JP2008041352A - Gas diffusion layer and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion layer allowing a drainage property at high temperatures to be controlled without degrading power generation performance; and a fuel cell having the gas diffusion layer. <P>SOLUTION: This gas diffusion layer 10 comprises a surface layer 3 and a conductive porous base material layer 1, and is structured such that a pore diameter-varying layer 2 is arranged on the side opposite to the surface layer 3 in the conductive porous base material layer 1; and a high-thermal-expansion material having a coefficient of thermal expansion higher than that of the conductive porous base material layer 1 is arranged in a part of the conductive porous base material layer 1. EPDM is used as the high-thermal-expansion material provided for the gas diffusion layer 10, and the pore diameter-varying layer 2 is formed by applying paste containing the EPDM and carbon black particles to the conductive porous base material and drying it. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gas diffusion layer and a fuel cell, and more particularly to a gas diffusion layer capable of controlling drainage at a high temperature and a fuel cell including the gas diffusion layer.

  A polymer electrolyte fuel cell (hereinafter, sometimes referred to as “PEFC (Polymer Electrolyte Fuel Cell)”) is an electrolyte membrane and electrodes (anode and cathode) disposed on both sides of the electrolyte membrane, respectively. Current collectors disposed on both sides of the MEA, respectively, by the electrical energy generated by the electrochemical reaction in the membrane electrode assembly (hereinafter sometimes referred to as “MEA (Membrane Electrode Assembly)”). For example, it is taken out through a separator. Among fuel cells, PEFCs used for home cogeneration systems and automobiles can be operated in a low temperature region. In addition, PEFC has attracted attention as an optimal power source for electric vehicles and portable power sources because of its high energy conversion efficiency, short start-up time, and small and lightweight system.

  A single cell of PEFC includes an electrolyte membrane including an ionomer having proton conductivity, a cathode and an anode including at least a catalyst layer, and a theoretical electromotive force thereof is 1.23V. However, since such low electromotive force is insufficient as a power source for electric vehicles and the like, usually, a single cell is laminated in series to form a laminated body, and end plates or the like are formed at both ends of the laminated body in the lamination direction. A fuel cell in the form of a stack formed by arranging is used. Then, from the viewpoint of reducing the contact resistance, a fastening pressure is applied from both ends of the stack type fuel cell.

  During operation of the PEFC, a hydrogen-containing gas (hereinafter referred to as “hydrogen”) is supplied to the anode, and an oxygen-containing gas (hereinafter referred to as “oxygen”) is supplied to the cathode. The hydrogen supplied to the anode is separated into protons and electrons on the catalyst contained in the catalyst layer of the anode (hereinafter also referred to as “anode catalyst layer”), and the protons generated from the hydrogen are separated from the anode catalyst layer. And reaches the cathode catalyst layer (hereinafter also referred to as “cathode catalyst layer”) through the electrolyte membrane. On the other hand, electrons reach the cathode catalyst layer through an external circuit, and PEFC can take out electric energy through such a process. Then, the protons and electrons that have reached the cathode catalyst layer react with oxygen supplied to the cathode catalyst layer, thereby generating water.

  The water generated during the operation of the PEFC can be used, for example, to keep the electrolyte membrane or the like in a water-containing state. On the other hand, when the PEFC is operated with a high load, the temperature of the single cell rises and water tends to evaporate. Since the evaporated water is easily discharged to the outside of the single cell together with hydrogen and / or oxygen supplied to the single cell, the electrolyte membrane and the like are easily dried when the temperature of the single cell rises. Here, at least the ionomer provided in the electrolyte membrane exhibits proton conduction performance in a water-containing state. Therefore, when the electrolyte membrane or the like is dried, the proton conduction performance is lowered, and the power generation performance of the PEFC is lowered. Therefore, in order to improve the power generation performance of PEFC, it is important to suppress drying of the electrolyte membrane and the like during high load operation.

Techniques aimed at suppressing drying of electrolyte membranes and the like have been disclosed so far. For example, Patent Document 1 includes a membrane electrode assembly and a porous gas diffusion material layer disposed together with the membrane electrode assembly, and the porosity of the porous gas diffusion material in a localized region on the porous gas diffusion layer is A fuel cell is disclosed that varies from a first value to a second value in response to a trigger condition at a corresponding region on the membrane electrode assembly adjacent to the porous gas diffusion layer. According to this fuel cell, hot spots that tend to occur in the fuel cell membrane electrode assembly can be suppressed.
JP 2005-508069 gazette

  According to the technique disclosed in Patent Document 1, it is considered that the excessive temperature rise can be suppressed by suppressing the supply of gas. However, if the gas supply is suppressed, an electrochemical reaction is less likely to occur at the location where the gas supply is suppressed, so that the technique disclosed in Patent Document 1 tends to reduce the power generation performance of the fuel cell. There was a problem.

