JP2001281205A - Co2 sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CO2 sensor superior in stability capable of reducing the effects of humidity and improving drifts without the need for a complicated correcting circuit. SOLUTION: In the CO2 sensor provided with a detecting electrode and counter electrode each in contact with a solid electrolyte, the solid electrolyte contains an alkaline metal ion and/or alkaline earth metal ion conductor, and the detecting electrode comprises a metal oxide layer and collector. A metal hydrogen carbonate and/or metal carbonate and metal salt with water of crystallization at room temperature to 100 deg.C are made present between the detecting electrode and solid electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide sensor for use in bio-related fields such as indoor and outdoor environment control, agricultural and industrial processes such as facility horticulture, disaster prevention, and measurement of metabolic functions on living bodies, and medical fields. About.

[0002]

2. Description of the Related Art In recent years, there is a need for a carbon dioxide sensor mainly for detection of indoor air pollution accompanying the spread of air conditioning, detection of air pollution in facilities in livestock farming, plant growth control in horticultural facilities, various industrial processes, and the like. And various types of carbon dioxide sensors have been proposed.

Specifically, for example, an infrared absorption type carbon dioxide sensor has been put to practical use. However, this type of sensor has not been widely used due to its large size and high cost. A sensor using a semiconductor has also been proposed, but since this sensor has poor selectivity for carbon dioxide, it is difficult to measure the concentration of only carbon dioxide.

[0004] On the other hand, some sensors using a solid electrolyte have been proposed as small and inexpensive sensors.

[0005] Maruyama et al. The 10th Solid Ionics Symposium
Abstracts 69 (1983)｝ show dissociation equilibrium with carbon dioxide
Forming a pair of electrodes on a solid electrolyte such as potassium carbonate
Is formed, and one of them is brought into contact with a reference gas having a known concentration to form an atmosphere.
A density-polarized cell for measuring the electromotive force due to the concentration difference of ambient gas.
A sensor. In addition, Maruyama et al.
In addition to polarization type sensors, NASICON (Sodium Super)
-Ion conductor: Na _ThreeZr_TwoSi_TwoPO₁₂Al)
Forming a pair of electrodes on a potassium metal ion conductive solid electrolyte
And dissociation equilibrium with carbon dioxide such as sodium carbonate
A metal carbonate layer that forms
A so-called electromotive force detection type cell
Has also proposed.

In Japanese Patent Publication No. 4-79542, a pair of electrodes is formed on a solid electrolyte having metal ion conductivity of a metal salt forming a dissociation equilibrium with carbon dioxide, and one of the electrodes is coated with the metal salt. A carbon dioxide sensor has been proposed in which the other electrode and the remaining solid electrolyte surface are coated with a gas barrier layer.

Japanese Patent Application Laid-Open No. 7-63726 proposes a solid reference electrode type carbon dioxide sensor in which a solid reference electrode, which is a conductor of electrons and oxygen ions, is pressed against a solid electrolyte made of an alkali ion conductor. .

A problem with a small and inexpensive carbon dioxide sensor using a solid electrolyte is that, first, the metal carbonate used as a material is easily affected by humidity. In order to solve this problem, it is necessary to seal the portion other than the gas detecting portion of the sensor element, or to heat the sensor with a heater to increase the operating temperature to reduce the influence of humidity. The operating temperature of the above sensor is as high as 400 to 700 ° C. When the operating temperature is high, problems such as a large power consumption of the whole sensor and a thermal degradation of the material occur. Further, there is also a problem that heat of several hundred degrees Celsius has a subtle effect on the measurement environment, such as heating around the sensor even if it is from a small heater and generating convection of air.

Further, since the metal carbonate is easily affected by humidity, it is necessary to store the element in a dry atmosphere when the use of the sensor is stopped. Furthermore, during use, baking is necessary to remove moisture that has entered the element during stoppage, and it takes a long time for the output voltage of the sensor to stabilize, and there is a problem of workability and energy. These are inevitable problems when operating the sensor at a high temperature, and a sensor operating at a lower temperature is required.

In response to this problem, S. Breikhin et al. [Applied
PhysicsA 57, 37-43 (1993)] reports a carbon dioxide sensor in which a solid electrolyte and a semiconductor are bonded. This carbon dioxide sensor uses a SnO ₂ semiconductor doped with Sb or V as a detection electrode, and a sodium ion conductor, NASICON, is joined as a solid electrolyte to this. A Na _x CoO ₂ as a reference electrode is provided on the opposite side of the detection electrode. Has been arranged. This carbon dioxide sensor can be operated at low temperature (-35 ° C. to room temperature), but has a problem that it takes more than 4 minutes until a response is observed. In addition, the moisture resistance is poor, and the response time and sensitivity change depending on the relative humidity (humidity), and it is difficult to obtain stable performance.

In view of such a situation, the present inventors have previously provided a detection electrode and a counter electrode in contact with a solid electrolyte such as NASICON, respectively, and the detection electrode has a current collector;
In addition, a carbon dioxide sensor that preferably includes a metal oxide layer containing a predetermined metal oxide and detects carbon dioxide by a detection electrode in the presence of hydrogen carbonate ions has been proposed (Japanese Patent Application No. 10-96604). , Japanese Patent Application No. 10-272608, Japanese Patent Application No. 10-27
2609, Japanese Patent Application No. 10-272610, etc.).

However, with such a carbon dioxide sensor,
Is greatly affected by humidity, and CO _TwoResponse to concentration change
It was found that a drift of the response electromotive force value was observed.

Hitherto, in order to cancel the influence of humidity and drift, it is necessary to carry out arithmetic processing by a complicated and expensive correction circuit.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly stable carbon dioxide sensor capable of reducing the influence of humidity and improving drift without requiring a complicated correction circuit. It is to provide.

[0015]

This and other objects are achieved by the present invention described below. (1) In a carbon dioxide sensor in which a detection electrode and a counter electrode are respectively provided in contact with a solid electrolyte, the solid electrolyte contains an alkali metal ion and / or an alkaline earth metal ion conductor, and the detection electrode is a metal oxide. Having a material layer and a current collector, between the detection electrode and the solid electrolyte,
Metal bicarbonate and / or metal carbonate, at room temperature to 1
A carbon dioxide sensor in which a metal salt having water of crystallization is interposed at a temperature of 00 ° C. (2) a metal oxide layer of the sensing electrode is located on the solid electrolyte side, and between the metal oxide layer and the solid electrolyte, a metal bicarbonate and / or a metal carbonate;
The carbon dioxide sensor according to the above (1), wherein a metal salt having crystallization water is interposed at a temperature of room temperature to 100 ° C. (3) The carbon dioxide sensor according to (1) or (2), wherein the solid electrolyte is a sodium ion conductor. (4) the solid electrolyte is _{Na 1 + x Zr 2 Si x} P 3-x O 12
The carbon dioxide sensor according to the above (3), wherein (x = 0 to 3). (5) The metal salt having water of crystallization at a temperature of room temperature to 100 ° C. is a phosphoric acid salt of an alkali metal, a phosphoric acid salt of an alkaline earth metal, or a phosphoric acid aluminum. (1) to (1) to which are at least one of a salt, a metal sulfate, a metal nitrate, a metal acetate, a metal hydroxide (however, excluding an alkali metal hydroxide) and a metal chloride.
The carbon dioxide sensor according to any one of (4). (6) The metal salt having water of crystallization at a temperature of from room temperature to 100 ° C. is a phosphoric acid salt of an alkali metal having water of crystallization, and a phosphoric acid salt of an alkali metal having water of crystallization is Alkali metal phosphate (orthophosphate), phosphonate, phosphinate, diphosphate, with water of crystallization,
The above (1) to (5), which are one or more of metaphosphate, hypophosphate, phosphite, and any of these acid salts
Any of the carbon dioxide sensors. (7) The alkali metal phosphoric acid-based salt having crystallization water is one or more of alkali metal phosphoric acid (orthophosphate) salts having crystallization water and any one of these acid salts. A) Carbon dioxide sensor. (8) The carbon dioxide sensor according to (7), wherein the alkali metal phosphoric acid-based salt having crystallization water is a sodium phosphate (orthophosphate) salt having crystallization water. (9) The metal bicarbonate and / or metal carbonate is a metal bicarbonate, and the metal bicarbonate is at least one of sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate, and cesium bicarbonate The carbon dioxide sensor according to any one of the above (1) to (8). (10) The carbon dioxide sensor according to (9), wherein the metal bicarbonate is sodium bicarbonate.

