JP2006339064A - Polybenzimidazole-based proton-conducting polymer film, manufacturing method of the same, and fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new proton-conducting polymer film as a polymeric electrolyte film, capable of operating in a condition of high temperature and non-humidification, superior in proton conductivity and workability at assembling of the fuel cell, showing fully practical characteristics in durability. <P>SOLUTION: The polybenzimidazole-based proton conducting polymer film is formed by impregnating the polymeric film composed of polybenzimidazole expressed by Formula (1) as the main component with an acidic molecule, wherein X denotes one kind selected from -O-, -SO<SB>2</SB>-, -S-, -CO-, -C(CH<SB>3</SB>)<SB>2</SB>-, -C(CH<SB>3</SB>)<SB>2</SB>-, and -O-Ph-O-, and Ph denotes one kind selected from among orthophenylene, metaphenylene, and paraphenylene. The manufacturing method of the proton conductive film and the fuel cell, using the same, are provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-temperature non-humidified fuel cell membrane obtained by impregnating a polybenzimidazole compound with an acidic compound, a method for producing the membrane, and a fuel cell using the membrane.

  As a new energy source, a polymer electrolyte fuel cell membrane has attracted attention. The polymer membrane used therein must exhibit good proton conductivity as a cation exchange membrane and be sufficiently stable chemically, thermally, electrochemically and mechanically. For this reason, perfluorocarbon sulfonic acid membranes, mainly “Nafion (registered trademark)” manufactured by DuPont, USA, have been used as long-term usable products. However, when a perfluorocarbon sulfonic acid membrane is used, if it is attempted to operate at a temperature exceeding 100 ° C., the moisture content of the membrane will drop drastically, and the membrane will soften significantly, thereby exhibiting sufficient performance as a fuel cell. I can't.

  In order to operate a fuel cell in a high temperature region of 100 ° C. or higher, a fuel cell membrane made of a polymer having high heat resistance is basically required. Polybenzimidazole can be said to be a polymer having high thermal stability, but there is a report that when it is impregnated with phosphoric acid, the thermal stability is further increased (see, for example, Non-Patent Document 1), and polybenzimidazole is impregnated with phosphoric acid. A high-temperature fuel cell electrolyte membrane having an ion conduction function extracted by phosphoric acid has been reported (see, for example, Patent Document 1).

  However, since polybenzimidazole itself does not have ionic conductivity, it requires a large amount of phosphoric acid to be impregnated, and phosphoric acid, which is a low-molecular compound, gradually flows out and the ionic conductivity decreases with time. There was a problem. Furthermore, since the membrane swelling increases as the phosphoric acid impregnation amount increases, there is a problem that becomes an obstacle when assembling the fuel cell. In this, it is also described that a polybenzimidazole structure using a dicarboxylic acid monomer having a pyridine skeleton is used, but the tetramine monomer used at the same time is only 3,3′-diaminobenzidine, and this combination polymer There was also a tendency to show the same defects as described above.

  On the other hand, it is conceivable to introduce acid groups into aromatic polyazole polymers such as polybenzimidazole to suppress outflow of acid components, and polymer electrolyte membranes using polybenzimidazole polymers containing sulfonic acid groups or phosphonic acid groups Was synthesized (see, for example, Patent Document 2). These polymers are not so high in proton conductivity around 80 ° C., but are expected to exhibit conductivity at high temperatures. However, a polymer having a structure in which a sulfonic acid group is introduced as an acidic group has good processability because it has good solubility in an organic solvent, but has a tendency that proton conductivity is not so high. On the other hand, a polymer with a structure in which a phosphonic acid group is introduced as an acidic group tends to increase proton conductivity by increasing the amount of acidic groups, but it still cannot be said to exhibit practically sufficient proton conductivity. . Moreover, since it is necessary to make it a humidification condition in order for these polymers to show proton conductivity, it could be said that it was impossible to use it without humidifying at a temperature of 100 ° C. or higher.

In this way, by simply introducing an acidic group such as a sulfonic acid group or a phosphonic acid group into a polymer, practical proton conductivity cannot be exhibited in a high temperature region of 100 ° C. or higher and no humidification. A sulfonic acid group-containing polybenzimidazole polymer film containing an organic acid has been reported (see, for example, Patent Document 3). Since these have acidic groups in the molecule, they can be expected to exhibit proton conductivity with a small amount of phosphoric acid impregnation, but the processability and fuel cell membrane characteristics are not sufficient. Further, in these studies, the polymer structure having a pyridine skeleton has not been studied.
Japanese National Patent Publication No. 11-503262 WO 02/38650 pamphlet JP 2003-327826 A E. J. et al. Powers et al., High Performance Polymers: Their Origin and Development, Elsevier, New York (1986), p. 355

  The present invention has been made in order to solve the above-mentioned problems, and its object is not only to exhibit excellent proton conductivity as a polymer electrolyte membrane that can be operated under high temperature and non-humidified conditions, The present invention is to provide a novel proton conductive polymer membrane that is excellent in processability when assembling a fuel cell and exhibits sufficient practical characteristics in terms of durability.

  As a result of intensive studies, the present inventors have found that a polymer film that achieves the above object can be obtained by impregnating a specific polybenzimidazole compound having a pyridine ring with an acidic molecule. That is, the present invention is as follows.

  The polybenzimidazole proton conductive polymer membrane of the present invention is characterized in that an acidic molecule is impregnated into a polymer membrane composed of polybenzimidazole having a structure represented by the following formula (1) as a main component.

(Where X is a group consisting of —O—, —SO ₂ —, —S—, —CO—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—Ph—O—). And at least one selected from orthophenylene, metaphenylene, and paraphenylene.)
In the polybenzimidazole proton conductive polymer membrane of the present invention, it is preferable that the polybenzimidazole has a structure represented by the following formula (2) and / or (3) as a main component.

