Dynamics of copper electrodeposition onto fibrous carbon electrodes with electrical conductivity varying across their thickness

Distribution of copper in its electrodeposition from a sulfuric acid solution onto fibrous carbon electrodes with electrical conductivity varying across their thickness, the deposition rate of copper, and the current efficiency by copper were studied in relation to the electrolysis duration, electrical conductivity of the electrode, geometric current density, and solution flow rate. The main factors governing the distribution of copper across the electrode thickness and the electrolysis parameters beginning from the process onset till the “clogging” of a part of the electrode by the metal were determined.     

Parameters of electrolysis in 3D flow electrode in limiting diffusion current mode

The analytical expressions were derived to calculate thickness of a three-dimensional flow electrode (TFE) working in limiting diffusion current mode in the cases of unidirectional and multidirectional electric field and solution flow for the given degree of metal extraction. The algorithm was suggested on the basis on the derived formulas and earlier published mathematical models of nonstationary electrolysis at TFE to calculate the whole electrode working conditions at the limiting diffusion current with parallel electrochemical reactions. The calculations and experimental studies were carried out on copper electrodeposition from sulfate electrolyte on TFE working in the limiting diffusion current mode. The effect of major electrochemical reactions to the distribution of potential and partial current densities by the electrode thickness was demonstrated. The process potential distribution was given for various electrode conductivities. A good compliance was shown between the results of calculations and experimental studies.     

Dynamics of copper deposition from a sulfuric acid solution onto electrically isoconducting electrodes made of fibrous carbon materials

Effect of the initial electrical conductivity of an electrically isoconducting flow-through electrode made of a fibrous carbon material on the dynamics of copper electrodeposition from a sulfuric acid solution was studied. The distribution of the copper deposit across the electrode thickness and the variation of the electrolysis parameters (copper deposition rate, current efficiency, uniformity of distribution, and mass of a deposited metal per unit mass of the fibrous carbon material) were considered.     

Effect of Cathodic and Anodic Polarization in a Lithium Sulfate Solution on the Electrical Conductivity of Carbonized Fibrous Carbon Materials

The effect of cathodic and anodic polarization of carbonized fibrous carbon materials of the KNM and NT-1 types in a Li₂SO₄ solution on their properties: electrical conductivity, steady-state electrode potential, electrical conductivity profile across the electrode thickness in relation to the electrolysis time, current density, Li₂SO₄ concentration, electrode thickness, and current reversal, was studied. The stability of the resulting electrical conductivity profile across the electrode thickness with time and in the course of the subsequent electrolysis was assessed. The reduction of Fe³⁺ in the ferri-ferrocyanide system on electrically iso- and nonisoconducting fibrous carbon electrode was considered.     

Insights into analyte electrolysis in an electrospray emitter from chronopotentiometry experiments and mass transport calculations

Insights into the electrolysis of analytes at the electrode surface of an electrospray (ES) emitter capillary are realized through an examination of the results from off-line chronopotentiometry experiments and from mass transport calculations for flow through tubular electrodes. The expected magnitudes and trends in the interfacial potential in an ES emitter under different solution conditions and current densities, using different metal electrodes, are revealed by the chronopotentiometry data. The mass transport calculations reveal the electrode area required for complete analyte electrolysis at a given volumetric flow rate. On the basis of these two pieces of information, the design of ES emitters that may maximize and those that may minimize analyte electrolysis during ES mass spectrometry are discussed.     

Joint Destruction of Cadmium and Copper at Alternating Current Electrolysis in Sodium Hydroxide Solution

The dependence of the metal oxidation rate on the current density and temperature of joint destruction in sodium chloride was studied. It is established that the dependence of the oxidation rate of copper is linear and generally do not differ from the dependencies established at individual oxidation of copper in the solution of sodium chloride with concentration 46.5% wt. In contrast to the oxidation rate of copper, the oxidation rate dependence of cadmium has extreme character and the oxidation rate of cadmium at its joint oxidation of copper increased in 2-3 times indicating that the mutual influence of electrodes at the electrochemical process with alternating current. Thus, the obtained dependences can predict operating electrolysis parameters a obtain copper-cadmium oxide system of the given composition.     

