JP2007179870A - Gas diffusion electrode, membrane-electrolyte assembly, polymer electrolyte fuel cell and methods for producing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion electrode, a membrane-electrolyte assembly, a polymer electrolyte fuel cell and methods for producing the same, that retain favorable gas permeability and mechanical strength, and thus can favorably maintain cell properties. <P>SOLUTION: The gas diffusion electrode 10 includes a fluororesin film in which at least carbon material has been dispersed, in which the fluororesin film has a plurality of through-holes 11. A method for producing the fluororesin film includes a process for forming the fluororesin film by drying fluid in which the carbon material is dispersed in a fluororesin solution and a process for making the through-holes in the fluororesin film. The fluororesin film contains olefin fluoride resin and a rate of hole area in the fluororesin film is in a range of 20% to 95%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gas diffusion electrode, a membrane-electrode assembly, a polymer electrolyte fuel cell, and methods for producing them.

  A fuel cell is a power generation system that continuously supplies fuel and an oxidant, and extracts chemical energy as electric power when the fuel and an oxidant react with each other. Fuel cells using this electrochemical power generation method use the reverse reaction of water electrolysis, that is, a mechanism in which hydrogen and oxygen are combined to produce electrons and water, and have high efficiency and excellent environmental characteristics. In recent years it has been in the spotlight.

  Fuel cells are classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, alkaline fuel cells, and solid polymer fuel cells depending on the type of electrolyte. In recent years, solid polymer fuel cells that have advantages such as startup at room temperature and extremely short startup time have attracted attention. The basic structure of a single cell constituting this polymer electrolyte fuel cell is such that a catalyst layer is bonded to both sides of a solid polymer electrolyte membrane, a gas diffusion electrode is bonded to the outside, and a separator is further arranged to the outside. .

  In such a polymer electrolyte fuel cell, first, hydrogen supplied to the fuel electrode side is guided to the gas diffusion electrode through the gas flow path in the separator. Next, the hydrogen is uniformly diffused by the gas diffusion electrode and then led to the catalyst layer on the fuel electrode side, where it is separated into hydrogen ions and electrons by a catalyst such as platinum. Then, hydrogen ions are guided to the catalyst layer in the oxygen electrode on the opposite side through the electrolyte membrane and sandwiching the electrolyte membrane. On the other hand, electrons generated on the fuel electrode side are led to a gas diffusion layer on the oxygen electrode side through a circuit having a load, and further to a catalyst layer on the oxygen side. At the same time, oxygen introduced from the separator on the oxygen electrode side passes through the gas diffusion electrode on the oxygen electrode side and reaches the catalyst layer on the oxygen electrode side. Then, water is generated from oxygen, electrons, and hydrogen ions to complete the power generation cycle. In addition, examples of the fuel other than hydrogen used in the polymer electrolyte fuel cell include alcohols such as methanol and ethanol, and these can be directly used as fuel.

  Conventionally, carbon paper or carbon cloth made of carbon fiber has been used as a gas diffusion layer of a polymer electrolyte fuel cell. In this carbon paper or carbon cloth, for the purpose of preventing flooding due to humidified water during fuel cell operation or water generated by electrode reaction at the cathode, such as polytetrafluoroethylene (PTFE) is formed on the surface or inside the gap. Water repellent treatment is performed with a water repellent binder. However, since these carbon paper and carbon cloth have a very large pore diameter, water may stay in the pores without obtaining a sufficient water repellent effect.

In order to improve this point, a gas diffusion electrode in which a porous resin containing a conductive filler made of carbon or the like is contained in carbon paper has been proposed (for example, see Patent Document 1).
However, such a gas diffusion electrode is prepared by directly applying a coating material constituting a porous resin containing a conductive filler made of carbon or the like on the surface of carbon paper, and impregnating, extracting a solvent, and drying. In other words, the gap in the carbon paper is blocked, so that the gas permeability inside the gap is lowered and the battery performance is lowered.

Further, it has been proposed to form a water repellent layer by applying a mixture of carbon black and PTFE to a stainless steel mesh (for example, see Patent Document 2).
However, the one formed by applying such a mixture has a problem in that the gap in the stainless steel mesh is blocked, and thus the gas permeability inside the gap is lowered, and the battery performance is lowered. Further, during the manufacture of the fuel cell, in order to make the gas diffusion electrode adhere to the electrolyte or to adhere it with an adhesive, in the process of applying pressure to the gas diffusion electrode, There was also a problem that the gaps were crushed and gas / water discharge was hindered.

