JP5672752B2 - Method for producing carbon-supported core-shell type catalyst fine particles, and method for producing catalyst ink using core-shell type catalyst fine particles obtained by the production method - Google Patents

Description

The present invention relates to a method for producing carbon-supported core-shell type catalyst fine particles, and a method for producing catalyst ink using core-shell type catalyst fine particles obtained by the production method .

  A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes.

  Conventionally, supported platinum and platinum alloy materials have been employed as electrolytic catalysts for anodes and cathodes of fuel cells. However, the amount of platinum required for current state-of-the-art electrocatalysts is still too expensive to make mass production of fuel cells commercially feasible. Therefore, studies have been made to reduce the amount of platinum contained in fuel cell cathodes and anodes by combining platinum with less expensive metals.

  One study of the combination of platinum and cheaper metals is to deposit an atomic monolayer of platinum on palladium nanoparticles. As a technique to which such research is applied, Patent Document 1 discloses a method for producing metal-coated palladium or palladium alloy particles, which includes hydrogen absorbing palladium or palladium alloy particles as a metal salt or metal salt. Contacting with the mixture and depositing a quasi-monoatomic or monoatomic metal coating or quasi-monoatomic or monoatomic metal alloy coating on the surface of said hydrogen-absorbing palladium or palladium alloy particles, thereby forming a metal coating or metal alloy coated palladium or palladium A method is disclosed that includes the step of producing alloy particles.

Special table 2008-525638 gazette

Patent Document 1 also discloses a method of bonding metal coating particles to a support. However, Patent Document 1 does not describe any adverse effect of the support when producing metal coating particles bonded to the support.
The present invention has been accomplished in view of the above circumstances, a method for producing core-shell type catalyst fine particles supported on a carrier, a method for producing catalyst ink using core-shell type catalyst fine particles obtained by the production method, and It aims at providing the catalyst layer containing the catalyst ink obtained by the said manufacturing method.

The method for producing carbon-supported core-shell type catalyst fine particles of the present invention is a method for producing carbon-supported core-shell type catalyst fine particles comprising a core part and a shell part that covers the core part, and the carbon carrier on which the core fine particles are supported A deactivation step of deactivating functional groups present on the surface of the carbon support by mixing the carbon support on which the core fine particles are supported and an inactivating agent; and After the deactivation step, the method has a step of covering the core portion with the core portion using the core fine particles as a core portion.

  In the manufacturing method having such a configuration, when the shell portion is coated on the core portion, the shell metal material constituting the shell portion does not have an affinity with the surface of the carbon carrier. Precipitation of the shell metal material in can be suppressed. As a result, an increase in the amount of shell metal material used can be prevented and costs can be reduced.

In one aspect of the method for producing carbon-supported core-shell type catalyst particles of the present invention, the deactivator is a protective group introducing agent, and the deactivation step includes a carbon support on which the core particles are supported , By mixing with a protecting group introducing agent, it is possible to adopt a constitution in which it is a protecting group introducing step for bonding a protecting group to a functional group present on the surface of the carbon support.

  In the production method having such a configuration, the functional group present on the surface of the carbon support can be deactivated accurately and simply by selecting an appropriate protecting group introducing agent.

  As one aspect of the method for producing carbon-supported core-shell type catalyst particles of the present invention, the protective group-introducing agent may be a cationic surfactant.

  In the production method having such a configuration, the cationic surfactant reacts with the functional group on the carbon support, whereby the functional group can be inactivated.

In one aspect of the method for producing carbon-supported core-shell type catalyst particles of the present invention, the deactivator is a reducing agent, and the deactivation step includes a carbon support on which the core particles are supported, and the reducing agent. Can be configured to be a reduction process for reducing functional groups present on the surface of the carbon support.

  In the manufacturing method having such a configuration, the functional group present on the surface of the carbon support can be deactivated accurately and simply by selecting an appropriate reducing agent.

  The method for producing the catalyst ink of the present invention is a hydrophilic ink that hydrophilizes functional groups present on the surface of the carbon carrier by mixing the carbon-supported core-shell type catalyst particles obtained by the above production method with a hydrophilizing agent. And a step of mixing at least the carbon-supporting core-shell type catalyst particles that have undergone the hydrophilic step and an electrolyte.

  In the manufacturing method having such a configuration, the affinity at the time of mixing the carbon-supporting core-shell type catalyst fine particles and the electrolyte can be increased by hydrophilizing the functional group present on the surface of the carbon support.

  As one aspect of the method for producing a catalyst ink of the present invention, the hydrophilizing agent is a deprotecting agent, and the hydrophilizing step removes a protecting group from a functional group present on the surface of the carbon support. It can take the composition of being.

  The manufacturing method having such a configuration can hydrophilize the functional group by deprotecting the functional group present on the surface of the carbon support.

  As one aspect of the method for producing the catalyst ink of the present invention, the deprotecting agent may be a strong acid.

