Electrode catalyst for hydrogen fuel cell anode

Abstract

To provide an electrocatalyst for a hydrogen fuel cell anode, which enables suppression of generation of hydrogen peroxide in a hydrogen fuel cell generating power using hydrogen as fuel, which can consequently contribute to improvement in long-term durability of the fuel cell.SOLUTION: An electrocatalyst for a hydrogen fuel cell anode is provided in which Pt particles and WO3 particles are carried by a carbon carrier, the WO3 particles include monoclinic crystal structure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrode catalyst for a hydrogen fuel cell. The electrode catalyst of the present invention is an electrode catalyst for use in the anode of a hydrogen fuel cell that generates electricity using hydrogen as fuel. [Background technology]

[0002] Research and development of fuel cells is underway to prevent air pollution, curb greenhouse gas emissions, and meet the demand for alternative energy sources to petroleum. Fuel cells have the advantages of being clean, having a high energy density, and not requiring charging, and are therefore expected to be the next generation energy source.

[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] In a hydrogen fuel cell, for example, a solid ion exchange membrane fuel cell, power is generated by the following electrochemical reactions (1) and (2) occurring at the anode (hydrogen electrode) and cathode (air electrode), respectively: Hydrogen electrode: 2H2 → 4H + +4e - (1) Air electrode: O2+4H + +4e - →2H2O (2)

[0005] However, hydrogen peroxide may be generated as a side reaction. The generated hydrogen peroxide is dissolved in impurities (e.g., iron ions, Fe 2+ When it comes into contact with the electrolyte membrane, it generates hydroxyl radicals (·OH), which have extremely high oxidizing power, and these radicals attack and deteriorate the electrolyte membrane, electrode materials, etc., thereby reducing the durability of the fuel cell.

[0006] In this regard, Patent Document 1 proposes adding an oxide catalyst selected from, for example, MnO2, RuO2, ZnO, WO3, MnO2-Al2O3, RuO2-Al2O3, ZnO-Al2O3, and WO3-Al2O3 to the electrolyte membrane or oxidizer electrode (air electrode) of a fuel cell, and explains that this suppresses the generation of hydrogen peroxide. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-106203 Summary of the Invention [Problem to be solved by the invention]

[0008] The technology of Patent Document 1 focuses on the fact that, as a mechanism for generating hydrogen peroxide, in addition to the four-electron reaction shown in the above-mentioned electrochemical reaction (2), a two-electron reaction shown in the following electrochemical reaction (3) occurs at the cathode (air electrode). Air electrode: O2 + 2H + +2e - →H2O2(3)

[0009] However, some of the oxygen supplied to the cathode may permeate the electrolyte membrane (solid ion exchange membrane) and reach the anode. This oxygen that reaches the anode is converted into hydrogen atoms (H ad ) to generate hydrogen peroxide via the following electrochemical reaction (4): Hydrogen electrode: 2H ad +O2→H2O2(4)

[0010] Furthermore, at the air electrode, the four-electron reaction represented by electrochemical reaction (2) is thought to take precedence, with the two-electron reaction represented by electrochemical reaction (3) contributing less. In contrast, oxygen that permeates the electrolyte membrane (solid ion exchange membrane) and reaches the hydrogen electrode is likely to generate hydrogen peroxide through electrochemical reaction (4). Therefore, electrochemical reaction (4) at the hydrogen electrode is thought to play a major role in the generation of hydrogen peroxide in hydrogen fuel cells.

[0011] The present invention was made based on the above considerations, and its object is to provide an electrode catalyst for a hydrogen fuel cell that can suppress the generation of hydrogen peroxide in a hydrogen fuel cell that generates electricity using hydrogen as fuel, thereby contributing to improving the long-term durability of the fuel cell. [Means for solving the problem]

[0012] The present invention is as follows.

[0013] Aspect 1: An electrode catalyst for a hydrogen fuel cell anode, comprising Pt particles and WO particles supported on a carbon support, the WO particles comprise a monoclinic crystal structure; Electrocatalyst for hydrogen fuel cell anodes. Aspect 2: The electrocatalyst according to aspect 1, wherein the ratio of the molar amount of WO3 to the molar amount of Pt (WO3 / Pt) in the electrocatalyst is 0.05 or more and 5.0 or less. Aspect 3: The electrocatalyst according to aspect 2, wherein the ratio of the molar amount of WO3 to the molar amount of Pt (WO3 / Pt) in the electrocatalyst is 0.1 or more and 3.0 or less. Aspect 4: The electrode catalyst according to any one of Aspects 1 to 3, wherein the WO3 particles have an average particle size of 0.1 nm or more and 5.0 nm or less. Aspect 5: The electrode catalyst according to any one of Aspects 1 to 4, wherein the Pt particles have an average particle size of 2.0 nm or more and 10.0 nm or less. Aspect 6: A method for producing the anode electrode catalyst for a hydrogen fuel cell according to any one of Aspects 1 to 5, comprising: Supporting Pt particles on a carbon support to obtain a Pt-supported carbon support; A WO precursor is supported on the Pt-supported carbon support to obtain a pre-calcined catalyst; and The pre-calcined catalyst is calcined in an inert atmosphere at a temperature of more than 400°C and not more than 650°C to convert the WO3 precursor into WO3 particles having a monoclinic crystal structure, thereby obtaining a calcined catalyst. A method for producing an electrode catalyst for a hydrogen fuel cell anode, comprising: Aspect 7: The method according to aspect 6, wherein the pre-calcined catalyst is calcined at a temperature of 450°C or higher and 600°C or lower. Aspect 8: The method according to aspect 6 or 7, further comprising contacting the calcined catalyst with an acid to perform an acid treatment. [Effects of the Invention]

