JP6191326B2 - ELECTRODE CATALYST PARTICLE FOR FUEL CELL, ELECTRODE CATALYST FOR FUEL CELL USING THE SAME, ELECTROLYTE-ELECTRODE ASSEMBLY, FUEL CELL, AND METHOD FOR PRODUCING CATALYTIC PARTICLE AND CATALYST - Google Patents

Description

  The present invention relates to an electrode catalyst particle for a fuel cell, an electrode catalyst for a fuel cell using the same, an electrolyte-electrode assembly, a fuel cell, and a method for producing the catalyst particle and the catalyst.

  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. In general, the polymer electrolyte fuel cell has a structure in which an electrolyte membrane-electrode assembly 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 a polymer electrolyte fuel cell having an electrolyte membrane-electrode assembly (MEA) as described above, the following reaction formulas are used depending on the polarity of both electrodes (cathode and anode) sandwiching the polymer electrolyte membrane. Electric energy is obtained by advancing the electrode reaction indicated by. 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 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 or a platinum alloy having a high platinum content 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 non-platinum-based 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 durability.

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

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

  Another object of the present invention is to provide a catalyst particle and a method for producing the catalyst of the present invention.

  As a result of intensive studies to solve the above problems, the present inventors focused on the atomic arrangement around non-platinum atoms, and non-platinum with respect to the average number of bonds of non-platinum metal atoms-non-platinum metal atoms. The inventors have found that catalyst particles having an average ratio of the number of bonds of metal atoms to platinum atoms of 2.0 or more can solve the above-mentioned problems, and have completed the present invention.

  According to the present invention, as a result of an increase in the coverage of non-platinum atoms by platinum atoms, elution of non-platinum atoms is suppressed, and the durability of the catalyst is improved.

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. (A) is a XANES spectrum of the Co-K end of the catalyst particles obtained in Example 1. (B) is an XANES spectrum of Co foil, ie, Co—Co bond, (C) is an XANES spectrum of CoO particle, ie, Co—O bond, and (D) is Co / Pt = 1/9 ( It is a XANES spectrum of Co—Pt alloy of atomic ratio), that is, Co—Pt bond and Co—Co bond. It is a graph explaining an oxidation degree.

  The catalyst particle of the present invention is an alloy particle having a platinum atom and a non-platinum metal atom, and the average value of the number of bonds of non-platinum metal atom-platinum atom to the average value of the number of bonds of non-platinum metal atom-non-platinum metal atom. The ratio is 2.0 or more.

  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. . In contrast, the alloy particles according to the present invention are excellent in durability (having high activity even after the durability test). 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.

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. This intermetallic compound having the L1 ₀ structure is stable as an alloy. However, since the platinum layer and the metal layer have a repeated structure, the structure stability is inferior. In addition, since the platinum-metal alloy described in Patent Document 1 contains a metal other than platinum on the surface of the catalyst particles, the metal chain is formed under acidic conditions, for example, under a strongly acidic electrolyte (for example, PEFC). Elution cannot be sufficiently suppressed, and metal is eluted. For this reason, the catalyst of patent document 1 is inferior to durability.

  As a result of intensive studies by the present inventors, in the case of using platinum-non-platinum metal alloy particles as catalyst particles, in order to improve long-term durability performance, the structure around the non-platinum metal atoms that are relatively easy to elute is atomized. I thought it was necessary to design at the level. From such a technical point of view, it has been found that long-term durability is improved by adopting an atomic design that increases the coverage of platinum atoms with respect to non-platinum metal atoms. As an indicator of the coverage, in the present invention, the ratio of the average number of non-platinum metal atoms-platinum atoms to the average number of non-platinum metal atoms-non-platinum metal atoms (hereinafter simply referred to as the bond number ratio). Adopted). As a result of various investigations, it has been found that the use of catalyst particles having a bond number ratio of 2.0 or more significantly improves the long-term durability of the battery (see Examples described later).

  Here, the conventional catalyst had a mass specific activity reduced to less than half after a durability test such as a potential cycle. The main cause of the decrease is a decrease in area specific activity (ia), and the decrease in ECA (electrochemical area) is relatively small compared to the decrease in area specific activity. For this reason, it is important that the absolute value of the area specific activity after the potential cycle endurance test is high, but the catalyst particles of the present invention have a high absolute value of the area specific activity even after the endurance test.

  Therefore, since the catalyst particles of the present invention have high elution resistance, chain elution of non-platinum metal can be suppressed / prevented even under acidic conditions, for example, under a strongly acidic electrolyte (for example, PEFC). For this reason, the electrode catalyst using the catalyst particles of the present invention, the electrolyte membrane-electrode assembly having the electrode catalyst, and the fuel cell are excellent in durability.