(Where X is a group consisting of —O—, —SO ₂ —, —S—, —CO—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—Ph—O—). And at least one selected from orthophenylene, metaphenylene, and paraphenylene.)
In the polybenzimidazole proton conductive polymer membrane of the present invention, it is preferable that the polybenzimidazole further contains a sulfonic acid group and / or phosphonic acid group-containing component represented by the following structure.

(Where X is a direct bond, —O—, —SO ₂ —, —S—, —CO—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—Ph—O—). One or more selected from the group consisting of Ar, one or more selected from aromatic units, Ph represents one or more selected from orthophenylene, metaphenylene and paraphenylene, Y represents a sulfonic acid group , One or more selected from phosphonic acid groups, all may be in the form of an acid, or part or all of it may be in the form of a derivative thereof, and n represents an integer of 1 to 4. To do.)
The polybenzimidazole proton conductive polymer membrane of the present invention also preferably contains acidic molecules in the range of 10 to 1000% by weight with respect to the membrane weight of the polymer membrane.

  The present invention provides a method for producing the above-described polybenzimidazole-based proton conductive polymer membrane of the present invention, wherein any one of the above-described polymer membranes containing polybenzimidazole as a main component is an acidic molecular liquid or acidic molecule. A method for producing a polybenzimidazole-based proton conductive polymer membrane is provided, which includes a step of immersing in a solution containing.

  The present invention also includes an oxygen electrode, a fuel electrode, and a solid polymer electrolyte membrane that is sandwiched between the oxygen electrode and the fuel electrode and is any of the polybenzimidazole proton conductive polymer membranes described above. There is also provided a fuel cell in which an oxidant flow plate having an oxidant flow path is provided on the oxygen electrode side and a fuel flow plate having a fuel flow path is provided on the fuel electrode side as a unit cell.

  According to the polymer electrolyte membrane in which acidic molecules are impregnated with polybenzimidazole having a pyridine ring according to the present invention, not only exhibits excellent proton conductivity, but also has excellent processability when assembling a fuel cell and is durable. In particular, the polymer electrolyte membrane which is suitable for a fuel cell operating under high temperature and non-humidified conditions and a fuel cell using the same can be provided.

  The polybenzimidazole proton conductive polymer membrane of the present invention is characterized in that an acidic molecule is impregnated into a polymer membrane composed of polybenzimidazole having a structure represented by the following formula (1) as a main component.

In the above formula (1), X represents —O—, —SO ₂ —, —S—, —CO—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—Ph. 1 or more types chosen from the group which consists of -O- are shown. Ph represents one or more selected from orthophenylene, metaphenylene, and paraphenylene.

  In the present invention, the polybenzimidazole having the structure represented by the above formula (1) as a main component is represented by the following formula (2) and / or from the high reactivity as a monomer and the ease of handling of the obtained polymer. Or it is preferable to have as a main component the structure shown by (3).

(In the above formulas (2) and (3), X is the same as described above.)
The polybenzimidazole having the above structure can be synthesized by a polymerization reaction between monomers in which an aromatic tetramine or a derivative thereof and a dicarboxylic acid having a pyridine ring or a derivative thereof are combined. Specific examples of the aromatic tetramine that gives the structure of the above formula (1) (preferably the formulas (2) and (3)) include 3,3 ′, 4,4′-tetraaminodiphenyl ether, and 3,3 ′. , 4,4′-tetraaminodiphenylsulfone, 3,3 ′, 4,4′-tetraaminodiphenylthioether, 3,3 ′, 4,4′-tetraaminobenzophenone, 2,2-bis (3,4 Diaminophenyl) propane, 2,2-bis (3,4-diaminophenyl) hexafluoropropane, 1,4-bis (3,4-diaminophenoxy) benzene, 1,3-bis (3,4-diaminophenoxy) Examples include benzene, 1,2-bis (3,4-diaminophenoxy) benzene and derivatives thereof. Specific examples of these aromatic tetramine derivatives include salts with acids such as hydrochloric acid, sulfuric acid and phosphoric acid. These compounds may contain known antioxidants such as tin (II) chloride and phosphorous acid compounds as necessary. In addition, these aromatic tetramines and derivatives thereof may be used as a single compound, but a plurality of compounds may be mixed and used.

  Examples of the dicarboxylic acid that gives the structure of the above formula (1) (preferably the formulas (2) and (3)) include 2,5-pyridinedicarboxylic acid, 2,6-pyridinecarboxylic acid, 2,3-pyridinecarboxylic acid, 2,4-pyridinecarboxylic acid, 3,4-pyridinecarboxylic acid, 3,5-pyridinecarboxylic acid and derivatives thereof. Specific examples of the derivatives include acid chlorides and ester compounds with various lower alcohols. These dicarboxylic acids and derivatives thereof may be used as a single compound, or a plurality of compounds may be mixed and used.

  The polybenzimidazole polymer film of the present invention may contain a polybenzimidazole structure other than that represented by the above formula (1). The aromatic tetramine used at that time is not particularly limited, but 1,2,4,5-tetraaminobenzene, 3,3′-diaminobenzidine, bis (3,4-diaminophenyl) methane, etc. , And derivatives thereof. Other dicarboxylic acids that can be used include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, biphenyl dicarboxylic acid, terphenyl dicarboxylic acid, and 2,2-bis (4-carboxyphenyl). Common aromatic dicarboxylic acids reported as polyester raw materials such as hexafluoropropane and derivatives thereof can be used. In addition, 2,5-dicarboxybenzenesulfonic acid, 3,5-dicarboxybenzenesulfonic acid, 2,5-dicarboxy-1,4-benzenedisulfonic acid, 4,6-dicarboxy-1,3-benzenedisulfone Sulfonic acid-containing dicarboxylic acids such as acids, 2,2′-disulfo-4,4′-biphenyldicarboxylic acid, 3,3′-disulfo-4,4′-biphenyldicarboxylic acid, and derivatives thereof, 2,5-di Aromatic dicarboxylic acids having a phosphonic acid group such as carboxyphenylphosphonic acid, 3,5-dicarboxyphenylphosphonic acid, 2,5-bisphosphonoterephthalic acid, 4,6-bisphosphonoisophthalic acid, and derivatives thereof Can be used.

