Copper chloride modified copper electrode: Application to electrocatalytic oxidation of methanol

Copper chloride modified copper (CCMC) electrode was prepared as a new electrode. For the preparation of the modified electrode, the polished copper electrode was placed in 0.1 M CuCl₂ solution for 20 s. In this step, a layer of copper (I) chloride was formed at the surface of copper electrode. Then, the electrode was placed in 0.1 M NaOH and the electrode potential was cycled between −250 and 1000 mV (vs. SCE) at a scan rate of 50 mV s⁻¹ for 5 cycles in a cyclic voltammetry regime until a featureless voltammogram was obtained. Surface physical characteristics of the modified electrode were studied by scanning electron micrographs (SEM). Results showed that considerable amounts of microcrystals have been formed on the copper surface during the modification. Surface elemental analysis of electrode were performed by energy dispersive X-ray (EDX) technique. The results showed that in addition to copper and chloride elements, there is also oxygen at the surface of CCMC electrode. This indicates that a layer of (ClCu)₂O was formed at the surface of the modified electrode. The electrocatalytic activity of the modified electrode for the oxidation of methanol, in aqueous basic solution was studied by using cyclic voltammetry. Results showed that, copper chloride modified electrode can improve the activity of Cu towards the oxidation of this small organic molecule, showing the possibility of attaining good electrocatalytic anodes for fuel cells. The modified electrode shows a stable and linear response in the concentration range of 5 × 10⁻³ to 8 × 10⁻² M with a correlation coefficient of 0.9958.     

Synthesis of porous and nanostructured particles of CuO via a copper oxalate route

CuO have potential applications in various fields, such as gas sensors, solar energy and catalysis. With the aim of trying to obtain CuO with a high specific surface area, an oxalate precipitation route followed by thermal decomposition was studied. Four different copper salts (nitrate, sulfate, chloride, and acetate) were precipitated with sodium oxalate to form copper oxalate, before being decomposed at 275 °C into copper oxide. The different reagent salts all gave very high specific surface areas (> 70 m²/g) with slight differences in the copper oxide morphology. The effect of the initial reagent concentration had a more significant effect on morphology and surface area; cushions were obtained at low concentrations (0.02 M), and spheres at high concentrations (0.10 M with surface areas < 20 m²/g). Also the use of hydroxypropylmethylcellulose (HPMC) gave the expected cubic morphology previously shown due to specific adsorption of the polymer onto the growing crystal. The low specific surface area measured for samples synthesized at high concentration of reagent was related to a significant amount of a secondary phase Cu₂O obtained after thermal decomposition, attributed to local inhomogeneities in the precipitated oxalate due to increased precipitation kinetics at the higher concentrations. Finally a very small amount of copper carbonate could be identified by FTIR which did not affect the main powder characteristic (S_BET), but helped validate the precipitation mechanism predicted by a previous thermodynamic study.     

Development of highly sensitive non-enzymatic sensor for the selective determination of glucose and fabrication of a working model

Copper oxide (CuO)/copper oxalate (CuOx) modified non-enzymatic electrochemical sensor for the detection of glucose in alkaline medium was fabricated by electrochemical anodisation of copper electrodes in potassium oxalate solution. Morphology of the modified copper electrode was studied by Scanning Electron Microscopy (SEM) and its electrochemical behaviour by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The formation of CuOx on the copper electrode was confirmed by the Infra-red Reflection Absorption Spectrum (IRRAS). The modified electrodes were found to be microporous and rough. Linear Sweep Voltammetry (LSV) and amperometry were adopted to investigate the direct electrocatalytic oxidation of glucose on CuO/CuOx modified electrode in alkaline medium which showed excellent catalytic activity. The best performance of the sensor was obtained at 0.7 V and in 0.1 M sodium hydroxide (NaOH). At this optimum potential, the sensor was highly selective to glucose in the presence of ascorbic acid (AA) and uric acid (UA) which are common interfering species in biological fluids. The sensitivity was found to be very high (1890 μA mM⁻¹ cm⁻²) with excellent linearity (R = 0.9999) up to 15 mM having a low detection limit of 0.05 μM (S/N = 3). The modified electrode was tested for glucose level in blood serum. Based on the optimised conditions, a working model of the sensor was made and successfully tested for glucose.     

