JP2005327675A - Gas diffusion layer and mea for fuel cell using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion layer which can improve corrosion resistance of the conductive material constituting a conductive water repellent layer and can demonstrate a stable performance for a long period. <P>SOLUTION: The problem is solved by a gas diffusion layer which has a conductive water repellent layer and a conductive base material containing a conductive material of which combustion temperature in the air atmosphere is 650°C or more. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas diffusion layer, and more particularly to a gas diffusion layer that can exhibit stable performance over a long period of time.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, solid 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. Yes. The solid polymer electrolyte fuel cell is characterized by using an electrolyte layer made of a film-like solid polymer electrolyte membrane.

  The configuration of a solid polymer electrolyte fuel cell generally has a structure in which a plurality of unit cells each having a membrane-electrode assembly (MEA) sandwiched between separators are stacked. The MEA has a structure in which an electrolyte layer is sandwiched between electrode catalyst layers in which an electrode catalyst is highly dispersed.

  In MEA, the following electrochemical reaction proceeds. First, hydrogen contained in the fuel gas supplied to the fuel electrode (anode) side electrode catalyst layer is oxidized by the catalyst particles to become protons and electrons. Next, the produced protons pass through the proton conductive electrolyte contained in the 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 anode-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 gas separator, and It reaches the cathode electrode catalyst layer through an external circuit. The protons and electrons that have reached the cathode-side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side to generate water. In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

  The electrochemical reaction proceeds at a three-phase interface in the electrode catalyst layer where the electrode catalyst, the solid polymer electrolyte, the fuel gas, or the oxidant gas contacts. In order to make the electrochemical reaction proceed uniformly in the electrode catalyst layer, the gas supplied through the separator is uniformly supplied to the electrode catalyst layer, and the water generated by the chemical reaction is promptly discharged to the outside. It is necessary to discharge.

  Therefore, it is common to arrange gas diffusion layers on both sides of the MEA. The gas diffusion layer is formed using a conductive base material made of carbon fiber or the like, and is porous. Due to the presence of the gas diffusion layer, appropriate gas diffusion, water movement, and current collection can be realized.

  In addition, the water repellent treatment may be performed on the conductive substrate constituting the gas diffusion layer for the purpose of more quickly discharging water and the like of the electrode catalyst layer by further improving the water repellency of the gas diffusion layer. It is effective to dispose a conductive water repellent layer containing a conductive material such as carbon particles or PTFE on a conductive base material (see, for example, Patent Document 1).

In general, the conductive water-repellent layer has a powdery conductive material as an aggregate, and has a denser structure than a conductive substrate made of fibers or the like. As a result, sufficient contact with the electrode catalyst layer can be maintained, which is advantageous for current collection, and the supplied gas can be diffused and supplied to the electrode catalyst layer more uniformly. It is possible to promote the discharge of water generated by a chemical reaction to the outside. Furthermore, when the conductive substrate is made of carbon fiber or the like, the electrode catalyst layer and the solid polymer electrolyte membrane may be damaged, but the conductive water-repellent layer can prevent damage.
JP 2002-289204 A

  However, when the electrode potential changes to a high potential due to various causes such as continuous operation and start / stop of the MEA for a long period of time, the conductive material constituting the conductive water repellent layer is electrochemical. As a result, the number of sites that function as a gas diffusion layer decreases due to oxidation and corrosion, leading to a problem that the performance of the MEA deteriorates over time.

  The MEA is required to exhibit desired power generation performance over a long period of time, and is said to be 5000 hours for automobiles and 40,000 hours for home use. Therefore, in order to exhibit the performance of MEA over a long period of time, it is necessary to keep the constituent members of the gas diffusion layer in a stable state.

  Accordingly, an object of the present invention is to provide a gas diffusion layer that can exhibit stable performance for a long period of time by using a conductive material having high corrosion resistance for the conductive water-repellent layer.

  In the present invention, as a result of intensive studies to ensure the corrosion resistance of the members constituting the conductive water-repellent layer in the gas diffusion layer, it has been found that a conductive material having a predetermined combustion temperature is excellent in corrosion resistance.

  That is, the present invention is a gas diffusion layer having a conductive water repellent layer containing a conductive material having a combustion temperature of 650 ° C. or higher in an air atmosphere, and a conductive base material.

