JP4135880B2 - Proton conductor gas sensor, gas detector using the same, and self-diagnosis method of proton conductor gas sensor - Google Patents

Description

[0001]
[Field of the Invention]
The present invention relates to a self-diagnosis of a proton conductor gas sensor.
[0002]
[Prior art]
The proton conductor film used for the proton conductor gas sensor can be used for electrolysis of water, and when a DC voltage is applied, hydrogen is generated at the hydrogen electrode and oxygen is generated at the air electrode. Thus, it has been proposed to self-diagnose a proton conductor gas sensor using hydrogen generated (USP 5668, 302, USP 6200, 443). USP 5668,302 states that it is difficult to guide hydrogen generated at the hydrogen electrode to the electrolyte side for gas detection through a small hole for diffusion control, and bypasses the small hole for diffusion control. , It is disclosed to lead to the electrolyte side for gas detection.
[0003]
[Problems of the Invention]
An object of the present invention is to provide a new self-diagnosis technique for a proton conductor gas sensor that does not use hydrogen generated by electrolysis of water .
An additional object of the present invention is to generate a self-diagnosis gas at a voltage of 1.23 V or less, which is an electrolysis voltage of water, and to extend the life of the MEA for gas generation.
An additional problem in the invention of claim 2 is to simplify the configuration of the MEA for generating self-diagnosis gas.
An additional object of the invention of claim 3 is to provide a specific structure of a proton conductor gas sensor with a self-diagnosis function.
[0004]
[Terminology]
In this specification, MEA means a composite of a proton conductor membrane and at least a pair of electrodes, and the electrodes may be tripolar. Regarding the generation of diagnostic gas, the hydrogen electrode is an electrode to which a negative potential is applied and generates hydrogen, and the air electrode is an electrode to which a positive potential is applied. The detection electrode (working electrode) is an electrode for dissociating or reacting a detection gas, and the counter electrode is an electrode for reacting protons with oxygen. Nafion is a registered trademark of DuPont.
[0005]
[Structure of the invention]
The present invention relates to a proton conductor gas sensor in which diagnostic gas is generated from a proton conductor and self-diagnosis is performed.
Proton conductor film for the generation of diagnostic gas and a first MEA comprising a hydrogen electrode and an air electrode, and a second MEA consisting of a sensing electrode and the counter electrode proton conductor film for detecting gas separate from Provided in
A negative potential to the hydrogen electrode of the first MEA for diagnostic gassing, a positive potential to the cathode, such that the voltage of the hydrogen electrode and the air interpole becomes 1. Less than 23 V in the electrolysis voltage of water In addition, the gas from the air electrode is introduced into the detection electrode of the second MEA for gas detection . Incidentally it may be provided three or more electrodes to those of the MEA.
[0006]
The voltage between the hydrogen electrode and the air electrode applied to the first MEA for generating diagnostic gas is less than 1.23 V of the electrolysis voltage of water, for example 0.5 to 1.2 V, more preferably 1.15 to 0 .8V, particularly preferably 1.1 to 0.9V .
[0007]
Preferably, the first MEA for generating a diagnostic gas is different from the first MEA for generating a diagnostic gas and the MEA for detecting a gas, and the first MEA for generating a diagnostic gas is simplified. To.
[0008]
Preferably, the air electrode of the first MEA for generating diagnostic gas and the detection electrode of the MEA for gas detection are arranged to face each other, and a gas passage for introducing an atmosphere outside the sensor between them is provided. Furthermore, a diffusion control means is provided for guiding the gas generated in the first MEA for generating diagnostic gas and the atmosphere introduced from the gas passage to the detection electrode of the gas detecting MEA under diffusion control .
[0009]
The gas detector of the present invention is a device for generating diagnostic gas from a proton conductor to self-diagnose a proton conductor gas sensor.
