Electrochemical gas sensor

Abstract

Electrochemical gas sensor, comprehensive: a flat ceramic housing with a recess; an MEA which is equipped with an ion-conducting membrane, a first electrode on one surface of the ion-conducting membrane, and a second electrode on an opposite surface of the ion-conducting membrane: a first electrically conductive gas diffusion membrane and a second electrically conductive gas diffusion membrane; and a metal cover that is attached to the housing and covers the recess, wherein the housing is provided with a first electrical connection extending from a bottom surface of the recess to a bottom surface of the housing, and a second electrical connection extending from a top surface of the housing surrounding the recess to the bottom surface of the housing; wherein the first electrically conductive gas diffusion membrane is arranged between the MEA and the bottom surface of the recess and is electrically connected to the first electrical connection; wherein the second electrically conductive gas diffusion membrane is arranged between the MEA and the lid and is electrically connected to the lid; wherein the lid is attached to the top surface and is electrically connected to the second electrical connection; wherein the second electrically conductive gas diffusion membrane is pressed against the MEA by the lid; and where a gas inlet is provided in the lid or in the base of the housing.

Description

Field of the invention

[0001] The present invention relates to a housing structure for electrochemical gas sensors. Technical background

[0002] Gases such as CO are detected by electrochemical gas sensors (see JP 5 693 496 B2, WO 01 / 14 864 A1). A membrane electrode assembly (MEA), the main component of the gas sensor, comprises a proton-conducting membrane, a retaining plate for an electrolyte solution or an ionic solution, or the like, and a sensing and counter electrode on both surfaces of the membrane or plate. Upon contact with gases, an electric current or electromotive force is generated between the electrodes and output by the gas sensor.On the two sides of the MEA, two permeable conductive membranes (electrically conductive gas diffusion membranes) are stacked on top of each other, the atmosphere to be detected is supplied through one of the conductive membranes adjacent to the sensing electrode, oxygen is supplied through the other conductive membrane adjacent to the counter electrode, and the generated water vapor is exhausted from the counter electrode (JP 5 693 496 B2).

[0003] Regarding the housing structure of electrochemical gas sensors, JP 5 693 496 B proposes a construction similar to button-type cells; the conductive membranes and the MEA are arranged between two metal plates insulated from each other by a gasket and pressed together with a sealant. The pressing pressure ensures the electrical contact of the MEA with the two metal plates.

[0004] According to WO 01 / 14 864 A1, two housings, each having a recess, are stacked on top of each other so that the recesses face each other and the MEA is accommodated in the recesses. According to WO 01 / 14 864 A1, a liquid electrolyte is embedded in the recesses, and the electrodes protrude exposed through holes or the like in the housing to ensure connection to the outer part. Electrochemical gas sensors with an MEA are also known from US 2006 / 0 091 007 A1, US 2006 / 0 196 770 A1, CN 1 00 350 237 C, and US 2004 / 0 134 780 A1. Summary of the inventionProblems to be solved by the invention

[0005] The housing according to JP 5 693 496 B2 uses a gasket and sealant, making it difficult to reduce the size of the gas sensors compared to current standards. Furthermore, since the compression with sealant can lead to fluctuations in the MEA positions, production control is difficult.

[0006] In the housing of WO 01 / 14864 A1, the connection between the electrodes and a peripheral circuit is difficult. When using permeable, electrically conductive membranes, it is also difficult to compress the membranes at a predetermined pressure to ensure contact between the electrodes and the membranes.

[0007] The object of the invention is to provide an electrochemical gas sensor which can be easily manufactured compactly, has uniform performance characteristics and can be easily mounted on a substrate. Means to solve the problems

[0008] An electrochemical gas sensor according to the invention comprises: a flat ceramic housing with a recess; an MEA provided with an ion-conducting membrane, a first electrode on one surface of the ion-conducting membrane, a second electrode on an opposite surface of the ion-conducting membrane; a first electrically conductive gas diffusion membrane and a second electrically conductive gas diffusion membrane; and a metal cover that is attached to the housing and covers the recess, wherein the housing is provided with a first electrical connection extending from a bottom surface of the recess to a bottom surface of the housing, and a second electrical connection extending from a cover surface of the housing surrounding the recess to the bottom surface of the housing; the first electrically conductive gas diffusion membrane is disposed between the MEA and the bottom surface of the recess and is electrically connected to the first electrical connection; the second electrically conductive gas diffusion membrane is arranged between the MEA and the lid and is electrically connected to the lid: the cover is attached to the cover surface and is electrically connected to the second electrical connection; the second electrically conductive gas diffusion membrane is pressed against the MEA by the lid; and a gas inlet is provided in the lid or in the bottom surface of the housing.

