JP2014035797A - Membrane electrode assembly and fuel cell, and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane electrode assembly including a gas diffusion layer that can balance water repellency, water holding property and conductivity well with a thickness thinner than conventional, and can enhance power generation performance furthermore, and to provide a fuel cell and a manufacturing method therefor.SOLUTION: An anode gas diffusion layer and a cathode gas diffusion layer are composed, respectively, of a porous member containing conductive particles and a polymer resin as main components. The porous member is a porous film formed by laminating more than one sheet having different porosity.

Description

  The present invention relates to a fuel cell that uses a reducing agent such as pure hydrogen or methanol as a fuel gas, or reformed hydrogen from a fossil fuel, and uses air (oxygen) or the like as an oxidant gas. More specifically, the present invention relates to a gas diffusion layer provided in the fuel cell and a manufacturing method thereof.

  2. Description of the Related Art A fuel cell, for example, a polymer electrolyte fuel cell, causes a fuel gas containing hydrogen and an oxidant gas containing oxygen such as air to react electrochemically in a gas diffusion layer having a catalyst layer such as platinum. By this, it is an apparatus which generates electric power and heat simultaneously. A fuel cell is generally configured by stacking a plurality of cells and pressurizing them with a fastening member such as a bolt. One cell is configured by sandwiching a membrane electrode assembly (hereinafter referred to as MEA: Membrane-Electrode-Assembly) between a pair of plate-like conductive separators.

  FIG. 4 is a schematic diagram showing a basic configuration of a conventional polymer electrolyte fuel cell.

  In the figure, a unit cell (also referred to as a cell) 100 of a polymer electrolyte fuel cell includes a membrane electrode assembly 110 (hereinafter referred to as MEA), and a pair of plates disposed on both sides of the MEA 110. And a conductive separator 120 in the form of a conductor.

  The MEA 110 includes a polymer electrolyte membrane (ion exchange resin membrane) 111 that selectively transports hydrogen ions, and a pair of electrode layers 112 formed on both surfaces of the polymer electrolyte membrane 111. The pair of electrode layers 112 are formed on both surfaces of the polymer electrolyte membrane 111, and are formed on the catalyst layer 113, which is mainly composed of carbon powder carrying a white metal catalyst, and on the catalyst layer 113. A gas diffusion layer 114 having both gas permeability and water repellency. The gas diffusion layer 114 includes a porous base material 115 made of carbon fibers and a coating layer (water-repellent carbon layer) 116 made of carbon and a water repellent material (see, for example, Patent Document 1).

  The pair of separators 120 are provided with a fuel gas flow path 12 for flowing fuel gas and an oxidant gas flow path 122 for flowing oxidant gas on the main surface in contact with the gas diffusion layer 114. . The pair of separators 120 is provided with a cooling water passage 123 through which cooling water or the like passes. When the fuel gas and the oxidant gas are supplied to the pair of electrode layers 112 through the gas flow paths 121 and 122, respectively, an electrochemical reaction occurs, and electric power and heat are generated.

  As shown in FIG. 4, one or more cells 100 configured as described above are generally stacked, and the cells 100 adjacent to each other are generally connected in series and used. At this time, the stacked cells 100 are applied with a predetermined fastening pressure by a fastening member 130 such as a bolt in order to prevent the fuel gas and the oxidant gas, which are reaction gases, from leaking and to reduce the contact resistance. Fastened with pressure. Therefore, the MEA 110 and the separator 120 are in surface contact with a predetermined pressure.

  At this time, the separator 120 has current collecting properties for electrically connecting the MEAs 110 and 110 adjacent to each other in series. In order to prevent the gas necessary for the electrochemical reaction from leaking to the outside, a sealing material (gasket) 117 is provided between the pair of separators 120 and 120 so as to cover the side surfaces of the catalyst layer 113 and the gas diffusion layer 114. Has been placed.

  In recent years, in order to improve the power generation performance of fuel cells, studies have been conducted to increase the heat recovery temperature by raising the power generation temperature higher than before. Further, in order to simplify the fuel cell system, it has been studied to operate with a reduced amount of humidification supplied to the electrode layer of the MEA than in the past (low humidification operation). When performing such a high temperature / low humidification operation, in the conventional fuel cell having the above-described configuration, the porous base material made of carbon fibers of the gas diffusion layer is not limited to the weaving and knitting methods of the fabric. Since the porosity of carbon fiber woven fabric or paper is usually as high as 80% or more, the water retention in the gas diffusion layer cannot be kept sufficiently high. Therefore, there is a problem that the inside of the electrode layer is dried, the proton conduction resistance of the polymer electrolyte membrane is increased, and the power generation performance (voltage) is lowered.

  For this reason, in order to improve the water retention of a gas diffusion layer, it is calculated | required to make porosity low. In order to reduce the porosity of the gas diffusion layer, it is necessary to form the gas diffusion layer without using carbon fiber as a base material. An example of a gas diffusion layer that does not use carbon fiber as a substrate is disclosed in Patent Document 2.

