JP2001330585A - Carbon monoxide sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon monoxide sensor having quick response. SOLUTION: This sensor is equipped with a proton conductive electrolyte film 1, electrodes 2 having catalysts disposed on both faces of the proton conductive electrolyte film 1, a positive electrode collector plate 8 equipped with a gas passage 7 having an inlet and an outlet of gas and disposed so that the gas passage 7 is brought into contact with the surface of one of the electrodes 2, a negative electrode collector plate 10 having plural holes 9 disposed in contact with the surface of the other of the electrodes 2, a direct current power source connected so that the positive electrode collector plate 8 becomes a positive electrode and that the negative electrode collector plate 10 becomes a negative electrode, and a current detection means for detecting a current changing corresponding to the concentration of carbon monoxide gas in the detection gas including hydrogen and flowing in the gas passage 7.

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 in a fuel gas containing a large amount of hydrogen used for a fuel cell, for example.

[0002]

2. Description of the Related Art In recent years, fuel cells using solid polymer proton conductive membranes for home use, automobile use, and the like have been actively developed. Since this fuel cell uses hydrogen gas as a fuel gas when operating, a reformer for reforming a liquid fuel such as methanol or a city gas to extract hydrogen gas is required. However, the fuel gas containing a large amount of hydrogen gas coming out of the reformer contains a very small amount of carbon monoxide gas at a level of several tens of ppm. When the carbon monoxide gas is adsorbed on the platinum catalyst constituting the electrode of the fuel cell (this phenomenon is called poisoning), the electromotive force of the fuel cell decreases. Therefore, it is necessary to monitor the concentration of carbon monoxide gas in the fuel gas and control the fuel cell system.

[0003] As a carbon monoxide sensor for detecting carbon monoxide gas in a fuel gas containing a large amount of hydrogen gas supplied to a fuel cell, one described in Japanese Patent Application Laid-Open No. 11-219716 is known. .

FIG. 6 shows an exploded perspective view of a schematic structure of the carbon monoxide sensor. Reference numeral 50 denotes an electrolyte membrane made of a polymer having proton conductivity as a proton exchange membrane {for example, NAFI
ON (a trademark of DuPont)}, having an anode 42 and a cathode 44 containing catalyst particles on both sides. Reference numerals 43 and 45 denote conductive diffusion portions made of carbon paper, which are arranged to be in contact with the anode 42 and the cathode 44, respectively. The conductive diffusion section 43 contacts a housing 54 having a gas inlet 59 to be detected, an anode flow channel 46 through which the gas to be detected flows, and an outlet 51 of the gas to be detected. Cathode 44 is exposed to ambient air through opening 52 in housing 54. A plurality of perforated metal current collectors 49 are in contact with the conductive diffusion 45 and conduct current to its terminals 47. The terminal 47 projects out of the housing 54 through the slot 55.

Next, the operation of the carbon monoxide sensor will be described. The gas to be detected containing a large amount of hydrogen gas (same as the fuel gas) reaches the anode flow channel 46 through the gas to be detected inlet 59. From here, it passes through the conduction diffusion part 43 and is discharged from the outlet 51. On the other hand, the cathode 44 is always in contact with oxygen gas in the atmosphere. Therefore, the anode 42 and the cathode 44
A chemical reaction similar to that of a fuel cell that generates electricity using hydrogen gas and oxygen gas as fuel occurs on the surface of the electrolyte membrane 50 in contact with the anode, and an electromotive force is generated between the anode and the cathode. The current and voltage at this time are detected by a current detection device and a voltage detection device (not shown) connected to the terminal 47 and the housing 54.

In this state, if carbon monoxide gas is mixed in the gas to be detected, the carbon monoxide gas is adsorbed on the catalyst particles in the anode 42 and the anode 42 is poisoned. As a result, the battery reaction by the hydrogen gas and the oxygen gas is inhibited, and the anode 42 and the cathode 4
The electromotive force during 4 decreases. Since the concentration of the carbon monoxide gas is reflected in the degree of poisoning, the concentration of the carbon monoxide gas in the detected gas can be known by measuring the current fluctuation and the voltage fluctuation accompanying the decrease in the electromotive force.

[0007]

The results of measuring the output characteristics of such a carbon monoxide sensor are shown by the dotted lines in FIG.
When a gas to be detected containing 50 ppm of carbon monoxide gas was introduced into this carbon monoxide sensor, it was found that it took several minutes for the sensor output, that is, the electromotive force, to change after the gas to be detected was introduced. During that time, no change in the voltage or current from the carbon monoxide sensor is recognized, so that voltage fluctuations and current fluctuations cannot be measured. Therefore, the concentration of the carbon monoxide gas cannot be known.

An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide a fast-response carbon monoxide sensor.

