JP2003254937A - Solid electrolyte type carbon dioxide sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte type carbon dioxide sensor element for measuring highly accurately even when the operation temperature is lowered to a low temperature, for example, 200°C, with shortened response time, and causing no change of an electromotive force even when left for long hours in the non-heated state. <P>SOLUTION: In this solid electrolyte type carbon dioxide sensor element having a basic structure wherein a working electrode and a reference electrode are bonded onto the surface of a solid electrolyte layer such as NASICON, an alkali metal compound oxide such as Li<SB>2</SB>Ni<SB>8</SB>O<SB>10</SB>or LiLaO<SB>2</SB>is added as well as an electronic conduction material such as platinum or gold included in the working electrode as an indispensable component and an auxiliary electrode material such as an alkali metal carbonate or an alkaline earth metal carbonate. <P>COPYRIGHT: (C)2003,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention
Solid oxide carbon dioxide sensor element for measuring gas concentration
About the child. [0002] 2. Description of the Related Art In recent years, there has been a demand for a living environment, particularly an indoor environment.
For example, monitor the concentration of carbon dioxide in the room
Rings and automatically changes when the carbon dioxide concentration rises.
Air cleaner equipped with a carbon dioxide sensor element
Purification equipment has been developed. Pollution prevention or countermeasures
From the viewpoint of measures, always measure the change in carbon dioxide concentration in the environment.
The so-called environmental measurement has become increasingly important. These sky
Control device or alarm device such as air purifier, or environmental measurement
As a carbon dioxide sensor element to be built in
Has high gas selectivity, easy miniaturization, wide operating conditions,
Solid electrolyte type charcoal with superior maintainability
Acid gas sensor elements are suitable. A solid electrolyte type carbon dioxide sensor element is generally used.
In addition, (a) the “solid electrolyte layer”, which is an ion conductor,
Equilibrium reaction between the proton conducting material and carbon dioxide as the gas to be measured.
"Action involving auxiliary electrode material that can cause response
Electrode "and (c) a" reference electrode "containing an electron conducting material.
It has a joined basic structure. Such carbon dioxide
For the sensor element, 400
The gas to be measured while being heated to a constant temperature of
Contained in the working electrode layer when left in an atmosphere containing
Dissociation between the auxiliary electrode material and the gas to be measured, carbon dioxide
Equilibrium reaction proceeds until equilibrium is reached and near the working electrode layer
A change occurs in the mobile ion concentration of the solid electrolyte layer, resulting in a change.
Between the working electrode layer and the reference electrode layer via the solid electrolyte layer
A certain electromotive force is generated according to the measured gas concentration
So, by measuring the electromotive force,
You can know. Conventionally, a generally known solid electrolyte type
In a carbon dioxide sensor element, a solid electrolyte layer is formed.
NASICON (Na_{1 + A}Zr₂
Si _AP_3-AO₁₂Where 0 ≦ A ≦ 3), β-Al₂
O₃Such as sodium ion conductive material and Li₂TiSi
O₅, LiTi₂(PO₄)₃Lithium ion conduction
Substances contained in the working electrode and the reference electrode
Conductive material (the material is necessary to detect electromotive force
Is excellent in heat resistance and oxidation resistance such as gold and platinum
Noble metal material is further included in the working electrode
As alkali metal carbonate or alkaline earth metal carbonate
Is generally used. However, the above-mentioned auxiliary electrode substance is
Solid state electricity using lithium metal carbonate and alkaline earth metal carbonate
Dissolved carbon dioxide sensor stopped operation by interrupting heating
Moisture concentration such as high humidity atmosphere or dew condensation atmosphere
If it is left in a high atmosphere, it will start operating again
Electromotive force is significantly lower than before leaving
(Hereafter, it is assumed that such a phenomenon is likely to occur.
It is also called low humidity. ). As a method for solving such a problem,
A method of adding a rare earth metal oxide to a working electrode is known.
(Japanese Unexamined Patent Publication No. H11-174023), the working electrode is La
₂O ₃, Nd₂O₃, Y₂O₃, CeO₂Rare earth gold
High humidity in non-heated state by adding metal oxide
Electromotive force is almost the same as before
Can be prevented from starting
The time until the power stabilizes can be within 2 hours
Noh. [0007] SUMMARY OF THE INVENTION A solid electrolyte
Type carbon dioxide gas sensor,
Separately from the above, reduce the operating temperature from the viewpoint of energy saving.
For certain applications, such as carbonic acid
In environmental measurement where gas concentration fluctuates drastically,
When the carbon dioxide concentration fluctuates, the electromotive force value changes quickly.
