JP2002221509A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor having excellent durability. SOLUTION: In this gas sensor, a detection part 3 has a detection electrode 5 including a detection electrode reaction layer 51 and a detection electrode gas diffusion layer 52; a counter electrode 6 including a counter electrode reaction layer 61 and a counter electrode gas diffusion layer 62; and an electrolyte layer 4 provided between them, contacting with the detection electrode reaction layer 51 and the counter electrode reaction layer 61. The detection electrode reaction layer 51 has a function oxidizing CO and/or H2 in a test gas and is disposed with plural detection electrode reaction layer units 511 mainly composed of a catalyst promoting oxidization of CO and/or H2 apart from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a gas sensor for measuring the CO concentration of the H ₂ rich subject gas.

[0002]

2. Description of the Related Art A conventional CO gas sensor has a detection unit having a detection electrode and a counter electrode arranged via an electrolyte layer.

In this CO gas sensor, for example, CO is adsorbed and oxidized on a detection electrode, and the CO concentration in the test gas is measured from the obtained current value.

Further, in the conventional CO gas sensor, the detection electrode and the counter electrode are each made of a material in which a catalyst is supported on a carrier and formed in a flat plate shape.

[0005] Such a CO gas sensor may be used by bringing a test gas of high temperature and high humidity into contact with a detection unit. Each member constituting the detection unit is exposed to the humidity change and repeats expansion and contraction.

Accordingly, in the conventional CO gas sensor,
For example, there is a problem that the catalyst is dropped from the carrier at the detection electrode or the counter electrode, or the detection electrode or the counter electrode is separated from the electrolyte layer, and as a result, the sensor output (measurement accuracy) is reduced.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a gas sensor having excellent durability.

[0008]

This and other objects are achieved by the present invention which is defined below as (1) to (13).

(1) It has a detection electrode reaction layer for reacting a predetermined component in a test gas, a counter electrode reaction layer provided opposite to the detection electrode reaction layer, and an electrolyte layer provided therebetween. A gas sensor comprising a detection unit, wherein the detection electrode reaction layer is formed by disposing a plurality of detection electrode reaction layer units mainly composed of a catalyst via a gap.

(2) The gas sensor according to (1), wherein a concave portion reaching the inside of the electrolyte layer is formed, and the concave portion forms the gap of the detection electrode reaction layer.

(3) On the detection electrode reaction layer side of the electrolyte layer, a plurality of irregularities are formed, and each of the detection electrode reaction layer units is provided on a convex portion of the electrolyte layer. The gas sensor according to 1) or 2).

(4) The ratio of the area occupied by the gap to the entire area of the detection electrode reaction layer when viewed from a direction perpendicular to the detection electrode reaction layer is 0.01 to 60%. The gas sensor according to any one of (1) to (3).

(5) The gas sensor according to any one of (1) to (4), wherein the detection electrode reaction layer is formed on the electrolyte layer.

(6) The gas sensor according to any one of the above (1) to (5), wherein the counter electrode reaction layer is made of a material containing a catalyst.

(7) The gas sensor according to (6), wherein the catalyst of the counter electrode reaction layer is carried on a carrier.

(8) The gas sensor according to any one of (1) to (7), wherein the specific surface area of the counter electrode reaction layer is 10 to 1000 times the specific surface area of the detection electrode reaction layer.

(9) The method according to any one of (1) to (8), wherein a gas diffusion layer is provided on each of the detection electrode reaction layer and the counter electrode reaction layer on a side opposite to the electrolyte layer. Gas sensor.

(10) The gas sensor according to any one of (1) to (9), wherein the electrolyte layer is formed of an ion exchange resin.

(11) The gas sensor according to any one of (1) to (10), further including a control unit that controls a voltage applied to the detection unit.

(12) The gas sensor according to any one of (1) to (11), further including a gas sampling container for sampling the test gas, wherein the detection unit is provided in the gas sampling container.

(13) The gas sensor according to any one of (1) to (12), which is used for measuring a CO concentration in the test gas.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventor has conducted intensive studies to solve the above problems, and as a result, has found that a gas sensor (C
In the case of the O gas sensor), when the catalyst in the detection electrode reaction layer (detection electrode) drops off from the carrier and the detection electrode reaction layer separates from the electrolyte layer, a significant decrease in sensor output (measurement accuracy) occurs. As a result, the present invention has been completed.

Hereinafter, a gas sensor according to the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings. In the following, CO (carbon monoxide) is used as a predetermined component in the test gas.
The case where is measured will be described.

First, before describing the gas sensor of the present invention, a fuel cell system will be described as an example of a system incorporating and using the gas sensor of the present invention.

FIG. 6 is a schematic diagram showing the overall configuration of the fuel cell system. Fuel cell system 100 shown in FIG.
Are a methanol tank 110, a water / methanol tank 120, a reformer 130, a CO remover 140,
It includes a fuel cell 150 and the gas sensor 1 of the present invention.

The methanol tank 110 stores the raw material methanol, while the water / methanol tank 120 stores the raw water / methanol mixed solution.

The methanol tank 110 and the water / methanol tank 120 are respectively provided with a pump 111,
It is connected to the reformer 130 via 121.

In this reformer 130, the raw materials introduced from the methanol tank 110 and the water / methanol tank 120 are reformed into a reformed gas containing about 75% of hydrogen gas.

The reformed gas is sent to a CO removing device 140 connected to the reforming device 130, and a part of the reformed gas is a bypass line in which a line connecting the reforming device 130 and the CO removing device 140 is branched. Gas sensor 1 installed on top
And the CO concentration in the reformed gas is measured.

The CO removal device 140 processes the reformed gas based on the measurement result of the CO concentration in the reformed gas by the gas sensor 1. As a result, CO is removed from the reformed gas, and the processed reformed gas is supplied as hydrogen gas fuel to the fuel cell 150 connected to the CO removal device 140.
Then, the fuel cell 150 generates electricity using the hydrogen gas fuel.

By using such hydrogen gas fuel, the power generation efficiency of the fuel cell 150 is improved.

Next, the gas sensor of the present invention will be described. FIG. 1 is a schematic diagram showing the entire configuration of the gas sensor of the present invention, and FIG. 2 is an enlarged cross-sectional view showing the configuration of a detection unit provided in the gas sensor of the present invention.

A gas sensor 1 shown in FIG. 1 includes a gas sampling container 2 for sampling a test gas therein, a detection unit 3 installed in the gas sampling container 2, and a control for controlling a voltage applied to the detection unit 3. And a unit 7. Hereinafter, each component will be described.

