Chronopotentiometric Studies Research Articles

Anodic Reactions of Borohydride in Sodium Hydroxide Solutions

Borohydrides present interesting options for electrochemical power generation acting either as hydrogen sources or anodic fuels for direct borohydride fuel cells and batteries. Though there have been several papers concerning electrochemical determination of relevant thermodynamic and kinetic parameters to the borohydride system, there are a number of basic aspects that have not been yet systematically studied. This paper reports chronopotentiometric studies of the electrooxidation of sodium borohydride at a gold sphere electrode in 2 M NaOH solutions, at temperatures ranging from 25 to 65 ºC. Gold displayed a rather good borohydride oxidation activity, and the overall oxidation process was shown to be irreversible involving a number of electrons very close to the theoretically expected value of 8. The results suggested that the rate-determining step is an irreversible, diffusion controlled, one-electron oxidation step, for which the transfer coefficients were calculated.

Chronopotentiometric Study of the Electrooxidation of Borohydride Anion in Alkaline Medium

Borohydrides present interesting options for electrochemical power generation acting either as hydrogen sources or anodic fuels for direct borohydride fuel cells and batteries. Though there have been several papers concerning electrochemical determination of relevant thermodynamic and kinetic parameters to the borohydride system, a number of its basic aspects have not been yet systematically studied. In this paper we report chronopotentiometric studies of the electrooxidation of sodium borohydride at a gold sphere electrode in 2M NaOH solutions, at temperatures ranging from 25 to 55 °C. Gold displayed a rather good BH4 - oxidation activity, and the overall oxidation process was shown to be irreversible involving a number of electrons very close to the theoretically expected value of 8. The results suggested that the rate-determining step is an irreversible, diffusion controlled, one-electron oxidation step, for which the transfer coefficients were calculated.

Aluminium anodising in low acidity sulphate baths: growth mechanism and nanostructure of porous anodic films

Overall kinetic and chronopotentiometric studies were performed during Al anodising in H2SO4, 0–5% w/v, bath solutions pure and saturated by Al2(SO4)3. Peculiarities in film growth mechanism and nanostructure in these cases appeared, like significant differences of porosity and its dependence on film thickness, different critical current density above which pitting appears, salt deposition on pitted surface regions in saturated bath, etc. The different conditions inside pores are responsible for this behaviour like almost depletion of H+ during a long initial transient stage in the first case, supersaturation and formation of Al2(SO4)3 nanoparticle micelles on pore surface in the second case, etc. Differences in film growth mechanism also appeared between these and alike baths at higher acidity. Anodising in low acidity saturated baths shows superiority for growing low porosity films at specific conditions. New technologies may be suggested to produce optimal films of desired structure.

Electrochemical Behavior of Solid Lithium Manganate (LiMn2O4) in Aqueous Neutral Electrolyte Solutions

Lithium manganate (LiMn2O4) was synthesized by a very simple low-temperature solution combustion technique. The product was characterized for its phase formation and composition by X-ray diffraction and inductively coupled plasma spectroscopy. The electrochemical behavior of this material in aqueous neutral electrolyte solutions was investigated in an effort to find a means of making it a usable electrode material for rechargeable battery systems in aqueous electrolytes. Cyclic voltammetric and chronopotentiometric studies of solid LiMn2O4 immobilized on a paraffin-impregnated graphite electrode were carried out in various aqueous neutral electrolyte solutions. LiMn2O4 was shown to undergo reversible insertion of K+, Li+, and NH4+ ions from neutral electrolyte solutions. Energy-dispersive X-ray (EDX) detection of electrochemically treated LiMn2O4 proved the presence of the intercalated K+ ion. The intercalation of the K+ ion was partial, as is shown by the weight percent analysis of EDX detection results.

Concentration effect of the solutions for alumina template ac filling by metal arrays

The influence of the c Me z+ in acidic solutions of Cu, Ni, Co, and Sn salts on the amount of deposited metal, m Me, by ac electrolysis in the pores of various alumina templates grown in commonly used aluminium anodizing solutions of sulfuric, oxalic, phosphoric and chromo-boric acids was investigated. Behaviour of the porous alumina under ac voltage control manifests itself through m Me– c Me z+ parabola dependencies. The peaks of m Me– c Me z+ plots was found to be dependent on the alumina pore diameter, d p, and composition of the metal salt solution used. An increase in d p and decrease in a solution pH shifts m Me versus c Me z+ dependencies and the optimal c Me z+ toward smaller solution concentrations. From the results of the voltammetric and chronopotentiometric studies a surprisingly large value of a few seconds of the transition time for hydrogen ions discharge, occurring before the metal ion reduction at the bottom of alumina pores, was obtained. This result makes it reasonable to suggest that the amount of Me(OH) x , formed in the pore base region due to the hydrogen evolution from the acidic solutions with bulk concentration 0.1–0.2 M, is the most favourable to the deposition of metal arrays at the highest rate if 13.5≤ d p≤37.5 nm.

