JP2013130481A - Hydrogen gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen gas sensor capable of detecting hydrogen gas and measuring a hydrogen gas concentration by a simple structure without requiring application of reference gas or voltage, and to provide a coin cell type hydrogen gas sensor using the hydrogen gas sensor.SOLUTION: In the hydrogen gas sensor configured by laminating a first electrode 11 and a second electrode 12 through a solid electrolyte film 13, the first electrode 11 and the second electrode 12 contain metal having catalysis capable of dissociating hydrogen to protons, the film thickness of the first electrode 11 is 1 to 25 nm, and the film thickness of the second electrode 12 is thicker than the film thickness of the first electrode 11.

Description

The present invention relates to a hydrogen gas sensor capable of detecting hydrogen gas and measuring the hydrogen gas concentration with a simple structure without requiring application of a standard gas or voltage, and a coin battery type hydrogen gas sensor using the hydrogen gas sensor. .

In recent years, fuel cells have attracted attention as energy sources for electric vehicles. A fuel cell is a chemical cell that can continuously extract electric power by continuously supplying a fuel such as hydrogen and an oxidant such as oxygen.
Hydrogen molecules, which are energy sources for fuel cells, are stable at room temperature, but are highly reactive and easily cause chemical reactions with various substances. For example, it is known that when hydrogen and oxygen are mixed at a volume ratio of 2: 1 and ignited, a violent explosion occurs. Therefore, in a place where hydrogen is used, there is an extremely high need for a hydrogen gas sensor that can accurately detect the hydrogen concentration by a simple method.

As such a hydrogen gas sensor, an electromotive force measurement method using a proton conductor is conventionally known. For example, Patent Document 1 discloses that a gas having a known hydrogen concentration partial pressure value (standard gas) is exposed to a second electrode (reference electrode), thereby determining the hydrogen concentration in the gas exposed to the first electrode. A hydrogen gas sensor that can be calculated and measured from an electromotive force between one electrode and a second electrode is disclosed.

Further, in Patent Document 2, a working electrode, a reference electrode, and a counter electrode are provided on an insulating substrate, a gas permeable proton conductor film that integrally covers the electrode is formed, and a gas that has permeated the proton conductor film is used. A hydrogen gas sensor that can measure the hydrogen concentration by measuring a current at which protons generated on the surface of the working electrode are reduced at the counter electrode is disclosed.

JP 2003-270200 A Japanese Examined Patent Publication No. 7-31153

However, the hydrogen gas sensor disclosed in Patent Document 1 has a problem of requiring a standard gas. When such a standard gas is used, various problems such as a complicated sensor structure and difficulty in miniaturization may occur.
In addition, the hydrogen gas sensor disclosed in Patent Document 2 generates protons on the surface of the working electrode after the detection gas permeates the proton conductor membrane, and is reduced again to gas at the counter electrode and then permeates the proton conductor membrane. Therefore, it had to be discharged to the outside, and there was a problem in sensitivity and responsiveness.
In addition, a voltage must be applied between the working electrode and the counter electrode, and a reference electrode is required for controlling the voltage, resulting in a problem that the detection circuit is complicated.
The present invention solves the above-described problems, and provides a hydrogen gas sensor capable of detecting hydrogen gas and measuring the hydrogen gas concentration with a simple structure without requiring application of a standard gas or voltage. With the goal.

The present invention is a hydrogen gas sensor in which a first electrode and a second electrode are laminated via a solid electrolyte membrane, wherein the first electrode and the second electrode are made of a metal having a catalytic action capable of dissociating hydrogen into protons. The hydrogen gas sensor is characterized in that the first electrode has a thickness of 1 to 25 nm, and the second electrode has a thickness greater than that of the first electrode.
The present invention is described in detail below.

The inventors use a metal having a catalytic action capable of dissociating hydrogen into protons as the material of the first electrode and the second electrode, and by setting the first electrode and the second electrode to a predetermined film thickness, The present inventors have found that hydrogen gas can be detected and the hydrogen gas concentration can be measured with a simple structure without applying a voltage or voltage, and the present invention has been completed.

