Progressive Nucleation Mechanism 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.
 

Facet‐Dependent Interfacial and Photoelectrochemical Properties of TiO2 Nanoparticles

AbstractThe photoelectrochemical properties of titanium dioxide (TiO2) nanoparticles are directly related to the presence of certain facets. The synthesis of such particles is challenged using volatile and sensitive precursors utilizing shape capping agents. In this study, an easier two‐step synthesis technique for the preparation of well‐specified morphology TiO2 nanocrystals from TiO2 powder is demonstrated. The facet‐dependent Fermi level and flat band potential of the prepared particles are calculated and their photoelectrochemical properties are investigated by Cu2+ and Pb2+ photo/electrodeposition. From Cu2+ electrodeposition, it is shown that the presence of {100} and {001} facets in cubic morphology facilitates the electrodeposition with progressive nucleation mechanisms, while the presence of {101} facet in octahedral geometry follows instantaneous nucleation mechanisms. The activity of electroreduction is also related to the flat‐band potential which shows the highest activity in Pb2+ electrodeposition for octahedron nanostructure due to the alignment of the reduction potential to the edge of the flat band. Photodeposition of Cu2+ and Pb2+ ions shows identical trends to electrodeposition indicating the facets influence in ion adsorption and structure of the bandgap of morphological TiO2. The findings emphasize the importance of facet‐dependent surface adsorption and bandgap structure designing faceted TiO2 nanoparticles for tailored applications.

Effect of ultrasonic field on the mechanism of electrodeposited Cu nucleation and growth

Electrodeposition technology is widely used in the surface treatment of copper foil. The unique “mechanical disturbance effect” and “cavitation effect” of ultrasonic field can effectively control the electrodeposition process of Cu and improve the quality of electrodeposited layer. In this paper, Linear Sweep Voltammetry (LSV), Cyclic Voltammetry (CV), Chronoamperometry (CA) and Chronocoulometry (CC) were used to study the electrochemical behavior of electrodeposited Cu in ultra-high acidity sulfate systems under different ultrasonic field powers. The nucleation and growth mechanism of Cu were discussed, and the surface morphology of electrodeposited layer was analyzed. The results show that the electrodeposition of Cu under the static condition (0 W) follows the diffusion controlled progressive nucleation and 3D growth mechanism, and the deposits are in the cylindrical shape with spherically agglomerated. The ultrasonic field significantly improves the mass transfer rate in the electrodeposition process, and the fine dispersion effect is obvious. The uniform and dense micro-nano layers are formed, following the 3D growth mechanism. With the increasing of ultrasonic field power, the nucleation mechanism gradually changes from the diffusion controlled progressive nucleation to the electrochemistry controlled instantaneous nucleation. In addition, there appear peeling, grooving and local microcracks on the electrodeposited layer under higher ultrasonic power condition, and it is easier to form a smooth and uniform electrodeposited layer with the ultrasonic power of 60 W compared to that with the ultrasonic power of 100 W.

A mechanistic study of Pt particle electrodeposition and growth on a self-assembled monolayer as an active template

