Electrochemical reduction of polymeric carbon

It was found that the electrochemical reduction of poly (tetrafluoroethylene) with lithium amalgam leading to the mixture of polymeric carbon and lithium fluoride as solid product is followed by a consecutive electrochemical reaction via a polymeric anion radical, [$\text{(}\text{?}$C_n$\text{)}\text{?}$^?]_m. The value of n was determined as 4.75 and was found to be independent of the reaction conditions. The charge of this radical is during the reaction neutralised with Li⁺ ions diffusing through the solid phase to form a chemical compound $\text{(}\text{?}$C_nLi$\text{)}\text{?}$_m whose CLi bonds have a localized character. Therefore, this compound does not evolve hydrogen in contact with water as the intercalation compounds C_nLi, but hydrolyses to a solid hydrocarbon $\text{(}\text{?}$C_nH$\text{)}\text{?}$_m.     

Electrochemical reduction of polyaromatic compounds

The electrochemical hydrogenation of several polycyclic aromatic compounds was investigated in aqueous tetrabutylammonium hydroxide electrolytes at different concentrations. Appropriate electrochemical conditions were determined on the basis of polarization curves, and electrolyses were there-after carried out at different cathodes, Hg, Pb, Zn and graphite. It was found that anthracene as a model compound can be reduced in a divided cell into 9,10-dihydroanthracene, not only on Hg, but also on other electrodes. At low current density more than 90% conversion can be reached. Octahydroanthracene was produced only at the mercury electrode. The possibility of electrochemical reduction of phenanthrene, fluoranthene and fluorene was also investigated.Author to whom correspondence should be addressed.     

Electrochemical reduction of sulphur in dimethylacetamide

The electrochemical reduction of sulphur into S^2?₈ and S^?₃, then into S^2?₄ has been studied in dimethylacetamide in order to prove that neither the disproportionation of S^2?₈, nor the direct electroreduction of S^2?₈ could be neglected to explain the mechanism of the electroreduction of S₈. A good fit between calculated and experimental visible absorbance or electrochemical curves recorded during coulometric experiments could be obtained without introducing the S^?₄ radical proposed in the literature.Equilibrium constants have been determined

.An estimation of the basicity of S^2?₈ and S^2?₃ ions is deduced from voltammetric curves recorded during the electrolysis of S₈ solutions.     

Electrochemical reduction of chemically passivated iron

Iron passivated chemically in chromate solutions over a range of pH was electrochemically reduced in phosphate-borate buffer solution of pH 8.5. According to the chronopotentiometry, the passive film became thinner as the pH diminished, which was in agreement with the ellipsometric result. The rest potential became more positive with decreasing pH, and the pH dependence was ?0.11 V/pH and ?0.07 V/pH in acid and alkaline solutions, respectively. The shift of the rest potential towards more positive values did not lead to an increase in the thickness of the passive film, and in this it differs from the behaviour of the passive film formed anodically. This discrepancy can be rationalized by the idea that most of the potential drop appears not across the passive film, but at the passive film-solution interface. In chemical passivation, a positive shift of the electrode potential is not associated with the growth of the passive film, provided that the rest potential is more positive than the Flade potential. The most influential factor for passive film growth is the environment, in which the iron initially dissolves readily and the passive film retains its stability.     

Electrochemical oxygen reduction on oxide catalysts

The process of oxygen electroreduction and adsorption in alkaline medium on nickel and cobalt oxides has been studied by the potentiodynamic and the disc-ring electrode methods. The oxide films were formed on the surface of metal specimens by thermal or electrochemical oxidation.After oxidation, the surface was examined by X-ray diffraction and electron diffraction. It was found that, depending on the oxidation conditions, simple or complex oxides are formed on the surface of metal specimens. Nickel and Cobalt oxide films obtained by thermal oxidation at t° ?300°C are more active than pure metals. The oxides of spinel structure Co₃O₄ and NiCo₂O₄ have an optimum activity. It is shown that oxygen adsorbed during the heat treatment of the specimens accelerates the process of the molecular oxygen reduction. On the oxides of spinel structure the oxygen reduction reaction proceeds to OH^?, whereas on simple nickel oxides the final product of oxygen reduction is HO^?₂.     

Electrochemical reduction of derivatives of 2,3-butanediol

Electrochemical reduction of cyclic and acyclic derivatives of 2,3-butanediol to C₄-hydrocarbons was examined. Among the derivatives, the cyclic sulphate was directly reduced to 2-butene; the diacetate and dimethanesulphonate also gave 2-butene but by indirect reduction with electrogenated amalgam.     

Electrochemical reduction processes in indigo dyeing

The application of indirect electrolysis as a reduction technique in indigo dyeing is described. Various reversible redox systems were tested to determine whether they are suitable for indigo dyeing. The results of the dyeing trials confirm that the process engineering involved can be applied to the production of denim. The new process offers environmental benefits and offers the prospects of improved process stability, because the reduction state in the dyebath can be readily monitored by measuring reduction potential.     

