Solid electrolyte gas sensor element, manufacturing method thereof, and solid electrolyte gas sensor

Abstract

To provide a solid electrolyte gas sensor element using a zeolite dense body which has a small environmental impact and can reduce manufacturing costs, a manufacturing method thereof, and a solid electrolyte gas sensor.SOLUTION: The solid electrolyte gas sensor element of the present invention comprises a first electrode layer, a gas sensing layer, a solid electrolyte layer, and a second electrode layer in that order. The gas sensing layer contains a metal inorganic acid salt, and the solid electrolyte layer contains a dense body of zeolite represented by the following general formula (1): (M1 / n)x(AlxSiyO2(x+y))*zH2O ... (1) (In formula (1), M=Na, Li, K; 0≤x≤y, 0≤z≤216, and n is the valence.) The ionic conductivity of the dense body of zeolite is 1.0×10-3S cm-1 or greater, and the bulk density of the dense body of zeolite is 1.7 g / cm3 or greater and 2.0 g / cm3 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid electrolyte gas sensor element using a dense body of zeolite as a solid electrolyte, a method for manufacturing the same, and a solid electrolyte gas sensor. [Background technology]

[0002] Gas sensors have been used in a variety of fields to measure inorganic gases such as carbon dioxide in the atmosphere, and have been used for combustion control, environmental measurement, etc. Solid electrolyte gas sensors using ion-conductive solid electrolytes have been proposed as small, simple, and inexpensive gas sensors. For example, Patent Document 1 lists solid electrolyte gas sensors using Li-β alumina, Li5AlO4, Na-β alumina, Na3Zr2Si2P0 12 Gas sensors using solid electrolytes such as Na3Zr2Si2P0 12 is called NASICON 1+x Zr2Si x P 3-x O 12 It is a type of solid electrolyte. Non-Patent Document 1 reports a gas sensor that uses a NASICON solid electrolyte.

[0003] Zeolites are extremely inexpensive and environmentally friendly, and are therefore commonly used as catalysts and adsorbents for purposes such as petroleum reforming, purification of exhaust gases from internal combustion engines, and hydrocarbon synthesis. Zeolites are often used in the form of powders in catalysts and adsorbents. Because zeolites are non-sinterable, they are rarely used in bulk form. On the other hand, it has been reported that zeolite can be successfully densified by a method called hydrothermal hot pressing, which involves simultaneously carrying out a hydrothermal reaction process and a pressure process (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 1985 / 05681 [Patent Document 2] Japanese Patent Publication No. 2021-107317 [Non-patent literature]

[0005] [Non-Patent Document 1] Sheng Yao, Youichi Shimizu, Norio Miura, Noboru Yamazoe: Solid Electrolyte CO2 Sensor Using Binary Carbonate Electrode, Chemistry Letters, Volume 19, Issue 11, November 1990, Pages 2033-2036. Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned Patent Document 1 and Non-Patent Document 1, these solid electrolytes are usually used after being densified by high-temperature heat treatment. Therefore, in manufacturing gas sensors, electrode components such as a gas sensing layer are baked onto a pre-fabricated dense body of solid electrolyte. In the highly competitive sensor development field, reducing the cost of the manufacturing process is an issue. On the other hand, although Patent Document 2 mentioned above succeeded in densifying zeolite, there is no report on the application of densified zeolite to a solid electrolyte gas sensor, and there are issues regarding the possibility of achieving the same level of performance as conventional solid electrolytes, and how to attach the gas detection layer when using zeolite as a solid electrolyte.

[0007] The object of the present invention is to provide a solid electrolyte gas sensor element using a dense zeolite body, which has a small environmental impact and can reduce manufacturing costs while maintaining the performance of solid electrolyte gas sensors using conventional solid electrolytes, a manufacturing method thereof, and a solid electrolyte gas sensor. [Means for solving the problem]

[0008] The gist and configuration of the present invention are as follows. [1] First electrode layer a gas sensing layer capable of generating electricity in response to a gas to be measured; a solid electrolyte layer having ion conductivity; a second electrode layer, and a second electrode layer in this order, the gas sensing layer comprises a metal inorganic acid salt, the solid electrolyte layer contains a dense body of zeolite represented by the following general formula (1), The ion conductivity of the zeolite dense body is 1.0 × 10 -3 S cm -1 That's all, The bulk density of the zeolite dense body is 1.6 g / cm 3 More than 2.0g / cm 3 The solid electrolyte gas sensor element is as follows: (M 1 / n ) x (Al x Si y O 2(x+y) )·zH2O ···(1) (In formula (1), M is one or more metal elements selected from Na, Li, and K, 0≦x≦y, 0≦z≦216, and n is a valence number.) [2] The solid electrolyte gas sensor element according to [1], wherein the relative density measured by comparing the theoretical density with the bulk density is 80% or more. [3] Bulk density: 1.6 g / cm 3 More than 2.0g / cm 3 The solid electrolyte gas sensor element according to [1] or [2], which is: [4] Log(σ / S cm) calculated from ionic conductivity between room temperature and 450°C -1 ) is not less than −3. [5] The solid electrolyte gas sensor element according to any one of [1] to [4], which has an A-type or X-type skeleton structure. [6] The gas sensing layer contains at least one metal carbonate selected from the group consisting of Li2CO3, Na2CO3, K2CO3, BaCO3, SrCO3, CaCO3, MgCO3, PbCO3, FeCO3, and ZnCO3, The solid electrolyte gas sensor element according to any one of [1] to [5], wherein the solid electrolyte gas sensor element is a carbon dioxide gas sensor. [7] The solid electrolyte gas sensor element according to any one of [1] to [6], wherein the gas detection layer contains at least one composite metal carbonate selected from the group consisting of Na2CO3-BaCO3 and Li2CO3-BaCO3. [8] The solid electrolyte gas sensor element according to any one of [1] to [7], wherein the gas sensing layer is formed by collectively molding the solid electrolyte layer and the gas sensing layer. [9] The solid electrolyte gas sensor element according to any one of [1] to [8], a device for measuring an electromotive force between the first electrode layer and the second electrode layer; and a device for introducing a gas to be measured into the gas sensing layer.

