JP2010009853A - Electrolyte membrane for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte membrane for a fuel cell which maintains high proton conductivity and has a high thermal stability. <P>SOLUTION: The electrolyte membrane for the fuel cell contains a proton conductive material in which an electrolyte resin is filled into inorganic particulates of hollow shape having a through-hole on the surface and a polymer which has a siloxane based repeating unit having a siloxane structure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrolyte membrane for a fuel cell that maintains high proton conductivity and has high thermal stability.

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source for the body.

In the solid polymer electrolyte fuel cell, when hydrogen is used as the fuel, the reaction of the formula (1) proceeds at the anode (fuel electrode).
_{^{H 2 → 2H + + 2e -}} ... (1)
The electrons generated by the equation (1) reach the cathode (oxidant electrode) after working with an external load via an external circuit. Then, the proton generated in the formula (1) moves by electroosmosis from the anode side to the cathode side in the solid polymer electrolyte membrane in a state of being hydrated with water.

Further, when oxygen is used as the oxidizing agent, the reaction of the formula (2) proceeds at the cathode.
_{^{2H + + (1/2) O 2}} + 2e - → H 2 O ... (2)
The water produced at the cathode mainly passes through the gas diffusion layer and is discharged to the outside. As described above, the fuel cell is a clean power generation device having no emission other than water.

  A polymer electrolyte membrane operable in a temperature range of a commonly used solid polymer electrolyte fuel cell is composed of an organic polymer type proton conductive material having a polymer as a basic skeleton or main chain. Problems with the proton-conducting material include dimensional changes such as expansion and contraction of the membrane during water absorption and drainage, and creep or thermal contraction due to heat. Under the operating environment of fuel cells, it is known that the balance of water and heat changes more frequently depending on the load and the external environment, but the accompanying dimensional change of the membrane is important to shorten the life of the electrolyte membrane. This is a problem and is a very difficult problem to solve for the current organic polymer type proton conductive material.

  On the other hand, an electrolyte membrane combining an inorganic proton conductor and a non-proton conductive polymer, which is different from the electrolyte membrane using the organic polymer type proton conductive material, has been proposed. Patent Document 1 is typified by tungsten oxide or tin oxide hydrate in order to maintain stable proton conductivity and mechanical strength even at a temperature of 100 ° C. or more, which is the heat resistance limit of conventional fluorine-based electrolyte membranes. A proton conducting membrane containing a metal oxide hydrate and an aprotic conducting polymer is disclosed.

Japanese Patent Laid-Open No. 2002-289051

  When the proton conductive membrane disclosed in Patent Document 1 is used as an electrolyte membrane for a fuel cell, the proton conductivity is stable under high temperature and low humidification conditions. However, in comparison with Nafion, which is an organic polymer that has been used in the past, the value of proton conductivity itself, in particular, the proton conductivity in the operating environment (temperature, humidity) with the highest power generation efficiency for fuel cells is not sufficient. There wasn't. Further, the invention of Patent Document 1 does not pay attention to the dimensional stability of the electrolyte membrane.

As a result of intensive studies on the proton conductive material, the present inventors have developed a material in which hollow inorganic fine particles having through holes on the surface are filled with an electrolyte resin, and the material impairs mechanical properties and shape. It has been found that high proton conductivity is exhibited without any patent application (Japanese Patent Application No. 2007-246203).
In the above patent application, hollow inorganic fine particles having through holes on the surface are mixed with a monomer having a sulfonic acid group or a precursor group thereof, and the monomer is filled in the inorganic fine particles under reduced pressure. A method for producing a proton conductive material for polymerizing the monomer is also proposed. According to this method, the polymer is filled into the inorganic fine particles by the subsequent polymerization reaction by a simple operation of filling the inorganic fine particles into the inorganic fine particles from the through holes of the inorganic fine particles, without impairing the mechanical properties and shape. A proton conductive material capable of improving proton conductivity can be provided.

  The present inventors have further studied the above proton conductive material and found an electrolyte membrane for a fuel cell exhibiting high proton conductivity and dimensional stability. That is, the present invention has been accomplished through the above-described research, and an object of the present invention is to provide a fuel cell electrolyte membrane that maintains high proton conductivity and has high thermal stability.

  The electrolyte membrane for a fuel cell of the present invention contains a proton conductive material in which hollow inorganic fine particles having through holes on the surface are filled with an electrolyte resin, and a polymer having a siloxane-based repeating unit having a siloxane structure. It is characterized by.

The electrolyte membrane for a fuel cell having such a configuration is an infinite number of the electrolyte resins filled in the cavities of the inorganic fine particles that are the outer shells of the proton conductive material in the proton conductive material contained in the electrolyte membrane. Since the proton conductive group is exposed from the through-holes on the surface of the inorganic fine particles, the proton conductivity is high, and the electrolyte resin is confined in the inorganic fine particles having a fixed particle diameter. Since there is no swelling and shrinkage of the proton conductive material, there is no dimensional change due to water and heat balance.
Further, the electrolyte membrane for a fuel cell according to the present invention can be used in the present invention even if it is normally in a state of high fluidity such as introducing a large amount of proton conductive groups into the structure of the electrolyte resin. Since it is held in the cavity of the inorganic fine particles, it is possible to achieve both improvement in shape retention and proton conductivity in the proton conductive material.
Furthermore, the electrolyte membrane for a fuel cell according to the present invention can uniformly disperse the proton conductive material in the electrolyte membrane by using the polymer having affinity for the proton conductive material as a binder resin. .

