JP2008181696A - Catalyst for fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide catalyst of high activity as one for a solid polymer fuel cell, and its manufacturing method and a membrane electrode assembly using it. <P>SOLUTION: The catalyst for a fuel cell has metal oxide fine particles and platinum system metal catalyst fine particles carried by a carbon carrier, with a mean particle diameter of the metal oxide fine particles measured by an X-ray diffraction method of 20 nm or less. The manufacturing method of the catalyst for a fuel cell having the carbon carrier carry metal oxide and platinum system metal catalyst fine particles comprises a process 1 of having the carbon carrier carry a metal compound to be metal oxide by calcining and calcine it at 300°C or less and at a temperature at which the metal compound turns to be metal oxide, and a process 2 of having the carrier thus obtained in the process 1 carry platinum system catalyst fine particles. The membrane electrode assembly has the above catalyst contained at least in either of the electrode catalyst layers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell catalyst in which a metal oxide and platinum-based metal catalyst fine particles are supported on a carbon support.

  In recent years, solid polymer fuel cells have been improved in performance, and their development has been accelerated with the expectation that they will be applied to power sources for electric vehicles, household cogeneration, portable devices and the like. However, for full-scale practical application, further efficiency improvement, downsizing, cost reduction, and reliability improvement are required. In particular, as a catalyst for oxygen reduction used for the air electrode, most power generation systems are platinum catalysts and platinum alloy catalysts (hereinafter referred to as platinum-based metal catalysts) having the highest activity and excellent durability in any application. It is used for. However, platinum is a scarce resource with limited reserves, and for the full-scale commercialization of fuel cells, further improvement in activity and reduction in the amount of platinum-based metal catalysts are required.

  The above platinum-based catalyst is usually in an electrically conductive and high specific surface area carbon black, and the electrode catalyst layer is thinned to ensure gas diffusibility. Many of the rates. Accordingly, it has been reported that the catalyst metal fine particles are likely to aggregate under a high temperature environment, and that the carrier itself is oxidatively deteriorated by radicals generated due to the reaction on the catalyst layer particularly under low humidification. Furthermore, in the case of automobiles, hydrogen in the battery is purged with air when the fuel cell is stopped, and it has been reported that the catalyst deteriorates drastically if the start and stop are repeated frequently, and improving the durability of the catalyst is also a major issue. ing. Regarding the oxidation of the carrier, it has been reported that the catalyst fine particles themselves exhibit a catalytic action, and measures for improving the oxidation resistance of the carrier are required.

  Non-Patent Documents 1 to 3 show that the corrosion of the carbon support is a major cause of the performance deterioration of the polymer electrolyte fuel cell at a high potential. The relationship between Pt and carrier deterioration is also mentioned. Non-Patent Document 4 discusses a model relating to oxygen generation and carbon deterioration on the cathode side that occurs due to frequent start and stop in a fuel cell for an automobile in a polymer electrolyte fuel cell. Non-Patent Document 5 shows a comparison between carbon black as a carrier and carbon nanofibers, and it is reported that the former has a greater deterioration of the Pt catalyst than the latter.

M.M. Roen, C.I. H. Paik, T .; D. Jarvi, Electrochem. Solid-State Lett. 7, A19 (2004). J. et al. P. Meyers and R.M. M.M. Darling, J.M. of the Electrochem. Soc. , 153, A1432 (2006). Z. Siroma, K.M. Ishii, K .; Yasuda, Y. et al. Miyazaki, M .; Inaba, A.M. Tasaka, Electrochem. Commun. , 7, 1153 (2005). D. A. Stevens, M.M. T.A. Hicks, G. M.M. Haugen and J.H. R. Dahn, J. et al. of the Electrochem. Soc. , 152, A2309 (2005). Y. Shao, G .; Yin, Y. Gao, and P.M. Shi, J. et al. of the Electrochem. Soc. , 153, A1093 (2006).

  The present invention has been made in view of the above-described conventional technology, and the stability of the catalyst can be improved even when a carrier having a remarkably high activity and a low crystallinity is used, compared to a platinum catalyst supported on a conventional carbon carrier. The purpose is to provide a technology that can ensure safety.

  As a result of intensive studies, the present inventors have supported metal oxides on a carbon support, and further supported platinum-based metal catalyst fine particles, so that even if a carbon support having a high activity and a high specific surface area is used, the present invention is stable. The inventors have found that characteristics can be obtained, and have reached the present invention.

  The present invention relates to a fuel cell catalyst in which metal oxide and platinum-based metal catalyst fine particles are supported on a carbon support, a production method thereof, and a membrane electrode assembly using the fuel cell catalyst.

  A catalyst for fuel cells in which metal oxide fine particles and platinum-based metal catalyst fine particles are supported on a carbon support, wherein the average particle diameter of the metal oxide fine particles measured by X-ray diffraction method is 20 nm or less. Fuel cell catalyst.

