JP2008123860A - Metal oxide-carrying carbon and fuel cell electrode employing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide metal oxide-carrying carbon which is highly corrosion-resistant, enables an amount of use of a catalyst to be reduced and can be used for a fuel cell catalyst or the like and to provide a fuel cell electrode of high output and high durability employing it. <P>SOLUTION: The metal oxide-carrying carbon contains carbon particles, amorphous platinum oxide carried by the carbon particles, and metal oxide particles containing cerium carried by the carbon particles. Also, the fuel cell electrode contains the metal oxide-carrying carbon. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a metal oxide-supporting carbon and a fuel cell electrode using the same.

  Conventionally, metal particles, alloy particles, metal oxide particles and the like supported on carrier particles are widely used as various catalysts for deodorizing, antibacterial, purification of automobile exhaust gas, fuel cells, NOx reduction and the like. As the carrier particles of this type of catalyst, metal oxides such as titanium oxide, zirconium oxide, iron oxide, nickel oxide and cobalt oxide, carbon and the like are mainly used. In particular, a catalyst using conductive carbon particles as a carrier is effective as a catalyst for an electrode of a fuel cell.

Among them, platinum and ruthenium alloy particles supported on a carbon carrier, and specific metal oxide particles such as molybdenum oxide and cerium oxide as a cocatalyst are supported on a carbon carrier together with metal platinum fine particles. Is known as an excellent catalyst for fuel cell electrodes. Further, a fuel cell catalyst that can suppress aggregation of platinum particles by supporting platinum particles on corrosion-resistant oxide particles such as cerium oxide and zirconium oxide on a carbon carrier has been proposed. (Patent Document 1). Furthermore, an electrode catalyst for a fuel electrode that can be produced without using hydrogen gas or the like in the production process by supporting both platinum oxide and ruthenium oxide on carbon has been proposed (Patent Document 2).
JP 2004-363056 A Japanese Patent No. 2890486

  However, conventional catalysts in which metal particles, alloy particles, metal oxide particles and the like as described above are supported on carrier particles are still insufficient in corrosion resistance when used as electrode catalysts for fuel cells and the like. There was a problem. For example, in the conventional catalyst for fuel cell electrodes using platinum metal particles, platinum is deteriorated due to CO poisoning of the platinum metal particles in the process of use, or by repeating a heat cycle between a temperature atmosphere of 100 ° C. and normal temperature. There was a problem in that the catalytic ability of the particles was remarkably lowered because the adhesion between the particles and the growth of the particles could not be prevented completely. For this reason, in the conventional fuel cell electrode, it was necessary to use a large amount of catalyst in order to compensate for the decrease in the catalytic performance in anticipation of the decrease in the catalytic performance in advance.

  In addition, even when platinum is used as an oxide, in order to improve its catalytic ability to the same level as that of metal platinum, an expensive noble metal element such as ruthenium oxide must be used repeatedly, and the total catalyst amount There was a problem that increased.

  The present invention solves the above-described problems, and provides a metal oxide-supported carbon that can be used for a catalyst for a fuel cell that has high corrosion resistance and can reduce the amount of the catalyst used, and a fuel cell electrode using the same. Is.

  The metal oxide-supported carbon of the present invention includes carbon particles, amorphous platinum oxide supported on the carbon particles, and metal oxide particles containing cerium supported on the carbon particles. .

  An electrode for a fuel cell according to the present invention includes the metal oxide-supported carbon according to the present invention.

  The present invention provides a metal oxide-supporting carbon that can be used for a battery catalyst or the like that has high corrosion resistance and can reduce the amount of catalyst used, and a high-power and highly durable fuel cell electrode using the same. it can.

(Embodiment 1)
First, the metal oxide-supported carbon of the present invention will be described. The metal oxide-supported carbon of the present invention includes carbon particles, amorphous platinum oxide supported on the carbon particles, and metal oxide particles containing cerium supported on the carbon particles.

  Usually, platinum used for an electrode catalyst is said to exhibit high catalytic ability unless it exists in the state of metal particles. In the present invention, platinum having catalytic ability is used as metal particles or oxide particles. Instead, by supporting the carbon particles in the form of amorphous platinum oxide, and simultaneously supporting the metal oxide particles containing at least cerium (Ce) on the carbon particles, it is possible to prevent the adhesion and growth of the platinum particles. In addition, it is possible to provide an electrode catalyst that has high corrosion resistance and that does not lower the catalytic performance even when the amount of the catalyst used is reduced. Thereby, the usage-amount of platinum which is a valuable resource can be reduced significantly compared with the conventional electrode catalyst.

  That is, platinum oxide can be supported in an amorphous state to provide a more efficient contact with metal oxide particles and carbon particles. As described above, in general, platinum has almost no activity in the form of oxide particles as compared with metal platinum particles. For example, platinum does not exhibit catalytic ability as an electrode catalyst for a polymer electrolyte fuel cell, but is oxidized. By making platinum amorphous, when it is used as an electrode catalyst in an oxide state, the same activity as when metal platinum particles are used can be extracted. At this time, since platinum is in an oxide state, particle coarsening due to adhesion, deterioration due to oxidation, poisoning due to CO, and the like do not occur.

  The metal oxide-supported carbon of the present invention is mainly used as an electrode catalyst. In addition to the electrode catalyst, it functions as a catalyst for hydrogenation, dehydrogenation, and oxidation reactions. Can also be used.

