JP2006228502A - Electrode catalyst for fuel cell, its manufacturing method, and electrode and fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode catalyst for fuel cell which is high in catalytic activity and resistance to poisoning, its manufacturing method and an electrode and a fuel cell that uses this catalyst. <P>SOLUTION: The electrode catalyst for fuel cell includes a porous carbon, where 10 nm or less of diameter of pores have 0.6 to 1.2 ml/g of pore capacity, and 90 or higher vol.% of the pores are in the dimensions of 1.2 to 5.0 nm, and 0.5 to 3.0 nm of Pt particles are dispersed on the surface of the pores. The electrode for fuel cell and the fuel cell that use it are also disclosed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrode catalyst for a fuel cell using electric power generated by electrode oxidation / reduction reaction, and relates to an electrode and a fuel cell using the same.

  A fuel cell is a cell that directly uses energy generated by an electrochemical reaction of fuel as an electromotive force. Therefore, the fuel cell is expected to be a power source that has high power generation efficiency and reduces energy consumption. The main ones are those that use hydrogen as fuel, and are being developed as power sources for automobiles and stationary use. There are various types of fuel cells, depending on the electrolyte used. Among them, solid polymer fuel cells have a high output density, a low operating temperature, and superior mobility compared to other fuel cells. Have.

  In addition, direct methanol fuel cells, which are classified as one of the polymer electrolyte fuel cells, use methanol, which is liquid at room temperature, as a direct fuel and do not require a reformer for fuel processing. Can be a battery. In addition, its energy density can be more than 10 times that of lithium ion secondary batteries. In addition, it is expected to be a power source for portable devices that can replace lithium ion secondary batteries, including the advantage of not requiring charging time.

  Each of these fuel cells includes a negative electrode that is a fuel electrode, a positive electrode that is an air electrode, and an electrolyte sandwiched between them. The electrode has a structure in which a metal such as platinum (Pt) which is an oxidation / reduction catalyst is supported on conductive carbon.

  Carbon black is generally known as an electrode carrier. Carbon black has a porous structure in which primary particles with a diameter of about several tens of nanometers are aggregated on a bead, and by supporting Pt particles on this, an electrode in which Pt is dispersed on carbon black can be obtained. However, considering the use as an energy source for portable devices, those having higher energy density are desired, and in order to increase the output of the fuel cell, it is desired to study a carrier that can further disperse Pt particles. ing. Therefore, for example, active research using activated carbon as a carrier has been actively conducted, and research has been conducted in which activated carbon raw materials and heat treatment conditions for carbonization are controlled (see, for example, Patent Document 1).

  In a fuel cell, when carbon black or activated carbon is used as a carrier for an electrode catalyst, the surface area is large, but mesopores that are three-dimensionally connected are difficult to grow and control of the pore structure is difficult. It is difficult to improve the Pt utilization rate by further increasing the dispersion of Pt as a component and to improve the diffusion of substances such as fuel and protons by optimizing the pore size.

  In recent years, there have also been reports of examples using carbon nanohorns, which are a type of carbon nanotubes found (see, for example, Non-Patent Document 1 and Patent Document 2). Carbon nanohorns have a minute and unique structure, and a large number of nanohorns gather to form aggregates (secondary particles) with a surface area of about 100 nm and a very large surface area. Therefore, when compared under the same conditions as those of conventionally used carbon black and activated carbon, the size of the Pt particles can be reduced to half or less. Therefore, it has been reported that the activity can be improved by further dispersing Pt. However, at present, carbon nanohorns have a problem that they are more expensive than carbon black and activated carbon.

  In 1999, a method for producing porous carbon using mesoporous silica as a template was reported (for example, see Non-Patent Document 2). This mesoporous carbon is known to be able to control the pore structure more precisely among porous carbons. Mesoporous silica used as a template is a silica characterized by having mesopores that are uniformly and regularly arranged. A part of Si in the silica skeleton is substituted with Al, B, Ti, etc. A generic term that includes silicates. In general, mesoporous silica itself is a silica obtained by performing a sol-gel reaction using a surfactant aggregate structure (for example, rod-like micelles) as a template and using a suitable silica source, for example, tetraethoxysilane (TEOS) as a raw material around the surface (surface). And then, the surfactant as a template is removed by baking or the like to leave a silica skeleton.

Since mesoporous carbon uses mesoporous silica as a template, mesoporous silica has a structure in which mesoporous silica is arranged uniformly and regularly, and has a high specific surface area of 1000 m ² / g or more and a mesoporous region. It has a very narrow pore size distribution. The pore diameter of this mesoporous carbon can be controlled in the range of about 1.2 to 10 nm by controlling the pore diameter of mesoporous silica as a template.