[0009]

In order to solve this problem, a carbon monoxide sensor according to the present invention comprises a proton conductive electrolyte membrane and electrodes having catalysts disposed on both sides of the proton conductive electrolyte membrane. A gas flow path having a gas inlet and a gas outlet, and a positive electrode current collector arranged such that the gas flow path is in contact with one surface of the electrode, and so as to be in contact with the other surface of the electrode. A negative electrode current collector having a plurality of holes disposed therein, a DC power supply in which the positive electrode current collector is connected to the positive electrode such that the negative electrode current collector becomes the negative electrode, and hydrogen flowing through the gas flow path. And a current detecting means for detecting a current that changes in accordance with the concentration of the carbon monoxide gas in the gas to be detected.

With this configuration, a carbon monoxide sensor having a fast response can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention provides a proton conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the proton conductive electrolyte membrane, an inlet and an outlet for gas. A positive electrode current collector plate provided so that the gas flow path is in contact with one surface of the electrode, and a gas flow path having the gas flow path having the same, and is provided so as to be in contact with the other surface of the electrode. A negative electrode current collector having a plurality of holes, a DC power supply connected such that the positive electrode current collector is a positive electrode, the negative electrode current collector is a negative electrode, and hydrogen flowing through the gas flow path. Current detection means for detecting a current that changes in accordance with the concentration of carbon monoxide gas in the gas to be detected, so that the gas to be detected quickly diffuses through a gas flow path to an electrode having a catalyst, Poisoning occurs quickly and air (oxygen)
Is not supplied, so a chemical reaction with a low reaction rate of generating water from protons, electrons, and oxygen does not occur. Instead, detection using proton conduction is performed, which has an effect of increasing responsiveness. .

According to a second aspect of the present invention, in the first aspect of the invention, since the gas flow path is provided only within the area of the electrode, the entire amount of the gas to be detected is introduced only into the electrode having the catalyst. This has the effect that the catalyst can be poisoned efficiently.

According to a third aspect of the present invention, in the first aspect of the present invention, since a gold plating layer is formed on the surfaces of the positive electrode current collector and the negative electrode current collector, the positive electrode current collector and the negative electrode current collector are provided. This has the effect of improving the electrical contact between the plate and the electrode having the catalyst and obtaining a low-noise output.

According to a fourth aspect of the present invention, in the first aspect of the present invention, a gas chamber having a gas outlet is provided on a side of the negative electrode current collector plate which is not in contact with the electrode, and the gas outlet is provided at the gas outlet. Because of the provision of the means, the atmosphere in the gas chamber becomes only pure hydrogen and water vapor generated by proton conduction, and has an effect that a stable output can be obtained.

According to a fifth aspect of the present invention, there is provided a proton conductive electrolyte membrane, a positive electrode having a catalyst made of an alloy of platinum and gold and disposed on one surface of the proton conductive electrolyte membrane, A negative electrode having a catalyst made of platinum or an alloy of platinum and another noble metal disposed on the other surface of the membrane, a direct current connected so that the positive electrode is a positive electrode and the negative electrode is a negative electrode A power supply; and a current detection means for detecting a current that changes in accordance with the concentration of carbon monoxide gas in the gas to be detected containing hydrogen flowing near the positive electrode. Since air (oxygen) is not supplied, proton There is no slow chemical reaction in which water is generated from oxygen, electrons and oxygen, and the response is fast because it is detected using proton conduction.The alloy of platinum and gold is extremely poisoned by carbon monoxide gas. Easy to be Because a material, by using this catalyst in the positive electrode, has the effect that response is higher speed.

According to a sixth aspect of the present invention, there is provided a fuel cell system comprising: a first electrolyte membrane having proton conductivity; and a catalyst comprising a platinum and gold alloy disposed on one surface of the first electrolyte membrane. A first detection unit including a positive electrode and a first negative electrode having a catalyst made of platinum or an alloy of platinum and another noble metal disposed on the other surface of the first electrolyte membrane;
A first direct-current power supply in which a positive electrode is connected to a positive electrode and a first negative electrode is connected to a negative electrode, and according to the concentration of carbon monoxide gas in a gas to be detected containing hydrogen flowing near the first positive electrode. A first current detecting means for detecting a changing current, a second electrolyte membrane having proton conductivity, and a catalyst comprising an alloy of platinum and ruthenium provided on one surface of the second electrolyte membrane. A second positive electrode, and a second detection unit including a second negative electrode having a catalyst made of platinum or an alloy of platinum and another noble metal disposed on the other surface of the second electrolyte membrane, A second DC power supply in which the second positive electrode is connected to the positive electrode and the second negative electrode is connected to the negative electrode, and a current that changes according to the concentration of hydrogen gas in the gas to be detected flowing near the second positive electrode Second current detecting means for detecting
By obtaining the hydrogen concentration in the gas to be detected from the current obtained from the current detecting means, the fluctuation amount of the hydrogen concentration in the current obtained from the first current detecting means is corrected and converted into the concentration of carbon monoxide gas. Therefore, there is an effect that the concentration of carbon monoxide can be detected with high accuracy regardless of the fluctuation of the concentration of hydrogen in the gas to be detected.

