JP2005174786A - Electrode for fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain proton conductivity of an electrode and activity of an electrocatalyst in a good condition and improve characteristics of a fuel cell equipped with the electrode by suppressing remarkable change of the water content of a cation exchange resin contained in the electrode depending on the increase or the decrease of the water content contained in a reactive gas since the thickness of the electrode is very thin, in the electrode for a fuel cell in which a catalyst metal is selectively held in a contact surface between a proton conduction path of the cation exchange resin and a carbon surface. <P>SOLUTION: In the electrode for the fuel cell including a first layer containing the cation exchange resin, first carbon and a catalyst metal, a second layer comprising second carbon and a fluororesin, a third layer which is formed between the first layer and the second layer and contains first carbon, the catalyst metal, second carbon and the fluororesin, the catalyst metal contained in the first layer is held in the contact surface between the proton conduction path of the cation exchange resin and the surface of the first carbon. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrochemical cell using a solid polymer electrolyte, particularly to an electrode for a solid polymer fuel cell and a method for producing the same.

  A single cell of a polymer electrolyte fuel cell (PEFC) has a structure in which a membrane / electrode assembly is sandwiched between a pair of separators. In this membrane / electrode assembly, an anode is bonded to one surface of a polymer electrolyte membrane, and a cathode is bonded to the other surface. A gas flow path is processed in the separator. For example, electric power can be obtained by supplying hydrogen as fuel to the anode and oxygen as oxidant to the cathode. In the anode and the cathode, the following electrochemical reaction proceeds.

Anod: 2H ₂ → 4H ⁺ + 4e ⁻
Cathode: O ₂ + 4H ⁺ + 4e ⁻ → H ₂ O
The electrochemical reaction as described above is performed at an interface where a reactant such as an oxidant or a fuel, protons (H ⁺ ), and electrons (e ⁻ ) exist (hereinafter, this interface is referred to as a reaction interface). proceed. In addition, protons move the polymer electrolyte membrane from the anode to the cathode with several hydrated waters. For this reason, the PEFC electrode requires both the supply of water to the anode and the discharge of water from the cathode.

  The anode and cathode of the polymer electrolyte fuel cell are provided with a catalytic metal in order to facilitate the electrochemical reaction. Electrons, reactants and water involved in the reaction are transferred to the catalytic metal via the conductive porous body. This conductive porous body is disposed between the electrode and the separator. For the conductive porous body, porous carbon paper or the like imparted with water repellency is used to facilitate the conduction of electrons, the diffusion of reactants, and the movement of water.

  A conventional PEFC electrode is manufactured, for example, by applying a mixture of a carbon powder carrying a catalyst metal and a polymer electrolyte solution to a polymer electrolyte membrane or a conductive porous body. In the conventional electrode, since the catalytic metal is present outside the reaction interface, the utilization factor of the metal is remarkably low. That is, Non-Patent Document 1 reports that the utilization rate is about 10%.

  The polymer electrolyte fuel cell electrode is a mixture of a cation exchange resin, which is a solid polymer electrolyte, carbon, and a catalyst metal. A fuel cell electrode in which the catalytic metal is selectively supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface has been developed and reported in Patent Document 1, Patent Document 2, and Non-Patent Document 2. . Since the catalytic metal of this electrode is selectively supported on the reaction interface where the electrochemical reaction proceeds, the utilization factor of the metal is significantly higher than that of the conventional fuel cell electrode.

Furthermore, since the thickness of the electrode selectively supporting the catalytic metal on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface can be reduced to 20 μm or less, the usage amount of the catalytic metal is further reduced. be able to. Although this electrode has a very small amount of catalyst used per unit area of 0.05 mg / cm ² or less, the characteristics of PEFC including the electrode are superior to those of the conventional electrode.

JP 2000-012041 A JP 2000-173626 A Edson A. Ticianelli, J. et al. Electroanal. Chem, 251, 275 (1988) Shuji Hitomi et al., 40th Battery Discussion Meeting, 167-168, (1999)

  However, since the thickness of the fuel cell electrode in which the catalytic metal is selectively supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface is very thin, the amount of moisture contained in the reaction gas The water content of the cation exchange resin contained in the electrode was remarkably changed by the increase / decrease. Due to this change in water content, the proton conductivity of the electrode or the activity of the electrode catalyst is reduced, causing a problem that the output voltage of the fuel cell equipped with the electrode is lowered.

  Therefore, an object of the present invention is to improve the proton conductivity of the electrode and the activity of the electrode catalyst by suppressing the change in the water content of the cation exchange resin in the electrode due to the increase or decrease in the amount of water contained in the reaction gas. In addition to maintaining a stable state, it is to improve the characteristics of a fuel cell including the electrode.

