JP2007141776A - Method of manufacturing electrode for fuel direct type fuel cell, electrode for fuel direct type fuel cell obtained by method, fuel direct type fuel cell, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for a fuel direct type fuel cell, which can obtain a high catalyst utilization factor and therefore can obtain the characteristics of higher output power using a smaller amount of catalyst, and to provide a method of manufacturing the electrode for the fuel direct type fuel cell. <P>SOLUTION: The method of manufacturing the electrode for the fuel direct type fuel cell comprises: a first process for producing a catalyst layer precursor by mixing a proton conducting material and an electron conducting material; a second process for making the catalyst layer precursor adsorb a solution of a catalyst active material precursor; and a third process for electrochemically reducing the catalyst active material precursor adsorbed in the catalyst layer precursor, which is obtained in the second process, in order to electrolytically deposit the catalyst active material on the electron conducting material in the catalyst layer precursor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a direct fuel cell electrode manufacturing method using methanol, ethanol, dimethyl ether or the like as a fuel, and a direct fuel cell electrode obtainable by the manufacturing method.

  In recent years, attention has been focused on direct fuel cells using methanol, ethanol, dimethyl ether or the like as fuel. This is mainly because the energy density of these liquid fuels is high and effective in constructing a power supply for a long time.

  Among these direct fuel cells, for example, a polymer electrolyte fuel cell is provided with a fuel electrode (anode electrode) on one surface of a polymer solid electrolyte membrane and an air electrode (cathode electrode) on the other surface. The membrane-electrode assembly is a basic structure. This electrode is usually composed of a catalyst layer and a gas diffusion layer, and the catalyst layer is in contact with the electrolyte membrane. In the fuel cell having such a structure, the reaction mechanism is that when fuel (such as methanol) is supplied to the fuel electrode and oxidant (such as air) is supplied to the air electrode, hydrogen ions generated at the fuel electrode are converted into electrolytes. The electric energy is taken out using an electrochemical reaction that moves to the air electrode through the air and becomes water at the air electrode.

Such an electrode reaction of the fuel cell proceeds on the electrode catalyst. For example, the electrode reaction in the case of a methanol-oxygen fuel cell is as follows.
Positive electrode) 3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O
Negative electrode) CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
As is apparent from these equations, the reaction of each electrode can proceed only at a three-phase interface that can contact with reactants such as methanol and oxygen and can exchange electrons and protons. Therefore, in order for the catalytically active material to function as a reaction field, it is necessary for the catalytically active material to contact both the electron conductive material and the proton conductive material.

  As a conventional method for producing a fuel cell electrode having such a function, a catalytically active material such as platinum (Pt) is usually supported on a carrier of an electron conductive material such as carbon black, and the catalyst is supported. A carrier and a proton conductive material such as a polymer solid electrolyte are mixed to form a layer of the mixture on the surface of the gas diffusion layer and the electrolyte membrane so that a layer structure of electrolyte membrane / catalyst layer / gas diffusion layer is obtained. The procedure of joining to is common. That is, the manufacturing process proceeds by a procedure in which a catalytically active substance is first supported on an electron conductive substance and then mixed with a proton conductive substance.

  The catalyst layer formed by the method for manufacturing a fuel cell electrode as described above is not packed closely with a catalyst-supporting carrier and a proton-conducting substance, but is a pore that becomes a passage for reactants such as methanol and oxygen. is required. In order to form such pores, there is a suitable range for the mixing ratio of the catalyst-supporting support and the proton-conducting substance, and within this preferable mixing ratio range, all the catalyst-supporting support surfaces are placed on the proton-conducting substance. It is difficult to cover with.

  However, since the catalytically active substance is uniformly supported on the surface of the support, there may be a catalytically active substance that does not come into contact with the proton conductive substance. In addition, even when the catalytically active substance is in contact with the proton conductive substance, the catalytically active substance and the proton conductive substance are not in contact with the reactant, or the catalyst support carrier itself conducts electrons from the electrode to the terminal. May be isolated from other networks. In any of these cases, such a catalytically active substance cannot function effectively as an electrode catalyst.

