JP2005243295A - Gas diffusion layer and fuel cell MEA using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon water repellent layer in which both diffusion polarization and resistance polarization are reduced.
A gas diffusion layer characterized by having a carbon water repellent layer containing carbon particles coated with a water repellent and water repellent particles on the surface of the gas diffusion substrate.
[Selection figure] None

Description

  The present invention relates to a gas diffusion layer, and more particularly to a gas diffusion layer having a carbon water repellent layer.

  In recent years, in response to social demands and trends against the background of energy and environmental issues, polymer electrolyte fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. . The solid polymer fuel cell is characterized by using a film-like solid polymer electrolyte membrane.

  The polymer electrolyte fuel cell generally has a structure in which a membrane-electrode assembly (hereinafter also referred to as “MEA”) is sandwiched between separators. The MEA has a structure in which a solid polymer electrolyte membrane is sandwiched between two electrodes and is further sandwiched between gas diffusion layers. The electrode is a porous material formed of a mixture of an electrode catalyst and a solid polymer electrolyte, and is also called an electrode catalyst layer.

  In a fuel cell, electricity can be taken out through the following electrochemical reaction or the like. First, hydrogen contained in the fuel gas supplied to the fuel electrode (anode) side is oxidized by the catalyst particles to become protons and electrons. Next, the generated protons pass through the solid polymer electrolyte contained in the fuel electrode side electrode catalyst layer and the solid polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the oxygen electrode (cathode) side electrode catalyst layer. . Electrons generated in the fuel electrode side electrode catalyst layer include a conductive carrier constituting the electrode catalyst layer, a gas diffusion layer in contact with a different side of the electrode catalyst layer from the solid polymer electrolyte membrane, a separator, and It reaches the oxygen electrode side electrode catalyst layer through an external circuit. The protons and electrons that reach the oxygen electrode side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the oxygen electrode side to generate water. Such an electrochemical reaction mainly proceeds at a three-phase interface where the catalyst particles, the proton conductive electrolyte, and the supply gas are in contact. Therefore, the gas diffusion layer is required to uniformly supply the supplied gas to the electrodes.

  In addition, a solid polymer electrolyte membrane in a fuel cell does not exhibit high proton conductivity unless it is wet. Therefore, it is necessary to make the humidity distribution of the solid polymer electrolyte membrane uniform by humidifying the gas supplied to the solid polymer fuel cell using a gas humidifier or the like.

  Under operating conditions such as high humidification and high current density, the amount of water that moves with protons that move through the polymer electrolyte membrane from the anode to the cathode, and the amount of water that is generated in the oxygen electrode side electrode catalyst layer and aggregates The amount of generated water increases. At this time, these produced waters particularly stay in the oxygen electrode-side electrode catalyst layer and cause a flooding phenomenon that closes the pores that have become the reaction gas supply path. As a result, the diffusion polarization is increased in order to inhibit the diffusion of the reaction gas. In contrast, under operating conditions such as low humidification and low current density, there is little risk of flooding due to the small amount of water produced, but the amount of water supplied is insufficient and the polymer electrolyte membrane dries out. This causes a dry-out phenomenon in which proton conductivity decreases.

  Therefore, conventionally, a gas diffusion layer having a carbon water-repellent layer made of conductive particles, a water repellent and the like on the surface of the gas diffusion base material has been used for the fuel cell MEA. The carbon water repellent layer has a porous structure made of an aggregate of conductive particles such as carbon. Therefore, it is possible not only to diffuse the gas supplied by humidification and uniformly supply the gas to the electrode catalyst layer, but also to quickly discharge excess water.

Patent Document 1 discloses a method of inclining the water repellent content in the carbon water repellent layer in accordance with the gas flow direction in order to keep the humidity distribution of the solid polymer electrolyte membrane uniform.
JP 2003-92112 A

  However, in the gas diffusion layer of Patent Document 1, resistance polarization, which is a basic factor that degrades the performance of the fuel cell, may increase. From the viewpoint of increasing the output of the fuel cell, it is necessary to reduce not only diffusion polarization but also resistance polarization, and further improvement is desired.

  Accordingly, an object of the present invention is to provide a gas diffusion layer in which both diffusion polarization and resistance polarization are reduced.

  The present invention solves the above problems by a gas diffusion layer characterized in that it has a carbon water repellent layer containing carbon particles coated with a water repellent and water repellent particles on the surface of the gas diffusion substrate. It is.

