Russian Journal of Electrochemistry

In the present study an electrochemical sensor, based on glassy carbon electrode (GCE) modified by polyluminol (PLum)/functionalized multi-walled carbon nanotube (f-MWCNTs) was introduced for the determination of paracetamol. Modified electrode was made by casting the f-MWCNTs on GCE and electropolymerization of luminol on its surface. The surface morphology was investigated by scanning electron microscopy (SEM) and impedance electrochemical spectroscopy (EIS). The effective parameters on the response of the modified electrode were optimized, and the square wave anodic stripping voltammetry (SWASV) was applied for drug determination. Under the optimized conditions, at least two linear dynamic ranges (0.04–32.2 and 32.2–172.2 µM) were observed between the anodic peak currents and concentrations of PCM when PLum/f-MWCNTs/GCE was used, and its detection limit was 25 nM. The proposed electrode was successfully applied to determine PCM in pharmaceutical formulations, urine and serum samples.

The results of studying the effect of solution pH on the electrode process that occurs on the gold electrode in solutions of sodium sulfite, sulfuric acid, and alkali, and also in the universal buffer of Britton–Robinson (pH 2–14) are shown. In sodium sulfite solutions, this electrode process represents a combination of the oxidation of sulfite species and the formation of oxides on the gold surface that proceeds simultaneously in the same potential region. It is shown that the solution pH and the oxidation of sulfite species have no effect on the amount of gold α-oxide formed. At the same time, the solution pH has a strong effect on the oxidation of sulfite species. Thus, the voltammograms measured in solutions with pH approximately between 2 and 11 are identical, i.e., the process rate is independent of the solution acidity and its partial composition. These results suggest that in this pH region, the oxidation of sulfite ions can be interpreted by the overall reaction \(2{\text{SO}}_{3}^{{2 - }} \to {{{\text{S}}}_{{\text{2}}}}{\text{O}}_{6}^{{2 - }} + 2{\text{e}}\) to produce dithionate ions. In strongly alkaline solutions (pH 12.5–14), the oxidation potential shifts in the negative direction and the current decreases with increasing pH. These results suggest that in strongly alkaline solutions, the oxidation of sulfite ions can proceed on the partly blocked electrode surface by the reaction \({\text{SO}}_{3}^{{2 - }} + 2{\text{O}}{{{\text{H}}}^{ - }} \to {\text{SO}}_{4}^{{2 - }} + {{{\text{H}}}_{{\text{2}}}}{\text{O}} + 2{\text{e}}\) to form sulfate ions. The changeover of the mechanism of oxidation of sulfite ions takes place in a narrow potential region in solutions with pH from 11 to 12.5 and is accompanied by anomalously sharp changes in the measured current. The latter anomalies are associated with the peculiar dynamics of the process of passivation/depassivation of the electrode surface by gold oxides.

The electrochemical method for synthesizing multilayer graphene oxide by the anodic oxidation of disperse graphite in sulfuric acid is proposed. The possibility of sequential dispersion of graphite in the course of its electrochemical oxidation, hydrolysis, and thermolysis is demonstrated. It is shown that the resulting nanostructured materials tend to form agglomerates in aqueous dispersions. When treated with supersonic, the size of oxidized graphite particles decreases noticeably and they form multilayer graphene oxide. Thermolysis (250°С) leads to a considerable expansion of oxidized graphite particles (the inflation coefficient 1490 cm³ g^–1) and reduction of oxygen-containing functional groups. The structure of thus obtained material includes polygraphene sheets with the thickness of 0.01–0.1 µm and contains pores of 1–10 µm.

Black phosphorus nanosheets (BPNS) were synthesized through liquid exfoliation method coupling with ultrasonication. The synthesized BPNS were characterized by transmission electron microscopy, size-distribution analysis, and Raman spectroscopy. The results revealed that few layers BP nanosheets with an average lateral size of 240 nm were obtained. BPNS modified glassy carbon electrode (BPNS/GCE) was fabricated, and used to study the electrochemical reaction of ascorbic acid (AA). The oxidation current of AA increased nearly 6-times and the oxidation potential was negatively shifted compared with the bare GCE, which should be result from the large surface area and good charge transfer ability of BPNS film. Several impacting factors including the amount of modified BPNS, the pH value, and the potential scan rate, were investigated. Under the optimal condition, differential pulse voltammetry was used to detect AA in the range of 1–35 nM with a detection limit of 0.3 nM. The obtained results revealed the potential electrochemical sensing application of BP nanomaterials, which should promote the further analytical application of two-dimensional nanomaterials.