Moreover, as a gas diffusion layer in which at least two types of carbon particles having different particle size distribution centers are mixed, graphite is used for the carbon particles having a larger particle size, and the carbon particles having a smaller particle size are coated with a fluororesin. Thus, it has been proposed to use carbon particles imparted with water repellency (see, for example, Patent Document 3).
However, the diffusion layer formed by this method has a problem that the strength is low and the water repellency is not sufficient.

  Further, a gas diffusion electrode made of a porous fluororesin containing a carbon material has been proposed (see, for example, Patent Document 4). Specifically, a porous structure is formed using a solvent component in which the fluororesin is soluble and a solvent component insoluble in the fluororesin. However, a solvent component in which the fluororesin is not soluble is essential for forming the porous material. In addition, since the porous fluororesin produced by this method has dispersed voids inside the membrane, there is a limit to the mechanical strength such as pressure resistance and tensile strength. There was a problem that was easy to collapse.

A conventional technique will be described with reference to FIGS.
FIG. 4 is a schematic perspective view of a conventional gas diffusion electrode, and FIG. 5 is a schematic cross-sectional view of the conventional gas diffusion electrode.
20 is a gas diffusion electrode, and 21 is a gap.
As shown in the figure, there are a large number of voids 21 in the gas diffusion electrode 20 and they are connected to form a hole, so that the gas permeability is excellent, but it is difficult to achieve and adjust the mechanical strength.

JP 2003-303595 A JP 2000-058072 A JP 2001-057215 A JP 2004-281363 A

  The present invention has been made in view of the above-described problems, and the object of the present invention is to maintain good gas permeability and mechanical strength, thereby improving battery characteristics. An object of the present invention is to provide a gas diffusion electrode, a membrane-electrode assembly, a polymer electrolyte fuel cell, and a production method thereof that can be maintained.

  The present invention has solved the above problems by the following technical configuration.

(1) A gas diffusion electrode having a fluororesin film in which at least a carbon material is dispersed, wherein the fluororesin film has a plurality of through holes.
(2) The gas diffusion electrode according to (1), wherein the fluororesin film contains a fluorinated olefin resin.
(3) The gas diffusion electrode according to (1), wherein the carbon material includes at least one of a particulate carbon material and a fibrous carbon material.
(4) The gas diffusion electrode according to (3), wherein the particulate carbon material is carbon black.
(5) The gas diffusion electrode according to (4), wherein the carbon black is acetylene black.
(6) The gas diffusion electrode according to (1) or (2), wherein the porosity of the fluororesin film is in the range of 20% to 95%.
(7) The gas diffusion electrode according to (1) or (2), wherein the density of the fluororesin film is in the range of 0.10 to 1.55 g / cm ³ .
(8) The gas diffusion electrode according to (1) or (2), wherein the porosity of the fluororesin film is in the range of 20% to 95%.
(9) Any of (1), (2), (6), (7) and (8) above, wherein the fluororesin film contains inorganic fine particles or organic fine particles having hydrophilicity as fillers The gas diffusion electrode as described.
(10) The weight ratio of the fluororesin and the carbon material in the fluororesin film is 1/3 to 10 parts by weight of the carbon material with respect to 1 part by weight of the fluororesin (1) ), (2), (6), (7), (8) and (9).
(11) A sheet-like conductive porous material is laminated on the fluororesin film according to any one of (1), (2), (6), (7), (8), (9) and (10). A gas diffusion electrode characterized by being made.
(12) A membrane-electrode assembly, wherein the gas diffusion electrode according to any one of (1) to (11) is provided with a polymer electrolyte membrane through a catalyst layer.
(13) A polymer electrolyte fuel cell comprising the membrane-electrode assembly according to (12) and a separator.
(14) Manufacturing of a gas diffusion electrode comprising: a step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution; and a step of opening a through hole in the fluororesin film. Method.
(15) forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, forming a through-hole in the fluororesin film, and forming a catalyst layer on the fluororesin film. A method for producing a membrane-electrode assembly, comprising: a step of obtaining a gas diffusion electrode with a catalyst layer; and a step of bonding the gas diffusion electrode with a catalyst layer and a polymer electrolyte membrane.
(16) A step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, a step of opening a through hole in the fluororesin film, and a polymer electrolyte with the fluororesin film and a catalyst layer A method for producing a membrane-electrode assembly, comprising the step of joining a membrane.
(17) A step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, a step of opening a through hole in the fluororesin film, and joining the fluororesin film and the catalyst layer. The step of obtaining a gas diffusion electrode with a catalyst layer, the step of joining the gas diffusion electrode with a catalyst layer and a polymer electrolyte membrane to obtain a membrane-electrode assembly, and the membrane-electrode assembly and the separator are simply combined. And a step of incorporating the polymer into a cell.
(18) A step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, a step of opening a through hole in the fluororesin film, and a polymer electrolyte with the fluororesin film and a catalyst layer A method for producing a solid polymer fuel cell, comprising: a step of joining a membrane to obtain a membrane-electrode assembly; and a step of incorporating the membrane-electrode assembly and a separator into a single cell.
(19) The manufacturing method according to any one of (14) to (18), wherein the step of opening a through hole in the fluororesin film comprises irradiating the fluororesin film with a laser.

