing sulphate anions, was performed. Voltammetric results indicated that Cu electrodeposition follows a diffusion-controlled nucleation and crystal growth model for three solutions studied (Na2SO4, H2SO4 and Na2SO4+H2SO4). Na2SO4 solution was found to be most effective because the copper reduction occurs at most positive potential value, reaching the highest current density. Analysis of potentiostatic current transients revealed that the process can be described predominantly by a model involving 3D-progressive nucleation mechanism, which was corroborated by scanning electron microscopy (SEM) analysis. SEM images showed high density of hemispherical shaped Cu particles of different sizes (mostly between 80-150 nm), randomly distributed on the HOPG surface for Na2SO4 electrolyte solution. In the presence of H2SO4, the size dispersion decreased, resulting in particles with greater diameters (up to 339 nm). The use of electrolyte solution with Na2SO4+H2SO4 revealed lower particle density with a considerable crystal size dispersion, where very small crystallites are prevailing. Cyclic voltammetry was used to evaluate qualitatively the catalytic activity of CuNPs deposited from three electrolyte solutions towards the nitrate reduction reaction. An enhanced catalytic effect was obtained when copper particles were prepared from either Na2SO4 or H2SO4 supporting electrolytes.

Electrochemical formation of copper phosphide from aqueous solutions of Cu(II) and hypophosphite ions

The electrochemical formation of copper phosphide phases on vitreous carbon electrodes from Cu(II) and hypophosphite acid aqueous solutions has been studied. It was found that the main component in the deposits was Cu, that their composition was independent of the electrodeposition potential, and that the P content increased with the proportion of hypophosphite with respect to Cu(II) in solution. Analysis of potentiostatic current transients recorded during deposition and the microscopic observation of the surface indicated that the mechanism of electrocrystallization occurs through copper electrodeposition, inducing the reduction of hypophosphite with concomitant formation of copper phosphide clusters followed by their aggregation, leading to the nucleation of three-dimensional centers with a growth rate controlled by the diffusion of electrodepositing species from the solution bulk, with generation also of byproducts of hypophosphite reduction.

Electrochemical Nucleation and Growth of Rhenium on Glassy Carbon in the KF-KBF4-B2O3-KReO4 Melt

The initial stages of rhenium electrocrystallization on the glassy carbon electrode from the KF-KBF4-B2O3-KReO4 (0.88 wt% Re) melt at 773 K were studied using cyclic voltammetry, chronoamperometry, and scanning electron microscopy (SEM). Cyclic voltammetry data indicated the presence of a nucleation process. Analysis of potentiostatic current transients and SEM images demonstrated that the electrocrystallization process occurs by the three-dimensional instantaneous nucleation with diffusion-controlled growth under the studied conditions. The Scharifker–Hills and Scharifker–Mostany theoretical models were used to calculate the nucleation parameters and the diffusion coefficient of rhenium ions.

Analysis of Potentiostatic Current Transients for Multiple Nucleation with Diffusion and Kinetic Controlled Growth

The theoretical aspects of the electrocrystallization on an inert electrode under potentiostatic conditions are considered. The common growth theory of a single new-phase nucleus is analyzed. Two theoretical approaches to the mathematical description of 3D multiple nucleation with diffusion or kinetic controlled growth and their basic assumptions are discussed. Significant differences between above mechanisms of phase formation illustrates in detail. The formulas for obtaining the main nucleation and growth parameters in these models are given.

Fundamental aspects of lead electrodeposition processes: Nucleation and growth

In this comprehensive study, the processes of nucleation and growth of lead from electrolytes of various kind and compositions have been analyzed. The processes of Pb nucleation were examined by the analysis of potentiostatic current transients, while the growth process was examined by the scanning electron microscopic (SEM) analysis of the obtained deposits. It was found that nucleation of lead follows Scharifker and Hills (SH) model based on the 3-D instantaneous nucleation with the diffusion controlled growth. Morphologies of lead particles starting from granules produced at the low overpotentials from the dilute electrolytes to very branchy dendrites at the higher ones were formed by the electrodeposition processes. The obtained surface morphologies were correlated with the corresponding polarization characteristics. It was found that regular hexagonal particles are formed by electrodeposition in the ohmic control, while irregular crystals denoted as precursors of dendrites and dendrites of various types (the needle-like, the primary (P) and the secondary (S) dendrites) were formed in the mixed ohmicdiffusion and diffusion controlled electrodeposition. The needle-like and primary (P) dendrites were primarily formed from the basic (nitrate), while the secondary (S) and the tertiary (T) dendrites were formed from the complex (acetate and hydroxide) electrolytes.

