Influence of Ge4+ and Pb2+ ions on the kinetics of zinc electrodeposition in acidic sulphate electrolyte

The effect of Ge⁴⁺ ions, a deleterious impurity for zinc deposition in acidic sulfate electrolytes, and that of Pb²⁺ ions, which inhibit hydrogen evolution, have been investigated by means of steady-state polarization curves and impedance analysis. Typical impedance plots have been shown to characterize the processes of zinc deposition, hydrogen evolution on zinc, and hydrogen evolution on adsorbed germanium. From changes in the double layer capacitance, the charge transfer resistance and the low-frequency relaxation processes, it is concluded that lead adsorbed on zinc generates a lessened activation of hydrogen evolution with increasing cathodic potential, and enhances the formation of H_ad on the zinc deposit. With the addition of Pb²⁺ ions to the Ge⁴⁺-containing electrolyte, the features characteristic of zinc deposition are observed to prevail in the electrode impedance.     

Response surface modeling and optimization to study the influence of deposition parameters on the electrodeposition of Cu–Zn alloys in citrate medium

Copper–zinc alloy coatings were deposited on mild steel substrates using sodium citrate electrolytes at room temperature and under direct current. For the bath composition studied, factorial design was used to verify the influence of deposition parameters, such as current density and mechanical stirring, on the cathodic efficiency, the contents of copper and zinc, and the amount of hydrogen evolution. Moreover, the four responses were simultaneously studied by using an optimization methodology. The results suggest that the optimum point for reaching good quality copper–zinc alloy deposits from the proposed citrate electrolytes are 29 A m⁻² and 247 rpm for bath 3 and 13 A m⁻² and 67 rpm for bath 4. Applying these conditions, a yellow-reddish coating was obtained from bath 3, while a bright red deposit was produced from bath 4.     

Effect of brighteners on hydrogen evolution during zinc electroplating from zincate electrolytes

Hydrogen evolution during zinc electrodeposition on a steel substrate from zincate electrolytes containing different additives was studied using various experimental techniques.The hydrogen evolution reaction is limited by the electron transfer step. Hydrogen evolution is most intensive during the first seconds from the beginning of electrodeposition due to the lower overpotential of hydrogen on steel as compared with that on zinc. The evolved hydrogen is dissipated in three ways. Most is dissipated to the atmosphere via gas bubbles at a constant rate. Some is dispersed in the electrolyte some diffuses into the steel substrate, predominantly at the commencement of deposition. The additives affect both the total amount of evolved hydrogen and its distribution. The highest amount of hydrogen is evolved in the presence of the anisaldehyde bisulphite containing composite additive. The highest amount of hydrogen included in the substrate and remaining in the electrolyte corresponds to the use of the Na–N-benzylnicotinate containing additive. In this case blistering is observed.     

Optimization of the hydrogen evolution activity on zinc-nickel deposits using experimental strategies

The experimental strategies including the fractional factorial design (FFD), path of the steepest ascent study, and the central composite design (CCD) coupled with the response surface methodology (RSM) was adopted to optimize the hydrogen evolution activity of Zn-Ni deposits. The key deposition variables, pH, the Zn/Ni ionic ratio and the TEPA concentration in the plating solutions, influencing the hydrogen evolution activity of Zn-Ni cathodes were found in the FFD investigation. These variables were subjected to the steepest ascent study to approach the vicinity of the optimal deposition conditions for plating the Zn-Ni deposits with the highest hydrogen evolution activity. In the CCD investigation, the optimal deposition settings, where the temperature of 50 °C, the current density of 2500 A m⁻², pH of 13.0, the Zn/Ni ionic ratio of 0.89 and the TEPA concentration of 0.58 M, were obtained by means of a regression model. This highest activity of the Zn-Ni deposits mainly consisting of the γ phase structure for hydrogen evolution is due to a combination of their good electrocatalytic activity and relatively high surface area. The electrocatalytic activity of these cathodes mainly composed of the γ phase Zn-Ni alloy was damaged by the selective dissolution of Zn from the deposits in 5 M KOH.     

Electrodeposition of Zn and In onto vitreous carbon

The deposition of indium and zinc on vitreous carbon was studied by voltammetric, galvanostatic and single potentiostatic pulse techniques. The morphology and composition of deposits were analysed by SEM/EDX. The codeposition process occurs without the formation of alloys or intermetallic compounds. On the one hand under stagnant conditions or at low electrode rotation speeds, localized alkalization produced by the hydrogen evolution reaction (HER) favours deposition through an indium hydroxide layer, and deposits with the same atomic percentage of In and Zn are attained. On the other hand, under electrode rotation, preferred deposition of Zn takes place. In this case, the reduction of H⁺ by the In⁺ species, intermediate in the In³⁺ reduction process, diminishes the electrochemical HER on the substrate thus favouring Zn deposition. The higher nucleation rate on metallic deposits previously formed on the vitreous carbon surface is also likely.     