  A method for producing a fuel cell catalyst comprising a carbon support carrying a metal oxide and platinum-based metal catalyst fine particles, the method comprising:

        Step 1: A step of supporting a metal compound that becomes a metal oxide by firing on a carbon support and firing at a temperature of 300 ° C. or less and at which the metal compound becomes a metal oxide.

        Step 2: A step of supporting platinum-based metal catalyst fine particles on the support obtained in Step 1 above.

  A polymer electrolyte fuel cell comprising: an electrolyte membrane; an electrode catalyst layer including an electrolyte and a catalyst provided on both surfaces of the electrolyte membrane; and a gas diffusion layer provided outside each of the electrode catalyst layers. A membrane electrode assembly for a polymer electrolyte fuel cell, wherein the catalyst contained in at least one of the electrode catalyst layers is the fuel cell catalyst.

  The catalyst of the present invention is a catalyst that has a significantly higher activity than conventional catalysts and has high catalyst stability even when a carrier having a low crystallinity is used, and is a catalyst that can be used for fuel cells for automobiles and the like. is there.

  The fuel cell catalyst of the present invention is a fuel cell catalyst in which fine particles of a metal oxide such as zirconium oxide are supported on a carbon carrier such as carbon black, and further, platinum-based metal catalyst fine particles such as a platinum catalyst are supported. Moreover, the average particle diameter obtained by measuring the particle diameter of the metal oxide fine particles supported on the carbon support by an X-ray diffraction method is 20 nm or less.

  The average particle diameter of the metal oxide fine particles in the fuel cell catalyst of the present invention is an average particle diameter obtained by measurement by an X-ray diffraction method. In addition, the average particle diameter of the platinum-based metal catalyst fine particles described later is also an average particle diameter obtained by measurement by this method.

  Measurement of the particle diameter of fine particles by X-ray diffraction (XRD) is known (for example, see “Technology for Fine Particle Engineering Vol. I, Basic Technology”, pages 333 to 335 published by Fuji Techno System Co., Ltd. in October 2001). This is a method of estimating the size of fine particles by analyzing the diffraction line width of a line (line broadening analysis; LBA). The relationship between the particle diameter of the fine particle and the width of the diffraction line is given by the Debye-Scherrer equation, and the average particle diameter (volume average particle diameter) of the fine particle is obtained from the measured value of the width of the diffraction line. This measurement in the present invention was performed as follows.

  RINT-2100 manufactured by Rigaku Corporation was used as the diffraction device. In order to analyze the X-ray diffraction line width, the XRD data analysis software used JADE, and obtained the half-value width using the base line formed by the main peak and the adjacent peak as the base line. The diffraction angle 2θ was scanned in the range of 20 to 60 ° for oxide and 34 to 46 ° for platinum.

In the present invention, the average particle diameter of the metal oxide fine particles by the above measuring method needs to be 20 nm or less. When the average particle diameter of the metal oxide fine particles is larger than 20 nm, the catalytic activity as a fuel cell catalyst tends to be lowered. The metal oxide fine particles in the present invention cannot always clearly grasp the particles by observation with a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM). Further, for example, in a carrier having a large specific surface area (Ketjen Black: specific surface area 800 m ² / g), the metal oxide is supported by 10 to 20% by mass with respect to the total amount of the metal oxide and the carbon carrier. From the fact that the specific surface area after supporting the oxide is 550 m ² / g, it is presumed that very fine oxide particles are thinly formed inside the pores. In such a state where the metal oxide fine particles and the platinum-based metal catalyst fine particles are directly joined or in the vicinity thereof, it is presumed that the catalytic activity is influenced by their interaction.

  The average particle diameter of the metal oxide fine particles obtained by measurement by the X-ray diffraction method is preferably 15 nm or less, more preferably 10 nm or less. Moreover, an average particle diameter is 0.1 nm or more, More preferably, it is 1 nm or more. This is because the catalyst activity tends to improve as the average particle size of the metal oxide is smaller. Although the shape of the metal oxide fine particles is unknown, it is presumed that the shape hardly affects the catalyst activity. Therefore, the shape may be any of spherical, flat plate, rod shape, etc., and is not particularly limited.

  In the fuel cell catalyst of the present invention, the average particle diameter of platinum-based metal catalyst fine particles (obtained by measurement by X-ray diffraction method) is a carbon-supported platinum-based metal catalyst conventionally used as a catalyst for fuel cells. The average particle diameter of the platinum-based metal catalyst fine particles in is used. The average particle diameter is preferably 1 to 10 nm, and particularly preferably 1 to 5 nm.

