JP2015159058A - Gas diffusion electrode base material and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas diffusion electrode base material for a fuel cell, excellent in conductivity and thermal conductivity and also capable of achieving both suppression of flooding due to drainage from a gas diffusion electrode, etc. and suppression of dry up by moisture retention of an ionomer of an electrolyte membrane and a catalyst layer, etc. at a high level.SOLUTION: In a gas diffusion electrode base material including a microporous layer disposed on one surface of an electrode base material, the electrode base material has a recessed part that does not penetrate to a surface of the electrode material where the microporous layer is not disposed, or a cavity at the inside thereof, and the microporous layer includes linear carbon.

Description

  The present invention relates to a gas diffusion electrode substrate suitably used for a fuel cell, particularly a polymer electrolyte fuel cell, and a fuel cell using the same.

  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 An electrode base material, a catalyst layer, an electrolyte membrane, a catalyst layer, a gas diffusion electrode base material, and a separator are laminated in order. The gas diffusion electrode base material has high in-plane direction gas diffusivity and high in-plane direction gas diffusivity for diffusing the gas supplied from the separator to the catalyst layer, and liquid water generated with electrochemical reaction High drainage for discharging (hereinafter referred to as generated water) to the separator and high conductivity for taking out the generated current are required, and electrode substrates made of carbon fiber or the like are widely used.

  In polymer electrolyte fuel cells, the generated water blocks the catalyst layer and gas diffusion electrode base material, so that hydrogen or air transport is prevented, so-called flooding occurs, and high power generation efficiency may not be obtained. is there. On the other hand, when the so-called dry-up occurs because the electrolyte membrane or the catalyst layer is not sufficiently humidified and the drying proceeds, high power generation efficiency cannot be obtained. In response to these problems, attempts have been made to improve water discharge by methods such as a method of water-repellent treatment with a fluororesin on the gas diffusion electrode substrate, a method of forming a microporous layer made of fluororesin and conductive particles on the gas diffusion electrode, etc. However, the effect is not sufficient and further improvement is required.

  For example, Patent Documents 1 and 2 disclose a technique that can smoothly discharge generated water through a hole by using carbon paper having a hole having an opening on the channel side as a gas diffusion electrode base material.

  In Patent Documents 2 and 3, the electrode substrate is formed with a non-through hole having a depth of 20 to 80% of the thickness by laser processing, so that the water content of the generated water and the ionomer of the electrolyte membrane and the catalyst layer are moisturized. A technique for achieving both is disclosed.

  Further, Patent Document 4 discloses an electrode base material having pores of 50 μm or more continuous in the planar direction from the viewpoint of improving gas diffusibility, although there is no description of suppression of flooding and the like.

  On the other hand, Patent Document 5 proposes a gas diffusion electrode base material in which a microporous layer made of carbon black and a water-repellent resin is formed on the catalyst layer side of the electrode base material. According to the fuel cell using this gas diffusion electrode substrate, since the microporous layer has water repellency, discharge of liquid water to the cathode side is suppressed, and flooding tends to be suppressed. Further, since the generated water is pushed back to the electrolyte membrane side (hereinafter referred to as reverse diffusion), the electrolyte membrane tends to be wet and dry-up is also suppressed.

  In Patent Document 6, in a gas diffusion electrode base material in which a microporous layer is formed on the catalyst layer side of the electrode base material, a void suitable for gas diffusion is formed in the microporous layer. Techniques for containing glassy carbon are disclosed.

  As described above, there are known techniques (Patent Documents 1 to 4 and 6) for improving the discharge of generated water and gas diffusibility through holes and voids, and a technique for reversely diffusing the generated water (Patent Document 5). The expected flooding and dry-up suppression and gas diffusibility improvement effects were not sufficient.

JP-A-8-111226 JP 2009-211928 A JP 2011-96385 A JP 2013-206704 A JP 2000-123842 A JP 2006-120506 A

  Patent Document 1 describes that a through hole is provided in the thickness direction of the electrode base material as a preferable aspect. Although this has the effect of suppressing flooding, the problem of dry-up due to drying of the ionomer of the electrolyte membrane and the catalyst layer remains. Moreover, the technique by non-through-hole and the space | gap formation currently disclosed by patent documents 2-4 has an effect which can control dry up rather than a through-hole, suppressing flooding.

  As a means for suppressing flooding and dry-up, a means for forming a microporous layer disclosed in Patent Document 5 is also effective.

  The inventors of the present invention have tried to investigate the formation of a microporous layer on an electrode base material in which non-through holes and voids are formed, which has hardly been studied so far. This study expected high flooding and dry-up suppression effects, but it was found difficult to achieve the expected effects. The present invention provides a gas diffusion electrode substrate in which a microporous layer is formed on an electrode substrate in which holes and voids are formed, and has a high flooding and dry-up suppression effect. Let it be an issue.

  In order to achieve the above object, the present invention provides a gas diffusion electrode base material in which a microporous layer is disposed on one side of an electrode base material, and the electrode base material includes a microporous layer of an electrode base material. It is a gas diffusion electrode base material having a non-penetrating recess on a non-penetrating surface or having a void inside and the microporous layer contains linear carbon.

  According to the present invention, it is excellent in conductivity and thermal conductivity, and at the same time achieves high humidification by achieving high levels of suppression of flooding due to drainage from gas diffusion electrodes, etc. and suppression of dry-up by ionomer moisturization of electrolyte membranes and catalyst layers. It is possible to provide a gas diffusion electrode substrate for fuel cells that can exhibit high power generation performance even under low humidification conditions.

<Gas diffusion electrode substrate>
In general, an electrode base material not provided with a microporous layer is often called a gas diffusion electrode base material. However, in the present invention, for the sake of distinction, for convenience, a base material without a microporous layer is simply referred to as an “electrode base material”. The electrode substrate provided with a microporous layer is referred to as a “gas diffusion electrode substrate”.

[Electrode substrate]
The electrode base material has high in-plane gas diffusivity for diffusing the gas supplied from the separator to the catalyst, gas diffusivity in the direction perpendicular to the surface, and discharges liquid water generated by the electrochemical reaction to the separator. It is necessary to have a high drainage property and high conductivity to take out the generated current.

  For this reason, as an electrode base material in the present invention, a carbon fiber woven fabric, a carbon fiber non-woven fabric, a porous body containing carbon fibers such as a carbon fiber paper body (so-called carbon paper), a fired sintered metal, a metal mesh, an expanded metal, etc. It is preferable to use a metal porous body, and it is preferable to use a porous body containing carbon fibers because of excellent corrosion resistance. Among these, a carbon fiber nonwoven fabric is preferable from the viewpoints of low cost, easy formation of recesses and voids, and the like.

  The substrate pore diameter of the porous body used for the electrode substrate in the present invention is preferably 35 μm or more, more preferably 40 μm or more, and further preferably 50 μm or more. Although an upper limit is not specifically limited, 100 micrometers or less are preferable and 80 micrometers or less are more preferable. When the substrate pore diameter is 35 μm or more, high performance can be obtained by gas diffusion and drainage even if a microporous layer is disposed. In particular, the tendency becomes remarkable at 40 μm or more. Moreover, if the substrate hole diameter is 100 μm or less, there is an advantage that dry-out is easily prevented. In the present invention, the substrate pore diameter is a value measured by a mercury intrusion method. This can be measured using, for example, PoreMaster (manufactured by Quantachrome), etc. In the present invention, the value calculated by assuming that the surface tension σ of mercury is 480 dyn / cm and the contact angle between mercury and the carbon fiber nonwoven fabric is 140 °. Use. The peak when the horizontal axis is the pore diameter (D) and the vertical axis is the volume difference (dV) is the substrate pore diameter.

  The electrode substrate in the present invention has a non-penetrating recess on the surface where the microporous layer is not disposed, or has a void inside the electrode substrate. Examples of the shape of the concave portion include a hole shape dispersed on the surface and a continuous groove shape, but are not particularly limited. It is preferable that it is a hole-shaped non-through-hole formed by dispersing on the surface. Non-penetrating means having an opening on one surface of the electrode substrate and not reaching the other surface. By setting it as a non-penetrating recessed part, dry-up can be suppressed more than the case where it penetrates.

