Russian Journal of Electrochemistry最新文献

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.

Abstract

The applicability of calcium–borosilicate glass-ceramics with high boron oxide content as a sealant for solid oxide fuel cells is studied. Chemical composition of the studied materials is: 33 mol % CaO, 21 mol % B₂O₃, and 46 mol % SiO₂. The material is studied as an alternative to the existing calcium– and barium–aluminosilicate-based sealants because of the latters’ limited adhesion to steel interconnects in fuel cells. The studied sealant is shown to have a softening point of about 920–930°C, which allows using it for sealing of fuel cells at 925°C. Use of relatively low sealing temperature allows avoiding overheating of the cell during the sealing and avoiding the accompanying degradation of the battery operational characteristics. The studied sealant demonstrated excellent adhesion to the surface of interconnect materials (the Crofer 22 APU steel). Furthermore, the studied sealant is found to be thermomechanically compatible with the Crofer 22 APU steel and ZrO₂-based electrolytes.

Abstract

Lead Sulfide (PbS) nanoparticle-decorated silicon (Si) pyramids array on Si-based photocathodes are fabricated by using pure chemical methods. The PbS thin layers were synthesized by chemical solution deposition onto flat Silicon (Si) and pyramidal textured Silicon (SiPY) obtained from alkaline Si substrate etching. Scanning Electron Microscopy (SEM) was used to carry out the morphological characterization, while UV–Vis-NIR Spectroscopy was used to study the optical properties. The Linear sweep voltammetry (LSV) was conducted to study the catalytic activity in dark and under white light irradiation using a potentiostat station. Cyclic voltammetry in the presence of and without purging CO₂ was also investigated. The LSV investigations showed the synergy effect between PbS thin films and Si for the rising and transport of the charge carriers. The results showed a higher photocatalytic towards CO₂ reduction of PbS/SiPY compared to Silicon substrate without surface texturization and sensitization. The photoelectrode based on PbS/SiPY could efficiently be used as a photocathode for the photoelectrochemical (PEC) reduction of CO₂ to Methanol.

Abstract

The article explores the features of Pt(0) nanoparticle formation at the interface of nickel-aqueous solution of reagents and a similar interface containing nanoflakes of Co(OH)₂. The synthesis was carried out under Successive Ionic Layers Deposition (SILD) conditions, and solutions of Na₂PtCl₆, CoCl₂, and NaBH₄ were used as the reagents. Pt(0) nanolayers were produced on the nickel surface using Na₂PtCl₆ and NaBH₄ solutions, and for Co(OH)₂ nanolayers CoCl₂ and NaBH₄ solutions were used. Structural chemical studies of the samples synthesized were performed by HRTEM, FESEM, EDX, SAED, XPS, FT-IR, and Raman spectroscopy. It was shown that Pt(0) nanolayers consist of separate nanoparticles, while Co(OH)₂ nanolayers consist of nanoflakes. The main attention in the work is paid to the formation features of Pt(0) nanoparticles on a nickel surface to which a nanolayer of Co(OH)₂ was previously applied. The study of the electrocatalytic properties of such samples in the hydrogen evolution reaction (HER) during water electrolysis in the alkaline medium showed that the best properties are exhibited by nanoparticles synthesized after 20–40 SILD cycles and on nickel substrates with Co(OH)₂ nanolayers applied in advance. Also, it was found that among these samples the best properties are displayed by those containing Co(OH)₂ layers synthesized after 5 SILD cycles. One of the best examples of this series was obtained from 40 SILD cycles and is characterized by the overpotential value at 29 mV of current density at 10 mA/cm², the Tafel slope value at 29.5 mV/dec, and high stability of these values at multiple cycle potential. It is noted that the Pt(0) nanoparticles synthesized after 40 SILD cycles are 4–8 nm in size and are located on the surface of the nanoflakes at a distance of about 10 nm from each other for the nickel foam sample, on the surface of which a Co(OH)₂ nanolayer was synthesized as a result of 5 SILD cycles. These features contribute to the formation of a set of Pt(0) nanoparticle contact points with the surface of Co(OH)₂ nanoflakes, which determines the high electrocatalytic activity and stability of properties of such structures.