(11) The metal oxide is indium oxide, tin oxide, cobalt oxide, tungsten oxide, zinc oxide, lead oxide, copper oxide, iron oxide, nickel oxide, chromium oxide, cadmium oxide, bismuth oxide, manganese oxide , Yttrium oxide, zirconium oxide, antimony oxide, aluminum oxide, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, silver oxide, lithium oxide, sodium oxide, potassium oxide, rubidium oxide, cesium oxide, magnesium oxide, calcium oxide, oxide The carbon dioxide sensor according to any one of (1) to (10), which is at least one of strontium and barium oxide. (12) The carbon dioxide sensor according to (11), wherein the metal oxide is indium oxide. (13) The above (1), wherein the metal oxide layer is porous.
A carbon dioxide sensor according to any one of (12) to (12). (14) The above (1) to (1), wherein the current collector is a porous metal.
The carbon dioxide sensor according to any one of (13). (15) The above (1) to (14), wherein the current collector is provided to face the solid electrolyte with the metal oxide layer interposed therebetween.
Any of the carbon dioxide sensors. (16) The carbon dioxide sensor according to any one of (1) to (15), wherein the detection electrode and the counter electrode are provided on the same surface of the solid electrolyte. (17) The carbon dioxide sensor according to any one of (1) to (16), wherein the counter electrode contains one or more of a metal and a metal oxide. (18) The metal bicarbonate and / or metal carbonate and a metal salt having crystallization water at a temperature of room temperature to 100 ° C. are interposed by forming a mixture layer of these compounds on the surface of the solid electrolyte. The above (1) to (17)
Any of the carbon dioxide sensors. (19) A porous material provided on the solid electrolyte as a solution or paste of these compounds, wherein the metal bicarbonate and / or metal carbonate and a metal salt having water of crystallization at a temperature of room temperature to 100 ° C. The carbon dioxide sensor according to any one of the above (12) to (17), which is interposed by passing through the metal oxide layer and the porous current collector to reach the surface of the solid electrolyte.

[0017]

The carbon dioxide sensor of the present invention is of a type in which a detection electrode and a counter electrode are provided in contact with a solid electrolyte containing a metal ion conductor, respectively. Having a body. As the metal ion conductor, an alkali metal ion and / or alkaline earth metal ion conductor, preferably a sodium ion conductor is used, and a metal bicarbonate and / or metal carbonate is provided between the solid electrolyte and the sensing electrode. A salt and a metal salt having crystallization water at a temperature of room temperature to 100 ° C. (for example, a phosphate salt of an alkali metal) are interposed.

As described above, by using a metal salt having water of crystallization at a temperature of room temperature to 100 ° C., a metal oxide layer is provided on the sensing electrode, and a metal hydrogen carbonate and / or a metal carbonate is present. Maintaining the effect of improving responsiveness,
While the rapid measurement at a low temperature is enabled, the influence of humidity can be reduced, and the drift can be improved. Therefore, in order to reduce the influence of humidity and improve drift, a complicated and expensive correction circuit is provided, which eliminates the need for arithmetic processing, thereby simplifying the element structure and reducing the cost.

The metal salt having water of crystallization at a temperature of room temperature to 100 ° C. is considered that, due to the presence of the water of crystallization, the influence of humidity is reduced and the drift is improved by changing the state of addition of the water of crystallization. Can be

The carbon dioxide sensor of the present invention is preferably of a type having a metal oxide layer on the surface of the solid electrolyte in contact with the detection electrode, and a metal oxide layer is provided between the metal oxide layer and the solid electrolyte. It is preferable to interpose a bicarbonate and / or a metal carbonate and a metal salt having crystallization water at a temperature of room temperature to 100 ° C. Thereby, the effect of the present invention is improved.

A metal bicarbonate and / or a metal carbonate having a water of crystallization at a temperature between room temperature and 100 ° C.
In order to intervene between the solid electrolyte and the sensing electrode (preferably a metal oxide layer), a mixture layer of these compounds may be provided. Specifically, it may be applied using a solution or paste of these compounds. In this case, the metal oxide layer provided on the mixture layer may be obtained by baking, and it is necessary to perform the application of water later.
Since the current collector and the metal oxide layer are made porous in order to provide the sensing electrode itself with a function as a gas diffusion layer and obtain a quick response, it is easy to apply water. Water can also be applied as a solution or paste using this as a solvent or dispersion medium. In the case where the current collector and the metal oxide are made porous, the current collector and the metal oxide layer may be formed, and then the compound may be impregnated as a solution or paste through the layers.

In any case, the above compound needs to be present at the interface between the solid electrolyte and the sensing electrode (preferably a metal oxide layer), and the compound is required to be present at the interface between the solid electrolyte and the sensing electrode (preferably a metal oxide layer). Layer), and may be diffused into both or one of the solid electrolyte and the sensing electrode (preferably a metal oxide layer).

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The carbon dioxide sensor of the present invention is of a type in which a detection electrode and a counter electrode are respectively provided in contact with a solid electrolyte, and the solid electrolyte is an alkali metal ion and / or an alkaline earth metal ion conductor, preferably sodium. An ion conductor is contained, the detection electrode has a metal oxide layer and a current collector, and a metal bicarbonate and / or a metal carbonate is provided between the detection electrode and the solid electrolyte; A metal salt having crystallization water at a temperature of 100 ° C. (for example, a phosphate salt of an alkali metal) is interposed. In the present invention, the current collector is provided so as to face the solid electrolyte with the metal oxide layer interposed therebetween so that the metal oxide layer of the detection electrode is located on the solid electrolyte side, for example, to obtain a quick response. However, in such an embodiment, it is preferable to interpose the above compound between the metal oxide layer and the solid electrolyte. However, since the current collector is usually a porous body such as a metal mesh, the present invention is not limited to this mode, and even in a mode in which the current collector is provided on the solid electrolyte side and then the metal oxide layer is provided. Since the coated material of the metal oxide penetrates into the current collector, it is possible to interpose the above compound between the metal oxide layer and the solid electrolyte, and the present invention is effective in such an embodiment. is there.

<Solid Electrolyte> In the carbon dioxide sensor of the present invention, an alkali metal ion and / or an alkaline earth metal ion conductor, preferably a sodium ion conductor, is used as the metal ion conductor in the solid electrolyte. When the counter electrode is exposed to the same environment as the detection electrode, the solid electrolyte cannot take an electromotive force. Further, those having no electronic conductivity are preferable.

