JP2013152927A - Fuel cell gas diffusion layer, membrane electrode assembly and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas diffusion layer which is excellent in resistance to flooding and plugging, excellent in dry-up resistance and capable of exhibiting high power generation performance over a wide temperature range from low temperature to high temperature and furthermore excellent in mechanical characteristics, conductivity and thermal conductivity.SOLUTION: A fuel cell gas diffusion layer is formed by adjoining and arranging a microporous part [A], an electrode substrate and a microporous part [B] in this order. A carbonaceous powder constituting the microporous part [A] includes carbon nanotubes whose average diameter is 1 to 1000 nm and a carbonaceous powder constituting a microporous part [B] includes granular carbon whose particle size is 3 to 500 nm.

Description

  The present invention relates to a gas diffusion layer suitably used for a fuel cell, particularly a polymer electrolyte fuel cell. More specifically, it has excellent anti-flooding and plugging properties, and also has excellent dry-up resistance, can exhibit high power generation performance over a wide temperature range from low to high temperatures, and has mechanical properties, electrical conductivity, and thermal conductivity. It relates to an excellent gas diffusion layer.

  A polymer electrolyte fuel cell that supplies a fuel gas containing hydrogen to the anode and an oxidizing gas containing oxygen to the cathode to obtain an electromotive force by an electrochemical reaction occurring at both electrodes is generally a separator, gas diffusion A layer, a catalyst layer, an electrolyte membrane, a catalyst layer, a gas diffusion layer, and a separator are sequentially laminated. The gas diffusion layer has a high gas diffusibility for diffusing the gas supplied from the separator to the catalyst, a high drainage property for discharging water generated by the electrochemical reaction to the separator, and taking out the generated current. Therefore, a gas diffusion electrode substrate (hereinafter referred to as an electrode substrate) made of carbon fiber or the like is widely used.

  However, as problems, (1) when the polymer electrolyte fuel cell is operated in a relatively low temperature of less than 70 ° C. and in a high current density region, the electrode base material is clogged with a large amount of liquid water, and fuel gas is supplied. As a result, the power generation performance is reduced as a result of shortage (hereinafter referred to as flooding). (2) When a polymer electrolyte fuel cell is operated at a relatively low temperature of less than 70 ° C. and in a high current density region, a large amount is generated. The problem is that the power generation performance is instantaneously reduced (hereinafter referred to as plugging) (3) 80 as a result of the gas flow (hereinafter referred to as flow path) of the separator being blocked by the liquid water to be supplied and the fuel gas supply being insufficient. When operating at a relatively high temperature of ℃ or higher, the electrolyte membrane is dried by water vapor diffusion, and proton conductivity is reduced, resulting in a problem that power generation performance is reduced (hereinafter referred to as dry-up). To have. Many efforts have been made to solve these problems (1) to (3).

  Patent Document 1 proposes a gas diffusion layer in which a microporous portion made of carbon black and a hydrophobic resin is formed on the catalyst layer side of an electrode substrate. According to the fuel cell using this gas diffusion layer, since the microporous portion forms a small pore structure having water repellency, drainage of liquid water to the cathode side is suppressed and flooding tends to be improved. . Further, since moisture is pushed back into the electrolyte membrane (hereinafter referred to as reverse diffusion), the electrolyte membrane tends to be wet and dry-up tends to be improved. However, suppression of flooding and dry-up is still insufficient, and there is a problem that plugging is not improved at all.

  Patent Document 2 proposes a gas diffusion layer in which a microporous portion made of carbon nanofibers and a hydrophobic resin is formed on the catalyst layer side of an electrode substrate. According to the fuel cell using this gas diffusion layer, the water repellency of the microporous portion is improved, the discharge of liquid water to the cathode side is suppressed, and the flooding is improved. Also, the reverse diffusion of moisture into the electrolyte membrane tends to wet the electrolyte membrane and improve dry-up. However, the suppression of dry-up is still insufficient, and there is a problem that plugging is not improved at all.

  Patent Documents 3 to 5 propose fuel cells using gas diffusion layers in which microporous portions made of carbon black and hydrophobic resin are formed on both surfaces of an electrode base material. According to the fuel cell using this gas diffusion layer, the microporous portion on the separator side is smooth and has high water repellency, so that liquid water does not easily stay in the flow path, and plugging is improved. Further, the back diffusion of moisture to the electrolyte membrane is suppressed by the microporous portion on the catalyst layer side, and the diffusion of water vapor is further suppressed by the microporous portion on the separator side. As a result, the electrolyte membrane is wet and dry-up is improved. However, since the drainage from the electrode substrate to the separator is hindered by the microporous portion on the separator side, there is a problem that flooding becomes remarkable.

  Although many such efforts have been made, a gas diffusion layer having excellent flooding / plugging resistance and excellent dry-up resistance has not yet been found.

JP 2000-123842 A JP 2006-120506 A Japanese Patent Laid-Open No. 9-245800 JP 2008-293937 A JP-A-2005-174607

  In view of the background of such conventional technology, the object of the present invention is excellent in flooding / plugging resistance, excellent in dry-up resistance, and capable of expressing high power generation performance over a wide temperature range from low temperature to high temperature. The object is to provide a gas diffusion layer having excellent mechanical properties, electrical conductivity, and thermal conductivity.

  The inventors of the present invention focused on improving dry-up and plugging when a gas diffusion layer having microporous portions provided on both sides of an electrode substrate is used in a fuel cell. However, when carbon black is used for the carbonaceous powder constituting the microporous portion as in the prior art, there is a problem that flooding is remarkable. On the other hand, as a result of diligent investigation, dry carbonization and plugging were improved by using granular carbon having a particle diameter of 3 to 500 nm for the microporous part on one side and carbon nanofibers for the microporous part on the other side. The present inventors have found that the drainage can be rather improved and have completed the present invention.

  In the method of providing microporous portions having the same composition on both surfaces as in the prior art, it is difficult to achieve both plugging resistance, dry-up resistance, and flooding resistance.

  Based on this idea, the gas diffusion layer of the present invention has the following characteristics. That is, the microporous part [A], the electrode base material, and the microporous part [B] are arranged adjacently in this order, and the carbonaceous powder constituting the microporous part [A] has an average diameter of 1 to 1000 nm. This is a fuel cell gas diffusion layer in which the carbonaceous powder comprising the carbon nanofibers and constituting the microporous part [B] contains granular carbon having a particle diameter of 3 to 500 nm.

  In the present invention, it is necessary to form a microporous portion having conductivity, a so-called microporous layer, on both surfaces of the electrode substrate. The microporous portion on one side of the electrode substrate is referred to as a microporous portion [A], and the microporous portion on the opposite surface side is referred to as a microporous portion [B]. Since the microporous part [A] contains carbon nanofibers, the porosity is high, and the drainage and air permeability are high. As a result, even if the microporous portion [A] is provided on the separator side of the fuel cell, drainage from the electrode base material is not hindered but rather promoted, so that low temperature performance is improved. In order to solve the above problems, the membrane electrode assembly of the present invention has a catalyst layer on both sides of the electrolyte membrane, and further has the fuel cell gas diffusion layer outside the catalyst layer. This fuel cell has separators on both sides of the membrane electrode assembly.

  The present invention achieves both flooding / plugging resistance and dry-up resistance, can exhibit high power generation performance over a wide temperature range from low temperature to high temperature, and has excellent mechanical properties, electrical conductivity, and thermal conductivity. A gas diffusion layer can be obtained.

  In the gas diffusion layer of the present invention, the microporous part [A], the electrode substrate, and the microporous part [B] are arranged adjacently in this order. Hereinafter, each component will be described.

