JP2006216385A - Electrode catalyst layer for fuel cell and fuel cell using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode catalyst layer for a fuel cell excellent in power generating performance with inner resistance reduced. <P>SOLUTION: The electrode catalyst layer 100 for a fuel cell contains conductive fiber having conductive nano-fibers 112, catalyst particles 113 carried at least by the conductive nano-fibers 111, and solid polymer electrolyte 114. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrode catalyst layer for a fuel cell, and more particularly to an electrode catalyst layer for a fuel cell whose power generation performance is improved by reducing internal resistance.

  In recent years, in response to social demands and trends against the background of energy and environmental issues, polymer electrolyte 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. . The solid polymer fuel cell is characterized by using a film-like solid polymer electrolyte membrane.

  The polymer electrolyte fuel cell generally has a structure in which a membrane-electrode assembly (hereinafter also referred to as “MEA”) is sandwiched between separators.

  The MEA has a solid polymer electrolyte membrane sandwiched between a pair of gas diffusion electrodes, that is, an anode (fuel electrode) side gas diffusion electrode and a cathode (oxygen electrode) side gas diffusion electrode. Each gas diffusion electrode has an electrode catalyst layer containing a solid polymer electrolyte and an electrode catalyst and a gas diffusion layer, and at least one surface of the electrode catalyst layer is in contact with the solid polymer electrolyte membrane.

  Conventionally, to produce the gas diffusion electrode, a catalyst slurry containing an electrode catalyst in which catalyst particles such as platinum particles are supported on a conductive carrier such as carbon particles and a solid polymer electrolyte is applied to a screen printing method or the like. A method of forming an electrode catalyst layer on a gas diffusion layer by applying and drying on a gas diffusion layer made of carbon paper or the like has been used. Further, a method is generally used in which an MEA is manufactured by hot pressing after sandwiching a solid polymer electrolyte membrane with the electrode catalyst layer inside using the prepared gas diffusion electrode.

  In the MEA, 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. The electrons generated in the anode-side electrode catalyst layer include a conductive carrier constituting the anode-side electrode catalyst layer, and a gas diffusion layer in contact with a different side of the anode-side electrode catalyst layer from the solid polymer electrolyte membrane The cathode side electrode catalyst layer is reached through the gas separator and the 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.

  The electrochemical reaction mainly occurs at a three-phase interface where the catalyst particles, the solid polymer electrolyte, and the feed gas are in contact. Therefore, in order to form a dense three-phase interface, the fuel gas and the oxidant gas need to be uniformly diffused in the electrode catalyst layer.

In order to improve the power generation performance of the fuel cell, it is important to reduce the internal resistance of the fuel cell. For example, Patent Document 1 discloses a fuel cell in which a layer made of conductive fine particles is disposed between an electrode catalyst layer and a gas diffusion layer. According to the document 1, it is possible to reduce the contact resistance between the electrode catalyst layer and the gas diffusion layer by improving the adhesion, thereby improving the power generation performance of the fuel cell.
JP 2000-123842 A

  Conventionally, catalyst particles have been included in an electrode catalyst layer as an electrode catalyst supported on a conductive carrier such as carbon particles. An electrochemical reaction in the electrode catalyst layer proceeds on the surface of the catalyst particles, and electrons generated by the reaction flow to an external circuit through a conductive carrier, a gas diffusion layer, and the like included in the electrode catalyst layer. However, the contact area between the conductive carriers is small, and in some cases, a solid polymer electrolyte or the like is interposed between them. For this reason, the electrical resistance due to the constituent members constituting the electrode catalyst layer has also been a factor that deteriorates the power generation characteristics of the fuel cell.

  Therefore, there is a possibility that a fuel cell having sufficient power generation performance may not be obtained even with the conductive fine particle layer disposed between the electrode catalyst layer and the gas diffusion layer.

  Accordingly, an object of the present invention is to provide a fuel cell electrode catalyst layer having excellent power generation performance by reducing internal resistance.

  As a result of intensive studies in view of the above problems, the present inventor can secure an electron conduction path composed of the same member continuous in the electrode catalyst layer by using an electrode base material composed of conductive fibers, and the conventional gas It has been found that the probability that electrons generated in the diffusion electrode move between the carriers can be greatly reduced.

  That is, the present invention is a fuel cell electrode catalyst layer, comprising a conductive fiber having conductive nanofibers, at least catalyst particles supported on the conductive nanofibers, and a solid polymer electrolyte. The battery electrode catalyst layer solves the above problems.

  According to the present invention, excellent electrical conductivity is exhibited by reducing the electrical resistance due to the constituent members, and the electrochemical reaction area is improved by highly dispersing the catalyst particles, resulting in a fuel having excellent power generation characteristics. A battery electrode catalyst layer can be obtained.

  A first aspect of the present invention is an electrode catalyst layer for a fuel cell, which includes conductive fibers having conductive nanofibers, at least catalyst particles supported on the conductive nanofibers, and a solid polymer electrolyte. It is an electrode catalyst layer for a fuel cell (hereinafter also simply referred to as “electrode catalyst layer”).

  First, a preferred embodiment of the electrode catalyst layer of the present invention will be described with reference to the schematic view of FIG. In the electrode catalyst layer 100 of FIG. 1 (A), the bundle of conductive fibers is woven by crossing and plain weaving, so that the conductive fibers used as the weft 111 have a wave-like shape. The conductive fiber used as the warp 111 ′ is schematically shown only in cross section. In FIG. 1B, the solid polymer electrolyte 114 is omitted for convenience of explanation.

  The electrode catalyst layer 100 in FIG. 1A is prepared by preparing a plurality of bundles made of a predetermined number of conductive fibers 111 and 111 ′, and weaving the obtained bundles into a sheet shape to form an electrode catalyst layer. It carries 100 skeleton parts. As shown in FIG. 1B, conductive nanofibers 112 are formed on the conductive fibers 111 and 111 '. Further, catalyst particles 113 are supported on the conductive fibers 111 and 111 ′ and the conductive nanofiber 112. Thus, in the electrode catalyst layer 100, the catalyst particles 113 are directly supported on the electrode base material composed of the conductive fibers 111 and 111 ′ in which the conductive nanofibers 112 are formed, and further includes the proton conductive electrolyte 114. .

  The electrode catalyst layer of the present invention has a configuration in which catalyst particles are directly supported on at least conductive nanofibers. As a result, when the electrons generated by the electrode reaction in the electrode catalyst layer move to the gas diffusion layer, a continuous electron conduction path can be secured without interposing a solid polymer electrolyte, etc. The probability of moving between different carriers that has occurred in the electrode can be greatly reduced.

  In addition, by forming conductive nanofibers on the conductive fibers, the surface area of the carrier on which the catalyst particles are supported can be increased. Thereby, it becomes possible to suppress the aggregation of the catalyst particles in the electrode catalyst layer and highly disperse it, and it is possible to improve the electrochemical reaction area and exhibit high power generation performance. Furthermore, by forming conductive nanofibers on the conductive fibers, it becomes possible to improve the contact property with the gas diffusion layer that can be disposed adjacently when the MEA is assembled. Can be secured.

  As described above, the gas diffusion electrode of the present invention exhibits excellent conductivity by reducing the electric resistance due to the constituent members, and the electrochemical reaction area is improved by highly dispersing the catalyst particles, resulting in As a result, a gas diffusion electrode excellent in power generation characteristics can be obtained.

  Hereinafter, the gas diffusion electrode of the present invention will be described in more detail.

(Conductive fiber)
As the conductive fiber used in the electrode catalyst layer of the present invention, one containing at least carbon is preferably used. As described above, the conductive fiber has conductive nanofibers and catalyst particles, and conducts electrons generated on the surface of the catalyst particles contained in the anode-side electrode catalyst layer to the gas diffusion layer and moves from the gas diffusion layer. It is necessary to conduct the generated electrons to the catalyst particles contained in the cathode side electrode catalyst layer. Therefore, it is desirable to use a highly conductive fiber such as one containing at least carbon as a member constituting the electrode catalyst layer.

