DE2347033A1 - METHOD AND DEVICE FOR OPTIMIZING THE OPERATION AND YIELD OF ELECTROCHEMICAL CELLS - Google Patents

Description

Dr. Marco V. Ginatta Turin, Italy

Method and device for optimizing the operation and the yield of electrochemical Cells

When using electrochemical cells, especially when electroplating various substrates with Metals and / or in the extraction of elements, compounds or substances by means of electrochemical processes, the methods of monitoring the process are known to be inadequate, as there is no possibility of precise determination certain parameters and influencing variables that are essential for the results are given.

It is especially with the currently known procedures are not possible, the value of the electric charge transfer coefficient ß (which is to be distinguished from the charge transfer coefficient in heterogeneous chemical reactions) to determine. In fact, this coefficient is usually taken to be constant with a value of 0.5, namely for every type of reaction, at every potential difference, at every cell temperature, etc.

Such an assumption of the coefficient β as constant must obviously lead to imprecise conclusions, in particular considering that it appears as an exponent in the expression describing the rate of reaction and that slightest changes in the value of this coefficient

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significant changes in the resulting rate of response to lead.

What has been said above results directly from the relationship mentioned

K - Kre "(kT / h) exp (- 4G * / RT) exp (-ßnF4 0 / RT) exp (-ßnF ₇ ro ο rev _{/ RT)} L

with

K * specific speed of the electrochemical reaction

K * classic transfer coefficient

Γ = quantum transfer coefficient

e = elementary electric charge

k = Boltzmann constant

T = absolute temperature

h = Planck ¹ see constant

G * = activation energy

R = gas constant

ß ■ electrical charge transfer coefficient

η »number of charges transferred

F = »Faraday's see constant
0 = reversible potential and

ti a applied overpotential.

The reason that the value ß by means of traditional Electrochemistry cannot be calculated because ß is a function of many variables (Type of electrochemical reaction, applied potential difference, cell temperature, composition of the electrolyte etc.). In the method of the present invention the value β is reduced to a function of only two variables: the excess energy and the electron transfer level.

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Figure 1 is a schematic representation of the field of electron reactions and the energetic pathway of the reactant products during the electrochemical reaction. The symbols mean:

Ep = * Fermi energy level,

E _T = energy level of the active participant at the moment of electron transfer,

E. * Energy level of the atom in the crystal structure of the electrode

Tbsp. “Energy level of the new atom at the moment of impact on the surface of the electrode,

E "= value of excess energy

PTE »electron transmission level (piano di trasferimento dell ¹ elettrone),

Εγ = ion energy level.

To calculate the excess energy of a given reaction Given the electrochemical conditions, the energy of the electrode surface must be measured.

The present invention relates to calculating the value of the coefficient β with the greatest possible accuracy

a thermoelectric process for optimization

the operation and yield (efficiency) of electrochemical cells and the specification of means for carrying out the procedure.

The proposal according to the invention is based on the excess energy generated by the reaction, which is used for the determination of the coefficient ß is determined.

Nessung belongs to the proposal according to the invention the temperature of the electrode surface, on the basis of which the value of the excess energy can be determined, from which in turn, the coefficient β can be calculated precisely.

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To carry out the proposed method, a thermoelectric element is used as a working electrode with which Information can be obtained that allow the determination of the energy of the electrode surface. Other variants of the proposed invention result from the subclaims.

The invention is described further below using an exemplary embodiment. It shows:

Fig. 2 schematically shows a thermocouple to be used in the context of the invention and

3 shows an electrochemical plant which is operated according to the invention.

The thermocouple, generally designated 5 in FIG. 2, has four wires 1 to 4 of the pairing platinum-rhodium.

The direct current source 8 has one connection) with a cylindrical counter electrode 6 and with the other connection connected to the wire 1 of the thermocouple 5 acting as an electrode (thermoelectrode).

The thermoelectrode 5 and the counter electrode 6 are immersed in the electrolyte in the vessel 7, in an in the vertical symmetrical, concentric arrangement.

To allow the electrolyte to circulate, is located the upper edge 6a of the counter electrode is below the electrolyte level.