  The amorphous platinum oxide and the metal oxide particles may form a composite. Here, forming a composite means a state in which amorphous platinum oxide and metal oxide particles are in contact with each other or fixed. Even in the case where the composite is formed, part of the amorphous platinum oxide may be present on the carbon particles without contacting or fixing with cerium oxide.

  Examples of the carbon particles include, but are not limited to, carbon black, activated carbon, carbon nanotube, carbon nanohorn, and the like.

  The metal oxide particles containing cerium include zirconium (Zr), iron (Fe), tin (Sn), samarium (Sm), hafnium (Hf), gadolinium (Gd), yttrium (Y), ytterbium (Yb), It may further contain at least one element selected from the group consisting of lanthanum (La), holmium (Ho) and erbium (Er). By including these, if it is used as a catalyst for an electrode, it will give electrical conductivity to the oxide of cerium that has essentially no electrical conductivity, without interfering with electrical conduction between carbon particles. Can expect higher output.

  The particle diameter of the metal oxide particles is preferably 1 nm or more and 20 nm or less, more preferably 1 nm or more and 10 nm or less. Even if the particle diameter of the metal oxide particles is less than 1 nm, it is considered that the characteristics as a catalyst are not greatly affected. However, the metal oxide lattice spacing is usually around 0.5 nm. When the diameter is less than 1 nm, the number of lattice points in the crystal structure is too small, so that stable bonding does not occur and it is difficult to maintain the oxide structure, so that metal oxide particles having a crystal structure are produced. It becomes difficult to do. When the particle diameter of the metal oxide particles exceeds 20 nm, the characteristics as a catalyst are not completely lost, but the performance as a catalyst tends to be lowered because a sufficient specific surface area cannot be obtained. Usually, metal oxide particles are supported on carbon particles as primary particles in a monodispersed state.

  In the present invention, the particle diameter of the metal oxide particles can be determined by measuring the size of particles in a transmission electron microscope (TEM) photograph. However, in a fine particle of less than 20 nm, it is rare to take a polycrystalline structure within one particle, and in most cases, it becomes a single crystal particle. Therefore, the particle diameter of the supported metal oxide particles can be obtained from the average crystallite size obtained from the powder X-ray diffraction spectrum in addition to the method obtained from the TEM photograph. In particular, in the case of fine particles having a particle diameter of several nanometers or less, a measurement error when the particle diameter is visually determined from a TEM photograph or the like is large, and it is preferable to determine from the average crystallite size. However, if coarse particles with a polycrystalline structure are present, the size of the crystallites contained in the coarse particles may be measured, so the particle diameter determined from the average crystallite size It is necessary to confirm whether or not the particle size observed by the TEM is consistent.

  In addition, in the metal oxide-supported carbon of the present invention, since platinum oxide is in an amorphous state, it is difficult to discriminate platinum oxide even when a TEM photograph is taken, and only carbon particles and supported metal oxide particles are observed. Is done. Furthermore, even in structural analysis such as powder X-ray diffraction, the diffraction line of platinum oxide does not appear in the amorphous state. For these reasons, when analyzing the presence of platinum oxide, first, the presence of a substantial amount of platinum element must be confirmed by compositional analysis such as X-ray fluorescence analysis (XRF) or ICP emission spectroscopic analysis. After confirming that any structure derived from platinum does not appear by powder X-ray diffraction (XRD) and has an amorphous structure, X-ray photoelectron spectroscopy (XPS) or X-ray absorption fine structure analysis (XAFS) is used. It is necessary to confirm the oxidation state of platinum.

  The average particle diameter of the carbon particles is preferably 20 nm to 70 nm, and more preferably 30 nm to 50 nm. Even if the average particle size of the carbon particles is less than 20 nm, there is no problem in the catalytic ability of the metal oxide-supported carbon as the final product, but the particle size is small in the synthesis process, so that the aggregation is intense and difficult to disperse uniformly. Therefore, the average particle diameter of the carbon particles is preferably 20 nm or more. Further, when the average particle diameter of the carbon particles exceeds 70 nm, the catalytic ability of the final product metal oxide-supported carbon is not completely lost, but the catalytic ability may be lowered because the specific surface area becomes small. Therefore, the average particle diameter of the carbon particles is preferably 70 nm or less.

  In the present invention, the average particle diameter is determined from the arithmetic average of the particle diameters of 100 particles observed from a transmission electron microscope (TEM) photograph.

  The average particle diameter of the metal oxide-supported carbon of the present invention is 20 nm or more and 90 nm or less when the metal oxide particles having the above particle diameter and the carbon particles having the above average particle diameter are used.

  The supported amount of platinum oxide is preferably 5% by weight or more and 50% by weight or less based on the total weight of platinum oxide and metal oxide particles. Even if it is less than 5% by weight, the catalytic action is not completely lost, but its catalytic ability may be difficult to express, and in order to obtain sufficient output, the total amount of catalyst must be increased, Therefore, it is necessary to increase the electrode film thickness, and the electrode performance is lowered with the increase in film thickness. Even if it exceeds 50% by weight, the action as a catalyst is recognized, but some platinum oxide does not become amorphous but crystallizes and precipitates in the form of particles, and all platinum elements are effectively catalyzed. This is not preferable because it cannot be acted on.

