JP2021156675A - Hydrogen sensor element - Google Patents

Abstract

To provide a hydrogen sensor element which comprises a hydrogen detection membrane containing an organic substance and offers good reversibility.SOLUTION: A hydrogen sensor element is provided, comprising a pair of electrodes and a hydrogen detection membrane disposed in contact with the pair of electrodes, where the hydrogen detection membrane contains a conjugated polymer and an organic dopant containing a dopant with a molecular volume of 0.20 nm3 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a hydrogen sensor element.

As conventional hydrogen sensor elements, contact combustion type and semiconductor type are mainly known.
The contact combustion type hydrogen sensor element uses a noble metal such as platinum or palladium as a combustion catalyst and tin oxide or alumina as a carrier material in the detection unit, and hydrogen is detected by detecting an increase in the element temperature due to catalytic reaction combustion of hydrogen. Is detected.
The semiconductor hydrogen sensor element uses a platinum wire coil coated with fine particles such as indium oxide as a detection unit. When a hydrogen oxidation reaction occurs in the detection unit, oxygen adsorbed by negative ionization is consumed on the surface of the fine particles, and free electrons are generated accordingly to reduce the electric resistance value. The semiconductor hydrogen sensor element detects hydrogen by detecting the decrease in the electric resistance value.

In both the contact combustion type and the semiconductor type, since the detection unit needs to be heated to several hundred degrees or more, the power consumption is large and there is room for improvement in terms of safety. Further, in any of the methods, since an inorganic sintered body is used, it is usually difficult to give the hydrogen sensor element flexibility.

Non-Patent Document 1 describes a hydrogen sensor element including a hydrogen detection membrane composed of a composite of _{polyaniline and TiO 2 doped with camphorsulfonic acid.}

Subodh Srivastava, Sumit Kumar, V.N. Singh, M. Singh, Y.K. Vijay, Synthesis and characterization of TiO2 doped polyaniline composites for hydrogen gas sensing, International Journal Of Hydrogen Energy 36 (2011) 6343-6355

The hydrogen sensor element that detects hydrogen based on the increase or decrease of the electric resistance value preferably has good reversibility of the electric resistance value from the viewpoint of enhancing the function and / or reliability as a sensor. The hydrogen sensor element described in Non-Patent Document 1 has room for improvement in terms of reversibility of electrical resistance value.

In the present specification, the reversibility of the electric resistance value means the same sensitivity when the hydrogen concentration in an object (for example, the environment) for which the hydrogen concentration is measured by using the hydrogen sensor element changes, if the change in the hydrogen concentration is the same. Means the ability to show. For example, when the hydrogen concentration to be measured changes from A to B to A to B, the sensitivity to the first change in hydrogen concentration from A to B is the same as the sensitivity to the second change in hydrogen concentration from A to B. If the difference between them is small, it can be said that the hydrogen sensor element has good reversibility.
The sensitivity here means the rate of change of the electric resistance value indicated by the hydrogen sensor element.

An object of the present invention is to provide a hydrogen sensor element provided with a hydrogen detection film containing an organic substance and having good reversibility.

The present invention provides the hydrogen sensor element shown below.
[1] A hydrogen sensor element including a pair of electrodes and a hydrogen detection film arranged in contact with the pair of electrodes.
The hydrogen detection film contains a conjugated polymer and an organic dopant, and contains a conjugated polymer and an organic dopant.
The organic dopant is a hydrogen sensor element containing a dopant having a molecular volume of 0.20 nm ^{3 or less.}
[2] The hydrogen sensor element according to [1], wherein the conjugated polymer is a polyaniline-based polymer.
[3] The hydrogen sensor element according to [1] or [2], wherein the organic dopant is an organic acid.
[4] The hydrogen sensor element according to any one of [1] to [3], wherein the hydrogen detection membrane contains nanofibers of the conjugated polymer.

It is possible to provide a hydrogen sensor element provided with a hydrogen detection film containing an organic substance and having good reversibility.

It is a schematic top view which shows an example of the hydrogen sensor element which concerns on this invention. It is a schematic top view which shows the manufacturing method of a hydrogen sensor element. It is a schematic top view which shows the manufacturing method of a hydrogen sensor element. It is a schematic diagram which shows the structure of the measurement system for evaluating the sensitivity of a hydrogen sensor element, and the reversibility of an electric resistance value.

The hydrogen sensor element according to the present invention (hereinafter, also simply referred to as “hydrogen sensor element”) includes a pair of electrodes and a hydrogen detection film arranged in contact with the pair of electrodes.
The hydrogen detection film may be in contact with the pair of electrodes. Preferably, the pair of electrodes are arranged so as to be separated from each other, and the hydrogen detection film is arranged so as to be in contact with each electrode between the pair of electrodes arranged so as to face each other.

