Products Of Electrochemical Reduction Research Articles

Effect of electrolysis voltage on electrochemical reduction of titanium oxide to titanium in molten calcium chloride

The electrochemical reduction of solid TiO 2 directly to solid metal is a promising alternative to the current Kroll process. The present work is aimed at studying the effect of electrolysis voltage on the rate of electrochemical reduction. The products of electrochemical reduction of TiO 2 and Ti 2O were examined using the scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The results show that Ti 2O was reduced to low valent titanium oxide at 1.5–1.7 V, which was the result of ionization of oxygen. TiO 2 and Ti 2O were reduced to titanium metal at 2.1–3.1 V, which was the co-action of ionization of oxygen and calciothermic reduction. The oxygen content decreased rapidly with voltage increasing from 2.1 to 2.6 V, while it changed little from 2.6 to 3.1 V. The optimized cell voltage was 2.6–3.1 V.

Chemical reduction of three-dimensional silica micro-assemblies into microporous silicon replicas

The carbothermal reduction of silica into silicon requires the use of temperatures well above the silicon melting point (> or =2,000 degrees C). Solid silicon has recently been generated directly from silica at much lower temperatures (< or =850 degrees C) via electrochemical reduction in molten salts. However, the silicon products of such electrochemical reduction did not retain the microscale morphology of the starting silica reactants. Here we demonstrate a low-temperature (650 degrees C) magnesiothermic reduction process for converting three-dimensional nanostructured silica micro-assemblies into microporous nanocrystalline silicon replicas. The intricate nanostructured silica microshells (frustules) of diatoms (unicellular algae) were converted into co-continuous, nanocrystalline mixtures of silicon and magnesia by reaction with magnesium gas. Selective magnesia dissolution then yielded an interconnected network of silicon nanocrystals that retained the starting three-dimensional frustule morphology. The silicon replicas possessed a high specific surface area (>500 m(2) g(-1)), and contained a significant population of micropores (< or =20 A). The silicon replicas were photoluminescent, and exhibited rapid changes in impedance upon exposure to gaseous nitric oxide (suggesting a possible application in microscale gas sensing). This process enables the syntheses of microporous nanocrystalline silicon micro-assemblies with multifarious three-dimensional shapes inherited from biological or synthetic silica templates for sensor, electronic, optical or biomedical applications.

Assignment of Molecular Structures to the Electrochemical Reduction Products of Diiron Compounds Related to [Fe−Fe] Hydrogenase: A Combined Experimental and Density Functional Theory Study

The reduction chemistry of (mu-bridge)[Fe(CO)3]2 [bridge = propane-1,3-dithiolate (1) and ethane-1,2-dithiolate (2)] is punctuated by the formation of distinct products, resulting in a marked difference in CO inhibition of electrocatalytic proton reduction. The products formed following reduction of 2 have been examined by a range of electrochemical, spectroelectrochemical, and spectroscopic approaches. Density functional theory has allowed assessment of the relative energies of the structures proposed for the reduction products and agreement between the calculated spectra (IR and NMR) and bond distances with the experimental spectra and EXAFS-derived structural parameters. For 1 and 2, one-electron reduction is accompanied by dimerization, but the structure, stability, and reaction with CO of the dimer is different in the two cases, and this is responsible for the different CO inhibition response for electrocatalytic proton reduction. Calculations of the alternate structures of the two-electron, one-proton reduced forms of 2 show that the isomers with terminally bound hydrides are unlikely to play a significant role in the chemistry of these species. The hydride-transfer chemistry of the 1B species is more reasonably attributed to a hydride-bridged form. The combination of experimental and computational results provides a solid foundation for the interpretation of the reduction chemistry of dithiolate-bridged diiron compounds, and this will underpin translation of the diiron subsite of the [FeFe] hydrogenase H cluster into an abiological context.

Integration of EXAFS, Spectroscopic, and DFT Techniques for Elucidation of the Structure of Reactive Diiron Compounds

Strategies for modelling the EXAFS of a range of compounds with structural features common to the diiron subsite of the [FeFe] hydrogenase H-centre are compared, and this has allowed identification of highly constrained models that still permit expression of the main structural characteristics of the compounds. Despite giving self-consistent values of the iron–scatterer distances, the EXAFS analysis fails to give unambiguous identification of the stereochemistry and composition of the compounds, and this necessitates the integration of results obtained using other spectroscopic and computational approaches. The combination of infrared spectroscopy, EXAFS, and ab initio DFT calculations are shown to provide a particularly potent approach for the study of metal carbonyl compounds of this class. In this case the EXAFS-derived iron–scatterer distances provide the basis of the starting point for DFT geometry optimization calculations, and the final distances together with the calculated infrared spectrum provides a means of validating the computed geometry. The approach is applied both to compounds of known structure and to the examination of the unstable products of chemical or electrochemical reduction.

