KR101042960B1 - Solid Polymer Electrolyte and Fuel Cell for Fuel Cell - Google Patents

Abstract

Provided are a solid polymer electrolyte for a fuel cell excellent in proton conductivity, heat resistance, and mechanical strength, and a fuel cell having the electrolyte. A solid polymer electrolyte for a fuel cell is employed in which a main chain made of an aromatic polyurea resin is provided with a proton conductive resin in which side chains R ¹ , R ² , R ³ , and R ⁴ are bonded.

Description

 Solid polymer electrolyte for fuel cell and fuel cell using the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 that can be suitably used in a fuel cell that generates electricity while humidifying the electrolyte membrane.

In recent years, as the global environment worsens, the development of the spread of clean energy has become a very small task worldwide. For example, in traffic relations, urban air pollution due to exhaust gas from internal combustion engines such as automobiles has become a problem due to an increase in the number of vehicles driven due to the development of the transportation network. As a countermeasure, electric vehicles and automobiles for electric and internal combustion engines, called hybrid cars, have been developed. The use of fuel cells, etc., is also promising as an energy source that is lightweight and easy to handle and does not pollute the atmosphere. In addition, the introduction of fuel cells into the home is the same as in the transportation sector.

There are various types of fuel cells, such as alkali type, phosphoric acid type, molten carbonate type, solid electrolyte type, solid polymer type, etc., depending on the type of electrolyte, which can operate at low temperature, is easy to handle, and has a high output density. High solid polymer type is attracting attention as an energy source for electric vehicles and households.

A proton conductive membrane is used for the electrolyte of this solid polymer fuel cell. Proton conductive membranes require high ion conductivity for protons involved in the electrode reaction of a fuel cell. As such proton conductive membranes, super acidic acid-containing fluorine-based polymers have been known for a long time. However, such a polymer electrolyte material is very expensive because it is a fluorine-based polymer, and there is a problem in that it is necessary to always supply water by humidifying from the fact that the medium for proton conduction is water.

Incidentally, in order to provide proton conductivity, it is described in Japanese Patent Application Laid-Open No. 2002-280019 or No. 2002-358978 to include an ionic dissociation group such as a carboxylic acid group, a sulfonic acid group, or a phosphoric acid group in an aromatic skeleton. However, these ion dissociation groups are particularly susceptible to desorption at high temperatures, deteriorate the flexibility of the proton conductive membrane, and also have problems such as low proton conductivity. JP-A-8-504293 also discloses related descriptions, but it does not disclose proton conductivity.

In addition, 'Development of Ion Exchange Membrane for Solid Polymer Fuel Cell' (GMC, published in May 2000, p.98) describes a method for introducing active hydrogen groups by reacting sultone with polybenzimidazole. Although described, only sulfonic acid groups can be introduced by the above method, and are not applicable to other active hydrogen groups.

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

In order to achieve the above object, the present invention employs the following configurations.

The solid polymer electrolyte for fuel cells of the present invention includes a proton conductive resin represented by the following general formula [1] in which a side chain R ¹ , R ² , R ³ , and R ⁴ are bonded to a main chain made of an aromatic polyurea resin. It features.

However, X <^1> and X <^2> in following General formula [1] are respectively any of S, O, a sulfonyl group, a C1-Cm linear group, a difluoromethylene group, a hexafluoropropylene group, and a heteroaromatic ring, 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 alkylsulfonic acid groups or carboxylic acid groups.

[Formula 1]

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

In the present invention, at least one of R ¹ , R ² , R ³ , R ⁴ in the general formula [1] is an alkyl sulfonic acid group or a carboxylic acid group, and the remainder is hydrogen, an alkyl group having 1 to 4 carbon atoms, an aromatic group having 6 to 9 carbon atoms. It may be a substituent of any one or more of the functional group containing a ring.

In addition, the solid polymer electrolyte for fuel cells of the present invention is the above-described solid polymer electrolyte for fuel cells, and is characterized in that the proton conductive resin is impregnated with at least one acid.