[0009] Since no sealant or gasket is required, the electrochemical gas sensor is manufactured compactly. The cover presses the first and second electrically conductive membranes and the MEA against the bottom surface of the recess, thus creating an electrical path from the MEA via the second electrically conductive membrane to the cover and an electrical path from the MEA via the first electrically conductive membrane to the first electrical connection. The cover is further electrically connected to the bottom surface of the housing via the second electrical connection, and the first electrical connection also extends to the bottom surface. This allows the two electrodes of the gas sensor to be connected to a peripheral circuit on the bottom surface of the housing. In this description, the direction is specified so that the cover is on the top and the bottom surface of the recess is on the bottom.

[0010] Preferably, a metal layer is provided on the cover surface, and the cover is welded to this metal layer. By welding the cover to the metal layer, the cover can be easily attached to the housing and electrically connected to the metal layer in a reliable and airtight manner.

[0011] The cover is preferably provided with an opening that serves as a gas inlet, and the bottom surface of the housing is airtight. Since the cover is made of metal, the small gas inlet opening can be inserted with high precision, thus maintaining a constant permeability to the interior of the gas sensor. Since the gas inlet opening is located in the cover, the bottom surface of the housing is also designed to be airtight.

[0012] An electrically conductive, flat gas adsorption filter is preferably provided between the second electrically conductive gas diffusion membrane and the lid. This applies to electrically conductive activated carbon, and most gas adsorbents such as silica gel, zeolite, and mesoporous silicon dioxide can be rendered electrically conductive by adding electrically conductive particles such as carbon black. This ensures an electrically conductive path from the second electrically conductive gas diffusion membrane via the gas adsorption filter to the lid. Furthermore, it is sufficient for the gas adsorption filter to treat a small amount of gas diffused through the gas inlet opening, thereby improving the filter's service life.

[0013] The MEA, the first electrically conductive gas diffusion membrane, the second electrically conductive gas diffusion membrane, the recess, the housing, and the cover preferably all have a quadrangular shape in plan view, for example, the shape of a rectangle or square. Instead of a round MEA from JP 5 693 496 B, a quadrangular MEA is used, thereby reducing cutting loss during MEA production when the MEA is punched from a flat starting material. Since the MEA is manufactured quadrangularly, the housing, the cover, the recess, and the first and second electrically conductive gas diffusion membranes are also all quadrangular.

[0014] The recess is preferably provided with the bottom surface, a first wall surrounding the bottom surface, a flat surface surrounding an upper edge of the first wall, and a second wall surrounding the flat surface, wherein the top surface is provided above the second wall and surrounds the second wall; the first electrically conductive gas diffusion membrane is in contact with the bottom surface of the recess and is surrounded by the first wall; the second electrically conductive gas diffusion membrane is surrounded by the second wall; and

[0015] Edges of the MEA or edges of the second electrically conductive gas diffusion membrane are arranged on the flat surface.

[0016] The electrically conductive membranes are compressed by the pressure from the lid, and this pressure ensures contact between the first electrically conductive membrane and the MEA, contact between the second electrically conductive membrane and the MEA, and contact between the second membrane and the first electrical connection. The flat surface between the bottom surface and the top surface of the recess divides the recess in the depth direction, from the top surface to the flat surface on the one hand, and from the flat surface to the bottom surface on the other. The compressed thickness of the first electrically conductive membrane and the compressed thickness of the second electrically conductive membrane can thus be regulated.Since edges of the MEA or edges of the second electrically conductive gas diffusion membrane are located on the flat surface, the two electrically conductive gas diffusion membranes are not in contact with each other and the atmosphere between the top of the flat surface and the bottom is sealed off. Brief description of the drawings Fig. 1 Cross-sectional view of an electrochemical gas sensor according to an embodiment. Fig. 2 Top view of the electrochemical gas sensor according to the embodiment. Fig. 3 Exploded view of an electrochemical gas sensor in plan view without cover according to the embodiment. Fig. 4 Cross-sectional view of a package for the electrochemical gas sensor according to the embodiment. Fig. 5 Enlarged partial cross-sectional view of the electrochemical gas sensor according to the embodiment. Fig. 6 Cross-sectional view of an electrochemical gas sensor according to a modified embodiment. Fig. 7 Cross-sectional view of an electrochemical gas sensor according to a second modified embodiment. Embodiments of the invention

[0017] The best mode for carrying out the invention is described below. Embodiments

[0018] Fig. Figures 1-5 show one embodiment. An electrochemical gas sensor 2 is provided with a ceramic housing 4, an MEA 6, electrically conductive gas diffusion membranes 8, 10 arranged above and below the MEA 6, and a metal cover 12. These parts 4-12 are rectangular or square in plan view, and the conductive gas diffusion membranes 8, 10 are mounted in a recess 13 of the housing 4.