  In the electrolyte membrane for a fuel cell of the present invention, when the content of the proton conductive material and the polymer is 100 parts by weight of the total of these two components, the proton conductive material is 70 to 30 parts by weight, The polymer is preferably 30 to 70 parts by weight.

  The electrolyte membrane for a fuel cell having such a configuration can sufficiently have a film forming property for forming an electrolyte membrane while maintaining high proton conductivity and shape retention.

  In the fuel cell electrolyte membrane of the present invention, the electrolyte resin in the inorganic fine particles preferably has a Si—O skeleton.

  In the fuel cell electrolyte membrane having such a configuration, in the proton conductive material contained in the electrolyte membrane, the inorganic fine particles are filled with a monomer that is a raw material of the electrolyte resin, and polymerized to synthesize the electrolyte resin. In this case, since the polymerization reaction can be easily caused, the production is easy. In the electrolyte membrane for a fuel cell of the present invention, since the monomer has a high affinity with the inorganic fine particles and can be easily filled, the synthesis of the proton conductive material contained in the electrolyte membrane can be performed quickly. It can be carried out.

In the fuel cell electrolyte membrane of the present invention, the inorganic fine particles are preferably SiO ₂ .

The electrolyte membrane for a fuel cell having such a structure has mechanical characteristics because the inorganic fine particles, which are the outer shells of the proton conductive material, are formed of SiO ₂ which is a chemically stable and rigid inorganic material. And can maintain a stable shape without contraction / expansion due to the balance of water and heat.

  In the electrolyte membrane for a fuel cell of the present invention, the proton conductive material preferably has an ion exchange capacity larger than the ion exchange capacity of the inorganic fine particles.

  The electrolyte membrane for a fuel cell having such a configuration can ensure proton conductivity higher than that of the inorganic fine particles by filling the electrolyte resin in the inorganic fine particles.

  In the fuel cell electrolyte membrane of the present invention, the proton conductive material preferably has an ion exchange capacity of 0.5 meq / g or more.

  The fuel cell electrolyte membrane having such a configuration can have sufficient proton conductivity.

  In the fuel cell electrolyte membrane of the present invention, the proton conductive material preferably has an average particle size of 0.05 to 10 μm.

  The electrolyte membrane for a fuel cell having such a configuration can be formed with an appropriate thickness.

  In the fuel cell electrolyte membrane of the present invention, the polymer includes at least an aromatic ring and a cyclic imide condensed or not condensed with the aromatic ring, and the aromatic ring and the cyclic imide are directly or It is preferable that it is a copolymer polymer formed by linking an aromatic repeating unit having a structure bonded through only one atom and a siloxane repeating unit having a siloxane structure.

  The electrolyte membrane for a fuel cell having such a structure has an affinity between the electrolyte resin filled with inorganic fine particles and the copolymer having cyclic imide, and the proton conductive group of the electrolyte resin is the imide group. Since the proton conductive material is trapped in the substrate, the proton conductive group can be kept stable without being brought into contact with the siloxane-based repeating unit portion. Further, the electrolyte membrane for a fuel cell of the present invention increases the membrane strength and suppresses the dimensional change by attracting the copolymer polymers by the π-π interaction between the aromatic rings of the aromatic repeating unit. The effect can be further improved.

According to the present invention, in the proton conductive material contained in the electrolyte membrane of the present invention, the countless proton conductivity of the electrolyte resin filled in the cavity of the inorganic fine particles, which is the outer shell of the proton conductive material. Since the group is exposed from the through-holes on the surface of the inorganic fine particles, the proton conductivity is high, and the electrolyte resin is confined in the inorganic fine particles having a determined particle size. Therefore, there is no dimensional change due to the balance of water and heat.
Further, according to the present invention, even if the fluidity is normally high, such as introducing a large amount of proton conductive groups into the structure of the electrolyte resin, Since it is held in the cavity, it is possible to achieve both improvement in shape retention and proton conductivity in the proton conductive material.
Furthermore, according to the present invention, the proton conductive material can be uniformly dispersed in the electrolyte membrane by using the polymer having an affinity for the proton conductive material as a binder resin.

  The electrolyte membrane for a fuel cell of the present invention contains a proton conductive material in which hollow inorganic fine particles having through holes on the surface are filled with an electrolyte resin, and a polymer having a siloxane-based repeating unit having a siloxane structure. It is characterized by.

  Hereinafter, the proton conductive material contained in the fuel cell electrolyte membrane of the present invention will be described in detail with reference to the drawings. FIG. 1 is a view showing a typical example of a proton conductive material contained in an electrolyte membrane for a fuel cell according to the present invention, and is a view obtained by cutting a particulate proton conductive material. The lower right circle is an enlarged view of the cross section, and is a diagram schematically showing the structural formula of the electrolyte resin. The broken line connecting the silicon atom and the sulfonic acid group in the lower right circle represents an alkyl chain. The proton conductive material 100 includes an electrolyte resin 1 and inorganic fine particles 2, and the hollow inorganic fine particles 2 are filled with the electrolyte resin 1. The inorganic fine particles 2 have innumerable through holes, and the electrolyte resin 1 is exposed on the particle surface through the through holes.

