Electrochemical gas sensor and method for manufacturing an electrochemical gas sensor

Abstract

An electrochemical gas sensor (1) as an embodiment of the present invention comprises an insulating substrate (10), an electrolyte layer (11) formed on the insulating substrate (10), a first metal layer (12) formed on the insulating substrate (10), and a second metal layer (13) formed on the insulating substrate (10) so as not to contact the first metal layer (12). The electrochemical gas sensor (1) also comprises a working electrode (20) formed covering the electrolyte layer (11) and the first metal layer (12) on the insulating substrate (10) so as to extend over the electrolyte layer (11) and the first metal layer (12), and a counter electrode (21) formed covering the electrolyte layer (11) and the second metal layer (13) so as to extend over the electrolyte layer (11) and the second metal layer (13).

Description

Technical Field

[0001] The present invention relates to an electrochemical gas sensor and a method for manufacturing the sensor.

Background Art

[0002] Conventionally, an electrochemical gas sensor including a working electrode, a counter electrode, and an ion conductor has been known. In an electrochemical gas sensor, for example, the working electrode and the counter electrode are connected via an external circuit, and when a detection target gas such as carbon monoxide flows into the sensor, cations and electrons are generated at the working electrode. The electrons flow through the external circuit to the counter electrode, and the gas concentration can be detected by measuring the short-circuit current at this time.

[0003] Electrochemical gas sensors are roughly classified into sensors using a liquid electrolyte as an ion conductor and sensors using a solid electrolyte. For example, Patent Document 1 discloses an electrochemical gas sensor including a polymer solid electrolyte membrane, a working electrode, a counter electrode, a gas diffusion layer, and a filter. This sensor is characterized in that a conductive and porous gas diffusion layer covers the working electrode, and the gas diffusion layer is hydrophilic or the filter is composed of hydrophilic activated carbon. Patent Document 1 describes an effect that the decrease in sensitivity in a dry atmosphere can be suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Incidentally, cost reduction, miniaturization, and increased sensitivity are important challenges for electrochemical gas sensors. To achieve high sensor sensitivity, it is necessary to stabilize the baseline output when the target gas is not present. Our investigations have shown that if the contact resistance of the sensor's laminated structure is unstable, the baseline noise increases, and the sensor's sensitivity decreases. One possible way to stabilize the contact resistance of the laminated structure is to attach a fastening member to the sensor and strongly press the laminated structure, but in this case, problems such as the sensor structure becoming more complex and the sensor becoming larger are anticipated.

[0006] The objective of the present invention is to provide an electrochemical gas sensor that has a structure that does not require special fastening fixtures or the like, while exhibiting excellent baseline stability.

[0007] An electrochemical gas sensor according to one aspect of the present invention comprises an insulating substrate, an electrolyte layer formed on the insulating substrate, a first metal layer formed on the insulating substrate, a second metal layer formed on the insulating substrate so as not to contact the first metal layer, a working electrode that covers the surfaces of the electrolyte layer and the first metal layer facing away from the insulating substrate, or is interposed between the electrolyte layer and the first metal layer and the insulating substrate, and is formed across the electrolyte layer and the first metal layer, and a counter electrode that covers the surfaces of the electrolyte layer and the second metal layer facing away from the insulating substrate, or is interposed between the electrolyte layer and the second metal layer and the insulating substrate, and is formed across the electrolyte layer and the second metal layer.

[0008] A method for manufacturing an electrochemical gas sensor according to one aspect of the present invention includes the steps of forming a first metal layer and a second metal layer on an insulating substrate so as not to contact each other, forming an electrolyte layer on an edge substrate, and forming a working electrode and a counter electrode on an insulating substrate so as not to contact each other, wherein the working electrode is formed across the electrolyte layer and the first metal layer, and the counter electrode is formed across the electrolyte layer and the second metal layer.

[0009] In a method for manufacturing an electrochemical gas sensor according to one aspect of the present invention, the working electrode and the counter electrode are formed, for example, by coating an electrode material onto an insulating substrate.

[0010] According to one aspect of the present invention, it is possible to provide an electrochemical gas sensor that has excellent baseline stability while having a structure that does not require special fastening jigs or the like. According to one aspect of the present invention, for example, it is possible to achieve cost reduction, miniaturization, and high sensitivity of the electrochemical gas sensor. [Brief explanation of the drawing]

[0011] [Figure 1] This is an exploded perspective view of an electrochemical gas sensor, which is an example of an embodiment. [Figure 2] This is a plan view of an electrochemical gas sensor, which is an example of an embodiment. [Figure 3] This is a cross-sectional view of an electrochemical gas sensor, which is an example of an embodiment. [Figure 4] This is a cross-sectional view showing a modified example of an electrochemical gas sensor. [Figure 5] This is a cross-sectional view showing a modified example of an electrochemical gas sensor. [Figure 6] This is a cross-sectional view showing a modified example of an electrochemical gas sensor. [Figure 7] This is a cross-sectional view showing a modified example of an electrochemical gas sensor. [Figure 8] This is a cross-sectional view showing a modified example of an electrochemical gas sensor. [Figure 9] This is a cross-sectional view showing a modified example of an electrochemical gas sensor. [Figure 10] This is a cross-sectional view showing a modified example of an electrochemical gas sensor. [Figure 11] This is a diagram illustrating a method for manufacturing an electrochemical gas sensor, which is an example of an embodiment. [Figure 12] This figure shows an example of an electrochemical gas sensor equipped with a drying prevention filter. [Figure 13] This diagram shows the arrangement patterns of the drying prevention filters. [Figure 14]It is a diagram showing an example of a drying countermeasure filter. [Figure 15] It is a diagram showing another example of a drying countermeasure filter. [Figure 16] It is a diagram showing the surface of the substrate of the dried and countermeasure filter that has been subjected to serialization treatment. [Figure 17] It is a diagram showing the surface of the substrate of the drying countermeasure filter on which a silane compound has been deposited. [Figure 18] It is a cross-sectional view showing the electrochemical gas sensor used in the example. [Figure 19] It is a diagram showing the change in sensitivity over time of the electrochemical gas sensor in a dry atmosphere.

Mode for Carrying Out the Invention

[0012] Hereinafter, an example of an embodiment of an electrochemical gas sensor according to the present invention will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining a plurality of embodiments and modification examples described below are included in the present invention.

[0013] FIG. 1 is an exploded perspective view of an electrochemical gas sensor 1 which is an example of an embodiment. FIG. 2 is a plan view of the electrochemical gas sensor 1, in which the illustration of the sealing layer 30 is omitted. FIG. 3 is a cross-sectional view of the electrochemical gas sensor 1. Note that the drawings are schematically drawn, and the dimensional ratios of the respective components are based on the following description.

[0014] As shown in FIGS. 1 to 3, the electrochemical gas sensor 1 includes an insulating substrate 10, an electrolyte layer 11 formed on the insulating substrate 10, and a metal layer formed on the insulating substrate 10. Further, the electrochemical gas sensor 1 includes a working electrode 20 and a counter electrode 21 formed on the insulating substrate 10. The metal layer includes a first metal layer 12 and a second metal layer 13, and each metal layer functions as a lead electrode that electrically connects each electrode to an external circuit (not shown). The second metal layer 13 is formed on the insulating substrate 10 so as not to contact the first metal layer 12.

[0015] The working electrode 20 and the counter electrode 21 are arranged to conduct ions via the electrolyte layer 11. The working electrode 20 is the electrode into which the gas to be detected flows, and is also called the detection electrode. The counter electrode 21 is formed on the insulating substrate 10 so as not to be in contact with the working electrode 20. In this embodiment, the working electrode 20 covers the electrolyte layer 11 and the first metal layer 12 on the insulating substrate 10 and is formed across the electrolyte layer 11 and the first metal layer 12. The counter electrode 21 covers the electrolyte layer 11 and the second metal layer 13 on the insulating substrate 10 and is formed across the electrolyte layer 11 and the second metal layer 13.

