JP5825005B2 - Polymer electrolyte, polymer electrolyte membrane, fuel cell, and ionic material - Google Patents

Description

  The present invention relates to a polymer electrolyte, a polymer electrolyte membrane, a fuel cell, and an ionic material, and is suitable for, for example, a polymer electrolyte having excellent durability and excellent low humidification characteristics.

  The polymer electrolyte fuel cell (hereinafter referred to as PEFC) is being researched and developed as a power source that can reduce the release of environmentally hazardous gases as a power source for fuel cell vehicles, stationary cogeneration, and mobile phones. In PEFC, a power generation reaction proceeds by conduction of protons in the battery. The presence of water is indispensable for proton conduction in PEFC. Therefore, a humidifier is required to advance the power generation reaction of PEFC. When a fuel cell is applied to a vehicle or the like, since it is desired that the humidification is small from the viewpoint of in-vehicle performance, an electrolyte that can perform proton conduction well even under low humidification is required. Fluorine resin electrolytes typified by Nafion (registered trademark, manufactured by DuPont) and Aciplex (registered trademark, manufactured by Asahi Kasei) are excellent in proton conductivity under low humidification and are widely used in PEFC It is.

  However, since the fluororesin electrolyte is a polymer material made of fluorine, there is a problem in terms of recycling. Considering the widespread use of fuel cell vehicles, the question of whether or not it can be recycled is important, and the environmental impact of materials that cannot be recycled cannot be ignored. Furthermore, when a fluorine resin electrolyte is applied alone as an electrolyte membrane, there is a problem in terms of durability. Therefore, the need for an alternative material for the fluororesin electrolyte is increasing.

  In recent years, hydrocarbon-based electrolytes have been developed as an alternative material. Hydrocarbon materials are generally more durable than fluororesin electrolytes and are expected to replace fluororesin electrolytes. In order to have high proton conductivity with low humidification using a hydrocarbon-based electrolyte, for example, in Patent Document 1 below, a sulfonic acid group network is formed using a material having a liquid crystal skeleton, and high proton conductivity with low humidification. It is described that sex is expressed.

JP 2003-55337 A

However, in the sulfonated liquid crystal polymer material obtained by increasing the molecular weight of the sulfonic acid type liquid crystal monomer material described in Patent Document 1, the mesogen of the side chain is biphenyl, and hydrogen atoms in the ortho position cause electron repulsion between the ortho-positioned hydrogen atoms. Since the two rings are twisted, stacking between mesogens becomes unstable. Along with this, there is a concern that formation of a network of acid groups is hindered and higher proton conductivity cannot be achieved. In addition, since the main chain is a methacryl group or an acrylic skeleton, it is difficult to expect an improvement in performance by thinning.
An object of the present invention is to solve the above-mentioned problems, and promotes stacking of mesogens in the side chain, and has an excellent proton conductivity by using a rigid skeleton in the main chain to enable thinning. It is to provide a polymer electrolyte, a polymer electrolyte membrane, a fuel cell, and an ionic material.

As a result of intensive studies to achieve the above object, the present inventors have focused on a polymer electrolyte membrane material in which the side chain mesogen is changed to a 2,2′-bipyridine skeleton and the main chain is changed to a phenylene skeleton. did.
The polymer electrolyte according to claim 1 of the present invention is a polymer electrolyte characterized by having a polymer unit represented by the following formula 1. However, A _1, A ₂ is an alkylene group - (CH _{2) m} - and is, m is an integer of 1 or more, B is a protonic acid group, n is an integer of 10 to 10,000.

The polymer electrolyte according to claim 2 of the present invention is the polymer electrolyte according to claim 1, wherein the protonic acid group B is a sulfonic acid group or a phosphonic acid group. .
The polymer electrolyte membrane according to claim 3 of the present invention is a polymer electrolyte membrane using the polymer electrolyte according to claim 1 or 2.

