Russian Journal of Electrochemistry最新文献

The effect of the electrolysis mode on internal stresses in zinc, tin–zinc, and nickel electroplates is studied experimentally. The stationary, unipolar galvanostatic pulse, reverse galvanostatic pulse, and potentiostatic pulse electrolysis modes are compared. It was found that the reverse pulse mode provides the maximum stress reduction, viz., by 71% (from 350 to 100 MPa) for nickel electroplates deposited from the Watts electrolyte and the transition from tensile (+25 MPa) to compressive stresses (–5 MPa) for the tin–zinc alloy. The possibility of minimizing the use of organic additives through application of pulse methods is demonstrated. The results highlight the potential of pulse electroplating technologies for improving coating quality under environmental requirements.

Al³⁺-doped vanadium oxide is synthesized by hydrothermal method. The Al : V atomic ratio determined by inductively coupled plasma optical emission spectroscopy is 0.036 : 1, which corresponds to the formula Al_0.072V₂O₅. The layered structure of Al³⁺-doped vanadium oxide is determined by the powder X-ray diffraction analysis. The electrochemical properties of Al³⁺-doped-vanadium-oxide-cathodes are studied in magnesium-containing propylene carbonate electrolyte 1 M Mg(ClO₄)₂ using cyclic voltammetry and galvanostatic charge–discharge. Due to the large interlayer distance of 12.11 Å, the Al³⁺-doped vanadium oxide can reversibly intercalate magnesium ions into its crystal lattice. In addition to the electrochemical characterization of the cathodes, their structural changes after charge–discharge cycling are investigated by X-ray diffraction analysis, and the magnesium content of the cathode in the discharged state is estimated.

The recently proposed express-method for experimental determination of transport characteristics of ion-exchange membranes (Russ. J. Electrochem., 2022, vol. 58, p. 1103) is based on the comparison of measurements of the current transients in an electrode/membrane/electrolyte solution system after applying a large-amplitude potential step with theoretical predictions for this dependence. In previous studies, this approach was used in the study of the transport of bromide anions through a membrane under conditions of its pure diffusional mechanism owing to the electric-field suppression by background ions, for which analytical solutions are available. In this paper, both the solution and the membrane contain only two mobile single-charge ionic species: background cation (counterion) M and electroactive anion (co-ion) X which is subject to the redox-transformation into a neutral product at the electrode/membrane boundary. Then, the non-stationary electrodiffusion transport of these ions inside the membrane as a result of applying a potential step from the equilibrium state of the whole system to the transport-limited current regime is considered. Equilibrium with respect to the exchange of each ion across the membrane/solution boundary is assumed to be retained. It is established that within a short-time interval after the potential step, when the non-stationary diffusion layer thickness is significantly shorter than that of the membrane, the distributions of ion concentrations and electric field strength can be represented as functions of a self-similar variable, х/t^1/2, where x is the spatial coordinate, t is the time. Dependence of these functions on the system parameters are found by numerical integration. The limiting current varies over time according to the Cottrell formula: I ~ t^–1/2. The dependence of the dimensionless current amplitude on the system characteristics is found by numerical calculation. Explicit analytical formulas are derived for the cases of high and low cation concentrations in the membrane as compared with the concentration of immobile charged groups. If the counterion mobility strongly exceeds that of the electroactive component, an approximate analytical formula is proposed that is applicable within a wide range of system parameters. Estimates of the limits of applicability of the expressions obtained are given.

Samples of palladium foil with thickness of 1000 and 40 μm obtained at the initial and final stages of cold rolling, respectively, are studied. The influence of the deformation degree in the formation of the substructure and structure was revealed by the studying of hydrogen permeability processes. Electrochemical studies were carried out by cyclic voltammetry and cathodic–anodic chronoamperometry in 0.1 M H₂SO₄ deaerated solution. Different deformation degrees are found not to affect the substructure of the obtained samples, but manifested themselves in surface processes. At the same time, the rate constants of the atomic hydrogen injection and extraction increased. The values of the hydrogen-permeability diffusion parameters for the studied samples confirm that the movement of atomic hydrogen in the solid phase mainly occurs through the crystallite bodies, while the grain boundaries act as trapping defects.

The performance and durability of proton exchange membrane fuel cells (PEMFCs) are closely related to their operating temperature. Although existing studies have revealed the macroscopic relationship between temperature and performance, the degradation mechanisms of the membrane electrode assembly (MEA) are complex and involve mesoscale structures. These mechanisms are difficult to analyze in detail using conventional experimental methods. In this study, a multiscale numerical model was developed to couple the common degradation mechanisms of PEMFC MEAs, including carbon corrosion, platinum (Pt) oxidation, dissolution, redeposition, and changes in structural characteristics. The model was used to investigate the effects of different operating temperatures on MEA degradation. The results show that operating temperature significantly affects the relative humidity distribution, carbon corrosion rate, Pt dissolution rate, and degradation of the proton exchange membrane (PEM) in PEMFCs. Specifically, at low temperatures (45°C), higher relative humidity leads to more severe carbon corrosion, while at high temperatures (85°C), the dissolution rate of Pt and the degradation rate of PEM increase. For every 1°C increase in temperature, the average Pt dissolution rate increases by 5.8 × 10⁻⁸ g/m². Moreover, the membrane degradation exhibits a higher degradation rate as the temperature decreases at temperatures below 90°C, with the degradation rate at 45°C being faster than at 85°C.This study provides a theoretical basis for optimizing the operating temperature of PEMFCs to enhance their performance and durability and offers new insights into the relationship between temperature and degradation mechanisms.