  Specific examples of conductive fibers include PAN-based carbon fibers made from acrylic fibers; pitch-based carbon fibers made from petroleum, pitch, or naphthalene-based pitches; phenol-based carbon fibers made from phenolic resins; rayon-based materials Examples thereof include carbon fibers such as carbon fibers.

  Since the conductive fiber only needs to have high conductivity, metal fibers such as stainless steel can be used in addition to the carbon fiber described above.

  A conductive fiber having a diameter of 1 to 30 μm, preferably 5 to 15 μm is suitably used. If the diameter is less than 1 μm, the mechanical strength of the obtained electrode catalyst layer may be reduced, and if it exceeds 30 μm, the porosity of the obtained electrode catalyst layer may be reduced. In addition, the diameter of a conductive fiber can be measured from the cross-sectional observation image of a gas diffusion electrode using a scanning electrochemical microscope (SEM) etc., for example.

The basis weight of the conductive fiber is 10 to 500 g / m ² , preferably about 30 to 200 g / m ² . If the weight per unit area is less than 10 g / m ² , the strength of the electrode catalyst layer may be reduced, and if it exceeds 500 g / m ² , the electrode catalyst layer may be thickened, resulting in a decrease in power generation characteristics or an increase in size of the MEA. is there.

  The conductive fibers used in the electrode catalyst layer of the present invention are used after being formed into a sheet having a porous structure, such as a woven fabric, a paper-like papermaking body, and a non-woven fabric.

(Conductive nanofiber)
Next, in the electrode catalyst layer of this invention, it has electroconductive nanofiber on the electroconductive fiber mentioned above. In addition, although the said electrode catalyst layer contains the conductive fiber in which the conductive nanofiber was formed, in addition to this, the conductive fiber mentioned above in which the conductive nanofiber was not formed is included in part. You may go out.

  In the present invention, the conductive nanofiber refers to a fiber having a diameter of 200 nm or less and a nanometer-sized diameter.

  The conductive nanofibers preferably include at least carbon. Since the conductive nanofibers are members constituting the electrode catalyst layer, high electronic conductivity can be obtained by using conductive nanofibers containing at least carbon, as described above in the description of the conductive fibers.

  Specific examples of the conductive nanofibers include carbon nanofibers, carbon nanotubes, and carbon nanohorns.

  The carbon nanofiber is made of a fibrous carbon material having a predetermined diameter as described above. The carbon nanotube is made of a tubular carbon material having the above-mentioned predetermined diameter and having a cavity at the center of the fiber. Specifically, the carbon nanotube has a structure in which graphite is rolled into a cylindrical shape, the cylinder is a single-walled carbon nanotube (SWNTs), and the multi-walled carbon nanotube in which the cylinder is multi-layered concentrically. (MWNT). The carbon nanohorn is made of single-layer graphite, and is made of an aggregate of conical structures having the predetermined diameter described above.

  By using conductive nanofibers with a nanometer-sized diameter in this way, it is possible to improve the area as a carrier for supporting catalyst particles without blocking the voids for gas diffusion in the electrode catalyst layer. It becomes.

  The diameter of the conductive nanofiber is 200 nm or less, preferably 100 nm or less, more preferably 50 nm or less. If the diameter of the conductive nanofiber exceeds 200 nm, the porosity of the electrode catalyst layer may be reduced, or the surface area of the conductive nanofiber may be reduced.

  The length of the conductive nanofiber is 20 to 0.1 μm, preferably 10 to 1 μm. If the length is less than 0.1 μm, the area as a carrier for supporting catalyst particles in the electrode catalyst layer may not be sufficiently increased. If the length exceeds 20 μm, the porosity of the electrode catalyst layer is reduced. There is a fear.

The content of the conductive nano fibers in the electrode catalyst layer, to a unit area of the electrode catalyst layer ^{(cm 2), 0.1~2.5mg / cm} 2, preferably 0.5 to 1.5 mg / cm ^It should be about ² . If the content is less than 0.1 mg / cm ² , there is a possibility that the effect of containing conductive nanofibers may not be sufficiently obtained. If the content exceeds 2.5 mg / cm ² , voids in the electrode catalyst layer may be obtained. There is a risk of reducing the rate.

The conductive fiber and / or conductive nanofiber contained in the electrode catalyst layer is preferably modified to have water repellency and / or hydrophilicity. Specifically, surface treatment is performed on the conductive fibers and / or conductive nanofibers to modify the surface of each fiber, thereby imparting water repellency or hydrophilicity to the conductive fibers and / or conductive nanofibers. It is preferable for the electrode catalyst layer to maintain a good three-phase interface by quickly discharging water generated by the electrode reaction to the outside. Therefore, in the conventional electrode catalyst layer, a water repellent material such as PTFE has been added. However, since the water repellent material does not have electrical conductivity, the addition of the water repellent agent to the electrode catalyst layer may lead to an increase in MEA internal resistance.

  On the other hand, in the present invention, in order to impart water repellency to the electrode catalyst layer, preferably, conductive fibers and / or conductive nanofibers whose surfaces are modified to be water repellant are used. Thereby, each fiber can be made into the fiber which has water repellency and electroconductivity, and it becomes possible to provide water repellency to an electrode catalyst layer, without impairing electroconductivity. Therefore, a gas diffusion electrode capable of exhibiting excellent performance can be obtained even under operating conditions where a large amount of water is likely to be generated such as high humidification and high current density.

  Also, the solid polymer electrolyte membrane tends to dry under operating conditions such as low humidification and low current operating density. Drying of the solid polymer electrolyte membrane decreases proton conductivity, resulting in a decrease in power generation performance. Therefore, in the present invention, conductive fibers and / or conductive nanofibers whose surfaces are modified to be hydrophilic are used. Thereby, a fiber having both hydrophilicity and conductivity can be obtained, and it is possible to quickly achieve high humidification of the solid polymer electrolyte membrane and to prevent the solid polymer electrolyte membrane from being dried.

  The surface of the conductive fiber and / or conductive nanofiber in the electrode catalyst layer may be modified to be hydrophilic and / or water-repellent in consideration of operating conditions and power generation performance. For example, the electrocatalyst layer is one of a conductive fiber and / or conductive nanofiber modified to be hydrophilic and a conductive fiber and / or conductive nanofiber modified to be water repellent. Should be included. However, the electrocatalyst layer uses conductive fibers and / or nanofibers modified to be hydrophilic and conductive fibers and / or nanofibers modified to be water-repellent. preferable. Thereby, it can be set as the electrode catalyst layer which has water repellency and hydrophilic property, and it becomes possible to exhibit high power generation performance stably in a wide range of operating conditions.

  For example, under operating conditions where a large amount of generated water such as high current density and high humidification is likely to be generated, the content of conductive fibers and / or conductive nanofibers modified to be water-repellent should be increased. In addition, the content of the conductive fibers and / or conductive nanofibers modified to hydrophilicity should be increased under operating conditions that tend to cause drying of the solid polymer electrolyte membrane such as low humidification.

  The method for modifying the surface of conductive fibers and / or conductive nanofibers to be water-repellent is to use conductive fibers and / or conductive fibers formed with conductive nanofibers at 2000 ° C. or higher, particularly 2500 ° C. or higher. It can be obtained by, for example, a heat treatment method. By such heat treatment, hydrophilic surface functional groups such as a carboxyl group, a lactone group, a hydroquinone group, and a quinone group existing on the surface of each fiber are reduced, and the fiber surface can be modified to be water repellent. The heat treatment atmosphere may be an inert gas atmosphere such as nitrogen, helium, or argon, or a reducing gas atmosphere such as hydrogen or a mixed gas of hydrogen and an inert gas. The method for modifying the fiber surface to be water-repellent is not limited to the above-mentioned method. If the surface can be modified to be water-repellent without impairing the conductivity of each fiber, a conventionally known method can be used as appropriate. Also good.

