Cathodic Transfer Research Articles

Delivering protons with electrons

Electrochemistry Many chemical reactions involve concurrent transfer of a proton and an electron. In electrochemical synthesis, this mechanism could prove useful in lowering the energy necessary for cathodic electron transfer alone, but it is hindered by competing direct coupling of the protons and electrons to make hydrogen instead. Chalkley et al. now report a molecular mediator consisting of a dimethylaniline base tethered to a cobaltocenium electron acceptor. This construct can deliver both a proton and an electron to a substrate from an acid and a cathode while skirting the hydrogen pathway. Science , this issue p. [850][1] [1]: /lookup/doi/10.1126/science.abc1607

Electricity generation from paddy soil for powering an electronic timer and an analysis of active exoelectrogenic bacteria

In farmlands, most electronic devices have no connection to a power source and have to work on batteries. To explore paddy soil as an in situ power source, herein, we in the present study constructed sediment microbial fuel cells (SMFCs) in paddy soil. An open circuit voltage of 1.596 V and a maximum power density of 29.42 mWm−2 were obtained by serially connecting three SMFCs. Electrochemical impedance spectroscopy showed that the internal resistance which comprised ohmic resistance and anodic and cathodic charge transfer resistance was approximately 400 Ω for each of the three individual SMFCs. We used the serially connected SMFCs to power an electronic timer through a 1 F capacitor. The SMFCs had powered the timer for 80 h until the potential of the SMFCs dropped below 0.936 V. Then, RNA was extracted from anode samples and 16S rRNA was sequenced following reverse transcription. The results showed that the relative abundance of active exoelectrogenic bacteria-associated genera on the anode was 13.03%, 27.78%, and 16.17% for the three SMFCs with Geobacter and Anaeromyxobacter being the dominant genera. Our findings provide the possibility of powering electronic devices in the field by using soil as a power source.

Dual kinetic curves in reversible electrochemical systems

We introduce dual kinetic chronoamperometry, in which reciprocal relations are established between the kinetic curves of electrochemical reactions that start from symmetrical initial conditions. We have performed numerical and experimental studies in which the kinetic curves of the electron-transfer processes are analyzed for a reversible first order reaction. Experimental tests were done with the ferrocyanide/ferricyanide system in which the concentrations of each component could be measured separately using the platinum disk/gold ring electrode. It is shown that the proper ratio of the transient kinetic curves obtained from cathodic and anodic mass transfer limited regions give thermodynamic time invariances related to the reaction quotient of the bulk concentrations. Therefore, thermodynamic time invariances can be observed at any time using the dual kinetic curves for reversible reactions. The technique provides a unique possibility to extract the non-steady state trajectory starting from one initial condition based only on the equilibrium constant and the trajectory which starts from the symmetrical initial condition. The results could impact battery technology by predicting the concentrations and currents of the underlying non-steady state processes in a wide domain from thermodynamic principles and limited kinetic information.

Cathodic Aromatic C,C Cross-Coupling Reaction via Single Electron Transfer Pathway.

We have successfully developed a novel cathodic cross-coupling reaction of aryl halides with arenes. Utilization of the cathodic single electron transfer (SET) mechanism for activation of aryl halides enables the cross-coupling reaction to proceed without the need for any transition metal catalysts or single electron donors in a mild condition. The SET from a cathode to an aryl halide initiates a radical chain by giving an anion radical of the aryl halide. The following propagation cycle also consists entirely of anion radical intermediates.

Voltammetric Investigation of Iron(III) Interactions with Phytate

ABSTRACT The electrochemical behavior of Fe(III) in the presence of phytate ligand was investigated by cyclic voltammetry on the polycrystalline gold and mercury drop electrodes in the pH range between 1.5 and 10, and ligand to metal molar ratio from 0 to 20. Complexation of Fe(III) and Fe(II) by phytate ligand (L) reflects in (i) shift of the formal potential E 0′ of the Fe(III)/Fe(II) redox couple into the negative direction, and (ii) an increased irreversibility of the redox processes. Change of the formal potential originate from higher stability of the Fe(III)L complex with respect to Fe(II)L complex, however, due to the slow charge transfer control of the redox processes apparent stability constants calculated from voltammetric data may lead to an overestimation of their true values. Irreversible reduction of Fe(III)L to Fe(II)L is diffusion controlled and involves one proton per one electron on both electrodes. Reduction of Fe(III) phytate complex to Fe(II)L depends on the pH and at pH III H 5 L] 4– species, but at higher pH less protonated [Fe III H 3 L] 6– become the major reacting species. An almost stepwise change of the reduction peak potential for more than 0.8 V into the negative direction around pH 5 indicate that both reactants have quite different stability and/or structure. We predicted that electronic configuration and affinity of Fe(III) ions for the octahedral coordination induce the inversion of phytate ligand from its equatorial to the axial conformation which form more than ten orders of magnitude more stable Fe(III)L complexes. Fe(II)L intermediate generated on the electrode is strongly adsorbed on both gold and mercury electrodes, and totally irreversible reduction of Fe(II)L complex to the Fe metal was observable at mercury electrode as well. From Fe(III/II)L peak analysis on the mercury electrode the cathodic charge transfer coefficient of 0.68 was found, for [Fe III H 3 L] 6– reacting species the diffusion coefficient of (9.1 ± 0.1) × 10 −7 cm 2 /s was estimated, and the rate constant k 0 of 7.8 × 10 −5 cm/s was calculated.

