JP2001041925A - CO gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten start time and improve stability over a long time period of a sensor outputs by setting a CO oxidation potential and a CO adsorption potential of a voltage impressing apparatus to be a specific values respectively. SOLUTION: This gas sensor has a detection part, having a solid electrolyte film 3 held between a detect electrode 1 and a counter electrode 2, and a voltage impress device for impressing a CO oxidation potential and a CO adsorption potential to between the detect electrode 1 and a counter electrode 2. The detect electrode 1 includes an electrochemically active first catalyst in a conductive porous base, forming a reaction layer of density range of 1 ng/cm2-100 μg/cm2 and a thickness of 0.3 nm-15 μm. The counter electrode 2 has an electrochemically active second catalyst carried by a conductive porous base. The CO oxidation potential and CO adsorption potential of the voltage impress device are set to 0.8-0.9 V and 0.3-0.07 V respectively. According to the thus constituted gas sensor, the CO oxidation potential and CO adsorption potential can be properly set, so that the reproducibility of the sensor can be maintained over a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CO gas sensor. INDUSTRIAL APPLICABILITY The CO gas sensor according to the present invention is suitable for detecting a small concentration of CO gas in a hydrogen gas-rich atmosphere, and is suitably used in a fuel cell device using a methanol reformed gas as a fuel gas.

[0002]

2. Description of the Related Art In WO 97/40371, a new gas sensor is proposed. FIG. 1 shows the principle of executing the pulse method in this gas sensor.
The description will be made based on Nos. As shown in FIG.
The gas sensor has a configuration in which an electrolyte membrane 3 is interposed between a detection electrode 1 and a counter electrode 2. The sensor controller 5 applies a positive voltage to the detection electrode 1 side. When the voltage applied to the detection electrode is changed from a relatively high CO oxidation potential to a relatively low CO adsorption potential as shown in the upper part of FIG. 2, a transient current (response current) flows as shown in the lower part of FIG. This reduction rate of the response current corresponds to the CO concentration in the test gas. That is, as the CO concentration increases, the rate of decrease in the response current increases. Therefore, as shown in FIG. 3, a calibration curve indicating the relationship between the current reduction rate and the CO concentration is obtained in advance, and the measured current reduction rate is compared with the calibration curve to obtain a CO curve.
The concentration can be specified.

[0003]

The present inventors have intensively studied to improve the above gas sensor. As a result, they have found that the gas sensor has the following problem to be solved. In the CO gas sensor disclosed in the above-mentioned International Publication, no specific pulse pattern is described when the pulse method is executed. According to the study of the present inventor, if an inappropriate CO oxidation potential is set as a pulse pattern, CO may not be sufficiently oxidized on the surface of the detection electrode, and the cleaning may be insufficient. In particular, this insufficient cleaning is likely to occur when the CO gas sensor is started. In addition, if an inappropriate CO adsorption potential is set, the reproducibility and long-term stability of the sensor may be affected by the influence of hydrogen diffusion.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve at least one of the above-mentioned problems, and the configuration thereof is as follows. A CO gas sensor comprising a detection unit having a solid electrolyte membrane sandwiched between a detection electrode and a counter electrode, and a voltage applying device for applying a CO oxidation potential and a CO adsorption potential between the detection electrode and the counter electrode. The detection electrode is formed on a conductive porous substrate by an electrochemically active first electrode.
1 ng / cm ^{2 to} 100 μg / c
A reaction layer having a density of 0.3 nm to 15 μm is formed at a density of m ² , and the counter electrode is supported on a conductive porous base material by an electrochemically active second catalyst. A CO gas sensor, wherein the application device sets the CO oxidation potential to 0.8 to 0.9 V and sets the CO adsorption potential to 0.03 V to 0.07 V.

According to the CO gas sensor configured as described above, since the CO oxidation potential and the CO adsorption potential are appropriately set, a remarkable improvement in the shortening of the start-up time and the maintenance of reproducibility was observed. It is considered that the start-up time was shortened mainly because the CO oxidation potential was appropriately set. It is considered that maintaining the reproducibility for a long period of time, that is, the stability of the sensor output is mainly due to appropriately setting the CO adsorption potential.

[0006]

Embodiments of the present invention will be described below. FIG. 4 shows a basic configuration of the CO gas sensor 10 of the present invention. Hereinafter, each component will be described. Detection electrode 11 The detection electrode 11 is composed of a porous base material and a reaction layer. Here, any material can be used as long as the substrate is conductive and electrochemically inert. As a material of such a base material, conductive carbon and the like can be mentioned. Electrochemically inert means that no charge is exchanged with CO or hydrogen within the range of the voltage applied to the sensor. The reason why the base material is made porous is to obtain a larger surface area with a smaller volume and to carry more catalyst on the surface. The porosity of the substrate is 10 to 90
% Is preferable. More preferably, 20 to 60%
And still more preferably 35 to 45%. The average pore diameter of the substrate is preferably from 1 nm to 100 μm. More preferably, it is 1 nm to 1 μm, and still more preferably 10 nm to 0.3 μm.

