JP2007213947A - Manufacturing method of catalyst support powder for polymer electrolyte fuel cell, and polymer electrolyte fuel cell having catalyst support powder provided by same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of catalyst support powder capable of suppressing operating voltage drop in an endurance test of a polymer electrolyte fuel cell (PEFC), and to provide a PEFC using the catalyst support powder. <P>SOLUTION: This manufacturing method of catalyst support powder for a polymer electrolyte fuel cell goes through: a first process for manufacturing a mixture of a cation exchange resin, a carbonaceous material, a fluororesin, and a solvent; a second process for providing mixed powder of the cation exchange resin, the carbonaceous material, and the fluororesin by drying the mixture; a third process for adsorbing cations of a catalyst metal to fixed ions of the cation exchange resin in the mixed powder; and a fourth process for chemically reducing the cations. The manufacturing method is characterized in that not less than 30 mass% of any of methanol, acetone and (methanol+acetone) is included in the solvent of the mixture in the first process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a catalyst-supported powder for a polymer electrolyte fuel cell and a polymer electrolyte fuel cell comprising a catalyst-supported powder obtained by the method.

  A single cell of a polymer electrolyte fuel cell (PEFC) has a structure in which a membrane / electrode assembly is sandwiched between a pair of gas flow plates. The membrane / electrode assembly is obtained by joining an anode on one side of a cation exchange membrane and a cathode on the other side. A gas flow path is processed in the gas flow plate. For example, power is obtained by supplying hydrogen as fuel to the anode and oxygen as oxidant to the cathode. In the anode and cathode, the following electrochemical reaction proceeds.

Anod: 2H ₂ → 4H ⁺ + 4e ⁻ (1)
Cathode: O ₂ + 4H ⁺ + 4e ⁻ → H ₂ O (2)
The above-described electrochemical reaction proceeds at a region where hydrogen or oxygen and protons (H ⁺ ) are transmitted and an interface with the catalyst (hereinafter, this interface is referred to as a reaction interface). Since the catalyst is in contact with the electron conductive member, the electrons (e ⁻ ) are collected through the member.

  As a conventional PEFC catalyst-supported powder, there is a patent consisting of a mixture of an electrode catalyst (supporting active catalyst metal particles on a catalyst carrier such as carbon black), PTFE (polytetrafluoroethylene) and an ion exchanger. Carbon powder disclosed in Document 1 and carbon powder in which catalyst metal is supported, carbon powder obtained by adding PTFE to a colloidal dispersion of solid polymer electrolyte and water-repellent treatment, and carbon powder supporting platinum catalyst. A manufacturing method to be added is disclosed in Patent Document 2.

  Recently, Patent Documents 3 and 4 disclose that a catalytic metal is mainly supported on a contact surface between a proton conduction path of a cation exchange resin and a surface of a carbonaceous material. The catalyst-supported powder (ultra-low platinum loading carbon, hereinafter referred to as ULPLC) in which the catalyst metal is mainly supported on the contact surface between the proton conduction path of the cation exchange resin and the surface of the carbonaceous material is the utilization rate of the catalyst metal. Is excellent in reducing costs by reducing the amount of catalyst metal used.

Also, in the ULPLC production method, in order to improve the wettability of the carbon particle surface, first, carbon particles containing alcohol such as methanol are first prepared, and a technique of passing through this and a cation exchange resin solution is mixed. Is disclosed. However, the electrode obtained in Patent Document 5 did not contain a fluororesin other than the cation exchange resin.
Japanese Patent Laid-Open No. 06-068880 Japanese Patent Application Laid-Open No. 08-088007 JP 2000-012041 A JP 2003-257439 A JP 2005-222812 A

  However, the PEFC equipped with this ULPLC has a drawback that the operating voltage drop in the durability test is large and the practicality is poor. The cause was not clear, and there was a strong demand for improvement. The inventor has intensively studied the cause of the decrease in the operating voltage of the PEFC equipped with the ULPLC and found that the main cause of the decrease is due to the flooding phenomenon.

