Number Density Of Active Sites Research Articles

Study on the Palladium Nucleation and Growth Mechanism in A Deep Eutectic Solvent by Electrochemical Method

By using cyclic voltammetry (CV) and chronoamperometry (CA) techniques, the thermodynamics and kinetics of palladium electrodeposition on glassy carbon electrode (GCE) in deep eutectic solvent were studied. The Pd electrodeposition process via progressive 3D nucleation mechanism was controlled by the diffusion. Non-linear fitting methods were applied to obtain the kinetic parameters in the light of Harrison – Thirsk (H-T) and Scharifker – Hills (S-H) models for 3D nucleation and growth process. From that, the diffusion coefficient of Pd (II) in reline at ambient temperature was calculated by two different ways, and the obtained results showed that it is of cm2/s by using CV. Moreover, some important parameters such as the number density of active sites on the electrode surface (No) and the nucleation frequency per active site (A) were estimated by fitting experimental CAs data with Scharifker-Mostany model.
 Electrodeposition, thermodynamic, electrochemical, progressive, palladium, deep eutectic solvent.
 

Electrochemical Nucleation and Growth of Pd-Co Alloy Nanoparticles from the Reline Deep Eutectic Solvent

Electrochemical formation of Pd-Co alloy nanoparticles, PdCoNPs, onto a glassy carbon electrode, GCE, from their metallic precursors dissolved in the reline deep eutectic solvent, is reported for the first time. Potentiodynamic and potentiostatic studies indicated that PdCoNPs were electrodeposited by multiple nucleation of 3D bimetallic centers with mass transferred-controlled growth. Potentiostatic current density transients, j–t, were adequately fitted by a theoretical model that describes the kinetics of nucleation and diffusion-controlled growth of bimetallic phases and the number density of active sites for PdCoNPs nucleation, N 0, and their nucleation frequency, A, was determined as a function of the applied potential. SEM image recorded on the GCE electrodeposited with PdCoNPs showed that sizes and particle number density of these PdCoNPs depend on both the applied potential and the deposition time considered. At −0.42 V and 10 s the PdCoNPs had (30 ± 4) nm as average size and a particle number density of (4.23 ± 0.33) x1010 PdCoNPs cm–2. EDS, XRD and XPS observations indicated the presence of Pd and Co. forming a PdCo alloy as zero and bivalenced oxidation states. GCE/PdCoNPs depict higher mass activity towards FAOR than GCE/PdNPs and other modified electrodes reported in the literature where the electrocatalysts were synthesized by different means.

Electrodeposition of Nanostructured Chromium Conglomerates from Cr(III) Dissolved in a Deep Eutectic Solvent: Influence of Forced Convection

In this work, Cr electrodeposition onto a glassy carbon rotating disk electrode (GCRDE) was studied from Cr(III) ions dissolved in the choline chloride and ethylene glycol eutectic mixture (ethaline) under different GCRDE angular speeds, ω, at 343 K. The ethaline kinematic viscosity, = 0.17 was estimated, for the first time, from potentiodynamic plots under forced convection conditions, using the Levich equation. Cr electrodeposition was studied from the analysis of potentiostatic current density transients, j-t plots, recorded at different ω. This study was based on the model proposed by Hyde et al. (J. Electroanal. Chem., 534, 13 (2002)) for analysis of j-t plots due to 3D nucleation and diffusion-controlled growth under forced convection, j dc-fcon(t), complemented by a previous adsorption step, j ad(t), and the residual water reduction, jWR (t), taking place on the growing surfaces of the Cr nuclei; thus, j total (t) = j ad(t) + j dc-fcon(t) + j WR(t). The kinetic parameters, namely: nucleation frequency and number density of active sites for chromium nucleation onto the GCRDE showed small dependence on ω; however, the term j WR (t) clearly depends on the ω value. Scanning Electron Microscopy, Energy Dispersive Spectroscopy and X-ray Photoelectron Spectroscopy techniques were used to characterize the Cr electrodeposited on the GCRDE surfaces. It was observed that the electrodeposits were formed by quasi-spherical conglomerates (ca. 50 and 200 nm diameter for 0 and 1500 rpm, respectively) of nanoparticles (sized less than 30 nm diameter, in both cases). Moreover, these electrodeposits were formed by chromium and oxygen and its content increases with ω. These nanoparticles exhibit a core–shell structure, where the core was formed by metallic, zero valence chromium, and the shell of Cr(III) (as Cr(OH)3 and Cr2O3), which was consistent with the theoretical mechanism used for the analysis of the j-t plots.

