JP5291349B2 - Proton conducting membrane, membrane-electrode assembly, and polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton conductive membrane capable of improving power generation performance while maintaining a high proton conductivity, high impact resistance, and achieving thermal cycle resistance, and high wet and dry cycle resistance, to provide a membrane-electrode assembly, and to provide a solid polymer fuel cell. <P>SOLUTION: The proton conductive membrane has: a silicon-oxygen bond structure (A) which includes a cross-linking structure by silicon-oxygen bonding; and an acid group-containing structure (B) which has a covalent bond with a silane compound and has a sulfide bond, a sulfoxide bond or a sulfone bond. Here, the acid group-containing structure (B) can be synthesized from a compound (&alpha;) containing silicon and a thiol group and a compound (&beta;) containing any of an acid group, its metal salt or an acid precursor group, and an unsaturated double bond. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a proton conductive membrane, a membrane-electrode assembly, and a polymer electrolyte fuel cell.

  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, a polymer electrolyte fuel cell (hereinafter referred to as “PEFC”) is smaller and smaller than any other type. It is a high-output, small-scale on-site power source for the next generation as a power source for mobile objects such as a power source for vehicles and for portable use.

  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 of the PEFC. Among these, electrons are supplied to the outside, used as electricity, and circulated to the cathode side of the PEFC. On the other hand, protons are supplied to the proton conductive membrane (electrolyte membrane) and move to the cathode side through the proton conductive membrane. On the cathode side, protons, circulating electrons, and oxygen introduced from the outside are supplied by the catalyst to generate water. In other words, when viewed as a single PEFC, PEFC is a very clean energy source that extracts electricity when making water from hydrogen and oxygen.

  In recent years, fuel cells that use fuels other than hydrogen such as alcohols, ethers, hydrocarbons, and the like as fuels for fuel cells and that extract protons and electrons from these fuels using a catalyst have been studied. A typical example of such a fuel cell is a direct methanol fuel cell (hereinafter referred to as “DMFC”) using methanol (usually used as an aqueous solution) as fuel. Since DMFC does not require an external reformer and fuel is easy to handle, it is most expected as a compact and portable power source among various types of fuel cells.

  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, the main proton conductive membrane used in PEFC is a fluororesin membrane having perfluoroalkylene as a main skeleton and partially having a sulfonic acid group at the end of a perfluorovinyl ether side chain. Examples of such a sulfonated fluororesin membrane include Nafion (Nafion (registered trademark) membrane (Du Pont: Du Pont, see Patent Document 1)), Dow (Dow Chemical: Dow Chemical, Patent). Reference 2)), Aciplex (Aciplex (registered trademark) membrane (Asahi Kasei Kogyo Co., Ltd., see Patent Document 3)), Flemion (Flemion (registered trademark) membrane (Asahi Glass Co., Ltd.)), etc. Are known.

  These fluororesin-based membranes are said to have a glass transition temperature (Tg) near 130 ° C. in a wet state where the fuel cell is used, and so-called creep phenomenon occurs from around this temperature, and as a result, The proton conduction structure in the membrane changes, and stable proton conduction performance cannot be exhibited. Furthermore, the membrane is transformed into a swollen form, becomes jelly-like, and is very easily damaged, leading to a failure of the fuel cell.

  For the reasons described above, the maximum temperature that can be used stably for a long period of time is usually 80 ° C.

  Since fuel cells use chemical reactions in principle, energy efficiency is higher when operated at high temperatures. 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. Accordingly, the operating temperature of the fuel cell is preferably higher when it is lower than the glass transition temperature or thermal decomposition temperature of the proton conductive membrane to be used, and usually 100 ° C. or higher, particularly 120 ° C. or higher is preferable.

  In addition, if the supplied hydrogen is not sufficiently purified, the catalyst used on the anode side may lose its activity due to fuel impurities (for example, carbon monoxide) (so-called catalyst poisoning). It is a big issue that affects the lifespan. It is known that this catalyst poisoning can also be avoided if the fuel cell can be operated at a high temperature. From this point, it can be said that the fuel cell is preferably operated at a higher temperature. Furthermore, if operation at higher temperatures becomes possible, the catalyst itself can be replaced with an alloy of various metals, instead of the pure expensive precious metal such as platinum that has been used in the past, in terms of cost or resources. This is also very advantageous.

  As described above, despite the demand for high-temperature operation of the PEFC, that is, high-temperature heat resistance of the proton conductive membrane in various aspects such as power generation efficiency, cogeneration efficiency, cost and resources, sufficient protons are required. There is no proton conducting membrane that has both conductivity and heat resistance.

  On the other hand, in a DMFC that uses methanol as a fuel instead of hydrogen, methanol directly contacts the membrane. In sulfonated fluororesin membranes such as Nafion (registered trademark) currently used, the affinity between the membrane and methanol is high, the membrane swells extremely due to absorption of methanol, and in some cases dissolves. It may cause failure. In addition, there has been a serious problem that the so-called methanol crossover (MCO) that permeates the proton-conductive membrane in which methanol swells and leaks to the cathode side is generated, and the output of the fuel cell is greatly reduced. Furthermore, a system that can be used at a high methanol concentration such as 30% by weight or 64% by weight is required for DMFC to be able to be driven for a long time with less fuel. However, a general fluororesin-based membrane can be operated only at a concentration of several percent or less because the crossover increases as the methanol concentration increases.

  As described above, even in DMFC, there is no proton conductive membrane that is efficient and durable at present.

  Against this background, in order to increase the operating temperature of PEFC, and to achieve high output using high concentration methanol in DMFC, there are also membranes for fuel cells other than sulfonated fluororesins. Various types of membranes such as hydrocarbons and inorganics have been actively developed. For example, since an organosilicon compound is composed of a silicon-oxygen bond having a strong binding energy, it has high chemical stability, heat resistance and oxidation resistance, and can impart many unique properties depending on its composition. It is used in all industrial fields such as electronics, office equipment, architecture, food, medicine, textile, plastic, paper, pulp, and paint rubber. A proton conductive membrane using this organosilicon compound and having a crosslinked structure composed of a silicon-oxygen bond has been disclosed (for example, see Patent Document 4). The cross-linked structure composed of silicon-oxygen bonds is relatively stable even when exposed to high temperature and high humidity under strong acidic (proton presence) conditions like the proton conductive membrane, and the cross-linked structure inside the fuel cell membrane Can be suitably used. Furthermore, even when an alcohol such as methanol is used as a fuel, the silicon-oxygen cross-linking structure can suppress the swelling and can be expected to reduce the MCO.

However, the silicon-carbon bond contained in the film is slightly weaker in intermolecular force than the silicon-oxygen bond, and has an impact resistance against external pressure such as rapid temperature change, humidity change, and rapid swelling. Low. For this reason, when a certain type of organosilicon compound is used as the fuel cell electrolyte membrane, there are cases in which, for example, performance degradation of proton conductivity and fuel barrier properties is caused by repeated cooling and drying.
British Patent No. 4,330,654 JP-A-4-366137 JP-A-6-342665 Japanese Patent No. 3679104

  The present invention provides a proton conductive membrane, a membrane-electrode assembly, and a high solids material that can achieve high cold-heat repeatability and high dry-wet repeatability while maintaining high proton conductivity and high heat resistance, and can improve power generation performance. An object is to provide a molecular fuel cell.

