JP2003287514A - Microelectrode structure and measuring instrument using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and lightweight microelectrode structure by which an electrochemical measurement in a high-resistance medium is performed with high sensitivity and by which an electrode reaction product and/or an electrode reaction intermediate product are detected and to provide an electrochemical measuring instrument using the microelectrode structure. <P>SOLUTION: An electrochemical active species in the high-resistance medium is detected with high sensitivity, and the reaction intermediate product or the reaction product is detected by the electrochemical measuring instrument which is provided with the microelectrode structure formed in such a way that at least a working electrode and a reference electrode as a pair and a counter electrode used as required are brought into contact on a plane and/or a curved surface via an ion conductive material, a means used to apply a voltage or a current to the microelectrode structure, and a current or voltage measuring means. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel microelectrode structure in which a working electrode, a reference electrode, and optionally a counter electrode are integrated via an ion conductive material. The present invention also relates to an apparatus capable of mainly performing electrochemical measurement in a high resistance medium using the integrated microelectrode.

[0002]

2. Description of the Related Art Microelectrodes (microelectrodes) are measuring means capable of performing measurements that cannot be measured with normal size electrodes. In other words, it is known that the local region can be analyzed and that the measurement current is small and therefore the measurement is not affected even if the solution resistance is high. In order to perform these characteristic measurements, the microelectrode and the counter electrode must be electrically conductive through the ion conductive medium. As such an electrolytic solution, usually 0.01 Scm
An electrolyte having a conductivity of ^-1 or more is used, and a supporting electrolyte is used by dissolving it in a medium for expressing such conductivity.

For the measurement of a minute amount of a subject, for example, Japanese Patent Laid-Open No. 223772/1993 discloses Japanese Patent Laid-Open No.
JP-A-1-187865, JP-A-2000-266717.
Japanese Patent Publication discloses an array-shaped, band-shaped, or dot-shaped electrode assembly. These electrodes have a structure for the purpose of efficiently detecting or amplifying a small amount of reaction product, and have a different structure, action, and purpose from the present invention. On the other hand, a microelectrode intended for a gas detector for gas chromatography is described in Journal of Electroanalytical Chemistry, Vol. 244, p. 81, Electrochemical and Industrial Physics, Vol. 61, p. 825. There is. They detect gas after column separation with a bipolar microelectrode, but since they do not have a reference electrode, they cannot measure the current with respect to the electrochemical electrode potential, and the absolute value of the detected current. Has the drawback of being small.

In measuring the electrode reaction in a high resistance medium having a microelectrode, the working electrode, the reference electrode and the counter electrode, which are independent of each other, are arranged close to each other in the medium containing the redox species, and the electrical resistance between the electrodes is measured. Is measured by reducing
Journal of Electroanalytical Chemistry, Vol. 456, p. 239. This method requires the operation of controlling the position of each electrode in order to minimize electric resistance.

As described above, various electrode structures and measuring methods utilizing the characteristics of the microelectrode have been proposed. However, in the measurement in a high resistance medium, the observed current value is small, and for example, when trying to suppress the iR drop by using a minute electrode, there is a drawback that the current value is small due to the minute electrode size.

[0006]

The usual electrochemical measurement means a measurement that reveals the current-potential relationship.
The potential here means an electrode potential, and it is essential to use a reference electrode capable of defining the electrode potential. In order to enable the analysis of the local region and the electrochemical measurement in the high resistance medium, it is necessary to construct an electrode structure capable of extracting the characteristics of the microelectrode as described above.

On the other hand, the microarray electrode can perform high-sensitivity measurement based on the redox cycling reaction even when the concentration of the reactant is low. This is because the reaction intermediate or the reaction product generated in one electrode is measured in the other electrode. Based on what can be detected in. Such an array electrode has been usually used for electrochemical measurement in a low resistance solution prepared by dissolving an electrolyte. However, it is impossible to perform electrochemical measurement in a high resistance medium with such a conventional array electrode. Because the array electrode and the reference electrode,
Since the distance between the counter electrodes, which is used as needed, is usually 1 mm to several cm, the so-called iR drop is large, so only the resistance between the electrodes is reflected, and the reaction that occurs at the electrode-solution interface can be observed. This is because it cannot be done.