  Then, this invention makes it a subject to provide a gas diffusion layer which can control the drainage property at the time of high temperature, and a fuel cell provided with the said gas diffusion layer, without reducing electric power generation performance.

In order to solve the above problems, the present invention takes the following means. That is,
The invention described in claim 1 includes a conductive porous substrate, and a high thermal expansion material having a higher coefficient of thermal expansion than the conductive porous substrate is provided in a part of the conductive porous substrate. It is a gas diffusion layer characterized.

  Here, “a high thermal expansion material having a higher coefficient of thermal expansion than the conductive porous substrate” means a high thermal expansion measured by a method defined in JIS C2161: 1997 “Method for Testing Powder Coating for Electrical Insulation”. It means that the value of the coefficient of thermal expansion of the material is larger than the value of the coefficient of thermal expansion of the conductive porous substrate. In other words, it means a material (high thermal expansion material) that expands more easily than the conductive porous substrate at a high temperature (for example, 80 ° C. or higher).

  The invention according to claim 2 is characterized in that, in the gas diffusion layer according to claim 1, the conductive porous substrate is provided with a carbon material, and the high thermal expansion material is an organic polymer material.

  Specific examples of the “carbon material” include carbon fiber and carbon black. Furthermore, the “organic polymer material” means a material having a higher coefficient of thermal expansion than the carbon material and capable of withstanding the environment in the single cell during fuel cell operation.

  The invention according to claim 3 is the gas diffusion layer according to claim 2, wherein the organic polymer material is ethylene-propylene-diene rubber (hereinafter referred to as “EPDM”).

  According to a fourth aspect of the present invention, there is provided a membrane electrode structure comprising an electrolyte membrane, an anode catalyst layer provided on one side of the electrolyte membrane, and a cathode catalyst layer provided on the other side of the electrolyte membrane , “MEA”), a first current collector provided on one side of the membrane electrode structure, and a second current collector provided on the other side of the membrane electrode structure, A first gas diffusion layer disposed between the first current collector and the membrane electrode structure and / or a second gas disposed between the second current collector and the membrane electrode structure. A fuel diffusion layer, wherein the first gas diffusion layer and / or the second gas diffusion layer is the gas diffusion layer according to any one of claims 1 to 3. It is a battery.

  Here, the “electrolyte membrane” is not particularly limited as long as it has a polymer (proton conductive polymer) that conducts protons, but at least a sulfonic acid group and a phosphonic acid group with a fluorinated polymer as a skeleton. And a polymer having one of phosphoric acid groups (for example, Nafion et al. (Nafion is a registered trademark of DuPont, USA). In addition, it has a hydrocarbon-based polymer such as polyolefin. In addition, the form of the catalyst layer is not particularly limited as long as the catalyst layer includes a proton conductive polymer and a catalyst material, and the catalyst material is used for the oxidation reaction of hydrogen and the reduction reaction of oxygen at the anode and the cathode. As long as it has an action, it is not particularly limited. Specific examples include carbon as a carrier (for example, carbon In addition to platinum supported on a rack, etc., platinum black particles, alloys thereof, etc. Further, the proton conductive polymer contained in the catalyst layer includes a proton conductive polymer contained in the electrolyte membrane and In addition, specific examples of the “first current collector” and the “second current collector” may include separators, etc. Specific examples of the material constituting the “second current collector” include carbon materials and conductive resins, as well as metals such as titanium alloys and stainless steel.

  Further, “the first gas diffusion layer disposed between the first current collector and the membrane electrode structure and / or the second gas collector disposed between the second current collector and the membrane electrode structure”. “Two gas diffusion layer” refers to a case where a gas diffusion layer is provided between the first current collector and the MEA and between the second current collector and the MEA (hereinafter referred to as “form A”). Means a first gas diffusion layer and a second gas diffusion layer. In addition, a gas diffusion layer is provided only between the first current collector and the MEA, and a gas diffusion layer is not provided between the second current collector and the MEA (hereinafter referred to as “form B”). ) Means a first gas diffusion layer, a gas diffusion layer is not provided between the first current collector and the MEA, and a gas diffusion layer is provided only between the second current collector and the MEA. In the case (hereinafter referred to as “form C”), it means the second gas diffusion layer. Furthermore, “the first gas diffusion layer and / or the second gas diffusion layer is the gas diffusion layer according to any one of claims 1 to 3” means that in the case of the above-described form A, First gas diffusion layer and second gas diffusion layer (hereinafter referred to as “form A1”), only the first gas diffusion layer (hereinafter referred to as “form A2”), or only the second gas diffusion layer ( Hereinafter, “form A3”) means that it is the gas diffusion layer according to any one of claims 1 to 3. On the other hand, in the case of the form B, it means that the first gas diffusion layer is the gas diffusion layer according to any one of claims 1 to 3, and in the case of the form C, It means that a 2nd gas diffusion layer is a gas diffusion layer of any one of the said Claims 1-3.

