JP4581253B2 - Gas sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to H₂The present invention relates to a gas sensor that measures the CO concentration in a rich test gas.
[0002]
[Prior art]
A conventional CO gas sensor includes a detection unit having a detection electrode and a counter electrode arranged via an electrolyte layer.
[0003]
In this CO gas sensor, CO concentration in the test gas is measured from the obtained current value by, for example, adsorbing and oxidizing CO on the detection electrode.
[0004]
In the conventional CO gas sensor, the detection electrode and the counter electrode are each formed by forming a material in which a catalyst is supported on a carrier into a flat plate shape.
[0005]
Such a CO gas sensor may be used by bringing a test gas having a high temperature and high humidity into contact with the detection unit. In this case, the detection unit may change drastically in temperature and humidity during use and when not in use. Each member that is exposed and constitutes the detection unit repeats expansion and contraction.
[0006]
Thereby, in the conventional CO gas sensor, for example, the catalyst is detached from the carrier at the detection electrode or the counter electrode, the separation from the electrolyte layer of the detection electrode or the counter electrode, and the like, and as a result, the sensor output (measurement accuracy) is reduced. There's a problem.
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a gas sensor having excellent durability.
[0008]
[Means for Solving the Problems]
  Such purposes are as follows (1) to (12This is achieved by the present invention.
[0009]
  (1) a detection unit having a detection electrode reaction layer that reacts a predetermined component in the test gas, a counter electrode reaction layer that is installed to face the detection electrode reaction layer, and an electrolyte layer that is installed therebetween The voltage applied to the detection unit is controlled and H by voltage application is controlled.₂Detected with the oxidation reaction of₂A controller for measuring the ionization current,
  The detection electrode reaction layer comprises a plurality of detection electrode reaction layer units mainly composed of a catalyst.A recess formed to reach the inside of the electrolyte layerIt is arranged through a gap,
  The control unit detects the H detected between when a CO oxidation potential that adsorbs and oxidizes CO is applied to the detection unit and when a CO adsorption potential that adsorbs CO but does not oxidize is applied.₂A gas sensor that measures a CO concentration in the test gas based on a change amount of an ionization current.
[0010]
(2) a detection unit having a detection electrode reaction layer that reacts with a predetermined component in the test gas, a counter electrode reaction layer installed opposite to the detection electrode reaction layer, and an electrolyte layer installed therebetween The voltage applied to the detection unit is controlled and H by voltage application is controlled. ₂ Detected with the oxidation reaction of ₂ A controller for measuring the ionization current,
The detection electrode reaction layer is composed of a plurality of detection electrode reaction layer units mainly composed of a catalyst with a gap therebetween, and a plurality of irregularities are formed on the detection electrode reaction layer side of the electrolyte layer. And each of the detection electrode reaction layer units is provided on a convex portion of the electrolyte layer,
The control unit detects the H detected between when a CO oxidation potential that adsorbs and oxidizes CO is applied to the detection unit and when a CO adsorption potential that adsorbs CO but does not oxidize is applied. ₂ A gas sensor that measures a CO concentration in the test gas based on a change amount of an ionization current.
[0011]
(3) a detection unit having a detection electrode reaction layer that reacts with a predetermined component in the test gas, a counter electrode reaction layer that is disposed to face the detection electrode reaction layer, and an electrolyte layer that is disposed therebetween. The voltage applied to the detection unit is controlled and H by voltage application is controlled. ₂ Detected with the oxidation reaction of ₂ A controller for measuring the ionization current,
The detection electrode reaction layer is formed by arranging a plurality of detection electrode reaction layer units mainly composed of a catalyst with a gap between them,
The specific surface area of the counter electrode reaction layer is 10 to 1000 times the specific surface area of the detection electrode reaction layer,
The control unit detects the H detected between when a CO oxidation potential that adsorbs and oxidizes CO is applied to the detection unit and when a CO adsorption potential that adsorbs CO but does not oxidize is applied. ₂ A gas sensor that measures a CO concentration in the test gas based on a change amount of an ionization current.
[0012]
(4) When viewed from a direction perpendicular to the detection electrode reaction layer, the ratio of the area occupied by the gap to the total area of the detection electrode reaction layer is 0.01 to 60%. The gas sensor according to any one of the above.
[0013]
(5) The gas sensor according to any one of (1) to (4), wherein the detection electrode reaction layer is formed on the electrolyte layer.
[0014]
(6) The gas sensor according to any one of (1) to (5), wherein the counter electrode reaction layer is made of a material containing a catalyst.
[0015]
(7) The gas sensor according to (6), wherein the catalyst of the counter electrode reaction layer is supported on a carrier.
[0017]
  (8)  The gas diffusion layers are respectively installed on the opposite sides of the detection electrode reaction layer and the counter electrode reaction layer from the electrolyte layer.(7)The gas sensor according to any one of the above.
[0018]
  (9)  The electrolyte layer is composed of an ion exchange resin (1) to (1) above.(8)The gas sensor according to any one of the above.
[0019]
  (10)  The control unit is configured to₂The rate of change per unit time is calculated from the amount of change in ionization current, and the calculated rate of change is calculated using the known CO concentration and H₂It is applied to a calibration curve with the rate of change of the ionization current, and is configured to calculate the CO concentration (1) to (1)(9)The gas sensor according to any one of the above.
[0020]
  (11)  The above (1) to (1), further comprising a gas collection container for collecting the test gas, wherein the detection unit is installed in the gas collection container(10)The gas sensor according to any one of the above.
[0021]
  (12)  (1) to (1) used for measuring the CO concentration in the test gas(11)The gas sensor according to any one of the above.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
As a result of intensive research in order to solve the above problems, the present inventor, as a result, in the gas sensor (CO gas sensor), in the detection electrode reaction layer (detection electrode), the catalyst falls off from the carrier, the electrolyte layer of the detection electrode reaction layer As a result, it has been found that the sensor output (measurement accuracy) is remarkably lowered when peeling from the substrate occurs, and the present invention has been completed.
[0023]
Hereinafter, a gas sensor of the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings. Hereinafter, a case where CO (carbon monoxide) is measured as a predetermined component in the test gas will be described.
[0024]
First, before describing the gas sensor of the present invention, a fuel cell system will be described as an example of a system incorporating and using the gas sensor of the present invention.
[0025]
FIG. 6 is a schematic diagram showing the overall configuration of the fuel cell system.
A fuel cell system 100 shown in FIG. 6 includes a methanol tank 110, a water / methanol tank 120, a reforming device 130, a CO removing device 140, a fuel cell 150, and the gas sensor 1 of the present invention.
[0026]
The methanol tank 110 stores methanol as a raw material, while the water / methanol tank 120 stores a mixed solution of water / methanol as a raw material.
[0027]
The methanol tank 110 and the water / methanol tank 120 are connected to the reformer 130 via pumps 111 and 121, respectively.
[0028]
In this reformer 130, the raw materials introduced from the methanol tank 110 and the water / methanol tank 120 are reformed into a reformed gas containing about 75% hydrogen gas.
