JP5565135B2 - Method for producing catalyst-supported carrier and method for producing electrode catalyst - Google Patents

Description

  The present invention relates to a method for producing a catalyst-carrying carrier that forms an electrode catalyst for a fuel cell, and a method for producing an electrode catalyst using the catalyst-carrying carrier produced by this method.

  A fuel cell of a polymer electrolyte fuel cell includes a membrane electrode assembly (MEA: Membrane) composed of an ion-permeable electrolyte membrane and anode and cathode electrode catalyst layers (electrode catalysts) sandwiching the electrolyte membrane. An electrode assembly (MEGA: MEA and GDL) is formed by providing a gas diffusion layer (GDL) on the outside of each electrode catalyst layer to promote gas flow and increase current collection efficiency. A separator is arranged outside the gas diffusion layer to form a fuel cell. Actually, these fuel cells are stacked in the number corresponding to the power generation performance to form a fuel cell stack.

  The above-described conventional method for forming a catalyst layer includes, for example, a catalyst-supported carrier supporting a catalyst, a polymer electrolyte (ionomer), and a dispersion solvent on the surface of a substrate such as a Teflon sheet (Teflon: registered trademark, DuPont). The catalyst layer is formed by applying the catalyst solution (catalyst ink) and then drying the surface of the catalyst solution with a hot plate or the like (wet coating method). In addition, in this coating operation, there are a method of applying by spray, a method of using a doctor blade, and the like.

  By the way, in order to increase the efficiency or activity of the electrocatalyst, which is an important factor for improving the power generation performance of the fuel cell, this is achieved by an approach from the production method of the electrocatalyst and the production method of the catalyst-supporting carrier constituting this electrocatalyst. Various technologies have been proposed.

  As one of the developed technologies, instead of supporting the catalyst metal alone on the surface of the conductive support, the highly active platinum or the like is left only on the surface (shell or shell) of the catalyst particles, and the particles do not contribute greatly to the catalytic action. Attention has been focused on the production and development of a catalyst-supported carrier on which a so-called core-shell catalyst is supported, in which the inside (core or core) of the catalyst is made of a low activity metal different from platinum.

  This core-shell catalyst can reduce the amount of extremely expensive and rare platinum used as much as possible, and can form the same level of fine particles as the conventional platinum catalyst, and expect the same or higher catalytic activity. it can.

  Here, a technique disclosed in Patent Document 1 can be cited as a conventional published technique related to a method for producing an electrode catalyst having a core-shell catalyst. The method for producing an electrocatalyst disclosed herein comprises mixing a reverse micelle solution containing a solution containing rhodium chloride inside a micelle and a reverse micelle solution containing a solution containing platinum ions inside the micelle, A reducing agent and a reducing agent of platinum ions are added, and the conductive support is dispersed in the solution, and the composite metal particles are supported on the conductive support.

  As can be understood from the production method disclosed in Patent Document 1, when a core-shell catalyst composed of different metals is to be formed on the surface of the conductive support, it is necessary to use a reducing agent specific to each of the different metals, Problems such as manufacturing management required for the reduction process, processing time for the reduction process, and material cost required for the reducing agent occur, such as the timing of the metal reduction process.

  Therefore, although not related to the core-shell catalyst, in Patent Document 2, for example, an alloy precursor made of platinum and a metal other than platinum is manufactured by the reverse micelle method, and this and carbon powder are added to a solvent, and an inert gas is introduced. Thus, there is a disclosure of a technique for producing an electrode catalyst made of an alloy catalyst without using a reducing agent by heat treatment.

  However, this technique has a big problem that a process with a high degree of difficulty in processing such as manufacturing an alloy precursor by applying a reverse micelle method is added to the production of an electrode catalyst.

JP 2005-196972 A JP 2008-130325 A

  The present invention has been made in view of the above problems, and relates to a method for producing a catalyst-carrying carrier in which a core-shell catalyst is carried on a conductive carrier, making it unnecessary to use a reducing agent specific to each different metal, There is no need for production management for reduction treatment and no processing time therefor, and there is no need for a process for producing an alloy precursor in advance, and a catalyst-supported carrier that can form an efficient and excellent core-shell catalyst. It is an object of the present invention to provide a production method and a production method of an electrode catalyst using the catalyst-supported carrier obtained by this method.

  In order to achieve the above object, a method for producing a catalyst-carrying carrier according to the present invention is a method for producing a catalyst-carrying carrier in which a catalyst is carried on a conductive carrier, wherein the first catalyst metal is carried on the conductive carrier. The catalyst-supported carrier intermediate is mixed in a solvent to form a suspension, and the suspension is heat treated to lower the liquid potential of the suspension. The second catalyst metal is mixed with the suspension, and the second catalyst metal modifies the surface of the intermediate first catalyst metal with the second catalyst metal.

  In the production method of the present invention, a first catalyst metal (for example, a core catalyst) is previously supported on the surface of a conductive support, and this is mixed in a solvent such as pure water to form a suspension. Before mixing the catalyst metal (for example, shell catalyst) into the suspension, the suspension is subjected to a heat treatment to lower the liquid potential of the suspension. Is added to the suspension and mixed to modify the first catalyst with the second catalyst to form, for example, a core-shell catalyst, which is produced on a conductive carrier. The first catalytic metal serving as the core catalyst can be a simple substance such as Pd, Ir, Rh, or an alloy thereof.

