JP2016054065A - Manufacturing method of electrode catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an electrode catalyst with superior durability.SOLUTION: The manufacturing method of the electrode catalyst that is formed by supporting a catalyst particle in a conductive carrier is disclosed. The catalyst particle is an alloy particle comprised of a platinum atom and a non-platinum metal atom, where the alloy particle has an L1structure as an internal structure and comprises: a core part that is comprised of the platinum atom and the non-platinum metal atom; and a skin layer comprised of the platinum atom covering the core part. The method includes: adding a reductant to a mixture solution of a platinum precursor and a non-platinum metal precursor; obtaining a platinum-non-platinum metal alloy particle by simultaneously reducing the platinum precursor and the non-platinum metal precursor; preparing a catalyst precursor particle supporting carrier by supporting the platinum-non-platinum metal alloy particle in a carbon carrier containing on a surface at least one or more functional groups selected from among a lactone group, hydroxy group, ether group and carbonyl group for 0.5 μmol/mas a total amount; obtaining a heat treatment catalyst particle carrier by implementing first heat treatment on the catalyst precursor particle supporting carrier; obtaining a heat/acid treatment catalyst particle carrier by performing acid treatment on the heat treatment catalyst particle carrier; and then implementing second heat treatment on the heat/acid treatment catalyst particle carrier.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing an electrode catalyst. In particular, the present invention relates to a method for producing an electrode catalyst having excellent durability.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power source for electric vehicles because it operates at a relatively low temperature. The polymer electrolyte fuel cell generally has a structure in which an electrolyte membrane-electrode assembly (MEA) is sandwiched between separators. In the electrolyte membrane-electrode assembly, a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers and a gas diffusing electrode (gas diffusion layer; GDL).

In the polymer electrolyte fuel cell having the electrolyte membrane-electrode assembly as described above, both the electrodes (cathode and anode) sandwiching the polymer electrolyte membrane are represented by the following reaction formulas according to their polarities. Electrode reaction proceeds to obtain electrical energy. First, hydrogen contained in the fuel gas supplied to the anode (negative electrode) side is oxidized by the catalyst component to become protons and electrons (2H ₂ → 4H ⁺ + 4e ⁻ : reaction 1). Next, the generated protons pass through the solid polymer electrolyte contained in the electrode catalyst layer and the solid polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the cathode (positive electrode) side electrode catalyst layer. In addition, the electrons generated in the anode-side electrode catalyst layer include the conductive carrier constituting the electrode catalyst layer, the gas diffusion layer in contact with the side of the electrode catalyst layer different from the solid polymer electrolyte membrane, the separator, and the outside. The cathode side electrode catalyst layer is reached through the circuit. The protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water (O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O: Reaction 2). . In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

  Here, in order to improve the power generation performance, it is important to improve the activity and durability (activity after the durability test) of the catalyst particles of the electrode catalyst layer. Conventionally, it was necessary to use platinum as a catalyst component of an electrode catalyst from the viewpoint of improving activity and durability. However, since platinum is very expensive and a rare metal, it is necessary to develop a platinum alloy catalyst with reduced platinum content in the catalyst particles while maintaining activity and durability. ing.

  For example, Patent Document 1 includes a platinum-metal alloy having a face-centered tetragonal structure, and shows a broad peak or a peak divided into two at a 2θ value of 65 to 75 degrees in an XRD pattern of the platinum-metal alloy. Catalysts have been reported. According to Patent Document 1, a platinum-metal alloy having a face-centered tetragonal structure has a stable structure and thus has excellent durability.

JP 2010-282947 A

  However, although the platinum-metal alloy described in Patent Document 1 has a stable structure as an alloy, a metal other than platinum is present on the surface of the catalyst particles, so that a metal other than platinum is eluted under acidic conditions. . For this reason, the catalyst of patent document 1 is inferior to activity and durability.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing an electrode catalyst having excellent durability.

  Another object of the present invention is to provide an electrolyte membrane-electrode assembly and a fuel cell using the electrode catalyst according to the present invention.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by focusing on the structure of the catalyst and configuring the catalyst particle surface with a skin layer of only platinum atoms. The present invention has been completed.

  According to the method of the present invention, it is possible to produce an electrode catalyst composed of only platinum atoms whose surface is excellent in dissolution resistance. Therefore, the electrode catalyst according to the present invention is excellent in durability.

It is a schematic sectional drawing which shows the basic composition of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention.

The method for producing an electrode catalyst in which the catalyst particles of the present invention are supported on a conductive carrier has the following steps (i) to (v):
(I) A reducing agent is added to a mixed solution of a platinum precursor and a non-platinum metal precursor, and the platinum precursor and the non-platinum metal precursor are simultaneously reduced to obtain platinum-non-platinum metal alloy particles (step) (I));
(Ii) The platinum-non-platinum metal alloy particles have a total amount of at least one functional group selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group on the surface of 0.5 μmol / m ^2. The catalyst precursor particle-supported carrier is prepared by being supported on the carbon carrier having the above (step (ii));
(Iii) The catalyst precursor particle-supported carrier is subjected to a first heat treatment to obtain a heat-treated catalyst particle carrier (step (iii));
(Iv) acid-treating the heat treated catalyst particle carrier to obtain a heat / acid treated catalyst particle carrier (step (iv)); and (v) performing a second heat treatment on the heat / acid treated catalyst particle carrier. (Step (v)); The catalyst particles are alloy particles composed of platinum atoms and non-platinum metal atoms. In this case, the alloy particles have an L1 ₂ structure as an internal structure, and composed of a skin layer made of platinum atoms which covers the core portion and the core portion composed of platinum atoms and a non-platinum metal atoms.

In the present specification, "having an L1 ₂ structure as an internal structure" refers to those rules of the L1 ₂ structure (Extent of ordering) is greater than 0%. Here, the "rules of the L1 ₂ structure (Extent of ordering)", which indicates the degree of L1 ₂ structure, rules of the L1 ₂ structure, the volume ratio of the L1 ₂ structure in the entire alloy grain structure (% By volume). The greater this degree of order (with an L1 ₂ structure at a high volume rate) higher regularity means that an intermetallic compound. Further, in this specification, also referred to as the "rule of the L1 ₂ structure" simply "order parameter".

  The platinum-metal alloy constituting the catalyst of Patent Document 1 cannot exhibit sufficient activity and cannot prevent chain elution of a metal (for example, Co) that forms an alloy with platinum, resulting in poor durability. . On the other hand, the electrode catalyst (alloy particles) produced by the method according to the present invention is excellent in durability (the activity before and after the durability test can be effectively maintained). The reason why the above effect can be achieved is unknown, but is estimated as follows. In addition, this invention is not limited by the following estimation. Hereinafter, the electrode catalyst produced by the method according to the present invention is also simply referred to as “electrode catalyst according to the present invention”. Similarly, alloy particles having a specific structure manufactured by the method according to the present invention are also simply referred to as “alloy particles according to the present invention”. Further, in the present specification, “alloy particles” and “catalyst particles” are used synonymously.

That is, the platinum-metal alloy constituting the catalyst of Patent Document 1 has a face-centered tetragonal structure, an XRD pattern using a CuKα line, and a 2θ value of 65 to 75 degrees and two broad peaks or apexes. Separate peaks are shown. Therefore, the platinum Patent Document 1 - metal alloy is an intermetallic compound having an L1 ₀ structure. Intermetallic compound having an L1 ₀ structure, as the alloy is stable. However, to take the platinum layer and the metal layer is repeated structure, as compared to the intermetallic compound having a L1 ₂ structure, poor structural stability. In addition, since the platinum-metal alloy described in Patent Document 1 contains a metal other than platinum (for example, Co) on the surface of the catalyst particles, under acidic conditions, for example, under a strongly acidic electrolyte (for example, PEFC). The chain elution of the metal cannot be sufficiently suppressed, and the metal is eluted. For this reason, the catalyst of patent document 1 is inferior to activity and durability.

  On the other hand, the electrode catalyst (alloy particles) according to the present invention is produced by the above steps (i) to (v). The electrode catalyst (alloy particle) according to the present invention sequentially carries a platinum precursor and a non-platinum metal precursor on a support, heat treatment (first heat treatment), and acid treatment → heat treatment (second heat treatment) sequentially. Manufactured by. The electrode catalyst (alloy particles) according to the present invention thus produced is composed of a core portion made of platinum atoms and non-platinum metal atoms, and a skin layer made of platinum atoms covering the core. Hereinafter, the core part composed of platinum atoms and non-platinum metal atoms is also referred to simply as “core part”, and the skin layer composed of platinum atoms covering the core is also referred to simply as “skin layer”. By adopting such a configuration, the catalyst particles are excellent in durability (that is, the activity can be maintained for a long time). Specifically, a conventional alloy (catalyst) particle composed of platinum atoms and non-platinum metal atoms has non-platinum metal on the outermost surface. The non-platinum metal constituting the alloy particles is usually easier to elute than platinum. For this reason, when an electrode catalyst in which such alloy particles are supported on a conductive carrier is placed in an environment such as a potential cycle, the non-platinum metal on the outermost surface is easily eluted and the catalytic performance is reduced (ie, Inferior in durability). Further, as described above, in the conventional catalyst particles, in contact with a strongly acidic electrolyte (for example, an electrolyte such as perfluorosulfonic acid generally used in PEFC) under acidic conditions, Non-platinum metal elutes in a chain. On the other hand, in the alloy particles according to the present invention, a skin layer made of platinum atoms having high resistance to electric potential cycles covers a core part made of platinum atoms and non-platinum metal atoms. That is, the alloy particles according to the present invention have no or almost no non-platinum metal on the outermost surface. For this reason, the skin layer suppresses / prevents elution of non-platinum metal even under an environment such as a potential cycle (after an endurance test) or under acidic conditions. Therefore, the catalyst particles and the electrode catalyst on which such catalyst particles are supported can effectively suppress and prevent a decrease in activity (area specific activity, mass specific activity, particularly mass specific activity), and is excellent in durability.