The reaction layer includes a first catalyst that includes a first electrochemically active material. On the surface of the catalyst, adsorption and oxidation of CO and oxidation of H ₂ are performed within the range of the voltage applied to the sensor. Thus, the catalyst acts as a substantial electrode. In this respect, the conventional technology (WO97 / 4037)
No. 1) discloses an example in which platinum itself is used as a base material of the electrode. The reason why the catalyst is used in the present invention is to obtain a larger electrochemically active area with a smaller weight, that is, an area capable of electrochemically adsorbing and oxidizing CO and H ₂ . Thus, the amount of the heavy and expensive first catalyst material used can be reduced. The first material constituting the first catalyst includes Pt, Au,
A material containing one or more metals selected from Cu, Ni, Pd, Ag, Rh, and Ru or an alloy of one or more selected metals can be used. Among them, Pt is preferable. A fine powder of such a material is included in the catalyst according to the present invention, even if it is not sold as a catalyst. That is,
Compared to an electrode composed of a simple metal, a larger electrochemically active area with a smaller weight, that is, an area capable of electrochemically adsorbing and oxidizing CO and H ₂ can be obtained by supporting it on a substrate. Should be fine.

According to the study of the present inventors, the density of the first catalyst is preferably 1 ng / cm ^{2 to} 10 mg / cm ² . If the density of the first catalyst is less than 1 ng / cm ² , the response current is not stable, and if it exceeds 10 mg / cm ² , the response current becomes too large, which is not preferable. A more preferred density of the first catalyst is 10 ng / cm ²
１1 mg / cm ² , more preferably 0.1 μm
g / cm ^{2 to} 10 μg / cm ² . In the above solution, the upper limit of the density of the first catalyst is 100 μg / cm ² , which is a value obtained by comparison with the comparative example. Considering practical use as a CO sensor, as described above, it is preferable that the concentration be 1 ng / cm ^{2 to} 10 mg / cm ² . More importantly, the loading amount of the first catalyst is as follows.
By controlling the total carrying amount, that is, the total area, the amount of response current flowing to the sensor is controlled. CO
In order to improve sensitivity, durability, and the like, it is preferable to reduce the response current. Therefore, the smaller the supported amount of the first catalyst that defines the electrochemically effective electrode area in the detection electrode 11, the better.

In the above description, the supported amount of the catalyst is defined by the weight per unit area of the base material, that is, the density. Depending on the catalyst, the surface area per unit weight may be different. Therefore, the amount of the catalyst is defined as follows based on the surface area. That is, the specific surface area of the reaction layer with respect to the substrate is preferably substrate: catalyst = 1: 0.001 to 100. More preferably, the specific surface area of the base material: catalyst = 1: 0.
01 to 10. More preferably, the specific surface area is set to 1: 0.1 to 1 for the base material and the catalyst. Here, the specific surface area is a ratio between the unit area of the substrate and the total surface area of the catalyst supported per unit area.

[0010] The thickness of the reaction layer is preferably 0.3 nm to 1 cm. If the thickness of the reaction layer is less than 0.3 nm, a sufficient electrochemically active surface area cannot be obtained even with the catalyst constituting the reaction layer. The thickness of the reaction layer is 1c
If it exceeds m, the test gas may not sufficiently diffuse into the reaction layer. That is, even when the CO concentration changes, the test gas may not quickly and uniformly diffuse into the reaction layer. The more preferable thickness of the reaction layer is 1 μm to 1 mm, and further more preferably 5 μm to 10 μm. In the above solution, the thickness of the reaction layer is set to 0.3 nm to 15 nm.
μm, which is a numerical value determined in comparison with the comparative example. By thus reducing the thickness of the reaction layer of the detection electrode 11, there is also an effect of reducing the surface area (total area of the supported catalyst) of the detection electrode 11. Considering practical use as a CO gas sensor, it is preferable that the thickness of the reaction layer of the detection electrode 11 be 0.3 nm to 1 cm as described above.

Counter Electrode 12 The counter electrode 12 has a structure in which a second catalyst containing a second material that is electrochemically active is supported on a conductive porous base material. The same substrate as the detection electrode can be used. In addition, it is preferable to use the same substrate as the detection electrode from the viewpoint of common use of components. The second material constituting the second catalyst includes P as in the first material constituting the first catalyst.
One or more metals selected from t, Au, Cu, Ni, Pd, Ag, Rh, and Ru or an alloy of one or more selected metals can be used. Such a catalyst may be entirely dispersed in the base material, or may be configured to form a reaction layer on the base material as in the case of the first catalyst.