  The gas diffusion layer of the present invention can reduce not only diffusion polarization but also resistance polarization by having the carbon water-repellent layer. Therefore, when the gas diffusion layer of the present invention is used for a fuel cell, not only can the flooding phenomenon be suppressed, particularly at the cathode, but also a high power generation amount can be stably supplied.

  A first aspect of the present invention is a gas diffusion layer characterized by having a carbon water repellent layer containing carbon particles coated with a water repellent and water repellent particles on the surface of the gas diffusion substrate.

  The carbon water-repellent layer not only has the function of supplying water uniformly to the solid polymer electrolyte membrane and discharging excess water to the gas diffusion layer side, but also has the function of improving the power generation characteristics by lowering the electrical resistance. It is required to have. However, the conventional carbon water-repellent layer can reduce the diffusion polarization by promoting the discharge of water, but there is a problem that the resistance polarization increases.

  In the present invention, as a result of intensive studies in view of such problems, the following has been found. As a conventional method for producing a carbon water repellent layer, a method is used in which a slurry prepared by mixing a solvent, a water repellent such as carbon particles and polytetrafluoroethylene is applied to the surface of a gas diffusion substrate. . Therefore, the carbon particles 1 are covered with a water repellent 2 as shown in FIG. Since the water repellent agent can also act as a binder, the carbon particles can be entangled and the physical binding between the electrode and the gas diffusion substrate can be enhanced. Moreover, when promoting discharge | emission of water etc., it is necessary to increase content of the water repellent of a carbon water repellent layer. In this case, conventionally, since the carbon water-repellent layer is produced using the slurry adjusted by increasing the water-repellent concentration, as shown in FIG. 1B, the water-repellent agent 2 that coats the carbon particles 1 is used. The thickness increases.

  Electrons generated in the electrode flow to the gas diffusion base material, the external circuit, etc. via the carbon particle surface in the carbon water-repellent layer. Moreover, polytetrafluoroethylene generally used as a water repellent is an insulator. Therefore, in the conventional carbon water repellent layer, it is conceivable that the electrical resistance between the carbon particles increases due to the increase in the thickness of the water repellent, resulting in an increase in resistance polarization.

  On the other hand, the carbon water repellent layer of the present invention further includes water repellent particles 3 in addition to the carbon particles 1 coated with the water repellent 2 as shown in FIG. In the carbon water repellent layer, in order to increase the content of the water repellent, the content of the water repellent particles may be increased, and the thickness of the water repellent covering the carbon particles can be reduced. Therefore, the carbon water-repellent layer not only promotes the discharge of water and ensures gas permeability, but also reduces the electrical resistance between the carbon particles, realizing both reduction of diffusion polarization and resistance polarization. It becomes possible to make it.

  Hereinafter, the gas diffusion layer of the present invention will be described in order.

  The gas diffusion layer of the present invention is as described above, and has a carbon water-repellent layer on the surface of the gas diffusion substrate.

  The gas diffusion base material is not particularly limited, and examples thereof include a base material made of a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric.

  In addition, the gas diffusion base material may be subjected to water repellency treatment using a known means in order to enhance water repellency and prevent a flooding phenomenon or the like. Examples of the water repellent treatment include a method in which a gas diffusion base material is immersed in a dispersion of a water repellent such as a fluorine-based resin such as polytetrafluoroethylene and then heated and dried in an oven or the like. Moreover, the rigidity of a gas diffusion base material can also be improved by performing water-repellent treatment.

  Next, the carbon water repellent layer disposed on the gas diffusion substrate further includes water repellent particles in addition to the carbon particles coated with the water repellent.

  The carbon particles may be those having excellent electron conductivity, and examples thereof include carbon black powder, graphite powder, expanded graphite powder, metal powder, and ceramic powder. Carbon blacks such as oil furnace black, channel black, lamp black, thermal black, and acetylene black are preferred because of their excellent electron conductivity and large specific surface area.

  Commercially available products can be used as the carbon particles, such as Cabot Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Legal 400, Ketjen Black EC manufactured by Lion. Oil furnace black such as # 3150 and # 3250 manufactured by Mitsubishi Chemical Corporation; acetylene black such as Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd. and the like. In addition to carbon black, there are artificial graphite and carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin and furan resin. In order to improve the corrosion resistance and the like, the carbon particles may be subjected to processing such as heat treatment.

  The average particle diameter of the carbon particles is 1 to 10 μm, preferably about 3 to 7 μm. If the average particle size is less than 1 μm, the porosity of the carbon water-repellent layer may decrease. If the average particle size exceeds 10 μm, the thickness of the carbon water-repellent layer may increase, leading to a decrease in gas permeability, electronic conductivity, and the like. is there.

