Electrode catalyst for fuel cell

Abstract

To provide an electrode catalyst for a fuel cell having both high catalytic activity and high durability.SOLUTION: An electrode catalyst for a fuel cell in which PtSn alloy particles are supported on conductive support particles, wherein a ratio R (cryst) of a crystalline PtSn alloy calculated by the following mathematical formula (1) is 0.40% or less: R (cryst) = R (Pt3Sn) + R (PtSn) + R (Pt2Sn3) + R (Pt2Sn) (1) (In Equation (1), R (Pt3Sn), R (PtSn), R (Pt2Sn3), and R (Pt2Sn) are the proportions (%) of the respective crystalline structures in the PtSn particles. ) SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode catalyst for a fuel cell. [Background technology]

[0002] Research and development of fuel cells is underway to address the needs for preventing air pollution, reducing greenhouse gas emissions, and providing alternative energy sources to petroleum. Fuel cells have the advantages of being clean, having a high energy density, and not requiring charging.

[0003] A fuel cell has a structure in which an anode and a cathode are arranged opposite each other with an ion exchange membrane interposed between them. When a fuel (e.g., hydrogen) is supplied to the anode side and an oxidant (e.g., air) is supplied to the cathode side, a predetermined electrochemical reaction occurs at each of the electrodes, generating electricity.

[0004] Fuel cells use, for example, an electrode catalyst having a structure in which catalytic metal particles are supported on the surface of a conductive support. Carbon black, which has excellent conductivity, is often used as the conductive support, and Pt, which has excellent catalytic activity, is often used as the catalytic metal particles.

[0005] In an attempt to improve the catalytic activity of electrode catalysts for fuel cells, the use of alloys of Pt and transition metals as catalytic metal particles has been investigated.

[0006] For example, Patent Document 1 describes the use of a Pt-Co alloy as catalytic metal particles in an electrode catalyst for a fuel cell, and Patent Document 2 describes the use of a Pd-Co-W alloy as catalytic metal particles. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2016 / 063968 [Patent Document 2] Japanese Patent Application Publication No. 2019-067766 Summary of the Invention [Problem to be solved by the invention]

[0008] When alloys of Pt and transition metals such as Co are used as catalytic metal particles in fuel cell electrode catalysts, it is true that higher catalytic activity than Pt can be obtained. However, the catalytic activity of fuel cell electrode catalysts using catalytic metal particles made of these alloys decreases over time with continued use.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode catalyst for a fuel cell that combines high catalytic activity with high durability. [Means for solving the problem]

[0010] The present invention is as follows.

[0011] Aspect 1: An electrode catalyst for a fuel cell, comprising PtSn alloy particles supported on conductive support particles, The proportion R(cryst) of the crystalline PtSn alloy calculated by the following formula (1) is 0.40% or less. Electrode catalyst for fuel cells. R(cryst)=R(Pt3Sn)+R(PtSn)+R(Pt2Sn3)+R(Pt2Sn) (1) (In formula (1), R(PtSn), R(PtSn), R(PtSn), and R(PtSn) are the proportions (%) of each crystal structure in the PtSn alloy particles, calculated by the following formula, R(Pt3Sn)={I(Pt3Sn) / I(total)}×100 R(PtSn)={I(PtSn) / I(total)}×100 R(Pt2Sn3)={I(Pt2Sn3) / I(total)}×100 R(Pt2Sn)={I(Pt2Sn) / I(total)}×100 I(PtSn) is the peak intensity of the peak based on the PtSn (111) plane observed near 2θ=31.565° in the XRD data measured for the fuel cell electrode catalyst, I(PtSn) is the peak intensity of the peak due to the PtSn (202) plane observed near 2θ = 62.271°, I(Pt2Sn3) is the peak intensity of the peak based on the Pt2Sn3 (205) plane observed around 2θ = 60.794°, I(Pt2Sn) is the peak intensity of the peak based on the Pt2Sn (220) plane observed around 2θ = 65.421°, I(total) is I(Pt3Sn) + I(PtSn) + I(Pt2Sn3) + I(Pt2Sn) + I(Pt), I(Pt) is the peak intensity of the Pt(111) plane peak observed around 2θ=39.735°. Aspect 2: The fuel cell electrode catalyst according to Aspect 1, wherein the R(Pt3Sn) is 0.15% or less. Aspect 3: The fuel cell electrode catalyst according to Aspect 1, wherein the R(Pt2Sn3) is 0.15% or less. Aspect 4: The fuel cell electrode catalyst according to Aspect 1, wherein the Sn content in the PtSn alloy particles is 0.5 atomic % or more and less than 10.0 atomic %. Aspect 5: The fuel cell electrode catalyst according to Aspect 1, wherein the particle size of the PtSn alloy particles is 2.0 nm or more and 5.0 nm or less, as calculated by the Scherrer equation from a peak based on the Pt(220) plane observed around 2θ=67.424° in XRD data measured on the fuel cell electrode catalyst. Aspect 6: The fuel cell electrode catalyst according to Aspect 1, wherein the conductive support particles are carbon particles. Aspect 7: The specific surface area of ​​the carbon particles is 100 m 2 / g or more 1,500m 2 7. The fuel cell electrode catalyst according to claim 6, wherein the electrocatalyst has a .DELTA. / g or less. Aspect 8: The fuel cell electrode catalyst according to Aspect 1, wherein the ratio of the mass of Pt in the PtSn alloy particles to the sum of the mass of the conductive support particles and the mass of Pt in the PtSn alloy particles is 20% by mass or more and 55% by mass or less. Aspect 9: The fuel cell electrode catalyst according to any one of Aspects 1 to 8, which is a cathode catalyst for a fuel cell. Aspect 10: A fuel cell electrode comprising the fuel cell electrode catalyst according to any one of Aspects 1 to 8. Aspect 11: The electrode of aspect 10, which is a cathode of a fuel cell. Aspect 12: A method for producing the fuel cell electrode catalyst according to any one of Aspects 1 to 8, comprising: supporting Pt particles on the conductive support particles to obtain Pt-supported conductive support particles; contacting the Pt-supported conductive support particles with a solution of an Sn precursor to obtain a mixed solution of the Pt-supported conductive support particles and the Sn precursor; placing a mixed solution of the Pt-supported conductive support particles and the Sn precursor under alkaline conditions to support Sn particles on the Pt-supported conductive support particles, thereby obtaining Pt-Sn-supported conductive support particles; and The Pt-Sn-supported conductive support particles are fired to alloy the Pt particles and the Sn particles on the Pt-supported conductive support particles, thereby obtaining PtSn alloy-supported conductive support particles. and When the Pt-supported conductive support particles are brought into contact with the Sn precursor solution, the Pt-supported conductive support particles are mixed with a solution containing the Sn precursor and an acid. A method for producing an electrode catalyst for a fuel cell. Aspect 13: The method according to aspect 12, further comprising heating the PtSn alloy-supported conductive support particles in the presence of nitric acid. [Effects of the Invention]