  First, the electrode base material which is a component of the present invention will be described.

  In the present invention, the electrode base material has a high gas diffusibility for diffusing the gas supplied from the separator to the catalyst, and a high drainage property for discharging the water generated along with the electrochemical reaction to the separator. High conductivity is required to extract current. For this reason, it is preferable to use a porous body having conductivity and an average pore diameter of 10 to 100 μm. More specifically, for example, a porous body containing carbon fibers such as a carbon fiber woven fabric, a carbon fiber papermaking body, and a carbon fiber nonwoven fabric, and a porous metal body such as a foam sintered metal, a metal mesh, and an expanded metal are preferably used. Among them, it is preferable to use a porous body containing carbon fiber because of its excellent corrosion resistance, and furthermore, because of its excellent property of absorbing dimensional change in the thickness direction of the electrolyte membrane, that is, “spring property”, carbon fiber. It is preferable to use a base material obtained by binding a paper body with a carbide, that is, “carbon paper”. In the present invention, a substrate formed by binding a carbon fiber papermaking body with a carbide is usually obtained by impregnating a carbon fiber papermaking body with a resin and carbonizing it, as will be described later.

  Examples of the carbon fiber include polyacrylonitrile (PAN) -based, pitch-based, and rayon-based carbon fibers. Of these, PAN-based and pitch-based carbon fibers are preferably used in the present invention because of excellent mechanical strength.

  In the carbon fiber of the present invention, the average diameter of the single fibers is preferably in the range of 3 to 20 μm, and more preferably in the range of 5 to 10 μm. When the average diameter is 3 μm or more, the pore diameter is increased, drainage is improved, and flooding can be suppressed. On the other hand, when the average diameter is 20 μm or less, the water vapor diffusibility becomes small, and dry-up can be suppressed. Moreover, it is preferable to use two or more types of carbon fibers having different average diameters because the surface smoothness of the electrode substrate can be improved.

  Here, the average diameter of the single fiber in the carbon fiber is taken with a microscope such as a scanning electron microscope, the carbon fiber is magnified 1000 times or more, and 30 different single fibers are randomly selected. The diameter was measured and the average value was obtained. As a scanning electron microscope, S-4800 manufactured by Hitachi, Ltd. or an equivalent thereof can be used.

  In the carbon fiber of the present invention, the average length of single fibers is preferably in the range of 3 to 20 mm, and more preferably in the range of 5 to 15 mm. When the average length is 3 mm or more, the electrode base material is preferable because it has excellent mechanical strength, electrical conductivity, and thermal conductivity. On the other hand, when the average length is 20 mm or less, the dispersibility of carbon fibers during papermaking is excellent, and a homogeneous electrode substrate is obtained, which is preferable. Carbon fibers having such an average length can be obtained by a method of cutting continuous carbon fibers into a desired length.

  Here, the average length of the carbon fiber is taken with a microscope such as a scanning electron microscope, the carbon fiber is magnified 50 times or more, and 30 different single fibers are selected at random. Is measured and the average value is obtained. As a scanning electron microscope, S-4800 manufactured by Hitachi, Ltd. or an equivalent thereof can be used. In addition, although the average diameter and average length of the single fiber in carbon fiber are normally measured by observing the carbon fiber directly about the carbon fiber used as a raw material, you may observe and measure an electrode base material.

In the present invention, it is preferable that the density of the electrode substrate is in the range of 0.2-0.4 g / cm ^3, more preferably in the range of 0.22~0.35g / cm ^3, further Is preferably in the range of 0.24 to 0.3 g / cm ³ . When the density is 0.2 g / cm ³ or more, the water vapor diffusibility is small, and dry-up can be suppressed. Further, the mechanical properties of the electrode substrate are improved, and the electrolyte membrane and the catalyst layer can be sufficiently supported. In addition, the conductivity is high, and the power generation performance is improved at both high and low temperatures. On the other hand, when the density is 0.4 g / cm ³ or less, drainage is improved and flooding can be suppressed. The electrode base material having such a density can be obtained by controlling the carbon fiber basis weight in the pre-impregnated body, the blending amount of the resin component with respect to the carbon fiber, and the thickness of the electrode base material in the production method described later. In the present invention, a paper body containing carbon fibers impregnated with a resin composition is referred to as a “pre-impregnated body”. Among these, it is effective to control the carbon fiber basis weight in the pre-impregnated body and the blending amount of the resin component with respect to the carbon fiber. Here, a low-density substrate is obtained by reducing the carbon fiber basis weight of the pre-impregnated body, and a high-density substrate is obtained by increasing the carbon fiber basis weight. Moreover, a low density base material is obtained by reducing the compounding quantity of the resin component with respect to carbon fiber, and a high density base material is obtained by increasing the compounding quantity of the resin component. Moreover, a low density base material is obtained by increasing the thickness of the electrode base material, and a high density base material is obtained by reducing the thickness.

  Here, the density of the electrode base material is obtained by dividing the basis weight (mass per unit area) of the electrode base material weighed using an electronic balance by the thickness of the electrode base material when pressed with a surface pressure of 0.15 MPa. Can be obtained.

  In the present invention, the pore diameter of the electrode substrate is preferably in the range of 30 to 80 μm, more preferably in the range of 40 to 75 μm, and further preferably in the range of 50 to 70 μm. When the pore diameter is 30 μm or more, drainage can be improved and flooding can be suppressed. When the pore diameter is 80 μm or less, the conductivity is high, and the power generation performance is improved at both high and low temperatures. In order to design within such a pore diameter range, it is effective to include both carbon fibers having an average single fiber diameter of 3 μm to 8 μm and carbon fibers having an average single fiber diameter exceeding 8 μm.

  Here, the pore diameter of the electrode substrate is obtained by determining the peak diameter of the pore diameter distribution obtained by measuring in the measurement pressure range of 6 kPa to 414 MPa (pore diameter 30 nm to 400 μm) by mercury porosimetry. When a plurality of peaks appear, the peak diameter of the highest peak is adopted. As a measuring device, Autopore 9520 manufactured by Shimadzu Corporation or an equivalent product thereof can be used.

  In this invention, it is preferable that the thickness of an electrode base material is 60-200 micrometers. More preferably, it is 70-170 micrometers, More preferably, it is 70-160 micrometers, Most preferably, it is 80-110 micrometers. When the thickness of the electrode substrate is 60 μm or more, the mechanical strength becomes high and handling becomes easy. By being 200 μm or less, the cross-sectional area of the electrode base material is reduced, and the amount of gas through which the liquid water flows in the separator channel increases, so that plugging can be suppressed. In addition, the drainage path is shortened, flooding is improved, and power generation performance at low temperatures is improved.

  Here, the thickness of the electrode base material can be determined using a micrometer in a state where the surface pressure is 0.15 MPa.

  Next, the microporous parts [A] and [B], which are constituent elements of the present invention, will be described.

  The microporous part has high gas diffusibility for diffusing the gas supplied from the separator to the catalyst, high drainage for discharging water generated by the electrochemical reaction to the separator, and taking out the generated current. In addition, it is necessary to promote the reverse diffusion of moisture into the electrolyte membrane. For this reason, it is preferable to use a porous body having conductivity and an average pore diameter of 1 to 10 μm. More specifically, for example, it is preferable to use a mixture of carbonaceous powder and hydrophobic resin.

