Vol 52, No 1 (2016)

The process of deposition of the Re–Ni alloy, its current efficiency, and the alloy composition are studied as a function of the current density and the solution temperature. The hydrogen content in the deposits, their surface morphology, internal structure, and properties as the cathodic material for HER are examined. It is assumed that besides the high rhenium content, the high catalytic activity of nickel–rhenium alloys is associated with the high degree of their structural disordering.

Electrochemical properties of new electrode material—compact of boron-doped synthetic diamond—is studied for the first time. Cylindrical samples 3.5–4 mm in diameter and 2.5 mm in height were obtained by thermobaric processing of graphite–boron carbide mixtures in the diamond thermodynamic stability region (at the pressure of 8–9 GPa and temperature of ~2500 K). Their electrode behavior is studied using cyclic voltammetry and electrochemical impedance spectroscopy techniques. The cyclic voltammograms of the compact samples showed that their electrode characteristics are similar to those of traditional thin-film diamond electrodes obtained by the chemical vapor deposition (CVD) technique. In particular, they demonstrate rather wide potential window, low background current in indifferent electrolytes, and good reproducibility. It can be concluded that the diamond compacts practically are not inferior to the thin-film CVD-diamond electrodes and can serve as indicator electrodes, e.g., in electroanalysis. At the same time their compact form may be a convenience in the designing of electrolyzers and other electrochemical devices.

The electrochemical behaviors of copper ions complexed with picolinic, nicotinic and isonicotinic acids (2-, 3- and 4-pyridinecarboxylic acids) in Britton–Robinson buffer (pH 7.4) was studied by polarographic and voltammetric techniques on a mercury electrode. This study showed that the reduction of complexed copper ions in the presence of nicotinic acid (NA) was carried out in two one-electron steps [Cu(II)/Cu(I) and Cu(I)/Cu(0)] whereas this cathodic process in the presence of picolinic acid (PA) or isonicotinic acid (INA) occurred in one two-electron step [Cu(II)/Cu(0)]. The stability of the Cu(I) complex can be sourced from the positions of carboxylate substituents on these isomeric ligands, binding to the copper center.

Poly(o-toluidine) (sodium dodecyl sulfate) (POT(SDS)) film was electrosynthesized on carbon paste electrode (CPE) by using the cyclic voltammetry technique in aqueous solution containing o-toluidine (OT), sulfuric acid and SDS. Then, copper oxide was incorporated by immersion of POT(SDS)/CPE in a solution of copper sulfate and using constant potential method. Then, the electrochemical characterization of the modified electrode is presented in alkaline solution. For the first time, electrochemical behaviour of amoxicillin (AMX) at the Cu/POT(SDS)/CPE has been investigated using cyclic voltammetry (CV) and chronoamperometric method. The experimental results suggest that the modified electrode exhibits electrocatalytic effect on the oxidation of AMX resulting in a marked enhancement of the anodic peak current response. Under the selected conditions, the anodic peak current was linearly dependent on the concentration of AMX in the range 80–200 and 5–150 μM with CV and amperometric method, respectively. The detection limits (2δ) were also estimated to be 60 and 3 μM. Some kinetic parameters such as the transfer second-order rate constant (k = 4.9 × 10⁶ cm³ mol^–1 s^–1) of AMX was calculated. Therefore, this modified electrode was a simple, rapid and new electrode to determine AMX in pharmaceutical preparations.

A mathematical model of a hydrogen–oxygen (air) fuel cell that takes into account the phenomena of degradation of the cathodic platinum catalyst is presented. For potential cycling from 0.6 to 1.1 V with a scan rate of 0.1 V/s, depending on the platinum loadings, the following factors are found to prevail in the mechanism of electroactive surface degradation: the coalescence of platinum nanoparticles at large loadings and the platinum dissolution/redeposition and diffusion to the membrane at medium and low loadings. Based on mathematical simulation, the data on the discharge curves are calculated. The observed decrease in the discharge characteristics is attributed to the degradation of the catalyst active surface and the increased transport losses during accelerated stress testing.

A recently proposed method using constant current steps were applied for a period of time on a reticulated vitreous carbon cathode. The current steps were calculated from a theoretical analysis of the metal concentration profile assuming that the metal was deposited under mass transport control. A model was developed to predict the concentration decay of metal ions during the process. The current required to reduce the metal at the mass transfer limit at each time step was predicted from the concentration decay obtained from the model. This process should enable one to maintain high metal recovery rates whilst maximizing current efficiency. This concept was tested on Cu(II) deposition from an acidified sulfate electrolyte using a flowby reactor system with a reticulated vitreous carbon electrode. The model was good for predicting copper metal removal using a three dimensional cathode in dilute rinse waters. Also, the predicted current efficiency was in good agreement with that obtained using the experimental data.

The SnO₂|ZhK-440|SnO₂ system, where the ZhK-440 is a liquid crystal mixture consisting of 2/3 parts of p-butyl-p'-methyloxyazoxybenzene and 1/3 part of p-butyl-p'-heptanoyloxyazoxybenzene, was studied by impedance spectroscopy. The impedance spectrum of the system contained the contributions from electric conductivity and bulk and electrode polarizations. The models of bulk and electrode impedance were discussed.