The effect of hydrogen codeposition on the morphology of copper electrodeposits. I. The concept of effective overpotential

Various iron group alloys have been electrodeposited and evaluated for properties including corrosion resistance, microstructure, electrical resistivity, magnetoresistance and other magnetic properties. Corrosion resistance depends on deposit composition and microstructure, which are controlled by solution composition and deposition variables. Maximum corrosion resistance was observed for 50Ni50Fe and 70Co30Ni binary alloys. The corrosion resistance of electrodeposited CoFe films was an order of magnitude lower than CoNi and NiFe films. Substantially increased corrosion resistance was obtained by adding Ni to CoFe alloys. However, addition of B only slightly increased corrosion resistance. For electrodeposited NiFe and CoNi thin film alloys, three distinct structural regions were observed: for NiFe alloys, fcc, mixed fcc and bcc, and bcc phases as deposit Fe content increased; for CoNi alloys, fcc, mixed fcc and hcp, and hcp as deposit Co content increased. The smallest grain size was obtained in the mixed phase region of both NiFe and CoNi alloys, For CoFe alloys, a mixed phase region was not observed; only fcc and bcc phases were obtained. Electrodeposited NiFe films from sulfate baths show superior soft magnetic properties including both lower coercivity and higher squareness than from chloride baths. Magnetic saturation (M S ) of electrodeposited NiFe films follow bulk alloys where magnetic saturation increased with increased deposit Fe content.

Electrodeposited Iron Group Thin-Film Alloys: Structure-Property Relationships

High concentrations of copper chloride solutions (in the molar range) are used in several industrial applications. In this work, we investigated the species distribution of copper chloride complexes and how to measure the copper concentration precisely at high concentrations using electrochemical methods, by including migrational effects. The latter, in fact, can be useful in determining the nature of the species in solution undergoing electron transfer at the electrode. The study indicates that the main species of Cu(II) complexes in high chloride concentration is CuCl42– and the main species of Cu(I) complexes are CuCl2– and CuCl32–. However insoluble CuCl is an intermediate in the process and can deactivate the electrode surface. This can be ameliorated by increasing the temperature or Cl– concentration. Under these conditions, voltammetry with an ultramicroelectrode (UME) can measure copper concentration with good precision even at 1 M Cu(II) concentrations in a few molar chloride. The main charge of ...

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Electrochemistry of high concentration copper chloride complexes.

A review of effects of silver, lead, sulfide and carbonaceous matter on gold cyanidation and mechanistic interpretation

Redox enzymes, which catalyze reactions involving electron transfers in living organisms, are very promising components of biotechnological devices, and can be envisioned for sensing applications as well as for energy conversion. In this context, one of the most significant challenges is to achieve efficient direct electron transfer by tunneling between enzymes and conductive surfaces. Based on various examples of bioelectrochemical studies described in the recent literature, this review discusses the issue of enzyme immobilization at planar electrode interfaces. The fundamental importance of controlling enzyme orientation, how to obtain such orientation, and how it can be verified experimentally or by modeling are the three main directions explored. Since redox enzymes are sizable proteins with anisotropic properties, achieving their functional immobilization requires a specific and controlled orientation on the electrode surface. All the factors influenced by this orientation are described, ranging from electronic conductivity to efficiency of substrate supply. The specificities of the enzymatic molecule, surface properties, and dipole moment, which in turn influence the orientation, are introduced. Various ways of ensuring functional immobilization through tuning of both the enzyme and the electrode surface are then described. Finally, the review deals with analytical techniques that have enabled characterization and quantification of successful achievement of the desired orientation. The rich contributions of electrochemistry, spectroscopy (especially infrared spectroscopy), modeling, and microscopy are featured, along with their limitations.

https://hal-amu.archives-ouvertes.fr/hal-01793660/document

Controlling Redox Enzyme Orientation at Planar Electrodes

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.

https://link.springer.com/content/pdf/10.1023/B:RUEL.0000035261.95595.e9.pdf

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

Effect of lead hydroxy compounds on the process of electrodeposition of silver from cyanide electrolytes is studied on an electrode whose surface is renewed in solution by cutting off a thin layer of metal. This permitted to perform the study on both the freshly renewed electrode and at controlled values of the time of the electrode contact with solution Δt. Shown is that on the freshly renewed electrode (Δt<1 s) the presence in the solution of lead ions in concentrations c1 on the order of 10–5 M leads to the process depolarization only in the initial portion of a polarization curve. With c1 increased to 10–4 M the effect of depolarization extends on the entire polarization curve. Keeping the electrode in solution after the renewal of the metal surface magnifies depolarization, and the greater the concentration c1, the shorter the time period Δt required to achieve the same effect. These regularities are attributed to catalytic influence of lead adatoms, whose surface concentration depends on c1 and Δt, as well as on the intensity of their incorporation in the silver deposit.