It is desired to change and stabilize in response to movement. [0008] However, Japanese Patent Application Laid-Open No.
Of the solid electrolyte type carbon dioxide sensor disclosed in
The problem of moisture resistance during non-heating has been solved
The operating temperature and response speed of conventional solid electrolyte type
It is the same as the acid gas sensor, and it is not always satisfactory.
There was no. For example, to make reliable measurements
It is difficult to keep the operating temperature below 200 ° C,
The electromotive force changes and stabilizes following the fluctuation of carbon dioxide concentration
Time (response time) was 10 minutes or more. Therefore, the present invention has a high moisture resistance when not heated.
And high-precision measurement is possible even when the operating temperature is lowered
Response to changes in carbon dioxide concentration
Provide a solid electrolyte type carbon dioxide sensor with short response time
The purpose is to: [0010] The present inventor has solved the above-mentioned problems.
As a result of repeated research to solve it, formed on the surface of the solid electrolyte layer
If a specific compound is added to the working electrode
Solid electrolyte type carbon dioxide gas that satisfies all of the above required performance
Have been found to lead to the present invention.
Was. That is, the present invention provides an electron conductive material, an auxiliary electrode
Working electrode containing substance and alkali metal composite oxide, and
The reference electrode, which contains an electron conductive material, is in contact with the surface of the solid electrolyte layer.
Solid electrolyte type carbon dioxide gas
Sensor element. [0012] BEST MODE FOR CARRYING OUT THE INVENTION The solid electrolyte type carbon dioxide gas
In a sensor element, an alkali metal composite oxide,
Working electricity containing complex oxides of rukari metal and other elements
It is important to use poles. The working electrode layer
Operating temperature below 200 ° C when no complex oxides are contained
, The fluctuations of the electromotive force and sensitivity with time increase.
Measurement of carbon dioxide concentration becomes difficult and response time
10 minutes or more, and no heating in a high humidity environment
Value is significantly lower than before
I will drop it. The alkali metal composite oxide used in the present invention
Means one or more alkali metals, alkalis
One or more elements that are neither metals nor oxygen (others
And an oxide composed of oxygen. Effect
From the point of view, other elements are transition metals or rare earth elements.
The use of element, especially Ni, Ti or La,
It is preferable to use Li as the potassium metal element. Book
Composite oxide of alkali metal and other elements used in the invention
As long as the above conditions are satisfied,
Known compounds can be used without particular limitation, and are suitably used in the present invention.
Specific examples of the composite oxide that can be used include Li₂
Ni₈O₁₀, LiLaO₂, Li₂TiO₃, LiC
oO₂, Li₂Fe₃O₄, Li₃NaTiO₄, Li
₂NiZrO₄, Na₂CrO₄, Na₄GeO₄, N
aNiO₂, Na₂Ti₃O₇, Na₂CoSiO₄,
K₉Ni₂O₇, K₃TaO₄, K₂WO₄, KNa₂
CuO₂, And mixtures thereof. Among these oxides, the operating temperature of the device is low.
Reduction effect, response time reduction effect, and non-heating moisture resistance improvement effect
Because the fruit is particularly high, Li₂Ni₈O₁₀And Li
LaO₂Composite of metallic lithium and other elements such as
At least one oxide selected from the group consisting of oxides
It is preferably used. Alkali metal and other elements used in the present invention
Commercially available compounds can be used as they are.
In addition, it can be easily obtained according to a general manufacturing method of a composite oxide.
For example, Li, Na, Ni, Ti, La
Etc., and by firing, these elements
Compounds such as carbonates that give oxides, or lithium oxide,
Oxides of these elements such as titanium oxide
Theoretically, when the reaction has proceeded,
Mixing and firing; or Li, Na, Ni, Ti,
Use carbonates and metal alkoxides containing constituent elements such as La
The desired composition is obtained when the reaction proceeds stoichiometrically.
Mix in a volume ratio such that
Heating in a solution of enic acid, by the so-called citrate method
More preferably, it can be obtained. Alkali metal contained in the working electrode layer and other
The amount of the composite oxide with the element is not particularly limited, but the effect
From the viewpoint of the electron conducting material and the auxiliary electrode material in the working electrode
1 to 50 parts by weight, based on 100 parts by weight of the total quality,
In particular, the amount is preferably 2 to 30 parts by weight. The solid electrolyte type carbon dioxide sensor element of the present invention
Is a complex acid of alkali metal and other elements as a working electrode
Other than using a working electrode containing
There is no particular difference from the quality type carbon dioxide sensor element. That is,
The solid electrolyte type carbon dioxide sensor element of the present invention is
As with the solid electrolyte type carbon dioxide sensor element, the solid electrolyte layer
Has a basic structure in which the working electrode and reference electrode are joined to the surface of
You. FIG. 1 shows a typical solid electrolyte gas sensor element of the present invention.