FIG. 1 is a schematic top view showing an example of a hydrogen sensor element. The hydrogen sensor element 100 shown in FIG. 1 has a pair of electrodes composed of a first electrode 101 and a second electrode 102, and a hydrogen detection film 103 arranged in contact with both the first electrode 101 and the second electrode 102. include. The hydrogen detection film 103 is in contact with these electrodes by forming both ends thereof on the first electrode 101 and the second electrode 102, respectively.
The hydrogen sensor element can further include a substrate 104 that supports the first electrode 101, the second electrode 102, and the hydrogen detection film 103 (see FIG. 1).

The hydrogen sensor element 100 shown in FIG. 1 detects hydrogen by detecting a decrease / increase in the electric resistance value caused by doping / dedoping hydrogen in the conjugated polymer contained in the hydrogen detection film 103.

[1] First Electrode and Second Electrode As the first electrode 101 and the second electrode 102, those having a sufficiently smaller electric resistance value than the hydrogen detection film 103 are used. Specifically, the electric resistance values of the first electrode 101 and the second electrode 102 included in the hydrogen sensor element are preferably 500 Ω or less, more preferably 200 Ω or less, and further preferably 100 Ω or less at a temperature of 25 ° C. Is.

The materials of the first electrode 101 and the second electrode 102 are not particularly limited as long as an electric resistance value sufficiently smaller than that of the hydrogen detection film 103 can be obtained, and for example, a single metal such as gold, silver, copper, platinum, or palladium; An alloy containing two or more kinds of metal materials; a metal oxide such as indium tin oxide (ITO) and indium zinc oxide (IZO); a conductive organic substance (a conductive polymer or the like) or the like can be used.
The material of the first electrode 101 and the material of the second electrode 102 may be the same or different.

The method for forming the first electrode 101 and the second electrode 102 is not particularly limited, and may be a general method such as vapor deposition, sputtering, or coating (coating method). The first electrode 101 and the second electrode 102 can be formed directly on the substrate 104.
The thickness of the first electrode 101 and the second electrode 102 is not particularly limited as long as an electric resistance value sufficiently smaller than that of the hydrogen detection film 103 can be obtained, but is, for example, 50 nm or more and 1000 nm or less, preferably 100 nm or more and 500 nm or less. ..

[2] Substrate The substrate 104 is a support for supporting the first electrode 101, the second electrode 102, and the hydrogen detection film 103.
The material of the substrate 104 is not particularly limited as long as it is non-conductive (insulating), and may be a resin material such as a thermoplastic resin, an inorganic material such as glass, or the like. When a resin material is used as the substrate 104, the hydrogen detection film 103 typically has flexibility, so that the hydrogen sensor element can be imparted with flexibility.

The thickness of the substrate 104 is preferably set in consideration of the flexibility and durability of the hydrogen sensor element. The thickness of the substrate 104 is, for example, 10 μm or more and 5000 μm or less, preferably 50 μm or more and 1000 μm or less.

[3] Hydrogen Detection Film The hydrogen detection film 103 contains a conjugated polymer and an organic dopant, and preferably contains a conjugated polymer doped with an organic dopant. The hydrogen detection film 103 is preferably made of a conjugated polymer and an organic dopant, and more preferably made of a conjugated polymer doped with an organic dopant.

The hydrogen detection film 103 preferably has a shape having a large surface area from the viewpoint of increasing the reactivity with hydrogen gas and improving the sensitivity.
The hydrogen detection film having the above shape is, for example, a film composed of nanofibers of a conjugated polymer and doped (adsorbed) by an organic dopant on the nanofibers; Membranes to which an organic dopant is doped (adsorbed); a film containing a porous material and the porous material is impregnated with a conjugated polymer and an organic dopant.
The hydrogen detection film 103 is preferably a membrane containing nanofibers of a conjugated polymer and having an organic dopant doped (adsorbed) on the nanofibers, and more preferably the nanofibers of the conjugated polymer and the nanofibers. It is a film made of an organic dopant that is doped with.
The hydrogen detection film 103 exposes the conjugated polymer to the surface from the viewpoint of enabling contact between the conjugated polymer and hydrogen, preferably from the viewpoint of enabling contact between the conjugated polymer and hydrogen on the largest possible surface area. It is preferable to do so.

[3-1] Conjugated Polymer A conjugated polymer usually has extremely low electrical conductivity of its own, and exhibits almost no electrical conductivity ^{, for example, 1 × 10-6 S / m or less.} The electrical conductivity of the conjugated polymer itself is low because the electrons are saturated in the valence band and the electrons cannot move freely. On the other hand, since the electrons of the conjugated polymer are delocalized, the ionization potential of the conjugated polymer is significantly smaller than that of the saturated polymer, and the electron affinity is very large. Thus, conjugated polymers are prone to charge transfer with suitable dopants, such as electron acceptors or donors, and the dopant pulls electrons out of the valence band of the conjugated polymer. Alternatively, electrons can be injected into the conduction band. Therefore, in a conjugated polymer doped with a dopant, there are a small number of holes in the valence band or a small number of electrons in the conduction band, and these can move freely, so that the conductivity tends to be dramatically improved. It is in.