  According to the present invention, when the shell portion is coated on the core portion, the shell metal material constituting the shell portion does not have an affinity with the surface of the carbon support. The deposition of the material can be suppressed. As a result, an increase in the amount of shell metal material used can be prevented and costs can be reduced.

It is the figure which showed typically the process of coat | covering a shell part on a core part in the manufacturing method of this invention. It is a figure which shows an example of a fuel cell provided with the catalyst layer of this invention, Comprising: It is the figure which showed typically the cross section cut | disconnected in the lamination direction. It is the figure which showed typically the conventional method which coat | covers platinum on the palladium fine particle carry | supported by carbon, and manufactures a support core-shell type catalyst fine particle.

1. Method for Producing Carbon-Supported Core-Shell Type Catalyst Fine Particles The method for producing carbon-supported core-shell type catalyst fine particles of the present invention is a method for producing carbon-supported core-shell type catalyst fine particles comprising a core part and a shell part covering the core part. A step of preparing core fine particles supported on a carbon support, an inactivation step of inactivating functional groups present on the surface of the carbon support by mixing the core fine particles and an inactivating agent, And after the said inactivation process, it has the process of coat | covering the said shell part to the said core part by making the said core microparticle into a core part.

  In the present invention, “deactivating the functional group present on the surface of the carbon support” means that the functional group is in an inactive state with respect to adsorption of the shell metal material that is the raw material of the shell portion and its ions. It means to convert.

  As a conventional method for producing the carbon-supported core-shell type catalyst fine particles, there is a method in which the core fine particles supported on the carbon support are coated with a shell portion using a shell metal material as a raw material of the shell portion. However, in such a conventional method, the shell metal material is deposited on the core fine particles, and also on a place other than the core fine particles, for example, on the carbon support, resulting in an increase in the amount of the shell metal material used. There was a demerit.

The inventors have studied the mechanism by which the shell metal material or the ions thereof are directly adsorbed on the carbon support by adsorbing the shell metal material or ions thereof to a functional group such as a carboxyl group present on the surface of the carbon support. Hereinafter, the case where palladium is used as the core fine particles and platinum is used as the shell metal material will be described as an example.
FIG. 3 is a diagram schematically showing a conventional method for producing supported core-shell type catalyst fine particles by coating platinum on palladium fine particles supported on carbon. The double wavy line means that the drawing is omitted. Moreover, about the palladium fine particle coat | covered with platinum, the cross section is shown typically.
FIG. 3A is a schematic view showing a state where palladium fine particles are supported on carbon. In addition to the carbon-carbon double bond and carbon-carbon single bond, functional groups such as a carboxyl group formed by partially oxidizing carbon are present on the carbon surface.
FIG. 3B is a schematic view showing a state in which copper is coated on palladium fine particles by the Cu-UPD method described later from the state of FIG. Although not shown in the figure, at this time, the proton (H ⁺ ) on the carboxyl group may be replaced with copper ions (Cu ²⁺ ).
FIG. 3C is a schematic view showing a state in which copper is replaced with platinum by the replacement plating method described later from the state of FIG. By the displacement plating method, copper coated on the palladium fine particles is dissolved, and platinum is deposited on the palladium. In addition to depositing on palladium, platinum ions may be adsorbed on carboxyl groups. At this time, electrons generated when copper is oxidized reach the platinum ions adsorbed on the carboxyl group via the conductive carbon.
FIG. 3D is a schematic diagram showing a state at the end of displacement plating. The platinum ions adsorbed on the carboxyl group are reduced by electrons when copper is oxidized. As a result, platinum fine particles are generated on the supported carbon separately from the core-shell type catalyst fine particles, resulting in an increase in the amount of platinum used and an increase in cost.

  The inventors have found that by inactivating functional groups on the surface of the carbon support, the affinity between the shell metal material and the surface of the carbon support can be reduced, and precipitation of the shell metal material on the surface of the carbon support can be suppressed. Was completed.

The present invention includes (1) a step of preparing core fine particles supported on a carbon carrier, (2) a step of inactivating a functional group present on the surface of the carbon carrier, and (3) a shell portion in the core portion. A step of coating. The present invention is not necessarily limited to only the above three steps, and may include, for example, a filtration / washing step, a drying step, a pulverizing step and the like as described later in addition to the above three steps.
Hereinafter, the steps (1) to (3) and other steps will be described in order.

1-1. Step of preparing core fine particles supported on a carbon carrier In this step, a commercial product of core fine particles supported on a carbon carrier may be purchased to proceed to the next step, or a core fine particle and a carbon carrier may be prepared separately. Then, the core fine particles may be supported on a carbon carrier. The core fine particles can be supported on the carbon support by a conventional method.

  As the core fine particles used in this step, a metal crystal having a cubic crystal system and a lattice constant of a = 3.60 to 4.08Å can be employed. Examples of such metal crystals include crystals of metal materials such as palladium, copper, nickel, rhodium, silver, gold and iridium, and alloys thereof. Among these, palladium crystals are used as core fine particles. Is preferred.