  Next, the method of modifying the surface of the conductive fibers and / or conductive nanofibers to hydrophilic is performed by changing the conductive fibers and / or conductive fibers on which the conductive nanofibers are formed, oxygen gas, water vapor, etc. It is obtained by a method of oxidizing the surface using a known technique such as vapor phase method or plasma irradiation. Oxidation increases the amount of hydrophilic surface functional groups such as carboxyl groups, phenol groups, and ketone groups at the end of the C-C bond on the surface of the conductive fiber, and the hydrophilic surface functional groups are removed from the water molecule vapor. It can act as an active site that promotes adsorption, and can promote water condensation through hydrogen bonds between adsorbed water molecules. Thereby, each fiber surface can be modified to be hydrophilic and wettability can be improved.

  For example, in order to obtain hydrophilic conductive fibers by a vapor phase method, the surface of conductive fibers and / or conductive nanofibers is oxidized in an oxygen gas atmosphere at 350 to 400 ° C. or in water vapor at 700 to 1000 ° C. What is necessary is just to process.

  Further, in order to modify the surface of each fiber to be hydrophilic by plasma irradiation, a conventional general apparatus may be used. For convenience, a corona discharge treatment apparatus that discharges in air at normal temperature and pressure is used. Just do it.

  The method for modifying the surface of each fiber to be hydrophilic is not limited to the above-described method. For example, a pyrogenic method (hydrogen combustion) using water vapor generated by reacting hydrogen and oxygen; potassium permanganate; Conductive fiber such as liquid phase method using strong oxidizing aqueous solution containing nitric acid, chlorate, persulfate, perborate, percarbonate, hydrogen peroxide, etc .; gas phase method using ozone, nitrogen oxide, air, etc. Various known techniques for oxidizing the surface can be used as appropriate.

  When metal fibers are used as the conductive fibers, the surface of the conductive fibers can be modified to be hydrophilic by oxidizing the surface of the metal fibers by plasma irradiation in an oxygen atmosphere in the same manner as described above. can get. The conductive fiber surface can be modified to be water repellent by treating the metal fiber surface with plasma irradiation in a fluorine-based gas atmosphere.

  In the electrode catalyst layer, it is desirable that the gas supplied from the outside is uniformly diffused. Therefore, it is preferable that the electrode catalyst layer has a function of quickly discharging the generated water without being localized. However, the generated water tends to localize in the electrode catalyst layer along the flow of gas supplied from outside, such as oxidant gas, making it difficult to diffuse the gas uniformly in the electrode catalyst layer, resulting in reduced power generation performance. There is a risk of inviting.

  Therefore, in the electrode catalyst layer of the present invention, the content of conductive fibers and / or conductive nanofibers modified to have water repellency from the gas introduction part to the gas discharge part may be increased. Thereby, it becomes possible to eliminate generated water and the like more efficiently. In such a case, the properties of the surface of each fiber supporting the catalyst particles are not particularly limited, and the conductive fibers and / or conductive nanofibers modified to be water-repellent, and hydrophilically modified. The conductive fibers and / or the conductive nanofibers may be supported on either or either of them, and may be appropriately determined so as to obtain a desired power generation performance.

(Catalyst particles)
In the electrode catalyst layer of the present invention, the catalyst particles may be supported on any one of the above-described conductive fibers or conductive nanofibers, but it is preferable that the catalyst particles are supported on at least the conductive nanofibers. Thereby, the catalyst particles can be highly dispersed and supported in the electrode catalyst layer. More preferably, the catalyst particles are supported on both the conductive nanofibers and the conductive fibers.

  The catalyst particles are not particularly limited as long as they have a catalytic action with respect to an oxidation reaction of hydrogen and / or a reduction reaction of oxygen. For example, one kind selected from metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof. The above is mentioned. The catalyst particles may be used alone, but may be an alloy containing platinum as a main component in order to increase the catalytic activity of the catalyst particles, stability to heat, carbon monoxide, and the like.

  The average particle diameter of the catalyst particles is preferably 1 to 30 nm. The catalyst particles are estimated to have a higher specific surface area as the average particle size is smaller, so the catalytic activity is also improved. However, in practice, even if the catalyst particle size is extremely small, catalyst activity commensurate with the increase in specific surface area is obtained. Therefore, the above range is preferable. The “average particle diameter of catalyst particles” in the present invention is measured by an average value of catalyst particle diameters determined from crystallite diameters or transmission electron microscope images determined from the half-value widths of diffraction peaks of catalyst metals in X-ray diffraction. can do.

Supported amount of the catalyst particles in the electrode catalyst layer, 0.001~10mg / cm ^2, and it is preferably a 0.005~1mg / cm ² approximately. If the supported amount is too small, there is a fear that the desired power generation amount of the gas diffusion electrode cannot be obtained, and even if the supported amount is too large, the manufacturing cost may be increased. The supported amount is, for example, the amount (g) of the catalyst particles contained in the electrode catalyst layer measured by inductively coupled plasma emission spectrometry as the area (cm ² ) of the surface of the electrode catalyst layer in contact with the solid polymer electrolyte membrane. The divided value.

  The catalyst particles contained in the electrode catalyst layer are preferably supported on the conductive nanofibers modified to have at least water repellency. As a result, while the catalyst particles are highly dispersed and supported in the electrode catalyst layer, water near the catalyst particles can be quickly removed and gas such as hydrogen can be efficiently brought into contact with the catalyst particles, thereby improving the power generation performance of the MEA. Can be made. Furthermore, carbon-containing fibers and the like are likely to be corroded at portions where moisture comes into contact. Therefore, by supporting the catalyst particles on the fiber modified to have water repellency, the corrosion of the fiber can be prevented, and stable power generation performance can be exhibited over a long period of time. More preferably, the catalyst particles are supported on the conductive fibers and the conductive nanofibers modified to have water repellency.

(Solid polymer electrolyte)
The solid polymer electrolyte contained in the electrode catalyst layer is not particularly limited as long as it is generally used in conventional electrode catalyst layers. Specifically, the polymer skeleton is a fluorinated polymer in which all or a part of the polymer skeleton is fluorinated and has an ion exchange group, or a polymer polymer skeleton that does not contain fluorine. And solid polymer electrolytes having ion exchange groups.

Examples of the ion-exchange group is not particularly _{limited, -SO 3 H, -COOH, -PO} (OH) 2, -POH (OH), - SO 2 NHSO 2 -, - Ph (OH) (Ph represents a phenyl group A cation exchange group such as —NH ₂ , —NHR, —NRR ′, —NRR′R ″ ⁺ , —NH ₃ ^{+ and the} like (R, R ′, R ″ represent an alkyl group, cycloalkyl Anion exchange groups such as a group, an aryl group, and the like.

  Specific examples of the solid polymer electrolyte having an ion exchange group as the fluoropolymer include 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.), etc., perfluorocarbon sulfonic acid polymers, polytrifluorostyrene sulfonic acid polymers, perfluorocarbon phosphonic acid polymers, trifluorostyrene sulfonic acid polymers, ethylenetetrafluoroethylene-g-styrene sulfonic acid polymers Polymers, ethylene-tetrafluoroethylene copolymers and the like are preferable examples.

  Specific examples of the solid polymer electrolyte having an ion exchange group as the hydrocarbon polymer include polysulfonesulfonic acid, polyaryletherketonesulfonic acid, polybenzimidazolealkylsulfonic acid, polybenzimidazolealkylphosphonic acid, and the like. Is a suitable example.

  In the electrode catalyst layer, the solid polymer electrolyte preferably covers the surfaces of conductive fibers, conductive nanofibers, and catalyst particles. This makes it possible to obtain a high-density three-phase interface. The thickness covered by the solid polymer electrolyte may be appropriately determined in consideration of the power generation performance of the obtained electrode catalyst layer, but if it is too thick, there is a possibility that the gap of the electrode catalyst layer is blocked. In addition, the solid polymer electrolyte does not need to cover all of the surfaces of the conductive fibers, conductive nanofibers, and catalyst particles contained in the electrode catalyst layer, and may be at least partially covered.

  If the thickness of the electrode catalyst layer is too thin, a desired power generation amount cannot be obtained, and if it is too thick, a high output cannot be obtained.

(Buffer layer)
The electrode catalyst layer of the present invention preferably has a buffer layer. The buffer layer may be disposed on at least one surface of the electrode catalyst layer. Preferably, when the MEA is produced using the electrode catalyst layer, the electrode catalyst layer may be disposed on a surface that can come into contact with the solid polymer electrolyte membrane.

