JP6357923B2 - Gas diffusion electrode, manufacturing method and manufacturing apparatus thereof - Google Patents

Description

  A fuel cell is a mechanism that electrically extracts the energy generated when water is produced by reacting hydrogen and oxygen, and is expected to be clean energy because it has high energy efficiency and only emits water. . TECHNICAL FIELD The present invention relates to a gas diffusion electrode used for a fuel cell, a method for manufacturing the same, and a manufacturing apparatus, and more particularly, to a gas diffusion electrode used for a polymer electrolyte fuel cell used as a power source for a fuel cell vehicle. The present invention relates to a manufacturing method and a manufacturing apparatus.

  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 fibers, 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, when the electrical load increases, that is, when 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 amount of gas (oxygen or hydrogen) supplied to the catalyst layer decreases, and finally When all the pores are blocked, power generation stops (this phenomenon is called flooding).

  In other words, in order to prevent the flooding from occurring as much as possible, the gas diffusion electrode is required to have drainage in order to increase the current value causing the 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). In order to impart water repellency to this microporous layer, it is known to contain a fluorine-based resin as a water repellent material (Patent Documents 1, 2, and 3). In addition to the above, the role of the microporous layer is to prevent the catalyst layer from penetrating into the gas diffusion electrode base material with a coarse mesh (Patent Document 4), and the roughness of the conductive porous base material to the electrolyte membrane There is a retouching effect to prevent transfer.

  Since the water repellent material preferably has as high a water repellency as possible, a fluorine-based resin is preferably used. Of these, PTFE, FEP, etc., which can obtain particularly high water repellency, are preferably used. These fluororesins are usually marketed in a dispersion state in which they are dispersed in a water-based dispersion medium with a surfactant. Water-based coating is also preferable from the viewpoint of reducing environmental burden.

  On the other hand, in a fuel cell for a fuel cell vehicle, power generation performance under high temperature operation conditions is also required. At high temperatures, the electrolyte membrane is likely to dry (this phenomenon is called dry-up), so that the ionic conductivity of the electrolyte membrane is reduced and the power generation performance is reduced.

  As a technique for preventing this dry-up, Patent Document 5 discloses that a second microporous layer having a lower porosity and a smaller thickness is further laminated on the surface of the microporous layer. A technique for suppressing water permeability by a porous layer is disclosed.

Japanese Patent No. 3382213 JP 2002-352807 A JP 2000-123842 A Japanese Patent No. 3773325 JP 2008-277093 A

  However, with the techniques disclosed in Patent Documents 1 to 4, it is difficult to achieve both flooding resistance and dry-up resistance. In Patent Document 5, the second microporous layer having a low porosity is used. It cannot be said that the conditions for sufficiently exhibiting the water vapor permeation suppressing effect have been studied, and a method for efficiently carrying out industrial mass production has not been studied. Therefore, with the technology disclosed in Patent Document 5, it has been difficult to obtain high performance in a wide temperature range as intended in applications that require a large output such as being mounted on a fuel cell vehicle. .

  The present invention overcomes the disadvantages of the prior art and provides a gas diffusion electrode that has both dry-up resistance and flooding resistance and has good power generation performance as a gas diffusion electrode. Is to provide a production method and a production apparatus capable of mass production at a low cost with high productivity.

In order to solve the above problems, the gas diffusion electrode of the present invention employs the following means. That is, a gas diffusion electrode used in a fuel cell in which a first microporous layer in contact with a conductive porous substrate and a second microporous layer are sequentially arranged on one side of the conductive porous substrate. The conductive porous substrate has a thickness of 150 μm or less, a porosity of 80% or more, a pore diameter of 10 μm or more and 100 μm or less, and a sliding angle of 40 ° or less.
The first microporous layer has a porosity of 70% or more and a pore diameter of 0.1 μm or more and less than 10 μm,
The second microporous layer has a thickness of 0.1 μm or more and 7 μm or less, a porosity of 40% or more and less than 70%, a pore diameter of less than 0.1 μm, and the total thickness of the microporous layer is 40 μm. The gas diffusion electrode is as follows.

In order to solve the above-mentioned problems, the gas diffusion electrode manufacturing method of the present invention employs the following means. That is, a gas diffusion electrode used in a fuel cell, in which a first microporous layer in contact with a conductive porous substrate and a second microporous layer are sequentially arranged on one side of the conductive porous substrate. A method of manufacturing, wherein a first microporous layer coating liquid having a viscosity of 5000 mPa · s to 20 Pa · s is applied to one side of a conductive porous substrate, and the first microporous layer coating liquid is applied After applying a second microporous layer coating liquid having a viscosity lower than that of the first microporous layer coating liquid and not more than 10 Pa · s without being substantially dried, the first microporous layer coating liquid and This is a method for manufacturing a gas diffusion electrode, in which the second microporous layer coating liquid is collectively dried to obtain a gas diffusion electrode.

  Furthermore, in order to solve the above problems, the gas diffusion electrode manufacturing apparatus of the present invention employs the following means. That is, a gas diffusion electrode used in a fuel cell, in which a first microporous layer in contact with a conductive porous substrate and a second microporous layer are sequentially arranged on one side of the conductive porous substrate. An apparatus for continuously manufacturing, a first unwinding machine for unwinding a long conductive porous substrate wound in a roll, and a conductive porous substrate unwound by an unwinding machine. A first coating machine for applying the microporous layer coating liquid, a second microporous layer on a conductive porous substrate which is coated with the first microporous layer coating liquid and which is not substantially dried A second coating machine, a first microporous layer coating liquid, and a second fine coating layer disposed on the same side of the substrate surface on which the first coating machine is disposed for applying the coating liquid. It consists of a dryer for drying the conductive porous substrate coated with the porous layer coating liquid, and a winder that winds up the resulting gas diffusion electrode. An apparatus for producing gas diffusion electrodes.

  By using the gas diffusion electrode of the present invention, it is possible to provide a fuel cell with high power generation performance in a wide temperature range because it has high gas diffusibility, good drainage, and can achieve both flood resistance and dry-up resistance. be able to.

  Further, by using the production method and production apparatus of the present invention, the gas diffusion electrode can be produced with high productivity, low loss and low cost.

Schematic which shows the structure of the gas diffusion electrode of this invention. The schematic arrangement figure showing the example of the desirable mode of the manufacture device of the gas diffusion electrode in the present invention. The schematic arrangement | positioning figure which shows another preferable example of a manufacturing apparatus of the gas diffusion electrode in this invention. The schematic arrangement drawing of the water-repellent treatment apparatus used in the Example and the comparative example.

  In the gas diffusion electrode of the present invention, a first microporous layer in contact with the conductive porous substrate and a second microporous layer are sequentially arranged on one side of the conductive porous substrate.

  First, the conductive porous substrate will be described. As the electrode substrate, a conductive porous substrate is used. Usually, a fluororesin is applied to the conductive porous substrate to form an electrode substrate.

