JP4899454B2 - Carbon particle composite for fuel cell and production method - Google Patents

Description

  The present invention relates to a carbon particle composite used for an electrode of a fuel cell, for example, a polymer electrolyte fuel cell, and a production method thereof.

  A fuel cell directly converts the chemical energy of fuel into electrical energy, and has high conversion efficiency into electrical energy. In particular, a polymer electrolyte fuel cell is capable of generating high output at a relatively low temperature. It is expected as a small mobile power source and a stationary power source including an automobile power source.

  The structure of a polymer electrolyte fuel cell is generally composed of an electrolyte membrane made of a polymer ion exchange membrane such as a fluororesin ion exchange membrane having a sulfonic acid group, and a catalyst electrode in which a catalyst such as platinum is supported on both surfaces thereof. And tens to hundreds of layers of single cells consisting of separators and the like provided with concave and convex grooves for supplying a reaction gas for supplying a fuel gas such as hydrogen or an oxidant gas such as oxygen or air to each electrode. It consists of a stack and two current collectors provided outside the stack.

  As shown in FIG. 1, the structure of the single cell includes a pair of catalyst electrodes 2 and 3, that is, an anode 4 and a cathode 5 with a solid polymer electrolyte membrane 1 made of, for example, a fluorine-based resin ion exchange membrane interposed therebetween, The anode-side gas diffusion layer 6 and the cathode-side gas diffusion layer 7 formed on the outer side thereof, and a separator 8 made of a dense and gas-impermeable carbon material or metal material sandwiching these layers from both sides.

  The catalyst electrodes 2 and 3 are formed of a conductive carbonaceous porous body supporting a catalyst such as a noble metal such as platinum or ruthenium or an organometallic complex. As the carbonaceous porous body, for example, carbon short fiber or carbon black is used. A porous body bound with a resin is used.

The separator 8 is provided with a plurality of grooves 9, a flow path of fuel gas (for example, hydrogen gas) is formed by the grooves 9 and the anode side gas diffusion layer 6, and an oxidant gas (by the groove 9 and the cathode side gas diffusion layer 7). For example, the hydrogen gas supplied from the groove 9 diffuses through the anode-side gas diffusion layer 6 and is ionized by the reaction of H ₂ → 2H ⁺ + 2e ⁻ to become H ⁺ in the anode 4. It passes through the membrane 1.

On the other hand, the oxygen gas supplied from the groove 9 diffuses through the cathode-side gas diffusion layer 7 and generates water by the reaction of 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O at the cathode 5. The power generation mechanism of the fuel cell takes out the flow of electrons (e ⁻ ) generated by this electrochemical reaction as electric energy to an external circuit.

That is, the hydrogen gas supplied to the anode side is ionized on the catalyst electrode 4 to become H ⁺ , and H ⁺ moves through the electrolyte membrane to the cathode side together with water (xH ₂ O), and oxygen gas (O ₂ ) at the cathode. Reacts with water to produce water. Therefore, in order to make this battery reaction proceed smoothly, it is necessary to ionize the hydrogen gas while maintaining the electrolyte membrane in an appropriate wet state. Usually, the fuel gas and the oxidant gas are saturated at a temperature close to the operating temperature of the battery. Water vapor is supplied to keep the electrolyte membrane in a proper wet state.

  On the other hand, when water is excessively contained, the supersaturated water vapor is condensed as water droplets. When water droplets are generated in the reaction gas in this way, the surface tension of the water is so great that it stagnates in the gas flow path of the separator, and a flooding phenomenon occurs that condensate blocks the flow path and inhibits the flow of the reaction gas. As a result, the battery reaction does not proceed smoothly, resulting in a problem that power generation performance is degraded.

  In order to solve this problem, water repellency is imparted using a fluorine-based resin. For example, Patent Document 1 proposes improving the performance of a fuel cell by devising a mixing method of a fluororesin and a catalyst. However, the catalyst surface is covered with a fluororesin, and there is a drawback that the battery performance cannot be sufficiently exhibited.

