JP2005171086A - Proton-conductive electrolyte and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton-conductive membrane excellent in proton conductance, heat resistance and mechanical strength, and to provide a fuel cell using the membrane. <P>SOLUTION: The proton-conductive membrane comprises a proton-conductive electrolyte characterized in that a side-chain polymer 4 having proton-dissociable groups and/or a side-chain polymer 5 composed of a dendrimer is(are) added to the main-chain polymer 3 having hard segments 1 and soft segments 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a proton conductive electrolyte and a fuel cell, and particularly to a proton conductive electrolyte excellent in heat resistance and proton conductivity.

  In recent years, with the deterioration of the global environment, the spread and development of clean energy has become a serious issue worldwide. For example, in traffic relations, urban air pollution caused by exhaust gas from internal combustion engines such as automobiles has become an issue along with the development of the traffic network and the increase in the number of vehicles. Electric vehicles and hybrid vehicles have been developed as countermeasures for this, including electric and internal combustion engines, and the use of fuel cells as an energy source that does not pollute the atmosphere for lightweight and easy-to-use vehicles. Can be mentioned. The introduction of fuel cells to homes is similar to the transportation sector.

  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 they can operate at low temperatures and are easy to handle. Solid polymer type with high output density is attracting attention as an energy source for electric vehicles and homes.

  Proton conducting membranes used in solid polymer fuel cells are required to have high ionic conductivity for protons involved in electrode reactions of fuel cells. As such a proton conducting membrane, a membrane made of a super strong acid group-containing fluorine-based polymer is known. However, since these polymer materials are fluorine-based polymers, they are very expensive, and since the proton conducting medium is water, there is a problem that it is necessary to always humidify and replenish water.

Patent Document 1 and Patent Document 2 describe 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 eliminated particularly at high temperatures, so that they have low heat resistance, the membrane is not flexible, and proton conductivity is low.
Further, although there is a description related to Patent Document 3, there is no disclosure about proton conductivity.
JP 2002-280019 A JP 2002-358978 A Japanese National Patent Publication No. 8-504293

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a proton conductive membrane excellent in proton conductivity, heat resistance and mechanical strength, and a fuel cell using the same.

In order to achieve the above object, the present invention employs the following configuration.
The proton conductive electrolyte of the present invention is obtained by adding either or both of a side chain polymer having a proton dissociating group or a side chain polymer having a dendrimer to a main chain polymer having a hard segment portion and a soft segment portion. It is characterized by that.

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

  Further, the proton conductive electrolyte of the present invention is the proton conductive electrolyte described above, wherein the hard segment portion has any one of an aromatic ring, a heterocyclic ring, and an alicyclic ring, an acid anhydride, and a polyamine compound. The polyisocyanate and the compound are formed by a reaction with any one of the polyol compounds, and are bonded with a group selected from the group consisting of an imide group, a urea group, and a urethane group. Features.

  According to the above configuration, a proton conducting membrane excellent in proton conductivity and flexibility can be obtained.

  The proton conductive electrolyte of the present invention is the proton conductive electrolyte described above, wherein the soft segment portion has a polyoxyalkylene chain, and the hard segment is formed by one or both of a urea group and a urethane group. It is combined with the part.

According to the above configuration, a proton conducting membrane having high proton conductivity can be obtained.

The proton conductive electrolyte of the present invention is the proton conductive electrolyte described above, wherein the main chain polymer has a thermal decomposition temperature of 220 ° C. or higher and a storage elastic modulus at 200 ° C. of 1 × 10 ⁷ Pa or higher. It is characterized by being in a range of 1 × 10 ⁹ Pa or less.

  According to said structure, the proton conductive film excellent in heat resistance can be obtained.

  The proton conductive electrolyte of the present invention is the proton conductive electrolyte described above, wherein the proton dissociation group is any one of a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group. .

  According to said structure, the proton conductive membrane which has high proton conductivity can be obtained.

  The proton conductive electrolyte of the present invention is the proton conductive electrolyte described above, wherein the side chain polymer composed of the dendrimer has at least a polyethylene oxide chain, and an amino group, a hydroxyl group, and a terminal at the end of the polyethylene oxide chain. It is a polyacrylate having two or more sulfonic acid groups.

  According to the above configuration, a proton conducting membrane having high proton conductivity can be obtained.

  Next, a fuel cell according to the present invention includes a pair of electrodes and an electrolyte membrane disposed between the electrodes, wherein the electrolyte membrane is the proton conductive electrolyte according to any one of the above, and The proton conductive electrolyte is contained in a part of the electrode.