Proton conductor film for the generation of diagnostic gas and a first MEA comprising a hydrogen electrode and an air electrode, to separate the second MEA consisting of a sensing electrode and the counter electrode proton conductor film for detecting gas Provided,
A negative potential to the hydrogen electrode of the first MEA for diagnostic gassing, a positive potential to the cathode, such that the voltage of the hydrogen electrode and the air interpole becomes 1. Less than 23 V in the electrolysis voltage of water in addition,
When introducing the gas from the air electrode to the sensing electrode of the second MEA for gas detection, and characterized in that the output of the second MEA for gas detection, and a proton conductor gas sensor such that self-diagnosis To do.
[0010]
The self-diagnosis method of the proton conductor gas sensor according to the present invention is a method in which a diagnostic gas is generated from the proton conductor to self-diagnose the proton conductor gas sensor.
Proton conductor film for the generation of diagnostic gas and a first MEA comprising a hydrogen electrode and an air electrode, to separate the second MEA consisting of a sensing electrode and the counter electrode proton conductor film for detecting gas Provided,
A negative potential to the hydrogen electrode of the first MEA for diagnostic gassing, a positive potential to the cathode, such that the voltage of the hydrogen electrode and the air interpole becomes 1. Less than 23 V in the electrolysis voltage of water In addition, the gas from the air electrode is introduced to the detection electrode of the second MEA for gas detection,
The self-diagnosis is performed from the response of the second MEA for gas detection to the gas from the air electrode .
[0011]
[Operation and effect of the invention]
In the proton conductor gas sensor according to the present invention, a negative potential is applied to the hydrogen electrode of the first MEA for generating a diagnostic gas , and a positive potential is applied to the air electrode. Self-diagnose the second MEA . According to the inventor's experience, it was difficult to self-diagnose the second MEA for gas detection with hydrogen generated at the hydrogen electrode. For example, even when the hydrogen electrode is arranged on the detection electrode side of the second MEA for gas detection, the output signal obtained by the self-diagnosis is very small. Therefore, in order to perform self-diagnosis reliably, it is necessary to apply a large voltage to the first MEA for gas generation. However, if this is done, the damage to the first MEA for gas generation becomes significant, and self-diagnosis occurs. The number of times it can be limited. However, when the gas from the air electrode is introduced into the detection electrode of the second MEA for gas detection, a large self-diagnosis signal can be obtained. For this reason, the self-diagnosis of the gas sensor can be performed using the gas generated at the air electrode of the first MEA for generating diagnostic gas .
[0012]
In the present invention, the voltage applied to the first MEA for generating diagnostic gas is less than 1.23 V of the electrolysis voltage of water . For example, the inventor has found that self-diagnosis can be performed even when a voltage of about 1.0 V is applied between the hydrogen electrode and the air electrode. And since the voltage applied to the first MEA for gas generation can be reduced, suppressing deterioration of the first MEA for gas generation, it is possible to increase the gas sensor life.
Although the details of the generated gas are unknown, it is estimated to be ozone or hydrogen peroxide gas because it is generated on the air electrode side. When ozone or hydrogen peroxide gas touches the detection electrode of the first MEA for detection, O ₃ + H ₂ O → H ₂ O ₂ + O ₂ H ₂ O ₂ → HO ₂ + H ⁺ + e ⁻ It is presumed that the reaction such as HO ₂ → O ₂ + H ⁺ + e ⁻ proceeds and self-diagnosis is possible.
[0013]
The MEA is generally an expensive material, but the first MEA for gas generation may be less reliable than the second MEA for gas detection. Therefore, for example, as the proton conductor film of the first MEA for gas generation, an inexpensive proton conductor film of hydrocarbon type such as a styrene butadiene copolymer into which a sulfonic acid group is introduced is used. For this, an inexpensive electrode such as a thin film Pt electrode or a C electrode can be used.
[0014]
Preferably, both the gas generated in the first MEA for gas generation and the atmosphere to be detected are guided to the detection electrode of the second MEA for gas detection through the diffusion control means under diffusion control. In other words, it is preferable not to provide a bypass passage for introducing the generated diagnostic gas in the diffusion control means to the detection electrode. When the bypass passage is provided, for example, when CO permeates through the first MEA for gas generation, diffusion control is not performed. When the bypass passage is not provided, the self-diagnosis signal is hardly obtained with hydrogen generated from the hydrogen electrode of the first MEA for gas generation. On the other hand, when gas from the air electrode is used, self-diagnosis can be performed without providing a bypass passage.