  The total supported amount of the platinum oxide and the metal oxide particles is preferably 5% by weight or more and 50% by weight or less based on the total weight of the metal oxide-supported carbon. If the total supported amount is less than 5% by weight, the amount of platinum oxide decreases, so that its catalytic ability may be difficult to be expressed. If it exceeds 50% by weight, the content of metal oxide increases. There is a possibility that metal oxide particles may overlap or aggregate without being deposited as a single layer on the surface of carbon particles.

  Next, an example of the manufacturing method of the metal oxide carrying carbon of this invention is demonstrated.

  First, an aqueous solution containing platinum ions and cerium ions is prepared. When a metal element other than cerium is included as a metal element constituting the metal oxide particles, ions of metals such as zirconium, iron, tin, samarium, hafnium, gadolinium, yttrium, ytterbium, lanthanum, holmium, erbium, etc. Include in aqueous solution. Moreover, as long as it is an element which can be stably contained in the cerium oxide structure of the final product, metal ions other than the metal ions can be included in the aqueous solution. However, in the case where amorphous platinum oxide and metal oxide particles are simultaneously supported, in order to maximize the function as a catalyst, the aqueous solution preferably contains at least cerium ions and zirconium ions.

  Next, carbon particles such as carbon black are dispersed in the aqueous solution containing the metal ions. At this time, in the aqueous solution, the total supported amount of platinum oxide and metal oxide particles is 5% by weight or more and 50% by weight or less with respect to the total weight of the metal oxide-supported carbon as the final product. Disperse the carbon particles in.

  As the carbon particles, it is preferable to use those subjected to surface treatment in order to increase dispersibility in an aqueous solution. The surface treatment of the carbon particles is performed as follows. That is, carbon particles are dispersed in an aqueous nitric acid solution at about 90 ° C., stirred for 3 to 5 hours and oxidized, and then subjected to hydrothermal treatment in the range of 120 to 200 ° C. Thereafter, the surface-treated carbon particles are obtained by washing with water and filtering. The temperature of the nitric acid aqueous solution in the oxidation treatment may be slightly different as long as it is about 90 ° C. However, when the temperature is 100 ° C., the transpiration of water becomes severe, and therefore it is preferably less than 100 ° C. Hydrothermal treatment is not a problem as long as it is in the range of 120 to 200 ° C., but in order to perform more effective treatment, it is preferable to perform treatment at 150 ° C. or higher for 4 hours or longer.

  After the carbon particles are dispersed in an aqueous solution containing metal ions as described above, a general alkali agent such as sodium hydroxide, potassium hydroxide, or ammonia is added to neutralize the carbon particles to form the surface. After the metal compound is deposited, the precursor fine particles are deposited on the surface of the carbon particles by drying. The atmosphere to be dried is not particularly limited, but drying in air is most convenient and inexpensive because it is preferable.

  Further, the fine particle-supported carbon thus obtained is dried and then subjected to heat treatment. As the heat treatment, it is preferable to perform a heat treatment in air at a temperature of 300 ° C. or lower, or a heat treatment in an inert gas atmosphere such as nitrogen or argon. Under the present circumstances, in the atmosphere where oxygen exists, when it exceeds 300 degreeC, there exists a possibility that the combustion of the carbon particle which is a support | carrier may be unpreferable. Further, in a reducing atmosphere, the adsorbed precursor fine particles do not become oxides and metal platinum may be deposited, which is not appropriate. In particular, when heat treatment is performed at a high temperature in a reducing atmosphere containing hydrogen or the like, alloy particles of platinum and a metal such as cerium may be precipitated. The temperature of the heat treatment in an inert gas atmosphere is preferably in the range of 200 to 1000 ° C.

  By the above production method, metal oxide-supported carbon in which amorphous platinum oxide and metal oxide particles containing at least cerium are supported on carbon particles can be obtained. Note that only the platinum oxide becomes amorphous because the crystallization conditions of the platinum oxide are different from the crystallization conditions of the metal oxide particles containing cerium or the like, and the crystallization conditions of the metal oxide particles containing cerium or the like. It seems that only platinum oxide was formed in an amorphous state by heat treatment or the like.

(Embodiment 2)
Next, an example of the fuel cell electrode of the present invention will be described with reference to the drawings. In this embodiment, a membrane electrode assembly (MEA) that is an electrode for a fuel cell manufactured using the metal oxide-supported carbon of Embodiment 1 will be described.

  FIG. 1 is a schematic cross-sectional view showing an example of a membrane electrode assembly. In FIG. 1, a membrane electrode assembly 10 is disposed outside the air electrode 2, the air electrode 2 disposed on one side in the thickness direction of the solid polymer electrolyte membrane 1, the fuel electrode 3 disposed on the other side, and the air electrode 2. The air electrode gas diffusion layer 4 and the fuel electrode gas diffusion layer 5 disposed outside the fuel electrode 3 are provided.

  Examples of the solid polymer electrolyte membrane 1 include a polyperfluorosulfonic acid resin membrane, specifically “Nafion” (trade name) manufactured by DuPont, “Flemion” (trade name) manufactured by Asahi Glass Co., Ltd., and Asahi Kasei Kogyo. A membrane such as “Aciplex” (trade name) manufactured by the company can be used. For the gas diffusion layers 4 and 5, porous carbon cloth or carbon sheet can be used.