  A schematic diagram of the electrode catalyst layer 100 having the buffer layer 120 is shown in FIG. The electrode catalyst layer 100 in FIG. 2 is manufactured in the same manner as the electrode catalyst layer 100 shown in FIG. 1, and a buffer layer 120 is formed on the electrode catalyst layer 100. By having the buffer layer in this manner, the contact property between the electrode catalyst layer and the solid polymer electrolyte membrane can be improved when the MEA or the like is assembled, and the internal resistance of the MEA can be reduced. Further, it is possible to prevent the solid polymer electrolyte membrane from being damaged by the conductive fibers constituting the electrode catalyst layer due to an impact applied during cell assembly or during operation of the fuel cell.

  Examples of the buffer layer include those containing a proton conductive electrolyte. By constituting the buffer layer with a material having proton conductivity, it is possible to suitably ensure proton conductivity between the solid polymer electrolyte membrane and the catalyst particles.

  Preferred examples of the proton conductive electrolyte include organic compounds and / or inorganic compounds.

  The organic compound is not particularly limited as long as it is conventionally used as a solid polymer electrolyte in an electrode catalyst layer or the like. Specifically, the organic compound contained in the electrode catalyst layer described above is specifically limited. The thing similar to what was enumerated in description of molecular electrolyte is mentioned. Among them, those having at least a cation exchange group such as a sulfonic acid group or a carboxyl group are preferable because they have high proton conductivity. Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, Asahi Kasei Co., Ltd.) Perfluorocarbon sulfonic acid polymers such as Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.) and the like are particularly preferred.

The inorganic compound preferably includes any one of P ₂ O ₅ , SiO ₂ , B ₂ O ₃ , GeO ₂ , or As ₂ O ₃ . Of these, P ₂ O ₅ and SiO ₂ are preferable. In addition, a second component such as an alkali metal or an alkaline earth metal may be included in order to ensure the stability of the obtained buffer layer. For example, P ₂ O ₅ —ZrO ₂ —SiO ₂ water-containing glass is characterized by high proton conductivity by absorbing a large amount of water, and does not dissolve in water. There is a merit that the nature is high.

  Further, in order to improve not only proton conductivity but also durability and flexibility, the buffer layer may be composed of a mixture of the organic compound and the inorganic compound.

  Although it does not specifically limit as a form of the said mixture, The form etc. with which the inorganic type compound is disperse | distributed to the film | membrane comprised from an organic type compound are mentioned. In such a case, the shape of the inorganic compound may be powder, plate, needle, sphere, fiber, etc., and the dispersion state of the inorganic compound may be unevenly distributed in the buffer layer. It may be. It is preferable that the organic compound and the inorganic compound are combined by a covalent bond or the like, such as a form in which the organic compound is bonded to the surface of the inorganic compound.

  The proton conductive electrolyte such as an organic compound and / or an inorganic compound constituting the buffer layer is preferably in contact with the solid polymer electrolyte contained in the electrode catalyst layer. As a result, a proton conduction path communicating with the buffer layer and the electrode catalyst layer can be secured, and the proton conductivity of the MEA can be improved.

  The thickness of the buffer layer is 0.1 to 20 μm, preferably about 1 to 10 μm. If the thickness is less than 0.1 μm, the effect as expected by the buffer layer may not be obtained, and if it exceeds 20 μm, the proton conductivity may be reduced instead. preferable.

  The size of the buffer layer is preferably larger than that of the electrode catalyst layer. As a result, the buffer layer can be disposed outside the outer flange portion of the electrode catalyst layer, and damage to the solid polymer electrolyte membrane due to conductive fibers contained in the electrode catalyst layer can be more effectively prevented. .

  The buffer layer may have voids. As a result, a buffer layer excellent in stress absorption can be obtained, and breakage of the solid polymer electrolyte membrane can be prevented more effectively. Moreover, since water etc. can be absorbed in the said space | gap, water retention can be provided to a buffer layer and it becomes possible to control the water | moisture content of an electrode catalyst layer.

  It describes below about the manufacturing method of the electrode catalyst layer of this invention. However, the method described below shows a preferred embodiment of the present invention, and the production method of the electrode catalyst layer of the present invention is not limited to the following method, and conventionally known methods are appropriately applied. May be.

(Method for producing electrode catalyst layer)
As a method for producing the electrode catalyst layer, first, conductive nanofibers are formed on conductive fibers, and then catalyst particles are supported on at least the conductive nanofibers. Next, the conductive fibers having the conductive nanofibers and the catalyst particles are twisted together in a predetermined number to form a bundle, and a plurality of the bundles are used to form a sheet by plain weaving or the like. Examples include a method of preparing an electrode catalyst layer precursor containing catalyst particles and impregnating the electrode catalyst layer precursor with a solid polymer electrolyte.

(1) Formation of conductive nanofibers To form conductive nanofibers on conductive fibers, when carbon nanotubes (hereinafter also referred to as “CNT”) are used as the conductive nanofibers, for example, A thermal chemical vapor deposition method (thermal CVD method) in which carbon nanotubes are grown by thermochemical vapor deposition from a CNT-forming catalyst is used.

  Specifically, first, a conductive fiber is loaded with a CNT-forming catalyst. The method for supporting the CNT-forming catalyst is not particularly limited, such as physical or chemical vapor deposition, and the conductive fiber is immersed in a solution containing a compound containing an element constituting the CNT-forming catalyst. A method of adsorbing to the conductive fiber may be used.

  The CNT-forming catalyst is not particularly limited as long as it is a commonly used catalyst. Ni, Co, Fe, Y, Rh, Pd, Pt, La, Ce, Pr, Nd, Gd, Tb, Dy, Examples include at least one selected from the group consisting of Ho, Er, and Lu, and these may be used alone or in combination of two or more.

  Examples of the compound containing an element constituting the CNT-forming catalyst include acetylacetonate, acetate, and nitrate of the elements constituting the CNT-forming catalyst. The solution containing the compound can be prepared by dissolving the compound in water and / or an alcohol solvent such as ethyl alcohol.

  The conductive fiber can be adsorbed to the conductive fiber by immersing the conductive fiber in a solution containing the compound and allowing it to stand for a certain period of time. At this time, means such as stirring and ultrasonic irradiation may be used.

  The conductive fiber on which the compound is adsorbed is preferably heat-treated in a reducing gas atmosphere such as hydrogen or an inert gas atmosphere such as nitrogen, argon, helium, or a mixed gas thereof. Thereby, the conductive fiber carrying the CNT-forming catalyst is obtained. Although it does not restrict | limit especially as heat processing conditions, It is about 300-1000 degreeC, and is about 10 to 100 minutes.

  The supported amount and average particle diameter of the CNT-forming catalyst in the conductive fiber may be appropriately determined so that CNTs having desired characteristics such as the formation amount, length, diameter, and hollow diameter can be obtained.

  As a method for supporting the CNT-forming catalyst on the conductive fiber, a magnetron sputtering method, a vapor deposition method by resistance heating, or the like can be used in addition to the above-described method.

  Next, the conductive fibers carrying the CNT-forming catalyst are set in a container of a thermal CVD apparatus, a hydrocarbon gas is sent to the CNT-forming catalyst together with a carrier gas, and the hydrocarbon gas is thermally decomposed. Carbon nanotubes are formed.

  As the hydrocarbon gas, any gas containing carbon such as acetylene gas, alcohols, carbon monoxide, and methane gas can be used. Moreover, what is necessary is just to select the preferable flow volume with a furnace as the flow volume of gas. As the carrier gas, an inert gas such as nitrogen, argon or helium can be used, and an etching gas such as ammonia or hydrogen can be added. Moreover, what is necessary is just to select the preferable flow volume with a furnace as the flow volume of gas. The temperature of the thermal CVD apparatus is preferably 400 to 1200 ° C. If the temperature of the thermal CVD apparatus is out of this range, the carbon nanotubes tend not to grow.

  The conductive fibers on which CNTs are formed as described above may be subjected to a purification treatment using a known method such as an acidic aqueous solution or an air oxidation treatment in order to remove impurities such as the remaining CNT-forming catalyst.