[0015]
In the gas detection device and the self-diagnosis method of the present invention, a positive potential is applied to the air electrode of the first MEA for generating a diagnostic gas, a negative potential is applied to the hydrogen electrode, and self-diagnosis is performed using the gas from the air electrode. .
[0016]
【Example】
1 to 9 show an embodiment and its modification. In these figures, 2 is a proton conductor gas sensor, which detects the current flowing from the detection electrode 43 to the counter electrode 42 with an ammeter 4 or the like, thereby detecting gas. Reference numeral 6 denotes a DC 1V power source for applying a voltage to the MEA for gas generation. An AC power supply may be used instead of the DC power supply. A switch 8 closes the switch 8 during self-diagnosis and applies a voltage from the power source 6 to the MEA 14 for gas generation.
[0017]
In the gas detection MEA 10, reference numerals 11 and 12 are conductive sheets such as carbon sheets. 14 is an MEA for gas generation, and 16 is a breathable sheet between the MEAs 10 and 14, but it may be a ring-like member having air permeability. Further, when the breathable sheet 16 is made conductive, the detection electrode of the gas generating MEA 14 and the air electrode of the gas detecting MEA 10 can be connected to a common electrode plate.
[0018]
Reference numerals 18 to 24 are electrode plates made of stainless steel, and 26 to 32 are openings provided therein. Of these, the opening 28 is an opening for diffusion control, and the opening 26 is for introducing water vapor from a water reservoir (not shown). Is the opening. The opening 32 is a large opening having a diameter of about 2 mm, for example, for introducing the diagnostic gas generated in the MEA 14 into the opening 28 through the breathable sheet 16. The opening 30 is an opening for discharging a gas such as hydrogen generated in the MEA 14, but may not be provided.
[0019]
The package 34 of the proton conductor gas sensor 2 is shown in FIG. The package 34 is composed of a pair of plastic films 35 and 36, and these are thermally bonded together to form a simple package. The package 34 is provided with openings 37 and 38, the opening 38 side is connected to a water reservoir 39, and water vapor is introduced from the water reservoir opening 40. An opening 33 is provided in the electrode plate 22 ′ so that an external atmosphere can be introduced from the side surface of the MEA 14 to the breathable sheet 16.
[0020]
The configuration of the MEA 10 for detection is shown in FIG. 3. The MEA 10 is provided with Pt—C electrodes 42 and 43 on both sides of a fluororesin proton conductor film 41. Among these, the electrode 42 is a counter electrode, and the electrode 43 serves as a detection electrode, and a detection gas or a diagnostic gas is introduced to the detection electrode 43 side through the opening 28 and the conductive sheet 12. The proton conductor film 41 is an expensive film for a fuel cell such as a Nafion film. The electrodes 42 and 43 are expensive electrodes containing about 25 to 40 wt% Pt.
[0021]
The configuration of the MEA 14 for gas generation is shown in FIG. 50 is a hydrocarbon resin-based proton conductor membrane, for example, an inexpensive proton conductor membrane sulfonated from a styrene-butadiene copolymer. The strength and durability of the membrane is low, so gas is continuously detected for several years. Not suitable for. However, such a proton conductor membrane 50 is extremely inexpensive and can be used for an acceptable gas generating MEA 14 even if there is some variation in performance.
[0022]
Reference numerals 51 and 52 denote Pt thin film electrodes, and the Pt amount is, for example, about 0.01 mg / cm ^{2 and} about 1/10 of the Pt-C electrodes 42 and 43. The electrodes 51 and 52 are not limited to Pt thin films, and C electrodes and other appropriate electrodes can be used. This is because the efficiency of the electrode reaction at the electrodes 51 and 52 is not particularly problematic.
[0023]
In FIGS. 1 and 2, both sides of the MEA 14 are sandwiched between electrode plates 22 and 24. However, as shown in FIG. 5, Ti meshes 53 and 54 may be substituted for the electrode plates.
