Electrolysis Regimes Research Articles

Energy Efficiency of Steady DC and Half Sine Pulsed DC in the High Voltage Pre-Plasma and Plasma Alkaline Water Electrolysis

The research addresses the contrasting views on the energy efficiency of alkaline water electrolysis using the regular DC vs the pulsed DC. We compare the high voltage steady DC electrolysis with the high voltage half-wave rectified (HWR) AC (or the half Sine pulsed DC, an unexplored form of the pulsed DC) across a wide range of voltage regimes, with a particular focus on the less explored Plasma electrolysis (PE) regime. In addition, the current-voltage characteristics are mapped across the voltage regimes (NE to PE) using a novel high-voltage 3-electrode circuit, which allows better control over the working electrode potential. The experimental design considers critical parameters such as energy efficiency, Faradaic efficiency, and current density, providing a comprehensive evaluation of the regular DC Vs. the half-wave rectified AC electrolysis.Pulsed electrolysis can facilitate bubble removal and ensure timely replenishment of reactant during the low-bias phase and this is expected to diminish over potential losses due to mass transfer resistance. However, the preliminary energy efficiency assessment suggests that the regular DC is ~13% higher at 33 V bias and ~24% higher at 26.5 V bias than the half sine pulsed DC(50 Hz) electrolysis. This suggests that for these particular reaction conditions, the fluctuations in the current leading to reactive losses in the circuit and other internal losses overwhelm any enhancement in the mass transfer characteristic of pulsed electrolysis. The study also points to regimes where significant thermal decomposition results in a significant increase in the apparent Faradaic efficiency.

АНАЛИЗ МОРФОЛОГИИ ПРИ ВОЗДЕЙСТВИИ ЭЛЕКТРОЛИТИЧЕСКОЙ СТРУИ НА ПОВЕРХНОСТЬ НЕРЖАВЕЮЩИХ СТАЛЕЙ

The article is devoted to the study of the effect of an electrolytic jet on the surface of a metal anode. The studies were carried out in the electrolysis mode with a study of the transition to the electrolyte-plasma treatment mode. Special attention is paid to the mechanisms of formation of the morphology of the surface of stainless steels 08X18H9T, AISI 301, AISI 304. It is shown that for different steels, the process of electro-chemical dissolution of the anode material is accompanied by different mechanisms of dissolution of the micronerities of the microprofile. The current-voltage characteristics of the process in the voltage range in the range of 20-250 V. The effect of the decrease in the mass of the anode material on the current value is considered. The morphology of steels has been studied under different technological conditions and at different points of contact of the electrolytic jet with the surface. The criteria accompanying the transition to the electrolyte-plasma regime from the electrolysis regime are considered.The effect of an electrolytic jet on the risks formed by mechanical treatment on the anode surface is investigated. The influence of stress on the formed surface roughness parameter Ra is considered. The calculation of the electric field strength for surface nanodefects was performed in the Comsol Multithisics program. The results of this work can be used for the development of turbine blade processing technology, electrochemical cutting and nanoobrabotation of materials.

DBD-like and electrolytic regimes in pulsed and AC driven discharges in contact with water

The interaction of an ambient air plasma with a water surface in a pin–water electrode configuration is presented in a polydiagnostic study. A discharge was generated by applying different high-voltage (HV) waveforms to a metallic pin electrode, positioned 2 mm above the water surface of a Petri dish filled with demineralized water. For pulsed discharge operation, a clear distinction is observed between a dielectric barrier discharge regime featuring a transient discharge at the rising as well as at the falling slope of the HV pulse, while a steady discharge is present in the gap during the complete HV pulse for the electrolysis regime. The occurrence of those two regimes is coupled to the increasing conductivity of the water over time, which additionally results in a quick rise of the dissipated discharge power and an increase of the gas temperature. The AC driven discharges exhibit only the electrolysis regime and do not significantly evolve over the treatment time. The resulting water conductivity was found to be a function of the total dissipated energy, irrespective of the discharge driving mode. Additionally, the resulting water conductivity shows a strong correlation with the total transferred charge in the gas phase. The total dissipated energy can potentially be used as a global measure to compare different experiments involving plasma–water interaction across different setups in different research groups.