  According to a fifth aspect of the present invention, in the fuel cell according to the fourth aspect, high thermal expansion is provided on the first current collector side of the first gas diffusion layer and / or on the second current collector side of the second gas diffusion layer. Material is provided.

  Here, “a high thermal expansion material is provided on the first current collector side of the first gas diffusion layer and / or the second current collector side of the second gas diffusion layer” means that in the case of the above-described form A1 This means that a high thermal expansion material is provided on the first current collector side of the first gas diffusion layer and on the second current collector side of the second gas diffusion layer. In addition, in the case of the form A2 or the form B, a high thermal expansion material is provided on the first current collector side of the first gas diffusion layer. In the case of the form A3 or the form C, the second gas diffusion is provided. It means that a high thermal expansion material is provided on the second current collector side of the layer.

  According to the first aspect of the present invention, the high thermal expansion material is provided on a part of the conductive porous substrate. Therefore, it is possible to provide a gas diffusion layer that can control drainage by the expanded high thermal expansion material while ensuring gas diffusibility at high temperatures.

  According to the second aspect of the present invention, the conductive porous substrate is provided with a carbon material such as carbon fiber, and an organic polymer material is used as the high thermal expansion material. Therefore, a gas diffusion layer having the above effects can be easily obtained.

  According to the invention described in claim 3, EPDM is used as the organic polymer material. Since EPDM has a large coefficient of thermal expansion and a large difference from the coefficient of thermal expansion of the carbon material provided in the conductive porous substrate, it is possible to provide a gas diffusion layer that can easily control the movement of water at high temperatures.

  According to the invention described in claim 4, the gas diffusion layer of the present invention is provided on the anode side and / or the cathode side. Therefore, it is possible to provide a fuel cell capable of improving the power generation performance by controlling the drainage by the expanded high thermal expansion material while ensuring the gas diffusibility at high temperature and suppressing the decrease in the power generation performance.

  According to the invention described in claim 5, the high thermal expansion material is provided on the current collector side of the gas diffusion layer. Therefore, in addition to the above effects, a fuel cell that can further suppress the occurrence of flooding can be provided.

  In order to obtain electric energy using PEFC, it is necessary to cause an electrochemical reaction in MEA, and in order to cause an electrochemical reaction, it is necessary to transfer protons generated in the anode catalyst layer to the cathode catalyst layer. is there. From this point of view, the PEFC electrolyte membrane, anode catalyst layer, and cathode catalyst layer are provided with a substance having proton conductivity, and perfluorosulfonic acid ionomers are known as the substance. Since this ionomer expresses proton conducting performance in a water-containing state, it is necessary to keep the MEA in a water-containing state during PEFC operation. However, the temperature of the single cell rises at the time of high load operation or the like, and the MEA tends to dry especially near the gas flow path inlet of the single cell. As a conventional technique for suppressing the drying of MEA, for example, there is a technique for suppressing the supply of gas. However, if the supply of gas is suppressed, an electrochemical reaction hardly occurs, and the power generation performance of PEFC is likely to deteriorate. There was a problem. Therefore, there is a demand for a technique that can suppress drying of MEA without reducing the power generation performance of PEFC.

  The present invention has been made from such a viewpoint, and the first gist of the present invention is to control drainage while ensuring gas diffusibility by adopting a form in which a part of the base material is provided with a high thermal expansion material. It is to provide a gas diffusion layer that can be used. Furthermore, the second gist is to provide a fuel cell capable of controlling drainage while ensuring gas diffusibility by adopting a configuration in which the gas diffusion layer is provided.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

1. Gas Diffusion Layer FIG. 1 is an enlarged schematic view showing an example of the gas diffusion layer of the present invention. 2 and 3 are enlarged views of a portion indicated by a broken line in FIG. 1, and in order to facilitate understanding of the present invention, the structure of the portion where the high thermal expansion material is provided is shown more specifically, The structure of the part is shown in a simplified manner. 2 and 3 are schematic diagrams for explaining the concept of the present invention in an easy-to-understand manner. FIG. 2 shows the form of the gas diffusion layer in a temperature environment of 60.degree. C., and FIG. The form of the gas diffusion layer is shown respectively.