The average particle diameter of the core fine particles is not particularly limited as long as it is equal to or smaller than the average particle diameter of carbon-supported core-shell type metal nanoparticles described later. When palladium fine particles are used as the core fine particles, the average particle size of the palladium fine particles is preferably 10 to 100 nm, and particularly preferably 10 to 20 nm.
In addition, the average particle diameter of the particle | grains in this invention is computed by a conventional method. An example of a method for calculating the average particle size of the particles is as follows. First, in a TEM (transmission electron microscope) image having a magnification of 400,000 times or 1,000,000 times, a particle size is calculated for a certain particle when the particle is considered to be spherical. Calculation of the average particle diameter by such TEM observation is performed for 200 to 300 particles of the same type, and the average of these particles is taken as the average particle diameter.

In particular, when carbon-supported core-shell type catalyst particles are used in the catalyst layer of a fuel cell, the carbon carrier is preferably a conductive material from the viewpoint of imparting conductivity to the catalyst layer.
Specific examples of the conductive material that can be used as the carbon carrier include Ketjen black (trade name: manufactured by Ketjen Black International Co., Ltd.), Vulcan (product name: manufactured by Cabot), and Nolit (trade name: manufactured by Norit). And carbon particles such as black pearl (trade name: manufactured by Cabot), acetylene black (trade name: manufactured by Chevron), and conductive carbon materials such as carbon fiber.

1-2. The step of inactivating the functional groups present on the surface of the carbon support In this step, the functional groups present on the surface of the carbon support are mixed by mixing the core fine particles supported on the carbon support with an inactivating agent. This is a step of inactivation.

On the surface of the carbon support, there are functional groups formed by oxidizing carbon-carbon double bonds and / or carbon-carbon single bonds. The functional group mainly has a carbon-oxygen bond and has an unshared electron pair derived from an oxygen atom. The functional group may have Bronsted acidity and / or Lewis acidity. Therefore, the shell metal material or its ion is added to the functional group by a neutralization reaction between the functional group and the shell metal material ion, electron donation from the lone pair of the functional group to the shell metal material or its ion, or the like. There is a possibility of adsorption.
Examples of the functional group on the surface of the carbon carrier include a carboxyl group, a hydroxyl group, a lactone group, a quinone group, an aldehyde group, an acid anhydride group, an acyl group, an ester group, and a ketone group. Among these, a carboxyl group, a hydroxyl group, a lactone group, and the like are considered to have a particularly strong adsorption action because the shell metal material or its ions are adsorbed by a neutralization reaction.

  Examples of inactivating the functional group present on the surface of the carbon support include a method for introducing a protective group into the functional group and a method for reducing the functional group. Hereinafter, these two methods will be described in detail.

1-2-1. Method for Introducing Protecting Group into Functional Group Specifically, this method protects the functional group present on the surface of the carbon carrier by mixing the core fine particles supported on the carbon carrier and the protecting group introducing agent. This is a method of bonding groups.
The protecting group introducing agent is preferably one in which all or part of the protecting group-introducing agent reacts with the functional group, and the protecting group as a residue is bonded to the functional group. The protecting group introduction agent also includes a catalyst that temporarily activates the functional group to facilitate the introduction of the protecting group.
Examples of the protecting group introducing agent include cationic surfactants. A cationic surfactant becomes a cation when ionized in water, and can neutralize the functional group by neutralizing the functional group.
Examples of the cationic surfactant include a quaternary ammonium salt type surfactant, an alkylamine type surfactant, and a pyridinium salt type surfactant.