  In a polymer electrolyte fuel cell, the gas diffusion electrode has a high gas diffusibility for diffusing the gas supplied from the separator to the catalyst, and a high drainage for discharging the water generated by the electrochemical reaction to the separator. In order to take out the generated electric current, high conductivity is required. For this reason, as the gas diffusion electrode, a conductive porous substrate, which is a substrate made of a porous body having conductivity and an average pore diameter of usually 10 μm or more and 100 μm or less, is used as an electrode substrate. The pore size can be determined by measuring the pore size distribution with a mercury porosimeter. The pore diameter of the conductive porous substrate may be measured directly using the conductive porous substrate, or may be measured using a gas diffusion electrode. Using a gas diffusion electrode, each layer structure is confirmed by scanning electron microscope (SEM) observation of a cross section of the gas diffusion electrode, and the diameter of the pore part of the SEM image is roughly determined. By determining the pore diameter of each layer in correspondence with the pore diameter peak, the pore diameter of the conductive porous substrate, the pore diameter of the first microporous layer, and the pore diameter of the second microporous layer can be efficiently obtained. it can.

  Specific examples of the conductive porous substrate include, 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, and firing and firing. It is preferable to use a porous metal substrate such as a bonded 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 base material obtained by binding a carbon fiber papermaking body with a carbide, that is, carbon paper.

  In the present invention, the porosity of the conductive porous substrate is set to 80% or more, preferably 85% or more in order to enhance the gas diffusibility of the gas diffusion electrode and enhance the power generation performance of the fuel cell as much as possible. The upper limit of the porosity is about 95% as the limit that the porous substrate can maintain its structure.

  About the porosity of a base material, the plane cross section of the thickness direction is cut out with an ion milling apparatus (IM4000 type | mold by Hitachi High-Technologies Corporation and its equivalent), and it observes with a scanning electron microscope (SEM). It can be defined by binarizing the void portion and the non-void portion in contact with the cross section and setting the area ratio of the area of the void portion to the entire area as the void ratio (%). The porosity of the conductive porous substrate may be measured directly using the conductive porous substrate, or may be measured using a gas diffusion electrode. If a porosity is measured for each region of the conductive porous substrate, the first microporous layer, and the second microporous layer in the cross section of the gas diffusion electrode, the conductive porous substrate , The porosity of the first microporous layer, and the porosity of the second microporous layer can be obtained efficiently.

  Moreover, since gas diffusibility can also be improved by reducing the thickness of the conductive porous substrate, the thickness is set to 150 μm or less. The thickness is preferably 120 μm or less, but if it is too thin, the mechanical strength becomes weak and handling in the manufacturing process becomes difficult, so 70 μm is usually the lower limit.

  In order to efficiently manufacture a gas diffusion electrode using such a base material, the material in a state in which such a base material is wound in a long length is unwound and continuously processed until it is wound up. It is preferable.

  In the present invention, the electrode substrate is usually formed by applying a water-repellent treatment to a conductive porous substrate by applying a fluororesin. The fluororesin acts as a water repellent material. Examples of fluororesins include PTFE (polytetrafluoroethylene) (for example, “Teflon” (registered trademark)), FEP (tetrafluoroethylene hexafluoropropylene copolymer), PFA (perfluoroalkoxy fluororesin), ETFA (ethylene Examples thereof include tetrafluoroethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), and the like, and PTFE or FEP expressing strong water repellency is preferable.

  The amount of the water repellent material is not particularly limited, but is suitably about 0.1% by mass or more and 20% by mass or less with respect to the conductive porous substrate. If the amount is less than 0.1% by mass, the water repellency is not sufficiently exhibited. If the amount exceeds 20% by mass, pores serving as gas diffusion paths or drainage paths may be blocked, or electrical resistance may be increased. .

  In the present invention, the sliding angle of the conductive porous substrate needs to be 70 ° or less, for example, by water repellent treatment. This sliding angle is an index of water repellency, and if it seems to exceed 70 °, it is an operating condition in which the fuel cell generates power at a high output at a low temperature (corresponding to a case where a fuel cell vehicle is started). There is a possibility that the condensed water generated inside the battery cannot be sufficiently drained and high output cannot be obtained. The sliding angle is preferably 50 ° or less, more preferably 40 ° or less. The sliding angle is measured using the sliding angle measurement mode of the automatic contact angle meter DM501 manufactured by Kyowa Interface Science Co., Ltd. or its equivalent, and a predetermined amount (for example, 10 μl) of water drops is dropped on the equipment placed on a horizontal stage. It can be evaluated by increasing the inclination of the stage in a stepwise manner from the horizontal state and measuring the angle at which the water droplet slides.

  As a method for the water repellent treatment, a coating technique such as die coating and spray coating can be applied in addition to a treatment technique of immersing in a generally known water repellent dispersion. Further, processing by a dry process such as sputtering of a fluororesin can also be applied. However, in order to keep the sliding angle below 70 °, it is necessary to uniformly disperse the water-repellent material inside the conductive porous substrate. For this purpose, the application of a water-repellent material dispersion by die coating and the repellent property by spraying are required. It is desirable to apply a water material dispersion or to coat the water repellent material by sputtering. In addition, you may add a drying process and also a sintering process as needed after water-repellent treatment.

  Next, the microporous layer will be described. In the present invention, the microporous layer is disposed on one side of the conductive porous substrate. At that time, the first microporous layer in contact with the conductive porous substrate and the second microporous layer in this order. Laminate and place. First, common items for the microporous layer will be described.

  The microporous layer comprises conductive fine particles such as carbon black, carbon nanotubes, carbon nanofibers, chopped fibers of carbon fibers, graphene, and graphite. As the carbon black, acetylene black is preferably used because it has few impurities and hardly reduces the activity of the catalyst. In addition, the microporous layer has characteristics such as conductivity, gas diffusivity, water drainage, moisture retention, and thermal conductivity, as well as strong acid resistance on the anode side inside the fuel cell and oxidation resistance on the cathode side. Therefore, the microporous layer preferably contains a water-repellent resin such as a fluororesin in addition to the conductive fine particles. Examples of the fluororesin used for the microporous layer include PTFE, FEP, PFA, ETFA, and the like, similar to the fluororesin used for the electrode substrate. PTFE or FEP is preferred because of its particularly high water repellency.

  In order to provide a microporous layer on a gas diffusion electrode, it is common to apply a coating liquid for forming a microporous layer on the electrode substrate, that is, a microporous layer coating liquid. The microporous layer coating liquid usually comprises the above-mentioned conductive fine particles and a dispersion medium such as water or alcohol, and a surfactant or the like is often blended as a dispersant for dispersing the conductive fine particles. In addition, when the water repellent resin is included in the microporous layer, it is preferable to add a water repellent resin to the microporous layer coating liquid in advance.

  The concentration of the conductive fine particles in the microporous layer coating solution is preferably 5% by mass or more, more preferably 10% by mass or more from the viewpoint of productivity. There is no upper limit for the concentration if the viscosity, dispersion stability of the conductive particles, applicability of the coating liquid, etc. are appropriate, but in practice, if it exceeds 50% by mass, the suitability as a coating liquid may be impaired. . In particular, when acetylene black is used as the conductive fine particles, the upper limit is about 25% by mass in the case of an aqueous coating liquid in the study by the present inventors. When the concentration exceeds this, the acetylene blacks reaggregate. In other words, so-called percolation occurs, and the applicability of the coating liquid is impaired due to a sudden increase in viscosity.

  The role of the microporous layer is as follows: (1) protection of the catalyst, (2) re-dressing effect that prevents the surface of the rough conductive porous substrate from being transferred to the electrolyte membrane, and (3) water vapor generated at the cathode. This is an effect of preventing condensation. Among the above, a certain amount of thickness is required in order to exhibit the retouching effect.

