Alkaline Zincate Solutions Research Articles

Effect of minor nickel alloying with zinc on the electrochemical and corrosion behavior of zinc in alkaline solution

The electrochemical and corrosion behavior of pure zinc and Zn–0.5Ni alloy in strong alkaline solution (7 M KOH) was investigated by Tafel plot, potentiodynamic, potentiostatic and electrochemical impedance spectroscopy (EIS) methods, and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Measurements were conducted under different experimental conditions. The results of both Tafel plot extrapolation and the electrochemical impedance spectroscopy (EIS) measurements exhibited the same trend, which the cathodic and anodic processes on the alloy surface are less significant compared with those on the pure zinc. The results revealed that, the shift in steady state of open-circuit potential ( E corr) to more negative potential in the case of the studied alloy compared with that of pure zinc has a positive effect on both charge efficiency and self-discharge. The anodic potentiodynamic measurements demonstrated that the polarization curves exhibited active/passive transition. The active dissolution of both pure zinc and its alloy increases with increasing temperature and scan rate. The activation energy ( E a) value of active region and peak current ( I AI) of the two studied electrodes in the investigated alkaline solution is calculated and compared. In the case of alloy, the results obtained at certain positive potential (+425 mV vs. SCE), exhibited high current density indicating that the most passive layer was destroyed. This indicates that the addition of small amount from Ni to Zn promotes the electrochemical reaction (in the passive region), acting as so-called self catalysis. Accordingly, one can conclude that, the electrochemical behavior of the investigated alloy in strong alkaline solution contributes to suppression of hydrogen gas evolution and increases the corrosion resistance. In addition, reactivation of the alloy surface takes place in the passive region.

The anodic dissolution of zinc and zinc alloys in alkaline solution. I. Oxide formation on electrogalvanized steel

The polarization behaviour of zinc in alkaline solution has been investigated using atomic emission spectroelectrochemistry. By independently measuring the oxidation rate of zinc (electrical current) and the rate of Zn 2+ dissolution (partial elemental current) it is possible to calculate the amount of insoluble zinc cations produced at any instant. Assuming the insoluble cations are present as a zinc oxide film, the growth of this film as a function of potential and time was determined. On the basis of kinetic evidence, it was found that at least three forms of zinc based oxide/hydroxide films form during polarization experiments. Type I oxide formation occurs when the metal/electrolyte interface becomes locally saturated with Zn 2+ ions. Type II oxide forms on the metal surface underneath the film of Type I oxide but has little inhibiting effect on zinc dissolution. Type III oxide is produced in much smaller quantity and results in a transition to the passive state. This may be due to a potential induced transition of Type II → Type III oxide.

Morphology Control of Electrodeposited Zinc from Alkaline Zincate Solutions for Rechargeable Zinc Air Batteries

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Effect of alkaline electrolysis conditions on current efficiency and morphology of zinc powder

The deposition of electrolytic zinc from alkaline zincate solution was investigated and the effects of process parameters on current efficiency, morphology and specific surface area of zinc powders were analysed, based on excess potential and hydrogen release. Experiments were carried out with specific zincate and KOH concentrations under different current densities and current efficiencies were calculated based on powder weight. SEM imaging was used to study the effects of various conditions on powder morphology and the specific surface area was measured by BET. The highest specific surface area obtained was 9.14 m 2/g.

The inhibition of the spongy electrocrystallization of zinc from doped flowing alkaline zincate solutions

Abstract The effects of the presence of additives like lead and tungstate ions in flowing alkaline zincate solutions on suppressing spongy zinc electrogrowth are examined. The results show that the two additives with optimal concentrations in flowing electrolytes can suppress spongy zinc initiation and propagation. And, the two additives can bring about more uniform and compact deposits and, thereby, reduce spongy zinc growth. The influence of lead and tungstate ions on the zinc deposition/dissolution is evaluated by cyclic voltammetry. It also shows that the addition of the two additives is largely a blocking action, and the co-deposition of lead and zinc ions may occur. The performance of the zinc-air flow battery with zinc regeneration electrolysis is determined. It shows that by the addition of 0.6 M Na 2 WO 4 or 10 −4 M to 10 −3 M lead, compact or mixed compact–spongy zinc deposits are created and the favorable charge/discharge performance of the battery is achieved with an energy efficiency of approximately 60%.

Current efficiency improvement of Zn-Fe alloy electrodeposition by hydrogen inhibitor

In order to inhibit hydrogen evolution and enhance current efficiency of Zn-Fe alloy electrodeposition from alkaline zincate solution, hydrogen inhibitors composed of the sulfur group elements were optimized on the basis of atom structures analysis. The effects of hydrogen inhibitor on the current efficiency of Zn-Fe alloy electroplating and their electrochemical behaviors were studied. The results indicate that hydrogen inhibitor can increase the current efficiency of Zn-Fe alloy electroplating evidently, from 63.28% without hydrogen inhibitor up to 83.54% with a hydrogen inhibitor at a volume fraction of 2.0%, while it has a minor influence on that of pure Zn plating, which maintains at 80%. The optimum volume fraction of hydrogen inhibitor is 2.0%.