High-sensitivity electrochemical measurement in a high resistance medium, detection of electrochemical reaction intermediates, and products are carried out by specifically measuring gas electrode reaction of fuel cell, reaction analysis of polymer battery, and electrochemical capacitor. It is expected to be indispensable for measurement. However, an electrode structure capable of performing such electrochemical measurement has not been proposed yet, and its development has been long awaited.

In view of such potential requirements, in the present invention, a highly sensitive detection electrode structure capable of defining an electrode potential in a high resistance medium, a reaction intermediate, and an electrode structure capable of detecting a product, and An object is to provide an electrode reaction measuring device to be used.

[0010]

As a result of intensive studies to solve the above problems, the inventors of the present invention have found that (1) at least a pair of working electrode and reference electrode are ion-conductive on a plane and / or curved surface. Microelectrode structure contacted via a conductive material, (2) at least a pair of working electrode, reference electrode and counter electrode contacted on a plane and / or curved surface via an ion conductive material (1) (3) The microelectrode structure according to (1) or (2), characterized in that the pair of working electrodes is an alternating array electrode, (4) on a flat surface and / or a curved surface. A microelectrode structure in which at least a pair of working electrode and reference electrode are in contact with each other via an ion conductive material, means for applying voltage or current between the electrodes, and current or voltage measuring means. (5) A microelectrode structure in which at least a pair of working electrodes, a reference electrode and a counter electrode are in contact with each other via an ion conductive material on a flat surface and / or a curved surface. And means for applying a voltage or current between the electrodes and means for controlling the current or voltage (4)
Measuring device using the microelectrode structure described in (6)
The microelectrode structure according to (1) or (2), characterized in that the pair of working electrodes are alternating array electrodes.
A measuring device using the microelectrode structure according to any one of (4) to (5), characterized in that it comprises means for applying voltage or current between electrodes and current or voltage measuring means.
However, they have found that the above problems can be solved, and have completed the present invention.

That is, the inventors of the present application focused on the shape of the electrode assembly and the conductivity between the electrodes, and highly sensitively detected the electrochemical reaction in the high resistance medium, or detected the reaction intermediate and / or the product. We have completed an integrated microelectrode structure that can be used and a measuring device using the same.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of a microelectrode structure of the present invention, in which a pair of working electrodes 2 and 3 and a reference electrode 4 which are electrically isolated from each other are provided on an insulating substrate 1, and this electrode is provided. The groups are in contact with each other via the ion conductive membrane 5. Figure 2
Represents the plan view of FIG. FIG. 3 is a cross-sectional view showing another microelectrode structure of the present invention.
A pair of electrically isolated working electrodes 2 and 3, a reference electrode 4 and a counter electrode 6 are arranged on top of this, and this electrode group is in contact via an ion-conducting membrane 5. FIG. 4 shows a plan view of FIG. FIG. 5 is a cross-sectional view showing another example of the microelectrode structure of the present invention, in which an ion conductive film 5 is provided on an insulating substrate 1, and a pair of working electrodes 2 are formed in contact with the ion conductive film 5. And 3 and the reference electrode 4 are formed.

As the insulating substrate 1, 10^ThreeΩ cm^-1
Any known material with the above resistivity can be used
Good. Examples of such materials include polytetrafluoroe
Known pluses such as ethylene and polyethylene
Glass materials such as tic material, quartz glass, hard glass, soft glass
Fee, Al_TwoO_Three, Metal oxides represented by MgO, Si
_ThreeO_Four, Metal nitride represented by AlN, represented by SiC
Known materials such as metal carbides are used.
Used. The substrate may be flat or curved.
It may be concave or convex, but a pair of
The electrodes 2 and 3 are directly or through the ion conductive material 5.
And place it in a space where it can contact the desired high resistance medium.
It is desirable to be able to place it.