As the carbon carrier, an electrically conductive material such as carbon black or carbon nanofiber is desirable. The specific surface area of the carbon support is not particularly limited, and a carbon support having a specific surface area of about 10 m ² / g, a specific surface area of 800 m ² / g, or a carbon support having a larger specific surface area can be used. Even if the carbon support has a small specific surface area, it is considered that the specific surface area of the support is expanded by supporting the metal oxide. A carbon support having a specific surface area of 800 m ² / g or a larger carbon support can be used. However, the specific surface area of the carbon support in the case of PEFC catalyst to envisage the loading of catalytic metal than 40-50% is, 5~1000m ² / g are suitable, 200~1000m ² / g are preferred. This is because if the specific surface area is less than 200 m ² / g, it is difficult to make catalyst metal fine particles. This is because, if it exceeds 1000 m ² / g, the oxidation resistance of the carrier tends to decrease basically, although the oxidation resistance imparting effect by the oxide loading is effective. In addition, the specific surface area in this invention means the specific surface area (JISK6217-2: 2001) measured by the nitrogen adsorption method (nitrogen BET method).

  In the fuel cell catalyst of the present invention, the supported amount of the metal oxide fine particles depends on the carbon support used, but the amount of the metal element of the metal oxide relative to the total amount of the metal oxide and the carbon support. 1-50 mass% is preferable. A more preferable loading amount is 5 to 35% by mass. If the amount is less than 1% by mass, the effect of improving the catalytic activity is not sufficient, and if it exceeds 50% by mass, the increase in electric resistance due to the metal oxide cannot be ignored, which is undesirable as an electrode material.

  In the fuel cell catalyst of the present invention, the supported amount of platinum-based metal catalyst fine particles depends on the carbon support used, but is 10% relative to the total amount of carbon support, metal oxide particles, and platinum-based metal catalyst particles. -70 mass% is preferable. A more preferable loading is 25 to 60% by mass. If it is less than 10% by mass, the catalytic activity per unit volume is not sufficient, and if it exceeds 70% by mass, formation of platinum catalyst fine particles becomes difficult, and aggregation and characteristic deterioration of the fine particles easily occur with use. Therefore, it is not desirable as a fuel cell electrode material.

  As the metal oxide in the present invention, a metal oxide containing a metal element selected from Group 4 (Ti, Zr, Hf) and Group 5 (V, Nb, Ta) is preferable, and zirconium oxide is particularly preferable. The metal oxide may be a metal oxide containing two or more metal elements, and in that case, a combination of two or more metal elements selected from Group 4 and Group 5, or a group selected from Group 4 and Group 5 A metal oxide containing two or more metal elements composed of a combination of one or more metal elements and another metal element is preferable. In particular, a metal oxide containing Zr and at least one other metal element is preferable. The metal oxide containing two or more metal elements is preferably a composite metal oxide, but may be a mixture of separate metal oxides.

  Preferred metal oxides in the present invention are metal oxides (zirconium oxide) containing substantially only Zr as a metal element, and metal oxides containing Zr and other metal elements and mainly containing Zr. . The metal element combined with Zr is preferably at least one selected from the group consisting of Ti, Y, Nb, Sn, Ta, W, Mo, V, Al, and Ce. By using such a metal element in combination, it is possible to adjust the acid resistance and isoelectric point of the metal oxide, and the catalytic activity and stability may be improved as compared to the case of Zr alone. is there. However, since the acid resistance of the metal oxide may be lowered if the proportion of other metal elements is too high, the number of Zr atoms in the metal oxide is preferably larger than the number of other metal atoms. In terms of acid resistance, the other metal elements are preferably W, Sn, and Ti. The ratio of the number of Zr atoms to the total metal atoms in zirconium oxide which may contain a metal element other than Zr is preferably 50 to 100%, particularly preferably 70 to 100%. In addition, acid resistance is judged from the amount of eluted metal ions after holding the metal oxide-supported carbon support in 10% sulfuric acid at 80 ° C. for 5 days.

  The particulate platinum-based metal catalyst in the present invention includes a catalyst composed essentially of only platinum, an alloy of two or more metals including platinum, a solid solution, an intermetallic compound, and a part of oxides of component elements. It may be. The platinum-based metal catalyst fine particles are platinum catalyst fine particles substantially consisting of only Pt, or from the group consisting of Cr, Fe, Co, Ni, Ru, Rh, Pd, Re, Ir, Cu, Ag and Au. Metal catalyst fine particles comprising at least one selected from Pt are preferable. The ratio of the number of Pt atoms to the total metal atoms in the platinum-based metal catalyst fine particles is preferably 1 to 100%, particularly preferably 10 to 100%.

  The method for producing a catalyst for a fuel cell according to the present invention includes a step 1 for supporting a metal oxide on a carbon support and a step 2 for supporting platinum-based metal catalyst fine particles on a carbon support on which the metal oxide is supported. . Step 1 is a step in which a metal compound that becomes a metal oxide by firing is supported on a carbon support and is fired at a temperature of 300 ° C. or less and at which the metal compound becomes a metal oxide. Step 2 is a step of supporting the platinum-based metal catalyst fine particles on the carrier obtained in Step 1 above.