  According to the first invention of the present application, there is provided a proton conductive membrane having a crosslinked structure by silicon-oxygen bonds, and a silicon-oxygen bond type structure represented by the following general formula in the proton conductive membrane: There is provided a proton conductive membrane characterized by having (A) and an acid group-containing structure (B) represented by the following general formula.

_{A: (R 2) n X} (3-n) -Si-R 1 -Si-X (3-n) (R 2) n
(Wherein X represents an —O— bond or an OH group, R ₁ is selected from an oxygen atom and an optionally substituted chain hydrocarbon group that may contain a hetero atom having 1 to 50 carbon atoms; ₂ is a methyl, ethyl, propyl or phenyl group, where n = 0, 1, or 2.)
_{B: (R 4) m X} (3-m) -Si-R 3 -Y
(In the formula, X represents an —O— bond or an OH group, Y represents an acid group, R ₃ represents a sulfide bond, a sulfoxide bond, or an organic group having 3 or more carbon atoms including a sulfone bond, provided that the main group of R ₃ The chain consists of either a C—C bond or a C—S—C bond, or a combination thereof, and R ₄ represents a methyl, ethyl, propyl, or phenyl group, where m = 0, 1, or 2)
Here, the oxygen atom of X is involved in the formation of a silicon-oxygen bond bridge.

R ₃ in the formula is (CH ₂ ) ₃ —S— (CH ₂ ) ₂ , (CH ₂ ) ₃ —S (═O) — (CH ₂ ) ₂ , (CH ₂ ) ₃ —SO ₂ — (CH _{2) 2, (CH 2)} 3 -S- (CH 2) 3, (CH 2) 3 -S (= O) - (CH 2) 3, and _{(CH 2) 3 -SO 2 -} (CH 2) ₃ can be selected.

  Y in the formula can be a sulfonic acid group.

  The structure B is composed of a compound (α) containing silicon and a thiol group, and a compound (β) containing either an acid group, a metal salt thereof, or an acid group precursor group and an unsaturated double bond.

R ₁ in the formula is a chain hydrocarbon group having 1 to 50 carbon atoms, or a chain hydrocarbon group having 1 to 50 carbon atoms including a sulfide bond, a sulfoxide bond, or a sulfone bond. However, the main chain of R ₁ consists of either a C—C bond only or a C—S—C bond alone, or a combination of a C—C bond and a C—S—C bond only.

R ₁ in the formula may be a hydrocarbon group having 2 carbon atoms.

  The proton conductive membrane may be reinforced with the porous material. The porous material may be glass fiber, but is not limited thereto.

  Further, a membrane-electrode assembly is provided by using any one of the above proton conductive membranes and bonding a gas diffusion electrode thereto.

  Furthermore, a polymer electrolyte fuel cell comprising the membrane-electrode assembly is provided.

  Furthermore, the membrane-electrode assembly is a unit cell, a pair of separators serving as fuel and oxygen passages are installed outside the unit cell, and a plurality of adjacent unit cells are connected to each other. A polymer electrolyte fuel cell is provided.

<Proton conductive membrane>
The proton conductive membrane of the present invention has a cross-linked structure composed of a silicon-oxygen bond with high heat resistance and high dimensional stability. Therefore, under a strong acidic (proton presence) condition like an electrolyte membrane for fuel cells, In addition, a proton conductive membrane having high output and excellent durability can be formed even at high temperatures and in high humidity including a polar solvent such as an aqueous methanol solution. In addition, since the silicon-oxygen bond can be easily formed and is relatively inexpensive, it can be suitably used as a composition for an electrolyte membrane for fuel cells.

  Furthermore, the proton conductive membrane of the present invention has a silicon-oxygen cross-linking structure and an acid group covalently bonded thereto with an organic group having 3 or more carbon atoms including a sulfide, sulfoxide, or sulfone bond having high oxidation resistance. Since they are connected, deterioration due to OH radicals, which are said to occur inside the fuel cell, is small, and the membrane structure is not easily destroyed by repeated heating and cooling and drying and drying, so that a highly durable proton conductive membrane can be provided. Further, the acid group-containing structure (B) is converted into a compound (α) containing a silicon and a thiol group, a compound containing an acid group, a metal salt thereof, or an acid group precursor group and an unsaturated double bond ( If the method of synthesis by β) is selected, various materials can be obtained relatively inexpensively and the reaction is easy.

1. Silicon-oxygen bond structure (A)
The proton conductive membrane according to the embodiment of the present invention includes a silicon-oxygen bond type structure (A) as a crosslinked structure. The silicon-oxygen bond structure (A) is a structure represented by the following general formula.

_{A: (R 2) n X} (3-n) -Si-R 1 -Si-X (3-n) (R 2) n
X represents an —O— bond or an OH group involved in crosslinking, R ₁ is selected from an oxygen atom and an optionally substituted chain hydrocarbon group that may contain a heteroatom having 1 to 50 carbon atoms; R ₂ is selected from methyl, ethyl, propyl and phenyl groups, where n = 0, 1, or 2.

  The cross-linked structure composed of the silicon-oxygen bond structure (A) is less likely to soften at high temperature or swell due to aqueous methanol solution, and can realize a fuel cell using high temperature operation or high concentration aqueous methanol solution as fuel.

  Some of the crosslinkable precursors forming these structures are commercially available as they are, and further, for example, by hydrosilylation reaction between a hydrocarbon compound having an unsaturated bond and the corresponding silyl compound, It can be synthesized by a reaction between a compound having an amino group or the like and a silane compound having a functional group capable of reacting with these groups.

  As represented by the above general formula, the silicon-oxygen bond structure (A) may be composed of only an inorganic substance, or may be composed of an organic-inorganic composite in which an organic compound is combined. is there. When the organic compound is combined, a fuel cell membrane having both the heat resistance of the inorganic substance and the flexibility of the organic substance can be formed. When such a compound is contained, the physical properties of each film including flexibility can be adjusted by designing the molecular structure between the crosslinked structures. Proton conductivity and fuel barrier properties, which are important characteristics as an electrolyte membrane for fuel cells, can also be controlled by the acid group concentration, molecular structure, and crosslinking density.

  For example, bis (triethoxysilyl) methane, 1,2-bis (trimethoxysilyl) ethane, 1,2-bis (triethoxysilyl) ethane, 1,6 is used as a raw material for the silicon-oxygen bond structure (A). -Bis (triethoxysilyl) hexane, 1,8-bis (triethoxysilyl) octane, 1,8-bis (diethoxymethylsilyl) octane, 1,8-bis (ethyldimethoxysilyl) octane, 1,9- Bis (triethoxysilyl) nonane, 1,4-bis (triethoxysilyl) benzene, 1,4-bis (trimethoxysilylmethyl) benzene, bis (trimethoxysilylethyl) benzene, tetramethoxysilane, tetraethoxysilane, Tetraisopropoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxy Silane, ethyltrimethoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, n-propyltrimethoxysilane, i-propyltrimethoxysilane, n-butyltri A crosslinked structure obtained by hydrolysis and polycondensation of alkoxysilane such as methoxysilane can be preferably used. Of these, one type or two or more types may be used as raw materials. In addition, the alkoxy group of the above compound may not be completely reacted, but it is more heat resistant, fuel barrier property, mechanical, more fully reacting and forming a dense structure when O-Si is formed. From the viewpoint of mechanical strength. Moreover, what substituted the alkoxy group of the enumerated compound by the other alkoxy group can be used similarly.

