Parameters of electrolysis in 3D flow electrode in limiting diffusion current mode

The analytical expressions were derived to calculate thickness of a three-dimensional flow electrode (TFE) working in limiting diffusion current mode in the cases of unidirectional and multidirectional electric field and solution flow for the given degree of metal extraction. The algorithm was suggested on the basis on the derived formulas and earlier published mathematical models of nonstationary electrolysis at TFE to calculate the whole electrode working conditions at the limiting diffusion current with parallel electrochemical reactions. The calculations and experimental studies were carried out on copper electrodeposition from sulfate electrolyte on TFE working in the limiting diffusion current mode. The effect of major electrochemical reactions to the distribution of potential and partial current densities by the electrode thickness was demonstrated. The process potential distribution was given for various electrode conductivities. A good compliance was shown between the results of calculations and experimental studies.     

The behaviour of an electrochemical detector used in liquid chromatography and continuous flow voltammetry: Part III. Potential dependent current

The potential dependence of the steady-state current at a channel electrode has been calculated approximately. Six regions of behavior can be described from a consideration of the characteristic times of diffusion, fluid flow and electrochemical reaction. Wave shapes and half-wave potential shifts are as expected for amperometric cells under all values of the heterogeneous reaction rate constant, and for reversible electrochemical reactions in a coulometric cell. The wave adopts a peculiar shape for irreversible reactions at a coulometric electrode. This is caused by the inapplicability of the concept of mass transfer control in these systems.     

Interaction of DNA with echinomycin at the mercury electrode surface as detected by impedance and chronopotentiometric measurements

The capacitance measurement (dependence of the differential capacitance C of the electrode double layer on potential E, C-E curves), electrochemical impedance spectroscopy (frequency response of the impedance Z of the electrode double layer-EIS) and constant current chronopotentiometry (dependence of dt/dE on potential at constant current, chronopotentiometric stripping analysis-CPSA) have been used for electrochemical study of echinomycin and its interaction with single-stranded (ss) and double-stranded (ds) DNA at the hanging mercury drop electrode (HMDE). The capacitance measurement showed that echinomycin gives a pseudocapacitance redox peak strongly dependent on the a.c. voltage frequency at the potential of -0.53 V. This peak is observed with dsDNA-echinomycin complex as well, but not with ssDNA treated by echinomycin. Similar results were obtained using CPSA measurements. Thus capacitance measurements and CPSA can distinguish with the aid of the bis-intercalator echinomycin the single-stranded and double helical form of DNA adsorbed at the mercury electrode surface. Impedance measurement in connection with adsorptive transfer technique can find the differences between ssDNA and dsDNA, which promise to use this technique for detection of dsDNA in hybridisation reactions.     

Analysis of Turbulent Noise Spectra of Electrochemical Reactions in Different Experimental Conditions

The Ershler–Randles impedance model is used to analyze the physical foundations of potentiostatic and galvanostatic spectra of turbulent noise of electrochemical redox reactions as a function of the frequency range of measurements and the electrode potential. On the whole, the theoretically calculated and experimentally measured spectra are in satisfactory agreement. A computer simulation of the dependence of characteristic frequencies on the electrode potential, reaction parameters, and experimental conditions is realized. The approach allows one to tentatively estimate the in-principle possibility of experimental realization of spectrum sections, which are located in different frequency ranges and contain information on the characteristic frequencies and kinetic parameters of the reaction under study, and to formulate conditions required for performing an experiment and extracting data on the process kinetics.     

How to avoid interfering electrochemical reactions in ESI‐MS analysis

The presence of electrochemical reactions occurring in an electrospray processes at the point where the current enters the liquid is discussed since the early 1990's. This current transfer to the liquid results in oxidation or reduction of either electrolyte species in the liquid sprayed or of the electrode material in contact with the liquid. As a result, new chemical species are generated. These products of the electrochemical reaction might be detected as altered species in mass spectra; they might be volatile and not recognized at all or accumulate on the electrode surface and cause cross contamination later on. In other cases, it might happen that the products of the electrochemical reactions are the only detectable species formed from an otherwise nondetectable analyte. An electrospray setup in which electrochemical reactions do not interfere with the analyte under investigation excludes the electrochemical reaction as source of sample contamination and sample altering and may serve as reference setup for experiments focused on the electrochemical reaction itself. We present a simple and inexpensive current coupling approach and specify operation conditions for which any impact of the electrochemical reaction on the sample under investigation is inherently excluded. On the basis of a practical example, we show the impact of the electrochemical reaction on sample composition and demonstrate the benefit of using the proposed current coupling method. Because of the obvious benefit of this method and its simple realization, it has the potential to be employed as standard feeding approach, especially for electrosprays operated at small flow rates.     