[0029]
This reformed gas is sent to the CO removing device 140 connected to the reforming device 130, but a part of the reformed gas is installed on a bypass line where a line connecting the reforming device 130 and the CO removing device 140 is branched. Is sent to the gas sensor 1 and the CO concentration in the reformed gas is measured.
[0030]
Based on the measurement result of the CO concentration in the reformed gas of the gas sensor 1, the CO removal device 140 processes the reformed gas. Thereby, CO is removed from the reformed gas, and the treated reformed gas is supplied as hydrogen gas fuel to the fuel cell 150 connected to the CO removing device 140. The fuel cell 150 generates electricity using this hydrogen gas fuel.
[0031]
By using such hydrogen gas fuel, power generation efficiency is improved in the fuel cell 150.
[0032]
Next, the gas sensor of the present invention will be described.
FIG. 1 is a schematic diagram showing the overall configuration of the gas sensor of the present invention, and FIG. 2 is an enlarged cross-sectional view showing the configuration of a detection unit provided in the gas sensor of the present invention.
[0033]
A gas sensor 1 shown in FIG. 1 includes a gas sampling container 2 that collects a test gas inside, a detection unit 3 installed in the gas sampling container 2, and a control unit 7 that controls a voltage applied to the detection unit 3. It has. Hereinafter, each component will be described.
[0034]
The gas sampling container 2 has a casing 21 and a lid 22. The casing 21 has a space 211 formed therein, and a detection unit 3 described later is installed in the space 211. In this gas sensor 1, a test gas is introduced (purged) into the space 211, and the CO concentration in the test gas is measured.
[0035]
Further, in the space 211, water is stored in order to keep the gas sampling container 2 (space 211) in a humidified state. Although it does not specifically limit as humidity in the space 211, For example, it is preferable that it is about 30-100% RH.
[0036]
In addition, instead of holding the gas sampling container 2 in a humidified state, a humidified test gas may be introduced into the gas sampling container 2.
[0037]
The housing 21 is provided with a flat lid 22 so as to hermetically close the upper opening. The lid 22 includes an introduction line (introduction means) 23 for introducing the test gas into the gas sampling container 2 (space 211), and an exhaust line (exhaust means) for discharging the test gas from the gas sampling container 2 24).
[0038]
Further, the introduction line 23 is provided with a pressure adjusting device 231 for adjusting the pressure in the gas sampling container 2 in the middle thereof, and an end portion of the introduction line 23 is connected to the reformer 130 described above.
[0039]
On the other hand, the end of the exhaust line 24 is connected to the CO removal device 140 described above.
[0040]
Such a gas sampling container 2 (housing 21 and lid 22) includes, for example, various resin materials such as polycarbonate, polymethyl methacrylate, polyimide, polysulfone, polyphenylene sulfide, aluminum or aluminum alloy, stainless steel, titanium, or titanium alloy. It can comprise with various metal materials, such as various ceramic materials, various glass materials, etc.
[0041]
The detector 3 is installed in the gas sampling container 2 (space 211).
As shown in FIG. 2, the detection unit 3 includes a detection electrode 5 including a detection electrode reaction layer 51 and a detection electrode gas diffusion layer 52, a counter electrode 6 including a counter electrode reaction layer 61 and a counter electrode gas diffusion layer 62, The electrolyte layer 4 is disposed between them and is in contact with the detection electrode reaction layer 51 and the counter electrode reaction layer 61.
[0042]
In such a detection unit 3, when the test gas comes into contact, in the detection electrode reaction layer 51, predetermined components in the test gas (in this embodiment, CO and / or H).₂) Are adsorbed and oxidized (reacted), and in the counter electrode reaction layer 61, hydrogen ions (H⁺) And electrons (e^-) And reassociate (reducing hydrogen ions). At this time, a response current (hereinafter referred to as “CO ionization current”) obtained by CO oxidation reaction directly or indirectly by an ammeter 73 provided in the control unit 7 described later, or indirectly, H₂Response current obtained by oxidation reaction of (hydrogen) (hereinafter referred to as “H₂Ionization current ". ) Changes over time (decreases) in accordance with the adsorption of CO to the detection electrode reaction layer 51, whereby the CO concentration in the test gas can be measured.
[0043]
A specific method for measuring the CO concentration in the test gas using the gas sensor 1 (usage method: operation of the gas sensor 1) will be described later.
[0044]
The electrolyte layer 4 has a function as a hydrogen ion transfer medium, and has a film shape (layer shape).
[0045]
The electrolyte layer 4 is impregnated (supported) with a water retention material (for example, woven fabric, nonwoven fabric, paper, etc.) with an electrolyte solution such as proton conductive ion exchange resin (solid electrolyte) such as Nafion (registered trademark) or sulfuric acid. However, among these, it is preferable to use a proton conductive ion exchange resin that is easy to handle and has a wide use environment.
[0046]
Thereby, in the gas sensor 1, while the measurement accuracy improves more, response time (measurement time) can be shortened more.
[0047]
Although the average thickness of the electrolyte layer 4 is not specifically limited, For example, it is preferable that it is about 1-1000 micrometers, and it is more preferable that it is about 10-100 micrometers. Thereby, the electrolyte layer 4 can exhibit the said effect more suitably.
[0048]
On one surface (left side in FIG. 2) of the electrolyte layer 4, a detection electrode 5 having a film shape (layer shape) as a whole is joined (installed).
[0049]
The detection electrode 5 includes a detection electrode reaction layer 51 on the electrolyte layer 4 side, and a detection electrode gas diffusion layer 52 joined to the detection electrode reaction layer 51.
[0050]
The detection electrode reaction layer 51 includes CO and / or H in the test gas.₂Which has a function of oxidizing CO and mainly CO and / or H₂A plurality of detection electrode reaction layer units 511 composed of a catalyst that promotes oxidation of the catalyst are arranged (arranged).
[0051]
Each of these detection electrode reaction layer units 511 is installed (arranged) via a gap (micro gap) 512, that is, at a predetermined interval.
[0052]
By making the detection electrode reaction layer 51 (detection electrode reaction layer unit 511) mainly composed of a catalyst, that is, by making the carrier not carry the catalyst, the sensor output (measurement accuracy) of the conventional CO gas sensor is lowered. Catalyst desorption from the carrier, which is one of the causes, can be prevented, and excellent durability can be obtained in the detection unit 3 (gas sensor 1).
[0053]
In addition, by configuring the detection electrode reaction layer 51 with a plurality of detection electrode reaction layer units 511 installed via the gaps 512, stress (deformation) due to expansion / contraction of the electrolyte layer 4 is applied to the detection electrode reaction layer 51. The influence exerted can be reduced. Accordingly, it is possible to suitably prevent (or reduce) the separation of the detection electrode reaction layer 51 from the electrolyte layer 4 which is one of the causes of a decrease in the sensor output of the conventional CO gas sensor, and the detection unit 3 (gas sensor 1 ) Provides excellent durability.
[0054]
Furthermore, in the detection part 3 (gas sensor 1), durability can be remarkably improved by the synergistic effect by the combination of these structures.