[10] A method for producing the solid electrolyte gas sensor element according to any one of [1] to [8], a first step of forming a first laminate including a precursor layer of the gas sensing layer and a precursor layer of the solid electrolyte layer; a second step of placing the first laminate in an enclosed space configured to be capable of being heated and pressurized, and producing a second laminate including the zeolite dense body by a hydrothermal hot pressing method; A method for manufacturing a solid electrolyte gas sensor element comprising:

[11] A method for manufacturing a solid electrolyte gas sensor element as described in claim 10, further comprising a third step of forming the first electrode layer on the gas sensing layer side of the second laminate and forming the second electrode layer on the opposite side thereof.

[12] The method for manufacturing a solid electrolyte gas sensor element according to

[10] or

[11] , further comprising a third step of dehydrating the second laminate after the second laminate is produced by the hydrothermal hot pressing method in the second step.

[13] The method for manufacturing a solid electrolyte gas sensor element according to any one of [9] to

[12] , wherein in the second step, the first laminate is heated and pressurized at a temperature of 100°C or higher and 200°C or lower, at a pressure of 50 MPa or higher and 600 MPa or lower, and for a holding time of 0.5 hours or higher and 24 hours or lower.

[14] The method for manufacturing a solid electrolyte gas sensor element according to any one of [9] to

[13] , wherein the precursor layer of the solid electrolyte layer is made using a mixture of a powder of the zeolite represented by the general formula (1) and water or an alkaline aqueous solution. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a solid electrolyte gas sensor element using a dense zeolite body, which has a small environmental impact and can reduce manufacturing costs while maintaining the performance of a solid electrolyte gas sensor using a conventional solid electrolyte, a manufacturing method thereof, and a solid electrolyte gas sensor. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a layer structure of a solid electrolyte gas sensor element according to one embodiment of the present invention; [Figure 2] 2(a) to 2(c) are schematic diagrams illustrating an example of a method for manufacturing the solid electrolyte gas sensor element according to this embodiment. [Figure 3] FIG. 3 is a scanning electron microscope (SEM) image showing the interface between the gas detection layer 40 and the solid electrolyte layer 60 of the solid electrolyte gas sensor element 100 obtained in Example 1. As shown in FIG. [Figure 4] FIG. 4 is a scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX) image showing the interface between the gas detection layer 40 and the solid electrolyte layer 60 of the solid electrolyte gas sensor element obtained in Example 1. [Figure 5] FIG. 5 is a diagram showing the results of calculating the ionic conductivity at each temperature of the solid electrolyte layer 60 of the solid electrolyte gas sensor elements 100 obtained in Examples 1 to 5. [Figure 6]FIG. 6 is a graph showing the sensor response recovery curves for each CO 2 concentration in the solid electrolyte gas sensor element 100 obtained in Example 1. [Figure 7] FIG. 7 is a graph showing the change in the sensor electromotive force in response to each CO 2 concentration in the solid electrolyte gas sensor element 100 obtained in Example 1. [Figure 8] FIG. 8 is a diagram showing the results of a cycle experiment on the solid electrolyte gas sensor element 100 obtained in Example 1. As shown in FIG. [Figure 9] FIG. 9 is a graph showing the sensor response recovery curve for 10,000 ppm CO 2 in the solid electrolyte gas sensor element obtained in Example 13. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic parts enlarged for the sake of convenience in order to make the features of the present invention easier to understand. Therefore, the dimensional ratios of each component may differ from the actual ones.

[0012] (Solid electrolyte gas sensor element) As shown in Fig. 1, a solid electrolyte gas sensor element 100 according to one embodiment of the present invention comprises, in this order, a first electrode layer 20, a gas sensing layer 40 capable of generating electricity in response to a gas to be measured, a solid electrolyte layer 60 having ion conductivity, and a second electrode layer 80. The gas sensing layer contains a metal inorganic acid salt. The solid electrolyte layer contains a dense body of zeolite represented by the following general formula (1), and the ionic conductivity of the dense body of zeolite is 1.0 x 10 -3 S cm -1 or more, and the bulk density of the zeolite dense body is 1.6 g / cm 3 More than 2.0g / cm 3 The following is the result. (M 1 / n ) x (Al x Si y O 2(x+y) )·zH2O ···(1) (In formula (1), M is one or more metal elements selected from Na, Li, and K, 0≦x≦y, 0≦z≦216, and n is a valence number.) The solid electrolyte gas sensor element is preferably a carbon dioxide gas sensor for measuring carbon dioxide. In the solid electrolyte gas sensor element, the solid electrolyte layer and the gas sensing layer are preferably formed in a single unit, and more preferably formed in a single unit using a hydrothermal hot press. It is further preferable that the solid electrolyte gas sensor element is obtained by the "Method for manufacturing a solid electrolyte gas sensor element" described later.