  The non-penetrating recess preferably has an opening area larger than the substrate hole area of the electrode substrate. Here, the base material hole area of an electrode base material means the area of the circle | round | yen which makes the base material hole diameter of the electrode base material mentioned above a diameter. The opening area of the concave portion referred to in the present invention is the thickness of the electrode base material when the electrode base material is pressed at 1 MPa in the thickness direction in order to eliminate the influence of unevenness on the surface of the electrode base material (hereinafter simply referred to as “when pressurized” It may be referred to as “thickness.”) It means an opening area when it is assumed that the recess forming surface of the electrode base material is trimmed until the thickness becomes the same as the thickness. When pressed, the electrode base material cut to 2.5 cm x 2.5 cm is sandwiched between metal plates with a surface of 3 cm or more x 3 cm or more and a thickness of 1 cm or more, and a pressure of 1 MPa is applied to the electrode substrate. And ask. Moreover, the opening area of a recessed part can be calculated | required by observing an electrode base material with a laser microscope etc., and measuring the cross-sectional area of each recessed part in the height equivalent to thickness at the time of pressurization using a shape analysis application. .

The opening area of the recess, in order to ensure the drainage, preferably at 1000 .mu.m ² or more, and more preferably 2000 .mu.m ² or more. Moreover, it is preferable that it is 100 mm < ² > or less from a viewpoint of ensuring a contact area with a separator and giving sufficient electroconductivity and thermal conductivity, and it is more preferable that it is 1 mm < ² > or less.

  Examples of the cross-sectional shape when the recess is a non-through hole (cross-sectional shape when cut by a plane parallel to the electrode substrate surface) include a circle, an ellipse, a quadrangle, a triangle, a polygon, and a star. It is done.

  The vertical cross-sectional shape of the recess (the cross-sectional shape when cut by a plane perpendicular to the electrode substrate surface) is not particularly limited, and the diameter changes in the depth direction even if the diameter does not change in the depth direction. It may be a substantially trapezoidal shape, a substantially triangular shape, or a substantially arc shape. A reverse trapezoidal shape or an arcuate shape whose diameter decreases with increasing depth is preferable in that drainage efficiency can be improved. From the viewpoint of ease of hole formation, it is preferable that such a recess has an arcuate shape with a cross section in the depth direction being a first chord. That is, when the recess is a non-through hole, it is preferably a hole having a substantially spherical cross section.

  The depth of the recess is not particularly limited, but from the viewpoint of ensuring drainage, it is preferably 5% or more, more preferably 10% or more, with respect to the thickness when the electrode substrate is pressed. The absolute value of the depth of the recess is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more.

  The upper limit of the depth of the recess is not particularly limited and can be appropriately set according to the thickness of the electrode substrate. From the viewpoint of ensuring the strength of the electrode substrate and maintaining the uniformity of gas supply, the electrode substrate It is preferable that it is 80% or less with respect to the thickness at the time of pressurization, and it is more preferable that it is 50% or less. Further, since the fuel cell becomes large when the thickness of the electrode base material itself is increased, the electrode base material is preferably thin as long as it exhibits its function, and is generally about 50 μm to 500 μm. In the present invention, the thickness of the electrode substrate is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 140 μm or less. Moreover, it is more preferable that it is 60 micrometers or more, and it is still more preferable that it is 70 micrometers or more. When the thickness of the electrode substrate is 50 μm or more, gas diffusion in the in-plane direction is further improved even when a microporous layer is disposed, and gas can be more easily supplied to the catalyst under the ribs of the separator. The power generation performance is further improved at both low temperature and high temperature. Further, the mechanical strength of the electrode base material is further improved, and the electrolyte membrane and the catalyst layer can be supported more preferably. On the other hand, when the thickness of the electrode base material is 300 μm or less, the drainage path becomes shorter, so that the drainage performance is further improved, flooding can be further suppressed, and the conduction path is shortened, and the conductivity is further improved. The power generation performance is further improved at both high and low temperatures. In particular, the thickness is preferably 200 μm in that the effect that high performance can be obtained even when the microporous layer of the present invention is disposed. 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.

  The depth of the recess means the depth when it is assumed that the recess forming surface of the electrode base material has been trimmed to the thickness at the time of pressurization, similarly to the opening area. The depth of such a recess is observed with a laser microscope or the like, and is present on the opening surface side by a height corresponding to the thickness of the electrode substrate when pressed from the non-opening surface of the recess using a shape analysis application. Assuming a plane, it can be obtained by measuring the depth of the portion of the recess that is present on the non-opening surface side of the plane.

  The recessed part of the electrode base material in this invention exists in the surface in which the microporous layer is not arrange | positioned. And as above-mentioned, it is preferable that a recessed part is a non-through-hole, and it is preferable that a non-through-hole is disperse | distributed and formed in the electrode base-material surface. “Dispersed and formed” refers to a state in which a plurality of recesses are arranged on the surface of the electrode substrate without the peripheries of the openings contacting each other. The arrangement pattern of the recesses is not particularly limited, but is preferably formed so that the recesses are distributed substantially uniformly in the plane.

  The area ratio of the recesses with respect to the electrode substrate surface is preferably 1.5% to 60%. When the area ratio of the recesses is 1.5% or more, sufficient drainage can be ensured, and when it is 60% or less, the conductivity and thermal conductivity can be excellent. . The area ratio of the recesses is more preferably 3% or more, and more preferably 40% or less. Here, the area of a recessed part is an area at the time of assuming that the electrode base-material surface was trimmed to the thickness at the time of pressurization as above-mentioned. The area ratio of the recesses can be obtained by observing the recess forming surface of the electrode substrate with a laser microscope or the like, and dividing the total area of the recesses within a fixed visual field by the visual field area using a shape analysis application.

When the recesses are non-through holes, the number of recesses (non-through holes) per unit area is preferably 30 / cm ^{2 to} 5000 / cm ^{2, and} more preferably 100 / cm ^{2 to} 1500 / cm ² .

  Moreover, the electrode base material in this invention may have a space | gap inside an electrode base material instead of the above-mentioned non-penetrating recessed part. In this case, the average void diameter is preferably 20 μm or more, more preferably 30 μm or more, and further preferably 40 μm or more. When the average pore diameter is 20 μm or more, higher gas permeability can be expected. In particular, when a microporous layer is disposed, the effect is remarkable. The upper limit of the average void diameter is not particularly limited, but is preferably smaller than the thickness of the electrode substrate. Moreover, in order to improve electroconductivity, it is preferable that an average space | gap diameter is less than 600 micrometers, It is more preferable that it is 150 micrometers or less, It is further more preferable that it is 100 micrometers or less.

  Here, the value calculated | required with the following method was used for the average space | gap diameter. Using a microscope such as a scanning electron microscope, the gap in the cross section of the electrode substrate (in the direction perpendicular to the surface forming the surface) was enlarged 1000 times or more, and after taking a picture, 30 different locations were randomly selected. The diameter of the maximum inscribed circle of each void was measured by selecting the void, and the average value was obtained as the average void. As a scanning electron microscope, S-4800 manufactured by Hitachi, Ltd. or an equivalent thereof can be used.

  Moreover, in order to exhibit the effect more, it has a non-penetrating recessed part and may have a space | gap inside an electrode base material.

  Hereinafter, a case where a porous body containing carbon fiber is used as the electrode substrate will be described.

  Examples of the carbon fiber used for the porous body containing carbon fiber include polyacrylonitrile (PAN) -based, pitch-based, and rayon-based carbon fibers. Among 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 single fiber diameter of 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 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.

  The carbon fiber in the present invention can be appropriately changed depending on the structure of the porous body, but in the case of a papermaking body, the average length of the single fiber is preferably in the range of 3 to 100 mm, and in the range of 5 to 15 mm. More preferably. 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 fibers during papermaking is excellent, and a homogeneous electrode substrate is obtained, which is preferable. Moreover, in the case of a carbon fiber nonwoven fabric, it is preferable to exceed 20 mm, more preferably 50 mm or more, and further preferably 70 mm or more. By exceeding 20 mm, the strength can be improved by entanglement of the carbon fibers. Moreover, it is preferable that it is 150 mm or less, and it is more preferable that it is 100 mm or less. By setting it to 150 mm or less, a nonwoven fabric excellent in productivity can be obtained. The carbon fiber having such an average length is obtained by a method of cutting a continuous carbon fiber or a carbon fiber precursor to a desired length.

  Here, the average length of the carbon fiber is calculated based on the length of the cut fiber at the time of manufacture and converted into the fiber length of the fiber by converting the expansion and contraction in each process, or by using a microscope such as a scanning electron microscope. A photograph obtained by enlarging the fiber by 50 times or more, taking 30 different single fibers at random, measuring the length thereof, and calculating the average value thereof can be used. 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.