R ₁ is a molecular chain that is selected from an oxygen atom and an optionally substituted chain hydrocarbon group that can contain a hetero atom having 1 to 50 carbon atoms, and that controls film properties such as flexibility, In the case of atoms, a dense cross-linked structure is formed, and in the case of a carbon atom-containing molecular chain group, flexibility and flexibility can be imparted. However, when the number of carbon atoms exceeds 50, crosslinking is insufficient and heat resistance and swelling resistance cannot be expected.

  Particularly preferably, a hydrocarbon group has high oxidation resistance and can be suitably used. Examples of the hydrocarbon group include an alkylene group and an aromatic hydrocarbon group. Among these, a linear molecular chain composed of a polymethylene chain having no branching is particularly preferable.

R ₁ may have any heteroatom, but in this case, R ₁ is preferably an organic group containing a sulfide bond, a sulfoxide bond, or a sulfone bond. However, the main chain of R ₁ is composed of either a C—C bond alone or a C—S—C bond alone, or a combination of a C—C bond and a C—S—C bond alone. The bond of R ₁ is stable against acid and heat. In addition, a sulfide bond, a sulfoxide bond, or a sulfone bond refers to —R—S—R′—, —R ″ —S (═O) —R ″ ′ —, —R ″ ″ — SO ₂ —R ″ ″, respectively. It is a bonding group represented by '-. Provided that R, R ′, R ″, R ″ ′, R ″ ″, or R ″ ″ ′ are any groups selected from an alkylene group, an arylene group, an aralkylene group, and the like, and are the same. Or different. The sulfide bond and the sulfoxide bond may be oxidized to form a sulfone bond depending on conditions. However, once the sulfone bond is converted to a sulfone bond, it is not further oxidized and is very stable against heat and acid. That is, even a sulfide bond or a sulfoxide bond is sufficiently stable as it is, and forms a stable sulfone bond without being cleaved by stress such as oxidation. As a result, it can be said that these bonds are extremely stable with respect to any of strong acid conditions, oxidation conditions, and high temperature conditions that are experienced during fuel cell operation.

  Such a sulfide bond, sulfoxide bond, or sulfone bond can be easily obtained by, for example, an addition reaction of a thiol group to a carbon-carbon unsaturated bond. That is, a bond can be easily formed by mixing a material having an unsaturated bond and a material having a thiol group and heating or irradiating an actinic ray such as light.

  Further, as the silicon-oxygen bond structure (A), for example, both-end silanol polydimethylsiloxane, both-end silanol polydiphenylsiloxane, both-end silanol polydimethylsiloxane-polydiphenylsiloxane copolymer available from Gelest Co., Ltd. , Both ends chloropolydimethylsiloxane, diacetoxymethyl-terminated polydimethylsiloxane, methoxy-terminated polydimethylsiloxane, dimethoxymethylsilyl-terminated polydimethylsiloxane, trimethoxysilyl-terminated polydimethylsiloxane, methoxymethylsiloxane-dimethylsiloxane copolymer, etc. However, the present invention is not limited to these.

2. Acid group-containing structure (B)
In the proton conductive membrane, it is important that acid groups are present in a high concentration in the membrane and / or that acid groups are efficiently arranged for efficient proton conduction.

  During fuel cell operation, protons generated at the anode are supplied to the membrane, while protons in the membrane are consumed at the cathode. Some protons are present in advance in the proton conducting membrane. At the anode, the proton concentration increases due to proton supply, and at the cathode, the proton concentration decreases due to proton consumption. The proton concentration gradient generated in the membrane in this way is the driving force for proton diffusion from the anode to the cathode. If there are not enough protons in the membrane, there will be insufficient protons on the cathode side, and stable fuel cell operation cannot be expected. In addition, in a membrane that is softened at a high temperature or swelled with methanol, efficient proton conduction may be hindered. Therefore, in order to provide a proton-conducting membrane that operates stably, it is important that the acid groups are present in a high concentration and that the efficient arrangement of the acid groups is difficult to change depending on the environment.

  In the present invention, by including the acid group-containing structure (B) having a silicon-oxygen bond and having an acid group, there is a problem of dissolution, softening, and swelling even if the acid group is present in a high concentration in the film. The proton concentration in the membrane can be increased, and a fuel cell that stably exhibits high proton conductivity can be realized.

  The acid group-containing structure (B) in the present invention is a structure represented by the following general formula.

_{B: (R 4) m X} (3-m) -Si-R 3 -Y
X represents an —O— bond or OH group involved in crosslinking, Y represents an acid group, R ₃ represents a sulfide bond, a sulfoxide bond, or an organic group having 4 or more carbon atoms including a sulfone bond, R ₄ represents methyl, ethyl, Propyl or phenyl group, m = 0, 1, or 2. However, the backbone of _{R 3} consists only of C-C bonds and C-S-C bond.

  Examples of the acid group Y include sulfonic acid, carboxylic acid, phosphoric acid, phosphonic acid, phosphinic acid, and the like. The sulfonic acid group has a very low pKa value and can be particularly preferably used as a proton conductivity-imparting group. The sulfonic acid group can be obtained by previously introducing a compound having a sulfonic acid group into the membrane, for example, by oxidation of a thiol group, a polysulfide group such as a disulfide group or a tetrasulfide group, or a thioacetoxy group. Therefore, it can also be formed by introducing a sulfide such as a thiol group, a polysulfide group or a thioacetoxy group into the molecule and then oxidizing it. As described above, the sulfonic acid group can be easily introduced and has high acidity, thermal stability and oxidation resistance, and can be preferably used as a proton conductivity-imparting group of the proton conductive membrane.

As R ₃ , (CH ₂ ) ₃ —S— (CH ₂ ) ₂ , (CH ₂ ) ₃ —S (═O) — (CH ₂ ) ₂ , or (CH ₂ ) ₃ —SO ₂ — ( _{CH 2) 2, (CH 2} ) 3 -S- (CH 2) 3, (CH 2) 3 -S (= O) - (CH 2) 3, or _{(CH 2) 3 -SO 2 -} (CH 2 ₃ is preferably used.

  Such a sulfide bond is, for example, a compound (α) containing a silicon and a thiol group and a compound (β) containing either an acid group, a metal salt thereof, or an acid group precursor group and an unsaturated double bond. Bonds can be easily formed by heating the mixture or irradiating with actinic rays such as light. Similarly, it can be synthesized from a mixture of a silane compound (γ) having an unsaturated double bond and an acid group-containing compound (δ) having a thiol group and an acid group. The C—S—C bond (sulfide bond) thus formed is stable against acid and heat. In addition, as described above, sulfide bonds may undergo oxidation or the like depending on conditions to become sulfoxide bonds and further sulfone bonds. However, once a sulfone bond is formed, it does not undergo further oxidation, compared to ether bonds or ester bonds. It is very stable against heat and acid.

  Examples of the compound (α) containing silicon and thiol group include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltripropoxysilane, 3-mercaptopropyltributoxysilane, 2-mercaptoethyltri Methoxysilane, 2-mercaptoethyltriethoxysilane, 2-mercaptoethyltripropoxysilane, 2-mercaptoethyltributoxysilane, mercaptomethyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane 3-mercaptopropylmethyldipropoxysilane, 3-mercaptopropylmethyldibutoxysilane, 3-mercaptopropylethyldimethoxysilane, 3-mercaptopro Examples include pyrbutyldiethoxysilane, 3-mercaptopropylphenyldimethoxysilane, mercaptomethylmethyldiethoxysilane, and the like, but the present invention is not limited thereto.