  The manufacturing method of the membrane electrode assembly 10 is not particularly limited, and the following general method can be applied. That is, the metal oxide-supporting carbon of the first embodiment, a polymer material, and, if necessary, a binder or the like are mixed in a solvent having a lower alcohol such as ethanol or propanol as a main component, and a magnetic stirrer, ball mill, or the like. The catalyst paint is prepared by dispersing using a general dispersing device such as an ultrasonic disperser. At this time, the amount of the solvent is adjusted so that the viscosity of the paint is optimized in accordance with the application method. The metal oxide-supported carbon of Embodiment 1 may be used for both the air electrode catalyst coating and the fuel electrode catalyst coating, but may be used for only one of them. For the electrode not using the metal oxide-supported carbon of the first embodiment, a conventionally used catalyst such as platinum-supported carbon particles can be used.

  Next, the air electrode 2 or the fuel electrode 3 is formed by using the obtained catalyst paint, and the following procedures generally include the following three methods (1) to (3). .

  (1) Using the obtained catalyst paint, a polytetrafluoroethylene (PTFE) film, a polyethylene terephthalate (PET) film, a polyimide film, a PTFE-coated polyimide film, a PTFE-coated silicon sheet, a PTFE-coated glass cloth, etc. An electrode film is formed on the releasable substrate by uniformly coating on the releasable substrate and drying. Next, the electrode film is peeled off and cut into a predetermined electrode size. Such an electrode film is produced, and each is used as an air electrode and a fuel electrode. Thereafter, the electrode membrane is bonded to both sides of the solid polymer electrolyte membrane by hot pressing or hot roll pressing, and then gas diffusion layers are arranged on both sides of the air electrode and the fuel electrode, and are integrated by hot pressing. A membrane electrode assembly is produced.

  (2) The obtained catalyst paint is applied to the air electrode gas diffusion layer and the fuel electrode gas diffusion layer, respectively, and dried to form the air electrode and the fuel electrode. At this time, the coating method is a method such as spray coating or screen printing. Next, the polymer electrolyte membrane is sandwiched between the gas diffusion layers on which these electrode membranes are formed and integrated by hot pressing to produce a membrane electrode assembly.

  (3) The obtained catalyst paint is applied to both surfaces of the solid polymer electrolyte membrane by a method such as spray coating and dried to form an air electrode and a fuel electrode. Thereafter, gas diffusion layers are arranged on both sides of the air electrode and the fuel electrode and integrated by hot pressing to produce a membrane electrode assembly.

  In the membrane electrode assembly 10 obtained as described above, a current collector plate (not shown) is provided on each of the air electrode 2 side and the fuel electrode 3 side for electrical connection, and hydrogen is supplied to the fuel electrode 3. Can be operated as a fuel cell by supplying air (oxygen) to the air electrode 2, respectively.

  Metal oxide-supported carbon was produced as follows.

(Example 1)
<CeO ₂ : PtO = 90: 10 (weight ratio) · 40 wt% / carbon>
First, carbon black “Vulcan XC-72” (registered trademark, average particle diameter of 30 nm) manufactured by CABOT, which is carbon particles, was dispersed in a 3 mol / L nitric acid aqueous solution at 90 ° C. and stirred for 4 hours, and then 150 ° C. Was subjected to hydrothermal treatment heated for 4 hours, and then washed with water and filtered to obtain surface-treated carbon particles.

  Next, 2.57 g of cerium chloride heptahydrate and 0.32 g of chloroplatinic acid hexahydrate were dissolved in 300 mL of water to prepare an aqueous solution containing cerium ions and platinum ions. Separately from this, 100 g of an equivalent sodium hydroxide aqueous solution was prepared. After adding 2 g of the surface-treated carbon particles to the aqueous solution containing the cerium ion and platinum ion and dispersing with ultrasonic waves, the sodium hydroxide aqueous solution is dropped over 1 hour with stirring, and cerium and platinum are added. A compound containing was deposited on the surface of the carbon particles. Thereafter, it was washed with water, filtered, and dried at 90 ° C. to obtain carbon particles carrying a precursor compound of cerium and platinum.

  Subsequently, the carbon particles were calcined at 280 ° C. for 1 hour in air, then heat-treated at 600 ° C. in a nitrogen atmosphere, and again heat-treated at 250 ° C. for 1 hour in air. And metal oxide-supported carbon particles were obtained.

The carbon particles thus obtained were subjected to powder X-ray diffraction spectrum measurement. The result is shown in FIG. From FIG. 2, it was confirmed that a clear single-phase peak having a cerium oxide structure appeared in the carbon particles of this example. FIG. 2 also shows the spectrum of the cerium oxide (CeO ₂ ) -supported carbon particles obtained in Comparative Example 1 described later for comparison. The spectrum of this example and the spectrum of Comparative Example 1 almost coincide. From this, it was confirmed that cerium oxide (CeO ₂ ) was supported on the carbon particles of this example. Moreover, although the platinum particles are contained in the carbon particles of this example, the peak representing the platinum oxide structure shown by the bar graph in FIG. 2 does not appear, and the platinum may be in an amorphous state. confirmed. At this time, the average crystallite size of cerium oxide obtained from the half width of the diffraction peak was 6.9 nm. Further, when X-ray photoelectron spectroscopy (XPS) analysis was performed on the carbon particles of this example, the peak of the Pt-4f orbit of the XPS spectrum appeared at about 73 eV as shown in FIG. From this result, it was confirmed that Pt is an oxide that takes a divalent state. As a result of TEM observation, it was confirmed that particles of about 5 to 8 nm were supported on the surface of the carbon particles. From the above, the carbon particles of this example are supported by amorphous platinum oxide and cerium oxide particles on the surface of the carbon particles, and further, the amorphous platinum oxide and cerium oxide particles form a composite. I found out.

