JP2011222350A - Method of manufacturing oxygen reduction reaction electrode and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a fuel-cell electrode which can retard increase in diameter of catalyst particles and their dropping, and which can secure high power generation characteristics for a long period by preventing dissolution and dissipation of noble metal catalyst particles under an acidic condition.SOLUTION: This invention is regarding a method of manufacturing an oxygen reduction reaction electrode for fuel cells and is regarding the fuel cells using the same. The oxygen reduction reaction electrode comprises catalyst powder whose surface at least has catalyst particles, and a layer with thickness of 0.5-5nm for retarding dissolution of platinum which is formed on the surface of the catalyst powder. The layer comprises a compound whose molecules include alkyl sulfonic acid group and a group represented by formula (RO)Si-(Rrepresents hydrogen atoms or a 1C-4C alkyl group). The spaces between the catalyst covered with the layer for retarding dissolution of platinum are filled with electrolyte.

Description

  The present invention relates to a method for producing an oxygen reduction reaction electrode, and more particularly to a method for producing an electrode for a polymer electrolyte fuel cell.

  A fuel cell generates electric power by electrochemically reacting a fuel capable of generating protons such as hydrogen and an oxidant containing oxygen such as air.

  In the cathode of the fuel cell, a catalytic reaction in which water is generated on the surface of the catalyst particles is generated by gaseous oxygen, liquid protons, and electrons from conductive fine powder that is solid.

  The reaction center in which the catalytic reaction occurs is generally called a three-phase interface. The area of this three-phase interface is proportional to the effective surface area (ECA, called electrochemical surface area) of the catalyst particles in contact with the electrolyte layer that can efficiently supply protons. If this ECA can be maintained, long-term High battery output characteristics can be obtained. However, the platinum catalyst undergoes oxidative dissolution when exposed to acid by protons supplied from the electrolyte. Under strong acidic conditions in a normal fuel cell electrode, the dissolution reaction accelerates and ECA is lowered. In addition, since efficient supply of oxygen to the catalyst surface is essential for electrode reactions, various material developments are needed from the viewpoints of both ECA and oxygen diffusivity in order to obtain stable and high battery characteristics over the long term. Has been made.

  In general, a catalyst layer of a fuel cell electrode is formed by mixing a catalyst powder in which platinum particles are supported on a porous carbon fine powder such as ketjen black or acetylene black and a polymer electrolyte. Under these circumstances, in order to ensure both ECA and oxygen diffusivity, studies have been made on a method of mixing a polymer electrolyte and catalyst particles. For example, a method is proposed in which the polymer electrolyte is overcoated on the catalyst powder by changing the dispersion state of the electrolyte on the catalyst while gradually adjusting the dispersibility of the polymer electrolyte in the solvent. (Patent Documents 1 and 2). There is also a method in which a polymer electrolyte is chemically bonded using a polymerizable functional group fixed on the surface of a catalyst powder as a base point (Patent Document 3). However, since the battery characteristics used as an actual machine are insufficient, or because a perfluoroalkyl sulfonic acid polymer electrolyte is used, the catalyst platinum particles are acid-dissolved due to potential fluctuations, causing catalyst deterioration. There was a problem that stability could not be secured.

  In addition, materials have been proposed to ensure the stability of platinum nanoparticles as a catalyst. However, in order to use materials that reduce catalytic activity in the first place, in addition to ECA and oxygen diffusivity, There is a problem with respect to electrical conduction, and it cannot be an effective method for obtaining satisfactory initial characteristics of a battery (Patent Document 4).

  Thus, in the development of fuel cell electrodes, the development of materials that simultaneously ensure both power generation characteristics and long-term stability has become a major issue.

  In addition, Patent Document 5 may relate to the present invention.

Japanese Patent Laid-Open No. 11-126615 Japanese Patent Laid-Open No. 7-254419 JP 2007-165005 A JP 2007-5292 A JP 2005-032668 A

  In the conventional electrode configuration, a perfluorocarbon sulfonic acid polymer must be used for the polymer electrolyte in the catalyst layer in order to enhance the output characteristics of the fuel cell. The sulfonic acid group that the electrolyte has in its molecular structure has a very large acid dissociation constant, and the dispersed platinum nanoparticles in the electrode easily cause acidic dissolution. Therefore, the problem is that the catalyst gradually deteriorates during the operation of the fuel cell and it is difficult to ensure the stability of ECA.