Cathodic Processes in Uranium Containing Molybdate Melts

Cathodic processes in Li2MoO4–K2MoO4–MoO3 and K2MoO4–MoO3 melts containing added UO2MoO4 were investigated at 550–800 °C using cyclic voltammetry, cathodic polarization and bulk electrolysis. Cathodic reduction of molybdate melts (not containing uranium) resulted in formation of molybdenum dioxide. Products of the cathodic reactions in the melts containing uranium molybdate predominantly consisted of crystalline uranium oxides (mostly UO2 and U4O9) and MoO2. Minor products formed included other uranium oxides (U3O8, U13O34), mixed uranium-molybdenum oxides (U1.5Mo10O32, Mo2UO8) and molybdates (provisionally attributed to K2U(MoO4)3). Effect of temperature, cathodic current density 0.05–1 A cm−2), excess MoO3 concentration (30–50 mol%) on the composition of the cathodic reaction products were analyzed. Oxygen-to-uranium atomic ratio (oxygen coefficient) for primary uranium oxide phases was determined and varied from 1.963 to 2.161 for UO2±x and from 2.209 to 2.287 for U4O9±y. The effect of the electrolysis regime on the composition of the cathodic product was also considered. Constant-current and constant-potential electrolysis, as well pulsed-current, pulsed-potential and pulsed-reversed-current electrolysis were investigated with varying the parameters of alternating pulses (duration, current density or potential). Chemical and phase composition of the products produced by bulk electrolysis was fully characterized.

Deuterodehalogenation Under Net Reductive or Redox‐Neutral Conditions Enabled by Paired Electrolysis

AbstractInterest in deuterated active pharmaceutical ingredients (APIs) is increasing as deuteration holds promise for kinetic isotope effect (KIE) regulated fine‐tuning of API performance. Moreover, deuterium isotope labeling is frequently carried out to study organic and bioorganic reaction mechanisms and to facilitate complex target synthesis. As such, methods for highly selective deuteration of organic molecules are highly desirable. Herein, we present an electrochemical method for the selective deuterodehalogenation of benzylic halides via a radical‐polar crossover mechanism, using inexpensive deuterium oxide (D2O) as the deuterium source. We demonstrate broad functional group compatibility across a range of aryl and heteroaryl benzylic halides. Furthermore, we uncover a sequential paired electrolysis regime, which permits switching between net reductive and overall redox‐neutral reactions of sulfur‐containing substrates simply by changing the identity of the sacrificial reductant employed.

Deuterodehalogenation Under Net Reductive or Redox-Neutral Conditions Enabled by Paired Electrolysis.

Interest in deuterated active pharmaceutical ingredients (APIs) is increasing as deuteration holds promise for kinetic isotope effect (KIE) regulated fine-tuning of API performance. Moreover, deuterium isotope labeling is frequently carried out to study organic and bioorganic reaction mechanisms and to facilitate complex target synthesis. As such, methods for highly selective deuteration of organic molecules are highly desirable. Herein, we present an electrochemical method for the selective deuterodehalogenation of benzylic halides via a radical-polar crossover mechanism, using inexpensive deuterium oxide (D2 O) as the deuterium source. We demonstrate broad functional group compatibility across a range of aryl and heteroaryl benzylic halides. Furthermore, we uncover a sequential paired electrolysis regime, which permits switching between net reductive and overall redox-neutral reactions of sulfur-containing substrates simply by changing the identity of the sacrificial reductant employed.