Further, as described above, alloy particles according to the present invention has an L1 ₂ structure as an internal structure. L1 ₂ structure, fcc structure (α (000), β ( 1/2 1/2 0), γ (1/2 0 1/2), δ (0 1/2 1/2)) 4 one secondary of Only one of the lattices is different and forms a regular structure with a composition ratio of 3: 1. The atomic arrangement of the L1 ₂ structure has a cubic symmetry. In the alloy (catalyst) particles having the above structure, non-platinum metal atoms are not coordinated with each other, and many platinum atoms are present on the surface of the catalyst particles. For this reason, the alloy (catalyst) particles according to the present invention have high elution resistance, and contacted, for example, a strongly acidic electrolyte (for example, an electrolyte such as perfluorosulfonic acid used in PEFC) under acidic conditions. Even in the state, chain elution of non-platinum metal can be suppressed / prevented.

Therefore, the electrode catalyst according to the present invention (alloy particles) that have an L1 ₂ structure and the skin layer, (activity can be maintained before and after the durability test) excellent durability. That is, the activity (area specific activity, mass specific activity, particularly mass specific activity) can be maintained after the durability test. In addition, the electrode catalyst (alloy particles) according to the present invention can exhibit high activity even with a small platinum content. For this reason, the membrane electrode assembly and fuel cell which have a catalyst layer containing the electrode catalyst which concerns on this invention are excellent in electric power generation performance. The above effect is particularly noticeable when the degree of order of the L1 ₂ structure in or particle skin layer composed of 1-5 platinum atomic layers is 30% or more.

  Hereinafter, an embodiment of the catalyst particles of the present invention, and an embodiment of an electrode, an electrolyte membrane-electrode assembly (MEA) and a fuel cell using the same will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited only to the following embodiments. Each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may be different from the actual one. Further, in the case where the embodiment of the present invention is described with reference to the drawings, the same reference numerals are given to the same elements in the description of the drawings, and redundant description is omitted.

  In the present specification, “X to Y” indicating a range means “X or more and Y or less”, and “weight” and “mass”, “wt%” and “mass%”, “part by weight” and “ “Part by mass” is treated as a synonym. Unless otherwise specified, the operation and physical properties are measured under conditions of room temperature (20 to 25 ° C.) / Relative humidity 40 to 50%.

[Fuel cell]
A fuel cell comprises a pair of separators comprising an electrolyte membrane-electrode assembly (MEA), an anode side separator having a fuel gas flow path through which fuel gas flows, and a cathode side separator having an oxidant gas flow path through which oxidant gas flows. And have. The fuel cell of the present invention is excellent in durability and can exhibit high power generation performance.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention. The PEFC 1 first includes a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute an electrolyte membrane-electrode assembly (MEA) 10 in a stacked state. To do.

  In PEFC1, the MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5 a, 5 c) are illustrated so as to be positioned at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another adjacent PEFC. These descriptions are omitted in FIG.

  The separators (5a, 5c) are obtained, for example, by forming a concavo-convex shape as shown in FIG. 1 by subjecting a thin plate having a thickness of 0.5 mm or less to a press treatment. The convex part seen from the MEA side of the separator (5a, 5c) is in contact with the MEA 10. Thereby, the electrical connection with MEA10 is ensured. Further, a recess (space between the separator and the MEA generated due to the concavo-convex shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for circulating gas during operation of the PEFC 1 Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) is circulated through the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated through the gas flow path 6c of the cathode separator 5c.

  On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) serves as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  In addition, in embodiment shown in FIG. 1, the separator (5a, 5c) is shape | molded by the uneven | corrugated shape. However, the separator is not limited to such a concavo-convex shape, and may be any form such as a flat plate shape and a partially concavo-convex shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. Also good.

  The fuel cell having the MEA of the present invention as described above exhibits excellent power generation performance. Here, the type of the fuel cell is not particularly limited. In the above description, the solid polymer fuel cell has been described as an example. However, in addition to the above, an alkaline fuel cell and a direct methanol fuel cell are used. And a micro fuel cell. Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. Among them, it is particularly preferable to use as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long time of operation stop.

  The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used in that high output is possible.

  Further, the application application of the fuel cell is not particularly limited, but it is preferably applied to a vehicle. The electrolyte membrane-electrode assembly of the present invention is excellent in power generation performance and durability, and can be downsized. For this reason, the fuel cell of this invention is especially advantageous when this fuel cell is applied to a vehicle from the point of in-vehicle property.

  Hereinafter, although the preferable form of the manufacturing method of this invention is demonstrated, the technical scope of this invention is not restrict | limited only to the following form.

(Process (i))
In this step, a reducing agent is added to a mixed solution of a platinum precursor and a non-platinum metal precursor, and the platinum precursor and the non-platinum metal precursor are simultaneously reduced to obtain platinum-non-platinum metal alloy particles.

Although it does not restrict | limit especially as a platinum precursor which can be used in this process (i), A platinum salt and a platinum complex can be used. More specifically, chloroplatinic acid (typically its hexahydrate; H ₂ [PtCl ₆ ] · 6H ₂ O), nitrates such as dinitrodiammine platinum, sulfates, ammonium salts, amines, tetraammine platinum and Use ammine salts such as hexaammineplatinum, carbonates, bicarbonates, halides such as platinum chloride, inorganic salts such as nitrite and oxalic acid, carboxylates such as formate, hydroxides, alkoxides, etc. Can do. In addition, the said platinum precursor may be used individually by 1 type, or may be used as a 2 or more types of mixture.

Moreover, it does not restrict | limit especially as a non-platinum metal precursor which can be used in this process (i). Here, the non-platinum metal atom is not particularly limited, catalytic activity, from the viewpoint of forming easiness of L1 ₂ structure is preferably a transition metal atom. Here, the transition metal atom refers to a Group 3 element to a Group 12 element, and the type of the transition metal atom is not particularly limited. Catalytic activity, from the viewpoint of forming easiness of L1 ₂ structure, the transition metal atom, vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu) And selected from the group consisting of zinc (Zn) and zirconium (Zr). The transition metal atom is more preferably cobalt (Co). Since the transition metal atom easily forms an intermetallic compound with platinum (Pt), the specific mass activity can be further improved while reducing the amount of platinum used. The above transition metal atom and platinum alloy achieves higher area specific activity (activity per unit area) and mass specific activity (activity per unit mass) and excellent durability (activity after endurance test). it can. The transition metal atom may be alloyed with platinum alone, or two or more of them may be alloyed with platinum.

  As the non-platinum metal precursor, non-platinum metal salts and non-platinum metal complexes can be preferably used. More specifically, non-platinum metals such as nitrates, sulfates, ammonium salts, amines, carbonates, bicarbonates, halides such as bromides and chlorides, inorganic salts such as nitrites and oxalic acid, formates, etc. And carboxylates, hydroxides, alkoxides, oxides, and the like can be used. That is, a compound in which the non-platinum metal can be converted into a metal ion in a solvent such as pure water is preferable. Of these, halides (particularly chlorides), sulfates and nitrates are more preferred as the non-platinum metal salts. In addition, the said non-platinum metal precursor may be used individually by 1 type, or may be used as a 2 or more types of mixture. The non-platinum metal precursor may be in the form of a hydrate.

  The solvent used for the preparation of the mixed solution containing the platinum precursor and the non-platinum metal precursor is not particularly limited, and is appropriately selected depending on the kind of the platinum precursor and the non-platinum metal precursor to be used. The form of the mixed solution is not particularly limited, and includes a solution, a dispersion, and a suspension. From the standpoint that uniform mixing is possible, the mixed solution is preferably in the form of a solution. Specific examples include water such as tap water, pure water, ultrapure water, ion exchange water, and distilled water, organic solvents such as methanol, ethanol, 1-propanol, and 2-propanol, acids, and alkalis. Among these, water is preferable from the viewpoint of sufficiently dissolving the platinum / non-platinum metal ion compound, and it is particularly preferable to use pure water or ultrapure water. The said solvent may be used independently or may be used with the form of a 2 or more types of mixture.

  The concentration in the mixed solution of the platinum precursor and the non-platinum metal precursor is not particularly limited, but is preferably 0.1 to 50 (mg / 100 mL), more preferably 0.5 to 20 (mg) in terms of metal. / 100 mL). The concentration in the mixed solution of the platinum precursor and the non-platinum metal precursor may be the same or different.

The mixing ratio of the platinum precursor and the non-platinum metal precursor is not particularly limited, but is preferably a mixing ratio that can achieve the following alloy composition. Specifically, the ratio of the non-platinum metal precursor to 0.4 to 20 mol, more preferably 0.4 to 15 mol, and particularly preferably 0.5 to 10 mol with respect to 1 mol of the platinum precursor ( It is preferable to mix by metal conversion. With such a mixing ratio, it can be preferably maintained an L1 ₂ structure. The supported concentration of the catalyst particles supported on the finally prepared carrier is adjusted by the amount of platinum precursor and non-platinum metal precursor. However, even if the same preparation is performed before the heat treatment, the loading concentration may be slightly different if the heat treatment conditions are different.

  In the step (i), the method for preparing the mixed solution containing the platinum precursor and the non-platinum metal precursor is not particularly limited. For example, a platinum precursor and a non-platinum metal precursor are added together in a solvent; a platinum precursor is dissolved in a solvent, and then a non-platinum metal precursor is added thereto; a non-platinum metal precursor is dissolved in a solvent Thereafter, a platinum precursor may be added thereto; the platinum precursor and the non-platinum metal precursor may be separately dissolved in a solvent and then mixed together. The mixed solution is preferably stirred in order to mix uniformly. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by applying ultrasonic waves such as an ultrasonic dispersion device using an appropriate stirrer such as a stirrer or a homogenizer. The stirring temperature is preferably 0 to 50 ° C, more preferably 5 to 40 ° C. Moreover, what is necessary is just to set suitably so that dispersion | distribution may fully be performed as stirring time, Usually, it is 1 to 60 minutes, Preferably it is 5 to 40 minutes.