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

  According to the proton conductive electrolyte of the present invention, proton conductivity, heat resistance, and mechanical strength can be improved. Moreover, according to the fuel cell of the present invention, a high-performance fuel cell excellent in power generation characteristics can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows the structure of the proton conductive electrolyte of the present invention.
As shown in FIG. 1, the proton conductive electrolyte according to the present invention has a side chain consisting of a side chain polymer 4 having a proton dissociating group or a dendrimer in a main chain polymer 3 having a hard segment portion 1 and a soft segment portion 2. Either one or both of the polymers 5 are added.

  The hard segment portion 1 is formed by a reaction between a polyisocyanate and any one of an acid anhydride, a polyamine compound, and a polyol compound. Further, the hard segment portion 1 is connected to the soft segment portion 2 by either one or both of a urea group and a urethane group. The combination of the hard segment and the soft segment is made in the range of NCO index 90-110. By providing this hard segment part 1, the heat resistance of the proton conductive electrolyte is improved.

  The polyisocyanate constituting the hard segment part 1 has any one of an aromatic ring, a heterocyclic ring and an alicyclic ring. Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a fullerene ring, and a benzene ring and a naphthalene ring are particularly preferable. Examples of the heterocyclic ring include those having oxygen, nitrogen and sulfur, and those having oxygen and nitrogen are particularly preferable. Examples of the alicyclic ring include ordinary ones and are not particularly limited.

  Further, the acid anhydride, polyamine compound, and polyol compound constituting the hard segment portion 1 react with polyisocyanate to form an imide group, a urea group, and a urethane group, respectively. That is, an imide group is formed by a reaction between polyisocyanate and a polyvalent acid anhydride, a urea group is formed by a reaction between polyisocyanate and a polyamine compound, and a urethane group is formed by a reaction between polyisocyanate and a polyol compound.

  The following are mentioned as an example of polyisocyanate. Examples of the compound having an aromatic ring include tolylene diisocyanate, diphenylmethane diisocyanate (hereinafter abbreviated as MDI), xylylene diisocyanate, naphthalene diisocyanate, and the like. Examples of the compound having an alicyclic ring include isophorone diisocyanate and cyclohexane diisocyanate. Furthermore, examples of the aliphatic compound include hexamethylene diisocyanate and lysine diisocyanate. Furthermore, derivatives of the compounds described in these can also be used. These may be used in combination if necessary. The NCO% of the polyisocyanate is usually 20 to 48%, preferably 25 to 48%. Outside this range, heat resistance and mechanical strength are poor.

  Examples of polyhydric acid anhydrides include pyromellitic anhydride, trimetic acid benzenetetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, and the like.

  Polyamine compounds include aliphatic diamines (ethylene diamine, propylene diamine, etc.), alicyclic diamines (isophorone diamine, etc.), aromatic diamines [(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) and the like. These may be used as a mixture. Of the polyamine compounds, alicyclic diamines and aromatic diamines are particularly preferable. The amine value is usually 250 to 500, preferably 300 to 500. Outside this range, heat resistance and mechanical strength are poor.

  Examples of the polyol compound include aliphatic diols (such as ethylene glycol and propylene glycol) and aromatic diols (such as hydroquinone and bisphenol A). The hydroxyl value is usually 250 to 500, preferably 300 to 500. Outside this range, heat resistance and mechanical strength are poor.

  Next, the soft segment portion 2 has a polyoxyalkylene chain, and is bonded to the hard segment portion 1 by one or both of a urea group and a urethane group. By providing this soft segment portion 2, flexibility is imparted to the main chain polymer 3, and proton conductivity is improved.

  Examples of the polyoxyalkylene chain constituting the soft segment part 2 include a polyethylene oxide chain, a polypropylene oxide chain, and a polytetrahydrofuran oxide chain. Particularly, the polyethylene oxide chain and the polytetrahydrofuran oxide chain have proton conductivity and mechanical properties. It is preferable from the viewpoint.

  The soft segment part 2 has a polyoxyalkylene chain in the molecule and has a hydroxyl group or an amino group at the end. Specifically, the hydroxyl value of polyoxyalkylene glycol or polyalkylene oxide-di-P-aminobenzoate is used. Or an amine value is 28-200 normally, Preferably it is 28-150. Outside this range, the mechanical strength is poor.

The main chain polymer 3 preferably has a thermal decomposition temperature of 220 ° C. or higher and a storage elastic modulus at 200 ° C. of 1 × 10 ⁷ Pa or more and 1 × 10 ⁹ Pa or less. Outside this range, preferable heat resistance and mechanical properties cannot be obtained.

  Next, the side chain polymer 4 has a proton dissociation group at the terminal. Examples of the proton dissociation group include one or more selected from the group consisting of a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group. Of these, preferred are a sulfonic acid group and a phosphoric acid group. Although there is no limitation in particular as the kind of side chain polymer 4, poly (meth) acrylate is preferable.

