JP2005197195A - Solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means to achieve both the effective supply of a reaction gas to a catalyst contained in a catalyst layer and the suppression of an increase in electron transfer resistance of the catalyst layer. <P>SOLUTION: The catalyst layers (120a, 120c) are made to have a laminate structure of a layer (122a, 122c) in which cavities are formed and a layer (121a, 121c) in which cavities are not formed, the layers (122a, 122c) being disposed on the sides of gas diffusion layers (130a, 130c). Due to the cavities (123a, 123c), gases are effectively supplied to the catalysts. Besides, due to the no-cavity layers, electron transfer resistance is suppressed low. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte fuel cell. More specifically, the present invention relates to a technique for improving a catalyst layer of a polymer electrolyte fuel cell.

  In recent years, fuel cells have attracted attention as one of power sources. A fuel cell refers to a device that generates electricity by oxidizing a fuel such as hydrogen or methanol. The power generation efficiency of fuel cells is very high. Moreover, the discharge from the fuel cell using hydrogen as a fuel is water, which is a very useful power source from the viewpoint of protecting the global environment.

  Various fuel cells such as a polymer electrolyte fuel cell, a solid oxide fuel cell, a molten carbonate fuel cell, and a phosphoric acid fuel cell have been proposed as fuel cells. Among these, the polymer electrolyte fuel cell can be operated at a relatively low temperature, and is expected to be used as a power source for moving bodies such as automobiles, and is being developed.

  The polymer electrolyte fuel cell is a fuel cell using a proton conductive polymer electrolyte, also called a polymer electrolyte fuel cell or PEFC. In the following description, it is also referred to as PEFC. In PEFC, a catalyst layer containing a catalyst for promoting a power generation reaction is formed on both sides of a proton-conductive polymer electrolyte membrane. A gas diffusion layer and a separator are disposed outside the catalyst layer. A gas flow path through which gas flows is formed on the surface of the separator, and the gas used for the power generation reaction is supplied to the catalyst layer through the gas flow path and the gas diffusion layer. Moreover, the water produced | generated with the electric power generation reaction is discharged | emitted outside PEFC through a gas diffusion layer and a gas flow path.

  In addition to the catalyst, the catalyst layer includes a carrier supporting the catalyst and a proton conductive polymer electrolyte. From the viewpoint of increasing the utilization rate of the catalyst, it is desirable that the catalyst layer be as dense as possible. On the other hand, in order to make the power generation reaction proceed smoothly, it is desirable that the reaction gas is efficiently supplied to the catalyst. That is, in order to improve the utilization rate of the catalyst, it is only necessary to form a dense catalyst layer. However, if it is dense enough to prevent the reaction gas from flowing, the power generation characteristics of the PEFC are deteriorated.

As a technique for solving this problem, a technique has been proposed in which a void for intentionally improving gas diffusibility is provided in the catalyst layer surface to secure a reaction gas flow path (see Patent Document 1). . However, the voids formed in the catalyst layer reduce the electron transfer path in the catalyst layer and increase the electron transfer resistance of the catalyst layer. In particular, when the catalyst deteriorates due to long-term use, the electron transfer resistance tends to increase.
Japanese Patent Laid-Open No. 2002-270187

  Accordingly, an object of the present invention is to provide means for achieving both efficient supply of reaction gas to the catalyst contained in the catalyst layer and suppression of increase in electron transfer resistance of the catalyst layer.

  The present invention provides a polymer electrolyte membrane, a pair of catalyst layers sandwiching the polymer electrolyte membrane, and the polymer electrolyte membrane and the catalyst layer on a surface of the catalyst layer facing the polymer electrolyte membrane. A pair of gas diffusion layers disposed so as to sandwich the electrode assembly, wherein at least one of the catalyst layers is laminated in a direction in which the components of the membrane electrode assembly are laminated. In addition, the two or more layers constituting the catalyst layer are formed of a layer in which a gap for promoting the gas supply is formed, and a gap for promoting the gas supply is not formed. The membrane electrode assembly is a membrane electrode assembly in which the layer in which the voids are formed is disposed on the gas diffusion layer side.

  In the membrane electrode assembly of the present invention, the reaction gas is efficiently supplied to the catalyst contained in the catalyst layer. Further, the increase in the electron transfer resistance of the catalyst layer due to the means for efficiently supplying the reaction gas is suppressed to the minimum.

  Hereinafter, the membrane electrode assembly of the present invention will be described in detail with reference to the drawings. In the present invention, the material used in the conventional membrane electrode assembly except that the catalyst layer is constituted from the layer in which the void is formed and the layer in which the void is not formed, It can be used as well. For this reason, basic configurations other than the catalyst layer, such as a polymer electrolyte membrane and a gas diffusion layer (hereinafter referred to as “GDL”), will be briefly described, but these materials are limited to the exemplified materials and shapes. I don't mean.

  First, an outline of the basic configuration of the membrane electrode assembly will be described. FIG. 1 is a schematic cross-sectional view of one embodiment of the membrane electrode assembly of the present invention.

