Fast Electrochemical Reaction Research Articles

Electroanalytical chemistry of metal complexes with S-containing ligands

The main types of electrochemical reactions of complexes in organic and mixed solvents are considered. Fast electrochemical reactions (ks=n×10−2 cm · s−1) were used to reduce the minimal concentrations (cmin) in a.c. voltammetry. The role of pre- and post-chemical reactions in the formation of the analytical signal in extraction voltammetry is elucidated. The principles of the influence of the special structure of the complexes on their redox properties are determined using complexes of the transition metals with phosphorus dithioacids and bidentate heterocyclic amines. The features of the electrooxidation and electroreduction of inert complexes of the platinum metals with heterocyclic dithioacids and organic sulphides in nonaqueous media are discussed. The products of the electrochemical reaction of these compounds in protic media catalyze the hydrogen evolution on the mercury electrode. Kinetic data of the chelate formation are used for developing highly selective methods for the determination of the platinum metals with cmin=2×10−9−5×10−8 mol/l.

Data-aquisition system for cyclic voltammetry at a microelectrode and application to fast electrode kinetics

A data-aquisition system for fast micro-electrode voltammetry is described. The computer-controlled system can be used at scan rates up to 10 000 V s −1. The response of the system was examined by monitoring fast electrochemical reactions. A heterogeneous rate constant of 1.1 cm s −1 was obtained for oxidation of ferrocene in acetonitrile. Oxidation of anthracene in acetonitrile was also studied; the enthalpy of activation was evaluated as 13 kJ mol −1 for the reaction of the anthracene radical cation with acetonitrile.

A Versatile Microcomputer-Controlled System for Data Acquisition and Analysis in Voltammetry

A versatile microcomputer-controlled electrochemical system for data acquisition and analysis was constructed. The system is presently programmed for cyclic and normal pulse voltammetry, and can be used with other transient electrochemical techniques with a slight modification of the programme for data acquisition. The system can also be used with fast transient techniques; cyclic voltammograms were recorded at scanning rates of up to 1200V s-1. The response of the system was examined by monitoring of the fast electrochemical reactions of quinone/ semiquinone systems, and the collected data were analyzed by finite difference methods. The system could work with a microelectrode assembly, and the signal-to-noise ratio was high enough.

Use of hexamminecobalt(III)-tricarbonatocobaltate(III) as a redox titrant for the potentiometric estimation of some organic compounds

Hexamminecobalt(III)-tricarbonatocobaltate(III) was prepared, and its bicarbonate solution was standardized against ferrous ammonium sulfate using Ferroin indicator. The Co solution was used as an oxidimetric reagent for the determination of organic systems. Hydroquinone as a reversible system undergoes fast electrochemical reactions, so it can be determined with the Co(III) complex, which acts as an irreversible titrant. Thus it can be determined with both visual and potentiometric methods. Standardized hydroquinone solutions in H 2SO 4 medium gave very similar results when determined potentiometrically against standard Co(III) solution. The acid medium is important for liberating Co(III) ions. Hydrochloric acid behaves similarly but perchloric acid interferes with the reaction. Diluting the hydroquinone solutions had no effect on the determinations. The potentiometric endpoint coincides with the discharge of the color if Ferroin has been present. p-Aminophenol, p-phenylenediamine, and Metol ( p-hydroxy- N-methylaniline), which slow or hinder the electrochemical reaction, do not indicate a distinct potential change at the endpoint, so cannot be determined potentiometrically. Their chemical reactions are fast enough to be titrated visually against Co(III) complex using Ferroin indicator. Titration curves representing biamperometric measurements of these solutions fulfill these results. Hydrazine sulfate and isonicotinic acid hydrazide as irreversible systems cannot react with Co(III) and thus cannot be determined either potentiometrically or visually as both electrochemical and chemical reactions are slow to be recognized.

