Copper electrodeposition into ion-exchange materials

Electrodeposition of copper into spherical granules of ion-exchange materials KU-23 and KU-2 out of acid sulfate solutions is studied by a method of cyclic voltammetry. It is discovered that the discharge of copper ions in an ion-exchange matrix is characterized by a cathodic overvoltage that is higher than the overvoltage of the same process on a graphite substrate by 0.08 V, which is most probably connected with a limited mobility of ions localized at fixed groups [RSO ₃ ^? ]. The cyclic voltammogram exhibits an additional cathodic peak in the potential region corresponding to the reduction of single-charged copper ions that form as a result of their accumulation inside pores of the ion-exchange matrix during anodic dissolution of metal deposited previously. It is fixed microscopically that the process of deposition begins at the graphite substrate/ion-exchanger interface and passes into bulk upon the formation of an electron-conducting layer saturated with copper. Preliminary saturation of the ion-exchanger by copper deposited chemically facilitates uniform electrodeposition of copper over the entire volume of pores of the ion-exchange matrix.     

Synthesis and Characterization of Sol-Gel Cu-ZrO2 and Fe-ZrO2 Catalysts

Fe-ZrO₂ and Cu-ZrO₂ xerogels were prepared by a sol-gel method. The effect of the hydrolysis catalyst during the gelation step, namely H₂SO₄ or NH₄OH, on the properties of the resulting materials was investigated by XRD, BET, TGA/DTA, TPD of ammonia, FTIR, and TPR. Fe-ZrO₂ and Cu-ZrO₂ xerogels, with sulfuric acid introduced as the hydrolysis catalyst, mainly crystallyzed in the tetragonal phase and exhibited larger surface area and acid amount than those obtained with NH₄OH. Ammonia TPD shows that copper promoted sulfated zirconia is the most acidic material. TGA and FTIR reveal that under oxidizing conditions sulfated zirconia promoted with iron and copper retains more sulfate species than unpromoted sulfated zirconia. Regardless of the hydrolysis catalyst employed, copper promoted catalysts calcined at 600°C, contain a large fraction of copper oxide specieseasily reduced at low temperatures. These copper oxide species are believed to have different environment and interactions with the surface oxygen vacancies of the zirconia support. A FeO-like phase appears to be the most probable one after reduction of Fe-ZrO₂ catalysts prepared with NH₄OH as the hydrolysis catalyst. The formation of Fe° species may be hindered by the high dispersion and interaction of Fe²⁺ ions with the zirconia support. On the other hand, the reduction peaks of iron oxide and sulfate species exhibit a considerable overlap in the TPR profiles of sulfated Fe-ZrO₂ samples. Hence, the nature of the supported phase in the latter samples is rather uncertain.     

Changes in surface stress of gold electrode during underpotential deposition of copper

The changes in surface stress of the evaporated gold electrode (mainly oriented to the (111) plane) during underpotential deposition (UPD) of copper in 0.1 M sulfuric acid medium or 0.1 M perchloric acid medium with and without sulfate or chloride were measured using a bending beam method. The surface stress maximum of gold electrode appeared during Cu-UPD. The co-adsorption of (bi)sulfate or chloride ions with copper atoms induced the compressive surface stress to promote the Cu-UPD. The factors influencing the surface stress or surface elastic strain were discussed in relation to the Cu-UPD structure. Dedicated to Professor Su-Il Pyun on the occasion of his 65th birthday.     

Peculiarities of copper underpotential deposition and nucleation on polycrystalline platinum in the presence of acetonitrile: Rotating ring-disk electrode

The initial stages of copper electrocrystallization on polycrystalline platinum in 0.5 M H₂SO₄ + 10 mM CuSO₄ + 0–200 mM acetonitrile (AcN) solutions are studied by the methods of cyclic voltammetry and potentiostatic current transients on a ring-disk electrode. Adsorbed AcN molecules accelerate both the underpotential deposition and the bulk deposition of copper due to the local electrostatic effects on the charged interface. With the increase in the additive concentration in solution, the contribution of the production of copper ions Cu⁺ is observed to increase due to the formation of Cu(AcN) _x ⁺ comlexes, particularly, for [AcN] ≥ 4 mM when the concentrations of acetonitrile and copper sulfate become comparable. In the presence of AcN, as well as in the copper sulfate supporting electrolyte, the adatomic layer is formed via the mechanism of the two-dimensional growth of Cu(1 × 1) phase islets.     