  A polymer electrolyte membrane 110 is disposed in the center of the membrane electrode assembly 10. On the anode side of the polymer electrolyte membrane, the catalyst layer 120a and the GDL 130a are arranged in this order. The catalyst layer 120a includes a layer 121a that is disposed on the polymer electrolyte membrane 110 side and in which no voids such as cracks are formed, and a layer 122a that is disposed on the GDL 130a side and in which voids 123a such as cracks are formed. . On the other hand, the catalyst layer 120c and the GDL 130c are also arranged in this order on the cathode side of the polymer electrolyte membrane 110. Similar to the anode side, the catalyst layer 120c is formed with a layer 121c disposed on the polymer electrolyte membrane 110 side where no voids such as cracks are formed, and a void 123c such as cracks disposed on the GDL 130c side. Layer 122c. In the present application, the “membrane electrode assembly” is an assembly having a polymer electrolyte membrane, a pair of catalyst layers that sandwich the polymer electrolyte membrane, and a pair of GDLs that sandwich the polymer electrolyte membrane and the catalyst layer. Means the body. The “layer in which voids are formed” means a layer in which voids are artificially formed. A layer including only voids inevitably generated when forming a layer does not correspond to “a layer in which voids are formed” in the present application, but corresponds to “a layer in which voids are not formed”.

  When a PEFC is manufactured using the membrane electrode assembly 10, a pair of separators is arranged outside the membrane electrode assembly 10 so as to sandwich the membrane electrode assembly 10 (not shown). The separator has a gas flow path on the surface in contact with the GDL. In addition, various members can be installed as necessary. For example, a sealing material that prevents leakage of gas supplied to the PEFC to the outside is disposed (not shown).

  In the membrane electrode assembly 10 of the present invention, at least one of the catalyst layers (120a, 120c) is composed of two or more layers laminated in the direction in which the components of the membrane electrode assembly are laminated. As shown in FIG. 1, both catalyst layers may be composed of two or more layers. And the layer (122a, 122c) arrange | positioned at the GDL (130a, 130c) side has the space | gap (123a, 123c) for promoting supply of gas. On the other hand, the layers (121a, 121c) arranged on the polymer electrolyte 110 side do not have voids for promoting gas supply.

  As described above, at least one of the catalyst layers on the anode side or the cathode side has a laminated structure including two or more layers, and the catalyst layers (122a, 122c) in contact with the GDL (130a, 130c) have cracks or the like. A space | gap (123a, 123c) is provided. Due to the gaps (123a, 123c), the diffusibility of the gas supplied through the gas flow path provided in the separator and the GDL is improved, and the gas is efficiently supplied to the catalyst disposed in the catalyst layer (120a, 120c). The Moreover, the water produced | generated by the battery reaction in a catalyst layer can be efficiently excluded by the space | gap (123a, 123c) by the side of GDL (130a, 130c).

  On the other hand, voids for promoting gas supply are not formed in the catalyst layers (121a, 121c) in contact with the polymer electrolyte membrane 110. The presence of the catalyst layer having no voids secures an electron transfer path and suppresses an increase in electron transfer resistance of the catalyst layer to a minimum.

  In this way, the catalyst layer has a laminated structure composed of two or more layers, the GDL side layer improves the gas diffusion and generated water discharge function, and the polymer electrolyte membrane side layer secures the electronic electric function. Thus, the reaction gas is efficiently supplied to the catalyst included in the catalyst layer, and an increase in the electron transfer resistance of the catalyst layer is suppressed to a minimum.

  Then, the member which comprises a membrane electrode assembly is demonstrated in order.

  The polymer electrolyte membrane 110 is a polymer membrane having proton conductivity. Various materials have been proposed for the polymer electrolyte membrane. For example, the polymer electrolyte membrane includes a membrane made of a perfluorocarbon polymer having a sulfonic acid group. As the polymer electrolyte membrane, a membrane synthesized by itself may be used, or a commercially available product may be used.

  The catalyst layers (120a, 120c) are portions where a catalyst that mediates an electrode reaction is disposed. The catalyst layer generally includes a catalyst, a carrier supporting the catalyst, and a proton conductive polymer electrolyte. In the present invention, the catalyst layers (120a, 120c) are composed of two or more layers. Each of the two or more layers stacked has a function as a catalyst layer. In the present invention, in principle, the “catalyst layer” refers to the entire layer having a function as a catalyst layer. The polymer electrolyte membrane is sandwiched between the catalyst layers. That is, the layers are laminated in the order of catalyst layer 120a / polymer electrolyte membrane 110 / catalyst layer 120c. In the present invention, “clamping” means a state in which a certain member is interposed between two other members. The contact area between the members is not particularly limited.

  In the membrane / electrode assembly of the present invention, a layer having voids is disposed on the GDL side, and a layer having no voids is disposed on the polymer electrolyte membrane side. The layer having voids and the layer not having voids may each be a laminate composed of two or more layers. In the membrane electrode assembly of the present invention, if the layer having voids is disposed in the outermost layer on the GDL side, and the layer not having voids is disposed in the outermost layer on the polymer electrolyte membrane side, There is no particular limitation. For example, two or more layers having voids are disposed on the GDL side, and two or more layers having no voids are disposed on the polymer electrolyte membrane side. The porosity of two or more layers having voids may gradually decrease as the distance from the GDL to the polymer electrolyte membrane is approached.

