JP2011113882A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of stably obtaining a high power by decreasing a temperature difference. <P>SOLUTION: The fuel cell includes a membrane electrode assembly 2 having an electrolyte membrane 17, an anode 13 arranged on one surface of the electrolyte membrane 17, and a cathode 16 arranged on the other surface of the electrolyte membrane 17; a fuel supply mechanism 3 arranged on the anode side of the membrane electrode assembly 2 and supplying fuel to the anode; and a heat conductor 40 arranged between the fuel supply mechanism 3 and the anode 13 and coming in contact with the fuel supply mechanism 3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technology of a fuel cell using a liquid fuel.

  In recent years, attempts have been made to use a fuel cell as a power source for portable electronic devices such as notebook computers and mobile phones so that they can be used for a long time without being charged. A fuel cell is characterized in that it can generate electric power simply by supplying fuel and air, and can generate electric power continuously for a long time if fuel is replenished. For this reason, if the fuel cell can be reduced in size, it can be said that the system is extremely advantageous as a power source for portable electronic devices.

  In a fuel cell that operates at a high temperature, a technique is disclosed in which the outer surface of a heat insulator that covers the fuel cell is covered with a heat transfer body in order to prevent the casing of a device that houses the fuel cell from becoming high temperature ( For example, see Patent Document 1).

  On the other hand, a thermally conductive molded article having high thermal conductivity suitable for uses such as a fuel cell separator has been disclosed (for example, see Patent Document 2). In particular, according to this thermally conductive molded body, it is disclosed that it is useful in a heat dissipation design of a housing when it is used as a housing or member for an electric / electronic device due to anisotropy of thermal conductivity. Yes.

  In a fuel cell formed by laminating a plurality of unit cells to form a laminate, a gas separation plate and a unit cell whose thermal conductivity in the planar direction is larger than the thermal conductivity in the laminating direction for the purpose of uniform temperature distribution Are alternately stacked, and a cooling plate is disposed on the upper and lower ends (for example, see Patent Document 3).

JP 2006-202611 A JP 2006-49878 A JP-A-9-289026

  As a fuel cell, for example, a direct methanol fuel cell (DMFC) using methanol as a fuel can be miniaturized and can be easily handled as a power source for portable electronic devices. Promising.

  As the liquid fuel supply method in the DMFC, there are known an active method such as a gas supply type and a liquid supply type, and a passive method such as an internal vaporization type in which the liquid fuel in the fuel container is vaporized inside the cell and supplied to the fuel electrode. It has been. Among these, passive methods such as an internal vaporization type are advantageous for downsizing the DMFC. The passive DMFC includes a membrane electrode assembly (MEA) having a fuel electrode, an electrolyte membrane, and an air electrode, for example.

  An unintended temperature variation may occur in the surface of such a membrane electrode assembly. In particular, heat dissipation is relatively promoted in the peripheral part of the membrane electrode assembly, whereas heat is difficult to escape in the central part, and a large temperature difference tends to occur between the peripheral part and the central part.

  In addition, due to such a temperature difference, a difference occurs in the vapor pressure of the vaporized component of the fuel generated by the vaporization of the liquid fuel, and the transfer of the fuel necessary for the power generation reaction in the membrane electrode assembly is hindered. There is a risk of lowering output or destabilization. Such unstable supply of vaporized components does not occur much when the temperature of the entire fuel cell is high and the vapor pressure of the vaporized fuel is kept high throughout. However, in a fuel cell used as a power source for portable electronic devices and the like, it is necessary to suppress the temperature of the entire fuel cell from the viewpoint of safety and the like. In this case, the vapor pressure of the vaporized component is low overall. A difference in vapor pressure due to a slight temperature difference greatly affects the output stability.

  An object of the present invention is to provide a fuel cell capable of stably obtaining a high output.

According to one aspect of the invention,
A membrane electrode assembly comprising: an electrolyte membrane; an anode disposed on one surface of the electrolyte membrane; and a cathode disposed on the other surface of the electrolyte membrane;
A fuel supply mechanism disposed on the anode side of the membrane electrode assembly and supplying fuel toward the anode;
A heat conductor disposed between the fuel supply mechanism and the anode and in contact with the fuel supply mechanism;
A fuel cell comprising: is provided.

According to another aspect of the invention,
A membrane electrode assembly comprising: an electrolyte membrane; an anode disposed on one surface of the electrolyte membrane; and a cathode disposed on the other surface of the electrolyte membrane;
A fuel supply mechanism disposed on the anode side of the membrane electrode assembly and supplying fuel toward the anode;
A gas-liquid separation membrane disposed between the fuel supply mechanism and the anode;
A heat conductor disposed between the fuel supply mechanism and the gas-liquid separation membrane and spaced from the gas-liquid separation membrane;
A fuel cell comprising: is provided.

  According to the present invention, a fuel cell capable of stably obtaining a high output can be provided.

FIG. 1 is a plan view showing the appearance of the cathode side of a fuel cell according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a structure in which the fuel cell shown in FIG. 1 is cut along the first direction. FIG. 3 is a top view of the fuel distribution plate in the fuel supply mechanism of the fuel cell shown in FIG. 2 as viewed from the top where the membrane electrode assemblies overlap. FIG. 4 is a perspective view schematically showing a structure of a heat conductor applicable to the fuel cell shown in FIG. FIG. 5 is a cross-sectional view schematically showing a structure in which a fuel cell according to another embodiment is cut along a first direction. FIG. 6 is a cross-sectional view schematically showing a structure in which a fuel cell according to another embodiment is cut along a first direction. FIG. 7 is a cross-sectional view schematically showing a structure in which a fuel cell according to another embodiment is cut along a first direction. FIG. 8 is a cross-sectional view schematically showing a structure in which a fuel cell according to another embodiment is cut along a first direction. FIG. 9 is a cross-sectional view schematically showing a structure in which a fuel cell according to another embodiment is cut along a first direction. FIG. 10 is a cross-sectional view schematically showing a structure in which a fuel cell according to another embodiment is cut along a first direction. FIG. 11 is a diagram illustrating a measurement result of the output density when the performance evaluation is performed.

