JP5045503B2 - Proton conducting membrane - Google Patents

Description

  The present invention relates to a proton conducting membrane, and more specifically, various types such as a polymer electrolyte fuel cell, a water electrolysis device, a hydrohalic acid electrolysis device, a salt electrolysis device, an oxygen and / or hydrogen concentrator, a humidity sensor, and a gas sensor. The present invention relates to a proton conductive membrane suitable as an electrolyte membrane used in an electrochemical device.

  A polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) in which a cathode electrode is provided on one side of a solid polymer electrolyte membrane and an anode electrode is provided on the other side. A plurality of single cells sandwiched between conductive separators are stacked. Each separator is formed with a flow path through which the reaction gas passes. An oxidant gas (air) is supplied to the flow path of the separator facing the cathode electrode, and a fuel gas containing hydrogen is supplied to the flow path of the separator facing the anode electrode, and an electrochemical reaction between oxygen and hydrogen occurs. The generated current is taken out. At the same time, water is generated at the cathode electrode, and the generated excess water is discharged outside through the flow path of the separator.

  When an electrolyte membrane mounted on this type of fuel cell is dried, its function as an ion exchange membrane is lowered. Therefore, the electrolyte membrane is humidified by a humidifier before the reaction gas is sent to the fuel cell. However, if a humidifier for humidifying the reaction gas is provided, a heat source such as a heater for heating water is required, or the humidifying temperature is strictly controlled so as to be the operating temperature of the fuel cell. The system configuration becomes complicated because it is necessary. Therefore, if these systems can be eliminated, the efficiency of the battery can be greatly improved.

  On the other hand, a low EW (equivalent weight) type electrolyte membrane has been proposed as an electrolyte membrane exhibiting high proton conductivity with low humidification. However, most of the low EW type electrolyte membranes have a high water content, swell significantly in water, and are easily broken during battery operation.

In order to solve this problem, various proposals have conventionally been made.
For example, in Patent Document 1, a silica porous membrane having a pore diameter of 500 nm and a porosity of 74% is prepared using polystyrene as a template, and a sulfonic acid group is introduced into the pore surface of the silica porous membrane. An ionic conductor impregnated with ethyl imidazolium triflate (2EtHImTf) is disclosed.
This document describes that impregnation of a porous silica membrane whose surface is modified with a sulfonic acid group is improved in ionic conductivity as compared with ionic liquid alone.

In Patent Document 2, a porous silica film having a pore diameter of 500 nm was prepared using polystyrene as a template, and impregnated with 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF ₄ ) in the pores. An ionic conductor is disclosed.
This document describes that when a porous silica membrane is impregnated with an ionic liquid, the ionic conductivity is improved over both the ionic liquid alone and the ionic conductor obtained by impregnating polyimide with an ionic liquid.

JP 2007-311311 A JP 2007-035301 A

The ionic liquid is durable even at 100 ° C. or higher and exhibits high proton conductivity. When the porous silica membrane is impregnated with such an ionic liquid, a self-supporting proton conducting membrane that can be used in an intermediate temperature range is obtained.
Here, when the porous membrane is filled with an electrolyte such as an ionic liquid, in general, the larger the pore diameter, the easier the electrolyte flows out. Moreover, the increase in the pore diameter causes a decrease in the strength of the porous film. Therefore, the smaller the pore diameter of the porous membrane, the better as long as the electrolyte can be filled in the pore and the proton conduction in the pore can be achieved.
However, a porous silica film using polystyrene as a mold can only obtain a porous film having a relatively large pore diameter (about 500 nm) because the pore diameter is determined by the particle diameter of the polystyrene particles. Therefore, in the composite membrane obtained by the conventional method, the ionic liquid may flow out from the pores or the membrane strength may be reduced.

In addition, in order to reduce the proton conduction resistance in the membrane, the shorter the proton conduction path, the better. However, the pores in the porous silica membrane using polystyrene as a mold have a shape in which spherical pores communicate with each other through a narrow passage. For this reason, not only protons that travel linearly, but also those that diverge to the surrounding spheres, and there is a waste in the proton conduction path.
Furthermore, in order to produce an MEA using a conventional electrolyte membrane, two steps are necessary: a step of producing a self-supporting membrane and a step of joining the membrane and an electrode. Such a two-step manufacturing process may decrease the adhesion between the electrode and the electrolyte membrane, or may increase the manufacturing cost.

The problem to be solved by the present invention is to provide a proton conductive membrane that has no risk of electrolyte flowing out from the pores, has high strength, and is excellent in proton conductivity.
Another problem to be solved by the present invention is to provide a proton conducting membrane that exhibits high proton conductivity in the middle temperature range.
Furthermore, another problem to be solved by the present invention is to provide a proton conducting membrane that has high electrode / electrolyte membrane adhesion and can reduce manufacturing costs.

