Initial stages of copper electrocrystallization from sulfate electrolytes: Cyclic voltammetry on a platinum ring-disk electrode

Initial stages of copper electrocrystallization on platinum rotating and stationary ring-disk electrodes are studied in sulfate electrolytes of different acidities by cyclic voltammetry with a variable cathodic limit. In a weakly acid sodium sulfate solution of pH 3.7, copper deposition occurs at a higher rate than in a sulfuric acid electrolyte, which is due to an acceleration of the discharge of copper ions caused by local electrostatic effects that occur during the specific adsorption of sulfate anions and hydroxyl ions and to alterating nature of electroactive species. The mechanism of the formation of intermediate species (ions Cu⁺) during the deposition and dissolution of copper in solutions of different acidities is established.     

Kinetics and mechanism of nitrate and nitrite electroreduction on Pt(100) electrodes modified by copper adatoms

Kinetics and mechanism of nitrate and nitrite reduction on Pt(100) electrode modified by Cu adatoms have been studied in solutions of sulfuric and perchloric acids by means of cyclic voltammetry and in situ IR-spectroscopy. It has been shown that the surface redox process with participation of ammonia or hydroxylamine at 0.5–0.9 V occurs only on the Cu-free platinum. The causes of this effect could be low adsorption energy of nitrate reduction products on copper or changes in the composition of the products (ammonia for Pt(100) and N₂O for Pt(100)+Cu). Nitrate reduction on Pt(100)+Cu electrode is much faster in the perchloric acid solution (by several orders of magnitude) as compared with unmodified platinum as a result of induced adsorption of nitrate anions in the presence of partly charged Cu atoms. In the solutions of sulfuric acid the rate of nitrate reduction is considerably lower as copper adatoms facilitate adsorption of sulfate anions, which block the adsorption sites for the nitrate.     

Electrochemical quartz crystal microbalance study of copper ad-atoms on gold and platinum electrodes Part I. Adsorption of anions in sulfuric acid

The deposition and dissolution processes of copper ad-atoms on a gold or a platinum electrode in sulfuric acid electrolyte solution were investigated by using the electrochemical quartz crystal microbalance. It was found that the weight loss in the removal of the Cu-adlayer from the Au substrate was considerably larger than that expected from Faraday's law whereas the deviation for the Pt substrate was very small. The adsorption of bisulfate or sulfate anions both on Cu ad-atoms and on the electrode substrates was discussed quantitatively. It was demonstrated that higher coverage with Cu ad-atoms and lower adsorbability with bisulfate or sulfate anions were obtained on the Pt electrode than on the Au, and these effects could be ascribed to the difference in electronegativity between Pt and Au substrates.     

Methodical aspects of studying the electroreduction of nitrate on modified single crystal Pt(hkl) + Cu electrodes

Technique of modification of basal faces Pt(hkl) by adatoms and epitaxial copper deposits is developed. Analysis of potentiostatic current transients of copper deposition/dissolution and atomic force microscopy showed that the activity of Pt(hkl) faces regarding the processes of copper nucleation and epitaxial growth increases in the sequence of Pt(111) < Pt(110) < Pt(100). The reaction of nitrate anion reduction is sensitive towards the surface structure, not only in the case of platinum, but also in the case of copper deposits (including a monolayer of adatoms). The highest process rate is observed for the Pt(100) electrode modified by a monolayer of adatoms or islands of bulk copper; nitrate reduction at the lowest rate occurs at Pt(111) + Cu electrodes. Structure-sensitive competitive adsorption of background electrolyte and nitrate anions is the factor that largely determines the kinetics of nitrate reduction on different faces of platinum single crystal and copper deposits.     

Morphological aspects of sulfate-induced reconstruction of Cu(1 1 1) in sulfuric acid solution: in situ STM study