Effect of anion adsorption on early stages of copper electrocrystallization at Au(111) surface

The monolayer and submonolayer deposition of copper on Au(111) electrode surface in the presence of chloride and sulfate ions was studied by in situ X-ray absorption and electrochemical techniques. The anions coadsorb with the deposited copper adatoms and have a strong influence on the structure of these mixed overlayers. Copper deposited in the presence of chloride forms a bilayer in which copper atoms are sandwiched between the gold substrate and the top layer of chloride ions. The bilayer is well ordered and has a (5×5) long range structure. The copper atoms are packed in registry with the top layer of chloride ions. In contrast, copper adatoms deposited in the presence of sulfate ions are packed in registry with respect to the Au(111) substrate. The coadsorbed copper and sulfate form a highly corrugated overlayer. The copper adatoms assume a honeycomb (√3×√3) structure with the center of the honeycomb occupied by sulfate. The sulfate ion adsorbs with three of its four oxygens directed towards the hexagon of copper adatoms. The bond angle between the copper adatom and the oxygen of the sulfate ion is approximately equal to 45 °. Our data indicate that, in contrary to the literature reports, the (√3×√3) structure observed on STM and AFM images corresponds to the corrugation of adsorbed sulfate ions rather than copper adatoms.     

Copper in Acid Chloride Solutions: Electrochemical Behavior by Quartz Microgravimetry and Voltammetry

The cathodic deposition of copper on a gold electrode and its subsequent anodic dissolution in an acid chloride solution, where two successive stages of a one-electron transfer are distinguishable because of the stability of chloride complexes of Cu(I), is studied by voltammetry and quartz microgravimetry. The formation of a film of an intermediate compound of Cu(I) during the deposition and dissolution of copper is revealed experimentally. Techniques for identifying the intermediate solid species are suggested. During a cathodic polarization, a film of intermediate compound CuCl forms at a reduced concentration of chloride ions in the Cu(II)/Cu(I) process, while during the anodic dissolution of the copper deposit formed during the cathodic polarization the intermediates appear in the Cu(0)/Cu(I) process, the concentration of chloride ions notwithstanding. The change in the electrochemical behavior of the system caused by a decrease in the concentration of chloride ions is explained.     

Initial Stages of Copper Electrocrystallization on a Glassy-Carbon Ring–Disk Electrode from Sulfate Electrolytes of Various Acidity: Potentiostatic Current Transients

Initial stages of copper electrocrystallization on glassy carbon from sulfuric acid electrolytes of pH 0.3 and 3.7 are studied by the method of potentiostatic current transients on rotating and stationary ring–disk electrode. The rate of copper deposition in a 0.5 M Na₂SO₄ + 0.01 CuSO₄ (pH 3.7) solution is marginally higher than in a 0.5 M H₂SO₄ + 0.01 CuSO₄ acid electrolyte (pH 0.3) at the expense of adsorption of sulfate and hydroxide ions on the substrate surface and the copper crystals. Regularities governing the multistage discharge of copper ions, the formation of the new phase nuclei, and the deposit dissolution are analyzed. The results of the study are compared with the data on the kinetics of copper electrocrystallization on a platinum electrode. The acceleration of the copper deposition on glassy carbon in the acid solution of pH 0.3, as compared with platinum, is due to accelerated discharge of copper ions and increased number of univalent copper ions in the near-electrode layer of solution. The oxygen-containing surface groups of glassy carbon (quinone–hydroquinone, carbonyl, etc.) are probably active centers for the discharge of copper ions and three-dimensional nucleation.     

Traveling fronts of copper deposition

We report the experimental observation of traveling fronts during the electroless deposition of copper on passive steel substrates. The low-carbon steel samples are passivated in nitric acid prior to the plating experiment, thus creating a thin, protective oxide layer on the steel surface. The deposition experiments are carried out from slightly acidic (pH 3.2) copper sulfate solution and copper nitrate solution with the latter showing front propagation only in the presence of chloride ions. For up to 30 s, fronts propagate with constant velocities in the range from 0.5 to 5 mm/s depending on the experimental conditions. This phase of constant-speed propagation gives way to accelerating fronts and very rapid, spatially unstructured deposition. Front-mediated plating is observed over a wide range of cupric ion concentration and constitutes a striking and unexpected example for pattern formation in electrochemical systems.     