  Next, examples of the water repellent include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and polypropylene. And polyethylene. Of these, fluororesins are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction.

  In the carbon particles coated with the water repellent, the content of the water repellent is 5 to 40% by mass, preferably about 10 to 20% by mass. If the water repellent content is less than 5% by mass, the carbon particles may not be sufficiently bound. If the content exceeds 40% by mass, the electrical resistance may increase, that is, the resistance polarization may increase. Not desirable. The “carbon particles coated with a water repellent” are preferably coated with the water repellent on the entire surface of the carbon particles, but a part of the surface may not be coated with the water repellent. .

  The average particle diameter of the water repellent particles used in the carbon water repellent layer is 1 to 10 μm, preferably about 3 to 7 μm. If the average particle size is less than 1 μm, the porosity of the carbon water-repellent layer may decrease. If the average particle size exceeds 10 μm, the thickness of the carbon water-repellent layer may increase, leading to a decrease in gas permeability, electronic conductivity, and the like. is there.

  The thickness of the carbon water-repellent layer may be 50 to 150 μm, preferably 75 to 100 μm. However, it is not particularly limited to this, and it may be determined in consideration of gas permeability, electron conductivity, and the like of the obtained gas diffusion layer.

  The carbon water-repellent layer of the present invention preferably has at least one layer composed of only carbon particles coated with a water-repellent agent over the entire length of the carbon water-repellent layer. A schematic diagram of such a carbon water repellent layer is shown in FIG.

  In the carbon water repellent layer 6 of FIG. 2, the carbon particles 1 coated with the water repellent 2 are communicated from the electrode 5 to the gas diffusion base material 7. By having such a structure, the electron conduction path from the electrode to the gas diffusion base material can be secured without being hindered by the electrical resistance of the water repellent, and the resistance polarization can be further reduced. .

  Further, the gas diffusion base material and the carbon water-repellent layer may have different average pore diameters to promote water discharge. That is, the average pore diameter of the carbon water repellent layer is made smaller than the average pore diameter of the gas diffusion base material. Thereby, the water absorption power by capillary force increases, it becomes easy to move water, and it can promote that it is diffused and discharged | emitted to a gas diffusion base material.

  In general, in a fuel cell, a gas supplied as fuel is humidified in order to wet a solid polymer electrolyte membrane. In addition, a large amount of water is generated by the electrode reaction, particularly at the cathode. Therefore, the moisture content gradually increases from the gas inlet portion toward the gas outlet portion, and the moisture content increases considerably in the vicinity of the gas outlet portion to increase diffusion polarization. Therefore, it is desirable to reduce the diffusion polarization by increasing the water repellency of the portion that causes water flooding easily in the carbon water repellent layer and causes the flooding phenomenon.

  In consideration of this point, in the carbon water repellent layer, the content of the water repellent may be increased in the surface direction from the gas inlet portion to the gas outlet portion. The content of the water repellent may be increased stepwise or may be gradually increased with an inclination. In the former case, for example, only carbon particles in which the first half of the carbon water-repellent layer is coated with a water repellent are disposed, and the latter half in the same manner as in FIG. Examples thereof include, but are not limited to, a carbon water repellent layer in which liquid agent particles are arranged. The water repellent content may be determined in consideration of the water repellency of the obtained carbon water repellent layer, but may be gas outlet / gas inlet = 1-4, preferably about 1-2.

  Furthermore, the carbon water-repellent layer, when used on the cathode side of the fuel cell, discharges water from the electrode to the gas diffusion base material and conducts electrons transmitted through the external circuit from the gas diffusion base material to the electrode. There is a need. Therefore, as shown in FIG. 3, it is preferable to reduce the content of the water repellent in the thickness direction from the electrode side to the gas diffusion base material side. Thereby, not only is the water repellency improved, but since many carbon particles are arranged on the gas diffusion base material side, electrons transmitted from the external circuit can be efficiently conducted to the electrode. Further, the content may be increased stepwise, or may be gradually increased with an inclination. At this time, the water repellent content may be determined in consideration of the water repellency of the carbon water repellent layer to be obtained, and the vicinity of the electrode / near the gas diffusion substrate = 1 to 4, preferably about 1-2. do it.

