Constant Potential Electrolysis Research Articles

Binary composite ionic liquids [bmim][BF4] and [bmim][Ac] for electrochemical reduction of nitrobenzene

The binary composite ionic liquid mixtures composed of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) and 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) were studied and used in electroreduction of nitrobenzene for the first time. 1H NMR and Fourier transform infrared (FTIR) spectroscopy were carried out to acquire a deep understanding of the interaction of binary ionic liquids, and UV/Vis spectroscopy was used to study the interaction between the mixture of ionic liquids and nitrobenzene. It was found that chemical shifts of all protons were changed and significant changes in the anion IR bands were induced, and the UV maximum absorption wavelength and absorbance of nitrobenzene in binary ionic liquids were different from those in the neat ionic liquid. The electrochemical reduction behavior of nitrobenzene in binary composite ionic liquids on platinum electrode was studied by cyclic voltammetry, in situ Fourier transform infrared spectroscopy, and constant potential electrolysis. Results indicated that the reduction of nitrobenzene in binary composite ionic liquids demonstrated higher current densities with a more positive potential, and the product (azobenzene) showed higher yield and selectivity in the composite ionic liquids than in the neat ionic liquids; the concentrations of water in the binary mixtures of ionic liquids had great effect on the electrochemical behavior of nitrobenzene. In the end, the mechanism of reduction of nitrobenzene in binary mixtures of ionic liquids was discussed.

Electrochemical reduction of nitrobenzene in ionic liquid BMImAc

Ionic liquid, 1-butyl-3-methylimidazolium acetate(BMImAc), was used in the electrochemical reduction of nitrobenzene. The electro-reduction of nitrobenzene on platinum electrode was studied by cyclic voltammetry(CV), in situ Fourier transform infrared(FTIR) spectroscopy and constant-potential electrolysis. The experimental results show that electrochemical reduction process of nitrobenzene was controlled by diffusion, the main reduction product was azobenzen at −1.45 V, and the influences of scan rate and temperature on the electrochemical behaviors were obviously. A reduction mechanism of nitrobenzene in an ionic liquid was a probable ‘nitrobenzene→nitroso-benzene→azobenzene→aniline’ main reductive reaction route.

Electrodeposition of cobalt with tunable morphology from reverse micellar solution

Electrodeposition of cobalt on a copper electrode was successfully performed from aqueous and reverse micellar solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), using constant potential electrolysis method. The potential to be applied for electrodeposition was judged from the cyclic voltammetric behavior of cobalt(II) in aqueous and reverse micellar solutions of CTAB at different compositions. The morphology, dimension, and crystallinity of cobalt deposited onto a copper substrate were evaluated from scanning electron microscopy (SEM) images and X-ray diffraction technique. The cobalt deposited on copper from aqueous solution does not show any definite shape and size, while the deposition from reverse micellar solutions occurred with definite shapes such as star-, flower-, and nanorod-like structures depending on the composition. The slow kinetics governed by the reverse micelles associated with the deposition brings about oriented growth of cobalt onto the copper substrate and offers the potential to electrochemically tune cobalt deposit with desirable morphology.

废气监测二氧化硫过程中遇到的问题及解决方法

废气的温度、含湿量、高负压和干扰气体都会对定电位电解法监测二氧化硫产生干扰，根据不同的干扰原因提出了不同的解决方法，并推荐应广泛采用非分散红外吸收法对废气二氧化硫进行监测。Temperature, humidity ratio, high negative pressure and interfering gas of the exhaust gas interfere with constant potential electrolysis' monitoring sulfur dioxide. Different solutions are being proposed according to different disturbing causes. And non-dispersive infrared absorption method which is being widely adopted is also recommended to monitor the sulfur dioxide.

Electrochemical control of the conversion of cellulose oligosaccharides into glucose

This paper presents a novel method to convert cellulose oligosaccharides to glucose by using constant-potential electrolysis. Firstly experiments were performed to seek the optimum conditions and catalyst dosage to make the catalytic electrode, and it is found that the most active catalytic electrode (γ-MnO2/graphite/PTFE) can be made using 5% γ-MnO2 as catalysts which is prepared at calcinations temperature of 500°C and calcinations time of 3h. Following this, experiments were conducted to find the optimum operation conditions for the maximum glucose yield using the above-developed catalytic electrode. The results show that the maximum glucose yield of 72.4% can be achieved under the following operation conditions: electrolysis potential vs. SEC −1.0V, pH value of 3 and electrolytic reaction time of 8h. The cyclic voltammetry performance on MnO2/graphite/PTFE electrode suggests that γ-MnO2 acts not only as electrode material but also as a catalyst. The γ-MnO2 displays high electrocatalytic activity toward the breakage of β-1,4-glycoside bond of oligosaccharides and gives 100% selectivity to glucose.