  In the present invention, at least the first microporous layer and the second microporous layer are included as the microporous layer, but the total thickness of the microporous layer is that of the current conductive porous substrate. Considering the roughness, it is necessary that the dry film thickness is 10 μm or more and less than 60 μm. When the total thickness of the microporous layer is less than 10 μm, the above-described re-dressing effect is insufficient, and when it is 60 μm or more, the gas diffusibility (permeability) of the gas diffusion electrode itself decreases or the electrical resistance increases. From the viewpoint of increasing gas diffusibility or decreasing electric resistance, it is preferably 50 μm or less, more preferably 40 μm or less.

  The total thickness of the microporous layer referred to here is the total thickness of the microporous layer on one side of the conductive porous substrate on which the first microporous layer and the second microporous layer are arranged. Okay, even when the microporous layer is arranged on both sides of the conductive porous substrate, only on one side of the conductive porous substrate on which the first microporous layer and the second microporous layer are arranged Intended for microporous layers.

  The thickness of the substrate (gas diffusion electrode or conductive porous substrate) can be obtained by measuring using a micrometer or the like while applying a load of 0.15 MPa to the substrate. The thickness of the microporous layer can be determined by subtracting the thickness of the conductive porous substrate from the thickness of the gas diffusion electrode. Further, regarding the thickness of the second microporous layer, as shown in FIG. 1, when the second microporous layer is applied on the conductive porous substrate on which the first microporous layer is applied, The difference between the portion where the second microporous layer is applied and the portion where the second microporous layer is not applied can be the thickness of the second microporous layer.

  In the case of obtaining the thickness of each layer in the state of the gas diffusion electrode in which the conductive porous substrate, the first microporous layer, and the second microporous layer are laminated, IM4000 manufactured by Hitachi High-Technologies Corporation, etc. The gas diffusion electrode is cut in the thickness direction by using an ion milling apparatus, and a method of calculating a surface cross section from an SEM image observed with a scanning electron microscope (SEM) can be employed.

  As described above, the microporous layer coating liquid is usually prepared by dispersing conductive fine particles in a dispersion medium (water in the case of an aqueous system) using a dispersant. In order to disperse the conductive fine particles, a dispersant may be added in an amount of 0.1 to 5% by weight based on the content of the conductive fine particles. However, in order to stabilize this dispersion for a long time to prevent the increase in the viscosity of the coating liquid and prevent the liquid from separating, it is effective to increase the amount of the dispersant added.

  Further, as described above, when the total thickness of the microporous layer is 10 μm or more with a dry coating film, it is preferable to keep the viscosity of the coating liquid at least 1000 mPa · s or more. When the viscosity is lower than this, the coating liquid flows on the surface of the electrode base material, and the coating liquid flows into the pores of the conductive porous base material to cause back-through. On the contrary, if the viscosity is too high, the applicability deteriorates, so the upper limit is about 25 Pa · s. A preferable viscosity range is 3000 mPa · s or more and 20 Pa · s or less, and more preferably 5000 mPa · s or more and 15 Pa · s or less. In the present invention, after forming the first microporous layer, the second microporous layer is then applied to form the second microporous layer. In this case, the second microporous layer is applied. The viscosity of the liquid is even lower and is desirably 10 Pa · s or less.

  In order to keep the viscosity of the coating liquid at a high viscosity as described above, it is effective to add a thickener.

  The thickener used here may be a well-known one. For example, methyl cellulose, polyethylene glycol, polyvinyl alcohol and the like are preferably used.

  These dispersants and thickeners may have two functions for the same substance, and materials suitable for the respective functions may be selected. However, when the thickener and the dispersant are separately selected, it is necessary to select one that does not break the dispersion system of the conductive fine particles and the dispersion system of the fluororesin that is the water repellent material. The dispersant and the thickener are collectively referred to as a surfactant herein. In the scope of the present invention, the total amount of the surfactant is preferably 50% by mass or more, more preferably 100% by mass or more, and further preferably 200% by mass or more of the added mass of the conductive fine particles. The upper limit of the addition amount of the surfactant is usually 500% by mass or less of the addition mass of the conductive fine particles, and if it exceeds this, a large amount of vapor or decomposition gas is generated in the subsequent sintering process, which is safety. , May reduce productivity.

  Application of the microporous layer coating liquid to 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, comma coater coating, etc. can be used. Die coater coating is preferred because the amount of coating can be quantified regardless of the surface roughness of the material. In addition, when a gas diffusion electrode is incorporated in a fuel cell, a blade coater or a comma coater is preferably used in order to obtain smoothness of the coated surface in order to improve adhesion with the catalyst layer. The coating methods exemplified above are only for illustrative purposes, and are not necessarily limited thereto.

  After applying the microporous layer coating liquid, the dispersion medium of the coating liquid (water in the case of an aqueous system) is removed by drying as necessary. In the case of an aqueous system, the drying temperature is preferably from room temperature (around 20 ° C.) to 150 ° C. or less, more preferably from 60 ° C. to 120 ° C. The dispersion medium (for example, water) may be dried all at once in the subsequent sintering step.

  After applying the microporous layer coating liquid, sintering may be performed for the purpose of removing the surfactant used in the microporous layer coating liquid and for binding the conductive fine particles by once dissolving the water-repellent resin. It is common.

  The sintering temperature is preferably 250 ° C. or more and 400 ° C. or less, although it depends on the boiling point or decomposition temperature of the added surfactant. If the sintering temperature is less than 250 ° C., the removal of the surfactant cannot be sufficiently achieved, or it takes an enormous time to completely remove the surfactant, and if it exceeds 400 ° C., the water-repellent resin may be decomposed. is there.

  The sintering time is as short as possible from the viewpoint of productivity, preferably within 20 minutes, more preferably within 10 minutes, and even more preferably within 5 minutes. Steam and degradable organisms are generated abruptly, and there is a danger of ignition if performed in the atmosphere.

  The sintering temperature and time also affect the sliding angle, which is the index of water repellency of the conductive porous substrate described above, so it is optimal in view of the melting point or decomposition temperature of the water-repellent resin and the decomposition temperature of the surfactant. Select the correct temperature and time. The drying and sintering may be performed after the application of the first microporous layer coating solution and after the application of the second microporous layer coating solution, respectively. It is preferable to carry out all at once after the application of the porous layer coating liquid and the second microporous layer coating liquid.

  In the present invention, at least two layers of the microporous layer provided on the conductive porous substrate are laminated on at least one surface of the conductive porous substrate. The microporous layer in contact with the conductive porous substrate is the first microporous layer, and the microporous layer laminated outside the first microporous layer when viewed from the conductive porous substrate side is the second microporous layer. This is called a layer.

  The microporous layer will be described in detail with reference to FIG.

  The first microporous layer 201 is provided by directly applying a first microporous layer coating liquid, which is a coating liquid for forming the first microporous layer, to the electrode substrate. The first microporous layer is required to have a high porosity and a relatively large pore diameter in order to improve gas diffusion and drainage. Specifically, the porosity needs to be 70% or more, preferably 75% or more. The higher the porosity, the better. However, the upper limit for maintaining the structure of the microporous layer when incorporated in a fuel cell is about 95%. The pore diameter can be defined by the peak value of the distribution in the mercury porosimeter, and 0.1 μm or more is required to make the gas diffusibility high. However, if it becomes larger than the pore diameter of the conductive porous substrate, water vapor is condensed inside the first microporous layer, and water droplets may be generated to inhibit gas diffusion. To do.