  Patent Document 2 includes a fluororesin and carbon particles for the purpose of more reliably supplying gas and discharging generated water, and has a porosity (corresponding to the porosity of the present invention) of 60% or less. A gas diffusion layer is disclosed. According to the gas diffusion layer of Patent Document 2, since the porosity is as low as 60% or less, the water retention in the gas diffusion layer can be kept high even when performing a high temperature and low humidification operation. The power generation performance of the fuel cell can be improved.

  Patent Document 3 discloses a composition and manufacturing method of a porous member having a structure (so-called self-supporting structure) supported by conductive particles and a polymer resin without using carbon fiber as a base material. Proposed. Further, Patent Document 4 proposes a manufacturing method for forming an uneven shape on the porous member described in Patent Document 3. There has also been proposed a manufacturing method in which two porous members are combined to form an uneven shape on one surface.

Japanese Patent Laid-Open No. 2003-197202 JP 2007-242444 A Japanese Patent No. 4773582 Japanese Patent No. 4818486

  Further, in recent years, especially fuel cell systems are required to be smaller and have higher output, and while MEA performance is improved and power generation efficiency is being improved, the resistance of the gas diffusion layer is required to be reduced. Attempts have been made to reduce the film thickness.

  However, in order to try to reduce the thickness of the gas diffusion layer, the carbon fiber base material on which the gas diffusion layer is formed is thinned using the same method as in Patent Document 1, and the carbon for improving the water retention property is further added. An attempt was made to provide a coating layer made of a water repellent material, but there was a problem that it was difficult to peel the coating layer from the release film because the strength of the carbon fiber-based gas diffusion layer was reduced. .

  In addition, a gas diffusion layer containing a fluororesin and carbon particles prepared by using the same method as in Patent Document 2 on which the carbon fiber substrate is thinned and having a porosity of 60% or less is added. Although an attempt was made to bond them together by pressing, there was a problem that the gas diffusion layer was broken because pressure was applied to the gas diffusion layer made of the carbon fiber substrate.

  On the other hand, as shown in Patent Document 3, while pressing a gas diffusion layer sheet containing a fluororesin and carbon particles to a thickness of 150 μm or less, the film cannot be self-supported due to insufficient film strength. There was a problem that the shape could not be maintained by breaking.

  While studying the thinning of these gas diffusion layers, in order to increase the film strength of the gas diffusion layer, it is sufficient to lower the porosity (higher density). In this case, however, the gas diffusibility is hindered. In particular, the reaction gas did not reach the catalyst layer vertically below the rib portion of the separator, causing variations in the power generation distribution in the catalyst layer surface, resulting in a problem of voltage reduction. That is, it has become clear that the water repellency, water retention and conductivity as functions of the gas diffusion layer are more strongly required than before to maintain a good balance in the thin layer.

  As a result of earnestly researching the above problems, the inventors of the present invention have achieved the conventional by overlapping and pressing at least two types of gas diffusion layer sheets having different thicknesses that are self-supporting and have different shapes. It is possible to find a method for manufacturing a gas diffusion layer that can maintain water repellency, water retention, and conductivity in a well-balanced manner with a thinner thickness and can further improve power generation performance.

  In order to achieve the above object, the present invention is configured as follows.

  A polymer electrolyte membrane, a pair of catalyst layers facing each other across the polymer electrolyte membrane, and an anode gas diffusion layer and a cathode gas diffusion layer facing each other across the polymer electrolyte membrane and the pair of catalyst layers, The anode gas diffusion layer and the cathode gas diffusion layer are composed of a porous member mainly composed of conductive particles and a polymer resin, and are formed by laminating at least two layers having different porosity. It is characterized by a membrane electrode assembly comprising a membrane and a method for producing the same.

  With this configuration, it is possible to form a gas diffusion layer with a thickness thinner than before and with a porosity gradient in the thickness direction, and it is possible to maintain a balance between water repellency, water retention and conductivity, and improve power generation performance. This can be further improved.

  According to the membrane electrode assembly, the fuel cell, and the method for producing the same according to the present invention, the gas diffusion layer is made of at least two layers of porous members mainly composed of conductive particles and a polymer resin. Since the film is laminated and rolled, it becomes possible to reduce the thickness of the gas diffusion layer without impairing the water retention and water repellency of the gas diffusion layer, and the power generation performance is further improved compared to conventional membrane electrode assemblies and fuel cells. Can be improved.

Sectional drawing which shows the basic composition of the fuel cell in embodiment of this invention The figure which shows the manufacturing method (flowchart) of the gas diffusion layer comprised by the porous member which has as a main component the electroconductive particle shown in Embodiment 1 of this invention, polymer resin, and carbon fiber. The figure which shows the manufacturing method (flowchart) of the gas diffusion layer comprised with the porous member which has as a main component the electroconductive particle shown in Embodiment 2 of this invention, polymer resin, and carbon fiber. Schematic sectional view showing the structure of a conventional fuel cell

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all of the following drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a cross-sectional view showing a basic configuration of a fuel cell according to an embodiment of the present invention.