[0016] Specifically, the working electrode 20 is formed on the surface of the electrolyte layer 11 and the first metal layer 12 facing away from the insulating substrate 10, and the counter electrode 21 is formed on the surface of the electrolyte layer 11 and the second metal layer 13 facing away from the insulating substrate 10. The working electrode 20 and the counter electrode 21 are formed only on the surfaces of the electrolyte layer 11 and each metal layer facing away from the insulating substrate 10, so that they do not come into contact with each other.

[0017] As will be explained in more detail later, the electrochemical gas sensor 1 has a laminated structure in which the main components of the sensor—the electrolyte layer 11, the electrode, and the metal layer (extraction electrode)—are directly formed and integrally bonded to one surface (first surface 10a) of the insulating substrate 10. In other words, the electrolyte layer 11, the electrode, and the metal layer are deposited on the first surface 10a. This provides good adhesion of the laminated structure, and the resistance value of the sensor decreases and stabilizes without the need for special fastening jigs, etc., greatly improving the stability of the baseline. Furthermore, it is easy to manufacture and enables cost reduction of the sensor.

[0018] The electrochemical gas sensor 1 detects the gas concentration by introducing the gas to be detected into the working electrode 20, oxidizing or reducing the gas molecules on the working electrode 20, and measuring the change in current or potential associated with this oxidation-reduction reaction. The electrochemical gas sensor 1 may be a potential-detecting type, but in this embodiment, a current-detecting type sensor is exemplified. When gas molecules are oxidized or reduced at the working electrode 20, electrons are generated or consumed, and a current flows between the working electrode 20 and the counter electrode 21. Since this current value is proportional to the gas concentration, the gas concentration can be detected by measuring the current value. When electrons are generated or consumed by the oxidation-reduction reaction at the working electrode 20, cations or anions are generated, and the generated ions move to the counter electrode 21 via the electrolyte layer 11.

[0019] The electrochemical gas sensor 1 further comprises a third metal layer 14 and a reference electrode 22 formed across the electrolyte layer 11 and the third metal layer 14. The third metal layer 14 is formed on the insulating substrate 10 so as not to be electrically connected to the first metal layer 12 and the second metal layer 13. The reference electrode 22 is in contact with the electrolyte layer 11 and is formed so as not to be in contact with the working electrode 20 and the counter electrode 21.

[0020] The reference electrode 22 is a reference electrode used to control and measure the potential of the working electrode 20, and is also called the reference electrode. The working electrode 20 is connected to the reference electrode 22 via an external circuit, and the external circuit is configured to maintain a constant potential with respect to the reference electrode 22. The potential of the working electrode 20 is maintained at a potential that can oxidize, for example, the gas to be detected. In this embodiment, the working electrode 20, the counter electrode 21, and the reference electrode 22 are all formed on the same surface of the electrolyte layer 11.

[0021] In the following explanation, carbon monoxide (CO) will be used as an example of the target gas for detection. However, the configuration of the electrochemical gas sensor according to the present invention is not limited to carbon monoxide sensors. The configuration of the electrochemical gas sensor according to the present invention can be widely applied to electrochemical gas sensors using a solid electrolyte membrane, and can be applied to sensors that detect gases such as hydrogen sulfide (H2S), nitric oxide (NO), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), ammonia (NH3), etc.

[0022] When the gas detected by the electrochemical gas sensor 1 is CO, the oxidation reaction of CO shown in equation (1) occurs at the working electrode 20. CO + H2O → CO2 + 2H + +2e - ...(1) CO that flows into the working electrode 20 reacts with water molecules to produce CO2, and protons (H + ) and electrons are generated. The protons move to the counter electrode 21 via the electrolyte layer 11, and the electrons move via the external circuit. At the counter electrode 21, the reaction shown in equation (2) takes place. 1 / 2 O2 + 2H + +2e - →H2O···(2) The protons and electrons generated at the working electrode 20 react with oxygen in the air at the counter electrode 21 to produce water. At this time, the current flowing through the external circuit is proportional to the amount of CO flowing into the working electrode 20, so the concentration of CO can be detected by measuring this current.

[0023] The electrochemical gas sensor 1 further comprises a sealing layer 30 covering the electrolyte layer 11, the working electrode 20, the counter electrode 21, and the reference electrode 22. The sealing layer 30 is placed on an insulating substrate 10 and is bonded to the first surface 10a of the insulating substrate 10 on which the electrolyte layer 11 and each electrode are laminated.

[0024] The sealing layer 30 is preferably made of a material with low gas (CO) permeability and may include a gas barrier layer such as a metal layer or an inorganic compound layer. The sealing layer 30 has a gas inlet hole 30a, which is a through hole for introducing CO into the working electrode 20. The sealing layer 30 covers the entire electrolyte layer 11 and each electrode so that CO flows in only from the gas inlet hole 30a, and the peripheral edge of the sealing layer 30 is joined to the first surface 10a. The electrolyte layer 11 and each electrode are arranged in the space surrounded by the insulating substrate 10 and the sealing layer 30. Note that the location of the gas inlet hole (through hole) is not limited to the sealing layer. The through hole may be formed, for example, in the insulating substrate.

[0025] The sealing layer 30 is made of, for example, a resin with low gas permeability. Examples of resins that make up the sealing layer 30 include olefin resins such as polyethylene, polypropylene, and polyvinyl chloride, polyesters such as polyethylene terephthalate, acrylic resins, polycarbonate, polyimide, and polyphenylene sulfide. The sealing layer 30 may also be a single-layer structure made mainly of these resins.

[0026] The sealing layer 30 may be composed of a sheet including a base layer and an adhesive layer. The base layer may be a resin film mainly composed of the above-mentioned resin, a metal sheet, etc. A gas barrier layer may be formed on the surface of the resin film, such as a metal layer such as aluminum, or an inorganic compound layer such as silica, silicon nitride, or alumina. For the adhesive layer, for example, epoxy adhesives, acrylic adhesives, urethane adhesives, silicone adhesives, etc. The adhesive may be tacky at room temperature, or it may be a hot-melt adhesive that becomes tacky when heated, or a curing type adhesive.

[0027] The following describes in more detail the configurations of the insulating substrate 10, the electrolyte layer 11, the metal layer, and the electrodes.

[0028] As shown in Figures 2 and 3, the electrolyte layer 11, the first metal layer 12, the second metal layer 13, and the third metal layer 14 are formed directly on the first surface 10a of the insulating substrate 10. The three metal layers are formed on the first surface 10a in areas that do not come into contact with each other. In the example shown in Figure 2, the first surface 10a has a rectangular shape in plan view, with the electrolyte layer 11 formed in the center of the first surface 10a and the three metal layers formed at the edges of the first surface 10a, flanking the electrolyte layer 11. Furthermore, the edges of the electrolyte layer 11 and the edges of each metal layer are in contact with each other, and there are no gaps between the electrolyte layer 11 and the metal layers.

[0029] On the first surface 10a of the insulating substrate 10, a working electrode 20, a counter electrode 21, and a reference electrode 22 are formed so as to cover the electrolyte layer 11 and the metal layer. That is, all three electrodes are formed on the surface of the electrolyte layer 11 opposite to the surface facing the insulating substrate 10. A laminated structure is formed on the first surface 10a of the insulating substrate 10, with the electrolyte layer 11 and the metal layer as the lower layer and the three electrodes as the upper layer, and the upper layer (electrode layer) is bonded to the first surface 10a via the lower layer. The electrode layer covers a portion of the electrolyte layer 11 and the metal layer.