According to the present invention, a gas diffusion electrode, a membrane-electrode assembly, a polymer electrolyte fuel cell, and their fuel cells that can maintain good gas permeability and mechanical strength, thereby maintaining good battery characteristics. A manufacturing method can be provided.
That is, the gas diffusion electrode of the present invention maintains good gas permeability by providing a through-hole, and can maintain mechanical strength by leaving a columnar structure, so that voids are not easily crushed during hot pressing, It is excellent in water repellency to prevent flooding due to humidified water or generated water during fuel cell operation, to quickly supply and remove reaction gas, and to conduct electricity efficiently.
In addition, since it has a smooth surface with water repellency / drainage by fluororesin and conductivity by carbon material, there is also an effect that the catalyst layer and the polymer solid electrolyte membrane are not damaged or destroyed.
Furthermore, according to the present invention, a simple method for producing a gas diffusion electrode, a membrane-electrode assembly, and a polymer electrolyte fuel cell can be provided.
That is, it does not require a solvent component in which the fluororesin is not soluble to form holes in the fluororesin, and can form arbitrary holes later, and control the gas permeability and mechanical strength by controlling the hole area ratio. Is also easy.

Hereinafter, the present invention will be specifically described.
First, the structure of the gas diffusion electrode of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic perspective view of a gas diffusion electrode of the present invention, and FIG. 2 is a schematic cross-sectional view of the gas diffusion electrode of the present invention.
10 is a gas diffusion electrode, and 11 is a through hole.
As shown in the figure, by providing the through holes 11 in the gas diffusion electrode 10, the gas permeability is excellent, and the mechanical strength can be maintained by leaving the columnar structure.

  Examples of the fluororesin used as a raw material for the gas diffusion electrode of the present invention include vinylidene fluoride, tetrafluoroethylene, tetrafluoroethylene-fluoroalkyl vinyl ether copolymer, fluoroethylene-hexafluoropropylene copolymer, and the like. A fluororesin comprising at least one of the above can be selected and used. Among these, a fluorinated olefin resin is particularly preferable because it has high heat resistance and good mechanical strength. The fluorinated olefin resin has an advantage that a fluororesin film can be formed with high accuracy, and humidified water inside the fluororesin film and water generated at the cathode can be drained well. The fluorinated olefin-based resin as used in the present invention includes a vinylidene fluoride homopolymer, one or more monomers selected from the group consisting of ethylene tetrafluoride, propylene hexafluoride, and ethylene, and vinylidene fluoride. Includes copolymers and multi-component polymers of 3 or more. In addition to the case where these resins are used alone, it is also included in the present invention to use a mixture of two or more resins.

The fluororesin preferably has a mass average molecular weight in the range of 100,000 to 1,200,000.
If the mass average molecular weight is less than 100,000, the strength may be low. On the other hand, if it exceeds 1,200,000, the solubility in a solvent is inferior, making it difficult to form a paint, and uneven viscosity of the paint. As a result, the thickness accuracy of the final gas diffusion electrode may decrease, and the adhesion with the catalyst layer may become non-uniform.

Any carbon material dispersed in the fluororesin can be used as long as it is particulate, and for example, so-called carbon black typified by furnace black, channel black, acetylene black and the like can be used. Carbon black, particularly acetylene black, is preferably used because of its high conductivity and good dispersibility in the coating liquid. Carbon black can be used in any grade regardless of the specific surface area and particle size. For example, Lion Akzo: Ketjen EC, Cabot: Vulcan XC72R, Electrochemical Industry: For example, Denka Black. In the present invention, these carbon materials preferably have an average primary particle diameter in the range of 10 to 100 nm. The particulate carbon material includes graphite, but it may be included.
A fibrous carbon material can also be used. Furthermore, a particulate carbon material and a fibrous carbon material may be mixed.
Examples of fibrous carbon materials include carbon fibers, Showa Denko's carbon nanofibers (trade name: VGCF), and carbon nanotubes.