According to a seventh aspect of the present invention, in the sixth aspect of the present invention, the detected gas is introduced into the first detecting portion, and the carbon monoxide gas in the detected gas is extremely reduced by the first detecting portion. After being removed to a low concentration, it is introduced into the second detection unit, and thus has the effect of not poisoning the catalyst of the second detection unit.

According to an eighth aspect of the present invention, in the first, fifth and sixth aspects of the present invention, a DC power supply is turned on with the gas to be detected flowing through the carbon monoxide sensor, and the concentration of the carbon monoxide gas is increased. Therefore, the poisoning of the catalyst starts immediately after the DC power supply is turned on, and the response of the sensor using the poisoning characteristic is further increased.

According to a ninth aspect of the present invention, in the first, fifth and sixth aspects of the present invention, a switching valve for introducing air is provided in a gas introduction portion for introducing a gas to be detected, so that poisoning is performed. It has the effect that the catalyst can be recovered quickly.

According to a tenth aspect of the present invention, in the invention according to the ninth aspect, after the gas to be detected is introduced into the gas introduction section for a predetermined time, air is introduced into the gas introduction section by the switching valve. This has the effect that the catalyst is poisoned with good reproducibility and the concentration of carbon monoxide can be detected with high accuracy.

According to an eleventh aspect of the present invention, when air is introduced into the gas introduction part in the tenth aspect,
Because the DC power supply is cut off and the voltage change rate is obtained by voltage detection means connected to the positive electrode and the negative electrode, the switching valve is switched when the change rate of the voltage becomes negative, and the gas to be detected is introduced. It has the effect that the poisoned catalyst can be recovered quickly and with good reproducibility.

According to the twelfth aspect of the present invention,
In the inventions described in (6) and (7), a valve is provided in the gas introduction unit and the gas discharge unit that discharges the gas to be detected, and the valve is opened during operation and the valve is closed during non-operation. The trapped air stays in the gas flow path, prevents the electrolyte membrane from drying, and has the effect of stably detecting the concentration of carbon monoxide.

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

(Embodiment 1) FIG. 1 is an exploded perspective view for explaining a schematic structure of a carbon monoxide sensor according to Embodiment 1 of the present invention. FIG. 2 is a block diagram illustrating the configuration of the sensor. FIG. 3 is an output characteristic diagram of the sensor and a conventional carbon monoxide sensor.

In FIG. 1, reference numeral 1 denotes a proton conductive electrolyte membrane made of a fluorine-based polymer material having a diameter of 1.4 cm, and a catalyst alloyed on both surfaces thereof so that the ratio of platinum to gold is 3: 1. Is loaded with carbon powder having a diameter of 1c.
The upper and lower two electrodes 2 are fixed on a carbon cloth of m with a fluorine-based polymer material. A thickness of 0.25 m is provided outside each of the two electrodes 2 to prevent gas leakage.
A sealing material 3 made of a silicon-based polymer of m is provided. The proton conductive electrolyte membrane 1 sandwiched between the two electrodes 2 and the sealing material 3 is fixed by hot pressing at a temperature of 130 ° C. Thus, the detection element 4 is composed of the proton conductive electrolyte membrane 1 and the two electrodes 2 and 2
And three sealing materials 3.

In FIG. 2, a positive electrode current collector 8 is provided on one surface of the detection element 4 so that a gas flow path 7 having a gas inlet 5 and an outlet 6 is in contact with the gas collector 7. The gas flow path 7
The width and pitch are set to 0.5 so as to fit within the area of the electrode 2.
mm, depth 0.3 mm, stainless steel (for example, J
It is formed by cutting the surface of a positive electrode current collector 8 made of IS standard SUS304). The gas flow path 7
Is not limited to the above dimensions as long as a predetermined gas flow rate (50 cc / min in the first embodiment) can be secured. After cutting, a gold plating layer having a thickness of 1 μm is formed on the surface of the positive electrode current collector plate 8.

The other surface of the detecting element 4 has a diameter of 1.5
A negative electrode current collector plate 10 made of stainless steel (for example, SUS304 of JIS standard) provided with a large number of holes 9 of mm is provided. A gold plating layer having a thickness of 1 μm is also formed on the surface of the negative electrode current collector plate 10.

On the side where the negative electrode current collector plate 10 is not in contact with the detection element 4, that is, in FIG. 2, above the negative electrode current collector plate 10, a stainless steel having a gas outlet 11 (for example, JIS standard SUA304) is cut. Thus, a gas chamber 12 formed is provided. An orifice 13 having a diameter of 0.8 mm is connected to the gas outlet 11 as flow suppression means.