Anodic dissolution of electronegative component during the process of metal codeposition in a flow-through porous cathode

Possible magnitude of the electronegative component (M₂) dissolution during a two metal (M₁ and M₂) codeposition inside a porous electrode is studied theoretically (by modeling) and experimentally. Model calculations based on the substituting of the pure metal (M₂) dissolution rate for its selective dissolution rate from the alloy gave an overestimated evaluation of the effect. The dissolution effect is shown to be small when the porous electrode is filled up with metal deposited from a solution large single portion; however, it increased significantly when the solution is divided into smaller portions. Experimental studies of Ag and Cu deposition dynamics in thiosulfate solution showed that the turning from a direct-flow to a circulation mode results in significant increase in the Cu mass and widening its deposition zone up to the porous electrode entire thickness. When the 2nd and 3rd portions of the solution are subjected to electrolysis, the solution is temporarily enriched with Cu ions, which evidences the copper partial dissolution whose scale is close to calculated estimates. The explanation of specific features of Cu dissolution in repeated cycles of the metal recovery was suggested and experimentally proved.     

Hydrodynamic voltammetry at channel electrodes: Part VIII. Theory of reversible voltammograms for chronoamperometry and linear sweep voltammetry

An expression for the reversible transient current at a channel flow electrode was derived when a potential with any time variation was applied to the electrode. First, the expression was adapted to chronoamperometry. As the electrolysis time elapses, the current density distribution varies from a Cottrellian uniform distribution to a non-uniformly steady-state distribution. Second, the expression for the reversible linear sweep voltammogram was derived. For small values of a dimensionless potential sweep rate, the voltammograms are in a sigmoidal form similar to the steady-state curve. As the values become large, the voltammograms have a peak which is often observed in quiescent solution. The dependence of the peak current and the potential at the half peak current on the dimensionless potential sweep rate was examined.     

Electrolysis of ammonia for hydrogen production catalyzed by Pt and Pt-Ir deposited on nickel foam

Electrolysis of ammonia in alkaline electrolyte solution was applied for the production of hydrogen. Both Pt-loaded Ni foam and Pt-Ir loaded Ni foam electrodes were prepared by electrodeposition and served as anode and cathode in ammonia electrolytic cell, respectively. The electrochemical behaviors of ammonia in KOH solution were individually investigated via cyclic voltammetry on three electrodes, i.e. bare Ni foam electrode, Pt-loaded Ni foam electrode and Pt-Ir loaded Ni foam electrode. The morphology and composition of the prepared Ni foam electrode were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Effects of the concentration of electrolyte solution and temperature of electrolytic cell on the electrolysis reaction were examined in order to enhance the efficiency of ammonia electrolysis. The competition of ammonia electrolysis and water electrolysis in the same alkaline solution was firstly proposed to explain the changes of cell voltage with the electrolysis proceeding. At varying current densities, different cell voltages could be obtained from galvanostatic curves. The low cell voltage of 0.58 V, which is less than the practical electrolysis voltage of water (1.6 V), can be obtained at a current density of 2.5 mA/cm². Based on some experimental parameters, such as the applied current, the resulting cell voltage and output of hydrogen gas, the power consumption per gram of H₂ produced can be estimated.     

Dynamics of the codeposition of metals in a porous electrode in the presence of an oxidant

The oxidant effect on the codeposition of two metals in a porous electrode (PE) was studied experimentally and by numerical calculations. The presence of an oxidant in a solution always leads to degradation of the dynamics and final characteristics of the target process, namely, to a decrease in the current efficiency, the final mass, and the average rate of metal deposition and to a less uniform distribution of metals in the PE. The effect depends on the PE operating conditions and involves less uniform potential distribution in PE and anodic dissolution of metals. The former component of the effect dominates when the concentrations of the metal ions and oxidant are comparable. A considerable deceleration of silver deposition in the presence of an oxidant and anodic dissolution of copper at the first stage of the electrolysis of the second and subsequent portions of solution were confirmed experimentally using as an example Ag and Cu extraction from an alkaline thiosulfate solution in the presence of a Fe³⁺ trilonate complex used as an oxidant.     

Effect of solution flow rate and direction on copper electrodeposition process from sulfuric acid electrolyte on porous electrode with high electric conductivity

The effect of solution flow direction and rate on the dynamics of copper electrodeposition onto a premetallized coal-graphite VINN-250 material from a dilute copper sulfate sulfuric acid solution is experimentally studied in the direct-flow mode. A light effect of solution supply on the copper deposit final mass for high and low solution flow rates is found, while the effect of this parameter on the metal distribution within the porous electrode is significant. The most uniform copper deposit distribution throughout the porous electrode is observed in the case of intermediate solution flow rates at its rear supply. The obtained experimental data agree qualitatively with the earlier published mathematical simulation results. Small systematic deviations from numeric calculations can be due to the process disregarded in the mathematical model: the effect of gas phase formed within the porous cathode due to the simultaneous hydrogen evolution.     