The self-diagnosis and gas detection mechanism in the embodiment will be described. Water vapor is supplied from the water reservoir 39 through the openings 40 and 38 to the counter electrode of the MEA 10, and the water vapor is distributed in the conductive sheet 11 and supplied to the entire surface of the electrode 42 serving as the counter electrode. The gas to be detected enters the air-permeable sheet 16 from the periphery of the MEA 14 and is introduced to the detection electrode 43 through the opening 28. The opening 28 is an opening having a diameter of about 100 μm, and introduces the gas to be detected to the detection electrode under diffusion rate control. Thus, the electrode plate 20 also serves as a diffusion control means.
[0025]
The self-diagnosis of the gas sensor 2 is performed at a predetermined cycle, for example, once a month, and each time a voltage of about 1 V is applied to the MEA 14 by closing the switch 8 for a predetermined time, for example, about 30 seconds to 1 minute. . The voltage is applied so that the air electrode 51 close to the MEA 10 is positive and the hydrogen electrode 52 from the opening 30 is negative. Ozone and hydrogen peroxide gas generated at the air electrode are discharged from the opening 32 to the breathable sheet 16 and the opening 28. In addition, it is introduced into the detection electrode via the conductive sheet 12. For this reason, the opening 32 is preferably a large opening. Since the hydrogen generated at the hydrogen electrode of the MEA 14 diffuses quickly, it can be discharged freely without providing the opening 30.
[0026]
In the package 34 of FIG. 2, the side surface of the MEA 14 is easily covered with the package. Therefore, the electrode plate 22 ′ has a larger diameter than the MEA 14, and a bypass opening 33 is provided outside the MEA 14 so as not to overlap the MEA 14. In this way, the detection target gas can reach the breathable sheet 16 through the side surface of the MEA 14. Also in this case, the diagnostic gas is introduced through the opening 32, the air permeable sheet 16, and the opening 28 for diffusion control.
[0027]
FIG. 6 shows a modified proton conductor gas sensor 62. In this proton conductor gas sensor 62, a common electrode plate 64 is used, MEA 10 and MEA 14 are separately provided on the common electrode plate 64, and gas generated at the air electrode of MEA 14 is supplied to the detection electrode side of MEA 10 through pipe 66. 64 is a common electrode plate made of stainless steel or the like, and 66 is a pipe for introducing the gas generated at the air electrode of the MEA 14 to the vicinity of the opening 28 of the MEA 10. A member that provides a gas flow path such as a breathable sheet may be used instead of the pipe.
[0028]
FIG. 7 shows waveforms during self-diagnosis with the gas sensor of FIG. Vcc means a DC voltage applied to the self-diagnosis, and is added so that the air electrode side (near MEA 10) is positive and the hydrogen electrode side is negative. The numbers such as 100, 300 on the right side of the figure indicate the CO concentration (in ppm). FIG. 7 shows the output waveforms of two sensors, a normal sensor and a sensor with a clogged opening 28.
[0029]
When Vcc is about 1V, an output capable of sufficient self-diagnosis is obtained, and the output at MEA 10 increases as Vcc is increased. Even if self-diagnosis is performed, the baseline in the detection MEA does not change, and CO can be detected. Since the response time of the MEA for detection is about 30 seconds, the time width of the voltage applied to the self-diagnosis is preferably about 30 seconds to 1 minute. Next, the smaller the voltage applied to the MEA 14 for gas generation, the smaller the damage to the MEA 14, so the applied voltage is preferably less than 1.23 V, which is the electrolysis voltage of water, for example 0.5 V to 1.2 V, more preferably 0. 0.8V to 1.15V, most preferably 1.1V to 0.9V, and 1.0V in the embodiment.
[0030]
FIG. 8 shows the characteristics when the polarity of the voltage is reversed during self-diagnosis. Here, Vcc + means that a positive voltage is applied to the air electrode according to the embodiment, and Vcc − means that a negative voltage is applied to the air electrode. When hydrogen is generated at the air electrode, the output for self-diagnosis is small and a voltage of about -2V is required. When such a large voltage is applied, the MEA for gas generation is significantly damaged. When hydrogen is generated by applying a voltage of -2 V, the output undershoot after self-diagnosis is remarkable. On the other hand, if the voltage is applied with the air electrode side negative and the positive hydrogen electrode side negative, sufficient self-diagnosis can be performed at about 1.0V, and even if a large voltage of 2.0V is applied, the self-diagnosis can be performed Hysteresis is small.