  Among these, 3-mercaptopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) can be obtained in large quantities and at low cost, and can be preferably used.

  As the compound (β) containing either an acid group, its metal salt, or an acid group precursor group and an unsaturated double bond, vinyl sulfonic acid, allyl sulfonic acid, acrylic acid, methacrylic acid, vinyl phosphoric acid, allyl phosphorus, etc. And metal salts thereof. Moreover, the compound which substituted the sulfonic acid group of the said sulfonic acid compound by the thiol group can also be used conveniently.

  Examples of the silane compound (γ) having an unsaturated double bond include trimethoxyvinylsilane, triethoxyvinylsilane, trimethoxyallylsilane, triethoxyallylsilane, trimethoxyvinylsilane, triethoxyvinylsilane, p-styryltrimethoxysilane, p-styryltri. An ethoxysilane etc. are mentioned.

  Examples of the acid group-containing compound (δ) having a thiol group and an acid group include mercaptomethanesulfonic acid, mercaptoethanesulfonic acid, mercaptopropanesulfonic acid, mercaptobutanesulfonic acid, and the like.

  Further, an unsaturated double bond of a compound (β) having an unsaturated double bond and a silane compound (γ) having an unsaturated double bond and either an acid group, a metal salt thereof, or an acid group precursor group and an unsaturated double bond. Even if it connects with the compound represented by the following general formula, the acid group containing structure (B) in this invention is obtained.

HS- _{(CH 2)} n -SH
(In the formula, n represents an integer of 1 to 20)
Here, in the above formula, a methylene chain having no branch between two thiol groups is preferable. If there is a branch, the branch portion is more likely to be oxidized under oxidizing conditions during fuel cell operation, which is not preferable. In addition, the stability is higher when neither the aromatic ring nor the unsaturated bond is contained in the molecular chain.

  Similarly, the thiol group of the compound (α) containing silicon and a thiol group and the thiol group of the acid group-containing compound (δ) having a thiol group and an acid group may be communicated by a compound represented by the following general formula.

_{CH 2 = CH- (CH 2)} n -CH = CH 2
(In the formula, n represents an integer of 0 to 20)
Since this compound consists of a linear methylene chain and does not have a polar group or a branched structure, it has good oxidation resistance, acid resistance, and heat resistance. As specific compounds, butadiene, 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, 1,9-decadiene, 1,13-tetradecadiene and the like are easily available.

  FIG. 1 shows a schematic diagram of an example of the structure of a proton conductive membrane. Here, a silicon-oxygen bond type structure (A) that is a crosslinked basic structure (skeleton) and a compound (α) containing silicon and a thiol group are combined with an acid group, a metal salt thereof, or an acid group precursor group and an inert group. And an acid group-containing structure (B) covalently bonded to a compound (β) containing a saturated double bond.

  FIG. 2A shows a structural example of precursors of A and B, and FIG. 2B shows a structural example in which A and B are connected by a silicon-oxygen bond.

  Here, it is preferable that A and B are connected by a silicon-oxygen bond, and at this time, an acid group responsible for proton conduction can exist more stably.

  In general, silicon-oxygen crosslinked structures have a rigid structure, so if there are a large number of highly polar parts such as acid groups, stress concentration occurs due to rapid temperature fluctuations or rapid solvent intrusion, resulting in structural breakdown or molecular chain breakage. In some cases, performance degradation such as proton conductivity and fuel barrier property of the proton conductive membrane may occur due to.

In the present invention, the distance between the acid group and the silicon atom forming the silicon-oxygen cross-linked structure can be separated by a certain amount or more by R ₃ , so that while maintaining the characteristics of the film such as high fuel barrier property and strength, The membrane structure is not easily destroyed by repeated drying and drying, and a highly durable proton conductive membrane can be provided.

  Furthermore, since the acid group-containing structure (B) has many organic sites, flexibility is imparted to the proton conductive membrane, and impact resistance is enhanced.

  In the proton conductive membrane according to the present invention, the atomic group of the acid group in the acid group-containing structure (B) is bonded to silicon having a siloxane bond via a distance of at least four or more carbon bonds. Preferably it is. Thereby, it becomes possible to suppress the destruction of the film and the deterioration of the characteristics due to the rapid penetration of the polar solvent which may occur when the acid group-silicon bond distance is short.

3. Porous material In order to increase the strength of the proton conductive membrane and suppress swelling due to water content, the porous material may be impregnated to form a membrane. Examples of the porous material include polymer materials such as polyethylene, ultrahigh molecular weight polyethylene, polypropylene, a fluororesin typified by polytetrafluoroethylene, polyimide, and a polyarylate liquid crystal polymer. Among these porous materials, a porous material having a film thickness of 20 to 100 μm, a pore diameter of 0.05 to 10 μm, and a porosity of 60% or more is used. The porous material is preferably subjected to a hydrophilic treatment. Among them, a porous film made of polyethylene, ultrahigh molecular weight polyethylene, and polypropylene is excellent in oxidation resistance, very flexible, and can be suitably used because it is relatively easy to obtain at a low cost.

  More preferably, inorganic materials such as glass fiber nonwoven fabric and glass fiber cloth have high heat resistance and are easily available, and thus can be used preferably.

  As the glass woven fabric, there are weaves such as a plain woven fabric, a twill woven fabric, a Turkish satin woven fabric, a copying woven fabric, a leash fabric, etc. In the present invention, a plain woven fabric is particularly preferable for preventing elongation. In addition, it is not preferable to use an excessively dense woven fabric in order to reduce the inhibition of the conductivity of the proton conductive membrane with respect to the plain woven fabric. This is because the ion conduction path may be blocked by the dense texture. Therefore, a coarser weaving method in which every other yarn is pulled out is preferable. In the present invention, such a weaving method is referred to as a plain weave.

  In order to define the structure of the plain woven fabric, there are a single yarn count, a woven density (pitch), and the like. In the proton conductive membrane of the present invention, those in the following ranges are suitable. The single yarn is obtained by bundling about 50 to 1000 glass fibers and twisting them, and the count of the single yarn is called Tex. The unit of Tex is g / 1000 m, which is the mass per 1000 m. A suitable count is 3 to 50 Tex. Although it is preferable that it is thin, if it is too thin, it will be easy to cut in the process, and even if it exceeds 50 Tex, it becomes difficult to produce a thin film-like substrate suitable for a proton conductive membrane.

  The weaving density is also called the driving density or pitch, and means the number of single yarns per 25 mm width. When the woven density is coarse, the reinforcing effect is lost, and on the contrary, the production of a dense one is limited by the fineness of the single yarn described above. A suitable weave density is selected in the range of 40 to 200/25 mm width.

The thickness of the plain woven fabric is substantially determined by the above specifications, and the thickness in the above specifications is 20 to 100 μm. The basis weight (mass per m ² ) is related to the above thickness, but is usually 10 to 50 g / m ² , preferably 15 to 25 g / m ² .

  In the case of a sheet made of a glass fiber nonwoven fabric, the film thickness is preferably 10 μm or more and 100 μm or less. Particularly preferably, the thickness is 20 μm to 60 μm. A higher porosity is preferable because a larger amount of electrolyte can be filled. However, the strength of the sheet is lowered, and this is a balance with that, and the porosity is 30% or more and 99% or less, more preferably 50% or more and 95% or less. It is. The glass material is preferably acid resistant glass or alkali resistant glass.

