JPH11174024A - Solid electrolyte type carbon dioxide sensor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte type carbon dioxide sensor in which a time from the start of operation to stabilization of electromotive force is shortened and, even if it is left under non-heated condition in an atmosphere high in moisture concentration such as high humidity or dew condensation, an electromotive force stabilizing time is almost kept unchanged. SOLUTION: A solid electrolyte type carbon dioxide sensor element comprises a working electrode layer 1 including electronic conductive substance and auxiliary electrode substance and a reference electrode layer 3 including electronic conductive substance formed on the surface of a fixed electrolyte layer 2. Also the working electrode layer 1 includes a zeolite of 0.1 to 8 wt.% relative to a working electrode of 100 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor device using a solid electrolyte for measuring the concentration of carbon dioxide in an atmosphere, which is incorporated in an air purifying facility, an environmental measuring facility, and the like. The present invention relates to a solid oxide carbon dioxide sensor element in which the stability of the carbon dioxide sensor is improved and the stabilization time of the electromotive force is shortened.

[0002]

2. Description of the Related Art In recent years, there has been an increasing interest in environmental issues, and a sensor for measuring and controlling the concentration of carbon dioxide gas released into the atmosphere has attracted attention. Among such sensors, a solid electrolyte type carbon dioxide sensor element utilizing a change in electromotive force of the solid electrolyte is small, simple, and inexpensive, and therefore its practical application is eagerly desired.

At present, a solid electrolyte type carbon dioxide sensor element which is being considered for practical use includes a solid electrolyte layer which is an ion conductor, a working electrode layer containing an electron conductive material and an auxiliary electrode material, and a reference electrode layer containing an electron conductive material. And a heater for heating them.

[0004] This sensor element is usually 100 ° C to 600 ° C.
When it is heated and operated at a constant temperature of ℃ and left in an atmosphere containing carbon dioxide gas, a certain electromotive force according to the carbon dioxide gas concentration is generated between the working electrode layer and the reference electrode layer via the solid electrolyte layer. Occur. When the concentration of carbon dioxide in the atmosphere left undisturbed, the dissociation equilibrium reaction between the auxiliary electrode substance and carbon dioxide contained in the working electrode layer progresses until equilibrium is reached, and the mobile ions of the solid electrolyte layer near the working electrode layer Changes occur in concentration.

Since this change in concentration appears as a change in electromotive force, the electromotive force at that time is measured with a voltmeter, and a calibration curve showing the correlation between the electromotive force and the carbon dioxide gas concentration is used. You can know the gas concentration.

In general, NASICON (Na _{1 + A} Zr ₂ Si _A P _3-A) is formed on the solid electrolyte layer of such a carbon dioxide gas sensor.
A cationic conductor such as O ₁₂ , where 0 ≦ A ≦ 3) and β-Al ₂ O ₃ is used.

The electron conductive substance contained in the working electrode layer is a substance necessary for detecting an electromotive force, and a noble metal material having excellent heat resistance and oxidation resistance such as gold and platinum is used.

The auxiliary electrode substance contained in the working electrode layer is a substance capable of causing an equilibrium reaction with carbon dioxide in an atmosphere containing carbon dioxide, and an alkali metal having a dissociation equilibrium with carbon dioxide. Carbonates and alkaline earth metal carbonates are used.

Further, as the electron conductive material contained in the reference electrode layer, the same material as the electron conductive material contained in the working electrode layer is used.

The solid electrolyte type carbon dioxide sensor that operates with the above configuration has an advantage that it can accurately measure the concentration of carbon dioxide contained in the atmosphere and can be made small and inexpensive, so that it has high versatility. Accepted as a sensor element.

[0011]

However, in the solid electrolyte type carbon dioxide gas sensor using an alkali metal carbonate or an alkaline earth metal carbonate as the auxiliary electrode material, the time from the start of operation until the electromotive force is stabilized is reduced. Those that take 6 to 8 hours and are left unheated in an atmosphere having a high moisture concentration such as high humidity and dew condensation are 20 to 4 hours.
There was a problem that it took 0 hours.

Since the measurement cannot be performed until the electromotive force is stabilized, this problem is a factor that hinders the practical use of the solid electrolyte type carbon dioxide sensor. Therefore, the time from the start of operation to the stabilization of the electromotive force (hereinafter, referred to as stabilization time) is shortened, and the apparatus is left unheated in an atmosphere having a high moisture concentration such as high humidity or dew. Even so, it has been desired to develop a solid electrolyte type carbon dioxide sensor whose stabilization time does not change from a normal state.