[0031]
The type of gas generated at the air electrode during self-diagnosis is assumed to be ozone or hydrogen peroxide gas. Since the electrolysis voltage of water is 1.23 V, water cannot be constantly electrolyzed at a voltage lower than this, and the mechanism of gas generation is unknown. Therefore, as a gas generation mechanism at the air electrode, for example,
・ The hydroxyl groups adsorbed on the air electrode are converted into protons, electrons, and adsorbed oxygen, and the adsorbed oxygen adheres to the surrounding water and hydrogen peroxide is generated.
・ Or adsorbed oxygen is added to oxygen molecules to generate ozone,
It is possible. In addition to ozone and hydrogen peroxide, oxygen should also be generated on the air electrode side. When ozone reaches the detection electrode of MEA 10, hydrogen peroxide is generated by the reaction of O ₃ + H ₂ O → O ₂ + H ₂ O ₂ . When hydrogen peroxide comes into contact with the sensing electrode, a reaction of H ₂ O ₂ → HO ₂ + H ⁺ + e ⁻ HO ₂ → O ₂ + H ⁺ + e ⁻ releases a proton to the sensing electrode and performs self-diagnosis. be able to.
[0032]
The MEA 10 for detection and the MEA 14 for gas generation need to be separated. Further, in order to allow the diagnostic gas generated in the MEA 14 for gas generation to be introduced into the MEA 10, they are preferably arranged oppositely or in parallel. Here, it is not preferable that the MEA 10 and the MEA 14 share a proton conductor film. The inventor examined an example in which a proton conductor film is shared between two MEAs. In this way, the gas sensor can be easily manufactured. FIG. 10 shows such a gas sensor. Reference numeral 41 is a common proton conductor film, 70 is an air electrode in the gas generating section, 71 is a hydrogen electrode, and 11 and 12 are the conductive sheets. Reference numeral 72 denotes a new electrode plate.
[0033]
The gas sensor of FIG. 10 is manufactured by laminating detection electrodes 42 and 43, gas generation electrodes 70 and 71, and conductive sheets 11 and 12 on one proton conductor film 41. The gas generation part and the detection part share the same electrode and conductive sheet material. Here, when a voltage is applied from the electrodes 70 and 71 to the proton conductor film 41 during gas generation, this voltage also affects the region between the electrodes 42 and 43.
[0034]
FIG. 9 shows an example in which the voltage from the power source 6 is applied to the MEA 10 side in the gas sensor of FIG. The voltage was applied between the electrode plates 18 and 20 and 1 V × 30 seconds. FIG. 9 shows the response waveform to CO of one normal gas sensor to which no voltage is applied and three sensors to which a voltage of 1 V × 30 seconds is applied. The response waveform to CO was measured about 1 hour after the voltage was applied, but the same waveform was obtained even after 3 days. As is apparent from FIG. 9, the characteristics of the MEA change significantly when a voltage is applied. Therefore, as shown in FIG. 10, it is considered dangerous to use a common proton conductor film for gas detection and gas generation, and separate MEA is used for gas generation and detection. .
[Brief description of the drawings]
FIG. 1 is a principle diagram of self-diagnosis of a proton conductor gas sensor according to an embodiment. FIG. 2 is a cross-sectional view showing a main part of the proton conductor gas sensor according to the embodiment. Side view [Fig. 4] Cross-sectional view of MEA for gas generation in the embodiment [Fig. 5] Cross-sectional view showing a state in which a Ti mesh is attached to the MEA for gas generation [Fig. Sectional view [Fig. 7] Shows the output waveform during self-diagnosis in the example, Vcc indicates the voltage applied to the MEA for gas generation, and CO concentration indicates the CO concentration contacted after self-diagnosis in ppm units [Fig. 8] Indicates the effect of voltage polarity applied to the MEA for gas generation during self-diagnosis, Vcc + is self-diagnostic with the gas generated on the air electrode side with the polarity of the example,-is hydrogen electrode with polarity in the conventional example This is a characteristic for self-diagnosis with hydrogen generated on the side.
