JP2006086037A - Electrocatalyst for fuel cell and electrocatalyst layer for fuel cell using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrocatalyst for fuel cell which can increase an area of a three layer interface in an electrocatalyst layer. <P>SOLUTION: The problem is solved by the electrocatalyst for the fuel cell in which photocatalyst particle expressing hydrophilic property by being irradiated by light is carried on a conductive carrier in the electrocatalyst for the fuel cell constituted by having catalyst particles carried on the conductive carrier. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrode catalyst for a fuel cell, and more particularly to an electrode catalyst for a fuel cell that can improve the power generation performance of the fuel cell.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, the polymer electrolyte fuel cell is expected as a power source for electric vehicles because it operates at a relatively low temperature.

  The polymer electrolyte fuel cell generally has a structure in which a membrane-electrode assembly (hereinafter also simply referred to as “MEA”) is sandwiched between separators. The MEA is obtained by sandwiching a solid polymer electrolyte membrane between a pair of electrode catalyst layers and a gas diffusion layer.

  The electrode catalyst layer includes at least an electrode catalyst in which catalyst particles are supported on a conductive carrier and a solid polymer electrolyte, and is generally prepared by mixing an electrode catalyst and a solid polymer electrolyte solution. The produced electrode catalyst slurry is applied to a substrate and dried.

  In such a polymer electrolyte fuel cell, the following electrochemical reaction proceeds. First, hydrogen contained in the fuel gas supplied to the anode side is oxidized by the catalyst particles to become protons and electrons. Next, the generated protons pass through the solid polymer electrolyte contained in the anode-side electrode catalyst layer, and further through the solid polymer electrolyte membrane in contact with the anode-side electrode catalyst layer, and reach the cathode-side electrode catalyst layer. Electrons generated in the anode-side electrode catalyst layer include a conductive carrier constituting the electrode catalyst layer, a gas diffusion layer in contact with a different side of the anode-side electrode catalyst layer from the solid polymer electrolyte membrane, and a separator And reaches the cathode-side electrocatalyst layer through an external circuit. The protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water. In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

  A solid polymer electrolyte membrane in a fuel cell does not exhibit high proton conductivity unless it is wet. Therefore, conventionally, means for preventing drying of the solid polymer electrolyte membrane has been used by humidifying the gas supplied to the fuel cell using a gas humidifier or the like. However, under operating conditions such as high current density and high humidification, there is a risk of causing a flooding phenomenon that agglomerates a lot of moisture and closes the pores that have become reaction gas supply paths in the electrode catalyst layer.

  Therefore, Patent Document 1 discloses an electrode catalyst layer including at least an electrode catalyst in which catalyst particles are supported on hydrophilic carbon particles, a solid polymer electrolyte, and a hydrophobic carbon material. As a result, the wet state in the electrode catalyst layer is moderately maintained, and excess generated water can be quickly discharged by the adjacent hydrophobic carbon material.

  In a conventional electrode catalyst, both a cathode and an anode are used in which carbon particles are used as a carrier and platinum or the like is supported thereon as catalyst particles. As the carbon particles in the electrode catalyst, those having a large specific surface area are often used in order to carry finely dispersed catalyst particles in a highly dispersed manner. Thereby, the electrode reaction area of the catalyst particles can be increased, and high catalytic activity can be obtained.

  However, the conductive support in the electrode catalyst may corrode and disappear due to various causes, such as when the cathode-side electrode catalyst layer becomes a noble potential environment (about 0.8 V). The disappearance of the corrosion of the conductive carrier leads to the release and aggregation of the supported catalyst particles, and the electrode reaction area is reduced.

  The polymer electrolyte fuel cell has a problem with the cost, but the life of the cell. Battery life is said to be 5000 hours for automobiles and 40,000 hours for home use, and it is required to maintain desired power generation performance over a long period of time.

Therefore, graphitized carbon particles having improved corrosion resistance by graphitizing the carbon particles used as a conductive carrier by heat treatment or the like to bring the crystal structure closer to the graphite structure is used as the conductive carrier.
JP 2000-243404 A

  In the fuel cell, the electrochemical reaction occurs on a three-phase interface in the electrode catalyst layer where catalyst particles, a solid polymer electrolyte, and a reaction gas exist. Therefore, in order to obtain a fuel cell having high power generation performance, it is extremely important how to make the electrode catalyst and the solid polymer electrolyte in an appropriate state in the electrode catalyst layer to increase the three-layer interface.

  In particular, when graphitized carbon particles that are effective in improving the durability of a fuel cell are used as an electrode catalyst, the affinity between the solid polymer electrolyte and the electrode catalyst is poor, and the area of the three-layer interface may be reduced. Therefore, in order to obtain higher power generation performance, it is necessary to increase the amount of catalyst particles to be used in order to compensate for the reduced utilization rate of catalyst particles such as platinum.

  In general, graphitized carbon particles and the like have a tendency that hydrophilic surface functional groups such as carboxyl groups are reduced by a heat treatment process during production, and the surface of the graphitized carbon particles becomes hydrophobic. On the other hand, in addition to the electrode catalyst, the solid polymer electrolyte constituting the electrode catalyst layer has a hydrophilic group such as a sulfonic acid group. Therefore, when the electrode catalyst layer ink is prepared, the affinity between the electrode catalyst and the solid polymer electrolyte decreases due to the electrode catalyst repelling the solid polymer electrolyte, and as a result, in the produced electrode catalyst layer, It is considered that the three-phase interface decreases.