  There are reports of using this mesoporous carbon as a carrier for fuel cell electrode catalysts. In the research conducted by Ryong Ryoo et al. (For example, see Non-Patent Document 3), by supporting Pt on mesoporous carbon, the activity is greatly improved, and the activity is maximized when the amount of Pt supported is 30 to 40 wt%. Has been reported. However, it has also been shown that the activity decreases when Pt is supported.

  There is also a report that uses a carbon material partially containing mesoporous carbon particles as a carrier (see, for example, Patent Document 3). In this example, the mesoporous carbon has narrow pores with a distribution having a peak near 3 nm, but most of the pores of 2 to 4 nm disappear when Pt is supported. Therefore, the gas diffusibility is not sufficient with only mesoporous carbon, and the gas diffusivity is improved by mixing a carbon material other than mesoporous carbon. That is, gas diffusibility is improved by mixing other carbon materials with mesoporous carbon at 1: 1.

    In addition, an example using mesoporous silica as a template is also reported. First, a catalyst preparation method in which catalyst component particles are first produced on mesoporous silica as a template, carbon precursors are adsorbed and carbonized, and finally the template is removed is reported. (See, for example, Patent Document 4). In this example, the power generation characteristics are improved by improving the contact between the Pt particles and the electrolyte, but the Pt particle diameter is 6.8 nm, which is the same level as the conventional preparation method.

  In the negative electrode, which is the fuel electrode, even if Pt is highly dispersed for high performance, carbon monoxide (CO) generated in the raw material or reaction is adsorbed and poisoned by the Pt catalyst. There is a problem that the battery performance deteriorates. In particular, in the case of a direct methanol fuel cell, poisoning is unavoidable because CO is generated as an intermediate during the oxidation process of methanol, which is a raw material, and the performance deterioration is more noticeable.

To avoid this problem, what is commonly done is to facilitate the oxidation of residual CO by activating the H ₂ O, the Ru metal having an effect of suppressing the poisoning of the Pt catalyst, the two Co-supported as the next metal. Although development of an electrocatalyst that suppresses such a decrease in activity has been actively carried out, it is not sufficient yet, so a highly active electrocatalyst with further enhanced resistance to poisoning is desired.
JP-A-2004-217507 WO2002 / 075831 JP2004-71253A JP 2004-178859 A NEC Press Release 2001-8-30-02 (2001) J. Phys. Chem. B 103, 7743-7746 (1999) Nature 412 169-172 (2001)

  Current fuel cells, particularly direct methanol fuel cells, are not yet sufficiently powerful and efficient. It is an object of the present invention to develop a fuel cell catalyst having high catalytic activity and poisoning resistance, a method for producing the same, and an electrode and a fuel cell using the catalyst.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention required a porous carbon having mesopores with high dispersion of Pt, a narrow pore size distribution range, and three-dimensional expansion. Accordingly, the present inventors have found that a fuel cell catalyst having high catalytic activity and high resistance to poisoning can be obtained by complexing silica having a hydrophilic group.

  That is, the fuel cell electrode catalyst of the present invention has pores with a diameter of 10 nm or less having a pore volume of 0.6 to 1.2 ml / g, and 90% by volume or more of the pores. Is in the range of 1.2 to 5.0 nm in size, and includes porous carbon in which Pt particles having a size of 0.5 to 3.0 nm are dispersed on the pore surface. .

  The present invention also provides the method for producing an electrode catalyst for a fuel cell, wherein the porous carbon is formed with pores using porous silica as a template.

  The present invention also provides a fuel cell electrode and a fuel cell using the above fuel cell electrode catalyst.

  According to the present invention, an electrode catalyst having both excellent activity and poisoning resistance can be provided, which can be suitably used for a fuel cell.

Hereinafter, the present invention will be specifically described.
(Electrocatalyst for fuel cell)
In the fuel cell electrode catalyst of the present invention, pores having a diameter of 10 nm or less have a pore volume of 0.6 to 1.2 ml / g. The pore volume is preferably 0.7 to 1.2 ml / g, more preferably 0.8 to 1.2 ml / g. When the pore volume is in this range, material diffusion is facilitated with the structure being solid. Here, the pore volume can be determined by a generally known nitrogen adsorption method.

  In the fuel cell electrode catalyst of the present invention, 90% by volume or more of pores having a diameter of 10 nm or less have a diameter of 1.2 to 5.0 nm. Preferably, it is 1.2-4.0 nm, More preferably, it is 2.0-4.0 nm. When the diameter of the pore is within this range, the reaction on the catalyst component can be facilitated without decreasing the substance diffusion. Here, the diameter of the pores can also be determined by the nitrogen adsorption method in the same manner as the pore volume.