For the conjugated polymer, the value of the linear resistance R of a single product when the distance between the lead rods is set to several mm to several cm and measured with an electric tester is preferably in the range of 0.01 Ω or more and 300 MΩ or less at a temperature of 25 ° C. Is. Such a conjugated polymer has a conjugated system structure in the molecule, for example, a molecule having a skeleton in which double bonds and single bonds are alternately connected, and a polymer having a conjugated unshared electron pair. And so on. As described above, such a conjugated polymer can be easily imparted with electrical conductivity by doping. The conjugated polymer is not particularly limited, and for example, polyacetylene; poly (p-phenylene vinylene); polypyrrole; poly (3,4-ethylenedioxythiophene) [PEDOT] or other polythiophene-based polymer; polyaniline-based polymer. And so on. Here, the polythiophene-based polymer is a polymer having a polythiophene skeleton, a polythiophene skeleton, and a substituent introduced into a side chain, a polythiophene derivative, or the like. In the present specification, the term "polymer" means a similar molecule.
Only one type of conjugated polymer may be used, or two or more types may be used in combination.

From the viewpoint of easiness of polymerization and identification, the conjugated polymer is preferably a polyaniline-based polymer.

[3-2] Organic Dopant As the organic dopant, an organic compound that functions as an electron acceptor (acceptor) for the conjugated polymer and an organic compound that functions as an electron donor (donor) for the conjugated polymer are included. Can be mentioned.
In general, conjugated polymers are imparted with conductivity by abstracting electrons with a dopant or donating electrons.

The doping / dedoping behavior of the dopant on the conjugated polymer is a reversible redox reaction. The doping state is an oxidation state and its chemical potential is high. The conjugated polymer in the doped state acts as an oxidant, but its potential differs depending on the type of the conjugated polymer.
In addition, the doping rate of the dopant on the conjugated polymer varies, and the chemical potential increases as the doping rate increases. If the doping rate is too high, oxidative decomposition of the conjugated polymer itself will occur. The upper limit doping rate that does not cause oxidative decomposition depends on the type of conjugated polymer.

H ⁺ A is a dopant that functions as an electron acceptor ^- cited doped polyaniline example, hydrogen detecting film containing a conjugated polymer and the dopant is a mechanism for detecting the hydrogen will be described using the following equation. In addition, polyaniline becomes conductive only in the emeraldine salt state.
When the polyaniline doped with the dopant H ⁺ A ⁻ is exposed to hydrogen gas, it is further doped with hydrogen, and as a result, the electric resistance value is lowered. Hydrogen gas can be detected by detecting such fluctuations in the electric resistance value.

The doped hydrogen molecule acts on a nitrogen atom having a positive charge of two polyaniline molecules (formulas (a) and (b) below). Then, when an NH bond is formed between the hydrogen molecule and the polyaniline two molecule, the HH bond in the hydrogen molecule is dissociated (the following formula (c)). After that, in each polyaniline diatomic molecule, electrons and A- move between adjacent N atoms (formulas (c) and (d) below), and at that time, the hydrogen atom dissociates from the N atom to form a hydrogen molecule. Occurs (formula (e) below).

As shown by the above mechanism, the hydrogen detection membrane can reversibly react with the hydrogen gas, which makes it possible for the hydrogen sensor element to exhibit the reversibility of the electric resistance value.
Further, since the hydrogen sensor element provided with the hydrogen detection film containing the conjugated polymer and the dopant detects hydrogen based on the above mechanism, it can be driven at room temperature.

The organic dopant contained in the hydrogen detection film 103 includes a dopant having a molecular volume of 0.20 nm ³ or less (hereinafter, this organic dopant is also referred to as “dopant (A)”). Thereby, the reversibility of the electric resistance value of the hydrogen sensor element can be improved.
The organic dopant contained in the hydrogen detection film 103 may contain only one kind of dopant (A), or may contain two or more kinds of dopant (A).

When the organic dopant contained in the hydrogen detection film 103 contains the dopant (A), the reversibility of the electric resistance value of the hydrogen sensor element is improved. It is presumed that this is partly due to the ease of approaching and moving away.
Further, when the molecular volume of the organic dopant is 0.20 nm ³ or less, it is considered that hydrogen gas easily penetrates into the hydrogen detection film 103, which is considered to be advantageous for improving the sensitivity of the hydrogen sensor element. Be done.

The use of an organic dopant is advantageous in making the doping rate an appropriate value. When an inorganic dopant such as an inorganic acid having a high acidity function is used, the doping rate becomes too high and oxidative decomposition of the conjugated polymer is likely to occur.

From the viewpoint of improving the reversibility of electrical resistance, the molecular volume of the dopant (A) is preferably not 0.18 nm ³ or less, more preferably 0.16 nm ³ or less, more preferably 0.15 nm ³ or less Is.
The molecular volume of the dopant (A) is usually 0.05 nm ^{3 or more, and is preferably 0.06 nm 3} or more from the viewpoint of improving the long-term stability of the hydrogen detection film 103.
When a polymer dopant is used as the organic dopant, the polymer tends to embrace moisture and the influence of humidity on the electric resistance value detected by the hydrogen detection film 103 becomes large, and the reliability of the hydrogen sensor element tends to decrease.

