JP2002243697A - Carbon monoxide sensor and fuel cell system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon monoxide sensor of high accuracy having few sudden changes in the output current. SOLUTION: Electrodes 2, having a catalyst arranged on both surfaces of a proton conductive electrolyte film, are housed in the gas chamber 7 provided between first and second collector plates 5 and 8, and a DC power supply 16 is connected, so that the first collector plate 5 becomes a positive electrode and the second collector plate 8 becomes a negative electrode, and an ammeter 17 is provided as a current detecting means for detecting a current changing corresponding to the concentration of the carbon monoxide gas in the hydrogen- containing gas to be detected which is introduced into the gas chamber 7. The detection of a current at a measuring voltage of not less than carbon monoxide oxidation potential and not more than the decomposition potential of water and the refreshing of the catalyst at a refreshing voltage of not less than the decomposition potential of water are set to one cycle, to change the voltage of the DC power supply 16, so as to calculate the concentration of the carbon monoxide gas by the repetition of the cycle.

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 reformed gas of a fuel cell system using a reformer, and a fuel cell system using the same. It is about.

[0002]

2. Description of the Related Art In recent years, fuel cells using solid polymer proton conductive membranes for home use and automobile use have been actively developed. Since this fuel cell uses hydrogen gas when operating, a reformer for extracting hydrogen gas by reforming liquid fuel such as methanol or city gas is required. However, the fuel gas coming out of the reformer contains a very small amount of carbon monoxide gas at a level of tens of ppm in addition to hydrogen gas, water (generated as steam), carbon dioxide gas, and the like. When this carbon monoxide gas is adsorbed on the platinum catalyst constituting the electrode of the fuel cell (this phenomenon is called poisoning),
The electromotive force 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 described above, a fuel gas (contains a large amount of hydrogen gas) supplied to function as a fuel cell
As a carbon monoxide sensor for detecting carbon monoxide gas therein, a sensor (CO gas sensor) described in WO97 / 40371 is known.

FIG. 12 shows a schematic structure of the CO gas sensor. The CO gas sensor 111 has a gas sampling container 116 which contains water 112 for keeping the inside in a humidified state, purges a gas to be detected, and also serves as a room for measuring the concentration of carbon monoxide gas. I have. Gas sampling container 11
A detection unit 130 for detecting the concentration of carbon monoxide gas is provided in 6.
Is installed, and an extraction lead wire of the detection unit 130 is connected to a voltage application device 119 disposed outside the gas collection container 116.
It is connected to the. An inlet 117 for introducing a gas to be detected (same as fuel gas) into the CO gas sensor 111,
An outlet 118 for discharging the gas to be detected is provided. Further, in order to adjust the pressure in the CO gas sensor 111, the pressure adjusting device 100 is connected to the inlet 117.

FIG. 13 shows a schematic sectional view of the structure of the detecting section 130. The detection unit 130 includes a detection electrode 113 made of a material in which a platinum catalyst is supported on porous carbon, and a detection electrode 113.
The solid polymer electrolyte membrane 120 is laminated by a counter electrode 114 or a reference electrode 115 disposed opposite to the above.

Next, a method of measuring the concentration of carbon monoxide gas in the gas to be detected by the CO gas sensor will be described.

The gas to be detected is introduced from the inlet 117 in the direction of the arrow in FIG.
Touch 30. The oxidation potential (0.65 to 1 V) of the carbon monoxide gas and the adsorption potential (0.65 V or less, for example, 0.4 V) of the carbon monoxide gas are held on the detection electrode 113 of the detection unit 130 for a certain period of time. The pulse potential is repeatedly applied by the voltage application device 119. When the gas to be detected comes into contact with the detection electrode 113 in this state, the detection electrode 1
A large amount of hydrogen contained in the gas to be detected is separated into hydrogen ions (hereinafter, protons) and electrons according to the formula (1) of Chemical Formula 1 on the platinum catalyst in No. 13. Protons pass through the solid polymer electrolyte membrane 120, and electrons reach the counter electrode 114 from the lead through an external circuit. Then, it returns to hydrogen again according to the formula (2) of the chemical formula (1). However, since the gas to be detected also contains a trace amount of carbon monoxide gas, the carbon monoxide gas is adsorbed on the platinum catalyst in the detection electrode 113 while the adsorption potential of the carbon monoxide gas is applied ( Poisoning) and inhibits the reaction of formula (1) of formula (1). As a result, the generated electrons are reduced, and the current flowing through the circuit is reduced. Since the degree of decrease in the current varies depending on the degree of adsorption of the carbon monoxide gas to the platinum catalyst, that is, the concentration of the carbon monoxide gas, the concentration of the carbon monoxide gas can be measured from the current value and the time change of the current. it can. When the oxidation potential of the carbon monoxide gas is applied to the detection electrode 113, the adsorbed carbon monoxide is oxidized to become carbon dioxide gas and desorbed from the platinum catalyst. (Hereinafter, this operation is called refresh).

[0008]

Embedded image

FIG. 14 shows an output current (response current) characteristic diagram of the CO gas sensor by the above operation. FIG. 14A shows the state of the applied voltage (pulse potential), and FIG. 14B shows the response current according to the applied voltage. FIG. 14B shows that when the adsorption potential of carbon monoxide gas is applied to the detection electrode 113, carbon monoxide is adsorbed on the platinum catalyst, and the response current decreases with time. In the conventional CO gas sensor, the response current drop characteristics (current I0 at time t0, current I1 at time t1, current I2 at time t2,...) Are used to calculate the carbon monoxide gas using the difference or ratio of the current values. The concentration is calculated.

[0010]

When a conventional CO gas sensor was prototyped and evaluated, the output current (response current) suddenly changed in long-term continuous measurement at the same carbon monoxide gas concentration or in repeated reproducibility evaluation measurement. It became clear that dots appeared repeatedly. FIG. 1 shows the output current characteristics at that time.
It is shown in FIG. As shown by the dotted line in the figure, the output current sharply increases while the adsorption potential of the carbon monoxide gas is applied, that is, while the current value characteristic for determining the concentration of the carbon monoxide gas is measured. There was a point where the current value changed, and the subsequent change in the current value drawn a curve having a different slope from the previous one.
Therefore, I0, I1, I2,... Described in FIG.
Will vary in spite of the same concentration of carbon monoxide gas, and it is clear that the correct carbon monoxide gas concentration cannot be determined from these data even if the difference or ratio is calculated.

As a result of investigating the cause of such a rapid rise in output current, the following model is considered to be the main cause.
In other words, when water molecules accompanying transport during proton conduction reach the counter electrode 114, water condenses in the porous carbon (carbon paper) constituting the counter electrode 114, liquefies, and gradually clogs. However, since water molecules are transported one after another, the condensed water in the carbon paper is pushed out of the carbon paper at a stretch when a certain amount is collected, and is discharged out of the detection unit 130 as water droplets. As a result, the clogging of the carbon paper is rapidly eliminated, and the hydrogen gas generation reaction {Formula (2)} on the counter electrode 114 is smoothly performed. Therefore, it is considered that the amount of proton conduction increases, and as a result, the output current sharply increases.

The present invention solves this problem,
It is an object of the present invention to provide a highly accurate carbon monoxide sensor without an abrupt change in output current and a fuel cell system using the same.