[0030] The working electrode 20, the counter electrode 21, and the reference electrode 22 are formed on the electrolyte layer 11 and the metal layer, separated from each other so as not to contact each other. As described above, the working electrode 20 is formed across the electrolyte layer 11 and the first metal layer 12, the counter electrode 21 is formed across the electrolyte layer 11 and the second metal layer 13, and the reference electrode 22 is formed across the electrolyte layer 11 and the third metal layer 14. A portion of the electrodes may also be formed directly on the first surface 10a of the insulating substrate 10.

[0031] As will be described in more detail later, it is preferable that the working electrode 20, the counter electrode 21, and the reference electrode 22 are formed by coating the electrode material onto the first surface 10a of the insulating substrate 10 on which the electrolyte layer 11 and the metal layer are formed. In this case, electrode formation is easy, good adhesion of the electrodes to the electrolyte layer 11 and the metal layer can be obtained without using special fastening jigs, and the improvement effect on baseline stability becomes more pronounced.

[0032] [Insulating substrate] The insulating substrate 10 is a substrate that ensures insulation in at least the portion on which the electrochemical gas sensor 1 is constructed. The insulating substrate 10 functions as a support member for the electrolyte layer 11, the metal layer, and the electrodes, and also functions as a sealing member that seals the electrolyte layer 11 and the electrodes together with the sealing layer 30. In the examples shown in Figures 2 and 3, the insulating substrate 10 has a rectangular shape in plan view, and the first surface 10a is a flat substrate. The shape, dimensions, etc. of the insulating substrate 10 are not particularly limited, and any substrate can be used for the insulating substrate 10.

[0033] The insulating substrate 10 may be a substrate specifically for the electrochemical gas sensor 1, or it may be a circuit board (commonly also called a "printed wiring board") on which other electronic components are mounted. The insulating substrate 10 is, for example, a substrate on which wiring is formed on at least one of the surface and interior, and on which multiple electronic components are mounted. The electrochemical gas sensor 1 may be connected to other electronic components mounted on the same circuit board, and processing based on the sensor's detection information may be performed within this circuit board. That is, the electrochemical gas sensor 1 can be built on a circuit board on which other electronic components are mounted.

[0034] [Electrolyte layer] The electrolyte layer 11 is an ion-conducting membrane that transmits ions generated at the working electrode 20 to the counter electrode 21, and is a layer made of an insulating membrane that does not have electronic conductivity. The electrolyte layer 11 may be constructed by absorbing a liquid electrolyte into a holding member such as a porous sheet, but it is preferably composed of a solid electrolyte made of a polymer material. In this embodiment, a solid electrolyte having proton conductivity is used. An example of a proton-conducting solid electrolyte is a hydrocarbon polymer or a fluorine polymer into which proton-conducting groups such as sulfonic acid groups have been introduced. A commercially available product such as Nafion (registered trademark: manufactured by DuPont) may be used for the electrolyte layer 11.

[0035] The thickness of the electrolyte layer 11 is not particularly limited, but as an example, it ranges from 1 μm to 400 μm. μm. Figure 2 shows an electrolyte layer 11 with a rectangular shape in plan view, but the shape of the electrolyte layer 11 is not particularly limited and can be changed as appropriate according to the shape of the insulating substrate 10, etc. The electrolyte layer 11 may be formed by attaching a solid electrolyte film to the first surface 10a of the insulating substrate 10, but it is preferably formed by coating the constituent material of the solid electrolyte.

[0036] [Metal layer] As described above, the metal layers include a first metal layer 12 to which the working electrode 20 is connected, a second metal layer 13 to which the counter electrode 21 is connected, and a third metal layer 14 to which the reference electrode 22 is connected. Each metal layer functions as an extraction electrode, electrically connecting each electrode to an external circuit (not shown), with a portion of it covered by the sealing layer 30 and the remaining portion extending from the area covered by the sealing layer 30. Wiring, for example, that connects to the external circuit is connected to the metal layers.

[0037] Each metal layer is formed, for example, by forming a thin metal film on the first surface 10a of the insulating substrate 10, and then pattern etching the thin film into the shape of each metal layer. Each metal layer may also be formed by depositing a plating layer on top of the patterned thin metal film. An example of a metal layer is a nickel / gold plated layer on top of copper foil. The thickness of each metal layer is substantially the same. An example of the thickness of each metal layer is 1 μm to 100 μm. The layers They may also be formed by methods such as vapor deposition.

[0038] From the viewpoint of miniaturizing the electrochemical gas sensor 1, it is preferable that each metal layer be formed around the electrolyte layer 11. In the example shown in Figure 2, the first metal layer 12, the second metal layer 13, and the third metal layer 14 are formed separately on both sides of the insulating substrate 10 in the first direction, flanking the electrolyte layer 11. The second metal layer 13 and the third metal layer 14 are formed side by side in the second direction (a direction perpendicular to the first direction) of the insulating substrate 10 with a gap between them. The first metal layer 12 may also be formed over a larger area than the second metal layer 13 and the third metal layer 14.

[0039] [Electrodes (working electrode, counter electrode, reference electrode)] The working electrode 20 is formed on the electrolyte layer 11 and the first metal layer 12 formed on the first surface 10a of the insulating substrate 10, and is in strong contact with the electrolyte layer 11 and the first metal layer 12. In addition, a portion of the working electrode 20 is directly formed on the first surface 10a. The working electrode 20, together with the electrolyte layer 11 and the first metal layer 12, is in strong contact with the first surface 10a and is integrated with the insulating substrate 10. Therefore, a good contact state can be obtained even with a small force pressing the working electrode 20 against the electrolyte layer 11 and the first metal layer 12. As a result, it is thought that the contact resistance is reduced and stabilized, and noise in the base current is suppressed.

[0040] As described above, the working electrode 20 is formed across the electrolyte layer 11 and the first metal layer 12. In other words, the working electrode 20 is continuous from the electrolyte layer 11 to the first metal layer 12, and is formed across the two layers so as to connect the electrolyte layer 11 and the first metal layer 12. In the example shown in Figure 2, the working electrode 20 is formed in a rectangular shape in plan view and broadly covers the first metal layer 12. Also, the working electrode 20 covers a wider area of ​​the electrolyte layer 11 compared to the counter electrode 21 and the reference electrode 22, and is formed over a large area. The thickness of the working electrode 20 is, for example, greater than the thickness of the first metal layer 12 and less than or equal to the thickness of the electrolyte layer 11. An example of the thickness of the working electrode 20 is 1 μm to 300 μm, or 10 μm to 100 μm.

[0041] The counter electrode 21 is formed on the electrolyte layer 11 and the second metal layer 13 formed on the first surface 10a of the insulating substrate 10, and is in strong contact with the electrolyte layer 11 and the second metal layer 13. Similarly, the reference electrode 22 is formed on the electrolyte layer 11 and the third metal layer 14, and is in strong contact with the electrolyte layer 11 and the third metal layer 14. As a result, a good contact state is obtained between each electrode and the electrolyte layer 11 and each metal layer, the contact resistance is reduced, and noise in the base current is suppressed. The counter electrode 21 and the reference electrode 22 are formed, for example, in a rectangular shape in plan view with substantially the same area, and a portion is directly formed on the first surface 10a.

[0042] The counter electrode 21 is formed across the electrolyte layer 11 and the second metal layer 13, and the reference electrode 22 is formed across the electrolyte layer 11 and the third metal layer 14. In other words, the counter electrode 21 is continuous from the electrolyte layer 11 to the second metal layer 13, and is formed across the two layers so as to connect the electrolyte layer 11 and the second metal layer 13. Similarly, the reference electrode 22 is continuous from the electrolyte layer 11 to the third metal layer 14, and is formed across the two layers so as to connect the electrolyte layer 11 and the third metal layer 14. The counter electrode 21 and the reference electrode 22, like the working electrode 20, are tightly attached to the first surface 10a together with the electrolyte layer 11, the second metal layer 13, and the third metal layer 14, and are integrated with the insulating substrate 10. The thickness of the counter electrode 21 and the reference electrode 22 is substantially the same as, for example, the thickness of the working electrode 20.

