Vol 54, No 12 (2018)

The purpose of this study was to evaluate the effects of press pressure and sintering temperature on the microstructure and electrochemical performance of silver oxide-graphene oxide composite as a novel electrode produced by the powder metallurgy (PM) route. Scanning electron microscopy method used to investigate the microstructure of electrodes and energy dispersive X-ray spectroscopy analysis method was used for point analysis. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were used to research the effects of sintering temperature and press pressure on the electrochemical behaviour in the 1.4 wt % KOH solution and electrical discharge test was used for evaluate the ultimate electrical capacity of silver oxide-zinc batteries with electrolyte of the 1.4 wt % KOH solution.

Determination of tryptophan was performed by using of an easy to prepared electrode. Basically, the electrode was prepared by using of ionic liquid and multi-walled carbon nanotube as main constituents. Then, the electrode surface was activated by cycling the potential. The activated multi-walled ionic liquid electrode shows facile electro-oxidation and good stability for determination of tryptophan. Linear range and limit of detection were obtained as 5 × 10^–6 to 1 × 10^–3 and 2.3 × 10^–6 M, respectively. Finally, determination of tryptophan in real samples (commercial amino acid injection and blood serum) was performed successfully. The high activity of the proposed electrode is attributed to the simultaneous presence of ionic liquid and multi-walled carbon nanotube in the electrode content.

The electroreduction of indium on indium electrode (99.98%) in perchlorate-containing chloride electrolytes is studied by the methods of linear sweep and cyclic voltammetry, impedance spectroscopy, and chronoamperometry. The indium electroreduction is limited by diffusion, the reaction rate constant is 1.3 10^–4 cm/s at the indium salt concentration of 0.1 M. The values of the apparent rate constant for the charge transfer stage found by linear sweep and cyclic voltammetry and also by impedance spectroscopy are 2.37 × 10^–3, 3.62 × 10^–3, 3.06 × 10^–3 cm/s, respectively. The values of diffusion coefficient of indium(III) ions calculated according to the Cottrell equation based on chronoamperametric measurements and from the Warburg impedance found by impedance spectroscopy are in good agreement. The presence of the Gerischer impedance is stated, which suggests that a homogeneous reaction of formation of indium chloride complexes proceeds and its mechanism is chemical-electrochemical.

Nanostructured germanium samples prepared by electrochemical deposition from aqueous solution of 0.05 М germanium oxide onto titanium substrate are tested as the negative electrodes of lithium-ion batteries. The reversible capacity in the process of lithium insertion-extraction is found to be about 1180 mA h/g, which corresponds to the formation of Li_3.05Ge alloy. The effective diffusion coefficient of lithium in germanium is shown to be 1.2 × 10^–11 cm²/s. The degradation of the germanium electrode upon cycling at 0.6 С rate is less than 0.3% per cycle.

Polarization and microcoulometric measurements at fixed potential on the erythrocyte suspension in neutral solutions of sodium chloride with additions of sodium sulfite revealed the presence of electroreduction and electrooxidation processes at potentials E < –150 mV and > +200 mV vs. Ag/AgCl reference electrode. These results are the direct evidence for the presence of electron transport at the charged surface/cell’s membrane interface. It is noteworthy that the potential region from –150 to +200 mV, which is characterized by the absence of electron transport at the contact of platinum with erythrocytes, closely coincides with the region of the absence of interaction between electrodes of carbon materials and blood cells.

A graphene/Au nanoparticles composite modified glassy carbon electrode (GR/AuNPs/GCE) was developed. Electrochemical behavior of acetaminophen (ACOP) at this modified electrode was studied by liner sweep voltammetry (LSV) in pH 6.0 phosphate buffer solution. The effect factors of the electrochemical response of ACOP were optimized by LSV. Under the optimum conditions, a linear calibration curve of the oxidation peak current of ACOP and concentration was obtained in the range of 1.0 × 10^–6 to ~2.2×10^–4 M. The peak current increases linearly with the scan rate, indicating that the reaction of ACOP at the modified electrode is adsorption-controlled process. This new proposed method has been successfully employed to determine acetaminophen in pharmaceutical preparation.

Paraquat dichloride commonly used as herbicide was determined by differential pulse cathodic stripping voltammetry technique. Experimental parameters, such as pH, accumulation time, accumulation potential and initial potential were optimized. In this analysis, paraquat dichloride exhibited a well-defined tworeduction peaks at −0.35 and −0.90 V in the pH range from 2.0 to 12.0. The 0.04 mol L^–1 BR buffer at pH 2.0 was found a suitable medium for electroanalytical determination of the paraquat dichloride. Interfering ions effect was not significant. Linear calibration plots for standard solutions of paraquat dichloride were obtained in the range of 0.25 to 1.75 × 10^–6 mol L^–1. Detection limit was 3.66 × 10^–8 mol L^–1. The optimized parameters were effectively applied for the determination of commercial paraquat dichloride and in artificial samples. Artificial samples were prepared by spiking paraquat dichloride into tap water and drinking water dispenser samples. The recovery value was 90.5% in drinking water dispenser samples and 91.7% in tap water samples at the concentration range of 1.00 × 10^–6 to 1.75 × 10^–6 mol L^–1.

