JP7114858B2 - Gas diffusion electrode and fuel cell - Google Patents

Description

A fuel cell is a method of obtaining energy by reacting hydrogen and oxygen, and since it emits only water, it is expected to spread as a next-generation clean energy. TECHNICAL FIELD The present invention relates to a gas diffusion electrode used in a fuel cell, and more particularly to a gas diffusion electrode having controlled micropores in a microporous layer and excellent catalyst coating properties.

Among the electrodes used in fuel cells, the electrodes used in solid polymer electrolyte fuel cells are arranged in a state sandwiched between two separators. It has a structure consisting of a catalyst layer formed on the surface of the electrolyte membrane and a gas diffusion electrode formed outside the catalyst layer. Performances required for the gas diffusion electrode include, for example, gas diffusibility, electrical conductivity for collecting electricity generated in the catalyst layer, and drainage performance for efficiently removing moisture generated on the surface of the catalyst layer. As a member used to obtain such a gas diffusion electrode, a conductive porous substrate having both gas diffusion ability and electrical conductivity is commonly used.

Specifically, carbon paper, carbon felt, and carbon cloth made of carbon fiber are often used as the conductive porous substrate described above. considered the most preferred.

In addition, the fuel cell is a system that electrically extracts the energy generated when hydrogen and oxygen react to produce water. (Water vapor) is generated, and this water vapor condenses into water droplets at low temperatures, and when the pores of the gas diffusion electrode are blocked, the amount of gas (oxygen or hydrogen) supplied to the catalyst layer decreases, and finally If all the pores are blocked, power generation will stop (this phenomenon is called flooding).

The gas diffusion electrode is required to have drainage properties so as to prevent this flooding from occurring as much as possible. As a means for enhancing the water repellency, a gas diffusion electrode substrate obtained by subjecting a conductive porous substrate to a water repellent treatment is usually used to enhance the water repellency.

In addition, when the conductive porous substrate treated with water repellency as described above is used as it is as a gas diffusion electrode, the fibers are coarse, and when water vapor condenses, large water droplets are generated and flooding is likely to occur. For this reason, a layer called a microporous layer (microporous layer) is formed by applying a coating liquid in which conductive fine particles such as carbon black are dispersed on a conductive porous substrate that has been subjected to a water-repellent treatment, followed by drying and sintering. layer) may be provided.

Patent Literature 1 discloses a method in which the presence of penetrating holes on the surface of a microporous layer improves drainage and makes flooding less likely to occur.

Further, Patent Document 2 discloses a gas diffusion electrode capable of preventing permeation by making the conductive porous substrate thick and dense.

Furthermore, Patent Literature 3 discloses that it is possible to improve drainage performance by intentionally providing holes penetrating through the microporous layer.

JP 2015-195111 A Japanese Unexamined Patent Application Publication No. 2011-080160 JP 2013-015226 A

However, the gas diffusion electrode described in Patent Document 1 is a technique focusing only on the drainage of the gas diffusion electrode, and even if the drainage is maintained, it may not be sufficient for coating the catalyst layer.

In the gas diffusion electrode described in Patent Document 2, from the viewpoint of suppressing permeation into the base material, there is a possibility that the coatability of the catalyst is sufficient, but drainage is not considered. However, there are cases in which the performance is insufficient, and there are cases in which excessive cracking (hereinafter referred to as cracks) in the gas diffusion electrode causes the catalyst to come off, resulting in insufficient coatability.

In addition, the gas diffusion electrode described in Patent Document 3 can intentionally create holes to improve performance, but there is a problem that the catalyst layer cannot be applied stably. has an inverse relationship with

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a gas diffusion electrode that achieves both performance and coatability by suppressing pores that hinder catalyst coatability while improving drainage.

In order to solve the above problems, the present invention employs the following means.

A gas diffusion electrode having a microporous layer on at least one side of a conductive porous substrate,
The total area ratio of the regions penetrating the microporous layer in the thickness direction is 0.05% or more and 0.7% or less,
If a region having an aspect ratio of 0.33 or less or 2.0 or more in the penetrating region is defined as a non-hole region, the total area ratio of the non-hole region in the penetrating region is 90% or more and 99% or less. A gas diffusion electrode characterized by:

According to the gas diffusion electrode of the present invention, it is possible to obtain a gas diffusion electrode capable of maintaining high yield and performance even when a catalyst is applied to the surface of the gas diffusion electrode.