  In the fuel cell electrode catalyst of the present invention, Pt particles having a size of 0.5 to 3.0 nm are dispersed on the pore surface. The size of the Pt particles is preferably 0.5 to 2.5 nm, more preferably 0.5 to 2.0 nm. When the size of the Pt particles is in this range, a highly active catalyst can be obtained. Here, the size of the Pt particles can be determined by an X-ray diffraction method or the like.

  The fuel cell electrode catalyst of the present invention is preferably combined with 0.01 to 120% by weight of silica based on the porous carbon. The amount of composite silica is more preferably 0.1 to 100% by weight, particularly preferably 0.1 to 80% by weight. Since the porous carbon and the silica are combined in the above-described range, it is possible to suppress a decrease in catalytic activity due to poisoning of the catalyst by CO. In the present invention, it was found that by promoting CO oxidation using a silica surface complexed with porous carbon as an adsorption point of water, reduction in catalytic activity due to CO poisoning can be suppressed without using Ru. The amount of silica combined with porous carbon can be determined by ICP analysis after dissolving the silica with hydrofluoric acid or the like.

  Furthermore, the fuel cell electrode catalyst of the present invention preferably has a Pt particle content of 0.01 to 100% by weight based on the porous carbon. When the content of Pt particles is within this range, the catalyst cost can be reduced. The content of Pt particles can be determined by ICP analysis after dissolving Pt with aqua regia.

  As described above, the porous carbon which is a carrier of the electrode catalyst in the present invention is a porous carbon having a three-dimensional structure with a controlled pore diameter, and thereby, high dispersion of the active ingredient and improvement of its utilization rate, and Increased material diffusion and high activity. In addition, it has a characteristic that it can form a complex with silica as appropriate and can suppress a decrease in Pt catalyst activity due to CO poisoning.

(Method for producing electrode catalyst for fuel cell)
In the present invention, it is preferable to use porous carbon prepared using porous silica, particularly mesoporous silica as a template, as the electrode catalyst carrier in both the negative electrode and the positive electrode. However, the porous silica used as a template is not limited to mesoporous silica as long as it has three-dimensional pores. When the above-described mesoporous silica is used as a template, a structure in which the pores are three-dimensionally connected, for example, a cubic type regular pore structure represented by MCM-48, SBA-1, etc. , HMS, SBA-15, MSU-H, and other mesopores represented by worm-eaten structures connected by micropores, and in addition to regularly arranged mesopores, more Bimodal mesoporous silica or the like in which secondary pores having a large pore diameter coexist is desirable.

  That is, the pore shape of the porous carbon is controlled by controlling the pore shape of the porous silica serving as a template. For example, it is possible to produce porous silica with different pore diameters by utilizing the fact that the size of the micelle to be formed is changed by changing the length of the hydrophobic group of the surfactant as a template. By controlling the pore shape of silica, porous carbon with a controlled pore shape can be prepared.

The physical properties of the porous silica used as a template include a specific surface area of 400 m ² / g or more, a pore volume of 0.4 ml / g or more, and a pore diameter of 1.5 to 10 nm, and further a specific surface area of 600 m ² / g. g or more, a pore volume of 0.6 ml / g or more, and a pore diameter of 1.5 to 5.0 nm are preferable, and a specific surface area of 600 m ² / g or more, a pore volume of 0.8 ml / g g or more and a pore diameter of 1.5 to 5.0 nm are preferable.

  As a method for preparing the porous carbon, first, the pores of the porous silica are filled with a precursor organic substance serving as a carbon source. Examples of the method include the following two methods. It can also be prepared by other methods.

(I) Method of using a precursor organic substance as a carbon source as a surfactant used as a template when forming porous silica As a surfactant used as a template of porous silica, the following general formula (1), Those represented by (2), (3) or (4) may be mentioned. In the general formula (1), X represents an ionic hydrophilic functional group or atomic group. Examples of the ionic hydrophilic functional group include a quaternary ammonium ion, a pyridinium ion, an imidazolium ion, a sulfonate ion, and a carboxylate ion, and among them, a quaternary ammonium ion, a pyridinium ion, and an imidazolium ion are preferable. X in the general formulas (2) and (3) and X ′ in the general formula (3) represent a neutral hydrophilic functional group or atomic group. Examples of the neutral hydrophilic functional group include an amino group, a polyethylene oxide group, a nitroso group, and a hydroxyl group. Among them, an amino group and a polyethylene oxide group having a polymerization degree of 2 to 150 are preferable. In the general formulas (1) to (3), Y is a hydrophobic part conventionally known as a constituent component of the surfactant. Specific examples include an alkyl group, an alkenyl group, an alkynyl group, an alicyclic hydrocarbon group, a phenyl group, or an alkylene oxide group. Among them, an alkyl group having 8 to 24 carbon atoms or an average degree of polymerization of 10 is particularly preferable. ~ 200 polypropylene oxide groups are preferred. In the general formula (1), Z represents a counter ion of the ionic hydrophilic functional group X. Examples of Z include halide ions, nitrate ions, sulfate ions, hydroxide ions, tetrafluoroborate ions, hexafluorophosphate ions, alkali metal ions, alkaline earth metal ions, ammonium ions, among others. Chloride ion, bromide ion, fluoride ion and hydroxide ion are preferred. Specific examples of the surfactants represented by the general formulas (1) to (3) include cationic surfactants such as cetyltrimethylammonium salt, Triton-X (C ₁₄ H ₂₂ O (C ₂ H ₄ O) _n H), Brij30 (C ₁₂ H ₂₅ O (C ₂ H ₄ O) ₄ H), Pluronic P123 (HO (C ₂ H ₄ O) ₂₀ (C ₃ H ₆ O) ₇₀ (C ₂ H ₄ O) ₂₀ Nonionic surfactants such as H).

