JP2011090987A - Manufacturing method of electrode for fuel cell - Google Patents

Abstract

An object of the present invention is to produce an electrode for a fuel cell in which an ultrathin polymer electrolyte is uniformly coated on a catalyst support.
A fuel cell electrode comprising: mixing a catalyst-supporting carrier and a polymer electrolyte with a binder having a functional group capable of reacting with the catalyst-supporting carrier and a functional group capable of reacting with the polymer electrolyte. Production method.
[Selection figure] None

Description

  The present invention relates to a method for producing an electrode for a fuel cell, a fuel cell comprising an electrode obtained by the method, and a binder used in the method.

  Modern life consists of consuming enormous energy. However, most of this energy depends on fossil fuels such as petroleum, and CH, CO, NOx, etc. emitted when fossil fuels are burned are problematic. Under such circumstances, an efficient and clean energy source is demanded, and fuel cells are attracting attention as one of them.

  Currently known fuel cells include polymer electrolyte fuel cells (PEFC), alkaline electrolyte fuel cells (AFC), and phosphoric acid fuel cells (PAFC). Molecular fuel cells are particularly promising because they can be reduced in size and weight and have excellent environmental characteristics.

  A polymer fuel cell is composed of a single cell in which an electrode / electrolyte membrane assembly, in which electrodes are bonded to both sides of a polymer electrolyte membrane, is sandwiched between a gas diffusion layer and a separator. It is configured. The fuel cell electrode includes a catalyst, a carrier, and an electrolyte, and forms a three-phase interface. Since the three-phase interface is involved in the catalytic reaction, electron conduction, and proton conduction, it is important how many three-phase interfaces are formed in order to improve the characteristics of the fuel cell.

  Patent Document 1 has both a catalyst and an electron-proton conductivity for the purpose of increasing the reaction area inside the electrode by bringing the catalyst and the electrolyte into sufficient and uniform contact and thereby exhibiting higher performance. A fuel cell electrode comprising a mixed conductive material is disclosed.

  In Patent Document 2, for the purpose of producing a gas diffusion composition in which the inner wall of the primary pores of the primary aggregate formed by the catalyst-supporting carbon is uniformly coated with the polymer electrolyte thin film, the catalyst-supported carbon is used as a non-electrolyte polymer. A method of coating with a compound and then ionizing the polymer compound using an ionizing agent is disclosed.

  Patent Document 3 discloses a method in which catalyst particles are pretreated with an oxidant for the purpose of sufficiently coating the catalyst particles with an electrolyte to improve the catalyst coverage with the electrolyte.

JP 2001-110428 A JP 2008-53089 A JP-A-10-189003

  Usually, an electrode (catalyst layer) of a fuel cell is made of a catalyst-supporting carrier and a polymer electrolyte (ionomer). The catalyst support has a structure coated with an electrolyte, and the coating structure is formed by an intermolecular force between the catalyst support and the electrolyte.

  The electrolyte is responsible for transport of protons, oxygen, and water in the catalyst layer, and these transports are greatly influenced not only by the physical properties of the electrolyte but also by the structure of the catalyst layer, particularly the coating structure of the electrolyte. However, in the conventional method for producing a catalyst layer, a non-uniform coating structure is formed such that the coating thickness varies, or there are portions that are not coated on the carrier. As a result, the oxygen diffusion resistance was large at the location where the electrolyte was thickly coated, and the voltage was lowered at high output (concentration overvoltage) due to insufficient oxygen supply to the catalyst. Moreover, the function as a catalyst cannot be exhibited in the location which is not coat | covered with electrolyte.

  Accordingly, an object of the present invention is to produce a fuel cell electrode in which an ultrathin polymer electrolyte is uniformly coated on a catalyst support.

  As a result of diligent studies, the present inventor has found that the problem can be solved by mixing a catalyst-supporting carrier and a polymer electrolyte with a binder to produce a fuel cell electrode.

That is, the gist of the present invention is as follows.
(1) Production of an electrode for a fuel cell comprising mixing a catalyst-supporting carrier and a polymer electrolyte with a binder having a functional group capable of reacting with the catalyst-supporting carrier and a functional group capable of reacting with the polymer electrolyte. Method.
(2) The method according to (1), wherein the binder has a basic functional group.
(3) A fuel cell comprising an electrode obtained by the method according to (1) or (2).
(4) A binder for producing an electrode for a fuel cell having a functional group capable of reacting with a catalyst-supporting carrier and a functional group capable of reacting with a polymer electrolyte.

