JP2008047472A - Electrode catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode body capable of effectively suppressing/preventing the elution of Pt which is a catalyst component, and enhancing electrode catalytic activity. <P>SOLUTION: In an electrode catalyst containing the catalyst component and a carbon-containing conductive material, the catalyst component contains at least Pt, and the difference between the N<SB>2</SB>-BET specific surface area and the CTAB adsorption specific surface area of the carbon-containing conductive material is 100 m<SP>2</SP>/g or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode catalyst used for a battery, and more particularly to an electrode catalyst used for a polymer electrolyte fuel cell.

  In relation to effective use of fossil fuels and environmental problems, fuel cells have high energy exchange efficiency and clean exhaust gas, and these fuel cells are installed in comparison with gasoline vehicles. The superiority of the energy saving efficiency of a car that can be realized at low cost depends on how inexpensive the battery can be and the high performance. Among them, the polymer electrolyte fuel cell (PEFC) can be activated at room temperature, has few problems of electrolyte dissipation, and has advantages such as high current density.

  However, the current PEFC uses a platinum-based catalyst with excellent activity as an electrode catalyst. However, if mass production is premised, there is a problem in the supply of platinum resources. Needed. Therefore, the electrode catalyst is dispersed and supported on the carbon-containing conductive material carrier having a large surface area in the form of ultrafine particles of nanometer order for the purpose of increasing the surface area per mass of the catalyst metal. Irreversible changes that occur in the catalyst metal ultrafine particles and the carbon-containing conductive material on the carrier include (1) agglomeration of catalyst particles, (2) dissolution and reprecipitation of platinum particles, and (3) the carbon-containing conductive material. Corrosion (corrosion of carrier carbon when a carbon material is used for the carbon-containing conductive material), (4) platinum particles falling off due to corrosion of the carbon-containing conductive material, and the like can be considered. Among these irreversible changes, the problem of dissolution and reprecipitation of platinum particles in (2) above is a problem directly related to the problem of platinum resource supply, assuming the above-mentioned mass production. For example, the following conventional examples exist.

Patent Document 1 describes an electrode catalyst using a platinum alloy including platinum-nickel-cobalt ternary alloy particles having a regular structure by heating at a temperature of 600 ° C. or higher and lower than 800 ° C. Further, the regular structure is confirmed by the fact that the peaks of (100) or (001) and (110) or (100) appear on the lower diffraction angle 2θ side than the main diffraction peak of (111) or (101) ( Patent Document 1 Table 1, FIG. 1), the platinum alloy having a face-centered cubic ordered structure or a face-centered tetragonal ordered structure has little performance deterioration even when used at a relatively high temperature for a long period of time. It also describes that high activity can be maintained.
JP-A-6-176766

  However, when the alloy catalyst of the above-mentioned Patent Document 1 is actually used, even if the alloy catalyst is made into a regular alloy, a large amount of the metal component below the second component elutes, and the catalyst metal composition changes significantly over time. In addition, high elution resistance cannot be maintained for a long time, and the elution metal tends to promote deterioration of the electrolyte and the carbon support. In particular, it has been found that elution resistance is insufficient as a catalyst metal for automotive fuel cell applications where the amplitude of power generation load fluctuation is large and the fluctuation frequency is high. Further, the eluted catalyst metal promotes the deterioration of other element materials such as the electrolyte membrane and the carbon support.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode body that can effectively suppress and prevent elution of Pt and is excellent in electrocatalytic activity.

  In general, the larger the particle size, the more stable the elution is due to the decrease in volume energy according to the Ostwald growth theory, but the larger the particle size, the higher the cost because the amount of catalyst metal used increases. However, in the present invention, by optimizing the physical properties of the carbon support and applying heat treatment, the Pt elution resistance is greatly improved even with the same catalyst component particle size. Furthermore, pure Pt, which is one of the catalyst components in the electrode catalyst of the present invention, has the highest elution resistance. However, 10 at. If it is about% or less, even if the second component is contained, no significant decrease in elution resistance is observed. Therefore, it is possible to provide an electrode catalyst with high elution resistance of the catalyst component.

That is, the above object is an electrode catalyst including a catalyst component and a carbon-containing conductive material, wherein the catalyst component includes at least Pt, and the N ₂ -BET specific surface area and CTAB adsorption ratio of the carbon-containing conductive material. It is achieved by an electrocatalyst characterized by a difference in surface area of 100 m ² / g or less.

(Electrode catalyst)
The first of the present invention is an electrode catalyst comprising a catalyst component and a carbon-containing conductive material, wherein the catalyst component contains at least Pt, and the N ₂ -BET specific surface area and CTAB adsorption of the carbon-containing conductive material The electrode catalyst is characterized in that the difference in specific surface area is 100 m ² / g or less.

Since N ₂ and CTAB have different adsorption occupation areas, a difference in both specific surface areas occurs due to the fine structure of the surface of the carbon-containing conductive material. In other words, the numerical value of the nitrogen adsorption specific surface area includes the surface area of the fine irregularities on the surface of the carbon-containing conductive material. On the other hand, since the adsorption cross-sectional area of cetyltrimethylammonium bromide (CTAB) is considerably larger than that of nitrogen molecules, the surface area due to minute irregularities that cannot be penetrated by CTAB molecules is not reflected in the numerical value of CTAB adsorption specific surface area. From this, it can be said that the difference between both adsorption specific surface areas represents the number of undulations of minute irregularities on the surface of the carbon-containing conductive material.

Therefore, when the difference between the adsorption specific surface areas is 100 m ² / g or less, the number of small catalyst components supported on the minute irregularities on the surface of the carbon-containing conductive material is moderately small. Not only the effect of reducing the particle size variation but also the detailed mechanism is not clear, but the surface of the support having such physical property values is more uniform and stable, and the interaction between the catalyst component and the support This is considered to stabilize the catalyst component. For the above reasons, it is considered that elution of the catalyst component, particularly Pt, is suppressed / prevented even when a high potential at which the catalyst component such as Pt is eluted or a large potential oscillation is applied.

_{Incidentally,} the difference between the N 2 BET specific surface area and the CTAB adsorption specific surface area is preferably 1 to 100 m ² / g, more preferably 2~80m ² / g, is 5 to 50 m ² / g More preferably.

  A catalyst using a carbon-containing conductive material having a physical property value range as described above as a carrier can provide an electrode catalyst having sufficient elution resistance by the production method of the present invention.

  When the electrode catalyst according to the present invention is used in, for example, a polymer fuel cell, the electrode catalyst contains a catalyst component and a carbon-containing conductive material, and may contain additives as necessary. Furthermore, as a matter of course, the electrode catalyst according to the present invention is a concept including a cathode electrode catalyst and / or an anode electrode catalyst. In the electrode catalyst according to the present invention, the catalyst component is preferably supported on the carbon-containing conductive material, and more preferably the catalyst component is dispersedly supported on the carbon-containing conductive material.

As the N ₂ -BET specific surface area of the carbon-containing conductive material according to the present invention, a value measured according to a known BET specific surface area measurement method using nitrogen can be used. Specifically, first, a sample is placed in a sample tube. While heating at 250 to 350 ° C., the surface is evacuated to clean the surface, and the weight of the sample after that is measured. The adsorption cell is attached to the apparatus again, the sample is cooled to the liquid nitrogen temperature, and nitrogen gas is sent into the cell. When nitrogen gas is adsorbed on the sample surface and the amount of gas blown is increased, the sample surface is covered with gas molecules. The state in which the gas molecules are adsorbed in a multiple manner is plotted as a change in the adsorption amount with respect to a change in pressure. From this graph, the adsorption amount of gas molecules adsorbed only on the sample surface is obtained from the BET adsorption isotherm. The surface area of the sample can be measured from the amount of adsorbed gas because the adsorption occupation area of nitrogen molecules is known in advance. Actually, the present invention is obtained according to the standard measurement method of the apparatus using ChemBET 3000 of Quantachrome.