  Moreover, it is preferable that the porous body containing a carbon fiber, especially a carbon fiber nonwoven fabric, contains a carbon fiber having a curved portion with a curvature radius of 1 mm or less. In general, the conductivity and thermal conductivity of carbon fibers are superior in the fiber axis direction to the fiber cross-sectional direction. A fiber having a curved portion with a small radius of curvature has a long fiber length within a certain area, and can be expected to impart high conductivity and thermal conductivity to the electrode substrate. The electrode base material in the present invention preferably includes carbon fibers having a curved portion with a curvature radius of 500 μm or less, and more preferably includes carbon fibers having a curved portion with a curvature radius of 200 μm or less.

  The inclusion of such a carbon fiber having a curved portion can be confirmed by observing the carbon fiber on the surface of the electrode substrate. The radius of curvature of the carbon fiber can be obtained as the radius of the circumscribed circle of the three points by observing the carbon fiber on the surface of the carbon fiber nonwoven fabric with an optical microscope or an electron microscope, taking three arbitrary points at the curved portion of the carbon fiber. . In the present invention, when an area of 1.5 mm × 1.5 mm on the surface of the carbon fiber nonwoven fabric is observed with an optical microscope or an electron microscope, 10 or more carbon fibers having a curved portion with such a curvature radius can be confirmed. Preferably, 30 or more can be confirmed. Moreover, when an area of 1.5 mm × 1.5 mm on the surface of the carbon fiber nonwoven fabric is observed with an optical microscope or an electron microscope, and this field of view is divided into 25 regions of 0.3 mm × 0.3 mm, There are preferably 5 or more regions where the curved portion of the radius of curvature can be confirmed, and more preferably 10 or more.

  In an electrode base material composed of a porous body containing carbon fibers, if a carbide is attached as a binder to the contact points between the carbon fibers, the contact area becomes large at the contact points between the carbon fibers, and excellent conductivity and thermal conductivity. Can be obtained. Examples of a method for applying such a binder include a method in which a binder solution is impregnated or sprayed on a porous body after carbonization treatment, and the binder is carbonized by heat treatment again under an inert atmosphere. In this case, as the binder, a thermosetting resin such as a phenol resin, an epoxy resin, a melamine resin, or a furan resin can be used, and among them, the phenol resin is particularly preferable in terms of a high carbonization yield. Further, as described later, a method of blending a thermoplastic resin with a carbon fiber precursor nonwoven fabric or the like is also preferable. In order to improve the conductivity, carbon black or the like can be further added to the binder.

  Moreover, in the electrode base material which consists of a porous body containing a carbon fiber, it is preferable that at least one part carbon fiber is orientating in the height direction of a recessed part among the carbon fibers which comprise the wall surface in a recessed part. The carbon fiber constituting the wall surface of the recess is a carbon fiber in which at least a part of the fiber is exposed on the inner wall surface of the recess. And the said carbon fiber is orientating in the height direction of a recessed part, when a recessed part is divided into 3 equally in a height direction, carbon fiber is divided into two equal surfaces (a plane parallel to the electrode base-material surface). ) Means that it penetrates both.

  The presence of carbon fibers oriented in the height direction of the recess is observed by observing the surface of the electrode substrate with a laser microscope or the like, and using a shape analysis application to divide the divide plane into 1/3 depth of the recess and the recess This can be confirmed by observing the carbon fiber that crosses both the intersection line with the inner wall surface and the intersection line between each bisector of the 2/3 depth of the recess and the inner wall surface of the recess. In addition, an arbitrary cross section including the concave portion of the electrode substrate is observed with a scanning electron microscope or the like, and two straight lines parallel to the surface of the electrode substrate crossing the concave portion at positions 1/3 and 2/3 of the depth of the concave portion. This can also be confirmed by observing carbon fibers that intersect both of the two straight lines. Two or more such carbon fibers are preferably present in one recess, and more preferably five or more.

  In general, when the concave portion is formed, the contact area with the gas supply side member (for example, a separator) becomes smaller than when the concave portion is not formed, and the conductivity and thermal conductivity are lowered. However, since carbon fiber is superior in conductivity in the fiber axis direction and thermal conductivity than in the fiber cross-sectional direction, when carbon fibers constituting the wall surface of the recess are oriented in the height direction of the recess, The conductivity and thermal conductivity in the thickness direction of the electrode base material are improved, and the decrease in conductivity and thermal conductivity due to the formation of the recess can be compensated.

  Similarly, it is preferable that the carbon fiber penetrates all three equal surfaces when the concave portion is divided into four equal parts in the height direction, and the four equal surfaces when divided into five equal parts. More preferably, it penetrates all. It is preferable that at least some of the carbon fibers constituting the wall surface of the recess are continuous along the wall surface from the opening to the bottom of the recess.

  Moreover, it is preferable that the carbon fibers oriented in the height direction of the recesses are continuous to the bottom surface of the recesses because the effect of improving the conductivity and thermal conductivity in the height direction of the recesses is enhanced. That the carbon fiber is continuous to the bottom surface of the recess means that the tip of the carbon fiber constituting the wall surface of the recess is bent or curved, and at least a part of the carbon fiber is the bottom surface of the recess. Also refers to the state of being exposed. In addition, when a wall surface and a bottom face cannot be distinguished in a recessed part, such as when a recessed part is spherical, the deepest part of a recessed part is considered as a bottom face. When observing a cross section of the electrode base material, at least a part of the carbon fibers constituting one wall surface of the recess is continuous to the bottom surface of the recess and further configures another wall surface. Preferably it is. That is, it is preferable that the carbon fiber which comprises a wall surface in two places in a recessed part and continues to the bottom face exists.

  In the present invention, it is not necessary for all the carbon fibers constituting the wall surface of the recess to be oriented in the height direction of the recess, and such carbon fiber only needs to be present. Moreover, although it is preferable that such a carbon fiber can be confirmed in each recessed part, it does not make it out of the scope of the present invention that such a recessed part which cannot confirm a carbon fiber exists.

  Furthermore, in the electrode base material which consists of a porous body containing a carbon fiber, it is preferable that a fiber cross section is not observed in the peripheral part of a recessed part in planar view. In general, the electrode base material tends to have greater in-plane air permeability than thickness-direction air permeability. The presence of a fiber cross section at the peripheral edge of the recess means that electrical conductivity or heat conduction in the fiber axis direction cannot be expected at that portion. As described above, since carbon fibers have excellent electrical conductivity and thermal conductivity in the fiber axis direction, the fact that there is no fiber cross section can further improve these performances.

  It can be confirmed by observing the surface of the electrode substrate with an optical microscope, an electron microscope or the like that the fiber cross section is not observed at the peripheral edge of the recess. Here, it is most desirable that the fiber cross section is not observed in the peripheral portion of all the concave portions, but the number of fibers in which the fiber cross section is not observed in the peripheral portion of the concave portion is the number of fibers in which the fiber cross section is observed in the peripheral portion of the concave portion. It may be more than the number.

  The number of fibers in which the fiber cross section is not observed is preferably 70% or more of the fibers constituting the peripheral portion, more preferably 80% or more, and further preferably 90% or more.

When a porous body containing carbon fibers is used as the electrode substrate in the present invention, the basis weight is not particularly limited, but is preferably 10 g / m ² or more, and more preferably 20 g / m ² or more. By setting it as 10 g / m < ² > or more, electroconductivity can be improved, mechanical strength can improve, and the conveyance property in a manufacturing process, and the support property of an electrolyte membrane or a catalyst layer can be made favorable. On the other hand, it is preferably 120 g / m ² or less, more preferably 60 g / m ² or less. By setting it to 120 g / m ² or less, the gas diffusibility in the direction perpendicular to the surface of the electrode base material is further improved, and the gas diffusibility in the direction perpendicular to the surface of the obtained gas diffusion electrode base material is increased. The power generation performance is further improved at any low temperature. Here, the basis weight is obtained by dividing the weight by the area.

Moreover, it is preferable that an apparent density is 0.2-1.0 g / cm < ³ >. 0.3 to 0.9 g / cm ³ is more preferable, and 0.4 to 0.8 g / cm ³ is more preferable. By setting it to 0.2 g / cm ³ or more, the conductivity can be improved, and the structure is not easily destroyed by the pressure applied as the electrode substrate. Moreover, the permeability | transmittance of gas and a liquid can be improved by setting it as 1.0 g / cm < ³ > or less. Here, the apparent density is obtained by dividing the basis weight by the thickness.