[0043] The working electrode 20 and the counter electrode 21 include, for example, a catalyst, a conductive support, and an ionomer. In this embodiment, the reference electrode 22 is also made of the same material as the working electrode 20 and the counter electrode 21, for example, each electrode is made of the same material. The catalyst promotes the oxidation reaction of CO, and the reaction of formula (1) above occurs on the catalyst of the working electrode 20. Examples of catalysts include platinum (Pt), palladium (Pd), gold (Au), silver (Ag), ruthenium (Ru), rhodium (Rh), iridium (Ir), cobalt (Co), iron (Fe), nickel (Ni), etc. Among these, it is preferable to use a precious metal catalyst such as Pt or PtRu alloy.

[0044] The conductive support described above is a conductive material that holds the catalyst. Examples of suitable conductive support materials include carbon materials such as carbon black, acetylene black, Ketjenblack, graphite carbon, and carbon nanotubes. The catalyst is, for example, fixed to the particle surface of the carbon material. The ionomer described above is an ionic conductive material that enables the movement of protons generated by the reaction. An example of a suitable ionic conductive material is Nafion (registered trademark: manufactured by DuPont), which has the same composition as the electrolyte layer 11.

[0045] As shown in Figure 3, the electrochemical gas sensor 1 includes a lower layer consisting of an electrolyte layer 11 and a metal layer, and an electrode layer formed on the lower layer. The lower layer and the electrode layer are bonded to the first surface 10a of the insulating substrate 10 and integrated with the insulating substrate 10. That is, the electrolyte layer 11, the metal layer, and the electrode layer are formed as films on the first surface 10a of the insulating substrate 10.

[0046] In this embodiment, the electrolyte layer 11 and the metal layer are formed on the same plane so that they do not overlap. If the electrolyte layer 11 and the metal layer overlap, for example, a large step is formed in the overlapping portion. However, by forming the electrolyte layer 11 and the metal layer so that they do not overlap, the step can be reduced, thereby reducing the impact on the shape of the electrode layer. In Figure 3, the electrolyte layer 11, the first metal layer 12, and the second metal layer 13 are shown with the same thickness, but generally, the thickness of the electrolyte layer 11 is greater than the thickness of the metal layer.

[0047] As shown in Figure 4, the electrolyte layer 11 may be arranged on the insulating substrate 10 overlapping with the first metal layer 12 and the second metal layer 13. The electrolyte layer 11 may also overlap with the third metal layer 14. When the electrolyte layer 11 overlaps with the metal layers, it is preferable that the electrolyte layer 11 is arranged on top of the metal layers. In this case, compared to the embodiment illustrated in Figure 3, it is easier to increase the contact area between the electrolyte layer 11 and the electrode, which is advantageous for increasing the sensitivity and miniaturization of the sensor. The thickness of the electrolyte layer 11 in the region overlapping with the metal layer may be thinner than the thickness of the electrolyte layer 11 in other regions (regions not overlapping with the metal layer).

[0048] As shown in Figure 5, the electrolyte layer 11 may be formed so as not to overlap with or in contact with the metal layer. In the example shown in Figure 5, the electrolyte layer 11 and the first metal layer 12 are formed with a predetermined gap between them, and the working electrode 20 is in close contact with the first surface 10a of the insulating substrate 10 between the electrolyte layer 11 and the first metal layer 12. In this case, compared to the configuration in which the electrolyte layer 11 and the metal layer are in contact (the configuration shown in Figure 3), it is not necessary to control the positional relationship of each layer, making manufacturing easier.

[0049] As shown in Figures 6 and 7, the first surface 10a of the insulating substrate 10 on which the laminated structure of the electrochemical gas sensor 1 is formed is not limited to being flat, but may have irregularities. In the example shown in Figures 6 and 7, a recess 10b is formed on the first surface 10a of the insulating substrate 10. The recess 10b is a depression formed in a part of the first surface 10a. At least one of the electrolyte layer 11, the first metal layer 12, the second metal layer 13, and the third metal layer 14 may be formed in the recess 10b.

[0050] In the example shown in Figure 6, the electrolyte layer 11 is formed in a recess 10b on the first surface 10a of the insulating substrate 10, while the first metal layer 12 and the second metal layer 13 are formed in a region where the recess 10b does not exist (hereinafter sometimes referred to as the "surface" of the first surface 10a). By forming the electrolyte layer 11 in the recess 10b, the step difference formed in the electrode layer can be reduced. The electrolyte layer 11 may also be formed flush with the surface of the first surface 10a.

[0051] In the example shown in Figure 7, both the electrolyte layer 11 and the metal layer are formed in recesses 10b on the first surface 10a of the insulating substrate 10. The recess 10b in which the electrolyte layer 11 is formed may be deeper than the recess 10b in which the metal layer is formed. Furthermore, the electrolyte layer 11 and the metal layer may be formed flush with the surface of the first surface 10a. In this case, the step difference formed in the electrode layer can be reduced more effectively.

[0052] As shown in Figure 8, the electrolyte layer 11 and the metal layer may be formed so as to cover the electrode layer formed on the insulating substrate 10. That is, in the example shown in Figure 8, the working electrode 20, which is formed across the electrolyte layer 11 and the first metal layer 12, is interposed between the electrolyte layer 11 and the first metal layer 12 and the insulating substrate 10. Also, the counter electrode 21, which is formed across the electrolyte layer 11 and the second metal layer 13, is interposed between the electrolyte layer 11 and the second metal layer 13 and the insulating substrate 10. In this case as well, the electrode layer, the electrolyte layer 11, and the metal layer are formed on one surface of the insulating substrate and integrated together.

[0053] In the example shown in Figure 8(a), a gas introduction hole 40 for introducing CO into the working electrode 20 is formed in the insulating substrate 10. Only one gas introduction hole 40 is formed, penetrating the insulating substrate 10 and overlapping with the working electrode 20. In the example shown in Figure 8(b), a gas introduction hole 30a is formed in the sealing layer 30 at a position opposite the working electrode 20. In the embodiment illustrated in Figure 8, the gas introduction hole 30a penetrates the electrolyte layer 11 and is formed so that CO is introduced into the working electrode 20 which is located below the electrolyte layer 11.

[0054] As shown in Figure 9, it is also possible to arrange the working electrode 20 and the counter electrode 21 so as to sandwich the electrolyte layer 11 and the metal layer. In the example shown in Figure 9, the working electrode 20 is formed to cover the sides of the electrolyte layer 11 and the first metal layer 12 that are facing away from the insulating substrate 10, and the counter electrode 21 is interposed between the electrolyte layer 11 and the first metal layer 12 and the insulating substrate 10. In this case, there may be a portion where the counter electrode 21, the electrolyte layer 11, and the working electrode 20 are stacked. The reference electrode 22 may be placed either above or below the electrolyte layer 11. It is also possible to reverse the arrangement of the working electrode 20 and the counter electrode 21.

[0055] In the example shown in Figure 10, the first metal layer 12 and the second metal layer 13 (not shown) are formed separately from the electrolyte layer 11, while the third metal layer 14 is formed overlapping the electrolyte layer 11. A portion of the third metal layer 14 extends beneath the electrolyte layer 11 and is interposed between the insulating substrate 10 and the electrolyte layer 11. As with the other embodiments described above, the third metal layer 14 is formed on the insulating substrate 10 so as not to be electrically connected to the first metal layer 12 and the second metal layer 13. The metal layer can also be used as a reference electrode; in the example shown in Figure 10, the third metal layer 14 is in contact with the electrolyte layer 11 and functions as a reference electrode.