[0014] According to the present invention, there is provided an electrode catalyst for a hydrogen fuel cell anode, which can suppress the generation of hydrogen peroxide in a hydrogen fuel cell that generates electricity using hydrogen as fuel, and can contribute to improving the long-term durability of the fuel cell. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 shows XRD spectra (2θ=52 to 64° range, after subtraction from Comparative Example 1) obtained for the samples of Examples 1 to 4 and Comparative Examples 3 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Electrode catalyst for hydrogen fuel cell anode> The hydrogen fuel cell anode electrode catalyst of the present invention comprises: An electrode catalyst for a hydrogen fuel cell anode, comprising Pt particles and WO particles supported on a carbon support, The WO3 particles contain a monoclinic crystal structure, This is an electrode catalyst for hydrogen fuel cell anodes.

[0017] The inventors discovered that a highly active electrode catalyst for hydrogen fuel cells, which has Pt particles supported on a carbon support, has WO particles with a monoclinic crystal structure arranged in the vicinity of the Pt particles, which are the active species, and that using such an electrode catalyst as an anode reduces the amount of hydrogen peroxide generated, leading to the present invention.

[0018] The mechanism by which the hydrogen fuel cell electrode catalyst of the present invention reduces the amount of hydrogen peroxide generated is not clear, but the present inventors speculate as follows.

[0019] As mentioned above, hydrogen peroxide generation at the anode of a hydrogen fuel cell requires the hydrogen atoms (H ad Therefore, if the amount of hydrogen atoms adsorbed to the Pt particles in the anode can be reduced, the generation of hydrogen peroxide from the anode can be suppressed.

[0020] Here, the WO3 particles have the property of absorbing hydrogen atoms through the following electrochemical reaction (5) near the potential at which the catalytic action of the electrode catalyst at the anode is manifested. WO3+xH + +xe - →H x WO3(5)

[0021] The hydrogen storage capacity of WO3 is particularly pronounced when it includes a monoclinic crystal structure. Therefore, it is presumed that by placing WO3 particles with a monoclinic crystal structure, which has high hydrogen storage capacity, near Pt particles, the amount of hydrogen atoms adsorbed onto the Pt particles is reduced, resulting in a decrease in the amount of hydrogen peroxide generated.

[0022] <Carbon support> The carbon support in the fuel cell electrode catalyst of the present invention may be, for example, carbon black, graphite, carbon fiber, activated carbon, amorphous carbon, nanocarbon material, etc. Graphite may be natural graphite or artificial graphite. Natural graphite includes lump graphite, amorphous graphite, flake graphite, etc. Artificial graphite includes graphitized carbon obtained by graphitizing any carbon material, etc. Nanocarbon materials include carbon nanotubes, graphene, fullerene, etc.

[0023] The carbon support in the present invention has a specific surface area of ​​10 m2 or less, as measured by the BET method using nitrogen as an adsorbate. 2 / g or more, 30m 2 / g or more, 50m 2 / g or more, 100m 2 / g or more, 150m 2 / g or more, or 200m 2 / g or more, and 2 / g or less, 800m 2 / g or less, 600m 2 / g or less, 500m 2 / g or less, or 400m 2 / g or less.

[0024] The particle size of the carbon support may be 10 nm or more, 20 nm or more, 50 nm or more, 100 nm or more, or 300 nm or more, as the number-average primary particle size measured by electron microscope observation, and may be 800 nm or less, 600 nm or less, 500 nm or less, or 400 nm or less.

[0025] The particle size of the carbon support 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 the same perimeter as the perimeter of the object being measured.

[0026] <Pt particles> In the hydrogen fuel cell electrode catalyst of the present invention, Pt particles are supported on a carbon support together with WO3 particles, which will be described later.