Specific examples of the side chain polymer 4 include the following. Examples of the proton dissociation group being a sulfonic acid group include poly (2-acrylamido-2-methylpropanesulfonic acid (hereinafter abbreviated as TBAS), polystyrene sulfonic acid, and the like.
Examples of the proton dissociation group being a carboxylic acid group include polyacrylic acid, poly (β-methacryloyloxyethyl hydrogen succinate), poly (β-methacryloyloxyethyl hydrogen phthalate), and the like.
Furthermore, poly [mono (2-acryloyloxyethyl) acid phosphate], poly [mono (2-methacryloxyethyl) acid phosphate] and the like are examples in which the proton dissociation group is a phosphate group.
These can be obtained from each monomer by a known method by radical polymerization or photopolymerization.

  Next, the side chain polymer 5 made of a dendrimer is a poly (meth) acrylate having at least a polyethylene oxide chain and having two or more amino groups, hydroxyl groups, or sulfonic acid groups at its terminals. Specifically, an alkylene oxide containing ethylene oxide is added to a compound having three or more hydroxyl groups in the molecule (trimethylolpropane, pentaerythritol, etc.), reacted with methacrylic isocyanate, and subjected to radical polymerization or photopolymerization. The thing obtained by the known method can be used.

  The side chain polymer 4 and the side chain polymer 5 may be polymerized from the respective monomers in the main chain polymer 5.

  The ratio of the main chain polymer 3, the side chain polymer 4, and the side chain polymer 5 is not particularly limited, but is usually 0.1 to 1 part by weight of the side chain polymer 4 with respect to 1 part by weight of the main chain polymer 3. The polymer 5 is preferably 0.01 to 1 weight. More preferably, the side chain polymer 4 is 0.3 to 1 part by weight and the side chain polymer 5 is 0.01 to 0.5 part by weight with respect to 1 part by weight of the main chain polymer 3.

  Next, the fuel cell according to the present invention will be specifically described. The fuel cell according to the present invention includes a pair of electrodes and an electrolyte membrane disposed between the electrodes, and the electrolyte membrane is a proton conductive electrolyte according to the present invention, and a part of the electrodes To contain the proton conductive electrolyte.

That is, the fuel cell includes an electrolyte membrane made of a proton conductive electrolyte, an air electrode (electrode) and a fuel electrode (electrode) disposed in contact with both sides of the electrolyte membrane.
At the fuel electrode, the hydrogen of the fuel is electrochemically oxidized to generate protons and electrons. The generated protons are transported by the electrolyte membrane and move to the air electrode. Further, the electrons generated at the fuel electrode pass through the load connected to the fuel cell and flow to the air electrode. Oxygen is supplied to the air electrode, and protons, oxygen, and electrons react in the air electrode to generate water.

  The fuel electrode and air electrode constituting the fuel cell are 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.

  The catalyst is not particularly limited as long as it promotes a hydrogen oxidation reaction and an oxygen reduction reaction. For example, lead, iron, manganese, cobalt, chromium, gallium, vanadium, tungsten, ruthenium, iridium. , Palladium, platinum, rhodium or alloys thereof.

As the binder, it is desirable to use the above proton conductive electrolyte. In addition to the proton conductive electrolyte, other resins can be used in combination with the binder. In that case, the other resin is preferably a fluororesin having water repellency. 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.

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

  Proton conductivity: Two platinum wires (diameter 0.2 mm) are pressed against the surface of a sample formed into a strip shape at intervals of 5 mm to form an electrode, and the resistance when alternating current (1 kHz) is applied to this electrode is an impedance analyzer. Measured with The proton conductivity was determined by 1 / (R × t × D) from the electrode interval and resistance slope (R), sample thickness (t), and sample width (D). The measurement was performed at 80 ° C. and a humidity of 95%.

  Storage elastic modulus: Using a viscoelasticity measuring device (Rheogel-E4000 manufactured by UBM Co., Ltd.), the heating rate was 2 ° C./min, the temperature range was 20 ° C. to 230 ° C., the frequency was 100 Hz, and the displacement was 5 μm.

(Example 1)
20.8 parts by weight of MDI and 100 parts by weight of polytetramethylene oxide-di-P-aminobenzoate (amine number 89) are mixed and dissolved in 400 parts of tetrahydrofuran, and the solution is placed in a petri dish made of fluororesin. The main chain polymer of Example 1 was obtained by pouring and removing tetrahydrofuran.
As a result of measuring the viscoelasticity of the obtained main chain polymer, the storage elastic modulus at 200 ° C. was 4 × 10 ⁷ Pa and the thermal decomposition temperature was 250 ° C.