The weight ratio of the fluororesin and the carbon material (particulate and / or fibrous) is preferably in the range of 1/3 to 10 parts by weight of the carbon material with respect to 1 part by weight of the fluororesin. More preferably, it is in the range of 2/3 to 6 parts by weight. When the carbon material is a particulate carbon material, a range of 2/3 to 3/2 parts by weight is preferable. When the carbon material is a fibrous carbon material, a range of 1 to 6 parts by weight is preferred. preferable. When the carbon material is less than 1/3 parts by weight, the conductivity of the gas diffusion layer is lowered. When the carbon material is more than 10 parts by weight, the mechanical strength of the fluororesin film becomes too weak to withstand the gas diffusion pressure. .
In either case, the result is a reduction in fuel cell performance.

  The thickness of the fluororesin film is preferably 5 μm to 150 μm, more preferably 10 μm to 100 μm, and still more preferably 15 μm to 50 μm. If the thickness is less than 5 μm, the water retention effect is not sufficient, and if it is greater than 150 μm, it is too thick and the gas diffusing capacity and drainage capacity are reduced, leading to battery performance degradation.

  In the present invention, the shape of the through-hole provided in the fluororesin film may be simply a cylindrical shape, or may have a structure in which a portion near the surface of the fluororesin film expands and the inside becomes narrow. Alternatively, a mortar shape in which the hole diameter on one surface is wide and the hole diameter on the opposite side is narrow may be used. Furthermore, although the through hole may be perpendicular to the fluororesin film, depending on the gas inflow path, it may be better to be disposed obliquely with respect to the fluororesin film surface. The diameter of the through hole is preferably 50 μm or less so that the gas is uniformly dispersed.

The fluororesin film constituting the present invention can be evaluated by the open area ratio, density, and porosity, which are scales for measuring the structure of the film having through holes.
The hole area ratio can be obtained by the following equation.
Opening ratio (%) = (pore area per unit area / unit area) × 100
The porosity of the fluororesin film of the present invention is preferably in the range of 20% to 95%, more preferably 50% or more, and particularly preferably 70% or more. If the open area ratio is less than 20%, the gas diffusing capacity and water discharge are insufficient, and if it exceeds 95%, the mechanical strength is remarkably lowered and the fuel cell is easily damaged in the process until it is assembled.

As shown below, the density can be determined by the thickness of the fluororesin film and the mass per unit area.
Density (g / cm ³ ) = mass per unit area / (film thickness × unit area)
The density of the fluororesin film constituting the present invention is preferably in the range of 0.10 to 1.55 g / cm ³ .

The porosity can be obtained by the following formula.
Porosity (%) = [{(a + b + c + d) −density of fluororesin film} / (a + b + c + d)] × 100
(Where, a = (specific gravity of fluororesin of fluororesin film) × (mass content of fluororesin of fluororesin film), b = (specific gravity of particulate carbon material) × (particulate carbon material in fluororesin film) ), C = (specific gravity of filler) × (mass content of filler in fluororesin film), d = (specific gravity of fibrous carbon material) × (mass content of fibrous carbon material in fluororesin film) ))
The porosity of the fluororesin film constituting the present invention is preferably in the range of 20% to 95%, more preferably 50% or more, and particularly preferably 70% or more. If the porosity is less than 20%, the gas diffusing capacity and water discharge are insufficient, and if it exceeds 95%, the mechanical strength is remarkably lowered and the fuel cell is easily damaged in the process until it is assembled.
In the present invention, since the through holes are provided, the open area ratio and the porosity are closely related. Therefore, the porosity can be controlled by setting the hole area ratio to a target value during processing.

  In the fluororesin film constituting the present invention, a filler may be included in addition to the carbon material. By adding this filler, it becomes possible to control the discharge of gas and water and the dispersion of the carbon material, which greatly affects the fuel cell performance. As the filler used in the present invention, those having hydrophilicity are preferable. When a hydrophilic filler is added to a fluororesin having water repellency, the water-repellent part and the hydrophilic part are microscopically intricate, and a carbon material and an agglomerate are formed to form an inside of the through hole. This is because gas and water can be discharged well by being exposed to. As a result, it is possible to prevent a decrease in battery performance due to the flooding phenomenon. Further, either inorganic fine particles or organic fine particles can be used, but inorganic fine particles are preferable in consideration of the environment inside the gas diffusion electrode in the fuel cell.

  As such a filler, inorganic oxide fine particles such as titanium dioxide and silicon dioxide are preferable. This is because they can withstand the environment inside the gas diffusion electrode in the fuel cell and have sufficient hydrophilicity. Any particle size of the filler can be used, but if it is very small, dispersion in the paint becomes difficult, and if it is very large, the resulting fluororesin The problem of decreasing the conductivity of the film occurs. Therefore, generally, a particle size range similar to the particle size of the particulate carbon material, that is, a range of 10 to 100 nm is used.

