Proton Conductor Gas Sensor

Abstract

A counter electrode-side gas diffusion layer, a membrane electrode composite, a sensing electrode-side gas diffusion layer, a diffusion control plate, and a sealing body are arranged in this order on the inside bottom of the metal can. Both the counter electrode-side gas diffusion layer and the sensing electrode-side gas diffusion layer contain adsorbents. The diameter of the membrane electrode composite is equal to or greater than that of the sensing electrode-side gas diffusion layer, and the sensing electrode-side gas diffusion layer is larger in both diameter and thickness than the counter electrode-side gas diffusion layer. An insulating and acid-resistant ring-shaped coating having an outer diameter larger than that of the membrane electrode composite and an inner diameter smaller than that of the counter electrode-side gas diffusion layer is provided on the inside bottom surface of the metal can. [Effect] The poisoning resistance of the proton conductor gas sensor is improved.

Description

[Technical Field]

[0001] The present invention relates to a proton conductor gas sensor, and more particularly to an improvement in the poisoning resistance of the gas sensor. [Background technology]

[0002] The applicant manufactures proton conductor gas sensors. In the applicant's proton conductor gas sensors, poisons such as siloxane are removed using a filter such as activated carbon, and a diffusion control plate with controlled air permeability is placed after the filter to control the amount of atmosphere supplied to the MEA (membrane electrode assembly). The MEA is a three-layer membrane consisting of a central proton conductor membrane and a sensing electrode and counter electrode on either side, and the sensing electrode and counter electrode are covered with a GDL (gas diffusion layer). The GDL is air permeable and supplies atmospheric gas while also discharging gas generated by the electrode reaction. The GDL is also electronically conductive and is electrically connected to the sensing electrode and counter electrode.

[0003] The applicant proposed using hydrophilized carbon for the GDL (Patent Document 1: WO2017 / 047316). The thickness of the GDL on both the sensing electrode side and the counter electrode side is, for example, 200 μm, and the material is, for example, activated carbon bound with a hydrophilic polymer binder. In this gas sensor, the GDL adsorbs water vapor in the atmosphere and prevents the MEA from drying out. As a result, the durability of the gas sensor in dry atmospheres is improved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2017 / 047316 Summary of the Invention [Problem to be solved by the invention]

[0005] Providing a filter such as activated carbon on a proton conductor gas sensor can prevent poisoning by siloxane, etc. Furthermore, proton conductor gas sensors equipped with a filter such as activated carbon are less likely to be poisoned by VOCs with boiling points below 100°C, such as benzene and toluene. However, even with a filter such as activated carbon, proton conductor gas sensors can be poisoned by VOCs with high boiling points, such as terpenes such as pinene.

[0006] An object of the present invention is to improve the poisoning resistance of a proton conductor gas sensor. [Means for solving the problem]

[0007] The proton conductor gas sensor of the present invention comprises: On the inside bottom of the metal can, a counter electrode-side gas diffusion layer having breathability and conductivity; a membrane electrode assembly including a counter electrode, an acidic solid polymer proton conductor membrane, and a sensing electrode; a gas diffusion layer on the sensing electrode side that is breathable and conductive; a metal diffusion control plate having gas diffusion holes for supplying atmospheric gas to the gas diffusion layer on the sensing electrode side; a sealing body overlapping the diffusion control plate and having an opening larger than the gas diffusion holes in a portion facing the gas diffusion; and are arranged in this order, A proton conductor gas sensor, wherein the counter electrode side gas diffusion layer, the membrane electrode assembly, and the sensing electrode side gas diffusion layer are all disk-shaped, and the sealing body is crimped to the metal can with a gasket, The counter electrode side gas diffusion layer and the sensing electrode side gas diffusion layer each contain an adsorbent that adsorbs poisonous gases, the diameter of the membrane electrode assembly is equal to or greater than the diameter of the sensing electrode side gas diffusion layer, The sensing electrode side gas diffusion layer is larger in both diameter and thickness than the counter electrode side gas diffusion layer. The metal can is characterized in that an insulating and acid-resistant ring-shaped coating is provided on the inner bottom surface of the metal can, the outer diameter of which is larger than the diameter of the membrane electrode assembly and the inner diameter of which is smaller than the diameter of the counter electrode side gas diffusion layer.

