JP2017171550A - Conductive porous substrate, gas diffusion electrode, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive porous substrate in which, when it is used for a fuel cell, a short circuit is unlikely to occur and a fuel cell having high durability can be obtained.SOLUTION: A conductive porous substrate is a conductive porous substrate including carbon fiber, and in which, characterized, when setting the in-plane direction of the conductive porous substrate as 0° and the thickness direction as 90°, and letting the number of carbon fibers oriented in the direction of 0° or more and less than 10° be N1 and the number of carbon fibers oriented in the direction of 10° or more and 90° or less be N2, N1/N2 is 85/15 to 100/0. Here, both N1 and N2 are integer from 0 to 100, and the sum of N1 and N2 is 100.SELECTED DRAWING: None

Description

  A fuel cell is a mechanism that electrically extracts the energy generated when water is produced by reacting hydrogen and oxygen. It is highly energy efficient and has only water, so it is expected to spread as clean energy. Has been. The present invention relates to a conductive porous substrate that can be applied to a gas diffusion electrode used in a fuel cell, and in particular, a conductive material suitable for a polymer electrolyte fuel cell used as a power source for a fuel cell vehicle among fuel cells. Relates to a porous porous substrate.

  An electrode used in a polymer electrolyte fuel cell is sandwiched between two separators in a polymer electrolyte fuel cell, and is disposed between the two separators. On both surfaces of the polymer electrolyte membrane, the electrode is on the surface of the polymer electrolyte membrane. It has a structure comprising a formed catalyst layer and a gas diffusion layer formed outside the catalyst layer. A gas diffusion electrode is distributed as an individual member for forming a gas diffusion layer on the electrode. The performance required for the gas diffusion electrode includes, for example, gas diffusivity, conductivity for collecting electricity generated in the catalyst layer, and drainage for efficiently removing moisture generated on the surface of the catalyst layer. can give. In order to obtain such a gas diffusion electrode, generally, a conductive porous substrate having gas diffusion ability and conductivity is used.

  Specifically, carbon felt made of carbon fiber, carbon paper, carbon cloth, and the like are used as the conductive porous substrate, and carbon paper is most preferable from the viewpoint of mechanical strength.

  In addition, since a fuel cell is a system that electrically extracts energy generated when hydrogen and oxygen react to produce water, if the electrical load increases, that is, if the current taken out of the cell increases, a large amount of water When (water vapor) is generated and the water vapor condenses into water droplets at low temperatures and closes the pores of the gas diffusion electrode, the supply amount of gas (oxygen or hydrogen) to the catalyst layer decreases, and finally If all the pores are blocked, the power generation stops (this phenomenon is called flooding).

  The gas diffusion electrode is required to have drainage so as not to generate this flooding as much as possible. As means for improving the drainage, the water repellency is usually increased by using a gas diffusion electrode base material obtained by subjecting the conductive porous base material to water repellency treatment.

  Further, if the conductive porous substrate subjected to the water repellent treatment as described above is used as a gas diffusion electrode as it is, the fiber has a coarse mesh, so that when water vapor is condensed, 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. (Also referred to as a layer).

  If the carbon fiber fluff of the conductive porous base material penetrates the polymer electrolyte membrane, the performance of the fuel cell may be reduced due to short circuit or deterioration of the polymer electrolyte membrane starting from the penetrated portion. In particular, even if the impact on the initial power generation is small, the shortage and deterioration of the polymer electrolyte membrane progress due to repeated swelling and shrinkage of the polymer electrolyte membrane due to repeated starting and stopping of the fuel cell, thereby improving the durability of the fuel cell. Reduce.

  Therefore, Patent Document 1 discloses a conductive porous substrate in which a gas is sprayed on at least one surface of the conductive porous substrate, and the carbon short fibers from which the binding due to the resin carbide is removed are sufficiently removed. The manufacturing method is shown.

  Further, in Patent Document 2, an insulating member having a plurality of communication holes is disposed on the water repellent layer side of a gas diffusion layer formed by laminating a carbon fiber layer and a water repellent layer, and further insulated from the gas diffusion layer. The member is sandwiched between a pair of electrodes, a pair of surface pressure plates are disposed and sandwiched between the back surfaces of the pair of electrodes, and the gas diffusion layer is pressurized by the pair of surface pressure plates. When a voltage is applied to the pair of electrodes in a pressurized state, an electric current is passed through the protruding portion of the carbon fiber that is in contact with the electrode on the water repellent layer through the communication hole of the insulating member, and the protrusion due to Joule heat A method for burning and removing the carbon fibers is shown.