  Hereinafter, an embodiment of the catalyst of the present invention, and an embodiment of a catalyst layer, a 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, measurement of operation and physical properties is performed under conditions of room temperature (20 to 25 ° C.) / Relative humidity 40 to 50%.

[Fuel cell]
A fuel cell includes a membrane electrode assembly (MEA), a pair of separators including 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. 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 a membrane electrode assembly (MEA) 10 in a stacked state.

  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. 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 member which comprises the fuel cell of this invention is demonstrated easily, the technical scope of this invention is not restrict | limited only to the following form.

[Catalyst particles]
The catalyst particles used in the present invention are alloy particles having platinum atoms and non-platinum atoms.

  In addition, the catalyst particle here refers to the catalyst particle used as a catalyst, For example, the catalyst particle carry | supported on the electroconductive support | carrier may be sufficient.

  Although it does not specifically limit as a non-platinum metal atom, A transition metal atom, a typical metal element, etc. are mentioned. The non-platinum metal atom is preferably a transition metal atom, among which selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ta, and W Is preferably at least one. 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. Moreover, the alloy of the said transition metal atom and platinum can achieve higher area specific activity (activity per unit area) and durability (activity after an endurance test). The transition metal atom may be alloyed with platinum alone, or two or more of them may be alloyed with platinum, but is preferably alloyed with platinum alone.

  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 alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. In this application, any form may be sufficient. However, the catalyst particles of the present invention preferably contain at least platinum atoms and non-platinum atoms forming an intermetallic compound, and are substantially composed of an intermetallic compound of platinum atoms and non-platinum atoms. For this reason, the catalyst particles of the present invention have an average value of the number of bonds of non-platinum metal atoms-platinum atoms (hereinafter also simply referred to as the number of M-Pt bonds) and the average number of bonds of non-platinum metal atoms-non-platinum metal atoms. A value (hereinafter also simply referred to as the number of MM bonds) is calculated.

  The catalyst particles have an average value of the number of M-Pt bonds / the average value of the number of M-M bonds is 2.0 or more. When the bond number ratio is 2.0 or more, the non-platinum metal atoms are dispersed, and the platinum atoms effectively cover the non-platinum metal atoms. For this reason, even after the durability test, the catalyst particles are suppressed in activity, particularly in area specific activity, and exhibit high area specific activity. From the viewpoint of exhibiting high activity even after the durability test, the bond number ratio is preferably 2.0 or more, and more preferably 3.0 or more. Since the ratio of the number of atoms of platinum and non-platinum atoms is preferably 0.11 or more, assuming the FCC structure, the coordination number is 12 at the maximum, and a random alloy of Pt0.89 to Co0.11 is assumed. Then, the ratio of Co—Pt is 10.7, the ratio of Co—Co is 1.3, and the upper limit of the bond number ratio is preferably 8.23 or less, and more preferably 7.0 or less.

  In the present invention, the average number of bonds is a value obtained from the spectrum of the K absorption edge of a nonmetallic atom in an XANES spectrum obtained by an X-ray absorption fine structure (XAFS) analysis method. A sample for spectrum measurement was prepared as follows. Preparation method of measurement sample and actual measurement method are XC-ray absorption spectroscopy-XAFS and its application-published by IPC, X-ray absorption fine structure-XAFS measurement and analysis ) Etc. can be referred to. As a sample preparation method, boron nitride powder and a carbon-supported electrocatalyst were mixed well while grinding on an agate mortar to form a pellet. It is necessary to mix a predetermined amount of electrode catalyst so that the edge jump Δμt is in the range of 0.5 to 1.5 at the absorption edge of the non-platinum metal to be noted.

  In addition, for example, a pellet is placed in the optical path in a beam line such as BL16B2 of SPring8, and sweeping is started from the low energy side of about 500 eV lower than the target absorption edge of the target element, and about 1000 eV from the absorption end to the high energy side. The absorbance should be measured in increments of approximately 0.2 eV. As a sample preparation method, boron nitride powder and carbon-supported electrocatalyst were mixed well while grinding on an agate mortar to form a pellet. The equipment and other conditions used to obtain the spectrum are shown below.

  In the analysis, the background is obtained by extrapolating the obtained spectrum by performing a least-squares fitting on the pre-absorption region (flat pre-edge region) using the Victorine or Macmaster formula. After subtraction, differentiation is performed. For example, when M is Co, SPring 8 was used to calibrate the spectrum so that the Co-K absorption edge (maximum change rate) of the Co foil was 7709 eV. The XAFS data processing is not particularly limited, but can be performed using, for example, Rigaku REX2000 Inc.

