JP2006040709A - Electrolyte membrane for fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte membrane for a fuel cell excellent in proton conductivity, heat resistance, and mechanical strength. <P>SOLUTION: The electrolyte membrane for a fuel cell, composed of proton conductive resin formed by bonding side chains, on a terminal part of which an active hydrogen group is bonded, to a principal chain composed of poly-urea resin, is adopted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolyte membrane for a fuel cell and a fuel cell using the same.

  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 Japanese National Patent Publication No. 8-504293 “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 an electrolyte membrane for a fuel cell excellent in proton conductivity, heat resistance, and mechanical strength, and a fuel cell provided with the electrolyte membrane. To do.

In order to achieve the above object, the present invention employs the following configuration.
The electrolyte membrane for a fuel cell according to the present invention is characterized in that it is composed of a proton conductive resin in which a side chain in which an active hydrogen group is bonded to a terminal is bonded to a main chain made of a polyurea resin.

  According to said structure, the electrolyte membrane for fuel cells excellent in proton conductivity, heat resistance, and mechanical strength can be obtained.

The electrolyte membrane for a fuel cell according to the present invention is the electrolyte membrane for a fuel cell described above, wherein an acrylic isocyanate compound is combined with one or both of a urea group and a urethane group contained in the polyurea resin, An active hydrogen group-containing acrylate compound is combined with the combined acrylic isocyanate compound.
The acrylic isocyanate compound also includes a methacryl isocyanate compound in which a methyl group is bonded to the α-position. The active hydrogen group-containing acrylic isocyanate compound also includes an active hydrogen group-containing methacrylic isocyanate compound in which a methyl group is bonded to the α-position.

  According to said structure, the electrolyte membrane for fuel cells excellent in proton conductivity can be obtained.

  The fuel cell electrolyte membrane of the present invention is the fuel cell electrolyte membrane described above, wherein the active hydrogen group is any one of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, and a hydroxyl group. It is characterized by.

  According to said structure, the electrolyte membrane for fuel cells excellent in proton conductivity and a softness | flexibility can be obtained.

  The electrolyte membrane for a fuel cell according to the present invention is the electrolyte membrane for a fuel cell described above, wherein a sultone compound is combined with one or both of a urea group and a urethane group contained in the polyurea resin. It is characterized by that.

  According to said structure, the electrolyte membrane for fuel cells excellent in proton conductivity can be obtained.

  The fuel cell electrolyte membrane of the present invention is the fuel cell electrolyte membrane described above, wherein the hydroxyl group is bonded to a polyoxyalkylene chain.

  According to said structure, the electrolyte membrane for fuel cells excellent in proton conductivity can be obtained.

The fuel cell electrolyte membrane of the present invention is the fuel cell electrolyte membrane described above, having a thermal decomposition temperature of 180 ° C. or higher and a storage elastic modulus at 150 ° C. of 1 × 10 ⁷ Pa or higher and 1 ×. It is the range of 10 ⁹ Pa or less.

  According to the said structure, the electrolyte membrane for fuel cells which has heat resistance can be obtained.

  Next, a fuel cell of the present invention is characterized by including any one of the electrolyte membranes for fuel cells described above.

  According to said structure, the high performance fuel cell excellent in the electric power generation characteristic can be provided.

  According to the electrolyte membrane for a fuel cell of the present invention, a proton conducting membrane excellent in proton conductivity, heat resistance, and mechanical strength can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
The electrolyte membrane 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, in the electrolyte membrane for fuel cells of the present invention, the acrylic isocyanate compound is obtained by combining an acrylic isocyanate compound with one or both of the urea group and the urethane group contained in the polyurea resin, and further combining them. Are combined with an active hydrogen group-containing acrylate compound. The combined active hydrogen group-containing acrylate compound has an active hydrogen group of any one of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, and a hydroxyl group. Proton conduction is achieved by the presence of this active hydrogen group. Occurs, and proton conductivity is imparted to the fuel cell electrolyte membrane. The active hydrogen group may be a mixture of any of the above active hydrogen groups. Of these, sulfonic acid groups and phosphoric acid groups are particularly preferred.

  In addition, the polyurea resin constituting the main chain is characterized by excellent heat resistance and chemical resistance, and can increase the heat resistance and mechanical strength of the electrolyte membrane for fuel cells.