1 is a schematic cross-sectional view of a gas diffusion electrode of the present invention; FIG.

The present invention provides a gas diffusion electrode having a microporous layer on at least one side of an electrically conductive porous substrate, wherein the total area ratio of regions penetrating through the microporous layer in the thickness direction is 0.05% or more. 7% or less, and if a region having an aspect ratio of 0.33 or less or 2.0 or more in the penetrating region is defined as a non-hole region, the total area ratio of the non-hole region in the penetrating region is The gas diffusion electrode is characterized by being 90% or more and 99% or less.

Specific examples of the conductive porous substrate used in the gas diffusion electrode of the present invention include carbon fibers such as carbon fiber fabric, carbon fiber paper, carbon fiber nonwoven fabric, carbon felt, carbon paper, and carbon cloth. It is preferable to use a metal porous substrate such as a porous substrate containing, foamed sintered metal, metal mesh, expanded metal. Among them, it is preferable to use a porous substrate such as carbon felt containing carbon fiber, carbon paper, carbon cloth, etc., because of its excellent corrosion resistance. In other words, it is most preferable to use a base material containing a resin charcoal, that is, carbon paper, which is obtained by binding carbon fiber paper bodies with a charcoal because of its excellent "springiness".

In the present invention, a microporous layer is provided on at least one side of the conductive porous substrate. Here, the microporous layer is a layer having pores and containing conductive fine particles such as carbon black, carbon nanotube, carbon nanofiber, chopped carbon fiber, graphene, and graphite.

As the conductive fine particles, carbon black is preferably used from the viewpoint of low cost, safety and stability of product quality. Acetylene black is most often used because it contains few impurities and does not easily reduce the activity of the catalyst. As a measure of the content of impurities in carbon black, the ash content is cited, and it is more preferable to use carbon black with an ash content of 0.1% by mass or less. In addition, the lower the ash content in the carbon black is, the more preferable it is, and carbon black containing 0% by mass of ash, that is, carbon black containing no ash is most preferable.

In addition, the microporous layer has properties such as electrical conductivity, gas diffusion, water drainage, moisture retention, and thermal conductivity. Therefore, the microporous layer preferably contains a water-repellent resin such as fluororesin in addition to the conductive fine particles. Examples of the fluororesin contained in the microporous layer include PTFE, FEP, PFA, ETFA, and the like, which are the same as fluororesins that are preferably used for water-repellent conductive porous substrates. PTFE or FEP is preferable in terms of particularly high water repellency.

In the present invention, the microporous layer has a region penetrating through the microporous layer in the thickness direction. The region penetrating in the thickness direction may have a hole shape, a crack (crack, split) shape, or a mixture of holes and cracks. In the region penetrating the microporous layer in the thickness direction, when light is applied from the conductive porous substrate side of the gas diffusion electrode, the light penetrates to the microporous layer side. Therefore, the presence or absence of a region penetrating through the microporous layer in the thickness direction can be determined based on the presence or absence of light detected from the microporous layer side when light is applied from the conductive porous substrate side of the gas diffusion electrode. can be done.

In the present invention, the total area ratio of the regions penetrating the microporous layer in the thickness direction is 0.05% or more and 0.7% or less, and the non-hole region in the region penetrating the microporous layer in the thickness direction is The total area ratio is 90% or more and 99% or less.

Here, the non-hole region means a region having an aspect ratio of 0.33 or less or 2.0 or more in the region penetrating the microporous layer in the thickness direction. Incidentally, among the regions penetrating the microporous layer in the thickness direction, regions other than the non-hole regions are called hole regions. When the total area ratio of the regions penetrating the microporous layer in the thickness direction is 0.05% or more and 0.7% or less, when there are a plurality of regions penetrating the microporous layer in the thickness direction, each region , and the ratio of the sum to 100% of the entire surface of the microporous layer is 0.05% or more and 0.7% or less. Furthermore, the expression that the total area ratio of the non-hole regions in the region penetrating the microporous layer in the thickness direction is 90% or more and 99% or less means that when there are a plurality of non-hole regions, the sum of these regions is obtained, and the microporous layer is When there are a plurality of regions penetrating the layer in the thickness direction, the sum of these regions is calculated, and the sum of the regions penetrating the microporous layer in the thickness direction is taken as 100%, and the ratio of the sum of the non-hole regions is 90%. % or more and 99% or less.