Electrochemical Nucleation of Silicon in Ionic Liquid-Based Electrolytes

Silicon is widely applied in a high number of industrial technologies, including different types of electronics, solar energy conversion and electrochemical energy storage. This extensively studied material has an exceptionally high theoretical capacity, more than ten times higher compared to the currently used graphite anodes in Li-ion batteries [1]. However, its main disadvantage is the huge volume expansion upon alloying with lithium, inducing disintegration of the electrode material, loss of electrical contact, poor reversibility and a rapid capacity fade [1]. It has been established that Si applied in a nanostructured or nanoparticulate form displays an enhanced electrochemical stability. Therefore, advanced production technologies have to be implemented in order to obtain cost-effectively the required electrochemically stable Si morphologies.Electrochemical methods offer a simple and low-cost deposition process. Furthermore, the electrodeposition is a versatile technique, allowing control of the morphology by adjusting the experimental conditions and obtaining deposits on different substrate geometries. However, due to the very low reduction potential and high reactivity of silicon precursors, it is impossible to deposit this element in aqueous electrolytes. Therefore, a broad variety of alternative media, including high temperature molten salts (HTMS) [2], conventional organic solvents [3] and ionic liquids (ILs) [4] has been researched.It is established that the initial stages of electrodeposition play an important role for the physical properties, stability and functional behavior of the final deposit. For example, homogeneous distribution of a high number density of small Si crystals would be beneficial for the electrochemical stability of the deposit during lithiation. Therefore, the nucleation and growth process of silicon deserves a special attention. Initial studies on the formation of Si nuclei in HTMS have been recently reported [2]. It was found that the diffusion limited nucleation process in HTMS (i.e. KF-LiF-K2SiF6) is instantaneous, followed by 3D growth [2]. However, due to the high temperatures (T > 800oC) and difficulties to perform the Si deposition economically in these electrolytes the research interest has turned to low temperature molten salts (LTMS).In our study we analyze the initial stages of Si electrodeposition in IL electrolytes by interpreting the chronoamperometric data (fig.1a) with a model accounting nucleation and growth under diffusion limitation, established by Scharifker et al. [5-7], eq.1. Vitreous carbon was selected as an inert substrate for the experiments and 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide [BMP][TFSI] containing SiCl4 was chosen as an electrolyte.The current transients were quantitatively interpreted by a non-linear fitting procedure, applying a model equation for three-dimensional nucleation, eq.1. Eq.1 was modified with a term describing the surface charging phenomena, observed at the beginning of the silicon reduction, approximated to an exponential decay after Langmuir adsorption kinetics, eq.2. To prove the validity of this procedure, we extracted the charging currents (fig.1b) and fitted the resulting curves with the non-modified equation for 3D nucleation, where the respective output parameters remained nearly identical. According to eq.(3), the data for P1 should be constant for all fitted curves (i.e. potentials) since this parameter does not depend on other variables. This allows the value of the diffusion coefficient D =1.3×10−8 cm2 s−1 to be calculated. D was additionally confirmed by the analysis of the current maxima [5,6]. The data for the nucleation frequency, A and the number density of active sites, N0 obtained from the best fit are presented in Fig. 1c and show the typically observed linear increase as a function of the overpotential,η [7].Furthermore, we characterized the nucleation process by analyzing the current maxima in dimensionless coordinates (fig. 1d). According to the analysis the initial stages of the Si phase formation display an instantaneous behavior, showing a progressive character with decreasing the applied overpotential. The theoretically evaluated values for N0 correlate well with the crystal number density N, acquired by scanning electron microscopy. The talk will cover the main aspects of the electrochemical nucleation of Si in non-aqueous electrolytes and will provide a discussion on the major challenges towards understanding this process.

