Potentiodynamic Mode Research Articles

ВЛИЯНИЕ КАЛЬЦИЯ НА АНОДНОЕ ПОВЕДЕНИЕ АЛЮМИНИЕВОГО ПРОВОДНИКОВОГО СПЛАВА AlTi0.1 В СРЕДЕ ЭЛЕКТРОЛИТА NaCl

The article presents the results of an experimental study of the effect of calcium on the anodic behavior of the aluminum alloy AlTi0.1, in the medium of NaCl electrolyte. The study was carried out by the potentiostatic method in the potentiodynamic mode at the potential sweep rate of 2 mV / s. It is shown that the modification of the aluminum alloy AlTi0.1 with calcium promotes the displacement of the potentials of free corrosion, pitting formation, and repassivation to the positive range of values. The corrosion rate of the aluminum alloy AlTi0.1 when modified with 0.01-0.5 wt % calcium decreases by 10-17 %.

Electrochemical oxidation of pyrrole on the surface of the amorphous alloy of Al87Ni8Y5 composition in the 0.5 M sulfate acid solution

Polypyrrole films were deposited on the surface both of the outer and contact sides of the Al 87 Ni 8 Y 5 amorphous alloy electrodes by potentiodynamic oxidation of 0.25 M pyrrole in 0.5 M H 2 SO 4 aqueous solution. It is determined that already in the first anode cycle of potential scanning a nanofilm of polypyrrole is formed on Al 87 Ni 8 Y 5 amorphous alloy electrodes. The further pyrrole oxidation in potentiodynamic mode occurs easily and film of polypyrrole actively formed on the surface of the working electrode. Cyclic voltammogramms has been analyzed and the process of electrochemical oxidation of pyrrole and redox transformations of polypyrrole at these electrodes is described. It is shown that the difference in film topology is due to the surface topology of electrodes, which determines stability of surface oxide films on these surfaces. Studies of the electrode surface topology and also morphology, structure and composition of polypyrrole films produced on an amorphous alloy electrode were carried out using Fourier-transform infrared spectroscopy with attenuated total reflection (FTIR-ATR), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). It has been confirmed using FTIR analysis that the films deposited on the surface of the Al 87 Ni 8 Y 5 electrodes corespond to polypyrrole which are in the form of hydrosulfate salt. The analysis of the received electron microscopy images shown that a polypyrrole films produced both on the contact and outer sides of the working electrodes has developed surface topology, which depends on surface quality and nature of amorphizing additive in electrode alloy. The peculiarity of pyrrole oxidation and redox transformations of deposited polypyrrole on the Al 87 Ni 8 Y 5 electrode is mainly due to the high concentration of pyrrole in the solution and to a lesser extent to the properties of the electrode surfaces and naturally formed oxide films. Electrochemical oxidation of pyrrole on the Al 87 Ni 8 Y5 electrode in the potentiodynamic mode accompanied by the formation of quasi-spherical nanoaggregates, which form a dense primary film of polypyrrole. The formed nanoaggregates in the following cycles of potential scanning act as peculiar polymer electrodes. Keywords: pyrrole, amorpfous alloys, electrochemical oxidation, polypirrole, structure.

Mathematical modeling of nonstationary 1:1 electrolyte transfer and study of the space charge region in membrane systems taking into account electric convection and water dissociation/recombination reactions

The article formulates a mathematical model of non-stationary transfer of 1:1 electrolyte in potentiodynamic mode, taking into account electroconvection and non-catalytic reaction of dissociation/recombination of water molecules in membrane systems, which are considered the channel of desalting of the electrodialysis apparatus. Using this model, the main regularities of the space charge distribution are theoretically established, the influence of the input parameters is determined: initial concentration, potential sweep rate, etc. It is shown that the desalination channel consists of narrow quasi-equilibrium regions of space charge adjacent to ion-exchange membranes; an electric double layer appears in the central part, caused by the recombination reaction. Regions of electroneutrality are located between this double electric layer and the near-membrane space charge regions. This study will further be used to analyze the combined effect of the noncatalytic reaction of dissociation of water molecules and recombination and electroconvection on the current-voltage characteristic of the desalting channel.