The molecular volume of an organic dopant varies depending on the size of atoms constituting the dopant, the three-dimensional structure, and the like.

The hydrogen detection film 103 may further contain an organic dopant other than the dopant (A) together with the dopant (A), but preferably contains only the dopant (A).

The molecular volume of the dopant can be obtained by DFT (Density Functional Theory; B3LYP / 6-31G + g (d)) calculation using general calculation software based on its molecular structure. Examples of the calculation software include a quantum chemistry calculation program "Gaussian series" manufactured by HULINKS.

The dopant (A) preferably has a high boiling point from the viewpoint of suppressing a decrease in sensitivity of the hydrogen sensor element by suppressing desorption from the conjugated polymer. The boiling point of the dopant (A) at atmospheric pressure is preferably 80 ° C. or higher, more preferably 100 ° C. or higher, and even more preferably 130 ° C. or higher.
When the hydrogen detection film 103 contains two or more kinds of dopants (A), it is preferable that at least one kind has a boiling point in the above range, and it is more preferable that all the dopants (A) have a boiling point in the above range.

As described above, the dopant (A) may be a compound that functions as an acceptor for the conjugated polymer, or may be a compound that functions as a donor for the conjugated polymer.

Examples of the organic dopant having a molecular volume of 0.20 nm ³ or less and being an acceptor include organic acids (excluding phenolic compounds), organic cyano compounds, phenolic compounds, and organic metal compounds.

When the conjugated polymer is a polyaniline-based polymer, an organic acid such as an organic carboxylic acid, an organic sulfonic acid, or an organic phosphonic acid is preferably used as the organic dopant having a molecular volume of 0.20 nm ^{3 or less and being an acceptor.} , Organic sulfonic acid is more preferably used. When the conjugated polymer is a polyaniline-based polymer, the organic acid has a low proton donating property, so that the polyaniline-based polymer is less likely to be oxidatively decomposed, and the long-term stability of the hydrogen detection film 103 tends to be improved.

Examples of the organic acid include ethanesulfonic acid, hydroxypropanesulfonic acid, 2-fluorobenzenesulfonic acid, 3-fluorobenzenesulfonic acid, 4-fluorobenzenesulfonic acid, pyridine-2-sulfonic acid, and pyridine-3-sulfonic acid. , Pyridine-4-sulfonic acid, ethanedisulfonic acid, 3-amino-1-propanesulfonic acid, aminoethylsulfonic acid, malonic acid, succinic acid and the like.

Examples of the organic cyano compound having a molecular volume of 0.20 nm ³ or less and being an acceptor include tetracyanoethylene, tetracyanoethylene oxide, and tetracyanobenzene.
Examples of the phenolic compound having a molecular volume of 0.20 nm ³ or less and being an acceptor include methoxyphenol and ethoxyphenol.

Examples of the organic dopant having a molecular volume of 0.20 nm ³ or less and being a donor include alkylamine and alkylammonium salt, and specifically, methylamine, ethylamine, butylamine, ethylenediamine, tetramethylammonium salt and dimethyl. Examples thereof include diethylammonium salt.

A preferable example of the hydrogen detection membrane 103 is that the conjugated polymer is a polyaniline-based polymer, the organic dopant is the dopant (A), and the dopant (A) is the acceptor.
Another preferred example of the hydrogen detection film 103 is that the conjugated polymer is a polyaniline-based polymer, the organic dopant is the dopant (A), and the dopant (A) is an organic acid as an acceptor.

The dopant (A) preferably does not contain a fluorine atom from the viewpoint of improving the sensitivity of the hydrogen sensor element.

The dopant (A) contained in the hydrogen detection film 103 preferably has a dipole moment of 6D (Debye) or less. As a result, the humidity dependence of the electric resistance value indicated by the hydrogen sensor element can be reduced (the electric resistance value can be less affected by the humidity of the measurement environment), and thus the function and / or the function of the hydrogen sensor element and / or The reliability can be further improved.
When the dipole moment of the dopant (A) is 6D or less, the humidity dependence of the electric resistance value can be reduced because the dopant has a low affinity with water, which is a polar molecule. It is presumed that one of the reasons is that it is difficult to attract water.

From the viewpoint of reducing the humidity dependence of the electric resistance value, the dipole moment of the dopant (A) is preferably 5D or less, more preferably 4.5D or less, still more preferably 4D or less, and particularly preferably. Is 3.5D or less.
The dipole moment of the dopant (A) is usually 0.1 D or more, and preferably 1 D or more from the viewpoint of compatibility with the conjugated polymer.

The dipole moment of an organic dopant changes depending on the electronegativity, three-dimensional structure, etc. of the atoms constituting the dopant.