  The conductive material of the present invention has excellent corrosion resistance even in a noble potential environment or a strongly acidic atmosphere. Therefore, according to the conductive water repellent layer using such a conductive material, it is possible to provide a gas diffusion layer that can exhibit stable performance over a long period of time. According to the gas diffusion layer of the present invention, it is possible to stabilize the performance and extend the life of the MEA for fuel cells.

  As described above, the present invention is a gas diffusion layer having a conductive water repellent layer containing a conductive material having a combustion temperature in an air atmosphere of 650 ° C. or higher and a conductive base material.

  In the present invention, the combustion temperature is a physical property value of the conductive material, and specifically, the mass of the conductive material is rapidly increased by burning the conductive material when the temperature is equal to or higher than a predetermined temperature in an air atmosphere. It means the temperature that starts to decrease. More specifically, as shown in FIG. 1, in the thermogravimetric analysis of the conductive material in an air atmosphere, the mass rapidly decreases when the horizontal axis is plotted as the temperature and the vertical axis as the mass reduction rate. The intersection of the tangent in the previous range and the tangent in the range where the mass rapidly decreases is defined as the combustion temperature.

As the conductive material, a material having a characteristic that the combustion temperature in an air atmosphere is 650 ° C. or higher, preferably 700 ° C. or higher, more preferably 740 ° C. or higher is used. Such a conductive material can suppress corrosion even in a noble potential environment or a strongly acidic atmosphere, and can maintain a stable state for a long period of time. Therefore, by using the conductive material for the conductive water-repellent layer, a gas diffusion layer having excellent durability can be obtained. Also, a conductive material obtained by heat-treating a carbon material described later in an inert gas atmosphere. The combustion temperature can be increased. This is because the conductive material graphitized by heat treatment has a graphitized layer consisting of a three-dimensional crystal lattice resembling the graphite structure on the surface, and as the graphitization proceeds, there are fewer fine voids between the crystal lattices. This is because the crystal structure of the surface of the conductive material approaches the crystal structure of graphite.

  Specifically, the heat treatment of the carbon material is preferably performed at 2000 ° C. or more, particularly 2500 ° C. or more in an inert atmosphere such as nitrogen, helium, or argon. Thus, by performing heat processing in inert gas atmosphere, it can graphitize and, thereby, the combustion temperature of an electroconductive material can be raised.

The conductive material may have a BET specific surface area of 500 m ² / g or less, preferably 300 m ² / g or less, more preferably 150 m ² / g or less. In the present invention, as a result of examining the corrosion resistance of the conductive material, the conductive material having a BET specific surface area of more than 500 m ² / g has a thin graphitized layer formed on the surface, and the desired corrosion resistance is obtained. It turns out that there is a fear of not being able to. Therefore, it is preferable to use a conductive material having a BET specific surface area of 500 m ² / g or less.

The conductive material may have a lattice spacing d ₀₀₂ of 0.350 nm or less, preferably 0.336 to 0.350 nm. Such a conductive material has a sufficiently developed surface graphitized layer and has high corrosion resistance, electronic conductivity, and the like.

In the present invention, the “lattice plane distance d ₀₀₂ ” is the plane distance of the hexagonal mesh plane based on the graphite structure of the conductive material, and is a ½ layer of the lattice constant in the c-axis direction that is perpendicular to the hexagonal mesh plane Means the average distance.

  The conductive material used for the conductive water repellent layer of the present invention needs to use a material having high electron conductivity. This is because the gas diffusion layer arranged on the anode side has a role of taking out electrons generated in the anode-side electrocatalyst layer to an external circuit, and the gas diffusion layer arranged on the cathode side passes through the external circuit. Therefore, the internal resistance of the fuel cell can be reduced by using a material having high electron conductivity.

  Specific examples of the conductive material constituting the conductive water repellent layer include a carbon material containing carbon as a main component as a material having high electron conductivity, and more specifically, carbon black, activated carbon, coke. , Carbon materials such as graphite and carbon fiber. Of these, carbon black is preferably used because of its excellent electron conductivity, corrosion resistance, and the like.