[0027] The average particle size of the Pt particles may be 20.0 nm or less, 15.0 nm or less, 10.0 nm or less, 8.0 nm or less, 5.0 nm or less, or 4.0 nm or less, or may be 0.5 nm or more, 1.0 nm or more, 1.5 nm or more, or 2.0 nm or more. Pt particles with an average particle size of 5.0 nm or less have the advantage of a high ECSA (Electrochemically Active Surface Area). Pt particles with an average particle size of 0.5 nm or more have the advantage of excellent ECSA retention during long-term operation of a hydrogen fuel cell. These advantages are particularly advantageous when the hydrogen fuel cell electrode catalyst of the present invention is used in the anode (hydrogen electrode).

[0028] Those skilled in the art use terms such as "electrochemically active surface area" and "effective Pt reaction area" as technical terms in Japanese that correspond to the above ECSA.

[0029] The average particle size of the Pt particles may typically be, for example, 2.0 nm or more and 10.0 nm or less.

[0030] The average particle size of the Pt particles in the electrode catalyst for hydrogen fuel cells of the present invention can be calculated by the Scherrer equation from the line width of the diffraction peak in powder XRD measurement of the electrode catalyst for hydrogen fuel cells. The average particle size of the Pt particles may be calculated by the Scherrer equation from the line width of the diffraction peak of the Pt (220) plane in powder XRD measurement of the electrode catalyst for hydrogen fuel cells.

[0031] The amount of Pt particles supported in the hydrogen fuel cell electrode catalyst of the present invention may be 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more, or 50% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less, as a percentage of the total mass of the hydrogen fuel cell electrode catalyst. A Pt particle support amount of 5% by mass or more ensures sufficiently high catalytic activity. Furthermore, a Pt particle support amount of 50% by mass or less can prevent aggregation of the Pt particles, resulting in excellent long-term catalytic activity.

[0032] The hydrogen fuel cell electrode catalyst of the present invention may have a metal other than Pt supported on a carbon support together with Pt particles and WO particles (described below). The metal other than Pt may be, for example, one or more metals selected from the group consisting of Ti, Cr, Mn, Fe, Co, Ni, Cu, Ga, Zr, Hf, Ir, Pd, Os, and Rh.

[0033] Metals other than Pt may form metal particles separate from Pt particles and be supported on the carbon support, or may form an alloy with Pt particles and be supported on the carbon support as Pt alloy particles.

[0034] The hydrogen fuel cell electrode catalyst of the present invention may contain, in addition to Pt particles and WO particles described below, particles of a metal other than Pt selected from the above, in a range such that the mass ratio of the metal other than Pt to the total mass of Pt and the metal other than Pt is 5 mass% or less, 3 mass% or less, 1 mass% or less, or 0.5 mass% or less.

[0035] The hydrogen fuel cell electrode catalyst of the present invention may contain ruthenium (Ru), but in that case, it is preferable that Ru does not form an alloy with the Pt particles. If the Pt particles form an alloy with Ru, there is a concern that the catalytic activity and durability will decrease. The hydrogen fuel cell electrode catalyst of the present invention may not substantially contain Ru.

[0036] Here, the phrase "substantially does not contain Ru" for the electrode catalyst for hydrogen fuel cells of the present invention means that the mass ratio of Ru to the total mass of Pt and Ru is 3 mass% or less, 1 mass% or less, 0.5 mass% or less, 0.3 mass% or less, or 0.1 mass% or less, or that the electrode catalyst for hydrogen fuel cells does not contain Ru at all.

[0037] When the Pt particles are Pt alloy particles in which Pt is alloyed with other metals, the average particle size of the Pt alloy particles may be calculated by small-angle X-ray scattering or transmission electron microscopy (TEM).

[0038] <WO3 particles> The hydrogen fuel cell electrode catalyst of the present invention comprises WO3 particles supported on a carbon support. The WO3 particles contained in the hydrogen fuel cell electrode catalyst of the present invention have a monoclinic crystal structure.

[0039] The concept that WO3 particles contain a monoclinic crystal structure encompasses not only cases where the entire WO3 particle is made up of monoclinic crystals, but also cases where the WO3 particles are a mixture of monoclinic crystals and one or more types selected from crystals of other crystal systems and amorphous crystals.

[0040] The fact that the WO3 particles contain a monoclinic crystal structure can be confirmed by X-ray diffraction (XRD) measurement of the hydrogen fuel cell electrode catalyst. This XRD measurement may be performed, for example, by the following method.

[0041] XRD measurements are performed, for example, in the range of 2θ = 10 to 90°, on a hydrogen fuel cell electrocatalyst containing WO particles and a comparative electrocatalyst with the same composition but without WO particles. Next, to eliminate peaks derived from components other than WO particles from the XRD spectrum of the hydrogen fuel cell electrocatalyst containing WO particles and to smooth the baseline as much as possible, the difference between the XRD spectrum of the hydrogen fuel cell electrocatalyst containing WO particles and the XRD spectrum of the comparative electrocatalyst is extracted. The differential spectrum extracted in this way can be considered to be a spectrum derived solely from the WO particles in the hydrogen fuel cell electrocatalyst.

