JP4684620B2 - Solid polymer electrolyte for fuel cell and fuel cell - Google Patents

Description

  The present invention relates to a solid polymer electrolyte for a fuel cell and a fuel cell using the same, and more particularly to a solid polymer electrolyte suitably used for a fuel cell that generates power while humidifying an electrolyte membrane.

  In recent years, with the deterioration of the global environment, the widespread development of clean energy has become a serious issue worldwide. For example, in traffic relations, urban air pollution due to exhaust gas from an internal combustion engine such as an automobile has become a problem due to an increase in the number of vehicles traveling with the development of a traffic network. As countermeasures, electric vehicles and vehicles with electric / internal combustion engines called hybrid cars have been developed, but the use of fuel cells as an energy source that is lightweight and easy to handle and does not pollute the atmosphere is one of them. As promising. The introduction of fuel cells into the home is the same as in the transportation field.

  There are various types of fuel cells, such as alkaline type, phosphoric acid type, molten carbonate type, solid electrolyte type, solid polymer type, etc., depending on the type of electrolyte, but it can operate at low temperatures and is easy to handle. In addition, a solid polymer type having a high output density is attracting attention as an energy source for electric vehicles, homes and the like.

  A proton conductive membrane is used for the electrolyte of this polymer electrolyte fuel cell. The proton conducting membrane is required to have high ionic conductivity for protons involved in the electrode reaction of the fuel cell. As such a proton conducting membrane, a super strong acid group-containing fluorine-based polymer has been conventionally known. However, since these polymer electrolyte materials are fluoropolymers, they are very expensive, and since the proton conducting medium is water, it is necessary to always humidify and replenish water. .

  By the way, Patent Document 1 or 2 discloses that an aromatic skeleton contains an ionic dissociation group such as a carboxylic acid group, a sulfonic acid group, and a phosphoric acid group in order to impart proton conductivity. However, these ion dissociation groups are liable to be removed particularly at high temperatures, there is a risk that the flexibility of the proton conductive membrane may be impaired, and there are further problems such as low proton conductivity. Although there is a description related to Patent Document 3, proton conductivity is not disclosed.

Non-Patent Document 1 describes a method of introducing an active hydrogen group by reacting sultone with polybenzimidazole. However, only a sulfonic acid group can be introduced by this method, and other active hydrogen groups can be introduced. Not applicable to the group.
JP 2002-280019 A JP 2002-358978 A JP 2002-358978 A “Development of ion exchange membrane for polymer electrolyte fuel cell”, issued by CMC Co., Ltd., May 2000, p. 98

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a solid polymer electrolyte for a fuel cell excellent in proton conductivity, heat resistance, and mechanical strength, and a fuel cell provided with the electrolyte. And

In order to achieve the above object, the present invention employs the following configuration.
The solid polymer electrolyte for a fuel cell according to the present invention has a proton conduction represented by the following formula [1] in which side chains R ¹ , R ² , R ³ and R ⁴ are bonded to a main chain made of an aromatic polyurea resin. It is characterized by comprising a functional resin.
However, in the following formula [1], X ¹ and X ² are S, O, a sulfonyl group, a linear methylene group having 1-3 carbon atoms, a difluoromethylene group, a hexafluoropropylene group, a heteroaromatic ring, respectively. Any one of them, at least one of R ¹ , R ² , R ³ , and R ⁴ is an alkylsulfonic acid group or a carboxylic acid group, and n is in the range of 20-1000.
In the present invention, all of R ¹ , R ² , R ³ , and R ⁴ may be an alkyl sulfonic acid group or a carboxylic acid group.

According to the above configuration, since the aromatic polyurea resin containing an aromatic ring is provided as the main chain of the proton conductive resin, the heat resistance and strength of the solid polymer electrolyte can be improved. Moreover, since at least one of the side chains R ¹ , R ² , R ³ , R ⁴ is an alkylsulfonic acid group or a carboxylic acid group, the proton conductivity of the electrolyte can be improved.