  The fuel cell according to the present embodiment is a polymer electrolyte type that generates electric power and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen and an oxidant gas containing oxygen such as air. It is a fuel cell. The present invention is not limited to the polymer electrolyte fuel cell, but can be applied to various fuel cells.

  As shown in FIG. 1, the fuel cell according to this embodiment includes a membrane electrode assembly 10 (hereinafter sometimes referred to as MEA) and a pair of plate-like conductive separators (anodes) disposed on both surfaces of the MEA 10. A cell (unit cell) 1 having a separator 20A and a cathode separator 20C) is provided. Note that the fuel cell according to the present embodiment may be configured by stacking a plurality of the fuel cells 1. In this case, the stacked fuel cells 1 are applied with a predetermined fastening pressure by a fastening member (not shown) such as a bolt so that the fuel gas and the oxidant gas do not leak and the contact resistance is reduced. It is preferable that it is pressure-fastened.

  The MEA 10 includes a polymer electrolyte membrane 11 that selectively transports hydrogen ions, and a pair of electrode layers formed on both surfaces of the polymer electrolyte membrane 11. One of the pair of electrode layers is an anode electrode (also referred to as a fuel electrode) 12A, and the other is a cathode electrode (also referred to as an air electrode) 12C. The anode electrode 12A is formed on one surface of the polymer electrolyte membrane 11, and is formed on the anode catalyst layer 13A and a pair of anode catalyst layers 13A mainly composed of carbon powder carrying a white metal catalyst. And an anode gas diffusion layer 14A having both current collecting action, gas permeability and water repellency.

  In FIG. 1, the anode gas diffusion layer 14 </ b> A includes three layers, and is formed of a plurality of layers 141 </ b> A, 142 </ b> A, 143 </ b> A from the side close to the polymer electrolyte membrane 11. The cathode electrode 12C is formed on the other surface of the polymer electrolyte membrane 11, and is formed on the cathode catalyst layer 13C and a pair of cathode catalyst layers 13C mainly composed of carbon powder carrying a white metal catalyst. And a cathode gas diffusion layer 14C having both current collecting action, gas permeability and water repellency. Similarly to the anode gas diffusion layer, the cathode gas diffusion layer 14C is formed of a plurality of layers 141C, 142C, and 143C from the side close to the polymer electrolyte membrane 11.

  The anode separator 20A disposed on the anode electrode 12A side is provided with a fuel gas flow path 21A for flowing fuel gas on the main surface in contact with the anode gas diffusion layer 143A. The fuel gas channel 21A is constituted by, for example, a plurality of grooves that are substantially parallel to each other. The cathode separator 20C disposed on the cathode electrode 12C side is provided with an oxidant gas flow path 21C for flowing an oxidant gas on the main surface in contact with the cathode gas diffusion layer 143C.

  The oxidant gas flow path 21C is constituted by, for example, a plurality of grooves that are substantially parallel to each other. The anode separator 20A and the cathode separator 20C may be provided with a cooling water passage (not shown) through which cooling water or the like passes. The fuel gas is supplied to the anode electrode 12A through the fuel gas flow channel 21A, and the oxidant gas is supplied to the cathode electrode 12C through the oxidant gas flow channel 21C, whereby an electrochemical reaction occurs, and electric power and heat are generated. Occur.

  In the above description, the fuel gas passage 21A is provided in the anode separator 20A, but the present invention is not limited to this. For example, the fuel gas channel 21A may be provided in the anode gas diffusion layer 14A. In this case, the anode separator 20A may be flat. Similarly, in the above description, the oxidant gas flow path 21C is provided in the cathode separator 20C, but the present invention is not limited to this. For example, the oxidant gas channel 21C may be provided in the cathode gas diffusion layer 14C. In this case, the cathode separator 20C may be flat.

  Between the anode separator 20A and the polymer electrolyte membrane 11, an anode gasket 15A is disposed as a sealing material so as to cover the side surfaces of the anode catalyst layer 13A and the anode gas diffusion layer 14A in order to prevent fuel gas from leaking to the outside. Has been. Further, between the cathode separator 20C and the polymer electrolyte membrane 11, a cathode gasket is used as a sealing material so as to cover the side surfaces of the cathode catalyst layer 13C and the cathode gas diffusion layer 14C in order to prevent the oxidant gas from leaking to the outside. 15C is arranged.

  As the anode gasket 15A and the cathode gasket 15C, a general thermoplastic resin, thermosetting resin, or the like can be used. For example, as the anode gasket 15A and the cathode gasket 15C, silicon resin, epoxy resin, melamine resin, polyurethane resin, polyimide resin, acrylic resin, ABS resin, polypropylene, liquid crystalline polymer, polyphenylene sulfide resin, polysulfone, glass fiber reinforced resin Etc. can be used.