[0012] According to the present invention, there is provided an electrode catalyst for a fuel cell which has both high catalytic activity and high durability. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a graph showing the relationship between the proportion R(cryst) of crystalline PtSn alloy and the atomic proportion of Sn. DETAILED DESCRIPTION OF THE INVENTION

[0014] 《Electrode catalyst for fuel cells》 The fuel cell electrode catalyst of the present invention comprises: An electrode catalyst for a fuel cell, comprising PtSn alloy particles supported on conductive support particles, The proportion R(cryst) of the crystalline PtSn alloy calculated by the following formula (1) is 0.40% or less. Electrode catalyst for fuel cells. R(cryst)=R(Pt3Sn)+R(PtSn)+R(Pt2Sn3)+R(Pt2Sn) (1) (In formula (1), R(PtSn), R(PtSn), R(PtSn), and R(PtSn) are the proportions (%) of each crystal structure in the PtSn alloy particles, calculated by the following formula, R(Pt3Sn)={I(Pt3Sn) / I(total)}×100 R(PtSn)={I(PtSn) / I(total)}×100 R(Pt2Sn3)={I(Pt2Sn3) / I(total)}×100 R(Pt2Sn)={I(Pt2Sn) / I(total)}×100 I(PtSn) is the peak intensity of the peak based on the PtSn (111) plane observed near 2θ=31.565° in the XRD data measured for the fuel cell electrode catalyst, I(PtSn) is the peak intensity of the peak due to the PtSn (202) plane observed near 2θ = 62.271°, I(Pt2Sn3) is the peak intensity of the peak based on the Pt2Sn3 (205) plane observed around 2θ = 60.794°, I(Pt2Sn) is the peak intensity of the peak based on the Pt2Sn (220) plane observed around 2θ = 65.421°, I(total) is I(Pt3Sn) + I(PtSn) + I(Pt2Sn3) + I(Pt2Sn) + I(Pt), I(Pt) is the peak intensity of the Pt(111) plane peak observed around 2θ=39.735°.

[0015] The reason why fuel cell catalysts in conventional technology have poor durability is thought to be that the transition metals that form alloys with Pt in the catalyst metal particles gradually dissolve with continued use of the catalyst, reducing catalytic activity, and that the dissolved transition metals undergo an ion exchange reaction with the ionomer contained in the fuel cell, worsening the proton resistance of the fuel cell.

[0016] The fuel cell catalyst of the present invention is characterized by using a PtSn alloy with low crystallinity as catalytic metal particles.

[0017] Sn is less likely to be eluted than other transition metals such as Co. Therefore, the fuel cell catalyst of the present invention, which uses a PtSn alloy as catalytic metal particles, can maintain its activity for a long period of time even when used continuously.

[0018] Furthermore, in the fuel cell catalyst of the present invention, the proportion of crystalline PtSn alloy in the PtSn alloy of the catalyst metal particles is low, which allows the fuel cell catalyst of the present invention to exhibit excellent oxygen reduction activity.

[0019] It is believed that the fuel cell catalyst of the present invention achieves both high catalytic activity and high durability due to the above-mentioned mechanism of action, although the present invention is not limited to any particular theory.

[0020] <Conductive carrier particles> The fuel cell catalyst of the present invention contains conductive support particles.

[0021] The conductive support particles in the present invention may be conductive or semiconductive metal oxide particles or carbon particles.

[0022] The conductive or semiconductive metal oxide may be one or more selected from, for example, TiO, VO, Ti2O3, V2O3, VO2, NbO2, CrO2, MoO2, WO2, ReO2, RuO2, OsO2, RhO2, IrO2, SnO2, ReO2, LaTiO3, SrMoO3, SrRuO3, LaRhO3, and the like.

[0023] These metal oxides may be doped with a specific impurity element, which may be one or more elements selected from the group consisting of lithium (Li), niobium (Nb), tantalum (Ta), tungsten (W), antimony (Sb), and bismuth (Bi), and may be appropriately selected depending on the type of conductive or semiconductive metal oxide.

[0024] The carbon particles may be, for example, particles of carbon black, graphite, carbon fiber, activated carbon, amorphous carbon, nanocarbon material, or the like.

[0025] The carbon black may be, for example, furnace process carbon black, channel process carbon black, acetylene process carbon black, thermal process carbon black, etc., and in particular may be furnace process conductive carbon black.

[0026] Nanocarbon materials are a concept that encompasses carbon nanotubes, graphene, fullerenes, and the like.

[0027] The conductive support particles in the present invention may be carbon particles. In one embodiment of the present invention, the conductive support particles are carbon black particles. In another embodiment, the conductive support particles are furnace-process conductive carbon black particles.

[0028] When carbon particles are used as the conductive support particles in the present invention, the specific surface area of ​​the carbon particles is 50 m 2 / g or more, 70m 2 / g or more, 100m 2 / g or more, 150m 2 / g or more, 200m 2 / g or more, 400m 2 / g or more, or 600m 2 / g or more, and 2 / g or less, 1,500m 2 / g or less, 1,200m 2 / g or less, 1,000m 2 / g or less, 900m 2 / g or less, 800m 2 / g or less, 700m 2 / g or less, 500m 2 / g or less, 300m 2 / g or less, or 200m 2 / g or less.

[0029] The specific surface area of ​​carbon particles is, in particular, 100m 2 / g or more 1,500m 2 / g or less.

[0030] The specific surface area of ​​the carbon particles is a value measured by the BET method using nitrogen as an adsorbate.

[0031] The particle size of the carbon particles may be 5 nm or more, 10 nm or more, 20 nm or more, 30 nm or more, or 50 nm or more, as the number average primary particle size measured by electron microscope observation, and may be 300 nm or less, 200 nm or less, 100 nm or less, or 50 nm or less.

[0032] The particle size of the carbon particles can be calculated as the number average of the equivalent diameter based on an electron microscope image of the fuel cell electrode catalyst. The "equivalent diameter" refers to the diameter of a perfect circle having an area equal to the projected area of ​​the shape being measured.

[0033] <PtSn alloy particles> In the fuel cell catalyst of the present invention, PtSn alloy particles are supported on the above-mentioned conductive support particles.