Quaternary ammonium salt type surfactants include tetramethylammonium chloride (N ⁺ (CH ₃ ) ₄ Cl ⁻ ), tetramethylammonium hydroxide (N ⁺ (CH ₃ ) ₄ OH ⁻ ), tetrabutylammonium chloride ( _{^{N + (C 4 H 9)}} 4 Cl -) tetraalkylammonium salts, such as _{^{(N + R 4 X -)}} ; octyl trimethylammonium chloride _{^{(N + (C 8 H 17}} ) (CH 3) 3 Cl -), chloride Decyltrimethylammonium (N ⁺ (C ₁₀ H ₂₁ ) (CH ₃ ) ₃ Cl ⁻ ), dodecyltrimethylammonium chloride (N ⁺ (C ₁₂ H ₂₅ ) (CH ₃ ) ₃ Cl ⁻ ), tetradecyltrimethylammonium chloride (N _{^{+ (C 14 H 29) (}} CH 3) 3 Cl -), hexadecyltrimethylammonium chloride _{^{N + (C 16 H 33)}} (CH 3) 3 Cl -), stearyl trimethyl ammonium chloride _{^{(N + (C 18 H 37}} ) (CH 3) 3 Cl -), hexadecyltrimethylammonium bromide ^(N + (C ₁₆ H ₃₃ ) (CH ₃ ) ₃ Br ⁻ ) and other alkyltrimethylammonium salts (N ⁺ R (CH ₃ ) ₃ X ⁻ ); didecyldimethylammonium chloride (N ⁺ (C ₁₀ H ₂₁ ) ₂ (CH ₃ ) ₂ Cl ^-), distearyl dimethyl ammonium chloride _{^{(N + (C 18 H 37}} ) 2 (CH 3) 2 Cl -) dialkyl dimethyl ammonium salts such as _{^{(N + RR '(CH 3}} ) 2 X -); dodecyl chloride Alkyl such as dimethylbenzylammonium (N ⁺ (C ₁₂ H ₂₅ ) (CH ₃ ) ₂ (CH ₂ C ₆ H ₅ ) Cl ⁻ ) Le benzyl dimethyl ammonium salts _{^{(N + R (CH 2 C}} 6 H 5) (CH 3) 2 X -); benzyl trimethyl ammonium chloride _{^{(N + (CH 2 C 6}} H 5) (CH 3) 3 Cl -), benzyltriethylammonium chloride _{^{(N + (CH 2 C 6}} H 5) (C 2 H 5) 3 Cl -) benzyl trialkyl ammonium salts such as _{^{(N + (CH 2 C 6}} H 5) R 3 X -); chloride Benzalkonium (N ⁺ (CH ₂ C ₆ H ₅ ) (CH ₃ ) ₂ RCl ⁻ ) (R═C _{8 to} C ₁₇ ), Benzalkonium Bromide (N ⁺ (CH ₂ C ₆ H ₅ ) (CH ₃ ) Benzalkonium salts such as ₂ RBr ⁻ ) (R═C _{8 to} C ₁₇ ); benzethonium chloride (N ⁺ (CH ₂ C ₆ H ₅ ) (CH ₃ ) ₂ {(CH ₂ CH ₂ O) ₂ C ₆ H ₄ C ₈ H ₁₇ } Cl ⁻ ); In the structural formulas of the above examples, X ⁻ represents a counter anion.

Examples of the alkylamine surfactant include monomethylamine hydrochloride (CH ₃ NH ₂ .HCl), dimethylamine hydrochloride ((CH ₃ ) ₂ NH.HCl), trimethylamine hydrochloride ((CH ₃ ) ₃ N · HCl) Etc. can be illustrated.
Examples of the pyridinium salt type surfactant include butylpyridinium chloride (C ₅ H ₅ N ⁺ (C ₄ H ₉ ) Cl ⁻ ), dodecylpyridinium chloride (C ₅ H ₅ N ⁺ (C ₁₂ H ₂₅ ) Cl ⁻ ), and chloride. hexadecyl pyridinium ^{_{(C 5 H 5 N + (}} C 16 H 33) Cl -) and the like.

In addition to using a cationic surfactant, a protective group can be selectively introduced with respect to a specific functional group.
Among the functional groups, the carboxyl group can be inactivated by converting it to an ester group or the like. Examples of ester groups include methyl ester groups, ethyl ester groups, alkynyl methyl ester groups, benzyl ester groups, t-butyl ester groups, and the like. The protecting group-introducing agent is an alcohol corresponding to these ester groups, and an acid or base that temporarily activates the carboxyl group if necessary.

Among the functional groups, the hydroxyl group can be inactivated by converting it to an ether group, an acetal group, an acyl group, a silyl ether group, or the like.
Examples of the ether group include a methyl ether group, a benzyl ether group, a p-methoxybenzyl ether group, and a t-butyl ether group. The protecting group introducing agent for converting the hydroxyl group into an ether group is an alcohol corresponding to the ether group and, if necessary, an acid or a base that temporarily activates the hydroxyl group.
Examples of acetal protection include methoxymethyl (MOM) protection, ethoxyethyl (EE) protection, 2-tetrahydropyranyl (THP) protection, and the like. Examples of the protective group-introducing agent for converting a hydroxyl group into an acetal include an alcohol corresponding to the acetal and, if necessary, an acid or a base that temporarily activates the hydroxyl group.
Examples of the acyl group include an acetyl group, a pivaloyl group, and a benzoyl group. The protecting group-introducing agent for converting a hydroxyl group into an acyl group includes an acid anhydride group and / or an acid chloride corresponding to the acyl group, and an acid or a group that temporarily activates the hydroxyl group if necessary. Bases and the like.
Examples of silyl ether groups include trimethylsilyl (TMS) group, triethylsilyl (TES) group, t-butyldimethylsilyl (TBDMS) group, triisopropylsilyl (TIPS) group, t-butyldiphenylsilyl (TBDPS) group and the like. Can be mentioned. Protecting group introducing agent for converting hydroxyl group to silyl ether group includes silyl chloride and / or silyl triflate corresponding to silyl ether group, and acid or base that temporarily activates hydroxyl group if necessary Etc.

Of the functional groups, aldehyde groups and ketone groups can be inactivated by conversion to acetal groups or the like.
Examples of acetal protection include those described above, dimethyl acetal protection, cyclic acetal protection, dithioacetal protection, and the like. Protecting group introducing agent for converting aldehyde group or ketone group to acetal is alcohol, diol and / or thiol corresponding to the acetal, and acid or base that temporarily activates the hydroxyl group if necessary It is.