[0013]

The inventor of the present invention has conducted various studies to develop a solid electrolyte type carbon dioxide gas sensor having such characteristics, and as a result, the working electrode layer formed on the surface of the solid electrolyte layer has a thickness of 0.1 to 0.1%. By containing 8% by weight of zeolite, the time from the start of operation to the stabilization of the electromotive force is within 0.5 hours, and non-heating in an atmosphere with high moisture concentration such as high humidity and dew condensation The present inventors have found that a solid electrolyte type carbon dioxide gas sensor having almost no change in the stabilization time of the electromotive force can be obtained even if the sensor is left in this state, and have come to propose the present invention.

That is, the present invention provides a solid electrolyte type carbon dioxide sensor element comprising a working electrode layer containing an electron conductive material and an auxiliary electrode material and a reference electrode layer containing an electron conductive material formed on the surface of the solid electrolyte layer. 0.1 to working electrode layer
A solid electrolyte type carbon dioxide sensor element comprising 8% by weight of zeolite.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the structure of a solid oxide carbon dioxide sensor element of the present invention will be described in detail.

In the present invention, the working electrode layer has a thickness of 0.1 to
It is important to include 8% by weight of zeolite, preferably 0.5 to 5% by weight of zeolite.

When the amount of zeolite contained in the working electrode layer is less than 0.1% by weight based on 100% by weight of the total weight of the working electrode, the stabilization time of the electromotive force is reduced in the working electrode containing no zeolite. The object of the present invention cannot be achieved without changing the stabilization time of the solid electrolyte type carbon dioxide sensor element having the layer. Further, when the amount of zeolite contained in the working electrode layer is more than 8% by weight, the stabilization time of the electromotive force at normal time is shortened, but in an atmosphere having a high moisture concentration such as high humidity or dew. When left unheated, like the solid electrolyte type carbon dioxide sensor element having a working electrode layer containing no zeolite, it has a long time to stabilize the electromotive force and achieves the object of the present invention. Can not do.

The zeolite used in the present invention is:
Known ones are used without any limitation. For example, type A,
In addition to X-type, Y-type, USY, ZSM-5, and the like, those obtained by exchanging cations contained in these zeolites with other cations can be mentioned.

Among the above zeolites, U containing Na ⁺
SY (hereinafter abbreviated as Na-USY) and Na-US
It is preferable that Na ⁺ contained in Y is replaced with Li ⁺ or K ⁺ , because the effect of the present invention is more easily exerted. In particular, Na ⁺ contained in Na-USY is replaced with Li ⁺ (hereinafter, referred to as “Li ^+”) . Li-USY) is preferred.

The method of exchanging cations contained in zeolite for other cations is not particularly limited,
As a typical method, there may be mentioned a method in which the zeolite powder before ion exchange is immersed in an aqueous solution containing a cation to be exchanged, stirred, dried, and fired.

In the present invention, the rate at which the cations contained in the zeolite are exchanged for other cations is not particularly limited. It is preferable that 70% or more is exchanged with respect to 100%.

In the present invention, the auxiliary electrode substance contained in the working electrode layer is a substance capable of causing an equilibrium reaction with carbon dioxide in an atmosphere containing carbon dioxide.
Known materials are used without limitation. For example, alkali metal carbonates such as sodium carbonate and lithium carbonate and mixtures thereof, or alkaline earth metal carbonates such as calcium carbonate and magnesium carbonate and mixtures thereof are employed. It is preferable to use an alkali metal carbonate, particularly sodium carbonate or lithium carbonate, because it easily occurs.

The content of the auxiliary electrode substance in the working electrode layer is not particularly limited, but is preferably 1 to 70% by weight, more preferably 3 to 50% by weight based on 100% by weight of the total weight of the working electrode. Is preferable because it is easy to stably output the electromotive force of the sensor element.

In the present invention, the electron conductive material contained in the working electrode layer is a substance necessary for outputting an electromotive force of the sensor element, similarly to the electron conductive material contained in the later-described reference electrode layer. Material is used without restriction. For example, noble metal elements such as platinum, gold, palladium, and silver and alloys thereof, or a mixture of two or more of the above noble metal elements are employed. In particular, platinum, gold, and mixtures and alloys thereof are resistant. It is suitable because of its excellent corrosiveness.

In the present invention, the structure of the working electrode layer including the electron conductive material, the auxiliary electrode material and the zeolite is not particularly limited. To illustrate a typical structure,
A structure in which the auxiliary electrode material and zeolite are dispersed in the electron conductive material of the working electrode layer, and the electron conductive material covers part or all of the mixture layer of the auxiliary electrode material and zeolite formed on the surface of the solid electrolyte layer. The structure includes a structure in which a mixture layer of the auxiliary electrode material and the zeolite covers part or all of the layer of the electron conductive material formed on the surface of the solid electrolyte layer.In particular, the auxiliary electrode material and the The structure in which the zeolite is dispersed is preferred because the working electrode layer can be easily formed.