Silver Electrodeposition from Cyanide Solutions: Effect of Lead Ions

The potentialities of electrochemical method of removal of adsorbed octanethiol layer from gold electrode surface are considered. The dependence of a degree of gold macro- and microelectrode cleaning on the electrolyte composition, potential cycling range, and the number of cycles is studied. It is shown that the commonly used method of cleaning by multiple potential cycling in the perchloric acid solution in the potential range from 0 to 1400 mV (SCE) is not sufficiently efficient. Cycling in the water-ethanol solution of perchloric acid promotes the octanethiol desorption and leads to the complete regeneration of surface even after 6–8 cycles. This is evidenced by comparing with the voltammograms, which were obtained on pure Au surface in 4 mM potassium ferri-ferrocyanide and 0.1 M HClO4 solutions. A range of ethanol concentrations, which provides the highest degree of gold surface cleaning, is determined. The electrochemical method of cleaning by using water-ethanol solution of perchloric acid enables one to perform multiple electrode regeneration without destruction of thin gold layer (for example, in the quartz microbalance), which takes place in the case of chemical regeneration in the “piranha” solution based on sulfuric acid and hydrogen peroxide.

Desorption of octanethiol from gold electrode surface during its electrochemical cleaning

Regularities of silver dissolution in acid thiocarbamide electrolytes are studied. The kinetics of the process is shown to be severely affected by the admixture of hydrogen sulfide molecules that form upon inserting sodium sulfide or accumulate in electrolyte with the passage of time elapsed since its preparation. Catalytic effect increases with increasing length of time of the electrode’s contact with solution prior to the beginning of experiment or following an increase in the concentration of sulfide ions. Experiments with the surface renewed in the course of potential scans show that the catalytic effect is connected with the adsorption of sulfide ions on an interface. At large values of the surface coverage with sulfide ions, the dissolution rate increases so much that the dissolution process starts to be limited largely by the process of supply of thiocarbamide molecules toward the electrode surface.

Silver dissolution in acid thiocarbamide solutions containing sulfide ions

Quartz microgravimetry is used to determine the ratio between coefficients of mass transfer (1 : 0.54 : 0.48), which characterizes relative values of rates of diffusion of hydroxy complexes of thallium, lead, and bismuth in alkaline solutions. The ratio is used when refining the condition under which on a renewable electrode in solutions containing these ions at the concentration c
i the electrode coverage by relevant adatoms Θ
 i
 with increasing duration of contact of the electrode with solution reaches constant values: (c
Tl
t) = (0.54c
Pb
t) = (0.48c
Bi
t). Measured are i,t curves on a renewable gold electrode at E = const in solutions containing 0.1 M KCN, 0.1 M KOH, 0.01 M KAu(CN)2, and 8 × 10–6 M compounds of thallium or 1.5 × 10–5 M, lead, or 1.6 × 10–5 M, bismuth. Shown is that at (Θ, E) = const the currents of dissolution of gold in these solutions increase in the series Tl < Pb < Bi, which evidences an increase in this series of the catalytic activity of adatoms of these metals. Shown is that at Θ = const the catalytic action of adatoms of thallium and bismuth has an approximately additive character. The obtained data are analyzed with allowance made for the explanation offered earlier for the catalytic effect of adatoms on the anodic dissolution of gold based on the hypothesis about the shift of the potential of the free zero charge in the negative direction after substituting a metal atom for chemisorbed cyanide ions.

S. N. Ovchinnikova

Papers

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

Silver Electrodeposition from Cyanide Solutions: Effect of Lead Ions

Desorption of octanethiol from gold electrode surface during its electrochemical cleaning

Silver dissolution in acid thiocarbamide solutions containing sulfide ions

Catalytic Activity of Thallium, Lead, and Bismuth Adatoms in the Gold Dissolution Reaction in Cyanide Solutions: A Comparative Characterization