  The present invention solves the above-described problem, and prevents dissolution and dissipation of metal nanoparticles and suppresses catalyst deterioration, so that ECA of a fuel cell can be kept stable, and power generation performance can be stabilized accordingly. It aims at providing the manufacturing method of an electrode.

  In order to solve the above-described conventional problems, the method for producing an electrode for a fuel cell according to the present invention includes a step of preparing a slurry by mixing a catalyst powder having catalyst particles on the surface and a platinum elution suppressing material, and drying under reduced pressure. By performing a polymerization reaction of the platinum elution suppression material in the slurry by performing a treatment and a heat drying process, a platinum elution suppression layer made of a polymer of the ECA lowering suppression material is formed on the surface of the catalyst powder. Forming a suppression layer-covered catalyst, and mixing the suppression layer-coated catalyst, a solvent, and an electrolyte to prepare a paste.

  A platinum elution suppression layer having a thickness of several nanometers can be formed on the platinum surface and the carbon surface by polymerizing in situ using a certain amount or more of a low molecular state platinum elution suppression material at the time of slurry preparation.

  According to the oxygen reduction reaction electrode and the manufacturing method thereof of the present invention, an electrode having a high level and stable ECA can be manufactured over a long period of time.

Process drawing shown in the manufacturing method of the oxygen reduction reaction electrode in Embodiment 1 of this invention

  Embodiments of the present invention will be described below with reference to the drawings.

  In the present embodiment, an oxygen reduction reaction electrode is manufactured by performing steps S11 to S15.

  First, in step S11, a polymerizable electrolyte precursor (1) and a polymerizable spacer precursor (2) are mixed with a solvent 1 (3) to prepare a platinum elution suppressing material (4).

  The polymerizable electrolyte precursor (1) is a low molecular compound having a polymerizable functional group. Specifically, it is a compound having both a proton acidic functional group and a polycondensable functional group in the same molecule. The proton acidic functional group is a functional group possessed by a material having a function of supplying protons onto the platinum catalyst surface where oxygen reduction reaction proceeds. A sulfonic acid group is particularly preferable.

  The platinum elution suppressing material (4) has at least a polymerizable electrolyte precursor (1) as a constituent element in order to have proton supply ability.

The polycondensable functional group refers to a functional group that undergoes a polycondensation reaction by reaction under conditions such as heating and / or reduced pressure, and a silicon group having a hydroxyl group and / or an alkoxyl group is particularly preferable. This silicon group is specifically represented by the formula: (R ¹ O) ₃ Si— (wherein R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms). Since the platinum elution suppressing material (4) has this polycondensable functional group, it can be polymerized in step S12 described later to form a polymer. In the polymerization, silicon atoms are bonded to each other through an oxygen atom to form a siloxane bond and release water or R ¹ OH.

  Examples of the alkyl group having 1 to 4 carbon atoms in the above formula include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and a t-butyl group. Of these, an ethyl group is preferred because of its high reactivity and ease of removal after polymerization.

Specifically, as the platinum elution suppressing material (4), the formula: (R ¹ O) ₃ Si—R ² —SO ₃ H (wherein R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms). , R ² represents an alkylene group having 1 to 15 carbon atoms). Three R ¹ present in one molecule may be the same or different.

The alkylene group represented by R ² can be appropriately selected from alkylene groups having 1 to 15 carbon atoms. This alkylene group may be linear or branched. Preferably it is a C2-C10 alkylene group.

  The solvent 1 (3) is used to dissolve the platinum elution suppressing material (4) or the polymerizable spacer precursor (2). Such a solvent is preferably a polar solvent so that each compound can be dissolved. Specifically, acetone, alcohol having 1 to 4 carbon atoms (methanol, ethanol, propanol, butanol), dimethylacetamide, ethyl acetate. , Butyl acetate, tetrahydrofuran and the like. As the solvent (3), only one type may be used, or a plurality of types may be used in combination.

  The amount of the solvent used is not particularly limited as long as the platinum elution suppressing material (4) or the polymerizable spacer precursor (2) can be dissolved.

  Next, in step S12, a slurry (7) composed of catalyst powder (5), platinum elution inhibiting material (4), and solvent 2 (6) is prepared. At this time, the mixing method is not particularly limited, and the suppression material (4) in a low molecular state is uniformly and uniformly disposed in the fine pores and the powder surface of the catalyst powder.