(Example 2)
25.7 parts by weight MDI, 50 parts by weight polytetramethylene oxide-di-P-aminobenzoate (amine number 89), 50 parts by weight polytetramethylene oxide-di-P-aminobenzoate (amine number 132) ) Were dissolved in 400 parts of tetrahydrofuran, the solution was poured into a petri dish made of fluororesin, and tetrahydrofuran was removed to obtain the main chain polymer of Example 2.
As a result of measuring the viscoelasticity of the obtained main chain polymer, the storage elastic modulus at 200 ° C. was 8 × 10 ⁷ Pa, and the thermal decomposition temperature was 270 ° C.

(Example 3)
1 part by weight of the main chain polymer produced in Example 1 above, 1 part by weight of TBAS (50% aqueous solution) as the side chain polymer 4, and 0.02 of 2-hydroxy-2-methylpropiophenone as the polymerization initiator. 01 parts and 6 parts of tetrahydrofuran were mixed and degassed, and then irradiated with ultraviolet rays (400 W mercury lamp) for 7 minutes. Thereafter, the product was washed with hot water (80 ° C.) for 1 hour and then dried. In this way, the proton conductive electrolyte of Example 3 was produced.
The proton conductivity of the obtained proton conductive electrolyte was 6.1 × 10 ⁻³ S / cm.

The proton conductivity of the main chain polymer of Example 1 was 3 × 10 ⁻⁶ S / cm. Therefore, it can be seen that proton conductivity can be improved by adding the side chain polymer 4 to the main chain polymer.

Example 4
1 part by weight of the main chain polymer prepared in Example 2 above, 2 parts by weight of TBAS (50% aqueous solution) as the side chain polymer 4, and 0. 2-hydroxy-2-methylpropiophenone as the polymerization initiator. 0.3 part of a reaction product of 01 parts, 10 parts of ethylene oxide added to pentaerythritol as side chain polymer 5 to give a hydroxyl value of 545, and 3.7 parts of 2-methacryloyloxyethyl isocyanate, A proton conducting electrolyte of Example 4 was produced in the same manner as in Example 3 except that 6 parts of tetrahydrofuran was mixed.
The proton conductivity of the obtained proton conductive electrolyte was 1 × 10 ⁻³ S / cm.

The proton conductivity of the main chain polymer of Example 1 was 3 × 10 ⁻⁶ S / cm. Therefore, it can be seen that the proton conductivity can be improved by adding the side chain polymer 4 and the side chain polymer 5 to the main chain polymer.

(Example 5)
A fuel cell was constructed using the proton conductive electrolyte in Example 3. The electrode used was a Pt / C catalyst on which 30% of platinum was supported, dispersed in a polymer solution of this catalyst and tetrahydrofuran (solution in Example 3), and the solution was removed to form a catalyst layer. . Moreover, the electrolyte membrane which consists of a proton conductive electrolyte of Example 3 was arrange | positioned between electrodes. When power was generated at 80 ° C. using air and hydrogen, a cell voltage of 0.66 V was obtained at a current density of 0.3 A / cm ² .

The schematic diagram which shows the molecular structure of the proton-conductive electrolyte which is embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hard segment part, 2 ... Soft segment part, 3 ... Main chain polymer, 4 ... Side chain polymer which has a proton dissociation group, 5 ... Side chain polymer which consists of dendrimers

Claims (7)

  A proton conductive electrolyte comprising a main chain polymer having a hard segment part and a soft segment part, to which one or both of a side chain polymer having a proton dissociation group or a side chain polymer comprising a dendrimer is added. .   The hard segment portion is formed by a reaction between a polyisocyanate having any one of an aromatic ring, a heterocyclic ring, and an alicyclic ring and any one of an acid anhydride, a polyamine compound, and a polyol compound, and the polyisocyanate. 2. The proton conductive electrolyte according to claim 1, wherein the compound is bonded to a group selected from the group consisting of an imide group, a urea group, and a urethane group.   The said soft segment part has a polyoxyalkylene chain, and is couple | bonded with the said hard segment part by any one or both of a urea group and a urethane group, The Claim 1 or Claim 2 characterized by the above-mentioned. Proton conducting electrolyte. The thermal decomposition temperature of the main chain polymer is 220 ° C. or higher, and the storage elastic modulus at 200 ° C. is in the range of 1 × 10 ⁷ Pa to 1 × 10 ⁹ Pa. 4. The proton conductive electrolyte according to any one of 3.   The proton conductive electrolyte according to claim 1, wherein the proton dissociation group is any one of a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group.   The side chain polymer comprising the dendrimer is a polyacrylate having at least a polyethylene oxide chain and having two or more of an amino group, a hydroxyl group, and a sulfonic acid group at the end of the polyethylene oxide chain. 1. The proton conductive electrolyte according to 1. It is comprised from a pair of electrode and the electrolyte membrane arrange | positioned between each electrode, The said electrolyte membrane is the proton conductive electrolyte in any one of Claim 1 thru | or 6, and one of the said electrodes A fuel cell characterized in that the proton conductive electrolyte is contained in the part.

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