JP2004117123A - Gas sensor - Google Patents

Abstract

A gas sensor capable of reversibly and continuously measuring a gas concentration such as a CO concentration without a recovery means such as a heater.
A gas sensor communicates with an atmosphere of a gas to be measured via a proton conducting layer (1) that conducts protons, a diffusion-limiting section (21) that controls the diffusion of the gas to be measured, and a diffusion-controlling section (21). A measuring chamber (15), a first electrode (3) in contact with the proton conducting layer (1) in the measuring chamber (15) and containing a catalyst, and a proton conducting layer (1) outside the measuring chamber (15). And a second electrode (5) and a reference electrode (7) that are in contact with the first electrode. Then, based on the voltage Vp applied between the first electrode (3) and the second electrode (5) such that the potential difference Vs between the first electrode (3) and the reference electrode (7) becomes constant. Then, the concentration of the catalyst poison gas (CO) in the gas to be measured is determined.
[Selection diagram] Fig. 1

Description

前記測定結果を図４に示す。図４から、触媒として金を添加したものは、白金のみのものに比べて感度が大きく、金を添加することにより、感度を向上させることができることが分かる。
【００６４】
ここで、第１電極に用いた電極触媒は、前記実験例２と同様に、ＰｔとＡｕを重量比で１：１とし、カーボン粉末に担持したものを用いた。添加した金は、合金化処理されていても良いし、混合物として含まれていてもよい。尚、実験例３においても、前記実験例２と同様に、この実験例３の実施形態に限定されるものではない。
【００６５】
▲４▼実験例４
本実験例４は、前記実施例１のガスセンサを用い、下記測定条件４にて、水素濃度測定を行ったものである。つまり、ＣＯ濃度が異なる場合における水素濃度を測定したものである。
【００６６】

前記測定結果を図５に示す。図５から、水素濃度に応じて、第１電極と第２電極との間に流れる電流値が変化しており、更に、その電流値は、ＣＯ濃度によって変化しないことが分かる。
【００６７】
すなわち、上述したガスセンサにより、ＣＯ濃度と水素濃度とを同時に測定できることが分かる。
尚、実験例４においても、前記実験例２、３と同様に、この実験例４の実施形態に限定されるものではない。
（実施例２）
次に、実施例２について説明するが、前記実施例１と同様な箇所の説明は省略する。
【００６８】
本実施例のガスセンサは、前記実施例１と同様に、プロトン伝導層４１、第１電極４３、第２電極４５、拡散律速部４７等を備えているが、特に、第２電極４５が参照電極の機能を兼ね備え、参照電極と一体になっている点に特徴がある。図６に示す様に、本実施例では、ガスセンサの電気的構成として、第１電圧計５９にて、第１電極４３と第２電極４５との間の電位差Ｖｓを測定し、電源（電池）６１にて、第１電極４３と第２電極４５との間に電圧を印加し、第２電圧計６３にて、第１電極４３と第２電極４５との間に印加される電圧Ｖｐを測定し、電流計６５にて、第１電極４３と第２電極４５との間に流れる電流Ｉｐを測定する回路を備えるとともに、第１電極４３側に対して第１電圧計５９側又は電流計６５側に接続を切り替えるスイッチング素子６７を備えている。
【００６９】
そして、このスイッチング素子６７によって回路を切り替えることにより、第１電極４３と第２電極４５（このときは参照電極として機能）との間の電位差Ｖｓを測定する工程（スイッチング素子６７をＳ１に接続）と、第１電極４３と第２電極４５（参照電極の機能）との間の電位差Ｖｓを一定にするように、第１電極４３と第２電極４５との間に電圧を印加する工程（スイッチング素子６７をＳ２に接続）とを周期的に切り替える。
【００７０】
これにより、第１電極４３と第２電極４５（参照電極の機能）との間の電位差Ｖｓを一定にするように、第１電極４３と第２電極４５との間に電圧Ｖｐが印加されるため、この電圧Ｖｐを測定することにより、前記実施例１と同様に、被測定ガス中のＣＯ等の触媒毒ガスの濃度の測定が可能になる。また、限界電流Ｉｐにより、水素濃度を測定することもできる。
【００７１】
また、本実施例では、第２電極４５が参照電極と一体となっているので、ガスセンサの構造を単純化することができるという利点がある。
尚、本発明は前記実施例になんら限定されるものではなく、本発明の要旨を逸脱しない範囲において種々の態様で実施しうることはいうまでもない。
【図面の簡単な説明】
【図１】実施例１のガスセンサを破断して示す説明図である。
【図２】実験例１における電位差Ｖｓと電流値との関係を示すグラフである。
【図３】実験例２におけるＣＯ濃度と印加電圧Ｖｐとの関係を示すグラフである。
【図４】実験例３における触媒の違いによるセンサ感度の違いを示すグラフである。
【図５】実験例４におけるＣＯ濃度と水素濃度と電流値との関係を示すグラフである。
【図６】実施例２のガスセンサを破断して示す説明図である。
【符号の説明】
１、４１…プロトン伝導層
３、４３…第１電極
５、４５…第２電極
７…参照電極
１５…測定室（第１凹部）
２１、４７…拡散律速部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas sensor suitable for measuring the concentration of a catalyst poison gas such as CO or sulfur-containing substance (especially, the CO concentration) in a fuel gas, and for measuring the hydrogen concentration in a fuel gas, for example, in a fuel cell.