Study of zinc electrodes for single flow zinc/nickel battery application

Zinc deposition from alkaline zincate solution in single flow zinc/nickel battery has been investigated. The effect of different substrates such as copper, cadmium and lead were examined by using cyclic voltammetry and cathodic polarization technique. It was found that the cadmium substrate is better than the others. Zinc deposition was carried out by using galvanostatic technique, and the deposits were examined by SEM. The results demonstrated that there is no zinc dendrite on the cadmium substrate in flowing electrolyte. Coulombic and voltage efficiencies of 98 and 88%, respectively, are obtained in a small laboratory cell.

Characterization and Growth Mechanism of Filamentous Zinc Electrodeposits

The morphology of mossy zinc deposits from alkaline zincate solutions was investigated using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The composition and orientation of the mossy deposits were examined using powder X-ray diffraction (XRD), and selected area XRD (SAD). Morphologically, the deposits appear as spongy at the micrometer scale, but filamentous at the nanometer scale. Filamentous mossy zinc was determined to consist of pure metallic zinc. Individual deposit filaments were found to be single crystals which grow in the <0001> direction. The BET specific surface area of filamentous deposits was determined to be 5-11 m2 g-1 (BET). This high surface area makes filaments highly active and can spontaneously oxidize in the air.

Mechanism of zinc electroplating in alkaline zincate solution

The cathodic deposition properties and mechanism of Zn in alkaline zincate solution were studied by electrochemical techniques. The results show that Zn(superscript 2+) exists in the alkaline solution in the form of Zn(OH)4(superscript 2-). The apparent activation energy of the electrode reaction is 38.93 kJ/mol, which indicates that the discharge of Zn(OH)4(superscript 2-) on cathode is controlled by electrochemical polarization, and accompanied by a preceding chemical reaction. The diffusion coefficient of Zn(OH)4(superscript 2-) is 2.452×10^(-6) cm^2/s. Zn(OH)2 is the species directly discharged on the cathode surface. Based on the above results the mechanism of zinc electroplating in alkaline zincate solution was put forward. The discharged species is Zn(OH)2 formed from the preceding chemical reaction, which becomes Zn(OH) (subscript ad) when gaining one electron, and then gaining the second electron to become Zn. The first electron gaining step is rate determining one.

Kinetics of Zn cathodic deposition in alkaline zincate solution

Kinetic parameters of the electrode reactions were measured by investigating steady-state current-potential behaviors. The Tafel slopes of cathodic and anodic processes are −0.113 8 V and −0.041 18 V, the anodic and cathodic apparent transfer coefficients are 0.519 3 and 1.435 2, respectively, and the stoichiometric number of rate-determining step is 1. The theoretical kinetics equation of electrode reaction was deduced, from which the dynamic parameters can be calculated as follows: the cathodic and anodic Tafel slopes are −0.118 V and −0.039 4 V, respectively, consisting with the experimental values. Finally, the correctness of the mechanism was further demonstrated using apparent transfer coefficient according to the electrochemical dynamic equation of multi-electron reaction.

Nature of the potential of nonpolarized zinc electrode in zincate solutions

The effect of components of alkaline zincate solution and surface compounds, which form on metal zinc in the alkaline solutions, on the nature of nonpolarized electrode potential (E) is studied. It is proposed to determine the nature of E by taking into account more rigorously the activities of all solution components. It is found that in the zincate solutions, the potential of nonpolarized metal zinc is the potential of Zn/Zn(OH)2, OH− electrode of the second kind.

Electrochemical and Surface Studies of Zinc in Alkaline Solutions Containing Organic Corrosion Inhibitors-From Lab Studies to a Metal-Air Battery

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Effects of Deposition Conditions on the Morphology of Zinc Deposits from Alkaline Zincate Solutions

The morphology of zinc deposits from alkaline zincate solutions was systematically investigated over a wide range of conditions. Zinc deposit morphology was categorized as heavy spongy, dendritic, boulder, layerlike, and filamentous mossy. The formation of dendritic, layerlike, and mossy deposits is under single-factor control, and these morphologies are defined as type I. The formation of heavy spongy and boulder deposits is under multiple-factor control, and they are defined as type II. Within type I, dendrite initiation and growth are both under diffusion control, while layer and mossy formation is under activation control. Based on the effects of deposition conditions, morphology diagrams were constructed. These diagrams demonstrate that the control factors are not independent, and no universal critical overpotential for a specific deposit morphology exists.

Ionic Mass Transfer Accompanying Anodic Dissolution of Zinc in Alkaline Solution

Holographic interferometry was applied in situ to measure the ionic mass-transfer rates near upward-facing zinc anodes dissolving at high current densities in aqueous KOH solutions. The time-varying interference fringe patterns were converted to individual concentration profiles of , , and ions. The measured ionic concentration profiles agreed well with those predicted by a transient diffusion model for a multicomponent electrolyte. When a zinc anode was electrochemically dissolved in KOH electrolyte, the anode potential abruptly shifted in the noble direction, immediately followed by gas evolution. The onset time for this potential rise and accompanying gas evolution agreed well with the calculated time interval required to drive the ion concentration to zero at the zinc electrode surface. The present model can be applied to not only optimize zinc cell designs but also develop a control method for trouble-free, safe operation of a zinc battery without gas evolution.