Effect of plating mode, thiourea and chloride on the morphology of copper deposits produced in acidic sulphate solutions

The influence of plating mode, chloride and thiourea (TU) on morphology of copper deposits has been studied. All experiments were conducted on disc electrodes rotating at 500 rpm and an average current density of 4 A dm⁻² to produce 10 μm thick deposits. In additive-free solutions, the use of pulsed current (PC) improved deposit morphology and brightness over DC plating. In the presence of thiourea (no Cl⁻), the deposits obtained by DC and PC plating were similar under most plating conditions. The presence of thiourea generally improved deposit quality over that obtained in additive-free solutions, but caused the formation of microscopic nodules and the deposits to appear slightly cloudy, resulting in lower reflectances than that of a polished uncoated copper surface. The addition of Cl⁻ to thiourea-containing solutions strongly influenced deposit morphology at both microscopic and macroscopic scales depending on chloride concentration and pulse conditions. It prevented nodule formation and created microscopically bright and reflective deposits, but caused extreme macroscopic roughness. Nevertheless, PC plating at 50 Hz in solutions containing appropriate amounts of thiourea and Cl⁻ was found to yield macroscopically and microscopically smooth deposits with reflectance similar to that of a polished uncoated copper substrate.     

Electrochemical and surface analytical studies of the self-assembled monolayer of 5-methoxy-2-(octadecylthio)benzimidazole in corrosion protection of copper

5-Methoxy-2-(octadecylthio)benzimidazole (MOTBI) monolayer was self-assembled on fresh copper surface obtained after etching with nitric acid at ambient temperature. The optimum conditions for formation of self-assembled monolayer (SAM) were established using impedance studies. The optimum conditions are methanol as solvent, 10 mM concentration of the organic molecule and an immersion period of 24 h. The MOTBI SAM on copper surface was characterized by contact angle measurements, X-ray photoelectron spectroscopy and reflection absorption FTIR spectroscopy and it is inferred that chemisorption of MOTBI on copper surface is through nitrogen. Corrosion protection ability of MOTBI SAM was evaluated in aqueous NaCl solution using impedance, electrochemical quartz crystal nanobalance, potentiodynamic polarization and weight-loss studies. While bare copper showed a charge-transfer resistance (R_ct) value of 1.89 kΩ cm² in 0.20 M NaCl aqueous environment, the R_ct value for SAM covered copper surface is 123.4 kΩ cm². The MOTBI SAM on copper afforded corrosion inhibition efficiency of 98-99% in NaCl solution in the concentration range and in the temperature range studied. The SAM functions as a cathodic inhibitor. Quantum chemical calculations showed that MOTBI has relatively small ΔE between HOMO and LUMO and large negative charge in its benzimidazole ring, which facilitate formation of a polymeric [Cu⁺-MOTBI] complex on copper surface.     

Hydrometallurgical process for the recycling of copper using anodic oxidation of cuprous ammine complexes and flow-through electrolysis

Flow-through electrolysis for copper electrowinning from cuprous ammine complex was studied in order to develop a hydrometallurgical copper recycling process using an ammoniacal chloride solution, focusing on the anodic oxidation of cuprous to cupric ammine complexes. The current efficiency of this anodic oxidation was 96% at a current density of 200 A m⁻² under a batch condition. In a flow-through electrolysis using a sub-liter cell and a carbon felt anode, the anodic current efficiency increased with the flow rate and was typically higher than 97%. This tendency was explained by the backward flow of the cupric ammine complex, which was formed on the anode, through the diaphragm. The anodic overpotential was lower than 0.3 V even at an apparent current density of 1500 A m⁻². A similar current efficiency and overpotential were also achieved in a liter scale cell, which indicates the scale flexibility of this electrolysis. The power consumption requirements for copper electrowinning in this cell were 460 and 770 kWh t⁻¹ at the current densities of 250 and 500 A m⁻², respectively, which were much lower than that of the conventional copper electrowinning despite the longer interpolar distance.     

