JP6979167B2 - Impurity sensor for fuel cell and how to use it - Google Patents

Description

The present invention relates to an impurity sensor for protecting a fuel cell.

In recent years, fuel cells have been attracting attention as a next-generation power generation system. A fuel cell is a power generation system that uses hydrogen and oxidizer gas (air, oxygen-enriched air, oxygen, etc.) as fuel to generate electricity by causing the reverse reaction of electrolysis of water, and is an environmental load on the global environment. Is low. Further, as compared with the conventional power generation system, the energy conversion efficiency is high and the noise is low. In particular, polymer electrolyte fuel cells (PEFCs) that can operate even at low temperatures such as around room temperature are expected to be used in in-vehicle power sources, home stationary power sources, regional power generation systems, and the like.

FIG. 3 is a schematic configuration diagram of PEFC. As described above, in the PEFC 100, the cathode electrode 103 and the anode electrode 105 are arranged so as to sandwich the solid polymer electrolyte membrane 101.

The solid polymer electrolyte membrane 101 is a cation exchange membrane (cation exchange membrane), which is (A) a membrane obtained by cross-linking styrene-divinylbenzene to a fluorocarbon matrix and then sulphonized, (B) and (A). Various types of membranes such as (C) trifluorostyrene sulphonic acid polymer film, (D) fluorocarbon matrix grafted with trifluoroethylene, (E) perfluorocarbon sulphonic acid resin film, etc. Has been proposed. Specifically, a fluorine-based cation exchange membrane (for example, a Nafion membrane manufactured by DuPont) is often used.

The cathode electrode 103 includes a gas diffusion layer 111 and a catalyst layer 113 constituting an electrode base material. Examples of the material constituting the catalyst layer 113 include platinum (Pt), an alloy containing platinum, or palladium, and these are used alone or in a plurality of types thereof supported on carbon particles. Since these precious metals are expensive, they are used, for example, by being supported on the surface of powdery conductive carbon black.

In the gas diffusion layer 111, carbon particles such as carbon black are used as a catalyst carrier. More specifically, the gas diffusion layer 111 is applied to a gas diffusion electrode in which a catalyst layer containing a catalyst particle in which a noble metal, that is, an active metal is supported on carbon particles, an electrolyte and a water repellent agent is formed on a paper or a sheet. To. The gas diffusion layer 111 is formed by mixing a platinum-supported carbon black with a fluororesin having a binding function and water repellency, for example, a polytetrafluoroethylene-based polymer and an ionomer having the same composition as the polymer film.

The anode electrode 105 has a structure substantially similar to that of the cathode electrode 103. That is, the anode electrode 105 is configured to have a gas diffusion layer 121 and a catalyst layer 123 constituting the electrode base material. In addition to Pt, ruthenium (Ru) may be used for the catalyst layer 123 on the anode side.

A wire mesh terminal portion is provided on the surface of each of the cathode electrode 103 and the anode electrode 105. It is desirable to use gold as the material of the wire mesh terminal portion. When the material of the wire mesh terminal portion is stainless steel, an oxide film is formed non-uniformly on the surface of the terminal portion. Therefore, when the stainless steel wire mesh terminal portion is attached to each electrode, there is a problem that the electric resistance changes according to the contact condition between the two.

Usually, the PEFC 100 shows a structure in which the solid polymer electrolyte membrane 101, the cathode electrode 103, and the anode electrode 105 are integrated. Such a structure is particularly called MEA (Membrane Electrode Assembly).

The PEFC100 generates electricity as follows.

First, the fuel gas containing hydrogen gas is supplied to the anode electrode 105 from the gas passage 133 provided in the anode side terminal portion 131. The supplied fuel gas (hydrogen-containing gas) passes through the gas diffusion layer 121 on the anode side and reaches the catalyst layer 123 on the anode side. The fuel gas (hydrogen-containing gas) that reaches the catalyst layer 123 on the anode side is oxidized to protons (H ⁺ ) and electrons (e ⁻ ) according to the following formula.
H ₂ → 2H ⁺ + 2e ⁻

Protons (H ⁺ ) pass through the solid polymer electrolyte membrane 101 in contact with the catalyst layer 123 on the anode side and reach the catalyst layer 113 on the cathode side in contact with the solid polymer electrolyte membrane 101. On the other hand, the electron (e ⁻ ) reaches the catalyst layer 113 on the cathode side via the anode side terminal portion 131, the load 110, and the cathode side terminal portion 141.