Lithium Ethylene Dicarbonate Identified as the Primary Product of Chemical and Electrochemical Reduction of EC in 1.2 M LiPF6/EC:EMC Electrolyte

Lithium ethylene dicarbonate ((CH2OCO2Li)2) was chemically synthesized and its Fourier transform infrared (FTIR) spectrum was obtained and compared with that of surface films formed on Ni after cyclic voltammetry (CV) in 1.2 M lithium hexafluorophosphate (LiPF6)/ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7, w/w) electrolyte and on metallic lithium cleaved in-situ in the same electrolyte. By comparison of IR experimental spectra with that of the synthesized compound, we established that the title compound is the predominant surface species in both instances. Detailed analysis of the IR spectrum utilizing quantum chemical (Hartree-Fock) calculations indicates that intermolecular association through O...Li...O interactions is very important in this compound. It is likely that the title compound in the passivation layer has a highly associated structure, but the exact intermolecular conformation could not be established on the basis of analysis of the IR spectrum.

An investigation into electrochemical reduction of TiO2 pellet

The electrolytic reduction of solid TiO2 directly to the solid metal is a promising alternative to the current Kroll process. The products of electrochemical reduction of TiO2 in the present work were examined by SEM, EDX and XRD, which showed that TiO2 was reduced progressively from outside to inside of a pellet and from a high valence oxide to a lower one until the metallic state was achieved. From the analysis of anode gases and the measurement of current during the electrolysis, it was observed that the average current efficiency was relatively low and decreased with electrolysis time. Secondary reaction between Ca and CO, CO2 evolution at the anode and a short circuit caused by the black carbon product were considered as the main reasons for low current efficiency. There are two methods to improve the current efficiency. One is to separate the anode region from the cathode region to limit the secondary reaction. The other is to drain the molten salt containing black carbon at the surface continuously or to cut off the short circuit caused by black carbon bridging between anode and cathode.

Electrochemical reduction of pyrite in aqueous NaCl solution

Optimum conditions for pyrite removal from a high-sulfur coal by electrochemical reduction during flotation are determined by orthogonal experiments. The electrochemical reduction process of pure pyrite is examined with XRD, electrochemical and chemical analysis. The results show that the electrochemical reduction products of pyrite are FeS and S 2−. During this process, the reactions at cathode are: FeS 2+2e→FeS+S 2− and 2H ++2e→H 2. The corresponding electrode potentials and kinetic equation are determined. The conversion of hydrophobic pyrite to hydrophilic FeS and S 2− by electrochemical reduction is beneficial to desulfurization from coal in floatation process.

Studies on the Reduction of [(C5Me5)2Mo2O5] in Methanol/Water/Acetate Solutions by On‐Line Electrochemical Flowcell and Electrospray Mass Spectrometry

AbstractThe complex [Cp*2Mo2O5] (Cp* = η5‐C5Me5) and its electrochemical reduction products in acetic acid/acetate‐buffered (pH = 4.0) water/methanol solutions were investigated by combined electrochemical (EC) flowcell and on‐line electrospray ionization mass spectrometry (ESI‐MS). Mono‐, di‐, tri‐, and tetranuclear organometallic molybdenum oxides were identified in the starting solution. The effect of the relevant ESI‐MS parameters (ionic mode, heated capillary voltage, and heated capillary temperature) and of the concentration on the observed distribution of ions in the mass spectrometer was studied in order to minimize side reactions in the ESI chamber. It was verified that reduction in the ESI‐MS is undetectable under open‐circuit conditions. The on‐line electrochemical study revealed the potential‐dependent formation of previously unknown mono‐, di‐, tri‐, and tetranuclear MoV, MoIV, and mixed‐valence complexes. The compounds were identified by their characteristic isotope patterns and their ion trap MSn fragmentations. The observed formation potentials reflect the higher stability of the multinuclear species relative to the mononuclear ones with the same oxidation state. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003)

Electrochemical reduction of As(III) and As(V) in acidic and basic solutions

The removal of As(III) and As(V) from acidic and basic solutions by electrochemical reduction was studied using a reticulated vitreous carbon cathode and a IrO2/Ti anode in an electrochemical reactor that could be operated divided or undivided. By using a cascade of 7–9 plug flow reactors, residual concentrations of arsenic less than 20 ppb were achieved upon reduction of 100 ppm As(III) in either acidic or alkaline solutions and for 100 ppm As(V) in acidic solution. The reduction of As(V), generally considered electrochemically inactive in alkaline solutions, was proved possible, but was much less efficient. In all cases, the only product of electrochemical reduction was arsine. A moderate improvement in reduction efficiency was achieved under conditions of electrocatalytic hydrogenation using 5% Pd on alumina as catalyst.