Au Electrodeposition at the Liquid-Liquid Interface: mechanistic aspects

The deposition mechanism of metallic gold was investigated based on charge transfer voltammetry at the water/1,2-dichloroethane (W/DCE) interface, and the corresponding redox voltammetry of the metal precursor in W and the reductant, triphenylamine (TPA), in DCE. The metal precursor was present as Au(III) (AuCl4−), or Au(I) (AuCl2−) in W or DCE. Electron transfer could be observed voltammetrically at the interface between W containing both Au precursors and DCE containing TPA. Au particles, formed by constant potential electrolysis at the W/DCE interface, were examined by transmission electron microscopy. It was shown that deposit size could be controlled via the applied potential and time, with specific conditions to form particles of less than 10nm identified.

Electrodeposited gold nanoparticles on glassy carbon: Correlation between nanoparticles characteristics and oxygen reduction kinetics in neutral media

Gold nanoparticles (AuNPs) were deposited onto glassy carbon (GC) by constant potential electrolysis (CPE) using various sets of potential and duration from −0.3 to 0.7V/SHE and 10 to 1800s, respectively. The physico-chemical characteristics of the as-obtained deposits were investigated by cyclic voltammetry (CV) in H2SO4, field emission gun scanning electron microscopy (FEG-SEM), and Pb underpotential deposition (UPD). Their performances toward the oxygen reduction reaction (ORR) in a NaCl–NaHCO3 (0.15M/0.028M, pH 7.4) neutral solution were examined and correlated to AuNPs size and density. The best results were obtained using the deposits which exhibited a high density (555±49μm−2) of relatively small AuNPs (25±12nm). The Koutecky–Levich treatment was systematically applied to all the deposits in order to determine the number of electrons n exchanged for the ORR in the potential range from 0.1 to −1.0V/SHE. The values of the cathodic transfer coefficients βn were also extracted and compared to the values reported for unmodified GC and bulk Au. A map of the βn values as a function of AuNPs electrodeposition potential and duration was also provided.

Electrochemical reductive degradation of chlorobenzene using galvanically replaced Pd/Fe nanoscale particles

Nanoscale Pd/Fe particles were fabricated on glassy carbon substrates by electrodeposition of Fe and the subsequently underwent galvanic replacement with Pd. Heterostructure was found by various characterizations of Pd/Fe particles. The process of electrochemical reduction of chlorobenzene on Pd/Fe particles were studied by cyclic voltammetry and constant-potential electrolysis. The removal rate of chlorobenzene on Pd/Fe particles reaches up to 90% within 120min using electrolysis at −0.1V in 0.1M H2SO4. Consequently, it shows that nanoscale Pd/Fe particles exhibited higher catalytic activity than bulk Pd for chlorobenzene reduction.

Poly(luminol) based sensor array for determination of dissolved chlorine in water

An optical sensor for determination of free chlorine content of drinking water was prepared and tested. The function of the sensor is based on detecting chemiluminescence signal provided by thin immobilized poly(luminol) reagent layer. The poly(luminol) reagent film was prepared by electropolymerization of luminol onto planar indium-tin-oxide (ITO) electrode. Different methods, like electrode potential cyclization (cyclic voltammetry, CV), pulsed potential electrolysis (pulsed amperometry, PA) and potentiostatic electrolysis (constant potential electrolysis, PSE) were employed for preparation of the poly(luminol) layer. The chemoluminescence (chemiluminescence) of the differently prepared films was investigated in the poly(luminol) – hypochlorite – hydrogen peroxide reaction. Highest luminescence signal was obtained by the films prepared with CV. Poly(luminol) layers deposited with pulsed potential showed 80% less luminescence while almost no signal was obtained in case of films made with constant potential technique. The effects of the buffer composition and pH on the analytical properties of the electro polymerized sensing layer were investigated. The lower concentration limit of free chlorine detection was 5×10−7M in phosphate buffer at pH=8.0. It was found that the chemiluminescence signal decreased significantly when hypochlorite concentrations over 1mM were applied. An array of 24 micro wells was fabricated on ITO glass slab of about microscope slide size. The individual micro wells had identical volume and the poly(luminol) layer immobilized on their bottom had identical activity. The wells could be used for “single shot” determination of free chlorine content of drinking water. The long storage stability, the simple measurement procedure and low feasible concentration range makes the array an attractive analytical tool. Its applicability was proved measuring dissolved chlorine concentration of tap water samples.