氨基磺酸盐-硫酸盐混合溶液中锌-锰合金的电沉积

本文研究了氨基磺酸盐-硫酸盐混合溶液中锌-锰合金的电沉积机理。实验结果显示，在低电流密度区获得哑光镀层，锰离子的催化析氢作用降低了合金沉积效率．玻璃化炭黑上的伏安试验显示锌沉积过程中的第一个电子转移较慢，阳极溶出伏安试验显示锌合金的异常共沉积导致富锌中间相的产生。     

Nucleation and growth of zinc on aluminum from acidic sulfate solution with [BMIM]HSO<Subscript>4</Subscript> 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.     

Evaluation of substrates for zinc negative electrode in acid PbO_2–Zn single flow batteries

An investigation was performed on the suitability of carbon materials, metallic lead and its alloys as substrates for zinc negative electrode in acid Pb O2–Zn single flow batteries. The zinc deposition process was carried out in the medium of 1 mol·L-1H2SO4 at room temperature. No maximum current appears on the potentiostatic current transients for the zinc deposition on lead and its alloys. With increasing overpotential, the progressive nucleation turns to be a 3D-instantaneous nucleation process for the resin-graphite composite. Hydrogen evolution on the graphite composite is effectively suppressed with the doping of a polymer resin. The hydrogen evolution reaction on the lead is relatively weak, while on the lead alloys, it becomes serious to a certain degree. Although the exchange current density of zinc deposition and dissolution process on the graphite composite is relatively low,the zinc corrosion is weakened to a great extent. With the increase of deposition time, zinc deposits are more compact. The cyclings of zinc galvanostatic charge–discharge on the graphite composite provide more than90% of coulombic and 80% of energy efficiencies, and exhibit superior cycling stability during the first 10 cycles.     

Activation of porous Ni cathodes towards hydrogen evolution by electrodeposition of Ir nuclei

Porous Ni electrodes were modified by electrodeposition of Ir nuclei from H₂IrCl₆ solutions at 70 °C, with the aim of activating them towards the hydrogen evolution reaction and comparing their performance with those of porous Ni electrodes activated by spontaneous deposition of noble metals (Ir and Ru). The current efficiency of Ir deposition was found to be very low (1% or lower, decreasing upon increasing deposition current density). Ir deposits characterised by SEM-EDX and XRD consisted of nanocrystals decorating the Ni dendrites forming the porous layers. Ir electrodeposition led to a strong activation of the hydrogen evolution reaction from aqueous 1 M NaOH. The electrocatalytic activity of the cathodes was independent of the Ir deposition charge above the minimum explored value of 1  C cm^?2. This charge is estimated to correspond to the deposition of ca. 2.5 10^?8 Ir moles cm^?2. The kinetic parameters for hydrogen evolution were similar for porous Ni electrodes modified by either spontaneous deposition (studied in a previous work) or electrodeposition of Ir.     

Influence of a perfluorinated surfactant on the mechanism of zinc deposition in acidic electrolytes

The influence of the non-ionic surfactant Forafac F1110 on the kinetics of zinc deposition in sulfate or chloride solutions is investigated by voltammetry and impedance spectroscopy. From a discussion of the results in terms of a reaction model, it is shown that the additive produces a significant inhibition of the corrosion process. In addition and in a specific way for each electrolyte, the additive (i) inhibits the different steps of charge transfer leading to the zinc deposit and (ii) modifies the kinetic parameters of the slow reactions involved in the formation and destruction of the active sites for zinc deposition.     

Influence de l'antimoine et du cuivre sur la cementation du cobalt par le zinc

Zinc sulphate solution (160g/l Zn²⁺) used for zinc electrowinning is purified for cobalt by cementation with metallic zinc powder. Industrial practice shows that considerable acceleration of this operation is achieved by the presence of trace impurities in solution. Eventually, CuSO₄ and Sb₂O₃ are deliberately added to the solution. The aim of this work is to elucidate the mechanism of action of those impurities.Zn²⁺ ions present in the solution are responsible for the slow speed of cobalt deposition (160g/l Zn²⁺; 10 mg/l Co²⁺).The cathodic part of the cementation reaction was simulated on a flat electrode through potentiostatic deposits at ?730 mV/ENH (potential at zero current of metallic zinc in the solution). The deposits were studied by anodic dissolution, radioactive tracers, X-ray diffraction and fluorescence, atomic absorption spectrophotometry, optical and electronic microscopy (transmission and scanning). The results were compared with cementation on zinc plate and zinc powder.Antimony and copper are deposited together with cobalt and form alloys with reduced cobalt activity. Total voltage available to overcome the inhibitor effect of zinc ions is thus increased and the reduction of cobalt ions accelerated. Antimony, copper and cobalt triple alloys resist particularly well to corrosion with hydrogen evolution. Copper has a higher accelerating effect on cobalt cementation than antimony, but the latter stabilizes the deposit very effectively.The electrochemical methods used and the knowledge of the mechanism of action of the impurities open new trends for industrial practice.     