In the present invention, in the above formula [1], at least one of R ¹ , R ² , R ³ , and R ⁴ is an alkylsulfonic acid group or a carboxylic acid group, and the remainder is hydrogen and has 1-4 carbon atoms. Or any one or more substituents of a functional group containing an aromatic ring having 6 to 9 carbon atoms.

The solid polymer electrolyte for fuel cells of the present invention is the solid polymer electrolyte for fuel cells described above, wherein the proton conductive resin is impregnated with one or more acids.
In particular, in the solid polymer electrolyte for a fuel cell of the present invention, the acid is preferably either one or both of phosphoric acid and phosphonic acid.

  According to the above configuration, proton conductivity can be further improved by impregnating the proton conductive resin with the acid.

Next, a fuel cell according to the present invention is characterized by including the solid polymer electrolyte for a fuel cell according to any one of the above.
According to this configuration, since the solid polymer electrolyte excellent in heat resistance and proton conductivity is provided, a high-performance fuel cell excellent in power generation characteristics can be provided.

  According to the present invention, it is an object to provide a solid polymer electrolyte for a fuel cell excellent in proton conductivity, heat resistance, and mechanical strength, and a fuel cell provided with the electrolyte.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The solid polymer electrolyte for a fuel cell of the present invention is composed of a proton conductive resin formed by bonding a main chain made of a polyurea resin with a side chain having an active hydrogen group bonded to the terminal. The side chain in the present invention is branched from a urea group and / or a urethane group in the main chain of the polyurea resin. Other than this structure, high proton conductivity cannot be obtained.

More specifically, the solid polymer electrolyte for a fuel cell according to the present invention includes side chains R ¹ , R ² , R ³ , and R ⁴ bonded to a main chain made of an aromatic polyurea resin [2] A proton conductive resin represented by the formula is provided. In the following formula [2], X ¹ and X ² are S, O, a sulfonyl group, a linear methylene group having 1-3 carbon atoms, a difluoromethylene group, a hexafluoropropylene group, a heteroaromatic ring, respectively. Any one of them, and n is in the range of 20-1000.

The side chains R ¹ , R ² , R ³ and R ⁴ are substituents bonded to one or both of a urea group and a urethane group contained in the polyurea resin, at least one of which is an alkyl sulfonic acid group or a carboxyl group It is an acid group, and the remainder is one or more substituents selected from hydrogen, an alkyl group having 1 to 4 carbon atoms, and a functional group containing an aromatic ring having 6 to 9 carbon atoms.
The alkylsulfonic acid group or carboxylic acid group constituting at least one of the side chains R ¹ , R ² , R ³ , R ⁴ contains an active hydrogen group, and proton conduction is caused by this active hydrogen group. And proton conductivity is imparted to the solid polymer electrolyte for fuel cells.

Further, all of the side chains R ¹ , R ² , R ³ and R ⁴ may be alkyl sulfonic acid groups or carboxylic acid groups, and some of the side chains R ¹ , R ² , R ³ and R ⁴ are alkyl. As long as it is a sulfonic acid group or a carboxylic acid group, not all may be an alkylsulfonic acid group or a carboxylic acid group. In this case, as substituents other than alkyl sulfonic acid group or a carboxylic acid group, hydrogen, an alkyl group having 1-4 carbon atoms, any one or more substituents of the functional groups comprising an aromatic ring of 6-9 carbon atoms Groups can be used. Here, the alkyl group having 1 to 4 carbon atoms refers to a methyl group, an ethyl group, a propyl group, and a butyl group. The functional group containing an aromatic ring having 6 to 9 carbon atoms refers to a phenyl group, a benzyl group, a phenylethyl group, and a phenylpropyl group. When the carbon number of the functional group containing an alkyl group or an aromatic ring exceeds 4 or 9, the crystallinity of the aromatic polyurea resin constituting the main chain by the side chains R ^{1 to} R ⁴ is lowered, and the heat resistance is lowered. Therefore, it is not preferable.

