JP2002296216A - Integrated micro-electrode and measuring method for electrode reaction in high-resistance medium using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode and a measuring method enabling the measurement of electrochemical current potential curve in a local region and for measuring electrochemical electrode reaction of an oxidation reduction material in a high-resistance medium, for example in a low-conductivity liquid containing no supporting electrolyte, in a solid polymer, or in a gas phase. SOLUTION: Electrochemical measurement in a local region or a high- resistance region is made possible by integrating at least a working electrode and a reference electrode through an insulator in a tip region of an micro-area, and covering with a solid ionic conductor containing no oxidation-reduction species, if necessary.

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, if necessary, a counter electrode are integrated in a microtip region. The present invention also relates to an electrode reaction measurement performed in a high-resistance medium using the integrated microelectrode.

[0002]

2. Description of the Related Art A microelectrode (microelectrode) is a measuring means capable of performing measurement that cannot be measured with a normal-sized electrode. In other words, it is possible to analyze a local area, and the measurement current is small, so that the measurement is not affected even if the solution resistance is high
It is known to have such features. In order to perform these characteristic measurements, when the microelectrode is used as a working electrode, it is necessary that the reference electrode and the counter electrode have electrical conductivity through an electrolyte having ionic conductivity. Such an electrolyte is usually 0.01 Scm ^-1.
An electrolyte having the above conductivity is used. In order to express such conductivity, a supporting electrolyte is dissolved in a medium and used. Heretofore, for the measurement of a local area, an electrochemical cell has been used in which a microelectrode as a working electrode is brought close to the relevant local area, and a reference electrode and a counter electrode are arranged via a relatively large amount of electrolyte solution. .

[0003] In the measurement of a very small amount of an analyte, for example, Japanese Patent Application Laid-Open No. 5-223772 discloses a method disclosed in
1-187865, JP-A-2000-266717
Japanese Patent Application Laid-Open Publication No. H11-139,086 discloses an array-like, band-like, and dot-like electrode assembly. These electrodes are configured to efficiently or amplify and detect a very small amount of a reactant, and are different in structure, operation, 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, 244, 81, Electrochemistry and Industrial Physical Chemistry, 61, 825. . In these methods, gas is detected after column separation by a microelectrode having a bipolar structure. However, since there is no reference electrode, current cannot be measured with respect to electrochemical electrode potential.

In order to measure the electrode reaction in a high-resistance medium of a microelectrode, a working electrode, a reference electrode and a counter electrode which are independent from each other in a medium containing a redox species are arranged close to each other, and the electric resistance between the electrodes is measured. The method of measuring by reducing
It is described in Journal of Electronic Analytical Chemistry, 456, 239. This method requires an operation to control the position of each electrode in order to minimize the electric resistance.

As described above, various electrode structures and measurement methods utilizing the characteristics of the microelectrode have been proposed. However, a microelectrode structure having a reference electrode capable of electrochemical measurement of a minute area, and an electrode structure for measuring electrode reaction in a high-resistance medium or a measurement method using the same have not been studied. Was.

[0006]

[0005] Ordinary electrochemical measurement means a measurement that reveals a current-potential relationship.
The term “potential” as used herein refers to an electrode potential, and it is essential to use a reference electrode capable of defining the electrode potential.
In order to enable analysis of a local region and electrochemical measurement in a high-resistance medium, it is necessary to construct an electrode structure capable of extracting the characteristics of the microelectrode as described above.
Such electrodes are indispensable for electrochemical measurement in a minute space, electrochemical measurement in a high-resistance medium, specifically, gas electrode reaction measurement of a fuel cell, reaction analysis of a polymer battery, measurement of an electrochemical capacitor, etc. Is not expected to be possible. However, an electrode structure capable of performing such electrochemical measurement has not yet been proposed, and its development has been awaited.

In view of such latent requirements, the present invention provides an electrode structure capable of defining an electrochemical potential in a minute space and / or an electrode potential in a high-resistance medium and an electrode reaction measuring method using the same. With the goal.