[0055]
From such a viewpoint, the ratio of the area occupied by the gap 512 to the total area of the detection electrode reaction layer 51 when viewed from the direction perpendicular to the detection electrode reaction layer 51 (from the left side in FIG. 2) is not particularly limited. However, for example, it is preferably about 0.01 to 60%, and more preferably about 1 to 30%. Thereby, in the detection electrode reaction layer 51, the diffusion of CO becomes better, the sensitivity to CO is improved, and peeling of the detection electrode reaction layer 51 from the electrolyte layer 4 can be suitably prevented (or reduced). .
[0056]
Further, the shape of the detection electrode reaction layer unit 511 is not particularly limited, and any shape may be used. That is, the shape of the gap 512 is not particularly limited and may be any shape, but is preferably configured by a groove. In the present embodiment, the gap 512 includes a plurality of grooves that are substantially equally spaced. They are arranged so as to be substantially orthogonal (in a lattice pattern).
[0057]
As a catalyst constituting the detection electrode reaction layer unit 511 (detection electrode reaction layer 51), for example, platinum (Pt), gold (Au), copper (Cu), nickel (Ni), palladium (Pd), silver (Ag) ), Rhodium (Rh), ruthenium (Ru), or the like, or an alloy containing at least one of them can be used alone or in combination.
[0058]
In such a detection electrode reaction layer 51, for example, the average thickness is preferably about 0.01 to 1000 μm, more preferably about 0.1 to 1 μm, and the surface of the electrolyte layer 4 is 1 cm.²The amount of the catalyst present around is preferably about 0.01 to 50 μg, and more preferably about 0.1 to 20 μg. If the detection electrode reaction layer 51 is too thin (that is, if the amount of the catalyst is too small), depending on the type of the catalyst, the CO ionization current and / or H₂In some cases, the ionization current decreases, making measurement difficult. On the other hand, when the thickness of the detection electrode reaction layer 51 exceeds the upper limit (that is, the amount of the catalyst exceeds the upper limit), the sensitivity to CO may decrease.
[0059]
A detection electrode gas diffusion layer 52 in the form of a film (layer) is joined (installed) on the opposite side of the detection electrode reaction layer 51 to the electrolyte layer 4.
[0060]
The detection electrode gas diffusion layer 52 diffuses the test gas and contacts the detection electrode reaction layer 51 with CO and / or H.₂It has a function to reduce unevenness. The detection electrode gas diffusion layer 52 also has a function of giving electrons generated in the detection electrode reaction layer 51 to the control unit 7 described later. Further, the detection electrode gas diffusion layer 52 has a function of improving the strength of the detection unit 3.
[0061]
The detection electrode gas diffusion layer 52 can be composed of, for example, a porous conductive material typified by a porous carbon material such as carbon fiber fabric (for example, carbon cloth, carbon felt, etc.), carbon paper, or the like. . Thereby, the detection electrode gas diffusion layer 52 can more suitably exhibit the above-described function.
[0062]
Among these, the detection electrode gas diffusion layer 52 is preferably made of a carbon fiber fabric such as carbon cloth or carbon felt. Carbon fiber fabrics are CO and H₂It is also excellent in terms of improving the strength of the detection unit 3.
[0063]
The average thickness of the detection electrode gas diffusion layer 52 is not particularly limited, but is preferably about 50 to 2000 μm, and more preferably about 100 to 800 μm. If the detection electrode gas diffusion layer 52 is made too thin, the strength of the detection unit 3 cannot be maintained at a suitable level depending on the degree of porosity of the detection electrode gas diffusion layer 52, the constituent material, and the like. CO and / or H to the catalyst of the reaction layer 51₂The electrical contact unevenness may become remarkable. On the other hand, if the detection electrode gas diffusion layer 52 is too thick, depending on the degree of porosity of the detection electrode gas diffusion layer 52, the detection electrode reaction layer 51 may be subjected to CO and / or H.₂May not be able to contact (reach) efficiently.
The detection electrode gas diffusion layer 52 may be omitted as necessary.
[0064]
A counter electrode 6 having a film shape (layer shape) as a whole is joined (installed) to the side opposite to the detection electrode 5 (right side in FIG. 2) via the electrolyte layer 4.
[0065]
The counter electrode 6 includes a counter electrode reaction layer 61 on the electrolyte layer 4 side and a counter electrode gas diffusion layer 62 joined to the counter electrode reaction layer 61.
[0066]
The counter electrode reaction layer 61 is composed of CO and / or H in the detection electrode reaction layer 51.₂It has a function of reassociating (reducing hydrogen ions) hydrogen ions and electrons generated by the oxidation reaction.
[0067]
The counter electrode reaction layer 61 can be made of, for example, a material containing a catalyst that promotes reduction of hydrogen ions.
[0068]
As the catalyst, the same catalysts as those mentioned in the detection electrode reaction layer 51 can be used. However, a catalyst which is not easily poisoned by CO, such as platinum-ruthenium alloy (Pt-Ru), is preferably used. Good.
[0069]
The detection electrode reaction layer 51 and the counter electrode reaction layer 61 have different functions and roles. Therefore, the catalyst of the detection electrode reaction layer 51 and the catalyst of the counter electrode reaction layer 61 are different. preferable. As a result, the detection electrode reaction layer 51 and the counter electrode reaction layer 61 exert their respective functions and roles as a result. As a result, in the gas sensor 1, the measurement accuracy is further improved and the measurement time is further shortened. Can do.
[0070]
The material of the counter electrode reaction layer 61 is preferably configured such that, for example, a powder (particle) catalyst is supported on a carrier. Thereby, in the obtained counter electrode reaction layer 61, the specific surface area of a catalyst can be increased and the reduction | restoration efficiency of a hydrogen ion improves more.
[0071]
In this case, the average particle diameter of the catalyst is not particularly limited, but is preferably about 0.1 to 1000 nm, for example. Thereby, the catalyst can increase the specific surface area more.
[0072]
Moreover, as a support | carrier which carry | supports this catalyst, carbon materials (carbon material of a high specific surface area), such as carbon powder, carbon fiber (carbon fiber), a mixture thereof, etc. can be used, for example. Such a carbon material is excellent in the carrying capacity of the catalyst.
[0073]
When a powdery carrier such as carbon powder is used as the carrier, the average particle diameter of the carrier is not particularly limited, but is preferably about 0.01 to 1 μm, for example. Thereby, the support | carrier can carry | support a catalyst so that a catalyst can exhibit the outstanding catalyst activity.
[0074]
Moreover, you may make it mix the material which comprises the electrolyte layer 4 in the material of the counter electrode reaction layer 61 as needed. Thereby, the adhesiveness of the electrolyte layer 4 and the counter electrode reaction layer 61 can be improved.
[0075]
The content of the catalyst (the amount of catalyst supported) in the material of the counter electrode reaction layer 61 is appropriately set depending on the type of the catalyst and / or the support, and is not particularly limited, but is preferably about 1 to 80 wt%, for example. 10 to 50 wt% is more preferable. When the catalyst content is less than the lower limit, the counter electrode reaction layer 61 may not sufficiently reduce hydrogen ions depending on the type of the catalyst and the like, and the measurement accuracy of the gas sensor 1 may decrease. On the other hand, even if the content of the catalyst is increased beyond the upper limit, the gas sensor 1 cannot obtain any further improvement in measurement accuracy. In this case, the cost of the catalyst is high, and as a result, the manufacturing cost of the entire gas sensor 1 increases, which is not preferable.