Electrochemical Impedance Spectroscopic Study on Eu 2+ and Sr 2+ Using Liquid Metal Cathodes in Molten Chlorides

Abstract For the pyrochemical reprocessing of spent metallic nuclear fuels in molten salt baths it is important to investigate the behavior of the electrochemically negative elements Eu and Sr, which are significant fission products. Voltammetric and chronopotentiometric studies have shown that the reduction of Eu 2+ and Sr 2+ on liquid Pb cathodes in molten chloride baths at 1073 K follows the alloy formation reaction: Eu 2+ + 2e− + 3Pb → EuPb 3 and Sr 2+ + 2e− + 3Pb → SrPb 3 . In the present work these alloy formation reactions were studiedby electrochemical impedance spectroscopy. Analysis of the spectra showed that the electronic exchange of Eu 2+ /Eu and Sr 2+ /Sr is quasi-re-versible. Moreover, the experimental results allowed the determination of the kinetic parameters of EU 2+ /EU and Sr 2+ /Sr, the diffusion coefficients of these species in molten chloride baths, and also the diffusion layer thickness.

Electrochemical behaviour of indium ions in molten equimolar CaCl2–NaCl mixture at 550 ∘C

The stability of indium chloride and oxide as well as the electrochemical behaviour of indium ions have been studied in the equimolar CaCl2–NaCl melt at 550 ∘C by X-ray diffraction (XRD) and different electrochemical techniques, using molybdenum and tungsten wires as working electrodes. Voltammetric and chronopotentiometric studies showed signals attributed to the presence of three oxidation states of indium, i.e. 0, i and iii. The standard potential of the redox couples, as well as the solubility products of indium oxides have been determined, showing that In(iii) ions are completely reduced to monovalent indium by the indium metal according to the reaction: In (Ш) + 2 In ↔ 3 In () and that In2O is a strong oxide donor according to the reaction: In2O(s)→ 2 In() + O2- These results have allowed the construction of E-pO2− equilibrium diagrams summarising the properties of In–O compounds. The electrodeposition of indium was uncomplicated at Mo and W electrodes. Very good adherence of liquid indium to the electrode materials was observed, with the formation of Na–In alloys at highly reducing potentials, and there was no evidence of indium dissolution into the melt. Moreover, the voltammograms corresponding to the electrochemical In(iii)/In(i) exchange were well defined. The two electrochemical steps were found to be quasi-reversible, and the values of the kinetic parameters, ko and α, for both reactions, as well as the diffusion coefficients, DIn(III) and DIn(I) were calculated.

ELECTROCHEMICAL BEHAVIOUR OF COPPER IONS IN MOLTEN EQUIMOLAR CaCI2-NaCI MIXTURE AT 550° C

The stability of indium chloride and oxide as well as the electrochemical behaviour of indium ions have been studied in the equimolar CaCl2–NaCl melt at 550 ∘C by X-ray diffraction (XRD) and different electrochemical techniques, using molybdenum and tungsten wires as working electrodes. Voltammetric and chronopotentiometric studies showed signals attributed to the presence of three oxidation states of indium, i.e. 0, i and iii. The standard potential of the redox couples, as well as the solubility products of indium oxides have been determined, showing that In(iii) ions are completely reduced to monovalent indium by the indium metal according to the reaction: In (Ш) + 2 In ↔ 3 In () and that In2O is a strong oxide donor according to the reaction: In2O(s)→ 2 In() + O2- These results have allowed the construction of E-pO2− equilibrium diagrams summarising the properties of In–O compounds. The electrodeposition of indium was uncomplicated at Mo and W electrodes. Very good adherence of liquid indium to the electrode materials was observed, with the formation of Na–In alloys at highly reducing potentials, and there was no evidence of indium dissolution into the melt. Moreover, the voltammograms corresponding to the electrochemical In(iii)/In(i) exchange were well defined. The two electrochemical steps were found to be quasi-reversible, and the values of the kinetic parameters, ko and α, for both reactions, as well as the diffusion coefficients, DIn(III) and DIn(I) were calculated.