According to a fourth aspect of the present invention, there is provided a fuel cell comprising either or both of the polymer electrolyte according to the first or second aspect and the polymer electrolyte membrane according to the third aspect. The fuel cell.
Moreover, the ionic material according to claim 5 of the present invention is an ionic material characterized by having a group capable of being polymerized represented by the following two formulas. However, A _1, A ₂ is an alkylene group - (CH _{2) m} - and is, m is an integer of 1 or more, B is a protonic acid group, a chlorine atom X _1, X ₂ are independently a , An odor atom, or an iodine atom.

The invention according to claim 1 of the present invention is characterized by having the polymer unit represented by the above-mentioned formula 1, has high proton conductivity, can be thinned, and has high power generation performance. There is a remarkable effect that a polymer electrolyte can be provided.
The invention according to claim 2 of the present invention is a polymer electrolyte characterized in that the protonic acid group B is a sulfonic acid group or a phosphonic acid group, promotes dissociation of protons, and conducts protons. There is a remarkable effect that the degree can be improved.

The invention according to claim 3 of the present invention is a polymer electrolyte membrane comprising the polymer electrolyte according to claim 1 or 2, and has high proton conductivity and power generation performance. There is a remarkable effect that a polymer electrolyte membrane can be provided.
Among the present inventions, the invention according to claim 4 uses either one or both of the polymer electrolyte according to claim 1 or 2 and the polymer electrolyte membrane according to claim 3. The fuel cell having high power generation performance can be provided.

It is a pi stack conceptual diagram of a benzene ring. FIG. 2 is a structural diagram of biphenyl. FIG. 2 is a structural diagram of 2,2′-bipyridine. It is sectional drawing of the membrane electrode assembly which formed the electrode catalyst layer on both surfaces of the polymer electrolyte membrane of this invention. It is an exploded view which shows the structure of the single cell of the fuel cell equipped with the membrane electrode assembly of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 4 is a cross-sectional view of a membrane electrode assembly 12 in which the air electrode side electrode catalyst layer 2 and the fuel electrode side electrode catalyst layer 3 are formed on both surfaces of the polymer electrolyte membrane 1 of the present invention. FIG. 5 is an exploded view of the unit cell 11 of the fuel cell equipped with the membrane electrode assembly 12 of FIG. 4, in which 4 is an air electrode side gas diffusion layer, 5 is a fuel electrode side gas diffusion layer, Reference numeral 6 denotes an air electrode, reference numeral 7 denotes a fuel electrode, reference numeral 8 denotes a gas flow path, reference numeral 9 denotes a cooling water flow path, and reference numeral 10 denotes a separator.

Below, the ion conductive polymer of this invention and a membrane electrode assembly using the same are demonstrated. The present invention is not limited to each embodiment described below, and modifications such as design changes can be added based on the knowledge of those skilled in the art, and such modifications have been added. Embodiments can also be included in the scope of the present invention.
As shown in FIG. 1, the aromatic compound is generally stacked between molecules so that the surfaces of the aromatic ring overlap with each other as the π electrons delocalized on the aromatic ring interact with each other. It is known to form (π stack). This figure shows an example of a conformation in which the carbon atoms of the upper and lower benzene rings overlap each other. The mesogen of the liquid crystal molecule uses this stack formation to form an ordered structure. That is, in order to form an aggregate of liquid crystal molecules, promotion of stack formation is important.

In the present invention, a protonic acid group is bonded to a mesogen via a linking group, and the mesogen network can directly be a proton network. Therefore, by further promoting the formation of the mesogen stack, the protons in the molecule can be transported efficiently, and the proton conductivity can be improved.
In general, biphenyl often used as a mesogen has an electron repulsion caused by hydrogen bonding to carbon adjacent to (ortho position) the carbon to which the benzene rings are bonded, as shown in FIG. It is known that they twist about 50 degrees. In order to make it easier to form a stack, it is necessary to eliminate this twist.

  In the polymer electrolyte of the present invention, mesogenic biphenyl is changed to 2,2'-bipyridine. As shown in FIG. 3, 2,2′-bipyridine has a structure in which the hydrogen at the ortho position of biphenyl is eliminated from each ring one by one, and can cause electron repulsion between hydrogens like biphenyl. Therefore, the twisting of adjacent rings hardly occurs, and the rings are almost on the same plane. In addition, the nitrogen atom of the pyridine ring forms a hydrogen bond with the hydrogen at the ortho position of the adjacent ring, and this planar structure without twist can be stabilized.

