KR20080105844A - Carbon monoxide gas sensor and manufacturing method thereof - Google Patents

Abstract

A carbon monoxide gas sensor capable of miniaturization and excellent detection characteristics and a method of manufacturing the same are provided. The carbon monoxide gas sensor includes a cation exchange membrane made of a solid electrolyte, a hygroscopic coating membrane formed on both sides of the cation exchange membrane, a reaction electrode formed on the first porous support and bonded to the hygroscopic coating membrane disposed on one surface of the cation exchange membrane, and the second porous membrane. And a counter electrode and a reference electrode formed on the support and coupled to the hygroscopic coating film disposed on the other side of the cation exchange membrane, and a housing accommodating the cation exchange membrane, the hygroscopic coating film, the reaction electrode, the counter electrode and the reference electrode.

Description

Carbon monoxide gas sensor and method of manufacturing the same

1 is a cross-sectional view of a carbon monoxide gas sensor according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of the gas detector of FIG. 1.

3 is a process flowchart of a method of manufacturing a carbon monoxide gas sensor according to an embodiment of the present invention.

Figure 4 is a graph measuring the output signal according to the carbon monoxide concentration in the carbon monoxide gas sensor according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10: housing 10a: upper housing

10b: lower housing 12: carbon monoxide inlet

14: oxygen inlet 20: first dust filter

22: second dust filter 30: filter for removing interference gas

35: O-ring 40: porous separator

50: gas detector 52a: first porous support

52b: second porous support 54a: reaction electrode

54b: corresponding electrode 54c: reference electrode

56: cation exchange membrane 58: hygroscopic coating membrane

58a: solid electrolyte resin 58b: hygroscopic ultrafine particles

60a, 60b, 60c: wiring 62a, 62b, 62c: output terminal

100: carbon monoxide gas sensor

The present invention relates to a carbon monoxide gas sensor and a method for manufacturing the same, and more particularly, to a carbon monoxide gas sensor capable of miniaturization and excellent detection characteristics and a method for manufacturing the same.

As industrial society is advanced, gas accident safety management is a serious problem because industrial sites are using not only various types of gases but also generating them. One of them is colorless and odorless and carbon monoxide can harm the human body even at low concentrations of 100 ppm. Therefore, research and development of carbon monoxide gas sensors that measure the concentration of carbon monoxide and detect whether it is above the limit concentration is actively being conducted. The carbon monoxide gas sensor may be classified into an electrochemical sensor, a semiconductor sensor, a colorimetric sensor, an infrared sensor, and the like. Electrochemical sensors are the most widely used because of their excellent sensing characteristics, simple manufacturing process and low manufacturing cost.

The electrochemical carbon monoxide gas sensor according to the prior art uses a strong acid solution or a strong base solution as an electrolyte. In the case of using such an electrolyte solution, there is a problem of harmfulness due to leakage of the electrolyte solution, and there is a fear that the internal parts of the sensor may be corroded. In addition, the space occupied by the electrolyte in the sensor interferes with the miniaturization of the sensor.

The technical problem to be achieved by the present invention is to provide a carbon monoxide gas sensor capable of miniaturization and excellent detection characteristics.

Another object of the present invention is to provide a method of manufacturing such a carbon monoxide gas sensor.

The technical problems of the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

Carbon monoxide gas sensor according to an embodiment of the present invention for achieving the above technical problem, a cation exchange membrane made of a solid electrolyte, a hygroscopic coating membrane formed on both sides of the cation exchange membrane, and formed on a first porous support and the cation exchange membrane A reaction electrode coupled to the hygroscopic coating membrane disposed on one surface of the reaction electrode, a corresponding electrode and a reference electrode formed on a second porous support and bonded to the hygroscopic coating membrane disposed on the other surface of the cation exchange membrane, the cation exchange membrane and the hygroscopicity And a housing accommodating a coating film, the reaction electrode, the corresponding electrode, and the reference electrode.

According to another aspect of the present invention, there is provided a method of manufacturing a carbon monoxide gas sensor, including: protonating a cation exchange membrane made of a solid electrolyte, and applying a hygroscopic coating membrane to both surfaces of the cation exchange membrane. Forming a reaction electrode on the first porous support, forming a corresponding electrode and a reference electrode on the second porous support, and sequentially placing the first porous support, the cation exchange membrane, and the second porous support. Compressing, thereby coupling the reaction electrode to the hygroscopic coating film disposed on one surface of the cation exchange membrane, and coupling the corresponding electrode and the reference electrode to the hygroscopic coating film disposed on the other surface of the cation exchange membrane.