Влияние электротоковых характеристик процесса формирования на свойства ПЭО-покрытий, получаемых на магниевом сплаве МА8 в потенциодинамическом режиме

Установлено, что в потенциодинамическом режиме формирования покрытий методом плазменного электролитического оксидирования (ПЭО) электрохимические и морфологические свойства получаемых поверхностей можно регулировать, используя максимальную плотность тока. Получены зависимости данной величины от таких параметров, как максимальное значение и скорость изменения напряжения, а также от размеров оксидируемого изделия. Исследована зависимость защитных свойств ПЭО-покрытий, получаемых на магниевом сплаве МА8, от максимальной плотности тока формирования. Проведены морфологические и электрохимические исследования полученных гетерооксидных слоев с целью выявления корреляции свойств покрытий с плотностью тока формирования. Методами сканирующей электронной микроскопии и потенциодинамической поляризации изучены основные защитные свойства ПЭО-покрытий. Результаты свидетельствуют об увеличении толщины и пористости покрытий при росте значений плотности тока формирования. Показано, что при переходе от низких (2 мА/мм2) к высоким (до 12 мА/мм2) максимальным значениям плотности тока поляризационное сопротивление имеет максимум в области значения 4 мА/мм2, что свидетельствует об оптимальном режиме формирования ПЭО-покрытий с высокими барьерными свойствами. It is established that in the potentiodynamic coating-formation mode by plasma electrolytic oxidation (PEO), the electrochemical and morphological properties of the resulting surfaces can be adjusted using the maximum current density. In this paper, the dependences of this value on such parameters as the maximum value and the rate of voltage change, as well as on the size of the oxidized product are obtained. The dependence of the protective properties of PEO-coatings obtained on magnesium alloy MA8 on the maximum density of the formation current is studied. Morphological and electrochemical studies of the obtained heteroxide layers were performed in order to identify the correlation of the coating properties with the density of the formation current. The main protective properties of PEO-coatings have been studied using scanning electron microscopy and potentiodynamic polarization. The results obtained indicate an increase in the thickness and porosity of coatings with an increase in the values of density of the formation current. It is shown that during the transition from low (2 mA/mm2) to high (up to 12 mA/mm2) maximum values of the current density, the polarization resistance has a maximum in range of 4 mA/mm2, which indicates the optimal mode of formation of PEO coatings with high barrier properties.

Investigation of electrochemical performance and stability of electrodeposited Mn3O4 thin films in different aqueous electrolytes for its application in flexible supercapacitors

An electrochemical capacitor has attracted significant attention, mainly due to its long life cycle, high power and energy densities. Among the various metal oxides, manganese oxide is well known and extensively studied as an electrode in an energy storage system. In our work, we present a simple, effective and inexpensive approache to deposit thin film under ambient temperature. The manganese oxide thin film is prepared on flexible stainless steel (SS) sheet as substrate by potentiodynamic mode of electrodeposition and employed for supercapacitor application. The deposition is carried out by repeating the number of cycles in the potential region between -1V to 1V at a scan rate of 50 mV/s. The effect of heat-treatment on the electrode is also examined. The electrochemical performance of the thin electrode is evaluated by using a cyclic voltammetry measurement and charge/discharge test in three different electrolytes i.e. 1M Na2SO4, 1M NaOH and mixed 1M KOH with 0.04 M K4Fe(CN)6. The material exhibits a large pseudo-capacitance with better stability over a potential window of -0.1V to 1V in 1 M Na2SO4 electrolyte as the phase of material has been changed. Hence it proves to be a good candidate material for the supercapacitor electrode.