  On the other hand, in Patent Document 3, a sheet having elasticity is disposed on at least one surface of a conductive porous base material in which short carbon fibers are bound by carbon, and a linear pressure is 5 kN using a continuous pressurizing means. Shows a method of continuously removing carbon powder adhering to the conductive porous substrate by a method such as brushing, sucking, or ultrasonic cleaning after pressurizing at / m to 30 kN / m. Has been.

JP 2010-70433 A JP 2012-33458 A JP 2012-204142 A

  However, in the method described in Patent Document 1, the surface of the gas diffusion layer can be cleaned to some extent, but when the gas diffusion layer is compressed, such as a joining process with a polymer electrolyte membrane, new carbon fiber protrusion occurs. As a result, they pierce the polymer electrolyte membrane and cause a large short-circuit current.

  In the method described in Patent Document 2, since the protruding portion of the carbon fiber that generates a large amount of heat is easy to burn or cut near the center in the longitudinal direction of the protruding carbon fiber that generates little heat, the gas diffusion layer and There is a problem that the carbon fibers protruding between the cut portions remain, or the protruding carbon fibers ahead of the cut portions are mixed to cause a short circuit of the polymer electrolyte membrane.

  Further, the method described in Patent Document 3 also has a problem that the effect of removing carbon short fibers by pressurization is reduced by disposing an elastic sheet on at least one surface of the conductive porous substrate.

  Accordingly, an object of the present invention is to overcome the above-described problems and to provide a conductive porous substrate that is less likely to cause a short circuit when used in a fuel cell.

In order to solve the above problems, the present invention employs the following means.
(1) A conductive porous substrate containing carbon fiber,
When the in-plane direction of the conductive porous substrate is 0 ° and the thickness direction is 90 °, the number of carbon fibers facing the direction of 0 ° to less than 10 ° is N1, 10 ° to 90 ° A conductive porous substrate, wherein N1 / N2 is 85/15 to 100/0, where N2 is the number of carbon fibers facing the direction.

Here, N1 and N2 are both integers of 0 to 100, and the sum of N1 and N2 is 100.
(2) A conductive porous substrate containing carbon fiber and resin carbide,
The resin carbide consists of a plurality of lumps, and
The conductive porous base material, wherein a short diameter of the mass of the resin carbide is 3% to 20% when the thickness of the conductive porous base material is 100%.

  When the conductive porous substrate of the present invention is used in a fuel cell, a short circuit is unlikely to occur and a highly durable fuel cell can be obtained.

  The present invention is a conductive porous substrate containing carbon fiber, and when the in-plane direction of the conductive porous substrate is 0 ° and the thickness direction is 90 °, it is 0 ° or more and less than 10 °. N1 / N2 is 85/15 to 100/0, where N1 is the number of carbon fibers facing the direction and N2 is the number of carbon fibers facing the direction of 10 ° to 90 °. A conductive porous substrate. Here, N1 and N2 are both integers of 0 to 100, and the sum of N1 and N2 is 100.

  Hereinafter, the present invention is referred to as a first aspect, and the first aspect and a second aspect described later are collectively referred to as the present invention.

  Specifically, as the conductive porous substrate of the present invention, for example, a porous substrate containing carbon fibers such as carbon fiber woven fabric, carbon fiber papermaking body, carbon fiber nonwoven fabric, carbon felt, carbon paper, carbon cloth, etc. It is preferable to use a porous metal substrate such as a foam sintered metal, a metal mesh, or an expanded metal. Among them, since the corrosion resistance is excellent, it is preferable to use a porous substrate such as carbon felt containing carbon fiber, carbon paper, carbon cloth, and moreover, a property of absorbing a dimensional change in the thickness direction of the electrolyte membrane, That is, since it is excellent in “spring property”, it is preferable to use a substrate containing a resin carbide obtained by binding a carbon fiber papermaking body with a carbide, that is, carbon paper.

  In the first aspect, when the in-plane direction of the conductive porous substrate is 0 ° and the thickness direction is 90 °, the number of carbon fibers facing the direction of 0 ° or more and less than 10 ° is N1. N1 / N2 is 85/15 to 100/0, where N2 is the number of carbon fibers facing in the direction of 10 ° to 90 °. N1 and N2 are both integers of 0 or more and 100 or less.

