Constant Current Electrolysis Research Articles

In situ FTIR studies on the electrochemical hydrodechlorination of 3,4,5,6-tetrachloropicolinic acid on Ag cathode

The electrochemical hydrodechlorination reaction from starting material 3,4,5,6-tetrachloropicolinic acid (3,4,5,6-TCP) to the end product 3,6-dichloropicolinic acid (3,6-DCP) was investigated by cyclic voltammetry and in situ Fourier transform infrared spectroscopy (in situ FTIR). Compared with copper and glassy carbon, Ag cathode showed a high electrocatalytic activity for the irreversible reduction process of 3,4,5,6-TCP in NaOH aqueous solution. In situ FTIR results suggested that electrochemical hydrodechlorination took place in the 4- or 5-position of 3,4,5,6-TCP on Ag cathode after receiving an electron to get mixed trichloropicolinic acid free radical, which could receive another electron and give 3,5,6-trichloropicolinic acid (3,5,6-TCP) and 3,4,6-trichloropicolinic acid (3,4,6-TCP) at the potential more positive than −1000 mV afterwards. Finally, 3,5,6-TCP and 3,4,6-TCP were further dechlorinated to produce 3,6-dichloropicolinic acid (3,6-DCP) at the potential more negative than −1000 mV. Further studies of preparative electrolysis experiments by constant current electrolysis were carried out. The results were in good agreement with those from in situ FTIR investigations.

ヒドロキノン／繊維状活性炭電極の電気二重層‐擬似容量複合キャパシタへの応用

Hydroquinone is known to show an oxidation-reduction reaction. Active carbon felt with adsorbed hydroquinone shows higher capacitance than normal activated carbon does. Adsorbed hydroquinone shows a rapid oxidation-reduction reaction that can match a capacitor’s rapid charge and discharge. Furthermore, active carbon felt with adsorbed hydroquinone has longer-term stability than normal active carbon felt has, as demonstrated using cyclic voltammetry and constant current electrolysis.

Voltammetric behaviour of o-nitrophenol in aqueous methanol medium at various electrodes

Voltammetric curves of o-nitrophenol in aqueous methanol medium for acidic, basic and neutral ranges using B.R. buffer for various concentrations (0.05, 0.1, 0.15, 0.2 mM) and scan rates were obtained. The prominent three reduction peaks corresponding to 3e- change of o-nitrophenol was characterized at 0.1 mM concentration in neutral medium at scan rate 90 mV/s. The reversibility of the reaction was also studied by the cyclic voltammetry. Constant current electrolysis of 0.02 mM o-nitrophenol in neutral medium gives o,o'-dihydroxyazobenzene at stainless steel (type 316) cathode and counter electrode of same size and material at constant current 1.8 ampere respectively, as a major product which were confirmed by spectral and chemical analysis.

Hg cathode-free electrochemical detosylation of N, N-disubstituted p-toluenesulfonamides: mild, efficient, and selective removal of N-tosyl group

Hg cathode-free electrochemical detosylation of N, N-disubstituted p-toluenesulfonamides was successfully carried out by a constant current electrolysis using an undivided cell equipped with a platinum cathode and a magnesium anode in the presence of an arene mediator. The deprotection proceeded efficiently and selectively under neutral and mild conditions with a stoichiometric amount of electricity without the use of an Hg cathode to obtain the corresponding secondary amines in good to excellent yields.

A study of tiron in aqueous solutions for redox flow battery application

In this study, the electrochemical behavior of tiron in aqueous solutions and the influence of pH were investigated. A change of pH mainly produces the following results. In acidic solutions of pH below 4, the electrode reaction of tiron exhibits a simple process at a relatively high potential with a favorable quasi-reversibility. The tiron redox reaction exhibits fast electrode kinetics and a diffusion-controlled process. In solutions of pH above 4, the electrode reaction of tiron tends to be complicated. Thus, acidic aqueous solutions of pH below 4 are favorable for the tiron as active species of a redox flow battery (RFB). Constant-current electrolysis shows that a part of capacity is irreversible and the structure of tiron is changed for the first electrolysis, which may result from an ECE process for the tiron electro-oxidation. Thus, the tiron needs an activation process for the application of a RFB. Average coulombic and energy efficiencies of the tiron/Pb battery are 93 and 82%, respectively, showing that self-discharge is small during the short-term cycling. The preliminary exploration shows that the tiron is electrochemically promising for redox flow battery application.

