Copper deposits obtained by pulsating overpotential regime with a long pause and pulse duration from sulfated solutions (original) (raw)
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Morphologies of copper deposits obtained by the electrodeposition at high overpotentials
Surface and Coatings Technology, 2006
Morphologies of copper deposits obtained at overpotentials belonging to the plateau of the limiting diffusion current density and at higher overpotentials were examined by the scanning electron microscopy (SEM) technique. Copper dendrites are formed at overpotentials belonging to the plateau of the limiting diffusion current density. The shape of copper dendrites depends on the electrodeposition overpotential. At higher overpotentials (800 and 1000 mV) and larger values of current densities, porous and very disperse copper deposits were obtained. These morphologies were a consequence of a very vigorous hydrogen evolution at these electrodeposition overpotentials. Also, the obtained copper structures consisted of agglomerates of copper grains. The size of copper grains is a function of the overpotential of electrodeposition, thus approaching to nano-sized dimensions is achieved when the electrodeposition overpotential is increased.
Chemical Engineering Science, 2008
The relative concentration of hydrogen ion (H +) as a function of sulfuric acid (H 2 SO 4) concentration (calculated using Pitzer's model) and the electrochemical processes by which irregular copper deposits are formed were correlated. Irregular deposits are formed by potentiostatic electrodeposition at a high overpotential where the hydrogen evolution reaction occurs parallel to copper electrodeposition. Two sets of acid sulfate solutions were analyzed. In one set of experiments, the concentration of CuSO 4 was constant while the concentration of H 2 SO 4 was varied. The other set of experiments was performed with a constant concentration of H 2 SO 4 and different concentrations of CuSO 4. Then, the volumes of the evolved hydrogen (calculated as the average current efficiencies of hydrogen evolution) and the morphologies of copper deposits, characterized by the SEM technique, obtained for the same ratio of CuSO 4 /H 2 SO 4 were mutually compared and discussed in terms of the relative concentrations of hydrogen ions (H +) as a function of the H 2 SO 4 concentration. Good agreement between the ionic equilibrium in the CuSO 4-H 2 SO 4-H 2 O system and the results of the electrochemical processes was obtained. In this way, it was shown how this ionic equilibrium can be applied to predict and analyze the solution composition in electrolytic copper deposition processes.
Effect of temperature on the electrodeposition of disperse copper deposits
Journal of the Serbian Chemical Society, 2007
The effect of temperature on the electrodeposition of copper at overpotentials belonging to the plateau of the limiting diffusion current density and higher was examined by the determination of the average current efficiency of hydrogen evolution and by scanning electron microscopic (SEM) analysis of the morphology of the formed copper deposits. Increasing the temperature of the solution led to a shift of both the beginning and the end of the plateau of the limiting diffusion current density towards lower electrodeposition overpotentials. Also, higher temperatures led to the formation of morphological forms of copper deposits characteristic for electrodeposition of copper at some higher overpotentials. The unexpected trend in the development of copper structures electrodeposited at an overpotential of 800 mV is discussed in terms of the effect of temperature on the viscosity and surface tension of the electroplating solution.
Journal of the Serbian Chemical Society, 2008
The ionic equilibrium of the species in the CuSO 4 -H 2 SO 4 -H 2 O system was employed to systematize the conditions of copper electrodeposition leading to the formation of the honeycomb-like structure. The reason why CuSO 4 concentrations higher than 0.15 M are unsuitable for the formation of honeycomb-like structures is shown. The range of H 2 SO 4 concentrations enabling the formation of this type of structure was also determined. The conditions leading to the formation of the honeycomb-like structures are: electrodeposition from solutions with lower concentrations of Cu(II) ions (0.15 M CuSO 4 and less) in a concentration range from 0.25 to 1.0 M H 2 SO 4 , at a temperature of 18.0±1.0 °C and at overpotentials outside the plateau of the limiting diffusion current density at which hydrogen evolution is vigorous enough to change the hydrodynamic conditions in the near-electrode layer.