Finally, when the composition ratio of the carbon particles of this example was confirmed by fluorescent X-ray analysis, the weight ratio of CeO ₂ and PtO was 90:10, and the total supported amount of CeO ₂ and PtO was carbon It was found to be 40% by weight with respect to the total weight of the particles.

(Example 2)
<CeO ₂ : PtO = 70: 30 (weight ratio) · 40 wt% / carbon>
In the method for producing metal oxide-supported carbon particles of Example 1, 2.01 g of cerium chloride heptahydrate and 0.98 g of chloroplatinic acid hexahydrate are dissolved in 300 mL of water, and contain cerium ions and platinum ions. Metal oxide-supported carbon particles were obtained in the same manner as in Example 1 except that an aqueous solution was prepared.

  The carbon particles thus obtained were subjected to powder X-ray diffraction spectrum measurement in the same manner as in Example 1. As a result, a clear single-phase peak having a cerium oxide structure appeared as in Example 1. It was confirmed that a peak representing a platinum oxide structure did not appear, and it was confirmed that platinum was in some amorphous state. At this time, the average crystallite size of cerium oxide obtained from the half width of the diffraction peak was 10.6 nm. Further, when XPS analysis was performed, it was confirmed that Pt was an oxide having a divalent state as in Example 1. As a result of TEM observation, it was confirmed that particles of about 10 nm were supported on the surface of the carbon particles. From the above, the carbon particles of this example are supported by amorphous platinum oxide and cerium oxide particles on the surface of the carbon particles, and further, the amorphous platinum oxide and cerium oxide particles form a composite. I found out.

Finally, when the composition ratio of the carbon particles of this example was confirmed by fluorescent X-ray analysis, the weight ratio of CeO ₂ and PtO was 70:30, and the total supported amount of CeO ₂ and PtO was carbon. It was found to be 40% by weight with respect to the total weight of the particles.

(Example 3)
<(Ce, Zr) O ₂ : PtO = 90: 10 (weight ratio) · 40 wt% / carbon>
In the method for producing metal oxide-supported carbon particles of Example 1, 2.13 g of cerium chloride heptahydrate, 0.56 g of chlorinated zirconium oxide octahydrate and 0.23 g of chloroplatinic acid hexahydrate were added to 300 mL of water. Metal oxide-supported carbon particles were obtained in the same manner as in Example 1 except that an aqueous solution containing cerium ions, zirconium ions and platinum ions was prepared by dissolution.

  The carbon particles thus obtained were subjected to powder X-ray diffraction spectrum measurement in the same manner as in Example 1. As a result, a clear single-phase peak of a cerium-zirconium oxide solid solution structure appeared. It was confirmed that cerium and zirconium were not separated but formed a solid solution, and no peak representing a platinum oxide structure appeared, and it was confirmed that platinum was in some amorphous state. At this time, the average crystallite size of the oxide particles determined from the half width of the diffraction peak was 12.1 nm. Further, when XPS analysis was performed, it was confirmed that Pt was an oxide having a divalent state as in Example 1. As a result of TEM observation, it was confirmed that particles of about 10 to 15 nm were supported on the surface of the carbon particles. As described above, in the carbon particles of this example, amorphous platinum oxide and metal oxide particles are supported on the surface of the carbon particles, and further, amorphous platinum oxide and metal oxide particles form a composite. I found out that

Finally, when the composition ratio of the carbon particles of this example was confirmed by X-ray fluorescence analysis, the weight ratio of (Ce, Zr) O ₂ and PtO was 90:10, and (Ce, Zr) O _2. It was found that the total supported amount of PtO and PtO was 40% by weight with respect to the total weight of the carbon particles.

Example 4
<(Ce, Zr, La) O ₂ : PtO = 90: 10 (weight ratio) · 40 wt% / carbon>
In the method for producing metal oxide-supporting carbon particles of Example 1, 1.92 g of cerium chloride heptahydrate, 0.51 g of chlorinated zirconium oxide octahydrate, 0.25 g of lanthanum chloride heptahydrate and hexachlorochloroplatinate A metal oxide-supported carbon particle was obtained in the same manner as in Example 1 except that 0.32 g of hydrate was dissolved in 300 mL of water to prepare an aqueous solution containing cerium ion, zirconium ion, lanthanum ion and platinum ion. .