  A fuel cell according to an embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is a plan view showing the appearance of the cathode side of a fuel cell (DMFC) 1 according to this embodiment.

  The fuel cell 1 is formed in a substantially rectangular flat plate shape. In the plan view shown in FIG. 1, the fuel cell 1 has a rectangular shape, a pair of long side L1 and long side L2 extending along the first direction X, and a second direction Y orthogonal to the first direction X. And a pair of short sides S1 and S2 extending along the line.

  The fuel cell 1 includes a membrane electrode assembly (MEA) 2 constituting an electromotive unit. The membrane electrode assembly 2 is formed in a substantially rectangular shape. The detailed structure of the membrane electrode assembly 2 will be described later, but here, a plurality of, for example, four single cells CL1 to CL4 are provided. Each of the single cells CL1 to CL4 has a substantially rectangular shape extending along the first direction X on the same plane, and is arranged side by side in the second direction Y.

  A cover plate 21 is disposed on the surface of the fuel cell 1 located on the cathode side of the membrane electrode assembly 2. The cover plate 21 has a substantially rectangular appearance, and is made of, for example, stainless steel (SUS). The cover plate 21 is formed with a plurality of openings 21 </ b> H that can mainly take in air as an oxidant, particularly oxygen.

  A fuel supply mechanism (not shown) that supplies fuel to the membrane electrode assembly 2 is disposed on the anode side of the membrane electrode assembly 2. The cover plate 21 is fastened to the fuel supply mechanism at each of the long sides L1 and L2 and the short sides S1 and S2 of the fuel cell 1 with the membrane electrode assembly 2 held between the cover plate 21 and the fuel supply mechanism. Yes.

  FIG. 2 is a view schematically showing a cross section of the fuel cell 1 shown in FIG. 1 cut along the first direction X. As shown in FIG.

  The fuel cell 1 includes a membrane electrode assembly 2. The membrane electrode assembly 2 includes an anode (fuel electrode) 13, a cathode (air electrode or oxidant electrode) 16, a proton (hydrogen ion) conductive electrolyte membrane 17 sandwiched between the anode 13 and the cathode 16, It is configured with. The anode 13 includes an anode catalyst layer 11 and an anode gas diffusion layer 12 laminated on the anode catalyst layer 11. The anode catalyst layer 11 is laminated on one surface 17A of the electrolyte membrane 17. The cathode 16 has a cathode catalyst layer 14 and a cathode gas diffusion layer 15 laminated on the cathode catalyst layer 14. The cathode catalyst layer 14 is laminated on the other surface 17C of the electrolyte membrane 17.

  Each of the single cells CL1 to CL4 shown in FIG. 1 includes an anode 13 and a cathode 16 that face each other with the electrolyte membrane 17 interposed therebetween. That is, in the membrane electrode assembly 2 including the four single cells CL1 to CL4 shown in FIG. 1, the four anodes 13 not described in detail are arranged in the second direction Y on the one surface 17A of the single electrolyte membrane 17. The four cathodes 16 are arranged on the other surface 17C of the electrolyte membrane 17 at intervals in the second direction Y.

  Such a membrane electrode assembly 2 is sandwiched between current collectors 18 in the present embodiment. The current collector 18 is disposed on the same surface where the base insulating layer BF, the anode current collector 18A disposed on the base insulating layer BF, and the anode current collector 18A of the base insulating layer BF are disposed. It has a cathode current collector 18C.

  The anode current collector 18A and the cathode current collector 18C are made of, for example, a porous layer (for example, a mesh) or a foil body made of a metal material such as gold, copper, or nickel, or a conductive metal material such as stainless steel (SUS). It can be formed by using a composite material coated with a highly conductive metal such as gold, or may be formed by using a carbonaceous material such as graphite (graphite).

  In the example shown in FIG. 2, the anode current collector 18 </ b> A is stacked on the anode gas diffusion layer 12. The anode current collector 18A is formed with an opening 18AH that enables supply of fuel necessary for power generation reaction toward the anode 13. The cathode current collector 18C is stacked on the cathode gas diffusion layer 15. The cathode current collector 18C can supply oxygen necessary for the power generation reaction toward the cathode 16, and can discharge carbon dioxide, excess water vapor, and other gases generated during the power generation reaction to the outside. A possible opening 18CH is formed. The current collector 18 having such a configuration electrically connects a plurality of single cells CL1 to CL4 provided in the membrane electrode assembly 2 as shown in FIG.

  The current collector 18 has a structure in which the current collector 18 is folded in half and the membrane electrode assembly 2 is sandwiched as in the present embodiment, but is not limited to this structure. For example, individual current collectors in which the anode current collector 18A and the cathode current collector 18C are individually provided are prepared, and the membrane electrode assembly 2 is sandwiched between the individual current collectors. The plurality of single cells CL1 to CL4 provided in the membrane electrode assembly 2 as shown in FIG. 1 may be electrically connected in series with each other by using a conductive connecting member.

  The membrane electrode assembly 2 includes rubber O-rings sandwiched between one surface 17A of the electrolyte membrane 17 and the current collector 18 and between the other surface 17C of the electrolyte membrane 17 and the current collector 18. It is sealed by a sealing member 19 such as. Thereby, fuel leakage and oxidant leakage from the membrane electrode assembly 2 are prevented. In the membrane electrode assembly 2, one or more electrolyte membranes 17 are not in contact with the anode catalyst layer 11 and the cathode catalyst layer 14 and at positions corresponding to the inside surrounded by the seal member 19. Individual gas discharge holes (not shown) may be provided.

  On the cathode 16 side of the membrane electrode assembly 2, a plate-like body 20 made of a breathable insulating material is disposed between the current collector 18 and the cover plate 21. This plate-like body 20 mainly functions as a moisture retaining layer. That is, the plate-like body 20 is impregnated with a part of the water generated in the cathode catalyst layer 14 to suppress water evaporation and to the cathode catalyst layer 14 of air taken in from the opening 21H of the cover plate 21. The amount of air taken in is adjusted and the uniform diffusion of air is promoted. Such a plate-like body 20 is comprised by the flat plate which consists of a polyethylene-made porous film etc., for example.