[0008]

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, (1) at least a working electrode and a reference electrode are provided at the front end region with a small area via an insulator. (2) an integrated microelectrode characterized in that at least a working electrode, a reference electrode and a counter electrode are integrated via an insulator in a tip region of a small area, 3) The integrated microelectrode according to (1) or (2), wherein the geometric area of the working electrode is 1 × 10 ⁻⁴ cm ² or less, (4)
(5) The integrated microelectrode according to (1) to (3), wherein at least the working electrode and the reference electrode are integrated within a projected area of 1 × 10 ⁻² cm ² or less.
At least an electrically insulated working electrode and a reference electrode,
The integrated microelectrodes according to (1) to (4), which are in contact with each other via a solid ionic conductor containing no oxidizing species and no reducing species, and (6) electrode reaction oxidizing species and / or reduction. An electrode in the high-resistance medium, wherein the effective electrode portion of the integrated microelectrode described in (1) to (5) is brought into contact with a seed-containing high-resistance medium to measure a relationship between current and potential. Reaction measurement method, (7) The method for measuring an electrode reaction in a high resistance medium according to (6), wherein the high resistance medium is a gas, solves the above-mentioned problem, and completes the present invention. Reached.

That is, the present inventors have focused on the shape of the electrode assembly, and have solved the above-mentioned problems by integrating the minimum necessary number of electrodes capable of achieving electrochemical measurement at the tip of the pin-shaped electrode body. The inventors have found that an electrode structure that can be solved and that an electrochemical measurement using the same can be performed, and the present invention has been completed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The electrode of the present invention has a structure that maximizes the characteristics of a microelectrode. Focusing on the microcurrent, which is the first feature of the microelectrode, when using it as a working electrode, it is possible to use a reference electrode, which is an essential requirement of the present invention, as a counter electrode. That is, the minimum configuration of the present invention can be satisfied by integrating the micro working electrode and the micro or semi-micro reference electrode in the micro tip region of the pin-shaped electrode body. Further, by providing a counter electrode in addition to this, more stable electrochemical measurement can be performed. In this case, the counter electrode may coexist on the same tip surface as the working electrode, or may be arranged near the tip surface. In any case,
The counter electrode needs to be arranged in a region near the working electrode.

The working electrode material used in the present invention includes:
Materials belonging to the group consisting of simple metals or alloys, the group consisting of metal oxides, the group consisting of semiconductors, the group consisting of carbon-based materials, and the group consisting of metal sulfides are used.

The group consisting of simple metals or alloys includes Ti, V, Fe, Co, Ni, Cu, Zn, Ge,
Nb, Ru, Rh, Pd, Ag, Cd, Sn, Ta,
Specific examples thereof include simple metals such as W, Os, Ir, Pt, Au, Hg, and Pb and alloys having a composition obtained by combining them. The group consisting of metal oxides includes TiO ₂ , Mn
Specific examples 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, and HOPG (highly oriented pyrolytic graphite). The group consisting of metal sulfides includes:
RuS ₂ , PdS, PdS ₂ , CdS, In ₂ S ₃ , O
Examples include sS ₂ , CoS ₂ , PbS, NiS ₂ , and MoS ₂ .

[0013] These working electrode materials come into contact with the subject.
The part has an appropriate shape, such as a disk, polygon, or hollow
It may take any shape such as a cylindrical shape. However, the desired
Working electrode to develop the characteristics as a microelectrode
Geometric area of 1 × 10^-Fourcm ^TwoBelow, preferably 2
× 10^-Fivecm^TwoThe following are preferable results. Work
Electrodes are arranged in the tip region of a small area of the insulating substrate.
By doing so, the shape desired by the present invention can be realized. Insulating
As a substrate, 10^ThreeΩcm^-1Public with the above resistivity
Any known material may be used. With such materials
Then, Teflon (registered trademark), polycarbonate
Well-known plastic materials, quartz glass, pirates
(Registered trademark) glass, glass materials such as soft glass, Al
_TwoO_Three, A metal oxide represented by MgO, Si_ThreeO_Four, Al
Metal nitride represented by N, metal charcoal represented by SiC
Known materials such as chlorides are used.
You.