^{The protons (H +} ) and electrons (e ⁻ ) that reach the catalyst layer 113 on _{the cathode side are oxygen (O 2} ) contained in the oxidant gas supplied from the gas passage 143 provided in the terminal portion 141 on the cathode side. To generate _{water (H 2} O) according to the following formula.
2H ⁺ + 2e ⁻ + (1/2) O ² → 2H ₂ O

PEFC100 makes it possible to take out electricity to the outside through such an electrochemical reaction.

As the fuel gas supplied to the PEFC 100, a reformed gas is generally used. More specifically, for example, a gas containing hydrogen extracted by reforming _{methane (CH 4} ), which is the main component of LNG (liquefied natural gas) or LPG (liquefied petroleum gas), is used as a fuel gas.

The reformed gas refers to a gas obtained by subjecting a fuel gas to a treatment called reforming. The reforming is performed by a predetermined fuel reformer. As an example, the fuel reformer is configured by arranging a desulfurizer, a fuel reformer, a CO transformer, and a CO remover in order from the upstream side.

A odorant (sulfur compound) containing a sulfur component is generally added to LNG or LPG for the purpose of safety in the event of a gas leak. The desulfurizer removes the above-mentioned odorant. The removal process consists of, for example, the following processes.

(1) The sulfur compound (H ₃ C—S—CH ₃ ) added to LNG and LPG is reacted with hydrogen on a catalyst to convert it into _{hydrogen sulfide (H 2 S).} The temperature at the time of reaction is, for example, 250 to 400 ° C.
(2) Hydrogen sulfide is reacted with zinc oxide (ZnO) to obtain zinc sulfide (ZnS), and sulfide is removed. The temperature at the time of reaction is, for example, 350 to 400 ° C.
Methane (CH ₄ ) is obtained by the above process.

_{The fuel reformer produces hydrogen (H 2} ), carbon dioxide (CO ₂ ), and carbon monoxide (CO) from the methane obtained in the above process. As a conversion process, for example, methane is reacted with water vapor on a catalyst _{to obtain H 2} , CO ₂ , and CO.

As described above, platinum (Pt) is often used as the catalyst (113,123) used in the fuel cell. Although the Pt catalyst is a catalyst having high activity for hydrogenation, it has a property of strongly adsorbing CO, and the Pt catalyst is easily poisoned by the CO. When poisoned by CO, the power generation efficiency of PEFC100 decreases. _{Therefore, it is desirable that the hydrogen (H 2} ) supplied to the PEFC 100 is hydrogen containing almost no CO.

The CO transformer reduces the concentration of CO among _{H 2} , CO ₂ , and CO obtained by the fuel reformer. In the reduction process, for example, CO and water vapor (H ₂ O) are reacted on a catalyst _{to convert the CO into H 2} and CO ₂ , thereby reducing the CO concentration.

The CO remover is for removing a trace amount of CO that could not be converted by the CO transformer. The removal process is, for example, oxidative removal of CO by adding air to the gas from the CO metaphor _{and reacting CO with oxygen (O 2} ) on a precious metal catalyst to convert CO to CO _2. Is.

As described above, hydrogen, which is a raw material gas for fuel cells such as PEFC100, needs to reduce the concentration of CO and the like in the raw material gas as much as possible in order to suppress the poisoning of the catalyst contained in the fuel cell. be. Therefore, it is required to monitor whether or not the fuel reformer with reduced impurities such as CO is functioning normally with an impurity sensor.

FIG. 4 is a configuration example of the impurity sensor described in Patent Document 1 below. The impurity sensor 150 has a structure equivalent to that of the PEFC 100 shown in FIG. That is, in the impurity sensor 150, the cathode electrode 153 and the anode electrode 155 are arranged so as to sandwich the solid polymer electrolyte membrane 151. Then, in the structure shown in FIG. 4, as described above, the MEA structure in which the solid polymer electrolyte membrane 151 and the electrodes (153, 155) are integrated is configured. The cathode electrode 153 includes a gas diffusion layer 161 and a catalyst layer 163 that constitute an electrode base material. The anode electrode 155 is also configured to have a gas diffusion layer 171 and a catalyst layer 173.