  The “flooding phenomenon” in PEFC means that the water produced by the reaction is not discharged and the catalyst surface is covered so that the catalyst does not participate in the reaction. This means that gas or oxygen gas is prevented from reaching the reaction interface from outside the system.

  That is, in the catalyst layer provided with this ULPLC, water generated by the reaction is not easily discharged out of the system, and the water becomes water droplets and blocks the gas diffusion path, so that hydrogen gas or oxygen gas as an active material is used in the system. Inhibits reaching the reaction interface from the outside. As a result, no reaction occurs at the reaction interface where these gases do not reach, and the current density is biased, so that the operating voltage of this PEFC is considered to decrease. Therefore, in order to put this ULPLC into practical use, it is indispensable to suppress this flooding phenomenon.

  The present inventor has found that the main cause of the decrease in PEFC operating voltage is due to the aggregation of fluororesin in ULPLC. That is, the water repellency is biased due to the aggregation of the fluororesin in the ULPLC, so that the water generated by the reaction is insufficiently discharged. Therefore, the water stays in the electrode as water droplets and blocks the gas diffusion path, thereby preventing the hydrogen gas or oxygen gas as the active material from reaching the reaction interface from outside the system.

  As a result, reaction does not occur at the reaction interface where these gases do not reach, and the current density is biased, which is considered to reduce the operating voltage of this PEFC. Therefore, it is necessary to uniformly disperse the fluororesin in the ULPLC.

  The present invention relates to the operating voltage of PEFC using a catalyst-supporting powder comprising a catalyst-supporting powder and a water-repellent material mainly comprising a catalyst metal on the contact surface between the proton conduction path of the cation exchange resin and the surface of the carbonaceous material. The reduction rate was found to be remarkably improved as compared with the conventional one, and it was made paying attention to that.

  An object of the present invention is to provide a method for producing a catalyst-supported powder capable of suppressing a decrease in operating voltage in a PEFC durability test and a polymer electrolyte fuel cell provided with the catalyst-supported powder obtained by the production method.

  The invention of claim 1 includes a first step of producing a mixture of a cation exchange resin, a carbonaceous material, a fluororesin and a solvent, and drying the mixture to obtain a cation exchange resin, a carbonaceous material and a fluororesin. A second step of obtaining a mixed powder of the catalyst, a third step of adsorbing a cation of a catalytic metal to a fixed ion of a cation exchange resin in the mixed powder, and a fourth step of chemically reducing the cation In the method for producing a catalyst-supported powder for a polymer electrolyte fuel cell that undergoes a step, methanol, acetone, or (methanol + acetone) is contained in an amount of 30% by mass or more in the solvent of the mixture of the first step. It is characterized by.

  According to a second aspect of the present invention, in the polymer electrolyte fuel cell, the catalyst-supported powder obtained by the manufacturing method according to the first aspect is provided.

  Since the catalyst-supported powder for polymer electrolyte fuel cells of the present invention has sufficient water repellency, the electron conductivity and the water repellency are optimal in the catalyst layer of the polymer electrolyte fuel cell using the same. . As a result, the flooding phenomenon during the operation of the polymer electrolyte fuel cell can be suppressed, and the decrease in cell voltage can be suppressed.

  Further, in the first step of the method for producing a catalyst-supporting powder for a polymer electrolyte fuel cell of the present invention, any of methanol, acetone and (methanol + acetone) is contained in an amount of 30% by mass or more in the solvent of the mixture. Thus, since the fluororesin is uniformly dispersed in the mixture, in the polymer electrolyte fuel cell using the obtained catalyst-carrying powder, the flooding phenomenon can be suppressed and the decrease in the cell voltage can be suppressed. .

  The method for producing the catalyst-supporting powder for a polymer electrolyte fuel cell of the present invention is as follows.

  First, in the first step, a mixture of a cation exchange resin, a carbonaceous material, a fluororesin, and a solvent is prepared. In the first step, in order to uniformly mix the cation exchange resin, the carbonaceous material, and the fluororesin, the cation exchange resin and the fluororesin are in the form of powder or dispersed or dissolved in a solvent. Preferably there is.