Examples of such an ionic conductor include Na-β ″ alumina, Na-β alumina, Na _{1 + x}
NAS represented by _{Zr 2 Si x P 3-x} O 12 (x = 0~3)
ICON (for example, Na ₃ Zr ₂ Si ₂ PO ₁₂ ), Na-βGa ₂ O ₃ , Na-Fe ₂ O ₃ , Na ₃ Zr ₂
PSi ₂ P ₂ O ₁₂ , Li-β alumina, Li ₁₄ Zn (Ce
_{O 4), Li 5 AlO 4} , Li 1.4 Ti 1.6 In 0.4 P
₃ O ₁₂ , K-β alumina, K _1.6 Al _0.8 Ti _7.2 O ₁₆ , K
₂ MgTi ₇ O ₁₆ , CaS and the like. These may deviate somewhat from the stoichiometric composition. As the solid electrolyte, a sodium ion conductor is preferable, and Na, Z
A composite oxide of r, Si and P is preferable, and among them,
ASICON is preferred, and Na ₃ Zr ₂ is particularly preferred.
Although it is Si ₂ PO ₁₂ , it may slightly deviate from the stoichiometric composition.

The method for producing the solid electrolyte may be any of the commonly used solid phase method, sol-gel method, coprecipitation method, etc., and preferably the solid phase method is used.

In the solid electrolyte, in addition to the metal ion conductor, aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ),
Zirconium oxide (ZrO ₂ ), silicon carbide (Si
C), silicon nitride (Si ₃ N ₄ ), iron oxide (Fe ₂ O ₃ ), and the like may be contained in a mass percentage of 50% or less. These may deviate somewhat from the stoichiometric composition.

<Detection electrode> In the carbon dioxide sensor of the present invention, the detection electrode comprises a metal oxide layer and a current collector.

<Metal oxide layer of sensing electrode> Metal oxide layer
Contains those with electronic conductivity as metal oxides
Preferably, indium oxide (In)_TwoO_Three),acid
Tin oxide (SnO_Two), Cobalt oxide (Co_ThreeO_Four), Oxidation
Tungsten (WO_Three), Zinc oxide (ZnO), lead oxide
(PbO), copper oxide (CuO), iron oxide (Fe_TwoO_Three, F
eO), nickel oxide (NiO), chromium oxide (Cr_Two
O_Three), Cadmium oxide (CdO), bismuth oxide (B
i_TwoO_Three), Manganese oxide (MnO)_Two, Mn_TwoO_Three), Oxidation
Yttrium (Y_TwoO_Three), Zirconium oxide (Zr
O_Two), Antimony oxide (Sb_TwoO_Three), Aluminum oxide
(Al_TwoO_Three), Lanthanum oxide (La_TwoO_Three), Oxidized sericin
Um (CeO)_Two), Praseodymium oxide (Pr₆O₁₁),acid
Neodymium (Nd_TwoO_Three), Silver oxide (Ag_TwoO), oxide
Titanium (Li_TwoO), sodium oxide (Na)_TwoO), oxidation
Potassium (K _TwoO), rubidium oxide (Rb_TwoO), oxidation
Cesium (Cs_TwoO), magnesium oxide (MgO),
Calcium oxide (CaO), strontium oxide (Sr
O) and at least one of barium oxide (BaO)
Is preferable. Among them, indium oxide,
Tin oxide, cobalt oxide, tungsten oxide, suboxide
Lead, lead oxide, copper oxide, iron oxide, nickel oxide, black oxide
, Cadmium oxide, bismuth oxide, zirconium oxide
And aluminum oxide are preferred, and especially indium oxide
, Tin oxide, copper oxide, and zinc oxide are preferred.
In order to obtain the effect, indium oxide is most preferable. Was
However, lithium oxide, sodium oxide, potassium oxide,
Rubidium oxide, cesium oxide, magnesium oxide, acid
Using calcium oxide, strontium oxide, barium oxide
Better response, but more sensitive to humidity
And it is preferable to use it in combination with other metal oxides.
No. Note that these deviate somewhat from the stoichiometric composition.
Is also good.

The metal oxide layer may contain a metal bicarbonate and / or a metal carbonate in addition to the metal oxide. Thereby, since the detection electrode can be formed by applying a stable paste, the adhesion of the detection electrode to the solid electrolyte is improved, and the response speed is improved. In addition, since the work such as screen printing becomes easy at the time of forming the detection electrode,
Productivity is improved. Further, the strength of the electrode also increases.
In this case, the amount of the metal bicarbonate and / or metal carbonate may be within the range of the amount of these compounds interposed between the solid electrolyte and the sensing electrode (described later), and can be added in portions. .

The method of forming the metal oxide layer of the sensing electrode is not particularly limited, but usually, a paste of metal oxide powder, metal bicarbonate powder and / or metal carbonate powder is applied to a solid electrolyte, and the metal oxide It is preferable to form by drying by heating for about 2 hours at a temperature lower than the melting point or decomposition point of the substance, metal bicarbonate, or metal carbonate. The average particle size of the metal oxide, metal bicarbonate, or metal carbonate used is preferably 10 nm to 100 μm. As a solvent for the paste, an organic solvent in which the metal oxide, the metal bicarbonate and / or the metal carbonate does not dissolve or react, and has a relatively low vapor pressure at room temperature and good workability may be used. . In particular, α-terpineol, ethylene glycol,
Glycerin and the like are preferred. The viscosity of the slurry is 0.1 ~ 100,0
00P is preferred.

The metal oxide layer may be made porous by a thin film process.

Since the metal oxide layer is preferably gas-permeable, it is preferably porous. The pore diameter is preferably from 0.01 to 100 μm.

<Current Collector of Detection Electrode> The carbon dioxide sensor of the present invention uses a current collector for the detection electrode.

The metal used for the current collector may be any one or more of gold, platinum, silver, rubidium, rhodium, palladium, iridium, nickel, copper, chromium and the like.

The current collector is preferably a porous metal. If the current collector is porous, the detection electrode itself functions as a gas diffusion layer, so that a quicker response can be obtained.

The porous metal is preferably a metal mesh or a powder electrode formed by pressing or screen printing a metal powder paste. In particular, powder electrodes are preferred. The mesh size of the metal mesh is not particularly limited as long as it has a holding force.

Screen printing is a method in which a paste of metal powder is applied to a substrate through a mesh screen. In this case, a porous electrode in which metal particles are connected to each other is formed. The average particle size of the metal powder used at this time is 10 nm to 100 μm, particularly 10 nm to 10 μm.
m is preferable because good printing can be performed. In addition, the solvent for the paste is an organic solvent in which the metal used does not dissolve or react, and has a relatively low vapor pressure at room temperature.
Anything that has good workability may be used. Particularly, α-terpineol, ethylene glycol, glycerin and the like are preferable.
The viscosity of the slurry is preferably 0.1 to 100,000P.

It is also preferable to apply a current collector metal powder paste on the upper surface of the metal oxide layer and take a lead.

The pore diameter of the porous electrode is 0.5 to 500 μm
Is preferred.

It is also possible to form an electrode having a porous surface by sputtering these metal materials. Ar, He, O ₂ , N ₂
And the like, and the pressure during film formation is preferably in the range of 0.1 to 66.5 Pa (0.1 to 500 mTorr). The electrode surface can also be made porous by resistance heating evaporation.

Further, in order to make the sensing electrode itself a gas diffusion layer and obtain a quicker response, the current collector may be provided to face the solid electrolyte with the metal oxide layer interposed therebetween.