  The solvent 2 (6) is used for securing the dispersibility of the slurry (7) and adjusting the viscosity. Such a solvent is preferably a polar solvent so that each compound can be dissolved. Specifically, acetone, alcohol having 1 to 4 carbon atoms (methanol, ethanol, propanol, butanol), dimethylacetamide, ethyl acetate. , Butyl acetate, tetrahydrofuran and the like. Only one type of solvent 2 (6) may be used, or a plurality of types may be used in combination.

The catalyst powder (5) refers to a powder provided on the surface of a conductive carrier with metal catalyst particles used in an electrode of a fuel cell, particularly a polymer electrolyte fuel cell. In particular, it refers to particles that catalyze the reaction at the cathode where protons, oxygen, and electrons react to produce water. Specifically, platinum nanoparticles can be used. The average particle diameter of the platinum nanoparticles is generally about 1 to 5 nm, and the specific surface area is about 50 to ²⁰⁰ m ² / g. Moreover, although the particle diameter of platinum nanoparticles generally used in view of the required performance of the fuel cell is 2-3 nm or less, platinum is easily eluted under proton acidic conditions, and the catalyst stability is extremely low. .

The conductive carrier refers to a porous carrier that supports catalyst particles. Since the porous carrier has a role of conducting electrons to the catalyst particles, it needs to have conductivity. Specifically, porous carbon particles can be used. Porous carbon particles have pores having a size of several nm at the minimum. The average particle diameter of the porous carbon particles is larger than the average particle diameter of the catalyst particles, and is usually about 20 to 100 nm, and has a specific surface area of about 100 to 1000 m ² / g.

  Porous carbon particles may use an organic polymer electrolyte to bind to the surface of a polymer electrolyte membrane or a gas diffusion layer such as carbon paper or carbon cloth to form a planar electrode. It is common.

  Examples of the mixing method at the time of preparing the slurry in the present invention include known methods such as a planetary ball mill, a bead mill, and a homogenizer, and are not particularly limited. The electrocatalyst ink is preferably dispersed in an inert gas, but it may be mixed in an air atmosphere.

As the polymerizable compound, only the platinum elution suppressing material (4) may be used. However, in order to control the acid group concentration of the obtained polymer, the polymerizable spacer precursor is compared with the platinum elution suppressing material (4). It is desirable to use the body (2) together. Since the polymerizable spacer precursor (2) has copolymerizability with the platinum elution suppressing material (4), it is incorporated into the resulting polymer by copolymerization. The polymerizable spacer precursor (2) is a compound having no proton acidic functional group and having a polycondensable functional group. Specifically, the formula: (R ³ O) _m SiR ⁴ _n (wherein R ³ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ⁴ represents an alkyl group having 1 to 10 carbon atoms). M represents 2, 3 or 4, and n represents 0, 1 or 2. However, the sum of m and n is 4. Two or four R ^{3 s in} one molecule may be the same or different. Moreover, when two R < ⁴ > exists in 1 molecule, these R < ⁴ > may be the same and may differ.

Examples of the alkyl group having 1 to 4 carbon atoms representing R ³ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and a t-butyl group as in the case of R ^1. It is done. Of these, a methyl group is preferred because of its high reactivity and ease of removal after polymerization.

R ⁴ is a platinum elution suppressing material obtained from the alkyl group having 1 to 10 carbon atoms in consideration of the structure of the platinum elution suppressing material (4), the amount of the polymerizable spacer precursor (2) used, and the like. (4) can select the suitable thing which has an acidic concentration which can suppress elution of platinum, without inhibiting a catalytic reaction.

  When the polymerizable spacer precursor is used, the usage ratio of the polymerizable electrolyte precursor (1) and the polymerizable spacer precursor (2) depends on the EW value of the platinum elution suppression layer obtained by polymerization, power generation characteristics, and the like. Although it can be appropriately determined in consideration of the above, a molar ratio of 1: 0.25 to 10 is usually desirable. In particular, the range of 1: 0.5 to 8 is more preferable.

  The EW is an abbreviation for Equivalent Weight and represents the dry electrolyte membrane weight per mole of sulfonic acid groups. The smaller the EW value, the greater the proportion of sulfonic acid groups contained in the electrolyte. It is not preferable that the platinum elution suppressing layer in the present invention has an EW value that is too large in order to ensure both the stability of the platinum catalyst and the power generation characteristics of the electrode. Specifically, since the electrolyte layer in the present invention preferably has an EW value of 4000 or less, the use ratio of the polymerizable electrolyte precursor (1) and the polymerizable spacer precursor is adjusted so as to satisfy this range. Is preferred.