Optimizing Surface-Enhanced Raman Scattering-Active Au Nanostructures Coated on Indium-Doped Tin Oxide Glass by Combining Chemical Assembly and Electrodeposition Methods

A combined strategy of chemical assembly and electrodeposition methods was used to prepare Au nanostructures as highly efficient surface-enhanced Raman scattering (SERS) substrates. Small Au colloids (3–5 nm) were firstly anchored on the amine-terminated indium-doped tin oxide (ITO) glass, followed by the electrodeposited growth of Au nanoparticles (NPs) using constant potential electrolysis. We systematically investigated the effect of deposition potentials and electrodeposited times on the morphology of Au nanostructures and their coupling states on the ITO glass. The isolated (unconnected) dense-packing Au nanostructure demonstrated highly efficient SERS signals of o-chlorothiophenol when compared to those of aggregated (connected) dense-packing Au nanostructure. SERS enhancement factor of isolated dense-packing Au nanostructure was calculated to be tenth order of magnitude higher than that of aggregated dense-packing Au nanostructure.

Copper Complexes Relevant to the Catalytic Cycle of Copper Nitrite Reductase: Electrochemical Detection of NO(g) Evolution and Flipping of NO2 Binding Mode upon CuII → CuI Reduction

Copper complexes of the deprotonated tridentate ligand, N-2-methylthiophenyl-2'-pyridinecarboxamide (HL1), were synthesized and characterized as part of our investigation into the reduction of copper(II) o-nitrito complexes into the related copper nitric oxide complexes and subsequent evolution of NO(g) such as occurs in the enzyme copper nitrite reductase. Our studies afforded the complexes [(L1)Cu(II)Cl]n (1), [(L1)Cu(II)(ONO)] (2), [(L1)Cu(II)(H2O)](ClO4)·H2O (3·H2O), [(L1)Cu(II)(CH3OH)](ClO4) (4), [(L1)Cu(II)(CH3CO2)]·H2O (5·H2O), and [Co(Cp)2][(L1)Cu(I)(NO2)(CH3CN)] (6). X-ray crystal structure determinations revealed distorted square-pyramidal coordination geometry around Cu(II) ion in 1-5. Substitution of the H2O of 3 by nitrite quantitatively forms 2, featuring the κ(2)-O,O binding mode of NO2(-) to Cu(II). Reduction of 2 generates two Cu(I) species, one with κ(1)-O and other with the κ(1)-N bonded NO2(-) group. The Cu(I) analogue of 2, compound 6, was synthesized. The FTIR spectrum of 6 reveals the presence of κ(1)-N bonded NO2(-). Constant potential electrolysis corresponding to Cu(II) → Cu(I) reduction of a CH3CN solution of 2 followed by reaction with acids, CH3CO2H or HClO4 generates 5 or 3, and NO(g), identified electrochemically. The isolated Cu(I) complex 6 independently evolves one equivalent of NO(g) upon reaction with acids. Production of NO(g) was confirmed by forming [Co(TPP)NO] in CH2Cl2 (λ(max) in CH2Cl2: 414 and 536 nm, ν(NO) = 1693 cm(-1)).