  Thus, the functional group present on the surface of the carbon support can be deactivated accurately and simply by selecting a cationic surfactant or other appropriate protective group-introducing agent. These protecting group introduction agents are preferably selected from those that can be reliably and easily deprotected in the deprotecting step described later.

1-2-2. Method of reducing functional group Specifically, this method is a method of reducing the functional group present on the surface of the carbon support by mixing the core fine particles supported on the carbon support with a reducing agent. The functional group herein includes a lactone group, a quinone group, an acid anhydride group, an acyl group, and an ester group in addition to a carboxyl group, a hydroxyl group, an aldehyde group, and a ketone group.
The reducing agent preferably reacts with the functional group to convert the functional group into a carbon-carbon double bond, a carbon-carbon single bond, or a carbon-hydrogen single bond. The reducing agent is preferably one that does not affect the environment on the carbon surface other than the functional group, for example, the electronic state of the core fine particles.
Specific examples of the reducing agent include hydride complexes such as lithium aluminum hydride (LiAlH ₄ ), sodium borohydride (NaBH ₄ ), and diisobutylaluminum hydride ([(CH ₃ ) ₂ CHCH ₂ ] ₂ AlH); sodium amalgam And alloys such as zinc amalgam; sulfites such as sodium bisulfite (NaHSO ₃ ) and sodium sulfite (Na ₂ SO ₃ ); acids such as oxalic acid and formic acid; hydrazine (H ₂ NNH ₂ ) and derivatives thereof Semicarbazide (H ₂ NNHC (═O) NH ₂ ) and thiosemicarbazide (H ₂ NNHC (═S) NH ₂ );

1-3. Step of covering the core portion with the shell portion This step is a step of covering the core portion with the core portion using the core fine particles as the core portion after the deactivation step.
The coating of the shell portion on the core portion may be performed through a one-step reaction or may be performed through a multi-step reaction.
Hereinafter, an example in which the shell portion is coated through a two-step reaction will be mainly described.

  As an example in which the shell part is coated on the core part through a two-step reaction, at least a step of coating the core part with a monoatomic layer using the core fine particles as a core part, and the monoatomic layer as a shell The example which has the process substituted to a part is given.

As a specific method of this example, there is a method in which a monoatomic layer is formed on the surface of the core portion in advance by an underpotential deposition method, and then the monoatomic layer is replaced with a shell portion. As the underpotential deposition method, it is preferable to use a Cu-UPD method.
In particular, when palladium fine particles are used as the core fine particles and platinum is used for the shell portion, core-shell type catalyst fine particles having a high platinum coverage and excellent durability can be produced by the Cu-UPD method.

Hereinafter, specific examples of the Cu-UPD method will be described.
First, palladium (hereinafter referred to as Pd / C) powder supported on the deactivated carbon support is dispersed in water, and the Pd / C paste obtained by filtration is applied to the working electrode of the electrochemical cell. . As the working electrode, platinum mesh or glassy carbon can be used.
Next, a copper solution is added to the electrochemical cell, the working electrode, the reference electrode, and the counter electrode are immersed in the copper solution, and a copper monoatomic layer is deposited on the surface of the palladium particles by the Cu-UPD method. An example of specific deposition conditions is shown below.
Copper solution: mixed solution of 0.05 mol / L CuSO ₄ and 0.05 mol / L H ₂ SO ₄ (nitrogen is bubbled)
-Atmosphere: Under nitrogen atmosphere-Sweep speed: 0.2-0.01 mV / sec-Potential: After sweeping from about 0.8 V (vsRHE) to about 0.4 V (vsRHE), at about 0.4 V (vsRHE) Fix the potential.
-Potential fixing time: 60-180 minutes

After the potential fixing time is completed, the working electrode is immediately immersed in a platinum solution, and copper and platinum are replaced by plating using the difference in ionization tendency. The displacement plating is preferably performed in an inert gas atmosphere such as a nitrogen atmosphere. The platinum solution is not particularly limited. For example, a platinum solution in which K ₂ PtCl ₄ is dissolved in 0.1 mol / L HClO ₄ can be used. The platinum solution is thoroughly stirred and nitrogen is bubbled through the solution. The displacement plating time is preferably secured for 90 minutes or more.
By the displacement plating, core-shell type catalyst fine particles in which a platinum monoatomic layer is deposited on the surface of palladium particles are obtained.

  As the shell metal material constituting the shell portion, a material that forms a metal crystal having a cubic crystal system and a lattice constant of a = 3.80 to 4.08４ can be employed. Examples of such a metal material include metal materials such as platinum, iridium and gold, and alloys thereof. Among these, platinum is preferably used as the shell metal material.