A study of the electrodeposition of Co–Cu alloys thin films on FTO substrate

In this work, the early stages and the properties of the electrodeposition process of Co–Cu alloys thin films on a fluorine-doped tin oxide (FTO)-coated conducting glass substrate from a sulfate bath were investigated using conventional electrochemical techniques and X-ray diffraction technique (XRD). FTO was chosen as a foreign substrate because of its high transparence and its properties as inert material. Within the potential range analyzed, the kinetics of the Co–Cu electrodeposition corresponded to a model including instantaneous nucleation on active sites and diffusion controlled cluster growth. The number of active sites of the substrate, N0, and the diffusion coefficient, D, were determined from the analysis of potentiostatic current transients on the basis of existing theoretical models. XRD patterns of the Co–Cu alloys thin films display fcc and hcp phase, with peaks quite close to those of the Co phase (fcc and hcp). Therefore, the variation of the composition of thin films alloy is possible depending on the deposition potential.

A Novel Mathematical Model for the Study of Electrochemical Nucleation of Metals on Foreign Substrates from the Analysis of Potentiostatic Current Transients

A numerical model has been developed in order to characterize the kinetics of electrochemical nucleation processes using chronoamperometric techniques. The main purpose has been to overcome the limitations of the Scharifker-Mostany model which is currently used to determine kinetics parameters and to reproduce current density profiles. The proposed model was validated using chronoamperometric data obtained for copper nucleation on gold electrodes in CuSO4 - H2SO4 solutions at pH 1.0, 25 ºC with 0.05 M copper concentrations for overpotentials in the range -100 and -300 mV.

A Novel Mathematical Model for the Study of Electrochemical Nucleation of Metals on Foreign Substrates from the Analysis of Potentiostatic Current-Transients

not Available.

Formation of Cu/Pd bimetallic crystals by electrochemical deposition

The early stages of the palladium electrodeposition process onto a vitreous carbon (VC) substrate as well as the deposition of Cu on such Pd/VC modified surface were investigated using classical electrochemical techniques, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Within the potential range considered the kinetics of the Pd electrodeposition from a PdCl 2 acid solution can be described by a model involving progressive nucleation on active sites and diffusion-controlled 3D growth. The nucleation rate constant, A 0, and the number of active sites of the substrate, N 0, were determined from the analysis of potentiostatic current transients on the basis of an existing theoretical model. The AFM images corroborated the progressive nucleation mechanism showing irregular palladium crystals randomly distributed over the VC surface, with different sizes and 3D morphological characteristics. The electrodeposition of Cu was carried out onto the characterized Pd/VC modified surface from a Cu 2+ containing solution using a well defined polarization routine. The SEM/EDX images confirmed the formation of Cu/Pd bimetallic crystals uniformly distributed on the VC surface and the in situ AFM images obtained during this process corroborated that Cu formed a core–shell structure with the Pd crystals. Nevertheless, the subsequent anodic stripping produced only a partial dissolution of the Cu deposits, and therefore, the formation of a Cu/Pd alloy could be inferred.