  The CTAB adsorption specific surface area according to the present invention is a specific surface area measurement method using CTAB (cetyltrimethylammonium bromide) as an adsorbent, and specifically uses the results obtained by measuring according to ASTM D3765-80. It was.

_N 2 BET specific surface area according to the present invention is preferably from 10 to 1000 m ² / g, more preferably 20 to 500 m ² / g, it is 50 to 300 m ² / g Further preferred.

Since the surface of the support having a N ₂ -BET specific surface area of more than 1000 m ² / g is mainly composed of fine irregularities, an electrode catalyst having a high resistance to Pt elution cannot be obtained, and is less than 10 m ² / g. Since a sufficient catalyst supporting area cannot be obtained, sufficient catalyst activity cannot be obtained.

The CTBA specific surface area according to the present invention is preferably 1 to 1000 m ² / g, more preferably 5 to 500 m ² / g, and still more preferably 10 to 200 m ² / g.

If the CTBA specific surface area does not exceed 1000 m ² / g, the primary particle diameter will not be too small, and the supported catalyst component will not be unnecessarily small. Therefore, an electrode catalyst having high resistance to Pt elution can be obtained. Moreover, if it is 1 m < ² > / g or more, since sufficient catalyst supporting area is obtained, sufficient catalyst activity can be obtained.

  The carbon-containing conductive material according to the present invention has a specific surface area for supporting the catalyst component in a desired dispersed state and has sufficient electronic conductivity as a current collector. It can be used, and the main component is preferably a carbon-containing conductive material. By using a carbon-containing conductive material for the carbon-containing conductive material according to the present invention, a high-performance anode electrode with little electrical resistance loss and substance diffusion loss can be obtained. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. Further, as such carbon materials, more specifically, acetylene black, Vulcan, Ketjen black, black pearl, graphitized acetylene black, graphitized Vulcan, graphitized Ketjen black, graphitized carbon, graphitized black pearl , Carbon nanotubes, carbon nanofibers, carbon nanohorns, and carbon fibrils as main components.

  In the present invention, “the main component is carbon” refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.

  The size of the carbon-containing conductive material is not particularly limited. However, from the viewpoint of controlling the ease of loading, the catalyst utilization, and the thickness of the electrode catalyst (layer) within an appropriate range, the primary particles The diameter is 2 to 100 nm, preferably 10 to 80 nm, more preferably about 20 to 50 nm.

  If the primary particle diameter of the conductive material according to the present invention is 2 nm or more, it becomes easy to maintain highly dispersed support without being too small with respect to the catalyst component particle diameter. Since the specific surface area is obtained, sufficient electrode performance can be obtained without aggregation of the catalyst components.

  In the present specification, the “primary particle” means a carbon-containing conductive material, for example, a carbon material such as the above-mentioned carbon black is generally agglomerated, but means individual particles. The individual particles that make up

  Moreover, 5-80 volume% is preferable and, as for the porosity of the carbon containing electroconductive material which concerns on this invention, 10-70 volume% is more preferable.

  As a measuring method of the primary particle diameter of the carbon-containing conductive material according to the present invention, all the particle diameters of the primary particles of the conductive material observed in any eight fields of the transmission electron microscope image are measured ( The total was N> 60), and the median value of the particle diameters was the primary particle diameter. However, the primary particle diameter can be calculated not only by this measuring method but also by a known method.

  The method for producing the carbon-containing conductive material according to the present invention as described above will be described in detail in the section (Method for producing electrode catalyst) described later.

  As the catalyst component used in the electrode catalyst according to the present invention, the cathode catalyst is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. The catalyst component used for the anode catalyst is not particularly limited as long as it has a catalytic action for the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. Specifically, platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, gold (Au), silver (Ag), cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, etc. It is selected from metals and their alloys. Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like.

  The catalyst component according to the present invention is represented by a composition formula PtaMb (a + b = 100), and M is one or more selected from the group consisting of Co, Cr, Fe, Ni, Ir, Rh, Pd, Ag, and Au. It is an element, and it is preferable that a = 90-100 and b = 0-10.

An electrode catalyst in which Pt metal alone, a Pt-based alloy, or Pt, another metal, or a metal composition is mixed is desirable because of its excellent electrode catalyst activity. The purpose of adding other metal components is mainly to increase the electrocatalytic activity. Specifically, the formula can be represented by the formula Pt _a M _b , where M is one or more elements selected from Co, Cr, Fe, Ni, Ir, Rh, Pd, Ag, and Au, and a = 90-100 and b = 0-10 are good. If b is 10 or less, the metal which a 2nd component occupies does not increase too much, and Pt elution tolerance does not fall easily. In addition, the electrolyte and the carbon support are less likely to deteriorate due to elution of the second component. b is preferably 0 to 8, more preferably 0 to 6. Moreover, if a is 90 or more, Pt elution tolerance is hard to fall. a is preferably 92 to 100, more preferably 94 to 100.

  In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties.

  The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the cathode catalyst (layer) and the catalyst component used for the anode catalyst (layer) can be appropriately selected from the above. In the following description, unless otherwise specified, the descriptions of the catalyst components for the cathode catalyst (layer) and the anode catalyst (layer) are the same definitions for both, and are collectively referred to as “catalyst components”. However, the catalyst components for the cathode catalyst (layer) and the anode catalyst (layer) do not have to be the same, and are appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be used, but the catalyst component is preferably granular. At this time, the smaller the average particle size of the catalyst component used in the electrode catalyst, the higher the effective electrode area where the electrochemical reaction proceeds, which is preferable because the oxygen reduction activity is also high, but actually the average particle size is too small On the other hand, a phenomenon in which the oxygen reduction activity decreases is observed. Therefore, the average particle size of the catalyst component according to the present invention is preferably 2 to 20 nm, more preferably 3 to 15 nm, and further preferably 4 to 10 nm. If the average particle diameter is 2 nm or more, the specific surface area is not too large and high mass activity can be obtained, and sufficient elution resistance of Pt can be obtained by the catalyst production method of the present invention. If it is 20 nm or less, it is considered that elution resistance is obtained, and the specific surface area is not too small so that sufficient mass activity can be obtained.

  Examples of the method for measuring the average particle diameter of the catalyst component according to the present invention include a method of measuring the particle diameter of particles observed in several to several tens of fields for a representative sample from a transmission electron microscope image. In this measurement method, there is a significant difference in the average particle diameter depending on the sample to be observed and the visual field. More simply, the crystallite diameter determined from the half width of a specific reflection peak from the X-ray diffraction profile can be used as the average particle diameter of the catalyst component.

  The average particle size of the catalyst component of the present invention was determined by measuring all the primary particle sizes of the conductive material observed in any 8 fields of the transmission electron microscope image (total N> 120). The test was carried out under the condition that the median was the average particle diameter of the catalyst component.

  The ratio of the particle size standard deviation of the catalyst component according to the present invention to the average particle size of the catalyst component is preferably 0.3 or less.

  The particle size standard deviation according to the present invention can be expressed by the following equation, and is a value representing the dispersion of the particle size when the catalyst component is assumed to be a particle, and is a square root of dispersion.

  Examples of the particle size standard deviation of the catalyst component according to the present invention include a method of statistically processing the particle size of particles observed in several to several tens of fields for a representative sample from a transmission electron microscope image. That is, the value of the particle size of the catalyst component observed in several to several tens of fields for the representative sample from the transmission electron microscope image and the probability of taking the value of the particle size of each catalyst component are calculated, and the particle size standard is calculated. Deviation can be obtained.

  When the ratio of the particle size standard deviation of the catalyst component to the average particle size of the catalyst component (= ratio of the particle size standard deviation of the catalyst component to the average particle size of the catalyst component) exceeds 0.3, the small particle size The proportion of catalyst metal particles increases and the amount of the eluted catalyst component increases. Therefore, the ratio between the particle size standard deviation of the catalyst component and the average particle size of the catalyst component is preferably 0.3 or less, more preferably 0.25 or less, and further preferably 0.2 or less.