[0002]
[Prior art]
2. Description of the Related Art In recent years, as environmental degradation on a global scale has been regarded as a problem, research on fuel cells as a highly efficient and clean power source has been actively conducted. Among them, polymer electrolyte fuel cells (PEFC) are expected for automobiles and homes due to advantages such as low temperature operation and high output density.
[0003]
In the case of this fuel cell, the use of a reformed gas such as methanol as a fuel gas is promising. However, since carbon monoxide (CO) is generated in the reforming reaction process depending on conditions such as temperature and pressure, the reformed gas is used. In some cases, CO may be present. In addition, sulfur-containing substances (eg, H ₂ S) may remain.
[0004]
However, specific substances such as CO and sulfur-containing substances act as catalyst poisons and poison platinum (Pt) or the like which is a fuel electrode catalyst of a fuel cell. A gas sensor that can directly detect the substance concentration is required. Further, a sensor that detects a catalyst poison gas such as CO or a sulfur-containing substance is required to be able to perform measurement in a hydrogen-rich atmosphere.
[0005]
Therefore, conventionally, a carbon monoxide detection device (CO sensor) capable of performing measurement in such a hydrogen-rich atmosphere has been proposed (see Patent Document 1). This carbon monoxide detection device includes an electrolyte membrane and two electrodes sandwiching the electrolyte membrane. A gas to be measured is introduced into one electrode and the atmosphere is introduced into the other electrode, and a predetermined load is applied between the two electrodes. Is to determine the CO concentration from the potential difference between the electrodes in the state where is connected.
[0006]
Separately from this, a carbon monoxide sensor for arranging a detection unit in a gas to be measured, applying a predetermined voltage between two electrodes, and calculating a CO concentration from a gradient of a change in a current value flowing at that time is known. It has been proposed (see Patent Document 2).
[0007]
[Patent Document 1]
JP-A-8-327590 (page 2, FIG. 1)
[Patent Document 2]
JP 2001-099809 A (Page 2, FIG. 1)
[0008]
[Problems to be solved by the invention]
However, in general, the fuel gas to be measured is pressurized in order to improve the efficiency of the fuel cell. However, in the apparatus described in Patent Document 1, the hydrogen-rich gas to be measured and the atmosphere containing oxygen are mixed. Are separated only by the electrolyte membrane, pressure is unevenly applied to the electrolyte membrane, and there is a risk that the electrolyte membrane may be damaged in long-term use.
[0009]
Also, this technology proposes a structure in which the pressure is released when the gas to be measured exceeds a predetermined pressure. Under the given conditions, the pressure on the electrolyte membrane remains uneven.
On the other hand, in the technique of Patent Document 2, the CO concentration is obtained from the gradient of the change in the current value flowing between the two electrodes. However, since the change in the current value due to CO is irreversible, the recovery means using a heater is used. Is required, and there is a problem that the sensor structure becomes complicated.
[0010]
In addition, this technique has a problem that it is difficult to perform continuous measurement because time is required for recovery after measurement.
The present invention has been made in order to solve the above-mentioned problems, and has an object to provide a device without a trouble such as a gas to be measured leaking into the atmosphere and to have a recovery unit such as a heater. An object of the present invention is to provide a gas sensor capable of reversibly and continuously measuring a gas concentration such as a CO concentration without a gas sensor.
[0011]
Means for Solving the Problems and Effects of the Invention
(1) The invention of claim 1 is characterized in that the proton (H ⁺ ), A diffusion-controlling portion that controls the diffusion of the gas to be measured, a measurement chamber that communicates with the gas-to-be-measured via the diffusion-controlling portion, The present invention relates to a gas sensor including a first electrode in contact with a conductive layer and containing a catalyst, and a second electrode and a reference electrode outside of the measurement chamber and in contact with the proton conductive layer. Based on a voltage (for example, Vp) applied between the first electrode and the second electrode such that a potential difference (for example, Vs) between the electrode and the reference electrode becomes a predetermined value (for example, constant). The concentration of a catalyst poison gas (gas poisoning the catalyst) in the measured gas is obtained.
