JP2007250411A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell in which its water content is controlled and its power generation efficiency is improved, and total efficiency of a fuel cell system is thereby improved. <P>SOLUTION: The fuel cell is provided with: a base material layer 18, 26 having a porosity and conductivity, and also having different water repelling properties depending on its positions; fine hole layers 16, 24 which contain a first member having a porosity and conductivity and a conductive second member made of particles, and have a higher density than the base material layer and catalyst layers 14, 22 containing a catalyst having a catalyst action. In another case, the fuel cell is provided with first diffusion layers 18, 26, second diffusion layers to control a capillary attraction, and catalyst layers 14, 22 containing a catalyst having a catalyst function. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more specifically to a fuel cell capable of controlling the amount of water in the fuel cell.

  Although it has become an era when new technologies such as IT and biotechnology are deployed on a global scale, the energy industry is still one of the largest core industries. Recently, expectations for so-called new energy are increasing with the spread of environmental awareness including prevention of global warming. In addition to environmental properties, new energy can be produced in a distributed manner in close proximity to power consumers, so there are advantages in terms of transmission loss and power supply security. In addition, the development of new energy can be expected to have a secondary effect of creating new peripheral industries. New energy initiatives began in earnest with the oil crisis about 30 years ago, and now, renewable energy such as solar power generation, recycling energy such as waste power generation, high-efficiency energy such as fuel cells, and clean energy Energy such as new field energy represented by cars is in the stage of development for practical application.

  Among them, fuel cells are one of the most noticeable energies in the industry. A fuel cell is a device that generates electricity and heat simultaneously by chemically reacting hydrogen produced by reacting water vapor with natural gas, methanol, etc., and oxygen in the air. It is highly efficient in the area, and power generation is stable without being affected by the weather. In particular, the polymer electrolyte fuel cell is regarded as one of the next generation standard power supplies in applications such as stationary, in-vehicle use, and portable use.

In Patent Document 1, in this polymer electrolyte fuel cell, the amount of water produced by the electrode reaction is different between the reaction gas inlet side portion and the outlet side portion in the electrode, and is thus applied to the substrate depending on the portion. Changing the amount of water repellent is disclosed. Further, Patent Document 2 discloses that a passage through which a gas flows and a passage through which a liquid flows are provided in the electrode by filling the substrate with carbon black or a water repellent.
JP-A-9-283153 Japanese Patent No. 3583897

  When the carbon black is filled with the water repellency gradient of the base material as in Patent Document 1 as in Patent Document 2, the filling amount of the carbon black is affected by the water repellency of the base material, It was difficult to fill uniformly. In addition, depending on the case, the filling amount of the carbon black may vary depending on the part on the inlet side and the part on the outlet side of the reaction gas, and an electrode (diffusion layer) having the required water repellency and porosity in each part will be prepared. However, since the filling amount of carbon black is affected by water repellency, it is difficult to produce an electrode having water repellency and porosity necessary for each part.

  The present invention has been made in view of the above problems, and controls the amount of water in a fuel cell (in-plane) by using an electrode having a required water repellency and / or porosity depending on a portion in the electrode. An object of the present invention is to provide a fuel cell that can improve the power generation efficiency of the fuel cell, and thus the overall efficiency of the fuel cell system.

  The present invention provides an electrode for a fuel cell for achieving the above object, wherein the substrate layer is porous and conductive, and has a water repellency that varies depending on the part, and is porous and conductive. It comprises a member and a particulate second conductive member, and comprises a microporous layer having a density higher than that of the base material layer, and a catalyst layer containing a catalyst having a catalytic action. The electrode for a fuel cell of the present invention includes a first diffusion layer for controlling water repellency, a second diffusion layer for controlling capillary action, a catalyst layer containing a catalyst having a catalytic action, It is characterized by providing. As a result, an appropriate amount of water can be held or discharged (controlled) in the plane of the electrode, so that the fuel cell using the fuel cell electrode of the present invention has an appropriate amount of water controlled from the anode. Protons move smoothly to the cathode, improving the power generation efficiency of the fuel cell.

  An invention according to claim 3 is a fuel cell comprising: an electrolyte layer; a first electrode provided on one surface of the electrolyte layer; and a second electrode provided on the other surface of the electrolyte layer. The first electrode is a fuel cell electrode according to claim 1 or 2. As a result, the amount of water is appropriately controlled over the entire surface of the fuel cell, protons are smoothly transferred from the anode to the cathode, and the power generation efficiency of the fuel cell is improved.