Since the structures of the solid polymer electrolyte membrane, the cathode, and the anode in the impurity sensor 150 are the same as those of the PEFC 100, the description thereof will be omitted. In the catalyst layer 173, for example, ruthenium (Ru) is not used, and only platinum (Pt) supported on carbon is used.

FIG. 5 is a drawing schematically showing a usage mode of the impurity sensor 150. As shown in FIG. 5, a voltage is applied to both electrodes (153, 155) of the impurity sensor 150, and the applied voltage is measured by a voltmeter 181. In addition, in FIG. 5, terminals (154,156) for applying a voltage to both electrodes (153, 155) are shown. The impurity sensor 150 is arranged in the impurity measurement space in the impurity measurement chamber 180.

A fuel gas (hydrogen-containing gas) 190 is introduced into the impurity measurement chamber 180, and a current is passed between the cathode electrode 153 and the anode electrode 155. FIG. 5 shows an example in which a direct current is passed between both electrodes (153, 155) by a direct current power supply 182, but an alternating current may be passed.

The supplied fuel gas 190 passes through the gas diffusion layer 171 of the anode electrode 155 and reaches the catalyst layer 173 (see FIG. 4). The fuel gas 190 that reaches the catalyst layer 173 of the anode electrode 155 is oxidized to protons (H ⁺ ) and electrons (e ⁻ ).

Of these, ^{only protons (H +} ) pass through the solid polymer electrolyte membrane 151 in contact with the catalyst layer 173 of the anode electrode 155, and pass through the catalyst layer 163 of the cathode electrode 153 in contact with the solid polymer electrolyte membrane 151. To reach. On the other hand, the electron (e ⁻ ) reaches the catalyst layer 163 of the cathode electrode 153 via the terminal portion on the anode electrode 155 side, the DC power supply 182, and the terminal portion on the cathode electrode 153 side. ^{As a result, the proton (H +} ) that has reached the catalyst layer 163 of the cathode electrode 153 reacts with an electron and _{returns to hydrogen (H 2} ).

That is, on the anode electrode 155 side, a hydrogen decomposition reaction as shown in the following formula occurs.
H ₂ → 2H ⁺ + 2e ⁻

On the other hand, on the cathode electrode 153 side, a hydrogen generation reaction as shown in the following formula occurs.
2H ^{+ +} 2e ^- → H ₂

When an alternating current flows between the electrodes, a hydrogen decomposition reaction or a hydrogen generation reaction occurs at the anode electrode 155 depending on the polarity of the current. Similarly, a hydrogen generation reaction or a hydrogen decomposition reaction occurs at the cathode electrode 153 depending on the polarity of the current.

Using this principle, the voltage between the anode electrode 155 and the cathode electrode 153 is measured by the voltmeter 181. _{The voltage V 0} when using pure hydrogen gas containing no impurities is _{compared with the voltage V 1} (≦ V ₀ ) when using hydrogen gas containing impurities (for example, CO), and the voltage drop V _0. -V ₁ corresponds to the concentration of impurities.

Japanese Patent No. 5957004

^{As described above, the proton (H +} ) passing through the contact surface between the anode electrode 155 and the solid polymer electrolyte membrane 151 passes through the solid polymer electrolyte membrane 151 and is converted into hydrogen at the cathode electrode 153. The impurity sensor 150 senses the amount of impurities in the fuel gas (hydrogen-containing gas) by measuring the voltage between the anode electrode 155 and the cathode electrode 153 with a voltmeter 181 at this time.

^{Therefore, the proton (H +} ) emitted from one electrode (anode electrode 155 in the above example) and passing through the solid polymer electrolyte membrane 151 surely reaches the other electrode (cathode electrode 153 in the above example). Is desirable.

FIG. 6 is a drawing schematically showing the configuration of the impurity sensor 150, and is illustrated in a mode different from that of FIG. In FIG. 6, the upper part is a schematic plan view when the impurity sensor 150 is viewed from a direction orthogonal to the plane of the solid polymer electrolyte membrane 151, and the lower part is a cross-sectional view of A1-A1.

From the above viewpoint, as shown in FIG. 6A, the anode electrode 155 and the cathode electrode 153 have the same shape, and both electrodes are positioned symmetrically with each other via the solid polymer electrolyte membrane 151. It is preferable to configure it so as to be in contact with the electrolyte membrane 151. In particular, in order to facilitate alignment, it is preferable that the shapes of both electrodes (153, 155) are disk-shaped.