  Next, a reducing agent is added to the mixed solution prepared above, and the platinum precursor and the non-platinum metal precursor are simultaneously reduced to contain a platinum-non-platinum metal alloy particle (catalyst precursor particle) -containing liquid (hereinafter, Simply referred to as “catalyst precursor particle-containing liquid”). By this step, platinum ions and non-platinum metal ions can be reduced simultaneously, and catalyst precursor particles (intermetallic compound of platinum and non-platinum metal) can be obtained. Here, however, the skin layer is not formed on the catalyst precursor particles. Further, at this stage, the catalyst precursor particles do not necessarily have a degree of order of 30 to 100%.

Examples of the reducing agent that can be used here include ethanol, methanol, propanol, formic acid, formate such as sodium formate and potassium formate, citrate such as formaldehyde, sodium thiosulfate, citric acid, and sodium citrate, hydrogen Sodium borohydride (NaBH ₄ ) and hydrazine (N ₂ H ₄ ) can be used. Of the above reducing agents, sodium citrate can also act as an aggregation inhibitor.

  The reducing agent may be added as it is, or may be added to the mixed solution prepared in the above step (i) in the form of a reducing agent solution dissolved in a solvent. A solution form is preferable because it can be easily and uniformly mixed. Here, the solvent is not particularly limited as long as it can dissolve the reducing agent, and is appropriately selected depending on the type of the reducing agent. Specifically, the same solvent as the solvent used for the preparation of the mixed solution can be used. However, the solvent used for the reducing agent solution and the solvent used for preparing the mixed solution need not be the same, but are preferably the same in consideration of uniform mixing properties.

  The addition amount of the reducing agent is not particularly limited as long as it is an amount sufficient to reduce metal ions. Specifically, the addition amount of the reducing agent is preferably 1 to 10 mol, more preferably 3 to 1 mol of metal ions (total mol of platinum ions and non-platinum metal ions (metal conversion)). 7 moles. With such an amount, metal ions (platinum ions and non-platinum ions) can be sufficiently reduced simultaneously. In addition, when using 2 or more types of reducing agents, it is preferable that these total addition amount is the said range.

  After adding the reducing agent (reducing agent-containing liquid) to the mixed solution prepared above, it is preferable to stir. Thereby, since a platinum precursor, a non-platinum metal precursor, and a reducing agent are mixed uniformly, a uniform reduction reaction becomes possible. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by applying ultrasonic waves such as an ultrasonic dispersion device using an appropriate stirrer such as a stirrer or a homogenizer. The stirring temperature is preferably 0 to 50 ° C, more preferably 5 to 40 ° C. The stirring time is not particularly limited as long as the platinum precursor, the non-platinum metal precursor, and the reducing agent can be mixed uniformly.

  Platinum-non-platinum metal alloy particles (catalyst precursor particles) are obtained by the reduction reaction. Here, if necessary, platinum-non-platinum metal alloy particles (catalyst precursor particles) may be isolated from the solution. Here, the isolation method is not particularly limited, and the catalyst precursor particles may be filtered and dried. If necessary, the catalyst precursor particles may be filtered and then washed (for example, washed with water). Further, the filtration and the washing step may be repeated if necessary. Further, the catalyst precursor particles may be dried after filtration or washing. Here, drying of the catalyst precursor particles may be performed in air or may be performed under reduced pressure. Moreover, although drying temperature is not specifically limited, For example, it can carry out in 10-100 degreeC, Preferably it is room temperature (25 degreeC)-about 80 degreeC. Also, the drying time is not particularly limited, but for example, it can be performed in the range of 1 to 60 hours, preferably about 5 to 50 hours.

(Step (ii))
In this step, the platinum-non-platinum metal alloy particles prepared in the above step (i) are supported on a carbon support to prepare a catalyst precursor particle-supported support. Here, the carbon carrier has 0.5 μmol / m ² or more in total on the surface of at least one functional group selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group. Preferably, the carbon support has a total amount of 0.8 to 5 μmol / m ² of at least one functional group selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group on the surface. By using such a carbon support, the degree of order of the obtained catalyst particles can be more easily controlled, and the activity (area and / or mass specific activity) and durability can be further improved. This is considered to be because the aggregation of the alloy particles can be suppressed even by the heat treatment for obtaining the catalyst particles, and the decrease in the specific surface area of the entire supported catalyst particles can be suppressed. Note that the carbon carrier has at least one selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group on the surface even after the heat treatment in the following step (iii) and / or (v). It preferably has a functional group.

The value measured by the temperature programmed desorption method is adopted as the method for measuring the functional group amount. The temperature programmed desorption method is a technique in which a sample is heated at a constant speed under an ultra-high vacuum and gas components (molecules / atoms) released from the sample are detected in real time by a quadrupole mass spectrometer. The temperature at which a gas component is released depends on the adsorption / chemical binding state of that component on the sample surface, ie, components that require large energy for desorption / dissociation are detected at relatively high temperatures. The surface functional groups formed on the carbon are discharged as CO or CO ₂ at different temperatures depending on the type. The temperature-programmed desorption curve obtained for CO or CO ₂ is peak-separated, the integrated intensity T of each peak is measured, and the amount (μmol) of each functional group component can be calculated from the integrated intensity T. From this amount (μmol), the functional group amount is calculated by the following formula.

Desorption gas and temperature due to temperature rise of each functional group are as follows; lactone group CO ₂ (700 ° C.), hydroxyl group CO (650 ° C.), ether group CO (700 ° C.), carbonyl group CO (800 ° C.) .

  Moreover, in this invention, the value measured with the following apparatus and conditions is employ | adopted.

  The conductive carrier functions as a carrier for supporting the above-described catalyst particles and an electron conduction path involved in the transfer of electrons between the catalyst particles and other members. Any conductive carrier may be used as long as it has a specific surface area for supporting the catalyst particles in a desired dispersed state and has sufficient electronic conductivity as a current collector. The main component is carbon. Is preferred. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by weight or less is allowed.

  Specific examples of the conductive carrier added to the catalyst precursor particle-containing liquid include acetylene black, channel black, oil furnace black, gas furnace black (for example, Vulcan), lamp black, thermal black, and ketjen black (registered) Carbon black such as trademark); black pearl; graphitized acetylene black; graphitized channel black; graphitized oil furnace black; graphitized gas furnace black; graphitized lamp black; graphitized thermal black; Examples include black pearl; carbon nanotube; carbon nanofiber; carbon nanohorn; carbon fibril; activated carbon; coke; natural graphite; In addition, examples of the conductive carrier include zeolite template carbon (ZTC) having a structure in which nano-sized band-shaped graphene is regularly connected in a three-dimensional manner.

The BET specific surface area of the conductive carrier may be a specific surface area sufficient to carry the catalyst particles in a highly dispersed manner, but is preferably 10 to 5000 m ² / g, more preferably 50 to 2000 m ² / g. Good. With such a specific surface area, sufficient catalyst particles are supported (highly dispersed) on the conductive support, and sufficient power generation performance can be achieved. The “BET specific surface area (m ² / g carrier)” of the carrier is measured by a nitrogen adsorption method. The BET specific surface area of the support means the BET specific surface area of the conductive support constituting the final electrode catalyst.

  In addition, the size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, catalyst utilization, and the thickness of the electrode catalyst layer within an appropriate range, the average particle size is 5 to 200 nm, The thickness is preferably about 10 to 100 nm. Moreover, if it is such a magnitude | size, a suitable magnitude | size can be ensured even after heat processing. The “average particle size of the carrier” is the average of the crystallite size obtained from the half-value width of the diffraction peak of the carrier particle in X-ray diffraction (XRD), or the average particle size of the carrier examined by a transmission electron microscope (TEM). It can be measured as a value. In the present specification, the “average particle size of the carrier” means the average particle size of the carrier particles examined from a transmission electron microscope image of a statistically significant number (for example, at least 200, preferably at least 300) of samples. Value. Here, the “particle diameter” means the maximum distance among the distances between any two points on the particle outline.

  The carbon support having a specific functional group may be commercially available or manufactured. In the latter case, the method for producing a carbon support having a specific functional group is not particularly limited. For example, the carbon materials listed above as a conductive support are brought into contact with an acidic solution (hereinafter, this treatment is referred to as an acid support). Vapor activation treatment; vapor phase oxidation treatment (ozone, fluorine gas, etc.); liquid phase oxidation treatment (permanganic acid, chloric acid, ozone water, etc.). Among these, it is preferable to perform a heat treatment after contacting the carbon material with an acidic solution.

  Hereinafter, the acid treatment which is a preferable form will be described.

  Although it does not specifically limit as an acid used for an acidic solution, Hydrochloric acid, a sulfuric acid, nitric acid, perchloric acid etc. can be mentioned. Especially, it is preferable to use at least 1 sort (s) of a sulfuric acid and nitric acid from the point of surface functional group formation.

  In addition, the carbon material to be contacted with the acidic solution is not particularly limited, and the same material as the conductive carrier can be used. Carbon black is preferable because it has a large specific surface area and is stable by acid treatment.

  The acid treatment may be repeated not only when the carrier is brought into contact with the acidic solution once, but also multiple times. Moreover, when performing acid treatment in multiple times, you may change the kind of acidic solution for every process. The concentration of the acidic solution is appropriately set in consideration of the carbon material, the type of acid, etc., but is preferably 0.1 to 10 mol / L.

  The method for bringing the carbon material into contact with the acidic solution (acid treatment method) is not particularly limited, but a step of preparing a carbon material dispersion by mixing the carbon material with the acidic solution (step (1)), and carbon material dispersion It is preferable to have a step (step (2)) of heating the liquid and imparting a functional group to the surface of the carbon material. In the said process (1), it is preferable to mix a carbon material with an acidic solution. Moreover, it is preferable to stir the carbon material dispersion in order to mix it sufficiently uniformly. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by applying ultrasonic waves such as an ultrasonic dispersion device using an appropriate stirrer such as a stirrer or a homogenizer. In the step (1), the stirring temperature is preferably 5 to 40 ° C. Moreover, what is necessary is just to set suitably so that dispersion | distribution may fully be performed as stirring time, and it is 1 to 60 minutes normally, Preferably it is 3 to 30 minutes. Moreover, in the said process (2), the carbon material dispersion liquid prepared at the process (1) is heated, and a functional group is provided to the surface of a carbon material. Here, the heating condition is not particularly limited as long as the functional group can be imparted to the surface of the carbon material. For example, the heating temperature is preferably 60 to 90 ° C. The heating time is preferably 1 to 4 hours. Under such conditions, sufficient functional groups can be imparted to the surface of the carbon material.