  The microporous part [A] needs to contain carbon nanofibers having an average diameter of 1 to 1000 nm. By including the carbon nanofiber, the porosity of the microporous portion [A] is large and the conductivity is also good. The average diameter of the fiber is more preferably 10 to 500 nm. When the average diameter of the fibers is 1 nm or less, the porosity of the microporous portion [A] is reduced, and the drainage performance is lowered. Further, when the average diameter of the fibers is 1000 nm or more, the smoothness of the microporous portion [A] is lowered, the resistance to plugging is lowered, and the contact resistance is increased. The average diameter of the carbon nanofibers was measured with a microscope such as a transmission electron microscope, and the carbon fibers were magnified 500,000 times or more, and 30 different single fibers were randomly selected. It is measured and the average value is obtained. As the transmission electron microscope, JEM-4000EX manufactured by JEOL Ltd. or an equivalent product can be used.

  In the present invention, the carbon nanofiber refers to a carbon atom ratio of 90% or more and an aspect ratio of 10 or more. When the carbon atomic ratio is 90% or more, the conductivity and mechanical properties of the microporous portion are improved. On the other hand, when the aspect ratio is 10 or more, the conductivity and mechanical characteristics of the microporous portion are improved.

  The carbon nanofibers in the present invention include single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanohorns, carbon nanocoils, cup-stacked carbon nanotubes, bamboo-like carbon nanotubes, vapor-grown carbon fibers, and graphite nanofibers. Is mentioned. Of these, single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and vapor-grown carbon fibers are preferably used because of their large aspect ratio and excellent electrical conductivity and mechanical properties. Vapor-grown carbon fiber is obtained by growing carbon in the gas phase with a catalyst, and those having an average diameter of 5 to 200 nm and an average fiber length of 1 to 20 μm are preferable.

  The microporous portion [A] can be used in combination with the carbon nanofiber and the hydrophobic resin in order to impart a hydrophobic resin to the microporous portion [A] to improve drainage. Here, as the hydrophobic resin, polychlorotrifluoroethylene resin (PCTFE), polytetrafluoroethylene resin (PTFE), polyvinylidene fluoride resin (PVDF), copolymer of tetrafluoroethylene and hexafluoropropylene (FEP) And fluoropolymers such as a copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether (PFA) and a copolymer of tetrafluoroethylene and ethylene (ETFE).

  The blending amount of the hydrophobic resin in the microporous part [A] is preferably 1 to 70 parts by mass, and 5 to 60 parts by mass with respect to 100 parts by mass of the carbonaceous powder of the microporous part [A]. Is more preferable. When the blending amount of the hydrophobic resin is 1 part by mass or more, the microporous part [A] is preferable because it is excellent in drainage and mechanical strength. On the other hand, when it is 70 parts by mass or less, the microporous part [A] is preferable because it has excellent conductivity.

  The microporous portion [A] can contain carbonaceous powder other than carbon nanofibers. Examples of the carbonaceous powder other than carbon nanofiber include graphite, furnace black, acetylene black, channel black, thermal black, graphene, and milled carbon fiber. The carbonaceous powder constituting the microporous portion [A] is, for example, carbon. A mixture of nanofibers and acetylene black may also be used. When the carbonaceous powder constituting the microporous part [A] is 100 parts by mass, 5 to 100 parts by mass are preferably carbon nanofibers, and 10 to 100 parts by mass are more preferably carbon nanofibers. More preferably, 50 to 100 parts by mass are carbon nanofibers. When the carbon nanofiber is 5 parts by mass or less, the porosity of the microporous part [A] is lowered, and thus a gas diffusion layer having low drainage and gas diffusibility is obtained.

  The thickness of the microporous portion [A] is preferably in the range of 1 to 20 μm, and more preferably 4 to 16 μm. When the thickness is 1 μm or more, when the microporous portion [A] is used as the gas diffusion layer of the fuel cell toward the separator, the gap between the separator and the gas diffusion layer can be reduced. Moreover, it is preferable for it to be 20 μm or less because the electrical resistance of the microporous portion [A] can be reduced.

  The microporous portion [A] preferably has a porosity of 70 to 90%, more preferably 75 to 90%. A porosity of 70% or more is preferable because drainage from the gas diffusion layer is high. Moreover, it is preferable that the porosity is 90% or less because the microporous portion [A] has excellent mechanical strength. The porosity can be adjusted by the mixing ratio of the carbon nanofibers and the mixing ratio of the hydrophobic resin.

  The porosity of the microporous part [A] and the microporous part [B] can be enlarged by about 20000 times by selecting five different locations from the cross section of the gas diffusion layer with a microscope such as a scanning electron microscope. A photograph was taken, the porosity of the microporous part [A] and the microporous part [B] was measured, and the average value of the porosity of the microporous part [A] and the microporous part [B] in each image was calculated. Point to. As a scanning electron microscope, S-4800 manufactured by Hitachi, Ltd. or an equivalent product can be used. As a method for producing the cross section of the gas diffusion layer, an ion milling device IM4000 manufactured by Hitachi High-Technologies Corporation or an equivalent product can be used.

  On the other hand, the microporous part [B] needs to contain granular carbon having a particle diameter of 3 to 500 nm. Thereby, the pore diameter of 1 micrometer or less and high electroconductivity are securable, controlling the porosity of a microporous part [B] to 30 to 70%. Granular carbon is carbon fine particles having a particle diameter of 3 to 500 nm, and usually has conductivity. Examples of the granular carbonaceous shape include a spherical shape, an elliptical sphere, and a scale shape. Specific examples include graphite, carbon black, and marimocarbon. Among these, carbon black is preferable. The particle size is more preferably 20 to 200 nm.

  In addition, the particle diameter of granular carbon means the particle diameter calculated | required with the transmission electron microscope. Observation is performed with a transmission electron microscope at a magnification of 500,000, the outer diameter of 100 particle diameters present on the screen is measured, and the average value is taken as the particle diameter of the granular carbon. Here, the outer diameter refers to the maximum diameter of the particles (that is, the long diameter of the particles, indicating the longest diameter in the particles). As the transmission electron microscope, JEM-4000EX manufactured by JEOL Ltd. or an equivalent product can be used.

  Examples of the carbonaceous powder other than the granular carbon having a specific particle diameter constituting the microporous part [B] include those similar to the microporous part [A]. May be used in combination. When the carbonaceous powder constituting the microporous part [B] is 100 parts by mass, 50 to 100 parts by mass is preferably granular carbon having a specific particle diameter, and 70 to 100 parts by mass is granular carbon having a specific particle diameter. More preferably. When the granular carbon having a specific particle diameter is 50 parts by mass or less, the porosity of the microporous part [B] increases, and thus the electrolyte membrane is easily dried. When carbon nanofibers are added to the microporous part [B], it is necessary to make it smaller than the carbon nanofiber blending ratio of the microporous part [A].

  In the present invention, carbon black refers to fine carbon particles having a carbon atom ratio of 80% or more and a primary particle diameter of about 3 to 500 nm. The particle diameter of primary particles means the diameter of one granular carbonaceous particle that is not aggregated. For example, in the case of carbon black, it refers to the diameter of one non-aggregated carbon black particle. When the carbon atom ratio is 80% or more, the conductivity and corrosion resistance of the microporous portion are improved. On the other hand, when the diameter is 500 nm or less, the conductivity and mechanical properties of the microporous portion are improved.

  In the present invention, examples of carbon black include furnace black, channel black, acetylene black, and thermal black. Among them, it is preferable to use acetylene black having high conductivity and low impurity content.

