JP2009187797A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell maintaining a stable output over a long period of time. <P>SOLUTION: The fuel cell is provided with a membrane electrode assembly 10 consisting of fuel electrodes 11, 12, air electrodes 13, 14, and an electrolyte membrane 15 pinched by the fuel electrodes 11, 12 and the air electrodes 13, 14, a fuel supply mechanism 40 arranged at a fuel electrode 11, 12 side of the membrane electrode assembly 10 for supplying fuel to the fuel electrodes 11, 12, a moisturizing layer 20 arranged at an air electrode 13, 14 side of the membrane electrode assembly 10 to be impregnated with moisture produced at the air electrodes 13, 14, and a heat radiating member 23 in contact with the surface of the moisturizing layer 20 to dissipate heat toward outside air. The heat radiating member 23 comprises a first heat radiating member 22 arranged in correspondence to a high-temperature area of the air electrodes 13, 14 in a plane direction of the membrane electrode assembly 10, and a second heat radiating member 21 arranged in correspondence to a low-temperature area of the air electrodes 13, 14, with a heat radiating volume from the first heat radiating member 22 set larger than that from the second heat radiating member 21. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell using 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 without being charged for a long time. A fuel cell is characterized in that it can generate electric power simply by supplying fuel and air, and can continuously generate electric power 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.

  The direct methanol fuel cell (DMFC) is expected to be a power source for portable electronic devices because it can be miniaturized and the fuel can be easily handled.

  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.

  Various methods can be adopted as means for supplying fuel to the anode (fuel electrode). For example, a liquid fuel such as an aqueous methanol solution can be directly circulated under the anode conductive layer, or a gas fuel can be generated by evaporating methanol etc. outside the fuel cell, and the gaseous fuel can be circulated under the anode conductive layer. An external vaporization type to be used, an internal vaporization type in which liquid fuel such as pure methanol or an aqueous methanol solution is accommodated in the fuel accommodating portion, and the liquid fuel is vaporized inside the cell and supplied to the anode, etc. are conceivable.

  In addition, as means for supplying air, which is an oxidant, to the cathode (air electrode), an active type that forcibly supplies air by a fan or blower, or a spontaneous breathing (passive) type that supplies only by natural diffusion from the atmosphere. And so on.

  Among these, a passive system such as an internal vaporization type is particularly advantageous for downsizing of the DMFC. In the passive DMFC, for example, a structure is proposed in which a membrane electrode assembly (fuel cell) having a fuel electrode, an electrolyte membrane, and an air electrode is disposed on a fuel containing portion made of a resin box-like container ( For example, see Patent Document 1). The membrane electrode assembly is sandwiched between an anode conductive layer disposed on the fuel electrode side and a cathode conductive layer disposed on the air electrode side.

  The liquid fuel supplied to the fuel supply unit from the fuel storage unit via the flow path remains as the liquid fuel or the fuel distribution layer and the anode conductive layer are formed in a state where the liquid fuel and the vaporized fuel in which the liquid fuel is vaporized are mixed. To the anode gas diffusion layer of the fuel cell. The fuel supplied to the anode gas diffusion layer is diffused in the anode gas diffusion layer and supplied to the anode catalyst layer. When methanol fuel is used as the liquid fuel, an internal reforming reaction of methanol represented by the following formula (1) occurs in the anode catalyst layer.

CH3OH + H2O → CO2 + 6H ⁺ + 6e ⁻ Formula (1)
When pure methanol is used as the methanol fuel, the methanol is reformed by the internal reforming reaction of the above formula (1) with water generated in the cathode catalyst layer or water in the electrolyte membrane, or It is modified by other reaction mechanisms that do not require water.

The electrons (e ⁻ ) generated by this reaction are guided to the outside via a current collector, and are operated to a cathode after operating a portable electronic device or the like as so-called electricity. In addition, protons (H ⁺ ) generated by the internal reforming reaction of the formula (1) are guided to the cathode through the electrolyte membrane. Air is supplied to the cathode as an oxidant gas through the moisture retention layer. The electrons (e ⁻ ) and protons (H ⁺ ) that have reached the cathode cause a reaction represented by the following formula (2) with oxygen in the air in the cathode catalyst layer, and water is generated in accordance with this power generation reaction.