FIG. In the solid electrolyte sensor element,
The heater 6 connected to the heating power supply 7 is
Ceramics made of alumina, aluminum nitride, etc.
A reference electrode 3 having a layered shape and a solid electrolyte layer
2 and a lamination in which the laminar working electrodes 1 are laminated in this order.
The surface of the reference electrode 3 of the laminate
Bonded with an adhesive 5 so as to be in contact with the substrate,
Further, the potential difference between the reference electrode 3 and the working electrode 1 was measured.
Voltmeter 8 is electrically connected to both electrodes
ing. It should be noted that the structure shown in FIG.
And its connection with the power supply, voltmeter, etc.
The connection styles of the various members are limited to those shown in FIG.
Not. For example, the working electrode and reference electrode
Is particularly limited as long as it is in contact with the electrode layer for use and the reference electrode layer.
The working electrode and the reference electrode on the same surface of the solid electrolyte layer.
May be formed at a certain distance. Also,
The operation of the sensor must also be inhibited
Is not particularly limited, and if the
To maintain the temperature of the element at a predetermined constant temperature.
If it is possible, the heater need not be used. The solid electrolyte type carbon dioxide gas sensor of the present invention
The working electrode, reference electrode, and these electrodes used for the
Especially the structure, material, shape, size, etc. of the constituent members
Not limited to conventional solid electrolyte gas sensor elements
What is adopted is not restricted at all and can be used. An example
For example, the carbon dioxide gas of the present invention having a structure as shown in FIG.
These are the following types of sensor elements.
It can be suitably used as a member. That is, as the working electrode, an electron conductive material,
Aid that can trigger an equilibrium reaction with the gas to be measured
Electrode materials and composite oxides of alkali metals and other elements
From a layered body with a total thickness of 0.001 to 0.05 mm including
Can be used. Here, the electron conductive material is described later.
As with the electron conductive material contained in the reference electrode layer
Pt is a substance that outputs the electromotive force of
Noble metal elements such as gold, palladium, silver, etc.
Gold or a mixture of two or more of these noble metal elements
Are generally used, but they must have excellent corrosion resistance.
From platinum, gold, their mixtures, or their alloys
It is particularly preferably employed. Also, as the auxiliary electrode material,
Is the equilibrium reaction with carbon dioxide in an atmosphere containing carbon dioxide.
Any substance that can cause a reaction is particularly restricted.
And alkali metals such as sodium carbonate and lithium carbonate
Carbonates or mixtures thereof, or calcium carbonate or charcoal
Alkaline earth metal carbonates such as magnesium acid
These mixtures are used, but the equilibrium reaction with carbon dioxide is
Sodium carbonate and / or carbonic acid
Lithium is preferably employed. The voltage contained in the working electrode
The proportions of proton conductive material and auxiliary electrode material are particularly limited.
There is no fluctuation in the electromotive force of the sensor element during continuous use.
Based on the total weight of both substances due to low stickiness
20 to 95% by weight, expressed in terms of% by weight of electron conductive material,
It is preferably 40 to 90%. The working electrode
The structure of (i) electron conductive material, auxiliary electrode
Substances and composite oxides of alkali metals and other elements
Structure stacked in layers on the surface of the body electrolyte layer, (ii) solid
Auxiliary electrode material formed on the surface of the electrolyte layer and alkali
Part or all of a layer containing a composite oxide of a metal and another element
(Iii) electron conductive material
The auxiliary electrode material and the complex of alkali metal and other elements
Use a known structure such as a structure in which
However, the structure of (iii) above is preferable from the viewpoint of ease of production.
No. The working electrodes of these structures are composed of an electron conductive material,
Auxiliary electrode material and complex oxidation of alkali metal and other elements
Solvents and biomass
Into a paste, and paste the
Baking on the solid electrolyte layer surface by the printing method
Method; Sputtering electron conductive material and auxiliary electrode material
And methods of forming by thin film forming technology such as evaporation
It can be formed by a method. As the reference electrode, the above-described electronic transmission is used.