The method for producing the porous silica using the surfactant as a template is not particularly limited, and can be produced by a generally known method. That is, from the surfactant which is a template of porous silica, a silica source such as sodium silicate and alkoxysilane, a sol-gel reaction catalyst of an acid such as HCl or a base such as NaOH or NH ₄ OH, water, an organic solvent, etc. A composite of a surfactant and silica is obtained by subjecting the constituted silica preparation liquid to a sol-gel reaction by a known method. Here, the sol-gel reaction catalyst is usually an acid or a base, but a sol-gel reaction promoting substance such as a hydrofluoric acid salt such as NaF or NH ₄ F or a tetrafluoroborate such as NaBF ₄ or NH ₄ BF ₄ is added thereto. Alternatively, an acid / base may be used alone. The organic solvent is not particularly limited, but hydrophilic alcohols and ethers are preferable. Moreover, you may add the easily carbonizable substance mentioned later to the said silica preparation liquid as needed. The obtained surfactant / silica composite is dried in air at 15 to 150 ° C. for 1 to 24 hours, preferably at 80 to 120 ° C. for 10 to 20 hours. Next, in order to carbonize the surfactant, the surfactant / silica complex is heated at a temperature of 300 to 1400 ° C. or higher, preferably 600 to 1100 ° C. in an inert atmosphere such as vacuum or nitrogen. The heating time is 1 to 24 hours, preferably 2 to 6 hours.

(Ii) A method of filling a porous silica pore with a readily carbonizable substance and then polymerizing and carbonizing the easily carbonizable substance In the present invention, the easily carbonizable substance is a molecule having an unsaturated bond, Polymeric molecules or molecular aggregates such as polyhydric alcohols, molecules or molecular aggregates containing aromatic rings / alicyclic hydrocarbons / heterocycles, or polymers having a molecular weight of 500 or more, such as sucrose Saccharides, furfuryl alcohol, styrene, divinylbenzene, petroleum pitch, phenol, formaldehyde, terephthalic acid, ethylene glycol, acrylonitrile, methyl acrylate, polyacrylate, naphthalene, triphenylene, etc. .

  As a specific method for filling these easily carbonizable substances into the porous silica pores, porous silica as a template is added to a solution containing the easily carbonized substance and, if necessary, a polymerization catalyst and a polymerization initiator. It is relatively easy to immerse and adsorb and impregnate.

  In this case, the polymerization catalyst includes acids such as sulfuric acid. Other than this, porous silica in which acid sites are introduced in advance, for example, metallosilicates in which a part of Si in the silica skeleton is substituted with Al or B to form acid sites, or the silica skeleton is modified with an organic group to form a sulfone. Substitution can also be made by using an organic modified product into which an acid group, a carboxylic acid group or the like is introduced. Examples of the polymerization initiator include 2,2'-azobis (isobutyronitrile), benzoyl peroxide, and the like. The liquid in which the porous silica is immersed is dried in air at 15 to 200 ° C. for 1 to 48 hours, preferably at 80 to 120 ° C. for 3 to 15 hours until the solvent is dried. In this way, the carbon source filled in the silica pores is polymerized by heat treatment at 40 to 300 ° C., preferably 100 to 200 ° C., if necessary. The atmosphere for the heat treatment is not particularly limited, but is preferably performed in an inert atmosphere such as nitrogen. The treatment time is 1 to 48 hours, preferably 5 to 15 hours. It is desirable to repeat the filling of the precursor organic material and the polymerization thereof appropriately and appropriately so that the carbon source is sufficiently filled in the silica pores.