  As a method for producing the carbon water repellent layer of the present invention, first, carbon particles, a water repellent, etc., in a solvent such as water, perfluorobenzene, dichloropentafluoropropane, methanol, ethanol and other alcohol-based organic solvents, A slurry is prepared by dispersing and mixing. Next, by masking a predetermined portion of the gas diffusion base material in advance, removing the mask after applying the slurry, performing another masking on the applied slurry, and spraying water repellent particles on the remaining portion A carbon water repellent layer is obtained.

  For example, when PTFE is used as a water repellent, the slurry can also be prepared by mixing carbon powder, PTFE dispersion, and, if necessary, water. Moreover, in order to make it easy to apply | coat to a gas diffusion base material, you may add a thickener etc. to a slurry.

  In order to apply the slurry, it may be applied using various known techniques such as spray, knife coater, and spin coater. In addition, after making the said slurry into powder by drying and grind | pulverizing, you may spread on the gas diffusion base material masked beforehand.

  The surface of the carbon water repellent layer is preferably smooth in order to improve adhesion to the electrode. Therefore, the produced carbon water-repellent layer is preferably formed by a known means such as extrusion or roll rolling through a release film coated with a polyethylene resin.

  The gas diffusion base material on which the carbon water-repellent layer is formed is preferably dried and then subjected to heat treatment at about 300 to 400 ° C. using a muffle furnace or a firing furnace. This makes it possible for the water repellent to ensure stable water repellency over a long period of time.

  In the above-described method, the carbon water-repellent layer is formed on the gas diffusion base material. However, the method is not particularly limited thereto. That is, on a release film such as a fluorine-based resin, a predetermined portion is masked and the slurry is applied, and then the masking is removed, and another portion of the slurry is applied to the remaining portion and water repellent is applied to the remaining portion. The gas diffusion layer of the present invention can also be produced by a method of spraying agent particles, disposing a gas diffusion base material on the surface, performing heat treatment, and peeling off the release film. The heat treatment performed at this time may be performed in the same manner as described above.

  In order to increase the water repellent content of the carbon water repellent layer from the gas inlet to the gas outlet, masking is performed so that more slurry is applied near the gas inlet and less toward the gas outlet. do it.

  In order to reduce the water repellent content of the carbon water repellent layer in the thickness direction from the electrode side to the gas diffusion substrate side, for example, first, (i) gas diffusion without masking Apply the slurry onto the substrate. Next, (ii) masking a predetermined part on it, applying the slurry again to remove the masking, masking only the part where the slurry is applied again, and then spraying the water repellent particles on the remaining part . Furthermore, the step (ii) may be repeated so that the content of the water repellent agent has a desired gradient. At this time, it is preferable to adjust a portion to be masked so that the slurry is applied in layers so that the obtained carbon water-repellent layer has at least one layer composed of only carbon particles over the entire length.

  As described above, the carbon water repellent layer of the present invention includes carbon particles coated with a water repellent and the water repellent particles, thereby covering the carbon particles that cause an increase in electrical resistance. The thickness of the liquid medicine can be reduced. Thereby, the distance between carbon particles becomes short, and it becomes possible to reduce resistance polarization. Further, in order to obtain a desired water repellent content in the carbon water repellent layer, the content of the water repellent particles may be increased without changing the thickness of the water repellent covering the carbon particles. Accordingly, since not only resistance polarization but also diffusion polarization can be reduced, if the gas diffusion layer having the carbon water-repellent layer of the present invention on the surface is used as the MEA for fuel cells, excellent power generation characteristics are exhibited. be able to.

  The second of the present invention is a fuel cell MEA having a solid polymer electrolyte membrane, an electrode, and a gas diffusion layer, wherein at least one of the gas diffusion layers is the above-described first gas diffusion layer of the present invention. The fuel cell MEA is characterized in that the carbon water-repellent layer is disposed on a surface in contact with the electrode.

  The solid polymer electrolyte membrane is not particularly limited, and any solid polymer electrolyte membrane can be used as long as it has been conventionally used in MEA. An example is a material composed of a member having at least high proton conductivity. Specifically, a perfluorocarbon polymer having a sulfonic acid group, an inorganic acid such as phosphoric acid is doped into a hydrocarbon polymer compound. A membrane made of a solid polymer electrolyte, such as an organic / inorganic hybrid polymer partially substituted with a proton conductive functional group, or a proton conductor obtained by impregnating a polymer matrix with a phosphoric acid solution or a sulfuric acid solution. Can be mentioned.

  Solid polymer electrolyte membranes include perfluorosulfonic acid membranes represented by various NAFION and Flemion manufactured by DuPont, ion exchange resins manufactured by Dow Chemical Company, ethylene-tetrafluoroethylene copolymer resin membranes, Commercially available products such as fluoropolymer electrolytes such as resin membranes based on fluorostyrene and hydrocarbon resin membranes having sulfonic acid groups may be used.