  As mentioned above, the constituent components of the proton conducting membrane have been mentioned. However, the reinforcing material, the softening agent, the stabilizer, the colorant, the antioxidant, the inorganic or organic filler, the proton conduction auxiliary, within the range not impairing the object of the present invention. Other optional ingredients such as agents can be added. These addition amounts are not limited as long as the performance as a film is not deteriorated, and depending on the structure of the film material, the addition amount that does not deteriorate the performance is largely different, so it cannot be generally stated. The total weight of the agent is preferably 50% by weight or less.

<Method for producing proton conductive membrane>
Crosslinkable proton conduction comprising a silicon-oxygen bond type structure (A) containing a cross-linked structure by a silicon-oxygen bond and an acid group-containing structure (B) covalently bonded to the silicon-oxygen bond and having an acid group The conductive film can be produced, for example, by using the following steps. The following two manufacturing methods are examples, and it is needless to say that they can be manufactured by various other manufacturing methods.

a) First production method A compound (α) containing silicon and a thiol group which is covalently bonded to a silicon-oxygen bond and which is a precursor of an acid group-containing structure (B) having an acid group, and a sulfonic acid group A step of mixing a compound (β) containing a saturated double bond and forming an acid group-containing structure (B) having a sulfide bond and / or a precursor thereof by heating or ultraviolet irradiation. A step of mixing the acid group-containing structure (B) and / or its precursor with the silicon-oxygen bond-type structure (A) and / or its precursor. Forming a film of the mixed solution; Heat curing the film.

b) Second production method Compound (α) containing silicon and thiol group which is covalent bond with silicon-oxygen bond and precursor of acid group-containing structure (B) having acid group, and thiol group and unsaturated A step of mixing a compound (β) containing a double bond and forming a thiol group-containing structure having a sulfide bond and / or a precursor thereof by heating or ultraviolet irradiation. A step of mixing the thiol group-containing structure and / or its precursor with the silicon-oxygen bond type structure (A) and / or its precursor. Forming a film of the mixed solution; Heat curing the film. Oxidizing the thiol group contained in the film.

  Next, examples of suitable methods for particularly important steps in the production method will be given.

1. Mixing method When preparing the said mixture, you may use a solvent (C). The solvent to be used is not particularly limited as long as the respective materials can be uniformly mixed. In general, water, methanol, ethanol, alcohol solvents such as 1-propanol, 2-propanol, and t-ptanol, ether solvents such as tetrahydrofuran and 1,4-dioxane, and the like can be preferably used.

  Although there is no restriction | limiting in particular about the ratio of a solvent, Usually, the density | concentration whose solid content concentration is about 90 to 10 weight% can be used preferably.

  Further, as described later, a catalyst (D) may be mixed.

  In addition to adding water as a solvent, water necessary for hydrolysis may be added. Water is usually added in an equimolar amount with respect to the hydrolyzable silyl group, but may be added in a large amount to accelerate the reaction, or may be added in a small amount to suppress the reaction.

  For mixing, a known method such as stirring and vibration may be used, and there is no particular limitation as long as sufficient mixing is possible. Moreover, you may perform a heating, pressurization, defoaming, deaeration, etc. as needed.

2. Method for Forming Sulfide Bond A sulfide bond can be easily obtained by, for example, an addition reaction of a thiol group to a carbon-carbon unsaturated bond. That is, it is obtained by mixing a material having an unsaturated double bond and a material having a thiol group, and heating or irradiation with actinic rays such as light. In the present invention, the formation of a sulfide bond and the crosslinking reaction of alkoxysilane may occur simultaneously. For example, a mixture of a compound (α) containing silicon and a thiol group and a compound (β) containing either an acid group, a metal salt thereof, or an acid group precursor group and an unsaturated double bond is gelled. The method of heating on the conditions which do not carry out, the method of forming a sulfide bond at the time of heat-hardening after film formation mentioned later, etc. are mentioned. Further, a method of forming a sulfide bond prior to hydrolysis / polycondensation of alkoxysilane under conditions where alkoxysilane does not easily react can be suitably used. In this case, a mixture of a compound (α) containing silicon and a thiol group and an acid group, a metal salt thereof, or an acid group precursor group and a compound (β) containing an unsaturated double bond at room temperature A method of irradiating ultraviolet rays while stirring at the following temperature can be preferably used. In particular, (β) is preferably a metal salt of an acid group or a compound containing an acid group precursor group and an unsaturated double bond.

  In the case of performing the ultraviolet irradiation, the ultraviolet irradiation amount and the ultraviolet irradiation time are appropriately determined depending on the intensity of the ultraviolet light, the type of the crosslinkable compound, and the like. The ultraviolet light source is not particularly limited, and for example, a general ultraviolet light source such as a fluorescent lamp or a high-pressure mercury lamp can be used. Moreover, as a light source, you may use a low pressure mercury lamp, a xenon lamp, a metal halide lamp, a germicidal lamp, a laser beam etc., for example.

  As described above, when compounds (γ) and (δ) are used instead of compounds (α) and (β), sulfide bonds can be formed in the same manner.

3. Film Forming Method In order to form the mixed solution prepared above into a film shape, a known method such as casting, coating, casting, or the like can be used. The method for forming the film is not particularly limited as long as a uniform film can be obtained. The thickness of the film is not particularly limited, but can be formed to have an arbitrary thickness between 10 μm and 1 mm. The proton conductive membrane for a fuel cell is appropriately determined from the proton conductivity, fuel barrier properties, and mechanical strength of the membrane, and usually a membrane having a thickness of 20 to 300 μm can be preferably used. The thickness of the proton conductive membrane of the invention is also produced according to this.

  Moreover, when performing this film-forming process, the above-mentioned porous materials, fibers, mats, fibrils and other supports and reinforcing materials may be added, or these supports may be impregnated.

  The impregnation method is not limited to a dipping method, a potting method, a roll press method, a vacuum press method, or the like, and a known method may be used, and heating, pressurization, or the like may be performed.

4). Heat-curing method A hydrolyzable silyl group contained in the film-formed material formed above is hydrolyzed and condensed, and / or a silanol group is condensed to form a structure composed of a silicon-oxygen crosslinked structure.

  The proton conductive membrane in the present invention is characterized in that a crosslinked structure is formed by hydrolysis and condensation of an alkoxysilyl group or the like, stably exhibits proton conductivity even at high temperatures, and has little shape change. Such generation of Si—O—Si bonds by hydrolysis or condensation of alkoxysilyl groups or the like is well known as a sol-gel reaction.

  In the sol-gel reaction, the catalyst (D) is usually used for reaction acceleration and control. As the catalyst, an acid or a base is usually used.

  The catalyst (D) used in the method for producing a proton conductive membrane of the present invention may be an acid or a base.

  When an acid catalyst is used, a Prinsted acid such as hydrochloric acid, sulfuric acid, phosphoric acid or acetic acid is used. The type, concentration, etc. of the acid are not particularly limited as long as it is within the available range. Of these, hydrochloric acid has a relatively low acid residue after the reaction and can be suitably used. When hydrochloric acid is used, the concentration and the like are not particularly limited, but those of 0.01 to 12N are usually used.

  In general, it is known that when an acid is used, hydrolysis and condensation compete with each other, so that the reaction proceeds evenly between Si molecules, resulting in a linear cross-linked structure with few branches.

  On the other hand, when a base is used as a catalyst, hydrolysis occurs all at once, and once a single Si molecule is hydrolyzed, the reaction proceeds intensively in that molecule, so that a dendritic structure with many branches is obtained. It has been. In the present invention, any method can be used in consideration of film physical properties. In order to highlight the characteristics of the formation of particles and their continuum, a base catalyst can be preferably used. In this case, it is preferable to salt the acid group-containing molecule (β or δ).