  The thickness of the first microporous layer may be set to be 10 μm or more as the total thickness of the microporous layer in order to express the effect of retouching the roughness of the conductive porous substrate. The thickness of the first microporous layer alone is preferably 9.9 μm or more, more preferably 10 μm or more. However, even if a second microporous layer having a low porosity, which will be described later, is laminated thereon, the thickness of the first microporous layer needs to be less than 50 μm because of the need to ensure gas diffusibility.

  The second microporous layer 202 is a second microporous layer that is a coating liquid for forming the second microporous layer outside the first microporous layer when viewed from the conductive porous substrate side. It is formed by applying a coating liquid. When the microporous layer is composed of only the first microporous layer and the second microporous layer, the second microporous layer coating solution is applied to the surface of the first microporous layer. The role of the second microporous layer is to contact the catalyst layer when it is incorporated in the fuel cell, to suppress the permeation of moisture (water vapor) generated in the catalyst layer at the cathode, and from the cathode side to the anode side at the anode. It is to prevent the potential modifying film from drying (drying up) by suppressing the permeation of moisture that is back-diffused. For this reason, the porosity of the second microporous layer is smaller than that of the first microporous layer and needs to be less than 70%, and it should be 40% or more from the viewpoint of not reducing the gas diffusibility. is necessary. The pore diameter of the second microporous layer is also smaller than that of the first microporous layer and is less than 0.1 μm, preferably 0.09 μm or less, more preferably 0.08 μm or less. The thickness of the second microporous layer needs to be 0.1 μm or more and 10 μm or less. If the thickness of the second microporous layer is less than 0.1 μm, the effect of suppressing the permeation of water vapor cannot be obtained, and if it exceeds 10 μm, the gas diffusibility is lowered. Preferably, it is 7 μm or less, more preferably 5 μm or less.

  Regarding the control of the porosity of the first microporous layer, the ratio of the longest diameter to the shortest diameter is adjusted as the conductive fine particles, which adjust the dispersion degree of the conductive fine particles blended in the first microporous layer coating liquid, ie, It is possible to increase the porosity by using a non-spherical material having a high aspect ratio, or by adding a substance that evaporates or decomposes during drying or sintering. Here, the value of the aspect ratio is preferably 30 to 5000, and more preferably 40 to 1000. Examples of conductive fine particles having a high aspect ratio include vapor-grown carbon fibers (such as “VGCF” (registered trademark) and “VGCF-S” (registered trademark) manufactured by Showa Denko KK) and carbon nanotubes. In the second microporous layer, a fine coating film is formed by adjusting the degree of dispersion of the conductive fine particles blended in the second microporous layer coating solution, or a conductive fine particle having a small particle diameter is used. Thus, a dense coating film having a low porosity is formed. When carbon black is used as the conductive fine particles, it cannot be dispersed up to the primary particle size, and therefore the porosity of the coating film is lowered depending on how fine the secondary particle size (the size in which particles are aggregated to some extent) can be dispersed.

  As described above, the basic form of the present invention is that the first microporous layer is formed on the conductive porous substrate (thickness 150 μm or less, pore diameter 10 μm to 100 μm, porosity 80% or more, sliding angle 70 ° or less). (Thickness less than 50 μm, pore diameter 0.1 μm or more and less than 10 μm, porosity 70% or more) and second microporous layer (thickness 0.1 μm or more and 10 μm or less, pore diameter less than 0.1 μm, porosity 40% or more 70% Less than) in this order, and the thickness of the entire microporous layer on one side of the conductive porous substrate (when the microporous layer consists of only two layers, the first microporous layer and the second microporous layer) The sum of the thickness of the first microporous layer and the thickness of the second microporous layer) is 10 μm or more and less than 60 μm. By using such a gas diffusion electrode, the gas diffusion property in the vertical direction of the entire laminate can be 30% or more.

  The first microporous layer or the second microporous layer should be divided into two or more layers when the porosity of each layer is inclined or the first microporous layer cannot be applied thickly at once. Is also possible. When the microporous layer is formed by laminating three or more individual microporous layers, another corresponding microporous layer is provided between the first microporous layer and the second microporous layer. These layers preferably have the same pore diameter and porosity as those of the first microporous layer or the second microporous layer or intermediate values thereof. In addition, the thickness of the entire microporous layer on one side of the conductive porous substrate must not be 60 μm or more. Even in such a case, the gas diffusion property in the vertical direction as the gas diffusion electrode is preferably 30% or more.

  The gas diffusibility of the gas diffusion electrode is defined as follows. Using a water vapor gas water vapor permeation diffusion evaluation device such as a water vapor gas water vapor permeation diffusion evaluation device (MVDP-200C) manufactured by Seika Sangyo Co., Ltd. Then, nitrogen gas is flowed to the other surface side (secondary side). The differential pressure between the primary side and the secondary side is controlled in the vicinity of 0 Pa (0 ± 3 Pa) (that is, there is almost no gas flow due to the pressure difference, and the gas movement phenomenon occurs only by molecular diffusion). The gas concentration when the equilibrium is reached is measured by the gas concentration meter, and this value (%) is used as an index of gas diffusivity.

  In the present invention, the first microporous layer coating solution is applied to the surface of the electrode substrate, and the second microporous layer coating solution is applied thereon so that the thickness of the second microporous layer is 10 μm or less. Apply to. In order to uniformly apply such a thin film, a first microporous layer coating solution is applied onto a substrate, and then a second microporous layer coating solution is continuously applied without drying. It is effective to apply Wet's multilayer technology. The surface of the conductive porous substrate is generally rough, and the unevenness may be as close as 10 μm. Even when the first microporous layer coating liquid is applied to the surface having such large irregularities, the irregularities cannot be completely eliminated after drying. Since the second microporous layer is a thin film of 10 μm or less, the viscosity of the coating liquid needs to be lowered to some extent. When trying to form a thin film on the uneven surface as described above with such a low-viscosity coating liquid, the liquid tends to accumulate in the concave and convex portions (that is, thick), and the liquid is deposited on the convex portions. In the extreme case, the thin film of the second microporous layer cannot be formed without riding. In order to prevent this, the surface of the first microporous layer is obtained by stacking the first microporous layer coating liquid and the second microporous layer coating liquid before drying, and then drying them together at a later time. A thin film of the second microporous layer can be formed uniformly.

  In this way, when multi-layer coating is not performed after each layer is coated, drying at once after the completion of multi-layer coating requires only one dryer and shortens the coating process, which reduces equipment costs and production space. It also saves money. Moreover, it becomes possible to reduce the loss of a generally expensive conductive porous substrate in the process by shortening the process.

  In the above multilayer coating, the first microporous layer coating solution is applied by a die coater, and the second microporous layer coating solution is also applied by a die coater. A method of performing coating with various roll coaters and a second microporous layer coating solution with a die coater, a first microporous layer coating solution with a comma coater, and a second microporous layer coating solution Using a die coater, applying a first microporous layer coating solution with a lip coater, applying a second microporous layer coating solution with a die coater, and using a slide die coater, A method of stacking the first microporous layer coating liquid and the second microporous layer coating liquid before applying to the material can be applied. In particular, in order to uniformly apply a high-viscosity coating solution, it is preferable to apply the first microporous layer coating solution with a die coater or a comma coater.

