JP2015022888A - Substrate for gas diffusion electrode, gas diffusion electrode, membrane-electrode assembly, and solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for a gas diffusion electrode which not only prevents a solid polymer membrane from being damaged but also being excellent in drainage of produced water and diffusivity of supplied gas, to provide the gas diffusion electrode using the same, to provide a membrane-electrode assembly, and to provide a solid polymer fuel cell.SOLUTION: A substrate for a gas diffusion electrode includes: a fine nonwoven fabric layer containing an organic resin-made conductive fine fiber containing a conductive particle; and a thick nonwoven fabric layer containing a conductive thick fiber which is made of organic resin containing the conductive particle and has a larger average fiber diameter than the conductive fine fiber. The gas diffusion electrode, a membrane-electrode assembly and a solid polymer fuel cell are equipped with a substrate for the gas diffusion electrode.

Description

  The present invention relates to a gas diffusion electrode substrate, a gas diffusion electrode, a membrane-electrode assembly, and a polymer electrolyte fuel cell.

  Regarding energy used in various forms, exploring alternative fuels and conserving resources are important issues due to concerns over the depletion of petroleum resources. In the midst of this, active development has continued for fuel cells that convert various fuels into chemical energy and extract them as electric power.

  As disclosed in, for example, page 5 of “Technological Trend Survey on Fuel Cells” (hereinafter, Non-Patent Document 1), the fuel cell is a phosphoric acid fuel cell (PAFC), melted, depending on the type of electrolyte used. There are four types: carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), and polymer electrolyte fuel cells (PEFC). These various fuel cells have a limited operating temperature range depending on the electrolyte, PEFC has a low temperature range of 100 ° C or lower, PAFC has a medium temperature range of 180-210 ° C, MCFC has a temperature of 600 ° C or higher, and SOFC has a temperature close to 1000 ° C. It is known to operate in the high temperature region. Among these, a general PEFC capable of outputting in a low temperature region takes out electric power generated by a combined reaction between hydrogen gas and oxygen gas (or air) as a fuel, but has a relatively small device configuration. There is an urgent need for practical use in that efficient power can be extracted.

  FIG. 1 is a schematic cross-sectional view of a main part of a fuel cell, showing the basic structure of a conventionally known PEFC. In the figure, components having substantially the same configuration or function as materials are indicated by the same hatching. The PEFC includes a membrane-electrode assembly (MEA) composed of a fuel electrode (gas diffusion electrode) 17a, a solid polymer film 19 and an air electrode (gas diffusion electrode) 17c as shown in FIG. It has a structure in which a plurality of cell units sandwiched between 11a and 11c are stacked. The fuel electrode 17a includes a catalyst layer 15a that decomposes into protons and electrons, and a gas diffusion layer 13a that supplies fuel gas to the catalyst layer 15a, and moisture management is provided between the catalyst layer 15a and the gas diffusion layer 13a. On the other hand, the air electrode 17c is composed of a catalyst layer 15c for reacting protons, electrons and oxygen-containing gas, and a gas diffusion layer 13c for supplying oxygen-containing gas to the catalyst layer 15c. A moisture management layer 14c is formed between the layer 15c and the gas diffusion layer 13c.

  Since the bipolar plate 11a has a groove capable of supplying a fuel gas, when the fuel gas is supplied through the groove of the bipolar plate 11a, the fuel gas diffuses through the gas diffusion layer 13a and permeates the moisture management layer 14a to pass through the catalyst layer 15a. To be supplied. The supplied fuel gas is decomposed into protons and electrons, and the protons move through the solid polymer film 19 and reach the catalyst layer 15c. On the other hand, the electrons pass through an external circuit (not shown) and move to the air electrode 17c. On the other hand, since the bipolar plate 11c has a groove capable of supplying an oxygen-containing gas, when the oxygen-containing gas is supplied through the groove of the bipolar plate 11c, the oxygen-containing gas diffuses through the gas diffusion layer 13c and permeates the moisture management layer 14c. And supplied to the catalyst layer 15c. The supplied oxygen-containing gas reacts with protons that have moved through the solid polymer membrane 19 and electrons that have moved through the external circuit, thereby generating water. The generated water is discharged out of the fuel cell through the moisture management layer 14c. In the fuel electrode, water that has been reversely diffused from the air electrode passes through the moisture management layer 14a and is discharged out of the fuel cell.

  The functions necessary for the gas diffusion layer 13a and the moisture management layer 14a, or the gas diffusion layer 13c and the moisture management layer 14c include a moisture retention property for keeping the solid polymer film 19 moist under a low humidification condition, and a high Under humidified conditions, water accumulates in the fuel cell, and has drainage to prevent flooding. Such gas diffusion layer 13a and moisture management layer 14a, or gas diffusion layer 13c and moisture management layer 14c are conventionally impregnated with a conductive porous substrate such as carbon paper with a fluorine-based resin such as polytetrafluoroethylene. Or by applying a paste in which carbon powder and fluororesin are mixed to form moisture management layers 14a and 14c in which fluororesin is present or carbon powder and fluororesin are present, and these are not present The regions were gas diffusion layers 13a and 13c. However, the moisture management layers 14a and 14c formed in this way are fluorinated resins or carbon powders and fluorinated resins applied to a conductive porous substrate. Carbon paper is used, and the carbon fibers that make up this carbon paper have high rigidity, so it penetrates the moisture management layers 14a and 14c and the catalyst layers 15a and 15c, damages the solid polymer film, and shorts. There was a case.

  The applicant of the present application also stated that “carbon black and a polytetrafluoroethylene resin or a polyvinylidene fluoride resin are applied to a base for a gas diffusion electrode comprising a glass nonwoven fabric in which a binder containing an acrylic resin and / or a vinyl acetate resin is adhered to glass fibers. Has been proposed "(Patent Document 1). Similar to the conventional carbon paper, the glass fiber has high rigidity, so the moisture management layers 14a and 14c and the catalyst layer In some cases, it penetrates 15a and 15c, damages the solid polymer film, and causes a short circuit.