In order to solve the above problems, the proton conducting membrane according to the present invention is:
An inorganic porous membrane having an average pore diameter of 1 nm or more and less than 20 nm ;
E Bei and an electrolyte filled in the pores of the inorganic porous membrane,
The inorganic porous membrane has a linear pore structure obtained by self-organizing a metal oxide precursor using a surfactant as a template and removing the surfactant.
And this is the gist.

In the proton conducting membrane according to the present invention, since the average pore diameter of the inorganic porous membrane is 1 to 20 nm, there is little risk of electrolyte leakage and the strength is high. Moreover, since it has a pore shape with few irregularities, the proton conduction resistance is relatively low. Furthermore, when an ionic liquid is used as the electrolyte impregnated in the pores, a proton conducting membrane exhibiting high proton conductivity in the middle temperature range can be obtained.
Such a proton conductive membrane can be formed by coating a sol solution on the electrode plate, and therefore has high adhesion between the electrode and the electrolyte membrane. Moreover, since the surface of the opposite surface of the proton conducting membrane is extremely smooth, the adhesion between the electrode formed on the opposite surface and the electrolyte membrane is high.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Proton conducting membrane]
The proton conducting membrane according to the present invention includes an inorganic porous membrane and an electrolyte.

[1.1 Inorganic porous membrane]
In the present invention, the inorganic porous membrane is one having an average pore diameter of 1 to 20 nm.
When the average pore diameter becomes too small, it becomes difficult to fill the electrolyte. Therefore, the average pore diameter is preferably 1 nm or more.
On the other hand, if the average pore diameter is too large, the electrolyte retention is reduced, or the strength of the inorganic porous membrane is reduced. Therefore, the average pore diameter is preferably 20 nm or less.

As described later, the inorganic porous membrane is obtained by self-organizing a metal oxide precursor (for example, alkoxide) using a surfactant as a template and removing the surfactant. When polystyrene beads are used as a template, a pore structure is formed in which pores having a relatively large inner diameter are connected by a tunnel having a relatively small inner diameter. On the other hand, when a surfactant is used as a template, a linear pore structure (a structure having unevenness of 20% or less of the diameter) with substantially less unevenness is obtained.
When the type of surfactant to be used and the production conditions are optimized, all or part of the pores are regularly arranged to form a proton conduction path having a linear pore structure.
For example, when a cationic surfactant is used, an inorganic porous film having a cubic structure, a 3d-hexagonal structure, or a 2-hexagonal structure is obtained. Further, when a nonionic surfactant is used, an inorganic porous film having a pore structure of 2d-hexagonal structure is obtained. Further, when an anionic surfactant is used, an inorganic porous film having a cubic structure, a 3d-hexagonal structure, or a 2-hexagonal structure is obtained.

The inorganic porous film contains a metal oxide as a main component. With the metal oxide, a porous film having the above-described pore diameter and pore shape can be obtained relatively easily.
Specific examples of the metal oxide constituting the inorganic porous film include alumina, silica, titania, zirconia, and the like. The inorganic porous film may be composed of any one of these, or may be a composite composed of two or more.

The inorganic porous membrane may have a proton donating functional group modified on the pore wall. If the pore wall is modified with a proton-donating functional group, the resistance due to the inorganic wall can be offset, so that the proton conductivity of the entire membrane may be improved.
Specific examples of the proton-donating functional group include a sulfonic acid group, a phosphonic acid group, and a carboxylic acid group. The pore wall may be modified with any one of these, or may be modified with two or more.

[1.2 Electrolyte]
In the present invention, the type of electrolyte filled in the pores is not particularly limited, and various electrolytes can be used. Specific examples of the electrolyte include a solid polymer electrolyte and an ionic liquid. The pores may be filled with any one of these, or may be filled with two or more.

Specifically, as a solid polymer electrolyte,
(1) Polyamide, polyacetal, polyethylene, polypropylene, acrylic resin, polyester, polysulfone, polyether, etc. in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains, or derivatives thereof (aliphatic carbonization) Hydrogen electrolyte),
(2) Polystyrene having an acid group such as a sulfonic acid group introduced into any of the polymer chains, polyamide having an aromatic ring, polyamideimide, polyimide, polyester, polysulfone, polyetherimide, polyethersulfone, polycarbonate, or the like, or , Derivatives thereof (partial aromatic hydrocarbon electrolytes),
(3) Polyetheretherketone, polyetherketone, polysulfone, polyethersulfone, polyimide, polyetherimide, polyphenylene, polyphenylene ether, polycarbonate, in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains, Polyamide, polyamideimide, polyester, polyphenylene sulfide, etc., or their derivatives (fully aromatic hydrocarbon electrolytes),
(4) Polystyrene-graft-ethylenetetrafluoroethylene copolymer, polystyrene-graft-polytetrafluoroethylene, etc. in which an acid group such as a sulfonic acid group is introduced into any of the polymer chains, or derivatives thereof (parts) Fluorine electrolyte),
(5) Nafion (registered trademark) manufactured by DuPont, Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., or their derivatives (perfluorinated electrolytes),
and so on.

