Potentialities of the Voltammetry of 2-Butyne-1,4-diol at Mechanically Renewed Solid Electrodes

The electrochemical behavior of 2-butyne-1,4-diol was studied at solid platinum, gold, silver, cobalt, nickel, copper, and graphite electrodes. The working surfaces of the electrodes were renewed by cutting a thin 0.5-µm layer in the test solution immediately before recording every voltammogram. 2-Butyne-1,4-diol was oxidized in alkaline solutions at graphite, nickel, silver, and copper electrodes at positive potentials; the voltammograms obtained at these electrodes were suitable for analytical purposes. The dependence of the anodic current of 2-butyne-1,4-diol on its concentration was linear in the range from 0.03 to 0.3 g/L.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 5, 2005, pp. 499–503.Original Russian Text Copyright © 2005 by Skvortsova, Aleksandrova, Kiryushov.     

Electrochemical investigation of NaOH—Na<Subscript>2</Subscript>O—Na<Subscript>2</Subscript>O2—H<Subscript>2</Subscript>O—NaH melt by EMF measurements and cyclic voltammetry

Thermodynamic activity of sodium oxide and oxidation potential in NaOH—Na₂O—Na₂O₂—H₂O—NaH melt at the temperature of 400°C was investigated. Galvanic cell for the potentiometric measurements consisted either of a sodium electrode formed by β and β″-alumina semi-closed tube filled with liquid sodium or a platinum wire and of an oxygen electrode made from ZrO₂ (Y₂O₃) solid electrolyte with the Bi—Bi₂O3 reference mixture. The number of exchanged electrons determined from the electromotive force measurements was in good agreement with the assumed reactions. The activity coefficient of sodium oxide was lower than one. Voltammetric measurements were carried out with a sodium reference electrode and a nickel auxiliary electrode. Behaviour of platinum, gold, silver and nickel as working electrodes was studied. The experiments were carried out in nitrogen atmosphere. Several types of zirconia semi-closed tubes were tested for long-term measurements under the process conditions.     

Electrochemical behaviour of lanthanum fluoride in molten fluorides

The electrochemical behaviour of lanthanum fluoride dissolved in molten lithium fluoride and in eutectic mixture LiF-CaF₂ was investigated by cyclic voltammetry and laboratory electrolysis. The cyclic voltammetry experiments were carried out at 900°C and 800°C, respectively, in a graphite crucible (counter electrode). Several types of working electrodes (Mo, W, Ni and Cu) were used. Ni/Ni(II) was used as a reference electrode. Laboratory electrolysis was carried out in the system LiF-CaF₂-LaF₃ at 800°C in galvanostatic (j _c = −0.21 A cm⁻²) and potentiostatic (E = 0.87 V) regimes. In both cases, nickel served as the cathode and graphite as the anode. It was found that no new separate reduction peak occurred on the molybdenum or tungsten electrodes in the investigated systems. When copper or nickel electrodes were used, new peaks corresponding to the reduction of lanthanum(III) to lanthanum metal appeared. This can be explained by the formation of alloys or intermetallic compounds of lanthanum with copper or nickel. X-ray microanalysis showed that lanthanum was electrodeposited together with calcium under formation of intermetallic compounds with the electrode materials in the galvanostatic regime. In the potentiostatic regime, mainly lanthanum was deposited, which enabled its separation.     

Electrochemical synthesis of halogen derivatives of bis(1,2-dicarbollyl)cobalt(III)

A convenient electrochemical method for the synthesis of 8,8-dihalogen derivatives of bis(1,2-dicarbollyl)cobalt(III) anion [8,8X₂-3,3-Co(1,2-C₂B₉H₁₀)]^– (X = Cl, Br, I) was developed. The method includes the electrolysis of a solution of alkaline metal halide and tetramethylammonium salt of bis(1,2-dicarbollyl)cobalt(III) in methanol at 50 °C in a one-compartment electrochemical cell with a nickel cathode and platinum anode.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2448–2451, November, 2004.     