  For example, when pure water is used as the solvent, the liquid potential is lowered as the temperature of the suspension is increased by heating the pure water until it becomes hot water of less than 100 ° C., which is close to 100 ° C. It has been specified by the present inventors that the liquid potential of the suspension decreases to a constant value of about 500 mV, for example, when the temperature is reached.

  Then, when the temperature of the suspension settles down to a constant value and the liquid potential drops below a certain value, the second catalyst metal that becomes a shell catalyst is charged into the suspension and mixed, A core-shell catalyst is obtained in which a shell catalyst having a layer with a uniform thickness as much as possible is formed on the surface of the core catalyst, and the surface of the conductive carrier is modified (attached, adsorbed, or chemically bonded) by the core-shell catalyst. The present inventors have found that a catalyst-supported carrier obtained by the above process can be obtained.

  For example, water, which is a solvent, is oxidatively decomposed by heat treatment, whereby electrons are released into the suspension and are adsorbed on the surface of the first catalytic metal. When the second catalytic metal is introduced into the suspension, the second catalytic metal is reduced and deposited on the surface of the first catalytic metal via the electrons, and the surface of the first catalytic metal is modified to modify the core shell. It has been specified by the present inventors to form a catalyst.

  In addition, Pt can be used for the second catalyst metal serving as the shell catalyst, and platinum as compared with a catalyst support in which only platinum is supported on the surface of a carbon support as in a conventional catalyst support. The amount used can be significantly reduced. And according to the verification by the present inventors, a result is obtained that the catalytic activity is better than that of the conventional catalyst while reducing the amount of platinum used. Therefore, it is possible to manufacture a fuel cell excellent in power generation performance while reducing the manufacturing cost as compared with the conventional manufacturing method.

  In a preferred embodiment of the method for producing a catalyst-supporting carrier according to the present invention, the suspension is subjected to a bubbling treatment with an inert gas at least in the first step.

  According to the present inventors, by performing heat treatment while bubbling the suspension with an inert gas such as nitrogen gas, the decrease in the liquid potential of the suspension mixed with the intermediate is more prominent. Proven. Note that “at least in the first step” may be a mode in which the bubbling process is performed only during the first step, or is performed over the entire first and second steps. It means that it may be a form.

  Then, by combining this inert gas bubbling and heat treatment to lower the liquid potential of the suspension and mixing this with the second catalytic metal, shell layer formation and thickness uniformity of this layer It has been found that the catalyst can be further improved and a catalyst having a higher quality core-shell structure can be formed. The inert gas used includes argon gas and helium gas in addition to nitrogen gas.

  If water, which is a solvent, is present around the first catalyst metal supported on the conductive support and is sufficiently saturated with nitrogen gas or the like, the entire surface of the first catalyst metal is easily metallized. The water is oxidatively decomposed on the entire surface. Electrons are generated by this oxidative decomposition, and the second catalytic metal is more easily reduced and deposited through the electrons.

  Further, in a preferred embodiment of the method for producing a catalyst-supporting carrier according to the present invention, in the first step, the suspension is subjected to a heat treatment to a temperature not higher than the boiling point of the solvent, and is in the range of 65 to 95 ° C. To adjust.

  As described above, the present inventors have specified that the liquid potential of the suspension also decreases to a constant value of, for example, about 500 mV when the temperature is close to 100 ° C. The production below tends to increase the production cost, and it is preferable to reduce the liquid potential as desired while reducing the temperature of the suspension as much as possible.

  According to the verification by the present inventors, when the temperature of the suspension is 60 ° C. or lower, for example, the reaction selectivity of Pt ions as the second catalyst metal on Pd as the first catalyst metal is lost, It is known that single particles such as Pt are deposited on carbon, and in a suspension in which the solvent is water, this is heat-treated and adjusted to a temperature range of 65 to 95 ° C. It has been found that core-shell particles can be produced at a low cost while suppressing single particle precipitation such as the above.

  In a preferred embodiment of the method for producing a catalyst-supporting carrier according to the present invention, the suspension is hydrotreated in the first step.

  This method can be used, for example, at a stage before the heat treatment in the first step, a stage after the heat treatment, a stage before bubbling with an inert gas, or a stage after bubbling. The surface of the first catalytic metal or the vicinity of the surface is hydrogenated (hydrogen ions are adsorbed or hydrogen ions are floating in the vicinity). Thus, the stage of performing the hydrogen treatment may be at any timing during the first step, but the treatment is performed so that there is no residual hydrogen when the second catalyst metal is added.

  According to the present inventors, the surface of the first catalyst metal or the vicinity of the surface is hydrogenated, so that the second catalyst metal is easily modified, and the resulting core-shell catalyst also has a catalytic activity. It has been proven to improve.

  Here, as the above-mentioned hydrogen treatment, the following two methods can be exemplified.

  One is a method of bubbling the suspension with hydrogen gas, and the other is a method of adding sodium borohydride to the suspension.

  In particular, in the method of adding sodium borohydride to the suspension, a part of the hydrogen (ions) of this sodium borohydride is adsorbed on the first catalytic metal surface, and the remaining sodium borohydride is It has been identified that it is broken down in suspension and no extra hydrogen is released into the suspension.

  The above manufacturing method in which the suspension is simply heat-treated before the second step by introducing the second catalyst metal into the suspension with hydrogen ions adsorbed on the surface of the first catalyst metal, or the heat treatment In addition to the above-described production method in which bubbling with an inert gas is performed, a high-quality core-shell catalyst in which the entire surface of the core catalyst is modified with a shell catalyst having a more uniform thickness can be obtained.