If the total area ratio of the regions penetrating through the microporous layer in the thickness direction is less than 0.05%, the non-hole region is small and the drainage may be insufficient. On the other hand, when the total area ratio of the regions penetrating the microporous layer in the thickness direction exceeds 0.7% and the total area ratio of the non-hole regions is less than 90%, the catalyst is applied from above the microporous layer. At that time, the catalyst liquid leaks from the hole, resulting in a defect. In addition, as power generation is repeated, the electrolyte membrane may deform along the irregularities of the microporous layer, causing holes or tears, which may reduce the durability of the fuel cell.

In the gas diffusion electrode of the present invention, the area of the region penetrating the microporous layer in the thickness direction is preferably 0.1 μm ² or more and 2000 μm ² or less. By setting the area of the region penetrating the microporous layer in the thickness direction to 0.1 μm ² or more, the drainage property can be maintained. In addition, by setting the area of the region penetrating the microporous layer in the thickness direction to 2000 μm ² or less, it is possible to prevent the catalyst liquid from leaking through the holes when the catalyst is applied onto the microporous layer. The area of the region penetrating the microporous layer in the thickness direction as used herein does not mean the total area of the penetrating regions, even if there are a plurality of the penetrating regions. means area.

In the present invention, of the microporous layer, the microporous layer that has permeated into the conductive porous substrate is hereinafter referred to as a permeated portion. The ratio of the thickness of the soaked portion to the thickness of the microporous layer being 100% is hereinafter referred to as the soaked amount, and in the present invention, the soaked amount is 50% or more and 90% or less. is preferred. By setting the penetration amount to 50% or more and 90% or less, the total area ratio of the regions penetrating the microporous layer in the thickness direction is 0.05% or more and 0.7% or less, and the non-holes in the penetrating region are This is because the total area ratio of the regions can be controlled to 90% or more and 99% or less.

In addition, in order to make the penetration amount 50% or more and 90% or less, the content of the water-repellent resin in 100% by mass of the microporous layer can be controlled by 5% or more and 15% or less by mass. . Alternatively, it can be controlled by controlling the distance between the application position of the microporous layer coating liquid and the conductive porous substrate to 70% or more and 110% or less of the film thickness of the microporous layer coating liquid. If the content of the water-repellent resin is less than 5% by mass, the permeation amount may exceed 90%, resulting in a decrease in the drainage performance of the gas diffusion electrode and a decrease in the power generation performance of the fuel cell. On the other hand, when the content of the water-repellent resin exceeds 15% by mass, the penetration amount is less than 50%, and the area penetrating the microporous layer exceeds 0.7%, resulting in poor catalyst coating properties. Otherwise, the durability of the fuel cell may be lowered. Further, when the distance between the application position of the microporous layer coating liquid and the conductive porous substrate is less than 70% of the film thickness of the microporous layer coating liquid, the amount of penetration exceeds 90%, and the gas diffusion electrode The drainage performance of the fuel cell may decrease, and the power generation performance of the fuel cell may decrease. On the other hand, if the distance between the application position of the microporous layer coating liquid and the conductive porous substrate exceeds 110% of the thickness of the microporous layer coating liquid, the catalyst may be poorly coated.

The permeation part and the method for measuring the permeation amount will be described later.

If the amount of impregnation is less than 50%, the penetrating area increases, which may cause problems in the coating of the catalyst. In addition, gas diffusion resistance occurs in the microporous layer, which may reduce the power generation performance of the fuel cell. If the penetration amount exceeds 90%, it becomes difficult for gas and water to diffuse in the conductive porous substrate, and the power generation performance of the fuel cell may deteriorate.

In the present invention, the thickness of the microporous layer is preferably 100 μm or less in consideration of the roughness of current conductive porous substrates. If the thickness exceeds 100 μm, the diffusibility of gas and water (permeability and drainage) of the gas diffusion electrode itself may be lowered, or the electrical resistance may be increased. The thickness of the microporous layer is preferably 80 μm or less, more preferably 40 μm or less, from the viewpoint of increasing permeability and drainage or decreasing electrical resistance. is preferably 15 μm or more.

