Russian Journal of Electrochemistry最新文献

The processes at platinum electrodes during the cathode polarization in an alcohol solution of erbium nitrate are discussed. The current density maxima on the cathode branch of voltammograms were found to correspond to the potentials of the hydrogen reduction reactions. The gel-like deposit Er(OH)_x(NO₃)_y(С₂Н₅О)_z·nH₂O, x + y + z = 3, formed during the cathode treatment was shown to be not a product of the electron exchange between the cathode and the solution components. The following formation mechanism of the erbium-containing deposit has been suggested. First, the electrochemical process of the hydrogen cathode reduction is implemented. This process leads to the ionic unbalance and causes the alkalinization of the cathode space. This creates conditions for the chemical process of the gel-like erbium hydroxide formation, which is physically adsorbed on the cathode surface as a precipitate.

The aim of this work is to study the possibility of suppressing the metallic lithium dendrite formation during the operation of lithium secondary batteries, including those with a metallic lithium anode. The electrochemical deposition of lithium on copper and lithium substrates in the presence or absence of two surfactants, cetyltrimethylammonium bromide and hexadecylpyridinium bromide, is studied by the current transient and electrochemical impedance measurements. A typical lithium-ion battery electrolyte based on lithium hexafluorophosphate in the mixture of ethylene carbonate and diethyl carbonate is used. The presence of the so-called SEI (solid electrolyte interphase) layer on the electrode surface is shown to have a significant effect on the electrodeposition process. It is also shown that the mechanism of lithium electrodeposition on copper and lithium substrates is different. It can be assumed that the observed effect of surfactants on the dendrite formation is associated not with the adsorption of surfactants on lithium and blocking the growth of deposits, but with the surfactant effect on the properties of the SEI layer formed at these substrates.

We developeda facile method to construct flexible, freestanding three dimensional hierarchical electrodes that consist of graphene encapsulated one-dimensional conducting polyaniline (PANi)@MnO₂ coaxial nanowires grown on electrospun carbon nanofibers (denoted as G-PANi@MnO₂/ECNFs). A combination of XRD, SEM, and TEM techniques were used to characterize the structures of G‑PANi@MnO₂/ECNFs. Electrochemical measurements confirmed that such nanostructured composites possessed higher electrochemical capacitance than that of each individual component due to synergistic effects. The G-PANi@MnO₂/ECNFs electrode exhibited extremely high specific capacitance (1364.3 F/g at 0.3 A/g) and superior cycling stability (89.2% retention rate after 2000 cycles) in a 1 M Na₂SO₄ aqueous solution. The excellent electrochemical performance of such nanoscale architectured electrodes provides a new route to develop flexible, freestanding, and high-performance supercapacitors.

The electrochemical behavior of the biologically active redox chemicals is essential in point of view antibacterial activity. In some cases, the electronic exchanges are coupled to chemical reactions that produce new oxidative or reductive species, which might form electrodeposits. This contribution presents a comparative study of the antibacterial activities and the anodic oxidation of S-triazino-benzimidazole derivatives substituted at the triazine ring with phenyl, 4-fluorophenyl and pentafluorophenyl groups. By combining bactericidal screening against E. coli, P. aeruginosa, S. aureus, and S. typhimurium, to a cyclic voltammetry investigation, it was revealed that the fluorine phenyl substituents in the S-triazine benzimidazole derivatives enhance the electrons ejection to the platinum disk and the subsequent chemical reactions. Additionally, by cycling of potential the non-fluorinated chemical produces a rather passive film on the electrode surface, whereas the fluorinated ones generate electroactive and electrocatalytic coatings. Comparing the results obtained with S-triazino-benzimidazole derivatives to those with 2-aminobenzimidazole, plausible mechanisms of their bactericidal action are suggested.

The kinetic features of electrodeposition of wear- and corrosion-resistant composite electrochemical coating (CEC) of nickel–cobalt–alumina from a chloride colloidal electrolyte are studied. The application of potentiodynamic, chronopotentiometric and temperature–kinetic methods, as well as the use of the calculated temperature coefficient of reaction rate and the diffusion coefficients of nickel ions, enabled us to determine the mechanism of CEC electrodeposition. The analysis of the data on the kinetic features of CEC electrodeposition showed that the nature of the slow stage of the process is associated with the electrophoretic transfer of electroactive particles to the cathode and the stage of the overgrowth of dispersed particles adsorbed on the cathode surface with the electrodeposited metals, which proceed at comparable rates.

A set of computational and experimental methods is used in the study of chemical side interactions in the LiMn₂O₄-based lithium-ion cathodic half-cell over the 25–60°C temperature range. The degradation of LiMn₂O₄-spinel-based electrodes is shown to start upon the LiMn₂O₄ granules contacting the standard (basic) electrolyte solution (1 m LiPF₆ in a mixture of ethylene carbonate and dimethyl carbonate (1 : 1, by wt)). It is established that under current-less conditions, the degradation of the LiMn₂O₄-based electrode is caused by the mutual thermodynamic instability between LiMn₂O₄ and the LiPF₆ lithium salt. The equilibrium interaction products are determined, and the mechanism of the critical temperature influence on the degradation of lithium-ion batteries with lithium–manganese spinel is refined. A model is proposed for the primary surface layer at the LiMn₂O₄/electrolyte interface formation and evolution, which explains the distinctive features of the degradation processes in this system.