  In the present invention, the “void” means a gap that promotes the supply of the gas supplied to the catalyst layer. The shape and size of the gap are not particularly limited as long as the supply of a gas such as hydrogen gas or air is promoted. The void may be cracked or porous. The porosity of the catalyst layer having voids is not particularly limited, but it has a porosity of about 0.1 to 40% in order to effectively promote gas supply and not greatly reduce the utilization rate of the catalyst. It is good to have.

  Regarding the film thickness of the layer in which the void is formed and the film thickness of the layer in which the void is not formed, the total film thickness of the layer in which the void is formed is preferably the total film thickness of the layer in which the void is not formed. That's it. In order to improve the diffusibility of the gas supplied to the catalyst layer and the discharge of produced water, the total film thickness of the layer in which the voids are formed is equal to or greater than the total film thickness of the layer in which no voids are formed. There should be. More preferably, the total film thickness of the layer in which voids are formed is 1.0 to 5.0 times the total film thickness of the layer in which voids are not formed. More preferably, the total film thickness of the layer in which the void is formed is 1.5 to 3.0 times the total film thickness of the layer in which the void is not formed. If it is such composition, both gas diffusion and discharge of generated water will advance effectively. Since the electron transfer path is sufficiently secured even in a relatively thin layer, the total film thickness of the layer in which no void is formed may be relatively thin. The “total film thickness of the layer in which voids are formed” means the total film thickness of the layers in which voids are formed. The film thickness is calculated as an average film thickness. For example, it is calculated as an average value when the film to be measured is divided into nine and the film thickness is measured for each of the nine regions.

  Specifically, the total film thickness of the layer in which voids are formed is preferably 25 to 45 μm. The total film thickness of the layer in which no void is formed is preferably 5 to 25 μm. By setting the total film thickness of the layer in which no voids are formed within this range, the amount of catalyst necessary for the power generation reaction is ensured. Further, an increase in battery size and an increase in electron transfer resistance are suppressed.

  The total film thickness of the layer in which voids are formed and the layer in which voids are not formed is preferably 50 μm or less. If the total thickness of the catalyst layer disposed between the polymer electrolyte membrane and the GDL is too thin, it may not be possible to secure a sufficient amount of catalyst necessary for the electrode reaction, and the battery performance and life characteristics may be deteriorated. There is. On the other hand, if the total film thickness of the catalyst layer is too thick, the power generation performance may be reduced. Therefore, the thickness of the catalyst layer should be determined in consideration of battery performance and life characteristics.

  Preferably, the porosity of the layer (122a, 122c) in which the void is formed varies within the layer. In the electrode of the polymer electrolyte fuel cell, the reaction gas is supplied to the catalyst layer (120a, 120c) through the flow path provided in the separator and the gas diffusion layer (130a, 130c). At this time, in the portion corresponding to the upstream side in the flow direction of the reaction gas, the inside of the catalyst layer (120a, 120c) is easily dried because the flow velocity of the reaction gas is high. On the other hand, at the site corresponding to the downstream side in the flow direction of the reaction gas, the flow rate of the reaction gas is slow, so that the water generated by the electrode reaction is not easily discharged and the flooding phenomenon is likely to occur. Drying of the catalyst layer reduces the proton transfer rate necessary for the electrochemical reaction, which in turn causes the battery characteristics to deteriorate. In addition, the flooding phenomenon hinders the diffusion of the reaction gas, and also causes the battery characteristics to deteriorate.

  This problem can be solved by changing the void ratio of the layer (122a, 122c) in which the void is formed inside the layer. Specifically, the porosity in the layers (122a, 122c) in which the voids are formed is determined from the gas inflow portion of the gas flow path of the separator through which the gas supplied to the layers in which the voids are formed to the gas discharge portion. Increase in the direction. Thus, by changing the porosity in the gas flow direction, it is possible to prevent drying of the electrode on the upstream side of the reactive gas and to prevent the flooding phenomenon on the downstream side of the reactive gas.

  An embodiment in which the porosity changes will be described with reference to the drawings. FIG. 2 is a plan view of the PEFC anode in which the porosity of the layer in which the voids are formed changes in the direction from the gas inlet 151a to the gas outlet 152a of the gas flow path of the separator 140a. FIG. 2 is a drawing in which the direction of the GDL 130a is observed from the contact surface between the layer 121a in which no void is formed and the layer 122a in which the void is formed. In FIG. 2, the GDL 130a is not shown for convenience of explanation. The flow path formed in the separator 140a is indicated by a broken line.

  The layer 122a in which the void is formed includes a first void portion 125a, a second void portion 126a, and a third void portion 127a. The first void portion 125a, the second void portion 126a, and the third void portion 127a have different void ratios, and the void ratio increases in this order.

  The separator 140a is formed with a gas flow path 150a through which a gas supplied to the catalyst layer 120a flows. Gas is supplied to the gas flow path 150a through the gas inflow portion 151a, and the gas is discharged through the gas discharge portion 152a. The gas inflow portion 151a means a portion where the gas supplied to the gas flow path 150a flows into the gas flow path 151a. The gas discharge part 152a means the site | part from which the gas which distribute | circulated the gas flow path 150a is discharged | emitted from a separator outside. “The porosity changes in the direction from the gas inflow part to the gas exhaust part” means that at least the gas is measured when the porosity of the layer in which the void is formed in the direction from the gas inflow part to the gas exhaust part. It means that the porosity is different between the inflow part and the gas discharge part.