  Like the microporous part [A], the microporous part [B] is used in combination with the carbon black and the hydrophobic resin in order to impart water repellency to the microporous part [B] and improve drainage. be able to. Here, as the hydrophobic resin, polychlorotrifluoroethylene resin (PCTFE), polytetrafluoroethylene resin (PTFE), polyvinylidene fluoride resin (PVDF), copolymer of tetrafluoroethylene and hexafluoropropylene (FEP) And fluoropolymers such as a copolymer of tetrafluoroethylene and perfluoropropyl vinyl ether (PFA) and a copolymer of tetrafluoroethylene and ethylene (ETFE).

  The blending amount of the hydrophobic resin in the microporous part [B] is preferably 1 to 70 parts by mass, and 5 to 60 parts by mass with respect to 100 parts by mass of the carbonaceous powder of the microporous part [B]. Is more preferable. When the blending amount of the hydrophobic resin is 1 part by mass or more, the microporous part [B] is preferable because it is excellent in drainage and mechanical strength. On the other hand, when it is 70 parts by mass or less, the microporous part [B] is preferable because it has excellent conductivity.

  The thickness of the microporous part [B] is preferably in the range of 1 to 40 μm, and more preferably 10 to 30 μm. When the thickness is 1 μm or more, when the microporous portion [B] is used as the gas diffusion layer of the fuel cell toward the separator, it is possible to reduce the gap at the interface between the separator and the gas diffusion layer. Moreover, it is preferable that it is 30 μm or less because the electric resistance of the microporous portion [B] can be reduced.

  The microporous part [B] preferably has a porosity of 30 to 70%, more preferably 40 to 70%. A porosity of 30% or more is preferable because drainage from the gas diffusion layer is high. On the other hand, a porosity of 70% or less is preferable because reverse diffusion is promoted and dry-up can be suppressed. The porosity can be adjusted by the mixing ratio of carbon black and the mixing ratio of hydrophobic resin.

  It is preferable that both surfaces of the gas diffusion layer in which the microporous portion [A] and the microporous portion [B] are formed have an arithmetic average surface roughness of 0.1 to 15 μm. More preferably, the arithmetic average surface roughness is 0.1 to 10 μm. Since the arithmetic average roughness of both surfaces of the gas diffusion layer is 15 μm or less, the gap between the separator and the gas diffusion layer becomes small when used as a gas diffusion layer of a fuel cell. Is preferable because it is less likely to stay and plugging can be suppressed. Further, it is preferable because the adhesion between the catalyst layer and the separator is improved and the electric resistance of the cell can be reduced. The arithmetic average surface roughness of the electrode substrate can be determined using a surface roughness meter, and as the surface roughness meter, Kosaka Laboratory Surfcoder SE-2300 or an equivalent thereof can be used. .

  The combination of using carbon nanofibers as the carbonaceous powder constituting the microporous part [A] and using carbon black as the carbonaceous powder constituting the microporous part [B] is high in the microporous part [A]. The gas diffusion layer has both flooding resistance, high dry-up resistance of the microporous portion [B], and high plugging resistance due to the microporous portions on both sides. A combination using vapor grown carbon fiber as the carbon nanofiber and acetylene black as the carbon black is more preferable. By making the carbonaceous powder of the microporous part [A] into vapor-grown carbon fiber, the porosity of the microporous part [A] is particularly increased and the drainage is improved. By using acetylene black as the carbonaceous powder in the microporous portion [B], the electrical resistance of the microporous portion [B] can be particularly reduced. Further, by using vapor grown carbon fiber for the carbonaceous powder of the microporous part [A] and acetylene black for the carbonaceous powder of the microporous part [B], the microporous part [A] and the microporous part [B] are used. The property of the gas diffusion layer is greatly changed, and the drainage can be inclined in the direction perpendicular to the surface of the gas diffusion layer, so that flooding in the gas diffusion layer is easily suppressed.

  Further, when the carbonaceous powder constituting the microporous part [A] is 100 parts by mass, 50 parts by mass or more are vapor-grown carbon fibers, and the carbonaceous powder constituting the microporous part [B] is 100 parts by mass. When 70 parts by mass or more is acetylene black, the above-mentioned flooding resistance, dry-up resistance, and plugging resistance are most remarkably exhibited, which is particularly preferable.

  As a combination of the thicknesses of the microporous part [A] and the microporous part [B], the total thickness of the microporous part [A] and the microporous part [B] is preferably 10 to 50 μm. The thickness of [B] is preferably 70% or more of the total thickness of the microporous portion [A] and the microporous portion [B]. By setting the total thickness of the microporous portions to 50 μm or less, the electrical resistance can be reduced. Further, by setting the thickness of the microporous portion [B] to the above ratio or more, flooding resistance, dry-up resistance, and plugging resistance are most remarkably exhibited.

  Next, a method suitable for obtaining the gas diffusion layer of the present invention will be specifically described.

<Paper making body and method for producing paper making body>
In the present invention, in order to obtain a papermaking body containing carbon fibers, a wet papermaking method in which carbon fibers are dispersed in a liquid and a dry papermaking method in which the carbon fibers are dispersed in air are used. Of these, the wet papermaking method is preferably used because of its excellent productivity.

  In the present invention, for the purpose of improving the drainage and gas diffusibility of the electrode substrate, paper can be made by mixing carbon fibers with organic fibers. As the organic fiber, polyethylene fiber, vinylon fiber, polyacetal fiber, polyester fiber, polyamide fiber, rayon fiber, acetate fiber, or the like can be used.

  In the present invention, an organic polymer can be included as a binder for the purpose of improving the form retainability and handling of the papermaking body. Here, as the organic polymer, polyvinyl alcohol, polyvinyl acetate, polyacrylonitrile, cellulose or the like can be used.

  The paper body in the present invention is preferably in the form of a sheet in which carbon fibers are randomly dispersed in a two-dimensional plane for the purpose of maintaining in-plane conductivity and thermal conductivity isotropic.

  The pore size distribution obtained from the papermaking body can be formed to a size of about 20 to 500 μm, although it is affected by the carbon fiber content and dispersion state.

Paper body is preferably the basis weight of the carbon fibers is in the range of 10 to 60 g / ^{m 2,} and more preferably in the range of 20 to 50 g / ^{m 2.} It is preferable that the basis weight of the carbon fiber is 10 g / m ² or more because the electrode base material has excellent mechanical strength. It is preferable that it is 60 g / m ² or less because the electrode base material has excellent gas diffusibility and drainage. In addition, when bonding a plurality of paper bodies, it is preferable that the basis weight of the carbon fibers after the bonding is in the above range.

Here, the weight per unit area of the carbon fiber in the electrode base material is the weight of the residue obtained by removing the organic matter by holding the paper body cut to 10 cm square in an electric furnace at a temperature of 450 ° C. for 15 minutes in a nitrogen atmosphere. , By dividing by the area of the paper body (0.01 m ² ).

<Impregnation of resin composition>
In the present invention, as a method of impregnating a paper composition containing carbon fibers with a resin composition, a method of immersing a papermaking article in a solution containing a resin composition, a method of applying a solution containing a resin composition to a papermaking article, a resin For example, a method of transferring a film made of the composition on a paper body is used. Especially, since productivity is excellent, the method of immersing a papermaking body in the solution containing a resin composition is used preferably.

  The resin composition used in the present invention is preferably one that is carbonized upon firing to become a conductive carbide. A resin composition means what added the solvent etc. to the resin component as needed. Here, the resin component includes a resin such as a thermosetting resin, and further includes additives such as a carbon-based filler and a surfactant as necessary.

  In the present invention, more specifically, the carbonization yield of the resin component contained in the resin composition is preferably 40% by mass or more. When the carbonization yield is 40% by mass or more, the electrode base material is preferable because it has excellent mechanical properties, electrical conductivity, and thermal conductivity.