In the working electrode material of the present invention, a single layer or a plurality of layers of a simple metal, an alloy, an inorganic compound, an organic compound, a polymer compound, a biological substance or the like may be modified at the electrode interface. As the modification method, an appropriate method is selected from physical modification such as electrolytic plating, electroless plating, vapor deposition, and sputtering, or chemical modification such as adsorption and covalent bonding. As a specific method of disposing the working electrode in the tip region of the insulating material, a method of inserting a linear electrode material into a capillary glass tube and heating and sealing the tip, or a method of inserting the working electrode into a heat-shrinkable plastic tube and heating and sealing the tip. And a method in which an electrode material is inserted into a suitable capillary and sealed with an organic or inorganic adhesive.

As the material used for the reference electrode, any material can be used as long as it stabilizes the potential. A well-known example of such a reference electrode is “R” edited by DJG Ives and GJ Janz.
eference Electrodes, Theory and Practice ", (Academ
ic Press, 1961) are used as representative examples. Specific examples of the reference electrode include a reversible hydrogen electrode, a silver / silver chloride electrode, a saturated calomel electrode, and a direct hydrogen electrode. It is also effective and effective to use silver as a reference material by thinly coating a silver paste on the electrode serving as the reference electrode. When it is necessary to separate the part generating the equilibrium potential from the working electrode as a constituent requirement of the reference electrode, both parts can be arranged via an appropriate liquid junction. Specific examples of liquid agar include agar containing an electrolytic solution and the formation of a liquid through a fine wire.
Examples of such are detailed in the literature.

The reference electrode should preferably be integrated with the working electrode via an insulator in a minute area at the tip of the pin-shaped electrode body. At least a working electrode and a reference electrode are provided in a micro area at the tip of the electrode body at 1 × 10 ⁻² cm ^2.
In the following, the object of the present invention can be achieved if the components are integrated within a projection area of preferably 3 × 10 ⁻³ cm ² or less. As described above, the reference electrode can be used also as the counter electrode.

As the counter electrode, all the above-mentioned materials for working electrodes are used, and particularly, materials having high corrosion resistance, such as platinum, glassy carbon, and diamond, are preferably used. Considering the operation characteristics of the counter electrode, it is desirable that the counter electrode has an area of at least twice, preferably at least 10 times, more preferably at least 50 times the area of the working electrode. As one method for achieving this, known platinum black, palladium black and the like are used. This is a widely known method capable of providing an effective area of about 100 times the apparent area by plating. The counter electrode may be provided with a working electrode and a reference electrode in a minute region at the distal end of the electrode body, or may be provided on a side surface of the electrode body. The counter electrode can be provided in the same manner as the working electrode.

An embodiment can be adopted in which the working electrode and the reference electrode are in contact with the tip of the integrated microelectrode thus produced via a solid ionic conductor containing no oxidizing species and no reducing species. Examples of such solid ion conductors include ion exchange resins such as Nafion, and Zr.
Examples include solid electrolytes such as ceramics such as O ₂ and polymer materials having an affinity for a suitable solvent. As a polymer having an affinity for a solvent, first, as a water-soluble polymer insolubilized, cellulose acetate, polyvinyl alcohol, poly N vinylpyrrolidone,
Polyacrylamide, cellulose, carboxymethylcellulose, nitrocellulose, cyanoethylcellulose, cellulose sulfate, heparin, pectin, alginic acid, hydroxymethylcellulose, isopropylcellulose, polyacrylic acid, heat-treated and crosslinked products such as polyethylene oxide, among the above water-soluble polymers Copolymers obtained by crosslinking two or more kinds of polymers can be mentioned. Further, there is also mentioned a film in which a water-insoluble polymer which hardly swells with water is copolymerized with the above-mentioned water-soluble polymer at an appropriate fraction to improve the degree of swelling in water. Further, a method of dissolving a photocrosslinkable monomer in a water-soluble polymer solution, irradiating light after film formation to form a crosslinked structure, and obtaining a superabsorbent polymer can be mentioned. Examples of these polymers include photocrosslinkable polyvinyl alcohol, photocrosslinkable polyethylene oxide, and photocrosslinkable polyethylene glycol. 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 restrict their movement, a large diffusion coefficient may not be obtained in the membrane. For this reason, it is possible to improve selectivity and sensitivity by coating these anionic polymers after coating the water-soluble polymer.
In a two-layer film, the upper film having the function of taking in the target substance is separated from the lower film which contributes to the electrode response. Is fine. Also, as the lower layer film,
A porous membrane can also be used. Further, other than polymers, amphoteric substances used for bilayer membranes and LB membranes can be dispersed in a porous membrane and used as a thin film.

