JP2010086931A - Electrode and electrolyte membrane-electrode assembly, manufacturing methods of those, and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode and a method of manufacturing the same, wherein a numerous number of minute micro-pores necessary for the material transportation into the interior of the electrode are fabricated, and an adhesiveness of a boundary face of the electrode and the electrolyte membrane is improved; and to provide the electrolyte membrane-electrode assembly and method of manufacturing the same. <P>SOLUTION: In the electrolyte membrane-electrode assembly 20 in which electrodes 2, 3 equipped with catalyst layers 6, 8 on both sides of the solid electrolyte membrane 4 are respectively crimped, the catalyst layers 6, 8 contain a mixture of nano-carbon to carry the catalyst and proton conductive material. The electrolyte membrane-electrode assembly 20 is used in the fuel cell 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode of a fuel cell.

  A fuel cell is one that converts chemical energy of a fuel into electric energy by electrochemically oxidizing a fuel such as hydrogen or methanol, and has attracted attention as a new electric energy supply source.

  Patent Documents 1 and 2 disclose the structure of this type of fuel cell. The electrode structure of the fuel cell is a five-layer structure in which an anode current collector, an anode, an electrolyte membrane, a cathode, and a cathode current collector are sequentially stacked. A fuel such as hydrogen or methanol is used on the anode (fuel electrode), Oxygen is supplied to the cathode (oxidant electrode) and electricity is generated by an electrochemical reaction. For example, an electrochemical reaction represented by the following chemical formula 1 occurs at each electrode of a direct methanol fuel cell.

  For the fuel electrode and the oxidizer electrode, a mixture of carbon particles carrying a catalyst metal and a proton conductive material is used, and this mixture is generally used as a carbon paper or the like serving as a fuel gas diffusion layer. It is configured to be applied on an electrode substrate. A fuel cell is formed by sandwiching an electrolyte membrane between these two electrodes and thermocompression bonding.

  In the fuel cell of this configuration, the methanol supplied to the fuel electrode passes through the pores in the electrode and reaches the catalyst, emits electrons to become protons and carbon dioxide, and the carbon dioxide passes through the pores in the electrode. Then discharged. The emitted electrons are led to the external circuit through the carbon particles in the fuel electrode and the proton conductive material, and flow into the cathode electrode from the external circuit.

  On the other hand, hydrogen ions generated in the fuel electrode reach the oxidant electrode through the proton conductive material in the fuel electrode and the electrolyte membrane sandwiched between the two electrodes, and from the oxygen supplied to the oxidant electrode and the external circuit It reacts with the flowing electrons to produce water as shown in the above reaction formula. The generated water passes through the pores in the electrode and is discharged. As a result, in the external circuit, electrons flow from the fuel electrode toward the oxidant electrode, and electric power is taken out.

  In order to improve the characteristics of the fuel cell configured as described above, it is important to have good adhesion at the interface between the electrode and the electrolyte membrane, and it is necessary for transporting substances such as methanol, carbon dioxide, and water. Existence of fine pores is important.

Japanese Patent No. 3608564 Japanese Patent No. 3608565

  Therefore, the technical problem of the present invention is to solve the above-mentioned problems of the prior art and provide an electrode, a manufacturing method thereof, an electrolyte membrane electrode assembly, a manufacturing method thereof, and a fuel cell using the same. There is.

  According to the present invention, there is provided an electrode having a catalyst layer on the surface of the substrate, the electrode having pores having a diameter of 1 nm to 100 nm inside, the catalyst layer comprising nanocarbon supporting the catalyst, proton An electrode is obtained which comprises a mixture with a conductive material.

  According to the present invention, an electrode having a catalyst and a carrier is immersed in a 30 to 55 vol% aqueous methanol solution for 2 to 24 hours in advance to elute a part of the electrode catalyst and the carrier into the aqueous methanol solution. An electrode manufacturing method characterized by forming pores is obtained.

  According to the present invention, in the method for producing an electrode, by immersing the electrode in the aqueous methanol solution, a portion of the proton conductive material contained in the electrode is eluted into the aqueous methanol solution, and pores are formed inside the electrode. An electrode manufacturing method characterized in that is formed.

  According to the present invention, in the electrode manufacturing method, the electrode manufacturing method is characterized in that the pores having a diameter of 1 nm to 100 nm are formed inside the electrode.

  According to the present invention, in the electrolyte membrane electrode assembly in which electrodes each having a catalyst layer on both sides of a solid electrolyte membrane are pressure-bonded, the catalyst layer includes a mixture of nanocarbon supporting the catalyst and a proton conductive material. An electrolyte membrane electrode assembly is obtained.

  According to the present invention, it is possible to obtain a fuel cell comprising the electrolyte membrane electrode assembly and a pair of separators sandwiching the electrolyte membrane electrode assembly.