  In the present invention, the carbon material containing carbon as a main component is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the gas diffusion layer and the like. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by mass or less is allowed.

  As the conductive material, in addition to the above-described carbon material, metals such as ITO and ATO, and metal oxides can also be used.

  In the present invention, the conductive water repellent layer preferably contains a water repellent material in addition to the conductive material. In order to efficiently supply the fuel gas and the oxidant gas to the electrode catalyst layer, it is necessary to efficiently drain the water generated in the electrode catalyst layer and suppress water clogging in the gas supply path. Therefore, when the conductive water repellent layer further contains a water repellent material, it is possible to provide a gas diffusion layer excellent in electron conductivity, gas diffusibility, and drainage.

  The water-repellent material is not particularly limited as long as it is a conventionally used material such as a fluorine material containing fluorine atoms, polypropylene, or polyethylene. Especially, since it has high water repellency, at least one selected from the group of PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), and PVDF (polyvinylidene fluoride). Specified fluorine materials are preferred.

  In the conductive water-repellent layer, the mixing ratio of the conductive material and the water-repellent material may be insufficient to obtain the water repellency as expected when there are too many conductive materials. There is a risk that sex may not be obtained. Considering these, the mixing ratio of the conductive material and the water-repellent material in the conductive water-repellent layer is preferably about 90:10 to 40:60 in terms of mass ratio.

  The thickness of the conductive water repellent layer is 10 to 300 μm, preferably 20 to 100 μm. If it is less than 10 μm, the effect of the conductive water repellent layer may not be obtained as expected, and if it exceeds 300 μm, it is too thick and gas diffusibility and water discharge may be reduced.

  The conductive base material used for the gas diffusion layer of the present invention is not particularly limited, and the base material is a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, and a nonwoven fabric. Etc. Moreover, what is marketed may be used as an electroconductive base material, for example, carbon paper TGP series by Toray Industries, Inc., carbon cloth by E-TEK, etc. are mentioned.

  The thickness of the conductive substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness is less than 30 μm, sufficient mechanical strength or the like may not be obtained, and if it exceeds 500 μm, the distance through which gas or water permeates is undesirably increased.

  The porosity of the conductive substrate may be appropriately determined in consideration of gas diffusibility, water dischargeability, mechanical strength, and the like of the obtained gas diffusion layer, and is within a range of 50 to 90%. It is good to do.

  The method for producing a gas diffusion layer of the present invention may be performed using a conventional general method. First, a conductive material such as carbon black, a water repellent material such as polytetrafluoroethylene, and the like, an alcohol solvent such as water, perfluorobenzene, dichloropentafluoropropane, perfluoro (2-butyltetrahydrofuran), methanol, and ethanol. A slurry is prepared by dispersing in a solvent such as.

  In addition, the conductive substrate is preferably subjected to a water repellent treatment in advance using a known means for the purpose of suppressing flooding by increasing water repellency. Examples of the water repellent treatment method include a method in which a conductive substrate is immersed in a dispersion of a fluorine material such as PTFE and then dried using an oven or the like. Although it does not specifically limit as a drying method, What is necessary is just to heat to 100 degrees C or less in air | atmosphere or nitrogen atmosphere.

  Next, the slurry is applied on a conductive substrate and dried, or the slurry is once dried and pulverized to form a powder, which is applied on the conductive substrate. Thereby, a gas diffusion layer in which a conductive water repellent layer is formed on a conductive substrate is obtained.

  As a method of applying the slurry to the gas diffusion layer, any method such as a doctor blade method, a screen printer method, or a spray method may be used.

  When the slurry is impregnated into a part of the pores of the conductive base material during application, the conductive water repellent layer obtained by the anchor effect and the conductive base material can be strongly bonded. The depth for impregnating the slurry should be such that the pores of the conductive substrate are not blocked and the gas diffusivity is not lowered, and the obtained conductive water repellent layer and conductive group are obtained. The shallower one is desirable if the material can be sufficiently fixed. In order to prevent the slurry from being so deeply impregnated, it is preferable to perform a water-repellent treatment on the conductive substrate first.

  The obtained gas diffusion layer may be heat-treated at about 300 to 400 ° C. using a muffle furnace or a firing furnace. As a result, the water repellent material is welded when the temperature is equal to or higher than the melting point, and the structure of the gas diffusion layer can be kept stable for a long time.