[0008] Because the gas diffusion layer contains an adsorbent, if the sensing electrode side gas diffusion layer is made thicker than the counter electrode side gas diffusion layer, it can adsorb and remove poisonous gases such as pinene. However, the pressure caused by the crimping is applied to the sealing body, and this pressure presses the gas diffusion layer toward the membrane electrode assembly. For example, if the sensing electrode side gas diffusion layer is made thicker while keeping the diameter of the membrane electrode assembly and pair of gas diffusion layers the same, this gas diffusion layer will expand radially outward (see Figure 7). This can cause the sensing electrode side gas diffusion layer to come into contact with the counter electrode side gas diffusion layer or the metal can, resulting in a loss of gas sensor output. Furthermore, solid polymer proton conductors are generally polymers made of perfluorosulfonic acid, which is a highly acidic sulfonic acid.

[0009] Therefore, by making the diameter of the membrane electrode assembly equal to or larger than the diameter of the sensing electrode-side gas diffusion layer and by making the diameter of the sensing electrode-side gas diffusion layer larger than the diameter of the counter electrode-side gas diffusion layer, the sensing electrode-side gas diffusion layer is prevented from contacting the counter electrode-side gas diffusion layer or the metal can. Because the membrane electrode assembly has a diameter equal to or larger than the sensing electrode-side gas diffusion layer, it may come into contact with the metal can. Furthermore, because the membrane electrode assembly is acidic, it may corrode the metal can. Therefore, an insulating, acid-resistant ring-shaped coating with an outer diameter larger than the diameter of the membrane electrode assembly and an inner diameter smaller than the diameter of the counter electrode-side gas diffusion layer is provided on the bottom surface of the metal can. This coating prevents corrosion of the metal can and short-circuiting between the metal can and the membrane electrode assembly.

[0010] Examples of the effects of this invention are shown in Figures 8 and 9. Figure 8 shows an example (shown in Figure 1), in which the thickness of the sensing electrode side gas diffusion layer was 900 µm, and the thickness of the counter electrode side gas diffusion layer was 540 µm. Figure 9 shows a comparative example, in which the thickness of the gas diffusion layer on both the sensing electrode side and the counter electrode side was 540 µm, and no protrusions 18 were provided around the gas diffusion holes 16. The gas diffusion layers on both the sensing electrode side and the counter electrode side were made into a film of powdered activated carbon bound with a binder. The diameter of the membrane electrode assembly was 8 mm, the diameter of the sensing electrode side gas diffusion layer was 7.8 mm, the diameter of the counter electrode side gas diffusion layer was 6 mm, the outer diameter of the coating was 10 mm, and the inner diameter was 4 mm. A filter made of powdered activated carbon was housed in the sealing body.

[0011] When a proton conductor gas sensor was exposed to saturated pinene vapor at room temperature (20°C) for five days, the gas sensitivity (CO sensitivity in this case) decreased by approximately 50% in the comparative example, while the decrease in gas sensitivity was less than 10% in the example. In this way, by making the gas diffusion layer on the sensing electrode side thicker than that on the counter electrode side, it was possible to reduce poisoning by pinene. If poisoning by pinene can be reduced, poisoning by other high-boiling-point VOCs should also be reduced.

[0012] The adsorbent of the gas diffusion layer is, for example, carbon, more specifically, powdered activated carbon, fibrous activated carbon, finely powdered graphite, carbon nanotubes, graphene, fullerene, carbon black, or other carbon, which has electronic conductivity and a large specific surface area and therefore gas adsorption ability. In the embodiment, activated carbon is used as the carbon. In addition to carbon, zeolite, silica gel, activated alumina, etc., which are made conductive by being mixed with carbon powder, can also be used as the adsorbent of the gas diffusion layer. The ring-shaped coating is, for example, annular.

[0013] Preferably, the metal can comprises a metal can body and a bottom plate disposed on the inner bottom surface of the metal can, the coating is provided on the bottom plate, and the counter electrode-side gas diffusion layer is in contact with the surface of the bottom plate and the coating. The bottom of the metal can is required to have a certain degree of strength because it is subjected to impacts when the sealing body is crimped via a gasket, pressure from the sealing body, and the like. Therefore, the bottom plate is disposed on the inner bottom surface of the metal can to reinforce the bottom of the metal can.