  The anode gasket 15A and the cathode gasket 15C are preferably partially impregnated in the peripheral portion of the anode gas diffusion layer 14A or the cathode gas diffusion layer 14C. Thereby, power generation durability and strength can be improved.

  Further, instead of the anode gasket 15A and the cathode gasket 15C, the polymer electrolyte membrane 11, the anode catalyst layer 13A, the anode gas diffusion layer 14A, the cathode catalyst layer 13C, and the cathode gas diffusion are provided between the anode separator 20A and the cathode separator 20C. A gasket may be disposed so as to cover the side surface of the layer 14C. Thereby, deterioration of the polymer electrolyte membrane 11 can be suppressed, and handling of the MEA 10 and workability during mass production can be improved.

  Next, the configuration of the gas diffusion layer according to the embodiment of the present invention will be described in more detail.

  The anode gas diffusion layer 14A and the cathode gas diffusion layer 14C are made of a sheet-like and rubber-like porous member mainly composed of conductive particles, polymer resin, and carbon fiber. Moreover, each of the anode gas diffusion layer 14A and the cathode gas diffusion layer 14C may be configured by a combination of at least two porous members. The anode gas diffusion layer 14A is formed of a plurality of layers 141A, 142A, 143A from the side close to the polymer electrolyte membrane 11. Similarly to the anode gas diffusion layer, the cathode gas diffusion layer 14C is formed of a plurality of layers 141C, 142C, and 143C from the side close to the polymer electrolyte membrane 11. The combined gas diffusion layer is designed with the porosity inclined in the thickness direction, for example, and the gas diffusion layer close to the catalyst layer has high porosity, and the gas diffusion layer close to the gas flow path side opposite to the catalyst layer The porosity of the layer can be set low.

  As a result, unlike conventional carbon fiber woven fabric and paper, the electrode surface is composed of a sheet-like and rubber-like porous member mainly composed of conductive particles, polymer resin, and carbon fiber. 14A is produced even when a high-temperature, low-humidification operation is performed, by exhibiting an effect that the moisture generated in the above is diffused and held from the electrode side with a high porosity to the gas flow path side with a low porosity. In addition, water retention in the cathode gas diffusion layer 14C can be kept high.

  Examples of the conductive particle material include carbon materials such as graphite, carbon black, and activated carbon. Examples of the carbon black include acetylene black (AB), furnace black, ketjen black, and vulcan.

  Of these, acetylene black is preferably used as the main component of carbon black from the viewpoint of low impurity content and high electrical conductivity. Examples of the main component of graphite include natural graphite and artificial graphite. Of these, artificial graphite is preferably used as the main component of graphite from the viewpoint of low impurities.

  Moreover, it is preferable that electroconductive particle is comprised by mixing two types of carbon materials from which an average particle diameter differs. As a result, particles having a small average particle diameter can enter the gaps between particles having a large average particle diameter, so that the overall porosity of the anode gas diffusion layer 14A can be easily reduced to 60% or less. Examples of the conductive particles that can easily form a filling structure include graphite. Therefore, the conductive particles are preferably configured by mixing acetylene black and graphite.

  In addition, as the polymer resin, PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), PVDF (polyvinylidene fluoride), ETFE (tetrafluoroethylene / ethylene copolymer), PCTFE (polychlorotrifluoroethylene), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) and the like can be mentioned. Among these, it is preferable from the viewpoint of heat resistance, water repellency, and chemical resistance that PTFE is used as the polymer resin. Examples of the raw material form of PTFE include dispersion and powder. Among these, it is preferable from the viewpoint of workability that the dispersion is adopted as a raw material form of PTFE.

  In addition, this invention is not limited to this Embodiment, It can implement in another various aspect. For example, in the anode gas diffusion layer 14A and the cathode gas diffusion layer 14C, in addition to the conductive particles and the polymer resin, a surfactant, a dispersion solvent, and the like that are used when the anode gas diffusion layer 14A and the cathode gas diffusion layer 14C are manufactured. A trace amount may be contained. Examples of the dispersion solvent include water, alcohols such as methanol and ethanol, and glycols such as ethylene glycol. Examples of the surfactant include nonionic compounds such as polyoxyethylene alkyl ethers and zwitterionic compounds such as alkylamine oxides.

  What is necessary is just to set suitably the quantity of the dispersion solvent used at the time of manufacture, and the quantity of surfactant according to the kind of electroconductive particle, the kind of polymer resin, those compounding ratios, etc. In general, the larger the amount of the dispersion solvent and the amount of the surfactant, the more easily the conductive particles and the polymer resin are uniformly dispersed, but the fluidity becomes higher and the gas diffusion layer is formed into a sheet. Tend to be difficult.

