FI103437B - Method and apparatus for carrying out electrochemical measurements - Google Patents

Description

103437

METHOD AND APPARATUS FOR CARRYING OUT THE ELECTROCHEMICAL MEASUREMENT

The invention relates to a method as defined in the preamble of claim 1 and to an apparatus as defined in the preamble of claim 5 for performing electrochemical measurements.

Electrochemical measurements are based on the measurement of the current flowing between the specimen and the counter electrode in the same solution, when the potential of the specimen 10 is controlled relative to the constant potential of the reference electrode. Of course, accordingly, the measurements may be based on the measurement of the potential when the current is controlled accordingly. In the following, the invention will be explained by means of the former case 15, however, with both alternatives included in the inventive idea limited by the application.

The basic condition for successful measurement is that the solution is even electrically conductive. If the electrical resistance of the solution is high, the product of the electrical resistance and the current of the solution is summed up by the measured potential difference between the reference 20 electrode and the test piece. iR potential losses. Such. controlling the specimen potential is inaccurate.

In addition, the power of the devices used is not sufficient to provide sufficient current between the specimen and the counter electrode. The disadvantage t «<* · 'can be controlled to a limited extent by seeking to measure:'. The magnitude of the iR potential loss in the country.

· * In certain practical processes, such as

In power plant water and in the production of organic compounds, the electrical resistance of the solution is so high that the current between the specimen and the counter electrode is: ·. using the old spacing is limited to a few micro-amps when it comes to taking measurements. The required current level is several milliamps.

In thin-film electrochemistry, a technique is known, whereby a thin layer of solution is provided on the surface of a specimen, for example, between a glass wall and a specimen. The thickness of the solution layer may be in the range of 2 to 100 µm. The counter electrode and the reference electrode are located outside the thin solution layer. The main goal of thin-film-5 electrochemistry is to increase the ratio of the specimen area to the volume of the solution, which significantly improves the resolution of the various electrochemical methods as the concentration of the reaction products in the solution increases. The disadvantage of this technique is the extremely large uneven current distributions and the high iR potential loss, although the counter electrode and the reference electrode are intended to be located as close as possible to the gap containing the thin solution layer. These test arrangements have been carried out and operate only at low temperatures and unpressurized equipment and do not operate at high pressure and temperature variations.

The object of the invention is to eliminate the above-mentioned drawbacks. In particular, it is an object of the present invention to provide a novel method and apparatus for carrying out electrochemical measurements in solutions at elevated temperatures and pressures, that is, under actual conditions of use of the materials, and to overcome the disadvantages of iR potential loss.

25 As to the features which characterize the invention, reference is made to the claims.

The method and apparatus of the invention are particularly intended for high temperatures (above. *, · 100 ° C) and high pressures (above 1 bar), i.e., real power plant and process conditions where current measurement methods do not. are not usable or do not produce accurate enough results.

In the electrochemical measurement method of the invention, current flowing between the specimen in the poorly conductive solution 35 and the counter electrode is measured while controlling the potential of the specimen relative to the constant reference electrode potential. According to the invention, the counter electrode and the test piece are arranged substantially close to each other so that current flows between them in practice, i.e. within the limits of measurement accuracy, only through 5 gaps between their respective counter surfaces. Here, the potential difference between the reference electrode and the specimen is measured through a portion of the substantially non-current solution, i.e., outside the field of action of the electric field 10 formed between the specimen and the counter electrode.

Preferably, the potential difference is measured at a certain distance from the gap between the counter electrode and the specimen, the distance being at least the width of the gap. Preferably, the distance is substantially greater than the width of the slot 15, more than five or even more than ten times the slot width, for example 20 to 1000 times the slot width. In practice, the width of the gap can be as small as the smallest, and at most only tens of micrometres.

Preferably, prior to measurement, the contact surfaces of the specimen and counter electrode are moved into electrical contact with one another, after which they are spaced apart at a desired short distance.

This allows the contact surfaces to be contacted after the electrical contact. , 25 accurately move the desired distance from each other, and · get virtually nanometers of the gap »· • · six desired.