  As the base catalyst, an aqueous solution of sodium hydroxide, potassium hydroxide, ammonia or the like can be used. Among these, ammonia that does not produce a residual salt can be preferably used. Furthermore, organic amines can also be preferably used in consideration of compatibility with the thiol group-containing compound.

  Organic amines can be used without any particular limitation, but usually those having a boiling point of 50 ° C. or higher are preferably used. Specific examples of organic amines within this range that are readily available include triethylamine, dipropylamine, and isobutyl. Examples thereof include amine, diethylamine, diethylethanolamine, triethanolamine, pyridine, piperazine, and tetramethylammonium hydroxide, and any of them can be suitably used.

  Further, fluorides such as potassium fluoride, ammonium fluoride, tetramethylammonium fluoride, and tetraethylammonium fluoride may be used as the condensation catalyst.

  The addition amount of the catalyst can be arbitrarily set, and is appropriately determined taking into consideration the reaction rate, compatibility with the film material, and the like.

  The timing of introducing the catalyst may be any timing. The simplest method is a method introduced when preparing the mixture. In this case, it is necessary to consider the pot life and the set time in the film formation.

  Although the condensation reaction can be performed at room temperature, it is preferable to perform heating in order to shorten the reaction time and perform more efficient curing. Heating may be performed by a known method, and heating by an oven, pressure heating by an autoclave, far infrared heating, electromagnetic induction heating, microwave heating, or the like can be used. Heating can be performed at any temperature from room temperature to 300 ° C., preferably 100 to 250 ° C. At this time, heating may be performed under an inert gas or the like under reduced pressure, nitrogen, or argon.

  In addition, a method of avoiding a sudden environmental change, such as heating after curing for some time at room temperature and then gradually raising the temperature to a high temperature, may be employed.

  Further, it may be carried out under steam in order to replenish water necessary for hydrolysis, and may be carried out under solvent vapor in order to prevent rapid membrane drying.

  The film that has been heat-cured may be subjected to ion exchange with sulfuric acid or the like after removing unreacted substances and effect catalysts by washing as necessary.

  The structure composed of a silicon-oxygen crosslinked structure formed in the heat curing step is preferably composed of a continuous pair of particles. Here, a method in which a more suitable particle structure is formed by using the polarity control agent (E) is shown.

  In the proton conductive membrane of the present invention, it is essential that a substance (hydrogen ion or its hydrate) can diffuse and move. Therefore, it is preferable to form a proton conduction path for transporting ions inside the membrane. The gap between them plays that role.

  In the proton conductive membrane of the present invention, a polarity control agent (E) may be used for the efficient formation of the particles and the gaps between the particles.

  Usually, if an inorganic material such as tetraethoxysilane is hydrolyzed / condensed and heated sufficiently (for example, at 800 ° C.), a dense glassy cross-linked product is obtained, and micropores corresponding to ion channels are formed. Not. Such hydrolysis, condensation, and gelation processes (sol-gel reaction) of alkoxysilanes have been studied in detail. For example, Blinker et al. (SOL-GEL SCIENCE) (Academic Press, Inc. 1990). ), “Chemistry of Sol-Gel Method” (Agune Jofusha, 1988). In the sol-gel reaction, particle growth, particle bonding, and densification occur in this order. Detailed analysis of typical alkoxysilane materials has been made, and reaction conditions have been clarified.

  In the proton conductive membrane of the present invention, the alkoxysilane material having a substituent is used as a raw material, and further, particle size control, particle bond control, and accompanying particle gap control are important, and this is achieved. As a result of various investigations, the inventors have found that the addition of the polarity control agent (E) enables the formation of particle continuum and the accompanying particle gap control.

  The polarity control agent (E) is an organic liquid and desirably water-soluble. When the above-mentioned solvent is used, it is possible to adjust the solubility of the thiol group-containing compound in the solvent, so that it is possible to appropriately control the particle diameter of the particles and the gap between the particles. Furthermore, there is an advantage that the membrane can be easily extracted by washing with water.

  Moreover, it is preferable that the polarity control agent (E) has a boiling point of 100 ° C. or higher and a melting point of 25 ° C. or higher. If the boiling point of the polarity control agent (E) is too low, it will volatilize during the condensation reaction (mainly performed under heating conditions) when forming the film, and particle size control and particle gap control will not be possible. Sufficient conductivity cannot be ensured. Accordingly, the boiling point of the polarity control agent (E) is preferably not less than the boiling point of the solvent when a solvent is used, particularly preferably not less than 100 ° C., more preferably not less than 150 ° C., still more preferably 200 ° C. That's it.

  In addition, when the intermolecular interaction of the polarity control agent (E) is too large, the polarity control agent (E) may solidify and form a large domain other than the gap between the particles. The fuel gas barrier property of the membrane may be lowered. The magnitude of the intermolecular interaction of the polarity control agent (E) is substantially correlated with the melting point, and the melting point can be used as an index. The melting point of the polarity control agent (E) used in the present invention is preferably 25 ° C. or less. When the melting point is 25 ° C. or lower, an appropriate intermolecular interaction can be expected and preferably used, and more preferably 15 ° C. or lower.

  Examples of such organic substances include those having a polar substituent such as a hydroxyl group, an ether group, an amide group, and an ester group, those having an acid group such as a carboxylic acid group and a sulfonic acid group, or salts thereof. Examples thereof include those having a base group such as amine or a salt thereof. Of these, acids, bases and salts thereof are more preferably nonionic since it is necessary to pay attention to the interaction with these catalysts when using catalysts during hydrolysis and condensation. Can be used.

  Specifically, glycerin and its derivatives, ethylene glycol and its derivatives, ethylene glycol polymers (diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycols of various molecular weights, etc.), glucose, fructose, mannitol, sorbit, sucrose, etc. Sugars, polyhydric hydroxyl compounds such as pentaerythritol, water-soluble resins such as polyoxyalkylene, polyvinyl alcohol, polyvinyl pyrrolidone and acrylic acid, carbonates such as ethylene carbonate and propylene carbonate, alkyl sulfur oxides such as dimethyl sulfoxide, Examples include amides such as dimethylformamide, and polyoxyethylene alkyl ethers such as ethylene glycol monomethyl ether, but the present invention is not limited thereto. Not.

  In addition, ethylene glycol (mono / di) alkyl ethers in which part or all of the terminal OHs of these ethylene glycols are alkyl ethers can also be preferably used. Examples of this include ethylene glycol monomethyl ether, dimethyl ether, monoethyl ether, diethyl ether, monopropyl ether, dipropyl ether, monobutyl ether, diptyl ether, monopentyl ether, dipentyl ether, monodicyclopentenyl ether, monoglycidyl. Examples include ether, diglycidyl ether, monophenyl ether, diphenyl ether, and monovinyl ether divinyl ether. Further, part or all of the terminal OH of ethylene glycol may be an ester. Examples thereof include ethylene glycol monoacetates and diacetates.

  In the case where an acid and a salt thereof may be used, an acid such as acetic acid, propionic acid, dodecyl sulfuric acid, dodecyl sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid, toluene sulfonic acid, and salts thereof may be used. In addition, when salts thereof may be used, ammonium salts such as trimethylbenzylammonium chloride, amines such as N, N-dimethylbenzylamine, and salts thereof are exemplified. Furthermore, zwitterionic compounds such as amino acids such as sodium glutamate can also be used.