  Furthermore, the present invention extends to a method for producing an electrode catalyst using the catalyst-supported carrier obtained by the above-described production method. The catalyst-supported carrier obtained by the above method and a separate polymer electrolyte are provided. A catalyst solution (catalyst ink) is generated by stirring in a separate dispersion solvent, and a catalyst solution (catalyst ink) is formed. A layer composed of the catalyst solution is formed on the surface of the base material and dried to produce an electrode catalyst.

  Here, the substrate means an electrolyte membrane, a gas diffusion layer, or the like, and a catalyst solution is stretched on the substrate in a layer shape by, for example, a coating blade to form a coating film. The anode-side and cathode-side catalyst layers (catalyst electrodes) are formed through a drying process such as high-temperature drying using an air drying furnace or the like.

  As already described, a catalyst ink is produced using the catalyst-supported carrier obtained by the production method of the present invention, and a fuel cell having an electrode catalyst obtained by using the catalyst-supported carrier is an electrode produced by a conventional production method. Compared to a fuel cell having a catalyst, its power generation performance is high, and it is obtained at a low production cost based on a reduction in the material cost of the catalyst metal.

  The fuel cell having the electrode catalyst manufactured by the method for manufacturing the conductive carrier of the present invention and the method for manufacturing the electrode catalyst using the conductive carrier manufactured by this method has the above-described effects. Therefore, its production has been increasing recently, and it is suitable for fuel cells for electric vehicles and hybrid vehicles that require higher performance and lower manufacturing costs for in-vehicle devices.

  As can be understood from the above description, according to the method for producing a catalyst-supporting carrier of the present invention, a suspension is produced by mixing an intermediate composed of a core catalyst of a core-shell catalyst and a conductive carrier in a solvent, thereby producing a shell catalyst. Before mixing with the suspension, more preferably by subjecting the suspension to bubbling with an inert gas in addition to the heat treatment, and more preferably with the heat treatment and the inert gas. By hydrogenating the surface of the core catalyst or its vicinity in addition to the bubbling treatment, it is possible to obtain a catalyst-carrying carrier in which a core-shell catalyst having excellent catalytic activity is carried on a conductive carrier as much as possible. it can.

(A) is the schematic diagram explaining the 1st process of one Embodiment of the manufacturing method of the catalyst carrying | support carrier of this invention, (b) is an electron in the 1st catalyst metal surface in a 1st process. It is the schematic diagram explaining the state which has adsorb | sucked. (A) is the schematic diagram explaining the 2nd process of one Embodiment of the manufacturing method of the catalyst carrying | support carrier of this invention, (b) is the 2nd catalyst metal by the electron of the 1st catalyst metal surface. It is the schematic diagram explaining the state attracted | sucked, (c) is the schematic diagram explaining the catalyst support | carrier which the 2nd catalyst metal was modified on the surface of the 1st catalyst metal, and the core-shell catalyst was formed. . It is the schematic diagram explaining the 1st process of other embodiment of the manufacturing method of the catalyst carrying | support carrier of this invention. (A) is the schematic diagram explaining the 1st process of further another embodiment of the manufacturing method of the catalyst carrying | support carrier of this invention, (b) is a 1st catalyst in which a hydrogen ion is 1st process. It is the schematic diagram explaining the state adsorb | sucking to the metal surface. It is the graph which demonstrated the manufacturing method of Example 1 in time series in the experiment which verified the oxygen reduction activity of the catalyst. It is the graph which demonstrated the manufacturing method of Example 2 in time series in the experiment which verified the oxygen reduction activity of the catalyst. It is a figure which shows the experimental result regarding the activity per unit mass of the catalyst support | carrier obtained by both the Example manufacturing method and the comparative example manufacturing method. (A) is a TEM-EDX photograph of the core-shell catalyst by the production method of Example 1, and (b) is a metal atom containing the core catalyst metal and the shell catalyst metal at points 1, 2, and 3 in (a). It is a figure which shows mass ratio. (A) is a TEM-EDX photograph of the core-shell catalyst according to the production method of Example 1, and (b) is a metal containing a core catalyst metal and a shell catalyst metal at points 1, 2, and area 1 in (a). It is a figure which shows the mass ratio of an atom. (A) is a TEM-EDX photograph figure of the core-shell catalyst by the manufacturing method of Example 2, (b) is a figure which shows the analysis result regarding the platinum intensity | strength and palladium intensity | strength in the EDX line 1 in (a). (A) is a graph showing potential changes under nitrogen saturation conditions in Examples 1 and 2 and Comparative Examples 3 and 4, and (b) shows potential changes under oxygen saturation conditions in Examples 1 and 2 and Comparative Examples 3 and 4. It is a graph which shows. It is a figure which shows the experimental result which verified the appropriate temperature range of the suspension liquid in a 1st process, (a) is a STEM photograph figure of the core-shell catalyst manufactured under the suspension of 80 degreeC, (b ) Is a graph showing the relationship between the distance from the surface of the core-shell catalyst and the amounts of Pt and Pd. (A), (b) is the STEM photograph figure of the core-shell catalyst manufactured under the suspension of 60 degreeC. It is a graph which shows the relationship between the hydrogen ion density | concentration in a solution required for the reduction | restoration precipitation of Pt, and solution temperature. (A), (b) is a STEM photograph figure of the core-shell catalyst manufactured under the suspension of 40 degreeC. (C), (d) is a STEM photograph of the core-shell catalyst produced under a suspension at 40 ° C. (A), (b) is a STEM photograph figure of the core-shell catalyst manufactured under the suspension of 60 degreeC. (C) is a STEM photograph of a core-shell catalyst produced under a suspension at 60 ° C. (A), (b) is a STEM photograph figure of the core-shell catalyst manufactured under the suspension of 80 degreeC. (C) is a STEM photograph of a core-shell catalyst produced under an 80 ° C. suspension.