  As in the structural formula schematically shown in the lower right circle of FIG. 1, the electrolyte resin 1 preferably has a Si—O skeleton. The electrolyte resin 1 has a proton conductive group such as a sulfonic acid group. The sulfonic acid group is preferably exposed on the surface of the proton conductive material 100 through the through holes of the inorganic fine particles 2 as shown in the lower right circle of FIG.

A typical example of the electrolyte resin having a Si—O skeleton is a polymer in which a Si—O skeleton is formed by polymerizing a monomer. Such a polymer can easily cause a polymerization reaction when the inorganic fine particles are filled with a monomer as a raw material of the electrolyte resin and polymerized to synthesize the electrolyte resin. Further, since the monomer has a high affinity with the inorganic fine particles and can be easily filled, the proton conductive material can be synthesized quickly. Furthermore, since the electrolyte resin has a strong polymer chain called a Si—O skeleton, proton conductive groups do not leak out of the proton conductive material.
The polymerization of the monomer here includes addition polymerization and polycondensation. In addition, a resin that is a polymer having a large molecular weight from the beginning cannot be used because it is difficult to fill at the time of decompression. Therefore, a monomer can be used for filling.

As the monomer, a compound that is a repeating unit of the electrolyte resin to be filled in the cavity of the hollow inorganic fine particles is used.
For example, when it is desired to fill inorganic fine particles with perfluorocarbon sulfonic acid conventionally used in the field of polymer electrolyte fuel cells, a monomer that forms a fluorocarbon skeleton such as fluoroethylene can be used.
When it is desired to fill the inorganic fine particles with an electrolyte resin having a Si—O skeleton, a hydrocarbonoxysilane compound and / or a silanol compound having a sulfonic acid group or a precursor group thereof can be used. The hydrocarbonoxysilane compound that can be used here is a sulfonic acid group or a precursor group thereof bonded directly or indirectly to a silicon atom, and a hydrocarbonoxy group that may contain a different atom is bonded to the same silicon atom. A compound having a bonded structure. The hydrocarbonoxy group is a group in which an oxygen atom is bonded to an aliphatic or aromatic hydrocarbon group such as an alkoxy group or an aryloxy group, and the oxygen atom is bonded to a silicon atom. is there. The hydrocarbonoxy group may contain a hetero atom. When the sulfonic acid group or its precursor group is indirectly bonded to the silicon atom, it may be bonded via, for example, an aliphatic or aromatic hydrocarbon group, and the hydrocarbon group is bonded to a hetero atom. May be included. The silanol compound that can be used here is a compound having a structure in which a sulfonic acid group or a precursor group thereof is bonded directly or indirectly to a silicon atom and a hydroxyl group is bonded to the same silicon atom.
Examples of the hydrocarbonoxysilane compound and / or the silanol compound include, for example, a Si atom, a sulfonic acid hydrocarbon group (which may contain a different atom), a hydroxyl group (—OH) and / or an alkoxy group or an aryl group. A silicon compound bonded to an oxy group (which may contain a different atom) is preferably used. More specifically, those having a structure represented by the following formula (1), formula (2) and formula (3) can be mentioned.

（式中、Ｒ^１は炭素数１〜４の脂肪族炭化水素基又は炭素数６〜１０の芳香族炭化水素基であり、且つ、ｎ＝１〜４である。）

(In the formula, R ¹ is an aliphatic hydrocarbon group having 1 to 4 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms, and n = 1 to 4).

  As the monomer having a sulfonic acid group precursor group, a compound that can be derived from the above-described monomer having a sulfonic acid group can be used. For example, in the above formulas (1), (2), and (3) Examples of the corresponding monomer include those having a structure represented by the following formula (4), formula (5), and formula (6).

（式中、Ｒ^２〜Ｒ^９は互いに独立であり、水素原子、異種原子を含んでいてもよく好ましくは炭素数１〜４の脂肪族炭化水素基、及び異種原子を含んでいてもよく好ましくは炭素数６〜１０の芳香族炭化水素基からなる群から選択される官能基である。また、ｎ＝１〜４である。Ｘ^１〜Ｘ^４は互いに独立であり、チオール基、スルフィニル基、スルホン酸フルオリド、スルホン酸クロリド、スルホン酸ブロミド、スルホン酸ヨージド、スルホン酸リチウム、スルホン酸カリウム又はスルホン酸ナトリウム等のスルホン酸基の前駆体基のうちのいずれかから選択される官能基である。）

(In the formula, R ^{2 to} R ⁹ are independent of each other, and may contain a hydrogen atom, a heteroatom, or preferably an aliphatic hydrocarbon group having 1 to 4 carbon atoms and a heteroatom. Is a functional group selected from the group consisting of aromatic hydrocarbon groups having 6 to 10 carbon atoms, and n = 1 to ^4. X ^{1 to} X ⁴ are independent of each other, and are a thiol group or a sulfinyl group. , Sulfonic acid fluoride, sulfonic acid chloride, sulfonic acid bromide, sulfonic acid iodide, lithium sulfonic acid, potassium sulfonate, sodium sulfonate, and other functional groups selected from precursor groups of sulfonic acid groups .)

