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.     

Initial stages of copper electrocrystallization on polycrystalline platinum and glassy carbon in the presence of acetonitrile

The kinetics of formation of copper adlayer, three-dimensional nucleation, and the deposit growth on polycrystalline platinum and glassy carbon in the 0.5 M H₂SO₄ + 10 mM CuSO₄ + (0–2) M acetonitrile (AcN) solutions at the cathodic overvoltages is studied using the methods of cyclic voltammetry and potentiostatic current transients on a ring-disc electrode. At [AcN] = 2 M, the process of formation of copper adatoms on platinum is significantly retarded. In the solutions with high contents of AcN, the processes of Cu⁺ ion production, the formation of their complexes with acetonitrile, hydrogen evolution, copper nucleation, and the deposit growth proceed in parallel. The contribution of any process to the overall current depends on the amount of adsorbed AcN at the surface of substrate and copper deposit and on the electrode potential. At [AcN] = 2 M, an increase in the cathodic overvoltage to 0.32 V leads to an abnormal increase in the current of Cu⁺ ion production on platinum, which is caused by insufficiently rapid formation of copper atoms in the reduction of Cu⁺(AcN) _x complexes.     

Stripping voltammetry with collection at a rotating ring-disk electrode

A new electroanalytical technique is described, called "stripping voltammetry with collection." The technique involves the use of a rotating ring-disk electrode and is an improvement over traditional voltammetric stripping at a single electrode in that it is characterized by a lower limit of detection and that the period of deposition before stripping can be shorter. The use of the technique is illustrated by the determination of 10(-10)M Ag(+) in 0.1 M H(2)SO(4) by use of a ring-disk electrode having a disk electrode constructed of glassy carbon and a ring electrode constructed of platinum.     

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.     

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.     

Cyclic voltammetry at microelectrodes in the absence of added electrolyte using a platinum quasi-reference electrode

The cyclic voltammetric behaviour of the ferrocene/ferricinium (Fc/Fc⁺) couple has been examined in acetonitrile without deliberately added electrolyte using scan rates over the range 5 mV/s to 50 V/s. Platinum (0.5 μm, 2.5 μm and 25 μm radius) and gold (5 μm radius) microelectrodes were used as working electrodes, with platinum wire quasi-reference electrodes to minimize contamination. At slow scan rates (5 to 500 mV/s) sigmoidal shaped steady state voltammograms were generally observed on the forward (oxidative) scan as is the case with electrolyte. Reverse (reductive) scans were not strictly sigmoidal and exhibited small peaks. This phenomenon is not observed in the presence of electrolyte and is attributed to ionic migration of the Fc⁺ cation. With a two electrode configuration, employing a platinum wire quasi-reference electrode, the forward and reverse scans of cyclic voltammograms were not superimposed at low scan rates unless small radii and low ferrocene concentrations are used. This distortion may be attributed to polarization of the reference electrode. Use of a three electrode platinum configuration, in a potentiostatic model while increasing the noise level, decreases this problem. At fast scan rates in excess of 1 V/s, planar diffusion terms are apparent. Additionally, iR (ohmic) distortions are considerable and are enhanced as the electrode radius and ferrocene concentration increase. Despite this problem, which mitigates against obtaining reliable thermodynamic data or assessment of electrochemical reversibility, the important diagnostic criterion of the presence of chemical reversibility or otherwise of an electrode process can still be clearly ascertained at fast scan rates, since the reduction current arising from the presence of the Fc⁺ ion in the reverse scan is observed, as is the case in the presence of electrolyte.     

Cyclic voltammetry and electrochemical quartz crystal microbalance studies of a rhodized platinum electrode in sulfuric acid solution

The adsorption properties of a rhodized platinum electrode in sulfuric acid were studied through simultaneous cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) measurements. The processes occurring at the Rh surface during the potential scan between 0.04 and 1.3 V were analyzed in terms of the changes in mass and charge. The apparent molar masses of the species adsorbed on Rh in different potential regions were determined from the mass–charge correlation. The results obtained suggest that the desorption of hydrogen UPD initially occurs in conjunction with the incorporation of mass due to the adsorption of bisulfate/sulfate ions between 0.04 V and 0.12 V; the apparent molar mass (M ₁) in this potential region is consistent with that of bisulfate ion, assuming that one sulfate species occupies the site originally occupied by five H atoms. Between 0.12 V and 0.20 V, the apparent molar mass, M ₂, is less than M ₁. This result may be associated with a structural rearrangement of the adsorbed sulfate species. The apparent molar mass, M ₃, was determined in the potential region of 0.20–0.56 V; the value obtained for M ₃ suggests that the adsorbed species are hydrated bisulfate ions (HSO₄⁻·4H₂O). Additionally, it was found that Rh oxides formed at the surface between 0.56 V and 1.3 V could not be directly identified from the correlation between charge and mass.     

Electrooxidation of vanillyl alcohol in acidic aqueous solution using rotating ring-disk electrode voltammetry.

The electrooxidation of benzylic alcohol derivative in acidic aqueous solution shows an oxidation pre-peak in the cyclic voltammogram, which means that the reaction is proceeding via an ECE mechanism where the second electron transfer occurs at a less positive potential. From the result of the rotating ring-disk electrode voltammetry, the initial oxidation response of the electrode reaction can be extracted.     