[0076]
In addition, when the support is included in the material of the counter electrode reaction layer 61, the content of the support is appropriately set depending on the type of the catalyst and / or the support and is not particularly limited. For example, about 5 to 60 wt% It is preferable to set it as about 10-50 wt%. Thereby, the catalyst can be more suitably supported on the carrier. In addition, the electrons can be moved more rapidly in the counter electrode reaction layer 61.
[0077]
The specific surface area of the counter electrode reaction layer 61 is not particularly limited. For example, the specific surface area of the detection electrode reaction layer 51 is preferably about 10 to 1000 times, and preferably about 100 to 1000 times. Thereby, the counter electrode reaction layer 61 is less likely to be poisoned by CO, and the reduction reaction of hydrogen ions can be performed more stably. For this reason, there exists an advantage that the electric potential control of the detection pole 5 can be performed more accurately.
[0078]
More specifically, the specific surface area of the counter electrode reaction layer 61 is 5 to 300 cm.²/ Cm²It is preferable that it is about. Thereby, the reduction efficiency of hydrogen ions is further improved.
[0079]
In such a counter electrode reaction layer 61, for example, the average thickness is preferably about 2 to 1000 μm, more preferably about 5 to 500 μm, and the surface of the electrolyte layer 4 is 1 cm.²The amount of the catalyst present around is preferably about 0.05 to 5 mg, and more preferably about 0.1 to 1 mg. If the counter electrode reaction layer 61 is made too thin (that is, if the amount of the catalyst is too small), the reduction efficiency of hydrogen ions may decrease depending on the material of the counter electrode reaction layer 61 (particularly, the type of catalyst). On the other hand, even if the thickness of the counter electrode reaction layer 61 exceeds the upper limit (that is, the amount of the catalyst exceeds the upper limit), the reduction efficiency of hydrogen ions cannot be further improved. .
[0080]
A counter electrode gas diffusion layer 62 having a film shape (layer shape) is joined (installed) to the surface of the counter electrode reaction layer 61 opposite to the electrolyte layer 4.
[0081]
The counter electrode gas diffusion layer 62 is H generated by reduction of hydrogen ions in the counter electrode reaction layer 61.₂Has a function of efficiently removing the. Further, the counter electrode gas diffusion layer 62 also has a function of imparting electrons supplied via the control unit 7 described later to the counter electrode reaction layer 61. Furthermore, the counter electrode gas diffusion layer 62 also has a function of improving the strength of the detection unit 3.
[0082]
The counter electrode gas diffusion layer 62 can have the same configuration (material, thickness, etc.) as the detection electrode gas diffusion layer described above.
The counter electrode gas diffusion layer 62 may be omitted as necessary.
[0083]
In such a detection unit 3, the wiring 74 is connected to the detection electrode gas diffusion layer 52, and the wiring 75 is connected to the counter electrode gas diffusion layer 62, whereby the control unit 7 is connected.
[0084]
The control unit 7 includes a power source 71, a voltage change circuit 72, and an ammeter 73. The voltage change circuit 72 controls the voltage applied to the detection unit 3, and the ammeter 73 detects the voltage. A response current generated between the detection electrode 5 (detection electrode reaction layer 51) and the counter electrode 6 (counter electrode reaction layer 61) in accordance with the oxidation-reduction reaction in the unit 3 is measured.
[0085]
In such a gas sensor 1, for example, a pulse method in which a pulse voltage is applied from the control unit 7 to the detection unit 3 to change the potential of the detection electrode reaction layer 51 between two potentials, and the control unit 7 continues to the detection unit 3. In this case, the detection electrode 5 (detection electrode reaction layer) is applied by using a potential regulating method such as a cyclic voltammetry method in which a voltage that varies with time is applied and the potential of the detection electrode reaction layer 51 is continuously changed. 51) and a response current generated between the counter electrode 6 (counter electrode reaction layer 61) is measured by the control unit 7. Based on the measured value of the response current, the CO concentration in the test gas is measured.
[0086]
Next, as an example of a method for measuring the CO concentration in the test gas using the gas sensor 1 (usage method: operation of the gas sensor 1), a case where the pulse method is used as the potential regulating method will be described as a representative.
[0087]
First, the test gas is supplied into the space 211 of the gas sampling container 2 through the introduction line 23. In this case, it is preferable that the test gas is supplied by adjusting the pressure and flow rate by the pressure adjusting device 231. Thereby, the contact efficiency of the test gas to the detection part 3 can be improved more.
[0088]
As a supply pressure of the test gas, for example, 0.5 to 5.0 kgf / cm²It is preferable to set the degree.
[0089]
The supply rate of the test gas is preferably about 50 to 150 L / min, for example.
[0090]
Further, the gas sampling container 2 is provided with a heater (not shown), and the temperature in the space 211 can be adjusted. Although it does not specifically limit as this temperature, ie, the measurement temperature of a test gas, For example, it is preferable to set it as about 50-100 degreeC.
[0091]
Next, a pulse voltage is applied from the control unit 7 to the detection unit 3. As a result, the potential of the detection electrode reaction layer 51 (detection electrode 5) is divided into two potentials: a CO oxidation potential capable of adsorbing and oxidizing CO and a CO adsorption potential capable of adsorbing CO but causing no oxidation reaction of CO. Vary between. These CO oxidation potential and CO adsorption potential vary depending on the type of catalyst constituting the detection electrode reaction layer 51, but when using, for example, platinum as the catalyst, for example, about 0.65 to 1.5V, 0 It is set to about 0.05 to 0.43V.
[0092]
Here, FIG. 3 shows an example of the transition (change) of the response current over time when the potential of the detection electrode reaction layer is changed in a pulse manner between the CO oxidation potential and the CO adsorption potential.
[0093]
When the detection electrode reaction layer 51 is maintained at the CO oxidation potential, reactions of the following formulas (i) and (ii) occur in the detection electrode reaction layer 51 by the action of the catalyst.
[0094]
H₂  → 2H⁺  + 2e^-  (I)
CO + H₂O → CO₂  + 2H⁺  + 2e^-   ... (ii)
[0095]
The electrons generated in the detection electrode reaction layer 51 pass through the detection electrode gas diffusion layer 52, the control unit 7, and the counter electrode gas diffusion layer 62 and move to the counter electrode reaction layer 61. At this time, electrons are measured as a response current in the ammeter 73 of the control unit 7. That is, at the CO oxidation potential, the CO ionization current and H₂The ionization current is measured as the response current.
[0096]
In the counter electrode reaction layer 61, the reaction of the following formula (iii) occurs by the action of the catalyst between the electrons moved from the detection electrode reaction layer 51 and the hydrogen ions moved through the electrolyte layer 4.
[0097]
2H⁺  + 2e^-  → H₂  (Iii)
[0098]
On the other hand, when the detection electrode reaction layer 51 is held at the CO adsorption potential, the above-described formula (ii) that is an oxidation reaction of CO does not occur in the detection electrode reaction layer 51.