[0034] (Ratio of crystalline PtSn alloy) In the PtSn alloy particles contained in the fuel cell electrode catalyst of the present invention, the proportion R(cryst) of crystalline PtSn alloy calculated by the following formula (1) is 0.40% or less: R(cryst)=R(Pt3Sn)+R(PtSn)+R(Pt2Sn3)+R(Pt2Sn) (1) (In formula (1), R(PtSn), R(PtSn), R(PtSn), and R(PtSn) are the proportions (%) of each crystal structure in the PtSn alloy particles, calculated by the following formula, R(Pt3Sn)={I(Pt3Sn) / I(total)}×100 R(PtSn)={I(PtSn) / I(total)}×100 R(Pt2Sn3)={I(Pt2Sn3) / I(total)}×100 R(Pt2Sn)={I(Pt2Sn) / I(total)}×100 I(Pt3Sn) is the peak intensity of the peak based on the Pt3Sn (111) plane observed near 2θ = 31.565° in the XRD data measured for the fuel cell electrode catalyst, I(PtSn) is the peak intensity of the peak due to the PtSn (202) plane observed near 2θ = 62.271°, I(Pt2Sn3) is the peak intensity of the peak based on the Pt2Sn3 (205) plane observed around 2θ = 60.794°, I(Pt2Sn) is the peak intensity of the peak based on the Pt2Sn (220) plane observed around 2θ = 65.421°, I(total) is I(Pt3Sn) + I(PtSn) + I(Pt2Sn3) + I(Pt2Sn) + I(Pt), I(Pt) is the peak intensity of the Pt(111) plane peak observed around 2θ=39.735°.

[0035] By keeping the proportion of crystalline PtSn alloy in the PtSn alloy, R(cryst), at a low level of 0.40% or less, the resulting fuel cell catalyst can exhibit excellent oxygen reduction activity. The reason for this is unclear, but the inventors speculate as follows.

[0036] That is, when the PtSn alloy crystallizes in the catalyst metal particles, it is thought that certain crystal faces are easily exposed. These crystal faces are chemically and thermally stable, but have poor oxygen reduction activity. Therefore, if the proportion of crystalline PtSn alloy in the PtSn alloy is low, the stable crystal faces are less exposed, which is thought to improve the oxygen reduction activity of the fuel cell catalyst.

[0037] However, the present invention is not bound by any particular theory.

[0038] R(cryst) may be 0.35% or less, 0.32% or less, 0.30% or less, 0.28% or less, 0.25% or less, 0.22% or less, 0.20% or less, 0.18% or less, or 0.15% or less, or the PtSn alloy particles may be completely free of crystalline PtSn alloy, with the value of R(cryst) being 0 (zero).

[0039] Among crystalline PtSn alloys, the Pt3Sn structure and the Pt2Sn3 structure are particularly easy to form and are therefore thought to contribute significantly to the inhibition of the oxygen reduction activity of fuel cell catalysts. For this reason, the proportions of these crystalline structures in the PtSn alloy may be low.

[0040] In view of the above, the proportion R(Pt3Sn) of the Pt3Sn structure in the PtSn alloy particles may be 0.15% or less, 0.12% or less, 0.10% or less, 0.08% or less, or 0.05% or less, or the PtSn alloy particles may not contain any Pt3Sn structure at all, and the value of R(Pt3Sn) may be 0 (zero).

[0041] From a similar perspective, the proportion R(Pt2Sn3) of the Pt2Sn3 structure in the PtSn alloy particles may be 0.15% or less, 0.12% or less, 0.10% or less, 0.08% or less, or 0.05% or less, or the PtSn alloy particles may not contain any Pt2Sn3 structure at all, and the value of R(Pt2Sn3) may be 0 (zero).

[0042] XRD measurement for estimating the proportion of each crystal structure in the PtSn alloy particles may be carried out by, for example, the method described in the examples below.

[0043] (Sn content in PtSn alloy particles) Sn is less likely to be eluted than other transition metals such as Co. Therefore, the fuel cell catalyst of the present invention, which uses a PtSn alloy as the catalytic metal particles, can maintain its activity for a long period of time even when used continuously. To effectively achieve this effect, the Sn content in the PtSn alloy particles may be low, as long as the effect of improving catalytic activity due to the addition of Sn can be enjoyed.

[0044] In PtSn alloys, the dissolution of Sn in Pt leads to an increase in oxygen reduction activity due to the supply of electricity from Sn to Pt, and a decrease in oxygen reduction activity due to crystal distortion resulting from the increase in the interatomic distance of Pt. Here, it is believed that the lower the Sn content in PtSn alloy particles, the more dominant the effect of supplying electricity from Sn to Pt becomes, and the more likely it is that the improvement in oxygen reduction activity will be realized.

[0045] From this viewpoint, the Sn content in the PtSn alloy particles may be less than 10.0 atomic %, 9.0 atomic % or less, 8.0 atomic % or less, 7.0 atomic % or less, 5.0 atomic % or less, or 3.0 atomic % or less, based on the total mass of the PtSn alloy particles, or may be 0.5 atomic % or more, 1.0 atomic % or more, 3.0 atomic % or more, or 5.0 atomic % or more.

[0046] The Sn content in the PtSn alloy particles may typically be equal to or greater than 0.5 atomic % and less than 10.0 atomic %.

[0047] (PtSn alloy particle size) The smaller the particle size of the PtSn alloy particles, the higher the specific activity of the resulting fuel cell electrode catalyst tends to be. On the other hand, the larger the particle size of the PtSn alloy particles, the better the retention of specific activity when the fuel cell electrode catalyst is operated for a long period of time. From the viewpoint of balancing these, the particle size of the PtSn alloy particles may be 2.0 nm or more, 2.2 nm or more, 2.4 nm or more, or 2.6 nm or more, and may be 5.0 nm or less, 4.8 nm or less, 4.5 nm or less, 4.3 nm or less, or 4.0 nm or less.

[0048] The particle size of the PtSn alloy particles may typically be 2.0 nm or more and 5.0 nm or less.

[0049] The particle size of the PtSn alloy particles is a value calculated by the Scherrer equation from the peak based on the Pt(220) plane observed around 2θ=67.424° in the XRD data measured for the fuel cell electrode catalyst. The XRD measurement at this time may be performed under the same conditions as the XRD measurement for estimating the proportion of each crystal structure in the PtSn alloy particles, for example, by the method described in the Examples below.

[0050] (Pt loading rate) The Pt loading rate in the fuel cell electrode catalyst of the present invention may be 20 mass% or more, 25 mass% or more, 30 mass% or more, 35 mass% or more, or 40 mass% or more, or 55 mass% or less, 50 mass% or less, 45 mass% or less, or 40 mass% or less, as the ratio of the mass of Pt in the PtSn alloy particles to the total mass of the conductive support particles and the mass of Pt in the PtSn alloy particles.

[0051] The Pt loading rate in the fuel cell electrode catalyst of the present invention may typically be 20 mass % or more and 55 mass % or less.

[0052] (optional ingredient) The fuel cell electrode catalyst of the present invention is constructed by supporting PtSn alloy particles on conductive support particles. However, the fuel cell electrode catalyst of the present invention may contain optional components other than the conductive support particles and PtSn alloy particles. Examples of such optional components include catalytic metal particles other than PtSn alloy particles, conductive particles not supporting PtSn alloy particles, Sn oxides, etc. The fuel cell electrode catalyst of the present invention does not need to contain optional components other than the conductive support particles and PtSn alloy particles.