  A fuel supply mechanism 3 is disposed on the anode 13 side of the membrane electrode assembly 2. That is, the membrane electrode assembly 2 is disposed between the fuel supply mechanism 3 disposed on the anode 13 side and the cover plate 21 disposed on the cathode 16 side. The fuel supply mechanism 3 is configured to supply fuel to the anode 13 of the membrane electrode assembly 2, but is not particularly limited to a specific configuration. Such a fuel supply mechanism 3 is connected to a fuel storage portion 4 that stores the liquid fuel F via a flow path 5.

  The flow path 5 is comprised by piping etc. The flow path 5 is not limited to piping independent of the fuel supply mechanism 3 and the fuel storage unit 4. For example, when the fuel supply mechanism 3 and the fuel storage unit 4 are laminated and integrated, a flow path of the liquid fuel F that connects them may be used. That is, the fuel supply mechanism 3 only needs to communicate with the fuel storage unit 4 through a flow path or the like.

  The liquid fuel F accommodated in the fuel accommodating portion 4 can be dropped and sent to the fuel supply mechanism 3 through the flow path 5 using gravity. Alternatively, the flow path 5 may be filled with a porous body or the like, and the liquid fuel F stored in the fuel storage unit 4 may be fed to the fuel supply mechanism 3 by capillary action. Further, the liquid fuel F stored in the fuel storage unit 4 may be forcibly sent to the fuel supply mechanism 3 by interposing a pump 6 in a part of the flow path 5.

  The applied pump 6 is not a circulation pump that circulates fuel, but is a fuel supply pump that sends liquid fuel F from the fuel storage unit 4 toward the fuel supply mechanism 3 to the last. The fuel supplied from the fuel supply mechanism 3 to the membrane electrode assembly 2 is used for the power generation reaction, and is not circulated thereafter and returned to the fuel storage unit 4. The type of the pump 6 is not particularly limited, but a pump that can feed a small amount of liquid fuel F with good controllability and can be reduced in size and weight is preferable.

  The fuel cell 1 of this embodiment is different from the conventional active method because it does not circulate the fuel, and does not impair the downsizing of the device. Further, the pump 6 is used to supply the liquid fuel, which is different from a pure passive system such as a conventional internal vaporization type. The fuel cell 1 shown in FIG. 2 employs a system called a semi-passive type, for example.

  In the fuel supply mechanism 3, a fuel cutoff valve may be disposed in series with the pump 6. Further, a balance valve that balances the pressure in the fuel storage unit 4 with the outside air may be attached to the fuel storage unit 4 and the flow path 5.

  Liquid fuel F corresponding to the membrane electrode assembly 2 is stored in the fuel storage portion 4. Examples of the liquid fuel F include methanol fuels such as methanol aqueous solutions having various concentrations and pure methanol. The liquid fuel F is not necessarily limited to methanol fuel. The liquid fuel F may be, for example, an ethanol fuel such as an ethanol aqueous solution or pure ethanol, a propanol fuel such as a propanol aqueous solution or pure propanol, a glycol fuel such as a glycol aqueous solution or pure glycol, dimethyl ether, formic acid, or other liquid fuel F. Good. In any case, the fuel containing portion 4 contains the liquid fuel F corresponding to the membrane electrode assembly 2.

  Hereinafter, an example of the fuel supply mechanism 3 will be described.

  The fuel supply mechanism 3 disperses and diffuses fuel in the surface direction of the container 30 formed in a box shape and the anode 13 of the membrane electrode assembly 2 (that is, the direction in the XY plane in the drawing). A fuel distribution plate 31 is provided. The container 30 has a fuel inlet (not shown) to which the flow path 5 is connected. Examples of the resin material forming such a container 30 include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), cyclic olefin copolymer, cycloolefin polymer, polymethylpentene, and polyphenyl sulfide (PPS). The container 30 can also be formed using a metal material such as stainless steel (SUS) or a metal clad material instead of the resin material.

  The fuel distribution plate 31 is disposed in a recess formed inside the container 30. The fuel distribution plate 31 is formed in a flat plate shape. The fuel distribution plate 31 has a plurality of fuel discharge ports 33 formed therein. Such a fuel distribution plate 31 discharges the liquid fuel supplied from the fuel introduction port of the container 30 toward the anode 13 from the fuel discharge port 33. Such a fuel distribution plate 31 is formed of a material that does not allow liquid fuel and its vaporized components to permeate. Is formed.

  The fuel distribution plate 31 may be constituted by a gas-liquid separation membrane that separates liquid fuel and its vaporized component and allows the vaporized component to permeate toward the membrane electrode assembly 2. Examples of the gas-liquid separation membrane include silicone rubber, low density polyethylene (LDPE) thin film, polyvinyl chloride (PVC) thin film, polyethylene terephthalate (PET) thin film, fluororesin (for example, polytetrafluoroethylene (PTFE), tetrafluoro An ethylene / perfluoroalkyl vinyl ether copolymer (PFA) or the like) microporous film or the like is applicable.

  A heat conductor 40 is disposed between the fuel supply mechanism 3 and the anode 13 of the membrane electrode assembly 2. The heat conductor 40 is in contact with the fuel supply mechanism 3. Such a heat conductor 40 is formed in a flat plate shape substantially parallel to the XY plane. Here, the state in which “the heat conductor 40 is in contact with the fuel supply mechanism 3” corresponds to a state in which the lower surface of the heat conductor 40 in the XY plane is in contact with the fuel supply mechanism 3. In the illustrated example, the heat conductor 40 is in contact with the fuel distribution plate 31.

  The above-described heat conductor 40 is desirably formed of a material that does not dissolve, corrode, oxidize, or the like due to liquid fuel, water, oxygen, or the like and that has high thermal conductivity. Moreover, the heat conductor 40 needs to ensure the air permeability for permeate | transmitting the vaporization component of a fuel at least, and is formed with the material which has a porous material or a through-hole. Among these, as the porous heat conductor 40, a carbon fiber material is suitable. For example, carbon paper (TGP-H series) manufactured by Toray Industries, Inc. or carbon paper (GDL series) manufactured by SGL Carbon Japan Co., Ltd. Etc. are applicable. Moreover, as the heat conductor 40 having a through hole, a through hole was formed in a graphite sheet (for example, a graphite sheet (eGraf series) manufactured by Graphtec Co., Ltd.) obtained by processing a carbonaceous material such as graphite into a sheet shape. A thing etc. are applicable.In the example shown in FIG.