As shown in FIG. 1, the gas diffusion layer 10 of the present invention comprises a surface layer 3 and a base material layer 1, and the base material layer 1 is provided with a pore diameter variable layer 2 on the side opposite to the surface layer 3. It is a configuration.
Here, the surface layer 3 can be formed of a material that has water repellency, good conductivity and air permeability, and can withstand the environment in the fuel cell. Specific examples include a mixture of a water-repellent resin and a conductive material. Examples of the water-repellent resin include polytetrafluoroethylene resin (PTFE) and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Fluorine-based resin can be mentioned. Examples of the conductive substance include carbon black and graphite. Here, the surface layer 3 is a layer formed for the purpose of improving the contact with the catalyst layer when the gas diffusion layer 10 is incorporated in the fuel cell.
The base material layer 1 can be formed of a material that has good conductivity and air permeability and can withstand the environment in the fuel cell. Specific examples include conductive porous nonwovens such as carbon paper, conductive porous woven fabrics such as carbon cloth, and other conductive porous metals such as foam metal and sintered metal. The base material layer 1 is preferably one that is impregnated with a water-repellent resin and a conductive material in order to stably generate power in the fuel cell. As the water repellent resin and the conductive material, those equivalent to those of the surface layer 3 can be used.
The pore diameter variable layer 2 is formed by impregnating and applying particulate EPDM and a conductive substance to the base material layer 2. A conductive material equivalent to that of the surface layer 3 can be used.

  As shown in FIG. 2, the pore diameter variable layer 2 includes carbon fibers 21, 21,... Constituting the carbon paper, particulate EPDMs 22, 22,..., And carbon black particles 23, 23,. Is provided. In a temperature environment of 60 ° C., the EPDMs 22, 22,... Do not expand so much, so that gas and water can easily move in the thickness direction of the gas diffusion layer 10 (up and down direction in FIG. 2).

  On the other hand, as shown in FIG. 3, in a temperature environment of 90 ° C., EPDM expands to become expanded EPDMs 22x, 22x,. When EPDM expands in this way, the pores provided in the variable pore diameter layer 2 become smaller than in the case of FIG. 2, so that the water in the thickness direction of the gas diffusion layer 10 (up and down direction in FIG. 3). Can be suppressed.

  In the present invention, as long as the pore diameter variable layer 2 is provided in a part of the substrate 1, the ratio of the pore diameter variable layer 2 to the substrate 1 is not particularly limited. However, if the ratio of the pore diameter variable layer 2 is excessively increased, the drainage suppression effect can be improved, but the gas diffusibility may be lowered. Therefore, from the viewpoint of improving the drainage suppression effect while ensuring gas diffusibility, the upper limit of the ratio of the pore diameter variable layer 2 to the base material 1 is preferably 50%. When the pore diameter variable layer 2 is formed by applying a paste containing particulate EPDM 22, 22,... And carbon black particles 23, 23,. The ratio of the pore diameter variable layer 2 can be controlled by controlling the degree of paste that enters the inside of the substrate 1 by adjusting the viscosity of the paste applied to the substrate 1.

  Moreover, in this invention, if the pore diameter variable layer 2 is provided in a part of the base material 1, the site | part in which the pore diameter variable layer 2 is provided is not specifically limited. However, when the gas diffusion layer 10 of the present invention is provided in the PEFC, the gas inlet side of the MEA is easily dried as described above. Therefore, a location corresponding to the vicinity of the gas inlet (for example, when the right side in FIG. 1 is the gas inlet side and the left side is the gas outlet side, and the length of the substrate 1 in the left-right direction on the paper surface is L, It is preferable that the pore diameter variable layer 2 is provided in a part of the base material 1 including the L / 3 region from the right end of the material 1.

  Furthermore, as the high thermal expansion material provided in the gas diffusion layer of the present invention, EPDM is used, and a paste containing EPDM and carbon black particles is applied to a conductive porous substrate and dried to form a variable pore size layer. In this case, the ratio of EPDM and carbon black contained in the paste is not particularly limited. However, EPDM is an insulator, and if a large amount of EPDM is added too much, the electron conductivity of the gas diffusion layer may be lowered. Therefore, from the viewpoint of suppressing the decrease in the electron conductivity of the gas diffusion layer, when the total mass of EPDM and carbon black particles contained in the paste is 100 parts by mass, EPDM should be 40 parts by mass or less. Is preferred.

2. Fuel Cell FIG. 4 is a cross-sectional view schematically showing an embodiment of the fuel cell of the present invention, and shows an enlarged part of the fuel cell. 4, components having the same configuration as the members shown in FIG. 1 are denoted by the same reference numerals as those used in FIG. 1, and description thereof is omitted as appropriate. Hereinafter, the fuel cell of the present invention will be described with reference to FIGS.

  As shown in FIG. 4, the fuel cell 40 of the present invention (hereinafter also referred to as “single cell 40”) includes an electrolyte membrane 41 and an anode 42 provided on one side of the electrolyte membrane 41. A cathode 43 provided on the other side, a first current collector (hereinafter referred to as “separator”) 45 provided on the anode 42 side, and a second current collector provided on the cathode 43 side (hereinafter “separator”). 46). The anode 42 is provided with the anode catalyst layer 42a and the first gas diffusion layer 10, the cathode 43 is provided with the cathode catalyst layer 43a and the second gas diffusion layer 10, respectively, and the MEA 44 is provided with the electrolyte membrane 41 and the anode A catalyst layer 42a and a cathode catalyst layer 43a are provided. Further, the separator 45 is provided with gas flow paths 47, 47,... Through which hydrogen can flow, and the separator 46 is provided with gas flow paths 48, 48,. Hereinafter, the first gas diffusion layer 10 provided in the anode 42 is referred to as “anode diffusion layer 42 b”, and the second gas diffusion layer 10 provided in the cathode 43 is referred to as “cathode diffusion layer 43 b”.

