Том 54, № 3 (2018)

The novel Ce doped MnO₂/rGO composite was fabricated by a simple two-step hydrothermal method reacted for different times. As results, the composite reacted for 1h exhibits better electrochemical performance and rate capacity, the capacitive retention is 85% from 130.44 F g^–1 for first cycle decrease to 111.11 F g^–1 after 1000 cycles at the current density of 1 A g^–1, and 14.7 W h kg^–1 of energy density. Moreover, the BET surface area is 243 m² g^–1, and the average pore size is 7.9 nm, which will be convenient for the quick transport and migration of electrolyte ions during the charge–discharge process, and further confirm good rate capability.

Supercapacitors, also called as ultracapacitors, are electrochemical energy-storage devices that exploit the electrostatic interaction between high-surface-area nanoporous electrodes and electrolyte ions, combining properties of conventional batteries and conventional capacitors. A symmetrical activated carbon (AC) electrode supercapacitor has been fabricated in a simple and inexpensive manner. The AC has been synthesized from Charcoal, has activated in a furnace at high temperatures. The electrode was fabricated by casting slurry made of AC and blended in a polymer solution on the counter electrode (current collector), appeared to have high mechanical strength. The electrochemical performance of the prepared samples was tested in 1 M KCl solution by cyclic voltammetry (CV), galvanostatic charge discharge technique, and impedance spectroscopy. The surface and cross-section of electrode was observed with SEM. Capacitance of fabricated supercapacitor has a favorable capacitance in the range of 65–70 F/g with low resistance. The AC electrode supercapacitor has excellent electro chemical reversibility, good cycle stability with a low fading rate of specific capacitance even after 500 cycles, which is promising for energy storage applications.

In the present study, the electrochemical oxidation of quercetin (QUR) was investigated using a graphite paste electrode (GPE) modified with multi-walled carbon nanotube and Lewatit FO36 nanoresin (LFONR-MWCNT/GPE). LFONR-MWCNT/GPE could effectively a sensitive anodic peak at around 0.23 V (vs. SCE) in a 0.10 M phosphate buffer solution. Modified electrode revealed that activated with multiwalled carbon nanotube and LFONR was capable of facilitating electron transfer and increasing surface area. The electrochemical oxidation of QUR was studied using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Some kinetic parameters for electrochemical oxidation of QUR including total number of electrons (n) and standard heterogeneous rate constant (k_s) were also determined. The calibration graph consisted of two linear segments of 1.8–25.0 μM, and 25.0–570.0 μM with a detection limit of 0.213 μM (based on 3S_b). The applicability of the method to juice of peach, red grape, sour cherry and Gincora tablets analysis was also evaluated.

The synthesis of catalytic coatings on porous titanium electrodes by the method of magnetron sputtering is considered. The content of dopant ions Fe³⁺ and F^– is optimized as regards the activity and stability of the PbO₂ catalyst in the reaction of ozone electrogeneration as well as the current efficiency with respect to ozone. It is shown that the best characteristics of the electrochemical ozone generator are observed on the PbO₂ catalyst doped with Fe³⁺ and F^– ions in the amount of 3–4 and 1–2 at %, respectively.

Ultra-fine gold (<2 nm), silver (5 ± 2 nm), and palladium (<1–2 nm) nanoparticles stabilized in polyvinylpyrrolidone shell were synthesized in N,N-dimethylformamide, using molecular oxygen dissolved in the electrolyte as mediator, by the reduction of the metals’ ions and complexes at the controlled potential of the oxygen reduction to its radical-anion. Pd-nanoparticles showed high catalytic activity in the reactions of p-nitrophenol reduction and Suzuki cross-coupling. Long-term ageing of spherical Ag-nanoparticles for 60 days in the post- electrolysis solution resulted in their consolidation (up to 17 ± 5 nm; the average size of crystallites 7.5 (3) nm). Upon similar exposure of Au-nanoparticles for 15 days, V-shaped nanoparticles were formed (length 112 ± 53 nm, width 58 ± 22 nm, crystallites 20(2)–31(1) nm); upon the isolation, dispersing into ethanol, and exposure for 48 h, hexagonal nanoparticles (105 ± 29 nm) and polygons (56 ± 25 nm, crystallites 24(2)–51(1) nm; upon dispersing into water and exposure for 8 h, spherical nanoparticles (13 ± 8 nm, crystallites 7(1)–13.4(5) nm). Thus obtained nanoparticles are characterized by methods of cyclic voltammetry, dynamic light scattering, scanning and high resolution transmission electron microscopy, and X-ray powder diffraction.

It is shown that the specific surface energy of metals, which are used as the coatings, linearly depends on the critical temperature of the corresponding metals. Therefore, in the absence of data on the surface energy, it can be estimated from the boiling, melting and critical temperatures.

New composite membranes based on commercial perfluorinated Nafion-115 membrane and cross-linked sulfonated polystyrene were synthesized and investigated. The membranes were prepared by radical polymerization of styrene in the presence of a cross-linking agent divinylbenzene in Nafion polymer matrix and subsequent sulfonation of formed polystyrene. The membranes containing approximately 5 and 10 wt % of cross-linked polystyrene with ion-exchange capacity of 1.1 to 1.3 mg-eq/g were obtained. Modification with sulfonated polystyrene leads to an increase in the moisture content and proton conductivity of membranes in the humidity range of 15 to 100 RH.