[0012]
In the present invention, the potential difference between the first electrode and the reference electrode is set to a predetermined value, that is, the hydrogen concentration (hydrogen gas concentration) on the first electrode (and thus the measurement chamber) is always set to a predetermined value (for example, constant). The voltage applied between the first electrode and the second electrode is adjusted so that
[0013]
Therefore, the hydrogen concentration on the first electrode is set to, for example, “CO + H ₂ O → CO ₂ + H ₂ If the potential difference between the first electrode and the reference electrode is set so as to be sufficient for reacting CO according to the formula (A), the CO can react constantly according to the formula (A). become.
[0014]
That is, by providing the diffusion-controlling part, the diffusion of the gas to be measured introduced into the measurement chamber can be limited, and the hydrogen in the measurement chamber is pumped (here, pumped out) from the measurement chamber through the proton conductive layer. The concentration can be reduced. Therefore, when the catalyst poison gas is CO, the H ₂ CO can be reacted according to the above formula (A) showing a shift reaction by O.
[0015]
Then, the voltage applied between the first electrode and the second electrode rises as CO reacts and hydrogen (accordingly, protons) as a reaction product is pumped through the proton conductive layer. However, the reacting CO depends on the CO concentration (CO gas concentration) because the diffusion of CO is restricted in the diffusion rate controlling section. Therefore, the CO concentration can be measured by detecting a change in the voltage applied between the first electrode and the second electrode.
[0016]
Further, the poisoning by the catalyst poison gas occurs because the introduced catalyst poison gas such as CO is adsorbed on the catalyst (electrode catalyst) and does not desorb. Therefore, as in the present invention, the catalyst such as the introduced CO is used. By ensuring that the poison can always react, irreversible poisoning can be prevented. This makes it possible to reversibly and continuously measure the concentration of the catalyst poison gas such as the CO concentration without the need for a recovery means such as a heater.
[0017]
Furthermore, in the present invention, it is not necessary to introduce a gas containing oxygen such as the atmosphere, and even in a pressurized atmosphere, the pressure applied to the sensor unit (proton conductive layer) does not become uneven, It is hard to break and can be measured for a long time.
The catalyst is a catalyst involved in the reaction of a specific gas (here, a catalyst poisonous gas such as CO to be measured or hydrogen) in the gas to be measured.
[0018]
(2) The invention of claim 2 is characterized in that the catalyst poison gas is CO or a sulfur-containing substance.
The present invention exemplifies a catalyst poison gas whose concentration can be measured by a gas sensor. That is, the gas sensor of the present invention allows CO or a sulfur-containing substance (for example, H ₂ The gas concentration of S) can be suitably measured.
[0019]
(3) The invention according to claim 3 is characterized in that the second electrode also has the function of the reference electrode, and the second electrode and the reference electrode are integrated.
In the present invention, since the second electrode is integrated with the reference electrode, the structure of the gas sensor can be simplified.
[0020]
(4) The invention according to claim 4 is characterized in that a potential difference between the first electrode and the reference electrode is 400 mV or more.
By setting the potential difference between the first electrode and the reference electrode to 400 mV or more as in the present invention, all catalyst poison gases such as CO can be reacted, so that irreversible poisoning by CO or the like is prevented. You can prevent it from happening.
[0021]
(5) The invention according to claim 5 is characterized in that a current flowing by a voltage applied between the first electrode and the second electrode is a limiting current.
In the present invention, since the hydrogen concentration on the first electrode can be further reduced by pumping the hydrogen to the limit current, the reaction of the above formula (A) can be more stably caused. Thereby, the gas concentration of the catalyst poison gas can be measured stably and accurately.
[0022]
In the present invention, when the voltage is applied so as to increase sequentially, the current that rises to a certain value and becomes the upper limit is referred to as a limit current.
(6) The invention of claim 6 is characterized in that the hydrogen concentration in the gas to be measured is obtained from the value of the limiting current.
[0023]
Since the above-described limit current value differs depending on the hydrogen concentration, the hydrogen concentration can be measured from the limit current value.
That is, when a voltage is applied between the first electrode and the second electrode so that the potential difference between the first electrode and the reference electrode becomes a predetermined value, hydrogen is dissociated into protons on the first electrode, Is pumped to the second electrode side via the proton conductive layer, becomes hydrogen again, and diffuses into the gas atmosphere to be measured. At that time, the current value (limit current value) flowing between the first electrode and the second electrode is proportional to the hydrogen concentration, so that the hydrogen concentration can be measured by measuring the current value.