  The platinum-non-platinum metal alloy particles prepared in the above step (i) are added to and mixed with the conductive carrier obtained as described above, and the platinum-non-platinum metal alloy particles are supported on the conductive carrier. Here, the mixing ratio of the catalyst precursor particles and the conductive carrier is not particularly limited, but is preferably such an amount that the following catalyst particle loading concentration (loading amount) is obtained. Specifically, in an electrode catalyst in which catalyst particles (alloy particles) are supported on a conductive support, the support concentration (supported amount) of the catalyst particles may be 2 to 70% by weight with respect to the total amount of the support. preferable. It is preferable to set the support concentration in such a range because aggregation of the catalyst particles is suppressed and an increase in the thickness of the electrode catalyst layer can be suppressed. More preferably, it is 5 to 60% by weight, still more preferably more than 5% by weight and 50% by weight or less, and particularly preferably 10 to 45% by weight. When the supported amount of the catalyst component is within such a range, the balance between the degree of dispersion of the catalyst component on the catalyst support and the catalyst performance can be appropriately controlled. The amount of the catalyst component supported can be examined by a conventionally known method such as inductively coupled plasma emission spectrometry (ICP atomic emission spectrometry), inductively coupled plasma mass spectrometry (ICP mass spectrometry), or fluorescent X-ray analysis (XRF). it can.

  Moreover, it is preferable to stir after adding a conductive support to the catalyst precursor particle-containing liquid. Thereby, since the catalyst precursor particles and the conductive carrier are uniformly mixed, the catalyst precursor particles can be highly dispersed and supported on the conductive carrier. In addition, since the reduction reaction of the unreduced platinum precursor and the non-platinum metal precursor with the reducing agent occurs simultaneously by the stirring treatment, it is possible to further promote the high dispersion and loading of the catalyst precursor particles on the conductive carrier. It is. Here, the stirring conditions are not particularly limited as long as they can be mixed uniformly. For example, the mixture can be uniformly dispersed and mixed by applying ultrasonic waves such as an ultrasonic dispersion device using an appropriate stirrer such as a stirrer or a homogenizer. The stirring temperature is preferably 0 to 50 ° C, more preferably 5 to 40 ° C. The stirring time is preferably 1 to 90 hours, more preferably 5 to 80 hours. Under such conditions, the catalyst precursor particles can be highly dispersed and supported by the conductive carrier. In addition, since the unreduced platinum precursor or non-platinum metal precursor can be further reduced with a reducing agent, the catalyst precursor particles can be efficiently dispersed and supported by the conductive carrier.

  By the above-described supporting treatment, a conductive carrier (catalyst precursor particle-supporting carrier or carrier) on which the catalyst precursor particles are supported can be obtained. Here, if necessary, this carrier may be isolated. Here, the isolation method is not particularly limited, and the supported carrier may be filtered and dried. If necessary, the supported carrier may be filtered and then washed (for example, washed with water). Further, the filtration and the washing step may be repeated if necessary. Further, after the filtration or washing, the supported carrier may be dried. Here, the support carrier may be dried in air or under reduced pressure. Moreover, although drying temperature is not specifically limited, For example, it can carry out in the range of about 10-100 degreeC, More preferably, room temperature (25 degreeC)-about 80 degreeC. Also, the drying time is not particularly limited, but is, for example, 1 to 60 hours, preferably 5 to 48 hours.

  In the above, the catalyst precursor particles are supported on the conductive support by the impregnation method, but the present invention is not limited to the above method. In addition to the above methods, known methods such as a liquid phase reduction support method, an evaporation to dryness method, a colloid adsorption method, a spray pyrolysis method, and a reverse micelle (microemulsion method) can be used.

(Process (iii))
In this step, the catalyst precursor particle-supported carrier obtained in the above step (ii) is subjected to a first heat treatment to obtain a heat-treated catalyst particle carrier. By this step (iii), an appropriate regular structure is imparted to the heat-treated catalyst particle carrier. With this structure, even when the acid treatment is performed in the next step (iv), the non-platinum metal atoms present inside the heat-treated catalyst particles are not dissolved or eluted, and the elution of excessive non-platinum metal atoms is suppressed / prevented. Therefore, the non-platinum metal atoms existing in the vicinity of the surface of the heat treatment catalyst particles can be selectively dissolved and eluted by the acid treatment in the next step (iv), and the alloy (catalyst) particles can be dissolved in the second heat treatment in the step (v). A skin layer composed of smooth platinum atoms can be efficiently formed on the outermost layer. In this step, the heat-treated catalyst particle carrier may not have a preferable degree of order as shown below. Even when the heat-treated catalyst particle carrier is lower than the lower limit of the preferred ordering degree described below, the ordering of the alloy (catalyst) particles can be adjusted to an appropriate range by the second heat treatment in step (v).

The first heat treatment condition is not particularly limited, but it is important to control the temperature and time of the heat treatment in consideration of control of the degree of order. Specifically, when the heat treatment temperature is 350 to 450 ° C., the heat treatment is preferably performed for 30 minutes or longer, more preferably for 1 hour or longer, and further preferably for 2 hours or longer. The upper limit of the heat treatment time at the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the conductive support, and is appropriately selected depending on the particle size and type of the catalyst particles. For example, the heat treatment time is usually 36 hours or less, preferably 24 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less. The heat treatment atmosphere when the heat treatment temperature is 350 to 450 ° C. is not particularly limited, but the heat treatment is to suppress and prevent oxidation of the alloy (platinum and non-platinum metal) and / or reduction to platinum or non-platinum metal. It is preferable to carry out in a non-oxidizing atmosphere in order to further advance the process. Examples of the non-oxidizing atmosphere include an inert gas atmosphere and a reducing gas atmosphere. Here, the inert gas is not particularly limited, but helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N ₂ ), and the like can be used. The said inert gas may be used independently or may be used with the form of 2 or more types of mixed gas. The reducing gas atmosphere is not particularly limited as long as the reducing gas is contained, but a mixed gas atmosphere of the reducing gas and the inert gas is more preferable. Here, the reducing gas is not particularly limited, but hydrogen (H ₂ ) gas and carbon monoxide (CO) gas are preferable. Further, the concentration of the reducing gas contained in the inert gas is not particularly limited, but the content of the reducing gas in the inert gas is preferably 10 to 100% by volume, more preferably 50 to 100% by volume. It is. With such a concentration, the oxidation of the alloy (platinum and non-platinum metal) can be sufficiently suppressed / prevented. Among the above, the heat treatment is preferably performed in an inert gas atmosphere. Under such conditions, the catalyst particles can be supported in a highly dispersed state without aggregating on the support. Moreover, if it is the said conditions, the regularity of the catalyst particle (alloy particle) obtained can be effectively controlled by 30 to 100%, suppressing the increase in a catalyst particle diameter.

  When the heat treatment temperature is higher than 450 ° C. and lower than or equal to 750 ° C., the heat treatment is preferably performed for 10 minutes or longer, more preferably for 20 minutes or longer. The upper limit of the heat treatment time at the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the conductive support, and is appropriately selected depending on the particle size and type of the catalyst particles. For example, the heat treatment time is usually 36 hours or less, preferably 24 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less. The heat treatment atmosphere when the heat treatment temperature is higher than 450 ° C. and lower than 750 ° C. is not particularly limited, but the heat treatment is performed to suppress and prevent oxidation of the alloy (platinum and non-platinum metal) and / or platinum or non-platinum metal. In order to make the reduction to more proceed, it is preferably performed in a non-oxidizing atmosphere. Here, since the non-oxidizing atmosphere has the same definition as that in the case where the heat treatment temperature is 350 to 450 ° C. or lower, description thereof is omitted here. Among the above, the heat treatment is preferably performed in an inert gas atmosphere or a reducing gas atmosphere, and more preferably performed in an inert gas atmosphere. Under such conditions, the catalyst particles can be supported in a highly dispersed state without aggregating on the support. Moreover, if it is the said conditions, the regularity of the catalyst particle (alloy particle) obtained can be effectively controlled by 30 to 100%, suppressing the increase in a catalyst particle diameter.

  Furthermore, when the heat treatment temperature exceeds 750 ° C., it is preferable to perform the heat treatment in a reducing gas atmosphere for 10 to 45 minutes, more preferably 20 to 40 minutes. Alternatively, when the heat treatment temperature exceeds 750 ° C., the heat treatment is performed in an inert gas atmosphere for 10 to 120 minutes, more preferably 30 to 100 minutes, particularly preferably more than 45 minutes and 90 minutes or less. It is preferable. The upper limit of the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the conductive support, and is appropriately selected depending on the particle size and type of the catalyst particles. Further, although the degree of order increases in proportion to the temperature and time during the heat treatment, the particle diameter tends to increase due to sintering. Considering the above points, for example, the heat treatment temperature may be 1000 ° C. or less. Under such conditions, the catalyst particles (alloy particles) obtained can be supported in a highly dispersed state without agglomeration on the carrier while suppressing an increase in the catalyst particle diameter. Moreover, if it is the said conditions, the regularity of the catalyst particle (alloy particle) obtained can be effectively controlled by 30 to 100%, suppressing the increase in a catalyst particle diameter. In the above, “inert gas atmosphere” and “reducing gas atmosphere” have the same definitions as those in the case where the heat treatment temperature is 350 to 450 ° C. or less, and thus the description thereof is omitted here.

(Process (iv))
In this step, the heat-treated catalyst particle carrier obtained in the above step (iii) is acid-treated to obtain a heat / acid-treated catalyst particle carrier. By this step, the non-platinum metal atoms exposed on the outermost surface of the heat treatment catalyst particles are dissolved and eluted, and voids (defects) are generated in the portion where the non-platinum metal (for example, cobalt) was present near the surface. . The voids (defects) are formed such that platinum is melted by the heat treatment in the next step (v) and a smooth skin layer made of platinum atoms covers the core portion.