  Next, an average value of the number of bonds is calculated from the spectrum. Separately, M, M-O, and a known proportion of M-Pt alloy are used as standard samples, and XANES spectra are similarly obtained. The XANES spectrum of the obtained sample is fitted by weighted addition of the XANES spectrum of the standard sample.

  The case where M is Co will be specifically described with reference to FIG. FIG. 2A is an XANES spectrum at the Co—K end of the catalyst particles obtained in Example 1 (PtCo alloy_exp). Since this sample contains Co, platinum, and oxygen, XANES is mixed by Co—Co, Co—O, and Co—Pt bonds. FIG. 2 (B) is an XANES spectrum of Co foil, ie, Co—Co bond, (C) is an XANES spectrum of CoO particle, ie, Co—O bond, and (D) is Co / Pt = 1 / 9 is an XANES spectrum of a Co—Pt alloy of 9 (atomic ratio), that is, a Co—Pt bond and a Co—Co bond.

  Next, fitting using the spectra (B) to (D) is performed on the spectrum (A) of the sample (FIG. 2 (A) PtCo alloy_Fitting). The fitting range is from EO (maximum change rate energy) to -10 eV to +30 eV (77 to 7750 eV when M is Co). The completion of the fitting is completed when the R-factor defined by the following formula 1 becomes 10% or less.

  Here, since the number of Co—Co bonds was 12, when the fitting was possible with the Co foil, the average value of the number of Co—Co bonds was 12, and the fitting was possible with the Co / Pt (1/9) foil. In this case, the average value of the number of Co—Co bonds is 12 × 0.1 = 1.2, the average value of the number of Co—Pt bonds is 12 × 0.9 = 10.8, and the bond number ratio is 10 8 / 1.2 = 9.

  In addition, when fitting was possible with Co foil 0.5 and Co / Pt (1/9) foil 0.5, the average value of the number of Co—Co bonds was 12 × 0.5 + 12 × 0.1 × 0. Since 5 = 6.6, and the average value of the number of Co—Pt bonds is 12 × 0.9 × 0.5 = 5.4, the bond number ratio is 5.4 / 6.6 = 0.82. It becomes.

  In the particles of Example 1, the weight was Co foil 0.1, CoO particles 0.09, and Co / Pt alloy 0.81 (FIG. 2). The number of bonds is calculated using this value. Since the number of Co bonds is 12, the average number of Co—Co bonds = 12 × 0.1 (weighting derived from Co foil) + 12 × 0.1 × 0.81 (weighting derived from Pt—Co alloy) = 2.1, the average number of Co—Pt bonds = 12 × 0.9 × 0.81 = 8.7, and the coupling ratio is 8.748 / 2.172 = 4.1.

  In the above description, Co has been described as an example, but the same can be obtained for other non-platinum atoms. Here, the total atomic average coordination number is as follows.

  In addition, when a non-platinum metal atom is comprised from multiple types, a bond number ratio is calculated as follows. For example, assuming an alloy particle of PtCoNi, first, when calculating the number of bonds between Co and Pt, four samples of Co foil, CoPt alloy foil, CoNi alloy foil, and CoO standard sample are prepared and fitting is performed on the Co absorption edge. . In addition, a NiPt alloy foil, a NiCo alloy foil, a Ni foil, and a NiO foil are prepared and the Ni absorption edge is calculated. The sum of Ni—Pt and Co—Pt bonds is the numerator, and the sum of the number of Co—Co, Co—Ni bonds and the number of Ni—Ni bonds comes to the denominator.

  The bond number ratio can also be calculated by EXAFS.

  The catalyst particles preferably have a non-platinum metal atom oxidation degree of 0 or more and 0.3 or less. If the oxidation degree of the non-platinum atom is 0 or more and 0.3 or less, that is, if the reduction degree of the non-platinum metal atom is high (the oxidation degree is low), the non-platinum atom becomes difficult to ionize, and the performance after the durability test is Since it improves more, it is preferable. The lower limit of the degree of oxidation is 0, that is, particles having no oxygen atom, but it is usually 0.1 or more because it is difficult to contain no oxygen for production.

  The oxidation degree of the non-platinum metal atom is a numerical value of x when the composition formula representing the oxide of the non-platinum metal is MOx (wherein M represents a non-platinum metal and O represents oxygen).