The aim of the present study is to evaluate the potential of both the use of zinc oxide (ZnO) nanoparticles as primary filler and graphene as secondary filler in carboxy methyl cellulose based polymer electrolyte. The films were characterized structurally and morphologically by X-ray diffraction (XRD), Fourier-transform infra red spectroscopy (FT-IR), scanning electron microscopy (XRD). XRD results showed that ZnO nanoparticles inclusion reduced the crystallinity of the prepared biopolymer electrolyte. Addition of graphene as secondary filler further reduced the crystallinity of the prepared biopolymer electrolyte film. The FTIR technique and SEM images confirmed the complexation of salts with the polymer matrix. Due to graphene’s ability to create conductive layers, the inclusion of a little amount of it as a supplementary filler increased the A.C. conductivity from 1.63 × 10^–5 to 2.6 × 10^–4 S cm^–1. The synergistic effects of both fillers contributed to raising the polymer electrolyte film’s electrical conductivity. Utilizing this polymer electrolyte layer enabled the creation of a solid state DSSC with an efficiency of 2.6%.

Voltammetry and chronoamperometry are used to study the effect of the solution composition on the desorption behavior of self-assembled monolayers of alkanethiols with approximately the same chain length but different terminal groups of thiols (R: –CH₃, –CH₂OH, and –NH₂). The hydrophilic properties of the terminal groups for the studied thiols increased in the –CH₃ ( ll ) –NH₂ ≤ –CH₂OH series. It is found that the anionic and cationic composition of electrolyte affected significantly the electrochemical stability and blocking ability of self-assembled monolayers of thiols with different terminal groups. It is established that the electrochemical stability and blocking ability of the self-assembled monolayers decreased in the Li⁺, Na⁺, K⁺ series in alkaline solutions regardless of the thiol terminal group. The cation nature in perchlorate and chloride solutions manifested itself only for thiol with the –NH₂ terminal group. The shape of cathodic voltammograms changed for this thiol when passing from alkaline to ({text{ClO}}_{4}^{ - }) and Сl^– medium, possibly owing to a change in the amino group protonation degree.

A comparative study of the electrochemical behavior of various forms of the antitumor antibiotic doxorubicin (DOX), both free and encapsulated in micelle-like nanoparticles of the biocompatible amphiphilic copolymer of N-vinylpyrrolidone (VP) and methacrylic acid, viz., triethylene glycol dimethacrylate (TEGDM), is carried out in aqueous neutral buffers on a glassy carbon electrode. The hydrodynamic radii R_h of the copolymer and the DOX polymeric nanostructures are determined using dynamic light scattering. Using cyclic and square wave voltammetry, for both forms of DOX at pH 7.24, the two main redox transitions are revealed namely, the irreversible oxidation/rereduction in the potential interval from 0.2 to 0.6 V and the reversible reduction/reoxidation in the interval from –0.4 to –0.7 V (vs. saturated Ag/AgCl), and their redox potentials are determined. For both redox transitions, the potential difference between the corresponding peaks does not exceed several tens (20–30) mV; and, moreover, the oxidation of the encapsulated form proceeds easier as compared with the free form, whereas its reduction is somewhat more difficult. The analysis of the dependence of the reduction current of both DOX forms on the potential scan rate shows that the electron transfer to a free DOX molecule is largely determined by the rate of reagent accumulation in the adsorption layer, whereas the electron transfer to the encapsulated form is characterized by the mixed adsorption-diffusion control. Based on voltammetric data and the results of quantum chemical modeling, it is concluded that a hydrogen bond is formed between the oxygen-containing groups of copolymer’s monomeric units and the H atoms in OH and NH₂ groups of DOX. The bond energy in these structures is calculated and shown to be close to the classical values, assuming that the carbonyl group in the VP lactam ring in the encapsulating polymer is the electron donor, and the hydrogen atoms in OH and NH₂ groups of DOX are the electron acceptors. At the same time, the bonds involving oxygen of the ester group in the TEGDM unit are extremely weak.

The effect of lithium polysulfides on the amount and ratio of electrochemically active metallic lithium, electrochemically inactive metallic lithium, and chemically formed lithium compounds in the cathodic deposits formed on a stainless-steel electrode during galvanostatic cycling in 1 М LiClO₄ solution in sulfolane at 15, 30, 45, and 60°C is studied using the method we have developed earlier. It is shown that the increase in temperature leads to increase in the Coulomb efficiency of cycling and the amount of electrochemically active metallic lithium; a decrease in the amount of electrochemically inactive metallic lithium, regardless of the presence of lithium polysulfides in the electrolyte. When lithium polysulfides have been introduced into the electrolyte, an increase in the Coulomb efficiency of the metallic lithium cycling and a change in the ratio of various forms of lithium in the cathodic deposits toward an increase in electrochemically active lithium by about 1.5 times are observed. The lithium polysulfides are assumed to contribute to the dissolution of electrochemically inactive metallic lithium, forming an interfacial “sulfide” film at the electrode, which possessed high ionic conductivity and good protective properties, the more so, at elevated temperatures.