JP6209515B2 - 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)

  The present invention has been made under such circumstances, and provides a gas diffusion electrode substrate, a gas diffusion electrode, a membrane-electrode assembly, and a solid polymer fuel cell that do not damage the solid polymer membrane. The purpose is to do.

The present invention
[1] A gas diffusion electrode base material comprising a nonwoven fabric containing conductive fibers containing conductive particles at least inside an organic resin;
[2] A gas diffusion electrode in which a catalyst is supported on the gas diffusion electrode substrate according to [1],
[3] A membrane-electrode assembly provided with the gas diffusion electrode substrate according to [1],
[4] The present invention relates to a polymer electrolyte fuel cell comprising the gas diffusion electrode substrate according to [1].

  The “base for gas diffusion electrode” of the present invention of [1], wherein the nonwoven fabric constituting the base for gas diffusion electrode contains conductive fibers containing conductive particles at least inside the organic resin, Since this conductive fiber contains an organic resin and is flexible, the conductive fiber does not damage the solid polymer film and short-circuit it.

  The “gas diffusion electrode” of the present invention of [2] is a gas diffusion electrode which can produce a fuel cell which is not easily short-circuited and has excellent power generation performance because a catalyst is supported on the base material for the gas diffusion electrode. It is.

  The “membrane-electrode assembly” of the present invention of [3] includes the gas diffusion electrode base material, and therefore it is difficult to short-circuit, and a membrane-electrode assembly that can produce a fuel cell with excellent power generation performance. Is the body.

  The “solid polymer fuel cell” of the present invention of [4] is a fuel cell that is not easily short-circuited and has excellent power generation performance because it comprises the base material for gas diffusion electrode.

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 nonwoven fabric containing conductive fibers containing conductive particles at least inside an organic resin. . Since the conductive fiber of this nonwoven fabric is flexible because it contains an organic resin, the conductive fiber does not damage the solid polymer film and short-circuit it. The “organic resin” of the present invention does not include diamond, graphite, and amorphous carbon.

  The organic resin constituting the conductive fiber may be a hydrophobic organic resin or a hydrophilic organic resin, and is not particularly limited. The former hydrophobic organic resin exhibits excellent water permeability without impregnating with a hydrophobic resin such as a fluororesin, and exhibits excellent drainage. 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. In particular, if only a hydrophilic organic resin is used, moisture can be retained and the solid polymer membrane can be kept moist even in a low-humidity environment, thus producing a solid polymer fuel cell that can exhibit sufficient power generation performance. can do.

  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 resin, for example, a polyethylene terephthalate (PET), polyethylene naphthalate (PEN). 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; polyacrylonitrile. Acrylic resin, polyvinyl alcohol resin, acrylic resin, for example, polyacrylic acid, polymethacrylic acid, resin having a hydrophilic group (amide group, carboxyl group, hydroxyl group, amino group, sulfonic acid group, etc.), for example, hydrophilic Mention may be made of water-soluble polyurethane and polyvinylpyrrolidone. 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 is not easily crushed by swelling of the solid polymer film. In the present invention, the hydrophobic organic resin and the hydrophilic organic resin may be mixed or combined.

  When used as a gas diffusion electrode, the conductive fiber of the present invention contains conductive particles at least inside the organic resin so that the electron mobility is excellent. That is, if the conductive particles are present only on the outer surface of the organic resin, the organic resin component becomes a resistance component and is inferior in conductivity. In the present invention, however, the conductive particles are contained inside the organic resin. Since it contains, it is excellent in electroconductivity. From the viewpoint of conductivity, the conductive particles are preferably exposed from the organic resin. “Containing conductive particles inside” does not only mean that the conductive particles are completely buried in the organic resin, but a part of the conductive particles is made of the organic resin. It also means an exposed state. Such conductive fibers containing conductive particles at least inside the organic resin can be produced, for example, by spinning a spinning solution containing the organic resin and conductive particles.