  Only one type of polymerizable spacer precursor may be used, or a plurality of types may be used in combination.

In this embodiment, although the case where a polymerizable spacer precursor is used is described, the polymerizable spacer precursor (5) may not be used. Even then, the structure of the lipophilic moiety with platinum dissolution inhibiting material (2) (e.g., number of carbon atoms of the alkylene group R ²⁾ by controlling the form of platinum elution suppressing layer having a controlled acid concentration (5) be able to.

  Further, since water is continuously produced by the oxygen reduction reaction at the catalytic site of the cathode electrode during the operation of the fuel cell, the platinum elution suppressing layer in the present invention exhibits water repellency that enables efficient drainage. It is also required. This water repellency is controlled by the structure of the platinum elution suppressing material (4) to be used, the structure and use ratio of the optional polymerizable spacer precursor (2), and the like.

  It is desirable to use the platinum elution suppressing material shown above at 0.3 to 0.7 with respect to the carbon weight of the platinum-supported carbon catalyst. Further, the weight ratio of the platinum elution suppressing material and carbon is hereinafter referred to as I / C.

  Subsequently, as shown in Step S13 to Step S14, the platinum elution suppression material (4) contained in the slurry undergoes a polycondensation reaction by subjecting the slurry (7) to reduced pressure or heat drying treatment, whereby a platinum elution suppression layer ( 8), the suppression layer-coated catalyst (9) is produced in such a manner that the suppression layer (8) covers the platinum particles and the carbon particles.

  In step S15, the paste (12) is produced by mixing the suppression layer-coated catalyst (9), the polymer electrolyte (10), and the solvent 3 (11). The polymer electrolyte to be used is a perfluoroalkylsulfonic acid polymer generally used in fuel cell catalyst electrodes, but there is no problem as long as the electrolyte material has a proton conductivity comparable to this. Not. When the weight ratio of platinum-supported carbon to carbon weight is expressed as N / C, the electrolytic mass used for preparing the paste is 0.9 to 1 in total with the previous period I / C (I / C + N / C). It is desirable to be in the range of.

Subsequently, as shown in step S16, the obtained paste (12) is applied onto a polymer film as a base material, and the solvent is removed by a drying treatment, whereby a catalyst and a platinum elution suppressing layer (8 ) And an electrolyte (10), a fuel cell electrode (12) can be formed. For example, by directly applying to an electrolyte membrane composed of a perfluorosulfonic acid polymer such as Nafion ^(R) (trade name manufactured by DuPont ⁾ and drying it, the fuel cell adheres to the membrane surface. It is also possible to form a working electrode.

  The fuel cell electrode (12) manufactured as described above has a structure in which platinum nanoparticles as a catalyst are first coated with a platinum elution suppression layer (8), and a polymer electrolyte is disposed on the outside thereof. ing. With this structure, a large amount of protons produced at the anode electrode are supplied to the surface of most of the catalyst present in the cathode electrode, and while having high power generation characteristics, deterioration of the catalyst metal due to acidic dissolution is suppressed. It will be.

  The electrode manufactured according to the present invention is used as a cathode electrode for a fuel cell. The cathode electrode is disposed to face the anode electrode with a perfluorosulfonic acid electrolyte membrane interposed therebetween, and can be configured as a fuel cell by being sandwiched between separators.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Formation of platinum elution suppressing layer in the present invention According to the above-described method, first, a polymerizable electrolyte precursor, which is a compound having a sulfonic acid group and a polycondensable silicon group, is diluted with an organic solvent. Thereafter, a low molecular weight material insoluble in water is added as a polymerizable spacer precursor and mixed to prepare a platinum elution suppressing material. Finally, a platinum elution suppression layer is obtained through a copolymerization reaction by removing volatile components such as a solvent by drying under reduced pressure and / or heating.

