Abstract: The state-of-the-art in realization of the method of distribution of relaxation times (DRT) as applied to the analysis of data of electrochemical impedance spectroscopy is briefly surveyed. The theoretical fundamentals of the DRT method are described, the methods of solving the Fredholm equation of the 1st order with respect to the unknown DRT function are considered as an ill-defined problem. The Tikhonov regularization method presently considered as the most suitable for solving this equation is discussed. For several numerical experiments, the high resolution of the DRT method and its stability with respect to noise in impedance spectra are demonstrated. Among the problems and limitations of the DRT methods, the choice of the optimal regularization coefficient is considered as the most significant. Particularly, it is shown that in those cases where several relaxation processes with the constant phase angle appear in the response of objects under study to ac disturbances, different regularization coefficients should be selected for each of these elements in order to obtain adequate results.

Abstract: The properties of electrolyte systems based on standard nonaqueous solvent composed of a mixture of dialkyl and alkylene carbonates and new commercially available lithium salts potentially capable of being an alternative to thermally unstable and chemically active lithium hexafluorophosphate LiPF6 in the mass production of lithium-ion rechargeable batteries are surveyed. The advantages and drawbacks of electrolytes containing lithium salts alternative to LiPF6 are discussed. The real prospects of substitution for LiPF6 in electrolyte solutions aimed at improving the functional characteristics of lithium-ion batteries are assessed. Special attention is drawn to the efficient use of new lithium salts in the cells with electrodes based on materials predominantly used in the current mass production of lithium-ion batteries: grafitic carbon (negative electrode), LiCoO2, LiMn2O4, LiFePO4, and also solid solutions isostructural to lithium cobaltate with the general composition LiMO2 (M = Co, Mn, Ni, Al) (positive electrode).

Abstract: The application of gold nanoparticles (AuNPs) modified glassy carbon electrode in the electrochemical detection of arsenic is presented. AuNPs were electrodeposited onto the surface of a glassy carbon electrode (GCE) by cyclic voltammetry in a potential range of–400 to 1100 mV for 10 cycles. The modification of the GCE with AuNPs resulted in increased redox current of [Fe(CN)6]3–/4– when compared to that obtained from bare GCE. As(III) detection was carried out using square wave anodic stripping voltammetry (SWASV) at the following optimised conditions: pH 1, deposition potential of–600 mV and pre-concentration time of 60 s. The GCE–AuNPs electrode detected As(III) to the limit of 0.28 ppb and was not susceptible to many interfering cations except Cd, Cu and Hg. The GCE–AuNPs electrode was used for the quantitative analysis of arsenic in real water sample. The results obtained were in good correlation with those obtained from inductively coupled plasma—optical emission spectroscopy technique, thus validating the reported method.

Abstract: A novel carbon paste electrode modified with ZnO nanorods and 2-(4-oxo-3-phenyl-3,4-dihydroquinazolinyl)-N′-phenyl-hydrazinecarbothioamide (2PHCZNCPE) was fabricated and employed to study the electrocatalytic oxidation of droxidopa, using cyclic voltammetry, chronoamperometry and square wave voltammetry as diagnostic techniques It has been found that the oxidation of droxidopa at the surface of modified electrode occurs at a potential of about 435 mV less positive than that of an unmodified carbon paste electrode Square wave voltammetry exhibits a linear dynamic range from 70 × 10–8 to 30×10−4 M and a detection limit of 450 nM for droxidopa Finally this modified electrode was used for simultaneous determination of droxidopa and carbidopa

Abstract: The problems of overcoming titanium passivity that hampers reaching high rates of its anodic dissolution, the optimization of electrolyte composition, and the mode of electrochemical machining (ECM) are considered. The anodic potentials of machining and the current efficiencies for titanium ionization reaction in relation to the anionic composition of electrolyte and the nature of solvent are presented. Some details of the mechanism of high-rate anodic dissolution of metal, which determine the main results of ECM, are considered. The examples of techniques of ECM of titanium and their biomedical and aircraft industry applications are presented.