[0013]

Means for Solving the Problems To solve this problem, the invention according to claim 1 of the present invention provides a proton conductive electrolyte membrane and an electrode having a catalyst disposed on both sides of the electrolyte membrane. An opening into which the gas to be detected is introduced, and a gas chamber having a cross-sectional area smaller than the area of the electrode connected to the opening, and the gas chamber is in contact with one surface of the electrode A first current collector disposed in such a manner as described above; a second current collector having the same shape as the first current collector disposed in contact with the other surface of the electrode; A DC power source connected so that the electric plate is a positive electrode and the second current collector is a negative electrode, and changes according to the concentration of carbon monoxide gas in the gas to be detected including hydrogen introduced into the gas chamber. Current detecting means for detecting a current flowing through the battery, and a power supply for decomposing water at a carbon monoxide oxidation potential or higher. And the current detection at the following measurement voltage, the catalyst refresh the decomposition potential than the refresh voltage of water changing the voltage of the DC power supply as one cycle,
Because the concentration of carbon monoxide gas was determined by repeating the above cycle, a large amount of water molecules were transported together with the protons due to the high measurement voltage, and were discharged from the detection element as water vapor without liquefaction in the carbon paper. This has the effect that the clogging of water in the carbon paper is eliminated and the output current does not suddenly change.

According to a second aspect of the present invention, in the first aspect of the present invention, the carbon monoxide is measured based on a value of a current flowing through the element after a predetermined time has passed after the application of the measurement voltage and a current change rate near the time point. Since the concentration of the gas is determined, there is an effect that the concentration of the carbon monoxide gas at a low concentration can be determined with high accuracy.

According to a third aspect of the present invention, in the first aspect of the present invention, the opening of the first current collector and the opening of the second current collector are arranged in the same direction. There is no need to distinguish between the first current collector plate and the second current collector plate when assembling the carbon monoxide sensor, which has an effect of facilitating assembly.

According to a fourth aspect of the present invention, there is provided a fuel cell system having a reformer for reforming a hydrocarbon fuel to generate hydrogen gas, wherein a reformed gas connecting the reformer to a fuel cell stack is provided. A bypass pipe for flowing a gas to be detected is provided in a part of the pipe, and a carbon monoxide sensor is disposed in the bypass pipe, so that the concentration of the carbon monoxide gas in the reformed gas immediately before being introduced into the fuel cell stack is detected. Can and
When the gas to be detected passes through the bypass pipe, the gas temperature is lowered, and the carbon monoxide sensor can be prevented from being deteriorated by heat.

According to a fifth aspect of the present invention, in the invention of the fourth aspect, the flow rate of the gas to be detected flowing through the bypass pipe is 0.1% or more and 1% or less of the flow rate of the reformed gas flowing through the main pipe. This has the effect that the concentration of the carbon monoxide gas can be detected with high response without waste of the reformed gas.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, since the orifice is provided in a part of the bypass pipe, the flow rate of the reformed gas flowing through the bypass pipe can be reduced to 0.1% of the main pipe. % To 1% or less.

According to a seventh aspect of the present invention, in the sixth aspect of the present invention, the orifice is provided upstream of the carbon monoxide sensor. Can be reduced, and the accuracy of the carbon monoxide sensor can be increased.

According to an eighth aspect of the present invention, in the invention according to the fourth aspect, a part of the bypass pipe is arranged in a direction perpendicular to the ground, and the gas to be detected flowing through the bypass pipe flows to the ground. Since the carbon monoxide sensor is arranged inside the vertical portion of the bypass pipe, the dew water generated in the bypass pipe flows in the ground direction, does not clog the bypass pipe, and has an effect that a stable output can be obtained.

According to a ninth aspect of the present invention, in the invention according to the eighth aspect, since the opening of the carbon monoxide sensor is arranged in the ground direction, the condensed water generated in the vicinity of the opening flows in the ground direction. This has the effect that the vicinity of the section is not clogged and a stable output is obtained.

According to a tenth aspect of the present invention, in the invention according to the fourth aspect, a part of the bypass pipe is inclined with respect to the ground, and the gas to be detected flowing through the bypass pipe flows toward the ground. Since the carbon monoxide sensor is disposed on the inclined portion, the dew water generated in the bypass pipe flows in the ground direction, so that the dew water does not become clogged in the bypass pipe, and a stable output is obtained.

According to an eleventh aspect of the present invention, in the invention of the tenth aspect, the opening of the carbon monoxide sensor is arranged in a direction perpendicular to the peripheral surface of the bypass pipe. Condensed water generated in the vicinity of the opening in the direction of the ground flows in the direction of the ground, so that the vicinity of the opening is not clogged and a stable output can be obtained.

According to a twelfth aspect of the present invention, in the eleventh aspect of the present invention, the carbon monoxide sensor is disposed such that the opening of the first current collector plate is on the upstream side of the bypass pipe.
The gas to be detected discharged from the second current collecting plate is no longer taken in again from the opening of the first current collecting plate, and has the effect that the concentration of the carbon monoxide gas can be detected with high accuracy.

According to a thirteenth aspect of the present invention, in the fourth aspect of the present invention, since the distal end of the bypass pipe is connected to the main pipe on the fuel cell stack outlet side, a pressure difference is generated upstream and downstream of the bypass pipe. In addition, the gas to be detected always flows from the upstream to the downstream, the influence of the backflow can be eliminated, and the effect of detecting the concentration of the carbon monoxide gas with high accuracy can be obtained.

According to a fourteenth aspect of the present invention, in the thirteenth aspect, the distal end of the bypass pipe is connected to the main pipe on the outlet side of the fuel cell stack vertically or at an angle to the ground. Condensed water generated at the tip of the bypass pipe flows in the direction of the ground, and there is no clogging of the condensed water at the tip of the bypass pipe, so that a stable output can be obtained.

According to a fifteenth aspect of the present invention, in the fourth aspect, a part of the carbon monoxide sensor or
Since a temperature sensor is provided in a part of the bypass pipe near the carbon monoxide sensor, fluctuations in output due to the temperature of the gas to be detected can be corrected, and even if the temperature fluctuates, the concentration of carbon monoxide gas can be detected with high accuracy. Has an action.

According to a sixteenth aspect of the present invention, in the fourth aspect, a part of the carbon monoxide sensor or
Since a pressure sensor is provided in a part of the bypass pipe near the carbon monoxide sensor, fluctuations in output due to the pressure of the gas to be detected can be corrected, and even if the pressure fluctuates greatly, the concentration of carbon monoxide gas can be detected with high accuracy. It has the action of:

According to a seventeenth aspect, in the fourth aspect, a carbon monoxide sensor mounting portion, a temperature sensor mounting portion, and a pressure sensor mounting portion on the bypass pipe are the same as the bypass pipe. Has the effect of preventing material corrosion due to the formation of a local battery due to the contact of dissimilar materials, especially dissimilar metal materials, and the presence of moisture.

According to the eighteenth aspect of the present invention, the carbon monoxide sensor, the temperature sensor, and the pressure sensor are attached to the bypass pipe in an electrically insulated state. This has the effect of reducing the influence of noise between the sensors and the noise mixed in from the bypass pipe, and of preventing material corrosion.