  The thickness of the solid polymer electrolyte membrane may be appropriately determined in consideration of the properties of the obtained MEA, but is preferably 5 to 300 μm, more preferably 10 to 200 μm, and particularly preferably 15 to 150 μm. If the thickness is less than 5 μm, it may be easily damaged during the manufacturing process or MEA operation, and if it exceeds 300 μm, the output characteristics of the resulting MEA may be deteriorated.

  Next, in the MEA of the present invention, the pair of electrodes sandwiching the solid polymer electrolyte membrane includes at least an electrode catalyst in which catalyst particles are supported on a conductive carrier, and a solid polymer electrolyte.

  The conductive carrier is preferably composed mainly of carbon. When the electrical resistance of the conductive carrier is high, the internal resistance of the electrode is increased, resulting in a decrease in battery performance. The conductive carrier can obtain a sufficiently high electronic conductivity by using carbon as a main component, and can reduce electric resistance.

  More specifically, as the conductive carrier, carbon black such as channel black, furnace black, and thermal black; activated carbon obtained by carbonizing and activating a material containing various carbon atoms; carbon such as graphitized carbon as a main component To do.

  Next, the catalyst particles in the electrode catalyst are required to have a catalytic action for hydrogen oxidation reaction and oxygen reduction reaction, such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, Examples thereof include one or more selected from metals such as iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, and aluminum, and alloys thereof. The catalyst particles may be used alone, but may be an alloy containing platinum as a main component in order to increase the stability and activity of the catalyst particles.

  The average particle diameter of the catalyst particles is preferably 1 to 30 nm. The catalyst particles are estimated to have a higher specific surface area as the average particle size is smaller, so the catalytic activity is also improved. However, in practice, even if the catalyst particle size is extremely small, catalyst activity commensurate with the increase in specific surface area is obtained. Therefore, the above range is preferable. The “average particle diameter of the catalyst particles” in the present invention is the average value of the particle diameter of the catalyst particles determined from the crystallite diameter or transmission electron microscope image obtained from the half width of the diffraction peak of the catalyst particles in X-ray diffraction. Can be measured.

  The catalyst particles can be supported on the conductive support by a known method. The amount of catalyst particles supported on the conductive support in the electrode catalyst is not particularly limited, but is 10 to 80% by mass, preferably 30 to 70% by mass, more preferably 40 to 40% by mass with respect to the total amount of the electrode catalyst in the electrode. It is good to set it as about 60 mass%. If the supported amount is less than 10% by mass, sufficient catalytic activity by the catalyst particles may not be obtained. For this reason, in order to obtain high activity, the electrode must be thickened, which is undesirable because the battery performance may be deteriorated due to an increase in the internal resistance of the electrode. On the other hand, when the amount exceeds 80% by mass, the overlapping of the catalyst particles supported on the surface of the conductive carrier increases, so that a sufficient reaction area of the catalyst particles cannot be obtained and the catalytic activity may be lowered. The amount of catalyst particles supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  Next, the solid polymer electrolyte contained in the electrode is not particularly limited as long as it is conventionally used for the electrode, and specifically, if the solid polymer electrolyte listed in the solid polymer electrolyte membrane is used. Good. Further, the solid polymer electrolyte used for the solid polymer electrolyte membrane and the electrode may be different, but it is preferable to use the same one in consideration of the contact resistance between the membrane and the electrode.

  The solid polymer electrolyte preferably covers an electrode catalyst as a binder polymer. Thereby, while being able to maintain the structure of an electrode stably, the sufficient reaction site (three-phase interface) where an electrode reaction advances can be ensured, and high catalyst activity can be acquired. Although content of the said solid polymer electrolyte contained in an electrode is not specifically limited, It is good to set it as 20-60 mass% with respect to the whole quantity of a catalyst particle.

  As an electrode manufacturing method, in addition to the catalyst particles and the proton conductive member, a water repellent, a pore former, a thickener, a diluting solvent, etc. are mixed as necessary to form a paste or slurry. Examples include a known method of forming an electrode by applying and drying to a desired thickness on a gas diffusion layer (carbon water repellent layer) or a solid polymer electrolyte membrane by a screen printing method, a deposition method, or a spray method. .

  The MEA of the present invention uses the above-described solid polymer electrolyte membrane and electrode, and further, a gas diffusion layer, gas diffusion layer / electrode (anode) / solid polymer electrolyte membrane / electrode (cathode) / gas diffusion. It is obtained by arranging so as to form a layer.