  Next, in the second step, the mixture obtained in the first step is dried, the solvent is removed, and a mixed powder of the cation exchange resin, the carbonaceous material, and the fluororesin is obtained. As a method for performing this drying, for example, there is a method of spray drying the mixture of the cation exchange resin, the carbonaceous material, the fluororesin and the solvent obtained in the first step.

  Next, in the third step, the cation of the catalytic metal is adsorbed on the fixed ions of the cation exchange resin in the mixed powder of the cation exchange resin, the carbonaceous material and the fluororesin obtained in the second step. Let

  In this third step, for example, a mixed powder containing a cation exchange resin, a carbonaceous material, and a fluororesin is immersed in an aqueous solution containing a cation of the catalytic metal element, and the cation of the catalytic metal and the cation exchange resin The cation of the catalytic metal is preferentially adsorbed on the cation exchange resin by an ion exchange reaction with the fixed ions.

As a cation containing a platinum group metal having such adsorption characteristics, a platinum group metal complex ion, for example, platinum ammine complex cation such as [Pt (NH ₃ ) ₄ ] ²⁺ and [Pt (NH ₃ ) ₆ ] ⁴⁺ Ions, or ruthenium ammine complex cations such as [Ru (NH ₃ ) ₄ ] ²⁺ and [Ru (NH ₃ ) ₆ ] ³⁺ .

  Further, in the fourth step, the catalyst-supported powder of the present invention is obtained by chemically reducing the cation of the catalyst metal adsorbed on the cation exchange resin using a reducing agent. As a reducing agent that can be used in this step, for example, hydrogen gas can be used. This hydrogen gas is preferably used as a mixed gas (hydrogen mixed gas) with an inert gas such as nitrogen, helium or argon. Further, the reduction temperature in this reduction is in the range of 100 ° C. or higher and 200 ° C. or lower, and particularly preferably 150 ° C. or higher and 180 ° C. or lower.

  In the method for producing a catalyst-supported powder for a polymer electrolyte fuel cell according to the present invention, in the mixture of the first step, 30% by mass or more of methanol, acetone, or (methanol + acetone) is contained in the solvent of the mixture. It is included.

  In the present invention, a dispersion containing a cation exchange resin, a carbonaceous material, and a fluororesin is a cation exchange resin solution in which a cation exchange resin is dissolved in alcohol in advance, a carbonaceous material, and an aqueous solution containing a surfactant. A solution in which the resin powder is dispersed can be obtained by mixing with methanol, acetone or a solution containing methanol and acetone. Alternatively, cation exchange resin powder, carbonaceous material, and fine powder of fluororesin can be obtained by mixing methanol, acetone, or a solution containing methanol and acetone.

  Here, methanol in the solution so that either 30% by mass or more of methanol, acetone, or (methanol + acetone) is contained in the solvent of the dispersion containing the cation exchange resin, the carbonaceous material, and the fluororesin. It is necessary to adjust the blending ratio of acetone and acetone. The reason is as follows.

  When the ratio of methanol, acetone or (methanol + acetone) contained in the solution is less than 30% by mass, the fluororesin is aggregated, and the resulting cation exchange resin, carbonaceous material, and mixture containing the fluororesin are mixed. In the powder, the fluororesin is biased. On the other hand, in the case of 30% by mass or more, since the fluororesin exists uniformly, the water repellency of the electrode is improved. Accordingly, since the discharge of water generated by the fuel cell reaction is promoted, hydrogen gas or oxygen gas as an active material can easily reach the reaction interface from outside the system. As a result, the current density becomes uniform and a decrease in the operating voltage of the PEFC is suppressed.

