JP2008004286A - Perovskite type oxide particulate, perovskite type oxide carrying particle, catalyst material, catalyst material for oxygen reduction, catalyst material for fuel cell, and electrode for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide catalyst for an electrode using none other than metal oxide particles capable of being used as a substitute of platinum-carrying carbon particles or metal platinum particles with a possibility of greatly reducing a volume of use of platinum. <P>SOLUTION: The transition metal oxide particulates having a perovskite structure expressed in a general formula of ABO<SB>3</SB>as a main phase is structured with a lattice constant satisfying a conditional expression of: 1.402<2b/(a+c)<1.422. Here, in the conditional expression, a and c denote a length of each minor axis of perovskite type crystal lattices, and b denotes a length of a major axis. Further, in the general formula, A denotes one or more elements selected from lanthanum, strontium, cerium, calcium, yttrium, erbium, praseodymium, neodymium, samarium, europium, silicon, magnesium, barium, niobium, lead, bismuth, and antimony, and B denotes one or more elements selected from iron, cobalt, manganese, copper, titanium, chromium, nickel, and molybdenum. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a perovskite oxide fine particle having a specific crystal lattice constant. More specifically, the present invention relates to a perovskite oxide crystal structure including a transition metal element in a constituent element and having a transition metal perovskite oxide crystal structure as a main phase. The present invention relates to perovskite-type oxide fine particles having a crystal lattice constant, perovskite-type oxide-supported particles in which the perovskite-type oxide particles are supported on a conductive carrier, and an electrode for a fuel cell produced using these.

  Conventionally, metal particles, alloy particles, metal oxide particles and the like supported on carrier particles have been widely used as various catalysts such as deodorizing, antibacterial, automobile exhaust gas purification, fuel cell, NOx reduction. As the carrier particles in this case, 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, the one in which platinum and ruthenium alloy particles are supported on a carbon carrier, and the one in which specific metal oxide particles such as molybdenum oxide and cerium oxide are supported on a carbon carrier together with metal platinum fine particles as a promoter. It is known as an excellent electrode catalyst. For example, Patent Document 1 describes that aggregation of platinum particles can be suppressed by supporting platinum particles supported on corrosion-resistant oxide particles such as cerium oxide and zirconium oxide on a carbon support. ing. Patent Documents 2 and 3 include examples in which noble metal particles such as platinum are supported on the surface of perovskite-type titanium oxide particles, and this noble metal-supported oxide paste is applied onto a carbon film and used as an electrode catalyst. It is described that the catalytic performance of perovskite-type titanium oxide is improved by acting as a promoter.

On the other hand, it is known that a perovskite oxide, which is a kind of transition metal oxide, having a specific structure has an action of decomposing NOx. In Patent Document 4, this is supported on a carrier. NOx contact catalysts have been proposed. Patent Document 5 describes that a perovskite-type Fe oxide as a carrier and a noble metal such as Pt, Pd, Rh supported thereon have excellent catalytic action even at a high temperature exceeding 500 ° C. Further, Patent Document 6 discloses that a perovskite type Fe oxide (represented by the general formula AFeO ₃ ) is partially replaced with a noble metal such as Pt, Pd, Rh, etc. It describes that it has an excellent catalytic action even at low temperatures, and further improves sulfur poisoning resistance.

  Some perovskite-type composite metal oxides containing transition metal elements such as iron, cobalt, and nickel have been put to practical use as air electrode catalysts for solid oxide fuel cells (SOFC). A solid oxide fuel cell is used at a high temperature of about 800 ° C. or higher. Under such a high temperature condition, the contained transition metal element itself may function as a catalyst having oxygen decomposability. Are known.

  Further, in Patent Document 7, platinum particles on a carrier are sintered by supporting both metal oxide particles such as alumina, silica, manganese oxide, iron oxide, cobalt oxide and platinum particles on carbon particles. It is described that it is possible to suppress and to reduce expensive platinum particles.

As a general method for supporting various metal oxides on the support surface, the following methods are mainly exemplified.
(1) A method of adsorbing metal colloidal particles on a carrier.
(2) A method in which carrier particles are dispersed in an aqueous metal salt solution, and a metal hydroxide is deposited on the carrier surface with an alkali agent.
(3) A method in which fine particles are fixed to the surface of a carrier from a fine particle dispersion in which fine particles are previously dispersed.

  Known examples using such a liquid phase method include Patent Document 8 and Patent Document 9. Among these, in Patent Document 8, carbon particles preliminarily supporting platinum are dispersed in a mixed solution of other predetermined metal salt, the metal hydroxide is deposited on the carbon particles with an alkali agent, and a reducing atmosphere is obtained. Under heating at 1000 ° C. or higher, alloy particles (four-element alloy particles of platinum, molybdenum, nickel, and iron) are supported on carbon particles. In this case, the supported fine alloy particles are about 3 nm or more.

  In Patent Document 9, in order to obtain particles in which vanadium pentoxide is supported on carbon, an organic solvent is added to the organic vanadium solution to solvate it to produce an organic complex, which is adsorbed and supported on carbon. It has been taken. In this case, the vanadium pentoxide supported on carbon is amorphous.