  In the present invention, examples of the resin constituting the resin component include thermosetting resins such as phenol resin, epoxy resin, melamine resin, and furan resin. Of these, a phenol resin is preferably used because of its high carbonization yield. Moreover, as an additive added to a resin component as needed, a carbon-type filler can be included in order to improve the mechanical characteristics, electroconductivity, and thermal conductivity of an electrode base material. Here, as the carbon-based filler, carbon black, carbon nanotube, carbon nanofiber, milled carbon fiber, graphite or the like can be used.

  The resin composition used in the present invention can use the resin component obtained by the above-described configuration as it is, and can contain various solvents as needed for the purpose of improving the impregnation property to the papermaking body. . Here, methanol, ethanol, isopropyl alcohol, or the like can be used as the solvent.

  The resin composition in the present invention is preferably in a liquid state at 25 ° C. and 0.1 MPa. When it is liquid, it is preferable because the paper body has excellent impregnation properties and the electrode base material has excellent mechanical properties, electrical conductivity, and thermal conductivity.

  In this invention, it is preferable to impregnate a resin component 30-400 mass parts with respect to 100 mass parts of carbon fibers, and it is more preferable to impregnate 50-300 mass parts. When the impregnation amount of the resin component is 30 parts by mass or more, the electrode base material is preferable because it has excellent mechanical properties, electrical conductivity, and thermal conductivity. On the other hand, when the impregnation amount of the resin component is 400 parts by mass or less, the electrode base material is preferable because it has excellent gas diffusibility.

<Lamination and heat treatment>
In the present invention, after a pre-impregnated body impregnated with a resin composition is formed on a papermaking body containing carbon fibers, prior to carbonization, the pre-impregnated body can be bonded or heat-treated.

  In the present invention, a plurality of pre-impregnated bodies can be bonded together for the purpose of setting the electrode substrate to a predetermined thickness. In this case, a plurality of pre-impregnated bodies having the same properties can be bonded together, or a plurality of pre-impregnated bodies having different properties can be bonded together. Specifically, a plurality of pre-impregnated bodies having different average diameters and average lengths of carbon fibers, a carbon fiber basis weight of the papermaking body, an impregnation amount of the resin component, and the like can be bonded together.

  In the present invention, the pre-impregnated body can be heat-treated for the purpose of thickening and partially cross-linking the resin composition. As a heat treatment method, a method of blowing hot air, a method of heating with a hot plate such as a press device, a method of heating with a continuous belt, or the like can be used.

<Carbonization>
In the present invention, after impregnating the paper composition containing carbon fibers with the resin composition, firing is performed in an inert atmosphere in order to carbonize the paper composition. For this firing, a batch type heating furnace can be used, or a continuous type heating furnace can be used. The inert atmosphere can be obtained by flowing an inert gas such as nitrogen gas or argon gas in the furnace.

  In the present invention, the maximum firing temperature is preferably in the range of 1300 to 3000 ° C, more preferably in the range of 1700 to 3000 ° C, and further in the range of 1900 to 3000 ° C. preferable. When the maximum temperature is 1300 ° C. or higher, the carbonization of the resin component proceeds, and the electrode base material is preferably excellent in conductivity and thermal conductivity. On the other hand, the maximum temperature of 3000 ° C. or lower is preferable because the operating cost of the heating furnace is reduced.

  In the present invention, the firing rate is preferably in the range of 80 to 5000 ° C./min for firing. A temperature increase rate of 80 ° C. or higher is preferable because productivity is excellent. On the other hand, when the temperature is 5000 ° C. or lower, the carbonization of the resin component gradually proceeds and a dense structure is formed. Therefore, the electrode base material is preferably excellent in conductivity and thermal conductivity.

  In the present invention, the carbonized paper impregnated with a resin composition and then carbonized is referred to as a “carbon fiber fired body”.

<Water repellent finish>
In the present invention, the carbon fiber fired body is preferably subjected to water repellent treatment for the purpose of improving drainage. The water-repellent finish can be performed by applying a hydrophobic resin to the carbon fiber fired body and heat-treating it. The application amount of the hydrophobic resin is preferably 1 to 50 parts by mass, and more preferably 3 to 40 parts by mass with respect to 100 parts by mass of the carbon fiber fired body. When the application amount of the hydrophobic resin is 1 part by mass or more, the electrode substrate is preferable because it has excellent drainage. On the other hand, when the amount is 50 parts by mass or less, the electrode base material is preferably excellent in conductivity.

  In the present invention, a carbon fiber fired body that has been subjected to water repellent treatment as necessary is referred to as a “gas diffusion electrode substrate” or “electrode substrate”. When the water repellent finish is not applied, the carbon fiber fired body and the “gas diffusion electrode substrate” or “electrode substrate” are the same.

<Formation of microporous part [A] and microporous part [B]>
The microporous portion [A] applies a carbon coating liquid [A], which is a mixture of the hydrophobic resin used in the above-described water-repellent processing and the carbonaceous powder containing carbon nanofibers, to one surface of the electrode substrate. The microporous portion [B] is formed on the other surface of the electrode base material with the hydrophobic resin used in the above-described water-repellent processing and a carbonaceous powder containing granular carbon having a particle diameter of 3 to 500 nm. It can form by apply | coating carbon coating liquid [B] which is a mixture of these.

  Thereby, the gas diffusion layer of the present invention is formed by arranging the microporous portion [A], the electrode substrate, and the microporous portion [B] in this order.

  The carbon coating solution [A] and the carbon coating solution [B] may contain a dispersion medium such as water or an organic solvent, or may contain a dispersion aid such as a surfactant. Water is preferable as the dispersion medium, and a nonionic surfactant is more preferably used as the dispersion aid.

  The coating of the carbon coating liquid [A] and the carbon coating liquid [B] onto the electrode substrate can be performed using various coating apparatuses such as commercially available. As the coating method, screen printing, rotary screen printing, spray spraying, intaglio printing, gravure printing, die coater coating, bar coating, blade coating, etc. can be used, but regardless of the surface roughness of the electrode substrate Die coater coating is preferred because the amount of coating can be quantified. The coating methods exemplified above are only for illustrative purposes, and are not necessarily limited thereto.

  The microporous part [A] and the microporous part [B] are formed by applying a coating material obtained by applying the carbon coating liquid [A] or the carbon coating liquid [B] on one side at a temperature of 80 to 120 ° C. It is preferable to carry out after drying.

  That is, the coated product is put into a dryer set at a temperature of 80 to 120 ° C. and dried in a range of 5 to 30 minutes. The amount of drying air may be determined as appropriate, but rapid drying is undesirable because it may induce micro cracks on the surface. The coated product after drying is put into a muffle furnace, a baking furnace or a high-temperature dryer, heated at 300 to 380 ° C. for 5 to 20 minutes to melt the hydrophobic resin, and a binder of carbonaceous powders. Thus, it is preferable to form the microporous part [A] and the microporous part [B].

  Next, a membrane electrode assembly and a fuel cell using the gas diffusion layer of the present invention will be described.

  In this invention, a membrane electrode assembly can be comprised by joining the above-mentioned gas diffusion layer to at least one side of the solid polymer electrolyte membrane which has a catalyst layer on both surfaces. In that case, it is preferable to arrange the membrane electrode assembly so that the microporous portion [B] is arranged on the catalyst layer side, that is, the microporous portion [B] is in contact with the catalyst layer. By arranging the microporous part [B] having a small porosity of the microporous part on the catalyst layer side, the reverse diffusion is promoted and the dry-up resistance is improved. When the microporous portion [A] is on the separator side, the porosity of the gas diffusion layer on the separator side does not become too small, so that gas diffusion with good drainage can be achieved.