  In the embodiment shown in FIG. 2, the layer 122a in which the void is formed includes the first void portion 125a positioned on the gas inflow portion 151a side of the separator gas flow path and the gas discharge portion 152a side of the separator gas flow path. The third gap portion 127a located at the first gap portion 125a and the second gap portion 126a existing between the first gap portion 125a and the third gap portion 127a. In the embodiment shown in FIG. 2, the layer 122a in which the voids are formed is composed of three portions (125a, 126a, 127a) having different void ratios, but may be composed of two portions having different void ratios. Further, it may be composed of four or more parts having different porosity. The aspect in which the porosity continuously changes may be used. The embodiment shown in FIG. 2 shows the anode side, but the same configuration can be adopted for the cathode side. In some cases, a configuration in which the porosity is changed only on the cathode side may be employed.

  By changing the porosity in this way, electrode drying and flooding are prevented, and deterioration of battery performance is prevented.

  The specific numerical value of the porosity is not particularly limited, but preferably, the porosity in the portion 125a corresponding to the gas inflow portion 151a is 1.5 to 2 of the porosity of the layer 121a in which the adjacent void is not formed. The porosity of the portion 127a corresponding to the gas discharge part 152a is 2.5 to 3.0 times the porosity of the layer 121a in which the adjacent void is not formed. By setting the porosity in this range, it is possible to effectively suppress a decrease in battery performance. Note that the void ratio means the ratio of voids per volume. For example, using an SEM, an enlarged photograph of an arbitrary part (several places) inside the electrode is taken, and image processing is performed to perform the image processing. It can be obtained by calculating the area of the hole portion and calculating the ratio with the area of the electrode portion. For example, as shown in FIG. 2, when the layer in which the void is formed is composed of three portions, the porosity of the first void portion 125a existing in the portion corresponding to the gas inflow portion 151a, the second void portion The porosity of 126a and the porosity of the second cavity 127a existing at the site corresponding to the gas discharge part 152a are 1.5 to 2.0 times the porosity of the layer 121a in which no cavity is formed, 2.0 to 2.5 times and 2.5 to 3.0 times.

  A method for producing a catalyst layer of a polymer electrolyte fuel cell, comprising a layer in which voids for promoting gas supply are formed and a layer in which voids for promoting gas supply are not formed, It is not limited. For example, the following method can be used.

  First, a slurry for preparing a layer in which voids are formed is prepared. A foaming agent is included in the slurry. As the foaming agent, camphor or the like can be used. In addition to the foaming agent, a material constituting the catalyst layer is blended in the slurry. For example, the slurry includes a carrier supporting a catalyst, a polymer electrolyte, and a blowing agent. The slurry may be formed on a predetermined sheet such as a water-repellent substrate and then transferred to the surface of the GDL, or the slurry may be applied to the surface of the GDL. Preferably, the slurry is applied to the surface of the GDL. Since GDL is porous, cracks are likely to occur. The method for applying the slurry is not particularly limited, and application methods such as a screen printing method, a doctor blade method, and a spray method can be used. The blowing agent disappears upon drying. Thereby, a layer in which voids are formed can be formed. The porosity of the layer can be controlled by the amount of foaming agent added.

  As shown in FIG. 2, when the layer in which the voids are formed is composed of a plurality of portions having different void ratios, two or more kinds of slurries having different types of foaming agents or blending amounts of the foaming agents are applied and dried. By doing so, a layer composed of two or more parts having different porosity may be formed.

  More specifically, in the case of forming three parts having different void ratios, first, the slurry for gas inflow part applied to the part corresponding to the gas inflow part and the part corresponding to the gas discharge part are applied. The slurry for the gas discharge part side and the slurry for intermediate parts applied to these intermediate parts are prepared. The gas inflow portion side slurry is applied to a one-third area corresponding to the gas inflow portion, and the coating film is dried. Thereafter, the intermediate portion slurry is applied to the adjacent one-third area, and the coating film is dried. Finally, the gas discharge part side slurry is applied to the remaining one-third area, and the coating film is dried. By such a method, a layer in which a void composed of three regions is formed can be produced. However, the technical scope of the present invention is not limited to the PEFC including the catalyst layer manufactured by such a manufacturing method.

  On the other hand, a slurry for preparing a layer in which no void is formed is prepared. The slurry does not contain a blowing agent. A material constituting the catalyst layer is blended in the slurry. For example, the slurry includes a carrier supporting a catalyst and a polymer electrolyte. The slurry may be formed on a predetermined sheet such as a water-repellent substrate, and then transferred to the surface of the polymer electrolyte membrane, or the slurry may be applied to the surface of the polymer electrolyte membrane. Preferably, the slurry is applied onto a water repellent substrate and the coating film is dried. A water-repellent substrate such as a polytetrafluoroethylene sheet is generally not porous and is advantageous in forming a layer in which no voids such as cracks are formed. The coating film formed on the water repellent substrate is transferred onto the polymer electrolyte membrane by hot pressing. After hot pressing, the water repellent substrate is peeled off.

  In the above description, the manufacturing method in which the foaming agent is used has been described. However, a layer in which voids are formed without using the foaming agent may be produced. For example, a slurry having a high water content is prepared, and after applying this slurry, it is heated and dried to generate cracks on the coating film surface. The degree of occurrence of cracks can be controlled by the moisture content and drying conditions.