  As a CNT formation method, the thermal CVD method has been described above. However, the method is not limited to such a method, and other CNT formation methods such as an arc discharge method and a laser evaporation method are generally used. Any method can be used without particular limitation.

(2) Support of catalyst particles Next, catalyst particles that promote electrode reaction are supported on conductive fibers on which conductive nanofibers are formed. At this time, since the catalyst particles have a large surface area and can be supported in a highly dispersed state, the catalyst particles are preferably supported at least on the conductive nanofibers, more preferably on both the conductive nanofibers and the conductive fibers.

  In order to support the catalyst particles on the conductive fibers on which the conductive nanofibers are formed, for example, after the conductive fibers on which the conductive nanofibers are formed are immersed in the catalyst compound solution, a reducing agent or the like is added. A method is mentioned. According to such a method, the catalyst particles can be highly dispersed and supported on the conductive nanofibers and the conductive fibers, and aggregation of the catalyst particles can be suppressed.

  The catalyst compound solution is a solution containing a compound containing elements constituting the catalyst particles (also simply referred to as “catalyst compound”). Specifically, when Pt is used as the catalyst particles, for example, a solution containing a catalyst compound such as chloroplatinic acid, chloroplatinum chloride, or dinitrodiammineplatinum can be used. In order to obtain a platinum alloy, other than platinum, a desired catalyst particle compound such as nitrate, chloride or sulfate may be dispersed in the solution. As the solvent to which the catalyst compound is added, water and / or alcohols such as ethanol and methanol can be used. Moreover, what is necessary is just to determine suitably the catalyst compound density | concentration in a catalyst compound solution, etc. so that the desired catalyst particle load may be obtained.

  The reducing agent is not particularly limited as long as it can reduce the catalyst compound. Sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, hydrazine, formaldehyde, methanol, ethanol, hydrogen, Ethylene, carbon monoxide and the like can be used. By adding the reducing agent, the catalyst compound can be supported as catalyst particles on the conductive fiber. After immersing the conductive fiber in the catalyst compound solution described above, an appropriate amount of the reducing agent is added, heated to 60 to 100 ° C. using a reflux reactor or the like, and then allowed to cool to room temperature to thereby form catalyst particles. Perform reduction loading.

  As described above, when alloying at least the catalyst particles supported on the conductive nanofibers, it is preferable to perform further firing. Moreover, you may dry as needed before baking.

  The method for drying the conductive fibers after the catalyst particles are reduced and supported is not particularly limited as long as a publicly known method such as vacuum drying, natural drying, rotary evaporator, and drying by a blow dryer is used. What is necessary is just to determine drying time etc. suitably according to the method to be used.

  Further, as a firing method in the case of alloying, the firing temperature is preferably 300 to 1000 ° C. in an air atmosphere, preferably in an inert atmosphere such as nitrogen, helium, and argon, or in a reducing atmosphere such as hydrogen. May be performed in the range of 300 to 600 ° C. for about 1 to 6 hours.

  In addition to the above-described method using a reducing agent, the impregnation method, coprecipitation method, competitive adsorption method, microemulsion (reverse micelle method), etc. can be used as a method for supporting the catalyst particles on the conductive fiber on which the conductive nanofibers are formed. The method can be applied. From the viewpoint that the catalyst particles can be highly dispersed and firmly supported on the conductive fibers and / or conductive nanofibers, a method using a reducing agent, a microemulsion (reverse micelle method), and the like are preferably used. Moreover, you may carry | support catalyst particles using PVD methods, such as sputtering and vapor deposition.

(3) Preparation of Electrode Catalyst Layer Precursor Next, the electrode catalyst layer precursor is prepared by forming into a sheet shape using conductive fibers having conductive nanofibers and catalyst particles prepared as described above. . Specifically, conductive fibers having conductive nanofibers and catalyst particles are twisted together in a predetermined number to form a bundle, and a plurality of the conductive fiber bundles are prepared and crossed with each other as warp and weft. It is sufficient to use a method such as plain weaving.

  The number of the conductive fibers twisted together may be appropriately determined in consideration of the thickness, porosity, etc. of the obtained electrode catalyst layer. A bundle of two or more conductive fiber bundles twisted together may be woven. Further, these bundles may contain conductive fibers in which conductive nanofibers are not formed.

  Specifically, the number of the conductive fibers twisted together is preferably 20 to 100, more preferably about 40 to 60, and the conductive fibers may be twisted together to form a bundle of conductive fibers. . If the number of conductive fiber bundles is less than 20, the strength of the electrode catalyst layer may be reduced, and if the number of conductive fiber bundles exceeds 100, the porosity of the electrode catalyst layer decreases and gas permeability and generation There is a risk of reducing water discharge.

  Moreover, in order to shape | mold into a sheet form using an electroconductive fiber, if a desired electrode catalyst layer is obtained, it will not specifically limit, In addition to the plain weave mentioned above, a well-known method, such as a twill weave and a satin weave, is used. May be formed into a sheet shape. The obtained electrode catalyst layer precursor may have a smooth surface using a roller, a press device or the like.

(4) Impregnation of the solid polymer electrolyte Next, the slurry containing the solid polymer electrolyte is added to the electrode catalyst layer precursor containing the catalyst particles prepared as described above, and the flow coating method, spray method, screen printing method, After applying using a doctor blade method or the like, it is impregnated and dried. Thereby, the electroconductive fiber, electroconductive nanofiber, and catalyst particle which are contained in an electrode catalyst layer precursor can be coat | covered with a solid polymer electrolyte, and the electrode catalyst layer of this invention is obtained.

  As the slurry, a solution obtained by dissolving a solid polymer electrolyte in water and / or a solvent such as methanol, ethanol, propanol, isopropyl alcohol, or the like is used.

  In order for the solid polymer electrolyte to have a desired thickness or the like covering the inside or surface of the electrode catalyst layer precursor, the operation of impregnating and drying the slurry is repeated, or the concentration of the slurry is adjusted. It can be done by making adjustments. In addition, after applying the slurry, the slurry may be sucked from the back surface of the electrode catalyst layer precursor using an aspirator or the like.

  Although it does not specifically limit in order to dry the apply | coated said slurry, What is necessary is just to carry out at 20-120 degreeC under inert atmosphere, such as nitrogen, argon, helium, Preferably it is 60-100 degreeC. As a result, the electrode catalyst layer can be formed while preventing oxidative degradation of the solid polymer electrolyte.

  Moreover, as a method of impregnating the solid polymer electrolyte, the electrode substrate is immersed in the slurry containing the solid polymer electrolyte, and then pulled up at a predetermined speed and dried. The slurry is applied to the electrode substrate. After applying, a method of impregnating with a roller or the like can also be used.

  As described above, after the catalyst particles are supported on the conductive fibers and / or the conductive nanofibers, the conductive fibers and the conductive nanofibers and the catalyst particles are impregnated with the solid polymer electrolyte. A suitable contact state in which no solid polymer electrolyte is interposed therebetween can be maintained.

(5) Others The conductive fiber and / or conductive nanofiber of the present invention may be a fiber whose surface is modified to be hydrophilic and / or water-repellent. Since the method for modifying each fiber surface to be hydrophilic and / or water-repellent is as described above, detailed description thereof is omitted here.

  There is no particular limitation on the timing of modifying each fiber surface to be hydrophilic and / or water repellent. For example, in the production of the electrode catalyst layer described above, conductive fibers that have been modified in advance to be hydrophilic and / or water-repellent may be used. After forming the conductive fibers into a sheet, the hydrophilic and / or water-repellent properties are used. It is also possible to carry out a modification process.

  When the CNTs are formed on the conductive fibers, the CNT-forming catalyst can be highly dispersed and supported if the surface of the conductive fibers is hydrophilic. Therefore, it is preferable to use the conductive fiber used for forming the CNTs whose surface has been modified to be hydrophilic first.

