Electroreduction Of Ions Research Articles

Electrochemical behaviour of selenite ions in tartaric electrolytes

<span lang="EN-GB">In recent years, a great interest has been emerged on electrochemical preparation of semiconductor films based on selenium. Therefore, a study of electrochemical reduction of selenium could be very important. In this work, the kinetics and mechanism of the electrochemical reduction of selenite ions on the Pt cathode have been studied in the electrolyte containing selenious and tartaric acids. The study shows that electroreduction of selenite ions from tartaric electrolytes proceeds in two stages. The effect of various factors on the cathodic reduction of selenium ions has also been studied. The effective activation energy was calculated using the polarization curves of the temperature dependence of the electroreduction process of selenite ions. It was established that the process of electroreduction under investigation is proceeding by mixed kinetics, at first by concentration and then by electrochemical polarization.</span>

Synthesis of nickel entities: From highly stable zerovalent nanoclusters to nanowires. Growth control and catalytic behavior

Non-noble metal nanoclusters synthesis is receiving increased attention due to their unique catalytic properties and lower cost. Herein, the synthesis of ligand-free Ni nanoclusters with an average diameter of 0.7 nm corresponding to a structure of 13 atoms is presented; they exhibit a zero-valence state and a high stability toward oxidation and thermal treatment. The nanoclusters formation method consists in the electroreduction of nickel ions inside an ordered mesoporous alumina; also, by increasing the current density, other structures can be obtained reaching to nanowires of 10 nm diameter. A seed-mediated mechanism is proposed to explain the growth to nanowires inside these mesoporous cavities. The size dependence on the catalytic behavior of these entities is illustrated by studying the reduction of methylene blue where the nanoclusters show an outstanding performance.

Experimental and Theoretical Studies of Anionic Surfactants Activity at Metal/Solution Interface: The Influence of Temperature and Hydrocarbon Chain Length of Surfactants on the Zinc Ions Electroreduction Rate

Abstract The effect of concentration of two anionic surfactants sodium 1-octanesulfonate and sodium 1-decanesulfonate in the temperature range 288–318 K on the kinetics and mechanism of electroreduction of Zn2+ ions was studied using electrochemical impedance spectroscopy (eis) and other electrochemical methods. It was found that the process of electroreduction proceeds in two steps. To describe the mechanism of Zn2+ amalgamation, the Fawcett’s models were considered: CE (chemical step C, electron transfer step E), IE (ion transfer step I, electron transfer step E) and IA (ion transfer step I, adsorption step A). The results of theoretical investigations suggest that the IE model is the most probable mechanism of the process. Both surfactants were found to exert a catalytic effect on the analyzed electrode process. The accelerating abilities of the surfactants were found to increase with the growth of the length of their hydrocarbon chain and with the increase of temperature. The observations concerning the mechanism of the electrode reaction and its acceleration caused by surfactants were confirmed by the parameters calculated from temperature dependencies.

Erratum to: Generalized Nernst Layer Model for Convective-Diffusion Transport. Numerical Solution for Bromate Ion Electroreduction on Inactive Rotating Disk Electrode under Steady State Conditions

Erratum to: Generalized Nernst Layer Model for Convective-Diffusion Transport. Numerical Solution for Bromate Ion Electroreduction on Inactive Rotating Disk Electrode under Steady State Conditions

Electrolytic synthesis of carbon from the captured CO2 in molten LiCl–KCl–CaCO3: Critical roles of electrode potential and temperature for hollow structure and lithium storage performance

In the present study, CaCO3-containing molten LiCl–KCl under CO2 atmosphere was investigated as the electrolyte for the preparation of electrolytic carbon. Varying the electrode potential and electrolysis temperature can manipulate the kinetics of the electro-deposition reaction of carbon, thereby allowing the formation of the carbon products with different morphologies. At 450 °C, high yields of micron-sized hollow carbon spheres (HCSs) and ultrathin sheets were obtained under 2.8 and 3.5 V cell voltages, respectively. At higher temperatures (550 and 650 °C) and cell voltages, the content of carbon sheets decreased, and various carbon materials, such as quasi–spherical particles, coral–like carbon and carbon nanofibers, could be observed. Micron-sized HCSs were only obtained with a moderate reaction rate (2.8 V and 450 °C), which allowed the occurrence of microbubble effect of the as-formed CO gas (one of the intermediates of electro-reduction of carbonate ions). The expansion of the CO gas shaped the plastic ultrathin carbon sheets, resulting in the formation of well-developed HCSs. Among the carbon products, the one deposited at 4.5 V and 650 °C exhibited the highest specific surface area of more than 400 m2 g−1, while the HCSs showed the best performance for lithium storage. The present study highlights the importance of manipulating electrode potential and working temperature to the preparation of value-added electrolytic carbon from the captured CO2 in molten salts.