[0014] Preferably, the diameter ratio of the sensing electrode side gas diffusion layer to the counter electrode side gas diffusion layer is 110% to 150% and the thickness ratio is 120% to 500%. The ratio of the diameter of the membrane electrode assembly to the diameter of the sensing electrode side gas diffusion layer is, for example, 100% to 110%. The membrane electrode assembly has a thickness of, for example, 100 μm or less, which is generally thinner than the counter electrode side gas diffusion layer. If the sensing electrode side gas diffusion layer is excessively thick, the pressure from the sealing member will not be transmitted to the counter electrode side gas diffusion layer. Therefore, the sensing electrode side gas diffusion layer preferably has a thickness of 700 μm to 1500 μm. The counter electrode side gas diffusion layer preferably has a thickness of 100 μm to 600 μm.

[0015] Preferably, the coating is made of a synthetic resin, such as an epoxy resin or a urethane resin, and an epoxy resin having high acid resistance is particularly preferred.

[0016] Preferably, the sealing body contains a filter to remove poisonous gases. As shown in Figures 8 and 9, even if a filter is placed in the sealing body, it is not sufficient to prevent poisoning by high-boiling-point VOCs. However, the filter in the sealing body can easily prevent poisoning by siloxane.

[0017] Preferably, the diffusion control plate has a portion surrounding the gas diffusion hole that protrudes into the opening of the sealing body, and a gap is provided between the portion surrounding the gas diffusion hole and the gas diffusion layer on the sensing electrode side.

[0018] The diffusion control plate is pressed toward the sensing electrode side gas diffusion layer by the pressure of the crimping through the sealing body. This pressure can cause material from the sensing electrode side gas diffusion layer to seep into the gas diffusion holes. This changes the amount of ambient gas supplied through the gas diffusion holes, which in turn changes the gas sensitivity. To address this issue, the periphery of the gas diffusion holes in the diffusion control plate can be protruded into the opening of the sealing body, creating a gap between the periphery of the gas diffusion holes and the sensing electrode side gas diffusion layer, thereby reducing the variation in gas sensitivity.

[0019] Preferably, a ring-shaped member having a hardness lower than that of the gasket is disposed between the gasket and the inner bottom of the metal can so as to surround the sensing electrode side gas diffusion layer, the membrane electrode assembly, and the counter electrode side gas diffusion layer, and the bottom of the ring-shaped member is in close contact with the inner bottom of the metal can.

[0020] Generally, metal cans are more rigid than sealing bodies, making them more susceptible to incomplete sealing with the gasket. If the gas sensor is subjected to mechanical shock, such as being dropped, the seal between the metal can and the gasket becomes incomplete, resulting in a change in gas sensitivity. Therefore, by providing the ring-shaped member described above, the pressure from the crimping causes the ring-shaped member to tightly contact the bottom of the metal can, blocking atmospheric gases that diffuse through the gap between the metal can and the gasket. This reduces changes in gas sensor sensitivity due to dropping or other factors.

[0021] Preferably, the diffusion control plate extends beyond the area facing the bottom of the sealing body to the area between the gasket and the ring-shaped member.

[0022] A small gap may exist between the diffusion control plate and the sealing member. Mechanical shock, such as dropping the gas sensor, can change the air permeability through the gap between the diffusion control plate and the sealing member. In contrast, if the diffusion control plate extends to the region between the gasket and the ring-shaped member, the ring-shaped member is soft and seals the gap between the gasket and the bottom of the metal can. As a result, atmospheric gas that has passed through the gap cannot move any further. This can further reduce changes in the sensitivity of the gas sensor due to dropping or other factors. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view of a main part of a proton conductor gas sensor according to an embodiment of the present invention; [Figure 2] Enlarged partial cross-sectional view of the MEA in the example [Figure 3] A plan view of the main part of the gas sensor shown in Figure 1. [Figure 4] A bottom view of the main part of the gas sensor shown in Figure 1, excluding the bottom plate. [Figure 5] Cross-sectional view of a gas sensor according to an embodiment [Figure 6] Enlarged cross-sectional view of the diffusion control plate, the opening of the sealing body, and the main part of the GDL on the sensing electrode side in Figure 5 [Figure 7] Cross-sectional photograph of a gas sensor according to another embodiment [Figure 8] A characteristic diagram showing the durability of the gas sensor of the example to pinene. [Figure 9] Characteristics diagram showing the durability of the gas sensor of the comparative example to pinene DETAILED DESCRIPTION OF THE INVENTION