Specific details of other embodiments are included in the detailed description and the drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and the general knowledge in the art to which the present invention belongs. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, a carbon monoxide gas sensor according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of a carbon monoxide gas sensor according to an embodiment of the present invention, Figure 2 is an enlarged cross-sectional view of the gas detection unit of FIG.

1 and 2, the carbon monoxide gas sensor 100 according to an exemplary embodiment of the present invention may include a housing 10, a carbon monoxide inlet 12 formed on the housing 10, and a housing ( 10) the interference gas removal filter 30, the porous separator 40 and the gas detector 50, which are sequentially disposed below the carbon monoxide inlet 12, and the oxygen inlet 14 formed in the lower portion of the housing 10. It includes.

The housing 10 is composed of the upper housing (10a) and the lower housing (10b) can be separated and combined, the interference gas removal filter 30, the porous separator 40 and the gas detector 50 therein. I can accept it. The upper housing 10a and the lower housing 10b may be completely hermetically coupled so that components contained therein do not leak to the outside.

One or more carbon monoxide inlets 12 are formed on the upper surface of the upper housing 10a so that external carbon monoxide gas flows into the housing 10. The cross-sectional area of the carbon monoxide inlet 12 is preferably about 0.01-1% of the cross-sectional area of the reaction electrode 54a of the gas detector 50. For example, when the diameter of the reaction electrode 54a is 13 mm, the diameter of the carbon monoxide inlet 12 may be about 1.1 mm, and the length may be about 2-4 mm in length.

The first dust filter 20 positioned on the outer surface of the housing 10 above the carbon monoxide inlet 12 serves to block foreign matter such as dust or water from entering the housing 10 through the carbon monoxide inlet 12. Do it. For example, the first dust filter 20 may be made of porous PTFE (PolyTetraFluoroEthylene).

The interference gas removal filter 30 located inside the housing 10 under the carbon monoxide inlet 12 serves to exclude the influence of interference gas that interferes with measuring the concentration of carbon monoxide. Such interference gases include, for example, H ₂ , H ₂ S, SO ₂ , and the like, and the interference gas removing filter 30 may be formed of a charcoal having a high adsorption force on the interference gas. The interference gas removing filter 30 may be made of a mesh type or powder type made of carbon fiber. For example, the interference gas removing filter 30 has a surface area of 900-1500 m 2 / g and may be made of activated carbon in a granular or fibrous form.

An o-ring 35 interposed between the interference gas removal filter 30 and the upper housing 10a along the edge of the interference gas removal filter 30 is provided with external components inside the housing 10. To prevent leakage.

The porous separator 40 is disposed below the interference gas removal filter 30. The porous separator 40 serves to control the inflow concentration of the gas flowing from the outside while separating the interference gas removal filter 30 from the gas detector 50. For example, PTFE may be used as the porous separator 40.

Under the porous separator 40, a gas detector 50 for measuring the concentration of carbon monoxide is disposed. The gas detection unit 50 is formed on the cation exchange membrane 56, the hygroscopic coating membrane 58 formed on both sides of the cation exchange membrane 56, and the first porous support 52 a, and is compressed on one side of the cation exchange membrane 56. The electrode 54a and the corresponding electrode 54b and the reference electrode 54c formed on the second porous support 52b and pressed on the other side of the cation exchange membrane 56 are included.

The cation exchange membrane 56 may be made of a solid polymer electrolyte having high ion conductivity and mechanical strength, and good chemical resistance and thermal stability. As the cation exchange membrane 56, for example, Nafion ™ (Du Pont Co.), Flemion ™ (Asahi Glass Co.), Aciplex ™ (Asahi Chemical Co.), Gore-Select ™ (Gore-Tex Co.), XUS ™ (Dow) Chemical Co., Ltd.) may be used, and embodiments of the present invention will be described using Nafion ™ for convenience of description below. In the case of using the cation exchange membrane 56 made of a solid electrolyte instead of the electrolyte, it is possible to prevent the problem of harmfulness due to leakage of the electrolyte.

The cation exchange membrane 56 changes its ion conductivity according to the water content. In order to operate the carbon monoxide gas sensor 100 stably, the relative humidity of the cation exchange membrane 56 needs to be kept constant, for example, about 100%. have. In the case of the carbon monoxide gas sensor 100 according to an embodiment of the present invention, a hygroscopic coating film 58 is formed on both sides of the cation exchange membrane 56 to maintain a stable water content of the cation exchange membrane 56 even in the absence of external humidification. It is.