  Moreover, the weight ratio of the filler to the fluororesin is preferably 3 parts by weight or less of the filler with respect to 1 part by weight of the fluororesin. More preferably, it is 3/2 parts by weight or less. If the blending amount of the filler is more than 3 parts by weight, the fluororesin film is filled too much, which causes a decrease in gas diffusion capacity and a decrease in conductivity, resulting in a decrease in fuel cell performance. .

  In the gas diffusion electrode of the present invention, a fluororesin film having through-holes may be used as a gas diffusion electrode as it is, or a sheet-like conductive porous body may be laminated to form a gas diffusion electrode. Examples of the sheet-like conductive porous material include carbon paper and carbon cloth made of carbon fiber, nickel foam, titanium fiber sintered body, and the like. Since the fluororesin film and the sheet-like conductive porous body have a laminated structure, the voids of the sheet-like conductive porous body are not blocked by the resin and the carbon material constituting the fluororesin film. Therefore, the gas permeability inside the voids is good, and the problem of reducing battery performance is eliminated.

Next, the membrane-electrode assembly of the present invention comprises a polymer electrolyte membrane on the gas diffusion electrode described above via a catalyst layer.
The catalyst layer and the gas diffusion electrode are laminated on at least one surface of the polymer electrolyte membrane. That is, the gas diffusion electrode of the present invention may be disposed on both sides of the polymer electrolyte membrane via the catalyst layer, or the catalyst layer and the gas diffusion electrode of the present invention are disposed on one side of the other surface. May be provided with a catalyst layer and a known gas diffusion electrode.
FIG. 3 shows an example of the structure of the membrane-electrode assembly of the present invention.
15 is a polymer electrolyte membrane, 16 is a catalyst layer, and 50 is a membrane-electrode assembly.
The polymer electrolyte fuel cell of the present invention has a structure in which carbon paper or carbon cloth is arranged outside the membrane-electrode assembly as necessary, and a separator is arranged outside the membrane-electrode assembly.
Since the polymer electrolyte fuel cell of the present invention includes the gas diffusion electrode, it has excellent power generation characteristics. As the separator, any separator can be used as long as it is used in a polymer electrolyte fuel cell.

Next, the manufacturing method of the gas diffusion electrode of this invention is demonstrated.
The gas diffusion electrode of the present invention can be manufactured by a step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, and a step of opening a through hole in the fluororesin film.

Specifically, first, a fluororesin is dissolved in a solvent, and particulate and / or fibrous carbon materials, and in some cases, fillers other than carbon materials are dispersed and mixed to produce a paint that is a solvent mixture. To do. Examples of the solvent in which the fluororesin dissolves include 1-methyl-2-pyrrolidone. For the dissolution / dispersion / mixing, commercially available stirrers and dispersers can be used.
A conductive fluororesin film can be formed by applying the obtained paint on a suitable substrate and drying. The substrate is removed when it is incorporated into a fuel cell. For example, a polyimide film, a polyethylene naphthalate film (PEN), or the like is preferably used.
Then, the obtained fluororesin film can be subsequently perforated to provide through holes, thereby obtaining a gas diffusion electrode that is a fluororesin film having through holes.
There is a method of irradiating the surface of the fluororesin film with a laser in order to produce a gas diffusion electrode of the present invention by making a through hole in the fluororesin film. Lasers include ultraviolet (UV) lasers, CO ₂ lasers, excimer lasers, etc., and are used for drilling holes in semiconductor circuit boards and flexible boards.
Further, as another method, the through hole can be formed by penetrating the fluororesin film by mechanical means such as an ultrafine needle or a drill.
In addition, since what is necessary is just to open a desired through-hole, it is not limited to these.

  In the case of producing a gas diffusion electrode in which a sheet-like conductive porous body is laminated, the sheet-like conductive porous body is stacked on the fluororesin film formed as described above, and hot pressing or the like. It can obtain by pressurizing and joining.

Next, the membrane-electrode assembly of the present invention includes a step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, a step of opening a through-hole in the fluororesin film, It can be manufactured by forming a catalyst layer on a fluororesin film to obtain a gas diffusion electrode with a catalyst layer and joining the gas diffusion electrode with a catalyst layer and a polymer electrolyte membrane.
The membrane-electrode assembly of the present invention includes a step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, a step of opening a through hole in the fluororesin film, and the fluorine It can also be produced by a step of joining the resin membrane and the polymer electrolyte membrane with a catalyst layer.