[0024]
(7) In the invention of claim 7, the catalyst contained in the first electrode adsorbs the catalyst poison gas in the gas to be measured, and decomposes, dissociates, or reacts with the hydrogen-containing substance, thereby producing hydrogen or hydrogen. It is a catalyst capable of generating protons.
[0025]
The present invention exemplifies a catalyst. That is, by using such a catalyst, a catalyst poison gas such as CO can be reacted, for example, as in the above formula (A), thereby preventing irreversible poisoning by CO or the like.
(8) The invention according to claim 8 is characterized in that the catalyst contains platinum and / or gold.
[0026]
The present invention exemplifies a catalyst. That is, by using platinum or gold as the catalyst, high sensor sensitivity can be obtained, and among them, gold is particularly preferable because the sensor sensitivity is high.
In the above-described inventions, the proton conductive layer may be made of a solid polymer electrolyte. By using this solid polymer electrolyte, it is possible to operate at a low temperature, so that the sensor structure can be simplified without requiring a heater or the like.
[0027]
-The gas sensor can be used for a polymer electrolyte fuel cell system. That is, in the polymer electrolyte fuel cell system, the concentration of the catalyst poison gas and the concentration of hydrogen in the fuel gas can be accurately measured by using the gas sensor.
[0028]
-Further, as the configuration of the gas sensor, a configuration in which the proton conductive layer, the first electrode, the second electrode, the reference electrode, and the diffusion-controlling portion are supported by a support can be adopted.
The diffusion-controlling portion is a communicating portion that controls the diffusion of the gas to be measured introduced from the atmosphere of the gas to be measured into the measurement chamber. For example, a hole (through hole) formed in the support or a hole formed in the support is provided. It can be realized by a filled gas-permeable porous body or the like.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an example (example) of an embodiment of the gas sensor of the present invention will be described.
(Example 1)
In the present embodiment, a gas sensor used for measuring the concentration of carbon monoxide (CO) and the concentration of hydrogen contained in the fuel gas of a polymer electrolyte fuel cell will be described as an example.
[0030]
a) First, the configuration of the gas sensor of the present embodiment will be described with reference to FIG. FIG. 1 is a longitudinal sectional view of the gas sensor.
As shown in FIG. 1, in the gas sensor of the present embodiment, a first electrode 3 is provided on one surface (the upper surface in FIG. 1) of the proton conductive layer 1 and the other surface (in FIG. On the lower surface), a second electrode 5 and a reference electrode 7 are provided so as to face the first electrode 3, and they are supported by a support 13 including a first support 9 and a second support 11. I have.
[0031]
That is, the proton conductive layer 1 is sandwiched between the first support 9 and the second support 11, and the first electrode 3 is covered with the first support 9 and in the first recess (measurement chamber) 15. The second electrode 5 is arranged and covered by the second support 11 and arranged in the second recess 17. The reference electrode 7 is covered by the second support 11 and arranged in the third recess 19. Have been.
[0032]
In addition, as a method of integrally configuring the gas sensor, a configuration in which the proton conductive layer 1 is fixed by a fixing member or the like (not shown) while the proton conductive layer 1 is sandwiched between the first support 9 and the second support 11 or a resin is used. A method of integrally fixing can be adopted.
Among these, the proton conductive layer 1 is provided with a proton (H) from one surface side to the other surface side, for example, from the first electrode 3 side to the second electrode 5 side. ⁺ ) Can be moved. As a material of the proton conductive layer 1, a material which operates at a relatively low temperature (for example, 150 ° C. or lower) is preferable, and for example, “Nafion” (trademark of DuPont) which is a fluororesin can be used.
[0033]
The support 13 is an insulator made of ceramics containing, for example, alumina as a main component. The support 13 is preferably an organic insulator made of a resin or the like, in addition to an inorganic insulator such as a ceramic, but may be a metal such as stainless steel as long as it is electrically insulated.
[0034]
Among the supports 13, the first support 9 is provided with a diffusion-controlling portion 21 that communicates the surrounding atmosphere with the first recess 15 (therefore, the first electrode 3).
In other words, the diffusion-controlling portion 21 is a small hole that introduces the fuel gas to be measured (accordingly, the contained CO gas and hydrogen gas) to the first electrode 3 and controls the diffusion thereof. The degree of diffusion can be controlled by setting the inner diameter of the diffusion control part 21 or filling the diffusion control part 21 with a porous material such as alumina.
[0035]
On the other hand, the second support 11 is provided with a hole 23 that communicates with the surrounding atmosphere and the second recess 17 (therefore, the second electrode 5).