  In step 1, first, a metal compound that becomes a metal oxide by firing is supported on a carbon support. The metal compound that becomes a metal oxide by firing may be any metal compound that has the property of easily becoming an oxide at a relatively low temperature. For example, metal alkoxide, metal nitrate, metal oxynitrate, metal hydroxide, and the like. It can be used suitably. Particularly preferred metal compounds are metal alkoxides and metal oxynitrates. A metal compound that can be converted into a metal oxide at a firing temperature of 300 ° C. or lower is used. If the temperature at which the metal oxide is formed is too high, the particle size of the generated metal oxide tends to increase, and if a metal oxide having a large particle size is present, the catalytic activity tends to decrease. The metal compound is preferably a compound that is easily dissolved in a solvent such as water or an organic solvent.

  Examples of the zirconium compound as the metal compound in the present invention include zirconium nitrates such as zirconium oxynitrate, zirconium ethoxide (same as tetraethoxyzirconium), zirconium alkoxides such as zirconium-n-propoxide, zirconium-n-butoxyzirconium, and the like. Is preferred. Titanium compounds such as titanium ethoxide (same as tetraethoxy titanium), titanium alkoxides such as titanium-i-propoxide, titanium-n-butoxy, titanium chelate compounds such as di-i-propoxybis (ethylacetoacetate) titanium Are preferable. As another metal compound, a metal alkoxide is preferable.

  A metal compound solution is brought into contact with the carbon support to attach the metal compound to the carbon support, and then the solvent is removed to support the metal compound on the carbon support. In the contact between the metal compound solution and the carbon support, the processing conditions such as contact time and stirring conditions are adjusted so that the metal compound is adsorbed by sufficiently penetrating the solution into the pores of the carbon support. The contact time is preferably 20 hours or longer, and particularly preferably 40 hours or longer. Stirring is preferably as intense as possible. In addition, it is preferable to adjust the pH of the solution in order to stabilize the metal compound in the solution. For example, in the case of an oxynitrate aqueous solution, it is preferable to add nitric acid to make an acidic aqueous solution. In the case of a metal alkoxide aqueous solution or an organic solvent (alcohol or the like) solution, a neutral vicinity is preferable. In order to improve the wettability between the carbon carrier and the solution, it is preferable to add an organic solvent such as alcohol in the case of an aqueous solution.

  After sufficiently bringing the metal compound solution into contact with the carbon support, the solvent is removed and the metal compound is attached to the carbon support. The removal of the solvent is usually performed by filtration separation or evaporation drying. Before removing the solvent, it is preferable to perform a treatment for fixing the metal compound on the surface of the carbon support. For example, when an acidic aqueous solution of oxynitrate is used, a part of the oxynitrate is converted into an oxide by neutralizing the acid with an alkali such as ammonia to make it more alkaline, thereby improving the adhesion to the surface of the carbon support. improves.

  After the metal compound is supported on the carbon support, firing is performed to form a metal oxide on the carbon support. The firing temperature is 300 ° C. or lower, and if the firing temperature is higher than this temperature, metal oxide fine particles having a large average particle diameter are likely to be generated. Although depending on the type of metal compound, the average particle size of the metal oxide produced can be controlled by adjusting the firing temperature. The lower limit of the calcination temperature is not particularly limited as long as the metal compound can be a metal oxide, but if the calcination temperature is too low, a metal oxide containing a large amount of metal hydrate is formed, and the catalytic activity may be lowered. The lower limit of the firing temperature is preferably 200 ° C. A preferable firing temperature is 200 to 260 ° C.

  As described above, the amount of the metal oxide supported on the carbon support is preferably 5 to 50% by mass, particularly preferably 10 to 25% by mass as the amount of the metal element of the metal oxide. The amount of metal oxide supported can be adjusted by the amount of metal compound supported on the carbon support. The amount of the metal compound supported on the carbon support can be adjusted by selecting the metal compound, the concentration of the metal compound solution, the contact time between the carbon support and the metal compound solution, and other metal compound support conditions.

