An important task of modern materials science is the development of highly efficient electrocatalysts for green hydrogen production. Specifically, this involves the urea oxidation reaction (UOR), which is an energetically advantageous and attractive alternative to the anodic oxygen evolution reaction, coupled with hydrogen evolution at the cathode. In this work, we present for the first time the use of systems based on a new generation of environmentally friendly room-temperature ionic liquids – deep eutectic solvents (DESs) – for the electrodeposition of electrocatalysts for UOR. The electrochemical performance of electrodeposited nanocomposite Ni–CeO2 electrocatalysts was evaluated in alkaline solution, showing an appreciable reduction in the anodic potential of UOR compared to oxygen evolution, reaching up to approximately 0.2 V at a current density of 0.1 mA cm–2. The obtained results are significant for the development of electrochemical synthesis methods for electrocatalysts used in green renewable energy.

The development of efficient and energy-saving electrochemical processes for "green" hydrogen generation represents one of the most crucial challenges in modern chemistry and technology. An effective approach to realizing such processes involves alkaline water electrolysis with cathodic hydrogen evolution coupled with anodic urea oxidation reaction. As extensively reported in the literature, this configuration allows for a significant reduction in cell voltage. In this work, we present thermodynamic analysis of the electrochemical reaction CO(NH2)(2) + 2OH(-) +/- 6e(-) = 3H(2) + N-2 + CO32-, for the first time accounting for the inevitable carbonate formation due to interaction of carbon dioxide with alkali. Standard changes in enthalpy, entropy, and Gibbs free energy, as well as the electromotive force were calculated over the temperature range of 298-338 K. The influence of pH on the electromotive force value was investigated. It was observed that the process under study is accompanied by heat release and an increase in entropy, becoming thermodynamically spontaneous at pH > 12.66. From a thermodynamic point of view, this suggests exceptionally favorable energy characteristics for the studied process, promoting the development of an energy-efficient "green" hydrogen generation technology. Additionally, we demonstrate that increasing the temperature further enhances the thermodynamic features of this reaction by reducing the energy consumption for its progression.

For the first time, we investigated the process of potentiostatic anodic treatment of the surface of a copper (≈55%)-nickel alloy in a eutectic mixture of urea and choline chloride (reline), which is a typical representative of a new generation of ionic liquids, deep eutectic solvents. The anodic behavior of the alloy in the used solvent was characterized by cyclic voltammetry, and the nature of the electrochemical dissolution reactions of individual components of the alloy corresponding to several anodic current waves registered in voltammograms was determined. It was established that the anodic dissolution of the alloy occurs under conditions of salt surface passivation due to the formation of a layer of poorly soluble products of the electrode reaction. It was shown that under conditions of prolonged (150 min) potentiostatic polarization of the alloy in reline for various values of the electrode potential (in the range from 0.1 to 1.7 V relative to the Ag reference electrode), the chemical composition of the surface remained unchanged (i.e., there was no selective etching of individual components of the alloy), but an evolution of surface morphology patterns was observed, the specific type of which depended on the value of the applied potential. Anodic treatment of the Cu-Ni alloy in the reline solvent at any of the investigated anodic potentials led to an increase in the surface roughness coefficient, and electrochemical polishing did not occur. Analysis of kinetic data related to the hydrogen evolution reaction on the surfaces of reline-treated copper-nickel alloys in a 1 M NaOH aqueous solution showed a significant increase in exchange current density. This indicates enhancement of electrocatalytic activity compared to the untreated surface. The observed effect is likely associated with an increase in the true surface area of the alloy available for electrochemical reaction and an increase in the surface concentration of electrocatalytic sites resulting from the anodic dissolution of the alloy. The obtained results can be used in the development of highly efficient and relatively inexpensive electrocatalysts for hydrogen energy.