Using in situ STM the atomic structure and the morphology of a Cu(1 1 1) surface exposed to a dilute sulfuric acid solution have been studied depending on the applied electrode potential. At anodic potentials near the onset of copper dissolution the electrode surface is reconstructed (expanded) caused by the specific adsorption of sulfate anions. The extent of the surface reconstruction strongly depends on the sulfate adsorption rate. Fast sulfate adsorption results in a mainly disordered sulfate adlayer on an unreconstructed copper surface. Conversely, slow sulfate adsorption produces a mainly reconstructed copper surface with a highly ordered sulfate/water coadsorption layer. This adsorbate structure shows an additional long-range Moiré modulation, due to a misfit between the first reconstructed and the second unreconstructed copper layer. This is verified by spectroscopy-like STM experiments, which allow the imaging not only of the adsorbate overlayer, but also of the underlying reconstructed substrate. This type of adsorbate-induced reconstruction is characterized by an expansion of the topmost copper layer. The kinetically slow process of reconstruction can be easily followed by dynamic STM measurements revealing a mass transport out of the topmost copper layer during the slow sulfate adlayer formation. Characteristically, new copper islands nucleate and grow, while the sulfate Moiré adlayer expands over the electrode surface. At cathodic electrode potentials the desorption of the sulfate adlayer is accompanied by the lifting of the surface reconstruction and the massive formation of surface defects, such as small pits and vacancy islands. A continuous cycling of the electrode potential leads to an enormous roughening of the surface morphology.     

A rational approach in the design of selective mesoporous adsorbents

Two MCM-41 derived adsorbents have been tailor-made for the separation of silver and copper ions using the hard-soft, acid-base (HSAB) principle as the design guideline. NH2-MCM-41 containing "hard" Lewis base adsorption sites (i.e., RNH2) was prepared for the adsorption of the "hard" Lewis acid, Cu2+, and SH-MCM-41 with a grafted "soft" thiolpropyl base was prepared for the selective removal of Ag+, a "soft" Lewis acid. Single- and binary-component adsorption studies were conducted at different metal concentrations, solution compositions, and pH values. The experimental results showed that SH-MCM-41 has excellent affinity and capacity for silver adsorption and adsorbed only the silver ions with copper remaining in the solution. The selectivity was not affected by the metal concentration and composition, anion, and pH. Under similar experimental conditions, NH2-MCM-41 selectively adsorbed copper from the binary solution. The selectivity of NH2-MCM-41 remained for the copper at different pH values, although the adsorption capacity diminished at lower pH values. The type of anions used affected copper adsorption on NH2-MCM-41 with an increased copper uptake in the presence of the sulfate ions. A simple Freundlich adsorption model was sufficient to describe metal adsorption on SH-MCM-41 and NH2-MCM-41, and the LeVan and Vermeulen model was successfully used to predict the adsorption capacity and selectivity for binary-component adsorptions.     

Adsorption of anions on ultra-thin metal deposits on single-crystal electrodes: II: Voltammetric and radiochemical study of bisulfate adsorption on Pt(111) and Pt(poly) electrodes containing copper adatoms

The formation of ultra-thin metal deposits of copper on Pt(111) and polycrystalline platinum electrodes, as well as the adsorption of bisulfate on the copper-covered platinum surfaces, were studied by cyclic voltammetry and radioactive labeling. The highest charge obtained by voltammetry in the underpotential stripping range nearly corresponds to a close-packed monolayer of copper. The radioactive labeling data indicate that there are inactive and active copper adlayers toward bisulfate adsorption. The transition from inactive to active behavior is interpreted in terms of an increase in surface—bisulfate interactions at the expense of surface—perchlorate interactions. Based on recent X-ray absorption near-edge spectroscopy (XANES) analysis of copper deposition onto platinum, the site for bisulfate adsorption is most probably a Cu⁺ surface species. Combining this spectroscopic information with coulometry shows that an additional electron is confined to surface platinum atom(s) covered by the copper species. The copper film attains bulk copper properties when approximately 2.5 monolayers of copper are deposited.     

Effect of sulfate ion adsorption on the rate of copper electrocrystallization on Ag(111) face

The process of copper electrocrystallization on the Ag(111) face was studied in acidic perchlorate-sulfate electrolytes. Enhanced rate of charge transfer in the course of nucleation and growth of epitaxial copper crystallites was observed in the solutions with additives of sulfate ion as a result of local electrostatic effects under specific adsorption of anions. Copper nucleation parameters were estimated in the framework of the diffusion models and atomistic theory of electrochemical nucleation.     

Zeolite ZSM-5 containing copper ions: The effect of the copper salt anion and NH<Subscript>4</Subscript>OH/Cu<Superscript>2+</Superscript> ratio on the state of the copper ions and on the reactivity of the zeolite in DeNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N₂O decomposition. The amount of Cu²⁺ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu²⁺ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO _x ) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO _x properties of Cu-ZSM-5 depend considerably on the NH₄OH/Cu²⁺ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH₄OH/Cu²⁺ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu²⁺ ions bonded with extraframework oxygen, which are more active in DeNO _x than isolated Cu²⁺ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH₄OH/Cu²⁺ = 3).     

