JP2001099809A - Carbon monoxide sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon monoxide sensor which will not leak a gas to be detected into an atmosphere. SOLUTION: The carbon monoxide sensor has a detecting part 1 comprised of a proton conductive electrolyte film 8, first electrodes 9 with a catalyst which are set to both faces of the electrolyte film 8 and second electrodes 11, a d.c. power source 12 connected to make one of the second electrodes 11 positive and the other negative, and an ammeter 13 as a current-detecting means for detecting a current changing in accordance with a concentration of a carbon monoxide gas in a gas to be detected while the detecting part 1 is set in the gas to be detected which includes a hydrogen gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide sensor for detecting the concentration of carbon monoxide gas contained in a fuel gas used for a fuel cell, for example.

[0002]

2. Description of the Related Art In recent years, fuel cells have been actively developed, and a fuel cell using a proton conductive membrane made of a solid polymer is most practically used. When the operating temperature is lower than 100 ° C., the device operates at a very low temperature as compared with other systems, and is easy to handle. Therefore, it is regarded as a favorite for home and automobile fuel cells.

As a fuel gas to be supplied to the fuel cell, pure hydrogen gas is desirable, but at present, almost no infrastructure has been provided for supplying pure hydrogen gas.
Therefore, a method of extracting hydrogen gas by reforming a liquid fuel such as methanol is becoming mainstream. In this case, the fuel gas coming out of the reformer is mostly hydrogen gas and carbon dioxide gas, but may contain a very small amount of carbon monoxide gas of several tens ppm level. If this carbon monoxide gas is adsorbed on a platinum catalyst constituting an electrode of a fuel cell even at a level of several tens of ppm (this phenomenon is called poisoning), the electromotive force is reduced. Therefore, it is necessary to constantly monitor the concentration of the carbon monoxide gas in the fuel gas and control the reformer to reduce the carbon monoxide gas. Therefore, a carbon monoxide sensor is an essential component in a fuel cell using a reformer.

As a carbon monoxide sensor for detecting a carbon monoxide gas in a fuel gas (containing a large amount of hydrogen gas) supplied to function as a fuel cell as described above, JP-A-8-327590 discloses Are known.

FIG. 8 shows a schematic cross section of the structure of the carbon monoxide sensor. Reference numeral 110 denotes an electrolyte membrane made of a polymer having proton conductivity, on both surfaces of which an electrode 1 is prepared by kneading carbon powder carrying platinum for a catalyst on a carbon cloth.
12, 114 are joined by hot pressing. Mesh-shaped metal plates 116 and 118 are provided on the surfaces of the electrodes 112 and 114 that are not joined to the electrolyte membrane 110. The electrolyte membrane 110, the electrodes 112 and 114, and the metal plates 116 and 118 are formed by metal flanges 120 provided inside cylindrical holders 120 and 122.
a, 122a. On the electrolyte membrane 110 side of the end face of the holder 122, an O-ring 126 for gas sealing is provided.

Screw portions 120b and 122b are formed on the outer periphery of the holders 120 and 122, respectively, and these are formed inside an insulating member 124 made of polytetrafluoroethylene {for example, Teflon (trademark of DuPont)}. The holders 120 and 122 are fixed by being screwed into the screw portions 124a and 124b.

A gas inflow passage 12 is provided at one end of the holder 120.
8 is connected to one end, from which a gas to be detected (same as fuel gas) is introduced into the carbon monoxide sensor. on the other hand,
The gas inflow passage 128 is not connected to one end of the holder 122, and is open to the atmosphere.

The other end of the gas inflow passage 128 is connected to a branch port 14 provided in a part of a fuel gas passage 140 introduced into the fuel cell.
0a.

The holders 120 and 122 are provided with detection terminals 120T and 122T, respectively, to which an electric circuit 130 is connected. The electric circuit 130 has a configuration in which a voltmeter 132 and a resistor 134 for adjusting a load current are connected in parallel. The detection terminal 120T is a voltmeter 1
The detection terminal 122T is connected to the negative electrode 32, and the positive terminal, respectively.