This second catalyst also serves as the first catalyst at the detection electrode.
Charge transfer is performed on the surface of the catalyst as shown in FIG. Thus, the second catalyst acts as a substantial electrode. The catalyst is used in the present invention in order to obtain a larger electrochemically active area with a smaller volume, that is, an area where H ⁺ can be electrochemically reduced. Thus, the amount of the heavy and expensive second catalyst material used can be reduced. It is preferable that the second catalyst supported on the counter electrode does not easily adsorb CO. This is because, as shown in FIG. 1, if CO is adsorbed on the surface of the counter electrode where hydrogen is reduced, the reduction action is hindered. As such a second catalyst, a Pt-Ru catalyst can be used.

According to the study of the present inventors, the amount of the second catalyst carried can be arbitrarily selected from the range of 1 ng / cm ^{2 to} 10 mg / cm ² . If the amount of the second catalyst carried is small, the response current may not be stable. Therefore, in the present invention, the amount of the second catalyst carried (total amount) is compared with the amount of the first catalyst carried by the detection electrode 11 (total amount).

According to the study of the present inventors, the counter electrode 12
Weight of the second catalyst such as Pt-Ru supported on the sensor: total weight of the first catalyst supported on the detection electrode 11 = 0.1 to 1
00000: 1 is preferable. More preferably, it is 1 to 10000: 1, and still more preferably 10 to 10,000.
1000: 1. This is also the relationship between the electrochemically effective (active) surface area of the counter electrode 12 and the electrochemically effective (active) surface area of the detection electrode 11.
That is, assuming that the surface area per unit weight of the catalyst supported on each electrode is equal, the electrochemically effective surface area of the counter electrode 12: the electrochemically effective surface area of the detection electrode 11 = 0.1 to It is preferably set to 100000: 1. A more preferred area ratio is 1 to 10,000: 1, and further more preferably 10 to 1000: 1.

Electrolyte Membrane 13 The electrolyte membrane 13 is a proton conductive ion exchange membrane formed of a solid polymer material, for example, a fluororesin.
For example, a Nafion (trade name: DuPont) film or the like can be used. The electrolyte membrane 13 must maintain a wet state in order to move protons. Therefore, when the current flowing through the CO gas sensor 10 increases, heat is generated, and the electrolyte membrane 13 may be excessively dried, which is not preferable. The humidity of the atmosphere in which the CO gas sensor 10 is placed is also important from the viewpoint of maintaining the electrolyte membrane 13 in a wet state. The thickness of the electrolyte membrane 13 is not particularly limited. Instead of the electrolyte membrane 13, an electrolytic solution such as a sulfuric acid aqueous solution can be used. In this case, the detection electrode and the counter electrode are immersed in the electrolytic solution.

Diffusion control film 14 (see FIG. 5) As shown in FIG. 5, the diffusion control film 14 can be provided on the surface of the detection electrode 11 so as to cover the reaction layer.
As the diffusion control film 14, a porous film (for example, the same porous carbon as the base material) or a liquid film (sulfuric acid aqueous solution) can be adopted, and the film thickness is arbitrary. By providing such a diffusion control film 14, the rate limiting of the detection speed of the sensor can be made dependent on the gas diffusion speed of the detection electrode 11 on the reaction layer. If the diffusion control film 14 is omitted, the temperature and humidity of the detection environment affect the Nafion film, and the ion conduction speed in the Nafion film may determine the detection speed of the sensor. When the performance of the sensor is to be improved by optimizing the reaction layer of the detection electrode, it is preferable that the performance of the reaction layer directly affects the performance of the entire sensor.

Sensor control unit 15 The sensor control unit 15 as a voltage application device includes a DC power supply 1
6, a voltage changing circuit 17 and an ammeter 18 are provided. The voltage changing circuit 17 applies the voltage of the DC power supply 16 as a rectangular wave pulse as shown in FIG. The ammeter 18 detects a response current flowing when the potential of the detection electrode changes from the CO oxidation potential to the CO adsorption potential. In the pulse of FIG. 6, the CO oxidation potential (High potential in the figure) applied to the detection electrode is preferably set to 0.8V to 0.9V. If the potential is less than 0.8 V, cleaning of the detection electrode surface by CO oxidation is not sufficiently performed, and the performance of the sensor is significantly reduced, which is not preferable. If the potential is increased beyond 0.9 V, the sensor is undesirably deteriorated.
Note that the potential in this specification indicates a potential difference between the detection electrode and the counter electrode.