Next, the aromatic polyurea resin constituting the main chain is characterized by excellent heat resistance and chemical resistance, and can improve the heat resistance and mechanical strength of the solid polymer electrolyte for fuel cells.
The aromatic polyurea resin has one or both of a urea group and a urethane group in its molecular structure depending on the type of raw material monomer. These urea groups and urethane groups have active hydrogen bonded to nitrogen. By reacting this active hydrogen with various functional groups, the side chain R ¹ -R ⁴ is bonded to the polyurea resin. For example, the alkylsulfone group is formed by cleavage of sultones or the like. In addition, the carboxylic acid group is formed by bonding of the terminal isocyanate group-containing ester compound and hydrolysis of the ester moiety. When the sultone is cleaved and bonded to the main chain, a sulfonic acid group is located at the end of the side chain. When the terminal isocyanate group-containing ester compound is bonded and the ester portion is hydrolyzed, a carboxylic acid group is located at the end of the side chain.

The aromatic polyurea resin is obtained, for example, by a reaction between an aromatic polyisocyanate and an aromatic polyamine.
Examples of aromatic polyisocyanates include tolylene diisocyanate, diphenylmethane diisocyanate (hereinafter abbreviated as MDI), 4,4′-diphenyl ether diisocyanate (ODI), xylylene diisocyanate, naphthalene diisocyanate, 4,4′-diphenyl sulfide diisocyanate, Examples include 4,4′-diphenyl sulfoxide diisocyanate, diphenylethane diisocyanate, diphenylpropane diisocyanate, diphenyldifluoromethane diisocyanate, diphenylhexafluoropropylene diisocyanate, and derivatives of the compounds described therein.
These aromatic polyisocyanates may be used in combination if necessary. The NCO% of the polyisocyanate is usually 20% or more and 48% or less, preferably 25% or more and 48% or less.

  Aromatic polyamines include 4,4′-diphenyl ether diamine (ODA), (polytetramethylene oxide-di-P-aminobenzoate), (4,4′-diamino-3,3′-diethylamino-5,5 ′). -Diaminodiphenylmethane), (2,2 ′, 3,3′-tetrachloro-4,4′-diaminodiphenylmethane), (3,3′-dichloro-4,4′-diaminodiphenylmethane), (trimethylene-bis ( 4-aminobenzoate)), (3,5′-dimethylthiotoluenediamine), 2,3-diaminopyridine, 2,5-diaminopyridine, 2,6-diaminopyridine, 3,4-diaminopyridine, and the like. It can be illustrated. These may be used as a mixture. Of these, 4,4'-diphenyl ether diamine (ODA) is particularly preferable. The amine value is usually preferably in the range of 28 to 200, more preferably 28 to 150. Outside this range, the mechanical strength of the solid polymer electrolyte for fuel cells decreases.

  The reaction between the aromatic polyisocyanate and the aromatic polyamine is usually an NCO index of 90 or more and 110 or less, preferably 95 or more and 105 or less. Outside this range, a film having good heat resistance and strength cannot be obtained.

The reaction between the urea group and / or the urethane group in the polyurea resin and the side chain R ¹ -R ⁴ is performed by a known reaction in polyurethane in the presence of a solvent.
When an alkyl sulfonic acid group is introduced as a substituent to be bonded to the side chain R ¹ -R ⁴ , a sultone or the like is cleaved and bonded to one or both of the urea group and the urethane group in the polyurea resin.

  An example of the reaction formula is shown in the following formula [3]. Specifically, sodium hydride or the like is added to the polyurea resin (3-1), and the active hydrogen bonded to nitrogen contained in the urea group or urethane group is replaced with sodium (3-2). The sodium is reacted with a sultone compound (3-3). At this time, the sultone compound is cleaved to form a side chain and compound (3-4) into a urea resin. Further, by substitution with an acid, a sulfonic acid group (3-5) derived from a sultone compound is formed at the end of the side chain. Examples of the sultone compounds include (alkyl) propane sultone and butane sultone.