[0099]
Therefore, in the ammeter 73, H₂The ionization current is measured as the response current.₂As the amount of CO adsorbed on the detection electrode reaction layer 51 increases as time elapses, the ionization current increases as H increases on the detection electrode reaction layer 51.₂Adsorption is inhibited and decreases (changes).
[0100]
Such H₂The decrease of the ionization current occurs almost simultaneously (or continuously) when the potential of the detection electrode reaction layer 51 is lowered (changed) from the CO oxidation potential to the CO adsorption potential. This H₂From the decrease rate of the ionization current (ΔI / t in FIG. 3), the CO concentration in the test gas can be measured.
[0101]
More specifically, in a standard gas having a known CO concentration, the CO concentration and H₂A calibration curve with the reduction rate of the ionization current is prepared, and H obtained in the test gas is added to the calibration curve.₂By applying the measured value of the reduction rate of the ionization current, the CO concentration in the test gas can be measured.
[0102]
The detection unit 3 included in the gas sensor 1 as described above can be manufactured as follows, for example.
[0103]
<1> First, an electrolyte layer 4 made of, for example, Nafion or the like is prepared.
[0104]
<2> Next, a plurality of detection electrode reaction layer units 511 are formed on one surface of the electrolyte layer 4. This can be done as follows.
[0105]
First, the material of the detection electrode reaction layer 51 made of, for example, platinum is applied to one surface of the electrolyte layer 4 by, for example, sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), molecular beam epitaxy. A film-like (thick film or thin film) film is obtained by various film forming methods such as (MBE).
[0106]
The film formation conditions vary depending on various film formation methods and are not particularly limited. For example, when a sputtering method is used, the temperature of the electrolyte layer 4 (sample) is about 5 to 30 ° C., and the Ar gas (inert gas) pressure is used. 1 × 10^-3~ 1.5 × 10^-2It is preferable that the pressure is about Torr, the plasma output is about 10 to 150 W, and the plasma irradiation time is about 10 to 120 seconds.
[0107]
Next, after forming a mask layer of a desired pattern shape on the surface (upper surface) of this film (in this embodiment, a mask layer in which a plurality of grooves arranged so as to be substantially equidistant and substantially orthogonal to each other is formed) For example, a part of the coating is removed by performing various etching processes such as a plasma etching process, a wet etching process, a reactive ion etching process, a beam etching process, and a light assist etching process.
[0108]
The treatment conditions differ depending on various etching treatments and are not particularly limited. For example, when plasma etching treatment is used, the temperature of the laminate (sample) of the coating film and the electrolyte layer 4 is about 5 to 30 ° C., Ar gas ( Inert gas) pressure 1 × 10^-3~ 1.5 × 10^-2It is preferable that the pressure is about Torr, the plasma output is about 10 to 150 W, and the plasma irradiation time is about 10 to 300 seconds.
Thereafter, the mask layer is removed from the surface of the electrolyte layer 4.
[0109]
Thus, by forming the detection electrode reaction layer 51 directly on the electrolyte layer 4, the adhesion between the detection electrode reaction layer 51 and the electrolyte layer 4 can be improved, and the electrolyte layer 4 of the detection electrode reaction layer 51. Can be prevented (or reduced) more reliably.
[0110]
From this point of view, prior to the film forming operation by the various film forming methods, the surface of the electrolyte layer 4 is subjected to, for example, chemical treatment (for example, acid treatment such as hydrochloric acid treatment), shot blasting, sand blasting, etc. The surface roughening treatment may be performed by such a method. Thereby, the adhesiveness of the detection pole reaction layer 51 and the electrolyte layer 4 can be improved more.
[0111]
<3> Next, the counter electrode reaction layer 61 is formed on the other surface of the electrolyte layer 4 (the surface opposite to the detection electrode reaction layer 51). This can be done as follows.
[0112]
First, for example, a carbon powder (carrier) carrying, for example, a platinum-ruthenium alloy (catalyst of the counter electrode reaction layer 61) is ultrasonically dispersed in a solution containing, for example, Nafion (proton conductive resin), and the counter electrode reaction layer is obtained. 61 materials are prepared.
[0113]
Next, the material of the counter electrode reaction layer 61 is applied on, for example, a polytetrafluoroethylene (PTFE) sheet (base material) by various application methods such as spin coating, brush coating, doctor blade, roll coater, etc. After drying, heat treatment is applied. The heat treatment conditions are not particularly limited, and for example, under reduced pressure (for example, 10^-6~ 5x10²It is preferable that the processing temperature is about 80 to 150 ° C. and the processing time is about 1 to 5 hours. Thereby, the counter electrode reaction layer 61 is obtained on the PTFE sheet.
[0114]
Next, the counter electrode reaction layer 61 is brought into contact with the other surface of the electrolyte layer 4 and subjected to a heating / pressing (hot pressing) process. Thereby, the counter electrode reaction layer 61 is joined to the other surface of the electrolyte layer 4. Although it does not specifically limit as this processing conditions, For example, heating temperature is about 100-200 degreeC, and pressurization pressure is 50-150 kgf / cm.²It is preferable to set the degree.
Thereafter, the PTFE sheet is removed from the counter electrode reaction layer 61.
[0115]
<4> Next, the detection electrode gas diffusion layer 52 and the counter electrode gas diffusion layer 62 such as carbon cloth are bonded to the surfaces of the detection electrode reaction layer 51 and the counter electrode reaction layer 61 opposite to the electrolyte layer 4, respectively. The detection unit 3 is completed.
[0116]
In this method, a laminate of the detection electrode reaction layer 51, the electrolyte layer 4 and the counter electrode reaction layer 61 is sandwiched between the detection electrode gas diffusion layer 52 and the counter electrode gas diffusion layer 62, and a heating / pressing (hot pressing) process is performed. Can be performed. Although it does not specifically limit as this process conditions, For example, a heating temperature is about 100-200 degreeC and a pressurization pressure is 50-150 kgf / cm.²It is preferable to set the degree.
The detection part 3 is manufactured through the above processes.
[0117]
Next, another configuration example of the detection unit provided in the gas sensor of the present invention will be described.
FIG. 4 is an enlarged cross-sectional view showing another configuration of the detection unit.
[0118]
Hereinafter, the detection unit 3 ′ illustrated in FIG. 4 will be described with a focus on differences from the detection unit 3, and description of similar matters will be omitted.
[0119]
The detection unit 3 ′ shown in FIG. 4 is the same as the detection unit 3 except for the configuration of the electrolyte layer 4.
[0120]
That is, a plurality of irregularities (concave part 41 and convex part 42) are formed on the detection electrode reaction layer 51 side of the electrolyte layer 4, and the detection electrode reaction layer unit 511 is provided on the convex part 42, respectively. . In other words, a recess reaching the inside of the electrolyte layer 4 is formed, and a gap 512 of the detection electrode reaction layer 51 is formed by the recess.