  Below, the manufacturing method of the polymer electrolyte membrane which can make the fuel cell of this invention thin film and was excellent in durability is demonstrated. The present invention is not limited to the embodiments described below, and modifications such as design changes can be added based on the knowledge of those skilled in the art, and such modifications have been added. Embodiments can also be included in the scope of the present invention.

[Synthesis of compounds]
A ₁ , A ₂ and B in the formula ₂ are the same as those defined in the formula _1, and X ₁ and X ₂ are each independently any one of a chlorine atom, a bromine atom or an iodine atom. is there. X ₁ and X ₂ may be the same or different, but are preferably the same.
For example, when A ₁ is an ethylene group — (CH ₂ ) ₂ —, A ₂ is a propylene group — (CH ₂ ) ₃ —, and B is a sulfonic acid group, It can be synthesized as follows. First, 4,4′dihydroxy-2,2′-bipyridine was prepared (see Journal of Medicinal Chemistry, 44, 1396 (2001) for synthesis), and this was reacted with an inorganic base and propane sultone to produce the following 3 The formula can be obtained.

  The reaction conditions at this time are not particularly limited, but the reaction temperature is preferably 25 to 80 ° C. The reaction time is preferably 10 to 48 hours. There is no problem in the reaction in an air atmosphere or a nitrogen atmosphere. The reaction solvent is preferably a good solvent, more preferably an alcohol solvent. Examples of the alcohol solvent include ethanol, methanol, 1-propanol, 2-propanol, and 1-butanol.

The base is preferably a strong base, and examples thereof include sodium hydroxide and potassium hydroxide. The amount of the base is preferably 50 to 100 mol% and more preferably 70 to 90 mol% with respect to 100 mol% of 4,4'-dihydroxy-2,2'-bipyridine.
Next, a compound represented by the following formula 4 is prepared. Here, each X is a base atom, a bromine atom, or an iodine atom.

  A monomer compound represented by the following formula (5) can be obtained by treating the compound represented by the formula (3) with an inorganic base and reacting the compound represented by the formula (4).

  The reaction conditions at this time are not particularly limited, but the reaction temperature is preferably 25 to 80 ° C. The reaction time is preferably 10 to 48 hours. There is no problem in the reaction in an air atmosphere or a nitrogen atmosphere. The reaction solvent is preferably a good solvent, more preferably a highly polar solvent. Examples of the highly polar solvent include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone and the like.

The base is preferably a strong base, and examples thereof include sodium hydroxide and potassium hydroxide. The amount of the base is preferably 50 to 100 mol% and more preferably 80 to 100 mol% with respect to 100 mol% of the compound represented by the above formula 4.
The polymerization of this monomer is not particularly limited, but it is preferable to react in the presence of a specific catalyst. The catalyst used in this case is a catalyst system containing a transition metal compound. This catalyst system includes a ligand component, a transition metal complex coordinated with a ligand, and a reducing agent as essential components. A salt may be added to increase the polymerization rate.

  Examples of the ligand component include triphenylphosphine, 2,2′-bipyridine, 1,5-cyclooctagene, 1,3-bis (diphenylphosphino) propane, and the like. Of these, triphenylphosphine and 2,2'-bipyridine are preferred. The compound which is the said ligand component may be used individually by 1 type, and may use 2 or more types together. The ligand component is preferably 1 to 100 mol% and more preferably 1 to 20 mol% with respect to 100 mol% of the monomer.

  Examples of transition metal complexes in which a ligand is coordinated include nickel chloride bis (triphenylphosphine), nickel bromide building (triphenylphosphine), nickel iodide bis (triphenylphosphine), and nickel nitrate bis (triphenyl). Phosphine), nickel chloride (2,2′-bipyridine), nickel bromide (2,2′-bipyridine), bis (1,5-cyclooctagene) nickel, tetrakis (triphenylphosphine) nickel, tetrakis (triphenyl) Phosphite) nickel, tetrakis (triphenylphosphine) palladium and the like. Of these, nickel chloride bis (triphenylphosphine) and nickel chloride (2,2'-bipyridine) are preferred. The transition metal complex is preferably 1 to 100 mol% and more preferably 1 to 20 mol% with respect to 100 mol% of the monomer.