  In the method described above, the method for producing the gas diffusion layer of the present invention is a method in which a conductive water repellent layer is formed directly on a conductive substrate, but in addition, a conductive repellent layer is formed on a film such as PTFE. After forming an aqueous layer, the method of transferring on a conductive substrate may be used.

  A second aspect of the present invention is an MEA for a fuel cell (hereinafter also simply referred to as “MEA”) having the gas diffusion layer described above. The gas diffusion layer of the present invention having a conductive water-repellent layer containing a conductive material excellent in corrosion resistance can exhibit stable performance over a long period of time because of its excellent durability, and is suitably used for MEA.

  The structure of the MEA is not particularly limited, and may be a general structure in which an electrode catalyst layer and a gas diffusion layer are disposed on both sides of the solid polymer electrolyte membrane.

  The first gas diffusion layer of the present invention may be used as at least one gas diffusion layer on the cathode side or anode side of the MEA. At this time, the gas diffusion layer is disposed so that the conductive water-repellent layer is disposed between the conductive substrate and the electrode catalyst layer.

  However, in order to improve the durability of the obtained MEA, it is more preferable that the first gas diffusion layer of the present invention is disposed on both the anode side and the cathode side.

  An example of other constituent elements in the fuel cell is described below, but the present invention is not limited to this and may be used by appropriately referring to various conventionally known techniques.

  The electrode catalyst layer used on the anode side and the cathode side includes at least an electrode catalyst in which catalyst particles are supported on a conductive carrier, and a solid polymer electrolyte.

  The conductive carrier may have any specific surface area for supporting the catalyst particles in a desired dispersed state and sufficient electronic conductivity as a current collector, such as carbon black, activated carbon. , Coke, natural graphite, artificial graphite, etc., as long as they are conventionally used.

  The size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the thickness of the electrode catalyst layer within an appropriate range, the average primary particle diameter is 5 to 200 nm, preferably about 10 to 100 nm. Is good.

  The catalyst particles are required to have a catalytic action in a hydrogen oxidation reaction and an oxygen reduction reaction, and preferably contain at least platinum.

  In addition, in order to improve the toxicity resistance, heat resistance, etc. against carbon monoxide, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, It may be an alloy of platinum and at least one metal selected from aluminum and the like.

  The average particle diameter of the catalyst particles supported on the conductive carrier is preferably 1 to 30 nm. Although it is speculated that the catalyst particles improve the catalyst activity because the specific surface area increases as the average particle size decreases, in fact, even if the catalyst particle size is extremely small, the catalyst activity commensurate with the increase in specific surface area is obtained. Therefore, the above range is preferable. Further, the supported amount of catalyst particles may be appropriately determined so that an electrode catalyst having a desired catalytic activity can be obtained.

  The average particle diameter of the catalyst particles can be measured by the crystallite diameter obtained from the half-value width of the diffraction peak of the catalyst particles in X-ray diffraction or the average value of the fine particle diameter of the catalyst particles determined from a transmission electron microscope image. it can.

  The solid polymer electrolyte used for the electrode catalyst layer is not particularly limited, and a known one can be used as long as it is a member having at least high proton conductivity. Specifically, a perfluorocarbon polymer having a sulfonic acid group such as NAFION (registered trademark of DuPont), a hydrocarbon polymer compound doped with an inorganic acid such as phosphoric acid, a part of which is proton conductive. Examples thereof include organic / inorganic hybrid polymers substituted with functional groups, proton conductors in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution, and the like.

  In the present invention, the electrode catalyst layer may be produced according to a conventionally known method. For example, a solid polymer electrolyte and an electrode catalyst are mixed with water or an alcohol solvent to form an electrode catalyst layer ink, which is applied onto a substrate such as a gas diffusion layer, a solid polymer electrolyte membrane or a PTFE sheet, It is a method of drying.

  The electrode catalyst layer ink may contain various additives such as a water repellent polymer such as PTFE, PFA, and PVDF in addition to the solid polymer electrolyte and the electrode catalyst. Thereby, the water repellency of the obtained electrode catalyst layer can be increased, and water generated at the time of power generation can be quickly discharged. The content of the water repellent polymer may be appropriately determined in consideration of the properties of the obtained MEA.