  In addition, the particle diameter of carbon particles mainly used as an electron conductive material is as small as 30 nm, and the state of the carbon particles mixed with the proton conductive material is a state in which a carbon aggregate in which dense irregularities are formed is formed. Become. Therefore, liquid fuel such as methanol or ethanol cannot penetrate into the catalytically active material located in the deep part of the carbon particle aggregate, and the catalytically active substance located in the deep part cannot participate in the electrode reaction.

  Due to these factors, the actual catalyst utilization rate of the conventional fuel cell electrode is limited to about 20 to 60%, and the power generation capacity commensurate with the actual usage amount of the catalytically active substance cannot be obtained.

  FIG. 2 shows a cross-sectional structure of the catalyst layer of such a conventional fuel cell electrode. In this figure, carbon particles, which are electron conductive materials carrying catalyst particles, which are catalytically active materials, aggregate to form an aggregate of carbon particles. The catalyst particles that are present on the contact surface between the carbon particles and the solid polymer electrolyte and that can come into contact with a liquid fuel such as methanol or ethanol can efficiently contribute to the electrode reaction. However, since the solid polymer electrolyte, which is a proton conductive substance, does not easily penetrate into the deep part of the concave portion of the carbon particle aggregate, the catalyst particles existing in this deep part cannot contact the solid polymer electrolyte and are effective for electrode reaction. Difficult to function. In addition, the carbon particle aggregate has a portion where the liquid fuel is difficult to permeate, and the catalyst particles located in this portion are difficult to contact the liquid fuel, so that it is difficult to function effectively for the electrode reaction.

  In order to solve such a problem, Patent Document 1 discloses that an electrode precursor including a catalyst layer precursor mixed with an electron conductive material after mixing a precursor of a catalytically active material and a proton conductive material is negatively polarized. A method of manufacturing a fuel cell electrode is disclosed.

FIG. 3 conceptually shows the cross-sectional structure of the catalyst layer of the fuel cell electrode disclosed in Patent Document 1. As shown in FIG. In this electrode catalyst layer, a catalytically active material such as Pt is concentrated on the contact surface between the proton conductive path of the proton conductive material and the electron conductive material, and other than the contact surface, for example, the electron conductive material is in the catalyst layer. It does not exist in the part facing the pores. In the case of the production method disclosed in Patent Document 1, carbon particles, which are electron conductive materials carrying catalyst particles, aggregate to form a carbon particle aggregate. The catalyst particles that are located on the contact surface between the carbon particles and the solid polymer electrolyte and that can come into contact with a liquid fuel such as methanol or ethanol can effectively contribute to the electrode reaction. However, since the liquid fuel is difficult to penetrate into the deep part of the carbon particle aggregate, the catalyst particles that are located on the contact surface between the carbon and the solid polymer electrolyte, but do not easily come into contact with the liquid fuel, work effectively for the electrode reaction. Is difficult. Therefore, the amount of catalytically active material that can be in contact with liquid fuel and can function as a reaction field that can be in contact with both proton conductive material and electron conductive material is limited, and the catalyst utilization rate is optimized. It has not been.
JP 2001-118583 A

  Therefore, an object of the present invention is to provide a novel and useful method for manufacturing a direct fuel cell electrode and a direct fuel cell electrode that can solve the above problems. Another object of the present invention is to provide a power supply system and an electronic device using such a direct fuel cell electrode.

The method for producing a direct fuel cell electrode of the present invention includes a first step of preparing a catalyst layer precursor by mixing a proton conductive material and an electron conductive material, and a catalyst activity in the catalyst layer precursor. A second step of adsorbing a precursor solution of the substance, and a catalytically active material precursor adsorbed on the catalyst layer precursor obtained in the second step is electrochemically reduced, And a third step of electrolytically depositing a catalytically active material on the electron conductive material.
The present invention is also an electrode for a direct fuel cell that can be obtained by the above production method.

Furthermore, this invention is a membrane-electrode assembly provided with the electrode for fuel direct fuel cells obtained using said manufacturing method.
Furthermore, the present invention is also a direct fuel fuel cell comprising the membrane-electrode assembly and an electronic device on which the fuel cell is mounted.