  As described above, N1 / N2 is 85/15 to 100/0, and when it is 84/16 or less, the number of carbon fibers oriented in the thickness direction of the conductive porous substrate increases, and short-circuiting easily occurs. N1 / N2 is preferably 85/15 or more.

  In the first aspect, in the carbon fibers existing inside the conductive porous substrate, the number of carbon fibers facing the direction of 0 ° to less than 10 ° is N3, the direction of 10 ° to 90 ° N3 / N4 is preferably 85/15 to 100/0, where N4 is the number of carbon fibers facing the surface. Here, N3 and N4 are both integers of 0 or more and 100 or less, and the sum of N3 and N4 is 100. Note that the inside of the conductive porous substrate is a portion that is 20% or more inside from the surface of the conductive porous substrate when the thickness of the conductive porous substrate is 100%. Say.

  In order to set N1 / N2 to 85/15 to 100/0 or N3 / N4 to 85/15 to 100/0, pressure treatment is performed so that the conductive porous substrate has a desired thickness. The pressure of the hour or the distance between the upper and lower press face plates can be adjusted.

  The conductive porous substrate of the present invention can be made into a carbon fiber sheet by using either a dry papermaking method or a wet papermaking method using carbon fibers having an average fiber length of 3 to 20 mm, for example. In the wet papermaking method using water as a papermaking medium, the carbon fibers are more easily oriented in the in-plane direction of the conductive porous substrate, that is, N1 / N2 is easily set to 85/15 to 100/0, and N3 / N4 is also set. Since it is easy to control to 85 / 15-100 / 0, it is preferable. That is, when the wet papermaking method is used, since the carbon fibers are difficult to face in the thickness direction, a short circuit penetrating the polymer electrolyte membrane hardly occurs, and the short circuit current can be suppressed low. Moreover, since a homogeneous sheet with good carbon fiber dispersibility can be obtained, the short-circuit current can be kept low at a large number of measurement points, which is preferable.

  In addition, the measuring method of N3 and N4 is the same as the measuring method of above-mentioned N1 and N2. However, when measuring N3 and N4, when the thickness of the conductive porous substrate is set to 100%, the portion that is 20% or more inside from the surface of the conductive porous substrate is observed. It shall be measured as a range.

  Moreover, in order to improve form retention property, handling property, etc., it is preferable to contain organic binders, such as polyvinyl alcohol, a cellulose, polyester, an epoxy resin, a phenol resin, an acrylic resin, in a carbon fiber sheet. In that case, it is preferable that the total of the organic binder is 1 to 30% by mass in 100% by mass of the carbon fiber sheet.

  The obtained carbon fiber sheet is impregnated with a resin having a residual carbon ratio of 35% (mass basis) or more, and the like, and a composition containing carbon fiber and resin (that is, a sheet in which a carbon fiber sheet is impregnated with resin Hereinafter, this is referred to as a precursor sheet), and the composition is heated to carbonize the resin, whereby a conductive porous substrate containing carbon fiber and resin carbide can be obtained.

  Here, the resin is carbonized during baking to become a conductive resin carbide. Therefore, after firing, a conductive porous substrate having a structure in which carbon fibers are bound with resin carbide can be obtained. A solvent or the like may be added to the resin as necessary. A residual carbon ratio of 35% by mass or more is preferable because the conductive porous substrate has excellent mechanical strength, conductivity, and thermal conductivity. The higher the carbonization yield, the better. However, in the current technical level, it is generally 70% by mass or less.

  Examples of the resin to be impregnated into the carbon fiber sheet to form the precursor sheet include thermosetting resins such as phenol resin, epoxy resin, melamine resin, and furan resin. Among these, a phenol resin is preferably used because of a high residual carbon ratio.

  The resin preferably contains carbon powder such as graphite powder, carbon black, and carbon nanotube. By containing carbon fiber in the resin, the conductive porous substrate obtained also contains carbon powder, and shrinkage and crack generation when the resin is carbonized are suppressed. Accordingly, it is possible to prevent the carbon fibers from dropping or the polymer electrolyte membrane from being short-circuited due to a decrease in the binding between the resin carbide and the carbon fiber, and the short-circuit current can be kept low.