  Next, the solid polymer electrolyte membrane used in the MEA of the present invention is not particularly limited, and examples thereof include those made of the same solid polymer electrolyte as listed in the description of the electrode catalyst layer. Examples include NAFION manufactured by DuPont, FLEMION manufactured by Asahi Glass Co., and ACIPLEX manufactured by Asahi Kasei. In addition, fluoropolymer electrolytes such as ion exchange resins manufactured by Dow Chemical Co., ethylene-tetrafluoroethylene copolymer resin membranes, resin membranes based on trifluorostyrene, and hydrocarbons having sulfonic acid groups A resin film or the like 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. From the viewpoint of strength during film formation and durability during MEA operation, it is preferably 5 μm or more, and from the viewpoint of output characteristics during MEA operation, it is preferably 300 μm or less.

  What is necessary is just to perform according to a conventionally well-known method as a manufacturing method of MEA of this invention. For example, as described above, a method of forming an electrode catalyst layer on a gas diffusion layer, sandwiching a solid polymer electrolyte membrane by using two electrode catalyst layers, and then hot pressing may be used.

  Hot pressing is preferably performed at 110 to 170 ° C. and a pressing pressure of 1 to 5 MPa with respect to the electrode surface. Thereby, the bondability between the solid polymer electrolyte membrane and the catalyst layer can be enhanced.

  When an electrode catalyst layer is formed on a PTFE sheet or the like, after sandwiching the solid polymer electrolyte membrane so that the electrode catalyst layer is on the inside, hot pressing is performed in the same manner as described above, and then PTFE It is only necessary to peel off the sheet.

  A third aspect of the present invention is a fuel cell using the above-described gas diffusion layer or MEA. According to the gas diffusion layer of the present invention described above or the MEA using the same, a fuel cell that can exhibit stable power generation performance over a long period of time can be provided. The fuel cell using the gas diffusion layer and the MEA is also suitably used under a high current density where a large amount of water is generated, operating conditions under high humidification, and the like.

  The type of the fuel cell is not particularly limited as long as desired battery characteristics can be obtained, but it is preferably used as a solid polymer electrolyte fuel cell (PEFC) from the viewpoints of practicality and safety. Thereby, a highly reliable fuel cell can be obtained as a power source for moving bodies and a stationary power source.

  The structure of the fuel cell is not particularly limited, and examples thereof include a structure in which MEA is sandwiched between separators.

  The separator has a function of separating air and fuel gas, and a gas flow groove may be formed in order to secure the flow path, and a conventionally known technique can be appropriately used. The shape of the separator is not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

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

  Hereinafter, the present invention will be specifically described based on examples. The present invention is not limited to the following examples.

<Example 1>
-Water-repellent treatment of conductive substrate First, a conductive substrate in which carbon paper (carbon paper TGP-H-090 manufactured by Toray Industries, Inc.) was punched into a 5 cm square was prepared. After immersing this conductive base material in a PTFE fluorine-based aqueous dispersion solution (polyflon D-1E manufactured by Daikin Industries, Ltd., containing 60 wt% PTFE) adjusted to a predetermined concentration with pure water, The PTFE was dispersed in the carbon paper by drying at 60 ° C. for 30 minutes. At this time, the PTFE content was 25 wt%. As a result, a water-repellent conductive substrate was obtained.

-Production of conductive water-repellent layer Subsequently, carbon black (Black Pearl manufactured by Cabot) was heat-treated in an argon atmosphere at about 2900 ° C for about 5 hours to produce graphitized carbon black (combustion temperature 700 ° C, specific surface area 260 m ^2). / g, lattice spacing d ₀₀₂ 0.349 nm). Mixing and stirring this graphitized carbon black as a conductive material and PTFE fluorine-based aqueous dispersion solution (containing Daikin Industries, Ltd., Polyflon D-1E, PTFE 60 wt%) in a mass ratio of 8: 2. A conductive water repellent layer ink was prepared.

