JP2005332801A - Proton conductive film, combined proton conductivity film, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton conductive film, a combined proton conductive film, and a fuel cell wherein they are superior in heat resistance, fluctuations of a proton conductive performance due to humidity changes are small, and proton conductive performance is superior under a high temperature and a low humidity. <P>SOLUTION: The proton conductive film consists of a continuous body of minute particles of a silicon-oxygen cross-linked structure having sulfonic acid groups on the surface, wherein pores penetrating the film are formed between the minute particles, the total pore volume of the pores measured by a BET method is 0.3 cm<SP>3</SP>/g or less, and the ion exchange capacity of the pores is 0.7 meq/g or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a proton conductive membrane, a composite proton conductive membrane, and a fuel cell that are excellent in heat resistance, have a small fluctuation in proton conductive performance due to changes in humidity, and are particularly excellent in proton conductive performance under high temperature and low humidity.

Since fuel cells have high power generation efficiency and excellent environmental characteristics, in recent years, fuel cells have attracted attention as next-generation power generation devices that can contribute to solving environmental problems and energy problems that have become major social issues.
Fuel cells are generally classified into several types according to the type of electrolyte. Among them, polymer electrolyte fuel cells (hereinafter also referred to as PEFC) are smaller and have higher output than any other type. In addition, it is regarded as the next-generation main power source for small-sized on-site type, for example, a mobile power source such as a power source of a vehicle, and a portable power source, and development for practical use is actively performed.

In PEFC, hydrogen is usually used as a fuel. Hydrogen is decomposed into protons (hydrogen ions) and electrons by a catalyst installed on the anode side. Electrons obtained by the decomposition are supplied to the outside and used as electricity, and then circulated to the cathode side. On the other hand, protons obtained by decomposition move to the cathode side through the proton conductive membrane (electrolyte membrane). On the cathode side, protons, circulated electrons, and oxygen supplied from the outside react with each other through a catalyst to form water. That is, PEFC is a very clean energy source that extracts electricity when making water from hydrogen and oxygen.
As the fuel for fuel cells, hydrogen is mainly used as described above, but fuel other than hydrogen such as alcohol, ether, hydrocarbons, etc. is used, and fuel that extracts protons and electrons from these fuels using a catalyst. Batteries are also being considered. Examples of such a fuel cell include a direct methanol fuel cell (hereinafter also referred to as DMFC) using methanol (usually used as an aqueous solution) as fuel.

In fuel cells such as PEFC and DMFC, the proton conductive membrane has a role of conducting protons generated on the anode side to the cathode side. This proton conduction occurs in concert with the flow of electrons. Therefore, in order to obtain a high output, that is, a high current density in the fuel cell, it is necessary to conduct protons through the proton conductive membrane sufficiently and at high speed. Thus, it is no exaggeration to say that the proton conductive membrane is a key material that determines the performance of the fuel cell.
The proton conductive membrane also serves as an insulating film that electrically insulates the anode side and the cathode side, and a fuel barrier that prevents fuel such as hydrogen supplied to the anode side from leaking to the cathode side. It also has a role as a membrane.

At present, sulfonated fluororesin membranes having perfluoroalkylene as the main skeleton and partially having a sulfonic acid group at the end of the perfluorovinyl ether side chain are mainly used as proton conductive membranes used in PEFC and the like. Such a proton conductive membrane has a non-polar / water-repellent main chain portion and a polar / hydrophilic side chain portion having a sulfonic acid group, and is separated into a sea part composed of the main chain portion. It shows a structure in which islands with a high concentration of acid groups are dispersed. It is considered that the island portion where the sulfonic acid group is accumulated at a high concentration functions as a proton conduction path (see Non-Patent Document 1).
Examples of commercially available sulfonated fluororesin membranes include Nafion (Nafion (registered trademark) membrane (DuPont: see Patent Document 1).
), Dow (Dow membrane (Dow Chemical: see Patent Document 2)), Aciplex (Aciplex (registered trademark) membrane (see Asahi Kasei Kogyo, Patent Document 3)), Flemion (registered trademark) ) Film (Asahi Glass Co., Ltd.)).

These sulfonated fluororesin membranes exhibit excellent proton conduction performance in a temperature range up to about 80 ° C. in a wet state. However, when the operating temperature exceeds 100 ° C., a so-called creep phenomenon occurs, and as a result, the proton conduction structure in the membrane changes. Furthermore, in a high temperature and high humidity region, the membrane swells to form a jelly, which is very easy to break, leading to the failure of the fuel cell.

However, fuel cells are required to operate at 100 ° C. or higher, preferably 120 ° C. or higher for the following reasons.
1) Since a fuel cell uses a chemical reaction in principle, energy efficiency is higher when operated at a high temperature. That is, given the same output, a device that can operate at a high temperature can be made smaller and lighter. In addition, when operating at a high temperature, the exhaust heat can also be used, so that so-called cogeneration (cogeneration) is possible, and the total energy efficiency is dramatically improved.
2) Since the reaction occurring during operation of the fuel cell is an exothermic reaction, the temperature rises due to the operation. At present, cooling is performed by a water cooling method, but the whole apparatus becomes large and heavy due to the cooling means, and the small size and light weight characteristics, which are the original characteristics of PEFC, cannot be fully utilized. If it can be operated at 100 ° C. or higher, the entire apparatus including the cooling apparatus can be drastically reduced in size.
3) When the supplied hydrogen is not sufficiently purified, the catalyst used on the anode side loses its activity due to fuel impurities (for example, carbon monoxide), so-called catalyst poisoning occurs. There is a big problem that affects the life of PEFC. It is known that this catalyst poisoning can be avoided if the fuel cell can be operated at a high temperature.
4) When operation at a higher temperature is possible, it is not necessary to use a pure noble metal such as platinum as a catalyst, and an inexpensive alloy or the like can be used.

In addition, some electrolyte membranes used in fuel cells also have a problem that their proton conduction performance is highly dependent on humidity. That is, high proton conductivity is exhibited under high humidity, but proton conductivity decreases when humidity decreases. For this reason, in the conventional PEFC, the fuel such as hydrogen gas is humidified, and the humidifier is always operated to control the humidity in order to keep the inside of the cell at a constant humidity. For this reason, a humidifier and a humidity controller are essential, which hinders downsizing and cost reduction of the apparatus.

As described above, in various aspects such as power generation efficiency, cogeneration efficiency, cost / resources, cooling efficiency, etc., the heat resistance of the proton conducting membrane is improved, and fluctuations in proton conducting performance due to changes in humidity are reduced. In particular, improvement of proton conduction performance under high temperature and low humidity has been demanded.

On the other hand, what consists of an aromatic polymer material is proposed as a proton conductive film | membrane excellent in heat resistance. For example, Patent Document 4 discloses a proton conductive membrane made of polybenzimidazole, Patent Documents 5 and 6 show a proton conductive membrane made of polyethersulfone, and Patent Document 7 shows a polyether ether ketone. A proton conducting membrane is disclosed. Proton conducting membranes made of these aromatic polymer materials have little structural change at high temperatures. However, since it has a structure in which a sulfonic acid group, a carboxylic acid group or the like is directly introduced between aromatics, a significant desulfonation reaction or decarboxylation reaction occurs at a high temperature, and proton conductivity may decrease. There was a problem. In addition, it swells greatly in the high temperature and high humidity state, and due to the change in the membrane form between the dry state and the wet state, stress is applied to the joint part of the membrane-electrode assembly, and the joint part of the film and the electrode peels off, There is a high possibility that the film is torn, and there is also a problem that the film may be broken due to a decrease in the film strength due to swelling.

Further, Patent Document 8 discloses that a crosslinked product obtained by combining a mercapto group-containing alkoxysilane (C), a boron oxide, and another alkoxysilyl compound is formed, and then oxidized to have heat resistance and A method for producing a proton conducting membrane having high conductivity is disclosed. However, in this method, the crosslinked structure of mercapto group-containing alkoxysilane (C) and boron oxide and the crosslinked structure of mercapto group-containing alkoxysilane (C), boron oxide and other alkoxysilyl compounds are: These films are obtained as powders and cannot be formed alone. Therefore, it is necessary to form a composite with another polymer material for film formation, but even if the crosslinked body itself has high heat resistance, the heat resistance of the composite polymer material is inferior, so the heat resistance as a film is not necessarily high. It was not. Non-Patent Document 2 also discloses a method of obtaining an electrolyte material by combining a mercapto group-containing alkoxysilane (C) with another alkoxysilyl compound, crosslinking, and oxidizing. However, although there is no detailed description of the material form and the like here, it has been clearly shown that it exhibits deliquescence at high humidity and cannot be used as a proton conductive membrane.