Next, the operation of the carbon monoxide sensor will be described. A gas to be detected containing a large amount of hydrogen gas (the same as the fuel gas) is supplied to the electrode 112 through the gas inflow passage 128.
To reach. On the other hand, the electrode 114 is always in contact with oxygen gas in the atmosphere. Therefore, on the surface of the electrolyte membrane 110 in contact with the electrodes 112 and 114, a battery reaction similar to that of a fuel cell that generates power using hydrogen gas and oxygen gas as fuel occurs, and an electromotive force is generated between the electrodes 112 and 114. Electrode 112,
Since a resistor 134 is connected between the electrodes 114, a predetermined load current flows. At this time, a potential difference between the electrodes 112 and 114 is detected by a voltmeter 132.

If carbon monoxide gas is mixed in the gas to be detected in this state, the carbon monoxide gas is adsorbed on the catalytic platinum in the electrode 112, and the electrode 112 is poisoned. As a result, the battery reaction by the hydrogen gas and the oxygen gas is inhibited, and the electrode 11
The potential difference between 2, 114 decreases. Since the concentration of carbon monoxide gas is reflected in the degree of poisoning, the electrodes 112, 114
The concentration of carbon monoxide gas in the gas to be detected can be known by measuring the potential difference between them.

[0012]

In this carbon monoxide sensor, the gas to be detected and the atmosphere are sealed by an extremely thin polymer electrolyte membrane 110. A pressure difference (usually several atmospheres) is applied. In such a state, when an unexpectedly large stress due to abnormally high pressure or vibration is concentrated and applied (especially to the circled portions in FIG. 8), the electrolyte membrane 11
0 may be damaged, and the gas to be detected containing a large amount of hydrogen gas may leak to the atmosphere. Further, as a means for avoiding damage to the electrolyte membrane 110, a configuration in which a safety valve for releasing a gas to be detected at an abnormal pressure is provided is also described.
In any case, leakage of the gas to be detected into the atmosphere is inevitable.

The present invention solves this problem,
It is an object of the present invention to provide a carbon monoxide sensor in which a gas to be detected does not leak into the atmosphere.

[0014]

According to the present invention, there is provided a carbon monoxide sensor comprising a proton conductive electrolyte membrane and electrodes having catalysts disposed on both sides of the electrolyte membrane. Part, and one of the electrodes is a positive electrode,
A power source connected so that the other side is a negative electrode, and the detection unit is installed in a gas to be detected including hydrogen gas, and detects a current that changes according to the concentration of carbon monoxide gas in the gas to be detected. And a current detecting means.

With this configuration, a carbon monoxide sensor in which the gas to be detected does not leak into the atmosphere can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a detecting section comprising a proton conductive electrolyte membrane, and electrodes having catalysts disposed on both sides of the electrolyte membrane; One of which is connected to a positive electrode and the other is connected to a negative electrode, and the detection unit is installed in a gas to be detected containing hydrogen gas, and is provided in accordance with the concentration of carbon monoxide gas in the gas to be detected. Current detecting means for detecting a current that changes in the detection gas, the detection unit itself is entirely in the gas to be detected, and even if the electrolyte membrane is damaged, the gas to be detected is essentially in the atmosphere. Do not leak to In addition, since a safety valve and the like are not required, the structure is extremely simplified.

According to a second aspect of the present invention, in the first aspect of the present invention, the electrode comprises two first electrodes each having a carbon powder carrying a catalyst fixed on a carbon cloth, and the two first electrodes. Since it is composed of two second electrodes disposed outside one electrode and having at least one through hole, the first
The first electrode and the second electrode can be brought into surface contact with each other without obstructing diffusion of the gas to be detected to the electrodes, and an effect of obtaining good output stability can be obtained.

According to a third aspect of the present invention, in the second aspect of the present invention, since the surface of the second electrode is processed smoothly and a gold plating layer is formed, the first electrode and the second electrode are formed. This has the effect of further improving the contact properties and obtaining a low-noise output.

According to a fourth aspect of the present invention, in the first aspect of the present invention, there is provided a concentration calculating means for obtaining the concentration of carbon monoxide gas in the gas to be detected from the current detected by the current detecting means. Therefore, there is an effect that conversion from the output current to the concentration can be performed with high accuracy.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the concentration calculating means has a calculating section for converting a rate of change of current into a concentration of carbon monoxide gas.
This has the effect of increasing the response speed.

According to a sixth aspect of the present invention, in the first aspect of the present invention, a heater is provided in a part of the detecting section, and a heater control circuit for controlling the heater is connected, so that the poisoning is performed. It has the function of recovering the first electrode.

According to a seventh aspect of the present invention, in the sixth aspect of the present invention, the heating element of the heater is sandwiched between fluoropolymer sheets, and a hole or a slit is provided through the heating element and the sheet. Therefore, the poisoned first electrode can be recovered by heating without disturbing the diffusion of the gas to be detected to the first electrode with a simple configuration.