  In the first step of the method for producing a catalyst-supporting powder for a polymer electrolyte fuel cell according to the present invention, the cation exchange resin and the fluororesin each include a cation exchange resin solution and a fluororesin in which the cation exchange resin is dissolved. A dispersion solution in which is dispersed in water containing a surfactant is used. Since the type of the solvent contained in the cation exchange resin solution is not disclosed, it is currently unknown, and the dispersion solution contains about 40% water. Therefore, when a commercially available cation exchange resin solution and fluororesin dispersion solution are used, the ratio of methanol, acetone or (methanol + acetone) contained in the solvent of the mixture of the first step is 100. %.

  However, in the future, when a cation exchange resin solution using only methanol or acetone as a solvent and a dispersion medium and a dispersion solution of a fluororesin are developed, in the first step of the present invention, as a solvent of the mixture, It is estimated that 100% methanol or acetone can be used. Therefore, in the present invention, the upper limit of the ratio of methanol, acetone or (methanol + acetone) contained in the solvent of the mixture in the first step is not particularly limited.

  The catalyst-supported powder for a polymer electrolyte fuel cell of the present invention comprises a catalyst metal, a cation exchange resin, a carbonaceous material, and a fluororesin, and the catalyst metal comprises a proton conduction path of the cation exchange resin, a carbonaceous material, It is mainly prepared for the contact surface. The reason is as follows.

  In the polymer electrolyte fuel cell electrode using the catalyst-supported powder for polymer electrolyte fuel cell of the present invention, the catalyst metal has a proton conduction path through which protons, water, hydrogen and oxygen involved in the reaction can mainly move. It is mainly supported on the surface in contact with the surface of the carbon material. Since this place is a place where electrons and protons can be exchanged at the same time, the catalyst metal supported on this contact surface is efficiently involved in the electrode reaction. Therefore, by increasing the proportion of the catalyst metal supported on the contact surface between the proton conduction path and the surface of the carbon material, the utilization rate of the catalyst metal is remarkably increased, and the amount of catalyst metal used can be reduced.

  In the catalyst layer of the polymer electrolyte fuel cell electrode of the present invention, "the catalytic metal is mainly provided on the contact surface between the proton conduction path of the cation exchange resin and the carbon material" means that the cation exchange resin It means that the amount of catalyst metal supported on the surface of carbon particles in contact with the proton conduction path is 50% by mass or more of the total amount of catalyst metal supported. That is, 50% by mass or more of the total catalytic metal loading is a catalytic metal active for the electrode reaction, so that the utilization rate of the catalytic metal is remarkably increased.

  In the present invention, the ratio of the amount of the catalyst metal supported on the surface of the carbon particles in contact with the proton conduction path of the cation exchange resin to the total amount of the catalyst metal supported is preferably as high as possible, particularly exceeding 80% by mass. preferable. In this way, the electrode is highly activated by supporting the catalytic metal at a high rate on the contact surface between the proton conduction path and the carbon particles.

  In the catalyst-supported powder of the present invention, the catalyst metal is mainly provided on the contact surface between the proton conduction path of the cation exchange resin and the carbon material, which is described in the literature (M. Komomoto et.al., GS Yuasa). As described in Technical Report, 1, 48 (2004)), it becomes clear from the change over time in the electrochemically active surface area and the mass activity of platinum as a catalyst in a polymer electrolyte fuel cell electrode.

  Regarding the time-dependent change in the electrochemically active surface area of platinum, in the conventional electrode, the electrochemically active surface area of platinum decreases due to aggregation due to the dissolution / precipitation reaction of platinum, but the electrode using the catalyst-supported powder of the present invention Then almost no aggregation occurs.

  When the polymer electrolyte fuel cell is operated at a low current density, all platinum is used for the electrochemical reaction, but when it is operated at a high current density, it exists in the proton conduction path of the cation exchange resin. Only platinum is used for the electrochemical reaction, and platinum present in the hydrophobic skeleton part does not participate in the electrochemical reaction.