In the present invention, the thickness of the solid ionic conductor which does not contain oxidizing species and reducing species, which is provided at the tip of the electrode as required, is 100 μm or less, preferably 50 μm or less.
μm or less.

The integrated microelectrode manufactured as described above can be used for the purpose of measuring the oxidation-reduction reaction in a specimen having ordinary conductivity. Further, the integrated microelectrode can exert its power in measuring a minute space. This does not need to be explained in consideration of the shape of the integrated electrode structure.
Furthermore, since the integrated microelectrode has a micro-sized working electrode, a reference electrode, and a counter electrode, if necessary, arranged close to each other, the integrated microelectrode can be used even when measuring the electrode reaction of electrode active species in a high-resistance medium. The spacing does not have to be adjusted each time and the resistance between the electrodes based on the medium can be minimized.

The medium to be measured by the integrated microelectrode of the present invention includes water, ethers such as diethyl ether, dimethoxyethane, tetrahydrofuran, tetrahydropyran, acetonitrile, dimethylformamide, dimethylsulfoxide, liquid ammonia, sulfuric acid and the like. Not only can be used, but also a molten salt, a supercritical fluid, and the like can be measured. These solvents include:
A conventional method of dissolving a known supporting electrolyte and lowering the solution resistance for measurement is applied. Examples of the high-resistance medium include the above-described solvents, solid polymers, and gases that do not contain a supporting electrolyte. Examples of the solid polymer include polyethylene glycol or a polymer similar to polyethylene glycol. By mixing lithium ion into the polymer, the electrochemical behavior of lithium ion in a high-resistance medium can be measured. Gas is also a measurement target of the integrated microelectrode 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 measured as an electrode reaction.

The measurement is performed by bringing the above-mentioned test medium into contact with the above-mentioned integrated microelectrode. As a measuring device,
In addition to potentiostats, galvanostats, coulostats and the like, appropriate measuring devices such as potential scanners, lock-in amplifiers, frequency response analyzers and the like can be connected to these for measurement.

[0023]

Next, the present invention will be described in detail with reference to examples. However, the examples are for describing the present invention in detail, and it is refused that the present invention is not limited by these examples. Not even.

(Example 1) Three glass capillaries having an outer diameter of 1.2 mm were bundled, and the ends were heated with a gas burner and squeezed.
Platinum wires having diameters of 25 mm and 100 mm were sealed to serve as a working electrode and a counter electrode, respectively. A 100 mm diameter platinum wire tip was similarly sealed in the tip of the remaining one capillary to form a liquid junction for the reference electrode. Further, a silver wire plated with silver chloride on its surface and potassium chloride saturated water were put into the capillary by a conventional method to obtain a silver / silver chloride (Ag / AgCl) reference electrode. The tip of the pin-shaped electrode with the three poles integrated at the tip was polished to complete the microelectrode with the three poles integrated on the same surface in the tip area with a small area. FIG. 1 shows a side view photograph of the integrated microelectrode. FIG. 2 shows a front photograph of the tip of the electrode, from which it can be seen that the diameter of the tip of the integrated electrode is about 500 mm. As a result of immersing the tip of the electrode in ultrapure water for one day and performing ICP analysis,
No ions derived from the reference electrode were detected in the water.