The influence of anodic potentiostatic treatment of nickel surface in deep eutectic solvents, ethaline and reline (eutectic mixtures of choline chloride with ethylene glycol and urea, respectively), on the electrocatalytic activity in the electrochemical reactions of oxygen evolution and urea oxidation in an aqueous alkaline medium (1 M NaOH) was investigated for the first time. It was shown that, depending on the chosen treatment potential and the nature of the eutectic solvent used, a significant increase in the rate of the studied processes was observed. Specifically, after anodic treatment of nickel under certain conditions, the polarization of the oxygen evolution reaction at a current density of 0.1 A/cm2 could be reduced by approximately 150–200 mV, and the maximum current density of urea oxidation could be increased by an order of magnitude (from 0.012 A/cm2 to 0.131 A/cm2 at a urea concentration of 0.33 mol/dm3 in alkaline solution). The observed increase in electrocatalytic activity after anodic treatment of nickel in deep eutectic solvents is likely related to changes in surface morphology patterns and the nature and concentration of relevant electroactive sites on the electrode surface. The results obtained in this work can be used for the development of highly efficient electrode materials for green hydrogen energy.

A heat-resistant superalloy from destroyed special equipment was used for further processing to extract valuable metals such as rhenium, nickel, cobalt, tungsten, molybdenum, niobium, tantalum, and others. The need to develop an effective method for the electrochemical dissolution of this superalloy is due to the shortage and high cost of the component metals, especially rhenium. The electrochemical dissolution method is effective for the rapid and complete dissolution of such hard alloys, optimizing the extraction process of valuable components. In the course of the work, the composition of the unknown superalloy was determined, and the possible grade of the alloy was identified as JS32-VI. For the first time, a comparison of the anodic behavior of the heat-resistant superalloy containing rhenium in various electrolyte solutions, including methanesulfonic acid, was carried out. This comparison helped determine which electrolyte is best suited for dissolving the superalloy and extracting valuable metals from it. The results showed that solutions containing chloride ions (NaCl and HCl) are the most effective for the electrochemical dissolution of the superalloy. These results are explained by the fact that chloride ions help remove the passive oxide film from the metal surface. Thus, chloride solutions provide more effective dissolution of the superalloy compared to methanesulfonic acid and sulfuric acid. The key finding of the study is the identification of chloride solutions as the most effective for dissolving the superalloy, which optimizes the process of extracting valuable metals. The application of these methods will contribute to resource conservation and the reduction of production costs, which is important for industries using such materials

Electrodeposited nickel-based coatings microalloyed with lanthanum (up to approximately 1.75 wt%) were investigated. Electrodeposition was carried out using a deep eutectic solvent containing dissolved anhydrous salts of Ni(II) and Ce(III) as precursors. Electrochemical impedance spectroscopy results revealed that microalloying the chemical composition of coatings with lanthanum leads to a significant enhancement in electrocatalytic activity towards the hydrogen evolution reaction in an alkaline medium, as well as an improvement in corrosion resistance, compared to coatings not doped with lanthanum. These findings may be used in the development of high-performance electrocatalysts for hydrogen energy.

CuFe2O4 cubic copper ferrite nanoparticles were synthesized by a new plasma method, the advantage of which is the short duration of processing and cost-effectiveness. To select optimal synthesis conditions, central compositional rotatable experimental planning was used. Using the methods of X-ray phase analysis, vibration magnetometry, electron microscopy, and UV spectroscopy, the sizes of crystallites, the intensity of peaks in X-ray diffraction patterns, dislocation density, saturation magnetization, coercive force, and the degree of degradation of 4-nitrophenol were determined. To study the effect of pH on the composition of the resulting copper ferrites, cyclic voltammetry was used. The kinetics of the ferritization process under the influence of a plasma discharge has also been studied. A mechanism for ferritization in the Cu2+-Fe2+-SO42--OH- system has been proposed. It was found that single-phase nanodispersed powders of cubic copper ferrites with a saturation magnetization Ms 78-93 Emu/g can be obtained by plasma treatment at 300 s and pH 12. Copper ferrite with an admixture of Cu2O is formed at pH = 8. The maximum values of the coercive force correspond to regimes in which the minimum dislocation density is observed. The saturation magnetization depends on the crystallite size. The crystallite size of the resulting powders is in the range of 225-500 A. The results showed that the processing time is the parameter that has the greatest impact on the structural and magnetic characteristics of copper ferrite; the pH of the reaction medium affects them to a lesser extent.