Moreover, the density of the conductive porous substrate is preferably 0.15 g/cm ³ or more and 0.5 g/cm ³ or less. If it is less than 0.15 g/cm ³ , the strength of the conductive porous substrate may be insufficient and the durability may be lowered. If the density of the conductive porous substrate exceeds 0.5 g/cm ³ , the drainage and gas permeability may be lowered.

Regarding the thickness of the gas diffusion electrode or the conductive porous substrate, an ion milling device such as IM4000 manufactured by Hitachi High-Technologies Corporation is used to cut the gas diffusion electrode in the thickness direction, and the perpendicular cross section (thickness direction Cross section) is obtained by a method of calculating from an image observed by SEM. The thickness of the microporous layer can be obtained by subtracting the thickness of the conductive porous substrate from the thickness of the gas diffusion electrode.

As a method for forming a microporous layer on at least one side of a conductive porous substrate, a coating liquid for forming a microporous layer (hereinafter referred to as a microporous layer coating liquid) may be applied by screen printing, rotary screen printing, spraying, or intaglio. A method of coating such as printing, gravure printing, die coater printing, bar coating, blade coating, knife coater, etc. is preferable, and the hole area in the penetrating area is reduced (that is, the area ratio of the non-hole area is increased), and the surface smoothness is improved. From this point of view, the coating method by screen printing or die coater printing is more preferable. From the viewpoint of productivity, the concentration of the conductive fine particles in the microporous layer coating liquid is preferably 5% by mass or more, more preferably 8% by mass or more, and still more preferably 12% by mass or more. There is no upper limit to the concentration as long as the viscosity, the dispersion stability of the conductive particles, the coating properties of the coating liquid, etc. are official. When it exceeds, the appropriateness as a coating liquid may be impaired. After applying the microporous layer coating liquid, it is common to perform sintering at 250° C. or higher and 400° C. or lower.

In the present invention, from the viewpoint of enhancing gas diffusion, it is preferable to reduce the thickness of the conductive porous substrate such as carbon paper. That is, the thickness of the conductive porous substrate such as carbon paper is preferably 220 μm or less, more preferably 150 μm or less, and particularly preferably 120 μm or less. Since it becomes difficult, 70 μm is usually the lower limit.

As the conductive porous substrate used in the gas diffusion electrode of the present invention, one to which a water-repellent treatment has been applied by applying a fluororesin is preferably used. Since the fluororesin acts as a water-repellent resin, the conductive porous substrate of the present invention preferably contains a water-repellent resin such as a fluororesin. Examples of the water-repellent resin contained in the conductive porous substrate, that is, the fluorine resin contained in the conductive porous substrate include PTFE (polytetrafluoroethylene) (for example, “Teflon” (registered trademark)), FEP (polytetrafluoroethylene), propylene hexafluoride copolymer), PFA (perfluoroalkoxy fluororesin), ETFA (ethylene tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), etc., but strong PTFE or FEP exhibiting water repellency is preferred.

Although the amount of the water-repellent resin is not particularly limited, it is suitably about 0.1% by mass or more and 20% by mass or less based on 100% by mass of the entire conductive porous substrate. If it is less than 0.1% by mass, sufficient water repellency may not be exhibited, and if it exceeds 20% by mass, the pores that serve as gas diffusion paths or drainage paths may be blocked, or electrical resistance may increase. be.

Methods for water-repellent treatment of conductive porous substrates include the commonly known treatment technique of immersing the conductive porous substrate in a dispersion containing a water-repellent resin, as well as die coating, spray coating, etc. A coating technique of coating a water-repellent resin on a flexible porous substrate is also applicable. Processing by a dry process such as sputtering of fluororesin can also be applied. After the water-repellent treatment, a drying step and a sintering step may be added as necessary.

Further, the fuel cell of the present invention is characterized by having the gas diffusion electrode of the present invention. Since the fuel cell of the present invention has the gas diffusion electrode of the present invention, it is characterized by high power generation performance.

EXAMPLES The present invention will be specifically described below with reference to Examples. The materials used in the examples, the method for producing the gas diffusion electrode, and the method for evaluating the power generation performance of the fuel cell are shown below.