  Therefore, in order to improve the area of the three-phase interface, the affinity between the solid polymer electrolyte and the electrocatalyst is improved by improving the hydrophilicity of the conductive carrier having a hydrophobic surface such as graphitized carbon particles. A means to make it possible is considered. As a method for hydrophilizing the surface of the conductive carrier, there is a method of forming a hydrophilic monomolecular film on the surface of the conductive carrier as described in Patent Document 1 described above. However, when the conductive carrier according to the above method is used, there is a possibility that the drainage of water from the vicinity of the electrode catalyst is lowered in the electrode catalyst layer during the operation of the fuel cell, resulting in a flooding phenomenon. Therefore, the conventional method has a limit in improving the three-phase interface in the electrode catalyst layer by improving the affinity between the solid polymer electrolyte and the electrode catalyst.

  This invention is made | formed in view of the said situation, and it aims at providing the electrode catalyst for fuel cells which can increase the area of the three-layer interface in an electrode catalyst layer.

  The present invention provides a fuel cell electrode catalyst in which catalyst particles are supported on a conductive support, wherein the photocatalyst particles that exhibit hydrophilicity when irradiated with light are supported on the conductive support. The above problem is solved by the fuel cell electrode catalyst.

  The electrode catalyst of the present invention can temporarily improve the hydrophilicity of the electrode catalyst surface when irradiated with light. If such an electrode catalyst is used, the affinity between the electrode catalyst and the solid polymer electrolyte can be increased, the three-layer interface in the electrode catalyst layer can be increased, and the power generation performance can be improved.

  The first aspect of the present invention is that, as described above, in the electrode catalyst for a fuel cell in which catalyst particles are supported on a conductive carrier, the photocatalyst particles that exhibit hydrophilicity when irradiated with light are formed on the conductive carrier. A fuel cell electrode catalyst (hereinafter, also simply referred to as “electrode catalyst”) characterized by being supported.

  The photocatalyst particles exhibit hydrophilicity when irradiated with light having a wavelength having energy greater than or equal to the band gap. In general, how much a substance repels water is determined by a contact angle between a water droplet and the substance surface. The photocatalyst particles have a contact angle with water of several tens of degrees or more before the light irradiation, but after the light irradiation, the contact angle with the water decreases and finally becomes almost 0 degrees to completely repel water. Eliminates and temporarily develops high hydrophilicity.

  When the photocatalyst particles are used as an electrode catalyst, the hydrophilicity of the electrode catalyst surface can be improved by irradiation with light, and the affinity with the solid polymer electrolyte can be increased. In addition, by supporting the catalyst particles and the photocatalyst particles on the conductive support, the photocatalyst particles are present near the catalyst particles, and the functional groups responsible for proton conductivity such as sulfonic acid groups of the solid polymer electrolyte are catalyzed. It becomes possible to arrange | position around a particle | grain and can form a three-phase interface in a more suitable state. Therefore, as shown in FIG. 1, according to the electrode catalyst of the present invention in which the catalyst particles 102 and the photocatalyst particles 103 are supported on the conductive carrier 101, the light is irradiated when the electrode catalyst ink is prepared. Thus, the degree of contact between the electrode catalyst and the solid polymer electrolyte 104 can be increased, and an electrode catalyst layer with an increased amount of three-phase interface can be provided.

  Furthermore, the hydrophilicity by the photocatalyst particles returns to the original after a certain time. Therefore, according to the electrode catalyst of the present invention using such photocatalyst particles, the area of the three-phase interface having a suitable state can be increased without hindering the drainage of the electrode catalyst layer during operation of the fuel cell. Is possible.

  Hereinafter, the electrode catalyst of the present invention will be described more specifically.

  As the photocatalyst particles used in the electrode catalyst of the present invention, it is preferable to use particles that can maintain the hydrophilicity that is developed when irradiated with light for several hours to several tens of hours, preferably 3 to 24 hours. As a result, it is possible to maintain a state in which the hydrophilicity of the electrode catalyst surface is increased, and light irradiation is performed once in the electrode catalyst ink preparation step without continuing to irradiate light in the electrode catalyst ink preparation step. Just to get better.

  In addition, in the electrode catalyst of the present invention, the fact that the hydrophilicity developed by irradiation with light can be maintained for a predetermined time means that the state where the contact angle is 10 degrees or less can be maintained for several hours to several tens of hours. .

Examples of the photocatalyst include oxide semiconductors, organic polymer semiconductors, and metal complexes. Among these, an oxide semiconductor having characteristics as an optical semiconductor is preferable because of its high hydrophilicity and chemical stability. Although it does not specifically limit as said oxide semiconductor, The thing which consists of an oxide semiconductor in any one of an alkali metal, alkaline-earth metal, a transition metal, noble metals, and rare earths can be used. More specifically, in addition to TiO ₂ , SrTiO ₂ , Al ₂ O ₃ , WO ₃ , BiYO ₃ , Fe ₂ O ₃ , Cu ₂ O, NiO, ZnO, SnO ₂ , NaTaO ₃ , InTaO ₄ , Nb ₂ O ₅ , CdS, ZrO ₂ , KTaO ₃ , CdSe, and the like, and a composite compound containing an N atom or an S atom in these compositions may be used. Moreover, these may be used independently and may be used in mixture of 2 or more types, as long as the effect of other photocatalyst particles is not impaired.

As the photocatalyst particles, titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), tungsten oxide (WO ₃ ), and tin oxide (SnO ₂ ) are particularly preferable because of their high hydrophilicity that is expressed upon light irradiation. Preferably mentioned, More preferably, a titanium oxide is mentioned. Although titanium oxide may be amorphous, it may have anatase type, rutile type, or industrially produced brookite type crystal structure, but it can form a suitable three-phase interface. It is preferable to have.

  In the electrode catalyst of the present invention, the average particle size of the photocatalyst particles is preferably 1 to 30 nm, more preferably 1 to 10 nm. If the average particle size is less than 1 nm, the desired effect of the photocatalyst particles may not be obtained, and if it exceeds 30 nm, the contact degree between the catalyst particles and the solid polymer electrolyte may be reduced.