ВОССТАНОВЛЕНИЯ ДЕТАЛЕЙ СЕЛЬСКОХОЗЯЙСТВЕННОЙ ТЕХНИКИ НАНЕСЕНИЕМ КОМПОЗИЦИОННЫХ ПОКРЫТИЙ НА ОСНОВЕ ЖЕЛЕЗА

Great opportunities for increasing the resource of parts of agricultural machinery that require restoration are opened up by technologies for applying hardening coatings. Options for obtaining galvanic deposits in various electrolytes, which allow depositing metal coatings with various special properties that ensure reliable operation of restored units under appropriate conditions, are considered in the article. Solutions of sulphate, chloride, and hydroboric fluoride salts of divalent iron were used as the electrolyte. Methods of chemical analysis of galvanic deposits were used. The hardness of the deposited layers was determined using a PMT-3 instrument. The effect of various alloying additives on the quality of the precipitates obtained is analyzed depending on the concentration of inclusions. The boundaries of inclusion concentrations are determined. It has been established that for controlled deposition of a composite coating, the concentration of inclusions in the deposited iron-containing coating should not exceed 20 g/l. It has been found that even an insignificant presence of manganese inclusions in an iron-based composite coating, which is of the order of the measurement error, doubles its hardness. The dependence of the concentration of ammonium chloride, as the base material for the extraction of pure manganese, on the hardness of the deposited galvanic precipitate, was studied in the framework of the described study. The highest hardness was achieved at a concentration of NH4Cl in the range of 100–150 g/l, and manganese - 0.4% by weight. Graphical dependences of the main quality indicators of the resulting coatings on the type and composition of the electrolytes used were obtained. The influence of the electrolyte temperature and electrolysis regimes on the hardness of the deposited metal is analyzed.

Morphology and Structure of Electrolytically Synthesized Tin Dendritic Nanostructures

The formation of tin dendritic nanostructures by electrolysis from the alkaline electrolyte has been investigated. Morphology and structure of Sn dendrites produced applying both potentiostatic and galvanostatic regimes of the electrolysis are characterized by SEM and XRD, respectively. Depending on the applied cathodic potentials, three types of Sn dendrites were obtained: (a) needle-like and spear-like, (b) fern-like, and (c) stem-like dendrites. The very branchy dendrites with branches of the prismatic shape obtained by the galvanostatic regime of electrolysis represented a novel type of Sn dendrites, not previously reported in the literature. To explain the formation of various dendritic forms, correlation with the polarization characteristics for this electrodeposition system is considered. The needle-like and the spear-like dendrites represented monocrystals of (200),(400) preferred orientation, the fern-like dendrites exhibited the predominant (220),(440) preferred orientation, while in the stem-like particles Sn crystallites were oriented to a greater extent in the (440) crystal plane than in other planes. The galvanostatically synthesized Sn particles possessed the strong (200),(400) preferred orientation. The strong influence of parameters and regimes of electrodeposition on structural characteristics of Sn dendrites is explained by the fundamental laws of electrocrystallization taking into consideration the concept of slow-growing and fast-growing crystal planes.

ВЗАИМОСВЯЗЬ ПАРАМЕТРОВ ЭЛЕКТРООСАЖДЕНИЯ И МОРФОЛОГИИ ПОВЕРХНОСТИ НИКЕЛЕВЫХ ПОКРЫТИЙ В ПРИСУТСТВИИ ИНГИБИТОРА РОСТА

On the one hand, nickel and nickel coatings are well-studied objects in terms of their wide practical application; on the other hand, the application of various approaches to their production and structuring gives new possibilities for changing their properties. At present, the research activities related to the change in nickel physicochemical properties through nanostructuring are being carried out. Methods and techniques for producing nanostructured materials are very diverse. However, many of them are considered energy-intensive and economically unviable. The work solves the problem of obtaining nickel coatings and changing their properties through electrodeposition from aqueous solutions of electrolytes. The paper studies the effect of additives to a nickel electrolyte on the habit of crystals formed in the coating and, consequently, the nickel coating morphology. The authors used sodium, potassium, and calcium chlorides in the same molar concentration to be additives. During the electrodeposition of coating samples, the substrate nature and the electrolysis regimes changed. The deposition was carried out in the stationary mode of electrodeposition within one or two stages of electrolysis. The authors studied the obtained samples by scanning electron microscopy methods using X-ray diffraction analysis. The study identified that chlorides can significantly change the coating surface morphology. Depending on chloride concentration and deposition regimes, the surface morphology of nickel coatings changes from the three-dimensional cone-shaped structures to the lamellar habit. Chlorides allow forming crystals with pentagonal symmetry as well. The addition of chlorides affects the growth of crystals in certain crystallographic directions (111), which may be the result of their inhibitory effect. The obtained nickel coatings have a regular microrelief.