  Examples of the reducing agent that can be used in the catalyst system include iron, zinc, manganese, aluminum, magnesium, sodium, and calcium. Of these, zinc, magnesium and manganese are preferred. These reducing agents can be used after being more activated by bringing them into contact with an acid such as an organic acid. The reducing agent is preferably 1 to 100 mol% and more preferably 10 to 30 mol% with respect to 100 mol% of the monomer.

  Examples of salts that can be used in the catalyst system include sodium compounds such as sodium fluoride, sodium chloride, sodium bromide, sodium iodide, and sodium sulfate; potassium fluoride, potassium chloride, potassium bromide, potassium iodide, sulfuric acid Examples include potassium compounds such as potassium; ammonium compounds such as tetraethylammonium fluoride, tetraethylammonium chloride, tetraethylammonium bromide, tetraethylammonium iodide, and tetraethylammonium sulfate. Of these, sodium bromide, sodium iodide, potassium bromide, tetraethylammonium bromide, and tetraethylammonium iodide are preferred. The salt is preferably 1 to 100 mol% and more preferably 10 to 30 mol% with respect to 100 mol% of the monomer.

  Examples of the catalyst used in the polymerization include tetrahydrofuran, cyclohexanone, dimethyl sulfoxide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, γ-butyrolactone, N, N- Examples thereof include dimethyl imidazolidinone. Of these, tetrahydrofuran, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, and N, N-dimethylimidazolidinone are preferred. These polymerization solvents are preferably used after sufficiently dried.

  The polymerization temperature and polymerization time during the polymerization are not particularly limited, and may be set as appropriate depending on the molecular weight, the polymerization concentration, and the like. For example, when it is intended to obtain a polymer having a weight average molecular weight of 100 to 500,000, the polymerization temperature is preferably 25 to 80 ° C., more preferably 40 to 70 ° C., and the polymerization time is preferable from the viewpoint of reaction efficiency. Is carried out in 8 to 40 hours, more preferably 16 to 32 hours. The polymerization pressure at the time of polymerization is not particularly limited, and may be any of under pressure, normal pressure (atmospheric pressure), and reduced pressure, and may be appropriately set according to circumstances, but is preferably under normal pressure.

  A method for producing a polymer electrolyte membrane using the polymer electrolyte thus obtained is not particularly limited. For example, the polyphenylene electrolyte of the present invention is dissolved in a solvent to form a solution, and then cast. Examples thereof include a method of coating on a substrate and forming it into a film, a method of applying and forming a film using an applicator controlled to a predetermined gap, and a method of forming a film using a die coater.

In film formation, the viscosity is preferably 10 to 10000 Pa · s, and more preferably 10 to 1000 Pa · s. When the viscosity is within this range, the residual amount of solvent is small, and the probability that a large amount of bubbles are generated when the solution is dried is low, and the unevenness in thickness can be reduced by the leveling effect, so that stable proton conductivity is achieved. Secured.
The electrolyte concentration at this time is usually 2.5 to 50% by mass, preferably 7 to 25% by mass, although it depends on the molecular weight. Within this concentration range, the film formability is excellent.

  Examples of the solvent used at this time include N-methyl-2-pyrrolidone, N, N-dimethylformamide, γ-butyllactone, N, N-dimethylacetamide, dimethylsulfoxide, dimethylurea, dimethylimidazolidinone, and the like. Aprotic polar solvents, alcohol solvents such as methanol, ethanol, propyl alcohol, iso-propyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and ketone solvents such as acetone, methyl ethyl ketone, and cyclohexanone. These solvents may be used alone or in combination of two or more. Moreover, you may use what added water to these solvents.