[0013] [Solid electrolyte layer] The solid electrolyte layer 60 included in the solid electrolyte gas sensor element 100 of this embodiment is preferably a dense body of zeolite represented by the general formula (1) above. It is preferable that the zeolite dense body (sometimes referred to as "zeolite dense body") is molded together with the gas sensing layer according to the present embodiment, which will be described later, using the hydrothermal hot pressing method, which will be described later. In this case, the heating and pressure conditions for the hydrothermal hot pressing method are not particularly limited, but are preferably, for example, a temperature of 100°C to 300°C, a pressure of 50 MPa to 600 MPa, and a holding time of 0.5 hours to 36 hours. It is more preferable that the temperature is 125°C to 175°C, a pressure of 200 MPa to 600 MPa, and a holding time of 10 hours to 25 hours. In the hydrothermal hot pressing method of Example 1, which will be described later, the heating temperature was 150°C, the pressure was 540 MPa, and the holding time was 24 hours.

[0014] <Dense zeolite body> The dense zeolite body according to this embodiment forms a dense aggregate of crystal grains, unlike conventional zeolite compacts such as zeolite powder compacts, due to the formation of bonds between the particles constituting the zeolite powder. This three-dimensional structure of dense aggregates allows for the formation of good ion conduction paths. Therefore, the ion conductivity of the dense zeolite body is 1.0 x 10 -3 S cm -1or more, preferably 0.5 × 10 -2 S cm -1 More preferably, it is 1.0×10 -2 S cm -1 The relative humidity of the atmosphere during use of the zeolite dense body is preferably 30% or more, more preferably 50% or more, and even more preferably 70% or more. By using the zeolite dense body of this embodiment in an environment where the relative humidity can be maintained within the above range, higher ionic conductivity can be achieved.

[0015] The dense zeolite body is composed of a framework of anionic crystalline aluminosilicate and a cationic metal element M supported on the framework. The metal element M is preferably Na or Li, since cationic species with a smaller ionic radius exhibit higher ionic conductivity.

[0016] In this zeolite dense body, the relative density measured from the theoretical density and bulk density is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. By having a relative density within the above range, more bonds are formed between particles, resulting in a zeolite bulk body with a relative density close to the theoretical density. Furthermore, a dense crystalline structure without impurities, voids, pinholes, etc. at the grain boundaries can be obtained.

[0017] The bulk density of the zeolite dense body is 1.6 g / cm 3 More than 2.0g / cm 3 Preferably, it is 1.8 g / cm or less. 3 More than 2.0g / cm 3 The bulk density of the compact made of zeolite powder is more preferably 0.9 g / cm or less. 3 More than 1.2g / cm 3 Since the bulk density of the zeolite dense body of this embodiment is larger than those of the above, a denser zeolite bulk body can be obtained. The bulk density can be measured from the shape and mass of the sample.

[0018] The dense zeolite body has the same skeletal structure as the zeolite powder used as the raw material. Examples of the skeletal structure of the dense zeolite body include A-type (LTA), X-type or Y-type (FAU), L-type (LTL), ZSM-5 (MFI), beta (BEA), ferrierite (FER), and mordenite (MOR). From the viewpoint that the more cations present in the dense zeolite body, the more cations that contribute to ionic conduction and thus the higher the ionic conductivity, the more preferred the skeletal structure is with a low silica / alumina ratio, and A-type or X-type is preferred.

[0019] A dense zeolite body has a plurality of pores with pore sizes corresponding to each skeletal structure. For example, when a dense zeolite body has an A-type skeletal structure, the pore size is 0.42 nm (4.2 Å), and when a dense zeolite body has an X-type skeletal structure, the pore size is 0.74 nm (7.4 Å). Among the above skeletal structures, the pore sizes increase in the order of X-type or Y-type, L-type, mordenite, beta, ZSM-5, ferrierite, and A-type.

[0020] The shape of the zeolite dense body can be bulk, sheet, membrane, or the like. The thickness of the zeolite dense body is preferably 10 μm or more and 2000 μm or less, and more preferably 50 μm or more and 1000 μm or less. By making the thickness of the zeolite dense body 50 μm or more, it is possible to prevent the dense body from being broken or short-circuited. Furthermore, by making the zeolite dense body thinner, it is possible to reduce the resistance to ion conduction and obtain high ion conduction properties.

[0021] In addition, for dense zeolite, the log(σ / S·cm) calculated from the ionic conductivity (σ) is -1 ) is -3 or more. In the fields of batteries and chemical sensors, log(σ / S·cm -1The region where the ionic conductivity (R) is -3 or greater is called the superionic conduction region, and is one of the indices that govern the electrical performance of each device. By exhibiting the ionic conductivity contained in this superionic conduction region at a relatively low temperature range, between room temperature and 450°C, it is possible to maintain significantly higher ionic conductivity within the allowable temperature range within the device, for example, the allowable temperature range for a lithium-ion secondary battery in a vehicle, thereby achieving excellent charge / discharge characteristics for the lithium-ion secondary battery.

[0022] [Gas sensing layer] The gas sensing layer 40 included in the solid electrolyte gas sensor element of this embodiment contains a metal inorganic acid salt. Examples of the metal inorganic acid salt include metal carbonates such as Li2CO3, Na2CO3, K2CO3, BaCO3, SrCO3, CaCO3, MgCO3, PbCO3, FeCO3, and ZnCO3. The metal inorganic acid salt preferably contains a complex metal carbonate such as X2CO3-YCO3 (X = Li, Na, or K; Y = Ca, Ba, or Sr). More preferably, the metal inorganic acid salt contains a complex metal carbonate such as Na2CO3-BaCO3 or Li2CO3-BaCO3. The gas sensing layer 40 is preferably formed using a complex metal carbonate such as Na2CO3-BaCO3 or Li2CO3-BaCO3. When the metal inorganic acid salt is a Na2CO3-BaCO3 composite metal carbonate, the Na2CO3 / BaCO3 blending ratio may be 1 / 1.5 (molar ratio), 1 / 1.7 (molar ratio), or 1 / 2 (molar ratio).