The influence of 2,2′-dipyridyl on non-formaldehyde electroless copper plating

High electroless copper deposition rates can be achieved using hypophosphite as the reducing agent. However, the high deposition rate also results in dark deposits. In the hypophosphite baths, nickel ions (0.0057 M with Ni²⁺/Cu²⁺ mole ratio 0.14) were used to catalyze hypophosphite oxidation. In this study, additives (e.g. 2,2′-dipyridyl) were investigated to improve the microstructure and properties of the copper deposits in the hypophosphite (non-formaldehyde) baths. The influence of 2,2′-dipyridyl on the deposit composition, structure, properties, and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The electroless deposition rate decreased with the addition of 2,2′-dipyridyl to the plating solution and the color of the deposits changed from dark brown to a semi-bright with improved uniformity. The deposits also had smaller crystallite size and higher (1 1 1) plane orientation with the use of 2,2′-dipyridyl. The resistivity and nickel content of the deposit were not affected by 2,2′-dipyridyl additions to the bath. The electrochemical current-voltage results show that 2,2′-dipyridyl inhibits the catalytic oxidation of hypophosphite at the active nickel site. This results in a more negative electroless deposition potential and lower deposition rate.     

Hydrodynamic effects on the performance of an electrochemical reactor for destruction of copper cyanide. Part 2—reactor kinetics and current efficiencies

An electrochemical reactor, with stainless-steel electrodes, was used for treatment of a wastewater containing dilute copper(I) cyanide. Both anodic cyanide oxidation and cathodic copper(I) reduction could be operated under mass transport control, when reactions rates and current efficiencies were influenced by hydrodynamic conditions created by pumping and gas sparging, used to enhance reactor performance. Pumping promoted the rate of Cu electrodeposition to a greater extent than sparging with compressed air, whereas the latter slightly enhanced the rate of cyanide destruction. A hypothesis of cathodic O₂ reduction generating oxidising species, which react homogeneously with cyanide, was verified experimentally. The specific electric energy consumption, calculated for typical values of current densities and current efficiencies, were 0.34 kWh mol^-1 Cu and 0.24 kWh mol^-1 CN^-).     

Preparation of environmental friendly coatings based on natural shellac modified by diamine and its applications for copper protection

An environmental friendly coating based on natural product—shellac was prepared by using aliphatic diamine as a crosslinking agent and ethanol as a solvent. The amide group appeared in FTIR spectra in the modified shellac structure suggested the 1,3-propanediamine could successfully react with the acid groups in shellac. The enhancement in anticorrosive performance of the modified shellac could be observed directly from the color changes of the surface images of copper, copper coated with shellac and modified shellac after 60 h salt spray test. The EIS results indicated that after 24 h immersion in 0.5 M NaCl solution, the ionic Cl⁻ and water had reached the copper electrode and the shellac lost its protection to copper. However, the corrosive behavior of the copper electrode coated with modified shellac immersed in 0.5 M NaCl solution for 24 h still showed a characteristic of middle period of immersion and the coating layer hindered the ionic and water penetrating onto the surface of the copper; while after 72 h immersion, the modified shellac began to lose its protection to copper. The improvement in anticorrosive performance of modified shellac was attributed to the formation of network structure and the introduction of hydrophobic aliphatic group in shellac structure, which slowed down the speed of the ionic and water moving onto the copper surface.     

Mass transport studies at rotating cylinder electrode: Influence of the inter-electrode gap