Effects of Temperature and Thiourea Addition on the Electrodeposition of Tin on Glassy Carbon Electrodes in Acid Solutions

The electrodeposition of tin on glassy carbon electrodes was studied in plain and thiourea-containing sulphuric acid solutions at different temperatures. Voltammograms exhibit a single cathodic current peak related to the electroreduction of tin ions on the glassy carbon substrate. The current of this peak increases linearly with the square root of the scan rate in the absence of thiourea, as expected for an electrochemical reaction under diffusion control. However, with the addition of thiourea, the peak current exhibits a semi-logarithmic dependence. Electrodeposition current transients show always a single peak that increases its height and appears at shorter times as the electrode potential is made more negative. The non-dimensional analysis of the current transients suggests the occurrence of an instantaneous nucleation and 3D growth under diffusion control in thiourea-free solutions. When thiourea is added, the transient current peak shifts to longer times and the non-dimensional analysis agrees with the presence of a progressive nucleation process. Seemingly, thiourea adsorbs on the electrode surface blocking active sites. This is consistent with the changes observed in the morphology of tin deposits, which change from well-distributed small crystallographic particles in the absence of thiourea, to complex and larger ones that exhibit branches at 900, in the presence of thiourea. Nyquist plots exhibit only two time constants at open circuit conditions, while in the potential range of tin electrodeposition two capacitive contributions appear at high an medium frequencies, followed by an inductance, assigned to a surface relaxation process, and a Warburg contribution, associated with the transport of ions to the interface, at low frequencies.

An ultrasonic-assisted process for copper recovery in a des solvent: Leaching and re-deposition

The continuous growth of the electronic equipment market has led to an increased amount of scraping that it becomes necessary to recover. A hydrometallurgical method for copper and precious metal recovery from e-waste must consist of a number of steps: leaching, ion separation and subsequent electrochemical re-deposition of the target metal. Although this task is achievable in aqueous solutions, it requires strong acid or cyanide solutions.The aim of the study is to develop a new environmentally benign process by using a Deep Eutectic Solvent (DES), a form of cheap and safe ionic liquid, as an electrolyte for both leaching and electrodeposition.The experiments were conducted in a mixture of choline chloride and ethylene glycol, under 20kHz ultrasonic agitation. In optimized temperature and sonication conditions, the leaching rate of copper attains 65mg/hcm2. An interesting feature is that, in this media, copper dissolves into the form of Cu(I) complex instead of Cu(II) complex, so that subsequent electroreduction of copper ions is energetically more favorable. Copper deposits obtained from CuI-DES solution present a sand-rose cluster morphology inducing a large developed surface. Application of ultrasound during electrodeposition allows for grain size reduction and crystallographic texture modifications, compared to silent conditions.

The Catalytic Impact of Ethionine on the Multi-Step Electroreduction of Bi(III) Ions in Chlorates(VII) Solutions

It was concluded that the presence and the protonation of the ethionine (Et) have effects on the rate of the multi-step process of Bi(III) electroreduction in the 2 mol dm−3 chlorates(VII). The catalytic activity of ethionine increases with increasing amounts of NaClO4 in the basic electrolyte solution. Increased amounts of HClO4 in chlorate(VII) solutions causes a decreased rate of the Bi(III) ion electroreduction process in the presence of ethionine. This confirms the assumption on the variety of active complexes mediating the passage of electrons.Graphical ᅟ

Ruthenium Nanoparticles Mediated Electrocatalytic Reduction of UO22+ Ions for Its Rapid and Sensitive Detection in Natural Waters.