  Hereinafter, a method for producing a catalyst-supporting carrier of the present invention will be outlined with reference to the drawings. Here, FIG. 1a is a schematic diagram illustrating a first step of an embodiment of the method for producing a catalyst-carrying carrier of the present invention, and FIG. 1b is a diagram showing that the first catalyst is an electron in the first step. It is the schematic diagram explaining the state adsorb | sucking to the metal surface. FIG. 2a is a schematic diagram illustrating the second step of the embodiment of the method for producing the catalyst-supporting carrier of the present invention subsequent to FIG. 1, and FIG. 2b is the electron on the surface of the first catalyst metal. FIG. 2C is a schematic diagram illustrating a state in which the second catalytic metal is sucked by the catalyst, and FIG. 2C is a catalyst-supporting carrier in which a core-shell catalyst is formed by modifying the second catalytic metal on the surface of the first catalytic metal. FIG. Further, FIG. 3 is a schematic diagram illustrating a first step of another embodiment of the method for producing a catalyst-supporting carrier of the present invention, and FIG. 4a is still another method for producing a catalyst-supporting carrier of the present invention. FIG. 4B is a schematic diagram illustrating a state in which hydrogen ions are adsorbed on the first catalytic metal surface in the first step.

  In the manufacturing method shown in FIG. 1a, first, as a first step, a first catalyst metal 2 serving as a core catalyst is formed on the surface of the conductive carrier 1 in a solvent W made of pure water contained in a container Y. The supported intermediate 10 is charged to produce a suspension, which is heat-treated.

  In the heat treatment of the suspension, since the solvent W is pure water, it is preferable that the temperature be adjusted to a range of 65 ° C. to 95 ° C., which is lower than the boiling point (experimental results indicating the basis thereof will be described later).

  As the suspension is heat treated and approaches, for example, 65 ° C. in the above temperature range, the liquid potential of the suspension gradually decreases. The timing of adding the second catalyst metal in the second step is such that a threshold value is provided for the liquid potential of the suspension, and the second catalyst metal is charged when the liquid potential falls below the threshold value. It is desirable to do. According to the present inventors, when pure water is used as a solvent, an intermediate is mixed with the solvent to produce a suspension, which is then heat-treated to lower its liquid potential. It has been specified that a liquid potential atmosphere effective for core-shell catalyst formation is obtained when the temperature reaches about 65 to 95 ° C. For example, it has been specified that the liquid potential falls below 500 mV when the liquid temperature of the suspension reaches about 95 ° C. Therefore, by introducing the second catalyst metal at a timing when the liquid temperature of the suspension is about 65 to 95 ° C. and the liquid potential is lower than the predetermined value, a core-shell catalyst having a higher quality than the conventional manufacturing method can be obtained. It has been found that it can be formed.

By heat-treating the suspension to the above temperature range, as shown in FIG. 1b, oxidative decomposition of H ₂ O → 2H ⁺ + 1 / 2O ₂ + 2e ⁻ occurs in water, and this electron: e ⁻ Is adsorbed on the surface of the core catalyst 2.

  In this state, as shown in FIG. 2a, when the second catalytic metal 3 serving as the shell catalyst is introduced into the suspension, the shell catalyst 3 is sucked into the surface of the core catalyst 2 as shown in FIG. As shown by 2c, the surface of the core catalyst 2 is modified with the shell catalyst 3 to form the core-shell catalyst 4, and the catalyst-supported carrier 20 in which the core-shell catalyst 4 is supported on the conductive carrier 1 is obtained.

  In the production method described above, no reductant specific to each of the core catalyst and the shell catalyst is used, and an extremely simple improved production method in which the suspension in which the intermediate is mixed in the first step is merely heat-treated. Is due to.

  Here, the conductive carrier 1 includes carbon materials such as carbon black, carbon nanotube (CNT), carbon nanofiber (CNF), graphite carbon, highly crystalline carbon, acetylene black, alumina, zirconia, titanium oxide, ceria. And ceramics.

  In addition, as the core catalyst metal, any one of Pd, Ir, Rh, Au, Re, Os, Ru, Ag, Fe, Co, Ni, Cr, Mn, Mo, Cu, Pt (single), or Two or more of these alloys can be used.

  On the other hand, as the shell catalyst metal, any one of Pt, Pd, Ir, Rh, Au, Re, Os, Ru, Ag, Fe, Co, Ni, Cr, Mn, Mo, Cu (single), or Two or more of these alloys can be used. As the shell catalyst metal, a tetravalent to monovalent metal salt can be used, and among them, a divalent to monovalent metal salt is preferable.

  The manufacturing method shown in FIG. 3 provides an inert gas such as nitrogen into the suspension through the introduction pipe K in parallel with the heat treatment of the suspension as in the first step shown in FIG. 1a. (X1 direction), and a bubbling process is performed.

  Here, when the target temperature of the suspension during heat treatment is set to about 65 to 95 ° C., the timing of the bubbling treatment may be before the suspension reaches the target temperature, It may be after reaching. Further, the inert gas may be subjected to a bubbling process over all the steps from the first step to the second step.

