Electrochemical reduction of tungsten (VI) oxide from a eutectic melt CaCl2-NaCl under potentiostatic conditions

An overview dedicates to the directions of scientific research and achieved results in the field of electrochemistry, initiated by scientific institutions and in higher educational institutions of Kyiv. Academician O.V. Plotnikov is the forerunner of the world- known Kyiv School of Electrochemistry, formed in the last century's twenties: M.I. Usanovych, V.O. Izbekov, Ya.A. Fialkov, Yu.K. Delimarskyi, I.A. Sheka, and many other scientists known to the general scientific community. O.V. Plotnikov and his followers are one of the first to attempt to combine the most progressive theoretical provisions on electrolytic dissociation, the chemical theory of solutions, and the chemistry of complex compounds for that time. World achievements of the Kyiv School of Electrochemistry were provided by the results of such fundamental research as the chemical theory of solutions, acid-base interactions (Usanovich's theory), the structure of the electric double layer (the Yesin-Markov effect, the reduced Antropov scale of potentials), physical chemistry and electrochemistry of molten electrolytes, kinetics electrode processes, electrometallurgy, electrochemical materials science, electrochemical power engineering. Representatives of our School significantly expanded the knowledge of mass transfer in electrochemical systems with molten electrolytes (the phenomenon of the transfer of metals from the anode to the cathode). New technological processes of obtaining and refining heavy non-ferrous metals (bismuth, lead, indium, etc.), finishing metal surfaces, extraction of radionuclides, electroplating technology, and environmental monitoring have been introduced into the practice of industrial production. Research in electrochemical materials science is closely connected to solving the problems of electrochemical energy, particularly, the creation of new sources of current, including solid-state, hydrogen generators, and converters of solar energy into electrical power. The studies of electrochemical aspects of the extraction of some refractory metals from natural raw materials, the creation of new materials with specified functional properties, catalysts, and electrocatalysts, the latest galvanic coatings, electrode and electrolyte materials for chemical current sources and supercapacitors, valuable inorganic compounds, metal and carbon nanophases, corrosion inhibitors are expanding the scientific direction of electrochemical materials science.

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Scientific Electrochemical School of Kyiv

Pekhnyo¹,

Омельчук

Linyucheva³

2022

Ukr. Chem. Journ.

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Electrolytic Catalysts Based on Tungsten and Carbon Compounds for the Hydrogen Evolution Reaction

Kuleshov,

Novoselova,

Medvezhynska

2023

Ukr. Chem. Journ.

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The hydrogen evolution reaction (HER) is one of the most promising methods of obtaining high-purity hydrogen. However, the high cost and limited resources of materials with low cathodic hydrogen evolution overvoltage values, such as platinum group metals, are the main obstacles to the use HER for obtaining hydrogen on an industrial scale. Therefore, it is necessary to develop new alternative materials and methods of their production. One of the promising materials are catalysts based on refractory metals, in particular tungsten carbides. Metal tungsten can also be used for these purposes. In our opinion, high-temperature electrochemical synthesis (HTES) in molten salts can be a promising method of obtaining materials with properties that meet the requirements for effective catalysts, namely: ultra-dispersity, high specific surface area, mesoporosity and defective structure, high chemical and electrochemical stability. Therefore, the purpose of this work is to evaluate the electrocatalytic activity of a group of materials for HER, which are obtained by HTES in melts. Four samples of electrolytic materials were chosen for the study: tungsten, carbon, tungsten mono- and semi-carbides (WC and W2С). All samples were characterized in detail using X-ray diffraction (phase composition), SEM (morphology), Raman spectroscopy (structure of carbon phases), DTG (free carbon content). Based on the analysis of the obtained data, it was established that all samples can be used as catalysts: crystallites have a nanometer size and a large number of structural defects; morphology provides increased surface area; tungsten carbide particles are covered with a layer of free carbon, which prevents oxidation of carbide to WO3, which has a lower catalytic activity; carbon particles are nanosized (20–30 nm) and contain a large number of structural defects; tungsten carbide-based samples contain free carbon, which increases the specific surface area, but does not cause clogging of pores. Polarization measurements were carried out at room temperature at a polarization rate of 5 mV/s in a standard three-electrode cell with an Ag|AgCl reference electrode. 1N H2SO4 was used as a base solution, which was bubbled with high-purity argon. Onset potentials for all samples are -0.05 – -0.25 V (in order WC/C – W2C/WC/C – C – W). The overvoltage and Tafel slope were calculated and WC/C composite was shown to have the lowest values of -0.2 V and -75 mV, respectively. Electrolytic composite of tungsten carbide/carbon have demonstrated the best characteristics, so we plan to continue the development of synthesis method of carbide compounds, which will allow us to reveal even greater potential of carbide catalysts and pave the way for their wide application in catalytic processes.

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Electrochemical Production of Tungsten: Status and Prospects

Medvezhynska,

Omelchuk

2023

Ukr. Chem. Journ.

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An overview of studies of the electrochemical reduction of tungsten compounds of different composition in various reaction media is presented. It is shown that among the variety of existing scientific and technical methods for obtaining tungsten, there are attractive prospects for the creation and development of a new industrial process that would ensure the direct electrochemical release of oxygen from its oxygen-containing compounds into molten mixtures based on chloride and calcium oxide. This scientific and technical solution is known in the literature as the FFC Cambridge process (FFC process).In contrast to the known methods of electrochemical reduction of tungsten compounds, this process allows the reduction of oxygen-containing tungsten compounds in the solid state and does not depend on the course of acid-base equilibria at the electrode/electrolyte phase separation boundary. The most favorable conditions for the reduction of oxygen-containing tungsten compounds are provided by electrolysis using a liquid gallium cathode in both galvanostatic and potentiostatic modes, and it is advisable to use the initial tungsten compounds in a finely dispersed state. The electrochemical reduction of tungsten trioxide in thee utectic melt of sodium and calcium chlorides occurs through the intermediate stage of calcium tungstate formation, so it is advisable to use CaWO4 instead of WO3 as the starting compound for reduction. Electrochemical reduction on a liquid gallium cathode in a molten eutectic mixture of sodium and calcium chlorides allows obtaining highly dispersed tungsten powder (11–35 nm) of high purity (99.9%) with a degree of extraction of at least 90.0% from both tungsten trioxide and from calcium tungstate. In addition, in this way it is possible to obtain not only pure tungsten, but also metal alloys and composites based on it.

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Electrochemical reduction of tungsten (VI) oxide from a eutectic melt CaCl2-NaCl under potentiostatic conditions

Cited by 3 publications

References 14 publications

Scientific Electrochemical School of Kyiv

Scientific Electrochemical School of Kyiv

Electrolytic Catalysts Based on Tungsten and Carbon Compounds for the Hydrogen Evolution Reaction

Electrochemical Production of Tungsten: Status and Prospects

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