[0024] The following examples are provided for carrying out the present invention. [Example]

[0025] 1 to 9 show examples and their characteristics. FIG. 1 shows the main components of a proton conductor gas sensor, from a bottom plate 4 to a diffusion control plate 14. The bottom plate 4 is, for example, a stainless steel plate, and on top of it, a counter electrode-side gas diffusion layer 10, a membrane electrode assembly (MEA) 6, a sensing electrode-side gas diffusion layer 8, and a diffusion control plate 14 are layered in this order. In addition, on the surface of the bottom plate 4, a coating 12 made of a printed epoxy resin film is provided in an annular shape so that its outer diameter is larger than that of the MEA 6 and its inner diameter is smaller than that of the counter electrode-side gas diffusion layer 10. In the following, the sensing electrode-side gas diffusion layer 8 is referred to as GDL8, and the counter electrode-side gas diffusion layer 10 is referred to as GDL10.

[0026] The structure of the MEA 6 is shown in Figure 2. A solid polymer proton conductor membrane 20 is located at the center of the MEA 6 in the thickness direction, and a counter electrode 21 is laminated on the surface of the membrane 20 on the GDL 10 side, and a sensing electrode 22 on the GDL 8 side. The counter electrode 21 and sensing electrode 22 are made of carbon black supporting an electrode catalyst such as Pt, and a solid polymer proton conductor such as perfluorosulfonic acid. The solid polymer proton conductor membrane 20 is made of a strongly acidic material such as perfluorosulfonic acid, and has a thickness of approximately 10 μm to 100 μm. The proton conductive membrane 20 is strongly acidic and corrodes the stainless steel bottom plate 4 when it comes into contact with the bottom plate 4 .

[0027] The GDLs 8 and 10 in the examples are both made of carbon that is electronically conductive, breathable, and gas-absorbing, and in the examples, are made by molding powdered activated carbon into a film using a fiber binder.

[0028] 3 is a plan view in which the GDL 8 is arranged at the top and the coating 12 at the bottom. FIG. 4 is a bottom view in which the coating 12 is arranged at the top and the GDL 8 at the bottom. The GDLs 8 and 10 and the MEA 6 are disk-shaped, and the coating 12 is annular. If the diameter of the MEA 6 is φ1, the diameter of the GDL 8 is φ2, and the diameter of the GDL 10 is φ3, then φ1≧φ2>φ3, and for example, 110%≧φ1 / φ2≧100%, 150%≧φ2 / φ3≧110%. If the thickness of GDL 8 is t1 and the thickness of GDL 10 is t2, then, for example, 500%≧t1 / t2≧120%. Thickness t1 is preferably 700 μm or more and 1500 μm or less, thickness t2 is preferably 100 μm or more and 500 μm or less, and t1+t2 is preferably 800 μm or more and 2000 μm or less. The inner diameter of coating 12 is smaller than the diameter of GDL 10, and the outer diameter is larger than the diameter of MEA 6.

[0029] 5 and 6 show the structure of the proton conductor gas sensor 2. 30 is a metal can with a bottom plate 4 placed on the top surface of the bottom. 32 is a metal sealing body that houses a filter 34 made of activated carbon, silica gel, zeolite, activated alumina, or the like, and has an opening 36 in the center of the bottom, through which atmospheric gas is introduced.