  The invention of claim 1 is a fuel cell electrode comprising a first layer comprising a cation exchange resin, a first carbon and a catalytic metal, and a second layer comprising a fluororesin and a second carbon, The catalytic metal contained in the first layer is supported on a contact surface between the proton conduction path of the cation exchange resin and the surface of the first carbon.

  According to a second aspect of the present invention, there is provided a method for producing an electrode for a fuel cell according to the first aspect, wherein a first step of forming a layer containing a cation exchange resin and a first carbon, and the pair of the cation exchange resin After forming the first layer through the second step of adsorbing the cation of the catalytic metal on the ions and the third step of chemically reducing the cation of the catalytic metal, the fluororesin and the second A fourth step of forming a second layer made of carbon and a fifth step of integrating the first layer and the second layer are characterized.

  The fuel cell comprising the fuel cell electrode of the present invention is characterized in that the fuel comprises only the first layer in which the catalytic metal is selectively supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. Research results show that it is superior to batteries.

  The electrode for a fuel cell of the present invention includes a cation exchange resin, a first carbon, and a catalyst metal, and the catalyst metal is supported on a contact surface between the proton conduction path of the cation exchange resin and the carbon surface. And a conductive second layer comprising a fluororesin and second carbon and having appropriate porosity and water repellency. In this conductive second layer, in addition to being able to hold an appropriate amount of moisture in the pores, the pores are not clogged by the retention of water by providing appropriate water repellency. Therefore, the layer can keep a smooth supply of the reaction gas while suppressing the drying of the electrode.

  Furthermore, since the reactive gas can be prevented from coming into direct contact with the electrode surface by the second layer, excessive drying of the electrode can be suppressed even when a dry reactive gas is supplied. That is, the second layer has a function of keeping the water content of the electrode constant. Therefore, an electrode with a constant water content maintains high proton conductivity, so it is possible to maintain a high activity for electrochemical reaction at the reaction interface that extends three-dimensionally inside the electrode. Thus, even when the water content of the cathode gas is low, a high cell voltage can be maintained.

  An electrode for a fuel cell of the present invention includes a first layer containing a cation exchange resin, a first carbon, and a catalyst metal, and a second layer made of a fluororesin and a second carbon, and the first layer The catalyst metal contained in is carried on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface, and the first layer and the second layer are integrated.

  A schematic view of the fuel cell electrode of the present invention is shown in FIG. In FIG. 1, 11 is a fuel cell electrode of the present invention, 12 is a first layer, and 13 is a second layer. The electrode 11 for a fuel cell according to the present invention includes a first layer 12 in which a catalytic metal is supported on a contact surface between a proton conduction path of a cation exchange resin and a surface of the first carbon, a fluororesin, and a second carbon. The conductive second layer 13 is provided with water repellency and porosity.

  The fuel cell is configured by providing the fuel cell electrode 11 of the present invention on at least one surface of the polymer electrolyte membrane. A cross section of the fuel cell is schematically shown in FIG. In FIG. 2, symbols 12 and 13 are the same as those in FIG. 1, 14 is a polymer electrolyte membrane, 15 is a conductive porous body, 16 is a gas supply path, 17 is a separator, 18 is a sealing material, and 19 is a fuel. It is a battery.

  The first layer 12 on which the catalyst metal of the fuel cell electrode of the present invention is supported is disposed so as to be in contact with each surface of the polymer electrolyte membrane 14. The other surface (second layer) of the fuel cell electrode is disposed so that one surface of the conductive porous body 15 having water repellency is in contact therewith. Further, a separator 17 including a gas supply path 16 is disposed on the other surface of the conductive porous body 15 so as to come into contact therewith. As shown in FIG. 2, the fuel cell 19 includes a polymer electrolyte membrane 14 including a pair of electrodes including a first layer 12 and a second layer 13, a pair of conductive porous bodies 15, and a pair of separators 17. It is comprised by pinching. Between the separators, a sealing material 18 such as a gasket or an O-ring is disposed, so that the reaction gas is kept airtight.

FIG. 3 shows a schematic diagram of the internal structure of the first layer 12 in which the catalytic metal is supported on the contact surface between the proton conduction path of the cation exchange resin and the surface of the first carbon. In FIG. 3, symbols 12 and 14 are the same as those in FIG. 2, 31 is a first carbon, 32 is a cation exchange resin, and 33 is a pore. The first layer 12 contains a first carbon 31 and a cation exchange resin 32. As the cation exchange resin 32, for example, a perfluorosulfonic acid resin or a styrene-divinylbenzenesulfonic acid resin can be used. As shown in FIG. 3, the first carbon 31 and the cation exchange resin 32 are mixed together, whereby the first carbon 3
1 and the cation exchange resin 32 are distributed three-dimensionally. Although not shown, fine particles of catalyst metal are supported on the surface of the first carbon 31. Furthermore, a plurality of pores 33 are formed in the mixture. In the first layer 12, the first carbon 31, the cation exchange resin 32, and the pores 33 form an electron conduction path, a proton conduction path, and a movement path between the reactant and water, respectively. Since these three paths are three-dimensionally formed in the first layer 12, the reaction interface where reactants, protons (H ⁺ ) and electrons (e ⁻ ) exist increases. In the fuel cell electrode, the first layer 12 is bonded to the polymer electrolyte membrane 14.