Oxygen reduction kinetics on graphite cathodes in sediment microbial fuel cells

Sediment microbial fuel cells (SMFCs) have been used as renewable power sources for sensors in fresh and ocean waters. Organic compounds at the anode drive anodic reactions, while oxygen drives cathodic reactions. An understanding of oxygen reduction kinetics and the factors that determine graphite cathode performance is needed to predict cathodic current and potential losses, and eventually to estimate the power production of SMFCs. Our goals were to (1) experimentally quantify the dependence of oxygen reduction kinetics on temperature, electrode potential, and dissolved oxygen concentration for the graphite cathodes of SMFCs and (2) develop a mechanistic model. To accomplish this, we monitored current on polarized cathodes in river and ocean SMFCs. We found that (1) after oxygen reduction is initiated, the current density is linearly dependent on polarization potential for both SMFC types; (2) current density magnitude increases linearly with temperature in river SMFCs but remains constant with temperature in ocean SMFCs; (3) the standard heterogeneous rate constant controls the current density temperature dependence; (4) river and ocean SMFC graphite cathodes have large potential losses, estimated by the model to be 470 mV and 614 mV, respectively; and (5) the electrochemical potential available at the cathode is the primary factor controlling reduction kinetic rates. The mechanistic model based on thermodynamic and electrochemical principles successfully fit and predicted the data. The data, experimental system, and model can be used in future studies to guide SMFC design and deployment, assess SMFC current production, test cathode material performance, and predict cathode contamination.     

Electrochemical Characterization of Nickel Electrodes in Phosphate and Carbonate Electrolytes in View of Assessing a Medical Diagnostic Device for the Detection of Early Diabetes

In view of optimizing a multi‐electrode device using proprietary technology for noninvasive assessment of eccrine sweat gland activity and thus the early detection of diabetes, we thoroughly explored the electrochemical behavior of a nickel electrode in a three‐electrode set up combining a nickel counter electrode and a nickel pseudo‐reference electrode in synthetic buffered phosphate and carbonate solutions in presence of chloride, lactate and urea that mimic the composition of physiological sweat. This approach provides insight into the origin of the onset of responses measured upon the application of low voltage potential with variable amplitudes to Ni electrodes on the skin. For low voltage amplitude of ca. ΔE=0.6 V, the electrochemical reactions measured at the electrodes are those related to the oxidation of Ni leading to the formation of a passive layer, as well as the reduction of this passive layer. For voltage amplitude higher than 1 V, or current densities higher than 1 mA/cm², the breakdown of the passive layer becomes the main electrochemical anodic reaction, while its reduction and the electrolytic solution govern the cathode reactions. This brings explanation of the nonlinear current‐voltage features measured during the clinic tests. Finally, the obtained results make possible the definition of the experimental electrochemical conditions where the Ni electrodes can be renewed.     

In situ electrochemical spectroscopy for boron-doped diamond electrode reactions: recent progress and perspectives

Over the past years, great attention has been given to the developments of boron-doped diamond (BDD) materials in various fields because of the advantages of electrochemical features, such as large potential range and low background current. This minireview aims to present the recent progress of in situ electrochemical spectroscopy for BDD electrode reactions. After a concise state of the widely used in situ electrochemical spectroscopy techniques, including in situ electrochemical Raman, infrared, and electron paramagnetic resonance spectroscopy, the current progress of BDD electrode reactions using in situ electrochemical spectroscopy has been summarized. Finally, challenges and perspectives for the tendency of the BDD study via in situ electrochemistry are provided, of which several potential electrochemical combined technologies relating to the mechanism exploration of BDD are proposed.     