Reduction of UO22+ ions to U4+ ions is difficult due to involvement of two axially bonded oxygen atoms, and often requires a catalyst to lower the activation barrier. The noble metal nanoparticles (NPs) exhibit high electrocatalytic activity, and could be employed for the sensitive and rapid quantifications of U022+ ions in the aqueous matrix. Therefore, the Pd, Ru, and Rh NPs decorated glassy carbon electrode were examined for their efficacy toward electrocatalytic reduction of UO22+ ions and observed that Ru NPs mediate efficiently the electro-reduction of UO22+ ions. The mechanism of the electroreduction of UO22+ by the RuNPs/GC was studied using density functional theory calculations which pointed different approach of 5f metal ions electroreduction unlike 4p metal ions such as As(III). RuNP decorated on the glassy carbon would be hydrated, which in turn assist to adsorb the uranyl sulfates through hydrogen bonding thus facilitated electro-reduction. Differential pulse voltammetric (DPV) technique, was used for rapid and sensitive quantification of UO22+ ions. The RuNPs/GC based DPV technique could be used to determine the concentration of uranyl in a few minutes with a detection limit of 1.95 ppb. The RuNPs/GC based DPV was evaluated for its analytical performance using seawater as well lake water and groundwater spiked with known amounts of UO22+.

Copper Crystallization from Aqueous Solution: Initiation and Evolution of the Polynuclear Clusters

The initial steps of copper electrocrystallization process from aqueous solutions have been studied at DFT level of theory. It has been shown that Cu(H2O) unit is the final product of Cu2+-ions electroreduction. From this particle clusters Cun·aq are formed and grow. Aggregation of copper atoms to the Cun·aq clusters consists of two steps. The first step includes condensation of Cu(H2O) units to hydrated clusters Cun(H2O)n (n = 2–6). At the second step bonding of Cu(H2O) particles is accompanied by dehydration of clusters yielding Cun(H2O)m structures (n > m). Cluster Cu7·aq has been singled out as key structure based on calculated values of energies and Cu–Cu bond distances of Cun·aq clusters. This cluster is of D5h symmetry which is typical for copper microcrystals formed from aqueous solutions in electrocrystallization processes on foreign surface. This key particle could be considered as a critical nucleus. Number of copper atoms therein matches average dimension of critical nucleus.

Electrochemical Deposition of Carbon Prepared on Cu and Ni Cathodes in CaCl2-LiCl Melts

Various carbon materials, including carbon nanotubes and amorphous carbon, were successfully deposited on the nickel and copper cathodes during the electrolysis in the molten CaCl2-LiCl at 3.0 V and 600°C. CaO serving as trapping agent of CO2 was added before the electrolysis. Electrode reactions were investigated by cyclic voltammetry and chronoamperometry in a three-electrode cell. The results show that the electro-reduction of carbonate ions is dominated by carbon deposition on Ni electrode accompanied with partial evolution of CO, while, on the contrary, the generation of CO is more preferable than carbon deposition on Cu electrode. Electro-reduction of solid carbon were carried out in two-electrode cell and short-time electrolysis were applied to study the formation and growth of the varied carbon microstructure. The formation of carbon nanotubes may be attributed to the evolution of CO. With a SnO2 anode, O2 gas was produced during the electrolysis.

Electrochemical Synthesis of Polypyrrole, Reduced Graphene Oxide, and Gold Nanoparticles Composite and Its Application to Hydrogen Peroxide Biosensor

Here we report a facile eco-friendly one-step electrochemical approach for the fabrication of a polypyrrole (PPy), reduced graphene oxide (RGO), and gold nanoparticles (nanoAu) biocomposite on a glassy carbon electrode (GCE). The electrochemical behaviors of PPy–RGO–nanoAu and its application to electrochemical detection of hydrogen peroxide were investigated by cyclic voltammetry. Graphene oxide and pyrrole monomer were first mixed and casted on the surface of a cleaned GCE. After an electrochemical processing consisting of the electrooxidation of pyrrole monomer and simultaneous electroreduction of graphene oxide and auric ions (Au3+) in aqueous solution, a PPy–RGO–nanoAu biocomposite was synthesized on GCE. Each component of PPy–RGO–nanoAu is electroactive without non-electroactive substance. The obtained PPy–RGO–nanoAu/GCE exhibited high electrocatalytic activity toward hydrogen peroxide, which allows the detection of hydrogen peroxide at a negative potential of about −0.62 V vs. SCE. The amperometric responses of the biosensor displayed a sensitivity of 40 µA/mM, a linear range of 32 µM–2 mM, and a detection limit of 2.7 µM (signal-to-noise ratio = 3) with good stability and acceptable reproducibility and selectivity. The results clearly demonstrate the potential of the as-prepared PPy–RGO–nanoAu biocomposite for use as a highly electroactive matrix for an amperometric biosensor.