  According to the present invention, it is possible to obtain a method for producing an electrolyte membrane electrode assembly, which includes a step of previously immersing in a 30 to 55 vol% methanol aqueous solution for 2 to 24 hours and then joining the electrolyte membrane.

  According to the present invention, in the method for producing an electrolyte membrane electrode assembly, the electrolyte is characterized in that, in the step, a part of the electrode catalyst and the carrier are eluted into the methanol aqueous solution to form pores inside the electrode. A method for producing a membrane electrode assembly is obtained.

  According to the present invention, in the method for manufacturing an electrolyte membrane electrode assembly according to any one of the above, in the step, a part of the proton conductive material contained in the electrode is eluted in the methanol aqueous solution and is finely divided in the electrode. A method for producing an electrolyte membrane electrode assembly, wherein holes are formed, is obtained.

  According to the present invention, in the method for producing an electrolyte membrane electrode assembly, the method for producing an electrolyte membrane electrode assembly is characterized in that the pores formed inside the electrode have a diameter of 1 nm to 100 nm. .

  According to the present invention, a fuel cell characterized by using any one of the electrolyte membrane electrode assemblies is obtained.

  That is, by immersing the electrode in a 30 to 55 vol% aqueous methanol solution for 2 to 24 hours in advance, a part of the electrode catalyst and carrier and a part of the proton conductive substance are eluted into the aqueous methanol solution and are finely divided inside the electrode. A hole is created, and an electrode optimal for mass transport can be produced.

  According to the present invention, an electrode, a manufacturing method thereof, and an electrolyte membrane, in which a large number of fine pores necessary for material transportation inside the electrode are produced and the interface has an excellent adhesion between the electrode and the electrolyte membrane. An electrode assembly and a manufacturing method thereof can be provided.

  Moreover, according to the present invention, a fuel cell capable of generating power efficiently can be provided by using the electrolyte membrane electrode assembly.

  Embodiments of the present invention will be described below.

  FIG. 1 is a cross-sectional view schematically showing an example of the structure of a fuel cell according to the present invention. Referring to FIG. 1, the electrolyte membrane electrode assembly 20 includes a fuel electrode 2, an oxidant electrode 3, and an electrolyte membrane 4. The fuel electrode 2 and the oxidant electrode 3 are collectively referred to as an electrode, and the electrode according to the present invention is used for at least one of the fuel electrode 2 and the oxidant electrode 3. The fuel electrode 2 includes a base 5 and a catalyst layer 6 containing a proton conductive material.

  Carbon paper is used as the base 2 constituting the fuel electrode 2, but a porous base such as a carbon molded body, a sintered body of carbon, a sintered metal, and a foam metal can be used. However, it is not limited to these as long as it is a good conductive material.

  The catalyst layer 6 includes a catalyst, a carrier that supports the catalyst, and a binder, for example, a conductive polymer, for binding the carrier that supports the catalyst.

  The catalyst is a noble metal such as gold, silver, palladium, rhodium, iridium, ruthenium, osmium, rhenium, alloys thereof, compounds containing them, iron group elements other than iron such as nickel, cobalt, alloys thereof, or Examples of such compounds include, but are not limited to, alkaline earth metals such as lithium, lanthanum, strontium, yttrium, rare earth metals, alloys thereof, compounds containing them, and the like.

  Moreover, as a support | carrier, carbon particles, such as nanocarbons, such as carbon nanohorn, a carbon nanotube, fullerene, and a graphite particle, are preferable.

  Further, the binder may be a solid polymer electrolyte, and is not particularly limited to the material.

  The oxidant electrode 3 includes a base 7 and a catalyst layer 8 containing a proton conductive material.

  The base 7 constituting the oxidant electrode 3 is made of the same material as the base 5 constituting the fuel electrode 2, but is not limited thereto as long as it is a conductive material with good oxygen gas permeation. .

  The catalyst layer 8 includes a catalyst, a carrier that supports the catalyst, and a binder, for example, a conductive polymer, for binding the carrier that supports the catalyst. As the catalyst and the carrier, the same catalyst and carrier used for the catalyst layer 6 can be used.

  Further, the binder may be a solid polymer electrolyte, and is not particularly limited to the material.

  The solid polymer electrolyte membrane 4 is not particularly limited to a material as long as it allows hydrogen ions and water molecules to pass therethrough. However, as shown in [0049] of Patent Document 2, sulfone is used. An organic polymer having a polar group such as a strong acid group such as a group, a phosphoric acid group, a phosphone group or a phosphine group, or a weak acid group such as a carboxyl group is preferably used. Examples of the organic polymer include aromatic-containing polymers such as sulfonated poly (4-phenoxybenzoyl-1,4-phenylene) and alkylsulfonated polybenzimidazole; polystyrene sulfonate copolymer, polyvinyl sulfonate copolymer, Copolymers such as cross-linked alkyl sulfonic acid derivatives, fluorine-containing polymers composed of a fluororesin skeleton and sulfonic acid; acrylamides such as acrylamide-2-methylpropane sulfonic acid and acrylates such as n-butyl methacrylate. Copolymer obtained by polymerization; sulfone group-containing perfluorocarbon (Nafion (registered trademark, manufactured by DuPont), Aciplex (manufactured by Asahi Kasei)); carboxyl group-containing perfluorocarbon (Flemion (registered trademark) S membrane (Asahi Glass Co., Ltd.) Made ); And the like are exemplified.