[0023] The thickness of the gas sensing layer may be 300 μm or more, 400 μm or more, or 500 μm or more. It may be 1000 μm or less, 700 μm or less, or 500 μm or less. The thickness of the gas sensing layer is preferably 300 μm or more and 1000 μm or less, and more preferably 400 μm or more and 700 μm or less. By keeping the thickness of the gas sensing layer within this range, it is possible to maintain a sufficient electromotive force in response to the gas to be measured and an appropriate response time.

[0024] Preferably, the gas sensing layer 40 is formed in one operation using a metal inorganic acid salt together with the solid electrolyte layer according to the present embodiment, which will be described later, by the hydrothermal hot pressing method described later. In this case, the heating and pressure conditions for the hydrothermal hot pressing method are not particularly limited, but are preferably, for example, a temperature of 100°C to 300°C, a pressure of 50 MPa to 600 MPa, and a holding time of 0.5 hours to 36 hours. More preferably, the temperature is 125°C to 175°C, the pressure is 200 MPa to 600 MPa, and a holding time of 10 hours to 25 hours. In the hydrothermal hot pressing method of Example 1 described later, the heating temperature was 150°C, the pressure was 540 MPa, and the holding time was 24 hours.

[0025] [Electrode layer] The first electrode layer 20 and the second electrode layer 80 (sometimes simply referred to as "the electrode layers according to this embodiment") included in the solid electrolyte gas sensor element of this embodiment are not particularly limited as long as they have high electronic conductivity, chemical stability, crystal-chemical stability, etc. Gold, silver, platinum, graphite, etc. can be used as the electrode layers according to this embodiment.

[0026] The thickness of the electrode layer according to this embodiment may be 10 nm or more, 15 nm or more, or 20 nm or more, and is preferably 10 nm or more and 25 nm or less.

[0027] The electrode layer according to this embodiment may be in the form of a solid film, a mesh film, or the like. In particular, the first electrode layer 20 is formed on the gas sensing layer 40. Therefore, the first electrode layer may be formed to be permeable to the gas so that the gas sensing layer 40 and the gas to be measured come into contact with each other. Furthermore, the first electrode layer may be formed only partially, rather than entirely, on the gas sensing layer 40 so that the gas sensing layer 40 and the gas to be measured come into contact with each other.

[0028] The first electrode layer and the second electrode layer may have the same composition or different compositions, the first electrode layer and the second electrode layer may have the same thickness or different thicknesses, and the first electrode layer and the second electrode layer may have the same shape or different shapes.

[0029] (Method of manufacturing a solid electrolyte gas sensor element) The method for manufacturing a solid electrolyte gas sensor element according to one embodiment of the present invention is a method for manufacturing the solid electrolyte gas sensor element 100 according to this embodiment shown in Fig. 1. The method for manufacturing a solid electrolyte gas sensor element according to this embodiment includes a first step of forming a first laminate P including a precursor layer 40P of the gas detection layer 40 and a precursor 60P of the solid electrolyte layer 60; and a second step of placing the first laminate P1 in an enclosed space configured to be capable of being heated and pressurized, and producing a second laminate M including the zeolite dense body by a hydrothermal hot pressing method (hereinafter also referred to as an HHP method) (see Figure 2). A third step (not shown) may be included in which a first electrode layer 20 is formed on the gas sensing layer 40 side of the second laminate M, and a second electrode layer 80 is formed on the opposite side. The method for manufacturing the solid electrolyte gas sensor element will now be described in detail.

[0030] <Hydrothermal hot pressing method> The manufacturing method of the solid electrolyte gas sensor element according to this embodiment involves introducing the first laminate P produced in the first step into an enclosed space configured to be capable of being heated and pressurized, and producing a second laminate M by hydrothermal hot pressing.

[0031] 2(a) to 2(c) are schematic diagrams illustrating an example of a manufacturing method for the solid electrolyte gas sensor element according to this embodiment. A hydrothermal hot pressing apparatus 10 (hereinafter also referred to as an HHP apparatus) used in this manufacturing method includes a reaction vessel body 11 having a through-hole 12 with a substantially circular cross section at its center, a lower rod 13A inserted into the through-hole 12 from below the reaction vessel body 11 and arranged to be movable in the vertical direction, an upper rod 13B inserted into the through-hole 12 from above the reaction vessel body 11 and arranged to be movable in the vertical direction, and a sealed space 14 provided between the lower rod 13A and the upper rod 13B within the through-hole 12. The sealed space 14 is defined by an upper surface 13a of the lower rod 13A, a lower surface 13b of the upper rod 13B, and an inner circumferential surface 12a of the through-hole 12, and functions as a mold when the second laminate M is manufactured. The hydrothermal hot press device 10 also includes a heating unit (not shown), such as a heater, that is arranged to surround the reaction vessel body 11 .