  In addition, the mass activity ratio of the electrode using the catalyst-supported powder of the present invention to the conventional electrode is approximately 1 in a high voltage region higher than 0.70 V during operation of the fuel cell, and 2. 7 On the other hand, in the cation exchange resin, the volume ratio of the proton conduction path in the polymer portion is about 2.5. Therefore, in the conventional electrode, in the high voltage region above 0.70 V, platinum in the proton conduction path of the cation exchange resin and platinum in the hydrophobic skeleton portion are active, but at 0.60 V, the cation exchange resin. It is clear that only platinum in the proton conduction pathway is active.

  The mass activity is obtained by dividing the current density at a certain voltage by the amount of the catalyst metal supported per unit area.

  The fluororesin that can be used in the catalyst-supporting powder of the present invention does not include a polymer having an ion exchange group such as a cation exchange resin. Specific examples thereof include FEP (tetrafluoroethylene-hexafluoropropylene copolymer, Tetrafluoroethylene hexafluoropropylene copolymer), PVdF (polyvinylidene fluoride) and PTFE (polytetrafluoroethylene, polyfluor, etc.). Among these, in order to make the dispersibility of the fluororesin in the mixture in the first step more uniform, it is preferable to use FEP or PTFE.

  Examples of the cation exchange resin that can be used in the catalyst-supported powder of the present invention include perfluorocarbon sulfonic acid type, styrene-divinylbenzene sulfonic acid type cation exchange resin, and cation exchange resin having a carboxyl group as an ion exchange group. Is preferred.

  As the carbonaceous material used in the present invention, carbon black, activated carbon, graphite, carbon nanotube, carbon nanofiber, and the like can be used, but carbon black is particularly preferable because of its large specific surface area. As the carbon black, furnace black, acetylene black, or the like can be used.

  The catalytic metal used in the catalyst-supporting powder of the present invention has high catalytic activity for electrochemical oxygen reduction reaction and hydrogen oxidation reaction, so platinum group metals such as platinum, rhodium, ruthenium, iridium, palladium and osnium are used. preferable. In particular, an alloy containing platinum and ruthenium is preferable as an anode catalyst because high CO poisoning resistance can be expected. Furthermore, an alloy containing at least one element selected from the group consisting of magnesium, aluminum, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, silver, or tungsten and a platinum group metal is used as the catalyst metal. Thus, a reduction in the amount of platinum group metal used, an improvement in CO poisoning resistance, and a high activity for oxygen reduction reaction can be expected.

  By the production method of the present invention, catalyst-supported carbon powder in which the catalyst metal is mainly supported on the contact surface between the carbonaceous material and the proton conduction path of the cation exchange resin can be obtained. The catalytic metal supported on the contact surface has a high activity for the electrode reaction. Therefore, the usage amount of the catalyst metal can be reduced by increasing the ratio of the catalyst metal supported on the contact surface. Furthermore, the aggregation of the fluororesin that functions as a water repellent contained in this powder is suppressed, so that the gas diffusibility is improved and the current density distribution is uniform, resulting in improved PEFC output and durability. To do.

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

[Examples 1-3 and Comparative Examples 1-3]
[Example 1]
A catalyst-supporting powder containing 100% by mass of a fluororesin and 67% by mass of a cation exchange resin with respect to the carbonaceous material was prepared. First, in the first step, carbon powder (Vulcan XC-72, manufactured by Cabot) 15 g, cation exchange resin solution (Nafion 5 mass% solution, manufactured by Aldrich) 200 g, FEP dispersion (54 mass%, Mitsui / Dupont Fluoro) A mixture containing 28 g of FEP120-J (chemical) and 600 g of methanol was prepared.

  In this mixture, the solvent contained in the cation exchange resin solution was 190 g, the solvent contained in the FEP dispersion was 12.9 g, and the total amount of the solvent was 802.9 g. Since the solvent contained in the cation exchange resin solution is unknown, when methanol is not contained, the ratio of methanol contained in the solvent in this mixture was 74.7% by mass.

  Next, in the second step, this mixture was dried by spray drying and granulated to produce a mixed powder containing a cation exchange resin, carbon powder and FEP. In this mixed powder, it is presumed that the carbon powder is coated with a cation exchange resin and FEP.