The silver(I)-copper reaction in acetonitrile-water mixtures

An electrochemical and kinetic study of the silver(I)-copper displacement (cementation) reaction in acidified acetonitrile-water mixtures is reported. The cathodic polarization curves for the reduction of silver(I) were found to be those of a fast electrochemical reaction. From the variation of limiting current with rotation speed, the diffusion coefficient of silver(I) as a function of acetonitrile concen- tration was determined. The anodic oxidation of copper gave a Tafel slope of 60 mV per decade of current and was rotation-speed-dependent. It is suggested that the slow step in the reaction mechanism is the diffusion of copper(I) from the electrode surface. At all acetonitrile concentrations investigated, the two polarization curves intersected at a point where the current is fixed by the diffusion of silver(I); this suggests that the displacement reaction will be diffusion-controlled, which was confirmed by kinetic studies. Provided the silver deposit was not too thick, there was good agreement between the measured kinetic rate and that calculated from the silver(I) limiting-current measurements. However, when the deposit became too thick, some increase in reaction rate due to surface roughening was observed.

A rapid on-line computer method for electrochemical investigations

It is demonstrated that a simple on-line computer technique can be used to measure the electrochemical characteristics of a fast electrochemical reaction at modest frequencies. The technique is very suitable for making rapid electrochemical measurements where time effects are involved, e.g. in metal deposition.

The use of rotating electrodes in the study of the different processes relevant in electrochemical engineering

The authors present recent results illustrating the developments in Electrochemical Engineering arising from the use of the rde system as devised by Levich since 1942. It is known, indeed, that when a fast electrochemical reaction is used, the control by mass transport from the bulk solution to the interface of the overall current, yields a way of studying hydrodynamics in the boundary layer thanks to the coupling due to convective diffusion. The examples presented below pertain in particular to boundary layer turbulence (measurement of eddy diffusivity and study of the local hydrodynamic drag reduction) as well as to convective diffusion in non Newtonian fluids with a prospect of application to Bioelectrochemistry. The authors underline also the improvements achieved in the methodology by describing recent non steady state methods.

Emploi d'electrodes a anneau tournant a l'etude du transport de matiere dans un fluide en regime hydrodynamique laminaire ou turbulent

We have studied the flux of matter to the surface of rings rotating in a fluid at high Schmidt number ( Sc $ ̃ 3000 ). The experimental method is based on the measurement of the limiting diffusion current given by a fast electrochemical reaction: Fe( CN) 6 3− + e − → Fe( CN) 6 4− in NaOH(2N). The results show that, for thick rings, the measured values of diffusion flux in function of Reynolds number Re, are in good agreement with the laws established by Levich for both laminar and turbulent flows. On the other hand, for very thin rings, the flux in turbulent flow, is no more represented by a function of Re 0,9 but a function of Re 0,6. This behaviour due to the sole influence of radial convection on the transport, has been compared to those shown by other types of flows with electrodes whose dimension according to flow direction is small. The experimental apparatus described here, thanks to a good definition of mechanical conditions, allowed us to show up in the case of thin rings, diffusion flux values for the laminar flow smaller than those predicted by Levich.

Thermal conductivity of fire-clay: J. K. Clement and W. L. Ecy. ( Met. and Cheni. Eng., viii, 414.)

Hexamminecobalt(III)-tricarbonatocobaltate(III) was prepared, and its bicarbonate solution was standardized against ferrous ammonium sulfate using Ferroin indicator. The Co solution was used as an oxidimetric reagent for the determination of organic systems.Hydroquinone as a reversible system undergoes fast electrochemical reactions, so it can be determined with the Co(III) complex, which acts as an irreversible titrant. Thus it can be determined with both visual and potentiometric methods. Standardized hydroquinone solutions in H2SO4 medium gave very similar results when determined potentiometrically against standard Co(III) solution. The acid medium is important for liberating Co(III) ions. Hydrochloric acid behaves similarly but perchloric acid interferes with the reaction. Diluting the hydroquinone solutions had no effect on the determinations. The potentiometric endpoint coincides with the discharge of the color if Ferroin has been present.p-Aminophenol, p-phenylenediamine, and Metol (p-hydroxy-N-methylaniline), which slow or hinder the electrochemical reaction, do not indicate a distinct potential change at the endpoint, so cannot be determined potentiometrically. Their chemical reactions are fast enough to be titrated visually against Co(III) complex using Ferroin indicator. Titration curves representing biamperometric measurements of these solutions fulfill these results.Hydrazine sulfate and isonicotinic acid hydrazide as irreversible systems cannot react with Co(III) and thus cannot be determined either potentiometrically or visually as both electrochemical and chemical reactions are slow to be recognized.