<Metal bicarbonate and / or metal carbonate> By supporting the metal bicarbonate and / or metal carbonate on the surface of the solid electrolyte, the generation of bicarbonate ions essential for the detection of carbon dioxide is further increased. Is promoted, and responsiveness such as sensitivity, response speed, and selectivity is improved. In addition,
It is considered that the metal carbonate reacts with carbon dioxide and water to form a metal bicarbonate, and promotes the generation of hydrogen carbonate ions derived from carbon dioxide. In any case, the existence of hydrogen carbonate ions is important for the function as a carbon dioxide sensor.

Examples of the metal bicarbonate include alkali metal bicarbonate and the like. Sodium bicarbonate (NaHCO ₃ ), potassium bicarbonate (KHCO ₃ ), rubidium bicarbonate (RbHCO ₃ ), cesium bicarbonate ( CsHCO ₃ ). These may be used alone or in combination of two or more. Among them, it is preferable to use sodium hydrogencarbonate and potassium hydrogencarbonate, particularly sodium hydrogencarbonate.

As the metal carbonate, for example, carbonate
Lithium (Li_TwoCO_Three), Sodium carbonate (Na_TwoC
O_Three), Potassium carbonate (K_TwoCO_Three), Rubidium carbonate
(Rb_TwoCO_Three), Cesium carbonate (Cs_TwoCO_Three), Carbonic acid
Gnesium (MgCO_Three), Calcium carbonate (CaC
O_Three), Strontium carbonate (SrCO_Three), Barium carbonate
(BaCO_Three), Manganese carbonate (Mn (CO_Three)_Two, M
n_Two(CO_Three)_Three), Iron carbonate (Fe _Two(CO_Three)_Three, FeCO
_Three), Nickel carbonate (NiCO_Three), Copper carbonate (CuC
O_Three), Cobalt carbonate (Co_Two(CO_Three)_Three), Chromium carbonate
(Cr_Two(CO_Three)_Three), Zinc carbonate (ZnCO_Three), Silver carbonate
(Ag_TwoCO_Three), Cadmium carbonate (CdCO_Three), Carbonated
Indium (In)_Two(CO_Three)_Three), Yttrium carbonate
(Y_Two(CO_Three)_Three), Lead carbonate (PbCO_Three), Bismuth carbonate
(Bi_Two(CO_Three)_Three), Lanthanum carbonate (La_Two(C
O_Three)_Three), Cerium carbonate (Ce (CO_Three)_Three), Carbonated plastic
Theodymium (Pr₆(CO_Three)₁₁), Neodymium carbonate (Nd_Two
(CO_Three)_Three) And the like. Use one kind of metal carbonate
Or two or more of them may be used in combination. Among them, Lithium carbonate
It is preferable to use sodium carbonate, potassium carbonate,
New When used in combination with metal bicarbonate,
It is preferable to use a carbonate of the same metal as the bicarbonate of the genus
No.

In particular, it is preferable to use bicarbonate or carbonate of the same metal as the mobile ion species of the solid electrolyte.

The metal bicarbonate and / or the metal carbonate may be used in combination of two or more kinds. In this case, the metal bicarbonate may be used between the metal bicarbonates or the metal carbonates, or the metal bicarbonate may be used. And a metal carbonate can be used in combination.

<Metal salt having water of crystallization at room temperature to 100 ° C.> A metal salt having water of crystallization at a temperature of room temperature to 100 ° C. (usually 15 ° C. to 100 ° C.) is supported on the surface of the solid electrolyte. Since these salts may have water of crystallization, they may play a role in controlling the partial pressure of water vapor, probably because of the change in the state of addition of the water of crystallization, and can reduce the effects of humidity. And drift is reduced.

The metal salt having water of crystallization at a temperature of room temperature to 100 ° C. is preferably a phosphoric acid-based salt of an alkali metal. These salts include those having water of crystallization. (Orthophosphoric acid) salt (PO ₄ ^3- salt), phosphonate (PHO ₃ ^2- salt), phosphinate (PH ₂ O
₂ ^- salts), diphosphate (pyrophosphate) salt (P ₂ O ₇ ^4-salts), metaphosphate, hypophosphate (P ₂ O ₆ ^4-salts), phosphites (PO ₃ ^3- Salts) and their acidic salts (hydrogen salts). Among them, phosphates, phosphonates, phosphinates, diphosphates, hypophosphates and those selected from acid salts thereof are preferred, and more preferably selected from phosphates and acid salts thereof. And particularly preferably a phosphate. Examples of the alkali metal include Li, Na, K, Rb, and Cs.
a and K are preferred, and Na is generally preferred because it is the same as the mobile ionic species of the solid electrolyte. Specifically, Na ₃ PO ₄ , Na ₂ HPO ₄ , NaPH ₂ O ₂ , N
_{a 2 PHO 3, NaHPHO 3,} Na 4 P 2 O 6, Na 2 H 2 P
_{There are 2} O ₆ , Na ₄ P ₂ O ₇ , Na ₂ H ₂ P ₂ O _{7 and the} like, most preferably Na ₃ PO ₄ .

As the above-mentioned phosphoric acid salts, in addition to alkali metal salts, alkaline earth metal salts such as Ca, Mg and Ba, and Al salts can be used.

In addition, sulfates (specifically, CuS
O_Four, ZnSO_Four, CoSO_Four, CaSO_Four, Ga_Two(S
O_Four)_Three), Nitrates (specifically, Cu (NO_Three)_Two, Co
(NO_Three)_Two, Mn (NO_Three)_TwoEtc.), acetate (specifically,
Mn (CH_ThreeCOO)_Two, Mg (CH _ThreeCOO)_Two, Co
(CH_ThreeCOO)_TwoEtc.), hydroxide (alkaline gold
Excluding genus salts. Specifically, Ba (OH)_Two, Ca (OH)_Two
Etc.), chlorides (specifically CuCl_Two, MgCl_Two, Ba
Cl_TwoEtc.) can also be used.

These compounds are usually used alone, but may be used in combination of two or more.

The metal salt having water of crystallization at a temperature from room temperature to 100 ° C. is shown in the above-mentioned specific example without the water of crystallization, and the compound itself to be added may be an anhydride. However, it is necessary to make water coexist at the initial stage of configuring the sensor.

The amount of the metal oxide, metal bicarbonate and / or metal carbonate, and the metal salt having water of crystallization at a temperature of room temperature to 100 ° C. can be appropriately determined according to the device configuration and size. Good.

The metal bicarbonate and / or metal carbonate is mixed with a metal salt having water of crystallization at a temperature between room temperature and 100 ° C.
In order to be interposed between the solid electrolyte and the sensing electrode (preferably a metal oxide layer), that is, supported on the surface of the solid electrolyte, saturation of the metal bicarbonate and / or metal carbonate
Using a supersaturated aqueous solution and a saturated to supersaturated aqueous solution of a metal salt having water of crystallization at a temperature of room temperature to 100 ° C., respectively, impregnating the solid electrolyte surface with a predetermined amount of each compound, A mixture layer may be formed, or a paste of metal bicarbonate and / or metal carbonate;
A predetermined amount is applied to the surface of the solid electrolyte using a paste of a metal salt having crystallization water at a temperature of room temperature to 100 ° C. and baked, and further, water (ion exchange water or the like) is dropped to form a mixed layer. May be. The amount of water added is about 0.001 ml to 1 ml per 1 cm ^{2 of} the solid electrolyte. Cellulose or a cellulose derivative (for example, ethylcellulose) or the like is used as a binder when forming the paste, and α-terpineol or the like is used as a solvent.
When forming a paste, the average particle size of each of the above compounds is preferably 10 nm to 100 μm, and the viscosity of the slurry is 0.1 μm.
~ 100,000P is preferred.