According to a nineteenth aspect of the present invention, in the invention of the fourth aspect, the surfaces of the carbon monoxide sensor, the temperature sensor, the pressure sensor, and the portion of the bypass pipe contacting the gas to be detected are subjected to hydrophilic treatment. Even if the moisture contained in the gas to be detected is condensed, the dew condensation water is prevented from being clogged.

According to a twentieth aspect of the present invention, since the unevenness surface is provided as the hydrophilic treatment in the nineteenth aspect, it is possible to prevent the clogging of dew condensation water with a simple configuration.

According to a twenty-first aspect of the present invention, the titanium oxide layer is provided as a hydrophilic treatment in the nineteenth aspect, so that adhesion of dew condensation water can be prevented from the initial stage of dew condensation, and the influence of clogging is minimized. It has the effect that it can be limited.

According to a twenty-second aspect of the present invention, in the twenty-first aspect, the titanium oxide layer has a structure having an anatase type crystal structure, so that the maximum effect in preventing the adhesion of dew condensation water is obtained. Have.

According to a twenty-third aspect of the present invention, the thickness of the titanium oxide layer is 0.1 μm.
Since the thickness is 1 μm or less, the titanium oxide layer has the effect of preventing the adhesion of dew water without peeling.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is an exploded perspective view for explaining a schematic structure of Embodiment 1 of a carbon monoxide sensor of the present invention. FIG. 2 is a partially cutaway perspective view when the sensor is attached to a pipe. FIG. 3 is a piping diagram of mounting the sensor on a fuel cell system. FIG. 4 is a characteristic diagram showing the carbon monoxide concentration dependency of the current immediately before refresh of the sensor. FIG. 5 is a characteristic diagram showing the carbon monoxide concentration dependency of the average poisoning rate of the sensor.

In FIG. 1B, reference numeral 1 denotes a proton conductive electrolyte membrane made of a fluorine-based polymer material and having a diameter of 14 mm, and both surfaces thereof are alloyed so that the ratio of platinum to gold is 3: 1. The carbon powder on which the catalyst is supported is
Two electrodes 2 having a structure fixed on a 0 mm carbon cloth with a fluorine-based polymer material are provided. A seal member 3 made of a silicon-based polymer having a thickness of 0.25 mm is provided on the outer periphery of each of the two electrodes 2 to prevent gas leakage. The electrolyte membrane 1 sandwiched between the two electrodes 2 and the sealing material 3 is fixed by a hot press at a temperature of 130 ° C.

Thus, the electrolyte membrane 1 and the two electrodes 2
As shown in FIG. 1A, a stainless steel (for example, JIS SUS316, hereinafter, all stainless steels are SUS316) is provided on one surface of the detection element 4 composed of the sealing material 3 and the two sealing materials 3. A first current collector plate 5 is provided. The first current collecting plate 5 is provided with a first current collecting plate opening 6 having a diameter of 4 mm serving as an inlet of a gas to be detected and a gas chamber 7 having a diameter of 8 mm connected to the first current collecting plate opening 6 by cutting. Have been. Since the cross-sectional area of the gas chamber 7 is smaller than the area of the electrode 2, the electrode 2 is in contact with the first current collector 5 so as to cover the gas chamber 7.

On the other surface of the detecting element 4, a first current collector 5
A second current collecting plate 8 having the same configuration as that described above is provided. The second current collecting plate 8 is also provided with a second current collecting plate opening 9 serving as a gas outlet and a gas chamber 7, and the electrode 2 is in contact with the second current collecting plate 8 so as to cover the gas chamber 7. I have.

The first current collector plate opening 6, gas chamber 7, and
The surface of the second current collector plate opening 9 is provided with an uneven surface by an acid treatment.

The first current collector, the detecting element 4 and the second current collector 8 are arranged such that the first current collector opening 6 and the second current collector opening 9 face in the same direction. The layers are stacked in this order, and the whole is fixed with resin screws 10 having insulating properties. With such a configuration, the first current collector plate 5 and the second current collector plate 8 have a symmetrical shape with the detection element 4 as a center, so that it is not necessary to distinguish them when assembling the carbon monoxide sensor. , Increased productivity.

The first current collector plate 5 and the second current collector plate 8 are provided with a female screw 11, and a washer 14 to which the positive electrode lead wire 12 and the negative electrode lead wire 13 are connected is provided with a washer fixing screw 15. Each is fixed.

A DC power supply 16 is connected to the positive lead wire 12 and the negative lead wire 13. First current collector 5
An ammeter 17 as a current detecting means is connected in series with the DC power supply 16 in order to detect a current flowing between the DC power supply 16 and the second current collector plate 8. The output of the ammeter 17 is connected to a microcomputer 18. Microcomputer 18
Performs a predetermined calculation from the current detected by the ammeter 17, outputs the concentration of carbon monoxide gas, and continuously controls the voltage of the DC power supply 16 to refresh the catalyst.

FIG. 2 shows the mounting state of the carbon monoxide sensor having such a configuration. Reference numeral 25 denotes a stainless steel bypass pipe branched from a part of a reformed gas main pipe connecting a fuel cell stack and a reformer for reforming a hydrocarbon-based fuel such as natural gas or methanol to generate hydrogen gas. The gas to be detected flows therein. The inner surface of the bypass pipe 25 is provided with irregularities by an acid treatment similarly to the gas chamber 7, the first current collector plate opening 6, and the second current collector plate opening 9.

The carbon monoxide sensor 20 is fixed inside the bypass pipe 25. At this time, the first current collector plate opening 6 and the second current collector plate opening 9 were fixed so as to face the downstream direction of the bypass pipe 25. In FIG. 2, the gas to be detected flows in the direction of the white arrow.

In the carbon monoxide sensor 20, a stainless steel positive electrode plate 21 and a negative electrode plate 22 as washers 14 are fixed by screws (not shown, the same as the screws 15 in FIG. 1). The positive electrode plate 21 and the negative electrode plate 22 are fixed by penetrating a positive electrode plate insulating material 23 made of Teflon (registered trademark) and a negative electrode plate insulating material 24 press-fitted into a part of a bypass pipe 25. Therefore, the carbon monoxide sensor 20 is
1 and the negative electrode plate 22 are mechanically fixed to the bypass pipe 25. At the same time, the positive electrode plate 21 and the negative electrode plate 22 are connected to the positive electrode lead 12 and the negative electrode lead 13, respectively. The connection is also made. Further, the carbon monoxide sensor 20 is connected to the bypass pipe 2.
5, but is electrically insulated.

FIG. 3 shows a schematic piping diagram of a fuel cell system including a carbon monoxide sensor with such a mounting.
The hydrocarbon-based fuel is mixed with steam,
0, a chemical reaction is caused on each catalyst by sequentially passing through a shift converter 31 and a carbon monoxide remover 32,
It becomes a hydrogen-rich reformed gas containing a large amount of water vapor. However, carbon monoxide gas is also generated in the course of the reaction, and remains slightly even through the carbon monoxide remover 32. Therefore,
In order to protect the fuel cell 34 from poisoning, when the concentration of the carbon monoxide gas in the reformed gas is high (20 ppm or more in the first embodiment), the switching valve 33 is set so as not to introduce the reformed gas. And the reformed gas having a high concentration of carbon monoxide gas needs to flow directly to the combustor 36. for that reason,
A bypass pipe 25 is provided between the main pipe connecting the carbon monoxide remover 32 and the fuel cell 34 to monitor the concentration of carbon monoxide gas in the reformed gas, and the concentration of carbon monoxide gas is less than 20 ppm. Then, the switching valve 33 is controlled to introduce the reformed gas into the fuel cell 34. Therefore, the carbon monoxide sensor 20 has a carbon monoxide gas concentration of 20 ppm.
It is arranged to output whether or not this is the case.