• Application of monolayers on gold as templates for deposition of Pt particles. • Evaluation of particle growth using cyclic voltammetry and chronoamperometry. • Evaluation of growth mechanism with SH model using chronoamperometric deposition. • Evaluation of growth mechanism using time dependant image J analysis of the SEM. • Comparing mechanism of growth evaluated using SH model with SEM analysis. Platinum is an essential component in many commercial catalytic processes. However, due to its cost and availability considerable effort is made to control the amount, location, and accessibility of the platinum species on an electrode surface. The current study investigates a low-cost, and versatile method for the deposition of Pt particles using a self-assembled monolayer (SAM) as an active assisted template on a gold electrode. Alkane (HSCH 2 (CH 2 ) 8 CH 3 ), alcohol (HSCH 2 (CH 2 ) 9 CH 2 OH) and carboxylate (HSCH 2 (CH 2 ) 8 CH 2 COOH) terminated monolayers were used to probe the impact of hydrophobicity on particle size, population density and growth mechanism. Cyclic voltammetry (CV) and chronoamperometry (CA) were employed to induce particle growth. From the CA data a dimensionless theoretical plot was calculated based on the Scharifker and Hills model to establish the mechanism as either progressive or instantaneous. The time-dependent study revealed a progressive nucleation mechanism for Pt particles synthesized on all three electrode surfaces, whereas microscopy and image analysis revealed an instantaneous nucleation mechanism for the alkane template only and progressive nucleation pathways for the alcohol and carboxylate SAM surfaces. The results indicated that SAM templating could be used to effectively control particle growth in a predictable fashion, however there is a limitation in application of the existing model due to a combination of factors including the migration of the SAM monomers on the electrode surface, the hydrophobicity of the terminal moieties and the occurrence of secondary and subsequent nucleation and growth phases. In addition, post-particle deposition CV was used to determine the impact of the SAM template on the active area of the Pt particles available for catalysis and showed that the hydrophobic SAM coatings gave significantly higher activity.

Influence of the electrochemical processing parameters on the photocurrent–voltage conversion characteristics of copper bismuth selenide photoactive films

Thin-film deposition using electrodeposition techniques is highly preferable because of its capability to deposit multi-component alloys at low temperatures. In this regard, copper bismuth selenide (CBSe) films were electrodeposited in two various ways, simultaneous and successive electrodeposition processes. The structural and morphological characterizations of the obtained films were performed using X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray analysis (EDX), and X-ray Photoelectron Spectrometer (XPS). The CBSe alloy films formed by successive electrodeposition revealed better crystallinity and more regular morphology in comparison with simultaneous electrodeposited CBSe films. The prepared CBSe film by successive electrodeposition exhibited high light absorptivity and low band gap energy value (Eg = 1.65 eV) resulting in a higher photoelectrical response. The crystallization of the ternary CBSe film electrodeposited via successive routine obeyed the instantaneous nucleation mechanism, while the CBSe film obtained by simultaneous electrodeposition agreed with the progressive nucleation mechanism. Successive electrodeposition of ternary CBSe alloy film achieved greater values of photocurrent–voltage conversion efficiency (η = 1.26%) in photoelectrochemical systems.Graphic abstract

Insight into the Nucleation Mechanism of p-Methoxybenzoic Acid in Ethanol-Water System from Metastable Zone Width.

The metastable zone width (MSZW) of p-methoxybenzoic acid (PMBA) in an ethanol-water system was measured using the polythermal method. The nucleation order m obtained by the Nývlt’s model indicates the nucleation of PMBA following a progressive nucleation mechanism at low saturation temperature (m = 3.18–7.50) and an instantaneous nucleation mechanism at high saturation temperature (m = 1.46–2.55). Then, combined with the metastable zone experiment and the Sangwal model, we found that the MSZW and the interfacial energy reached the maximum when the mass fraction of ethanol was 0.8, which resulted in the smallest crystal product size. Meanwhile, the maximum and obtained based on the modified Sangwal model indicating the PMBA needs to overcome a higher nucleation barrier in the ethanol mass fraction of 0.8. Finally, we proposed a preferential strategy for adjusting MSZW by correlating the interfacial energy with the change in ethanol mass fraction, saturation temperature, and cooling rate, respectively.

Effect of Thiourea Containing Composite Additives on Nickel Electrodeposition in Ammoniacal Solution