FIG. 9 shows the response waveform to CO after applying a DC voltage of 1 V × 30 seconds to the MEA for gas generation. FIG. 10 shows protons common to the MEA for gas generation and the MEA for gas detection. Side view of the main part of a gas sensor for comparison using a conductor film [Explanation of symbols]
2 Proton conductor gas sensor 4 Ammeter 6 Power supply 8 Switch 10 MEA for gas detection
11, 12 Conductive sheet 14 MEA for gas generation
16 Breathable sheet 18-24 Electrode plate 26-32 Opening 34 Package 35.36 Plastic film 37, 38 Opening 39 Water reservoir 40 Opening 41 Fluororesin proton conductor film 42, 43 Pt-C electrode 50 Hydrocarbon resin proton Conductor films 51, 52 Pt thin film electrodes 53, 54 Ti mesh 62 Proton conductor gas sensor 64 Common electrode plate 66 Pipe 70 Electrode 72 Electrode plate

Claims (5)

In the proton conductor gas sensor that generates diagnostic gas from the proton conductor and performs self-diagnosis,
Proton conductor film for the generation of diagnostic gas and a first MEA comprising a hydrogen electrode and an air electrode, and a second MEA consisting of a sensing electrode and the counter electrode proton conductor film for detecting gas separate from Provided in
A negative potential to the hydrogen electrode of the first MEA for diagnostic gassing, a positive potential to the cathode, such that the voltage of the hydrogen electrode and the air interpole becomes 1. Less than 23 V in the electrolysis voltage of water In addition , a proton conductor gas sensor is characterized in that gas from the air electrode is introduced into the detection electrode of the second MEA for gas detection. In the first MEA and the second MEA for detecting gas for diagnostic gas generation, the material of the material or the electrode of the proton conductor film are different from each other, the proton conductor gas sensor as claimed in claim 1. The air electrode of the first MEA for diagnosis gas generation and the detection electrode of the second MEA for gas detection are arranged opposite to each other, and a gas passage for introducing an atmosphere outside the sensor between them is provided. ,
Furthermore, a diffusion control means for guiding the gas generated in the first MEA for generating diagnostic gas and the atmosphere introduced from the gas passage to the detection electrode of the second MEA for gas detection under diffusion control. The proton conductor gas sensor according to claim 1, wherein the proton conductor gas sensor is provided. In an apparatus for generating diagnostic gas from a proton conductor to self-diagnose the proton conductor gas sensor,
Proton conductor film for the generation of diagnostic gas and a first MEA comprising a hydrogen electrode and an air electrode, to separate the second MEA consisting of a sensing electrode and the counter electrode proton conductor film for detecting gas Provided,
A negative potential to the hydrogen electrode of the first MEA for diagnostic gassing, a positive potential to the cathode, such that the voltage of the hydrogen electrode and the air interpole becomes 1. Less than 23 V in the electrolysis voltage of water in addition,
When introducing the gas from the air electrode to the sensing electrode of the second MEA for gas detection, and characterized in that the output of the second MEA for gas detection, and a proton conductor gas sensor such that self-diagnosis A gas detection device. In the method of generating diagnostic gas from the proton conductor and self-diagnosing the proton conductor gas sensor,
Proton conductor film for the generation of diagnostic gas and a first MEA comprising a hydrogen electrode and an air electrode, to separate the second MEA consisting of a sensing electrode and the counter electrode proton conductor film for detecting gas Provided,
A negative potential to the hydrogen electrode of the first MEA for diagnostic gassing, a positive potential to the cathode, such that the voltage of the hydrogen electrode and the air interpole becomes 1. Less than 23 V in the electrolysis voltage of water In addition, the gas from the air electrode is introduced into the detection electrode of the second MEA for gas detection,
A self-diagnosis method for a proton conductor gas sensor, characterized in that self-diagnosis is performed from a response of a second MEA for gas detection to gas from an air electrode.

Images