  Hereinafter, the case where a carbon fiber nonwoven fabric is used as the electrode substrate will be described.

  For carbon fiber nonwoven fabrics, dry parallel laid or cross laid web, air laid web, extruded spunbond web, melt blow web, electrospinning web, etc. are used. , Etc. can be used.

In the carbon fiber nonwoven fabric, it is preferable that at least some of the carbon fibers are oriented in the thickness direction. As described above, the carbon fiber has higher conductivity in the fiber axis direction than the conductivity in the fiber cross-sectional direction, so that when the carbon fiber is oriented in the thickness direction, higher conductivity is obtained. Can do. In the carbon fiber nonwoven fabric, it is more preferable that at least a part of the carbon fiber is continuous from the surface to the other surface. “Continuous from one surface to the other” means that fiber cutting cannot be confirmed between one surface and the other surface, and is observed by cutting with an ion beam or razor, This can be confirmed by evaluating the fiber in the cross-sectional direction with a transmission image using the above. The carbon fiber is sufficient if at least a part of the fibers is continuous from one surface to the other surface. However, the higher the frequency of continuous fibers, the easier it is to obtain higher conductivity, so 1 mm when viewed from the surface. It is preferable that a plurality of fibers are continuous in a range of ² (1 mm × 1 mm), and it is more preferable that a plurality of fibers are continuous in a range of 0.1 mm ² (0.3 mm × 0.3 mm).

  Moreover, in a carbon fiber nonwoven fabric, it is preferable that at least some carbon fibers are entangled with each other. Whether or not they are entangled with each other and oriented in the thickness direction, as described above, cut and observe with an ion beam or razor, and evaluate the fiber in the cross-sectional direction with a transmission image using X-rays, etc. This can be confirmed. It should be noted that those in which the fibers are simply crossed, in contact with each other, or intertwined via other fibers are not included in the intertwined ones in the present invention.

[Microporous layer]
The gas diffusion electrode substrate of the present invention has a microporous layer disposed on one side of the electrode substrate. The microporous layer promotes the reverse diffusion of moisture into the electrolyte membrane and has a function of wetting the electrolyte membrane, so that it has an effect of suppressing dry-up.

  As described above, according to the study by the present inventors, when a microporous layer is formed on an electrode base material in which voids and holes are formed by a conventional method, a high level of expected suppression of flooding and dry-up is achieved. It has been found that a new problem arises that it is difficult to achieve both. There are several possible reasons for this, but it is also considered that one of the reasons is that the resin flows into the voids and pores during the formation of the microporous layer and tends to block them. However, this can be solved at once by including linear carbon in the microporous layer.

  In general, the carbon fiber has an average diameter of 3 μm or more and an average fiber length of 1 mm or more depending on the cut length. The linear carbon in the present invention is different from these general carbon fibers, for example, vapor-grown carbon fiber, single-walled carbon nanotube, double-walled carbon nanotube, multi-walled carbon nanotube, carbon nanohorn, carbon nanocoil, cup laminated type Examples thereof include linear carbon selected from the group consisting of carbon nanotubes, bamboo-like carbon nanotubes, and graphite nanofibers. Of these, a plurality of types of linear carbon may be used in combination. Among these, vapor-grown carbon fibers, single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes are suitable as linear carbon for use in the present invention because the aspect ratio can be increased and the electrical conductivity and mechanical properties are excellent. Can be mentioned. By using such linear carbon, penetration of the carbon coating liquid, which is a precursor of the microporous layer, into the electrode base material is moderately suppressed, and blockage of recesses and voids in the electrode base material is also suppressed. Directional gas diffusivity and drainage are considered to be improved. Therefore, it is possible to suppress flooding while suppressing dry-up.

  The average diameter of the linear carbon is preferably 0.1 to 1000 nm, and the average fiber length is preferably 1 to 1000 μm. Further, vapor grown carbon fibers having an average diameter of 5 to 200 nm and an average fiber length of 1 to 20 μm are particularly preferable.

  In the present invention, the linear carbon preferably has an aspect ratio of 30 to 5,000. By setting the aspect ratio of the linear carbon to 30 or more, it is possible to further suppress the penetration of the carbon coating liquid into the electrode base material and the blocking of the recesses and voids due to the entanglement of the linear carbon in the carbon coating liquid. be able to. On the other hand, by setting the aspect ratio of the linear carbon to 5000 or less, it is possible to suppress aggregation and sedimentation of the solid content in the carbon coating liquid and perform more stable production. In the present invention, the linear carbon has an aspect ratio of preferably 3000 or less, and more preferably 1000 or less. Further, the aspect ratio of the linear carbon is more preferably 35 or more, and further preferably 40 or more.

  Here, the aspect ratio of the linear carbon means average length (μm) / average diameter (μm). The average length is taken with a microscope such as a scanning electron microscope or a transmission electron microscope, taking a picture with a magnification of 1000 times or more, selecting 10 linear carbons at random, measuring the length, The average value is obtained. The average diameter is taken with a microscope such as a scanning electron microscope or a transmission electron microscope, and the photograph is taken at a magnification of 10,000 times or more, 10 different linear carbons are selected at random, the diameter is measured, and the average is measured. The value is obtained. As a scanning electron microscope, S-4800 manufactured by Hitachi, Ltd. or an equivalent thereof can be used.

  In the present invention, the average length of the linear carbon is preferably in the range of 0.1 to 30 μm, more preferably in the range of 1 to 20 μm, and further preferably in the range of 2 to 15 μm. preferable. In such a linear carbon, when the average length is 0.1 μm or more, the viscosity of the carbon coating liquid becomes higher, and the effect of suppressing the back-through, the depression, and the clogging of the voids is achieved. The gas diffusibility and drainage in the in-plane direction can be further improved, and flooding can be further suppressed.

  In the present invention, the microporous layer may further contain various carbon-based fillers other than linear carbon. Examples thereof include carbon black such as furnace black, acetylene black, lamp black and thermal black, scaly graphite, scaly graphite, earth graphite, artificial graphite, expanded graphite, flake graphite and the like.

  When carbon black is used as the carbon-based filler, the mixing mass ratio of carbon black to linear carbon is preferably in the range of 0.5 to 20, more preferably in the range of 1 to 19. More preferably, it is in the range of -10. When the mixing mass ratio is 0.5 or more, the porosity of the microporous layer containing linear carbon and carbon black becomes a more appropriate size, so that the water vapor diffusibility is smaller and the dry-up is further suppressed. Can do. When the mixing mass ratio is 20 or less, penetration of the carbon coating liquid, which is a precursor of the microporous layer, into the electrode base material is moderately suppressed due to the effect of blending the linear carbon having a specific aspect ratio. Since the gas diffusibility and drainage in the direction are improved, flooding can be suppressed, and furthermore, a microporous layer having a sufficient thickness is formed on the surface layer of the electrode base material, and the reverse diffusion of the generated water is promoted. , Dry up can be suppressed.

  In the present invention, from the viewpoint of promoting drainage of liquid water, the microporous layer preferably contains a water repellent material in combination with linear carbon. Among them, it is preferable to use a fluorine-based polymer as the water repellent material because of its excellent corrosion resistance. Examples of the fluorine-based polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

  The microporous layer can contain various other materials in combination with linear carbon from the viewpoint of promoting liquid water discharge and suppressing water vapor diffusion. For example, a disappearing material can be used for the purpose of increasing the pore size of the microporous layer and promoting drainage of liquid water. Here, the disappearing material is heated at 300 to 380 ° C. for 5 to 20 minutes to melt the water repellent material, and burns away when forming a microporous layer as a binder between linear carbons. Means a material that disappears and forms voids. Specific examples include particles such as polymethyl methacrylate and polystyrene, and fibers.

  In the present invention, the porosity of the microporous layer is preferably in the range of 60 to 85%, more preferably in the range of 65 to 80%, and further preferably in the range of 70 to 75%. preferable. When the porosity is 60% or more, drainage is further improved, and flooding can be further suppressed. When the porosity is 85% or less, water vapor diffusibility is smaller, and dry-up can be further suppressed. In addition, the conductivity is high, and the power generation performance is improved at both high and low temperatures.