  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 is not particularly limited, but is preferably 10 to 90:90 to 10, more preferably 20 to 80:80 to 20, and 30 More preferably, it is -70: 70-30, and it is still more preferable that it is 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, it is preferable that electroconductive particle occupies 10-90 mass% of a nonwoven fabric, and it is more preferable that it occupies 20-80 mass% so that it may be excellent in electroconductivity.

  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, there are few contact points between the fibers in the electrode substrate, and the conductivity tends to be insufficient. On the other hand, when the average fiber diameter is less than 10 nm, it tends to be difficult to contain conductive particles inside the fiber. Because there is. 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.

  The “average fiber diameter” means the arithmetic average value of the fiber diameters at 40 points, and the “fiber diameter” is a value measured based on a micrograph, and the conductive particle exposed conductive particles. In the case of being composed only of conductive fibers, it means the diameter including the exposed conductive particles, and does not contain conductive fibers with exposed conductive particles or conductive fibers with exposed conductive particles In the case where it is configured to include a conductive fiber having a portion where the conductive particles are not exposed, the diameter at the portion where the conductive particles are not exposed is meant.

  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 a conductive continuous fiber is, for example, an electrostatic spinning method, a spunbond method, a melt blow method, or a spinning solution discharged from a liquid discharging unit as disclosed in JP2009-287138A. Thus, it is possible to produce the fiber by discharging the gas in parallel and applying a shearing force to the spinning solution in a straight line.

  The mass content ratio of the conductive fibers in the nonwoven fabric constituting the electrode substrate of the present invention is preferably 10% or more, more preferably 50% or more, and more preferably 70% or more so that the mobility of electrons is excellent. More preferably, it is more preferably 90% or more, and most preferably composed only of conductive fibers. Examples of fibers other than 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 be.

The nonwoven fabric constituting the electrode substrate of the present invention can contain fibers other than conductive fibers, but the electrode substrate has an electrical resistivity of 10 ⁷ Ω · cm or less so as to be excellent in conductivity. It is preferably 10 ⁶ Ω · cm or less, and more preferably 10 ⁵ Ω · cm or less. “Electrical resistivity” in the present invention refers to a value measured by a four-probe method using a resistivity meter (Loresta, manufactured by Mitsubishi Chemical Corporation).

  In addition, the nonwoven fabric which comprises the electrode base material of this invention may be couple | bonded by using an adhesive agent, and a form may be maintained, but by the coupling | bonding of the organic resin which comprises a conductive fiber so that it may be excellent in electroconductivity. It is preferable to maintain the form. Examples of suitable organic resin bonds include entanglement of fibers, bonding by plasticization with a solvent, and bonding by heat fusion.

The basis weight of the nonwoven fabric constituting 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 0.5 to 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).

Since the nonwoven fabric constituting the electrode substrate of the present invention is porous, a fuel cell with excellent drainage and gas diffusibility and high power generation performance can be produced even in the surface direction. The porosity is preferably 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 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 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 electrode base material of the present invention includes the nonwoven fabric as described above. However, since the nonwoven fabric is porous, the drainage property and gas also in the surface direction when nothing is filled in the voids of the nonwoven fabric. Excellent diffusivity.

  In addition, when the surface and / or space | gap of a nonwoven fabric contains a fluorine resin and / or carbon, supply of the fuel gas or the water | moisture content internally generated by containing the former fluorine resin or Emission 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 substrate of the present invention can be produced, for example, as follows.

  First, a fiber web is formed by spinning using a spinning solution in which an organic resin and conductive particles are mixed to form conductive fibers, and collecting and collecting the conductive fibers directly. If the fiber web itself is moderately entangled, the fiber web can be used as a non-woven fabric as long as it is strong enough to handle, and in order to impart or improve the strength, plasticizing with a solvent, melting by heat It can also be made into a non-woven fabric by bonding, adhesion with an adhesive or the like. In addition, it is preferable that the fiber which comprises the fiber web formed by directly collecting and accumulating conductive fibers is a continuous long fiber. 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.