  Furthermore, as the heat conductor 40, a metal such as gold, aluminum, copper, tungsten, and molybdenum having excellent heat conductivity, or an alloy of these metals such as stainless steel formed with a through hole is applicable. is there.

  When a metal material is used as the thermal conductor 40, there is a possibility that oxidation or corrosion may occur due to water generated at the cathode 16 or formic acid as a by-product of the reaction at the anode. In order to prevent this, the heat conductor 40 is made of a material that is not easily corroded, such as stainless steel, or the surface of the heat conductor 40 is plated with a metal that is not easily oxidized, such as gold, Alternatively, it may be coated with resin or rubber, or coated with a paint that does not dissolve in the vaporized component of the liquid fuel.

  As the resin or rubber for coating as described above, polyethylene, polypropylene, polystyrene, polyethylene terephthalate, nylon, polyetheretherketone (PEEK: trademark of Victorex), polytetrafluoroethylene (PTFE), tetrafluoroethylene -Resin such as perfluoroalkyl vinyl ether copolymer (PFA), polyvinyl chloride, polyimide, silicone resin, rubber such as ethylene / propylene rubber (EPDM), fluorine rubber, etc. can be used. Since these resins and rubbers have a lower thermal conductivity than metal materials, it is desirable to make the resin or rubber to be coated as thin as possible.

  Further, as in the example shown in FIG. 2, when the thermal conductor 40 is in contact with the anode current collector 18 </ b> A, the thermal conductor 40 is prevented in order to prevent a short circuit between the single cells of the membrane electrode assembly 2. Is configured as an insulator, or at least the surface of the heat conductor 40 that is in contact with the anode current collector 18A is preferably covered with an insulator such as resin or rubber as described above.

  This thermal conductor 40 has a thermal conductivity λpl of 10 W / mK or more in a plane direction parallel to the fuel supply mechanism 3 (that is, a direction parallel to the XY plane in the example shown in FIG. 2). desirable. This is because the greater the value of the thermal conductivity λpl, the greater the effect on the uniform heat distribution in the plane parallel to the XY plane.

  Further, in this thermal conductor 40, the thermal conductivity λpl in the plane is larger than the thermal conductivity λt in the thickness direction (that is, the Z direction in the example shown in FIG. 2). It is still desirable to have it. This is because, when the thermal conductivity λt in the thickness direction is larger than the thermal conductivity λpl in the plane, the movement of heat in the thickness direction is promoted, and in-plane, that is, the high-temperature portion of the membrane electrode assembly 2 This is because the movement of heat from the heat to the low temperature part may be hindered. The thermal conductivities λpl and λt described here are measured by a laser flash method.

  Moreover, in this heat conductor 40, it is desirable that the porosity (or aperture ratio) at the center portion thereof is smaller than the peripheral portion. That is, the heat conductor 40 disposed on the anode 13 side of the membrane electrode assembly 2 has air permeability so as not to inhibit the introduction of fuel into the anode 13. On the other hand, the porosity of the thermal conductor 40 is one of the factors that control the thermal conductivity. The higher the porosity, the more the inside of the thermal conductor 40 is filled with gas components, and the lower the heat dissipation performance. Invite. That is, the higher the porosity, the lower the thermal conductivity. As described above, the heat conductor 40 is required to ensure air permeability while ensuring heat conductivity.

  In many cases, the in-plane temperature distribution of the membrane electrode assembly 2 is high in the central portion and low in the peripheral portion (that is, the portion close to the container 30). In order to cope with this, in the heat conductor 40, it is desirable that the porosity at the central portion is smaller than the peripheral portion. That is, in the heat conductor 40, the portion facing the central portion of the membrane electrode assembly 2 has a relatively high thermal conductivity and promotes the movement of heat, and the portion facing the peripheral portion has a relatively high heat conductivity. On the other hand, the air permeability is high and the power generation reaction can be promoted.

  At this time, you may comprise the heat conductor 40 so that the porosity may become large continuously toward a peripheral part from a center part. In this case, the thermal conductivity in the plane of the heat conductor 40 is not constant, and continuously increases from the central portion to the peripheral portion.

  As shown in FIG. 2, the through hole 40 </ b> H formed in the heat conductor 40 is located immediately above the fuel discharge port 33 of the fuel distribution plate 31.

  FIG. 3 is a top view of the fuel distribution plate 31 in the fuel supply mechanism 3.

  The fuel distribution plate 31 is formed in a substantially rectangular shape extending in the first direction X. The fuel distribution plate 31 has a fuel inlet 32 and a fuel outlet 33 formed therein. The fuel injection port 32 is formed in one place, for example. The fuel inlet 32 communicates with the fuel inlet 30 </ b> A of the container 30. A plurality of fuel discharge ports 33, here 128 (16 × 8), are formed. These fuel discharge ports 33 are connected to the fuel injection port 32 via a flow path 34. The flow path 34 may be a groove formed on the surface of the fuel distribution plate 31 that is in close contact with the container 30 or may be a pipe that passes through the inside of the fuel distribution plate 31, and the form is not particularly limited. .

  FIG. 4 is a perspective view of the heat conductor 40.

  The heat conductor 40 is formed in a substantially rectangular shape extending in the first direction X. In such a heat conductor 40, a plurality of, here 128 (16 × 8) through holes 40H are formed. Each of these through holes 40H is located immediately above the fuel discharge port 33. Such a through hole 40H has a diameter equal to or larger than the diameter of the fuel discharge port 33. In addition to the 128 through holes 40H shown in the drawing, a plurality of through holes may be further formed in the heat conductor 40. The number of through holes 40H formed in the heat conductor 40 may be appropriately set in consideration of the heat conductivity required for the heat conductor 40.