  As a method for supporting the perovskite oxide on the support surface, there is a method in which an aqueous solution containing a metal salt is applied on the support, dried, and then subjected to heat treatment at a high temperature to be deposited on the support surface. For example, Patent Document 10 discloses that when perovskite-type iron oxide fine particles are supported on a carrier, perovskite-type iron oxide particles containing Pd in the crystal lattice are synthesized in advance, and a slurry prepared using this is prepared on the carrier. A method of applying a heat treatment after coating is described. In this case, the perovskite-type iron oxide particles synthesized in advance have a submicron size, and the carrier is a carrier having an area enough to apply the slurry.

  In addition, Patent Document 11 describes a method of supporting metal oxide particles on a carbon-based material by plasma treatment using microwaves. Specific examples thereof include an example in which titanium oxide, nickel oxide, and cobalt oxide are supported on carbon, and it is described in the text that it can be applied to perovskite-type composite metal oxides. According to this method, the metal oxide, which has been difficult to be supported on carbon because the oxidation temperature is high and carbon as the support burns, can be supported on the carbon-based support. Special equipment is required for plasma treatment.

JP 2004-363056 A JP 2005-50759 A Japanese Patent Laying-Open No. 2005-50760 Japanese Patent Laid-Open No. 5-261289 JP 2001-269578 A JP 2004-321986 A JP 2005-270873 A JP-A-5-217586 JP 2000-36303 A JP 2004-41866 A JP-A-11-28357

  As described above, the transition metal oxide itself is a known substance as various catalysts or as a co-catalyst for improving corrosion resistance, and in particular, the perovskite oxide is used as a catalyst for a solid oxide fuel cell. Furthermore, it can be said that the perovskite oxide in which a part of the constituent elements is replaced with a noble metal, in particular palladium, is a known material used as an exhaust gas purification catalyst.

  However, in a polymer electrolyte fuel cell (PEFC), a general metal oxide represented by MxOy, MOOH, Mx (OH) y, etc. (M is a transition metal element) is supported together with a noble metal element. Although there is an example used as a catalyst, there is no example in which these transition metal oxides themselves are used as an electrode catalyst.

  In particular, for perovskite oxides, a particulate material having conductivity, such as carbon black and other carbon particles, which is easily available at low cost, is used as a carrier, and perovskite oxide particles There are no products that support and use. What has been obtained so far is a case where the perovskite oxide particles themselves are used as a support or are supported because the application object is a solid oxide fuel cell (SOFC) or an exhaust gas purification catalyst. However, a heat-resistant oxide such as alumina or cerium is used as the carrier. This is because, when used as an exhaust gas purification catalyst for an automobile engine or the like, the carrier does not need to have conductivity like carbon black, and both the solid oxide fuel cell catalyst and the exhaust gas purification catalyst This is probably because carbon black burns and cannot be used as a carrier because the use environment is a high temperature close to 1000 ° C.

  Furthermore, until now, there has been no idea of using metal oxide particles themselves as a catalyst for an electrode of a polymer electrolyte fuel cell (PEFC). The reason is that in the case of a polymer electrolyte fuel cell, a polymer material is used as an electrolyte, so it is necessary to operate at a low temperature of 300 ° C. or less. For example, a perovskite oxide that is effective in a solid oxide fuel cell However, since the catalytic ability is not exhibited, it is considered that there is no catalytic effect other than the noble metal particles at such a low temperature. For these reasons, at present, platinum particles are mainly used as an electrode catalyst for a polymer electrolyte fuel cell, and in particular, reduction of the amount of platinum used in a cathode catalyst is a major issue.

  In light of the above circumstances, the main object of the present invention is to provide a catalyst for an electrode of a polymer electrolyte fuel cell using metal oxide particles per se in order to reduce the amount of platinum used.

  The present inventors have described transition metal oxides that do not have the activity of reducing oxygen molecules at a low temperature of not more than 300 ° C., usually under a use environment as an electrode catalyst for a polymer electrolyte fuel cell. It has been found for the first time that oxygen molecules can be reduced / dissociated under certain conditions, even at room temperature, in accordance with the oxidation / reduction activity of the contained transition metal element. Although the reason for these phenomena is not clear, the oxidation / reduction activity of transition metal elements occurs with the movement of oxygen atoms in the perovskite lattice, and this movement of oxygen atoms is caused by oxygen molecules adsorbed on the surface. It is also considered to have an effect on the reduction and dissociation of.

  Furthermore, the present inventors have found for the first time that the lattice constant of a perovskite oxide plays an important role as a condition that enables reduction and dissociation of oxygen molecules. Such phenomena and correlations have never been known before and are groundbreaking discoveries.

  Here, the range of lattice constants effective for reduction / dissociation of oxygen molecules is very narrow and limited, and the present inventors have developed a perovskite oxide having such a lattice constant. We studied diligently. The lattice constants of oxides change in a complex manner, including the ionic radius of constituent elements and their abundance, the amount of lattice defects, and, in the case of nanometer (nm) sized particles, the particle diameter. It is necessary to make fine adjustments.

  In the present invention, as a result of repeated detailed studies, as for the perovskite type oxide containing iron as the main element, lanthanum is mainly used as the A site element and platinum element is added to the iron site due to the ionic radius. It was found that a perovskite oxide having a lattice constant within a specific range was obtained.