According to an eighth aspect of the present invention, in the first aspect of the present invention, since the detection section is disposed in parallel to the flow of the gas to be detected, the detecting section of the gas to be detected applied to both surfaces of the electrolyte membrane is provided. This has the effect of minimizing the pressure difference and greatly reducing the possibility of damaging the electrolyte membrane.

According to a ninth aspect of the present invention, in the first aspect of the present invention, since the voltage of the power supply is set to 0.1 V or more and 1 V or less, the catalyst is stably poisoned, and good output stability is obtained. It has the effect that sensitivity can be obtained.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

(Embodiment 1) FIGS. 1A and 1B are a front sectional view and a side sectional view for explaining a schematic structure of a carbon monoxide sensor according to Embodiment 1 of the present invention. FIG. 2 is an exploded perspective view for explaining the configuration of the detection unit. FIG. 3 is a cross-sectional view for explaining the flow of the gas to be detected in the vicinity of the detection unit when the detection unit is installed in a pipe. FIG.
FIG. 3 is a block diagram for explaining a configuration of the detection circuit. FIG. 5 is an output current characteristic diagram of the carbon monoxide sensor of the present invention.

In FIG. 1, reference numeral 1 denotes a detecting section for detecting the concentration of carbon monoxide gas in the gas to be detected. The detecting unit 1 is fixed by a holder 2 and a ring 3 made of insulating polytetrafluoroethylene (for example, Teflon (trademark of DuPont)). A part of the holder 2 is inserted and fixed to a mounting screw 4 made of stainless steel (for example, SUS303 of JIS standard). The mounting screw portion 4 is screwed and fixed to the detected gas pipe 22 of the fuel cell via an O-ring (not shown). In FIG. 1, only the detected gas pipe 22 is cut off. Also, the detecting unit 1
Is fixed so as to be parallel to the flow of the gas to be detected (the direction of the black arrow in FIG. 1). An output lead wire 5 coated with Teflon is electrically connected to both surfaces of the detection unit 1 at a connection unit 6. The output lead wire 5 is connected to an output cable 7 connected to an external detection circuit.

In FIG. 2, reference numeral 8 denotes a proton conductive electrolyte membrane made of a fluorine-based polymer material having a diameter of 1.4 cm, and on both surfaces thereof, a carbon powder carrying a platinum catalyst is deposited on a carbon cloth having a diameter of 1 cm. And two first electrodes 9 fixed with a fluorine-based polymer material. The electrolyte membrane 8 sandwiched between the two first electrodes 9 has a capacity of 130
It is fixed by hot pressing under a temperature condition of ° C.
The reason why the diameter of the electrolyte membrane 8 is larger than the diameter of the first electrode 9 is to prevent the two first electrodes 9 from being partially short-circuited due to slight displacement when both are fixed by hot pressing. is there.

On both sides of the detecting element 10 composed of the electrolyte membrane 8 and the two first electrodes 9 in this way, stainless steel (for example, JIS standard) provided with two elongated through holes 15 is provided. SUS303) 1.3 cm in diameter,
Two disk-shaped second electrodes 11 having a thickness of 1 mm are provided. The surfaces of the two second electrodes 11 are smoothed so that the average surface roughness is 1.6 μm or less, and a 1 μm-thick gold plating layer is formed thereon. Also,
The shape and dimensions of the through-hole 15 are not limited to the present embodiment as long as the gas to be detected can pass therethrough.

The detecting section 1 constituted by the detecting element 10 and the two second electrodes 11 is put in the holder 2 and fixed by screwing the ring 3 from above the detecting section 1. .

FIG. 3 shows a positional relationship when the detecting section 1 thus constructed is attached to the gas pipe 22 to be detected. FIG. 3 is a diagram viewed from the direction of the white arrow A in FIG. 1, and shows only the detected gas pipe 22 cut away.
The black arrows in FIG. 3 indicate the direction of the flow of the gas to be detected. Since the detector 1 (which is sandwiched between the holder 2 and the ring 3) is disposed in parallel to the flow of the gas to be detected, the pressure of the gas to be detected is applied substantially equally from both sides of the detector 1. . Therefore, the pressure difference of several atmospheres between the gas to be detected and the atmosphere is not structurally applied to the electrolyte membrane 8 in the detection unit 1 as described in the conventional example. Therefore, the electrolyte membrane 8
Not only is the possibility of breakage of the electrolyte membrane reduced, but even if unexpected large stress is applied and the electrolyte membrane 8 is broken,
As a result, the gas to be detected does not leak into the atmosphere.