Abstract: In order to elucidate the mechanism of lithium transport in intercalation electrodes based on solid lithium-accumulating compounds and determine its parameters, the kinetic models are used which allow the combined analysis of electrode impedance spectroscopy, cyclic voltammetry, pulse chronoampero- and chronopotentiometry data to be carried out. The models describe the stages of consecutive lithium transport in the surface layer and bulk of electrode-material particles, including the accumulation of species in the bulk. The lithium transport stages that occur in the surface layer of an intercalation-material particle and in its bulk are both of the diffusion nature but substantially differ as regards their characteristic times and diffusion coefficients D. Taking account of this peculiarity and assessing adequately the geometrical configuration of intercalation system allow the diffusion parameters of lithium transport to be correctly determined.

Abstract: It is found that the variations in the structure (morphology and microrelief) and chemical composition of surface of heterogeneous ion-exchange membranes as a result of thermal modification have different effects on the current—voltage characteristics and conditions for the generation of electroconvective instability at the membrane/solution interface under intense current modes. After thermal treatment of strongly acidic sulfocation-exchange membrane, which is characterized by a low catalytic activity in the reaction of water dissociation and a high thermal stability of fixed groups, a fraction of conducting surface area increases and the membrane microrelief develops. As a result, the diffusion limiting current density increases and the length of plateau of the current—voltage curve decreases. Therewith, the thickness of the region of electroconvective instability of solution in the near-membrane region increases and the polarization of electromembrane system, at which the mode of unstable electroconvection is reached, decreases. The thermodestruction of strongly basic anion-exchange membranes, conversely, leads to suppression of electroconvection and an increase in the length of plateau of the current—voltage curve due to the formation of fixed weakly basic amino groups, which are catalytically active in the reaction of water dissociation. A linear correlation is found between the dimensions of the region of electroconvective instability and a fraction of weakly basic functional amino groups in the composition of strongly basic membranes.

Abstract: The concepts of total and free charge of platinum single crystal electrodes are revised in this paper, together with the associated concepts of potential of zero total and free charge. Total charges can be measured from CO displacement method. Results on solution of different pH are described. A novel buffer composition is used to attain pH values close to neutrality while avoiding interferences from anion adsorption processes. Stress is made on the fact that free charges are not accessible through electrochemical measurement for systems at equilibrium since adsorption processes (hydrogen and hydroxyl) interfere with free charge determination. Still, a model is described that allows, under some assumptions, extract free charge values and the corresponding potential of zero free charge for Pt(111) electrodes. On the other hand, fast measurement outside equilibrium can separate free charges from adsorption processes based on their different time constant. In this way, the laser induced temperature jump experiment allows determination of the potential of maximum entropy, a magnitude that is intimately related with the potential of zero free charge. Values of the potential of maximum entropy as a function of pH are given for the different basal planes of platinum.

Abstract: The processes contributing to degradation of characteristics of membrane-electrode assemblies (MEA) of water electrolyzers with solid polymer electrolyte (SPE) are considered. Particularly, the life tests of an electrolysis cell with SPE reveal the migration of platinum from the cathodic active layer and its deposition in membrane’s near-cathode region. In addition to platinum, several other elements (Ti, Ir, Fe, Ni, Si) are detected in the membrane, carried there with the water-reagent from the structural elements of MEA, electrolysis cell, and its outer framing (anodic electrocatalytic layer, half-cells, tubes, water tank-separator, etc.). The observed considerable loss of platinum in the cathodic catalytic layer leads to a decrease in its activity (due to the decrease in concentration of platinum nanoparticles and the loss of their cohesion), while the appearance in the membrane of platinum and other ions that have the lower mobility as compared with hydrogen ions gives rise to modifications in the membrane structure thus increasing the electrolysis potential in the course of life tests.