  The coating method of the above-mentioned die coater and comma coater is described in many existing documents such as “All about Converting” (edited by Processing Technology Research Group). The die coater is a type in which a pre-weighed coating liquid is applied onto a substrate via a die for uniformly distributing in the width direction. Also, the comma coater is a coating method that smoothens the coating surface regardless of the unevenness of the substrate by scraping off the thick coating liquid with a roll knife set at a certain height in the same way as the knife coater It is.

  What is important in the present invention is to form a surface layer such as the second microporous layer as uniformly as possible on a thin film of 0.1 μm or more and 10 μm or less. It is desirable to increase the adhesion between the applied electrolyte membrane and the gas diffusion electrode (contact area between the catalyst layer surface and the microporous layer surface of the gas diffusion electrode) as much as possible. For this purpose, it is desirable to make the surface of the microporous layer of the gas diffusion electrode as smooth as possible. In addition, a method of applying the catalyst ink to the gas diffusion electrode side is also generally known (GDE method). In this case, too, in order to apply the catalyst ink uniformly, the microporous layer of the gas diffusion electrode is formed. It is desirable to keep the surface as smooth as possible. As described above, when smoothness is required, the first microporous layer coating solution is applied with a comma coater or the like, and after the surface of the substrate is once roughened, the second microporous layer is used with a die coater. When a layer coating solution is applied, higher smoothness is obtained. As an index of smoothness, surface roughness Ra is used, and the surface of the second microporous layer desirably has a value of Ra of 6 μm or less, more preferably 4 μm or less. When Ra is larger than 6 μm, the adhesion to the catalyst layer is poor, and considering the case where the catalyst ink is applied to the surface of the microporous layer, the lower limit of the surface roughness Ra is considered to be about 0.1 μm. It is done.

  Various surface roughness meters can be applied to the measurement of the surface roughness. However, since the surface of the microporous layer is relatively fragile, it is preferable to use a non-contact type measuring instrument. An example of a non-contact type measuring instrument is a laser microscope VX-100 manufactured by Keyence Corporation.

  As described above, as a method for producing the gas diffusion electrode of the present invention, the first microporous layer coating liquid is applied to one side of the conductive porous substrate, and the first microporous layer coating liquid is applied. After the second microporous layer coating liquid is applied without substantially drying, the first microporous layer coating liquid and the second microporous layer coating liquid are collectively dried to obtain a gas diffusion electrode. It is effective. That is, (a) the step of applying the first microporous layer coating liquid to the conductive porous substrate, before drying the first microporous layer coating liquid, (b) the first microporous layer coating liquid A step of recoating the second microporous layer coating liquid on the substrate, and (c) a step of collectively drying the substrate coated with the first microporous layer coating liquid and the second microporous layer coating liquid. Adopt it. Furthermore, the first microporous layer coating liquid and the second microporous layer coating liquid may be dried together and then sintered to obtain a gas diffusion electrode. Even if a sintering process is a process (it is set as the heat processing 1) which removes organic substances, such as surfactant contained in the 1st microporous layer coating liquid and the 2nd microporous layer coating liquid, by heat processing. , (E) any of the steps of heat treatment (referred to as heat treatment 2) for binding the water repellent resin and the conductive fine particles contained in the first microporous layer coating liquid and the second microporous layer coating liquid In addition, the step (d) and the step (e) can be performed together. In addition, “substantially do not dry” means that it is not actively dried by a heat treatment machine such as a dryer in a heated state, and for a very short time (within 30 seconds, preferably within 20 seconds, It is preferable that it is naturally dried (preferably within 10 seconds).

  Since the conductive porous substrate can be obtained as a wound body wound in a long length, in the manufacturing process of the present invention, before the step (a), in order to increase the efficiency of mass production. The conductive porous substrate for unwinding the conductive porous substrate from the wound body (A) and applying the first microporous layer coating liquid is a long conductive layer. Is provided from the unwinding step of unwinding the porous porous substrate from a wound body, and after the step (c), a winding step (B) is taken up by a winder or the like. Thus, it is desirable to perform a so-called roll-to-roll process in which a winding process for winding the obtained gas diffusion electrode is included and the process from the winding process to the winding process is continuously performed. Thereby, it can be set as a continuous process and mass productivity can be improved. More preferably, steps (d) to (e) are incorporated after step (c) and before step (B).

  The production apparatus suitable for producing the gas diffusion electrode of the present invention includes an unwinding machine for unwinding a long conductive porous substrate wound in a roll shape, and an electrically conductive porous material unwound by an unwinding machine. A first coating machine for applying the first microporous layer coating liquid to the porous substrate, the first microporous layer coating liquid being applied to the conductive porous base material that is not substantially dried A second coating machine disposed on the same side of the substrate surface on which the first coating machine is disposed for applying the second microporous layer coating liquid, the first microporous layer coating A drying machine for drying the conductive porous substrate coated with the liquid and the second microporous layer coating liquid, and a winder that winds up the obtained gas diffusion electrode.

  2 and 3 exemplify a particularly preferred production apparatus according to the present invention.

  In the manufacturing apparatus shown in FIG. 2, the long conductive porous substrate 1 is unwound from the unwinding machine 2 and conveyed while being appropriately supported by the guide roll 3, and is the first coating machine. The first microporous layer coating solution is applied to one side of the conductive porous substrate by the die coater 4. At this time, the first microporous layer coating liquid is usually supplied from the coating liquid tank 12 to the die coater by the liquid feeding pump 13. Preferably, the filter 14 is used for filtration. The second microporous layer coating liquid is set to the first microporous layer coating liquid by the second die coater 5 which is a second coating machine installed on the same substrate surface side as the first die coater 4. After being coated on the coated surface, drying is performed by the dryer 7 in a lump, and the gas diffusion electrode is wound by the winder 9. The second microporous layer coating liquid is also usually supplied from the coating liquid tank 12 to the die coater by the liquid feed pump 13. Preferably, the filter 14 is used for filtration. Moreover, as shown in FIG. 2, it is preferable to install the sintering machine 8 after the dryer 7, and to sinter in-line. Further, the back roll 6 may be used when the microporous layer coating liquid is applied by the die coater, and the interleaf paper 10 unwound from the interleaf unwinding machine 11 is used for protecting the coated surface during winding. May be wound together with the product.

  In the manufacturing apparatus shown in FIG. 3, a comma coater 40 is installed in place of the first die coater 4 in FIG. When applying with a comma coater, the substrate is transported while supplying the coating material to the liquid dam 42, and the coating material is scraped off with the knife roll 41 so that a desired coating amount is obtained.

  As shown in FIG. 2 or 3, when a plurality of layers are provided on the base material, the drying of the plurality of layers can be simplified, and the dryer can be simplified. Since the process up to the removal can be shortened, the productivity is high and the loss can be reduced even when the substrate is broken.

  The gas diffusion electrode of the present invention is a fuel cell in which a single cell is assembled by assembling a member such as a separator by pressure bonding so that the catalyst layer and the gas diffusion electrode are in contact with both sides of an electrolyte membrane provided with catalyst layers on both sides. Used as. At that time, the second microporous layer may be assembled so as to be in contact with the catalyst layer.

  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 method for evaluating the cell performance of the fuel cell are shown below.

