Russian Journal of Electrochemistry最新文献

In pulsed electrochemical machining (PECM), it is difficult to control machining stability and surface quality numerous due to the interrelated variables with highly nonlinear and complex characteristics. Thus, how to determine the optimal process parameters to ensure optimal machining performance became a hot research. In this paper, we investigate the recurrence behavior of Ti–48Al–2Cr–2Nb alloy in PECM by recurrence plots and the quantitative analysis. Besides, the Technique for Order Preference by Similarity to Ideal Solution with Criteria Importance through Intercriteria Correlation (CRITIC-TOPSIS) is employed to determine the optimal process parameters for PECM. The results demonstrate that the recurrence plots exhibit periodic characteristics at the macro level, and effectively identify current density changes in different dissolution stages of the alloy at the micro level. Each pulse stage exhibits an inherent oscillation frequency, and the recurrence plots display a similar block structure with evident fractal features. The optimal result show that the optimal process parameters for the potential, the duty cycle, electrolyte pressure and the feed velocity is 16 V, 40%, 0.4 MPa and 0.9 mm/min, respectively. After optimization, the machining stability and the surface morphology uniformity improves by 29.82 and 72.78%, respectively, and the surface roughness decreases by 24.09%, providing a basis for establishing the quantitative relationship between the machining stability and the surface roughness.

The charge-transfer resistance R₁ as a function of the electrode potential Е for the hydrogen evolution reaction passing by the Volmer–Heyrovsky mechanism involving atomic hydrogen adsorbed according to Temkin isotherm is studied. For a quasiequilibrium Volmer reaction, logR₁,E-curves have a minimum and a maximum. With the increasing of the surface nonuniformity factor f the minimum has been shifted toward lower electrode potentials, the minimum region in the voltammogram is widened. The half-width of the minimum region allowed determining the f value. At the lowest and highest values of the surface coverage, the logR₁,E-dependence demonstrated the same regularities as the Langmuir isotherm.

La_{1 – x}Sr_xCoO₃ (x = 0.1, 0.2, 0.3, 0.4, and 0.5) were prepared by the alginic acid sol–gel route and characterized by thermo gravimetric analysis (TGA), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM) techniques. The electrocatalytic activity of fabricated oxide electrodes (Ni/oxide) was studied for oxygen evolution reaction (OER) in an alkaline medium. The cyclic voltammetry of oxide electrodes shows a pair of redox couple at anodic peak potential (E_pa) = 400 ± 6 mV and cathodic peak potential (E_pc) = 296 ± 8 mV. The observed values of electrode kinetic parameters such as the Tafel slope (b) lie between 91 and 126 mV dec^–1 and current density (j) lie between 17.0–73.1 mA cm^–2 at 0.85 V. The Sr-substitution in lanthanum cobaltate matrix improve electrocatalytic activity for OER in an alkaline medium and maximum improvement was observed in the case of 0.4 mol Sr-substituted oxide. The order of reaction (p) with respect to the concentration of [OH^–] is found unity and the highly negative value of entropy of the reaction indicated the oxygen evolution follows the same mechanism and involves the adsorption of the reaction intermediate.

The electrochemical behavior of manganese silicide-germanides with different ratios of germanium and silicon is studied using the methods of voltammetry and impedance spectroscopy in 0.5 M aqueous sodium sulfate solution. It is shown that the oxidation stability of materials decreases with an increase in the ratio of germanium, which, unlike silicon, is incapable of forming a layer of stable oxides on the material surface.

Using the method of polysulfone chloromethylation followed by quaternization, an anion-exchange membrane is synthesized for water electrolyzers with alkaline electrolyte. The characteristics of this membrane such as porosity, electrical conductivity, and gas-tightness are determined. A comparative analysis of characteristics of this membrane as compared with a porous diaphragm (analog of ZifronPerl) is carried out. The results of tests of the membrane within an alkaline electrolyzer battery are compared with the results for the porous diaphragm based on unmodified polysulfone with a hydrophilic filler (TiO₂) and synthesized by phase inversion. The possible mechanism of the degradation of the main chain in quaternized polysulfone is presented. The ways are proposed for the further development of the technology of anion-exchange membranes based on polysulfone.

The reduction of permanganate on a rotating disk electrode is accompanied by an inhibition of depositing birnessite. The addition of potassium ferrate(VI) leads to an increase of inhibition. The obtaining of electrode material based on Fe-doped birnessite under alkaline conditions is demonstrated in experiment with deposition at inhibition potentials. This birnessite is single phase and highly disordered. The Fe content varies from 0 to 10 mol % in respect to Mn with increasing ferrate(VI) content in deposition solution. Recharging potentials of birnessite are shifted which is manifested by cyclic voltammetry. Doping allows to increase the rate of oxygen evolution reaction. The specific currents increase with the iron content in birnessite. The Tafel slope is 53 mV/dec and by 2.5 times lower for birnessite containing 10 mol % Fe.

An hydrophobized gas-diffusion electrode with a tin catalyst deposited onto acetylene black A437E is tested with the aim of elucidation of its potential in intensifying the CO₂ electroreduction to formate in acidic and alkaline aqueous solutions. Porous electrodes with the fluoroplastic content of 40 wt %, a thickness of 0.5 mm, porosity of 60 vol %, and the tin content ≈0.7 mg/cm² of the total electrode surface are studied. It is shown that this type of electrodes can be used in electroreduction of CO₂ at a current density of up to 900 mA/cm², a temperature of 25–55°C with the current efficiency from 74 to 96% with respect to formate. The 4 h electrolysis at a current density of 190 mA/cm² produces a solution with the potassium formate concentration of 1.58 M. This is accompanied by the increase in the capacitance of the electric double layer from 7 to 17 mF/cm² and the decrease in the current efficiency from 96 to 58%.