Abstract: The rapid and simple detection of bisphenol A is very important for the safety and reproduction of organisms. Here, a sensitive and reliable electrochemical sensor was established for bisphenol A detection based on the high amplification effect of copper sulfide-multi-walled carbon nanotube (CuS–MWCNT) nanocomposites. The flower-like CuS–MWCNT were successfully synthesized by a simple hydrothermal method accompanied by polyvinylpyrrolidone (PVP). Compared with bare glassy carbon electrode (GCE), CuS–MWCNT modified GCE could amplify the electrochemical signals in about ten times, which was attributed to the synergistic effect of CuS and MWCNT. The MWCNT could increase the specific surface area of electrodes and improve the electrode activity. The integration of CuS could further enhance the electrode conductivity as well as accelerate the electron transfer rate. Raman spectra and transmission electron microscope (TEM) were used to characterize the successful fabrication of CuS–MWCNT nanocomposites and its uniform and monodispersed morphology. Under optimizing conditions, the oxidation currents of bisphenol A via the differential pulse voltammetric (DPV) showed a good linear relationship with its concentration in a wide range of 0.5–100 μM, with a detection limit of 50 nM. This electrochemical sensor of bisphenol A provided a convenient and economical platform with high sensitivity and reproducibility, which had great potential in environmental monitoring.

Abstract: Efficient synthesis of silver nanoparticles stabilized by cetyltrimethylammonium cations (Ag@CTA+) is carried out in aqueous medium by methylviologen-mediated electroreduction of silver chloride nanospheres stabilized by surface-active CTA+ cations (AgCl@CTA+, diameter ~330 nm), on a glassy carbon electrode at potentials of the MV2+/MV•+ redox couple. The nanospheres AgCl@CTA+ can be reduced immediately on the electrode at a low rate and the resulting metal is deposited on the electrode. In the mediated reduction, the metal is not deposited on the cathode but the quantitative reduction of AgCl to Ag@CTA+ nanoparticles proceeds completely in solution volume at the theoretical charge. In aqueous solution, the nanoparticles are positively charged (electrokinetic (zeta) potential is +74.6 mV), their characteristic absorption maximum is at 423 nm and the average hydrodynamic diameter is 77 nm. Isolated Ag@CTACl nanoparticles have the size of 39 ± 15 nm. The preferential form of metal nanoparticles is sphere with the diameter of 34 ± 24 nm; nanorods are also obtained in small amounts (4%); the average size of metal grains is 8–16 nm.

Abstract: Entire carbon nanofiber mats (carbon nanofiber paper) based on polyacrylonitrile pyropolymer composite were prepared by the preliminary oxidation (stabilization) of the initial polymer at 250–350°C in air and following pyrolysis at 800–1200°C under vacuum. The mats were tested as cathodes in a fuel cell on polybenzimidazole membrane. Properties of the pyropolymers which were obtained by polymer carbonization could be significantly changed by the addition of specific additives to polyacrylonitrile and also by changing thermal treatment. Particularly, the addition of Ketjen Black® or Vulcan® XC72 carbon blacks and polyvinyl pyrrolidone during electrospinning step resulted in increase of material electrical conductivity and inner porosity, which is important for improving fuel cell performance. Depending on oxidation and pyrolysis temperature, the physical properties of platinated carbon nanofiber paper and the efficiency of a fuel cell on polybenzimidazole membrane significantly change.

Abstract: This work is devoted to the studying of effects of La2NiO4 doping with alkaline-earth elements: Ca, Sr, and Ba (at an amount of 15 mol %) on its structural, electrical, and electrochemical properties. The effects of the alkaline-earth element nature, introduction of the Ce0.8Sm0.2O1.9-electrolyte (SDC) component to the functional layer, and the presence of collecting film onto electrochemical activity of the electrodes contacting the Ce0.8Sm0.2O1.9-electrolyte are examined. The doping was found to increase the La2NiO4 full conductivity due to increase in the hole conductivity. The maximal conductivity (at the sample density of 86–89%) was obtained for the Ca-doped composition: 85 S/сm at 700°C, as compared with 65 S/сm for undoped La2NiO4. at the same time, the doping was found to deteriorate the electrodes’ electrochemical activity which is likely to be due to loss of interstitial oxygen as a result of the doping. The using of composite electrodes allows increasing polarization conductivity markedly. For instance, at 700°С the conductivity of La2NiO4 is 0.25 S/сm2; of its based composite, 0.67 S/сm2.