  It has been found that due to nitrogen bubbling, the liquid potential of the suspension is significantly lower than in the case of the manufacturing method with only heat treatment shown in FIG. 1, and the structure of the core-shell catalyst obtained by this method is It has been found that a layer of shell catalyst having a more uniform thickness is formed on the surface of the catalyst, and the catalytic activity is further improved. The inert gas used includes argon gas and helium gas in addition to nitrogen gas, and these are preferably provided to the suspension in an amount of 10 to 1000 ml / min.

  In addition to the manufacturing method shown in FIG. 3, that is, the manufacturing method shown in FIG. 4, that is, the suspension is heat-treated in the first step, and in parallel with this, bubbling with an inert gas is performed. The suspension is treated with hydrogen to hydrogenate the surroundings of the first catalytic metal 2 forming the intermediate 10.

  Here, in addition to the method of bubbling hydrogen gas into the suspension, there is a method of charging sodium borohydride 5 into the suspension as shown in the figure.

The timing of the introduction of sodium borohydride 5 is the stage before the second process, for example, the stage before the heat treatment in the first process, the stage after the heat treatment, and the bubbling with the inert gas. Any of a stage and a stage after bubbling may be sufficient. By treating the suspension with hydrogen, as shown in FIG. 4 b, a state is formed in which hydrogen ions: H ⁺ are adsorbed on the surface of the first catalytic metal 2, and bubbling nitrogen: N ₂ Floating nearby.

  According to the present inventors, the surface of the first catalytic metal or the vicinity of the surface is hydrogenated, so that the second catalytic metal is easily modified, and the catalytic activity of the obtained core-shell catalyst is further increased. It has been proven to improve.

  The hydrogen ions adsorbed on the surface of the first catalyst metal 2 effectively reduce the second catalyst metal introduced into the suspension, and the thickness of the first catalyst metal surface is as uniform as possible. A layered shell catalyst is formed.

  A catalyst-carrying carrier in which a core-shell catalyst is carried on a conductive carrier is obtained by the various production methods described above, and an electrode catalyst is produced using the catalyst-carrying carrier.

  Specifically, the obtained catalyst-supporting carrier and polymer electrolyte (ionomer) are put into a dispersion solvent accommodated in a prepared container, and stirred using an ultrasonic homogenizer, a bead mill, a ball mill, or the like. As a result, a catalyst solution (catalyst ink) is generated.

  Here, the charged polymer electrolyte is a proton-conductive polymer, an ion exchange resin having an organic fluorine-containing polymer as a skeleton, such as perfluorocarbon sulfonic acid resin, sulfonated polyether ketone, sulfonated polyether. Sulfonated plastic electrolytes such as sulfone, sulfonated polyetherethersulfone, sulfonated polysulfone, sulfonated polysulfide, sulfonated polyphenylene, sulfoalkylated polyetheretherketone, sulfoalkylated polyethersulfone, sulfoalkylated polyetherethersulfone And sulfoalkylated plastic electrolytes such as sulfoalkylated polysulfone, sulfoalkylated polysulfide, and sulfoalkylated polyphenylene. It is also possible to use commercially available materials such as Nafion (registered trademark, manufactured by DuPont) and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.).

  Examples of the dispersion solvent include water, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, and diethylene glycol, acetone, methyl ethyl ketone, dimethylformamide, dimethylimidazolidinone, dimethyl sulfoxide, dimethylacetamide, Examples include N-methylpyrrolidone, propylene carbonate, esters such as ethyl acetate and butyl acetate, and various aromatic or halogen solvents, and these may be used alone or as a mixture. it can.

  Form the electrode catalyst on the surface of the substrate by applying the generated catalyst solution to any one of the electrolyte membrane, gas diffusion layer, and support film that is the substrate, followed by hot air drying, hot pressing, etc. Can do. Here, this electrolyte membrane is, for example, a non-fluorine ion exchange membrane having a sulfonic acid group or a carbonyl group, a substituted phenylene oxide, a sulfonated polyaryletherketone, a sulfonated polyarylethersulfone, a sulfonated phenylenesulfide or the like. It is formed from a fluorine-based polymer or the like. The gas diffusion layer is formed from a fired body made of polyacrylonitrile, a fired body made of pitch, carbon materials such as graphite and expanded graphite, nanocarbon materials thereof, stainless steel, molybdenum, titanium, and the like. Furthermore, examples of the support film include a polyethylene film, a polypropylene film, a polytetrafluoroethylene film, an ethylene / tetrafluoroethylene copolymer film, and the like. Also good. A commercially available material such as a Teflon sheet (Teflon: registered trademark, DuPont) may also be used.

[Experiment verifying oxygen reduction activity of catalyst and its results]
The inventors manufactured the catalyst-supported carrier by the following three types of inventive methods (Examples 1, 2, and 3), and also manufactured the catalyst-supported carrier by the methods of Comparative Examples 1 to 4 including the conventional manufacturing method. In addition to verifying these oxygen reduction activities, Examples 1 and 2 were subjected to TEM-EDX imaging to analyze the mass ratio of contained metal atoms.

First, in the method according to Example 1, 0.5 g of Pd-supported carbon (manufactured by BASF, Pd20% / C, C9-20) is suspended in 500 mL of pure water, and the suspension is refluxed at 95 ° C. with stirring. (At this stage, the liquid potential of the suspension is below 500 mV). Next, 0.122 g of K ₂ PtCl ₄ (corresponding to Pt1 atomic layer) is dissolved in 200 ml of pure water, added dropwise to the suspension over 1 hour, stirred for 4 hours, washed with water, filtered and air-dried at 80 ° C. A catalyst-supported carrier was obtained.