Electrochemical nucleation and optical characterization of highly oriented Bi clusters on Cu substrate

The electrochemical nucleation and growth of bismuth (Bi) crystallites on copper substrates were investigated using cyclic voltammetry and chronoamperometry measurements, and scanning electron microscopy (SEM). The experimental current transients were analyzed according to the Scharifker and Hills and Mirkin-Nilov and Heerman-Tarallo models. At relatively low overpotentials and low Bi concentration, Bi deposition can be described by a model involving progressive nucleation on active sites and 3D diffusion-controlled growth. At higher Bi concentration, the growth mechanism shifts to the instantaneous nucleation mode. These results were also confirmed by SEM analysis. The values of some kinetic parameters such as the nucleation rate, the number density of active sites and the diffusion coefficient of Bi3+ ions were also calculated using different theoretical approaches. X-ray diffraction measurements revealed that the Bi crystallites grow in the rhombohedral crystal structure along the [012] direction. The optical properties of the dispersed Bi nanoparticles on the Cu surface were discussed in the ultraviolet-visible (UV–Vis) wavelength range. It was found that the UV–Vis spectrum exhibit a strong resonant optical absorption on the surface with the smallest Bi crystallite size (200 nm).

Early stages of copper microparticles electrodeposition on polypyrrole film

Abstract In this work, we studied the electrodeposition of copper (Cu) microparticles on polypyrrole (PPy) films using cyclic voltammetry and chronoamperometry techniques. The initial stages of Cu deposition were investigated by performing current transients. Models based on Scharifker and Hills calculations were established to determine the nucleation and growth type. The results suggest that the deposition of Cu proceeds via an instantaneous nucleation followed by three-dimensional (3D) diffusion-limited growth. The values of the number density of active sites N∞ and diffusion coefficient D were also determined.

Copper Electrodeposition from a Deep Eutectic Solvent, Used for Nitrates Reduction

This research work studied Cu electrodeposition over a glassy carbon electrode (GC) using deep eutectic solventes (DESs) instead of conventional aqueous media to subsequently assess the electrodeposit catalytic properties during nitrates reduction. These are nitrogen’s most reduced form, typically present in residual waters from chemical industries, from human consumption and from agriculture, which represent a significant contamination problem; they are not at all easy to eliminate through conventional methods used in water treatment plants, because they can reach potable water sources provoking in humans the incidence of severe illnesses, like cancer among others. It has been shown, that catalysts based in Pd, Pt and Cu metal phases reduce the nitrate ions, where the Cu ones have been studied because of their attractive catalytic properties. There are various forms of synthesizing the Cu catalysts, where electrodeposition leads to better control of Cu nucleation and growth. Cu electrocristalization was carried out from DES to compare the influence of the medium over the nucleation and growth mechanism. The eutectic mixtures used were prepared from choline chloride as the ionic species while the hydrogen bond donnors were urea and ethylene glycol. Both the DES were prepared in a 1:2 molar ratio, taking particular care to establish the influence of the resulting liquid at the early stages of electrodeposition, which was studied from Cu (II) solutions. It was shown that its electrodeposition takes place through a separte stage during which Cu (II) reduces first to Cu (I). All media studied led to demonstrate that electrodeposition follows a nucleation and 3D diffusion controlled growth. The Cu (II) diffusion coefficient, the A (nucleation frequence) and N0 (number density of active sites) parameters were estimated from potentiostatic plots using the Heerman and Tarallo model. The nitrates reduction at different concentrations was studied via differential pulse voltammetry to determine analytical parameters, like sensibility, detection and quantification limits. The Cu-modified glassy carbon electrodes and a Cu bar served to reduce the nitrates, immersed in 100 mM NaCl supporting electrolyte at pH=1.4 set with HClO4 analytical grade, adding different KNO3 concentraciones. It was shown that in acid medium the nitrates ion can be quantified reliably. Figure 1