  The catalyst metal of the first layer 12 described above is supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. FIG. 4 schematically shows the vicinity of the surface of the first carbon. In FIG. 4, symbols 31 and 32 are the same as those in FIG. 3, 41 is a hydrophilic region (proton conduction path), 42 is a hydrophobic region, and 43 is a catalyst metal.

  In the first layer, the surface of the first carbon 31 is covered with a cation exchange resin 32. The cation exchange resin 32 includes a hydrophilic region (proton conduction path) 41 and a hydrophobic region 42. A catalytic metal 43 is supported on the contact surface between the hydrophilic region (proton conduction path) 41 and the surface of the carbon 31.

  By the way, cation exchange resins such as perfluorosulfonic acid resin are H.264. L. As described in the report of Yeager et al. (J. Electrochem. Soc., 128, 1880, (1981)) and Kokumi et al. (J. Electrochem. Soc., 132, 2601 (1985)), the main chain is assembled. It is known that the structure is microphase-separated into a hydrophobic region and a hydrophilic region in which side chains are assembled. Since the hydrophobic region is a structure similar to polytetrafluoroethylene, there is significantly less permeation of reactants and water. On the other hand, in the hydrophilic region, the ion exchange group bonded to the tip of the side chain forms a cluster, and when water is taken into the cluster, the counter ion becomes movable. That is, water, protons and reactants (hydrogen or oxygen) can move through the hydrophilic region.

  Therefore, since the catalytic metal 43 supported on the contact surface between the proton conduction path 41 of the cation exchange resin 32 and the surface of the carbon 31 can form a reaction interface, it is active against an electrochemical reaction. . On the contrary, the catalytic metal present on the surface of the hydrophobic region 42 of the cation exchange resin 32 and the carbon 31 does not supply reactants and protons, so that it is active for electrochemical reaction. Conversely, the catalytic metal present on the surface of the hydrophobic region 42 of the cation exchange resin 32 and the first carbon 31 is inert to the electrochemical reaction because the reactant and proton are not supplied. .

  The conductive second layer 13 provided in the fuel cell electrode according to the present invention is made of fluororesin and second carbon. The internal structure of the second layer 13 is schematically shown in FIG. In FIG. 5, symbols 12 and 13 indicate the same as in FIG. 1, 51 is second carbon, 52 is a fluororesin, and 53 is a gap.

  In the mixture contained in the second layer 13, the second carbon 51 is bound by the fluororesin 52. A gap 53 is formed between the aggregates of the second carbons 51. As the second carbon 51, powders such as carbon black and acetylene black having high electron conductivity, or electron conductive carbon fibers can be used.

  On the other hand, since the fluororesin 52 is chemically stable, it is suitable for use in the vicinity of the electrode of the fuel cell. For example, polytetrafluoroethylene is preferably used as the resin. Alternatively, polyhexafluoropropyleneylene, polyvinylidene fluoride, a copolymer of tetrafluoroethylene and hexafluoropropyleneylene, and a mixture of the aforementioned fluororesins can be used. Further, the size and occupancy ratio of the voids 53 can be controlled by a method using a pore forming agent or the like.

  A cation exchange resin such as perfluorosulfonic acid resin or styrene-divinylbenzenesulfonic acid resin can be used for the polymer electrolyte membrane of the polymer electrolyte fuel cell having the fuel cell electrode of the present invention. Furthermore, the conductive porous body of the polymer electrolyte fuel cell may be an electron conductive material such as carbon paper or carbon felt, and a porous electrode support layer may be used.

  The electrode for a fuel cell of the present invention comprises a first step of preparing a mixture containing a cation exchange resin and first carbon and then forming a layer containing the mixture, and a cation contained in the layer. The catalyst metal is converted into a cation exchange resin through a second step of adsorbing the cation of the catalyst metal on the counter ion of the exchange resin and a third step of chemically reducing the cation of the catalyst metal. After forming a first layer including the one supported on the contact surface between the proton conduction path and the carbon particle surface and preparing a mixture containing the fluororesin and the second carbon, a second layer comprising this mixture is prepared. It is manufactured through a fourth step of forming a layer and a fifth step of integrating the first layer and the second layer.