An example of the hydrogen gas sensor of the present invention is shown in FIG.
The hydrogen gas sensor 10 of the present invention includes a first electrode 11, a second electrode 12, and a solid electrolyte membrane 13, and the first electrode 11 and the second electrode 12 are laminated via the solid electrolyte membrane 13. It has become. The film thickness a of the first electrode 11 is 1 to 25 nm, and the film thickness b of the second electrode 12 is larger than the film thickness a of the first electrode 11 (b> a). The difference (b−a) between the film thickness b of the second electrode 12 and the film thickness a of the first electrode 11 is preferably 10 to 200 nm.

In the hydrogen gas sensor 10 of the present invention, the first electrode 11 and the second electrode 12 contain a metal having a catalytic action capable of dissociating hydrogen into protons. Thus, when hydrogen gas is present in the vicinity of the surfaces of the first electrode 11 and the second electrode 12, hydrogen is dissociated into protons and electrons as shown in the following formula (1).
H ₂ → 2H ⁺ + 2e ⁻ (1)
Protons generated by dissociation diffuse in the first electrode 11 and the second electrode 12 and reach the solid electrolyte membrane 13. At the same time, a reaction in which protons disappear due to oxygen present in the atmosphere near the surfaces of the first electrode 11 and the second electrode 12 as shown in the following formula (2).
2H ⁺ + 1 / 2O ₂ + 2e ⁻ → H ₂ O (2)
Therefore, in the hydrogen gas sensor 10 of the present invention, the reaction of the above formulas (1) and (2) is performed by electrically connecting the first electrode 11 and the second electrode 12 to the first electrode 11 and the second electrode 12. Therefore, after the hydrogen molecules contained in the atmosphere reach the electrode surface, the concentration of hydrogen molecules or protons decreases as they diffuse from the electrode surface to the inside.
Due to this phenomenon, in the present invention, by providing the first electrode 11 and the second electrode 12 having different thicknesses on the solid electrolyte membrane 13, a proton concentration gradient is formed in the solid electrolyte membrane 13, and the first electrode 11 side As a result, the proton concentration in the solid electrolyte membrane 13 moves to the second electrode 12 side. Since such a reaction occurs continuously, a current corresponding to the hydrogen concentration flows in the external circuit, and thus the hydrogen concentration can be measured by measuring the current.
In addition, the proton which moved to the 2nd electrode 12 side is reduce | restored with the electron through an external circuit by said reaction (2) Formula.

The first electrode and the second electrode contain a metal having a catalytic action capable of dissociating hydrogen into protons. As a result, the reactions of the above formulas (1) and (2) can be generated in the first electrode and the second electrode.
Examples of the metal include platinum group metals such as platinum, palladium, rhodium, ruthenium, iridium, and osmium.

The first electrode and the second electrode only need to contain a metal having a catalytic action capable of dissociating hydrogen into protons, and may be carbon carrying a metal having a catalytic action capable of dissociating hydrogen into protons. Specifically, it is preferable to use carbon carrying a platinum group metal.
Moreover, it is preferable to use what consists of a platinum group metal as a 1st electrode, and use what consists of carbon which carry | supported the platinum group metal as a 2nd electrode. As a result, even if the amount of catalytic metal is small, the area where the second electrode is in contact with oxygen and hydrogen in the atmosphere increases, so that the reaction (2) is further promoted and the proton concentration in the solid electrolyte membrane is reduced. Can be lowered.

In the present invention, the thickness of the second electrode is preferably larger than the thickness of the first electrode, and the difference between the thickness of the second electrode and the thickness of the first electrode is preferably 10 to 200 nm.
If the difference in film thickness is less than 10 nm, the proton concentration difference becomes small and the current corresponding to the hydrogen concentration becomes small, so the sensitivity may be low. If it exceeds 200 nm, the response speed decreases and the solid electrolyte membrane Curling or the like may occur.
More preferably, it is 30-80 nm.

The film thickness of the first electrode is 1 to 25 nm. If the film thickness of the first electrode is less than 1 nm, the electric resistance increases and it becomes difficult to take out the current. If the film thickness exceeds 25 nm, the number of protons reaching the solid electrolyte membrane decreases, so the current corresponding to the hydrogen concentration decreases. Sensitivity is lowered.
Preferably it is 5-10 nm.