In FIG. 4, the detecting unit 1 includes an output cable 7
Are connected to a DC power supply 12 and an ammeter 13 as current detecting means. The ammeter 13 is connected to a microcomputer 14 as a concentration calculating means for calculating the concentration of carbon monoxide gas in the gas to be detected from the detected current. The microcomputer 14 calculates a current difference (i.e., a current change speed) for each predetermined time (for example, one second), and previously calculates a correlation between the current change speed and the concentration of the carbon monoxide gas (stored in a ROM). ) Is converted to the concentration of carbon monoxide gas and output.

Next, the operation of the carbon monoxide sensor according to this embodiment will be described.

In the present embodiment, since the entire detecting section 1 is disposed in the gas to be detected, oxygen gas cannot be introduced. Therefore, a battery reaction unlike the conventional example cannot be caused.
Therefore, in the present embodiment, the concentration of carbon monoxide gas is detected based on the operation principle described below.

When a gas to be detected containing a large amount of hydrogen gas, such as fuel gas supplied to the fuel cell, reaches the detecting section 1, it reaches the detecting element 10 through the through hole 15 of the second electrode 11. Since most of the first electrode 9 constituting the detecting element 10 is made of carbon cloth, the gas to be detected diffuses in the carbon cloth to reach carbon powder carrying a platinum catalyst. Here, since the DC power supply 12 is connected such that one of the two first electrodes 9 is a positive electrode and the other is a negative electrode, the hydrogen gas in the detected gas is formed on each of the first electrodes 9. The reaction shown in 1) occurs.

[0036]

Embedded image

As shown in the formula (1) of the chemical formula (1), a hydrogen gas dissociation reaction occurs at the first electrode 9 on the positive electrode side, and the protons (H ⁺ ) generated here pass through the electrolyte membrane 8 to the negative electrode side. First
Electrons arrive at the electrode 9, where they again receive the electron e- and generate hydrogen gas as shown in the formula (2) of Chemical Formula 1. Therefore, in the presence of hydrogen gas, the detection element 10 and the DC power supply 12
An electric closed circuit is formed between them, and a current flows according to the proton conductivity.

Under such conditions, if the gas to be detected contains carbon monoxide gas, the carbon monoxide gas is adsorbed on the surface of the platinum catalyst and is poisoned. As a result, the reaction shown in the above (Chem. 1) is inhibited, and the current decreases. Therefore, an output corresponding to the concentration of the carbon monoxide gas can be obtained by monitoring this current.

FIG. 5 shows an output current characteristic diagram when the gas to be detected flows through the detection element 10. In FIG. 5, the horizontal axis represents time, and the vertical axis represents output current. The voltage applied to the detection element 10 was about 0.4V. The concentration of carbon monoxide gas is 0ppm
In the case of (1), the output current was constant, but when carbon monoxide gas was mixed into the gas to be detected, the output current decreased with time. As described above, the time during which the output current decreases (that is, the rate of change of the output current) varies depending on the concentration of the carbon monoxide gas. This is because the higher the concentration, the faster the platinum catalyst is poisoned. The rate of change of the output current is determined by the microcomputer 1
4, the concentration of the carbon monoxide gas could be known by obtaining from the change amount of the output current every fixed time (for example, one second). This indicates that the response of the present sensor is 1 second.

Here, for comparison, the response of a carbon monoxide sensor using a battery reaction based on hydrogen gas and oxygen gas as in the conventional example was measured. A few minutes later the output potential changed. From this result, it was found that the carbon monoxide sensor according to the present embodiment has much higher responsiveness than the conventional technology.

In the conventional example, the electrodes 112, 11
4 are in contact with the mesh-shaped metal plates 116 and 118, respectively, but since the contact portions are point contacts or line contacts,
The output voltage was unstable and there was much noise. On the other hand, in the present configuration, since the second electrode 11 is a flat plate, the surface of which is smoothed and plated with gold, the contact with the first electrode 9 becomes good, and an extremely stable output current is obtained. .

Although the present embodiment has been described using a general ammeter as the current detecting means, the present invention is not limited to this. For example, various ammeters such as those using a current transformer are used. It is possible.