[0053] (Applications of electrode catalysts for fuel cells) The fuel cell electrode catalyst of the present invention has a low ratio R(cryst) of crystalline PtSn alloy in the PtSn alloy particles and excellent oxygen reduction activity, and is therefore suitable for use as a cathode catalyst in fuel cells.

[0054] Fuel cell electrodes According to another aspect of the invention, a fuel cell electrode is provided.

[0055] The electrode of the fuel cell of the present invention comprises the fuel cell electrode catalyst of the present invention. More specifically, the electrode of the fuel cell of the present invention has a suitable substrate layer and a catalyst layer on the substrate layer, and the catalyst layer comprises the fuel cell electrode catalyst of the present invention.

[0056] The substrate layer may be appropriately selected from those having chemical and mechanical stability that can withstand the fuel cell electrode catalyst and solvent, as well as the heat treatment, pressure treatment, etc. that are preferably performed during electrode formation. Specifically, for example, a sheet of polyimide, polyethylene, polypropylene, polysulfone, polytetrafluoroethylene, etc. may be used.

[0057] The catalyst layer contains the fuel cell electrode catalyst of the present invention, but may also contain an ionomer and other optional components such as a binder. The ionomer may be, for example, NAFION (registered trademark, a sulfonated tetrafluoroethylene (co)polymer).

[0058] As described above, the fuel cell electrode catalyst of the present invention has excellent oxygen reduction activity. Therefore, the fuel cell electrode of the present invention containing such a fuel cell electrode catalyst of the present invention can be suitably used as a fuel cell cathode.

[0059] <<Method for producing an electrode catalyst for a fuel cell>> According to yet another aspect of the present invention, there is provided a method for producing an electrode catalyst for a fuel cell.

[0060] The method for producing an electrode catalyst for a fuel cell of the present invention is the method for producing an electrode catalyst for a fuel cell of the present invention described above, Pt particles are supported on the conductive support particles to obtain Pt-supported conductive support particles (Pt-supported conductive support particle manufacturing step); contacting the Pt-supported conductive support particles with a solution of a Sn precursor to obtain a mixed solution of the Pt-supported conductive support particles and the Sn precursor (mixed solution preparation step); A mixed solution of the Pt-supported conductive support particles and the Sn precursor is placed under alkaline conditions to support Sn particles on the Pt-supported conductive support particles, thereby obtaining Pt-Sn-supported conductive support particles (Pt-Sn-supported conductive support particle manufacturing step); and The Pt-Sn-supported conductive support particles are fired to alloy the Pt particles and the Sn particles on the Pt-supported conductive support particles, thereby obtaining PtSn alloy-supported conductive support particles (alloying step). and When the Pt-supported conductive support particles are brought into contact with the Sn precursor solution, the aqueous suspension of the Pt-supported conductive support particles is mixed with an aqueous solution containing the Sn precursor and an acid. A method for producing an electrode catalyst for a fuel cell.

[0061] The PtSn alloy-supported conductive support particles obtained by the above method may be used as an electrode catalyst for a fuel cell as is, or may be used as an electrode catalyst for a fuel cell after being heated in the presence of nitric acid (nitric acid treatment step).

[0062] <Pt-loaded conductive support particle manufacturing process> In the Pt-supported particle production process, conductive support particles are contacted with a Pt precursor, and then the Pt precursor is reduced to support Pt particles on the conductive support particles, thereby obtaining Pt-supported conductive support particles. This process may be carried out in a suitable solvent.

[0063] The conductive support particles may be appropriately selected depending on the type of conductive support particles contained in the desired fuel cell electrode catalyst, and for example, carbon particles may be used.

[0064] The Pt precursor may be appropriately selected from Pt compounds soluble in the solvents described below, such as PtCl, PtCl, PtBr, PtS, Pt(CN), and PtCl(NH) (dinitrodiammine platinum).

[0065] The ratio of the conductive support particles to the Pt precursor may be appropriately set depending on the desired Pt loading rate of the fuel cell electrode catalyst. According to the studies of the present inventors, when the Pt loading rate in the fuel cell electrode catalyst is within the above-mentioned range, the entire amount of the Pt precursor used is loaded on the conductive support particles.

[0066] As the solvent, water or a mixed solvent of water and a water-soluble organic solvent may be used, and typically water may be used.

[0067] The pH of the reaction solution containing the conductive support particles, the Pt precursor, and the solvent may be appropriately selected depending on the type of Pt precursor used, and may be, for example, acidic. An appropriate pH adjuster may be added to the reaction solution. The pH adjuster may be an inorganic acid or an inorganic base, and specific examples thereof include nitric acid, hydrochloric acid (hydrochloric acid), sodium hydroxide, and potassium hydroxide.

[0068] After the conductive support particles and the Pt precursor are brought into contact in a solvent, a suitable reducing agent is added to the reaction solution to reduce the Pt precursor, thereby supporting Pt particles on the conductive support particles.

[0069] The reducing agent used here may be, for example, ethanol, acetic acid, acetaldehyde, sodium borohydride, hydrazine, etc. The reduction may be carried out at a temperature of 10°C to 100°C for 0.5 hours to 8 hours. When sodium borohydride is used as the reducing agent, the reduction temperature is preferably 10°C to 50°C, and when ethanol, acetic acid, acetaldehyde, or hydrazine is used as the reducing agent, the reduction temperature is preferably 60°C to 100°C.

[0070] In this way, Pt-supported conductive support particles, in which Pt particles are supported on the conductive support particles, are obtained. The obtained Pt-supported conductive support particles may be isolated as necessary and then subjected to the subsequent mixed solution preparation step.

[0071] <Mixed liquid preparation process> Next, in the mixed solution preparation step, the Pt-supported conductive support particles obtained above are brought into contact with a solution of a Sn precursor to obtain a mixed solution of the Pt-supported conductive support particles and the Sn precursor. This step may be performed in an appropriate solvent.

[0072] This step is typically carried out by adding a solution of the Sn precursor to a suspension of Pt-loaded conductive support particles dispersed in a solvent.

[0073] As the solvent for the Pt-loaded conductive support particle suspension, water or a mixed solvent of water and a water-soluble organic solvent may be used, and typically water may be used.

[0074] The Sn precursor may be appropriately selected from Sn compounds soluble in the solvents described below, such as SnCl2, SnCl4, and Sn(SO4).

[0075] The proportion of the Sn precursor used may be appropriately set depending on the Sn content in the PtSn alloy particles in the desired fuel cell electrode catalyst. According to the studies of the present inventors, when the Sn content in the PtSn alloy particles is less than 10 atomic %, the entire amount of the Sn precursor used is supported on the conductive support particles.