Positive current collector 8, detecting element 4, negative current collector 1
The gas chamber 12 and the gas chamber 12 are fixed by four screws 14 in this order.

The gas inlet 5 and the gas outlet 15 are connected to the gas inlet 5 and the gas outlet 6, respectively. A switching valve 18 for switching between a gas to be detected and humidified air is provided at the end of the gas introduction unit 15. The humidified air is introduced into the switching valve 18 by partially branching the humidified air supplied to the fuel cell. The gas discharge part 16 and the outlet side of the orifice 13 are connected so as to merge with each other, and a valve 17 is provided at the end thereof.

A DC power supply 19 is connected to the positive current collector 8 and the negative current collector 10 so that the former is a positive electrode and the latter is a negative electrode. In order to detect a current flowing between the positive current collector 8 and the negative current collector 10, an ammeter 20 as current detection means is connected in series with the DC power supply 19. In order to detect a voltage between the positive current collector 8 and the negative current collector 10, a voltmeter 21 as a voltage detecting means is connected therebetween. The outputs of the ammeter 20 and the voltmeter 21 are connected to a microcomputer 22. The microcomputer 22 calculates, for example, the rate of change of the current per second from the current detected by the ammeter 20, and obtains a correlation between the rate of change of the current and the concentration of the carbon monoxide gas in advance (stored in the ROM). ), The output is converted into the concentration of carbon monoxide gas, and the DC power supply 19 is turned on and off in order to recover the function of the catalyst to which the carbon monoxide gas is adsorbed (hereinafter referred to as refresh). And switching valve 1
The switching control of 8 and the opening and closing of the valve 17 are performed.

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

In order to suppress the output fluctuation caused by the drying of the proton conductive electrolyte membrane 1, the microcomputer 22 first opens the two valves 17, switches the switching valve 18 to the humidified air side, and flows the humidified air for 30 seconds. . The flow rate of the humidified air was 50 cc / min. Here, the time of 30 seconds is the time required for the gas in the pipe and the gas flow path 7 of the carbon monoxide sensor of the first embodiment to be replaced with humidified air at a flow rate of 50 cc / min. . Therefore, since the replacement time varies depending on the flow rate and the size of the gas flow path 7, the replacement time is not limited to the time in the first embodiment.

Next, the microcomputer 22 switches the switching valve 18 to the gas to be detected. The flow rate of the gas to be detected was 50 cc / min. The gas to be detected passes through the valve 17, the gas introduction unit 15, and the inlet 5, and is guided to the gas channel 7. Gas flow path 7
Is in contact with the electrode 2, the gas to be detected flows through the gas flow path 7 and diffuses evenly into the carbon paper constituting the electrode 2 to reach a catalyst made of an alloy of platinum and gold. Thereafter, the detected gas is supplied to the outlet 6 and the gas discharge unit 1
6. Exhaust through valve 17;

After a lapse of 30 seconds from the above operation, the gas in the pipe and the gas flow path 7 is replaced with the gas to be detected, and then the microcomputer 22 switches on the DC power supply 19. As a result, a voltage is applied between the positive electrode current collector 8 and the negative electrode current collector 10. In the first embodiment, the voltage is set to 0.1V. By this operation, the hydrogen gas in the detected gas causes the following reactions on the catalyst of the electrode 2 for each of the positive electrode and the negative electrode. Positive electrode side: H ₂ → 2H ⁺ + 2e ⁻ (1) Formula Negative electrode side: 2H ⁺ + 2e ⁻ → H ₂ (2) Formula 2 At the positive electrode 2, a hydrogen gas dissociation reaction occurs as shown in the above formula (1). The protons (H ⁺ ) generated here reach the electrode 2 on the negative electrode side through the proton conductive electrolyte membrane 1, where they receive the electrons (e ⁻ ) again as shown in the above equation (2) and receive hydrogen gas. Generate. Therefore, in the presence of hydrogen gas, an electric closed circuit is formed between the detection element 4 and the DC power supply 19, and a current flows according to the proton conductivity.

In such a state, if the gas to be detected contains a carbon monoxide gas, the carbon monoxide gas is adsorbed and poisoned on the surface of the catalyst made of an alloy of platinum and gold. As a result, the reactions of equations (1) and (2) are inhibited, and the current decreases.
The microcomputer 22 calculates the rate of decrease of the current every second and outputs the concentration of the carbon monoxide gas with reference to a correlation table between the rate of change of the current and the concentration of the carbon monoxide gas.

When the above operation is continued, the catalyst is poisoned by the carbon monoxide gas, and the current becomes difficult to flow.
At this time, the change speed of the current is significantly slower than the change speed at the time of starting the sensor even if the concentration of the carbon monoxide gas is the same, which causes a large error. Therefore, the microcomputer 22 measures the decrease in the current of the catalyst due to the poisoning of the carbon monoxide gas for a predetermined time (1 minute in the first embodiment), and then performs the following refresh operation.