  Invention of Claim 4 is a fuel cell system, Comprising: The fuel cell of Claim 3, The hydrogen supply means which supplies hydrogen to the said fuel cell, The oxygen supply means which supplies oxygen to the said fuel cell, It is characterized by providing. In the best mode for carrying out the invention of the present specification, the hydrogen supply means will be described using a reformer that reforms LPG, city gas, etc., but is not limited to this, and protons ( Any means may be used as long as it supplies a hydrogen molecule or an organic substance containing a hydrogen atom as a source of (H +). The oxygen supply means is generally a system using air, but may be a supply means using an oxygen cylinder or the like for space use or deep sea use. In either case, water is generated by power generation, but the water content of the fuel cell is appropriately controlled by the present invention, so that the power generation efficiency of the fuel cell is improved, and the overall efficiency of the fuel cell system is also improved. .

  According to the present invention, the power generation efficiency of the fuel cell can be improved.

  Hereinafter, the fuel cell 10 of the present invention will be described in detail with reference to the drawings. FIG. 1 is a system configuration diagram of a household fuel cell cogeneration system 100 using a fuel cell 10 according to the present invention. The home fuel cell cogeneration system 100 reforms raw fuel (hydrocarbon fuel) such as LPG and city gas, and generates a reformed gas containing about 80% hydrogen (fuel); The fuel cell 10 that generates power by the reformed gas supplied from the reformer and oxygen (oxidant) in the air, and the heat generated from the reformer and the fuel cell 10 are converted into hot water (water at 40 ° C. or higher). ) And a hot water storage device that recovers and stores hot water in the form of a system that has both a power generation function and a hot water supply function.

  Raw fuels such as LPG and city gas installed in homes are usually odorized by sulfides as a safety measure against gas leakage, but this sulfide degrades the catalyst in the reformer. In the reformer, first, sulfide in the raw fuel is removed by the desulfurizer 52. The raw fuel desulfurized by the desulfurizer 52 is then mixed with steam, steam reformed by the reformer 54, and introduced into the transformer 56. The reformer 56 produces reformed gas of about 80% hydrogen, about 20% carbon dioxide, and 1% or less carbon monoxide, but is operated at a low temperature (100 ° C. or less) that is easily affected by carbon monoxide. In the present system 100 for supplying the reformed gas to the fuel cell 10 to be processed, the reformed gas and oxygen are further mixed, and the carbon monoxide is selectively oxidized by the CO remover 58. The carbon monoxide concentration in the reformed gas can be reduced to 10 ppm or less by the CO remover 58.

  The reformer includes at least a reformer 54 and a transformer 56. When the gas laid at home is used as a raw fuel as in the system 100, the desulfurizer 52 is used as the fuel cell 10. In the case of using a low temperature type fuel cell 10 such as a solid polymer fuel cell, a CO remover 58 is further included.

  Since steam reforming is an endothermic reaction, the reformer 54 is provided with a burner 60. When starting the reformer, the raw fuel is also supplied to the burner 60 to raise the temperature of the reformer 54. When the system 100 can be stably operated, the supply of the raw fuel to the burner 60 is stopped. Then, by supplying unreacted fuel discharged from the fuel cell 10 to the burner 60, heat is supplied to the reformer 54. Since the exhaust after supplying heat to the reformer 54 by the burner 60 still has a large amount of heat, this exhaust is heat-exchanged with the water in the hot water storage tank 62 by the heat exchangers HEX01 and HEX02. Then, the water exchanges heat (HEX03) with the exhaust gas from the cathode 14 of the fuel cell 10 and further exchanges heat (HEX04) with the exhaust gas from the anode 22 and returns to the hot water storage tank 62. The water pipe 64 passing through the heat exchangers HEX01, HEX02, HEX03, and HEX04 can be used for raising or cooling the cathode-side humidification tank 66 depending on the temperature of water (hot water) after passing through the heat exchanger HEX04. Further, a branch pipe 68 is provided. When the temperature of the cathode-side humidification tank 66 is low, such as when the present system 100 is activated, water passes through the heat exchanger HEX04 and then passes through the branch pipe 68 to heat the cathode-side humidification tank 66 with the heat exchanger HEX05. After supplying, the hot water storage tank 62 is returned.

  The cathode side humidification tank 66 also functions as a cooling water tank, and the water in the cathode side humidification tank 66 cools the fuel cell 10 and returns to the cathode side humidification tank 66. As described above, when the temperature of the fuel cell 10 is low, such as when the system 100 is started up, the fuel cell 10 can be warmed by supplying the coolant heated by the heat exchanger HEX05 to the fuel cell 10. . The cooling water passage 70 through which the cooling water passes is connected to a heat exchanger HEX06 provided in the anode-side humidification tank 72, and the cooling water serves to make the temperatures of the cathode-side humidification tank 66 and the anode-side humidification tank 72 substantially the same. Also plays.