Subsequently, in the third step, this mixed powder is impregnated with an aqueous solution of [Pt (NH ₃ ) ₄ ] Cl ₂ (50 mmol / l solution) and [Pt (NH ₃ ) ₄ ] ²⁺ is ^added to the cation exchange resin. It was made to adsorb | suck to a cluster part.

  Further, in the fourth step, the mixed powder was washed and dried, and reduced at 180 ° C. in a hydrogen atmosphere, thereby producing the catalyst-supporting powder A of Example 1. The amount of platinum contained in the catalyst powder was 2.15% by mass with respect to the catalyst-supported powder. This amount of platinum is a value obtained by extracting platinum of catalyst powder with aqua regia and then quantifying the amount of platinum in the aqua regia by ICP emission analysis. The amount of FEP contained in the catalyst-supporting powder A was 100% by mass with respect to the carbon powder.

A catalyst layer containing this catalyst-supported powder A was produced by the following method. First, a mixture containing 6.0 g of the catalyst-supporting powder A and 15 g of N-methyl-2-pyrrolidone (NMP, manufactured by Mitsubishi Chemical) was prepared, and this mixture was applied onto a titanium sheet and then dried. A layer was formed on the titanium sheet. Subsequently, the catalyst layer was cut into a square having a side of 5 cm to form a catalyst layer. In addition, when apply | coating a mixture, the thickness of application | coating was adjusted and the amount of platinum contained in this catalyst layer was 0.060 mg / cm < ² >.

  Furthermore, a membrane / electrode assembly for a polymer electrolyte fuel cell and a polymer electrolyte fuel cell were produced by the following method. First, the obtained catalyst layer and a cation exchange membrane (Nafion 112, manufactured by DuPont, film thickness of about 50 μm) were hot-pressed at 17.1 MPa and 160 ° C. to be transferred onto both surfaces of the cation exchange membrane, and titanium The sheet was peeled off to produce a membrane / electrode assembly.

  Next, this membrane / electrode assembly was washed with an aqueous sulfuric acid solution (0.5 mol / l) and water. Furthermore, after arranging carbon paper (TGP-H-060, manufactured by Toray) of a conductive porous body imparting water repellency to both surfaces of this bonded body, it is sandwiched between a pair of gas flow plates. The polymer electrolyte fuel cell (cell A) of Example 1 was produced by sandwiching it with a current collector plate.

[Example 2]
A catalyst-supported powder B was produced in the same manner as in Example 1 except that acetone was used instead of methanol. Then, in the same manner as in Example 1, using the catalyst-supported powder B, a polymer electrolyte fuel cell (cell B) of Example 2 was produced.

[Example 3]
A catalyst-carrying powder C was prepared in the same manner as in Example 1 except that a mixed solution of 300 g of methanol and 300 g of acetone was used instead of 600 g of methanol. Then, in the same manner as in Example 1, using the catalyst-supported powder C, a polymer electrolyte fuel cell (cell C) of Example 3 was produced.

[Comparative Example 1]
A catalyst-supported powder D was produced in the same manner as in Example 1 except that 2-propanol was used instead of methanol. Then, in the same manner as in Example 1, a solid polymer fuel cell (cell D) of Comparative Example 1 was produced using the catalyst-supported powder D.

[Comparative Example 2]
A catalyst-supported powder E was produced in the same manner as in Example 1 except that ethanol was used instead of methanol. Then, in the same manner as in Example 1, a solid polymer fuel cell (cell E) of Comparative Example 2 was produced using the catalyst-supported powder E.

[Comparative Example 3]
A catalyst-supported powder F was produced in the same manner as in Example 1 except that N-methyl-2-pyrrolidone (NMP) was used instead of methanol. Then, a polymer electrolyte fuel cell (cell F) of Comparative Example 3 was produced using the catalyst-supported powder F in the same manner as in Example 1.