  In the first step described above, for example, a paste-like dispersion is prepared by adding a carbon powder such as carbon black to a solution of a cation exchange resin and then mixing them. The dispersion is applied to a substrate and then dried to prepare a sheet-like mixture containing a cation exchange resin and carbon.

  As the cation exchange resin, for example, a perfluorocarbon sulfonic acid type or a styrene-divinylbenzene sulfonic acid type cation exchange resin can be used. What mixed water and alcohol in arbitrary ratios can be used for the solvent of the solution containing a cation exchange resin. The viscosity of the dispersion varies depending on the amount of solvent in the cation exchange resin. Accordingly, dispersions having various viscosities can be prepared by selecting the concentration of the cation exchange resin. For example, when the concentration of the cation exchange resin is high, the viscosity of the dispersion increases. Furthermore, the viscosity can be increased by removing the solvent from the low viscosity dispersion. A polymer sheet, a metal foil, or the like can be used as a substrate on which the dispersion is applied.

  In the second step, a solution is prepared by dissolving a compound containing a catalyst metal cation in water or water containing an alcohol. The solution contains a catalytic metal cation. Next, the cation of the metal element which becomes a catalyst metal is adsorbed to the cation exchange resin contained in the sheet by immersing the sheet-like mixture produced in the first step in the solution. This adsorption is due to an ion exchange reaction between the counter ion of the cation exchange resin and the cation. At that time, by using two or more types of cations to be ion-exchanged, two or more types of catalytic metal cations can be adsorbed to the mixture.

Cations are difficult to adsorb on the exposed carbon surface without being coated with the cation exchange resin, and are preferentially placed on the proton conduction path of the cation exchange resin by an ion exchange reaction with the counter ion of the cation exchange resin. What adsorbs is preferred. As a cation containing a platinum group metal having such an adsorption characteristic, platinum that can be expressed as a complex ion of a platinum group metal, particularly [Pt (NH ₃ ) ₄ ] ²⁺ or [Pt (NH ₃ ) ₆ ] ⁴⁺ Or [Ru (NH ₃ ) ₆ ] ₂₊ or [Ru (NH ₃ ) ₆ ] ³⁺ is preferable. In addition to the ammine complex, a platinum group metal complex ion coordinated with a nitrate group or a nitroso group can be used.

  In the third step, the cation contained in the sheet-like mixture obtained in the second step is chemically reduced. In this third step, it is preferable to use a chemical reduction method using a reducing agent suitable for mass production. In particular, a gas phase reduction method using hydrogen gas or a gas containing hydrogen or an inert gas containing hydrazine is used. A method of phase reduction is preferred. Here, the gas containing hydrogen gas is preferably a mixed gas of hydrogen gas and an inert gas such as nitrogen, helium, or argon, and preferably contains 10 vol% or more of hydrogen gas.

In this third step, since carbon has activity as a catalyst for the reduction reaction of the cation of the platinum group metal, the cation contained in the cation exchange resin can be reduced even at a temperature of 200 ° C. or lower. Can do. For example, the reduction temperature of platinum ammine complex ion [Pt (NH ₃ ) ₄ ] ²⁺ adsorbed in a perfluorocarbon sulfonic acid type cation exchange resin membrane with hydrogen is about 300 ° C. (Tetsuo Sakai, Osaka Industrial Technology Laboratory quarterly report, 36, 10 (1985)), but that of [Pt (NH ₃ ) ₄ ] ²⁺ adsorbed on the surface of carbon particles (Denka Black, Vulcan XC-72, Black Peal 2000, etc.) modified with an exchange group is 180 ° C. (K. Amine, M. Mizuhata, K. Oguro, H. Takenaka, J. Chem. Soc. Faraday Trans., 91, 4451 (1995)). Due to this activity, cations near the surface of the carbon are preferentially reduced to the catalytic metal, and a catalytic metal is generated on the surface of the carbon. Since the catalytic metal has a catalytic activity for the cation reduction reaction, the cations in the cation exchange resin are successively reduced to the catalytic metal. In this third step, the particle size and surface properties of the catalytic metal produced on the carbon surface can be controlled by adjusting the type of reducing agent, reducing agent concentration, reducing pressure, reducing time, and reducing temperature in a timely manner. it can.

  An example of the first to third steps will be described below. First, after preparing a dispersion from Vulcan XC-72 as carbon and a Nafion solution as a cation exchange resin solution, the dispersion is applied to a polymer sheet and dried to produce a sheet-like mixture.