  As the gas diffusion layer, the gas diffusion layer having the first carbon water repellent layer of the present invention may be used in at least one of the anode side gas diffusion layer and the cathode side gas diffusion layer. Used for diffusion layer. Thus, not only can water generated by the electrode reaction be discharged to suppress the flooding phenomenon, but also electrons can be efficiently conducted to the electrode, so that a fuel cell MEA having excellent power generation characteristics can be obtained. Further, since the gas diffusion base material is generally made of a fiber woven fabric or the like, there is a risk that the gas diffusion base material may pierce and break the electrode or the solid polymer electrolyte membrane. However, providing a carbon water-repellent layer also provides a secondary role as a buffer layer.

  A gas diffusion layer having no carbon water-repellent layer may be disposed in the anode side gas diffusion layer. As the gas diffusion layer in this case, only the gas diffusion substrate used in the first gas diffusion layer of the present invention may be used. In addition, since the said gas diffusion base material is as having mentioned above, detailed description is abbreviate | omitted here.

  As a manufacturing method of MEA, after forming an electrode directly on a solid polymer electrolyte membrane, a method of sandwiching this with a gas diffusion layer, a gas diffusion layer and an electrode are formed on a separator, and this is used as a solid polymer electrolyte membrane. Various methods such as a method of bonding, a method of forming an electrode on a flat plate such as a release film, transferring the electrode to a solid polymer electrolyte membrane, and sandwiching it with a gas diffusion layer can be used. When the electrode is formed separately from the solid polymer electrolyte membrane, the electrode and the solid polymer electrolyte membrane are preferably joined by a hot press method or the like.

  A third aspect of the present invention is a fuel cell having a fuel cell MEA capable of exhibiting the various characteristics described above. The fuel cell is useful as a power source for a moving body such as a vehicle, a stationary power source, and the like, and can stably supply a high power generation amount under a high current density operation condition.

  The type of fuel cell is not particularly limited as long as desired cell characteristics can be obtained, but it is used as a polymer electrolyte fuel cell (also simply referred to as “PEFC”) from the viewpoints of practicality and safety. Is preferred. The PEFC has a structure in which an MEA is sandwiched between separators.

  It does not specifically limit as a separator, What is necessary is just to use well-known things, such as a carbon separator and a metal separator. The separator 8 has a function of separating air and fuel gas, and in order to secure the flow paths thereof, as shown in FIG. 2, a flow path groove 9 extending in parallel along the gas flow is formed. A plurality may be formed. The gas channel groove 9 is partitioned by a plurality of convex portions 10 called ribs.

  The groove width and pitch of the flow path groove of the separator are not particularly limited, but the gas diffusibility to the electrode is improved as the thickness is reduced, and a groove width of about 0.5 to 1.0 mm is usually used. In addition, in order to prevent water generated at the cathode from staying in the separator flow path, the flow path can be lengthened to increase the flow rate, or the separator can be set up so that the generated water can easily flow from top to bottom. Good.

  In the fuel cell of the present invention, it is preferable that the layer made of only carbon particles coated with the water repellent in the carbon water repellent layer is disposed in a region facing the convex portion as shown in FIG. Thereby, the flow of electrons can be made smooth, and the electron conductivity can be improved.

  Furthermore, a stack in which a plurality of MEAs are stacked via a separator and connected in series may be formed so that a desired voltage or the like can be obtained by the PEFC. The shape of the PEFC is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  The fuel cell MEA and the fuel cell of the present invention described above include the first gas diffusion layer of the present invention. Therefore, what has been described above is merely an example regarding the other requirements, and other constituent components that can be used in the conventionally known technology can be used as appropriate for the fuel cell MEA and the fuel cell of the present invention.

  Hereinafter, the present invention will be specifically described based on examples. The following example shows only one preferred embodiment of the present invention, and it goes without saying that the present invention is not limited thereto.

<Example 1>
1. Formation of gas diffusion layer (1-1) Water repellent treatment of gas diffusion base material Carbon paper having a thickness of 270 μm (TGP-H-090 manufactured by Toray Industries, Inc.) was dispersed in a polytetrafluoroethylene (PTFE) dispersion (manufactured by Daikin Industries, Ltd.). Gas diffusion base material (PTFE content: 25 wt.) Obtained by dispersing PTFE in carbon paper and dipping it in carbon paper by drying in an oven at 80 ° C. for 1 hour after being immersed in Polyflon D-1E (60 wt%) %). Thereafter, the gas diffusion base material was cut into a square having a side of 6 cm.