  In addition, since fluororesin has no electrical conductivity, increasing the blending amount of fluororesin to increase water repellency decreases the conductivity. On the other hand, it is necessary to reduce the blending amount of fluororesin in order to ensure conductivity. As a result, there is a drawback that sufficient water repellency cannot be imparted.

  On the other hand, as a method of imparting hydrophilicity, Patent Document 2 discloses a method of binding a silane coupling agent having a hydrophilic site to a catalyst body. However, in this method, there is a problem that the hydrophilic coating covers even the noble metal catalyst support site and a problem that the conductivity is lowered because the carbon material is covered.

Patent Document 3 discloses a method of supporting a noble metal catalyst after imparting hydrophilicity to a catalyst support using a diazonium salt obtained by treating sulfanilic acid with sodium nitrite in an acidic aqueous solution. . However, there is a problem that it is difficult to fully support the catalyst because the modified functional group inhibits the support of the noble metal catalyst.
JP-A-8-264190 JP 2000-243404 A JP 2003-007308 A

  Therefore, the present invention aims to solve these problems, and has excellent hydrophilicity, high electronic conductivity and proton conductivity, a carbon particle composite for fuel cells, for example, a carbon particle composite suitable as a catalyst support. It aims at providing a body and its manufacturing method.

  In order to achieve the above object, the carbon particle composite for a fuel cell according to the present invention has a functional group on the surface of the carbon particle and one end isocyanate group of a diphenyl compound having an isocyanate group at both ends bonded to the other end of the diphenyl compound. A structural feature is that the isocyanate group is composed of carbon particles chemically modified with a sulfonic acid group bonded to a reactive group of a reactive alkylsulfonic acid.

  The functional group on the carbon particle surface is preferably a hydroxyl group and / or a carboxyl group.

  Also, the method for producing a carbon particle composite for a fuel cell according to the present invention comprises dissolving a diphenyl compound having an isocyanate group at both ends in a non-reactive solvent, mixing the carbon particles in the solution, and mixing one end of the diphenyl compound. After the isocyanate group is bonded to the functional group on the surface of the carbon particle by urethane and the unreacted diphenyl compound is removed, the reactive alkylsulfonic acid is added in a non-reactive solvent to add the other end isocyanate group and the reactive group of the diphenyl compound. Is a structural feature.

  This carbon particle composite is excellent in hydrophilicity, electronic conductivity and proton conductivity, and is suitably used, for example, as a fuel cell catalyst carrier.

  In the carbon particle composite for a fuel cell of the present invention, a functional group on the surface of the carbon particle, preferably a functional group such as a hydroxyl group or a carboxyl group, and one end isocyanate group of a diphenyl compound having an isocyanate group at both ends are bonded by a urethane bond. The diisocyanate is composed of carbon particles chemically modified with a sulfonic acid group in which the other end isocyanate group of the diphenyl compound is bonded to the reactive group of the reactive alkyl sulfonic acid, and both ends of the diphenyl compound having an isocyanate group at both ends. The carbon particle is chemically modified with a sulfonic acid group by bonding a group to the surface functional group of the carbon particle and a reactive group of the reactive alkylsulfonic acid. As a result, the hydrophilicity is improved and the wet state of the electrolyte is well maintained, the affinity between the electrolyte and the carbon particle composite is improved, and the three-phase interface is increased. For example, a fuel exhibiting excellent power generation performance It is suitably used as a battery catalyst support.

  Further, the method for producing a carbon particle composite for a fuel cell according to the present invention comprises dissolving a diphenyl compound having an isocyanate group at both ends in a non-reactive solvent, mixing the carbon particles in the solution, and mixing one end of the diphenyl compound. After the isocyanate group is bonded to the functional group on the surface of the carbon particle by urethane and the unreacted diphenyl compound is removed, the reactive alkylsulfonic acid is added in a non-reactive solvent to add the other end isocyanate group and the reactive group of the diphenyl compound. And the carbon particle surface is chemically modified with a sulfonic acid group. For example, a fuel cell catalyst carrier excellent in power generation performance can be produced.