JP 2008-204945 A

“Technological Trend Survey on Fuel Cells” (Edited by Technical Research Section, Patent Office, May 31, 2001, <URL> http://www.jpo.go.jp/shiryou/index.html)

  Therefore, the applicant of the present application has proposed “a base material for a gas diffusion electrode comprising a non-woven fabric containing conductive fibers containing conductive particles at least inside an organic resin” (Japanese Patent Application No. 2012-158122). This base material for a gas diffusion electrode is flexible because it contains conductive fibers containing an organic resin, and the conductive fibers did not damage the solid polymer film and cause a short circuit. However, this gas diffusion electrode substrate has insufficient drainage of generated water from the solid polymer membrane side to the bipolar plate side and the diffusibility of the supplied gas.

  The present invention has been made under such circumstances, and not only does the solid polymer membrane be damaged, but also provides a substrate for a gas diffusion electrode that is excellent in drainage of generated water and diffusibility of supplied gas. It is an object of the present invention to provide a gas diffusion electrode, a membrane-electrode assembly, and a polymer electrolyte fuel cell using the same.

The present invention
[1] A thin non-woven fabric layer containing conductive fine fibers made of organic resin containing conductive particles, and an organic resin made of organic resin containing conductive particles and having a larger average fiber diameter than the conductive fine fibers A gas diffusion electrode substrate comprising a thick nonwoven fabric layer containing thick fibers,
[2] A gas diffusion electrode in which a catalyst is supported on the base material for the gas diffusion electrode,
[3] A membrane-electrode assembly comprising the gas diffusion electrode substrate,
[4] A polymer electrolyte fuel cell comprising the gas diffusion electrode substrate,
About.

  [1] The gas diffusion electrode substrate of the present invention of [1] includes a fine nonwoven fabric layer containing conductive fine fibers made of organic resin and a conductive thick fiber made of organic resin. Since the conductive fibers constituting the nonwoven fabric layers are made of an organic resin and are flexible, the conductive fibers do not damage the solid polymer film and cause a short circuit.

  In addition, the generated water becomes liquid water and / or water vapor depending on the power generation conditions, but the gas diffusion electrode substrate of the present invention includes the fine nonwoven fabric layer and the thick nonwoven fabric layer, so that the liquid water moves. Since water vapor is condensed and liquid water tends to concentrate on a thick non-woven fabric layer having a larger pore size, and the density of liquid water can be increased, the action of pushing out the liquid water works and has excellent drainage, and the thick non-woven fabric layer In this case, it is possible to secure a gap in the base material for the gas diffusion electrode by draining, and as described above, liquid water is unlikely to exist in the thin nonwoven fabric layer, so that the diffusibility of the supplied gas is excellent. .

  In the gas diffusion electrode of the present invention [2], since the catalyst is supported on the base material for the gas diffusion electrode, it is difficult to short-circuit, and is excellent in drainage of generated water and diffusibility of supplied gas. Therefore, the gas diffusion electrode is capable of producing a fuel cell with excellent power generation performance.

  [3] Since the membrane-electrode assembly of the present invention includes the base material for gas diffusion electrode, it is difficult to short-circuit, and is excellent in drainage of generated water and diffusibility of supplied gas. A membrane-electrode assembly capable of producing a fuel cell with excellent power generation performance.

  Since the polymer electrolyte fuel cell of the present invention of [4] includes the gas diffusion electrode substrate, it is difficult to short-circuit, and is excellent in drainage of generated water and diffusibility of supplied gas. Therefore, the fuel cell has excellent power generation performance.

Schematic sectional view showing the schematic configuration of a polymer electrolyte fuel cell

  The base material for gas diffusion electrodes of the present invention (hereinafter sometimes simply referred to as “electrode base material”) includes a fine nonwoven fabric layer containing conductive fine fibers made of an organic resin containing conductive particles, and a conductive material. And a thick nonwoven fabric layer containing conductive thick fibers having an average fiber diameter larger than that of the conductive fine fibers.

  Conductive fibers (hereinafter simply referred to as “conductive fibers”) constituting these nonwoven fabric layers (hereinafter simply referred to as “nonwoven fabric layers” refer to both fine nonwoven fabric layers and thick nonwoven fabric layers) Since both conductive fine fibers and conductive thick fibers are made of an organic resin and are flexible, the conductive fibers do not damage and short-circuit the solid polymer film. Note that the organic resin constituting the conductive fiber of the present invention does not include diamond, graphite, or amorphous carbon.

  The organic resin constituting these conductive fibers may be a hydrophobic organic resin or a hydrophilic organic resin, and is not particularly limited. The former hydrophobic organic resin is preferable because it exhibits excellent drainage and gas diffusibility without impregnation with a hydrophobic resin such as a fluorine resin. On the other hand, since the hydrophilic organic resin can retain moisture, the solid polymer membrane can be kept moist and a solid polymer fuel cell capable of exhibiting sufficient power generation performance can be produced. it can.

  The conductive fiber may be composed only of the hydrophobic organic resin, may be composed of only the hydrophilic organic resin, or the hydrophobic organic resin and the hydrophilic organic resin are mixed or combined. However, it is particularly preferable that the conductive fiber is composed only of a hydrophobic organic resin because it exhibits excellent drainage and gas diffusibility.

  Further, the organic resin constituting the conductive fine fiber and the organic resin constituting the conductive thick fiber may both be composed of a hydrophobic organic resin or a hydrophilic organic resin, and either one is hydrophobic. It may be made of an organic resin and the other may be made of a hydrophilic organic resin. In addition, when all are comprised from hydrophobic organic resin or hydrophilic organic resin, they may be comprised from the same organic resin or different organic resin.

