WO1999054719A1

WO1999054719A1 - Method for influencing electro-chemical processes on electrodes by the application of an electric field

Info

Publication number: WO1999054719A1
Application number: PCT/DE1998/003156
Authority: WO
Inventors: Peter SCHÖNWEITZ
Original assignee: Schoenweitz Peter
Priority date: 1998-04-21
Filing date: 1998-10-29
Publication date: 1999-10-28

Abstract

The present invention relates to a method for influencing electro-chemical processes on electrodes by the application of an electric field without modifying the pre-set red-ox potential of the electrode relative to the electrolyte.

Description

Description:

Process for manipulating electrochemical processes on electrodes by means of a superimposed electrical field

The present invention relates to a method according to claim 1, with which electrochemical processes on electrodes can be influenced with an electric field.

The state of the art nowadays allows voltammetry in very poorly conductive solvents or even gas phases to determine currents of a few femtoamperes on very small disk electrodes of less than one micrometer in diameter.

In addition to the processes of adsorption, desorption, as well as oxidation or reduction processes on an electrode, which have been postulated for the responsibility of the current in voltammetry, a large part of the currents are superimposed as charging currents (Coulomb currents) with a corresponding change in potential . For current measurements with very small electrodes (smaller than 25 μm room diameter) an advantageous side effect is the strong reduction in charging currents.

Literature:

[1] P. Atkins, Physical Chemistry, Verlag Chemie, Weinheim 1987, 817. [2] H. Emons, Voltammetric Analysis with Microelectrodes, GIT Fachz. Lab.3 (1996)

204-208.

[3] R. Menzel, A voltammetric multifunction sensor system for aqueous media, dissertation TU Munich 1993, 97-103.

[4] K.R. Wehmeyer, M.R. Deakin, R.M. Wightman, Electroanalytical Properties of Band Electrodes of Submicrometer Width, 57 (1985) 1913-1916.

[5] P. Schönweitz, investigations of electrochemical measuring methods in aqueous

Media, dissertation TU Munich 1997, 78 - 80.

[6] Data sheet Specification for stripping the silver cover of Wollaston wire, Heraeus

Hanau, 1997. [7] filed patent, method for measuring the smallest currents in the

Voltammetry with few components, August 1997, file number 197 36224.9-35 A supplementary view and more detailed investigations that have been carried out in this regard describe the processes that take place on an electrode and have a current measured as follows:

First of all, by means of a potential presented at the electrode with respect to the electrolyte, some reaction partners for oxidation or reduction, i.e. moved to donate or accept electrons. However, no current has flowed with this process.

The charge of the reactant changes according to the potential of the electrode, e.g. an anode leads to oxidation, i.e. to positive ions. The resulting electrostatic interaction of the charge of the ion formed and that of the electrode causes a force that leads to spatial separation in the liquid medium. In this process, the electrical resistance, which is given by the electrolyte, is overcome. A current is flowing.

This process can also be described for the cathode. Correspondingly, ions already present in the electrolyte overcome the resistance on the way to the electrode in order to neutralize their charge at the electrode or to be further oxidized or reduced accordingly. This process also contributes to the current flowing at the electrode.

Since the mass transfer from or to the electrode is responsible for the measured electrical current and this depends on the charge of the electrode and the ions, the superimposed electrical field was a logical conclusion to influence the mass conversion at the electrode. To be able to implement this method, electrodes with a microscopic or symmetrical structure are necessary. This is the only way to achieve a homogeneous electric field, but above all parallel to the actual field (electrode - electrolyte). In addition, a metal tip, in which electrical charge collects, can support the field alignment and thus the establishment of a homogeneous field to the micro or even nanoelectrode. However, small electrodes only deliver very low currents, so that very expensive amplifiers had to be used. Support for this development was provided by a new, patent-pending circuit for measuring the smallest electrical currents in voltammetry with low component expenditure (Akz 197 6 224.9 - 35).

2 It is therefore an object of the present invention to build up an insulated electric field on an electrode and to set it up so as to exert an influence on the electrostatic interaction which exists between the charge of the ions and the electrode. The resulting change in the ion transport speed away from or towards the electrode thus has an immediate influence on the measured current without changing the preset redox potential of the electrode.

This object is achieved by the features of claim 1, a method for the electrochemical conversion of reactants in the electrolyte or the electrolyte itself on an electrode under the influence of an electric field. An electrical field is created perpendicular to the electrode surface, which is directed parallel to the assumed field of electrostatic interaction (electrolyte - electrode).

The influence of the electric field has so far only been observed on very small glass-coated disk electrodes with a diameter of 10 μm or smaller. Electrical currents of a few pico- or femtoamperes were measured in a Faraday cage. A controllable high-voltage field was placed between the electrode and a metallic tip (radius of curvature <50 μm), the distance between which is approx. 12 μm. The gap between the tip and the electrolyte was separated with a highly electrically insulating material of 10 μm thickness [FIG. 1].

There was a clear influence of the electric field on the measured current.

A further structure is shown in FIG. 2, in which the measuring cell is cylindrical and the electric field builds up correspondingly radially.

3 Further advantages and features of the present invention result from new measurement and synthesis options in electrochemistry:

Since the electrical current at the electrode can be set independently of the redox potential, new investigation methods with regard to the kinetics taking place and possibilities for observing electrode processes are pending.

This method can also be used to create new analytical processes. One draft provides for the current at the electrode to be kept constant with the electric field via a control system. In addition, as with voltammetry, a defined course of the electrolyte potential is scanned and the change in the resulting electric field is observed. Because the reactants in the electrolyte are oxidized or reduced at different potentials and thus contribute to the measured current, the electric field will also change in order to keep the current constant. This method can be used in both qualitative and quantitative analysis.

Other control systems of the electric field, which work, for example, galvanometrically or potentiometrically, can also provide information about the reaction kinetics taking place. Likewise, the electric fields could be generated or regulated (sine, triangular or rectangular courses, etc.) in such a way that they influence the double-layer area of the electrode in such a way that the charging currents can be manipulated. With this method, the current can be reversed regardless of the redox potential. For example, given a redox potential, both the anions and the cathions can be determined by special measuring cycles.

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Claims

Expectations:

1. Method with which electrochemical processes on electrodes can be manipulated by means of a superimposed electrical field,

characterized in that in addition to the predetermined potential difference between the electrolyte and the working electrode, an electric field is superimposed on this system,

characterized in that the one pole of the electric field is the electrode itself,

characterized in that the other pole of the electric field is brought so close to the electrode in an electrically insulated manner that a fluid exchange at the electrode is still possible,

characterized in that an electric field is set up perpendicular to the electrode surface, which is directed parallel to the assumed field of electrostatic interaction (electrolyte electrode),

characterized in that the electric field can be controlled by a controller depending on the potential of the electrode, the measured current or the time.

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