[0030] A stainless steel diffusion control plate 14 is mounted on top of the GDL 8, and a gas diffusion hole 16 with a diameter of 0.1 mm is located in the center. This plate controls the diffusion of atmospheric gas into the GDL 8. Around the gas diffusion hole 16, the diffusion control plate 14 protrudes toward the sealing body 32, forming a protrusion 18. A gap exists between the interior of the protrusion 18 and the GDL 8. The protrusion 18 is housed within an opening 36 in the sealing body 32 and does not contact the filter 34. As shown in FIG. 6 , pressure is applied to the GDL 8 through the sealing body 32 by crimping, as described below. If this pressure causes the material of the GDL 8 to infiltrate into the gas diffusion hole 16, the gas permeability of the diffusion hole 16 changes, and the gas sensitivity of the gas sensor 2 also changes. Therefore, by using the protrusion 18 to prevent the material of the GDL 8 from infiltrating into the gas diffusion hole 16, the gas permeability of the gas diffusion hole 16 can be made constant, thereby reducing variations in gas sensitivity.

[0031] A gasket 40 is placed between the sealing body 32 and the upper part of the inner surface of the metal can 30, and the metal can 30 and the sealing body 32 are crimped together via the gasket 40. A ring-shaped member 42 made of synthetic resin is placed between the bottom of the gasket 40 and the bottom plate 4, and the member 42 has a lower hardness than the gasket 40. The outer periphery of the disk-shaped diffusion control plate 14 is placed between the gasket 40 and the ring-shaped member 42.

[0032] The gasket 40 preferably has a Shore hardness D of 50 or more and 90 or less, more preferably a Shore hardness D of 55 or more and 90 or less, and particularly preferably a Shore hardness D of 60 or more and 90 or less. The ring-shaped member 42 preferably has a Shore hardness A of 50 or more and 90 or less, more preferably a Shore hardness A of 50 or more and 85 or less, and particularly preferably a Shore hardness A of 50 or more and 80 or less.

[0033] Shore hardness D is a unit that indicates the hardness of plastics, etc., while Shore hardness A is a unit that indicates the hardness of rubber, etc. Also, Shore hardness D of 40 is roughly equivalent to Shore hardness A of 90. Shore hardness is measured using a commercially available Shore hardness tester that complies with ASTM D2240.

[0034] The gasket 40 is preferably made of, for example, nylon 66, fluororesin such as PTFE, high-density polyethylene, etc. In this embodiment, the gasket 40 is made of high-density polyethylene. The ring-shaped member 42 is preferably made of NBR rubber, silicone rubber, Viton rubber, nitrile rubber, EPDM rubber, etc.

[0035] The metal can 30 is generally more rigid than the sealing body 32, and even if it is crimped, it does not necessarily provide sufficient adhesion to the gasket 40. If the gas sensor 2 is subjected to an impact, such as being dropped, a gap may form between the metal can 30 and the gasket 40, allowing unwanted atmospheric gas to be supplied to, for example, the GDL 8. This changes the gas sensitivity. In contrast, if a ring-shaped member 42 with low hardness is provided, the pressure from the crimping will cause the ring-shaped member 42 to come into close contact with the surface of the bottom plate 4, blocking out unwanted gas. This stabilizes the gas sensitivity.

[0036] The diffusion control plate 14 extends to between the gasket 40 and the ring-shaped member 42, and the portion of the diffusion control plate 14 that is outside the bottom of the sealing body 32 is called the extension 14b. When the extension 14b is provided, the atmosphere that passes through the interface between the diffusion control plate 14 and the sealing body 32 is blocked at the interface between the gasket 40 and the ring-shaped member 42 or the interface between the ring-shaped member 42 and the bottom plate 4, thereby blocking unnecessary gas flow paths from the opening 36 of the sealing body 32. The air permeability between the sealing body 32 and the diffusion control plate 14 changes when an impact is applied to the gas sensor 2, such as when it is dropped. Therefore, blocking this gas flow path with the extension 14b of the diffusion control plate 14 stabilizes gas sensitivity.

[0037] Figure 7 shows a cross-sectional photograph of a gas sensor 2 of another embodiment, which is the same as the embodiment in Figure 1 except that there are no protrusions 18 around the diffusion holes 16. A thin coating 12 can be seen on the bottom plate 4 below the outer edge of the upper GDL 8, and the GDL 8 has expanded in areas where there is no lower GDL 10. The MEA 6 prevents contact between the GDL 8 and GDL 6, and between the GDL 8 and the bottom plate 4. Furthermore, contact between the MEA 6 and the bottom plate 4 is prevented by the coating 12. Note that the GDL 8 below the gas diffusion holes 16 has been altered due to the resin injected into the gas sensor 2 for photography.