  In the electrode catalyst of the present invention, the supported amount of the photocatalyst particles is preferably 1 to 30% by mass, more preferably 5 to 10% by mass, based on the total amount of the electrode catalyst. If the supported amount is less than 1% by mass, the desired effect of the photocatalyst particles may not be obtained, and if it exceeds 30% by mass, the contact degree between the catalyst particles and the solid polymer electrolyte may be reduced. is there.

  As a light source for expressing hydrophilicity by the photocatalyst particles, sunlight, indoor lighting, fluorescent lamps and the like cannot exhibit high hydrophilicity, and the effects of the present invention may not be sufficiently obtained. Therefore, it is preferable that high hydrophilicity is expressed by irradiating photocatalyst particles with strong ultraviolet rays using a black light lamp, a xenon lamp, a high pressure sodium lamp, a metal halide lamp, a BLB lamp, a germicidal lamp, or the like.

Illuminance of the excitation light, ultraviolet rays UV-A region of 380nm or less of the wavelength in the electrode catalyst surface, preferably 50~1500μW / cm ^2, more preferably to irradiate 500~1000μW / cm ^2.

  Next, as the conductive carrier used in the electrode catalyst of the present invention, graphitized carbon particles obtained by graphitizing carbon particles by heat treatment or the like are preferably used. Thereby, it can be set as the electrode catalyst excellent in durability and water repellency. The heat treatment is preferably performed at 2000 ° C. or higher, particularly 2500 ° C. or higher in an inert atmosphere such as nitrogen, helium, or argon. Although the surface of the graphitized carbon particles has hydrophobicity, as described above, according to the present invention, the contact degree of the three-phase interface in the electrode catalyst can be increased even if the graphitized carbon particles are used.

  In the present invention, the conductive carrier is not limited to the graphitized carbon particles, and other than that, carbon particles that have not been graphitized, carboxyl groups that exist on the surface of the carbon particles by heat treatment in an inert atmosphere, etc. As long as it is conventionally used as a conductive carrier in an electrode catalyst, such as hydrophobic carbon particles whose surface has been modified to be hydrophobic by reducing the number of hydrophilic groups, it can be used without particular limitation. Even when these carbon particles are used, the three-phase interface in the electrode catalyst layer can be further improved.

  The carbon particles used in the conductive carrier are not particularly limited, but the main components include carbon black such as channel black, furnace black, and thermal black, and activated carbon obtained by carbonizing and activating various carbon atom-containing materials. What is carbon is mentioned preferably.

  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 contained in order to improve the properties of the electrode catalyst. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.

  Specific examples of the conductive carrier include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite, and the like. Can do.

  Commercially available products can be used as the carbon particles, such as Cabot Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Legal 400, Ketjen Black EC manufactured by Lion. Oil furnace black such as # 3150 and # 3250 manufactured by Mitsubishi Chemical Corporation; acetylene black such as Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd. and the like.

The specific surface area of the conductive carrier is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. The specific surface area, 20 m 2 / dispersibility of catalyst particles and a solid polymer electrolyte of ^g less than the that to the conductive support is lowered there is a possibility that sufficient power generation performance is obtained, a 1600 m 2 / ^g When it exceeds, there exists a possibility that the effective utilization factor of a catalyst particle and a solid polymer electrolyte may fall on the contrary.

  The size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the thickness of the electrode catalyst layer within an appropriate range, the average particle diameter is 5 to 200 nm, preferably about 10 to 100 nm. Is good.

  Next, the catalyst particles used in the electrode catalyst of the present invention may be those having a catalytic action for hydrogen oxidation reaction or oxygen reduction reaction, and those containing at least one of platinum, iridium, and palladium. preferable. Further, in order to improve the poisoning resistance, heat resistance, etc. with respect to carbon monoxide or the like, an alloy of platinum and other metals may be used. Specifically, the alloy is at least one selected from ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum. And an alloy of platinum and platinum.

  The average particle diameter of the catalyst particles is preferably 1 to 30 nm. Although it is speculated that the catalyst activity of the catalyst particles increases as the particle size decreases, the catalyst activity also improves. In fact, even if the particle size of the catalyst particles is extremely small, the catalyst activity commensurate with the increase in the specific surface area is not. Since it may not be obtained, the above range is preferable.

  In the present invention, the average particle diameter of the above-described photocatalyst particles and catalyst particles can be measured using a known method, for example, photocatalyst particles or catalyst particle diameters observed using a transmission electron microscope, Or it can obtain | require from the average value etc. of the crystallite diameter calculated | required from the half value width of the diffraction peak of the catalyst particle in X-ray diffraction.

  The supported amount of catalyst particles in the electrode catalyst of the present invention is 5 to 80% by mass, preferably 10 to 60% by mass, based on the total amount of the electrode catalyst. When the supported amount is less than 5% by mass, the amount of the electrode catalyst may be increased in order to obtain a desired catalytic activity. As a result, the electrode becomes thick, and there is a possibility that the battery performance may be deteriorated due to an increase in internal resistance or diffusion resistance of the reactant. On the other hand, when the amount exceeds 80% by mass, the overlapping of the catalyst particles supported on the surface of the conductive support increases, and the catalytic activity obtained with respect to the amount of catalyst particles used decreases, which may increase the cost. There is.

  In the present invention, the photocatalyst particles and the supported amount of the catalyst particles can be confirmed by ICP (inductively coupled plasma emission spectroscopy) or the like.