  The microporous layer having such a porosity is obtained by adjusting the basis weight of the microporous layer, the water repellent material, the blending amount of the carbon-based filler with respect to other materials, the type of the carbon-based filler, and the thickness of the microporous layer in the manufacturing method described later. It is obtained by controlling. Among them, it is effective to control the blending amount of the carbon-based filler with respect to the water repellent material and other materials and the type of the carbon-based filler. Here, by increasing the blending amount of the carbon-based filler with respect to the water-repellent material and other materials, a microporous layer having a high porosity can be obtained, and by reducing the blending amount of the carbon-based filler with respect to the water-repellent material and other materials. A low porosity microporous layer is obtained.

  Here, the porosity of the microporous layer is measured by using a sample for cross-sectional observation using an ion beam cross-section processing apparatus, and taking a photograph with a microscope such as a scanning electron microscope with a cross-section magnified 1000 times or more. The area of the portion was measured, and the ratio of the area of the void portion to the observation area was obtained. As a scanning electron microscope, S-4800 manufactured by Hitachi, Ltd. or an equivalent thereof can be used.

The basis weight of the microporous layer is preferably in the range of 10 to 35 g / m ² . It is more preferably 30 g / m ² or less, and further preferably 25 g / m ² or less. Further, more preferably 14 g / ^{m 2} or more, more preferably 16g / ^{m 2} or more. When the basis weight of the microporous layer is 10 g / m ² or more, the surface of the electrode substrate can be covered more, the back diffusion of generated water is further promoted, and the dry-up can be further suppressed. In addition, when the basis weight of the microporous layer is 35 g / m ² or less, the clogging of the recesses and voids is suppressed, the drainage is further improved, and flooding can be further suppressed.

  Moreover, it is preferable that a part of microporous layer has impregnated the electrode base material from a viewpoint that the electrical resistance between a separator and a gas diffusion electrode base material can be reduced.

[Others]
Since the basis weight of the gas diffusion electrode substrate of the present invention is composed of the electrode substrate and the microporous layer described above, 20 to 155 g / m ² is a preferable range.

  In the present invention, the thickness of the gas diffusion electrode substrate is preferably 60 to 400 μm. It is more preferably 200 μm or less, and further preferably 150 μm or less. Moreover, it is more preferable that it is 70 micrometers or more, and it is further more preferable that it is 80 micrometers or more. When the thickness of the gas diffusion electrode substrate is 60 μm or more, in-plane gas diffusion is more preferable, and gas can be more easily supplied to the catalyst under the ribs of the separator. The power generation performance is further improved. On the other hand, when the thickness of the gas diffusion electrode base material is 400 μm or less, the effects of the recesses and voids can be exhibited more, drainage performance can be improved, flooding can be further suppressed, and the path for conduction can be shortened. The conductivity is further improved, and the power generation performance at high and low temperatures is further improved. A gas diffusion electrode substrate having such a thickness can be obtained by controlling the thickness of the electrode substrate and the thickness of the microporous layer. Here, the thickness of the gas diffusion electrode substrate can be determined using a micrometer in a state where the thickness is increased at a surface pressure of 0.15 MPa.

The gas permeation resistance in the direction perpendicular to the plane of the gas diffusion electrode of the present invention is preferably in the range of 15 to 190 mmAq, more preferably 180 mmAq or less, and even more preferably 170 mmAq or less. The gas permeation resistance in the perpendicular direction is used as an index of gas diffusivity in the perpendicular direction. The smaller the gas diffusion resistance in the perpendicular direction of the gas diffusion electrode substrate, the higher the gas diffusivity in the perpendicular direction. Moreover, it is more preferable that it is 25 mmAq or more, and it is further more preferable that it is 50 mmAq or more. When the surface gas diffusion resistance is 15 mmAq or more, water vapor diffusibility can be further reduced and dry-up can be further suppressed. Further, when the surface gas diffusion resistance is 190 mmAq or less, the gas diffusibility in the surface direction is further improved, and high power generation performance is more easily exhibited over a wide temperature range from low temperature to high temperature. The surface gas permeation resistance of the gas diffusion electrode substrate was determined by using a circular sample with a diameter of 4.7 cm cut out from the gas diffusion electrode substrate, and air was supplied from the surface on the microporous layer side to the opposite surface at 58 cc / min / cm. ^The differential pressure between the surface on the microporous layer side and the opposite surface when it was permeated at a flow rate of ² was measured with a differential pressure gauge to obtain a surface direct gas permeation resistance.

<Method for producing gas diffusion electrode substrate>
Next, as an example of the method for producing the gas diffusion electrode substrate, the membrane electrode assembly, and the fuel cell of the present invention, an example using a carbon fiber nonwoven fabric having a non-penetrating recess that is a preferred embodiment as the electrode substrate of the present invention will be described. To do.

[Carbon fiber nonwoven fabric]
The carbon fiber nonwoven fabric having a non-penetrating recess in the present invention includes, as an example, a step of pressing the surface of the carbon fiber precursor fiber nonwoven fabric to form a recess and a step of carbonizing the obtained carbon fiber precursor fiber nonwoven fabric. And can be manufactured by.

  The carbon fiber precursor fiber is a fiber that is carbonized by carbonization, and is preferably a fiber having a carbonization rate of 15% or more, and more preferably 30% or more. The carbon fiber precursor fiber used in the present invention is not particularly limited, but polyacrylonitrile (PAN) fiber, pitch fiber, lignin fiber, polyacetylene fiber, polyethylene fiber, and a fiber in which these are infusible, polyvinyl Examples include alcohol fibers, cellulose fibers, and polybenzoxazole fibers. Among them, it is particularly preferable to use a PAN-based flame resistant fiber in which PAN having high strength and high workability is infusible. The fiber may be infusibilized either before or after the production of the nonwoven fabric, but it is preferable to infusibilize the fibers before forming into a sheet because the infusibilization treatment can be easily controlled uniformly.

  The carbonization rate can be obtained from the following equation.

Carbonization rate (%) = weight after carbonization / weight before carbonization × 100
A carbon fiber precursor fiber nonwoven fabric is a web or sheet formed of carbon fiber precursor fibers. As the web, a dry parallel laid web or cross laid web, an airlaid web, a wet papermaking web, an extruded spunbond web, a melt blow web, and an electrospinning web can be used. Moreover, as a sheet | seat, the sheet | seat which mechanically entangled these webs, the sheet | seat heat-fused, the sheet | seat adhere | attached with the binder, etc. can be used. When the PAN-based fiber obtained by the solution spinning method is infusibilized to form a web, a uniform sheet is easily obtained, and therefore, a dry web or a wet web is preferable. A sheet in which a dry web is mechanically entangled is particularly preferable. The basis weight and apparent density of the electrode substrate can be adjusted by the amount of fibers used here.

  In order to impart high electrical conductivity and thermal conductivity to the carbon fiber nonwoven fabric after carbonization, the carbon fiber precursor fiber in the carbon fiber precursor fiber nonwoven fabric preferably includes a curved portion having a curvature radius of 1 mm or less. . The carbon fiber precursor fiber nonwoven fabric preferably has a curved portion with a radius of curvature of 500 μm or less, and more preferably has a curved portion with a radius of curvature of 200 μm or less. Specifically, when an area of 1.5 mm × 1.5 mm on the surface of the carbon fiber precursor fiber nonwoven fabric is observed with an optical microscope or an electron microscope, the carbon fiber precursor fiber having a curved portion with such a curvature radius is obtained. It is preferable that 10 or more can be confirmed, and more preferably 30 or more can be confirmed. In addition, when an area of 1.5 mm × 1.5 mm on the surface of the carbon fiber precursor fiber nonwoven fabric was observed with an optical microscope or an electron microscope, this field of view was divided into 25 regions of 0.3 mm × 0.3 mm. There are preferably 5 or more regions where a curved portion having such a radius of curvature can be confirmed, and more preferably 10 or more.

  As a method of obtaining a carbon fiber precursor fiber non-woven fabric including carbon fiber precursor fibers having a curved portion with a radius of curvature of 1 mm or less, carbon that has been crimped in advance with a push-in type (using a stuffing box) crimper or the like. A method of forming a nonwoven fabric using fiber precursor fibers and a method of forming a web with carbon fiber precursor fibers and then entangling and bending the fibers by a mechanical treatment such as needle punching or water jet punching. Can do. It is a more preferable method to use a carbon fiber precursor fiber nonwoven fabric further subjected to needle punching or water jet punching treatment to the web obtained by crimping.