The effects of nickel and cobalt and their interaction with antimony on zinc electrowinning from industrial acid sulphate electrolyte

The effects of nickel and cobalt and their interaction with antimony on the electrowinning of zinc from industrial acid sulphate electrolyte were studied using X-ray diffraction, scanning electron microscopy and cyclic voltammetry. Concentrations of cobalt as high as 20 mgl^–1 had no effect on the zinc deposition current efficiency. The current efficiency decreased rapidly when the electrolyte contained >5 mgl^–1 nickel. Neither cobalt or nickel had an effect on the morphology of the 1-h zinc deposits. Nickel and cobalt caused characteristic changes in the cyclic voltammograms for zinc deposition. As a result this technique might provide a rapid means for evaluating the electrolyte prior to zinc electrowinning. The combined presence of cobalt and antimony in the zinc electrolyte was more deleterious to zinc electrowinning than was the combined presence of nickel and antimony. The presence of 0.08 mgl^–1 antimony in the electrolyte counteracted the effect of nickel both on the current efficiency for 1-h deposits and on the zinc deposition polarization curves.     

Synergistic effect of additives on bright nanocrystalline zinc electrodeposition

The influence of additives like cetyltrimethylammonium bromide (CTAB) and Ethyl vanillin (EV) on zinc electrodeposition from acid sulfate bath was systematically investigated by scanning electron microscopy, X-ray diffraction, and voltammetric techniques. The result shows the existence of interaction between CTAB and EV. They exhibited synergistic effect to produce bright nanocrystalline zinc coating on steel surface. The combined effects of these two compounds on deposition overpotential, hydrogen evolution, zinc ion diffusion, and surface coverage were discussed. The morphological and orientational changes occurred in electrodeposit were presented. Also the nucleation mechanism exhibited by zinc during electrodeposition in the presence of additive was examined.     

Impedance spectroscopy and modelling of zinc deposition in chloride electrolyte containing a commercial additive

The kinetics of zinc deposition from a concentrated chloride electrolyte containing a commercial additive are investigated by impedance spectroscopy. A reaction model formerly validated for zinc deposition in acidic sulphate medium has been adapted to the present electrolyte and closely related to the elementary steps involved in the crystal growth process. Simulation of the electrode kinetics shows that the additive modifies the deposit morphology by changing some specific rates of the surface steps: slowing down the charge transfer reactions, poisoning the active kink sites and increasing the deposition overpotential. Thus zinc deposition takes place on a surface where the intermediate adions Zn⁺ _ad and the active kink sites are more numerous and where the nucleation rate is increased, leading to refined grain size.     

The effect of germanium on zinc electrowinning from industrial acid sulphate electrolyte

The effect ofgermanium on the electrowinning of zinc from industrial acid sulphate electrolyte was studied using X-ray diffraction, scanning electron microscopy and cyclic voltammetry techniques. Germanium concentrations > 0.1 mgl^–1 results in severe re-solution of the zinc deposit and hence decreased the zinc deposition current efficiency. Extreme fluctuations in the current efficiency occurred as a function of electrolysis time. Cyclic voltammograms obtained for Ge-containing electrolytes were characterized by a shoulder in the reverse scan prior to the cross-over potential. Vigorous hydrogen gassing occurred at the shoulder. These results are interpreted in terms of the formation of local Zn-Ge galvanic cells. Germanium concentrations to 0.2 mgl^–1 had no effect on the morphology of the 1-h zinc deposits but the preferred orientation changed from [1 1 4] [1 1 2] for Ge-free electrolyte to [1 1 2] [1 1 0] for electrolytes containing Ge.     

Storage characteristics of mercury-free alkaline manganese batteries

The amount and distribution of additive species in zinc alloy particles containing 0.025wt% bismuth modified with 0.10wt% indium for mercury-free alkaline manganese batteries were examined after storage at various discharging levels at 60°C. The amount of hydrogen gas evolution due to the self-discharging reactions of zinc and the internal cell impedance were also evaluated. The amount of additive species in the zinc alloy particles was found to increase with increasing depth of discharge. Indium was homogeneously distributed on the surface even after partial discharge and also after storage for 1200h at 60°C. This behaviour is considered to contribute to the suppression of hydrogen gas evolution and increase in the internal cell impedance to the same level as when mercury is employed. As a result, mercury-free alkaline manganese batteries showed the same storage characteristics as conventional batteries containing mercury.     

