High-speed jet electrodeposition and microstructure of nanocrystalline Ni-Co alloys

The jet electrodeposition from watts baths with a device of electrolyte jet was carried out to prepare nano-crystalline cobalt-nickel alloys. The influence of the concentration of Co²⁺ ions in the electrolyte and electrolysis parameters, such as the cathodic current density, the temperature as well as the electrolyte jet speed, on the chemistry and microstructure of Ni-Co-deposit alloys were investigated. Experimental results indicated that increasing the Co²⁺ ions concentration in the bath, the electrolyte jet speed and decreasing of the cathodic current density and decrease of the electrolyte temperature all results in an increase of cobalt content in the alloy. Detailed microstructure changes upon the changes of alloy composition and experimental conditions were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD results show the Ni-Co solid solution was formed through the jet electrodeposition. Phase constitution of solid solution changes progressively under different electrolyte concentration. Alloys with low Co concentration exhibit single phase of face-centered cubic (fcc) structure; The Co concentration over 60.39 wt.%, the alloys are composed of face-centered cubic (fcc) phase and hexagonal close-packed (hcp) phase. Furthermore, the formation of the nanostructured Ni-Co alloy deposit is investigated. Increasing the Co²⁺ ions concentration in the bath, the cathodic current density, the electrolyte temperature and the electrolyte jet speed all result in the finer grains in the deposits. Additives such as saccharin in the electrolyte also favor the formation of the finer grains in the alloy deposits.     

Structure and electrochemical behaviors of a series of Co-B alloys

A series of Co_xB (x = 1, 2, 3) alloys were prepared by arc melting, the phase structure of the alloys were characterized by X-ray diffraction (XRD). The electrochemical experimental results demonstrated that the Co_xB (x = 1, 2, 3) series alloys showed excellent cycling stability, the capacity retention was 94.2%, 93.6% and 93.8% in the 100th cycle, respectively, as the cobalt content decreased. The CoB alloy electrode showed very good electrochemical reversibility in cyclic voltammetry (CV) curves, the oxidation and reduction peaks resembled the pure cobalt element powder electrode. The electrode mechanism was discussed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), using pure CoB alloy cast electrode. From the SEM, after first and second cycle, the surface became porous and pulverous; also, the oxidation state of Co changed through XPS, after second cycle, the Co of 0 oxidation state could not be found on the surface. Based on the experiment, a proper mechanism was proposed: on this condition, the discharge capacity may due to the Co(OH)₂/Co reaction, which happened on the porous surface as the boron dissolved when the cycle increased.     

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.     

Study of the electrochemical deposition of Sn-Ag-Cu alloy by cyclic voltammetry and chronoamperometry

The electrochemical deposition of Sn-Ag-Cu alloy from weakly acidic baths onto glassy carbon electrodes (GCE) was studied by cyclic voltammetry (CV) and chronoamperometry (CA). The properties of the electrodeposits were characterized by scanning electron microscopy (SEM), energy-dispersive spectrometery (EDS) and X-ray diffraction (XRD). Test results indicate that the two cathodic peaks in the CV curves, at −0.6 V and −0.85 V during the forward scan towards the negative potentials, correspond to the irreversible deposition of a solid solution of tin, silver and copper. The underpotential deposition (UPD) of Sn occurs at −0.6 V during the cathodic period and the amount of Ag and Cu in the Sn-Ag-Cu alloy decreases with increasingly negative cathodic potentials. During the forward scan, towards the positive potentials used in CV testing, cathodic peaks at −0.85 V appear in the CV curves for baths containing mixtures of tin salts and triethanolamine (TEA). This corresponds to a reduction of transient complex ions [Sn(TEA)_x]²⁺ on the surface of the cathode. Furthermore, the formation and reduction of [Sn(TEA)_x]²⁺ is a diffusion controlled process. On the surface of the GCE, the actual nucleus growth mechanism of the Sn-Ag-Cu alloy is represented by the progressive nucleation model.     

Study of phase composition of Zn-Ni alloy electrodeposited in acetate-chloride electrolyte at a temperature of 50 °C

The phase composition of Zn-Ni alloys electrodeposited under potentiodynamic and galvanostatic conditions in acetate-chloride plating solution with the ratio [Zn⁺²]/[Ni⁺²] = 1:12.8 at 50 °C has been investigated by the potentiodynamic stripping and XRD methods. It has been determined that two anodic peaks, which can be attributed to oxidation of the certain phases of Zn-Ni alloy emerged in potentiodynamic stripping curves (PDC) at E < 0 V and at E > 0 V. The Zn-Ni alloy phase that oxidized at E > 0 V was obtained by using cyclic voltammetry with the partial potentiodynamic stripping. This phase is ∼7 at.% Zn solid solution in Ni. The composition of Zn-Ni alloy phase that oxidized at E < 0 is ∼41.0 at.% Zn and ∼59.0 at.% Ni. The ratio of these phases in the alloys depends on the cathodic current density (i_c).     