[0032] <1st process> The first step forms a first laminate P including a precursor layer 40P of the gas sensing layer 40 and a precursor layer 60P of the solid electrolyte layer 60. For example, as shown in FIG. 2(a), the precursor layer 40P of the gas sensing layer 40 may be first formed on the upper surface 13a of the lower rod 13A of the hydrothermal hot-pressing apparatus 10, and then the precursor layer 60P of the solid electrolyte layer 60 may be formed thereon. Alternatively, the precursor layer 60P of the solid electrolyte layer 60 may be first formed, and then the precursor layer 40P of the gas sensing layer 40 may be formed thereon. Furthermore, the first laminate P may be formed by first molding the first laminate P including the precursor layer 40P of the gas sensing layer 40 and the precursor layer 60P of the solid electrolyte layer 60 using a known molding device, and then setting the first laminate P on the upper surface 13a of the lower rod 13A of the hydrothermal hot-pressing apparatus 10 shown in FIG. 2(a). The thickness and shape (diameter, if disk-shaped) of the precursor layer 40P of the gas sensing layer 40 and the precursor layer 60P of the solid electrolyte layer 60 are not particularly limited, as long as the thickness and shape after treatment by the hydrothermal hot pressing method described below are the same as the thickness and shape of the solid electrolyte gas sensor element of this embodiment. The thickness of the precursor layer 60P of the solid electrolyte layer 60 is preferably thicker than the precursor layer 40P of the gas sensing layer 40. The size (diameter, if disk-shaped) of the precursor layer 60P of the solid electrolyte layer 60 may be the same as or larger than the precursor layer 40P of the gas sensing layer 40.

[0033] <<Precursor layer of gas sensing layer>> The precursor layer 40P of the gas sensing layer 40 is formed by introducing a powder of an inorganic metal salt into a molding device and molding it into a shape such as a disk. The inorganic metal salt has the same components as the inorganic metal salt contained in the gas sensing layer of the solid electrolyte gas sensor element of this embodiment.

[0034] <<Precursor layer for solid electrolyte layer>> The precursor layer 60P of the solid electrolyte layer 60 is made using a powder of zeolite represented by the above general formula (1). A mixture of water or an alkaline aqueous solution and the zeolite powder is prepared as a raw material, and the precursor layer 60P of the solid electrolyte layer 60 can be formed using this mixture.

[0035] The type of zeolite powder used as a raw material is not particularly limited. Examples of the zeolite powder skeletal structure include A-type (LTA), X-type or Y-type (FAU), L-type (LTL), ZSM-5 (MFI), beta (BEA), ferrierite (FER), and mordenite (MOR), with A-type or X-type being preferred.

[0036] The alkaline aqueous solution may be, for example, an aqueous solution containing one or more selected from sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, calcium hydroxide, lithium hydroxide, sodium silicate (water glass), natural soda, etc.

[0037] The concentration of the alkaline aqueous solution can be appropriately selected depending on the type of alkali, the type of zeolite, etc., but is preferably from 0.1 mol / L to 10 mol / L, more preferably from 0.1 mol / L to 5.0 mol / L, even more preferably from 0.1 mol / L to 2.0 mol / L, and particularly preferably from 0.1 mol / L to 1.8 mol / L.

[0038] The blending ratio of water or alkaline aqueous solution in the mixture can be appropriately selected depending on the type of zeolite, the type and concentration of the alkaline aqueous solution, etc., but the mass of water or alkaline aqueous solution relative to the mass of the mixture is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 20% by mass or less.

[0039] The zeolite powder may be pulverized by a ball mill method before being mixed with water or an alkaline aqueous solution. By pre-pulverizing the zeolite powder by a ball mill method and then mixing the pulverized zeolite powder with water or an alkaline aqueous solution to prepare a mixture, the relative density of the zeolite dense body increases, and higher ionic conductivity can be obtained.

[0040] The particle size of the zeolite powder after ball milling is preferably 0.1 μm or more and 10 μm or less, more preferably 0.5 μm or more and 5.0 μm or less, and even more preferably 0.8 μm or more and 3.0 μm or less.

[0041] <Second process> In the second step, the first laminate P obtained in the first step is placed in an enclosed space configured to be capable of being heated and pressurized, and a second laminate M including the zeolite dense body is produced by a hydrothermal hot pressing method. The lower rod 13A is inserted from above into the through-hole 12 of the reaction vessel body 11, and the resulting first stack P is placed on the upper surface 13a of the lower rod 13A (FIG. 2(a)). Then, the upper rod 13B is inserted from above into the through-hole 12 of the reaction vessel body 11, forming an enclosed space 14 within the through-hole 12 (FIG. 2(b)). Then, the lower rod 13A and the upper rod 13B are moved close to each other to create a predetermined pressure within the enclosed space 14, and the enclosed space 14 is heated by a heating unit (not shown) (FIG. 2(c)). As a result, the first stack P within the enclosed space 14 is heated to a predetermined temperature and pressurized to a predetermined pressure by a hydrothermal hot pressing method. Then, the lower rod 13A and the upper rod 13B are removed from the through-hole 12, and a second stack M is obtained.

[0042] The heating and pressurizing conditions for the HHP method are not particularly limited, but it is preferable to heat and pressurize the mixture at a temperature of 100°C or higher and 300°C or lower, a pressure of 50 MPa or higher and 600 MPa or lower, and a holding time of 0.5 hours or higher and 24 hours or lower.