Abstract: Using the rotating ring (platinum)—disk (glassy carbon) electrode methodology, electrocatalytic activity of the microstructured copper centers (imbedded within the polyvinylpyrrolidone polymer matrix and deposited onto the glassy carbon disk electrode) has been monitored during electroreduction of carbon dioxide both in acid (HClO4) and neutral (KHCO3) media as well as diagnosed (at Pt ring) with respect to formation of the electroactive products. Combination of the stripping-type and rotating ring-disk voltammetric approaches has led to the observation that, regardless the overlapping reduction phenomena, the reduction of carbon dioxide at copper catalyst is, indeed, operative and coexists with hydrogen evolution reaction. Using the fundamental concepts of surface electrochemistry and analytical voltammetry, the reaction products (thrown onto the platinum ring electrode) could be considered and identified as adsorbates (on Pt) under conditions of the stripping-type oxidation experiment. Judging from the potentials at which the stripping voltammetric peaks appear in neutral CO2-saturated KHCO3 (pH 6.8), formic acid or carbon monoxide seem to be the most likely reaction products or intermediates. The proposed methodology also permits correlation between the CO2 electroreduction products and the potentials applied to the disk electrode. By performing the comparative stripping-type voltammetric experiments in acid medium (HClO4 at pH 1) with the adsorbates of formic acid, ethanol and acetaldehyde (on Pt ring), it can be rationalized that, although C2H5OH or CH3CHO are very likely CO2-reduction electroactive products, formation of some HCOOH, CH3OH or even CO cannot be excluded.

Abstract: The operation-mode stability and the catalytic activity in electrode reactions are the most important properties of electrocatalysts that determine the possibility of using them in fuel cells The negative linear correlations between stability and catalytic activity of a series of Pt/C and Pt–Cu/C materials in the oxygen electroreduction reaction are revealed and studied A method of selecting electrocatalysts with the optimal combination of activity and stability is proposed The Cu@Pt/C catalysts containing bimetallic nanoparticles with the core–shell architecture which demonstrate the anomalously high combination of activity and stability are synthesized

Abstract: A direct relationship is derived between the charge-transfer resistance and the resistive terms ascribable to diffusion for a faradaic reaction influenced by transport of the reacting species to the electrode. The charge-transfer resistance is shown to approach a finite value for potentials at which the current is limited by mass transfer and, conversely, the diffusion impedance approaches a finite value when the current is controlled by kinetics. Supporting experimental results are presented for both an irreversible (oxygen reduction reaction) and a quasi-reversible (ferrocyanide oxidation) electrochemical systems investigated with a rotating- disk electrode.

Abstract: Platinum nanoparticles (PtNPs) are synthesized by methylviologen-mediated reduction of PtCl2 at the potentials of the MV2+/MV•+ redox couple in 40% aqueous DMF solution In the absence of stabilizing agents and in the presence of a stabilizer in the form of spherical silica NPs or alkylamine-modified silica NPs (SiO2-NHR), a part of PtNPs (14–18%) are deposited on the electrode while the rest of particles remain in solution to form coarse aggregates which precipitate In the latter case, PtNPs are also partly bound to form individual ultrafine NPs (3 ± 2 nm) on the SiO2-NHR surface In the presence of polyvinylpyrrolidone (PVP), the generated PtNPs (18 ± 9 nm) neither aggregate nor deposit on the cathode but are completely stabilized in solution being encapsulated within the PVP matrix The obtained PtNPs are characterized by the methods of dynamic light-scattering and electron microscopy

Abstract: The work contains the results of studies of a promising composite material of Sr2Fe1.5Mo0.5O6 + Ce0.8Sm0.2O1.9 for electrodes of symmetrical solid oxide fuel cells. It is shown that conductivity of the composite at 800°C is about 10 and 15 S/cm, for air and humid hydrogen, respectively, and polarization resistance of the electrodes in contact with the electrolyte based on doped lanthanum gallate under the same conditions is about 0.26 and 0.12 Ohm cm2. Tests of a symmetrical fuel cell with a planar design and the supporting gallate electrolyte with the thickness of 300 μm show that the cell can develop the power of about 0.5 W/cm2 at 800°C when air is supplied to the cathode and humid hydrogen is supplied to the anode. Analysis of polarization losses shows that the polarization of the oxygen electrode considerably exceeds the polarization of the anode.