  Further, the anode gas diffusion layer 14A and the cathode gas diffusion layer 14C may contain carbon fibers having a weight smaller than that of the polymer resin contained in the anode gas diffusion layer 14A and the cathode gas diffusion layer 14C. That is, the anode gas diffusion layer 14A and the cathode gas diffusion layer 14C are sheet-like and rubber-like porous materials containing conductive particles and a polymer resin as main components and added with a weight of carbon fibers that cannot be formed as a base material. You may comprise with a quality member. In this case, since carbon fiber is not used as a base material, the cost of the fuel cell can be reduced. Moreover, since carbon fiber has a reinforcing effect, a high-strength gas diffusion layer can be produced by increasing the blending ratio of carbon fiber. Thereby, it becomes possible to reduce the compounding quantity of the high molecular resin which acts as a binder.

  In addition, since the blending ratio of the polymer resin that is an insulator can be reduced, the power generation performance can be improved. In addition, the electrical conductivity of the carbon fiber also makes it possible to improve the electrical conductivity of the gas diffusion layer, and the inclusion of carbon fiber in the gas diffusion layer is particularly effective when manufacturing a thin gas diffusion layer. is there.

  Examples of the carbon fiber material include vapor grown carbon fiber (hereinafter referred to as VGCF), milled fiber, cut fiber, and chop fiber. When VGCF is used as the carbon fiber, for example, a fiber having a fiber diameter of 0.15 μm and a fiber length of 15 μm may be used. Moreover, when using a milled fiber, a cut fiber, or a chop fiber as the carbon fiber, for example, a fiber having a fiber diameter of 5 to 20 μm and a fiber length of 20 to 100 μm may be used.

  The raw material of milled fiber, cut fiber, or chop fiber may be any of PAN, pitch, and rayon. The fiber is preferably used by dispersing a bundle of short fibers produced by cutting and cutting an original yarn (long fiber filament or short fiber stable). When the fiber diameter of VGCF is smaller than 0.15 μm, the fiber strength is lowered and the strength of the gas diffusion layer cannot be maintained. In addition, when the fiber length is greater than 15 μm, it is possible to improve the strength of the gas diffusion layer, but it is difficult to adjust the thickness by a pressing method such as press working.

  Moreover, it has become clear that similar problems arise even when milled fibers such as carbon fibers, cut fibers, or chop fibers are used.

  In order to improve power generation performance in fuel cells, the power generation temperature, fuel electrode side humidification dew point, air electrode side humidification dew point, fuel gas utilization rate, air utilization rate, separator channel shape, catalyst layer specifications, etc. Optimization is effective. In particular, among the physical property parameters constituting the gas diffusion layer, the thickness and porosity are highly sensitive to voltage fluctuations. For this reason, it is more effective to optimize the thickness or the porosity of the gas diffusion layer in order to improve the power generation performance under the operating conditions of high temperature and low humidification.

  The thickness of the anode gas diffusion layer 14A and the cathode gas diffusion layer 14C is preferably 100 μm or more and 600 μm or less. When the thickness of the gas diffusion layer is smaller than 100 μm, the gas diffusion layer becomes thin and the gas diffusibility increases, the water retention decreases, the polymer electrolyte membrane dries, and the membrane resistance increases. Therefore, it is considered that the power generation performance is significantly reduced. On the other hand, even when the thickness of the gas diffusion layer is larger than 600 μm, it is considered that the power generation performance is significantly reduced because the internal resistance of the gas diffusion layer increases due to the increase in the thickness of the gas diffusion layer.

(Embodiment 1)
Embodiment 1 of the present invention will be described below by a method as shown in FIG.

  First, in step s1, two types of carbon powders (conductive particles) having different average particle sizes, carbon fibers, a polymer resin, a surfactant, and water (dispersing solvent) are kneaded (kneading step). More specifically, the conductive particles, the polymer resin, the carbon fiber, the surfactant, and the dispersion solvent are put into a stirrer / kneader, kneaded, pulverized and granulated. Thereafter, the polymer resin material is added to these kneaded materials and further dispersed. Note that all the materials including the polymer resin material may be simultaneously fed into the kneader without feeding the polymer resin material separately from the other materials into the kneader.

  Next, in step s2, the kneaded product obtained by kneading is extruded and rolled into a sheet by a press (pre-rolling step).

  Next, in step s3, the kneaded material in sheet form is fired, and the surfactant and water are removed from the kneaded material (firing step).

  Next, in step s4, at least two kinds of fired sheets are superposed, the rolling force and gap of the press are adjusted, the sheet is re-rolled, and the porosity and thickness of the sheet are adjusted (re-run) Rolling process).

  Below, the manufacturing method of a specific gas diffusion layer is shown. First, 150 g of acetylene black (Denka Black: Denka Black: registered trademark manufactured by Denki Kagaku Kogyo Co., Ltd.), graphite (manufactured by Wako Pure Chemical Industries, Ltd.) and VGCF (manufactured by Showa Denko: fiber diameter 0.15 μm, fiber length 15 μm), interface 7.5 g of activator (Triton X: registered trademark) and 170 g of water are put into a mixer. Then, each said material is knead | mixed for 60 minutes by setting the rotation speed of a mixer to 100 rpm. After the elapse of 60 minutes, 70 g of PTFE dispersion (AD911 manufactured by Asahi Glass Co., Ltd.) as a polymer resin is mixed with the kneaded product obtained by the kneading and further stirred for 5 minutes.