ELECTRODEPOSITION OF METALS AND ALLOYS FROM AQUEOUS SOLUTIONS. REVIEW OF WORK OF EMPLOYEES FROM V.I. VERNADSKY NASU

The article examines in a historical perspective the issues that have been associated with the theory and practice of electrochemical deposition over the years of existence of the V.I. Vernadsky Institute of General and Inorganic Chemistry of NAS of Ukraine.
 Research in the field of electrochemistry of aqueous solutions, which was and is being carried out at the Institute, made a significant contribution to theoretical and applied electro­chemistry: the theory of electrode pro­cesses, electrochemistry of complex compounds, masstransfer, chemical power sources, electrocatalysis, electrochemical devices, theoretical and engineering electroplating, hydroelectro­metallurgy, electrochemical ecology and a number of other areas of modern chemistry. This article highlights issues related to research in the field of electrodeposition, namely: theo­retical research in the field of electrodeposition, electrodeposition of metals and alloys, hydroelectrometallurgy, corrosion and anticorrosion coatings. It is proved the effect of complexation leads to the formation of elect­rochemically active and inactive coordination ions, a mechanism for the discharge of ions during the formation of a film on the electrode surface is also proposed. The regularities leading to the formation of powders and black deposits of metals are analyzed. The conditions for a stable electrolysis regime were identified, the concept of the electrochemical resistance of the system was introduced, and the relationship between the kinetic parameters of elect­rolysis and the structure of the coatings was shown. The works in the field of hydroelectrometallurgy, corrosion-resistant and protective coatings are analyzed. It is noted that the scien­tific achievements of the Institute’s scientists are widely known around the world.

Correlation of Morphology and Crystal Structure of Metal Powders Produced by Electrolysis Processes

In this review paper, morphologies of metal powders produced by the constant (potentiostatic and galvanostatic) regimes of electrolysis from aqueous electrolytes are correlated with their crystal structure at the semiquantitative level. The main parameters affecting the shape of powder particles are the exchange current density (rate of electrochemical process) and overpotential for hydrogen evolution reaction. Depending on them, various shapes of dendrites (the needles, the two-dimensional (2D) fern-like, and the three-dimensional (3D) pine-like dendrites), and the particles formed under vigorous hydrogen evolution (cauliflower-like and spongy-like particles) are produced by these regimes of electrolysis. By decreasing the exchange current density value, the crystal structure of the powder particles is changed from the strong (111) preferred orientation obtained for the needle-like (silver) and the 2D (lead) dendrites to the randomly orientated crystallites in particles with the spherical morphology (the 3D dendrites and the cauliflower-like and the spongy-like particles). The formation of metal powders by molten salt electrolysis and by electrolysis in deep eutectic solvents (DESs) and the crystallographic aspects of dendritic growth are also mentioned in this review.

Preparation of fine copper powders by galvanostatic regime of electrolysis of copper scrap in a cylindrical electrochemical cell

A cylindrical electrochemical cell is designed. The mean residence time and volume fraction of stagnant zone under perpendicular inflow (PI) and tangential inflow (TI) are studied by hydraulics experiments. Fine copper powders are prepared by galvanostatic regime of electrolysis of copper scrap. The effects of current density on current efficiency, cell voltage, power consumption, and the particle size of copper powder (D50) are investigated both under PI and TI. The results show the residence time of fluid particles is prolonged with decreasing flow rate, which is beneficial to the reaction of substances, and volume fraction of stagnant zone decrease. Maximum current efficiency and minimum power consumption are obtained under PI, which corresponds to the maximum D50 particle size. According to SEM figures, deposits on the surface of cathode are honeycomb-like forms. There are more arborous secondary dendrites under PI, but more compact and stout dendrites under TI in comparison.