When a carboxylic acid group is introduced as a substituent to be bonded to the side chain R ¹ -R ⁴ , a terminal isocyanate group-containing ester compound is bonded to one or both of the urea group and the urethane group in the polyurea resin. The ester moiety is hydrolyzed.
Specific examples of the terminal isocyanate group-containing ester compound include butyl isocyanatoacetate, ethyl isocyanatoacetate, ethyl isocyanatobenzoate, and ethyl isocyanatopropionate.
The reaction between one or both of the urea group and the urethane group in the polyurea resin and the terminal isocyanate group-containing ester compound is performed by a known method in polyurethane in the presence of a solvent. An example of the reaction formula is shown in the following formula [4]. In this reaction, the solvent is preferably dimethylformamide, dimethyl sulfoxide, dimethylacetamide or the like. If necessary, urethane or a catalyst may be used. A tin compound is preferred as the urethanization catalyst.
In addition, in order to convert the ester part of the reaction product (4-2) of the urea group or the urethane group in the polyurea resin and the terminal isocyanate group-containing ester compound into a carboxylic acid, a known hydrolysis method is used. Is mentioned.

  In addition, the solid polymer electrolyte for a fuel cell according to this embodiment may be obtained by impregnating a proton conductive resin with one or more acids. The acid is preferably either one or both of phosphoric acid and phosphonic acid. The amount of impregnation (doping amount) of phosphoric acid or the like is preferably in the range of 4 mol to 32 mol per mol of the repeating unit of the proton conductive resin represented by the formula [2]. By impregnating the proton conductive resin with phosphoric acid or the like, the proton conductivity of the solid polymer electrolyte can be further increased.

  Next, the fuel cell according to the present invention will be specifically described. The fuel cell according to the present invention includes the above-described solid polymer electrolyte for a fuel cell as a polymer membrane having proton conductivity.

  The fuel cell is composed of a polymer film having proton conductivity and a positive electrode and a negative electrode (a pair of electrodes) arranged in contact with both sides. Fuel hydrogen is electrochemically oxidized at the negative electrode to produce protons and electrons. The protons are transported in the polymer membrane and reach the positive electrode to which oxygen is supplied. On the other hand, electrons generated at the negative electrode pass through an external load connected to the fuel cell and flow to the positive electrode, where protons, oxygen, and electrons react to generate water.

  The electrode constituting the fuel cell is composed of a conductive material, a binder and a catalyst. As the conductive material, any conductive material may be used, and various metals and carbon materials may be used. Examples thereof include carbon black such as acetylene black, activated carbon and graphite, and these are used alone or in combination.

  Moreover, although it is preferable to use the proton conductive resin of this invention as a binder, other resin can also be used. In that case, the other resin is preferably a fluororesin having hydrophobicity. Among the fluororesins, those having a melting point of 400 ° C. or lower are more preferable, and examples thereof include polytetrafluoroethylene and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers.

  The electrode catalyst is not particularly limited as long as it is a metal that promotes hydrogen oxidation reaction and oxygen reduction reaction. For example, lead, iron, manganese, cobalt, chromium, gallium, vanadium, tungsten, ruthenium. , Iridium, palladium, platinum, rhodium or an alloy thereof.

  As described above, according to the solid polymer electrolyte for fuel cells of the present invention, proton conductivity, heat resistance, and mechanical strength can be improved. Moreover, according to the fuel cell of the present invention, the power generation characteristics can be further improved.