  A combination in which the core fine particles are palladium or a palladium alloy and the shell metal material is platinum is particularly preferable. Platinum is excellent in catalytic activity, particularly oxygen reduction reaction (ORR) activity. In addition, the lattice constant of platinum is 3.92Å, whereas the lattice constant of palladium is 3.89Å, and the lattice constant of palladium is a value within a range of ± 5% of the lattice constant of platinum. There is no lattice mismatch between platinum and palladium, and palladium is sufficiently covered with platinum.

Hereinafter, the case where palladium is used as the core fine particles and platinum is used as the shell metal material will be described as an example.
FIG. 1 is a diagram schematically showing a process of covering a core part with a shell part in the manufacturing method of the present invention. The double wavy line means that the drawing is omitted. Moreover, about the palladium fine particle coat | covered with platinum, the cross section is shown typically.
FIG. 1A is a schematic view showing a state in which palladium fine particles are supported on carbon. Functional groups such as carboxyl groups on the carbon surface are previously inactivated by protective groups. In addition, “OP” in FIG. 1A indicates that the oxygen of the carboxyl group and the protecting group are bonded by a chemical bond.
FIG.1 (b) is a schematic diagram which shows a mode that copper was coat | covered on the palladium fine particle by the Cu-UPD method from the state of Fig.1 (a). At this time, since the protective group is bonded to the carboxyl group, the carboxyl group is not affected by copper ions (Cu ²⁺ ).
FIG.1 (c) is a schematic diagram which shows a mode that substitution plating of copper was carried out to platinum by the substitution plating method from the state of FIG.1 (b). By the displacement plating method, copper coated on the palladium fine particles is dissolved, and platinum is deposited on the palladium. At this time, since the carboxyl group is inactivated, platinum ions are not adsorbed to the carboxyl group.
FIG. 1D is a schematic diagram showing a state at the end of displacement plating. Unlike the conventional manufacturing method shown in FIG. 3, platinum fine particles are not generated separately from the core-shell type catalyst fine particles. Therefore, the amount of platinum used is reduced, and the cost can be reduced.

The average particle size of the carbon-supported core-shell type metal nanoparticles is preferably 4 to 10 nm. If the average particle size is less than 4 nm, the activity per catalyst surface area may be reduced, and if the average particle size exceeds 20 nm, the activity per catalyst surface area does not improve, but the use of the core metal material There is a risk that the amount will increase, resources will increase, but costs will increase.
Since the shell part of the core-shell type metal nanoparticle is preferably a monoatomic layer, the thickness of the shell part is preferably 0.17 to 0.23 nm. Therefore, it is preferable that the thickness of the shell portion is substantially negligible with respect to the average particle size of the core-shell type metal nanoparticle, and the average particle size of the core portion and the average particle size of the core-shell type metal nanoparticle are approximately equal.

1-4. Other Steps After the step of coating the core portion with the shell portion, the carbon-supported core-shell type catalyst fine particles may be filtered, washed, dried and pulverized.
The filtration and washing of the carbon-supported core-shell type catalyst fine particles are not particularly limited as long as the method can remove impurities without impairing the core-shell structure and the supported state of the produced fine particles. Examples of the filtration / washing include an example of adding ultrapure water and performing suction filtration. The operation of adding ultrapure water and performing suction filtration is preferably repeated about 10 times.
The drying of the carbon-supporting core-shell type catalyst fine particles is not particularly limited as long as the method can remove the solvent and the like. As an example of the drying, an example in which drying is performed for about 12 hours by a vacuum dryer under a temperature condition of about 60 ° C. is given.
The pulverization of the carbon-supporting core-shell type catalyst fine particles is not particularly limited as long as it is a method capable of pulverizing a solid. Examples of the pulverization include pulverization using a mortar and the like, and mechanical milling such as a ball mill, a turbo mill, a mechanofusion, and a disk mill.

2. Method for Producing Catalyst Ink The method for producing the catalyst ink of the present invention comprises the functional group present on the surface of the carbon carrier by mixing the carbon-supporting core-shell type catalyst fine particles obtained by the above production method with a hydrophilizing agent. And a step of mixing at least the carbon-supporting core-shell type catalyst particles that have undergone the hydrophilic step and an electrolyte.

  After synthesizing the carbon-supporting core-shell type catalyst fine particles, when producing a membrane / electrode assembly using the catalyst fine particles, it is preferable to disperse the catalyst in a dispersion medium or the like to form a catalyst ink. In order to improve the dispersibility of the catalyst in the ink and the affinity between the catalyst and the electrolyte, it is preferable to make the functional group on the surface of the carbon support hydrophilic.

The present invention includes (1) a step of hydrophilizing a functional group present on the surface of a carbon support, and (2) a step of mixing carbon-supporting core-shell type catalyst fine particles and an electrolyte. The present invention is not necessarily limited to the above two steps.
Hereinafter, the steps (1) and (2) will be described in order.

2-1. The step of hydrophilizing the functional group present on the surface of the carbon support This step exists on the surface of the carbon support by mixing the carbon-supported core-shell type catalyst particles obtained by the above production method with a hydrophilizing agent. This is a step of hydrophilizing the functional group.