As a method for forming the working electrode layer, a known method is used without any particular limitation. For example, the above electron conductive material, auxiliary electrode material and zeolite alone,
Or a method of kneading with a solvent and a binder after mixing to form a paste, and baking the paste on a solid electrolyte surface by a screen printing method or the like, an electron conductive material,
A method in which the auxiliary electrode material and zeolite are formed by a thin film forming technique such as sputtering or vapor deposition is suitably adopted.

Although the thickness of the working electrode layer is not particularly limited,
Generally, it is adopted from the range of 0.001 to 0.03 mm.

In the present invention, the electron conductive material contained in the reference electrode layer is a substance necessary for outputting an electromotive force of the sensor element, similarly to the above-mentioned electron conductive material contained in the working electrode layer. Material is used without restriction. For example, noble metal elements such as platinum, gold, palladium, and silver and alloys thereof, or a mixture of two or more of the above noble metal elements are employed. In particular, platinum, gold, and mixtures and alloys thereof are resistant. It is suitable because of its excellent corrosiveness.

As a method for forming the above-mentioned reference electrode layer, a known method is used without any particular limitation. For example, the method as described in the method for manufacturing the working electrode layer described above can be used. The thickness of the reference electrode layer is not particularly limited, but is generally adopted in the range of 0.001 to 0.03 mm.

In the present invention, the arrangement of the working electrode layer and the reference electrode layer is not particularly limited as long as the working electrode layer and the reference electrode layer are in contact with the solid electrolyte layer. For example, a structure in which a working electrode layer is formed on one surface of a solid electrolyte layer and a reference electrode layer is formed on the other surface, and both the working electrode layer and the reference electrode layer are fixed on one surface of the solid electrolyte layer. May have a structure formed at a distance of.

In the present invention, a known solid electrolyte is used for the solid electrolyte layer without any limitation. For example, N
ASICON, β-Al ₂ O _{3 and the} like.

As a method for forming the solid electrolyte layer, a known method is employed without any particular limitation. As a typical forming method,
After sintering the solid electrolyte synthesis raw material, molding and heating, forming the solid electrolyte synthesis raw material, sintering, and kneading the solid electrolyte synthesis raw material with a solvent and a binder to form a paste, A method in which the paste is printed on a ceramic or glass substrate by a screen printing method or the like and baked is used.

Although the thickness of the solid electrolyte layer is not particularly limited, it is generally adopted in the range of 0.02 mm to 2.0 mm.

The solid electrolyte type carbon dioxide sensor element is usually heated to a constant temperature of 100 to 600 ° C. in order to cause a dissociation equilibrium reaction between the auxiliary electrode substance and carbon dioxide. As a method for heating the sensor element, heating from a heat source external to the sensor element may be used, or a ceramic or glass substrate on which a heater is formed is joined to the sensor element, and a DC or AC voltage is applied to the heater. May be heated. The mounting position of the heater joined to the sensor element is not particularly limited as long as it does not hinder the operation of the sensor element, such as on the reference electrode layer.

[0035]

According to the solid electrolyte type carbon dioxide sensor element of the present invention, by using 0.1 to 8% by weight of zeolite for the working electrode in the working electrode layer, the time from the start of operation until the electromotive force is stabilized is obtained. Within 0.5 hours. Furthermore, even if the apparatus is left unheated in an atmosphere having a high moisture concentration such as high humidity or dew condensation, the stabilization time of the electromotive force is almost the same as that in the normal state. Therefore,
The present invention has great technical significance in that carbon dioxide gas can be quickly measured under any environment.

[0036]

EXAMPLES The present invention will be described specifically with reference to the following examples, but the present invention is not limited to these examples.

(1) Measurement of electromotive force stabilization time during normal operation The sensor element was placed in a constant temperature bath maintained at a temperature of 25 ° C. and a humidity of 40%, and was left unheated for seven consecutive days.

Immediately after the sensor element was taken out of the thermostat, the sensor element was immediately placed in a chamber in which the concentration of carbon dioxide was maintained at 350 ppm, and a DC voltage was applied from a power source to a heater to heat the sensor element to 450 ° C. The time from the start of heating until the value of the electromotive force of the sensor element became stable in the range of ± 4 mV was measured, and this was defined as the normal stabilization time of the sensor element.

(2) Measurement of electromotive force stabilization time after leaving high-humidity atmosphere unheated The sensor element was placed in a thermostat maintained at a temperature of 60 ° C. and a humidity of 90%, and was continuously heated for 7 days without heating. I left it.