  A fuel cell is configured by having separators on both sides of the membrane electrode assembly. In general, a polymer electrolyte fuel cell is constructed by laminating a plurality of sandwiched electrode separators on both sides of such a membrane electrode assembly. The catalyst layer is composed of a layer containing a solid polymer electrolyte and catalyst-supporting carbon. As the catalyst, platinum is usually used. In a fuel cell in which a reformed gas containing carbon monoxide is supplied to the anode side, it is preferable to use platinum and ruthenium as the catalyst on the anode side. As the solid polymer electrolyte, it is preferable to use a perfluorosulfonic acid polymer material having high proton conductivity, oxidation resistance, and heat resistance. Such a fuel cell unit and the configuration of the fuel cell itself are well known.

  Hereinafter, the present invention will be described specifically by way of examples. The production method of the electrode substrate used in the examples and the cell performance evaluation method of the fuel cell are shown below.

<Preparation of electrode substrate>
Polyacrylonitrile-based carbon fiber “TORAYCA” (registered trademark) T300 (average carbon fiber diameter: 7 μm) manufactured by Toray Industries, Inc. was cut to an average length of 12 mm, dispersed in water, and continuously made by wet paper making. . Further, a 10% by mass aqueous solution of polyvinyl alcohol as a binder was applied to the paper and dried to prepare a paper body having a carbon fiber basis weight of 15.5 g / m ² . The coating amount of polyvinyl alcohol was 22 parts by mass with respect to 100 parts by mass of the papermaking body.

  A thermosetting resin using a resin in which a resol type phenolic resin and a novolac type phenolic resin are mixed at a weight ratio of 1: 1 as a thermosetting resin, scaly graphite (average particle diameter of 5 μm) as a carbon filler, and methanol as a solvent. / Carbon-based filler / solvent = 10 parts by mass / 5 parts by mass / 85 parts by mass These were mixed and stirred for 1 minute using an ultrasonic dispersion device to obtain a uniformly dispersed resin composition. .

  The paper body cut into 15 cm × 12.5 cm is immersed in a resin composition filled with aluminum bat, and the resin component (thermosetting resin + carbon filler) becomes 130 parts by mass with respect to 100 parts by mass of the carbon fibers. After impregnating in this manner, it was dried by heating at 100 ° C. for 5 minutes to prepare a pre-impregnated body. Next, it heat-processed for 5 minutes at 180 degreeC, pressing with a flat plate press. In addition, a spacer was disposed on the flat plate press during the pressurization, and the interval between the upper and lower press face plates was adjusted so that the thickness of the pre-impregnated body after the heat treatment was 160 μm.

  The base material obtained by heat-treating the pre-impregnated body was introduced into a heating furnace having a maximum temperature of 2400 ° C. maintained in a nitrogen gas atmosphere in a heating furnace to obtain a carbon fiber fired body.

  5 parts by mass of PTFE resin was applied to 95 parts by mass of the carbon fiber fired body, heated at 100 ° C. for 5 minutes and dried to prepare an electrode substrate having a thickness of 160 μm.

<Production of microporous part [A] and microporous part [B]>
In order to form a microporous portion, a carbon coating liquid portion was formed on the electrode substrate. The carbon coating liquid for forming the microporous part [A] is referred to as carbon coating liquid [A], and the carbon coating liquid for forming the microporous part [B] is referred to as carbon coating liquid [B].

  The carbon coating solution [A] used here uses vapor-grown carbon fiber (“VGCF” (registered trademark), average diameter 0.15 μm, average fiber length 8 μm, manufactured by Showa Denko KK) as carbon fiber, Other materials include PTFE resin ("Polyflon" (registered trademark) D-1E manufactured by Daikin Industries, Ltd.), surfactant ("TRITON" (registered trademark) X-100 manufactured by Nacalai Tesque), and purified water. Used, vapor-grown carbon fiber / PTFE resin / surfactant / purified water = 7.7 parts by mass / 2.5 parts by mass / 14 parts by mass / 75.8 parts by mass with a mixture ratio thereof It was. The carbon coating solution [A] was coated on an electrode substrate using a die coater, and was heated and dried at 120 ° C. for 10 minutes.

  The carbon coating solution [B] used here uses acetylene black (“DENKA BLACK” (registered trademark), average primary particle size 35 nm) manufactured by Denki Kagaku Kogyo Co., Ltd.) as carbon black, and PTFE resin as other materials. (Daikin Kogyo Co., Ltd. “Polyflon” (registered trademark) D-1E), surfactant (Nacalai Tesque Co., Ltd. “TRITON” (registered trademark) X-100), purified water, carbon black / PTFE Resin / surfactant / purified water = 7.7 parts by mass / 2.5 parts by mass / 14 parts by mass / 75.8 parts by mass of these were mixed. The carbon coating solution [B] was coated on the opposite side of the surface coated with the carbon coating solution [A] using a die coater and dried by heating at 120 ° C. for 10 minutes.

  The heat-dried coated material is heated at 380 ° C. for 10 minutes to form a gas diffusion layer having a microporous part [A] on the surface of the electrode substrate and a microporous part [B] on the other surface. Produced.

<Measurement of electrode substrate thickness>
The thickness of the electrode substrate was determined using a micrometer in a state where the electrode substrate was pressurized at a surface pressure of 0.15 MPa.

<Measurement of thickness of microporous part [A] and microporous part [B]>
The thickness of the microporous part [A] and microporous part [B] is selected with a microscope such as a scanning electron microscope at 10 different locations randomly selected from the cross section of the gas diffusion layer. The thickness of the microporous part [A] and the microporous part [B] was measured, and the average value of the thickness of the microporous part [A] and the microporous part [B] in each image was shown. . As a scanning electron microscope, S-4800 manufactured by Hitachi, Ltd. was used. As a method for producing a gas diffusion layer cross section, an ion milling device IM4000 manufactured by Hitachi High-Technologies Corporation was used.

<Measurement of surface roughness of electrode substrate>
The surface roughness of the electrode substrate was indicated by the arithmetic average roughness obtained using a surface roughness meter. As a surface roughness meter, Kosaka Laboratory Surfcoder SE-2300 was used.

<Battery performance evaluation of polymer electrolyte fuel cells>
1.00 g of platinum-supported carbon (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum support: 50% by mass), 1.00 g of purified water, “Nafion” (registered trademark) solution (“Nafion” (registered trademark) 5 manufactured by Aldrich) (0.0 mass%) 8.00 g and isopropyl alcohol (manufactured by Nacalai Tesque) 18.00 g were sequentially added to prepare a catalyst solution.

Next, “Naflon” (registered trademark) PTFE tape “TOMBO” (registered trademark) No. 7 cut to 7 cm × 7 cm. A catalyst solution was applied to 9001 (manufactured by NICHIAS Corporation) by spraying and dried at room temperature to prepare a PTFE sheet with a catalyst layer having a platinum amount of 0.3 mg / cm ² . Subsequently, a solid polymer electrolyte membrane “Nafion” (registered trademark) NRE-211CS (manufactured by DuPont) cut to 10 cm × 10 cm is sandwiched between two PTFE sheets with a catalyst layer, and pressed to 5 MPa with a flat plate press. Pressing at 5 ° C. for 5 minutes transferred the catalyst layer to the solid polymer electrolyte membrane. After pressing, the PTFE sheet was peeled off to produce a solid polymer electrolyte membrane with a catalyst layer.