The Electrochemistry of Copper in Aqueous Sulphide Solutions
MRS Proceedings, 2006
Using a variety of electrochemical and surface analytical techniques, the mechanism and kinetics of Cu corrosion in anoxic, aqueous, sulphide-containing environments are being investigated. Under these conditions ([S] total = 10-4 to 3x10-3 mol/L), the anodic growth of a film (XRD identifies Cu 2 S/Cu 1.8 S as major/minor phases, respectively) is supported by the cathodic reduction of water thereby destabilizing the copper surface. For more oxidizing conditions, the subsequent growth of a partially passivating film is observed. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry at rotating disc electrodes show film growth occurring with negligible dissolution and under partial SHtransport control. Current-potential relationships as a function of [S] total give Tafel slopes of ~(40 mV)-1 suggesting reaction occurs via a 2 step process: An initial rapid adsorption of SHleading to an equilibrium surface concentration, followed by a rate determining electron transfer to form a sulphide film. It is proposed that film growth propagates via transport of Cu I through the film to the solution interface. The primary goal of this research is the development of a mathematical model which can be used to assess the performance of copper nuclear waste canisters in granitic repositories.
Sensors, 2007
Electrodeposition of copper from acid sulfate solutions at overpotentials on the plateau of the limiting diffusion current density and at higher overpotentials was examined. The average current efficiencies for hydrogen evolution reaction are determined by a measurement of the quantity of evolved hydrogen and the overall electrodeposition current as a function of electrodeposition time, while morphologies of copper deposits are examined by the use of the scanning electron microscopy (SEM) technique. It is found that the open and porous structures of copper deposits (denoted and as honeycomb-like copper structures), suitable for electrodes in electrochemical devices such as fuel cells and chemical sensors, were reached by electrodeposition processes from solutions with the lower concentrations of Cu (II) ions (0.15 M CuSO 4 and less in 0.50 M H 2 SO 4) at overpotentials outside the plateau of the limiting diffusion current density at which the quantity of evolved hydrogen was enough to change hydrodynamic conditions in the near-electrode layer. The main characteristics of these copper structures were craters or holes formed primarily due to the attachment hydrogen bubbles with agglomerates of copper grains between them.
Electrochemical behaviour of copper electrode in concentrated sulfuric acid solutions
Electrochimica Acta, 1993
The electrochemical behaviour of copper in 6.0moll-' sulfuric acid at 3o"C, was studied by means of the potentiodynamic method. At low potential sweep rates, u < ZOOmVs-', the data reveal that the anodic process is basically constituted of copper dissolution and a film formation which inhibits further metal oxidation and which may undergo further dissolution. For higher potential sweep rates, a modification in the passivation region of the voltammogram is observed. It can be ascribed to a change in the passivation mechanism which possibly involves different surface species. The kinetic relationships derived from the potentiodynamic l/E curves obtained at low u suggest a film formation via a dissolution/precipitation mechanism.