The film thickness of the second electrode is preferably 30 to 200 nm.
If the film thickness of the second electrode is less than 30 nm, the amount of protons that reach the solid electrolyte membrane increases, so that the current value corresponding to the hydrogen concentration decreases and the sensitivity may decrease. Decrease in speed or curling of the solid electrolyte membrane may occur.
More preferably, it is 40-100 nm.

Examples of the solid electrolyte membrane include perfluorinated polymers having high proton conductivity such as perfluorosulfonic acid and perfluorocarboxylic acid, and partially sulfonated styrene-olefins such as Poly (styrene-ran-ethylene) and sulfonated. It is preferable to employ a solid polymer electrolyte membrane made of copolymer. Specifically, Nafion (manufactured by DuPont, registered trademark: NAFION), Aciplex (manufactured by Asahi Kasei Corporation, registered trademark: ACIPLEX) and the like can be suitably used. Further, conductive particles may be dispersed in the solid electrolyte membrane.

The thickness of the solid electrolyte membrane is preferably 5 to 200 μm.
If the thickness of the solid electrolyte membrane is less than 5 μm, the mechanical strength may be low and it may be easily broken, or a short circuit may occur between the first electrode and the second electrode due to pinholes. When it exceeds 200 μm, the response speed may be lowered.
More preferably, it is 10-100 micrometers.

FIG. 2 shows an example of the method of extracting current and the application of the electrode shape in the hydrogen gas sensor of the present invention.
The hydrogen gas sensor 20 of the present invention includes a first electrode 21, a second electrode 22, and a solid electrolyte membrane 23, and a conductive wire 24 is connected to the first electrode 21 and the second electrode 22. Furthermore, by installing a current-voltage conversion circuit between the first electrode 21 and the second electrode 22, the first electrode and the second electrode can always be kept at the same potential while measuring the current.
The first electrode 21 is connected to the conductive wire 24 via a thick film portion 25 formed on the outside. For example, when a conducting wire is directly connected to the first electrode 21, the area in contact with hydrogen gas can be increased, but when the resistance of the electrode is high in order to extract the current from a part, the current cannot be extracted efficiently. . On the other hand, the formation of such a thick film portion 25 reduces the hydrogen gas reaction area, but the efficiency can be increased by reducing the resistance.
Examples of the pattern shape (in top view) of the thick film portion include a lattice shape, a radial shape, a vein shape, and the like.

An example to which the present invention is applied is shown in FIGS.
The hydrogen gas sensor 30 has an opening for exposing the first electrode 31 and the second electrode 32 having a bonding hole at an end portion of the laminated body including the first electrode 31, the second electrode 32, and the solid electrolyte membrane 33. It has the structure inserted | pinched between the SUS electrode plates 36 which have. Further, the SUS electrode plate 36 also has a function as an output output electrode by being electrically connected to the first electrode 31 and the second electrode 32, and by connecting the conducting wire 34, The function as a gas sensor can be exhibited. With such a configuration, it is possible to perform accurate hydrogen gas measurement while protecting the first electrode 31, the second electrode 32, and the solid electrolyte membrane 33 that are important for hydrogen gas measurement.

The hydrogen gas sensor 40 has a configuration in which a laminated body composed of a first electrode 41, a second electrode 42, and a solid electrolyte membrane 43 is sandwiched between SUS electrode plates 46 having a joining hole at an end and an opening at the center. It has become. In addition, the SUS electrode plate 46 is electrically connected to the first electrode 41 and the second electrode 42 through the gas permeable conductor 47, and thus has a function as an electrode for taking out the output. By connecting the lead wire 44, a function as a hydrogen gas sensor can be exhibited. With such a configuration, current can be taken out from the entire surface while supplying hydrogen to the first electrode 41 and the second electrode 42 which are important for hydrogen gas measurement. Furthermore, it is possible to measure the hydrogen gas while preventing adhesion of foreign matters.
As an application of the hydrogen gas sensor 40, the hydrogen gas sensor 40 may be installed on a printed circuit board.

The hydrogen gas sensor 50 is an example when the present invention is used as a coin battery type hydrogen gas sensor.
The hydrogen gas sensor 50 has a configuration in which a laminated body including a first electrode 51, a second electrode 52, and a solid electrolyte membrane 53 is sandwiched between a pair of SUS electrode covers 56. The SUS electrode cover 56 also has a function as an electrode by being electrically connected to the first electrode 51 and the second electrode 52 via the gas permeable conductor 57. Further, the pair of SUS electrode covers 56 are electrically insulated via insulating spacers 58. In this way, the electrode is clamped and fixed, so that the sensor becomes strong, and there is no loosening of screws or disconnection of the wiring, so the hydrogen gas sensor itself can be easily carried, and the detector replacement type It can also be used for a hydrogen gas sensor device.