A conductive material, preferably platinum, gold, a mixture thereof, or
0.001-0.03mm layer made of these alloys
The body thing is suitably adopted. The reference electrode is also the working electrode
It can be formed by the same method as described above. Further, as the solid electrolyte layer, the aforementioned NA
SICON, Li₂TiSiO₅Thick solid electrolyte
0.02mm to 2.0mm plate, cylinder, bottomed cylinder
What was shape | molded in the shape, such as a shape, can be used conveniently. What
The method for forming the solid electrolyte layer is not particularly limited, either.
For example, the solid electrolyte synthesis raw material is fired, molded and then heated.
Method: sintering after shaping the raw material for solid electrolyte synthesis
Or a solid electrolyte synthesis raw material with a solvent and a binder.
Into a paste by kneading
Printing on ceramic or glass substrates by printing method etc.
A method of printing and printing can be suitably employed. The carbon dioxide sensor element of the present invention has a constant temperature.
Contains carbon dioxide, which is the gas to be detected,
Used by leaving it in an atmosphere
Carbon dioxide in the atmosphere based on the electromotive force measured by a manometer
Although it can measure the concentration,
Not only high humidity, but also lower operating temperature to about 200 ℃
Measurement can be performed with high accuracy even when
It is possible. And when the carbon dioxide concentration changed greatly
Response time is very short, about 7 to 20 seconds. For this reason,
Carbon dioxide sensor for environmental measurement where the carbon dioxide concentration changes drastically
It can be particularly suitably used as an element. [0023] DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to specifically explain the present invention, the following examples
The present invention will be described by way of examples, but the present invention is not limited to these examples.
It is not done. Examples 1 to 3 First, C₂H₅ONa, Zr (C₄H₉O)₄, Si
(OC₂H₅)₄, (C ₂H₅O)₃PO in molar ratio
3: 2: 2: 1 mixture and metal alkoxide
After hydrolyzing the compound, it was dried at 100 ° C.
After firing at 00 ° C for 4 hours, it is uniaxially formed into pellets,
Sinter in an air atmosphere at 1200 ° C for 10 hours.
And a solid electrolyte layer made of NASICON
Done. Next, 5% by weight of ethyl cellulose is dissolved.
30 parts by weight of terpineol
Gold powder, Li as auxiliary electrode material₂CO₃Or
Na ₂CO₃, And Li₂Ni₈O₁₀The powder is shown in Table 1.
Kneaded at the same ratio to form a paste,
Screen printing on one side of the porous layer, after drying
Baking in air for 30 minutes, working voltage of 0.015mm
An extreme layer was formed. Li₂Ni₈O₁₀The powder is commercially available Li₂
CO₃Powder and NiCO₃1: 4 powder molar ratio
And fired in an air atmosphere at 600 ° C for 2 hours.
And produced. Then, the gold powder 10 as an electron conductive material
0% by weight of 5% by weight ethyl cellulose dissolved in ter
30 parts by weight of pinoeol were added and mixed to form a paste.
Later, this is the surface of the solid electrolyte layer on which the working electrode layer was formed.
Screen printing on the opposite surface to 650 ° C after drying
Fired in the air for 30 minutes and the thickness is 0.015mm
An electrode layer was formed. Next, using a commercially available platinum paste,
An electrode with a platinum heater formed by lean printing
The surface where the heater is not formed should be
Adhesive made of glass on the reference electrode layer so that
And connect an external AC power supply to the heater
And a voltmeter connected between the working electrode and the reference electrode.
Solid electrolyte type sensor having a sectional structure as shown in FIG.
A device was manufactured. The solid electrolyte type carbonic acid prepared as described above
For gas sensor elements, see (1) to (3) below.
And the operating temperature dependency test of the electromotive force and sensitivity
Measurement and a non-heating moisture resistance test were performed. Measurement result
Are shown in Table 2. (1) Dependence test on operating temperature of electromotive force and sensitivity
Method Immediately after producing the solid electrolyte type carbon dioxide sensor element,
Put in a chamber where gas concentration can be controlled freely, and supply power
By applying a DC voltage to the heater, the operating temperature of the element
To 200 ° C. and maintain the sensor element at that temperature.
Adjust the concentration of carbon dioxide in the chamber to 350ppm
And the electromotive force was measured. Next, carbon dioxide gas in the chamber
The concentration of the gas to 2000 ppm, and the electromotive force at the same temperature.
It was measured. After that, the element temperature (operating temperature) is set to 300 ° C.
And 450 ° C., and at the same temperature, 350 pp
The electromotive force at m and 2000 ppm was measured. Ma
In addition, 350 ppm at each temperature and 2000 pp
m, and calculate the difference between the electromotive forces at each operating temperature.
