Electrode Rotation Speed Research Articles

Extension of the voltammetric theory to inert, permeable thin-film coated rotating disc electrodes: Part I. General equations of voltammetric curves

The electrochemical behaviour of metallic electrodes coated with chemically inert, insulating and permeable thin films is examined in the case of steady-state mass transfer at a rotating electrode. The general equation of voltammetric curves is established: it is demonstrated that the classical equations describing the voltammetric curves may still be used with such electrodes, provided that the solution diffusion layer δ is replaced by a fictitious diffusion layer whose thickness is δ′= e+( D f/ D s)δ where e is the film thickness and D f and D s the diffusion coefficients in the film and in the solution. Two limiting behaviours are to be expected. In the first, the diffusion rate is slower in the solution than in the film ( D s/δ≪ D f/ e) and the usual voltammetric wave is obtained. In the second case, the diffusion rate is slower in the film than in the solution: the limiting current is then independent of the electrode rotation speed. It is shown that under such conditions a redox system may become more reversible on the coated electrode than on the bare one.

The response surface of an amperometric flow cell detector based on a rotating disk electrode for h.p.l.c.and continuous flow analysis

The amperometric detector flow cell based on a rotating disk electrode can be used in conjunction with continuous flow analysis as well as with h.p.l.c. The response surface of the detector as a function of flow rate, electrode rotation speed and concentration of electroactive species (hexacyanoferrate(II)) is measured in combination with continuous flow analysis. When the electrode is stationary, the detector behaves as a wall-jet detector. Rotating the electrode results in a completely different hydrodynamic flow pattern in the flow cell. The response becomes independent of the flow rate and is linearly related to the electrode rotation speed. The influence of nozzle height in the flow cell on the detector response in combination with h.p.l.c. is described. With certain combinations of nozzle height and rotation speeds, a favourable flow pattern appears to be created in the cell and the sensitivity is increased considerably.

ChemInform Abstract: ANODIC OXIDATION OF COPPER IN ALKALINE SOLUTIONS. 2. THE OPEN‐CIRCUIT POTENTIAL BEHAVIOR OF ELECTROCHEMICALLY FORMED CUPRIC HYDROXIDE FILMS

AbstractMit einem in LiOH‐Lösung (1 mol dm′3) potentiostatisch bei ‐250 mV gezüchteten Cu(OH)2‐Film bedeckte Cu‐Elektroden werden durch Röntgenbeugung, Rasterelektronenmikroskopie sowie elektrochemische Methoden untersucht.

ChemInform Abstract: THE DISSOLUTION OF CUPRIC HYDROXIDE FILMS FROM COPPER SURFACES

AbstractDie Auflösung von unter genau definierten potentiostatischen Bedingungen auf Cu gebildeten Cu(OH)2‐ Filmen in LiOH wird als Funktion von [OH′ ], der Rotationsgeschwindigkeit einer rotierenden Scheibenelektrode und des Bildungspotentials untersucht.

Anodic oxidation of copper in alkaline solutions 2—the open-circuit potential behavior of electrochemically formed cupric hydroxide films

Copper electrodes covered with Cu(OH) 2 films grown in 1 mol dm −3 LiOH solution have been examined using X-ray diffractometry, scanning electron microscopy and electrochemical techniques. A sharp change in potential on open-circuit, due to a change in phase from Cu(OH) 2 to Cu 2O, was observed. This phase change is accompanied by a substantial amount of film dissolution. The time required for transformation, and the final amount of Cu 2O formed, are functions of both hydroxide ion concentration and electrode rotation speed. A mechanism involving Cu(OH) 2 dissolution, disproportionation (Cu 2++Cu→2Cu +) and Cu 2O precipitation, is proposed to explain these observations.

The dissolution of cupric hydroxide films from copper surfaces

The dissolution of cupric hydroxide films grown under well defined potentiostatic conditions has been studied in lithium hydroxide as a function of hydroxide ion concentration, electrode rotation speed (at a rde, and formation potential. The dissolution reaction was followed by monitoring the amount of cupric hydroxide on the copper surface electrochemically at any given time. The open-circuit potential was used as an indication of when the dissolution of when the dissolution reaction was complete. The dissolution reaction was found to be jointly controlled by surface kinetics and diffusion of the dissolution product away from the surface. The effect of incomplete dissociation of LiOH was also considered.

Impédance électromécanique obtenue au courant limite de diffusion à partir d'une modulation sinusoidale de la vitesse de rotation d'une électrode à disque

We present an approach which permits the prediction of the limiting diffusion current of a polarographic reaction when the rotation speed of a disc electrode is sinusoidally modulated. For very low frequencies, we have calculated an expression for the electromechanical impedance making the assumption that the concentration profile is linear. After constructing high performance apparatus we have determined, in the case of a Newtonian medium, the numerical coefficient of a supplementary term extending the validity of the analytical expression of the electromechanical impedance to a wide range of frequencies. We have then been able to apply this method to the study of electrochemical kinetic problems in which the overall current is determined by convective diffusion. The case of the anodic behaviour of active iron in H 2SO 4 medium provides a good example. We determine then the diffusion component of a zero overall current (measured at the corrosion potential) and specify the value of the Schmidt number by the analysis of the electromechanical impedance as a function of frequency.