  In the fuel cell 1 described above, the liquid fuel F introduced into the fuel distribution plate 31 from the fuel storage unit 4 via the flow path 5 remains in the liquid component or in a state where the liquid component and the gas component are mixed. The fuel is discharged from the fuel discharge port 33 of the fuel distribution plate 31. The discharged fuel is supplied to the anode 13 of the membrane electrode assembly 2 through the heat conductor 40 and the anode current collector 18A of the current collector 18.

  The gaseous component of the fuel supplied to the anode 13 diffuses through the anode gas diffusion layer 12 and is supplied to the anode catalyst layer 11. When methanol fuel is used as the fuel, an internal reforming reaction of methanol shown in the following formula (1) occurs in the anode catalyst layer 11. When pure methanol is used as the methanol fuel, the water generated in the cathode catalyst layer 14 or the water in the electrolyte membrane 17 is reacted with methanol to cause the internal reforming reaction of the formula (1), or The internal reforming reaction is caused by another reaction mechanism that does not require water.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
The electrons (e ⁻ ) generated by this reaction are guided to the outside via the current collector 18, and after operating a portable electronic device or the like as so-called electricity, the electrons (e ⁻ ) Led. Proton (H ⁺ ) generated by the internal reforming reaction of the formula (1) is guided to the cathode 16 through the electrolyte membrane 17. Air is supplied to the cathode 16 as an oxidant. Electrons (e ⁻ ) and protons (H ⁺ ) that have reached the cathode 16 react with oxygen in the air in the cathode catalyst layer 14 according to the following formula (2), and water is generated with this reaction.

6e ⁻ + 6H ⁺ + (3/2) O ₂ → 3H ₂ O (2)
In the power generation reaction of the fuel cell 1 described above, in order to increase the power to be generated, the catalytic reaction is smoothly performed, and the fuel is uniformly supplied to the entire electrode of the membrane electrode assembly 2 so that the entire electrode becomes more effective. It is important to contribute to power generation.

  According to the present embodiment, in the surface of the membrane electrode assembly 2, the central portion is relatively difficult to dissipate heat and is likely to be at a high temperature, and conversely, the peripheral portion is likely to be at a lower temperature than the central portion. In this case, by disposing the heat conductor 40, heat transfer from the central part of the membrane electrode assembly 2 to the peripheral part is promoted, and the temperature difference between the central part and the peripheral part of the membrane electrode assembly 2 is reduced. It becomes possible to do. That is, the temperature distribution in the surface of the membrane electrode assembly 2 can be made uniform.

  In addition, the vapor pressure difference of the vaporized component of the liquid fuel due to the temperature difference is also reduced, and the exchange of substances necessary for the power generation reaction is promoted in both the central part and the peripheral part in the surface of the membrane electrode assembly 2. Is possible. In particular, in the fuel cell 1 used as a power source for a portable electronic device or the like, even if the temperature of the entire fuel cell is kept low, the vapor pressure difference is reduced, so that a high output can be stably obtained.

  Next, variations of the fuel cell 1 that can be employed in the present embodiment will be described. Note that the same components as those in the example shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 5 is a view schematically showing a cross section of the fuel cell 1 according to another embodiment cut along the first direction X. FIG.

  The example shown in FIG. 5 is different from the example shown in FIG. 2 in that an insulator 50 is disposed between the thermal conductor 40 and the current collector 18. The insulator 50 is in contact with the upper surface of the heat conductor 40 and in contact with the back side of the anode current collector 18A. As such an insulator 50, for example, one that functions as a fuel diffusion plate or a gas-liquid separation membrane can be applied. Further, the insulator 50 has substantially the same shape as the heat conductor 40 and has substantially the same outer dimensions.

  The insulator 50, which is a fuel diffusion plate, is composed of a flat plate made of, for example, a polyethylene porous film. Such an insulator 50 serves to promote the uniformity of the supply of vaporized fuel by diffusing in the plane direction of the vaporized fuel (direction parallel to the XY plane in FIG. 1).

  The insulator 50, which is a gas-liquid separation membrane, is composed of a flat plate made of various materials as described above, such as a microporous membrane made of polytetrafluoroethylene (PTFE). Such an insulator 50 separates liquid fuel and its vaporized component from the fuel supplied from the fuel supply mechanism 3 toward the anode 13, and transmits the fuel vaporized component toward the anode 13. is there.

  FIG. 6 is a view schematically showing a cross section of the fuel cell 1 according to another embodiment cut along the first direction X. FIG.

  The example shown in FIG. 6 differs from the example shown in FIG. 2 in that a spacer 60 for forming an air layer 61 is disposed between the heat conductor 40 and the current collector 18. is doing. The spacer 60 is disposed outside the path through which the fuel supplied from the fuel supply mechanism 3 is supplied toward the membrane electrode assembly 2.

  That is, the spacer 60 is in contact with the upper surface along the outer edge portion outside the through hole 40H of the heat conductor 40, and is in contact with the back surface side along the outer edge portion of the anode current collector 18A. Such a spacer 60 is formed of an insulating elastic body such as an O-ring, for example.

  FIG. 7 is a view schematically showing a cross section of the fuel cell 1 according to another embodiment cut along the first direction X. FIG.

  In the example shown in FIG. 7, compared with the example shown in FIG. 2, a gas-liquid separation film is disposed as the insulator 50 between the heat conductor 40 and the current collector 18, and the fuel supply mechanism 3. Is different in that it has a fuel diffusion plate 35 disposed between the fuel distribution plate 31 and the heat conductor 40.

  The insulator 50 is formed in a flat plate shape, is in contact with the upper surface of the heat conductor 40, and is in contact with the back surface side of the anode current collector 18A. Further, the insulator 50 has substantially the same shape as the heat conductor 40 and has substantially the same outer dimensions. Such an insulator 50 is made of various materials as described above, such as a microporous membrane made of polytetrafluoroethylene (PTFE).

  The fuel diffusion plate 35 is formed in a flat plate shape, is in contact with the upper surface of the fuel distribution plate 31, and is in contact with the back surface of the heat conductor 40. Such a fuel diffusion plate 35 is made of, for example, a polyethylene porous film.