Composite additives have an important influence on the process of metal electrodeposition and the quality of a metal deposited layer. In this work, the additive thiourea (TU) was compounded with cetyltrimethyl ammonium chloride (CTAC), sodium dodecyl sulfate (SDS) and polyethylene glycol 20,000 (PEG20000), and their effect on the cyclic voltammetric behavior, electrochemical nucleation mechanism, crystallographic orientations and surface morphology of the nickel electrodeposition in ammoniacal solution were experimentally investigated. The results show that the introduction of composite additives resulted in a stronger cathodic polarization and increased the nucleation overpotential (NOP) values significantly, which had an important impact on forming compact and smooth nickel deposits. The chronoamperometry analysis indicated that the reduction in nickel followed the 3D progressive nucleation mechanism in the presence of composite additives at the step potential of −1.16 V and −1.18 V. Smoother and finer nickel films were found using scanning electron microscopy (SEM) images as the composite additives were used. X-ray diffraction revealed that all nickel deposit samples had the face-centered cubic structure, and five main crystal planes were displayed by the presence of composite additives in the electrolyte. Furthermore, the diffraction peaks of (111) and (200) crystal planes were slightly shifted toward lower 2θ values when thiourea was used in combination with additive CTAC or PEG20000. These results were beneficial for understanding the mechanisms and facilitating the rational design of additives for metal nickel electrodeposition.

Influence of a polymeric additive on the crystallisability and nucleation mechanism for the model fuel system of eicosane crystallising from supersaturated toluene solutions

The impact of a commercially available cold flow improver additive (IA) on crystallisation within a model fuel system of eicosane in toluene solutions is investigated. Polythermal crystallisation method utilising turbidometric detection is used to assess the influence of IA addition upon eicosane solubility and nucleation inhibition at different solution IA treat rates, ranging from 0.1 to 10 wt%. Whilst IA is found to have negligible effect upon eicosane solubility, its nucleation is found to be disrupted, resulting in a reduction in crystallisation temperatures as a function of higher IA treat rate, with IA and eicosane phase separation also taking place at treat rates of 2 wt% IA and above. A change from an instantaneous to a progressive nucleation mechanism of eicosane in the absence and presence of IA within solution, respectively, is found. This behaviour is rationalised through the proposition that IA is incorporated within developing eicosane prenucleation clusters, hence disrupting their ability to readily grow to a critical size for nucleation. Nucleation kinetic analysis confirms that at given solution undercoolings, higher IA treat rate reduces the rate of nucleation due to an increase in the effective interfacial tension to nucleation, in line with a higher degree of thermodynamic control of the nucleation process, as might be expected for the progressive nucleation behaviour.

The Effect of Naphthalene‐Based Additives on the Kinetics of Tin Electrodeposition on Boron‐Doped Diamond Electrodes

AbstractThe effect of naphthalene‐based additives: naphthalene (NPT), naphthalenesulfonate (NPTS) and hydroxynaphthalenesulfonate (HNPTS) on the kinetics of tin electrodeposition on a boron‐doped diamond (BDD) electrode has been studied by means of chronoamperometry and scanning electron microscopy (SEM). Potentiostatic current transients in the absence and the presence of naphthalene‐based additives are analyzed by using the Scharifker‐Hills model. A strong decrease of the kinetics of tin nucleation on BDD was observed in the presence of naphthalene‐based additives, NPT showing the smallest effect and HNPTS showing the largest effect. From the long‐term Cottrell behavior of the transients, similar values of tin(II) diffusion coefficients were obtained for all additives, suggesting that there is no complexation of Sn(II) by the additives and that the charge‐transfer kinetics itself is not substantially influenced by the presence of the additives. In the absence of additives, tin deposition on BDD displays a progressive nucleation and growth mechanism at the least negative potentials, switching to instantaneous nucleation and growth at more negative potential. In the presence of NPTS and HNPTS, progressive nucleation and growth transients are observed. The growth mode results are confirmed by the tin features observed in the scanning electron micrographs. In conclusion, NPT, NPTS and HNPTS mainly decrease the rate of the nucleation of tin deposition, most likely by blocking or reducing access to active nucleation sites. In comparison, ethoxylated α‐napthalenesulfonic acid (ENSA, a commonly used additive in the tin plating industry) inhibits tin deposition process on BDD even more strongly. These observations show a striking similarity to our previous study of tin deposition on gold electrodes.