  A second aspect of the present invention is a conductive porous substrate containing carbon fibers and resin carbide, wherein the resin carbide is composed of a plurality of lumps, and the thickness of the conductive porous substrate is 100%. In this case, the conductive carbide base material is characterized in that a minor axis of the lump of the resin carbide is 3% to 20%.

  In addition, the first aspect of the present invention may include a resin carbide. And when the 1st mode of the present invention contains resin carbide, when the resin carbide consists of a plurality of lumps and the thickness of the conductive porous substrate is 100%, the resin carbide The conductive porous substrate is characterized in that the short axis of the lump is 3% to 20%.

  In order to control the short diameter of the resin carbide lump so that the short diameter of the resin carbide lump is 3% to 20% when the thickness of the conductive porous substrate is 100%, The pressure or the distance between the upper and lower press face plates can be adjusted.

  In the present invention, a resin carbide is preferably included. And it is preferable that this resin carbide becomes a plurality of lump. In this way, carbon fibers are bound together, improving the mechanical strength of the conductive porous substrate, while making it difficult to inhibit electrons, heat, gas, and water flowing in the conductive porous substrate. As a fuel cell, high power generation performance can be exhibited.

  In the present invention, when the thickness of the conductive porous substrate is 100%, the minor axis of the mass of the resin carbide is preferably 3% to 20%. If the short axis of the resin carbide block is less than 3% of the thickness of the conductive porous substrate, the resin carbide is too small to bind the carbon fibers, causing fluffing and short circuiting. To do. If the short diameter of the mass of resin carbide exceeds 20% of the thickness of the conductive porous substrate, the flow of electrons, heat, gas, and water in the conductive porous substrate is inhibited, and the power generation performance of the fuel cell Decreases.

  Furthermore, when the cross-sectional area of the conductive porous substrate is 100%, the cross-sectional area of the lump of resin carbide is preferably 1% to 5%. If the cross-sectional area of the mass of the resin carbide is less than 1% when the cross-sectional area of the conductive porous substrate is 100%, the amount of the resin carbide is too small to bind the carbon fibers sufficiently. If it exceeds 5%, the resin carbide is too large, obstructing the flow of electrons, heat, gas, and water in the conductive porous substrate, and lowering the power generation performance of the fuel cell.

  In order to control the size of the resin carbide lump so that the cross-sectional area of the resin carbide lump is 1% to 5% when the cross-sectional area of the conductive porous substrate is 100%, The pressure or the distance between the upper and lower press face plates can be adjusted.

  In the present invention, it is preferable to reduce the thickness of the conductive porous substrate such as carbon paper from the viewpoint of enhancing gas diffusibility. 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 of the present invention, a material subjected to water repellent treatment by applying a fluororesin is suitably 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. As the water-repellent resin contained in the conductive porous substrate, that is, the fluororesin contained in the conductive porous substrate, PTFE (polytetrafluoroethylene) (for example, “Teflon” (registered trademark)), FEP (tetrafluoroethylene) Hexafluoropropylene copolymer), PFA (perfluoroalkoxy fluoride resin), ETFA (ethylene tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), etc. are strong, but strong PTFE or FEP that exhibits water repellency is preferred.

  The amount of the water-repellent resin is not particularly limited, but about 0.1% by mass to 20% by mass is appropriate for 100% by mass of the entire conductive porous substrate. If the amount is less than 0.1% by mass, the water repellency may not be sufficiently exerted. If the amount exceeds 20% by mass, pores serving as gas diffusion paths or drainage paths may be blocked, and electrical resistance may increase. is there.

  The method of water-repellent treatment of the conductive porous base material is conducted by die coating, spray coating, etc. in addition to the treatment technique of immersing the conductive porous base material in a dispersion containing a generally known water-repellent resin. An application technique for applying a water-repellent resin to a porous porous substrate is also applicable. Further, processing by a dry process such as sputtering of a fluororesin can also be applied. In addition, you may add a drying process and also a sintering process as needed after water-repellent treatment.

  The conductive porous substrate of the present invention is preferably used as a gas diffusion electrode having a microporous layer on at least one surface thereof. Therefore, the microporous layer will be described below.

  The microporous layer is a layer containing conductive fine particles such as carbon black, carbon nanotube, carbon nanofiber, carbon chopped fiber, graphene, and graphite.