Polypyrrole microstructure deposited by chemical and electrochemical methods on cotton fabrics

Electrochemically and chemically coated cotton fabrics with polypyrrole are comparatively evaluated and characterized in order to produce the conducting fabrics/textiles. The polypyrrole coated fabric is obtained electrochemically by constant current electrolysis (2 mA cm −2) at room temperature for 4 h. The stability, electrical conductivity and electrochemical behaviour of such composite coating are evaluated by means of SEM, FTIR, TGA, DSC, four-probe conductivity, impedance spectroscopy and cyclic voltammetry. When compared to chemical method thicker films of polypyrrole with globular microstructure could be obtained by electrochemical technique and the conductivity of the polypyrrole film was also high (1.9 × 10 −2 to 3.3 × 10 −1 S cm −1). The weight uptake and the electrical conductivity of the coated fabric increase with concentration of pyrrole and time of electrolysis. Many other physico-chemical properties of the polypyrrole films obtained by the two methods were found to be qualitatively similar.

Preparation of LSM–YSZ composite powder for anode of solid oxide electrolysis cell and its activation mechanism

Sr-doped LaMnO 3 and Yttria stabilized zirconia (LSM–YSZ) composite powder is synthesized by the preparation of LSM on submicron-sized YSZ particles using an in-situ glycin–nitrate combustion method for solid oxide electrolysis cells (SOEC) in this paper. LSM–YSZ composite powder and the relevant LSM powder are characterized by XRD and FESEM. The results show that LSM–YSZ is net-porous composite powder while YSZ and LSM do not react with each other during synthesis process. The electrochemical test of the single button cells indicates that the in-situ LSM–YSZ powder shows better electrolysis performance and lower discharging capability than traditionally direct mixture LSM and YSZ oxygen electrode. When operating in SOEC mode with constant current electrolysis at a current density of 0.33 A cm −2 and 900 °C, the electrolytic voltage decreases from 1.21 V to 1.02 V, which indicates that LSM–YSZ electrode has an activation process at the initial testing stage. A mechanism which involves the incorporation of SrO segregated on the surface into the LSM lattice and the generation of oxygen vacancies in the LSM electrode is proposed for the activation process with O 2− oxidation on LSM electrodes.

Electrosynthesis of nitrogen heterocycles using environmentally friendly methodologies

Cyclic voltammetry and constant-current electrolysis in a one-compartment cell with a sacrificial anode has been used to study the indirect electroreduction of N-allyl-α-haloamides by electrogenerated Ni(I) complexes conducted in N, N-dimethylformamide (DMF) and acetonitrile (ACN) and the results were compared with those obtained in protic solvents such as EtOH and EtOH–H 2O mixtures. It was observed that the indirect electrochemical reduction of N-allyl-α-haloamides led to the corresponding lactams and the yields and selectivities obtained in EtOH and EtOH–H 2O were much better than those obtained in DMF or ACN.

Electro-organic synthesis of 1-(3-chloro-2-hydroxy propyl)-2-methyl-5-aminoimidazole in acidic medium

Electro-organic synthesis of 1-(3-chloro-2-hydroxy propyl)-2-methyl-5-aminoimidazole has been carried out by the constant current electrolysis at copper and amalgamated forms of copper and lead electrodes under acidic conditions. The electro reduction of 1-(3-chloro-2-hydroxy propyl)-2-methyl-5-nitroimidazole (Ornidazole) has been also studied by cyclic voltammetry at glassy carbon electrode under acidic conditions which indicate the reducible behaviour of it. Isolated product was characterized by TLC, usual laboratory qualitative tests and IR, NMR spectral analysis. Effect of different parameters like current density, temperature, depolarizer concentration and nature of cathode material on yield percentage and current efficiency have been investigated. Number of electrons have also been calculated to confirm the isolated product, which is 1-(3-chloro-2-hydroxy propyl)-2-inethyl-5-nitroimidazole.