  In synthesizing the electrolyte resin, two or more monomers may be used.

As a method for converting a precursor group of a sulfonic acid group into a sulfonic acid group, for example, when the precursor group is a thiol group or a sulfinyl group, it is converted into a sulfonic acid group by adding an oxidizing agent such as hydrogen peroxide. Or when the precursor group is sulfonic acid fluoride, sulfonic acid chloride, sulfonic acid bromide, sulfonic acid iodide, lithium sulfonic acid, potassium sulfonic acid, sodium sulfonic acid or the like, an acid such as hydrochloric acid or sulfuric acid, or It can be converted to a sulfonic acid group by adding a base such as an aqueous sodium hydroxide solution.
Further, the precursor group of the sulfonic acid group is not limited to the above, and includes, for example, the case where X ^{1 to} X ⁴ in the above formulas (4) to (6) are terminal olefins. In this case, it can be converted into an alkyl group having a sulfonic acid group at the terminal by treating with sulfur trioxide and then treating with a base.

  In addition, the electrolyte resin 1 may be a polymer electrolyte usually used in a fuel cell. Polyelectrolyte here refers to polyether polymer ketone, polyether ketone, polyether sulfone, polyphenylene sulfide, in addition to fluorine-based polymer electrolytes such as perfluorocarbon sulfonic acid resin represented by Nafion (trade name). Protonic acid groups such as sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, and boronic acid groups on hydrocarbon polymers such as engineering plastics such as polyphenylene ether and polyparaphenylene, and general-purpose plastics such as polyethylene, polypropylene, and polystyrene ( Hydrocarbon polymer electrolytes into which proton conductive groups) have been introduced.

  The inorganic fine particles 2 are required to have a sufficient filling amount inside the particles, and have a low internal resistance to flow and are easy to be filled when the monomer as the raw material of the electrolyte resin 1 is filled. It is not necessarily limited to a complete hollow body, and may have some internal structures in the form of partitions on the pillars.

  In addition, the through-holes on the surface of the inorganic fine particles 2 have a low resistance to flow when the monomer as the raw material of the electrolyte resin 1 is filled, and the monomer is addition-polymerized or polycondensed inside the particles. It is required that the electrolyte resin produced in this way has a size in an appropriate range that does not easily flow out.

In order to satisfy the properties of the inside of the inorganic fine particles 2 and the through holes as described above, the inorganic fine particles 2 are preferably SiO ₂ . Since the proton conductive material 100 has a rigid shell made of SiO _2, it has an advantage of excellent mechanical properties.

As the inorganic fine particles, it is preferable to use microcapsules (trade name: Washin microcapsules) whose main component is SiO ₂ , but other inorganic fine particle porous hollow bodies may be used. Specifically, in addition to the above SiO ₂ , silsesoxane, zeolite, and the like can be given. However, mesoporous silica does not correspond to the hollow inorganic fine particles used in the present invention because the electrolyte resin easily flows out from the inside of the particles and it is difficult to hold the electrolyte resin.
As a method for producing inorganic fine particles, styrene monomer is polymerized in the presence of a vinyl monomer having a cationic surfactant group to obtain polystyrene fine particles having an ionic group on the surface. The polystyrene fine particles are subjected to a hydrolytic condensation reaction of tetraethoxysilane to form silica on the surfaces of the polystyrene fine particles. Next, hollow silica microcapsules are obtained by dissolving and removing polystyrene with a solvent.
The microcapsules must be treated with an acid such as hydrochloric acid prior to the production of the proton conductive material to remove impurities in advance.

The proton conductive material 100 preferably has an ion exchange capacity larger than the ion exchange capacity of the inorganic fine particles 2 itself, and the ion exchange capacity of the proton conductive material 100 is 0.5 meq / g or more. Is preferred. If the ion exchange capacity of the proton conductive material 100 is smaller than the ion exchange capacity of the inorganic fine particles 2, no improvement in ion conductivity can be expected even if an ion conductive group is added. Further, if the proton exchange capacity of the proton conductive material 100 is less than 0.5 meq / g, sufficient power generation efficiency cannot be expected when the proton conductive material 100 is used for an electrolyte membrane of a fuel cell. .
Therefore, the proton conductive material having the ion exchange capacity as described above can ensure proton conductivity higher than that of the inorganic fine particles by filling the electrolyte resin in the inorganic fine particles, and the fuel. When used in an electrolyte membrane of a battery, sufficient proton conductivity can be exhibited.

The proton conductive material 100 preferably has an average particle size of 0.05 to 10 μm.
If the average particle size of the proton conductive material 100 is less than 0.05 μm, it is not large enough to hold a sufficiently filled electrolyte resin. Conversely, when the average particle size of the proton conductive material 100 exceeds 10 μm, it cannot be used for an electrolyte membrane having an appropriate thickness.
More preferably, from the viewpoint of avoiding particle destruction, the bulk density of the inorganic fine particles 2 may be 5% or more of the true density of the inorganic fine particles 2.