Electrochemical Interaction of a Heterotrophic Bacteria Alcaligenes faecalis with a Graphite Cathode

This study focused on the electrochemical interaction between a heterotrophic bacterium, Alcaligenes faecalis and a graphite cathode. The growth of Alcaligenes faecalis on the cathode surface was found to be stimulated by applying a polarization potential of −0.25 V (vs. SCE) to the cathode. Environmental scanning electron microscope (ESEM) showed a significant increase of the bacterial population on the poised-potential electrode and a notable change of the bacterial morphology from short rod to unusual long rod shape. Cyclic voltammetry (CV) curves of the biofilm-attached electrode showed two reductive peaks at around 0.4 V and −0.35 V vs. SCE, which were assigned to the redox potentials of outer membrane cytochromes and attached metabolites, respectively. Electrochemical impedance spectroscopy (EIS) indicated the attachment of active Alcaligenes faecalis reduced the charge transfer resistance of the electrode. The results conclusively indicated that both the bacteria and the metabolites on the electrode were involved in the electrochemical reactions, and Alcaligenes faecalis was bioelectrochemically active in cathodic electron transfer process.

Electrochemical Study of the Additive-Effect on Sn Electrodeposition in a Methansulfonate Acid Electrolyte

The effect of three organic additives in stannous methanesulfonate baths on cathodic overpotential and Faradaic impedance of tin-electrodeposition were studied by measuring cathodic polarization curves, galvanostatic responses and electrochemical impedance spectroscopy. The results show that the composite additive consisting of three organic compounds can significantly increase the cathodic polarization, crystallization overpotential and charge transfer resistance, which is very beneficial to improve coating quality and result in a fine-grained and smooth matt tin coating.

Kinetics of Zn cathodic deposition in alkaline zincate solution

Kinetic parameters of the electrode reactions were measured by investigating steady-state current-potential behaviors. The Tafel slopes of cathodic and anodic processes are −0.113 8 V and −0.041 18 V, the anodic and cathodic apparent transfer coefficients are 0.519 3 and 1.435 2, respectively, and the stoichiometric number of rate-determining step is 1. The theoretical kinetics equation of electrode reaction was deduced, from which the dynamic parameters can be calculated as follows: the cathodic and anodic Tafel slopes are −0.118 V and −0.039 4 V, respectively, consisting with the experimental values. Finally, the correctness of the mechanism was further demonstrated using apparent transfer coefficient according to the electrochemical dynamic equation of multi-electron reaction.

Electrode kinetics in cyanide silver-plating electrolytes at different surface coverages by lead adatoms

Effective values of exchange current i0, cathodic and anodic transfer coefficients α and β, and cathodic and anodic reaction orders with respect to cyanide ions (Pc, Pa) are measured in cyanide silver-plating electrolytes at different surface coverages by lead adatoms θ. With increasing coverage, i0 and α increase from 5 × 10−5 A cm−2 and 0.24 in pure solutions to 8 × 10−5 A cm−2 and 0.3 at θ = 0.4, with Pc and Pa hardly altering. The cathodic process markedly accelerates at θ = 0.6, while at θ ≃ 0.5 the kinetics of the cathodic process is unstable. Different effects of lead adatoms on cathodic and anodic gold and silver plating in cyanide solutions are due to lead salts not affecting the metal substrate dissolution mechanism in the latter case.

