A comprehensive study concerning the phase formation mechanism and growth/dissolution kinetics of sodium tungsten bronze crystals during the electrolysis of a 0.8Na2WO4–0.2WO3 melt was carried out. The regularities of deposit formation on a Pt(111) working electrode were investigated experimentally using cyclic voltammetry, chronoamperometry, scanning electron microscopy, and X-ray diffraction analysis. Models have been developed to calculate the current response during the formation, growth and dissolution of a two-phase deposit consisting of NaxWO3 and metallic tungsten or two oxide tungsten bronzes with different sodium content. These models consider mass transfer to the electrode and nuclei; chemical and electrochemical reactions with the participation of polytungstate ions, Na+, Na0, and O2−; as well as the ohmic drop effect. The approach was proposed to describe the dissolution of an NaxWO3 crystal with a nonuniform sodium distribution. The fitting of cyclic voltammograms was performed using the Levenberg–Marquardt algorithm. The NaxWO3 formation/growth/dissolution mechanism was determined. Concentration profiles and diffusion coefficients of [WnO3n]−, reaction rate constants, number density of nuclei, and time dependencies of crystal size were calculated. The proposed approaches and models can be used in other systems for the cyclic voltammogram analysis and study of the mechanism and kinetics of electrode processes complicated by phase formation; parallel and sequential electrochemical and chemical reactions; as well as the formation of a deposit characterized by a nonuniform phase and/or chemical composition.

Polytungstate melts are used for the electrodeposition of oxide tungsten bronzes (OTBs). The scarce information on the ionic composition and properties of these electrolytes hinders effective control of the electrochemical synthesis of OTBs with desired electrical and optical properties. In this work, a comprehensive study of Na2WO4–WO3 melts that contained up to 55 mol% of tungsten trioxide was performed in the temperature range from 983 to 1073 K. Melt densities were measured using the Archimedes method. DFT calculations were carried out for various tungsten-containing compounds, including WxO3x−12+, WxO3x+12−, NaWxO3x+1−, and Na2WxO3x+1. The calculated values of the W–O bond energy indicate that the tested compounds are stable in the specified temperature range, and the WO22+ cation is the most stable. The experimental dependences of the redox potential on the mole fraction of tungsten trioxide in the Na2WO4–WO3 melt were obtained using the EMF method. A model that considers the processes of interaction between tungsten-containing ions and O2− ions was proposed for the quantitative interpretation of these dependences. The equilibrium constants were found through fitting according to the Levenberg–Marquardt algorithm. The effect of the WO3 mole fraction and temperature on the concentrations of WO42−, W2O72−, W3O102−, W4O132−, WO22+, and O2− ions was analyzed.

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 feasibility of obtaining hybrid nanosystems consisting of copper, copper oxides, tetragonal or cubic oxide tungsten bronze (OTB) by means of electrodeposition from the polytungstate melts at 973 and 1023 K was studied. The formation regularities of various hybrid nanosystems were established based on a data of electrochemical techniques, X-ray diffraction phase analysis (XRD), and scanning electron microscopy (SEM). A Cu (mesh)/Cu2O/OTB hybrid system with catalase activity was obtained during electrodeposition from the K2WO4 - Na2WO4 (1:1) - 50 mol% WO3 melt at 973 K. (C) 2019 The Electrochemical Society.

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.

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.

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.

The phase composition of Na x M x Ti 8 – x O 16 (M = Al, Ga, In) materials was studied by x-ray diffraction. In the Al system, a hollandite phase was obtained in the composition range 0.67 ≤ x ≤ 2.0. The results are interpreted in terms of Goldschmidt's tolerance factor. It is shown that A 2 B 8 O 16 compounds with the hollandite or Na x TiO 2 -type structure are more difficult to prepare at smaller ionic radii of M. The assumption is made that the monoclinic Na x TiO 2 -type phase may, under certain conditions, have a channel structure.

The oxygen coefficient of uranium oxides, their structure, and current efficiency were studied as influenced by the electrolyte composition, deposition potential, and temperature of electrolysis. On passing from Na2WO4-UO2WO4 binary system to lower-melting ternary systems the dependences of the oxygen coefficient in the cathodic product on the electrolyte composition and electrolysis parameters remain essentially similar. Significant deviation of the experimental current efficiency with respect to uranium oxides from the theoretical value suggests significant chemical interaction between the cathodic product and electrolyte. The corrosion rate increases and the current efficiency decreases with increasing temperature and concentration of W2O72- ions. The structure of the resulting cathodic deposits is predominantly determined by their specific electrical conductivity, which is a function of the chemical composition of the electrolyte. The dendrite structure is typical for higher oxides.

The electrical conductivity and thermal expansion of SmBa2(Cu1-xFex 3O6+δ (x = 0-0.2) were measured in air in the temperature range from 20 to 900°C. The linear thermal expansion coefficient was determined to be (12.8–13.5) × 10-6 K-1 in the temperature range from 20 to 350°C and (16.2–17.8) × 10-6 K-1 in the range from 350 to 800°C. Between 400 and 900°C, the conductivity of SmBa2(Cu1-xFex)3O6+δ was found to decrease with increasingx, mainly in the rangex = 0–0.1. This finding was interpreted in terms of the Fe occupancies on the Cu(1) and Cu(2) sites.