  40 g of the kneaded material thus obtained is taken out from the mixer, and is rolled into a sheet by adjusting the gap using a stretching roll machine. Porosity control often depends on the amount of this material charged, particularly the amount of water added as a solvent. In order to create sheets with different porosities, the amount of water added was changed.

  Thereafter, the kneaded material in sheet form is baked at 300 ° C. for 30 minutes in a program-controlled baking furnace to remove the surfactant and water in the kneaded material. The kneaded product from which the surfactant and water have been removed is taken out of the firing furnace, and at least two kinds of gas diffusion layers having different porosities are stacked, and further rolled using a drawing roll machine to adjust the rolling force and gap. Then, after adjusting the thickness and reducing the thickness variation, it is cut into a 6 cm square. In this way, rubber-like gas diffusion layers having different thicknesses are produced. Thereby, a gas diffusion layer having a desired porosity and thickness can be manufactured.

  Table 1 shows the film thickness at step s2, the film thickness at step s4, and the porosity of the three types (a to c) of gas diffusion layer samples prepared in the first embodiment.

  In addition, the manufacturing method of a gas diffusion layer is not limited to the said method, Another method may be sufficient. For example, the kneaded material is rolled with a roll press or a flat plate press to produce a sheet-like porous member, but the present invention is not limited to this.

  For example, the kneaded material can be charged into an extruder and continuously formed from a die head of the extruder to produce a sheet-like porous member. Moreover, the kneaded product can be obtained without using the kneader by devising the shape of the screw provided in the extruder and giving the screw a kneading function. That is, stirring, kneading, and sheet forming of each carbon material can be performed integrally with a single machine.

  One manufacturing method is specifically as follows.

  First, as described above, the kneaded product obtained by kneading with a mixer is formed into a sheet having a width of 7 cm using an extrusion molding machine (biaxial full flight screw length 50 cm, T die width 7 cm, slit gap 1 mm). Then, after making a desired film thickness with a rolling roll, baking is performed at 300 ° C. for 30 minutes in a program-controlled baking furnace to remove the surfactant and water in the kneaded product. The kneaded product from which the surfactant and water have been removed is taken out from the firing furnace, adjusted again by adjusting the gap of the drawing roll machine, and adjusted in thickness and reduced in thickness variation. Thereafter, the re-rolled kneaded product is cut into a 6 cm square.

  The other manufacturing method is specifically the following method. First, a material having the same composition as in the first embodiment is kneaded using an extruder (biaxial full flight screw length: 100 cm, T-die width: 7 cm, gap: 1 mm) instead of the mixer, extruded, and desired Is formed into a sheet having a thickness of 1 mm.

  Thereafter, the kneaded material in sheet form is baked at 300 ° C. for 30 minutes in a program-controlled baking furnace to remove the surfactant and water in the kneaded material. The kneaded product from which the surfactant and water have been removed is taken out from the firing furnace, adjusted again by adjusting the rolling force and gap of the drawing roll machine, and adjusted in thickness and reduced in thickness variation. Thereafter, the re-rolled kneaded product is cut into a 6 cm square. In this way, a gas diffusion layer having a desired porosity and thickness was obtained.

  Next, a method for measuring (calculating) the porosity of the gas diffusion layer will be described. First, the true density of the manufactured gas diffusion layer is calculated from the true density and composition ratio of each material constituting the gas diffusion layer. Next, the weight, thickness, vertical and horizontal dimensions of the manufactured gas diffusion layer are measured, and the density of the manufactured gas diffusion layer is calculated. Next, the porosity is calculated by substituting the calculated density and true density of the gas diffusion layer into the equation of porosity = (density of gas diffusion layer) / (true density) × 100.

  As described above, the porosity of the produced gas diffusion layer can be measured. When the pore size distribution of the produced gas diffusion layer was measured using a mercury porosimeter, it was confirmed that the porosity calculated from the cumulative pore volume was consistent with the porosity calculated as described above. I have confirmed.

  Next, a method for measuring the internal resistance (electric conductivity) of the gas diffusion layer will be described. First, each sample is punched to have a diameter of 4 cm. Next, a compression load is applied to each sample using a compression tester (manufactured by Shimadzu Corporation, EZ-graph) so that the pressure (surface pressure) is 1.5 kg / cm 2. In this state, the internal resistance value [mΩ · cm 2] is measured using an AC four-terminal resistance meter (manufactured by Tsuruga Electric, MODEL 3566).