FIG. 7 shows a change in the response current (current value after a predetermined time after switching the potential) when the CO oxidation potential is shifted to the high potential side and then shifted to the low potential side. As is apparent from the figure, if the CO oxidation potential is increased beyond 0.9 V, the response current will not return to the original value when the potential is subsequently reduced. That is, hysteresis occurs between the CO oxidation potential and the response current. This is presumably because, when a potential exceeding 0.9 V is applied to the sensor, the base material and the catalyst of the detection electrode react and this irreversibly deteriorates. In order to clean a substance such as CO adsorbed on the surface of the detection electrode and prevent the deposition of the substance, it is preferable to apply a CO oxidation potential as high as possible to the detection electrode. Therefore, from the results of FIG. 7, it is preferable to adopt approximately 0.9 V as the CO oxidation potential.

In the pulse pattern of FIG. 6, the CO adsorption potential (Low potential in the figure) is preferably set to 0.03 to 0.07V. If the potential is less than 0.03 V, a current having the opposite sign is generated due to the reverse reaction of hydrogen ionization (2H ⁺ + 2e ⁻ → H ₂ ), and the measurement accuracy of the sensor is undesirably reduced. On the other hand, if the potential exceeds 0.07 V, the hydrogen diffusion rate on the detection electrode side greatly affects the value of the response current, which is not preferable. A more preferred CO adsorption potential is 0.04
０．０0.06 V, more preferably about 0.05
V.

FIG. 8 shows a change in the hydrogen ionization current when the potential applied to the detection electrode of the sensor is changed. FIG.
As can be seen from the graph, the hydrogen ionization current is saturated at a certain potential. This is presumably because the rate of diffusion of hydrogen to the surface of the detection electrode is the rate-limiting step of the rate of charge transfer in the entire sensor. In such a potential region, the response current changes with time due to hydrogen diffusion. This is because hydrogen diffusion is easily affected by external influences (vibration, temperature change, etc.). Therefore, a large error is included in the response current, so that the CO adsorption potential should be set as low as possible. However, the potential is 0 with respect to RHE (reversible hydrogen electrode).
As the voltage approaches V, the current reaches 0 in principle, making measurement impossible.

Therefore, in order to specifically determine the CO adsorption potential, the degree of influence of hydrogen diffusion rate-limiting on the potential was examined. This was performed by an operation of applying an appropriate potential to the detection electrode of the sensor, changing to 0 V after a certain time, and returning to the original potential again. FIG. 9 shows the results. As shown in FIG. 9A, when the applied potential is 0.01 V, a large noise enters the response current. Further, as shown in C and D of FIG. 9, when the applied potential is 0.1 and 0.2 V, the diffusion of hydrogen greatly affects the response current. On the other hand, as shown in FIG. 9B, when the applied potential is 0.05 V, noise is small and diffusion of hydrogen has almost no effect. Based on the results of FIG. 9, in the present invention, the range of the CO adsorption potential is 0.03 V
〜0.07V.

In FIG. 6, the holding time of the High potential can be set arbitrarily as long as it is necessary to clean the detection electrode. By shortening the holding time, the cycle of the output (response time) of the sensor is shortened.
If more outputs are obtained per unit time, it is possible to improve the accuracy of the output values by averaging them. According to the study of the present inventors, it is preferable that the holding time of the High potential be 0.3 seconds to 0.8 seconds. More preferably, it is between 0.4 seconds and 0.6 seconds, most preferably approximately 0.5 seconds.

In FIG. 6, the holding time of the Low potential can be arbitrarily set as long as it is necessary to calculate the reduction rate of the response current. Like the holding time of the High potential, it is desirable to shorten this holding time as much as possible from the viewpoint of shortening the cycle of the sensor output. According to the study by the present inventors, the retention time of this Low potential is 0.5 seconds to 2.
Preferably, it is 0 seconds. More preferably, it is between 0.8 seconds and 1.2 seconds, most preferably about 1.0 second.

FIGS. 10 and 11 show other pulse waveform patterns. If the requirements for the pulse height (potential) and width (holding time) described above are satisfied, a portion where the potential gradually increases (swept portion) as shown in FIG. 10 may be included. Further, the potential may be changed as shown in FIG. Note that the period of the pulse need not always be constant. Further, adjacent pulses may have a difference in amplitude.

From the response current thus obtained, CO 2
The density is determined by calculation. The principles for performing the calculation include a general-purpose calibration curve method, a calibration curve method for Langmuir-type CO adsorption, the reciprocal of the time required to reach a certain current reduction rate, and CO.
Calibration curve method based on concentration, initial current decrease rate and CO
There is a calibration curve method based on the relationship with the concentration. See WO for details
See JP 97/40371. Of course, a cyclic voltammetry method can also be performed.
In this case, the voltage is swept by the voltage changing circuit 17 within a predetermined range.

