JP2008210602A - Catalyst carrier for fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst carrier for a fuel cell excellent in power generating performance, and to provide its manufacturing method. <P>SOLUTION: The catalyst carrier for the fuel cell is made of a carbon particle chemically bonded to the reactive group of a compound having at least two or more Cl atoms, wherein one end isocyanate group of a diphenyl compound having isocyanate groups at both ends is urethane-bonded to a functional group on the surface of the carbon particle and the other end isocyanate group has a reactive group at its end. In its manufacturing method, the diphenyl compound having the isocyanate groups at both ends is dissolved in a non-reactive solvent; the carbon particle is mixed in the solution to urethane-bond the one end isocyanate group of the diphenyl compound to the functional group on the surface of the carbon particle; and a compound having the reactive group at its end and at least two of more Cl atoms is then added after removing the diphenyl compound which has not been reacted to chemically bond the reactive group at the end to the other end isocynate group of the diphenyl compound. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a catalyst carrier used for a fuel cell, for example, an electrode of a polymer electrolyte fuel cell, and a method for producing the same.

  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. The carbonaceous porous body is made of carbon short fiber or carbon black with a resin. A bonded porous body or the like 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 oxidant gas (oxygen) supplied from the groove 9 diffuses in the cathode side gas diffusion layer 7 and generates water in the cathode 5 by the reaction of 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O. 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.

  However, when moisture 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, for example, Patent Document 1 discloses that generated water is quickly discharged and removed by imparting water repellency using a fluorine-based resin. However, since the fluorine-based resin is not conductive, increasing the blending amount of the fluorine-based resin in order to increase the water repellency results in a decrease in conductivity. It is necessary to reduce the blending amount, and sufficient water repellency cannot be imparted.

  Thus, it has been proposed to use a silane coupling agent as another method for imparting water repellency. For example, Patent Document 2 discloses a fuel cell including a solid polymer electrolyte membrane and a pair of electrodes having a catalytic reaction layer sandwiching the solid polymer electrolyte membrane, wherein the electrodes are catalyst particles or catalyst particle carriers. An electrode for a fuel cell having a hydrogen ion diffusion layer formed by chemically bonding a silane compound on the surface is disclosed.

  Patent Document 3 discloses a water-repellent conductive material in which a water-repellent layer composed of a silane compound having at least one hydrocarbon chain or fluorocarbon chain is formed on at least a part of the surface of conductive particles or a conductive porous body. An electrode for a fuel cell having a functional material as a constituent element is disclosed.

Patent Document 4 discloses a reaction product obtained by reacting a silane compound in which an isocyanate group or a hydrolyzable group and a fluorine-containing organic group are bonded in the presence of moisture, a catalyst powder, and an ion exchange resin. A polymer electrolyte fuel cell electrode is disclosed.
JP-A-8-264190 JP 2000-228204 A JP 2000-239704 A JP 2001-135340 A

  However, since it is chemically bonded to the silane coupling agent by an ester bond, in the fuel cell in which the battery reaction is performed in the presence of a large amount of water vapor, the ester bond may be cleaved by hydrolysis. In addition, since the catalyst is covered with a silane coupling agent, the diffusion rate when the reaction gas reaches the catalyst surface is lowered, which causes a problem that the smooth progress of the cell reaction is hindered. Furthermore, the water repellency was not sufficient, and the permeability of oxidizing gas such as oxygen gas was insufficient.

  Therefore, the present inventor conducted intensive research to solve these problems, and the diphenylmethane group urethane-bonded via the functional group on the surface of the carbon particle is chemically bonded to the reactive group of the compound having at least two Cl atoms. It was confirmed that the carbon particles used were suitable as a catalyst carrier for a fuel cell in terms of conductivity, water repellency, and reaction gas permeability.

  That is, the present invention was developed based on this finding, and an object of the present invention is to provide a fuel cell catalyst carrier having excellent power generation performance and a method for producing the same.

  In order to achieve the above object, the catalyst carrier for a fuel cell according to the present invention has a diphenyl compound having an isocyanate group at both ends, one end isocyanate group of which is bonded to a functional group on the carbon particle surface, and the other end isocyanate group is terminated. It is characterized by comprising carbon particles chemically bonded to the reactive group of a compound having at least two Cl atoms having a reactive group.

  Further, the method for producing a fuel cell catalyst carrier according to the present invention comprises dissolving a diphenyl compound having an isocyanate group at both ends in a non-reactive solvent, mixing carbon particles in the solution, and mixing one end of the diphenyl compound. After the isocyanate group is urethane-bonded to the functional group on the surface of the carbon particles, and then the unreacted diphenyl compound is removed, a compound having at least two Cl atoms having a reactive group at the terminal is added, and the terminal reactive group is added. And the other end isocyanate group of the diphenyl compound are structurally characterized.

  According to the present invention, since the water repellency is high and the hydrophobicity is improved, the flooding phenomenon is suppressed, and since the conductivity is high, a fuel cell catalyst carrier having excellent power generation performance and a method for producing the same can be provided.