  According to the method for producing an electrode for a direct fuel cell of the present invention, a solution of a precursor of a catalytically active material is adsorbed on a catalyst layer precursor obtained by mixing a proton conductive material and an electron conductive material. Since the precursor of the catalytically active substance adsorbed on the catalyst layer precursor is electrochemically deposited, the catalytically active substance is always formed on the contact surface between the proton conducting path of the proton conducting substance and the electron conducting substance. It will be. On the other hand, no catalytically active material is formed in the deep part of the aggregate of particles of the electron conductive material to which liquid fuel is difficult to be supplied. By these things, it becomes possible to implement | achieve efficiently and simply the electrode for fuel direct shape | mold batteries which can obtain a higher output characteristic with a small catalyst amount with a high catalyst utilization factor.

  Further, according to the method for manufacturing an electrode for a direct fuel cell of the present invention, the catalytically active substance is mainly supported on the contact surface between the proton conducting path of the proton conducting substance and the electron conducting substance. Substantially all catalytically active substances used in the fuel cell electrode can participate in the supply and transmission of electrons and protons, and can function as a reaction field of the fuel cell. This makes it possible to realize an electrode for a direct fuel cell that has a high catalyst utilization rate and can extract a higher output with a smaller amount of catalyst.

  First, the structure of the fuel cell will be described. FIG. 1 is a conceptual diagram showing a single cell structure which is a single component of a general fuel cell. The direct fuel cell electrode obtained by the production method of the present invention can be suitably used in a fuel cell having such a structure. That is, FIG. 1 shows a preferred embodiment of a direct fuel cell using a direct fuel cell electrode obtainable by the direct fuel cell electrode manufacturing method of the present invention.

  Referring to FIG. 1, in a direct fuel cell, a fuel electrode 3 is provided on one surface with an ion exchange membrane 2 interposed, and an air electrode 4 is provided on the other surface. Current collectors (separators) 1a and 1b are disposed on the fuel electrode 3 and the air electrode 4, respectively, and a liquid fuel passage 5 through which liquid fuel such as methanol flows is formed on the fuel electrode 3 side. An oxidant flow path 6 through which an oxidant such as air flows is formed on the air electrode 4 side. This direct fuel cell can be used as a stacked fuel cell by assembling two or more fuel cells into a stack.

  As the above-mentioned ion exchange membrane, any one of anion conduction type and cation conduction type can be used, and a proton conduction type is preferably used. As the ion exchange membrane, all known materials including ion exchange resins represented by perfluoroalkylsulfonic acid polymers can be used. The film thickness is preferably 40 to 200 μm.

  As the fuel electrode 3 and the air electrode 4, an electrode for a direct fuel cell that can be obtained by the production method of the present invention described below can be suitably used. These electrodes are usually composed of an electrode base material provided with a predetermined catalyst layer. As the material for the electrode substrate, an electron conductive porous material is used. The porous material is not particularly limited as long as it has electronic conductivity and does not hinder the diffusion of liquid fuel or oxidant. For example, carbon paper, carbon cloth, or carbon powder is made of a high material such as polytetrafluoroethylene. A porous carbon-based material such as a sheet formed with a molecular binder is preferred. Such a carbon-based material has air permeability and a uniform pore size distribution. Among these, porous carbon paper is particularly preferable.

  As the current collector, it is preferable to use dense graphite that has high current collecting performance and is stable even in an acidic atmosphere.

  In the fuel cell of the present invention, the catalyst layer of the fuel electrode 3 and the air electrode 4 is formed with the ion exchange membrane 2 interposed, or the fuel electrode 3, the air electrode 4 and the ion exchange membrane 2 are joined by hot pressing. The membrane-electrode structure (MEA: Membrane Electrode Assembly) obtained in this way can be used.

As the liquid fuel of the direct fuel cell of the present invention, methanol, ethanol, hydrazine, dimethyl ether and the like can be suitably used. Among these, those using methanol as a fuel are preferable. In this case, the direct fuel cell is called DMFC (Direct Methanol Fuel Cell).
As the oxidant of the direct fuel cell of the present invention, air or oxygen gas is usually used.