Electrochemical Characterization of a Polypyrrole/Montmorillonite Nanocomposite

The electrochemical activities of films prepared from chemically synthesized polypyrrole and a polypyrrole/ montmonrillonite nanocomposite are examined using cyclic voltammetry and chronopotentiometry. The nanocomposite exhibits redox chemistry at potentials approximately 1 V more negative than in native polypyrrole. Chronopotentiometric studies show that the capacities of these two materials, when evaluated in terms of mass of polymer are similar and that the charge/discharge plateaus are also shifted by approximately 1 V. Two models are proposed to explain these results, one based on the inductive effect of the encasing anionic sheets, and one on a redox mechanism involving cation insertion.

Electrochemical impedance spectroscopy study of indium couples in LiCl-KCl eutectic at 450 °C

Voltammetric and chronopotentiometric studies have shown that the reduction of InCl 3 dissolved in molten LiCl-KCl at 450 °C follows a two step mechanism: In 3+ + 2 e − ⇔ In + and In + le − ⇔ In 0. The In 3+ In + and In + In 0 couples were studied separately by electrochemical impedance spectroscopy (EIS). Analysis of the spectra showed that the electronic exchanges are respectively reversible and quasi-reversible. Moreover, it allowed the determination of the rate constant of In + In 0 exchange, the diffusion coefficients of indium species in the LiCl-KCl eutectic, and also the diffusion layer thickness.

Stability and Electrochemistry of Lithium in Room Temperature Chloroaluminate Molten Salts

Addition of protons to buffered neutral melts allows elemental lithium to be deposited and stripped at a 250 μm tungsten electrode. Chronopotentiometric studies performed at current densities from 0.16 to 3.06 mA cm−2 show minimal overpotentials for lithium deposition and stripping. When the lithium is stripped immediately after deposition, the stripping to deposition efficiency approaches 80%; however, when the deposited lithium is allowed to contact the electrolyte at open circuit for several minutes, the efficiencies drop rapidly due to the reaction of lithium with the melt. In basic (chloride‐rich) melts, elemental lithium appears to be stable for long times with and without the addition of protons. In addition, the maximum lithium anodization current density achieved in basic melts is higher than the buffered neutral melts.

Investigation of the 1-methyl-3-ethylimidazolium chloride-AlCl3/LiAlCl4 system for lithium battery application Part I: Physical properties and preliminary chronopotentiometric study

The applicability of the 1-methyl-3-ethylimidazolium chloride — AlCl3 system for lithium battery application was investigated. Lithium chloride was found to dissolve up to 1.59 mole ratio of LiAlCl4/MeEtImAlCl4 upon reaction between LiCl and AlCl3 in the melt. Density, conductivity and viscosity of the melt upon addition of LiAlCl4 were determined. The density was found to increase monotonically from 1280 to 1480 kg m−3, while the conductivity decreased rapidly from the initial value of 5.6 mS to a steady plateau at 3.4 mS. The viscosity was varied from 1.46 Ns m−2 to a small but distinct initial fall prior to rising to 2.75 Ns m−2 when the mole ratio of LiAlCl4 increased from zero to 1.59. The chronopotentiometric studies indicate a satisfactory electrochemical behaviour with no apparent attack of the melt by the formation of the reactive lithium alloys. 350 cycles were achieved with cycling efficiency over 90% using an optimal c.d. of 6 mA cm−2 for lithium deposition on aluminium substrate in the melt. Prolonged cycling improved the nucleation rate but led to an increase in the internal resistance and a gradual reduction in the charge and discharge capacity.

Chronopotentiometric studies of certain biologically important compounds at tubular graphite electrode

The chronopotentiometric studies of certain phenothiazines in hydrodynamic systems at a solution flow-through tubular graphite electrode were carried out in sulfuric acid of different concentrations. A well-defined single wave (involving 2 electrons) in 0.1M H2SO4 and two waves (involving 1 electron each) in 2.0M H2SO4 were observed. Phenothiazines are oxidized trough the formation of a monocation radical by the elimination of one electron from the lone pair of N-atom. The monocation radical is stable in sulfuric acid of a moderate concentration and is unstable in neutral or less acidic solutions. The cation radical undergoes instantaneous hydrolysis yielding sulfoxide, thus presenting an overall two-electron oxidation of the phenothiazine derivatives. The suitability of the chronopotentiometric technique for their determination was established.