When the above-described production method is employed, since the metal oxide layer is usually formed by firing, the application of water (an aqueous solution or a paste using water) may be applied to fix the detection electrode. Because of the need to be performed later, the current collector and the metal oxide layer of the sensing electrode are generally porous, but when porous, after forming the sensing electrode, the aqueous solution or The paste may be carried on the solid electrolyte by passing through the sensing electrode. In such a case, the above compound remains partially in the sensing electrode (particularly, the metal oxide layer), but may remain even if it remains, which is rather preferable in terms of characteristics. The order in which the above compounds are added may be any order, and in some cases, they may be added after being mixed in advance.

When a mixed layer of the above compounds is formed, it is considered that the above compounds diffuse at the solid electrolyte interface and the sensing electrode (particularly, metal oxide layer) interface. preferable.

<Counter electrode> In the carbon dioxide sensor of the present invention,
A metal or metal oxide is used for the counter electrode. The metal or metal oxide used may be any one or more of the same metals or oxides thereof as the above-described current collector of the sensing electrode, and the same metal oxide as the metal oxide layer. By using a metal oxide for the counter electrode, the influence of the coexisting gas is reduced, and high carbon dioxide selectivity is obtained. Further, the moisture resistance is improved, and the influence of humidity, particularly at the time of measurement at a low temperature, is reduced.

The counter electrode is preferably made of a porous metal or a porous metal oxide, like the current collector. In particular, a powder electrode formed by pressing or screen printing a metal oxide powder paste is preferable. The mesh size of the metal mesh is not particularly limited as long as it has a holding force. The average particle size of the metal powder and the metal oxide powder used for the paste for forming the powder electrode is preferably from 10 nm to 100 μm, particularly preferably from 10 nm to 10 μm. The paste solvent may be any organic solvent that does not dissolve or react with the metal or metal oxide used, and has a relatively low vapor pressure at room temperature and good workability.
Particularly, α-terpineol, ethylene glycol, glycerin and the like are preferable. Slurry viscosity 0.1 ~ 100,000P
It is preferable that

The pore diameter of the porous electrode is 0.5 to 500 μm
Is preferred.

<Method of Measuring Carbon Dioxide Concentration>
In the presence of carbon dioxide, the sensor converts to carbon dioxide and moisture.
Bicarbonate ion (HCO_Three ^-) Is the sensing electrode metal
Supposedly formed on oxide surface or solid electrolyte surface
It is. Usually, it is thought that all of them are formed.
And the dissociation equilibrium of bicarbonate ion
Convert to changes in carbon dioxide concentration by converting to ion activity
Detect as force. Using NASICON for solid electrolyte
HCO_Three ^-Is the solid electrolyte surface, the solid electrolyte of the sensing electrode
Whether formed on a porous surface or a metal oxide surface,
Na, a mobile ion in the electrolyte⁺But HCO_Three ^-Pull to
And move to the vicinity of the detection pole. Also, ionic conductivity
Excellent HCO on metal oxide surface_Three ^-Is formed,
Na which is a mobile ion during the decomposition⁺Penetrate into the metal oxide layer
Enter. At this time, NaHCO_ThreeMay be generated
You. In addition, the solid electrolyte component in the sensing electrode also supplies mobile ions.
Acts as a feeder and changes in carbon dioxide concentration
It is quickly converted by a change in the activity of the metal ion.

When bicarbonate ions are formed on the surface of a metal oxide having excellent electron conductivity, the metal oxide acts as a conductor and generates an electromotive force. Examples of metal oxides having excellent electron conductivity include indium oxide, tin oxide,
Cobalt oxide, tungsten oxide, zinc oxide, lead oxide,
Examples include copper oxide, iron oxide, nickel oxide, and chromium oxide.

When bicarbonate ions are formed on the surface of a metal oxide having excellent ion conductivity, as described above, an electromotive force is generated when mobile ion species in the solid electrolyte penetrate into the metal oxide. Examples of the metal oxide having excellent ion conductivity include bismuth oxide and cerium oxide.

Even if the formed hydrogen carbonate ion is directly adsorbed or bonded to the metal oxide surface or the solid electrolyte surface of the sensing electrode, the surface of the solid electrolyte component of the sensing electrode,
It may be adsorbed or bonded directly to —OH groups on the surface of the metal oxide or the surface of the solid electrolyte or via water (H ₂ O).

The fact that HCO ₃ ⁻ is involved in the measurement of carbon dioxide in the sensor of the present invention can be confirmed from the results of infrared absorption spectrum (IR) and mass spectrometry. Also,
This is also suggested by the results of Experimental Example 2 described later.

In addition, the influence of humidity upon measurement is reduced,
In addition, in order to reduce drift, it is preferable to use indium oxide as the metal oxide, but the mechanism is not clear. In addition, the presence of a metal salt having water of crystallization at a temperature of room temperature to 100 ° C. on the surface of the solid electrolyte reduces the influence of humidity at the time of measurement and reduces drift. It is considered that the change of the state of addition of the water of crystallization of the metal salt having water of crystallization at the temperature is involved.

<Sensor Structure> FIGS. 1 and 2 show examples of the structure of the carbon dioxide sensor of the present invention. FIG. 1 shows a detection electrode 3 composed of a metal oxide layer 4 and a current collector 5 with a solid electrolyte 2 interposed therebetween.
And a separation-type carbon dioxide sensor 1 provided with a counter electrode 6 opposed thereto. And, between the solid electrolyte 2 and the current collector 5, a metal bicarbonate and / or a metal carbonate,
A mixture layer 7 with a metal salt having water of crystallization at a temperature between room temperature and 100 ° C. is interposed. At this time, the metal oxide layer 4 penetrating into the current collector 5 comprising the solid electrolyte 2 and the metal mesh
It is sufficient that these compounds exist at the interface with, and may be present in the form of being diffused and contained in the current collector 5 including the solid electrolyte 2 and / or the metal oxide layer 4.

FIG. 2 shows a non-separable carbon dioxide sensor 1 in which a detection electrode 3 and a counter electrode 6 composed of a metal oxide layer 4 and a current collector 5 are provided on one surface of a solid electrolyte 2. Also in this embodiment, similarly to FIG. 1, between the solid electrolyte 2 and the metal oxide layer 4 in the current collector 5, a metal bicarbonate and / or a metal carbonate is crystallized at a temperature of room temperature to 100 ° C. Metal salt with water is interposed. The non-separable type is preferable because the formation of the current collector and the removal of the lead can be simplified in the process and the manufacturing process is simplified, so that the production efficiency is increased.
Further, the size of the element can be reduced. Lead wires are drawn out from the detection electrode 3 and the counter electrode 6, respectively, and connected to a potentiometer.

Although the size of the carbon dioxide sensor of the present invention is not particularly limited, when the surface on which the detection electrode is formed is the upper surface of the solid electrolyte, the thickness of the solid electrolyte is usually 1 μm to 5 m.
m and the area of the upper surface of the solid electrolyte is about 1 μm ^{2 to} 200 mm ² . The thickness of the sensing electrode is about 0.1 to 100 μm, and the area of the sensing electrode is about 0.5 μm ^{2 to} 200 mm ² . The thickness of the counter electrode is about 0.1 to 100 μm, and the area of the counter electrode is about 0.5 μm ^{2 to} 200 mm ² .