  It can also be synthesized in a polymerization system in which two amino groups or a derivative thereof and a compound having one carboxyl group are mixed in the same molecule. Since the polybenzimidazole polymer membrane of the present invention has a structure represented by the above formula (1) (preferably, the above formula (2) and / or (3)) as a main component, The component is preferably less than 50% of the total.

  The polybenzimidazole compound having a pyridine ring in the present invention preferably further includes a sulfonic acid group and / or phosphonic acid group-containing component represented by the following formula (4).

In the above formula (4), X represents a direct bond, —O—, —SO ₂ —, —S—, —CO—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—. One or more selected from the group consisting of Ph—O—, Ar represents one or more selected from aromatic units, Ph represents one or more selected from orthophenylene, metaphenylene and paraphenylene, Y Is at least one selected from a sulfonic acid group and a phosphonic acid group, and all may be in the form of an acid, or part or all of it may be in the form of a derivative thereof. Examples of the derivatives include alkali metal salts such as sodium and potassium, and salt structures such as various metal salts, ammonium salts, and alkylammonium salts, but are not limited thereto.

  In said formula (4), n shows the integer of 1-4. A unit where n is 0 is not particularly useful for obtaining sufficient proton conductivity, and a unit where n is 5 or more lowers the water resistance of the polymer. However, as long as the structure includes the unit (1), there is no problem even if a unit where n is 0 or 5 or more partially coexists.

  The route for synthesizing the polybenzimidazole compound containing the structure represented by the above formula (4) is not particularly limited, but is usually selected from the group consisting of aromatic dicarboxylic acids capable of forming an imidazole ring in the compound and derivatives thereof. It can be synthesized by reaction with one or more compounds. At that time, by using a dicarboxylic acid containing a sulfonic acid group, a phosphonic acid group, or a derivative thereof in the dicarboxylic acid to be used, a sulfonic acid group and / or a phosphonic acid group is added to the resulting polybenzimidazole. Can be introduced. One or more dicarboxylic acids containing a sulfonic acid group or a phosphonic acid group can be used in combination. In that case, you may synthesize | combine simultaneously using the dicarboxylic acid which does not contain a sulfonic acid group, a phosphonic acid group, or those derivatives. By polymerization of the monomer giving these structures with the monomer giving the above formula (1) (preferably the formula (2) and / or (3)), the acidic group unit represented by the above formula (4) together with the pyridine ring Polybenzimidazole possessed can be synthesized.

  The sulfonic acid group-containing dicarboxylic acid that gives the structure of the above formula (4) can be selected from those containing 1 to 4 sulfonic acid groups in the aromatic dicarboxylic acid. For example, 2,5-dicarboxybenzenesulfonic acid, 3,5-dicarboxybenzenesulfonic acid, 2,5-dicarboxy-1,4-benzenedisulfonic acid, 4,6-dicarboxy-1,3-benzenedisulfone Examples thereof include sulfonic acid-containing dicarboxylic acids such as acid, 2,2′-disulfo-4,4′-biphenyldicarboxylic acid, 3,3′-disulfo-4,4′-biphenyldicarboxylic acid, and derivatives thereof. Examples of the derivatives include alkali metal salts such as sodium and potassium, ammonium salts, and alkyl ammonium salts. The structure of the sulfonic acid group-containing dicarboxylic acid is not particularly limited to these.

  The purity of the dicarboxylic acid containing a sulfonic acid group is not particularly limited, but is preferably 98% or more, and more preferably 99% or more. Polyimidazole polymerized using dicarboxylic acid containing sulfonic acid group as raw material tends to have a lower degree of polymerization than when dicarboxylic acid not containing sulfonic acid group is used. It is preferable to use a dicarboxylic acid having as high purity as possible.

  An aromatic dicarboxylic acid having a phosphonic acid group and a derivative thereof used for synthesizing a polybenzimidazole compound having a phosphonic acid group represented by the above formula (4) are not particularly limited, and aromatic A compound having 1 to 4 phosphonic acid groups in the dicarboxylic acid skeleton can be preferably used. Specific examples include phosphonic acid groups such as 2,5-dicarboxyphenylphosphonic acid, 3,5-dicarboxyphenylphosphonic acid, 2,5-bisphosphonoterephthalic acid, and 4,6-bisphosphonoisophthalic acid. And aromatic dicarboxylic acids and derivatives thereof. It is not preferable to have 5 or more phosphonic acid groups in the aromatic dicarboxylic acid skeleton because the water resistance of the polymer tends to be lowered. The structure of the aromatic dicarboxylic acid having a phosphonic acid group is not limited to these, but as described above, an aromatic dicarboxylic acid having a phenylenephosphonic acid group-type phosphonic acid group is preferable.

  Examples of phosphonic acid derivatives of aromatic dicarboxylic acids having these phosphonic acid groups include alkali metal salts such as sodium and potassium, ammonium salts and alkylammonium salts. These compounds may be used alone or in combination. Furthermore, these compounds may contain known antioxidants such as tin (II) chloride and phosphorous acid compounds as necessary.

  The purity of the aromatic dicarboxylic acid having a phosphonic acid group used for the synthesis of the polybenzimidazole compound of the present invention is not particularly limited, but is preferably 97% or more, more preferably 98% or more. A polybenzimidazole compound polymerized using an aromatic dicarboxylic acid having a phosphonic acid group as a raw material has a degree of polymerization as compared with the case where an aromatic dicarboxylic acid having no sulfonic acid group and phosphonic acid group is used as a raw material. Since it tends to be low, it is preferable to use an aromatic dicarboxylic acid having a phosphonic acid group as high as possible. That is, when the purity of the aromatic dicarboxylic acid is less than 97%, the degree of polymerization of the resulting polybenzimidazole compound tends to be low, making it unsuitable as a solid polymer electrolyte material.