Nucleation at three-phase junction lines: in situ atomic force microscopy of the electrochemical reduction of sub-micrometer size silver and mercury(I) halide crystals immobilized on solid electrodes

The electrochemical reduction of sub-micrometer size silver halide crystals immobilized on the surface of gold and platinum electrodes starts at the three-phase junction line where the three phases metal, silver halide and electrolyte solution meet. Following nucleation at this line the reaction advances within seconds on the surface of the silver halide crystals until the entire surface is covered with about 20 atomic layers of silver and the reduction is terminated. The silver layer can be oxidized anodically and the next layer of the silver halide crystals becomes accessible for further reduction. This sequence of reductions and oxidations can be repeated. The nucleation of silver at the three-phase junction line can be detected by atomic force microscopy (AFM) measurements when, after a short reduction pulse and dissolution of the remaining silver halide, a thin ring of silver is observed at the place where the three-phase junction line was situated. The entire scenario of electrochemical reduction of immobilized silver halide crystals depends on the crystal size. Large crystals (about 100 µm edge-length) immobilized on the surface of optically transparent indium tin oxide electrodes show the growing of silver whiskers on the crystal surface, similar to what is known for the reduction of silver halides with photographic developers. However, also in the case of the large crystals, the reduction starts at the three-phase junction line. The electrochemical reduction of immobilized sub-micrometer size crystals of Hg₂Cl₂ and Hg₂Br₂ starts also at the three-phase junction. In the case of gold electrodes the formation of liquid mercury is followed by the formation of a solid crystalline gold amalgam. In the case of platinum electrodes the liquid mercury wets the platinum surface but does not destroy it.     

Synthesis,characterization and thermal decomposition of double monomethylammonium sulfates of cobalt,nickel, copper and zinc

Double sulfates of cobalt(II), nickel(II), copper(II) and zinc with the monomethylammonium cation were obtained from the reaction mixture of the corresponding metal sulfate and monomethylammonium sulfate in a molar ratio of 13.The obtained compounds were studied by the methods of X-ray powder diffraction, TG and DSC analysis and elemental analysis.It was found that the double sulfates have the formula (CH₃NH₃)₂M(SO₄)₂· 6H₂O, and that the cobalt, nickel and zinc compounds are isostructural. The relationship between crystal structure and thermal decomposition is discussed.The financial support of the Research Council of Macedonia, Yugoslavia, is gratefully acknowledged.     

Synthesis of nanostructured carbon on graphite electrodes with a supported Co catalyst for preparing anodes for microbial fuel cells

The synthesis of nanostructured carbon (NSC) on graphite electrodes with a supported Co catalyst by C₃ and C₄ alkane pyrolysis in the presence of hydrogen has been investigated. Co(II) hydroxo compounds have been deposited onto graphite, and a Co/graphite catalyst has been prepared by the homogeneous precipitation of divalent cobalt from cobalt nitrate solutions in the presence of urea and compounds containing OH groups, namely, lower alcohols (ethanol, n-propanol, and n-butanol) and polyols (ethylene glycol, glycerol, and sorbitol). The effect of Co catalyst preparation conditions on the pyrolytic activity of the catalyst and on the morphology of the synthesized NSC has been investigated. An active Co/graphite catalyst forms in the presence of an alcohol containing 1-3 OH groups. A fairly uniform NSC layer on the graphite surface is obtained at Co(II) nitrate concentrations of 0.05–0.1 mol/L, a urea concentration of 1 mol/L, and glycerol concentrations of 5–20 vol %. The electrochemical characteristics of the electrodes prepared and those of a microbial fuel cell (MFC) involving an NSC/graphite anode and an activated-sludge microbial consortium have been determined. The maximum power of the MFC under the conditions examined is 4.8 mW per square meter of the anode’s geometric surface area.     

Hexacyanoferrate-based composite ion-sensitive electrodes for voltammetry

Composite electrodes made of graphite, paraffin and metal hexacyanoferrates exhibit a voltammetric response of the hexacyanoferrate ions, the potential of which depends linearly on the logarithm of concentration of alkali and alkaline-earth metal ions. This behaviour has been observed on account of the fact that the electrochemical reaction is accompanied by an exchange of these ions between the solution and the zeolitic lattice of the hexacyanoferrates for charge compensation. The voltammetric determination of the formal potential of these electrodes in a solution allows the quantitative analysis of the ions which are exchanged between the metal hexacyanoferrates and the aqueous solutions. Iron(III), copper(II), silver(I), nickel(II) and cadmium(II) hexacyanoferrates have been studied for the determination of H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, NH⁺₄, Mg²⁺, Ca²⁺ and Ba²⁺. In some cases, the selectivity constants are as low as 310^-4, or even so small that their exact value is inaccessible. Electrodes made of iron (III), copper (II), silver (I), nickel (II) and cadmium (II) hexacyanoferrates are most suitable for the determination of potassium ions. Electrodes with nickel (II) and cadmium (II) hexacyanoferrates are also suitable for the determination of caesium ions. The working range of the electrodes also depends on the conductivity of the solutions and can range from 10^-5 to 1 moll^-1. Typical standard deviations of the potential measurements are 3 mV.     