The paper reports the impact of anodic potentiostatic treatment of nickel in two representatives of a new type of eutectic ionic liquids (deep eutectic solvents), ethaline and reline, which are eutectic mixtures of choline chloride with ethylene glycol and urea, respectively. The influence of anodic treatment on surface morphology, roughness coefficients, and electrocatalytic activity towards the hydrogen evolution reaction is characterized. It is demonstrated that the current densities of nickel anodic dissolution in reline are approximately an order of magnitude lower than in ethaline under all other identical conditions. Significant differences in the kinetics of nickel anodic dissolution and passivation during anodic polarization in ethaline and reline have been established, which may be attributed to both a substantial difference in the viscosity of these solvents and differences in the chemical nature and composition of the ions present in them. It is found that anodic treatment in ethaline, at certain potentials, results in electrochemical polishing of the surface, confirmed by a decrease in measured roughness coefficients, while anodic treatment in reline does not allow effective electropolishing and only surface etching (increase in roughness coefficients) is observed. Anodic potentiostatic treatment of nickel in both investigated deep eutectic solvents at specific electrode potential values significantly enhances the electrocatalytic activity of the surface towards the hydrogen evolution reaction in an alkaline environment. This finding can be utilized in the development of electrocatalytic materials for the electrolytic synthesis of green hydrogen.

DESs, as new-generation room temperature ILs, are very promising to perform anodic processing of different metals and alloys. We report Ni-Cu alloy (45 wt.% Ni) anodic treatment in a DES, ethaline, for the first time. It is shown that the anodic dissolution originated the formation of sparingly soluble Ni and Cu chloride salts in the near-electrode layer. Ni-Cu alloy anodic treatment in ethaline resulted in changed patterns of the metallic surface morphology. Depending on the applied electrode E, star like crystallites, with sharply pointed shapes and thorns, may appear on the anodically etched surface, and surface morphology smoothing was observed, in some cases. The Ni-Cu alloy anodic processing in ethaline, which dramatically changed its surface morphology, contributed to a considerable increase in the electrocatalytic activity towards HER in an alkaline medium. Considering favorable environmental aspects of DES use and marked improvement in electrocatalytic properties, this treatment can be further used to develop high-efficient, eco-friendly and relatively inexpensive electrocatalysts methods for water electrolysis within H-2 energy concept.

In this work, nanocrystalline nickel and nickel-molybdenum alloys were electrodeposited from electrolytes based on deep eutectic solvents. Eutectic mixtures of choline chloride with ethylene glycol (ethaline) and urea (reline) were used as typical representatives of deep eutectic solvents. The deposited Ni and Ni-Mo films were evaluated as potential electrocatalytic materials for green hydrogen production via electrolysis of alkaline aqueous solutions. The electrodeposited samples were characterized by XRD, SEM and EDX techniques, and the electrochemical behavior was evaluated by means of linear voltammetry and Tafel analysis. It was shown that the deposition of nickel (without molybdenum) from the electrolytes based on ethaline provides a higher elec-trocatalytic activity of the material with respect to the hydrogen evolution reaction than the material deposited from the reline-based electrolytes. The reline-based plating electrolytes contribute to a greater inclusion of molybdenum in the fabricated Ni-Mo alloys and therefore ensure increased electrocatalytic activity as compared with the ethaline-based electrolytes. The electrocatalytic behavior well correlates with the molybdenum content in the coatings. Ni and Ni-Mo electrodeposits produced from the deep eutectic solvent-mediated plating baths exhibit improved electrocatalytic performance and can be considered as promising catalytic materials for water electrolysis in green hydrogen energy.

The effect of anodic treatment of a nickel -copper alloy (45 wt % Ni) in an ethanol solvent, which is a new type of room -temperature ionic liquids, on the morphological features of the surface and electrocatalytic properties is characterized. It is shown that the anodic etching of the alloy in ethaline has practically no effect on the chemical composition of the surface, but leads to the formation of a new type of surface morphology patterns: appearance of star -shaped and polyhedral asymmetric crystallites on a smoothed and defect -free surface. The anodic treatment of the nickel -copper alloy in ethaline at defined values of electrode potential allows significantly increasing the electrocatalytic activity towards the hydrogen evolution reaction in an aqueous alkaline medium, which can be used to create new highly efficient electrocatalytic materials for hydrogen energy.