  As a method for forming a fiber web, for example, an electrostatic spinning method, a spun bond method, a melt blow method, or a spinning solution discharged from a liquid discharging unit as disclosed in JP 2009-287138 A is used. On the other hand, there can be mentioned a method in which gas is discharged in parallel 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 Japanese Patent Application Laid-Open No. 2009-287138, since a conductive fiber having a small fiber diameter can be spun, a thin non-woven fabric can be produced, resulting in the resistance of the fuel cell. This is preferable because the volume of the fuel cell can be reduced. When the conductive particles are mixed with a solution in which an organic resin is dissolved in a solvent, as in the electrostatic spinning method or the method disclosed in JP2009-287138A, a solvent that does not easily volatilize during spinning is used. If the spinning solvent is removed by solvent substitution after forming the fiber web or nonwoven fabric, the conductive fibers tend to be in a plasticized state, and as a result, a highly conductive nonwoven fabric can be produced. It is preferable because the electrode substrate becomes dense and the contact resistance in the fuel cell tends to be low.

  In addition, after winding the conductive fiber as a continuous fiber and then cutting the conductive fiber into a desired fiber length to make a short fiber, a fiber web is formed by a known dry method or wet method, and plasticization with a solvent, heat It can also be made into a non-woven fabric by bonding by fusing, bonding with an adhesive or the like. However, as described above, since the conductive fibers constituting the nonwoven fabric are preferably continuous fibers, the nonwoven fabric is derived from a fiber web formed by collecting and collecting the continuous conductive fibers directly. preferable.

  In addition, when the organic resin which comprises a nonwoven fabric is an acryl oxide, it spins using the spinning solution which mixed the acrylic resin and electroconductive particle, forms electroconductive fiber, The fiber web containing this electroconductive fiber is formed. After forming directly or indirectly, by heating at a temperature of 200 to 300 ° C. in air, the conductivity of the nonwoven fabric can be further increased by using acrylic resin as acrylic oxide. Alternatively, after the conductive fiber spun using a spinning solution in which acrylic resin and conductive particles are mixed is heated in air at a temperature of 200 to 300 ° C., the acrylic resin is converted to acrylic oxide, It is also possible to form a nonwoven fabric using conductive fibers made of conductive particles.

  In addition, when the organic resin constituting the conductive fiber is a heat-resistant organic resin having a melting point exceeding 350 ° C., after immersing the nonwoven fabric in a fluorine-based dispersion such as a polytetrafluoroethylene dispersion, By sintering at a temperature of 300 to 350 ° C., a gas diffusion electrode substrate with improved water repellency can also be formed.

  In the gas diffusion electrode of the present invention, since the catalyst is supported on the above-described electrode base material, it is difficult to short-circuit, and a fuel cell with excellent power generation performance can be produced. Further, the gas diffusion electrode of the present invention has a catalyst supported on the surface of the conductive fiber, and not only the electron conduction due to the contact between the catalysts but also the electron conduction path by the conductive fiber is formed, so that it is isolated from the electron conduction path. Less catalyst. Furthermore, the electrode base material is a non-woven porous body and has excellent drainage and gas diffusivity, so that gas can be supplied sufficiently stably to the three-phase interface (reaction field where gas, catalyst, and electrolyte resin meet). be able to. 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.

  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 catalyst dispersion suspension can be coated or dispersed on the electrode base as described above, and dried to produce a gas diffusion electrode.

  The membrane-electrode assembly of the present invention is a membrane-electrode assembly that is capable of producing a fuel cell that is not easily short-circuited and has excellent power generation performance because it includes the above-described base material for gas diffusion electrode. 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 substrates 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 a fuel cell with excellent power generation 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.