Using COMSOL Multiphysics and a modified 3D model of a PEM fuel cell, a computational optimization of a hydrogen-air proton exchange membrane fuel cell is carried out. The influence of the bipolar plate profile (widths of gas channels and current-carrying ribs) on the fuel cell’s polarization curve is investigated. The model is validated using the authors’ own experimental data and shows good agreement between the simulation and experimental results. The fuel cell operational conditions and the parameters of its components are recommended, enabling the achievement of the high specific performance of the power system at current densities above 1 A/cm².

The electrochemical behavior of two single-phase alloys in the Al–Cu–Fe system prepared by mechanical activation is studied in acidic media using potentiodymanic measurements. The first alloy is crystalline and consists of the β-Al(CuFe) phase; the second alloy consists of a quasi-crystalline icosahedral phase. The second alloy with the quasi-crystalline icosahedral structure is more stable. The corrosion stability of samples decreases with a decrease in the solution pH.

This study explores the electrodeposition of Ni–Mn coatings on a copper substrate using a sulfate bath with varying Mn²⁺ ions concentration ([Mn²⁺] = 0.05, 0.1, 0.2, and 0.4 M). The effects of [Mn²⁺] and applied potential (E) on the nucleation mechanism were evaluated using the Scharifker and Hills (S–H) nucleation model. The results indicate that [Mn²⁺] and E significantly influence the electrochemical behavior of Ni–Mn coatings. The energy dispersive X-ray (EDX) examination confirmed the presence of Ni, Mn and S species in the coatings. Scanning electron microscopy (SEM) micrographs revealed the cauliflower-like morphology, globular shape particles and porous cracked surface. XRD analysis reveals the successful incorporation of Mn atoms into the Ni lattice, resulting in the formation of a face-centered cubic (FCC) substitutional Ni(Mn) solid solution. The linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) analyses demonstrate that the incorporation of a small amount of Mn into Ni significantly improved the corrosion resistance. The obtained Ni_96.9Mn_1.5 coating shows the highest corrosion resistance. SEM and XRD analyses of the oxide layer confirmed the formation of a porous, non-uniform microstructure composed of MnO₂ and Ni(OH)Cl which contributes to the protective properties of the coating.

A novel glassy carbon electrode modified with cerium dioxide (CeO₂) nanoparticles and hexadecylpyridinium bromide is developed for the voltammetric determination of propyl gallate. The hexadecylpyridinium acts as a dispersing agent that stabilized the nanomaterial and as a co-modifier of the electrode surface. Modification of the glassy carbon electrode lowered the propyl gallate oxidation peak potential by 20 mV and provided a 2.6-fold increase in the oxidation peak current. The bare and modified glassy carbon electrodes are characterized by scanning electron microscopy, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. A statistically significant increase in the effective surface area of the modified electrode is shown (32.4 ± 0.5 mm² as compared with 8.9 ± 0.3 mm² for the bare glassy carbon electrode). The electrochemical impedance data indicate a 2100-fold decrease in the charge transfer resistance as compared to the bare glassy carbon electrode, which confirms the increase in the electron transfer rate (k_et = 1.13 × 10^–5 and 2.42 × 10^–2 cm/s for glassy carbon electrode and CeO₂-nanoparticles/glassy carbon electrode, respectively). Propyl gallate electrooxidation occurred irreversibly with the participation of protons and is controlled by surface processes. The parameters of electrooxidation are calculated and a scheme of the electrode reaction is suggested. The linear dynamic ranges of propyl gallate in the differential pulse voltammetry are 0.10–2.5 and 2.5–50 μM, with a detection limit of 0.022 μM. The selectivity of the electrode response to propyl gallate in the presence of inorganic ions and carbohydrates is demonstrated. Since the propyl gallate is used to prevent oxidation of vegetable oils, α-tocopherol and other antioxidant additives (tert-butylhydroxyanisole and tert-butylhydroxytoluene) used together with propyl gallate are considered as potential interfering agents. A 5-fold excess of α-tocopherol, a 10-fold excess of tert-butylhydroxyanisole and equimolar amounts of tert-butylhydroxytoluene do not interfere with the propyl gallate determination. The method is tested on extracts of sunflower and sesame oils.

Magnesium alloys with rare-earth elements are widely used in industry due to their high specific strength; however, their low corrosion and wear resistance necessitate surface protection. It is studied how the WC and TiC nanoparticles (NPs) used as the dispersed phase in the electrolyte at the plasma-electrolytic oxidation (PEO) of magnesium alloys in the system Mg–Y–Zn–Zr–Nd–Yb containing the long-period staking-ordered (LPSO) phase affect the formation, composition, and properties of oxide layers. The inert incorporation of WC and TiC NPs into the oxide (without their involvement in chemical reactions and phase transitions) is observed as well as the increased productivity of the coating formation for certain concentrations of additives, without commensurate incorporation of nanoparticles into the coating. As compared with WC NPs, the TiC NPs added into the electrolyte induce greater changes in the conditions of coating formation, as reflected in the decrease in the anodic forming voltage of the PEO process up to ~20 V and the increase in the degree of crystallinity of oxide layers to ~80 vol %. The hardness and the adhesion strength of layers increase due to their modification with WC and TiC nanoparticles. The PEO allows reducing the corrosion rate of this alloy by three—four orders of magnitude. The addition of nanoparticles into the electrolyte in concentrations of 2 and 5 g/L WС and 1 g/L TiC makes it possible to additionally increase the charge transfer resistance across the alloy/coating interface by a factor of up to 1.5. At the same time, the high (4–5 g/L) concentration of the dispersed phase in the electrolyte has a negative effect on the long-term corrosion stability of samples. Hence, these coatings are more suitable for articles with limited service life.