Vol 54, No 11 (2018)

This article reports the electrochemical determination of paracetamol (PC) in the presence of ascorbic acid (AA) and caffeine (CF) using an electrochemically treated pencil graphite electrode. In this study, we describe the use of an electrode prepared by overoxidation between 0.0 and +2.1 V for paracetamol determination. The electrochemically treated pencil graphite electrodes (ETPGEs) were prepared using a cyclic voltammetric method. The electrode was characterized by Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectroscopy (EIS), and Resonance Raman Spectroscopy. The differences in oxidation peak potentials were large enough to determine PC in the presence of AA and CF. The electroactive areas of the bare electrode and 10 scan-ETPGE in 0.5 M H₂SO₄ were calculated to be 0.0031 and 0.0341 cm², respectively. The sensor (10 scan-ETPGE in 0.5 M H₂SO₄) was sensitive to the PC with 1.74 × 10^–7 M limits of detection (S/N = 3). Finally, the developed method and the prepared electrodes were used for determination of PC in the pharmaceutical samples.

In this work, we discuss the catalytic performance of poly(3,4-ethylenedioxythiophene) (PEDOT) counter electrode prepared via electro-polymerization (EP) method in Na₂SO₄ aqueous solution and [BMIM]BF₄ ionic liquid for dye-sensitized solar cells (DSSCs), respectively. The electrochemical and photoelectric conversion tests result show that [BMIM]BF₄ is more beneficial to dissolve EDOT and thereby promote the growth of 3D PEDOT which can increase the catalytic activity. Furthermore, the introduced graphite (Gr) buffer layer can improve the roughness of PEDOT and F-doped tin oxide substrate (FTO), However, in the [BMIM]BF₄ ionic liquid, the overgrowth PEDOT on Gr will reduced the properties of the counter electrode (CE) compare to CE without Gr buffer layer. Further, by using the Gr/ PEDOT_IL counter electrode, a 4.89% of photoelectric conversion efficiency(PCE, η) was obtained which was up to 82.3% of DSSC–Pt (η = 5.94%) at the same condition. Meanwhile, the electro-catalytic activity of FTO/PEDOT_IL and FTO/Gr/PEDOT_IL electrode are demonstrated by scanning electrochemical microscopy (SECM).

The effect of the carbon-material specific mass on the electrochemical parameters of electrodes for supercapacitors on neutral aqueous electrolytes is studied. It is shown that the highest specific capacitance of 11 F/g is observed for electrodes with the specific mass of 1 mg/cm². These electrodes are stable at the potential scan rate from 2 to 600 mV/s, in contrast to electrodes with the specific mass of 6 mg/cm². As the power increases, the decrease in the specific energy of the electrode with the mass of 1 mg/cm² is less pronounced as compared with the electrode with the mass of 6 mg/cm². The specific energy of the former electrode is 8 W h/kg for the specific power of 20000 W/kg, whereas for the specific energy of the latter electrode is 5 W h/kg for the specific power of 2000 W/kg.

A sensitive and convenient electrochemical sensor was developed for determination of epinephrine by using the Fe₃O₄@SiO₂/GR nanocomposite modified graphite screen printed electrode, and its electrochemical behaviour was investigated by cyclic voltammetry, chronoamperometry and differential pulse voltammograms. Differential pulse voltammetry results exhibited the linear dynamic range of 5.0–1000.0 μM, with detection limits (S/N = 3) of 1.0 μM. The prepared electrode was successfully applied for simultaneous determination of epinephrine and folic acid in real samples.

Image analysis gives us a new opportunity in corrosion science. Fuzzy Kolmogorov–Sinai (K–S) entropy is used to quantify the average amount of uncertainty of a dynamical system through a sequence of observations. The fuzzy K–S entropy for horizontal and vertical orientations is sensitive to distribution of corrosion product or corrosion degree, and the entropy values decrease as the corrosion becomes more and more serious. It is concluded that the fuzzy K–S entropy is illustrated as an effective feature for image analysis and corrosion classification.