  The conductive fibers and / or conductive nanofibers on which the catalyst particles that promote the electrode reaction are supported are desirably water-repellent. Accordingly, it is preferable to use conductive fibers formed with conductive nanofibers used for supporting the catalyst particles, which have been modified to be water-repellent in advance. Also, after forming conductive nanofibers using conductive fibers that have been modified to be hydrophilic, the conductive fibers formed with the conductive nanofibers are heat-treated in an inert gas atmosphere. Further, conductive nanofibers and conductive fibers that are further modified to have water repellency can also be used when supporting catalyst particles.

  Moreover, the part which is not carry | supporting a catalyst particle can also be made into a water-repellent conductive fiber by modifying after carrying | supporting a catalyst particle on electroconductive nanofiber.

  Conductive fibers and / or conductive nanofibers modified to be water repellent and conductive fibers and / or conductive nanofibers modified to hydrophilicity when formed into a sheet shape using conductive fibers And (i) what is mixed and bundled may be formed into a sheet shape, and (ii) those separately bundled may be mixed and formed into a sheet shape.

  In the gas diffusion electrode, in order to increase the content of the conductive fibers and / or conductive nanofibers modified to be water-repellent from the gas introduction portion toward the gas discharge portion, in the method (i) A plurality of bundles having different contents of conductive fibers and / or conductive nanofibers modified to have water repellency are easily selected, and these bundles may be appropriately selected and used when formed into a sheet. In the method (ii), when forming into a sheet, the conductive fibers and / or conductive nanofibers modified to be water-repellent, the conductive fibers modified to hydrophilicity and / or Electrode catalyst layers having different contents of conductive fibers and / or conductive nanofibers modified to be water-repellent can also be obtained by appropriately adjusting the density and the like of each bundle with the conductive nanofibers.

  In the above-described method, the conductive nanofibers and catalyst particles are first formed at a desired portion of the conductive fiber and then formed into a sheet shape. However, the method is not limited thereto. A method may be used in which conductive nanofibers and catalyst particles are supported on the obtained molded body after the conductive fibers are formed into a sheet shape in the same manner as described above. As the method, for example, after a predetermined number of conductive fibers are bundled and formed into a sheet shape, conductive nanofibers are formed on the obtained molded body, and further, a molded body on which the conductive nanofibers are formed is obtained. There is a method in which catalyst particles are supported on the conductive fibers and conductive nanofibers by immersing them in a catalyst compound solution and adding a reducing agent or the like. Since the method for forming conductive nanofibers, the method for supporting catalyst particles, and the method for impregnating solid polymer electrolyte can be performed in the same manner as described above, detailed description thereof is omitted here.

  The said molded object can also use directly what is marketed as a molded object previously shape | molded in the sheet form using the desired electroconductive fiber. Examples of such commercially available products include carbon paper TGP series manufactured by Toray Industries, Inc., carbon cloth manufactured by E-TEK, graphite fiber nonwoven fabric manufactured by SGL Carbon, and the like.

  In order to modify the surface of conductive fibers and / or conductive nanofibers constituting the molded body to be hydrophilic and / or water-repellent, the molded body is subjected to oxidation treatment or heat treatment in an inert gas atmosphere. You can do that. In addition, since the method and time for modifying each fiber surface constituting the molded body to be hydrophilic and / or water-repellent are the same as described above, detailed description thereof is omitted here.

(Preparation of buffer layer)
As a method for producing a buffer layer on the electrode catalyst layer, when producing a buffer layer made of only an organic compound, a solution obtained by dissolving the organic compound in a solvent such as water or alcohol is used on the electrode catalyst layer. Then, it is obtained by coating and drying.

  In the solution in which the organic compound is dissolved, the content of the organic compound is preferably about 1 to 20% by mass.

  The application method is not particularly limited, and may be performed by using a known method such as a flow coating method, a spray method, a screen printing method, or a doctor blade method by appropriately adjusting the concentration of the solution. In addition, the concentration of the solution, the number of coatings, the coating speed, and the like may be adjusted so that the obtained buffer layer has a desired thickness.

  Although it does not specifically limit as said drying method, What is necessary is just to carry out by 20-120 degreeC under inert gas atmosphere, such as nitrogen, argon, helium, Preferably it is about 60-100 degreeC.

When a buffer layer made of an inorganic compound is manufactured, at least one metal constituting the inorganic compound such as P ₂ O ₅ , SiO ₂ , B ₂ O ₃ , GeO ₂ , or As ₂ O _{3 is used.} Examples thereof include a method of sufficiently drying a sol solution containing a metal alkoxide to obtain a dry gel.

Examples of the metal alkoxide include tetramethoxysilane (TMOS, Si (OCH ₃ ) ₄ ), tetraethoxysilane (TEOS, Si (OC ₂ H ₅ ) ₄ ), glycidoxypropyltrimethoxysilane (GPTS, (OCH ₃ ) ₃ SiO (CH ₂ ) ₂ OCH ₂ CHO), triethyl phosphate (PO (OC ₂ H ₅ ) ₃ ), trimethyl phosphate (PO (OCH ₃ ) ₃ ), and the like.

  The sol solution can be obtained by adding a metal alkoxide to a solvent such as water and alcohol. In addition, an acid or base such as hydrochloric acid or ammonia may be added to the sol solution as a catalyst in order to adjust the gelation rate.

  After the sol solution is applied on the electrode catalyst layer by the same application method as described above, it is allowed to stand at room temperature for several weeks or at 150 ° C. for 1 to 24 hours. The dried gel can be used as the buffer layer.

  It is not limited to this, After applying the wet gel obtained by maintaining the said sol solution at about 30-80 degreeC and advancing the gelatinization reaction by hydrolysis on an electrode catalyst layer etc., this is 30-30. What was dried at about 50 degreeC and made into the dry gel can also be used as a buffer layer.

  The step of applying and drying the sol or the wet gel may be repeated so that the obtained buffer layer has a desired thickness.

  Further, a buffer layer is transferred onto the electrode catalyst layer by bonding a dry gel film separately produced on a PTFE sheet or the like using the sol or the wet gel onto the electrode catalyst layer by hot pressing or the like. May be. The dry gel membrane may be further heat-treated at a temperature of about 500 to 1000 ° C. in order to obtain stable high proton conductivity.

  When manufacturing a buffer layer composed of a mixture of an inorganic compound and an organic compound, for example, the organic compound is dissolved in a solvent such as water or alcohol used in the manufacture of the buffer layer composed only of the organic compound described above. For example, a method of adding an inorganic compound to the solution and applying and drying the compound may be used.

  At this time, examples of the shape of the inorganic compound include powder, plate, needle, sphere, and fiber, and are not particularly limited. What is necessary is just to determine suitably the addition amount etc. of the said inorganic type compound in consideration of durability, a softness | flexibility, etc. of the buffer layer obtained.

  The application and drying method is the same as that described in the production of the buffer layer made of only the organic compound, and therefore detailed description thereof is omitted here.

  In addition to such a method, a mixture of an inorganic compound and an organic compound can be obtained by adding an organic compound solution to a sol solution used in the production of a buffer layer made of an inorganic compound and drying the solution. You may manufacture the buffer layer which consists of.

  Examples of the organic compound solution include a solution in which an organic compound is dissolved in a solvent such as water or alcohol. Since this is the same as that described in the production of the buffer layer made of only the organic compound, the description thereof is omitted here.

  What is necessary is just to manufacture similarly to the buffer layer which consists of the above-mentioned inorganic type compound except adding the said organic type compound solution to the said sol solution.

  A method of contacting the buffer layer and the electrode catalyst layer in a state where the proton conductive electrolyte or the solid polymer electrolyte contained in at least one of the buffer layer and the electrode catalyst layer is wet may be used. Thereby, it can be set as the structure which the proton conductive electrolyte and solid polymer electrolyte which are contained in a buffer layer and an electrode catalyst layer connected, and can improve proton conductivity. Moreover, when making a buffer layer and an electrode catalyst layer contact, it is good for the electrode catalyst layer to apply | coat the solid polymer electrolyte not only to the inside but to the surface.