Next, the shapes of the pair of working electrodes will be described. First, it is necessary that the electrodes 2 and 3 be arranged in the vicinity area. The electrodes 2 and 3 may have any suitable shape, such as a disk shape, a polygonal shape, or a hollow cylindrical shape, at a portion in contact with the intended high resistance medium. By reducing the distance between the poles, iR drop can be reduced as much as possible. The electrode size may be any size, but if it is as small as possible, not only the iR drop can be reduced but also the size of the device can be reduced. Further, the reference electrode 4 is installed in the vicinity of the working electrode, and similarly contacts the working electrode via the ion conductive material. The reference electrode may have any shape such as a disk shape, a polygonal shape, and a hollow cylindrical shape. 1, 2, 5
Shows an example of the configuration of such an electrode. Also, in FIG.
In FIG. 4, a counter electrode 6 used as necessary is installed near the pair of working electrodes via an ion conductive material. The shape of the counter electrode 6 may be any shape such as a disk shape, a polygonal shape, and a hollow cylindrical shape.

FIG. 6 shows an example of the present invention when an alternating array electrode is used as a pair of working electrodes. Although this pair of working electrodes is small in size, the effective contact area between the two electrodes can be increased, so various applications as high-sensitivity electrodes are being studied, and each electrode potential is set to a different appropriate potential. By doing so, the reaction product or reaction intermediate produced at one electrode can be detected at the other electrode, which is known as an effective means for analyzing the electrode reaction. As the shape of the pair of working electrodes, all known shapes can be used, but an alternating array electrode is particularly preferably used.

The pair of working electrode materials used in the present invention include a group consisting of a single metal or an alloy, a group consisting of a metal oxide, a group consisting of a semiconductor, a group consisting of a carbonaceous material, and a metal sulfide. Materials belonging to different groups are used, but the pair of working electrode materials may be the same or different.

Ti, V, Fe, Co, Ni, Cu, Zn, Ge, and
Nb, Ru, Rh, Pd, Ag, Cd, Sn, Ta,
Specific examples include elemental metals such as W, Os, Ir, Pt, Au, Hg, and Pb, and alloys having a composition in which they are combined. The group consisting of metal oxides includes TiO ₂ , Mn
Specific examples thereof include O ₂ , PbO ₂ , WO ₃ , perovskite oxide, bronze oxide, spinel oxide, and pyrochlore oxide. In the group consisting of semiconductors,
Specific examples include Si, Ge, ZnO, CdS, TiO ₂ , and GaAs. Specific examples of the group consisting of carbon-based materials include graphite, carbon paste, glassy carbon, HOPG (highly oriented pyrolytic graphite), and the like. For groups consisting of metal sulfides,
RuS ₂ , PdS, PdS ₂ , CdS, In ₂ S ₃ , O
Examples include sS ₂ , CoS ₂ , PbS, NiS ₂ , MoS _{2 and the} like.

Any material may be used for the reference electrode as long as it stabilizes the potential. A known example of such a reference electrode is "R" by DJG Ives and GJ Janz.
eference Electrodes, Theory and Practice ", (Academ
The one described in ic Press, 1961) is used as a typical example. Specific examples of the reference electrode include a reversible hydrogen electrode, a silver / silver chloride electrode, a saturated calomel electrode, a direct hydrogen electrode and the like. It is also effective and effective to thinly coat the electrode serving as the reference electrode with silver paste to use silver as the reference substance. As a constituent element of the reference electrode, when it is necessary to separate the portion generating the equilibrium potential from the working electrode, they can be arranged via an appropriate liquid junction. As a specific example of the liquid material, those described in the above-mentioned documents are used, but it is desirable that the ion conductive material preferably plays a role. Furthermore, the ions involved in the potential-determining reaction of the reference electrode are
Good results are obtained when it is the same as the ion conductive material.
Examples of such a reference electrode include a proton conductive membrane having a silver / silver sulfate / sulfo group, which can be favorably used. It goes without saying that it is possible to provide a suitable reference electrode by using a known liquid junction in addition to the above.