  The catalyst is required to have a catalytic action in the oxidation reaction of hydrogen and / or the reduction reaction of oxygen. For example, metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, copper, silver, and alloys thereof. It can be used as a catalyst. Usually, the catalyst is contained as catalyst particles in a state of being supported on a carrier.

  Carrier means a material that can be used to support the catalyst. However, a carrier not carrying a catalyst may be included. The carrier is conductive and the generated electrons can move through the carrier. When a carrier that does not carry a catalyst is included, the carrier that does not carry a catalyst is preferably a carrier having low corrosion resistance. When a large number of catalysts are supported on a carrier having high corrosion resistance, a decrease in power generation characteristics when the carrier is corroded is suppressed.

  As the carrier, carbon materials such as carbon black, activated carbon, coke, and graphite can be used. As the carrier, a carrier synthesized by itself using a known method may be used, or a commercially available product may be used. Carriers modified from commercial products may be used. The particle diameter when the catalyst is supported on the carbon material is generally about 1 to 30 nm. From the viewpoint of ease of loading, it is preferably 1 nm or more, and from the viewpoint of catalyst utilization, it is preferably 30 nm or less. However, in some cases, the particle diameter may be out of this range.

  As the proton conductive polymer electrolyte, the same polymer as the polymer electrolyte membrane can be used. By including a proton conductive polymer electrolyte in the catalyst layer, protons generated around the catalyst on the anode side can be transported to the polymer electrolyte membrane, and protons can be transported to the periphery of the catalyst on the cathode side.

  The catalyst layer may contain other components. For example, a water-repellent polymer such as polytetrafluoroethylene, polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer can be included in the catalyst layer.

  There are no particular limitations on the amount of the catalyst, the carrier, and the proton conductive polymer electrolyte in the catalyst layer. An appropriate blending amount may be determined based on the knowledge already obtained. The blending amount may be different depending on the layer constituting the catalyst layer. Generally, based on the total mass of the catalyst layer, the total compounding amount of the catalyst is 20 to 40% by mass, the total compounding amount of the carrier is 25 to 40% by mass, and the total compounding amount of the proton conductive polymer electrolyte is 20%. It is -55 mass%.

  The concentration of the polymer electrolyte contained in the catalyst layer preferably increases in the direction from the adjacent GDL to the polymer electrolyte membrane. That is, the concentration of the polymer electrolyte contained in the catalyst layer increases as it approaches the polymer electrolyte membrane from the GDL. The method of increasing the concentration may be stepwise or continuous. Considering the ease of production, the concentration of the polymer electrolyte is preferably changed for each layer constituting the catalyst layer. As the polymer electrolysis mass in the catalyst layer increases, the proton transfer resistance decreases. For this reason, sufficient proton conductivity is ensured in the part close to the polymer electrolyte membrane by increasing the concentration of the polymer electrolyte. On the other hand, when there is much polymer electrolysis mass, there exists a possibility that gas diffusibility and drainage may fall. For this reason, in the part close | similar to GDL, it is good to reduce the density | concentration of a polymer electrolyte, and to ensure gas diffusibility and drainage. A gradient may be provided for the concentration of the polymer electrolyte, and a gradient may be provided for the concentration of the catalyst and the support.

  The GDL (130a, 130c) is generally made of a porous material, and the gas supplied to the fuel cell is dispersed by the porous gas diffusion layer and supplied to the catalyst layer. The GDL (130a, 130c) is disposed so as to sandwich the polymer electrolyte membrane and the catalyst layer on the surface of the catalyst layer facing the polymer electrolyte. That is, the GDL 130a is disposed on the surface of the catalyst layer 120a opposite to the surface on which the polymer electrolyte 110 is disposed. The GDL 130c is disposed on the surface of the catalyst layer 120c opposite to the surface on which the polymer electrolyte 110 is disposed. As a whole, the polymer electrolyte membrane 110 and the catalyst layers (120a, 120c) are sandwiched between the GDL 130a and the GDL 130c. As a result, an assembly is obtained in which GDL 130a / catalyst layer 120a / polymer electrolyte membrane 110 / catalyst layer 120c / GDL 130c are arranged in this order.

  As a material used for GDL (130a, 130c), a sheet-like material made of carbon paper, carbon cloth, nonwoven fabric, carbon woven fabric, paper-like paper body, felt or the like has been proposed. GDL is also required to have functions such as electron conductivity and water repellency. When GDL has excellent electron conductivity, efficient transport of electrons generated by a power generation reaction is achieved, and the performance of the fuel cell is improved. Moreover, if GDL has excellent water repellency, the generated water is efficiently discharged.

  In order to ensure high water repellency, a technique for water repellency treatment of a material constituting the GDL has also been proposed. For example, a solution containing a fluorine-based resin such as polytetrafluoroethylene (PTFE) is impregnated with a material constituting GDL such as carbon paper, and dried in the air or an inert gas such as nitrogen. Depending on the case, the hydrophilization treatment may be performed on the material constituting the GDL. After drying, a carbon layer formed of carbon black powder and PTFE may be disposed.