(3/2) O2 + 6e ⁻ + 6H ⁺ → 3H ₂ O Formula (2)
In order to smoothly perform the internal reforming reaction described above and obtain a high output and a stable output in the fuel cell, at least a part of the water (H 2 O) generated in the cathode catalyst layer by the formula (2) is an electrolyte. The cycle of permeating the membrane, diffusing into the anode catalyst layer and being consumed by the reaction of formula (1) needs to be performed smoothly.

In order to achieve this, a moisturizing layer that impregnates water generated in the cathode catalyst layer to suppress transpiration is disposed near the cathode, and the moisture retention amount of the cathode catalyst layer is greater than the moisture retention amount of the anode catalyst layer. The water generated in the cathode catalyst layer using the osmotic pressure phenomenon is supplied to the anode catalyst layer through the electrolyte membrane.
International Publication No. 2005/112172 Pamphlet

  In the fuel cell that promotes the supply of water from the cathode to the anode using the moisturizing layer as described above, in order to increase the amount of water supplied from the cathode to the anode, it contacts the membrane electrode assembly of the moisturizing layer. It is preferable that the temperature difference between the side and the side in contact with the outside air is increased to promote the action of water vapor condensing (liquefying) inside the moisture retaining layer to generate liquid water. For this purpose, the thicker the moisturizing layer, the better. However, as the moisturizing layer becomes thicker, the amount of oxygen that passes through the moisturizing layer from the outside air and is supplied to the cathode decreases, or from the cathode to the outside air. In some cases, the amount of heat dissipated decreased and the temperature of the cathode increased excessively.

  On the other hand, if the temperature difference in the thickness direction of the moisturizing layer becomes excessively large, the cathode catalyst layer always retains a large amount of moisture during the power generation of the fuel cell. In some cases, the pores of the cathode catalyst layer are blocked with water, the air diffusibility in the cathode catalyst layer deteriorates, and the power generation characteristics deteriorate.

  For this reason, there is an optimum value for the temperature difference in the thickness direction of the moisturizing layer in order to supply a sufficient amount of water from the cathode to the anode and prevent deterioration of air diffusibility in the cathode catalyst layer. The optimum value of the temperature difference in the thickness direction of the moisture retention layer is closely related to the temperature of the cathode during power generation of the fuel cell.

  When the temperature of the cathode is high, the vapor pressure of water in the cathode catalyst layer becomes high, and the water vapor easily permeates through the moisture retaining layer to the outside air. In order to suppress the transpiration and supply a sufficient amount of water to the anode, it is necessary to increase the temperature difference in the thickness direction of the moisturizing layer.

  On the other hand, when the temperature of the cathode is low, the vapor pressure of water in the cathode catalyst layer is low, and water vapor is prevented from evaporating to the outside air, condensing (liquefaction) in the cathode catalyst layer and closing the pores, so-called Flooding is likely to occur. Therefore, it is necessary to reduce the temperature difference in the thickness direction of the moisture retaining layer.

  However, the temperature of the cathode is not always the same at all locations, and a temperature distribution may occur in the planar direction of the membrane electrode assembly. The cause of such temperature distribution is that the amount of fuel supplied from the fuel distribution layer to the membrane electrode assembly is not uniform, and the amount of heat generated in the membrane electrode assembly is dissipated to the outside air. It may be non-uniform. In many cases, in the planar direction of the membrane electrode assembly, the temperature is high at the central portion of the cathode and the temperature is low at the peripheral portion.

  At this time, if the temperature difference in the thickness direction of the moisturizing layer is the same in the plane direction of the membrane electrode assembly, the amount of water supplied from the cathode to the anode is insufficient at the portion where the temperature of the cathode is high. There is a case. In that case, the reaction of the above formula (1) is not performed smoothly, and the output of the fuel cell is lowered. On the other hand, in the portion where the temperature of the cathode is low, water condenses easily in the cathode catalyst layer. In that case, the output of the fuel cell decreases with the power generation time.

  The present invention has been made in view of the above-described problems, and the amount of water held in the cathode constituting the membrane electrode assembly and the amount of water supplied from the cathode to the anode are flattened. An object of the present invention is to provide a fuel cell that maintains a stable output for a long period of time by maintaining it in an appropriate range in all parts of the direction.