  According to the present invention, the ultrathin polymer electrolyte can be uniformly coated in the primary particles and the secondary particles of the catalyst-supporting carrier, and the utilization efficiency of the catalyst can be improved. Therefore, the fuel cell characteristics can be improved by providing the fuel cell electrode manufactured according to the present invention.

1. Catalyst In the present invention, the catalyst means all catalysts that can be used for electrodes of fuel cells. For example, but not limited to, platinum, ruthenium, palladium, osmium, iridium, rhodium, gold, silver, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc as catalysts and catalyst components And metals such as zirconium, niobium, molybdenum, and tungsten. These catalysts can be used alone or in combination of two or more. When two or more kinds of catalysts are used, they can be used as a mixture or as an alloy.

The same catalyst or different catalysts can be used at the anode and cathode.
The catalyst is preferably used as fine particles, and in particular, catalyst particles having a particle size of 2 to 10 nm are preferably used.

2. Carrier In the present invention, the carrier means any carrier that can carry a catalyst and has electronic conductivity. Examples thereof include, but are not limited to, carbon, titania, silica, ceria, alumina, magnesia, zirconia, and yttria. These carriers can be used alone or in combination of two or more. In the present invention, carbon can be preferably used.

  The carrier is preferably used as fine particles, and in particular, carrier particles having a particle size of 10 to 50 nm are preferably used.

The weight ratio of the support to the catalyst is not particularly limited, but is preferably 90:10 to 40:60,
It is particularly preferable that the ratio is 80:20 to 70:30.

  Various methodologies for preparing a catalyst-supporting carrier are known as described in, for example, JP-A-2008-080322 and JP-A-2008-068228. Accordingly, those skilled in the art can appropriately prepare the catalyst-supporting carrier used in the present invention.

  When preparing a catalyst-supported support, it is obvious to those skilled in the art that functional groups resulting from the preparation method are formed on the support surface. For example, Pt / C used in the following examples is prepared by reducing and supporting platinum on carbon black and then hydrophilizing with nitric acid, and has a carboxyl group on the carbon surface. JP-T-2006-508501 discloses the surface characteristics of the carbon support, and it is possible to form functional groups such as hydroxyl groups, carboxyl groups, and aldehyde groups by oxidizing the carbon surface, and various It is described that the oxidization of the oxidized carbon surface is possible by the reaction using various agents. Accordingly, those skilled in the art can form an arbitrary functional group on the surface of the catalyst-supporting support. In the present invention, it is preferable that an acidic functional group is formed on the surface of the catalyst-supporting carrier, and it is particularly preferable that a carboxyl group is formed.

3. Polymer electrolyte In the present invention, the polymer electrolyte means a polymer (ionomer) having an acidic functional group such as a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group. Examples thereof include, but are not limited to, perfluorosulfonic acid polymer, perfluorocarboxylic acid polymer, perfluorophosphoric acid polymer, and the like. In the present invention, it is preferable to use an ionomer having a sulfonic acid group, and it is particularly preferable to use Nafion (registered trademark).

  The weight ratio between the polymer electrolyte and the catalyst-supporting carrier is not particularly limited, but is preferably 1:10 to 3: 2, and particularly preferably 1: 2 to 1: 1.

4). Binder In the present invention, the binder means a compound having a functional group capable of reacting with a functional group present on the surface of the catalyst-supporting carrier and a functional group capable of reacting with a functional group of the polymer electrolyte. means. Accordingly, the binder has at least two or more functional groups, preferably two functional groups.

  The binder can have two or more identical functional groups or different functional groups. Examples include, but are not limited to, amino groups, hydroxyl groups, thiol groups, epoxy groups, carboxyl groups, acid halides, acid anhydrides, halogens, and the like. In the present invention, the binder preferably has two or more basic functional groups, particularly preferably two basic functional groups, and more preferably two amino groups. A preferred binder in the present invention is p-phenylenediamine.