The optimum operating temperature of the carbon dioxide sensor of the present invention varies depending on the material constituting the sensor element, the type of coexisting gas, and the like, but is -70 ° C to 200 ° C, preferably -7 ° C.
The range is from 0 ° C to 150 ° C, more preferably from -50 ° C to 120 ° C. At a temperature higher than this, the change in electromotive force with respect to the carbon dioxide concentration becomes small, probably because the amount of adsorbed water decreases and bicarbonate ions are hardly formed, so that the carbon dioxide concentration cannot be measured. The performance of a sensor that cannot be measured at high temperature is restored when the temperature is lowered to about room temperature, and a response can be seen. The carbon dioxide sensor of the present invention can operate at a lower temperature than a conventional carbon dioxide sensor using a solid electrolyte, and can reduce power consumption. Since the temperature does not need to be high, the change in the measurement environment due to the heat of the heater can be sufficiently reduced.

The carbon dioxide sensor of the present invention has good responsiveness, and a response can be obtained in one second to three minutes.

In the element configuration, a heater is not necessary for a sensor that can be operated at room temperature, but it is preferable to provide a heater in consideration of a seasonal temperature difference.

[0073]

The present invention will be described below with reference to examples.
An experimental example will be described prior to the example. Comparative examples are also shown.

<Experimental example 1> NASICON of solid electrolyte
(Specifically, Na ₃ Zr ₂ Si ₂ PO ₁₂ ) pellets (10 m
A Pt mesh (100 mesh) was provided on the lower surface of (m diameter, 1 mm thickness) to serve as a counter electrode.

On the other hand, a current collector Au mesh (100 mesh) was provided on the upper surface of the solid electrolyte. Then, on top of that,
Metal oxide powder described later (average particle diameter: 10 nm to 1 each)
00 μm) was used as a paste [a mixture of 5% (mass percentage) of ethylcellulose and α-terpineol). Viscosity of 10,000 to 100,000P] was applied and baked to form a detection electrode.

Finally, a glass tube filled with dry standard air was bonded to the counter electrode side with an inorganic adhesive (Aron Ceramic C, manufactured by Toagosei Chemical Co., Ltd.) so that only the detection electrode surface was exposed. Then, a lead wire was connected from each electrode to obtain a separated carbon dioxide sensor (see FIG. 1).
However, there is no mixture layer). Further, a sensor in which the detection electrode was provided only with the Au mesh current collector without providing the metal oxide layer was manufactured.

The metal oxide is ZrO_Two, Co_ThreeO_Four,
CuO, ZnO, Al_TwoO_Three, In_TwoO _Three, SnO_Two, Bi_Two
O_ThreeWere used.

On the sensing electrode side, 10 synthetic air containing CO ₂ was applied.
Under an operating temperature of 30 ° C. and a relative humidity (RH) of 30 to 70%, a potential difference (electromotive force EMF) generated between the detection electrode and the counter electrode is measured by an electrometer as a sensor signal under a condition of a circulation of 0 cm ³ / min and a relative humidity (RH) of 30 to 70%. did. The partial pressure of water vapor in the test gas was controlled by bubbling dry air.

300 ppm CO _{2 at} 30 ° C. and 50% RH
Difference between each sensor and 3000ppmCO ₂ (ΔEMF =
EMF 3000 ppm-EMF 300 ppm).

All metal oxides showed higher CO ₂ sensitivity than Au alone. In particular, when SnO ₂ was used, the highest sensitivity was exhibited, but it was found that the sensitivity was greatly affected by humidity.

On the other hand, in a device using In ₂ O ₃ , SnO ₂
Although the same high CO ₂ sensitivity as in the case of was obtained, it was found that the influence of humidity was small. The electromotive force response of the sensor using In ₂ O ₃ at 30 ° C. was proportional to the logarithm of the CO ₂ concentration. Although its CO ₂ sensitivity (ΔEMF) is almost stable against changes in humidity, base gas (300 ppm CO ₂ )
It has been found that the electromotive force value for shifts greatly.

As described above, in the sensor of the type described above, unlike the conventional high-temperature-operated type CO ₂ sensor, an auxiliary phase (carbonate) responsive to CO ₂ is not added to the surface of the solid electrolyte. , CO ₂ response was obtained. This is because the interface between the solid electrolyte and the oxide at the time when the sensor is fabricated or during operation in the test gas
It is considered that ₂ sensitive substances were generated.

<Experimental Example 2> Among the sensors of Experimental Example 1, a sensor using In ₂ O ₃ as a metal oxide
Na ₂ CO ₃ , NaHC as CO ₂ sensitive substance on CON surface
Sensors formed with O ₃ and Na ₃ PO ₄ respectively were obtained (see FIG. 1).

Using these three types of sensors, the CO ₂ response characteristics were examined in the same manner as in Experimental Example 1.

As a result, the effect of increasing the CO ₂ sensitivity was Na ₂ C
It was found that NaHCO ₃ was slightly larger than O ₃ . Further, it was found that when Na ₂ CO ₃ and NaHCO ₃ were used as the sensor material, they were affected by water vapor.

On the other hand, in the sensor to which Na ₃ PO ₄ (anhydrous) was added, the following changes were observed in the sensor characteristics by adding water (ion-exchanged water) to the sensor surface. That is, in the measurement before adding water,
It was found that the response electromotive force drifted with respect to the CO ₂ concentration change, the response electromotive force was unstable, and the CO ₂ sensitivity (ΔEMF) did not increase. On the other hand, when moisture was added to the sensor surface, the sensitivity was increased, and the humidity dependency of the base electromotive force was considerably reduced.
FIG. 3 shows a CO ₂ response curve with respect to a change in the CO ₂ concentration when the humidity conditions were changed to 30% RH, 50% RH, and 70% RH at 30 ° C. for the Na ₃ PO ₄ added sensor to which water was added. . In addition, 300, 500, 100 in the figure
The numerical values of 0, 2000, and 3000 are CO ₂ concentrations, and the unit is ppm.

As described above, since the humidity dependency is reduced, it is considered that Na ₃ PO ₄ plays a role of controlling the partial pressure of water vapor near the interface.

[0088] The Na ₃ PO ₄ (anhydrous), the X-ray diffraction before and after the addition of water (XRD) analysis was performed to study the XRD pattern, Na ₃ PO ₄ (anhydrous) is the addition of water It turned out to change to Na ₃ PO ₄ .12H ₂ O. Further, from the result of thermogravimetric analysis (TG), it was also found that this Na ₃ PO ₄ .12H ₂ O was dehydrated even in dry air at room temperature, and at about 50 ° C., it was in a state close to an anhydrate. Because of this, Na ₃ PO
₄ is expected to reduce the humidity dependence by changing the state of addition of the crystallization water.

As described above, the CO ₂ sensitivity is lower than that of HCO ₃ ⁻
However, it is considered that Na ₃ PO ₄ contributes to the humidity dependency.

Next, examples based on this will be shown together with comparative examples.

Example 1 NASICON of Solid Electrolyte
(Specifically, Na ₃ Zr ₂ Si ₂ PO ₁₂ ) pellets (10 m
A Pt mesh (100 mesh) was provided on the lower surface of (m diameter, 1 mm thickness) to serve as a counter electrode.