• ·: · Because of the high accuracy used and the V * distances short, it is extremely difficult to mount the counter-electrode and specimen planar surfaces parallel to the nanometer. As a result, prior to transferring the surfaces into electrical contact with one another, they are preferably aligned. The alignment of the surfaces is preferably accomplished by means of a suitable flat-pack molten abrasive, such as abrasive paper, placed between the counter electrode and the counter surfaces of the specimen. In this case, by pulling the abrasive paper as the surfaces 103437 4 are pressed against the opposite abrasive surfaces of the paper, the surfaces become very precisely parallel.

The apparatus of the invention for conducting electrochemical measurements in poorly conductive solutions includes a specimen in the solution, a counter electrode, and a reference electrode. According to the invention, the counter electrode and the test piece have similarly shaped counter surfaces so that their spacing is constant over the entire region of the counter surfaces, and furthermore, according to the invention, the reference electrode is located substantially outside the electric field of action between the counter electrode and the test object.

Preferably, the mating surfaces are straight planes, whereby their distance is constant throughout the mating surfaces 15, even if the surfaces are moved, i.e. moved away or moved closer to one another. Thus, no current concentrates are formed between the surfaces, but a uniform electric field is applied between the surfaces in solution.

Preferably, the counter electrode, or at least its counter surface 20, is a non-stick electrically conductive material, so that when contacted at the beginning of the measurement with the counter surface of the test piece, the counter electrode does not adhere to or transfer material to the surface of the sample.

Preferably, the mating surface is a hard noble metal or a suitable alloy thereof, for example iridium or • · · • · l, rhodium. Likewise, it is possible that the mating surface is a metal having a relatively good oxide V conductivity.

There are several ways of adjusting the distance between the specimen and the counter electrode. For example, a stepper motor outside the pressurized space moves the spindle in the displacement control. Step-by-step motor controlled by computer. 35 The mandrel passes through a radial lip seal in the pressure plate Tian to a helical spring which converts the movement into force. The spiral spring transmits force to the spring to which the counter * 103437 5 electrode is fixed by a rigid screw connection. The force moves the parallelogram spring, whereby the distance between the counter electrode and the specimen can be changed. The trunnion spring is constructed as part of the second U-shaped shape of the test piece and counter electrode attachment, of which it forms the upper mandrel. A test piece is attached to the lower spindle and the lower spindle is stiff so it does not spring. The attachment has the advantage that the specimen and counter electrode can be positioned at exactly the desired distance before starting the test at room temperature and further that the alignment of the contact surfaces of the specimen and the counter electrode can be ensured by polishing the surfaces between the surfaces after mounting. The distance adjustment sensitivity can be easily changed for various purposes by appropriately selecting the spring constant of the coil spring. Devices based on, for example, piezo-crystals 20 may be used to move the spindle outside the pressure vessel in addition to the stepper motor.

The method and apparatus of the invention have significant advantages over the prior art. Electrochemical methods are widely used to characterize the properties of materials and their suitability for a particular environment. The method and apparatus of the invention allow for the first time the use of such methods under real operating conditions, such as in power plant environments.

In the following, the invention will be described in detail with reference to the accompanying drawings, in which: f. Fig. 1 shows a measuring arrangement according to the prior art and · Fig. 2 shows a measuring arrangement according to the invention.

Fig. 1 shows a conventional measuring system for conducting electrochemical measurement at high temperatures. Therein, a solution B, a counter electrode C, and a reference electrode D are embedded in solution A, the shape and distances of which vary from case to case, with distances usually in the order of centimeters. In general, when the electrical resistance of a solution is relatively high, the product of the electrical resistance and the current of the solution are added to the measured potential difference between the reference electrode and the test piece. Generally, the power used by the power supply equipment will be insufficient and no sufficient current will flow between the specimen and the counter electrode.

Figure 2 illustrates an arrangement 15 according to the invention. Therein, the test piece 2 and the counter electrode 3 are embedded in the solution 1, whose mating surfaces 6 and 5, i.e. the surfaces facing each other, are straight and parallel planar surfaces so that the gap between them is of constant thickness throughout its area. The thickness h of the gap 20, i.e. the distance h between the contact surfaces 5 and 6, can be adjusted by the transfer device 7 so that the surfaces can be electrically contacted with each other and then spaced apart at a suitable distance. As a transmission device, various arrangements known per se can be used, whereby controlled and accurate transmission is possible.

103437 7 the gap between them is of the order μτη, rounded edges are formed at the edges of the slits, i.e. the counter electrode and the specimen, with radii of curvature significantly larger than the width of the slit 5. As a result, no current concentrates are formed at the edges of the gap, but the electric field in the gap is very uniform over its entire area.