  The binder can form an ionic bond, a covalent bond (for example, an amide bond, an ester bond, an ether bond, etc.) by reacting with the catalyst-supporting carrier and the polymer electrolyte. The bonding mode between the binder and the catalyst support and the bonding mode between the binder and the polymer electrolyte may be the same or different. That is, the bond type between the binder and the catalyst-supporting carrier may be a covalent bond, and the bond type between the binder and the polymer electrolyte may be an ionic bond. However, in the present invention, preferably, the bonding mode between the binder and the catalyst-supporting carrier and the bonding mode between the binder and the polyelectrolyte are both ionic bonds.

  The functional group present on the surface of the catalyst-supporting support can be arbitrarily formed by those skilled in the art as described above. Further, the polymer electrolyte in the present invention has an acidic functional group. Accordingly, those skilled in the art can select an appropriate binder depending on the type of functional group present on the surface of the catalyst-supporting support and the functional group of the polymer electrolyte.

  The molar ratio of the binder to the acidic functional group of the polyelectrolyte is 1: 100 to 10: 100, preferably 5: 100.

  In one embodiment of the present invention, a binder for producing a fuel cell electrode having a functional group capable of reacting with a catalyst-supporting carrier and a functional group capable of reacting with a polymer electrolyte is provided. The binder may contain an optional component. For example, the binder may contain a catalyst, a solvent, a stabilizer, and the like, but is not limited thereto.

5. Production of Fuel Cell Electrode The fuel cell electrode of the present invention can be produced by mixing a catalyst carrier and a polymer electrolyte with a binder. The binder can be added to the mixture of the catalyst support and the polymer electrolyte. Alternatively, the binder can be mixed with one of the catalyst support and the polymer electrolyte, and then the other component can be added. In the present invention, the catalyst-supported carrier and the binder are first mixed, a bond is formed between the catalyst-supported carrier and the binder, and then the polymer electrolyte is mixed. It is preferred to form a bond.

  The bond formation reaction is preferably performed in an organic solvent. Examples of the organic solvent that can be used in this reaction include, but are not limited to, ethanol and propanol.

  The reaction time and reaction temperature of the bond forming reaction vary depending on the type of the functional group of the catalyst-supporting carrier, the polymer electrolyte, and the binder used. A person skilled in the art can appropriately adjust the reaction time and reaction temperature according to the type of functional group.

  A catalyst can be utilized to promote the bond formation reaction. For example, although not limited to these, an acid catalyst (hydrochloric acid, sulfuric acid, etc.) or a base catalyst (sodium hydroxide, etc.) can be used.

  In one embodiment of the present invention, a fuel cell electrode comprising reacting a catalyst-supporting carrier having an acidic functional group and a polymer electrolyte having an acidic functional group with a binder having two basic functional groups. A manufacturing method is provided.

  In one embodiment of the present invention, there is provided a method for producing an electrode for a fuel cell, which comprises reacting a catalyst-supporting carrier having a carboxyl group and a polymer electrolyte having a sulfonic acid group with a binder having two amino groups. provide.

  In one embodiment of the present invention, a catalyst-supporting carrier having a carboxyl group and a binder having two amino groups are reacted to form a bond between the catalyst-supporting carrier and the binder, and then a sulfonic acid group is contained. There is provided a method for producing an electrode for a fuel cell, comprising reacting a polymer electrolyte to form a bond between a binder and a polymer electrolyte.

6). Fuel Cell The present invention further provides a fuel cell comprising the above fuel cell electrode. A single cell of a fuel cell is formed by providing gas diffusion layers on both sides of a membrane electrode assembly (MEA) composed of a polymer electrolyte membrane and the electrodes (anode and cathode) of the present invention, and further providing separators on both sides thereof. can do. A fuel cell can be formed by stacking the single cells.