  There are no limitations on the type of carbon material used in the carbon particle composite for fuel cells of the present invention. For example, graphite, carbon black, glassy carbon, activated carbon, carbon aerogel, mesocarbon microbeads, carbon fibers, carbon nanotubes, Any of fullerenes can be used.

  The functional group on the surface of the carbon particle to which the one-end isocyanate group of the diphenyl compound having an isocyanate group at both ends is urethane-bonded is not particularly limited as long as it is reactive, and a functional group such as a hydroxyl group, a carboxyl group, an amino group, a sulfone group is present. Although it can illustrate, a hydroxyl group and a carboxyl group are preferable from reaction efficiency. Moreover, when these functional groups are not present or when the amount thereof is small, these functional groups can be generated and controlled by applying an appropriate surface treatment, which is preferable.

Examples of the surface treatment method include the following method.
(1) Hydroxyl and carboxyl groups are produced by exposing carbon particles to an oxidizing gas atmosphere such as ozone, oxygen, NOx, SOx, treating with low-temperature oxygen plasma, ozone water, hydrogen peroxide water, peroxo 2 Gas phase oxidation treatment or liquid phase oxidation treatment, such as a method of mixing and stirring carbon particles in an oxidizing agent aqueous solution such as acid or its salts, hypohalite, dichromate, permanganate, nitric acid, etc. Method.
(2) Amino group is generated by oxidizing with nitric acid / sulfuric acid mixed system to form nitro group and reducing with reducing agent such as formaldehyde.
(3) The sulfone group is formed by sulfonation with concentrated sulfuric acid.

  In addition, as for the grade of surface treatment, when producing | generating a hydroxyl group and a carboxyl group, for example, it is preferable to process to pH about 5 or less.

  By reacting these functional groups with a diphenyl compound having isocyanate groups at both ends, one end isocyanate group of the diphenyl compound is bonded to a functional group on the surface of the carbon particle by a urethane bond (OHOCN) to bond the diphenyl compound. .

  For this reaction, the reaction formula when the hydroxyl group on the carbon particle surface and one end isocyanate group of methyldiphenyl diisocyanate react with each other to form a urethane bond is taken as an example, using methyldiphenyl diisocyanate as the diphenyl compound having isocyanate groups at both ends. Indicated.

  The carbon particle composite for a fuel cell according to the present invention has one end isocyanate of a diphenyl compound (for example, methyldiphenyl diisocyanate) having a functional group (for example, hydroxyl group) on the surface of the carbon particle and an isocyanate group at both ends as shown in Chemical Formula 1. The group is bonded by a urethane bond, and the other unreacted isocyanate group is bonded to the reactive group of the reactive alkylsulfonic acid, and the carbon particle surface is chemically modified with the sulfonic acid group.

  That is, in the diphenyl compound having isocyanate groups at both ends, one end isocyanate group of the isocyanate groups at both ends is bonded to the functional group on the surface of the carbon particle, and the other unreacted other isocyanate group is a reactive alkylsulfone. A diphenyl compound having an isocyanate group at both ends functions as an intermediate substance for bonding a functional group on the surface of carbon particles and a reactive alkylsulfonic acid.

  This reaction formula is illustrated in Chemical Formula 2. In the chemical formula 2, the hydroxyl group on the surface of the carbon particles shown in chemical formula 1 and one end isocyanate group of methyldiphenyl diisocyanate are urethane-bonded, and the isocyanate group on the other end is a reactive alkylsulfonic acid and the amino group of 2-aminoethanesulfonic acid. The reaction formula at the time of bonding is illustrated.

  In this way, the diphenyl compound must have isocyanate groups at both ends, the isocyanate group at one end is bonded to the functional group on the surface of the carbon particle, and the isocyanate group at the other end is reacted. It couple | bonds with the reactive group of a functional alkylsulfonic acid.

  This composite carbon particle is excellent in electronic conductivity, proton conductivity, and hydrophilicity, and is suitably used as a material that imparts electron conductivity and proton conductivity by mixing with a catalyst carrier or catalyst layer of a fuel cell, for example. can do.