  Here, the definition of “degree of oxidation” in this specification will be described with reference to FIG. First, the X-ray absorption spectrum of the sample is measured, and the X-ray absorption fine structure is analyzed. In other words, the measured X-ray absorption spectrum is normalized by using a background region before the absorption edge and fitting with a Victorine polynomial to remove the background. Similarly, the X-ray absorption spectrum of the non-platinum metal itself and the X-ray absorption spectrum of the oxide of the metal are measured and normalized. FIG. 3 is a graph showing the results of normalizing the X-ray absorption spectra of metallic nickel, a sample (Pt / Ni alloy particles) and nickel oxide (NiO).

  Next, for each spectrum, the normalized peak height of the K absorption edge of the non-platinum metal is measured. At this time, the peak height of the metal (nickel in the case of FIG. 3, Ni—K absorption edge) is “X = 0”, and the peak height of the metal oxide (nickel oxide in the case of FIG. 3) is “X”. = 1 ”, the relative ratio of the peak height of the sample is defined as“ degree of oxidation ”. That is, as X approaches 1, it can be interpreted that many of the non-platinum metal atoms are oxidized.

  The method described in the following Example is employ | adopted for the value of specific oxidation degree.

  The catalyst particles preferably have a ratio (atomic ratio) of non-platinum metal atoms to platinum atoms of 0.11 or more. When the content of the non-platinum metal atom is in such a range, the activity of the catalyst can be improved by adding the non-platinum metal atom. The upper limit of the ratio of non-platinum metal atoms to platinum atoms is preferably 1.0 or less and more preferably 0.7 or less from the viewpoint of reducing the amount of expensive platinum used.

  The 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 fluorescent X-ray analysis (XRF). Specifically, the methods described in the following examples are employed.

  The size of the catalyst particles is not particularly limited. For example, the average particle diameter of the catalyst particles is preferably 1 to 10 nm, more preferably 2 to 8 nm, and further preferably 3 to 7 nm. When the 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. The “average particle diameter of the catalyst particles” is the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst particles in X-ray diffraction (XRD), or the particles of the catalyst metal particles determined by a transmission electron microscope (TEM). It can be measured as the average diameter. In the present specification, the “average particle diameter of the catalyst particles” is an average value of the particle diameters of the catalyst particles examined from a transmission electron microscope image for a statistically significant number (for example, at least 203 samples). Here, the “particle diameter” means the maximum distance among the distances between any two points on the particle outline.

[Method for producing catalyst particles]
The method for producing the catalyst particles is not particularly limited, and a step (1) of preparing a mixed solution by dispersing a platinum salt or a platinum complex and a non-platinum metal salt or a non-platinum metal complex in a solvent. And (2) adding a reducing agent to the mixed solution. Through such a process, platinum atoms and non-platinum metal atoms were mixed by reducing platinum ions and non-platinum ions at the same time in a situation where platinum ions and non-platinum ions were mixed. An intermetallic compound can be obtained.

  Hereinafter, the preferable method will be described in detail. However, the present invention is not limited to the following method.

(Process (1))
Although it does not restrict | limit especially as a platinum precursor which can be used in a process (1), 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.

  The non-platinum precursor that can be used in this step (1) is not particularly limited, but non-platinum metal salts and non-platinum metal complexes can be 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 precursor may be used individually by 1 type, or may be used as a 2 or more types of mixture. The non-platinum precursor may be in the form of a hydrate.

  The solvent used for the preparation of the mixed solution containing the platinum salt / complex (hereinafter also simply referred to as platinum precursor) and the non-platinum metal salt / complex (hereinafter also simply referred to as non-platinum precursor) is not particularly limited. The platinum precursor and non-platinum precursor used are appropriately selected. The form of the mixed solution is not particularly limited, and includes a solution, a dispersion, and a suspension. In view of uniform mixing, the mixed solution is preferably in the form of a solution. Specific examples include water, methanol, ethanol, organic solvents such as 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.

  Although the density | concentration in the liquid mixture of a platinum precursor and a non-platinum precursor is not restrict | limited, It is preferable that it is 0.1-50 (mg / 100 mL) in metal conversion, More preferably, it is 0.5-30 (mg / 100 mL). In addition, the density | concentration in the liquid mixture of a platinum precursor and a non-platinum precursor may be the same, or may differ.

  Alternatively, the metal ion concentration (total concentration of platinum ion concentration and non-platinum ion concentration) in the mixed solution (particularly the mixed solution) is not particularly limited, but is preferably 10.0 mM or less, and preferably 5 mM or less. More preferred. When the metal ion concentration is 5.0 mM or less, aggregation of mixed particles of synthesized platinum atoms and non-platinum atoms can be suppressed. The lower limit of the metal ion concentration in the mixed solution is not particularly limited, but is preferably 1 mM or more from the viewpoint of the reaction rate.