Diffusion of ionic species labeled with35S in various aqueous electrolyte solutions at 25°C

Composite diffusion coeffcients have been measured for the various species labeled with³⁵S which are present in a number of aqueous solutions due to the introduction of the labeled material as³⁵SO ₄ ^2– . The solutions were of two components consisting of water and either sodium sulfate. The diffusion coeffcient measured for sodium chloride solutions is similar to literature data for the corresponding diffusion in sodium sulfate solutions. The results for sulfuric acid and ammonium hydrogen sulfate have been interpreted using literature data for the relative concentrations of the hydrogen sulfate and sulfate ions to obtain estimates for the diffusion coefficents of those ions. The results for perchloric acid, regarded as representing the diffusion coefficient of the hydrogen sulfate ion, have a much different concentration dependence to that observed for the estimates for that ion in sulfuric acid and ammonuim hydrogen sulfate. The difference is attributed to the effect of the perchlorate ion on the water structure.     

Ligand and electrolyte effects in the electroreduction of copper-substituted heteropolyanions

Focus is put on the electrochemical behaviours of the Cu²⁺ centre in several copper-substituted heteropolyanions. These behaviours are found to depend clearly on the structure and composition of the precursor lacunary oxometalates. In sulfate medium, complete demetallation is easily observed upon reduction. However, quantitative recovery of the complex is obtained by reoxidation. Therefore, after the deposition process, the lacunary heteropolyanions retain their original properties and can be used again to capture metal ions in solution. Various behaviours of the copper deposition process are observed depending on the presence of chloride in the supporting electrolyte.     

Origin of active copper electrocrystallization centers on platinum

The activation of a platinum electrode in an acid sulfate solution is studied on rotating and stationary disk electrodes by means of cyclic voltammetry. Rates of the adatom layer formation and the phase copper deposition significantly increase following use of a slow potential scan and/or agitation of electrolyte as a result of the interaction between adatoms or ions of copper with adsorbed or dissolved oxygen. Oxide compounds of copper are active centers of a two-dimensional growth of an adatom layer and a three-dimensional nucleation in the course of electrocrystallization.     

Mutual Influence of Electrode Processes during Electrodeposition of Layered Structures by a Single-Bath Method: Effect of Nickel Deposition and Hydrogen Evolution on the Mass Transfer of Copper in a Sulfosalicylate Electrolyte

The work justifies the selection of a sulfosalicylate copper–nickel electrolyte and its composition for obtaining nanostructures comprising alternate magnetic and nonmagnetic layers by a single-bath method. According to calculations of an equilibrium composition of the electrolyte and electrodiffusion fluxes of discharging species, in a neutral region of pH copper exists in the form of multicharged anions CuSSA^3–, and the migration effects must reduce the rate of the mass transfer of copper-containing species with increasing current of the parallel reaction of discharge of nickel ions. Dependences of the partial current density of copper deposition on the electrode potential are studied at various values of pH of the copper and copper–nickel electrolytes. Experimental results are analyzed on the basis of modeling concepts. It is shown that the drop of the partial current density of copper deposition below its limiting value at potentials of deposition of a magnetic layer is connected with the emergence of migration effects.     

Copper Electrodeposition Dynamics at a Porous Flow-through Electrode

The dynamics of the copper electrodeposition out of a dilute sulfuric acid solution of copper sulfate (straight-through regime, solution supplied from the rear at a velocity of ～1 cm s^?1) onto preliminarily metallized carbonaceous felt of the VINN-250 brand is studied. The profile, which describes the final deposit distribution, qualitatively conforms to predictions made in terms of a dynamic model for a porous electrode described previously, as does the nonmonotonic variation of the gain in the copper weight and the current efficiency for copper with time in the first half of the deposition process. At later stages of the process, along with the enhancement of the tendency towards the forcing of the copper electrodeposition process towards the front end of the electrode, there appears a new factor, which is not taken into account by the method. This factor is the deposition of a loose rough copper layer outside the porous electrode at its front side.     

Initial stages of the copper electrocrystallization from a sulfuric acid electrolyte: Chronoamperometry at a platinum ring-disk electrode

Initial stages of the copper electrocrystallization on platinum from a sulfuric acid electrolyte are studied by measuring potentiostatic current transients (the chronoamperometry method) on a rotating and stationary ring-disk electrode. The number of active centers and the copper nucleation rate are shown to substantially depend on the electrochemical pretreatment of the electrode. The mechanism governing the formation of intermediate species (ions Cu⁺) during the nucleation of a new copper phase and the deposit dissolution is analyzed. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth.     