Palladium electrochemistry in the choline chloride-urea deep eutectic solvent at gold and glassy carbon electrodes

The electrochemical behaviour of Pd(II) in choline chloride-urea eutectic (ChCl-U) has been investigated at polycrystalline gold and glassy carbon electrodes at 60 °C using voltammetry (cyclic and hydrodynamic) and chronoamperometry. The voltammograms recorded at Au in the palladium solution show three reduction signals, assigned to Pd bulk deposition (around −0.2 V vs. Ag QRE), the formation of palladium hydrides PdHx (around −0.4 V vs. Ag QRE) and an underpotential deposition (upd) of Pd (around 0 V vs. Ag QRE). Two anodic peaks present in the cyclic voltammograms correspond to the oxidation of Pd hydrides and Pd deposits. In contrast to the results obtained at Au, no upd response is observed at a GC electrode and a crossover between the forward and backward scan, characteristic of a kinetic control by nucleation and growth, is clearly evidenced. Typical peaked transients are observed whose analysis unambiguously demonstrates that the deposition occurs through a 3D progressive nucleation mechanism.

Growth mechanism during the early stages of electrodeposition of bismuth telluride Bi2Te3 on ITO substrate

The electrochemical deposition mechanism of Bismuth telluride (Bi2Te3) by co-reduction of the telluryl (HTeO2+) and bismuth ions from the nitric acid medium on tin doped indium oxide (ITO) substrate was investigated using two electrochemical techniques: cyclic voltammetry (at different scan rates) and chronoamperometry (at different applied potentials). The thin films electrodeposited by chronoamperometry were characterized by X-Ray diffraction (XRD) and UV–Visible spectroscopy, the exploitation of UV–visible curves allowed us to calculate the gap energy. Surface morphology was examined using a scanning electron microscope (SEM) and atomic force microscope (AFM). These techniques have shown that the electrodeposition of Bi2Te3 has been performed at a negative potential around −0.18 V vs SCE, with a quasi-reversible reaction controlled by the diffusion process. Moreover, the measured current transient curves were compared to those calculated from Scharifker-Hills models. It was found that a progressive 3D nucleation mechanism governs the nucleation and growth of Bi2Te3 on ITO substrate.

Catalytic effects of NH4+ on hydrogen evolution and manganese electrodeposition on stainless steel

Abstract The effects of (NH4)2SO4 concentration (c((NH4)2SO4)) on hydrogen evolution and Mn electrodeposition on stainless steel (SS) in different potential ranges were investigated by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), potentiostatic polarization, chronoamperometry, scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. The results show that the NH4+ discharge reaction (NDR) intensifies the overall hydrogen evolution kinetics, and the NDR is catalyzed by increasing c((NH4)2SO4) and over-potential. The electro-crystallization of Mn on SS follows a three-dimensional progressive nucleation and diffusion-limited growth mechanism. Increasing the over-potential could accelerate the nucleation rate and also cause the decline of the nucleation density. The absorbed Mn2+ preferably discharges at low over-potential. Increasing c((NH4)2SO4) at medium over-potential could improve the current efficiency and produce more block-like grains. The nucleation process is suppressed by increasing c((NH4)2SO4) at high over-potential, at which the formation of columnar grains with higher hydrogen contents becomes prevailing.

Electrodeposition of 1-D tellurium nanostructure on gold surface from choline chloride-urea and choline chloride-ethylene glycol mixtures

The electrodeposition of Te on Au substrate was investigated in either choline chloride-urea and in choline chloride-ethylene glycol deep eutectic solvents, at a molar ration of 1:2, containing 0.05 mol L−1 TeCl4. The electrodeposition of Te on Au electrode followed a three-dimensional progressive nucleation mechanism in both eutectic solvents. The diffusion coefficients of Te4+ species as a function of temperature were well fitted by a like-Arrhenius equation in both plating solutions. The apparent activation energies were 22.20 and 22.55 kJ mol−1 for Scharifker-Hills and Cottrell's models, respectively, in 1ChCl:2EG. On the other hand, in 1ChCl:2 U these values were 59.20 and 57.80 kJ mol−1. In addition, SEM micrographs of Te electrodeposits from both revealed a large-scale Te rods-like morphology with hexagonal cross-section in nanoscale regime uniformly distributed on electrode surface. TEM investigation suggested that Te single-crystalline grew perpendicular direction of (100) planes which implied in the preferential growth direction of [001].