Next, as step 2, a step of supporting platinum-based metal catalyst fine particles on the metal oxide-supporting carbon support obtained in step 1 is performed. As a method for supporting the platinum-based metal catalyst fine particles, a conventionally well-known or known method for producing a carbon carrier supporting platinum-based metal catalyst fine particles can be used. For example, using a solvent-soluble platinum compound, bringing the platinum compound solution into contact with a metal oxide-supporting carbon support to attach the platinum compound to the support, removing the solvent, and then converting the platinum compound to metal platinum Thus, fine particles of metallic platinum are formed on the carrier. The reaction for converting a platinum compound into metallic platinum is usually a reduction reaction, and for example, metal fine particles can be formed by heating in hydrogen-containing nitrogen. In the present invention, when this reduction reaction is carried out at a high temperature, the metal oxide particles may become large. Therefore, this reduction reaction is preferably performed at 300 ° C. or lower. Using other metal compounds together with the platinum compound, metal fine particles such as alloys and solid solutions of platinum and other metals can be similarly formed. As the metal compound, a metal acid, a metal acid salt, a metal complex, or the like can be used. For example, in the case of a platinum compound, chloroplatinic acid, chloroplatinate, dinitrodiammine platinum [Pt (NH ₂ ) ₂ (NO ₂ ) ₂ ] and the like can be used.

  The membrane electrode assembly of the polymer electrolyte fuel cell of the present invention is provided with an electrolyte membrane, an electrode catalyst layer including an electrolyte and a catalyst provided on both surfaces of the electrolyte membrane, and outside each of the electrode catalyst layers. The membrane electrode assembly is characterized in that the catalyst contained in at least one of the electrode catalyst layers is the fuel cell catalyst. Of the two electrode catalyst layers, the electrode catalyst layer containing the fuel cell catalyst of the present invention is preferably at least a cathode (air electrode). In addition, an electrode catalyst layer containing the fuel cell catalyst of the present invention can also be used as the anode.

  The electrolyte of the electrolyte membrane and the electrode catalyst layer is made of a proton conductive resin. Examples of the proton conductive resin include a proton conductive fluororesin and a proton conductive hydrocarbon resin. From the viewpoint of durability, the proton conductive resin is used. Fluorine-based resin is preferable. The proton conductive group of the proton conductive resin is preferably a sulfonic acid group.

The proton conductive fluorine-based resin is preferably a perfluorosulfonic acid resin having a repeating unit having a sulfonic acid group and a repeating unit based on a perfluoroolefin. In particular, a perfluorosulfonic acid resin having a repeating unit represented by the following formula (1) and a repeating unit based on tetrafluoroethylene is preferable.
_{- [CF 2 -CF {(OCF} 2 CFX) m -Op- (CF 2) n-SO 3 H}] - ··· (1)
However, X is a fluorine atom or a trifluoromethyl group, m is an integer of 0 to 3, n is an integer of 1 to 12, and p is 0 or 1.

  Proton conductive hydrocarbon resins include sulfonated polyarylene, sulfonated polybenzoxazole, sulfonated polybenzothiazole, sulfonated polybenzimidazole, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, Sulfonated polyphenylene sulfone, sulfonated polyphenylene oxide, sulfonated polyphenylene sulfoxide, sulfonated polyphenylene sulfide, sulfonated polyphenylene sulfide sulfone, sulfonated polyether ketone, sulfonated polyether ether ketone, sulfonated polyether ketone ketone, sulfonated polyimide, etc. Is mentioned.

  The ion exchange capacity of the proton conductive resin is preferably 0.5 to 2.0 meq / g dry resin, more preferably 0.7 to 1.6 meq / g dry resin. If the ion exchange capacity is 0.5 meq / g dry resin or more, the electric resistance of the solid polymer electrolyte membrane can be sufficiently lowered. If the ion exchange capacity is 2.0 meq / g dry resin or less, the hydrophilicity of the resin is suppressed, and the electrolyte membrane does not dissolve during power generation.

A catalytic amount in the electrode catalyst layer including a fuel cell catalyst and electrolyte of the present invention is preferably 0.02~3mg / cm ² of platinum-based metal content, in particular 0.05 to 0.5 / cm ² preferably . The electrode catalyst layer can be formed by a conventionally known or known method. For example, a slurry containing a predetermined amount of the catalyst for the fuel cell of the present invention, an electrolyte, and a solvent is formed into a sheet to obtain a sheet that can be used as an electrode catalyst layer. This sheet can be formed and integrated on an electrolyte membrane or a gas diffusion layer sheet, and a membrane electrode assembly can be assembled by combining with other members. Moreover, after forming this sheet | seat alone, a membrane electrode assembly can also be assembled by laminating | stacking this sheet | seat on the electrolyte membrane and the sheet | seat for gas diffusion layers.

  The fuel cell catalyst of the present invention is suitable as a catalyst in the electrode catalyst layer of the cathode because of its high activity and good oxidation resistance. However, the catalyst is not limited to the cathode electrode catalyst layer, and can be used as a catalyst in the anode electrode catalyst layer. It can also be used as a catalyst in both the cathode and anode electrode catalyst layers. When the fuel cell catalyst of the present invention is not used as the catalyst in the anode electrode catalyst layer, a conventionally known carbon-supported platinum-based metal catalyst can be used as the anode electrode catalyst. The same applies when the fuel cell catalyst of the present invention is not used as the catalyst in the electrode catalyst layer of the cathode.