Computational electrochemo-fluid dynamics modeling in a uranium electrowinning cell

A computational electrochemo-fluid dynamics model has been developed to describe the electrowinning behavior in an electrolyte stream through a planar electrode cell system. Electrode reaction of the uranium electrowinning process from a molten-salt electrolyte stream was modeled to illustrate the details of the flow-assisted mass transport of ions to the cathode. This modeling approach makes it possible to represent variations of the convective diffusion limited current density by taking into account the concentration profile at the electrode surface as a function of the flow characteristics and applied current density in a commercially available computational fluid dynamics platform. It was possible to predict the conventional current–voltage relation in addition to details of electrolyte fluid dynamics and electrochemical variables, such as the flow field, species concentrations, potential, and current distributions throughout the galvanostatic electrolysis cell.     

Mass transport to and within porous electrodes. Linear sweep voltammetry and the effects of pore size: The prediction of double peaks for a single electrode process

We simulate an electrode modified with a conducting porous film, where the electrolysis occurs both at the surface of the film and within it, in order to study the effect of pore size on the peak current in linear sweep voltammetry. For redox systems with reversible electrode kinetics we find that for both very large and very small pores the peak current is given by the Randles-?ev?ik equation. For intermediate pore size, however, we observe a greatly enhanced peak current. When considering systems with irreversible electrode kinetics a very similar pattern is observed, except for the case of very small pores. In this case the peak current is actually smaller than expected from the Randles-?ev?ik equation because the peak splits into two distinct peaks; one due to ??thin layer?? diffusion within the film and another caused by planar diffusion from bulk solution. The experimental implications of this observation are significant given the widespread use of modified electrodes for analysis.     

Coulometric Anodic Stripping Voltammetry of Lead at Copper Column Electrode

A flow coulometric electroanalytical system using a copper column electrode with a copper wire inserted into a Nafion tube was developed to determine Pb(II) content based on anodic stripping voltammetry. The electrolysis efficiency of 5 μM Pb(II) was evaluated to be 100.4±4.5 % (n=5) when the length of the copper wire and flow rate of the Pb(II) solution were 50 cm and 0.1 mL min⁻¹, respectively. The amount of electricity due to the re-oxidation of Pb electrodeposited at the copper column electrode was proportional to the concentration of Pb(II) in the range between 0.1 to 100 μM, and the limit of detection for Pb(II) was 0.8 μM for a deposition time of 15 min. Interference from the presence of Cd(II) could be avoided and the selective determination of Pb(II) was successfully achieved by adjustment of the electrodeposition potential.     

Hydrodynamic voltammetry at channel electrodes: Part VII. Current transients at double channel electrodes

Expressions for the transient current at the downstream electrode in response to galvanostatic electrolysis at the upstream electrode in the channel flow cell were derived by applying double Laplace transformation when the electrode reaction at the upstream electrode is kinetically controlled. The ratio of the transient current to the steady state current or the transient collection efficiency was calculated as a function of electrode geometry and θ

, where U_m is the mean flow velocity in the channel cell, D the diffusion coefficient of the electroactive species, b the half height of the channel, x₁ the length of the upstream electrode and t the time elapsed since the beginning of the galvanostatic electrolysis at the upstream electrode. Curves for the transient collection efficiency can be applied to evaluating the amount of adsorption at the upstream electrode when metal at the electrode is anodically dissolved in solution. Digital simulation was carried out. Transient curves, obtained analytically, were in good agreement with those evaluated from the digital simulation. In order to allow one to draw transient curves readily, we derived a simple approximate equation.     

Regeneration by Membrane Electrolysis of an Etching Solution Based on Copper Chloride

Regeneration of an acid solution for copper etching, based on copper(II) chloride, hydrochloric acid, and ammonium chloride, by membrane electrolysis was studied. The concentrations of copper(I, II) ions in the cathode and anode spaces, current efficiency, degree of copper recovery, and specific consumption of electric power at different quantities of electricity passed through the electrolyzer were measured. The influence exerted by the current density on the electric power expenditure for recovery of metallic copper was examined. The anode current efficiency by chlorine was determined with a spent etching solution and an H₂SO₄ solution used as anolyte.     