  Using one or more compounds selected from the group consisting of the above-mentioned aromatic tetramines and derivatives thereof, and one or more compounds selected from the group consisting of aromatic dicarboxylic acids and derivatives thereof, a sulfonic acid group and The method for synthesizing a polybenzimidazole compound having a phosphonic acid group is not particularly limited. F. Wolfe, Encyclopedia of Polymer Science and Engineering, 2nd Ed. , Vol. 11. p. 601 (1988), and can be synthesized by dehydration and cyclopolymerization using polyphosphoric acid as a solvent. In addition, polymerization by a similar mechanism using a mixed solvent system of methanesulfonic acid / phosphorus pentoxide instead of polyphosphoric acid can be applied. In order to synthesize a polybenzimidazole compound having high thermal stability, polymerization using polyphosphoric acid that is commonly used is preferred.

  Furthermore, in order to obtain the polybenzimidazole compound of the present invention, for example, a precursor polymer having a polyamide structure or the like is synthesized by a reaction in a suitable organic solvent or in the form of a mixed raw material monomer melt. A method of converting to a target polybenzimidazole structure by a cyclization reaction by an appropriate heat treatment can also be used.

  In addition, the reaction time when synthesizing the polybenzimidazole compound of the present invention cannot be defined unconditionally because there is an optimum reaction time depending on the combination of individual raw material monomers, but it has a long time as previously reported. In the applied reaction, in the case of a system containing a raw material monomer such as an aromatic dicarboxylic acid having a sulfonic acid group or a phosphonic acid group, the thermal stability of the resulting polybenzimidazole compound may be lowered. In this case, it is preferable to shorten the reaction time as long as the effect of the present invention is obtained. Thus, by shortening reaction time, the polybenzimidazole type compound which has a sulfonic acid group and a phosphonic acid group can also be obtained in a state with high heat stability.

  In addition, after the synthesis of the polybenzimidazole compound of the present invention, when the raw material monomer constituting the repeating unit is composed of a plurality of types, the repeating units are subjected to random polymerization and / or alternating polymerization. By being bonded, it has the characteristic of showing stable performance as a polymer electrolyte membrane material. The alternating polymerization is a bonding mode in which the same repeating unit is essentially not continuously bonded, and is clearly distinguished from random polymerization and block polymerization described later (for example, NMR measurement). Can be confirmed using the linkage distribution evaluation by Here, in order to synthesize the polybenzimidazole compound of the present invention by random polymerization and / or alternating polymerization, all monomer raw materials are charged at a blending ratio that combines equivalence from the initial stage of polymerization. It is preferable to make.

  Polybenzimidazole compounds can also be synthesized by block polymerization rather than random polymerization or alternating polymerization, but in this case, the first component oligomer is used under the same conditions as the monomer raw material with a mixed proportion shifted. It is preferable to perform polymerization after adding a monomer raw material and adjusting the blending ratio so that the equivalence is matched including the second component.

  The molecular weight of the polybenzimidazole compound in the present invention is not particularly limited, but is preferably 2,000 or more, more preferably 4,000 or more. The molecular weight is preferably 1,000,000 or less, and more preferably 300,000 or less. When this molecular weight is less than 2,000, it becomes difficult to obtain a molded product having good properties from a polybenzimidazole compound due to a decrease in viscosity. On the other hand, when the molecular weight exceeds 1,000,000, it becomes difficult to mold a polybenzimidazole compound due to an increase in viscosity.

  In addition, the molecular weight of the polybenzimidazole compound in the present invention can be substantially evaluated by logarithmic viscosity when measured in methanesulfonic acid. And this logarithmic viscosity is preferably 0.3 or more, and more preferably 0.50 or more. The logarithmic viscosity is preferably 8 or less, more preferably 7 or less. When the logarithmic viscosity is less than 0.3, it is difficult to obtain a molded product having good properties from the polybenzimidazole compound due to the decrease in viscosity. On the other hand, when the logarithmic viscosity exceeds 8, it becomes difficult to mold the polybenzimidazole compound due to the increase in viscosity.

  The polybenzimidazole compound in the present invention can be suitably used even if it is blended as a main component in the resin composition. Examples of the polymer that can be used with the polybenzimidazole described above as the resin composition include polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, and polyamides such as nylon 6, nylon 6,6, nylon 6,10, and nylon 12. Acrylate resins such as polymethyl methacrylate, polymethacrylic acid esters, polymethyl acrylate, polyacrylic acid esters, polyacrylic acid resins, polymethacrylic acid resins, polyethylene, polypropylene, polystyrene and diene polymers Various polyolefins, polyurethane resins, cellulose resins such as cellulose acetate and ethyl cellulose, polyarylate, aramid, polycarbonate, polyphenylenes Fido, polyphenylene oxide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, polyimide, polyamideimide, polybenzimidazole, polybenzoxazole, polybenzthiazole and other aromatic polymers, epoxy resin, phenolic resin, novolak There are no particular restrictions on the resin and thermosetting resins such as benzoxazine resin.

  When used as these resin compositions, the polybenzimidazole compound is preferably contained in an amount of 50% by weight or more and less than 100% by weight based on the entire resin composition. More preferably, they are 60 weight% or more and less than 100 weight%, Most preferably, they are 70 weight% or more and less than 100 weight%. When the content of the polybenzimidazole compound is less than 50% by weight of the entire resin composition, the acidic molecule retention of the ion conductive membrane containing this resin composition tends to be reduced. The polybenzimidazole compound and the resin composition thereof according to the present invention are, for example, an antioxidant, a heat stabilizer, a lubricant, a tackifier, a plasticizer, a crosslinking agent, a viscosity modifier, and an antistatic agent. Various additives such as an antibacterial agent, an antifoaming agent, a dispersant, and a polymerization inhibitor may be included.