  That is, the present invention relates to a perovskite-type oxide fine particle containing a transition metal element and having a crystal lattice constant within a specific range, and has an optimum crystal lattice constant for reduction / dissociation of oxygen molecules at room temperature. The transition metal oxide particles themselves are configured to exhibit oxygen reduction activity. The realization of such perovskite oxide fine particles is a great clue to a solution for reducing the amount of platinum used.

  According to the present invention, the oxide is a perovskite oxide containing a transition metal element, and the oxygen reduction activity is expressed by the movement of the oxygen element in the crystal lattice by setting the crystal lattice constant within a specific range. The perovskite oxide fine particles can be obtained, and the obtained fine particles are useful as a cathode electrode for a fuel cell. Further, by supporting these perovskite oxide fine particles on a conductive carrier such as carbon, a more excellent effect as an electrode catalyst for a fuel cell is exhibited.

  In producing the perovskite type oxide particles of the present invention, any production method may be used, and a known production method can be applied. In the present invention, when a solution containing metal complex ions is prepared in advance and then supported on a conductive support, the metal complex ions are dispersed on the surface of the support particles by dispersing the support particles in the solution. The oxide fine particle precursor is precipitated on the surface of the carrier by drying it and then heat-treated to produce perovskite type oxide-supported particles.

In the present invention, for a perovskite type oxide crystal, a transition metal element that has a lattice constant satisfying the following formula (1) and can exist stably in the perovskite type crystal lattice is converted into a perovskite type oxide (general formula: ABO). ₃ ) It was found for the first time that the transition metal element in the crystal lattice has an oxidation / reduction activity and an oxygen reduction activity at room temperature. Perovskite-type oxide-supported particles obtained by being supported on a functional carrier are functional materials particularly suitable for use in cathode electrode catalyst applications for fuel cells.
1.402 <2b / (a + c) <1.422 (1)
Here, a and c represent the length of each short axis of the perovskite crystal lattice, and b represents the length of the long axis.

  In the present invention, the amount of use of a noble metal element such as platinum is reduced or used in order to utilize the entry / exit of oxygen atoms in the crystal lattice caused by the oxidation / reduction activity of a transition metal element as an electrode catalyst for a fuel cell. It can be expected that this will become a clue for developing the function of the catalyst without the use of the catalyst.

Hereinafter, the perovskite oxide fine particles of the present invention will be described in detail. Transition metal elements contained as main elements at the B site of the perovskite structure ABO ₃ include copper (Cu), manganese (Mn), iron (Fe), titanium (Ti), molybdenum (Mo), and cobalt (Co). One or more elements are selected from the transition metal elements such as, but it is preferable that at least one of iron, copper, and manganese is contained as an element that can easily have magnetism in the crystal lattice. In the examples to be described later, iron is used as the main element of the B site. In general, many perovskite oxides have magnetism by adding an additive element, and the range of options is limited to iron. It is considered wide. In any case, it is more preferable that an element having a possibility of becoming a ferromagnetic substance in the crystal lattice is a main element. This is because perovskite oxides, which are ferromagnetic materials, often exhibit excellent electrical conductivity and often have high ion mobility within the crystal lattice. A high ion mobility indicates that oxygen atoms in the crystal lattice easily move, and oxygen enters and exits the crystal surface more easily.

In the perovskite structure ABO ₃ , the metal element at the A site is not particularly limited as long as it can exist stably. For example, one or more transition metal elements different from the B site may be selected from the transition metal elements, and other metal elements include lanthanum (La), strontium (Sr), cerium (Ce), Calcium (Ca), yttrium (Y), erbium (Er), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), silicon (Si), magnesium (Mg), barium (Ba), One or more elements may be selected from elements such as chromium (Cr), nickel (Ni), niobium (Nb), lead (Pb), bismuth (Bi), and antimony (Sb). In the present invention, lanthanum elements are mainly used in response to the iron element as the main element, but these elements are appropriately selected according to the type of element selected as the B element.

  Next, an additive element is selected in order to manipulate the lattice constant within an optimum range. In the present invention, the platinum element is used for the lanthanum-iron-based perovskite type oxide in terms of the ionic radius, and thus the platinum element is used. Of course, the element is not limited to platinum element as long as it can have a composition. Any type can be used as long as it can exist stably in the crystal lattice.

  Since the perovskite oxide fine particles of the present invention have conductivity per se, they can be used as a catalyst for electrodes even if they are used, but in order to improve their characteristics, they are supported on a conductive carrier such as carbon. It can also be made. For example, in the case of carbon particles, acetylene black or ketjen black, furnace carbon, etc., such as Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd. and Vulcan (registered trademark) manufactured by CABOT, are used. Perovskite oxide particles are supported on a carrier. Any method may be used for supporting, and a general particle supporting method may be used.

  At this time, the average particle diameter of the perovskite oxide-supported particles as the final product is preferably 20 to 70 nm. Even if the average particle size is 20 nm or less, there is no problem in the catalytic performance of the perovskite type oxide-supported particles as the final product, but since the particle size is small in the synthesis process, the aggregation is intense and it becomes difficult to uniformly disperse. It is not preferable. Even if the average particle diameter is 70 nm or more, the catalytic ability of the final product is not completely lost, but the specific surface area is small, so that the catalytic ability is lowered, which is not preferable.