A Cu2+-Cu/glassy carbon system for glyphosate determination

Cu° electrocrystallization onto glassy carbon (GC) at potentials between −0.4 V and −0.7 V is consistent with a 3D progressive nucleation mechanism and diffusion-controlled growth. Cu/GC electrode prepared at −0.6 V is applied to the detection of a widely used herbicide such as glyphosate (Glyp). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods are applied in the Glyp determination in acetic acid buffer aqueous solution (ABS) at pH 5 or pH 6. Optimal herbicide detection properties are found for this electrode, arising from Cu°/Cu+ and Cu+/Cu2+ couples. An interesting phenomenon is detected by the DPV method, with Cu/GC electrode in presence of (0.03–0.2 mM) Cu2+ into the ABS at pH 6, when glyphosate is added. For an oxidation potential of −0,015 V vs. Ag/AgCl for Cu°/Cu+ couple (DPV), the current peak is sensitively affected by glyphosate concentration. A strong adsorptive effect between 6 and 30 μM of analyte leads to a linear decrease in the current peak at pH 6. This phenomenon is related to the formation of a barrier of adsorbed glyphosate molecules, which prevent Cu2+ ions diffusion towards the electrode’s surface. CVs and DPVs for Cu/GC electrode system in the presence of Glyp and Cu2+ ions are consistent with the transfer of one electron from Cu2+ to Cu+ and from Cu+ to Cu0, which is limited by diffusion of Cu2+ ions. A quantification limit (LOQ) for Glyp of (0.62 ± 0.02) μM [(105 ± 3) μg L–1], and a low determination limit (LOD) of (0.186 ± 0.004) μM (31 (μg L–1) (31g/L)) are obtained from Cu/GC system into ABS pH 6 and 0.1 mM Cu2+ ions. Glyp Determinations for Cu2+-Cu/GC in the presence of interfering cations and in drinking water demonstrated similar sensitivity and stability as in pure systems.

Electrochemical behaviour of passive film formed on the surface of Ti-6Al-4V alloys fabricated by electron beam melting

The microstructure, composition, semiconductive properties and electrochemical performance of passive film formed on the surface of Ti-6Al-4 V alloy produced by electron beam melting (Abbreviated as ET) were compared with conventional wrought counterpart (WT) in phosphate buffered saline at 37 °C. The results demonstrated a thinner and more compact passive film formed on ET, which was attributed to the small grain size and high density of grain boundaries in ET, these active sites increased the growth rate at the initial stage in the manner of 3D progressive nucleation mechanism of passive film, leading to superior corrosion resistance than WT.

Solubility and Nucleation of Methyl Stearate as a Function of Crystallization Environment

Crystallization studies of methyl stearate from supersaturated dodecane, kerosene, and toluene solutions reveal strong evidence that solvent choice influences solubility and nucleation behavior. Solute solubility is less than ideal with toluene, kerosene, and dodecane, respectively, exhibiting the closest behavior to ideality, the latter consistent with the highest solvation. Polythermal crystallization studies using the Kashchiev–Borissova–Hammond–Roberts (KBHR) model [Kashchiev et al. J. Phys. Chem. B 2010, 114, 5441; Kashchiev et al. J. Cryst. Growth 2010, 312, 698; Camacho et al. CrystEngComm 2014, 16, 974] reveal a progressive nucleation (PN) mechanism with crystallite interfacial tension (γeff) values between 0.94 and 1.55 mJ/m2, between 1.21 and 1.91 mJ/m2, and between 1.18 and 1.88 mJ/m2 for dodecane, kerosene, and toluene, respectively. Nucleation rates at the critical undercooling lie between 4.56 × 1016 and 1.79 × 1017 nuclei/mL·s, with the highest rates associated with crystallization from ker...