  Further, the mixing ratio of the platinum salt / complex and the non-platinum metal salt / complex is not particularly limited, but should be a mixing ratio that can achieve the above alloy composition (platinum atom / non-platinum atom ratio). preferable. Specifically, the non-platinum metal salt / complex may be mixed at a ratio (metal conversion) of 0.1 to 15 mol, more preferably 0.1 to 10 mol, with respect to 1 mol of the platinum salt / complex. preferable.

  In the step (1), the method for preparing the mixed solution containing the platinum salt / complex and the non-platinum metal salt / complex is not particularly limited. For example, platinum salt / complex and non-platinum metal salt / complex are added to the solvent; after the platinum salt / complex is dissolved in the solvent, the non-platinum metal salt / complex is added thereto; Any of the following methods may be used: a platinum salt / complex and a platinum salt / complex and a non-platinum metal salt / complex are separately dissolved in a solvent and then mixed with each other. Good. Moreover, it is preferable to stir in order for the said liquid mixture 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 10 to 50 ° C, more preferably 15 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.

(Process (2))
Next, in step (2), platinum ions and non-platinum metal ions can be simultaneously reduced by adding a reducing agent. By such a process, an intermetallic compound of platinum and a non-platinum metal can be obtained.

Examples of the reducing agent that can be used in the step (2) include ethanol, methanol, propanol, formic acid, formate such as sodium formate and potassium formate, and citric acid such as formaldehyde, sodium thiosulfate, citric acid, and sodium citrate. Salts, sodium borohydride (NaBH ₄ ), hydrazine (N ₂ H ₄ ), and the like can be used.

  Moreover, a reducing agent may be added to the liquid mixture prepared at the said process (1) with the form of the reducing agent solution melt | dissolved in the 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 need not be the same as the solvent used for preparing the mixed solution, but is 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 0.2 to 5 mol, preferably 0.4 to 3 mol, with respect to 1 mol of metal ions (total mol of platinum ions and non-platinum ions). It is. 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.

  In step (2), it is preferable to stir after adding the reducing agent-containing liquid. Thereby, since a platinum precursor, a non-platinum 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 0 to 30 ° 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.

  The catalyst precursor particles of the present invention are obtained by the reduction reaction. Here, if necessary, the catalyst precursor particles may be isolated. 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 can be performed, for example, in the range of 1 to 60 hours, preferably about 5 to 48 hours.

  The catalyst particles of the present invention are preferably produced by the steps (1) and (2). Here, the bond number ratio and the degree of oxidation can be controlled by appropriately adjusting the platinum / non-platinum content ratio, stirring conditions, reaction time, and the like. Further, the oxidation state and atomic bonding state of the catalyst particles can be changed also by heat treatment described later.

  In the present invention, the catalyst precursor particles obtained here may be used as catalyst particles as they are. However, as described later, by supporting the catalyst precursor particles on a conductive carrier, an electrode catalyst (in particular, a fuel cell) As an electrode catalyst for), it can be suitably used.

[Catalyst (Electrocatalyst)]
The catalyst particles described above are preferably supported on a conductive carrier to form an electrode catalyst.

  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 include carbon blacks such as acetylene black, channel black, oil furnace black, gas furnace black (for example, Vulcan), lamp black, thermal black, and ketjen black (registered trademark); black pearl Graphitized acetylene black; graphitized channel black; graphitized oil furnace black; graphitized gas furnace black; graphitized lamp black; graphitized thermal black; graphitized Ketjen black; graphitized black pearl; carbon nanotube; Carbon nanohorn, carbon fibril, activated carbon, coke, natural graphite, artificial graphite, and the like. 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.

  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.

  In the electrode catalyst in which the catalyst particles are supported on the conductive support, the support concentration of the catalyst particles is preferably 2 to 70% by mass with respect to the total amount of the support. 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, the supported concentration of the catalyst particles is 5 to 60% by mass with respect to the total amount of the carrier. 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 inductively coupled plasma emission spectroscopy (ICP).