[0042] The difference spectrum obtained is then examined for the presence of three peaks (55.2°, 60.5°, and 62.3°) specific to monoclinic WO crystals. If these peaks are confirmed in the difference spectrum, the WO particles contained in the hydrogen fuel cell electrode catalyst can be evaluated as having a monoclinic crystal structure.

[0043] Even if the peak specific to monoclinic WO3 is not clearly observed in the obtained difference spectrum, if a line is drawn between the point at 2θ=52.0° and the point at 2θ=63.0° and the spectrum exists above this line, the WO3 particles in the hydrogen fuel cell electrode catalyst can be evaluated as containing a monoclinic crystal structure.

[0044] The average particle size of the WO particles may be, for example, 0.1 nm or more, 0.5 nm or more, 1.0 nm or more, 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, or 3.0 nm or more, from the viewpoint of ensuring that the monoclinic crystal structure in the particles has a significant extent and effectively suppressing the generation of hydrogen peroxide. On the other hand, from the viewpoint of arranging the WO particles having the monoclinic crystal structure in the vicinity of as many Pt particles as possible and effectively suppressing the generation of hydrogen peroxide, the average particle size may be 10.0 nm or less, 8.0 nm or less, 6.0 nm or less, 5.0 nm or less, or 4.5 nm or less.

[0045] The average particle size of the WO3 particles may typically be, for example, 0.1 nm or more and 5.0 nm or less.

[0046] The average particle size of WO3 particles can be calculated by the Scherrer equation from the line width of the single diffraction peak of WO3 in powder XRD measurement of the electrode catalyst for hydrogen fuel cells.

[0047] In the hydrogen fuel cell electrode catalyst of the present invention, the ratio of the molar amount of WO to the molar amount of Pt (WO / Pt) may be 0.05 or more, 0.1 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.8 or more, or 1.0 or more from the viewpoint of effectively suppressing the generation of hydrogen peroxide. On the other hand, from the viewpoint of maintaining catalytic activity, the ratio WO / Pt may be 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, or 2.0 or less.

[0048] In the hydrogen fuel cell electrode catalyst of the present invention, the ratio of the molar amount of WO3 to the molar amount of Pt (WO3 / Pt) may typically be 0.05 or more and 5.0 or less, or 0.10 or more and 3.0 or less.

[0049] <<Method for producing an electrode catalyst for anodes of hydrogen fuel cells>> The anode electrode catalyst for a hydrogen fuel cell of the present invention may be produced by any method as long as it has the above-mentioned configuration. The anode electrode catalyst for a hydrogen fuel cell of the present invention may be produced, for example, by the following method.

[0050] Pt particles are supported on a carbon support to obtain a Pt-supported carbon support (Pt supporting step); A WO precursor is supported on a Pt-supported carbon support to obtain a pre-calcined catalyst (WO precursor supporting step); and The pre-calcined catalyst is calcined in an inert atmosphere at a temperature of more than 400°C and not more than 650°C to convert the WO3 precursor into WO3 particles containing a monoclinic crystal structure, thereby obtaining a calcined catalyst (calcination step). A method comprising:

[0051] The method for producing an electrode catalyst for a hydrogen fuel cell of the present invention comprises the steps of: The method may further include contacting the obtained calcined catalyst with an acid to perform an acid treatment (acid treatment step).

[0052] Each step in the method for producing an electrode catalyst for a hydrogen fuel cell of the present invention will be described below in order.

[0053] <Pt Supporting Step> In the Pt supporting step, Pt particles are supported on the carbon support to obtain a Pt-supported carbon support.

[0054] The Pt particles may be supported on the carbon support by, for example, a method in which a Pt precursor and a carbon support are brought into contact with a reducing agent in a suitable solvent, thereby reducing Pt ions in the Pt precursor to metallic Pt, and depositing the metallic Pt on the carbon support as Pt particles.

[0055] The carbon support used here may be appropriately selected depending on the carbon support in the target hydrogen fuel cell electrode catalyst. For example, a carbon material selected from carbon black, graphite, carbon fiber, activated carbon, amorphous carbon, nanocarbon material, etc. may be used as the carbon support.

[0056] The Pt precursor may be appropriately selected from solvent-soluble Pt compounds, such as PtCl, PtCl, PtBr, PtS, Pt(CN), and PtCl(NH) (dinitrodiammine platinum).