Electrocatalytical properties presented by Cu/Ni alloy modified electrodes toward the oxidation of glucose

This paper concerns the deposition of metal alloys formed by nickel and copper on electrode surface aiming at the development of electrocatalytic systems. Such alloys were formed on platinum electrodes by direct reduction of Ni²⁺ and Cu²⁺ sulfate salts in different proportions in a simple and straightforward electrochemical treatment. After the deposition, the conversion to the electrocatalytic oxide form was done in alkaline solutions by cyclic voltammograms. The experimental parameters, such as deposition time and the proportion of copper and nickel in the synthetic solution, were investigated toward the catalytic oxidation of glucose. The materials were characterized by electrochemical experiments, infrared and Raman spectroscopies, and X-ray diffraction, showing that the material is not a simple mixture of nickel and copper oxides. The modified electrodes showed remarkable electrocatalytic properties, indicating an interesting application in the sensor and fuel cell development.     

Unusual concentration impedance for catalytic copper deposition

Recently a new mechanism for copper deposition has been proposed by Gabrielli et al. [C. Gabrielli, P. Moçotéguy, H. Perrot, R. Wiart, J. Electroanal. Chem. 572 (2004) 367]. In this mechanism cupric ions are supposed to be reduced by two different paths. The first path is a direct discharge of cupric ions in two steps, and the second follows a parallel path through a catalytic complexation with chloride ions and adsorption of copper (I) chloride onto the copper surface. In the second path, chloride ions are consumed in the first step and produced in the second step, therefore chloride ions act as catalysts. The rates of the two steps of the second path are equal under steady-state condition and the concentration of Cl⁻ anion is constant in the electrolytic solution. In contrast the step rates are not equal under dynamic conditions causing a concentration impedance of chloride ions with a rather unusual expression. Such an impedance is calculated and thoroughly examined in this paper. Finally, decomposition of the Faradaic impedance into the sum of concentration impedances of adsorbed species and chloride ions makes it possible to determine the contribution of each concentration impedance to the global impedance of the electrode.     

Electrodeposition of thin Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> films

The electrochemical behavior of copper(II), zinc(II), and thiosulfate (S₂O₃ ^2-) ions on the molybdenum electrode in individual 0.2 М sodium sulfate solutions (рН 6.7) and with addition of either 0.1 М tartaric acid (рН 4.6) or 0.1 М citric acid (рН 4.7) is studied. A one-step electrochemical method is developed for the deposition of thin Cu₂ZnSnS₄ films, which is carried out on the molybdenum electrode at a constant potential in sodium sulfate solutions containing tartaric acid. The effect of the concentration of electrolyte components on the chemical composition of Cu₂ZnSnS₄ films is determined. The phase composition is confirmed by the Raman spectroscopy data. The surface morphology of synthesized films is studied by means of scanning-electron and atomic-force microscopes. The photoelectrochemical characteristics of Cu₂ZnSnS₄ films are determined. Samples of these coatings on the Mo electrode are found to be highly photosensitive.     

Influence of preliminary UV irradiation on the thermal decomposition of copper hypophosphite

The effect of the influence of preliminary UV irradiation on the kinetics of the thermal decomposition of crystalline copper hypophosphite has been discovered, revealing a decrease in the induction period. Spectral dependence of the effect was determined by absorption of copper hypophosphite in the 255 nm charge transfer band. Comparison of the quantum efficiency of the disappearance of ions of bivalent copper 10^?1–10^?2 ions per quantum and the quantum output of hydrogen 10^?4–10^?5 mole per quantum as well as acid formation during photolysis shows that a proton (acid) as well as the univalent copper is the main primary product of photolysis. Formation of acid in the course of photolysis participating in the nucleation during the investigated topochemical process of thermal decomposition is the reason for the discovered effect.     

H+-Cu2+ ion exchange on a Cu0-KU-23 sulfocation exchanger nanocomposite in solutions with various pH values

The influence of solution pH on H⁺-Cu²⁺ exchange equilibrium was studied for the disperse copper- KU-23 (15/100 S) macroporous strongly acid sulfocation exchanger nanocomposite. In dilute solutions of copper(II) sulfate in weakly acid media (pH 3–6), ion exchange limitation is related to the consumption of hydrogen counterions and the formation of copper counterions in a side reaction between copper particles and impurity oxygen. The concentration of hydrogen counterions in the nanocomposite is replenished as pH decreases because of their sorption from solution together with copper ions. Original Russian Text ? E.V. Zolotukhina, T.A. Kravchenko, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 934–938.     

Sorption Properties of Hematite for Copper Ions

Sorption properties of commercial hematite (α-Fe₂O₃) for divalent copper ions were studied. This was done with a model solution of copper(II) sulfate additionally containing 400 mg L^–1 of sodium sulfate. It was shown that the hematite sample under study is a good sorbent for removal of divalent copper ions from aqueous solutions. The process of Cu²⁺ sorption is described by the Langmuir equation. The parameters of this equation were determined at various pH values of the model solution and compared with similar published parameters for other hematite samples.