JPH01216262A - Electrochemical sensor - Google Patents

Abstract

PURPOSE:To increase the ion quantity which is concerned in the ionic conduction and to raise the sensitivity of the sensor by forming the thickness of a solid-state electrolytic layer between reaction parts of a working electrode and a counter electrode so as to become thicker than the sum of the thickness of the reaction parts of the working electrode and the counter electrode part and the thickness of the solid-state electrolytic layer for covering the reaction part. CONSTITUTION:On a rectangular insulating substrate 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 solid-state electrolytic layer 6. The solid-state electrolytic layer 6 consists of a comparatively thin part 61 on each reaction part 20, 30 and 40, and a pretty thick part 60 between each reaction part, and constituted so that thickness t1 extending from the surface of the insulating substrate 1 to the solid-state electrolytic layer 60 becomes larger than the sum t2 of thickness of the reaction part 20, etc. and thickness of the solid-state electrolytic layer 61 on said part.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electrochemical sensor, and more specifically, an electrochemical sensor that detects or quantifies a specific gas component using an electrolytic reaction. It is related to 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 the reaction is
Since the potential of the working electrode varies depending on the components of the detected gas, it is necessary to keep the potential of the working electrode constant depending on the detected gas. Therefore, the voltage applied to the working electrode is controlled with reference to the reference electrode.

In this way, in addition to the method of setting the potential of the working electrode to a constant value and selecting the gas component to be detected, the reaction can be performed selectively for each gas component by changing the potential of the working electrode of the same sensor. A method has also been adopted in which the target detection gas component is separated and selected using the so-called potential sweep method, which measures the detection current while changing the potential of 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.

This gas sensor has a sensing electrode (working electrode) and a reference electrode (reference electrode) on one side of the solid electrolyte membrane, and a reverse electrode (counter electrode) on the other side, making it more compact than the liquid electrolyte type. 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 micro-processing technology such as planar technology, and gas sensors used in combination with such elements have also been developed using ultra-miniaturized layers and high 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. 8 and 9 show structural examples of such a planar type gas sensor, in which a working electrode 2. A counter electrode 3 and a reference electrode 4 are provided, each of which consists of a reaction section 20.30.40 that performs an electrochemical action and a terminal section 21, 31.41 that is connected to an external circuit. A solid electrolyte layer 6 is provided to cover .40 and the space therebetween.

The solid electrolyte layer 6 thinly covers each reaction section 20 and the like so that the entire solid electrolyte layer 6 has a -like thickness, and the upper surface of the solid electrolyte layer 6 is flat. Therefore, 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.

The above gas sensor has all electrodes 2 on the same surface of an insulating substrate l.
．． 3.4, the electrodes and solid electrolyte layers can be formed extremely efficiently using micro-processing technology such as planar technology, making it possible to miniaturize the sensor and improve its performance. It has excellent characteristics.

[Problem to be solved by the invention]

However, in the solid electrolyte type sensor described above, the solid electrolyte that controls ion conduction from the working electrode to the counter electrode has a lower ion concentration and lower ion mobility than conventional liquid electrolytes, so the electrochemical reaction of the sensor is In this system, the movement of ions from the working electrode to the counter electrode is extremely slow and becomes a rate-limiting process, resulting in a small detection current and a problem in that the detection sensitivity of the sensor is low.

In addition, since the specific resistance of solid electrolytes is higher than that of liquid electrolytes, the electrical resistance between the working electrode and the counter electrode is large.
As a result, there is a problem that the time constant of the electrochemical reaction becomes large and the reaction rate becomes slow.

In particular, when implementing the above-described potential sweep method, if the reaction rate is slow, the potential cannot be swept quickly and a satisfactory detection result cannot be obtained.

In order to eliminate these drawbacks, as shown in Figure 1O,
It was also considered to increase the thickness of the solid electrolyte layer 6 to enable good ion conduction, but the reaction section 2
0 etc. is thickly covered with the solid electrolyte layer 6, making it difficult for the detection component to pass through the thick solid electrolyte layer 6, diffuse into the reaction area 2° of the working electrode 2, and cause a reaction. , on the contrary, the detection current decreases and the sensitivity decreases.