[0056] The following describes an example of a manufacturing method for the electrochemical gas sensor 1 having the above configuration, with reference to Figure 11. 11 This is a diagram illustrating the manufacturing process of an electrochemical gas sensor 1, showing how an electrode layer including the working electrode 20 is formed by spray coating of electrode material 50.

[0057] The electrochemical gas sensor 1 is manufactured, for example, through the following process. (1) A step of forming a first metal layer 12 and a second metal layer 13 on an insulating substrate 10 so as not to come into contact with each other. (2) A step of forming an electrolyte layer 11 on the insulating substrate 10. (3) A step of forming the working electrode 20 and the counter electrode 21 on the insulating substrate 10 so as not to come into contact with each other. (4) If the electrochemical gas sensor 1 has a sealing layer 30, the method further includes the step of forming a sealing layer 30 that covers the electrolyte layer 11, the working electrode 20, and the counter electrode 21.

[0058] In the manufacturing process of the electrochemical gas sensor 1, the working electrode 20 is formed across the electrolyte layer 11 and the first metal layer 12, and the counter electrode 21 is formed across the electrolyte layer 11 and the second metal layer 13. The order of steps (1) and (2) can be reversed, but from the viewpoint of productivity, it is preferable to proceed to step (2) after step (1).

[0059] In this embodiment, as shown in Figure 8, a working electrode 20, a counter electrode 21, and a reference electrode 22 are formed on an insulating substrate 10 on which an electrolyte layer 11 and a metal layer are formed. Preferably, each electrode is formed by coating an electrode material 50 onto the insulating substrate 10. The electrolyte layer 11, each metal layer, and each electrode are formed on the first surface 10a of the insulating substrate 10 and integrated with the insulating substrate 10, so that the baseline is stabilized without the use of special fastening jigs. The electrolyte layer 11 and the sealing layer 30 can also be formed by coating the constituent materials of the layers onto the insulating substrate 10.

[0060] In step (1) above, for example, a copper foil is formed on the first surface 10a of the insulating substrate 10, the copper foil is pattern-etched to the shape of each metal layer, and the remaining copper foil is plated to form the first metal layer 12, the second metal layer 13, and the third metal layer 14. A plating layer consisting of a two-layer structure of nickel and gold may be formed on the etched copper foil. When forming metal layers in this way, it is preferable to form the electrolyte layer 11 after forming the metal layers.

[0061] In step (2) above, for example, an ink containing the constituent materials of a solid electrolyte is applied to the first surface 10a of the insulating substrate 10, and the electrolyte layer 11 is formed by drying the coating film and volatilizing and removing the dispersion medium. That is, the electrolyte layer 11 is formed by applying a material containing an electrolyte. The dispersion medium contained in the ink is not particularly limited, but one example is a mixed solvent of water and a lower alcohol such as ethanol. Examples of ink coating methods include spray coating, screen printing, inkjet printing, electrolytic spray coating, and dispensing. Among these, spray coating or screen printing is preferred.

[0062] In step (3) above, for example, an ink containing electrode material 50 such as a catalyst, conductive carrier, and ionomer is coated onto the first surface 10a of an insulating substrate 10 on which an electrolyte layer 11 and a metal layer are formed, and the electrodes are formed by drying the coating film and volatilizing off the dispersion medium. The dispersion medium contained in the ink is not particularly limited, but one example is a mixed solvent of water and a lower alcohol such as ethanol. The same method as in step (2) can be applied to coat the ink.

[0063] In step (4) above, for example, an ink containing a resin with low gas permeability is applied to the first surface 10a of the insulating substrate 10 on which the metal layer, electrolyte layer 11, and each electrode layer are formed, and the coating film is dried to remove the dispersion medium by volatilization, thereby forming a sealing layer 30. That is, the sealing layer 30 is formed by applying a sealing material. By forming the sealing layer 30 by applying a sealing material, the ink (paint) penetrates into the irregularities of the first surface 10a, forming the sealing layer 30 even in areas with steps, and good adhesion of the sealing layer 30 to the first surface 10a is obtained. The dispersion medium contained in the ink and the coating method can be the same as those used in the other steps above.

[0064] The sealing layer 30 can also be formed by attaching a sheet (tape) containing a base layer and an adhesive layer to the first surface 10a of the insulating base material 10. In this case as well, the adhesive follows the irregularities of the first surface 10a, and good adhesion of the sealing layer 30 to the first surface 10a can be obtained.

[0065] As described above, the electrochemical gas sensor 1 having the above configuration has a laminated structure in which the electrolyte layer 11, electrodes, and metal layer are directly formed on the first surface 10a of the insulating substrate 10 and integrally bonded. As a result, good adhesion of the laminated structure is obtained, and the contact resistance of the laminated structure is reduced and stabilized. Therefore, noise in the base current is suppressed, and high sensitivity of the sensor can be achieved. With the electrochemical gas sensor 1, good contact conditions of each component can be ensured even with a small pressing force of the laminated structure, so special fastening members are not required, and the sensor can be miniaturized and cost-effective.

[0066] The electrochemical gas sensor 1 can be manufactured by a simple method of depositing an electrolyte layer 11, a metal layer, and electrodes on an insulating substrate 10. Therefore, it is possible to form the sensor structure in the empty space of a circuit board.

[0067] The above-described embodiments can be modified as appropriate without impairing the objectives of the present invention. For example, in the above-described embodiments, the working electrode 20, the counter electrode 21, and the reference electrode 22 were formed using the same electrode material, but each electrode may be made of different materials. Also, the structure of the electrochemical gas sensor may be a two-electrode structure that has only a working electrode and a counter electrode as electrodes. Alternatively, the counter electrode can also be used as a reference electrode to set the potential of the working electrode.

[0068] In the above-described embodiment, through-holes in the sealing layer for introducing gas are formed only at positions overlapping with the working electrode, but through-holes may also be formed at positions overlapping with the counter electrode. Since oxygen is required at the counter electrode, providing through-holes at positions overlapping with the counter electrode can prevent a decrease in oxygen concentration around the counter electrode.

[0069] The electrochemical gas sensor 1 may also include a gas diffusion layer 31 and a drying prevention filter 32 used as a means of preventing drying. As shown in Figure 12, the gas diffusion layer 31 and the drying prevention filter 32 are provided at least within the path through which the target gas reaches the working electrode 20 from the gas introduction hole 30a, and the structure has such that the gas diffusion layer 31, the drying prevention filter 32, and the sealing layer 30 are arranged in order on an electrode layer formed on a lower layer consisting of an electrolyte layer 11 and a metal layer. Here, the gas diffusion layer 31 and the drying prevention filter 32 may be joined to the insulating substrate 10 via an electrode layer or the like, or they may be sandwiched between the insulating substrate 10 and the sealing layer 30 in a non-joined state.

[0070] The gas diffusion layer 31 has the function of diffusing CO introduced from the gas introduction hole 30a over a wide area of ​​the working electrode 20. The gas diffusion layer 31 is composed of, for example, a gas-permeable porous membrane. The thickness of the gas diffusion layer 31 is not particularly limited, but one example is 20 μm to 200 μm. In the example shown in Figure 12, the gas diffusion layer 31 is arranged on the electrode layer so as to cover the entire electrode layer including the counter electrode 21 and the reference electrode 22, but it may also be arranged to cover only the working electrode 20. In this embodiment, it is preferable that the gas diffusion layer 31 is a non-conductive porous membrane. If the gas diffusion layer 31 is non-conductive, it can be arranged to cover the entire electrode layer.