硫氰酸盐电化学氧化的动力学复杂性

本文利用多种电化学方法研究了多晶电极上硫氰酸盐电化学氧化的动力学和机理,观察到电流和电位振荡。循环伏安测量表明氧化动力学分为二步过程。除了振荡现象,系统也展示双稳态,利用时间电位扰动,氧化反应可在高电位和低电位稳态之间转换,而且强烈吸附的惰性离子也可诱导从振荡转化为稳态。     

Scanning electrochemical mapping of spatially localized electrochemical reactions induced by surface potential gradients

The influence of a surface potential gradient on the location and extent of electrochemical reactions was examined using a scanning electrochemical microscope. A linear potential gradient was imposed on the surface of a platinum-coated indium tin oxide electrode by applying two different potential values at the edges of the electrode. The applied potentials were used to control the location and extent of several electrochemical reactions, including the oxidation of Ru(NH3)6(2+), the oxidation of H2, and the oxidation of H2 in the presence of adsorbed CO. Scanning electrochemical mapping of these reactions was achieved by probing the feedback current associated with the oxidation products. The oxidation of Ru(NH3)6(2+) occurred at locations where the applied potential was positive of the formal potential of the Ru(NH3)6(2+/3+) redox couple. The position of this reaction on the surface could be spatially translated by manipulating the terminal potentials. The rate of hydrogen oxidation on the platinum-coated electrode varied spatially in the presence of a potential gradient and correlated with the nature of the electrode surface. High oxidation rates occurred at low potentials, with decreasing rates observed as the potential increased to values where platinum oxides formed. The extent of oxide formation versus position was confirmed with in-situ ellipsometry mapping. In the presence of adsorbed carbon monoxide, a potential gradient created a localized region of high activity for hydrogen oxidation at potentials between where carbon monoxide was adsorbed and platinum oxides formed. The position of this localized region of activity could be readily translated along the surface by changing the terminal potential values. The ability to manipulate electrochemical reactions spatially on a surface has potential application in microscale analytical devices as well as in the discovery and analysis of electrocatalytic systems.     

Effect of Coulomb interaction between the electrons on two-electron redox-mediated tunneling

Two-electron non-adiabatic redox-mediated tunneling through a symmetric electrochemical contact with a bridge molecule having one electron energy level participating in tunneling is considered under ambient conditions. It is shown that the current/overpotential dependence in this system can disclose two distinct or overlapping clear-cut maxima depending on the value of the effective Coulomb repulsion energy. This new effect is due to the opening of the channel for tunneling of second electron with the variation of the electrode potential. The system manifests also a rectification effect in the current/bias voltage curve which depends on the value of the effective Coulomb repulsion energy.     

Activation energy of electrochemical reaction at a constant value of electrode potential

Equations were derived interrelating ideal activation energy W (determined at the constant Galvani potential value), real activation energy A (determined at a constant overpotential), and the so called formal activation energy Ω (calculated at a constant electrode potential vs. an arbitrarily chosen reference electrode). The obtained equations include only the parameters of the studied reaction and no characteristics of the reaction occurring on the reference electrode. The type of the Ω dependence on the electrode potential is established. Conditions are found, under which the real and formal activation energies of the electrochemical reactions can simultaneously remain constant in the given temperature range and it becomes possible to use them in the integral forms of the Arrhenius equation.     

Beyond the Butler-Volmer equation. Curved Tafel slopes from steady-state current-voltage curves

We report the discovery and analysis of curved Tafel slopes from the electrochemical reduction of hexamminecobalt(III) under steady-state conditions. In order to confirm the existence of the curvature, random assemblies of carbon microelectrodes (RAM? electrodes) were employed to obtain experimental data over more than three orders of magnitude, without significant double layer charging currents and without ohmic distortion. Since the rate-determining step in the reduction reaction is electron transfer, and no ligand substitution reactions occur on the timescale of experiments, the curvature of the Tafel plot is attributed to the dependence of the symmetry factor on electrode potential.     