  That is, first, a gas diffusion electrode is produced on a substrate as described above, and a catalyst layer-forming gas diffusion electrode is produced by applying a coating for forming a catalyst layer thereon, and then the obtained catalyst layer The attached gas diffusion electrodes are placed so that their catalyst layers are in contact with the polymer electrolyte membrane, and the polymer electrolyte membrane and the gas diffusion electrode with the catalyst layer are joined by hot pressing. Next, the membrane-electrode assembly of the present invention can be produced by peeling the substrate.

  Alternatively, a catalyst layer-forming coating material is applied to the polymer electrolyte membrane to form a catalyst layer, thereby preparing a polymer electrolyte membrane with a catalyst layer. Then, the gas diffusion electrode prepared as described above is arranged on the catalyst layer surface of the polymer electrolyte membrane with the catalyst layer, and the polymer electrolyte membrane with the catalyst layer and the gas diffusion electrode are joined by hot pressing. Subsequently, a membrane-electrode assembly can be produced by peeling the substrate.

  Such a membrane-electrode assembly manufacturing method simply bonds the polymer electrolyte membrane to the gas diffusion electrode through the catalyst layer and peels off the substrate, so that the membrane-electrode assembly can be manufactured very easily. can do. Further, since the formed membrane-electrode assembly is provided with the gas diffusion electrode described above, the gas / water discharge is good and the conductivity is excellent.

  In the polymer electrolyte fuel cell according to the present invention, carbon paper or carbon cloth is arranged on both sides of the membrane-electrode assembly as necessary, and a separator is arranged on the outside of the membrane-electrode assembly to be incorporated into a single cell. Can be manufactured. Any of the methods described above may be used as the method for producing the membrane-electrode assembly.

The present invention will be described with reference to examples and comparative examples.
A gas diffusion electrode was prepared as follows, and then a polymer electrolyte fuel cell in which the gas diffusion electrode was disposed on both the fuel electrode side and the oxygen electrode side was manufactured and evaluated.

(Manufacture of gas diffusion electrode)
First, the gas diffusion electrode of Examples 1-11 was manufactured.
30 parts by weight of vinylidene fluoride resin is dissolved in 600 parts by weight of 1-methyl-2-pyrrolidone, and acetylene black and / or carbon nanofibers having an average primary particle size of 40 nm (made by Showa Denko KK, trade name: VGCF (aspect ratio) 10 to 500)) were dispersed in parts by weight as shown in Table 1, and in Example 10, silicon dioxide was added as a filler, and in Example 11, titanium dioxide was added as a filler to obtain a coating material as a dispersion. The obtained paint was applied to a PEN substrate using an applicator to obtain a coating film and dried to obtain a fluororesin film.

Thereafter, an ultraviolet (UV) laser was applied to the fluororesin film to open fine through holes so that the aperture ratios (target values during processing) shown in Table 2 were obtained. The pore diameter was about 25 μm. Thus, gas diffusion electrodes of Examples 1 to 11 which are fluororesin films having through holes were obtained.
Next, gas diffusion electrodes of Comparative Examples 1 and 2 were manufactured.
Dissolve 30 parts by weight of vinylidene fluoride resin in 600 parts by weight of 1-methyl-2-pyrrolidone, disperse acetylene black having an average primary particle size of 40 nm as shown in Table 1, and then mix 45 parts by weight of diethylene glycol. A paint was obtained by stirring. The obtained paint was applied to a PEN substrate using an applicator to obtain a coating film and dried to obtain gas diffusion electrodes of Comparative Examples 1 and 2 which are porous fluororesins.

(Physical property measurement and through hole / void crushing confirmation test)
The mass per unit area and the film thickness (X) of the gas diffusion electrodes of Examples 1 to 11 and Comparative Examples 1 and 2 were measured. The density was calculated from the measured mass, and the aforementioned porosity was calculated. Further, in order to confirm the degree of crushing of through holes and voids by hot pressing, hot pressing (120 ° C., 10 MPa, 10 minutes) on PEN was performed, and the film thickness (Y) after hot pressing was measured. And (Y / X) * 100 was shown as mechanical strength (%).
Table 2 shows the physical property values.

In both Examples and Comparative Examples, the porosity is 20% or more, and the gas permeability is considered high. In particular, Examples 2, 3, 5, 6, 8, 9, 10, 11, and Comparative Examples 1 and 2 have a porosity of 55% or more and particularly high gas permeability.
As shown in Table 2, the film thickness after hot pressing does not change so much in Examples 1 to 11 as compared to that in Comparative Examples 1 and 2 which was very thin. In terms of mechanical strength, Examples 1 to 11 are 65% or more, while Comparative Examples 1 and 2 are less than 50%. This is considered to be because the mechanical strength is maintained by leaving the columnar structure in the embodiment, and the void collapse is prevented.