Composition control of ternary FeCoNi deposits using cyclic voltammetry

Ternary FeCoNi alloys were electroplated through mean of cyclic voltammetry in simple chloride baths with pH of 2.0. The anodic process in the voltammetric curves was found to completely depress the anomalous deposition of binary alloys while this anomaly was still obvious for the deposition of ternary FeCoNi alloys. From the energy-dispersive X-ray results, the Fe/Co ratio in the ternary FeCoNi deposits was equal to the Fe²⁺/Co²⁺ ratio in the deposition solutions when the Ni²⁺ content was continuously changed. The composition of ternary FeCoNi deposits could be precisely predicted and easily controlled by adjusting the Ni²⁺/(Fe²⁺+Ni²⁺+Co²⁺) ratio in the plating solutions although a synergistic effect in depressing the codeposition of Ni onto the FeCoNi matrix due to the coexistence of Co²⁺ and Fe²⁺ was clearly demonstrated in this work.     

Ni–Zn–P alloy deposition from sulfate bath: inhibitory effect of zinc

Electroless Ni–Zn–P alloy deposition from a sulphate bath, containing sodium hypophosphite as reducer, was investigated. To increase the plating rate, the deposition parameters were optimized. The effect of process parameters (T, pH and [Zn²⁺]) on the plating rate and deposit composition was examined and it was found that the presence of zinc in the bath has an inhibitory effect on the alloy deposition. As a consequence, the percentage of zinc in the electroless Ni–Zn–P alloys never reaches high values. Using cyclic voltammetry the electrodeposition mechanism of Ni–Zn–P alloys was investigated. It was observed that the zinc deposition inhibits the nickel discharge and, as a consequence, its catalytic activity on hypophosphite oxidation. It was also found that increase in temperature or pH leads to the deposition of nickel rich alloys.     

Electrodeposition of porous Co layers and their conversion to electrocatalysts for methanol oxidation by spontaneous deposition of Pd

Electrocatalysts for methanol oxidation were prepared through a two stage deposition process: porous cobalt layers were deposited, by cathodic reduction of Co²⁺ ions, and then modified by spontaneous deposition of Pd. A basic sulphate solution and a mildly acid chloride solution were compared as media for the electrodeposition of Co. Deposits with the highest surface roughness were obtained in the chloride solution, at large current densities. Pd was deposited onto the Co porous layers by immersing them in acid deaerated PdCl₂ solutions, at open circuit. The Pd loading and the Pd surface area were estimated by UV–visible spectroscopy and by cyclic voltammetry, respectively. The Pd-modified Co electrodes were tested as anodes for methanol oxidation and compared to the similarly prepared Pd-modified Ni electrodes. The former exhibited better stability of performance and higher methanol oxidation peak currents per unit Pd mass, ca. 200 A g⁻¹.     

Electrochemical and SEM investigations of the influence of gluconate on the electroless deposition of Ni-Cu-P alloys

The effect of gluconate on the deposition rate and the deposit composition was examined at low pH of solution. The deposition rate exhibit a maximum and the content of copper present a minimum when the gluconate concentration changes between 0 and 40 g/l. The kinetic study carried out by cyclic voltammetry and electrochemical impedance showed that the gluconate acts on the anodic and cathodic reactions. The activation energy of the alloy deposition was determined. In addition, gluconate does not affect the crystallinity of the Ni-Cu-P deposit.     

Zinc deposited polymer coatings for copper protection

Polypyrrole (PPy) and polyaniline (PAni) coatings were electrosynthesized on copper, by using cyclic voltammetry technique. Then, these coatings were modified with the deposition of zinc particles from aqueous zinc sulphate solution. The electrodeposition of zinc was achieved at a constant potential value of −1.20 V, in the amount of ∼0.75 mg/cm². The corrosion performance of zinc modified polymer coatings were investigated in 3.5% NaCl solution; by using the electrochemical impedance spectroscopy (EIS), and anodic polarization curves. The zinc particles improved the barrier property of polymer films, thanks to formation of voluminous zinc corrosion products within the pores of polymer coating. Also, the zinc particles provided cathodic protection to the substrate, where the polymer film played the role of conductance between zinc particles and copper.     