Specifically, the procedure is as follows. 10 mmol of a trihydroxyalkylsilane compound having a sulfonic acid group ((RO) ₃ Si— (CH ₂ ) ₃ —SO ₃ H, 30 wt% aqueous solution, Gelest) diluted with t-BuOH Prepare. Thereafter, 60 mmol of (MeO) ₃ Si— (CH ₂ ) ₅ —Me is added and stirred for 15 minutes, and further, t-BuOH is added and mixed to prepare a platinum elution inhibiting material as a colorless transparent solution. By this process, the polymerizable electrolyte precursor ((HO) ₃ Si— (CH ₂ ) ₃ —SO ₃ H) converted into a sulfonic acid group and the polymerizable spacer precursor (MeO) ₃ Si not having a sulfonic acid group - (CH _{2) 5} -Me molar ratio of 1: 6 homogeneous solution of the mixed is obtained. The EW (mass of material necessary to contain 1 mol of sulfonic acid group) value of this solution is 1070.

  Next, the polymerization reaction proceeded by gradually distilling off volatile components such as a solvent under reduced pressure from the above solution. As a result, a platinum elution suppressing layer was obtained as a water-insoluble polysiloxane solid. The polysiloxane solid has a siloxane (Si—O—Si) skeleton.

  In order to confirm the insolubility of the polysiloxane solid obtained as a film-like substance in water, the film-like substance was immersed in water and stirred for one day. The supernatant was taken and water was distilled off under reduced pressure, but no precipitation of the polysiloxane compound was confirmed.

In addition, solid-state NMR measurements were performed on the synthesized polysiloxane solids. They were measured in ¹³ C-DDMAS-NMR (single pulse & 1H decouple) and ²⁹ Si-CPMAS-NMR (1H → 13C cross polarization & 1H decouple). The chemical shift value of the signal peak was in good agreement with the theoretical value expected from its molecular structure, and it was found that the synthesized solid product was a copolymer having the target molecular structure.

In addition, various molar ratios 1: n (n = n = n) of (HO) ₃ Si— (CH ₂ ) ₃ —SO ₃ H and (MeO) ₃ Si—Me are obtained by using the above-described method for preparing the platinum elution suppressing material. It is possible to prepare platinum elution control materials mixed in 0, 0.5, 1, 2, 3). After transferring each platinum elution suppression material to the eggplant flask, the solvent was distilled off under reduced pressure using a diaphragm pump to obtain a bulk solid through a polymerization reaction.

  It was found that the polymers with n = 1, 2, 3, 4, 5 have insolubility in water.

  Further, when the solubility of the platinum elution suppression layer (n = 1, 2, 3) in an organic solvent was examined, the platinum elution suppression layer was immersed in acetone and ethyl alcohol and stirred all day and night. However, it did not dissolve at all and resulted in only a precipitate.

Further, (HO) ₃ Si— (CH ₂ ) ₃ —SO ₃ H and (MeO) ₃ Si—C ₆ H ₁₃ (manufactured by Tokyo Chemical Industry Co., Ltd.) having a C6 alkyl chain were mixed at a molar ratio of 1: n. The polymerizable electrolyte precursor thus prepared was dried and subjected to a polymerization reaction to obtain a platinum elution suppressing layer. The platinum elution suppression layer with n = 0.50,0.75,1,2,3,6,10 was immersed and stirred in acetone and ethyl alcohol all day and night, but it did not dissolve at all, and only a precipitate was obtained.

Also, (HO) ₃ Si— (CH ₂ ) ₃ —SO ₃ H and (MeO) ₃ Si—C ₁₀ H ₂₁ (made by Shin-Etsu Chemical Co., Ltd.) having a C10 alkyl chain are mixed at a molar ratio of 1: n. The platinum elution suppression material thus prepared was dried and subjected to a polymerization reaction to obtain a platinum elution suppression layer. The platinum elution suppression layers with n = 0.50,0.75,1,2,3,4,6,8 were immersed and stirred in acetone and ethyl alcohol all day and night, but did not dissolve at all, resulting in only a precipitate.

  Examples of the solvent capable of preparing the platinum elution suppressing material include lower alcohols such as acetone and ethanol, dimethylacetamide, and the like other than t-BuOH.