FIG. 12 shows a CO concentration calculating device 20 for specifying the CO concentration from the obtained response current. The CO concentration calculation device 20 includes a response current reduction rate calculation circuit 21 and a CPU 2
3 and a memory 25. The response current reduction rate calculation circuit 21 analyzes the waveform of the response current detected by the ammeter 18 and calculates the reduction rate per predetermined time. Memory 2
5 stores a calibration curve (see FIG. 3) necessary to execute any of the above-mentioned calibration curve methods, for example, in the form of a data table. The memory 25 also stores a control program that regulates the operation of the CPU 23. The CPU 23 refers to the data table of the current reduction rate-CO concentration stored in the memory 25 and specifies the CO concentration from the current reduction rate calculated by the response current reduction rate calculation circuit 21. The specified CO concentration is displayed on a display device 27 including a display and a printing device. Also, CO
When the concentration calculation device 20 is installed in the fuel cell device, the obtained CO concentration is sent to the control unit of the fuel cell device.

FIG. 13 shows a CO gas sensor 1 according to the present invention.
1 shows an example in which 0 is assembled in a fuel cell device. In the fuel cell device shown in FIG.
And methanol from the water tank 30 while the pump 3
6, water is introduced into a water / methanol tank 35, and water / methanol as a raw material is introduced from the tank 35 into a reformer 33 by a pump 34, where methanol reformed gas (H ₂ : 75%, CO ₂ : 25%, CO: several 100 ppm). The reformed gas is sent to the CO selective oxidizing unit 37, where CO in the reformed gas is selectively oxidized, and sent to the fuel cell 38. A part of the fuel gas discharged from the CO selective oxidizing unit 37 is sent to the CO gas sensor 10, where the CO concentration in the fuel gas is measured. CO
The CO concentration calculator 20 calculates the CO concentration based on the response current detected by the gas sensor 10. The obtained CO concentration is sent to the main control unit 39 of the fuel cell device. Obtained C
Based on the O concentration, the main control unit 39 determines the C value of the CO selective oxidation unit 37.
The O oxidation reaction conditions and the like are controlled. When the CO concentration exceeds a predetermined threshold, the supply of the fuel gas to the fuel cell 38 is stopped.

[0028]

Next, a preferred embodiment of the CO gas sensor according to the present invention will be described. It should be noted that the CO gas sensor of the comparative example in the following description can sufficiently withstand practical use, and it is first refused that the configuration is not a conventional example of the present invention.

The configurations of the CO gas sensor of the embodiment and the CO gas sensor of the comparative example are as shown in FIG. 4, and the specifications of each component are as shown in Table 1.

[Table 1] In the table, the specific surface area of each electrode indicates the total surface area of the catalyst supported on a unit area of the electrode substrate. In Examples and Comparative Examples, a Pt catalyst or a Pt-Ru catalyst is applied to the substrate of each electrode by a conventional method to form a reaction layer on the surface of the substrate. After that, the Nafion film is sandwiched between the opposing surfaces of the detection electrode and the opposing electrode, and the whole is hot-pressed to form a sensor detection section. Each electrode was connected to a sensor control unit to obtain a CO sensor having the configuration shown in FIG.

In comparison between the example and the comparative example, the amount of Pt catalyst carried on the detection electrode of the CO gas sensor was 100 μg /
cm ² or less. Similarly, the thickness of the detection electrode is preferably 15 μm or less. The catalyst supported on the counter electrode is preferably Pt-Ru.

A rectangular wave pulse shown in FIG. 6 was applied to the CO gas sensors of the above embodiment and the comparative example with the following patterns of amplitude and period, respectively. Example Comparative example CO oxidation potential (High potential) Potential 0.8 to 0.9 V 1.0 V Holding time 0.5 sec 1.0 sec CO adsorption potential (Low potential) Potential 0.05 V 0.4 V Holding time 1. 0 seconds 10 seconds to several minutes

The starting performance was compared between the CO gas sensor of the embodiment to which such a pulse pattern was applied and the CO gas sensor of the comparative example. FIG. 14 shows the results. FIG.
In the graph, the sensor output (%) on the vertical axis represents the difference between the response current reduction rate at each time and the response current reduction rate at each time on the basis of the response current reduction rate after 300 minutes (0%). The measurement conditions in FIG. 14 are as follows: CO concentration: 50 ppm, humidity:
42% RH, pressure: 1.5 atm, flow rate: 100 l / min. From the results shown in FIG. 14, it can be seen that the starting performance of the CO gas sensor of the example was significantly improved.

Similarly, the reproducibility was compared between the CO gas sensor of the embodiment and the CO gas sensor of the comparative example.
FIG. 15 shows the results. In FIG. 15, the sensor output (%) on the vertical axis is expressed as (0
%), And the difference between this and the response current decrease rate in each of the second and subsequent tests is expressed in%. In each test, the reduction rate of the response current 300 minutes after the pulse application was taken. The measurement conditions in FIG. 15 are as follows: CO concentration: 50 ppm,
Humidity: 42% RH, pressure: 1.5 atm, flow rate: 100 l / min. From the results shown in FIG. 15, it can be seen that the reproducibility of the CO gas sensor of the example was significantly improved. That is, it is understood that the performance is stable and the stability is maintained for a long period of time.