<Material>
A: A carbon paper having a conductive porous substrate with a thickness of 100 μm and a porosity of 85% was prepared as follows.
Polyacrylonitrile-based carbon fiber “Torayca” (registered trademark) T300-6K (average single fiber diameter: 7 μm, number of single fibers: 6,000 fibers) manufactured by Toray Industries, Inc. was cut to a length of 6 mm and exposed to hardwood from Arabara River With kraft pulp (LBKP) craft market pulp (hardwood), water is continuously made as a paper making medium, further immersed in a 10% by weight aqueous solution of polyvinyl alcohol and dried, and then wound into a roll. A long carbon fiber paper having a basis weight of carbon short fibers of 15 g / m ² was obtained. The amount of added pulp corresponds to 40 parts by mass, and the amount of polyvinyl alcohol attached corresponds to 20 parts by mass with respect to 100 parts by mass of carbon fiber paper.
Scale-like graphite BF-5A (average particle diameter: 5 μm, aspect ratio: 15), phenol resin and methanol (manufactured by Nacalai Tesque Co., Ltd.) mixed at a mass ratio of 2: 3: 25 manufactured by Chuetsu Graphite Industries Co., Ltd. A prepared dispersion was prepared. The carbon fiber paper is continuously impregnated with the dispersion so that the resin impregnation amount is 78 parts by mass of phenol resin with respect to 100 parts by mass of carbon short fibers, and dried at a temperature of 90 ° C. for 3 minutes. After passing through the resin impregnation step, it was wound into a roll to obtain a resin-impregnated carbon fiber paper. In the phenol resin, Arakawa Chemical Industries, Ltd. resol type phenol resin KP-743K and Arakawa Chemical Industries, Ltd. novolak type phenol resin “Tamanol” (registered trademark) 759 were mixed at a mass ratio of 1: 1. Things were used. The carbonization yield of this phenol resin (mixture of resol type phenol resin and novolac type phenol resin) was 43%.
Set a hot plate on a Kawatiri 100t press so that the hot plates are parallel to each other, place a spacer on the lower hot plate, and move up and down while repeatedly opening and closing the press at a hot plate temperature of 170 ° C and a surface pressure of 0.8 MPa. Then, the resin-impregnated carbon fiber paper sandwiched between the release papers was intermittently conveyed, and the same portion was subjected to compression treatment so as to be heated and pressurized for a total of 6 minutes. Moreover, the effective pressurization length LP of the hot plate was 1200 mm, the feed amount LF of the precursor fiber sheet when intermittently conveyed was 100 mm, and LF / LP was 0.08. That is, compression treatment was performed by repeating heating and pressing for 30 seconds, mold opening, and feeding of carbon fiber (100 mm), and the product was wound into a roll.
The compressed carbon fiber paper is used as a precursor fiber sheet, introduced into a heating furnace having a maximum temperature of 2400 ° C. maintained in a nitrogen gas atmosphere, and continuously running in the heating furnace at about 500 ° C./min. After passing through a carbonization step of firing at a heating rate of 400 ° C./min up to 650 ° C. and 550 ° C./min at a temperature exceeding 650 ° C., a carbon paper was obtained by winding in a roll. The obtained carbon paper had a density of 0.25 g / cm ³ and a porosity of 85%.
・ Similar to carbon paper with a thickness of 100 μm and a porosity of 85%, except for adjusting the weight of the carbon fiber and the thickness of the spacer during the compression treatment so that the thickness after carbonization is 150 μm, the thickness is 150 μm, the gap A carbon paper with a rate of 85% was obtained.
For further comparison, the carbon fiber weight per unit area and the thickness of the spacer during the compression treatment were adjusted to obtain carbon paper having a carbonized thickness of 180 μm.
B: Conductive fine particles / vapor-grown carbon fiber “VGCF” (registered trademark) having an aspect ratio in the range of 30 to 5000 (manufactured by Showa Denko KK, average diameter: 0.15 μm, average fiber length: 8 μm, (Aspect ratio: 50, a kind of linear carbon)
Vapor growth 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)
・ Multi-walled carbon nanotubes (Cheap Tubes, average diameter: 0.015 μm, average fiber length: 20 μm, aspect ratio: 1300, a kind of linear carbon)
・ Flake graphite “xGnP” (registered trademark) grade M (manufactured by XG Science, average particle size: 5 μm, average thickness: 0.006 μm, aspect ratio: 830)
C: Conductive fine particles and acetylene black “Denka Black” (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size: 0.035 μm, aspect ratio: 1 , A kind of carbon black)
D: Water repellent material “Polyflon” (registered trademark) PTFE dispersion D-210C (PTFE resin, manufactured by Daikin Industries, Ltd.)
"Polyflon" (registered trademark) FEP dispersion N-110 (PTFE resin, manufactured by Daikin Industries, Ltd.)
E: Surfactant “TRITON” (registered trademark) X-100 (manufactured by Nacalai Tesque)

<Measurement of thickness of substrate and microporous layer>
The thickness of the substrate (gas diffusion electrode and conductive porous substrate) was measured using a digital thickness gauge “Digimicro” manufactured by Nikon Corporation while applying a load of 0.15 MPa to the substrate. The thickness of the microporous layer was measured by subtracting the thickness of the conductive porous substrate from the thickness of the gas diffusion electrode. That is, with respect to the thickness of the first microporous layer, the thickness of the first microporous layer depends on the difference between the thickness of the substrate coated with only the first microporous layer and the thickness of the conductive porous substrate. did. As for the thickness of the second microporous layer, as shown in FIG. 1, when the second microporous layer is applied on the conductive porous substrate on which the first microporous layer is applied, The thickness of the second microporous layer was determined by the difference between the portion where the second microporous layer was applied and the portion where the second microporous layer was not applied.

<Measurement of viscosity of coating liquid>
In the viscosity measurement mode of the Spectris Borin rotary rheometer, the stress is measured using a circular cone plate having a diameter of 40 mm and an inclination of 2 ° while increasing the number of rotations of the plate (increase the share rate). At this time, the viscosity value at a shear rate of 0.17 (/ s) was taken as the viscosity of the coating liquid.

<Measurement of porosity>
Using S-4800 manufactured by Hitachi, Ltd. as the scanning electron microscope, each region of the conductive porous substrate, the first microporous layer, and the second microporous layer from the cross-sectional surface of the gas diffusion electrode , Randomly selected 20 different locations, magnified at a magnification of about 20000 times, photographed, and binarized the non-voided portion and the non-voided portion in each image to obtain an average value obtained by measuring the void ratio. In producing the cross section of the gas diffusion electrode, an ion milling apparatus IM4000 manufactured by Hitachi High-Technologies Corporation was used.

<Measurement of pore size>
The pore diameters of the conductive porous substrate and the microporous layer were obtained by measuring the peak diameter of the pore diameter distribution obtained by measuring in the measurement pressure range of 6 kPa to 414 MPa (pore diameter 30 nm to 400 μm) by mercury porosimetry. When a plurality of peaks appear in the near pore diameter region, the peak diameter of the highest peak was adopted. As a measuring device, Autopore 9520 manufactured by Shimadzu Corporation was used.

  In order to determine the pore diameter of each layer of the gas diffusion electrode in which the first microporous layer and the second microporous layer are laminated on the conductive porous base material, the structure of each layer is obtained by SEM observation of the cross section of the gas diffusion electrode. The pore diameter of each layer was determined while correlating with the pore diameter peak of each layer obtained by a mercury porosimeter. In the case of the gas diffusion electrode of the present invention, a small peak appears in the region of less than 0.1 μm, a relatively broad peak in the region of 0.1 μm or more and less than 10 μm, and a large and clear peak appears in the region of 10 μm or more and 100 μm or less. .