[0043] After producing the second laminate M by the HHP method, the second laminate M may be dehydrated, if necessary. From the viewpoint of electrical insulation, it is preferable that the water content of the solid electrolyte layer (zeolite dense body) contained in the second laminate M is low; however, if the water content of the zeolite dense body is too low, ionic conductivity may decrease. From the above viewpoint, the water content of the zeolite dense body is preferably 0% by mass or more and 25% by mass or less, and more preferably 10% by mass or more and 25% by mass or less, relative to the mass of the entire zeolite dense body.

[0044] A material such as carbon graphite powder may be applied to the upper surface 13a of the lower rod 13A, the lower surface 13b of the upper rod 13B, and / or the inner circumferential surface 12a of the through-hole 12 in the reaction vessel body 11. In addition, an inclined surface may be provided by chamfering or the like at the portion of the through-hole 12 that serves as the outlet for the second laminate M. This prevents the second laminate M from sticking to the reaction vessel body 11, and suppresses damage to the dense zeolite body M when the sample is taken out. Furthermore, a surface treatment such as carburizing may be applied to the upper surface 13a of the lower rod 13A, the lower surface 13b of the upper rod 13B, and / or the inner circumferential surface 12a of the through-hole 12 in the reaction vessel body 11. This makes it possible to suppress deformation and wear of the upper surface 13a of the lower rod 13A, the lower surface 13b of the upper rod 13B, and / or the inner circumferential surface 12a of the through-hole 12 in the reaction vessel body 11 during production of the second stack M.

[0045] <3rd process> In the third step, a first electrode layer 20 is formed on the gas sensing layer 40 side of the second laminate M, and a second electrode layer 80 is formed on the opposite side. In the third step, the method for forming the electrode layers is not particularly limited, and conventional techniques can be used. For example, the first electrode layer 20 and the second electrode layer 80 may be formed by sputtering.

[0046] <Solid electrolyte gas sensor> A solid electrolyte gas sensor according to one embodiment of the present invention includes the solid electrolyte gas sensor element according to the present embodiment, a device for measuring the electromotive force between the first electrode layer and the second electrode layer, and a device for introducing a gas to be measured into the gas detection layer. [Example]

[0047] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0048] Example 1 <First step: Formation of first laminate P>

[0049] "Precursor layer of gas sensing layer" 0.15 g of Na2CO3-BaCO3 powder (molar ratio 1.0:1.7) was ground in a mortar for one hour, and then the Na2CO3-BaCO3 powder was used to form a molded body with a diameter of 10 mm using a molding device manufactured by JASCO Corporation as the precursor layer 40P of the gas sensing layer 40. The molded body was placed on the upper surface 13a of the lower rod 13A of the hydrothermal hot press device 10 (inner diameter 20 mm) shown in Figure 2(a).

[0050] "Precursor layer for solid electrolyte layer" A mixture was obtained by uniformly mixing 0.75 g of A-type (LTA) zeolite powder (manufactured by Tosoh Corporation) and 150 μL of water. Using this mixture, a precursor layer 60P of the solid electrolyte layer 40 was formed on the NaCO—BaCO compact on the upper surface 13a of the lower rod 13A of a hydrothermal hot press apparatus 10 (inner diameter 20 mm) shown in FIG. 2(a).

[0051] <Second step: Formation of second laminate M> The first laminate P obtained in the first step was subjected to the hydrothermal hot pressing method shown in FIG. 2 to produce a second laminate M made of a dense A-type zeolite body. In the hydrothermal hot pressing method, the heating temperature was 150° C., the pressure was 540 MPa, and the holding time was 24 hours. The second laminate M includes a gas sensing layer (Na2CO3-BaCO3) 40 having a thickness of 500 μm and a solid electrolyte layer 60 (A-type zeolite dense body) having a thickness of 1000 μm.

[0052] <Third step: Formation of first electrode layer and second electrode layer> A Pt electrode was formed as the first electrode layer 20 on the gas sensing layer 40 side of the second laminate M, and a Pt electrode was formed as the second electrode layer 80 on the opposite side. The solid electrolyte gas sensor element 100 of this example was obtained. In this example, the first electrode layer and the second electrode layer were formed to a thickness of 15 nm using a sputtering apparatus (manufactured by Sanyu Electronics Co., Ltd., named "SC-701CT"). The first electrode layer 20 and the second electrode layer 80 (sometimes simply referred to as "the electrode layers according to this example") included in the solid electrolyte gas sensor element 100 of this example are not particularly limited as long as they have high electronic conductivity, chemical stability, crystal-chemical stability, etc. Other than Pt, for example, gold, silver, graphite, etc. may also be used for the electrode layers according to this example. Furthermore, platinum wires serving as leads were fixed to the first electrode layer 20 and the second electrode layer 80 using silver paste (Sylvest P-248, manufactured by Tokuriki Chemical Laboratory).

[0053] [Cross-sectional SEM image and SEM-EDX image of a solid electrolyte gas sensor element] The interface between the gas sensing layer 40 and the solid electrolyte layer 60 of the solid electrolyte gas sensor element 100 of Example 1 was confirmed by scanning electron microscope images (manufactured by JEOL Ltd., device name "JSM-6510A") and scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX) images. The results are shown in FIGS. 3 and 4. It was confirmed that a tightly adhered interface without cracks was obtained, and that the Ba and Si elements were uniformly dispersed.

[0054] [Evaluation of ionic conductivity] The solid electrolyte layer (zeolite dense body) 60 of the obtained solid electrolyte gas sensor element 100 was subjected to impedance measurement by an AC two-terminal method, and the ionic conductivity at each temperature was calculated. At 300°C, the ionic conductivity was 7.4×10 ―4 (S·cm -1 ) was.