[0071] The drying prevention filter 32 has the function of preventing an excessive decrease in humidity inside the sensor, and is preferably a porous structure with a homogeneous pore structure. In the example shown in Figure 12, the drying prevention filter 32 is arranged on the electrode layer so as to cover the entire electrode layer including the counter electrode 21 and the reference electrode 22, but it may also be arranged to cover only the working electrode 20. Furthermore, as shown in Figures 13(a) to (d), the drying prevention filter 32 may be arranged to cover the gas inlet hole 30a, or it may be placed inside the gas inlet hole 30a. In this case, the drying prevention filter 32 can be effective even if it is of the minimum size. Details of the drying prevention filter 32 will be described later.

[0072] In this embodiment, a drying prevention filter 32 is used as a means of preventing drying, but other methods can be employed as long as it is possible to prevent the humidity inside the sensor from decreasing or changing excessively. For example, the electrodes and electrolyte layer 11, including the working electrode 20, counter electrode 21, and reference electrode 22, which are the sensor components, may be made to be resistant to drying. In this case, the working electrode 20, counter electrode 21, reference electrode 22, and electrolyte layer 11 serve as the means of preventing drying, so it is not necessary to provide a drying prevention filter 32 separately.

[0073] For example, a sensor of When an electrode contains a catalyst, a conductive support, and an ionomer, mixing these with a hydrophilic material can improve drying resistance while maintaining the electrode's function. Examples of hydrophilic materials that can be mixed include metal oxide particles such as silica (SiO2), titania (TiO2), zirconia (ZrO2), and alumina (Al2O3). The hydroxyl groups present on the surface of these metal oxide particles are effective in retaining moisture, thus improving drying resistance.

[0074] It is also possible to improve drying resistance by selecting highly hydrophilic materials for conductive carriers, ionomers, etc., or by optimizing the mixing ratio of materials. For example, drying resistance can be improved by hydrophilizing the surface of carbon-based materials used as conductive carriers. Hydrophilization treatments include methods that generate hydrophilic functional groups such as hydroxyl groups and carboxyl groups on the material surface by oxidation treatment, and methods that generate hydrophilic functional groups such as hydroxyl groups and carboxyl groups on the material surface by plasma treatment.

[0075] In the case of ionomers, for example, proton-conducting materials containing sulfonic acid groups, a higher concentration of sulfonic acid groups in the ionomer is preferable for moisture retention, and selecting an ionomer with a high concentration of sulfonic acid groups can improve drying resistance. Furthermore, since ionomers generally have a higher moisture retention capacity compared to conductive carriers, drying resistance can also be improved by increasing the mixing ratio of ionomers to an extent that does not cause the electrode to lose its function.

[0076] The configuration of the drying prevention filter 32 is described in more detail below. The drying prevention filter 32 is a porous membrane having a hydrophobic surface and a pore diameter of less than 100 nm. A hydrophobic surface is preferably one in which, when the surface is smooth, the water contact angle of this surface is 80° or more. This water contact angle can be confirmed by forming a smooth surface from the same material as the material constituting the surface of the drying prevention filter 32 and measuring the water contact angle on this surface.

[0077] Pore ​​diameter is measured using either the mercury intrusion method or the nitrogen adsorption method, depending on its size. For example, if the pore diameter is 3 nm or larger, it is the volume-based average pore diameter measured by the mercury intrusion method; if it is less than 3 nm, it is the volume-based average pore diameter measured by the nitrogen adsorption method.

[0078] The pores in the drying prevention filter 28 may have a co-continuous structure as schematically shown in Figure 14, or they may have a cylindrical shape that penetrates the drying prevention filter 32 in the thickness direction, as schematically shown in Figure 15. Furthermore, the drying prevention filter 32 may have pores formed by stretching and finely splitting its material. The structure of the pores in the drying prevention filter 32 is not limited to the above structure, and the pores may have any appropriate structure.

[0079] To more effectively suppress the passage of water vapor by the drying prevention filter 32, the pore size of the drying prevention filter 32 is more preferably 80 nm or less, and even more preferably 60 nm or less. Furthermore, it is preferable that the pore size be adjusted according to the type of molecule to be passed through the drying prevention filter 32. For example, when passing carbon monoxide molecules through the drying prevention filter 32, the pore size is preferably 1 nm or more, and more preferably 10 nm or more. In this case, the drying prevention filter 32 can selectively allow carbon monoxide to pass through while effectively suppressing the passage of water vapor.

[0080] The drying prevention filter 32 is formed from, for example, a hydrophobic material. In this case, the drying prevention filter 32 may have a hydrophobic surface.

[0081] The hydrophobic material preferably contains a fluorine-containing resin. The fluorine-containing resin includes, for example, at least one molded from the group consisting of polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), perfluoroethylene propene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and polyvinyl fluoride (PVF). When the hydrophobic material contains a fluorine-containing resin, the drying prevention filter 32 is, for example, a porous sheet formed from the fluorine-containing resin.

[0082] The surface of the drying prevention filter 32 may be hydrophobic by applying a hydrophobic treatment to its surface. In this case, for example, the drying prevention filter 32 is manufactured by applying a hydrophobic treatment to the surface of a porous substrate.

[0083] The porous substrate may be made from any suitable material, provided that its pore size is within a desired range and its surface can be hydrophobized. The pore size of the substrate may be 100 nm or larger if the pore size of the drying prevention filter made by hydrophobizing the substrate is less than 100 nm.

[0084] The substrate is, for example, a sheet made of porous glass or a porous resin sheet. When producing porous glass, for example, a glass raw material can be treated at a high temperature to induce phase separation, and then one of the phases can be eluted and removed from the raw material to obtain porous glass consisting of the remaining phase.

[0085] The hydrophobic treatment is not particularly limited as long as it can make the surface of the substrate hydrophobic. Hydrophobic treatments include, for example, treatments including silylation, treatments including vapor deposition of silane compounds, or treatments to provide a water-repellent resin film.

[0086] Silylation treatment is a process that introduces silyl groups to the surface of a substrate using a silylating agent. Figure 16 schematically shows how the surface of a substrate becomes hydrophobic due to a silylating agent. The silyl group is, for example, a trialkylsilyl group such as a trimethylsilyl group, but is not limited to this. That is, the silyl group that the silylating agent possesses is not limited to a trialkylsilyl group such as a trimethylsilyl group. The silylation agent contains, for example, at least one selected from the group consisting of hexamethyldisilazane (HMDS), trimethylchlorosilane (TMCS), N-methyl-N-trimethylsilylacetamide (MTMSA), N-trimethylsilyldiethylamine (TMSDEA), N-trimethylsilyldimethylamine (TMSDMA), N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA), N,O-bis(trimethylsilyl)acetamide (BSA), N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA), N-trimethylsilylimidazole (TMSI), ethyldimethylchlorosilane, propyldimethylchlorosilane, dodecyldimethylchlorosilane, and phenyldimethylchlorosilane. The silylation treatment is carried out, for example, by immersing the substrate in the silylation agent, followed by washing and drying. Silylation treatment makes it possible to hydrophobize the surface of the substrate without significantly changing the pore size of the substrate, and also to silylate the surface inside the pores of the substrate.

[0087] The process of vapor-depositing a silane compound involves depositing the silane compound onto the surface of a substrate, thereby introducing hydrophobic groups (R) derived from the silane compound onto the substrate surface. Figure 17 schematically shows how the surface of the substrate becomes hydrophobic after the vapor-depositing process of a silane compound. The hydrophobic groups (R) are, for example, alkyl groups or alkyl fluorides. That is, it is preferable that the silane compound has an alkyl group or alkyl fluoride bonded to a silicon atom. It is also preferable that the silane compound has an alkoxy group. In this case, the alkoxy group of the silane compound deposited on the substrate can react with the surface of the substrate and bond to it, thereby maintaining the hydrophobicity of the surface of the drying prevention filter 32 over a long period of time. It is preferable that the silane compound has at least two alkoxy groups, and more preferably three alkoxy groups. In this case, not only can the alkoxy group of the silane compound react with the surface of the substrate and bond to it, but the silane compounds can also bond to each other through reactions between their alkoxy groups. Therefore, the hydrophobicity of the surface of the drying prevention filter 32 is maintained for a longer period of time, i.e., the durability of the drying prevention filter 32 is increased. The silane compound contains, for example, at least one selected from the group consisting of methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, (3,3,3-trifluoropropyl)trimethoxysilane, trimethoxy(1H,1H,2H,2H-nonafluorohexyl)silane, trimethoxy(1H,1H,2H,2H-tridecafluoro-n-octyl)silane, and trimethoxy(1H,1H,2H,2H-heptadecafluorodecyl)silane. Silane compounds are deposited by, for example, placing the substrate and the silane compound inside a sealed container and then heating the contents of the sealed container.