As the counter electrode 6, all of the above-mentioned working electrode materials are used, but particularly, a material having a high corrosion resistance such as platinum, glassy carbon or diamond is preferably used. In view of its operating characteristics, it is desirable that the counter electrode has an area that is at least twice the area of the working electrode, preferably at least 10 times, and more preferably at least 50 times. As a method for achieving this, publicly known platinum black, palladium black, etc. can be mentioned and used. This is a widely known method because it can provide an effective area of about 100 times the apparent area by plating. The counter electrode can be provided and used as needed, and is preferably arranged so as to come into contact with the pair of working electrode and reference electrode via the ion conductive material as in the case of the reference electrode. .

As the pair of working electrode and reference electrode, and the ion conductive material 5 contacting the counter electrode, an ion exchange resin such as Nafion, a solid electrolyte such as ceramics such as ZrO ₂ or a suitable solvent is used. Polymer materials having properties are listed. As a polymer having an affinity with a solvent, first, a water-soluble polymer is insolubilized, and cellulose acetate, polyvinyl alcohol, poly-N-vinylpyrrolidone, polyacrylamide, cellulose, carboxymethyl cellulose, nitrocellulose, cyanoethyl cellulose, cellulose sulfate , Heat-treated or crosslinked products of heparin, pectin, alginic acid, hydroxymethyl cellulose, isopropyl cellulose, polyacrylic acid, polyethylene oxide, etc., and copolymers obtained by cross-linking two or more of the above water-soluble polymers Can be mentioned. Further, a membrane in which a water-insoluble polymer that hardly swells with water is copolymerized with the above water-soluble polymer at an appropriate ratio to improve the degree of swelling in water is also included. Further, a method in which a photocrosslinkable monomer is dissolved in a water-soluble polymer solution, and after film formation is irradiated with light to form a crosslinked structure, a superabsorbent polymer can be obtained.
Examples of these polymers include photocrosslinkable polyvinyl alcohol, photocrosslinkable polyethylene oxide, and photocrosslinkable polyethylene glycol. Further, examples of the ionic polymer include polyvinyl sulfonic acid, polystyrene sulfonic acid, and Nafion. Since these anionic polymers take in a cationic target substance and restrain the movement, a large diffusion coefficient may not be obtained in the film. Therefore, it is possible to improve the selectivity and sensitivity by coating the water-soluble polymer and then coating these anionic polymers. In the two-layer film, the upper layer film having a function of taking in the target substance and the lower layer film contributing to the electrode response are separated.
The upper layer film may be a film having a large partition coefficient for the target substance. A porous film can also be used as the lower layer film. Furthermore, other than a polymer, an amphoteric substance used for a bilayer film or an LB film can be dispersed in a porous film and used as a thin film.

In the present invention, the thickness of the ion conductive film which contacts the pair of working electrodes is preferably 200 μm or less, more preferably 100 μm or less.

The microelectrode structure produced as described above is capable of measuring the redox reaction in a subject having ordinary conductivity. Furthermore, since the microelectrode structure can be designed to have an effective electrode area of a minute size of 0.05 cm ² or less, electrochemical measurement can be performed on a minute region or a small amount of the test medium. Further, the greatest feature of the microelectrode structure of the present invention is that the working electrode, the reference electrode, and, if necessary, the counter electrode are arranged close to each other, so that the electrode reaction of the electrode active species in the high resistance medium is measured. Also in this case, it is not necessary to adjust the electrode interval each time, and the resistance between the electrodes based on the medium can be suppressed to the minimum.