  As a method for forming a microporous layer on at least one side of a conductive porous substrate, a microporous layer coating solution is screen-printed, rotary screen printing, spray spraying, intaglio printing, gravure printing, die coater printing, bar coating, blade A coating method by coating, knife coater or the like is preferable. From the viewpoint of productivity, the concentration of the conductive fine particles in the microporous layer coating solution is preferably 5% by weight or more, more preferably 10% by weight or more. If the viscosity, dispersion stability of the conductive particles, and coating properties of the coating liquid are official, there is no upper limit to the concentration, but in practice, the concentration of the conductive fine particles in the microporous layer coating liquid is 50% by mass. When it exceeds, the appropriateness as a coating liquid may be impaired. Generally, after applying the microporous layer coating solution, sintering is performed at 250 ° C. or more and 400 ° C. or less.

  The fuel cell of the present invention is characterized by having the conductive porous substrate of the present invention. Since the fuel cell of the present invention has the conductive porous substrate of the present invention, the fuel cell has a characteristic that a short circuit hardly occurs.

  Hereinafter, the present invention will be described specifically by way of examples. The materials used in the examples, the method for producing the conductive porous substrate, and the short-circuit evaluation method are shown below.

Example 1
<Material>
A PAN-based carbon fiber “Torayca” (registered trademark) T300 (average diameter: 7 μm) manufactured by Toray Industries, Inc. was cut into an average length of 12 mm of short fibers, dispersed in water, and continuously made by wet paper making. Furthermore, a 10% by mass aqueous solution of polyvinyl alcohol as a binder was applied to the paper and dried to prepare a carbon fiber sheet having a carbon fiber basis weight of 26 g / m ² . The adhesion amount of polyvinyl alcohol was 18 parts by mass with respect to 100 parts by mass of the carbon fiber.

  Next, a phenolic resin in which a resol type phenolic resin and a novolac type phenolic resin are mixed as a thermosetting resin so as to have a mass ratio of non-volatile content of 1: 1, and scaly graphite powder (average particle size 5 μm) as a carbon powder And methanol as a solvent, and these are mixed at a blending ratio of thermosetting resin (non-volatile content) / carbon powder / solvent = 10 parts by mass / 5 parts by mass / 85 parts by mass, and uniformly dispersed resin composition ( A mixed solution) was obtained.

  Next, the carbon fiber sheet was continuously immersed in the mixed solution of the resin composition, followed by a resin impregnation step in which the carbon fiber sheet was squeezed between rolls and then wound up into a roll shape to obtain a precursor fiber sheet. At this time, the roll is a smooth metal roll having a structure capable of removing excess resin composition with a doctor blade. Two rolls are horizontally arranged with a certain clearance, and the carbon fiber sheet is pulled up vertically. Thus, the adhesion amount of the entire resin composition was adjusted. By sandwiching one surface side of the short carbon fiber sheet with a metal roll and the other surface side with a gravure roll and squeezing the impregnating liquid of the resin composition, the resin composition on one surface and the other surface of the carbon fiber sheet The amount of adhesion was different. The adhesion amount of the phenol resin in the precursor fiber sheet was 104 parts by mass with respect to 100 parts by mass of the carbon fiber.

  The hot plate was set in a press molding machine so as to be parallel to each other, a spacer was disposed on the lower hot plate, and the resin-impregnated carbon fiber paper sandwiched between release papers from above and below was intermittently conveyed and compressed. In that case, the space | interval of an up-and-down press face plate was adjusted so that it might become the thickness of a desired precursor fiber sheet after a pressurization process.

  Moreover, the compression process was performed by repeating heating and pressurization, mold opening, and sending of carbon fiber, and it wound up in roll shape. It was 171 micrometers when the thickness in 0.15 MPa of the precursor fiber sheet after the pressurization process in a compression process was measured.

  The precursor fiber sheet subjected to the pressure treatment was introduced into a heating furnace having a maximum temperature of 2400 ° C. maintained in a nitrogen gas atmosphere, and passed through a carbonization step of firing while continuously running in the heating furnace. It was wound up in a roll shape to obtain a conductive porous substrate. The thickness of the obtained conductive porous substrate at 0.15 MPa was 129 μm.

  Kraft paper was placed on both sides of this conductive porous substrate, and calendering was performed continuously. Using a non-contact type dust removing cleaner on the calendered conductive porous substrate, air was blown onto both surfaces of the conductive porous substrate, and air was sucked from both surfaces.