  In addition, although it is possible to use an inorganic salt or the like as the polarity control agent (E), in general, an inorganic salt has a strong cohesive force (high melting point), and even if added to a mixture containing a thiol group-containing compound, Fine dispersion at a level is difficult, resulting in large crystals and amorphous solids, and there is a high possibility of forming large aggregates that are disadvantageous to film physical properties and gas barrier properties.

  In the present invention, other ionic surfactants can be suitably used, and anionic, cationic, and amphoteric surfactants can also be used in consideration of the interaction with the catalyst.

  Among these, polyoxyalkylene which is a liquid water-soluble organic substance and has an appropriate compatibility (or appropriate incompatibility) with a thiol group-containing compound is preferable, and an ethylene glycol polymer is particularly preferable among them. Can do.

  As the polymer of ethylene glycol, dimer (diethylene glycol) to polyethylene glycol having various molecular weights are commercially available, and compatibility, viscosity, molecular size and the like can be appropriately selected and can be preferably used. In particular, in the present invention, diethylene glycol having a molecular weight of about 100 to polyethylene glycol having an average molecular weight of 600 can be more preferably used, and tetraethylene glycol or polyethylene glycol having a molecular weight of about 200 can be particularly preferably used.

  The size of the particles and the gaps between the particles are the compatibility with the thiol group-containing compound, the compatibility balance with the entire film-forming raw material system including the solvent and additives, the molecular weight of the polarity control agent (E), and Determined by blending amount. In the case of the present invention, there is a correlation between the average molecular weight of the polarity control agent (F) and the diameter of the particle gap, and when polyethylene glycol having a molecular weight of more than 600 is used, the diameter becomes large and gas barrier properties and physical properties are reduced. On the other hand, if the molecular weight is less than 100, the film has a small diameter and becomes too dense, and there is a tendency that sufficient particle gaps are not formed.

  The amount of the polarity control agent (E) added depends on the type and molecular weight of the polarity control agent (E) used, or the structure of the film. Add 3 to 150 parts by weight with respect to parts by weight. If the amount is less than 3 parts by weight, the effect of controlling the particle diameter and the particle gap is hardly observed. If the amount exceeds 150 parts by weight, the particle gap becomes too large, the film becomes brittle, and gas permeation becomes remarkable. Probability is high.

  As described above, the proton conductive membrane of the present invention can be designed and formed with a custom-made structure of the gap between particles, that is, the proton conduction path, by using the polarity control agent (E). A film having a good balance with various film properties such as permeability and film strength can be formed. This is a point that is different from a conventional sulfonated fluororesin membrane in which the proton conduction path is uniquely determined by the molecular structure.

  In addition, since the proton conduction path controlled in this way does not deform even in a high temperature / high humidity environment, stable operation is possible even when the fuel cell is operated at a high temperature.

5. Oxidation method of thiol group As described above, the membrane may be washed with water prior to oxidation. Further, when an organic amine is used as a catalyst, the membrane is coated with an acid such as hydrochloric acid or sulfuric acid prior to oxidation. May be contacted to remove the catalyst.

  The water used for washing is preferably water containing no metal ions, such as distilled water or ion exchange water. In washing with water, heating may be performed, and washing with water may be made more efficient by applying pressure or vibration. Furthermore, in order to promote the penetration into the membrane, a mixed solvent in which methanol, ethanol, n-propanol, i-propanol, acetone, tetrahydrofuran or the like is added to water may be used.

  The thiol group oxidation method used in the present invention is not particularly limited, but a general oxidizing agent can be used. Specifically, for example, as described in a new experimental chemistry course (Maruzen, 3rd edition, Vol. 15, 1976), nitric acid, hydrogen peroxide, oxygen, organic peracid (percarboxylic acid), bromine Oxidizing agents such as water, hypochlorite, hypobromite, potassium permanganate, and chromic acid can be used.

  Among these, hydrogen peroxide and organic peracids (peracetic acid and perbenzoic acids) can be suitably used because they are relatively easy to handle and have a good oxidation yield.

  Furthermore, in order to protonate the sulfonic acid group in the membrane obtained by oxidation, it may be contacted with a strong acid such as hydrochloric acid or sulfuric acid. In this case, protonation conditions such as acid concentration, immersion time, and immersion temperature are appropriately determined depending on the sulfonic acid group-containing concentration in the membrane, the porosity of the membrane, the affinity with the acid, and the like. A typical example is a method of immersing the film in 1N sulfuric acid at 50 ° C. for 1 hour.

  The oxidized film is preferably washed with water to remove the oxidizing agent in the film.

  Furthermore, the oxidized film may be subjected to acid treatment with hydrochloric acid, sulfuric acid or the like. It can be expected that impurities and unnecessary metal ions in the film are washed away by the acid treatment. It is preferable to perform water washing after the acid treatment.

<Evaluation method>
(1) Evaluation of proton conductivity In a conventional electrochemical cell obtained by the production method of the present invention (for example, the same as that described in FIG. 3 in JP-A-2002-184427) The proton conductive membrane and the platinum plate were brought into close contact with each other. The platinum plate was connected to an electrochemical impedance measuring device (1260 type, manufactured by Solartron), and impedance measurement was performed in a frequency range of 0.1 Hz to 100 kHz to evaluate the proton conductivity of the ion conductive membrane.

  In the above measurement, the sample is supported in an electrically insulated sealed container, and the cell temperature is changed from room temperature to 160 ° C. with a temperature controller in a water vapor atmosphere (95 to 100% RH). Comparative evaluation was carried out by proton conductivity.

(2) Shape stability test The proton conductive membrane obtained in this example was cut into a square having a side of 5 cm, held in a pressure cooker at 120 ° C. and 95% RH for 6 hours, and then returned to room temperature. The rate of change was measured.

(3) Impact resistance test The proton conductive membrane obtained in this example was cut into a square having a side of 5 cm, dried at 50 ° C. for 3 hours using a vacuum oven, and then heated to 80 ° C. hot water. Immersion and let stand for 3 hours. The membrane was sufficiently washed with water, and sandwiched between gas diffusion electrodes (E-TEK, USA, area 2.5 × 2.5 cm, platinum loading 0.5 mg / cm ² ), and this was electrochem (Electrochem). ) Was introduced into a single cell (membrane area: 5.25 cm ² ) manufactured by the company to produce a single cell fuel cell. Hydrogen was introduced into the anode side, oxygen was introduced into the cathode side, an electronic load was connected to the output, and a voltage-current curve was measured at 0 to 120 ° C.

  During measurement, hydrogen was humidified using a bubbler, and the humidity was 95% RH. The humidity was adjusted by changing the bubbler temperature, and 60% RH was adopted as the low humidity measurement. The impact resistance was evaluated from the OCV during power generation at 60% RH. In the measurement at 120 ° C., pressurization was performed. In any film, the OCV during power generation before the impact resistance test was 0.9 V or more.

Example 1
A liquid prepared by mixing 0.6 g of 3-mercaptopropyltrimethoxysilane, 0.40 g of sodium allylsulfonate, 1.5 g of isopropanol, and 1.32 g of water was prepared. While stirring this liquid, the surface of the liquid was irradiated with ultraviolet rays having a wavelength of 254 μm and 610 μW / cm ² at about 25 ° C. for 1 hour. This liquid was mixed with 0.98 g of 1,8-bis (diethoxymethylsilyl) octane (manufactured by Gelest), 1.5 g of isopropanol, and a liquid obtained by stirring 0.30 g of 1N hydrochloric acid for several minutes. Stir for several minutes.