  The “hydrophobic organic resin” is an organic resin having a contact angle with water of 90 ° or more, and examples thereof include fluororesins such as polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE). ), Polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer ( ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer, and a copolymer of various monomers constituting the resin; polyolefin resin, for example, Polyethylene (PE), polypropylene (PP); Ether-based resins, e.g., polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and the like. In addition, these resins can be used alone or in combination of two or more. Among these, in particular, a fluororesin can be suitably used because it has high heat resistance, chemical resistance, and hydrophobicity.

  On the other hand, the “hydrophilic organic resin” is an organic resin having a contact angle with water of less than 90 °. Examples thereof include cellulose, such as rayon; polyamide resin, such as nylon 6, nylon 66; acrylic resin. Resins such as polyacrylic acid, polymethacrylic acid; resins having hydrophilic groups (amide group, carboxyl group, hydroxyl group, amino group, sulfonic acid group, etc.) such as hydrophilic polyurethane, polyvinyl pyrrolidone; polyacrylonitrile, acrylic oxide , Polyvinyl alcohol resins, and the like. These resins can be used alone or in combination of two or more. Among these, polyacrylonitrile is preferable because it is excellent in heat resistance, and since the thickness is not easily crushed by swelling of the solid polymer film, voids are maintained, and as a result, gas diffusibility is maintained.

  In addition, since the rigidity of the conductive fiber is high and as a result, the rigidity of the electrode substrate is high, the solid polymer film can be prevented from swelling and shrinking to prevent cracking of the solid polymer film. The conductive fibers are thermoset by the hydrophobic organic resin and / or the hydrophilic organic resin so that the thickness of the electrode substrate is not easily crushed by the swelling of the film, and the gap is maintained. Resin may be used. The thermosetting resin may contain both conductive thick fibers and conductive fine fibers, or only one of them. In addition to the thermosetting resin, a curing accelerator may be included.

  Examples of the “thermosetting resin” include an epoxy resin, a thermosetting polyimide resin, a phenol resin, a melamine resin, an unsaturated polyester resin, and a diallyl phthalate resin. Among these, a phenol resin and an epoxy resin are preferable because they are excellent in heat resistance and acid resistance and can increase the rigidity of the electrode substrate by heat treatment. In addition, when the conductive fiber contains a thermosetting resin, it may be composed of only a thermosetting resin, two or more kinds of thermosetting resins may be mixed or combined, and thermosetting. One or more types of hydrophilic resins and one or more types of thermoplastic hydrophobic organic resins or hydrophilic organic resins may be mixed or combined.

  The conductive fiber of the present invention contains conductive particles so as to be excellent in electron mobility when used as a gas diffusion electrode. When conductive particles are present only on the outer surface of the conductive fiber, the organic resin component inside the conductive fiber becomes a resistance component and tends to be inferior in conductivity. It preferably contains particles. In addition, the conductive particles may be completely embedded in the organic resin, but some of the conductive particles are exposed from the organic resin constituting the conductive fiber so that the conductive property is excellent. Is preferred. The conductive fiber containing such conductive particles can be produced, for example, by spinning a spinning solution containing an organic resin and conductive particles.

  In addition, the conductive fiber may contain two or more types of conductive particles that differ in terms of material or average primary particle size. Moreover, the electroconductive particle which comprises electroconductive fine fiber, and the electroconductive particle which comprises electroconductive thick fiber may be the same in the point of a raw material or an average primary particle diameter, and may differ.

  The conductive particles are not particularly limited, and examples thereof include carbon black, carbon nanotubes, carbon nanofibers, metal particles, and metal oxide particles. Among these, carbon black is preferably used in terms of chemical resistance, conductivity, and dispersibility. The particle size of the carbon black which is suitable is not particularly limited, but those having an average primary particle size of 5 nm to 200 nm, more preferably 10 nm to 100 nm can be used. In addition, it is preferable that the average primary particle diameter of the conductive particles is smaller than the fiber diameter of the conductive fibers to be described later so that the average primary particle diameter does not easily fall off and easily forms a fiber form.

  The mass ratio between the conductive particles and the organic resin in such a conductive fiber is not particularly limited, but is preferably 10 to 90:90 to 10, and preferably 20 to 80:80 to 20. More preferably, it is 30-70: 70-30, still more preferably 40-70: 60-30. This is because if the conductive particles are less than 10 mass%, the conductivity tends to be insufficient, whereas if the conductive particles are more than 90 mass%, the fiber forming property tends to be lowered. In addition, the mass ratio of the conductive particles and the organic resin in the conductive fine fibers and the mass ratio of the conductive particles and the organic resin in the conductive thick fibers may be the same or different. .

  The conductive particles preferably occupy 10 to 90 mass% of the electrode base material, more preferably 20 to 80 mass%, and more preferably 30 to 70 mass% so that the conductivity is excellent. More preferably, it occupies 40 to 70 mass%.

  The average fiber diameter of the conductive fiber of the present invention is not particularly limited, but is preferably 10 nm to 10 μm. When the average fiber diameter exceeds 10 μm, the number of contact points between the conductive fibers in the electrode substrate tends to be low, and the conductivity tends to be insufficient. On the other hand, when the average fiber diameter is less than 10 nm, it is difficult to contain conductive particles inside the fibers. This is because there is a tendency. In addition, it is preferable that the average fiber diameter of a conductive fiber is 5 times or more of the primary particle diameter of an electroconductive particle so that an electroconductive particle cannot drop out easily.

  In the present invention, conductive thick fibers having an average fiber diameter larger than that of the conductive fine fibers are contained so that the liquid water can easily move and the water vapor is condensed and the liquid water is easily concentrated. A thick nonwoven fabric layer having a pore diameter larger than that of the thin nonwoven fabric layer is formed. Therefore, if the difference in the average fiber diameter between the conductive thick fiber and the conductive fine fiber is small, it tends to be difficult to selectively concentrate the liquid water in the thick nonwoven fabric layer. The difference in average fiber diameter from the fine fibers is preferably 100 nm or more.