On the other hand, as a proton conductive membrane with improved proton conduction performance under high temperature and low humidity, for example, Patent Document 9 discloses a polyfunctional sulfonate ionomer having a very large ion exchange capacity (high sulfonic acid group content). A method of ionic crosslinking with a basic compound (diamine oligomer) is disclosed. However, such a membrane cannot be used as a proton conductive membrane because it swells vigorously under high temperature and high humidity and exhibits deliquescence.

In Non-Patent Document 3, mercapto group-containing alkoxysilane (C) and tetraethoxysilane are mixed at various ratios, the mixture is crosslinked in the presence of a surfactant, etc., and then oxidized to form an ion channel. A method for obtaining an electrolyte material having working micropores is disclosed. However, even in the membrane obtained by this method, the influence of ion channels on proton conductivity under low humidity has not been studied.

U.S. Pat. No. 4,330,654 JP-A-4-366137 JP-A-6-342665 Japanese Patent Laid-Open No. 9-110982 JP 10-211943 A Japanese Patent Laid-Open No. 10-45913 JP-A-9-87510 Japanese Patent Laid-Open No. 14-184427 Japanese Patent Laid-Open No. 14-26041 Membrane, Vol. 28, p. 14, 2003 Solid State Ionics, Volume 74, Page 105, 1994 Kaliaguine, Microporous and Mesoporous Materials, 52, 29-37, 2002

In view of the above-described situation, the present invention provides a proton conductive membrane, a composite proton conductive membrane, and a fuel cell that are excellent in heat resistance, have small fluctuations in proton conductive performance due to changes in humidity, and are particularly excellent in proton conductive performance under high temperature and low humidity. The purpose is to provide.

The present invention is a proton conductive membrane comprising a continuum of fine particles of silicon-oxygen crosslinked structure having sulfonic acid groups on the surface, and pores penetrating the membrane are formed between the fine particles. The proton conductive membrane has a total pore volume of 0.3 cm ³ / g or less and an ion exchange capacity of 0.7 meq / g or more measured by the BET method of the pores.
The present invention is described in detail below.

The proton conductive membrane of the present invention comprises a continuum of silicon-oxygen crosslinked structure fine particles (hereinafter also simply referred to as fine particles) having sulfonic acid groups on the surface. Here, the continuum of fine particles means a structure in which the fine particles are continuously present so that they have contact portions with each other. The structure of the proton conductive membrane of the present invention will be described with reference to FIG.
FIG. 1 is a schematic view showing the structure of the proton conductive membrane of the present invention. In the proton conductive membrane of the present invention, as shown in FIG. 1, a large number of fine particles 1 made of a silicon-oxygen cross-linked structure are present in the membrane and are present densely and continuously. The bond between the fine particles is preferably a silicon-oxygen bond in which unreacted silicon-oxygen crosslinking groups present on the surface of the fine particles react with each other. Thus, the strength of the film is further improved by having a bond between fine particles in which the metal-oxygen crosslinking groups react with each other.

In the proton conductive membrane of the present invention, since it is difficult for the fine particles to have a geometrically perfect structure, gaps 2 are generated between the fine particles as shown in FIG. The gap 2 can be viewed as pores 2 formed in the membrane when viewed as the entire membrane. Since there are a large number of sulfonic acid groups on the wall surface of the pore 2 (that is, the boundary between the fine particles and the fine particles), the pore 2 can serve as a proton conduction path in which acid groups are accumulated. .

During operation of the fuel cell, protons generated on the anode side are conducted to the cathode side through the proton conductive membrane, while protons are consumed on the cathode side. In a proton conductive membrane containing protons in advance, the proton concentration is increased by supplying protons on the anode side, and the proton concentration is decreased by proton consumption on the cathode side, resulting in a proton concentration gradient in the membrane. This proton concentration gradient becomes a driving force for proton conduction from the anode side to the cathode side. If there are not enough protons in the proton conducting membrane, the protons on the cathode side are insufficient, and stable fuel cell operation cannot be expected. Therefore, a sufficient proton concentration is required in the membrane. On the other hand, in order to obtain a high output in the fuel cell, it is required that the conduction speed by the proton concentration gradient is sufficiently high. For this purpose, a proton conduction path needs to be secured so that efficient conduction is possible. Since protons normally move as hydrates, they have good affinity with water, and a continuous phase in which acids are accumulated at a high concentration where protons can exist stably is suitable as a proton conduction path.
In the proton conductive membrane of the present invention, since the pores having a large number of sulfonic acid groups play a role of this proton conduction path, it is possible to exhibit high proton conductivity extremely stably. Furthermore, since these pores are formed by bonding between stable silicon-oxygen crosslinked structure fine particles, stable proton conduction can be performed without deformation even at high temperatures.

The size and volume of the pores greatly affect the performance of the proton conductive membrane. That is, when the pore diameter is large and the volume is large, the water content increases, but on the other hand, it may not be able to serve as a fuel barrier film that restricts the movement of fuel such as hydrogen. Therefore, it is preferable that the pores are denser as long as sufficient proton conductivity can be expressed. In addition, the present inventors show that, when the pores are sufficiently dense, although proton conductivity performance is lowered according to relative humidity, stable proton conductivity performance can be maintained even during long-time operation. I found it.

In the proton conductive membrane of the present invention, the upper limit of the total pore volume measured by the BET method using a BET analyzer (for example, “Gemini 2375” manufactured by Shimadzu Corporation) is preferably 0.3 cm ³ / g. . If it exceeds 0.3 cm ³ / g, the stability of proton conduction under low humidification deteriorates. In addition, depending on the type of fuel, fuel leaks and power generation efficiency may decrease. A more preferable upper limit is 0.2 cm ³ / g. Although the minimum of the total pore volume of the said pore is not specifically limited, A preferable minimum is 0.001 cm < ³ > / g. When it is less than 0.001 cm ³ / g, there are substantially no through-holes, and sufficient proton conduction performance may not be obtained.

In addition, as the pore, the proportion of pores having a pore diameter of 2 to 10 nm is 80% or more and the proportion of pores having a pore diameter of 10 to 100 nm in the pore volume determined by the BET method Is preferably less than 20%. In the case where such a pore having a relatively small pore diameter is the center, high proton conduction performance can be obtained even under high temperature and low humidity.

However, although pores having a pore diameter of less than 2.0 nm cannot be evaluated by the BET method, pores having an extremely small pore diameter of, for example, about 2 to 6 mm below this, can retain moisture in the membrane under high temperature and low humidity. It is thought that there is an effect to increase In the case of having a large number of pores having such extremely small pore diameters, higher proton conduction performance can be obtained even under high temperature and low humidity.
Although it is difficult to directly observe the presence of such extremely small pores, it can be confirmed by an X-ray diffraction image. That is, when an X-ray diffraction image is measured, if a shoulder or a scattering peak is observed in the range of 2θ = 6 to 23 (deg), the presence of pores with extremely small pore diameters is confirmed.
Therefore, the proton conductive membrane of the present invention preferably has a shoulder or scattering peak observed in the range of 2θ = 6 to 23 (deg) when an X-ray diffraction image is measured.

Next, the fine particles constituting the proton conductive membrane of the present invention will be described.
The fine particles are made of a silicon-oxygen crosslinked structure. Here, the silicon-oxygen crosslinked structure is a structure formed by chemical bonding of at least silicon and oxygen, and means a so-called glass structure. In the proton conductive membrane of the present invention, this silicon-oxygen cross-linked structure is an important component and plays a role of mechanical strength, heat resistance, durability, dimensional stability, etc. of the membrane. That is, when a crosslinked structure having a sufficient degree of condensation is used, a large dimensional change is not observed and a strength change is not caused even in a wet state or a dry state.
A preferable lower limit of the degree of condensation measured by 29Si-NMR analysis of the silicon-oxygen crosslinked structure is 85%. If it is less than 85%, the amount of dimensional change accompanying a change in state may increase.

The fine particles may contain metals other than silicon, phosphorus, boron, etc. within a range not sacrificing the object and cost of the present invention, and the ease of the manufacturing method, and these metals, phosphorus, boron, etc. are oxygen. It may have a structure combined with.