  An ionic liquid consists of what a cation and an anion have ion-bonded. The combination of a cation and an anion is not specifically limited, It becomes various ionic liquids by combining various cations and anions.

Specifically, as the cation,
(1) Imidazolium such as 2-ethylimidazolium, 3-propylimidazolium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1,3-dimethylimidazolium,
(2) ammonium such as diethylmethylammonium, tetrabutylammonium, cyclohexyltrimethylammonium, methyltri-n-octylammonium, triethyl (2-methoxyethoxymethyl) ammonium, benzyldimethyltetradecylammonium, benzyltrimethylammonium,
(3) There are pyrrolidinium, pyridinium, phosphonium, sulfonium and the like.

Specifically, as an anion,
(1) Halogens such as Cl ⁻ , Br ⁻ and I ⁻ ,
(2) HSO ₄ ⁻ , MeSO ₄ ⁻ , CF ₃ SO ₃ ⁻ , C ₂ H ₅ SO ₄ ⁻ , C ₆ H ₁₃ SO ₄ ⁻ , C ₄ H ₉ SO ₄ ⁻ , C ₈ H ₁₇ SO ₄ ⁻ , C ₆ H ₄ SO ₃ ^- sulfates such as and sulfonic acids,
(3) Amides and imides such as (CN) ₂ N ⁻ , [N (CF ₃ ) ₂ ] ⁻ , [N (SO ₂ CF ₃ ) ₂ ] ⁻ ,
_{(4) [HC (SO 2} CF 3) 2] -, C (SO 2 CF 3) 3 - methanes such as,
(5) BF ₄ ⁻ , B (CN) ₄ ⁻ , borate salts such as compounds represented by the formulas (a) to (e),
(6) Phosphate such as (C ₂ F ₅ ) ₂ P (O) O ⁻ , PF ₆ ⁻ , (C ₃ F ₇ ) ₃ PF ₃ ⁻ , the compound represented by formula (f), and SbF ₆ ⁻ Antimony such as
(7) C ₁₀ H ₂₁ COO ⁻ , CF ₃ COO ⁻ , Co (CO) ₄ ⁻
and so on.
Among these, those in which the cation component is imidazolium or ammonium have high heat resistance and high proton conductivity, and are particularly suitable as an ionic liquid filled in the pores.

  The ionic liquid is usually in a state in which a cation component and an anion component are ionically bonded. When such an ionic liquid is introduced into the pores of the inorganic porous membrane, when the pore walls are modified with proton donating functional groups, after introducing the ionic liquid into the pores, all of the anionic components Or a part can be removed. The ion balance is maintained by ion exchange between the proton of the proton donating functional group and the cation component.

  The optimum filling amount of electrolyte in the pores is selected according to the purpose. In general, the higher the electrolyte filling amount in the pores, the higher the proton conductivity.

[2. Proton Conductive Membrane Manufacturing Method]
The proton conducting membrane according to the present invention can be produced by various methods. An example is shown below.
The method for producing a proton conductive membrane according to the present invention includes a first step for producing an inorganic porous membrane and a second step for impregnating the inorganic porous membrane with an electrolyte.

[2.1 First step]
First, an inorganic porous film that satisfies the above-described conditions is manufactured. Specifically, the inorganic porous membrane is obtained by partially polymerizing a metal oxide source (partial polymerization step), mixing this with a surfactant to form a complex (complex formation step), and including the complex. It is obtained by applying the solution to the substrate surface and drying it (thin film forming step). Moreover, after forming a thin film, a proton donating functional group can also be introduce | transduced into the inner wall of a pore (proton donating functional group introduction process).
The introduction of the proton-donating functional group and the introduction of the electrolyte into the pores are preferably performed after removing the surfactant from the thin film, but may be performed before removing the surfactant.

[2.1.1 Partial polymerization step]
The partial polymerization step is a step of obtaining a solution containing the partial polymer of the metal oxide source by reacting the metal oxide source in an acidic solvent.
When one or more compounds containing one type of metal element are used as the metal oxide source, an inorganic porous film made of a metal oxide containing one type of metal element can be obtained. On the other hand, when two or more compounds containing two or more metal elements are used as the metal oxide source, an inorganic porous film made of a metal oxide containing two or more metal elements can be obtained. In any case, in order to obtain a partial polymer, it is preferable to use an alkoxide as the metal oxide source.