The gas collection container 2 has a housing 21 and a lid 22. The housing 21 has a space 211 formed therein, and a detection unit 3 described below is installed in the space 211. In the gas sensor 1, a test gas is introduced (purged) into the space 211, and the CO concentration in the test gas is measured.

In the space 211, the gas collection container 2 is provided.
Water is stored to keep the (space 211) in a humidified state. The humidity in the space 211 is not particularly limited, but is preferably, for example, about 30 to 100% RH.

Instead of holding the inside of the gas sampling container 2 in a humidified state, a humidified test gas may be introduced into the gas sampling container 2.

The housing 21 is provided with a flat lid 22 so as to hermetically close the upper opening. The test gas is supplied to the lid 22 in the gas collection container 2 (space 211).
An introduction line (introduction means) 23 for introducing the gas into the inside and an exhaust line (exhaust means) 24 for exhausting the test gas from the gas sampling container 2 are provided.

The introduction line 23 is provided with a pressure adjusting device 23 for adjusting the pressure in the gas sampling container 2 on the way.
1 is installed, and the end of the introduction line 23 is connected to the reformer 130 described above.

On the other hand, the end of the exhaust line 24 is connected to the above-described CO removing device 140.

The gas sampling container 2 (housing 21 and lid 22) is made of various resin materials such as polycarbonate, polymethyl methacrylate, polyimide, polysulfone, and polyphenylene sulfide, aluminum or aluminum alloy, stainless steel, titanium Alternatively, it can be made of various metal materials such as a titanium alloy, various ceramic materials, various glass materials, and the like.

The detection unit 3 is provided in the gas collection container 2 (space 211). As shown in FIG. 2, the detection unit 3 includes a detection electrode 5 including a detection electrode reaction layer 51 and a detection electrode gas diffusion layer 52, a counter electrode reaction layer 61, and a counter electrode gas diffusion layer 6.
2 and an electrolyte layer 4 disposed between them and in contact with the detection electrode reaction layer 51 and the counter electrode reaction layer 61.

In the detection section 3, when the test gas comes into contact, the detection electrode reaction layer 51 adsorbs a predetermined component (CO and / or H _{2 in the} present embodiment) in the test gas to oxidize (react). ), In the counter electrode reaction layer 61, the hydrogen ions (H ⁺ ) generated by the oxidation reaction and the electrons (e ⁻ ) are reassociated (the hydrogen ions are reduced). At this time, a response current (hereinafter, referred to as “CO”) obtained by an oxidation
Ionization current. " ) Or, indirectly,
The response current obtained by the oxidation reaction of H ₂ (hydrogen)
It referred to as "H ₂ ionization current". ) Is measured over time (decrease) over time in accordance with the adsorption of CO to the detection electrode reaction layer 51, whereby the CO concentration in the test gas can be measured.

The specific method of measuring the CO concentration in the test gas using the gas sensor 1 (how to use the gas sensor 1: operation) will be described later.

The electrolyte layer 4 has a function as a transfer medium for hydrogen ions, and has a film shape (layer shape).

The electrolyte layer 4 is formed by adding an electrolyte solution such as a proton conductive ion exchange resin (solid electrolyte) such as Nafion (registered trademark) or sulfuric acid to a water-retentive material (eg, woven fabric, nonwoven fabric, paper, etc.). Although it can be constituted by impregnated (supported) or the like, among them, it is preferable to be constituted by a proton conductive ion exchange resin which is easy to handle and has a wide use environment condition.

As a result, in the gas sensor 1, the measurement accuracy can be further improved, and the response time (measurement time) can be further shortened.

The average thickness of the electrolyte layer 4 is not particularly limited, but is preferably, for example, about 1 to 1000 μm, and more preferably about 10 to 100 μm. Thereby, the electrolyte layer 4 can more suitably exhibit the above-described effects.

On one surface (left side in FIG. 2) of the electrolyte layer 4, a detection electrode 5 having a film shape (layer shape) as a whole is joined (installed).

The detection electrode 5 has a detection electrode reaction layer 51 on the electrolyte layer 4 side, and a detection electrode gas diffusion layer 52 joined to the detection electrode reaction layer 51.

The detection electrode reaction layer 51 has a function of oxidizing CO and / or H ₂ in the test gas.
A plurality of detection electrode reaction layer units 511 mainly composed of a catalyst for promoting the oxidation of CO and / or H ₂ are provided (arranged).

The detection electrode reaction layer units 511 are provided (arranged) via a gap (micro gap) 512, that is, at a predetermined interval.

The detection electrode reaction layer 51 (detection electrode reaction layer unit 51)
1) is mainly constituted by a catalyst, that is, by adopting a structure in which a catalyst is not supported on a carrier, the conventional C
Desorption of the catalyst from the carrier, which is one of the causes of a decrease in the sensor output (measurement accuracy) of the O gas sensor, can be prevented, and excellent durability can be obtained in the detection unit 3 (gas sensor 1).

Further, since the detection electrode reaction layer 51 is composed of a plurality of detection electrode reaction layer units 511 provided through the gap 512, stress (deformation) due to expansion and contraction of the electrolyte layer 4 is reduced. The effect on the layer 51 can be reduced. Thereby, it is possible to suitably prevent (or reduce) the separation of the detection electrode reaction layer 51 from the electrolyte layer 4 which is one of the causes of a decrease in the sensor output of the conventional CO gas sensor. In), excellent durability can be obtained.

Further, in the detecting section 3 (gas sensor 1),
The durability can be remarkably improved by the synergistic effect of the combination of these configurations.

From such a viewpoint, the detection electrode reaction layer 51
When viewed from a direction perpendicular to (from the left side in FIG. 2), the ratio of the area occupied by the gap 512 to the entire area of the detection electrode reaction layer 51 is not particularly limited.
It is preferably about 1 to 60%, and more preferably about 1 to 30%. Thereby, the detection electrode reaction layer 51
In this case, the diffusion of CO becomes better, the sensitivity to CO is improved, and the separation of the detection electrode reaction layer 51 from the electrolyte layer 4 can be suitably prevented (or reduced).

The shape of the detection electrode reaction layer unit 511 is as follows:
There is no particular limitation, and any one may be used. That is, the shape of the gap 512 is not particularly limited, and may be any shape. However, it is preferable that the gap 512 be formed of a groove. They are arranged so as to be substantially orthogonal (to form a grid).