Effects of cobalt, temperature and certain impurities upon cobalt electrowinning from sulfate solutions

The effects of cobalt concentration, temperature and the presence of zinc, copper and iron ions in the electrolyte on current efficiency and cathodic quality were investigated by cyclic voltammetry and galvanostatic methods during cobalt electrowinning. The results showed that high cathodic efficiency of cobalt deposition was obtained from solutions containing cobalt concentration in the range 30–60 g l^–1. Current efficiency increased from 94% to 97% with increase in cobalt concentration to 60 g l^–1 at 20 °C. It was also found that increase in temperature to 50 °C enhanced the cobalt deposition reaction, along with the rate of hydrogen evolution, resulting in little change in current efficiency. The presence of foreign cations in the electrolyte not only adversely affects current efficiency but also promotes cracking and peeling.     

Electrodeposition of noncrystalline cobalt–tungsten alloys from citrate electrolytes

Induced electrodeposition of Co–W alloys onto steel substrates from acid citrate baths has been investigated. The effects of some plating parameters, such as current density, pH and temperature on the potentiodynamic cathodic polarization curves, cathodic current efficiency of the alloy and the percentage tungsten in the alloy were studied. Highly adherent and compact Co–W alloys codeposited from citrate baths containing up to 28 mass % tungsten were obtained. The percentage W (w/w) in the alloy increases with increasing pH, bath temperature and Co²⁺ ion concentration. On the other hand, the percentage W in the alloy decreases with increasing current density. Anodic linear stripping voltammetry (ALSV) indicated that the alloy might consist of one phase solid solution. These alloys were determined to be noncrystalline by X-ray diffraction analysis.     

Electrochemical and AFM study of cobalt nucleation mechanisms on glassy carbon from ammonium sulfate solutions

Nucleation mechanisms of cobalt on a glassy carbon electrode (gce) from aqueous ammonium sulfate solutions were investigated through the electrochemical techniques of cyclic voltammetry (cv) and chronoamperometry (ca), coupled with atomic force microscopy (AFM) studies. The studied parameters were pH, cobalt concentration, temperature, scanning rate, and deposition potential. It was found that scanning in the cathodic direction produced two peaks, corresponding to cobalt and hydrogen reduction, respectively. Scanning in the anodic direction was characterized by cobalt dissolution, which was interrupted by formation of cobalt hydroxide, causing a second anodic peak. The amperometric study found progressive nucleation mechanisms, in contrast to the instantaneous nucleation mechanisms determined by the AFM study. An explanation for the contradictory nucleation mechanisms shown in the two studies is provided.     

Anomalous codeposition of Co–Ni: alloys from gluconate baths

Thin films of cobalt–nickel alloys were galvanostatically deposited onto steel substrates from gluconate baths. Cathodic polarization curves were determined for the parent metals and Co–Ni alloy. The effects of bath composition, current density and temperature on cathodic current efficiency (CCE) and alloy composition were studied. The deposition of Co–Ni alloy is of anomalous type, in which the less noble metal (Co) is preferentially deposited. The CCE of codeposition is high and increases with increase in temperature and current density, but it decreases as the [Co²⁺]/[Ni²⁺] ratio in the bath increases. The percentage of Co in the deposit increases with increasing cathodic current density, temperature and increasing Co²⁺ ion concentration. The structure and surface morphology of the deposit were studied by XRD, ALSV and SEM. The results showed that the alloys consisted of a single solid solution phase with a hexagonal close packed structure.     

Sonochemical intercalation synthesis of nano γ-nickel oxyhydroxide: Structure and electrochemical properties

Nano γ-nickel oxyhydroxide (nano γ-NiOOH), intended as a new positive electrode material for alkaline Zn/Ni batteries, was synthesized by a sonochemical intercalation method. Using NaClO as oxidant, 5 M NiCl₂ solution was added dropwise to a concentrated alkaline solution of NaClO + NaOH, which allows all four elementary reactions (precipitation, oxidation, cation exchange, and water molecule intercalation) to proceed simultaneously under low-frequency ultrasonic irradiation. XRD, SAXS, TEM, SEM, AAS, IR, TG, CT (complexometric titration), cyclic voltammetry (CV), and a charge-discharge test of imitative cell have been used to characterize the microstructural characteristics, composition and electrochemical properties of the synthesized material. The results showed that the lattice parameters of nano γ-NiOOH are a = 2.8256 Å and c = 20.7938 Å. The average oxidation state of Ni in the sample is 3.65 as measured by an indirect iodine method. The alkali metallic Na⁺ ions and water molecules have been inserted into sites between NiO₂ layers. The cyclic voltammogram of nano γ-NiOOH exhibited two cathodic peaks and two anodic peaks, which is in accord with the redox reaction between the various phases of Ni(OH)₂ and NiOOH. The charge-discharge test of imitative cells revealed that nano γ-NiOOH exhibited a higher discharge capacity than spherical β-NiOOH.     