  The polybenzimidazole compound or the resin composition thereof in the present invention is formed into a film shape by any method such as extrusion, rolling, and casting from a polymerization solution, an isolated polymer, a re-dissolved polymer solution, and the like. Can do. A preferred method for forming a film containing the polybenzimidazole compound or the resin composition thereof in the present invention includes casting from a solution. Soluble solvents include aprotic polar solvents such as N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, hexamethylphosphonamide, polyphosphoric acid, methanesulfonic acid, sulfuric acid A suitable acid can be selected from strong acids such as trifluoroacetic acid, but is not limited thereto. Among these, it is particularly preferable to mold from an organic solvent system. In particular, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone, in which the polybenzimidazole of the present invention is well dissolved, are preferably selected as the solvent. A plurality of these solvents may be used as a mixture within a possible range.

  As a means for improving solubility, a solvent obtained by adding a Lewis acid such as lithium bromide, lithium chloride, or aluminum chloride to an organic solvent may be used. The polymer concentration in the solution is preferably in the range of 0.1 to 50% by weight. If it is too low, the moldability will deteriorate, and if it is too high, the workability will deteriorate. The solvent is preferably dried from the viewpoint of film uniformity. Moreover, in order to avoid decomposition | disassembly and alteration of a polymer or a solvent, it can also dry at the lowest temperature possible under reduced pressure. As a substrate to be cast, a glass plate, a Teflon (registered trademark) plate, a metal plate, a polymer sheet, or the like can be used. When the viscosity of the solution is high, heating the substrate or the solution and casting at a high temperature lowers the viscosity of the solution and can be easily cast.

  The thickness of the solution at the time of casting is not particularly limited, but is preferably 30 to 1500 μm. If it is too thin, the shape of the film cannot be maintained, and if it is too thick, a non-uniform film can be easily formed. More preferably, it is 100-1000 micrometers. As a method for controlling the cast thickness of the solution, a known method can be used. For example, a certain thickness can be ensured by using an applicator, a doctor blade, or the like, or the cast area can be kept constant by using a glass petri dish or the like, and the thickness can be controlled by the amount and concentration of the solution. The cast solution can obtain a more uniform film by adjusting the solvent removal rate. For example, when the solvent is distilled off by heating, the evaporation rate can be reduced by lowering the temperature in the first stage. In addition, when immersed in a non-solvent such as water, the solidification rate of the polymer can be adjusted by leaving the solution in air or an inert gas for an appropriate time. The film of the present invention can have any film thickness depending on the purpose, but is preferably as thin as possible from the viewpoint of ion conductivity. Specifically, it is preferably 200 μm or less, and more preferably 50 μm or less. Moreover, it is preferable that a film thickness is 5 micrometers or more from the surface of the intensity | strength of a film | membrane or workability.

  The polybenzimidazole proton conductive polymer membrane of the present invention is characterized in that acidic molecules are impregnated in the polymer membrane having the structure described above. Examples of the inorganic acid that can be used as the acidic molecule include phosphoric acid, polyphosphoric acid, sulfuric acid, nitric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, and derivatives thereof. Moreover, organic sulfonic acid and organic phosphonic acid are used as the organic acid. Specific examples of organic sulfonic acids include methane sulfonic acid, ethane sulfonic acid, hexane sulfonic acid, octyl sulfonic acid, dodecyl sulfonic acid, cetyl sulfonic acid, sulfosuccinic acid, sulfoglutaric acid, sulfoadipic acid, sulfopimelic acid, sulfosuberin. Perfluoroalkyl sulfonic acids such as acid, sulfoazeleic acid, sulfosebacic acid and other alkyl sulfonic acids, trifluoromethane sulfonic acid, pentafluoroethane sulfonic acid, heptafluoropropyl sulfonic acid, benzene sulfonic acid, 1,3-benzene Sulfonic acid, toluenesulfonic acid, octylbenzenesulfonic acid, 2-methyl-5-isopropylbenzenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, naphthalenesulfonic acid, black Benzene sulfonic acid, phenol sulfonic acid, trichlorobenzene sulfonic acid, nitrotoluene sulfonic acid, nitrobenzene sulfonic acid, aromatic sulfonic acid such as sulfobenzoic acid, and derivatives thereof can be mentioned, but without limitation, various Organic sulfonic acids of the structure can be used. Specific examples of the organic phosphonic acid include phenylphosphonic acid, aromatic phosphonic acid such as 1,3-dicarboxyphenylphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, vinylphosphonic acid, and the like. Examples thereof include aliphatic phosphonic acids and derivatives thereof, but organic phosphonic acids having various structures can be used without being limited thereto. The acidic compound to be impregnated can be impregnated not only as a single species but also as a mixture of two or more species.

  The impregnation amount of the acidic molecule is preferably in the range of 10 to 1000% by weight, more preferably in the range of 50 to 800% by weight with respect to the film weight of the polymer film in the present invention. When the impregnation amount of the acidic molecule is less than 10% by weight with respect to the membrane weight of the polymer membrane, the proton conductivity tends to be lowered under high temperature and no humidification. Further, when the impregnation amount of acidic molecules exceeds 1000% by weight with respect to the weight of the polymer membrane, there is a tendency that acidic molecules ooze out from the polymer electrolyte membrane. The amount of impregnation is 100 × (membrane weight before extraction−membrane weight after extraction) / extraction from the difference in membrane weight before and after extraction, for example, by extracting all the acidic molecules from the membrane by hot water extraction of the polymer electrolyte membrane. It can be calculated as the weight of the back membrane (%).

  The method of impregnating a polymer film containing polybenzimidazole with acidic molecules in the present invention can be performed by impregnating the polymer film with a liquid acidic molecule itself or a solution containing acidic molecules. Under the present circumstances, acidic molecule content can be controlled by changing the temperature conditions and immersion time to immerse. Although acidic molecule content is determined by the combination of immersion temperature and immersion time, it is preferable to set it as the range of 20-150 degreeC as temperature to make it immersed. This is because when the temperature is less than 20 ° C., the impregnation rate tends to be slow, and when it exceeds 150 ° C., the membrane tends to be easily deformed during the impregnation. The immersion time is preferably in the range of 10 minutes to 20 hours. This is because when the time is less than 10 minutes, acidic molecules tend not to be impregnated sufficiently evenly, and when it exceeds 20 hours, productivity tends to decrease. When the immersion treatment is performed using a solution containing vinylphosphonic acid, a solvent that can be well mixed with acidic molecules, such as water and lower alcohol, can be used as the solvent. The solution concentration is preferably 50% or more.