  The primary particle diameter of the carbon-containing conductive material according to the present invention can be measured by using a known method using an electron microscope such as a scanning type or a transmission type, or an X-ray diffraction method. For example, the ratio of the average particle diameter with the catalyst component to the primary particle diameter of the carbon-containing conductive material calculated from the image taken by TEM is preferably 1 to 50, more preferably 1.5 to 15, and more preferably 2-10.

  If the ratio of the average particle size between the primary particle size of the carbon-containing conductive material and the catalyst component is 1 or more, the catalyst component particles will not be too large compared to the primary particle size of the carrier. Aggregation is unlikely to occur and high dispersion support is easy to maintain. For this reason, sufficient electrode performance can be obtained with respect to the amount of Pt used. If the ratio of the average particle size of the primary particle size of the carbon-containing conductive material to the catalyst component is 50 or less, the specific surface area of the carrier does not become too small and there is a sufficient area for supporting the catalyst component. For this reason, the agglomeration of the supported catalyst component particles hardly occurs as described above, and sufficient electrode performance can be obtained with respect to the used Pt amount.

  In the electrode catalyst in which the catalyst component is supported on the carbon-containing conductive material, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 60% by mass with respect to the carbon-containing conductive material. It is good to do. The amount of the catalyst component supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  In order to further suppress the elution of Pt, it is better to set the catalyst component loading in a certain range. If it is 10 mass% or more, the catalyst layer does not become too thick, and high electrode performance can be obtained. Further, when the content is 80% by mass or less, the elution of Pt is further suppressed, and the catalyst component becomes highly dispersed, so that the performance obtained with respect to the amount of the catalyst component becomes sufficient.

  The carbon-containing conductive material according to the present invention is preferably a powder or a porous structure composed of 85% by mass to 100% by mass of carbon, more preferably 90% by mass to 100% by mass, and more preferably 95% by mass to 100 mass% is more preferable.

  When the proportion of carbon in the carbon-containing conductive material is 85% by mass to 100% by mass, it is possible to obtain a high-performance electrode that can achieve both a sufficient specific surface area and electronic conductivity.

  A material composed of carbon carrying the catalyst component has sufficient electronic conductivity, and since it is necessary to easily disperse the catalyst component easily, a carbonaceous material is preferably used. Examples of elements other than carbon include, for example, fluorine and silicon for imparting water repellency, boron for improving the corrosion resistance of carbon-containing conductive materials, and hydrogen, oxygen and nitrogen contained in surface functional groups. In addition to the above, impurities such as impure metals are listed.

(Electrocatalyst production method)
The second aspect of the present invention is a method for producing an electrode catalyst comprising a carbon-containing conductive material carrying a catalyst component, and before the catalyst component is carried on the carbon-containing conductive material, the surface of the carbon-containing conductive material is surfaced. It is a manufacturing method of the electrode catalyst characterized by performing a processing process.

  By this production method, the Pt elution resistance is greatly improved as compared with the conventional electrode catalyst. Although the detailed elution suppression mechanism is not clear, for example, as described above, since the number of small catalyst components supported on the minute irregularities on the surface of the carbon-containing conductive material is moderately small, the particle size variation of the supported catalyst components Although the detailed mechanism is not clear, the surface of the support having such physical property values is more uniform and stable, and the catalyst component is supported by the interaction between the catalyst component and the support. Is considered to be more stable. For the above reasons, it is considered that elution of the catalyst component, particularly Pt, is suppressed / prevented even when a high potential at which the catalyst component such as Pt is eluted or a large potential oscillation is applied.

  The surface treatment step in the method for producing an electrode catalyst according to the present invention is not limited as long as it is a method of physically or chemically applying a load to the carbon-containing conductive material itself to adjust the microstructure of the carbon-containing conductive material. However, as a part of the surface treatment process according to the present invention, acid treatment, alkali treatment, and steam firing are listed as means for physically or chemically loading the carbon-containing conductive material itself. In the process of adjusting the microstructure of the carbon-containing conductive material by physically or chemically applying a load to the carbon-containing conductive material itself, such as alkali treatment and steam baking, a heat treatment step may be added as necessary. More preferably, heat treatment is particularly preferred after acid treatment, alkali treatment, and water vapor firing. In addition, the acid treatment, the alkali treatment, and the steam baking as part of the surface treatment process according to the present invention may be performed in one step or a plurality of steps, respectively. The heat treatment as a part may be performed once or a plurality of times, and the atmosphere in the heat treatment is preferably an inert gas atmosphere or a reducing gas atmosphere.

  The inert gas and reducing gas are the same as the inert gas and reducing gas used below, and will not be described here because they will be described in detail.

  The “surface treatment step” in this specification refers to a step of physically or chemically applying a load to the carbon-containing conductive material itself to adjust the fine structure of the carbon-containing conductive material, so-called corrosion treatment step. And a concept including a heat treatment step.

  The acid treatment which is a part of the surface treatment process according to the present invention is carried out by using a carbon-containing conductive material in a known acid solution such as acetic acid, hydrochloric acid, sulfuric acid, nitric acid, sulfuric acid, nitrous acid, phosphorous acid, hydrofluoric acid, and mixed acids thereof. And a method of spraying the acid aqueous solution onto the carbon-containing conductive material by spraying.

  Moreover, although the solvent used for said acid solution is mainly water, polar organic solvents, such as acetone and alcohol, may be included in order to make it easy to disperse | distribute a carbon containing electroconductive material. The concentration of the acid solution is preferably 1 to 80% by mass, more preferably 10 to 70% by mass, and still more preferably 15 to 65% by mass with respect to the solvent.

  The impregnation time in the case of forming a microstructure in the carbon-containing conductive material according to the present invention by the above-described impregnation method is not particularly limited, and is appropriately selected according to the pH of the acid solution, the size of the carbon-containing conductive material, and the like. For example, it is preferable to impregnate a predetermined amount of acid solution for about 5 to 100 hours. The heat treatment and firing time are appropriately determined according to various conditions such as the pH of the acid solution and the size of the carbon-containing conductive material.

  After the acid treatment which is a part of the surface treatment process according to the present invention, the acid may be removed by heat treatment, baking, washing or the like, if necessary. In this case, the heat treatment and firing temperature is preferably 100 to 500 ° C.

  Examples of the alkali treatment that is a part of the surface treatment process according to the present invention include a method of impregnating a known alkaline solution with a carbon-containing conductive material, a method of spraying the acid aqueous solution onto the carbon-containing conductive material by spraying, and the like. .

  The alkali solution used for the alkali treatment is not particularly limited and is preferably used as long as it is a known alkali solution. However, an alkali solution (including hydrogen) and an alkali solution containing an alkaline earth metal are more preferable, and sodium, An alkaline solution containing potassium is more preferable, and NaOH and KOH are particularly preferable.

  The solvent used in the alkaline solution is mainly water, but may contain a polar organic solvent such as acetone or alcohols for the purpose of easily dispersing the carbon-containing conductive material. The concentration of the alkaline solution is preferably 1 to 80% by mass, more preferably 10 to 70% by mass, and still more preferably 15 to 65% by mass with respect to the solvent.

  The impregnation time in the case of forming a microstructure in the carbon-containing conductive material according to the present invention by the above-described impregnation method is not particularly limited, and is appropriately selected according to the pH of the alkaline solution, the size of the carbon-containing conductive material, and the like. For example, it may be impregnated with a predetermined amount of alkaline solution for about 5 to 100 hours.

  After the alkali treatment which is a part of the surface treatment step according to the present invention, the acid may be removed by heat treatment, baking, washing or the like, if necessary. In this case, the heat treatment and firing temperature is preferably 100 to 500 ° C. The heat treatment and firing time are appropriately determined according to various conditions such as the pH of the alkaline solution and the size of the carbon-containing conductive material.