  The average particle diameter of the carbon particles is determined from the average of 100 particles observed with a transmission electron microscope (TEM) photograph. At this time, the amount of the metal element contained in the solution is set such that the amount of the perovskite oxide in the perovskite oxide-supporting particles as the final product is 5 to 50% by weight. There is no problem even if the amount of the perovskite oxide supported particles in the perovskite oxide supported particles is less than 5% by weight, but for example, when used as a catalyst, the effective catalyst amount as a whole decreases, The function may be difficult to develop, and there is no problem even if it is 50% by weight or more. However, if the content is increased, the fine particles may overlap or aggregate without being deposited as a single layer on the surface of the carrier particles. There is a risk that it may fall back.

  Further, when used as an electrode for a fuel cell, these perovskite oxide fine particles can be used alone, or a combination of perovskite oxide particles and noble metal particles can be used. .

  Although the basic particle configuration has been described above, it is necessary to select an optimal composition for the perovskite oxide. That is, the combination of elements constituting the perovskite oxide is not limited as long as it can exist stably, but the composition needs to be within a range where an optimum lattice constant can be obtained. However, the lattice constant is not determined only by the composition, and varies depending on the particle size, synthesis conditions, and the like. Therefore, regarding the combination of elements to be contained, composition, particle size, synthesis conditions, etc., all optimum conditions are different for each, and it is necessary to adjust each of them.

By optimally adjusting all of the above matters, a perovskite type oxidation containing a transition metal element, having a crystal lattice constant within the range of the following conditional expression (1), and a crystallite size in the range of 1 nm to 20 nm. Product particles and perovskite-type oxide-supported particles having an average particle diameter of 20 to 70 nm, which are supported on a conductive carrier.
1.402 <2b / (a + c) <1.422 (1)
Here, in the lattice constants a, b, and c, a and c are the lengths of the respective short axes, and b is the length of the long axis.

When the value of the lattice constant satisfies the conditional expression (1), it is effective as a fuel cell electrode. However, when taking a numerical value outside the boundary line, the performance gradually decreases, which is not preferable. . In addition, regarding the a and c axes of the lattice constant, a = c should be obtained when the crystal structure is completely symmetric, and in the case of a crystal such as LaFeO ₃ without any added element. Is quite symmetric, and the values of a and c are not coincident but close to each other. In the present invention, better characteristics are exhibited as the lattice constant is within the range represented by the above equation and the difference between the a and c axis lengths is large (the distortion is large and the symmetry is low).

  The reason for this is not clear, but since there is a tendency to involve not only the lattice constant but also the strain, the interatomic atoms contained in the A and B sites contained in the perovskite oxide crystal lattice It is presumed that the distance between oxygen atoms has a large influence, not the distance of. This is probably because the distance between oxygen atoms changes and the distance is not suitable for oxygen reduction / dissociation. In general, when the perovskite oxide has conductivity, the oxygen ion mobility in the crystal lattice is considered to be high. Therefore, when the composition has conductivity, the reduction and dissociation of surface adsorbed oxygen molecules is not possible. It tends to happen. However, in the present invention, since oxygen molecules are more excellently reduced and dissociated only within a specific lattice constant range, not only the composition has conductivity but also the perovskite type oxide crystals appearing on the surface. It can be considered that the distance between the oxygen atoms of has an important influence.

  The average particle diameter of each particle is determined from the average of 100 particles observed in the TEM photograph. At this time, even if the crystallite size of the perovskite-type oxide fine particles is 1 nm or less, it is considered that the characteristics as a catalyst are acceptable, but the lattice spacing of the perovskite-type oxide is usually around 0.5 nm (5Å). In many cases, the number of lattice points is too small due to the crystal structure, so that stable bonding does not occur and it is difficult to maintain the oxide structure, and at the same time, it is very difficult to manufacture the oxide itself. . Even when the crystallite size is 20 nm or more, the characteristics as a catalyst are not completely lost as long as oxygen atoms in the crystal lattice appear on the surface. However, a sufficient specific surface area cannot be obtained. As a result, the performance tends to deteriorate.

  For the above reasons, the crystallite size of the perovskite oxide fine particles is preferably 1 to 20 nm. At this time, in a fine particle of 20 nm or less, it is rare to take a polycrystalline structure in one particle, and in most cases, it becomes a single crystal particle. Therefore, the average particle diameter of the supported fine particles can be obtained from the average crystallite size obtained from the powder X-ray diffraction spectrum in addition to the method for obtaining the average from the TEM photograph. In particular, in the case of fine particles having a particle diameter of several nanometers or less, the measurement error when the particle diameter is visually determined from a TEM photograph or the like is large, and it is preferable to determine 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.

  For the obtained fine particles, a powder X-ray diffraction spectrum is measured, and a crystal lattice constant is calculated from the obtained peak position. The spectrum measurement range may be a range in which the lattice constant can be specified, and a range of 20 to 80 degrees is sufficient.