In particular, in the solid polymer electrolyte for fuel cells of the present invention, it is preferable that the acid is either or both of phosphoric acid and phosphonic acid.

According to the above structure, the acid is impregnated in the proton conductive resin, thereby further increasing the proton conductivity.

Next, the fuel cell of the present invention is provided with the solid polymer electrolyte for a fuel cell according to any one of the above.

According to this structure, since the solid polymer electrolyte which is excellent in heat resistance and proton conductivity is provided, the high performance fuel cell excellent in power generation characteristics can be provided.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail.

The solid polymer electrolyte for a fuel cell of the present invention is composed of a proton conductive resin formed by combining a main chain made of polyurea resin with a side chain having an active hydrogen group integrated at an end thereof. The side chains in the present invention branch from the urea group and / or urethane group in the main chain of the polyurea resin. Outside of this structure, high proton conductivity cannot be obtained.

More specifically, the solid polymer electrolyte for a fuel cell of the present invention comprises a proton conductive resin represented by the following general formula [2] 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 comprised. In addition, X <^1> and X <^2> in following General formula [2] are respectively S, O, a sulfonyl group, a linear methylene group of 1-3 carbon atoms, a difluoro methylene group, a hexafluoro propylene group, a heteroaromatic ring, and n Is in the range of 20-1000.

[Formula 2]

The side chains R ¹ , R ² , R ³ and R ⁴ are substituents bonded to any one or both of the urea group or urethane group included in the polyurea resin, at least one of which is an alkylsulfonic acid group or a carboxylic acid group, and the rest are hydrogen, It is a substituent of any one or more of the C1-C4 alkyl group and the functional group containing a C6-C9 aromatic ring.

The alkylsulfonic acid group or carbonic acid group constituting any one of the side chains R ¹ , R ² , R ³ , and R ⁴ contains an active hydrogen group, and the conduction of protons occurs by the active hydrogen groups, and the protons are used in the solid polymer electrolyte for fuel cells. Conductivity is imparted.

Further, all of the side chains R ¹ , R ² , R ³ , and R ⁴ may be alkylsulfonic acid groups or carboxylic acid groups, and if a part of the side chains R ¹ , R ² , R ³ , and R ⁴ is an alkylsulfonic acid group or a carboxylic acid group, all of them It may not be an alkylsulfonic acid group or a carboxylic acid group. In this case, as a substituent other than an alkyl sulfonic acid group or a carboxylic acid group, the substituent of any one or more of hydrogen, the C1-C4 alkyl group, and the functional group containing a C6-C9 aromatic ring can be used. Here, a C1-C4 alkyl group refers to a methyl group, an ethyl group, a propyl group, and a butyl group. In addition, the functional group containing a C6-C9 aromatic ring refers to a phenyl group, benzyl group, a phenylethyl group, and a phenylpropyl group. When the carbon number of the alkyl group exceeds 4 or the carbon number of the functional group containing an aromatic ring exceeds 9, the crystallinity of the aromatic polyurea resin constituting the main chain by side chains R ¹ -R ⁴ is lowered and heat resistance is lowered. not.

Subsequently, 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 either or both of a urea group and a urethane group in its molecular structure depending on the kind of the raw material monomer. In these urea and urethane groups, there are active hydrogens bound to nitrogen. Various functional groups react with this active hydrogen, and side chain R <^1> -R <^4> is couple | bonded with polyurea resin. For example, the alkyl sulfone group is formed by cleavage of sultones and the like. In addition, when a carbonic acid group has the terminal isocyanate group containing ester compound, and an ester part hydrolyzes, a carbonic acid group is located in the terminal of the side chain.

An aromatic polyurea resin is obtained by reaction of aromatic polyisocyanate with aromatic polyamine, for example.

