Cyclic Chronopotentiometry Research Articles

Application of the superposition principle to the study of a charge transfer reaction in cyclic chronopotentiometry. Part II

The general analytical expressions corresponding to the response obtained for a charge transfer process in cyclic chronopotentiometry are presented. The different geometries considered for the mass transport operator are planar, tubular and spherical. In the case of spherical electrodes (such as the dropping mercury electrode and the static mercury dropping electrode), we have analyzed the following two cases: solution soluble product and electrode soluble product or amalgamation. The solutions deduced here are independent of the method used in solving the differential equations system since we have applied the superposition principle for which we have only used the properties of the linear operators.

Application of Cyclic Chronopotentiometry to the Study of Slow Charge Transfer Reactions at the DME and the SMDE

In this work we apply cyclic chronopotentiometry to analyze charge transfer reactions at spherical electrodes, highlighting the influence of electrode curvature and the formation of amalgam on the potential-time response. Moreover, methods are proposed for determining the formal potential and the kinetic parameters of the electrode reaction. Equations obtained for the dropping mercury electrode are transformed to those corresponding to a static mercury drop electrode and a plane electrode.

Voltammetric Study of Silver in a Glass Melt

The redox reaction and the oxidation state of silver in a glass melt were studied by cyclic voltammetry and chronopotentiometry between 800° and 1200°C. Silver ions in glass were reduced at a less noble potential than the rest potential of a platinum electrode. A reversible redox reaction of silver in glass was indicated from the analysis of the cyclic voltammogram. An analysis based on the electron transference number revealed that the solubility of reduced silver increased with increasing temperature. Ag+/Ag0 equilibrium in glass was suggested because the rest potential of the platinum electrode in glass was a mixed potential. No relation was observed between the redox behavior of silver in glass and optical basicity. O‐type redox behavior of silver in glass was shown.

Aluminium deposition and redissolution at TiB2/C composite cathodes in cryolite based melts

Electrochemical techniques of cyclic voltammetry and current reversal chronopotentiometry (CRC) with delay were used to evaluate the current efficiency of aluminium deposition together with its dissolution rates on TiB2/C composite cathodes of ⩽ 40 wt % TiB2 in NaF-AlF3-Al2O3 molten baths. Experiments were conducted in both alumina-saturated and unsaturated melts. The working electrodes were titanium diboride-carbon composites and ATJ graphite. In general, the current efficiency for aluminium deposition was higher in unsaturated melts than in AL2O3-saturated melts. The rate of aluminium dissolution was found to be a diffusion-controlled process. The wettability of these composites by molten aluminium was found to be poor, this being attributed to the low surface TiB2 content and the large graphite particles which prevent the formation of a thin continuous aluminium film on the surface of the cathodes.

On the formation and oxidation of a heterogeneous amalgam of iron

Electrode processes involving the formation of a heterogeneous amalgam of iron during the electroreduction of Fe(II) ions on mercury and the oxidation of the iron amalgam were investigated by cyclic voltammetry, chronoamperometry and cyclic chronopotentiometry. The hanging mercury drop electrode and an iron plate placed on a mercury pool electrode were used in the experiments as working electrodes. It was established that particles of the electrodeposited iron are wetted by mercury and penetrate into the bulk of mercury electrodes forming a suspension. However, during electroreduction of Fe(II) ions from concentrated CaCl 2 and Ca(ClO 4) 2 solutions a small amount of metallic iron remains on the surface of mercury. Oxidation of the heterogeneous amalgam of iron occurs at potentials about 100–150 mV less positive than the onset potential of mercury oxidation in the solutions studied. At these potentials oxidation of mercury may become significant enough to uncover some parts of the iron microcrystals. These iron particles become partially passivated and their surface energy at the Fe/solution interface decreases; consequently, the spreading coefficient of mercury on iron decreases, microcrystals of iron are expelled from mercury and finally oxidized.

Analysis of molten industrial silicates by electrochemical techniques

Fused silicate glass is investigated in this work by electrochemical techniques, using platinum as a convenient material for reference, working and auxiliary electrodes. Cyclic voltammetry and chronopotentiometry are carried out whenever possible, mainly in the case of colourless glass. For more complex systems, square-wave voltammetry is preferred since its mathematical treatment allows the waves of interfering electrochemical reactions to be separated. So, the oxidation of oxygen anions, the reduction of sodium ions and Fe oxides are studied in some detail and the feasibility of the attempted techniques in the fused glass are discussed.