The fine particles have sulfonic acid groups on the surface. Since sulfonic acid is a very strong acid, it has a very high proton dissociation property. Therefore, if there are sulfonic acid groups in the pores, protons can be conducted with extremely high efficiency. In addition, sulfonic acid has high oxidation durability and is stable up to 180 ° C. in heat resistance.

The amount of sulfonic acid groups on the fine particles is not particularly limited, but proton conduction performance is enhanced when more sulfonic acid groups are present in the pores. The amount of sulfonic acid groups on the fine particles determines the ion exchange capacity of the proton conductive membrane. That is, it can be said that the larger the ion exchange capacity, the greater the amount of sulfonic acid groups contained in the membrane and the higher the proton conductivity. The proton conductive membrane of the present invention has a preferable lower limit of ion exchange capacity of 0.7 meq / g. If it is less than 0.7 meq / g, sufficient proton conduction efficiency cannot be obtained under high temperature and low humidity. A more preferred lower limit is 0.8 meq / g.

The ion exchange capacity of the proton conducting membrane of the present invention can be measured by the following method. That is, the proton conductive membrane is immersed in a high concentration sodium chloride solution to cause an ion exchange reaction between the sulfonic acid group in the membrane and sodium chloride. Therefore, sulfonic acid groups and hydrochloric acid generated at 1: 1 are directly titrated with an aqueous sodium hydroxide solution, and the following formula can be calculated from the titration amount.

The sulfonic acid group may be injected (doped) on the surface of the fine particles. However, when doped, the sulfonic acid group is dissipated from the proton conductive membrane when used in a fuel cell over a long period of time, resulting in a decrease in proton conduction efficiency. There is a possibility that. Accordingly, the sulfonic acid group is preferably covalently bonded to the atoms constituting the fine particles. When covalently bonded, stable proton conduction performance can be exhibited over a long period of time.
Although the structure in which the sulfonic acid group is covalently bonded to the atoms constituting the fine particles is not particularly limited, for example, it is preferably bonded to a silicon atom as represented by the following formula (1).

In the formula (1), X represents an —O— bond or an OH group involved in crosslinking, R ¹ represents a hydrocarbon group having 20 or less carbon atoms, R ² represents CH ₃ , C ₂ H ₅ , C ₃ H ₇ or C ₆ H ₅ is represented, and n represents an integer of 1 to 3. When n is 1, R ² may be a mixture of different substituents.
In the above fine particles, R ^1, R ² or n of the structure represented by the formula (1) may be used in combination different.

In the above formula (1), R ¹ is preferably a linear alkylene group having 20 or less carbon atoms. That is, the sulfonic acid group is preferably covalently bonded to the silicon atom via a linear alkylene group having 20 or less carbon atoms. The sulfonic acid group may be bonded to the silicon atom via, for example, an aromatic ring or a molecular chain having various heteroatoms, but is high when bonded via an alkylene group having 20 or less carbon atoms. Heat resistance, acid resistance, oxidation resistance, etc. are obtained.

The fine particles may be composed only of the structure represented by the above formula (1), but are preferably composed using various other crosslinking agents. By using a cross-linking agent, stronger cross-linking is formed, and particles become more stable even at high temperatures, and as a result, stability as a proton conductive membrane is improved.
As said crosslinking agent, what is represented by following formula (2), what is represented by following formula (3), etc. can be used, for example.

In Formula (2), R ³ represents an alkyl group having 20 or less carbon atoms, X represents an —O— bond or OH group involved in crosslinking, and n is an integer of 2 to 4.
The structure represented by the above formula (2) is a basic silica crosslinked structure and is very stable with respect to heat resistance and oxidation resistance. In addition, it is easy to obtain raw materials, and an inexpensive proton conductive membrane can be realized. In particular, when the number n of the cross-linking groups is 4, the structure represented by the above formula (1) is stably immobilized while forming a strong cross-linked structure and having high durability. be able to. In addition, when n is 2 or 3, the fine particles are given flexibility, and as a result, the flexibility of the proton conductive membrane can be improved.
In the above fine particles, R ³ or n may be used in combination with different ones of the structure represented by the formula (2).

In formula (3), X represents an —O— bond or OH group involved in crosslinking, R ⁵ represents a carbon atom-containing molecular chain group having 1 to 30 carbon atoms, and R ⁴ represents CH ₃ , C ₂ H _5. , C ₃ H ₇ , C ₄ H ₉ or C ₆ H ₅ , n is an integer of 0, 1 or 2.

The structure represented by the above formula (3) has a structure in which two crosslinkable silyl groups are bridged by a molecular chain R ⁵ . Such a crosslinked cross-linked structure has extremely high cross-linking reactivity, can form a strong cross-linked structure, and contributes to an improvement in the stability of the fine particles. In addition, physical properties such as flexibility can be adjusted depending on the molecular chain type, molecular chain length, number of cross-linking groups X (3-n), and the like of the bridge structure. For example, when the number of cross-linking groups (3-n) is 1 or 2 and R ⁴ is a methyl group, the entire film has flexibility and can be handled easily.
In addition, in the said microparticles | fine-particles, you may use together the thing from which R < ⁴ >, R < ⁵ > or n differs among the structures shown by the said Formula (3).

The shape of the fine particles is not particularly limited, and may be a spherical shape or a non-spherical shape such as a flat granular shape or a columnar shape. The preferable lower limit of the average particle diameter of the fine particles is 3 nm, and the preferable upper limit is 20 nm. If it is less than 3 nm, the diameter of the pores formed in the gaps between the fine particles becomes extremely small, and a sufficient proton conduction path may not be ensured. When it exceeds 20 nm, the above-mentioned pore volume may not be satisfied.
The particle diameter of the fine particles can be directly determined by observing with an electron microscope. It can also be obtained by a method such as small-angle X-ray scattering.

The particle size distribution of the fine particles is appropriately determined in consideration of the type of fuel gas and the required proton conductivity, fuel barrier properties, membrane strength, etc., and may be uniform or non-uniform. . Proton conductive membranes composed of uniform fine particles can easily form gaps geometrically and exhibit high proton conductivity. On the other hand, in the proton conductive membrane of the present invention comprising non-uniform fine particles, dense packing is possible, which contributes to improved fuel barrier properties and membrane strength.

The thickness of the proton conductive membrane of the present invention is appropriately determined in consideration of proton conductivity, fuel barrier properties, mechanical strength, and the like, and is not particularly limited. Usually, a thickness of about 20 to 300 μm is preferably used. .

The method for producing the proton conductive membrane of the present invention is not particularly limited. For example, it has a mercapto group and a hydrolyzable silyl group and / or silanol group capable of condensation reaction covalently bonded to the mercapto group. A first step of preparing a mercapto group-containing compound, and adding water, a catalyst, etc. to the mercapto group-containing compound, hydrolyzing and condensing, and / or condensing a silanol group to increase the viscosity and form a film A second step of forming a film composed of a continuum of silicon-oxygen crosslinked structure fine particles by heating and baking the hydrolyzable silyl group contained in the film, and the silicon- The mercapto group in the film composed of a continuous body of oxygen-crosslinked structure fine particles is oxidized to form sulfonic acid groups, and the sulfonic acid groups are introduced onto the surfaces of the silicon-oxygen crosslinked structure fine particles. Method having the fourth step is preferred.
Such a method for producing a proton conducting membrane of the present invention is also one aspect of the present invention.

In the method for producing a proton conductive membrane of the present invention, the degree of cross-linking of the obtained membrane, the particle diameter, the particle gap, etc. are adjusted by adjusting the type and amount of the cross-linking agent and polarity control agent in the first step. It is possible to control the film characteristics, including the film strength and the degree of flexibility.
Here, the polarity control agent plays a role of assisting hydrolysis of the mercapto group-containing compound, or remaining in the film in a state of being phase-separated in the film after curing, and promoting pore structure formation. For example, polyethers are suitable.

The proton conducting membrane of the present invention may be reinforced with a polymer material. When it consists only of the above-mentioned fine particles, it may be easily damaged due to its low flexibility. In particular, when power is generated using such a membrane, the gas may be broken due to the pressure of hydrogen gas. By combining with a polymer material, the strength of the proton conductive membrane is improved, and the handleability and stability are improved.
A composite proton conductive membrane in which the proton conductive membrane of the present invention is composite reinforced with a polymer material is also one aspect of the present invention.

As the polymer material, for example, a material having a sulfonic acid group may be used. In the composite proton conductive membrane of the present invention using such a polymer material, the polymer material itself exhibits proton conductivity, so that higher proton conductivity can be obtained as a whole.