Subsequently, after preparing an aqueous solution of [Pt (NH ₃ ) ₄ ] Cl ₂ as a compound containing a catalyst metal cation, the mixture is immersed in the solution. By this solution, the complex ion and the counter ion (H ⁺ ) of the cation exchange resin undergo an ion exchange reaction, so that [Pt (NH ₃ ) ₄ ] ²⁺ is adsorbed on the proton conduction path of the cation exchange resin. Subsequently, the mixture is reduced in a hydrogen gas atmosphere at 180 ° C. for 6 hours to selectively form platinum as a catalyst metal on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. . This production method makes it possible to produce a fuel cell electrode in which the amount of catalyst metal supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon particles exceeds 80 wt% of the total amount of catalyst metal supported.
In the fourth step described above, for example, a fluororesin and a carbon powder such as carbon black are added to a dispersion medium and then mixed to prepare a paste-like dispersion. The dispersion is applied to a substrate and then dried and fired to prepare a sheet-like mixture containing a fluororesin and carbon. Polytetrafluoroethylene is preferably used as the resin, but polyhexafluoropropylene ylene, polyvinylidene fluoride, a copolymer of tetrafluoroethylene and hexafluoropropylene ylene, and a mixture of the aforementioned fluororesins. Can be used. The resin powder or dispersion can be used. As the dispersion medium, water to which a small amount of a surfactant is added can be used. Further, by adding a thickener to the mixture of fluororesin, carbon and dispersion medium, a paste-like mixture having excellent coatability can be obtained. As the thickener, for example, a cellulose compound such as carboxymethylcellulose can be used. By baking the mixture at a temperature of 350 ° C. or higher, the thickener or surfactant can be removed. By removing them, voids are formed in the conductive layer.

  In the fifth step described above, for example, the catalytic metal is selectively supported on the contact surface between the proton conduction path of the cation exchange resin and the surface of the first carbon on at least one surface of the polymer electrolyte membrane. After joining the first layer, the first layer is composed of the first layer and the second layer by joining a conductive second layer made of a mixture of fluororesin and second carbon to the first layer. The fuel cell electrode of the present invention is formed on a polymer electrolyte membrane.

  For the polymer electrolyte membrane, for example, a proton conductive cation exchange resin such as perfluorocarbon sulfonic acid resin, styrene-vinylbenzene sulfonic acid resin, perfluorocarbon carboxylic acid resin, styrene-vinyl benzene carboxylic acid resin may be used. However, it is preferable to use a perfluorocarbon sulfonic acid resin having high chemical stability and high proton conductivity. For example, a DuPont Nafion membrane can be used as the polymer electrolyte membrane.

  Joining in this step can be performed by thermocompression bonding. The heating temperature is preferably 125 ° C. to 135 ° C., which is close to the glass transition temperature of the cation exchange resin. However, if the heating temperature is 0 ° C. or higher where freezing of water starts, the fuel cell electrode and polymer of the present invention can be used. The electrolyte membrane can be joined. A flat press or a roll press can be used for the thermocompression bonding.

  Further, the first layer including a catalyst metal supported on the contact surface between the proton conduction path of the cation exchange resin and the surface of the first carbon has a conductive first layer made of the fluororesin and the second carbon. By joining the two layers, the fuel cell electrode of the present invention comprising the first layer and the second layer can be produced.

  From the research results, it has been clarified that the characteristics of the fuel cell including the fuel cell electrode of the present invention are superior to those of the conventional case including the electrode. For example, a conventional electrode is prepared by preparing a mixture of carbon supporting a platinum as a catalyst and a cation exchange resin, and then applying the mixture to a polymer sheet and drying it, and then joining the polymer electrolyte membrane. It is manufactured by. However, since the utilization rate of platinum is low in the conventional electrode, a large amount of platinum is required.

  The reason for the decrease in platinum utilization will be described next. FIG. 6 shows a schematic diagram of the interface between the cation exchange resin and the surface of carbon carrying the catalyst metal in the conventional electrode. In FIG. 6, 31 is the first carbon, 32 is a cation exchange resin, 41 is a hydrophilic region (proton conduction path), 42 is a hydrophobic region, 43 and 61 are catalytic metals, and 62 is no catalytic metal particles. It is an area.

  In FIG. 6, the surface of the first carbon 31 is covered with a cation exchange resin 32. The cation exchange resin 32 includes a hydrophilic region (proton conduction path) 41 and a hydrophobic region 42. Catalytic metals 43 and 61 are randomly supported on the interface between the surface of the first carbon 31 and the cation exchange resin 32.

  Since the catalytic metal particles 43 are present on the contact surface between the surface of the first carbon 31 and the hydrophilic region (proton conduction path) 41, the catalytic metal particles 43 are active against an electrochemical reaction. On the other hand, since the catalyst metal 61 exists on the contact surface between the surface of the first carbon 31 and the hydrophobic region 42, the catalyst metal 61 is inactive to the electrochemical reaction. Therefore, the conventional electrode in which the catalyst metal 61 exists has a low utilization rate of the catalyst metal.