  Here, the acid treatment may be performed by any method, but is preferably performed by bringing the heat-treated catalyst particle carrier into contact with an acidic solution. Here, the method for contacting the heat-treated catalyst particle carrier with the acidic solution is not particularly limited. For example, the heat-treated catalyst particle carrier is immersed in the acidic solution, and the acidic solution is applied to the heat-treated catalyst particle carrier (for example, spray coating, Bar coat, etc.). Among these, dipping is preferable in consideration of ease of operation and mass production.

  Although it does not specifically limit as an acid used for an acidic solution, Aqueous solution, such as hydrochloric acid, nitric acid, perchloric acid, sulfuric acid, oxalic acid, acetic acid, formic acid, carbonic acid, phosphoric acid, citric acid, sulfamic acid, is mentioned . These acids may be used alone or in combination of two or more. Of these, hydrochloric acid, nitric acid, sulfuric acid, oxalic acid and sulfamic acid are preferred, perchloric acid, hydrochloric acid and sulfuric acid are more preferred, and perchloric acid is particularly preferred. In addition, the solvent used for the preparation of the acidic solution is not particularly limited as long as it dissolves the acid, and is appropriately selected depending on the type of acid. Specific examples include tap water, pure water, ultrapure water, ion exchange water, distilled water and the like, methanol, ethanol, tetrahydrofuran, and the like. These solvents may be used alone or in the form of a mixture of two or more. The concentration of the acidic solution is appropriately set according to the type of non-platinum metal in consideration of easiness of elution of non-platinum metal. The concentration (acid concentration) of the acidic solution is preferably 0.01 to 10 mol / L, more preferably 0.05 to 5 mol / L. At such a concentration, the non-platinum metal atoms exposed on the outermost surface of the heat treatment catalyst particles dissolve and elute without excessively eluting the non-platinum metal inside, and non-platinum metal ( For example, voids (defects) can be generated in portions where cobalt was present. Therefore, a smooth skin layer can be formed on the outermost layer of the alloy (catalyst) particles by the next second heat treatment step.

  The acid treatment conditions are not particularly limited. Specifically, the acid treatment temperature is preferably 5 to 50 ° C, more preferably 10 to 40 ° C. The acid treatment time is preferably 30 minutes to 50 hours, more preferably 5 to 40 hours, and more preferably 10 to 30 hours. Under these conditions, the non-platinum metal atoms exposed on the outermost surface of the heat treatment catalyst particles are dissolved and eluted without excessively eluting the non-platinum metal inside, and non-platinum metal (near the surface) ( For example, voids (defects) can be generated in portions where cobalt was present. Therefore, a smooth skin layer can be formed on the outermost layer of the alloy (catalyst) particles by the next second heat treatment step. In addition, the acid treatment may be repeated not only when the carrier is brought into contact with the acidic solution once, but also multiple times. Moreover, when performing acid treatment several times, you may change the kind of acidic solution and / or heat processing conditions for every process.

  Here, if necessary, this heat / acid-treated catalyst particle carrier may be isolated. Here, the isolation method is not particularly limited, and the heat / acid-treated catalyst particle carrier may be filtered and, if necessary, dried and washed (for example, washed with water). The above operations (filtration and drying and washing if necessary) may be repeated. Here, when drying is performed, the heat / acid-treated catalyst particle carrier may be dried in air or under reduced pressure. Moreover, although drying temperature is not specifically limited, For example, it can carry out in the range of about 10-100 degreeC, More preferably, room temperature (25 degreeC)-about 80 degreeC. Also, the drying time is not particularly limited, but is, for example, 1 to 60 hours, preferably 5 to 48 hours.

(Process (v))
In this step, a second heat treatment is performed on the heat / acid-treated catalyst particle carrier obtained in the step (iv). In the second heat treatment step, the voids (defects) generated by the dissolution and elution of the non-platinum metal atoms exposed on the outermost surface of the heat treatment catalyst particles are filled with platinum metal, and the outermost layer of the alloy (catalyst) particles is smoothed. A skin layer composed of platinum atoms is formed. Therefore, the electrode catalyst which concerns on this invention is obtained by the said process.

Here, the second heat treatment condition is not particularly limited as long as the platinum atoms can fill the voids (defects) generated in (iv) above, but control of the temperature and time of the heat treatment is important. Specifically, when the heat treatment temperature is 350 to 450 ° C., it is preferable to perform the heat treatment for 30 minutes or more, more preferably for more than 60 minutes, and even more preferably for 120 minutes or more. The upper limit of the heat treatment time at the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the conductive support, and is appropriately selected depending on the particle size and type of the catalyst particles. For example, the heat treatment time is usually 36 hours or less, preferably 24 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less. The heat treatment atmosphere when the heat treatment temperature is 350 to 450 ° C. is not particularly limited, but the heat treatment is to suppress and prevent oxidation of the alloy (platinum and non-platinum metal) and / or reduction to platinum or non-platinum metal. It is preferable to carry out in a non-oxidizing atmosphere in order to further advance the process. Examples of the non-oxidizing atmosphere include an inert gas atmosphere and a reducing gas atmosphere. Here, the inert gas is not particularly limited, but helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), nitrogen (N ₂ ), and the like can be used. The said inert gas may be used independently or may be used with the form of 2 or more types of mixed gas. The reducing gas atmosphere is not particularly limited as long as the reducing gas is contained, but a mixed gas atmosphere of the reducing gas and the inert gas is more preferable. Here, the reducing gas is not particularly limited, but hydrogen (H ₂ ) gas and carbon monoxide (CO) gas are preferable. Further, the concentration of the reducing gas contained in the inert gas is not particularly limited, but the content of the reducing gas in the inert gas is preferably 10 to 100% by volume, more preferably 50 to 100% by volume. It is. With such a concentration, the oxidation of the alloy (platinum and non-platinum metal) can be sufficiently suppressed / prevented. Among the above, the heat treatment is preferably performed in an inert gas atmosphere. Under such conditions, the catalyst particles can be supported in a highly dispersed state without aggregating on the support. Moreover, if it is the said conditions, the regularity of the catalyst particle (alloy particle) obtained can be effectively controlled by 30 to 100%, suppressing the increase in a catalyst particle diameter.

  When the heat treatment temperature is higher than 450 ° C. and lower than or equal to 750 ° C., the heat treatment is preferably performed for 10 minutes or longer, more preferably for 20 minutes or longer. The upper limit of the heat treatment time at the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the conductive support, and is appropriately selected depending on the particle size and type of the catalyst particles. For example, the heat treatment time is usually 36 hours or less, preferably 24 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less. The heat treatment atmosphere when the heat treatment temperature is higher than 450 ° C. and lower than 750 ° C. is not particularly limited, but the heat treatment is performed to suppress and prevent oxidation of the alloy (platinum and non-platinum metal) and / or platinum or non-platinum metal. In order to make the reduction to more proceed, it is preferably performed in a non-oxidizing atmosphere. Here, since the non-oxidizing atmosphere has the same definition as that in the case where the heat treatment temperature is 350 to 450 ° C. or lower, description thereof is omitted here. Among the above, the heat treatment is preferably performed in an inert gas atmosphere or a reducing gas atmosphere. Under such conditions, the catalyst particles can be supported in a highly dispersed state without aggregating on the support. Moreover, if it is the said conditions, the regularity of the catalyst particle (alloy particle) obtained can be effectively controlled by 30 to 100%, suppressing the increase in a catalyst particle diameter.

  Furthermore, when the heat treatment temperature exceeds 750 ° C., it is preferable to perform the heat treatment in a reducing gas atmosphere for 10 to 45 minutes, more preferably 20 to 40 minutes. Alternatively, when the heat treatment temperature exceeds 750 ° C., the heat treatment is performed in an inert gas atmosphere for 10 to 120 minutes, more preferably 30 to 100 minutes, particularly preferably more than 45 minutes and 90 minutes or less. It is preferable. The upper limit of the heat treatment temperature is not particularly limited as long as it is a temperature at which the catalyst particles can be supported on the conductive support, and is appropriately selected depending on the particle size and type of the catalyst particles. Further, although the degree of order increases in proportion to the temperature and time during the heat treatment, the particle diameter tends to increase due to sintering. Considering the above points, for example, the heat treatment temperature may be 1000 ° C. or less. Under such conditions, the catalyst particles (alloy particles) obtained can be supported in a highly dispersed state without agglomeration on the carrier while suppressing an increase in the catalyst particle diameter. Moreover, if it is the said conditions, the regularity of the catalyst particle (alloy particle) obtained can be effectively controlled by 30 to 100%, suppressing the increase in a catalyst particle diameter. In the above, “inert gas atmosphere” and “reducing gas atmosphere” have the same definitions as those in the case where the heat treatment temperature is 350 to 450 ° C. or less, and thus the description thereof is omitted here.

  By the above method, the electrode catalyst according to the present invention is produced. The catalyst particles thus produced are alloy particles composed of platinum atoms and non-platinum metal atoms. Here, an alloy is a general term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The catalyst particles of the present invention have an alloy structure in which a component element becomes a separate crystal, that is, a eutectic alloy that is a mixture, a component element completely melted into a solid solution, a component element is an intermetallic compound or Some form a compound of a metal and a nonmetal. In the present invention, the catalyst particles may be in any form, but include those in which at least a platinum atom and a non-platinum atom form an intermetallic compound.

  The catalyst particles according to the present invention include a core portion made of platinum atoms and non-platinum metal atoms, and a skin layer made of platinum atoms covering the core. According to the said structure, the skin layer which consists of a platinum atom with high solubility resistance has coat | covered the core part containing the non-platinum metal atom inferior to dissolution resistance. For this reason, in order to suppress and prevent elution of non-platinum metal under a potential cycle environment or acidic conditions, the catalyst particles can maintain activity (area specific activity, mass specific activity) for a long period of time. Here, the skin layer only needs to cover at least a part of the catalyst particles (alloy particles). However, in consideration of the suppression and prevention effect of non-platinum metal elution, the skin layer may cover the entire surface of the catalyst particles. preferable. The platinum atomic layer constituting the skin layer may be a single layer or a laminate of a plurality of layers. The skin layer is preferably composed of 6 platinum atomic layers exceeding 0, preferably 1 to 5 platinum atomic layers, and more preferably 1 to 3 platinum atomic layers. With such a number of layers, elution of non-platinum metal under a potential cycle environment or acidic conditions can be sufficiently suppressed / prevented. In addition, since the non-platinum metal is located in the vicinity of the surface of the catalyst particles, the catalyst particles can sufficiently exhibit the effect of the non-platinum metal, and thus can exhibit high activity.