Electrochemical Synthesis of Cobalt with Different Crystal Structures from a Deep Eutectic Solvent

The present paper shows experimental evidence of electrochemically synthetizing cobalt with hexagonal and face centered cubic structures from a choline chloride-based deep eutectic solvent. The nucleation and diffusion-controlled growth mechanisms of cobalt onto a copper electrode were studied through electrochemical means in order to determine several kinetic parameters of interest such as the nucleation rate, A, and the number density of active sites, N0. Current density transients were analyzed using a model comprising the simultaneous presence of cobalt 3D nucleation with diffusion-controlled growth and residual water reduction on the growing surfaces of the metallic nuclei. The massive electrodeposition of cobalt was carried out on copper substrates using potentiostatic and galvanostatic techniques. The analysis of results obtained from the surface deposit microstructure and morphology using scanning electron microscopy images and magnetic measurements, confirmed the existence of the hexagonal and cubic cobalt structures. It was found that fiber textures parallel to the electrodeposition axis are formed in the case of the cobalt cubic structure. Furthermore, mainly the current density and kinetics of crystallites nucleation are considered the key parameters to favor the crystal structure change, thus formation of the texture of cobalt from DES.

Iron Electrodeposition from Fe(II) Ions Dissolved in a Choline Chloride: Urea Eutectic Mixture

In this work, the Fe electrodeposition and nucleation and growth mechanisms onto a glassy carbon electrode from a choline chloride-based deep eutectic solvent (DES) were studied using electrochemical techniques and surface characterization techniques (SEM, EDS, and XPS). The current density transients were characterized by the strong effect of the induction-time during the Fe electrodeposition process. A model comprising 3D nucleation and diffusion-controlled growth that considers the induction-time offset was proposed and validated to analyze and explain the Fe nucleation and growth mechanism on the glassy carbon electrode. Kinetic parameters of Fe nucleation and diffusion-controlled growth such as the nucleation rate, A, the number density of active sites, N0, the diffusion coefficient, D, as well as induction-time were determined. Iron electrodeposit follows an electrochemical aggregative growth mechanism and was constituted by particles of Fe(0) and a mixture of FeO, Fe2O3 and Fe(OH)3.

INFLUENCE OF TEMPERATURE ON THE THERMODYNAMICS AND KINETICS OF COBALT ELECTROCHEMICAL NUCLEATION AND GROWTH

From potentiodynamic and potentiostatic experiments, the cobalt electrochemical nucleation and growth process, onto the glassy carbon electrode surfaces, from an aqueous solution containing 10−2M CoCl2 and 1M NH4Cl (pH=4.66) at different temperatures (15–60°C) is reported. It was found that while the equilibrium potential moves to more negative values as the temperature of the system was increased, the contrary was observed for the nucleation overpotential, ηnucleation, required for the onset of cobalt nucleation onto the surfaces of vitreous carbon. From Tafel plots recorded at the different temperatures considered, both: the transfer coefficient, α, and the exchange current density, j0, associated with the Co(II)/Co(0) system were assessed, and from the Arrhenius plot (ln j0 vs. T−1) the activation energy for Co(II) reduction of (27.9±0.3) kJmol−1 was estimated. From analysis of the potentiostatic current density transients according with the formalism proposed by Palomar-Pardavé et al. (Electrochim. Acta 50 (2005) 4736-4745), the total current density was de-convoluted into individual contributions, due to formation of multiple mass-transfer controlled 3D Co nuclei and that associated to the proton reduction occurring simultaneously on the growing surface of the Co nuclei. The latter contribution was practically null at 10°C, however, it drastically increased as the temperature of the system did, provoking that the cathodic efficiency for Co deposition diminished. Furthermore, it was found that both the number density of active sites, N0, and the nucleation rate, A, for Co nucleation depend exponentially with ηnucleation, regardless of temperature, except at 60°C where N0 diminished linearly with ηnucleation. From variations of the Co(II) ions diffusion coefficient with temperature, a value of (8.5±0.2) kJmol−1 was obtained for the activation energy for bulk diffusion. SEM analysis showed that the cobalt nuclei are bigger as the temperature increases; however, the coverage of the electrode surfaces becomes lower.