A new method for the calculation of electric field distributions in the systems with spatiallyrestricted regions filled with polar media with nonlocal dielectric characteristics is proposed. The presence of regions with different dielectric properties in the system (as exemplified by the presence of an ion-filled cavity in which there is no polar medium surrounding the ion) is automatically taken into account within this procedure. The field distribution inside a uniform and isotropic nonlocal dielectric medium outside the spherical cavity containing a spherically symmetric charge distribution (the system represents the ion inside the polar solvent) has illustrated this new approach. In contrast to the previously suggested approach (dielectric approximation), where calculations of this characteristic required complex numerical and analytical calculations, the new method requires only single integration in order to determine the distribution of the potential of the electric field inside the polar medium with an arbitrary law of spatial dispersion of its dielectric permittivity (which can be specified eithter analytically or numerically).

The properties of poly(3,4-ethylenedioxythiophene) (PEDOT) films were studied electrochemically at high positive potentials (from–0.3 to 1.5 V relative to the Ag/AgCl electrode). A cyclic voltammetry (CV) study revealed the range of potentials (up to 1.3–1.5 V) where the cycling leads to significant changes in the electrochemical, structural, and morphological properties of the polymer film due to overoxidation. When the upper cycling potential E_up exceeded 1.4 V, the anodic current significantly increased during the first cycle and then decreased, which suggests a loss of the electroactivity of the polymer and degradation of its properties. In the high-frequency region of the impedance spectra of the PEDOT films, a semicircle appears after overoxidation, which indicates a notable increase of the charge transfer resistance in the system, in contrast to the films subjected to potentiodymanic processing in a limited range of potentials from–0.3 to 1.3 V. The effect of overoxidation on the polymer morphology was studied by scanning electron microscopy. The chemical state of elements in the structure of the polymer film was determined by X-ray photoelectron spectroscopy. The obtained data indicate that–S=O groups formed at the thiophene sulfur in the polymer.

The interaction between thallium atoms and the Au(111) surface is studied using the cluster metal surface model and the density functional method. An adsorbed thallium atom forms a strong chemical bond with surface gold atoms. The adsorption energy barely depends on the location of the thallium atom. The electron density is appreciably displaced from thallium to gold in the process of adsorption. Thallium exists on the surface in the cationic form. The analysis of the density of state (DOS) spectra demonstrates that the atomic orbitals of thallium participate in the formation of lower molecular orbitals in the thallium–gold system when the surface is slightly filled with thallium. When the surface is filled to a substantial degree, the contribution of thallium to the molecular orbitals with the least negative energy appreciably grows. The possible change in the electronic work function upon the surface modification of gold with the adsorbed thallium is estimated.

The effects the anode material has on the rate of electrodeposition (current efficiency) and microhardness of Co–W alloys deposited from a boron–gluconate bath are studied in a broad range of bath ages Q (A h/L). We use nonconsumable (platinum and graphite) and consumable (tungsten, cobalt–tungsten) anodes. With the cobalt–tungsten double anode, the total concentration of W and Co species in the bath is maintained constant during electrodeposition. We find that, as Q increases, the anodic processes have a significant impact on both the rate of deposition and microhardness of the prepared coatings. Departing from the mechanism of induced codeposition in which the first stage is the formation of an intermediate species of the metal component that induces codeposition (Co), here we propose a model that takes into account the effects associated with the anodic processes. In this model, along with reduction at the cathode to give an alloy, this metal component can undergo oxidation at the anode.

The adsorption of serine anion on a smooth and platinized platinum electrode is investigated. The stationary and kinetic adsorption isotherms are plotted. For both smooth platinum electrodes and Pt(Pt) electrodes, the kinetics of the processes under investigation obeys the Roginsky–Zeldovich equation, and the stationary coverage is described by the Temkin isotherm. The main thermodynamic characteristics (adsorption equilibrium constant and change in the Gibbs free energy) of the process of adsorption of serine anion on both electrodes are found.