[0057] The solvent may be selected from those capable of dissolving the Pt precursor used. For example, when the Pt precursor is PtCl, hydrochloric acid may be used; when it is PtBr, aqueous hydrobromic acid may be used; when it is PtCl(NH), aqueous nitric acid may be used; and when it is PtCl, PtS, or Pt(CN), water may be used.

[0058] The reducing agent used to reduce the Pt ions in the Pt precursor to metallic Pt 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.

[0059] In this way, a Pt-supported carbon support is obtained in which Pt particles are supported on the carbon support. The obtained Pt-supported carbon support may be recovered from the reaction solution, washed and dried as necessary, and then used in the next step.

[0060] <WO3 precursor supporting step> In the WO3 precursor supporting step, a WO3 precursor is supported on the Pt-supported carbon support obtained in the Pt supporting step to obtain a pre-calcined catalyst. The WO3 precursor supported on the Pt-supported carbon support in this step is a precipitate of a tungsten (W) compound, a chemical species that has not yet been completely oxidized to the state of tungsten oxide (WO3).

[0061] The WO3 precursor loading step may be carried out in a suitable solvent.

[0062] The tungsten (W) compound for precipitating the WO precursor may be appropriately selected from those soluble in a solvent. Examples of W compounds that may be used include sodium tungstate, ammonium tungstate, and tungstic acid. A preferred W compound is one that exists as a stable solution in a solvent at a certain pH but precipitates when the pH is changed. A typical example is sodium tungstate, which exists as a solution in an alkaline aqueous solution but precipitates in an acidic solution.

[0063] The solvent may be selected from those capable of dissolving the W compound to be used. For example, when the W compound is sodium tungstate, water may be used. Here, in order to sufficiently dissolve the W compound in the solvent, an appropriate pH adjuster may be added to the solvent to adjust the pH of the solvent. For example, when the W compound is sodium tungstate, ammonia water may be added as a pH adjuster to the water solvent to adjust the pH of the solution to the alkaline side.

[0064] The WO precursor supporting step may be carried out, for example, by adding an appropriate pH adjuster to a reaction mixture consisting of a solvent containing dispersed Pt-supported carbon support and a dissolved W compound, to adjust the pH of the reaction mixture to a pH at which the W compound precipitates. This operation causes the dissolved W compound to precipitate as a WO precursor and be supported on the Pt-supported carbon support. For example, when the W compound is sodium tungstate, the pH of the reaction mixture can be adjusted to the acidic side by adding an appropriate acid (e.g., nitric acid, hydrochloric acid, etc.) to the alkaline reaction mixture.

[0065] By the above operations, a pre-calcined catalyst is obtained.

[0066] <Firing process> In the calcination step, the pre-calcined catalyst obtained in the WO3 precursor supporting step is calcined in an inert atmosphere at a temperature of more than 400°C and not more than 650°C, and the WO3 precursor supported on the carbon support is converted into WO3 particles having a monoclinic crystal structure, thereby obtaining a calcined catalyst.

[0067] In this calcination step, the calcination atmosphere and calcination temperature are important. Specifically, if the calcination temperature is below 400°C, the conversion from the WO3 precursor to WO3 is insufficient, and there is a concern that the hydrogen atom storage capacity of WO3 will not be fully realized. On the other hand, if the calcination temperature exceeds 650°C, part or all of the WO3 crystal form will become a more stable crystal system (e.g., cubic), and the hydrogen atom storage capacity of WO3 particles containing a monoclinic crystal structure will be impaired. Furthermore, if the calcination temperature is further increased, some of the W in WO3 will alloy with Pt, which will impair the hydrogen atom storage capacity of the WO3 particles and the catalytic activity of the electrode catalyst.

[0068] The temperature at which the pre-calcined catalyst is calcined may be 450°C or higher and 600°C or lower.

[0069] The calcination time in the calcination step may be 10 minutes or more, 20 minutes or more, 30 minutes or more, 40 minutes or more, 1 hour or more, 2 hours or more, or 4 hours or more, from the viewpoint of ensuring the conversion of the WO3 precursor to WO3. On the other hand, even if the calcination time is longer than necessary, the hydrogen atom storage capacity of WO3 will not be improved indefinitely. Therefore, the calcination time may be 24 hours or less, 12 hours or less, 6 hours or less, 4 hours or less, 3 hours or less, or 2 hours or less.

[0070] The ambient atmosphere during the firing step must be an inert atmosphere, preferably an argon atmosphere.

[0071] <Acid treatment process> The calcined catalyst obtained in the calcination step may be used as it is as the electrode catalyst for a hydrogen fuel cell of the present invention, or may be further subjected to an optional acid treatment step.

[0072] In the acid treatment step, the calcined catalyst obtained in the calcination step is brought into contact with an acid to perform an acid treatment. This acid treatment imparts hydrophilicity to the carbon support or improves the hydrophilicity of the carbon support, and is therefore expected to improve catalytic activity.