In the method according to Example 2, 0.5 g of Pd-supported carbon (manufactured by BASF, Pd20% / C, C9-20) was suspended in 500 mL of pure water, and suspended by refluxing at 95 ° C. with N ₂ bubbling and stirring. A liquid was produced. Next, 0.12 g of K ₂ PtCl ₄ (corresponding to a Pt1 atomic layer) was dissolved in 200 ml of pure water and bubbled with N ₂ and dropped into the suspension over 1 hour. Next, the mixture was stirred for 4 hours while bubbling with N ₂ , washed with water, filtered and blown and dried at 80 ° C. to obtain a catalyst-supported carrier.

On the other hand, in the method according to Example 3, 0.5 g of Pd-supported carbon (manufactured by BASF, Pd20% / C, C9-20) was suspended in 50 mL of pure water, and 0.082 g of sodium borohydride was added for 48 hours. The mixture was left stirring at room temperature and refluxed at 95 ° C. with N ₂ bubbling and stirring to form a suspension. Next, 0.12 g of K ₂ PtCl ₄ (corresponding to a Pt1 atomic layer) was dissolved in 200 ml of pure water and bubbled with N ₂ and dropped into the suspension over 1 hour. Next, the mixture was stirred for 4 hours while bubbling with N ₂ , washed with water, filtered and blown and dried at 80 ° C. to obtain a catalyst-supported carrier.

  In contrast to the manufacturing methods of Examples 1 to 3 described above, the method according to Comparative Example 1 is a method in which Pt was dropped in the method of Example 1 when the liquid potential of the suspension was 600 mV.

  The method according to Comparative Example 2 uses a material similar to that in Example 1 and synthesizes a core-shell catalyst by an electroless plating method.

  In the method according to Comparative Example 3, Pd / C (manufactured by BASF, Pd20% / C, C9-20) in which only palladium is supported on a carbon support, not a core-shell catalyst, was produced.

  Furthermore, the method according to Comparative Example 4 was the same as Comparative Example 3 except that Pt / C (manufactured by Tanaka Kikinzoku Co., Pt30% / C, TEC10E30E) in which only a platinum was supported on a carbon support was used instead of the core-shell catalyst. It is.

  Here, FIGS. 5 and 6 are graphs illustrating the manufacturing methods of Examples 1 and 2 in time series.

  First, in the method of Example 1 shown in FIG. 5, Pt is added to the suspension when the suspension falls below one threshold value of 500 mV by heat treatment.

  As is clear from the figure, the liquid potential of 500 mV is also the temperature at the stage where the temperature of the suspension reached 95 ° C., and the liquid potential starts to increase by adding Pt. Further, the pH of the suspension decreases as the temperature of the suspension increases, and becomes substantially constant in an acidic atmosphere where the pH is less than 4.

On the other hand, in the method of Example 2 shown in FIG. 6, heat treatment and N ₂ bubbling are simultaneously disclosed, and N ₂ bubbling is continuously performed after Pt addition.

  5 and 6, it is clear that in the method of Example 2, the lower limit peak value of the liquid potential of the suspension is lowered to about 300 mV compared to about 450 mV in Example 1. ing.

  In addition, the pH of the suspension is also more acidic in Example 2, and the tendency of the liquid potential after addition of Pt is gradually increased to about 600 mV in Example 1, whereas in Example 2, It shows a tendency to suddenly rise to near 700 mV and then suddenly drop through the upper limit peak.

  The verification results regarding the oxygen reduction activity of the catalyst-supported carriers produced by the production methods of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1 below.

  Regarding Table 1, the upper result is a unit mass activity value obtained by dividing the amount of power generation by the total amount of platinum and palladium in the catalyst (the amount of platinum in the case of platinum only, the amount of palladium in the case of palladium only), The result in the middle row is the unit mass activity value obtained by ignoring the amount of palladium and dividing the amount of power generation by the amount of platinum alone, and the result in the lower row assumes that the material cost of palladium is 1/4 of that of platinum. It is a unit mass activity value obtained by adjusting the catalyst amount by reflecting the ratio in the mass and dividing the power generation amount by the adjusted catalyst amount. From this, it can be said that it is preferable for the vehicle manufacturer to use the lower result showing the unit mass activity value in consideration of both the material cost and the catalyst activity.

  Table 1 shows that each of the examples has catalytic activity in the order of Examples 1, 2 and 3 as compared to Comparative Examples 4 and 3 showing a conventional catalyst-supported carrier in which platinum and palladium are supported alone on a conductive carrier. In particular, in Example 3, it has been demonstrated that the activity is improved by 2-3 times compared to Comparative Examples 4 and 3.

  Further, from the graph regarding the oxide peak potential shift and the oxygen reduction activity per unit mass shown in FIG. It can be confirmed that the activity of Example 3 is improved by about 2.5 times that of Comparative Example 4.

  8 and 9 show TEM-EDX photographs of the core-shell catalyst produced by the production method of Example 1, and FIG. 10 shows TEM-EDX photographs of the core-shell catalyst produced by the production method of Example 2, respectively. The analysis result regarding the mass ratio of the containing metal atom containing a catalyst metal and a shell catalyst metal is shown. In FIG. 8, the upper, middle, and lower stages of each mass ratio analysis graph shown in FIG. 8b show the results of points 1, 2, and 3 in FIG. 8a, respectively. In FIG. 9, the upper, middle, and lower stages of each mass ratio analysis graph shown in FIG. 9b show the results of points 1 and 2 and area 1 in FIG. 9a, respectively.