  Further, in the conventional electrode, a region 62 where no catalytic metal exists is partially formed at the interface between the surface of the first carbon 31 and the hydrophilic region (proton conduction path) 41. Since no reaction interface is formed in this region 62, the presence of this region 62 reduces the electrochemical activity of the conventional electrode.

  The present invention will be described below with reference to preferred embodiments.

[Example 1]
The fuel cell electrode of the present invention was manufactured by the following method. First, 80 g of a cation exchange resin solution (manufactured by Aldrich, Nafion 5 mass% solution) was collected in a container. After adding 6 g of Vulcan XC-72 (manufactured by Cabot Corp.) as the first carbon to the solution, a dispersion was prepared by stirring for 1 hour while irradiating ultrasonic waves using a wing stirrer. . Next, after the container was placed in a constant temperature water bath at 50 ° C., the dispersion was stirred with a wing stirrer. At this time, since the solvent of the dispersion evaporates, the dispersion is concentrated. By this concentration, the weight of the solid content relative to the weight of the dispersion (the sum of carbon and the solid content of the cation exchange resin) was adjusted to 14%.

  Subsequently, the dispersion was applied to a polymer (FEP) film using an applicator having a gap of 200 μm, and then dried at room temperature to prepare a sheet-like mixture. The thickness of the mixture was about 20 μm.

Meanwhile, an aqueous solution of [Pt (NH ₃ ) ₄ ] Cl ₂ having a concentration of 50 mmol / l was prepared. [Pt (NH ₃ ) ₄ ] ²⁺ was adsorbed on the proton conduction path of the cation exchange resin in the mixture by immersing the sheet-like mixture in the aqueous solution for 6 hours or more. Thereafter, the sheet-like mixture was sufficiently washed with deionized water and then sufficiently dried.

Subsequently, after the mixture was placed in a reducer, it was charged with 1 atmosphere of hydrogen. The reducer was maintained at 180 ° C. for 12 hours. Thereafter, the mixture taken out from the reducer was immersed in 0.5 mol / l sulfuric acid for 1 hour to elute the [Pt (NH ₃ ) ₄ ] ²⁺ that was not reduced in the reduction step, and then the mixture Was sufficiently washed with deionized water to obtain a first layer in which a catalytic metal was supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. Finally, the first layer was cut into a size of 5 cm × 5 cm. On the first layer on which the catalyst metal was selectively supported, 0.05 mg / cm ² of platinum as the catalyst metal was supported.

  Next, the electroconductive 2nd layer which comprises the electrode for fuel cells of this invention was manufactured with the following method. 8 g of Vulcan XC-72 (manufactured by Cabot) as the second carbon and 3 g of carboxymethyl cellulose (manufactured by Daicel Chemical Industries, Ltd.) as the thickener were mixed using a blender. After adding 140 g of deionized water to the mixture, the mixture was stirred for 5 minutes using a biaxial rotating stirrer. Next, 3 g of polytetrafluoroethylene dispersion (solid content: 60 mass%) was gradually added to the mixture while stirring with a wing stirrer, and then stirred for 5 minutes. Subsequently, the mixture was applied to an aluminum foil using an applicator with a gap of 250 μm, and then dried at room temperature. Furthermore, the electroconductive 2nd layer which comprises the electrode for fuel cells of this invention which is 25 micrometers in thickness was obtained by baking the coating material for 30 minutes at 380 degreeC using a nitrogen atmosphere furnace. Finally, the conductive second layer was cut into a size of 5 cm × 5 cm.

Next, after boiling the polymer electrolyte membrane (DuPont Nafion 115 membrane, film thickness of about 120 μm) with 0.5 mol / l sulfuric acid for 1 hour, the polymer electrolyte membrane is washed with deionized water five times. And boiled for 1 hour. Subsequently, after placing the first layer carrying the catalyst metal produced by the above-described method on both sides of the polymer electrolyte membrane, the polymer electrolyte membrane is subjected to thermocompression bonding (135 ° C., 50 kg / cm ² ). And the first layer were joined together. Thereafter, the polymer (FEP) film was peeled off from the first layer of the joined body.

Furthermore, after disposing a conductive second layer on each surface of the first layer, the first layer joined to the polymer electrolyte membrane by thermocompression bonding (100 ° C., 50 kg / cm ² ) The conductive second layer was integrally bonded. Thereafter, the aluminum foil was peeled off from the second layer of the joined body. In this way, a membrane / electrode assembly provided with the fuel cell electrode of the present invention was produced.