The carbon monoxide sensor 20 is provided in a part of the bypass pipe 25 as shown by a dotted line. Note that an enlarged cross-sectional view of a portion indicated by a dotted line corresponds to FIG. An orifice 35 made of stainless steel is arranged in a part of the bypass pipe 25 and upstream of the carbon monoxide sensor 20. This makes it very easy for the flow rate of the gas to be detected flowing in the bypass pipe 25 to fall within the range of 0.1% to 1% of the flow rate of the reformed gas flowing in the main pipe. As a result of a preliminary study at various flow rates, the flow rate in the above range does not significantly affect the rated power generation of the fuel cell 34 and is optimal for the gas replacement in the bypass pipe 25 to be performed sufficiently quickly. Met. Further, by providing the orifice 35 on the upstream side, the pressure change of the reformed gas due to the load fluctuation during the operation of the fuel cell was not directly received, and the influence of the pressure was reduced.

The carbon monoxide remover 32 and the fuel cell 3
Although a configuration in which the carbon monoxide sensor 20 is provided in a part of the main pipe connecting the pipes 4 is also conceivable, the temperature of the reformed gas exiting from the carbon monoxide remover 32 is as high as about 100 ° C. to 200 ° C. Then, the electrolyte membrane 1 made of a fluorine-based polymer deteriorates. Therefore, the bypass pipe 25 is provided, and the temperature is lowered by natural cooling while the gas to be detected flows through the bypass pipe 25. The gas temperature fluctuates depending on the operating conditions of the reformer.
The following is desired. Therefore, various operation states of the reformer are tried, and the carbon monoxide sensor 20 is arranged in a portion where the detected gas does not exceed 90 ° C. in the bypass pipe 25. Also,
Since the gas to be detected is cooled by the bypass pipe 25, a large amount of water vapor contained in the gas to be detected is always condensed.
5, the first current collector plate opening 6 of the carbon monoxide sensor 20, the second
Condensation water may be clogged at the current collector plate opening 9 and the like, and the gas to be detected may not flow. Therefore, the following configuration was adopted as a measure against dew condensation including the piping.

As shown in FIG. 3, the bypass pipe 25 is arranged so as to be perpendicular to the ground so that the gas to be detected flows in the ground direction. Further, the carbon monoxide sensor 20 was fixed such that the first current collector plate opening 6 and the second current collector plate opening 9 face the ground direction (downstream direction). As a result, water generated in the gas to be detected is dew-condensed in the bypass pipe 25, the first current collector plate opening 6, the second current collector plate opening 9, and the like, and the water generated by the gravity flows downstream due to gravity. Furthermore, the bypass pipe 2
Since the inner surface of 5 is provided with irregularities, even if water droplets adhere, the contact angle becomes smaller, and it becomes easier to flow downstream. Therefore, the gas to be detected could flow through the carbon monoxide sensor 20 without water clogging in the bypass pipe 25.

The tip of the bypass pipe 25 was connected to the main pipe on the outlet side of the fuel cell 34 so as to be perpendicular to the ground. As a result, the dew condensation water does not clog at the end of the bypass pipe 25. Note that a configuration in which the end of the bypass pipe 25 is returned to the main pipe connecting the carbon monoxide remover 32 and the fuel cell 34 again is conceivable, but in this case, since the pressure difference between the upstream and downstream of the bypass pipe 25 is extremely small, There is a possibility that the gas to be detected hardly flows, or the gas flows backward depending on the operation fluctuation of the reformer, so that the concentration of the carbon monoxide gas cannot be detected accurately. In the case of the first embodiment,
The distal end of the bypass pipe 25 is connected to the outlet main pipe of the fuel cell 34, and the outlet main pipe always has a lower pressure than the inlet main pipe due to pressure loss in the fuel cell 34, so that backflow does not occur. The concentration of carbon monoxide gas can be detected with high accuracy.

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

In FIG. 2, when the gas to be detected flows from the direction of the white arrow in a state where the carbon monoxide sensor 20 is in operation (voltage is applied), a part of the gas is connected to the positive electrode plate 21. The first current collector plate 5 is introduced into the first current collector plate opening 6. This is for the following reason.

Since a positive voltage is applied to the first current collecting plate 5, the hydrogen gas contained in the gas chamber 7 is filled on the catalyst in the electrode 2 in contact with the first current collecting plate 5 in FIG. It is separated into protons and electrons according to the formula (1) of the chemical formula 1). Both return to hydrogen gas on the catalyst in the electrode 2 which is in contact with the second current collector plate 8 which is a negative electrode, according to the formula (2). This means that the carbon monoxide sensor 20 performs an operation like a pump so as to transport hydrogen gas from the positive electrode side to the negative electrode side (hereinafter, referred to as pumping). As a result, pumping from the positive electrode side to the negative electrode side is always performed when the carbon monoxide sensor 20 is in the operating state,
The amount of hydrogen gas present in the gas chamber 7 provided in the first current collector 5 decreases, and the gas pressure becomes negative. Therefore, the gas to be detected is sucked from the first current collector plate opening 6.

Further, as a result of the pumping, hydrogen gas is sequentially generated in the gas chamber 7 provided in the second current collecting plate 8 to be in a pressurized state. Therefore, the generated hydrogen gas is discharged from the second current collector plate opening 9.

For these reasons, the gas to be detected is introduced only from the first current collector plate opening 6 on the positive electrode side, and does not enter through the second current collector plate opening 9. This means that the gas to be detected does not reach the catalyst in the electrode 2 that is in contact with the second current collector plate 8, and as a result, the catalyst is not poisoned by the carbon monoxide gas, and As shown in the example, a complicated operation of periodically applying a reverse potential to refresh the negative electrode 2 becomes unnecessary.

A DC power supply 16 is connected between the first current collector plate 5 and the second current collector plate 8, and the DC power source 16 is continuously operated by the microcomputer 18 without interruption of the measurement voltage and the refresh voltage. Is controlled so that it can be applied to the detection element 4. In the first embodiment, the measured voltage is 1 V, which is not less than the carbon monoxide oxidation potential and not more than the decomposition potential of water, that is, in the range of 0.65 V to 1.23 V.
And Also, the refresh voltage is higher than the decomposition potential of water,
That is, the voltage was set to 1.3 V which is 1.23 V or more. The default time of one cycle was 8 seconds for measurement and 2 seconds for refresh, for a total of 10 seconds.

By this operation, the hydrogen gas in the gas to be detected causes the reactions shown in the chemical formula 1 on the positive electrode and the negative electrode on the catalyst of the electrode 2 as described above.