Influence of Two-step Mechanism of Dissociation of H2SO4 on the Limiting Cathodic Current of Copper Deposition from Sulfate Solutions in Conditions of Natural Convection

The limiting cathodic current of copper deposition at a flat vertical electrode from solutions containing a mixture of copper sulfate and sulfuric acid (in excess) in conditions of natural convection is calculated. The possibility of the two-step dissociation of sulfuric acid is accounted for. The obtained formulas yield the limiting cathodic current at any ratio of bisulfate and sulfate anions in solution.     

Photoelectron spectroscopic studies of the adsorption of CO and CO2 on nickel,platinum and copper

The adsorption of CO and CO₂ on platinum, nickel and copper was studied by X-ray and UV photoelectron spectroscopy. The results indicate that CO₂ is physisorbed on platinum and copper and that the bonding of CO on all three metals involves the metal d-electrons and particularly the 5σ level of CO. It is suggested that the energy required to promote a copper d-electron to an unfilled level above the Fermi energy is responsible for the small heat of adsorption of CO on copper.     

Electrolyte Anion Affinity and Its Effect on Oxyanion Adsorption on Goethite

The influence of various types of background electrolytes (NaCl, NaNO(3), and NaClO(4)) on the proton adsorption and on the adsorption of sulfate and phosphate on goethite have been studied. Below the PZC the proton adsorption on goethite decreases in the order Cl>NO(3)>ClO(4). The decreasing proton adsorption affects the adsorption of oxyanions on goethite. Anion adsorption of strongly binding polyvalent anions is lower in the studied electrolytes in the order Cl相似文献   

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.     

Application of the Radiotracer Technique for the Study of the Specific Anion Adsorption on Al(2)O(3) in Acidic Medium

The specific adsorption of radiolabeled anions (sulfate, chloride) from perchlorate supporting electrolyte on gamma-Al(2)O(3) powder has been investigated. It was demonstrated that a measurable adsorption occurs only at pH values under pH 6. The adsorption capacity of a given amount of gamma-Al(2)O(3) powder tends to a limiting value with decreasing pH. A Langmuir-like adsorption isotherm describes the concentration dependence of the adsorption of sulfate species. It was found that the experimental results are very similar to those obtained in the case of hematite. Copyright 2000 Academic Press.     

Adsorption Studies of Copper Sulfate on Hydrogels of Poly(Amido-Amines)

Abstract

The interaction between the active groups of polymeric gels of poly(amido-amines) such as poly(acrylamide-diallyldiethyl ammonium chloride) “cationic gel p(AM-DADEAmCl)” and poly(acrylamide-sodium acrylate-diallyldiethyl ammonium chloride) “amphoteric gel p(AM-AANa-DADEAmCl” with copper sulfate have been carried out by using polymeric gels of different swelling degree and different amine percent.

The capacity toward cations decreases with increasing the amine percent and the swelling degree but the capacity toward anions such as (SO₄₎ ^2- decreases with increasing swelling degree and increases with increasing the amine percent. These polymeric gels interact with copper sulfate at pH value >5 to form a crosslinked structures. Spectroscopic studies showed that the mechanism of crosslinking formation is a bond formation between the active group of polymeric chains and copper sulfate. The bond formation depends on the nature of the polymer chain. It was also found that the amide groups form complexes with hydrated cations, while both carboxylate and ammonium groups interact by ion-exchange mechanisms.     

Parameters of the double electric layer and n-butanol adsorption on lead in methanesulfonate solutions

A differential capacity measurement showed that the zero charge potential of a lead electrode in a sodium methanesulfonate solution was ?0.69 V. Like sulfate anions, methanesulfonate anions had low specific adsorbability on lead. The adsorption of n-butanol from a methanesulfonate electrolyte on a lead electrode was approximated by the Frumkin isotherm equation. The parameters of n-butanol adsorption in a methanesulfonate solution were close to those reported for fluoride and sulfate solutions in the literature.     