First, the microcomputer 22 shuts off the switch of the DC power supply 19 and switches the switching valve 18 to the humidified air side. Thereby, the humidified air flows into the gas flow path 7.

On the other hand, until immediately before the switching valve 18 is switched, the gas chamber 12 is operated by the reactions shown in the above equations (1) and (2).
Hydrogen gas is generated inside. Further, since the orifice 13 is attached to the outlet 11 of the gas chamber 12,
The generated hydrogen gas is not immediately exhausted, and a certain amount of hydrogen gas exists in the gas chamber 12.

Accordingly, the detection element 4 forms a fuel cell composed of air in the gas flow path 7 and hydrogen gas in the gas chamber 12.
An electromotive force is generated in which the positive electrode current collector 8 serves as a positive electrode and the negative electrode current collector 10 serves as a negative electrode. In the case of the first embodiment, the voltage due to the electromotive force increases up to about 0.8 V and then gradually decreases. This is because the hydrogen gas existing in the gas chamber 12 is gradually consumed to generate an electromotive force.

By operating in this manner, the poisoned catalyst is supplied with oxygen gas in humidified air, reacts with carbon monoxide gas to form carbon dioxide gas, and leaves the catalyst. At the same time, the electrode 2 on the poisoned catalyst side generates an electromotive force of about 0.8 V. Therefore, a voltage of 0.68 V or more necessary for desorbing the carbon monoxide gas adsorbed on the catalyst is applied, and The carbon gas moves further away from the catalyst. Therefore,
By merely introducing humidified air into the gas passage 7, these oxidation reactions and electromotive forces act on the poisoned catalyst, and this catalyst is refreshed to almost its original state.

The voltage change due to the electromotive force is monitored by a voltmeter 21 connected between the positive current collector 8 and the negative current collector 10. The microcomputer 22 obtains the rate of change of the voltage from the output of the voltmeter 21, and if the rate of change becomes negative (decreases the voltage), determines that the refresh has been completed, and switches the switching valve 18 to the gas to be detected.

Next, the microcomputer 22 waits for the humidified air in the pipe and the gas flow path 7 to be replaced with the gas to be detected (30 seconds in the first embodiment),
The switch 9 is turned on and the measurement of the concentration of carbon monoxide gas is continued.

By repeating the above operation, the concentration of the carbon monoxide gas is detected.

When the operation of the carbon monoxide sensor is stopped, the microcomputer 22 switches the switching valve 18 to the humidified air side to perform the above-described refresh operation. When the rate of change of the voltage obtained from the output of the voltmeter 21 becomes negative, the microcomputer 22 closes the two valves 17 and cuts off the switch of the DC power supply 19. Since the carbon monoxide sensor is stopped in this manner, the detection element 4 is constantly exposed to humidified air, and output fluctuations due to drying of the proton conductive electrolyte membrane 1 can be suppressed.

In the carbon monoxide sensor according to the first embodiment, 50 cc of a gas to be detected having a carbon monoxide gas concentration of 20 ppm is applied.
An output characteristic diagram when flowing at a flow rate per minute is shown by a solid line in FIG. The horizontal axis is time, and the vertical axis is output current. When the time was 0, the DC power supply 19 was turned on. As soon as the DC power supply 19 was turned on, the output current began to decrease. The concentration of the carbon monoxide gas could be known by obtaining the rate of change by the microcomputer 22. The output voltage of the conventional example (broken line in FIG. 3) did not change for several minutes even when the same gas to be detected was supplied. As described above, a carbon monoxide sensor having much higher responsiveness than that of the conventional technology was realized. This is essentially a chemical reaction in which the gas to be detected quickly diffuses into the electrode 2 having a catalyst through the gas flow path 7 and poisoning occurs quickly, and a slow reaction rate in which water is generated from protons, electrons and oxygen. This is because an alloy of platinum and gold, which is extremely toxic to carbon monoxide gas, was used for the catalyst.

In the first embodiment, an alloy of platinum and gold poisoned by carbon monoxide was used as a catalyst constituting the electrode 2. However, since the catalyst used for the negative electrode current collector plate 10 that functions as the negative electrode may be toxic by carbon monoxide, platinum alone or an alloy of platinum and other noble metals, for example, platinum and ruthenium, may be used. The invention is not limited to gold alloy materials.

(Embodiment 2) FIG. 4 is a block diagram illustrating a configuration of a carbon monoxide sensor according to Embodiment 2 of the present invention. FIG. 5 shows a second embodiment of the carbon monoxide sensor of the present invention.
It is a perspective view which shows the structure of the 2nd detection element of FIG.