  Next, the solid polymer electrolyte membrane with a catalyst layer was sandwiched between two gas diffusion layers cut to 7 cm × 7 cm, and pressed at 130 ° C. for 5 minutes while being pressurized to 3 MPa with a flat plate press to produce a membrane electrode assembly. . The gas diffusion layer was disposed so that the surface having the microporous portion [B] was in contact with the catalyst layer side.

  The obtained membrane electrode assembly was incorporated into a single cell for fuel cell evaluation, and the voltage when the current density was changed was measured. Here, as the separator, a serpentine type single groove having a groove width of 1.5 mm, a groove depth of 1.0 mm, and a rib width of 1.1 mm was used. Further, evaluation was performed by supplying hydrogen pressurized to 210 kPa to the anode side and air pressurized to 140 kPa to the cathode side. Both hydrogen and air were humidified using a humidification pot set at 70 ° C. The utilization rates of hydrogen and oxygen in the air were 80% and 67%, respectively.

First, when the operating temperature was held at 65 ° C. and the current density was set at 2.2 A / cm ² , the output voltage was measured and used as an indicator of low temperature performance (flooding resistance).

The resistance to plugging was evaluated by counting the number of times the output voltage decreased when the current density was maintained at 2.2 A / cm ² for 30 minutes. In the evaluation for 30 minutes, the number of times that the output voltage became 0.2 V or less was evaluated as “x”, the number of 3-4 times was evaluated as “◯”, and the number of times less than 2 was evaluated as “◎”.

Next, the current density is set to 1.2 A / cm ² , the operating temperature is maintained from 80 ° C. for 5 minutes, the output voltage is measured while repeatedly raising 2 ° C. over 5 minutes, and the limit temperature at which power generation is possible is obtained. And used as an index of high-temperature performance (dry-up resistance).

Example 1
Example 1 is the same method as described in <Preparation of electrode substrate> and <Preparation of microporous part [A] and microporous part [B]>, and the thickness of microporous part [A] is 15 μm. The microporous part [B] was prepared to have a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 5 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery Performance Evaluation of Solid Polymer Fuel Cell>, the plugging resistance was extremely good. The output voltage is 0.35 V (operation temperature 65 ° C., humidification temperature 70 ° C., current density 2.2 A / cm ² ), limit temperature is 91 ° C. (humidification temperature 70 ° C., current density 1.2 A / cm ² ), Both flooding resistance and dry-up resistance were good.

(Example 2)
Example 2 is the same method as described in <Production of electrode substrate> and <Production of microporous part [A] and microporous part [B]>, and the thickness of microporous part [A] is 20 μm. The microporous part [B] was prepared to have a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 5 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery Performance Evaluation of Solid Polymer Fuel Cell>, the plugging resistance was extremely good. The output voltage is 0.34 V (operation temperature 65 ° C., humidification temperature 70 ° C., current density 2.2 A / cm ² ), limit temperature is 92 ° C. (humidification temperature 70 ° C., current density 1.2 A / cm ² ), Both flooding resistance and dry-up resistance were good.

(Example 3)
Example 3 is the same method as described in <Preparation of electrode base material> and <Preparation of microporous part [A] and microporous part [B]> except that the thickness of the electrode base material was 220 μm. The microporous part [A] was prepared to have a thickness of 20 μm and the microporous part [B] had a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 5 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the plugging resistance was good. The output voltage is 0.33 V (operation temperature 65 ° C., humidification temperature 70 ° C., current density 2.2 A / cm ² ), limit temperature 91 ° C. (humidification temperature 70 ° C., current density 1.2 A / cm ² ), Both flooding and dry-up resistance were good.

Example 4
Example 4 is the same method as described in <Preparation of electrode base material> and <Preparation of microporous portion [A] and microporous portion [B]>, and the thickness of microporous portion [A] is 2 μm. The microporous part [B] was prepared to have a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 20 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the plugging resistance was good. The output voltage is 0.36 V (operating temperature 65 ° C., humidification temperature 70 ° C., current density 2.2 A / cm ² ), limit temperature 91 ° C. (humidification temperature 70 ° C., current density 1.2 A / cm ² ), The flooding property was extremely good, and the dry-up resistance was also good.

(Example 5)
Example 5 is the same method as described in <Preparation of electrode base material> and <Preparation of microporous part [A] and microporous part [B]> except that the thickness of the electrode base material was 100 μm. The microporous part [A] was made to have a thickness of 15 μm and the microporous part [B] was made to have a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 5 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery Performance Evaluation of Solid Polymer Fuel Cell>, the plugging resistance was extremely good. Output voltage is 0.37V (operating temperature 65 ° C, humidification temperature 70 ° C, current density 2.2A / cm ² ), limit temperature 91 ° C (humidification temperature 70 ° C, current density 1.2A / cm ² ), anti-flooding The properties were extremely good and the dry-up resistance was also good.

(Example 6)
In Example 6, the thickness of the electrode substrate was set to 100 μm, and the carbon black of the carbon coating solution [B] was changed to a mixture having a ratio of 80 parts by mass of acetylene black to 20 parts by mass of flake graphite (average particle diameter: 5 μm). Is the same method as described in <Preparation of electrode substrate> and <Preparation of microporous portion [A] and microporous portion [B]>, and the thickness of microporous portion [A] is 15 μm. The part [B] was made to have a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 5 μm, and the microporous part [B] was 5 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the plugging resistance was good. Output voltage 0.34V (operating temperature 65 ° C, humidification temperature 70 ° C, current density 2.2A / cm ² ), limit temperature 92 ° C (humidification temperature 70 ° C, current density 1.2A / cm ² ), anti-flooding resistance Both resistance and dry-up resistance were good.

(Example 7)
Example 7 is the same method as described in <Preparation of Electrode Base> and <Preparation of Microporous Part [A] and Microporous Part [B]> except that the thickness of the electrode base is 100 μm. The microporous part [A] was prepared to have a thickness of 0.5 μm and the microporous part [B] had a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 25 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the plugging resistance was good. Output voltage 0.38V (operating temperature 65 ° C, humidification temperature 70 ° C, current density 2.2A / cm ² ), limit temperature 90 ° C (humidification temperature 70 ° C, current density 1.2A / cm ² ), anti-flooding The properties were extremely good and the dry-up resistance was also good.

(Example 8)
Example 8 is the same method as described in <Preparation of electrode base material> and <Preparation of microporous part [A] and microporous part [B]> except that the thickness of the electrode base material was 100 μm. The microporous part [A] was prepared to have a thickness of 30 μm and the microporous part [B] had a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 4 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery Performance Evaluation of Solid Polymer Fuel Cell>, the plugging resistance was extremely good. Output voltage 0.36V (operating temperature 65 ° C, humidification temperature 70 ° C, current density 2.2A / cm ² ), limit temperature 91 ° C (humidification temperature 70 ° C, current density 1.2A / cm ² ), anti-flooding The properties were extremely good and the dry-up resistance was also good.

Example 9
Example 9 is the same method as described in <Preparation of electrode base material> and <Preparation of microporous part [A] and microporous part [B]> except that the thickness of the electrode base material was 100 μm. The microporous part [A] was prepared to have a thickness of 30 μm and the microporous part [B] had a thickness of 15 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 4 μm, and the microporous part [B] was 4 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the plugging resistance was good. Output voltage 0.34V (operating temperature 65 ° C, humidification temperature 70 ° C, current density 2.2A / cm ² ), limit temperature 90 ° C (humidification temperature 70 ° C, current density 1.2A / cm ² ), anti-flooding resistance Both resistance and dry-up resistance were good.