The first step in the method for producing an electrode for a direct fuel cell of the present invention is a step of preparing a catalyst layer precursor by mixing a proton conductive material and an electron conductive material.
The proton conductive material is preferably a solid polymer electrolyte usually used in a fuel cell. For example, a copolymer of a trifluoroethylene derivative, a phosphoric acid-containing polybenzimidazole resin, a sulfonic acid group, a phosphonic acid group, a phenol-based material. Examples thereof include resins having a hydroxyl group or a fluorine-containing carbon sulfonic acid group as an ion exchange group, PSSA-PVA (polystyrene sulfonate polyvinyl alcohol copolymer), PSSA-EVOH (polystyrene sulfonate ethylene vinyl alcohol copolymer), and the like. Of these, ion exchange resins such as perfluoroalkylsulfonic acid polymers are preferred.

The above-mentioned electron conductive substance is not particularly limited as long as it is generally used for fuel cell electrodes and can obtain predetermined physical properties. The electron conductive substance is preferably a fine spherical or chain carbon material produced by gas phase pyrolysis or incomplete combustion of natural gas or hydrocarbon gas. As such a carbon material, any carbon black including furnace black, thermal black, acetylene black, ketjen black and the like can be used. Moreover, carbon particles such as activated carbon, activated carbon fiber, multi-walled carbon nanotube, and nanocarbon can be used as the carbon material having the same structure. In addition, as the electron conductive material, metal particles such as gold, silver, platinum, titanium, and niobium, and semiconductor particles such as n-type, p-type, or doped silicon can be used.
The electron conductive material preferably has an average particle size of 10 to 100 nm, more preferably 20 to 30 nm.

  When mixing the proton conductive material with the electron conductive material, it is preferable to dissolve or suspend the proton conductive material as described above in an appropriate solvent from the viewpoint of ease of mixing. The solvent that can be used is not particularly limited as long as it is inactive to the proton conductive material, and examples thereof include water, lower alcohols such as methanol and ethanol, and NN dimethylacetamide.

  When the proton conductive material is dissolved or suspended in a solvent, the electron conductive material can be mixed with the proton conductive material, for example, in the form of dry particles.

After the first step, a catalyst layer precursor obtained by mixing a proton conductive material and an electron conductive material is applied to the ion exchange membrane of the fuel cell and dried to form a membrane-electrode precursor junction. The body can also be pre-formed. The catalyst layer precursor is preferably applied so that the thickness of the catalyst layer precursor on the electrolyte membrane after drying is 10 to 100 μm, preferably 30 to 60 μm.
The drying time and temperature are preferably 40 to 80 ° C. and about 10 to 60 minutes.

The second step in the production method of the present invention is a step of adsorbing a solution of a precursor of a catalytically active substance on the catalyst layer precursor.
A precursor of a catalytically active substance is a compound that can be reduced to become a catalytically active substance. The shape and properties of such a compound are not particularly limited as long as it functions as a catalyst, but those in which catalytic metal particles are generated by reduction are preferably used. When a noble metal such as platinum, ruthenium, rhodium, iridium, palladium, or osmium is used as the catalytically active substance, the precursor of the catalytically active substance is preferably a salt or complex of these noble metals. For example, [Pt (NH ₃ ) ₄ ] Cl ₂ , H ₂ PtCl ₆ , RuCl _{3 and the} like.

  Moreover, when using a metal compound as a precursor of a catalytically active substance, the mixture of 2 or more types of the compound containing a metal may be used, and double salt may be used. For example, by using a mixture of a platinum compound and a ruthenium compound, a platinum-ruthenium alloy is formed as a catalytically active substance by electrolytic reduction in the following third step.

  In the catalyst active substance precursor solution, a solvent inert to the catalyst active substance precursor can be used, and a liquid fuel used for power generation of the fuel cell is preferably used as a solvent. . As the liquid fuel, methanol, ethanol, hydrazine, dimethyl ether and the like can be suitably used. Of these, methanol is preferable.

Examples of the method for adsorbing the catalyst active material precursor to the catalyst layer precursor include a method in which the catalyst layer precursor is immersed in a solution of the catalyst active material precursor. The soaking conditions are preferably 20 to 60 ° C. for about 6 to 24 hours, more preferably 25 to 40 ° C. for about 10 to 12 hours.
The adsorption is preferably performed by ion exchange of a proton conductive substance. For example, when an ion exchange resin of perfluorosulfonic acid polymer is used as the proton conductive material and [Pt (NH ₃ ) ₄ ] Cl ₂ is used as the precursor of the catalytically active material, [Pt (NH ₃ ) ₄ ] ²⁻ It will be adsorbed to the catalyst layer precursor by ion exchange. Due to such adsorption, the precursor of the catalytically active substance can exist on the contact surface between the proton conducting path of the proton conducting substance and the electron conducting substance.