In the second embodiment, a carbon monoxide sensor having the same configuration as that of the first embodiment (hereinafter, carbon monoxide detector 23)
And a hydrogen gas detector 24 similar to that of the first embodiment except that the catalyst material of the positive electrode is an alloy of platinum and ruthenium. The circuit of the hydrogen gas detector 24 is the same as the carbon monoxide gas detector 23 except that the voltmeter 21 is not connected.

Therefore, the same components and parts as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted.
In addition, when used for the carbon monoxide detection unit 23, “1” is added to the name, and when the same constituent part or part is used for the hydrogen gas detection unit 24, the name is “second”. And a is attached to the number to distinguish them.

In FIG. 5, reference numeral 25 denotes a carbon powder carrying a catalyst made of an alloy of platinum and ruthenium having a diameter of 1 c.
m, a proton conductive electrolyte membrane 1 other than this catalyst electrode fixed on a carbon cloth with a fluoropolymer material,
The electrode 2, the sealing material 3, and their configurations are the same as those described in FIG.

During the measurement with the carbon monoxide sensor described in the first embodiment, if the concentration of hydrogen gas in the gas to be detected changes greatly, the amount of protons flowing through the proton electrolyte membrane 1 changes. As a result, the output current changes. Therefore, it may not be possible to distinguish whether the change in the output current is due to a change in the concentration of carbon monoxide gas or a change in the concentration of hydrogen gas. For this reason, in the carbon monoxide sensor described in the first embodiment, the operation of the reformer is stabilized, and the concentration of the carbon monoxide gas in a state where the concentration of the hydrogen gas coming out of the reformer is almost constant is reduced. It functions satisfactorily in a limited state such as detection, but may be insufficient when the concentration of hydrogen gas fluctuates, for example, immediately after the reformer starts up.

Therefore, in the second embodiment, as shown in FIG. 4, a hydrogen gas detecting unit 24 for detecting only the concentration of hydrogen gas is connected to the first gas discharging unit 16 of the carbon monoxide gas detecting unit 23. And corrects the change in the concentration of the hydrogen gas and outputs the concentration of the carbon monoxide gas.

Next, the basic operation of the carbon monoxide sensor according to the second embodiment will be described. First, the microcomputer 22 opens the two valves 17 and 17a, switches the switching valve 18 to the humidified air side, and waits for 60 seconds. The flow rate of the humidified air was 50 cc / min.

Next, the microcomputer 22 switches the switching valve 18 to the detected gas side. The flow rate of the gas to be detected was 50 cc / min. The gas to be detected is the first valve 17, the first gas introduction unit 15, the first inlet 5 of the carbon monoxide gas detection unit 23.
Through the first gas flow path 7 to reach the catalyst in the electrode 2 made of an alloy of platinum and gold. Thereafter, the gas to be detected passes through the first outlet 6 and the first gas discharge unit 16, passes through the second gas introduction unit 15 a and the second inlet 5 a of the hydrogen gas detection unit 24, and passes through the second inlet 5 a.
It is led to the gas flow path 7a and reaches the catalyst electrode 25 in the second detection element 26 which is made of an alloy of platinum and ruthenium. Next, the gas to be detected is supplied to the second outlet 6a, the second gas discharging portion 16a,
The air is exhausted through the valve 17a.

Sixty seconds have passed since the switching valve 18 was switched to the gas to be detected, and the piping, the first gas flow path 7, and the second gas flow path 7
After the gas in a is replaced with the gas to be detected, the microcomputer 22 sends the first DC power supply 19 of the carbon monoxide gas detection unit 23 and the hydrogen gas detection unit 24 (hereinafter, both detection units) to the second
The switches of the DC power supply 19a are simultaneously turned on. As a result, a voltage is applied between the first positive electrode current collector 8 and the first negative electrode current collector 10 and between the second positive electrode current collector 8a and the second negative electrode current collector 10a. In the second embodiment, the voltages of both the detection units are set to 0.1 V. By this operation, the hydrogen gas in the gas to be detected in the two detection units causes the following reactions to occur on the positive electrode and the negative electrode on the catalyst of the electrode 2 and the catalyst electrode 25, respectively,
Accordingly, a current corresponding to the proton conductivity flows through both the detection units. Positive electrode side: H ₂ → 2H ⁺ + 2e ⁻ (1) formula Negative electrode side: 2H ⁺ + 2e ⁻ → H ₂ formula (2) Under these conditions, the carbon monoxide gas in the detected gas is carbon monoxide gas. The catalyst is adsorbed and poisoned on the surface of a catalyst made of an alloy of platinum and gold in the first detection element 4 of the detection unit 23. As a result, the carbon monoxide gas detector 23 detects (1)
The reaction shown in the equation (2) is inhibited, and the current decreases. On the other hand, as a result of the carbon monoxide gas being adsorbed on the catalyst of the carbon monoxide gas detection unit 23, the gas to be detected from which the carbon monoxide gas has been almost completely removed is introduced into the hydrogen gas detection unit 24, and the second detection element 26 has a catalyst electrode 25 made of an alloy of platinum and ruthenium which is hardly poisoned by carbon monoxide gas, and therefore outputs a current according to the concentration of hydrogen gas without being affected by carbon monoxide gas.