Preparation and electrochemical capacitance of cobalt oxide (Co3O4) nanotubes as supercapacitor material

Cobalt oxide (Co₃O₄) nanotubes have been successfully synthesized by chemically depositing cobalt hydroxide in anodic aluminum oxide (AAO) templates and thermally annealing at 500 °C. The synthesized nanotubes have been characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The electrochemical capacitance behavior of the Co₃O₄ nanotubes electrode was investigated by cyclic voltammetry, galvanostatic charge-discharge studies and electrochemical impedance spectroscopy in 6 mol L⁻¹ KOH solution. The electrochemical data demonstrate that the Co₃O₄ nanotubes display good capacitive behavior with a specific capacitance of 574 F g⁻¹ at a current density of 0.1 A g⁻¹ and a good specific capacitance retention of ca. 95% after 1000 continuous charge-discharge cycles, indicating that the Co₃O₄ nanotubes can be promising electroactive materials for supercapacitor.     

Voltammetric study of plating baths for electrodeposition of Co-W amorphous alloys

Cyclic voltammetry and chronoamperometry at glassy carbon and platinum microdisc electrodes have been used to study the electrodeposition of Co–W amorphous alloys. Voltammetric results show that cathodic deposition of Co–W alloy is accompanied by hydrogen evolution and the efficiency of Co–W electrodeposition does not exceed 20%. Voltammetric behaviour of cobalt (II) and tungstate in ammonium citrate solution depend strongly on composition of the plating bath. The concentration of Co(II) ions can be monitoredin situ during electroplating by means of anodic stripping voltammetry at a platinum microelectrode. The deposit of the alloy on the microelectrode is stable in the atmosphere and thus can be stored for subsequent comparison with a deposit obtained later in the life of the working bath.     

Effect of cathodic reduction on catalytic activity of amorphous alloy electrodes for electrooxidation of sulfite

Active electrode materials for a new zinc electrowinning process, in which the thermodynamic cell voltage is about half that of the conventional process by replacing oxygen evolution by anodic oxidation of SO₂ produced in the zinc smelting process have been studied. Immersion in HF solution and subsequent cyclic voltammetry (CV) in sulfuric acid are known to be effective surface activation treatments of the amorphous alloy electrodes. The galvanostatic cathodic reduction (CR) treatment was applied to obtain further activation for sulfite oxidation for HF- and CV-treated electrodes prepared from amorphous nickel-valve metal-platinum group metal alloys. This treatment has been found to be effective in enhancing the activity. Among the amorphous Ni-40Nb alloys containing platinum group elements, the platinum-containing electrode showed the highest catalytic activity, which was higher than that of platinized platinum. Furthermore, the electrocatalytic activities of CR-treated electrodes prepared from amorphous alloys containing platinum and rhodium, and platinum and ruthenium were higher than that of the electrode containing only platinum. According to XPS analysis of the amorphous Ni-40Nb-1Pt-1Ru alloy specimen the enrichment of platinum and ruthenium occurred by CV treatment, and a small amount of oxidized platinum and ruthenium species remained on the electrode surfaces, but most of them were cathodically reduced to the metallic state by CR treatment. High catalytic activities for sulfite oxidation can be attributed to the metallic state of platinum and ruthenium contained in the alloy electrodes, even though the activity of these electrocatalysts is higher than that of pure Pt or Ru.     

Electrooxidation of methanol on NiMn alloy modified graphite electrode

Nickel and nickel-manganese alloy modified graphite electrodes (G/Ni and G/NiMn) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) were employed. In CV studies, in the presence of methanol NiMn alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel hydroxide increase is followed by a decrease in the corresponding cathodic current in presence of methanol. The anodic peak currents show linear dependency upon the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of methanol was found to be 4 × 10⁻⁶ cm² s⁻¹. A mechanism based on the electro-chemical generation of Ni³⁺ active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. The charge transfer resistance accessible both theoretically and through the EIS have been used as criteria for derivation of the rate constant.     

镀镍溶液中甘氨酸对Ni^2＋,Zn^2＋电化学行为的影响

运用阴极极化法和循环伏安法研究了镀镍溶液中甘氨酸对Ｎｉ＾２＋，Ｚｎ＾２＋以及Ｎｉ＾２＋＋Ｚｎ＾２＋电化学行为的影响。结果表明，电沉积Ｎｉ，Ｎｉ－Ｚｎ合金过程中，甘氨酸能抑制Ｈ＾的放电；在低电流区，甘氨酸有去极化作用，在高电流区有增大极化作用。