A specific method for hydrophilizing the functional group present on the surface of the carbon support is to mix the carbon-supported core-shell type catalyst particles and the deprotecting agent to remove the protective group from the functional group present on the surface of the carbon support. It is a method of removing.
While the deprotection agent selectively reacts with the functional group and proceeds with deprotection, the carbon surface environment other than the functional group, for example, a carbon-carbon double bond or a carbon-carbon single bond of the supported carbon It is preferable that it does not react with.
Effective deprotecting agents depend on the functional group. Hereinafter, the deprotection of the protecting group described in “1-2-1. Method for Introducing Protecting Group into Functional Group” will be briefly described.

  When a cationic surfactant is used as a protecting group introducing agent, it is preferable to deprotect by applying an acid stronger than the functional group before protection. For example, when it is desired to deprotect a carboxyl group, it is preferable to act an acid stronger than carboxylic acid, specifically, perchloric acid, permanganic acid, chlorous acid, sulfuric acid, selenic acid and the like.

When the ester group is deprotected and converted to a carboxyl group, the deprotection proceeds under strongly acidic conditions, and a metal complex such as a palladium complex can be used if necessary.
When the ether group is deprotected and converted to a hydroxyl group, a strong Bronsted acid or Lewis acid can be used, and a metal complex such as a cobalt complex or a palladium complex can also be used.
When the acetal is deprotected and converted to a hydroxyl group, aldehyde group or ketone group, the deprotection proceeds by reaction with water under acidic conditions.
When the acyl group is deprotected and converted to a hydroxyl group, a base or a hydride reducing agent can be used.
When the silyl ether group is deprotected and converted to a hydroxyl group, the deprotection proceeds under acidic conditions or by applying a fluoride ion source such as tetra-n-butylammonium fluoride (TBAF). .

  In addition, this process can be performed anytime as long as it has passed through the above-mentioned “1-3. That is, this process is performed at any time during the process of covering the core part with the shell part and the filtration / washing process, between the filtration / washing process and the drying process, between the drying process and the grinding process, and after the grinding process. Yes.

2-2. Step of Mixing Carbon-Supported Core-Shell Type Catalyst Fine Particles and Electrolyte This step is a step of mixing at least the carbon-supported core-shell type catalyst fine particles and the electrolyte that have undergone the hydrophilic step.

The catalyst ink is obtained by dissolving the carbon-supported core-shell type catalyst fine particles, the electrode electrolyte and the like in a solvent or dispersing them in a dispersion medium. The solvent of the catalyst ink may be appropriately selected. For example, alcohols such as methanol, ethanol and propanol, organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO), or organic solvents such as these Mixtures and mixtures of these organic solvents and water can be used. In addition to the catalyst and the electrolyte, the catalyst ink may contain other components such as a binder and a water repellent resin as necessary.
As the electrode electrolyte, the same material as the polymer electrolyte membrane described later can be used.

3. Catalyst Layer The catalyst layer of the present invention is characterized by containing a catalyst ink produced by the above production method.

  FIG. 2 is a diagram showing an example of a fuel cell including the catalyst layer of the present invention, and is a diagram schematically showing a cross section cut in the stacking direction. A fuel cell 100 includes a membrane composed of a solid polymer electrolyte membrane (hereinafter sometimes referred to simply as an electrolyte membrane) 1 having hydrogen ion conductivity, and a pair of cathode electrode 6 and anode electrode 7 sandwiching the electrolyte membrane 1. A pair of separators 9 and 10 including the electrode assembly 8 and further sandwiching the membrane / electrode assembly 8 from the outside of the electrode. Gas flow paths 11 and 12 are secured at the boundary between the separator and the electrode. As the electrode, an electrode formed by laminating a catalyst layer and a gas diffusion layer in order from the electrolyte membrane side is used. That is, the cathode electrode 6 is formed by stacking the cathode catalyst layer 2 and the gas diffusion layer 4, and the anode electrode 7 is formed by stacking the anode catalyst layer 3 and the gas diffusion layer 5. The catalyst layer of the present invention can be used for either the cathode catalyst layer or the anode catalyst layer.

  The polymer electrolyte membrane is a polymer electrolyte membrane used in a fuel cell, and includes a fluorine polymer electrolyte membrane containing a fluorine polymer electrolyte such as perfluorocarbon sulfonic acid resin represented by Nafion (trade name). In addition, sulfonic acids can be added to hydrocarbon polymers such as engineering plastics such as polyetheretherketone, polyetherketone, polyethersulfone, polyphenylene sulfide, polyphenylene ether, and polyparaphenylene, and general-purpose plastics such as polyethylene, polypropylene, and polystyrene. And hydrocarbon polymer electrolyte membranes including hydrocarbon polymer electrolytes into which proton acid groups (proton conductive groups) such as groups, carboxylic acid groups, phosphoric acid groups, and boronic acid groups are introduced.