[Production method of catalyst (electrode catalyst)]
The method for producing a catalyst for a fuel cell is not particularly limited, but a step of preparing a mixed solution by dispersing a platinum salt or a platinum complex and a non-platinum metal salt or a non-platinum metal complex in a solvent (1 '), Adding a reducing agent to the mixed solution to obtain a reducing agent-containing liquid (2'), adding a conductive carrier to the reducing agent-containing liquid, and adding platinum and non-platinum metal-containing particles. And (3 ′) supporting on a conductive carrier. Further, in some cases, it is preferable to include a step (4 ′) of performing a heat treatment after the step (3 ′). Specifically, the electrode catalyst particles for a fuel cell supported on a conductive support are more than 100 degrees. It is preferable to include the process of heat-processing at the temperature of 700 degrees C or less.

  Hereinafter, although the said preferable method is explained in full detail, since the said process (1 ') and (2') is the same as that of the description in the manufacturing method of a catalyst particle, description is abbreviate | omitted here. The present invention is not limited to the following method.

(Process (3 '))
In this step, a conductive carrier is added to the reducing agent-containing liquid, and platinum and non-platinum metal-containing particles are supported on the conductive carrier to obtain catalyst precursor particle-supported carriers. Here, the platinum and non-platinum metal-containing particles are catalyst precursor particles containing a platinum-non-platinum intermetallic compound reduced by the reducing agent in step (2). The catalyst precursor particles may become catalyst particles supported on the carrier as they are, or may become catalyst particles supported on the carrier by changing the physical properties by the heat treatment described later.

The BET specific surface area of the conductive carrier used is preferably 10 to 5000 m ² / g in order to carry the catalyst component in a highly dispersed state. More preferably, it is 50-2000 m < ² > / g. The “BET specific surface area (m ² / g carrier)” of the carrier is measured by a nitrogen adsorption method.

  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 above-mentioned catalyst particle loading concentration (loading amount) is obtained.

  Moreover, it is preferable to stir after adding a conductive support | carrier to a reducing agent 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. Moreover, since the reduction reaction of the unreduced platinum precursor and the non-platinum precursor with the reducing agent also occurs simultaneously with the above stirring treatment, it is possible to further promote the high dispersion and loading of the catalyst precursor particles on the conductive support. is there. 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 and non-platinum 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 (4 '))
In this step, the catalyst particle-supported carrier obtained in the above step (3 ′) is heat-treated. Such heat treatment is preferably performed after catalyst particles are supported on a conductive support. The reduction of non-platinum metal can be promoted by heat treatment at a high temperature as required, and the bond number ratio and the degree of oxidation can be controlled. For example, when the bond number ratio of the catalyst particles is low (Comparative Example 2 described later), the bond number ratio can be increased to 2.0 or more (Example 1 described later) by heat treatment at a high temperature. The electrode catalyst thus obtained can exhibit high activity even with a small platinum content. Moreover, the said electrode catalyst is excellent also in durability (it has high activity maintenance property).

  The heat treatment conditions are not particularly limited as long as the bond number ratio or the oxidation degree can be controlled to a suitable range, but control of the heat treatment temperature and time is important. Specifically, the heat treatment temperature is preferably 100 to 1000 ° C, more preferably 100 to 700 ° C, and more preferably 400 to 700 ° C. Moreover, it is preferable that the heat processing time is 30 minutes or more. The upper limit of the heat treatment time is not particularly limited as long as it can maintain the state in which the catalyst particles are supported on the conductive support and does not cause an excessive increase in the particle diameter. Is appropriately selected.

The heat treatment is preferably performed in a non-oxidizing atmosphere in order to promote the reduction of the non-platinum metal. 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 in a reducing gas atmosphere (with respect to the total volume of the inert gas and the reducing gas), preferably 10 to 100% by volume, More preferably, it is 50-100 volume%. With such a concentration, the oxidation of the alloy (platinum and non-platinum metal) can be sufficiently suppressed / prevented.

[Electrolyte membrane-electrode assembly (MEA)]
The electrode catalyst described above can be suitably used for an electrolyte membrane-electrode assembly (MEA). That is, the present invention also provides an electrolyte membrane-electrode assembly (MEA) containing the electrode catalyst of the present invention, particularly a fuel cell electrolyte membrane-electrode assembly (MEA). The electrolyte membrane-electrode assembly (MEA) of the present invention can exhibit high 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 (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
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 room temperature (25 ° C.) for 5 minutes to prepare a mixed solution. The metal ion concentration in the mixture is 2.66 mM.

