JP4899453B2 - Composite carbon particles for fuel cells and method for producing the same - Google Patents

Description

  The present invention relates to a composite carbon particle for a fuel cell used for 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. 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 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. However, since the fluororesin has no electrical conductivity, increasing the blending amount of the fluororesin to increase water repellency decreases the conductivity. On the other hand, it is necessary to reduce the blending amount of the fluororesin in order to ensure conductivity. 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, in Patent Document 1, in 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, 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 2 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 3 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 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. There is also a problem that the water repellency is not sufficient.

  Therefore, the present invention solves these problems, maintains sufficient water repellency while maintaining high conductivity, has high reaction gas permeability and excellent power generation performance, for example, a catalyst layer of a fuel cell, that is, It aims at providing the composite carbon particle for fuel cells which can be used suitably as a catalyst support body or a gas diffusion layer, and its manufacturing method.

  In order to achieve the above object, the composite carbon particle 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 surface of the carbon particle, and the other end isocyanate group reacts. It is characterized in that it consists of carbon particles chemically bonded to a functional silicone polymer.

  Further, according to the present invention, this method for producing composite carbon particles for fuel cells comprises dissolving a diphenyl compound having isocyanate groups at both ends in a non-reactive solvent, and mixing the carbon particles in the solution to form a diphenyl compound. Constitutional features include one end isocyanate group urethane-bonded to the functional group on the carbon particle surface, removing the unreacted diphenyl compound, and then adding a reactive silicone polymer to chemically bond to the other end isocyanate group of the diphenyl compound. And

  In the composite carbon particles for a fuel cell of the present invention, 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 is a reactive silicone type. It consists of carbon particles chemically bonded to a polymer, and a diphenyl compound having isocyanate groups at both ends functions as an intermediate substance for bonding the carbon particles and the reactive silicone polymer. Further, according to the composite carbon particles, high water repellency is imparted, so that hydrophobicity is improved, and a flooding phenomenon is suppressed, and a fuel cell excellent in power generation performance is provided.

  According to the method for producing composite carbon particles for a fuel cell of the present invention, a diphenyl compound having isocyanate groups at both ends is dissolved in a non-reactive solvent, and the carbon particles are mixed in the solution to form a diphenyl compound. One end isocyanate group is urethane-bonded to the functional group on the surface of the carbon particles, unreacted diphenyl compound is removed, and reactive silicone polymer is added to chemically bond to the other one-end isocyanate group of the diphenyl compound Thus, it is possible to manufacture a fuel cell with excellent power generation performance.

  The carbon particles applied to the composite carbon particles for a fuel cell of the present invention are not limited to the type of carbon material. For example, graphite, carbon black, glassy carbon, activated carbon, carbon aerogel, mesocarbon microbeads, carbon Any of fibers, carbon nanotubes, fullerenes and the like 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.

Examples of the surface treatment method include the following method.
(1) Hydroxyl group and carboxyl group can be generated by exposing carbon particles to a gas atmosphere such as ozone, oxygen, NOx, SOx, treating with low temperature oxygen plasma, ozone water, hydrogen peroxide water, peroxodiacid or A method of vapor phase oxidation treatment or liquid phase oxidation treatment, such as a method of stirring and mixing in an aqueous solution of an oxidizing agent such as salts, hypohalite, dichromate, permanganate, nitric acid.
(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. .

  In this reaction, carbon black as carbon particles, and methyl diphenyl diisocyanate as an example of a diphenyl compound having isocyanate groups at both ends are used as an example. The reaction formula in this case is shown in Chemical Formula 1.

  The composite carbon particles for a fuel cell according to the present invention include one of a functional group (hydroxyl group) on the surface of carbon particles (carbon black particles) and a diphenyl compound (methyldiphenyl diisocyanate) having isocyanate groups at both ends as shown in Chemical Formula 1. One end isocyanate group is bonded by a urethane bond, and one unreacted other end isocyanate group is formed from carbon particles chemically bonded to a reactive silicone polymer.

  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 one unreacted other end isocyanate group is a reactive silicone type. 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 silicone polymer.

  This reaction formula is illustrated in Chemical Formula 2. Chemical formula 2 is the reaction of the hydroxyl group on the carbon black particle surface shown in chemical formula 1 and the methyldiphenyl diisocyanate to urethane bond the diphenylmethane group, and then the polysiloxane is reacted as a reactive silicone polymer to unbond the other end. This shows a chemical reaction formula in which an isocyanate group is chemically bonded to a polysiloxane group.

However, the formula in ^{R 2} is an alkylene group having 1 to 6 carbon ^atoms, R 3 ^{to R 13} represents the same or different aryl group, an alkyl group or an alkoxyl group having 1 to 10 carbon atoms having 1 to 6 carbon atoms, respectively, n represents an integer of 0 to 200.

  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 binds to the terminal reactive group of the conductive silicone polymer.

  The composite carbon particles are excellent in conductivity and water repellency, and can be suitably used, for example, as a material imparting conductivity by being mixed with a catalyst carrier or a catalyst layer of a fuel cell.