  After the immersion as described above, it is preferable that the catalyst layer precursor on which the precursor of the catalytically active substance is adsorbed is washed to remove an excessive solution of the precursor of the catalytically active substance. The washing is not particularly limited and can be performed at room temperature using purified water.

  When the membrane-electrode precursor assembly is not formed after the first step, the catalyst layer precursor that has adsorbed the precursor of the catalytically active material is used as the ion exchange membrane of the fuel cell after the cleaning. The membrane-electrode precursor assembly can also be formed by applying it on the substrate and drying it.

  In the third step of the production method of the present invention, the precursor of the catalytically active material adsorbed on the catalyst layer precursor obtained in the second step is electrochemically reduced, and electron conduction in the catalyst layer precursor is performed. In this step, the catalytically active substance is electrolytically deposited on the active substance.

  The conditions for electrolytic deposition of the catalytically active substance are to maintain the electrode potential at a sufficiently low potential, and at least lower than the oxidation potential of the catalyst component metal (zero valent) to be deposited. . Preferably, it is maintained at a base potential of 500 mV or more from the oxidation potential of the catalyst component metal (zero valence).

  The electrolytic deposition step is performed after the catalyst layer precursor containing the precursor of the catalytically active substance is in the form of a membrane-electrode precursor assembly joined to the ion exchange membrane of the fuel cell. preferable.

A preferred embodiment of the production method of the present invention will be described below.
Liquid fuel for a fuel cell using a membrane-electrode precursor assembly comprising a catalyst layer precursor formed from a mixture of a solid polymer electrolyte as a proton conductive material and carbon particles as an electron conductive material The precursor of the catalytically active substance such as Pt dissolved in the solution is immersed in the precursor and the precursor of the catalytically active substance is formed by adsorption by ion exchange of the proton conductive substance to form a membrane-electrode precursor assembly. And contained in the solid polymer electrolyte in the catalyst layer precursor. Then, the membrane-electrode precursor assembly including the catalyst layer precursor is electrolytically reduced, so that a catalytically active substance (such as Pt) is precipitated from the catalytically active substance precursor contained in the proton conductive substance. The The deposited catalytically active substance (Pt or the like) is electrolytically deposited on the contact surface between the proton conducting path of the proton conducting substance and the electron conducting substance. These catalytically active substances are not electrolytically deposited at a site where the liquid fuel in the deep part of the carbon particle aggregate is difficult to be supplied. This is because by using the liquid fuel to be used as a solvent for the precursor solution of the catalytically active material, the catalytically active material precursor is not adsorbed in the proton conductive material at the site where the liquid fuel is difficult to be supplied.

  In the direct fuel cell electrode that can be obtained by the production method of the present invention, the catalytically active substance is mainly interposed in the contact surface between the proton conducting path of the proton conducting substance and the electron conducting substance. Thus, an electrode having an excellent catalyst utilization rate can be obtained. Therefore, the direct fuel cell electrode obtained by the above manufacturing method is also one aspect of the present invention.

The direct fuel cell electrode of the present invention that can be obtained by the above production method comprises a proton conductive material, an electron conductive material, and a catalytically active material.
As the catalytically active substance used in the direct fuel cell electrode of the present invention, a metal having high fuel oxidation ability and oxygen reduction ability is preferably used, and noble metals such as platinum, ruthenium, rhodium, iridium, palladium, osmium and the like Two or more of these alloys are more preferred.

  FIG. 4 shows an example of a cross-sectional view of the catalyst layer of a preferred embodiment of the electrode for a direct fuel cell of the present invention. In this electrode catalyst layer, a catalytically active substance such as Pt is concentrated on the contact surface between the proton conducting path of the proton conducting substance and the electron conducting substance. For example, in the part of the catalyst layer facing the pores, etc. Virtually nonexistent. Furthermore, it does not exist in the deep part of the particle aggregate of the electron conductive material to which liquid fuel such as methanol or ethanol is difficult to be supplied. Therefore, the catalytically active substance in the fuel cell electrode catalyst layer of the present invention can function as a 100% reaction field.