[0073] The acid treatment step may be carried out by immersing the calcined catalyst in a solution containing an acid, such as an aqueous solution of nitric acid, hydrochloric acid, hydrofluoric acid, or sulfuric acid.

[0074] In the acid treatment step, the temperature of the acid-containing solution may be, for example, 40° C. or more, 50° C. or more, 60° C. or more, 70° C. or more, or 80° C. or more, and may be, for example, 100° C. or less, 95° C. or less, 90° C. or less, 85° C. or less, or 80° C. or less. The time for the acid treatment step may be, for example, 1 hour or more, 2 hours or more, or 4 hours or more, and may be, for example, 24 hours or less, 16 hours or less, 12 hours or less, 8 hours or less, or 6 hours or less.

[0075] The calcined catalyst after the acid treatment step may be recovered from the acid-containing solution, washed and dried as necessary, and then used as the electrode catalyst for a hydrogen fuel cell of the present invention.

[0076] <<Use of electrode catalyst for hydrogen fuel cell anode>> The hydrogen fuel cell anode electrode catalyst of the present invention is suitable as an electrode catalyst contained in a catalyst layer of a hydrogen fuel cell anode. An anode containing the hydrogen fuel cell electrode catalyst of the present invention suppresses the amount of hydrogen peroxide generated, and therefore, a hydrogen fuel cell electrode catalyst containing the anode can maintain high activity for a long period of time.

[0077] The anode of a hydrogen fuel cell may have a suitable substrate layer and a catalyst layer on the substrate layer, the catalyst layer comprising the hydrogen fuel cell electrode catalyst of the present invention.

[0078] The substrate layer may be appropriately selected from those having chemical and mechanical stability that can withstand the hydrogen 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.

[0079] The catalyst layer contains the hydrogen 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 (a sulfonated tetrafluoroethylene (co)polymer).

[0080] The anode containing the hydrogen fuel cell electrode catalyst of the present invention can be suitably applied to an electrode assembly for a hydrogen fuel cell having a structure in which the anode, a solid polymer electrolyte membrane, and a cathode are laminated in this order. The solid polymer electrolyte membrane used here may be, for example, a known proton exchange membrane. The cathode may be any known cathode used in hydrogen fuel cells.

[0081] The above-mentioned hydrogen fuel cell electrode assembly can be suitably applied to a hydrogen fuel cell having the fuel cell electrode assembly, a hydrogen channel arranged on the anode side of the fuel cell electrode assembly, and an air channel or an oxygen channel arranged on the cathode side of the fuel cell electrode assembly. This hydrogen fuel cell may be produced by a known method, except that an electrode containing the hydrogen fuel cell electrode catalyst of the present invention is used as the anode. [Example]

[0082] Example 1 (1) Preparation of electrode catalyst Specific surface area 300m 2 A dispersion was obtained by dispersing 1.13 g of carbon support (carbon black) at 1 / g in 80 mL of pure water. A dinitrodiammine platinum nitrate solution (equivalent to 0.4 g of Pt metal) was added dropwise to the dispersion as a Pt precursor, and the carbon support and Pt precursor were thoroughly mixed in the dispersion. Next, 30 g of ethanol was added as a reducing agent to the dispersion, and the mixture was maintained at 90°C for 2 hours to reduce the Pt precursor and support Pt particles on the carbon support. The solid content was filtered from the resulting dispersion, washed with pure water, and then dried in air at 80°C for 6 hours to obtain a Pt-supported carbon support.

[0083] The entire amount of the obtained Pt-loaded carbon support was dispersed in 80 mL of pure water to obtain a dispersion. Ammonia water was added to the dispersion to adjust the pH to 10. Next, sodium tungstate dihydrate was added as a W compound so that the molar ratio of WO3 to Pt (metal equivalent) was WO3 / Pt = 1.0, and the mixture was thoroughly stirred until the sodium tungstate dihydrate was dissolved.

[0084] After the sodium tungstate dihydrate was dissolved, a 0.1 mol / L aqueous nitric acid solution was slowly added dropwise to the reaction mixture using a pipette to adjust the pH to 2, thereby supporting the WO3 precursor on the Pt-loaded carbon support.

[0085] The solid content in the reaction solution was collected by filtration, washed with pure water, and dried in air at 80°C for 6 hours to obtain a pre-calcined catalyst.

[0086] The resulting pre-calcined catalyst was then calcined at 450° C. for 1 hour in an argon atmosphere to obtain a calcined catalyst.

[0087] The resulting calcined catalyst was immersed in a 0.5N aqueous nitric acid solution and subjected to acid treatment at 80° C. for 6 hours. Thereafter, the solid content was filtered, washed with pure water, and then dried in air at 80° C. for 6 hours to obtain the electrode catalyst of Example 1. The amount of Pt particles supported in this electrode catalyst was 20.0 mass %.