  A fuel cell according to an aspect of the present invention includes a membrane electrode assembly including a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode, and the fuel electrode side of the membrane electrode assembly. A fuel supply mechanism for supplying fuel to the fuel electrode, a moisturizing layer disposed on the air electrode side of the membrane electrode assembly and impregnating water generated at the air electrode, and the moisturizing layer A first heat radiating member disposed in correspondence with a region where the temperature of the air electrode is high in a planar direction of the membrane electrode assembly. And a second heat dissipating member disposed corresponding to a region where the temperature of the air electrode is low, and a heat dissipation amount from the first heat dissipating member is larger than a heat dissipation amount from the second heat dissipating member during power generation. It is comprised so that it may become.

  The present invention can provide a fuel cell that maintains a stable output over a long period of time.

  A fuel cell according to an embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the fuel cell according to the present embodiment has a membrane electrode assembly 10. The membrane electrode assembly 10 includes an anode (fuel electrode), a cathode (air electrode), and an electrolyte membrane 15 sandwiched between the anode and the cathode.

  The anode includes an anode gas diffusion layer 12 and an anode catalyst layer 11 disposed on the anode gas diffusion layer 12. The cathode has a cathode gas diffusion layer 14 and a cathode catalyst layer 13 disposed on the cathode gas diffusion layer 14. An anode conductive layer 16 is disposed on the anode side of the membrane electrode assembly 10. A cathode conductive layer 17 is disposed on the cathode side of the membrane electrode assembly 10.

  In the fuel cell according to this embodiment, the anode is manufactured, for example, by the following manufacturing method. First, to a carbon black supporting anode catalyst particles (Pt: Ru = 1: 1), a perfluorocarbon sulfonic acid solution as a proton conductive resin, water and methoxypropanol as a dispersion medium are added, and anode catalyst particles are prepared. A paste was prepared by dispersing the supported carbon black.

  By applying the paste obtained as described above to porous carbon paper as the anode gas diffusion layer 12, the anode catalyst layer 11 having a thickness of 100 μm can be formed.

  In the fuel cell according to this embodiment, the cathode is manufactured, for example, by the following manufacturing method. First, perfluorocarbon sulfonic acid solution as a proton conductive resin and water and methoxypropanol as a dispersion medium are added to carbon black supporting cathode catalyst particles (Pt), and the carbon black supporting cathode catalyst particles is dispersed. To prepare a paste.

  By applying the paste obtained as described above to porous carbon paper as the cathode gas diffusion layer 14, for example, the cathode catalyst layer 13 having a thickness of 100 μm can be formed.

  In the fuel cell according to this embodiment, the anode gas diffusion layer 12 and the cathode gas diffusion layer 14 are substantially the same shape and the same thickness, and the anode catalyst layer 11 applied to these gas diffusion layers. The cathode catalyst layer 13 is also substantially the same shape and size.

  Between the anode catalyst layer 11 and the cathode catalyst layer 13 formed as described above, a perfluorocarbon sulfonic acid membrane having a thickness of 30 μm and a water content of 10 to 20% by weight (trade name: nafion, for example) is used as the electrolyte membrane 15. Membrane electrode assembly 10 was manufactured by hot pressing in a state where the membrane was made by DuPont and aligned so that the anode catalyst layer 11 and the cathode catalyst layer 13 faced each other.

  In the fuel cell according to the present embodiment, in the membrane electrode assembly 10, the electrolyte membrane 15 is not in contact with the anode catalyst layer 11 and the cathode catalyst layer 13, and corresponds to the inside of the O-ring 19 described below. A gas discharge hole (not shown) may be provided at the position.

  Subsequently, the membrane electrode assembly 10 is made up of the anode conductive layer 16 and the cathode conductive layer 17 having a plurality of openings, respectively, the surface of the anode gas diffusion layer 12 opposite to the anode catalyst layer 11, and the cathode gas diffusion layer 14. It was formed on the opposite surface of the cathode catalyst layer 13.

  The anode conductive layer 16 and the cathode conductive layer 17 are, for example, a porous layer (for example, mesh) or a foil body made of a metal material such as gold or nickel, or a conductive metal material such as stainless steel (SUS) such as gold. A composite material coated with a highly conductive metal can be used.

  A rubber O-ring 19 was sandwiched between the electrolyte membrane 15 and the anode conductive layer 16 and between the electrolyte membrane 15 and the cathode conductive layer 17 to seal the membrane electrode assembly 10.