The medium to be measured by the microelectrode structure of the present invention includes water, ethers such as diethyl ether, dimethoxyethane, tetrahydrofuran, tetrahydropyran, acetonitrile, dimethylformamide, dimethylsulfoxide, liquid ammonia, sulfuric acid, etc. Not only can it be used, but molten salts, supercritical fluids, etc. can also be measured. These solvents include
A conventional method of dissolving a known supporting electrolyte to reduce the solution resistance and performing measurement is applied. In addition, examples of the high resistance medium include the above-mentioned solvents, solid polymers, and gases that do not contain a supporting electrolyte. As the solid polymer, for example, polyethylene glycol or a polymer similar thereto can be mentioned. By mixing lithium ion into the polymer, the electrochemical behavior of lithium ion in the high resistance medium can be measured. Further, a gas, which is a high resistance medium, is also a measurement target of the microelectrode structure according to the present invention. As an example, a gas such as hydrogen, oxygen, carbon monoxide, carbon dioxide, carbon disulfide, or a substance such as methanol, ethanol, dimethyl ether, or acetone can be vaporized and used as the measurement target of the electrode reaction.

The measurement is carried out by bringing the above-mentioned test medium into contact with the above-mentioned electrode structure. When the test medium is a gas, the measurement can be performed so that the target gas phase is brought into contact with the effective portion of the microelectrode structure (the portion where each electrode contacts the ion conductor). If the test medium is a liquid,
The target liquid may be brought into contact with the effective portion of the microelectrode structure. In either case, the fluid may be flowing or may be stationary with respect to the electrode. In the case of a liquid, the electrochemical measurement can be performed even if the test liquid is a very small amount (one drop).

FIG. 7 shows an example of the electrochemical measuring device of the present invention. The microelectrode structure 10 of the present invention is connected to an electrochemical measuring device 11. Reference numeral 12 is a control / data accumulation device of the measuring device 11. As the electrochemical measuring device 11, a DC constant voltage source, a DC constant current source, or an AC power source can be used. The response at this time can be measured with a DC ammeter, a voltmeter or an AC measuring instrument. Specifically, a known measuring device such as a potentiostat, a galvanostat or a bridge can be used. Measuring devices suitable for these, such as potential scanners,
It is also possible to connect a lock-in amplifier, a frequency response analyzer, etc. for measurement.

[0026]

EXAMPLES Next, the present invention will be described in detail with reference to examples, but the examples are for the purpose of explaining the present invention in detail, and it is refused that the present invention is not limited by these examples. There is no end.

Example 1 A microelectrode structure of the present invention having alternating microarray electrodes, reference electrodes and counter electrodes as shown in FIG. 6 was prepared by using a photolithography technique on a quartz glass substrate. First, a 0.1 mm thick platinum thin film deposited by sputtering was processed by photolithography, and the electrode width and interelectrode gap were 10 mm and the length was 2.4 mm.
An alternating type micro array electrode in which 20 mm band electrodes were alternately arranged was used. The counter electrode is platinum with an effective area of 0.5 cm ² provided by sputtering. Similarly, the reference electrode was formed by plating silver on the sputtered platinum, and then electrochemically forming a silver sulfate film on the surface thereof. On this electrode structure,
A Nafion film having a dry film thickness of 3 mm was provided by a spin coating method using a Nafion solution (manufactured by Aldrich Co.) to prepare the microelectrode structure of the present invention.

The prepared microelectrode structure was exposed to saturated and humidified nitrogen gas for 30 minutes or more, and then a pair of working electrodes were short-circuited to perform cyclic voltammogram measurement at a potential scanning rate of 10 mV / sec. The measurement result is shown by the solid line in FIG. Cyclic voltammograms similar to the behavior of the platinum electrode in acidic aqueous solution were obtained, and it was confirmed that the present microelectrode structure operates even in a high resistance medium.
The ionic conductivity of the Nafion membrane under the conditions is 0.12.
It was revealed from the impedance measurement results that it was × 10 ^-2 S / cm. That is, it can be seen that the electrochemical measurement can be performed in a high resistance medium whose conductivity is two orders of magnitude lower than that of a normal aqueous electrolyte.

Comparative Example 1 An electrode of Comparative Example 1 was produced in the same manner as in Example 1 except that the Nafion layer was not provided on the electrode. When the same measurement as in Example 1 was performed, the measurement result indicated by the dotted line in FIG. 8 was obtained. Since the electrode of Comparative Example 1 does not have an ion conductive film, it is clear that electrochemical measurement in an ultrahigh resistance medium (humidified nitrogen) cannot be performed.