In this embodiment, the voltage applied to the detection element 10 is set to about 0.4 V, for the following reason.

In order to determine the voltage of the DC power supply 12, the poisoning characteristic was measured by flowing a gas to be detected containing carbon monoxide gas while changing the applied voltage. When the applied voltage exceeded 1 V, the output current became very high. It turned out to be unstable. It is considered that this is because when the applied voltage is high, the platinum catalyst in the first electrode 9 is in a high activated state, and the desorption occurs simultaneously with the adsorption of the carbon monoxide gas. As described above, when the carbon monoxide gas is adsorbed (poisoned) by the platinum catalyst, the original function of the catalyst is impaired, and the output current decreases. However, the carbon monoxide gas is immediately desorbed and the output current increases again. Since this is repeated at random, the output current becomes extremely unstable.

From the above, it has been found that a voltage of 1 V or less is sufficient to obtain a stable output current. However, when the voltage is 0.1 V or less, the output current becomes too small, and it is difficult to discriminate the noise. Therefore, it is considered that an applied voltage in the range of 0.1 V to 1 V is appropriate for obtaining a good output current. However, the higher the applied voltage, the higher the output current and the higher the power consumption. Therefore, it is necessary to devise the shape and dimensions of the electrodes.

As a result of further detailed examination, in view of stability of output current, sensitivity, noise, optimization of electrode shape and size, etc., the range of applied voltage is 0.3 V to 0.8 V. Preferably, more preferably, from 0.4 V to 0.1 V.
It was in the range of 5V.

(Embodiment 2) FIG. 6 is an exploded perspective view for explaining a configuration of a detection unit according to Embodiment 2 of the carbon monoxide sensor of the present invention. FIG. 7 is a block diagram for explaining the configuration of the detection circuit.

In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, detailed description thereof will be omitted, and only different portions will be described in detail.

The carbon monoxide sensor described in the first embodiment does not include a means for forcibly desorbing the carbon monoxide gas from the platinum catalyst after the poisoning of the platinum catalyst. For this reason, it has sufficient functions as an alarm or switch to notify that the concentration of carbon monoxide gas has exceeded a certain value, but once poisoned, the reaction is irreversible, so it is reversible. It is not sufficient as a carbon monoxide sensor having a specific function. Therefore, in the present embodiment, a heater 16 for restoring the function of the platinum catalyst by heating the platinum catalyst to which the carbon monoxide gas has been adsorbed (poisoned) as shown in FIG. did. The heater 16 sandwiches a heating element 17 made of a nichrome wire processed into a shape as shown in FIG. 6 with a fluorine-based polymer sheet 18 such as Teflon also punched into a shape as shown in FIG. A heater cable 19 for supplying a current to the heating element 17 is connected, and is formed by hot pressing so as to be flat. Since the slits 20 are formed in the heater 16, the gas to be detected can be transmitted through the slits 20. Although the slit 20 is provided in the present embodiment, the slit 20 may be a through hole as long as the gas to be detected can pass therethrough. Further, the shapes and dimensions of the through holes and the slits are not limited to the present embodiment.

The heater 16 is connected to the detector 1 as shown in FIG.
The heater 16 and the detection unit 1 are further sandwiched and fixed by screwing the ring 3 into the holder 2 from above. The detecting unit 1 thus configured is inserted and fixed in the mounting screw unit 4 as in FIG.

The detection circuit shown in FIG. 7 is obtained by adding a heater control circuit 21 to the detection circuit shown in FIG. 4 described in the first embodiment.

Next, the basic operation principle of the carbon monoxide sensor according to this embodiment will be described. Although the basic operation of the carbon monoxide sensor of the present embodiment is the same as that of the first embodiment, there is a difference in the operation of the present embodiment due to the provision of the heater 16. That is, the carbon monoxide gas adsorbed on the platinum catalyst is desorbed by being heated by the heater 16, and can be operated again as a carbon monoxide sensor.

When the microcomputer 14 determines that the concentration of carbon monoxide gas is equal to or higher than a predetermined concentration, a signal is transmitted to the heater control circuit 21. As a result, the heater control circuit 21 supplies a current so that the temperature of the heater 16 becomes approximately 130 ° C. As a result, the detection unit 1 is heated, and the carbon monoxide gas adsorbed on the platinum catalyst is desorbed. The above operation suggests that even if the platinum catalyst is poisoned, it can be repeatedly used as a carbon monoxide sensor.