Electrochemical nanogravimetric studies of platinum in acid media

Electrochemical quartz crystal nanobalance (EQCN) is one of the most powerful tools to obtain information on the events occurring at the electrode surface. This method has been exploited to monitor the surface mass changes and hence to draw conclusions in respect of the formation and removal of adsorbed species and oxides as well as changes in the electrochemical double layer also in the case of platinum electrodes. However, the results that had been obtained so far are somewhat contradictory, and consequently diverse interpretations can be found in the literature. Therefore, it is worth to review the knowledge accumulated and to carry out systematic study in this respect. In this work smooth and platinized platinum electrodes in contact with acidic solutions were studied using EQCN technique. The effects of temperature, the nature of cations and anions, pH, concentrations, potential range were investigated on the electrochemical, and the simultaneously detected nanogravimetric responses. It is shown that in the underpotential deposition (upd) of hydrogen the adsorption/desorption of species from the solution phase is governed by the oxidative desorption/reductive adsorption of hydrogen; however, unambiguos conclusions cannot be drawn regarding the actual participation of anions and water molecules in the surface coverage. In the hydrogen evolution region a weak cation adsorption can be assumed and the potential of zero charge can be estimated. Cs⁺ cations affect the EQCN response in the hydrogen upd region. In some cases, e.g., in the case of upd of zinc the mass change can be explained by an induced anion adsorption. Two types of dissolution processes have been observed. A platinum loss was detected during the reduction of platinum oxide, the extent of which depends on the positive potential limit and the scan rate, and to a lesser extent on the temperature. The platinum dissolution during the electroreduction of oxide is related to the interfacial place exchange of the oxygen and platinum atoms in the oxide region. At elevated temperatures two competitive processes take place at high positive potentials: a dissolution of platinum and platinum oxide formation.     

Study of copper sulfide crystallization in PEO-SDS solutions

The crystallization of copper sulfide in aqueous supersaturated solutions in the presence of the polymer poly(ethylene oxide), PEO, and the surfactant sodium dodecyl sulfate, SDS, was investigated. In these systems, copper sulfide precipitation competes with the reaction between copper cations and dodecyl sulfate anions. The competition of the two reactions may affect the reaction products significantly; therefore it is important to study the properties of the surfactant salt, copper dodecyl sulfate (Cu(DS)2), in detail. The thermodynamic solubility constant of Cu(DS)2 was measured at 8 degrees C and was equal to (2.4 +/- 0.4) x 10(-10) M3. The Krafft point of Cu(DS)2 and its solubility curve (precipitation temperature for a range of concentrations) were also measured. The latter was found to be very close to room temperature. Temperature is thus a very significant parameter in these systems and must be carefully controlled in all experiments. The crystallization of copper sulfide in PEO-SDS solutions was investigated in solutions with compositions above and below the solubility curve. Copper sulfide nanoparticles predominate and are stabilized at temperatures above the solubility curve. Surprisingly, at temperatures below the solubility curve CuxS coexists with Cu(DS)2, which appears in the form of lamellar crystals. The system is further complicated by the presence of at least two different types of copper sulfides corresponding to different oxidation states of copper. Our results suggest that the predominance of Cu(DS)2 at lower temperatures is due to its limited solubility and is modified by the CuI/CuII redox equilibrium in combination with the solution pH.     

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.     

Surface and Subsurface Oxygen on Platinum in a Copper Perchlorate Solution

The formation of an adatom layer on polycrystalline platinum and the three-dimensional nucleation of copper in a copper perchlorate solution are studied by cyclic voltammetry at 0.1 V s^–1 while varying potential ranges and by recording potentiostatic current transients. About 0.6 monolayers of copper adatoms are deposited when cycling with anodic limit E _a = 1.35 V, the process is slower than that in an acid sulfate solution. Decreasing E _a accelerates the process (nearly one monolayer forms for E _a = 0.80–0.95 V in a cathodic scan) due to an increased number of active centers (metastable copper oxides) and, probably, to a change in the platinum surface microstructure. Oxygen for copper oxides is presumably supplied by water molecules adsorbed on a monolayer of copper adsorbed atoms and by subsurface oxygen (O_ss), which appears on the platinum surface after the destruction of complexes O_ss–Pt _n –ClO₄. Both the copper nucleation and the deposit growth accelerate at higher concentrations of copper oxides, which form at low E _a. High cathodic overvoltages decrease the number of active crystallization centers due to reduction or removal of copper oxides.