The present invention is not at all limited to the description of the above-described embodiments and examples. Various modifications are included in the present invention without departing from the scope of the claims and within the scope of those skilled in the art.

Hereinafter, the following matters will be disclosed. (2) A first catalyst for the substrate at the detection electrode
The specific surface area of the base material: the first catalyst = 1: 0.001 to 10
12. The method according to claim 1, wherein 0 is set.
2. The CO gas sensor according to 1. (3) A second catalyst for the substrate at the counter electrode
The specific surface area of the base material: the second catalyst = 1: 0.001 to 10
000, or 1 to 11 or
The CO gas sensor according to any one of (2). (4) Total weight of the second catalyst carried on the counter electrode
Is 10% of the total weight of the first catalyst supported on the detection electrode.
2. The method according to claim 1, wherein the number is up to 1000 times.
1, CO gas sensor according to any one of (2) to (3)
Sa. (5) The base material of the detection electrode has a porosity of 10 to 90%.
Having an average pore diameter of 1 nm to 100 μm.
Any of claims 1 to 11, and (2) to (4),
A CO gas sensor according to any of the preceding claims. (6) The detection electrode is provided with a diffusion control film.
14. The method according to claim 1, wherein (2) to (5).
The CO gas sensor according to any one of the above. (7) With the solid electrolyte membrane interposed between the detection electrode and the counter electrode
Between the detection electrode and the counter electrode.
And a voltage application device for applying the oxidation potential and the CO adsorption potential.
0.8-0.9V
0.03 V to 0.07 V from the CO oxidation potential
When changed to O adsorption potential, the detection electrode and the counter electrode
The value of the current flowing between the electrodes is 0.001 mA / cm²~ 1
A / cm² A CO gas sensor, characterized in that: (8) The current value is 0.01 mA / cm.²~ 0.1A
/ Cm²CO gas according to (7),
Sensor. (9) The current value is 0.1 mA / cm.²~ 0.01A
/ Cm²The CO according to claim 7, wherein
Gas sensor. (10) CO gas according to any of (2) to (9)
A fuel cell device equipped with a sensor. (11) An electrolyte is interposed between the detection electrode and the counter electrode.
Between the detection electrode and the counter electrode.
And apply the voltage between 0.8 V and 0.9 V to 0.03
And a voltage application device for changing the voltage between V and 0.07 V.
In the resulting CO gas sensor, the detection electrode is conductive.
First material electrochemically active on porous base material
Comprising a first catalyst comprising: 1 ng / cm²-10
0 μg / cm²0.3nm to 15μm thick at the density of
Characterized by the fact that a reaction layer having CO is formed.
Gas sensor. (12) CO oxidation potential of 0.8 V to 0.9 V and 0.0
Apply 3V to 0.07V CO adsorption potential to the detection electrode
Electrode for a CO gas sensor, comprising:
Is a conductive porous base material, and an electrochemically active first
1 ng / cm comprising a first catalyst comprising the following materials:²
~ 100 μg / cm²At a density of 0.3 nm to 15 μm
A reaction layer having a thickness is formed.
Detection electrode. (13) CO oxidation potential of 0.8 V to 0.9 V and 0.0
Apply 3V to 0.07V CO adsorption potential to the detection electrode
Electrode for a CO gas sensor, comprising:
Is electrochemically inert, conductive and porous
A substrate, and an electrochemically active catalyst supported on the substrate;
A counter electrode, comprising: (21) CO oxidation potential of 0.8 V to 0.9 V and 0.0
Apply 3V to 0.07V CO adsorption potential to the detection electrode
Electrode for a CO gas sensor,
A reaction layer having a thickness of about 1 cm.
Output electrode. (22) the thickness of the reaction layer is 1 μm to 1 mm,
(21) The detection electrode according to (21). (23) The thickness of the reaction layer is 5 μm to 10 μm.
The detection electrode according to (21), wherein (24) The reaction layer is made of Pt, Au, Cu, Ni, P
one or more metals selected from d, Ag, Rh, Ru, or
Comprising an alloy of one or more selected metals.
The detection power according to any one of (21) to (23),
very. (25) The reaction layer includes Pt.
(24). (31) CO oxidation potential of 0.8 V to 0.9 V and 0.0
Apply 3V to 0.07V CO adsorption potential to the detection electrode