  As a filling condition of the above-mentioned monomer into the inorganic fine particles, it is preferable to carry out 1 to 200 mmHg, 20 to 100 ° C., and 1 to 6 hours as the degree of vacuum. Moreover, as polymerization conditions in the inorganic fine particles of the monomer, it is preferable to perform heat treatment at 80 to 150 ° C. for 2 to 24 hours under reduced pressure.

  The polymer having a siloxane-based repeating unit having a siloxane structure includes at least an aromatic ring and a cyclic imide condensed or not condensed with the aromatic ring, and the aromatic ring and the cyclic imide are directly or It is preferable that it is a copolymer polymer formed by linking an aromatic repeating unit having a structure bonded through only one atom and a siloxane repeating unit having a siloxane structure.

  The aromatic repeating unit includes at least one cyclic imide and at least one aromatic ring constituting a chain structure of a main chain skeleton (here, the main chain includes a polymer side chain such as a graft chain). And has a chemical structure in which the aromatic ring occupies most of the spatial extent of the repeating unit.

  The aromatic ring may be either a mononuclear aromatic ring or a condensed polynuclear aromatic ring. In the case of a polynuclear structure, the number of aromatic rings to be fused and integrated is not limited, but in general, from the viewpoint of ease of synthesis. It is preferably a mononuclear aromatic ring or a condensed polynuclear aromatic ring in which 3 or less aromatic rings are condensed.

  The atoms forming the aromatic ring have π electrons delocalized in the aromatic ring, in addition to the σ electrons that form the bonds between the atoms. Due to the interaction between the π electrons (π-π interaction), the surfaces of the aromatic rings are stacked facing each other and stabilized. Therefore, by mixing the copolymer having an aromatic ring in the electrolyte membrane, the copolymer polymers attract each other by the π-π interaction between the aromatic rings, thereby increasing the membrane strength and suppressing the dimensional change. The effect can be further improved.

  A cyclic imide is a cyclic compound or a cyclic functional group in which two hydrogen atoms of ammonia are substituted with an acyl group, and is generally derived from an acid anhydride and an amine. Therefore, the basic structural formula of the imide moiety of the cyclic imide is —C (O) —N (R) —C (O) — (R is alkyl, aryl, etc.). Examples of the structural formula of the cyclic imide include monoimides represented by the following formulas (7) to (12).

  Further, as the cyclic imide, diimides represented by the following formulas (13) to (17) derived from tetracarboxylic acid anhydride can also be used.

  A phthalimide structure as shown in formulas (7) and (8), a succinimide structure as shown in formula (9), a glutarimide structure as shown in formulas (10) and (11), as shown in formula (12) Maleimide structure, benzenetetracarboxylic acid diimide structure as shown in formula (13), naphthalenetetracarboxylic acid diimide structure as shown in formulas (14) and (15), anthracene tetracarboxylic acid diimide as shown in formula (16) The structure and the polymer having a perylene tetracarboxylic acid diimide structure as shown in the formula (17) have an affinity for the electrolyte resin filled in the inorganic fine particles in the proton conductive material described above, and the proton conductivity of the electrolyte resin. Since the functional group is captured by the imide group and the proton conductive group is fixed, the proton conductive group is It can be kept stable without contacting the portion of the hexane-based repeating unit.

The cyclic imide may exist as a side chain of the repeating unit, but it is preferable to form a chain structure of the main chain skeleton by connecting or condensing with an aromatic ring.
The cyclic imide may appear repeatedly in the copolymer, and two or more different cyclic imide structures may form the same copolymer.
The cyclic imide is preferably a cyclic imide condensed with an aromatic ring.
Particularly preferred is a cyclic imide condensed with a benzene ring, such as the phthalimide structure represented by the above formulas (7) and (8).

In addition to the aromatic ring or cyclic imide moiety, the aromatic repeating unit includes atoms, substituents, side chains, and non-aromatic rings such as alicyclic hydrocarbons bonded between the aromatic ring and the cyclic imide. It may be included. However, from the viewpoint of not impairing the rigidity and π-π interaction expected for the aromatic repeating unit, it is preferable that the following conditions are satisfied as much as possible, and it is particularly preferable that at least the following condition 1 is satisfied. .
Condition 1: It is preferable that the aromatic ring and the cyclic imide are directly bonded or bonded via only one atom. However, the chemical structure for connecting the aromatic ring and the cyclic imide may not have two or more atoms in the chain direction connecting the rings, and may have a substituent or a side chain. For example, when an aromatic ring and a cyclic imide are bonded via a 2,2-propylidene group (or can be expressed as a dimethylmethylene group), the aromatic ring and the cyclic imide are bonded via only one atom. Become.
Condition 2: The substituent and the side chain may be either chain-like or cyclic, but preferably have a small size. In particular, the number of atoms constituting the substituent or the side chain excludes a hydrogen atom. The total is preferably 3 or less for each substituent or side chain.
Condition 3: When the aromatic repeating unit has a non-aromatic ring, the non-aromatic ring is preferably present as a pendant structure of a side chain, that is, a polymer chain. Further, the number of non-aromatic rings contained in the aromatic repeating unit is preferably smaller than the number of aromatic rings. The number of non-aromatic rings contained in one aromatic repeating unit is preferably 2 or less, particularly preferably 1 or less.