Zinc Electrodeposition from deep eutectic solvent containing organic additives

The effect of the addition of a group of organic additives on the electrodeposition behavior of zinc was investigated in choline chloride:ethylene glycol (ChCl:EG) eutectic mixture in the molar ratio of 1:2. Cyclic voltammograms recorded on steel electrode showed a cathodic peak is only observed after reversing of the scan. Chronoamperometric measurements indicated that the deposition of zinc occurs through 3D progressive nucleation mechanism. The morphology of the zinc deposits and was evident that additives influence the deposits morphologies. X-ray diffraction confirmed the presence of crystalline zinc and reveal the grain refinement effect obtained by using the additives selected where the smallest grain size of 31.7nm was obtained in the presence of Dimethyl sulfoxide (DMSO). Moreover the XRD data showed that the addition of additives modified the preferential growth plane. The corrosion resistance properties of the electrodeposited Zn coatings were evaluated in 3% NaCl aqueous solution using potentiodynamic polarization. The results showed that the zinc film deposited with DMSO was the best corrosion resistant coating.

CoNiMn magnetic films prepared by magnetic field induced codeposition technology

ABSTRACTMagnetic fields vertical to electric fields were applied during electrodeposition process to prepare CoNiMn magnetic thin films. Influences of different magnetic intensities on electrochemistry mechanism, nucleation, surface morphology and magnetic property of CoNiMn films were studied. Magnetohydrodynamics phenomenon caused by Lorentz forces during magnetic electrodeposition process tends to agitate the diffusion layer near cathode. It was found out that, CoNiMn films fabricated by magnetic electrodeposition process belonged to a kind of typical progressive nucleation mechanism. Anomalous codeposition phenomenon of CoNi was affected by magnetic fields. Higher magnetic intensity tended to obtain smooth surface of CoNiMn films with smaller and denser particles. Coercivity and remanence of CoNiMn alloy films increased sharply when magnetic field was induced. Magnetic property of vertical direction was better than parallel direction, which indicated that CoNiMn magnetic film possessed good vertical anisotropy.

Electrochemical Characterization of the Electrocrystalization of Bismuth on a Graphite Electrode

Bismuth electrocrystalization on a graphite electrode (GE) was studied by cyclic voltammetry and cronoamperometric techniques. Cyclic voltammetry shows that the electrocrystalization of is controlled by diffusion. Nucleation mechanisms depend on the imposed potential and time. Current transients were analyzed with the Sharifker-Hills model, the nucleation mechanism and growth of Bi on the GE is not a simple process, since at potentials between -210 and -240 mV, Bi electrocrystalization takes place in two different stages: at the first stage a 2D instantaneous mechanism can be recognized, followed in the second stage by a 3D progressive mechanism. For potentials lower than -260 mV only a 3D progressive nucleation mechanism can be recognize. These results imply that different characteristics for the Bi film can be obtained depending on the applied electrocrystalization potential, which can be considered for different applications.

A 3D Continuum-Kinetic Monte Carlo Simulation Study of Early Stages of Nucleation and Growth in Ni Electrodeposition

A 3D continuum code coupled with a kinetic Monte Carlo module has been developed for the simulation of Ni electrocrystallization in the initial stages of nucleation and growth. Mass transfer in solution was controlled by a finite-difference code which is distributed over an irregular nanoscale grid system in vertical direction to the substrate. Deposition events such as surface diffusion, chemisorption and crystallization in the system were considered in a KMC module that processes the output of a diffusion-controlled scheme in probability functions to model electrodeposition process on surface. Electrochemical data of this simulation was simultaneously generated according to analytical electrochemical equations to study nucleation and growth mechanism. In spite of minor dissimilarities at current transient coordinates, a reasonable agreement could be noticed between electroanalytical simulation data and experimental results, both of which showed that under presumed conditions nickel electrodeposition is prone to a progressive nucleation mechanism at initial seconds. A similar result has been achieved from the juxtaposition of experimental morphological studies and simulated snapshots. It was found that a balance between surface diffusion and charge transfer reaction rate is a critical factor in dominant nucleation mechanism and deviation from the equilibrium could remarkably alter the nucleation regime and also nanostructure of the deposit.