A membrane-electrode assembly can be obtained by joining the direct fuel cell electrode obtained by the above production method to the ion exchange membrane of the fuel cell. Such a membrane-electrode assembly is also one aspect of the present invention.
For joining the electrode for a direct fuel cell of the present invention and the ion exchange membrane, a method used for joining an electrode and a membrane of a normal fuel cell can be used.

As described above, the membrane-electrode assembly can be accommodated in a fuel cell container together with a current collector, liquid fuel, gas, and the like to obtain a direct fuel cell.
The size of the fuel cell container is usually about 40 to 200 mm in length, 40 to 200 mm in width, and about 5 to 50 mm in height.

  Furthermore, the fuel direct fuel cell can be suitably used for small electronic devices such as mobile devices such as mobile phones, electronic notebooks, and notebook computers.

The present invention will be described in more detail with reference to the following examples. However, these examples are for explaining the present invention in detail, and the present invention is not limited to these examples.
Example 1
An alcohol solution of Nafion (registered trademark, manufactured by DuPont), which is an ion exchange resin of a perfluorosulfonic acid polymer as a proton conductive substance, was measured as a polymer weight of 300 mg, and the electronic conductivity was measured. The material was mixed well with 250 mg of dried carbon black (average particle size 30 nm, manufactured by Cabot) to form a paste. This paste was uniformly applied to the surface of a carbon paper (or carbon cloth) diffusion layer as an electrode substrate having a size of 2.25 cm × 2.25 cm by screen printing, and dried at 60 ° C. for 15 minutes with a dryer. .

Next, two pieces of carbon paper coated with the mixture of carbon black and ion exchange resin are bonded to both sides of a Nafion (registered trademark) 117 membrane (manufactured by DuPont) as an ion exchange membrane of a fuel cell by hot pressing. A membrane-electrode precursor assembly was prepared. The prepared membrane-electrode precursor assembly was immersed overnight in a solution of [Pt (NH ₃ ) ₄ ] Cl ₂ , which is a catalytically active substance precursor, dissolved in methanol as a liquid fuel (equivalent to a Pt content of 20 mg). Then, [Pt (NH ₃ ) ₄ ] ²⁺ was adsorbed on the proton conduction path of the proton conducting substance by ion exchange, and then thoroughly washed with purified water. The membrane-electrode precursor assembly thus prepared was accommodated in a fuel cell container (size: 50 mm long, 100 mm wide, 100 mm high) to form a fuel cell single cell.

While flowing N ₂ gas through the bipolar gas flow path of this fuel cell single cell, energization was performed 10 times at −0.5 V (vs Ag / AgCl), 250 mSec between both electrodes, and Pt contained in the bipolar catalyst layer. The fuel was obtained by electrochemically reducing the salt and depositing it on the contact surface between the proton conducting path of the proton conducting substance and the carbon black.
Thereafter, air was supplied to the positive electrode and methanol (1M) was supplied to the negative electrode to generate power, and the relationship between current and voltage was examined.

Comparative Example 1
The same alcohol solution of Nafion (registered trademark) as used in Example 1 was weighed with a polymer weight of 300 mg, and Pt-supported carbon fine particles (average particle diameter) supporting Pt on carbon black so that the weight ratio was 20%. 30 mg (manufactured by Tanaka Kikinzoku Co., Ltd.) 250 mg (carbon equivalent) was mixed well to make a paste. This paste was uniformly applied to the surface of a carbon paper (or carbon cloth) diffusion layer having a size of 2.25 cm × 2.25 cm by screen printing, and dried by a dryer at 60 ° C. for 15 minutes.
Two electrodes were produced by this method, and bonded to both surfaces of the Nafion (registered trademark) 117 film by hot pressing to produce a membrane-electrode assembly. The membrane-electrode assembly was used in the same manner as in Example 1 to obtain a single fuel cell, and air was supplied to the positive electrode and methanol (1M) was supplied to the negative electrode to generate power, and the relationship between current and voltage was examined. .