The Influence of Viscosity on Diffusion at the Stationary Electrode

Abstract

The influence of viscosity on diffusion at the stationary electrode is studied. Relations between the maximum electrolysis time attainable without any disturbance by natural convection, the thickness of the diffusion layer and solution viscosity are presented and discussed in the case of constant current electrolysis at shielded electrodes. A re-examination of data existing in literature is made.     

氧分压对固体氧化物电解池性能的影响

High-temperature (700–900 ℃) steam electrolysis based on solid oxide electrolysis cells (SOECs) is valuable as an efficient and clean path for large-scale hydrogen production with nearly zero carbon emissions, compared with the traditional paths of steam methane reforming or coal gasification. The operation parameters, in particular the feeding gas composition and pressure, significantly affect the performance of the electrolysis cell. In this study, a computational fluid dynamics model of an SOEC is built to predict the electrochemical performance of the cell with different sweep gases on the oxygen electrode. Sweep gases with different oxygen partial pressures between 1.01 × 10³ and 1.0 × 10⁵ Pa are fed to the oxygen electrode of the cell, and the influence of the oxygen partial pressure on the chemical equilibrium and kinetic reactions of the SOECs is analyzed. It is shown that the rate of increase of the reversible potential is inversely proportional to the oxygen partial pressure. Regarding the overpotentials caused by the ohmic, activation, and concentration polarization, the results vary with the reversible potential. The Ohmic overpotential is constant under different operating conditions. The activation and concentration overpotentials at the hydrogen electrode are also steady over the entire oxygen partial pressure range. The oxygen partial pressure has the largest effect on the activation and concentration overpotentials on the oxygen electrode side, both of which decrease sharply with increasing oxygen partial pressure. Owing to the combined effects of the reversible potential and polarization overpotentials, the total electrolysis voltage is nonlinear. At low current density, the electrolysis cell shows better performance at low oxygen partial pressure, whereas the performance improves with increasing oxygen partial pressure at high current density. Thus, at low current density, the best sweep gas should be an oxygen-deficient gas such as nitrogen, CO₂, or steam. Steam is the most promising because it is easy to separate the steam from the by-product oxygen in the tail gas, provided that the oxygen electrode is humidity-tolerant. However, at high current density, it is best to use pure oxygen as the sweep gas to reduce the electric energy consumption in the steam electrolysis process. The effects of the oxygen partial pressure on the power density and coefficient of performance of the SOEC are also discussed. At low current density, the electrical power demand is constant, and the efficiency decreases with growing oxygen partial pressure, whereas at high current density, the electrical power demand drops, and the efficiency increases.     

Microdistribution of Electrolytic Nickel Deposits and Their Surface Topography: Effect of Hydrogen

The role of hydrogen and the near-electrode gas–liquid flows in the formation of the nickel surface microrelief on a smooth copper electrode in a sulfate electrolyte is studied at different values of solution pH, current density, and deposit thickness. Depending on the discharge kinetics of ions being reduced and the mechanism of removal of bubbles from the electrode surface, a nickel-plating electrolyte displays either ideal or poor microthrowing and leveling powers. The development of three- and two-dimensional microwaves discovered on the deposits is closely related to the nature of natural-convective motion of electrolyte and the influence exerted by mass transfer on the electrocrystallization process.     

碱性溶液中电聚酪胺-铜草酸盐纳米复合物修饰铜电极电催化甲醇氧化(英文)

A polytyramine-copper oxalate nanocomposite modified copper(PTCOxNMC) electrode prepared by electropolymerization was examined for electrocatalytic activity towards the oxidation of methanol in alkaline solution using cyclic voltammetry and impedance spectroscopy. The prepared PTCOxNMC electrode showed a significantly high response for adsorbed methanol oxidation. The effects of various parameters such as potential scan rate and methanol concentration on the electrocatalytic oxidation at the surface of the PTCOxNMC electrode were investigated. Spectrometry techniques such as Fourier transform infrared spectroscopy and scanning electron microscopy were used to determine the surface physical characteristics of the modified electrode and revealed that the polytyramine-copper oxalate nanocomposite particles were highly dispersed on the surface of the copper electrode with a narrow size up to 40 nm. The very high current density obtained for the catalytic oxidation may have resulted from the high electrode surface area caused by modification with the poly-tyramine-copper oxalate nanocomposite.