Examples of the polymer material include a silicone resin material, a fluororesin material, a cyclic polyolefin material, and an ultra-high molecular weight polyolefin material. However, the polymer resin is exposed to oxidation conditions inside the fuel cell, so that it has excellent chemical stability. A fluorine-based polymer material made of Although it does not specifically limit as said fluorine-type polymeric material, Since the chemical stability is excellent especially, what consists of polytetrafluoroethylene (PTFE) is suitable.

The composite mode is not particularly limited, and examples thereof include a mode in which a polymer material such as fiber, mat, or fibril is impregnated with a mixed liquid that is a raw material for the proton conductive membrane of the present invention. Among these, a mode in which a porous material made of a fluororesin is used and impregnated with the above mixed solution is suitable.
Examples of the porous material made of the fluororesin include those made of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and the like, which are easily available.

The preferable lower limit of the pore diameter of the porous material made of the fluororesin is 0.05 μm, and the preferable upper limit is 0.2 μm. If it is less than 0.05 μm, it may be difficult to impregnate the above mixed solution, and if it exceeds 0.2 μm, the resulting composite proton conductive membrane may have insufficient gas barrier properties.

The porosity of the porous material made of the fluororesin is preferably 60% or more. If it is less than 60%, the fine particles may not form a predetermined continuum in the composite proton conductive membrane obtained.

The preferable lower limit of the thickness of the porous material made of the fluororesin is 20 μm, and the preferable upper limit is 100 μm. When the thickness is less than 20 μm, the obtained composite proton conductive membrane may not have sufficient strength. When the thickness exceeds 100 μm, it may be difficult to uniformly impregnate the mixed solution to some extent.

The porous material made of the fluororesin is preferably subjected to a hydrophilic treatment. In order for the obtained composite proton conductive membrane of the present invention to exhibit stable conductivity even under high temperature and low humidity, a continuum is formed so that the fine particles have a predetermined total pore volume and ion exchange capacity. In order to do so, the fine particles must be filled in the pores of the porous material made of the fluororesin as much as possible without voids. Moreover, when the filling is insufficient, there is a risk that the gas barrier property and the like are lowered. By subjecting the porous material made of the fluororesin to a hydrophilization treatment, even when the viscosity of the mixed solution is high, the porous material can be sufficiently impregnated.

The hydrophilization method is not particularly limited. For example, a method of modifying by irradiating an energy beam such as an electron beam; a surface modifying method using an alkali metal material; a hydrophilic resin such as polyvinyl alcohol (PVA) Examples of the method include a method of cross-linking this after impregnation. Among these, a surface modification method using an alkali metal material is preferable. When a fuel cell is produced using the composite proton conductive membrane of the present invention, the hydrophilic resin deteriorates in the method using a hydrophilic resin because it is used in an environment that is acidic and under high temperature and low humidity. May turn brown and cause peeling or contamination. In addition, when trying to process the inside of the porous material by the energy beam irradiation method, there is a risk of uneven processing. According to the surface modification method using an alkali metal material, it is possible to perform a hydrophilic treatment that is uniform and excellent in durability.

The method for hydrophilizing the porous material composed of the fluororesin by the surface modification method using the alkali metal material is not particularly limited. For example, the fluorine material is dispersed in a dispersion in which a sodium-naphthalene complex is dispersed in a solvent. And a method of immersing a porous material made of a resin. In this case, so as not to damage the surface of the porous material made of the fluororesin, it is hydrophilized by immersing it in a relatively low concentration dispersion diluted with a solvent such as tetrahydrofuran (THF) for a long time. The method is preferred.

Whether or not the porous material made of the fluororesin has been hydrophilized can be easily confirmed by total reflection-infrared absorption measurement. The porous material made of a fluororesin hydrophilically treated with a sodium-naphthalene complex has an absorption peak of a band caused by a hydroxyl group in the vicinity of 3500 cm ⁻¹ as compared with an untreated one, and 1700 cm ⁻ Some carbonyl groups near ¹ are also seen. Absorption peaks of methyl groups and methylene groups in the vicinity of 3000 cm ⁻¹ that are seen when hydrophilized by, for example, complexing with a polyvinyl alcohol resin are not observed with this method. Therefore, the porous fluorine material used for the composite proton conductive membrane of the present invention has a peak due to a hydroxyl group in the vicinity of 3500 cm ⁻¹ when the total reflection-infrared absorption measurement is performed, and the vicinity of 3000 cm ^−1. It is preferable that no peak due to the methyl group or methylene group is observed.

In the case of producing the composite proton conductive membrane of the present invention by combining the proton conductive membrane material of the present invention and the porous material composed of the hydrophilic fluorine-based resin, silane is used as the proton conductive membrane material. It is preferable that a porous material to which a coupling agent is added or subjected to a hydrophilic treatment is surface-treated with a silane coupling agent. Thereby, the adhesiveness of a proton conductive membrane and a porous material improves more, and the gas barrier property of the composite proton conductive membrane of this invention obtained further improves.

Although it does not specifically limit as said silane coupling agent, For example, an epoxy silane and / or aminosilane are suitable. Also, commercially available silane coupling agents such as 3-glycididoxypropyltrimethoxysilane (manufactured by Chisso, trade name S510) and 3-aminopropyltrimethoxysilane (manufactured by Chisso, trade name S360) are preferably used. Can do.

The method of adding the silane coupling agent is not particularly limited. For example, a method of adding the silane coupling agent in advance to the mixed solution that is a raw material of the proton conductive membrane of the present invention; a porous material made of the hydrophilic hydrofluoric resin Examples include a method of immersing the material in a tetrahydrofuran-acid solution of a silane coupling agent; a method of immersing the composite proton conductive membrane in a methanol solution of a silane coupling agent, or the like.

The method for producing the composite proton conductive membrane of the present invention is not particularly limited. For example, a hydrolyzable silyl group and / or silanol group having a mercapto group and covalently bonded to the mercapto group and capable of condensation reaction. A first step of preparing a mercapto group-containing compound having water, adding water, a catalyst, etc. to the mercapto group-containing compound, hydrolyzing and condensing and / or condensing a silanol group to increase the viscosity, Impregnating a porous material made of a fluororesin that has been previously hydrophilized and forming a film, a second step of forming a film, a second step of forming a film, and a hydrolyzable silyl group contained in the film A third step of forming a film comprising a continuum of silicon-oxygen crosslinked structure fine particles by heating and baking; and a mercap in the film comprising the continuum of silicon-oxygen crosslinked structure fine particles. A sulfonic acid group by oxidation of groups, the silicon - method having a fourth step of introducing a sulfonic acid group on the surface of the oxygen cross-linked structure fine particles are preferred.
Such a method for producing a composite proton conductive membrane of the present invention is also one aspect of the present invention.

In the method for producing a composite proton conductive membrane of the present invention, in the first step, it is preferable to blend a silane coupling agent such as epoxysilane or aminosilane in the mixed solution. Although it does not specifically limit as a compounding quantity, A preferable minimum with respect to the whole liquid mixture is 1 weight%. If it is less than 1% by weight, the effect of improving the adhesion between the proton conductive membrane and the porous material subjected to the hydrophilic treatment may not be sufficiently obtained.

In the second step of the method for producing a composite proton conductive membrane of the present invention, the method for impregnating the porous material with the mixed liquid is not particularly limited, and examples thereof include stamping by a press and roll processing. Moreover, you may perform these processes under pressure reduction as needed. Moreover, it is preferable that the porous material which consists of a fluororesin which the hydrophilic treatment was performed previously used here was hydrophilized by being immersed in a metal sodium-naphthalene complex containing liquid.

The proton conducting membrane of the present invention is excellent in heat resistance, has little fluctuation in proton conducting performance due to changes in humidity, and is particularly excellent in proton conducting performance under high temperature and low humidity. In addition, the composite proton conductive membrane of the present invention is further improved in strength and barrier performance while maintaining the performance of the proton conductive membrane of the present invention.
The fuel cell using the proton conductive membrane of the present invention or the composite proton conductive membrane of the present invention is also one aspect of the present invention.
The fuel cell of the present invention can be stably operated even at a high temperature of about 120 ° C., and can be stably operated even at a high temperature and low humidity. For this reason, the fuel cell of the present invention has high energy efficiency and high output. In addition, cogeneration (cogeneration) will be possible and the total energy efficiency will be dramatically improved. Further, the cooling means and the humidity adjusting means can be simplified, and the entire apparatus can be reduced in size and weight. In addition, since there is no problem of catalyst poisoning, it is possible to use a fuel with a low degree of purification, and furthermore, it is possible to use a relatively inexpensive alloy or the like as a catalyst, which greatly increases the overall cost. Can be reduced.