Example 2
A Nafion (registered trademark) alcohol solution similar to that used in Example 1 was weighed out at a polymer weight of 300 mg and mixed well with 250 mg of carbon black used in Example 1 to obtain a paste. This paste was uniformly applied to the surface of a carbon paper (or carbon cloth) diffusion layer having a size of 2.25 cm × 2.25 cm by screen printing, and dried by a dryer at 60 ° C. for 15 minutes.
Next, two pieces of carbon paper coated with the above-described mixture of carbon black and ion exchange resin were bonded to both surfaces of the Nafion 117 film by hot pressing to prepare a membrane-electrode precursor assembly. The prepared membrane-electrode precursor assembly was immersed in a methanol solution of H ₂ PtCl ₆ (corresponding to Pt content of 13.5 mg) and RuCl ₃ (corresponding to Ru content of 6.5 mg) overnight, and washed thoroughly with purified water. Thus, the produced membrane-electrode precursor assembly was accommodated in the fuel cell container similar to Example 1, and the fuel cell single cell was formed.

While flowing N ₂ gas through the bipolar gas flow path of this single cell of the fuel cell, -1.0 V (vs Ag / AgCl), 250 mSec, energized 10 times to the negative electrode, -0.5 V (vs Ag / AgCl) to the positive electrode , 250 mSec, energized 10 times, electrochemically reduced Pt salt and Ru ions contained in the bipolar catalyst layer and deposited on the contact surface between the proton conducting path of the proton conducting material and the carbon black. A battery was obtained (by changing the applied voltage of each of the positive electrode and the negative electrode, Pt was selectively deposited on the positive electrode side and PtRu was selectively deposited on the negative electrode).

  Thereafter, air was supplied to the positive electrode and methanol (1M) was supplied to the negative electrode to generate power, and the relationship between current and voltage was examined.

Comparative Example 2
A Nafion (registered trademark) alcohol solution similar to that used in Example 1 having a polymer weight of 300 mg, H ₂ PtCl ₆ (corresponding to a Pt content of 13.5 mg) and RuCl ₃ (corresponding to a Ru content of 6.5 mg) were measured. The mixture was mixed well with 250 mg of carbon black similar to that used in Example 1 to obtain a paste. This paste was uniformly applied to the surface of a carbon paper (or carbon cloth) diffusion layer having a size of 2.25 cm × 2.25 cm by screen printing, and dried by a dryer at 60 ° C. for 15 minutes.

This electrode was used as the negative electrode, and the electrode produced by the same method as in Example 1 was used as the positive electrode, and was bonded to both surfaces of the Nafion 117 film by hot pressing to prepare a membrane-electrode precursor assembly. The membrane-electrode precursor assembly thus produced was accommodated in a fuel cell container to form a fuel cell single cell.
While flowing N ₂ gas through the bipolar gas flow path of this single cell of the fuel cell, both of the electrodes are energized 10 times alternately at 10A for 5 minutes, and the Pt salt and / or Ru salt contained in the bipolar electrode catalyst layer is supplied. Electrochemically reduced and precipitated. Thereafter, air was supplied to the positive electrode and methanol (1M) was supplied to the negative electrode, and the relationship between current and voltage was examined.

  Example 1 and Comparative Example 1 are both fuel cells using a Pt catalyst for the negative electrode catalyst layer and the positive electrode catalyst layer. In Example 1, the electrode catalyst layer of both the negative electrode and the positive electrode was obtained by depositing a Pt catalyst on the contact surface between carbon black as an electron conductive material and Nafion as a proton conductive material, as shown in FIG. In addition, a catalytically active substance such as Pt is concentrated on the contact surface between the proton conducting path of the proton conducting substance and the electron conducting substance, and other than the contacting face, for example, on the part facing the pores of the electron conducting substance. Is not present, and is not present in the deep part of the carbon particle aggregate to which liquid fuel such as methanol or ethanol is difficult to be supplied. On the other hand, in Comparative Example 1, the electrode catalyst layers of the negative electrode and the positive electrode were obtained by previously supporting Pt catalyst on carbon black and mixing it with a proton conductive material. As described above, the Pt catalyst is present not only on the contact surface between the proton conducting path of the proton conducting material and the electron conducting material, but also on the portion facing the pores of the electron conducting material.