[0055] From the ionic conductivity obtained above, log(σ / S cm -1 ) was calculated to evaluate the ionic conductivity. FIG. 5 shows the results of calculating the ionic conductivity of the solid electrolyte layer 60 of the solid electrolyte gas sensor element 100 at each temperature. Ionic conductivity log(σ / S·cm -1 ) was greater than -3 at temperatures above 300°C.

[0056] [Evaluation of bulk density and relative density] The bulk density and relative density of the solid electrolyte layer (zeolite dense body) 60 of the obtained solid electrolyte gas sensor element 100 were evaluated. The results are shown in Table 1.

[0057] Examples 2 to 11 The solid electrolyte gas sensor elements 100 of Examples 2 to 11 were fabricated in the same manner as Example 1, except that the amount of water used in forming the precursor layer of the solid electrolyte layer in the first step, and the heating temperature, pressure, and holding time in the second step were shown in Table 1. For Examples 2 to 5, the ionic conductivity was calculated at each temperature in the same manner as Example 1. The results are shown in FIG. In Examples 2 to 11, the bulk density and relative density were evaluated in the same manner as in Example 1. The results are shown in Table 1 (for comparison, Example 2 is listed multiple times in Table 1). [Table 1]

[0058] Example 12 "Evaluation of electromotive force of solid electrolyte gas sensor element" (1) Carbon dioxide concentration dependence The electromotive force was measured at the following concentrations of carbon dioxide using the solid electrolyte gas sensor element 100 obtained in Example 1. The time (response time) required for the electromotive force to reach 90% of the original value was also measured.

[0059] "Measuring device for solid electrolyte gas sensor elements" The gas sensor element was placed in a tubular furnace, and the change in potential due to the introduction of gas was measured with a digital multimeter. Three types of gas were introduced: N2, CO2, and O2. 600 seconds after the introduction of the gas, the introduction of CO2 gas was stopped, and the electromotive force was measured thereafter.

[0060] "Measurement conditions for solid electrolyte gas sensor elements" Measurement temperature: 450℃ CO2 concentration: 500ppm, 1000ppm, 3000ppm, 5000ppm, 10000ppm The results are shown in Table 2 and Figures 6 and 7. [Table 2]

[0061] (2) Cycle experiment A cycle experiment was carried out under the following measurement conditions using the gas sensor element obtained in Example 1. The electromotive force and response time were measured for each cycle.

[0062] "Measurement conditions" Measurement temperature: 450℃ CO2 concentration: 500ppm The results are shown in Table 3 and Figure 8.

[0063] [Table 3]

[0064] Example 13 "Creating a solid electrolyte gas sensor element" [Preparation of solid electrolyte] A mixture was obtained by uniformly mixing 0.75 g of A-type (LTA) zeolite powder (manufactured by Tosoh Corporation) and 150 μL of water. Using this mixture, a dense A-type zeolite body was produced by the hydrothermal hot pressing method shown in FIG. 2 on the upper surface 13a of the lower rod 13A of a hydrothermal hot pressing apparatus 10 (inner diameter 20 mm) shown in FIG. 2(a). In the hydrothermal hot pressing method, the heating temperature was 150° C., the pressure was 540 MPa, and the holding time was 24 hours.

[0065] [Fabrication of gas sensing layer] 0.15 g of Na2CO3-BaCO3 powder (molar ratio 1.0:1.7) was ground in a mortar and mixed with 90 μL of polyethylene glycol (manufactured by Co., Ltd.) to prepare a precursor paste for the gas sensing layer. A gas sensing layer with a diameter of 6 mm was formed on a dense zeolite A body by screen printing. The body was then heated to 400°C for 12 hours to bake the solid electrolyte and gas sensing layer. This produced a solid electrolyte gas sensor element.

[0066] "Evaluation of electromotive force of solid electrolyte gas sensor element" The solid electrolyte gas sensor element thus obtained was evaluated for its electromotive force and response time in the same manner as in Example 12.

[0067] "Measurement conditions for solid electrolyte gas sensor elements" Measurement temperature: 450℃ CO2 concentration: 10000ppm The results are shown in Table 4 and Figure 7.

[0068] [Table 4]

[0069] (Comparative Example 1) "Gas sensor using NASICON" In Non-Patent Document 1, Na2CO3-BaCO3 is used as the gas sensing layer, and Na, called NASICON, is used as the solid electrolyte layer. 1+x Zr2Si x P 3-x O 12 Gas sensors using solid electrolytes have been reported, and their response times are shown in Table 5.

[0070] [Table 5]

[0071] (Consideration) Figure 6 shows the sensor response recovery curves for each carbon dioxide concentration. It was found that an electromotive force was generated immediately upon introduction of carbon dioxide gas. Figure 6 also shows that the electromotive force changed according to the gas concentration. Table 2 shows the sensor response time for each carbon dioxide concentration. The results in Table 3 and Figure 8 show that the gas sensor operated stably during the seven cycle experiments, and no degradation in performance was observed. From the above results, it was found that the fabricated solid electrolyte gas sensor element functions as a gas sensor for measuring carbon dioxide. In particular, it was found that the zeolite dense body used as the solid electrolyte layer 40 in the solid electrolyte gas sensor element 100 functions as a solid electrolyte of the gas sensor.

[0072] In the gas sensor reported in Non-Patent Document 1 shown in Comparative Example 1, the same type of gas sensing layer as in Example 12 (Example 1) was used, but a pre-fabricated NASICON electrolyte layer was used. Comparing the response time between Comparative Example 1 and Example 1, it was found that the response time of the solid electrolyte gas sensor element of this embodiment was shorter.