(1-2) Formation of carbon water repellent layer 5.4 g of carbon particles (2800 ° C. heat-treated Ketjen black EC600JD), 1.0 g of the same PTFE dispersion used in (1-1), and 29.6 g of water were homogenizer. Was mixed and dispersed for 3 hours to form a slurry. As shown in FIG. 2, the part where the slurry is applied on one side of the gas diffusion base material that has been subjected to the water-repellent treatment is a width (w ₁ ) of 1 mm, a height (h ₁ ) of 100 μm, and an interval (w ₂ ) of 1 mm. Then, the slurry was applied using a bar coater, and then the masking was removed. Next, masking is performed only on the applied slurry, and PTFE powder (average particle size: 1 μm) is sprayed as water-repellent particles on the remaining portion, followed by drying in an oven at 80 ° C. for 1 hour, and further a muffle furnace At 350 ° C. for 1 hour.

2. Preparation of MEA (2-1) Preparation of electrode ink 10 g of platinum-supported carbon (platinum content 43 wt%) in which platinum is supported on carbon particles (2800 ° C. heat-treated Ketjen Black EC600JD manufactured by Ketjen Black International), solids high Water bath set to hold a molecular electrolyte solution (DuPont NAFION solution DE520, electrolyte content 5 wt%) 90 g, pure water 3 g, and 2-propanol (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) at 25 ° C. An electrode ink was obtained by mixing and dispersing in a glass container inside for 3 hours using a homogenizer.

(2-2) Electrode formation The electrode ink previously prepared using a screen printer was applied on one side of a 200 μm thick PTFE sheet (Naflon sheet manufactured by Nichias) and dried in an oven at 100 ° C. for 30 minutes. Then, it was cut into a square with a side of 5 cm to form an electrode-formed PTFE sheet.

(2-3) MEA conversion The electrode-forming side of the two electrode-forming PTFE sheets prepared earlier with a solid polymer electrolyte membrane (NAFION NR-111 made by DuPont) having a square of 8 cm on each side and a thickness of 25 μm is sandwiched between them. The electrodes are transferred to the solid polymer electrolyte membrane by stacking them so as to face each other and hot-pressing at 130 ° C. for 10 minutes at a pressure of 2.5 MPa per one-side PTFE sheet area, and then removing only the PTFE sheet after cooling. A laminate was obtained. At this time, the transfer rate of the electrode from the polytetrafluoroethylene sheet to the solid polymer electrolyte membrane was 100%, the platinum weight per 1 cm ² of the single-sided electrode area on the solid polymer electrolyte membrane was 0.40 mg, and the single-sided electrode The thickness was 10 μm. Two gas diffusion layers are stacked so that the carbon water-repellent layer faces each other with the produced laminate sandwiched therebetween, thereby forming an MEA, which has a height (h ₂ ) of 1 mm and a width (w ₃ ) as shown in FIG. A graphite separator having a gas flow channel groove provided with a 1 mm convex portion at an interval (w ₄ ) of 1 mm, and sandwiching the convex portion and a layer made of only carbon particles coated with a water repellent. Further, this was sandwiched between gold-plated stainless steel current collector plates to form single cells for evaluation.

<Example 2>
In (1-2) of Example 1, 3 cm from the gas inlet of the gas diffusion base material is not masked, the remaining part is masked in the same manner as in Example 1, and when the produced MEA is sandwiched between separators For evaluation in the same manner as in Example 1, except that the convex portion of the separator and the layer composed of only the carbon particles coated with the water repellent agent formed on the latter half of the gas diffusion base material were sandwiched to face each other. A single cell was assembled into a single cell for evaluation.

<Example 3>
In Example 1-2 (1-2), as shown in FIG. 3, the slurry was applied on one side of a water-repellent gas diffusion base material using a bar coater to a height (h ₁ ) of 20 μm. did. Next, masking is performed so that the part where the slurry is applied has a width (w ₁ ) of 1 mm, a height (h ₂ ) of 20 μm, and an interval (w ₂ ) of 1 mm. Another masking was performed only on the applied slurry, and PTFE (average particle size: 1 μm) was sprayed as water repellent particles on the remaining portion to remove the masking. Furthermore, masking was performed so that the part to which the slurry was applied had a width (w ₁ ) of 1 mm, a height (h ₃ ) of 20 μm, and an interval (w ₂ ) of 1 mm, and the slurry was further applied to remove the masking and further applied After another masking only on the slurry, PTFE (average particle size 1 μm) was sprayed as water repellent particles on the remaining portion to remove the masking. This was dried in an oven at 80 ° C. for 1 hour, and further heat-treated in a muffle furnace at 350 ° C. for 1 hour. As a result, as shown in FIG. 3, a carbon water-repellent layer (thickness: 60 μm) was obtained on the gas diffusion substrate.