  The obtained carbon source / porous silica composite is heated at a high temperature of 300 to 1400 ° C. or higher, preferably 600 to 1100 ° C. in an inert atmosphere such as vacuum or nitrogen as in the case of (i). Carburizing treatment is performed. The heating time is 1 to 24 hours, preferably 2 to 6 hours.

The carbon / silica composite obtained by the above method is immersed in a basic solution such as NH ₄ OH and NaOH or an HF solution to dissolve and remove the silica skeleton, thereby obtaining porous carbon. In the case of treatment with a basic solution such as NH ₄ OH or NaOH, the carbon / silica composite is immersed in an aqueous solution of 0.05 to 10 mol / l, preferably 0.5 to 2 mol / l, and 15 It is carried out at a temperature of ˜150 ° C., preferably 80 ° C. to 120 ° C., with reflux as necessary. The treatment time is 1 minute to 24 hours, preferably 10 minutes to 12 hours. On the other hand, in the case of treating with an HF solution, the carbon / silica composite is immersed in an aqueous solution of 0.01 to 2.0 mol / l, preferably 0.1 to 0.5 mol / l, and 0 to 50 mol. C., preferably 15 to 35.degree. C., left standing or stirred. The treatment time is within 3 hours, preferably 1 minute to 1 hour.

  Furthermore, in the present invention, as described below, it is possible to suppress a decrease in catalytic activity due to CO poisoning by appropriately forming a complex with silica.

In the present invention, it is preferable to leave the silica surface without removing all of the silica skeleton from the carbon / silica composite produced in the process of preparing the porous carbon.
That is, by adjusting the concentration and immersion time of a basic solution such as NaOH or HF solution and the immersion time of the produced carbon / silica composite, while maintaining an appropriate porous carbon pore shape, Silica can remain on the carbon surface within a range of ˜120 wt%, preferably 0.1 to 100 wt%, more preferably 0.1 to 80 wt%.

  When a solution containing a readily carbonizable organic substance is immersed in porous silica to be adsorbed and impregnated, the carbon is completely removed by controlling the degree of immersion of the easily carbonizable organic substance in the porous silica pores. It can be set as the structure which left the space | gap partly without making it fill. Here, if the weight ratio of carbon and silica is within the above range, the operation of removing silica as it is is not necessary. The degree of immersion can be controlled, for example, by changing the concentration of the easily carbonizable substance solution or the number of immersion treatments.

  Furthermore, in the case where an appropriate porous carbon pore shape is formed without removing silica due to shrinkage due to carbonization of the carbon source filled in the pores, if the above content rate is maintained, It is also possible to use without removing the silica.

  As the metal catalyst to be contained in the porous carbon support of the negative electrode, a Pt one-way system is used, but a two-way system in which a second metal such as Ru is added thereto may be used as appropriate. Further, a metal catalyst such as Pt can be used for the positive electrode as well as the negative electrode.

  Regarding the Pt dispersion method, after forming porous carbon, it can also be performed by a general Pt support method, but if heat treatment is performed to stabilize the catalyst, Pt particles tend to aggregate, making it difficult to achieve high dispersion It is. In this study, the problem of agglomeration of Pt particles was overcome by preparing a mixed solution of carbon precursor and Pt particle precursor in advance and filling the mixed solution in porous silica. That is, when the surfactant or the like in the above-described method (i) is used as a carbon source, a Pt precursor may be mixed with the surfactant in advance.

In the above-mentioned method (ii), a compound containing a precursor of Pt particles such as H ₂ PtCl ₆ or [Pt (NH ₃ ) ₄ ] Cl ₂ is mixed with the solution containing the easily carbonizable organic substance. , Pt particle precursors are formed in a highly dispersed state in carbon. At this time, the concentration of the Pt particle precursor in the solution containing the easily carbonizable organic substance is preferably 0.1 to 30% by weight, particularly preferably 1 to 10% by weight in terms of Pt element.