However, since the electrodes are generally opaque, it is difficult to easily align both electrodes (153, 155) at the positions shown in FIG. 6 (a). When the misalignment of both electrodes (153,155) occurs, the region where both electrodes (153,155) overlap (effective region 160) decreases via the solid polymer electrolyte membrane 151, as shown in FIG. 6B. Resulting in. As a result, some sensors may have insufficient electrical characteristics. Further, when a plurality of sensors are used, individual differences between the sensors may not be negligible. In FIG. 6, the effective region 160 is shown by hatching.

In view of the above problems, the present invention affects the electrical characteristics of the hydrogen impurity sensor that employs the MEA structure due to the positional deviation between the first electrode and the second electrode that sandwich the solid polymer electrolyte membrane during its manufacture. It is an object of the present invention to provide a suppressed impurity sensor.

The present invention is an impurity sensor for a fuel cell.
With the first electrode
The solid polyelectrolyte membrane formed on the upper surface of the first electrode and
It has a MEA type structure including a second electrode formed on a surface of the solid polymer electrolyte membrane opposite to the side on which the first electrode is formed.
The area of the first region where the first electrode and the solid polymer electrolyte membrane are in contact is smaller than the area of the second region where the second electrode and the solid polymer electrolyte membrane are in contact.
When viewed in a direction orthogonal to the plane of the solid polymer electrolyte membrane, the entire outer circumference of the first region is located inside the outer circumference of the second region.

As described above, conventionally, both the first electrode and the second electrode have the same shape and the same dimensions. Therefore, if the alignment is not performed strictly, the effective region may decrease as shown in FIG. 6 (b), and as a result, the area of the effective region may vary from individual to individual.

On the other hand, according to the above configuration, the region where the first electrode and the solid polymer electrolyte membrane are in contact (first region) and the region where the second electrode and the solid polymer electrolyte membrane are in contact (second region). ) And the area is different. All of the outer circumference of the first region is located inside the outer circumference of the second region. In the case of this configuration, when viewed in the direction orthogonal to the plane of the solid polymer electrolyte membrane, both electrodes may be arranged so that one electrode is inside the other electrode, so that the degree of freedom of alignment is greater than before. Can be enhanced. As long as it is arranged in this way, the area of the effective region is always defined as the area of the first region, so that the probability that individual differences will occur is greatly reduced.

When manufacturing an impurity sensor, a method may be adopted in which the first electrode and the second electrode are placed on the front and back surfaces of a sheet-shaped solid polymer electrolyte membrane and then fixed by applying heat and pressing. be. At this time, the relative positional relationship between the two electrodes may deviate from the state before fixing due to heat shrinkage of the sheet-shaped solid polymer electrolyte membrane or a decrease in the water content. As an example, when the solid polymer electrolyte membrane is composed of the Nafion membrane NR-211 manufactured by DuPont, it is immersed in water from a state of 50% RH (relative humidity) of 23 ° C, and when the temperature is raised to 100 ° C, it is about 15%. It has been confirmed that there is a dimensional change in.

However, according to the above configuration, it is sufficient that one electrode is arranged so as to be inside the other electrode when viewed in a direction orthogonal to the plane of the solid polymer electrolyte membrane, so that there is a margin. Is high. That is, even if the solid polymer electrolyte membrane contracts and the relative positional relationship between the two electrodes deviates from the state before fixing, it is possible to prevent the area of the effective region from changing before and after the fixing step.

In the impurity sensor, the area of the second region may be 6.5 cm ² or less. More specifically, if the second region is rectangular, it may be □ 1 inch or less, and if the second region is circular, it may be φ28 mm or less.

The electrical properties of solid polyelectrolyte membranes used in impurity sensors are sensitive to temperature and humidity. Therefore, strict temperature and humidity control is required in order to accurately measure the fluctuation amount of the voltage between electrodes at the time of measuring impurities. As an example, the temperature is controlled within 40 ° C. ± 1 ° C. and the humidity is controlled within 80% RH ± 1%. Further, since a current flows between the first electrode and the second electrode, Joule heat is generated between the electrodes. Therefore, it is necessary to control the above temperature in consideration of the influence of this Joule heat. If the Joule heat is large, the temperature control is adversely affected. Therefore, it is necessary to reduce the Joule heat, and for this purpose, it is necessary to reduce the detection voltage. Due to such a background, the impurity sensor has an extremely small size as compared with the fuel cell.