  The “average fiber diameter” in the present invention means an arithmetic average value of fiber diameters at 40 points, and the “fiber diameter” is a value measured based on a micrograph, and the conductive particles are exposed. Means a diameter including exposed conductive particles, and the conductive particles do not contain the exposed conductive fibers or the conductive particles are exposed. Even if it contains conductive fibers, when it is configured to include conductive fibers having portions where the conductive particles are not exposed, it means the diameter of the portions where the conductive particles are not exposed.

  The conductive fiber of the present invention is preferably a continuous fiber so that the electron mobility is excellent, and the end of the conductive fiber is small and the solid polymer film is hardly damaged. Such conductive continuous fibers can be produced, for example, by an electrostatic spinning method or a spunbond method.

  The electrode base material of the present invention comprises a fine nonwoven fabric layer containing conductive fine fibers as described above and a thick nonwoven fabric layer containing conductive thick fibers. As excellent, the mass content ratio in each layer of the conductive fine fiber or conductive thick fiber is preferably 10% or more, more preferably 50% or more, and further preferably 70% or more. 90% or more, more preferably composed of only conductive fine fibers or conductive thick fibers. In addition, the fibers other than the conductive fibers include hydrophobic organic fibers such as fluorine fibers and polyolefin fibers; hydrophilic organic fibers such as acrylic fibers and nylon fibers (for example, nylon 6 and nylon 66). Can do. Moreover, the mass content ratio of the conductive fine fibers in the fine nonwoven fabric layer and the mass content ratio of the conductive thick fibers in the thick nonwoven fabric layer may be the same or different.

Electrode substrate of the present invention may also containing fibers other than the conductive fibers, but as has excellent conductivity, is preferably an electric resistance of 150mΩ · cm ² or less, 100 m [Omega · cm ² or less It is more preferable that it is 50 mΩ · cm ² or less. “Electrical resistance” of the present invention is a method in which an electrode base material (25 cm ² ) cut into 5 cm square is sandwiched from both sides by a carbon plate, and a current (I) of 1 A is applied in the direction of carbon plate lamination under pressure of 2 MPa. In this state, the voltage (V) is measured. Then, resistance was (R = V / I) calculated, further, a value obtained by multiplying the area of the electrode substrate (25 cm ^2).

  In addition, although the thin nonwoven fabric layer or the thick nonwoven fabric layer which comprises the electrode base material of this invention may be adhere | attached with the adhesive agent, it is preferable not to adhere | attach with the adhesive agent so that it may be excellent in electroconductivity. For example, each layer is preferably formed by entanglement between conductive fibers, bonding by plasticizing an organic resin with a solvent, or bonding by fusing an organic resin by heat. Note that the bonding mode may be different for each layer.

The basis weight of the electrode substrate of the present invention is not particularly limited, but is preferably 0.5 to 200 g / m ² from the viewpoint of drainage, gas diffusibility, handleability and productivity, more preferably from 100 g / ^{m 2,} and even more preferably 0.5 to 50 g / ^{m 2.} Moreover, although thickness is not specifically limited, It is preferable that it is 1-1000 micrometers, It is more preferable that it is 1-500 micrometers, It is still more preferable that it is 1-300 micrometers.

“Weight” in the present invention is a value obtained by measuring the mass of a sample cut into a 10 cm square and converting it to a mass of 1 m ^2. “Thickness” is a thickness gauge (manufactured by Mitutoyo Corporation: Code No.) .547-401: Measurement force 3.5N or less).

  In addition, although the electrode base material of this invention is provided with the above-mentioned thin nonwoven fabric layer and a thick nonwoven fabric layer, the mass ratio of a thin nonwoven fabric layer and a thick nonwoven fabric layer is 1-99: 99-1. Is preferable, it is more preferable that it is 10-90: 90-10, and it is still more preferable that it is 20-80: 80-20. When the mass ratio of the fine nonwoven fabric layer is less than 1 mass%, gas diffusibility due to the fine nonwoven fabric layer tends to be deteriorated. On the other hand, when the mass ratio of the fine nonwoven fabric layer exceeds 99 mass%, concentrated liquid water in the thick nonwoven fabric layer This is because the discharge of gas cannot catch up and the gas diffusibility tends to decrease.

Since the electrode base material of the present invention is porous, a fuel cell having excellent drainage and gas diffusibility and high power generation performance can be produced even in the surface direction. It is preferable to have a porosity of 20% or more. Preferably, the porosity is 30% or more, more preferably the porosity is 50% or more. The upper limit of the porosity is not particularly limited, but is 99% or less from the viewpoint of form stability. The porosity P (unit:%) is a value obtained from the following equation.
P = 100- (Fr1 + Fr2 + .. + Frn)
Here, Frn indicates the filling rate (unit:%) of the component n constituting the electrode substrate, and is a value obtained from the following formula.
Frn = (M × Prn / T × SGn) × 100
Here, M is the basis weight (unit: g / cm ² ) of the electrode substrate, T is the thickness (cm) of the electrode substrate, and Prn is the component n (for example, organic resin, conductive particles) in the electrode substrate. The existing mass ratio, SGn, means the specific gravity (unit: g / cm ³ ) of component n.

  The average flow pore size of the fine nonwoven fabric layer constituting the electrode substrate of the present invention is preferably 10 nm to 3 μm, and preferably 100 nm to 3 μm, so that liquid water does not easily concentrate on the fine nonwoven fabric layer and is excellent in gas diffusibility. It is more preferable that On the other hand, the average flow pore size of the thick nonwoven fabric layer may be larger than the average flow pore size of the thin nonwoven fabric layer so that liquid water can easily concentrate on the thick nonwoven fabric layer, and is not particularly limited, but is 2 μm to 100 μm. Is preferable, and it is more preferable that it is 2 micrometers-50 micrometers.