Therefore, an object of the present invention is to improve the detection sensitivity and the reaction rate by enabling good ion conduction within the solid electrolyte layer.

Although all of the above explanations have been made regarding gas sensors, the structure of the gas sensor described above can be applied to electrochemical detection in various applications, such as by applying it to 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 problems, the present invention provides that the thickness of the solid electrolyte layer between the reaction parts of the working electrode and the counter electrode is smaller than the sum of the thickness of the reaction parts of the working electrode and the counter electrode and the thickness of the solid electrolyte layer covering the reaction part. I also try to make it thicker.

[For production]

In this way, if the thickness of the solid electrolyte layer between the reaction part of the working electrode and the counter electrode is made thicker than other parts, the amount of ions involved in ion conduction from the working electrode to the counter electrode will increase, and the mobility will increase. Therefore, ion movement is not the rate-limiting process,
A sufficient detection current can be obtained, and the electrical resistance between the working electrode and the counter electrode is also low.

Moreover, only the solid electrolyte layer between the reaction parts is thickened.
Since the thickness of the solid electrolyte layer at the reaction part may be as thin as in the conventional case, the diffusion of the detection component into the reaction part and the electrochemical reaction can be carried out as well as in the conventional case.

〔Example〕

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

1 and 2 schematically show the structure of a gas sensor according to the present invention, in which a working electrode 2 is placed on a rectangular insulating substrate 1. A counter electrode 3 and a reference electrode 4 are provided, and various 2
．． 3.4 are reaction sections 20.3 and 3.4, respectively, which perform electrochemical action.
30, 40, and terminal portions 21, 31 . . , which connect to external circuits.
41, and the solid electrolyte layer 6 covers the top and the space between each reaction section 20, 30, 40. This basic configuration is the same as that of a conventional gas sensor.

In the illustrated embodiment, the reaction parts 20.30 of the working electrode 2 and the counter electrode 3 have a relatively large rectangular shape, and their long sides face each other with a constant gap. The reaction section 40 of the reference electrode 4 has a small rectangular shape and is arranged between the reaction sections 20, 30 of the working electrode and the counter electrode. The various terminal parts 21, 31.41 are connected to the reaction parts 20, 30.
．． It is juxtaposed on the outside of the solid electrolyte layer 6 that covers the solid electrolyte layer 40 to facilitate connection to an external circuit.

The solid electrolyte layer 6 includes each reaction section 20, 30.40 and
The thickness of the solid electrolyte N6 that covers the space between them varies depending on the location. Each reaction section 20.30.40
The thickness of the solid electrolyte layer 61 at the zero reaction area is relatively thin at the area 61 corresponding to the top, and considerably thick at the area 60 between the reaction areas 20, 30, and 40. The solid electrolyte layer 61 is formed to be thin enough to allow gas and the like to quickly pass through the solid electrolyte layer 61 and diffuse into the reaction section 20 and the like. On the other hand, the solid electrolyte layer 60 between the reaction parts is formed to have a thickness that allows sufficiently good ion conduction. Therefore, the thickness 11 from the surface of the insulating substrate 1 to the solid electrolyte layer 60 between the reaction parts is larger than the sum t3 of the thickness of the reaction part 20 etc. and the thickness of the solid electrolyte layer 61 thereon.

In the above-mentioned gas sensor, the insulating substrate l is made of a common insulating substrate material for gas sensors or electronic circuit elements, such as aluminosilicate glass.

Platinum is preferably used as the material for the working electrode 2 and counter electrode 3, and gold is preferably used as the material for the reference electrode 4, but it is also possible to use other various electrode materials. It can be formed by ordinary electrode forming means, for example, 5
For the 0 reaction part 20, etc., which is carried out with 0 thickness for about 000 people,
It may be coated with platinum black or subjected to activating treatment such as oxidation treatment. The narrower the distance between the reaction parts, the easier the ion conduction and the lower the electrical resistance.

As the solid electrolyte N6, a gas-permeable polymer solid electrolyte such as sulfonated perfluorocarbon (trade name: Nafion, manufactured by DuPont) is used, but other solid electrolytes that are used in ordinary gas sensors can also be used. For example, sb, os' 4H, O, Zr (
HPO, )t'4HtO, etc. can also be used.