  In the fuel cell 40, the electrolyte membrane 41 is made of, for example, a solid polymer membrane including a perfluorosulfonic acid ionomer (hereinafter simply referred to as “ionomer”). Furthermore, the anode catalyst layer 42a and the cathode catalyst layer 43a are provided with, for example, a platinum catalyst supported on carbon (for example, carbon black) as a carrier and an ionomer. When the fuel cell 40 having such a configuration is operated, hydrogen supplied through the gas flow paths 47, 47,... Is separated into protons and electrons on the platinum catalyst provided in the anode catalyst layer 42a, and thus generated. The protons reach the platinum catalyst provided in the cathode catalyst layer 43a through the anode catalyst layer 42a and the electrolyte membrane 41. On the other hand, electrons generated in the anode catalyst layer 42a reach the platinum catalyst provided in the cathode catalyst layer 43a via an external circuit. And water is produced | generated when oxygen supplied through gas flow path 48,48, ... reacts with the said proton and electron on the platinum catalyst with which the cathode catalyst layer 43a is equipped.

  Thus, water is generated during operation of the fuel cell 40, but protons need to be conducted from the anode catalyst layer 42a to the cathode catalyst layer 43a in order to cause a water generation reaction. Since the ionomer provided in the anode catalyst layer 42a, the electrolyte membrane 41, and the cathode catalyst layer 43a exhibits proton conduction performance under water-containing conditions, normally, humidified hydrogen is present in the gas flow paths 47, 47,. .., And humidified oxygen is supplied to the gas flow paths 48, 48,. And the water produced | generated at the time of the driving | operation of the fuel cell 40 can be discharged | emitted from the exit of gas flow path 48,48, ... with the oxygen supplied via gas flow path 48,48, .... Further, the water that has permeated from the cathode catalyst layer 43a to the anode catalyst layer 42a through the electrolyte membrane 41, along with the hydrogen supplied through the gas channels 47, 47,. It can be discharged from the outlet. The water discharged from the fuel cell 40 is then recovered, for example, into a humidifier (not shown) provided outside the unit cell 40, and supplied through the gas flow paths 47, 47,. It can be used when humidifying oxygen supplied through the gas flow paths 48, 48,.

  Here, in general, the water generated during the operation of the fuel cell moves from the inlet side to the outlet side of the gas channel together with hydrogen and oxygen flowing through the gas channel. On the other hand, when excessive water is contained in the MEA, gas diffusion in the anode catalyst layer and the cathode catalyst layer is hindered, and power generation performance decreases. Therefore, during steady operation of the fuel cell, hydrogen and oxygen having a relative humidity of less than 100% are supplied. Therefore, compared with the outlet side of the gas channel, the inlet side of the gas channel is easily dried, and water tends to accumulate on the outlet side of the gas channel from which water that has moved from the inlet side is discharged. This tendency is particularly noticeable during high load operation of the fuel cell. Therefore, in the fuel cell 40 of the present invention, the anode 42 and the cathode 43 are provided with the anode diffusion layer 42 b and the cathode diffusion layer 43 b. If the fuel cell 40 includes the anode diffusion layer 42b and the cathode diffusion layer 43b, the movement of water in the thickness direction of the anode diffusion layer 42b and the cathode diffusion layer 43b (vertical direction in FIG. 4) at high temperatures. It is suppressed. Therefore, the amount of water taken out of the unit cell 40 together with hydrogen supplied to the gas flow paths 47, 47,... And / or oxygen supplied to the gas flow paths 48, 48,. (Controlling drainage) is possible, and drying of the MEA 44 at high temperatures can be suppressed. Further, since the anode diffusion layer 42b and the cathode diffusion layer 43b are provided with EPDMs 22, 22,... In a part of the base material 1, the anode diffusion layer and / or the cathode diffusion layer as in the conventional fuel cell are provided. A decrease in gas diffusibility due to thermal expansion of the whole can be suppressed. Therefore, according to the present invention, it is possible to provide the fuel cell 40 capable of controlling the drainage property at a high temperature while ensuring the gas diffusibility.