  The second of the present invention is a fuel cell MEA (also simply referred to as “MEA”) using the above-described first electrode catalyst layer of the present invention. That is, in an MEA having a configuration in which an anode-side electrode catalyst layer and an anode-side gas diffusion layer, and a cathode-side electrode catalyst layer and a cathode-side gas diffusion layer are arranged to face each other on both sides of a solid polymer electrolyte membrane. The MEA uses the first electrode catalyst layer of the present invention for at least one of the anode side electrode catalyst layer and the cathode side electrode catalyst layer. By using the first electrode catalyst layer of the present invention, an MEA having excellent power generation performance can be obtained.

  In the MEA of the present invention, the first electrode catalyst layer of the present invention may be used for at least one of the anode side electrode catalyst layer and the cathode side electrode catalyst layer. For example, when the above-described electrode catalyst layer is used for the cathode, a conventionally known anode electrode catalyst layer used for MEA may be applied to the anode in addition to the above-described electrode catalyst layer. However, it is more preferable that the above-described first electrode catalyst layer of the present invention is used for both the anode-side electrode catalyst layer and the cathode-side electrode catalyst layer because of its excellent electron conductivity.

  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, a membrane in which a polymer microporous membrane is impregnated with a liquid electrolyte, a membrane in which a porous body is filled with a polymer electrolyte, a membrane reinforced with porous Teflon, 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 100 μm, more preferably 10 to 50 μm. From the viewpoint of strength during film formation and durability during MEA operation, the thickness of the film is preferably 5 μm or more, and preferably from 100 μm or less from the viewpoint of output characteristics during MEA operation.

  As the gas diffusion layer, any conventionally known one can be used without particular limitation. Specifically, what consists of base materials, such as a sheet-like material which has electroconductivity and porosity, such as a carbon fabric, a paper-like paper body, a felt, and a nonwoven fabric, is mentioned. More specifically, carbon paper, carbon cloth, carbon nonwoven fabric and the like are preferable. A commercial item can also be used for the said base material, for example, carbon paper TGP series by Toray Industries, Inc., carbon cloth by E-TEK, etc. are mentioned.

  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.

  In order to further improve water repellency, the gas diffusion layer may have a conductive fine particle layer made of an aggregate of carbon particles containing a water repellent on the 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.

  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. In addition to carbon black, there are artificial graphite and carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin and furan resin.

  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 conductive fine 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 conductive fine particle layer, the mixing ratio between the carbon particles and the water repellent may be insufficient to obtain the water repellency as expected if there are too many carbon particles. May not be obtained. Considering these, the mixing ratio of the carbon particles and the water repellent in the conductive fine particle layer is preferably about 90:10 to 40:60 in terms of mass ratio.

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

  When a water repellent is contained in the gas diffusion layer, a general water repellent treatment method may be used. Examples include a method in which a base material used for a gas diffusion layer is immersed in an aqueous dispersion solution or an alcohol dispersion solution of a water repellent, and then heated and dried in an oven or the like. In view of ease of exhaust gas treatment during drying, it is preferable to use an aqueous dispersion solution of a water repellent.

  In the case of forming a gas diffusion layer having a conductive fine particle layer on the substrate, carbon particles, water repellent, etc. are used as alcohol, water, perfluorobenzene, dichloropentafluoropropane, methanol, ethanol, etc. A slurry is prepared by dispersing in a solvent such as a solvent, and the slurry is applied on a substrate and dried, or the slurry is dried and pulverized to form a powder, which is applied on the substrate. Or the like. The slurry can also be prepared by mixing carbon particles in an aqueous dispersion solution or alcohol dispersion solution of a water repellent. Then, it is preferable to heat-process at about 250-400 degreeC using a muffle furnace or a baking furnace.

  Also, the MEA production method is not particularly limited. For example, a method in which a solid polymer electrolyte membrane is sandwiched using an electrode catalyst layer and a gas diffusion layer and then bonded using a hot press method or the like. What is necessary is just to use suitably. 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, bondability can be improved.

  A third aspect of the present invention is a fuel cell using the above-described MEA. By using the second MEA of the present invention, a fuel cell having excellent power generation performance can be obtained. According to the fuel cell, the fuel cell system can be highly efficient, reduced in size, and reduced in weight, and 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 type of the fuel cell is preferably a polymer electrolyte fuel cell because it is small in size and high in density and high in output.

  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. 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, 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.

  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.

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

Example 1
(1) Formation of carbon nanotube An iron thin film was produced on the fiber surface using a sputtering method for carbon fiber (diameter 7 to 8 μm). Subsequently, it was placed in a quartz glass thermal CVD furnace, fired at 700 ° C. in an argon gas atmosphere, and then argon gas 400 SCCM and acetylene gas 40 SCCM were flowed to grow carbon nanotubes at 700 ° C.

(2) Supporting platinum particles Next, carbon fibers on which carbon nanotubes are formed are immersed in a dinitrodiammine platinum aqueous solution (Pt concentration: 1.0% by mass), and 50 ml of ethanol as a reducing agent is mixed with the solution to obtain 1 Stir for hours. Then, it heated up to 85 degreeC in 30 minutes, and also, after stirring and mixing at 85 degreeC for 6 hours, it cooled to room temperature in 1 hour. Subsequently, after pulling up the carbon fiber, the platinum particle was supported on the carbon fiber and the carbon nanotube by drying at 85 ° C. under reduced pressure for 12 hours.

(3) Production of electrode catalyst layer Next, 25 carbon fibers on which the platinum particles and the carbon nanotubes are formed are twisted together, and further, plain weaving is performed using a fiber bundle in which the two twisted yarns are twisted together. Thus, a carbon cloth was produced and punched into a 50 mm square to obtain an electrode catalyst layer precursor carrying platinum particles.

Further, a solid polymer electrolyte solution prepared by adjusting a Nafion (registered trademark) solution (DE520 manufactured by DuPont, containing Nafion 5 wt%) to a concentration of 3 wt% with isopropyl alcohol was applied to the electrode catalyst layer precursor by a flow coating method in a nitrogen atmosphere. Then, the electrode catalyst layer was prepared by applying and impregnating with the above, and drying in a nitrogen atmosphere at 60 ° C. for 60 minutes.
(4) Preparation of intermediate buffer layer A solid polymer electrolyte solution similar to the above was applied to one side of the electrode catalyst layer by a flow coating method in a nitrogen atmosphere, and then dried in a nitrogen atmosphere at 60 ° C for 60 minutes. The intermediate buffer layer was produced on one side of the electrode catalyst layer by repeating the step of causing the electrode catalyst layer 3 times.
(5) Production of Gas Diffusion Layer A gas diffusion base material was prepared by punching carbon paper (carbon paper TGP-H-060 manufactured by Toray Industries, Inc., thickness 190 μm) into a 50 mm square. This gas diffusion substrate was immersed for 5 minutes in a solution in which a PTFE fluorine-based aqueous dispersion solution (polyflon D-1E manufactured by Daikin Industries, Ltd., containing PTFE 60 wt%) was adjusted to a predetermined concentration with pure water, The PTFE was dispersed in the carbon paper by drying at 60 ° C. for 30 minutes. At this time, the PTFE content was 25 wt%. As a result, a water-repellent gas diffusion base material was obtained.

Subsequently, 5.4 g of carbon black (VULCAN (registered trademark) XC-72R manufactured by CABOT Co., Ltd.), 1.0 g of the same fluorine-based aqueous dispersion solution of PTFE as used above, and 29.6 g of water, A slurry was prepared by mixing and dispersing for 3 hours in a homogenizer. This slurry was uniformly applied to one surface of the previously prepared water-repellent gas diffusion base material by a bar coater, dried in an oven at 60 ° C. for 1 hour, and further subjected to 350 in a muffle furnace. A heat treatment was performed at 1 ° C. for 1 hour. Thereby, the gas diffusion layer in which the conductive fine particle layer was formed on the gas diffusion base material was obtained.
(6) Production of MEA and solid polymer electrolyte fuel cell After two electrode catalyst layers produced as described above were used and placed on both sides of Nafion 112 (100 mm square, thickness of about 50 μm) as a solid polymer electrolyte membrane Then, after hot pressing at 130 ° C. and 2.0 MPa for 10 minutes to form a joined body, the joined body is sandwiched by using two gas diffusion layers prepared earlier with the conductive fine particle layer inside. Thus, an MEA was produced.