Poly-N,N-diallylmorpholinium bromide is synthesized and characterized using the methods of IR and NMR spectroscopy. The surface modification of MA-41 industrial heterogeneous membranes (Russia) by this polyelectrolyte is carried out from an equivalent mixture of N-methylpyrrolidone and anhydrous formic acid and also from aqueous solutions. The electrochemical characteristics of the modified membranes are studied on the setup with a rotating membrane disk. It is found that the reaction of water dissociation on modified membranes occurs less intensively than on the initial membrane and the main mass transport mechanism in the superlimiting current modes in systems with modified membranes is electroconvection.

Stability is one of the most important characteristics of electrocatalysts used in low-temperature fuel cells with a proton exchange membrane. The corrosion-morphological stability of supported electrocatalysts containing platinum and platinum-copper nanoparticles with ~20 wt % Pt was evaluated under the conditions of voltammetry stress testing corresponding to different degradation mechanisms. The effect of the difference in the architecture of Pt–Cu nanoparticles on the stability of catalysts and changes in their composition as a result of stress tests were studied. At close values of the electrochemically active surface area (ECAS), the carbon-supported bimetallic catalysts demonstrated significantly higher stability compared to the commercial Pt/C catalysts. The Pt(Cu)/C catalyst obtained by sequential deposition of copper and platinum showed the highest resistance to the degradation and selective dissolution of copper during the testing.

Polymer-silver composites are prepared by in situ introducing silver(I) nitrate to the oxidative polymerization of aniline and polycondensation of aniline or melamine with formaldehyde. The data of the X-ray phase analysis and electron microscopy are used to study structure-phase changes and morphological features of the structure of composites after synthesis and in electrochemical systems, after their saturation with hydrogen and in the course of o-nitroaniline electrohydrogenation. It is shown that silver micro- and nanoparticles are formed as a result of chemical and/or electrochemical reduction of silver cations. A different electrocatalytic activity of the synthesized silver-containing composites as related to the structure of their polymer matrix is established.

Parameters that characterize the electric double layer structure on a renewable liquid (Cd–Ga) (0.3 at % Cd) electrode in solutions of surface-inactive electrolytes in a solvent with the low donor number, namely, acetonitrile (AN), are obtained. For the (Cd–Ga) electrode in AN, the following parameters: the potential of zero charge (PZC) unaffected by specific adsorption of ions, the value of “corrected electrochemical work function,” and the potential drop due to chemisorption of solvent, are obtained and compared with analogous results at Hg/AN, Ga/AN, (Cd–Ga)/gamma-butyrolactone (GBL), and (Cd–Ga)/dimethylformamide (DMF) interfaces. The AN chemisorption shifts the potential in the negative direction, which suggests that chemisorbed AN dipoles are oriented with their negative (nitrogen) ends to the metal surface. It is demonstrated that the solvent chemisorption potential drop on the (Cd–Ga) electrode increases in the series AN < GBL < DMF, i.e., with the increase in solvent’s donor number. The energy of chemisorption interaction metal–AN increases when going from (Cd–Ga) to Ga, i.e., with the increase in the work function. Based on the PZC shifts observed in 0.1 М LiBr and LiI solutions with respect to the PZC in solution of a surfaceinactive electrolyte, the adsorbability of halide ions on the (Cd–Ga)/AN interface is studied. The close values of the adsorption potential shift are obtained for Br^– and I^– ions, which suggests the stronger (Cd–Ga)–Br^– interaction as compared with (Cd–Ga)–I^–.

Several methods of enhancing the signal-to-noise ratio for instrumentation designed to measure electrochemical noise are practically tested. The experiments are carried out using model RC-circuits and lielectrolyte electrochemical cells. Strong limitations in the tested objects’ impedance values are found due to the input current noise of the instrumentation, especially during the parallel connection of several channels. The advantages of a two-channel scheme for automatically compensating the instrument’s self noise are demonstrated. Different methods of lowering the dispersion of the frequency dependences of the spectral power density of electrochemical noise are compared. It is shown that averaging over segments with an overlap is the most effective method but averaging over frequencies can lead to large distortions when investigating electrochemical systems.