[0073] The reason for the increased response speed of the solid electrolyte gas sensor element of this embodiment was unclear. At least, it was clear from the images in Figures 3 and 4 that the interface between the gas sensing layer and the solid electrolyte layer was in close contact. It is thought that the solid electrolyte gas sensor element of this embodiment is formed by simultaneously molding the gas sensing layer and the solid electrolyte layer using a hydrothermal hot press method, which causes some kind of physical or chemical change at the interface between the gas sensing layer and the solid electrolyte layer, allowing ions from the gas sensing layer to smoothly enter the solid electrolyte layer. [Industrial Applicability]

[0074] The solid electrolyte gas sensor element of the present invention maintains the performance of a solid electrolyte gas sensor using a conventional solid electrolyte, while using a dense zeolite body that has a small environmental impact and can reduce manufacturing costs, and therefore can be used as a sensor for gases such as carbon dioxide. [Explanation of symbols]

[0075] 10. Hydrothermal hot press equipment 11 Reaction vessel body 12 Through holes 12a Inner surface 13A Lower Rod 13a Top side 13B Upper rod 13b Bottom side 14 Closed space 20 1st electrode layer 40 Gas Sensing Layer 60 Solid electrolyte (dense zeolite) 80 Second electrode layer 40P Precursor layer of gas sensing layer 60P Solid electrolyte precursor layer (zeolite layer) 100 Solid electrolyte gas sensor element P 1st laminate M 2nd laminate

Claims

1. a first electrode layer; a gas sensing layer capable of generating electricity in response to a gas to be measured; a solid electrolyte layer having ion conductivity; a second electrode layer, and a second electrode layer in this order, the gas sensing layer comprises a metal inorganic acid salt, the solid electrolyte layer contains a dense body of zeolite represented by the following general formula (1), The ion conductivity of the zeolite dense body is 1.0 × 10 －３ S.cm. －１ That's all, The bulk density of the zeolite dense body is 1.6 g / cm ３ 2.0g / cm or more ３ The solid electrolyte gas sensor element is as follows: (M) １／ｎ ) ｘ (Al) ｘ Yes ｙ O ２（ｘ＋ｙ） )・vH ２ O ・・・(1) (In formula (1), M is one or more metal elements selected from Na, Li, and K, 0≦x≦y, 0≦z≦216, and n is a valence number.)

2. 2. The solid electrolyte gas sensor element according to claim 1, wherein the relative density measured by the theoretical density and the bulk density is 80% or more.

3. Bulk density: 1.6 g / cm ３ 2.0g / cm or more ３ 3. The solid electrolyte gas sensor element according to claim 1, wherein:

4. Log (σ / S cm) calculated from ionic conductivity at room temperature or higher and 450°C or lower －１ 3. The solid electrolyte gas sensor element according to claim 1, wherein the value of (a) is -3 or more.

5. 3. The solid electrolyte gas sensor element according to claim 1, having an A-type or X-type skeleton structure.

6. The gas sensing layer is ２ CO ３ , Na ２ CO ３ , K. ２ CO ３ , BaCO ３ , SrCO ３ , CaCO ３ , MgCO ３ , PbCO ３ , FeCO ３ , and ZnCO ３ At least one metal carbonate selected from the group consisting of 3. The solid electrolyte gas sensor element according to claim 1, wherein the solid electrolyte gas sensor element is a carbon dioxide gas sensor.

7. The gas sensing layer is ２ CO ３ -BaCO ３ and Li ２ CO ３ -BaCO ３ 3. The solid electrolyte gas sensor element according to claim 1, further comprising at least one composite metal carbonate selected from the group consisting of:

8. 3. The solid electrolyte gas sensor element according to claim 1, wherein the gas sensing layer is formed by molding the solid electrolyte layer and the gas sensing layer together.

9. The solid electrolyte gas sensor element according to claim 1 or 2, a device for measuring an electromotive force between the first electrode layer and the second electrode layer; and a device for introducing a gas to be measured into the gas sensing layer.

10. 2. A method for manufacturing the solid electrolyte gas sensor element according to claim 1, comprising the steps of: a first step of forming a first laminate including a precursor layer of the gas sensing layer and a precursor layer of the solid electrolyte layer; a second step of placing the first laminate in an enclosed space configured to be capable of being heated and pressurized, and producing a second laminate including the zeolite dense body by a hydrothermal hot pressing method; A method for manufacturing a solid electrolyte gas sensor element comprising:

11. 11. The method for manufacturing a solid electrolyte gas sensor element according to claim 10, further comprising a third step of forming the first electrode layer on the gas sensing layer side of the second laminate and forming the second electrode layer on the opposite side thereof.

12. 11. The method for manufacturing a solid electrolyte gas sensor element according to claim 10, further comprising a third step of dehydrating the second laminate after the second laminate is manufactured by the hydrothermal hot pressing method in the second step.

13. 11. The method for manufacturing a solid electrolyte gas sensor element according to claim 10, wherein in the second step, the first laminate is heated and pressurized at a temperature of 100° C. or higher and 200° C. or lower, a pressure of 50 MPa or higher and 600 MPa or lower, and a holding time of 0.5 hours or higher and 24 hours or lower.

14. 11. The method for manufacturing a solid electrolyte gas sensor element according to claim 10, wherein the precursor layer of the solid electrolyte layer is made using a mixture of a powder of the zeolite represented by the general formula (1) and water or an alkaline aqueous solution.

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