Examples of the aromatic polyisocyanate include tolylene diisocyanate, diphenylmethane diisocyanate (hereinafter referred to as MDI), 4, 4'-diphenylether diisocyanate (ODI), xylene diisocyanate, naphthalene diisocyanate, 4. 4 '-Diphenylsulfide diisocyanate, 4, 4'-diphenyl sulfoxide diisocyanate, diphenylethane diisocyanate, diphenylpropane diisocyanate, diphenyldifluoromethane diisocyanate, diphenylhexafluoropropylene diisocyanate, etc. It can illustrate, and also the derivative of the compound described in these can also be illustrated. These aromatic polyisocyanate can also be used together as needed. The NCO% of the polyisocyanate is usually 20% or more and 48% or less, preferably 25% or more and 48% or less. Outside this range, the heat resistance and mechanical strength of the solid polymer electrolyte for fuel cells are reduced.

As an aromatic polyamine, 4, 4'- diphenyl ether diamine (ODA), (polytetraethylene 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), (trimethylenebis (4-aminobenzoate)), (3, 5'-dimethylthiotoluenediamine), 2, 3-diaminopyridine, 2, 5-diaminopyridine, 2, 6- diaminopyridine, 3, 4-diaminopyridine, etc. can be illustrated. These can also be mixed and used. Among these, 4, 4'- diphenyl ether diamine (ODA) is preferable. The amine number is usually preferably in the range of 28 or more and 200 or less, more preferably 28 or more and 150 or less. Outside this range, the mechanical strength of the solid polymer electrolyte for fuel cells is lowered.

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

The reaction with the urea groups and / or urethane groups in the polyurea resin and the side chains R ¹ to R ⁴ is carried out by known reaction in the polyurethane in the presence of a solvent.

When introducing an alkylsulfonic acid group into the substituent which couple | bonds with side chain R <^1> -R <^4> , sultone etc. are cleaved and bonded to either or both of the urea group or urethane group in polyurea resin.

An example of reaction scheme is shown in following Chemical formula [3]. Specifically, sodium hydride and the like are added to the polyurea resin (3-1) to substitute active sodium bonded to nitrogen contained in the urea group or urethane group with sodium (3-2), and then to the sodium sultone compound (3). React -3). At this time, the sultone compound cleaves into side chains and is compounded to the urea resin (3-4). In addition, the sulfonic acid group (3-5) derived from a sultone compound is formed in the terminal of a side chain by substituting with an acid. Examples of the sultone compound include (alkyl) propane sultone and butane sultone.

(3)

In addition, when a carboxylic acid group is introduced as a substituent bonded to the side chains R ¹ -R ⁴ , a terminal isocyanate group-containing ester compound is bonded to one or both of a urea group or a urethane group in the polyurea resin to hydrolyze the ester moiety. .

Specific examples of the terminal isocyanate group-containing ester compound include isocyanate butyl acetate, isocyanate ethyl acetate, ethyl benzoate, ethyl isocyanatopropionate, and the like.

The reaction of either or both of the urea group or urethane group in the polyurea resin with the terminal isocyanate group-containing ester compound is carried out by a known method in polyurethane in the presence of a solvent. An example of the reaction scheme is shown in the following formula [4]. In this reaction, dimethylformamide, dimethyl sulfoxide, dimethylacetoamide, etc. are preferable as the solvent. A urethanation catalyst can also be used as needed. A tin compound is preferable as a urethanation catalyst.

Moreover, a well-known hydrolysis method is mentioned in order to convert the ester part of the reactant (4-2) of either or both of a urea group or a urethane group in a polyurea resin, and a terminal isocyanate group containing ester compound.

[Formula 4]

In addition, the solid polymer electrolyte for fuel cells of the present embodiment may be made by impregnating one or more acids with a proton conductive resin. The acid is preferably either one or both of phosphoric acid and phosphonic acid. It is preferable to make the impregnation amount (dope amount), such as phosphoric acid, into 4 mol-32 mol per mole of repeating unit of the proton conductive resin shown by the said General 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 concerning this invention is demonstrated concretely. The fuel cell according to the present invention is provided with a polymer electrolyte membrane having a proton conductivity as described above.