In addition, after immobilizing the precursor of Pt particles in a highly dispersed state in the porous silica pores in advance, filling the porous silica pores with a carbon source, and carbonizing the filled carbon source, If appropriate, Pt particles can be highly dispersed in carbon by performing a reduction treatment. Specifically, for example, by using a metallosilicate having a cation exchange point in which a part of Si in the skeleton as porous silica is a group IIIB element, in particular, Al or B is isomorphously substituted, A cationic Pt compound such as Pt (NH ₃ ) ₄ ] ²⁺ is preliminarily dispersed on porous silica. The isomorphous substitution rate of the metallosilicate is preferably 0.1 to 50 mol%, and particularly preferably 1 to 40 mol%, of Si before substitution. In this case, first, the metallosilicate is immersed in an aqueous solution such as NaNO ₃ containing an excess amount of Na ⁺ or an aqueous solution such as NH ₄ NO ₃ containing an excess amount of NH ₄ ⁺ with respect to the cation exchange point, and 10 to 90 ° C., Preferably, it is allowed to stand at a temperature of 10 to 40 ° C. for 1 to 24 hours to make all the ion exchange points Na type or NH ₄ type. The NH ₄ type may be appropriately baked at 200 to 1000 ° C., preferably 300 to 600 ° C. for 1 to 24 hours, to form an H type. An aqueous solution containing a metallosilicate in Na-type, NH ₄ -type or H-type, wherein a Pt compound cation such as [Pt (NH ₃ ) ₄ ] ²⁺ is 1 to 200%, preferably 20 to 120% of the ion exchange point. And is stirred at a temperature of 10 to 90 ° C, preferably 65 to 85 ° C for 1 to 24 hours. After supporting the Pt compound in this manner, the composite is obtained by immersing in the solution containing the easily carbonizable substance described above and adsorbing and impregnating the carbon source. By polymerizing this carbon source, heating it in an inert atmosphere and carbonizing it, and performing reduction treatment as necessary, Pt particles are partially embedded in carbon while being highly dispersed and supported on the carbon surface. It is formed. According to this method, since the Pt particle precursor is immobilized at the ion exchange point, compared to the case where the carbon source is adsorbed and impregnated after the Pt particles are generated on silica in advance, the Pt particle precursor is immobilized at the ion exchange point. Pt particles can be miniaturized.

  According to the method of the present invention, when the silica is completely dissolved, the porous structure of the porous carbon containing the Pt particles has the same physical properties as the above-mentioned porous structure of only the porous carbon. The Pt particle-containing porous carbon thus obtained has a structure in which the Pt particles are embedded in the porous carbon, so that during heat treatment, aggregation due to the movement of Pt hardly occurs and high dispersion can be maintained. . When silica is left, the pore diameter and pore volume become smaller in proportion to the amount of silica remaining, but there is no problem in material diffusion as long as it is within the range of the pore structure described above. The particle size of the Pt particles is within the above range regardless of the amount of silica.

Next, the fuel cell electrode will be described. The fuel cell electrode can be produced from the electrode catalyst prepared as described above, and the production method is not particularly limited. The Pt content is 0.1 to 0.5 mg, preferably 0.1 to 0.4 mg, more preferably 0.1 to 0.35 mg per 1 cm ^{2 of} electrode area.

  The solid electrolyte is most preferably a solid electrolyte membrane represented by polyperfluoroalkylsulfonic acids, but is not particularly limited as long as it is a membrane capable of conducting protons. Further, the method for joining the solid electrolyte and each electrode is not particularly limited.

    EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Example 1
After stirring a solution obtained by adding 50 ml of ion-exchanged water to 9.93 g of n-octylamine, 0.56 g of concentrated hydrochloric acid was added and stirred. A solution obtained by mixing 16.00 g of tetraethoxysilane (TEOS) with 30 ml of ethanol was added to this solution and stirred in a 35 ° C. water bath to obtain a white precipitate. This was subjected to suction filtration, filtered and washed with ion-exchanged water in the funnel until the filtrate did not become cloudy, and further washed with 20 ml of ethanol three times. The filter cake was air-dried at room temperature and then fired at 650 ° C. in air to obtain porous silica.

1.00 g of porous silica prepared by the above method is mixed with 1.25 g of sucrose, 0.14 g of concentrated sulfuric acid, 0.20 g of H ₂ PtCl ₆ .6H ₂ O, and 5.00 g of ion-exchanged water. The sample was immersed in the solution and dried in air at 100 ° C. while the silica was immersed in the solution, followed by heat treatment at 160 ° C. The obtained powder is again immersed in a solution in which 0.80 g of sucrose, 0.09 g of concentrated sulfuric acid, 0.20 g of H ₂ PtCl ₆ .6H ₂ O and 5.00 g of ion-exchanged water are mixed, and silica is immersed The solution thus obtained was similarly dried in air at 100 ° C., heat treated at 160 ° C., and further treated at 900 ° C. under vacuum to carbonize sucrose and reduce Pt. To 1 g of the sample after carbonization / reduction, 280 g of 1 mol / l NaOH aqueous solution was added, and the silica skeleton was removed by heating at 120 ° C. while refluxing in the flask. The black precipitate obtained by suction filtration of this liquid was repeatedly filtered and washed with ion-exchanged water twice in a funnel, and then air-dried as it was to prepare Pt-supported mesoporous carbon.

    FIG. 1 shows a pore distribution curve obtained by analyzing the result of the nitrogen adsorption measurement by the BJH method. From FIG. 1, it was found that the obtained Pt-supported mesoporous carbon (sample 1) had pores distributed around a pore diameter of 1.6 nm.