According to the present invention, there are provided a proton conductive membrane, a composite proton conductive membrane, and a fuel cell, which are excellent in heat resistance, have small fluctuations in proton conduction performance due to changes in humidity, and are particularly excellent in proton conduction performance under high temperature and low humidity. Can do.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
0.8 g of copolymer of 3-mercaptopropyltrimethoxysilane and tetraethoxysilane (X-41-1805, manufactured by Shin-Etsu Chemical Co., Ltd.), 0.3 g of tetraethoxysilane as a cross-linking agent, and polyethylene glycol as a polarity control agent (# 200) 0.08 g was weighed into a beaker. In another beaker, 0.3 g of diethylamine as a sol-gel catalyst, 0.12 g of 1 wt% potassium fluoride methanol solution and 0.3 g of water were weighed.
While thoroughly stirring a beaker containing a silane raw material and polyethylene glycol with a stirrer, separately weighed catalyst and water were added all at once and stirred so as to uniformly hydrolyze.

After confirming that the mixed solution became transparent, the mixture was poured into a Petri dish made of fluororesin having an inner diameter of 9.0 cm (made by Freon Chemical Co., Ltd.), and the Petri dish was covered with a glass plate. The solution was allowed to stand at room temperature for 170 hours and gelled.
The gelled film is placed in an oven at 80 ° C. for 2 hours in a desiccator containing water. After heating the oven to 270 ° C. at 20 ° C. per hour, the film is further heated at 270 ° C. for 4 hours. I got a thing. The obtained film-like material was transferred to a glass petri dish and immersed in 1N hydrochloric acid aqueous solution and water at 80 ° C. for 1 hour, respectively, to extract unreacted materials, catalyst, and polarity control agent from the film.

The extracted membrane was immersed in peracetic acid mixed with 125 mL of acetic acid and 100 mL of 30% hydrogen peroxide, and heated on a hot plate at 80 ° C. for 1 hour. Thereafter, the peracetic acid solution was sufficiently removed by dipping in 80 ° C. water for 1 hour and 3 times to obtain a transparent hard film. This was used as a proton conductive membrane.
The obtained proton conductive membrane was a circle of about 4 cm, and the thickness was 200 μm.

(Example 2)
21.2 g of 3-mercaptopropyltrimethoxysilane, 52.5 g of tetraethoxysilane and 10.7 g of methanol were weighed in a flask and stirred at room temperature for 5 minutes. A solution obtained by mixing 6.2 g of 0.1N hydrochloric acid and 8.2 g of methanol was added thereto, and further stirred at room temperature for 3 hours. Next, a mixed solution of 0.057 g of potassium fluoride and 9.7 g of methanol was added, and the mixture was stirred for 3 hours while being heated to 80 ° C. in an oil bath. The mixed solution was cooled to 5 ° C, and then methanol was fractionally distilled at 35 ° C in vacuum. 120 mL of diethyl ether was added to the resulting solution, stirred at room temperature for 10 minutes, cooled to 5 ° C., and filtered using a filter paper (quantitative filter paper No. 5C manufactured by ADVANTEC). Diethyl ether was fractionally distilled from the obtained filtrate at 35 ° C. under vacuum to obtain a mercapto group-containing silane oligomer.

To a liquid obtained by mixing 4.37 g of the obtained mercapto group-containing silane oligomer and 0.51 g of tetraethoxysilane, 0.16 g of water and 0.06 g of triethylamine were added dropwise. After stirring at room temperature for 10 minutes, this solution was impregnated on a fluororesin film into a PTFE porous membrane (Millipore Corporation OMWP14225: hydrophilized type by PVA) having a film thickness of about 50 μm and a diameter of 15 cm. The impregnated film was covered with a fluororesin film, and the film was leveled with an applicator from above. After curing for 80 hours at room temperature with the fluororesin film covered, the film was peeled off and further cured for 36 hours at room temperature. The film after curing is sandwiched between two glass plates, put in a glass container in this state together with 500 mL of water, heat cured at 80 ° C. for 24 hours using a gear oven, and then from 100 ° C. to 200 ° C. for 1 hour The temperature was raised at a rate of 20 ° C., and further calcined at 200 ° C. for 3 hours.

The film obtained by baking was transferred to another glass container, and 7 g of tetraethoxysilane, 5 g of water and 3 g of triethylamine contained in separate glass bottles were put in this container in a gear oven. The film was heated from 120 ° C. to 120 ° C. at a rate of 20 ° C. per hour, and further heated at 120 ° C. for 2 hours to obtain a film-like product.
The obtained film-like material was transferred to a glass petri dish and immersed in 1N hydrochloric acid aqueous solution and water at 80 ° C. for 1 hour, respectively, to extract unreacted materials and catalyst from the membrane. After removing the extract, the membrane was immersed in peracetic acid prepared by mixing 125 mL of acetic acid and 100 mL of 30% aqueous hydrogen peroxide, and heated on a hot plate at 80 ° C. for 1 hour. The obtained film was taken out from the peracetic acid solution and immersed in water at 80 ° C. for 1 hour and 3 times to sufficiently remove the peracetic acid solution to obtain a translucent film. This was used as a proton conductive membrane.
The obtained proton conductive membrane had a diameter of about 14 cm and a thickness of about 50 μm, and was highly flexible.

(Example 3)
11.8 g of 3-mercaptopropyltrimethoxysilane, 62.5 g of tetraethoxysilane, and 12.3 g of methanol were weighed in a flask and stirred at room temperature for 5 minutes. The solution which mixed 5.4g of 0.1N hydrochloric acid and 7.2g of methanol was added there, and also it stirred at normal temperature for 3 hours. Next, a solution obtained by mixing 0.073 g of potassium fluoride and 10.9 g of methanol was added, and the mixture was stirred for 3 hours while being heated to 80 ° C. in an oil bath. The mixed solution was cooled to 5 ° C, and then methanol was fractionally distilled at 35 ° C in vacuum. Next, 120 mL of diethyl ether was added and stirred at room temperature for 10 minutes. The mixed solution was cooled to 5 ° C and filtered using a filter paper (manufactured by ADVANTEC, quantitative filter paper No. 5C). Diethyl ether was fractionally distilled from the filtrate at 35 ° C. under vacuum to obtain a mercapto group-containing silane oligomer.

1.0 g of the obtained mercapto group-containing silane oligomer and 0.08 g of diethylene glycol as a polarity control agent were weighed in a beaker. In another beaker, 0.3 g of diethylamine as a sol-gel catalyst, 0.12 g of 1 wt% potassium fluoride methanol solution and 0.28 g of water were weighed. Separately weighed catalyst and water were added all at once and stirred so as to hydrolyze uniformly.

After confirming that the mixed solution became transparent, the mixture was poured into a Petri dish made of fluororesin having an inner diameter of 9.0 cm (made by Freon Chemical Co., Ltd.), and the Petri dish was covered with a glass plate. The solution was allowed to stand at room temperature for 170 hours and gelled.
The gelled membrane was placed in an 80 ° C oven in a desiccator containing water for 2 hours, and then the oven was heated to 270 ° C in increments of 20 ° C per hour, followed by heating at 270 ° C for 4 hours. A film was obtained. The obtained film-like material was transferred to a glass petri dish and immersed in 1N hydrochloric acid aqueous solution and water at 80 ° C. for 1 hour, respectively, to extract unreacted materials, catalyst, and polarity control agent from the film.

The extracted membrane was immersed in peracetic acid mixed with 125 mL of acetic acid and 100 mL of 30% hydrogen peroxide, and heated on a hot plate at 80 ° C. for 1 hour. Thereafter, the peracetic acid solution was sufficiently removed by dipping in 80 ° C. water for 1 hour and 3 times to obtain a transparent hard film. This was used as a proton conductive membrane.
The obtained proton conductive membrane was a circle of about 4 cm and the thickness was 150 μm.

(Comparative Example 1)
11.8 g of 3-mercaptopropyltrimethoxysilane, 62.5 g of tetraethoxysilane, and 12.3 g of methanol were weighed in a flask and stirred at room temperature for 5 minutes. The solution which mixed 5.4g of 0.1N hydrochloric acid and 7.2g of methanol was added there, and also it stirred at normal temperature for 3 hours. Next, a solution obtained by mixing 0.073 g of potassium fluoride and 10.9 g of methanol was added, and the mixture was stirred for 3 hours while being heated to 80 ° C. in an oil bath. The mixed solution was cooled to 5 ° C, and then methanol was fractionally distilled at 35 ° C in vacuum. Next, 120 mL of diethyl ether was added and stirred at room temperature for 10 minutes. The mixed solution was cooled to 5 ° C and filtered using a filter paper (manufactured by ADVANTEC, quantitative filter paper No. 5C). Diethyl ether was fractionally distilled from the filtrate at 35 ° C. under vacuum to obtain a mercapto group-containing silane oligomer.

