Electroreduction Of Ions Research Articles

Studies of the mixed adsorption layer on a mercury electrode in the systemp-toluidine-polyethyleneglycol-1M NaClO4

The properties of the mixed adsorption layer on a mercury electrode in the system 1M NaClO4-p-toluidine-polyethyleneglycol (average molecular masses of polyethyleneglycols: 400 or 10000) are discussed. The parameters of theFrumkin and virial isotherms were determined in the range of strong adsorption potentials. In the range of more negative potentials, a mixed adsorption layer was found by investigating the kinetics of the reduction of Zn(II) ion as a pilot ion. Depending on the concentration ratio of the studied organic substances, inhibition, acceleration, or compensation of both with respect to Zn(II) electroreduction was observed. In the presence of polyethyleneglycol, the efficiency of the Zn(II) ion electroreduction increases due to a greater adsorption lability ofp-toluidine molecules on the mercury surface.

Effects of pulsating magnetic fields on electrolytic mass transfer around cylindrical cathodes.

The influence of pulsating magnetic fields on mass transfer was studied experimentally in the electroreduction of ferrocyanide ions around an inclined cylindrical cathode under diffusion-controlled conditions. The mass transfer rate is increased by applying the pulsating magnetic field as well as the static one. The time-averaged enhancement of the mass transfer rate is dependent markedly on duty cycle (ON-time ratio), peak magnetic flux density of the applied pulsating magnetic fields in a range of 20 to 200 mHz, and slightly on its frequency. The mass transfer coefficient was correlated well by two types of non-dimensional regression equations with and without a duty-cycle factor, by using the “magneto-diffusion factor” to express the contribution of the applied magnetic flux density.

Electrolytic mass transfer around inclined cylinders in static magnetic fields

The influence of static magnetic fields on mass transfer rates in the electroreduction of ferocyanide ions around an inclined cylindrical cathode was studied experimentally with a supporting electrolyte. The mass transfer rate was found to be increased by applying the magnetic field. The obtained mass transfer coefficient was correlated well be a non-dimensional regression equation by using a new dimensionless term, “magneto-diffusion factor”, instead of the Hartmann number to express the contribution of the applied magnetic flux density.

On-line mass spectroscopy applied to electroreduction of nitrite and nitrate ions at porous Pt electrode in sulfuric acid solutions

On-line mass spectroscopy was applied to detect volatile products of the electroreduction of NO − 2 and NO − 3 at Pt in 0.5M H 2SO 4. It provided important information, particularly on the transient behavior. Nitrite is reduced stepwise to NO (at 0.6–1 V, rhe), N 2O (0.2–0.8 V) and N 2 (0.1–0.6 V) in the potential ranges indicated. On the other hand, nitrate reduction takes place at much lower potentials ( E <0.4 V), simultaneously yielding N 2O and N 2 but no NO, and terminated at prolonged polarization time.

Electrocatalysis of S 2O 82− ion reduction : The effect of underpotential deposition on the kinetics of the cathodic process on platinum

The effect of underpotential-deposited (upd) monolayers of heavy metals (i.e. Pb, Tl and Bi) on the rate of persulphate ion electroreduction on Pt has been studied in aqueous acid, neutral and alkaline media. It was found that upd adlayers improve significantly the electrocatalytic activity of platinum for S 2O 8 2- ion reduction. The enhancement in the electrocatalytic activity is characterized by a shift of the Tafel region for S 2O 8 2− ion reduction towards more positive potentials and by the attainment of diffusion-controlled limiting current densities within the upd range of the metals used. The catalytic effect has been interpreted in terms of preventing the covering of the Pt surface with chemisorbed species resulting from the dissociative chemisorption of S 2O 8 2− ions, thus leading to faster electron exchange for the charge-transfer step involved in the reaction mechanism.

Electrochemical studies of magnesium ions in magnesium chloride containing chloride melt at 710 ± 10°C

The electroreduction of magnesium ions on stainless steel and graphite substrates in magnesium chloride containing sodium chloride-rich NaCl + KCl + CaCl 2 melt at 710 ± 10° C has been studied using steady state voltanunetry, cyclic voltammetry, chronopotentiometry and chronoamperometry. The experiments were done in a controlled argon atmosphere cell with safety features. It is concluded that the mechanism of electrodeposition of magnesium in a purified melt is a reversible two-electron process in which the rate-determining step is the mass-transfer process. The non-steady state data also indicate minor effects of electron-transfer and electrocrystallization steps on the overall electrowinning process. The calculated values of the formal potential for the Mg/Mg 2+ electrode reaction and the diffusion coefficient of Mg 2+ ion are 2.75 ± 0.02 V vs. Cl −/Cl 2 (ref.) and (6.0±1.0)×10 −5 cm 2 s −1, respectively.