  In both Example 2 and Comparative Example 2, a mixed catalyst of PtRu was used for the negative electrode catalyst layer, and a Pt catalyst was used for the positive electrode catalyst layer. In Example 2 and Comparative Example 2, similar to Example 1, catalytically active materials such as Pt are concentrated on the contact surface between the proton conductive path of the proton conductive material and the electron conductive material, and other than the contact surface For example, it exists in the state which does not exist in the part which faced the pores of the electron conductive substance. The difference between Example 2 and Comparative Example 2 is that the electrode catalyst layer of the negative electrode of Comparative Example 2 is located on the contact surface between the carbon particles and the solid polymer electrolyte as shown in FIG. This is because there are catalyst particles that do not work effectively in the electrode reaction because they exist in the deep part of the carbon particle aggregate that is difficult for fuel to penetrate.

FIG. 5 shows the results of a power generation test performed on the direct fuel cell using the electrodes of Examples 1 and 2 and Comparative Examples 1 and 2. As is apparent from FIG. 5, when the fuel cell of Example 1 is used, a higher output is obtained than the fuel cell of Comparative Example 1, and the fuel cell of Example 2 is the fuel cell of Comparative Example 2. It can be seen that a higher output can be obtained.
From these results, the fuel cell using the direct fuel cell electrode of the present invention has a higher catalyst utilization rate than the conventional fuel cell using the direct fuel cell electrode. It is considered that the improvement of the battery led to the improvement of the battery characteristics.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for direct fuel cell of a fuel with a favorable catalyst utilization factor can be obtained. Using such an electrode, methanol, ethanol, dimethyl ether, etc., which can be easily handled and the material and shape of the fuel container can be easily selected, can be mounted on various electric machines, electronic devices and precision devices. A direct fuel cell can be obtained. By using such a fuel cell, not only high output can be continuously exhibited, but also the cost of the battery can be reduced by reducing the amount of expensive catalyst.

It is a figure which shows the structure of preferable embodiment of the fuel direct fuel cell of this invention. It is the figure which showed notionally the cross-section of the electrode catalyst layer of the conventional fuel cell. It is the figure which showed notionally the cross-sectional structure of the electrode catalyst layer of the fuel cell disclosed by Unexamined-Japanese-Patent No. 2001-118583. It is the figure which showed notionally the cross-section of the catalyst layer of the electrode for fuel direct fuel cells of this invention. It is the figure which showed the current-voltage characteristic of the fuel cell using the electrode catalyst of Example 1 and 2 and Comparative Example 1 and 2.

Explanation of symbols

1a Current collector (separator)
1b Current collector (separator)
2 Electrolyte membrane 3 Fuel electrode 4 Air electrode 5 Liquid fuel flow path 6 Oxidant gas flow path

Claims (9)

A first step of preparing a catalyst layer precursor by mixing a proton conductive material and an electron conductive material;
A second step of adsorbing a catalyst active material precursor solution onto the catalyst layer precursor;
The catalyst active material precursor adsorbed on the catalyst layer precursor obtained in the second step is electrochemically reduced, and the catalyst active material is electrolytically deposited on the electron conductive material in the catalyst layer precursor. And a third step of manufacturing a direct fuel cell electrode for a fuel cell.   The method for producing a direct fuel cell electrode according to claim 1, wherein the catalyst active substance precursor solution uses a liquid fuel used for power generation of the fuel cell as a solvent.   3. The method for producing an electrode for a direct fuel cell according to claim 1, wherein the precursor of the catalytically active material is a mixture of metal salts containing at least one kind of noble metal.   The method of manufacturing an electrode for a direct fuel cell according to any one of claims 1 to 3, wherein the adsorption in the second step is adsorption by ion exchange of a proton conductive material.   It can obtain by the manufacturing method of any one of Claims 1-4, and a catalytically active substance is mainly interposed in the contact surface of the proton conduction path | route of a proton conductive substance, and the said electronic conductive substance. A fuel direct fuel cell electrode.   6. The direct fuel cell electrode according to claim 5, wherein the catalytically active substance is a noble metal or an alloy thereof.   The direct fuel cell electrode or the direct fuel cell electrode according to claim 5 or 6, which can be obtained by the method for manufacturing the direct fuel cell electrode according to any one of claims 1 to 4. A membrane-electrode assembly comprising an electrode.   A direct fuel cell comprising the membrane-electrode assembly according to claim 7.   An electronic apparatus comprising the direct fuel cell according to claim 8.