HIGH TEMPERATURE AND ELECTROCHEMICAL CORROSION OF Zn0.5Al ALLOY DOPED WITH CALCIUM IN VARIOUS MEDIA

The article presents the results of a study of high-temperature and electrochemical corrosion of Zn0.5Al alloy doped with calcium in the various media. The thermogravimetric method was used to study the interaction of the Zn0.5Al alloy doped with calcium with atmospheric oxygen in the temperature range 523–623 K in the solid state. The kinetic and energy parameters of the process of high-temperature oxidation of alloys are determined. The process of high-temperature oxidation of Zn-Al-Ca alloys system is characterized by a monotonic decrease in the true oxidation rate and an increase in the effective activation energy when the alloying component in the initial Zn0.5Al alloy is up to 1.0 wt% doping with zinc-aluminum alloy 0.5 and 1.0 wt%. Calcium shows a slight increase in the oxidation rate of alloys. It was revealed that the oxidation process of the studied alloys with oxygen of the gas phase obeys the hyperbolic law. It was found that calcium supplements in the range of 0.01 - 0.1 wt%. The oxidizability of the initial Zn0.5Al alloy is reduced significantly, and the oxidation products of the alloys were ZnO, Al2O3, Al2O3 ∙ ZnO, CaO, Al2O3 ∙ CaO. By potentiostatic methods in the potentiodynamic mode with a potential sweep speed of 2 mV/s, it has been shown that for all samples of the Zn0.5Al-Ca alloys system in the acidic, neutral, and alkaline media, electrochemical potentials of corrosion, pitting formation, and repassivation are shifted to the region of negative values. It was revealed that zinc-aluminum alloys doped with calcium are most resistant to pitting corrosion in all studied media, respectively, in acidic (0.01n.), neutral (0.03-, 0.3-, 3.0 wt%) and alkaline (0.01n.) electrolytes of HCl, NaCl and NaOH. It has been established that calcium additions in the range of 0.01 - 0.1 wt.% reduce the corrosion rate of zinc-aluminum alloy Zn0.5Al by a factor of 2–3. Calcium alloys are recommended as anodic coatings and protectors for corrosion protection of steel products and structures operating at high temperatures.

Changes in electrochemical properties of a heavy tungsten alloy during its processing under the influence of DC current in ammonia-alkali solutions

The method of linear voltammetry in the potentiodynamic mode was used to study the change in the anode behavior of a heavy tungsten VNZh alloy (in wt.%: 78.8 W; 15.2 Ni; 6.0 Fe), as well as the phase composition and morphology of its surface during its electrochemical dissolution under the influence of DC current. It was determined, that the phase composition of VNZh alloy surface is a solid solution of iron-nickel after tungsten dissolution from the surface of the alloy. It has been established, that in ammonia-alkali electrolytes the process of tungsten passing into solution does not stop after dissolution of the metal from the alloy surface, but continues both due to diffusion of the metal from the depth of the sample and the pits formation in the processed alloy.

ОСОБЕННОСТИ КАТОДНЫХ И АНОДНЫХ РЕАКЦИЙ НА УГЛЕРОДИСТОЙ СТАЛИ В ЗАВИСИМОСТИ ОТ ГЛУБИНЫ ПОГРУЖЕНИЯ В НЕЙТРАЛЬНЫЙ РАСТВОР

The investigation of the depth immersion of the specimens on corrosion rate of steel St3 in 3 % NaCl solution. Simulation of atmospheric corrosion (humid and wet) was performed by immersing of a steel sample by the size of (50×10×2) mm in a neutral solution of 3% NaCl at different depths. By leading the lower boundary of the working surface of the sample to the level of the solution (about 0 mm), humid corrosion was simulated, submerged to a depth of 2 mm (up to the upper boundary), wet corrosion, and 10 mm from the upper boundary - the electrolyte volume. The developed method allowed to carry out electrochemical researches by the method of polarization curves. The polarization curves were measured in the potentiodynamic mode with the potential scanning rate of 5∙10-4 V/s .The working electrode was a sample of steel St3 by the size (10×50×2) mm. A work surface (10×2) mm was separated on the sample, the rest of the surface was isolated with a non-conductive varnish. The results of the investigation of the effect of depth immersion of samples into electrolyte solution on corrosion rate of St3 steel are presented. The conditions of “humid” and “wet” atmospheric corrosion of the metal were simulated by the immersion of samples on a depth from 0 to 10 mm into 3% sodium chloride solution. It was found, that on the base on determination of the rate of particular electrode reactions occurring on the electrode at various depths of its immersion into the solution, the corrosion rate of steel St3 was determined by the value of the limiting diffusion current.It was shown that the value of limiting current increases from 0.51 to 2 A/m2 with decreasing of the film thickness. It has been established that the cathodic process rate depends both on the concentration of oxygen in the layers of the solution, which are at different distances from the solution/air boundary, and on the speed of its diffusion to the metal surface. Because the method of polarization resistance allows to measure the currents smaller than the currents of oxygen reduction in thin films of the solution, it can be used to estimate the rate of atmospheric corrosion of steel. Based on simulation of humid and wet atmospheric corrosion the effect of immersion depth of the specimens on the cathodic reaction rate of steel St3 in 3 % NaCl solution was established. The cathodic current density (limit diffusion current) is raised from 0,51 to 2 A/m2 under decreasing of immersion depth. The suggested method of simulation of atmospheric corrosion may be used for electrochemical investigations in thin films of moisture of different thickness which are form on the metals and sensors surfaces. The possibility of application of polarization resistance method for atmospheric conditions was presented.