  The steam baking which is a part of the surface treatment process according to the present invention can be performed by a known method. For example, the steam concentration is preferably 20 to 100%, more preferably relative humidity 50 to 95%, and still more preferably relative. Baking is preferably performed for about 1 to 6 hours under a temperature condition of 600 to 1200 ° C., more preferably 700 to 1100 ° C., and even more preferably 800 to 1000 ° C. in an atmosphere with a humidity of 60 to 90%. As the balance gas added to the water vapor, an inert gas or carbon dioxide can be used.

  After performing the heat treatment in the surface treatment step, a high-temperature heat treatment step may be performed to further adjust the surface structure of the carrier as appropriate and stabilize a part of the surface destabilized by the surface treatment step. The high temperature heat treatment step may be performed in place of the heat treatment or firing. The high-temperature heat treatment step for achieving such an object is performed under a temperature condition of 1500 to 3000 ° C., more preferably 1600 to 2800 ° C., and further preferably 1800 to 2600 ° C. in an inert gas atmosphere or a reducing gas atmosphere. It is preferable to bake for about 1 to 4 hours.

  In addition, regarding the catalyst component and carbon-containing conductive material used in the following (Electrocatalyst production method) in this specification, the “catalyst component” and “carbon-containing conductive material” used in the above-mentioned (electrode catalyst). The description is omitted here because of the same materials and physical properties.

  The method for producing an electrode catalyst according to the present invention preferably further includes a step (A) of applying a heat treatment after supporting the catalyst component on the carbon-containing conductive material.

  By this production method, the Pt elution resistance is greatly improved as compared with the conventional electrode catalyst. Although the detailed elution suppression mechanism is not clear, the combination of carbon support species and catalyst metal species having physical properties as shown in the present invention and the catalyst loading method contributes to the formation of a catalyst metal structure with high elution resistance during heat treatment. it is conceivable that.

  The catalyst component can be supported on the carbon-containing conductive material according to the present invention by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used.

  In particular, the raw material of the catalyst component according to the present invention is more preferably supported on the carbon-containing conductive material by being reduced in a state dissolved or dispersed in the liquid phase.

  The catalyst component is supported on the carbon-containing conductive material according to the present invention when the metal salt is dissolved or dispersed in the liquid phase and the metal salt is reduced by the reducing agent. The manufacturing method is more preferable. Therefore, a liquid phase reduction support method, a colloid adsorption method, and a reverse micelle method are particularly preferable.

  For example, in order to support the catalyst component on the surface of the carbon-containing conductive material by an impregnation method, a step of adding the carbon-containing conductive material to a solution containing the catalyst component (hereinafter also referred to as catalyst solution), and the carbon-containing conductive material The method includes a step of impregnating the surface of the material with the catalyst solution, and a catalyst component supporting step of supporting the catalyst component on the carbon-containing conductive material. Thereby, the catalyst component can be highly dispersed and supported on the surface of the carbon-containing conductive material, and an electrode catalyst having sufficient initial performance and excellent durability can be obtained.

  The solution containing the catalyst component is a solution containing an element of the catalyst component to be supported on the carbon-containing conductive material. Since the catalyst component exhibits high catalytic activity, the solution according to the present invention described above is used. The same elements as the catalyst component used for the electrode catalyst (layer) can be mentioned.

  The raw material of the catalyst component according to the present invention is preferably Pt chloride, Pt nitrate, or Pt dinitrodiammine complex salt.

  The method for reducing the metal salt used as the catalyst component raw material should have an appropriate reduction rate, and the carbon-containing conductive material in this application is supported by carrying the catalyst components listed in the description of the above catalyst components such as Pt. In the method, chloride, nitrate, dinitrodiammine complex salt and the like are preferably used. Thereby, the catalyst component can be supported in a highly dispersed manner on the surface of the carbon-containing conductive material.

  Specifically, as the raw material of the catalyst component, for example, when Pt is used as the catalyst component, chloroplatinic acid, platinum chloride, dinitrodiammine platinum; when iridium is used, iridium chloride, etc .; palladium When used, such as a solution in which a compound containing an element of a desired catalyst component such as palladium chloride (hereinafter also simply referred to as “catalyst compound”) is dissolved in water and / or an organic solvent at a predetermined concentration. It is. It does not specifically limit as an organic solvent, Alcohols, such as water, methanol, ethanol, propanol, isopropyl alcohol, ketones, such as acetone, etc. are mentioned, These may be used individually by 1 type, or 2 types. You may mix and use the above.

  It does not specifically limit as a density | concentration of the catalyst compound in a catalyst solution, What is necessary is just to determine suitably so that a desired electrode catalyst may be obtained, but 0.01-5 mass% with respect to a solvent, Preferably it is 0.05-1 mass. It may be about%.

  After the carbon-containing conductive material is added to the catalyst solution, when the carbon-containing conductive material is a powder, the carbon-containing conductive material is added to the catalyst solution by an appropriate dispersing means such as a homogenizer or an ultrasonic dispersing device. It may be sufficiently dispersed, and these dispersing means may be appropriately combined. When the carbon-containing conductive material is a porous structure, it may be added to the solution, and then a means for penetrating the catalyst solution in detail by ultrasonic irradiation or vacuum degassing may be added as necessary. By these means, the surface of the carbon-containing conductive material can be impregnated with the catalyst solution.

  The addition amount of the carbon-containing conductive material to be added to the catalyst solution according to the present invention is not particularly limited, and may be appropriately determined so that a desired electrode catalyst is obtained. It may be about 15% by mass, preferably about 0.1 to 10% by mass.

  Next, the carbon-containing conductive material impregnated with the catalyst solution is filtered and dried using a known means such as a separating means such as suction filtration. Thereafter, the electrode mixture of the present invention can be obtained by filtering the mixed solution and drying the resulting precipitate.

  The method for drying the electrode catalyst of the present invention may be any known method such as vacuum drying, natural drying, rotary evaporator, and drying by a blower dryer, and is not particularly limited. What is necessary is just to determine drying time etc. suitably according to the method to be used.

  Further, for example, in order to support the catalyst component on the surface of the carbon-containing conductive material by the liquid phase reduction support method, a step of adding the carbon-containing conductive material to the catalyst solution and a step of adding a reducing agent to the resulting mixed solution A method including a catalyst supporting step of supporting a catalyst component on the carbon-containing conductive material may be used. The step of adding the carbon-containing conductive material to the catalyst solution may be performed in the same manner as described in the impregnation method.

  Next, in the step of adding a reducing agent to the resulting mixed liquid, the reducing agent is capable of reducing the catalyst compound and has an appropriate reduction rate, and is not particularly limited. Examples of the reducing agent include sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, hydrazine, formaldehyde, methanol, ethanol, hydrogen, ethylene, carbon monoxide and the like. The amount of the reducing agent added to the catalyst solution is not particularly limited, and may be determined as appropriate.

  After the reducing agent is added to the mixed solution, it may be heated to 30 to 100 ° C. using a reflux reactor or the like to carry out reduction loading of catalyst particles such as platinum. Then, after allowing to cool to room temperature if necessary, the carbon-containing conductive material carrying the catalyst component may be filtered and dried by a separating means such as suction filtration. The drying method and the filtration method are publicly known. This method may be the same as the above method.

  For example, to support the catalyst component on the surface of the carbon-containing conductive material by the colloid adsorption method, a step of adding the carbon-containing conductive material to the catalyst colloid solution and a step of adsorbing the catalyst colloid to the carbon-containing conductive material Thus, a method including a catalyst supporting step of supporting a catalyst component on the carbon-containing conductive material may be used.

  Examples of the solvent used in the liquid phase according to the present invention include water, alcohols such as methanol, ethanol, propanol, and isopropyl alcohol, and ketones such as acetone. In this application, water is most preferably used.