  The second of the present invention is a fuel cell electrode catalyst layer (hereinafter, also simply referred to as “electrode catalyst layer”) using the first electrode catalyst of the present invention. As described above, according to the electrode catalyst of the present invention, the hydrophilicity of the electrode catalyst surface can be improved by using the photocatalyst particles, and the area of the three-layer interface having a suitable state can be increased. An electrode catalyst layer having excellent power generation performance can be provided. In addition, since the high hydrophilicity due to the photocatalyst particles is temporarily improved, the hydrophilicity only has to be expressed at the time of preparation of the electrode catalyst ink. At the time of power generation, the hydrophilicity of the photocatalyst particles returns to before the light irradiation, and flooding occurs. There is no risk of incurring phenomena. Therefore, high power generation performance can be exhibited even under operating conditions where a large amount of generated water such as high humidification and high current density can be generated.

  The electrode catalyst layer of the present invention includes at least the electrode catalyst in which catalyst particles and photocatalyst particles are supported on a conductive carrier, and a solid polymer electrolyte.

  Since the electrode catalyst is the same as that of the first aspect of the present invention, detailed description thereof is omitted here.

  The solid polymer electrolyte is not particularly limited, and a known one can be used as long as it is a member having at least high proton conductivity. Specifically, a perfluorocarbon polymer having a sulfonic acid group such as Nafion (registered trademark), an inorganic acid such as phosphoric acid doped into a hydrocarbon polymer compound, a part of which is a proton conductive functional group And an organic / inorganic hybrid polymer substituted with a proton conductor in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution.

In the electrode catalyst layer, the mass of the catalyst particles per unit area is about 0.01 to 1.0 mg / cm ² , preferably about 0.05 to 0.35 mg / cm ² . According to the present invention, an electrode catalyst layer in which the amount of catalyst particles in the electrode catalyst layer has at least high power generation performance can be obtained.

Here, the area in “per unit area” in the electrode catalyst layer means the area of the surface of the electrode catalyst layer that contacts the solid polymer electrolyte membrane. Therefore, the “mass of catalyst particles per unit area” in the electrode catalyst layer means the amount (g) of catalyst particles contained in the electrode catalyst layer by the area (cm ² ) of the electrode catalyst layer on the solid polymer electrolyte membrane. The divided value.

  The thickness of the electrode catalyst layer may be appropriately determined so as to obtain an electrode catalyst layer having desired performance, but is preferably 1 to 40 μm, more preferably 2 to 15 μm. If the thickness is less than 1 μm, uniform film formation may be difficult and a desired function may not be obtained. If the thickness is more than 40 μm, not only the flooding phenomenon is likely to occur, but also gas diffusibility and electrical resistance are reduced. Is also undesirable.

  Since the electrode catalyst according to the present invention and the electrode catalyst layer using the electrode catalyst have the above-described various characteristics, the MEA having excellent power generation performance can be obtained by using as the MEA.

  The basic configuration of the MEA is not particularly limited, and any conventional configuration may be used. That is, the cathode-side electrode catalyst layer and the anode-side electrode catalyst layer are disposed so as to face both surfaces of the solid polymer electrolyte membrane, and are further sandwiched between the gas diffusion layers.

  The electrode catalyst of the present invention and the electrode catalyst layer using the electrode catalyst may be used for at least one of the anode side electrode catalyst layer and the cathode side electrode catalyst layer, but the cathode side electrode is required because the required amount of the three-phase interface is large. It is preferable to use it for the catalyst layer. When the electrode catalyst layer according to the present invention is used only for the cathode-side electrode catalyst layer, the anode-side electrode catalyst layer may be a conventional one containing at least a solid polymer electrolyte and an electrode catalyst.

  The solid polymer electrolyte membrane used in the MEA of the present invention is not particularly limited, and examples thereof include a membrane made of the same solid polymer electrolyte as that used for the electrode catalyst layer. In addition, perfluorosulfonic acid membranes represented by various Nafion (registered trademark) and Flemion (registered trademark) manufactured by DuPont, ion exchange resins, ethylene-tetrafluoroethylene copolymer resin membranes manufactured by Dow Chemical Company, Fluoropolymer electrolytes such as resin membranes based on trifluorostyrene, and hydrocarbon polymer resin membranes with sulfonic acid groups, such as solid polymer electrolyte membranes that are generally commercially available, polymer microporous A membrane in which a membrane is 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 solid polymer electrolyte used for the solid polymer electrolyte membrane and the solid polymer electrolyte used for the electrode catalyst layer may be the same or different, but the electrode catalyst layer and the solid polymer electrolyte membrane From the viewpoint of improving the adhesiveness, it is preferable to use the same one.

  The thickness of the solid polymer electrolyte membrane may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 150 μm. From the viewpoint of strength during film formation and durability during MEA operation, it is preferably 5 μm or more, and from the viewpoint of output characteristics during MEA operation, it is preferably 300 μm or less.

  The gas diffusion layer used in the MEA of the present invention is not particularly limited, and is based on a sheet-like material having conductivity and porosity, such as carbon woven fabric, paper-like papermaking body, felt, and non-woven fabric. Is mentioned.

  The thickness of the gas diffusion layer may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness is less than 30 μm, sufficient mechanical strength or the like may not be obtained, and if it exceeds 500 μm, the distance through which gas or water permeates is undesirably increased.

  The gas diffusion layer preferably contains a water repellent in the base material in order to further improve water repellency and prevent a flooding phenomenon. Although it does not specifically limit as said water repellent, It is fluorine-type, such as a polytetrafluoroethylene (PTFE), a polyvinylidene fluoride (PVDF), a polyhexafluoropropylene, a tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples thereof include polymer materials, polypropylene, and polyethylene.

  Moreover, in order to improve water repellency more, the said gas diffusion layer may have a carbon particle layer which consists of an aggregate | assembly of the carbon particle containing a water repellent on the said base material.