For example, it is preferable to use a silicon alkoxide represented by the following formula (1) as the silica source.
A _(4-a) -Si- (OR) _a (1)
However, R is a hydrocarbon group. A is a hydrogen atom, a halogen atom, a hydroxyl group, or a hydrocarbon group. a is an integer of 1 to 4.
The hydrocarbon group R may be any of a chain type, a return type, and a fat return type. The hydrocarbon group R is preferably a chain alkyl group having 1 to 5 carbon atoms, and particularly preferably a methyl group or an ethyl group.
When A is a hydrocarbon group, the hydrocarbon group A is preferably an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 1 to 10 carbon atoms, a phenyl group, a substituted phenyl group, or the like.

As silicon alkoxide, specifically,
(1) Tetraalkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, dimethoxydiethoxysilane,
(2) Trimethoxysilanol, triethoxysilanol, trimethoxymethylsilane, trimethoxyvinylsilane, triethoxyvinylsilane, triethoxy-3-glycidoxypropylsilane, 3-mercaptopropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, γ- (methacryloxypropyl) trimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, etc. Trialkoxysilane,
(3) dialkoxysilanes such as dimethoxydimethylsilane, diethoxydimethylsilane, diethoxy-3-glycidoxypropylmethylsilane, dimethoxydiphenylsilane, and dimethoxymethylphenylsilane;
and so on.
Among these, tetramethoxysilane (Si (OCH ₃ ) ₄ ) and tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) are particularly useful as silica sources because a silica porous film with good crystallinity can be obtained. Is preferred.

Specifically, as a metal oxide source other than the silica source,
(1) Al-containing alkoxides such as aluminum butoxide (Al (OC ₄ H ₉ ) ₃ ), aluminum ethoxide (Al (OC ₂ H ₅ ) ₃ ), aluminum isopropoxide (Al (OC ₃ H ₇ ) ₃ ) ,
(2) Ti such as titanium isopropoxide (Ti (Oi-C ₃ H ₇ ) ₄ ), titanium butoxide (Ti (OC ₄ H ₉ ) ₄ ), titanium ethoxide (Ti (OC ₂ H ₅ ) ₄ ), etc. Containing alkoxide,
(3) Zr such as zirconium isopropoxide (Zr (Oi-C ₃ H ₇ ) ₄ ), zirconium butoxide (Zr (OC ₄ H ₉ ) ₄ ), zirconium ethoxide (Zr (OC ₂ H ₅ ) ₄ ) Containing alkoxide,
and so on.

When the metal oxide source described above is blended at a predetermined ratio and then hydrolyzed and polycondensed under acidic conditions, a partial polymer of the metal oxide source is obtained.
When an acid is added to a solution containing an alkoxide (aqueous solution, alcohol solution, etc.), all or part of the alkoxyl group (—OR) is hydrolyzed to a hydroxyl group (—OH), and the hydroxyl group is condensed to increase the molecular weight. . In the partial polymer, some alkoxyl groups and / or hydroxyl groups remain unreacted.
As the acid, hydrochloric acid, nitric acid, boric acid, bromic acid, fluorine acid, sulfuric acid, phosphoric acid and the like can be used. These acids are used after being diluted with a suitable solvent (for example, water, alcohol, etc.).
The optimum pH, reaction temperature, reaction time, etc. of the solution are selected according to the type of metal oxide source, the mixing ratio, and the like. For example, in the case of silicon alkoxide, hydrolysis and polycondensation can be promoted as the pH decreases. The reaction temperature is preferably 15 to 25 ° C., and the reaction time is preferably 30 to 90 minutes.

[2.1.2 Complex formation step]
The complex forming step is a step of adding a surfactant to a solution containing a partial polymer to obtain a solution containing a complex in which the partial polymer is adsorbed around the micelle of the surfactant.
When a surfactant is added to the solution containing the partial polymer, the surfactant forms micelles in the solution. This micelle becomes a supramolecular template, and a complex is formed by adsorbing a partial polymer around it. Since the partial polymer does not enter the interior of the micelle, the interior of the micelle eventually becomes a pore portion. Therefore, the pore diameter in the thin film can be controlled by controlling the molecular chain length of the surfactant.

  The surfactant may be any of a cationic surfactant, an anionic surfactant, or a nonionic surfactant. Depending on the type of surfactant to be used, the pore structure when the film is formed can be changed.