Abstract: The results on optimizing the procedure of preparation of the electrode system within membrane–electrode assemblies (MEA) of solid-oxide fuel cells (SOFC) by joint sintering of electrodes at the enhanced temperature close to that of anode sintering are presented. The MEA are prepared based on membranes of the anionic conductor HionicTM (Fuel Cell Materials, USA); the cathode is formed based on cation–deficient lanthanum-strontium manganite (La0.8Sr0.2)0.95MnO3 with addition of activated carbon for optimizing its microstructure; the anode is formed on the basis of cermet NiO/10Sc1CeSZ (89 mol % ZrO2, 10 mol % Sc2O3, 1 mol % CeO2). The results of electrochemical testing of model MEA are also shown.

Abstract: Different graphitic carbon-based electrode materials were evaluated for direct electro-oxidation of clindamycin and electroanalytical parameters such as sensitivity, residual background current, and signal-tobackground current ratio were compared to select the best one for the clindamycin electroanalysis. Such electrode materials include glassy carbon, carbon paste, pyrolytic graphite (edge-plane and basal-plane), carbon nanotube, reduced graphene oxide, and carbon black. The edge-plane pyrolytic graphite electrode after a simple and fast electrochemical pretreatment showed superior performance compared with the other carbon electrodes. Raman and Fourier transform infrared spectroscopy were employed to analyze the surface microstructure and chemical bonding of the carbon materials and scanning electron microscopy was used to study their surface morphologic features. The applicability of the electrochemically activated edge-plane pyrolytic graphite electrode for the determination of clindamycin in pharmaceutical formulations and human urine samples was evaluated.

Abstract: Peculiarities of open-circuit interaction between the surface of electronegative NdFeB magnet and electrolytes containing pyrophosphate and ammonia complexes of copper are studied. It is shown that in the first minutes of the magnet immersion, the rate of open-circuit contact exchange in the pyrophosphate- ammonia electrolyte is close to its value in the pyrophosphate electrolyte (0.98 and 0.90 mA/cm2, respectively) being gradually halved. Although the contact-exchange rate in pyrophosphate-ammonia electrolyte is higher as compared with the ammonia electrolyte, the contact exchange does no become the reason for the loss of adhesion of the deposited copper-containing coatings to the substrate. This is associated with both the formation of a strongly adhered copper layer on cathodic domains of the magnet surface and the absence of poorly soluble products of magnet dissolution formed on the surface of anodic sites.

Abstract: The work studies chemical stability and thermal compatibility of composite electrodes in contact with proton electrolyte based on calcium zirconate. Composite of electrolytes of CaZr0.95Sc0.05O3–δ and CaZr0.9Y0.1O3–δ with Fe, Ni, Cu, and Pd metals and also with the perovskite oxide of SrTi0.8Fe0.2O3–δ are considered. Temperature dependences of resistance of porous electrodes made of these materials are studied.

Abstract: The Ag–Ge–Se system was studied in the range of compositions Ag2Se–GeSe2–Se by measuring the EMF of the concentration (relative to the silver electrode) circuits with a solid electrolyte Ag4RbI5 in the temperature range 290–430 K The polymorphic transition temperature of Ag8GeSe6 (320 K) was determined and the partial molar functions of silver were calculated for both crystal modifications of this compound based on the EMF measurements The thermodynamic functions of formation and entropy of both modifications of Ag8GeSe6 and the thermodynamic functions of its polymorphic transition were calculated

Abstract: We present a model Hamiltonian for electrochemical electron transfer, and use Green’s functions as the starting point for three different approaches to the calculation of rate constants: first order perturbation theory, which is equivalent to the Levich and Dogonadze theory, the calculation of adiabatic free energy surfaces, and propagation in time. We discuss the similarities and differences between these methods.