Electrochemical reduction of alkoxychlorosilanes for Si–Si bond formation

Electrochemical reduction of alkoxychlorosilanes was studied. Constant current electrolysis of alkoxychlorosilanes in DME using tetrabutylammonium perchlorate as the supporting electrolyte and Cu–Cu as the electrodes led to the formation of homo-coupling products, dialkoxydisilanes, together with small amounts of dialkoxysilanes. When similar electrolysis was carried out in the presence of excess amounts of chloromono- and disilanes under the same conditions alkoxydi- and trisilanes were obtained, respectively, as the corresponding cross-coupling products. A dialkoxychlorosilane was also co-electrolyzed with chlorosilanes to give the respective 1,1-dialkoxydi- and trisilanes.

Cathodic C–H electro-activation in ionic liquid: An improved electrochemical method for the conjugate addition of 1,3-dicarbonyl compounds

The constant current electrolysis of 1,3-dicarbonyl compounds in 1-ethyl-3-methylimidazolium ethylsulfate (EMIMEtSO4) ionic liquid provided the direct deprotonation of the methylene active functionality to the cathode: the corresponding enolates efficiently underwent to the one-pot Michael addition with activated olefins.

Determination of Sugars by LC with On-Line Electrogenerated Cu(HIO6)2]5−–Luminol Chemiluminescence Detection

A novel method was developed for the determination of sugars such as glucose, fructose and lactose by column liquid chromatography coupled with chemiluminescence detection. The LC separation used a Kromasil NH2 column (250 × 4.6 mm, i.d.: 5 μm, pore size, 100 A) with a mobile phase consisting of acetonitrile and water. The chemiluminescence detection was based on the enhancement effect of the selected sugars on the chemiluminescence intensity between luminol and [Cu(HIO6)2]5−, which was on-line electrogenerated by constant current electrolysis. The limits of detection for determination of glucose, fructose and lactose were 4, 3 and 20 μg mL−1, respectively. The proposed method has been successfully applied to the determination of glucose and fructose in grape samples and lactose in milk samples.

Electrochemical inhibitor injection for control of reinforcement corrosion in carbonated concrete

AbstractThis paper describes preliminary investigations into the effectiveness of an electrochemical method of injecting organic base corrosion inhibitors into carbonated concrete containing embedded steel bars on which corrosion had been pre‐initiated. The corrosion inhibitors studied were pure compounds of ethanolamine (pKa ∼ 9.5) and guanidine (pKa ∼ 13.6). They were injected from aqueous solutions placed in contact with the surfaces of the water‐saturated concrete specimens by applying constant current electrolysis between anodes located within the inhibitor solutions and embedded steel bars acting as cathodes. The concentration profiles of the inhibitors penetrating the concrete cover were examined and the influence of the various treatments on the corrosion rates of the embedded steel bars was estimated by linear polarisation resistance measurements, carried out repeatedly during exposure of the treated specimens to cyclic wetting and drying over several months. The stability of the concentration profiles of the inhibitors was evaluated and measurements of corrosion weight losses of the steel bars were also undertaken on completion of the exposure regimes. It was found that the specimens treated with the inhibitors showed significantly reduced corrosion when compared with untreated control specimens that were subjected to similar exposure.

The role of acid catalysis in the electrosynthesis of N-(2,5-dimethoxyphenyl)azoles

The influence of the acid components of the medium on the anodic 2,5-dimethoxy-phenylation of various azoles at the nitrogen atom was studied for constant-current electrolysis of the mixture azole—1,4-dimethoxybenzene in an undivided cell. Elimination of azole functions in the key steps of the process can be catalyzed by such electrophilic species as Bronsted (AcOH) and Lewis acids (ZnCl2) and even the radical cation generated in the anodic oxidation of 1,4-dimethoxybenzene. The data obtained provided evidence for the existence of the arenonium cation as a key reaction intermediate.