  Finally, a conductive porous carbon paper imparted with water repellency is disposed on each surface of the membrane / electrode assembly, and then sandwiched by a pair of separators, thereby allowing the fuel cell electrode of the present invention to A fuel cell provided (hereinafter, this fuel cell will be referred to as the fuel cell of the present invention) was manufactured.

[Comparative Example 1]
For comparison, a fuel cell having a conventional electrode was manufactured by the following method. First, 80 g of a cation exchange resin solution (manufactured by Aldrich, Nafion 5 mass% solution) was collected in a container. After adding 14 g of carbon catalyst (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., TEC10V50E) supported by 50 mass% of platinum to the solution, the dispersion was stirred for 1 hour while irradiating ultrasonic waves using a wing stirrer Prepared. Next, after the container was placed in a constant temperature water bath at 50 ° C., the dispersion was further stirred with a wing stirrer. At this time, since the solvent of the dispersion evaporates, the dispersion is concentrated. By this concentration, the weight of the solid content relative to the weight of the dispersion (the sum of carbon and the solid content of the cation exchange resin) was adjusted to 14%. Subsequently, the dispersion was applied to a polymer (FEP) film using an applicator having a gap of 200 μm, and then dried at room temperature, thereby producing a conventional electrode. Finally, the electrode was cut into a size of 5 cm × 5 cm. The thickness of the obtained conventional electrode was about 20 μm, and the supported amount of platinum was 0.5 mg / cm ² .

Next, after boiling the polymer electrolyte membrane (DuPont Nafion 115 membrane, film thickness of about 120 μm) with 0.5 mol / l sulfuric acid for 1 hour, the polymer electrolyte membrane is washed with deionized water five times. And boiled for 1 hour. Subsequently, the polymer electrolyte membrane and the conventional electrode are formed by placing the conventional electrode manufactured by the above-described method on each surface of the polymer electrolyte membrane and then heat-pressing (135 ° C., 50 kg / cm ² ). Were joined together. Thereafter, the polymer (FEP) film was peeled off from the conventional electrode of the joined body. In this way, a membrane / electrode assembly provided with a conventional electrode was manufactured.

  Finally, a carbon cell, which is a conductive porous body imparted with water repellency, is disposed on each surface of the membrane / electrode assembly, and then sandwiched between a pair of separators, thereby providing a fuel cell having a conventional electrode (Hereinafter, this fuel cell will be referred to as the fuel cell of Comparative Example 1).

[Comparative Example 2]
For comparison, a fuel cell was manufactured by the method described below, in which the catalyst metal was provided with only the first layer supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface as an electrode. First, the first layer was manufactured in the same procedure as in Example 1. Next, the first layer cut into a size of 5 cm × 5 cm was used as an electrode. This electrode supported 0.05 mg / cm ² of platinum as a catalyst metal.

Subsequently, after placing the electrode of Comparative Example 2 on each surface of the polymer electrolyte membrane (DuPont, Nafion 115 membrane, film thickness of about 120 μm) pretreated by the same procedure as in Example 1. The membrane and the electrode were integrally joined by thermocompression bonding (135 ° C., 50 kg / cm ² ). Thereafter, the polymer (FEP) film was peeled off from the first layer of the joined body. In this way, a membrane / electrode assembly including the electrode of Comparative Example 2 was produced.

  Finally, a conductive porous carbon paper imparted with water repellency is disposed on each surface of the membrane / electrode assembly, and then sandwiched between a pair of separators, thereby providing a fuel cell (hereinafter referred to as a fuel cell) equipped with the electrode. This fuel cell will be referred to as the fuel cell of Comparative Example 2).

  FIG. 7 shows the results of evaluating the voltage-current characteristics of the fuel cell of the present invention, the fuel cell of Comparative Example 1, and the fuel cell of Comparative Example 2. The conditions for this evaluation were as follows: the cell temperature was 80 ° C., the anode gas was pure hydrogen, the anode utilization rate was 80%, the anode humidification temperature was 80 ° C., the cathode gas was air, the cathode utilization rate was 40%, and the cathode humidification temperature was 80 ° C. did. In FIG. 8, curve A shows the voltage-current characteristic of the fuel cell of the present invention, curve C shows the voltage-current characteristic of the fuel cell of Comparative Example 1, and curve B shows the voltage-current characteristic of the fuel cell of Comparative Example 2.

  FIG. 7 shows that the voltage-current characteristics of the fuel cell of Comparative Example 2 are excellent even though the amount of platinum used in the fuel cell of Comparative Example 2 is about 1/10 that of Comparative Example 1. As a result, in the electrode provided in the fuel cell of Comparative Example 2, the catalytic metal is selectively supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface. This is probably due to the dramatic improvement in utilization.