[0019] The housing 4 is provided with a recess 13, which is rectangular or square when viewed from above. 14 denotes the bottom surface of the recess 13, 15 denotes a flat intermediate surface surrounding the bottom surface 14, and 25 denotes a cover surface surrounding the flat surface 15. Between the cover surface 25 and the flat surface 15 there is a wall surface 17, which is, for example, vertical, and between the flat surface 15 and the bottom surface 14 there is another wall surface 18, which is, for example, vertical. The cover surface 25 is covered, for example, completely covered, by a metal layer 16; the metal layer 16 can be manufactured by simultaneously firing a metal material for the layer and a ceramic material for the housing 4, or by soldering a metal plate onto the cover surface 25.The metal layer 16 is electrically connected to an electrical connection 21 on the bottom surface 19 of the housing 4 via another electrical connection 20.

[0020] An electrical connection 22 is provided entirely or partially on the bottom surface 14 of the recess and is extended on the bottom surface 19 of the housing 4 via electrical connections 23, 24. The electrical connections 20-24 are produced by simultaneously firing a metal material for the connections and the ceramic material for the housing 4. While the electrical connection 20, 23 extends along the side surfaces of the housing 4, electrically conductive, airtight through-holes can be provided in the housing 4 instead.

[0021] The cover 12 has one or more gas inlet openings 26, and the size of the gas inlet opening 26 is designed to be constant, so that the permeability to the interior of the gas sensor 2 is constant. Since the inlet openings are introduced into the metal plate using a hole-making process, the desired gas inlet openings 26 are manufactured in a constant size. Instead of the gas inlet opening in the cover 12, the layer from the bottom surface 19 to the bottom surface 14 of the recess 13 of the housing 4 can be manufactured as a permeable ceramic layer.

[0022] As on the left side of Fig. As shown in Figure 1, the MEA 6 comprises a proton-conducting membrane 34, a sensing electrode 35 laminated to the top of the membrane, and a counter electrode 36 laminated to the bottom. Instead of the proton-conducting membrane 34, a sheet metal retaining an electrolyte solution or an ion solution can be used. The MEA 6 is the most complex part of the gas sensor 2, and the MEA 6 is punched from a flat MEA template. The rectangular or square MEA 6 eliminates cutting waste.

[0023] The electrically conductive gas diffusion membranes 8, 10 are permeable surface elements containing carbon black, carbon fiber, or other electrically conductive particles, and high electrical conductivity is not required for them. While the diffusion membranes 8, 10 can be made hydrophobic by adding fibers such as PTFE, they contain hydrophilic fibers such as polyamide, methylcellulose, and polyvinyl alcohol to adjust the humidity in the housing and reduce the humidity dependence of the gas sensor 2.

[0024] 28 denotes a permeable, electrically conductive filter made of a sheet material containing activated carbon; it is arranged between the cover 12 and the first electrically conductive membrane 8, electrically connecting them. The filter 28 may be a sheet material containing a mixture of electrically conductive particles and another adsorbent such as zeolite, silica gel, or mesoporous silicon dioxide, and formed with a fiber-like binder.

[0025] Now, the method for manufacturing the gas sensor 2 will be described. As in Fig. As shown in Figure 5, the housing 4 comprises three layers 30-32. For example, the electrical connections 21, 22, and 24 are provided on both sides of layer 30, the metal layer 16 is provided on top 25 of layer 32, and the layers 30-32 are stacked and fired to form the housing. The electrical connections 20, 23 can be formed and fired simultaneously with the layers 30-32, or they can be formed after the firing of the layers 30-32.

[0026] The electrically conductive gas diffusion membranes 8, 10 are layered both below and above the MEA 6, and the electrically conductive gas diffusion membrane 10 is arranged on the bottom surface 14 of the recess 13. The MEA 6 and / or the electrically conductive membrane 8 rest on the flat surface 15, thereby preventing contact between the electrically conductive membranes 8, 10 and dividing the atmosphere into the upper space and the lower space of the flat surface 15.

[0027] The filter 28 is layered over the gas diffusion membrane 28, and the cover 12 covers the recess 13. The cover 12 is welded to the metal layer 16 by seam welding. Since seam welding is used to encapsulate IC chips in ceramic package housings, the cover 12 is easily and hermetically sealed to the housing 4. However, instead of seam welding, attachment with an electrically conductive adhesive or the like is also possible.