  An evaluation single cell was assembled into an evaluation single cell in the same manner as in Example 1 except that the gas diffusion layer thus prepared was used.

<Comparative Example 1>
In Example 1-2 (1-2), the prepared slurry was applied to one side of a water-repellent gas diffusion substrate without masking using a bar coater (thickness: 100 μm), and the slurry was 80 in an oven. Except for obtaining a carbon water-repellent layer on the gas diffusion substrate by drying it at 350 ° C. for 1 hour in a muffle furnace and then cutting it into a square of 6 cm on each side after drying at 350 ° C. for 1 hour. Similarly, an evaluation single cell was assembled into an evaluation single cell.

<Evaluation>
The performance measurement of the single cell for evaluation produced by each Example and the comparative example was performed according to the following.

In this measurement, when the fuel cell was operated for power generation, hydrogen was supplied as fuel to the anode side and air was supplied to the cathode side. The supply pressure of both gases is atmospheric pressure, hydrogen is saturated and humidified at 80 ° C, air is saturated and humidified at 80 ° C, the temperature of the fuel cell body is set at 80 ° C, the hydrogen utilization rate is 70%, and the air utilization rate Was 40%, and the power generation characteristics of the single cell were evaluated by observing the change in cell voltage when the current density was changed from 0 A / cm ² to 1.2 A / cm ² . The obtained results are shown in FIGS.

  4-6, it turns out that the single cell of each Example is excellent in a power generation characteristic. The single cell using the gas diffusion layer according to the present invention is considered to have the resistance polarization of the gas diffusion layer suppressed and the optimal arrangement of the water repellent. In particular, even under high humidification and high current density, where flooding is generally likely to occur, the generated water can be discharged to suppress diffusion polarization, and the gas diffusion layer of the present invention exhibits excellent power generation characteristics. It can be seen that it is possible.

It is the schematic diagram which showed the comparison of the structure of the conventional example of a carbon water repellent layer, and this invention. The schematic cross section of the air electrode side single side | surface of MEA produced in Example 1 is shown. The schematic cross section of the air electrode side single side | surface of MEA produced in Example 3 is shown. The evaluation result of each single cell produced in Example 1 and the comparative example is shown. The evaluation result of each single cell produced in Example 2 and the comparative example is shown. The evaluation result of each single cell produced in Example 3 and the comparative example is shown.

Explanation of symbols

1 ... carbon particles,
2 ... water repellent,
3 ... water repellent particles,
4 ... Solid polymer electrolyte membrane,
5 ... Electrode,
6 ... carbon water repellent layer,
7: Gas diffusion substrate,
8 ... separator,
9: Gas channel groove,
10: Convex part (rib).

Claims (9)

  A gas diffusion layer having a carbon water repellent layer containing carbon particles coated with a water repellent and water repellent particles on the surface of the gas diffusion substrate.   The gas diffusion layer according to claim 1, wherein the carbon water repellent layer has at least one layer composed of only the carbon particles over the entire length of the thickness of the carbon water repellent layer.   The gas diffusion layer according to claim 1, wherein the carbon water repellent layer has an average pore diameter smaller than that of the gas diffusion base material.   The gas diffusion layer according to any one of claims 1 to 3, wherein the carbon water repellent layer has a large content of the water repellent in a surface direction from a gas inlet portion to a gas outlet portion.   The gas diffusion layer according to any one of claims 1 to 4, wherein the carbon water repellent layer has a small content of the water repellent in the thickness direction from the electrode side to the gas diffusion base material side. In an MEA for a fuel cell having a solid polymer electrolyte membrane, an electrode, and a gas diffusion layer,
6. The fuel cell MEA according to claim 1, wherein at least one of the gas diffusion layers is the gas diffusion layer according to claim 1, and the carbon water-repellent layer is disposed on a surface in contact with the electrode.   A fuel cell comprising the fuel cell MEA according to claim 6.   8. The fuel cell according to claim 7, wherein the fuel cell MEA is sandwiched between separators having convex portions forming gas flow channel grooves.   The fuel cell according to claim 8, wherein the layer made of only the carbon particles is disposed in a region facing the convex portion.

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