0.8 g of the obtained mercapto group-containing silane oligomer, 0.3 g of tetraethoxysilane as a crosslinking agent, 0.2 g of polyethylene glycol (# 200) as a polarity control agent, and 1.8 mL of THF as a solvent were weighed in a beaker. In a separate beaker, 0.3 g of triethylamine, 0.12 g of 1 wt% potassium fluoride methanol solution, 0.28 g of water and 0.6 mL of methanol were weighed as a sol-gel catalyst.
While thoroughly stirring a beaker containing a silane raw material and polyethylene glycol with a stirrer, separately weighed catalyst and water were added all at once and stirred so as to uniformly hydrolyze.

After confirming that the liquid mixture became transparent, it was poured into a fluororesin Petri dish (Freon Chemical Co., Ltd.) having an inner diameter of 9.0 cm, and the Petri dish was covered with a glass plate. The film-like material was allowed to stand for 170 hours at room temperature to be gelled.
The gelled film was heated in an oven at 80 ° C. in a desiccator containing water for 24 hours. The obtained film-like material was transferred to a glass petri dish and immersed in a 1N hydrochloric acid aqueous solution and water at 80 ° C. for 1 hour each to extract unreacted materials, catalyst, and polarity control agent from the membrane.

After removing the extract, it was immersed in peracetic acid prepared by mixing 125 mL of acetic acid and 100 mL of 30% aqueous hydrogen peroxide, and heated at 80 ° C. for 1 hour on a hot plate.
The obtained film was taken out from the peracetic acid solution, immersed in 80 ° C. water for 3 hours each for 1 hour, and the peracetic acid solution was sufficiently removed to obtain a transparent hard film. This was used as a proton conductive membrane.
The obtained proton conductive membrane was a circle of about 4 cm, and the thickness was 200 μm.

(Evaluation)
The proton conducting membranes produced in Examples 1 to 3 and Comparative Example 1 were evaluated by the following methods.
The results are shown in Table 1.

(1) Particle structure evaluation The surface of the proton conductive film was observed using a field emission scanning electron microscope (S-4100, manufactured by Hitachi, Ltd.), and the presence or absence of a continuum structure of fine particles was evaluated according to the following criteria.
◯: A continuum structure of fine particles was observed ×: A continuum structure of fine particles was not recognized

(2) Evaluation of pore volume and pore size distribution The proton-conductive membrane was dried at room temperature for 48 hours, and then further vacuum-dried at 50 ° C. for 4 hours for evaluation.
The volume of pores having a pore diameter of 2 to 100 nm on the proton conductive membrane was analyzed using a BET evaluation apparatus (Shimadzu Corporation, Gemini 2375). The analysis was performed by the BJH method in the pore volume evaluation mode. Further, the ratio of the pores having a pore diameter of 2 to 10 nm in the total pore volume and the ratio of the pores having a pore diameter of 10 to 100 nm were determined.

(3) X-ray diffraction evaluation The proton conductive membrane was subjected to wide-angle X-ray diffraction evaluation using an X-ray diffraction evaluation apparatus (RINT2400, manufactured by Rigaku Corporation). That is, the dried sample was irradiated with X-rays generated under conditions of 50 kV and 100 mA for 60 minutes to obtain a scattering spectrum. The scattering intensity I is plotted on the vertical axis and the scattering angle is plotted 2θ on the horizontal axis, and each axis is converted into a logarithmic display to confirm the presence or absence of a scattering peak or shoulder near 2θ = 6 to 23 (deg).

(4) Evaluation of ion exchange capacity The proton conductive membrane was immersed in a 1N aqueous hydrochloric acid solution for 4 hours and washed thoroughly with distilled water. After confirming that the sample was sufficiently washed using a pH test paper, the sample was allowed to dry at room temperature for 24 hours and further dried at 50 ° C. under vacuum for 6 hours, and then the weight of the sample was measured. Next, the sample was immersed in a 2 mol / L sodium chloride aqueous solution and allowed to stand for 6 hours. Thereafter, neutralization titration was performed using a 0.01N aqueous sodium hydroxide solution, and the ion exchange capacity was calculated from the titration amount.

(5) NMR analysis The proton conductive membrane was crushed and a spectrum was obtained using this as a sample using solid 29Si-NMR (JNM-LA500, manufactured by JEOL Ltd.). The obtained spectrum was classified into T0-3 and Q0-4, and the area ratio was determined. The calculated area ratio is 0 for the T0 and Q0 regions, 0.33 for the T1 region, 0.66 for the T2 region, 0.25 for the Q1 region, 0.5 for the Q2 region, and 0 for the Q3 region. Multiply by 75 to get the total. The degree of condensation was obtained by dividing this value by the total area ratio.

(6) Evaluation of proton conductivity in high temperature region The proton conductive membrane is set in an electrochemical cell (the same as that described in FIG. 3 in JP-A-2002-184427), and the proton conductive membrane and platinum are set. The plate was brought into close contact. An electrochemical impedance measuring device (Solartron Co., 1260 type) was connected to the platinum plate, impedance was measured in a frequency range of 0.1 Hz to 100 kHz, and the proton conductivity of the proton conductive membrane was evaluated.
In the measurement, the sample is supported in an electrically insulated sealed container, the cell temperature is set to 120 ° C. by the temperature controller, and the humidity is 100% RH and 40% RH from the start of measurement until 100 hours later. The change in conductivity was obtained. In the measurement, the inside of the measurement tank was pressurized.
The change in conductivity at 120 ° C.-100% RH is shown in FIG. 2, and the change in conductivity at 120 ° C.-40% RH is shown in FIG.

From Table 1 and FIGS. 1 and 2, the proton conductive membranes obtained in Examples 1 to 3 and Comparative Example 1 each having a continuum structure of fine particles having sulfonic acid groups on the surface are 120 ° C.-100% RH. Below, it showed very good proton conductivity and was very stable over time.
However, while the proton conductive membranes obtained in Examples 1 to 3 in which pore volume and pore distribution are in a certain range showed stable proton conductivity even at 120 ° C.-40% RH, In the proton conductive membrane obtained in Comparative Example 1, a decrease in conductivity was observed over time.
Note that no change in dimension due to shrinkage or the like was observed in any proton conductive membrane.

Example 4
3-Mercaptopropyltrimethoxysilane (17.7 g), tetraethoxysilane (168.7 g) and methanol (28.5 g) were weighed in a flask and stirred at 0 ° C. for 10 minutes. A solution obtained by mixing 14.6 g of 0.1N hydrochloric acid and 19.5 g of methanol was added thereto, stirred at 0 ° C. for 1 hour, heated to 40 ° C., and further stirred for 2 hours. Next, a solution obtained by mixing 0.190 g of potassium fluoride and 28.5 g of methanol was added, stirred at 40 ° C. for 1 hour, heated to 80 ° C., and further stirred for 2 hours. The mixed solution was cooled to 0 ° C, and then the alcohol was fractionally distilled at 40 ° C in vacuum. The obtained solution was cooled to 0 ° C., 200 mL of diethyl ether was added, and the mixture was stirred at 0 ° C. for 10 minutes, followed by filtration using a membrane filter (MILLIPORE, Omnipore membrane pore size 0.2 μm). Diethyl ether was fractionally distilled from the obtained filtrate at 40 ° C. under vacuum to obtain a mercapto group-containing silane oligomer.

100 g of a sodium-naphthalene complex-based fluorine surface treatment agent (manufactured by Technos, Fluorobonder E01) was poured into a stainless steel vat, and 120 mL of THF was added as a diluting solvent, and this surface treatment agent mixture was thoroughly stirred.
A PTFE porous material (manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) having an average pore diameter of 0.1 μm and a thickness of 50 μm was cut into a square shape with a side of 10 cm, and immersed in a surface treatment agent mixed solution for 30 minutes. The PTFE porous material was taken out and rinsed thoroughly with THF to remove the complex component adhering to the surface. Thereafter, it was further thoroughly washed with methanol and dried to obtain a hydrophilic treatment porous material.