  The carbon particles are not particularly limited, and may be conventional ones such as carbon black, graphite, and expanded graphite. Of these, carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are preferred because of their excellent electron conductivity and large specific surface area.

  The particle size of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with an electrode catalyst layer.

  Examples of the water repellent used for the carbon particle layer include the same water repellents as those described above used for the substrate. Of these, fluorine-based polymer materials are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction.

  In the carbon particle layer, the mixing ratio between the carbon particles and the water repellent may be insufficient to obtain the water repellency as expected when the carbon particles are too much. There is a risk that it will not be obtained. Considering these, the mixing ratio of the carbon particles and the water repellent in the carbon particle layer is preferably about 90:10 to 40:60 in terms of mass ratio.

  The thickness of the carbon particle layer may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer.

  The electrode catalyst described above, and the electrode catalyst layer and MEA using the electrode catalyst have high power generation performance by forming many three-layer interfaces in a suitable state. Therefore, by using these for a fuel cell, it is possible to provide a fuel cell with excellent power generation performance. 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. However, in addition to the above, a phosphoric acid fuel cell, a direct methanol fuel cell, etc. Is mentioned. Among these, the formation of a three-phase interface greatly affects the performance, and therefore a polymer electrolyte fuel cell is preferred. The fuel cell is useful as a power source for a moving body such as a vehicle having a limited mounting space in addition to a stationary power source.

  The configuration of the fuel cell is not particularly limited, and a conventionally known technique may be used as appropriate. Generally, the fuel cell has a structure in which an MEA is sandwiched between separators.

  A fuel cell according to the present invention having a preferred embodiment will now be described with reference to FIG. In FIG. 2, a polymer electrolyte fuel cell 260 includes an anode side electrode catalyst layer 220a and an anode side gas diffusion layer 230a, a cathode side electrode catalyst layer 220b and a cathode side gas diffusion layer on both sides of the solid polymer electrolyte membrane 210. 230b has an MEA 200 disposed so as to face each other, and the MEA 200 is further sandwiched between an anode side separator 250a and a cathode side separator 250b. The fuel gas and the oxidant gas supplied to the MEA are supplied to the anode side separator 250a and the cathode side separator 250b through gas supply grooves 251a and 251b provided at a plurality of locations, respectively.

  As the separator for sandwiching the MEA, any conventionally known separator such as a carbon made of dense carbon graphite, a carbon plate, or a metal such as stainless steel can be used without limitation. 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 and the like, the shape of the channel groove, and the like are not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Furthermore, a stack in which a plurality of MEAs 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.

  3rd of this invention is a manufacturing method of the 1st electrode catalyst of this invention mentioned above. The order in which the catalyst particles and the photocatalyst particles are supported on the conductive carrier is not particularly limited. For example, (1) after the catalyst particles are supported on the conductive carrier, light is irradiated to express hydrophilicity. And a method of supporting the photocatalyst particles, and (2) a method of supporting the catalyst particles after supporting the photocatalyst particles exhibiting hydrophilicity by irradiating the conductive carrier with light. As a result, the catalyst particles and the photocatalyst particles can be supported close to each other, and in the production of the electrode catalyst layer, a large number of sulfonic acid groups and the like responsible for proton conductivity of the solid polymer electrolyte are arranged around the catalyst particles. Can do. Among these, the method (1) is preferably used because the catalyst particles can be highly dispersed and supported.

  As the catalyst particle loading method, known methods such as impregnation method, liquid phase reduction loading method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) and the like are used without particular limitation.

  For example, as a method of supporting the catalyst particles on the conductive support using the liquid phase reduction support method, there may be mentioned a method of adding a reducing agent after adding the conductive support to the catalyst particle solution.

  The catalyst particle solution is a solution containing an element of catalyst particles. Examples of the catalyst particles include at least one selected from Pt, Ir, and Pd because of high catalytic activity. Specific examples of the catalyst particle solution include, for example, when Pt is used as the catalyst particles, chloroplatinic acid, platinum chloride, dinitrodiammine platinum; iridium chloride when iridium is used, and the like when palladium is used. Is a solution in which a compound containing elements of desired catalyst particles 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 does not specifically limit as an organic solvent, Ethanol, methanol, propanol, etc. are mentioned, These may be used individually by 1 type and may be used in mixture of 2 or more types.

  After adding a conductive carrier to the catalyst particle solution, it may be sufficiently dispersed by an appropriate dispersing means such as a homogenizer or an ultrasonic dispersing device, and these dispersing means may be appropriately combined.

  Next, the reducing agent added to the resulting mixture is not particularly limited as long as it can reduce the catalyst compound. For example, sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, borohydride Sodium, hydrazine, formaldehyde, methanol, ethanol, hydrogen, ethylene, carbon monoxide and the like can be mentioned. The amount of the reducing agent added to the catalyst particle solution is not particularly limited, and may be determined by appropriately adjusting. After the reducing agent is added to the mixed solution, it may be heated to 20 to 100 ° C. using a reflux reactor or the like to carry out reduction loading of catalyst particles such as platinum.

  Then, the electrode catalyst of the present invention can be obtained by filtering the mixed solution using a known means such as a separating means such as suction filtration and drying the obtained precipitate. The drying method 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.

  After drying, further baking may be performed, or only baking may be performed without going through a drying step. Although it does not specifically limit as baking conditions performed as needed, In air, nitrogen atmosphere, inert gas atmospheres, such as argon atmosphere, or reducing atmosphere containing flammable gas like hydrogen, 300- What is necessary is just to carry out at 1000 degreeC for about 1 to 6 hours.

  Next, as a method for supporting the photocatalyst particles on the conductive support, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, metal alkoxide hydrolysis method, reverse micelle (microemulsion method) and the like are available. It is used without particular limitation.