  The carbon particles thus obtained were subjected to powder X-ray diffraction spectrum measurement in the same manner as in Example 1. As in Example 3, a single phase with a clear cerium-zirconium oxide solid solution structure was obtained. It was confirmed that a peak appeared, and a shift in peak position due to substitution of lanthanum was observed compared to the peak position in Example 3. From this, it was found that cerium, zirconium and lanthanum were not separated but formed a solid solution. Furthermore, no peak representing the platinum oxide structure appeared, and it was confirmed that platinum was in some amorphous state. At this time, the average crystallite size of the oxide particles determined from the half width of the diffraction peak was 5.1 nm. Further, when XPS analysis was performed, it was confirmed that Pt was an oxide having a divalent state as in Example 1. As a result of TEM observation, it was confirmed that particles of about 5 nm were supported on the surface of the carbon particles. As described above, in the carbon particles of this example, amorphous platinum oxide and metal oxide particles are supported on the surface of the carbon particles, and further, amorphous platinum oxide and metal oxide particles form a composite. I found out that

Finally, when the composition ratio of the carbon particles of this example was confirmed by fluorescent X-ray analysis, the weight ratio of (Ce, Zr, La) O ₂ and PtO was 90:10, and (Ce, Zr, La) The total supported amount of O ₂ and PtO was found to be 40% by weight with respect to the total weight of the carbon particles.

(Example 5)
<(Ce, Zr, Ho) O ₂ : PtO = 90: 10 (weight ratio) · 40 wt% / carbon>
In the method for producing metal oxide-supported carbon particles of Example 1, 1.92 g of cerium chloride heptahydrate, 0.51 g of zirconium chloride octahydrate, 0.22 g of holmium chloride hexahydrate and hexachlorochloroplatinate A metal oxide-supported carbon particle was obtained in the same manner as in Example 1 except that 0.32 g of hydrate was dissolved in 300 mL of water to prepare an aqueous solution containing cerium ion, zirconium ion, holmium ion and platinum ion. .

  The carbon particles thus obtained were subjected to powder X-ray diffraction spectrum measurement in the same manner as in Example 1. As in Example 3, a single phase with a clear cerium-zirconium oxide solid solution structure was obtained. It was confirmed that a peak appeared, and a shift in peak position due to substitution of holmium was observed as compared with the peak position in Example 3. From this, it was found that cerium, zirconium and holmium formed a solid solution without being separated. Furthermore, no peak representing the platinum oxide structure appeared, and it was confirmed that platinum was in some amorphous state. At this time, the average crystallite size of the oxide particles determined from the half width of the diffraction peak was 7.2 nm. Further, when XPS analysis was performed, it was confirmed that Pt was an oxide having a divalent state as in Example 1. As a result of TEM observation, it was confirmed that particles of about 5 to 10 nm were supported on the surface of the carbon particles. As described above, in the carbon particles of this example, amorphous platinum oxide and metal oxide particles are supported on the surface of the carbon particles, and further, amorphous platinum oxide and metal oxide particles form a composite. I found out that

Finally, when the composition ratio of the carbon particles of this example was confirmed by fluorescent X-ray analysis, the weight ratio of (Ce, Zr, Ho) O ₂ and PtO was 90:10, and (Ce, Zr, It was found that the total supported amount of Ho) O ₂ and PtO was 40% by weight with respect to the total weight of the carbon particles.

(Comparative Example 1)
<CeO ₂ · 30% by weight / carbon>
In the method for producing metal oxide-supported carbon particles of Example 1, only 1.85 g of cerium chloride heptahydrate was dissolved in 300 mL of water without using chloroplatinic acid hexahydrate, and an aqueous solution containing cerium ions was prepared. Except for the preparation, metal oxide-supporting carbon particles were obtained in the same manner as in Example 1.

  The carbon particles thus obtained were subjected to powder X-ray diffraction spectrum measurement in the same manner as in Example 1. The result is shown in FIG. From FIG. 2, it was confirmed that a clear single-phase peak having a cerium oxide structure appeared in the carbon particles of this comparative example. At this time, the average crystallite size of cerium oxide obtained from the half width of the diffraction peak was 7.3 nm. As a result of TEM observation, it was confirmed that particles of about 7 to 8 nm were supported on the surface of the carbon particles.

  Finally, when the composition ratio of the carbon particles of this comparative example was confirmed by fluorescent X-ray analysis, it was found that the amount of cerium oxide supported was 30% by weight with respect to the total weight of the carbon particles.

(Comparative Example 2)
<PtO · 10wt% / carbon>
In the method for producing metal oxide-supported carbon particles of Example 1, only 0.55 g of chloroplatinic acid hexahydrate was dissolved in 300 mL of water without using cerium chloride heptahydrate, and an aqueous solution containing platinum ions was prepared. A carbon particle carrying a platinum compound as a precursor was obtained in the same manner as in Example 1 except that 2 g of “Vulcan XC-72” was added and dispersed in the aqueous solution without subjecting to surface treatment. It was. Next, the carbon particles were heat-treated at 270 ° C. for 1 hour in the air to obtain metal oxide-supported carbon particles.

  The carbon particles thus obtained were subjected to powder X-ray diffraction spectrum measurement in the same manner as in Example 1. As a result, it was confirmed that a broad single-phase peak having a platinum oxide structure appeared. . At this time, the average crystallite size of platinum oxide determined from the half width of the diffraction peak was 3.6 nm. As a result of TEM observation, it was confirmed that particles of about 3 nm were carried on the surface of the carbon particles.

  Finally, when the composition ratio of the carbon particles of this comparative example was confirmed by fluorescent X-ray analysis, it was found that the supported amount of platinum oxide was 10% by weight with respect to the total weight of the carbon particles.