Composite of Cu metal nanoparticles-multiwall carbon nanotubes-reduced graphene oxide as a novel and high performance platform of the electrochemical sensor for simultaneous determination of nitrite and nitrate

In the present research, we aimed to fabricate a novel electrochemical sensor based on Cu metal nanoparticles on the multiwall carbon nanotubes-reduced graphene oxide nanosheets (Cu/MWCNT/RGO) for individual and simultaneous determination of nitrite and nitrate ions. The morphology of the prepared nanocomposite on the surface of glassy carbon electrode (GCE) was characterized using various methods including scanning electron microscopy (SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy. Under optimal experimental conditions, the modified GCE showed excellent catalytic activity toward the electro-reduction of nitrite and nitrate ions (pH=3.0) with a significant increase in cathodic peak currents in comparison with the unmodified GCE. By square wave voltammetry (SWV) the fabricated sensor demonstrated wide dynamic concentration ranges from 0.1 to 75μM with detection limits (3Sb/m) of 30nM and 20nM method for nitrite and nitrate ions, respectively. Furthermore, the applicability of the proposed modified electrode was demonstrated by measuring the concentration of nitrite and nitrate ions in the tap and mineral waters, sausages, salami, and cheese samples.

The effects of homocysteine protonation on double layer parameters at the electrode/chlorates (VII) interface, as well as the kinetics and the mechanism of Bi (III) ion electroreduction

The influence of homocysteine on double layer parameters at the electrode/chlorates (VII) interface and multi-step Bi (III) ion electroreduction was investigated using both voltammetry and impedance methods. The catalytic activity of homocysteine increases with an increasing amount of NaClO4 in a basic electrolyte solution. The highest catalytic activity of homocysteine was observed for 2mol·dm−3 chlorates (VII). The multistage process is confirmed by the not rectilinear lnkf=f(E) dependences. In this mechanism, the chemical stages of Bi–Hg(SR)2 complexes formation with the participation of homocysteine, which is a mediator in the formation of these complexes, and water can be distinguished. The composition of these complexes is diversified in solutions that differ in the degree of amino acid protonation.

Studying the electrochemical deposition process of molybdenum from aqueous solution of molybdate ions

<span lang="EN-US">In this study, the tracing of the electroreduction process of molybdate ions in aqueous media at different conditions is achieved for obtaining molybdenum metal in a simple and easy way. The kinetics and the mechanism of the electroreduction of molybdate ions are studied using cathodic polarization technique. It is observed that, the speed of the electroreduction process depends on the speed of the change of the cathodic potential sweep as well as on the temperature of the electrodeposition bath. Moreover, it is observed that, at the potential range from the stationary potential (E<sub>st</sub> = 0.25V) to −0.7 V, the electroreduction of molybdate ions occurs into two steps. Moreover it is observed that, after −0.7 V the electroreduction process of molybdate is accompanying with evolution of hydrogen.</span>

Growth of single gold nanofilaments at the apex of conductive atomic force microscope tips.

This paper describes a fast and one-step technique to grow single gold filaments at the apex of commercial conductive AFM tips. It is implemented with an atomic force microscope in air with a high relative humidity at room temperature and is based on a bias-assisted electro-reduction of gold ions directly at the tip apex. The technique requires only ad hoc substrates made of a mesoporous silica layer loaded with gold salt deposited on a conductive electrode. It leads to the growth, at the tip apex, of filaments whose length can be monitored and controlled during the growth between tens and hundreds of nanometers and whose radius of curvature can be as low as 3 nm. Made of polycrystalline gold nanostructures, the filaments are chemically and mechanically stable and conductive.

