JP6193669B2 - Base material for gas diffusion electrode, gas diffusion electrode, membrane-electrode assembly, and polymer electrolyte fuel cell - Google Patents

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] Conductive fine continuous fibers made of an organic resin containing conductive particles, and conductive thick continuous fibers made of an organic resin containing conductive particles and having a larger average fiber diameter than the conductive fine continuous fibers , A non-woven fabric having a mixed region in which gas is mixed, and a base material for a gas diffusion electrode,
[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.

  The base material for a gas diffusion electrode according to the present invention of [1] is a nonwoven fabric having a mixed region where the base material for a gas diffusion electrode is a mixture of conductive fine fibers made of organic resin and conductive thick fibers made of organic resin. Since the conductive fine fibers and the conductive thick fibers constituting the nonwoven fabric are made of an organic resin and are flexible, the solid polymer film is not damaged and short-circuited.

  Further, the produced water becomes liquid water and / or water vapor depending on the power generation conditions, but the nonwoven fabric constituting the gas diffusion electrode substrate of the present invention has a mixed region in which conductive fine fibers and conductive thick fibers are mixed. In this mixed region, conductive fine fibers and conductive thick fibers are mixed, so that the mixed regions are relatively small voids compared to the regions composed only of conductive fine fibers or only conductive thick fibers. Since it is mixed up to large gaps, liquid water moves or water vapor condenses, and it is easy to concentrate liquid water in a larger area of the gap and increase the density of liquid water. Extrusion works and excels in drainage, and it is possible to secure voids by draining, and liquid water is unlikely to exist in areas consisting of relatively small voids, so supply even under conditions where liquid water is likely to exist Of gas It is considered to be excellent in dispersibility.

  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 electrode of the present invention (hereinafter sometimes simply referred to as “electrode base material”) is composed of conductive fine fibers made of organic resin containing conductive particles, and organic containing conductive particles. A non-woven fabric having a mixed region in which conductive thick fibers made of resin and having an average fiber diameter larger than that of the conductive fine fibers is mixed is provided.

  The conductive fibers constituting the nonwoven fabric of the present invention (hereinafter simply referred to as “conductive fibers” indicate both conductive fine fibers and conductive thick fibers) are flexible by being made of organic resin. Therefore, the conductive fiber does not damage the solid polymer film and short-circuit it. 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 water permeability without impregnating with a hydrophobic resin such as a fluororesin, and exhibits excellent drainage and gas diffusibility. 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 a phenol resin, an epoxy resin, a thermosetting polyimide 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, in the mixed region of conductive fine fibers and conductive thick fibers, by forming a relatively large void from a relatively small void, the action of increasing the density of liquid water and increasing drainage, The difference in average fiber diameter between the conductive thick fibers and the conductive fine fibers is preferably 100 nm or more so that the density of liquid water is low and the diffusibility of the supplied gas can be expected.

  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 substrate of the present invention includes a nonwoven fabric having a mixed region in which conductive fine fibers and conductive thick fibers are mixed as described above, but the total amount of conductive fine fibers and conductive thick fibers in the nonwoven fabric. Is preferably 10% by mass or more of the whole nonwoven fabric, more preferably 50% by mass or more, further preferably 70% by mass or more, and 90% by mass or more so as to have excellent conductivity. More preferably, it is most preferably composed of only conductive fine fibers and 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.

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 nonwoven fabric 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, the bonding is preferably performed by entanglement between the conductive fibers, bonding by plasticizing the organic resin with a solvent, or bonding by fusing the organic resin with heat. In addition, you may couple | bond together by these combined use.

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, the nonwoven fabric which comprises the electrode base material of this invention has the mixed area | region where the above-mentioned conductive fine fiber and conductive thick fiber are mixed, but the conductive fine fiber and conductivity in a mixed area | region are mentioned. The mass ratio to the thick fibers is preferably 1 to 99:99 to 1, more preferably 10 to 90:90 to 10, and still more preferably 20 to 80:80 to 20. When the mass ratio of the conductive fine fibers is less than 1 mass%, there is a tendency that the relatively small voids are too small and the gas diffusibility tends to deteriorate. When the mass ratio of the conductive fine fibers exceeds 99 mass%, the relatively large voids This is because there are too few discharge paths for liquid water and the drainage tends to be poor.

  In addition, the mixed region may exist over the entire thickness direction of the nonwoven fabric, or may exist only in a part in the thickness direction of the nonwoven fabric, so that the water dischargeability and gas diffusibility are excellent. It is preferable that 1% or more of the thickness of the nonwoven fabric is composed of the mixed region.