(Comparative Example 3)
<CeO ₂ : Pt = 90: 10 (weight ratio) · 40 wt% / carbon>
In the method for producing metal oxide-supported carbon particles of Example 1, 2.57 g of cerium chloride heptahydrate was dissolved in 300 mL of water without using chloroplatinic acid hexahydrate, and an aqueous solution containing cerium ions was prepared. Except that 2.13 g of platinum-supported carbon particles (platinum supported amount 6.2 wt%, average particle diameter of platinum particles 5 nm) in which platinum particles were previously supported on carbon particles was added and dispersed in the aqueous solution. In the same manner as in Example 1, platinum-carrying carbon particles carrying a precursor cerium compound were obtained. Next, this carbon particle was heat-treated at 550 ° C. for 1 hour in a nitrogen atmosphere to obtain metal oxide-supported carbon particles.

  The carbon particles thus obtained were subjected to powder X-ray diffraction spectrum measurement in the same manner as in Example 1. As a result, it was confirmed that the peak of the cerium oxide structure and the peak of platinum metal appeared. It was. At this time, the average crystallite sizes of cerium oxide and metal platinum obtained from the half width of the diffraction peak were 11.8 nm and 5.6 nm, respectively. As a result of TEM observation, it was confirmed that about 10 nm of cerium oxide particles and about 5 nm of platinum metal particles were supported on the surface of the carbon particles.

Finally, when the composition ratio of the carbon particles of this comparative example was confirmed by fluorescent X-ray analysis, the weight ratio of CeO ₂ and Pt was 90:10, and the total supported amount of CeO ₂ and Pt was carbon It was found to be 40% by weight with respect to the total weight of the particles.

  Next, in order to evaluate the catalytic properties of the metal oxide-supported carbon particles obtained in Examples 1 to 5 and Comparative Examples 1 to 3, membrane electrode assemblies (MEA) for fuel cells were prepared and used. The output characteristics of the fuel cell were investigated. When the metal oxide-supported carbon particles as described above are used for the electrodes constituting the membrane electrode assembly, the oxide composition of the metal oxide-supported carbon particles (carbon The composition of the metal oxide supported on the particles is different. Therefore, in order to perform uniform evaluation, an electrode film using metal oxide-supported carbon particles was used for the fuel electrode, and a standard electrode film shown below was used for the air electrode.

<Production of metal oxide-supported carbon particle electrode film>
1 part by weight of the metal oxide-supported carbon particles of Examples 1 to 5 and Comparative Examples 1 to 3 is “Nafion” (manufactured by Aldrich) which is a 5% by weight solution of polyperfluorosulfonic acid resin. Product name, EW = 1000) 9.72 parts by weight and polyperfluorosulfonic acid resin 20% by weight “Nafion” (trade name) 2.52 parts by weight from DuPont and water The mixture was added to 1 part by weight, and the mixture was stirred well so as to be uniformly dispersed to prepare a catalyst paint. Next, this catalyst coating was applied onto a PTFE film so that the platinum loading was 0.03 mg / cm ² and dried, and then peeled off to obtain a metal oxide-supporting carbon particle electrode film.

<Preparation of standard electrode film>
A catalyst coating material was prepared in the same manner as described above using a platinum-supporting carbon “10E50E” (trade name) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. supporting 50% by weight of platinum. After coating and drying so as to be 5 mg / cm ² , it was peeled off to obtain a standard electrode film.

<Preparation of membrane electrode assembly>
As the solid polymer electrolyte membrane, a polyperfluorosulfonic acid resin membrane “Nafion 112” (trade name) manufactured by DuPont was cut into a predetermined size and used. The metal oxide-supported carbon particle electrode film prepared above and the standard electrode film are superposed on both surfaces of this solid polymer electrolyte membrane, and hot pressing is performed at a temperature of 160 ° C. and a pressure of 4.4 MPa, and these are joined. did. Next, a carbon non-woven fabric “TGP-H-120” (trade name) manufactured by Toray Industries, Inc., which has been subjected to water repellent treatment in advance, is bonded to both surfaces of the solid polymer electrolyte membrane on which the electrode membrane is formed by hot pressing, and a membrane electrode A joined body was produced.

<Evaluation of output characteristics>
Using the membrane electrode assembly obtained as described above, the maximum output density (mW / cm ² ) was measured as the output characteristics of the fuel cell. In the measurement, the measurement system including the membrane electrode assembly is held at 60 ° C., 60 ° C. humidified / heated hydrogen gas is supplied to the fuel electrode side, and 60 ° C. humidified / heated is supplied to the air electrode side. The measurement was performed with the supplied air supplied. The results are shown in Table 1. Table 1 also shows the composition and particle size (supported particle size) of the metal oxide particles.

  As is clear from Table 1, the fuel cells using the metal oxide-supported carbon particles of Examples 1 to 5 showed a decrease in the maximum output density despite using the carbon particles supporting platinum oxide. I can't understand. This is because, in the metal oxide-supported carbon particles of Examples 1 to 5, platinum oxide is amorphous and forms a complex with metal oxide particles containing at least cerium, so that the catalytic ability is sufficiently exerted. It seems that it was done.

  On the other hand, in Comparative Example 1 in which only cerium oxide particles are supported without supporting platinum oxide, the characteristics as an electrode hardly appear, and it can be seen that only cerium oxide particles have no catalytic ability. Further, even in Comparative Example 2 in which only platinum oxide particles are supported, the characteristics as an electrode do not endure the use, and as conventionally considered, there is almost no catalytic ability in the state of mere platinum oxide particles. I understand.