The dipole moment of an organic dopant can be obtained by DFT (Density Functional Theory; B3LYP / 6-31G + g (d)) calculation using general calculation software based on its molecular structure. Examples of the calculation software include a quantum chemistry calculation program "Gaussian series" manufactured by HULINKS.

Examples of organic dopants having a molecular volume of 0.20 nm ³ or less and a dipole moment of 6D or less include ethanesulfonic acid, hydroxypropanesulfonic acid, pyridine-3-sulfonic acid, 4-fluorobenzenesulfonic acid, and the like. Examples thereof include 3-amino-1-propanesulfonic acid, aminoethylsulfonic acid, malonic acid and succinic acid.

From the viewpoint of further reducing the humidity dependence of the electric resistance value, the dopant (A) more preferably satisfies any one or more of the following in addition to having a dipole moment of 6D or less.
(A) It has a hydrophobic group such as an alkyl group in the molecule.
(B) When the conjugated polymer has an aromatic ring (for example, a benzene ring) such as a polyaniline-based polymer, it has at least one, preferably two or more aromatic rings (for example, a benzene ring) in the molecule.

By satisfying the above (a), the water insolubility of the dopant (A) can be increased, so that the humidity dependence can be further reduced. However, it tends to be difficult to attract water when the dipole moment is small and the degree of uneven distribution of electric charges is small rather than being water-insoluble.
It is presumed that the humidity dependence can be further reduced by satisfying the above (b) because the packing property of the dopant (A) with the conjugated polymer is improved.

In addition to the above, the molecular structure of the organic dopant and the type of functional group it has can affect the humidity dependence. For example, having a hydrophilic group tends to increase the humidity dependence.

The dopant (A) contained in the hydrogen detection film 103 is an atom having an acid group and having an absolute value of negative charge of 0.55 or more (hereinafter, this atom is also referred to as “atom a”). It is preferably contained in a molecular structure other than the acid group. Thereby, the sensitivity of the hydrogen sensor element can be improved. As the atom a, the atom having the largest absolute value of negative charge among the atoms contained in the molecular structure other than the acid group is usually selected.

In order to increase the sensitivity (reactivity to hydrogen) of the hydrogen sensor element, it is important to reduce the positive charge of the conjugated polymer. Reducing the positive charge in the conjugated polymer means reducing the attraction of electrons from the conjugated polymer by the dopant, which leaves room in the conjugated polymer for electrons to be attracted by doping with hydrogen gas. Can be done. In the dopant (A) containing the atom a in the molecular structure other than the acid group, the charge of the atom around the atom a is positively large, and the positive charge of the acid group is small accordingly. As a result, the dopant (A) has a weaker ability to extract electrons from the conjugated polymer, and therefore the positive charge of the conjugated polymer doped with the dopant (A) becomes smaller. As a result, the sensitivity of the hydrogen sensor element can be increased by including the dopant (A) containing the atom a in the molecular structure other than the acid group.

From the viewpoint of improving the sensitivity of the hydrogen sensor element, the absolute value of the negative charge of the atom a is preferably 0.6 or more, more preferably 0.65 or more.
The absolute value of the negative charge of the atom a is usually 1.5 or less, and is preferably 1.2 or less from the viewpoint of imparting a function as an acceptor.

The charge of the dopant is calculated by DFT (Density Functional Theory; APFD / 6-31G + g (d)) using general calculation software based on its molecular structure, and then the MK method of the Electrostatic potential fitting (esp) method. Can be determined by optimizing the charge using. Examples of the calculation software include a quantum chemistry calculation program "Gaussian series" manufactured by HULINKS.

Examples of organic dopants having a molecular volume of 0.20 nm ³ or less and having an acid group and containing the atom a in a molecular structure other than the acid group include pyridine-3-sulfonic acid and hydroxypropanesulfonic acid. , 3-Amino-1-propanesulfonic acid, aminoethylsulfonic acid and the like.

The dopant (A) contained in the hydrogen detection film 103 has an absolute value | ΔG | of the energy difference between the lowest empty orbital (LUMO) of the dopant (A) in the ground state and the highest occupied orbital (HOMO) of the conjugated polymer. It is preferably selected so as to be 4.5 eV or more. Thereby, the sensitivity of the hydrogen sensor element can be improved. | ΔG | is expressed by the following equation.
| ΔG | = | (LUMO energy of dopant (A))-(HOMO energy of conjugated polymer) |

By setting | ΔG | to 4.5 eV or more, the interaction between the conjugated polymer and the dopant (A) can be reduced, thereby reducing the attraction of electrons from the conjugated polymer by the dopant (A). be able to. Therefore, the positive charge of the conjugated polymer doped with the dopant (A) becomes small. As a result, when | ΔG | is 4.5 eV or more, the sensitivity of the hydrogen sensor element can be increased.

From the viewpoint of improving the sensitivity of the hydrogen sensor element, | ΔG | is preferably 4.6 eV or more, more preferably 4.7 eV or more, and further preferably 4.8 eV or more.
| ΔG | is usually 10 eV or less, and is preferably 8 eV or less from the viewpoint of facilitating the interaction between the conjugated polymer and the dopant (A).