The need to develop new electrochemical energy storage and conversion devices requires the creation of new, available, low-cost and high-performance electrocatalytic materials, which can be produced as coatings by electrodeposition technique. The electrodeposited composite coatings based on nickel seem to be very promising in this context. We studied the corrosion resistance of electrocatalytic Ni–TiO2 composite coatings fabricated by electrodeposition method using a plating solution based on deep eutectic solvents, a new environmentally friendly and affordable type of room-temperature ionic liquids. We investigated the corrosion behavior of Ni and Ni–TiO2 coatings (5 and 10 wt.% of TiO2) in a 3% NaCl aqueous solution as a corrosive medium. The corrosion parameters were determined by linear voltammetry and electrochemical impedance spectroscopy. It was established that the inclusion of titania particles in the Ni matrix and an increase in their content in the coating leads to a shift in corrosion potential towards positive values, a decrease in corrosion current density and an increase in polarization resistance. The observed effects of improving the corrosion resistance of coatings are associated with the barrier action of particles of the dispersed phase and the formation of corrosion microcells contributing to the inhibition of local corrosion.

Kinetics of electrodeposition of composite Ni/TiO2 coatings was studied using the electrolyte based on a deep eutectic solvent (DES) containing choline chloride, ethylene glycol, water additive, and nickel chloride. Degussa P 25 nanopowder was used as a dispersed phase in the electrolyte (1–10 g/dm3). The developed electrolyte allows depositing composite coatings with the content of titanium dioxide reaching 10 wt

Ni-TiO2 composite electrolytic deposits were fabricated from an electrolyte based on ethylene glycol-containing deep eutectic solvent (the so-called ethaline, which is a typical representative of a new generation of room temperature ionic liquids). The electrolyte contained dissolved nickel (II) chloride salt and the addition of water that ensures an increase in electrical conductivity, a decrease in viscosity, and an increase in the content of the dispersed TiO2 phase in the coating (up to 10 wt%). The influence of the content of water and titanium dioxide in the electrolyte on the composition of the composite coating has been investigated. X-ray phase analysis and study of surface morphology (by scanning electron microscopy) were carried out. An increase in the electrocatalytic activity in the reaction of hydrogen evolution was detected, which was explained by the introduction of particles of the TiO2 dispersed phase into the electrodeposited nickel matrix. Copyright (C) 2022 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the EastWest Chemistry Conference 2021.

To determine the conditions for the maximum degree of precipitation, thermodynamic diagrams of the solubility of cobalt(II) hydroxides were calculated. Experimental studies of the precipitation of cobalt (II) hydroxide were carried out by the methods of finite concentrations, potentiometric titration, measurement of the apparent volume of the precipitate and electrical conductivity. The residual concentrations of Co(II) in model solutions were determined, the composition of the precipitates was determined, and the existence of cobalt hydroxocomplexes in solution was substantiated depending on the pH of the solution. The results of thermodynamic calculation showed that the pH of cobalt(II) hydroxide precipitation is 9.5. Methods of potentiometric titration, cyclic voltammetry showed that the formation of hydroxides is a stepwise process. At the initial stage, aqua ions are formed, then the main salt, the composition of which depends on the initial concentration of the solution, and then polyhydroxocomplexes.