  For example, as a method for supporting photocatalyst particles on a conductive support using a hydrolysis method of metal alkoxide, a metal alkoxide solution in which a metal alkoxide constituting photocatalyst particles is dissolved in a solvent such as an organic solvent or water is used. After the carrier is immersed and impregnated for a certain period of time, the conductive carrier is separated by filtration, centrifugation, or the like. Thereafter, a method of hydrolyzing the metal alkoxide by air drying or performing steam treatment as necessary, followed by drying and firing, and the like can be mentioned.

  The photocatalyst particles are as described above in the first aspect of the present invention, and preferred examples include titanium oxide, zirconium oxide, tungsten oxide, and tin oxide. In the case of titanium oxide, examples of the metal alkoxide include titanium isopropoxide, titanium tetramethoxide, titanium tetraethoxide, titanium tetranormal propoxide, titanium tetraisopropoxide, titanium tetranormal butoxide, titanium tetraisobutoxide, and titanium tetraoxide. Tertiary butoxide, traisopropyl titanate, tetrabutyl titanate, diisopropoxybis (ethylacetoacetate) titanium, diisopropoxybis (acetylacetate) titanium and the like can be used. In addition to the metal alkoxide, titanyl sulfate, titanium tetrachloride, titanium peroxide, titanium nitrate, and the like are used in the same manner. However, metal alkoxide is preferably used because it hydrolyzes easily.

  Examples of the organic solvent used in the metal alkoxide solution include methanol, ethanol, isopropyl alcohol (IPA), normal propanol, n-butanol, etc. as lower aliphatic alcohols, ethylene glycol, ethylene glycol monobutyl ether, etc. as ethylene glycol derivatives. As the diethylene glycol derivative, diethylene glycol, diethylene glycol monobutyl ether or the like can be used.

The firing condition is not particularly limited, but is 200 to 600 ° C. in an atmosphere, an inert gas atmosphere such as a nitrogen atmosphere or an argon atmosphere, or a reducing atmosphere containing a combustible gas such as hydrogen. It may be performed for about 6 hours. If the calcining temperature is less than 200 ° C., the crystallinity may not be sufficiently increased. If the calcining temperature is higher than 600 ° C., the specific surface area may be decreased, and the hydrophilicity may be decreased.

  Further, the average particle diameter, supported amount, etc. of the conductive carrier, the catalyst particles, and the photocatalyst particles are as described above in the first of the present invention, and are prepared so as to obtain an electrode catalyst having desired characteristics. An electrode catalyst may be prepared.

  Next, the 4th of this invention is a manufacturing method of the electrode catalyst layer using the 1st electrode catalyst of this invention. That is, in the method for producing an electrode catalyst layer comprising the steps of dispersing an electrode catalyst in a solid polymer electrolyte solution to prepare an electrode catalyst ink and applying the electrode catalyst ink to a substrate, the electrode catalyst for fuel cells and / or It is a manufacturing method of the electrode catalyst layer including the process of irradiating the said electrode catalyst ink with light.

  The above-mentioned solid polymer electrolyte solution is a solution obtained by mixing a solid polymer electrolyte with water or an alcohol solvent, and can be used without particular limitation as long as it is generally used conventionally. Further, since the solid polymer electrolyte and the electrode catalyst are as described above, detailed description thereof is omitted here.

  The hydrophilicity of the photocatalyst can be expressed by irradiating the electrode catalyst with light. In the method of the present invention, the hydrophilicity due to the photocatalyst only has to be expressed only in the preparation step of the catalyst electrode catalyst ink. Since the hydrophilicity due to the photocatalyst is restored after a certain period of time, there is no possibility of causing a flooding phenomenon due to the photocatalyst when the produced electrode catalyst layer is generated.

  Therefore, light irradiation to the electrode catalyst can be performed by (1) irradiating the electrode catalyst with light before preparing the electrode catalyst ink, or (2) an electrode obtained by mixing the electrode catalyst and the solid polymer electrolyte solution. The catalyst ink is preferably irradiated with light. You may perform light irradiation to an electrode catalyst by both said (1) and (2). If a photocatalyst capable of developing hydrophilicity for several hours to several tens of hours after light irradiation is used, light irradiation to the electrode catalyst may be performed only in the above (1). In the case of (2), it is preferable to perform light irradiation while mixing the electrode catalyst ink.

  As a light source for expressing hydrophilicity by the photocatalyst particles, sunlight, indoor lighting, fluorescent lamps and the like cannot exhibit high hydrophilicity, and the effects of the present invention may not be sufficiently obtained. Therefore, it is preferable that high hydrophilicity is expressed by irradiating photocatalyst particles with strong ultraviolet rays using a black light lamp, a xenon lamp, a high pressure sodium lamp, a metal halide lamp, a BLB lamp, a germicidal lamp, or the like.

The illuminance of the excitation light is not particularly limited, in the electrode catalyst surface, so that ultraviolet rays UV-A region of a wavelength 380nm becomes preferably 50~1500μW / cm ^2, more preferably the 500~1000μW / cm ² It is good to make it. Thereby, high hydrophilicity due to the photocatalyst particles can be expressed. Moreover, what is necessary is just to determine suitably irradiation time etc. so that the hydrophilicity after light irradiation may be hold | maintained only while desired.

  In addition to the solid polymer electrolyte membrane, the electrode catalyst ink is applied on a base material such as a gas diffusion layer or a PTFE sheet, and then dried to obtain an electrode catalyst layer.