  In addition, when the mixed region exists only in a part in the thickness direction of the nonwoven fabric, the region including one surface of the nonwoven fabric may be a mixed region, or the mixed region is in a region between both surfaces. May exist. However, since the region including the one surface is a mixed region, the mixed region is brought into contact with the catalyst layer, and therefore, drainage and gas diffusibility are excellent. In other words, when the mixed region is in contact with the catalyst layer, it is easy to discharge the water generated by the reaction in the catalyst or the water that has been reversely diffused, and the fuel gas or oxygen-containing gas necessary for the reaction can be supplied uniformly. As a result, since it is considered that the power generation performance is excellent, it is preferable that the mixed region is in contact with the catalyst layer.

  Thus, when the mixed region exists only in a part in the thickness direction of the nonwoven fabric, the remaining region is a region composed only of conductive fine fibers, a region composed only of conductive thick fibers, or conductive fine fibers. It can be a region composed of fibers other than fibers and conductive thick fibers, or a region composed of fibers other than conductive thick fibers and conductive thin fibers.

  In addition, the nonwoven fabric which comprises the electrode base material of this invention should just have one mixed area | region in the thickness direction of a nonwoven fabric, and may have it in two or more places. In the case of having two or more mixed regions, it is preferable to provide a mixed region in which the average fiber diameter is sequentially larger or smaller in the thickness direction from the viewpoint of drainage and gas diffusibility. For example, when there are three mixed regions, the first mixed region, the second mixed region having an average fiber diameter larger (or smaller) than the first mixed region, and the average fiber diameter larger (or smaller) than the second mixed region. It is preferable that it is a nonwoven fabric provided with the 3rd mixing area | region. Such a mixed region of nonwoven fabrics can be confirmed by taking an electron micrograph in the thickness direction of the electrode substrate.

  Furthermore, when the mixed region exists only in a part of the nonwoven fabric, the mixed region does not need to exist only in a part in the thickness direction of the nonwoven fabric, and exists only in a part in the surface direction of the nonwoven fabric. May be. Thus, when it exists only in one part in the surface direction of a nonwoven fabric, it is preferable that 1% or more of the whole main surface of a nonwoven fabric consists of a mixed area | region so that it may be excellent in water discharge property and gas diffusibility.

  In addition, when the mixed region exists only in a part in the surface direction of the nonwoven fabric, the mixed region may be regularly present in a staggered pattern, a lattice intersection, or may be present at random. . However, it is a preferable aspect that the mixed region regularly exists because it is excellent in drainage and gas diffusibility. In addition, when the mixed region exists only in a part in the surface direction of the nonwoven fabric, if the mixed region exists so as to be located at a position that coincides with or overlaps the flow path of the bipolar plate, In addition, it is a preferred embodiment because of its excellent gas diffusibility.

  Thus, when the mixed region exists only in a part in the surface direction of the nonwoven fabric, the remaining region is a region composed only of conductive fine fibers, a region composed only of conductive thick fibers, or conductive fine fibers. And a region composed of fibers other than conductive thick fibers, and a region composed of fibers other than conductive thick fibers and conductive thin fibers.

Since the nonwoven fabric constituting the electrode substrate 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. This porosity preferably has a porosity of 20% or more in terms of porosity. 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 preferably 99% or less from the viewpoint of form stability. The porosity P (unit:%) is a value obtained from the following formula.
P = 100- (Fr1 + Fr2 + .. + Frn)
Here, Frn indicates the filling rate (unit:%) of component n constituting the nonwoven fabric, and is a value obtained from the following formula.
Frn = [M × Prn / (T × SGn)] × 100
Here, M is the basis weight of the nonwoven fabric (unit: g / cm ² ), T is the thickness (cm) of the nonwoven fabric, Prn is the mass ratio of component n (for example, organic resin, conductive particles) in the nonwoven fabric, and SGn is It means the specific gravity (unit: g / cm ³ ) of component n.

  The average flow pore size of the nonwoven fabric constituting the electrode substrate of the present invention is preferably 10 nm to 100 μm, and more preferably 100 nm to 50 μm so as to be excellent in liquid water discharge and gas diffusibility. . This average flow rate pore size is a value measured using a porous material automatic pore size distribution measurement system (Palm Porometer; Porous Materials) using a surface energy of 15.7 dyn / cm standard solution as the measurement liquid.