  One or a plurality of catalyst electrolyte membrane electrode assemblies 20 are electrically connected via the fuel electrode side separator 9 and the oxidant electrode side separator 10 to constitute the fuel cell 1. Note that methanol 11 as fuel is supplied into the fuel electrode side separator 9, and oxygen gas 12 as oxidant is supplied into the oxidant side separator 9.

  In the present invention, the fuel electrode 2 and the oxidizer electrode 3 are immersed in a 30 to 55 vol% methanol aqueous solution in advance for 2 to 24 hours so that the electrode catalyst, a part of the carrier, and the proton conductive material are in the methanol aqueous solution. And the pores are formed inside the electrode.

  The electrode treated with the methanol aqueous solution is thermocompression bonded to the solid polymer electrolyte membrane 4 to produce an electrolyte membrane electrode assembly 20 having fine pores advantageous for transporting substances such as fuel, carbon dioxide and water. can do.

  In the embodiment of the present invention, by immersing the electrode in a 30 to 55 vol% methanol aqueous solution in advance for 2 to 24 hours, the electrode catalyst and a part of the carrier and the proton conductive substance are eluted in the methanol aqueous solution, A pore is created inside the electrode.

  When the aqueous methanol solution is less than 30% by volume, the catalyst and a part of the carrier and part of the proton conductive material are not eluted from the electrode, so the effect is remarkably low. As a result of peeling off, the electrode cannot be produced.

  Especially, the effect is particularly high when the concentration of the aqueous methanol solution is 45 to 55 vol%. In addition, when the immersion time in an aqueous methanol solution is shorter than 2 hours, the proton conductive material swells and has an effect of improving the adhesion between the electrode and the electrolyte membrane. There is little effect of elution of part of the catalyst, and if it exceeds 24 hours, the catalyst layer of the electrode is peeled off, or the amount of elution of the catalyst, the carrier, and the proton conductive substance is excessive, and the performance as an electrode is deteriorated. .

  The effect is particularly high when immersed for 12 hours or more at room temperature. A fuel cell using an electrode produced according to the present invention is excellent in catalytic characteristics, conductive characteristics and proton conductive characteristics, and can generate power efficiently.

  Examples of the present invention will be shown below, and the present invention will be illustrated and explained in more detail. However, the present invention is not limited to the following examples.

(Example)
The carbon nanohorn catalyst was prepared by a colloid method. Reduced by adding sodium hydrogen sulfite while maintaining the temperature of the chloroplatinic acid aqueous solution with a stoichiometric ratio of carbon to Pt of 2: 3 at 50 ° C, and adjusted the pH to 5 with 1N sodium hydroxide solution did. The obtained solution was diluted with water, carbon nanohorn aggregates were added, and the mixture was stirred for 30 minutes using a homogenizer. A 30% hydrogen peroxide solution was added little by little to change the platinum compound in the solution into a platinum oxide colloid and simultaneously adsorbed onto the carbon powder. While maintaining the liquid temperature at 75 ° C., the pH of the solution was adjusted to 5 and stirred for 12 hours. The solution was boiled for 10 minutes, and after natural cooling, unnecessary salts were removed by centrifugation and washing with water, and kept at 70 ° C. for 12 hours and dried to obtain a carbon powder adsorbed with platinum oxide. Thereafter, reduction was carried out in hydrogen for 2 days. The sample carrying the catalyst was observed with a scanning transmission electron microscope image (SEM), and the black point in the SEM image was analyzed by energy dispersive X-ray spectroscopy (EDS). confirmed. From the STEM image, it was estimated that the average Pt particle diameter of the sample was 4.5 nm. As for the loading rate, as a result of thermogravimetric analysis in an oxygen atmosphere, Pt could be confirmed to be 60% by weight with respect to the carbon nanohorn.

  Isopropanol was added to the 60% Pt-supported catalyst of carbon nanohorn prepared above in a nitrogen atmosphere from which oxygen was removed, and the carbon nanohorn catalyst was dispersed. Further, in order to further improve the dispersibility of the carbon nanohorn catalyst, ultrasonic dispersion treatment at a frequency of 20 kHz was performed. A 5% Nafion (registered trademark) solution manufactured by DuPont was added to the carbon nanohorn catalyst dispersed in an organic solvent and kneaded to prepare a carbon nanohorn catalyst paste.