Immediately after the sensor element was taken out of the constant temperature bath, the sensor element was placed in a chamber in which the concentration of carbon dioxide was maintained at 350 ppm, and a DC voltage was applied from a power source to a heater to heat the sensor element to 450 ° C. The time from the start of heating until the value of the electromotive force of the sensor element was stabilized in the range of ± 4 mV was measured, and this was defined as the stabilization time of the sensor element after leaving it in a high-humidity atmosphere without heating.

Examples 1 to 15 Elements having a sectional structure as shown in FIG. 1 were produced as solid electrolyte type carbon dioxide sensors. In this solid electrolyte type gas sensor element, a working electrode layer 1 is formed on one surface of a solid electrolyte layer 2 and a reference electrode layer 3 is formed on the other surface, and a ceramic plate 4 is bonded on the reference electrode layer 3 with an adhesive 5. ing. Furthermore, the ceramic plate 4 on the opposite side to the surface to which the reference electrode layer 3 is bonded
A heater 6 is formed on the surface of the device, and is supplied with electricity from a power supply 7. Further, lead wires are drawn out from the working electrode layer 1 and the reference electrode layer 3, and connected to a voltmeter 8 to measure the electromotive force.

The solid electrolyte powder for forming the solid electrolyte layer is made of zirconium silicate and sodium phosphate.
₃ Zr ₂ SiPO ₁₂ was mixed to give a composition of 1100
It was obtained by baking for 6 hours in an air atmosphere at a temperature of ° C.

The solid electrolyte layer 2 was formed into a disk-shaped pellet by uniaxially molding the above-mentioned solid electrolyte powder and then sintering at 1200 ° C. in an air atmosphere for 10 hours.

The working electrode layer was kneaded with terpineol in which 5% by weight of ethylcellulose was dissolved and gold powder as an electron conductive material, an auxiliary electrode material and zeolite at a ratio shown in Table 1 to form a paste. Was formed by screen printing, drying, and baking for 30 minutes in the air at 650 ° C. Thus, when the film thickness is 0.015
mm of working electrode layer was obtained.

Of the zeolites, Li-USY is Na
-USY was stirred for 12 hours in an aqueous solution of lithium nitrate at 25 ° C, washed with water, and then calcined in the air at 500 ° C for 8 hours. By this processing, it was confirmed by a fluorescent X-ray analyzer that Li-USY in which 90% of Na ⁺ in Na-USY was replaced with Li ⁺ was obtained.

As the A-type and ZSM-5 zeolites, commercially available zeolites were used as they were.

The reference electrode layer is obtained by kneading gold powder as an electron conductive material and terpineol in which 5% by weight of ethylcellulose is dissolved to form a paste, which is opposite to the surface of the solid electrolyte layer on which the working electrode layer is formed. It was formed by screen printing, drying, and baking for 30 minutes in the air at 650 ° C. on the surface. Thus, a reference electrode layer having a thickness of 0.015 mm was obtained.

On the above-mentioned reference electrode layer, an alumina substrate mounted with a platinum heater formed by a screen printing method using a commercially available platinum paste is made of glass such that the surface on which the heater is not formed becomes a bonding surface. Bonded with adhesive.

With respect to the solid electrolyte type carbon dioxide sensor element manufactured by the above-described method, the electromotive force stabilization time was measured at normal time and after non-heating and leaving in a high humidity atmosphere.

The results are shown in Table 1.

Comparative Examples 1 to 8 The solid electrolyte type carbon dioxide sensor elements of Comparative Examples 1 to 8 were produced in the same manner as in Examples 1 to 15.

The working electrode layers of Comparative Examples 1 to 8 were prepared by mixing terpineol in which 5% by weight of ethylcellulose was dissolved with gold powder as an electron conductive material, an auxiliary electrode material, and the same zeolite as in the examples shown in Table 1. To form a paste, which was formed on one surface of the solid electrolyte layer by screen printing, drying, and baking for 30 minutes in the air at 650 ° C.

The electromotive force stabilization time of the fabricated sensor element was measured at normal time and after leaving it in a high humidity atmosphere without heating. The results are shown in Table 1.

[0054]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a typical embodiment of a solid oxide carbon dioxide sensor element.

[Explanation of symbols]

 1. Working electrode layer 2. Solid electrolyte layer 3. 3. Reference electrode layer Ceramic plate 5. Adhesive 6. Heater 7. Power supply 8. voltmeter

Claims (1)

[Claims] 1. A solid electrolyte type carbon dioxide sensor element in which a working electrode layer containing an electron conducting material and an auxiliary electrode material and a reference electrode layer containing an electron conducting material are formed on the surface of a solid electrolyte layer. A solid oxide carbon dioxide sensor element comprising 0.1 to 8% by weight of zeolite.