  In the example shown in FIG. 7, a gas-liquid separation membrane is applied as the insulator 50. However, a fuel diffusion plate may be applied as the insulator 50 as in the example shown in FIG. In this example, the insulator 50 is disposed between the heat conductor 40 and the current collector 18, but the spacer 60 for forming the air layer 61 is disposed as in the example shown in FIG. 6. May be.

  FIG. 8 is a view schematically showing a cross section of the fuel cell 1 according to another embodiment cut along the first direction X. FIG.

  8 is different from the example shown in FIG. 2 in that a gas-liquid separation membrane and an anode film 70 as the insulator 50 are disposed between the heat conductor 40 and the current collector 18. Is different.

  The anode film 70 is formed in a flat plate shape and is in contact with the upper surface of the heat conductor 40. The anode film 70 has substantially the same shape as the heat conductor 40 and has substantially the same outer dimensions.

  A plurality of apertures 70H are formed in the anode film 70. Here, the anode film 70 is formed with 128 (16 × 8) openings 70 </ b> H that are the same number as the fuel discharge ports 33 of the fuel distribution plate 31. Each of these openings 70 </ b> H is located immediately above the fuel discharge port 33. Such an opening 70 </ b> H has a diameter equal to or larger than the diameter of the fuel discharge port 33. The anode film 70 may be further formed with a plurality of openings in addition to the 128 openings 70H.

  Such an anode film 70 is formed of a material having sufficient resistance to a fuel such as methanol. For example, polyphenyl sulfide (PPS), polyimide (PI), polyethylene terephthalate (PET), polypropylene (PP), It is formed of polyethylene naphthalate (PEN), polyetheretherketone (PEEK: trademark of Victorex), liquid crystal polymer (LCP), or the like. The anode film 70 may be formed using a metal plate whose surface is subjected to acid resistance treatment, glass, silicon, or the like.

  The insulator 50 is formed in a flat plate shape, is in contact with the upper surface of the anode film 70, and is disposed so as to close the opening 70 </ b> H of the anode film 70. The insulator 50 has substantially the same shape as the heat conductor 40 and the anode film 70 and has substantially the same outer dimensions.

  FIG. 9 is a diagram schematically showing a cross section of the fuel cell 1 according to another embodiment cut along the first direction X. FIG.

  9, the spacer 60 for forming the insulator 50 and the air layer 61 is disposed between the heat conductor 40 and the current collector 18, as compared with the example shown in FIG. It is different in point.

  The insulator 50 is a gas-liquid separation film, for example, and is formed in a flat plate shape. The insulator 50 is in contact with the back side of the anode current collector 18A.

  As in the example shown in FIG. 6, the spacer 60 is located outside the path through which the fuel supplied from the fuel supply mechanism 3 is supplied toward the membrane electrode assembly 2, and the spacer 60 is a through hole of the heat conductor 40. It is in contact with the upper surface along the outer edge portion outside 40H and in contact with the back surface along the outer edge portion of the insulator 50.

  FIG. 10 is a view schematically showing a cross section of the fuel cell 1 according to another embodiment cut along the first direction X. FIG.

  In the example shown in FIG. 10, compared with the example shown in FIG. 2, a gas-liquid separation membrane and an anode film 70 as the insulator 50 are disposed between the heat conductor 40 and the current collector 18, and The fuel supply mechanism 3 is different in that it has a fuel diffusion plate 35 disposed between the fuel distribution plate 31 and the heat conductor 40.

  The fuel diffusion plate 35 is formed in a flat plate shape, is disposed on the fuel distribution plate 31, and overlaps all the fuel discharge ports 33 formed in the fuel distribution plate 31. The heat conductor 40 is disposed on the fuel diffusion plate 35. In the illustrated example, the fuel diffusion plate 35 and the heat conductor 40 are in contact with each other. The through hole 40 </ b> H formed in the heat conductor 40 is located immediately above the fuel discharge port 33.

  The anode film 70 is disposed on the heat conductor 40. In the illustrated example, the heat conductor 40 and the anode film 70 are in contact with each other. The opening 70 </ b> H formed in the anode film 70 is located immediately above the fuel discharge port 33. That is, the fuel discharge port 33, the through hole 40H, and the opening 70H are coaxially positioned along the Z direction.

  The insulator 50, which is a gas-liquid separation membrane, is formed in a flat plate shape, is in contact with the upper surface of the anode film 70, and is disposed so as to close the opening 70H of the anode film 70. In the illustrated example, the insulator 50 is in contact with the back side of the anode current collector 18A.

  As described above, the same effects as described above can be obtained in the variations shown in FIGS.

<Performance evaluation>
Example 1
To the carbon black supporting the anode catalyst particles (Pt: Ru = 1: 1), a perfluorocarbon sulfonic acid solution as a proton conductive resin and water and methoxypropanol as a dispersion medium were added to support the anode catalyst particles. A paste was prepared by dispersing carbon black. The obtained paste was applied to porous carbon paper (55.5 mm × 8.7 mm rectangle) as the anode gas diffusion layer 12 to obtain an anode catalyst layer 11 having a thickness of 100 μm.

  To the carbon black carrying the cathode catalyst particles (Pt), a perfluorocarbon sulfonic acid solution as a proton conductive resin and water and methoxypropanol as a dispersion medium are added to disperse the carbon black carrying the cathode catalyst particles. A paste was prepared. The obtained paste was applied to porous carbon paper as the cathode gas diffusion layer 15 to obtain a cathode catalyst layer 14 having a thickness of 100 μm.

  The anode gas diffusion layer 12 and the cathode gas diffusion layer 15 have the same shape and the same size, the same thickness, and the anode catalyst layer 11 and the cathode catalyst layer 14 applied to each gas diffusion layer have the same shape. And the same size.