The hygroscopic coating film 58 has a structure in which hygroscopic ultrafine particles 58b are dispersed in the solid electrolyte resin 58a. Further, in addition to the hygroscopic ultrafine particles 58b in the solid electrolyte resin 58a, a small amount of platinum ultrafine particles catalyst may be added.

The solid electrolyte resin 58a serves as an adhesive having a cationic conductivity, and may be formed by, for example, heat treating a Nafion solution in which 5 wt% Nafion ™ is dissolved in an ethanol solvent.

In addition, the hygroscopic ultrafine particles 58b absorb water (H ₂ O) formed in the corresponding electrode 54b to replenish moisture in the cation exchange membrane 56 to maintain a constant relative humidity. As the hygroscopic ultrafine particles 58b, an oxide such as SiO ₂ , TiO ₂ , or ZrP may be used. The hygroscopic ultrafine particles 58b range in size from tens to hundreds of nm, and the concentration may be used in the range of about 2-10% relative to the dry mass of Nafion in the Nafion solution. When the concentration of the hygroscopic ultrafine particles 58b is lower than the above range, the moisture adsorption rate is low, so that it is difficult to maintain a constant relative humidity. Destructive structures can destroy the ionic conductivity.

The reaction electrode 54a formed on the first porous support 52a is pressed onto the cation exchange membrane 56. The first porous support 52a may be formed of, for example, PTFE, and may have a pore size of about 0.3 to 5 μm and a thickness of about 100 to 300 μm.

The reaction electrode 54a may be formed of a material having catalytic properties for the oxidation reaction of carbon monoxide, for example, platinum black, platinum (Pt), gold (Au), silver (Ag), and the like. The first porous support 52a serves to control the diffusion rate of the carbon monoxide gas flowing from the carbon monoxide inlet 12 into the reaction electrode 54a and also serves as a support for forming the reaction electrode 54a. For example, PTFE may be used as the first porous support 52a. The reaction electrode 54a may be formed on the first porous support 52a by a method such as screen printing, compression coating, sputtering, or evaporation. The reaction electrode 54a is pressed together with the first porous support 52a to the hygroscopic coating layer 58 positioned on the cation exchange membrane 56 and mechanically coupled thereto.

Under the cation exchange membrane 56, the corresponding electrode 54b and the reference electrode 54c formed on the second porous support 52b are compressed. The second porous support 52b may be formed of, for example, PTFE, and may have a pore size of about 0.3 to 5 μm and a thickness of about 100 to 300 μm.

As the counter electrode 54b and the reference electrode 54c, for example, Ag, AgO, Ru, RuO ₂ , Pt, or the like may be used. The second porous support 52b serves to control the diffusion rate of the oxygen gas introduced from the oxygen inlet 14 into the counter electrode 54b, and at the same time, the support for forming the counter electrode 54b and the reference electrode 54c. Plays a role. For example, PTFE may be used as the second porous support 52b. The counter electrode 54b and the reference electrode 54c may be formed on the second porous support 52b by a method such as screen printing, compression coating, sputtering, or evaporation. The corresponding electrode 54b and the reference electrode 54c are pressed together with the second porous support 52b by a hygroscopic coating film 58 positioned under the cation exchange membrane 56 and mechanically coupled to each other.

The principle of the carbon monoxide gas sensor according to an embodiment of the present invention is the same as the following scheme 1.

Scheme 1

_{CO + H 2 O → CO 2} + 2H + + 2e -

Scheme 2

_{^{2H + + 1/2 O 2 + 2e}} - → H 2 O

The carbon monoxide gas introduced through the carbon monoxide inlet 12 is decomposed at the reaction electrode 54a as in Scheme 1 to generate hydrogen ions (H ⁺ ). Hydrogen ions generate water (H ₂ O) as shown in Scheme 2 at the counter electrode 54b through the hygroscopic coating membrane 58 and the cation exchange membrane 56. Oxygen required for the reaction at the corresponding electrode 54b is introduced through the oxygen inlet 14. In addition, the water generated by the reaction scheme 2 is adsorbed by the hygroscopic coating film 58 formed on both sides of the cation exchange membrane 56 so that the relative humidity of the cation exchange membrane 56 is kept constant.