[0076] The Sn precursor may be added in the form of a solution containing the Sn precursor and an acid to a suspension in which Pt-supported conductive support particles are dispersed. The acid contained in this solution may be an inorganic acid, specifically, for example, nitric acid, hydrochloric acid, etc. The pH of the solution may be appropriately set depending on the solubility of the Sn precursor used, and may be, for example, an acidic pH of 5.0 or less, 4.0 or less, or 3.0 or less.

[0077] As the solvent for the Sn precursor solution, water or a mixed solvent of water and a water-soluble organic solvent may be used, and typically water may be used.

[0078] After adding the Sn precursor solution to the Pt-loaded conductive support particle suspension, the mixture may be stirred, if necessary, at a temperature of, for example, 0°C or higher and 100°C or lower for, for example, 5 minutes or longer and 2 hours or shorter.

[0079] <Pt-Sn-loaded conductive support particle manufacturing process> In the Pt-Sn-supported conductive support particle manufacturing process, a mixed solution of Pt-supported conductive support particles and a Sn precursor is placed under alkaline conditions to support Sn particles on the Pt-supported conductive support particles, thereby obtaining Pt-Sn-supported conductive support particles.

[0080] This step may be carried out by adding an alkaline solution to the mixture obtained in the mixture preparation step.

[0081] The alkaline compound contained in the alkaline solution to be added may be either an inorganic base or an organic base, and specific examples thereof may include ammonia, sodium hydroxide, potassium hydroxide, hydrazine, triethylamine, etc. As the solvent for the alkaline solution to be added, water or a mixed solvent of water and a water-soluble organic solvent may be used, and typically water may be used.

[0082] The amount of alkaline solution added may be an amount that makes the pH of the reaction solution after addition alkaline, for example, 8.0 or more, 8.5 or more, or 9.0 or more.

[0083] After adding the alkaline solution to the mixed solution, the mixed solution may be stirred, if necessary, at a temperature of, for example, 0° C. or higher and 100° C. or lower for, for example, 10 minutes or longer and 48 hours or shorter.

[0084] In this manner, Pt—Sn-supported conductive support particles are obtained. The obtained Pt—Sn-supported conductive support particles may be isolated and washed as necessary, and then subjected to the subsequent alloying step.

[0085] <Alloying process> In the alloying step, the Pt-Sn-supported conductive support particles are fired to alloy the Pt particles and Sn particles on the Pt-supported conductive support particles, thereby obtaining PtSn alloy-supported conductive support particles.

[0086] The firing temperature may be, for example, 400° C. or more, 500° C. or more, 600° C. or more, or 700° C. or more, and may be, for example, 1,200° C. or less, 1,100° C. or less, 1,000° C. or less, or 900° C. or less. The firing time may be, for example, 10 minutes or more, 20 minutes or more, or 30 minutes or more, and may be, for example, 6 hours or less, 4 hours or less, 3 hours or less, or 2 hours or less.

[0087] The ambient atmosphere during firing may be an inert atmosphere or a reducing atmosphere, and particularly may be an inert atmosphere. Specifically, the alloying step may be carried out in, for example, nitrogen, argon, or the like.

[0088] In this manner, PtSn alloy-supported conductive support particles are obtained, in which a PtSn alloy is supported on the conductive support particles. The obtained PtSn alloy-supported conductive support particles may be used as an electrode catalyst for a fuel cell as is, or may be used as an electrode catalyst for a fuel cell after being subjected to the nitric acid treatment step described below.

[0089] <Nitric acid treatment process> In the optional nitric acid treatment step, the PtSn alloy-loaded conductive support particles are heated in the presence of nitric acid.

[0090] This step may be carried out by dispersing the PtSn alloy-loaded conductive support particles in a nitric acid solution and maintaining the solution at a predetermined temperature for a predetermined period of time.

[0091] The solvent for the nitric acid solution may be water or a mixed solvent of water and a water-soluble organic solvent, typically water. The concentration of the nitric acid solution may be appropriately determined by those skilled in the art.

[0092] The treatment temperature may be, for example, 80° C. or higher, 90° C. or higher, or 95° C. or higher, and may be, for example, 120° C. or lower, 110° C. or lower, or 105° C. or lower. The nitric acid treatment may typically be carried out under reflux using water as a solvent. The treatment time may be, for example, 10 minutes or higher, 30 minutes or higher, or 1 hour or higher, and may be, for example, 12 hours or lower, 6 hours or lower, or 4 hours or lower.

[0093] The PtSn alloy-supported conductive support particles after the nitric acid treatment may be used as an electrode catalyst for a fuel cell after isolation and washing. [Example]

[0094] I. Evaluation of the crystallinity of the electrode catalyst Example 1-1 (1) Preparation of electrode catalyst As the carbon support particles, acetylene black manufactured by Denka Co., Ltd., "OSAB-D" (specific surface area 800 m 2 / g) was used.

[0095] 6.0 g of the heat-treated carbon support particles were dispersed in 480 mL of 0.1 N aqueous nitric acid solution to obtain a carbon support particle dispersion. Dinitrodiammine platinum (II) nitric acid solution was added to the obtained carbon support particle dispersion and stirred for 30 minutes to obtain a C-Pt mixture. The amount of dinitrodiammine platinum (II) nitric acid solution was adjusted so that the mass of Pt, calculated as metallic Pt, was 40 mass% relative to the total mass of metallic Pt and the carbon support particles.

[0096] To the resulting C-Pt mixture, 73.4 g of ethanol was added as a reducing agent, and the mixture was heated under reflux for 2 hours to support Pt on the carbon support particles. The solids were collected by filtration, washed with pure water, and then dried at 80°C for 15 hours to obtain Pt-supported carbon particles (Pt / C).

[0097] 5.0 g of the Pt / C obtained above was dispersed in 270 g of pure water to obtain a Pt / C dispersion. Meanwhile, stannous chloride (SnCl2) was dissolved in 0.5 N hydrochloric acid to prepare a stannous chloride hydrochloric acid solution. The amount of stannous chloride was adjusted so that the amount of Sn was 1.0 atomic % relative to the total amount of Sn and Pt. The entire amount of the obtained stannous chloride solution was added to the Pt / C dispersion and stirred for 30 minutes to obtain a Pt / C-Sn mixed solution.

[0098] A 3.0N aqueous ammonia solution was added to the resulting Pt / C-Sn mixture to adjust the pH to 9.0, and the mixture was stirred overnight at room temperature to further load Sn onto the Pt-loaded carbon particles (Pt / C). The solids were then collected by filtration, washed with pure water, and dried at 80°C for 15 hours to obtain Pt-Sn-loaded carbon particles ((Pt,Sn) / C).

[0099] The obtained (Pt, Sn) / C was fired in an argon atmosphere at 800°C for 60 minutes to alloy Pt and Sn.

[0100] Five grams of the calcined (Pt, Sn) / C was dispersed in a 0.5 N aqueous nitric acid solution, and then heated to reflux at 100°C for 6 hours to perform a nitric acid treatment. The solid content was then recovered by filtration, washed with pure water, and dried at 80°C for 15 hours to prepare the electrode catalyst of Example 1-1.