(Production of polymer electrolyte fuel cell)
(1) Production method 1 of a polymer electrolyte fuel cell
Two 50 mm square gas diffusion electrodes (with substrate) obtained in Examples 1 to 11 and Comparative Examples 1 and 2 were prepared. A catalyst coating composed of a carbon / ion conductive resin carrying platinum catalyst and a mixed solvent of water and ethanol is applied and dried on the surface of the fluororesin film of the two gas diffusion electrodes to form a catalyst layer. A gas diffusion electrode with a layer was obtained. The amount of each platinum catalyst was 0.3 mg / cm ² . Next, a gas diffusion electrode with a catalyst layer was arranged on both sides of the polymer electrolyte membrane so that the catalyst layer surface was in contact with the polymer electrolyte membrane (DuPont, product name: Nafion 117), and hot press (120 ° C., 10 MPa) 10 minutes), the catalyst layer and the polymer electrolyte membrane were joined, and the PEN film, which was the substrate used in the production of the gas diffusion electrode, was peeled off to obtain a membrane-electrode assembly. A carbon paper is disposed on both sides of the obtained membrane-electrode assembly, a graphite separator is disposed on the outside thereof, and a solid polymer fuel cell for evaluation (Example 1-1 to Example) is incorporated into a single cell. 11-1, Comparative Example 1-1 to Comparative Example 2-1) were obtained. In addition, Example 1-1 to Example 11-1 are polymer electrolyte fuel cells using the gas diffusion electrodes of Examples 1 to 11, respectively. Comparative Example 1-1 to Comparative Example 2-1 These are polymer electrolyte fuel cells using the gas diffusion electrodes of Comparative Examples 1 and 2, respectively.

(2) Production method 2 of polymer electrolyte fuel cell
A catalyst coating composed of carbon carrying an platinum catalyst, an ion conductive resin and a solvent is applied and dried on both surfaces of a polymer electrolyte membrane (DuPont, Nafion 117) to form a catalyst layer. A polymer electrolyte membrane with a catalyst layer was obtained. The amount of each platinum catalyst was 0.3 mg / cm ² . Next, the gas diffusion electrodes (with a substrate) obtained in Examples 1 to 11 and Comparative Examples 1 and 2 were placed so that the gas diffusion electrode surface was in contact with the catalyst layer, and hot pressing (120 ° C., 10 MPa, 10 MPa Min)), the catalyst layer and the gas diffusion electrode were joined, and the PEN film, which was the substrate used in the production of the gas diffusion electrode, was peeled off to obtain a membrane-electrode assembly. Carbon paper is arranged on both surfaces of the obtained membrane-electrode assembly, a graphite separator is arranged on the outside thereof, and a polymer electrolyte fuel cell for evaluation (Examples 1-2 to Examples) incorporated in a single cell. 11-2, Comparative Example 1-2 to Comparative Example 2-2) were obtained. Examples 1-2 to 11-2 are polymer electrolyte fuel cells using the gas diffusion electrodes of Examples 1 to 11, respectively. Comparative Examples 1-2 to 2-2 These are polymer electrolyte fuel cells using the gas diffusion electrodes of Comparative Examples 1 and 2, respectively.

(Evaluation of polymer electrolyte fuel cells)
The polymer electrolyte fuel cells (Example 1-1 to Example 11-1, Comparative Example 1-1 to Comparative Example 2-1, Example 1-2 to Example 11-2, Comparative Example 1-2) The power generation characteristics of Comparative Example 2-2) were evaluated in the following manner.
Hydrogen gas was used on the fuel electrode side and oxygen gas was used on the oxygen electrode side as the supply gas for the polymer electrolyte fuel cell. Hydrogen gas was supplied at a humidification temperature of 85 ° C. so as to be 500 mL / min and 0.1 MPa, and oxygen gas was supplied so as to be 1000 mL / min and 0.1 MPa at a humidification temperature of 70 ° C. Under this condition, the voltage at a current density of 1 A / cm ² was measured.
The results are shown in Table 3.