The thickness of the solid electrolyte layer 6 is, for example, approximately 2 pH at the reaction part 61 and approximately 20 μm between the reaction parts 60, but it depends on the spacing between the reaction parts 20, 30, the characteristics of the solid electrolyte, the application and required performance of the sensor. The thickness can be changed as appropriate by taking this into account.

In the above embodiment, as shown in FIG. 3, when the thickness of the various reaction parts 20, etc. is increased, the opposing areas of the reaction parts 20, 30, etc. become wider, and the solid electrolyte layer 60 between the reaction parts becomes larger.
Since more parts are arranged between the opposing surfaces, the electrochemical reaction and ion conduction between the reaction parts 20 and 30 become better, and sensitivity can be improved. As a specific example of dimensions, the thickness of various reaction parts 20 etc. is 5 μm.
, the thickness of the solid electrolyte N60 between the reaction parts is set to 25p1.

In the embodiment described above, the solid electrolyte layer 60 between each electrode is formed to have the same thickness, but only the area between the reaction areas 20 and 30 of the working electrode and the counter electrode, which is most important for ion conduction, is formed thick. The effect of this invention can be exhibited just by keeping it in place.

A method for manufacturing a solid electrolyte layer 6 in which the thickness is different between the reaction parts is, for example, by covering the parts where the thickness should be reduced, such as each reaction part 20, with masking tape, and then coating it with an appropriate solvent. The melted solid electrolyte material is cast to a predetermined thickness between the reaction sections, and is dried and solidified to form a thick solid electrolyte 1i60 between the reaction sections. Thereafter, the tape is peeled off and the solid electrolyte is thinly cast on the remaining reaction area, thereby forming a thin solid electrolyte layer 61.

In addition to the illustrated embodiments, various shapes and arrangements can be made with appropriate structures employed in ordinary gas sensors. For example, the structure shown in FIG.
0.30 are formed in a comb-teeth shape and are arranged so as to mesh with each other at intervals. With this structure, the opposing areas involved in the electrochemical reaction in the reaction parts 20.30 of the working electrode and the counter electrode increase, and the spacing between the reaction parts 20.30 can be narrowed, so detection sensitivity can be improved. Can be done. The solid electrolyte layer 6 has a shape that matches the formation pattern of the reaction parts 20 and the like, and the solid electrolyte layer 6 between the reaction parts
0 (the hunting part in the figure) is formed thickly.

To show the specific dimensions of the above embodiment, for example, the line width of each comb tooth to
o n, line spacing 200 n, line length 3c11, thickness 5000
For a person, the number of tubes is 50 tubes for each reaction part 20.30 mm, total 100 tubes.
A book will be provided. The thickness of the solid electrolyte Fi61 at the reaction part is 2n, and the thickness of the solid electrolyte layer 60 between the reaction parts is 10#.
1 will be implemented.

Another embodiment of the invention is shown in FIGS. 5 and 6, in which a solid electrolyte layer 6 is provided only between the various reaction sections, and a solid electrolyte layer 6 is provided above each reaction section 20, 30, 40. There is no electrolyte layer. Thickness of solid electrolyte Jif6 between reaction parts 1. teeth,
It is formed thickly so that ion conduction can be performed well, and is considerably thicker than the thickness t of the reaction section 20 and the like.

In this way, if the solid electrolyte layer 6 is not above the reaction section 20 etc. and the reaction section 20 etc. is exposed, the detected gas etc. will not be obstructed by the solid electrolyte layer 6 and will directly reach the reaction section 20 etc. The so-called three phases coexist: a gas phase containing the detection gas, a solid phase in the reaction area where the detection gas undergoes an electrochemical reaction, and an electrolyte phase that carries the ions generated by the reaction. A three-phase interface is formed, and electrochemical reactions such as the reaction of the detection gas and the movement of ions generated by the reaction occur very efficiently, further improving the sensitivity and response speed of the sensor.