Electroreduction of nitrate ions in concentrated sodium hydroxide solutions at lead, zinc, nickel and phthalocyanine-modified electrodes

The electrochemical reduction of nitrate in strongly alkaline solution has been studied using nickel, lead, zinc and iron cathodes. Intermediate formation of nitrite ion and ammonia product was observed for all electrode materials. Coating a nickel sponge electrode with phthalocyanine renders it less active toward nitrate reduction, while iron electrodes appear to be activated. Electrolysis between a lead cathode and a nickel anode is an efficient means of removing nitrate from strongly alkaline solutions.

ChemInform Abstract: Kinetics of Electroreduction of Lithium Ions in Tetrahydrofuran at Mercury and Mercury Amalgam Electrodes.

AbstractKinetic parameters of reaction A are measured in various electrolytes (tetrabutylammonium salts in THF) and at electrodes of varying composition (Hg and Hg(In)).

The kinetics of electroreduction of lithium ions in tetrahydrofuran at mercury and mercury amalgam electrodes

Kinetic parameters of the reaction Li + + e − → Li(Hg) have been measured at mercury and indium amalgam electrodes in tetrahydrofuran solutions containing various tetrabutylammonium salts. The standard rate constant at Hg decreased when the anion of the electrolyte was changed in the series AsF − 6 > ClO − 4 > BF − 4. This observation is attributed to a decrease in the activity of Li + ion at constant concentration due to increasing ion pairing in the series AsF − 6 < ClO − 4 < BF − 4. For a given electrolyte, the standard rate constant increased markedly with increase in indium content in the electrode. This effect is attributed to a corresponding increase in Li atom activity in the metallic phase. On the basis of a detailed analysis of the kinetic data it is concluded that altering the composition of the solution or the electrode has no influence on the transition state for the reaction. It was also shown that the logarithm of the standard rate constant for this reaction measured in six different aprotic solvents with widely varying dielectric properties is a linear function of the solvent's ability to act as a Lewis base as estimated by its donor number, DN.

Electroreduction mechanism for transition metals

The similarity of the structures and of the compositions of the intermediate reduction products of such transition metals as copper, manganese, chromium, nickel, rhenium, molybdenum, tungsten and zirconium indicates that their reduction from aqueous solution takes place by the same mechanism. The presence of low valency compounds in the solid phase indicates that they exist in the cathodic zone, i.e. in the material of the cathode film which is formed as a result of the accumulation of a sufficient amount of low valency compounds of the respective metals at a given polarization value, the cathode layer being alkalized at the same time. The cathode film is a source material for a deeper reduction reaction to proceed and it serves as a barrier that separates the reaction zone from the bulk electrolyte, preventing the oxidation of low valency compounds that have already formed there. The nature of the ligand determines the rate of dissolution of incomplete reduction products formed in the cathode layer on the electrolyte side and the rate of formation of these products as a result of alkalization. These chemical reactions parallel the electrochemical reactions. The physicochemical properties of the cathode film determine the technological parameters of the electroreduction of the corresponding metal ions. The formation of real bifunctional systems makes it possible to produce functional coatings and to electrocrystallize metals with deposition potentials that are more negative than with hydrogen.

Electrochemical oscillations of the system Hg, HSO −4, BrO −3 and phenol

The electrochemical oscillations of the system Hg, HSO − 4, BrO − 3 and phenol are described. These oscillations arise at the dme in the range of potentials from +0.06 V to +0.01 V against a potential of a 1.5 mol dm −3 Hg/Hg 2SO 4 electrode in a solution of sulphuric acid, sodium bromate and phenol. The temporal change of the limiting current and that of surface-tension of mercury oscillate in an anodic, anodic—cathodic or cathodic range depending on the concentration of phenol and on the value of the dme potential. The probable mechanism is also discussed. This is based on the simultaneous electroreduction of bromate ions and the electro-oxidation of mercury as the surface-tension changes, produced by the film of Hg 2SO 4 and Hg 2Br 2 formation and by the adsorption of phenol and/or its oxidation products.

Amperometric determination of metal ions in a flow-injection system witha a copper-amalgam electrode

The direct electroreduction of metal ions in an ammoniacal buffer as complexing carrier stream is demostrated at a copper amalgam working electrode in a flow-injection system. Injection of 0.02–80 μg of cadmium(II) in volumes of 1–40 μl gave sharp response peaks; the relative standard deviation for peak-height measurements was 0.6% and the response time was 12 s for baseline resolution. After deaeration of the ammoniacal buffer and sample solutions, detection limits of 2–3 ng were obtained for copper, cadmium, and zinc at working potential of −0.60 V, −1.00 V and −1.40 V (vs. SCE), respectively.