Example 1
Under an argon atmosphere, 1.040 g of 4,4′-diphenyl ether diamine (ODA) was dissolved in 15 mL of N-methylpyrrolidone, and further 1.250 g of diphenylmethane diisocyanate (MDI) was slowly added dropwise under an argon atmosphere. Then, after making it react at 120 degreeC for 3 hours, the reaction solution was reprecipitated in methanol and white aromatic polyurea resin (henceforth PU-MDOD) was collect | recovered.
Next, 0.120 g of sodium hydride was dispersed in 10 mL of N-methylpyrrolidone at 80 ° C. in an argon atmosphere. Moreover, 1.035 g of PU-MDOD obtained previously was dissolved in 10 mL of N-methylpyrrolidone solution. And the N-methylpyrrolidone solution of PU-MDOD was gradually dripped at the N-methylpyrrolidone solution of sodium hydride. After the dropped solution became transparent, 1,81-butanesultone (0.681 g) was added dropwise. After dropping, the precipitated solid is collected by vacuum filtration and washed with ethanol to obtain a pale yellow solid proton conductive resin sodium salt (hereinafter referred to as s-PU-MDOD (Na)). It was. The obtained s-PU-MDOD (Na) was dissolved in dimethylacetamide (hereinafter referred to as DMAc), and then the solution was cast on a glass substrate and dried at 80 ° C. to obtain a pale yellow transparent film. It was. By immersing this film in a 1 mol / L hydrochloric acid aqueous solution for 12 hours or more, Na ions were replaced with hydrogen ions to obtain a film made of a proton conductive resin (hereinafter referred to as s-PU-MDOD (H)). . In this way, a solid polymer electrolyte membrane of Example 1 made of an aromatic polyurea resin having an alkylsulfonic acid group introduced into the side chain was produced. The obtained polymer film had a thickness of 37 μm. The reaction scheme from the synthesis of the aromatic polyurea resin to the synthesis of the proton conductive resin in the present Example is shown in the following formula [5]. Moreover, structural formula of s-PU-MDOD (H) of Example 1 is shown in the following formula [6]. The structure represented by the following formula [6] is the same as the structure represented by the formula [2], in which X ¹ is O, X ² is CH ₂ , R ¹ -R ³ is H, and R ⁴ is OC ₃ H ₆ SO _3. H.

(Example 2)
A proton conducting resin (hereinafter referred to as s-PU-ODOD (H)) is used in the same manner as in Example 1 except that diphenylmethane diisocyanate (MDI) is changed to 4,4′-diphenyl ether diisocyanate (ODI). A film was obtained. In this way, a solid polymer electrolyte membrane of Example 2 made of an aromatic polyurea resin having an alkylsulfonic acid group introduced into the side chain was produced. The film thickness of the obtained polymer film was 41 μm. The reaction scheme from the synthesis of the aromatic polyurea resin to the synthesis of the proton conductive resin in the present Example is shown in the following formula [7]. Moreover, structural formula of s-PU-ODOD (H) of the present Example 2 is shown in the following formula [8]. The structure represented by the following formula [8] is the same as the structure [2], in which X ¹ and X ² are O, R ¹ -R ³ is H, and R ⁴ is OC ₃ H ₆ SO ₃ H. Is.

(Example 3)
The solid polymer electrolyte membrane of Example 3 in which the proton conductive resin is impregnated with phosphoric acid by immersing the s-PU-MDOD (Na) obtained in Example 1 in 85% phosphoric acid for 12 hours Manufactured. The film thickness of the obtained polymer film was 35 μm.

(Comparative Example 1)
Into the flask, 25 g of commercially available polyether ether ketone and 125 ml of concentrated sulfuric acid were added, and the mixture was stirred at room temperature for 48 hours under a nitrogen stream to sulfonate the polyether ether ketone. The reaction solution after stirring was slowly added dropwise to 3 liters of deionized water to precipitate sulfonated polyether ether ketone, which was collected by filtration. The obtained precipitate was formed into a film in the same manner as in Example 1, and a yellow transparent film was obtained. Thus, the solid polymer electrolyte membrane of Comparative Example 1 was obtained.