  The average flow pore size is a value measured using a porous material automatic pore size distribution measurement system (Palm Porometer; Porous Material) and using a standard solution with a surface energy of 15.7 dyn / cm as the measurement liquid.

  The electrode base material of the present invention includes the fine nonwoven fabric layer and the thick nonwoven fabric layer as described above. However, since these layers are porous, when the voids of the electrode base material are not filled with anything, The liquid water is easy to move to the thick nonwoven fabric layer, and the water vapor of the generated water is condensed in the thick nonwoven fabric layer having a larger pore size to become liquid water, and the density of the liquid water in the thick nonwoven fabric layer can be increased. The action of pushing out water works, and it has excellent drainage properties in the thickness direction of the electrode base material, and in the thick nonwoven fabric layer, the voids of the electrode base material can be secured by draining, and the thin nonwoven fabric layer As described above, since liquid water hardly exists, the diffusibility of the supplied gas is also excellent. In addition, since it is porous when the space | gap of an electrode base material is not filled at all, it is excellent in the drainage property and gas diffusibility also in the surface direction of an electrode base material.

  In addition, when the fluorine-based resin and / or carbon is contained in the voids of the fine nonwoven fabric layer or the thick nonwoven fabric layer of the electrode base material, liquid water is easily pushed out by containing the former fluorine-based resin. Further, drainage and gas diffusibility can be enhanced, and the conductivity can be enhanced by containing the latter carbon.

  Examples of the fluororesin include polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene. Ethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride / tetrafluoroethylene / hexafluoro Examples thereof include a propylene copolymer and a copolymer of various monomers constituting the resin.

  Examples of carbon include carbon black, carbon nanotube, and carbon nanofiber.

  In addition, the electrode base material of this invention should just be equipped with at least 1 layer of a thin nonwoven fabric layer and a thick nonwoven fabric layer, and may be equipped with two or more layers of a thin nonwoven fabric layer or a thick nonwoven fabric layer. From the viewpoint of property, it is preferable to provide a nonwoven fabric layer having an average fiber diameter that is successively larger or smaller in the thickness direction. For example, in the case of an electrode substrate composed of three nonwoven fabric layers, the first nonwoven fabric layer, the second nonwoven fabric layer having an average fiber diameter larger (or smaller) than the first nonwoven fabric layer, and the average fiber diameter larger than the second nonwoven fabric layer. It is preferable that it is an electrode base material provided with the (or small) 3rd nonwoven fabric layer. In addition, since the electrode base material of this invention has a layer structure, if an electron micrograph in the thickness direction of an electrode base material is image | photographed, a layer structure can be confirmed clearly.

  The electrode base material which consists of one thin nonwoven fabric layer of this invention and one thick nonwoven fabric layer can be manufactured as follows, for example.

  First, by spinning using a first spinning solution in which the first organic resin and the first conductive particles are mixed, conductive thick fibers are formed, and the conductive thick fibers are directly collected and accumulated. To form a thick fiber web. If the thick fiber web itself has strength, the thick fiber web can be used as it is as a thick non-woven fabric layer, and in order to impart or improve strength, plasticization of the first organic resin with a solvent, A thick nonwoven fabric layer can also be formed by bonding by heat fusion, adhesive bonding, or the like. The conductive thick fibers constituting the thick fiber web formed by directly collecting and accumulating conductive thick fibers are preferably continuous long fibers. This is because the continuous long fibers are not only excellent in terms of conductivity and strength, but also have few fiber ends and are difficult to damage the solid polymer film.

  Next, spinning is performed using a second spinning solution in which the second organic resin and the second conductive particles are mixed to form conductive fine fibers, and the conductive fine fibers are directly collected on the thick nonwoven fabric layer. The fine fiber web is formed by accumulating. If the fine fiber web itself has strength, the fine fiber web can be used as a thin non-woven fabric layer as it is, and in order to impart or improve strength, plasticization of the second organic resin with a solvent, The thin non-woven fabric layer can also be bonded by heat fusion, adhesive bonding, or the like. The conductive fine fibers constituting the fine fiber web are preferably continuous long fibers. This is because the continuous long fibers are not only excellent in terms of conductivity and strength, but also have few fiber ends and are difficult to damage the solid polymer film.

  The above method is a method of laminating a fine fiber web on a thick non-woven fabric layer after forming the thick non-woven fabric layer, and laminating a fine fiber web on the thick fiber web, and the thick fiber web and the fine fiber web simultaneously. They may be bonded to form an electrode substrate. Moreover, although the said method is a method of forming a thin nonwoven fabric layer after forming a thick nonwoven fabric layer, you may form a thick nonwoven fabric layer after forming a thin nonwoven fabric layer.

  As a method for forming a thick fiber web or a fine fiber web, for example, an electrostatic spinning method, a spun bond method, a melt blow method, or a discharge from a liquid discharge unit as disclosed in JP 2009-287138 A A method may be mentioned in which a gas is discharged in parallel to the spinning solution and a fiber is formed by applying a shearing force to the spinning solution in a straight line. Among these, according to the electrostatic spinning method or the method disclosed in JP-A-2009-287138, conductive thin fibers or conductive thick fibers having a small fiber diameter can be spun, so that a thin electrode substrate can be produced. As a result, the resistance of the fuel cell can be lowered, and the volume of the fuel cell can be reduced, which is preferable.

  When the conductive particles are mixed with a solution in which the first organic resin or the second organic resin is dissolved in a solvent, as in the electrostatic spinning method or the method disclosed in JP2009-287138A, as the solvent, After using a material that is difficult to volatilize during spinning and forming a thick fiber web or a fine fiber web, removing the spinning solvent by solvent replacement will result in conductive thick fibers, conductive fine fibers, or conductive thick fibers and conductive As a result, a highly conductive electrode base material can be produced, and the electrode base material becomes dense, resulting in low contact resistance in the fuel cell. It is suitable because it is easy.