<Evaluation of oxidation resistance>
In order to evaluate the resistance of metal oxide-carrying carbon particles to oxidation in air, the metal oxide-carrying carbon particles of Example 5 and Comparative Example 3 were used as those having typical compositions, and these airs. Changes in physical properties were measured. In the measurement, each carbon particle was previously oxidized in air at 150 ° C. for 48 hours.

  About each metal oxide carrying | support carbon particle after the said oxidation process, when powder X-ray-diffraction spectrum measurement was performed and the crystal structure was investigated, the cerium oxide structure appeared in the metal oxide carrying | support carbon particle of Example 5, and before a process There was no change compared with. On the other hand, the metal oxide-supported carbon particles of Comparative Example 3 had two phases of “cerium oxide structure + metal platinum structure” before the treatment, but after the oxidation treatment, “cerium oxide structure + metal platinum structure + platinum oxide ( Three phases of “PtO)” were observed.

  Furthermore, when TEM observation was performed for each particle, it was observed that about 7 to 8 nm of particles were supported on the carbon particles in the metal oxide-supported carbon particles of Example 5, compared with before the treatment. There was almost no change in the particle size. On the other hand, in the metal oxide-supported carbon particles of Comparative Example 3, it was observed that about 10 nm oxide particles and about 8-9 nm platinum particles were supported on the carbon particles, and about 5 nm platinum particles before treatment. It was observed that the particle size was increased compared to.

Next, using each metal oxide-supported carbon particle after the oxidation treatment, a membrane / electrode assembly was prepared in the same manner as described above, and the output characteristics were evaluated. As a result, when the metal oxide-supported carbon particles of Example 5 were used, the maximum output density was 179 mW / cm ² , and in Comparative Example 3, it was 91 mW / cm ² . Table 2 shows the results of the above oxidation resistance evaluation and output characteristic evaluation.

  As is apparent from Table 2, after the oxidation in the air, the metal oxide-supported carbon particles of Example 5 have almost no change in the crystal structure and the supported particle diameter, whereas the metal of Comparative Example 3 It can be seen that in the oxide-supported carbon particles, the crystal structure changes from “metal platinum” to “metal platinum + platinum oxide”, and the supported particle diameter increases. For this reason, the output of the fuel cell using the metal oxide-supported carbon particles of Example 5 is less decreased, whereas the output of the fuel cell using the metal oxide-supported carbon particles of Comparative Example 3 is significantly reduced. It seems to have done.

  As described above, the metal oxide-supported carbon of the present invention in which platinum element is platinum oxide in an amorphous state and is supported on carbon together with metal oxide particles having a cerium oxide structure is an electrode of a solid polymer fuel cell. It can be seen that the catalyst is useful as a catalyst. In addition, amorphous platinum oxide cannot be deteriorated due to further oxidation, and since there is no metal bond between platinum and platinum, deterioration due to coarsening of particles due to adhesion cannot occur. The metal oxide-supported carbon of the invention can prevent deterioration of the catalyst, increase durability, and reduce the amount of catalyst used.

  As described above, the metal oxide-supported carbon of the present invention can exhibit excellent catalytic ability as an electrode catalyst, and can provide a high-power fuel cell electrode using the same.

It is a schematic cross section which shows an example of the membrane electrode assembly which is an electrode for fuel cells of this invention. FIG. 3 is a graph showing powder X-ray diffraction spectra of the metal oxide-carrying carbon particles of Example 1 and the metal oxide-carrying carbon particles of Comparative Example 1. FIG. 4 is a diagram showing XPS measurement results of Pt-4f orbits in the metal oxide-supported carbon particles of Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Air electrode 3 Fuel electrode 4 Gas diffusion layer for air electrodes 5 Gas diffusion layer for fuel electrodes 10 Membrane electrode assembly (MEA)

Claims (8)

  A metal oxide-supported carbon comprising carbon particles, amorphous platinum oxide supported on the carbon particles, and metal oxide particles containing cerium supported on the carbon particles.   The metal oxide-supported carbon according to claim 1, wherein the amorphous platinum oxide and the metal oxide particles form a composite.   3. The metal according to claim 1, wherein the metal oxide particles further include at least one element selected from the group consisting of zirconium, iron, tin, samarium, hafnium, gadolinium, yttrium, ytterbium, lanthanum, holmium, and erbium. Oxide-supported carbon.   The metal oxide-supported carbon according to any one of claims 1 to 3, wherein a particle diameter of the metal oxide particles is 1 nm or more and 20 nm or less, and an average particle diameter of the carbon particles is 20 nm or more and 70 nm or less. .   The metal oxide-supporting carbon according to any one of claims 1 to 4, wherein an average particle size of the metal oxide-supporting carbon is 20 nm or more and 90 nm or less.   The metal oxidation according to any one of claims 1 to 5, wherein the supported amount of the platinum oxide is 5 wt% or more and 50 wt% or less with respect to a total weight of the platinum oxide and the metal oxide particles. Material-supporting carbon.   The total supported amount of the platinum oxide and the metal oxide particles is 5% by weight or more and 50% by weight or less based on the total weight of the metal oxide supported carbon. The metal oxide-carrying carbon described in 1.   A fuel cell electrode comprising the metal oxide-supporting carbon according to any one of claims 1 to 7.

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