[0088] The obtained electrode catalyst was measured by X-ray diffraction (XRD) and, in accordance with JIS K0131, the average particle size of Pt particles calculated from the peak intensity of the Pt metal alone in the XRD chart was 3.0 nm. The average particle size of WO3 particles calculated from the peak intensity of the WO3 alone in the XRD chart using the same method as for Pt above was 4.0 nm.

[0089] (2) Evaluation of electrode catalysts Ultrapure water and isopropanol were added to the electrode catalyst obtained above, and then Nafion (NAFION, registered trademark, manufactured by DuPont) was added in an amount equal to the mass of the electrode catalyst. The resulting dispersion was subjected to ultrasonic dispersion to obtain an electrode catalyst slurry for application.

[0090] The above electrode catalyst slurry was dropped onto the disk electrode portion of the working electrode of a rotating ring disk electrode device (manufactured by Hokuto Denko Corporation) using a micropipette, and air-dried to obtain an electrode with the electrode catalyst uniformly dispersed therein.

[0091] The electrode catalyst was evaluated using the above electrode as the working electrode, a standard hydrogen electrode (RHE) as the reference electrode, and a 0.1 mol / L aqueous perchloric acid solution as the electrolyte. The specific operating procedures were as follows.

[0092] The electrolyte was subjected to oxygen bubbling to dissolve oxygen to a saturated concentration before being used for evaluation.

[0093] The rotating ring-disk electrode device was operated, and the working electrode was rotated at 1,600 rpm to agitate the electrolyte at an electrolyte temperature of 30°C. A constant potential of 1.2 V (vs. RHE) was applied to the ring electrode while sweeping the potential of the disk electrode to measure the hydrogen peroxide production rate (X H2O2 The results are shown in Table 1.

[0094] Hydrogen peroxide generation rate (X H2O2 The potential was scanned continuously from 0 V (vs. RHE) to 1.0 V in the noble direction, and then from 1.0 V to 0 V in the noble direction. The scanning rate was 10 mV / s in both directions. To calculate the hydrogen peroxide production rate, the current value at 0.07 V (vs. RHE) was used when scanning in the noble direction, which simulates the anode environment of a fuel cell. The measured solution resistance of the electrolyte was used to perform iR compensation.

[0095] Hydrogen peroxide generation rate (X H2O2 ) was calculated according to the following formula in accordance with the method described in J. Electrochem. Soc., 134, 495 (2001). Hydrogen peroxide generation rate X H2O2 =(2I R / N)÷(I D +I R / N) {where, I R is the ring current value, and I D is the disk current value and N is the capture rate.

[0096] The capture rate N is calculated as follows:

[0097] Rotating electrode measurements were performed in an argon atmosphere in an aqueous solution of potassium ferricyanide K3 [Fe(CN)6]. 3- From [Fe(CN)6] 4- in the reduction to |I R / I D The value of | was calculated and used as the capture rate N. R / I D|" is the number I R / I D Represents the absolute value of .

[0098] In addition, the hydrogen peroxide generation rate (X H2O2 ) is shown as a relative value, with the value of Comparative Example 1, in which the electrode catalyst did not contain a tungsten compound, being 1.00.

[0099] The sweep for measuring the electrochemically active specific surface area (ECSA) was performed sequentially from 0 V (vs. RHE) to 1.2 V in the noble direction, and then from 1.2 V to 0 V in the less noble direction. The scan rate was 50 mV / s in both directions. The effective platinum reaction area (ECSA) was calculated from the results of the CV measurement during this sweep.

[0100] Examples 2 to 8 and Comparative Examples 2 to 6 In "(1) Preparation of electrode catalyst", the amounts of the Pt precursor (dinitrodiammine platinum nitrate solution) and W compound (sodium tungstate dihydrate) used were adjusted so that the amount of Pt particles supported was 20.0 mass % and the molar ratio of WO / Pt was as shown in Table 1, and further the calcination temperature was changed as shown in Table 1. Except for this, an electrode catalyst was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0101] Comparative Example 1 A Pt-supported carbon support was obtained in the same manner as in Example 1, except that in "(1) Preparation of electrode catalyst," the amount of carbon support used was 1.60 g. This Pt-supported carbon support was recovered by filtration from the reaction solution, washed with pure water, dried in air at 80°C for 6 hours, and then calcined in an argon atmosphere at 450°C for 1 hour to obtain a calcined catalyst. This calcined catalyst was subjected to acid treatment, pure water washing, and drying in the same manner as in Example 1 to prepare and evaluate an electrode catalyst of Comparative Example 1. The results are shown in Table 1.