Methodical aspects of studying the electroreduction of nitrate on modified single crystal Pt(hkl) + Cu electrodes

Technique of modification of basal faces Pt(hkl) by adatoms and epitaxial copper deposits is developed. Analysis of potentiostatic current transients of copper deposition/dissolution and atomic force microscopy showed that the activity of Pt(hkl) faces regarding the processes of copper nucleation and epitaxial growth increases in the sequence of Pt(111) < Pt(110) < Pt(100). The reaction of nitrate anion reduction is sensitive towards the surface structure, not only in the case of platinum, but also in the case of copper deposits (including a monolayer of adatoms). The highest process rate is observed for the Pt(100) electrode modified by a monolayer of adatoms or islands of bulk copper; nitrate reduction at the lowest rate occurs at Pt(111) + Cu electrodes. Structure-sensitive competitive adsorption of background electrolyte and nitrate anions is the factor that largely determines the kinetics of nitrate reduction on different faces of platinum single crystal and copper deposits.

Analysis of potentiostatic current transients at metal/liquid interfaces: resolving the effects of a finite step interval

AbstractPotentiostatic current transients are used routinely for electrochemical analysis of metal/liquid interfaces. These measurements can be affected by both the electrochemical cell and the potentiostat used for such experiments. We demonstrate this in the present report with double‐layer charging experiments using a gold electrode in aqueous electrolytes of NaF and NaNO3. By employing a high‐resolution potentiostat, we show that the apparently instantaneous voltage step actually has a finite temporal width. The double‐layer charging current develops an additional feature due to this behavior of the voltage step. We present a theoretical framework to resolve these instrumental effects from the actual electrical response of the double layer. The results are compared with a set of independent measurements of the same quantities using impedance spectroscopy. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Formation Mechanisms and Characterization of Black and White Cobalt Electrodeposition onto Stainless Steel

Cobalt electrodeposition onto a stainless steel substrate from 1.17 M Co(II) aqueous solution containing , 0.56 M KCl, and was evaluated in the absence (i) and presence (ii) of . Cobalt electrodeposited from the electrolytic bath (i) was white‐gray colored, whereas deposition from bath (ii) formed a black‐colored surface. SEM‐WDX, AFM, and XRD analysis of the steel surfaces covered with these two deposits revealed distinct characteristics for black and white cobalt films. Although both deposits were composed of metallic cobalt, the white cobalt deposit was a smooth, 2D film while the black deposit consisted of many dispersed, nano‐sized clusters of 150 to 250 nm in diameter. Analysis of potentiostatic current transients (I-t curves) indicated that formation of white cobalt was carried out by multiple 3D nucleation limited by lattice incorporation of cobalt adatoms to the growth centers. Formation of black cobalt was shown to involve the simultaneous processes of 3D nucleus formation and growth, limited by mass transfer, and the reduction of nitrates in the medium onto the surfaces of these nuclei. It is shown that, beside this cobalt‐nitrate interaction, ions in solution can block active sites for cobalt reduction and the effect of this phenomenon strongly depends on the nitrate concentration. These facts could explain the observed dispersion of the black cobalt coating. © 2000 The Electrochemical Society. All rights reserved.

The kinetics of mercury nucleation from Hg22+ and Hg2+ solutions on vitreous carbon electrodes

The kinetics of the electrochemical nucleation of Hg onto vitreous carbon were studied from analysis of potentiostatic current transients obtained at different overpotentials in Hg22+ and Hg2+ solutions. Similar sizes of critical nuclei and number densities of sites on the surface were found for nucleation of Hg from both solutions, indicating, in agreement with nucleation theory, that the rates of nucleation are controlled by surface energies and deposit–substrate interactions. Saturation number densities of nuclei were deduced from the kinetic analysis, and their relationship with those obtained from direct observation of the electrode surface is discussed. It was found that at low overpotentials, the nuclei deposited from both solutions were uniformly distributed on the electrode surface, whereas their distribution was affected by inhibition of the nucleation rates close to already established nuclei at high overpotentials. This inhibition was enhanced during deposition from Hg2+ solution.