On the other hand, a mixture of 5% (mass percentage) of ethyl cellulose and α-terpineol in 5% (mass percentage) of Na ₃ PO ₄ powder (average particle size: 0.1 to 100 μm) was added to the upper surface of the solid electrolyte. Then, a paste (with a viscosity of 10,000 to 100,000 P) was applied and baked. The baking temperature was 800 ° C. for 2 hours. A current collector Au mesh (100 mesh) was provided on the upper surface.

Then, a mixture of 5% (mass percentage) of ethylcellulose and α-terpineol was added to 50 mg of In ₂ O ₃ powder (average particle size: 50 nm), and the mixture was mixed. Nishimono (viscosity 10,000-100,00
0P) was applied and baked.

NaHCO ₃ powder (average particle size: 0.1 to 1)
00 μm) and water to form a paste, impregnated into the above In ₂ O ₃ layer, supported on a solid electrolyte, and then dried. Thus, a detection electrode was produced.

Finally, a glass tube filled with dry standard air on the counter electrode side was coated with an inorganic adhesive (Aron Ceramic C, manufactured by Toagosei Chemical Co., Ltd.) so that only the surface of the detection electrode was exposed. Then, a lead wire was connected from each of the electrodes to obtain a separation-type carbon dioxide sensor as shown in FIG. The response characteristics were examined as follows.

On the detection electrode side, synthetic air containing CO ₂
Under the condition that the operating temperature is 30 ° C. and the relative humidity (RH) is 30 to 70%, the potential difference (electromotive force EMF) generated between the detection electrode and the counter electrode is used as a sensor signal (output) at a flow rate of 0 cm ³ / min. It was measured with a meter. The partial pressure of water vapor in the test gas was controlled by bubbling dry air. CO
₂ 300 ppm, 500 ppm, 1000 ppm, 2000
FIG. 4 shows the relationship between the relative humidity and the electromotive force (EMF) for the test gas set to 3000 ppm and 3000 ppm. Also, 3
FIG. 5 shows the relationship between the logarithm of the CO ₂ concentration and the electromotive force (EMF) under the condition of 0 ° C. and 50% RH. FIG. 6 shows the relationship between the electromotive force (EMF) and the oxygen concentration (% by volume) under the conditions of a CO ₂ concentration of 1000 ppm and a temperature of 30 ° C. and a relative humidity of 40%.

As a result, it was found that not only the sensitivity of CO ₂ was improved, but also that the electromotive force for each CO ₂ concentration was almost stable even when the relative humidity was changed between 30% and 70%. (FIG. 4). Further, as shown in FIG. 5, the response electromotive force of the sensor of the present invention was proportional to the logarithm of the CO ₂ concentration. Further, as shown in FIG. 6, it was found that the response electromotive force of the sensor of the present invention did not depend on the O ₂ concentration.

Further, using a test gas having a CO ₂ concentration of 1000 ppm, an electromotive force (EMF) 500 hours after the sensor reached an equilibrium state at 30 ° C. and 40% RH was examined, and a change from an initial value was obtained. When the rate (%) was determined, it was about 5%, and it was found that the drift was small.

<Example 2> A Pt mesh (100 mesh) was provided on the upper surface of the pellet, that is, on the surface of the solid electrolyte in the same plane as the detection electrode in the same manner as in Example 1 so as not to be in contact with the detection electrode. did.

In the same manner as in Example 1, as shown in FIG. 2, a paste of Na ₃ PO ₄ was
It was applied to a region smaller than about half of the upper surface of the N pellet (diameter: 10 mm, thickness: 1 mm) and baked in the same manner as in Example 1. Then, a current collector Au mesh (10
0 mesh). Next, an In ₂ O ₃ paste (same as in Example 1) was applied and baked so as to cover a region of about half of the upper surface of the NASICON pellet. Further, the same Na ₃ PO ₄ paste as in Example 1 was impregnated into the above-mentioned In ₂ O ₃ layer, supported on the solid electrolyte, and then dried.

Then, a lead wire was connected from each electrode to obtain a non-separable carbon dioxide sensor as shown in FIG.

The CO ₂ response characteristics of this sensor were examined in the same manner as in Example 1. As a result, good results equivalent to or better than those of Example 1 were obtained.

<Embodiment 3> In Embodiment 1, a counter electrode is used.
Example on the opposite surface of the solid electrolyte provided with the Pt mesh
1. An Au mesh was provided in the same manner as in No. 1, and further,
In same as Example 1 _TwoO_ThreeApply paste and apply 2 at 650 ° C
Burned for hours. And NaHCO_ThreeOversaturated
Aqueous solution and Na_ThreePO_FourAnd the supersaturated aqueous solution of
In_TwoO_ThreeImpregnated from above the layer and supported on the solid electrolyte
Was. Otherwise, in the same manner as in Example 1,
A sample was prepared. In this regard, the CO_TwoResponse characteristics
Upon examination, the same results as in Example 1 were obtained.

The NaHCO on the solid electrolyte surface
_{3 The} supported amount is 1 to 50 mg / cm ² , and the Na ₃ PO ₄ supported amount is 1 to 5
It is considered to be 0 mg / cm ^2, and a part of the detection electrode (particularly, the In ₂ O ₃ layer) is impregnated.

<Embodiment 4> Structure of Embodiment 2 (non-separable type)
Example 3
According to the same method as above, an Au mesh was provided, and 650 ° C.
Baking the In ₂ O ₃ layer under conditions of 2 hours, In ₂ O ₃ layer is impregnated with an aqueous solution supersaturated aqueous solution and Na ₃ PO ₄ supersaturated of NaHCO ₃ from the top of, in addition to be carried on the solid electrolyte Produced a carbon dioxide sensor in the same manner as in Example 2. When the CO ₂ response characteristics were examined in the same manner, the same results as in Example 2 were obtained.

<Comparative Example 1> In the sensor of Example 1,
A sensor was obtained in the same manner except that Na ₃ PO ₄ was not added,
When the response characteristics were examined, it was found that the effect of humidity was large as shown in Experimental Example 2. Further, the drift was large, and it was found that a change of about 10% was exhibited in the same manner as in Example 1.

<Comparative Example 2> In the sensor of Example 1,
A sensor was obtained in the same manner except that NaHCO ₃ was not added, and the response characteristics were examined. As expected from Experimental Example 2, the sensitivity was not sufficient.

<Comparative Example 3> In the sensor of Example 3,
Instead of Na ₃ PO ₄ aqueous solution, 0.1 mol / l NaOH
Except for injecting the aqueous solution, a sensor was obtained in the same manner, and the characteristics were examined. As a result, no influence by humidity and no improvement in drift were found.

<Example 5> In Examples 1-4, potassium phosphate, lithium phosphate, rubidium phosphate, and cesium phosphate (all of which were obtained by adding water of crystallization) instead of sodium phosphate A sensor was produced in the same manner except that each of the above-mentioned (salts) was used, and the characteristics were examined in the same manner. As a result, similar results were obtained depending on the element structure.

<Example 6> In Examples 1 to 4, Na ₂ HPO ₄ , NaH ₂ PO ₄ , NaPH ₂ O ₂ , Na ₂ P in which a water of crystallization may be present instead of sodium phosphate.
HO ₃ , NaHPHO ₃ , Na ₄ P ₂ O ₆ , Na ₂ H ₂ P
_A sensor was fabricated in the same manner except that ₂ O ₆ , Na ₄ P ₂ O ₇ , and Na ₂ H ₂ P ₂ O ₇ were used, respectively, and the characteristics were examined in the same manner. Obtained.