  As a material for the gas diffusion layer, a porous carbon material sheet is preferable, and a carbon fiber nonwoven fabric or woven fabric is particularly preferable. As the material of the gas diffusion layer, a material subjected to treatment such as imparting water repellency can also be used.

  The thickness of each layer in the membrane / electrode assembly is not particularly limited, but an electrolyte membrane of 15 to 50 μm, an electrode catalyst layer (one layer) of 5 to 20 μm, and a gas diffusion layer (one layer) of 100 to 350 μm are preferable. The membrane / electrode assembly may have other thin film layers besides these. For example, a water repellent layer can be provided between the electrode catalyst layer and the gas diffusion layer. The total thickness of the membrane electrode assembly including such a thin film layer is preferably 225 to 790 μm.

  A fuel cell is assembled by attaching a fuel supply system member such as a separator and an oxygen supply system member such as air to both sides of the membrane electrode assembly.

  Hereinafter, the present invention will be described with specific embodiments, but is not limited to the embodiments described below. Examples 1 to 10 are examples, and examples 11 to 16 are comparative examples.

  In the following examples, the particle diameters of the metal oxide fine particles and the metal fine particles are average particle diameters measured by the X-ray analysis method (hereinafter referred to as XRD method). The BET specific surface area is a specific surface area measured by a nitrogen adsorption method. The perfluorosulfonic acid resin used in the following examples has a repeating unit represented by the above formula (1) and a repeating unit based on tetrafluoroethylene having an ion exchange capacity of 1.2 meq / g dry resin. It is a copolymer resin.

(Example 1)
6 g of zirconium oxynitrate was dissolved in a solution prepared by mixing 400 cm ³ of pure water and 40 cm ³ of ethanol and adjusting the pH to 2 with nitric acid. Carbon black (Ketjen black: BET specific surface area 800 m ^{2 /} g) 12.6 g is added to this solution, and an ultrasonic disperser is used for 10 minutes to mix zirconium oxynitrate with pure water, nitric acid and ethanol. And dispersed. Thereafter, carbon black (Ketjen Black: BET specific surface area 800 m ² / g) was further added, and the mixture was vigorously stirred for 2 days with a red devil stirrer manufactured by CBC Corporation. Then, after adding an aqueous ammonia solution and stirring for 6 hours, the precipitate was filtered while being sucked by a water pump. The obtained solid was dried and fired at 230 ° C. in air. The obtained zirconium oxide-supported carbon black had a Zr atom support ratio of 9.9% by mass, and a BET specific surface area of 524 m ² / g. To measure the BET specific surface area, SA-9600 manufactured by Horiba Ltd. was used. The particle diameter of zirconium oxide measured by the XRD method was 7 nm. Using the obtained zirconium oxide-supported carbon black as a carrier, dinitrodiammine platinum was supported on this carrier by a conventional method, and then reduced at 200 ° C. The obtained carbon black carrying zirconium oxide and platinum was one that carried 38.1% by mass of platinum with respect to the total amount. The platinum particle diameter measured by the XRD method was 2.5 nm, and the metal surface area by the CO adsorption method was 134 m ² / g.

  The obtained catalyst powder was supported on a rotating electrode, and the oxygen reduction activity was measured in a 0.5 M sulfuric acid solution. Further, the potential of the electrode supporting the catalyst was repeatedly swept 20 times between 0.05 V and 1.2 V with reference to RHE, and the subsequent reduction activity was measured. These measurement results are shown in Table 1.

  A catalyst electrode for a hydrogen electrode was prepared using TEC10E50E (50% platinum-supported carbon catalyst) manufactured by Tanaka Kikinzoku Co., Ltd. and a perfluorosulfonic acid resin solution. On the other hand, the catalyst obtained above and perfluorosulfonic acid resin are mixed and stirred in a mixed solvent of ethanol / water (1/1 by mass ratio), and the solid content (total amount of catalyst and resin) of the resulting liquid is concentrated. Was adjusted to be 10% by mass to prepare a catalyst ink for an air electrode.

After a catalyst layer using these inks is formed on both sides of a perfluorosulfonic acid film (film thickness: 20 microns), the membrane electrode assembly is sandwiched between two gas diffusion layers made of carbon cloth having a thickness of 300 μm. Was set in a single cell having an electrode action area of 25 cm ² , and cell characteristics were measured under normal pressure conditions using hydrogen and air humidified at a cell temperature of 80 ° C. and a dew point of 80 ° C. The results are shown in FIG.