The reference electrode 54c serves to form a reference voltage in the reaction.

The reaction electrode 54a, the corresponding electrode 54b and the reference electrode 54c are connected to the output terminals 62a, 62b and 62c through the wirings 60a, 60b and 60c, respectively. Since the current flowing between the reaction electrode 54a and the corresponding electrode 54b through the reaction equations 1 and 2 is proportional to the external carbon monoxide concentration, the current is measured through the output terminals 62a, 62b, and 62c to determine the external carbon monoxide concentration. Can be measured.

The second dust filter 22 positioned on the oxygen inlet 14 serves to block foreign matter such as dust or water from entering the housing 10 through the oxygen inlet 14. For example, the second dust filter 22 may be made of porous PTFE.

Hereinafter, a method of manufacturing a carbon monoxide gas sensor according to an embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3. 3 is a process flowchart of a method of manufacturing a carbon monoxide gas sensor according to an embodiment of the present invention. In particular, the manufacturing method of the gas detection unit included in the carbon monoxide gas sensor according to an embodiment of the present invention will be described in detail.

Referring to FIGS. 2 and 3, first, the cation exchange membrane 56 is cut to an appropriate size, and then boiled for about 40 minutes at 100 to 150 ° C. in an aqueous solution of 3-5 wt% H ₂ O ₂ , and then washed with distilled water to clean the cation exchange membrane 56. ) Surface impurities, in particular, organic impurities are removed (S110).

In order to increase the ion conductivity of the cleaned cation exchange membrane 56, it is boiled for about 200-250 ° C for 1-2 hours in hydrochloric acid (HCl) or sulfuric acid (H ₂ SO ₄ ) aqueous solution, and then washed with distilled water to treat protons or protons. The process proceeds (S120). The protonation treatment will be described in detail using Nafion ™ as the cation exchange membrane 56 as an example. The chemical structure of Nafion ™ is shown in Chemical Formula 1 below.

[Chemical Structural Formula 1]

As shown in formula 1 Nafion ™ is a side chain addition sulpu acid group ^{_{(sulfuric acid group, SO 3 -}} H +) with the main chain structure has the added PTFE. That is, Nafion ™ has a structure in which hydrophilic groups and hydrophobic groups are clearly distinguished by forming clusters between the highly hydrophobic main chain portion and the hydrophilic side chain portion, thereby having high hydrogen ion conductivity when hydrated. The protonation treatment using an aqueous hydrochloric acid or sulfuric acid solution has the effect of supplementing the side chain portion to be hydrophilic by supplying hydrogen ions to the sulfuric acid group of the side chain portion, thus increasing the delivery channel of the hydrogen ions.

Subsequently, a hygroscopic coating film 58 is applied to both surfaces of the cation exchange membrane 56 (S130). First, hygroscopic ultrafine particles 58b are added to the Nafion solution and stirred to disperse uniformly. The Nafion solution mixed with the hygroscopic ultrafine particles 58b is applied onto the cation exchange membrane 56 using a method such as spray coating or spin coating.

Subsequently, the cation exchange membrane 56 and the applied Nafion solution are cured by heat treatment at a temperature of about 90 to 130 ° C. for 1 hour (S140). The Nafion solution and the hygroscopic ultrafine particles solidify to form a hygroscopic coating film 58.

Subsequently, the aforementioned protonation treatment is also performed on the hygroscopic coating film 58 (S150). Accordingly, the hygroscopic coating membrane 58 together with the cation exchange membrane 56 also has high ion conductivity.

The reaction electrode 54a is formed on the first porous support 52a using screen printing or the like (S160). The corresponding electrode 54b and the reference electrode 54c are formed on the second porous support 52b by using screen printing or the like (S170).

Subsequently, the reaction electrode 54a, the counter electrode 54b and the reference electrode 54c are pressed onto the hygroscopic coating film 58 formed on both surfaces of the cation exchange membrane 56, specifically, both surfaces of the cation exchange membrane 56. Combined into (S180). In this case, the reaction electrode 54a, the corresponding electrode 54b, and the reference electrode 54c may be pressed at a pressure range of about 50 to 150 kg / cm 2 for stable bonding of the hygroscopic coating film 58.

The self-humidifying cation exchange membrane 56 thus prepared is adsorbed and repaired by the hygroscopic coating membrane 58 of water formed from the reaction at the corresponding electrode 54b to prevent the ion conductivity of the cation exchange membrane 56 from decreasing.