(Example 2)
2.00 g of a surfactant having the structure of HO (C ₂ H ₄ O) ₂₀ (C ₃ H ₆ O) ₇₀ (C ₂ H ₄ O) ₂₀ H, ion-exchanged water 52.40 g, concentrated hydrochloric acid 8 .60 g was added and stirred until uniform. After adding 4.30 g of TEOS to this solution, it was immersed in an oil bath at 40 ° C. and stirred. The obtained white slurry was transferred to an autoclave, sealed, and stirred in a thermostat at 100 ° C. for 2 days. This was subjected to suction filtration, and filtration and washing with ion-exchanged water was repeated 5 times in the funnel, followed by air drying. The collected white powder was dried at 100 ° C. in the air and then baked at 550 ° C. in the air to remove the surfactant and obtain porous silica.

1.00 g of porous silica prepared by the above method was added to 1.25 g of sucrose, 0.14 g of concentrated sulfuric acid, 0.20 g of H ₂ PtCl ₆ .6H ₂ O, and 5.00 g of ion-exchanged water. It was immersed in the mixed solution, dried in air at 100 ° C. with the silica immersed in the solution, and then heat-treated at 160 ° C. The obtained powder is again immersed in a solution in which 0.80 g of sucrose, 0.09 g of concentrated sulfuric acid, 0.20 g of H ₂ PtCl ₆ .6H ₂ O and 5.00 g of ion-exchanged water are mixed, and silica is immersed The solution thus obtained was similarly dried in air at 100 ° C., heat-treated at 160 ° C., and further treated at 900 ° C. under vacuum to carbonize sucrose and reduce Pt. To 1 g of the sample after carbonization / reduction, 280 g of 1 mol / l NaOH aqueous solution was added, and the silica skeleton was removed by heating at 120 ° C. while refluxing in the flask. The black precipitate obtained by suction filtration of this liquid was repeatedly filtered and washed with ion-exchanged water twice in a funnel, and then air-dried as it was to prepare Pt-supported mesoporous carbon.

  FIG. 1 shows a pore distribution curve obtained by analyzing the result of the nitrogen adsorption measurement by the BJH method. From FIG. 1, it was found that the obtained Pt-supported mesoporous carbon (sample 2) had pores distributed around a pore diameter of 3.5 nm.

(Example 3)
The same operation as in the preparation of porous silica in Example 2 was performed except that TEOS 3.01 g and Al (OC ₃ H ₇ ) ₃ 1.26 g were added when TEOS was added in the preparation of porous silica in Example 2. And Al-containing porous silica was obtained.

1.00 g of Al-containing porous silica prepared by the above method was immersed in 200 ml of 1 mol / l NaNO ₃ aqueous solution and allowed to stand at room temperature until all the ion exchange points were converted to Na type. After filtration under reduced pressure, it was filtered and washed five times with ion-exchanged water in the funnel, and further immersed in 200 ml of 1 mol / l NH ₄ NO ₃ aqueous solution and allowed to stand at room temperature until the ion exchange points were all NH ₄ type. The same was filtered and washed. This sample was calcined in air at 400 ° C. to make the ion exchange point H ⁺ type, then immersed in 200 ml of 4 mmol / l [Pt (NH ₃ ) ₄ ] Cl ₂ aqueous solution and stirred in an oil bath at 80 ° C. did. After cooling to room temperature, the powder obtained by filtration was dried in air at 100 ° C. After drying, it was immersed in a solution in which 0.83 g of phenol, 0.80 g of formaldehyde and 5.00 g of ethanol were mixed, and after removing ethanol at 50 ° C. while the silica was immersed in the solution, heat treatment was subsequently performed at 100 ° C. The obtained powder was immersed again in a solution in which 0.83 g of phenol, 0.80 g of formaldehyde and 5.00 g of ethanol were mixed, and the solution in which silica was immersed was similarly removed at 50 ° C., and then at 100 ° C. The mixture was heat-treated and further treated at 900 ° C. under vacuum to carbonize sucrose and reduce Pt. 280 g of 1 mol / l NaOH aqueous solution was added to 1 g of the sample after carbonization / reduction, and the silica skeleton was removed by heating in a flask while refluxing at 120 ° C. The black precipitate obtained by suction filtration of this liquid was repeatedly filtered and washed with ion-exchanged water twice in a funnel, and then air-dried to prepare Pt-supported mesoporous carbon (sample 3).