  The nonwoven fabric constituting the electrode substrate of the present invention has a mixed region in which conductive fine fibers and conductive thick fibers are mixed as described above. When nothing is filled, the liquid water is likely to move to a relatively large area in the mixed area, and the water vapor of the generated water is condensed in the relatively large area to become liquid water. Since the density of liquid water in areas with large voids can be increased, the action of pushing out liquid water works, it has excellent drainage properties, and it is possible to secure voids by draining, and it is a region consisting of relatively small voids Since liquid water does not easily exist, the diffusibility of the supplied gas is excellent.

  In addition, if the voids of the nonwoven fabric constituting the electrode base material contain fluorine-based resin and / or carbon, liquid water is easily pushed out by containing the former fluorine-based resin. Gas diffusibility can be increased, and the conductivity can be increased 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.

  The electrode base material which consists of a nonwoven fabric which has the mixed area | region where the conductive fine fiber and conductive thick fiber of this invention are mixed can be manufactured as follows, for example.

  First, a first spinning solution in which the first organic resin and the first conductive particles are mixed and a second spinning solution in which the second organic resin and the second conductive particles are mixed are prepared. Next, the first spinning solution is spun to form conductive thick fibers, and at the same time, the second spinning solution is spun to form conductive fine fibers, and these conductive fibers are directly collected and accumulated. A mixed fiber web in which conductive thick fibers and conductive fine fibers are mixed is formed. If the mixed fiber web itself has strength, the mixed fiber web can be used as a nonwoven fabric as it is, and in order to impart or improve strength, plasticization of the first organic resin and / or the second organic resin with a solvent, The first organic resin and / or the second organic resin may be bonded by heat, bonded by an adhesive, or the like to form a nonwoven fabric. In addition, it is preferable that the conductive fine fiber and the conductive thick fiber constituting the mixed fiber web are 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.

  Before forming the mixed fiber web, only the first spinning solution is spun and the conductive thick fiber region consisting only of the conductive thick fiber, or only the second spinning solution is spun and consists of only the conductive fine fiber. The conductive fine fiber region can be formed, and after the mixed fiber web is formed, the conductive thick fiber region or the conductive fine fiber region can be formed in the same manner as described above.

  In addition, as a spinning method of the conductive thick fiber or the conductive fine fiber, for example, an electrostatic spinning method, a spun bond method, a melt blow method, or a liquid discharge unit as disclosed in JP 2009-287138 A And a method in which a gas is discharged in parallel to the spinning solution discharged from the fiber, and a fiber is formed by applying a shearing force to the spinning solution in a single straight line. Among these, according to the electrostatic spinning method or the method disclosed in JP-A-2009-287138, conductive thin fibers or conductive fine 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, If a spinning fiber is removed by solvent replacement after using a material that does not easily volatilize during spinning and then the solvent is replaced by solvent substitution, the conductive thick fibers and conductive fibers tend to be in a plasticized state, resulting in a conductive property. It is preferable because a non-woven fabric having a high thickness can be produced, and the non-woven fabric becomes dense and the contact resistance in the fuel cell tends to be low.

  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 mixed fiber web can be formed and bonded by plasticizing an organic resin with a solvent, fusing an organic resin with heat, adhering with an adhesive, or the like to form a nonwoven fabric. However, as described above, the conductive thick fibers or the conductive fine fibers are preferably continuous fibers, and therefore the nonwoven fabric derived from the mixed fiber web directly collecting the continuous conductive thick fibers or the conductive fine fibers. Preferably there is.

  In the case where the organic resin constituting the conductive thick fiber and the conductive fine fiber is acryl oxide, spinning obtained by mixing polyacrylonitrile (PAN) and / or polyacrylonitrile (PAN) copolymer and conductive particles. The mixture is spun using a liquid to form a mixed fiber web in which conductive thick fibers and conductive fine fibers are mixed, and then heated in air at a temperature of 200 to 300 ° C., so that polyacrylonitrile (PAN) and It is also possible to further increase the conductivity of the nonwoven fabric by using a polyacrylonitrile (PAN) copolymer as acrylic oxide. Alternatively, conductive thick fibers or conductive fine fibers spun using a spinning solution in which polyacrylonitrile (PAN) and / or polyacrylonitrile (PAN) copolymer and conductive particles are mixed are heated in air at a temperature. After forming conductive thick fibers or conductive fine fibers in which polyacrylonitrile (PAN) and / or polyacrylonitrile (PAN) copolymer is made of acrylic oxide by heating at 200 to 300 ° C., this conductivity Thick fibers or conductive fine fibers can be mixed to form a mixed fiber web to produce a nonwoven fabric.

  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 nonwoven fabric is immersed in a fluorine-based dispersion such as polytetrafluoroethylene dispersion. Then, by sintering at a temperature of 300 to 350 ° C., it is possible to obtain a nonwoven fabric with improved water repellency and excellent drainage and gas diffusibility.