[0038] The effects of the example are shown in Figures 8 and 9. Figure 8 shows the results of the example, in which the thickness of the sensing electrode-side gas diffusion layer 8 was 900 µm and the thickness of the counter electrode-side gas diffusion layer 10 was 540 µm. Figure 9 shows the results of the comparative example, in which the thickness of the gas diffusion layer was 540 µm on both the sensing electrode side and the counter electrode side. The gas diffusion layers 8 and 10 on both the sensing electrode side and the counter electrode side were made of powdered activated carbon formed into a film using a binder. The diameter of the membrane electrode assembly 6 was 8 mm, the diameter of the sensing electrode-side gas diffusion layer 8 was 7.8 mm, the diameter of the counter electrode-side gas diffusion layer 10 was 6 mm, the outer diameter of the coating 12 was 10 mm, and the inner diameter was 4 mm. The sealing body 32 contained a filter 34 made of powdered activated carbon.

[0039] When the proton conductor gas sensor 2 was exposed to saturated pinene vapor at room temperature (20°C) for 5 days, the gas sensitivity (CO sensitivity in this case) decreased by approximately 50% in the comparative example, while the decrease in gas sensitivity was less than 10% in the example.

[0040] Table 1 shows the variation in initial CO sensitivity depending on whether or not there is a protrusion 18. By providing the protrusion 18, the variation in initial CO sensitivity was reduced to a fraction of the original value. There were 10 samples for each.

[0041] Table 1 Distribution of initial CO sensitivity (nA / ppm; N=10) around the protrusions of the gas diffusion layer Sample A Yes Min 2.3 Max 2.5 Sample B None Min 1.6 Max 2.3 *Sample A was provided with the protrusions 18 around the gas diffusion holes 16, the gasket 40, the ring-shaped member 42, and the extension portion 14b of the diffusion control plate. *Sample B did not have the protrusions 18 around the gas diffusion holes 16 or the extensions 14b of the diffusion control plate, and had only a single gasket, not a combination of the gasket 40 and the ring-shaped member 42.

[0042] Table 2 shows the difference in drop durability of the gas sensor 2 depending on whether or not the ring-shaped member 42 and the extension 14b of the diffusion control plate 14 are present. The drop test involved dropping the gas sensor 2 five times from a height of 2.1 mm onto a concrete floor, after which the gas sensitivity was measured. In sample A, high-density polyethylene (Shore hardness D: 70) was used for the gasket 40, and rubber (Shore hardness A: 70) was used for the ring-shaped member 42. In sample B, the gasket 40 and the ring-shaped member 42 were combined into a single high-density polyethylene gasket, and the extension 14b of the diffusion control plate 14 was not provided. In sample C, the gasket 40 and the ring-shaped member 42 were the same as in sample A, but the extension 14b of the diffusion control plate 14 was not provided.

[0043] The durability to the drop test was increased by the ring-shaped member 42, and the durability to the drop test was further increased by providing the diffusion control plate 14b. The number of samples N was 3 for each.

[0044] Table 2 Ring-shaped element Extension of diffusion control plate Increase in CO sensitivity due to drop test Sample A Yes Yes 1~ 2% (N=3) Sample B None None 80-100% (N=3) Sample C Presence / absence 2~10% (N=3) * Samples A and B are the same as Table 1. *Sample C was provided with the protrusions 18 around the gas diffusion holes 16, the gasket 40 and the ring-shaped member 42, but was not provided with the extension portion 14b of the diffusion control plate.