Metallurgical and Materials Transactions B, 2003
A study on cathodic deposition of copper in acidic aqueous sulfate solution has been carried out using a stainless steel cathode and a graphite anode. The individual and the combined effects of added [H 2 SO 3и aq] and [Co 2ϩ и aq] on cathode potential, current efficiency, crystal orientations, and deposit morphology have been investigated and are compared. The maximum decrease of ഡ50 pct in cathode potential is more pronounced in the presence of ഡ10.25 g/L of H 2 SO 3 alone in the electrolyte than that (ഡ30 pct) in the presence of ഡ100 ppm of added Co 2ϩ (aq) alone; however, the presence of added Co 2ϩ (aq) along with H 2 SO 3 (aq) does not cause further decrease in cathode potential in comparison to that observed in the presence of only H 2 SO 3 (aq) in the electrolyte. The current efficiency is found to decrease in the presence of [H 2 SO 3и aq] in the range of 1.32 to 30.75 g/L or in the presence of added [Co 2ϩ и aq] in the range of ഡ10 ppm to 600 ppm, while the decrease of about 4 pct in current efficiency is more pronounced in the presence of only H 2 SO 3 (aq) in the electrolyte, it is about 2 pct in the presence of only added Co 2ϩ (aq) in the same electrolyte. The addition of Co 2ϩ (aq) to the electrolyte containing H 2 SO 3 (aq) does not alter the current efficiency (94 pct) of copper at the cathode. The linear sweep voltammetry (LSV) method was used to study the effect of added [H 2 SO 3и aq], [Co 2ϩ и aq], or both, on the copper deposition at the cathode. The presence of each of these two additives or both causes a depolarization effect; the extent of the depolarization depends on the concentration of H 2 SO 3 (aq), Co 2ϩ (aq), and the current density. X-ray diffraction (XRD) data suggest that there is a change in the order of the preferred crystal orientations (viz., from the (220) plane in the absence of added H 2 SO 3 (aq) and Co 2ϩ (aq) to the (111) plane in the presence of added H 2 SO 3 (aq) and Co 2ϩ (aq) in the electrolyte solution) due to a change in the preferred plane of relative crystal growth. Results of scanning electron microscopy (SEM) indicate that cathode deposits of better surface morphology due to small-sized crystallites are found in the presence of added H 2 SO 3 (aq) ϩ Co 2ϩ (aq) in the electrolyte solution.
Electrochimica Acta, 1985
The electrochemical behaviour of copper electrodes in NaOH solutions with the addition of Na,S was studied through the analysis of current transients under constant potential and complementary voltammetric and scanning electron microscopy data including energy dispersive X-ray analysis. The overall process can be described by the following three stages. The First stage corresponds to the nucleation and growth of a complex copper sulphide layer at potential values close to the equilibrium potentials of the Cu/Cu2S and Cu/CuS reversible electrodes. The second stage is related to the rupture of the copper sulphide film at potentials more positive than a certain critical value leading to pitting corrosion of copper metal and yielding a poorly protective copper sulphide layer. The third stage occurs in the copper oxide electroformation range, where the presence of copper sulphide accelerates the electrodissolution of the base metal and copper oxide hinders the sulphidization processes. The current transients of each stage are interpreted through a model based on the nucleation and growth mechanism.
Langmuir, 2000
We report in situ scanning tunneling microscopy (STM) results of underpotential deposition (UPD) of copper at well-ordered Pt(111) and Rh(111) electrodes in sulfuric acid solutions. Cyclic voltammograms of Pt(111) at 1 mV/s in 0.05 M H2SO4 and 5 mM CuSO4 reveal two well-defined UPD peaks at 0.65 and 0.61 V, whereas one doublet UPD peak at 0.44 V is observed for Rh(111). Real-time STM imaging revealed that the two sharp UPD features for Pt(111) correspond to the formation of a (3 × 3)R30°structure and a disorder phase, respectively. A long-range ordered (3 × 7)oblique structure was imaged after a full monolayer of Cu was deposited, tentatively assigned to the (bi)sulfate anions lying atop the Cu adlayer. In contrast, a monolayer of Cu was deposited in a single step on Rh(111), where (bi)sulfate anions also actively participated in the process. In situ STM revealed a well-ordered (3 × 7)oblique structure throughout the deposition process, likely because of the coadsorbed (bi)sulfate anions. A series of timedependent in situ STM images were acquired to unveil the deposition processes of Cu. Deposition of Cu preferentially began at defect sites, particularly upper step ledges. Lateral growth and coalescence of Cu islands followed to cover nearly the whole surface. Decreasing potential to the bulk deposition region led to the formation of local Cu islands with a thickness of 4-5 layers of Cu, on which a well-ordered (3 × 7)oblique structure was still observed. All the STM results indicate that sulfate anions were heavily involved in the UPD processes of Cu at these two electrodes. The different adsorption energies of Cu adatoms on Pt and Rh electrodes also affect the deposition processes.