ESR parameters and transformations of the products of reduction of methanofullerenes

Paramagnetic products of chemical (by diazabicycloene derivatives) and electrochemical reduction of the dicarbethoxy derivative and phosphorylated methane[60]fullerenes were studied by ESR. In all cases, one-electron reduction affords radical anions (g = 1.9998—1.9999, ΔH = 0.20—0.28 mT), and further reduction produces the secondary radicals (g = 2.0004—2.0010, ΔH = 0.020—0.028 mT). The rate constants for formation and decay of the radical anions in chemical reduction depend slightly on the nature of the reducing agent and substituents in the methanofullerenes. The retro-Bingel reaction occurs during two-electron reduction.

Electrochemical stability and transformations of fluorinated poly(2,6-dimethyl-1,4-phenylene oxide)

Fluorination of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) leads to narrowing of its window of electrochemical stability in a cathodic range of potentials. It is found this is connected with appearance of both perfluorinated and incompletely fluorinated units in the polymer. The former units are liable to electrochemical reduction (at potentials <−2.0 V) followed by elimination of fluorine anions and the latter react with basic products (generated at potentials <−1.8 V) of electrochemical reduction of the background solution. In the both cases this results in appearance of conjugated multiple bonds in the fluorinated macromolecules. Quantities of these units in fluorinated PPO were determined with a help of direct and indirect electrochemical reductive degradation techniques.

Electrochemical conversion of carbon dioxide to formic acid on Pb in KOH/methanol electrolyte at ambient temperature and pressure

The electrochemical reduction of CO 2 in KOH/methanol-based electrolyte has been investigated on a lead wire electrode at ambient temperature and pressure. The major products of electrochemical reduction of CO 2 were formic acid, CO and methane. The formation of formic acid from CO 2 predominated in the potential range −1.8 to −2.5 V vs Ag/AgCl (saturated KCl). Hydrogen evolution in competition with CO 2 reduction was observed at only 3.5% faradaic efficiency. The partial current density for CO 2 reduction was more than 22 times larger than that for hydrogen evolution. Study of the Tafel plot showed that the reduction of CO 2 to formic acid and CO was not limited by mass transfer in this potential range.

Indirect electrochemical reductive degradation of polycarbonates

We have studied the kinetic characteristics of degradation of polycarbonates with different structures in dimethylformamide when treated with the products of electrochemical reduction of a (C4H9)4NClO4 solution in dimethylformamide (supporting solution). We have shown that this process (which can be described as indirect electrochemical reductive degradation) occurs according to a nucleophilic catalytic mechanism.

Indirect Electrochemical Dehydrochlorination of Polyvinylchloride

Abstract The initiation of electrochemical reductive degradation (ECRD) of polyvinylchloride (PVC) by the active products of electrochemical reduction of dimethylformamide (DMF) and acetonitrile (MeCN) has been investigated. It was determined that ECRD leads to dehydro-chlorination of PVC and brings into appearance polyconjugated double bonds that are able to further chemical conversion. The kinetics of indirect electrochemical dehydrochlorination process depends on a phase state of the polymer. This process occurs immediately at the interaction of solute PVC with the DMF electrolysis products. The kinetics of dehydrochlorination of the solid-phase polymer in MeCN is determined by the penetration of the active particles into the polymer volume. The possibility to apply the process of the indirect electrochemical dehydrochlorination for both the PVC surface modification to impart the hydrophilicity and to increase the PVC membranes productivity was revealed.

An integrated calcium fluoride crystal ir thin-layer cell and its application to identification of electrochemical reduction product of bilirubin

An integrated CaF 2 crystal optically transparent infrared ( ir) thin-layer cell was designed and constructed without using any soluble adhesive materials. It is suitable for both aqueous and nonaqueous systems, and can be used not only in ir but also in uv-vis studies. Excellent electrochemical and spectroelecrochemical responses were obtained in evaluating this cell by cyclic voltammetry and steady-state potential step measurements for both ir and uv-vis spectrolectrochemistry with ferri/ferrocyanide in aqueous solution, and with ferrocene/ferrocenium in organic solvent as the testing species, respectively. The newly designed ir cell was applied to investigate the electrochemical reduction process of bilirubin in situ, which provided direct information for identifying the structure of the reduction product and proposing the reaction mechanism.