Analysis of the theoretical CVC of electromembrane systems

In a number of recent studies, the authors derived and substantiated a formula for calculating the theoretical current voltage curve (CVC) of electromembrane systems (EMS). This formula was created for the flow cell of desalination of the electrodiaysis apparatus formed by an anion exchange (AEM) and a cation exchange membranes (CEM) in the potentiodynamic mode based on the charge conservation law. In this paper, the formula for the CVC (I –V characteristic) is investigated, its physical meaning, and the contribution of various factors to the CVC are revealed. A new simplified formula is proposed for calculating CVC, stable with respect to rounding errors. The critical values of the current density were determined and the current voltage curve was divided into separate sections. In the article, we showed that for characteristic values of the average flow rate of the electrolyte solution, the initial concentration in all sections of the CVC, the contribution of the convective current is small. The main role belongs to the electromigration (ohmic) current, especially in the overlimiting sections of the current – voltage curve. The contribution of the diffusion current in limiting and underlimiting sections is quite significant, although less than the ohmic current.

Constructing Bifunctional 3D Holey and Ultrathin CoP Nanosheets for Efficient Overall Water Splitting.

Pursuing cost-effective water-splitting catalysts is still a significant scientific challenge to produce renewable fuels and chemicals from various renewable feedstocks. The construction of controllable binder-free nanostructures with self-standing holey and ultrathin nanosheets is one of the promising approaches. Herein, by employing a combination of the potentiodynamic mode of electrodeposition and low-temperature phosphidation, three-dimensional (3D) holey CoP ultrathin nanosheets are fabricated on a carbon cloth (PD-CoP UNSs/CC) as bifunctional catalysts. Electrochemical tests show that the PD-CoP UNSs/CC exhibits outstanding hydrogen evolution reaction performance at all pH values with overpotentials of 47, 90, and 51 mV to approach 10 mA cm-2 in acidic, neutral, and alkaline media, respectively. Meanwhile, only a low overpotential of 268 mV is required to drive 20 mA cm-2 for the oxygen evolution reaction in alkaline media. Cyclic voltammetry and impedance studies suggest the enhanced performance is mainly attributed to the unique 3D holey ultrathin nanosheets, which could increase the electrochemically active area, facilitate the release of gas bubbles from electrode surfaces, and improve effective electrolyte diffusion. This work suggests an efficient path to design and fabricate non-noble bifunctional electrocatalysts for water splitting at a large scale.

Simultaneous voltammetric determination of gallic and ellagic acids in cognac and brandy using electrode modified with functionalized SWNT and poly(pyrocatechol violet)

Voltammetric approach for the simultaneous determination of gallic and ellagic acids using glassy carbon electrode modified with polyaminobenzene sulfonic acid functionalized single-walled carbon nanotubes (f-SWNT) and poly(pyrocatechol violet) (polyPCV/f-SWNT/GCE) has been developed. The electrochemical PCV polymerization has been performed in potentiodynamic mode. The optimization of electrolysis conditions (supporting electrolyte, PCV concentration, polarization window, number of cycles, and potential scan rate) has been performed. The best voltammetric characteristics of gallic and ellagic acids oxidation have been registered on the poly(PCV)-modified electrode obtained by tenfold potential scanning from − 0.2 to 1.1 V at 50 mV s−1 using 50 μmol L−1 PCV in 0.1 mol L−1 H2SO4. The electrode is characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The statistically significant changes in the effective surface area of modified electrodes (38.9 ± 0.6 mm2 for f-SWNT/GCE and 49.0 ± 0.2 mm2 for polyPCV/f-SWNT/GCE vs. 8.2 ± 0.3 mm2 for GCE) have been confirmed. EIS data have shown 2.6-fold decrease of the charge transfer resistance in comparison to GCE. Under conditions of differential pulse voltammetry (DPV), the analytical ranges of 0.75–10 and 10–100 μmol L−1 for gallic acid and 0.75–7.5 and 7.5–100 μmol L−1 for ellagic acid have been obtained. The limits of detection (LOD) and quantification (LOQ) of 0.12 and 0.41 μmol L−1 for gallic acid and 0.11 and 0.37 μmol L−1 for ellagic acid have been achieved. The approach developed has been applied for the simultaneous determination of the gallic and ellagic acids in cognac and brandy. The results obtained agree well to chromatography data.