  The EPDMs 22, 22,... Provided in the anode diffusion layer 42b and the cathode diffusion layer 43b should be provided if they are provided only in a part of the base materials 1 and 1 constituting the anode diffusion layer 42b and the cathode diffusion layer 43b. The location is not particularly limited. However, as described above, the MEA 44 includes at least the inlet side of the gas passages 47, 47,... And the inlet side of the gas passages 48, 48,. It is preferable that EPDMs 22, 22,. Here, the “gas channel inlet side” is, for example, opposed to a region from the gas channel inlet to the length L / 3 when the total length of the gas channel provided in the separators 45 and 46 is L. Means the part of the gas diffusion layer.

  Furthermore, if EPDMs 22, 22,... Are provided only on a part of the base materials 1, 1, the positions in the thickness direction of the anode diffusion layer 42b and the cathode diffusion layer 43b to be provided with the EPDMs 22, 22,. There is no particular limitation. However, if EPDMs 22, 22,... Are provided on the surface in contact with the MEA 44, the movement of water from the MEA 44 to the anode diffusion layer 42b and the cathode diffusion layer 43b is suppressed, so that the MEA 44 enters a so-called flooding state. Cheap. Therefore, in addition to the above-described effect that the drainage property at high temperature can be controlled while ensuring gas diffusibility, the separator 45 side surface of the anode diffusion layer 42b is also able to suppress the occurrence of flooding. It is preferable that the pore diameter variable layers 2 and 2 including EPDMs 22, 22,... Are provided on the separator 46 side surface of the cathode diffusion layer 43 b.

  In the above description regarding the fuel cell of the present invention, the anode 42 and the cathode 43 are illustrated as being provided with the gas diffusion layer (the anode diffusion layer 42b and the cathode diffusion layer 43b) of the present invention. However, the present invention is not limited thereto, and the gas diffusion layer of the present invention may be provided only on the anode or the cathode. However, when the single cell is exposed to a high temperature state, the MEA tends to dry on the anode side and the cathode side. Therefore, from the viewpoint of enabling control of drainage properties at high temperatures without deteriorating power generation performance, the anode and cathode are provided with the gas diffusion layers (anode diffusion layer 42b and cathode diffusion layer 43b) of the present invention. The fuel cell 40 is preferable.

1. Preparation of sample 1.1. Example 1
<Preparation of base material layer>
Carbon black particles (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black) and fibrous carbon (manufactured by Showa Denko KK, VGCF (“VGCF” is a registered trademark of Showa Denko KK), PTFE particles) and PTFE particles and a dispersant ( The paste was prepared by dispersing (surfactant) in water. Then, this paste was impregnated and applied to carbon paper (TGP-H-060, manufactured by Toray Industries, Inc.) to prepare a 200 μm thick base material layer. The amount of paste applied was 1 mg / cm ² .
<Preparation of surface layer>
On one surface of the base material layer produced by the above process, carbon black particles (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black), fibrous carbon (manufactured by Showa Denko KK, VGCF), PTFE particles, and a dispersant (surfactant) ) Was dispersed in water to apply a paste prepared to form a surface layer. The amount of paste applied was 4 mg / cm ² . Then, 360 degreeC heat processing was implemented, and the gas diffusion layer provided with a base material layer and a surface layer was produced.
<Preparation of pore diameter variable layer>
A paste was prepared by dispersing carbon black particles, organic polymer particles (EPDM latex) and a dispersant (surfactant) in water. Then, the surface of the base material layer opposite to the surface on which the surface layer is formed is impregnated with a paste and dried at 130 ° C., thereby providing a 50 μm thick pore diameter variable layer. A gas diffusion layer was produced. The amount of paste applied was 1.2 mg / cm ² .

1.2. Example 2
A gas diffusion layer including a base material layer and a surface layer was produced in the same procedure as in Example 1. On the other hand, a paste was prepared by dispersing carbon black particles, organic polymer particles (EPDM latex) and a dispersant (surfactant) in water. Then, the gas according to Example 2 including the pore diameter variable layer having a thickness of 100 μm by impregnating and applying the paste to the surface of the base material layer opposite to the surface layer-formed surface and drying at 130 ° C. A diffusion layer was prepared. The amount of paste applied was 2.4 mg / cm ² .

1.3. Comparative Example 1
A gas diffusion layer including a base material layer and a surface layer was produced in the same procedure as in Example 1. On the other hand, a paste was prepared by dispersing carbon black particles (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black), PTFE particles, and a dispersant (surfactant) in water. And the gas diffusion layer and porosity according to Example 1 (ratio of V1 / V2 when the total pore volume of the gas diffusion layer is V1, and the total volume including the pores is V2, the same applies hereinafter). Thus, the paste was impregnated and applied to the surface of the base material layer opposite to the surface on which the surface layer was formed, and a heat treatment at 360 ° C. was performed to prepare a diffusion layer according to Comparative Example 1. The amount of paste applied was 1.5 mg / cm ² .