As described above, the alloy particles may have a portion where the skin layer made of platinum atoms is not formed on the surface. However, the alloy particles have an L1 ₂ structure between non-platinum metal atoms are not coordinated as internal structure. For this reason, non-platinum metal atoms in the vicinity of the surface are eluted under acidic conditions during use (operation) even if there is a portion where the skin layer does not exist on the surface of the catalyst particles during production (before operation). On the other hand, since platinum atoms coordinated to non-platinum metal atoms stop chain elution of non-metal metal atoms, an additional skin layer of platinum metal atoms is formed on the surface of the alloy particles, and a higher proportion The surface of the catalyst particles can be covered with a skin layer. Therefore, the alloy (catalyst) particles according to the present invention have high elution resistance and are in contact with a strongly acidic electrolyte (for example, an electrolyte such as perfluorosulfonic acid used in PEFC) under acidic conditions. Even so, chain elution of non-platinum metals can be more effectively suppressed / prevented. That is, according to this configuration, in the alloy (catalyst) particles, the skin layer made of platinum atoms having high dissolution resistance covers the core portion containing non-platinum metal atoms that are poor in dissolution resistance. For this reason, elution of non-platinum metal under a potential cycle environment or acidic conditions can be suppressed / prevented, and the catalyst particles can maintain activity (area specific activity, mass specific activity) over a long period of time. Therefore, the catalyst particles of the present invention can exhibit the effect of non-platinum metal over a long period of time.

  Here, the number of platinum atomic layers constituting the skin layer of the catalyst particles (alloy particles) can be measured by a known method. For example, Energy Dispersive X-ray Spectroscopy (EDX) that performs elemental analysis and composition analysis by detecting characteristic X-rays generated by electron beam irradiation and performing spectral analysis with energy Can be used. In the present specification, the number of platinum atomic layers constituting the skin layer of catalyst particles (alloy particles) is measured by STEM-EDX analysis. Specifically, using a STEM-EDX analyzer (trade name: HD-2700, manufactured by Hitachi High-Technologies Corporation), platinum metal elements and non-platinum constituting the catalyst particles from the surface of the catalyst particles toward the center. Characteristic X-rays peculiar to metal elements are detected and the intensity is measured. Here, the thickness when the characteristic X-ray peculiar to the non-platinum metal element is detected for the first time becomes the skin layer thickness (nm). The skin layer thickness is divided by the atomic diameter of platinum (0.27 nm), and the obtained value is the number of platinum atomic layers constituting the skin layer of the catalyst particles (alloy particles). For example, when platinum-cobalt alloy particles are analyzed by STEM-EDX, when cobalt element is detected for the first time at a point 0.68 nm from the surface, the number of platinum atomic layers is about 2.5 (= 0.68 / 0. 27) It becomes a layer.

Further, the alloy particles according to the present invention has an L1 ₂ structure as an internal structure. “Having an L1 ₂ structure” means that the degree of ordering of the L1 ₂ structure exceeds 0%. The catalyst particles having the above configuration can exhibit high activity and durability even with a small platinum content. Here, regulations of the L1 ₂ structure is not particularly limited, preferably from 30% to 100%, preferably 40 to 100%, more preferably 45-100%, 47-95 % Is even more preferable, and 50 to 90% is particularly preferable. Thereby, the activity (area specific activity and mass specific activity, particularly mass specific activity) and durability (activity after the durability test) of the catalyst particles can be further improved.

"Rules of the L1 ₂ structure (Extent of ordering) (%)" is, J Mater Chem, 2004, 14 , 1454 -... 1460 The methods described can be determined based on, in this specification , Defined as the ratio of the peak area (Ia) of the maximum intensity of the X-ray diffraction (XRD) pattern to the peak area (Ib) characteristic of the intermetallic compound. Specifically, "rules of the L1 ₂ structure (Extent of ordering) (%)" is a value measured by the following methods.

<Measurement method of degree of order of the L1 ₂ structure (Extent of ordering)>
The catalyst particles are subjected to X-ray diffraction (XRD) under the following conditions to obtain an XRD pattern. In the obtained XRD pattern, the peak area (Ia) observed in the range of 2θ value of 39 to 41 ° and the peak area (Ib) observed in the range of 31 to 34 ° are measured. Here, the peak observed in the range of 2θ value of 39 to 41 ° is a peak inherent to the lattice plane of platinum. The peak observed in the range of 39 to 41 ° is a peak representing the entire alloy particle structure. Also, peak 2θ value is observed in the range of 31 to 34 ° is the inherent peak L1 ₂ structure of the alloy particles.

Using the peak areas Ia and Ib, the following equation (1), and calculates the degree of order of the L1 ₂ structure.

  In the above formula (1), X is a value specific to the non-platinum metal atom constituting the alloy particle. Specifically, X is a value shown in the following table.

The composition of the catalyst particles is not particularly limited. Catalytic activity, from the viewpoint of forming easiness of L1 ₂ structure, the composition of the catalyst particles to non-platinum metal atom 1 mol, platinum atom is preferably a 1.5 to 15 moles, 1. The amount is more preferably 6 to 10 mol, still more preferably 1.7 to 7 mol, and particularly preferably 2.2 to 6 mol. With such a composition, the catalyst particles have a high enough degree of order L1 ₂ structure can exhibit and maintain a high activity. The composition of the catalyst particles (content of each metal atom in the catalyst particles) is determined by inductively coupled plasma emission spectrometry (ICP atomic emission spectrometry), inductively coupled plasma mass spectrometry (ICP mass spectrometry), and X-ray fluorescence analysis (XRF). It can be determined by a conventionally known method.

The size of the catalyst particles is not particularly limited. For example, the number average particle diameter (d _N ) of the catalyst particles is preferably 1 to 10 nm, more preferably 2 to 8 nm, and further preferably 2 to 7 nm. When the number average particle diameter of the catalyst particles is within such a range, the dissolution / aggregation of the catalyst metal during power generation can be suppressed while increasing the activity per unit platinum amount. In the present specification, the number average particle diameter (d _N ) of the alloy particles is measured as follows. First, n alloy particles are observed with a TEM, and the particle diameter (equivalent circular diameter) when the area is a perfect circle is calculated backward from the projected area of each particle to calculate the particle diameter (d) of each alloy particle. Measure. Using the particle diameter (d) of the alloy particles thus obtained, the number average particle diameter (d _N ) of the alloy particles is calculated by the following formula (A). The number of measured alloy particles (n) is not particularly limited, but is preferably a statistically significant number, preferably at least 200, and more preferably at least 300. .

  As described above, the electrode catalyst according to the present invention can maintain high activity (area specific activity and mass specific activity) even after the durability test, and is excellent in durability. In addition, the electrode catalyst can exhibit high activity (area specific activity and mass specific activity) even with a small platinum content.

[Electrolyte membrane-electrode assembly (MEA)]
The above-described electrode catalyst according to the present invention can be suitably used for an electrolyte membrane-electrode assembly (MEA). That is, the present invention includes using an electrolyte membrane-electrode assembly (MEA) including the electrode catalyst according to the present invention, particularly an electrolyte membrane-electrode assembly (MEA) for a fuel cell, and the electrode catalyst according to the present invention. A method for producing an electrolyte membrane-electrode assembly (MEA), particularly an electrolyte membrane-electrode assembly (MEA) for a fuel cell is also provided. The electrolyte membrane-electrode assembly (MEA) according to the present invention can exhibit high power generation performance and durability.

  The electrolyte membrane-electrode assembly (MEA) of the present invention can have the same configuration except that the electrode catalyst (catalyst) of the present invention is used instead of the conventional electrode catalyst. Although the preferable form of MEA of this invention is demonstrated below, this invention is not limited to the following form.

  The MEA includes an electrolyte membrane, an anode catalyst layer, an anode gas diffusion layer, a cathode catalyst layer, and a cathode gas diffusion layer that are sequentially formed on both surfaces of the electrolyte membrane. In this electrolyte membrane-electrode assembly, the electrode catalyst of the present invention is used for at least one of the cathode catalyst layer and the anode catalyst layer.

(Electrolyte membrane)
The electrolyte membrane is composed of, for example, a solid polymer electrolyte membrane. For example, the solid polymer electrolyte membrane has a function of selectively allowing protons generated in the anode catalyst layer during operation of a fuel cell (such as PEFC) to permeate the cathode catalyst layer along the film thickness direction. The solid polymer electrolyte membrane also has a function as a partition for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  It does not specifically limit as electrolyte material which comprises a solid polymer electrolyte membrane, A conventionally well-known knowledge can be referred suitably. For example, the fluorine-based polymer electrolyte and the hydrocarbon-based polymer electrolyte described as the polymer electrolyte in the following catalyst layer can be used in the same manner. At this time, it is not always necessary to use the same polymer electrolyte used for the catalyst layer.

  The thickness of the electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte membrane is usually about 5 to 300 μm. When the thickness of the electrolyte membrane is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

(Catalyst layer)
The catalyst layer is a layer where the battery reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer, and the reduction reaction of oxygen proceeds in the cathode catalyst layer. Here, the catalyst of the present invention may be present in either the cathode catalyst layer or the anode catalyst layer. Considering the necessity of improving the oxygen reduction activity, it is preferable to use at least the cathode catalyst layer of the electrode catalyst of the present invention. However, the catalyst layer according to the above embodiment may be used as an anode catalyst layer, or may be used as both a cathode catalyst layer and an anode catalyst layer, and is not particularly limited.

  The catalyst layer includes the electrode catalyst of the present invention and an electrolyte. The electrolyte is not particularly limited, but is preferably an ion conductive polymer electrolyte. Since the polymer electrolyte plays a role of transmitting protons generated around the catalyst active material on the fuel electrode side, it is also called a proton conductive polymer.