(Example 1)
<Material>
A. Conductive porous substrate Polyacrylonitrile-based carbon fiber “Torayca” (registered trademark) T300 (average diameter: 7 μm) manufactured by Toray Industries, Inc. was cut into short fibers with an average length of 6 mm, dispersed in water, and subjected to a wet papermaking method. Paper was continuously made by Further, a 10% by mass aqueous solution of polyvinyl alcohol as a binder was applied to the paper and dried to produce a carbon fiber sheet having a carbon fiber basis weight of 26 g/m ² . The adhered amount of polyvinyl alcohol was 18 parts by mass with respect to 100 parts by mass of the carbon fibers.

Next, a phenolic resin obtained by mixing a resol-type phenolic resin and a novolac-type phenolic resin as a thermosetting resin so that the non-volatile matter has a mass ratio of 1:1, and a flaky graphite powder (average particle size 5 μm) as a carbon powder. And, using methanol as a solvent, thermosetting resin (non-volatile matter) / carbon powder / solvent = 10 parts by weight / 5 parts by weight / 85 parts by weight, these are mixed to form a uniformly dispersed resin composition ( mixture) was obtained.

Next, the carbon fiber sheet was continuously immersed in the mixed liquid of the resin composition, sandwiched between rolls and squeezed, and then wound into a roll to obtain a precursor fiber sheet. At this time, the roll is a smooth metal roll having a structure that allows removal of excess resin composition with a doctor blade. Thus, the adhesion amount of the entire resin composition was adjusted. The amount of phenol resin attached to the precursor fiber sheet was 130 parts by mass with respect to 100 parts by mass of carbon fibers.

The press molding machine was set so that the hot plates were parallel to each other, a spacer was placed on the lower hot plate, and the resin-impregnated carbon fiber paper sandwiched between the release papers from above and below was intermittently conveyed and compressed. At that time, the distance between the upper and lower pressing plates was adjusted so that the precursor fiber sheet had a desired thickness after the pressure treatment.

Further, compression treatment was performed by repeating heating and pressurization, mold opening, and feeding of carbon fibers, and the carbon fiber was wound into a roll. When the thickness at 0.15 MPa of the precursor fiber sheet after pressure treatment in the compression step was measured, it was 180 µm.

The pressurized precursor fiber sheet is introduced into a heating furnace with a maximum temperature of 2400° C. maintained in a nitrogen gas atmosphere, and passed through a carbonization step in which it is fired while continuously running in the heating furnace. A conductive porous substrate was obtained by winding up into a roll. The thickness of the resulting conductive porous substrate at 0.15 MPa was 145 μm.

Further, the conductive porous substrate obtained above was continuously transported while being pressed at a constant pressure at normal temperature, and wound into a roll. The thickness of the resulting conductive porous substrate at 0.15 MPa was 135 µm.

B. Microporous layer carbon black, water-repellent resin (“Neofuron” (registered trademark) FEP dispersion ND-110 (FEP resin, manufactured by Daikin Industries, Ltd.)), surfactant (“TRITON” (registered trademark) X-100 (manufactured by Nacalai Tesque Co., Ltd.) and water were used.

<Evaluation>
A. Method for measuring the amount of penetration First, an ion milling device (Model IM4000, manufactured by Hitachi High-Technologies Co., Ltd.) was used to cut out a vertical cross section (cross section in the thickness direction), and a scanning electron microscope (SEM, S-4800, manufactured by Hitachi, Ltd.) was used. , the image was observed at a magnification of 200 times.

Next, a method for determining the boundary between the microporous layer and the conductive porous substrate will be described with reference to FIG. Starting from the point (11) existing on the outermost surface of the microporous layer, a line parallel to the outermost surface (10) of the conductive porous substrate was drawn, and the line was defined as the outermost surface (12) of the microporous layer. In the portion where the microporous layer permeates into the conductive porous substrate (infiltration portion), starting from the point (13) where the microporous layer penetrates to the outermost surface side of the conductive porous substrate, the conductive A line parallel to the outermost surface (10) of the porous substrate was drawn, and the line was defined as the innermost surface (14) of the microporous layer. In the outermost surface of the conductive porous substrate on the microporous layer side, starting from the point (15) closest to the outermost surface of the microporous layer, parallel to the outermost surface (10) of the conductive porous substrate A line was drawn and the line was taken as the innermost surface (16) of the conductive porous substrate.

The distance between the outermost surface (10) of the conductive porous substrate and the innermost surface (16) of the conductive porous substrate is the thickness (a) of the conductive porous substrate, the innermost surface of the microporous layer The distance between (14) and the innermost surface (16) of the conductive porous substrate is the thickness (b) of the infiltrated portion, and the outermost surface (12) of the microporous layer and the innermost surface of the microporous layer (14) was defined as the thickness (c) of the microporous layer.