Depending on the type of raw material monomer, the polyurea resin has either or both of a urea group and a urethane group in its molecular structure. These urea groups and urethane groups have active hydrogen bonded to nitrogen. By reacting the isocyanate group of the acrylic isocyanate compound with this active hydrogen, a side chain composed of the acrylic isocyanate compound is formed in the polyurea resin. This combined acrylic isocyanate compound has a carbon double bond in the molecule. An active hydrogen group-containing acrylate compound having a carbon double bond in the molecule is polymerized with respect to the carbon double bond. The active hydrogen group-containing acrylate compound contains the active hydrogen group described above, and is located almost at the end of the side chain where the active hydrogen group is formed.
The acrylic isocyanate compound also includes a methacryl isocyanate compound in which a methyl group is bonded to the α-position. The active hydrogen group-containing acrylic isocyanate compound also includes an active hydrogen group-containing methacrylic isocyanate compound in which a methyl group is bonded to the α-position.

  As described above, a proton conductive resin is formed in which a side chain formed by binding an active hydrogen group to a terminal is bonded to a main chain formed of a polyurea resin. By forming this proton conductive resin into a membrane, the fuel cell electrolyte membrane according to the present invention is obtained.

A polyurea resin is obtained by reaction of polyisocyanate and polyamine, for example.
The following are mentioned as an example of polyisocyanate. Tolylene diisocyanate, diphenylmethane diisocyanate (hereinafter abbreviated as MDI), xylylene diisocyanate, naphthalene diisocyanate, etc. as an aromatic ring compound, isophorone diisocyanate, cyclohexane diisocyanate, etc. as an alicyclic compound, hexamethylene diisocyanate as an aliphatic compound, Lysine diisocyanate and the like. Furthermore, derivatives of the compounds described in these can also be used.
These 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.

  Polyamines include aliphatic diamines (ethylene diamine, propylene diamine, etc.), alicyclic diamines (isophorone diamine, etc.), aromatic diamines ((polytetramethylene oxide P-aminobenzoate), (4,4'-diamino-3). , 3′-diethylamino-5,5′-diaminodiphenylmethane), (2,2 ′, 3,3′-tetrachloro-4,4′-didiaminodiphenylmethane), (3,3′-dichloro-4,4′-diaminodiphenylmethane) ), (Trimethylene-bis (41-aminobenzoate)), (3,5′-dimethylthiotoluenediamine) and the like. These may be used as a mixture. Of the polyamines, aromatic diamines are particularly preferred, and polyalkylene oxide P monoaminobenzoate is particularly preferred. 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 fuel cell electrolyte membrane decreases.

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

  Specific examples of the acrylic isocyanate compound include 2-methacryloyloxyethyl isocyanate, MOI (2-isocyanatoethyl methacrylate) and the like.

  Examples of the active hydrogen group-containing acrylate compound include 2-acrylamido-2-monomethylpropane sulfonic acid (hereinafter abbreviated as TBAS), styrene sulfonic acid and the like as examples having a sulfonic acid group. Examples having a carboxylic acid group include acrylate β-methacryloyloxyethyl hydrogen succinate β-methacryloyloxyethyl hydrogen phthalate. Examples of having a phosphate group include mono (21-acryloyloxyethyl) acid phosphate, mono (21-methacryloxyethyl) acid phosphate, and the like. Monofunctional polyethylene glycol mono (meth) acrylate having a hydroxyl group, polypropylene glycol mono (meth) acrylate, etc., bifunctional polyoxyalkylene diglycol mono (meth) acrylate, etc., trifunctional polyoxyalkylene triglycol mono ( And (meth) acrylate. Of these, those having two or more functional groups are preferred.

  The reaction between the urea group (1) and / or the urethane group in the polyurea resin and the acrylic isocyanate compound (2) is carried out by a known reaction in polyurethane in the presence of a solvent. An example of the reaction is shown below. In this reaction, the solvent is preferably dimethylformamide, dimethylsulfoxide, dimethylacetamide or the like. If necessary, a urethanization catalyst may be used. A tin compound is preferred as the urethanization catalyst.