Electrode for a CO gas sensor,
Electrochemically inert, conductive and porous material
And the porosity of the substrate is 10 to 90%.
Characterized by a uniform pore diameter of 1 nm to 100 μm
Detection electrode. (32) The porosity is 20 to 60%, and the average porosity is
(31) wherein the diameter is 1 nm to 1 μm.
The detection electrode as described. (33) The porosity is 35 to 45%, and the average porosity is
The diameter is from 10 nm to 0.3 μm (3
The detection electrode according to 1). (34) The base material is made of conductive carbon.
Detection according to any one of (31) to (33), which is a feature.
electrode. (41) CO oxidation potential of 0.8 V to 0.9 V and 0.0
Apply 3V to 0.07V CO adsorption potential to the detection electrode
Electrode for a CO gas sensor, comprising:
Is electrochemically inert, conductive and porous
A substrate made of a material, and 1 ng / cm²-10m
g / cm²A supported electrochemically active first material;
A detection electrode comprising: (42) The loading amount of the first material is 10 ng / cm.²
~ 1mg / cm²(41), which is characterized in that
The detection electrode as described. (43) The loading amount of the first material is 0.1 μg / cm.
²-10 μg / cm²(4)
The detection electrode according to 1). (44) CO oxidation potential of 0.8 V to 0.9 V and 0.0
Apply 3V to 0.07V CO adsorption potential to the detection electrode
Electrode for a CO gas sensor, comprising:
Is electrochemically inert, conductive and porous
A base material made of a material, and an electrochemically
An active first material comprising:
The specific surface area of the first material is as follows: substrate: first material = 1: 0.
001 to 100, a detection electrode. (45) The specific surface area is as follows: base material: first material = 1: 0.
01 to 10, characterized by the above-mentioned (44).
Detection electrode. (46) The specific surface area is as follows: base material: first material = 1: 0.
The detection according to (44), wherein the number is 1 to 1.
electrode. (47) The first material is Pt, Au, Cu, Ni,
One or more metals selected from Pd, Ag, Rh, Ru
Comprises an alloy of one or more selected metals.
The detection according to any one of (41) to (46), which is a feature.
electrode. (48) The first material comprises Pt.
The detection electrode according to (47), which is characterized in that: (51) One selected from the descriptions of (21) to (25)
Requirements, one of which is selected from the descriptions of (31) to (33)
Requirement, one requirement selected from the descriptions of (41) to (48)
Detection device that meets at least two of the requirements
very. (52) The detection according to any one of (21) to (51).
CO sensor with electrodes. (53) A fuel comprising the CO sensor according to (52).
Battery device. (61) CO oxidation potential of 0.8 V to 0.9 V and 0.0
Apply 3V to 0.07V CO adsorption potential to the detection electrode
Electrode for a CO gas sensor, comprising:
Is electrochemically inert, conductive and porous
Substrate and relatively hard to adsorb CO supported on the substrate
And a second material, wherein the second material is (4)
1) comparing with the first material according to any of (48)
The total weight ratio is 0.1 to 100000 times
A counter electrode. (62) The total weight ratio is 1 to 10,000 times.
The counter electrode according to (61), wherein: (63) The total weight ratio is 10 to 1000 times,
The counter electrode according to (61), wherein: (64) CO oxidation potential of 0.8 V to 0.9 V and 0.0
Apply 3V to 0.07V CO adsorption potential to the detection electrode
Electrode for a CO gas sensor, comprising:
Is electrochemically inert, conductive and porous
Substrate and relatively hard to adsorb CO supported on the substrate
A second material; and
The chemically active surface area is any of (41) to (48)
0.1 to 100 in area ratio compared to the detection electrode described in
A counter electrode characterized by a factor of 000. (65) The area ratio is 1 to 10,000 times.
The counter electrode according to (64), wherein: (66) The area ratio is 10 to 1000 times.
The counter electrode according to (65), wherein: (67) The second material is a Pt-Ru catalyst.
(61) to (66).
Counter electrode. (71) The facing member according to any one of (61) to (67).
CO sensor with electrodes. (72) A fuel cell equipped with the CO sensor according to (71).
Pond equipment.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the operation principle of a CO gas sensor.