Also, the permeation amount was determined from the formula: thickness of permeated portion (b)/thickness of microporous layer (c) x 100. Three permeation portions of the microporous layer were defined from three images, and the permeation amount was determined as the average value of the three values.

B. Method for measuring the total area ratio of the regions penetrating the microporous layer in the thickness direction To obtain the total area of the regions penetrating the microporous layer in the thickness direction, the gas diffusion electrode is examined from the microporous layer side of the gas diffusion electrode under an optical microscope. The microporous layer was observed, and light was irradiated from the side of the conductive porous substrate to illuminate a region penetrating the microporous layer in the thickness direction, and an image was taken. After that, it is imported into image processing software (JTrim), and the sum of the number of pixels with a brightness level of 240 or more, that is, the sum of the number of pixels in the white area is divided by the total number of pixels. The total area ratio (%) of the regions penetrating the layer in the thickness direction was obtained.

C. Measurement of Area Penetrating Microporous Layer and Its Aspect Ratio The obtained gas diffusion electrode was set horizontally in an apparatus combining a transmission optical system and a reflection optical system. Set a magnifying glass perpendicular to the gas diffusion electrode, visually from the top, check the area that penetrates the microporous layer, mark it, and measure the flow direction of the base material during continuous transportation (hereinafter referred to as the X direction ), and the position in the width direction (hereinafter referred to as Y direction) of the substrate was measured. After that, the marked portion was observed with an optical microscope, and the area of each region penetrating through the microporous layer was calculated.

Furthermore, the aspect ratio of each region penetrating through the microporous layer (here, the aspect ratio is determined in the longest direction and the shortest direction) was determined, and the total area ratio of the non-hole regions was calculated.

D. Method for measuring the density of the conductive porous substrate The density of the conductive porous substrate is obtained by weighing the mass of the conductive porous substrate with an electronic balance and measuring the thickness of the conductive porous substrate obtained in Section A. It was obtained by dividing by (a).

E. Method of measuring water permeation pressure Using a perm porometer (CFP-1500AEXLC) manufactured by Porous Materials Co., Ltd., water is dropped on the microporous layer, and compressed air is blown from the microporous layer side toward the conductive porous substrate side. The water permeation pressure (kPa) was measured by increasing the pressure of the compressed air and measuring the pressure of the compressed air when the air began to flow toward the conductive porous substrate.

F. Measurement method of gas diffusivity in the thickness direction Using a water vapor gas vapor permeation diffusion evaluation device (MVDP-200C) manufactured by Seika Sangyo, oxygen gas whose diffusivity is to be measured is measured on one side (primary side) of the gas diffusion electrode. A mixed gas of nitrogen gas was flowed, and nitrogen gas was flowed to the other side (secondary side). The differential pressure between the primary side and the secondary side is controlled to about 0 Pa (0±3 Pa) (that is, there is almost no gas flow due to the pressure difference, and the gas movement phenomenon occurs only by molecular diffusion), and the secondary side The gas concentration when equilibrium was reached was measured using an oxygen concentration meter, and this value (%) was used as an index of gas diffusion in the thickness direction.

(Example 1)
While transporting the carbon paper wound into a roll using a winding-type transport device, it is placed in an immersion tank filled with a water-repellent resin dispersion dispersed in water so that the concentration of fluororesin is 2% by mass. The substrate was immersed for water-repellent treatment, dried in a dryer set at 100° C., and wound up by a winder to obtain a water-repellent conductive porous substrate. As the water-repellent resin dispersion, FEP Dispersion ND-110 was diluted with water so that the concentration of FEP was 3 mass %.

Next, a winding-type continuous coater equipped with a die coater, a dryer and a sintering machine was prepared in a conveying device equipped with an unwinder, a guide roll, a back roll, an interleaf unwinder and a winder.

As the water-repellent conductive porous substrate, a 400-m rolled roll of carbon paper was set in an unwinder.

The original fabric was conveyed by drive rolls installed in the unwinding section, the winding section, and the coater section. First, using a die coater, the distance between the coating position of the microporous layer coating liquid and the conductive porous substrate was set to 90% of the thickness of the microporous layer coating liquid, and then the coating liquid was dried with hot air at 140°C in a dryer. After drying the water content and sintering in a sintering machine set at a temperature of 350° C., it was wound up with a winder.