The microcomputer 22 calculates the rate of decrease of the current of the carbon monoxide gas detector 23 per second, and determines the concentration of the carbon monoxide gas determined from the current change rate and the output current of the hydrogen gas detector 24. And outputs the concentration of the carbon monoxide gas with reference to the correlation table.

After the output of the carbon monoxide gas concentration is continued for a predetermined time (60 seconds in the second embodiment), the microcomputer 22 performs the same refresh operation as in the first embodiment.

Next, the microcomputer 22 operates until the humidified air in the pipe, the first gas flow path 7 and the second gas flow path 7a is replaced with the gas to be detected (in the second embodiment, 60 μm).
Second), the first DC power supply 19 and the second DC power supply 1
The switch 9a is turned on at the same time, and the measurement of the concentration of carbon monoxide gas is continued for a predetermined time (60 seconds in the second embodiment).

By repeating the above operation, the concentration of carbon monoxide gas is detected.

When the operation of the carbon monoxide sensor is stopped, the microcomputer 22 switches the switching valve 18 to the humidified air side and performs the above-described refresh operation as in the first embodiment. When the rate of change of the voltage obtained from the output of the voltmeter 21 becomes negative, the microcomputer 22 closes the two valves 17, 17a and cuts off the switches of the first DC power supply 19 and the second DC power supply 19a. In order to stop the carbon monoxide sensor in this manner, the first detection element 4 and the second detection element 26 are always exposed to humidified air, and the first proton conductive electrolyte membrane 1 and the second proton conductive electrolyte membrane Output fluctuations due to drying of 1a can be suppressed.

In the carbon monoxide sensor according to the second embodiment, 50 cc of a gas to be detected having a carbon monoxide gas concentration of 20 ppm was applied.
When the output at a flow rate of / min was measured, it was confirmed that the same high responsiveness as in the first embodiment was obtained. This is because the gas to be detected quickly diffuses through the first gas flow path 7 to the first electrode 2 having a catalyst, poisoning occurs quickly, and the reaction rate is low such that water is generated from protons, electrons, and oxygen. This is because a chemical reaction essentially does not occur, and an alloy of platinum and gold, which is very easily poisoned by carbon monoxide gas, is used for the catalyst. In addition, the carbon monoxide gas concentration could be accurately detected even when the measurement was performed with the gas to be detected in which the hydrogen gas concentration was changed.

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, a carbon monoxide sensor having a quick response can be realized. Further, a carbon monoxide sensor capable of accurately detecting the concentration of carbon monoxide gas even when the concentration of hydrogen gas in the gas to be detected changes can be realized.

[0065]

As described above, the present invention provides a gas channel having a proton conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the proton conductive electrolyte membrane, and a gas inlet and an outlet. A positive electrode current collector plate disposed so that the gas flow path is in contact with one surface of the electrode, and a plurality of holes disposed so as to be in contact with the other surface of the electrode. A negative electrode current collector plate, a DC power supply in which the positive electrode current collector plate is connected to the positive electrode and the negative electrode current collector plate as the negative electrode, and carbon monoxide in the gas to be detected containing hydrogen flowing in the gas flow path. With the provision of a current detecting means for detecting a current that changes in accordance with the concentration of the gas, the gas to be detected quickly diffuses to the electrode having the catalyst through the gas flow path, and poisoning of the catalyst occurs quickly, In addition, since the air (oxygen) is not supplied, the prototype And the chemical reaction does not occur slow reaction rate of producing water and electricity from electrons and oxygen, since the detection using the proton conductive Instead, fast carbon monoxide sensor responsive obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view illustrating a schematic structure of a detection unit according to a first embodiment of a carbon monoxide sensor of the present invention.

FIG. 2 is a block diagram illustrating the configuration of the sensor.

FIG. 3 is an output characteristic diagram of the sensor and a conventional carbon monoxide sensor.

FIG. 4 is a block diagram illustrating a configuration of a carbon monoxide sensor according to a second embodiment of the present invention.

FIG. 5 is an exploded perspective view for describing a detection element structure according to a second embodiment of the carbon monoxide sensor of the present invention.