  Furthermore, although the amount of platinum used in the fuel cell of the present invention is similar to that in Comparative Example 2, it can be seen that the cell voltage was improved in the fuel cell of the present invention. This improvement is achieved by an electrode in which the catalytic metal is selectively supported on the contact surface between the proton conduction path of the cation exchange resin and the carbon surface by the conductive second layer having appropriate water repellency and porosity. Since the water-containing state was maintained in a good state, it is considered that the catalyst metal was improved in activity for electrochemical reaction.

  FIG. 8 shows the relationship between the cell voltage of the fuel cell of the present invention and the fuel cell of Comparative Example 2 and the cathode humidification temperature. The measurement conditions of this relationship are as follows: the cell temperature is 80 ° C., the anode gas is pure hydrogen, the anode utilization is 80%, the anode humidification temperature is 80 ° C., the cathode gas is air, the cathode utilization is 40%, and the cathode humidification temperature is 55. The temperature was varied between 0 ° C and 95 ° C. In FIG. 8, curve D shows the relationship between the cell voltage of the fuel cell of the present invention and the cathode humidification temperature, and curve E shows the relationship between the cell voltage of the fuel cell of Comparative Example 2 and the cathode humidification temperature.

  From FIG. 8, the cell voltage of the fuel cell of Comparative Example 2 significantly decreases as the cathode humidification temperature becomes lower than the cell temperature. Conversely, the fuel cell of the present invention has a higher cell voltage than that of Comparative Example 2. However, it can be seen that a high cell voltage can be maintained even when the humidified state of the cathode gas is low. This result shows that in the fuel cell of the present invention, the reduction in the cell voltage due to the decrease in the water content of the cathode gas is suppressed.

  The suppression of the cell voltage reduction is achieved by the conductive second layer having appropriate water repellency and porosity, so that the catalytic metal is selectively brought into contact with the proton conduction path of the cation exchange resin and the carbon surface. This is probably due to the fact that drying of the supported electrode is prevented. In other words, since a layer having a water retention function is disposed between the electrode and the gap of the conductive porous body through which the cathode gas flows, the dried cathode gas is prevented from directly contacting the electrode. The This prevention seems to suppress the excessive drying of the electrode. Furthermore, because of the suppression effect, the water content of the electrode was maintained in a good state, so that the activity of the catalytic metal against the electrochemical reaction was improved, and the cell voltage was high even with a low humidified cathode gas. This is considered to be a cause.

The schematic diagram of the cross section of the electrode for fuel cells of this invention. The schematic diagram of the cross section of a fuel cell provided with the electrode for fuel cells of this invention. The schematic diagram of the internal structure of a 1st layer. The schematic diagram of the surface vicinity of the carbon by which the catalyst metal of the 1st layer was carry | supported by the contact surface of the proton conduction path | route of cation exchange resin, and the carbon surface. The schematic diagram of the internal structure of a 2nd layer. The schematic diagram of the interface of the carbon which carry | supported the cation exchange resin and the catalyst metal in the conventional electrode. The figure which showed the voltage-current characteristic of the fuel cell provided with the electrode for fuel cells of this invention, the fuel cell of the comparative example 1, and the fuel cell of the comparative example 2. FIG. The figure which showed the relationship between the cell voltage of the fuel cell provided with the electrode for fuel cells of this invention, and the fuel cell of the comparative example 2, and cathode humidification temperature.

Explanation of symbols

11 Electrode for Fuel Cell of the Present Invention 12 First Layer 13 Second Layer 14 Cation Exchange Membrane 15 Conductive Porous Body Provided with Water Repellency 31 First Carbon 32 Cation Exchange Resin 33 Pore 41 Cation Exchange Resin Hydrophilic region (proton conduction pathway)
42 Hydrophobic region of cation exchange resin 43, 61 Catalytic metal 51 Second carbon 52 Fluoro resin 53 Void 62 Region where catalyst metal particles do not exist

Claims (2)

A first layer containing a cation exchange resin, a first carbon, and a catalyst metal; and a second layer made of a fluororesin and a second carbon, wherein the catalyst metal contained in the first layer is a cation An electrode for a fuel cell, which is supported on a contact surface between the proton conduction path of the exchange resin and the surface of the first carbon. A first step of forming a layer containing a cation exchange resin and a first carbon; a second step of adsorbing a cation of a catalyst metal to a counter ion of the cation exchange resin; A fourth step of forming a second layer composed of a fluororesin and a second carbon after forming the first layer through a third step of chemically reducing ions; and the first layer; The method for producing a fuel cell electrode according to claim 1, wherein a fifth step of integrating the second layer is performed.

Images