  When the transition metal element has a high oxidation / reduction activity, that is, when the mobility of oxygen ions in the crystal lattice is high, about 0.6 to 0.00 on the cyclic voltammetry (CV) curve of this powder. An oxidation-reduction peak considered to be derived from iron appears in the range of 8V. At this time, the higher the activity, the clearer the activity peak appearing on the CV curve, and the smaller the difference between the redox activity energies. Conversely, when the activity decreases, the activity peak on the CV curve becomes broader, and the energy difference between the redox activity energies increases, or the activity peak itself does not appear. is there.

  Next, as a specific example of a fuel cell electrode using the perovskite oxide fine particles according to the present invention as a catalyst material for electrodes, a membrane electrode assembly for fuel cells produced using the perovskite oxide fine particles ( MEA) will be described.

  FIG. 1 schematically shows a cross-sectional structure of a membrane electrode assembly (MEA) for a fuel cell. The membrane electrode assembly 10 includes an air electrode 2 disposed on one side in the thickness direction of the solid polymer electrolyte membrane 1, a fuel electrode 3 disposed on the other side, and an air disposed outside the air electrode 2. The electrode gas diffusion layer 4 and the fuel electrode gas diffusion layer 5 disposed outside the fuel electrode 3 are provided. Among these, as the solid polymer electrolyte membrane 1, a polyperfluorosulfonic acid resin membrane, specifically, “Nafion” (trade name) manufactured by DuPont, “Flemion” (trade name) manufactured by Asahi Glass Co., Ltd., Asahi Kasei A membrane such as “Aciplex” (trade name) manufactured by Kogyo Co., Ltd. can be used. As the gas diffusion layers 4 and 5, porous carbon cloth or carbon sheet can be used. As a manufacturing method of the membrane electrode assembly 10, the following general methods can be applied.

  General solvents such as magnetic stirrers, ball mills, ultrasonic dispersers, etc. are mixed with catalyst-supporting carbon particles, polymer materials, and binders as necessary in solvents based on lower alcohols such as ethanol and propanol. A catalyst paint is produced by dispersing using a dispersing device. 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. Next, the air electrode 2 or the fuel electrode 3 is formed by using the obtained catalyst paint, and the following three methods (1) to (3) are generally used as the subsequent procedure. Can be mentioned. Any means may be used as the means for evaluating the fine particle-supporting carbon particles of the present invention, but it is important that the production methods are unified and evaluated when performing comparative evaluation.

  (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. The electrode film is peeled off and cut into a predetermined electrode size. Two kinds of such electrode films are produced and used as an air electrode and a fuel electrode, respectively. 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 application method is a spray application method or a screen printing method. 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 as shown in FIG. 1 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, By supplying hydrogen to the fuel electrode 3 and air (oxygen) to the air electrode 2, the fuel cell can be operated.

_<< La (Fe _0.95 Pt _0.05 ) O ₃ / C, 40 wt% supported >>
2.23 g of lanthanum nitrate hexahydrate, 1.98 g of iron nitrate nonahydrate and 0.14 g of chloroplatinic acid hexahydrate were dissolved in a mixed solution of 80 ml of water / 20 ml of ethanol to obtain 2.16 g of citric acid. Was added to prepare an aqueous solution containing citrate complex ions of lanthanum, iron and platinum.

Next, 2 g of Vulcan XC-72 (registered trademark, carbon black manufactured by CABOT, average particle diameter of 30 nm, the same shall apply hereinafter) as carbon particles is impregnated with an aqueous solution containing the citrate complex ion. The compound was adsorbed on the Vulcan surface. The carbon particles were heat-treated at 600 ° C. in nitrogen and then washed with water to obtain perovskite complex oxide fine particles La (Fe _0.95 Pt _0.05 ) O ₃ -supported carbon particles.

As a result of the powder X-ray diffraction spectrum measurement of the La (Fe _0.95 Pt _0.05 ) O ₃ -supported carbon particles obtained in this way, as shown in FIG. 2, a clear single-phase peak with a perovskite structure is obtained. And the lattice constant determined from the peak position was 5.5672 × 7.867 × 5.5437 (Å), and it was confirmed that 2b / (a + c) = 1.416. In the powder X-ray diffraction spectrum, although the peak representing the structure due to platinum did not appear despite the inclusion of platinum element, it can be seen that platinum element was incorporated in the lattice of the perovskite structure. At this time, the average crystallite size obtained from the half width of the diffraction peak was 10.3 nm. Further, as a result of observation with a transmission electron microscope (TEM), it was confirmed that about 10 nm of composite metal oxide fine particles were supported on the surface of the carbon particles. The composition analysis and the loading amount analysis were performed using fluorescent X-ray analysis and XPS.

_<< La (Fe _0.95 Pt _0.05 ) O ₃ / C, 40 wt% supported >>
In the method for producing fine particle-supporting carbon particles of Example 1, lanthanum nitrate hexahydrate, iron nitrate nonahydrate and chloroplatinic acid hexahydrate were dissolved in 100 ml of water in the same manner as in Example 1. Then, an aqueous solution containing iron and platinum citrate complex ions was prepared, carbon particles were impregnated with a total of 100 ml of an aqueous solution containing citrate complex ions, and the complex compound was adsorbed on the Vulcan surface. Thereafter, heating was performed at 90 ° C. for about 2 hours in a nitrogen atmosphere, and further heat treatment was performed at 600 ° C. in a nitrogen atmosphere to obtain perovskite-type composite oxide fine particles La (Fe _0.95 Pt _0.05 ) O ₃ -supported carbon particles.