Decolourisation of real textile waste using electrochemical techniques: Effect of electrode composition

The present paper presents the study of the decolourisation of real textile effluent by constant current electrolysis in a flow-cell using a DSA ® type material. The effect of using different anode materials (Ti/Ru 0.3Ti 0.7O 2; Ti/Ir 0.3Ti 0.7O 2; Ti/Ru X Sn 1− X O 2, where X = 0.1, 0.2 or 0.3) on the efficiency of colour removal is discussed. Attempts to perform galvanostatic oxidation (40 and 60 mA cm −2) on the as-received effluent demonstrate that colour removal and total organic carbon (TOC) removal are limited. In this case the greatest degree of colour removal is achieved when anode containing 90% SnO 2 is used. If the conductivity of the effluent is increased by adding NaCl (0.1 mol L −1) appreciable colour/TOC removal is observed. The efficiencies of colour and TOC removal are discussed in terms of the energy per order ( E EO/kW h m −3 order −1) and energy consumption ( E C/kW h kg −1 TOC), respectively. Finally, the extent of colour removal is compared to consent levels presented in the literature.

Synthesis and electrocoating of indole–thiophene comonomer on carbon fiber microelectrode, and surface topography by AFM

5,2-Thiophenylindole(5,2 In–Th) comonomer is synthesized by means of palladium catalyzed Stille cross-coupling reaction with an aim of obtaining extensively conjugated, low oxidation potential comonomer relative to its corresponding monomer. The comonomer is characterized by UV–Visible, FTIR, and NMR spectroscopic techniques, and the resulting conjugated copolymer exhibited the properties of both polyindole and polythiophene (having low oxidation potential and high conductivity). 5,2 In–Th comonomer was electropolymerized onto carbon fiber microelectrodes. The copolymer was electrochemically coated (grafted) onto micron size carbon fiber by constant potential electrolysis and cyclic voltammetry (CV) and the resulting nanosize thin films of polymers were characterized using atomic force microscopy (AFM), and FTIR spectroscopy. The efficiency of the electrocopolymerization process on the carbon fiber surfaces under preparative constant current electrolysis and potentiodynamic conditions, was evaluated in order to ascertain the effects of copolymer thickness, dopant and morphology.

Development of an Analytical Method for the Determination of β2-Agonist Residues in Animal Tissues by High-Performance Liquid Chromatography with On-line Electrogenerated [Cu(HIO6)2]5--Luminol Chemiluminescence Detection

A novel method was developed for the simultaneous determination of beta2-agonist residues such as terbutaline, salbutamol, and clenbuterol by high-performance liquid chromatography (HPLC) coupled with chemiluminescence (CL) detection. The procedure was based on the enhancement effect of beta2-agonists on the CL reaction between luminol and the complex of trivalent copper and periodate ([Cu(HIO6)2]5-), which was on-line electrogenerated by constant current electrolysis. The HPLC separation used a Nucleosil RP-C18 column (250 mm x 4.6 mm i.d., 5 microm; pore size, 100 A) with a mobile phase consisting of 90% acetonitrile and 10% aqueous ammonium acetate (20 mmol L-1, pH 4.0) at a flow rate of 1.0 mL min-1. The effects of several parameters on the HPLC resolution and CL emission were studied systematically. Liver samples were hydrolyzed with beta-glucuronidase followed by a solid-phase extraction procedure using Waters OasisMCX cartridges. Under optimum conditions, the limits of detection at a signal-to-noise ratio of 3 ranged from 0.007 to 0.01 ng g-1 and the limits of quantification at a signal-to-noise ratio of 10 ranged from 0.023 to 0.033 ng g-1 for three beta2-agonists. The relative standard deviations (RSDs) of intra- and interday precision were below 4.5%. The average recoveries for beta2-agonists (spiked at the levels of 0.05-5.0 ng g-1) in pig liver ranged from 84 to 110%, and the RSDs of the quantitative results were from 1.6 to 7.2%. The proposed method was successfully applied to the determination of beta2-agonist residues in pig liver samples.