  Simultaneously with or subsequent to the production of the above gas diffusion layer, platinum supported carbon (TEC10E50E manufactured by Tanaka Kikinzoku Co., Ltd.) and ions are formed on both sides of the polymer electrolyte membrane (Dupont Nafion112: registered trademark) as a catalyst layer. A mixture of exchange resins (Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd.) is applied. Thereafter, the mixture is dried to obtain a membrane / catalyst layer assembly.

  At this time, the size of the polymer electrolyte membrane is 15 cm square, and the size of the catalyst layer is 5.8 cm square. The amount of platinum used is 0.35 mg / cm2 on the anode electrode side and 0.6 mg / cm2 on the cathode electrode side.

  Next, the manufactured gas diffusion layer is disposed on both surfaces of the membrane / catalyst layer assembly, and hot press bonding (80 ° C., 10 kgf / cm 2) is performed to manufacture an MEA. Next, the manufactured MEA is sandwiched between a pair of separators (manufactured by Tokai Carbon Co., Ltd.) and is pressed until the fastening pressure becomes 10 kgf / cm 2 so as not to be displaced in this state. As described above, the unit cell (cell) of the fuel cell is manufactured.

(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to a method as shown in FIG.

  In the figure, first, in step S1, two types of carbon powders (conductive particles) having different average particle sizes, a polymer resin, carbon fibers, a surfactant, and water (dispersing solvent) are kneaded (kneading step). More specifically, the conductive particles, the polymer resin, the surfactant, and the dispersion solvent are put into a stirrer / kneader, kneaded, pulverized and granulated. Thereafter, the polymer resin material is added to these kneaded materials and further dispersed. Note that all the materials including the polymer resin material may be simultaneously fed into the kneader without feeding the polymer resin material separately from the other materials into the kneader.

  Next, in step S2, the kneaded product obtained by kneading is extruded and rolled with a press to form a sheet (pre-rolling step).

  Next, in step S3, at least two kinds of sheets are superposed, the rolling force and gap of a press machine are adjusted and the sheets are superposed and rolled, and the porosity and thickness of the sheets are adjusted (rolling) Process). Next, in step S4, the kneaded material that has been superposed and formed into a sheet is fired, and the surfactant and water are removed from the kneaded material (firing step).

  Next, in step S5, the sheet is rolled by adjusting the rolling force and gap of the press, and the porosity and thickness of the sheet are adjusted (re-rolling step).

  Thereby, a gas diffusion layer having a desired porosity and thickness can be manufactured. Table 2 shows the film thickness in step s2), the film thickness in step s5, and the porosity of the two types (d, e) of the gas diffusion layer sample prepared in the second embodiment.

  By superimposing sheets after the preliminary rolling process, the rolling process is performed in a wet state, so that the effect of increasing the bonding force between layers and completing the firing process in one can be obtained. Moreover, there is a concern that the bonding force between the sheets may be insufficient by laminating without sticking the adhesiveness expressed in the film after firing in the first embodiment.

  Examples are shown below. Here, the resistance value of the fuel cell prepared by combining eight types (a to h) of the gas diffusion layer samples prepared according to the first and second embodiments with the mixing ratio of acetylene black, graphite, and carbon fiber being constant, and The voltage value was measured.

  Next, a method for measuring the voltage value will be described. First, an electronic load machine (PLZ-4W manufactured by Kikusui Electric) is connected to each sample. Pure hydrogen is supplied as a fuel gas to the anode electrode, and air is supplied as an oxidant gas to the cathode electrode. At this time, the utilization rates are 70% and 40%, respectively. The gas humidification dew point is set at an anode electrode 65 ° C. and a cathode electrode 65 ° C. The cell temperature is set to 90 ° C. Next, the voltage value [V] at a current density of 0.2 A / cm 2 is measured.

  The voltage value was obtained as described above.

Example 1
As the gas diffusion layer, a fuel cell was prepared using the sample a prepared in the first embodiment for the anode and the sample a prepared in the first embodiment for the cathode.

(Example 2)
As the gas diffusion layer, a fuel cell was prepared by using the sample d prepared in the second embodiment for the anode and the sample a prepared in the first embodiment for the cathode.

(Example 3)
As the gas diffusion layer, a fuel cell was prepared using the sample a prepared in the first embodiment for the anode and the sample d prepared in the second embodiment for the cathode.

Example 4
As the gas diffusion layer, a fuel cell was prepared using the sample d prepared in the second embodiment for the anode and the sample d prepared in the second embodiment for the cathode.

(Example 5)
As the gas diffusion layer, a fuel cell was prepared by using the sample b prepared in the first embodiment for the anode and the sample a prepared in the first embodiment for the cathode.

(Example 6)
As the gas diffusion layer, a fuel cell was prepared by using the sample c prepared in the first embodiment for the anode and the sample a prepared in the first embodiment for the cathode.

(Example 7)
As the gas diffusion layer, a fuel cell was prepared using the sample c prepared in the first embodiment for the anode and the sample e prepared in the second embodiment for the cathode.