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.

塩酸中におけるアルミニウムの交流エッチングのサイクリッククロノポテンショメトリーによる検討

The AC etching of aluminum foil (99.99%) in 5% hydrochloric acid solution was studied by cyclic chronopotentiometry, SEM observation and electrostatic capacity measurement. Prolonged cyclic chronopotentiograms at a frequency of 50Hz were measured under different current densities and temperatures, and expressed in three-dimensional graphics as a function of cycle number. Potentialcycle number curves were also derived from the chronopotentiograms at arbitrary times.Change in the peak potential at anodic half cycles was closely related to the potential in the subsequent cathodic half cycles. The time, tp, at which the anodic peak is attained and the value of the anodic peak potential, Ep, varied with cycle number. The potential -cycle number curve was greatly affected by the current density at the cathodic half cycles and changes in tp and Ep became greater as the electrolyte temperature was increased. When the etching was carried out with a high anodic peak potential and without large fluctuation in the potential-cycle number curve, the pits were densely formed on the aluminum foil, providing high electrostatic capacity.

A Study of Chemically Synthesized Polypyrrole as Electrode Material for Battery Applications

We have studied the behavior of a chemically synthesized polypyrrole as electrode material. The different electrochemical methods that we have used for this characterization, namely, cyclic voltammetry, ac impedance measurements, and cyclic chronopotentiometry, have evidenced the role of the low frequency capacitance characteristic of the doped state of polypyrrole. This capacitance seems independent of the synthesis conditions of the polymer, and we show that it partially explains the large value of the total charge stored in this polypyrrole. Analyzing the effect of residual water in the polymer, we show that a water content of about 3% (w/w) increases the total charge and lowers the redox potential . A quasi linear relationship has been found between and , the massic capacity: increases when decreases. This relation can be also attributed to the charging of the capacitance , where is the degradation potential. We discuss the origin of this capacitance .

A Voltammetric Investigation of AC Corrosion Phenomena at an Aluminum Electrode in Hydrochloric Acid

Abstract The electrochemical behavior of Al in HCl has been studied by cyclic voltammetry, square-wave chronoamperometry, and square-wave chronopotentiometry. High speed cyclic voltammetry was studied thoroughly, and the effects of temperature, HCl concentration, potential sweep rate, and cathodic potential limit were examined. Relevant parameters that can be determined from the cyclic voltammetric i-V curve include the breakdown and protection potentials for Al, the onset potential for hydrogen evolution, and the magnitude of the anodic and cathodic currents. The degree of passivity, which is reflected in the anodic breakdown potential and the magnitude of the anodic current, decreased with increasing solution temperature and HCl concentration, and increased with higher sweep rates. The nature of the Al passivation that occurs during the cathodic half-cycle depends on the cathodic potential limit. These processes and their relationship to the voltammetric curves are discussed in detail.

Electrochemical reactions of nickel cyanide complexes

The reduction of the nickel(II) cyanide complex in aqueous solutions, with and without an excess of free cyanide, was studied using the techniques of cyclic chronopotentiometry aided with computer simulation. The mechanism of reduction is an e.c.e. sequence, the chemical rate determining step being a dissociation reaction. Superimposed onto this reaction sequence is a fast equilibrium disproportionation reaction. The rate coefficient of the chemical reaction was determined by fitting working curves, generated by numerical simulation of the reaction sequence, to experimental data. In solutions containing an excess of free cyanide (0.1 mol l −1 KCN +0.1 mol l −1 KCl) the rate coefficient of the chemical reaction is κ c =0.34 s −1 P2 for any equilibrium constant of the disproportionation reaction, K , between 10 and 100. Corresponding values for 0.1 mol l −1 KCl solutions, in absence of free cyanide, are: κ c =0.03 s −1 , and K =10 −3 . P2

Electrochemical reactions of nickel cyanide complexes

The reduction of the nickel(II) cyanide complex in aqueous solutions, with and without an excess of free cyanide, was studied using the techniques of cyclic chronopotentiometry aided with computer simulation. The mechanism of reduction is an e.c.e. sequence, the chemical rate determining step being a dissociation reaction. Superimposed onto this reaction sequence is a fast equilibrium disproportionation reaction. The rate coefficient of the chemical reaction was determined by fitting working curves, generated by numerical simulation of the reaction sequence, to experimental data. In solutions containing an excess of free cyanide (0.1 mol l −1 KCN +0.1 mol l −1 KCl) the rate coefficient of the chemical reaction is κ c=0.34 s −1 P2 for any equilibrium constant of the disproportionation reaction, K, between 10 and 100. Corresponding values for 0.1 mol l −1 KCl solutions, in absence of free cyanide, are: κ c=0.03 s −1, and K=10 −3. P2

A differential derivative chronopotentiometric method for evaluating γ

Two-cell differential methods are described for obtaining τ. Results are compared with those obtained from the derivative of the chronopotentiogram, the minimum of which is related to τ. Data are obtained under conditions of low double-layer charging. With the described apparatus cyclic chronopotentiometry does not give the expected values of τ n/τ i.