Electrochemical reduction of cerium oxide into metal

The Fray Farthing and Chen (FFC) and Ono and Suzuki (OS) processes were developed for the reduction of titanium oxide to titanium metal by electrolysis in high temperature molten alkali chloride salts. The possible transposition to CeO₂ reduction is considered in this study. Present work clarifies, by electro-analytical techniques, the reduction pathway leading to the metal. The reduction of CeO₂ into metal was feasible via an indirect mechanism. Electrolyses on 10 g of CeO₂ were carried out to evaluate the electrochemical process efficiency. Ca metal is electrodeposited at the cathode from CaCl₂–KCl solvent and reacts chemically with ceria to form not only metallic cerium, but also cerium oxychloride.     

Electrochemical reduction of dichloromethane to higher hydrocarbons

The electroreduction of CH2Cl2 at Ni, Cu, Pt and Ag electrodes in acetonitrile and (C4H9)4NI 0.1m as supporting electrolyte was studied. The half-wave potential was found to be in the range –2.2 to –2.5V vs SCE at room temperature. From the analysis of the gaseous products it was found that methane, ethylene, chloromethane, propene and butene isomers were the main products, while at silver and platinum cathodes methane was mainly produced. The effect of the potential on the current efficiency of the gaseous products was also studied. The current efficiency of the products increases at concentration levels of CH2Cl2 up to 0.2m, whereas at higher values its CE is not significantly influenced. The application of the Schultz–Flory distribution analysis to the experimental data showed that the hydrocarbons are mainly formed via polymerization of methylene radicals on the surface of Ni and Cu electrodes. At Ag and Pt electrodes the mechanism appears to be different.     

Electrochemical reduction of 2-chloro-2-cyclohexenones

The electrochemical reduction of the 2-chloro-2-cyclohexenones 2a–2c (mercury cathode, CH₃CN,Bu₄NBF₄) was studied by means of cyclic voltammetry, dc polarography, coulometry and chemical product analysis. The results were compared to those obtained with the analogous 2-cyclohexenones 1a–1c. Due to the chloro-substituent on C—2 the half wave potentials E_1/2 for the first electron transfer step become less cathodic and the overall mechanism of reduction of a chloro-substituent on C—6 is modified. In addition, strong inhibition effects were observed in the cyclic voltammograms of compound 2 and it was found that other 2-halogeno-2-cycloalkenones exhibit a similar behaviour.     

Electrochemical reduction of diphenyl 4-nitrobenzyl phosphate

The electroreduction of diphenyl 4-nirobenzyl phosphate in non-aqueous media has been examined by polarography, cyclic voltammetry, controlled-potential coulometry and electron spin resonance spectroscopy. A 1-electron reduction (half-wave potential in ACETONITRILE = −0·880 V vs aqueous saturated calomel reference) gives the anion radical of the phosphate, but this species decomposes rapidly to give the diphenyl phosphate anion and a neutral 4-nitrobenzyl radical. This neutral radical dimerises to give 4,4′-dinitrobibenzyl as the major product although some 4-nitrotoluene is also produced, presumably by hydrogen atom abstraction from the solvent.     

Electrochemical reduction of lanthanides in propylene carbonate

The electrochemical reduction of europium, ytterbium and samarium in propylene carbonate was investigated by cyclic voltammetry. These reactions proceed in two stages, where the first is due to the formation of divalent ions. The influence of the water content in the stability of Sm²⁺ is analysed, since Sm²⁺ is partly oxidised by the wter present in the propylene carbonate. The stability of the divalent species decreases in the order: Eu²⁺ > Yb²⁺ > Sm²⁺.     

Electrochemical reduction of derivatives and isomers of ethylpicolinate

Electrolysis of picolinic acid, 2-formylpyridine, 2-hydroxymethylpyridine, ethylnicotinate and ethylisonicotinate in aqueous sulfuric acid solutions was performed on a lead cathode in galvanostatic mode. Electrolyses of picolinic acid, ethylnicotinate and ethylisonicotinate were performed in aqueous solutions to prepare the different hydroxymethylpyridine isomers. Results were compared with those for ethylpicolinate: the chemical yield in 2-hydroxymethylpyridine is lower than that in 3-hydroxymethylpyridine while that in 4-hydroxymethylpyridine is better. Electrolyses of the intermediates 2-formylpyridine and 2-hydroxymethylpyridine in aqueous solutions were performed with a view to understanding the competition between the reduction of the side chain and that of the pyridine nucleus. Study of medium acidity, current density, concentration and temperature shows that electroreduction occurs on the pyridinic nucleus of the formylpyridine and the picoline principally and less on the other derivatives.     

Electrochemical reduction of nickel ions from dilute solutions

Electrochemical reduction of nickel ions in dilute solution using a divided GBC-cell is of interest for purification of waste waters. A typical solution to be treated is the effluent from steel etching processes which contain low quantities of nickel, chromate and chromium ions. Reduction of chromate in a divided GBC-cell results in effluent containing Cr³⁺ ions. This paper examines the limitations to further treatment of the effluent by electrochemical reduction of nickel ions. Nickel current efficiency has been determined by varying temperature, pH, current density and concentration of supporting electrolyte. It was found that the presence of a complexing agent, e.g. NH₄ ⁺ is necessary. To deposit nickel, complete removal of Cr³⁺ ions from the solution is inevitable. Optimum nickel current efficiencies are obtained at pH 5 and current density 10 mA cm^–2.     