Aqueous alkaline zincate solutions and methods

Aqueous alkaline zincate solutions and methods

Electrochemical behaviors of Zn-Fe alloy and Zn-Fe-TiO2 composite electrodeposition

Electrochemical behaviors of Zn-Fe alloy and Zn-Fe-TiO2 composite electrodeposition in alkaline zincate solutions were studied respectively by the methods of linear potential sweep and cyclic voltammetry. From the results it can be concluded that Zn shows under potential deposition, Zn-Fe alloy codeposition is anomalous codeposition and Zn-Fe alloy cathode polarization is increased with the introduction of additive. From the view point of electrochemistry, the reasons that the content of Fe in the Zn-Fe coating changes with the composition of the electrolyte and the process conditions altering and the relationship between the content of Fe and the appearance of the coating are interpreted. The cathode polarization of Zn-Fe alloy codeposition is enhanced obviously with addition of additive. In the course of composite electrodeposition, TiO2 has less promotion to electrodeposition of zinc ions than to iron ions, while the electrodeposition of iron ions improves the content of TiO2 in composite coating, which is in agreement with the results of process experiments.

Influence of alloying additives on the performance of commercial grade aluminium as galvanic anode in alkaline zincate solution for use in primary alkaline batteries

The self-corrosion of different grades of commercial aluminium such as 2S, 3S, 26S and 57S in 4 M NaOH containing 0.6 M ZnO has been determined by weight loss measurements. It is found that 26S and 57S aluminium exhibit negligible corrosion rates in the range 0.05–0.06 mg cm−2 min−1, which can be attributed to the formation of a zincate coating on the aluminium surface. The influence of zincating on the performance of binary and ternary alloys of 26S and 57S aluminium obtained by incorporating alloying elements such as zinc, indium, thallium, gallium and tin as galvanic anode in 4 M NaOH containing 0.6 M ZnO has been examined by studying self corrosion, steady state open circuit potential, galvanostatic polarization and anode efficiency. It is found that zincated ternary alloys of 26S and 57S aluminium containing zinc and indium can serve as good galvanic anodes in alkaline medium. AC impedance measurements and X-ray diffraction studies have been carried out to understand the nature of the film formed on the aluminium surface.

Electrochemical and surface studies of zinc in alkaline solutions containing organic corrosion inhibitors

The electrochemical behavior of zinc in strong alkaline solutions containing 8.5 M of potassium hydroxide (KOH) and polymeric organic inhibitors was evaluated. The concentrations of the organic inhibitors studies were in the range of 400–4000 ppm and included polyethylene glycol (PEG), with a molecular weight of 600, and polyoxyethylen alkyl phosphate ester acid form (GAFAC RA600). The electrochemical studies included anodic, cathodic, and linear polarization along with potentiostatic studies. It was found that the inhibition properties of PEG, in the strong alkaline solution, are by far much more efficient than the inhibition capability of GAFAC RA600. Surface analysis obtained with the use of high resolution scanning electron microscopy (HRSEM) revealed different morphology characteristic developed at the zinc surface in the presence of the two inhibitors. A methodology employing electrochemical tests is proposed to quickly and conveniently evaluate inhibitors for Zn in alkaline media.

Effects of coprecipitated zinc on the structure and electrochemical performance of Ni/Al-layered double hydroxide

The effects of zinc on the structure and electrochemical performance of Ni/Al-layered double hydroxides (LDHs) prepared by a coprecipitation method were studied. The experimental results showed that the addition of zinc in Ni/Al-LDHs improved the electrochemical performance of the samples such as discharge potential, cycle stability and reversibility. The maximum specific discharge capacity of 425 mAh g −1 of nickel hydroxide was obtained for the Ni/Al-LDHs without zinc. The maximum discharge mediate potential of 413 mV and the lowest capacity deterioration rate of <5% after 398 charge–discharge cycles at 1C rate were gained for the 6.4 wt% Zn-containing sample. The results of electrochemical impedance spectroscopy and powder X-ray diffraction measurements indicated that the advantageous performance of Ni/Al-LDHs with high zinc content resulted from the decrease of electron transfer resistance ( R t) and the number of cells per crystallite in the direction of c-axis and slow dissolution of zinc in alkaline solution.

Effects of bismuth ion and tetrabutylammonium bromide on the dendritic growth of zinc in alkaline zincate solutions

The effectiveness of bismuth ion and tetrabutylammonium bromide (TBAB) as deposit-enhancing additives of zinc electrode has been investigated by means of current–time technique, potentiodynamic polarization and scanning electron microscopy. The experimental results showed that the dendritic growth of zinc in alkaline zincate solution was inhibited by the addition of Bi 3+ and TBAB, respectively. However, at a higher cathodic overpotential TBAB produced little effective suppression on zinc dendrites. Obvious synergistic effect of Bi 3+ and TBAB on the dendrite inhibition of zinc electrode was also found.