Oxide tungsten bronzes (OTB) of cubic, tetragonal and hexagonal structure were electrodeposited under galvanostatic conditions. Electrolysis of polytungstate melts 0.8Na2WO4–0.2WO3, 0.25Na2WO4–0.25K2WO4–0.5WO3 and 0.1K2WO4–0.55Li2WO4–0.35WO3 was performed at a temperature of 973 K and a cathode current density of 25 mA cm–2 for 20 min. The synthesized OTB powders were studied by X-ray diffraction analysis, laser diffraction, and scanning electron microscopy coupled with energy dispersive spectroscopy. To determine the upper limit of the thermal stability range, the phase composition of OTB powders with an average particle size of 40–50 μm was studied after isothermal annealing at 373–1173 K for 2 h in an air or argon atmosphere. OTB powders with a tetragonal structure were additionally studied by synchronous thermal analysis. The electrical resistance of the samples sintered at 473 K was measured in air using direct and alternating current. It has been established that the most stable are the hexagonal OTBs isostructural to K0.3WO3, since their phase composition does not change up to 773 K during heat treatment in air and remains constant over the entire studied temperature range in an inert atmosphere. Tetragonal OTB powders isostructural to K0.475WO3 and Na0.28WO3 are stable up to 1073 K in argon and partially oxidize in air above 673 K to form OTBs with lower alkali metal content, WO3 and Na2W2O7. The phase composition of cubic OTB isostructural to Na0.74WO3, is stable up to 673 K in air and up to 873 K in argon. Conductivity studies of all samples indicate mixed ion-electron conductivity with a predominance of the electronic component. Аt 298–573 K, the specific electrical conductivity values vary within the range of 0.035–0.051, 0.012–0.030 and 0.005–0.019 (Ohm⋅cm)–1 for the OTB samples of tetragonal, cubic and hexagonal structures, respectively.

The problem of the cyclic voltammetry investigation of the initial stages of electrochemical phase formation is considered. Analytical expressions are derived for the cyclic voltammograms and the sizes of the independent new-phase nuclei having formed on an indifferent electrode under linear potential sweep conditions for the cases of instantaneous and progressive nucleation followed by diffusion-controlled growth. The current as a function of the overpotential is found to have different dependences on the scan rate for the given limiting cases of nucleation. The results of a numerical simulation are presented. The logarithmic dependences of the maximum and minimum currents on the scan rate are shown to have a slope of –1/2 if nuclei appear in a narrow time interval long before the reverse, their number does not change when the scan rate changes, and their growth is controlled by diffusion. The slope of the dependences is –3/2 when nuclei form before and after the reverse and their number decreases with increasing scan rate. The possibility of using the proposed criteria for the interpretation of the experimental cyclic voltammograms is analyzed and confirmed for the model system (KNO3–NaNO3–AgNO3 melt/iridium substrate/silver) at low concentrations of depositing ions, which provide diffusion control of the process. Both instantaneous nucleation and progressive nucleation are shown to occur in this system, depending on other experimental conditions.

Texturing silicon wafers is one way to increase the performance of solar cells. This work is the first to report on the surface modification of Si wafers by processing in polytungstate melts. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction analysis (XRD), the Brunauer–Emmett–Teller (BET) method, and photoelectrochemical measurements were used to elucidate the effect of texturing conditions in the Na2WO4—K2WO4 (1:1) melt containing 35 or 50 mol% WO3 at 973 K in air. As a result of cathodic treatment in the melt containing 50 mol% WO3 at the potential of –0.92 V (vs Pt) for 15 s, upright pyramids were formed on the Si surface. In addition, inverted pyramids appeared at the OTB/Si contact points. The photocurrent density of these samples was several times higher than that for the initial Si wafer or the Si wafer etched in 5 M NaOH solution at 353 K for 20 min. Mechanisms for the formation of upright and inverted pyramids were proposed. Unusual eight-faceted pyramids were formed on the Si surface during cathodic treatment in the melt containing 35 mol% WO3 at –1.19 V for 15 s, but the photocurrent density of such samples was low.

The electrochemical behavior of nickel in the K 2 WO 4 –Na 2 WO 4 (1 : 1)–WO 3 (35 mol %) and K 2 WO 4 –Na 2 WO 4 (1 : 1)–WO 3 (50 mol %) polytungstate melts was studied by the cyclic voltammetry. Based on a comparison of the obtained cyclic voltammograms with the data of SEM, EDS and XRD conclusions were drawn about the sequence of processes proceeding on the nickel substrate. Equations of the electrolysis products formation are proposed.

A general scheme is used to consider the initial stages of electrocrystallization under potentiodynamic and galvanostatic conditions. Proposed theoretical models are shown to agree well with the experimental results obtained during the electrodeposition of silver crystals on an iridium microelectrode from nitrate melt containing an excess background electrolyte.