On the cathode conductive layer 17, as the moisture retaining layer 20, for example, the thickness is 0.75 mm, the air permeability is 1.7 seconds / 100 cm ³ (according to the measurement method defined in JIS P-8117), and the moisture permeability Is a polyethylene porous film having a Shore hardness of D44 and 3000 g / (m ² · 24 h) (according to the measurement method defined in JIS L-1099 A-1).

  The air supplied from the outside air to the cathode will pass through the moisture retaining layer 20. A surface cover 23 was laminated as a heat radiating member on the moisture retaining layer 20. In the fuel cell according to the present embodiment, the surface cover 23 is a stainless steel plate (SUS304) having a thickness of 1.0 mm, in which, for example, 48 square air inlets 24 each having a length of 3 mm are uniformly formed.

  In the fuel cell according to the present embodiment, the surface cover 23 includes a first heat radiating member 22 and a second heat radiating member 21. The first heat radiating member 22 and the second heat radiating member 21 are configured such that the amount of heat radiated from the first heat radiating member 22 is larger than the amount of heat radiated from the second heat radiating member 21 during power generation.

  In order to make the amount of heat released from the first heat radiating member 22 larger than the amount of heat radiated from the second heat radiating member 21, for example, the surface area of the first heat radiating member 22 in contact with the outside air is larger than that of the second heat radiating member 21. It may be configured as follows. Further, the first heat radiating member 22 may be configured to have a larger area in contact with the surface of the moisture retaining layer 20 than the second heat radiating member 21. The first heat radiating member 22 may be made of a material having a higher thermal conductivity than the second heat radiating member 21.

  The first heat radiating member 22 is arranged in the plane direction (XY direction) of the membrane electrode assembly 10 so as to correspond to the first region where the temperature of the cathode increases during power generation. The second heat radiating member 21 is disposed corresponding to the second region where the temperature of the cathode is lower than that of the first region during power generation.

  The heat dissipating member is preferably made of a material having high thermal conductivity without being dissolved, corroded, oxidized, or the like by liquid fuel, water, oxygen, or the like. Specifically, metals such as stainless steel, copper, aluminum, tungsten, and molybdenum, or alloys of these metals, ceramics such as alumina ceramics, aluminum nitride, ceramics, and glass can be used. A heat conductive resin in which a powder of carbon, metal, or the like is mixed with a resin can also be used.

  Moreover, as a heat radiating member, a metal is most desirable from the viewpoint of high heat conductivity and high strength even when the wall thickness is thin. In particular, copper (thermal conductivity at 20 ° C .: 370 W / mK), aluminum (thermal conductivity at 20 ° C .: 204 W / mK), and tungsten (thermal conductivity at 20 ° C .: 198 W / mK) are preferable because of high thermal conductivity. Preferably, the surface further anodized (anodized) is used. In order to increase the emissivity to the outside air, it is particularly preferable to treat the surface with black alumite.

  However, when a metal material is used as the heat conducting material, there is a possibility that oxidation or corrosion may occur due to water generated at the cathode, oxygen or water vapor contained in the atmosphere. In order to prevent this, a material that does not corrode easily such as stainless steel (thermal conductivity at 20 ° C. of 15 W / mK) is used, or a metal that is not easily oxidized such as gold is plated on the surface of the heat radiating member, or a resin or rubber. For example, the coating may be performed or the coating may be performed with a paint that does not dissolve in the liquid fuel vapor.

  The resin or rubber for coating as described above is polyethylene, polypropylene, polystyrene, polyethylene terephthalate, nylon, polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE), tetrafluoroethylene / perfluoroalkyl vinyl ether. Resins such as copolymer (PFA), polyvinyl chloride, polyimide, and silicone resin, and rubbers such as ethylene / propylene rubber (EPDM) and fluororubber can be used. Since these resins and rubbers have lower thermal conductivity than metals, it is desirable to make the resin or rubber to be coated as thin as possible.

  The first heat radiating member 22 and the second heat radiating member 21 may be formed by cutting from a block of material, or may be integrally formed with the surface cover 23 main body in a predetermined shape by casting, forging, extrusion, or the like, or You may create combining a board | plate material, a square, a wire.

  In the case where the first heat radiating member 22 and the second heat radiating member 21 are formed by a combination of plate materials or the like, the members may be configured to contact with each other in as large an area as possible in order to improve heat conduction at the joint portion between the members. desirable. Furthermore, it is desirable to fix the contacted members by welding or the like. When fixing by welding or the like is difficult, or when it is difficult to take a large area for direct contact between members, heat conductive grease (commonly called thermal grease) is applied between the members, or a heat conductive adhesive It may be fixed with.