Preparation and Properties of Graphite Nitrate-Modified Composite Electrochemical Coatings Based on a Nickel–Chromium Alloy

We have prepared graphite nitrate-modified composite electrochemical coatings based on a nickel–chromium alloy. The electrodeposition process used to grow the coatings has been studied in potentiodynamic mode. We have assessed the influence of disperse-phase concentration and cathode current density on the microhardness of the nickel–chromium–graphite nitrate coatings.

ELECTROCHEMICAL SYNTHESIS OF POROUS CRYSTALLINE TANTAL OXIDE

Self-organization of nanoscale structures during electrochemical processing is most pronounced during the formation of porous anodic metal oxides (aluminum, titanium, tungsten, niobium, tantalum). These oxides contain arrays oriented perpendicular to the pore substrate. A distinctive feature of these films is a high degree of orderliness in the arrangement of pores and the possibility of controlled variation of the pore diameter in a wide range (from 10 to 150 nm). In this work, the features of the electrochemical formation of nanoporous oxide coatings on tantalum in acid-fluoride and organic electrolytes are investigated. Tantalum foil with a thickness of 0.1 mm and a purity of 99.99 % was used as a working electrode. For the formation of tantalum oxides, 1 M H2SO4 solutions with the addition of HF (0.1 M; 0.25 M; 0.5 M; 1 M) and an organic electrolyte were used: EG + 5.5 М H2O + 0.05 М H3PO4 + 0.8 М NH4F, EG + 5.5 М H2O + 0.05 М H3PO4 + 0.8 М NaF. Polarization studies were carried out on a P-45X potentiostat. in potentiodynamic mode. The reference electrode is saturated silver chloride. The magnitudes of the potentials are given relative to the normal hydrogen electrode. The morphology of the obtained coatings was studied using scanning electron microscopy using a JSM-7001F microscope. It is shown that the use of fluoride ion activator and electrolytes of different nature allows at the initial stage of anodizing to provide conditions for the formation of a crystalline anodic oxide film with different surface morphology. By varying the anodizing regime on tantalum, it is possible to synthesize porous films of amorphous or crystalline types. To obtain a crystalline porous oxide of tantalum with a developed surface, it is advisable to use an organic aprotic electrolyte composition: EG + 5.5 М H2O + 0.05 М H3PO4 + 0.8 М NH4F.

Electrochemical Oxidation of a Heavy Tungsten-Containing VNZh-Type Alloy and Its Components in Ammonia–Alkali Electrolytes

Linear voltammetry in the potentiodynamic mode is used to study the electrochemical behavior of a heavy tungsten-containing VNZh alloy (in wt %: 90 W, 7 Ni, 3 Fe) and its components in ammonia–alkali electrolytes. The anodic oxidation of individual tungsten and nickel is found to be activated when NH4OH is introduced into the composition of an alkaline electrolyte. Galvanostatic electrolysis is used to perform electrochemical processing of a VNZh-type alloy with a current efficiency of about 100% for tungsten and a specific energy consumption of ~1.5 kW h/kg.

1D Mathematical Modelling of Non-Stationary Ion Transfer in the Diffusion Layer Adjacent to an Ion-Exchange Membrane in Galvanostatic Mode.