A model of conductivity of nanocomposite ceramics consisting of solid-electrolyte and dielectric phases is proposed based on the assumption that the conductivity of grain boundaries between the solid-electrolyte and dielectric phases is higher than the conductivity of the volume of particles in the solid-electrolyte phase and its grain boundaries. Taking into account the size of particles, the thickness of grain boundaries, and the bulk and grain-boundary conductivities, the grain size of composite ceramics for which the conductivity may exceed the conductivity of single-phase solid-electrolyte ceramics is assessed. For testing this model, the composite samples are synthesized based on dielectric magnesium oxide and solid-electrolyte cerium oxide doped with samarium oxide. It is shown that introduction of 50 mol % magnesium oxide into composite ceramics has virtually no effect on its conductivity as compared with single-phase solid-electrolyte ceramics. This result can be explained by assuming the appearance of accelerated transport routes for oxygen ions in grain boundaries between dielectric and solid-electrolyte phases. Further dispersion, optimization of the ratio, and increase in distribution homogeneity of components can confirm the validity of the proposed conductivity model and open up the possibility of preparation of oxide solid-electrolyte materials with higher conductivity.

The relationship between the leveling power of electrolytes, the primary current distribution, and the microdistribution of the metal deposition rate is considered. For electrolytes with positive, zero, and negative leveling power, the calculations of microdistribution of metal deposition rate are carried out with regard to the data on the primary current distribution obtained experimentally for a macromodel of the microprofile under study. Good agreement is demonstrated between the microdistribution calculated using the described method and the results of direct measurements of metal distribution over the surface with the regular twodimensional microprofile.

PtCu/C electrocatalysts with similar compositions but different distributions of components in bimetallic nanoparticles were obtained by simultaneous and sequential reduction of copper(II) and platinum( IV) in a carbon suspension. The catalyst obtained by multistage synthesis while sequentially increasing the Pt(IV) concentration in the precursor solution added at each stage showed the highest stability and activity in oxygen electroreduction in acidic media. This catalyst was least liable to selective dissolution of copper during its operation. The influence of the architecture of bimetallic PtCu nanoparticles on the electrochemical behavior of the catalysts is due to the peculiarities of the structure rearrangement of nanoparticles during the enrichment of the protective surface layer with platinum.

The oxidation of a 10 mM aqueous solution of sodium bromide in a sulfuric acid medium on the surface of a platinum electrode in a cell with separated spaces was studied. The process is important in view of the use of the bromine–bromide redox couple in redox flow batteries. The study was performed by cyclic voltammetry, potentiostatic chronoamperometry with optical absorption spectrum recording, and measurements of the potential of the redox reference electrode. A numerical procedure for processing the experimental spectra of the solution was developed to separate them into the spectrum of molecular bromine and the residual signal. The latter was attributed to the absorption of the tribromide anion based on the literature data. The experimental dependences of the Br₂ and Br₃^- concentrations for the oxidative electrolysis of the NaBr solution in the sulfuric acid medium agreed well with the theoretical predictions. The current efficiency of bromine formation was evaluated.

Here we are presenting complete electrochemical studies on redox activities of 1,2-dinitrobenzene (DNB) in the presence of antioxidants–quercetin, morin, rutin, ascorbic acid and β-carotene. Bimolecular rate constants (k₂), antioxidant activities (K_a) and diffusion coefficients (D_o) were evaluated from changes in voltammeric responses and electrochemical parameters in the presence of antioxidant’s concentrations. Theoretical charge calculations by PM3 parameterization were done which further justified our experimental electrochemical work and proposed scavenging mechanism. Present findings were also compared in details with our previously reported studies on 1,3- and 1,4-dinitrobenzene systems for their interactions with antioxidants.

Electrochemical oxidation of catechol has been studied in the presence of ketamine as a drug in phosphate buffer solution mixed with ethanol using voltammetric techniques. The obtained results indicated that the o-quinone formed from electro-oxidation of catechol participated in a 1,4-Michael addition reaction to form the corresponding new 2-(2-chlorophenyl)-2-[(3,4-dihydroxyphenyl)(methyl)amino]cyclohexanone under ECE mechanism. The electro-organic synthesis has been successfully performed under mild condition in a divided cell in good yield.

We study the effect of the treatment by an electric current of two-layer gas diffusion electrodes made of porous (66–68 vol %) composite material based on A-437E acetylene black and polytetrafluoroethylene. Polarization is carried out cyclically in the range 0.0 ± 2.0 V by anodic and cathodic currents, respectively, in 1 M H₂SO₄ and 0.5 M KOH with the addition of tetrabutylammonium bromide (TBAB). In both cases, the increase in the charge passed leads to an increase in the volume of electrolyte pores and the electrical capacitance of the electrodes. Under anodic polarization, the increase in the wettability and capacitance of the electrodes is larger than under the cathodic process; however, in the latter case, the carbon surface does not undergo oxidation. As the charge passed and the TBAB concentration increases, the ohmic loss grows. The possible causes of the observed phenomena are considered.

For correctly analyzing the nucleation processes during metal electrodeposition under galvanostatic conditions, we must take into account that the deposition and dissolution processes are of nonequilibrium character, which is associated with deviation of the electrode potential from equilibrium. Ignorance of this factor substantially affects the results of calculations. The experimental dependences potential vs. time obtained under galvanostatic conditions make it possible to determine the equilibrium concentration of adatoms, the electrode-reaction transfer coefficient, and, in certain cases, the exchange current density if the latter is not too high.