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

The electrode constituting the fuel cell is composed of a conductive material, a binder, and a catalyst. Any conductive material may be used as long as it is electrically conductive, and various metals and carbon materials may be mentioned. For example, carbon black, such as acetylene black, activated carbon, graphite, etc. are mentioned, These are used individually or in mixture.

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 fluorine resin having water repellency. It is further more preferable that melting | fusing point is 400 degrees C or less among fluororesins, For example, a polytetrafluoro ethylene, a tetrafluoro ethylene- perfluoro alkyl vinyl ether copolymer, etc. are mentioned.

The catalyst of the electrode is not particularly limited as long as it is a metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen, but for example, lead, iron, manganese, cobalt, chromium, gallium, vanadium, tungsten, ruthenium, iridium, palladium, Platinum, rhodium or their alloys.

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. In addition, according to the fuel cell of the present invention, the power generation characteristics can be further improved.

[Example]

(Example 1)

1.040 g of 4,4'-diphenyletherdiamine (ODA) was dissolved in 15 ml of N-methylpyrrolidone under argon atmosphere, and 1.250 g of diphenylmethane diisocyanate (MDI) was slowly added dropwise under argon atmosphere. Then, after making it react at 120 degreeC for 3 hours, the reaction solution was precipitated again in methanol, and white aromatic polyurea resin (it calls it PU-MDOD hereafter) was collect | recovered.

Subsequently, under argon atmosphere, 0.120 g of sodium hydride (NaH) was dispersed in 10 ml of N-methylpyrrolidone at 80 ° C. In addition, 1.035 g of the previously obtained PU-MDOD was dissolved in 10 ml of N-methylpyrrolidone solution. And the N-methylpyrrolidone solution of PU-MDOD was dripped gradually to the N-methylpyrrolidone solution of sodium hydride. 0.681 g of 1, 4-butanesulfons were dripped after the solution after dripping became transparent. After dropping, the precipitated solid was collected by filtration under reduced pressure and washed with ethanol to obtain a sodium salt of a pale yellow solid proton conductive resin (hereinafter referred to as s-PU-MDOD (Na)). The resulting s-PU-MDOD (Na) was dissolved in dimethylacetoamide (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. The film was immersed in 1 mol / L aqueous hydrochloric acid solution for 12 hours or longer to replace Na ions with hydrogen ions to obtain a film made of a proton conductive resin (hereinafter referred to as s-PU-MDOD (H)). Thus, the solid polymer electrolyte membrane of Example 1 which consists of aromatic polyurea resin in which the alkyl sulfonic acid group was introduce | transduced into the side chain was produced. The film thickness of the obtained polymer film was 37 micrometers. The following reaction scheme is shown in the following general formula [5] from the synthesis | combination of the aromatic polyurea resin to the synthesis | combination of a proton conductive resin. Moreover, the structural formula of s-PU-MDOD (H) of Example 1 is shown to following General formula [6]. In the structure [6], X ^{1 is represented} by O, X ^{2 is represented} by CH ₂ , R ¹ -R ^{3 is represented} by H, and R ^{4 is represented} by OC ₃ H ₆ SO _3. H was done.

[Chemical Formula 5]

[Formula 6]

(Example 2)

Proton conductive resin (hereinafter, referred to as s-PU-ODOD (H)) in the same manner as in Example 1 except that diphenylmethane diisocyanate (MDI) was changed to 4, 4'-diphenyl ether diisocyanate (ODI). Obtained a film made of. Thus, the solid polymer electrolyte membrane of Example 2 which consists of the aromatic polyurea resin by which the alkyl sulfonic acid group was introduce | transduced into the side chain was produced. The film thickness of the obtained polymer film was 41 micrometers.

The following reaction scheme is shown in the following general formula [7] from the synthesis of the aromatic polyurea resin to the synthesis of the proton conductive resin. Moreover, the structural formula of s-PU-ODOD (H) of this Example 2 is shown by following General formula [8]. In the structure [2], X ¹ and X ² are represented by O, R ^{1 to} R ³ are represented by H, and R ^{4 is represented} by OC ₃ H ₆ SO ₃ H.