  Separately, 1.6 g of trisodium citrate dihydrate and 0.6 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, and the mixture is stirred and mixed with a stirrer at room temperature (25 ° C.) for 30 minutes to cause reduction precipitation, and catalyst precursor particles (containing Pt—Co). A solution containing particles) was obtained. Next, 100 mL of an aqueous dispersion containing 0.2 g of a carbon support (Ketjen Black (registered trademark) KettjenBlackEC300J, average particle size: 40 nm, BET specific surface area: 800 m ² / g, manufactured by Lion Corporation) is added to this solution. Then, the mixture was stirred and mixed with a stirrer at room temperature (25 ° C.) for 48 hours to support the catalyst precursor particles on the support. 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 a catalyst particle-supporting carrier. The catalyst particle-supported carrier was dried at 60 ° C. for 12 hours, and then subjected to a heat treatment step at 600 ° C. for 2 hours in a 100% by volume hydrogen gas atmosphere. Thereby, the electrode catalyst 1 was obtained. With respect to this electrode catalyst 1, the bond number ratio, the oxidation degree, and the non-platinum atom / platinum atom ratio were measured and calculated. The results are shown in Table 2 . Also, support concentration of the catalyst particles of the electrode catalyst 1 (weight bearing), to the carrier, 34.0 (Pt: 30.7, Co : 3.3) percent by weight, average particle diameter 4. It was 4 nm.

Example 2
To a 1000 ml ultrapure water in a beaker, 10.9 mL of 0.105 M cobalt chloride (CoCl ₂ .6H ₂ O) aqueous solution (67.5 mg in Co amount), 1.32 M chloroplatinic acid (H ₂ [PtCl ₆ ] · 6H ₂ O) was charged with an aqueous solution 0.36 mL (92 mg of platinum amount). This was stirred and mixed with a stirrer at room temperature (25 ° C.) for 5 minutes to prepare a mixed solution. The metal ion concentration in the mixed solution is 1.60 mM.

  Separately, 1.6 g of trisodium citrate dihydrate and 0.6 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 room temperature (25 ° C.) for 30 minutes, and reduced and precipitated to obtain catalyst precursor particles (Pt—Co mixed). A solution containing particles) was obtained. Next, 100 mL of an aqueous dispersion containing 0.2 g of a carbon carrier (Ketjen Black (registered trademark) KetjenBlackEC, average particle size: 40 nm, BET specific surface area: 800 m ² / g, manufactured by Lion Corporation) is added to this solution. Then, the mixture was stirred and mixed with a stirrer at room temperature (25 ° C.) for 48 hours to support the catalyst precursor particles on the support. 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 a catalyst particle-supporting carrier. The catalyst particle-supported carrier was dried at 60 ° C. for 12 hours to obtain an electrode catalyst 2. For this electrode catalyst 2, the bond number ratio, the oxidation degree, and the non-platinum atom / platinum atom ratio were measured and calculated. The results are shown in Table 2 . Also, support concentration of the catalyst particles of the electrode catalyst 1 (carrying amount), with respect to the support, 32.7 (Pt: 31.5, Co : 1.2) percent by weight and an average particle diameter of 2. It was 8 nm.

Example 3
In Example 2, a 0.105 M aqueous solution of cobalt chloride (CoCl ₂ · 6H ₂ O) 43.6 mL (270 mg in Co amount) and a 1.32 M aqueous solution of chloroplatinic acid (H ₂ [PtCl ₆ ] · 6H ₂ O) An electrode catalyst 3 was obtained in the same manner as in Example 2 except that 0.36 mL (92 mg in platinum amount) was used to prepare a mixed solution (metal ion concentration: 4.9 mM). For this electrode catalyst 3, the bond number ratio, the oxidation degree, and the non-platinum atom / platinum atom ratio were measured and calculated. The results are shown in Table 2 . Also, a support concentration (supported amount) of the catalyst particles of the electrode catalyst 3, with respect to the support, 34.0 (Pt: 31.6, Co : 2.4) percent by weight and an average particle diameter of 2. It was 8 nm.

Comparative Example 1
In Example 2, 0.105M cobalt chloride (CoCl ₂ .6H ₂ O) aqueous solution 32.7 mL (202 mg in Co amount), 1.32 M chloroplatinic acid (H ₂ [PtCl ₆ ] · 6H ₂ O) aqueous solution An electrode catalyst 4 was obtained in the same manner as in Example 2 except that a mixed solution was prepared using 0.54 mL (138 mg in platinum amount). For this electrode catalyst 4, the bond number ratio, the oxidation degree, and the non-platinum atom / platinum atom ratio were measured and calculated. The results are shown in Table 2 . Also, support concentration of the catalyst particles of the electrode catalyst 4 (weight bearing), to the carrier, 43.2 (Pt: 40.2, Co : 3.0) percent by weight and an average particle diameter of 3. It was 0 nm.