  In both the core-shell catalysts of Examples 1 and 2 shown in FIGS. 8 and 10, it can be confirmed that a shell catalyst is formed around the central core catalyst metal. 8 and 10, it is clear that the core-shell catalyst of Example 2 is more dominant than Example 1 in terms of the atomic weight of palladium in the core, and the atomic weight of platinum in the shell is increased. It can be seen that a core-shell structure composed of a palladium core and a platinum shell is formed with higher accuracy.

Further, FIGS. 11a and 11b show potential changes of the core-shell catalyst according to the manufacturing methods of Examples 1 and 2, respectively. Here, FIG. 11a is the result under the condition of 0.1M HClO ₄ , 27 ° C., N ₂ saturation, 100 mV / sec, and FIG. 11b is the result of 0.1M HClO ₄ , 27 ° C., O ₂ saturation, 10 mV / sec. Results under conditions.

  From FIG. 11, it can be confirmed that Examples 1 and 2 have similar electrochemical characteristics when the catalyst metal is platinum alone.

[Experiment verifying the appropriate temperature range of the suspension in the first step and its results]
The present inventors conducted an experiment for verifying an appropriate temperature range of the suspension in the first step. This is because the suspension is heat-treated and adjusted to a desired temperature range to lower its liquid potential, and the second catalyst metal constituting the shell of the core-shell catalyst is added to the suspension to thereby improve the quality of the core-shell catalyst. This is because the can be formed.

  First, the core-shell catalyst was formed by using two types of suspensions that were heat-treated and adjusted to 60 ° C. and 80 ° C., respectively.

More specifically, 0.3 g of Rd-supported carbon was prepared and charged into 300 g of ion-exchanged water, and after N2 bubbling, each ion-exchanged water was heated to 60 ° C. and 80 ° C., and then K ₂ PtCl ₄ 0.083 g (0.20 mmol) dissolved in 200 g of ion-exchanged water was added, and the temperature of each solution was maintained at 60 ° C. and 80 ° C. for 5 hours while stirring.

  Next, it was filtered, washed with 500 mL of ion exchange water at 60 ° C. three times, and blown and dried at 80 ° C. for 15 hours to obtain a catalyst-supported carrier.

  FIG. 12a is a STEM photograph of the core-shell catalyst produced under a suspension at 80 ° C., and FIG. 12b is a graph showing the relationship between the distance from the surface of the core-shell catalyst and the amounts of Pt and Pd. Table 2 below shows the Pd and Pt composition ratios of the manufactured core-shell catalyst.

  From FIG. 12 and Table 2, core-shell particles can be confirmed, and single particles of Pd and Pt do not exist.

  On the other hand, FIGS. 13a and 13b are STEM photographs of core-shell catalysts produced under a suspension at 60 ° C., and Table 3 below shows the Pd and Pt composition ratios of the produced core-shell catalysts.

  From FIG. 13 and Table 3, core-shell particles could not be confirmed, and single particles of Pt existed. That is, it has been proved that the reaction selectivity of Pt ions onto Pd is lost when the temperature is 60 ° C. or lower, and the target core-shell particles cannot be produced.

  From the above experimental results, it can be seen that it is difficult to form core-shell particles when the suspension is heat-treated at 60 ° C, and it is necessary to adjust the temperature of the suspension to 65 ° C or higher, which is at least higher than that. Therefore, it can be concluded that the temperature should be adjusted to the above-described 95 ° C range which is 65 ° C or higher.

  However, the temperature of the suspension is as low as possible among the temperatures at which the core-shell particles can be formed, which leads to a reduction in manufacturing cost. An example of the trial calculation result is shown below.

  First, the amount of heat that can be saved when the temperature during production is changed from 95 ° C to 80 ° C is obtained. Assuming that 1J (joule) is the amount of heat required to raise 1g of water by 1K (1 ° C), when the temperature is 95 ° C to 80 ° C, 500g of water (amount used in the example) x 15 (temperature difference) = The amount of heat that can be saved when the temperature rises is 7500J.

Next, a cost corresponding to this amount of heat is obtained. Here, the calculation is based on 22 yen / kWh. Generally, 1kWh = 1 x 1000W x 3600s = 3.6 x 10 ⁶ J, and 1J = 2.78 x 10 ^-7 kWh, so 7500J is 7500 J x 2.78 x 10 ^-7 kWh / J = 2.1 x 10 ^-3 kWh It becomes.

The cost at this time is 22 yen / kWh x (2.1 x 10 ^-3 kWh) = 0.046 yen (cost reduction unit price).

  In mass production of fuel cells, if the scale is increased 100,000 times to produce 30 kg of catalyst, water will also be used 100,000 times, so that it will be 0.046 yen x 100,000 = 4600 yen, which is a trial calculation that can reduce the cost by about 4600 yen in one production. Furthermore, when the temperature is maintained for about 5 hours, it is possible to expect a cost reduction unit cost × time cost reduction.

By the way, it is possible to produce a core-shell catalyst in which Pd particles are coated with a Pt layer by reducing and precipitating Pt ions on Pd particles using electrons obtained by oxidative decomposition of H ₂ O. As described above, The core-shell catalyst is synthesized by adjusting the suspension temperature to around 95 ° C. and then adding Pt and stirring. However, in practice, when the core-shell catalyst is synthesized under this temperature condition, although Pt is reduced and deposited on Pd, it does not have an ideal core-shell structure. One of the causes is Pt deposition on the carbon material (Ketjen), and H ₂ O oxidative decomposition on the carbon is generated by high temperature heating around 95 ° C. Therefore, the present inventors have found that the oxidative decomposition on Pd is promoted more than the H ₂ O oxidative decomposition on carbon by adjusting the heating temperature in the range of 65 to 80 ° C. According to the temperature condition of this suspension, as shown in the above calculation, the core-shell catalyst is synthesized at a lower temperature than in the case of high-temperature heating near 95 ° C., so that the cost during production can be reduced. You can also. Accordingly, the temperature range of the suspension in the first step of the production method of the present invention is preferably adjusted to a range of 65 ° C to 95 ° C, but is preferably adjusted to a range of 65 ° C to 80 ° C. It can be concluded.