  In this composite carbon particle for fuel cells, a diphenyl compound having an isocyanate group at both ends is dissolved in a non-reactive solvent, and the carbon particle is mixed in the solution so that one end isocyanate group of the diphenyl compound is functionalized on the surface of the carbon particle. After the unreacted diphenyl compound is removed by urethane bonding with the group, a reactive silicone polymer is added and chemically bonded to the other end isocyanate group of the diphenyl compound.

  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 that is non-reactive with the diphenyl compound, for example, an ester compound such as ethyl acetate or butyl acetate, or a ketone solvent such as methyl ethyl ketone, and carbon particles are added to this solution for 10 to 100. By stirring and mixing at a temperature of ° C., the isocyanate group at one end of the diphenyl compound reacts with the functional group on the surface of the carbon particle, and the diphenyl compound is bonded to the functional group on the surface of the carbon particle with 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 silicone polymer 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. The reactive silicone polymer is dissolved again in this non-reactive solvent, and the solution is stirred and mixed at a temperature of 10 to 100 ° C. for an appropriate time.

  For reactive silicone polymers, polysiloxanes with reactive functional groups such as amino groups, hydroxyl groups, carboxyl groups, and epoxy groups are used at the ends, and reactive silicone polymers with reactive functional groups at both ends are reactive. Since it has low property, those having a reactive functional group only at one end are preferred.

  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 silicone polymer, Diphenyl compound having isocyanate groups at both ends binds carbon particles and reactive silicone polymer as an intermediate, so when used as a catalyst support for a fuel cell, for example, the catalyst is supported without covering the catalyst metal A catalyst carrier for a fuel cell is produced that is directly bonded to the carbon carrier to form a water-repellent portion and efficiently causes a cell reaction without causing a decrease in power generation efficiency.

In this case, after the above reaction is performed on carbon particles on which no catalyst is supported , the resulting composite carbon particles may support the catalyst. However, a compound bonded to the surface hinders catalyst support. Since it is easy, it is preferable to cause the carbon particles carrying the catalyst to carry out the above reaction .

  Hereinafter, examples of the present invention will be specifically described using a catalyst carrier of a fuel cell as an example and compared with comparative examples. However, the present invention is not limited to the following examples.

Comparative Example 1
Using carbon black (Vulcan XC72-R, manufactured by Cabot Corp., USA) as carbon particles for supporting the catalyst, the platinum compound is supported on the surface by dipping in a chloroplatinic acid aqueous solution, and reduced to 30% by weight of the platinum catalyst. A supported fuel cell catalyst carrier was produced.

Comparative Example 2
A silane coupling agent was adsorbed on the surface of the fuel cell catalyst carrier of Comparative Example 1 to form a monomolecular film made of the silane coupling agent. As a silane coupling agent, CH ₃ — (CH ₂ ) _n —SiCl ₃ (n is an integer of 10 or more and 25 or less) having a linear hydrocarbon film is used and dissolved in a concentration of 1% by weight. And carbon black was immersed. Subsequently, a catalyst support for a fuel cell in which a water-repellent film of a silane coupling agent was formed by dehydrochlorination was produced.

Example 10 g of a fuel cell catalyst carrier of Comparative Example 1 was placed in a methyl ethyl ketone solution in which diphenylmethane-4,4'-diisocyanate (MDI) was dissolved to a concentration of 10% by weight and stirred at 40 ° C. for 2 hours. The diphenylmethane group was urethane-bonded by reaction. Thereafter, the solvent and unreacted MDI were separated by centrifugation.

  Subsequently, 3 g of a reactive silicone polymer (GE TSF4709, manufactured by GE Toshiba Silicones) was added to the solution by redispersion in methyl ethyl ketone, and the mixture was reacted at 40 ° C. for 2 hours with stirring. Thereafter, unreacted reactive silicone polymer was removed by centrifugation to produce a fuel cell catalyst carrier. A fuel cell was constructed using the fuel cell catalyst carrier, a fluorine-based electrolyte membrane, carbon paper as a diffusion layer, and a metal separator.

  A fuel cell was prepared by kneading these catalyst carriers with an electrolyte material to form a cathode electrode, and a power generation test of the cell 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. In addition, when flooding occurs, the voltage drop increases. 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 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)

  A fuel cell comprising a diphenyl compound having an isocyanate group at both ends, one end isocyanate group of which is bonded to a functional group on the surface of the carbon particle by urethane bonding, and the other end isocyanate group chemically bonded to a reactive silicone polymer. Composite carbon particles.   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. A method for producing composite carbon particles for a fuel cell, comprising removing a diphenyl compound and then adding a reactive silicone polymer to chemically bond with the other end isocyanate group of the diphenyl compound.   A fuel cell catalyst carrier comprising the composite carbon particles according to claim 1.   A method for producing a catalyst carrier for fuel cells, wherein the composite carbon particles according to claim 2 are catalyst carriers.

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