Cyclic voltammetry of copper in sodium hydroxide solutions

The cyclic voltammograms of the Cu electrode were, obtained in NaOH solution as a function of the voltage scanning rate, electrolyte concentration and voltage range. A correlation was made between three well-defined anodic peaks and their corresponding cathodic ones. The anodic peaks were found to correspond successively to the formation of a monolayer of Cu₂O, formation of a thick multilayer film of CuO and finally Cu₂O₃ upon which O₂ is evolved. It is suggested that CuO is formed from the oxidation of Cu₂O and/or direct oxidation of metallic copper.Below 0.1 M NaOH the ratio of anodic to cathodic charges was found to be about unity, indicating the quantitative reduction of solid oxidation products, while at higher alkali concentrations higher charge ratios were obtained due to increasing proportions of soluble reaction products.The behaviour of the copper electrode in NaOH was found to be quite complicated. Thus, no simple relations were found between the voltage scanning rate and both the peak current and peak potential or between the peak current and the alkali, concentration. Further work is needed to obtain a definitive explanation of this behaviour.     

Initial stages of copper electrodeposition from acidic sulfate solution in the presence of alklpyridinium hydrosulfate ionic liquids

The effect of two alklpyridinium hydrosulfate based ionic liquids(ILs)including N-butylpyridinium hydrogen sulfate(BpyHSO4)and N-hexylpyridinium hydrogen sulfate(HpyHSO4)as additives on the nucleation and growth of copper from acidic sulfate bath was investigated using cyclic voltammetry,chronoamperometric and scanning electron microscopy techniques.Results from cyclic voltammetry indicated that the two studied additives had a blocking effect on copper electrodeposition process and this effect initiated by HpyHSO4was more pronounced in comparison to BpyHSO4.Dimensionless chronoamperometric current-time transients for the electrodeposition of copper from the bath free of additives were in good accord with the theoretical transients for the limiting case of instantaneous three-dimensional nucleation with diffusion-controlled growth of the nuclei.However,the instantaneous nucleation mechanism observed in the additive-free bath was changed to a more progressive one when additives were present in the bath.Surface morphology analysis indicated that alklpyridinium hydrosulfate ILs can induce the formation of leveled and finer grained deposits by the adsorption of additive at the first stages of deposition process,leading to decrease of the nucleation and growth rate of nuclei.     

铋膜电极伏安法测定硫酸软骨素

硫酸软骨素是一种天然酸性粘多糖,属生物高分子化合物,其结构如下图所示.硫酸软骨素具有许多重要的生理活性和药理作用,如促进冠状动脉循环、降血脂、抗凝血、抗肿瘤和防止血管硬化等[1,2].     

Electrochemical reactions at a copper electrode in copper-conducting solid electrolytes

Potentiostatic measurements are used to show that, depending on the overvoltage sign, either electrochemical deposition or dissolution of copper occurs at the Cu/Cu₄RbCl₃I₂ interface at overvoltages η > 8–10 mV. At η = 10–100 mV, the reaction rate is limited by the formation and expansion of dissolution centers at the copper surface during anodic polarization and crystallization centers, during cathodic polarization. At η > 120 mV, the reaction rate is limited by charge transfer; the exchange current density is 2.7 mA cm^?2 and the anodic transfer coefficient is ～0.45. Under anodic polarization, formation of electron holes in the electrolyte occurs in parallel with the copper anodic dissolution. Therefore, nonstoichiometry of the electrolyte emerges in the near-electrode layer and divalent copper accumulates there.     

Cyclic voltammetry of Tifluadom at a C18-modified carbon-paste electrode

Tifluadom, N-[5-(2-fluorophenyl)-2,3-dihydro-methyl-1H-1,4-benzodiazepine]-2-4-methyl-3-thiophene carboxamide, was determined by using a carbon-paste electrode modified with C₁₈ μBondapak. Adsorption on the electrode served as a preconcentration step which improved the limit of detection. Preconcentration for 5 min (open circuit) gave a linear range of 2.2×10^?7 M?4.5×10^?6 M with a detection limit of 1.3×10^?7 M (%C₁₈=25, w/w) for Tifluadom in Britton-Robinson buffer pH 6. The determination of Tifluadom added to urine required no preliminary treatment; the detection limit was 1.3×10^?6 M.     

Differential-pulse anodic stripping voltammetry of copper with a chemically-modified glassy carbon electrode

Copper at the low or fractional ng g^?1 level in 0.1 M oxalic acid solutions at pH 1.6 is electrodeposited on a chemically-modified glassy carbon electrode with surface-bound

groups at ?0.6 V vs. Ag/AgCl (3.3 M KCl). The deposit is then anodically stripped in the same solution, a current-potential curve being recorded by the differential-pulse technique. The advantages of this electrode over an unmodified glassy carbon electrode include higher sensitivity, precision and selectivity; the modified electrode can be used 50–100 times without further treatment.     

Electrochemical processes on the copper electrode in water-ethanol solutions of copper sulfate

The system Cu/H₂O-C₂H₅OH-CuSO₄ was studied in a wide range of organic component concentrations by the impedance spectroscopy method. In the studied range of ethanol concentrations the diffusion of ions to an electrode is the limiting stage of the electrode process. An increase in the ethanol concentration results in a decrease in the double electrical layer capacity, which is caused by a change in the double electrical layer structure at the electrode-solution boundary.     

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.     

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.