An investigation of the electrochemical intercalation of lithium into a Li 1− δCoO 2 electrode based upon numerical analysis of potentiostatic current transients

Lithium insertion into a porous Li 1− δ CoO 2 electrode was investigated by numerical analysis of potentiostatic cathodic current transients. As lithium was intercalated, the current transients at first exhibited two-stage behavior in the presence of a single phase. This was later replaced by a three-stage character when a Li-diluted α phase coexisted with a Li-concentrated β phase. From the comparison of derivatives of the experimental logarithmic current transients with those numerically simulated, it is suggested that the chemical diffusivity of lithium ion predominantly determines the shapes of the first stage of the current transients when the two phases coexist and of the later stage of the current transients when only a single phase exists. The derivatives of the second stages of the linear and logarithmic current transients during the coexistence of two phases were observed to be characterized by an upward concave shape, indicating that lithium insertion proceeds via phase boundary movement (PBM). Transition times t tr (1) and t tr (2) were determined as the times of the local maxima on the derivatives of the experimental linear and logarithmic transients, respectively. These time values correspond to the onset and end of the PBM. The current transient and its derivative were simulated as functions of equilibrium stoichiometry through the numerical analysis for lithium transport under the condition for potentiostatic lithium injection into the electrode subjected to the limitation placed by the `pinning' of the phase boundary and the impermeable constraint to lithium. The numerically simulated current transient and the derivative of the second stage of the transient qualitatively matched those experimentally determined as functions of applied potential in their three-stage character and upward concave shape, respectively.

Spatial distributions and saturation number densities of lead nuclei deposited on vitreous carbon electrodes

The nucleation of lead onto vitreous carbon electrodes has been investigated. Diffusion-controlled growth of nuclei inhibits nucleation, giving rise to saturation with nuclei and introducing correlations in their location on the electrode surface. Similar nuclear number densities were obtained from direct, microscopic observation of the surface and from analysis of potentiostatic current transients considering the development of nucleation exclusion zones around already established nuclei. At low overpotentials nuclei were found to be uniformly distributed on the surface, whereas at high overpotentials the results were found to be consistent with simulations of the process that allowed for the existence of exclusion zones around nuclei, with radii proportional to the square root of their age.

Electrochemical behaviour of copper in potassium thiocyanate solution—II. Analysis of potentiostatic current transients

The kinetics of passivity and pitting corrosion of copper in borate-boric acid buffer containing potassium thiocyanate is studied at 25°C by means of potentiostatic transients recorded at different constant potential values. Three different potential regions are distinguished. Region I, as the applied potential is increased, implies the successive formation of cuprous thiocyanate, cuprous and cupric oxide. This corresponds to the formation of a composite anodic layer. Region II extends from the potential of the third anodic voltammetric peak up to the breakdown potential. Region III involves the breakdown of the passive layer caused by thiocyanate ions, and the formation of different copper salts in the pits. The kinetics of the various stages is discussed in terms of an extension of the nucleation and growth mechanism following an approach which was earlier applied for explaining the initiation and growth of pitting corrosion of metals.

ChemInform Abstract: Corrosion aml Passivity of Copper in Solutions Containing Sodium Sulphide. Analysis of Potentiostatic Current Transients.

AbstractDas elektrochemische Verhalten von Cu‐Elektroden in NaOH‐Lösung mit Na2S‐Zusatz läßt sich als 3‐Stufen‐Prozeß beschreiben.

Corrosion and passivity of copper in solutions containing sodium sulphide. Analysis of potentiostatic current transients

The electrochemical behaviour of copper electrodes in NaOH solutions with the addition of Na 2S was studied through the analysis of current transients under constant potential and complementary voltammetric and scanning electron microscopy data including energy dispersive X-ray analysis. The overall process can be described by the following three stages. The first stage corresponds to the nucleation and growth of a complex copper sulphide layer at potential values close to the equilibrium potentials of the Cu/Cu 2S and Cu/CuS reversible electrodes. The second stage is related to the rupture of the copper sulphide film at potentials more positive than a certain critical value leading to pitting corrosion of copper metal and yielding a poorly protective copper sulphide layer. The third stage occurs in the copper oxide electroformation range, where the presence of copper sulphide accelerates the electrodissolution of the base metal and copper oxide hinders the sulphidization processes. The current transients of each stage are interpreted through a model based on the nucleation and growth mechanism.