  Hereinafter, the results of verifying the feasibility of synthesizing the core-shell catalyst when using three types of suspensions prepared by heat-treating the suspension to 40 ° C., 60 ° C., and 80 ° C. will be shown.

Overview of the experiment was suspended Pd30mass% / Ketjen0.3g in deionized water 500 mL, then heated to reflux with stirring and N ₂ bubbling, K ₂ PtCl ₄ 0.083 g of (Pt1 atomic layers) in ion-exchanged water 200mL The melted and bubbled N ₂ solution was added dropwise to 500 mL of ion exchange water over 1 hour, heated and stirred as it was for 4 hours, filtered, washed with water, blown and dried at 80 ° C. to synthesize a core-shell catalyst.

Here, the hydrogen ion concentration (oxidative decomposition of H ₂ O) in the solution necessary for the reduction precipitation of Pt was traced with a pH meter, and the result of obtaining the relationship between the hydrogen ion concentration and the solution temperature is shown in FIG. .

From the figure, the amount of H ⁺ produced when the temperature of the suspension is about 55-80 ° C is Pd / Ketjen> Ketjen, and it is inferred that oxidative decomposition preferentially proceeds on Pd / Ketjen Pd in this temperature range. Is done.

Moreover, it was specified that the H ₂ O oxidative decomposition by carbon can be suppressed at less than 55 ° C., and that the H ₂ O oxidative decomposition on Pd occurs preferentially at 55 to 88 ° C.

  The experimental results regarding the feasibility of synthesizing the core-shell catalyst when using three types of suspensions adjusted to 40 ° C., 60 ° C., and 80 ° C. are shown in FIG. 15 (results of 40 ° C.) and 16 (60 ° C.). The results are shown in the following Tables 4, 5 and 6 along with STEM photographs at 17 (results at 80 ° C.). Table 6 includes Table 2, and Table 5 includes Table 3.

  From FIGS. 15 and 16 and Tables 4 and 5, it is observed that both the synthetic product having a suspension temperature of 40 ° C. and the synthetic product having a suspension temperature of 60 ° C. have single Pt particles present in the observed metal particles. It was found that the Pt coating on the particles was not performed sufficiently.

  On the other hand, from FIG. 17 and Table 6, in the synthesized product having a suspension temperature of 80 ° C., the single metal particles of Pt are not observed in the observed metal particles, and the core-shell catalyst in which the Pd particles are sufficiently covered with Pt. It was found that it was formed.

  From the above results, in the first step of the production method of the present invention, the temperature of the suspension in which the solvent is water is adjusted to be in the range of 65 ° C to 95 ° C, more preferably in the range of 65 ° C to 80 ° C. It was proved that a high quality core-shell catalyst can be synthesized by adjusting to. It has also been demonstrated that when the temperature of the suspension is 60 ° C. or less, single particles of Pt are generated, and the core-shell catalyst cannot be sufficiently synthesized.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 ... Conductive support | carrier, 2 ... 1st catalyst metal (core catalyst), 3 ... 2nd catalyst metal (shell catalyst), 4 ... Core shell catalyst, 3 '... Film | membrane (film | membrane which consists of polymer electrolytes), 5 ... Sodium borohydride, 10 ... Intermediate, 20 ... Catalyst support carrier, Y ... Container, W ... Solvent (pure water), K ... Inlet tube

Claims (8)

A method for producing a catalyst-carrying carrier in which a catalyst is carried on a conductive carrier,
An intermediate of the catalyst-carrying carrier in which the first catalyst metal is carried on the conductive carrier is mixed in a solvent to form a suspension, and the suspension is heat-treated at a temperature below the boiling point of the solvent. The first step of adjusting the range to 65 to 95 ° C. and lowering the liquid potential of the suspension;
The second catalyst metal is mixed with the suspension having the lowered liquid potential, and the surface of the intermediate first catalyst metal is modified by the second catalyst metal. Production method.   The method for producing a catalyst-supporting carrier according to claim 1, wherein the solvent comprises pure water.   The method for producing a catalyst-supporting carrier according to claim 1 or 2, wherein the suspension is bubbled with an inert gas at least in the first step.   The method for producing a catalyst-supporting carrier according to claim 3, wherein bubbling with an inert gas is also performed in the second step. The method for producing a catalyst-supporting carrier according to any one of claims 1 to 4 , wherein the suspension is hydrotreated in the first step. The method for producing a catalyst-supporting carrier according to claim 5 , wherein the hydrogen treatment is for bubbling the suspension with hydrogen gas. The method for producing a catalyst-supporting carrier according to claim 5 , wherein the hydrogen treatment is to add sodium borohydride to the suspension. A catalyst solution is produced from the catalyst-supported carrier produced by the production method according to any one of claims 1 to 7 , a polymer electrolyte and a dispersion solvent,
A method for producing an electrode catalyst, wherein a layer comprising the catalyst solution is formed on a surface of a substrate and dried to produce an electrode catalyst.

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