Hereinafter, the sensing characteristics of the carbon monoxide gas sensor according to the exemplary embodiment of the present invention will be described in detail with reference to FIG. 4. 4 is a graph measuring the output signal according to the carbon monoxide concentration change in the carbon monoxide gas sensor according to an embodiment of the present invention.

Specifically, the carbon monoxide was leaked between 200 and 600 seconds, and at this time, the output signal detected from the carbon monoxide gas sensor was measured. The concentration of carbon monoxide is 100 ppm for A sample, 200 ppm for B sample, 300 ppm for C sample, 400 ppm for D sample, and 500 ppm for E sample.

As shown in FIG. 4, it can be seen that as the carbon monoxide concentration increases, the output signal of the carbon monoxide gas sensor increases linearly. Therefore, the concentration of carbon monoxide gas can be measured accurately.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above embodiments but may be manufactured in various forms, and having ordinary skill in the art to which the present invention pertains. It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

As described above, according to the carbon monoxide gas sensor and the manufacturing method thereof according to the present invention, by using a cation exchange membrane made of a solid electrolyte, it is easy to miniaturize and prevent the problem of harmfulness due to electrolyte leakage. In addition, by forming a hygroscopic coating film on both sides of the cation exchange membrane, it is possible to implement a self-humidifying carbon monoxide gas sensor to keep the relative humidity of the cation exchange membrane constant to prevent the ion conductivity from decreasing.

Claims (12)

Cation exchange membrane made of a solid electrolyte; Hygroscopic coating film formed on both sides of the cation exchange membrane; A reaction electrode formed on a first porous support and coupled to the hygroscopic coating film disposed on one surface of the cation exchange membrane; A counter electrode and a reference electrode formed on a second porous support and coupled to the hygroscopic coating film disposed on the other surface of the cation exchange membrane; And And a housing accommodating the cation exchange membrane, the hygroscopic coating membrane, the reaction electrode, the corresponding electrode, and the reference electrode. According to claim 1, The hygroscopic coating film is a carbon monoxide gas sensor made of a solid electrolyte resin in which hygroscopic ultrafine particles are dispersed. The method of claim 2, The hygroscopic ultrafine particles are composed of SiO ₂ , TiO ₂ , or ZrP. The method of claim 2, The solid electrolyte resin is a carbon monoxide gas sensor made by heat-treating a Nafion solution in which Nafion is dissolved in an ethanol solvent. The method of claim 4, wherein The concentration of the hygroscopic ultra-fine particles of carbon monoxide gas sensor has a range of 2 to 10% based on the dry mass of the Nafion. According to claim 1, The first and second porous support is a carbon monoxide gas sensor made of PTFE. According to claim 1, The carbon monoxide gas sensor further comprises an interference gas removal filter disposed on the first porous support in the housing to absorb the interference gas. The method of claim 7, wherein Carbon monoxide gas further comprises a porous separator interposed between the interference gas removing filter and the first porous support to control the inflow concentration of the gas flowing from the outside while isolating the interference gas removing filter from the first porous support. sensor. Protonating a cation exchange membrane made of a solid electrolyte; Applying a hygroscopic coating film to both sides of the cation exchange membrane; Forming a reaction electrode on the first porous support, and forming a corresponding electrode and a reference electrode on the second porous support; And By sequentially placing and compressing the first porous support, the cation exchange membrane, and the second porous support, the reaction electrode is bonded to the hygroscopic coating membrane disposed on one surface of the cation exchange membrane, and the corresponding electrode and the reference electrode are bonded to each other. The method of manufacturing a carbon monoxide gas sensor comprising the step of bonding to the hygroscopic coating film disposed on the other surface of the cation exchange membrane. The method of claim 9, The protonation step is a method of producing a carbon monoxide gas sensor to boil the cation exchange membrane in an aqueous solution of hydrochloric acid or sulfuric acid. The method of claim 9, wherein the applying the hygroscopic coating film, Dispersing hygroscopic ultrafine particles in a Nafion solution in which Nafion is dissolved in an ethanol solvent; Coating the Nafion solution on the cation exchange membrane; And The method of manufacturing a carbon monoxide gas sensor comprising the step of heat-treating the Nafion solution. The method of claim 9, wherein after applying the hygroscopic coating film, The method of manufacturing a carbon monoxide gas sensor further comprises the step of protonating the hygroscopic coating film.

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