The LUMO energy of the dopant and the HOMO energy of the conjugated polymer can be obtained by DFT (Density Functional Theory; APFD / 6-31G + g (d)) calculation using general calculation software based on their molecular structures. can. Examples of the calculation software include a quantum chemistry calculation program "Gaussian series" manufactured by HULINKS.

Examples of the combination of the conjugated polymer having | ΔG | of 4.5 eV or more and the dopant (A) include polyaniline and ethanesulfonic acid, polyaniline and hydroxypropanesulfonic acid, and polyaniline and 3-amino-1-propanesulfonic acid. , Polyaniline and aminoethyl sulfonic acid, polyaniline and malonic acid, polyaniline and succinic acid and the like.

The content of the dopant (A) is preferably 0.1 mol or more, more preferably 0.4 mol or more, with respect to 1 mol of the conjugated polymer, from the viewpoint of increasing the sensitivity of the hydrogen sensor element. The content is preferably 3 mol or less, more preferably 2 mol or less, with respect to 1 mol of the conjugated polymer, from the viewpoint of film forming property when forming the hydrogen detection film 103.

[3-3] Thickness of Hydrogen Detection Film The thickness of the hydrogen detection film 103 is not particularly limited, but is, for example, 0.3 μm or more and 50 μm or less. From the viewpoint of the flexibility of the hydrogen sensor element, the thickness of the hydrogen detection film 103 is preferably 0.3 μm or more and 40 μm or less.

[4] Hydrogen sensor element For the hydrogen sensor element, for example, a substrate 104 on which a pair of electrodes composed of a first electrode 101 and a second electrode 102 is formed is prepared, and is in contact with both the first electrode 101 and the second electrode 102. It can be manufactured by forming the hydrogen detection film 103 so as to be arranged.

The hydrogen detection film 103 can be produced, for example, by subjecting a substrate 104 to a polymerization reaction to form a film (layer) of a conjugated polymer and then impregnating it with an organic dopant.
Examples of the polymerization reaction on the substrate 104 include a method in which a liquid containing a monomer forming a conjugated polymer and a liquid containing a polymerization initiator are placed on the substrate 104 in an overlapping manner. The substrate may be heated as needed to accelerate the polymerization reaction.

The hydrogen sensor element can include other components other than those described above. Other components include, for example, antioxidants, metal microparticles, metal oxide microparticles, graphite and the like.
The antioxidant may contribute to the antioxidant of the hydrogen detection film 103. Metal fine particles, metal oxide fine particles, and graphite can contribute to improving the sensitivity of the hydrogen sensor element.

The hydrogen sensor element according to the present invention is excellent in reversibility of electric resistance value. The reversibility of the electric resistance value can be evaluated by, for example, the following method. First, as shown in FIG. 2, a pair of electrodes (first electrode 101 and second electrode 102) made of Au are formed on one surface of a glass substrate (substrate 104), and then as shown in FIG. A hydrogen sensor element is manufactured by forming a hydrogen detection film 103 so as to be in contact with both of these electrodes.
Next, referring to FIG. 4, the pair of Au electrodes of the hydrogen sensor element 100 and a commercially available digital multimeter are connected by a lead wire 401, and the hydrogen sensor element 100 is housed in the tubular container 402. Then, both ends of the container are sealed with a rubber stopper 403 provided with an outlet of the lead wire 401 and a gas inlet / outlet.

While monitoring the electric resistance value with a digital multimeter, a test is conducted in which gas is flowed into the container 402 in the order of the following [1] to [4] for the following time. The following test is carried out in an environment with a temperature of 23 ° C.
[1] Dry air with a flow rate of 10 L / min only (hydrogen concentration 0 vol%) for 10 minutes [2] Dry air with a flow rate of 10 L / min and dry air with a flow rate of 0.2 L / min (mixed gas with a hydrogen concentration of 2 vol%) for 10 minutes [3] Dry air with a flow rate of 10 L / min only (hydrogen concentration 0 vol%) for 10 minutes [4] Dry air with a flow rate of 10 L / min and dry air with a flow rate of 0.2 L / min (mixed gas with a hydrogen concentration of 2 vol%) for 10 minutes

In the above test, the operations of [1] and [2] are referred to as the first cycle, and the operations of [3] and [4] are referred to as the second cycle.
Then, for each of the first cycle and the second cycle, the electric resistance value change rate Z (%) is obtained based on the following formula. The electric resistance value change rate Z obtained for the first cycle is referred to as an electric resistance value change rate Z1, and the electric resistance value change rate Z obtained for the second cycle is referred to as an electric resistance value change rate Z2.

In the above formula, the electric resistance value H2 is an average value of the electric resistance values from 3 minutes to 10 minutes after switching the gas introduced into the container 402 to a mixed gas having a hydrogen concentration of 2 vol%. The electric resistance value H0 is the average value of the electric resistance values from 3 minutes to 10 minutes after introducing only the dry air into the container 402 or after switching the gas to be introduced into the container 402 to only the dry air. Is.