[0121]
By adopting such a configuration, the generation of stress (deformation) due to expansion / contraction of the electrolyte layer 4 can be relaxed, and the influence of this stress on the detection electrode reaction layer 51 can be further reduced. Peeling of the detection electrode reaction layer 51 from the electrolyte layer 4 is more preferably prevented (or reduced), and more excellent durability is obtained in the detection unit 3 ′.
[0122]
Further, the shape of the detection electrode reaction layer unit 511 is not particularly limited, and any shape may be used. That is, the shape of the recess 41 (gap 512) is not particularly limited and may be any shape, but is preferably configured by a groove. In this embodiment, the recess 41 includes a plurality of grooves, They are arranged so as to be substantially equidistant and substantially orthogonal (in a lattice shape).
Such a detection unit 3 ′ can be manufactured as follows, for example.
[0123]
<1 ′> First, an electrolyte layer 4 made of, for example, Nafion or the like is prepared.
[0124]
<2 ′> Next, a plurality of irregularities are formed on one surface of the electrolyte layer 4. This can be done as follows.
[0125]
First, a mask layer having a desired pattern shape (in this embodiment, a mask layer formed with a plurality of grooves arranged at almost equal intervals and substantially orthogonally) is formed on the surface (upper surface) of the electrolyte layer 4. Thereafter, a part of the electrolyte layer 4 is removed by performing various etching processes such as a plasma etching process, a wet etching process, a reactive ion etching process, a beam etching process, and a light-assisted etching process.
[0126]
The processing conditions differ depending on various etching processes, and are not particularly limited. For example, when plasma etching is used, the temperature of the electrolyte layer 4 (sample) is about 5 to 30 ° C., and the Ar gas (inert gas) pressure is set. 1 × 10^-3~ 1.5 × 10^-2It is preferable that the pressure is about Torr, the plasma output is about 10 to 300 W, and the plasma irradiation time is about 10 to 300 seconds.
Thereafter, the mask layer is removed from the surface of the electrolyte layer 4.
[0127]
Next, various materials such as a sputtering method, a physical vapor deposition method (PVD), a chemical vapor deposition method (CVD), and a molecular beam epitaxy (MBE) are used as materials for the detection electrode reaction layer 51 made of, for example, platinum. It is formed into a film shape (thick film or thin film) by a film method or the like.
[0128]
The film formation conditions vary depending on various film formation methods and are not particularly limited. For example, when a sputtering method is used, the temperature of the electrolyte layer 4 (sample) is about 5 to 30 ° C., and the Ar gas (inert gas) pressure is used. 1 × 10^-3~ 1.5 × 10^-2It is preferable that the pressure is about Torr, the plasma output is about 10 to 150 W, and the plasma irradiation time is about 10 to 300 seconds.
[0129]
Thereby, a plurality of detection electrode reaction layer units 511 are formed on one surface of the electrolyte layer 4 corresponding to the plurality of convex portions 41.
[0130]
<3 ′> A step similar to the above step <3> is performed.
[0131]
<4 '> The same step as the above step <4> is performed.
The detection unit 3 ′ is manufactured through the above processes.
[0132]
As mentioned above, although the gas sensor of this invention was demonstrated based on embodiment of illustration, this invention is not limited to this. Each part constituting the gas sensor can be replaced with any part that can exhibit the same function.
[0133]
For example, the gas sampling container can be omitted if necessary. In this case, for example, the detection unit can be directly installed in the flow path of exhaust gas discharged from an internal combustion engine, a combustion furnace, or the like. .
[0134]
Further, for example, between the detection electrode gas diffusion layer and the detection electrode reaction layer, between the detection electrode reaction layer and the electrolyte layer, between the electrolyte layer and the counter electrode reaction layer, and between the counter electrode reaction layer and the counter electrode gas diffusion layer. Each may be provided with an intermediate layer.
[0135]
In the above embodiment, the case where the CO concentration in the test gas is measured using the gas sensor has been described. For example, the potential of the detection electrode reaction layer (for example, CO₂Reduction potential, etc.), the type of catalyst in the detection electrode reaction layer, the constituent material of the electrolyte layer (for example, oxygen ion conductive ion exchange resin, etc.), etc., or a combination of them as appropriate. Thus, the gas sensor of the present invention can be used to measure the concentration of gas components other than CO.
[0136]
【Example】
Next, specific examples of the present invention will be described.
[0137]
Example 1
First, a detection unit as shown in FIG. 2 was produced as follows.
[0138]
<Configuration of detection unit>
▲ 1 ▼ Detection pole
Detection electrode reaction layer
・ Component material: Platinum
Average thickness: 0.2 μm (the amount of platinum present on the electrolyte layer is 20 μg / cm²)
-Ratio of the area occupied by the gap to the total area of the detection electrode reaction layer when viewed from the direction perpendicular to the detection electrode reaction layer: 1%
・ Specific surface area: 1cm²/ Cm²
Detection electrode gas diffusion layer
・ Component material: Carbon cloth
・ Average thickness: 500μm
(2) Electrolyte layer
-Constituent material: Nafion 112 (Du Pont)
・ Average thickness: 50μm
(3) Counter electrode
Counter electrode reaction layer
-Constituent material: Platinum-ruthenium alloy (average particle size 5 nm) 26 wt%
Carbon powder (average particle size 75nm) 40wt%
Nafion (Aldrlich) 34wt%
Average thickness: 20 μm (the amount of platinum-ruthenium alloy present on the electrolyte layer is 0.5 mg / cm²)
Specific surface area: 100cm²/ Cm²
Counter electrode gas diffusion layer
・ Component material: Carbon cloth
・ Average thickness: 500μm
[0139]
<Preparation of detector>
-1- The detection electrode reaction layer (detection electrode reaction layer unit) having the above-described configuration was produced on one surface of the electrolyte layer.
[0140]
First, the amount of platinum deposited by sputtering is 40 μg / cm.²A platinum film was formed so that The sputtering method was performed under the following conditions.
[0141]
Sample temperature: 25 ° C., Ar gas pressure: 7 × 10^-3Torr, plasma output: 100 W, plasma irradiation time: 60 seconds
[0142]
Next, after forming a mask layer having a plurality of grooves provided at equal intervals and orthogonally on the surface of the platinum coating, the portion of the platinum coating where the mask layer was not formed was removed by plasma etching. The plasma etching process was performed under the following conditions. Thereafter, the mask layer was removed.
[0143]
Sample temperature: 25 ° C., Ar gas pressure: 7 × 10^-3Torr, plasma output: 100 W, plasma irradiation time: 60 seconds
[0144]
-2- On the other surface of the electrolyte layer, a counter electrode reaction layer having the above-described configuration was produced.
First, carbon powder carrying a platinum-ruthenium alloy was ultrasonically dispersed in a Nafion 5 wt% solution so as to obtain the above composition ratio, thereby preparing a counter electrode reaction layer material.
[0145]
Next, this material was applied and dried on a PTFE sheet by brush coating (coating method), and heat-treated at 130 ° C. for 3 hours under reduced pressure (450 Torr). The counter electrode reaction layer formed on the PTFE sheet is brought into contact with the other surface of the electrolyte layer, and 140 ° C., 100 kgf / cm.²Then, the PTFE sheet was removed from the counter electrode reaction layer.