The electrode has a catalyst layer and a gas diffusion layer.
Both the anode catalyst layer and the cathode catalyst layer can be formed using the catalyst ink according to the present invention described above.

  The method for forming the catalyst layer is not particularly limited. For example, the catalyst layer may be formed on the surface of the gas diffusion layer sheet by applying and drying the catalyst ink on the surface of the gas diffusion layer sheet, or the electrolyte membrane. A catalyst layer may be formed on the surface of the electrolyte membrane by applying a catalyst ink on the surface and drying. Alternatively, a transfer sheet is prepared by applying and drying a catalyst ink on the surface of the transfer substrate, and the transfer sheet is joined to the electrolyte membrane or the gas diffusion sheet by thermocompression bonding or the like. The catalyst layer may be formed on the surface of the electrolyte membrane or the catalyst layer may be formed on the surface of the gas diffusion layer sheet.

  The method for applying the catalyst ink, the drying method, and the like can be selected as appropriate. For example, examples of the coating method include a spray method, a screen printing method, a doctor blade method, a gravure printing method, and a die coating method. Examples of the drying method include vacuum drying, heat drying, and vacuum heat drying. There is no restriction | limiting in the specific conditions in reduced pressure drying and heat drying, What is necessary is just to set suitably. The thickness of the catalyst layer is not particularly limited, but may be about 1 to 50 μm.

  As the gas diffusion layer sheet for forming the gas diffusion layer, a gas diffusion property that can efficiently supply fuel to the catalyst layer, conductivity, and strength required as a material constituting the gas diffusion layer, for example, Carbonaceous porous bodies such as carbon paper, carbon cloth, carbon felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium , Tantalum, iron, stainless steel, gold, platinum, and the like, and those made of a conductive porous material such as a metal mesh or a metal porous material. The thickness of the conductive porous body is preferably about 50 to 500 μm.

The gas diffusion layer sheet may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, water-repellent resin such as polytetrafluoroethylene (PTFE), and the like. The water-repellent layer is not always necessary, but it can improve the drainage of the gas diffusion layer while maintaining an appropriate amount of water in the catalyst layer and the electrolyte membrane. There is an advantage that electrical contact can be improved.
The electrolyte membrane and gas diffusion layer sheet on which the catalyst layer has been formed by the above-described method are appropriately overlapped and subjected to thermocompression bonding or the like, and joined together to obtain a membrane / electrode assembly.

  The produced membrane / electrode assembly is preferably held by a separator having a reaction gas flow path to form a single cell. The separator has conductivity and gas sealing properties, and can function as a current collector and gas sealing body, for example, a carbon separator containing a high concentration of carbon fiber and made of a composite material with resin, metal A metal separator using a material can be used. Examples of the metal separator include those made of a metal material excellent in corrosion resistance, and those coated with a coating that enhances the corrosion resistance by coating the surface with carbon or a metal material excellent in corrosion resistance. .

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Cathode catalyst layer 3 Anode catalyst layer 4, 5 Gas diffusion layer 6 Cathode electrode 7 Anode electrode 8 Membrane / electrode assembly 9, 10 Separator 11, 12 Gas flow path 100 Fuel cell

Claims (7)

A method for producing carbon-supported core-shell type catalyst fine particles, comprising a core part and a shell part covering the core part,
A step of preparing a carbon support on which core fine particles are supported ;
An inactivation step of inactivating a functional group present on the surface of the carbon support by mixing the carbon support on which the core fine particles are supported and an inactivating agent; and
A method for producing carbon-supported core-shell type catalyst fine particles, comprising, after the deactivation step, a step of covering the core part with the shell part using the core fine particle as a core part. The deactivator is a protecting group introducing agent,
In the inactivation step, a protective group introduction step of bonding a protective group to a functional group present on the surface of the carbon support by mixing the carbon support carrying the core fine particles and the protective group introduction agent. The method for producing carbon-supported core-shell type catalyst fine particles according to claim 1, wherein   The method for producing carbon-supported core-shell type catalyst particles according to claim 2, wherein the protecting group introducing agent is a cationic surfactant. The deactivator is a reducing agent;
The deactivation step is a reduction step in which a functional group present on the surface of the carbon support is reduced by mixing the carbon support on which the core fine particles are supported and the reducing agent. A method for producing the carbon-supported core-shell type catalyst fine particles as described. A functional group present on the surface of the carbon carrier is obtained by mixing the carbon-supporting core-shell type catalyst fine particles obtained by the production method according to any one of claims 1 to 4 and a hydrophilizing agent. A hydrophilization step for hydrophilization, and
A method for producing a catalyst ink, comprising: a step of mixing at least the carbon-supported core-shell type catalyst particles that have undergone the hydrophilization step and an electrolyte. The hydrophilizing agent is a deprotecting agent;
The method for producing a catalyst ink according to claim 5, wherein the hydrophilization step is a deprotection step of removing a protective group from a functional group present on the surface of the carbon support.   The method for producing a catalyst ink according to claim 6, wherein the deprotecting agent is a strong acid.

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