Decolorisation of real textile waste using electrochemical techniques: Effect of the chloride concentration

The present paper presents the study of the decolorisation of real textile effluent by constant current electrolysis in a flow-cell using a Ti/Ru 0.3Ti 0.7O 2 DSA ® type electrode. The effect of increasing the chloride ion concentration on the efficiency of colour removal is discussed. Attempts to perform galvanostatic oxidation (40 and 60 mA cm −2) on the as-received effluent demonstrate that colour removal and total organic carbon (TOC) removal are limited. If the conductivity of the effluent is increased by adding 0.033 mol L −1 Na 2SO 4, little increase in the extent of colour/TOC removal is observed. However, when Na 2SO 4 is substituted, stepwise, with NaCl (while maintaining the ionic strength constant) appreciable colour/TOC removal is observed. The study of the effect of increasing the current density demonstrates that total colour removal is possible at high currents. The efficiencies of colour and TOC removal are discussed in terms of the Energy per order ( E EO/kW h m −3 order −1) and Energy consumption ( E C/kW h kg −1TOC), respectively. Finally, the extent of colour removal is compared to consent levels presented in the literature.

Electrochemical destruction of p-chlorophenol and p-nitrophenol – Influence of surfactants and anode materials

The electrochemical oxidative removal of p-chlorophenol and p-nitrophenol was studied by cyclic voltammetry (CV) and constant current electrolysis on commercially available graphite and titanium substrate insoluble anodes (TSIA). The effect of cationic cetyl trimethylammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and non-ionic polyoxyethylene(23)lauryl ether (Brij-35) surfactants, which prevent adherent film formation on the electrode surface were also studied. CV experiments indicate that p-chlorophenol exhibits a relatively higher tendency for film formation on graphite and that sodium chloride is a better medium for the destruction of phenols. The electrochemical oxidation of phenols under galvanostatic conditions in chloride medium with CTAB enhanced the detoxification process with significantly lower fouling effects on TSIA. The surfactants, however, did not improve phenol removal on graphite under identical experimental conditions. A charge of 2.5 F per mol was found to be sufficient to achieve 44–48% removal of phenol on both the electrodes in the absence of the surfactants. A 55–65% removal was achieved in the presence of the cationic surfactant on the TSIA electrode. Phenol was removed as a low molecular weight polymer (MW ≈ 4450).

Detection of glucocorticoid residues in pig liver by high-performance liquid chromatography with on-line electrogenerated [Cu(HIO 6) 2] 5−—luminol chemiluminescence detection

A novel method was developed for the simultaneous determination of glucocorticoid residues such as triamcinolone (TR), prednisolone (PR), hydrocortisone (HC), cortisone (CO), methylprednisolone (MP), dexamethasone (DE) and triamcinolone acetonide (TA) by high-performance liquid chromatography (HPLC) coupled with chemiluminescence (CL) detection. The procedure was based on the enhancement effect of glucocorticoids on the chemiluminescence reaction between luminol and the complex of trivalent copper and periodate ([Cu(HIO 6) 2] 5−), which was on-line electrogenerated by constant current electrolysis. The HPLC separation used a Nucleosil RP-C 18 column (250 mm × 4.6 mm i.d., 5 μm, pore size, 100 Å) with a mobile phase consisting of acetonitrile and 1.0 mmol L −1 ammonium acetate (pH 6.8, 40:60,v/v) at a flow rate of 0.8 mL min −1. The effects of several parameters on the HPLC resolution and CL emission were studied systematically. Liver samples were hydrolyzed with Helix pomatia juice followed by a solid-phase extraction procedure. Under optimum conditions, the limits of detection (LOD) at a signal-to-noise of 3 ranged from 0.08 to 1.0 ng g −1 and the limits of quantification (LOQ) at a signal-to-noise of 10 ranged from 0.27 to 3.33 ng g −1 for seven glucocorticoids. The relative standard deviations (RSD) of intra- and inter-day precision were below 6.8%. The average recoveries for glucocorticoids (spiked at the levels of 5–50 ng g −1) in pig liver ranged from 88 to 106%, and the relative standard deviations of the quantitative results were from 2.0 to 6.9%. The proposed method had been successfully applied to the determination of glucocorticoid residues in pig liver.