  The reformed gas from the reformer is humidified (bubbling in the case of the present system 100) in the anode-side humidification tank 72 and supplied to the anode 22. Unreacted fuel that has not contributed to power generation at the anode 22 is discharged from the fuel cell 10 and supplied to the burner 60. The fuel cell 10 is normally operated to generate power in the range of 70 to 80 ° C., and the exhaust gas discharged from the fuel cell 10 has a heat of about 80 ° C. Therefore, as described above, the heat exchanger HEX04 After the heat exchange at, the temperature of the water supplied to the cathode-side humidification tank 66 and the anode-side humidification tank 72 is further raised by the heat exchanger HEX07 and then supplied to the burner 60.

  The water supplied to the cathode-side humidification tank 66 and the anode-side humidification tank 72 is preferably clean water having low electrical conductivity and low contamination with organic substances. Supplied after water treatment with membrane and ion exchange resin. The water subjected to this water treatment is also used for steam reforming of the reformer 54. The clean water is also supplied to the hot water storage tank 62. At this time, the clean water is supplied from the lower part of the hot water storage tank 62. The water pipe 64 also draws water having a low temperature from the lower part of the hot water storage tank 62 and returns the water exchanged with each heat exchanger to the upper part.

  HEX10 is a total heat exchanger. Since the exhaust gas containing unreacted oxygen that has not contributed to power generation at the cathode 14 contains heat of about 80 ° C. and produced water generated by the reaction, it is supplied to the cathode 14 by the total heat exchanger HEX10. Supply heat and moisture to the air. The air supplied to the cathode 14 is further humidified (bubbling in the case of the present system 100) in the cathode-side humidification tank 66 and then supplied to the cathode 14, while heat and moisture are supplied to the total heat exchanger HEX10. The supplied exhaust gas is further subjected to heat exchange with water in the heat exchanger HEX03 and then discharged to the outside of the system 100.

  FIG. 2 is a schematic configuration diagram showing the configuration of the fuel cell 10 according to the present invention. In the fuel cell 10 of the present invention, the diffusion layers 20 and 28 are made of carbon black on base layers (first diffusion layers) 18 and 26 made of carbon paper having a thickness of about 110 μm and roll carbon having a thickness of about 100 μm. It is composed of microporous layers (second diffusion layers) 16 and 24 coated with a carbon paste having a main viscosity. Carbon paper is a flat, relatively hard porous (nonwoven fabric) conductive member, and roll carbon is a porous conductive member similar to carbon paper, but there are woven and non-woven fabric types, It is a member that is more flexible than carbon paper and is commercially available in a rolled state. Carbon black is generally made of fine particles of amorphous carbon (amorphous carbon).

  As shown in FIG. 2, in consideration of productivity, the diffusion layers 20 and 28 use a common carbon paper and roll carbon, respectively, and a water repellent dispersion in which carbon paper is immersed or a carbon paste applied to roll carbon. By adjusting the blending, water repellency and porosity required for each part are adjusted. Specifically, the cathode side is adjusted to have a lower water repellency than the anode side, and when a highly humidified reaction gas of 85% RH or more is supplied to the fuel cell 10, the reaction gas inlet side is The water repellency is higher than the reaction gas outlet side. Conversely, when the low humidified reaction gas is supplied to the fuel cell 10 or in the case of an internal humidified fuel cell, the water repellency is lower on the reaction gas inlet side than on the reaction gas outlet side. To be adjusted.

  However, when the water repellency treatment is performed so that the water repellency is different between the reaction gas inlet side and the reaction gas outlet side, the carbon paste to be applied thereafter may be applied uniformly or not depending on the water repellency. It becomes difficult. Therefore, by producing the diffusion layers 20 and 28 as follows, the diffusion layers 20 and 28 having the water repellency and porosity (density) necessary for each part are provided.