[0101] (2) Evaluation of the crystalline structure ratio of PtSn alloy The crystalline structure proportion of the PtSn alloy was determined from the peak intensity ratio using the XRD data measured on the electrode catalyst, employing the following peaks for each crystalline structure. Pt3Sn:2θ=31.565°, Pt3Sn(110) plane PtSn:2θ=62.271°, PtSn(202) surface Pt2Sn3:2θ=60.794°, Pt2Sn3(205) plane Pt2Sn:2θ=65.421°, Pt2Sn(220) plane Pt:2θ=39.735°, Pt(111) surface

[0102] The peak intensity I(PtSn) of the PtSn(110) plane was determined using a cubic approximation curve calculated from data at 2θ = 30.0 to 30.4° and 2θ = 35.6 to 36.0° as a baseline. The peak intensity I(PtSn) of the PtSn(202) plane and the peak intensity I(PtSn) of the PtSn(205) plane were both determined using a cubic approximation curve calculated from data at 2θ = 58.5 to 58.8° and 2θ = 63.2 to 63.5° as a baseline. The peak intensity I(PtSn) of the PtSn(()) plane was determined using a cubic approximation curve calculated from data at 2θ = 62.85 to 63.15° and 2θ = 72.85 to 73.15° as a baseline. Furthermore, the maximum value of the peak near 2θ=39.735° was used as the peak intensity I(Pt) of the Pt(111) plane.

[0103] The peak intensity ratio of each crystal structure was calculated using the following formula. Ratio of Pt3Sn R(Pt3Sn) = I(Pt3Sn) / I(total) Ratio of PtSn R(PtSn) = I(PtSn) / I(total) Ratio of Pt2Sn3 R(Pt2Sn3) = I(Pt2Sn3) / I(total) Ratio of Pt2Sn R(Pt2Sn) = I(Pt2Sn) / I(total) I(total)=I(Pt3Sn)+I(PtSn)+I(Pt2Sn3)+I(Pt2Sn)+I(Pt)

[0104] Based on the above results, the proportion R(cryst) of the crystalline PtSn alloy was calculated using the following formula. R(cryst)=R(Pt3Sn)+R(PtSn)+R(Pt2Sn3)+R(Pt2Sn)

[0105] The XRD measurement was carried out under the following conditions. Detector: Rigaku Corporation, horizontal sample type powerful X-ray diffractometer "RINT-TTR III" Tube:CuK α (Wavelength 1.5418Å) Output: 50kV-300mA Measurement angle range (2θ): 20 to 90° Sampling interval: 0.02°

[0106] (3) Evaluation of the average particle size of PtSn particles The average particle size of the PtSn particles was calculated by the Scherrer equation from the peak corresponding to the Pt(220) plane near 2θ=67.5° using the XRD data of the electrode catalyst measured under the above conditions.

[0107] (4) Evaluation of the composition of PtSn particles (Sn content) After thorough drying, the electrode catalyst was ashed in air. This operation burned away the carbon support particles in the electrode catalyst, and Sn became SnO2, which became insoluble in aqua regia. Next, Pt was dissolved from the resulting ashed material using aqua regia to obtain a Pt-containing solution. The amount of Pt ions in the resulting solution was quantified using an inductively coupled plasma (ICP) optical emission spectrometer (Shimadzu Corporation, model "ICPV-8100"), and the mass of Pt in the electrode catalyst was calculated. The mass of Pt was then subtracted from the mass of the ashed material to calculate the mass of SnO2, and the resulting value was converted to the mass of metallic Sn. The Pr and Sn loading ratios in the electrode catalyst and the Sn content in the PtSn alloy particles (the atomic ratio (%) of Sn to the total of Sn and Pt) were then calculated from the resulting Sn mass, the Pt mass, and the original mass of the electrode catalyst.

[0108] Examples 1-2 to 1-5 and Comparative Examples 1-1 to 1-4 In "(1) Preparation of electrode catalyst", the amount of stannous chloride solution was varied to adjust the atomic ratio (%) of Sn to the total of Sn and Pt to the ratio (atomic %) shown in Table 1, and the firing conditions of (Pt, Sn) / C were changed as shown in Table 1. Except for this, an electrode catalyst was prepared and evaluated in the same manner as in Example 1. In Comparative Example 1-1, no stannous chloride solution was used in "(1) Preparation of electrode catalyst".

[0109] Comparative Example 1-5 Pt-supported carbon particles (Pt / C) were prepared in the same manner as in Example 1-1, and 5.0 g of the particles were dispersed in 270 g of pure water to obtain a Pt / C dispersion. Meanwhile, stannous chloride (SnCl) was added to water and stirred to prepare a stannous chloride aqueous solution. The amount of stannous chloride was adjusted so that the amount of Sn was 3.0 atomic % relative to the total amount of Sn and Pt. The entire amount of the obtained stannous chloride solution was added to the Pt / C dispersion and stirred for 30 minutes. After stirring, a 3.0 N aqueous ammonia solution was added to adjust the pH of the solution to 8.2, and the solution was stirred for another 30 minutes to obtain a Pt / C-Sn mixed solution.

[0110] Next, the resulting Pt / C-Sn mixed solution was heated to 96°C with stirring to precipitate tin oxide on the Pt / C. The solid content was then collected by filtration, washed with pure water, and then heat-treated at 900°C for 30 minutes in a mixed gas flow consisting of 20% by volume of hydrogen and 80% by volume of nitrogen, to obtain the electrode catalyst of Comparative Example 1-5.

[0111] The obtained electrode catalyst was evaluated in the same manner as in Example 1-1.

[0112] In addition, Comparative Example 1-5 differs from Example 1-1 in that when the Pt-supported carbon particles (Pt / C) and the Sn precursor were brought into contact, the Sn precursor was added to the Pt / C dispersion in the form of a simple aqueous solution rather than as a hydrochloric acid solution.

[0113] Comparative Examples 1-6 to 1-9 In "(1) Preparation of electrode catalyst", the amount of stannous chloride aqueous solution was varied to adjust the amount of Sn relative to the total amount of Sn and Pt to the ratio shown in Table 1. Except for this, electrode catalysts were prepared and evaluated in the same manner as in Comparative Examples 1-5.

[0114] Comparative Example 1-10 (1) Preparation of electrode catalyst Pt-supported carbon particles (Pt / C) were prepared in the same manner as in Example 1-1, and 5.0 g of the particles were dispersed in 270 g of pure water to obtain a Pt / C dispersion. Meanwhile, cobalt nitrate (Co(NO3)2) was dissolved in pure water to prepare a cobalt nitrate aqueous solution. The amount of cobalt nitrate was adjusted so that the amount of Co was 7.2 atomic % relative to the total amount of Co and Pt. The entire amount of the obtained cobalt nitrate aqueous solution was added to the Pt / C dispersion and stirred for 30 minutes. Next, a 3.0 N ammonia aqueous solution was added to adjust the pH of the solution to 9.0, and the mixture was stirred for an additional 30 minutes to obtain a Pt / C-Co mixed solution.