The obtained conductive water-repellent layer ink was uniformly applied to one surface of the previously prepared water-repellent conductive substrate by the doctor blade method and dried in an oven at 60 ° C. for 30 minutes. Thereafter, it was further fired at 350 ° C. for 30 minutes in a muffle furnace. Thereby, the gas diffusion layer in which the electroconductive water repellent layer was formed on the electroconductive base material was obtained. The weight of the conductive water repellent layer formed per 1 cm ² of the conductive substrate was about 3 mg.

  In order to evaluate the produced gas diffusion layer, an MEA was produced according to the following, and performance evaluation was performed.

-Production of MEA 1 g of conductive carrier powder obtained by heat-treating carbon black (Vulcan XC72 manufactured by Cabot) at about 2900 ° C. for about 5 hours in an argon atmosphere in 250 g of an aqueous chloroplatinic acid solution containing 0.4% platinum. After sufficiently dispersing using a homogenizer, 20 ml of formaldehyde was added thereto and heated to 50 ° C. using a reflux reactor to carry out reduction loading of platinum particles. And after standing to cool to room temperature, the electroconductive support | carrier with which the platinum particle was carry | supported is separated by filtration, and it is made to dry at 85 degreeC for 12 hours, and an electrocatalyst (Pt: particle size 2-3 nm, carrying amount about 50 wt%) Got.

  10 g of the obtained electrode catalyst, 90 g of Nafion / isopropyl alcohol solution (manufactured by DuPont, containing 5 wt% of Nafion), 25 g of pure water, and 10 g of isopropyl alcohol (special grade reagent manufactured by Wako Pure Chemical Industries, Ltd.) are set to be kept at 20 ° C. The electrode catalyst slurry was obtained by mixing and dispersing in a glass container in the water bath using a homogenizer for 3 hours. This electrocatalyst slurry is applied on one side of a PTFE sheet (Naflon (registered trademark) sheet manufactured by NICHIAS Corporation, thickness 200 μm, 5 cm square) using a screen printer and dried in an oven at 100 ° C. for 30 minutes. Thus, an electrode catalyst layer was formed on the PTEF sheet.

With the solid polymer electrolyte membrane (DuPont NAFION NR-112, thickness of about 50 μm, 10 cm square) sandwiched between the two electrode catalyst layer forming PTFE sheets prepared earlier, the electrode catalyst layer forming side is on the inside The electrode catalyst layer is transferred to the solid polymer electrolyte membrane and bonded by hot pressing at 150 ° C. for 10 minutes at a pressure of 20 Kg / cm ² per PTFE sheet, cooling, and then removing only the PTFE sheet after cooling. Got the body. At this time, the transfer rate of the electrode catalyst layer from the PTFE sheet to the solid polymer electrolyte is 100%, and the platinum weight per 1 cm ² of the single-sided electrode catalyst layer area on the solid polymer electrolyte membrane is 0.50 mg. did.

  Subsequently, the gas diffusion layer prepared earlier was arranged on both surfaces of the joined body so that the conductive water-repellent layer was on the inside, thereby forming an MEA.

  Thereafter, a gas separator with a gas flow path and a sealing material are arranged on the manufactured MEA, and are further clamped by a gold-plated stainless steel current collector plate so as to have a predetermined surface pressure. The solid polymer electrolyte shown in FIG. Type fuel cell.

-Performance evaluation The single cell was temperature-controlled at 80 degreeC, hydrogen (dew point 80 degreeC) was supplied as fuel gas to the anode side, and air (dew point 60 degreeC) was supplied as an oxidizing agent to the cathode side. The exhaust pressure on the single cell was atmospheric pressure.

Subsequently, power generation was stopped for 1 hour at a current density of 1 A / cm ² (hydrogen utilization rate 70%, air utilization rate 40%). After stopping, the supply of hydrogen and air was stopped, the single cell was replaced with nitrogen gas, and the system was on standby for 30 minutes. Thereafter, hydrogen gas was supplied to the anode side and air was supplied to the cathode side again, and power was generated again at a current density of 1 A / cm ² for 1 hour.

This power generation / stop operation was repeated to evaluate the durability of the single cell. FIG. 3 shows the change (decrease rate with respect to the initial value) with respect to the number of power generation-stop cycles of the cell voltage of the single cell (when generating power at 1 A / cm ² ).