  A fuel supply mechanism 40 for supplying the liquid fuel F to the fuel distribution layer 30 is disposed on the anode side of the membrane electrode assembly 10. As shown in FIG. 1, the fuel supply mechanism 40 that supplies the liquid fuel F to the fuel distribution layer 30 mainly includes a fuel storage part 41, a fuel supply part 42, and a flow path 43.

  The fuel storage unit 41 stores liquid fuel F corresponding to the fuel battery cell. 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. In any case, the fuel storage unit 41 stores liquid fuel corresponding to the fuel cell.

  The fuel supply unit 42 is connected to the fuel storage unit 41 via a flow path 43 of the liquid fuel F configured by piping or the like. Liquid fuel F is introduced into the fuel supply unit 42 from the fuel storage unit 41 via the flow path 43, and the introduced liquid fuel F and / or the vaporized component of the liquid fuel F vaporized are the fuel distribution layer 30 and It is supplied to the membrane electrode assembly 10 through the anode conductive layer 16. The flow path 43 is not limited to piping independent of the fuel supply unit 42 and the fuel storage unit 41. For example, when the fuel supply unit 42 and the fuel storage unit 41 are stacked and integrated, a flow path of the liquid fuel F that connects them may be used. That is, the fuel supply unit 42 only needs to communicate with the fuel storage unit 41 through a flow path or the like.

  The liquid fuel F accommodated in the fuel accommodating part 41 can be dropped and sent to the fuel supply part 42 via the flow path 43 using gravity. Alternatively, the flow path 43 may be filled with a porous body or the like, and the liquid fuel F stored in the fuel storage section 41 may be fed to the fuel supply section 42 by capillary action. Further, the pump 44 may be interposed in a part of the flow path 43 to forcibly send the liquid fuel F stored in the fuel storage unit 41 to the fuel supply unit 42.

  The fuel distribution layer 30 is configured by, for example, a flat plate in which a plurality of openings 31 are formed, and is sandwiched between the anode gas diffusion layer 12 and the fuel supply unit 42. The fuel distribution layer 30 is made of a material that does not allow the vaporized component of the liquid fuel F or the liquid fuel F to permeate. Specifically, for example, a polyethylene terephthalate (PET) resin, a polyethylene naphthalate (PEN) resin, or a polyimide resin. Etc.

  Further, the fuel distribution layer 30 may be constituted by, for example, a gas-liquid separation membrane that separates the vaporized component of the liquid fuel F and the liquid fuel F and permeates the vaporized component to the membrane electrode assembly 10 side. 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), tetrafluoroethylene). -Perfluoroalkyl vinyl ether copolymer (PFA) etc.) A microporous film etc. are used.

[Example]
Hereinafter, a fuel cell according to an embodiment of the present invention will be described with reference to the drawings. In the following description, the same components as those of the fuel cell according to the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

(First embodiment)
A fuel cell according to this example was prepared as follows. First, to the carbon black carrying 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 are added. A paste was prepared by dispersing carbon black carrying bismuth.

  Next, porous carbon paper (80 mm × 10 mm rectangle) is prepared as the anode gas diffusion layer 12, and the thickness obtained by applying the paste obtained as described above to the anode gas diffusion layer 12 is 100 μm. The anode catalyst layer 11 was formed.

  Subsequently, to the carbon black supporting 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, and the carbon black supporting the catalyst particles for the cathode is added. A paste was prepared by dispersing.

  Next, porous carbon paper is prepared as the cathode gas diffusion layer 14, and the cathode gas diffusion layer 14 is coated with the paste obtained as described above, whereby the cathode catalyst layer 13 having a thickness of 100 μm is formed. Formed.

  The anode gas diffusion layer 12 and the cathode gas diffusion layer 14 have the same shape and size, and the anode catalyst layer 11 and the cathode catalyst layer 13 applied to the gas diffusion layers 12 and 14 have the same shape and 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 15 between the anode catalyst layer 11 and the cathode catalyst layer 13 produced as described above. , Manufactured by DuPont), each of the four anode catalyst layers 11 and the cathode catalyst layers 13 facing each other, and between the adjacent anode catalyst layers and between the cathode catalyst layers is 1 mm. The membrane electrode assembly 10 was formed by performing hot pressing in a state in which the positions were aligned so as to be parallel to each other.