  Various reducing agents can be applied as the reducing agent depending on the type of metal salt used, the metal species, and the reducing conditions. For example, organic reducing agents such as alcohols, formic acid, aldehydes, and borohydride salts. An inorganic reducing agent, hydrogen, a reducing gas such as carbon monoxide, or the like is applicable. Other specific examples of the reducing agent include molecular hydrogen, yellow phosphorus, hydrazine, sodium tetrahydroborate, sodium citrate, tannic acid, sodium bisulfite, and the like. Instead of reduction with the reducing agent, reduction by light irradiation or ultrasonic irradiation is also possible.

  In addition to the method of reducing with a reducing agent, a method of electrochemical reduction can also be used. That is, a method of supporting the carrier surface by electrolysis or migration of the charged catalyst component precursor at a potential lower than the reduction potential of the metal salt in a state where the metal salt is dissolved or dispersed in the liquid phase is also exemplified.

  The catalyst colloid solution is a solution in which nano-sized catalyst components are uniformly dispersed in the solution. As a method for preparing the catalyst colloid solution, a known technique may be used as appropriate. For example, in a solution containing a salt containing an element of a catalyst component that is reduced to become colloidal particles (hereinafter also simply referred to as “catalyst salt”) It can be obtained by adding a reducing agent or the like.

  Note that the concentration of the catalyst salt in the solution containing the catalyst salt is not particularly limited and may be any saturation concentration or less. However, since it is necessary to repeat the above steps until the desired loading is achieved at low concentrations, the necessary concentration may be determined as appropriate. Moreover, what is necessary is just to determine suitably as addition amount of the carbon containing electroconductive material added to the solution containing a catalyst salt so that a desired electrode catalyst may be obtained.

  In addition to the reducing agent, a colloid stabilizer or the like may be added to the catalyst colloid solution. The colloid stabilizer is not particularly limited as long as it has a protective colloid action. Preferred examples thereof include poly (N-vinyl-2-pyrrolidone), polyvinyl alcohol, N-vinyl-2-pyrrolidone and acrylamide. Alternatively, a copolymer with methyl acrylate, poly (methyl vinyl ether), gelatin, sodium caseinate, gum arabic, and the like can be given.

  By adding a carbon-containing conductive material to the catalyst component colloid solution and setting an appropriate temperature and pH, the catalyst component can be adsorbed and supported on the surface of the carbon-containing conductive material. The conditions vary depending on the type of catalyst component used, the type of carbon-containing conductive material, and the type of solution, but it is preferable to adjust the temperature appropriately in the range of 10 to 40 ° C. and the pH of 2 to 10. If it is the temperature of this range, it will become a desirable range, without worrying that adsorption | suction is accelerated | stimulated because it is too high, and there is no fear that the solution will freeze. Further, if the pH is within the above range, the catalyst component is likely to be adsorbed on the carrier, and the catalyst component in the solution is less likely to be degraded or aggregated.

  The form of the catalyst component supported on the surface of the carbon-containing conductive material is not particularly limited, and a catalyst component precursor such as a hydroxide of the catalyst component may be supported on the surface of the carbon-containing conductive material.

  The amount of the reducing agent and colloid stabilizer added to the solution containing the catalyst salt and the amount of the carbon-containing conductive material added to the catalyst component colloid solution are appropriately determined so that the desired electrode catalyst can be obtained. Just decide.

  After the catalyst component is adsorbed and supported in this manner, if the catalyst colloid solution does not contain a substance that inhibits the catalytic activity, the electrode catalyst of the present invention can be obtained only through the filtration and drying steps. I can do it. The drying method may be performed in the same manner as described in the impregnation method described above.

  The method for producing an electrode catalyst according to the present invention comprises a step (I) of heat-treating in an inert gas atmosphere during the step (A) of applying a heat treatment after supporting the catalyst component on a carbon-containing conductive material, a reducing property. It is preferable to include at least one stage selected from the group consisting of the step (II) of heat treatment under a gas atmosphere and the step (III) of heat treatment under an oxidizing gas atmosphere.

  Not only is it difficult to reduce the ratio between the particle size of the catalyst component and the average particle size to 0.3 or less by only the method of supporting the catalyst component on the above-mentioned various carbon-containing conductive materials, but it is also practically high elution. I cannot gain resistance. By applying a predetermined heat treatment in an inert gas, an oxidizing gas, or a reducing gas, particles that are too small relative to the average can be adjusted in particle size by sintering, and high elution resistance can be obtained.

It is preferable that the temperature of the process (I) heat-processed in the inert gas atmosphere which concerns on this invention, and the process (II) heat-processed in a reducing gas atmosphere is 300-1200 degreeC.
If the heat treatment is lower than 300 ° C., the catalyst metal does not calcinate and a catalyst metal that realizes high elution resistance cannot be obtained. On the other hand, if the heat treatment is higher than 1200 ° C., the sintering of the particles is excessive and the desired catalyst metal particle size cannot be obtained. In addition, the temperature of the process (I) heat-processed in the inert gas atmosphere which concerns on this invention, and the process (II) heat-processed in a reducing gas atmosphere becomes like this. More preferably, it is 400-1000 degreeC, More preferably, it is 500-900 degreeC. It is.

The inert gas according to the present invention is one or more selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and nitrogen (N ₂ ). It is preferable that

The reducing component of the reducing gas according to the present invention is hydrogen, the hydrogen concentration is 1 to 100% by volume, and the balance gas is helium (He), neon (Ne), argon (Ar), krypton (Kr), One or more selected from the group consisting of xenon (Xe) and nitrogen (N ₂ ) are preferred.

  It is preferable that the temperature of the process (III) heat-processed in the oxidizing gas atmosphere which concerns on this invention is 500 to 150 degreeC, More preferably, it is 400 to 180 degreeC, More preferably, it is 300 to 200 degreeC .

  If the temperature of the heat treatment in an oxidizing gas atmosphere is 500 ° C. or lower, oxidation (combustion) of the carbon-containing conductive material as a carrier does not proceed, and the catalyst is unlikely to deteriorate. Moreover, if it is 150 degreeC or more, the effect which Pt elution tolerance improves is fully acquired.

The oxidizing component of the oxidizing gas according to the present invention is oxygen, the oxygen concentration is 0.1 to 30% by volume, and the balance gas is helium (He), neon (Ne), argon (Ar), krypton (Kr). ), Xenon (Xe), and nitrogen (N ₂ ).

  3rd invention is the membrane-electrode assembly which has the electrode catalyst manufactured by said 2nd of this invention, and the 1st electrode catalyst of this invention. The “membrane-electrode assembly” in the present specification refers to a polymer electrolyte membrane in which an anode catalyst layer is disposed on one side and a cathode catalyst layer is disposed on the other side.

  The polymer electrolyte membrane used for the membrane-electrode assembly of the present invention is not particularly limited, and examples thereof include a membrane made of the same polymer electrolyte as that used for the electrode catalyst layer. In addition, various Nafion (registered trademark of DuPont) manufactured by DuPont and perfluorosulfonic acid membranes represented by Flemion, ion exchange resins manufactured by Dow Chemical, ethylene-tetrafluoroethylene copolymer resin membrane, trifluoro Fluorine polymer electrolytes such as styrene-based polymer membranes, hydrocarbon-based resin membranes with sulfonic acid groups, etc. A membrane impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, or the like may be used. The polymer electrolyte used for the polymer electrolyte membrane and the polymer electrolyte used for each electrode catalyst layer may be the same or different, but the adhesion between each electrode catalyst layer and the polymer electrolyte membrane From the viewpoint of improving the properties, it is preferable to use the same one.

  The thickness of the polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained membrane / electrode assembly, but is preferably 10 to 75 μm, more preferably 15 to 70 μm, and particularly preferably 20 to 60 μm. . The thickness is preferably 10 μm or more from the viewpoint of strength during film formation and durability during operation of the membrane electrode assembly, and is preferably 75 μm or less from the viewpoint of output characteristics during operation of the membrane electrode assembly.