Specific examples of the cationic surfactant include alkyl quaternary ammonium salts represented by the following formula (2).
CH ₃ — (CH ₂ ) _n —N ⁺ (R ₁ ) (R ₂ ) (R ₃ ) X ⁻ (2)
(2) wherein, R _1, R _2, R ₃ each represent an alkyl group having 1 to 3 carbon atoms. R ₁ , R ₂ and R ₃ may be the same as or different from each other. In order to facilitate aggregation (formation of micelles) between alkyl quaternary ammonium salts, it is preferable that R ₁ , R ₂ , and R ₃ are all the same. Further, at least one of R ₁ , R ₂ , and R ₃ is preferably a methyl group, and all are preferably methyl groups.
(2) In the formula, X represents a halogen atom. Although the kind of halogen atom is not particularly limited, X is preferably Cl or Br in view of availability.
(2) In formula, n represents the integer of 7-21.

Specific examples of the anionic surfactant include fatty acid salts, alkyl sulfonates, and alkyl phosphates.
Specific examples of nonionic surfactants include polyethylene oxide nonionic surfactants and primary alkylamines.

  When adding a surfactant to a solution containing a partial polymer, the reaction conditions such as the molar ratio of the partial polymer to the surfactant, the amount of solvent, and the concentration of acid in the solution affect the crystallinity of the thin film. . These conditions are selected optimally according to the type and blending ratio of the metal oxide source.

For example, when silicon alkoxide is used as the main metal oxide source and a cationic surfactant is used as the surfactant, the reaction is preferably performed under the following conditions.
If the amount of the surfactant with respect to the metal oxide source is too small, the amount of the surfactant is insufficient and continuous micelles cannot be formed. Therefore, the surfactant is preferably 0.005 mol or more with respect to 0.1 mol of the metal oxide source.
On the other hand, when the amount of the surfactant is excessive, a lamellar substance is generated, and when the surfactant is removed, only a laminate of sheets is obtained, and an inorganic porous film is not obtained. Accordingly, the surfactant is preferably 0.02 mol or less with respect to 0.1 mol of the metal oxide source.
The reaction temperature is preferably 10 to 30 ° C., and is preferably stirred for 30 to 90 minutes.

  The amount of the solvent is preferably 0.2 to 10 mol with respect to 0.1 mol of the metal oxide source. It is preferable to use water, alcohol or the like as the solvent. The solvent preferably contains at least 0.2 mol of water. If the amount of the solvent is too small, it becomes difficult to condense the silicon alkoxide in a chain form. On the other hand, when the amount of the solvent is excessive, the concentration of the metal oxide source in the solution and the viscosity of the solution are lowered, and a uniform thin film cannot be obtained.

In the case of producing a composite, if the acid concentration in the solution is too low, the hydrolysis rate and polycondensation rate are slowed, making it difficult to produce a thin film. Accordingly, the acid concentration is preferably 0.00057 eq / L or more. The concentration of the acid is more preferably 0.00059 eq / L or more.
On the other hand, if the acid concentration is excessive, the hydrolysis rate and polycondensation rate become too fast, and a homogeneous polymer cannot be obtained. Further, the crystallinity of the thin film, the smoothness of the surface, and the orientation of the pores are insufficient. Accordingly, the acid concentration is preferably 0.0086 eq / L or less. The concentration of the acid is more preferably 0.0080 eq / L or less.

Similarly, if the acid content in the solution is too small, the hydrolysis rate and polycondensation rate are slowed, making it difficult to produce a thin film. Therefore, the acid content is preferably 2.3 × 10 ⁻⁴ mol or more with respect to 0.1 mol of the metal oxide source. The acid content is more preferably 2.4 × 10 ⁻⁴ mol or more.
On the other hand, when the acid content is excessive, the hydrolysis rate and the polycondensation rate become too fast, and a homogeneous polymer cannot be obtained. Further, the crystallinity of the thin film, the smoothness of the surface, and the orientation of the pores are insufficient. Accordingly, the acid content is preferably 3.8 × 10 ⁻⁴ mol or less. The content of the acid is more preferably 3.5 × 10 ⁻⁴ mol or less.

  Furthermore, the viscosity of the solution containing the composite is preferably 10 Pa · s or less, and more preferably 5 Pa · s or less. When the viscosity of the solution is too high, not only thinning becomes difficult, but also the uniformity of the pore arrangement of the thin film decreases.

In the case of producing a composite, the pore structure when formed into a film can be controlled by controlling the type and addition amount of the surfactant.
For example, in the case of producing a mesoporous silica thin film, when tetramethoxysilane is used as the silicon alkoxide and alkyltrimethylammonium chloride is used as the surfactant, alkyltrimethylammonium chloride is added in an amount of 0.04 to 0.04 to 1 mol of tetramethoxysilane. When the amount is 0.15 mol, a thin film having a pore structure of 3d-hexagonal structure can be obtained.
For example, when alkyltrimethylammonium chloride is 0.15 to 0.19 with respect to 1 mol of tetramethoxysilane, a thin film having a cubic pore structure can be obtained.
For example, when tetramethoxysilane is used as the silicon alkoxide and nonionic Pluronic P123 is used as the surfactant, 2d-hexagonal is obtained when the surfactant is 0.005 to 0.15 mol with respect to 1 mol of silicon alkoxide. A thin film having a pore structure can be obtained.