[0115] Sodium borohydride dissolved in pure water was added dropwise to the resulting Pt / C-Co mixed solution, and the mixture was stirred to further support Co on the Pt-supported carbon particles (Pt / C). The solids were then collected by filtration, washed with pure water, and dried at 80°C for 15 hours to obtain Pt-Co-supported carbon particles ((Pt,Co) / C).

[0116] The obtained (Pt, Co) / C was fired in an argon atmosphere at 800°C for 60 minutes to alloy Pt and Co.

[0117] Five grams of the calcined (Pt, Co) / C was dispersed in a 0.5 N aqueous nitric acid solution and then heated to reflux at 100°C for 6 hours for nitric acid treatment. The solid content was then recovered by filtration, washed with pure water, and dried at 80°C for 15 hours to prepare the electrode catalyst of Comparative Example 1-10.

[0118] Note that the nitric acid treatment causes some of the Co to be eluted, so the Co content in the final electrode catalyst is smaller than the value calculated from the amounts of the raw materials charged.

[0119] (2) Evaluation of electrode catalysts The electrocatalyst obtained above was evaluated in the same manner as in Example 1-1. The average particle size of the PtCo particles was calculated by the Scherrer equation from the peak corresponding to the Pt(220) plane near 2θ=67.5° in the XRD data of the electrocatalyst, as in the case of the PtSn particles. The composition of the PtCo particles (Co content) was determined by ICP emission spectroscopy of a solution prepared by dissolving the PtSn particles from the electrocatalyst using aqua regia, and the amount of Pt ions and Co ions in the solution was quantified, and the Co content in the PtCo particles (the atomic ratio (%) of Co to the total of Co and Pt) was calculated, in accordance with the procedure in Example 1-1.

[0120] Comparative Examples 1-11 and 1-12 In "(1) Preparation of electrode catalyst", the amount of cobalt nitrate aqueous solution was varied to adjust the amount of Co relative to the total amount of Co and Pt to the ratio shown in Table 1. Except for this, electrode catalysts were prepared and evaluated in the same manner as in Comparative Examples 1-10.

[0121] Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-3 In "(1) Preparation of electrode catalyst," acetylene black manufactured by Denka Co., Ltd. and "Denka Black Li-435" (average particle size 23 nm, specific surface area 133 m) were used as carbon support particles instead of "OSAB-D." 2 An electrode catalyst was prepared and evaluated in the same manner as in Example 1-1, except that carbon particles (wt. / g, bulk density 0.05 g / mL) that had been heat-treated in air at 520°C for 3 hours were used, and the amount of stannous chloride solution was varied to adjust the amount of Sn relative to the total amount of Sn and Pt to the ratios (atomic %) shown in Table 2. In Comparative Example 2-1, no stannous chloride solution was used in "(1) Preparation of electrode catalyst".

[0122] Comparative Examples 2-4 and 2-5 In "(1) Preparation of electrode catalyst", acetylene black manufactured by Denka Co., Ltd., carbon particles obtained by heat-treating "Denka Black Li-435" in air at 520°C for 3 hours were used instead of "OSAB-D" as the carbon support particles, and the amount of cobalt nitrate aqueous solution was changed so that the ratio of Co to the total amount of Co and Pt was adjusted to be as shown in Table 2. Except for this, electrode catalysts were prepared and evaluated in the same manner as in Comparative Examples 1-10.

[0123] All of the above results are shown in Tables 1 and 2. Also, a graph showing the relationship between the crystalline PtSn alloy ratio R(cryst) and the atomic ratio of Sn for Examples 1-1 to 1-5, Examples 2-1 to 2-5, Comparative Examples 1-2 to 1-9, and Comparative Examples 2-2 and 2-3 relating to PtSn alloy particles is shown in Figure 1.

[0124] [Table 1]

[0125] [Table 2]

[0126] The following can be understood from Tables 1 and 2 and FIG.

[0127] In the comparative example, the electrode catalyst in which the Sn precursor was added to the Pt / C dispersion in the form of a simple aqueous solution when the Pt-supported carbon particles (Pt / C) came into contact with the Sn precursor showed only a small decrease in R(cryst) even when the atomic ratio of Sn decreased to less than 10 atomic %.

[0128] In contrast, it was verified that the R(cryst) of the electrode catalyst of the example, in which the Sn precursor was dissolved in acidic water and added to the Pt / C dispersion, rapidly decreased when the atomic ratio of Sn decreased to less than 10 atomic %.

[0129] II. Evaluation of electrocatalytic performance In the above "(2) Evaluation of the crystalline structure ratio of PtSn alloy," the electrocatalysts of Examples 1-1 to 1-5 and 2-1 to 2-5, in which the crystalline PtSn alloy ratio R(cryst) was 0.40 or less, were evaluated for electrocatalytic performance by the following procedure.

[0130] (1) Manufacturing of a single cell for catalytic activity evaluation The obtained electrode catalyst of Example 1-1 was dispersed in water, and then ethanol was added, followed by the addition of an aqueous dispersion containing Nafion as an ionomer, followed by ultrasonic dispersion to prepare a coating liquid for forming a cathode (air electrode) catalyst layer. The obtained coating liquid for forming a cathode catalyst layer was applied to one side of a Teflon (registered trademark) sheet and then dried to form a cathode catalyst layer on the sheet.

[0131] An anode (hydrogen electrode) catalyst layer forming coating solution was prepared in the same manner as the cathode catalyst layer forming coating solution, except that a catalyst powder in which Pt was supported on Ketzen Black (manufactured by Lion Specialty Chemicals Co., Ltd., product name "Carbon ECP") was used instead of the electrode catalyst in Example 1-1. The amount of Pt supported in the catalyst powder used in this anode catalyst layer was 18 mass % based on the mass of the catalyst powder.

[0132] Teflon sheets bearing the cathode and anode catalyst layers obtained above were laminated on both sides of the polymer electrolyte membrane, with the catalyst layer-forming surfaces facing each other, and then transferred by hot pressing. The Teflon sheets were then peeled off to obtain an MEA in which the cathode catalyst layer, polymer electrolyte membrane, and anode catalyst layer were laminated in this order. Next, a diffusion layer was placed on the surface of each catalyst layer to produce a single cell for evaluating catalytic activity.

[0133] (2) Evaluation of electrochemically effective specific surface area (ECSA) Using an electrochemical measurement system "HZ-5000" manufactured by Hokuto Denko Corporation, the single cell for evaluating catalytic activity manufactured above was subjected to cyclic voltammetry (CV) measurement at a voltage of 0.01 to 1.20 V under conditions of a cell temperature of 90°C and humidity of 90%, while supplying nitrogen to the cathode side at 2.0 L / min and hydrogen to the anode side at 0.5 L / min, and the area C value of the hydrogen desorption wave was calculated. The obtained C value and the Pt coverage (mg-Pt / cm) of the evaluation sample were used. 2 -MEA) and ECSA(m 2 / g-Pt) was calculated.