As shown in the formula (1) of the chemical formula 1, a dissociation reaction of hydrogen gas occurs at the electrode 2 on the positive electrode side, and the proton (H ⁺ ) generated here passes through the electrolyte membrane 1 and the electrode on the negative electrode side. 2 where the electron (e ⁻ ) is received again as shown in the formula (2) of the chemical formula (1) to generate hydrogen gas. Therefore, in the presence of hydrogen gas, an electric closed circuit is formed between the detection element 4 and the DC power supply 16, and a current flows according to the proton conductivity. This current is detected by the ammeter 17 and the ammeter 17
And outputs a signal corresponding to the concentration of the carbon monoxide gas.

Next, the signal processing calculated in the microcomputer 18 will be described in detail below.

Assuming the gas state of the reformer immediately after startup, the concentration of the carbon monoxide gas is set to 1% in the carbon monoxide sensor 20.
30 minutes, 0.1% 10 minutes, 100 ppm 10 minutes, 50p
pm 10 minutes, 20 ppm 10 minutes, 10 ppm 10 minutes, 5
I tried to introduce it by decreasing step by step in the order of ppm 40 minutes.
The other components of the gas to be detected are hydrogen 80%, nitrogen 5%,
The balance is adjusted to be carbon dioxide. These simulated gases to be detected were humidified by a bubbler and introduced. The gas flow rate at the time of measurement was the gas flow rate (about 3
(0 l / min), 300 cc / min corresponding to 1%, and the gas temperature was 80 ° C.

The current value detected by the ammeter 17 in the above measurement gradually decreases from the time when the refresh voltage is applied for 2 seconds and then switched to the measured voltage. This is because carbon monoxide in the gas to be detected is adsorbed on the catalyst in the electrode 2, and the reaction of the formula (1) of Chemical Formula 1 is inhibited.

The microcomputer 18 stores the current value being measured in a memory every second. The current value is referred to as I (i). Here, i is the time (second) after the start of measurement.
In the first embodiment, i = 1, 2,..., 8.

When the measurement is completed for a predetermined time (8 seconds),
The microcomputer 18 raises the voltage of the DC power supply 16 to the refresh voltage (1.3 V), and within a predetermined time from the obtained current value data I (i) (the first embodiment).
In this case, the current change speed (hereinafter, referred to as an average poisoning speed) MV is calculated according to (Equation 1). That is, MV corresponds to the gradient of the current value near the predetermined time of the measurement (between immediately before refreshing and 2 seconds before).

[0066]

(Equation 1)

When a refresh voltage is applied, the electrode 2
On the catalyst inside, the hydroxyl groups and oxygen generated by electrolysis of water vapor contained in the gas to be detected react with the adsorbed carbon monoxide to produce carbon dioxide gas as shown in (Chem. 2). Carbon monoxide can be removed from the catalyst.
In (Chemical Formula 2), (g) indicates gas, and (a) indicates adsorption to the catalyst.

[0068]

Embedded image

By repeating such an operation, the concentration of carbon monoxide gas can be measured while refreshing the catalyst.

Next, the results of the above measurements are shown in FIGS. FIG. 4 shows the current value after the lapse of the predetermined measurement time (8 seconds), that is, the current RI immediately before refresh {RI = I (8) in the first embodiment} dependence on the carbon monoxide concentration. FIG. 5 shows the average poisoning rate M calculated from (Equation 1).
4 shows the dependence of V on carbon monoxide concentration. In addition, the measurement was performed 5 times under the same conditions, and the results were collectively shown in each figure.

FIG. 4 shows that when the concentration of the carbon monoxide gas is high, the current immediately before the refresh changes greatly when the gas concentration is switched, and the concentration dependency is obtained. However, when the concentration becomes low, the variation between the measurements becomes larger than the change due to the concentration of the carbon monoxide gas.
In the region indicated by the middle and thin dotted lines, it was found that the current immediately before refreshing overlapped even at a different concentration, and it was not possible to discriminate the concentration at or above the target of 20 ppm or more.

Therefore, the concentration dependency of the average poisoning rate MV is examined from FIG.
From 10 to 10 ppm, the MV has clearly changed,
In addition, it was found that there was almost no influence of the variation due to five measurements. Therefore, a threshold (-0.3 mA / s) as shown by a thick dotted line in FIG. 5 is provided, and it is determined whether or not the concentration of the carbon monoxide gas is 20 ppm or more based on whether or not the MV is not less than the threshold. I knew I could do it.

However, in FIG. 5, when the concentration of the carbon monoxide gas is 1%, MV may almost depend on the threshold value. This is because when a high concentration of carbon monoxide gas as high as 1% is introduced, it is almost instantaneously adsorbed on the catalyst, and the current change (slope: MV) after 6 to 8 seconds becomes extremely gentle. This is because it becomes impossible to distinguish from a gradual change in current when the concentration of carbon oxide gas is low. Therefore, when the MV alone determines the concentration of carbon monoxide gas,
Even at 1%, a signal of less than 20 ppm may be output. Therefore, as shown in FIG. 4, when the concentration of the carbon monoxide gas is high, the catalyst is heavily poisoned, and the current RI immediately before the refresh is obviously reduced. A rough judgment is made, and in a thin region (for example, the threshold indicated by a thick dotted line in FIG. 4 = 130 mA or more), the comparison judgment with the MV threshold is performed as described above. As a result, 20
It was possible to output whether it was not less than ppm.

Further, in the first embodiment, the sudden change in the output current (response current), which was a problem of the conventional example, did not occur even during five measurements, as can be seen from FIG. This is because the measurement voltage was set to 1 V which is equal to or higher than the carbon monoxide oxidation potential and equal to or lower than the decomposition potential of water. The reason will be described below.

The following model is considered as a cause of the sudden change in the output current as shown in FIG. 15 in the conventional example. When protons conduct through the electrolyte membrane made of a fluorine-based solid polymer, several molecules of water are simultaneously conducted, and the water precipitates in the carbon paper used for the negative electrode and gradually liquefies. . However, during the operation of the carbon monoxide sensor, water molecules are further conducted, and when a certain amount of water accumulates, the water is suddenly discharged from the carbon paper. as a result,
It is considered that the gas flow on the negative electrode side suddenly improves and the output current increases.

Therefore, in order to avoid a sudden change in the output current, it is sufficient that the precipitated water is discharged in a gaseous state before being liquefied in the carbon paper. For this purpose, if the measurement voltage is set to a voltage (1 V) higher than 0.4 V shown in the embodiment and water molecules are transported in large quantities one after another with protons, the water molecules are not liquefied in the carbon paper, and It is considered to be discharged as it is.

Since the voltage of 1 V is a region in which the oxidation wave of the adsorbed carbon monoxide is detected from the cyclic Holtogram shown in the conventional example, the carbon monoxide adsorbed on the catalyst undergoes an oxidation reaction. It desorbs from the catalyst as carbon dioxide gas. However, in the study of the inventors, as shown in FIG. 4, the value of the current flowing through the detection element clearly changes according to the concentration of the carbon monoxide gas. It is thought that not all can be oxidized by an applied voltage of 1V. In other words, although there is carbon monoxide that is partially oxidized and removed, at the same time, there is also adsorbed carbon monoxide, and the current value determined by the balance of adsorption and desorption depending on experimental conditions such as the concentration and temperature of carbon monoxide gas is observed. A model that has been considered.