This study shows the effect of using two different inter-electrode gaps on the RCE mass transport characterization. The average mass transport coefficient was calculated using the limiting current technique, using the soluble reduction of triiodide (smooth RCE interface) and the copper deposition (roughness RCE interface) in KNO₃ and H₂SO₄, respectively. Based on the analysis of the Sh = aRe^bSc^0.356 correlation, the values of the constant a, associated with shape and cell dimensions, were 0.89 and 3.8, in the soluble system (I₃⁻/I⁻), for the gaps of 2.4 and 3.2 cm, respectively, indicating that this coefficient increases with inter-electrode space. While for copper deposition, these values were 0.00081 and 0.014, for the gaps of 2.4 and 3.2 cm. The constant b, associated with hydrodynamic regime, exhibits values of 0.43 and 0.33 for the gaps of 2.4 and 3.2 cm, respectively, in the system I₃⁻/I⁻, indicating that hydrodynamics on the smooth RCE diminishes according to the inter-electrode space. While for the system (Cu(II)/Cu), the values of b were 0.91 and 0.88, for the gaps of 2.4 and 3.2 cm. These values were higher for the copper deposition than for the soluble system, due to microturbulence at the roughened (and often powdery deposits) RCE interface. From the analysis performed in this paper is clear that inter-electrode gap and hydrodynamics on the smooth and roughness RCE interface (given by the nature of reduction reaction) modify the mass transport correlation.     

Formation and electrochemical performance of copper/carbon composite nanofibers

Copper-loaded carbon nanofibers are fabricated by thermally treating electrospun Cu(CH₃COO)₂/polyacrylonitrile nanofibers and utilized as an energy-storage material for rechargeable lithium-ion batteries. These composite nanofibers deliver more than 400 mA g⁻¹ reversible capacities at 50 and 100 mA g⁻¹ current densities and also maintain clear fibrous morphology and good structural integrity after 50 charge/discharge cycles. The relatively high capacity and good cycling performance of these composite nanofibers, stemmed from the integrated combination of metallic copper and disordered carbon as well as their unique textures and surface properties, make them a promising electrode candidate for next-generation lithium-ion batteries.     

Overpotential deposition of copper on an iodine-modified Au(1 1 1) electrode

Cyclic voltammetry, chronoamperometry and in situ electrochemical scanning tunneling microscopy were used to study the kinetics of nucleation and crystal growth during the initial stages of copper overpotential deposition (OPD) on a previously iodine-modified Au(1 1 1) electrode, from an aqueous solution 10⁻³ M CuSO₄ in 0.05 M H₂SO₄. The starting potential during step experiments was chosen in the region where the gold electrode was completely free of the copper deposit. The recorded current transients for copper deposition onto the iodine-modified Au(1 1 1) electrode surface appear to be very complex, with the unusual presence of two or more current maxima. A new method was used for quantitative evaluation of current transients that involves the transition UPD-OPD, developed by our group [M. Palomar-Pardavé, I. González, N. Batina, J. Phys. Chem. B 104 (2000) 3545], was used for the quantitative interpretation. Our results show that, within a single current transient, copper adsorption and two types of nucleation process: two-dimensional (2D) and three-dimensional (3D) limited by lattice incorporation of copper adatoms and diffusion of Cu(II) ion, respectively, take place simultaneously. STM images revealed the enhanced growth of 3D copper on edge of I-Au(1 1 1) during the early stages of deposition. Moreover, our results strongly suggest that the iodine adlayer is constantly present, even after the striping Cu that was overpotential deposited.     

Oxygen and hydrogen peroxide reduction catalyses in neutral aqueous media using copper ion loaded glassy carbon electrode electrolyzed in ammonium carbamate solution

An aminated glassy carbon electrode (AGCE) can be obtained by the electrode oxidation of glassy carbon electrode in ammonium carbamate solution. In the cyclic voltammetric experiments, the electrode reduction of the dissolved oxygen began from −0.15 V vs. Ag/AgCl in neutral aqueous media when the aminated glassy carbon electrode was used as a working electrode although it began from −0.40 V vs. Ag/AgCl when a polished GCE was used. The nitrogen containing groups introduced by the electrode oxidation of carbamic acid must be related with the acceleration of the electron transfer rate of oxygen. Moreover, the new reduction wave of the dissolved oxygen appeared at +0.15 V vs. Ag/AgCl when copper (II) ion was coordinated to AGCE surface. This reduction potential of oxygen coincided with that of copper (II) ion and this fact suggests that the coordinated copper ion to the aminated carbon surface works as a redox mediator of oxygen. The reduction product of oxygen was monitored by rotating platinum ring - aminated glassy carbon disk electrode, and it was found that most of oxygen was reduced to water in a potential range negative than −0.4 V vs. Ag/AgCl. By using AGCE, it was recognized that the catalytic reduction of hydrogen peroxide was also taken place as well as oxygen reduction.     