  Various improvements may be made to the GDL (130a, 130c) in order to improve performance. For example, GDL gas diffusibility and compressibility may be improved by forming a layer composed of a fluororesin and carbon black on the surface of a carbon fiber woven fabric (for example, JP-A-10-261421). Gazette, JP-A-11-273688).

  The membrane electrode assembly is used for the production of PEFC. When manufacturing PEFC, a pair of separators are arranged so as to sandwich the membrane electrode assembly of the present invention. In addition, various members can be installed as necessary. For example, a gasket that prevents leakage of gas supplied to the PEFC to the outside is disposed.

  The separator has a function of transmitting a current generated in the membrane electrode assembly to an adjacent fuel cell. When the PEFC is arranged at the end of a stack composed of a large number of PEFCs, current is taken out from the separator arranged at the outermost part, or current flows into the separator arranged at the outermost part.

  The separator is disposed so as to sandwich the polymer electrolyte membrane, the catalyst layer, and the separator on the surface facing the GDL catalyst layer. That is, one separator is arrange | positioned on the surface on the opposite side to the surface where the catalyst layer 120a of GDL130a is arrange | positioned. The other separator is disposed on the surface opposite to the surface on which the catalyst layer 120c of the GDL 130c is disposed. As a whole, the polymer electrolyte membrane 110, the catalyst layers (120a, 120c), and the GDL (130a, 130c) are sandwiched by two separators. As a result, PEFCs arranged in the order of separator / GDL 130a / catalyst layer 120a / polymer electrolyte membrane 110 / catalyst layer 120c / GDL 130c / separator are obtained.

  A gas channel is formed on the GDL side surface of the separator, and a predetermined gas is supplied to the gas channel. The gas flowing through the gas flow path flows into the GDL, is diffused by the GDL, and is finally supplied to the membrane electrode assembly. The gas flow path is also used for discharging water generated along with the power generation reaction in the membrane electrode assembly to the outside. Water generated in the membrane electrode assembly is transported to the gas flow path of the separator via the GDL, and is discharged to the outside of the PEFC through the gas flow path. The gas flow path is formed by irregularities that the separator has on the surface on the GDL side.

  The method for producing PEFC is not particularly limited. Obtained knowledge and known techniques can be referred to as appropriate. The PEFC of the present invention can be used for various applications. Preferred applications include vehicles. A vehicle equipped with the PEFC of the present invention has excellent power generation characteristics.

  Hereinafter, although the present invention is explained using an example, the technical scope of the present invention is not limited to the following example.

[Example 1]
First, a slurry for preparing a catalyst layer was prepared. For 1 part by mass of Pt-supported carbon particles in which 50% by mass of Pt having a particle diameter of 2 to 3 nm is supported on carbon particles having an average particle diameter of about 30 nm, 2.5 parts by mass of pure water and 5% by mass Nafion solution (DuPont) (Registered trademark) 9 parts by mass and 1 part by mass of isopropyl alcohol were mixed to obtain slurry A for preparing a catalyst layer. Next, 2 parts by mass of pure water and 1 part by mass of isopropyl alcohol were added to the slurry A to obtain a slurry B for preparing a catalyst layer.

  The slurry A was applied onto the polytetrafluoroethylene sheet using a screen printer. After applying the slurry A, it was naturally dried in a desiccator for about 40 minutes to form a film in which no voids such as cracks were generated. This operation was repeated, and finally, a first catalyst layer having a total film thickness of 10 μm and having no voids such as cracks was obtained.

  On the other hand, slurry B was applied onto the gas diffusion layer using a doctor blade. After applying the slurry B, the slurry on the gas diffusion layer was dried at 40 ° C. for about 10 minutes, further heated to 60 ° C. and dried for about 20 minutes, thereby forming a film in which cracks were formed. This operation was repeated, and finally a second catalyst layer having a total film thickness of 20 μm and having cracks formed was obtained.

  The first catalyst layer having no voids formed on the polytetrafluoroethylene sheet was transferred to both surfaces of the proton conductive polymer electrolyte membrane by hot pressing. The polytetrafluoroethylene sheet was peeled off from the catalyst layer after hot pressing. A polymer electrolyte membrane in which a first catalyst layer having no voids is formed on both surfaces, and two gas diffusion layers on the surface of which the second catalyst layer having voids is disposed on the surface, the first catalyst layer and the second catalyst layer. It arrange | positioned so that a catalyst layer might contact and it integrated by the hot press. Thereby, gas diffusion layer / second catalyst layer (with voids) / first catalyst layer (without voids) / polymer electrolyte membrane / first catalyst layer (without voids) / second catalyst layer (with voids) / gas diffusion A membrane electrode assembly in which the layers were laminated in this order was obtained.

[Example 2]
For 1 part by mass of Pt-supported carbon particles in which 50% by mass of Pt having a particle diameter of 2 to 3 nm is supported on carbon particles having an average particle diameter of about 30 nm, 2.5 parts by mass of pure water and 5% by mass Nafion solution (DuPont) (Registered trademark) 7 parts by mass and 1 part by mass of isopropyl alcohol were mixed to obtain slurry C for preparing a catalyst layer.

  The slurry A was applied onto the polytetrafluoroethylene sheet using a screen printer. After applying the slurry A, it was naturally dried in a desiccator for about 40 minutes to form a film in which no voids such as cracks were generated. This operation was repeated, and finally, a first catalyst layer having a total film thickness of 10 μm and having no voids such as cracks was obtained.