  Commonly used catalysts such as platinum and ruthenium are used as the catalyst. Examples of the carbon particles supporting the catalyst include graphite, carbon black, glassy carbon, activated carbon, carbon aerogel, mesocarbon microbeads, carbon fibers, and carbon nanotubes. Carbon particles such as fullerene are used.

  The functional group on the surface of the carbon particle that is urethane-bonded to the one-end isocyanate group of the diphenyl compound having an isocyanate group at both ends may be a reactive group that chemically bonds to the isocyanate group, such as hydroxyl group, carboxyl group, amino group, etc. A functional group can be exemplified, but a hydroxyl group and a carboxyl group are preferable from the viewpoint of reaction efficiency. In addition, when it does not have these functional groups or when the amount is small, it is preferable to generate and control these functional groups by performing an appropriate surface treatment.

  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, 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. For example, MDI, TDI, and HDI are preferably used.

  The diphenyl compound having an isocyanate group at both ends reacts with a functional group on the surface of the carbon particle, and one end isocyanate group of the diphenyl compound is bonded to the functional group on the surface of the carbon particle by a urethane bond (OHOCN) to bond the diphenyl compound. .

  In this reaction, carbon black as carbon particles and diphenylmethane-4,4'-diisocyanate as diphenyl compounds having isocyanate groups at both ends are used as examples. One end of hydroxyl group on carbon black particle surface and diphenylmethane-4,4'-diisocyanate The reaction formula when the isocyanate group reacts to form a urethane bond is shown in Chemical Formula 1.

  In the catalyst support for fuel cell of the present invention, the one-end isocyanate group of the diphenyl compound having isocyanate groups at both ends as in Chemical Formula 1 is urethane-bonded to the functional group on the surface of the carbon particles, and one unreacted isocyanate group at the other end Is formed from carbon particles chemically bonded to a compound having at least two Cl atoms having a reactive group at the terminal.

  Examples of reactive groups include amino groups, hydroxyl groups, carboxyl groups, and epoxy groups. Specific examples of compounds having at least two Cl atoms having a reactive group at the terminal include the following. Is done.

  2-amino-2,6-dichlorophenol, 2-amino-3,5 dichloropyridine, 2-amino-4,6-dichloropyrimidine, 5-amino-4,6-dichloropyrimidine, 2,4-dichlorobenzyl alcohol 2,5-dichlorobenzyl alcohol, 2,6-dichlorobenzyl alcohol, 2,3-dichloroaniline, 2,4-dichloroaniline, 2,5-dichloroaniline, 2,6-dichloroaniline, 3,4-dichloro Aniline, 3,5-dichloroaniline, 2,4-dichlorobenzoic acid, 2,5-dichlorobenzoic acid, 3,4-dichlorobenzoic acid, 3,5-dichlorobenzoic acid, 2,3-dichlorophenol, 2, 4-dichlorophenol, 2,5-dichlorophenol, 2,6-dichlorophenol, 3,4-dichlorophenol, 2 4,5-trichloroaniline, 2,4,6-trichloroaniline, 3,4,5-trichloroaniline, 2,3,5-trichlorophenol, 2,3,6-trichlorophenol, 2,4,5-trichloro Phenol, 2,3,6-trichlorophenol, 2,2,2-trichloroethanol.

  For example, in the case where the hydroxyl group on the surface of the carbon black particle and one end isocyanate group of diphenylmethane-4,4′-diisocyanate are urethane-bonded, one unbound other isocyanate group has a reactive hydroxyl group at the end. The reaction formula in the case of chemical bonding with 2,2,2-trichloroethanol having 3 Cl atoms is shown in Chemical Formula 2.

  As described above, in the fuel cell catalyst carrier of the present invention, the one-end isocyanate group of the diphenyl compound having an isocyanate group at both ends is urethane-bonded to the functional group on the surface of the carbon particle, and the unbonded other-end isocyanate group is Cl atom. Are composed of carbon particles chemically bonded to a reactive group of a compound having two or more, and the diphenyl compound functions as an intermediate substance that bonds the carbon particles and a compound having two or more Cl atoms. Since the Cl atom has high electronegativity, it has high catalyst activation and oxygen gas permeability, high conductivity and water repellency, and exhibits excellent performance as a catalyst carrier for a fuel cell.

  The catalyst carrier for a fuel cell of the present invention is prepared by dissolving a diphenyl compound having isocyanate groups at both ends in a non-reactive solvent, mixing carbon particles in the solution, and converting one end isocyanate group of the diphenyl compound to the surface of the carbon particles. After removing the unreacted diphenyl compound and adding a compound having at least two Cl atoms having a reactive group at the terminal, the terminal reactive group and the other end of the diphenyl compound It is produced by chemically bonding with an isocyanate group.