Electrochemical study on the inhibitory effect of the underpotential deposition of zinc on Zn-Co alloy electrodeposition

Zn-Co alloy electrodeposition from chloride baths containing different Zn²⁺/Co²⁺ ratios was investigated by cyclic voltammetry and anodic linear sweep voltammetry using a Pt electrode. The peaks were attributed by means of EDX analysis, SEM and TEM observations performed on some alloys potentiostatically deposited. In the range of potential where zinc deposits underpotential, cyclic voltammetry showed a complex cathodic peak with one maximum and two shoulders, correlated with the deposition of different cobalt rich alloys. Up to four anodic peaks, two correlated with zinc oxidation from η and γ phases and two correlated with oxidation of solid solutions of zinc in cobalt, were observed. ALSV and TEM indicated that the remarkable increase in Zn content of the alloy, which occurs with a strong inhibition of the process at potentials more negative than that of the cathodic peak and more positive than the bulk deposition potential of zinc, is due to the deposition of γ phase. No inhibition of the alloy deposition process was observed with very low concentrations of zinc (<0.015 M) in the bath containing 0.19 M Co²⁺.     

Zinc electrodeposition in the presence of polyethylene glycol 20000

The influence of polyethylene glycol 20000 (PEG₂₀₀₀₀) on the mechanism of zinc deposition and nucleation was studied by voltammetry, chronoamperometry, and atomic force microscopy (AFM). The electrodeposition of zinc in an electrolytic bath containing PEG₂₀₀₀₀ occurs via two reduction processes with different energies that involve the same species, ZnCl₄²⁻: the first reduction process occurs at E_PI′c = −1.25 V, SCE, whereas the second process, which corresponds to the bulk deposition of Zn, occurs at E_PII′c = −1.6 V, SCE without significant interference from the hydrogen evolution reaction. Analysis of chronoamperograms obtained in the absence and presence of PEG₂₀₀₀₀ indicates that distinct nucleation mechanisms are involved during the initial stages of Zn deposition. In the absence of PEG₂₀₀₀₀, the transients are consistent with the model of 3D diffusion-controlled nucleation. In the presence of PEG₂₀₀₀₀, however, the transients exhibit a more complex form involving two simultaneous nucleation and growth processes: 2D instantaneous nucleation limited by the incorporation of adatoms (2D_i-li) and a diffusion-controlled 3D nucleation mechanism (3D_-dc). Characterization of the surface morphologies of the zinc deposits by AFM imaging confirmed our conclusions drawn from the electrochemical studies. SEM analysis showed that the zinc coatings obtained in the presence of PEG₂₀₀₀₀ at −1.6 V, SCE are smoother and more compact.     

Role of polyethylene glycol in electrodeposition of zinc–chromium alloys

The role of polyethylene glycol (PEG) as an additive in the electrodeposition of zinc–chromium alloys was investigated in sulfate baths containing trivalent chromium. PEG with high molecular weight enabled the codeposition of metallic chromium with zinc, while chromium(III) was present in the deposits obtained from the baths containing PEG with lower molecular weight as well as the PEG-free bath. The polarization curves for the alloy deposition revealed that PEG with high molecular weight polarized the deposition potential of zinc to the reduction potential of chromium to permit the codeposition of chromium with zinc.     

Zinc deposition and dissolution in methanesulfonic acid onto a carbon composite electrode as the negative electrode reactions in a hybrid redox flow battery

Electrodeposition and dissolution of zinc in methanesulfonic acid were studied as the negative electrode reactions in a hybrid redox flow battery. Cyclic voltammetry at a rotating disk electrode was used to characterize the electrochemistry and the effect of process conditions on the deposition and dissolution rate of zinc in aqueous methanesulfonic acid. At a sufficiently high current density, the deposition process became a mass transport controlled reaction. The diffusion coefficient of Zn²⁺ ions was 7.5 × 10⁻⁶ cm² s⁻¹. The performance of the zinc negative electrode in a parallel plate flow cell was also studied as a function of Zn²⁺ ion concentration, methanesulfonic acid concentration, current density, electrolyte flow rate, operating temperature and the addition of electrolytic additives, including potassium sodium tartarate, tetrabutylammonium hydroxide, and indium oxide. The current-, voltage- and energy efficiencies of the zinc-half cell reaction and the morphologies of the zinc deposits are also discussed. The energy efficiency improved from 62% in the absence of additives to 73% upon the addition of 2 × 10⁻³ mol dm⁻³ of indium oxide as a hydrogen suppressant. In aqueous methanesulfonic acid with or without additives, there was no significant dendrite formation after zinc electrodeposition for 4 h at 50 mA cm⁻².