As the gas permeable conductor, carbon paper, foam metal or the like can be used.
The carbon paper is a porous body made of carbon fiber and carbon, and is also used for a gas diffusion layer of a fuel cell, etc., and therefore has excellent gas permeability and conductivity. Foam metal is used for battery electrode materials, filters, and the like, and those having a porosity of 90% or more have particularly good gas permeability, and also have low resistance because they are metal.
As an electrode used for the coin battery type hydrogen gas sensor, an electrode press-molded to a standard size such as CR2032 or CR2016 can be used, but when used for a hydrogen sensor, a vent hole is provided for gas permeation. As the insulating spacer, a molded one that matches the shape of the battery case made of polypropylene or the like is used.

As a method for manufacturing the hydrogen gas sensor of the present invention, for example, a step of forming a first electrode and a second electrode having a predetermined thickness on both sides of a solid electrolyte membrane, and the obtained laminate is cut into a predetermined size. Manufactured by a process.

Examples of the method for forming the first electrode and the second electrode include methods capable of forming a thin film such as sputtering, vapor deposition, and laser ablation.

According to the present invention, a hydrogen gas sensor capable of detecting hydrogen gas and measuring a hydrogen gas concentration with a simple structure without requiring application of a standard gas or voltage, and a coin battery type hydrogen using the hydrogen gas sensor A gas sensor can be provided.

It is a schematic diagram which shows an example of the hydrogen gas sensor of this invention. It is a schematic diagram which shows an example of the hydrogen gas sensor of this invention. It is a schematic diagram which shows an example of the hydrogen gas sensor of this invention. It is a schematic diagram which shows an example of the hydrogen gas sensor of this invention. It is a schematic diagram which shows an example of the hydrogen gas sensor of this invention. 3 is a graph showing the output current of the sensor obtained in Example 1. 4 is a graph showing the relationship of output current to hydrogen concentration of the sensor obtained in Example 1. 3 is a graph showing the output current of the sensor obtained in Example 1.

Examples of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1
A perfluorosulfonic acid polymer membrane (manufactured by DuPont) having a thickness of 50 μm was used as the solid electrolyte. A platinum film having a thickness of 10 nm was laminated as a first electrode on one surface of the perfluorosulfonic acid polymer film by sputtering (input power of 0.5 KW in Ar gas 0.4 Pa). Further, a platinum film having a thickness of 70 nm was stacked as the second electrode on the other side of the surface on which the first electrode was stacked by a sputtering method. Thereafter, it was punched into a circular shape having a diameter of 13 mm.
A carbon paper (Toray, 11 mm diameter circular shape, about 0.2 mm thickness) is placed so as to sandwich the obtained laminate, and further sandwiched between 20 mm diameter stainless steel plates from both sides, and then a stainless steel plate The sensors as shown in FIG. 4 were obtained by fastening them together with resin screws and fixing the whole.

The sensor obtained in Example 1 was placed in a glass tube, and the change in the current value when air with changed hydrogen concentration was supplied was measured via a current-voltage conversion circuit. FIG. 6 shows the response waveform, and FIG. 7 shows the relationship between the output current and the hydrogen concentration.
6 and 7, it can be seen that the output current and the hydrogen concentration have a straight line (linear function) relationship, and the hydrogen concentration can be measured from the current value.

FIG. 8 shows an output when nitrogen containing 1% hydrogen is supplied to the sensor used in Example 1 and an output current (response waveform) when air containing 1% hydrogen is supplied.
As shown in FIG. 8, when air containing 1% hydrogen (1% hydrogen in the air) was supplied, steady current was confirmed, whereas nitrogen containing 1% hydrogen (hydrogen concentration in nitrogen 1 %), A steady current did not flow, and a slight current flowed due to a change in concentration when the supply was switched. This was thought to be because the above formula (2), which consumes protons reaching the second electrode, does not proceed steadily due to the absence of oxygen in nitrogen containing 1% hydrogen.