<Surface roughness measurement>
With respect to the surface of the microporous layer of the gas diffusion electrode to be measured, a roughness measurement is performed by using a laser microscope VK-X100 manufactured by Keyence Co., Ltd. with an objective lens 10 times without cutoff, and an arithmetic average roughness Ra is obtained. The surface roughness was averaged for the field of view.

<Sliding angle of conductive porous substrate>
Using the sliding angle measurement mode of the automatic contact angle meter DM501 manufactured by Kyowa Interface Science Co., Ltd., a 10 μl water droplet is dropped on the sample, and the sample stage is gradually inclined from a horizontal state (1 ° / second) The angle at which the water droplet slipped and disappeared from the measurement screen was defined as the sliding angle.

<Gas diffusivity>
Using a water vapor permeation evaluation apparatus (MVDP-200C) manufactured by Seika Sangyo Co., Ltd., the gas whose diffusibility is to be measured is flowed to one side (primary side) of the gas diffusion electrode, and the other side (secondary side) Nitrogen gas is allowed to flow through. The differential pressure between the primary side and the secondary side is controlled in the vicinity of 0 Pa (0 ± 3 Pa) (that is, there is almost no gas flow due to the pressure difference, and the gas movement phenomenon occurs only by molecular diffusion). The gas concentration when the equilibrium was reached was measured with the gas concentration meter of No. 1 and this value (%) was used as an index of gas diffusivity.

<Evaluation of power generation performance>
The obtained gas diffusion electrode was formed by integrating an electrolyte membrane / catalyst layer integrated product (Nippon Gore's electrolyte membrane “Gore Select” (registered trademark) and Nippon Gore's catalyst layer “PRIMEA” (registered trademark) on both sides. The membrane electrode assembly (MEA) was manufactured by sandwiching the catalyst layer and the microporous layer so that the catalyst layer and the microporous layer were in contact with each other and hot pressing. This membrane electrode assembly is incorporated into a single cell for a fuel cell. The cell temperature is 40 ° C., the fuel utilization efficiency is 70%, the air utilization efficiency is 40%, the hydrogen on the anode side, and the air on the cathode side are 75 ° C. and 60 ° C., respectively. The value of current density (limit current density) at which power generation is stopped when the current density is increased by humidifying the temperature to be 0 ° C. is used as an index for flooding resistance. Moreover, the measurement was similarly performed at a battery temperature of 80 ° C., and used as an index of dry-up resistance. Furthermore, the power generation performance under normal operating conditions (battery temperature 70 ° C.) was also measured.

Example 1
The carbon paper wound in a roll shape having a thickness of 100 μm and a void ratio of 85% is unwound from the unwinder 2 using the take-up type conveying device shown in FIG. While being immersed in an immersion tank 15 filled with a water-repellent material dispersion dispersed in water so that the fluororesin concentration becomes 2% by mass, water-repellent treatment is performed, and drying is performed with a dryer 7 set at 100 ° C. Then, the film was wound up by a winder 9 to obtain a water-repellent conductive porous substrate. As the water repellent dispersion, a FEP dispersion ND-110 diluted with water so that the FEP concentration was 2% by mass was used. The sliding angle after sintering of this base material was 34 °.

  Next, as schematically shown in FIG. 2, two die coaters (4, 5) are provided in a conveying device including an unwinding machine 2, a guide roll 3, a back roll 6, an interleaf unwinding machine 11, and a winding machine 9. ), And a winding type continuous coater equipped with a dryer 7 and a sintering machine 8 was prepared.

  As the conductive porous substrate subjected to the water repellent treatment, a raw material obtained by winding carbon paper having a thickness of 100 μm, a porosity of 85%, and a width of about 400 mm into a 400 m roll was set in the unwinding machine 2.

  The raw material was conveyed by drive rolls installed at the unwinding unit, the winding unit, and the coater unit. First, after the first microporous layer coating solution is applied using the first die coater 4, the second microporous layer coating solution is continuously applied by the second die coater 5. Moisture was dried with hot air at 100 ° C., and further sintered in a sintering machine 8 set at 350 ° C., and then wound up with a winder 9.

The microporous layer coating solution was prepared as follows.
First microporous layer coating solution:
Vapor growth carbon fiber "VGCF" (registered trademark) 7 parts by mass, FEP dispersion ("Polyflon" (registered trademark) ND-110) 2.5 parts by mass, surfactant ("TRITON" (registered trademark) X- 100) 15 parts by mass and 80.5 parts by mass of purified water were kneaded with a planetary mixer to prepare a coating solution. The coating liquid viscosity at this time was 6 Pa · s.
Second microporous layer coating solution:
Acetylene black "Denka Black" (registered trademark) 7.7 parts by mass, FEP dispersion ("Polyflon" (registered trademark) ND-110) 2.5 parts by mass, surfactant ("TRITON" (registered trademark) X- 100) 5 parts by mass and 75.8 parts by mass of purified water were kneaded with a planetary mixer to prepare a coating solution. The kneading time in the planetary mixer took twice as long as that of the first microporous layer coating liquid to increase the dispersion degree of the conductive fine particles. The coating liquid viscosity at this time was 3.6 Pa · s.

In applying the first microporous layer coating solution, the basis weight of the microporous layer after sintering was adjusted to 13 g / m ² . At this time, the thickness of the first microporous layer was 25 μm. Furthermore, in applying the second microporous layer coating liquid, the thickness of the second microporous layer was adjusted to 5 μm.

  Further, the gas diffusion electrode prepared as described above was thermocompression-bonded so that the microporous layer and the catalyst layer were in contact with both sides of the electrolyte membrane provided with the catalyst layer on both sides, and incorporated into a single cell of the fuel cell. The power generation performance (limit current density) was evaluated at a temperature of 70 ° C.

(Example 2)
In Example 1, a gas diffusion electrode was obtained in the same manner as in Example 1 except that carbon paper having a porosity of 85% and a thickness of 150 μm was used as the conductive porous substrate. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

(Comparative Example 1)
In Example 1, a gas diffusion electrode was obtained in the same manner as in Example 1 except that carbon paper having a porosity of 85% and a thickness of 180 μm was used as the conductive porous substrate. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

(Example 3)
In Example 1, the second microporous layer coating solution was changed to the following, and when the second microporous layer coating solution was applied, the thickness of the second microporous layer was 0.8 μm. Except for the preparation, a gas diffusion electrode was obtained in the same manner as in Example 1. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.
Second microporous layer coating solution:
"Denka Black" (registered trademark) 7.7 parts by mass, FEP dispersion ("Polyflon" (registered trademark) ND-110) 2.5 parts by mass, surfactant ("TRITON" (registered trademark) X-100) 2 parts by mass and 75.8 parts by mass of purified water were used, and the dispersion time of the conductive fine particles was increased by taking 3 times as long as the kneading time with the planetary mixer in the case of the coating liquid of the first microporous layer. The coating liquid viscosity at this time was 0.9 Pa · s.

Example 4
In the apparatus of FIG. 2, the water-repellent conductive porous substrate obtained in Example 1 (thickness 100 μm, porosity 85%, width of about 400 mm of carbon paper rolled into a 400 m roll) is wound. Set in dispenser 2.