<Evaluation>
A. The short-circuit probability conductive porous substrate has a measuring point of 90% or more when a short-circuit current density in the thickness direction is measured by applying a voltage of 2V while pressing a pressure of 5 MPa on a polymer electrolyte membrane having a thickness of 25 μm. It is preferable that a short circuit current density is 111 mA / cm < ² > or less. Here, the short-circuit probability defined in the present invention means a value specified by the following procedures (1) to (3).

  (1) The polymer electrolyte membrane “Nafion” (registered trademark) NR211 (manufactured by DuPont) is sandwiched on both sides by a conductive porous substrate with a film thickness of 25 μm. Here, the conductive porous substrate is a square having a side of 5 cm, the polymer electrolyte membrane is a square having a side of 6 cm or more, and each side of the polymer electrolyte membrane is parallel to each side of the conductive porous substrate. Then, the polymer electrolyte membrane is overlaid so that the center of the polymer electrolyte membrane coincides with the center of the conductive porous substrate.

(2) The stacked polymer electrolyte membrane and the conductive porous base material are sandwiched between two gold-plated stainless steel block electrodes (the surface to be sandwiched is a 3 cm square), and the conductive porous base material has an area of 9 cm ² . The pressure is increased to 5 MPa. At this time, each side of the surface sandwiched by the stainless steel block electrode and each side of the conductive porous substrate are parallel, and the stainless block electrode is sandwiched so that the center of the stainless steel block electrode coincides with the center of the conductive porous substrate.

(3) Using a digital multimeter (KEITHLEY Model196 SYSTEM DMM), apply a DC voltage of 2 V between the gold-plated stainless steel block electrodes, measure the current between the electrodes, and use the obtained value as the short-circuit current. The short-circuit current density is obtained by dividing the short-circuit current at an area of 9 cm ² where pressure is applied to the conductive porous substrate.

The short-circuit probability is obtained by the probability that the obtained value exceeds 111 mA / cm ² by changing the measurement sample of the conductive porous substrate and repeating (1) to (3) 10 times.

When the measured short-circuit current density exceeds 111 mA / cm ² , there is a possibility that a short circuit occurs in the polymer electrolyte membrane due to the protrusions such as carbon fibers protruding from the conductive porous substrate, and the long-term of the fuel cell It may cause a decrease in power generation performance under operation. Therefore, the conductive porous substrate of the present invention is preferably 111 mA / cm ² or less at a measurement point where the short-circuit current density measured by the above method is 90% or more.

B. Method for Measuring the Thickness of the Conductive Porous Base Material When producing the cross section of the conductive porous base material, an ion milling device IM4000 manufactured by Hitachi High-Technologies Corporation was used. The magnification of the SEM image was 200 times.

  The thickness of the conductive porous substrate was measured at five locations within the field of view of the SEM image, and the average value was taken as the thickness of the conductive porous substrate.

C. Measuring method of N1, N2, N3, and N4 The method of measuring the inclination of carbon fiber, that is, the measuring method of N1, N2, N3, and N4 is as follows. One carbon fiber when the cross section of the conductive porous substrate is observed in the same manner as described in B, the in-plane direction of the conductive porous substrate is 0 °, and the thickness direction is 90 ° Each angle was measured. It should be noted that the observation range when counting N1 and N2 was determined so that at least one surface of the conductive porous substrate was observed. On the other hand, when observing N3 and N4, the observation range is determined so that a portion entering 20% of the thickness of the conductive porous substrate from the surface of the conductive porous substrate is observed. did. Furthermore, when the carbon fiber is bent or bent, the angle of the line segment formed by connecting the ends of one carbon fiber with a straight line is defined as the angle of the carbon fiber.

  The number of carbon fibers facing in the direction of 0 ° or more and less than 10 ° in the region where at least one surface of the conductive porous substrate is observed, the region where at least one surface of the conductive porous substrate is observed The number of carbon fibers facing in the direction of 10 ° or more and 90 ° or less, and 0 ° or more in a portion that enters the inside of 20% of the thickness of the conductive porous substrate from the surface of the conductive porous substrate The number of carbon fibers facing in the direction of less than 10 °, and 10 ° or more and 90 ° in the portion that enters the length of 20% of the thickness of the conductive porous substrate from the surface of the conductive porous substrate The numbers of carbon fibers facing in the following directions were N1, N2, N3, and N4, respectively.