  Since the gas diffusion electrode of the present invention has a catalyst supported on the electrode base material provided with the nonwoven fabric as described above, it is difficult to short-circuit, and is excellent in drainage of generated water and diffusibility of the supplied gas. A fuel cell with excellent performance can be produced. 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 material as described above is used. However, in the electrode base material as described above, liquid water tends to concentrate in a region having a relatively large gap in the mixed region. It is considered to be excellent in gas diffusibility through the presence of a relatively small void area in the mixed area through the void generated by the drainage and excellent drainage due to the extruded liquid water. When the region includes one surface of the nonwoven fabric, it is preferable to dispose the region so that the mixed region side is the catalyst layer side.

  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. And, when the mixed region includes one surface of the nonwoven fabric on the electrode base as described above, the catalyst dispersion suspension is coated or sprayed on the mixed region side surface and dried. A gas diffusion electrode can be manufactured.

  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. When the base material and the mixed region include one surface of the nonwoven fabric, it can be manufactured by a method in which the mixed region side surface is laminated so as to come into contact with the catalyst layer and hot pressed.

  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
<Production of base material for gas diffusion electrode>
The first spinning solution is used to spin conductive thick fibers (average fiber diameter: 800 nm) by electrostatic spinning, and the second spinning solution is used to spin conductive fine fibers (average) by electrostatic spinning. (Fiber diameter: 300 nm) is spun and accumulated directly on the stainless steel drum as the counter electrode, and only the mixed region where continuous conductive thick fibers and continuous conductive fine fibers are mixed (thickness direction, surface) A mixed fiber web consisting of only mixed regions in any direction) is prepared, and the mixed fiber web in which nothing is filled in the voids is made of a nonwoven fabric, that is, an electrode substrate (weight per unit: 24 g / m ² , Thickness: 119 μm, porosity: 89%, electric resistance: 23 mΩ · cm ² , carbon black content: 40 mass%, mass ratio of conductive thick fibers to conductive fine fibers = 50: 50).

  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, and the conductive thick fiber and the conductive fine fiber are integrated. Sometimes intertwined and joined. In addition, the electrospinning conditions of any conductive fiber 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

(Comparative Example 1)
Conductive thick fibers obtained by spinning the first spinning solution by the electrospinning method are directly accumulated on a stainless drum as a counter electrode to produce a thick fiber web composed only of continuous conductive thick fibers. A thick fiber web in which nothing is filled in the voids is a non-woven fabric, that is, a gas diffusion electrode substrate (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%).

  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)
A fine fiber web consisting only of continuous conductive fine fibers was produced in the same manner as in Comparative Example 1 except that the second spinning solution was used, and a fine fiber web in which nothing was filled in the voids was made into a nonwoven fabric, That is, the base material for gas diffusion electrodes (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%) did.

  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)
Gas diffusion electrodes of Example 1 and Comparative Examples 1 and 2 using a porous material automatic pore size distribution measurement system (Palm Porometer; Porous Materials Co., Ltd.) and using a surface energy 15.7 dyn / cm standard solution as a measurement liquid The average flow pore size of the base material for measurement was measured. 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 material of Example 1 or Comparative Examples 1 and 2 was disposed on both surfaces of the solid polymer membrane-catalyst layer assembly, the membrane-electrode assembly (MEA) was respectively formed by hot pressing. Produced.

  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 cell using the electrode substrate of Example 1 has a voltage at a current density of 2.0 A / cm ^{2 as} compared with the fuel cell using the electrode substrate of Comparative Examples 1 and ^2. It was expensive. From this, the electrode base material provided with the nonwoven fabric having the mixed region in which the conductive fine fiber and the conductive thick fiber of the present invention are mixed is also capable of drainage and gas even under a situation where a large amount of water is generated. It was found that a fuel cell that can maintain diffusibility and has excellent power generation performance can be produced.

<Evaluation of leakage current>
The membrane-electrode assembly (MEA, electrode area 25 cm ² ) using the electrode base material of Example 1 or Comparative Examples 1 and 2 prepared in the above <Power generation test> is sandwiched between carbon plates and 2MP in the stacking direction. Each cell unit was fabricated by fastening at a pressure of 1 m. 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)

An organic resin of the conductive fine continuous fibers containing conductive particles, organic resin containing conductive particles, and than the conductive fine continuous fibers and thick conductive thick continuous fibers having an average fiber diameter are mixed A base material for a gas diffusion electrode comprising a non-woven fabric having a mixed region. 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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