The detection electrode reaction layer unit 511 (detection electrode reaction layer 5
Examples of the catalyst constituting 1) include platinum (Pt),
Metals such as gold (Au), copper (Cu), nickel (Ni), palladium (Pd), silver (Ag), rhodium (Rh), ruthenium (Ru), or at least one of these metals
One or more of alloys including seeds can be used in combination.

In such a detection electrode reaction layer 51, for example, the average thickness thereof is preferably 0.01 to 1000 μm.
m, more preferably about 0.1 to 1 μm, and the amount of catalyst present per 1 cm ² of the surface of the electrolyte layer 4 is preferably about 0.01 to 50 μg,
More preferably, the amount is about 0.1 to 20 μg.
When the detection electrode reaction layer 51 is too thin (that is, when the amount of the catalyst is too small), the CO ionization current and / or the H ₂ ionization current decrease depending on the type of the catalyst, and the like.
It may be difficult to measure. On the other hand, the detection electrode reaction layer 51
When the thickness is larger than the upper limit (that is, the amount of the catalyst is larger than the upper limit), the sensitivity to CO may decrease.

The electrolyte layer 4 of such a detection electrode reaction layer 51
On the opposite side, the detection electrode gas diffusion layer 5 in the form of a film (layer) is provided.
2 are joined (installed).

The detection electrode gas diffusion layer 52 has a function of diffusing the test gas and reducing unevenness of CO and / or H ₂ contacting the detection electrode reaction layer 51. The detection electrode gas diffusion layer 52 also has a function of giving electrons generated in the detection electrode reaction layer 51 to the control unit 7 described later. Further, the detection electrode gas diffusion layer 52 also has a function of improving the strength of the detection unit 3.

The detection electrode gas diffusion layer 52 is made of, for example, a porous conductive material typified by a porous carbon material such as carbon fiber fabric (for example, carbon cloth, carbon felt, etc.) and carbon paper. be able to. Thereby, the detection electrode gas diffusion layer 52 can more suitably exhibit the above-described function.

Among them, the detection electrode gas diffusion layer 52 is
Made of carbon fiber fabric such as carbon cloth and carbon felt
It is preferred that it is implemented. Carbon fiber fabrics are
And H _TwoIs excellent in the diffusion property of the
It is also excellent.

The average thickness of the detection electrode gas diffusion layer 52 is not particularly limited, but may be, for example, 50 to 2000 μm.
It is preferably about 100 μm, more preferably about 100 to 800 μm. If the detection electrode gas diffusion layer 52 is too thin, the strength of the detection unit 3 cannot be maintained at a suitable level depending on the degree of porosity of the detection electrode gas diffusion layer 52, the constituent materials, and the like, or the detection electrode The unevenness of the electrical contact of CO and / or H ₂ to the catalyst of the reaction layer 51 may be significant. On the other hand, if the detection electrode gas diffusion layer 52 is too thick, depending on the degree of porosity of the detection electrode gas diffusion layer 52, etc., the CO and / or H ₂ can be efficiently contacted (attained) with the detection electrode reaction layer 51. May not be possible. Note that the detection electrode gas diffusion layer 52 can be omitted as necessary.

A counter electrode 6 having a film shape (layer shape) as a whole is joined (installed) to the opposite side (the right side in FIG. 2) of the detection electrode 5 via the electrolyte layer 4.

The counter electrode 6 has a counter electrode reaction layer 61 on the electrolyte layer 4 side and a counter electrode gas diffusion layer 62 joined to the counter electrode reaction layer 61.

The counter electrode reaction layer 61 has a function of re-associating (reducing hydrogen ions) electrons with hydrogen ions generated by the oxidation reaction of CO and / or H ₂ in the detection electrode reaction layer 51.

The counter electrode reaction layer 61 can be made of, for example, a material containing a catalyst for promoting the reduction of hydrogen ions.

As the catalyst, the detection electrode reaction layer 51 is used.
Although it is possible to use the same catalyst as mentioned in the above section, it is preferable to use a catalyst which is hardly poisoned by CO, for example, a platinum-ruthenium alloy (Pt-Ru).

The detection electrode reaction layer 51 and the counter electrode reaction layer 61
Because each has a different function and role,
The catalyst of the detection electrode reaction layer 51 and the catalyst of the counter electrode reaction layer 61 are:
Preferably they are different. As a result, the detection electrode reaction layer 51 and the counter electrode reaction layer 61 exert their respective functions and roles, and as a result, in the gas sensor 1, the measurement accuracy is further improved and the measurement time is further shortened. Can be.

The material of the counter electrode reaction layer 61 preferably has, for example, a structure in which a powder (particle) catalyst is supported on a carrier. Thereby, in the obtained counter electrode reaction layer 61, the specific surface area of the catalyst can be increased, and the hydrogen ion reduction efficiency is further improved.

In this case, the average particle size of the catalyst is not particularly limited, but is preferably, for example, about 0.1 to 1000 nm. Thereby, the specific surface area of the catalyst can be further increased.

As the carrier for supporting the catalyst, for example, a carbon material (carbon material having a high specific surface area) such as carbon powder, carbon fiber (carbon fiber), and a mixture thereof can be used. Such a carbon material is excellent in a catalyst supporting force.

When a powdery carrier such as carbon powder is used as the carrier, the average particle size of the carrier is not particularly limited, but is preferably, for example, about 0.01 to 1 μm. Thereby, the carrier can support the catalyst so that the catalyst can exhibit excellent catalytic activity.

Further, the material of the electrolyte layer 4 may be mixed with the material of the counter electrode reaction layer 61, if necessary. Thereby, the electrolyte layer 4 and the counter electrode reaction layer 61
And the adhesiveness with the adhesive can be improved.

The content of the catalyst in the material of the counter electrode reaction layer 61 (the amount of the supported catalyst) is appropriately set depending on the type of the catalyst and / or the carrier, and is not particularly limited.
８０80 wt%, preferably 10-50 wt%.
% Is more preferable. When the content of the catalyst is less than the lower limit, depending on the type of the catalyst, the counter electrode reaction layer 61 cannot sufficiently reduce the hydrogen ions, and the gas sensor 1
Measurement accuracy may decrease. On the other hand, even if the content of the catalyst is increased beyond the upper limit, the gas sensor 1
No further improvement in measurement accuracy can be obtained. Further, in this case, the cost of the catalyst is high, and the gas sensor 1
It is not preferable because the whole manufacturing cost increases.