  In addition, after winding a conductive thick fiber or a conductive fine fiber as a continuous fiber, and then cutting the conductive thick fiber or the conductive fine fiber into a desired fiber length to make a short fiber, a known dry method or wet method is used. A fiber web can be formed and bonded by plasticizing an organic resin with a solvent, fusing the organic resin with heat, adhering with an adhesive, or the like to form a thick nonwoven fabric layer or a thin nonwoven fabric layer. However, as described above, it is preferable that the conductive thick fibers or conductive fine fibers are continuous fibers. Therefore, the thick fibers formed by directly collecting and collecting the continuous conductive thick fibers or conductive thin fibers. A thick nonwoven fabric layer or a fine nonwoven fabric layer derived from a web or a fine fiber web is preferred.

  When the organic resin constituting the conductive thick fiber or the conductive fine fiber is an acrylic oxide, the conductive thick fiber or the conductive fine fiber is spun using a spinning solution in which the acrylic resin and the conductive particles are mixed. After forming the fiber and forming the fiber web containing the conductive thick fiber or conductive fine fiber directly or indirectly, the acrylic resin is oxidized by heating at a temperature of 200 to 300 ° C. in air. As the acrylic, the conductivity of the electrode substrate can be further increased. Alternatively, conductive acrylic fibers and conductive fine fibers spun using a spinning solution in which acrylic resin and conductive particles are mixed are heated in air at a temperature of 200 to 300 ° C., thereby converting the acrylic resin to acrylic oxide. After that, a thick nonwoven fabric layer or a thin nonwoven fabric layer can be formed using conductive thick fibers or conductive fine fibers made of acrylic oxide and conductive particles.

  In addition, when the organic resin constituting the conductive thick fiber and the conductive fine fiber is a heat-resistant organic resin having a melting point exceeding 350 ° C., the electrode base material is a fluorine-based dispersion such as polytetrafluoroethylene dispersion. After being immersed in and applied, sintering is performed at a temperature of 300 to 350 ° C., so that the electrode substrate can be improved in water repellency and excellent in drainage and gas diffusibility.

  Since the gas diffusion electrode of the present invention has a catalyst supported on the electrode base material described above, it is difficult to short-circuit, and is excellent in the drainage of generated water and the diffusibility of the supplied gas. A battery can be fabricated. In addition, the gas diffusion electrode of the present invention has a catalyst supported on the surface of conductive fibers (surface of conductive fine fibers or conductive thick fibers), and not only the electron conduction caused by contact between the catalysts but also the electron conduction path caused by the conductive fibers. Is also formed, so there are few catalysts isolated from the electron conduction path. Furthermore, since the electrode substrate of the present invention is excellent in drainage and gas diffusibility, gas can be sufficiently stably supplied to the three-phase interface (reaction field where the gas, catalyst, and electrolyte resin are associated). For these reasons, the catalyst can be used efficiently and the amount of catalyst can be reduced.

  The gas diffusion electrode of the present invention has the same structure as that of a conventional gas diffusion electrode except that it includes the electrode base as described above. Examples of the catalyst include platinum, platinum alloy, palladium, palladium alloy, titanium, manganese, magnesium, lanthanum, vanadium, zirconium, iridium, rhodium, ruthenium, gold, nickel-lanthanum alloy, titanium-iron alloy, and the like. It is possible to carry one or more kinds of catalysts selected from these.

  In addition to the catalyst, it is preferable that an electron conductor and a proton conductor are included, and as the electron conductor, conductive particles similar to the conductive particles contained in conductive fibers such as carbon black are suitable. The catalyst may be supported on the conductive particles. Moreover, an ion exchange resin is suitable as the proton conductor.

  In the gas diffusion electrode of the present invention, the electrode base as described above is used, but in the electrode base as described above, liquid water tends to concentrate on the thick nonwoven fabric layer, and the concentrated liquid water is the bipolar plate. Extruded to the side with excellent drainage, thick nonwoven fabric layer is excellent in gas diffusivity through voids generated by drainage, and thin nonwoven fabric layer is unlikely to have liquid water and is considered to be excellent in gas diffusibility Therefore, it is preferable to arrange the fine nonwoven fabric layer side to be the solid polymer film side. Therefore, the catalyst is preferably supported on the fine nonwoven fabric layer side of the electrode substrate.

  The gas diffusion electrode of the present invention can be produced, for example, by the following method.

  First, a catalyst (for example, carbon powder carrying a catalyst such as platinum) is added and mixed in a single or mixed solvent composed of ethyl alcohol, propyl alcohol, butyl alcohol, ethylene glycol dimethyl ether, etc., and this is mixed with an ion exchange resin. The solution is added and mixed uniformly by ultrasonic dispersion or the like to obtain a catalyst dispersion suspension. Then, the gas dispersion electrode can be produced by coating or spraying the catalyst dispersion suspension on the electrode substrate as described above, preferably on the fine nonwoven fabric layer side of the electrode substrate, and drying the solution. it can.

  Since the membrane-electrode assembly of the present invention includes the base material for gas diffusion electrode as described above, it is difficult to short-circuit, and also has excellent drainage of generated water and excellent diffusibility of supplied gas. This is a membrane-electrode assembly capable of producing a fuel cell excellent in.

  The membrane-electrode assembly of the present invention can be exactly the same as the conventional membrane-electrode assembly except that the membrane-electrode assembly is provided with the base material for gas diffusion electrode as described above.

  Such a membrane-electrode assembly can be manufactured, for example, by sandwiching a solid polymer membrane between the catalyst support surfaces of a pair of gas diffusion electrodes and hot pressing. Further, after applying the catalyst dispersion suspension as described above to the support to form a catalyst layer, this catalyst layer is transferred to a solid polymer film, and then the catalyst layer is used for the gas diffusion electrode as described above. It can also be produced by a method of laminating the base material, preferably the thin nonwoven fabric layer side surface of the base material for gas diffusion electrode so as to contact the catalyst layer, and hot pressing.

