JPH01216263A - Electrochemical sensor - Google Patents

Abstract

PURPOSE:To raise the detection sensitivity, and also, to stabilize the detecting reaction by placing successively and repeatedly reaction parts of each electrode, in the electrochemical sensor in which a solid-state electrolytic layer is provided among a working electrode, a counter electrode and a reference electrode. CONSTITUTION:On an insulating electrode 1, reaction parts 20, 30 and 40 for executing an electrochemical action and a working electrode 2, a counter electrode 3 and a reference electrode 4 consisting of terminal parts 21, 31 and 41 which are connected to an external circuit are provided, and the upper part of each reaction part 20, 30 and 40 and the parts among them are covered with a slid-state electrolytic layer 6. The reaction parts 20, 30 and 40 of the working electrode 2, the counter electrode 3 and the reference electrode 4 consist of those which are formed in a thin spiral line shape, and these spiral-like reaction parts 20, 30 and 40 have the same center, and also, placed at a prescribed interval between each other. The outside peripheral ends of each reaction part 20, 30 and 40 are connected to the rectangular surface-like terminal parts 21, 31 and 41, and can be connected easily to the external circuit.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electrochemical sensor, and more specifically, an electrolytic sensor that detects or quantifies a specific gas component using an electrolytic reaction. This relates to chemical sensors.

[Conventional technology]

The general basic structure of an electrolytic gas sensor is that three electrodes, a working electrode, a counter electrode, and a reference electrode, are provided in an electrolyte, and its working mechanism is that a constant voltage is applied to the working electrode. When applied, the gas component to be detected undergoes an oxidation or reduction reaction at the working electrode, and the ions generated at this time move within the electrolyte and undergo a reduction or oxidation reaction at the counter electrode. By measuring the current flowing between the working electrode and the counter electrode accompanying this redox reaction, it is possible to detect and quantify the target gas. ″ The potential of the working electrode required to cause a reaction varies depending on the components of the detected gas, so it is necessary to keep the potential of the working electrode constant depending on the detected gas. to control the voltage applied to the working electrode.

By the way, conventional electrolytic gas sensors use the electrolyte as
For example, since liquid electrolytes such as H, So, etc. are used,
There are problems such as electrolyte change over time, liquid leakage, and material corrosion.
Because it requires a tightly sealed structure, it is difficult to miniaturize it, and its sensitivity and output decrease over time, resulting in poor long-term stability and short lifespan.
There were drawbacks such as difficulty in handling and management.

Therefore, instead of liquid electrolytes, gas sensors using solid polymer electrolytes such as sulfonated perfluorocarbons have been developed; for example, U.S. Pat.
It is disclosed in Japanese Patent No. 115293 and the like.

child? Gas sensors have a sensing electrode (working electrode) and a reference electrode (reference electrode) on one side of a solid electrolyte membrane, and a reverse electrode (counter electrode) on the other side, making them more compact than liquid electrolyte types. It has excellent performance such as stability over time, and is easy to handle.

However, in this gas sensor, an electrode made of a gas-permeable membrane supporting a fine particle mixture of Pt, Au, etc. and polytetrafluoroethylene is bonded to a soft solid electrolyte membrane, which makes manufacturing difficult. In addition, there was a problem in that it was difficult to miniaturize and form a sensor array.

In recent years, electronic circuit elements such as semiconductors have been miniaturized using microfabrication technology such as planar technology, and the -i5 has become ultra-miniaturized and highly sophisticated as a gas sensor used in combination with such elements. Performance is required.

Therefore, the applicant has developed a planar gas sensor that solves the problems of the prior art described above and can be manufactured using the same microprocessing technology as semiconductor devices. Figure 5 shows
An example of the structure of such a planar gas sensor is shown, in which a working electrode 2. A counter electrode 3 and a reference electrode 4 are provided, each consisting of a reaction part 20.30.40 for performing electrochemical action and a terminal part 21.31.41 connected to an external circuit. The reaction parts 20.30 of the working electrode 2 and the counter electrode 3 are formed in a mutually intricate comb-shaped structure, and by increasing the reaction area, the sensitivity of the sensor is improved. The reaction section 40 of the reference electrode 4 is disposed on the side of the comb-shaped reaction sections 20, 30 of the working electrode 2 and counter electrode 3. A solid electrolyte layer 6 is provided to cover these various reaction sections 20, 30, 40 and the spaces therebetween. The detection gas and the like pass through the solid electrolyte layer 6 and diffuse onto the reaction part 20 of the working electrode, causing an electrochemical reaction.

In the above gas sensor, all the electrodes 2, 3 and 4 are provided on the same side of the insulating substrate 1, so the formation of the electrodes and solid electrolyte layer is extremely difficult using micro-processing technology such as planar technology. It has many excellent features, such as efficient processing, miniaturization and high performance of the sensor.