(Example 10)
Example 10 is the same method as described in <Preparation of electrode base material> and <Preparation of microporous part [A] and microporous part [B]> except that the thickness of the electrode base material was 100 μm. The microporous part [A] was made to have a thickness of 10 μm and the microporous part [B] was made to have a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 6 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery Performance Evaluation of Solid Polymer Fuel Cell>, the plugging resistance was extremely good. Output voltage 0.38V (operating temperature 65 ° C, humidification temperature 70 ° C, current density 2.2A / cm ² ), limit temperature 91 ° C (humidification temperature 70 ° C, current density 1.2A / cm ² ), anti-flooding The properties were extremely good and the dry-up resistance was also good.

  Tables 1 and 2 collectively show the evaluation results in the examples.

(Comparative Example 1)
In Comparative Example 1, the thickness of the electrode base material was 220 μm, and the microporous part [A] was not provided. <Preparation of electrode base material> and <Preparation of microporous part [A] and microporous part [B]> The microporous part [B] was made to have a thickness of 30 μm by the same method as described in 1 to obtain a gas diffusion layer. When the surface roughness was measured, the microporous portion [B] was 3 μm. As a result of evaluating the power generation performance of the gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the plugging resistance was low. This is because the surface of the gas diffusion layer on the separator side is rough, so that liquid water is less likely to stay in the flow path. The output voltage is 0.35 V (operation temperature 65 ° C., humidification temperature 70 ° C., current density 2.2 A / cm ² ), limit temperature 88 ° C. (humidification temperature 70 ° C., current density 1.2 A / cm ² ), Although the flooding property was good, the dry-up resistance was low.

(Comparative Example 2)
In Comparative Example 2, the thickness of the electrode substrate was 220 μm, the microporous portion [A] was not provided, and the carbon black of the carbon coating solution [B] was changed to vapor-grown carbon fiber. And <Manufacture of microporous part [A] and microporous part [B]>, the microporous part [B] is prepared to have a thickness of 30 μm, and a gas diffusion layer is formed. Obtained. When the surface roughness was measured, the microporous portion [B] was 3 μm. As a result of evaluating the power generation performance of the gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the plugging resistance was low. This is because the surface of the gas diffusion layer on the separator side is rough, so that liquid water is less likely to stay in the flow path. The output voltage is 0.34 V (operating temperature 65 ° C., humidification temperature 70 ° C., current density 2.2 A / cm ² ), limit temperature 86 ° C. (humidification temperature 70 ° C., current density 1.2 A / cm ² ), Although the flooding property was good, the dry-up resistance was low.

(Comparative Example 3)
In Comparative Example 3, the electrode substrate had a thickness of 220 μm, and the vapor-grown carbon fiber of the carbon coating solution [A] was acetylene black (“DENKA BLACK” (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.), with an average primary particle size of 35 nm. The thickness of the microporous portion [A] is the same as described in <Production of electrode base material> and <Formation of microporous portion [A] and microporous portion [B]>. Was produced so that the thickness of the microporous part [B] was 30 μm, and a gas diffusion layer was obtained. When the surface roughness was measured, the microporous part [A] was 5 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the output voltage could not be taken out (operation temperature 65 ° C., humidification temperature 70 ° C., current density 2. 2A / cm ² ), limit temperature 89 ° C. (humidification temperature 70 ° C., current density 1.2 A / cm ² ), and both flooding resistance and dry-up resistance were reduced. The low flooding resistance is due to the low porosity of the microporous part [A] on the separator side of the electrode substrate, which impedes drainage of liquid water, and the low dry-up resistance is the porosity on both sides. This is because the basic performance is low because it is difficult to supply gas because it has a microporous portion with a low rate.

(Comparative Example 4)
In Comparative Example 4, the thickness of the electrode substrate was 220 μm, and acetylene black of the carbon coating solution [B] was vapor-grown carbon fiber (“VGCF” (registered trademark) manufactured by Showa Denko KK, average diameter 0.15 μm, average The microporous part [A] is the same as described in <Preparation of electrode substrate> and <Preparation of microporous part [A] and microporous part [B]> except that the fiber length is changed to 8 μm). Was prepared so that the thickness of the microporous part [B] was 30 μm, and a gas diffusion layer was obtained. When the surface roughness was measured, the microporous part [A] was 5 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the plugging resistance was good. The output voltage is 0.30 V (operation temperature 65 ° C., humidification temperature 70 ° C., current density 2.2 A / cm ² ), limit temperature 87 ° C. (humidification temperature 70 ° C., current density 1.2 A / cm ² ), Both flooding and dry-up resistance decreased. The low flooding resistance is due to the high porosity of the microporous part [B] on the catalyst layer side and the weak back diffusion, resulting in an increase in the amount of liquid water flowing into the cathode, resulting in a decrease in dry-up resistance. This is because the back diffusion is weak and the electrolyte membrane is easy to dry.

(Comparative Example 5)
In Comparative Example 5, the thickness of the electrode substrate is 220 μm, and the vapor-grown carbon fiber of the carbon coating liquid [A] is milled carbon fiber (MLD-30 manufactured by Toray Industries, Inc., average fiber diameter 7 μm, average fiber length 30 μm). Other than the change, the thickness of the microporous part [A] is 20 μm in the same manner as described in <Preparation of electrode substrate> and <Preparation of microporous part [A] and microporous part [B]>. The microporous part [B] was prepared to have a thickness of 30 μm to obtain a gas diffusion layer. When the surface roughness was measured, the microporous part [A] was 5 μm, and the microporous part [B] was 3 μm. As a result of evaluating the power generation performance of this gas diffusion layer by the method described in <Battery performance evaluation of polymer electrolyte fuel cell>, the output voltage could not be taken out (operation temperature 65 ° C., humidification temperature 70 ° C., current density 2. 2A / cm ² ) and a limiting temperature of 88 ° C. (humidification temperature of 70 ° C., current density of 1.2 A / cm ² ), both the flooding resistance and the dry-up resistance were lowered.

  Table 3 summarizes the evaluation results of the comparative examples.

Claims (9)

The microporous part [A], the electrode substrate, and the microporous part [B] are arranged adjacent to each other in this order, and the carbonaceous powder constituting the microporous part [A] is carbon having an average diameter of 1 to 1000 nm. A fuel cell gas diffusion layer containing nanofibers, wherein the carbonaceous powder constituting the microporous part [B] contains granular carbon having a particle diameter of 3 to 500 nm. The gas diffusion layer for a fuel cell according to claim 1, wherein the granular carbon is carbon black. The gas diffusion layer for a fuel cell according to claim 1 or 2, wherein the microporous portion [A] has a porosity of 70 to 90%, and the microporous portion [B] has a porosity of 30 to 70%. The gas diffusion layer for a fuel cell according to any one of claims 1 to 3, wherein the thickness of the microporous portion [A] is 1 µm or more and 20 µm or less. The gas diffusion layer for a fuel cell according to any one of claims 1 to 4, wherein both surfaces have an arithmetic average surface roughness of 0.1 to 15 µm. 6. The fuel cell gas diffusion layer according to claim 1, wherein the electrode substrate has a thickness of 60 to 200 [mu] m. The membrane electrode assembly which has a catalyst layer on both sides of electrolyte membrane, and also has the gas diffusion layer for fuel cells in any one of Claims 1-6 outside the said catalyst layer. The membrane electrode assembly according to claim 7, wherein the microporous portion [B] is disposed on the catalyst layer side. The fuel cell which has a separator on both sides of the membrane electrode assembly of Claim 8.