The work presents the results of measurements of specific conductivity in aqueous solutions of low–molecular alcohols: mono-, di-, tri-, and nonaethylene glycols, glycerol, ethanol, sorbitol, and acetone in the full concentration range. It is shown that not only hydroxyl groups should be considered as the donor–active charge carrier centers in the studied systems, but also oxygen atoms, which is illustrated by a linear dependence of the conductivity maximum on the number of hydration centers. A new method of normalization of specific conductivity is suggested that allows extracting the component corresponding to the charge carrier donor.

The electroreduction of oxygen on thin-film metal–polymer nanocomposites that differ in the metal (Ag, Cu, Pd), content, particle size of the metal component, and ionic form of the Lewatit K2620 matrix (H⁺, Na⁺) was studied. The limiting oxygen diffusion current and effective number of electrons involved in oxygen electroreduction were determined. The limiting current and the number of electrons increased with the content of metal nanoparticles and transition to larger nanoparticles. The oxygen electroreduction occurs by the four-electron mechanism, whereby the hydrogen peroxide intermediate product does not accumulate, and oxygen is reduced directly to water molecules. The electrochemical reduction of the metal oxidation products and hydrogen evolution can be observed depending on the ionic form of the matrix.

In the work, new lithium-conducting solid electrolytes based on lithium zirconate are synthesized. They are obtained by doping Li₈ZrO₆ phase with isostructural Li₇TaO₆. It is shown that in the Li_{8– x}Zr_{1– x}Ta_xO₆ system, a series of solid solutions х = 0−0.5 based on Li₈ZrO₆ form. The conductivity of synthesized Li_8 ‒ xZr_{1 – x}Ta_xO₆ solid solutions increases by 1–2 orders of magnitude as compared with undoped zirconate Li₈ZrO₆ due to the formation of lithium vacancies in the tetra- and octahedral layers of the structure. All-solid-phase electrochemical cells with Li_7.85Zr_0.85Ta_0.15O₆ electrolyte, 0.75Li₂SnMo₃O₁₂ ∙ 0.25B₂O₃ glass-ceramic anode, and 0.2Li₂O · 0.2LiF · 0.45V₂O₅ · 0.25B₂O₃ cathode are electrochemically tested. It is shown that the resistance of 0.75Li₂SnMo₃O₁₂ · 0.25B₂O₃|Li_7.85Zr_0.85Ta_0.15O₆|0.2Li₂O · 0.2LiF · 0.45V₂O₅ · 0.25B₂O₃ cell decreases after the charge—discharge cycling.

Technical carbon CH210 was processed by chemical reduction of the diazo derivative of anthraquinone for surface modification. The presence of anthraquinone groups on the carbon surface was confirmed by attenuated total internal reflection (ATR) IR spectroscopy. Carbon with the anthraquinone-modified surface was deposited on a glassy carbon support using a polymer binder. The behavior of the thus obtained catalyst in oxygen electroreduction in an alkaline medium was studied by the rotating disk electrode method. The kinetic characteristics of the reaction were determined: half-wave potential, limiting current, number of electrons, Tafel slope, exchange current, and charge transfer coefficient. Hydrogen peroxide is formed on the surface of the carbon–polymer composite at higher positive potentials than on technical carbon and glassy carbon electrodes. Therefore, the proposed material can be used as an effective electrocatalyst for this reaction.

Based on the reaction of electron-hole separation in perovskite solar cells, we derived the mathematical relationship between current and voltage from the viewpoint of electrochemical kinetics and, moreover, by using this relation, we successfully fitted the i–E curves. We found that the nonlinear relationships between the activation energy and the potential of the recombination reaction are the fundamental reason for the appearance of the hysteresis loop.