<Preparation of the first spinning solution>
In a solution of polyacrylonitrile (weight average molecular weight 200,000) dissolved in N, N-dimethylformamide (DMF), carbon black [Denka Black granular product, manufactured by Denki Kagaku Kogyo Co., Ltd., average primary particle size as conductive particles] : 35 nm] is mixed and stirred, and further diluted with DMF to disperse the carbon black, and the first spinning with a solid mass ratio of carbon black to polyacrylonitrile of 40:60 and a solid content concentration of 20 mass%. A solution was prepared.

<Preparation of second spinning solution>
A second spinning solution was prepared in the same manner as the first spinning solution except that the solid content mass ratio of carbon black and polyacrylonitrile was 50:50 and the solid content concentration was 25 mass%.

<Preparation of third spinning solution>
A third spinning solution was prepared in the same manner as the first spinning solution except that the solid mass ratio of carbon black and polyacrylonitrile was 60:40 and the solid content concentration was 25 mass%.

<Preparation of the fourth spinning solution>
A fourth spinning solution was prepared in the same manner as the first spinning solution except that the solid content mass ratio of carbon black and polyacrylonitrile was 30:70 and the solid content concentration was 25 mass%.

<Preparation of fifth spinning solution>
After mixing and stirring carbon black [Denka Black granular product, Denki Kagaku Kogyo Co., Ltd., average primary particle size: 35 nm] as conductive particles in a solution in which polyethersulfone is dissolved in dimethylacetamide (DMAc) Further, DMAc was added for dilution to disperse the carbon black, and a fifth spinning solution having a solid mass ratio of carbon black to polyethersulfone of 40:60 and a solid content concentration of 25 mass% was prepared.

Example 1
<Production of base material for gas diffusion electrode>
Conductive 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 non-woven fabric (for gas diffusion electrodes) consisting only of continuous conductive fibers. A base material, basis weight 18 g / m ² , thickness 90 μm, porosity 85%, average fiber diameter: 700 nm, electric resistivity: 1.09 × 10 ⁵ Ω · cm) was prepared. The carbon black constituting this conductive fiber was partially exposed from the fiber surface, and the 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: 1 g / hour Distance between nozzle tip and stainless steel drum: 5 cm
Applied voltage: 10 kV
Temperature / humidity: 25 ° C / 40% RH

(Example 2)
Conductive fibers obtained by spinning the second spinning solution by the same electrospinning method as in Example 1 except that the distance between the nozzle tip and the stainless steel drum was 10 cm was placed on the stainless steel drum as the counter electrode. Non-woven fabric consisting of only conductive fibers that are directly integrated (gas diffusion electrode substrate, basis weight 20 g / m ² , thickness 140 μm, porosity 92%, average fiber diameter: 600 nm, electrical resistivity: 2 .3 × 10 ⁴ Ω · cm). The carbon black constituting this conductive fiber was partially exposed from the fiber surface, and the fibers were in a state of being bonded at the time of accumulation.

(Example 3)
A non-woven fabric consisting of only continuous conductive fibers (gas diffusion electrode substrate, basis weight 20 g / m ² , thickness 140 μm, porosity 92%, except that the third spinning solution was used) Average fiber diameter: 450 nm, electrical resistivity: 2.3 × 10 ⁴ Ω · cm). The carbon black constituting this conductive fiber was partially exposed from the fiber surface, and the fibers were in a state of being bonded at the time of accumulation.

Example 4
A non-woven fabric consisting of only continuous conductive fibers (gas diffusion electrode substrate, basis weight 20 g / m ² , thickness 175 μm, porosity 93%, except that the fourth spinning solution was used) Average fiber diameter: 800 nm, electrical resistivity: 3.4 × 10 ⁵ Ω · cm). The carbon black constituting this conductive fiber was partially exposed from the fiber surface, and the fibers were in a state of being bonded at the time of accumulation.