The express-method proposed recently for experimental determination of diffusion coefficients of electroactive ions inside a membrane and their distribution coefficients at the membrane/solution boundary (Russ. J. Electrochem., 2022, 58, 1103) is based on the comparison of the measured non-stationary current for the electrode/membrane/electrolyte solution system upon the applying of a potential step with the theoretical expressions for the current–time dependence. Application of this method for the study of bromide-anion transport across the membrane was performed in the previous work under the condition of the membrane permselectivity where the amplitude of the electric field inside the membrane was suppressed owing to a high concentration of non-electroactive counterions. Then, the coion (bromide anion) transport occurred by the diffusional mechanism, for which the solution was available in an analytical form. The present study considers for the first time a non-stationary electrodiffusional transmembrane transport of two singly charged ions (e.g., background cation М⁺ as the counterion and electroactive anion X^– as the coion) having identical diffusion coefficients where the current passage induced a transient electric field in this space, resulting in a deviation from predictions for the diffusional mechanism. It is found that within the short time interval after the applying of the potential step from the membrane equilibrium state to the limiting current regime (where the thickness of the non-stationary diffusion layer is significantly smaller than that of the membrane) the non-stationary distributions of the ion concentrations and of the electric field strength as a function of two variables (the spatial and temporal ones, x and t) can be expressed via a function of one variable, Z(z), where z = x/(4Dt)^1/2. The form of the expression, depending on the ratio of the surface concentration of component X to the fixed charge density inside the membrane (X_m/C_f) has been found by numerical integration. The limiting current varies with time according to the Cottrell formula (I ~ t^–1/2); the dependence of the dimensionless current amplitude, i, on the X_m/C_f ratio is found by numerical calculation; an approximate analytical formula has also been proposed. In particular, the passing current is shown to be close to the diffusion-limited one for a low coion concentration at the membrane/electrolyte solution boundary as compared with the concentration of immobile charged groups inside the membrane (X_m/C_f ( ll ) 1), whereas the migration contribution to the ionic fluxes doubles the limiting current when the opposite condition (X_m/C_f ( gg ) 1) is fulfilled.

The nanocomposite of a resorcinol–formaldehyde xerogel and carbon nanotubes after carbonation was obtained in the form of a composite carbon nanopaper (CCNP) with the thickness of 100–300 microns, the density from 0.1 to 0.5 g/cm³ and the electronic conductivity of more than 10 S/cm. The microporous structure of the nanopaper is formed by carbonized resorcinol–formaldehyde xerogel, and the mesoporous structure is formed by the nanotube framework. Previously, the characteristics of nanopaper electrodes in an aqueous electrolyte of 1M H₂SO₄ were measured, where the maximum capacitance was 155 F/g (56 F/cm³). To work with an organic electrolyte, a method for activating CCNP with potassium hydroxide has been developed. In this paper the characteristics of electrodes made of activated nanopaper (a-CCNP) in an organic electrolyte 1 M 1,1-Dimethylpyrrolidinium tetrafluoroborate (DMPBF₄)/acetonitrile solution were measured. The capacitance in this electrolyte has been reached 70 F/g (27 F/cm³). According to measurements on a laboratory assembly of a symmetrical supercapacitor (SC) with electrodes made of CCNP, the characteristics are calculated when the SC operates in the mode of short pulse switching with an efficiency of EF = 95%. In an aqueous electrolyte of 1 M H₂SO₄ (U₀ = 1.0 V), the volumetric energy density was E_0.95,SC = 0.9 W h/L and the volumetric power density was P_0.95,SC = 2.1 kW/L. In 1 M DMPBF₄/acetonitrile electrolyte (U₀ = 2.7 V), the design characteristics of the capacitor were: volumetric energy density E_0.95,SC = 3.8 W h/L and volumetric power density P_0.95,SC = 2.0 kW/L. The specific characteristics of power SCs are compared with electrodes made of activated CCNP and of other carbon materials. In mass production, nanocomposite electrodes are estimated to be cheaper than activated carbon microfibers and significantly cheaper than graphene electrodes.

Transition metals, one of the many modifiers used in enzyme-free sensors, have received impressive attention among the various modification materials for urea electrochemical sensors with low cost. Textiles represent a flexible material for collecting sweat samples for non-invasive urea detection. In our study, we developed a nonwoven fabric-based modified carbon paste electrode using Ag-doped NiO (Ag/NiO) as a sensitive non-enzymatic electrochemical urea sensor. A variety of techniques were used to characterize synthesized Ag/NiO, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), electrochemical impedance spectroscopy (EIS), diffuse reflectance spectroscopy (DRS), and X-ray diffraction (XRD). The electrochemical properties of the Ag/NiO nanocomposite modified carbon paste on a textile electrode were studied using electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry. The electrode was able to oxidize urea in alkaline solutions with high sensitivity, a wide linear range (2.5 × 10^–3 to 5 mM), a low detection limit (8 µM), long-term stability, and good selectivity. Finally, urea concentrations in human sweat samples and plasma were determined by the sensor.