Direct Electro-oxidation of Toluene Derivations on Graphite Electrode

Direct electro-oxidation behaviors of toluene derivations(p-methoxy methylbenzene,p-xylene,p-chloro methylbenzene,p-tert-butyl methylbenzene) were studied by cyclic voltammetry(CV),in situ Fourier transform infrared spectroscopy(in situ FTIR),and constant potential electrolysis on graphite electrode in sulfuric acid and acetone solutions.The direct electro-oxidation behaviors of the four toluene derivations were similar.The negative-going band at 1710 cm-1is the stretching vibration peak of carboxyl group of aromatic aldehydes,and the positive-going band at 1130 cm-1shows the consumption peak of methyl of toluene derivations.The main electro-oxidation products are aromatic aldehydes detected by gas chromatography-mass spectrometry(GC-MS).The yield of p-methoxy benzaldehyde could reach up to 70.9% in the sulfuric acid system at 40 ℃.

An XPS depth-profile study on electrochemically deposited TaO x

Through the use of XPS and controlled Ar+ etching, the surface composition and oxide species of tantalum oxides (TaO x ), which were electrodeposited on glassy carbon electrodes by cyclic voltammetric and constant-potential electrolyses, are quantified along the depth profile. Electrodeposition exhibits efficacy in depositing TaO x with a distribution of various TaO x : TaO, TaO2, and Ta2O5. The distribution gradient from the outer surface of TaO x is such that Ta2O5 > TaO2 > TaO. TaO is found to be the dominant species in the underlying layer of TaO x . Such a unique structure of the electrode surface is analogous to that of nanoparticles with a core–shell structure, with the core being suboxides and the surface being that of the saturated pentoxide, Ta2O5. The electrochemically induced nonhydrolytic condensation route is proposed to be capable of producing TaO x with a distribution gradient of Ta2O5, TaO2, and TaO in the depth direction.

Fabrication of a Polyaniline Ultramicroelectrode via a Self Assembled Monolayer Modified Gold Electrode

Herein, we report a simple and inexpensive way for the fabrication of an ultramicroelectrode and present its characterization by electrochemical techniques. The fabrication of polyaniline UME involves only two steps: modification of a gold (Au) electrode by self assembled monolayers (SAM) and then electrodeposition of polyaniline film on this thiol-coated Au electrode by using cyclic voltammetry and constant potential electrolysis methods. Two types of self-assembled monolayers (4-mercapto-1-butanol, MB, and 11-mercaptoundecanoic acid, MUA) were used, respectively, to see the effect of chain length on microelectrode formation. Microelectrode fabrication and utility of the surface was investigated by cyclic voltammetric measurements in a redox probe. The thus prepared polyaniline microelectrode was then used for DNA immobilization. Discrimination between double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) was obtained with enhanced electrochemical signals compared to a polyaniline-coated Au electrode. Different modifications on the electrode surfaces were examined using scanning electron microscopy (SEM).

Ni/NiFe2O4 Composite Electrode Prepared by Electro-deposition and Its Electro-catalytic Performance Towards Oxygen Evolution Reaction

The spinel-type NiFe2O4 powders have been synthesized by a hydroxide co-precipitation method.The Ni/NiFe2O4 composite coating was prepared through electro-deposition in Watt nickel plating by adding some NiFe2O4 powders.The optimized plating conditions for the composite electro-deposition were investigated by varying parameters,such as the plating solution pH and the cathode current density jk.The composition and structure of the Ni/NiFe2O4 composite coating were characterized by scanning electron microscopy(SEM),energy X-ray diffraction(XRD) and dispersive spectrometer(EDS).The results show that the NiFe2O4 mass content in the Ni/NiFe2O4 composite coating is the highest(55.15%) at optimized plating conditions of a solution pH = 5.8 ～ 6.0 and a cathodic current density jk = 40 × 10-3 ～ 60 × 10-3 A/cm2.In 5 mol/L KOH solution,the electro-catalytic properties towards the oxygen evolution reaction(OER) of the Ni/NiFe2O4 composite electrode was studied using cyclic voltammetry,steady-state polarization,and chronoamperometry.Compared with the nickel electrode,the electro-catalytic properties towards OER of the Ni/NiFe2O4 electrode is higher and the apparent activation energy is decreased by 62.07 kJ/mol,and its specific surface area is 23.02 times as large as that of the nickel electrode.The constant-potential electrolysis with long time for OER shows that the stability of the Ni/NiFe2O4 composite electrode is good.