The first support 9 and the second support 11 are formed by laminating and firing ceramic-containing sheets, and for example, lead portions (for example, platinum (Pt)) between the sheets (not shown). Are formed.
[0036]
The first electrode 3, the second electrode 5, and the reference electrode 7 are, for example, porous electrodes containing carbon as a main component, and are formed in the concave portions 15, 17, 19, respectively, and are electrically connected to the respective lead portions. I have. In each of the electrodes 3, 5, and 7, a catalyst layer (not shown) of Pt or the like is formed on the side in contact with the proton conductive layer 1 by coating.
[0037]
Although the reference electrode 7 is formed separately from the other electrodes 3 and 5 so as to reduce the influence of the hydrogen concentration in the gas to be measured, the hydrogen concentration at the reference electrode 7 is further stabilized. For this purpose, the reference electrode 7 is preferably used as a self-generated reference electrode.
In particular, in the present embodiment, the first electrode 3, the second electrode 5, and the reference electrode 7 are connected to the circuit shown in the drawing via lead portions, respectively, and are connected to the first electrode 3 by the first voltmeter 25. A potential difference (Vs) between the first electrode 3 and the second electrode 5 is measured by a power supply (battery) 27, and a voltage is applied between the first electrode 3 and the second electrode 5 by a power source (battery) 27. A voltage (Vp) applied between the first electrode 3 and the second electrode 5 is measured, and a current Ip flowing between the first electrode 3 and the second electrode 5 is measured by the ammeter 31. .
[0038]
In this embodiment, the potential difference between the first electrode 3 and the reference electrode 7 is, for example, 400 mV or more, so that the potential difference Vs between the first electrode 3 and the second electrode 5 is 450 mV. Is adjusted, and at this time, the voltage Vp applied between the first electrode 3 and the second electrode 5 is measured, and the current flowing between the first electrode 3 and the second electrode 5 is adjusted. (Limit current) Ip is measured.
[0039]
Further, the CO concentration is determined from the voltage Vp between the first electrode 3 and the second electrode 5, and the hydrogen concentration is determined from the limit current Ip flowing between the first electrode 3 and the second electrode 5.
In addition, the processing for obtaining the CO concentration from the voltage Vp between the first electrode 3 and the second electrode 5 and the processing for obtaining the hydrogen concentration from the limit current Ip flowing between the first electrode 3 and the second electrode 5 are as follows. The present invention can be implemented by an electronic control unit mainly including a well-known microcomputer to which those data are input.
[0040]
b) Next, the measurement principle and the measurement procedure of the gas sensor of the present embodiment will be described. When the gas sensor according to the present embodiment is exposed to the fuel gas, basically, the hydrogen that has reached the first electrode 3 from the ambient atmosphere outside the gas sensor through the diffusion-controlling portion 21 is generated between the first electrode 3 and the reference electrode 7. Then, an electromotive force is generated in accordance with the hydrogen concentration (specifically, the difference in hydrogen concentration between the two electrodes 3 and 7).
[0041]
Then, the voltage Vp is applied between the first electrode 3 and the second electrode 5 by the power supply 27 so that the potential difference Vs between the first electrode 3 and the reference electrode 7 becomes constant.
As a result, the catalyst in the first electrode 3 dissociates hydrogen in the gas to be measured in the first concave portion (measurement chamber) 15 into protons, and converts CO of the catalyst poison gas into protons through the above formula (A). The protons are dissociated and pumped out to the second electrode 5 side through the proton conductive layer 1, become hydrogen again, and diffuse into the gas atmosphere to be measured.
[0042]
At this time, since the voltage Vp applied between the first electrode 3 and the second electrode 5 changes depending on the concentration of the catalyst poison gas such as CO, the concentration of the catalyst poison gas such as CO can be measured by the voltage Vp. Become.
When the concentration of the catalyst poison gas such as CO is sufficiently lower than the hydrogen concentration, the current value due to the pumping of the catalyst poison gas such as CO as protons is so small as to be almost negligible. Since the current Ip flowing between the third electrode 3 and the second electrode 5 changes according to the hydrogen concentration, it is possible to measure the hydrogen concentration from the current value Ip.
[0043]
That is, the current value Ip flowing between the first electrode 3 and the second electrode 5 (that is, the limit current that increases to a certain value and becomes the upper limit when the voltage Vp is applied so as to increase sequentially) is hydrogen. Since the concentration is proportional to the concentration, measuring the current value Ip makes it possible to measure the hydrogen concentration.