Example 4
A surfactant having a structure of HO (C ₂ H ₄ O) ₂₀ (C ₃ H ₆ O) ₇₀ (C ₂ H ₄ O) ₂₀ H is added to 1.50 g of phenol, 10.0 g of ethanol, 52.40 g of ion-exchanged water, 8.60 g of concentrated hydrochloric acid and 0.49 g of H ₂ PtCl ₆ .6H ₂ O were added, and the mixture was immersed in an oil bath at 40 ° C. and stirred. To this solution, 4.30 g of TEOS and 1.44 g of formaldehyde were added, followed by stirring at 40 ° C. for 1 day. The obtained white slurry was transferred to an autoclave and sealed, and stirred for 2 days in a thermostatic bath at 100 ° C., and then the precipitate was suction filtered, and the residue was filtered and washed with ion exchange water in a funnel 5 times. Repeatedly air dried. The collected white powder was dried in air at 100 ° C. and then treated under vacuum at 800 ° C. to carbonize the phenol resin and reduce Pt. 280 g of 1 mol / l NaOH aqueous solution was added to 1 g of the sample after carbonization / reduction, and the silica skeleton was removed by heating in a flask while refluxing at 120 ° C. The black precipitate obtained by suction filtration of this liquid was repeatedly filtered and washed with ion-exchanged water twice in a funnel, and then air-dried to prepare Pt-supported mesoporous carbon (Sample 4).

(Comparative Example 1)
1.00 g of the porous silica prepared in Example 2 was immersed in a solution in which 1.25 g of sucrose, 0.14 g of concentrated sulfuric acid and 5.00 g of ion-exchanged water were mixed, and the silica was immersed in the solution while being immersed in the solution. After drying at 100 ° C. until the liquid was dried, heat treatment was continued at 160 ° C. The obtained powder was again immersed in a solution in which 0.80 g of sucrose, 0.09 g of concentrated sulfuric acid and 5.00 g of ion-exchanged water were mixed, and the solution in which silica was immersed was similarly dried at 100 ° C. in air. The sucrose was carbonized by heat treatment at 160 ° C. and further under vacuum at 900 ° C. 280 g of 1 mol / l NaOH aqueous solution was added to 1 g of the carbonized sample, and the silica skeleton was removed by heating at 120 ° C. in a flask while refluxing. The black precipitate obtained by suction filtration of this liquid was subjected to filtration and washing with ion-exchanged water twice in a funnel, and then air-dried to prepare mesoporous carbon. In a solution prepared by adding 0.40 g of H ₂ PtCl ₆ · 6H ₂ O to 200 ml of ion-exchanged water, 0.90 g of the mesoporous carbon prepared by the above method is immersed, and while the carbon is immersed in the solution, air After drying at 100 ° C. until the liquid was dried, Pt was reduced by treatment at 300 ° C. under a flow of H _{2 of} 50 ml / min to prepare Pt-supported mesoporous carbon (Sample 5).

  Table 1 shows the pore volume of the Pt-supported mesoporous carbon (samples 1 to 4) prepared in Examples and Comparative Examples, the pore volume ratio of the pore diameter of 1.2 to 5.0 nm in the total pore volume, and the average Pt The measurement result of a particle diameter is shown. In the Pt-supported mesoporous carbon prepared according to the present invention, it was found that there was no pore clogging due to Pt support, and the Pt particle diameter was 3.0 nm or less and highly dispersed.

The pore distribution curve of Pt-supported mesoporous carbon (Samples 1 and 2) prepared according to the present invention.

Claims (9)

A pore having a diameter of 10 nm or less has a pore volume of 0.6 to 1.2 ml / g, and 90% by volume or more of the pore has a size of 1.2 to 5.0 nm. An electrode catalyst for a fuel cell, comprising porous carbon in which Pt particles having a size of 0.5 to 3.0 nm are dispersed on the pore surface. The electrode catalyst for a fuel cell according to claim 1, wherein the porous carbon is complexed with 0.01 to 120% by weight of silica based on the porous carbon. 3. The fuel cell electrode catalyst according to claim 1, wherein the content of the Pt particles is 0.01 to 100% by weight with respect to the porous carbon. The method for producing an electrode catalyst for a fuel cell according to claim 1, wherein the porous carbon forms pores using porous silica as a template. The Pt particles are formed from a precursor of Pt particles dispersed in a carbon source of porous carbon, and the porous carbon is dispersed on the carbon surface after the formation. The method for producing a fuel cell electrode catalyst according to claim 4. The Pt particles are formed from Pt or / and a Pt compound fixed in advance in the pores of the porous silica, and are dispersed on the carbon surface after the porous carbon is formed. A method for producing an electrode catalyst for a fuel cell according to claim 4 or 5, wherein: The electrode for fuel cells formed using the electrode catalyst of any one of Claims 1-3. The fuel cell electrode according to claim 7, wherein the amount of Pt metal used is 0.1 to 0.5 mg per 1 cm ^{2 of} electrode area. A fuel cell comprising the electrode according to claim 7 or 8 as a constituent element.

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