  Subsequently, the membrane / electrode assembly 10 was sandwiched between gold foils having a plurality of openings to form an anode conductive layer 16 and a cathode conductive layer 17. In addition, the anode conductive layer 16 and the cathode conductive layer 17 are arranged outside the membrane electrode assembly 10 so that the four anode catalyst layers and the cathode catalyst layer are electrically connected in series. Wiring is applied. A rubber O-ring 19 was sandwiched between the electrolyte membrane 15 and the anode conductive layer 16 and between the electrolyte membrane 15 and the cathode conductive layer 17 for sealing.

Subsequently, the thickness was 0.75 mm, the porosity was 26%, the air permeability was 1.7 seconds / 100 cm ³ (according to the measurement method specified in JIS P-8117), and the moisture permeability was 3000 g / (m ² · 24h) A polyethylene porous film (measured in accordance with JIS L-1099 A-1) is cut into a rectangle having a length of 84 mm and a width of 47 mm, and laminated on the cathode conductive layer 17 to form the moisture retaining layer 20. Formed.

  If there is a space between the cathode conductive layer 17 and the moisturizing layer 20, the water vapor is condensed in the space to generate liquid water, blocking the pores of the cathode gas diffusion layer 14 and the cathode catalyst layer 13. Since there is a risk of flooding, it is desirable that the cathode conductive layer 17 and the moisturizing layer 20 be adhered as much as possible.

  Subsequently, a 1 mm thick stainless steel plate (SUS304) in which 120 square air inlets 24 each having a side length of 3 mm were uniformly formed on the moisturizing layer 20 was laminated to form a surface cover 23. In addition, if there is a space between the moisturizing layer 20 and the surface cover 23, heat conduction from the moisturizing layer 20 to the surface cover 23 is not smoothly performed, so the moisturizing layer 20 and the surface cover 23 are in close contact as much as possible. It is desirable.

  The surface cover 23 includes a first heat radiating member 22 and a second heat radiating member 21 as shown in FIGS. 1 and 2. In the fuel cell according to the present embodiment, in the planar direction (XY direction) of the membrane electrode assembly 10, the first heat radiating member 22 has a central portion (first region) of the surface cover 23 body where the temperature of the cathode increases during power generation. The second heat dissipating member 21 is disposed in the peripheral part (second region) of the main body of the surface cover 23 where the cathode temperature is lower than the central part during power generation.

  That is, as shown in FIG. 2, the first heat radiating member 22 and the second heat radiating member 21 are arranged between the long side direction (Y direction) of the membrane electrode assembly 10 between the air introduction holes 24 provided in the main body of the surface cover 23. It arrange | positions so that it may extend substantially in parallel.

  Further, in the fuel cell according to the present embodiment, as the first heat radiating member 22, three stainless steel plates (SUS304, thermal conductivity 15 W / mK at 20 ° C.) having a thickness of 0.5 mm, a length of 50 mm, and a height of 20 mm are provided. As the second heat radiation member 21, four stainless steel (SUS304) plates having a thickness of 0.5 mm, a length of 50 mm, and a height of 10 mm were used.

  In FIGS. 1 and 2, the thickness of the first heat radiating member 22 and the second heat radiating member 21 is the length in the X direction, the length is the length in the Y direction, and the height is the Z direction. Is the length of Therefore, the first heat radiating member 22 is configured to have a larger surface area in contact with the outside air than the second heat radiating member 21. That is, in the fuel cell according to this example, the heat radiation area at the center in the planar direction (XY direction) of the membrane electrode assembly 10 is larger than that at the periphery. The first heat radiating member 22 and the second heat radiating member 21 are fixed by welding so as to be in close contact with the surface of the front cover 23 main body.

  With this configuration, all of the front cover 23 main body, the first heat radiating member 22, and the second heat radiating member 21 function as a heat radiating member, and the planar direction (XY) of the membrane electrode assembly 10 It is possible to increase the heat radiation area in the center portion than the heat radiation area in the peripheral portion in the direction).

  Pure methanol having a purity of 99.9% by weight was supplied to the fuel cell prepared as described above in an environment having a temperature of 25 ° C. and a relative humidity of 50%. A constant voltage power supply was connected to control the current flowing through the fuel cell so that the output voltage of the fuel cell was constant at 0.3V.