TiO2 nanotube arrays co-loaded with Au nanoparticles and reduced graphene oxide: Facile synthesis and promising photocatalytic application

Au nanoparticles and reduced graphene oxide co-loaded TiO2 nanotube arrays (Au/RGO–TiO2 NTs) were prepared through a simple one-step constant-potential electrolysis of chloroauric acid and graphene oxide on TiO2 NTs. Compared with Au–TiO2 NTs, RGO–TiO2 NTs and un-modified TiO2 NTs, the Au/RGO–TiO2 NTs exhibited high efficiency in photocatalytic degradation of methyl orange (MO) under simulated solar light irradiation. The highly efficient photocatalytic activity is associated with broad absorption in the visible light region, increased photoinduced charge separation through transferring photogenerated electrons from TiO2 NTs to both Au and RGO, as well as the strong adsorption ability of RGO to MO molecules. Moreover, the Au/RGO–TiO2 NTs has an excellent stability. This work provides an insight into designing and synthesizing new TiO2 NTs-based hybrid materials for effective visible light-activated photocatalysis.

Preconcentration and electroanalysis of silver at pt electrode modified with poly(2-aminothiazole)

Conducting poly(2-aminothiazole) (PAT) films were electrodeposited on a platinum disc electrode surface by constant potential electrolysis of 2-aminothiazole (AT) for the stripping voltammetric determination of Ag(I). Ag(I) was preconcentrated on the polymer matrix by dipping the modified Pt electrode (PAT-Pt electrode) into Ag(I)(aq) solution. Effects of the film thickness, reduction potential, pH, preconcentration time, Ag(I) concentration and the interference of some other metal ions on the oxidation peak current of silver were studied. Cu(II) interference observed to be significant for the stripping voltammetric determination of Ag(I). The detection limit was calculated on the basis of signal to noise ratio of 3 as 2 × 10−7 mol L−1.

Electrochemical oxidation of aldehyde-N-arylhydrazones into symmetrical-2,5-disubstituted-1,3,4-oxadiazoles

A convenient, efficient and one-pot synthesis of chemically and pharmaceutically interesting symmetrical-2,5-disubstituted-1,3,4-oxadiazoles is reported. The protocol involves anodic oxidation of aldehyde-N-arylhydrazones in anhyd. MeCN–LiClO4. Constant potential electrolysis carried out in an undivided cell and platinum electrodes leads to the formation of the corresponding oxadiazoles under ambient condition and the mechanism was deduced from voltammetry studies. The reaction proceeded smoothly with high atom economy.

Preparation and Oxygen Evolution Reaction Performance of Ni/NiCo<sub>2</sub>O<sub>4</sub> Electrode

Spinel-type NiCo2O4 powders were prepared by a sol-gel method, and Ni/NiCo2O4 electrode was prepared through composite sol method combined with sintering. The composition and structure of Ni/ NiCo2O4 were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy- dispersive X-ray spectroscopy (EDS). Electrocatalytic properties of the Ni/NiCo2O4 electrode in the oxygen evolution reaction (OER) were studied in 5 mol·L - 1 KOH solution, using cyclic voltammertry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), chronoamperometry, and extended duration constant potential electrolysis. The Ni/NiCo2O4 electrode exhibited a lower OER over- potential, higher specific surface area, and better stability than a porous Ni electrode. The specific surface area of the Ni/NiCo2O4 electrode was 28.69 times greater than that of the porous Ni electrode, and its apparent activation energies decrease 166.78 and 162.15 kJ·mol - 1 at different overpotentials, respectively. (Article)

Efficient Oxidative Cycloreversion Reaction of Photochromic Dithiazolythiazole

Electrochemical response of photochromic tearylenes was surveyed by means of cyclic voltammetry, DFT calculations, and spectroelectrochemistry. 4,5-Bis(2-phenyl-5-methylthiazolyl)-2-phenylthiazole was found to show electrochemical oxidative ring-cycloreversion reaction. The net current efficiency of the cycloreversion reaction under constant potential electrolysis was as high as 900%, which is ascribed to an electrochemical local-cell mechanism and a chain reaction mechanism. Electron transfer stopped-flow study using a chemical oxidant successfully identified radical cation intermediates of both closed- and open-ring isomers, involved in the oxidative cycloreversion process. The significantly long-lived radical cation of open-ring isomer with the lifetime of 33 s takes part in the indirect electron transfer process from the neutral closed-ring isomer to the radical cation of open-ring isomer in the chain reaction manner.