Intensification of the recovery of hydraulic equipment parts by iron in the electrolyte flow

The technology of bath-free ironing of parts in an electrolyte flow with simultaneous hydromechanical activation of the growing surface is proposed. Its advantages over the traditional type of coating are introduced. The structure, some physicomechanical and operational properties of iron coatings were studied depending on the electrolysis regimes and the composition of electrolytes. The possibility of high-speed electrodeposition of iron with a wide range of physical and mechanical properties is shown. There were shown the electrolysis modes, which make it possible to obtain high-quality strong-adhered pure-iron coatings with a wear resistance several times higher than hardened alloy steels and a precipitation growth rate tens of times higher than with traditional ironing. A typical technological process of parts ironing was developed. It was tested on the example of restoration of hydraulic valve spools of agricultural machinery. The design of an installation and an electrochemical cell for ironing the valve hydraulic distributors, providing optimal hydrodynamic conditions when applying coatings to worn surfaces, was proposed. Recommendations for the post-electrolysis treatment of restored parts by iron are given. Bench and field tests of hydraulic valves with remanufactured valves were carried out. They confirmed the results of laboratory studies, and showed that no malfunctions were identified during the operation period. Technical and economic calculations have shown the high efficiency of the proposed technology in comparison with traditional ironing. The introduction of the technology in production will reduce the production area and the time spent on restoring parts by increasing the productivity of the iron process and reducing the number of operations, reducing the cost of materials for preparing electrolytes by reducing the operation of anodic treatment and washing, and increasing the reliability of the technology by improving its structural scheme.

Lead Dioxide Based Oxide-Surfactant Composites

Great attention is paid to various electrochemical methods of coatings synthesizing in connection with the simplicity of their implementation, low cost equipment and the ability to control the composition and properties of the materials obtained by changing the electrolysis regimes and the composition of electrolytes [1, 2]. Composite materials based on lead dioxide, containing surfactants are of considerable interest for research, since while maintaining the basic properties of PbO2, the composition, physico-chemical properties, and electrocatalytic activity of such materials can vary widely. At the same time, there is a lack of information [4, 5] regarding the effect of surfactants on the regularities of electrodeposition of materials based on lead dioxide, especially the physico-chemical properties of the oxides obtained and their electrocatalytic activity. In this connection, herein, we report the regularities of synthesizing, the effect of deposition conditions on the composition, physico-chemical properties of composite PbO2-sodium laureth sulfate (SLES) materials obtained from nitrate electrolytes. The addition of surfactants has a significant impact on the kinetics of lead dioxide electrodeposition, without changing the mechanism of the process. In this way, at low anodic polarizations second electron transfer stage is rate determining, whereas at high anodic polarizations such stage is diffusion transport of the lead ions to the electrode surface. The presence of sodium laureth sulfate in the deposition electrolyte leads to a slight inhibition of the deposition of lead dioxide. The content of the additive in lead dioxide is determined mainly by its adsorption on the oxide. An increase in the adsorption of additive due to an increase in its concentration in the solution and an increase in electrostatic attraction (an increase in the anodic current density and the acid content in the deposition electrolyte) leads to the enrichment of the composite material with organic substance. Anionic surfactants, SLES in particular, are included in the growing lead dioxide. The content of organic substance in the oxide can vary from 3.4 to 12.5 w.%, forming a surfactant-oxide composite coating. The changing in deposition conditions (temperature, pH and anodic current density) allows one to control the content of surfactant in the resulting oxide. Based on the data obtained, a colloidal-electrochemical mechanism for the formation of composites was proposed, according to which the process proceeds in several stages: the formation of colloidal oxide particles in the near-electrode zone; adsorption of anionic polyelectrolyte on colloidal particles; electrophoretic delivery of oxide particles with adsorbed surfactant to the electrode surface; sedimentation and crystallization of the composite at the interface. The surface morphology and chemical composition of obtained materials were investigated by SEM, EDAX, phase composition and texture was determined by X-Ray powder diffraction. The morphology and structure of composite materials differs significantly from lead dioxide. With an increase in the additive content in the composite, there is a transition from large-grained deposits to materials with submicron and nano-sized crystals. The electocatalytic activity of the materials involved was investigated in respect to oxygen evolution reaction and the oxidation of 4-chlorophenol. The calculated value of Tafel slope is 229 on nonmodified PbO2, while on 10.2 wt.% SLES-PbO2 it is 178 mV/dec. Slope decreasing in the case of PbO2-SLES denotes the increasing of lead dioxide infilling degree by oxygen-containing radicals, which are directly involved in the electrochemical stages of oxygen evolution. The most likely, surfactants on the electrode surface play the role of mediators in the process of oxygen evolution and inhibit the surface blocking by sulfate ions on such materials. The processes of electrooxidation of 4-chlorophenol on lead dioxide and PbO2-based composite materials proceed qualitatively in the same way and differ only in the rate. Thus, lead dioxide based surfactant-oxide composite coatings are of great interest because of high electrocatalytic activity in respect to oxygen transfer reactions. References R. Vargas, C. Borras, D. Mendez, J. Mostany, B.R. Scharifker, J. Solid State Electrochem. 20, 875 (2016).M. Krishna, E. J. Fraser, R. G. A. Wills, F. C. Walsh, J. Energy Storage, 15, 69 (2018).X. Li, H. Xu, W. Yan, J. Alloy Compd., 718, 386 (2017).A. B. Velichenko, T. V. Luk'yanenko, N. V. Nikolenko, R. Amadelli, F. I. Danilov, Russ. J. Electrochem., 43, 118 (2007).