  In this carbon particle composite for a fuel cell, a diphenyl compound having isocyanate groups at both ends is dissolved in a non-reactive solvent, and carbon particles are mixed in the solution to convert one end isocyanate group of the diphenyl compound to the surface of the carbon particles. By removing the unreacted diphenyl compound with a functional group and urethane, and then adding a reactive alkylsulfonic acid in a non-reactive solvent to chemically bond the other end isocyanate group and the reactive group of the diphenyl compound. Manufactured.

  Examples of diphenyl compounds having isocyanate groups at both ends include paraphenylene diisocyanate, 2-chloro-1,4-phenyl diisocyanate, 2,4-toluene diisocyanate (TDI), 2,6-toluene diisocyanate, and 1,5-naphthalene diisocyanate. Hexamethylene diisocyanate (HDI), diphenylmethane-4,4'-diisocyanate (MDI), 1,3-xylene-4,6-diisocyanate, diphenyl sulfide-4,4'-diisocyanate, 1,4-naphthalene diisocyanate, etc. Illustratively, MDI, TDI, and HDI are preferably used.

  These diphenyl compounds are dissolved in a solvent non-reactive with the diphenyl compound, for example, an ester compound such as ethyl acetate or butyl acetate or a solvent such as ketones such as methyl ethyl ketone, and carbon particles are added to this solution to 25 to 100. The isocyanate group at one end of the diphenyl compound reacts with the functional group on the carbon particle surface by stirring and mixing at a temperature of ℃, preferably 40 to 80 ° C. for an appropriate time, for example, 1 to 3 hours. A diphenyl compound is bonded by a functional group and a urethane bond.

  In this case, if the unreacted diphenyl compound remains, the carbon particles are easily aggregated and bonded, and the reaction with the reactive alkylsulfonic acid is also inhibited. Therefore, the unreacted diphenyl compound is removed and purified. Removal of the diphenyl compound is performed, for example, with a high-speed centrifuge, and the operation of adding a solvent and centrifuging is repeatedly performed for removal and purification.

  Carbon particles in which the functional groups on the surface of the carbon particles and one end isocyanate group of the diphenyl compound having an isocyanate group at both ends are bonded by a urethane bond are the above-mentioned ester compounds such as ethyl acetate and butyl acetate or ketones such as methyl ethyl ketone. By re-dissolving in a non-reactive solvent, adding a reactive alkylsulfonic acid and stirring and mixing at a temperature of 25 to 100 ° C., preferably 40 to 80 ° C. for an appropriate time, for example, 1 to 3 hours, The carbon particle surface can be chemically modified with a sulfonic acid group by combining the reactive group of the reactive alkylsulfonic acid with an unreacted one-end isocyanate group.

  The reactive alkylsulfonic acid is not particularly limited as long as it is a compound having a reactive group and a sulfonic acid group, and examples of the reactive group include a hydroxyl group, an amino group, a carboxyl group, and an active methylene group. Specific examples of the reactive alkylsulfonic acid include, for example, 2-aminoethanesulfonic acid, 2-aminopropanesulfonic acid, N- (2-hydroxyethyl) piperazine-N ′-(2-ethanesulfonic acid), 4 Examples include-(2-hydroxyethyl) -1-piperazinepropanesulfonic acid.

  In this way, the isocyanate group at one end of the diphenyl compound having isocyanate groups at both ends is bonded to the surface functional group of the carbon particles, and the isocyanate group at the other end is bonded to the reactive functional group of the reactive alkylsulfonic acid, Since the diphenyl compound having isocyanate groups at both ends binds carbon particles and reactive alkylsulfonic acid as an intermediate, for example, when used as a catalyst support for a fuel cell, the catalyst is not covered with a catalyst metal. A catalyst carrier of a fuel cell having excellent hydrophilicity is produced by directly bonding to the carbon carrier to be supported.

In these treatments , after the above reaction is performed on carbon particles on which no catalyst is supported , the resulting composite carbon particles may support the catalyst, but the compound bonded to the surface prevents the catalyst from being supported. Therefore, it is preferable to cause the carbon particles carrying the catalyst to carry out the above reaction .