The use of the Nernst–Planck and Poisson (NPP) equations allows computation of the space charge density near solution/electrode or solution/ion-exchange membrane interface. This is important in modelling ion transfer, especially when taking into account electroconvective transport. The most solutions in literature use the condition setting a potential difference in the system (potentiostatic or potentiodynamic mode). However, very often in practice and experiment (such as chronopotentiometry and voltammetry), the galvanostatic/galvanodynamic mode is applied. In this study, a depleted stagnant diffusion layer adjacent to an ion-exchange membrane is considered. In this article, a new boundary condition is proposed, which sets a total current density, i, via an equation expressing the potential gradient as an explicit function of i. The numerical solution of the problem is compared with an approximate solution, which is obtained by a combination of numerical solution in one part of the diffusion layer (including the electroneutral region and the extended space charge region, zone (I) with an analytical solution in the other part (the quasi-equilibrium electric double layer (EDL), zone (II). It is shown that this approach (called the “zonal” model) allows reducing the computational complexity of the problem tens of times without significant loss of accuracy. An additional simplification is introduced by neglecting the thickness of the quasi-equilibrium EDL in comparison to the diffusion layer thickness (the “simplified” model). For the first time, the distributions of concentrations, space charge density and current density along the distance to an ion-exchange membrane surface are computed as functions of time in galvanostatic mode. The calculation of the transition time, τ, for an ion-exchange membrane agree with an experiment from literature. It is suggested that rapid changes of space charge density, and current density with time and distance, could lead to lateral electroosmotic flows delaying depletion of near-surface solution and increasing τ.

INFLUENCE OF ALKALINE – EARTH METALS ON ANODIC BEHAVIOR OF ALLOY ССУЗ IN NEUTRAL ENVIRONMENT OF THE ELECTROLYTE NaCl

The anodic behavior of a lead-antimony alloy (3 wt% Sb) doped with alkaline-earth metals was investigated in potentiostatic method in the potentiodynamic mode at a potential sweep rate of 2 mV/s and it was shown that with an increase in the content of alkaline earth metals in the alloy (SSUZ), the potentials of free Corrosion and pitting are slightly shifted to the positive region. As the concentration of the chloride ion in the electrolyte increases, these potentials decrease. The current density of corrosion and, accordingly, the corrosion rate of alloys with an increase in the content of alkaline earth metals are reduced by 75–85%, and the concentration of chloride ion increases.In transition from alloys with calcium to alloys with strontium, the corrosion rate of alloys increases by 20–30%, and to alloys with barium it decreases by 25–30%.

Comparison of the Tendency to Pitting Corrosion of Casting of Al6Ca, Al1Fe, and Al6Ca1Fe Experimental Alloys and AK12M2 Industrial Alloy

The electrochemical and corrosion behavior of four alloys (wt %) is investigated: Al–6Ca (further Al6Ca), Al–6Ca–1Fe (further Al6Ca1Fe), Al–1Fe (further Al1Fe), and Ak12M2. An increased iron content (up to 1%) in alloys is necessary for the high productivity of casting under pressure. Electrochemical studies are performed in a 3% aqueous NaCl solution at 26 ± 0.5°C using an IPC-Pro 3A digital potentiostat (IPC-2000). Anodic polarization is performed in a potentiodynamic mode with a potential scan rate of 1 mV/s. The initial polarization potential is–800 mV with respect to the standard hydrogen electrode. The direction of the potential scan was changed to inverse upon the “critical” current density icr = 10 mA/cm2 performing polarization with the same rate. The tendency of the alloy to form pits was judged by the ratio of amounts of electricity that passed through the electrode before pitting formation and their repassivation (Qfor/Qinv) and values of pitting resistance bases: the difference in the pitting formation potential and stationary potential and the difference in the repassivation potential and stationary potential. Corrosion tests of casting aluminum alloys were performed holding the samples in a salt fog chamber and in a 3% aqueous NaCl solution for 700 h. After these holdings, the surface morphology of the samples was investigated using an Olympus GX51 optical microscope. It is established that Al6Ca1Fe and Al6Ca experimental alloys, in contrast to the AK12M2 industrial alloy and Al1Fe alloy, are not subjected to pitting corrosion in a 3% aqueous NaCl solution. It is assumed that the increased corrosion resistance of Al6Ca1Fe alloy is caused by the fact that iron enters the Al10CaFe2 intermetallic compound, which is not an efficient cathode because of the considerable negative potentials of Al and Ca. Due to the high casting and mechanical properties of the Al6Ca1Fe alloy, which are no worse than the properties of eutectic silumin and surpass them by the corrosion resistance, the Al6Ca1Fe alloy is promising for use in an industrial scale.