As shown in Table 3, the polymer electrolyte fuel cells of Example 1-1 to Example 11-1 and Example 1-2 to Example 11-2 are Comparative Example 1-1 to Comparative Example 2-1. The voltage at a current density of 1 A / cm ² was higher than that of the polymer electrolyte fuel cells of Comparative Examples 1-2 to 2-2, and the power generation characteristics were excellent.
Specifically, in the example, the voltage was maintained at 0.64 V or higher, but in the comparative example, the voltage was 0.63 V or lower.
This is because the gas diffusion electrode of the present invention has a mechanical strength by providing a through-hole so as to have a predetermined porosity in a fluororesin containing carbon, particularly acetylene black. In addition to preventing flooding due to humidified water or generated water, gas permeability is also improved, and battery performance is improved.
Among them, Examples 2-1, 2-2, 3-1, 3-2, 6-1, 6-2, 8-1, 8-2, 9-1, 9-2, 10-1 In 10-2, 11-1, and 11-2, the voltage was 0.67 V or more, which was good.
This is probably because the battery strength was particularly good because both the mechanical strength and the porosity were high.
In contrast between Examples 1-1 to 11-1 and Examples 1-2 to 11-2, the voltages in Examples 1-2 to 11-2 tended to increase.
This is presumably because the degree of void collapse slightly changed due to the difference in the manufacturing method.

Schematic perspective view of the gas diffusion electrode of the present invention Schematic sectional view of the gas diffusion electrode of the present invention The figure which shows an example of the structure of the membrane-electrode assembly of this invention Schematic perspective view of a conventional gas diffusion electrode Schematic sectional view of a conventional gas diffusion electrode

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Gas diffusion electrode 11 Through-hole 15 Polymer electrolyte membrane 16 Catalyst layer 20 Gas diffusion electrode 21 Void 50 Membrane-electrode assembly

Claims (19)

  A gas diffusion electrode having a fluororesin film in which at least a carbon material is dispersed, wherein the fluororesin film has a plurality of through holes.   The gas diffusion electrode according to claim 1, wherein the fluororesin film contains a fluorinated olefin resin.   The gas diffusion electrode according to claim 1, wherein the carbon material includes at least one of a particulate carbon material and a fibrous carbon material.   The gas diffusion electrode according to claim 3, wherein the particulate carbon material is carbon black.   The gas diffusion electrode according to claim 4, wherein the carbon black is acetylene black.   The gas diffusion electrode according to claim 1 or 2, wherein a hole area ratio of the fluororesin film is in a range of 20% to 95%. The gas diffusion electrode according to claim 1 or 2, wherein the density of the fluororesin film is in a range of 0.10 to 1.55 g / cm ³ .   The gas diffusion electrode according to claim 1 or 2, wherein a porosity of the fluororesin film is in a range of 20% to 95%.   The gas diffusion electrode according to any one of claims 1, 2, 6, 7, and 8, wherein the fluororesin film contains inorganic fine particles or organic fine particles having hydrophilicity as a filler.   The weight ratio between the fluororesin and the carbon material in the fluororesin film is 1/3 to 10 parts by weight of the carbon material with respect to 1 part by weight of the fluororesin. The gas diffusion electrode according to any one of 6, 7, 8, and 9.   A gas diffusion electrode comprising a sheet-like conductive porous body laminated on the fluororesin film according to any one of claims 1, 2, 6, 7, 8, 9, and 10.   12. A membrane-electrode assembly comprising the gas diffusion electrode according to claim 1 and a polymer electrolyte membrane through a catalyst layer.   A polymer electrolyte fuel cell comprising the membrane-electrode assembly according to claim 12 and a separator.   A method for producing a gas diffusion electrode, comprising: forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution; and forming a through hole in the fluororesin film.   A step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, a step of forming a through-hole in the fluororesin film, and forming a catalyst layer on the fluororesin film with a catalyst layer A method for producing a membrane-electrode assembly, comprising: a step of obtaining a gas diffusion electrode; and a step of bonding the gas diffusion electrode with a catalyst layer and a polymer electrolyte membrane.   A step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution; a step of opening a through-hole in the fluororesin film; and the fluororesin film and a polymer electrolyte membrane with a catalyst layer. And a step of bonding the membrane-electrode assembly.   A step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution, a step of opening a through-hole in the fluororesin film, and joining the fluororesin film and the catalyst layer to form a catalyst layer A step of obtaining a gas diffusion electrode with a catalyst, a step of obtaining a membrane-electrode assembly by joining the gas diffusion electrode with a catalyst layer and a polymer electrolyte membrane, and incorporating the membrane-electrode assembly and a separator into a single cell. And a process for producing a polymer electrolyte fuel cell.   A step of forming a fluororesin film by drying a liquid in which a carbon material is dispersed in a fluororesin solution; a step of opening a through-hole in the fluororesin film; and the fluororesin film and a polymer electrolyte membrane with a catalyst layer. A method for producing a polymer electrolyte fuel cell, comprising: a step of bonding to obtain a membrane-electrode assembly; and a step of incorporating the membrane-electrode assembly and a separator into a single cell.   19. The manufacturing method according to claim 14, wherein the step of forming a through-hole in the fluororesin film comprises irradiating the fluororesin film with a laser.

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