  In order to react the active hydrogen group-containing acrylate compound (4) with the reaction product (3) of the urea group and / or urethane group and the acrylic isocyanate compound in the polyurea resin, known thermal polymerization and / or ultraviolet polymerization is performed. Is mentioned. Of these, ultraviolet polymerization is particularly preferred. Examples of reaction formulas are shown below. In this way, a proton conductive resin (5) is obtained.

  In addition to the above-described method, the sulfonic acid group among the active hydrogen groups may be introduced by reacting a sultone compound with one or both of the urea group and the urethane group in the polyurea resin. Can do. An example of the reaction formula is shown below. Specifically, sodium hydride or the like is added to the polyurea resin (6), the active hydrogen bonded to nitrogen contained in the urea group or urethane group is replaced with sodium (7), and then sultone is added to the sodium. Compound (8) is reacted. At this time, the sultone compound is cleaved to form a side chain and combine (9) with the urea resin. Furthermore, by substituting with an acid, a sulfonic acid group (10) 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.

  Further, among the active hydrogen groups, a hydroxyl group may be bonded to a polyoxyalkylene chain. Examples of the polyoxyalkylene chain include a polyethylene oxide chain, a polypropylene oxide chain, and a polytetramethylene oxide chain. Among these, a polyethylene oxide chain and a polytetramethylene oxide chain are preferable from the viewpoint of proton conductivity and mechanical properties. An example of a reaction for introducing a polyoxyalkylene chain is shown below. In this example, an acrylic isocyanate compound (12) is combined with a polyurea resin (11), and a branched acrylate (13) having an ethylene oxide chain is polymerized on the terminal carbon double bond of the combined acrylic isocyanate compound. Let

  Another example of the reaction for introducing a polyoxyalkylene chain is shown below. In this example, an acrylic isocyanate compound (12) is combined with a polyurea resin (11), and a polyfunctional acrylate (14) and an ethylene oxide chain are added to the terminal carbon double bond of the combined acrylic isocyanate compound. The branched acrylate (13) is polymerized.

The thermal decomposition temperature of the fuel cell electrolyte membrane is 180 ° C. or higher, and the storage elastic modulus at 150 ° C. is in the range of 1 × 10 ⁷ Pa to 1 × 10 ⁹ Pa. Outside this range, preferred heat resistance and mechanical properties cannot be obtained.

  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 electrolyte membrane 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 electrolyte 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 electrolyte membrane 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.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to this.
In addition, the measurement conditions of the physical properties in the following examples are as follows.

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%.
Storage modulus: A viscoelasticity measuring device (Rheogel-E4000 manufactured by UBM Co., Ltd.) was used, and the heating rate was 2 ° C., the temperature range was 20 ° C. to 300 ° C., the frequency was 100 Hz, and the displacement was 5 μm.
Thermal decomposition temperature: A thermal analyzer (thermal analysis system WSOO2 manufactured by Max Science) was used and the temperature was increased at a rate of 5 ° C./min.

Example 1
20.8 parts by weight of MDI and 100 parts by weight of polytetramethylene oxide P monoaminobenzoate (amine number 89) are mixed and dissolved in 400 parts by weight of tetrahydrofuran (hereinafter abbreviated as THF), and fluorine A polyurea resin was obtained by pouring into a petri dish and removing THF.

Dissolve 1 g of the resulting polyurea resin in 10 ml of THF, add 0.4 g of MOI (2-isocyanatoethyl methacrylate) and 0.002 g of dibutyltin dilaurate, and react at room temperature to eliminate isocyanate groups. It was confirmed. 1 part by weight of a TBAS aqueous solution having a mass concentration of 50%, 0.002 part by weight of 21-hydroxy-2-methylpropiophenone as a polymerization initiator, and 6 parts by weight of THF are mixed with respect to the total amount of the solution. After deaeration, ultraviolet rays (400 W) were irradiated for 7 minutes. Thereafter, the reaction product was washed with hot water (80 ° C.) for 1 hour and then dried. In this way, the proton conductive resin of Example 1 was obtained.
The resulting resin was molded into a sheet to form an electrolyte membrane, and the proton conductivity was measured.
It became 4 × 10 ⁻⁴ S / cm.