The coulomb meter 9 measures the number of charges flowing to the thermoelectrode. The voltmeter 10 measures the potential difference between thermo electrode 5 and counter electrode

An electrometer 11 measures the electromotive force generated by the thermocouple 2-3 belonging to the thermoelectrode is produced; the reference temperature junction -5-

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at 12 is electrically insulated below the counter electrode 6 near the entry of the electrolyte flow

The flow rate of the electrolyte relative to the The spherical cap 5a of the thermoelectrode 5 is monitored by means of a suitable sensor 13 by the device 13a, which affects the pump 14. The sensor 13 is also located near the electrolyte inlet.

Finally, there is still near the electrolyte inlet a sensor 15 for the temperature of the electrolyte, which acts on the device 15a for monitoring the same, which in turn influences the heat exchanger 16.

The concentration of the ions present in the electrolyte is selectively determined by the devices 18a and 19a of the specific ion electrodes 18 and 19 are measured.

The above-mentioned signals are recorded by a suitable device on a printout 20 so that a log of the course of the respective electrochemical reaction is obtained.

Before starting an electrochemical cell with the system described, the thermoelectrode 5 must be calibrated.

The electrometer 11 connected to the thermocouple must have a sensitivity of the order of microvolts, as the order of magnitude for many electrode reactions

-2 of the excess energy flow is 10 ¥ cm.

Precisely because of its high sensitivity, however, the electrometer 11 also measures very small potential differences between two points of the spherical caps 5a, as they are caused by the electron flow in the operation of the electrochemical Cell result in * -6-

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This contribution to the total signal measured by the electrometer 11 must be eliminated so that the measured emf, which is directly proportional to the temperature of the thermoelectric pair is, can be taken as a measure of the energy of the surface of the thermoelectrode.

It must therefore first be outside of each thermoelectrode of the electrochemical system, a calibration curve can be recorded as a function of the current intensity. This curve will of course be different for different geometrical designs of thermoelectrodes.

In the case of the in Fig. The training shown may be sufficient Calibration outside the electrolyte can be carried out by using wire no. 1 to feed the electron current to the thermocouple and wire # 4 for dissipating the same. The relationship between the the thermoelectrode The amount of current flowing through and the value of the associated EMF is then the norm for the respective thermocouple given its geometrical training.

The entirety of the thermoelectrode is made of a material suitable for the electrochemical process taking place isolated, with the exception of the dome 5a. After isolating wire # 4 and using wire No. 1 as the power supply, the thermoelectrode is brought into the electrochemical cell, the dome 5a as The working electrode is used.

During the course of the electrochemical reactions with or without the application of a potential difference, the protocol device stops all information necessary to calculate the value of the energy surplus for the given reaction, the given electrochemical conditions and the properties of the given reactants are necessary.

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The most important value, which is concerned according to the present invention, is that of the electrometer 11 measured signal of the thermoelectric pair. The simultaneous Recording of all electrochemical conditions at every point in time allows the interpretation of the output signal the thermoelectrode and thus the determination of the temperature of the electrode surface, which is a precise Display of the energetic situation on the electrode surface at the given moment is possible.

The device proposed according to the invention therefore makes it possible to determine the energy of the electrode surface and thus at any given moment it can be said under what conditions the desired electrochemical reaction takes place. This includes e.g. the prediction of the crystal structure of the moment separating substances, which are the stable and which are the unstable products, etc. All of these statements depend on the prevailing dynamic equilibrium, which is determined by the values of the electrochemical influencing variables is known at every moment.

Because of the inventive provision, problems can arise which could not be solved with the currently known techniques. For example, it is known that in the galvanic deposition of metal at high current densities dendrites and irregular structures are obtained, while using low current densities smooth deposits are obtained. Further is the mechanism It is not known how the gloss agents have their known influence on the improvement of the galvanic deposits. It is also unknown why some electroplated metal coatings exhibit internal tensile stresses during show other internal compressive stresses and finally it is unknown why the concept of hydrogen overstress is used is so confused.