On Wetting Angles and Nucleation Energies during the Electrochemical Nucleation of Cobalt onto Glassy Carbon from a Deep Eutectic Solvent

This work deals with the electrochemical nucleation of cobalt, onto a glassy carbon electrode, from a deep eutectic solvent formed by choline chloride and urea in a 1:2 molar ratio. The nucleation mechanism was studied through electrochemical techniques. From the analysis of the experimental potentiostatic current transients, the kinetic parameters such as the nucleation frequency, A, and the number density of active sites, N0, were determined. In this work, A was also expressed as a function of the wetting angle, θ, (A(θ)) where the local distribution of θ was calculated through a stochastic simulation of the misorientation angle distribution derived from a created random texture. The A(θ) obtained from such a stochastic approach was in good agreement with the experimental data thus leading to determination of the Gibbs free energy of nucleation ΔG(nc) and the critical nucleus size nc, aside from other kinetic parameters such as the transfer coefficient α, the exchange current density j0, and the surface tension σ. Furthermore, a new method of calculating the nucleation energy from a voltammetric trace recorded during cobalt nucleation onto glassy carbon was proposed and validated. This method provides a novel tool to assess the experimental magnitude and to measure the nucleation energy.

Electrochemical nucleation and three-dimensional growth under mixed kinetic-diffusion control: analytical approximation of the current transient

An analytical expression is derived for the current transient generated by electrochemical nucleation and three-dimensional growth of metal nanoparticles under mixed kinetic-diffusion control. The expression is the approximate solution of a novel mathematical model and describes the dependence of the current transient on nucleation rate, number density of active sites and charge transfer kinetic constant. Relative difference between the current predicted by the analytical expression and numerical solution of the original model is invariably lower than 0.1.

Methanol Reforming over Cobalt Catalysts Prepared from Fumarate Precursors: TPD Investigation

Temperature-programmed desorption (TPD) was employed to investigate adsorption characteristics of CH3OH, H2O, H2, CO2 and CO on cobalt-manganese oxide catalysts prepared through mixed Co-Mn fumarate precursors either by pyrolysis or oxidation and oxidation/reduction pretreatment. Pyrolysis temperature and Co/Mn ratio were the variable synthesis parameters. Adsorption of methanol, water and CO2 was carried out at room temperature. Adsorption of H2 and H2O was carried out at 25 and 300 °C. Adsorption of CO was carried out at 25 and 150 °C. The goal of the work was to gain insight on the observed differences in the performance of the aforementioned catalysts in methanol steam reforming. TPD results indicated that activity differences are mostly related to variation in the number density of active sites, which are able to adsorb and decompose methanol.