The siloxane repeating unit is composed of two or more siloxane structures (—Si (<Si) in the chain structure constituting the main chain skeleton (the main chain includes a polymer side chain such as a graft chain)). ) O-) has a chemical structure including a polysiloxane structure linked.
The polysiloxane structure is a chain polysiloxane structure— (R) ₂ Si—O — {(R) ₂ Si—O—} _n — (R) ₂ Si— or a cyclic polysiloxane structure (— (R) ₂ Si -O-) Expressed by a general formula such as _n . In particular, a polysiloxane structure in which R is a methyl group is generally well known. In addition, R is an ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, sec C1-C8 linear or branched alkyl groups such as -butyl group, n-pentyl group, n-hexyl group, etc., and C1-C8 hydroxyalkyl groups such as hydroxymethyl group, hydroxyethyl group, etc. Is mentioned.

The siloxane-based repeating unit of the polymer is preferable because the affinity between the polymer and the proton conductive material is highest, especially when the inorganic fine particles of the proton conductive material described above are SiO ₂ .

The polysiloxane structure of the siloxane-based repeating unit is preferably formed by connecting 3 to 20 siloxane structures from the viewpoint of increasing the affinity with the proton conductive material.
In the middle of the polysiloxane structure, the chain of the siloxane structure may be interrupted by other atoms, but in that case, there is a portion in which 2 to 20 siloxane structures are continuous in one repeating unit. It is preferable that at least one is included.

  The siloxane-based repeating unit may have a structure serving as a linking group with another repeating unit at one end or both ends thereof. Examples of the linking group present at the end of the siloxane-based repeating unit include a divalent hydrocarbon group, a divalent organic group such as an ester group and an ether group, an organic group such as an ester group and an ether group, or a heterogeneous group. Examples thereof include a hydrocarbon group containing an atom. In the case of the hydrocarbon group, the size of the linking group can be exemplified by a hydrocarbon group (for example, a propylene group) having about 1 to 8 carbons linked in the chain direction of the main chain. Similarly, when the linking group contains different atoms, the number of atoms linked in the chain direction of the main chain is preferably about 1 to 8.

Regarding the carbon-carbon bond which is the main chain skeleton of a normal hydrocarbon chain, the bond angle of C—C—C is 109 ° and the bond distance of C—C is 0.140 nm, whereas the polysiloxane structure With respect to the silicon-oxygen bond, which is the main chain skeleton, the Si—O—Si bond angle is as wide as 143 ° and the Si—O bond distance is as long as 0.165 nm. energy: 0.8kJmol ^-1), silicon - oxygen bond can freely rotate. That is, the polysiloxane structure can maintain moderate flexibility as compared with a normal hydrocarbon chain.

  The copolymer may be a block copolymer in which a block in which the same number of repeating units of the aromatic repeating unit and the siloxane repeating unit are linked to each other may be copolymerized, or different repeating units. May be an alternating copolymer that alternately polymerizes. Further, it may be a random copolymer having no order in the arrangement of repeating units.

  The copolymer may contain other repeating units, but if the amount is too large, the properties expected of the copolymer may not be fully exhibited. Therefore, the copolymerization ratio of other repeating units contained in the copolymer is preferably 30 mol% or less, more preferably 10 mol% or less, and particularly no other repeating units are contained. preferable.

  A typical example of a polymer having a siloxane-based repeating unit having a siloxane structure contained in the electrolyte membrane of the present invention is poly (dimethylsiloxane) etherimide (hereinafter abbreviated as PDSEI) represented by the following formula (18). Can do.

  Although the values of x, y, and n, which are the degree of polymerization of PDSEI shown in the above formula (18), can be set freely, in view of the roles played by the aromatic repeating unit and the siloxane repeating unit as described above. X = 1 to 3, y = 1 to 12, and n = 8 to 10.

When the content of the proton conductive material and the polymer having a siloxane repeating unit having a siloxane structure is 100 parts by weight of the total of these two components, the proton conductive material is 70 to 30 parts by weight, The polymer is preferably 30 to 70 parts by weight. When the proton conductive material is less than 30 parts by weight, it is difficult to obtain high proton conductivity and shape retention of the electrolyte membrane, which are the effects of the present invention. Moreover, when the said polymer is less than 30 weight part, the film forming property for forming an electrolyte membrane may become inadequate.
More preferably, the proton conductive material is 65 to 40 parts by weight and the polymer is 35 to 60 parts by weight, the proton conductive material is 60 to 50 parts by weight, and the polymer is 40 to 50 parts by weight. Most preferably it is.

As a method for forming an electrolyte membrane, after dissolving the polymer having a siloxane-based repeating unit having a siloxane structure in an appropriate solvent, the proton conductive material is added and stirred well, and the solution is smoothed on a glass plate or the like. It is preferable to perform drying under an inert gas stream such as nitrogen gas or argon gas after spreading the film almost uniformly. In addition, when a solvent remains in a film | membrane, high temperature vacuum drying can also be performed. At this time, as a solvent, dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), dimethylacetamide (DMA), or a mixed solvent thereof can be used.
In addition to this, a conventionally used method can be employed as a method for forming the electrolyte membrane, and the main methods include a melt extrusion method, a doctor blade method, and the like.