Rotating electrode d.c. solution conductivity device

In an electrochemical cell with one electrode rotating asymmetrically with respect to a second fixed electrode, a constant current produces an a.c. component of the voltage between the pair at the rotational frequency. This a.c. signal arises from the varying iR drop between the extremes of rotational position and thus is a measure of the conductivity of the cell electrolyte. When such a rotating electrode is added to an operating two-electrode cell (e.g. a plating bath), the a.c. signal derived from the rotating element may be used additionally to map the spatial current distribution in the cell. The filtered and amplified signal in either system has also been used to trigger a counter for digital measurement of electrode rotational speed.

ChemInform Abstract: THE INDIUM ELECTRODE IN PERCHLORATE ELECTROLYTES, A ROTATING DISC AND IMPEDANCE STUDY

AbstractDie Ergebnisse einer Untersuchung der In/In(III)‐Reaktion im Perchloratmedium unter Anwendung rotierender Scheibenelektroden und Impedanzmessungen werden beschrieben.

The indium electrode in perchlorate electrolytes a rotating disc and impedance study

The results of an investigation of the In/In(III) reaction in perchlorate media, using rotating disc and impedance techniques, are presented. It was not possible to obtain satisfactory data in the region where a cathodic current flows due to the intrusion of the h.e.r., which accounted for all the observed current at the more negative potentials. The rotating disc measurements showed that at high pH the anodic current was independent of the electrode rotation speed. Lowering the pH resulted in a rotation speed dependence of the observed anodic currents. This dependence indicated that at the electrode equilibrium existed between In(0) and In(I) at the more negative anodic potentials and between In(0) and In(III) at the more positive potentials. There was an indication that at the more negative potentials the kinetic current was controlled by a one-electron change (In/In(I)) and at more positive potentials the Tafel slope indicated a change in mechanism. Impedance measurements in solutions of varying pH are in satisfactory agreement with the rotating disc data.

The Electrochemical Response of a Disk Electrode to Angular Velocity Steps

An experimental study has verified the prediction that the establishment of a boundary layer at the surface of an impulsively started disk is complete in less than three tenths of a rotation. A similar result was found for a rotating disk electrode whose speed was stepped between two values. The current transient produced by a step change of the rotation speed of a disk electrode held in the convective‐diffusion limiting current region of some electroactive species has been derived. Studies of the reduction of Ag+, Fe3+, and are in good agreement with theory and show that the relaxation process is limited by the convective‐diffusion of the electroactive species rather than the hydrodynamic relaxation phenomenon.

Detection and identification of intermediate and final products of electrochemical reactions by means of the rotating ring-disc electrode method

This paper discusses the principles of identification of intermediate and final products of electrochemical reactions on the basis of kinetic information obtained by means of the rotating ring-disc electrode method. Most important information about the nature of the products may be obtained by investigating the relationship between the ring collection efficiency for the appropriate product and the electrode rotation speed, disc potential, concentration of the initial reactant in the solution, temperature and pH of the solution. This approach was used for identification of the products of nitroferrocene alkaline reduction. It was demonstrated that the cathodic reduction of this compound involves formation of anion-radicals of nitroferrocene, unstable ferrocenylhydroxylamine and amino-ferrocene.

Effects of alkyl amine surfactants on the corrosion of a rotating copper cylinder

The corrosion of a rotating copper cylinder in saline solution has been studied in terms of the rest potential and the limiting current density for optimum cathodic protection of the metal. A comparison of these electrochemical parameters has been made in the absence and the presence of alkyl amine surfactants of various chain lengths. Alkyl amines were found to reduce both the tendency of the metal to corrode and the current requirement for cathodic protection. An attempt has been made to explain the inhibition phenomenon and its dependency on such variables as the electrode rotational speed, surfactant concentration and chain length.

The anodic dissolution of vanadium in acid solutions

Summary The anodic dissolution of vanadium in perchloric acid and hydrochloric acid has been studied using wire, rotating disc and ring-disc electrodes. The product of the reaction is V(IV). The rate of reaction is independent of the hydrogen ion concentration and the nature of the anion. The dissolution currents are also independent of the rotation speed of a disc electrode. The experimental data suggest that the rate-determining step is V → V(I) ads + e with an exchange current density at the V/V(IV) reversible potential of 8.0×10 −11 mA cm −2 .

The anodic dissolution of vanadium in acid solutions

The anodic dissolution of vanadium in perchloric acid and hydrochloric acid has been studied using wire, rotating disc and ring-disc electrodes. The product of the reaction is V(IV). The rate of reaction is independent of the hydrogen ion concentration and the nature of the anion. The dissolution currents are also independent of the rotation speed of a disc electrode. The experimental data suggest that the rate-determining step is V → V(I)ads + e with an exchange current density at the V/V(IV) reversible potential of 8.0×10−11 mA cm−2.