  In addition, as described above, when the carbide adheres to the intersections between the carbon fibers of the carbon fiber nonwoven fabric, the carbon fiber precursor fiber nonwoven fabric preferably contains a binder because the conductivity and thermal conductivity are excellent. The method of including the binder in the carbon fiber precursor fiber nonwoven fabric is not particularly limited, but the carbon fiber precursor fiber nonwoven fabric is impregnated or sprayed with a binder solution, or the carbon fiber precursor fiber nonwoven fabric is made of a thermoplastic resin that serves as a binder in advance. A method of blending fibers is mentioned.

  When carbon fiber precursor fiber nonwoven fabric is impregnated or sprayed with binder solution, thermosetting resin such as phenol resin, epoxy resin, melamine resin, furan resin can be used as binder, and the carbonization yield is high. Resins are preferred. However, when impregnated with a binder resin solution, the difference in shrinkage behavior between the carbon fiber precursor fiber and the binder resin occurs in the carbonization process, and the smoothness of the carbon fiber nonwoven fabric tends to be reduced. Since a migration phenomenon in which the solution moves to the electrode substrate surface is also likely to occur, uniform processing tends to be difficult.

  On the other hand, the method of previously blending the fiber made of thermoplastic resin as a binder with the carbon fiber precursor fiber nonwoven fabric can make the ratio of the carbon fiber precursor fiber and the binder resin uniform in the nonwoven fabric, This is the most preferable method because the difference in shrinkage behavior between the fiber precursor fiber and the binder resin hardly occurs. Such thermoplastic resin fibers are preferably relatively inexpensive polyester fibers, polyamide fibers, and polyacrylonitrile fibers.

  The blending amount of the binder is preferably 0.5 parts by mass or more with respect to 100 parts by mass of the carbon fiber precursor fiber in order to improve the strength, conductivity, and thermal conductivity of the electrode substrate, and is 1 part by mass or more. It is more preferable that Moreover, it is preferable that it is 80 mass parts or less for drainage improvement, and it is more preferable that it is 50 mass parts or less.

  The binder can also be applied by impregnating or spraying a binder solution after forming a concave portion in the carbon fiber precursor fiber nonwoven fabric. Moreover, it can carry out also by passing through the process of impregnating or spraying a binder solution to the electrode base material after carbonizing, and carbonizing again. However, if a binder is applied after the formation of the recess, the binder solution tends to accumulate around the recess and the amount of adhesion tends to be non-uniform.

  It is more preferable from the viewpoint of improving the conductivity to add a conductive additive to the thermoplastic resin fibers used as a binder or a solution to be impregnated or sprayed. As such a conductive aid, carbon black, carbon nanotube, carbon nanofiber, milled fiber of carbon fiber, graphite, or the like can be used.

  As a means for forming the concave portion, it is preferable to form the concave portion on the surface of the carbon fiber precursor fiber nonwoven fabric by pressing or the like to obtain a carbon fiber precursor fiber nonwoven fabric having the concave portion. The recess can also be formed by performing laser processing or machining on the carbonized electrode base material, but it is inevitable that the carbon fiber is cut at the wall surface of the recess, so that the conductivity and thermal conductivity are further improved. In this respect, the above method is preferable.

  The pressing method is preferably a method that does not involve cutting of carbon fibers, and a method of pressing a shaping member having a convex portion corresponding to the concave portion, a method of pressing with a needle-like member, a method of pressing with water, or the like is used. Can do. The area of the concave portion of the final electrode substrate can be adjusted by the pattern of the convex portion, the water treatment area, and the like.

  Among these, a method of pressing a shaping member having a convex portion corresponding to the concave portion to be formed on the surface of the carbon fiber precursor fiber nonwoven fabric is preferable. In this method, a concave portion can be formed while preventing cutting of the carbon fiber precursor fiber by physically pushing a part of the surface of the carbon fiber precursor fiber nonwoven fabric with the shaping member. As a result, at least some of the carbon fiber precursor fibers constituting the wall surface of the recess are oriented in the height direction of the recess.

  More specific means are not particularly limited, but embossing is preferable, a method of continuously pressing with an embossing roll and a flat roll formed with a convex shape corresponding to the concave portion, or a batch with a plate and a flat plate with the same convex shape formed The method of pressing can be mentioned. At the time of pressing, it is preferable to use heated rolls and plates so that the shape is not restored (there is no recess) in the subsequent carbonization treatment. The heating temperature at this time is preferably 160 ° C. to 280 ° C., more preferably 180 ° C. to 260 ° C., from the viewpoint of the shape stability of the recess formed in the nonwoven fabric structure of carbon fiber precursor fibers.

  Moreover, in order to control the density and thickness of the electrode base material finally obtained, it is also a preferable aspect that the pressing with a roll or plate without a convex part is performed before or after forming the concave part, or both. .

In order to form the recess without causing fiber breakage, it is preferable to deform the carbon fiber precursor fiber nonwoven fabric having a relatively low density. Therefore, the carbon fiber precursor fiber nonwoven fabric before forming the recess has an apparent appearance. preferably a density of 0.02~0.20g / cm ^3, more preferably 0.05~0.15g / cm ^3.

Moreover, in order to set it as the preferable apparent density of the gas diffusion electrode base material of this invention, it is preferable that the apparent density of the carbon fiber precursor fiber nonwoven fabric before carbonization shall be 0.20-1.00 g / cm < ³ >. In order to control the apparent density of the carbon fiber precursor fiber nonwoven fabric, after forming the recesses, it can be adjusted by pressing with a flat roll or flat plate, but from the viewpoint of controlling the shape of the recesses, the recess portion It is preferable that the apparent density of the carbon fiber precursor fiber nonwoven fabric is 0.20 to 1.00 g / cm ³ by simultaneously pressing the entire carbon fiber precursor nonwoven fabric.

  The carbon fiber precursor fiber nonwoven fabric thus obtained is then carbonized. The method of carbonization is not particularly limited, and a known method in the carbon fiber material field can be used, but firing in an inert gas atmosphere is preferably used. Firing in an inert gas atmosphere is preferably performed at 800 ° C. or higher while supplying an inert gas such as nitrogen or argon. The firing temperature is preferably 1500 ° C. or higher and more preferably 1900 ° C. or higher in order to easily obtain excellent electrical conductivity and thermal conductivity. On the other hand, in view of the operating cost of the heating furnace, it is preferably 3000 ° C. or lower.

In addition, when the carbon fiber precursor nonwoven fabric is formed with the carbon fiber precursor fiber before infusibilization, it is preferable to infusibilize before carbonization treatment. Such an infusibilization step is usually performed in air in a processing time of 10 to 100 minutes and a temperature of 150 to 350 ° C. In the case of a PAN-based infusible fiber, the density is preferably set to be in the range of 1.30 to 1.50 g / cm ³ .

  As mentioned above, although an example of the manufacturing method in the case of using a carbon fiber nonwoven fabric as an electrode base material was shown, it can manufacture according to the above, applying a well-known method suitably also in another aspect. For example, in the case of a porous body made of carbon fibers having recesses, a method of producing a paper body or fabric made of a carbon fiber precursor by a known method and then carbonizing after forming the recesses, or carbon fiber papermaking Examples thereof include a method of producing a body, a nonwoven fabric, and a woven fabric and then forming a recess.

  In the present invention, the porous body is preferably subjected to water repellent treatment for the purpose of improving drainage. The water repellent process can be performed by applying a water repellent material to the porous body and heat-treating it. Here, as the water repellent material, it is preferable to use a fluorine-based polymer because of its excellent corrosion resistance. Examples of the fluorine-based polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). The application amount of the water repellent material 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 porous body. When the application amount of the water repellent material 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.

[Microporous layer]
A microporous layer can be formed by applying a carbon coating liquid containing linear carbon to one surface of the electrode base material obtained as described above.

  The carbon coating liquid 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. Moreover, you may contain various carbon-type fillers other than linear carbon, and a water repellent material.

  The coating of the carbon coating liquid onto the electrode substrate can be performed using various commercially available coating apparatuses. As the coating method, screen printing, rotary screen printing, spray spraying, intaglio printing, gravure printing, die coater coating, bar coating, blade coating and the like can be used. The coating methods exemplified above are only for illustrative purposes, and are not necessarily limited thereto.

  It is preferable to dry the coating liquid at a temperature of 80 to 120 ° C. after the carbon coating liquid is applied to the electrode substrate. 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.

  In this way, solids (carbon-based filler, water repellent material, surfactant, etc.) in the carbon coating liquid remain after drying to form a microporous layer.