[0044]
Note that the voltage Vp is represented by an equation (B) showing “Vp = RIp + Vs”, where R is the internal resistance between the first electrode 3 and the second electrode 5. That is, in this equation (B), Ip is constant as the limit current, and Vs is also constant because of the set potential between the first electrode 3 and the reference electrode 7, so that Vp of Vp measured here is constant. It can be said that the change is detecting a rise in the internal resistance R that changes because the catalyst poison gas such as CO is turned into protons and pumped out through the proton conductive layer 1.
[0045]
That is, in the present embodiment, the rise of the resistance value R is detected by the applied voltage Vp. However, the potential difference Vs between the first electrode 3 and the reference electrode 7 is kept constant, and the rise of the internal resistance R is measured by AC measurement or the like. The concentration of the catalyst poison gas can be obtained by directly detecting the concentration of the catalyst poison gas.
[0046]
c) Next, a brief description will be given of a method of manufacturing the gas sensor of the present embodiment.
For example, the second support 11 is disposed on a base (not shown) with the second recess 17 side facing upward.
Next, the proton conductive layer 1 on which the first electrode 3, the second electrode 5, and the reference electrode 7 are disposed on both sides is disposed thereon. That is, the second electrode 5 and the reference electrode 7 are arranged so as to be accommodated in the second recess 17 and the third recess 19, respectively.
[0047]
Next, the first support 9 is disposed on the proton conductive layer 1 so as to surround the first electrode 3 with the first recess 15.
In this state, that is, in a state where the proton conductive layer 1 is sandwiched between the first support 9 and the second support 11, the gas sensor is pressed and fixed in a thickness direction (up and down direction in the figure) of the gas sensor by a fixing member or the like (not shown). And a gas sensor.
[0048]
The side surface of the gas sensor is covered with, for example, a resin or the like, and is airtight. However, it is only necessary to vent the gas from the part other than the diffusion control part 21 (to the first electrode 3 side). Not something.
d) Next, the effect of the gas sensor of the present embodiment will be described.
[0049]
In the gas sensor according to the present embodiment, the voltage Vp applied between the first electrode 3 and the second electrode 5 is adjusted so that the potential difference Vs between the first electrode 3 and the reference electrode 7 becomes constant. I have. Since this voltage Vp depends on the CO concentration, the CO concentration can be obtained from the voltage Vp. Note that the concentration of the catalyst poison gas other than CO can also be measured according to the same principle as in this embodiment.
[0050]
Further, as in the present embodiment, irreversible poisoning can be prevented by allowing the CO introduced into the measurement chamber 15 to always react. Thereby, the CO concentration can be reversibly and continuously measured without requiring a recovery means such as a heater.
[0051]
Further, in this embodiment, since the potential difference Vs between the first electrode 3 and the reference electrode 7 is 400 mV or more, all the CO introduced into the measurement chamber 15 can be reacted, and from this point, Can also prevent irreversible poisoning by CO.
In addition, in the present embodiment, it is not necessary to introduce a gas containing oxygen, such as the air, and the pressure applied to the sensor unit (proton conductive layer 1) may be uneven even in a pressurized atmosphere. Since it is not, it is hard to be damaged and can be measured for a long time.
[0052]
Further, in the present embodiment, the current flowing by the voltage Vp applied between the first electrode 3 and the second electrode 5 is a limiting current, so that the reaction of the above formula (A) can be more stably caused. Can be. Thus, the CO concentration can be measured stably and accurately.
[0053]
Further, since the limit current Ip flowing between the first electrode 3 and the second electrode 5 is proportional to the hydrogen concentration in the measurement chamber 15, in the present embodiment, not only the measurement of the CO concentration but also the first electrode 3 The hydrogen concentration in the gas to be measured can also be determined from the limit current Ip flowing between the second electrode 5 and the second electrode 5.
[0054]
e) Next, an experimental example performed to confirm the effect of the present embodiment will be described.
(1) Experimental example 1
The first experimental example is for setting the potential difference Vs at which the CO concentration can be measured stably.
[0055]
Here, using the gas sensor of Example 1 shown in FIG. 1 and monitoring the potential difference Vs generated between the first electrode and the reference electrode under the following measurement conditions 1, the first electrode and the second electrode were measured. When the voltage Vp applied between the electrodes is changed, that is, when the voltage Vp is increased so that the potential difference Vs is sequentially increased, the current flowing between the first electrode and the second electrode is measured. did.
[0056]
<Measurement condition 1>
-Gas composition: CO = 5000 ppm, CO ₂ = 15%, H ₂ O = 25%, N ₂ = Bal.