The measurement according to the invention is carried out as follows. The apparatus and method 10 of the invention can be used in various electrochemical measurements that control either current or potential, for example, impedance spectroscopy. In the arrangement of Figure 2, a suitable abrasive or polishing tool 15 is placed between the test piece 2 and the counter electrode 3, and by pulling it against the surfaces, a precise alignment of the counter surfaces is ensured. The surfaces are then moved into electrical contact with one another, that is, they are moved by the transfer device 7 so close to each other that the resistance between the counter electrode and the test piece is removed. This gives the exact position of the mating surfaces 5 and 6 relative to each other. The transfer device 7 is then used to move the surfaces apart at a desired distance, for example 5-10 μιη.

Thus, with the matching surfaces at exactly the desired distance throughout the gap, the actual measurements can be carried out. There is then a current in solution 1 between the test piece 2 and the counter electrode 3, which passes substantially through only a thin gap 30 between the contact surfaces. The electric field in the solution extends only to a minimal extent just outside the gap, and even at the distance of the gap thickness from the gap, it can be said, within the limits of the measuring accuracy, that solution 1 is non-current. Therefore, the reference electrode 4 is disposed at a suitable distance from the gap, whereby it can measure the potential difference between the reference electrode and the test piece without affecting the measurement in any way due to the electric field between the test piece and the counter electrode 8 103437.

The invention has been described above by way of example with reference to the accompanying drawings, in which various embodiments of the invention are possible within the scope of the claimed inventive concept. 1 ·

Claims (12)

1. A method for conducting electrochemical measurements in a solution that conducts electricity poorly, in which method the current which likes between the test piece and the counter electrode in the solution is measured, since the potential of the test piece is checked in relation to the potential of the reference electrode which is constantly poured, or in the corresponding way of the test piece. potential is measured in relation to the potential of the reference electrode that is constantly poured, where the current that likes between the sample piece and the counter electrode is controlled, characterized in that the counter electrode and sample piece are arranged substantially in proximity to each other, so that the current between them in practice is only via a gap between their counter faces directed, wherein the potential difference between the reference electrode and the sample is measured outside the electric field between the sample and the counter electrode. 2. A method according to claim 1, characterized in that the potential difference is measured at least one distance from the gap determined by the width of the gap. 3. A method according to claim 1, characterized in that the potential difference is measured at a distance from the gap which is above 5; over 10, for example 20 - 1000 times the width of the gap • * ··. 4. A method according to any one of claims 1 to 3, characterized in that before the measurement, the counter surfaces of the test piece and counter electrode are displaced in electrical contact with each other, after which they are removed from each other to the desired distance. 5. A method according to claim 4, characterized in that prior to the electrical contact, the counter surfaces of the test piece and counter electrode are paralleled. 103437 13 6. A method according to claim 5, characterized in that the parallel position is made by an even thicker slidable slider between the counter surfaces. Apparatus for conducting electrochemical measurements in a solution that conducts electricity poorly, to which device belongs a solution (1) wherein there is a test piece (2), a counter electrode (3) and a reference electrode (4), the switching frame between the sample piece and the counter electrode are measured since the potential of the sample piece is controlled relative to the potential of the reference electrode that is constantly poured, or correspondingly the potential of the sample piece is measured in relation to the potential of the reference electrode that is constantly poured, as the current which likes between the sample piece and the counter electrode is controlled, (3) and the specimen (2) belong to counter surfaces (5, 6. which correspond to each other in the form such that the distance (h) between them is constant in the whole area of the counter surfaces and that the reference electrode (4) is located late outside the range of operation of the electric field between the electrode and the sample. 8. Device according to claim 7, characterized in that the counter surfaces are straight planar surfaces. Device according to claim 7, characterized in - I '' '; t e c k n a d that the counter surface (6) of the counter electrode is made of electrically conductive material that does not stick. 10. Apparatus according to claim 9, characterized in that the counter surface (6) consists of hardened precious metal or mixtures thereof, for example iridium or rhodium. • · · V 1 11. Device according to claim 9, characterized in that the counter surface (6) consists of metal, the oxide of which is a good electrical conductor. 12. Device according to claim 7, characterized in that the device includes a sliding device (7) for controlling the distance between the counter surfaces between 0-1 mm. • · • · • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·