Electrochemical Reduction of CO 2 on a Cu Electrode under High Pressure: Factors that Determine the Product Selectivity

The selectivity of the electrochemical reduction products of on a Cu electrode in aqueous solution depended remarkably on the pressure (<60 atm), stirring condition, and the current density. As the flux of to the Cu electrode surface was increased by increasing pressure and/or by stirring, the main reduction product was changed in the order of and/or . On the other hand, the selectivity of the reduction products was changed in the order of and/or by increasing the current density. From these results, it was concluded that the balance between the flux of from the bulk solution to the electrode surface and the current density determines which reduction products are produced. Hydrocarbon formation was preferential when the current density was comparable to the maximum flux under given condition. The partial current density for maximum hydrocarbon formation occurred at 375 mA cm−2 under pressure at 30 atm.

Electrochemical reduction products of azido nucleosides, including zidovudine (AZT): mechanisms and relevance to their intracellular metabolism.

Previous studies on electrochemical reduction of the HIV reverse transcriptase inhibitor, 3'-azido-3'-deoxythymidine (Zidovudine, AZT) and several of its analogues, have been extended to 2'-AZdT and two of the intracellular metabolites of AZT, the 5'-O-glucuronide (GAZT) and the 5'-phosphate (AZTMP). Also investigated were azido nucleosides with aglycons susceptible to electrochemical reduction, cytosine and adenine. The surface activities of these compounds at the mercury electrode were examined. In all instances, reduction of the azido group was a two-electron process, with conversion to an amino group. For an azido adenine nucleoside, it proved possible to reduce the azido group without affecting the aglycon. Electrochemical reduction is shown to provide a simple one-step synthesis of amino nucleosides from the available azido nucleosides. The reduced compounds, several hitherto unknown, are useful reference standards for following intracellular metabolism of azido nucleosides, and may also prove of interest as new potential antimetabolites.

Mechanism and products of electrochemical reduction of 4-(nitrophenyl) substituted 1,4-dihydropyridines

Electrochemical reduction of isomeric 4-(nitrophenyl)-1,4-dihydropyridines (I) on mercury and solid electrodes leads to free radicals of the nitro- and nitrosobenzene type as evidenced by ESR spectroscopy. The dihydropyridine cycle undergoes reduction only in cases of N-substituted para - and meta -nitrophenyl derivatives of 1,4-dihydropyridine. 1,6-Dimethyl-3,5-dicyano-4-( para -, meta -nitrophenyl)-2-pyridonemethide (VIa, b) was identified as intermediate. The primary and secondary chemical reactions occurring during electrochemical reduction of the title compounds are discussed. The electroreduction does not involve the occurrence of an intramolecular redox system between the 1,4-dihydropyridine and nitrophenyl moieties in the molecule.

A Highly Sensitive Analysis of Electrochemical Reduction Products of CO2 on Gold by New Differential Electrochemical Mass Spectroscopy (DEMS)

Abstract The products of electrochemical reduction of CO2 on gold were analyzed in-situ by new DEMS with a stationary gas-permeable gold electrode sputtered on a porous water-repellent membrane in a rotational flow produced by a rotating rod.

INTER AND INTRAMOLECULAR INTERACTIONS OF PORPHYRINS WITH 5,5'-DITHIOBIS(2-NITROBENZOIC ACID)

meso-Tetraphenylporphyrin and its metal [zinc(II) and copper(II)] derivatives form both inter and intramolecular complexes with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB). The nature of interaction is predominantly charge transfer (CT) in origin, with the porphyrin functioning as a II-donor and DTNB as an acceptor. Among the covalently linked intramolecular systems, the magnitude of CT interaction varies with the position (of one of the aryl groups of the porphyrin) to which DTNB is attached as ortho meta > para. Steady-state and time-resolved fluorescence studies revealed electron transfer to be the dominant pathway for the fluorescence quenching in these systems. Steady-state photolysis experiments probed using EPR and optical absorption studies have shown that electron transfer (from the excited singlet state of the porphyrin) to DTNB results in the formation of thiyl radical and production of free thiolate anion. It is found that the products of electrochemical reduction of covalently linked porphyrin-DTNB systems are different from those observed for the photochemical studies.