・ Gas temperature: 80 ° C
-Gas flow rate: 10 L / min
・ Applied voltage Vp: 0 to 1000 mV
-Electrode catalyst of first electrode: Pt-supported carbon catalyst
-Electrode catalyst of the second electrode: Pt-supported carbon catalyst
FIG. 2 shows the measurement results. In FIG. 2, the vertical axis indicates the value of the flowing current Ip, and the horizontal axis indicates the monitored potential difference Vs.
[0057]
Here, the potential difference Vs on the horizontal axis indicates a value resulting from the hydrogen concentration on the first electrode which has been reduced by increasing the voltage Vp applied between the first electrode and the second electrode. A large value indicates that the hydrogen concentration on the first electrode is low.
From FIG. 2, it can be seen that as the potential difference Vs increases, the current flowing between the first electrode and the second electrode increases, and becomes constant (limit current) at Vs = 400 mV or more.
[0058]
This result indicates that when the hydrogen concentration on the first electrode decreases, the reaction proceeds to the right according to the above equation (A), that is, a current flows by the hydrogen generated by the reaction of CO. I have. Furthermore, since the limiting current is reached in the region where Vs = 400 mV or more, it can be seen that when Vs = 400 mV or more, all of the introduced CO has reacted.
[0059]
In addition, as described above, poisoning occurs because the introduced catalyst poison gas such as CO adsorbs on the electrode catalyst and does not desorb. Therefore, in order to prevent poisoning, the introduced catalyst poison gas such as CO is used. It is evident from this experimental example that if CO is set to Vs = 400 mV or more, all of the CO and the like will react, and it will be stable without irreversible poisoning. It can be seen that the CO concentration can be reversibly measured.
[0060]
(2) Experimental example 2
In Experimental Example 2, CO concentration was measured under the following measurement conditions 2 using the gas sensor of Example 1 described above.
<Measurement condition 2>
・ Gas composition:
CO = 0 → 1000 → 2000 → 3000 → 4000 → 5000 → 4000 → 3000 → 2000 → 1000 → 0ppm
H ₂ = 35%, CO ₂ = 15%, H ₂ O = 25%, N ₂ = Bal.
・ Gas temperature: 80 ° C
-Gas flow rate: 10 L / min
-Set potential (potential difference) Vs between the first electrode and the reference electrode: 900 mV
-Electrode catalyst of first electrode: Pt-Au supported carbon catalyst
-Electrode catalyst of second electrode and reference electrode: Pt-supported carbon catalyst
Sensor output: applied voltage Vp between the first electrode and the second electrode
FIG. 3 shows the measurement results. From FIG. 3, the sensor output is reversibly and continuously changed according to the change in the CO concentration, and the above-described gas sensor is used to measure the CO concentration reversibly and continuously without any means such as a heater. It can be seen that is possible.
[0061]
The electrode catalyst used for the first electrode was Pt and Au in a weight ratio of 1: 1 and supported on carbon powder. The added gold may be alloyed or may be contained as a mixture.
The electrode catalyst used for the first electrode is a catalyst that can generate hydrogen or proton by adsorbing a catalyst poison gas in a gas to be measured and decomposing, dissociating, or reacting with a hydrogen-containing substance. Well, it is not limited to this experimental example. Further, the catalyst used for the second electrode and the reference electrode is not limited to this experimental example. In addition, as will be described later, the second electrode may also function as a reference electrode, and may be integrated with the reference electrode.
[0062]
(3) Experimental example 3
In Experimental Example 3, it was confirmed that the sensitivity was improved by adding gold as an electrode catalyst of the first electrode under the following measurement conditions 3 using the gas sensor of Example 1 described above.
[0063]

FIG. 4 shows the measurement results. From FIG. 4, it can be seen that the sensitivity of the catalyst to which gold was added was higher than that of the catalyst to which only platinum was added, and the sensitivity could be improved by adding gold.
[0064]
Here, as the electrode catalyst used for the first electrode, a Pt and Au were used in a weight ratio of 1: 1 and supported on carbon powder, as in Experimental Example 2. The added gold may be alloyed or may be contained as a mixture. Note that, in Experimental Example 3, as in Experimental Example 2, the embodiment is not limited to the embodiment of Experimental Example 3.
[0065]
(4) Experimental example 4
In Experimental Example 4, hydrogen concentration was measured under the following measurement conditions 4 using the gas sensor of Example 1 described above. That is, the hydrogen concentration is measured when the CO concentration is different.
[0066]

FIG. 5 shows the measurement results. FIG. 5 shows that the value of the current flowing between the first electrode and the second electrode changes according to the hydrogen concentration, and that the current value does not change according to the CO concentration.
[0067]
That is, it is understood that the CO concentration and the hydrogen concentration can be measured simultaneously by the above-described gas sensor.