[0028] The cover 12 presses the filter 28, the electrically conductive gas diffusion membrane 8, the MEA 6, and the electrically conductive gas diffusion membrane 10 against the bottom surface 14 of the recess 13, thereby electrically connecting these parts and securing them in the recess. The electrically conductive gas diffusion membranes 8, 10 become thinner due to the pressure exerted by the cover; the pressurized thickness of the electrically conductive gas diffusion membrane 10 is determined by the height of the wall surface 18, and the pressurized thickness of the gas diffusion membrane 8 is determined by the height of the wall surface 17. Furthermore, the edges of both the MEA 6 and the conductive gas diffusion membrane 8 rest on the flat surface 15, and thus the conductive gas diffusion membranes 8, 10 are not in contact with each other.In addition, the gap between the wall surface 18 and the conductive gas diffusion membrane 10 is covered by the MEA 6 and the conductive gas diffusion membrane 8, and thereby the atmosphere surrounding the detection electrode is prevented from penetrating to the counter electrode.

[0029] Since the detection electrode and the counter electrode of the MEA 6 are electrically connected to the electrical connections 21, 24 located on the bottom surface of the housing 4, the gas sensor 2 can be mounted on a substrate such as a printed circuit board by reflow soldering, electrically conductive adhesive, or the like.

[0030] Fig. Fig. 6 shows an electrochemical gas sensor 42 according to a first modified example which, unless otherwise stated, corresponds to the embodiment of the Fig. 1 to 5. In the gas sensor 42, a filter 48 comprising a gas adsorbent is positioned above the gas inlet opening 26 of the cover 12. The filter 48, which exceeds the size of filter 28, is necessary because the gas is treated before the gas flow rate through the gas inlet opening 26 is throttled.

[0031] Fig. Fig. 7 shows an electrochemical gas sensor 52 according to a second modified example which, unless otherwise stated, corresponds to the embodiment of Fig. 1 to 5. Instead of the two-stage recess 13 with the flat intermediate surface 15, a rectangular or square single-stage recess 53 is provided, and the recess accommodates the MEA 6, the gas diffusion membranes 8, 10, and the filter 28. Reference numeral 57 is a wall surface of the recess 53. Description of reference symbols 2 electrochemical gas sensor 4 housings 6 MEA 8, 10 electrically conductive gas diffusion membrane 12 lids 13 Recess 14 Bottom surface of the recess 15 flat surface 16 metal layer 17, 18 wall surface 19 Bottom surface of the housing 20-24 electrical connection 25 deck area 26 Gas inlet opening 28, 48 filters 30-32 shift 34 Proton conductor membrane 35 Detection electrode 36 Counter electrode 42, 52 electrochemical gas sensor 53 recess 57 wall area

Claims

[1] Electrochemical gas sensor comprising: a flat ceramic housing with a recess; an MEA provided with an ion-conducting membrane, a first electrode on one surface of the ion-conducting membrane, a second electrode on an opposite surface of the ion-conducting membrane: a first electrically conductive gas diffusion membrane and a second electrically conductive gas diffusion membrane; and a metal cover that is attached to the housing and covers the recess, wherein the housing is provided with a first electrical connection extending from a bottom surface of the recess to a bottom surface of the housing, and a second electrical connection extending from a cover surface of the housing surrounding the recess to the bottom surface of the housing; wherein the first electrically conductive gas diffusion membrane is disposed between the MEA and the bottom surface of the recess and is electrically connected to the first electrical connection; wherein the second electrically conductive gas diffusion membrane is disposed between the MEA and the lid and is electrically connected to the lid; wherein the cover is mounted on the cover surface and is electrically connected to the second electrical connection; wherein the second electrically conductive gas diffusion membrane is pressed against the MEA by the lid; and wherein a gas inlet is provided in the lid or in the bottom surface of the housing. [2] An electrochemical gas sensor according to claim 1, wherein a metal layer is provided on the cover surface and the cover is welded to the metal layer. [3] An electrochemical gas sensor according to claim 1 or claim 2, wherein the cover is provided with an opening serving as a gas inlet, and wherein the bottom surface of the housing is airtight. [4] An electrochemical gas sensor according to any one of claims 1 to 3, wherein an electrically conductive and planar gas adsorption filter is provided between the second electrically conductive gas diffusion membrane and the cover. [5] An electrochemical gas sensor according to any one of claims 1 to 4, wherein the MEA, the first electrically conductive gas diffusion membrane, the second electrically conductive gas diffusion membrane, the recess, the housing and the cover all preferably have a quadrangular shape in plan view. [6] An electrochemical gas sensor according to any one of claims 1 to 5, wherein the recess is provided with the bottom surface, a first wall surrounding the bottom surface, a flat surface surrounding an upper edge of the first wall, and a second wall surrounding the flat surface, and wherein the cover surface is provided above the second wall and surrounds the second wall; wherein the first electrically conductive gas diffusion membrane is in contact with the bottom surface of the recess and is surrounded by the first wall; wherein the second electrically conductive gas diffusion membrane is surrounded by the second wall; and wherein edges of the MEA or edges of the second electrically conductive gas diffusion membrane are arranged on the flat surface.

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