抗坏血酸在铂纳米粒子/碳纳米管/聚吡咯复合修饰电极上的电化学行为

研究了抗坏血酸在铂纳米粒子/碳纳米管/聚吡咯复合膜修饰电极上的电化学行为,发现复合修饰电极对抗坏血酸的电化学反应具有较好的电催化作用,与空白电极相比电化学氧化电流增加了7倍。用电化学阻抗谱研究了电子在修饰电极界面上的传输过程,发现修饰电极的电催化性能与修饰电极可以提高界面电子传输能力是相关的。同时研究了碳纳米管用量、支持电解质、扫速、电沉积条件等因素对抗坏血酸在修饰电极上电化学行为的影响。     

活性氯在316L不锈钢电极表面的阴极行为研究

利用电化学方法研究了活性氯在3.5%NaCl溶液中316L不锈钢电极表面的阴极还原反应及其反应机制.实验表明,随着溶液中活性氯浓度的增加,316L不锈钢的自腐蚀电位正移,阴极反应的极限扩散电流明显增大,说明活性氯对316L不锈钢电极表面的两个阴极反应,即HClO还原和ClO-还原具有明显的促进作用.本文的研究确定了产生这两个还原反应的电位范围,并进一步探索了该还原反应速度的控制步骤.     

Voltammetric determination of Tartrazine in food

A possibility of using voltammetry for the direct determination of yellow synthetic food dye Tartrazine, included in the list of substances regulated in food, is demonstrated. The electrochemical behavior of the dye is studied by direct current voltammetry using a glassy carbon electrode. It is shown that the signal of Tartrazine electrochemical reduction is the most pronounced in an acidic medium at pH 2.0, accumulation potential of 0.1 V, and time of 10 s. The dependence of the electrochemical reduction current of the dye at a potential of–0.25 V on its concentration is linear in the range 0.05–0.50 mg/L with the determination limit 0.034 mg/L and detection limit 0.011 mg/L. A procedure for quantifying the dye in food is proposed.     

Comparative electrochemical study of self-assembly of octanethiol from aqueous and aqueous ethanol solutions on a gold electrode

The self-assembly of octanethiol (OT) on the surface of a polycrystalline gold electrode in aqueous and aqueous ethanol thiol-containing (1 × 10^–4 М) 0.1 М NaClO₄ solutions was studied. The blocking properties and electrochemical stability of monolayer OT films were studied by chronopotentiometry during OT adsorption under the open circuit conditions (chronoamperometry at a fixed potential) combined with cyclic voltammetry for modified Au/OT electrodes. It was found from the change in the rate of electrochemical reactions in the range of monolayer stability potentials that in aqueous media, compact insulating OT monolayer films formed at a open circuit potential within ~100 s, and the shift of the adsorption potential toward negative values (to–0.6 V) allowed a considerable decrease in the monolayer self-assembly time. The potential shift toward higher negative values (–0.9 V) leads to a removal of OT from the electrode surface during the reductive desorption, with a multipeak current signal recorded on the voltammograms. A transition from aqueous to aqueous ethanol solutions accelerated the formation of an insulating OT monolayer (≈6 s) and led to a change in the shape of the desorption current peak, whose value was almost independent of the ОТ accumulation time and potential.     

The application of ultrasonic waves to the electrochemical polymerization of thiophene

The electrochemical polymerization of thiophene was carried out both in the presence and absence of ultrasonic waves. Without irradiation, the anode potential increased with increasing current density. Polymerization at high potential gave a low polymer yield and produced macroscopically heterogeneous films. Ultrasonic irradiation resulted in an improvement of polymer yield and in a lowering of the anode potential during polymerization. The effects were especially marked when the polymerizations were carried out at low temperature, low monomer concentration, and high current density. These results are explained by the formation of diffusion layer in the vicinity of the electrode during electrochemical reactions.     

Electrochemical oxidation of 3-methylpyridine at a boron-doped diamond electrode: application to electroorganic synthesis and wastewater treatment

The electrochemical oxidation of 3-methylpyridine (3-MP) at synthetic boron-doped diamond (BDD) thin film electrode has been studied in acid media by cyclic voltammetry and bulk electrolysis. The results have shown that in the potential region of water stability there can occur direct electron transfer reactions on BDD surface that result in electrode fouling due to the formation of a polymeric film on its surface. While during electrolyses in the potential region of water decomposition, indirect oxidation reactions can take place by electrogenerated active intermediates, probably hydroxyl radicals that can avoid electrode fouling. Depending on the values of applied current density, it is possible to obtain the partial oxidation of 3-MP to nicotinic acid or the complete combustion of 3-MP to CO₂.