Furthermore, FIG. 7 shows another embodiment, in which an insulating substrate 1 is used in which an insulating film 11 of silicon dioxide is coated on silicon lO as a base material. Also,
The insulating substrate 1 is dug into a groove shape between the reaction part 20 of the working electrode and the reaction part 30 of the counter electrode, and the inner surface of this 12 is also covered with the insulating film 11, and each reaction part 20
etc. are formed to extend from the upper surface of the insulating substrate 1 to the side walls of the groove 12. The solid electrolyte layer 61 at the reaction part is formed thinly as in the previous embodiment, and the solid electrolyte layer 60 between the reaction parts covers the inside of the groove 12, and the upper surface is higher than the reaction part 61. It has become. Therefore, the specific dimensions of the sensor in which the thickness tl of the solid electrolyte layer 60 between the reaction parts is thicker than the thickness t8 of the reaction part 20 etc. including the extension part to the groove 12 are, for example, 11
The depth of the solid electrolyte layer 61 at the reaction part is about 2iIs, and the thickness of the solid electrolyte layer 60 between the reaction parts is about 30 μm including the groove 12 part. shape, the thickness of the solid electrolyte 6, or the groove 12.
The formation method etc. can be changed as appropriate depending on the purpose. Further, the materials and shapes of the insulating substrate 1 and the various 2.degree.

With this structure, as in the embodiment shown in FIG. 3, the opposing areas of the reaction parts 20, 30, etc. become wider, and the thickness of the solid electrolyte layer 60 between them also increases, which improves the sensitivity of the sensor. It is effective for Note that, compared to the embodiment shown in FIG. The embodiment shown in FIG. 3 is superior in terms of ease of manufacture because it requires time and effort to form the solid electrolyte layer.Furthermore, in each of the embodiments described above, a gas selective permeability filter is provided on the solid electrolyte layer 6. By placing a water reservoir layer on top of the solid electrolyte layer 6, the target detection gas can be selectively sent to the solid electrolyte layer 6 or the working electrode 2 side, thereby partially increasing the detection accuracy. Sensitivity can be improved.

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. Note that when used in a liquid, the solid electrolyte does not need to be gas permeable, and the structure may be changed as appropriate depending on the application.

〔Effect of the invention〕

In the present invention described above, the thickness of the solid electrolyte layer covering between the reaction parts of the working electrode and the counter electrode is greater than the sum of the thicknesses of the reaction part and the solid electrolyte layer covering it.

By making it large, ion conduction accompanying electrochemical reactions is performed well, and the detection current becomes large, thereby improving the sensitivity of the sensor. In addition, since the specific resistance becomes smaller, the electrical resistance between the working electrode and the counter electrode becomes smaller, and the response speed of the sensor becomes faster.Therefore, it is suitable for applications that require a fast response speed, such as the potential sweep method. It becomes possible to do so.

[Brief explanation of the drawing]

1 is a schematic structural perspective view of a gas sensor according to the present invention, FIG. 2 is a sectional view, FIG. 3 is a sectional view of another embodiment, FIG. 4 is a plan view of another embodiment, and FIG. 6 is a sectional view, FIG. 7 is a sectional view of another embodiment, FIG. 8 is a perspective view of a conventional example, FIG. 9 is a sectional view, and FIG. 10 is a sectional view of another embodiment. FIG. 3 is a sectional view of another conventional example. 1... Insulating substrate 2... Working electrode 20. 30.
40...Reaction part 3...Counter electrode 4...Reference electrode 6
...Solid electrolyte layer 60...Solid electrolyte layer between reaction parts 61...Solid electrolyte layer agent at reaction part Patent attorney Takehiko Matsumoto Figure 4 Figure 7 Figure 9 Figure 10 Figure 1986 April 27th

Claims (1)

[Claims] 1. In an electrochemical sensor in which a working electrode, a counter electrode, and a reference electrode are provided on the same surface of an insulating substrate, and a solid electrolyte layer is provided covering at least the space between the reaction parts of each electrode, the reaction part between the working electrode and the counter electrode is An electrochemical sensor characterized in that the thickness of the solid electrolyte layer between the working electrode and the counter electrode is greater than the sum of the thickness of the reaction part of the working electrode and the counter electrode and the thickness of the solid electrolyte layer covering the reaction part.