Example 2 In Example 1, the following measurement was performed by using a humidified hydrogen gas instead of the humidified nitrogen gas. One of the working electrodes was fixed at -0.85 V with respect to the reference electrode to serve as a supplementary electrode. The other working electrode was subjected to potential scanning at a scanning rate of 2 mV per second in the same manner as in ordinary cyclic voltammetry. The results are shown in Fig. 9. As can be seen from the comparison with the results in FIG. 8, it is clear that hydrogen oxidation occurs at the generation electrode. On the other hand, at the trapping electrode, a reduction current is observed as the hydrogen oxidation current increases. This is a result showing that the hydrogen oxidation reaction product is captured by the trapping electrode, and by using the microelectrode structure of the present invention, the electrode reaction product can be electrochemically treated only in a high resistance medium. I was able to catch.

Comparative Example 2 Using the electrode of Comparative Example 1, the same electrochemical measurement was carried out under the conditions of Example 2, and as a result, the same current response as in Comparative Example 1 was not observed.

[0032]

The microelectrode structure of the present invention comprises at least a pair of working electrode and reference electrode on a flat surface and / or a curved surface, and a counter electrode which is optionally provided on the flat surface and / or a curved surface, which are in contact with each other through an ion conductive material. Therefore, high-sensitivity electrochemical measurement can be performed by means for applying voltage or current thereto and current or voltmeter means. This is due to a kind of amplification effect based on the redox cycling reaction at the pair of working electrodes. Secondly, in the microelectrode structure of the present invention, the reaction intermediate and / or the product produced at one working electrode is adjusted to an appropriate value in which the electrode potential of the other working electrode is different from the potential of the working electrode. It can be detected by setting, and the electrode reaction mechanism can be investigated in detail even in a high resistance medium.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an electrode structure of the present invention.

FIG. 2 shows a plan view of the electrode structure of FIG.

FIG. 3 is a cross-sectional view showing another example of the electrode structure of the present invention.

FIG. 4 shows a plan view of the electrode structure of FIG.

FIG. 5 is a cross-sectional view showing another configuration example of the electrode structure of the present invention.

FIG. 6 is a plan view showing an example in which the electrode structure of the present invention has an alternating array electrode.

FIG. 7 is a block diagram showing an electrochemical measurement device diagram of the present invention.

FIG. 8 shows current-potential curves of an example of the present invention and a comparative example.

FIG. 9 shows a current-potential curve of an example of the present invention.

[Explanation of symbols]

1. Electrically insulating substrate 2. One of a pair of working electrodes 3. One of a pair of working electrodes 4. Reference electrode 5. Ion conductive membrane 6. Opposite pole 10. Micro electrode structure 11. Electrochemical measuring device 12. Control / data collection device

Claims (6)

[Claims] 1. A microelectrode structure in which at least a pair of working electrodes and reference electrodes are in contact with each other on a flat surface and / or a curved surface via an ion conductive material. 2. The microelectrode structure according to claim 1, wherein at least a pair of a working electrode, a reference electrode and a counter electrode are in contact with each other on a flat surface and / or a curved surface via an ion conductive material. 3. The microelectrode structure according to claim 1, wherein the pair of working electrodes are alternating array electrodes. 4. A microelectrode structure in which at least a pair of working electrodes and a reference electrode are in contact with each other on a flat surface and / or a curved surface via an ion conductive material, and means and current for applying a voltage or current between the electrodes. Alternatively, a measuring device using a microelectrode structure, characterized by comprising a voltage regulation means. 5. A microelectrode structure in which at least a pair of a working electrode, a reference electrode and a counter electrode are in contact with each other on a flat surface and / or a curved surface via an ion conductive material, and a means for applying a voltage or current between the electrodes. 5. The measuring device using the microelectrode structure according to claim 4, characterized by comprising: 6. The microelectrode structure according to claim 1, wherein the pair of working electrodes are alternating array electrodes, a means for applying voltage or current between the electrodes, and a current or voltmeter. The measuring device using the microelectrode structure according to claim 4, further comprising a regulation means.