When the above-mentioned carrier is contained in the material of the counter electrode reaction layer 61, the content of the carrier is appropriately set depending on the type of the catalyst and / or the carrier, and is not particularly limited. It is preferably about 60 wt%, more preferably about 10 to 50 wt%. Thereby, the catalyst can be more appropriately supported on the carrier. In addition, the electrons can move more quickly in the counter electrode reaction layer 61.

The specific surface area of the counter electrode reaction layer 61 is as follows:
Although not particularly limited, for example, it is preferably about 10 to 1000 times the specific surface area of the detection electrode reaction layer 51,
It is preferably about 0 to 1000 times. This allows
The counter electrode reaction layer 61 is less likely to be poisoned by CO, and can more stably perform a reduction reaction of hydrogen ions. For this reason,
There is an advantage that the potential control of the detection electrode 5 can be performed more accurately.

[0078] More specifically, the specific surface area of the counter electrode reaction layer 61 is preferably a 5~300cm ² / cm ² or so. Thereby, the hydrogen ion reduction efficiency is further improved.

In such a counter electrode reaction layer 61, for example,
The average thickness is preferably about 2 to 1000 μm, more preferably about 5 to 500 μm, and the amount of the catalyst existing per 1 cm ² of the surface of the electrolyte layer 4 is 0.05 to 5 μm.
The amount is preferably on the order of mg, and more preferably on the order of 0.1 to 1 mg. If the counter electrode reaction layer 61 is too thin (that is, if the amount of the catalyst is too small),
Depending on the material of the counter electrode reaction layer 61 (particularly, the type of catalyst), the reduction efficiency of hydrogen ions may decrease. On the other hand, even if the thickness of the counter electrode reaction layer 61 is thicker than the upper limit (that is, the amount of the catalyst is larger than the upper limit), the reduction efficiency of hydrogen ions cannot be further improved. .

On the surface of the counter electrode reaction layer 61 opposite to the electrolyte layer 4, a film-shaped (layered) counter gas diffusion layer 6 is formed.
2 are joined (installed).

The counter electrode gas diffusion layer 62 has a function of efficiently releasing H ₂ generated by the reduction of hydrogen ions in the counter electrode reaction layer 61. The counter electrode gas diffusion layer 62 also has a function of giving electrons supplied via the control unit 7 described later to the counter electrode reaction layer 61. further,
The counter electrode gas diffusion layer 62 also has a function of improving the strength of the detection unit 3.

The counter electrode gas diffusion layer 62 can have the same configuration (material, thickness, etc.) as the detection electrode gas diffusion layer described above. The counter electrode gas diffusion layer 62 can be omitted as necessary.

In the detection section 3, a wiring 74 is connected to the detection electrode gas diffusion layer 52, and a wiring 75 is connected to the counter electrode gas diffusion layer 62, thereby connecting the control section 7.

The control section 7 has a power supply 71, a voltage changing circuit 72, and an ammeter 73.
In 2, the voltage applied to the detection unit 3 is controlled, and in the ammeter 73, the detection electrode 5 (detection electrode reaction layer 51) and the counter electrode 6 (counter electrode reaction layer 61) are caused by the redox reaction in the detection unit 3. And measure the response current generated between them.

In such a gas sensor 1, for example, a pulse method in which a pulse voltage is applied from the control unit 7 to the detection unit 3 to change the potential of the detection electrode reaction layer 51 between two potentials, Applying a continuously changing voltage to 3
At this time, a detection electrode 5 (detection electrode reaction layer 51) and a counter electrode 6 are used by using a potential regulation method such as a cyclic voltammetry method in which the potential of the detection electrode reaction layer 51 is continuously changed.
(Control electrode 7)
Measured in The CO concentration in the test gas is measured based on the measured value of the response current.

Next, a method of measuring the CO concentration in the test gas using the gas sensor 1 (how to use the gas sensor 1: operation)
Will be described with reference to a case where a pulse method is used as a potential regulation method.

First, a test gas is supplied into the space 211 of the gas sampling container 2 via the introduction line 23. in this case,
It is preferable that the test gas be supplied under pressure and flow rate adjusted by the pressure adjusting device 231. Thereby, the contact efficiency of the test gas with the detection unit 3 can be further improved.

As the supply pressure of the test gas, for example,
It is preferred to be about 0.5 to 5.0 kgf / cm ² .

The supply rate of the test gas is, for example, 5
It is preferably set to about 0 to 150 L / min.

Further, a heater (not shown) is provided in the gas sampling container 2 so that the temperature in the space 211 can be adjusted. This temperature, that is, the measurement temperature of the test gas is not particularly limited.
The temperature is preferably set to about 00 ° C.

Next, a pulse voltage is applied from the control unit 7 to the detection unit 3. Thus, the potential of the detection electrode reaction layer 51 (detection electrode 5) is set at two potentials, namely, a CO oxidation potential at which CO can be adsorbed and oxidized, and a CO adsorption potential at which CO is adsorbed but no CO oxidation reaction occurs. Vary between. The CO oxidation potential and the CO adsorption potential vary depending on the type of the catalyst constituting the detection electrode reaction layer 51. When, for example, platinum is used as the catalyst, for example,
It is set to about 0.65 to 1.5V and about 0.05 to 0.43V.

FIG. 3 shows the potential of the detection electrode reaction layer as C
An example of a temporal change (change) of the response current when the O-oxidation potential and the CO adsorption potential are changed in a pulsed manner is shown.

When the detection electrode reaction layer 51 is maintained at the CO oxidation potential, the reaction of the following formulas (i) and (ii) occurs in the detection electrode reaction layer 51 by the action of a catalyst.

[0094] _{^{H 2 → 2H + + 2e -}} ··············· (i) CO + H 2 O → CO 2 + 2H + + 2e - ··· (ii)

The electrons generated in the detection electrode reaction layer 51 are supplied to the detection electrode gas diffusion layer 52, the control unit 7, and the counter electrode gas diffusion layer 62.
And moves to the counter electrode reaction layer 61. At this time, the electrons are measured by the ammeter 73 of the control unit 7 as a response current. That is, at the CO oxidation potential, the CO ionization current and the H ₂ ionization current are measured as response currents.

In the counter electrode reaction layer 61, the reaction of the following formula (iii) is caused by the action of the catalyst between the electrons transferred from the detection electrode reaction layer 51 and the hydrogen ions transferred via the electrolyte layer 4.