  In addition, as a method for producing MEA, a conventionally known method such as a method in which an electrode catalyst layer is produced on both sides of a solid polymer electrolyte membrane and this is sandwiched between gas diffusion layers and then hot-pressed is used as appropriate. Can do. At this time, the method for producing the electrode catalyst layer described above may be used for at least one of the cathode side electrode catalyst layer and the anode side electrode catalyst layer. In addition, for example, when an electrode catalyst layer is formed only on the cathode side electrode catalyst layer by the method of the present invention, the anode side electrode catalyst layer may be formed using a conventional general method.

  The hot pressing is preferably performed at 110 to 170 ° C. and a pressing pressure of 1 to 5 MPa with respect to the electrode surface. Thereby, the bondability between the solid polymer electrolyte membrane and each electrode catalyst layer can be enhanced. When an electrode catalyst layer produced on a substrate such as a PTFE sheet is used, the PTFE sheet may be peeled off after hot pressing, and then a gas diffusion layer may be disposed.

  Moreover, what is necessary is just to perform using a general water-repellent processing method, when making a gas diffusion layer used for MEA contain a water-repellent agent. For example, after immersing the base material used for a gas diffusion layer in the dispersion liquid of a water repellent agent, the method of heat-drying with oven etc. is mentioned.

  When the carbon particle layer is formed on the substrate in the gas diffusion layer, the carbon particles, the water-repellent polymer, and the like are used as a solvent such as water, alcohol solvents such as perfluorobenzene, dichloropentafluoropropane, methanol, and ethanol. A slurry is prepared by dispersing in, and the slurry is applied on a substrate and dried, or the slurry is dried and pulverized to form a powder, and this is applied onto the gas diffusion layer, etc. May be used. Then, it is preferable to heat-process at about 300-400 degreeC using a muffle furnace or a baking furnace.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited only to the following Example.

<Example 1>
1. Production of cathode-side electrode catalyst layer (1) Production of electrode catalyst Titanium isopropoxide dissolved in Pt-supported graphitized carbon catalyst (platinum average particle diameter 5 nm, platinum-supported amount 50 wt%) and ethanol: Ti (O-i- C ₃ H ₇ ) ₄ (manufactured by Aldrich) was mixed and held for 2 hours with stirring, then the Pt-supported graphitized carbon catalyst was filtered, thoroughly washed with distilled water at about 70 ° C., and dried at 110 ° C. As a result, a platinum / titanium oxide-supported graphitized carbon catalyst (titanium oxide: average particle diameter 3 nm, supported amount 5 wt%, crystal structure anatase type) having titanium oxide supported on the surface as a photocatalyst was obtained.

(2) Preparation of cathode-side electrode catalyst ink The platinum / titanium oxide-supported graphitized carbon catalyst prepared in (1), a Nafion solution (manufactured by Du Pont) containing 5 wt% Nafion (registered trademark), water, IPA Are mixed so as to have a mass ratio of 1: 0.5: 2.5: 1, and light having an illuminance in the UV-A region of 500 μW / cm ² by a black light (Eishin Chemical Co., Ltd., UV minilight). Were continuously stirred for 3 hours while stirring and pulverizing with a homogenizer for fine pulverization, to obtain a cathode side electrode catalyst ink.

(3) Application of cathode-side electrode catalyst ink The obtained cathode-side electrode catalyst ink was applied onto a Teflon (registered trademark) sheet having a thickness of 0.2 mm using a screen printer, and dried, whereby a cathode-side electrode catalyst ink was applied. A catalyst layer was obtained. The cathode side electrode catalyst layer had a Pt loading of 0.40 mg / cm ² , a thickness of 10 μm, and a size of 50 × 50 mm.

2. Preparation of anode-side electrode catalyst layer Pt-supported graphitized carbon catalyst (platinum average particle diameter 5 nm, platinum support amount 50 wt%), Nafion solution (manufactured by Du Pont) containing 5 wt% Nafion (registered trademark), water, IPA Were mixed at a mass ratio of 1: 0.5: 2.5: 1 and stirred and pulverized with a fine pulverizing homogenizer to obtain an anode side electrode catalyst ink.

The obtained anode side electrode catalyst ink was applied onto a Teflon (registered trademark) sheet having a thickness of 0.2 mm using a screen printer and dried to obtain an anode side electrode catalyst layer. The anode side electrode catalyst layer had a Pt loading of 0.40 mg / cm ² , a thickness of 10 μm, and a size of 50 × 50 mm.

3. Assembly of MEA and single cell Using the produced anode side electrode catalyst layer and cathode side electrode catalyst layer, a solid polymer electrolyte membrane (manufactured by DuPont, Nafion 111, thickness 25 μm, size 80 × 80 mm) is sandwiched, After hot pressing at 130 ° C. and 20 kgf / cm ² for 10 minutes, the Teflon (registered trademark) sheet was peeled off, and the water-repellent treatment was performed on carbon paper (TGP-H-60 manufactured by Toray Industries, Inc.) treated with a PTFE solution. The MEA was sandwiched between gas diffusion layers coated with a carbon layer. This was sandwiched between a carbon separator and a current collector plate to obtain an evaluation cell.

<Example 2>
(1) Production of Electrocatalyst Graphitized carbon (average particle size 0.5 μm) and titanium isopropoxide dissolved in ethanol: Ti (OiC ₃ H ₇ ) ₄ (manufactured by Aldrich) are mixed. After holding for 2 hours with stirring, the graphitized carbon is filtered, washed thoroughly with distilled water at about 70 ° C., and dried at 110 ° C., thereby supporting titanium oxide with titanium oxide supported on the surface as a photocatalyst. Graphitized carbon (titanium oxide: average particle size 3 nm, supported amount 5 wt%, crystal structure anatase type) was obtained.