(Example 2)
After adding 3.3 g of zirconium ethoxide to 300 cm ³ of ethanol, 7 g of ketjen black was added and stirred with a magnetic stirrer for 4 hours. Ethanol and an equivalent amount of pure water were added thereto and hydrolyzed to precipitate a precipitate. After filtration, the film was dried at 80 ° C. overnight and then fired at 300 ° C. to prepare zirconium oxide-supported carbon black. The supporting rate of Zr atoms was 10.1% by mass, and the BET specific surface area was 550 m ² / g. Using this as a carrier, a catalyst supporting 41.5% by mass was obtained in the same manner as in Example 1. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 3)
A support was prepared in the same manner as in Example 2 except that a mixture of zirconium ethoxide and titanium ethoxide (molar ratio 8: 2) was used instead of zirconium ethoxide. The total loading of Zr atoms and Ti atoms was 12.1% by mass, and the BET specific surface area was 530 m ² / g. Using this as a carrier, a catalyst supporting 41.5% by mass of platinum was obtained in the same manner as in Example 1. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 4)
A support was prepared in the same manner as in Example 2 except that a mixture of zirconium ethoxide and niobium ethoxide (8: 2 in molar ratio) was used instead of zirconium ethoxide. The total loading of Zr atoms and Nb atoms was 30.2% by mass, and the BET specific surface area was 510 m ² / g. Using this as a carrier, a catalyst supporting 42.5% by mass of platinum was obtained in the same manner as in Example 1. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 5)
A support was prepared in the same manner as in Example 2 except that a mixture of zirconium ethoxide and tantalum ethoxide (8: 2 in molar ratio) was used instead of zirconium ethoxide. The total loading of Zr atoms and Ta atoms was 22.1% by mass, and the BET specific surface area was 490 m ² / g. Using this as a carrier, a catalyst carrying 43.3% by mass of platinum was obtained in the same manner as in Example 1. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 6)
A support was prepared in the same manner as in Example 2 except that a mixture of zirconium ethoxide and tin ethoxide (molar ratio 8: 2) was used instead of zirconium ethoxide. The total loading of Zr atoms and Sn atoms was 18.3% by mass, and the BET specific surface area was 560 m ² / g. Using this as a carrier, a catalyst carrying 42.4% by mass of platinum was obtained in the same manner as in Example 1. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 7)
A support was prepared in the same manner as in Example 2 except that a mixture of zirconium ethoxide and aluminum ethoxide (9: 1 molar ratio) was used instead of zirconium ethoxide. The total loading of Zr and Al atoms was 19.1% by mass, and the BET specific surface area was 570 m ² / g. Using this as a carrier, a catalyst carrying 41.4% by mass of platinum was obtained in the same manner as in Example 1. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 8)
A support was prepared in the same manner as in Example 2 except that a mixture of zirconium ethoxide and cerium ethoxide (9: 1 molar ratio) was used instead of zirconium ethoxide. The total loading of Zr and Ce atoms was 20.1% by mass, and the BET specific surface area was 565 m ² / g. Using this as a carrier, a catalyst carrying 41.4% by mass of platinum was obtained in the same manner as in Example 1. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 9)
A catalyst was prepared in the same manner as in Example 1 except that dinitrodiammine platinum (nitric acid solution) and cobalt chloride were used as the platinum-based metal catalyst raw material. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 10)
A catalyst was prepared in the same manner as in Example 1 except that dinitrodiammine platinum (nitric acid solution) and dinitrodiammine palladium (nitric acid solution) were used as the platinum-based metal catalyst raw material. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 11)
The same carbon black as in Example 1 (Ketjen Black: BET specific surface area 800 m ² / g) was used as a carrier, metal oxide was not supported, and dinitrodiammine platinum (nitric acid solution) was used to form platinum in the same manner as in Example 1. A catalyst supporting 1% by mass was obtained. The platinum particle diameter measured by the XRD method was 2.5 nm, and the specific surface area of platinum by the CO adsorption method was 134 m ² / g. When this catalyst powder was supported on a rotating electrode and the oxygen reduction activity was measured in a sulfuric acid solution, the results shown in Table 1 were obtained.

(Example 12)
IFPC40-II (platinum supported amount: 40% by mass) manufactured by Ishifuku Metal Co., Ltd., which uses ketjen black as a carrier, was supported on a rotating electrode, and the oxygen reduction activity was measured in a sulfuric acid solution. The result was obtained. Using this catalyst, a membrane electrode assembly was prepared in the same manner as in Example 1, and the current-voltage curve was measured. The results are shown in FIG.

(Example 13)
IFPC40-III (platinum supported amount: 40% by mass) manufactured by Ishifuku Metal Co., Ltd. using ketjen black as a carrier was supported on a rotating electrode, and the oxygen reduction activity was measured in a sulfuric acid solution. The result was obtained.

(Example 14)
The same carbon black as in Example 1 (Ketjen Black: BET specific surface area 800 m ² / g) was used as a carrier, and no platinum oxide was supported in the same manner as in Example 9, except that a metal oxide was not supported. When the oxygen reduction activity was measured in a sulfuric acid solution supported on a rotating electrode, the results shown in Table 1 were obtained.