Electrochemical cell with the reversible electrode–solid electrolyte or ionic melt interface in galvanodynamic and potentiodynamic operating modes

This work is aimed at studying the kinetics of the following two simultaneous processes: charging of the double electrical layer and the charge transfer at the reversible silver electrode–sulfate solid electrolyte or corresponding ionic melt interface in two operating modes of electrochemical cell, namely, galvanodynamic and potentiodynamic ones. The electrochemical kinetics has been studied by the method of operational impedance based on the Ohm law of interaction between Laplace transformed current, voltage, and complex resistance (impedance). Using appropriate mathematical calculations, analytical expressions are obtained for the current passing via a cell during linear potential scanning (potentiodynamic mode) as a function of time and for the interface potential as a function of time in the galvanodynamic mode (linear current scanning). The time dependence of the potential of the electrode–solid electrolyte or ionic melt interface is described by an exponential function in the potentiodynamic mode of the cell operation. An analysis and comparison of the results of the two independent electrochemical modes demonstrate that the behavior of the electrochemical cells containing a reversible metallic electrode, i.e., a solid electrolyte or the corresponding ionic melt, obeys the classical Randles–Ershler equivalent circuit. This statement can be proved by both the alternating current method (impedance method) and relaxation galvanodynamic and potentiodynamic methods (linear scanning of potential and current).

Microstructure and corrosion behavior of electrodeposited Ni-based nanocomposite coatings reinforced with Ni60Cr10Ta10P16B4 metallic glass particles

Ni-based nanocomposite coatings reinforced with Ni60Cr10Ta10P16B4 metallic glass powders have been successfully deposited by a direct current electrodeposition method in a typical Watt's bath. The effect of the glassy particles content on the microstructure, micro-hardness and corrosion behavior of the coatings have been evaluated. The structural investigations have been conducted by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The corrosion behavior of the coatings has been investigated in a 3.5 wt % NaCl solution by a potentiostat-galvanostat device in the potentiodynamic polarization mode. The composite coatings with the negligible amounts of porosity and crack, homogeneous distribution of the glassy particles, and appropriate bonding at the matrix/reinforcement interface are obtained. The results demonstrate that the crystallographic texture and surface morphology of the coatings are significantly changed by the addition of the glassy particles into the bath. A minimum matrix crystallite size of 31 nm and maximum glassy particles incorporation of about 6.4 vol% are obtained for the particles concentration of 10 g/L in the deposition bath. The microhardness of the coating is enhanced with increasing the content of the reinforcing particles in the bath and reaches a maximum value of 475 HV for the particles concentration of 10 g/L. Moreover, the corrosion current density and corrosion rate are significantly reduced from 2.25 μA/cm2 and 0.958 MPY for the pure Ni coating to 0.05 μA/cm2 and 0.021 MPY for the nanocomposite coating.

Ultrathin Mesoporous RuCo2 O4 Nanoflakes: An Advanced Electrode for High-Performance Asymmetric Supercapacitors.

A new ruthenium cobalt oxide (RuCo2 O4 ) with a unique marigold-like nanostructure and excellent performance as an advanced electrode material has been successfully prepared by a simple electrodeposition (potentiodynamic mode) method. The RuCo2 O4 marigolds consist of numerous clusters of ultrathin mesoporous nanoflakes, leaving a large interspace between them to provide numerous electrochemically active sites. Strikingly, this unique marigold-like nanostructure provided excellent electrochemical performance in terms of high energy-storage capacitance (1469 F g-1 at 6 A g-1 ) with excellent rate proficiency and long-lasting operating cycling stability (ca. 91.3 % capacitance retention after 3000 cycles), confirming that the mesoporous nanoflakes participate in the ultrafast electrochemical reactions. Furthermore, an asymmetric supercapacitor was assembled using RuCo2 O4 (positive electrode) and activated carbon (negative electrode) with aqueous KOH electrolyte. The asymmetric design allowed an upgraded potential range of 1.4 V, which further provided a good energy density of 32.6 Wh kg-1 (1.1 mWh cm-3 ). More importantly, the cell delivered an energy density of 12.4 Wh kg-1 even at a maximum power density of 3.2 kW kg-1 , which is noticeably superior to carbon-based symmetric systems.