[0045] In the proton conductor gas sensor 2, the risk of siloxane poisoning is inherently low. For example, we tested the siloxane durability of a proton conductor gas sensor in which GDLs 8 and 10 were both 180 μm thick and 800 μm in diameter, and siloxane was removed solely by the activated carbon filter 34 in the sealing body 32. This gas sensor lacked the protrusions 18 around the gas diffusion holes 16, the extension 14b of the diffusion control plate 14, and a single gasket was used instead of the gasket 40 and ring-shaped member 42. The proton conductor gas sensor was exposed to an atmosphere containing 10 ppm each of linear siloxane M3 and cyclic siloxanes D4 and D5 (30 ppm total) for two weeks, with the siloxane atmosphere replaced daily. The change in CO sensitivity after two weeks was less than 10% for all ten gas sensors. Thus, siloxane poisoning was easily prevented by the activated carbon filter in the sealing body 32. [Explanation of symbols]

[0046] 2. Proton Conductor Gas Sensor 4 Bottom plate 6 Membrane electrode assembly (MEA) 8 Gas diffusion layer on the sensing electrode side 10 Counter electrode gas diffusion layer 12 Coating 14 Diffusion control plate 14b Extension 16 Gas diffusion holes 18 protrusions 20 Solid polymer proton conductor membrane 21 Opposite 22 detection pole 30 Metal cans 32 Sealing body 33,36 aperture 34 Filters 40 gasket 42 Ring-shaped member

Claims

1. On the inside bottom of the metal can, a counter electrode-side gas diffusion layer having breathability and conductivity; a membrane electrode assembly including a counter electrode, an acidic solid polymer proton conductor membrane, and a sensing electrode; a gas diffusion layer on the sensing electrode side that is breathable and conductive; a metal diffusion control plate having gas diffusion holes for supplying atmospheric gas to the gas diffusion layer on the sensing electrode side; a sealing body overlapping the diffusion control plate and having an opening larger than the gas diffusion holes in a portion facing the gas diffusion; and are arranged in this order, A proton conductor gas sensor, wherein the counter electrode side gas diffusion layer, the membrane electrode assembly, and the sensing electrode side gas diffusion layer are all disk-shaped, and the sealing body is crimped to the metal can with a gasket, The counter electrode side gas diffusion layer and the sensing electrode side gas diffusion layer each contain an adsorbent that adsorbs poisonous gases, the diameter of the membrane electrode assembly is equal to or greater than the diameter of the sensing electrode side gas diffusion layer, The sensing electrode side gas diffusion layer is larger in both diameter and thickness than the counter electrode side gas diffusion layer. and a ring-shaped insulating and acid-resistant coating having an outer diameter larger than the diameter of the membrane electrode assembly and an inner diameter smaller than the diameter of the counter electrode-side gas diffusion layer is provided on the inner bottom surface of the metal can.

2. The metal can comprises a metal can body and a bottom plate disposed on the inner bottom surface of the metal can, The coating is provided on a bottom plate, 2. The proton conductor gas sensor according to claim 1, wherein said counter electrode gas diffusion layer is in contact with the surface of said bottom plate and said coating.

3. 2. The proton conductor gas sensor according to claim 1, wherein the ratio of the diameter of the sensing electrode side gas diffusion layer to the counter electrode side gas diffusion layer is 110% or more and 150% or less, and the ratio of the thickness of the sensing electrode side gas diffusion layer to the counter electrode side gas diffusion layer is 120% or more and 500% or less.

4. 2. The proton conductor gas sensor according to claim 1, wherein said coating is made of a synthetic resin.

5. 2. The proton conductor gas sensor according to claim 1, wherein said sealing body contains a filter for removing poisonous gases.

6. The diffusion control plate has a portion around the gas diffusion hole protruding into the opening of the sealing body, 2. The proton conductor gas sensor according to claim 1, wherein a gap is provided between the periphery of the gas diffusion hole and the gas diffusion layer on the sensing electrode side.

7. a ring-shaped member having a hardness lower than that of the gasket is disposed between the gasket and an inner bottom of the metal can so as to surround the sensing electrode side gas diffusion layer, the membrane electrode assembly, and the counter electrode side gas diffusion layer; 2. A proton conductor gas sensor according to claim 1, wherein the bottom of the ring-shaped member is in close contact with the bottom of the inside of the metal can.

8. 8. The proton conductor gas sensor according to claim 7, wherein said diffusion control plate extends beyond the area facing the bottom of said sealing body to the area between said gasket and said ring-shaped member.

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