The microporous layer coating liquid was prepared as follows.

Microporous layer coating liquid:
15 parts by mass of carbon black, 9 parts by mass of water-repellent resin (FEP dispersion, "Neophron" (registered trademark) ND-110), 7 parts by mass of surfactant ("TRITON" (registered trademark) X-100), purified water 69 parts by mass were kneaded with a planetary mixer to prepare a coating liquid.

In applying the microporous layer coating liquid, the basis weight of the microporous layer after sintering was adjusted to 25 g/m ² .

Table 1 shows the measured physical properties.

(Example 2)
Carbon black 15 parts by mass, water-repellent resin (FEP dispersion, "Neophron" (registered trademark) ND-110) 13 parts by mass, surfactant ("TRITON" (registered trademark) X-100) 7 parts by mass, purified water A gas diffusion electrode was obtained in the same manner as in Example 1, except that 65 parts by mass were kneaded in a planetary mixer to prepare a coating liquid. Table 1 shows the measured physical properties.

(Example 3)
Using a die coater, apply the microporous layer coating liquid so that the distance between the coating position and the conductive porous substrate is 110% of the thickness of the microporous layer coating liquid, and then dry with hot air at 140 ° C. A gas diffusion electrode was obtained in the same manner as in Example 1, except that after drying and sintering in a sintering machine set at a temperature of 350° C., it was wound up with a winder. Table 1 shows the measured physical properties.

(Example 4)
A gas diffusion electrode was obtained in the same manner as in Example 1, except that the density of the conductive porous substrate was 0.53 g/cm ³ . Table 1 shows the measured physical properties.

(Comparative example 1)
15 parts by mass of carbon black, 17 parts by mass of water-repellent resin (FEP dispersion, "Neophron" (registered trademark) ND-110), 7 parts by mass of surfactant ("TRITON" (registered trademark) X-100), purified water A gas diffusion electrode was obtained in the same manner as in Example 1, except that 61 parts by mass were kneaded in a planetary mixer to prepare a coating liquid. Table 1 shows the measured physical properties.

(Comparative example 2)
Using a die coater, apply the microporous layer coating liquid so that the distance between the coating position and the conductive porous substrate is 130% of the thickness of the microporous layer coating liquid, and then dry with hot air at 140 ° C. A gas diffusion electrode was obtained in the same manner as in Example 1, except that after drying and sintering in a sintering machine set at a temperature of 350° C., it was wound up with a winder. Table 1 shows the measured physical properties.

1 microporous layer 2 carbon fiber 10 outermost surface of conductive porous substrate 11 points present on outermost surface of microporous layer 12 outermost surface of microporous layer 13 most conductive porous substrate in permeated portion 14 The innermost surface of the microporous layer 15 The point closest to the outermost surface of the microporous layer among the outermost surfaces of the conductive porous substrate on the microporous layer side 16 The conductive porous innermost surface of the base material

Claims (5)

A gas diffusion electrode having a microporous layer on at least one side of a conductive porous substrate that is a porous substrate containing carbon fibers, wherein the microporous layer is formed when light is applied from the conductive porous substrate side. The total area ratio of the regions through which light is transmitted to the side is 0.05% or more and 0.7% or less,
If a region having an aspect ratio of 0.33 or less or 2.0 or more in the light -transmitting region is defined as a non-hole region, the total area ratio of the non-hole region in the light-transmitting region is 90%. A gas diffusion electrode, characterized in that the ratio is 99% or more. The microporous permeated into the conductive porous substrate when the thickness of the microporous layer defined as the distance between the outermost surface of the microporous layer and the innermost surface of the microporous layer is 100% 2. The gas diffusion electrode according to claim 1, wherein the thickness ratio of the layer (hereinafter referred to as the infiltration portion) (hereinafter referred to as the infiltration amount) is 50% or more and 90% or less. 3. The gas diffusion electrode according to claim 1, wherein the conductive porous substrate has a density of 0.15 g/cm ³ or more and 0.5 g/cm ³ or less. 4. The gas diffusion electrode according to claim 1, wherein said microporous layer has a thickness of 100 μm or less. A fuel cell comprising the gas diffusion electrode according to any one of claims 1 to 4.

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