  The cathode-side carbon paper is immersed in an FEP dispersion liquid having a weight ratio of carbon paper: tetrafluoroethylene-hexafluoropropylene copolymer (FEP) = 95: 5. On the other hand, the anode-side carbon paper is immersed in an FEP dispersion liquid having a weight ratio of carbon paper: FEP = 60: 40, and both carbon papers are dried at 60 ° C. for 1 hour. Next, half of the cathode-side carbon paper in the longitudinal direction is immersed in an FEP dispersion liquid having a weight ratio of carbon paper: FEP = 60: 40, and half of the anode-side carbon paper in the longitudinal direction is carbon paper: Immerse in an FEP dispersion such that the weight ratio of FEP = 30: 70. In the present embodiment, the one that is dipped twice in the FEP dispersion and has high water repellency is disposed on the reaction gas inlet side. After the second immersion, the film is dried at 60 ° C. for 1 hour, and then heat-treated at 380 ° C. for 15 minutes. As a result, the cathode-side base material layer 18 and the anode-side base material layer 26 that are inclined in water repellency can be produced. In this embodiment, the reaction gas that is easy to dry because the amount of generated water is small. Since the site | part with high water repellency of the base material layers 18 and 26 is arrange | positioned at the entrance side, produced | generated water is confined by the solid polymer film 12 side, and the moisture content of this part can be hold | maintained.

  Next, carbon black (manufactured by CABOT: Vulcan XC72R), terpineol (manufactured by Kishida Chemical Co., Ltd.) as a solvent and triton (manufactured by Kishida Chemical Co., Ltd.) as a solvent, and a weight ratio of carbon black: terpineol: triton = 20: 150: 3 In a universal mixer (manufactured by DALTON), the mixture is mixed uniformly at room temperature for 60 minutes to prepare a carbon paste. The weight ratio of the low molecular fluorine resin (made by Daikin: Lubron LDW40E) and the high molecular fluorine resin (made by DuPont: PTFE30J) to the fluorine resin contained in the dispersion is low molecular fluorine resin: high molecular fluorine resin = 20. : Mix to make 3 to produce a mixed fluororesin for cathode. The carbon paste is put into a hybrid mixer container and cooled until the carbon paste reaches 10 to 12 ° C. The above-mentioned mixed fluororesin for cathode is added to the cooled carbon paste so that the weight ratio is carbon paste: mixed fluororesin for cathode (fluorine resin component contained in the dispersion) = 65: 2, and a hybrid mixer (KEYENCE) Mix for 12 to 18 minutes in EC500) mixing mode. The mixing stop timing is set until the paste temperature reaches 50 to 55 ° C., and the mixing time is adjusted appropriately. After the paste temperature reaches 50 to 55 ° C., the hybrid mixer is switched from the mixing mode to the defoaming mode and defoamed for 1 to 3 minutes. The paste after defoaming is naturally cooled to complete the cathode diffusion layer paste.

  The carbon mixer and the low molecular fluororesin are mixed in a hybrid mixer container with a weight ratio of carbon paste: low molecular fluororesin (hereinafter referred to as anode fluororesin) (a fluororesin component contained in the dispersion) = 13. : 1 and mix for 15 minutes in the mixing mode of the hybrid mixer. After mixing, the hybrid mixer is switched from the mixing mode to the defoaming mode and defoamed for 4 minutes. When the supernatant liquid accumulates on the upper part of the paste after defoaming, the supernatant liquid is discarded and the paste is naturally cooled to complete the anode diffusion layer paste.

  The cathode-side roll carbon is cut in advance so as to have the same dimensions as the cathode-side base layer 18 and the anode-side roll carbon has the same dimensions as the anode-side base layer 26. As shown in FIG. 2, the solid polymer film 12 is arranged so that the edges do not overlap over the entire circumference so that the solid polymer film 12 does not break due to concentrated stress from the edge of the electrode, and the solid due to the lack of protons on the cathode side. In order to prevent the polymer film 12 from deteriorating, the cathode side and the anode side are designed so that the anode side becomes larger over the entire circumference. The cathode side diffusion layer paste cooled to room temperature is applied to the surface of the cathode side roll carbon, and similarly, the anode side diffusion layer paste is applied to the surface of the anode side roll carbon, and dried at 60 ° C. for 1 hour. This operation is repeated once more, and both roll carbons are sufficiently filled with the diffusion layer paste. Finally, by performing heat treatment at 360 ° C. for 2 hours, the cathode-side microporous layer 16 and the anode-side microporous layer 24 in which carbon black is sufficiently filled in the voids of the roll carbon fibers can be produced. As a result, since the microporous layers 16 and 24 are filled with carbon black in the gaps, the density is higher than that of the base material layers 18 and 26, and fine pores are present, and the capillary phenomenon is more likely to occur. Become. Therefore, the water generated by the power generation reaction or the water introduced into the fuel cell 10 from the humidification tanks 66 and 72 and condensed is moved to a lower water vapor partial pressure by the capillary action of the microporous layers 16 and 24. It becomes easy.