The electrogeneration of solvated metal atoms—II. Analyses of the stabilities of solvated cations and atoms

The purpose of this paper is to investigate mechanical models of ionic and atomic solvation in order to suggest a part of mechanism of the electroreduction of metal ions. We use a Morse potential, the parameters for which are determined with the use of spectroscopic information, to try to predict the mechanical properties of a solvated atom. In particular, the solvated ionic and atomic systems are allowed to approach and interact with a metallic surface. Changes in the positions of the equilibria and changes in the calculated force constants are determined. We define accurate adionic and adatomic states. In these states the ion or atom occupies an expanded cage which includes the solvent and the surface of the metal. The activation energies for the formation of adions may be much larger than the activation energies for the formation of the related adatoms. Thus, if a reduction should occur at the outer Helmholtz plane, a solvated atom can be formed. In the vicinity of the surface, such a solvated atom can desolvate much more readily than the ion. The strength with which solvent or ligand is associated with a zero-valent metallic species, we believe, influences strongly the character of the metallic deposit formed.

ChemInform Abstract: ELECTROREDUCTION OF URANYL ION IN AQUEOUS CALCIUM NITRATE SOLUTIONS

AbstractDie Elektro‐ ‐ reduktion des UOätlons wird in Acetat‐gepufferter (pH 3.65 oder 4.65) und ungepufferter 0.5 M Ca(NO3)2 ‐Lösung mit Hilfe polarographischer, cyclisch voltammetrischer, chronopotentiometrischer Methoden untersucht.

Electroreduction of uranyl ion in aqueous calcium nitrate solutions

The electroreduction of uranyl ions in buffered and unbuffered 0.5 M calcium nitrate has been studied using polarography, cyclic voltammetry, chronopotentiometry, and chronoamperometry. The results are compared with those in molten calcium nitrate tetrahydrate.

Electrode process in the presence of a surface active substance with accelerating-inhibiting properties

The electrode process in the presence of a surface active substance with accelerating-inhibiting properties is considered. The rate constant of the process k σ 1, θ is expressed as a sum of the rate corresponding to the electrostatic effect k σ 1 and that corresponding to the blocking effect k θ; k σ 1,θ = k σ 1 + k θ. The relations derived describe the experimental data for electroreduction of cadmium ions from a 3 M H 2SO 4 solution in the presence of benzenesulfonate ions.

Some trends in the influence of surface-active substances on electrode processes

Suggestions for the origin of an additional energy barrier during discharge at high degrees of surface coverage with an adsorbate are expounded. The influence of pH and background anions on the rate of inhibited electrode reactions is discussed. The effects of the inhibition of electrode processes by the adsorption of complexes of reacting ions with addition agents are considered. The main trends in the action of various classes of surface-active substances and their effect on the kinetics of electroreduction of metal ions and technological characteristics of electrocrystallization processes (current efficiency, diffusibility, the structure of cathodic deposits and others) are discussed. The main principles in choosing surface-active substances and background anions for the electrodeposition of metals in electroplating and hydroelectrometallurgy are formulated.

The rate of cadmium reduction of the DME in sulphate media and the role of hydrolytic products

Using a.c. phase-sensitive polarography the rate constants of electroreduction of cadmium ions were measured in neutral sulphate solutions which were successively acidified (pH range 5 to 1.5). The rate constant of charge-transfer reaction increased considerably with pH, the dependence of log k o vs. pH yielded a slope with a value close to 0.5. From this dependence, from reported data on hydrolysis of cadmium ions and from the double-layer effect at a constant pH value it is supposed that Cd 2 (OH) 3+ is the most probable complex governing the reduction rate via the hydrolyzed form of cadmium. The results could contribute to the explanation of a large scatter in rate constants found in the literature measured in the so-called neutral supporting electrolytes.

The rate of cadmium reduction on the DME in sulphate media and the role of hydrolytic products

Using a.c. phase-sensitive polarography the rate constants of electroreduction of cadmium ions were measured in neutral sulphate solutions which were successively acidified (pH range 5 to 1.5). The rate constant of charge-transfer reaction increased considerably with pH, the dependence of log k o vs. pH yielded a slope with a value close to 0.5. From this dependence, from reported data on hydrolysis of cadmium ions and from the double-layer effect at a constant pH value it is supposed that Cd 2(OH) 3+ is the most probable complex governing the reduction rate via the hydrolyzed form of cadmium. The results could contribute to the explanation of a large scatter in rate constants found in the literature measured in the so-called neutral supporting electrolytes.

Effects of adsorbed ions on simple electrode reactions. Part 1.—Reduction of periodate ion in the presence of toluene-p-sulphonate anions

The influence of adsorbed toluene-p-sulphonate ions on the rate of electroreduction of periodate ions at mercury has been studied as a function of electrode potential and bulk concentration of the adsorbing ions in solutions of constant ionic strength. The ratio of the reduction rate in the presence of adsorbed anions to that in their absence at constant potential was found to be a function of the surface concentration of the adsorbed species independent of electrode potential, bulk concentration of the adsorbing species and their orientation on the electrode surface. An analysis of the decelerating effect of the adsorbed ions in terms of an electrostatic model of the interface which considers discreteness-of-charge effects is presented. The results of the analysis indicate that the reacting anion pairs with non-adsorbed cations in the vicinity of the reaction site before entering the activated state.