[Membrane electrode assembly]
In this invention, a membrane electrode assembly can be comprised by joining the above-mentioned gas diffusion electrode base material to at least one side of a solid polymer electrolyte membrane having a catalyst layer on both sides. At that time, by arranging the microporous layer on the catalyst layer side, the back diffusion of the generated water is more likely to occur, and the contact area between the catalyst layer and the gas diffusion electrode substrate increases, reducing the contact electrical resistance. can do. In an electrode substrate having a non-penetrating recess on one surface or a void, and having a microporous layer on the other surface, it is possible to suppress flooding as well as dry-up.

〔Fuel cell〕
The fuel cell of the present invention has separators on both sides of the membrane assembly. That is, a fuel cell is constituted 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.

  The physical property values in the examples were measured by the following methods.

1. Structure of electrode substrate (1) Measurement was performed using a substrate pore diameter PoreMaster (manufactured by Quantachrome), and the surface tension σ of mercury was 480 dyn / cm, and the contact angle between mercury and the carbon fiber nonwoven fabric was 140 °. The peak when the horizontal axis is the pore diameter (D) and the vertical axis is the volume difference (dV) is the substrate pore diameter.

(2) Based on the cut fiber length at the time of manufacturing the fiber length, the fiber length of the fiber constituting the carbon fiber nonwoven fabric was calculated by converting the expansion and contraction in each step.

(3) Thickness and apparent density Ten specimens of 5 cm x 5 cm were collected according to JIS L1913 6.1 (thickness (Method A)), and fully automatic compression elasticity / thickness measuring instrument (Daiei Co., Ltd.) The thickness of each test piece after 10 seconds was measured under a pressure of 0.15 kPa using a model manufactured by Kagaku Seiki Seisakusho, model: CEH-400). And after calculating | requiring the average value of a measured value as thickness, it rounded off to the third decimal place from this thickness, a dimension (5 cm x 5 cm), and weight, and calculated | required the apparent density.

(4) Shape of concave portion The opening area and depth of the concave portion are observed with a laser microscope (VK-9710, manufactured by Keyence Corporation), and a shape analysis application (VK-Analyzer Plus, manufactured by Keyence Corporation) is used. It was measured. The measurement and analysis of the concavo-convex part is performed with a field of view of 1000 μm × 1400 μm, and a plane that exists on the opening surface side by a height corresponding to the thickness at the time of pressurization of the electrode substrate from the non-opening surface of the concave part is assumed, The average value of the cross-sectional areas of the recesses was defined as the opening area of the recesses, and the average value of the depths existing on the non-opening surface side from the plane was defined as the depth (absolute value) of the recesses. At this time, the height threshold value was the value of the electrode substrate thickness when pressurized at 1 MPa. Areas smaller than 1000 μm ² were ignored as minute regions. Moreover, the opening ratio was calculated | required as a percentage with respect to the area of an electrode base material of the sum total of the opening area of all the recessed parts.

(5) Orientation in the height direction of carbon fiber on the wall surface of the recess Whether the carbon fiber constituting the wall surface of the recess is oriented in the height direction of the recess is determined by a laser microscope (VK-9710, Inc. Observation by Keyence Co., Ltd., and determination was performed using a shape analysis application (VK-Analyzer Plus, Keyence Co., Ltd.). Observe the field of view of 1000 μm × 1400 μm, and cross both the line of intersection of the 1/3 depth divide surface and the inner wall surface of the recess, and the line of 2/3 depth divide surface and the wall surface of the recess. If even one carbon fiber was observed, it was judged that there was a fiber oriented in the height direction of the recess.

(6) Presence or absence of fiber cross-section to the peripheral edge of the non-through hole In the scanning electron microscope, among the 20 or more adjacent non-through holes, the fiber cross-section is not observed at the peripheral edge in the majority of the non-through holes, It was judged that there was no fiber cross section.

(7) Orientation in the height direction of the carbon fiber on the wall surface of the non-through hole Whether the carbon fiber constituting the wall surface of the non-through hole is oriented in the height direction of the non-through hole is determined by a laser microscope ( VK-9710 (manufactured by Keyence Co., Ltd.), and was determined using a shape analysis application (VK-Analyzer Plus, Keyence Co., Ltd.). Observe a field of view of 1000 μm × 1400 μm, intersect line between 1/3 depth of the non-through hole and the inner wall of the non-through hole, and 2/3 depth of the surface of the non-through hole and the inner wall of the non-through hole If even one carbon fiber crossing the crossing line is observed, it was judged that there was a fiber oriented in the height direction of the non-through hole.

(8) Average void diameter Using a scanning electron microscope (S-4800, manufactured by Hitachi, Ltd.), the void in the cross section of the electrode base material cut with an ion beam (in the direction perpendicular to the surface forming surface) is 1000 Next, 30 different voids were selected at random, and the diameter of the maximum inscribed circle of each void was measured, and the average value was taken as the average void hole.

(9) Number of carbon fibers having a curved portion with a curvature radius of 1 mm or less An area of 500 μm × 500 μm on the surface of the electrode substrate was observed with a scanning electron microscope. Three points were taken at the curved portion of the carbon fiber, and the radius of curvature of the curved portion was determined as the radius of the circumscribed circle at the three points. When 10 or more fibers having a curved portion with a radius of curvature of 1 mm or less were confirmed, the number was set to a large number. In addition, the smallest curvature radius among the curvature radii measured on the carbon fiber made into object was made into the curvature radius of the carbon fiber.

2. Power generation performance A catalyst layer (platinum amount 0.2 mg / cm ² ) made of platinum-supported carbon and “Nafion” is bonded to both sides of a fluorine-based electrolyte membrane “Nafion” 212 (manufactured by DuPont) by hot pressing to cover the catalyst layer An electrolyte membrane (CCM) was created.

  Two gas diffusion electrode substrates were placed on both sides of the CCM, and hot pressing was performed again to obtain a membrane electrode assembly (MEA). At this time, the gas diffusion electrode substrate was arranged so that the surface having the microporous layer was in contact with the catalyst side.

MEA in which a gasket (thickness 70 μm) was arranged around the gas diffusion electrode was set in a single cell (5 cm ² , serpentine flow path) manufactured by Electrochem.

(1) Voltage under humidification conditions The cell temperature is 60 ° C., the dew point of hydrogen and air is 60 ° C., the flow rates are 1000 cc / min and 2500 cc / min, respectively, the gas outlet is open (no pressure applied), and 0.6 A / Electric power was generated at a current density of cm ² , and the voltage at that time was the voltage under humidification conditions.

(2) Voltage under low humidification conditions The cell temperature is 90 ° C, the dew point of hydrogen and air is 60 ° C, the flow rates are 100 cc / min and 250 cc / min, respectively, and the gas outlet is open (no pressure), 0.6 A Electric power was generated at a current density of / cm ² , and the voltage at that time was defined as a voltage under low humidification conditions.

[Example 1]
After crimping the PAN-based flameproof yarn to a number average fiber length of 76 mm, it was formed into a sheet with a card and a cross layer, and then needle punching with a needle density of 300 / cm ² was performed to obtain a carbon fiber precursor fiber nonwoven fabric. .

  Cylindrical convex portions having a diameter of 150 μm and a height of 150 μm are dispersedly formed on one surface of the carbon fiber precursor fiber nonwoven fabric, and the pitch of the convex portions is 0.5 mm for both MD and CD. Embossing was performed using a metal embossing roll having a dot pattern in which the area ratio of the convex portion to the area was 3% and a metal flat roll. The heating temperature of the embossing roll and the flat roll was 220 ° C., and the linear pressure was 50 kN / m.

Thereafter, the temperature is raised from room temperature to 1500 ° C. over 3 hours in a nitrogen atmosphere and heated at 1500 ° C. for 15 minutes to perform carbonization treatment. The weight is 31 g / m ² having a recess ^{, the} thickness is 121 μm, the apparent density is 0.256 g. A carbon fiber nonwoven fabric of / cm ³ was obtained. When the surface was observed with a battery microscope, the carbon fibers were entangled with each other, and there was no fiber cross section at the periphery of the non-through holes. The carbonization rate determined from the weight change before and after the carbonization treatment was 52%.

  A PTFE resin aqueous dispersion (“Polyflon” (registered trademark) PTFE dispersion D-1E (manufactured by Daikin Industries, Ltd.)) is used for the carbon fiber nonwoven fabric, and PTFE is added to 95 parts by mass of the carbon fiber fired body. Mass parts were given.