Electrochemical reduction of trinitrotoluene on core-shell tin-carbon electrodes

In this work, we studied the electrochemical process of 2,4,6-trinitrotoluene (TNT) reduction on a new type of electrodes based on a core-shell tin-carbon Sn(C) structure. The Sn(C) composite was prepared from the precursor tetramethyl-tin Sn(CH₃)₄, and the product contained a core of submicron-sized tin particles uniformly enveloped with carbon shells. Cyclic voltammograms of Sn(C) electrodes in aqueous sodium chloride solutions containing TNT show three well-pronounced reduction waves in the potential range of −0.50 to −0.80 V (vs. an Ag/AgCl/Cl⁻ reference electrode) that correspond to the multistep process of TNT reduction. Electrodes containing Sn(C) particles annealed at 800 °C under argon develop higher voltammetric currents of TNT reduction (comparing to the as-prepared tin-carbon material) due to stabilization of the carbon shell. It is suggested that the reduction of TNT on core-shell tin-carbon electrodes is an electrochemically irreversible process. A partial oxidation of the TNT reduction products occurred at around −0.20 V. The electrochemical response of TNT reduction shows that it is not controlled by the diffusion of the active species to/from the electrodes but rather by interfacial charge transfer and possible adsorption phenomena. The tin-carbon electrodes demonstrate significantly stable behavior for TNT reduction in NaCl solutions and provide sufficient reproducibility with no surface fouling through prolonged voltammetric cycling. It is presumed that tin nanoparticles, which constitute the core, are electrochemically inactive towards TNT reduction, but Sn or SnO₂ formed on the electrodes during TNT reduction may participate in this reaction as catalysts or carbon-modifying agents. The nitro-groups of TNT can be reduced irreversibly (via two possible paths) by three six-electron transfers, to 2,4,6-triaminotoluene, as follows from mass-spectrometric studies. The tin-carbon electrodes described herein may serve as amperometric sensors for the detection of trace TNT.     

Electrochemical reduction of niobium ions in molten LiF-NaF

The mechanism of the electrochemical reduction of niobium ions in molten LiF-NaF (11 mol) has been studied in detail at 750 and 800° C by the use of cyclic voltametry, chronoamperometry and chronopotentiometry. In the solution of niobium ions in LiF-NaF, it is concluded that the mechanism for the electrochemical reduction of fluoroniobate is: Nb^v+eNb^IV Nb^IV+4eNb⁰ at potentials of about –0.06 and –0.17 V, respectively (referred to the reliable Ni/NiF₂ (1 mol%) electrode [1]. The electrochemical reaction Nb^IV+4eNb⁰ is a (quasi)reversible and diffusion-controlled process.The conclusion has also been confirmed by analysis of the cathodic product obtained at constant potential with a scanning electron microscope.     

Electrochemical reduction of graphene oxide in organic solvents

Graphene oxide (GO) cast on conductive substrates was electrochemically reduced in some organic solvents. The amount of electricity required for the almost complete reduction of GO was 2.0 C for 1 mg GO, corresponding to attaching of a one-electron reducible species to each benzene ring in graphene. The electrochemically reduced GO film gave an electrical conductivity of about 3 S cm⁻¹ and exhibited a relatively high specific capacitance of 147.2 F g⁻¹ in propylene carbonate. The electrochemical reduction of GO was feasible on Al foils as well.     

Electrochemical reduction of nitrate in weakly alkaline solutions

The electrocatalytic activity of several materials for the nitrate reduction reaction was studied by cyclic voltammetry on a rotating ring disc electrode in solutions with different concentrations of sodium bicarbonate. Copper exhibited highest catalytic activity among the materials studied. Nitrate reduction on copper was characterized by two cathodic shoulders on the polarization curve in the potential region of the commencement of hydrogen evolution. In this potential range an anodic current response was observed on the Pt ring electrode identified as nitrite to nitrate oxidation. This indicates that nitrite is an intermediate product during nitrate reduction. These conclusions were verified by batch electrolysis using a plate electrode electrochemical cell. Copper and nickel, materials representing the opposite ends of the electrocatalytic activity spectra, were used in batch electrolysis testing.     

Electrochemical reduction of dimanganese decacarbonyl and dirhenium decacarbonyl

The electrochemical reduction of Mn₂(CO)₁₀ and Re₂(CO)₁₀ at mercury electrodes has been studied in organic solvents by classical polarography, coulometry, chronopotentiometry and cyclic voltammetry. The mechanism is electrochemical—chemical and the kinetic parameters of the electrochemical step are given. The reduction products are identified as clusters of manganese and rhenium carbonyls by ir spectroscopy and proton NMR spectroscopy.