(Example 15)
The same carbon black as in Example 1 (Ketjen black: BET specific surface area 800 m ² / g) was used as a carrier, and no platinum oxide was supported in the same manner as in Example 10 except that a metal oxide was not supported. When the oxygen reduction activity was measured in a sulfuric acid solution supported on a rotating electrode, the results shown in Table 1 were obtained.

(Example 16)
A carrier was prepared in the same manner as in Example 1 except that the zirconium oxynitrate supported on ketjen black was calcined at 320 ° C. The particle size of zirconia was 34 nm. Platinum was supported on this carrier, a catalyst was prepared, and the oxygen reduction activity by the rotating electrode was measured. The results shown in Table 1 were obtained.

An MEA was produced in the same manner as in Example 1 using the above catalyst, and the voltage characteristics were examined. The output voltage becomes lower with respect to Example 1, was 0.74V at 0.1 A / cm ² 0.78 V, at 0.2 A / cm ^2.

  As shown in Table 1, the mass activity obtained as the current value per unit platinum-based metal amount is shown, the catalyst of the present invention has a remarkable activity improvement effect as compared with the catalyst in which platinum is directly supported on carbon black. It was confirmed that Further, it was confirmed that excellent current-voltage characteristics were obtained with respect to the conventional catalysts of Examples 12 and 13.

  The fuel cell catalyst produced from the method for producing a fuel cell catalyst of the present invention has extremely high activity. Therefore, the polymer electrolyte fuel cell comprising the fuel cell catalyst of the present invention has high current-voltage characteristics and can be used for fuel cell automobiles and the like.

The graph which shows the current-voltage characteristic of the membrane electrode assembly in Example 1 and Example 12.

Claims (12)

  A catalyst for fuel cells in which metal oxide fine particles and platinum-based metal catalyst fine particles are supported on a carbon support, wherein the average particle diameter of the metal oxide fine particles measured by X-ray diffraction method is 20 nm or less. Fuel cell catalyst.   2. The fuel cell according to claim 1, wherein the amount of the metal oxide fine particles supported is 1 to 50 mass% with respect to the total amount of the metal oxide and the carbon support as the amount of metal atoms of the metal oxide fine particles. Catalyst.   The metal element in the metal oxide fine particles is composed of Zr, or composed of Zr and at least one selected from the group consisting of Ti, Y, Nb, Sn, Ta, W, Mo, V, Al, and Ce. The catalyst for fuel cells according to claim 1 or 2.   The metal element in the platinum-based metal catalyst fine particles is composed of Pt, or at least one selected from the group consisting of Cr, Fe, Co, Ni, Ru, Rh, Pd, Re, Ir, Cu, Ag, and Au. The catalyst for a fuel cell according to claim 1, comprising Pt and Pt.   The fuel cell catalyst according to any one of claims 1 to 4, wherein the carbon support is carbon black. A method for producing a fuel cell catalyst comprising a carbon support carrying a metal oxide and platinum-based metal catalyst fine particles, the method comprising:
Step 1: A step of supporting a metal compound that becomes a metal oxide by firing on a carbon support and firing at a temperature of 300 ° C. or less and at which the metal compound becomes a metal oxide.
Step 2: A step of supporting platinum-based metal catalyst fine particles on the support obtained in Step 1 above.   The amount of the metal oxide supported is 1 to 50% by mass with respect to the metal oxide-supported carbon support obtained in the step 1 as the amount of metal atoms of the metal oxide. Production method.   The production method according to claim 6 or 7, wherein the metal oxide in the fuel cell catalyst has a fine particle shape having an average particle diameter of 20 nm or less as measured by an X-ray diffraction method.   The metal element in the metal oxide is composed of Zr, or composed of Zr and at least one selected from the group consisting of Ti, Y, Nb, Sn, Ta, W, Mo, V, Al, and Ce. The manufacturing method according to claim 6, 7 or 8.   The metal element in the platinum-based metal catalyst fine particles is composed of Pt, or at least one selected from the group consisting of Cr, Fe, Co, Ni, Ru, Rh, Pd, Re, Ir, Cu, Ag, and Au. The manufacturing method in any one of Claims 6-9 which consists of and Pt.   The production method according to claim 6, wherein the carbon support is carbon black.   A polymer electrolyte fuel cell comprising: an electrolyte membrane; an electrode catalyst layer including an electrolyte and a catalyst provided on both surfaces of the electrolyte membrane; and a gas diffusion layer provided outside each of the electrode catalyst layers. A membrane electrode assembly for a polymer electrolyte fuel cell, wherein the catalyst contained in at least one of the electrode catalyst layers in the membrane electrode assembly is the fuel cell catalyst according to any one of claims 1 to 5. body.

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