Sensitivity. (2) Response time measuring method Immediately after the measurement in the above test (1), the solid electrolyte type carbon dioxide
A sensor that can freely control the carbon dioxide concentration
Insert the battery into the bar and apply DC voltage to the heater from the power supply.
To heat the element to 450 ° C and heat the sensor element to 450 ° C.
While holding, the concentration of carbon dioxide in the chamber
pm and confirm that the electromotive force is constant
The gas concentration is instantaneously changed to 2000ppm,
The time until stabilization (response time) was measured. Then cha
The concentration of carbon dioxide in the chamber is increased from 2000ppm to 350p
pm until the electromotive force stabilizes
(Response time) was measured. (3) Moisture resistance test method without heating Immediately after the measurement in the above test (2), the solid electrolyte type carbon dioxide
A sensor that can freely control the carbon dioxide concentration
Insert the battery into the bar and apply DC voltage to the heater from the power supply.
And the element is heated to 450 ° C. and the temperature of the sensor element is set to 45 ° C.
While maintaining the temperature at 0 ° C., the concentration of carbon dioxide in the chamber was adjusted to 3
Adjusted to 50 ppm and 2000 ppm, and
Measure the electromotive force at the concentration and use this as the initial electromotive force.
Was. The electromotive force at 350 ppm and 2000 pp
m and the difference between the electromotive force value at the time of
Initial sensitivity at ° C. When the device temperature is 450 ° C
After measuring the initial sensitivity, remove the sensor element from the chamber.
It was taken out and kept at a temperature of 60 ° C. and a humidity of 90%.
After putting in a thermostat and leaving it unheated for 7 days
Take out of the thermostat, 3 when the element temperature is 450 ° C
Electromotive force at 50 ppm and 2000 ppm (
Power) in the same way and calculate the sensitivity (sensitivity after test)
did. [0033] [Table 1] [0034] [Table 2]Examples 4 to 6 Li added to the working electrode₂Ni₈O₁₀LiLa powder
O₂Except for changing to powder, the same as in Examples 1-3
A solid electrolyte type carbon dioxide sensor was produced, and
Evaluation was performed in the same manner. LiLaO₂Powder is commercially available
Li₂O powder and La₂(CO₃)₃Powder in molar ratio
Mix so that the mixture becomes 1: 1 and mix in air at 600 ° C.
It was produced by firing for an hour. Table of composition of working electrode
1 and Table 2 show the evaluation results. Examples 7 and 8 Li added to the working electrode₂Ni₈O₁₀Li powder₂T
iO₃Same as Examples 1 to 3 except that the powder is changed.
To produce a solid electrolyte type carbon dioxide sensor, Examples 1-3
Evaluation was performed in the same manner as described above. Li₂TiO₃The powder is
A commercially available product was used as it was. Table 1 shows the composition of the working electrode.
Table 2 shows the evaluation results. Comparative Examples 1-4 Examples 1 to 3 except that the working electrode having the composition shown in Table 1 was used.
Prepare a solid electrolyte type carbon dioxide sensor in the same way
Evaluation was performed in the same manner as in Examples 1 to 3. Working electrode composition
Table 1 shows the evaluation results together with Table 2. Comparative Examples 1 and 2 correspond to Example 2 respectively.
And Li₂Ni₈O₁₀Is a rare earth oxide, L
a₂O₃But the moisture resistance when not heated is high
Response time is long, and at low temperatures of 200 ° C
The carbon dioxide concentration could not be measured. Ma
Comparative Examples 3 and 4 are electron conductive materials and auxiliary electrode materials.
This is an example using a working electrode consisting only of
Has a low moisture resistance when not heated. [0039] The solid electrolyte type carbon dioxide sensor element of the present invention
Not only has high moisture resistance when not heated, but also
For example, high-precision measurement is possible even if the temperature is lowered to 200 ° C.
Furthermore, the response time is as short as 7 to 20 seconds. For this reason, long term
Not only enables reliable measurement during
Energy expenditure can be reduced. Furthermore, charcoal
For environmental measurement where acid gas concentration change may be severe
It is fully usable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a typical solid oxide carbon dioxide sensor element of the present invention. [Explanation of reference numerals] Working electrode 2. 2. solid electrolyte layer Reference electrode4. Ceramic plate5. Adhesive 6. Heater 7. Power supply 8. voltmeter

Claims (1)

Claims 1. A working electrode including an electron conductive material, an auxiliary electrode material, and an alkali metal composite oxide, and a reference electrode including an electron conductive material are bonded to a surface of a solid electrolyte layer. A solid electrolyte type carbon dioxide sensor element characterized by the above-mentioned.