  The polymer electrolyte membrane includes polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) in addition to the above-described fluorine-based polymer electrolyte and membranes made of hydrocarbon resins having sulfonic acid groups. For example, a porous thin film formed from a material impregnated with an electrolyte component such as phosphoric acid or ionic liquid may be used.

  Next, a preferred embodiment of the method for producing a membrane electrode assembly of the present invention will be described below, and the above membrane electrode assembly will be described. In addition, the following aspects show the preferable aspect of this invention, and the manufacturing method of the membrane electrode assembly of this invention is not limited to the following method.

  The electrode catalyst of the present invention has been described in detail above. For example, in addition to an aqueous catalyst component ion solution such as platinum, a conductive carrier such as carbon black is dispersed with a homogenizer and then reduced and supported. Next, after obtaining a carbon-containing conductive material carrying a heated and dried component, heat treatment is performed in an inert gas, acidic gas, or reducing gas atmosphere. Thereafter, an electrode catalyst in which a catalyst component is supported on a conductive carrier and a proton conductive polymer such as Nafion are added to a solvent such as water or alcohol as necessary to prepare a catalyst slurry.

  The catalyst slurry of the present invention is applied to a transfer mount and dried to form an electrode catalyst layer. In this case, as the transfer mount, a known sheet such as a PTFE (polytetrafluoroethylene) sheet, a PET (polyethylene terephthalate) sheet, or a polyester sheet can be used. The transfer mount is appropriately selected according to the type of catalyst slurry used (particularly, a conductive carrier such as carbon in ink). In the above process, the thickness of the electrode catalyst layer is not particularly limited as long as it can sufficiently exhibit the catalytic action of the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). Thickness can be used. Specifically, the thickness of the electrode catalyst layer is 1 to 50 μm, more preferably 5 to 20 μm.

  The catalyst slurry on the transfer mount is not particularly limited, and a known method such as a screen printing method, a deposition method, or a spray method can be similarly applied. The applied electrode catalyst layer drying conditions are not particularly limited as long as the polar solvent can be completely removed from the electrode catalyst layer. Specifically, the coating layer (electrode catalyst layer) of the catalyst slurry is dried at room temperature to 100 ° C., more preferably 50 to 80 ° C. for 30 to 60 minutes in a vacuum dryer. At this time, if the thickness of the catalyst layer is not sufficient, the coating and drying process is repeated until a desired thickness is obtained. Next, the process proceeds to the following steps.

  That is, after sandwiching the solid polymer electrolyte membrane thus produced, hot pressing is performed on the laminate. At this time, the hot press conditions are not particularly limited as long as the electrode catalyst layer and the solid polymer electrolyte membrane can be joined sufficiently closely, but are 110 to 150 ° C., more preferably 120 to 140 ° C., with respect to the electrode surface. The press pressure is preferably 1 to 5 MPa. Thereby, bondability with a solid polymer electrolyte membrane and an electrode catalyst layer can be improved.

  After hot pressing, the transfer mount is peeled off to obtain a membrane-electrode assembly including the electrode catalyst layer and the solid polymer electrolyte membrane.

  As will be described below, in the method for producing a fuel cell using the membrane-electrode assembly according to the present invention, it is necessary to provide a pair of gas diffusion layers on both sides of the membrane-electrode assembly. This gas diffusion layer is produced by impregnating carbon paper, carbon non-woven fabric or carbon cloth in a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) as necessary, and in the atmosphere or an inert gas such as nitrogen. After drying inside, a gas diffusion layer is prepared.

  Then, the membrane electrode assembly is produced by sandwiching the electrode including the electrode catalyst layer and the solid polymer electrolyte membrane using the two gas diffusion layers produced above.

  In the catalyst slurry of the present invention, the electrode catalyst may be used in any amount as long as it can sufficiently exhibit the desired action, that is, the action of catalyzing the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). , May be used. It is preferable that the electrode catalyst is present in the catalyst slurry in an amount of 5 to 75% by mass, more preferably 10 to 60% by mass.

  The catalyst slurry of the present invention includes a water repellency such as polytetrafluoroethylene, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer, if necessary, in addition to the electrode catalyst, the ion conductive polymer, and the solvent. Polymers, thickeners and the like may be included. Thereby, the water repellency of the obtained electrode catalyst layer can be increased, and water generated at the time of power generation can be quickly discharged.

  The ion conductive polymer in the electrode catalyst layer according to the present invention is not particularly limited, and a known one can be used. Examples thereof include the same materials as those used for the polymer electrolyte membrane, and at least high proton conductivity. Any material can be used. The cathode catalyst (layer) / anode catalyst (layer) (hereinafter, also simply referred to as “catalyst (layer)”) of the present invention includes a polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte that can be used in this case is roughly classified into a fluorine-based electrolyte containing fluorine atoms in the whole or a part of the polymer skeleton and a hydrocarbon-based electrolyte not containing fluorine atoms in the polymer skeleton.

  Specific examples of the fluorine electrolyte include perfluorocarbon sulfonic acids such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), and Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.). Polymer, polytrifluorostyrene sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene Preferred examples include polymers and polyvinylidene fluoride-perfluorocarbon sulfonic acid polymers.

  Specific examples of the hydrocarbon electrolyte include polysulfone sulfonic acid, polyaryl ether ketone sulfonic acid, polybenzimidazole alkyl sulfonic acid, polybenzimidazole alkyl phosphonic acid, polystyrene sulfonic acid, polyether ether ketone sulfonic acid, polyphenyl. A suitable example is sulfonic acid.

  The polymer electrolyte preferably contains a fluorine atom because of its excellent heat resistance and chemical stability. Among them, Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) Fluorine electrolytes such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) are preferred.

  The catalyst component can be supported on the carbon-containing conductive material by a known method. As will be described in the following (Electrocatalyst production method) column, for example, impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method), etc. Known methods can be used.

  In the case where the electrode according to the present invention is used as a membrane-electrode assembly (MEA), the polymer electrolyte used in the polymer electrolyte membrane and the electrode layer may be different, but the contact resistance between the membrane and the electrode, etc. In consideration, it is preferable to use the same one. In addition, when the electrode catalyst according to the present invention is used as a membrane-electrode assembly (MEA), the thickness of the electrode catalyst layer is preferably 1 to 50 μm, more preferably about 5 to 20 μm.

  The polymer electrolyte is preferably coated with an electrode catalyst as a polymer that functions as an adhesive. Thereby, while being able to maintain the structure of an electrode stably, the sufficient three-phase interface where an electrode reaction advances can be ensured, and high catalyst activity can be obtained. Although content of the said ion conductive polymer contained in an electrode is not specifically limited, It is good to set it as 20-60 mass% with respect to the whole quantity of a catalyst component.

  The use of a thickener is effective when the catalyst slurry or the like cannot be successfully applied onto the transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, (EG (ethylene glycol), PVA (polyvinyl alcohol)), and the like. The amount of the thickener added when using the thickener is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 0 to 10 with respect to the total mass of the catalyst slurry. % By mass. Furthermore, the solvent constituting the catalyst slurry used in the present invention is not particularly limited, and ordinary solvents used for forming the catalyst layer can be used in the same manner. Specifically, water, lower alcohols such as cyclohexanol, ethanol and 2-propanol can be used.

  The amount of the solvent used in the present invention is not particularly limited as long as the electrolyte can be completely dissolved, but the electrolyte is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% in the solvent. The amount is such that the concentration becomes mass%. At this time, if the concentration of the electrolyte is 20% by mass or less, it is unlikely that the electrolyte is completely dissolved and colloid is formed. Moreover, since the electric field mass contained in it being 0.1 mass% or more is an appropriate amount, the molecular chains of the electrolyte polymer are entangled well. For this reason, the mechanical strength of the electrode catalyst layer formed is excellent. Moreover, in the catalyst slurry, the concentration of the solid content including the electrode catalyst and the solid polymer electrolyte is preferably 5 to 50% by mass, more preferably about 10 to 40% by mass in the catalyst slurry.