A theoretical model for nucleate boiling of nanofluids considering the nanoparticle Brownian motion in liquid microlayer

The forming of a porous layer of deposited nanoparticles on the heater surface is one of the unique phenomena in nucleate boiling of nanofluids. As the deposition of nanoparticles is induced by the evaporation of liquid microlayer, the average nanoparticle concentration in the microlayer is much higher than that in the bulk liquid. Therefore, the Brownian motion of nanoparticles in the microlayer may play an important role in dissipating heat from the heater surface. In this study, a new heat flux partitioning (HFP) model was proposed, in which a new heat flux component was incorporated to account for the heat transfer by nanoparticle Brownian motion in the liquid microlayer. The new heat flux component was formulated based on the latest experimental and theoretical research outcomes of microlayer evaporation. Comparison of the numerical results against the experimental data available in the literature proved that the new HFP model performs better than the classic HFP model. This study also demonstrated that the importance of nanoparticle Brownian motion is mainly controlled by the applied heat flux as it directly affects the number density of active sites on the heater surface. Finally, the effects of nanoparticle concentration, size and materials were also analyzed.

Visualization study of nucleate pool boiling of liquid nitrogen with quasi-steady heat input

A visualization experimental device has been built to investigate the bubble behaviors in the nucleate pool boiling of cryogenic fluids at atmospheric pressure. The general morphologies of the bubbles are analyzed based on the captured films using a high-speed camera. The bubble behaviors leaving the wall at different heat flux can be divided into three regimes (low heat flux regime, fully developed nucleate boiling regime and intermediate regime) according to the availability of bubble parameters. In the low heat flux regime, the bubble is discrete and the interactive effects are ignorable. In the fully developed nucleate boiling regime close to CHF, the bubbles depart in the form of bubble cluster with a neck. In the intermediate regime, the interactive effect between the bubbles is significant and the bubbles follow a random pattern neither discretely nor as cluster neck. The information about the bubble departure diameter, the detachment frequency and the number density of activated sites are specially investigated. These data are used to evaluate the existing semi-empirical correlations widely applied to either the room-temperature or cryogenic fluids. It is found that the Kim’s correlation for the departure diameter predicts a satisfactory agreement with the experimental results in the isolated bubble regime. For the predictions of the detachment frequency, the correlation by Katto and Yokoya is recommended after comparison. The relation between the diameter and frequency can also be well determined by the correlation proposed by Mcfadden et al. The number density of active sites for liquid nitrogen still can be considered to be linearly proportional to ΔTm as it is for water, except that the exponent absolute m is much smaller.

Platinum-decorated carbon nanotubes for hydrogen oxidation and proton reduction in solid acid electrochemical cells.

Pt-decorated carbon nanotubes (Pt-CNTs) were used to enhance proton reduction and hydrogen evolution in solid acid electrochemical cells based on the proton-conducting electrolyte CsH2PO4. The carbon nanotubes served as interconnects to the current collector and as a platform for interaction between the Pt and CsH2PO4, ensuring minimal catalyst isolation and a large number density of active sites. Particle size matching was achieved by using electrospray deposition to form sub-micron to nanometric CsH2PO4. A porous composite electrode was fabricated from electrospray deposition of a solution of Pt-CNTs and CsH2PO4. Using AC impedance spectroscopy and cyclic voltammetry, the total electrode overpotential corresponding to proton reduction and hydrogen oxidation of the most active electrodes containing just 0.014 mg cm-1 of Pt was found to be 0.1 V (or 0.05 V per electrode) at a current density of 42 mA cm-2 for a measurement temperature of 240 °C and a hydrogen-steam atmosphere. The zero bias electrode impedance was 1.2 Ω cm2, corresponding to a Pt utilization of 61 S mg-1, a 3-fold improvement over state-of-the-art electrodes with a 50× decrease in Pt loading.