[0146]
-3- The detection electrode was completed by joining the detection electrode gas diffusion layer having the above configuration and the counter electrode gas diffusion layer having the above configuration to the surfaces of the detection electrode reaction layer and the counter electrode reaction layer opposite to the electrolyte layer, respectively.
[0147]
The detection electrode reaction layer, the electrolyte layer, and the counter electrode reaction layer are sandwiched between the detection electrode gas diffusion layer and the counter electrode gas diffusion layer at 140 ° C., 100 kgf / cm.²Was hot pressed under the conditions of
[0148]
Next, a control unit was attached to the detection unit, and the detection unit was housed in a gas sampling container to assemble the gas sensor shown in FIG.
[0149]
(Example 2)
First, a detection unit as shown in FIG. 4 was produced as follows.
[0150]
<Configuration of detection unit>
▲ 1 ▼ Detection pole
Detection electrode reaction layer
・ Component material: Platinum
Average thickness: 0.2 μm (the amount of platinum present on the electrolyte layer is 1 μg / cm²)
-Ratio of the area occupied by the gap to the total area of the detection electrode reaction layer when viewed from the direction perpendicular to the detection electrode reaction layer: 5%
・ Specific surface area: 1cm²/ Cm²
Detection electrode gas diffusion layer
・ Component material: Carbon cloth
・ Average thickness: 500μm
(2) Electrolyte layer (a plurality of irregularities are formed on the detection electrode reaction layer side)
-Constituent material: Nafion 112 (Du Pont)
・ Average thickness: 50μm
(3) Counter electrode
Counter electrode reaction layer
-Constituent material: Platinum-ruthenium alloy (average particle size 5 nm) 26 wt%
Carbon powder (average particle size 75nm) 40wt%
Nafion (Aldrlich) 34wt%
Average thickness: 20 μm (the amount of platinum-ruthenium alloy present on the electrolyte layer is 0.5 mg / cm²)
Specific surface area: 100cm²/ Cm²
Counter electrode gas diffusion layer
・ Component material: Carbon cloth
・ Average thickness: 500μm
[0151]
<Preparation of detector>
-1- The detection electrode reaction layer (detection electrode reaction layer unit) having the above-described configuration was produced on one surface of the electrolyte layer.
[0152]
First, after forming a mask layer having a plurality of grooves provided at equal intervals and perpendicularly on one surface of the electrolyte layer, the portion of the electrolyte layer where the mask layer is not formed is removed by plasma etching, Formed. The plasma etching process was performed under the following conditions. Thereafter, the mask layer was removed.
[0153]
Sample temperature: 25 ° C., Ar gas pressure: 7 × 10^-3Torr, plasma output: 100 W, plasma irradiation time: 60 seconds
[0154]
Next, a platinum deposition amount of 1 μg / cm is formed on the convex portion of the electrolyte layer by sputtering.²Thus, a detection electrode reaction layer unit was obtained. The sputtering method was performed under the following conditions.
[0155]
Sample temperature: 25 ° C., Ar gas pressure: 7 × 10^-3Torr, plasma output: 30 W, plasma irradiation time: 30 seconds
[0156]
-2- On the other surface of the electrolyte layer, a counter electrode reaction layer having the above-described configuration was produced.
This was performed in the same manner as in Example 1.
[0157]
-3- The detection electrode was completed by joining the detection electrode gas diffusion layer having the above configuration and the counter electrode gas diffusion layer having the above configuration to the surfaces of the detection electrode reaction layer and the counter electrode reaction layer opposite to the electrolyte layer, respectively.
This was performed in the same manner as in Example 1.
[0158]
Next, a control unit was attached to the detection unit, and the detection unit was housed in a gas sampling container to assemble the gas sensor shown in FIG.
[0159]
(Comparative example)
First, the detection part was produced as follows.
[0160]
<Configuration of detection unit>
▲ 1 ▼ Detection pole
Detection electrode reaction layer
Average thickness: 0.1 μm (the amount of platinum present on the electrolyte layer is 0.56 μg / cm²)
・ Specific surface area: 1cm²/ Cm²
Detection electrode gas diffusion layer
・ Average thickness: 300μm
(2) Electrolyte layer
-Constituent material: Nafion 112 (Du Pont)
・ Average thickness: 50μm
(3) Counter electrode
Counter electrode reaction layer
-Constituent material: Platinum-ruthenium alloy (average particle size 5 nm) 26 wt%
Carbon powder (average particle size 75nm) 40wt%
Nafion (Aldrlich) 34wt%
Average thickness: 20 μm (the amount of platinum-ruthenium alloy present on the electrolyte layer is 0.5 mg / cm²)
Specific surface area: 100cm²/ Cm²
Counter electrode gas diffusion layer
・ Component material: Carbon cloth
・ Average thickness: 500μm
[0161]
<Preparation of detector>
-1- A detection electrode having the above-described configuration was produced.
[0162]
First, a solution containing platinum (average particle size: 5 nm) is applied to one surface of a detection electrode gas diffusion layer obtained by forming a mixture of carbon powder and polytetrafluoroethylene (PTFE) into a sheet shape, thereby supporting platinum. I let you.
[0163]
Next, a Nafion 5 wt% solution is applied to the surface of the detection electrode gas diffusion layer coated with platinum at 1 mg / cm.²The detection electrode reaction layer having the above-described structure was obtained by coating and drying so as to be.
Note that a part of the detection electrode gas diffusion layer constitutes a part of the detection electrode reaction layer.
[0164]
-2- On the one surface of the electrolyte layer, the counter electrode reaction layer having the above-described configuration was produced.
This was performed in the same manner as in Example 1.
[0165]
-3- The detection electrode was completed by joining the detection electrode to the other surface of the electrolyte layer, and the counter electrode gas diffusion layer having the above structure to the surface of the counter electrode reaction layer opposite to the electrolyte layer.
[0166]
The detection electrode reaction layer of the detection electrode is brought into contact with the other surface of the electrolyte layer, and the counter electrode gas diffusion layer is brought into contact with the counter electrode reaction layer, and 140 ° C., 100 kgf / cm.²Was hot pressed under the conditions of
[0167]
Next, a control unit was attached to the detection unit, and the detection unit was housed in a gas sampling container to assemble the gas sensor shown in FIG.
[0168]
(Experiment)
In the gas sampling containers of the gas sensors manufactured in Examples 1 and 2 and Comparative Example, air (Wet state) prepared at a humidity of 30% RH was maintained at 100 ° C. and supplied for 8 hours. An operation of supplying air prepared in 100% RH and 2 mol% of methanol (Dry state) at 25 ° C. and supplying for 16 hours was performed. This operation was performed as one cycle, and each gas sensor was repeated for a predetermined cycle.
[0169]
(Evaluation)
For each gas sensor, the sensor output at the end of any cycle was measured. The sensor output is measured using the pulse method, and the H at the CO adsorption potential is measured.₂The sensor output was determined by the time change (ΔI / t) of the ionization current. The evaluation conditions were set as follows.