The electric resistance value change rate Z is an index (sensitivity index) indicating the sensitivity of the hydrogen sensor element, and for example, the electric resistance value change rate Z1 can be used as an index of the sensitivity of the hydrogen sensor element.
From the viewpoint of enhancing the function and / or reliability as a hydrogen sensor element, it is preferable that the electric resistance value change rate Z is high. For example, the rate of change in electrical resistance value Z1 can be 1% or more at 23 ° C., preferably 4% or more, more preferably 6% or more, and further preferably 8% or more. The rate of change in electrical resistance Z1 may be 25% or less at 23 ° C.
According to the present invention, it is possible to provide a hydrogen sensor element having good sensitivity for various purposes and usage environments.

Using the obtained electrical resistance value change rates Z1 and Z2, the index value (%) of the reversibility of the electrical resistance value is obtained based on the following formula.

The smaller the difference between the electric resistance value change rate Z2 and the electric resistance value change rate Z1, the larger the index value of reversibility. Therefore, it can be said that the higher the index value of reversibility, the more excellent the hydrogen sensor element is.
The index value of reversibility is preferably 80% or more, more preferably 84% or more, further preferably 90% or more, and particularly preferably 95% or more at 23 ° C. The index value of reversibility may be 100% or less or less than 100% at 23 ° C.

The humidity dependence of the electric resistance value of the hydrogen sensor element can be evaluated by, for example, the following method.
After manufacturing the hydrogen sensor element, the hydrogen sensor element is exposed to dry air overnight, and a pair of Au electrodes of the hydrogen sensor element and a commercially available digital multimeter are connected by a lead wire.
Next, the hydrogen sensor element is allowed to stand for 30 minutes in an atmosphere of a temperature of 30 ° C. and a relative humidity of 30% RH while monitoring the electric resistance value with a digital multimeter. Next, the hydrogen sensor element is allowed to stand for 30 minutes in an atmosphere of a temperature of 30 ° C. and a relative humidity of 80% RH while monitoring the electric resistance value with a digital multimeter. From the electric resistance value under each atmosphere, the humidity dependence index value (%) of the electric resistance value is obtained based on the following formula.

In the above formula, the electric resistance value RH30 is an electric resistance value when the product is allowed to stand in an atmosphere having a temperature of 30 ° C. and a relative humidity of 30% RH. Is the average value of. The electric resistance value RH80 is an electric resistance value when left standing in an atmosphere of a temperature of 30 ° C. and a relative humidity of 80% RH. Specifically, it is an average value of electric resistance values from a standing time of 15 minutes to 30 minutes. be.

The smaller the difference between the electric resistance value RH80 and the electric resistance value RH30, the smaller the index value of humidity dependence. Therefore, it can be said that the smaller the index value of humidity dependence, the smaller the humidity dependence of the hydrogen sensor element.
The humidity dependence index value is preferably less than 30%, more preferably 25% or less, still more preferably 20% or less, still more preferably 15% or less, and particularly preferably 10% or less. Is. The index value of humidity dependence may be 1% or more.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these examples. In the examples,% and parts representing the content or the amount used are based on mass unless otherwise specified.

<Example 1>
With reference to FIG. 2, by sputtering using an ion coater (“IB-3” manufactured by Eiko Co., Ltd.) on one surface of a square glass substrate (“Eagle XG” manufactured by Corning Inc.) having a side of 5 cm. , A pair of rectangular Au electrodes having a length of 2 cm and a width of 3 mm were formed.
The thickness of the Au electrode by cross-sectional observation using a scanning electron microscope (SEM) was 200 nm.

Solution A in which 0.029 g of ammonium persulfate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was dissolved in 1.55 mL of 1M hydrochloric acid, and 0.48 g of aniline (manufactured by Tokyo Chemical Industry Co., Ltd.) were xylene (Tokyo Chemical Industry Co., Ltd.). A solution B dissolved in 1.2 mL (manufactured by Co., Ltd.) was prepared.

90 μL of the A solution was added dropwise between the pair of Au electrodes formed on the glass substrate, and 10 μL of the B solution was further added dropwise thereto, and the mixture was allowed to stand for 5 minutes to carry out the polymerization reaction.
After that, the glass substrate is moved to a spin coater (“MS-A100” manufactured by Mikasa) and rotated under the condition of 3000 rpm / 30 s to remove the polymerization field from the glass substrate, and the polyaniline emeral represented by the following formula (1) is removed. A film of gin salt was obtained. After drying at room temperature for 20 minutes, it was immersed in 25% aqueous ammonia (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) diluted twice. When the polyaniline was dedoped and the membrane changed from green to blue, it was removed from the aqueous ammonia and the membrane was washed with water.
Then, the membrane was dried to obtain a nanofiber membrane of a polyaniline emeraldine base in a dedoped state represented by the following formula (2). The formed film was in contact with both electrodes (Fig. 3).