  The polymer electrolyte is not particularly limited, and conventionally known knowledge can be appropriately referred to. Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes depending on the type of ion exchange resin that is a constituent material.

  Examples of ion exchange resins constituting the fluorine-based polymer electrolyte include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride-per Examples thereof include fluorocarbon sulfonic acid polymers. From the viewpoint of excellent heat resistance, chemical stability, durability, and mechanical strength, these fluorine-based polymer electrolytes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. Is used.

  Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon polymer electrolytes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the selectivity of the material is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

  Proton conductivity is important in polymer electrolytes responsible for proton transmission. Here, when the EW of the polymer electrolyte is too large, the ionic conductivity in the entire catalyst layer is lowered. Therefore, it is preferable that the catalyst layer of this embodiment contains a polymer electrolyte having a small EW. Specifically, the catalyst layer of this embodiment preferably has an EW of 1500 g / eq. The following polymer electrolyte is contained, More preferably, it is 1200 g / eq. The following polymer electrolyte is included, and particularly preferably 1000 g / eq. The following polymer electrolytes are included. On the other hand, if the EW is too small, the hydrophilicity is too high, making it difficult to smoothly move water. From such a viewpoint, the EW of the polymer electrolyte is preferably 600 or more. Note that EW (Equivalent Weight) represents the equivalent weight of the exchange group having proton conductivity. The equivalent weight is the dry weight of the ion exchange membrane per equivalent of ion exchange group, and is expressed in units of “g / eq”.

  Further, the catalyst layer includes two or more types of polymer electrolytes having different EWs in the power generation surface. At this time, the polymer electrolyte having the lowest EW among the polymer electrolytes has a relative humidity of 90% or less of the gas in the flow path. It is preferable to use in the region. By adopting such a material arrangement, the resistance value becomes small regardless of the current density region, and the battery performance can be improved. The EW of the polymer electrolyte used in the region where the relative humidity of the gas in the flow channel is 90% or less, that is, the polymer electrolyte having the lowest EW is 900 g / eq. The following is desirable. Thereby, the above-mentioned effect becomes more reliable and remarkable.

  Further, it is desirable to use a polymer electrolyte having the lowest EW in a region higher than the average temperature of the cooling water inlet and outlet. As a result, the resistance value is reduced regardless of the current density region, and the battery performance can be further improved.

  Furthermore, from the viewpoint of reducing the resistance value of the fuel cell system, the polymer electrolyte having the lowest EW is within 3/5 from the gas supply port of at least one of the fuel gas and the oxidant gas with respect to the flow path length. It is desirable to use it in the range area.

  If necessary, the catalyst layer may be a water repellent such as polytetrafluoroethylene, polyhexafluoropropylene or tetrafluoroethylene-hexafluoropropylene copolymer, a dispersant such as a surfactant, glycerin, ethylene glycol (EG). ), A thickener such as polyvinyl alcohol (PVA) and propylene glycol (PG), and an additive such as a pore-forming agent may be contained.

  The film thickness (dry film thickness) of the catalyst layer is preferably 0.05 to 30 μm, more preferably 1 to 20 μm, and still more preferably 2 to 15 μm. The above applies to both the cathode catalyst layer and the anode catalyst layer. However, the cathode catalyst layer and the anode catalyst layer may be the same or different.

(Gas diffusion layer)
The gas diffusion layers (anode gas diffusion layer 4a, cathode gas diffusion layer 4c) are catalyst layers (3a, 3c) of gas (fuel gas or oxidant gas) supplied via the gas flow paths (6a, 6c) of the separator. ) And a function as an electron conduction path.

  The material which comprises the base material of a gas diffusion layer (4a, 4c) is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. The thickness of the substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing a flooding phenomenon or the like. Although it does not specifically limit as a water repellent, Fluorine-type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Examples thereof include molecular materials, polypropylene, and polyethylene.

  In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer; MPL, not shown) made of an aggregate of carbon particles containing a water repellent agent on the catalyst layer side of the substrate. You may have.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle size of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  Examples of the water repellent used in the carbon particle layer include the same water repellent as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

  The mixing ratio of the carbon particles and the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) in weight ratio in consideration of the balance between water repellency and electron conductivity. It is good. In addition, there is no restriction | limiting in particular also about the thickness of a carbon particle layer, What is necessary is just to determine suitably in consideration of the water repellency of the gas diffusion layer obtained.

(Method for producing electrolyte membrane-electrode assembly)
The method for producing the electrolyte membrane-electrode assembly is not particularly limited, and a conventionally known method can be used. For example, a method of joining a gas diffusion layer to a catalyst layer transferred or applied to an electrolyte membrane by hot pressing and drying it, or a microporous layer side of the gas diffusion layer (when a microporous layer is not included) First, two gas diffusion electrodes (GDE) are prepared by applying a catalyst layer on one side of a base material layer in advance and drying, and then bonding the gas diffusion electrodes to both sides of a solid polymer electrolyte membrane by hot pressing. The application and joining conditions such as hot pressing can be adjusted appropriately according to the type of polymer electrolyte in the solid polymer electrolyte membrane or catalyst layer (perfluorosulfonic acid type or hydrocarbon type). Good.

[Fuel cell]
The above-mentioned electrolyte membrane-electrode assembly (MEA) can be suitably used for a fuel cell. That is, the present invention also provides a fuel cell using the electrolyte membrane-electrode assembly (MEA) of the present invention. The fuel cell of the present invention can exhibit high power generation performance and durability. Here, the fuel cell of the present invention has a pair of anode separator and cathode separator that sandwich the electrolyte membrane-electrode assembly of the present invention.

(Separator)
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these flow paths, as described above, each of the separators is preferably provided with a gas flow path and a cooling flow path. As a material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

  The manufacturing method of the fuel cell is not particularly limited, and conventionally known knowledge can be appropriately referred to in the field of the fuel cell.

  Furthermore, a fuel cell stack having a structure in which a plurality of electrolyte membrane-electrode assemblies are stacked and connected in series via a separator may be formed so that the fuel cell can exhibit a desired voltage. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  The PEFC and the electrolyte membrane-electrode assembly described above use a catalyst layer that is excellent in power generation performance and durability. Therefore, the PEFC and the electrolyte membrane-electrode assembly are excellent in power generation performance and durability.

  The PEFC of the present embodiment and the fuel cell stack using the PEFC can be mounted on a vehicle as a driving power source, for example.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples. Unless otherwise specified, each operation is performed at room temperature (25 ° C.) / Relative humidity of 40 to 50%.

Example 1
² g of carbon support (Ketjen Black (registered trademark) KetjenBlackEC300J, average particle size: 40 nm, BET specific surface area: 800 m ² / g, manufactured by Lion Corporation) is added to 500 mL of 0.5 M HNO ₃ solution in a beaker. The mixture was stirred and mixed with a stirrer at 300 rpm for 30 minutes at room temperature (25 ° C.). Subsequently, an acid treatment was performed at 80 ° C. for 2 hours under stirring at 300 rpm to obtain a carbon support. Then, after filtering the carbon support, it was washed with ultrapure water. The above filtration and washing operations were repeated a total of 3 times. The carbon support was dried at 60 ° C. for 24 hours, and then an acid-treated carbon support A was obtained.

The amount of at least one functional group selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group formed on the surface of the obtained acid-treated carbon carrier A is 1.25 μmol / m ² . The BET specific surface area was 850 m ² / g, and the average particle size was 40 nm.

0.2 g of acid-treated carbon carrier A was added to 100 ml of ultrapure water placed in a beaker, and sonication was performed for 15 minutes to obtain carrier suspension A. The carrier suspension A was continuously stirred at 150 rpm at room temperature (25 ° C.) until it was added to the catalyst precursor particles. To 1000 ml ultrapure water in a beaker, 21.8 mL of 0.105 M cobalt chloride (CoCl ₂ .6H ₂ O) aqueous solution (135 mg in Co amount), 1.32 M chloroplatinic acid (H ₂ [PtCl ₆ ]. 6H ₂ O) aqueous solution 0.36 mL (92 mg in terms of platinum) was added. This was stirred and mixed with a stirrer at 10 ° C. for 5 minutes to prepare a mixed solution.

  Separately, 1.2 g of trisodium citrate dihydrate and 0.4 g of sodium borohydride were dissolved in 100 mL of ultrapure water to prepare a reducing agent solution.

  100 mL of the reducing agent solution prepared above is added to the mixed solution obtained above, stirred and mixed with a stirrer at 10 ° C. for 30 minutes, and reduced and precipitated to obtain catalyst precursor particles (Pt—Co mixed particles; platinum). -A solution containing non-platinum metal alloy particles 1) was obtained. Next, the carrier suspension A containing 0.2 g of the acid-treated carbon carrier A was added to this solution, and stirred and mixed with a stirrer at room temperature (25 ° C.) for 72 hours to carry the catalyst precursor particles on the carrier. . Thereafter, the catalyst precursor particle-supported carrier was filtered and washed with ultrapure water. The filtration and washing operations were repeated a total of 3 times, followed by filtration to obtain catalyst particle-supporting carrier 1 (catalyst precursor particle-supporting carrier 1). The catalyst particle-supported carrier was dried at 60 ° C. for 12 hours, and then subjected to a first heat treatment at 600 ° C. for 120 minutes in an argon gas atmosphere. Thereby, the heat-treated catalyst particle carrier 1 was obtained.

Next, the heat-treated catalyst particle carrier 1 was immersed (acid treatment) in an aqueous 0.1 M perchloric acid (HClO ₄ ) solution at room temperature (25 ° C.) for 24 hours, filtered, and subjected to heat / acid treatment. A catalyst particle carrier 1 was obtained.

  Further, the heat / acid-treated catalyst particle carrier 1 was subjected to a heat treatment (second heat treatment) at 600 ° C. for 120 minutes in an argon gas atmosphere, whereby an electrode catalyst 1 (average particle diameter: 5.1 nm) was obtained. ) The supported concentration (supported amount) of the catalyst particles of this electrode catalyst 1 was 36.5% by weight (Pt: 33.0% by weight, Co: 3.5% by weight) with respect to the support. The supported concentration was measured by ICP analysis. The same applies hereinafter.