2H ⁺ + 2e ⁻ → H ₂ (iii)

On the other hand, when the detection electrode reaction layer 51 is maintained at the CO adsorption potential, the above equation (ii), which is a CO oxidation reaction, does not occur in the detection electrode reaction layer 51.

[0099] Thus, the ammeter 73, the H ₂ ionization current is measured as a response current in accordance with the H ₂ ionization current over time, detected electrode reaction layer 51
As the amount of CO adsorbed on the electrode increases, the detection electrode reaction layer 51
The adsorption of H _{2 on} the surface is inhibited and the H ₂ decreases (changes).

Such a decrease in the H ₂ ionization current occurs almost simultaneously (or continuously) with decreasing (changing) the potential of the detection electrode reaction layer 51 from the CO oxidation potential to the CO adsorption potential. The reduction rate of this H ₂ ionization current (ΔI in FIG. 3)
/ T), the CO concentration in the test gas can be measured.

More specifically, in a standard gas having a known CO concentration, a calibration curve between the CO concentration and the reduction rate of the H ₂ ionization current is prepared in advance, and the calibration curve is obtained in the test gas. By applying the measured value of the reduction rate of the H ₂ ionization current, the CO concentration in the test gas can be measured.

The detection section 3 provided in the gas sensor 1 described above can be manufactured, for example, as follows.

<1> First, an electrolyte layer 4 made of, for example, Nafion is prepared.

<2> Next, a plurality of detection electrode reaction layer units 511 are formed on one surface of the electrolyte layer 4. This can be done as follows.

First, the material of the detection electrode reaction layer 51 made of, for example, platinum or the like is coated on one surface of the electrolyte layer 4 by, for example,
A film (thick film or thin film) is obtained by various film forming methods such as sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), and molecular beam epitaxy (MBE).

The film forming conditions are different depending on various film forming methods and are not particularly limited. For example, when a sputtering method is used, the temperature of the electrolyte layer 4 (sample) is set to 5 to 30.
℃, Ar gas (inert gas) pressure is 1 × 10 ^-3 ~
1.5 × 10 ^-2 Torr, plasma output 10-1
It is preferable to set the plasma irradiation time to about 50 W and the plasma irradiation time to about 10 to 120 seconds.

Next, a mask layer having a desired pattern shape (in this embodiment, a mask layer in which a plurality of grooves arranged at substantially equal intervals and substantially perpendicular to each other) is formed on the surface (upper surface) of the film. After that, a part of the film is removed by performing various etching processes such as a plasma etching process, a wet etching process, a reactive ion etching process, a beam etching process, and a light assisted etching process.

The processing conditions are different for various etching processes and are not particularly limited. For example, when a plasma etching process is used, the temperature of the laminate (sample) of the coating film and the electrolyte layer 4 is set to about 5 to 30 ° C. Ar gas (inert gas) pressure is 1 × 10 ^{−3 to} 1.5 × 10 ⁻² Torr
Preferably, the plasma output is about 10 to 150 W, and the plasma irradiation time is about 10 to 300 seconds. After that, the mask layer is removed from the surface of the electrolyte layer 4.

As described above, by forming the detection electrode reaction layer 51 directly on the electrolyte layer 4, the adhesion between the detection electrode reaction layer 51 and the electrolyte layer 4 can be improved. Separation from the electrolyte layer 4 can be more reliably prevented (or reduced).

From such a viewpoint, prior to the film forming operation by the above-mentioned various film forming methods, the surface of the electrolyte layer 4 is subjected to, for example, chemical treatment (for example, acid treatment such as hydrochloric acid treatment), shot blasting, or the like. The surface may be roughened by a method such as sandblasting. This allows
The adhesion between the detection electrode reaction layer 51 and the electrolyte layer 4 can be further improved.

<3> Next, a counter electrode reaction layer 61 is formed on the other surface of the electrolyte layer 4 (the surface opposite to the detection electrode reaction layer 51). This can be done as follows.

First, for example, a carbon powder (carrier) supporting, for example, a platinum-ruthenium alloy (catalyst of the counter electrode reaction layer 61) is ultrasonically dispersed in a solution containing, for example, Nafion (proton conductive resin). Counter electrode reaction layer 61
Prepare the ingredients for

Next, the material of the counter electrode reaction layer 61 is applied to, for example, a polytetrafluoroethylene (PTFE) sheet (substrate) by, for example, various coating methods such as spin coating, brush coating, doctor blade, and roll coater. After applying and drying, heat treatment is performed. The heat treatment conditions are not particularly limited. For example, the treatment temperature is set to 8 under reduced pressure (for example, about 10 ^{−6 to} 5 × 10 ² Torr).
It is preferable to set the temperature to about 0 to 150 ° C. and the processing time to about 1 to 5 hours. Thereby, the counter electrode reaction layer 61 is obtained on the PTFE sheet.

Next, the counter electrode reaction layer 61 is connected to the electrolyte layer 4.
And subjected to a heat and pressure (hot press) treatment. Thereby, the counter electrode reaction layer 61 is joined to the other surface of the electrolyte layer 4. The processing conditions are not particularly limited. For example, the heating temperature is preferably about 100 to 200 ° C., and the pressure is preferably about 50 to 150 kgf / cm ² . Thereafter, the PTFE sheet is removed from the counter electrode reaction layer 61.

<4> Next, the surfaces of the detection electrode reaction layer 51 and the counter electrode reaction layer 61 on the side opposite to the electrolyte layer 4 are respectively
For example, the detection electrode gas diffusion layer 52 such as a carbon cloth and the counter electrode gas diffusion layer 62 are joined to complete the detection unit 3.

In this method, a laminate of the detection electrode reaction layer 51, the electrolyte layer 4, and the counter electrode reaction layer 61 is combined with the detection electrode gas diffusion layer 52.
The heating and pressurizing (hot pressing) treatment can be performed by sandwiching the gas diffusion layer 62 and the counter electrode gas diffusion layer 62. The processing conditions are not particularly limited. For example, the heating temperature is about 100 to 200 ° C., and the pressurizing pressure is 50 to 15
Preferably, the pressure is about 0 kgf / cm ² . Through the steps described above, the detection unit 3 is manufactured.

Next, another example of the configuration of the detection unit provided in the gas sensor of the present invention will be described. FIG. 4 is an enlarged cross-sectional view illustrating another configuration of the detection unit.

Hereinafter, the detection unit 3 'shown in FIG.
The following description focuses on differences from the detection unit 3, and a description of similar items will be omitted.