[0170]
[Test gas]
Composition: H₂/ CO₂/CO=75/24.999/0.001
Humidity: 40% RH
Supply pressure: 1.5 kgf / cm²
Supply speed: 100L / min
Measurement temperature: 90 ° C
[Detection electrode reaction layer]
CO oxidation potential: 1.0V
CO adsorption potential: 0.4V
[0171]
(result)
FIG. 5 is a graph showing changes in sensor output of each gas sensor. In FIG. 5, the sensor output at the end of an arbitrary cycle is shown as a relative value (rate of change) with respect to the sensor output before the experiment (0 cycle).
[0172]
As is apparent from FIG. 5, the gas sensor of the first embodiment can obtain a sufficient sensor output even at the end of 42 cycles, and the gas sensor of the second embodiment can provide a sufficient sensor output even at the end of 48 cycles. Was obtained. That is, in any of the gas sensors of the present invention, the sensor output was suitably maintained (maintained) and excellent in durability.
[0173]
On the other hand, in the gas sensor of the comparative example, from the start of the experiment (first cycle), the catalyst is detached from the support in the detection electrode reaction layer or the detection electrode reaction layer is peeled off from the electrolyte layer. A decrease in sensor output was observed, and measurement of sensor output became impossible at the end of 5 cycles. For this reason, the experiment of the gas sensor of the comparative example was stopped at the end of 5 cycles. That is, the gas sensor of the comparative example was inferior in durability.
[0174]
【The invention's effect】
As described above, according to the present invention, the durability of the detection unit is achieved by the synergistic effect of the detection electrode reaction layer unit mainly composed of a catalyst and the detection electrode reaction layer unit disposed through a gap. Therefore, it is possible to provide a gas sensor that can remarkably improve the durability and durability.
[0175]
Moreover, the said effect can be improved more by forming a some unevenness | corrugation in the surface at the side of the detection pole reaction layer of an electrolyte layer.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the overall configuration of a gas sensor of the present invention.
FIG. 2 is an enlarged cross-sectional view showing a configuration of a detection unit provided in the gas sensor of the present invention.
FIG. 3 is a graph showing a change (change) of the response current over time when the potential of the detection electrode reaction layer is changed in a pulse manner between a CO oxidation potential and a CO adsorption potential.
FIG. 4 is an enlarged cross-sectional view showing another configuration of the detection unit.
FIG. 5 is a graph showing changes in sensor output of each gas sensor.
FIG. 6 is a schematic diagram showing an overall configuration of a fuel cell system.
[Explanation of symbols]
1 Gas sensor
2 Gas storage container
21 Case
211 space
22 Lid
23 Introduction line
231 Pressure regulator
24 Exhaust line
3 detector
4 Electrolyte layer
41 recess
42 Convex
5 Detection pole
51 Detection electrode reaction layer
511 Detection electrode reaction layer unit
512 gap
52 Detection electrode gas diffusion layer
6 Counter electrode
61 Counter electrode reaction layer
62 Counter electrode gas diffusion layer
7 Control unit
71 power supply
72 Voltage change circuit
73 Ammeter
74, 75 wiring
100 Fuel cell device
110 Methanol tank
111 pump
120 water / methanol tank
121 pump
130 reformer
140 CO remover
150 Fuel cell

Claims (12)

A detection unit having a detection electrode reaction layer for reacting a predetermined component in the test gas, a counter electrode reaction layer disposed to face the detection electrode reaction layer, and an electrolyte layer disposed therebetween, and the detection A control unit that controls an applied voltage to the unit and measures an H ₂ ionization current detected in association with an oxidation reaction of H ₂ by the application of the voltage,
The detection electrode reaction layer is formed by arranging a plurality of detection electrode reaction layer units mainly composed of a catalyst through a gap formed by a recess formed so as to reach the inside of the electrolyte layer ,
The control unit detects the H ₂ detected between when a CO oxidation potential that adsorbs and oxidizes CO is applied to the detection unit and when a CO adsorption potential that adsorbs CO but does not oxidize is applied. A gas sensor that measures a CO concentration in the test gas based on a change amount of an ionization current. A detection unit having a detection electrode reaction layer for reacting a predetermined component in the test gas, a counter electrode reaction layer disposed to face the detection electrode reaction layer, and an electrolyte layer disposed therebetween, and the detection The voltage applied to the part is controlled and H by voltage application ₂ Detected with the oxidation reaction of ₂ A controller for measuring the ionization current,
  The detection electrode reaction layer is composed of a plurality of detection electrode reaction layer units mainly composed of a catalyst with a gap, and a plurality of irregularities are formed on the detection electrode reaction layer side of the electrolyte layer. And each of the detection electrode reaction layer units is provided on a convex portion of the electrolyte layer,
  The control unit detects the H detected between when a CO oxidation potential that adsorbs and oxidizes CO is applied to the detection unit and when a CO adsorption potential that adsorbs CO but does not oxidize is applied. ₂ A gas sensor that measures a CO concentration in the test gas based on a change amount of an ionization current. A detection unit having a detection electrode reaction layer for reacting a predetermined component in the test gas, a counter electrode reaction layer disposed to face the detection electrode reaction layer, and an electrolyte layer disposed therebetween, and the detection The voltage applied to the part is controlled and H by voltage application ₂ Detected with the oxidation reaction of ₂ A controller for measuring the ionization current,
  The detection electrode reaction layer is formed by arranging a plurality of detection electrode reaction layer units mainly composed of a catalyst through a gap,
  The specific surface area of the counter electrode reaction layer is 10 to 1000 times the specific surface area of the detection electrode reaction layer,
  The control unit detects the H detected between when a CO oxidation potential that adsorbs and oxidizes CO is applied to the detection unit and when a CO adsorption potential that adsorbs CO but does not oxidize is applied. ₂ A gas sensor that measures a CO concentration in the test gas based on a change amount of an ionization current.   The ratio of the area occupied by the gap to the entire area of the detection electrode reaction layer when viewed from a direction perpendicular to the detection electrode reaction layer is 0.01 to 60%. Gas sensor.   The gas sensor according to claim 1, wherein the detection electrode reaction layer is formed on the electrolyte layer.   The gas sensor according to claim 1, wherein the counter electrode reaction layer is made of a material containing a catalyst.   The gas sensor according to claim 6, wherein the catalyst of the counter electrode reaction layer is supported on a carrier. The gas sensor according to any one of claims 1 to 7 , wherein a gas diffusion layer is provided on each side of the detection electrode reaction layer and the counter electrode reaction layer opposite to the electrolyte layer. The electrolyte layer is gas sensor according to any one of claims 1 to 8 is constituted by an ion-exchange resin. The control unit, the amount of change in the H ₂ ionization current, calculates a rate of change per unit time, the calculated rate of change, by applying the calibration curve of a known CO concentrations and H ₂ ionization current change rate the gas sensor according to any one of claims 1 is configured to calculate the CO concentration 9. The gas sensor according to any one of claims 1 to 10 , further comprising a gas collection container for collecting the test gas, wherein the detection unit is installed in the gas collection container. The gas sensor according to any one of claims 1 to 11 , which is used for measuring a CO concentration in the test gas.

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