Next, vapor-grown carbon fiber “VGCF” (registered trademark) (manufactured by Showa Denko Co., Ltd., average diameter: 0) is used as linear carbon on the smooth surface of the carbon fiber nonwoven fabric (the surface on which no recess is formed). .15 μm, average fiber length: 8 μm, aspect ratio: 50, a kind of linear carbon) 7.7% by weight and PTFE resin (“Polyflon” (registered trademark) PTFE Disperser which is an aqueous dispersion containing 60 parts by mass of PTFE resin) John D-1E (made by Daikin Industries, Ltd.) 2.5% by weight, surfactant “TRITON” (registered trademark) X-100 (made by Nacalai Tesque) 14.0% by weight, The mixture was applied using a slit die coater. After the carbon coating solution was applied, it was heated at 120 ° C. for 10 minutes and 380 ° C. for 10 minutes to form a microporous layer. In this way, a gas diffusion electrode substrate having a basis weight of 50 g / m ² , a thickness of 140 μm, and an apparent density of 0.357 g / cm ³ was obtained.

[Example 2]
In Example 1, instead of vapor grown carbon fiber “VGCF” (registered trademark), vapor grown carbon fiber “VGCF-S” (registered trademark) (manufactured by Showa Denko KK, average diameter: 0.10 μm, Average fiber length: 11 μm, aspect ratio: 110, a kind of linear carbon) 2.3 wt%, acetylene black “Denka Black” (registered trademark) (manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size: 0.035 μm) A gas diffusion electrode substrate was obtained in the same manner as in Example 1 except that 5.4% by weight was used.

[Example 3]
In Example 2, instead of vapor grown carbon fiber “VGCF-S” (registered trademark), multi-walled carbon nanotubes (manufactured by Cheap Tubes, average diameter: 0.015 μm, average fiber length: 20 μm, aspect ratio: 1300) The gas diffusion electrode base material was obtained in the same manner as in Example 2 except that it was a kind of linear carbon.

[Example 4]
A flame resistant yarn having a number average fiber length of 76 mm as in Example 1 and a nylon staple having a number average fiber length of 37 mm were mixed at a ratio of 80% by weight and 20% by weight, respectively, and then a card, a cross layer and a needle density of 300 / A cm ² needle punch was performed to obtain a carbon fiber precursor fiber nonwoven fabric. An electrode substrate was obtained in the same manner as in Example 1 except that the carbon fiber precursor fiber nonwoven fabric was used.

  Then, the gas diffusion electrode base material was obtained like Example 1 using the said electrode base material.

[Example 5]
A wet nonwoven fabric was obtained by a papermaking method using a PAN-based flame resistant fiber having a fiber length of 10 mm. The wet nonwoven fabric was embossed and carbonized in the same manner as in Example 1 to obtain a carbon fiber papermaking body. Subsequently, it was impregnated with 10% by weight of a phenol resin, pressed, and carbonized again. The carbon fiber papermaking body was subjected to water repellent treatment in the same manner as in Example 1 to obtain an electrode substrate.

  Then, the gas diffusion electrode base material was obtained like Example 1 using the said electrode base material.

[Example 6]
The carbon fiber precursor fiber nonwoven fabric obtained in the same manner as in Example 4 was irradiated with a YAG laser having a beam diameter of 100 μm, and both MD and CD were drilled at a frequency of one hole of 0.5 mm. Then, it carbonized by heating at 1500 degreeC for 15 minutes in nitrogen atmosphere, and obtained the electrode base material. The holes formed in the obtained electrode substrate were non-through holes, and the substrate hole diameter was 40 μm.

  Then, the gas diffusion electrode base material was obtained like Example 1 using the said electrode base material.

[Example 7]
A PET (polyethylene terephthalate) component having an intrinsic viscosity of 0.66 was spun and drawn to obtain 56 dtex 48 filament fibers. This was twisted by S twisting at 2400 T / m and steam set at 75 ° C. Similarly, a yarn that was twisted at 2400 T / m by Z twisting and steam-set at 75 ° C. was produced. S warp yarn and Z twist yarn are alternately arranged on the warp yarn, the S twist yarn is used for the weft yarn, the weave structure is plain weave, and a fabric is produced with a weave density of 93 × 64 / 2.54 cm. Thus, a woven fabric (fiber fabric) having a basis weight of 60 g / m ² was produced.

Next, the carbon fiber precursor fiber nonwoven fabric obtained by the same method as in Example 1 was laminated and needle punched (NP) from the direction of the carbon fiber precursor fiber nonwoven fabric so that the carbon fiber precursor fiber penetrated the fabric. And penetrated to the other surface. In this way, a composite sheet having an apparent density of 0.10 g / cm ³ was obtained. The obtained composite sheet was compressed with a press machine heated to 200 ° C. to give an apparent density of 0.50 g / cm ³ . Next, the temperature was raised to 1500 ° C. in a nitrogen atmosphere and fired (first carbonization) to obtain a PAN-based carbon fiber nonwoven fabric.

This PAN-based carbon fiber nonwoven fabric, respectively phenolic resin and ^{graphite, 40g / m 2, 15g /} m 2 was applied.

Again, in an electric furnace at 1500 ° C., carbonization treatment (second carbonization) was performed in an N ₂ atmosphere to obtain a carbon fiber nonwoven fabric. When the obtained carbon fiber nonwoven fabric was observed using X-ray CT, it was confirmed that the fibers constituting the dry web were continuous from one surface to the other surface. Further, it was confirmed that the fibers were entangled with each other and the fibers were oriented in the thickness direction. The obtained carbon fiber nonwoven fabric had a basis weight of 64 g / m ² , a thickness of 163 μm, an apparent density of 0.392 g / cm ³ , and an average pore diameter of 70 μm.

  The carbon fiber nonwoven fabric was used as an electrode base material to make a gas diffusion electrode base material in the same manner as in Example 1.

[Comparative Example 1]
In the same manner as in Example 4, a carbon fiber precursor fiber nonwoven fabric was obtained. An electrode substrate was obtained in the same manner as in Example 6 except that the obtained carbon fiber precursor fiber nonwoven fabric was irradiated with a YAG laser 10 times longer than that in Example 6. The hole formed in the obtained electrode base material was a through hole.

  Then, the gas diffusion electrode base material was obtained like Example 1 using the said electrode base material.

[Comparative Example 2]
In Example 1, instead of linear carbon, acetylene black “Denka Black” (registered trademark) (manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size: 0.035 μm, aspect ratio: 1, kind of carbon black) is 7 A gas diffusion electrode substrate was obtained in the same manner as in Example 1 except that the content was changed to 7% by weight.

[Comparative Example 3]
In Example 1, an electrode substrate was obtained in the same manner as in Example 1 except that the microporous layer was not formed. This electrode substrate was used as it was instead of the gas diffusion electrode substrate.

[Comparative Example 4]
A gas diffusion electrode substrate was obtained in the same manner as in Example 1 except that no recess was formed.

  Table 1 shows the structure of the base material of the gas diffusion electrode and the power generation performance of the fuel cell prepared in each example and comparative example.

Claims (8)

A gas diffusion electrode base material in which a microporous layer is disposed on one side of an electrode base material, wherein the electrode base material has a non-penetrating recess on a surface of the electrode base material on which the microporous layer is not disposed. Or a gas diffusion electrode substrate having voids inside and wherein the microporous layer contains linear carbon. The gas diffusion electrode substrate according to claim 1, wherein the non-penetrating recesses are non-penetrating holes formed in a dispersed manner. The gas diffusion electrode substrate according to claim 1 or 2, wherein an aspect ratio of the linear carbon is within a range of 30 to 5,000. The gas diffusion electrode substrate according to any one of claims 1 to 3, wherein the electrode substrate is made of a carbon fiber nonwoven fabric. The microporous layer having a basis weight is in the range of 10~35g / m ^2, gas diffusion electrode substrate according to any one of claims 1 to 4. The membrane electrode assembly containing the gas diffusion electrode base material in any one of Claims 1-5. A fuel cell comprising the gas diffusion electrode substrate according to any one of claims 1 to 5 or the membrane electrode assembly according to claim 6. A gas diffusion electrode substrate characterized in that a microporous layer is formed by applying a carbon coating liquid containing linear carbon to an electrode substrate having a non-penetrating recess on one side or having a void inside. Manufacturing method.