The experimental example 4 is not limited to the embodiment of the experimental example 4, as in the experimental examples 2 and 3.
(Example 2)
Next, a second embodiment will be described, but the description of the same parts as in the first embodiment will be omitted.
[0068]
The gas sensor according to the present embodiment includes the proton conductive layer 41, the first electrode 43, the second electrode 45, the diffusion-controlling portion 47, and the like, similarly to the first embodiment. It is characterized in that it has the function of (1) and is integrated with the reference electrode. As shown in FIG. 6, in the present embodiment, as an electrical configuration of the gas sensor, a first voltmeter 59 measures a potential difference Vs between the first electrode 43 and the second electrode 45 and supplies a power (battery). At 61, a voltage is applied between the first electrode 43 and the second electrode 45, and at the second voltmeter 63, a voltage Vp applied between the first electrode 43 and the second electrode 45 is measured. In addition, the ammeter 65 includes a circuit for measuring the current Ip flowing between the first electrode 43 and the second electrode 45, and the first voltmeter 59 or the ammeter 65 with respect to the first electrode 43. A switching element 67 for switching the connection is provided on the side.
[0069]
Then, the circuit is switched by the switching element 67 to measure the potential difference Vs between the first electrode 43 and the second electrode 45 (in this case, functioning as a reference electrode) (connecting the switching element 67 to S1). And applying a voltage between the first electrode 43 and the second electrode 45 (switching) so as to make the potential difference Vs between the first electrode 43 and the second electrode 45 (function of the reference electrode) constant. (The element 67 is connected to S2) periodically.
[0070]
Thereby, the voltage Vp is applied between the first electrode 43 and the second electrode 45 so that the potential difference Vs between the first electrode 43 and the second electrode 45 (function of the reference electrode) is constant. Therefore, by measuring the voltage Vp, it becomes possible to measure the concentration of the catalyst poison gas such as CO in the gas to be measured, as in the first embodiment. Also, the hydrogen concentration can be measured by the limit current Ip.
[0071]
Further, in this embodiment, since the second electrode 45 is integrated with the reference electrode, there is an advantage that the structure of the gas sensor can be simplified.
It should be noted that the present invention is not limited to the above-described embodiment at all, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention.
[Brief description of the drawings]
FIG. 1 is an explanatory view of a gas sensor according to a first embodiment, which is cut away.
FIG. 2 is a graph showing a relationship between a potential difference Vs and a current value in Experimental Example 1.
FIG. 3 is a graph showing a relationship between a CO concentration and an applied voltage Vp in Experimental Example 2.
FIG. 4 is a graph showing a difference in sensor sensitivity due to a difference in catalyst in Experimental Example 3.
FIG. 5 is a graph showing a relationship between a CO concentration, a hydrogen concentration, and a current value in Experimental Example 4.
FIG. 6 is an explanatory view showing the gas sensor of the second embodiment in a cutaway manner.
[Explanation of symbols]
1, 41 ... proton conductive layer
3, 43 ... first electrode
5, 45 ... second electrode
7 ... Reference electrode
15 Measurement chamber (first recess)
21, 47 ... diffusion controlling part

Claims (8)

A proton conducting layer that conducts protons,
A diffusion-controlling part that controls the diffusion of the gas to be measured;
Via the diffusion-controlling unit, a measurement chamber communicating with the measured gas atmosphere,
A first electrode in contact with the proton conductive layer and including a catalyst in the measurement chamber;
Outside the measurement chamber, a second electrode and a reference electrode in contact with the proton conductive layer,
With
Based on a voltage applied between the first electrode and the second electrode such that a potential difference between the first electrode and the reference electrode becomes a predetermined value, a catalyst poison gas in the gas to be measured is A gas sensor characterized by obtaining a concentration. The gas sensor according to claim 1, wherein the catalyst poison gas is CO or a sulfur-containing substance. The gas sensor according to claim 1, wherein the second electrode has a function of the reference electrode, and the second electrode and the reference electrode are integrated. 4. The gas sensor according to claim 1, wherein a potential difference between the first electrode and the reference electrode is 400 mV or more. 5. The gas sensor according to any one of claims 1 to 4, wherein a current flowing by a voltage applied between the first electrode and the second electrode is a limit current. The gas sensor according to claim 5, wherein a hydrogen concentration in the gas to be measured is obtained from the value of the limit current. The catalyst contained in the first electrode is a catalyst that can generate hydrogen or protons by adsorbing a catalyst poison gas in the gas to be measured and decomposing, dissociating, or reacting with a hydrogen-containing substance. The gas sensor according to claim 1, wherein: The gas sensor according to claim 7, wherein the catalyst includes platinum and / or gold.

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