High performance liquid chromatographic separation and UV determination of cobalt, copper iron and platinum in pharmaceutical preparations using bis(isovalerylacetone)ethylenediimine as complexing reagent

The reagent bis(isovalerylacetone)ethylenediimine(H₂IVA₂en) has been examined for HPLC separation and UV determination of cobalt, copper, iron and platinum using off-line precolumn derivatization and extraction in chloroform. The complexes of cobalt(II), cobalt(III), iron(II), iron(III) and the reagent have been subsequently separated on a Microsorb C-18 column. The complexes were eluted isocratically using ternary mixtures of methanol/water/acetonitrile. Detection was achieved by UV monitoring. Detection limits for Co(II), Co(III), Fe(II) and Fe(III) were 2.5–5.0 ng/injection, based on 0.5–1.0 g/ml with 5 l/injection. The concentration of cobalt(II) and cobalt(III) in aqueous solution have been determined. The presence of oxovanadium(IV), platinum(II), and nickel(II) did not affect the determinations. The HPLC method developed has been applied to the determination of cobalt, copper, iron and platinum in pharmaceutical preparations at the 30 g/g to 15 mg/g level and the obtained results were compared to those of atomic absorption spectrometry.     

Automatic coulometric titration of acids

An apparatus is described for the automatic titration of acids by the constant current coulometric technique. The generator electrodes comprise a platinum cathode and a silver/silver bromide anode. The increase in pH resulting from the reduction of hydrogen ion at the cathode is indicated by a glass electrode, in conjunction with a Beckman Automatic Titrator which automatically monitors the titration and interrupts the generating current when the equivalence point pH is reached. Quantities of hydrochloric acid in the neighborhood of 0.12 millimole in 50 ml were titrated with a mean error of ^-0.07% and an average deviation from the mean of ±0.15%. The technique is applicable to any strong or weak acid, and to acid mixtures, provided that no substance is present which is either reducible at the platinum cathode or reactive in any way at the silver anode.     

ToF‐SIMS study of 1‐dodecanethiol adsorption on Au,Ag, Cu and Pt surfaces

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) has been used to perform a chemical analysis of long‐chain thiol (CH₃(CH₂)₁₁SH)‐treated gold, silver, copper and platinum surfaces. All the mass peaks from positive and negative ion spectra within the range m/z = 0–2000 u are studied. ToF‐SIMS data revealed that on gold, silver and copper substrates 1‐dodecanethiol form dense standing‐up phases, but on platinum being a catalytically active substrate, we were able to identify also surface‐aligned parallel lying molecules in addition to a standing thiolate layer. Our study shows that when ToF‐SIMS spectra are analyzed, not only the existence of oligomers but also metal + hydrocarbon fragments give information about the order of SAM. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrocatalytic carboxylation of aliphatic halides at silver cathode in acetonitrile

A simple and efficient electrocarboxylation reaction of aliphatic halides has been developed using silver as cathode, magnesium as anode and CH₃CN saturated CO₂ as solvent in an undivided cell. The influence of some key factors (such as the nature of electrode materials, supporting electrolytes and temperature) on this reaction was investigated. Under the optimized condition, the corresponding carboxylic acids were obtained in moderate to good yields (22-89%). The electrochemical behaviour was studied at different electrodes (Ag, Cu, Ni and Ti) by cyclic voltammetry, which showed significant electrocatalytic effect of the silver electrode towards the reductive carboxylation of aliphatic halides.     

Correlation of the electrochemical reversibility and resolution of the anode and cathode peaks of the electrode processes of hydroquinone and metol on graphite and platinum

Cyclic and direct voltammetry with linear potential sweep was used to study the potential difference of the anode and cathode peaks for hydroquinone and metol in the cyclic voltammograms (CVA) of their individual solutions on the main factors affecting the reversibility of the electrochemical process on electrodes of a graphite-epoxy composite (GEC), namely, the state of the surface of the indicator electrode, the pH of the buffer solution, and the mode of polarization. The surface state of the GEC electrode was affected by its passivation in air for various periods of time; the reversibility of the electrode process was judged by the difference between the anode and cathode potentials on the CVAs of hydroquinone and metol. A correlation was found between the degree of reversibility and the difference of peak potentials for similar electrode processes of hydroquinone and metol on the GEC electrode and other solid electrodes made of graphite materials and platinum.     

正极集流体对可充镁电池电化学性能的影响

以目前常用的Chevrel相Mo₆S₈作为正极材料, 涂覆在不同集流体(不锈钢、镍、铜、钛) 上, 以镁为负极,研究了在(PhMgCl)₂-AlCl₃/四氢呋喃(简称THF)“二代”电解液中集流体对可充镁电池电化学性能的影响. 恒流放电-充电结果显示在不锈钢集流体上电池电压极化最小, 并且具有较好的循环稳定性; 镍、铜次之; 钛集流体上的极化最大, 循环稳定性也最差. 并通过对比放电-充电循环前后电极和集流体表面的微观结构, 探讨了集流体对电池性能显著影响的原因. 电解液对集流体会造成腐蚀, 不同集流体在电解液中的稳定性有差异; 正极材料涂覆在不同集流体上, 电极表面状况有差异; 负载活性材料后集流体发生腐蚀的电位有所降低, 使集流体更易受到电解液的腐蚀.     