As a result of the powder X-ray diffraction spectrum measurement of the La (Fe _0.95 Pt _0.05 ) O ₃ -supported carbon particles obtained in this way, a single peak with a perovskite structure appeared as in Example 1, and its lattice The constant was 5.5645 × 7.8348 × 5.5536 (×), and it was confirmed that 2b / (a + c) = 1.410. At this time, the average crystallite size obtained from the half width of the diffraction peak was 14.7 nm. As a result of TEM observation, it was confirmed that about 15 nm of composite metal oxide fine particles were supported on the carbon particle surfaces.

_<< La (Fe _0.98 Pt _0.02 ) O ₃ / C, 40% by weight supported >>
In the method for producing fine particle-supporting carbon particles of Example 1, except that iron nitrate nonahydrate was changed from 1.98 g to 2.04 g and chloroplatinic acid hexahydrate was changed from 0.14 g to 0.06 g. Prepared an aqueous solution containing iron and platinum citrate complex ions in the same manner as in Example 1, impregnated with a total of 100 ml of an aqueous solution containing citrate complex ions, and adsorbed the complex compound on the Vulcan surface. Thereafter, heat treatment was performed at 600 ° C. in a nitrogen atmosphere to obtain perovskite-type composite oxide fine particles La (Fe _0.98 Pt _0.02 ) O ₃ -supported carbon particles.

As a result of the powder X-ray diffraction spectrum measurement of the La (Fe _0.98 Pt _0.02 ) O ₃ -supported carbon particles obtained in this way, a single peak of a perovskite structure appeared as in Example 1, and its lattice The constant was 5.5407 × 7.8400 × 5.5468 (Å), and it was confirmed that 2b / (a + c) = 1.414. At this time, the average crystallite size obtained from the half width of the diffraction peak was 12.6 nm. As a result of TEM observation, it was confirmed that about 10 to 15 nm of composite metal oxide fine particles were supported on the surface of the carbon particles.

_<< La (Fe _0.97 Pt _0.03 ) O ₃ / C, 40% by weight supported >>
In the production method of fine particle-supporting carbon particles of Example 1, except that iron nitrate nonahydrate was changed from 1.98 g to 2.02 g and chloroplatinic acid hexahydrate was changed from 0.14 g to 0.08 g. Prepared an aqueous solution containing iron and platinum citrate complex ions in the same manner as in Example 1, impregnated with a total of 100 ml of an aqueous solution containing citrate complex ions, and adsorbed the complex compound on the Vulcan surface. Thereafter, heat treatment was performed at 600 ° C. in a nitrogen atmosphere to obtain perovskite-type composite oxide fine particles La (Fe _0.97 Pt ₀₁₀₃ ) O ₃ -supported carbon particles.

As a result of the powder X-ray diffraction spectrum measurement of the La (Fe _0.97 Pt _0.03 ) O ₃ -supported carbon particles obtained in this way, a single peak with a perovskite structure appeared as in Example 1, and the lattice The constant was 5.5899 × 7.8246 × 5.5524 (×), and it was confirmed that 2b / (a + c) = 1.404. At this time, the average crystallite size obtained from the half width of the diffraction peak was 16.6 nm. As a result of TEM observation, it was confirmed that about 15 nm of composite metal oxide fine particles were supported on the carbon particle surfaces.

[Comparative Example 1]
_<< La (Fe _0.95 Pt _0.05 ) O ₃ / C, 40 wt% supported >>
In the method for producing fine particle-supporting carbon particles of Example 1, before heat treatment at 600 ° C. in nitrogen, heat treatment is performed at 250 ° C. in air for 1 hour, and then heat treatment at 600 ° C. in nitrogen is performed to obtain a perovskite type. Composite oxide fine particles La (Fe _0.95 Pt _0.05 ) O ₃ -supported carbon particles were obtained.

As a result of the powder X-ray diffraction spectrum measurement of the La (Fe _0.95 Pt _0.05 ) O ₃ -supported carbon particles obtained in this way, a single peak with a perovskite structure appeared as in Example 1, and its lattice The constant was 5.6220 × 7.73939 × 5.5979 (Å), and it was confirmed that 2b / (a + c) = 1.384. At this time, the average crystallite size obtained from the half width of the diffraction peak was 7.5 nm. As a result of TEM observation, it was confirmed that about 5 to 10 nm of composite metal oxide fine particles were supported on the carbon particle surfaces.

[Comparative Example 2]
_<< La (Fe _0.99 Pt _0.01 ) O ₃ / C · 40 wt% supported >>
Iron and platinum were changed in the same manner as in Example 1 except that iron nitrate nonahydrate was changed from 1.98 g to 2.06 g and chloroplatinic acid hexahydrate was changed from 0.14 g to 0.03 g. An aqueous solution containing a citrate complex ion was prepared, impregnated with a total of 100 ml of an aqueous solution containing a citrate complex ion, and the complex compound was adsorbed on the vulcanized surface. Thereafter, heat treatment was performed at 550 ° C. in a nitrogen atmosphere to obtain perovskite-type composite oxide fine particles La (Fe _0.99 Pt _0.01 ) O ₃ -supported carbon particles.