A possible mechanism of formation of flower-like MgO/Mg(OH)2 structures by galvanostatic molten salt electrolysis: The concept of local diffusion fields

The processes of electrodeposition from magnesium nitrate hexahydrate melt by galvanostatic regime of electrolysis have been analyzed. The structure of the formed particles was examined by X-ray diffraction (XRD), which revealed formation of MgO/Mg(OH)2 mixture by molten salt electrolysis. Morphologies of the produced deposits were characterized by scanning electron microscopy (SEM) technique. The flower-like forms constructed from very thin needles with sharp tips were predominately formed by electrodeposition at various current densities and with various amounts of electricity. Aside from that, holes formed from detached hydrogen bubbles of various shapes and sizes, from dish-like holes to those resulting in honeycomb-like structures were also observed. Mechanism of formation of the flower-like forms has been elucidated applying the general theory of disperse deposits formation which is based on the concept of local (spherical and cylindrical) diffusion fields. It is shown that the growth of the needles occurs under the conditions of predominant spherical diffusion control, while the contribution of the cylindrical diffusion to the final shapes was negligible. Comparison with morphologies of deposits obtained by electrodepositions from aqueous magnesium salt electrolytes was also made and discussed.

Modern Methods for Synthesis of Few-Layer Graphene Structures by Electrochemical Exfoliation of Graphite

Abstract—A review of methods for synthezing few-layer graphene structures (FGS) by electrochemical exfoliation of graphite in aqueous solutions of inorganic substances and ionic liquids is conducted. The expected mechanisms of the processes are considered, as well as the influence of the electrolysis regimes on the quality characteristics of the product obtained. In general, the method of electrochemical exfoliation of graphite is based on the destruction of graphite-containing materials in solutions of certain substances containing ions that can undergo intercalation into graphite under the action of electric current. The procedure of electrochemical exfoliation of graphite contains two stages, the first of which corresponds to the intercalation of ions from the electrolyte solution into the space between the graphene sheets to form covalent or ionic bonds, and the second involves the separation of the material as a result of the electrochemical reaction. At first, a potential, as a rule, smaller compared to the operating one, is applied to the electrode to be destroyed in order to achieve good surface wetting and preliminary intercalation of graphite. At the next step, the main stage of obtaining the FGS begins, which is characterized by imposing an operating voltage. Then, as a rule, surfactants are added to the solution, facilitating exfoliation, as well as reducing the agglomeration of the obtained FGS suspensions. The stages of separation and purification of the obtained product are described.