  Next, as a result of measuring the number of platinum atom layers of the skin layer of this electrode catalyst 1, it was 1 to 3 layers. In addition, the electrode catalyst 1 was subjected to potential scanning from 0.2 V to 1.2 V at a rate of 10 mV / s in 0.1 M perchloric acid saturated with oxygen at 25 ° C., and then the skin layer was measured. After all, it was 1-3 layers. Furthermore, when the degree of order of the electrode catalyst 1 was measured, it was 39%.

Example 2
In Example 1, the first heat treatment was performed at 400 ° C. for 120 minutes in an argon gas atmosphere, and the second heat treatment was performed at 600 ° C. for 120 minutes in a 100% by volume hydrogen gas atmosphere. Except for the above, the same operation as in Example 1 was performed to obtain an electrode catalyst 2 (average particle size: 5.1 nm). The supported concentration (supported amount) of the catalyst particles of the electrode catalyst 2 was 33.5% by weight (Pt: 31.4% by weight, Co: 2.1% by weight) with respect to the support.

  Next, as a result of measuring the number of platinum atomic layers in the skin layer of the electrode catalyst 2, it was 1 to 2 layers. In addition, the electrode catalyst 2 was subjected to potential scanning from 0.2 V to 1.2 V at a rate of 10 mV / s in 0.1 M perchloric acid saturated with oxygen at 25 ° C., and then the skin layer was measured. After all, it was 1-2 layers. Furthermore, when the degree of order of the electrode catalyst 2 was measured, it was 37%.

Example 3
In Example 1, the first heat treatment was performed at 600 ° C. for 120 minutes in an argon gas atmosphere, and the second heat treatment was performed at 600 ° C. for 120 minutes in a 100% by volume hydrogen gas atmosphere. Except for the above, the same operation as in Example 1 was performed to obtain an electrode catalyst 3 (average particle size: 5.3 nm). The supported concentration (supported amount) of the catalyst particles of the electrode catalyst 3 was 33.5% by weight (Pt: 29.3% by weight, Co: 4.2% by weight) with respect to the support.

  Next, as a result of measuring the number of platinum atomic layers of the skin layer of this electrode catalyst 3, it was 1 to 4 layers. In addition, the electrode catalyst 3 was subjected to potential scanning from 0.2 V to 1.2 V at a rate of 10 mV / s in 0.1 M perchloric acid saturated with oxygen at 25 ° C., and then the skin layer was measured. After all, it was 1-4 layers. Furthermore, when the degree of order of the electrode catalyst 3 was measured, it was 52%.

Comparative Example 1
In the same manner as described in Example 1, catalyst precursor particle-supported carrier 1 was obtained.

  Next, the catalyst precursor particle-supported carrier 1 was dried at 60 ° C. for 12 hours, and then heat-treated at 400 ° C. for 120 minutes in a 100% by volume hydrogen gas atmosphere. This obtained the comparative electrode catalyst 1 (average particle diameter: 5.7 nm). The supported concentration (supported amount) of catalyst particles of this comparative electrode catalyst 1 was 33.8% by weight (Pt: 28.4% by weight, Co: 5.4% by weight) with respect to the support.

  Next, as a result of measuring the skin layer of this comparative electrode catalyst 1, no skin layer was observed (the number of platinum atomic layers: 0 layer). Further, this comparative electrode catalyst 1 was subjected to potential scanning at a rate of 10 mV / s from 0.2 V to 1.2 V in 0.1 M perchloric acid saturated with oxygen at 25 ° C. there were. Furthermore, when the degree of order of the comparative electrode catalyst 1 was measured, it was 24%.

(Catalyst performance evaluation)
<Durability test>
The following tests were conducted on the electrode catalysts of the examples and comparative examples. In 0.1 M perchloric acid at 60 ° C. saturated with N ₂ gas, the electrode potential was held at 0.6 V for 3 seconds with respect to the reversible hydrogen electrode (RHE), and then the potential was instantaneously raised to 1.0 V, The cycle of holding 1.0 V for 3 seconds and then instantaneously returning it to 0.6 V was repeated 10,000 cycles.

<Measurement of mass specific activity>
Each of the electrocatalysts of the example and the comparative example had a supported amount per unit area of 34 μg / cm ² on a rotating disk electrode (geometric area: 0.19 cm ² ) composed of a glassy carbon disk having a diameter of 5 mm. The electrode for performance evaluation was prepared by uniformly dispersing and supporting with Nafion.

  Next, using an electrochemical measurement device, a potential scan was performed from 0.2 V to 1.2 V at a rate of 10 mV / s in 0.1 M perchloric acid saturated at 25 ° C. with oxygen. Furthermore, the current value at 0.9 V was extracted from the current obtained by the potential scan after correcting the influence of mass transfer (oxygen diffusion) using the Koutecky-Levich equation. And the value which remove | divided the obtained electric current value by the total platinum carrying amount (6.5 micrograms) computed from the platinum carrying amount per said unit area was made into mass specific activity (A / g Pt). The method using the Koutecky-Levich equation is described, for example, on “4 Pt / C catalyst of Electrochemistry Vol.79, No.2, p.116-121 (2011) (convection voltammogram (1) oxygen reduction (RRDE)). Is described in “Analysis of Oxygen Reduction Reaction”.

  The mass specific activity was measured for the electrode catalysts before and after the durability test, and the retention rate (%) was determined from the results according to the following formula. The results are shown in Table 2 below. In Table 2 below, the maintenance ratio of mass specific activity for the electrode catalysts before and after the durability test is referred to as “mass specific activity maintenance ratio (%)”.

<Measurement of area specific activity>
The electrocatalysts of Examples and Comparative Examples were uniformly dispersed together with Nafion so as to be 34 μg · cm ⁻² on a rotating disk electrode (geometric area: 0.19 cm ² ) composed of a glassy carbon disk having a diameter of 5 mm. The electrode for performance evaluation was produced.

With respect to the electrodes of Examples and Comparative Examples, in a potential range of 0.05 to 1.2 V with respect to the reversible hydrogen electrode (RHE) in 0.1 M perchloric acid at 25 ° C. saturated with N ₂ gas. Cyclic voltammetry at a scanning speed of 50 mVs ⁻¹ . From the area of the hydrogen adsorption peak appearing at 0.05 to 0.4 V in the obtained voltammogram, the electrochemical surface area (cm ² ) of each electrode catalyst was calculated.

Next, using an electrochemical measurement device, a potential scan was performed from 0.2 V to 1.2 V at a rate of 10 mV / s in 0.1 M perchloric acid saturated at 25 ° C. with oxygen. Furthermore, the current value at 0.9 V was extracted from the current obtained by the potential scan after correcting the influence of mass transfer (oxygen diffusion) using the Koutecky-Levich equation. A value obtained by dividing the obtained current value by the above-described electrochemical surface area was defined as area specific activity (μA · cm ⁻² ). The method using the Koutecky-Levich equation is described, for example, on “4 Pt / C catalyst of Electrochemistry Vol.79, No.2, p.116-121 (2011) (convection voltammogram (1) oxygen reduction (RRDE)). Is described in “Analysis of Oxygen Reduction Reaction”. The area specific activity is calculated by dividing the extracted current value of 0.9 V by the electrochemical surface area.

  The area specific activity of the electrode catalyst before and after the durability test was measured, and the retention rate (%) was determined from the result according to the following formula. The results are shown in Table 2 below. In Table 2 below, the area specific activity maintenance rate of the electrode catalyst before and after the durability test is referred to as “area specific activity maintenance rate (%)”.

  From the above Table 2, it is shown that the electrode catalyst (catalyst particles) obtained by the production method of the present invention can maintain both mass specific activity and area specific activity significantly as compared with Comparative Example 1 having no skin layer. .

1 ... Polymer electrolyte fuel cell (PEFC),
2 ... Solid polymer electrolyte membrane,
3 ... Catalyst layer,
3a ... anode catalyst layer,
3c ... cathode catalyst layer,
4a ... anode gas diffusion layer,
4c ... cathode gas diffusion layer,
5a ... anode separator,
5c ... cathode separator,
6a ... anode gas flow path,
6c ... cathode gas flow path,
7: Refrigerant flow path,
10: Electrolyte membrane-electrode assembly (MEA).

Claims (7)

A method for producing an electrode catalyst in which catalyst particles are supported on a conductive carrier,
The catalyst particles are alloy particles of platinum atom and a non-platinum metal atoms, this time, the alloy particles, the core portion has an L1 ₂ structure as an internal structure, and platinum atoms and a non-platinum metal atoms and It is composed of a skin layer made of platinum atoms covering the core part,
The method
A reducing agent is added to a mixed solution of a platinum precursor and a non-platinum metal precursor, and the platinum precursor and the non-platinum metal precursor are simultaneously reduced to obtain platinum-non-platinum metal alloy particles.
The platinum-non-platinum metal alloy particles have a total amount of at least one functional group selected from the group consisting of a lactone group, a hydroxyl group, an ether group, and a carbonyl group on the surface of 0.5 μmol / m ² or more. Supported on a carbon support to prepare a catalyst precursor particle support,
The catalyst precursor particle-supported carrier is subjected to a first heat treatment to obtain a heat-treated catalyst particle carrier,
After the heat treatment catalyst particle carrier is acid-treated to obtain a heat / acid-treated catalyst particle carrier,
Performing a second heat treatment on the heat / acid treated catalyst particle support;
The manufacturing method which has.   The said carbon support | carrier is a manufacturing method of Claim 1 obtained by performing heat processing, after making a carbon material contact an acidic solution.   The said skin layer is a manufacturing method of Claim 1 or 2 comprised from 1-5 platinum atomic layers. The alloy particles are rules of the L1 ₂ structure is 30% to 100%, the production method according to any one of claims 1 to 3.   The manufacturing method of any one of Claims 1-4 whose said non-platinum metal atom is a transition metal atom.   The transition metal atom is selected from the group consisting of vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn) and zirconium (Zr). The manufacturing method according to claim 5.   The manufacturing method according to claim 6, wherein the transition metal atom is cobalt (Co).