As a result of the powder X-ray diffraction spectrum measurement of the La (Fe _0.99 Pt _0.01 ) O ₃ -supported carbon particles obtained in this way, a single peak of a perovskite structure appeared as in Example 1, and its lattice It was confirmed that the constant was 5.5852 × 7.8352 × 5.6060 (Å) and 2b / (a + c) = 1.400. At this time, the average crystallite size obtained from the half width of the diffraction peak was 18.2 nm. As a result of TEM observation, it was confirmed that about 20 nm of composite metal oxide fine particles were supported on the surface of the carbon particles.

[Comparative Example 3]
<< La (Fe _0.8 Pt _0.2 ) O ₃ / C, 40% by weight supported >>
Except for changing the iron nitrate nonahydrate from 1.98 g to 1.67 g and changing the chloroplatinic acid hexahydrate from 0.14 g to 0.56 g, iron and platinum An aqueous solution containing a citrate complex ion was prepared, impregnated with a total of 100 ml of an aqueous solution containing a citrate complex ion, and the complex compound was adsorbed on the vulcanized surface. Thereafter, heat treatment was performed at 270 ° C. for 4 hours in air, and then heat treatment was performed at 600 ° C. in a nitrogen atmosphere to obtain perovskite-type composite oxide fine particles La (Fe _0.8 Pt _0.2 ) O ₃ -supported carbon particles.

As a result of powder X-ray diffraction spectrum measurement of the La (Fe _0.8 Pt _0.2 ) O ₃ -supported carbon particles obtained in this way, a single peak of a perovskite structure appeared as in Example 1, and its lattice The constant was 5.5056 × 7.88846 × 5.5728 (Å), and it was confirmed that 2b / (a + c) = 1.423. At this time, the average crystallite size obtained from the half width of the diffraction peak was 20.3 nm. As a result of TEM observation, it was confirmed that about 20 nm of composite metal oxide fine particles were supported on the surface of the carbon particles.

  Next, in order to evaluate the catalytic characteristics of the fine particle-supported carbon particles obtained in each of the above-described examples and comparative examples, a membrane electrode assembly (MEA) for a fuel cell was produced and used as a fuel cell The output characteristics were examined. When the fine particle-supported carbon particles as described above are used for the electrodes constituting the membrane electrode assembly (MEA), the oxide composition of the fine particle-supported carbon particles (carbon particles) that can achieve the maximum effect between the air electrode and the fuel electrode. The composition of the oxide fine particles supported on the particles is different. Therefore, in this example, in order to perform uniform evaluation, a particulate-supported carbon particle electrode film was used for the fuel electrode, and a standard electrode film shown below was used for the air electrode.

<Fine particle supported carbon electrode film>
1 part by weight of the fine particle-supported carbon particles obtained in each of the above examples and comparative examples was replaced with “Nafion” (trade name, manufactured by Aldrich) which is a 5% by mass solution of polyperfluorosulfonic acid resin. EW = 1000) Added to 9.72 parts by mass of a solution and 2.52 parts by mass of “Nafion” (trade name) manufactured by DuPont, which is a 20% by mass solution of polyperfluorosulfonic acid resin, and 1 part by mass of water Then, the catalyst coating material was prepared by sufficiently stirring the mixed solution so as to disperse uniformly. Next, the catalyst paint was applied onto the PTFE film so that the platinum loading was 0.03 mg / cm ² , dried and peeled off to obtain a fine particle-supporting carbon particle electrode film.

<Standard electrode membrane>
As a standard electrode, a platinum-supported carbon “10E50E” (trade name) manufactured by Tanaka Kikinzoku Kogyo Co., Ltd. supporting 50% by mass of platinum was used, and after adjusting the catalyst paint in the same manner as described above, on the PTFE film, It was applied so that the amount of platinum supported was 0.5 mg / cm ² , dried and then peeled off to obtain a standard electrode film.

<Membrane electrode assembly>
As the solid polymer electrolyte membrane, a polyperfluorosulfonic acid resin membrane “Nafion112” (trade name) manufactured by DuPont was cut into a predetermined size and used. The fine particle-supporting carbon particle electrode film prepared above and the standard electrode film were superposed on both surfaces of the solid polymer electrolyte membrane, and hot pressing was performed under the conditions of a temperature of 160 ° C. and a pressure of 4.4 MPa to join them. Next, a carbon non-woven fabric (TGP-H-120, manufactured by Toray Industries, Inc.) that has been subjected to water-repellent treatment in advance and a solid polymer electrolyte membrane having electrode films formed on both sides thereof are joined by hot pressing, and a membrane electrode assembly is obtained. Produced.

[Battery characteristics evaluation]
Using the membrane electrode assembly obtained as described above, cyclic voltammetry (CV) measurement was performed to obtain a CV curve, and the output characteristics (maximum output density in this case) as a fuel cell were measured. When measuring output characteristics, the measurement system including the membrane electrode assembly is held at 60 ° C., hydrogen gas humidified and heated to a dew point of 60 ° C. is supplied to the fuel electrode side, and 60 ° to the air electrode side. The measurement was performed by supplying air that was humidified and heated to a dew point of ° C.