Electrochemical Production of Hydrogen and Sulfur by Low‐Temperature Decomposition of Hydrogen Sulfide in an Aqueous Alkaline Solution

Electrolysis of hydrogen sulfide to its constituents in a solution containing equimolar concentrations of and has been carried out at 80°C. In a double‐compartment cell employing Nafion membrane as a separator, both crystalline elemental sulfur and high‐purity hydrogen have been produced at high current efficiencies. Only minimal, if any, passivation of the anode by sulfur product was observed. According to solution composition, electrolysis could result in gas evolution at the anode, passivation of the anode by sulfur deposition, or oxidation of sulfide (S2−) or polysulfide to sulfur oxyanions. However, in an optimized solution, electrolysis gave only anodic sulfur via bisulfide (HS−) and sulfide oxidation. Voltammetric and chronopotentiometric studies showed that sulfide, bisulfide, and polysulfide oxidation occurred at about the same potential.

Cyclic chronopotentiometric studies of the LiAl anode in methyl acetate

The applicability of methyl acetate as a solvent for ambient temperature lithium secondary batteries was investigated using cyclic chronopotentiometry. Methyl acetate was found to be stable towards lithium-aluminium alloys and cycling up to more than 300 cycles was obtained with about 90% cycling efficiency. Water and other organic impurities have been identified in methyl acetate and a thorough purification procedure has been used to reduce these to acceptable levels. LiAsF6, LiPF6, LiClO4 and LiBF4 were investigated for use as supporting electrolytes and LiAsF6 was found to be the best in terms of cycling efficiency, longer cycling numbers and yielding the lowest corrosion capacity loss rate. The development of the LiAl anode upon cycling was observed in parallel with the reduction in nucleation polarization potential, the increase in cycling efficiency, the lowering of concentration polarization at the electrode surface and the more ready acceptance of lithium deposition at the developed electrode. The optimum conditions for the development of the LiAl anode were found to exist at a current density of 5 mA cm−2 and a charge density of 0.5 C cm−2.

Electrochemical Study of Halides and Oxyhalides in LiAlCl4, 3 SO 2 Electrolyte: II . Comparison Between , , and

The comparison of the three systems, , , and has been made using the solvate as an electrolyte. The similar behavior of and solutions was underlined. For all these chlorinated oxidizers, the electrochemical reduction is a diffusion‐limited process. Comparisons between chronopotentiometric reduction of on glassy carbon and constant current discharges of porous cathodes have underlined the validity of chronopotentiometric studies on microelectrodes to analyze the behavior of actual liquid cathode cells.

On a Homogeneous Electrochemical Reaction of Prussian Blue/Everitt's Salt System: A Model of System

Voltammetric, chronopotentiometric, and spectroelectrochemical studies on the homogeneous‐phase (single phase) reaction of Prussian blue (PB)/Everitt's salt (ES) system in aqueous solution were carried out as a model for understanding the homogeneous electrochemical reaction of manganese dioxide. Analytical results of voltammetric and chronopotentiometric studies on PB/ES system indicated that the electrode potential was represented by the empirical formulawhere the observed value was 0.5, not 1.0. Results on spectroelectrochemical studies supported the above formulation, and the value, 0.5, indicated that the effect was thermodynamic, not kinetic. A possible explanation of the problem was given, emphasizing the role of charge carrier in a solid matrix in an electrochemical reaction, and the specific differences between a redox reaction of soluble species in a solution and a redox reaction in a solid matrix were discussed. The electrochemical behavior of system was deduced in terms of a homogeneous (single phase) electrochemical reaction from the analogy of PB/ES system.

The reduction of In 3+ in the presence of I − ion from Ca(NO 3) 2.4H 2O at 60°C

Iodide ions form two complexes InI + 2 and InI − 4 in molten Ca(NO 3) 2.4H 2O. An anion induced adsorption of the complex is also inferred from polarographic, linear sweep voltammetric and chronopotentiometric studies. The surface excess of adsorption is evaluated.

ChemInform Abstract: CHRONOPOTENTIOMETRIC STUDIES OF THE TETRABUTYLAMMONIUM ION TRANSFER FROM WATER TO 1,2‐DICHLOROETHANE

Chemischer InformationsdienstVolume 11, Issue 31 Article ChemInform Abstract: CHRONOPOTENTIOMETRIC STUDIES OF THE TETRABUTYLAMMONIUM ION TRANSFER FROM WATER TO 1,2-DICHLOROETHANE Z. KOCZOROWSKI, Z. KOCZOROWSKISearch for more papers by this authorG. GEBLEWICZ, G. GEBLEWICZSearch for more papers by this author Z. KOCZOROWSKI, Z. KOCZOROWSKISearch for more papers by this authorG. GEBLEWICZ, G. GEBLEWICZSearch for more papers by this author First published: August 5, 1980 https://doi.org/10.1002/chin.198031079AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue31August 5, 1980 RelatedInformation

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Voltammetric and chronopotentiometric studies of the quinone and hydroquinone system in anhydrous formic acid