(Example 2) The tip of a glass capillary having an outside diameter of 1.2 mm and the inside of which was separated into two chambers by a glass partition was heated with a burner and squeezed. And a liquid junction for a reference electrode. A silver wire plated with silver chloride on its surface and potassium chloride-saturated water were put into the capillary for reference electrode by a conventional method to prepare a reference electrode.
Prior to the completion of the reference electrode, a platinum film having a thickness of about 100 nm was provided on the outer wall of the glass capillary by sputtering to serve as a counter electrode. Polish the tip of the pin-shaped electrode,
The integrated microelectrode of the present invention in which the working electrode and the reference electrode are formed on the tip micro-plane and the counter electrode is formed on the side surface is completed. An electron micrograph of the tip of the integrated microelectrode is shown in FIG. 3, which shows that the tip diameter of the integrated electrode is about 60 mm. Immerse the tip of the electrode in ultrapure water for one day,
As a result of ICP analysis, ions derived from the reference electrode were not detected in the water.

(Example 3) Ferrocenylmethyl trimethylammonium bromide was dissolved in ultrapure water prepared using a Millipore filter to prepare a 4 mM aqueous solution. The ionic conductivity of this aqueous solution was measured by an alternating current method (TOA conductivity meter CM-7B) and found to be 44.5 μSc.
m ⁻¹ , which was about 1/1000 of the conductivity of a solution that enables normal electrochemical measurement. The tip of the integrated microelectrode prepared in Example 1 was immersed in this high-resistance test solution, and a potentiostat (Hokuto Denko HA) was used using three electrodes.
150), and a cyclic voltammogram was measured at a potential scanning speed of 50 mVs ^-1 . The results are shown by the solid line in FIG. 4, and an S-shaped current-potential curve was obtained, indicating that the electrode oxidation reaction of ferrocenylmethyl trimethylammonium cation was measured.

Comparative Example 1 In Example 3, a platinum microelectrode having a diameter of 25 μm, a silver-silver chloride (Ag / AgCl) reference electrode, and an effective area of 0.5 cm ² were used instead of the integrated microelectrode.
Of three platinum foil counter electrodes were independently used. Example 3 except that the distance between the electrodes was reduced to a distance of about 2 mm.
The cyclic voltammogram was measured in the same manner as described above. The results are shown by the dotted line in FIG. 4, and it is apparent that only a monotonic increase in the current with respect to the potential was observed, and the electrode oxidation reaction of ferrocenylmethyltrimethylammonium cation could not be measured.

Example 4 In Example 3, only the working electrode and the reference electrode were used without using the counter electrode. That is, when the reference electrode was used as both a reference electrode and a counter electrode, the same measurement results as in Example 3 were obtained.

(Example 5) Nafion solution (manufactured by Aldrich) was applied to the tip of the integrated microelectrode prepared in Example 1.
Was coated by dip coating, and all three poles at the tip were covered with a Nafion membrane. The electrode thus treated was immersed in ultrapure water in which hydrogen gas was bubbled, and the cyclic voltammogram was measured in the same manner as in Example 3. The results are shown in FIG. 5, where a current potential curve for hydrogen oxidation was observed. Thus, the measurement of the current-potential curve was possible even in ultrapure water having no conductivity.

(Embodiment 6) A Nafion solution (manufactured by Aldrich) was applied to the tip of the integrated microelectrode prepared in Embodiment 1.
Was coated by dip coating, and all three poles at the tip were covered with a Nafion membrane. The electrode thus treated was contacted with hydrogen gas which was bubbled in ultrapure water and humidified, and a cyclic voltammogram was measured in the same manner as in Example 5. The results are shown in FIG. 6, where the current potential pole of hydrogen oxidation is observed. In this way, it is possible to measure the gas-phase electrode reaction even in a gas. (Comparative Example 2) When the independent three electrodes used in Comparative Example 1 were used instead of the integrated electrode used in Example 5, the potential regulation by the potentiostat was impossible (the electrode potential could not be measured). The cyclic voltammogram could not be measured.