<Embodiment 7> In Embodiments 1 to 6, paste obtained by adding α-terpineol to Au powder (average particle size: 0.1 to 100 μm) instead of providing an Au mesh on the current collector of the detection electrode. (Viscosity 10,000-100,00
0P) was applied, and a heat treatment was performed at 700 ° C. for 2 hours to provide a porous powder electrode, except that a sensor was prepared and characteristics were examined in the same manner as in Examples 1 to 6. It was found that similar results were obtained and the response speed was increased depending on each element structure.

<Embodiment 8> In Embodiments 1 to 6, instead of providing a Pt mesh or Au mesh on the counter electrode, α-terpineol was added to the surface of the NASICON pellet to In ₂ O ₃ powder (average particle size: 50 nm). The paste was applied, and a heat treatment was performed at 650 ° C. for 2 hours to provide a porous powder electrode. It was found that similar results were obtained and that the CO ₂ selectivity increased according to each device structure.

[0113]

As described above, according to the present invention, the influence of humidity is small and drift can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one configuration example of a separation-type carbon dioxide sensor of the present invention.

FIG. 2 is a cross-sectional view showing another configuration example of the non-separable carbon dioxide sensor of the present invention.

[Figure 3] CO ₂ when varying the humidity and CO ₂ concentration
It is a graph which shows a response curve.

FIG. 4 is a graph showing a relationship between an electromotive force (CO ₂ response characteristic) and humidity at each CO ₂ concentration.

FIG. 5 is a graph showing the relationship between the logarithm of the CO ₂ concentration and the electromotive force (CO ₂ response characteristic).

FIG. 6 is a graph showing a change in electromotive force (CO ₂ response characteristic) with respect to O ₂ concentration.

[Description of Signs] 1 Carbon dioxide sensor 2 Solid electrolyte 3 Detecting electrode 4 Metal oxide layer 5 Current collector 6 Counter electrode 7 Mixture layer

Continued on the front page (72) Inventor Noriyoshi Nanba 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (72) Inventor Yamazoe Noboru ▼ 4-32 Matsugaoka, Kasuga-shi, Fukuoka Prefecture (72) Inventor Miura Norio 1-111-181402 Hirao, Chuo-ku, Fukuoka Prefecture (72) Inventor Kengo Shimanoe 2-18-2 Tsukinoura, Onojo-shi, Fukuoka F-term (reference) 2G004 ZA04

Claims (19)

[Claims] 1. A carbon dioxide sensor in which a detection electrode and a counter electrode are provided in contact with a solid electrolyte, wherein the solid electrolyte contains an alkali metal ion and / or an alkaline earth metal ion conductor, and the detection electrode is A metal salt having a metal oxide layer and a current collector, and having a metal bicarbonate and / or a metal carbonate between the sensing electrode and the solid electrolyte and crystal water at a temperature of room temperature to 100 ° C. And a carbon dioxide sensor interposed. 2. A metal oxide layer of the sensing electrode is located on the side of the solid electrolyte, and a metal bicarbonate and / or a metal carbonate is provided between the metal oxide layer and the solid electrolyte. 2. The carbon dioxide sensor according to claim 1, wherein a metal salt having water of crystallization is interposed at a temperature of about 100 [deg.] C. 3. The carbon dioxide sensor according to claim 1, wherein said solid electrolyte is a sodium ion conductor. Wherein said solid electrolyte is _{Na 1 + x Zr 2 Si x} P
The carbon dioxide sensor of the _{3-x O 12 (x =} 0~3) at a third aspect. 5. The phosphoric acid salt of an alkali metal, the phosphoric acid salt of an alkaline earth metal, and the phosphoric acid of aluminum, wherein the metal salt having water of crystallization at a temperature of from room temperature to 100 ° C. has a water of crystallization. System salts, metal sulfates, metal nitrates, metal acetates,
The carbon dioxide sensor according to any one of claims 1 to 4, wherein the carbon dioxide sensor is at least one of a metal hydroxide (however, excluding an alkali metal hydroxide) and a metal chloride. 6. The metal salt having crystallization water at a temperature of room temperature to 100 ° C. is an alkali metal phosphate salt having crystallization water, and the alkali metal phosphate salt having crystallization water. An alkali metal phosphate (orthophosphate) salt, phosphonate, phosphinate, diphosphate, metaphosphate, hypophosphate, phosphite, or an acid salt thereof having a water of crystallization The carbon dioxide sensor according to any one of claims 1 to 5, which is at least one of the following. 7. The alkali metal phosphoric acid-based salt having water of crystallization is at least one of an alkali metal phosphoric acid (orthophosphate) salt having water of crystallization and an acid salt thereof. Item 6. A carbon dioxide sensor according to item 6. 8. The carbon dioxide sensor according to claim 7, wherein the alkali metal phosphate salt having water of crystallization is a sodium phosphate (orthophosphate) salt having water of crystallization. 9. The metal bicarbonate and / or metal carbonate is a metal bicarbonate, and the metal bicarbonate is selected from the group consisting of sodium bicarbonate, potassium bicarbonate, rubidium bicarbonate and cesium bicarbonate. The carbon dioxide sensor according to claim 1, wherein the carbon dioxide sensor is at least one. 10. The carbon dioxide sensor according to claim 9, wherein said metal bicarbonate is sodium bicarbonate. 11. The method according to claim 11, wherein the metal oxide is indium oxide,
Tin oxide, cobalt oxide, tungsten oxide, zinc oxide, lead oxide, copper oxide, iron oxide, nickel oxide, chromium oxide, cadmium oxide, bismuth oxide, manganese oxide, yttrium oxide, zirconium oxide, antimony oxide,
Aluminum oxide, lanthanum oxide, cerium oxide, praseodymium oxide, neodymium oxide, silver oxide, lithium oxide,
The carbon dioxide sensor according to any one of claims 1 to 10, wherein the carbon dioxide sensor is at least one of sodium oxide, potassium oxide, rubidium oxide, cesium oxide, magnesium oxide, calcium oxide, strontium oxide, and barium oxide. 12. The carbon dioxide sensor according to claim 11, wherein said metal oxide is indium oxide. 13. The carbon dioxide sensor according to claim 1, wherein said metal oxide layer is porous. 14. The carbon dioxide sensor according to claim 1, wherein said current collector is a porous metal. 15. The collector according to claim 1, wherein the current collector is provided to face the solid electrolyte with the metal oxide layer interposed therebetween.
Any of the carbon dioxide sensors. 16. The carbon dioxide sensor according to claim 1, wherein said detection electrode and said counter electrode are provided on the same surface of said solid electrolyte. 17. The carbon dioxide sensor according to claim 1, wherein the counter electrode contains at least one of a metal and a metal oxide. 18. The method according to claim 1, wherein the metal bicarbonate and / or the metal carbonate is mixed with a metal salt having water of crystallization at a temperature of room temperature to 100 ° C. by forming a mixture layer of these compounds on the surface of the solid electrolyte. The carbon dioxide sensor according to any one of claims 1 to 17, which is interposed. 19. The method according to claim 19, wherein the metal bicarbonate and / or metal carbonate and a metal salt having water of crystallization at a temperature of room temperature to 100 ° C. are used as a solution or paste of these compounds.
The carbon dioxide sensor according to any one of claims 12 to 17, wherein the sensor is interposed by passing through a porous metal oxide layer and a porous current collector provided on the solid electrolyte and reaching the surface of the solid electrolyte.