FIG. 6 is an exploded perspective view of a schematic structure of a conventional carbon monoxide sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Proton conductive electrolyte membrane 2 Electrode 3 Sealing material 4 Detecting element 5 Inlet 6 Outlet 7 Gas flow path 8 Positive electrode current collector 9 Hole 10 Negative electrode current collector 11 Gas outlet 12 Gas chamber 13 Orifice 14 Screw 15 Gas introduction part 16 Gas Discharge unit 17 Valve 18 Switching valve 19 DC power supply 20 Ammeter 21 Voltmeter 22 Microcomputer 23 Carbon monoxide gas detection unit 24 Hydrogen gas detection unit 25 Catalyst electrode 26 Second detection element

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Ida 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. F-term (reference) 5H027 AA02 BA01 KK51

Claims (12)

[Claims] 1. A fuel cell comprising a proton-conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the proton-conductive electrolyte membrane, and a gas flow channel having a gas inlet and an outlet. A positive electrode current collector disposed in contact with the gas flow path; a negative electrode current collector having a porosity disposed in contact with the other of the electrodes; A direct current power supply connected so that the electric plate becomes a negative electrode, and current detection means for detecting a current that changes according to the concentration of carbon monoxide gas in the gas to be detected including hydrogen flowing in the gas flow path. Carbon monoxide sensor. 2. The carbon monoxide sensor according to claim 1, wherein the gas flow path is provided only within an area of the electrode. 3. The carbon monoxide sensor according to claim 1, wherein a gold plating layer is formed on surfaces of the positive electrode current collector and the negative electrode current collector. 4. The carbon monoxide sensor according to claim 1, wherein a gas chamber having a gas outlet is provided on a side of the negative electrode current collector plate which is not in contact with the electrode, and the gas outlet is provided with a flow rate suppressing means. 5. A proton conductive electrolyte membrane, a positive electrode having a catalyst made of an alloy of platinum and gold disposed on one surface of the proton conductive electrolyte membrane, and the other of the proton conductive electrolyte membrane A negative electrode having a catalyst comprising platinum or an alloy of platinum and another noble metal disposed on the surface,
A direct current power supply in which the positive electrode is connected to the positive electrode and the negative electrode is connected to the negative electrode, and a current that changes according to the concentration of carbon monoxide gas in the gas to be detected including hydrogen flowing near the positive electrode is detected. A carbon monoxide sensor comprising: 6. A first electrolyte membrane having proton conductivity, a first positive electrode having a catalyst made of an alloy of platinum and gold disposed on one surface of the first electrolyte membrane, and said first electrolyte membrane A first detection unit including a first negative electrode having a catalyst made of platinum or an alloy of platinum and another noble metal disposed on the other surface of the membrane; and the first positive electrode being a positive electrode and the first negative electrode being a first negative electrode. A first direct-current power supply connected so as to be a negative electrode, and a first current for detecting a current that changes in accordance with the concentration of carbon monoxide gas in the gas to be detected containing hydrogen flowing near the first positive electrode Detecting means, a second electrolyte membrane having proton conductivity, a second positive electrode provided on one surface of the second electrolyte membrane and having a catalyst made of an alloy of platinum and ruthenium, and the second electrolyte membrane With platinum or platinum disposed on the other surface of A second detection unit comprising a second negative electrode having a catalyst comprising another noble metal alloy;
A second DC power supply in which the positive electrode is connected to the positive electrode and the second negative electrode is connected to the negative electrode, and a current that changes in accordance with the concentration of hydrogen gas in the gas to be detected flowing near the second positive electrode is detected. A second current detecting means for determining the hydrogen concentration in the gas to be detected from the current obtained from the second current detecting means, thereby obtaining a variation amount of the hydrogen concentration in the current obtained from the first current detecting means. A carbon monoxide sensor having a correction operation unit that corrects and converts to a concentration of carbon monoxide gas. 7. The carbon monoxide sensor according to claim 6, wherein the gas to be detected is introduced into the first detector and then into the second detector. 8. The carbon monoxide sensor according to claim 1, further comprising a detection procedure for turning on a DC power supply with the gas to be detected flowing through the carbon monoxide sensor and obtaining a concentration of the carbon monoxide gas. . 9. The carbon monoxide sensor according to claim 1, wherein a switching valve for introducing air is provided in a gas introduction section for introducing a gas to be detected. 10. The carbon monoxide sensor according to claim 9, wherein a gas to be detected is introduced into the gas introduction unit for a predetermined time, and then air is introduced into the gas introduction unit by the switching valve. 11. When air is introduced into the gas introduction unit, the DC power supply is shut off, and a voltage change rate is obtained by voltage detection means connected to the positive electrode and the negative electrode, and when the change rate of the voltage becomes negative, The carbon monoxide sensor according to claim 10, wherein the switching valve is configured to switch to a gas to be detected. 12. The apparatus according to claim 1, wherein a valve is provided in the gas introduction section and the gas discharge section for discharging the gas to be detected, and the valve is opened when operating and the valve is closed when not operating.
7. The carbon monoxide sensor according to claim 6.