According to the present invention, in the proton conductive material contained in the electrolyte membrane, the infinite number of proton conductive groups of the electrolyte resin filled in the cavity of the inorganic fine particles that are the outer shell of the proton conductive material are Since the proton conductivity is high and the electrolyte resin is confined in the inorganic fine particles having a fixed particle size, the proton conductive material does not swell and contract. Dimensional change does not occur due to heat balance.
Further, according to the present invention, even if the fluidity is normally high, such as introducing a large amount of proton conductive groups into the structure of the electrolyte resin, Therefore, it is possible to achieve both improvement in shape retention and proton conductivity in the proton conductive material.
Furthermore, according to the present invention, the proton conductive material can be uniformly dispersed in the electrolyte membrane by using the polymer having an affinity for the proton conductive material as a binder resin.

1. Pretreatment of inorganic fine particles 10.0 g of microcapsules (trade name: Washin Microcapsule) as hollow inorganic fine particles having through-holes on the surface were added to 200 mL of 0.1N hydrochloric acid and stirred for one day. Thereafter, the mixture was allowed to stand to precipitate microcapsules, and the supernatant was removed. After adding 200 mL of distilled water and stirring well, it was allowed to stand and the supernatant was removed in the same manner. Thus, addition of distilled water, stirring, and removal of the supernatant were repeated until pH = 7.
Finally, the remaining precipitate was dried under reduced pressure at 120 ° C. under vacuum for 6 hours.

2. Proton conductive material production [Synthesis example]
0.10 g of the pre-treated microcapsules described above was added to 1.54 g of a 3- (trihydroxysilyl) -1-propanesulfonic acid solution (manufactured by Gelest) having a concentration of 30 wt% as a monomer having a sulfonic acid group. Thereafter, pressure reduction (100 mmHg, 25 ° C., 2 hours) was performed to fill the microcapsules with the monomer. The pressure was further reduced for 3 hours to remove moisture. Subsequently, the monomer was polymerized by heating at 80 ° C. for 12 hours under reduced pressure. Then, after homogenizing using a mortar, it wash | cleaned 3 times with ion-exchange water, and reduced-pressure drying (120 degreeC, 6 hours) was performed. As a result, 0.36 g of a proton conductive material which was a white solid was obtained.

3. Production of Electrolyte Membrane Hereinafter, the proton conductive material described above and the electrolyte membrane (Examples 1 to 3) containing PDSEI which is a kind of polymer having a siloxane-based repeating unit, the proton conductive material described above, and non A method for producing an electrolyte membrane (comparative example) containing polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), which is a kind of proton conductive polymer, will be described. The inventors have already filed a patent application for the invention relating to the electrolyte membrane cited as a comparative example (Japanese Patent Application No. 2007-289844), and the electrolyte membrane of the comparative example has sufficient proton conductivity and high dimensions. It has become clear that it has a change suppressing effect.

[Example 1]
In an eggplant flask, 0.10 g of PDSEI (manufactured by Gelest, product number: SSP-85, 40 parts by weight), which is a type of polymer having a siloxane-based repeating unit, is dissolved in 1.5 mL of DMA under nitrogen. 0.15 g (60 parts by weight, average particle size of 3 to 5 μm) of the synthesized proton conductive material was added and stirred at room temperature for 1 day under nitrogen.
After confirming that it was well dispersed visually, stirring was terminated and the solution was spread almost uniformly on the glass plate. When the solution on the glass plate was allowed to stand at 60 ° C. for 24 hours under a nitrogen stream, a wet gel film was obtained. In order to remove the residual solvent in the wet gel film, it was dried under reduced pressure at 120 ° C. under vacuum for 12 hours to obtain a translucent and flexible electrolyte film.

[Example 2]
In an eggplant flask under nitrogen, 0.10 g (50 parts by weight) of PDSEI, which is a kind of polymer having a siloxane-based repeating unit, was dissolved in 1.5 mL of DMA, and 0.10 g (50 g of proton conductive material synthesized in the above synthesis example (50 Parts by weight and an average particle diameter of 3 to 5 μm) were added, and the mixture was stirred at room temperature for 1 day under nitrogen.
After confirming that it was well dispersed visually, the stirring was terminated and a film was formed by the same method as in Example 1.

[Example 3]
Under nitrogen, under a nitrogen atmosphere, PDSEI 0.10 g (60 parts by weight), which is a type of polymer having a siloxane-based repeating unit, was dissolved in DMA 1.5 mL, and the proton conductive material synthesized in the above synthesis example was 0.067 g (40 Parts by weight and an average particle diameter of 3 to 5 μm) were added, and the mixture was stirred at room temperature for 1 day under nitrogen.
After confirming that it was well dispersed visually, the stirring was terminated and a film was formed by the same method as in Example 1.