(Examples 2 to 4)
A sensor was obtained in the same manner as in Example 1 except that the film thickness of the first electrode was changed as shown in Table 1 and the film thickness of the second electrode was changed to 55 nm.

(Examples 5 to 8)
A sensor was obtained in the same manner as in Example 1 except that the film thickness of the first electrode was 8 nm and the film thickness of the second electrode was changed as shown in Table 1.

Example 9
8 mL of water was added to 2.5 g of a catalyst for a polymer electrolyte fuel cell (product number: TEC10E60TPM, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) in which 60% by weight of platinum was supported on Kettin black carbon, and the mixture was stirred for 1 minute with a ball mill. Thereto were added 1.2 g of a perfluorosulfonic acid polymer membrane (manufactured by DuPont), 8 mL of isopropyl alcohol, and 8 mL of normal propyl alcohol, and the mixture was stirred with a ball mill for 50 minutes. Then, it was left to stand in a refrigerator at 5 ° C. for 3 days to prepare a catalyst solution.
The obtained catalyst solution was applied onto a polytetrafluoroethylene (PTFE) sheet with a bar coater and dried in an oven at 60 ° C. for 15 minutes to form an electrode layer. The obtained electrode layer had a thickness of 12 μm.
Next, a 50-μm thick perfluorosulfonic acid polymer film (manufactured by DuPont) as a solid electrolyte was prepared by laminating a platinum film having a thickness of 10 nm as the first electrode by sputtering. The surface where one electrode was not formed and the electrode layer (side where the PTFE sheet was not laminated) were overlapped, and the electrode layer was transferred by hot pressing at 120 ° C. to laminate the second electrode. Thereafter, the PTFE sheet was peeled off.
Using the obtained laminate, a sensor as shown in FIG. 4 was obtained in the same manner as in Example 1.

(Comparative Example 1)
Instead of the 70 nm-thick platinum film as the second electrode, the sensor was formed in the same manner as in Example 1 except that a 100 nm-thick gold film was laminated by sputtering (input power of 0.5 kW in Ar gas 0.4 Pa). Obtained.

(Comparative Examples 2 to 4)
A sensor was obtained in the same manner as in Comparative Example 1 except that the film thickness of the second electrode was changed as shown in Table 1.

(Comparative Examples 5 and 6)
A sensor was obtained in the same manner as in Example 1 except that the film thickness of the first electrode was changed as shown in Table 1 and the film thickness of the second electrode was changed to 55 nm.

(Evaluation)
The following evaluation was performed about the sensor obtained by the Example and the comparative example. The results are shown in Table 1.

(1) Output current About the obtained sensor, the output current value in the air of hydrogen concentration 1% was measured.
In the sensors obtained in Comparative Examples 1 to 4, a steady current did not flow, and only a small amount of current flowed when the concentration changed at the time of air supply switching.
This is considered to be because the reaction that consumes the protons that reached the second electrode does not proceed steadily because the gold electrode has low catalytic action.

According to the present invention, a hydrogen gas sensor capable of detecting hydrogen gas and measuring a hydrogen gas concentration with a simple structure without requiring application of a standard gas or voltage, and a coin battery type hydrogen using the hydrogen gas sensor A gas sensor can be provided.

Claims (5)

A hydrogen gas sensor in which a first electrode and a second electrode are stacked via a solid electrolyte membrane,
The first electrode and the second electrode contain a metal having a catalytic action capable of dissociating hydrogen into protons,
The film thickness of the said 1st electrode is 1-25 nm, The film thickness of the said 2nd electrode is thicker than the film thickness of a 1st electrode, The hydrogen gas sensor characterized by the above-mentioned. The hydrogen gas sensor according to claim 1, wherein a difference between a film thickness of the second electrode and a film thickness of the first electrode is 10 to 200 nm. The hydrogen gas sensor according to claim 1 or 2, wherein the metal having a catalytic action capable of dissociating hydrogen into protons is a platinum group metal. 4. The hydrogen gas sensor according to claim 1, wherein the first electrode is made of a platinum group metal, and the second electrode is made of carbon carrying the platinum group metal. 5. A coin cell type hydrogen gas sensor comprising the hydrogen gas sensor according to claim 1, 2, 3 or 4.

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