  The raw material was conveyed by drive rolls installed at the unwinding unit, the winding unit, and the coater unit. First, after applying the first microporous layer coating solution using the first die coater 4, the moisture was dried with hot air at 100 ° C. in the dryer 7, and then wound up by a winder. The substrate coated with the first microporous layer coating solution is set again on the unwinder 2, and the second microporous layer coating solution is applied by the second die coater 5. Moisture was dried by hot air at 0 ° C., and further sintered in a sintering machine set at 350 ° C., and then wound up by a winder 9. Except for this, a gas diffusion electrode was obtained in the same manner as in Example 3. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

  In Example 4, the first microporous layer coating liquid was dried, so that the second microporous film was in a state where the surface of the first microporous layer traced the irregularities on the surface of the carbon paper. Since the layer coating liquid was applied, the film thickness of the second microporous layer was varied, and there were some portions that were hardly covered by the second microporous layer in the uneven protrusions of the first microporous layer. As a result, the barrier effect of water vapor is locally weakened, and it is considered that in power generation evaluation at a high temperature (80 ° C.), dry-up occurs and the power generation performance slightly decreases.

(Comparative Example 2)
In Example 1, all the steps were performed except that the coating amount was changed so that the thickness of the first microporous layer was 50 μm, the thickness of the second microporous layer was 10 μm, and the total thickness of the microporous layer was 60 μm. A gas diffusion electrode was obtained in the same manner as in Example 1. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

(Comparative Example 3)
In Example 1, a gas diffusion electrode was obtained in the same manner as in Example 1 except that the coating amount of the coating liquid was changed so that the thickness of the second microporous layer was 10 μm and the total thickness of the microporous layer was 35 μm. It was. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

(Comparative Example 4)
In Example 1, the gas was changed in the same manner as in Example 1 except that the coating amount of the coating liquid was changed so that the thickness of the first microporous layer was 30 μm, and the second microporous layer was not applied. A diffusion electrode was obtained. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

(Comparative Example 5)
In Example 1, the water-repellent material dispersion used for the water-repellent treatment of the base material is PTFE dispersion (“Polyflon” (registered trademark) D-210C) with water so that the PTFE concentration is 0.1% by mass. A gas diffusion electrode was obtained in the same manner as in Example 1 except that it was changed to a thinner one. The sliding angle of this substrate was 90 ° or more. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

(Comparative Example 6)
In Example 1, a gas diffusion electrode was obtained in the same manner as in Example 1 except that the second microporous layer coating liquid was changed to the same coating liquid as that used as the first microporous layer coating liquid. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

(Example 5)
A gas diffusion electrode was obtained in the same manner as in Example 1 except that the apparatus shown in FIG. 3 was used, and in Example 1, the first microporous layer coating solution was applied using a comma coater 40 instead of the die coater. Got. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

(Example 6)
In Example 5, after the first microporous layer coating solution was applied by the comma coater 40, the second microporous layer coating solution was dried without coating (without sintering) and wound again. The base material is set in the take-out machine, the coating liquid of the liquid dam 42 of the comma coater is changed to the second microporous layer coating liquid, the second microporous layer coating liquid is applied by the comma coater 40, dried and A gas diffusion electrode was obtained in the same manner as in Example 5 except that sintering was performed and winding was performed last. This gas diffusion electrode was incorporated into a single cell for fuel cells in the same manner as in Example 1, and power generation performance was evaluated.

  In Examples 5 and 6, coating was performed by filling the liquid dam 42 in FIG. 3 with the coating liquid for the first microporous layer. However, the coating liquid soaked into the carbon paper a little (thickness was reduced). However, the gas diffusivity inside the carbon paper was slightly impaired, and the power generation performance was slightly lowered at low temperatures (40 ° C) and medium temperatures (70 ° C). It was. However, the smoothness (surface roughness Ra) on the surface of the microporous layer was smaller than that of the die-coated product and could be made smooth.

  Table 1 shows the main conditions and results of power generation performance evaluation in each example and comparative example. It can be seen that the fuel cells using the gas diffusion electrodes prepared by the manufacturing method of the present invention all have better power generation performance than those prepared by the prior art. In the table, W / W is WET ON WET (stacking another coating material on top without drying the coating film), W / D is WET ON DRY (after drying the coating film) It means to laminate another coating material on top).

DESCRIPTION OF SYMBOLS 1 Conductive porous base material 2 Unwinding machine 3 Guide roll (non-drive)
4 First die coater 5 Second die coater 6 Back roll 7 Dryer 8 Sintering machine 9 Winding machine (drive)
10 Interleaf 11 Unwinder (for interleaf)
DESCRIPTION OF SYMBOLS 12 Coating liquid tank 13 Liquid feed pump 14 Filter 15 Immersion tank 40 Comma coater 41 Knife roll 42 Liquid dam 201 1st microporous layer 202 2nd microporous layer

Claims (8)

A gas diffusion electrode used in a fuel cell, wherein a first microporous layer in contact with a conductive porous substrate and a second microporous layer are sequentially disposed on one side of the conductive porous substrate. ,
The conductive porous substrate has a thickness of 150 μm or less, a porosity of 80% or more, a pore diameter of 10 μm or more and 100 μm or less, and a sliding angle of 40 ° or less.
The first microporous layer has a thickness of 10 μm or more , a porosity of 70% or more, and a pore diameter of 0.1 μm or more and less than 10 μm,
The second microporous layer has a thickness of 0.1 μm or more and 7 μm or less, a porosity of 40% or more and less than 70%, and a pore diameter of less than 0.1 μm,
Furthermore, the gas diffusion electrode whose total thickness of a microporous layer is 40 micrometers or less . The gas diffusion electrode according to claim 1, wherein the second microporous layer has a thickness of 0.8 µm or more and 7 µm or less. The gas diffusion electrode according to claim 1 or 2 , wherein the gas diffusion property in the vertical direction is 30% or more. The gas diffusion electrode according to any one of claims 1 to 3, wherein the second microporous layer has a surface roughness of 6 µm or less.
A gas diffusion electrode for use in a fuel cell is manufactured in which a first microporous layer in contact with a conductive porous substrate and a second microporous layer are sequentially arranged on one side of the conductive porous substrate. A method,
Applying the first microporous layer coating liquid having a viscosity of 5000 mPa · s to 20 Pa · s on one side of the conductive porous substrate without substantially drying the first microporous layer coating liquid , After applying a second microporous layer coating liquid having a viscosity of 10 Pa · s or less and lower than the first microporous layer coating liquid ,
Drying the first microporous layer coating liquid and the second microporous layer coating liquid together to obtain a gas diffusion electrode;
A method for producing a gas diffusion electrode. The method for producing a gas diffusion electrode according to claim 5 , wherein the first microporous layer coating solution is applied by a die coater or a comma coater. The gas diffusion electrode according to claim 5 or 6 , wherein the first microporous layer coating liquid and the second microporous layer coating liquid are collectively dried and then sintered to obtain a gas diffusion electrode. Production method. The conductive porous substrate for applying the first microporous layer coating liquid is supplied from an unwinding step of unwinding from a wound body in which a long conductive porous substrate is wound into a roll shape. The method for producing a gas diffusion electrode according to any one of claims 5 to 7 , further comprising a winding step of winding up the obtained gas diffusion electrode, and continuously performing from the unwinding step to the winding step.