  As the solid polymer film, for example, a perfluorocarbon sulfonic acid resin film, a sulfonated aromatic hydrocarbon resin film, an alkylsulfonated aromatic hydrocarbon resin film, or the like can be used.

  Since the polymer electrolyte fuel cell of the present invention is provided with the base material for gas diffusion electrode as described above, it is difficult to short-circuit, and is excellent in drainage of generated water and diffusibility of supplied gas. It is a fuel cell with excellent performance.

  The fuel cell of the present invention can be exactly the same as a conventional fuel cell except that it includes the gas diffusion electrode substrate as described above. For example, it has a structure in which a plurality of cell units sandwiching a membrane-electrode assembly as described above between a pair of bipolar plates are stacked. For example, a plurality of cell units can be stacked and fixed.

  The bipolar plate is not particularly limited as long as the bipolar plate has high conductivity, does not transmit gas, and has a flow path capable of supplying gas to the gas diffusion electrode. A carbon-resin composite material, a metal material, or the like can be used.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

(Example)
<Preparation of the first spinning solution>
A vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer was added to N, N-dimethylformamide (DMF) and dissolved using a rocking mill to obtain a solution having a concentration of 10 mass%.

  Next, carbon black (Denka Black granular product, manufactured by Denki Kagaku Kogyo Co., Ltd., average primary particle size: 35 nm) is mixed with the above solution as the conductive particles, stirred, and further diluted with DMF to obtain carbon. Black was dispersed to prepare a first spinning solution having a solid mass ratio of carbon black and vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymer of 40:60 and a solid content concentration of 13 mass%.

<Preparation of second spinning solution>
A second spinning solution was prepared in the same manner as the first spinning solution except that the solid concentration of the spinning solution was 8 mass%.

Example 1
<Preparation of base material for gas diffusion electrode>
Conductive thick fibers obtained by spinning the first spinning solution by an electrostatic spinning method are directly accumulated on a stainless drum, which is a counter electrode, and a thick non-woven fabric layer consisting only of continuous conductive thick fibers ( Average fiber diameter: 800 nm, basis weight: 17 g / m ² , thickness: 80 μm).

Subsequently, the conductive fine fibers obtained by spinning the second spinning solution by the electrospinning method are directly accumulated on the thick nonwoven fabric, and the fine nonwoven fabric layer (average fiber) consisting only of continuous conductive fine fibers is collected. An electrode base material having a diameter of 300 nm, a basis weight of 6 g / m ² , and a thickness of 30 μm, in which a thick nonwoven fabric layer and a thin nonwoven fabric layer are connected, and nothing is filled in the voids (weight basis: 23 g / m) ² , thickness: 110 μm, porosity: 89%, electric resistance: 25 mΩ · cm ² , carbon black content: 40 mass%). Both the conductive thick fiber and the conductive fine fiber contain carbon black inside the fiber, and a part of the carbon black is exposed from the fiber surface, the conductive thick fibers, the conductive fine fibers, In addition, the conductive thick fibers and the conductive fine fibers were in a state of being bonded at the time of accumulation. The electrospinning conditions were as follows.

Electrode: Metal nozzle (inner diameter: 0.33 mm) and stainless steel drum Discharge amount: 2 g / hour Distance between nozzle tip and stainless steel drum: 10 cm
Applied voltage: 10 kV
Temperature / humidity: 25 ° C / 35% RH

(Example 2)
The thick nonwoven fabric layer was formed in the same manner as in Example 1 except that the basis weight of the thick nonwoven fabric layer was 13 g / m ² , the thickness was 63 μm, the basis weight of the thin nonwoven fabric layer was 10 g / m ² , and the thickness was 50 μm. And a thin non-woven fabric layer connected to each other, and the gap is not filled with any electrode base material (weight per unit: 23 g / m ² , thickness: 113 μm, porosity 88%, electric resistance: 25 mΩ · cm ² , carbon black Content: 40 mass%). Both the conductive thick fiber and the conductive fine fiber contain carbon black inside the fiber, and a part of the carbon black is exposed from the fiber surface, the conductive thick fibers, the conductive fine fibers, In addition, the conductive thick fibers and the conductive fine fibers were in a state of being bonded at the time of accumulation.

(Comparative Example 1)
The conductive thick fibers obtained by spinning the first spinning solution by the electrostatic spinning method are directly accumulated on the stainless drum as the counter electrode, and only from the thick nonwoven fabric layer composed only of continuous conductive thick fibers. The gas diffusion electrode base material in which nothing is filled in the voids (average fiber diameter: 800 nm, basis weight: 23 g / m ² , thickness: 108 μm, electric resistance: 23 mΩ · cm ² , porosity: 88%, Carbon black content: 40 mass%) was produced. This conductive thick fiber contained carbon black inside the fiber, a part of the carbon black was exposed from the fiber surface, and the conductive thick fibers were in a state of being bonded together. The electrospinning conditions were as follows.

Electrode: Metal nozzle (inner diameter: 0.33 mm) and stainless steel drum Discharge amount: 2 g / hour Distance between nozzle tip and stainless steel drum: 10 cm
Applied voltage: 15 kV
Temperature / humidity: 25 ° C / 30% RH

(Comparative Example 2)
Similar to Comparative Example 1 except that the second spinning solution was used, a gas diffusion electrode base material consisting of only a thin non-woven fabric layer consisting only of continuous conductive fine fibers, in which no voids were filled ( Average fiber diameter: 300 nm, basis weight: 25 g / m ² , thickness: 110 μm, electric resistance: 24 mΩ · cm ² , porosity: 87%, carbon black content: 40 mass%). This conductive fine fiber contained carbon black inside the fiber, and a part of the carbon black was exposed from the fiber surface, and the conductive fine fibers were in a state of being bonded together.