The smaller the size of both electrodes, the higher the effect on the electrical characteristics due to the misalignment between the first electrode and the second electrode. In a normal fuel cell, even if the positions of both electrodes are slightly displaced, the generated voltage itself is high, so the fluctuation range is about an error and does not pose a problem. However, when it is used as an impurity sensor as described above, since the magnitude of the detection voltage itself is small, it is expected that a slight misalignment will have a large effect on the detection result. The above configuration is particularly effective in suppressing the influence on the electrical characteristics due to the misalignment in a small impurity sensor having an area of the second region of 6.5 cm ^{2 or less.}

In the impurity sensor, the difference between the area of the first region and the area of the second region may be 10% or more of the area of the first region.

With such a configuration, it is possible to sufficiently increase the margin of alignment.

In the impurity sensor, the first region and the second region may have similar shapes to each other. In this case, both the first region and the second region may be circular.

With such a configuration, it is possible to further increase the margin of alignment.

When both the first electrode and the second electrode have a plate shape having the same front and back surfaces, the area of the first region can be read as the area of the first electrode, and the area of the second region is It can be read as the area of the second electrode.

According to the impurity sensor of the present invention, even if the position shift between the first electrode and the second electrode sandwiching the solid polymer electrolyte membrane occurs during manufacturing, the influence on the sensing result can be suppressed. can.

It is a drawing which shows typically the impurity sensor of one Embodiment of this invention. It is a drawing which shows typically the impurity sensor of another embodiment of this invention. It is a schematic block diagram of PEFC. It is a schematic block diagram of an impurity sensor. It is a schematic block diagram of an impurity measurement chamber including an impurity sensor. It is a drawing which shows typically the conventional impurity sensor.

The structure of the impurity sensor according to the present invention will be described with reference to the drawings. FIG. 1 is a drawing schematically showing the structure of an impurity sensor according to the present embodiment, which is illustrated following FIG.

In the present embodiment, the impurity sensor 1 includes a solid polymer electrolyte membrane 2, a first electrode 3, and a second electrode 4. In this embodiment, both the electrodes (3, 4) have a disk shape. Note that FIG. 1B corresponds to a case where the positional relationship between the first electrode 3 and the second electrode 4 deviates from the state of FIG. 1A. The impurity sensor 1 of the present embodiment is used in the same manner as the impurity sensor 150 shown in FIG. 4, for example.

Similar to the conventional impurity sensor 150 described above with reference to FIGS. 4 to 6, the first electrode 3 and the second electrode 4 are arranged so as to sandwich the solid polymer electrolyte membrane 2. That is, the impurity sensor 1 shows a MEA type structure. The first electrode 3 may be an anode electrode and the second electrode 4 may be a cathode electrode, and conversely, the first electrode 3 may be a cathode electrode and the second electrode 4 may be an anode electrode.

The solid polymer electrolyte membrane 2 may be made of the same material as the solid polymer electrolyte membrane 151 included in the conventional impurity sensor 150. The electrodes (3, 4) may be made of the same material as the electrodes (153, 155) included in the conventional impurity sensor 150.

As shown in FIG. 1, the first electrode 3 has a smaller area than the second electrode 4. Then, when viewed in a direction orthogonal to the surface of the solid polymer electrolyte membrane 2, all the outer circumferences of the first electrode 3 are arranged so as to be located inside the outer circumference of the second electrode 4. In this case, the region where both electrodes (3, 4) overlap via the solid polymer electrolyte membrane 2 (effective region 10) corresponds to the region where the first electrode 3 comes into contact with the solid polymer electrolyte membrane 2. In FIG. 1, the effective domain 10 is shown by hatching.

In this configuration, as shown in FIG. 1 (b), even when the positional relationship between the first electrode 3 and the second electrode 4 is displaced, in the effective region 10, the first electrode 3 is still a solid polymer. Since it corresponds to the region in contact with the electrolyte membrane 2, its area does not change. That is, according to the impurity sensor 1 of the present embodiment, the entire outer periphery of the first electrode 3 is located inside the outer periphery of the second electrode 4 when viewed in a direction orthogonal to the surface of the solid polymer electrolyte membrane 2. As long as it is, the area of the effective region 10 does not change, and the voltage value measured by the voltmeter 181 does not fluctuate.