Abstract: The types of cells and methods of electrochemical reduction of graphene oxide films were described. The possibility of creating ultrathin membrane–electrode assemblies of supercapacitor cells was demonstrated. The peculiarities of the electrochemical behavior of films of different thicknesses that contact with carbon and metal current collectors were shown. The limiting charge (1500–2000 C/g) for complete electrochemical reduction of graphene oxide was determined. Possible mechanisms of proton conductivity along the basal faces of graphene oxide flakes were proposed. The nature of the current collector was shown to affect the electron–hole conductivity of graphene oxide films and the observed contact potential difference.

Abstract: It is shown that the liquid oxidative treatment of microporous active carbon (AC) of the Norit DLC Supra 30 grade by nitric acid in the presence of carbamide results in an increase in the content of hydroxy groups on the AC surface at the practically unchanged content of carboxyl groups. Redox functionalization and appearance of pseudocapacity result in an increase in the carbon electrode capacity by 26%. The surface state of the carbon material is characterized using the infrared spectroscopy and Boehm titrimetry techniques, while the electrochemical characteristics are studied using the method of cyclic voltammetry in 3 M sulfuric acid solution. Studies of degradation of the electrodes of the initial and modified active carbons show that capacity decreases by 3 and 8%, accordingly, after 1 thousand charging–discharge cycles.

Abstract: A facile approach has been established to prepare PPy via in situ polymerization with different metal sulfate as dopants. The morphology and structure of PPy and doped PPy were characterized by scanning electron microscopy (SEM) and fourier transform infrared (FT-IR). It was found that doped PPy has different morphology and a slight structure change. The electrochemical performance of the samples has been illustrated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and AC impedance measurements. Compared with the PPy, the specific capacitance of PPy/Cu2+ has been improved to 224 F g–1 at the current density of 0.6 A g–1. Also, the relationship between electrochemical properties of doped PPy and various parameters of metal ions has been investigated.

Abstract: Lithium-containing bismuth titanates with the pyrochlore-type structure Bi1.6LixTi2O7–δ were obtained for the first time. The formation of the pyrochlore phase was confirmed by X-ray diffraction analysis, scanning electron microscopy and local microanalysis. In Bi1.6MxTi2O7–δ, the lithium and indium are occupied the bismuth sites, primarily. The electrophysical properties of doped bismuth titanates were studied by impedance spectroscopy in the frequency range 1–106 Hz. In the low-temperature range (of up to ~400°C), electron conductivity predominates; above 400°C, the oxygen-ion type of conductivity is revealed. In the range p(O2) = 0.21–1 atm, the average value of the sum of ion transport numbers is 0.5 at 500–550°C. The relaxation process was found from the frequency dependences of the dielectric parameters (e', tan δ, M''), which was of the same type for systems with different dopants (In, Li) probably due to the hopping mechanism of oxygen conductivity.

Abstract: Overlimiting current modes are of considerable interest for the practice of electrodialysis (ED). However, the economical expedience of such ED modes is evident only for desalination of dilute solutions. Here, we show the theoretical analysis of the effect of concentration on the behavior of an ED cell with homogeneous ion-exchange membranes. The study is based on numerical solution of the two-dimensional system of coupled equations of Nernst–Planck–Poisson–Navier–Stokes. It is shown that as the electrolyte concentration in solution that enters the ED desalination chamber increases, the intensity of electroconvection decreases, which induces a decrease in the relative mass-transfer rate (the decrease in the ratio of current density to its limiting value). This effect is stronger in the region of high potential differences where the electroconvective instability of Rubinstein–Zaltzman is realized under the conditions of a nonuniform concentration field caused by solution desalination. In contrast, the increase in the counterion concentration at the membrane surface (associated with the increase in the surface charge) intensifies the electroconvection.