(Measurement of average flow hole diameter)
Gases of Examples 1 and 2 and Comparative Examples 1 and 2 using a porous material automatic pore size distribution measuring system (Palm Porometer; Porous Materials Co., Ltd.) and using a surface energy of 15.7 dyn / cm standard solution as a measuring liquid. The average flow pore size of the diffusion electrode substrate was measured. In addition, the average flow pore diameters of the thick nonwoven fabric layer and the fine nonwoven fabric layer of Examples 1 and 2 are different from those of Examples 1 and 2 in that only conductive thick fibers or only conductive fine fibers are used in Example 1 or Example 2. These are the average flow pore diameters when the fiber webs are formed so as to have the same basis weight as the thick nonwoven fabric layer or the thin nonwoven fabric layer, and the respective fiber webs are regarded as the thick nonwoven fabric layer or the fine nonwoven fabric layer. The results are shown in Table 1.

<Power generation test>
To 10.4 g of ethylene glycol dimethyl ether, 0.8 g of commercially available platinum-supported carbon particles (Ishifuku Metal Co., Ltd., platinum-supported amount of 40% by mass with respect to carbon) was added and dispersed by ultrasonic treatment. As a resin solution, 4.0 g of a commercially available 5% by mass Nafion solution (trade name, manufactured by Sigma-Aldrich, USA) was added, further dispersed by ultrasonic treatment, and further stirred with a stirrer to prepare a catalyst paste.

Next, this catalyst paste was applied to a 25 cm ² support (trade name: Naflon PTFE tape, manufactured by Nichias Co., Ltd., thickness 0.1 mm), dried at 60 ° C. with a hot air dryer, and platinum on the support A catalyst layer having a loading amount of 0.4 mg / cm ² was produced.

On the other hand, Nafion NRE-212CS (trade name, manufactured by DuPont, USA) was prepared as a solid polymer film. The catalyst layers were transferred and laminated on both surfaces of the solid polymer membrane, and then joined by hot pressing under conditions of a temperature of 135 ° C., a pressure of 2.6 MPa, and a time of 10 minutes, and a solid polymer having an electrode area of 25 cm ² . A membrane-catalyst layer assembly was produced.

  And the membrane-electrode assembly (MEA) was produced using the said solid polymer membrane-catalyst layer assembly. That is, after the gas diffusion electrode base materials of Examples 1 and 2 or Comparative Examples 1 and 2 are arranged on both surfaces of the solid polymer membrane-catalyst layer assembly, the membrane-electrode assembly (MEA) is formed by hot pressing. Were prepared. In addition, when the base material for gas diffusion electrodes of Examples 1 and 2 was used, it arrange | positioned so that a fine nonwoven fabric layer might contact | abut with a catalyst layer.

  After that, each was assembled in a polymer electrolyte fuel cell “As-510-C25-1H” (trade name, manufactured by NF Circuit Design Block Co., Ltd.) with a clamping pressure of 1.5 N · m, and each power generation performance was evaluated. .

  This standard cell includes a bipolar plate and is used for an evaluation test of a membrane-electrode assembly (MEA). For power generation, a hydrogen gas utilization rate of 70% was supplied to the fuel electrode side and an air gas utilization rate of 45% was supplied to the air electrode side, and the potential-current curve was measured under full humidification conditions at a cell temperature of 80 ° C and a bubbler temperature of 80 ° C. . The results are shown in Table 2.

From the results in Table 2, the fuel cells using the electrode base materials of Examples 1 and 2 were compared with the fuel cells using the electrode base materials of Comparative Examples 1 and ² at a current density of 2.0 A / cm ² . The voltage was high. From this, the electrode base material provided with the fine nonwoven fabric layer and the thick nonwoven fabric layer of the present invention can maintain drainage and gas diffusibility even under a situation where a large amount of water is generated, and has excellent power generation performance. It has been found that a fuel cell can be produced.

<Evaluation of leakage current>
The membrane-electrode assembly (MEA, electrode area 25 cm ² ) using the electrode base material of Examples 1-2 or Comparative Examples 1-2 prepared in the above <Power generation test> is sandwiched between carbon plates, and the lamination direction Each of the cell units was fabricated by fastening with a pressure of 2MP. Next, a voltage of 0.2 V was applied to these cell units, and leakage currents were measured. As a result, in all the membrane-electrode assemblies, the leakage current was 0.5 mA or less.

  Similarly, the leakage current was measured for the membrane-electrode assembly after <Power generation test>, but the leakage current was 0.5 mA or less, and no increase in leakage current before and after power generation was confirmed. . From these results, it was found that the electrode substrate of the present invention did not damage the solid polymer film.

  The electrode base material of the present invention not only does not damage the solid polymer membrane, but also has excellent drainage and gas diffusibility, so that a polymer electrolyte fuel cell having excellent power generation performance can be produced.

11a (Fuel electrode side) Bipolar plate 11c (Air electrode side) Bipolar plate 13a (Fuel electrode side) Gas diffusion layer 13c (Air electrode side) Gas diffusion layer 14a (Fuel electrode side) Moisture management layer 14c (Air electrode side) Moisture Management layer 15a (fuel electrode side) catalyst layer 15c (air electrode side) catalyst layer 17a Fuel electrode (gas diffusion electrode)
17c Air electrode (gas diffusion electrode)
19 Solid polymer membrane

Claims (4)

A thin non-woven fabric layer containing conductive fine fibers made of organic resin containing conductive particles, an organic resin containing conductive particles, and conductive thick fibers having an average fiber diameter larger than that of the conductive fine fibers The base material for gas diffusion electrodes provided with the thick nonwoven fabric layer to contain. A gas diffusion electrode in which a catalyst is supported on the gas diffusion electrode substrate according to claim 1. A membrane-electrode assembly comprising the gas diffusion electrode substrate according to claim 1. A polymer electrolyte fuel cell comprising the gas diffusion electrode substrate according to claim 1.

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