1.4. Comparative Example 2
A gas diffusion layer including a base material layer and a surface layer was produced in the same procedure as in Example 1. Then, in order to align the porosity with the gas diffusion layer according to Example 2, carbon black particles (Acetylene Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) are formed on the surface of the base material layer opposite to the surface on which the surface layer is formed. A diffusion layer according to Comparative Example 2 was prepared by impregnating and applying a paste prepared by dispersing PTFE particles and a dispersant (surfactant) in water and performing heat treatment at 360 ° C. The amount of paste applied was 3.0 mg / cm ² .

2. Fabrication of fuel cell <Production of MEA>
A paste was prepared by dispersing a catalyst (platinum-supported carbon having a platinum mass ratio of 60% with respect to the total mass) and an electrolyte solution (Nafion solution, manufactured by DuPont, USA) in a mixed solvent of water, ethanol and propylene glycol, After apply | coating the said paste on a PTFE sheet | seat, the catalyst application | coating sheet | seat provided with a catalyst layer was produced by making it dry at 100 degreeC. Thereafter, by placing the catalyst coated sheet on both sides of the electrolyte membrane (Nafion, manufactured by DuPont, USA) so that the catalyst layer of the catalyst coated sheet and the electrolyte membrane are in contact with each other, and hot pressing at 130 ° C. The electrolyte membrane and the catalyst-coated sheet were joined. Thereafter, the PTFE sheet was peeled off from the catalyst-coated sheet to prepare an MEA. The area of the contact surface between the electrolyte membrane and the catalyst layer was 36 cm ² .
<Fabrication of fuel cell>
A gas diffusion layer according to Example 1 is arranged on both sides of the MEA produced by the above process to produce a laminate including the MEA and the gas diffusion layer, and a serpentine-shaped gas flow is provided on both sides of the laminate. The fuel cell concerning Example 1 was produced by arrange | positioning the separator provided with a path | route. Further, the fuel cell according to Example 2 was manufactured in the same manner as the fuel cell manufacturing procedure according to Example 1, except that the gas diffusion layer according to Example 2 was arranged instead of the gas diffusion layer according to Example 1. Produced. The fuel cell according to Comparative Example 1 was prepared in the same manner as the fuel cell manufacturing procedure according to Example 1, except that the gas diffusion layer according to Comparative Example 1 was disposed instead of the gas diffusion layer according to Example 1. A fuel cell according to Comparative Example 2 was prepared in the same manner as the fuel cell manufacturing procedure according to Example 1, except that the gas diffusion layer according to Comparative Example 2 was arranged instead of the gas diffusion layer according to Example 1. Was made.

3. Evaluation of Physical Properties of Gas Diffusion Layer The porosity of the gas diffusion layer according to Example 1, the gas diffusion layer according to Example 2, the gas diffusion layer according to Comparative Example 1, and the gas diffusion layer according to Comparative Example 2 was measured using a mercury porosimeter. (Measured by Yuasa Ionics, model number PoleMaster-60). In addition, with respect to the gas diffusion layer according to Example 1 and the gas diffusion layer according to Example 2, the pore diameter is further variable using SEM-EDX (manufactured by JEOL Ltd., model number JSM-5610LV, JED-2201). The layer thickness was measured. These results are also shown in Table 1.

4). Performance Evaluation of Fuel Cell The fuel cell according to Example 1 is kept at 80 ° C., hydrogen and air having a relative humidity of 100% are supplied to the anode side and the cathode side of the fuel cell, respectively, and the current density is 1.0 A / cm ^2. And the voltage was measured (hereinafter, the test under the conditions is referred to as “80 ° C. full humidification test”). Meanwhile, the fuel cell according to Example 1 was kept at 90 ° C., and hydrogen and air humidified so that the dew point was 60 ° C. were supplied to the anode side and the cathode side of the fuel cell, respectively, and the current density was 1.0 A / The voltage was measured while holding at cm ² (hereinafter, the test under the conditions is referred to as “90 ° C. humidification test”). The fuel cell according to Example 2, the fuel cell according to Comparative Example 1, and the fuel cell according to Comparative Example 2 were also subjected to the 80 ° C. full humidification test and the 90 ° C. humidification test. These results are also shown in Table 2.

5. Results From the results of the 80 ° C. full humidification test of the fuel cell according to Example 1 and the fuel cell according to Comparative Example 1, the fuel cell of the present invention is similar to the conventional fuel cell even if the pore diameter variable layer is provided. It was confirmed that the power generation performance can be expressed. Furthermore, from the result of the 90 ° C. humidification test of the fuel cell according to Example 1 and the fuel cell according to Comparative Example 1, according to the present invention (Example 1), compared with the conventional fuel cell (Comparative Example 1). It was confirmed that the power generation performance during operation at 90 ° C. was improved.