  Then, it was poured into a polystyrene petri dish (manufactured by Yamamoto Seisakusho) with an inner diameter of 8.4 cm, heated at room temperature (20 ° C.) for 15 hours, under 80 ° C. saturated steam for 10 hours, and further heated in a 100 ° C. oven, A transparent and flexible film was obtained. Before evaluation and measurement, the sample was immersed in 10% sulfuric acid and further washed several times with purified water. The evaluation results of the film are shown in Table 1.

(Example 2)
A 50 μm-thick glass fiber mesh plain weave “WEA05E” (manufactured by Nitto Boseki Co., Ltd.) is immersed in an aqueous solution of trihydroxysilylpropane sulfonic acid (manufactured by Gelest), which is a silane coupling agent, for 1 hour in advance. The mixture was heated in an oven at 80 ° C. for 12 hours. The obtained dry glass fiber was washed with water for 2 hours to remove excess silane coupling agent.

Next, after stirring the mixed solution prepared in Example 1, the surface-treated glass fiber mesh plain weave placed on a Teflon (registered trademark) sheet was impregnated using a roll. The impregnation amount was adjusted to 50 g / m ² and roll impregnation was performed twice. Another Teflon (registered trademark) sheet was placed thereon, and the sheet was cured at room temperature (20 ° C.) for 15 hours while being sandwiched between two glass plates. Subsequent treatment was carried out in the same manner as in Example 1 to obtain a film. The film did not break even when pulled or repeatedly bent. The evaluation results of the film are shown in Table 1.

(Example 3)
A membrane was prepared in the same manner as in Example 2, except that 0.9 g of 1,2-bis (triethoxysilyl) ethane (manufactured by Gelest) was used instead of 1,8-bis (diethoxymethylsilyl) octane. The evaluation results of the film are shown in Table 1.

(Comparative Example 1)
0.50 g of 1,8-bis (triethoxysilyl) octane (manufactured by Gelest) and 0.50 g of tetraethoxylane were dissolved in 1.5 g of isopropanol. To 1.8 g of 33% aqueous solution of 3- (trihydroxysilyl) propanesulfonic acid, 1.5 g of isopropanol was added. Both were combined and stirred for several minutes.

  Thereafter, a transparent and hard film was obtained in the same manner as in Example 1.

(Comparative Example 2)
A commercially available Nafion 117 membrane, which is an electrolyte membrane for PEFC, was used as it was.

  Below, the outline | summary of a mixing | blending of the obtained Example and a comparative example is shown.

(Example 1): Basic proton conductive membrane of the present invention (Example 2): Composite membrane reinforced with the membrane of Example 1 (Example 3): R _{1 of the} structure (A) Glass fiber composite reinforced membrane when CH is CH ₂ CH ₂ (Comparative Example 1): As a structure (B), it is composed of a structure in which silicon and sulfur of a sulfonic acid group are linked by a hydrocarbon group having 3 or less carbon atoms. Porous membrane reinforced membrane (Comparative Example 2): Conventional typical fluorinated sulfonic acid (here, Nafion 117) membrane The results obtained are shown in Table 1 below.

  From the comparison between Examples 1, 2, and 3 and Comparative Examples 1 and 2, according to the present invention, it has high proton conductivity and dimensional stability even at high temperatures, and further changes in the environment such as repeated wet and dry cycles and repeated cold and hot cycles. It was found that the OCV did not decrease even when receiving. As a result, it was shown that the generation of cracks in the film and the removal of the acid component did not occur, and stable power generation performance was exhibited.

  In the above-described embodiment, the case of power generation using hydrogen and oxygen has been described. However, the present invention can also be applied to the case where air is used instead of oxygen or a methanol aqueous solution is used as fuel.

It is a schematic diagram which shows the image structural example of the proton conductive film | membrane which concerns on this embodiment. FIG. 2A is a structural diagram of each component before producing the proton conductive membrane according to the present embodiment, and FIG. 2B shows an example of a bonded state after producing the proton conductive membrane (Example 1). FIG.

Claims (10)

A proton conductive membrane having a crosslinked structure by a silicon-oxygen bond, wherein the proton conductive membrane includes a silicon-oxygen bond type structure (A) represented by the following general formula, and the following general formula: acid group-containing structure represented and (B), possess,
In the crosslinked structure by the silicon-oxygen bond, the substituent X of the silicon-oxygen bond structure (A) and the substituent X of the acid group-containing structure (B) are hydrolyzed and condensed or condensed. proton conducting membrane, wherein the structure der Rukoto formed by.
_{A: (R 2) n X} (3-n) -Si-R 1 -Si-X (3-n) (R 2) n
(Wherein X represents an —O— bond or an OH group, R ₁ is selected from an oxygen atom and an optionally substituted chain hydrocarbon group which may contain a hetero atom having 1 to 50 carbon atoms; R ₂ is selected from methyl, ethyl, propyl and phenyl groups, where n = 0, 1, or 2.)
_{B: (R 4) m X} (3-m) -Si-R 3 -Y
(In the formula, X represents an —O— bond or an OH group, Y represents an acid group, R ₃ is selected from a sulfide bond, a sulfoxide bond, and an organic group having 3 or more carbon atoms including a sulfone bond, provided that R The main chain of ₃ consists of either a C—C bond or a C—S—C bond, or a combination thereof, R ₄ is selected from methyl, ethyl, propyl, and phenyl groups, and m = 0, Or 2) R ₃ is (CH ₂ ) ₃ —S— (CH ₂ ) ₂ , (CH ₂ ) ₃ —S (═O) — (CH ₂ ) ₂ , (CH ₂ ) ₃ —SO ₂ — (CH ₂ ) _2. , (CH ₂ ) ₃ —S— (CH ₂ ) ₃ , (CH ₂ ) ₃ —S (═O) — (CH ₂ ) ₃ , and (CH ₂ ) ₃ —SO ₂ — (CH ₂ ) ₃ The proton conductive membrane according to claim 1, wherein   The proton conductive membrane according to claim 1 or 2, wherein Y is a sulfonic acid group.   The structure (B) is synthesized from a compound (α) containing a silicon and thiol group and a compound (β) containing either an acid group, a metal salt thereof, or an acid group precursor group and an unsaturated double bond. The proton conductive membrane according to claim 1. R ₁ is a chain hydrocarbon group having 1 to 50 carbon atoms, or a chain hydrocarbon group having 1 to 50 carbon atoms including a sulfide bond, a sulfoxide bond, or a sulfone bond, provided that R ₁ The main chain consists of either a C—C bond alone or a C—S—C bond alone, or a combination of a C—C bond and a C—S—C bond alone. Proton conducting membrane. The proton conductive membrane according to claim 5, wherein R ₁ is a hydrocarbon group having 2 carbon atoms.   The proton conductive membrane according to any one of claims 1 to 6, which is composite-reinforced with a porous material.   A membrane-electrode assembly, wherein a gas diffusion electrode is joined to the proton conducting membrane according to any one of claims 1 to 7.   A polymer electrolyte fuel cell comprising the membrane-electrode assembly according to claim 8.   The membrane-electrode assembly according to claim 8 is used as a unit cell, and a pair of separators serving as fuel and oxygen passages are installed outside the unit cell, and a plurality of adjacent unit cells are connected to each other. A solid polymer fuel cell, characterized in that:

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