(Comparative Example 1)
As the gas diffusion layer, a fuel cell was prepared by using SBC carbon 25BC (thickness 190 μm) for each of the anode and the cathode.

  Table 3 shows the film thickness, porosity, and resistance value of the gas diffusion layer when the thickness of the sheet-like kneaded material in the middle step of the gas diffusion layer is changed, and the fuel cell prepared using these gas diffusion layers. Voltage values are shown.

  As can be seen from Table 3, according to the membrane electrode assembly, the fuel cell, and the manufacturing method thereof according to this embodiment, the gas diffusion layer has at least two porous members mainly composed of conductive particles and a polymer resin. Since sheets having different porosities of layers or more are prepared and then laminated and rolled, a thin film can be formed without impairing the water retention and water repellency of the gas diffusion layer. As a result, the resistance value can be lowered and the voltage can be increased as compared with the conventional membrane electrode assembly and the fuel cell, and the power generation performance can be further improved.

  Since the membrane electrode assembly and the fuel cell according to the present invention can further improve the power generation performance, the membrane electrode assembly and the fuel cell are used, for example, as a driving source for a mobile body such as an automobile, a distributed power generation system, and a home cogeneration system. Useful for fuel cells.

DESCRIPTION OF SYMBOLS 1 Fuel cell 10 Membrane electrode assembly 11,111 Polymer electrolyte membrane 12A Anode electrode 12C Cathode electrode 13A Anode catalyst layer 13C Cathode catalyst layer 15A Anode gasket 15C Cathode gasket 20A Anode separator 20C Cathode separator 21A, 12 Fuel gas flow path 21C , 122 Oxidant gas flow path

Claims (12)

A polymer electrolyte membrane;
A pair of catalyst layers disposed opposite to each other across the polymer electrolyte membrane;
An anode gas diffusion layer and a cathode gas diffusion layer provided opposite to each other across the polymer electrolyte membrane and the pair of catalyst layers,
The anode gas diffusion layer and the cathode gas diffusion layer are composed of a porous member mainly composed of conductive particles and a polymer resin, and the porous member is formed by laminating at least two layers having different porosity. A porous membrane formed by
A membrane electrode assembly characterized by the above. The thickness of the anode gas diffusion layer and the cathode gas diffusion layer is:
The membrane electrode assembly according to claim 1, which is 100 μm or more and 600 μm or less. The conductive particles contained in the anode gas diffusion layer and the cathode gas diffusion layer are:
The membrane electrode assembly according to claim 1 or 2, comprising at least two kinds of carbon materials and carbon fibers having different average particle diameters. The anode gas diffusion layer and the cathode gas diffusion layer are:
The membrane electrode assembly according to any one of claims 1 to 3, comprising carbon fibers having a weight less than that of the polymer resin. The anode gas diffusion layer and the cathode gas diffusion layer are:
Each is composed of a combination of at least two layers of porous members, the porosity is inclined in the thickness direction from the side close to the polymer electrolyte membrane, the porosity is high, and the porosity of the gas diffusion layer near the gas flow path side is low The membrane electrode assembly according to any one of claims 1 to 4, which is set. The membrane electrode assembly according to any one of claims 3 to 5, wherein the carbon fiber includes at least one of vapor grown carbon fiber, milled fiber, cut fiber, and chop fiber. A fuel cell comprising: the membrane electrode assembly according to any one of claims 1 to 6; and a pair of separators disposed so as to sandwich the membrane electrode assembly. A membrane electrode comprising an anode gas diffusion layer and a cathode gas diffusion layer provided opposite to each other with a polymer electrolyte membrane and a pair of catalyst layers arranged opposite to each other with the polymer electrolyte membrane interposed therebetween A method for manufacturing a joined body, comprising:
The anode gas diffusion layer and the cathode gas diffusion layer are composed of a porous member mainly composed of conductive particles and a polymer resin, and
Laminating at least two or more layers of sheet-like porous members having different porosities;
Rolling the laminated sheet-like porous member,
A method for producing a membrane electrode assembly, characterized in that The conductive particles contained in the anode gas diffusion layer and the cathode gas diffusion layer are:
It is composed of at least two kinds of carbon materials and carbon fibers having different average particle sizes,
The manufacturing method of the membrane electrode assembly of Claim 8. The anode gas diffusion layer and the cathode gas diffusion layer contain carbon fibers having a weight less than that of the polymer resin.
The manufacturing method of the membrane electrode assembly of Claim 8 or 9. The anode gas diffusion layer and the cathode gas diffusion layer are each composed of a combination of at least two porous members, and
The porosity is inclined in the thickness direction from the side close to the polymer electrolyte membrane and the porosity is high, and the porosity of the gas diffusion layer near the gas flow path side is set low.
The manufacturing method of the membrane electrode assembly as described in any one of Claims 8-10. The membrane electrode assembly according to any one of claims 9 to 11, wherein the carbon fiber comprises at least one of vapor grown carbon fiber, milled fiber, cut fiber, and chop fiber. Production method.

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