We are the first to synthesize nanofilms of tetragonal oxide tungsten bronze (OTB) on a Pt(110) substrate by the electrolysis of the K 2 WO 4 –Na 2 WO 4 –WO 3 melt at 700 and 750°C. The composition and the morphology of OTB are shown to depend on the deposition potential and the WO 3 concentration in the melt. The laws of formation of tetragonal OTB films are discussed. The synthesized OTB samples are found to have a good thermal stability in the temperature range 20–800°C.

Cyclic voltammetry is used to study the formation of tetragonal oxide tungsten bronze of the composition K x Na y WO 3 on a Pt(110) substrate during electrodeposition from a K 2 WO 4 –Na 2 WO 4 –WO 3 melt. The potential ranges in which cathode products of various compositions and morphologies form are found. K x Na (0.66– x ) WO 3 crystals are shown to form according to the nucleation/growth mechanism. A general scheme is proposed and used to write equations for cathode reactions.

The initial stages of electrocrystallization in melts are considered. The nucleation and growth rates of metal nanocrystals during electrodeposition are calculated. The diffusion coefficients in the size space in the Fokker–Planck equation, which describes phase formation, are found. The method of calculating the number of nanoclusters formed on an electrode has been proposed. The concentration dependence of the phase formation under potentiostatic and galvanostatic electrodeposition conditions in melts is considered.

Tungsten oxide bronzes were produced by an original method of high-temperature electrochemical deposition. Their catalytic properties in a model process of desulfurization of petroleum products-benzothiophene peroxidation were studied. The effect of the particle size on the catalytic and catalase activity of samples was shown.

Исследовано окислительное обессеривание негидроочищенной прямогонной дизельной фракции, содержащей бензотиофен, дибензотиофен, их алкилзамещенные и тиаксантен, с пределом выкипания 178–342°C действием пероксида водорода в присутствии соединений переходных металлов Na2MoO4, Na2WO4, NaVO3, WO3, вольфрамовой кислоты и гетерополивольфрамомолибдата H3PMo6W6O40 в двухфазной системе с последующей экстракцией продуктов окисления диметилформамидом (ДМФА). Oкисление углеводородной фракции в присутствии гетерополивольфрамомолибдата (ГПВМ) в двухфазных условиях обеспечивает удаление до 82% общей серы.

The oxidative desulfurization of a straight-run, nonhydrotreated diesel fraction (boiling range 178–342°C) containing benzothiophene, dibenzothiophene, their alkyl-substituted derivatives, and thioxanthene by the action of hydrogen peroxide in the presence of transition metal compounds (Na2MoO4, Na2WO4, NaVO3, WO3, tungstic acid, and heteropoly tungstate/molybdate H3PMo6W6O40) in a biphasic system followed by the extraction of the oxidation products with dimethylformamide has been studied. The oxidation of the hydrocarbon fraction in the presence of heteropoly tungstate/molybdate under biphasic conditions provides for the removal of up to 82% of total sulfur.

Оригинальным высокотемпературным методом электрохимического осаждения из расплава соответствующих солей получены оксидные вольфрамовые бронзы. Изучены их каталитические свойства в модельном процессе “обессеривание нефтепродуктов – перекисное окисление бензотиофена”. Показано влияние размера частиц на каталитическую и каталазную активность образцов.

Оригинальным высокотемпературным методом электрохимического осаждения из расплава соответствующих солей получены оксидные вольфрамовые бронзы. Изучены их каталитические свойства в модельном процессе “обессеривание нефтепродуктов – перекисное окисление бензотиофена”. Показано влияние размера частиц на каталитическую и каталазную активность образцов.

The regularities of the initial stages of growth of silver nano- and microcrystals during electrodeposition from the AgNO3-KNO3-NaNO3 melt with an excess background electrolyte are studied. A model for the electrocrystallization process is proposed. Experimental and theoretical time dependences of the overpotential (supersaturation) and the crystal size are obtained. The applicability of this model is discussed. The main electrodeposition parameters are found to be the specific capacity of a double electrical layer, the equilibrium concentration of single adatoms at the electrode, and the diffusion coefficient of depositing ions in the melt.

The nucleation and growth of new phase clusters have been studied under galvanostatic conditions. Time dependences of the overpotential, number, and size of clusters formed on the electrode have been calculated from a model of the electrocrystallization process.

Nanocrystalline samples of K (x) Li (y) WO3 with hexagonal structure obtained by electrodeposition of molten salts were several times more active in catalytic decomposition than the coarse-grained materials.

Silver crystal nucleation is studied in AgNO 3 melts containing Pb(NO 3 ) 2 and HNO 3 at 250°C by the galvanostatic method. The maximum nucleation overpotential is higher as compared with pure AgNO 3 and the exchange current of silver deposition-dissolution is lower. It is found that the added substances and the products of their reactions with the melt are strong oxidants, take part in the electrochemical processes, and induce passivation of the cathodic substrate and the surface of growing silver crystals. Substantial changes in the morphology of the cathodic deposit and certain changes in the silver lattice parameter were observed depending on the oxidant content.