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Another essential aspect of the invention is that, knowing the characteristics of electrodes and electrolytes knowing the energy of the surface of the electrode calculating the value of the excess energy allowed, which represents one of the two variables on which the value ß depends. However, the following must be done beforehand Quantities can be determined under the given conditions and properties in the system:

1) The one passing through the surface of the electrode
Heat flow through the various, with the
electrochemical reaction related phenomena
is generated, and

2) the contribution of the thermoelectric effects
Joule, Thomson and Peltier, which are caused by the migration of electrons through the interphase electrode /
Electrolyte is created.

The algebraic addition of the values for 1) and 2) and des
The value of the energy of the surface of the electrode determines the value of the Seebeck effect, which is generated _{exclusively by the excess energy Ej 5.}

The second variable, on which the value β depends, is the electron transfer plane PTE, which is also graphically
can be obtained by means of the energy path if the
Value of excess energy is known.

For the construction of the curve of the energy path can
proceed as follows:

As shown in Fig. 1, the abscissa is the distance

ο ο
in Angstrom (A) and on the ordinate the energy in

Electron volts (eV) plotted.

In the intermediate phase a-b, the electrode body with uniform characteristics, there is constant energy with the level E .. In the intermediate phase b-c, the surface layer of the electrode, an energy gradient occurs

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E _n - E _A , which depends on the properties of the electrode and the value E ". The intermediate phase cd is the one where the electrochemical reaction takes place. In the intermediate phase de the participants are in a diffuse layer, which is determined by the properties of the electrolyte. In the final intermediate phase ef, the energy of the participants corresponds to the level Ej.

Only now can the value β be obtained, including two methods of different accuracy and different effort the following are proposed:

The simpler and less precise graphic method. Here ß is defined as the ratio between the Distance on the reaction path from the beginning of the diffuse intermediate phase (point e in Fig. 1) to the PTE and the Distance between point e and the beginning of the surface intermediate phase of the electrode (point b).

A mathematical method, namely the search for the minimum value of the total potential energy under inclusion any mutual interference between the reactants in the area where the electrode reaction takes place. Here, β is defined as the ratio between the change in the minimum value of the total potential energy mentioned above and the value of the applied potential difference. This method is more complicated but more precise than the graphical method and allows a more exact value to be set for the Electron transfer plane.

In working with the present invention, an electrochemical Process to be carried out on an industrial scale with its real conditions in the laboratory reproduced. The exact calculation of the data necessary to optimize the process and achieve maximum Yield can then be carried out in advance,

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which is a considerable economic advantage connected is.

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Claims (11)

2347Ü33 PATENT CLAIMS 1. Process for optimizing the operation of and the yield of electrochemical cells, characterized in that the temperature of the surface of the electrode is measured, from this the value of the energy surplus is determined and from this the value of the electrical charge transfer coefficient ß is determined. 2. Device for performing the method according to claim characterized by a thermoelectric pair (5) as the working electrode. 3. Device according to claim 2, characterized in that the thermoelectrode (5) Obtained signals are recorded in advance of the optimal conditions for a given process to be determined in industrial application. 4. Device according to claims 2 and 3, characterized in that the thermoelectrode (5) has four parallel conductors (1, 2, 3, 4) which are used to generate of thermoelectric voltages are electrically connected to one another at one of their ends. 5. Device according to claims 2 and 3, characterized by a pair at the ends with one another connected electrical conductor made of different materials. -12- A09815 / 0767 6. Device according to claims 2 and 3, characterized in that the thermoelectrode (5) consists of three or more connected to one another at their ends electrical conductors, at least one of which is different in relation to the rest of the conductors Material. 7. Device according to claims 2 and 3, characterized by four interconnected at the ends electrical conductors, two pairs of different materials being formed. 8. Device according to claims 2 to 7, characterized in that the thermoelectrode (5) consists of a plurality of lamellar, one on top of the other Consists of ladders, at least one of which is made of a different material. 9. Apparatus according to claim 8, characterized in that the thermoelectrode (5) from consists of a plurality of electrically conductive layers obtained by deposition, one of the layers consists of a material different from the material of the other layers. 10. Device according to claims 2 and 3, characterized in that the thermocouple of the thermoelectrode (5) is formed in that with the electrode an electrical conductor of a material different from the material is connected. 11. Device according to claims 2 and 3, characterized in that the elements of the thermoelectrode (5) are made of metals, alloys, intermetallic Connections or combinations thereof exist. 409815/0767 Blank page