Therefore, even if the measured voltage is equal to or higher than the carbon monoxide oxidation potential, the concentration can be detected. However, the higher the measurement voltage, the better. That is, when the measurement is performed at a voltage equal to or higher than the decomposition potential of water, the reaction shown in (Chem. 2) occurs from the side where carbon monoxide is adsorbed, which corresponds to measurement while refreshing. Even at this potential, the dependency on the concentration of carbon monoxide can be obtained, but the sensitivity is low and the accuracy is lowered. Accordingly, the upper limit of the measurement voltage is set to be equal to or lower than the decomposition potential of water, and the refresh voltage is set to be equal to or higher than the decomposition potential of water. When the measurement voltage was in the range of the carbon monoxide oxidation potential or higher and the water decomposition potential or lower, there was no sudden change in the output current, and practical sensitivity could be obtained.

With the above configuration and operation, a high-precision carbon monoxide sensor having no sudden change in output current was obtained.

(Embodiment 2) FIG. 6 is a partial cross-sectional view of a carbon monoxide sensor according to Embodiment 2 of the present invention attached to a bypass pipe. FIG. 7 is a characteristic diagram showing the carbon monoxide concentration dependency of the current just before refresh of the same sensor when the gas flow rate is changed. FIG. 8 is a characteristic diagram showing the carbon monoxide concentration dependency of the average poisoning rate of the sensor when the gas flow rate is changed. FIG. 9 is a characteristic diagram showing the carbon monoxide concentration dependency of the current immediately before refresh of the same sensor when the gas temperature is changed. FIG. 10 is a characteristic diagram showing the carbon monoxide concentration dependency of the average poisoning rate of the sensor when the gas temperature is changed. FIG. 11 is an output calculation and control flowchart of the sensor. (Table 1) is a threshold value table of the current just before refreshing and the average poisoning rate depending on the gas temperature.

Since the structure of the second embodiment is exactly the same as the structure of the carbon monoxide sensor described in the first embodiment, the same portions are denoted by the same reference numerals and the detailed description of the structure is omitted.

That is, the feature of the second embodiment is that FIG.
The carbon monoxide sensor 20 is not built in the bypass pipe 25 as shown in FIG. By adopting such a configuration, the position and dimensions of the bypass pipe 25 are not affected, and the degree of freedom in mounting the carbon monoxide sensor 20 is increased.

Hereinafter, the carbon monoxide sensor according to the present embodiment will be described in detail.

In FIG. 6, the carbon monoxide sensor 20 is made of stainless steel (for example, J
SUS316 of IS standard, all stainless steel below
Washer fixing screw 1 in case 40
5 is fixed together with the washer 14. Where 2
The washer fixing screws 15 are screwed through an insulating material (not shown) made of Teflon pressed into a part of the case 40 so as not to short-circuit each other. Both ends of the case 40 are threaded, and are connected and fixed to the bypass pipe 25 and a stainless steel nut 41, respectively.

Incidentally, as shown in FIG.
Is bent so as to have a part inclined with respect to the ground, and the carbon monoxide sensor 20 is arranged on the inclined part. The gas to be detected flows in the direction of the white arrow in FIG. 6, that is, in the direction of the ground. Also, the bypass pipe 25 and the case 40
Has a 0.5 μm-thick titanium oxide layer having an anatase crystal structure as a hydrophilic treatment. The titanium oxide layer was formed by immersing the bypass tube 25 and the case 40 in a titanium-containing organic complex solution and then sintering at 500 ° C. in the atmosphere until a predetermined thickness was obtained. Here, if the thickness of the titanium oxide layer is too small, the effect of the hydrophilic treatment does not appear, and if it is too large, there is a possibility of peeling. As a result of the examination, the thickness is preferably 0.1 μm or more and 1 μm or less.
It has been found that the range between 2 μm and 0.5 μm is optimal. Also, titanium oxide is originally known to exhibit a hydrophilic effect by irradiation with ultraviolet energy, but as a result of examination, it has been found that titanium oxide has a certain degree of hydrophilic effect even in a portion of the pipe where ultraviolet light does not strike as in the second embodiment. I found it. This is because the gas to be detected flowing in the bypass pipe 25 is obtained by branching off a part of the reformed gas flowing from the carbon monoxide remover 32, and thus has a high temperature of about 100 ° C. or more. Since a part of the titanium atoms on the surface of the titanium layer can be brought into an excited state, it is considered that a hydrophilic effect was obtained by attaching a hydroxyl group thereto. Although this hydrophilic effect was lower than that during irradiation with ultraviolet rays, it was sufficient for suppressing the clogging of dew water, which is the purpose of the hydrophilic treatment. Note that the crystal structure of the titanium oxide layer was higher in hydrophilic effect in anatase type than in rutile type. This is because the latter has a narrower band gap and can be easily excited as compared with the former.

As a result, even if water vapor in the gas to be detected is condensed in the pipe, the condensed water flows in the direction of the ground due to gravity, and water droplets due to the dew condensation on the surface of the pipe and the like also become hydrophilic in the titanium oxide layer. The effect reduces the contact angle and facilitates flow, so that dew condensation does not clog the piping.

The carbon monoxide sensor 20 is mounted so that the first current collector plate opening 6 and the second current collector plate opening 9 are in a direction perpendicular to the peripheral surface of the bypass pipe 25 and the first current collector plate The opening 6 is arranged on the upstream side. With this mounting, even if dew water is generated in the first current collector plate opening 6 and the second current collector plate opening 9, as shown in FIG.
Since the current collector plate opening 6 and the second current collector plate opening 9 always face in a direction inclined with respect to the ground, the bypass pipe 2 is moved by gravity.
5 flows downstream. Accordingly, the first current collector plate opening 6 and the second current collector plate opening 9 are no longer clogged with dew condensation water. Further, the first current collector plate opening 6 is connected to the second current collector plate opening 9.
The second current collector plate opening 9
6 flows downstream as indicated by the small arrow in FIG. 6, and is not introduced again through the first current collector plate opening 6. Therefore, only the gas to be detected on the upstream side is always the first gas.
Since the gas is introduced from the current collector plate opening 6, the concentration of the carbon monoxide gas can be accurately detected.

The case 40 is provided with a temperature sensor 42 in which the thermistor is protected by stainless steel, and a semiconductor pressure sensor 43 having a stainless steel pressure receiving portion. Since both sensors are made of the same material as the case 40, even if dew condensation water adheres, a local battery that is formed when water adheres to the dissimilar metal contact portion does not form. Therefore,
The structure was resistant to corrosion. In addition, since all the sensors are fixed via a Teflon sealing material (not shown), it is possible to reduce the influence of noise in the electric signal between the sensors and the noise mixed in from the bypass pipe,
At the same time, the structure is such that no material corrosion occurs. The above-mentioned hydrophilic treatment is also applied to the portions of these sensors in contact with the gas to be detected in order to prevent clogging of dew condensation water.

The connection of the bypass pipe 25 in the fuel cell system is the same as that of FIG. 3 described in the first embodiment, and the carbon monoxide sensor of FIG. 6 is arranged at the dotted line in FIG. Therefore, a detailed description of the connection of the bypass pipe 25 is omitted.