Electrochemical properties of active carbon in acid and alkaline electrolytes

A comparative study of active carbon in 1 N H 2SO 4 and in 1 N KOH using chronovoltammetry and cyclic chronopotentiometry has been carried out. Chronovoltammetric curves of active carbon in both electrolytes are analogous with those of other forms of carbon. At potentials exceeding 0.8 V/reversible hydrogen electrode two oxidation processes probably take place on the carbon surface. One of them leads to the formation of oxygen containing redox surface groups on the carbon and the other to oxygen adsorbed on the surface in a form which can be reduced only at much lower potentials.

Cyclic chronopotentiometry of nickel(II) at mercury electrodes in acidic perchlorate solutions: Case of higher order nonregenerative reactions following electron transfer

The reduction of Ni 2+ ions at mercury electrodes in acidic perchlorate solutions, at perchlorate concentrations below 0.2 M, is characterized by absence of kinetic control in the preceding step, and by a complex reaction mechanism following the electron transfer. This reaction sequence is known to involve intermetallic compound formation between Ni and Hg and is best described, as shown here, by a parallel second and third order kinetic scheme. Apparent rate coefficients for this kinetic scheme were determined using cyclic chronopotentiometric data and fitting by digital simulation. A linearization test of computed kinetic rate coefficients versus the number of transitions permits quantitative tests of validity of assumptions made.

An investigation of the dismutation of uranium(V) in sodium bicarbonate-carbonate solutions with cyclic chronopotentiometry

The dismutation of uranium(V) in carbonate-bicarbonate solutions has been studied by means of cyclic chronopotentiometry. The aim of the investigation has been to elucidate the actual reaction mechanism. There is evidence from the data on the concentration and pH dependence of the rate coefficients for the dismutation of uranium(V) that the disproportionation reaction is paralleled by an e.c.e. mechanism. The e.c.e. path contributes significantly to the overall reaction rate for concentrations of free carbonate ion of 5×10−3 M and of U(VI) of 1 and 3×10−3 M. For higher concentrations of either the free carbonate or of U(VI) in the bulk of solution the disproportionation is the predominant mechanism. It is difficult, if not even impossible, with the presently available electrochemical techniques, to estimate the relative contributions of either reaction mechanism.

An investigation of the dismutation of uranium(V) in sodium bicarbonate-carbonate solutions with cyclic chronopotentiometry

The dismutation of uranium(V) in carbonate-bicarbonate solutions has been studied by means of cyclic chronopotentiometry. The aim of the investigation has been to elucidate the actual reaction mechanism. There is evidence from the data on the concentration and pH dependence of the rate coefficients for the dismutation of uranium(V) that the disproportionation reaction is paralleled by an e.c.e. mechanism. The e.c.e. path contributes significantly to the overall reaction rate for concentrations of free carbonate ion of 5×10 −3 M and of U(VI) of 1 and 3×10 −3 M . For higher concentrations of either the free carbonate or of U(VI) in the bulk of solution the disproportionation is the predominant mechanism. It is difficult, if not even impossible, with the presently available electrochemical techniques, to estimate the relative contributions of either reaction mechanism.

Starting and switching problems and their solution in instruments for fast cyclic chronopotentiometry

Starting and switching problems and their solution in instruments for fast cyclic chronopotentiometry

Starting and switching problems and their solution in instruments for fast cyclic chronopotentiometry

Summary Problems of non-destructive starting and switching in instruments for fast cyclic chronopotentiometry have been studied. The solution of the problem has been implemented by using a specially designed programming unit connected to fast and precise linear gates.

An investigation into the reaction mechanism of uranium(VI) reduction in acidic solutions by cyclic chronopotentiometry

An investigation into the reaction mechanism of uranium(VI) reduction in acidic solutions by cyclic chronopotentiometry