To a solution obtained by mixing 4.07 g of a copolymer of 3-mercaptopropyltrimethoxysilane and tetraethoxysilane (X-41-1805, manufactured by Shin-Etsu Chemical Co., Ltd.) and 1.0 g of the obtained mercapto-containing silane oligomer, 0.12 g and 0.06 g of triethylamine were added dropwise. After stirring for about 20 minutes until clear, this solution was developed on a fluorine film.
The solution is covered with a hydrophilized porous material and impregnated with the solution, and in a portion where the solution is not sufficiently impregnated due to bubbles or the like, the solution is hydrophilized with a spatula made of polyethylene. The material was impregnated so that there was no unevenness. Then, the fluororesin film was covered and it leveled with the applicator from it on top so that a film thickness might be set to 50 micrometers. After curing for 80 hours at room temperature with the fluororesin film covered, the fluororesin film was peeled off and further cured for 36 hours. After the cured film is sandwiched between fluororesin films, they are further sandwiched between two glass plates, put into a glass container with 500 mL of water in this state, and heat cured at 80 ° C. for 24 hours using a gear oven. In a nitrogen atmosphere, the temperature was raised from 100 ° C. to 260 ° C. at a rate of 20 ° C. per hour, and further calcined at 260 ° C. for 3 hours.

The film after baking was transferred to another glass container and immersed in a 1N hydrochloric acid aqueous solution and water at 80 ° C. for 1 hour, respectively, to extract unreacted substances and catalyst from the film. After removing the extract, the membrane was immersed in peracetic acid prepared by mixing 125 mL of acetic acid and 100 mL of 30% aqueous hydrogen peroxide, and heated on a hot plate at 60 ° C. for 1 hour. The obtained film was taken out from the peracetic acid solution and immersed in water at 80 ° C. for 1 hour and 3 times to sufficiently remove the peracetic acid solution to obtain a translucent film. This was used as a composite proton conductive membrane.
The obtained composite proton conductive membrane had a side of 9 cm and a thickness of about 50 μm.

(Example 5)
3-Mercaptopropyltrimethoxysilane (35.3 g), tetraethoxysilane (150.0 g) and methanol (26.5 g) were weighed in a flask and stirred at 0 ° C. for 10 minutes. A solution obtained by mixing 15.6 g of 0.1N hydrochloric acid and 20.8 g of methanol was added thereto, stirred at 0 ° C. for 1 hour, heated to 40 ° C., and further stirred for 2 hours. Next, a solution in which 0.195 g of potassium fluoride and 29.7 g of methanol were mixed was added, stirred at 40 ° C. for 1 hour, heated to 80 ° C., and further stirred for 2 hours. The mixed solution was cooled to 0 ° C, and then the alcohol was fractionally distilled at 40 ° C in vacuum. The obtained solution was cooled to 0 ° C., 200 mL of diethyl ether was added, and the mixture was stirred at 0 ° C. for 10 minutes, followed by filtration using a membrane filter (MILLIPORE, Omnipore membrane pore size 0.2 μm). Diethyl ether was fractionally distilled from the obtained filtrate at 40 ° C. under vacuum to obtain a mercapto group-containing silane oligomer.

To a liquid obtained by mixing 4.07 g of the obtained mercapto group-containing silane oligomer, 1.0 g of the mercapto-containing silane oligomer prepared in Example 3, and 0.12 g of a silane coupling agent (manufactured by Chisso Corporation, S510), water 0.12 g and 0.06 g of triethylamine were added dropwise. After stirring at room temperature for about 10 minutes, this solution was developed on a fluororesin film.
This solution was covered with the hydrophilized porous material obtained in Example 3, and impregnated so as not to be uneven by the same method as in Example 3. Then, the fluororesin film was covered and it leveled with the applicator from it on top so that a film thickness might be set to 50 micrometers. After curing for 80 hours at room temperature with the fluororesin film covered, the fluororesin film was peeled off and further cured for 36 hours. After the cured film is sandwiched between fluororesin films, they are further sandwiched between two glass plates, put into a glass container with 500 mL of water in this state, and heat cured at 80 ° C. for 24 hours using a gear oven. In a nitrogen atmosphere, the temperature was raised from 100 ° C. to 260 ° C. at a rate of 20 ° C. per hour, and further calcined at 260 ° C. for 3 hours.

The film | membrane obtained by baking was transferred to another glass container, and each 1 hour hydrochloric acid and water were immersed in 80 degreeC conditions for 1 hour, respectively, and the unreacted substance and the catalyst were extracted from the film | membrane. After removing the extract, the membrane was immersed in peracetic acid prepared by mixing 125 mL of acetic acid and 100 mL of 30% aqueous hydrogen peroxide, and heated on a hot plate at 60 ° C. for 1 hour. The obtained film was taken out from the peracetic acid solution and immersed in water at 80 ° C. for 1 hour and 3 times to sufficiently remove the peracetic acid solution to obtain a translucent film. This was used as a composite proton conductive membrane.
The obtained composite proton conductive membrane had a side of 9 cm and a thickness of about 50 μm.

(Example 6)
3-mercaptopropyltrimethoxysilane 53.0 g, tetraethoxysilane 131.
2 g and 26.5 g of methanol were weighed into a flask and stirred at 0 ° C. for 10 minutes. A solution obtained by mixing 15.6 g of 0.01N hydrochloric acid and 20.8 g of methanol was added thereto, stirred at 0 ° C. for 1 hour, heated to 40 ° C., and further stirred for 2 hours. Next, a solution obtained by mixing 0.114 g of potassium fluoride and 29.7 g of methanol was added, stirred at 40 ° C. for 1 hour, heated to 80 ° C., and further stirred for 2 hours. The mixed solution was cooled to 0 ° C, and then the alcohol was fractionally distilled at 40 ° C in vacuum. The obtained solution was cooled to 0 ° C., 200 mL of diethyl ether was added, and the mixture was stirred at 0 ° C. for 10 minutes, followed by filtration using a membrane filter (MILLIPORE, Omnipore membrane pore size 0.2 μm). Diethyl ether was fractionally distilled from the obtained filtrate at 40 ° C. under vacuum to obtain a mercapto group-containing silane oligomer.

100 g of a sodium-naphthalene complex-based fluorine surface treating agent (manufactured by Technos, Fluorobonder E01) was poured into a stainless steel vat, and 120 mL of THF was added as a diluting solvent, and this surface treating agent mixed solution was well stirred.
A PTFE porous material (manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) having an average pore size of 0.2 μm and a thickness of 50 μm was cut into a square having a side of 10 cm and immersed in a surface treatment agent mixed solution for 30 minutes. The treated PTFE porous material was taken out and thoroughly rinsed with THF to remove the complex component adhering to the surface. Thereafter, it was thoroughly washed with methanol and dried to obtain a hydrophilic porous material.

To a liquid obtained by mixing 4.37 g of the obtained mercapto group-containing silane oligomer and 0.51 g of tetraethoxysilane, 0.11 g of water and 0.05 g of triethylamine were added dropwise. After stirring for 10 minutes at room temperature, this solution was developed on a fluororesin film. The obtained hydrophilized porous material was placed on this solution and impregnated by the same method as in Example 3. Then, the fluororesin film was covered and it leveled so that the film thickness might be set to 50 micrometers with the applicator from it. After curing for 80 hours at room temperature with the fluororesin film covered, the film was peeled off and further cured for 24 hours at room temperature. The film after curing is sandwiched between two glass plates via a fluororesin film, put in a glass container with 500 mL of water in this state, heated and cured at 80 ° C. for 24 hours using a gear oven, and then 100 ° C. From 200 to 200 ° C. at a rate of 20 ° C. per hour, and further calcined at 200 ° C. for 3 hours.

The film | membrane obtained by baking was transferred to another glass container, and each 1 hour hydrochloric acid and water were immersed in 80 degreeC conditions for 1 hour, respectively, and the unreacted substance and the catalyst were extracted from the film | membrane. After removing the extract, the membrane was immersed in peracetic acid prepared by mixing 125 mL of acetic acid and 100 mL of 30% aqueous hydrogen peroxide, and left at 23 ° C. for 24 hours. The obtained film was taken out from the peracetic acid solution and immersed in water at 80 ° C. for 1 hour and 3 times to sufficiently remove the peracetic acid solution to obtain a translucent film. This was used as a composite proton conductive membrane.
The obtained composite proton conductive membrane had a side of 9 cm and a thickness of about 50 μm.