FIG. 2 shows a relationship between an applied voltage and a response current in the pulse method.

FIG. 3 shows a calibration curve of CO concentration and reduction rate of response current.

FIG. 4 is a schematic configuration diagram of a CO gas sensor of the present invention.

FIG. 5 is a schematic configuration diagram of another type of CO gas sensor.

FIG. 6 shows a pulse pattern applied to the CO gas sensor.

FIG. 7 shows a hysteresis between a CO oxidation potential and a response current.

FIG. 8 shows the relationship between the CO adsorption potential and the hydrogen ionization reaction current.

FIG. 9 shows the effect of hydrogen diffusion on various CO adsorption potentials.

FIG. 10 shows another pulse pattern applied to the CO gas sensor.

FIG. 11 shows another pulse pattern applied to the CO gas sensor.

FIG. 12 is a block diagram illustrating a configuration of a CO concentration calculation device.

FIG. 13 is a block diagram showing a configuration of a fuel cell device to which a CO gas sensor of the present invention is assembled.

FIG. 14 is a graph showing starting characteristics of each of the CO gas sensors of the example and the comparative example.

FIG. 15 shows the CO gas sensor of FIG. 15 and the comparative example C
It is a graph which compares the stability of the output with an O gas sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 Detection electrode 2, 12 Counter electrode 3, 13 Electrolyte membrane 5, 15 Sensor control part 10 CO gas sensor 14 Diffusion control film 20 CO concentration calculation device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuhiko Saguchi 2-19-12 Sotokanda, Chiyoda-ku, Tokyo Inside Equos Research Co., Ltd. (72) Keiji Kunimatsu 2-19 Sotokanda, Chiyoda-ku, Tokyo 12 Equos Research Co., Ltd.

Claims (14)

[Claims] 1. A detection unit comprising a detection electrode and a counter electrode sandwiching a solid electrolyte membrane, and a voltage application device for applying a CO oxidation potential and a CO adsorption potential between the detection electrode and the counter electrode. In the CO gas sensor, the detection electrode includes a conductive porous base material and an electrochemically active first catalyst, and has a concentration of 1 ng / cm ² to 1 ng / cm ^2.
A reaction layer having a thickness of 0.3 nm to 15 μm is formed at a density of 00 μg / cm ² , and the counter electrode is supported on a conductive porous base material by a second electrochemically active catalyst. The voltage applying device sets the CO oxidation potential at 0.8 to 0.9.
V, and the CO adsorption potential is 0.03 V to 0.07 V. 2. The method according to claim 1, wherein the first catalyst and the second catalyst are Pt,
The CO gas sensor according to claim 1, comprising one or more metals selected from Au, Cu, Ni, Pd, Ag, Rh, and Ru, or an alloy of one or more selected metals. . 3. The CO gas sensor according to claim 1, wherein the first catalyst is made of Pt, and the second catalyst is made of Pt-Ru. 4. The method according to claim 1, wherein the CO adsorption potential is 0.04 V to 0.04 V.
The CO gas sensor according to any one of claims 1 to 3, wherein the voltage is 6V. 5. The CO gas sensor according to claim 1, wherein the CO adsorption potential is approximately 0.05 V. 6. The CO gas sensor according to claim 1, wherein the CO oxidation potential is approximately 0.9 V. 7. The reaction layer of the detection electrode has a thickness of 5-10.
μm, and the density of the first catalyst is 0.1 μg / cm.
The CO gas sensor according to claim 1, wherein the CO gas sensor has a concentration of ^{2 to} 1.0 μg / cm ² . 8. The CO gas sensor according to claim 1, wherein the CO oxidation potential and the CO adsorption potential are repeatedly applied as a rectangular wave pulse. 9. The application time of the CO oxidation potential is from 0.3 to
0.8 seconds, and the application time of the CO adsorption potential is 0.5
The CO gas sensor according to any one of claims 1 to 8, wherein the time is from 2.0 to 2.0 seconds. 10. The application time of the CO oxidation potential is approximately 0.5 seconds, and the application time of the CO adsorption potential is approximately 1 second.
The CO gas sensor according to claim 1, wherein the time is seconds. 11. C according to claim 1, wherein
A fuel cell device comprising an O gas sensor. 12. A detection unit comprising a solid electrolyte membrane sandwiched between a detection electrode and a counter electrode, and applying a voltage between the detection electrode and the counter electrode to obtain a voltage of 0.8%.
A CO gas sensor comprising: a voltage application device that repeatedly applies a CO oxidation potential of 0.9 V to a CO adsorption potential of 0.03 V to 0.07 V to the detection electrode. 13. The value of a response current flowing between the detection electrode and the counter electrode is 0.1 mA / cm ^{2 to} 0.01 A.
C / cm ^2.
O gas sensor. 14. A detection unit comprising a detection electrode and a counter electrode sandwiching a solid electrolyte membrane, and a voltage application device for applying a CO oxidation potential and a CO adsorption potential between the detection electrode and the counter electrode. In the CO gas sensor, the detection electrode includes a conductive porous base material containing an electrochemically active first material, and is 1 ng / cm ² to 1 ng / cm ^2.
Forming a reaction layer having a thickness of 0.3 nm to 15 μm at a density of 00 μg / cm ² , wherein the counter electrode is supported on a conductive porous substrate, and an electrochemically active second material is supported on the conductive electrode; The voltage applying device sets the CO oxidation potential at 0.8 to 0.9.
V, and the CO adsorption potential is 0.03 V to 0.07 V.