Comparative Example 2
An electrode catalyst 5 was obtained in the same manner as in Example 1 except that the heat treatment was not performed in Example 1. For this electrode catalyst 5, the bond number ratio, the degree of oxidation, and the non-platinum atom / platinum atom ratio were measured and calculated .併 allowed, Co content are also shown in Table 2. The supported concentration (supported amount) of the catalyst particles of the electrode catalyst 5 is 34.1 (Pt: 31.9, Co: 2.2)% by weight with respect to the support, and the average particle size is 2.4 nm. Met.

[Measurement of degree of oxidation]
The EXAFS was measured for the electrode catalysts of the examples and comparative examples. The measurement of EXAFS was performed in the transmission mode using a deflecting electromagnet beam line BL16B2 of SPring8. Next, using the background region before the absorption edge, the obtained absorption spectrum was fitted with a Victorine polynomial to remove the background, thereby obtaining a standardized absorption spectrum. Similarly, normalized absorption spectra were obtained for cobalt foil and cobalt oxide (CoO).

  And the oxidation degree of the electrode catalyst of an Example and a comparative example was computed by comparing the normalized peak height of the Co-K absorption edge in the electrode catalyst of an Example and a comparative example, cobalt foil, and cobalt oxide.

[Measurement of atomic ratio]
The atomic ratio was measured using an inductively coupled plasma emission spectrometer SPS-3520 manufactured by SII Nanotechnology.

(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 potential of the reversible hydrogen electrode (RHE) was maintained at 0.6 V for 3 seconds, and then the potential was instantaneously increased 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 area specific activity>
The electrocatalysts of Examples and Comparative Examples were uniformly dispersed together with Nafion so as to be 5 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 each Example and Comparative Example, 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. And 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 (μAcm ⁻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 after the durability test was measured. The results are shown in Table 2 below.

  Table 1 above shows that the electrode catalyst (catalyst particles) of the present invention has significantly higher activity after the durability test than that of the comparative example.

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 (13)

Alloy particles having platinum atoms and non-platinum metal atoms,
Non-platinum metal atoms - non-platinum metal atoms relative to the average value of the bonding number of the non-platinum metal atoms - Ri der ratio of the average value of the number of bonds is 2.0 or more platinum atoms,
Fuel cell electrode catalyst particles wherein the non-platinum metal atom is at least one selected from the group consisting of Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ta, and W .   The electrode catalyst particle for a fuel cell according to claim 1, wherein the oxidation degree of the non-platinum metal atom is 0 or more and 0.3 or less.   The electrode catalyst particle for a fuel cell according to claim 1 or 2, wherein a ratio of the non-platinum metal atom to the platinum atom (atomic ratio) is 0.11 or more. The electrode catalyst particle for fuel cells according to any one of claims 1 to 3 , wherein the non-platinum metal atom is Co. A fuel cell electrode catalyst, wherein the fuel cell electrode catalyst particles according to any one of claims 1 to 4 are supported on a conductive carrier. The electrode catalyst for a fuel cell according to claim 5 , wherein the supported concentration of the catalyst particles is 2 to 70 mass% with respect to the carrier. An electrolyte membrane-electrode assembly comprising the electrode catalyst according to claim 5 or 6 . A fuel cell using the electrolyte membrane-electrode assembly according to claim 7 . A step of preparing a mixed solution by dispersing a platinum salt or a platinum complex and a non-platinum metal salt or a non-platinum metal complex in a solvent;
The method for producing electrode catalyst particles for a fuel cell according to any one of claims 1 to 4 , comprising a step of adding a reducing agent to the mixed solution. The manufacturing method of the electrode catalyst particle for fuel cells of Claim 9 whose metal ion concentration in the said liquid mixture is 5.0 mM or less. A step of preparing a mixed solution by dispersing a platinum salt or a platinum complex and a non-platinum metal salt or a non-platinum metal complex in a solvent;
Adding a reducing agent to the mixed solution to obtain a reducing agent-containing liquid;
Adding a conductive carrier to the reducing agent-containing liquid, and supporting platinum and non-platinum metal-containing particles on the conductive carrier;
The manufacturing method of the electrode catalyst for fuel cells of Claim 5 or 6 containing these. The method for producing an electrode catalyst for a fuel cell according to claim 11 , wherein the conductive support has a specific surface area of 10 to 5000 m ² / g. Furthermore, the manufacturing method of the electrode catalyst for fuel cells of Claim 11 or 12 including the process of heat-processing the electroconductive support | carrier with which platinum and the non-platinum metal containing particle | grains were carry | supported at the temperature of 100 degreeC or more and 700 degrees C or less.