  The titanium oxide-supported graphitized carbon and the dinitrodiammine platinum solution, formic acid are mixed and held for 83 hours with stirring, and then the titanium oxide-supported graphitized carbon is filtered and thoroughly washed with distilled water at about 70 ° C., By drying at 110 ° C., a platinum / titanium oxide-supported graphitized carbon catalyst (platinum: average particle diameter 6 nm, supported amount 50 wt%) on which platinum was supported was obtained.

  An MEA and a single cell for evaluation were assembled in the same manner as in Example 1 except that the obtained platinum / titanium oxide-supported graphitized carbon catalyst was used for the cathode-side electrode catalyst layer.

<Comparative Example 1>
Pt-supported graphitized carbon catalyst (platinum average particle diameter 5 nm, platinum support amount 50 wt%), Nafion solution (manufactured by Du Pont) containing 5 wt% Nafion (registered trademark), water, and IPA in a mass ratio The mixture was mixed at 1: 0.5: 2.5: 1, and stirred and pulverized with a fine pulverization homogenizer to obtain a cathode side electrode catalyst ink.

The obtained cathode side electrode catalyst ink was applied on a Teflon (registered trademark) sheet having a thickness of 0.2 mm using a screen printer and dried to obtain a cathode side electrode catalyst layer. The cathode side electrode catalyst layer had a Pt loading of 0.40 mg / cm ² , a thickness of 10 μm, and a size of 50 × 50 mm.

  An MEA and an evaluation single cell were assembled in the same manner as in Example 1 except that the cathode side electrode catalyst layer was used.

<Performance evaluation>
In each of the evaluation single cells prepared in Examples 1 and 2 and Comparative Example 1, hydrogen gas having a dew point of 70 ° C. was supplied to the anode side at 500 cc / min, and nitrogen gas having a dew point of 70 ° C. was supplied to the cathode side at 500 cc / min. Then, using the anode side as a reference electrode, the cathode side as a working electrode, a potentiostat and a function generator are connected, and the cathode-side electrode catalyst layer is formed at a potential sweep rate of 50 mV / sec in the range of 0.05 to 0.9 V. Cyclic voltammetry (CV) was measured. Table 1 shows the ECA calculated from each cyclic voltammogram.

In addition, ECA in Table 1 is a specific surface area (m ² / g) of platinum adsorbed with hydrogen per unit platinum mass, measured by a cyclic voltammetry method within a potential range of 0.05 to 0.45 V. Is a calculated value.

  From Table 1, it can be seen that ECA is improved in Examples 1 and 2 of the present invention as compared with Comparative Example 1. That is, it can be seen that the cathode-side electrode catalyst layer of the present embodiment has a larger amount of hydrogen adsorbed on the surface of the catalyst particles (platinum) and a higher oxygen reduction reaction than the conventional one. Thereby, in the cathode side electrode catalyst layer of an Example of this application, it turns out that the area of a three-layer interface has increased by using the electrode catalyst with which the photocatalyst was carry | supported.

  By using photocatalyst particles for the electrode catalyst, it becomes possible to increase the amount of formation of the three-phase interface in the electrode catalyst layer, which is useful as a fuel cell excellent in power generation performance.

It is explanatory drawing which showed the contact state before and behind light irradiation of the electrode catalyst and solid polymer electrolyte of this invention. The cross-sectional schematic diagram of the solid polymer electrolyte fuel cell which is one preferable embodiment of this invention is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Electroconductive support | carrier, 102 ... Catalyst particle, 103 ... Photocatalyst particle, 104 ... Solid polymer electrolyte, 200 ... MEA, 210 ... Solid polymer electrolyte membrane, 220a ... Anode side electrode catalyst layer, 120b, 220b ... Cathode side electrode Catalyst layer, 230a, 230b ... gas diffusion layer, 260 ... solid polymer electrolyte fuel cell, 250a, 250b ... separator, 251a, 251b ... gas supply groove.

Claims (11)

In an electrode catalyst for a fuel cell in which catalyst particles are supported on a conductive carrier,
An electrode catalyst for a fuel cell, characterized in that photocatalyst particles that exhibit hydrophilicity when irradiated with light are supported on the conductive carrier.   2. The fuel cell electrode catalyst according to claim 1, wherein the photocatalyst particles are an oxide semiconductor.   3. The fuel cell electrode catalyst according to claim 1 or 2, wherein the photocatalyst particles are at least one selected from the group consisting of titanium oxide, zirconium oxide, tungsten oxide, and tin oxide.   The electrode catalyst for a fuel cell according to any one of claims 1 to 3, wherein the light is ultraviolet light.   The electrode catalyst for a fuel cell according to any one of claims 1 to 4, wherein the catalyst particles contain at least one of platinum, iridium, and palladium.   A fuel cell electrode catalyst layer using the fuel cell electrode catalyst according to any one of claims 1 to 5.   A fuel cell comprising the fuel cell electrode catalyst layer according to claim 6.   A method for producing an electrode catalyst for a fuel cell, comprising a step of supporting photocatalyst particles that exhibit hydrophilicity when irradiated with light after supporting the catalyst particles on a conductive carrier.   A method for producing an electrode catalyst for a fuel cell, comprising a step of supporting photocatalyst particles that exhibit hydrophilicity when irradiated with light on a conductive support, and then supporting the catalyst particles. A fuel cell electrode catalyst comprising a step of dispersing the electrode catalyst for a fuel cell according to any one of claims 1 to 5 in a solid polymer electrolyte solution to prepare an electrode catalyst ink, and applying the electrode catalyst ink to a substrate. In the method for producing the layer,
A method for producing an electrode catalyst layer for a fuel cell, comprising a step of irradiating the electrode catalyst for fuel cell and / or the electrode catalyst ink with light.   The method for producing an electrode catalyst layer for a fuel cell according to claim 10, wherein the light is ultraviolet light.

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