  Pt-supported carbon and an electrolyte solution (20% Nafion (registered trademark) solution) are mixed at a ratio of Pt-supported carbon: electrolyte solution = 3: 8 to prepare a cathode side catalyst paste. On the other hand, the anode side catalyst paste is prepared by mixing Pt—Ru supported carbon and an electrolyte solution (20% Nafion (registered trademark) solution) in a ratio of Pt—Ru supported carbon: electrolyte solution = 1: 2. Each catalyst paste is applied to the surface of the microporous layers 16 and 24 on the side where the diffusion layer paste is applied, thereby producing catalyst layers 14 and 22. The fuel cell 10 has a cathode-side catalyst layer 14 and a cathode-side microporous layer 16 disposed so that the cathode-side catalyst layer 14 is in contact with one surface of a solid polymer membrane (Nafion 112 manufactured by DuPont). The anode-side catalyst layer 22 and the anode-side microporous layer 24 are arranged so that the anode-side catalyst layer 22 is in contact with this surface. On the other hand, the cathode side substrate layer 18 is disposed outside the cathode side microporous layer 16, and the anode side substrate layer 26 is disposed outside the anode side microporous layer 24 while paying attention to the inlet / outlet of the reaction gas. Hot pressing is performed while sandwiched between the base material layers 18 and 26.

  In a conventional fuel cell, a method of directly applying a diffusion layer paste mainly composed of carbon black to carbon paper subjected to water repellent treatment has been adopted. However, in such a configuration, when the water repellency of the carbon paper varies depending on the site, as in the fuel cell 10 of the present invention, the diffusion layer paste is formed depending on the binding property of the water repellent, depending on the water repellent used. Many of them were applied, or the diffusion layer paste was not so much applied due to water repellency. In the present invention, since the diffusion layer paste is applied to the roll carbon that has not been subjected to the water repellent treatment, the diffusion layer paste can be applied uniformly, and the diffusion layer paste can be adjusted by adjusting the number of times of application and the site. The coating amount can be adjusted without being affected by the water repellency of the base material layers 18 and 26. Further, in the conventional fuel cell configuration, the coating depth of the diffusion layer paste could be controlled to some extent by the strength of the coating device. However, according to the configuration of the present invention, the diffusion layer paste sufficiently filled with the diffusion layer paste can be controlled. By laminating the pore layers 16 and 24 on the base material layers 18 and 26, the application depth of the diffusion layer paste can be made uniform.

  In the present embodiment, the description has been given using the domestic fuel cell cogeneration system in which the raw fuel is reformed by the reformer and supplied to the fuel cell. However, the present invention is not limited to this, and pure hydrogen is used for the fuel cell. It can also be used in an in-vehicle fuel cell system that supplies fuel to a direct methanol fuel cell system for portable equipment that supplies organic fuel directly to the fuel cell without reforming.

1 is a system configuration diagram of a household fuel cell cogeneration system using a fuel cell according to the present invention. 1 is a schematic configuration diagram showing the configuration of a fuel cell according to the present invention.

Explanation of symbols

10 Fuel cell 12 Solid polymer membrane (electrolyte layer)
14 Cathode side catalyst layer 16 Cathode side microporous layer (second diffusion layer)
18 Cathode side base material layer (first diffusion layer)
20 Cathode side diffusion layer 22 Anode side catalyst layer 24 Anode side microporous layer (second diffusion layer)
26 Anode-side base material layer (first diffusion layer)
28 Anode side diffusion layer 52 Desulfurizer 54 Reformer 56 Transformer 58 CO remover 60 Burner 62 Hot water storage tank 64 Water piping 66 Cathode side humidification tank 68 Branch piping 70 Cooling water passage 72 Anode side humidification tank 74 Water treatment device 76 Cooling Water flow path 78 Hot water supply pipe 100 Household fuel cell cogeneration system HEX01, HEX02, HEX03, HEX04, HEX05 Heat exchanger

Claims (4)

A base material layer that is porous and conductive and has different water repellency depending on the site;
A microporous layer having a higher density than the base material layer, comprising a porous and conductive first member and a particulate conductive second member;
A catalyst layer containing a catalyst having a catalytic action;
An electrode for a fuel cell comprising: A first diffusion layer for controlling water repellency;
A second diffusion layer for controlling capillary action;
A catalyst layer containing a catalyst having a catalytic action;
An electrode for a fuel cell comprising: In a fuel cell comprising an electrolyte layer, a first electrode provided on one surface of the electrolyte layer, and a second electrode provided on the other surface of the electrolyte layer,
The fuel cell according to claim 1, wherein the first electrode is a fuel cell electrode according to claim 1. A fuel cell according to claim 3;
Hydrogen supply means for supplying hydrogen to the fuel cell;
Oxygen supply means for supplying oxygen to the fuel cell;
A fuel cell system comprising:

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