  On the other hand, according to the result of the 80 ° C. full humidification test of the fuel cell according to Example 2 and the fuel cell according to Comparative Example 2, the fuel cell according to the present invention has the conventional fuel cell and It was confirmed that equivalent power generation performance could be expressed. Furthermore, from the result of the 90 ° C. humidification test of the fuel cell according to Example 2 and the fuel cell according to Comparative Example 2, according to the present invention (Example 2), compared with the conventional fuel cell (Comparative Example 2). It was confirmed that the power generation performance during operation at 90 ° C. was improved.

  Further, comparing the result of the 80 ° C. full humidification test and the result of the 90 ° C. humidification test of each fuel cell, the fuel cell according to Example 1 has a voltage difference of 0.12 V, and the fuel cell according to Example 2 Then, the voltage difference was 0.07V. In contrast, in the fuel cell according to Comparative Example 1, the voltage difference was 0.20V, and in the fuel cell according to Comparative Example 2, the voltage difference was 0.12V. When the result of the fuel cell according to Example 1 and the result of the fuel cell according to Comparative Example 1 in which the values of the porosity of the gas diffusion layer are made uniform are compared, the fuel cell according to Example 1 is associated with an increase in temperature. Performance degradation was suppressed. Similarly, when the result of the fuel cell according to Example 2 is compared with the result of the fuel cell according to Comparative Example 2, the performance of the fuel cell according to Example 2 due to the temperature rise was suppressed. This is considered to be because in the fuel cell according to Example 1 and the fuel cell according to Example 2 including the variable pore size layer, the decrease in proton conduction performance was suppressed as a result of the suppression of drying of the MEA. .

  On the other hand, when the results of the 80 ° C. full humidification test and the 90 ° C. humidification test of the fuel cell according to Example 1 and the fuel cell according to Example 2 are compared, the result of the 80 ° C. full humidification test is the fuel cell according to Example 1. The fuel cell according to Example 2 was superior in the results of the 90 ° C. humidification test. This is because the fuel cell according to Example 2 contains more EPDM than the fuel cell according to Example 1, and since EPDM is an insulator, the fuel cell according to Example 1 corresponds to Example 2. It is considered that the power generation performance was better than that of the fuel cell. On the other hand, when the temperature rises to 90 ° C., the water contained in the MEA easily evaporates and the MEA becomes easy to dry. However, the fuel cell according to the second embodiment has more fuel cells than the fuel cell according to the first embodiment. Therefore, it is considered that the effect of suppressing the drying of MEA increased, and as a result, the power generation performance better than that of the fuel cell according to Example 1 was exhibited.

  As described above, according to the present invention, it is possible to provide a gas diffusion layer capable of controlling drainage at a high temperature without reducing power generation performance, and a fuel cell including the gas diffusion layer.

It is the schematic which expands and shows the example of the form of the gas diffusion layer of this invention. It is the schematic which expands and shows the example of a form of the gas diffusion layer in a 60 degreeC temperature environment. It is the schematic which expands and shows the example of a form of the gas diffusion layer in a 90 degreeC temperature environment. It is sectional drawing which shows schematically the example of a form of the fuel cell of this invention.

Explanation of symbols

1 Substrate (conductive porous substrate)
2 Pore diameter variable layer 3 Surface layer 10 Gas diffusion layer 21 Carbon fiber 22, 22x EPDM (high thermal expansion material)
23 Carbon black particles 40 Fuel cell (single cell)
41 Electrolyte membrane 42 Anode 42a Anode catalyst layer 42b Anode diffusion layer (first gas diffusion layer)
43 Cathode 43a Cathode catalyst layer 43b Cathode diffusion layer (second gas diffusion layer)
44 MEA (membrane electrode structure)
45 Separator (first current collector)
46 Separator (second collector)
47, 48 Gas flow path

Claims (5)

A gas diffusion layer comprising a conductive porous substrate, and a high thermal expansion material having a higher coefficient of thermal expansion than the conductive porous substrate is provided in a part of the conductive porous substrate. . The gas diffusion layer according to claim 1, wherein the conductive porous substrate is provided with a carbon material, and the high thermal expansion material is an organic polymer material. The gas diffusion layer according to claim 2, wherein the organic polymer material is ethylene-propylene-diene rubber. A membrane electrode structure comprising an electrolyte membrane, an anode catalyst layer provided on one side of the electrolyte membrane, and a cathode catalyst layer provided on the other side of the electrolyte membrane, and one side of the membrane electrode structure A first current collector provided in the second current collector, a second current collector provided on the other side of the membrane electrode structure, and the first current collector and the membrane electrode structure. A first gas diffusion layer, and / or a second gas diffusion layer disposed between the second current collector and the membrane electrode structure,
The fuel cell according to claim 1, wherein the first gas diffusion layer and / or the second gas diffusion layer is the gas diffusion layer according to claim 1. 5. The high thermal expansion material is provided on the first current collector side of the first gas diffusion layer and / or the second current collector side of the second gas diffusion layer, according to claim 4. The fuel cell as described.

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