Electrochemical Extraction of Tungsten Derived from WC Scrap and Electrochemical Properties of Tungsten Ion in LiCl-KCl Molten Salt

Tungsten carbide (WC) scrap was used as a consumable anode to produce metallic tungsten in LiCl-KCl molten salts at 773 K. The feasibility of direct electrochemical dissolution of the WC anode to metallic tungsten was analyzed by thermodynamic calculations and experimental verifications. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were applied to investigate the dissolution of the WC anode, and the electrochemical properties of the issued tungsten ions in LiCl-KCl melts were studied by cyclic voltammetry (CV), square wave voltammetry, and chronopotentiometry. The results revealed that the WC anode could be used as a consumed anode to produce tungsten powder and the electroreduction of tungsten ions in the melts was achieved through a one-step reaction involving four exchanged electrons. Furthermore, it was found that the reaction was limited by the diffusion of tungsten ions in the solution with a diffusion coefficient estimated as 5.9 × 10−7 cm2/s at 773 K. Finally, analysis of the cathode products using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and energy dispersive spectroscopy (EDS) showed that tungsten powders could be prepared from a molten salt bath.

Electroreduction of yttrium ions in an equimolar NaCl–KCl molten mixture

The behavior of yttrium ions in an equimolar NaCl–KCl melt is studied in a temperature range of 973–1123 K using cyclic voltammetry at an inert electrode containing 5 wt % YCl3 in the range of potential sweep rates from 0.02 to 0.2 V/s. A cathodic reaction proceeds via the scheme Y(III) + 3e = Y. The diffusion coefficients of yttrium ions are determined, and the activation energy of the diffusion of yttrium ions is estimated.

Hybrid electrode materials based on ion-exchange matrix containing copper nanoparticles and carbon fibers for the electroreduction of nitrate ions

Copper-containing composite electrodes have been obtained by the chemical deposition of copper into the film on an electrode composed of an ion-exchange matrix and carbon fibers. The size of copper particles determined by X-ray diffraction analysis amounts to 23–29 nm and is not practically changed with a growth in the copper concentration in the electrode material. The active area of the surface of copper particles is determined electrochemically using the underpotential electrodeposition of lead ions. It is shown that the rate of electrochemical reduction of nitrate ions increases with the concentration of copper particles and reaches its maximum at 90 μg/cm2. The electroreduction of nitrate ions proceeds in the mode of mixed kinetics and is an irreversible process.

(Invited) Electrochemical CO2 Reduction By Violarite (FeNi2S4) As a Prebiotic Core of Carbon Monoxide Dehydrogenase

The discovery of deep-sea hydrothermal vents on the late 1970’s has led to many hypotheses concerning chemical evolution in the prebiotic ocean. Such studies are motivated by the desire to understand microbial ecosystems which are isolated from energy input from photosynthesis and thereby sustained by geochemical energy sources, such as H2S and H2, emitted from hydrothermal vents. Simultaneously, the continuous emission and mineralization of strongly reducing iron sulfides (pirite and greigite etc) in hydrothermal environments leads to the “iron-sulfur world” concept, an idea that the surface of iron sulfides with trace metals such as Ni, Cu, and Mo in the vicinity of hydrothermal vents played an extensive role in prebiotic CO2reduction on the early Earth. To deepen understanding of prebiotic CO2 reduction, we have examined geochemical processes associated with iron sulfides from the view point of the electrochemical functionalities. In 2010, we obtained a portion of mineral crust from the Mariner hydrothermal field in Black smoker chimney, and found that natural minerals themselves display an excellent metallic electrical conduction over a 10-cm distance and promotes electrocatalytic oxidation of H2S and H2 as well as electroreduction of O2 and ferric ions. [1] This finding promptly led us to propose the new type of CO2 reduction and carbon assimilation in the deep floor. Namely, not only the reductive chemicals such as H2 and H2S emitted from hydrothermal vents, but the high-energy electrons directly delivered from hot reduced hydrothermal trigers the electrocatalytic CO2 reduction with the same operation principal of an electrochemical fuel cell. [1-3] To confirm the validity of this hypothesis, here, we examined the energetics of electrocatalytic CO2 reduction by iron sulfide (FeS) at slightly acidic pH. Our analyses demonstrated that FeS functions as efficient electrocatalysts for CO2 reduction upon the substitution of Fe with Ni to form FeNi2S4, and that the faraday efficiency for CO2 reduction is further increased by modification of the catalytic surface with amine compounds. [3] These findings are consistent with the concept that Ni/greigite serves as a prebiotic catalyst for CO2 reduction due to its structural similarity with the catalytic centers of carbon monoxide dehydrogenase (CODH) enzyme. [4] Thus, the findings in the present study are expected to provide great insights into the electron conduction and electrocatalytic functions of bisulfide-bearing hydrothermal for triggering and maintaining the electrosynthesis of organic compounds prior to the emergence of the primordial living forms.