[0088] When the hydrophobic treatment includes a process to provide a water-repellent resin film, the resin film is made from a resin such as a fluorine-containing resin or silicone. However, the resin contained in the resin film is not limited to these. A water-repellent resin film exhibits water repellency by having, for example, fluorine-containing groups or silicone-containing groups on its surface. The presence of fluorine-containing groups or silicone-containing groups on the surface of the resin film can be confirmed, for example, by energy-dispersive X-ray spectroscopy (EDX). A water-repellent resin film is made by, for example, applying a coating solution containing a resin such as a fluorine-containing resin or silicone to a substrate using a known method such as dip coating, die coating, bar coating, spray coating, or spin coating. Dip coating is more preferable in order to allow the coating solution to penetrate into the pores of the substrate. When providing a water-repellent resin film, the pore size in the drying prevention filter 32 can also be adjusted by adjusting the amount of coating solution applied to the substrate.

[0089] The thickness of the drying prevention filter 32 is preferably 0.1 mm or more. In this case, the drying prevention filter 32 can more effectively suppress the passage of water vapor. The thickness of the drying prevention filter 32 is more preferably 0.2 mm or more, and even more preferably 0.5 mm or more. Furthermore, the thickness of the drying prevention filter 32 is preferably 2 mm or less. In this case, the drying prevention filter 32 can be made smaller, and the passage of molecules that the drying prevention filter 32 should pass through is less likely to be obstructed. The thickness of the drying prevention filter 32 is more preferably 1.5 mm or less, and even more preferably 1 mm or less. Example of a drying prevention filter

[0090] The following describes specific examples of the drying prevention filter. However, this embodiment is not limited to the examples described below.

[0091] 1. Fabrication of a drying prevention filter (1) Examples 1-3 Porous glass manufactured by Akagawa Hard Glass Industry Co., Ltd. (planar dimensions 20 mm x 20 mm, thickness 1 mm) was prepared. In Example 1, porous glass with a pore size of 50 nm was prepared, in Example 2, porous glass with a pore size of 70 nm was prepared, and in Example 3, porous glass with a pore size of 15 nm was prepared. The porous glass was immersed in trimethylchlorosilane overnight, then washed with hexane and dried to perform a silylation treatment on the porous glass. This produced a drying prevention filter.

[0092] (2) Example 4 Porous glass manufactured by Akagawa Hard Glass Industry Co., Ltd. (planar dimensions 20mm x 20mm, thickness 1mm, pore size 50nm) and trimethoxy(1H,1H,2H,2H-heptadecafluorodecyl)silane were placed in a sealed container and heated at 120°C for 20 minutes to deposit the silane compound onto the porous glass. This created a filter for preventing drying.

[0093] (3) Example 5 The porous glass prepared in Example 1 was subjected to silylation treatment using ethyldimethylchlorosilane instead of chlorotrimethylsilane. A gas filter was then fabricated.

[0094] (4) Example 6 In Example 1, the porous glass prepared was immersed in a coating solution and then dried at 140°C for 1 hour to form a resin film. As the coating solution, a mixture of Panasonic Environmental Engineering Co., Ltd.'s water-repellent coating MK-FSO-200 and butyl acetate as a solvent was added to adjust the solid content to 10% by mass. A gas filter was then fabricated.

[0095] (5) Comparative Examples 1-3 In each of Examples 1 to 3, the porous glass prepared was used as a drying filter without any hydrophobic treatment.

[0096] 2. Fabrication of an electrochemical gas sensor (1) Example 7 An electrochemical gas sensor 1 for testing, having the structure shown in Figure 18, was fabricated as follows. An insulating substrate 10 was prepared, and a metal layer and an electrolyte layer 11 were fabricated on the insulating substrate 10. Furthermore, a working electrode 20, a counter electrode 21, and a reference electrode (not shown) were fabricated so as to straddle the metal layer and the electrolyte layer 11, and so as not to be in contact with each other. Each of the working electrode 20, the counter electrode 21, and the reference electrode (not shown) was fabricated by coating and drying a composition prepared by mixing the catalyst TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., the solid electrolyte dispersion solution DE2020 CS manufactured by Fujifilm Wako Chemical Co., Ltd., and water and ethanol as solvents. Furthermore, a sealing layer 30 having a gas introduction hole 30a was formed on one surface of the insulating substrate 10. Furthermore, the drying prevention filter 32 of Example 1 was placed on the side of the sealing layer 30 opposite to the side on which the working electrode 20, counter electrode 21, and electrolyte layer 11 were installed, so as to cover the gas introduction hole 30a.

[0097] (2) Comparative Example 4 In Example 7 described above, the drying prevention filter of Comparative Example 1 was used instead of the drying prevention filter of Example 1.

[0098] (3) Reference example In Example 7, a device without a drying filter was prepared as an electrochemical gas sensor.

[0099] 3. Evaluation (1) Water contact angle The contact angle of the surface of the drying prevention filters in Examples 1-6 and Comparative Examples 1-3 was confirmed by the following method. A glass plate with a smooth surface was subjected to the same surface treatment conditions as in each of Examples 1 to 6. The water contact angle of the treated surface was measured using a fully automatic contact angle meter DMo-701 manufactured by Kyowa Interface Science Co., Ltd., in accordance with JIS R3257. The water contact angle of the surface of the glass plate with a smooth surface was also measured in the same manner. The water contact angles obtained were defined as the water contact angles for each of Comparative Examples 1 to 3.

[0100] (2) Evaluation of drying prevention filters The carbon monoxide and water vapor transmission rates of the drying prevention filters in Examples 1-6 and Comparative Examples 1-3 were measured using the following method. The results are shown in Table 1. Carbon monoxide transmission rate: In accordance with JIS K7126-2, the carbon monoxide permeation rate through the drying prevention filter was evaluated using the following method. As gas permeation cells, a first chamber and a second chamber, each with an inner diameter of 50 mm and a length of 100 mm, were made from 5 mm thick acrylic plate. Each chamber had a rim at its opening, and with a gasket attached to the rim, a sample could be fixed between the openings of the two chambers. The sample was prepared by sandwiching the drying prevention filter between two pieces of aluminum tape with 16 mm diameter circular holes and then bonding them together. This allowed the carbon monoxide permeation area in the drying prevention filter to be increased to 2 cm². 2 The procedure was as follows: A carbon monoxide gas cylinder was connected to the first chamber, and a NAP-508 carbon monoxide gas sensor manufactured by Nemoto Sensor Engineering Co., Ltd. was placed in the second chamber to detect the carbon monoxide concentration in the second chamber at 1-second intervals. In this state, the sample was fixed between the two chambers. Carbon monoxide gas was introduced into the first chamber from the carbon monoxide gas cylinder to a concentration of 150 ppm, and the change in carbon monoxide concentration in the second chamber was measured using the carbon monoxide gas sensor. From the measurement results from the carbon monoxide gas sensor during the first minute after the introduction of the carbon monoxide gas, the rate of increase in carbon monoxide concentration in the second chamber [ppm / s] was calculated using the least squares method, and this was defined as the carbon monoxide permeation rate.