  Non-reactive solvents with diphenyl compounds having isocyanate groups at both ends include, for example, ester compounds such as ethyl acetate and butyl acetate or ketones such as methyl ethyl ketone, and diphenyl compounds having isocyanate groups at both ends are used as these solvents. Next, by adding carbon particles to this solution and stirring and mixing at a temperature of 10 to 100 ° C., preferably 20 to 60 ° C. for about 1 to 10 hours, an isocyanate at one end of the diphenyl compound The group and the functional group on the surface of the carbon particle are reacted to bond the diphenyl compound with the functional group on the surface of the carbon particle and a urethane bond.

  In this case, when the unreacted diphenyl compound remains, the carbon particles are easily aggregated and bonded, and the reaction with the compound having at least two Cl atoms having a reactive group at the terminal is also inhibited. Remove and purify compound. The removal of the diphenyl compound can be performed by, for example, a high-speed centrifuge, and can be removed and purified by repeatedly performing the operation of adding the solvent and centrifuging.

  Carbon particles in which the functional group 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 The compound is dissolved again in a non-reactive solvent, and a compound having at least two Cl atoms having a reactive group at the terminal is added to the solution, and the temperature is 10 to 100 ° C., preferably 20 to 60 ° C. Then, the terminal reactive group and the other end isocyanate group of the diphenyl compound are chemically bonded by stirring and mixing for about 1 to 10 hours.

  In this way, the isocyanate group at one end of the diphenyl compound having an isocyanate group at both ends is bonded to the surface functional group of the carbon particle, and the isocyanate group at the other end has at least two Cl atoms having a reactive group at the end. The diphenyl compound having an isocyanate group at both ends binds to a carbon particle as an intermediate and a compound having at least two Cl atoms having a reactive group at the end, for example, fuel. When used as a catalyst support for a battery, it does not cover the catalyst metal, and is directly bonded to the carbon support for supporting the catalyst to form a water-repellent part, so that the power generation efficiency is not lowered efficiently. A catalyst carrier for a fuel cell that causes a cell reaction is produced.

  In addition, these treatments, that is, one end isocyanate group of a diphenyl compound having an isocyanate group at both ends are urethane-bonded to a functional group on the surface of the carbon particle, and then the other end isocyanate group of the unbonded diphenyl compound is reactive at the end. The reaction for chemically bonding to the reactive group of the compound having at least two Cl atoms having a group may be carried out on carbon particles on which no catalyst is supported, and then the catalyst may be supported. Since it tends to hinder the loading of the catalyst, it is preferably carried out on the carbon particles carrying the catalyst.

  Examples of the present invention will be specifically described below.

Comparative Example Carbon black (Vulcan XC72-R, manufactured by Cabot Corp., USA) was used as the carbon particles for supporting the catalyst. The carbon black was placed in an aqueous chloroplatinic acid solution, stirred and mixed, and then filtered and separated on the carbon black surface. A platinum compound was deposited. Subsequently, the catalyst support for fuel cells which carried 30 weight% of platinum catalysts by heating and reduction | restoration was manufactured.

Example 10 g of a fuel cell catalyst carrier (carbon black carrying a platinum catalyst) of a comparative example was placed in a methyl ethyl ketone solution in which diphenylmethane-4,4'-diisocyanate (MDI) was dissolved to a concentration of 10% by weight. The reaction was carried out at 40 ° C. for 2 hours while stirring to urethane bond the isocyanate groups. Thereafter, methyl ethyl ketone and unreacted MDI were separated by centrifugation.

  Subsequently, it was re-dispersed in methyl ethyl ketone, 3 g of 2,2,2-trichloroethanol was added to the solution, and the mixture was reacted at 40 ° C. for 2 hours with stirring. Thereafter, unreacted 2,2,2-trichloroethanol and methyl ethyl ketone were removed by centrifugation to produce a catalyst support for a fuel cell.

  A fuel cell using these catalyst carriers as cathode electrodes was prepared and a power generation test was conducted 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 80 ° C., and a cathode dew point of 80 ° C.

  When the current density is high, the higher the diffusibility of the fuel gas, the oxidant gas, or the water vapor, the more the reaction at the catalyst electrode is promoted, so the voltage drop is suppressed. Moreover, when flooding occurs, a voltage drop occurs. Therefore, it can be seen from FIG. 2 that in the example, as compared with the comparative example, flooding is suppressed due to the improvement in hydrophobicity, and even when the current density is increased, the voltage decrease is small and the battery performance is 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 of the fuel cell produced using the catalyst support body for fuel cells of the Example and comparative example of this invention, and a voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte membrane 2 Catalyst electrode 3 Catalyst 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 (2)

  A reactive group of a compound having at least two Cl atoms in which one end isocyanate group of a diphenyl compound having an isocyanate group at both ends is bonded to a functional group on the surface of the carbon particle and the other end isocyanate group has a reactive group at the end A catalyst support for a fuel cell, comprising carbon particles chemically bonded to the catalyst.   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 then unreacted. After the diphenyl compound is removed, a compound having at least two Cl atoms having a reactive group at the terminal is added to chemically bond the reactive group at the terminal and the other isocyanate group of the diphenyl compound. A method for producing a catalyst carrier for a fuel cell.

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