  Moreover, the assembly of the ion conductive polymer film of the present invention and the electrode can be obtained by installing the above-described ion conductive polymer film of the present invention on the electrode. As a method for producing this joined body, a conventionally known method can be used. For example, an adhesive is applied to the electrode surface and the ion conductive film and the electrode are bonded, or the ion conductive film and the electrode are bonded. There is a method of heating and pressing. An oxygen electrode, a fuel electrode, and a solid polymer electrolyte membrane of the present invention sandwiched between the oxygen electrode and the fuel electrode, and an oxidant distribution plate formed in the oxidant channel provided on the oxygen electrode side, By using a unit cell with a fuel flow distribution plate having a flow path formed on the fuel electrode side, a fuel cell that can be operated at a high temperature of 100 ° C. or higher and does not require humidification conditions can be obtained.

<Example>
EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example, this invention is not limited to these Examples. Various measurements were performed as follows.

(1) Solution viscosity A polybenzimidazole compound powder is dissolved in methanesulfonic acid at a concentration of 0.5 g / dl, and the viscosity is measured using an Ostwald viscometer in a constant temperature bath at 30 ° C. (Ta / tb)] / c (ta is the number of seconds the sample solution falls, and c is the polymer concentration).

(2) Ionic conductivity A polymer electrolyte membrane is sandwiched between platinum electrodes (diameter: 13 mm), complex impedance is measured using an electrochemical measurement system 12608W manufactured by Solartron, and ion conduction is determined from the obtained resistance value. The temperature dependence of degree (unit: S / cm) was determined.

(3) Fuel cell characteristics A polymer electrolyte membrane is sandwiched between commercially available fuel cell electrodes (manufactured by Electrochem) to form a membrane electrode assembly. Measurements were made.

<Example 1>
3,3 ′, 4,4′-tetraaminodiphenylsulfone 6,000 g (2.1557 × 10 ⁻² mole), 2,6-pyridinedicarboxylic acid 3.6602 g (2.1557 × 10 ⁻² mole), polyphosphorus 36.86 g of acid (phosphorus pentoxide content: 75%) and 29.54 g of phosphorus pentoxide are weighed into a polymerization vessel. The temperature is raised to 100 ° C. while slowly stirring on an oil bath while flowing nitrogen. After maintaining at 100 ° C. for 1 hour, the temperature was raised to 150 ° C. for 1 hour, and the temperature was raised to 200 ° C. and polymerized for 5 hours. After completion of the polymerization, the mixture was allowed to cool, water was added, the polymer was taken out, and washing with water was repeated until the pH test paper became neutral using a household mixer. The obtained polymer was dried under reduced pressure at 80 ° C. overnight. The logarithmic viscosity of the polymer was 1.78.

  1 g of the obtained polymer was dissolved in 10 g of N-methyl-2-pyrrolidone (NMP) on an oil bath, cast on a glass plate on a hot plate, NMP was distilled off until a film was formed, and then overnight in water. Soaked above. The obtained film was immersed in dilute sulfuric acid (concentrated sulfuric acid 6 ml, water 300 ml) for 1 day or longer, and further immersed and washed several times with pure water to obtain a polymer film 1 having a thickness of 21 μm.

  This polymer membrane 1 was immersed in orthophosphoric acid (purity: 85%, manufactured by Tokyo Chemical Industry Co., Ltd.) at 30 ° C. for 3 hours to obtain a polybenzimidazole proton conductive polymer membrane to which orthophosphoric acid was added. At this time, the content of orthophosphoric acid was 230% by weight based on the weight of the polymer film 1 calculated from the change in weight. With respect to the obtained polybenzimidazole proton conductive polymer membrane, the temperature dependence of the ionic conductivity and the fuel cell power generation characteristics were measured by the method described above.

Table 1 indicates the open circuit voltage at the initial stage of power generation and after 500 hours and the output voltage at a current density of 0.3 A / cm ² . FIG. 1 shows the temperature dependence of ion conductivity, and FIG. 2 shows the current-voltage characteristics at the initial stage of power generation. FIG. 3 shows changes with time in the output voltage at an open circuit voltage and a current density of 0.3 A / cm ² .

<Example 2>
A polybenzimidazole proton conductive polymer in which the polymer membrane 1 obtained in Example 1 was immersed in vinylphosphonic acid (purity: 85%, manufactured by Tokyo Chemical Industry Co., Ltd.) at 50 ° C. for 3 hours and vinylphosphonic acid was added. A membrane was obtained. The vinylphosphonic acid content at this time was 280% by weight based on the weight of the polymer film 1 calculated from the change in weight. Using this polybenzimidazole proton conductive polymer membrane, ion conductivity and fuel cell power generation characteristics were measured in the same manner as in Example 1. Table 1 shows the value of the ionic conductivity at 150 ° C. and the output voltage of the fuel cell at the initial stage of power generation and after 500 hours at an open circuit voltage and a current density of 0.3 A / cm ² .

<Example 3>
A polymer film 2 having a thickness of 23 μm was prepared in the same manner as in Example 1 except that 2,5-pyridinedicarboxylic acid was used instead of 2,6-pyridinedicarboxylic acid. The logarithmic viscosity of the polymer obtained by the reaction was 1.39. Orthophosphoric acid was added to this polymer membrane 2 in the same manner as in Example 1 to obtain a polybenzimidazole proton conductive polymer membrane. The orthophosphoric acid content at this time was 220% by weight based on the weight of the polymer film 2 calculated from the change in weight. Using this polybenzimidazole proton conductive polymer membrane, ion conductivity and fuel cell power generation characteristics were measured in the same manner as in Example 1. Table 1 shows the value of the ionic conductivity at 150 ° C. and the output voltage of the fuel cell at the initial stage of power generation and after 500 hours at an open circuit voltage and a current density of 0.3 A / cm ² .