[Problem to be solved by the invention]

However, in the conventional sensors described above, the reaction part of the reference electrode, which is important for setting the potential of the working electrode, is provided at a position away from the reaction parts of the working electrode and the counter electrode, making it difficult to set the potential of the working electrode. There was a problem with getting enough. In other words, since an electrochemical reaction takes place between the reaction parts of the working electrode and the counter electrode,
In order to accurately set the potential of the working electrode, it is best for the reaction part of the reference electrode to be located between the working electrode and the counter electrode.

However, 1. If the reaction part of the reference electrode is located far from the reaction parts of the working and counter electrodes, and the potential setting of the working electrode becomes inaccurate or unstable, accurate detection current will not be obtained. This results in a lack of reliability and stability in the detection results, which reduces the detection performance of the sensor.

Note that when using a liquid electrolyte as the electrolyte, the potential within the electrolyte is approximately constant, so no matter where the reaction part of the reference electrode is located within the electrolyte, it does not have much of an effect; however, when using a solid electrolyte Since the potential varies considerably depending on the position within the solid electrolyte and a potential distribution occurs, the position where the reaction part of the reference electrode is provided has an extremely large effect on the potential setting of the working electrode.

Note that if the reaction part of the reference electrode is installed between the reaction parts of the working electrode and the counter electrode, the potential of the working electrode can be set accurately. This is undesirable since it interferes with the electrochemical reaction between the working electrode and the counter electrode, which is undesirable as it has a negative effect on the detection sensitivity, etc. Therefore, the object of this invention is to
The purpose is to enable accurate setting of the potential of the working electrode.

Although all of the above explanations have been made regarding gas sensors, the structure of the gas sensor described above can be used as an ion sensor if the detection target that causes a reaction at the working electrode is ions in a liquid. This invention is applicable to sensors in general, including gas sensors.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention arranges that various reaction parts are arranged repeatedly in sequence. Where the reference electrode reaction area is located between the working electrode reaction area and the counter electrode reaction area, the potential of the working electrode can be accurately set based on the reference electrode, and the working electrode reaction area and the counter electrode reaction area are In a location where the electrodes are directly opposed to each other without sandwiching the reference electrode reaction section between them, the electrochemical reaction can be performed satisfactorily between the working electrode reaction section and the counter electrode reaction section.

〔Example〕

Next, the present invention will be described in detail below with reference to drawings showing embodiments.

1 and 2 show a schematic structure of a gas sensor according to the present invention, in which a working electrode 2. A counter electrode 3 and a reference electrode 4 are provided, and various 2, 3.4
are reaction parts 20.30.4 that perform electrochemical action, respectively.
0 and terminal portions 21, 31, and 41 connected to an external circuit, and the top and the space between each reaction portion 20, 30, 40 is covered with a solid electrolyte M6. This basic configuration is the same as that of a conventional gas sensor.

In the illustrated embodiment, various reaction sections 20.30
．． 40 is formed into a thin spiral line,
These spiral reaction sections 20... have the same center and are arranged with a constant interval between them. The outer peripheral end of each reaction section 20... is connected to a rectangular terminal section 21, 31, 41 to facilitate connection to an external circuit.

The cross-sectional structure of this reaction part is shown in FIG. 2, in which a working electrode reaction part 20. Counter electrode reaction section 30. Reference electrode reaction section 40. Again, the working electrode reaction section 20, the three-pole reaction section 20, and so on are repeatedly arranged one after another. That is, areas where the working electrode reaction area 20 and the counter electrode reaction area 30 directly face each other and areas where the reference electrode reaction area 40 is disposed between the working electrode reaction area 20 and the counter electrode reaction area 30 are formed alternately. Become.

In the gas sensor as described above, the insulating substrate 1 is made of a ceramic substrate such as an alumina ceramic plate, or a glass substrate, which is the material of the working electrode 2 and the counter electrode 3, in which an insulating substrate material for ordinary gas sensors or electronic circuit elements is used. Although platinum is used and gold is preferably used as the material of the reference electrode 4, it is also possible to use other various electrode materials. Each electrode can be formed by a normal electrode forming method such as a sputtering method, and for example, platinum black is applied to the 0 reaction part 20, etc., which is performed with a zero thickness of about 5,000 people.

, activation treatment such as oxidation treatment may be performed.

- Specific dimensions of each reaction section 20 include, for example, the line width IQOIIN and the distance between adjacent reaction sections 100. lol,
The number of turns of the spiral is 1.0.

For the solid electrolyte layer 6, a gas-permeable polymer solid electrolyte such as sulfonated perfluorocarbon (trade name: Nafion, manufactured by DuPont) is used, but in addition, various solids used in ordinary gas sensors etc. are used. Electrolytes can be used, for example, sb, o% 4H, OlZr
(HPO4)t 4Hi O etc. can also be used. The thickness of the solid electrolyte layer 6 is, for example, approximately 2μ, but
It may be changed as appropriate depending on the purpose and structure of the sensor, or the type of solid electrolyte.