This work reports about the kinetics and mechanism of the anodic oxygen evolution reaction occurring in an aqueous alkaline solution on two types of nickel electrodes obtained by electrodeposition technique. The first type of nickel coating was deposited from "ordinary" aqueous chloride nickel plating bath. The second type of nickel coating was deposited from an electrolyte based on ethaline (a eutectic mixture of choline chloride and ethylene glycol), which is a typical representative of the so-called deep eutectic solvents (a new generation of room-temperature ionic liquids). The electrocatalytic activity of Ni coatings towards the oxygen evolution reaction was evaluated by linear voltammetry and electrochemical impedance spectroscopy. Under conditions of moderate polarization, the rate-determining step at both types of electrodes is the transfer of the second electron. As the polarization increases, the transfer of the first electron becomes the rate-controlling step. Ni coating electrodeposited from an ethaline-based electrolyte exhibits higher electrocatalytic activity than the coating obtained from an aqueous electrolyte, which is confirmed by higher exchange current densities and lower polarization resistances. The observed effects are due to the manifestation of "true" electrocatalytic activity, rather than a consequence of an increase in the surface area available for the electrochemical process.

Kinetics of electrodeposition of composite Ni/TiO2 coatings was studied using the electrolyte based on a deep eutectic solvent (DES) containing choline chloride, ethylene glycol, water additive, and nickel chloride. Degussa P 25 nanopowder was used as a dispersed phase in the electrolyte (1–10 g dm3). The developed electrolyte allows depositing composite coatings with the content of titanium dioxide reaching ~ 10 wt.%. The electrolytic deposition of the composite was shown to obey Guglielmi's kinetic model. The main parameters of co-deposition of TiO2 particles into a nickel matrix were determined in the framework of this kinetic model. The co-deposition of titanium dioxide was found to inhibit the reaction of the nickel ions discharge. Electrocatalytic properties of the prepared composite Ni/TiO2 coatings were evaluated with respect to the hydrogen evolution reaction in an aqueous alkaline solution. A noticeable improvement in the electrocatalytic activity was observed when titanium dioxide particles were introduced into an electrodeposited nickel matrix.

Two groups of pigments were obtained by coprecipitation in the Fe-Al-Mg-O system. With the help of experimental studies, the influence of cations of chromophores and heat treatment on the color tone, color purity, anti-corrosion properties of pigments in the Fe-Al-Mg-O system has been established, which allows further targeted synthesis of pigments in beige, red and yellow colors. It is shown that the main technological properties of pigments are determined by the anionic and cationic composition. Color characteristics are determined by the cation occupying a tetrahedral position in the crystal lattice. For all considered systems, an increase in covalence after heat treatment leads to a shift in color to the long-wavelength region of the spectrum and to an increase in color intensity. The anticorrosive properties of pigments are largely determined by the hydrolysis of the formed compounds. The protective effect is mainly determined by the slowing down of the anodic process. In this case, anions containing aluminum atoms accelerate corrosion processes.

Purpose The purpose of this paper is to study the patterns of formation of anti-corrosion properties, the development of compositions for pigments by using the method of co-precipitation and subsequent heat treatment. Design/methodology/approach To obtain co-precipitated hydroxides, aqueous solutions of salts were used. The conditions of synthesis varied according to the following parameters: the nature of the starting salts of metals; and the ratio of metal cations. The anticorrosive activity of the pigments was evaluated by the potentiodynamic method, by comparing the anodic and cathodic polarization curves, and calculated potentials and corrosion currents on the basis of regions of Tafel on curves. Polarization curves were obtained by using Potentiostat/Galvanostat/ZRA Gamry, which connected to the PC, and by using the program Gamry Framework. The measurement results were processed by using the method of simplex-lattice planning. X-ray diffractograms of pigments were recorded on a DRON – 2.0 diffractometer (monochromatic copper radiation with a nickel filter). Findings The paper deals with the results of research the dependence of colour characteristics and anticorrosion properties of synthesized compositions on their nature and composition. The presence of aluminium cations leads to the formation of solid solutions of ferrum and aluminium oxyhydroxides. Originality/value The main technological properties of pigments are determined by the anionic and cationic composition. Colour characteristics are determined by the cation-chromophore. The anti-corrosive properties of non-calcined pigments are determined to a greater extent by the presence of the formed hydroxyl ions and the composition of the compounds. The greatest protective effect is observed when using double compounds of metals, the dissociation constants of which differ significantly. The protective effect is mainly determined by the slowdown of the anode process. Anions containing aluminium atoms accelerate the corrosion processes.