  The fuel cell comprising the fuel cell electrode according to the present invention can be used in various applications. For example, the present invention can be used for, but not limited to, automobiles, motorcycles, mobile devices (notebook computers, mobile phones, video cameras, etc.), home / business cogeneration systems, and the like.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by this.
Example 1 : Preparation of catalyst-supported support (Pt / C) Carbon black “Ketjen EC (Ketjen Black International Co., Ltd.)” (2.0 to 4.5 g) was suspended and stirred in distilled water, and 15% chloroplatinic acid was added to 3 to 20%. g was added dropwise. Next, 5 to 30 g of ethanol was dropped as a reducing agent to deposit platinum on the carbon. The obtained mixture was filtered, and the solid was dried to obtain platinum-supporting carbon. 10 to 60 wt% Pt / C can be prepared by this method. The obtained Pt-supported carbon powder was stirred in an aqueous nitric acid solution at a low temperature to perform a hydrophilic treatment.

Example 2 Production of Fuel Cell Electrode In a nitrogen atmosphere, 40 wt% Pt / C (8.3 g) prepared in Example 1 was added and dispersed in ethanol (50 g), and then p-phenylenediamine ( 24.5 mg) / ethanol (10 g) solution was added, and the mixture was stirred at room temperature for 24 hours. Then, Nafion (registered trademark) DE2020 (5.0 g) was added and stirred at room temperature for 24 hours, and then pure water (40 g) was added and stirred.
Using the obtained mixture, an electrode was formed on a transfer substrate (Teflon sheet) by a blade coating method. The electrode was transferred to the electrolyte membrane by a transfer method to prepare a membrane electrode assembly.

Example 3 : Measurement of BET specific surface area Using a BELSORP-mini apparatus manufactured by Nippon Bell Co., Ltd., the electrode prepared in Example 2 was vacuum degassed at 120 ° C for 8 hours, and nitrogen was applied using a constant volume method. The adsorption isotherm was measured, and the specific surface area was calculated by the BET multipoint method. The results are shown in Table 1.

Example 4 Measurement of Oxygen Diffusion Resistance Using the membrane electrode assembly prepared in Example 2, Air-IV (IV when air flows through the cathode) and O ₂ -IV (O in the cathode) in full humidification _The oxygen diffusion resistance was measured by the O ₂ gain method from IV) when ₂ was applied. The results are shown in Table 1.

Example 5 : Measurement of power generation performance Using the membrane electrode assembly prepared in Example 2, IV measurement was performed under the following conditions.
Cathode: 80 ° C full humidification, Air
Anode: 80 ° C full humidification, O ₂
ESCA was calculated from CV measurements. The results are shown in Table 1.

Comparative Example 1 Production of Fuel Cell Electrode Under a nitrogen atmosphere, 40 wt% Pt / C (8.3 g) prepared in Example 1 was added to ethanol (50 g) and dispersed therein, and then Nafion (registered trademark). DE2020 (5.0 g) was added and stirred at room temperature for 24 hours. Then, pure water (40 g) was added and stirred.
Using the obtained mixture, an electrode was formed on a transfer substrate (Teflon sheet) by a blade coating method. The electrode was transferred to the electrolyte membrane by a transfer method to prepare a membrane electrode assembly.

Comparative Example 2 : Measurement of BET specific surface area, oxygen diffusion resistance, and power generation performance Using the electrode and membrane electrode assembly prepared in Comparative Example 1, BET specific surface area, oxygen diffusion resistance, And the power generation performance was measured. The results are shown in Table 1.

結果：
結合剤を使用して製造した燃料電池用電極は、結合剤を使用しないものと比較して、良好なBET比表面積、酸素拡散抵抗、及び発電性能を示した。従って、本発明により製造した燃料電池用電極を備えることにより燃料電池の特性を向上させることが可能である。

Result :
The fuel cell electrode produced using the binder showed better BET specific surface area, oxygen diffusion resistance, and power generation performance than those without the binder. Accordingly, it is possible to improve the characteristics of the fuel cell by providing the fuel cell electrode manufactured according to the present invention.

Claims (4)

  A method for producing an electrode for a fuel cell, comprising mixing a catalyst-supporting carrier and a polymer electrolyte with a binder having a functional group capable of reacting with the catalyst-supporting carrier and a functional group capable of reacting with the polymer electrolyte.   The method according to claim 1, wherein the binder has a basic functional group.   A fuel cell comprising an electrode obtained by the method according to claim 1.   A binder for producing an electrode for a fuel cell, having a functional group capable of reacting with a catalyst-supporting carrier and a functional group capable of reacting with a polymer electrolyte.