Furthermore, in the embodiment described above, if a gas selective permeability filter is provided on the solid electrolyte layer 6, the target detection gas can be selectively sent to the solid electrolyte N6 or the working electrode 2 side, thereby improving detection accuracy. Some can be increased. Furthermore, by providing a water reservoir layer on the solid electrolyte M6,
Sensitivity can be improved.

In addition to the above-mentioned embodiments, methods for forming the various reaction sections 20 in a spiral shape include, for example, using a flexible material such as cotton impregnated with an aqueous sulfuric acid solution as the electrolyte layer 6; If this sulfuric acid-impregnated cotton and platinum thin plates are alternately laminated in triple layers and this laminated body is wound into a spiral shape several times, each platinum thin plate can be formed into various spiral reaction parts 2.
A sensor configured as 0... is created.

Next, FIG. 3 and FIG. 4 show another embodiment, in which sulfuric acid-impregnated cotton is used as the electrolyte N6, and a platinum thin plate is used as the electrode material for the reaction section 20. is used. Then, from the center, the electrolyte layer 6, the working electrode reaction part 2
0, the electrolyte layer 6, the reference electrode reaction section 40, the electrolyte M6, and the counter electrode reaction section 30. Each reaction section 20... is provided with five layers, the outermost layer is wrapped with a fluorocarbon resin film 9, and the whole is formed into a concentric cylindrical shape. Respective lead wires 23, 33, 43 are connected to each reaction section 20 at one end surface of the cylindrical outer shape to establish electrical connection with an external circuit.

In addition, in the above embodiment, as the electrolyte N6, a solid polymer electrolyte can also be used in addition to sulfuric acid impregnated cotton. Further, as in the embodiment shown in FIG. 1, an insulating substrate 1 is used, and each reaction section 20 is formed concentrically on this insulating substrate 1 by means such as sputtering, and a solid electrolyte is placed on top of the reaction section 20. It may also be covered with N6. In this case, the reaction parts of the same polarity may be connected with a lead wire or the like.

As in each of the examples illustrated above, each reaction section 20...
If it is formed in a spiral or concentric cylindrical shape, the reaction area of the working electrode 2, counter electrode 3, etc. can be made very large within a certain area or volume, which is effective for improving detection sensitivity and reducing size. This makes the sensor highly stable and reliable.

However, if each reaction section 20... is arranged repeatedly in order, the reaction section 20... in a concentric arc shape with a part of the cylinder missing, a concentric polygon shape, or a linear reaction section 20... will be repeatedly arranged. This can be done even if the devices are installed side by side.

In addition, unless the gist of the present invention is changed, various structures or shapes employed in ordinary gas sensors can be combined and implemented.

Furthermore, although each of the above-mentioned embodiments has been described with respect to a gas sensor, it is also possible to apply the same configuration to various electrochemical sensors such as ion sensors and biosensors that react to ionic components in a liquid. In addition, when used in a liquid, the solid electrolyte does not need to be gas permeable, etc.
Change the structure as appropriate depending on the application and implement it.

〔Effect of the invention〕

As explained above, this invention has various reaction parts arranged repeatedly in sequence, and the counter electrode reaction part directly faces one side of the working electrode reaction part, so that electrochemical reactions and ion conduction can be performed well. The reference electrode reaction area is placed between the counter electrode reaction area and the counter electrode reaction area on the opposite side of the working electrode reaction area.
It becomes possible to accurately set the potential of the working electrode.

Therefore, the detection sensitivity is high and at the same time the detection reaction is stable, making it possible to provide a sensor with excellent reliability and stable performance.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of a gas sensor according to the present invention;
2 is a sectional view, FIG. 3 is a perspective view of another embodiment, FIG. 4 is a side view, and FIG. 5 is a perspective view of a conventional example. 2... Working electrode 20... Working electrode reaction part 3... Counter electrode 30... Counter electrode reaction part 4... Reference hole 40...
Reference electrode reaction section 6...Electrolyte layer agent Takehiko Matsumoto, patent attorney Figure 1 Figure 2 Figure 13 Figure 4 Figure 5 rfWm 42854 No. 2, Name of the invention Electrochemical sensor 3, Relationship to the amended person case Patent applicant address Address 1048 Kadoma, Kadoma City, Osaka Prefecture Name of the invention
Name (583) Representative of Matsushita Electric Works Co., Ltd. In the line ``Aqueous sulfuric acid solution as a material'' should be corrected to ``Aqueous sulfuric acid solution as a liquid electrolyte''. ■ In line 5 of page 12 of the specification, ``In addition to sulfuric acid impregnated cotton'' should be changed to ``Aqueous sulfuric acid etc. "It's made by impregnating cotton with liquid electrolyte."

Claims (1)

[Claims] 1. An electrochemical sensor comprising a working electrode, a counter electrode, and a reference electrode, with an electrolyte layer provided between at least the reaction parts of each electrode, characterized in that the reaction parts of each electrode are arranged repeatedly in sequence. Chemical sensor.