Production of an Electrolytic Alloy Nickel-Tin-Bor

A method for the preparation and properties of an alloy based on nickel is discussed. An electrolyte for the deposition of a tin-nickel alloy has been developed. The influence of electrolysis regimes and electrolyte composition on the physical and mechanical properties (microhardness, spreading coefficient of solder, transient electrical resistance, coating ability to soldering, phase composition, porosity, adhesion, corrosion resistance) of an electrolytic coating based on nickel-tin alloy precipitated from a chloride electrolyte. The possibility of using a tin-nickel alloy as a solderable coating instead of gold and silver is shown.

Overpotential controls a morphology of electrolytically produced copper dendritic forms

The morphologies of copper dendritic forms obtained in both potentiostatic and galvanostatic regimes of electrolysis with various amounts of the electricity were analyzed by the scanning electron microscopy (SEM) technique. Irrespective of amount of passed electricity, 3D (three dimensional) pine-like dendrites with sharp tips were formed in the potentiostatic regime of electrolysis. On the other hand, the amount of passed electricity had a strong effect on the shape of the 3D pine-like dendrites formed in the galvanostatic regime of electrolysis. Dendrites with sharp tips were formed with smaller amount of passed electricity, while dendrites with globular tips were formed with larger amounts. The change in the shape of the galvanostatically synthesized 3D pine-like dendrites was explained by comparison with copper deposits obtained potentiostatically at overpotentials that corresponded to the final overpotentials during galvanostatic regime of electrolysis for the analyzed amounts of electricity. Based on the similarity of the obtained morphologies at the macro level, it was concluded that the overpotential plays a crucial role in the formation of the electrolytically synthesized dendrites and that the controlled conditions of electrolysis could represent a suitable way for a synthesis of spherical Cu particles by electrolysis.

Influence of A- and B-Site Modifications of (La1-xSrx)yCr0.5-zMn0.5-wNiz+wO3-δ on Electrochemical Impedance Characteristics of Reversible Solid Oxide Cell

Influence of A-site deficiency and chemical composition of B-site (concentration of Ni, Mn, and Cr) on electrochemical performance of hydrogen electrode in (La1-xSrx)yCr0.5-zMn0.5-wNiz+wO3-δ|(Sc2O3)0.10(CeO2)0.01(ZrO2)0.89|La0.8Sr0.2FeO3-δ reversible solid oxide fuel cell has been studied. Electrochemical characterization has been carried out in fuel cell and electrolysis regimes. Results indicate that in fuel cell regime most notable limiting steps were detected around 0.5 Hz frequency range and were attributed to gas-solid adsorption-desorption processes. pO2 variation in the oxygen electrode compartment led to small variations in a total impedance of single cells but was not the limiting process. In electrolysis mode, the dissociative adsorption was shown as an important limiting stage and limitations in kinetic region of charge transfer step were remarkable. Increase of A-site deficiency caused a significant increase in high-frequency series resistance as well as some increase of total polarization resistance. Variation in B-site composition had a significant influence on electrochemical performance with very different frequency dependence of impedance. Highest current density values of 0.27 and 0.66 A cm−2 at unit cell potentials of 0.9 and 1.5 V, respectively, at 850°C were measured for La0.75Sr0.25Cr0.3Mn0.5Ni0.2O3-δ (fuel cell mode) and (La0.8Sr0.2)xCr0.49Mn0.49Ni0.02O3-δ (electrolysis mode) in hydrogen fuel gas with pH2O = 0.03 and 0.30 atm, respectively.

Generation of nonporous crystalline Ta oxide

Features of electrochemical formation of nonporous oxide coating on tantalum in acid fluoride-containing and organic electrolytes have been investigated. It has been shown that the morphology of the surface of the formed oxide films depends significantly on the electrolysis regime and the composition of the solution. Under certain anodizing conditions, a nanostructured crystalline-type oxide coating is formed.