<Example 2>
In preparation of the conductive water-repellent layer ink of Example 1, graphitized carbon black (combustion temperature) obtained by heat-treating carbon black (Ketjen Black manufactured by Lion Corporation) at about 2900 ° C. for about 5 hours in an argon atmosphere. 710 ° C., specific surface area 100 m ² / g, lattice spacing d ₀₀₂ 0.347 nm) was used as a conductive material, and a gas diffusion layer and MEA were produced in the same manner as in Example 1 and the performance evaluation was performed. went. The obtained results are shown in FIG.

<Example 3>
In preparation of the conductive water-repellent layer ink of Example 1, graphitized carbon black (combustion temperature 740 ° C.) obtained by heat-treating carbon black (Vulcan XC72 manufactured by Cabot Corporation) in an argon atmosphere at about 2900 ° C. for about 5 hours. The gas diffusion layer and the MEA were prepared in the same manner as in Example 1 except that the specific surface area was 80 m ² / g and the lattice spacing d _{002 was} 0.340 nm), and the performance evaluation was performed. . The obtained results are shown in FIG.

<Comparative Example 1>
In the production of the conductive water repellent layer ink of Example 1, except that carbon black (Ketjen Black manufactured by Lion Corporation, combustion temperature 620 ° C., specific surface area 800 m ² / g) was used as the conductive material without heat treatment, A gas diffusion layer and MEA were prepared in the same manner as in Example 1, and performance evaluation was performed. The obtained results are shown in FIG.

In addition, Table 1 below summarizes the combustion temperature, specific surface area, and lattice spacing d ₀₀₂ of each conductive material used in Examples 1 to 3 and Comparative Example 1.

  Compared with Comparative Example 1 from FIG. 3, the fuel cell single cell produced using the gas diffusion layers of Examples 1 to 3 has an improved cell performance degradation rate when the power generation-stop cycle is repeated. I understand. By repeating the operation-stop cycle, the durability of the conductive material that is likely to be corroded by electrochemical oxidation in the fuel cell gas diffusion layer surface is improved, and a stable gas diffusion layer can be formed for a long time. It is thought that there is. Thus, it can be seen that a solid polymer fuel cell having excellent durability and stable performance for a long time can be provided.

It is a graph which shows the thermogravimetric analysis of the electroconductive material in an air atmosphere by setting a horizontal axis as temperature and a vertical axis | shaft as a mass decreasing rate. The schematic of the single cell of the solid polymer electrolyte fuel cell produced in the Example is shown. The time-dependent change characteristic of the cell voltage at the time of operation-stop operation | movement of the single cell using each gas diffusion layer produced in Examples 1-3 and the comparative example 1 is shown.

Explanation of symbols

10 ... conductive substrate,
15 ... conductive water repellent layer,
20 ... Electrocatalyst layer,
30 ... Solid polymer electrolyte membrane,
50 ... sealing material,
60 ... Gas separator,
61: Gas flow path.

Claims (9)

  A gas diffusion layer comprising: a conductive water repellent layer containing a conductive material having a combustion temperature of 650 ° C. or higher in an air atmosphere; and a conductive base material.   The gas diffusion layer according to claim 1, wherein the conductive material has a combustion temperature in an air atmosphere of 700 ° C or higher. The gas diffusion layer according to claim 1 or 2, wherein the conductive material has a specific surface area of 500 m ² / g or less. The gas diffusion layer according to claim 1, wherein the conductive material has a lattice spacing d ₀₀₂ of 0.350 nm or less.   The gas diffusion layer according to any one of claims 1 to 4, wherein the conductive material includes at least one carbon material selected from the group consisting of carbon black, activated carbon, coke, and graphite.   The gas diffusion layer according to claim 1, wherein the conductive water repellent layer includes a water repellent material.   The gas diffusion layer according to claim 6, wherein the water repellent material includes at least one fluorine material selected from the group of PTFE, PFA, and PVDF. In a fuel cell MEA having an electrode catalyst layer and a gas diffusion layer on both sides of a solid polymer electrolyte membrane,
An MEA for a fuel cell, wherein at least one of the gas diffusion layers is the gas diffusion layer according to any one of claims 1 to 7.   A fuel cell using the gas diffusion layer according to claim 1 or the MEA for fuel cell according to claim 8.