Potassium sorbate as an inhibitor in copper chemical mechanical planarization slurries. Part II: Effects of sorbate on chemical mechanical planarization performance

This study reports on the effects of potassium sorbate (K[CH₃(CH)₄CO₂]) on copper chemical mechanical planarization (CMP) performance and demonstrates how the performance can be controlled by the inhibitor concentration in the slurry. The study is a continuation of a recent report on the copper polishing mechanism in H₂O₂/glycine-based slurries using sorbate as an inhibitor. CMP performance with respect to the inhibitor concentration in the slurry is evaluated in terms of surface roughness, polishing uniformity and dishing values. CMP results obtained from blanket wafers show that an increased sorbate concentration provides lower roughness values. CMP data obtained from patterned wafers shows that an increased sorbate concentration provides better polishing uniformity and lower dishing values for copper lines. The high solubility of sorbate in water (up to 9 M) is a major advantage for CMP processing.     

Influence of 8-aminoquinoline on the corrosion behaviour of copper in 0.1 M NaCl

The corrosion behaviour of copper in aerated 0.1 M NaCl solution in presence of 8-aminoquinoline (8-AQ), using open circuit potential (OCP) measurements, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) measurements and atomic force microscopy (AFM), was studied. The measurements revealed that the effect of 8-AQ is dependent on its concentration. For concentrations up to 10⁻³ M, the organic compound displaces the corrosion potential following no trend and also reduces the anodic current. In contrast, for concentrations higher than 10⁻³, 8-AQ reduces markedly both, the anodic and cathodic currents and consequently, the corrosion current density of copper. After 9 days of exposure in chloride solution, containing the organic compound, potentiodynamic polarization analyses showed a significant reduction in the anodic response and a less significant reduction in the cathodic response, which is associated with a film formed at the copper surface of about 10 μm in thickness and visually observed by a colour change of the copper surface.In order to elucidate the most likely interaction between the 8-AQ molecule and the different molecular structures probably present on copper surfaces in chloride solutions, some results obtained from theoretical calculations are presented. The following molecular structures were considered: CuCl molecule, CuCl₂⁻ complex, and little copper clusters defect representation built as five atoms on C_4v symmetry. Thus, based on the geometric, energetic, frontier orbital, and Total Electronic Density analysis done for the optimized states found for the systems investigated, we suggest that the most probable interaction of 8-AQ proceeds above CuCl units and free copper sites.     

Impedance studies of copper foil and graphite-coated copper foil electrodes in lithium-ion battery electrolyte

The electrochemical impedance spectroscopy of battery grade copper foil and graphite-coated copper foil electrodes in 1 M LiPF₆ in a ternary organic carbonate electrolyte has been obtained. Detailed studies showed that both electrodes gave similar impedance spectra of two successive semicircular arcs. When overpotential was increased for both electrodes, the high frequency semicircles remained the same on each electrode, but the second semicircle increased for both electrodes. Based on the impedance spectra results of the electrodes, it appeared that the high frequency response represented a surface oxidation layer. At low frequency further oxidation occurs at both electrodes, but is kinetically controlled for bare copper, while the graphite-coated copper undergoes diffusional blocking through the porous carbon layer. An equivalent circuit of the impedance spectrum was then proposed.     