Gas-phase removal of hydrogen sulfide using iron oxyhydroxide at low temperature: Measurement of breakthrough curve and modeling of sulfidation mechanism

Abstract With the aim of removing hydrogen sulfide (H2S) from a gaseous phase around room temperature, we studied the performance of an iron oxyhydroxide (ferrihydrite) adsorbent by measuring a packed bed breakthrough curve (BTC) in a constant gas flow. We determined the amount of H2S adsorbed on the adsorbent by integrating BTCs measured under different experimental conditions. These conditions included the initial concentration of H2S, the superficial gas velocity and the temperature of the packed bed. Under the experimental conditions, it was found that the amount of H2S adsorbed was almost unchanged by the superficial gas velocity, whereas the adsorbed amount depended on the initial concentration of H2S and temperature. To solve the mass transfer equations in the packed bed, we developed a model considering such parameters as the kinetic constant of the sulfidation reaction, the intragranular diffusivity of H2S, and the number density of active sites on the adsorbent. By fitting the calculated BTC to the measured BTC under one of the experimental conditions, the set of parameters could be estimated. Using the same set of estimated parameters, we calculated the BTCs under the other experimental conditions. As a result, we confirmed that the calculated BTC coincided with the BTC measured under a different initial H2S concentration and gas velocity. We also found that the number density of the active sites increased with increases in temperature.

Zn Electrodeposition from an Acidic Chloride Bath Containing Polyethyleneglycol (Mw 200) and Benzylideneacetone as Additives

The influence of Polyethylene Glycol 200 (PEG200) or a PEG200/benzylideneacetone (BDA) mixture on the mechanism of Zn deposition and nucleation kinetics was studied by voltammetry, chronoamperometry and atomic force microscopy (AFM). The addition of PEG200 or PEG200/BDA to the solution partially inhibited the reduction of Zn(II) at E =− 1.135 V vs. SCE. In the presence of PEG200/BDA, an additional reduction process was observed at E =− 1.24 V vs. SCE. Analysis of the nucleation processes indicated that, in all systems studied, the initial stage of Zn deposition was dominated by 3D diffusion-controlled nucleation. At E =− 1.132 V vs. SCE, the addition of PEG200 caused a reduction in the nucleation rate constant (A) and the number density of active sites (N0) with respect to the values obtained without additives. AFM analysis of coatings obtained at E =− 1.132 V vs. SCE, showed the formation of Zn clusters with different sizes distributed randomly on the surface. At E =− 1.243 V vs. SCE, both A and N0were higher for the solution containing the PEG200/BDA mixture than for the systems with PEG200 alone or without additives. AFM analysis revealed the formation of similarly sized Zn clusters uniformly distributed on the surface.

Nucleation and growth of zinc on aluminum from acidic sulfate solution with [BMIM]HSO4 as additive

The nucleation and first stages of the growth of zinc on aluminum from acidic sulfate solution in the absence and presence of 1-butyl-3-methylimidazolium hydrogen sulfate-[BMIM]HSO4 as additive were investigated using cyclic voltammetry, chronoamperometric current–time transients, and scanning electron microscopy techniques. The dimensionless chronoamperometric current–time transients for the zinc electrodeposition on aluminum electrode from the solution free of [BMIM]HSO4 showed the zinc deposition can be interpreted by a model involving instantaneous nucleation with hemispherical diffusion controlled growth of nuclei. The addition of [BMIM]HSO4 induced a blocking effect on the zinc electrocrystallization process through its cathodic adsorption on the electrode surface. This effect led to increase the number density of active sites, decrease the nucleation and growth rate of these nuclei, and produce more leveled and fine-grained cathodic deposits without affecting the instantaneous nucleation mechanism. Surface morphology analysis revealed the crystal structure of the zinc deposits formed did not change by the adsorption of [BMIM]HSO4 at the first stages of deposition.

Effect of potential on the early stages of nucleation and growth during cobalt electrocrystallization in sulfate medium onto FTO surface

The electrodeposition of Co thin films onto a fluorine-doped tin oxide (FTO)-coated conducting glass substrate from sulfate solutions was investigated using cyclic voltammetry, and chronoamperometry measurements. The Scharifker and Hills model was used to analyze current transients. At relatively low overpotentials, the Co deposition can be described by a model involving instantaneous nucleation on active sites and diffusion-controlled 3D growth. The values of kinetic parameters, number density of active sites N∞, and diffusion coefficient D for Co2+ ions are also calculated.