  With respect to the solid polymer electrolyte membranes of Examples 1-3 and Comparative Example 1, proton conductivity and ion exchange capacity were measured. The results are shown in Table 1. The proton conductivity and ion exchange capacity were measured according to the following procedure.

  Proton conductivity: A platinum wire (diameter 0.2 mm) was pressed against the surface of a strip-shaped electrolyte membrane at an interval of 5 mm to form an electrode, and the resistance when alternating current (1 kHz) was applied was measured with an impedance analyzer. The proton conductivity was determined by 1 / (R × T × D) from the electrode interval and the slope of resistance (R), the thickness (t) of the electrolyte membrane, and the width (D) of the electrolyte membrane. The measurement was performed at 80 ° C. and a humidity of 95%.

  Ion exchange capacity: A strip-shaped electrolyte membrane is dried at 80 ° C. under reduced pressure for 12 hours and weighed, and this film is immersed in 40 mL of a 1 mol / L sodium chloride aqueous solution for 12 hours or more. 20 mL of a sodium chloride aqueous solution in which the membrane was immersed was collected, and the acid in the system was titrated with a 0.05 mol / L aqueous sodium hydroxide solution. The ion exchange capacity (meq / g) was determined by M / W from the number of moles of acid in the system (M) and the weight of the membrane during drying (W).

  Furthermore, proton conductivity was measured at 100 ° C. for the solid polymer electrolyte membranes of Example 3 and Comparative Example 1. The results are shown in Table 2.

As shown in Table 1, in Examples 1 and 2, although proton exchange capacity is smaller than that in Comparative Example 1, it can be seen that proton conductivity is high. The ion exchange capacity is proportional to the amount of the side chain bonded to the main chain of the proton conductive resin. In Examples 1 and 2, although the amount of the side chain is small, high proton conductivity is exhibited. Yes. In general, the smaller the resin side chain, the better the crystallinity of the resin itself and the higher the heat resistance. Therefore, in Examples 1 and 2, it can be assumed that the heat resistance is also excellent.
Furthermore, as shown in Table 2, it can be seen that the electrolyte membrane of Example 3 impregnated with phosphoric acid has a significantly higher proton conductivity than Comparative Example 1 at a relatively high temperature of 100 ° C. Thus, an electrolyte membrane obtained by impregnating proton conductive resin with phosphoric acid is considered to exhibit excellent power generation characteristics in a fuel cell operated at a temperature of 100 ° C. or higher.

Claims (5)

It is characterized by comprising a proton conductive resin represented by the following formula [1] in which side chains R ¹ , R ² , R ³ , and R ⁴ are bonded to a main chain made of an aromatic polyurea resin. Solid polymer electrolyte for fuel cells.
However, in the following formula [1], X ¹ and X ² are S, O, a sulfonyl group, a linear methylene group having 1-3 carbon atoms, a difluoromethylene group, a hexafluoropropylene group, a heteroaromatic ring, respectively. Any one of them, at least one of R ¹ , R ² , R ³ , and R ⁴ is an alkylsulfonic acid group or a carboxylic acid group, and n is in the range of 20-1000.

In the formula [1] of claim ¹ , at least one of R ¹ , R ² , R ³ , and R ⁴ is an alkylsulfonic acid group or a carboxylic acid group, and the remainder is hydrogen and an alkyl group having 1 to 4 carbon atoms. 2. The solid polymer electrolyte for a fuel cell according to claim 1, which is one or more substituents selected from functional groups containing an aromatic ring having 6 to 9 carbon atoms.   The solid polymer electrolyte for a fuel cell according to claim 1 or 2, wherein the proton conductive resin is impregnated with one or more acids.   4. The solid polymer electrolyte for a fuel cell according to claim 3, wherein the acid is either one or both of phosphoric acid and phosphonic acid. A fuel cell comprising the solid polymer electrolyte for a fuel cell according to any one of claims 1 to 4, and a positive electrode and a negative electrode arranged in contact with both sides thereof.