D. Method of measuring the minor axis of resin carbide chunks The minor axis of resin carbide chunks is to observe the cross section of the conductive porous substrate prepared in B, approximating each of the chunks as an ellipse. Obtained by measuring. The average value of the short diameter of each of the obtained resin carbide lumps was calculated, and the obtained value was defined as the short diameter of the resin carbide lumps.

E. Method of measuring cross-sectional area of conductive porous substrate The cross-sectional area of the conductive porous substrate was determined by observing the cross-section of the conductive porous substrate prepared in B and determining the average value of five locations. A value obtained by multiplying the thickness of the porous substrate by the width of the SEM image was taken as the cross-sectional area of the conductive porous substrate.

F. Method for Measuring Cross Section Area of Resin Carbide Mass The cross sectional area of the resin carbide mass was determined as follows. Using the image of the cross section used in E, first, image processing software (JTrim) is used to divide the maximum and minimum brightness by 256 levels, and the threshold is 1 when the resin carbide is black and the carbon fiber appears white. By subtracting the number of pixels of level 20 or less at the time of threshold 2 from the number of pixels of level 20 or less at the time of threshold 2 as threshold 2 at which both the resin carbide and carbon fiber appear white, the breakage of a plurality of masses of resin carbide The total area was determined. By dividing the total value of the cross-sectional areas by the number of masses of resin carbide, and further dividing by the value obtained by multiplying the thickness of the conductive porous substrate by the width of the SEM image, the section of the conductive porous substrate is cut. The ratio (%) of the cross-sectional area of the mass of resin carbide when the area was 100% was determined.

  Table 1 shows the measured physical properties.

(Example 2)
A conductive porous substrate was obtained in the same manner as in Example 1 except that the obtained conductive porous substrate was pressurized so that the thickness at 0.15 MPa was 136 μm. Table 1 shows the measured physical properties.

(Example 3)
A conductive porous substrate was obtained in the same manner as in Example 1 except that the obtained conductive porous substrate was pressurized so that the thickness at 0.15 MPa was 143 μm. Table 1 shows the measured physical properties.

(Comparative Example 1)
A conductive porous substrate was obtained in the same manner as in Example 1 except that the obtained conductive porous substrate was pressurized so that the thickness at 0.15 MPa was 161 μm. Table 1 shows the measured physical properties.

(Comparative Example 2)
A conductive porous substrate was obtained in the same manner as in Example 1 except that the obtained conductive porous substrate was pressurized so that the thickness at 0.15 MPa was 152 μm. Table 1 shows the measured physical properties.

Claims (7)

A conductive porous substrate comprising carbon fibers,
When the in-plane direction of the conductive porous substrate is 0 ° and the thickness direction is 90 °, the number of carbon fibers facing the direction of 0 ° to less than 10 ° is N1, 10 ° to 90 ° A conductive porous substrate, wherein N1 / N2 is 85/15 to 100/0, where N2 is the number of carbon fibers facing the direction.
Here, N1 and N2 are both integers of 0 to 100, and the sum of N1 and N2 is 100. In the carbon fibers existing inside the conductive porous substrate, the number of carbon fibers facing the direction of 0 ° or more and less than 10 ° is N3, and the number of carbon fibers facing the direction of 10 ° or more and 90 ° or less The conductive porous substrate according to claim 1, wherein N3 / N4 is 85/15 to 100/0, where N4 is a number.
Here, N3 and N4 are both integers of 0 or more and 100 or less, and the sum of N3 and N4 is 100. Including resin carbide,
The resin carbide consists of a plurality of lumps, and
3. The conductive material according to claim 1, wherein when the thickness of the conductive porous substrate is 100%, the minor axis of the mass of the resin carbide is 3% to 20%. 4. Porous substrate. A conductive porous substrate containing carbon fiber and resin carbide,
The resin carbide consists of a plurality of lumps, and
The conductive porous base material, wherein a short diameter of the mass of the resin carbide is 3% to 20% when the thickness of the conductive porous base material is 100%.   The conductive property according to claim 3 or 4, wherein a cross-sectional area of the mass of the resin carbide is 1% to 5% when a cross-sectional area of the conductive porous substrate is 100%. Porous substrate.   A gas diffusion electrode comprising a microporous layer on at least one surface of the conductive porous substrate according to claim 1.   A fuel cell comprising the conductive porous substrate according to claim 1.