Example 7 A current potential pole was measured in exactly the same manner except that oxygen gas was used instead of hydrogen gas used in Example 6. The results are shown in FIG. 7. The current potential curve of oxygen reduction was measured in the gas phase.

(Examples 8 to 11) Methanol was put into an air-washing bottle, and nitrogen gas was passed therethrough to obtain a methanol-saturated gas (methanol partial pressure: 97.5 mmHg). On the other hand, a water-saturated gas (steam partial pressure of 17.4 mmHg) was obtained by filling the cleansing bottle with ultrapure water and passing nitrogen gas through. Both were mixed at an arbitrary ratio using a gas mixer, and the current potential pole was measured in the same manner as in Example 6. However, the potential scanning speed is 5 mV
s ^-1 . The gas flow rate was 0.4 liter / min, and the mixing ratio of the gas was methanol-saturated gas: water vapor = 1: 3.
(Example 8) 2: 2 (Example 9), 3: 1 (Example 1)
0), 4: 0 (Example 11). The result is shown in Fig. 8
The numbers in the figure indicate the numbers of the examples. Also,
The solid line represents potential scanning in the anode direction, and the dotted line represents potential scanning in the cathode direction. This indicates that the current potential pole of the electrode oxidation of gaseous methanol can be measured in the gas phase.

[0033]

According to the integrated microelectrode of the present invention, since an electrode group is integrated in the tip region having a small area, electrochemical measurement in a local region can be performed. Further, when the integrated microelectrode of the present invention is used, it is possible to perform an electrochemical measurement in a high-resistance medium, for example, ultrapure water, gas, polymer, or the like. Furthermore, by using the integrated microelectrode of the present invention, qualitative and quantitative analysis of gas becomes possible, and application as a gas detector is also possible.

[Brief description of the drawings]

FIG. 1 is an optical microscope photograph showing a side surface of an integrated microelectrode of Example 1 of the present invention. One division of the scale is 1 mm.

FIG. 2 is an optical microscope photograph showing the tip of the integrated microelectrode of Example 1 of the present invention. W, R, and C represent a working electrode, a reference electrode, and a counter electrode, respectively.

FIG. 3 is a scanning electron micrograph showing a tip surface of an integrated microelectrode according to Example 2 of the present invention.

FIG. 4 shows Example 3 of the present invention (solid line) and Comparative Example 1 (dotted line).
1 shows a cyclic voltammogram.

FIG. 5 shows a cyclic voltammogram of Example 5 of the present invention.

FIG. 6 shows a cyclic voltammogram of Example 6 of the present invention.

FIG. 7 shows a cyclic voltammogram of Example 7 of the present invention.

FIG. 8 shows cyclic voltammograms of Examples 8 to 11 of the present invention.

Claims (7)

[Claims] 1. An integrated microelectrode characterized in that at least a working electrode and a reference electrode are integrated in a tip area having a small area via an insulator. 2. An integrated microelectrode, wherein at least a working electrode, a reference electrode and a counter electrode are integrated in a tip area having a small area via an insulator. 3. The geometric area of the working electrode is 1 × 10 ⁻⁴ cm.
^3. The integrated microelectrode according to claim 1, wherein the number is ² or less. 4. At least 1 × 1 working electrode and reference electrode
0 ^-2 cm ² or less of Integrated Micro electrode according to claim 1 to 3, characterized in that it is integrated in the projection area. 5. The method according to claim 1, wherein at least the electrically insulated working electrode and the reference electrode are in contact with each other via a solid ionic conductor containing no oxidized or reduced species. Integrated microelectrodes. 6. An electrode reaction The effective electrode portion of the integrated microelectrode according to claim 1 is brought into contact with a high-resistance medium containing an oxidizing species and / or a reducing species to measure the relationship between current and potential. A method for measuring an electrode reaction in a high-resistance medium, comprising: 7. The method for measuring an electrode reaction in a high-resistance medium according to claim 6, wherein the high-resistance medium is a gas.