The detector 3 'shown in FIG. 4 differs from the detector 3 in the structure of the electrolyte layer 4 except for the above.

That is, the detection electrode reaction layer 51 of the electrolyte layer 4
On the side, a plurality of irregularities (the concave portion 41 and the convex portion 42) are formed, and the detection electrode reaction layer unit 511 is provided on the convex portion 42, respectively. In other words, a concave portion reaching the inside of the electrolyte layer 4 is formed, and the concave portion forms a gap 512 of the detection electrode reaction layer 51.

With such a configuration, the generation of stress (deformation) due to expansion and contraction of the electrolyte layer 4 can be reduced, and the influence of this stress on the detection electrode reaction layer 51 can be further reduced. Separation of the detection electrode reaction layer 51 from the electrolyte layer 4 is more suitably prevented (or reduced), and more excellent durability is obtained in the detection unit 3 '.

The shape of the detection electrode reaction layer unit 511 is as follows.
There is no particular limitation, and any one may be used. That is, the shape of the concave portion 41 (the gap 512) is not particularly limited, and may be any shape. However, it is preferable that the concave portion 41 is formed of a groove. They are arranged so as to be substantially equally spaced and substantially orthogonal (to form a grid). Such a detecting unit 3 ′
For example, it can be manufactured as follows.

<1 ′> First, an electrolyte layer 4 made of, for example, Nafion is prepared.

<2 ′> Next, a plurality of irregularities are formed on one surface of the electrolyte layer 4. This can be done as follows.

First, on the surface (upper surface) of the electrolyte layer 4, a mask layer having a desired pattern shape (in the present embodiment, a mask layer in which a plurality of grooves arranged at substantially equal intervals and substantially perpendicular to each other) is formed. Is formed, for example, various etching processes such as a plasma etching process, a wet etching process, a reactive ion etching process, a beam etching process, and a photo-assisted etching process are performed to remove a part of the electrolyte layer 4. .

The processing conditions are different for various etching processes and are not particularly limited. For example, when plasma etching is used, the temperature of the electrolyte layer 4 (sample) is about 5 to 30 ° C., and Ar gas (inert gas) is used. ) Pressure of about 1 × 10 ^{−3 to} 1.5 × 10 ⁻² Torr, plasma output of about 10 to 300 W, plasma irradiation time of 10 to 3
It is preferably set to about 00 seconds. After that, the mask layer is removed from the surface of the electrolyte layer 4.

Next, the material of the detection electrode reaction layer 51 made of, for example, platinum or the like is used, for example, by sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), or molecular beam epitaxy (MBE). It is formed in a film shape (thick film or thin film) by various various film forming methods and the like.

The conditions for the film formation differ depending on various film formation methods and are not particularly limited. For example, when a sputtering method is used, the temperature of the electrolyte layer 4 (sample) is set to 5 to 30.
℃, Ar gas (inert gas) pressure is 1 × 10 ^-3 ~
1.5 × 10 ^-2 Torr, plasma output 10-1
It is preferable to set the plasma irradiation time to about 50 W and the plasma irradiation time to about 10 to 300 seconds.

Thus, a plurality of detection electrode reaction layer units 51
1 is formed on one surface of the electrolyte layer 4 corresponding to the plurality of protrusions 41.

<3 ′> The same step as the step <3> is performed.

<4 ′> The same step as the step <4> is performed. Through the steps described above, the detection unit 3 'is manufactured.

Although the gas sensor according to the present invention has been described based on the illustrated embodiment, the present invention is not limited to this. Each component of the gas sensor can be replaced with any component that can exhibit the same function.

For example, if necessary, the gas collection container
In this case, for example, the detection unit can be directly installed and used in a flow path of exhaust gas discharged from an internal combustion engine, a combustion furnace, or the like.

Also, for example, between the detection electrode gas diffusion layer and the detection electrode reaction layer, between the detection electrode reaction layer and the electrolyte layer, between the electrolyte layer and the counter electrode reaction layer, and between the counter electrode reaction layer and the counter electrode gas diffusion layer. And an intermediate layer may be provided between them.

In the above embodiment, the gas sensor is used to
Although the case where the CO concentration in the test gas is measured has been described, for example, the potential of the detection electrode reaction layer (eg, CO ₂ reduction potential), the type of catalyst of the detection electrode reaction layer, or the constituent material of the electrolyte layer (eg, The gas sensor of the present invention is also used for measuring the concentration of gas components other than CO by appropriately changing the oxygen ion conductive ion exchange resin or the like, or by appropriately combining them. be able to.

[0136]

Next, specific examples of the present invention will be described.

(Example 1) First, as shown in FIG.
The detection unit shown in FIG.

<Structure of the detection section> Detection electrode Detection electrode reaction layer-Constituent material: platinum-Average thickness: 0.2 µm (amount of platinum present on the electrolyte layer: 20 µg / cm ² )-Perpendicular to the detection electrode reaction layer Ratio of the area occupied by the gap to the entire area of the detection electrode reaction layer when viewed from various directions: 1% ・ Specific surface area: 1 cm ² / cm ² Detection electrode gas diffusion layer ・ Constituent material: carbon cloth ・ Average thickness: 500 μm Electrolyte layer • Constituent material: Nafion 112 (manufactured by Du Pont) • Average thickness: 50 μm Counter electrode Counter electrode reaction layer • Constituent material: Platinum-ruthenium alloy (average particle size 5 nm)
26 wt% carbon powder (average particle diameter 75 nm) 40 wt% Nafion (manufactured by Aldrlich) 34 wt% ・ Average thickness: 20 μm (amount of platinum-ruthenium alloy present on the electrolyte layer 0.5 mg / cm ² ) ・ Specific surface area: 100 cm ² / cm ² counter electrode gas diffusion layer ・ Constituent material: carbon cloth ・ Average thickness: 500 μm

<Preparation of Detection Section> -1- A detection electrode reaction layer (detection electrode reaction layer unit) having the above-described structure was formed on one surface of the electrolyte layer.

First, a platinum film was formed by a sputtering method so that the amount of platinum deposited was 40 μg / cm ² . Note that the sputtering method was performed under the following conditions.

Sample temperature: 25 ° C., Ar gas pressure: 7
× 10 ^-3 Torr, plasma output: 100 W, plasma irradiation time: 60 seconds

Next, after forming a mask layer in which a plurality of grooves were provided at equal intervals and orthogonally on the surface of the platinum film, the portion of the platinum film where the mask layer was not formed was removed by plasma etching. Note that the plasma etching treatment was performed under the following conditions. Thereafter, the mask layer was removed.