That is, according to the impurity sensor 1 of the present embodiment, the positional relationship between the first electrode 3 and the second electrode 4 is the outer periphery of the first region 3 when viewed in the direction orthogonal to the surface of the solid polymer electrolyte membrane 2. All of the above may be located inside the outer periphery of the second electrode 4, in other words, misalignment is allowed within the range in which this condition is satisfied. As a result, according to the impurity sensor 1 of the present embodiment, strict alignment is not required as compared with the conventional impurity sensor 150. Further, according to the impurity sensor 1 of the present embodiment, the problem of deterioration of sensing accuracy due to individual difference of the sensor is solved as compared with the conventional impurity sensor 150.

Hereinafter, another embodiment will be described.

<1> The first electrode 3 and the second electrode 4 do not necessarily have to have similar figures. For example, one may have a circular plate shape and the other may have a rectangular plate shape. However, by making both electrodes (3, 4) similar figures, the allowable range of misalignment can be sufficiently increased.

<2> The areas of the front and back surfaces of the first electrode 3 and the second electrode 4 do not necessarily have to be the same. FIG. 2 is a diagram showing an impurity sensor 1 in the case where the area of one surface of both the first electrode 3 and the second electrode 4 is larger than the area of the other surface, following FIG. In this case, when viewed in a direction orthogonal to the plane of the solid polymer electrolyte membrane 2, the entire outer periphery of the region (first region) 11 in which the first electrode 3 contacts the solid polymer electrolyte membrane 2 is the second electrode 4. The area of the effective region 10 does not change as long as is located inside the outer periphery of the region (second region) 12 in contact with the solid polymer electrolyte membrane 2. When the areas of the front and back surfaces of the first electrode 3 are the same, the area of the first region 11 matches the area of the first electrode 3, and when the areas of the front and back surfaces of the second electrode 4 are the same, the area is the same. , The area of the second region 12 corresponds to the area of the second electrode 4.

1: Impurity sensor 2: Solid polyelectrolyte membrane 3: First electrode 4: Second electrode 10: Effective region 11: First region 12: Second region 100: PEFC
101: Solid polymer electrolyte film 103: Cathode electrode 105: Cathode electrode 110: Load 111: Gas diffusion layer 113: Catalyst layer 121: Gas diffusion layer 123: Catalyst layer 131: Cathode side terminal part 133: Gas passage 141: Cathode side Terminal part 143: Gas path 150: Impure sensor 151: Solid polymer electrolyte membrane 153: Cathode electrode 154: Cathode electrode terminal 155: Anodic electrode 156: Anodic electrode terminal 160: Effective region 161: Gas diffusion layer 163: Catalyst layer 171: Gas diffusion layer 173: Cathode layer 180: Electrode measurement chamber 181: Voltage meter 182: DC power supply 190: Fuel gas

Claims (7)

Impurity sensor for fuel cell
With the first electrode
The solid polyelectrolyte membrane formed on the upper surface of the first electrode and
Of the solid polymer electrolyte membrane, wherein the first electrode is formed side Rutotomoni and a second electrode formed on the opposite side, the first electrode and the electrodes other than the second electrode Has a MEA type structure that does not have
The area of the first region where the first electrode and the solid polymer electrolyte membrane are in contact is smaller than the area of the second region where the second electrode and the solid polymer electrolyte membrane are in contact.
When viewed in a direction orthogonal to the plane of the solid polymer electrolyte membrane, the entire outer circumference of the first region is located inside the outer circumference of the second region .
An impurity sensor characterized in that a voltage between the first electrode and the second electrode is measurable for detecting an impurity concentration. The impurity sensor according to claim 1, wherein the area of the second region is 6.5 cm ^{2 or less.} The impurity sensor according to claim 1 or 2, wherein the difference between the area of the first region and the area of the second region is 10% or more of the area of the first region. The impurity sensor according to any one of claims 1 to 3, wherein the first region and the second region have similar shapes to each other. The impurity sensor according to claim 4, wherein both the first region and the second region have a circular shape. The method of using the impurity sensor according to any one of claims 1 to 5.
A method of using an impurity sensor, which comprises measuring a voltage between the first electrode and the second electrode while passing a gas to be measured for an impurity concentration. The method for using an impurity sensor according to claim 6, wherein the temperature of the impurity sensor is controlled within 40 ° C. ± 1 ° C. and the humidity is controlled within 80% RH ± 1% when the gas is flowing.

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