  A gas separator with a gas flow path and a sealing material were arranged on both sides of the MEA produced as described above and tightened to a predetermined surface pressure to obtain a polymer electrolyte fuel cell.

(Example 2)
The surface of the carbon fiber was modified to be hydrophilic by heat-treating the carbon fiber (diameter 7 to 8 μm) at about 900 ° C. in an inert gas atmosphere of argon gas containing water vapor for 5 hours. Carbon nanotubes were formed on the obtained hydrophilic carbon fibers in the same manner as in Example 1. The surface of the carbon nanotube and the hydrophilic carbon fiber was modified to be water repellent by further heat-treating the hydrophilic carbon fiber on which the carbon nanotube was formed at 2800 ° C. for 3 hours in a hydrogen atmosphere. Next, using this water-repellent carbon fiber, platinum particles were supported on the water-repellent carbon fiber and the carbon nanotube in the same manner as in Example 1.

  Next, using carbon fibers (diameter 7 to 8 μm), hydrophilic carbon fibers obtained by modifying the surface of the carbon fibers to be hydrophilic were obtained in the same manner as described above.

  As described above, each of the 25 water-repellent carbon fibers carrying platinum particles and the hydrophilic carbon fibers is twisted together, and a fiber bundle in which the two twisted yarns are twisted together. A carbon cloth was produced by plain weaving and punched into a 50 mm square to obtain an electrode catalyst layer precursor carrying platinum particles.

  The electrode catalyst layer was prepared by impregnating and drying the solid catalyst electrolyte solution in the same manner as in Example 1.

  An MEA and a fuel cell were produced in the same manner as in Example 1 except that the electrode catalyst layer obtained as described above was used.

(Example 3)
The surface of the carbon fiber was modified to be hydrophilic by heat-treating the carbon fiber (diameter 7 to 8 μm) at about 900 ° C. in an inert gas atmosphere of argon gas containing water vapor for 5 hours. Carbon nanotubes were formed on the obtained hydrophilic carbon fibers in the same manner as in Example 1.

  In the same manner as described above, a hydrophilic carbon fiber on which carbon nanotubes are formed is separately prepared, and this hydrophilic carbon fiber is heat-treated at 2800 ° C. for 3 hours in a hydrogen atmosphere, so that the surfaces of the carbon nanotube and the hydrophilic carbon fiber are obtained. Was modified to water repellency.

  Next, platinum particles were supported on the hydrophilic carbon fiber and the water-repellent carbon fiber on which the carbon nanotubes were formed in the same manner as in Example 1.

  A predetermined number of hydrophilic carbon fibers and water repellent carbon fibers carrying carbon nanotubes and platinum particles are twisted together, and a fiber bundle in which the two twisted yarns are twisted together is formed into a water repellent carbon fiber and a hydrophilic fiber. A plurality of fiber bundles made of carbon fiber were prepared. At this time, the total number of water-repellent carbon fibers and hydrophilic carbon fibers in the fiber bundle was 50, and a plurality of fiber bundles having different ratios of the water-repellent carbon fibers and the hydrophilic carbon fibers were prepared.

  A carbon cloth was produced by plain weaving the obtained fiber bundle, and the carbon cloth was produced such that the density of the water-repellent carbon fibers in the gas discharge portion of the carbon cloth obtained at this time was increased. This carbon cloth was punched into a 50 mm square to obtain an electrode catalyst layer precursor having platinum particles. The density of the water-repellent carbon fiber and the hydrophilic carbon fiber in the electrode catalyst layer precursor is set to 1: 2 in terms of the number ratio of the water-repellent carbon fiber and the hydrophilic carbon fiber on the gas introduction side (50 mm × 25 mm). Moreover, the ratio of the water-repellent carbon fiber and the hydrophilic carbon fiber was 2: 1 in terms of the number of fibers on the gas discharge part side (50 mm × 25 mm).

  An electrode catalyst layer was prepared by impregnating and drying the solid electrolyte solution in the same manner as in Example 1 on the electrode substrate.

  An MEA and a fuel cell were produced in the same manner as in Example 1 except that the electrode catalyst layer obtained as described above was used.

(Comparative Example 1)
10 g of platinum-supporting carbon (TEC10E50E, Tanaka Kikinzoku Kogyo Co., Ltd., platinum content 46.5 wt%), 90 g of Nafion / isopropyl alcohol solution (manufactured by DuPont, containing 5 wt% of Nafion, ion exchange group equivalent weight 1100 g / mol), 25 g of pure water, 10 g of isopropyl alcohol (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) was mixed and dispersed for 3 hours using a homogenizer in a glass container in a water bath set to be kept at 20 ° C. to obtain an electrode catalyst ink.

  This electrode catalyst ink was applied onto a Teflon sheet using a screen printer, dried in an oven at 100 ° C. for 30 minutes, and then cut into a square having a side of 50 mm to obtain an electrode catalyst layer.

  Using each of the two electrocatalyst layers thus prepared, they were placed as solid polymer electrolyte membranes on both sides of Nafion 112 (100 mm square, thickness of about 50 μm), and hot pressed at 130 ° C. and 2.0 MPa for 10 minutes by a hot press method. After the Teflon sheet was peeled off, the electrode catalyst layers were transferred to both surfaces of the solid polymer electrolyte membrane to obtain a joined body.

  An MEA and a fuel cell were produced in the same manner as in Example 1 except that the electrode catalyst layer obtained as described above was used.

  The electrode catalyst layer of the present invention with reduced internal resistance and the like is useful for fuel cells and the like where high power generation performance is desired over a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the electrode catalyst layer which is preferable one Embodiment of this invention (FIG. 1 (A) shows the schematic diagram of the said electrode catalyst layer, FIG.1 (B) shows the conductive fiber which comprises an electrode catalyst layer. An enlarged schematic diagram is shown). It is a schematic diagram of the electrode catalyst layer which is preferable one Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Electrode catalyst layer, 120 ... Buffer layer, 111 ... Conductive fiber (weft), 111 '... Conductive fiber (warp), 112 ... Conductive nanofiber, 113 ... Catalyst particle, 114 ... Solid polymer electrolyte

Claims (13)

An electrode catalyst layer for a fuel cell,
An electrode catalyst layer for a fuel cell, comprising conductive fibers having conductive nanofibers, at least catalyst particles supported on the conductive nanofibers, and a solid polymer electrolyte.   The electrode catalyst layer for a fuel cell according to claim 1, wherein the conductive fiber contains at least carbon.   The fuel cell electrode catalyst layer according to claim 1, wherein the conductive nanofiber contains at least carbon.   The electrode catalyst layer for a fuel cell according to any one of claims 1 to 3, wherein the conductive fiber and / or the conductive nanofiber is modified to have water repellency and / or hydrophilicity.   5. The fuel cell according to claim 1, wherein the content of the conductive fiber and / or the conductive nanofiber modified to have water repellency increases from a gas introduction part toward a gas discharge part. Electrocatalyst layer.   The electrode catalyst layer for a fuel cell according to any one of claims 1 to 5, wherein the catalyst particles exhibit catalytic action for hydrogen oxidation and / or oxygen reduction.   The catalyst particles are made of platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, copper, silver, and alloys containing these. The electrode catalyst layer for a fuel cell according to any one of claims 1 to 6, which is at least one selected from the group.   The electrode catalyst layer for a fuel cell according to any one of claims 1 to 7, wherein the catalyst particles are supported on the conductive nanofiber modified to have at least water repellency.   The electrode catalyst layer for a fuel cell according to any one of claims 1 to 8, further comprising a buffer layer containing a proton conductive electrolyte.   The fuel cell electrode catalyst layer according to claim 9, wherein the proton conductive electrolyte is an organic compound and / or an inorganic compound. The organic compound includes at least a sulfonic acid group or a carboxyl group, and the inorganic compound is at least one selected from the group consisting of P ₂ O ₅ , SiO ₂ , B ₂ O ₃ , GeO ₂ , and As ₂ O _3. The electrode catalyst layer for a fuel cell according to claim 9 or 10, which is a seed.   A fuel cell MEA using the fuel cell electrode catalyst layer according to claim 1.   A fuel cell using the fuel cell MEA according to claim 12.