Sample temperature: 25 ° C., Ar gas pressure: 7
× 10 ^-3 Torr, plasma output: 100 W, plasma irradiation time: 60 seconds

-2- A counter electrode reaction layer having the above structure was formed on the other surface of the electrolyte layer. First, a carbon powder carrying a platinum-ruthenium alloy was ultrasonically dispersed in a 5 wt% Nafion solution so as to have the above composition ratio to prepare a material for the counter electrode reaction layer.

Next, such a material is placed on a PTFE sheet.
Apply and dry by brush coating (coating method),
(Torr) at 130 ° C. for 3 hours. The counter electrode reaction layer formed on such a PTFE sheet was brought into contact with the other surface of the electrolyte layer, and was heated at 140 ° C. and 100 kgf /
After hot pressing under the condition of cm ² , P
The TFE sheet was removed.

-3- The detection electrode gas diffusion layer having the above-described structure and the counter electrode gas diffusion layer having the above-described structure are joined to the surface of the detection electrode reaction layer and the counter electrode reaction layer opposite to the electrolyte layer, respectively, to complete the detection section. did.

The detection electrode gas diffusion layer and the counter electrode gas diffusion layer
Hot pressing was performed at 140 ° C. and 100 kgf / cm ² with the laminate of the detection electrode reaction layer, the electrolyte layer, and the counter electrode reaction layer interposed therebetween.

Next, a control unit was attached to the detection unit, and the detection unit was housed in a gas sampling container to assemble the gas sensor shown in FIG.

(Embodiment 2) First, FIG.
The detection unit shown in FIG.

<Structure of the detection section> Detection electrode Detection electrode reaction layer-Constituent material: platinum-Average thickness: 0.2 µm (amount of platinum existing on the electrolyte layer: 1 µg / cm ² )-Perpendicular to the detection electrode reaction layer Ratio of the area occupied by the gap to the entire area of the detection electrode reaction layer when viewed from various directions: 5% ・ Specific surface area: 1 cm ² / cm ² Detection electrode gas diffusion layer ・ Constituent material: carbon cloth ・ Average thickness: 500 μm Electrolyte layer (a plurality of irregularities are formed on the detection electrode reaction layer side)-Material: Nafion 112 (manufactured by Du Pont)-Average thickness: 50 µm Counter electrode Counter electrode reaction layer-Material: Platinum-ruthenium alloy ( (Average particle size 5 nm)
26 wt% carbon powder (average particle diameter 75 nm) 40 wt% Nafion (manufactured by Aldrlich) 34 wt% ・ Average thickness: 20 μm (amount of platinum-ruthenium alloy present on the electrolyte layer 0.5 mg / cm ² ) ・ Specific surface area: 100 cm ² / cm ² counter electrode gas diffusion layer ・ Constituent material: carbon cloth ・ Average thickness: 500 μm

<Preparation of Detection Portion> -1- A detection electrode reaction layer (detection electrode reaction layer unit) having the above-described structure was formed on one surface of the electrolyte layer.

First, a mask layer in which a plurality of grooves are provided at equal intervals and orthogonally is formed on one surface of the electrolyte layer.
The portion of the electrolyte layer where the mask layer was not formed was removed by plasma etching to form irregularities. In addition,
The plasma etching was performed under the following conditions. Thereafter, the mask layer was removed.

Sample temperature: 25 ° C., Ar gas pressure: 7
× 10 ^-3 Torr, plasma output: 100 W, plasma irradiation time: 60 seconds

Next, a detection electrode reaction layer unit was obtained on the projections of the electrolyte layer by sputtering so that the amount of platinum deposited was 1 μg / cm ² . Note that the sputtering method was performed under the following conditions.

Sample temperature: 25 ° C., Ar gas pressure: 7
× 10 ^-3 Torr, plasma output: 30 W, plasma irradiation time: 30 seconds

-2- A counter electrode reaction layer having the above structure was formed on the other surface of the electrolyte layer. This was performed in the same manner as in Example 1.

-3- The detection electrode gas diffusion layer having the above configuration and the counter electrode gas diffusion layer having the above configuration are respectively joined to the surfaces of the detection electrode reaction layer and the counter electrode reaction layer opposite to the electrolyte layer to complete the detection section. did. This was performed in the same manner as in Example 1.

Next, a control unit was attached to this detection unit, and the detection unit was housed in a gas sampling container to assemble the gas sensor shown in FIG.

(Comparative Example) First, a detector was manufactured as follows.

<Structure of the detector> Detection electrode Detection electrode reaction layer Average thickness: 0.1 μm (amount of platinum present on the electrolyte layer: 0.56 μg / cm ² ) Specific surface area: 1 cm ² / cm ² Electrode gas diffusion layer ・ Average thickness: 300 μm Electrolyte layer ・ Material: Nafion 112 (manufactured by Du Pont) ・ Average thickness: 50 μm Counter electrode Counter electrode reaction layer ・ Material: Platinum-ruthenium alloy (average particle size 5 nm)
26 wt% carbon powder (average particle diameter 75 nm) 40 wt% Nafion (manufactured by Aldrlich) 34 wt% ・ Average thickness: 20 μm (amount of platinum-ruthenium alloy present on the electrolyte layer 0.5 mg / cm ² ) ・ Specific surface area: 100 cm ² / cm ² counter electrode gas diffusion layer ・ Constituent material: carbon cloth ・ Average thickness: 500 μm

<Preparation of Detector> -1- A detection electrode having the above-described configuration was prepared.

First, platinum (average particle diameter: 5) was formed on one surface of a detection electrode gas diffusion layer formed by molding a mixture of carbon powder and polytetrafluoroethylene (PTFE) into a sheet.
nm) was applied to carry platinum.

Next, a 5 wt% Nafion solution was applied to the platinum-coated surface of the detection electrode gas diffusion layer so as to have a concentration of 1 mg / cm ² and dried to obtain a detection electrode reaction layer having the above structure. A part of the detection electrode gas diffusion layer constitutes a part of the detection electrode reaction layer.

-2- A counter electrode reaction layer having the above structure was formed on one surface of the electrolyte layer. This was performed in the same manner as in Example 1.

-3- A detection electrode is provided on the other surface of the electrolyte layer.
Further, the counter electrode gas diffusion layer having the above configuration was joined to the surface of the counter electrode reaction layer opposite to the electrolyte layer to complete the detection unit.