[2.1.3 Thin film formation process]
The thin film forming step is a step in which a solution containing the composite is applied to the substrate surface and dried.
When the solution is applied to the substrate surface, the complex in which the partial polymer surrounds the surfactant micelle is arranged in a stable direction. When this is dried, polycondensation occurs between the arranged complexes.

The substrate is not particularly limited, and various substrates can be used according to the purpose. Specific examples of the substrate include a plate made of a metal, a resin, or the like, a metal oxide such as a film or glass.
The method for applying the solution is not particularly limited, and various coating methods can be employed. Specifically, as a coating method, a bar coater, a roll coater, a gravure coater, a dip coater, a spin coater, a spray coater, or the like can be used.

  After the solution is applied to the substrate to form a thin film, the thin film is air-dried or heat-dried. When drying by heating, the drying temperature is preferably 70 to 150 ° C, more preferably 100 to 120 ° C. As the drying time, an optimal time is selected according to the drying temperature.

When the surfactant is removed from the thin film after drying, an inorganic porous film having pores with few irregularities (pores with irregularities of 20% or less of the diameter) is obtained. As a method for removing the surfactant,
(1) A firing method for firing a thin film at 300 to 1000 ° C. (preferably 300 to 600 ° C.) for 30 minutes or longer (preferably 1 hour or longer) in the air or under an inert atmosphere,
(2) The thin film is immersed in a good solvent for the surfactant (for example, methanol containing a small amount of hydrochloric acid), stirred while heating at a predetermined temperature (for example, 50 to 70 ° C.), and the surfactant in the thin film Extract the ion exchange method,
and so on.

[2.1.4 Proton-donating functional group introduction step]
The obtained inorganic porous membrane may be used for electrolyte filling as it is, or before that, a proton donating functional group may be introduced into the pore inner wall surface. There are various methods for introducing a proton-donating functional group.

For example, in the method of introducing a sulfonic acid group into the pore inner wall surface,
(1) A method of producing an inorganic porous film using an alkoxide having a mercapto group as a starting material, and oxidizing the mercapto group with hydrogen peroxide,
(2) An inorganic porous film is produced using an alkoxide having an organic group capable of introducing a sulfonic acid group (for example, an aromatic ring) as a starting material, and a sulfonated agent such as fuming sulfuric acid, sulfuric anhydride, chlorosulfonic acid, etc. A method of sulfonating an organic group using
(3) A method in which an inorganic porous film is placed in a mixed solution of 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethanesulfonic acid sultone and anhydrous toluene and heated to reflux at 120 ° C. for 6 hours.
(4) A method of introducing an organic group into the inner wall surface of the pore using a silane coupling agent, and sulfonating the organic group,
and so on.

Moreover, as a method of introducing a phosphate group into the pore inner wall,
(1) An inorganic porous membrane is prepared using an alkoxide having an organic group capable of introducing a phosphate group as a starting material, and a phosphate group is introduced into the organic group using a phosphorylating agent such as phosphorus oxychloride. Method,
(2) A method in which an organic group introduced into an inorganic porous membrane is chloromethylated, and a chloromethyl group and triethyl phosphite are reacted and hydrolyzed (3) Using a silane coupling agent on the inner wall surface of the pore A method of introducing an organic group and phosphorylating the organic group,
and so on.

Furthermore, in the method of introducing a carboxylic acid group into the pore inner wall surface,
(1) A method of producing an inorganic porous film using an alkoxide having an organic group whose side chain group or terminal group is a methyl group as a starting material, and oxidizing the methyl group,
(2) A method of oxidizing an organic group by introducing an organic group having a methyl group on the inner wall surface of the pore using a silane coupling agent,
and so on.

[2.2 Second step]
The second step is a step of impregnating the inorganic porous membrane with the electrolyte.
When a polymer electrolyte is used as the electrolyte, the polymer electrolyte is dissolved in an appropriate solvent, and the solution is filled in the pores. If the solvent is removed after filling, the proton conducting membrane according to the present invention is obtained. Further, the solid polymer electrolyte may be melted and the melt may be filled in the pores.

Similarly, when an ionic liquid is used as the electrolyte, the ionic liquid may be liquefied as it is or by heating, and filled in the pores, or may be dissolved in an appropriate solvent and the solution filled in the pores. good.
Furthermore, after filling the ionic liquid, the anion component can be selectively removed by washing the membrane with a good solvent for the anion component. As the solvent for removing the anion component, an optimum solvent is selected according to the kind of the ionic liquid.