  Among these, as an example in which the iron oxidation / reduction peak clearly appears on the CV curve, FIG. 3 shows the CV measurement results when the particles obtained in Example 1 are used. In addition, FIG. 4 shows a CV measurement result when the particles obtained in Comparative Example 1 are used as an example in which the oxidation / reduction peak of iron is very weak and the catalytic ability is inferior.

  Table 1 shows the measurement results for the fine particle-supported carbon particles obtained in Examples 1 to 4 and Comparative Examples 1 to 3, and the membrane electrodes produced in Example 5 using these fine particle-supported carbon particles. The measurement result about a joined_body | zygote is shown collectively. However, the CV measurement results are obtained by relatively evaluating the state of the peak due to the iron atom, and those having a clear peak as represented by FIG. Those showing a very broad peak were marked with × and the intermediate state was marked with Δ.

Next, in the graph shown in FIG. 5, when the lattice constants of the perovskite structure are a, b, c and the long axis is b, the horizontal axis of the graph indicates the average length of the a axis and the c axis, It is the graph which plotted the perovskite type oxide obtained by taking each axis and b axis length in each example and a comparative example. In the figure, the band shown in gray represents a region that satisfies the following formula (1).
1.402 <2b / (a + c) <1.422 (1)

  As is apparent from Table 1 and FIG. 5, the fine particle-supporting carbon particles having a lattice constant within a specific range obtained in each example are attributed to iron elements on the CV curve in any case. Possible oxidation / reduction peaks appear, indicating that the contained iron element has oxidation / reduction activity and is effective as a cathode catalyst for fuel cells. On the other hand, in each comparative example, although the composition and structure are similar to each example, the lattice constant is out of a specific range, so the transition metal element contained is very weakly oxidized. It can be seen that it has only reducing activity and is inappropriate as a cathode catalyst for fuel cells.

It is sectional drawing which shows typically one structural example of the membrane electrode assembly (MEA) for fuel cells. It is a schematic cross section of a general membrane electrode assembly. FIG. 3 is a graph showing a powder X-ray diffraction spectrum of carbon particles (perovskite oxide-carrying particles) carrying 10 nm La (Fe _0.95 Pt _0.05 ) O ₃ particles produced in Example 1. It is a figure showing the CV curve obtained in Example 5 using the particle | grains produced in Example 1. FIG. It is a figure showing the CV curve obtained in Example 5 using the particle | grains produced by the comparative example 1. FIG. It is the graph showing the lattice constant about the particle | grains obtained by each Example and the comparative example.

Claims (13)

General formula ABO ₃ (wherein the element represented by A is selected from lanthanum, strontium, cerium, calcium, yttrium, erbium, praseodymium, neodymium, samarium, europium, silicon, magnesium, barium, niobium, lead, bismuth, antimony) The element represented by B represents one or more elements selected from iron, cobalt, manganese, copper, titanium, chromium, nickel, and molybdenum.) A perovskite oxide fine particle, which is a transition metal oxide fine particle in a phase and the lattice constant of the oxide fine particle satisfies the following conditional expression (1).
1.402 <2b / (a + c) <1.422 (1)
Here, a and c represent the length of each short axis of the perovskite crystal lattice, and b represents the length of the long axis.   The perovskite-type oxide fine particles according to claim 1, which mainly contain iron as the element represented by B (B element).   The perovskite oxide fine particles according to claim 1 or 2, having an average particle diameter of 1 to 20 nm.   The perovskite oxide fine particles according to any one of claims 1 to 3, wherein the fine oxide particles contain a noble metal.   The noble metal, as a noble metal element, replaces part of the elements constituting the oxide crystal lattice, or as a noble metal crystal, forms a complex with an oxide crystal, or as a noble metal particle, an oxide surface The perovskite-type oxide fine particles according to claim 4, which are deposited on.   The perovskite oxide fine particles according to claim 4 or 5, wherein the content of the noble metal is 1 to 20% in terms of element ratio with respect to the total amount of the B element.   A perovskite oxide-carrying particle comprising the perovskite oxide fine particle according to any one of claims 1 to 6 supported on a conductive carrier.   The perovskite oxide-carrying particles according to claim 7, wherein the conductive carrier is conductive carbon particles.   The supported amount of the perovskite type oxide fine particles in the perovskite type oxide supported particles is 5 to 50% by weight in a weight ratio (“weight of perovskite type oxide fine particles” / “weight of the whole oxide supported particle”). The perovskite type oxide-supporting particles according to claim 7 or 8, wherein   The catalyst material which has the perovskite type oxide fine particle as described in any one of claims 1 to 9 as a main component.   A catalyst material for oxygen reduction comprising the perovskite oxide fine particles according to any one of claims 1 to 9 as a main component.   A catalyst material for a fuel cell utilizing the oxygen reduction action of the catalyst material for oxygen reduction according to claim 11.   A fuel cell electrode comprising the fuel cell catalyst material according to claim 12.

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