  For the polymer electrolyte fuel cells A to F of Examples 1 to 3 and Comparative Examples 1 to 3, the cell temperature was 70 ° C., the anode gas was pure hydrogen, the anode utilization rate was 80%, and the anode humidification temperature was 70 ° C. The voltage-current characteristics were measured under conditions where the cathode gas was air, the cathode utilization rate was 40%, and the cathode humidification temperature was 70 ° C.

  FIG. 1 shows voltage-current curves of the PEFC of Example 1 (Cell A) and the PEFC of Comparative Example 1 (Cell D). In FIG. 1, the symbol ◯ indicates the characteristics of Example 1, and the symbol Δ indicates the characteristics of Comparative Example 1.

  1 that the voltage-current characteristic of the PEFC of Example 1 is superior to that of Comparative Example 1. FIG. In addition, the voltage-current curve of PEFC of Example 2 and Example 3 is substantially the same as the voltage-current curve of PEFC of Example 1, and the voltage-current curve of PEFC of Comparative Example 3 and Comparative Example 4 is It was almost the same as the voltage-current curve of the PEFC of Comparative Example 1.

  This means that in the mixture of the first step, when methanol or acetone is used as the solvent, FEP is uniformly dispersed in the catalyst layer, so that water discharge is improved, and as a result, the current distribution is uniform. This is thought to be due to the fact that

Next, for the polymer electrolyte fuel cells of Examples 1 to 3 and Comparative Examples 1 to 3, the cell voltage when operated at a current density of 300 mA / cm ^{2 under} the same conditions as the voltage-current characteristics were measured. Was measured over time. The results are shown in Table 1.

  From the results in Table 1, it was found that the cell voltage reduction rate was considerably better than that of Comparative Examples 1 to 3 using NMP, ethanol or 2-propanol alone when methanol or acetone was used.

  This is because, when methanol or acetone is used, FEP is uniformly dispersed in the catalyst layer, and as a result, sufficient water repellency was obtained, and as a result, a decrease in cell voltage due to flooding could be suppressed. Conceivable. In particular, in the case of methanol, a decrease in cell voltage can be remarkably suppressed. From the above, it was found that the fuel cell characteristics can be remarkably improved by using methanol or acetone in the mixture in the first step of the method for producing the catalyst-supporting powder of the present invention.

[Examples 4 to 10]
In Examples 4 to 10, since the solvent contained in the cation exchange resin solution is unknown, the ratio of methanol contained in the solvent of the mixture was determined on the assumption that methanol was not contained.

[Example 4]
In the mixture prepared in the first step, a catalyst was prepared in the same manner as in Example 1 except that a mixed solution of water and methanol was used as the solvent, and the ratio of methanol contained in the solvent in the mixture was 10% by mass. A carrier powder G was produced. Then, in the same manner as in Example 1, using the catalyst-supported powder G, a polymer electrolyte fuel cell (cell G) of Example 4 was produced.

[Example 5]
In the mixture prepared in the first step, a catalyst was prepared in the same manner as in Example 1 except that a mixed solution of water and methanol was used as the solvent, and the proportion of methanol contained in the solvent in the mixture was 20% by mass. Support powder H was produced. Then, in the same manner as in Example 1, using the catalyst-supported powder H, a polymer electrolyte fuel cell (cell H) of Example 5 was produced.

[Example 6]
In the mixture prepared in the first step, a catalyst was prepared in the same manner as in Example 1 except that a mixed solution of water and methanol was used as the solvent, and the ratio of methanol contained in the solvent in the mixture was 30% by mass. Support powder I was prepared. Then, in the same manner as in Example 1, using the catalyst-supported powder I, a polymer electrolyte fuel cell (cell I) of Example 6 was produced.

[Example 7]
In the mixture prepared in the first step, a catalyst was prepared in the same manner as in Example 1 except that a mixed solution of water and methanol was used as the solvent, and the proportion of methanol contained in the solvent in the mixture was 40% by mass. Support powder J was prepared. Then, in the same manner as in Example 1, using the catalyst-supported powder J, a polymer electrolyte fuel cell (cell J) of Example 7 was produced.