[3. MEA Manufacturing Method]
The method for producing MEA using the proton conducting membrane according to the present invention includes:
(1) a first method of joining a separately produced proton conducting membrane and an electrode;
(2) a second method in which an electrode is used as a substrate, a solution containing the above-described composite is applied to the electrode surface to form an inorganic porous film, and the inorganic porous film is impregnated with an electrolyte;
and so on. In the case of the second method, the other electrode can be formed on the surface of the proton conducting membrane by a method of applying or printing a catalyst ink, a method of transferring an electrode sheet, a vapor deposition method, a sputtering method, or the like.

In either method, the electrode
(1) A catalyst ink containing a carrier carrying an electrode catalyst (for example, Pt / C) and a polymer electrolyte is applied to the substrate surface and dried.
(2) A hydrogen selective permeable membrane made of Pd or the like is formed on the surface of a porous support made of Ni or the like, and an electrode catalyst is supported as required,
(3) A carbon membrane having pores that can selectively permeate hydrogen and, if necessary, an electrode catalyst supported thereon,
(4) On the surface of a porous support made of Ni or the like, a carbon film having pores capable of selectively permeating hydrogen is formed, and an electrode catalyst is supported as necessary,
Etc. can be used.
When the electrode includes a porous support, the porous support includes a first layer having an average pore diameter d ₁ of 0.1 μm ≦ d ₁ ≦ 0.5 μm, and an average pore diameter d ₂ of 0.5 μm ≦ d. Those having a two-layer structure of the second layer satisfying ₂ ≦ 3.0 μm are preferable. In this case, the hydrogen selective permeable membrane or the carbon membrane is formed on the first layer.

When the electrode includes a carbon film, the carbon film preferably has an average pore diameter of 1 nm or less. Such a carbon film is, for example,
(1) A polyimide precursor solution is applied to the surface of a suitable substrate (for example, Ni porous film), and kept at 60 ° C. for 4 hours to volatilize the solvent,
(2) Hold at 350 ° C. for 1 hour in a non-oxidizing atmosphere to advance the imidization reaction to form a polyimide film,
(3) Hold at 600 ° C. for 1 hour in a non-oxidizing atmosphere to carbonize the polyimide film.
Can be manufactured.

The porous support for supporting the hydrogen permselective membrane such as Pd or carbon membrane is obtained by, for example, press-molding a metal powder (for example, Ni powder) having an appropriate particle size at an appropriate pressure and sintering it. Can be manufactured.
A multilayer porous support having different average pore diameters can be produced by filling metal powders having different particle diameters into a multilayer, press-molding at an appropriate pressure, and sintering.

[4. Action of proton conducting membrane according to the present invention]
In the proton conducting membrane according to the present invention, since the average pore diameter of the inorganic porous membrane is 1 to 20 nm, there is little risk of electrolyte leakage and the strength is high. Moreover, since it has a pore shape with few irregularities, the proton conduction resistance is relatively low. Furthermore, when an ionic liquid is used as the electrolyte impregnated in the pores, a proton conducting membrane exhibiting high proton conductivity in the middle temperature range can be obtained.
Such a proton conductive membrane can be formed by coating a sol solution on the electrode plate, and therefore has high adhesion between the electrode and the electrolyte membrane. Moreover, since the surface of the opposite surface of the proton conducting membrane is extremely smooth, the adhesion between the electrode formed on the opposite surface and the electrolyte membrane is high.

(Examples 1 and 2)
[1. Preparation of sample]
[1.1 Example 1]
Four Pt electrodes were vapor-deposited on the glass substrate. A sol solution mainly composed of tetramethylorthosilicate (TMOS) and octadecyltrimethylammonium chloride (ODCTMA) was prepared on this glass substrate. The composition of the sol solution was TMOS / ODCTMA / H ₂ O / HCl = 1 / 0.1 / 7.8 / 3.4 / 0.006 (molar ratio).
This sol solution was dip-coated on a glass substrate and baked at 400 ° C. for 4 hours to burn off ODCTMA, thereby preparing a mesoporous silica thin film having pores with a 3d-hexagonal structure. On this thin film, 3-propylimidazolium trifluoromethanesulfonylimide (ionic liquid) represented by the formula (3) was applied with a brush. For the purpose of degassing the air in the pores and filling the ionic liquid, the sample was placed in a vacuum desiccator and the vacuum atmosphere was repeated.
Then, it was left still for half a day under atmospheric pressure, the film surface was washed with hexane (an ionic liquid poor solvent), and the thin film surface was wiped down.