Effects of copper trifluoromethanesulphonate as an additive to propylene carbonate-based electrolyte for lithium-ion batteries

Addition of copper trifluoromethanesulphonate (CuTF) to propylene carbonate (PC)-based electrolyte effectively suppresses the cointercalation and decomposition of PC in the mesocarbon microbeads (MCMB) electrodes during the first lithiation process. During the first charging cycle, copper ions are reduced at a higher potential (2 V versus Li/Li⁺) than the potential of PC cointercalation and decomposition (0.6-0.8 V versus Li/Li⁺), and predominately form a porous copper layer over the MCMB surface, thereby obstructing PC to cointercalate. An increase in reversible capacity can be achieved by increasing the amount of CuTF. However, above a critical value, the copper layer inhibits the intercalation of lithium ions and lowers the capacity. The AC impedance data reveal that the passivation film and the charge-transfer resistance are both increased when the deposited copper is in excess. An optimum result may be obtained when the addition is approximately 5 wt.%. CuTF is a possibility for PC-based electrolyte additive in lithium-ion batteries.     

Electrochemical characterization of screen-printed and conventional carbon paste electrodes

This work compares the electroactivity of a conventional carbon paste electrode and non-pretreated commercially available screen-printed carbon electrodes (from Alderon Biosciences, University of Florence and DropSens) towards some benchmark redox couples like hexaammineruthenium (III), ferricyanide, p-aminophenol and hydroquinone. While cyclic voltammograms of Ru³⁺ did not show significative electron transfer reactivity differences between the electrodes tested, the other redox systems exhibited higher reversible behaviours on DropSens electrodes. Scanning electron microscopy and roughness analysis with a profilometer were applied to detect the surface morphology of the working electrodes. The roughness evaluated of the screen-printed carbon working electrodes increased in this order Alderon < University of Florence < DropSens. Finally, the most electrochemically active and rough unpretreated electrode (DropSens commercial screen-printed electrode) was used to study the electrochemical-chemical reaction mechanism of indigo carmine oxidation in 0.1 M sulphuric acid. This study showed that the adsorption of the oxidation product of indigo carmine is stabilized when it is adsorbed on the surface of the electrode.     

Spectroelectrochemical study of perchloroethylene reduction at copper electrodes in neutral aqueous medium

The potential-dependent chemical reaction of perchloroethylene (PCE) on copper in neutral noncomplexing aqueous media is explored by means of surface-enhanced Raman spectroscopy (SERS), linear sweep voltammetry and preparative electrolysis at controlled potential. Voltammetric peaks associated with copper oxide reduction in Na₂SO₄ solution in the presence and the absence of Cl⁻ are correlated with simultaneously acquired SER spectra. Perchloroethylene undergoes a dechlorination process at potentials at E ≤ −0.3 V vs. Ag/AgCl/KCl (3 M), as shown by the emergence of an intense CuCl stretching band at 290 cm⁻¹ and a CH stretching band together with the presence of Cl⁻ in the catholyte. In the potential region between 0 and −0.9 V vs. Ag/AgCl/KCl (3 M) a broad band assigned to CC structures is observed in the triple-bond region (∼1900 cm⁻¹, FWHM = 180 cm⁻¹). In addition, dichloroethylene (DCE) is detected (but not trichloroethylene (TCE)) in this potential region during preparative electrolysis. At potentials lower than −1 V vs. Ag/AgCl/KCl (3 M) carbon residues are the main product, detected on the copper surface by SERS (and confirmed by XPS), whereas in solution higher levels of dichloroethylene and trichloroethylene are detected with a DCE/TCE ratio below 1.     

Influence of pulse plating parameters on the electrocodeposition of matrix metal nanocomposites

Electrocodeposition of alumina particles with copper and nickel from acidic electrolytes has been investigated using different deposition techniques. Compared to direct current (DC) deposition, both pulse plating (PP) and pulse-reverse plating (PRP) facilitated higher amounts of particle incorporation. With conventional DC plating the maximum alumina incorporation is ∼1.5 wt% in a nickel and ∼3.5 wt% in a copper matrix. However, the implementation of rectangular current pulses can give considerably higher particle contents in the metal layer. A maximum incorporation of 5.6 wt% Al₂O₃ in a copper matrix was obtained by PP at a peak current of 10 A dm⁻², a duty cycle of 10% and a pulse frequency of 8 Hz. In general, low duty cycles and high pulse frequencies lead to an enhanced particle codeposition. The microstructure and the hardness of both pure metal films and nanocomposite coatings showed only a weak dependence on the PP and PRP conditions.