(Example 2)
A polyurea resin was produced in the same manner as in Example 1.
1 g of the resulting polyurea resin was dissolved in 10 ml of THF, 0.4 g of MOI and 0.002 g of dibutyltin dilaurate were added and reacted at room temperature, and disappearance of isocyanate groups was confirmed. 1.18 parts by weight of polyethylene glycol 400 monoacrylate, 0.002 parts by weight of 21-hydroxy-2-methylpropiophenone as a polymerization initiator, and 6 parts by weight of THF are mixed with respect to the total amount of the solution. After deaeration, ultraviolet rays (400 W) were irradiated for 7 minutes. Thereafter, the reaction product was washed with hot water (80 ° C.) for 1 hour and then dried. In this way, the proton conductive resin of Example 2 was obtained.
The obtained resin was molded into a sheet shape to form an electrolyte membrane, and when proton conductivity was measured, it was 8 × 10 ⁻³ S / cm.

(Example 3)
A polyurea resin was produced in the same manner as in Example 1.
2.5 g of the resulting polyurea resin was dissolved in 50 ml of dimethylformamide (DMF) and placed in a reaction vessel, and the atmosphere in the vessel was replaced with nitrogen. Next, 195 mg of NaH having a purity of 60% was added to the reaction vessel and reacted at −5 ° C. for 15 minutes. Next, a solution in which 360 mg of 1,3 propane sultone was dissolved in 5 ml of DMF was added and reacted at 50 ° C. for 2 hours. The reaction was filtered and transferred to 300 ml diethyl ether to precipitate the polymer. The supernatant was removed by centrifuging, dissolved again in 5 ml of DMF, and proton exchange was performed by adding 200 ml of a 15 vol% hydrochloric acid aqueous solution. Further, after washing and drying, the product was dissolved in THF, cast into a petri dish, dried, washed with hot water and further dried to obtain the proton conductive resin of Example 3.

The obtained resin was molded into a sheet shape to form an electrolyte membrane, and the proton conductivity was measured to be 5.4 × 10 ⁻⁴ S / cm.
Moreover, the thermal decomposition temperature of the obtained proton conductive resin was 230 degreeC. Furthermore, the storage elastic modulus at 150 ° C. was 1.0 × 10 ⁸ Pa.

Example 4
0.5 g of each of the proton conductive resins of Example 2 and Example 3 was dissolved in THF and cast into a petri dish to obtain an electrolyte membrane of Example 4. When proton conductivity was measured, it was 5.4 × 10 ⁻⁴ to 8 × 10 ⁻³ S / cm.

(Comparative Example 1)
A polyurea resin was produced in the same manner as in Example 1. This polyurea resin was dissolved in THF and cast into a petri dish to obtain an electrolyte membrane of Comparative Example 1. When proton conductivity was measured, it was 3 × 10 ⁻⁶ S / cm.

As described above, it can be seen that the proton conductivity of the electrolyte membranes of Examples 1 to 4 is significantly improved as compared with the electrolyte membrane of Comparative Example 1.

Claims (7)

  An electrolyte membrane for a fuel cell comprising a proton conductive resin in which a side chain formed by binding an active hydrogen group to a terminal is bonded to a main chain made of a polyurea resin.   An acrylic isocyanate compound is combined with one or both of a urea group and a urethane group contained in the polyurea resin, and an active hydrogen group-containing acrylate compound is combined with the combined acrylic isocyanate compound. The electrolyte membrane for fuel cells according to claim 1.   The fuel cell electrolyte membrane according to claim 1 or 2, wherein the active hydrogen group is any one of a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, and a hydroxyl group.   The electrolyte membrane for a fuel cell according to claim 1, wherein a sultone compound is combined with one or both of a urea group and a urethane group contained in the polyurea resin.   The electrolyte membrane for a fuel cell according to claim 3, wherein the hydroxyl group is bonded to a polyoxyalkylene chain. 6. The thermal decomposition temperature is 180 ° C. or higher, and the storage elastic modulus at 150 ° C. is in the range of 1 × 10 ⁷ Pa to 1 × 10 ⁹ Pa. The electrolyte membrane for fuel cells as described. A fuel cell comprising the fuel cell electrolyte membrane according to any one of claims 1 to 6.