(Example 1) Production of fuel cells A to G A method for producing an electrode for a fuel cell using a platinum elution suppressing material obtained by the method described in the formation of a platinum elution suppressing layer will be described. Platinum elution suppression material (4) is composed of polymerizable electrolyte precursor (1) (HO) ₃ Si— (CH ₂ ) ₃ —SO ₃ H and polymerizable spacer precursor (2) (R′O) ₃ Si—R. Each of the two types (R: alkyl group, R ′: Me or Et) is contained in a predetermined molar ratio. 5 g of ultrapure water and 6.5 g of t-BuOH are added as solvent 1 (3) to 1 g of a mixture of these two types of monomers (1) and (2), which are solids, resulting in an 8% weight concentration. A solution of (4) was prepared. Regarding the mixing ratio of the polymerizable electrolyte precursor and the polymerizable spacer precursor, an appropriate molar composition having current-voltage characteristics is selected as the electrode in the range of materials having water insolubility in the formation of the electrolyte layer . But this is not the case. Each component of (HO) ₃ Si— (CH ₂ ) ₃ —SO ₃ H / (R′O) ₃ Si—R (R: alkyl group, R ′: Me or Et) contained in this electrolyte precursor is Solvated in a low molecular state.

  Next, the catalyst powder (5), the platinum elution suppressing material (4), and the solvent 2 (6) are mixed to prepare a slurry (7). A case where the electrode A is manufactured as a typical example will be described below. First, using platinum supported carbon (TEC10E50E) manufactured by Tanaka Kikinzoku Co., Ltd. as catalyst powder (5), weigh 5 g in a polypropylene beaker, add 5 g of solvent t-BuOH to this, and stir and mix so that the solvent can be used as a whole. To do. Next, after adding 10 g of platinum elution suppression material (8 wt% solution), 15 g of t-BuOH and 5 g of pure water were further added, and the slurry (7) was prepared by processing with an ultrasonic homogenizer. In the slurry (7) prepared for producing the electrode A, I / C was adjusted to about 0.4. The catalyst powder used here has a porous structure in which platinum nanoparticles of about 2 to 3 nm are supported on carbon black particles on the surface of fine carbon powder.

  Each of the slurries (7) for producing the electrode E from the electrode B was also prepared so that the I / C was 0.3 to 0.7.

  When the slurry (7) prepared from the polymerizable electrolyte precursor (1), the polymerizable spacer precursor (2), and the solvent 1 (3) was stirred at room temperature under reduced pressure, most of the solvent was distilled off. The elution suppression material changes into a platinum elution suppression layer (8) as the polycondensation reaction proceeds. Furthermore, the suppression layer coating catalyst (9) provided with (8) in the vicinity of the platinum particles was synthesized by treatment at 1 Torr and 80 ° C. for 2 hours. As a method for removing volatile components such as a solvent contained in the slurry, a spray drying method or freeze drying can be used, and the method is selected according to the required material shape of the catalyst.

Next, paste (12) was prepared by kneading the suppression layer-coated catalyst (9), the electrolyte (10), and the solvent 3 (11). Specifically, 3 g of Nafion ^(R) dispersion liquid (10 wt%, manufactured by Aldrich) as a perfluorocarbon sulfonic acid polymer electrolyte is added to the electrolyte (10) as a solvent with respect to 1 g of the suppression layer coating catalyst (9). A catalyst electrode paste for the fuel cell cathode electrode A was prepared by setting N / C = 0.7, and further adding water and alcohol to adjust the viscosity and stirring.

  In addition, in order to manufacture the electrode E from the electrode B, each was prepared so that I / C + N / C might be set to 0.9-1.2.

On the other hand, the anode electrode paste was prepared by the following method. 2 g of platinum-supported carbon (TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) was dispersed in 10 g of Nafion ^(R) dispersion (10 wt%, manufactured by Aldrich Co.), and then viscosity was adjusted by adding water and ethanol to obtain a paste. .

Further, a membrane-electrode assembly (MEA) is prepared using the above-described catalyst electrode paste for cathode electrode A, polymer electrolyte membrane Nafion ^(R) NR-211 (manufactured by DuPont), and catalyst electrode paste for anode electrode. A single fuel cell was constructed.

Each electrode was formed by die-coating the paste (12) so that the amount of platinum supported on both electrodes was cathode electrode: 0.3 mg / cm ² and anode electrode: 0.2 mg / cm ² .

  In addition, although the electrode was formed by die-coating a paste with respect to a polymer electrolyte membrane according to the manufacturing method of MEA for general fuel cells, it is not this limitation.

  For the other electrodes B to E, after preparing an electrode paste in the same manner as in the case of the electrode A, an MEA was prepared to constitute a fuel cell single cell.