  The catalyst slurry of the present invention may be used for only one or both of the cathode side electrode catalyst layer and the anode side electrode catalyst layer, but the cathode side is particularly affected by changes in the amount of water produced due to output fluctuations. At least the anode-side electrode catalyst layer because there is a high risk that the porous structure of the electrode catalyst layer in the initial state collapses due to changes in dryness and moisture, the porosity decreases, and the amount of reaction gas supplied to the electrode catalyst layer decreases. It is preferable to be used for.

  A fourth invention is a fuel cell using the membrane electrode assembly of the third invention.

The fuel cell using the membrane electrode assembly according to the present invention generally further has a gas diffusion layer as described in detail below. At this time, the gas diffusion layer is It is preferable that the transfer mount is peeled off, and the obtained joined body is further sandwiched between gas diffusion layers so that the electrode catalyst layer and the solid polymer electrolyte membrane are further joined to each electrode catalyst layer. Alternatively, after an electrode catalyst layer is formed on the surface of the gas diffusion layer in advance to produce an electrode catalyst layer-gas diffusion layer assembly, the electrode catalyst layer-gas diffusion layer assembly is solid as described above. It is also preferable to sandwich and bond the polymer electrolyte membrane by hot pressing.
In addition to the hot pressing method, a method of laminating an electrode catalyst layer, a polymer electrolyte membrane, an electrode catalyst layer, and a gas diffusion layer on the gas diffusion layer by sequential coating may be used.

  As a material used for the gas diffusion layer (hereinafter referred to as GDL) according to the present invention, a sheet-like material made of carbon paper, non-woven fabric, carbon woven fabric, paper-like paper body, felt or the like has been proposed. When GDL has excellent electron conductivity, efficient transport of electrons generated by a power generation reaction is achieved, and the performance of the fuel cell is improved. Further, if the GDL has an excellent water repellency, the generated water is efficiently discharged.

  In order to ensure high water repellency, a technique for water repellency treatment of a material constituting the GDL has also been proposed. For example, a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) is impregnated with a material constituting GDL such as carbon paper, and dried in the air or an inert gas such as nitrogen. Depending on the case, the hydrophilization treatment may be performed on the material constituting the GDL.

  In addition, carbon particles and a binder may be disposed on a sheet-like GDL made of carbon paper, nonwoven fabric, carbon fabric, paper-like paper body, felt, etc., and both may be used as a gas diffusion layer. You may use the film itself which consists of particle | grains and a binder as a gas diffusion layer. As a result, since the water repellent material and the carbon particles are uniformly formed on the film itself, the water repellent efficiency is increased as compared with the above application.

Examples of the water repellent material include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polypropylene, polyethylene, and the like. Is mentioned. Of these, fluororesins are preferred because they are excellent in water repellency and corrosion resistance during electrode reaction.
Incidentally, the “binder” refers to a substance having a role of adhesion, and in the examples according to the present invention, a fluororesin having both a role of a binder and a role of water repellency is used, but it is not necessarily limited thereto. Alternatively, the binder and the water repellent material may be mixed and used as independent substances.

  The anode side electrode catalyst layer and the cathode side electrode catalyst layer according to the present invention include a catalyst component, an ion conductive polymer, and a water repellent material.

  The porosity of the electrode catalyst layer is preferably 30 to 70%, more preferably 35 to 50%. If the porosity is 30% or more, gas diffusion is improved, and the cell voltage in the high current region does not decrease. In addition, when the porosity is 70% or less, the strength of the electrode catalyst layer is increased, and the porosity is not easily lowered in the transfer process.

  The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell has been described as an example, but in addition to this, a representative example is an alkaline fuel cell and a phosphoric acid fuel cell. Examples thereof include an acid electrolyte fuel cell, a direct methanol fuel cell, and a micro fuel cell. Among them, a solid polymer electrolyte fuel cell is preferable because it is small in size and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. However, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be particularly preferably used.

  The polymer electrolyte fuel cell is useful not only as a stationary power source but also as a power source for a moving body such as an automobile having a limited mounting space. In particular, moving bodies such as automobiles that are susceptible to corrosion of the carbon support due to the high output voltage required after a relatively long shutdown, and deterioration of the polymer electrolyte due to the high output voltage being taken out during operation. It is particularly preferred to be used as a power source.

  The configuration of the fuel cell is not particularly limited, and a conventionally known technique may be appropriately used. Generally, the fuel cell has a structure in which a membrane electrode assembly is sandwiched between separators.

  The separator can be used without limitation as long as it is conventionally known, such as those made of carbon such as dense carbon graphite and a carbon plate, and those made of metal such as stainless steel. The separator has a function of separating air and fuel gas, and a channel groove for securing the channel may be formed. The thickness and size of the separator, the shape of the flow channel, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Further, in order to prevent the gas supplied to each catalyst layer from leaking to the outside, a gas seal portion may be further provided at a portion where the catalyst layer is not formed on the gasket layer. Examples of the material constituting the gas seal portion include rubber materials such as fluoro rubber, silicon rubber, ethylene propylene rubber (EPDM), polyisobutylene rubber, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoro. Fluorine polymer materials such as propylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and thermoplastic resins such as polyolefin and polyester. The thickness of the gas seal portion may be 2 mm to 50 μm, preferably about 1 mm to 100 μm.

  Furthermore, a stack in which a plurality of membrane electrode assemblies are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples. In the examples, “%” represents a mass percentage unless otherwise specified.

(Production of electrode catalyst)
(A) Pretreatment of carbon-containing conductive material The pretreatment (surface treatment step) of carbon black was performed by appropriately combining the following various corrosion treatments and heat treatment steps. The corrosion treatment and heat treatment steps applied to the examples are as follows.

Surface treatment (I)
Carbon black was immersed in a 40% nitric acid aqueous solution, heated to 60 ° C., and stirred for 24 hours. After heating and stirring, carbon was collected by filtration and washed with pure water until the pH of the filtrate reached 5 or higher.

Corrosion treatment (II)
Carbon black was immersed in a 42% aqueous potassium hydroxide solution, heated to 40 ° C. and stirred for 24 hours. After heating and stirring, carbon was collected by filtration and washed with pure water until the pH of the filtrate was 10 or less.

Surface treatment (III)
Carbon black is placed in a fixed-bed flow type electric furnace, 0.5 g / min water is added to 200 ml / min high-purity argon as a flow gas, and evaporated in the heating section in front of the core, thereby changing the steam-containing gas. Using. The heating rate was 3 ° C./min, the holding temperature was 900 ° C., and the holding time was 2 hours.

Surface treatment (heat treatment (I))
Heat treatment was performed at 1800 ° C. for 30 minutes under a flow of high purity argon gas.

Surface treatment (heat treatment (II))
Heat treatment was performed at 2400 ° C. for 30 minutes under a high purity argon gas flow.
Carbon blacks 1 to 4 shown below were prepared by combining the above various corrosion treatments and heat treatments.

Surface treatment (I) was performed on the surface treatment step Vulcan XC-72 (manufactured by Cabot Corporation: specific surface area of about 250 m ² / g) of carbon black 1. (Surface treatment (heat treatment (I) and (II) are not implemented))
Surface treatment step of carbon black 2 Vulcan XC-72 (manufactured by Cabot: specific surface area of about 250 m ² / g) was subjected to surface treatment (II) and then surface treatment (heat treatment (I)).

Surface treatment process of carbon black 3 Vulcan XC-72 (manufactured by Cabot: specific surface area of about 250 m ² / g) After performing corrosion treatment (III), surface treatment (heat treatment (II)) was performed.