<Example 4>
Vinyl phosphonic acid was added to the polymer membrane 2 obtained in Example 3 in the same manner as in Example 2 to obtain a polybenzimidazole proton conductive polymer membrane. The vinylphosphonic acid content at this time was 300% by weight based on the weight of the polymer film 2 calculated from the change in weight. Using this polybenzimidazole proton conductive polymer membrane, ion conductivity and fuel cell power generation characteristics were measured in the same manner as in Example 1. Table 1 shows the value of the ionic conductivity at 150 ° C. and the output voltage of the fuel cell at the initial stage of power generation and after 500 hours when the open circuit voltage and current density are 0.3 A / cm ² .

<Example 5>
In Example 1, instead of 2,6-pyridinedicarboxylic acid, 2.5218 g (1.5090 × 10 ⁻² mole) of 2,5-pyridinedicarboxylic acid and monosodium 2,5-dicarboxybenzenesulfonate (purity) : 99%) A polymer film 3 having a thickness of 20 μm was produced using 1.7343 g (0.6467 × 10 ⁻² mole). The logarithmic viscosity of the polymer obtained by the reaction was 1.89. Orthophosphoric acid was added to the polymer membrane 3 in the same manner as in Example 1 to obtain a benzimidazole proton conductive polymer membrane. At this time, the content of orthophosphoric acid was 200% by weight based on the weight of the polymer film 3 as calculated from the change in weight. Using this benzimidazole-based proton conductive polymer membrane, ion conductivity and fuel cell power generation characteristics were measured in the same manner as in Example 1. Table 1 shows the value of the ionic conductivity at 150 ° C. and the output voltage of the fuel cell at the initial stage of power generation and after 500 hours at an open circuit voltage and a current density of 0.3 A / cm ² .

<Example 6>
In Example 3, instead of 2,5-pyridinedicarboxylic acid, 2,8821 g (1.7246 × 10 ⁻² mole) of 2,6-pyridinedicarboxylic acid and 3,5-dicarboxyphenylphosphonic acid (purity: 98 %) 1.0615 g (0.4311 × 10 ⁻² mole) was used to prepare a polymer film 4 having a thickness of 21 μm. The logarithmic viscosity of the polymer obtained by the reaction was 1.66. Vinyl phosphonic acid was added to the polymer membrane 4 in the same manner as in Example 2 to obtain a benzimidazole proton conductive polymer membrane. The vinylphosphonic acid content at this time was 300% by weight based on the weight of the polymer film 4 calculated from the change in weight. Using this benzimidazole-based proton conductive polymer membrane, ion conductivity and fuel cell power generation characteristics were measured in the same manner as in Example 1. Table 1 shows the value of the ionic conductivity at 150 ° C. and the output voltage of the fuel cell at the initial stage of power generation and after 500 hours when the open circuit voltage and current density are 0.3 A / cm ² .

<Example 7>
A benzimidazole proton conductive polymer membrane to which vinylphosphonic acid was added was obtained in the same manner as in Example 2 except that the polymer membrane 1 was immersed in vinylphosphonic acid at 30 ° C. for 1 hour. The vinylphosphonic acid content at this time was 210% by weight based on the weight of the polymer film 1 calculated from the change in weight. Using this benzimidazole-based proton conductive polymer membrane, ion conductivity and fuel cell power generation characteristics were measured in the same manner as in Example 1. Table 1 shows the value of the ionic conductivity at 150 ° C. and the output voltage of the fuel cell at the initial stage of power generation and after 500 hours at an open circuit voltage and a current density of 0.3 A / cm ² .

<Example 8>
Benzimidazole proton conductive high conductivity obtained by adding vinylphosphonic acid in the same manner as in Example 2 except that polymer membrane 1 is immersed in vinylphosphonic acid (purity: 85%, manufactured by Tokyo Chemical Industry Co., Ltd.) at 50 ° C. for 10 hours. A molecular film was obtained. The vinylphosphonic acid content at this time was 390% by weight based on the weight of the polymer film 1 calculated from the change in weight. Using this benzimidazole-based proton conductive polymer membrane, ion conductivity and fuel cell power generation characteristics were measured in the same manner as in Example 1.

<Comparative Example 1>
Poly-2,2 ′-(m-phenylene) -5,5′- with reference to the production methods described in US Pat. No. 3,313,783, US Pat. No. 3,509,108, US Pat. No. 3,555,389, and the like. Bibenzimidazole was obtained. 1 g of this polymer was dissolved in 10 g of dimethylacetamide (DMAC) on an oil bath, cast on a glass plate on a hot plate, and DMAC was distilled off until a film was formed. Furthermore, it vacuum-dried at 120 degreeC for 12 hours, and obtained the polymer film 5 of the thickness of 20 micrometers from which DMAC was distilled off completely.

  The polymer membrane 5 was immersed in orthophosphoric acid at room temperature for 3 hours to obtain a proton conductive polymer membrane to which orthophosphoric acid was added. The orthophosphoric acid content at this time was 410% by weight based on the weight of the polymer film 5 calculated from the change in weight. For the obtained proton conductive polymer membrane, the temperature dependence of the ionic conductivity and the fuel cell power generation characteristics were measured in the same manner as in Example 1.

Table 2 shows the open circuit voltage at the initial stage of power generation and after 500 hours, and the output voltage at a current density of 0.3 A / cm ² . FIG. 1 shows the temperature dependence of ion conductivity, and FIG. 2 shows the current-voltage characteristics at the initial stage of power generation. FIG. 3 shows changes with time in the output voltage at an open circuit voltage and a current density of 0.3 A / cm ² .