(Comparative Example 1) Production of fuel cell a
Using a platinum elution inhibitor material having an EW of 1070, a suppression layer-coated catalyst with I / C = 0.2 was prepared. Further, a paste was prepared in the same manner as in the example using Nafion ^(R) dispersion (10 wt%, manufactured by Aldrich ⁾ so that N / C = 0.9. Using this paste and the anode paste in the examples, a membrane-electrode assembly (MEA) was produced to constitute a single fuel cell.

(Comparative Example 2) Production of fuel cell b
Using a platinum elution inhibitor material having an EW of 1070, a suppression layer-coated catalyst with I / C = 0.8 was prepared. Further, a paste was prepared in the same manner as in Example using a Nafion ^(R) dispersion (10 wt%, manufactured by Aldrich ⁾ so that N / C = 0.1. Using this paste and the anode paste in the examples, a membrane-electrode assembly (MEA) was produced to constitute a single fuel cell.

In addition, each electrode was formed by die-coating the paste so that the amount of platinum supported on both electrodes was cathode electrode: 0.3 mg / cm ² and anode electrode: 0.2 mg / cm ² .

Change in catalytic reaction area (ECA) of fuel cell electrode Hydrogen gas (65 ° C., 100% RH) at the anode electrode and nitrogen gas (65% at the cathode electrode ) for fuel cells A to E and fuel cells a and b (Centigrade, 100% RH) was supplied while conducting a catalyst deterioration test. The protocol for the catalyst degradation test is as follows. The potential load fluctuation of 1 cycle of 0.6 V: 3 seconds / 1.0 V: 3 seconds for 6 seconds and 1 cycle is performed for a total of 5000 cycles. And the electrochemical surface area (ECA) of platinum was measured by the cyclic voltammetry method about the cathode electrode before and behind a test, and ECA retention after the test was computed. Table 1 summarizes the results of the electrochemical surface area (ECA, assuming an initial value of 100%) after the catalyst deterioration test for each fuel cell.

表１に示したとおり、Ｉ／Ｃが０．３から０．７の燃料電池において電位サイクル後のＥＣＡ変化が比較例１及び２の燃料電池と比較して大きく抑制されているのが分かる。Ｉ／Ｃ＝０．２においてはＥＣＡ低下抑制の効果があまり得られなかった。Ｉ／Ｃ＝０．８においては、ＥＣＡ低下抑制効果は得られたものの出力特性が低かった。

As shown in Table 1, it can be seen that the ECA change after the potential cycle in the fuel cell having an I / C of 0.3 to 0.7 is greatly suppressed as compared with the fuel cells of Comparative Examples 1 and 2. When I / C = 0.2, the ECA lowering suppression effect was not obtained so much. At I / C = 0.8, although the ECA reduction suppressing effect was obtained, the output characteristics were low.

  The fuel cell electrode manufacturing method according to the present invention can enable long-term maintenance of ECA due to catalyst deterioration suppressing effect and maintenance of power generation performance associated therewith. Useful for fuel cells. Further, it is effective in reducing the amount of precious metal electrode particles and catalyst particles finely dispersed in the porous structure and ensuring reliability, and can be widely applied to uses such as stable and inexpensive electrochemical electrodes.

Claims (5)

A method for producing an oxygen reduction reaction electrode, which is represented by an alkylsulfonic acid group and (R ¹ O) ₃ Si— (wherein R ¹ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms) in the molecule. A platinum elution suppressing layer having a thickness of 0.5 to 5 nm made of a compound having a group formed on the surface of the catalyst powder having at least the catalyst particles on the surface, A method for producing an oxygen reduction reaction electrode having a structure filled with a molecular electrolyte.   2. The method for producing an oxygen reduction reaction electrode according to claim 1, wherein a weight ratio of the platinum elution suppressing material to a weight of carbon particles of a platinum-supported carbon catalyst which is a catalyst powder is 0.3 to 0.7.   2. The weight ratio of the electrolyte material that fills the gap between the platinum elution suppression layer-coated platinum-supported carbon catalyst to the weight of the carbon particles of the platinum elution suppression layer-coated platinum-supported carbon catalyst is 0.5 to 0.9. A method for producing an oxygen reduction reaction electrode.   2. The oxygen reduction according to claim 1, wherein the total weight of the platinum elution inhibiting material and the electrolyte material filling the platinum elution inhibiting layer-covered platinum-supported carbon catalyst is 0.9 to 1.2 with respect to the carbon weight of the catalyst powder. A method for producing a reaction electrode.   The fuel cell using the electrode for fuel cells obtained by the manufacturing method in any one of Claims 1-4.

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