(Example 5)
Conductive fibers obtained by spinning the fifth spinning solution by an electrostatic spinning method are directly accumulated on a stainless drum, which is a counter electrode, and a non-woven fabric made of only continuous conductive fibers (for gas diffusion electrodes) A substrate, a basis weight of 20 g / m ² , a thickness of 100 μm, a porosity of 87%, an average fiber diameter: 500 nm, and an electric resistivity: 2.1 × 10 ⁴ Ω · cm) were produced. The carbon black constituting this conductive fiber was partially exposed from the fiber surface, and the 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: 1 g / hour Distance between nozzle tip and stainless steel drum: 10 cm
Applied voltage: 10 kV
Temperature / humidity: 25 ° C / 30% RH

(Comparative example)
Carbon paper [TGP-H-030, manufactured by Toray Industries, Inc., thickness: 110 μm] was prepared as a gas diffusion electrode substrate.

<Evaluation of piercing property to solid polymer film>
To 10.4 g of ethylene glycol dimethyl ether, 0.8 g of commercially available platinum-supported carbon particles (manufactured by Ishifuku Metal Co., Ltd., platinum-supported amount of 40% by mass with respect to carbon) is added and dispersed by ultrasonic treatment, and then the electrolyte 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.

The produced polymer membrane-catalyst layer assembly is sandwiched between carbon plates in a state where it is sandwiched between the gas diffusion electrode substrates (25 cm ² ) of Examples 1 to 5 or the comparative example, and fastened at a pressure of 2 MPa in the stacking direction. A cell unit was produced.

  Next, a voltage of 0.2 V was applied to the cell unit, and the leakage current was measured. The results are shown in Table 1.

  From the results shown in Table 1, the cell unit using the gas diffusion electrode substrate of the present invention has a very low leakage current, and the solid polymer membrane is formed by piercing the conductive fibers constituting the gas diffusion electrode substrate. The damage was found to be very small.

<Power generation test>
After laminating the gas diffusion electrode base material of Example 1 or Example 4 on both surfaces of the polymer membrane-catalyst layer assembly produced in the same manner as in the above <Evaluation of piercing property to solid polymer membrane> Membrane-electrode assemblies (MEA) were respectively produced by pressing.

After that, it was assembled to 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 and cell resistance were assembled. 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. . Further, the resistance value between the anode side and cathode side bipolar plates at a current density of 2.0 A / cm ² was measured. The results are shown in Table 2.

セル抵抗はガス拡散電極用基材の抵抗だけではなく、固体高分子膜、セパレータ、及びその他の電子伝導材料の合計値を示すが、発電をフル加湿下で行ったため、燃料電池で抵抗の多くを占める固体高分子膜の抵抗が低くなる。そのため、セル抵抗はガス拡散電極用基材の違いを反映する。
前記表２から、実施例１のガス拡散電極用基材の方が低いセル抵抗を示している。これは、実施例１における導電性粒子であるカーボンブラック量が４０ｍａｓｓ％と、実施例４のガス拡散電極用基材よりも多いためであると考えられた。

The cell resistance indicates not only the resistance of the gas diffusion electrode base material but also the total value of the solid polymer membrane, separator, and other electronic conductive materials. The resistance of the solid polymer film that occupies is reduced. Therefore, the cell resistance reflects the difference in the base material for the gas diffusion electrode.
From the said Table 2, the cell resistance of the base material for gas diffusion electrodes of Example 1 is low. This was considered to be because the amount of carbon black, which is the conductive particles in Example 1, was 40 mass%, which was larger than the gas diffusion electrode substrate of Example 4.

Since the electrode base material of the present invention does not damage the solid polymer membrane, it can be suitably used for polymer electrolyte fuel cell applications.
As mentioned above, although this invention was demonstrated along the specific aspect, the deformation | transformation and improvement obvious to those skilled in the art are included in the scope of the present invention.

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 base material for a gas diffusion electrode comprising a non-woven fabric containing only conductive fibers containing conductive particles at least inside an organic resin (excluding those having a thickness of 1 μm or less) .   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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