[Formula 7]

[Formula 8]

(Example 3)

The solid polymer electrolyte membrane of Example 3 was prepared by impregnating s-PU-MDOD (Na) obtained in Example 1 with 85% phosphoric acid for 12 hours to impregnate the proton conductive resin with phosphoric acid. The film thickness of the obtained polymer film was 35 micrometers.

(Comparative Example 1)

25 g of commercially available polyether ether ketone and 125 ml of concentrated sulfur were added to the flask, and the mixture was stirred for 48 hours at room temperature under 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 to obtain a yellow transparent film. Thus, the solid polymer electrolyte membrane of Comparative Example 1 was obtained.

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

Proton Conductivity: A platinum wire (0.2 mm in diameter) was pressed on the surface of an electrolyte membrane in the form of a short booklet to form an electrode, and resistance when alternating current (1 kHz) was applied was measured by an impedance analyzer. Proton conductivity was calculated by 1 / (R x T x D) from the electrode spacing, the slope of the resistance (R), the thickness (t) of the electrolyte membrane, and the width (D) of the electrolyte membrane. The measurement was performed at 80 degreeC and 95% of humidity.

Ion-exchange capacity: A short booklet-type electrolyte membrane was dried at 80 ° C. under reduced pressure for 12 hours, and weighed, and the film was immersed in 40 mL of 1 mol / L aqueous sodium chloride solution for at least 12 hours. 20 mL of the sodium chloride aqueous solution which deposited the film | membrane was extract | collected, and the acid in the system was measured with 0.05 mol / L sodium hydroxide aqueous solution. The ion exchange capacity (meq / g) was determined by M / W from the number of moles of acid (M) in the system and the weight (W) of the membrane during drying.

TABLE 1

Proton Conductivity (S / cm) Ion exchange capacity (meq / g) Example 1 7.8 × 10 ^-2 1.71 Example 2 7.2 × 10 ^-2 1.69 Example 3 7.6 × 10 ^-3 - Comparative Example 1 4.2 × 10 ^-3 2.91

In addition, 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.

TABLE 2

Proton Conductivity (S / cm) Example 3 1.5 × 10 ^-4 Comparative Example 1 7.8 × 10 ^-8

As shown in Table 1, it can be seen that in Examples 1 and 2, although the ion exchange capacity is smaller than that of Comparative Example 1, the proton conductivity is higher. The ion exchange capacity is proportional to the amount of side chains bound to the main chain of the proton conductive resin. In Examples 1 and 2, the amount of the side chains is high, but the proton conductivity is high. In general, the fewer the side chains of the resin, 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.

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. The electrolyte membrane impregnated with phosphoric acid in the proton conductive resin is considered to exhibit excellent power generation characteristics in a fuel cell operated at a temperature of 100 ° C. or higher.

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

Claims (5)

A solid polymer electrolyte for a fuel cell, comprising a proton conductive resin represented by the following general formula [1] to which a side chain R ¹ , R ² , R ³ , and R ⁴ are bonded to a main chain made of an aromatic polyurea resin. However, X <^1> and X <^2> in following General formula [1] are respectively any of S, O, a sulfonyl group, a C1-Cm linear group, a difluoromethylene group, a hexafluoropropylene group, and a heteroaromatic ring, 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. [Formula 1]

The method of claim 1, In general formula [1] of Claim 1, at least one of R <^1> , R <^2> , R <^3> and R <^4> is an alkyl sulfonic acid group or a carboxylic acid group, and the remainder is hydrogen, a C1-C4 alkyl group, C6-C9 aromatic Solid polymer electrolyte for a fuel cell, characterized in that any one or more substituents of the functional group containing a ring. The method of claim 1, Solid polymer electrolyte for a fuel cell, characterized in that the proton conductive resin is impregnated with at least one acid. The method of claim 3, wherein And said acid is at least one selected from the group consisting of phosphoric acid and phosphonic acid. A fuel cell comprising the fuel cell solid polymer electrolyte according to any one of claims 1 to 4.