[0134] (3) Evaluation of specific activity (SA) Using a fuel cell evaluation system manufactured by Toyo Corporation, the single cell for evaluating catalytic activity manufactured above was subjected to a current density of 0.01 to 0.20 A / cm while supplying air to the cathode side at 2.0 L / min and hydrogen to the anode side at 0.5 L / min under an environment of a cell temperature of 90°C and humidity of 90%. 2The voltage value was measured in the range of 0.9 V. The current density at which the voltage was calculated from the obtained data was taken as the catalytic activity. This value was divided by the ECSA obtained above to obtain SA (μA / m 2 -Pt) was calculated.

[0135] (4) Evaluation of power generation performance Using a fuel cell evaluation system manufactured by Toyo Corporation, the single cell for evaluating catalytic activity manufactured above was measured for its current density in the voltage range of 0.1 to 0.95 V, while supplying air to the cathode side at 2.0 L / min and hydrogen to the anode side at 0.5 L / min, in an environment of a cell temperature of 90°C and humidity of 90%. The current density calculated from the obtained data was 0.2 A / cm. 2 The voltage at which this was observed was taken as the power generation performance (V).

[0136] (5) Voltage maintenance rate The single cell for evaluating catalytic activity produced above was subjected to 40,000 cycles of potential scanning in the range of 0.1 to 0.90 V, while supplying nitrogen to the cathode at 1.0 L / min and hydrogen to the anode at 0.25 L / min, in an environment with a cell temperature of 90°C and humidity of 90%. At this time, in measurements at the 20,000th and 40,000th cycles, the current density was 0.2 A / cm. 2 The voltage (V) at which this was observed was determined, and the ratio of this to the power generation performance (V) obtained in "(4) Evaluation of power generation performance" was calculated to obtain the voltage retention rates (%) at the 20,000th cycle and the 40,000th cycle, respectively.

[0137] The above results are shown in Table 3.

[0138] [Table 3]

[0139] The results in Table 2 demonstrate that the electrode catalyst of the present invention exhibits excellent durability even after 40,000 cycles of potential scanning.

Claims

1. An electrode catalyst for a fuel cell, comprising PtSn alloy particles supported on conductive support particles, The ratio R (cryst) of the crystalline PtSn alloy calculated by the following formula (1) is 0.40% or less. Electrode catalyst for fuel cells. R(cryst)=R(Pt ３ Sn)+R(PtSn)+R(Pt ２ Sn ３ )+R(Pt ２ Sn) (1) (In formula (1), R(Pt ３ Sn), R(PtSn), R(Pt ２ Sn ３ ), and R(Pt ２ Sn) are the proportions (%) of each crystal structure in the PtSn alloy particles calculated by the following formula, R(Pt ３ Sn)={I(Pt ３ Sn) / I(total)}×100 R(PtSn)={I(PtSn) / I(total)}×100 R(Pt ２ Sn ３ )={I(Pt ２ Sn ３ ) / I(total)}×100 R(Pt ２ Sn)={I(Pt ２ Sn) / I(total)}×100 I (Pt ３ Sn) is a Pt observed near 2θ=31.565° in the XRD data measured for the fuel cell electrode catalyst. ３ is the peak intensity of the peak based on the Sn(111) plane, I(PtSn) is the peak intensity of the peak based on the PtSn (202) plane observed near 2θ = 62.271°, I (Pt ２ Sn ３ ) is Pt observed around 2θ = 60.794° ２ Sn ３ is the peak intensity of the peak based on the (205) plane, I (Pt ２ Sn) is Pt observed around 2θ = 65.421° ２ is the peak intensity of the peak based on the Sn(220) plane, I(total) is I(Pt ３ Sn)+I(PtSn)+I(Pt ２ Sn ３ ) + I(Pt ２ Sn)+I(Pt), I(Pt) is the peak intensity of the peak based on the Pt (111) plane observed near 2θ = 39.735°.

2. Said R(Pt ３ 2. The fuel cell electrode catalyst according to claim 1, wherein the content of Sn is 0.15% or less.

3. Said R(Pt ２ Sn ３ 2. The fuel cell electrode catalyst according to claim 1, wherein the content of Cr is 0.15% or less.

4. 2. The fuel cell electrode catalyst according to claim 1, wherein the Sn content in the PtSn alloy particles is 0.5 atomic % or more and less than 10.0 atomic %.

5. 2. The fuel cell electrode catalyst according to claim 1, wherein the particle size of the PtSn alloy particles calculated by the Scherrer equation from a peak based on the Pt(220) plane observed around 2θ=67.424° in XRD data measured for the fuel cell electrode catalyst is 2.0 nm or more and 5.0 nm or less.

6. 2. The fuel cell electrode catalyst according to claim 1, wherein the conductive support particles are carbon particles.

7. The specific surface area of ​​the carbon particles is 100 m ２ / g or more 1,500m ２ The fuel cell electrode catalyst according to claim 6, wherein the Mo content is 1 / g or less.

8. 2. The fuel cell electrode catalyst according to claim 1, wherein a ratio of the mass of Pt in the PtSn alloy particles to the total mass of the conductive support particles and the mass of Pt in the PtSn alloy particles is 20 mass% or more and 55 mass% or less.

9. The fuel cell electrode catalyst according to any one of claims 1 to 8, which is a cathode catalyst for a fuel cell.

10. A fuel cell electrode comprising the fuel cell electrode catalyst according to any one of claims 1 to 8.

11. 11. The electrode of claim 10, which is a cathode in a fuel cell.

12. A method for producing the fuel cell electrode catalyst according to any one of claims 1 to 8, comprising: supporting Pt particles on the conductive support particles to obtain Pt-supported conductive support particles; bringing the Pt-supported conductive support particles into contact with a solution of an Sn precursor to obtain a mixed solution of the Pt-supported conductive support particles and the Sn precursor; placing a mixed solution of the Pt-supported conductive support particles and the Sn precursor under alkaline conditions to support Sn particles on the Pt-supported conductive support particles, thereby obtaining Pt-Sn-supported conductive support particles; and The Pt-Sn-supported conductive support particles are fired to alloy the Pt particles and the Sn particles on the Pt-supported conductive support particles, thereby obtaining PtSn alloy-supported conductive support particles. and When the Pt-supported conductive support particles are brought into contact with the Sn precursor solution, the Pt-supported conductive support particles are mixed with a solution containing the Sn precursor and an acid. A method for producing an electrode catalyst for a fuel cell.

13. The method of claim 12, further comprising heating the PtSn alloy-loaded conductive support particles in the presence of nitric acid.

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