[Example 8]
In the mixture prepared in the first step, a catalyst was prepared in the same manner as in Example 1 except that a mixed solution of water and methanol was used as the solvent, and the proportion of methanol contained in the solvent in the mixture was 50% by mass. A supported powder K was produced. Then, in the same manner as in Example 1, using the catalyst-supported powder K, a polymer electrolyte fuel cell (cell K) of Example 8 was produced.

[Example 9]
In the mixture prepared in the first step, a catalyst was prepared in the same manner as in Example 1 except that a mixed solution of water and methanol was used as the solvent, and the proportion of methanol contained in the solvent in the mixture was 60% by mass. A supported powder L was produced. Then, in the same manner as in Example 1, a solid polymer fuel cell (cell L) of Example 9 was produced using the catalyst-supported powder L.

[Example 10]
In the mixture prepared in the first step, a catalyst was prepared in the same manner as in Example 1 except that a mixed solution of water and methanol was used as the solvent, and the proportion of methanol contained in the solvent in the mixture was 70% by mass. A supported powder M was produced. Then, in the same manner as in Example 1, a solid polymer fuel cell (cell M) of Example 10 was produced using the catalyst-supported powder M.

For the polymer electrolyte fuel cells of Examples 4 to 10, the cell voltage at a current density of 300 mA / cm ² was measured under the same conditions as the voltage-current characteristics measured in Example 1. The relationship between the ratio of methanol contained in the solvent in the mixture in the first step and the cell voltage is shown in FIG.

  FIG. 2 shows that the cell voltage is remarkably improved when the proportion of methanol is 30% by mass or more. This is because when the amount is less than 30% by mass, since the proportion of methanol in the dispersion is small, the FEP aggregates and the FEP is localized in the obtained catalyst-supporting carbon powder, so that sufficient water repellency is obtained. As a result, it is considered that flooding occurs and a sufficient output voltage cannot be obtained.

  On the other hand, when the proportion of methanol is 30% by mass or more, FEP is uniformly dispersed in the powder, so that sufficient water repellency is obtained, and as a result, discharge of water generated by the fuel cell reaction is promoted. Therefore, hydrogen gas or oxygen gas, which is an active material, easily reaches the reaction interface from outside the system, so that it is considered that the current distribution becomes uniform and a high voltage is exhibited. Therefore, in the mixture prepared in the first step, it has been clarified that the performance of the polymer electrolyte fuel cell is remarkably improved when the proportion of methanol in the solvent in the mixture is 30% by mass or more.

  Furthermore, when PTFE was used in place of FEP, the same experiment was conducted. When the solvent of the mixture in the first step contained methanol, acetone or (methanol + acetone), the same result as FEP was obtained. Obtained. That is, the polarization characteristics and durability performance are superior to those of 2-propanol, ethanol, or NMP, and the effect is that the ratio of methanol, acetone or (methanol + acetone) is 30% by mass or more in the solvent. It was confirmed to be remarkable when I was.

The figure which shows the voltage-current curve of the polymer electrolyte fuel cell of Example 1 and Comparative Example 1. FIG. The figure which shows the relationship between the ratio of the methanol contained in the solvent of the mixture of a 1st process, and a cell voltage.

Claims (2)

A first step of producing a mixture of a cation exchange resin, a carbonaceous material, a fluororesin, and a solvent; and a second step of drying the mixture to obtain a mixed powder of the cation exchange resin, the carbonaceous material, and the fluororesin. A solid polymer form that has undergone the following steps: a third step of adsorbing a cation of a catalytic metal to fixed ions of a cation exchange resin in the mixed powder; and a fourth step of chemically reducing the cation. In the method for producing a catalyst-supporting powder for a fuel cell, the solid polymer, wherein the solvent of the mixture in the first step contains at least 30% by mass of methanol, acetone, or (methanol + acetone) Of a catalyst-supporting powder for a fuel cell. A polymer electrolyte fuel cell comprising the catalyst-supported powder obtained by the production method according to claim 1.

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