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

In FIG. 6, when the gas to be detected flows from the direction of the white arrow in the operating state of the carbon monoxide sensor 20 (the state in which a voltage is applied, and the operating conditions are the same as in the first embodiment). , A part of which is introduced into the first current collector plate opening 6 as indicated by the small arrow, and reaches the gas chamber 7. The hydrogen gas in the gas to be detected is conducted as protons to the negative electrode side by the detection element 4, returns to the hydrogen gas at the negative electrode, and is discharged from the second current collector plate opening 9 as indicated by the small arrow. At this time, if the gas to be detected contains carbon monoxide gas, the first embodiment
As described above, the poisoning of the catalyst occurs, and the current flowing through the carbon monoxide sensor 20 changes. Since this change corresponds to the concentration of the carbon monoxide gas, the concentration of the carbon monoxide gas in the gas to be detected can be detected. Note that the operation of refreshing the poisoned element by the microcomputer is the same as that of the first embodiment, and a detailed description thereof will be omitted.

The same simulated gas to be detected as in the first embodiment was humidified and introduced into such a carbon monoxide sensor. The results are shown in FIG. 7 and FIG. FIG. 7 shows the carbon monoxide concentration dependency of the current immediately before refresh RI described in the first embodiment {RI = I (8)} also in the case of this embodiment, and FIG. 8 shows the average poisoning rate MV of carbon monoxide. The concentration dependence is shown. 7 and 8, the gas temperature is set to 80 ° C. and 200, 300, 4
Gas flow dependence at 00 cc / min was also measured.

FIG. 7 shows that there was little difference in RI depending on the gas flow rate, and no large gas flow rate dependence was observed. this is,
The amount of gas introduced from the first current collector plate opening 6 is determined by the detection element 4.
And the flow rate flowing through the bypass pipe 25 has no direct effect. Also, from FIG. 8, the target detection concentration is 20 ppm to 10 p.
The change in MV to pm was not significantly affected by the flow rate, and the two could be clearly distinguished.

From the above, the same threshold value (RI = 130 mA, MV = −0 .0) as in the first embodiment can be obtained in the carbon monoxide sensor of the second embodiment without being affected by the gas flow rate.
3 mA / s, indicated by thick dotted lines in FIGS. 7 and 8, respectively), it was possible to output whether or not the concentration of the carbon monoxide gas was 20 ppm or more.

Further, assuming that the gas flow rate is 300 cc / min,
FIG. 9 shows the carbon monoxide concentration dependency of the current RI immediately before refresh when the gas temperature is changed, and FIG. 10 shows the carbon monoxide concentration dependency of the average poisoning rate MV. In each case, it was found that the value fluctuated depending on the gas temperature. However, from FIG. 9, the threshold value of RI does not greatly affect the rough density determination which is the purpose of the present invention, and there is no problem with the above-described threshold value of 130 mA (shown by a thick dotted line in FIG. 9). . M
For V, the concentration of carbon monoxide gas was 20 ppm and 10 ppm.
In order to distinguish ppm, it is necessary to change the threshold value (shown by a thick dotted line in FIG. 10) according to the gas temperature. Therefore, in the second embodiment, the temperature of the gas to be detected is monitored by the temperature sensor 42 attached to the case 40, and the threshold value of the MV is changed according to the temperature. M
Table 1 shows the threshold values according to the temperature of V.

[0096]

[Table 1]

The contents of Table 1 are stored in the nonvolatile memory of the microcomputer, and an appropriate threshold value is selected from the signal of the temperature sensor 42 to determine the concentration of the carbon monoxide gas.
0 ppm and 10 ppm are distinguished.

In the second embodiment, the pressure sensor 43
3, the tip of the bypass pipe 25 is connected to the combustor 36, and the pressure loss in this portion was extremely small in this study, so that the pressure near the carbon monoxide sensor was almost constant. And there was almost no influence of the pressure on the output. However, pressure fluctuations may not be negligible depending on the fuel cell system configuration, operating conditions, abnormal times, and the like. In that case, the pressure sensor 43
By correcting the threshold value also from the signal (1), the concentration of the carbon monoxide gas can be accurately determined.

Since the carbon monoxide sensor of the second embodiment is measured under the same conditions as those of the first embodiment, a sudden change in the output current (response current), which is a problem of the conventional example, is not observed at all. Did not.

From the above, it has been clarified that a highly accurate carbon monoxide sensor can be obtained.

FIG. 11 is a flowchart summarizing the control and calculation method of the carbon monoxide sensor for judging whether or not the concentration is 20 ppm or more.

When the power of the carbon monoxide sensor is turned on,
In step 1, a refresh voltage of 1.3 V is applied to the electrode 2. Then, in step 2, a predetermined time is waited for 2 seconds. In step 3, it is checked whether or not a signal for stopping the fuel cell is transmitted from a fuel cell control circuit (not shown). If
In step 4, the voltage applied to the electrode 2 is turned off, and the operation of the carbon monoxide sensor is terminated.

On the other hand, if there is no signal for stopping the fuel cell, a voltage of 1 V is applied to the electrode 2 in step 5 as a measurement voltage. Thereafter, in step 6, the current value is taken into the memory of the microcomputer 18 at a predetermined time interval (1 second in this embodiment). At this time, the current value taken in last ｛I
(8) Let｝ be the current RI immediately before refresh.

When the current value data for a predetermined time of 8 seconds is taken in, the temperature signal of the gas to be detected at that time is taken in from the temperature sensor 42 in step 8. Step 9
, A pressure signal is also fetched from the pressure sensor 43. Next, in step 10, the average poisoning rate MV is calculated according to (Equation 1). Then, in step 11, predetermined values of RI and MV determined by the temperature and the pressure are obtained from a threshold value table.

In step 12, whether the obtained RI and MV are equal to or larger than the respective predetermined values is compared, and if both are equal to or larger than the predetermined values, in step 13 the current carbon monoxide concentration is equal to or lower than 20 ppm. An ON signal is output as there is, and a jump is made to A (return to S1). On the other hand, if either of them is less than the predetermined value, in step 14, the current carbon monoxide concentration is 20 ppm.
An off signal is output as a darker color, and a jump is made to A (return to S1).

By repeating such an operation, it is possible to output whether or not the concentration of the carbon monoxide gas is 20 ppm or more.

With the above configuration and operation, a high-precision carbon monoxide sensor having no sudden change in output current was obtained.

Note that the specific material names described in Embodiments 1 and 2 are examples for constructing the carbon monoxide sensor of the present invention and a fuel cell system including the same. The material is not limited at all. Also, specific numerical values are not limited to the numerical values described in the first and second embodiments except for those limited by the claims.

[0109]

As described above, the present invention provides a proton conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the electrolyte membrane, an opening through which a gas to be detected is introduced, and the opening. A first current collector having a gas chamber having a smaller cross-sectional area than the area of the electrode connected to the first current collector, and a first current collector disposed so that the gas chamber is in contact with one surface of the electrode;
A second current collector having the same shape as the first current collector disposed to be in contact with the other surface of the electrode; the first current collector serving as a positive electrode; and the second current collector serving as a positive electrode. A DC power supply connected to be 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 introduced into the gas chamber; Current detection at a measurement voltage equal to or higher than the carbon oxide oxidation potential and equal to or lower than the decomposition potential of water;
A sudden change in the output current is generated by changing the voltage of the DC power supply with the catalyst refresh at a refresh voltage higher than the decomposition potential of water as one cycle and obtaining the concentration of carbon monoxide gas by repeating the cycle. Thus, a highly accurate carbon monoxide sensor can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a partially cutaway perspective view of the sensor when the sensor is attached to a pipe.