Ice Melting to Release Reactants in Solution Syntheses

Aqueous solution syntheses are mostly based on mixing two solutions with different reactants. It is shown that freezing one solution and melting it in another solution provides a new interesting strategy to mix chemicals and to significantly change the reaction kinetics and thermodynamics. For example, a precursor solution containing a certain concentration of AgNO₃ was frozen and dropped into a reductive NaBH₄ solution at about 0 °C. The ultra‐slow release of reactants was successfully achieved. An ice‐melting process can be used to synthesize atomically dispersed metals, including cobalt, nickel, copper, rhodium, ruthenium, palladium, silver, osmium, iridium, platinum, and gold, which can be easily extended to other solution syntheses (such as precipitation, hydrolysis, and displacement reactions) and provide a generalized method to redesign the interphase reaction kinetics and ion diffusion in wet chemistry.     

Electro-oxidation of d-mannose on platinum, gold and nickel electrodes in aqueous medium

The oxidation of d-mannose is studied on platinum, gold and nickel in alkaline medium. The electro-reactivity of this compound and the rate determining step of the reactions were determined by cyclic voltammetry. Lead adatoms have important effect on the oxidation of d-mannose on platinum electrode. Five folder of increase in current densities was observed after the addition of 10⁻⁶ M Pb²⁺. Electrolyses carried out on upd-lead modified platinum, and gold electrodes show good conversion yields (75% and 80%, respectively) and reasonable selectivities towards mannonic acid. High amount of cleavage products were detected at the end of the electrolysis at nickel electrode. The reactivity-functional group relationship has been discussed considering the results of the electrolyses.     

A study of the effect of some pollutant gases on cathodes used in membrane-covered amperometric oxygen detectors

The effects of various gaseous pollutants on the electrochemical activity of materials used as cathodes for membrane-covered amperometric oxygen detectors are described. It is shown that gold and platinum cathodes are not unduly affected by concentrations of sulphur dioxide and chlorine many times greater than those likely to be encountered in test solutions, and that a gold cathode is also unaffected by hydrogen sulphide. A platinum cathode is rapidly and significantly poisoned on contact with hydrogen sulphide; an analysis of the fall in the rate of oxygen reduction as a function of time indicates that the poisoning occurs by the blocking of surface sites by sulphide. The effect of hydrogen sulphide on silver, nickel and nickel sulphide electrodes is also reported. Of these materials, only nickel sulphide is an effective electrocatalyst for oxygen reduction in the presence of sulphide.     

Electrocatalytic properties of surface oxides on gold,platinum, and stainless steel electrodes in electrooxidation of malic acid

Electrocatalytic properties of oxides formed at gold, platinum, and stainless steel electrodes in the malic acid electrooxidation in 0.1 M Na₂SO₄ are studied. Gas chromatographic analysis of the electrolyte after holding the potential at 1.0 V for 8 h shows that on platinum and gold electrodes 2 mmol of acetaldehyde are produced and on stainless steel, 45 mmol. The acetaldehyde yield is the highest on stainless steel.From Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 304–309.Original English Text Copyright © 2005 by Avramov Ivi, Popi, Antonovi.This article was submitted by the authors in English.     

The analysis of copper refinery slimes

Methods are reviewed for the determination of the following constituents of copper refinery slimes: aluminium, antimony, arsenic, barium, bismuth, calcium, cobalt, copper, gold, iron, lead, magnesium, manganese, molybdenum, nickel, platinum metals, selenium, silicon, silver, sulphur, tellurium, tin and zinc.     

Electrode materials based on lanthanum ferrite cobaltite for molten carbonate fuel cells

New cathode and anode materials for fuel cells with an electrolyte based on alkali carbonate melts have been studied. The regions of the orthorhombic and rhombohedral phases in the LaFe_1–yCo_yO₃ + x/2Li₂O system in air and in contact with molten (Li_0.68K_0.32)₂CO₃ electrolyte were investigated. The electric conductivity was analyzed in the range 300–1020 K. The electrocatalytic activity in oxygen reduction was analyzed for the new cathode materials. A method for introducing the Al₂O₃ additive in the anode material was suggested. The polarization characteristics of the porous gas-diffusion electrodes were determined.