When such a carbon monoxide sensor was manufactured and evaluated, basic output current characteristics similar to those shown in FIG. 5 were obtained. Further, after the poisoning, the heater 16 was operated and heated to 130 ° C., and then the power supply to the heater 16 was stopped and the heater 16 was allowed to cool. The original output current value has been restored. From this, it was proved that a reversible carbon monoxide sensor capable of recovering the detection function even if poisoned could be constituted.

In the first and second embodiments, the detection unit 1 is disposed in parallel to the flow of the gas to be detected. However, the pressure of the gas to be detected is applied to both sides of the detection unit 1 substantially equally. If it is in a state, it may be arranged in any direction.

Further, the specific material names described in the first and second embodiments are merely examples for constituting the carbon monoxide sensor of the present invention, and are not limited to these materials. Absent.

As described above, it is possible to realize a carbon monoxide sensor which has a very simple structure and does not leak the gas to be detected into the atmosphere.

Further, a carbon monoxide sensor capable of recovering the detection function even if poisoned can be realized.

[0059]

As described above, according to the present invention, a detection section comprising a proton conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the electrolyte membrane, and one of the electrodes serving as a positive electrode A power supply connected so that the other side is a negative electrode, and the detecting unit is installed in a gas to be detected including hydrogen gas, and detects a current that changes according to the concentration of carbon monoxide gas in the gas to be detected. With such a configuration, a carbon monoxide sensor having a very simple structure and having no detected gas leaking into the atmosphere can be obtained.

[Brief description of the drawings]

FIG. 1A is a schematic front sectional view of a carbon monoxide sensor according to a first embodiment of the present invention. FIG.

FIG. 2 is an exploded perspective view of the detection unit.

FIG. 3 is a cross-sectional view for explaining a flow of a gas to be detected in the vicinity of the detection unit.

FIG. 4 is a block diagram illustrating a configuration of the detection circuit.

FIG. 5 is a graph showing the output current characteristics.

FIG. 6 is an exploded perspective view of a detection unit according to a second embodiment of the carbon monoxide sensor of the present invention.

FIG. 7 is a block diagram for explaining a configuration of the detection circuit.

FIG. 8 is a schematic sectional view of a conventional carbon monoxide sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detecting part 2 Holder 3 Ring 4 Mounting screw part 5 Output lead wire 6 Connecting part 7 Output cable 8 Proton conductive electrolyte membrane 9 First electrode 10 Detecting element 11 Second electrode 12 DC power supply 13 Ammeter 14 Microcomputer 15 Through hole Reference Signs List 16 heater 17 heating element 18 polymer sheet 19 heater cable 20 slit 21 heater control circuit 22 detected gas pipe

Claims (9)

[Claims] 1. A detection unit comprising a proton conductive electrolyte membrane and electrodes having catalysts disposed on both sides of the electrolyte membrane, such that one of the electrodes is a positive electrode and the other is a negative electrode. A power supply connected thereto, and the detection unit is provided in a gas to be detected including hydrogen gas, and includes a current detection unit that detects a current that changes according to a concentration of the carbon monoxide gas in the gas to be detected. Carbon monoxide sensor. 2. The electrode comprises two first electrodes having carbon powder supporting a catalyst fixed on a carbon cloth, and at least one or more through-holes disposed outside the two first electrodes. The carbon monoxide sensor according to claim 1, comprising two second electrodes. 3. The carbon monoxide sensor according to claim 2, wherein the surface of the second electrode is processed smoothly and a gold plating layer is formed. 4. The carbon monoxide sensor according to claim 1, further comprising a concentration calculating means for calculating a concentration of the carbon monoxide gas in the gas to be detected from a current detected by the current detecting means. 5. The carbon monoxide sensor according to claim 4, wherein said concentration calculating means has a calculating section for converting a rate of change of the current into a concentration of carbon monoxide gas. 6. The carbon monoxide sensor according to claim 1, wherein a heater is provided in a part of the detection unit, and a heater control circuit for controlling the heater is connected. 7. The carbon monoxide sensor according to claim 6, wherein the heating element of the heater is sandwiched between fluoropolymer sheets, and a hole or a slit penetrating the heating element and the sheet is provided. 8. The carbon monoxide sensor according to claim 1, wherein the detection unit is provided in parallel with the flow of the gas to be detected. 9. The carbon monoxide sensor according to claim 1, wherein the voltage of the power supply is 0.1 V or more and 1 V or less.