The detection electrode reaction layer of the detection electrode was brought into contact with the other surface of the electrolyte layer, the counter electrode gas diffusion layer was brought into contact with the counter electrode reaction layer,
Hot pressing was performed at 140 ° C. and 100 kgf / cm ² .

Next, a control unit was attached to the detection unit, and the detection unit was housed in a gas sampling container to assemble the gas sensor shown in FIG.

(Experiment) Air (wet state) adjusted to a humidity of 30% RH was supplied to each of the gas sampling containers of the gas sensors manufactured in Examples 1 and 2 and Comparative Example for 8 hours while maintaining the temperature at 100 ° C. Then, air (Dry state) adjusted to a humidity of 100% RH and methanol of 2 mol% was added to 25%.
An operation of supplying at 16 ° C. for 16 hours was performed. This operation was defined as one cycle, and a predetermined cycle was repeated for each gas sensor.

(Evaluation) For each gas sensor, the sensor output at the end of an arbitrary cycle was measured. The measurement of the sensor output is performed using the pulse method.
Time variation of H ₂ ionization current at adsorption potential (ΔI /
t) was used as the sensor output. The evaluation conditions were set as follows.

[Test gas] Composition: H ₂ / CO ₂ /CO=75/24.999/
0.001 Humidity: 40% RH Supply pressure: 1.5 kgf / cm ² Supply rate: 100 L / min Measurement temperature: 90 ° C. [Detection electrode reaction layer] CO oxidation potential: 1.0 V CO adsorption potential: 0.4 V

(Results) FIG. 5 is a graph showing changes in the sensor output of each gas sensor. In FIG. 5, the sensor output at the end of an arbitrary cycle is shown as a relative value (rate of change) with respect to the sensor output before the experiment (0 cycle).

As is clear from FIG. 5, the gas sensor of the first embodiment can obtain a sufficient sensor output even at the end of the 42th cycle, and the gas sensor of the second embodiment has a sufficient output even at the end of the 48th cycle. Sensor output was obtained. That is, the gas sensor of the present invention
In each case, the sensor output was suitably maintained (sustained), and the durability was excellent.

On the other hand, in the gas sensor of the comparative example, the separation of the catalyst from the carrier in the detection electrode reaction layer or the separation of the detection electrode reaction layer from the electrolyte layer was caused immediately after the start of the experiment (first cycle). A conceivable remarkable decrease in the sensor output was observed, and measurement of the sensor output became impossible at the end of the five cycles. For this reason, the gas sensor of the comparative example
The experiment was stopped at the end of 5 cycles. That is, the gas sensor of the comparative example was inferior in durability.

[0174]

As described above, according to the present invention, the detection electrode reaction layer unit is mainly composed of a catalyst, and the detection electrode reaction layer unit is provided with a gap therebetween to provide a synergistic effect. In addition, the durability of the detection unit can be significantly improved, and a gas sensor having excellent durability can be provided.

The above effect can be further improved by forming a plurality of irregularities on the surface of the electrolyte layer on the side of the detection electrode reaction layer.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the overall configuration of a gas sensor according to the present invention.

FIG. 2 is an enlarged cross-sectional view illustrating a configuration of a detection unit included in the gas sensor of the present invention.

FIG. 3 is a diagram showing a transition (change) of a response current over time when the potential of a detection electrode reaction layer is changed to a CO oxidation potential and a CO adsorption potential in a pulsed manner.

FIG. 4 is an enlarged cross-sectional view illustrating another configuration of the detection unit.

FIG. 5 is a graph showing a change in sensor output of each gas sensor.

FIG. 6 is a schematic diagram showing an overall configuration of a fuel cell system.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 gas sensor 2 gas storage container 21 housing 211 space 22 lid 23 introduction line 231 pressure regulator 24 exhaust line 3 detection unit 4 electrolyte layer 41 concave portion 42 convex portion 5 detection electrode 51 detection electrode reaction layer 511 detection electrode reaction layer unit 512 Gap 52 Detection electrode gas diffusion layer 6 Counter electrode 61 Counter electrode reaction layer 62 Counter electrode gas diffusion layer 7 Control unit 71 Power supply 72 Voltage changing circuit 73 Ammeter 74, 75 Wiring 100 Fuel cell device 110 Methanol tank 111 Pump 120 Water / methanol tank 121 Pump 130 reformer 140 CO removal device 150 fuel cell

Claims (13)

[Claims] 1. A detection system comprising: a detection electrode reaction layer for reacting a predetermined component in a test gas; a counter electrode reaction layer provided opposite to the detection electrode reaction layer; and an electrolyte layer provided therebetween. A gas sensor, comprising: a plurality of detection electrode reaction layers, each of which is mainly composed of a catalyst, and is disposed via a gap. 2. The gas sensor according to claim 1, wherein a concave portion reaching the inside of the electrolyte layer is formed, and the concave portion forms the gap of the detection electrode reaction layer. 3. A plurality of concavities and convexities are formed on the detection layer reaction layer side of the electrolyte layer, and the detection electrode reaction layer unit comprises:
The gas sensor according to claim 1, wherein each of the gas sensors is provided on a convex portion of the electrolyte layer. 4. A ratio of an area occupied by the gap to an entire area of the detection electrode reaction layer when viewed from a direction perpendicular to the detection electrode reaction layer is 0.01% to 60%.
4. The gas sensor according to any one of claims 3 to 3. 5. The gas sensor according to claim 1, wherein the detection electrode reaction layer is formed on the electrolyte layer. 6. The gas sensor according to claim 1, wherein the counter electrode reaction layer is made of a material containing a catalyst. 7. The gas sensor according to claim 6, wherein the catalyst of the counter electrode reaction layer is supported on a carrier. 8. The specific surface area of the counter electrode reaction layer is 10 to 1000 times the specific surface area of the detection electrode reaction layer.
8. The gas sensor according to any one of claims 7 to 7. 9. The gas sensor according to claim 1, wherein a gas diffusion layer is provided on each of the detection electrode reaction layer and the counter electrode reaction layer on a side opposite to the electrolyte layer. 10. The gas sensor according to claim 1, wherein the electrolyte layer is made of an ion exchange resin. 11. The gas sensor according to claim 1, further comprising a control unit that controls a voltage applied to the detection unit. 12. The gas sensor according to claim 1, further comprising a gas sampling container for sampling the test gas, wherein the detection unit is provided in the gas sampling container. 13. The gas sensor according to claim 1, which is used for measuring the CO concentration in the test gas.