  A perfluorocarbon sulfonic acid membrane (trade name: nafion membrane) having a thickness of 30 μm and a water content of 10 to 20% by weight as the electrolyte membrane 17 between the anode catalyst layer 11 and the cathode catalyst layer 14 produced as described above. , Manufactured by DuPont), the four anode gas diffusion layers 12 and the four cathode gas diffusion layers 15 are arranged side by side so that the longitudinal directions thereof are substantially parallel and the distance between them is 1.2 mm. Membrane electrode assembly 2 was obtained by performing hot pressing in a state where the positions were adjusted so that layer 11 and cathode catalyst layer 14 face each other.

  The membrane electrode assembly 2 thus prepared is sandwiched by the current collector 18, the anode gas diffusion layer 12 and the anode current collector 18A are opposed to each other, and the cathode gas diffusion layer 15 and the cathode current collector 18C are connected to each other. Opposite. That is, a gold foil was laminated on the cathode gas diffusion layer 15 as the cathode current collector 18C. Further, a gold foil was laminated on the anode gas diffusion layer 12 as the anode current collector 18A. The anode current collector 18A and the cathode current collector 18C are formed so that the four pairs of the anode catalyst layer 11 and the cathode catalyst layer 14 are electrically connected in series. The anode current collector 18A has an opening at a position corresponding to the fuel discharge port 33 of the fuel distribution plate 31. The cathode current collector 18C has an opening at a position corresponding to the opening 21H of the cover plate 21.

  Between the electrolyte membrane 17 and the current collector 18 of the membrane electrode assembly 2, a rubber O-ring having a width of 2 mm is sandwiched between the anode side and the cathode side as seal members 19, respectively. gave.

On the cathode current collector 18C, as a plate-like body 20, the thickness is 0.75 mm, and the air permeability is 3.0 seconds / 100 cm ³ (according to the measurement method specified in JIS P 8117: 2009). Yes, a polyethylene porous film having a moisture permeability of 3000 g / (m ² · 24 h) (according to the measurement method defined in JIS L 1099: 2006 A-1) is formed into a rectangle having a length of 59.5 mm and a width of 42.4 mm. Cut and laminated. Air supplied from the outside air to the cathode 16 passes through the plate-like body 20.

  On the plate-like body 20, a stainless plate (SUS304) having a rectangular outer shape of 64.5 mm × 44.5 mm and a thickness of 0.3 mm was laminated as the cover plate 21. The cover plate 21 is uniformly formed with 64 rectangular openings 21H of 5.6 mm × 2.8 mm.

  On the fuel distribution plate 31, as a heat conductor 40, a graphite sheet having a thickness of 80 μm (manufactured by Graphtec; model number SS400) was cut into a rectangular shape of 59.5 mm × 42.4 mm and laminated. The graphite sheet as the thermal conductor 40 has a thermal conductivity λpl of 400 W / mK in the plane direction (direction parallel to the XY plane shown in FIG. 5), and its thickness direction (Z direction in FIG. 5). Has a thermal conductivity λt of 3.5 W / mK. An opening having a diameter of 1.8 mm is formed in the heat conductor 40 at a position corresponding to the fuel discharge port 33 of the fuel distribution plate 31.

  Between the heat conductor 40 and the anode current collector 18A, a polyethylene porous film having a thickness of 0.5 mm and a porosity of 26% was inserted as an insulator 50 which is a fuel diffusion plate. The insulator 50 has the same shape and the same size as the heat conductor 40. The insulator 50 plays a role of diffusing the vaporized fuel in the planar direction together with electrical insulation and promoting the uniformity of the supply of the vaporized fuel.

  The first embodiment having the above-described configuration corresponds to the fuel cell 1 shown in FIG.

(Example 2)
In Example 2, in the fuel cell 1 described in Example 1, instead of disposing the insulator 50 between the heat conductor 40 and the anode current collector 18A, the heat conductor 40 and the anode current collector 18A In the same manner as in Example 1, except that a spacer 60 for forming the air layer 61 having a distance in the Z direction of 0.5 mm is provided.

  The second embodiment having the above-described configuration corresponds to the fuel cell 1 shown in FIG.

(Example 3)
In the third embodiment, in the fuel cell 1 described in the first embodiment, the fuel diffusion plate 35 is disposed between the fuel distribution plate 31 and the heat conductor 40, and between the heat conductor 40 and the anode current collector 18A. Example 1 is the same as Example 1 except that the insulator 50, which is a gas-liquid separation membrane, is disposed. As the insulator 50, a microporous film made of polytetrafluoroethylene (PTFE) having a thickness of 0.1 mm and a porosity of 68% was applied.

  The third embodiment having the above-described configuration corresponds to the fuel cell 1 shown in FIG.

(Comparative example)
The fuel cell 1 described in the first embodiment is the same as the first embodiment except that the heat conductor 40 is not provided.

  Performance evaluation was performed about each fuel cell 1 of Examples 1 thru | or 3 mentioned above and a comparative example.

  First, pure methanol having a purity of 99.9% by weight was supplied to each fuel cell 1 produced as described above in an environment where the temperature was 25 ° C. and the relative humidity was 50%. Here, a thermocouple was attached to the surface of the central portion of the cover plate 21, and the case where the supply amount of pure methanol was controlled so that the temperature measured with this thermocouple was constant at 45 ° C. was measured with a thermocouple. The following measurements are performed under two conditions, that is, when the supply amount of pure methanol is controlled so that the temperature is constant at 50 ° C.

  Then, a constant voltage power supply is connected, and the current flowing through the fuel cell 1 is controlled so that the output voltage of the fuel cell 1 is constant at 0.35 V per pair in the four pairs of single cells connected in series. At this time, the output density obtained from the fuel cell 1 was measured.

Here, the output density (mW / cm ² ) of the fuel cell 1 refers to the current density flowing through the fuel cell 1 (current value per 1 cm ² area (mA / cm ² ) of the power generation unit) and the output voltage of the fuel cell 1. Multiplied by. Further, the area of the power generation unit is the area of the portion where the anode catalyst layer 11 and the cathode catalyst layer 14 face each other. In each of the examples and comparative examples described here, the areas of the anode catalyst layer 11 and the cathode catalyst layer 14 are equal and completely opposed to each other, so that the area of the power generation unit is equal to the areas of these catalyst layers.