Next, a dedoped polyaniline nanofiber film formed on a glass substrate was immersed in a dopant solution 1 in which 1 g of ethanesulfonic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 19 g of distilled water at a temperature of 23 ° C. Redoping was performed by allowing the mixture to stand for 2 hours. Then, the membrane (hydrogen detection membrane) was dried with dry air for 12 hours to obtain a hydrogen sensor element. The thickness of the hydrogen detection film was measured with Dektak KXT (manufactured by BRUKER) and found to be 30 μm.

<Example 2>
Examples except that as the dopant solution for immersing the polyaniline nanofiber film, a dopant solution 2 in which 1 g of hydroxypropanesulfonic acid (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was dissolved in 19 g of distilled water was used instead of the dopant solution 1. A hydrogen sensor element was manufactured in the same manner as in 1. When the thickness of the hydrogen detection film was measured in the same manner as in Example 1, it was 30 μm.

<Example 3>
As the dopant solution for immersing the polyaniline nanofiber film, a dopant solution 3 in which 1 g of 4-fluorobenzenesulfonic acid (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) was dissolved in 19 g of distilled water was used instead of the dopant solution 1. A hydrogen sensor element was produced in the same manner as in Example 1 except for the above. When the thickness of the hydrogen detection film was measured in the same manner as in Example 1, it was 30 μm.

<Example 4>
As the dopant solution for immersing the polyaniline nanofiber film, a dopant solution 4 in which 1 g of pyridine-3-sulfonic acid (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was dissolved in 19 g of distilled water was used instead of the dopant solution 1. A hydrogen sensor element was produced in the same manner as in Example 1. When the thickness of the hydrogen detection film was measured in the same manner as in Example 1, it was 30 μm.

<Comparative example 1>
Example 1 except that a dopant solution 5 in which 1 g of camphor sulfonic acid (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was dissolved in 19 g of distilled water was used instead of the dopant solution 1 as the dopant solution for immersing the polyaniline nanofiber film. A hydrogen sensor element was manufactured in the same manner as in the above. When the thickness of the hydrogen detection film was measured in the same manner as in Example 1, it was 30 μm.

Table 1 shows the types of organic dopants used in Examples and Comparative Examples and their molecular volumes.
The molecular volume of the organic dopant was determined by DFT (Density Functional Theory; B3LYP / 6-31G + g (d)) calculation using the quantum chemistry calculation program "Gaussian 16" manufactured by HULINKS based on its molecular structure.

[Evaluation of hydrogen sensor element]
The sensitivity and reversibility of the hydrogen sensor elements obtained in Examples and Comparative Examples were evaluated by the following tests.
With reference to FIG. 4, the produced hydrogen sensor element is exposed to dry air overnight, and a pair of Au electrodes of the hydrogen sensor element 100 and a digital multimeter (“XDM3051” manufactured by OWON) are connected by a lead wire 401. , The hydrogen sensor element 100 was housed in an acrylic cylinder (container 402). Next, both ends of the cylinder were sealed with a rubber stopper 403 provided with an outlet of the lead wire 401 and a gas inlet / outlet.

While monitoring the electric resistance value with a digital multimeter, a test was conducted in which gas was flowed into the container 402 in the order of the following [1] to [4] for the following time. The test was carried out in an environment with a temperature of 23 ° C.
[1] Dry air with a flow rate of 10 L / min only (hydrogen concentration 0 vol%) for 10 minutes [2] Dry air with a flow rate of 10 L / min and dry air with a flow rate of 0.2 L / min (mixed gas with a hydrogen concentration of 2 vol%) for 10 minutes [3] Dry air with a flow rate of 10 L / min only (hydrogen concentration 0 vol%) for 10 minutes [4] Dry air with a flow rate of 10 L / min and dry air with a flow rate of 0.2 L / min (mixed gas with a hydrogen concentration of 2 vol%) for 10 minutes

Based on the results of the above test, the electrical resistance value change rates Z1 and Z2 defined as described above, and the index value of reversibility were determined according to the above formula. Table 1 shows the index value of reversibility and the rate of change of electrical resistance value Z1 (sensitivity index).

100 Hydrogen sensor element, 101 1st electrode, 102 2nd electrode, 103 Hydrogen detection membrane, 104 Substrate, 401 Lead wire, 402 Cylindrical container, 403 Rubber stopper.

Claims (4)

A hydrogen sensor element including a pair of electrodes and a hydrogen detection film arranged in contact with the pair of electrodes.
The hydrogen detection film contains a conjugated polymer and an organic dopant, and contains a conjugated polymer and an organic dopant.
The organic dopant is a hydrogen sensor element containing a dopant having a molecular volume of 0.20 nm ^{3 or less.} The hydrogen sensor element according to claim 1, wherein the conjugated polymer is a polyaniline-based polymer. The hydrogen sensor element according to claim 1 or 2, wherein the organic dopant is an organic acid. The hydrogen sensor element according to any one of claims 1 to 3, wherein the hydrogen detection membrane contains nanofibers of the conjugated polymer.

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