The polymer solution whose viscosity is adjusted is cast onto a substrate, for example. Examples of the base material to be cast include metal materials, glass, ceramics, and plastics. The shape of the substrate is not particularly limited.
The film formed on the substrate is preferably heated at 25 to 140 ° C. for 0.1 to 24 hours to obtain a polymer electrolyte membrane.
Examples and comparative examples will be described. EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to this.

[Composition of Formula 3]
Under a nitrogen atmosphere, 94 g (0.5 mol) of 4,4′-dihydroxy-2,2′-bipyridine, 61 g (0.5 mol) of propane sultone, 16 g (0.4 mol) of sodium hydroxide, and 200 ml of methanol were added. Stir for hours. Then, it reprecipitated with diethyl ether and filtered. The filtrate was washed with methanol to obtain the above three formulas.
[Synthesis of Formula 6]
Under a nitrogen atmosphere, 166 g (0.5 mol) of the above formula 3, 127 g (0.5 mol) of 2- (2,5-dichlorophenyl) -1-bromoethane, 20 g (0.5 mol) of sodium hydroxide, and 200 ml of dimethyl sulfoxide were added, Stir for 48 hours. Then, it reprecipitated with methanol and filtered. The filtrate was washed with methanol to obtain the following six formulas.

[Example 1]
[Synthesis of Formula 7]
Under a nitrogen atmosphere, 7.6 g (15 mmol) of the above formula 6, 1.5 g (5.6 mmol) of triphenylphosphine, 0.3 g (2 mmol) of sodium iodide, 1.3 g (20 mmol) of zinc, bis (triphenylphosphine) Nickel (II) dichloride 0.31 g (0.48 mmol) was added, 20 ml of dimethylformamide was added as a solvent, and the mixture was stirred at 60 ° C. for 24 hours. The reaction product was reprecipitated with methanol, the solid was filtered off, and then proton-foamed with concentrated hydrochloric acid. Further, after washing with pure water until the pH of the filtrate reached 7, the solid was dried under reduced pressure to obtain the following formula 7.

Hereinafter, although this invention is demonstrated in detail by a comparative example, this invention is not limited to these.
[Synthesis of 9-bromo-1-decene]
To a 500 ml Erlenmeyer flask, 100 ml of benzene and 1.0 g of pyridine were added to dissolve 25 g (0.16 mol) of 9-decene-1-ol. Next, 100 ml of a benzene solution in which 43.2 g (0.16 mol) of phosphorus tribromide was dissolved was slowly added dropwise under ice cooling, followed by stirring at room temperature for 18 hours. Thereafter, the reaction solution was poured into ice water and extracted with 300 ml of diethyl ether. The ether-benzene mixed solution obtained here was dehydrated overnight with anhydrous sodium sulfate. Sodium sulfate was removed by suction filtration, ether-benzene was removed under reduced pressure, and the residue was distilled under reduced pressure to obtain the desired product 9-bromo-1-decene.

[Synthesis of 4- (9-decenyloxyphenyl) phenol]
3.40 g (0.08 mol) of sodium hydroxide was dissolved in 100 ml of ethanol. This solution was added little by little to 100 ml ethanol in which 14.9 g (0.08 mol) of 4,4′-biphenol was dissolved, and ethanol was removed under reduced pressure. The residue was dissolved in 150 ml dimethylformamide by heating under a nitrogen stream (solution A). 15.8 g (0.072 mol) of 9-bromo-1-decene prepared as described above and 0.1 g of phenothiazine were dissolved in 30 ml of DMF (solution B). Liquid B was added to liquid A over about 30 minutes while stirring well in a nitrogen atmosphere, and reacted at 40 ° C. for 24 hours. After completion of the reaction, the reaction solution was cooled, washed with 300 ml of 10% cold hydrochloric acid, extracted with 300 ml of ether, and then washed with 100 ml of cold distilled water. The ether layer is dehydrated with anhydrous sodium sulfate overnight. 300 ml of hexane is added to the residue and a precipitate is obtained by filtration. Next, 200 ml of benzene was added, and the benzene-soluble portion was purified by column chromatography using benzene to obtain 4- (9-decenyloxyphenyl) phenol.