  FIG. 11 collectively shows the above measurement results. The result of measuring the output density of the fuel cell 1 is shown as a relative value with the value of the comparative example measured at each control temperature as 100.

  When the fuel supply is controlled so that the surface temperature of the cover plate 21 is 45 ° C., when the output density of the comparative example is 100%, it is 107% in Example 1, 109% in Example 2, In Example 3, it was 102%, and it was confirmed that in any Example, a higher output density than that of the comparative example was obtained.

  When the fuel supply is controlled so that the surface temperature of the cover plate 21 is 50 ° C., when the output density of the comparative example is 100%, it becomes 104% in the first example and 105% in the second example. In Example 3, it was 102%, and it was confirmed that in any Example, a higher output density than that of the comparative example was obtained.

  Thus, particularly when the fuel supply is controlled to be lower than 50 ° C., the configurations of Examples 1 to 3 have a higher output density than the configuration of the comparative example. High effect.

  In the measurement results shown in FIG. 11, only the relative value with respect to the comparative example is shown. However, in the absolute value of the output density, the output of 50 ° C. control is higher than that of 45 ° C. control in any configuration. Density is obtained.

  As described above, according to this embodiment, even when the temperature of the fuel cell 1 is kept low, it is possible to stably obtain a high output.

  The fuel cell 1 according to the embodiment described above is effective when various liquid fuels are used, and the type and concentration of the liquid fuel are not limited. However, the fuel distribution plate 31 that supplies fuel while being dispersed in the plane direction is particularly effective when the fuel concentration is high. For this reason, the fuel cell 1 of the embodiment can exert its performance and effects particularly when methanol having a concentration of 80 wt% or more is used as the liquid fuel. Therefore, the embodiment is suitable for the fuel cell 1 using a methanol aqueous solution having a methanol concentration of 80 wt% or more or pure methanol as a liquid fuel.

  Furthermore, although embodiment mentioned above demonstrated the case where this invention was applied to the semi-passive type fuel cell 1, this invention is not restricted to this, It is with respect to an internal vaporization type pure passive type fuel cell. Is applicable.

  The present invention can be applied to various fuel cells using liquid fuel. Further, the specific configuration of the fuel cell, the supply state of the fuel, and the like are not particularly limited, and all the fuel supplied to the membrane electrode assembly is the vapor of the liquid fuel F, all the liquid fuel F, or one The present invention can be applied to various forms such as a vapor of the liquid fuel F supplied in a liquid state. In the implementation stage, the constituent elements can be modified and embodied without departing from the technical idea of the present invention. Furthermore, various modifications are possible, such as appropriately combining a plurality of constituent elements shown in the above embodiment, or deleting some constituent elements from all the constituent elements shown in the embodiment. Embodiments of the present invention can be expanded or modified within the scope of the technical idea of the present invention, and these expanded and modified embodiments are also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Fuel cell 2 ... Membrane electrode assembly 13 ... Anode 16 ... Cathode 17 ... Electrolyte membrane 18 ... Current collector 18A ... Anode current collector 18C ... Cathode current collector 21 ... Cover plate 21H ... Opening 3 ... Fuel supply mechanism DESCRIPTION OF SYMBOLS 30 ... Container 31 ... Fuel distribution plate 35 ... Fuel diffusion plate 40 ... Thermal conductor 40H ... Through-hole 50 ... Insulator (gas-liquid separation membrane or fuel diffusion plate)
60 ... Spacer 61 ... Air layer 70 ... Anode film 70H ... Open hole

Claims (10)

A membrane electrode assembly comprising: an electrolyte membrane; an anode disposed on one surface of the electrolyte membrane; and a cathode disposed on the other surface of the electrolyte membrane;
A fuel supply mechanism disposed on the anode side of the membrane electrode assembly and supplying fuel toward the anode;
A heat conductor disposed between the fuel supply mechanism and the anode and in contact with the fuel supply mechanism;
A fuel cell comprising: And a cathode current collector that is in contact with the cathode and an anode current collector that is disposed between the anode and the thermal conductor and is in contact with the anode of the membrane electrode assembly,
An insulator composed of a gas-liquid separation membrane or a fuel diffusion plate disposed between the anode current collector and the heat conductor, or an air layer formed between the heat conductor and the anode current collector A spacer for
The fuel cell according to claim 1, further comprising: A membrane electrode assembly comprising: an electrolyte membrane; an anode disposed on one surface of the electrolyte membrane; and a cathode disposed on the other surface of the electrolyte membrane;
A fuel supply mechanism disposed on the anode side of the membrane electrode assembly and supplying fuel toward the anode;
A gas-liquid separation membrane disposed between the fuel supply mechanism and the anode;
A heat conductor disposed between the fuel supply mechanism and the gas-liquid separation membrane and spaced from the gas-liquid separation membrane;
A fuel cell comprising: And a cathode current collector that is in contact with the cathode and an anode current collector that is disposed between the anode and the gas-liquid separation membrane and is in contact with the anode of the membrane electrode assembly,
An anode film disposed between the gas-liquid separation membrane, or a spacer for forming an air layer between the thermal conductor and the gas-liquid separation membrane;
The fuel cell according to claim 3, further comprising:   The fuel supply mechanism is disposed between a fuel distribution plate formed with a plurality of fuel discharge ports for discharging fuel toward the anode, the fuel distribution plate and the heat conductor, and the heat conductor. The fuel cell according to claim 1, further comprising a fuel diffusion plate in contact with the fuel cell.   6. The fuel cell according to claim 5, wherein the heat conductor is formed with a plurality of through holes located immediately above a fuel discharge port formed in the fuel distribution plate.   The fuel cell according to claim 4, wherein the anode film is formed with a plurality of apertures.   4. The fuel cell according to claim 1, wherein the thermal conductor has a thermal conductivity of 10 W / mK or more in a planar direction parallel to the fuel supply mechanism.   4. The fuel cell according to claim 1, wherein the heat conductor is formed of a porous member or a member having a through hole.   4. The fuel cell according to claim 1, wherein the thermal conductor has a porosity or an opening ratio at a central portion thereof smaller than that of a peripheral portion.

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