[1.2 Example 2]
3-Mercaptopropyltrimethoxysilane (MPTMS) 0.80g and TMOS: 0.91g were fractioned so that it might become MPTMS / TMOS = 2/3 (molar ratio), and it stirred for 10 minutes. Then, 5 ml of EtOH was added and stirred for 10 minutes, and an aqueous hydrochloric acid solution was further added and stirred for 1 hour.
In this solution,
(1) ODCTMA: 1.1 g, EtOH: 10 mL, H ₂ O: 100 μL, 2N-HCl: 10 μL previously mixed, and
(2) 30% hydrogen peroxide water 5g
Was added and stirred for another 2 hours to prepare a sol solution.
A glass substrate with a Pt electrode similar to that in Example 1 was coated with a sol solution using a dip coater. The coated substrate was allowed to stand for 1 day and then dried at 100 ° C. for 1 hour. Next, the surfactant was removed by immersing in HCl-added EtOH at 60 ° C. for 2 hours. Further, the substrate was immersed in a 10% hydrogen peroxide solution to oxidize mercapto groups (—SH) and convert them into sulfonic acid groups (—SO ₃ H). In the case of the above composition ratio, the acid amount is estimated to be 1.8 mmol / g.

[2. Test method]
The proton conductivity was measured by a 4-terminal DC method. The measurement conditions are as follows.
Humidity: 0%
Temperature: 25-180 ° C
Gas atmosphere: H ₂ 10% ・ N ₂ bal.
In addition, the measurement measured the initial value and the value after 45 minutes at each temperature. Moreover, the measurement was sequentially performed from a low temperature.

[3. result]
FIG. 1 shows the result. The proton conductive membrane obtained in Example 1 showed higher proton conductivity as the temperature was higher. In addition, the proton conductivity membrane obtained in Example 2 increased in proton conductivity at room temperature as compared with Example 1.

(Example 3, Comparative Example 1)
[1. Preparation of sample]
[1.1 Example 3]
A proton conducting membrane was produced according to the same procedure as in Example 1. The film thickness was about 800 nm.
[1.2 Comparative Example 1]
A sol solution mainly composed of TMOS and polystyrene bead (φ90 nm) dispersion was dip coated on a glass substrate with a Pt electrode. Next, the glass substrate was baked at 400 ° C. × 4 h and 700 ° C. × 3 h to burn out the beads, thereby producing a porous silica film. The film thickness was about 900 nm. Thereafter, in the same manner as in Example 1, the porous silica membrane was filled with the ionic liquid.

[2. Test method]
Of the four Pt electrodes, 0.5 V was applied to the two end electrodes, and the current flowing through the both end electrodes and the voltage between the two center electrodes were measured continuously. The conductivity was calculated from the continuously measured current and voltage.
In this state, 0.5 mL of EtOH (an ionic liquid good solvent) was gently dropped onto the film surface on the glass substrate. EtOH wetted the entire membrane instantly. Immediately after that, the sample was set up vertically, and EtOH and the ionic liquid eluted therein were allowed to flow.

[3. result]
A change in conductivity was observed by flowing EtOH from the membrane surface. Table 1 shows the results. From Table 1, in Comparative Example 1 with large pores, the decrease in conductivity by EtOH cleaning is about 1/1000, while in Example 3 with mesopores, conduction by EtOH cleaning. It can be seen that the degree of decrease is about ½. This indicates that the ionic fluid in the pores tends to flow out more in the large pore membrane.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

  The proton conducting membrane according to the present invention is used in various electrochemical devices such as solid polymer fuel cells, water electrolysis devices, hydrohalic acid electrolysis devices, salt electrolysis devices, oxygen and / or hydrogen concentrators, humidity sensors, and gas sensors. It can be used as an electrolyte membrane to be used.

It is a figure which shows the relationship between the temperature of the proton conductive membrane obtained in Example 1 and Example 2, and proton conductivity.

Claims (6)

An inorganic porous membrane having an average pore diameter of 1 nm or more and less than 20 nm ;
An electrolyte filled in the pores of the inorganic porous membrane;
With
The inorganic porous membrane has a linear pore structure obtained by self-organizing a metal oxide precursor using a surfactant as a template and removing the surfactant.
Flop proton-conducting membrane. The inorganic porous membrane include alumina, silica, titania, and the proton conducting membrane according to claim 1 comprising at least one of the metals oxide selected from zirconia.   The proton conductive membrane according to claim 1 or 2, wherein the inorganic porous membrane has a proton donating functional group modified on a pore wall.   The proton conductive membrane according to any one of claims 1 to 3, wherein the electrolyte is an ionic liquid.   The proton conductive membrane according to claim 4, wherein the ionic liquid comprises at least one cation component selected from imidazolium and ammonium.   The proton conductive membrane according to claim 4 or 5, which is obtained by filling the inorganic porous membrane with the ionic liquid and then removing all or part of an anionic component constituting the ionic liquid.

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