[Synthesis of 3- [6- (9-decenyloxy) biphenyloxy] propylsulfonic acid]
In 30 ml of dimethylformamide, 0.05 g of a polymerization inhibitor phenothiazine was dissolved. There, 1,8-diazabicyclo [5,4,0] -7-undencene (DBU) 1.22 g (0.008 mol) and 4- (9-decenyloxyphenyl) phenol 0.65 g (0.002 mol) ), 1.8 g (0.008 mol) of sodium 3-bromopropanesulfonate was dissolved and stirred at 50 ° C. for 48 hours under a nitrogen atmosphere. After completion of the reaction, the solvent was concentrated, diethyl ether was added and filtered to obtain a precipitate. Next, the precipitate was washed well with distilled water. Next, the washed precipitate was stirred in 6 mol / L HCl for 24 hours, and then a precipitate was obtained by a centrifuge. The precipitate was washed with diethyl ether, dried, and then dried with 3- [6- (9-decenyloxy]. ) Biphenyloxy] propylsulfonic acid was obtained.

[Comparative Example 1]
[Molecularization of 3- [6- (9-decenyloxy) biphenyloxy] propylsulfonic acid]
Under a nitrogen atmosphere, 488 mg (1 mmol) of 3- [6- (9-decenyloxy) biphenyloxy] propylsulfonic acid, 6.6 mg (0.04 mmol) of AIBN as an initiator, and 4.8 ml of dimethyl sulfoxide were added. It was. Then, it polymerized by heat polymerization at 60 ° C. for 60 hours. Thereafter, reprecipitation was performed with acetone to obtain a polymer.

[Polymer film formation]
The formula 7, 3- [6- (9-decenyloxy) biphenyloxy] propyl sulfonic acid polymer is dissolved in dimethyl sulfoxide, cast into glass, 12 hours at 45 ° C., 12 hours at 80 ° C., 1 hour at 80 ° C. A film was obtained by vacuum drying.
[Thinning]
The polymer film represented by the above formula 7 has a mechanical strength that can produce a membrane electrode assembly even when it is thinned, compared with a film obtained from 3- [6- (9-decenyloxy) biphenyloxy] propylsulfonic acid polymer. Had.

[Measurement of proton conductivity]
The AC resistance of the denatured membrane was determined from the measurement of AC impedance between platinum wires by pressing a platinum wire against the surface of a strip-shaped proton conducting membrane sample having a width of 10 mm and holding the sample in a constant temperature and humidity device. That is, the impedance was measured in an environment at a temperature of 80 ° C. and a relative humidity of 30%. The proton conductivity of Example 1 was greatly improved as compared with Comparative Example 1.

  The present invention relates to a polymer constituting a polymer electrolyte fuel cell used as a power generation source for automobiles such as electric vehicles and fuel cell vehicles, mobile devices such as notebook computers, mobile phones and personal digital assistants, and household power generators. It can be used as an electrolyte membrane.

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte 2 Air electrode side electrode catalyst layer 3 Fuel electrode side electrode catalyst layer 4 Air electrode side gas diffusion layer 5 Fuel electrode side gas diffusion layer 6 Air electrode 7 Fuel electrode 8 Gas flow path 9 Cooling water flow path 10 Separator 11 Single Cell 12 Membrane electrode assembly

Claims (5)

A polymer electrolyte comprising a polymer unit represented by the following formula 1. However, A _1, A ₂ is an alkylene group - (CH _{2) m} - and is, m is an integer of 1 or more, B is a protonic acid group, n is an integer of 10 to 10,000.

  The polymer electrolyte according to claim 1, wherein the protonic acid group B is a sulfonic acid group or a phosphonic acid group.   A polymer electrolyte membrane using the polymer electrolyte according to claim 1.   A fuel cell using one or both of the polymer electrolyte according to claim 1 and the polymer electrolyte membrane according to claim 3. An ionic material having a group capable of being polymerized represented by the following two formulas. However, A _1, A ₂ is an alkylene group - (CH _{2) m} - and is, m is an integer of 1 or more, B is a protonic acid group, a chlorine atom X _1, X ₂ are independently a , An odor atom, or an iodine atom.

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