FIG. 3 is a piping diagram of mounting the sensor on a fuel cell system.

FIG. 4 is a characteristic diagram showing a carbon monoxide concentration dependency of a current immediately before refresh of the sensor.

FIG. 5 is a characteristic diagram showing the carbon monoxide concentration dependency of the average poisoning rate of the sensor.

FIG. 6 is a partial cross-sectional view of the carbon monoxide sensor according to the second embodiment of the present invention attached to a bypass pipe.

FIG. 7 is a characteristic diagram showing a carbon monoxide concentration dependency of a current immediately before refresh when the gas flow rate of the sensor is changed.

FIG. 8 is a characteristic diagram showing the dependency of the average poisoning rate on the carbon monoxide concentration when the gas flow rate of the sensor is changed.

FIG. 9 is a characteristic diagram showing a carbon monoxide concentration dependency of a current immediately before refresh when the gas temperature of the sensor is changed.

FIG. 10 is a characteristic diagram showing the carbon monoxide concentration dependency of the average poisoning rate when the gas temperature of the sensor is changed.

FIG. 11 is a block diagram showing an output calculation and control flowchart of the sensor.

FIG. 12 is a schematic structural diagram of a conventional carbon monoxide sensor.

FIG. 13 is a schematic structural cross-sectional view of a detection unit of the sensor.

14A and 14B are output current (response current) characteristic diagrams of the same sensor.

FIG. 15 is a graph showing a rapidly changing output current (response current) characteristic of the sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Proton conductive electrolyte membrane 2 Electrode 3 Sealing material 4 Detector 5 First current collector 6 First current collector opening 7 Gas chamber 8 Second current collector 9 Second current collector opening 10 Screw 11 Female thread 12 Positive lead wire 13 Negative lead wire 14 Washer 15 Washer fixing screw 16 DC power supply 17 Ammeter 18 Microcomputer 20 Carbon monoxide sensor 21 Positive plate 22 Negative plate 23 Positive plate insulating material 24 Negative plate insulating material 25 Bypass tube 30 Reformer 31 transformer 32 carbon monoxide remover 33 switching valve 34 fuel cell 35 orifice 36 combustor 40 case 41 nut 42 temperature sensor 43 pressure sensor

Claims (23)

[Claims] 1. An electrode having a proton conductive electrolyte membrane, electrodes having catalysts disposed on both sides of the electrolyte membrane, an opening through which a gas to be detected is introduced, and an area of the electrode connected to the opening. A first current collector provided with a gas chamber having a small cross-sectional area and arranged such that the gas chamber is in contact with one surface of the electrode, and in contact with the other surface of the electrode; Current collector plate having the same shape as the first current collector plate, and a DC power source connected such that the first current collector plate is a positive electrode and the second current collector plate is a negative electrode And a current detecting means for detecting a current that changes in accordance with the concentration of carbon monoxide gas in the gas to be detected containing hydrogen introduced into the gas chamber, wherein the potential is equal to or higher than the carbon monoxide oxidation potential and the decomposition potential of water. Current detection at the following measurement voltage and touch at a refresh voltage higher than the decomposition potential of water A carbon monoxide sensor in which the voltage of the DC power supply is changed with medium refresh as one cycle, and the concentration of carbon monoxide gas is obtained by repeating the cycle. 2. The carbon monoxide sensor according to claim 1, wherein a concentration of the carbon monoxide gas is determined from a current value flowing through the element after a predetermined time has elapsed after the application of the measurement voltage and a current change rate near the time point. 3. The carbon monoxide sensor according to claim 1, wherein the opening of the first current collector and the opening of the second current collector are arranged in the same direction. 4. In a fuel cell system having a reformer for reforming a hydrocarbon-based fuel to generate hydrogen gas, a part of a reformed gas main pipe connecting the reformer and a fuel cell stack is detected. A fuel cell system comprising a bypass pipe through which a gas flows, and a carbon monoxide sensor disposed in the bypass pipe. 5. The fuel cell system according to claim 4, wherein the flow rate of the gas to be detected flowing in the bypass pipe is 0.1% or more and 1% or less of the flow rate of the reformed gas flowing in the main pipe. 6. The fuel cell system according to claim 5, wherein an orifice is provided in a part of the bypass pipe. 7. The fuel cell system according to claim 6, wherein the orifice is provided upstream of the carbon monoxide sensor. 8. A part of the bypass pipe is disposed in a direction perpendicular to the ground, a gas to be detected flowing in the bypass pipe flows in the direction of the ground, and a carbon monoxide sensor is disposed inside the vertical part of the bypass pipe. The fuel cell system according to claim 4. 9. The fuel cell system according to claim 8, wherein the opening of the carbon monoxide sensor is arranged in the ground direction. 10. The apparatus according to claim 4, wherein a part of the bypass pipe is inclined with respect to the ground, the gas to be detected flowing through the bypass pipe flows toward the ground, and a carbon monoxide sensor is disposed on the inclined part. Fuel cell system. 11. The fuel cell system according to claim 10, wherein the opening of the carbon monoxide sensor is arranged in a direction perpendicular to the peripheral surface of the bypass pipe. 12. The carbon monoxide sensor is arranged so that the opening of the first current collector plate is located on the upstream side of the bypass pipe.
3. The fuel cell system according to item 1. 13. The fuel cell system according to claim 4, wherein the end of the bypass pipe is connected to the main pipe on the fuel cell stack outlet side. 14. The fuel cell system according to claim 13, wherein the tip of the bypass pipe is connected to the main pipe at the outlet side of the fuel cell stack at right angles to the ground or with an inclination. 15. The fuel cell system according to claim 4, wherein a temperature sensor is provided in a part of the carbon monoxide sensor or a part of a bypass pipe near the carbon monoxide sensor. 16. The fuel cell system according to claim 4, wherein a pressure sensor is provided in a part of the carbon monoxide sensor or a part of a bypass pipe near the carbon monoxide sensor. 17. The fuel cell system according to claim 4, wherein the carbon monoxide sensor mounting portion, the temperature sensor mounting portion, and the pressure sensor mounting portion on the bypass pipe are made of the same material as the bypass pipe. 18. The fuel cell system according to claim 4, wherein the carbon monoxide sensor, the temperature sensor, and the pressure sensor are attached to the bypass pipe while being electrically insulated. 19. The fuel cell system according to claim 4, wherein the surfaces of portions of the carbon monoxide sensor, the temperature sensor, the pressure sensor, and the bypass pipe that are in contact with the gas to be detected are subjected to a hydrophilic treatment. 20. The fuel cell system according to claim 19, wherein an uneven surface is provided as the hydrophilic treatment. 21. The fuel cell system according to claim 19, wherein a titanium oxide layer is provided as the hydrophilic treatment. 22. The fuel cell system according to claim 21, wherein the titanium oxide layer has an anatase crystal structure. 23. The fuel cell system according to claim 21, wherein the thickness of the titanium oxide layer is 0.1 μm or more and 1 μm or less.