[0102] In "(2) Evaluation of electrode catalyst" in each example and comparative example, when the electrode catalyst slurry was dropped onto the disk electrode portion of the working electrode of the rotating ring-disk electrode device, the amount dropped was adjusted so that the amount of Pt obtained on the electrode would be constant.

[0103] <XRD measurement of electrode catalyst (confirmation of monoclinic crystals)> The electrode catalysts obtained in the above Examples and Comparative Examples were each subjected to XRD measurement in the range of 2θ = 10 to 90°. Next, in order to exclude peaks derived from components other than the tungsten compound from the XRD spectrum of the electrode catalyst containing a tungsten compound and to smooth the baseline as much as possible, the differences between the XRD spectra of the samples in all Examples and Comparative Examples 2 to 7 containing a tungsten compound and the XRD spectrum of Comparative Example 1, which did not contain a tungsten compound, were extracted, and this was taken as the spectrum derived only from the tungsten compound in each catalyst.

[0104] The spectrum derived from the obtained tungsten compound alone was then examined for the presence of three peaks (55.2°, 60.5°, and 62.3°) specific to monoclinic crystals of WO3, and samples in which these peaks were confirmed were evaluated as "containing monoclinic crystals."

[0105] The results are also shown in Table 1. Furthermore, the XRD spectra (2θ=52 to 64° range, after subtraction from Comparative Example 1) obtained for the samples of Examples 1 to 4 and Comparative Examples 3 to 5 are shown in Fig. 1 in the order of firing temperature.

[0106] [Table 1]

[0107] The results in Table 1 confirm that the electrocatalysts of Examples 1 to 8, which are configured by supporting monoclinic WO3 together with Pt particles on a carbon support, have a significantly reduced H2O2 generation rate compared to the electrocatalyst of Comparative Example 1, which does not contain a tungsten compound. In particular, it was verified that the electrocatalysts of Examples 1 to 7, which have a molar ratio of WO3 to Pt particles, WO3 / Pt, of 0.05 or more and 4.0 or less, have a significantly reduced H2O2 generation rate and a higher retention rate of the porous Pt reaction area compared to the electrocatalyst of Comparative Example 1.

[0108] In Table 1, the particle size of WO3 is not shown for the electrode catalysts obtained in Comparative Examples 2, 3, 5, and 6 because no WO3 peak was observed in the XRD chart. The reason why no WO3 peak was observed in the XRD chart in these Comparative Examples is presumed to be as follows.

[0109] In Comparative Examples 2 and 3, the calcination temperature was low, which presumably resulted in insufficient conversion of the WO3 precursor to WO3, and thus measurable particulate WO3 was not effectively produced. In Comparative Example 5, the calcination temperature was too high, which presumably resulted in at least some W atoms in the tungsten compound being alloyed with Pt. In Comparative Example 6, the amount of WO3 supported was insufficient, and thus measurable particulate WO3 was not effectively produced.

Claims

1. Pt particles and WO ３ 1. A particle-supported electrocatalyst for a hydrogen fuel cell anode, comprising: The WO ３ the particles comprise a monoclinic crystal structure; Electrocatalyst for hydrogen fuel cell anodes.

2. The ratio of WO to the molar amount of Pt in the electrode catalyst ３ The ratio of the molar amounts of (WO ３ 2. The electrode catalyst according to claim 1, wherein the ratio of Pt to Zn is 0.05 or more and 5.0 or less.

3. The ratio of WO to the molar amount of Pt in the electrode catalyst ３ The ratio of the molar amounts of (WO ３ 3. The electrode catalyst according to claim 2, wherein the ratio of Pt to Zn is 0.1 or more and 3.0 or less.

4. WO ３ 4. The electrode catalyst according to claim 1, wherein the particles have an average particle size of 0.1 nm or more and 5.0 nm or less.

5. 5. The electrode catalyst according to claim 1, wherein the average particle size of the Pt particles is 2.0 nm or more and 10.0 nm or less.

6. A method for producing the electrode catalyst for a hydrogen fuel cell anode according to any one of claims 1 to 5, comprising: Supporting Pt particles on a carbon support to obtain a Pt-supported carbon support; The Pt-supported carbon support was ３ supporting the precursor to obtain a pre-calcined catalyst; and The pre-calcined catalyst is calcined in an inert atmosphere at a temperature of more than 400°C and not more than 650°C, and the WO ３ The precursor was WO containing a monoclinic crystal structure. ３ Convert into particles to obtain catalyst after calcination A method for producing an electrode catalyst for a hydrogen fuel cell anode, comprising:

7. The method according to claim 6, wherein the pre-calcined catalyst is calcined at a temperature of 450°C or higher and 600°C or lower.

8. 8. The method of claim 6 or 7, further comprising contacting the calcined catalyst with an acid to perform an acid treatment.

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