[0101] Water vapor transmission rate: The water vapor permeation rate through the drying prevention filter was evaluated using the following method, in accordance with the cup method specified in JIS Z0208. A cup with an inner diameter of 56 mm and a height of 32 mm, made from a 1 mm thick stainless steel plate, was used. The cup opening had a rim, and a gasket and retaining lid could be attached to this rim to secure the sample. The sample was prepared by sandwiching the drying prevention filter between two pieces of aluminum tape with a 16 mm diameter circular hole and bonding them together. This allowed the water vapor permeation area of ​​the drying prevention filter to be 2 cm². 2 The procedure is as follows: A plastic dish containing 10g of calcium chloride was placed inside a cup, and the sample was then fixed in the cup. The initial weight of the cup was measured in this state. This cup was placed in a constant temperature and humidity chamber set to 25°C and 90% humidity, and after 24 hours it was removed and its weight was measured again. The weight increase [g] of the calcium chloride in the cup from the initial weight was calculated by calculating the difference between this measured weight and the initial weight. The water vapor transmission rate [g / h] was calculated by dividing the weight increase by 24.

[0102] [Table 1]

[0103] As shown in these results, compared to the drying filters of each comparative example, the drying filters of each embodiment maintain high carbon monoxide permeability while exhibiting lower water vapor permeability. This confirms that the drying filters of each embodiment suppress water vapor permeability while maintaining carbon monoxide permeability.

[0104] (3) Evaluation of electrochemical gas sensors The electrochemical gas sensors of Example 7, Comparative Example 4, and Reference Example were placed in an atmosphere at a temperature of 25°C and a relative humidity of 10%, and carbon monoxide was supplied to this atmosphere to adjust the carbon monoxide concentration to 10 ppm. Under these conditions, the short-circuit current flowing between the sensing electrode and the counter electrode in the sensing part of the electrochemical gas sensor was measured as the output of the electrochemical gas sensor. The output was continuously measured, and the sensitivity change rate was normalized with the initial output set to 1. The results are shown in Figure 19. In Figure 19, the vertical axis represents the sensitivity change rate, and the horizontal axis represents the elapsed time.

[0105] As shown in these results, in Example 7, the rate of change in sensitivity did not decrease as much compared to Comparative Example 4 and the Reference Example. Therefore, it was confirmed that the electrochemical gas sensor of Example 7 had improved durability in a dry atmosphere.

[0106] As is clear from the above embodiments and examples, the drying prevention filter 32 of the present invention can effectively suppress the passage of water vapor. Therefore, when applied to the electrochemical gas sensor 1, it can prevent the humidity inside the sensor from dropping excessively and improve the durability of the electrochemical gas sensor 1 in a dry atmosphere. [Explanation of Symbols]

[0107] 1 Electrochemical gas sensor, 10 Insulating substrate, 10a First surface, 10b Recess, 11 Electrolyte layer, 12 First metal layer, 13 Second metal layer, 14 Third metal layer, 20 Working electrode, 21 Counter electrode, 22 Reference electrode, 30 Sealing layer, 30a, 40 Gas introduction hole, 31 Gas diffusion layer, 32 Drying prevention filter

Claims

1. insulating substrate and An electrolyte layer formed on the insulating substrate, A first metal layer formed on the insulating substrate, A second metal layer is formed on the insulating substrate so as not to come into contact with the first metal layer, A third metal layer is formed on the insulating substrate so as not to be electrically connected to the first metal layer and the second metal layer, The electrolyte layer and the first metal layer cover the surfaces facing away from the insulating substrate, or are interposed between the electrolyte layer and the first metal layer and the insulating substrate, and the working electrode is formed across the electrolyte layer and the first metal layer, Covering the surface of the electrolyte layer and the second metal layer facing away from the insulating substrate, or interposed between the electrolyte layer and the second metal layer and the insulating substrate, and a counter electrode formed across the electrolyte layer and the second metal layer, A reference electrode formed across the electrolyte layer and the third metal layer, An electrochemical gas sensor equipped with the following features.

2. insulating substrate and An electrolyte layer formed on the insulating substrate, A first metal layer formed on the insulating substrate, A second metal layer is formed on the insulating substrate so as not to come into contact with the first metal layer, A third metal layer is formed on the insulating substrate so as not to be electrically connected to the first metal layer and the second metal layer, The electrolyte layer and the first metal layer cover the surfaces facing away from the insulating substrate, or are interposed between the electrolyte layer and the first metal layer and the insulating substrate, and the working electrode is formed across the electrolyte layer and the first metal layer, Covering the surface of the electrolyte layer and the second metal layer facing away from the insulating substrate, or interposed between the electrolyte layer and the second metal layer and the insulating substrate, and a counter electrode formed across the electrolyte layer and the second metal layer, Equipped with, The third metal layer is in contact with the electrolyte layer and functions as a reference electrode in an electrochemical gas sensor.

3. The working electrode is formed on the surface of the electrolyte layer and the first metal layer facing away from the insulating substrate. The electrochemical gas sensor according to claim 1 or 2, wherein the counter electrode is formed on the surface of the electrolyte layer and the second metal layer facing away from the insulating substrate.

4. The electrochemical gas sensor according to any one of claims 1 to 3, wherein the electrolyte layer is arranged so as not to overlap with the first metal layer and the second metal layer.

5. The electrochemical gas sensor according to any one of claims 1 to 4, further comprising a sealing layer disposed on the insulating substrate and covering the electrolyte layer, the working electrode, and the counter electrode.

6. The electrochemical gas sensor according to any one of claims 1 to 5, having a through hole for introducing gas into the working electrode.

7. An electrochemical gas sensor according to any one of claims 1 to 6, further comprising means for preventing drying.

8. The electrochemical gas sensor according to any one of claims 1 to 7, further comprising a gas diffusion layer provided at a position overlapping with at least the working electrode.

9. A recess is formed on the surface of the insulating substrate. The electrochemical gas sensor according to any one of claims 1 to 8, wherein at least one of the electrolyte layer, the first metal layer, and the second metal layer is formed in the recess.

10. The process involves forming a first metal layer, a second metal layer, and a third metal layer on the insulating substrate so that they do not come into contact with each other. The process of forming an electrolyte layer on the insulating substrate, The process of forming a working electrode, a counter electrode, and a reference electrode on the insulating substrate so that they do not come into contact with each other, Includes, The working electrode is formed across the electrolyte layer and the first metal layer, The counter electrode is formed across the electrolyte layer and the second metal layer, A method for manufacturing an electrochemical gas sensor, wherein the reference electrode is formed across the electrolyte layer and the third metal layer.

11. The process involves forming a first metal layer, a second metal layer, and a third metal layer on the insulating substrate so that they do not come into contact with each other. The process of forming an electrolyte layer on the insulating substrate, The process of forming an operating electrode and a counter electrode on the insulating substrate so that they do not come into contact with each other, Includes, The working electrode is formed across the electrolyte layer and the first metal layer, The counter electrode is formed across the electrolyte layer and the second metal layer, A method for manufacturing an electrochemical gas sensor, wherein the third metal layer is in contact with the electrolyte layer and functions as a reference electrode.

12. The method for manufacturing an electrochemical gas sensor according to claim 10 or 11, wherein the working electrode and the counter electrode are formed by coating an electrode material onto the insulating substrate.

13. The method for manufacturing an electrochemical gas sensor according to any one of claims 10 to 12, wherein the electrolyte layer is formed by coating a material containing an electrolyte.

14. The process further includes the step of forming a sealing layer that covers the electrolyte layer, the working electrode, and the counter electrode, The method for manufacturing an electrochemical gas sensor according to any one of claims 10 to 13, wherein the sealing layer is formed by applying a sealing material.

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