  On the other hand, slurry C was applied onto the gas diffusion layer using a doctor blade. After applying the slurry C, the slurry on the gas diffusion layer was dried at 40 ° C. for about 10 minutes, further heated to 60 ° C. and dried for about 20 minutes, thereby forming a film in which cracks were formed. This operation was repeated, and finally a second catalyst layer having a total film thickness of 20 μm and having cracks formed was obtained.

  The first catalyst layer having no voids formed on the polytetrafluoroethylene sheet was transferred to both surfaces of the proton conductive polymer electrolyte membrane by hot pressing. The polytetrafluoroethylene sheet was peeled off from the catalyst layer after hot pressing. A polymer electrolyte membrane in which a first catalyst layer having no voids is formed on both surfaces, and two gas diffusion layers on the surface of which the second catalyst layer having voids is disposed on the surface, the first catalyst layer and the second catalyst layer. It arrange | positioned so that a catalyst layer might contact and it integrated by the hot press. Thereby, gas diffusion layer / second catalyst layer (with voids) / first catalyst layer (without voids) / polymer electrolyte membrane / first catalyst layer (without voids) / second catalyst layer (with voids) / gas diffusion A membrane electrode assembly in which the layers were laminated in this order was obtained.

[Comparative Example 1]
The slurry A prepared in Example 1 was applied onto a polytetrafluoroethylene sheet using a screen printer. After applying the slurry A, it was naturally dried in a desiccator for about 40 minutes to form a film in which no voids such as cracks were generated. This operation was repeated, and finally, a catalyst layer having a total film thickness of 30 μm and having no voids such as cracks was obtained.

  The catalyst layer having no voids formed on the polytetrafluoroethylene sheet was transferred onto both surfaces of the proton conductive polymer electrolyte membrane by hot pressing. The polytetrafluoroethylene sheet was peeled off from the catalyst layer after hot pressing. A polymer electrolyte membrane in which a catalyst layer without voids was formed on both surfaces and two gas diffusion layers were laminated and integrated by hot pressing. As a result, a membrane electrode assembly was obtained in which the gas diffusion layer / catalyst layer (no voids) / polymer electrolyte membrane / catalyst layer (no voids) / gas diffusion layer were laminated in this order.

[Comparative Example 2]
On the gas diffusion layer, the slurry B prepared in Example 1 was applied using a doctor blade. After applying the slurry B, the slurry on the gas diffusion layer was dried at 40 ° C. for about 10 minutes, further heated to 60 ° C. and dried for about 20 minutes, thereby forming a film in which cracks were formed. This operation was repeated, and finally a catalyst layer having a total film thickness of 30 μm and having cracks formed was obtained.

  The polymer electrolyte membrane and the two gas diffusion layers having the above-described void catalyst layer disposed on the surface were laminated and integrated by hot pressing. As a result, a membrane electrode assembly was obtained in which the gas diffusion layer / catalyst layer (with voids) / polymer electrolyte membrane / catalyst layer (with voids) / gas diffusion layer were laminated in this order.

[Example 3]
A slurry for preparing a catalyst layer was prepared. For 1 part by mass of Pt-supported carbon particles in which 50% by mass of Pt having a particle diameter of 2 to 3 nm is supported on carbon particles having an average particle diameter of about 30 nm, 2.5 parts by mass of pure water and 5% by mass Nafion solution (DuPont) 9 parts by mass of (registered trademark) and 1 part by mass of isopropyl alcohol were mixed to obtain slurry D for preparing a catalyst layer. Next, camphor was added as a foaming agent to slurry D to obtain slurries E, F, and G for preparing a catalyst layer. Slurries E, F, and G had different amounts of added camphor, and the camphor content was set to slurry E <slurry F <slurry G.

  Slurry E, slurry F, and slurry G were applied onto the polytetrafluoroethylene sheet using a screen printer. As shown in FIG. 2, slurry E with a low foaming agent content is applied to a third of the part corresponding to the gas inflow part, and slurry G with a high foaming agent content is applied to the gas discharge part. The slurry F was applied to the middle part of the coating. Then, it was dried at room temperature in a desiccator to obtain a film in which voids were formed.

  Slurry D was applied on the film in which voids were formed, using a screen printer. Then, it was dried at room temperature in a desiccator to obtain a catalyst layer in which a layer in which voids were formed and a layer in which voids were not formed were laminated. The catalyst layer formed on the polytetrafluoroethylene sheet is transferred to both surfaces of the proton conductive polymer electrolyte membrane by hot pressing and sandwiched between a pair of gas diffusion layers, whereby a gas diffusion layer / second layer is formed. Catalyst layer (with voids; composed of a plurality of parts having different void ratios) / first catalyst layer (without voids) / polymer electrolyte membrane / first catalyst layer (without voids) / second catalyst layer (with voids; void ratio) A membrane electrode assembly in which gas diffusion layers were laminated in this order was obtained.

  The structures of the catalyst layers of Examples and Comparative Examples are summarized in Table 1.