Surface treatment process of carbon black 4 After surface treatment (I) was performed on ketjen black EC (manufactured by ketjen black international Co., Ltd .: specific surface area of about 800 m ² / g), surface treatment (heat treatment (II)) was further performed. .
(B) Loading of catalyst component on carbon-containing conductive material Loading of the catalyst metal component on the carbon black produced in (A) was performed using the following method.

  After thoroughly dispersing in 250 g of chloroplatinic acid aqueous solution containing 0.4% platinum with respect to 1.0 g of each carbon black powder using a homogenizer, 3 g of sodium citrate was added thereto, and the reflux reactor was It was used and heated at 85 ° C. for 6 hours to carry out reduction loading of platinum. And after standing to cool to room temperature, platinum carrying | supported carbon was separated by filtration, and Pt carrying | support carbon powder was obtained by fully wash | cleaning with a pure water. Pt—Co alloy-supported carbon is obtained by impregnating a Pt-supported carbon prepared by the above method with a cobalt component using a predetermined amount of cobalt nitrate aqueous solution and firing (alloying heat treatment) at 800 ° C. for 4 hours in a nitrogen atmosphere. Obtained.

(Production of electrode catalyst layer)
The production of the electrode catalyst layer was performed as follows.
After adding 5 times the amount of purified water to the weight of each catalyst metal-supported carbon material powder, 0.5 times the amount of isopropyl alcohol is added, and further, the Nafion is 0.8 times the weight of Nafion. A solution (containing 5 wt.% Nafion manufactured by Aldrich) was added. The mixed slurry was well dispersed with an ultrasonic homogenizer, followed by addition of a vacuum degassing operation to prepare a catalyst ink. A predetermined amount of catalyst ink is printed on one side of carbon paper (TGP-H-060 manufactured by Toray Industries, Inc.), which is a gas diffusion layer (GDL), and dried at 60 ° C. for 24 hours to produce an electrode layer. did.

(Production of MEA)
For the production of MEA (membrane-electrode assembly), MEA was produced by performing hot pressing at 120 ° C. and 1.2 MPa for 10 minutes with the surface coated with the catalyst aligned with the electrolyte membrane. In all cases, the catalyst of Comparative Example 1 was used as the anode catalyst.
The MEA used in both the comparative example and the example was 0.3 mg for the anode and 0.5 mg for the cathode per 1 cm ^{2 of the} apparent electrode area, and the electrode area was 25 cm ² . In addition, Nafion 112 (thickness: about 50 μm) was used as the electrolyte membrane.

(Single cell evaluation)
A fuel cell single cell was constructed using the produced MEA, and a potential cycle application test simulating power generation load fluctuation was performed by the following method.
Hydrogen was supplied to the anode side of the single fuel cell and nitrogen was supplied to the cathode side. The supply pressure for both gases was atmospheric pressure, the temperature of the fuel cell body was set to 70 ° C., and both gases were humidified to a dew point of 70 ° C., the hydrogen flow rate was 500 ml / min, and the nitrogen flow rate was 100 ml / min. . In this state, a rectangular wave with a potential range of 0.95 V to 0.60 V was applied at intervals of 10 seconds per cycle, and the electrochemical effective surface area (ECA) of Pt before and after 5000 cycles was compared. The Pt average particle size increases as the number of applied potential cycles increases due to repeated elution and reprecipitation of Pt by applying potential cycles. From this, it can be said that the larger the Pt ECA reduction rate, the lower the resistance to Pt elution and the faster the deterioration rate of the electrode performance. The ECA of the cathode was estimated from the hydrogen adsorption wave area by cyclic voltammetry.

Table 1 is a graph showing the results. The carrier carbon of Examples 1 and 2 is carbon black 1, the carrier carbon of Example 3 is carbon black 2, and the carrier carbons of Examples 4 and 6-9 are carbon black. 3. The carrier carbon of Example 5 is carbon black 4, the carrier carbon of Comparative Example 1 is Ketjen Black EC without surface treatment, and the carrier carbon of Comparative Example 2 is Vulcan XC-72 without surface treatment. ing. Compared with the comparative example, it was found that the example had a larger ECA reduction rate, and that the use of the example catalyst can significantly improve the Pt elution resistance, and the electrode performance can be maintained for a long time.
Further, Table 1 shows a comparison of the cathode Pt effective electrode area obtained by cyclic voltammetry before the start / stop test and after the 2000 cycle test. It can be seen that the amount of decrease in the effective electrode area is considerably small. This is consistent with the result of FIG.
From the above, it is considered that the decrease in the effective catalyst surface area could be suppressed because the Pt elution during operation was suppressed by completely reducing the Pt of the cathode at the start-up.

Claims (16)

In an electrode catalyst comprising a catalyst component and a carbon-containing conductive material,
The catalyst component contains at least Pt, and the difference between the N ₂ -BET specific surface area and the CTAB adsorption specific surface area of the carbon-containing conductive material is 100 m ² / g or less.   The catalyst component is represented by a composition formula PtaMb (a + b = 100), and M is one or more elements selected from the group consisting of Co, Cr, Fe, Ni, Ir, Rh, Pd, Ag, and Au. The electrode catalyst according to claim 1, wherein a = 90 to 100 and b = 0 to 10.   The electrode catalyst according to claim 1 or 2, wherein the catalyst component has an average particle size of 2 to 20 nm.   The electrode catalyst according to any one of claims 1 to 3, wherein a ratio between a particle size standard deviation of the catalyst component and an average particle size of the catalyst component is 0.3 or less. In a method for producing an electrode catalyst comprising a carbon-containing conductive material carrying a catalyst component,
Before carrying | supporting a catalyst component on a carbon containing conductive material, the surface treatment process is performed with respect to the said carbon containing conductive material, The manufacturing method of the electrode catalyst characterized by the above-mentioned.   The method for producing an electrode catalyst according to claim 5, further comprising a step (A) of applying a heat treatment after supporting the catalyst component on the carbon-containing conductive material.   The method for producing an electrode catalyst according to claim 5 or 6, wherein the raw material of the catalyst component includes Pt chloride, Pt nitrate, or Pt dinitrodiammine complex salt.   The method for producing an electrode catalyst according to any one of claims 5 to 7, wherein the raw material of the catalyst component is reduced by a reducing agent added in a state dissolved in a liquid phase and supported on a carbon material. In a method for producing an electrode catalyst comprising a carbon-containing conductive material carrying a catalyst component,
During the step (A) of applying a heat treatment after supporting the catalyst component on the carbon-containing conductive material,
Heat treatment under an inert gas atmosphere (I),
9. The method according to claim 5, comprising at least one step selected from the group consisting of a step (II) of heat-treating in a reducing gas atmosphere and a step (III) of heat-treating in an oxidizing gas atmosphere. A method for producing the electrode catalyst according to 1.   10. The method for producing an electrode catalyst according to claim 9, wherein the temperature of the step (I) of heat treatment in an inert gas atmosphere and the step of heat treatment (II) in a reducing gas atmosphere is 300 to 1200 ° C. 10.   The method for producing an electrode catalyst according to claim 9, wherein the temperature of the step (III) of heat treatment in an oxidizing gas atmosphere is 500 ° C. or less. The inert gas is at least one selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and nitrogen (N ₂ ). The method for producing an electrode catalyst according to claim 9 or 10. The reducing component of the reducing gas is hydrogen, the hydrogen concentration is 1 to 100% by volume, and the balance gas is helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe). ) And at least one selected from the group consisting of nitrogen (N ₂ ). The oxidizing component of the oxidizing gas is oxygen, the oxygen concentration is 0.1 to 30% by volume, and the balance gas is helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon. (Xe), and nitrogen (N ₂₎ is one or more selected from, method of producing an electrode catalyst according to claim 9 or 11.   The electrode catalyst obtained by the manufacturing method of Claims 5-14.   The membrane-electrode assembly which has the electrode catalyst of Claims 1-5 and Claim 15.