The activity of organoselenides as corrosion inhibitors for mild steel (MS) in 1.0 M hydrochloric acid was evaluated via electrochemical, surface examination and computational chemical methods. The results revealed that the corrosion inhibition percentage (% IE) of organoselenides reached more than 80% with little concentration. Tafel curves showed that organoselenides act as mixed-type inhibitors. EIS measurements indicated that organoselenides mitigate MS corrosion by adsorption on the surface. SEM and AFM analysis depicted the significant improvement in the MS surface in the presence of organoselenides, protecting the surface owing to the formation of an inhibitive film over the metallic surface. Also, DFT computations were conducted on the active form of the investigated compounds. Results from the practical experiments and theoretical calculations suggested that organoselenides are promising inhibitor candidates for corrosion of MS in 1.0 M hydrochloric acid.

An active coating, composed of a mixture of nanocrystals of RuO₂ with the rutile structure and nanocrystals of metal Pt, was thermally synthetized on a titanium substrate. Cyclic voltammograms and polarization curves showed that the catalytic activity of the coating for the formic acid oxidation in an acidic solution increased with an increase in the RuO₂ content, reaching the maximum value at 50 mol % RuO₂. Additionally, further increase in the RuO₂ content resulted in a decline of the catalytic activity. The catalytic effect was attributed to a bifunctional mechanism and an electronic effect. The bifunctional mechanism had a dominant role and was based on the fact that Ru–OH species were formed on Ru atoms of RuO₂ at more negative potentials than on Pt. Those species oxidized the adsorbed CO_ad and HCOO_ad—species on adjacent Pt atoms of clusters of metal Pt and thus discharge them to oxidize new HCOOH molecules.

Electrochemical oxidation of hydroquinones (1a–1b) were studied in the presence of meldrum’s acid (3) as a nucleophile in an ethanol-phosphate buffer (pH 7, 0.20 M) mixture (as a green media), by means of voltammetric techniques. The obtained results indicated that the p-quinones (2a–2b) are derived from 1a–1b participation in a 1,4-Michael addition reaction, with the meldrum’s acid (3) to form the corresponding new symmetric and asymmetric benzofurans (8a and 6b). The electrochemical synthesis of these new compounds (8a and 6b) has been successfully performed in an undivided cell with high yield and good purity.

The present study focused on remediation of clayey soil contaminated with two percentages of copper sulfate using washing-electrokinetics technique enhanced by purging solutions and mid compartment. The intact soil samples are obtained from Al-Ahdab oil field located in the southeast of Iraq, where the soil samples are contaminated synthetically with two percentages of copper sulfate (6666.66 and 26666.66) ppm for 30 days. The electrokinetics technique enhanced with a mid compartment to reduce the exist way of contaminant from the soil. Also, it is enhanced by purging solutions in the anode, mid, and cathode compartments to control the pH value of solutions in the resvoirs. The activated carbon is used to prevent the reverse osmotic flow from cathode to anode. The main results of physical model are the variation of electrical current with time, pH value, and the accumulated volume of osmotic flow. Increasing the concentration of copper causes raising the electrical current generated during the remediation process, so the chemical reaction occurred in the anode, mid and cathode compartments are increased. The removal efficiency of copper from soil samples ranged 98.4 to 99.6%, which indicated high efficiency within short time, but using washing process causes a reduction in the time required for remediation by 30% and causes a slight increase in the removal efficiency.

The fabrication and characterization of thin film humidity sensors based on orange dye (OD) and OD–graphene solid electrolytes cells were done in this paper. The 200 nm thick silver (Ag) and copper (Cu) electrodes were deposited on glass substrate by thermal evaporation. There was gap of 20 µm between the electrodes, where the 8 to 12 µm thick film of solid electrolyte was deposited. The pure OD and the OD–graphene composites with 40 and 60% (by weight) graphene were used as solid electrolytes. The dependences of the open-circuit voltage of the cells on humidity were measured in the humidity interval from 34 to 90% relative humidity (RH). It was found that with increase in humidity the open-circuit voltage of the cells increased. In the OD–graphene composite cells on increasing the concentration of graphene the open-circuit voltage increased accordingly.