Relationship between Erosion and Mechanical Characteristics of Fine-Grained Hard Alloy WC – 16% Co Obtained by Solid-Phase and Liquid-Phase Consolidation. Part 2. Mass Transfer (Cathode Mass Gain and Transfer Coefficient)

We investigate the erosion characteristics of hard alloys in spark alloying and their relation to the physical and mechanical properties. The WC – 16% Co alloys used were made by traditional vacuum sintering in the temperature range 950-1350°C or by sintering with subsequent high-energy treatment under pressure at the same temperatures. We show that how efficiently protective hard alloy coatings are formed on the substrate depends in more than one way on the porosity and the bending strength, definitely depends on the cracking resistance of the alloys, but is most clearly related to the resistivity which in turn is determined by the quality of the phase and grain boundaries. In addition, a linear relationship exists between the cathode mass gain, the transfer coefficient, and the erosion of the anode material. We demonstrate experimentally that the erosion resistance of hard alloys is a structure-sensitive characteristic to the extent that the structural factors affect the resistance.

Electrochemical corrosion kinetics of tin and tin amalgams in NaCl aqueous solutions

Electrochemical techniques were used to determine the corrosion rate of pure tin metal as compared to 80 Sn/20 Hg tin amalgam. X-ray diagrams showed that this amalgam was a crystalline γ2 phase, whereas a 50 Sn/50 Hg amalgam contained liquid alloy embedded in the same γ2 phase. Open circuit potential measurements, combined with narrow range potential scanning voltammetry, lead to the conclusion that amalgamation resulted in enhancement of the corrosion current, mainly by increasing the cathodic electron transfer reaction kinetics both in deaerated and in oxygen-saturated NaCl solution. When maintained at zero current potential in a solution containing dissolved O2 gas, the samples were gradually covered with an insulating oxide layer which was identified by a series of electrochemical impedance diagrams recorded at different time intervals. The oxide layer was firmly adherent to the bulk tin metal but was poor at protecting the amalgam electrode. Finally, at potential values where the anodic current reached a few mA/cm2, the pure tin metal surface was suddenly deteriorated by the formation of extremely deep pinhole corrosion pits, while this effect was smoothed down by amalgamation.

Polarization phenomena at the metal/proton conducting electrolyte interphase

The electrokinetics at the H2 - Pd/SrCe0.95Yb0.05O3−α interphase are presented. Current-overpotential (I-η) curves were obtained at 400–700 °C and at hydrogen partial pressures from 1 kPa to 100 kPa, using a three electrode single chamber cell. The present data were assumed to be free of mass transfer effects. The anodic and cathodic charge transfer coefficients as well as the exchange current density were calculated from the experimental results by using the Butler-Volmer equation. The high and low field approximations were used to simplify the analysis.

Effect of particles on Polarization during Electrocodeposition using a Rotating Cylinder Electrode

The influence of suspended submicrometric diameter alumina particles on polarization during electrocodeposition with copper at a rotating cylinder electrode was investigated. Cathodic polarization and mass transfer experiments were conducted as a function of electrode rotational speed and particle loading.

Direct cathodic reduction of Leuco Sulfur Black 1 and Sulfur Black 1

The electrochemical activity of Leuco Sulfur Black 1 in alkaline solution is shown by the means of voltammograms of the dyestuff recorded in a flow cell. The voltammograms indicate the possibility for further dyestuff reduction by cathodic electron transfer. In batch electrolysis experiments successful reduction of Leuco Sulfur Black 1 was achieved using a multi cathode cell. Applying similar experimental conditions cathodic reduction of the insoluble oxidized dyestuff Sulfur Black 1 was achieved. In a first step the dispersed Sulfur Black 1 is reduced to give an alkaline soluble form of the dyestuff that can be reduced further to yield Leuco Sulfur Black 1. Analogous to the electrochemical behaviour of technically produced Leuco Sulfur Black 1, which contains reducing agents, the solution of Leuco Sulfur Black 1 formed by electrolysis is able to undergo further cathodic electron transfer. The cathodic dyestuff reduction is of importance for the development of sulfur dyeing processes which do not require addition of reducing chemicals.