  The carbon nanohorn catalyst paste prepared above was applied onto a substrate, dried at 140 ° C., immersed in a 50 vol% methanol aqueous solution for 18 hours, and unnecessary substances were eluted in the methanol aqueous solution to prepare pores inside the electrode. . This was pressure-bonded to both surfaces of the electrolyte membrane to produce a fuel cell electrode. Using this electrode, a direct methanol fuel cell was made and its battery characteristics were measured at a temperature of 40 ° C. The results are shown in FIG.

(Comparative Example 1)
An electrode prepared by applying the carbon nanohorn catalyst paste prepared in the example onto a substrate and drying the catalyst layer dried at 140 ° C. without being immersed in an aqueous methanol solution was used. Otherwise, an MEA (electrolyte membrane electrode assembly) was prepared in the same manner as in the Examples, and the battery characteristics were evaluated. The results are shown in FIG.

(Comparative Example 2)
An electrode prepared by applying the carbon nanohorn catalyst paste prepared in the example onto a substrate, drying at 140 ° C., and immersing in a 10 vol% methanol aqueous solution for 18 hours was used. Otherwise, an MEA was produced in the same manner as in the Examples, and the battery characteristics were evaluated. The results are shown in FIG.

As shown in FIG. 2, the MEA produced by the conventional manufacturing method (Comparative Example 1) is an MEA using an electrode produced by immersing the catalyst layer in a 10 vol% methanol aqueous solution with a battery output of 12 mW / cm ² (Comparative Example). 2) battery output was 31 mW / cm ² , while MEA (Example) using an electrode prepared by immersing the catalyst layer in 50% aqueous methanol solution was 76 mW / cm ² and the battery output jumped. It was confirmed that it improved.

It is sectional drawing which shows typically an example of a structure of the fuel cell concerning this invention. MEA produced using a dry electrode of a conventional method, MEA produced using an electrode immersed in a 10 vol% methanol aqueous solution, and an electrode produced by dipping in a 50 vol% methanol aqueous solution according to the present invention to produce pores It is a figure which shows the output characteristic of MEA using.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Fuel electrode 3 Oxidant electrode 4 Solid polymer electrolyte membrane 5,7 Base | substrate 6,8 Catalyst layer 9,10 Separator 11 Methanol (fuel)
12 Oxygen gas (oxidizer)
20 Electrolyte membrane electrode assembly

Claims (11)

  An electrode having a catalyst layer on a substrate surface, the electrode having pores having a diameter of 1 nm to 100 nm inside, and the catalyst layer is a mixture of nanocarbon carrying a catalyst and a proton conductive material An electrode comprising:   An electrode having a catalyst and a carrier is immersed in a 30 to 55 vol% aqueous methanol solution for 2 to 24 hours in advance to elute a part of the electrode catalyst and the carrier into the aqueous methanol solution to form pores inside the electrode. An electrode manufacturing method characterized by the above.   3. The electrode manufacturing method according to claim 2, wherein a portion of the proton conductive material contained in the electrode is eluted into the methanol aqueous solution by immersing the electrode in the methanol aqueous solution, and pores are formed inside the electrode. A method for producing an electrode, comprising: forming the electrode.   4. The method for manufacturing an electrode according to claim 2, wherein the pores having a diameter of 1 nm to 100 nm are formed inside the electrode.   An electrolyte membrane electrode assembly in which electrodes each having a catalyst layer on both sides of a solid electrolyte membrane are pressure-bonded to each other, wherein the catalyst layer includes a mixture of nanocarbon supporting the catalyst and a proton conductive material. Electrode assembly.   6. A fuel cell comprising the electrolyte membrane electrode assembly according to claim 5 and a pair of separators sandwiching the electrolyte membrane electrode assembly.   A method for producing an electrolyte membrane electrode assembly, comprising a step of immersing in a 30 to 55 vol% aqueous methanol solution in advance for 2 to 24 hours and then joining the membrane with an electrolyte membrane.   8. The method for producing an electrolyte membrane / electrode assembly according to claim 7, wherein in the step, a part of the electrode catalyst and the carrier are eluted into the aqueous methanol solution to form pores inside the electrode. Manufacturing method of electrode assembly.   9. The method for producing an electrolyte membrane / electrode assembly according to claim 7 or 8, wherein in the step, part of the proton conductive material contained in the electrode is eluted into an aqueous methanol solution to form pores inside the electrode. A method for producing an electrolyte membrane electrode assembly comprising:   10. The method for producing an electrolyte membrane electrode assembly according to claim 8 or 9, wherein the pores formed in the electrode have a diameter of 1 nm to 100 nm.   A fuel cell using the electrolyte membrane electrode assembly according to any one of claims 7 to 10.

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