The membrane electrode assemblies of Examples and Comparative Examples were sandwiched between a pair of separators to produce PEFC single cells. When the membrane electrode assembly of Example 3 is used, as shown in FIG. 2, the gas inflow portion of the separator corresponds to the portion where the slurry E is applied, and the portion of the separator is applied to the portion where the slurry G is applied. A separator was arranged so that the gas discharge part corresponded. Battery characteristics of the obtained single cell of PEFC were investigated. When investigating battery characteristics, hydrogen gas was flowed to the fuel electrode (anode), air was flown to the air electrode (cathode), the cell temperature was 70 ° C., the fuel utilization rate was 67%, and the air utilization rate was 40%. Controlled. Further, the hydrogen gas and air were humidified so that the hydrogen gas was 60% RH and the air gas was 55% RH. Table 2 summarizes the cell voltages of each PEFC when currents of 0.2 A / cm ² and 1 A / cm ² were passed. As shown in Table 2, the PEFC of the present invention is excellent in power generation characteristics.

It is a cross-sectional schematic diagram about one Embodiment of the membrane electrode assembly of this invention. It is a top view of the anode of PEFC from which the porosity of the layer in which the space | gap was formed changes in the direction from the gas inflow part of the gas flow path of a separator to a gas discharge part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Membrane electrode assembly, 110 ... Polymer electrolyte membrane, 120a and 120c ... Catalyst layer, 121a and 121c ... Layer without voids, 122a and 122c ... Layer with voids, 123a and 123c ... Gaps , 125a: first gap portion, 126a ... second gap portion, 127a ... third gap portion, 130a and 130c ... gas diffusion layer (GDL), 140a ... separator, 150a ... gas flow path, 151a ... gas inflow portion, 152a ... gas discharge part.

Claims (13)

A polymer electrolyte membrane;
A pair of catalyst layers sandwiching the polymer electrolyte membrane;
A membrane electrode assembly having a pair of gas diffusion layers disposed on the surface of the catalyst layer facing the polymer electrolyte membrane so as to sandwich the polymer electrolyte membrane and the catalyst layer; ,
At least one of the catalyst layers is composed of two or more layers laminated in the direction in which the constituent elements of the membrane electrode assembly are laminated,
The two or more layers constituting the catalyst layer are composed of a layer in which a gap for promoting gas supply is formed and a layer in which no gap for promoting gas supply is formed. A membrane electrode assembly, wherein the formed layer is disposed on the gas diffusion layer side.   The membrane electrode assembly according to claim 1, wherein a total film thickness of the layer in which the void is formed is equal to or greater than a total film thickness of the layer in which the void is not formed.   The membrane electrode assembly according to claim 2, wherein the total film thickness of the layer in which the voids are formed is 1.0 to 5.0 times the total film thickness of the layer in which the voids are not formed.   The membrane electrode assembly according to claim 3, wherein the total film thickness of the layer in which the voids are formed is 1.5 to 3.0 times the total film thickness of the layer in which the voids are not formed.   The total thickness of the layer in which the void is formed is 25 to 45 μm, the total thickness of the layer in which the void is not formed is 5 to 25 μm, and the layer in which the void is formed and the void is not formed The membrane electrode assembly according to any one of claims 1 to 4, wherein a total film thickness with the layer is 50 µm or less.   The membrane electrode assembly according to any one of claims 1 to 5, wherein the concentration of the polymer electrolyte contained in the catalyst layer increases in the direction from the adjacent gas diffusion layer to the polymer electrolyte membrane. . The membrane electrode assembly according to any one of claims 1 to 6,
A solid polymer fuel cell comprising: a pair of separators disposed so as to sandwich the membrane electrode assembly.   The porosity of the layer in which the voids are formed increases from the gas inflow portion to the gas discharge portion of the gas flow path of the separator through which the gas supplied to the layer in which the voids are formed flows. The polymer electrolyte fuel cell according to claim 7. The porosity at the site corresponding to the gas inflow portion is 1.5 to 2.0 times the porosity of the layer in which the adjacent void is not formed,
9. The polymer electrolyte fuel cell according to claim 8, wherein a porosity in a portion corresponding to the gas discharge portion is 2.5 to 3.0 times a porosity of a layer in which the adjacent void is not formed. .   A vehicle on which the polymer electrolyte fuel cell according to any one of claims 7 to 9 is mounted. Membrane electrode assembly having a catalyst layer of a polymer electrolyte fuel cell, comprising a layer in which a gap for promoting gas supply is formed and a layer in which no gap for promoting gas supply is formed A manufacturing method of
Applying and drying a slurry containing a blowing agent to form a layer in which the voids are formed;
Forming a layer in which the voids are not formed by applying and drying a slurry containing no foaming agent, and a method for producing a membrane electrode assembly. The step of forming the layer in which the voids are formed is a step of applying and drying a slurry containing a foaming agent on the gas diffusion layer,
In the step of forming a layer in which no voids are formed, a slurry for forming a catalyst layer containing no foaming agent is applied and dried on a water-repellent substrate, and the formed coating film is hot-coated on the polymer electrolyte membrane. The method for producing a membrane electrode assembly according to claim 11, wherein the membrane electrode assembly is transferred by a press.   The step of forming the layer in which the voids are formed is performed by applying and drying two or more kinds of slurries having different kinds of foaming agents or blending amounts of the foaming agents, and drying a layer composed of two or more parts having different porosity. The manufacturing method of the membrane electrode assembly of Claim 11 or 12 which is a step of forming.

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