Transient methods: comparison of three methods employing the Cd2+|Cd(Hg) couple

Abstract A combination of three transient techniques (coulostatic, modified coulostatic and galvanostatic) has been applied for the study of the electrode reaction in aqueous solution, 1 M Na2SO4, pH 4. The techniques are applied under optimal conditions as determined by the information content curves. The modified coulostatic method, for which charging is performed by a galvanostatic pulse of a width of several τc, has been applied for the first time. The classical coulostatic method has not been applied in its pure form, i.e. tp ⪡ τc, but with somewhat longer pulses and smaller current densities, in order to avoid saturation of the measuring device during the charging step, and the evaluation of the results was performed using the equation for the coulostatic method with finite pulse width, derived for the modified coulostatic method. The three methods complement each other: with the classical coulostatic method the optimization of the experimental conditions is simplest; the modified coulostatic method ensures the highest accuracy in the determination of j0 and the galvanostatic method makes it possible to study the process on a longer time scale. With the three methods combined, the reaction can be studied in a time range of (1–40)τc or more, depending on the ratio of τ c τ d . A two-indicator electrode cell was used in order to increase the overpotential for which linearization of the overpotential/time plot is valid. The maximum value of the overpotential (not including IRs) was 6 mV. The exchange current density and the double layer capacitance were determined at different concentrations of Cd2+ and Cd(Hg). The stoichiometric number ν was estimated to be 1. Cathodic and anodic transfer coefficients were calculated and corrected for the diffuse-double-layer effect, according to Frumkin's theory. The transfer coefficients were found to be independent of temperature in the range 5–65 °C. αa = 1.59, αc = 0.23. The values corrected for diffuse double layer were found to be αo2 = 0a = 1.69, αo2 = 0c = 0.12. The values of the standard rate constant at 25 °C are: ksh = 0.026 cm s−1; ko2 = 0sh = 0.013 cm s−1. The standard enthalpy and entropy of activation are: ΔH≠ 0η = 0uncorr = 33 kJ mol−1, ΔH≠ 0η = 0corr = 32 kJ mol−1; ΔS≠ 0η = 0uncorr = 5 J (mol K)−1, ΔS≠ 0η = 0corr = −7 J (mol K)−1.

Problems of Anodic and Cathodic Mass Transfer in Copper Refining Electrolysis with Increased Current Density

AbstractFundamental problems of the impact of an increased current density on the conditions of mass transfer at the anode and the cathode are first discussed with special emphasis on the theoretical considerations of diffusion, natural convection and forced convection. An improved electro-chemical measurement technique using probe-type micro electrodes was employed to determine the Cu2+ concentration distribution in the boundary layers at the anode and the cathode. In the case of slime-covered anodes electrolyte sampling was carried out by means of capillaries introduced through bores. Resume Cet article discute des problemes fondamentaux associes a l’impact de l'augmentation de la densite de courant sur les conditions de transfert de matiere a l'anode et a la cathode, en insistant particulierement sur les considerations theoriques de la diffusion et de la convexion (naturelle et forcee). Une technique amelioree de mesure electrochimique, utilisant des microelectrodes de type sonde, a ete employee pour d...

ChemInform Abstract: Electroreductive “Barbier Type” Allylation of Imines with a Combination of a Pb(0)/Pb(II) Redox Mediator and Sacrificial Anode (Al).

Abstract An electroreductive “ Barbier Type ” allylation of imines with allyl bromide has been performed in a PbBr 2 /Bu 4 NBr/THF-(Al anode)-(Pt cathode) system. A combination of Pb(0)/Pb(II) redox and a sacrificial aluminum anode works as a mediator for both cathodic and anodic electron transfer processes, respectively.

Effect of anodically evolved gas bubbles on the rate of cathodic mass transfer in a vertical cylinder cell

Mass transfer coefficients were measured for the deposition of a copper from acidified copper sulphate solution at a vertical cylinder cathode stirred by oxygen evolved at a coaxial vertical cylinder lead anode placed upstream from the cathode and flush with it. The cathodic mass transfer coefficient was increased by a factor of 2.75–6.7 over the natural convection value depending on the rate of oxygen discharge at the lead anode and height of the cathode. The data were correlated by the equation:J=0.66(FrRe)−0.21

Effect of Heat Transfer on the Cathodic Polarisation of Steel in Saline Solution

AbstractAn apparatus is described for studying the effect of heat transfer on the cathodic polarisation of steel in flowing saline solutions.The effect of heat transfer on the diffusion-limited current for reduction of oxygen in 3·2% sodium chloride solution could be accounted for in terms of the effect of temperature at the metal/solution interface on the diffusion coefficient of oxygen.In sea water, the combined effect of cathodic polarisation and heat transfer enhanced the deposition of calcareous deposits on steel. Some implications of calcareous deposition on cathodic polarisation of steel are discussed.

Mass transfer characteristics of a novel gas-evolving electrochemical reactor

Mass transfer coefficients were measured for the deposition of copper from acidified copper sulphate solution at a vertical-plate cathode stirred by the oxygen evolved at a coplanar, vertical-plate lead anode placed upstream from the cathode. The variables studied were: oxygen discharge rate, electrolyte concentration and height of the cathode. The cathodic mass transfer coefficient was increased by a factor of the order of 2 to 5 over the natural convection value depending on the rate of oxygen discharge at the lead anode. The relationship between the mass transfer coefficient and the oxygen discharge rate was found to be logK=a+0.296 logV.