(Comparative Example 2)
Copolymer of 3-mercaptopropyltrimethoxysilane and tetraethoxysilane (X-41-1805, manufactured by Shin-Etsu Chemical Co., Ltd.) and 1.0 g of tetraethoxysilane were mixed with 0.12 g of water and triethylamine. 0.06 g was added dropwise. After stirring for about 20 minutes at room temperature, this solution was developed on a fluorine film. On this solution, a PTFE porous material (manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) having an average pore diameter of 0.1 μm and a thickness of 50 μm was cut into a 10 cm square. Here, since it was difficult for the solution to be impregnated into the material due to the water repellency of the PTFE porous material, the solution was impregnated so that there was no unevenness in the material by pressing a polyethylene spatula from above. Then, the fluororesin film was covered and it leveled with the applicator from it on top so that a film thickness might be set to 50 micrometers. After curing for 80 hours at room temperature with the fluororesin film covered, the fluororesin film was peeled off and further cured for 36 hours. After the cured film is sandwiched between fluororesin films, and further sandwiched between two glass plates, put in a glass container with 500 mL of water in this state, and heat cured at 80 ° C. for 24 hours using a gear oven In a nitrogen atmosphere, the temperature was raised from 100 ° C. to 260 ° C. at a rate of 20 ° C. per hour, and further calcined at 260 ° C. for 3 hours.

The film | membrane obtained by baking was transferred to another glass container, and each 1 hour hydrochloric acid and water were immersed in 80 degreeC conditions for 1 hour, respectively, and the unreacted substance and the catalyst were extracted from the film | membrane. After removing the extract, the membrane was immersed in peracetic acid prepared by mixing 125 mL of acetic acid and 100 mL of 30% aqueous hydrogen peroxide, and heated on a hot plate at 60 ° C. for 1 hour. The obtained film was taken out from the peracetic acid solution and immersed in water at 80 ° C. for 1 hour and 3 times to sufficiently remove the peracetic acid solution to obtain a translucent film. This was used as a composite proton conductive membrane.
The obtained composite proton conductive membrane had a side of 9 cm and a thickness of about 50 μm.

(Evaluation)
In addition to the evaluation similar to Example 1 etc. about the proton conductive film produced in Examples 4-6 and the comparative example 2, the helium gas permeation | transmission test was done with the following method.
The results are shown in Table 2.

(Helium gas permeation test)
A helium gas detector MSE-2000 type apparatus manufactured by Shimadzu Corporation was used to conduct a helium gas permeation test. The principle of this apparatus is that helium gas leaked from a sample is mixed in a nitrogen flow line having a constant flow rate, and a part of the mixed gas is introduced into the measurement unit at a constant flow rate. The measurement unit has a structure equivalent to that of a mass spectrometer, and is adjusted in advance to conditions for detecting only helium, so that the amount of helium in the mixed gas can be measured. A normal temperature and a helium gas pressure of 0.1 MPa were applied, and the amount of gas leaked after 30 seconds was evaluated.
Since this apparatus does not detect the total amount of helium mixed through the sample, the absolute value of the helium permeation amount of the sample cannot be measured, but a comparison is possible.

From Table 2, the composite proton conductive membrane obtained by impregnating the PTFE porous material subjected to the hydrophilization treatment showed high ion exchange capacity and gas barrier property, whereas the PTFE porous material not subjected to the hydrophilization treatment was used. The composite proton conductive membrane obtained by impregnating the porous material was inferior in both ion exchange capacity and gas barrier property. This is presumably because the impregnation was uneven.

According to the present invention, there are provided a proton conductive membrane, a composite proton conductive membrane, and a fuel cell, which are excellent in heat resistance, have small fluctuations in proton conduction performance due to changes in humidity, and are particularly excellent in proton conduction performance under high temperature and low humidity. Can do.

It is a schematic diagram which shows the structure of the proton conductive membrane of this invention. It is a figure which shows the change of the conductivity under 120 degreeC-100% RH of the proton-conductive film | membrane obtained in Examples 1-3 and Comparative Example 1. FIG. It is a figure which shows the change of the conductivity under 120 degreeC-40% RH of the proton conductive membrane obtained in Examples 1-3 and the comparative example 1. FIG.

Explanation of symbols

1 Fine particles composed of a silicon-oxygen crosslinked structure 2 Gaps and pores

Claims (17)

A proton conductive membrane comprising a continuum of fine particles of silicon-oxygen crosslinked structure having a sulfonic acid group on the surface,
Between the fine particles, pores penetrating the membrane are formed, and the total pore volume measured by the BET method of the pores is 0.3 cm ³ / g or less,
A proton conductive membrane having an ion exchange capacity of 0.7 meq / g or more. The proton conductive membrane according to claim 1, wherein the sulfonic acid group is covalently bonded to the silicon atom via a linear alkylene group having 20 or less carbon atoms. The proportion of pores having a pore diameter of 2 to 10 nm in the total pore volume is 80% or more, and the proportion of pores having a pore diameter of 10 to 100 nm is less than 20%. Item 3. The proton conductive membrane according to Item 1 or 2. 4. The proton conductive membrane according to claim 1, wherein a shoulder or scattering peak is observed in a range of 2 [theta] = 6 to 23 (deg) when an X-ray diffraction image is measured. 5. The proton conductive membrane according to claim 1, 2, 3 or 4, wherein the silicon-oxygen crosslinked structure has a degree of condensation measured by 29Si-NMR analysis of 85% or more. 6. A composite proton conductive membrane according to claim 1, wherein the proton conductive membrane according to claim 1 is composite reinforced with a polymer material. 7. The composite proton conductive membrane according to claim 6, wherein the polymer material has a sulfonic acid group. The composite proton conductive membrane according to claim 6 or 7, wherein the polymer material is a fluorine-based polymer material. 9. The composite proton conductive membrane according to claim 8, wherein the fluorine polymer material is made of polytetrafluoroethylene. The fluorine-based polymer material is a porous material having a film thickness of 20 to 100 µm, a pore diameter of 0.05 to 0.2 µm, and a porosity of 60% or more. Composite proton conductive membrane. The composite proton conductive membrane according to claim 10, wherein the porous material is subjected to a hydrophilic treatment. 12. The composite proton conductive membrane according to claim 11, wherein the composite proton conductive membrane is immersed in a metal sodium-naphthalene complex-containing liquid and a fluorine material into which hydrophilic groups such as hydroxyl groups are introduced on the surface of the base material is used. 13. The composite proton conductive membrane according to claim 12, wherein a silane coupling agent is added to the proton conductive membrane and the porous material subjected to hydrophilization treatment. 14. The composite proton conductive membrane according to claim 13, wherein the silane coupling agent is epoxy silane and / or amino silane. A first step of preparing a mercapto group-containing compound having a mercapto group and having a hydrolyzable silyl group and / or silanol group covalently bonded to the mercapto group, and water added to the mercapto group-containing compound; A second step of thickening the film by adding a catalyst, etc., and hydrolyzing and condensing and / or condensing a silanol group, and heating the hydrolyzable silyl group contained in the film. A third step of forming a pore structure by forming a film composed of a continuum of silicon-oxygen crosslinked structure fine particles by firing, and a film in a film composed of the continuum of silicon-oxygen crosslinked structure fine particles, Producing a proton conductive membrane comprising a fourth step of oxidizing a mercapto group to form a sulfonic acid group and introducing the sulfonic acid group onto the surface of the silicon-oxygen crosslinked structure fine particles. Method. A first step of preparing a mercapto group-containing compound having a mercapto group and having a hydrolyzable silyl group and / or silanol group covalently bonded to the mercapto group, and water added to the mercapto group-containing compound; Then, adding a catalyst, etc., hydrolyzing and condensing, and / or condensing silanol groups to increase the viscosity, impregnate a porous material made of a fluororesin that has been previously hydrophilized, and form a film And a second step of forming a pore structure by forming a film composed of a continuum of silicon-oxygen crosslinked structure fine particles by heating and baking the hydrolyzable silyl group contained in the film. And the step of oxidizing the mercapto group in the film composed of the continuum of the silicon-oxygen crosslinked structure fine particles to form a sulfonic acid group, and forming a sulfonic acid group on the surface of the silicon-oxygen crosslinked structure fine particle Method for producing a composite proton conducting membrane and having a fourth step of introducing. A proton conducting membrane according to claim 1, 2, 3, 4, or 5, or a composite proton conducting membrane according to claim 6, 7, 8, 9, 10, 11, 12, 13 or 14. A fuel cell characterized by comprising:

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