<Comparative Example 2>
Vinyl phosphonic acid was added in the same manner as in Example 2 except that the polymer film 5 obtained in Comparative Example 1 was immersed in vinyl phosphonic acid at 120 ° C. for 3 hours to obtain a proton conductive polymer film. The vinylphosphonic acid content at this time was 390% by weight based on the weight of the polymer film 5 calculated from the change in weight. Using this benzimidazole-based proton conductive polymer membrane, ion conductivity and fuel cell power generation characteristics were measured in the same manner as in Example 1. Table 2 shows the value of the ion conductivity at 150 ° C. and the output voltage at the initial power generation and after 500 hours of the open circuit voltage and the current density of 0.3 A / cm ² for the fuel cell.

Table 1 shows the benzimidazole proton conductive polymer membranes of Examples 1 to 8, Table 2 shows the ionic conductivity at 150 ° C. and the benzimidazole proton conductive polymer membranes of Comparative Examples 1 and 2. The initial open circuit voltage and the open circuit voltage after 500 hours, the initial battery voltage at a current density of 0.3 A / cm ^2, and the battery voltage after 500 hours were shown for the fuel cell produced using Table 1 also shows the reduction rate (%) after 500 hours when the initial voltage is 100%. From the results shown in Tables 1 and 2, in the initial state, there is no significant difference in the circuit voltage between the examples and the comparative examples, but there is a slight difference in the voltage with a current density of 0.3 A / cm ^2. There is a difference. Furthermore, it can be seen that the voltage of the comparative example is deteriorated with respect to the example after 500 hours.

  FIG. 1 shows the temperature dependence of the ionic conductivity for Example 1 and Comparative Example 1. It can be seen that the benzimidazole proton conductive polymer membrane of the present invention is equivalent in ion conductivity to the proton conductive polymer membrane of Comparative Example 1 although the acid content is small.

  FIG. 2 shows the relationship between the current density and the battery voltage at the initial measurement for Example 1 and Comparative Example 1. It can be seen that the benzimidazole proton conductive polymer membrane of the present invention has the same fuel cell characteristics although the amount of acid impregnation is small in proportion to the proton conductive polymer membrane of Comparative Example 1.

FIG. 3 shows the relationship between the open circuit voltage (OCV) and the battery voltage during power generation at a current density of 0.3 A / cm ² and the operation time of the fuel cell for Example 1 and Comparative Example 1. As shown in FIG. 3, it can be seen that in Comparative Example 1, both voltages decrease as the operation time becomes longer. On the other hand, almost no decrease in voltage is observed in the examples.

  As described above, the benzimidazole proton conductive polymer membranes of Examples 1 to 8 are superior in electrical characteristics and durability to the proton conductive polymer membranes of Comparative Examples 1 and 2. I understand.

  The benzimidazole proton conductive polymer membrane according to the present invention not only exhibits excellent proton conductivity as a polymer electrolyte membrane that can be operated under high-temperature and non-humidified conditions, but also has excellent processability when assembling a fuel cell. Thus, a novel polymer electrolyte membrane exhibiting sufficient practical characteristics in terms of durability can be obtained. Taking advantage of these characteristics, the proton conductive polymer membrane of the present invention can be used in a wide range of applications such as various battery electrolytes, sensors, capacitors, electrolytic membranes, and can contribute to the development and growth of industry. .

It is a graph which shows the temperature dependence of ion conductivity about Example 1 and Comparative Example 1. FIG. It is a graph which shows the relationship between the current density of a measurement initial stage, and a battery voltage about Example 1 and Comparative Example 1. FIG. 5 is a graph showing the relationship between the battery characteristics during power generation at an open circuit voltage and a current density of 0.3 A / cm ² and the operating time of the fuel cell for Example 1 and Comparative Example 1.

Claims (6)

A polybenzimidazole-based proton conductive polymer membrane, wherein a polymer membrane composed of polybenzimidazole having a structure represented by the following formula (1) as a main component is impregnated with an acidic molecule.

(Where X is a group consisting of —O—, —SO ₂ —, —S—, —CO—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—Ph—O—). And at least one selected from orthophenylene, metaphenylene, and paraphenylene.) The polybenzimidazole-based proton conductive polymer membrane according to claim 1, wherein the polybenzimidazole has a structure represented by the following formula (2) and / or (3) as a main component.

(Where X is a group consisting of —O—, —SO ₂ —, —S—, —CO—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—Ph—O—). And at least one selected from orthophenylene, metaphenylene, and paraphenylene.) The polybenzimidazole proton conductive polymer membrane according to claim 1 or 2, wherein the polybenzimidazole further contains a sulfonic acid group and / or phosphonic acid group-containing component represented by the following structure: .

(Where X is a direct bond, —O—, —SO ₂ —, —S—, —CO—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—Ph—O—). One or more selected from the group consisting of Ar, one or more selected from aromatic units, Ph represents one or more selected from orthophenylene, metaphenylene and paraphenylene, Y represents a sulfonic acid group , One or more selected from phosphonic acid groups, all may be in the form of an acid, or part or all of it may be in the form of a derivative thereof, and n represents an integer of 1 to 4. To do.)   The polybenzimidazole proton conductivity according to any one of claims 1 to 3, wherein an acidic molecule is contained within a range of 10 to 1000% by weight with respect to a film weight of the polymer film. Polymer membrane. A method for producing the polybenzimidazole-based proton conductive polymer membrane according to any one of claims 1 to 4,
A polybenzimidazole proton conduction comprising a step of immersing the polymer film comprising polybenzimidazole as a main component according to any one of claims 1 to 3 in an acidic molecule liquid or a solution containing acidic molecules. For producing a conductive polymer film. An oxygen electrode,
An anode,
A solid polymer electrolyte membrane, which is a polybenzimidazole-based proton conductive polymer membrane according to any one of claims 1 to 4, sandwiched between the oxygen electrode and the fuel electrode,
A fuel cell in which an oxidant flow plate having an oxidant flow path is provided on the oxygen electrode side and a fuel flow plate having a fuel flow path is provided on the fuel electrode side as a unit cell.

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