  Hereinafter, although the Example of this invention is described concretely compared with a comparative example, this invention is not restrict | limited to this Example at all.

Comparative Example Carbon black (Vulcan XC72-R, manufactured by Cabot Corp., USA) was used as the carbon particles for supporting the catalyst, immersed in an aqueous chloroplatinic acid solution to support the platinum compound on the surface, and reduced to 30 platinum catalyst. A fuel cell catalyst carrier supported by weight% was produced.

Example A solution having a concentration of 10 wt% was prepared by dissolving 0.4 g of diphenylmethane-4,4′-diisocyanate (MDI) in methyl ethyl ketone. After adding 10 g of the fuel cell catalyst carrier of the above comparative example to this solution and reacting at room temperature for 6 hours with stirring, the solvent and unreacted MDI were separated.

  Subsequently, the resultant was redispersed in methyl ethyl ketone, 0.3 g of N- (2-hydroxyethyl) piperazine-N ′-(2-ethanesulfonic acid) was added, and the mixture was reacted at room temperature for 6 hours with stirring. A fuel cell catalyst in which the solvent and unreacted N- (2-hydroxyethyl) piperazine-N '-(2-ethanesulfonic acid) are removed by centrifugation, and the surface of the carbon black particles is chemically modified with sulfonic acid groups A carrier was produced.

  Using these catalyst carriers as a fluorine-based electrolyte membrane, carbon paper as a diffusion layer, and a metal separator, a fuel cell using the catalyst carrier as a cathode electrode was prepared, and a power generation test of the battery was performed by the following method. The relationship between current density and voltage is shown in FIG.

Power generation test: Humidified hydrogen was supplied to the anode side and humidified air was supplied to the cathode side to evaluate the power generation performance. The flow rate is 272 ml / min for hydrogen and 866 ml / min for air for a cell area of 13 cm ² . The test conditions are a cell temperature of 80 ° C., an anode dew point of 60 ° C., and a cathode dew point of 60 ° C.

  When the current density is low, the power generation performance of the polymer electrolyte fuel cell is improved as the wet state of the polymer electrolyte membrane is suitably maintained. Therefore, the fuel cell produced using the catalyst carrier of the example from FIG. 2 has a better wet state of the electrolyte membrane due to improved hydrophilicity than the fuel cell produced using the catalyst carrier of the comparative example. As a result, it was found that when the current density was the same, the voltage was high and the battery performance was excellent.

It is a partial sectional view showing a schematic structure of a single cell of a polymer electrolyte fuel cell. It is the graph which showed the relationship between the current density and voltage of the fuel cell produced using the fuel cell catalyst support body of the Example of this invention, and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2 Catalytic electrode 3 Catalytic electrode 4 Anode 5 Cathode 6 Anode side gas diffusion layer 7 Cathode side gas diffusion layer 8 Separator 9 Reaction gas flow path 10 Sealing material

Claims (4)

  The functional group on the surface of the carbon particle and one end isocyanate group of the diphenyl compound having an isocyanate group at both ends are urethane-bonded, and the other end isocyanate group of the diphenyl compound is chemically bonded by the sulfonic acid group bonded to the reactive group of the reactive alkylsulfonic acid. A carbon particle composite for a fuel cell, comprising a modified carbon particle.   A fuel cell catalyst carrier comprising the fuel cell carbon particle composite according to claim 1 as a catalyst carrier.   A diphenyl compound having isocyanate groups at both ends is dissolved in a non-reactive solvent, carbon particles are mixed in the solution, and one end isocyanate group of the diphenyl compound is urethane-bonded to a functional group on the surface of the carbon particles, and unreacted. After removing the diphenyl compound, a reactive alkylsulfonic acid is added in a non-reactive solvent to chemically bond the other end isocyanate group and the reactive group of the diphenyl compound, and the carbon particle composite for fuel cells Manufacturing method.   A method for producing a fuel cell catalyst carrier comprising the fuel cell carbon particle composite of claim 3 as a catalyst carrier.

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