[Comparative example]
In an eggplant flask under nitrogen, 0.10 g (50 parts by volume) of polyvinylidene fluoride / hexafluoropropylene copolymer (PVDF-HFP), which is a kind of aprotic conductive polymer, 1.5 mL of dimethylacetamide (DMA) Then, 0.10 g (50 parts by volume, average particle size of 3 to 5 μm) of the proton conductive material synthesized in the above synthesis example was added and stirred at room temperature for 1 day under nitrogen. After completion of the stirring, the stirring bar was taken out and stirred for 30 minutes using an ultrasonic homogenizer to monodisperse PVDF-HFP and the proton conductive material in the solution.
The monodispersed solution was cast on a Teflon (registered trademark) petri dish and allowed to stand under a nitrogen stream at 60 ° C. for 24 hours to obtain a wet gel film. In order to remove the residual solvent in the wet gel film, it was dried under reduced pressure for 12 hours under the condition of 120 ° C. under vacuum, and 0.2 g of a translucent and flexible electrolyte film was obtained.

4). Measurement and Evaluation of Proton Conductivity of Electrolyte Membrane For the electrolyte membranes of Examples 1 to 3 described above, after standing for 3 hours at 95% relative humidity and each temperature (25 ° C., 50 ° C., 80 ° C.), the AC impedance method was used. Proton conductivity was measured. The results are shown in FIG.
In any of the electrolyte membranes of Examples 1 to 3, the common logarithm of proton conductivity σ is −2 or more, that is, σ is on the order of 10 ⁻² S / cm under the conditions of a relative humidity of 95% and a temperature of 25 ° C. or more. It was found that The higher the content of the proton conductive material of the present invention (ie, the proton conductive material obtained in the above synthesis example), the higher the proton conductivity, and the electrolyte membrane of Example 1 (ie, obtained in the above synthesis example). In the electrolyte membrane containing 60% by weight of the proton conductive material obtained, it was found that σ was on the order of 10 ⁻¹ S / cm under the conditions of a relative humidity of 95% and a temperature of 80 ° C.

5). Measurement and Evaluation of Temperature Dependence of Elastic Modulus of Electrolyte Membrane The electrolyte membranes of Example 1 and Comparative Example processed into a dumbbell shape were held in a constant temperature furnace in a state where they were fixed with light tension applied. Then, while increasing the temperature of the constant temperature furnace at a rate of temperature increase of 5 ° C./min, a load was repeatedly applied at 10 Hz between 0 and 0.1% strain, and the load at each temperature was set at 0.1% strain. The divided value was calculated as the elastic modulus, and the temperature dependence of the elastic modulus was obtained.
FIG. 3 is a graph showing the relationship between temperature (horizontal axis) and storage elastic modulus (vertical axis) for the electrolyte membranes of Example 1 and Comparative Example. From FIG. 3, a remarkable difference was seen in the storage elastic modulus of the electrolyte membrane of Example 1 and a comparative example especially in the temperature range of 150 degreeC or more. Therefore, it was found that the electrolyte membrane of Example 1 was obtained by further improving the electrolyte membrane of the comparative example from the viewpoint of mechanical strength (thermal stability).

6). Summary From the above measurement results, the electrolyte membrane of the present invention has higher proton conductivity and mechanical strength (thermal stability) than the electrolyte membrane containing the proton conductive material and the non-proton conductive polymer described above. ) Became clear.

It is the figure which showed the typical example of the proton-conductive material contained in the electrolyte membrane for fuel cells of this invention, and is the figure which cut the particulate proton-conductive material into pieces. It is the graph which showed the relationship between the reciprocal temperature (horizontal axis) in 95% of relative humidity, and the common logarithm of proton conductivity (vertical axis) about the electrolyte membrane of Examples 1-3 of this invention. It is the graph which showed the relationship between temperature (horizontal axis) and storage elastic modulus (vertical axis) about the electrolyte membrane of Example 1 and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte resin 2 ... Inorganic fine particle 100 ... Proton conductive material

Claims (8)

  A fuel cell electrolyte membrane comprising a proton conductive material in which hollow inorganic fine particles having through holes on the surface are filled with an electrolyte resin, and a polymer having a siloxane-based repeating unit having a siloxane structure .   When the content of the proton conductive material and the polymer is 100 parts by weight of the total of these two components, the proton conductive material is 70 to 30 parts by weight, and the polymer is 30 to 70 parts by weight. The electrolyte membrane for fuel cells according to claim 1.   The electrolyte membrane for a fuel cell according to claim 1 or 2, wherein the electrolyte resin in the inorganic fine particles has a Si-O skeleton. The electrolyte membrane for a fuel cell according to any one of claims 1 to 3, wherein the inorganic fine particles are SiO ₂ .   The electrolyte membrane for a fuel cell according to any one of claims 1 to 4, wherein the proton conductive material has an ion exchange capacity larger than that of the inorganic fine particles.   The electrolyte membrane for a fuel cell according to any one of claims 1 to 5, wherein an ion exchange capacity of the proton conductive material is 0.5 meq / g or more.   The electrolyte membrane for a fuel cell according to any one of claims 1 to 6, wherein the proton conductive material has an average particle size of 0.05 to 10 µm.   The polymer includes at least an aromatic ring and a cyclic imide condensed or not condensed with the aromatic ring, and the aromatic ring and the cyclic imide are bonded directly or via a single atom. The electrolyte membrane for a fuel cell according to any one of claims 1 to 7, which is a copolymer obtained by connecting an aromatic repeating unit having a structure and a siloxane repeating unit having a siloxane structure.

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