  Under the above conditions, the output density P1 of the fuel cell after 1000 hours of power generation and the output density P0 of the fuel cell when power generation was started were measured. Then, a ratio (P1 / P0) of the output density P1 to the output density P0 was calculated. The result is shown in FIG.

Here, the output density (mW / cm ² ) of the fuel cell is obtained by multiplying the current density flowing through the fuel cell (current value per 1 cm ² area of the power generation unit (mA / cm ² )) by the output voltage of the fuel cell. Is. The area of the power generation unit is the area of the portion where the anode catalyst layer 11 and the cathode catalyst layer 13 are opposed to each other. In this embodiment, since the anode catalyst layer 11 and the cathode catalyst layer 13 have the same area and are completely opposed to each other, the area of the power generation unit is equal to the area of these catalyst layers.

The ratio (P1 / P0) of the calculated output density P1 to the output density P0 was 0.90 (90%).

  In addition, as shown in FIG. 2, the cathode gas diffusion layer 14 and the cathode conductive layer 17 in the central measurement unit A2 and the peripheral measurement unit A1 in the planar direction (XY direction) of the membrane electrode assembly 10 A thermocouple was inserted between them, and the temperature of the surface of the cathode gas diffusion layer 14 when the fuel cell was generating power was measured. As a result of the measurement, the temperature of the surface of the cathode gas diffusion layer 14 in the measurement part A2 in the central part was 55 ° C., and the temperature of the surface of the cathode gas diffusion layer 14 in the measurement part A1 in the peripheral part was 50 ° C.

(Second embodiment)
Next, a fuel cell according to a second embodiment of the present invention will be described below with reference to the drawings. In the following description, the same components as those of the fuel cell according to the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In the fuel cell according to the present embodiment, the first heat radiating member 22 and the second heat radiating member 21 are arranged on the surface of the front cover 23 main body as shown in FIG. That is, the first heat dissipating member 22 is disposed at the center portion of the surface cover 23 main body where the cathode temperature is high during power generation, and the second heat dissipating member 21 is the surface cover 23 main body where the cathode temperature is lower than the central portion during power generation. Located in the periphery.

  Furthermore, in the fuel cell according to the present embodiment, as shown in FIG. 3, the first heat radiating member 22 and the second heat radiating member 21 are arranged between the air introduction holes 24 provided in the main body of the surface cover 23. It arrange | positions so that it may extend substantially in parallel with 10 short side directions (X direction).

  In the fuel cell according to the present embodiment, four stainless steel (SUS304) plates having a thickness of 0.5 mm, a length of 34 mm, and a height of 20 mm are used as the first heat dissipation member 22, and the thickness of the second heat dissipation member 21 is 0 mm. 6 stainless steel (SUS304) plates of 5 mm, 34 mm in length and 10 mm in height were used.

  In FIG. 3, the thickness of the first heat radiating member 22 and the second heat radiating member 21 is the length in the Y direction, the length is the length in the X direction, and the height is the length in the Z direction. It is. Therefore, in the fuel cell according to the present embodiment, the first heat radiating member 22 is configured to have a larger surface area in contact with the outside air than the second heat radiating member 21. That is, in the fuel cell according to this example, the heat radiation area at the center in the planar direction (XY direction) of the membrane electrode assembly 10 is larger than that at the periphery.

  In the fuel cell according to the second embodiment, when the ratio (P1 / P0) of the output density P1 to the output density P0 is calculated in the same manner as in the fuel cell according to the first embodiment, 0.92 (92 %)Met. Further, in the fuel cell according to the second example, the value of the output density P0 when power generation was started was 98% with respect to the value of the output density P0 of the fuel cell according to the first example.

  Further, as in the case of the fuel cell according to the first example, the temperature of the surface of the cathode gas diffusion layer 14 when the fuel cell according to the present example is generating power is measured. The temperature of the part A2 was 54 ° C., and the temperature of the peripheral measurement part A1 was 50 ° C.

(Third embodiment)
Next, a fuel cell according to a third embodiment will be described below with reference to the drawings. In the fuel cell according to this example, three sets of the first heat radiating members 22 and four pieces of the second heat radiating members 21 were arranged on the surface of the main body of the surface cover 23 as shown in the plan views shown in FIGS.

  In the fuel cell according to the present embodiment, the first heat radiating member 22 is formed by combining the first plate member 22A and the second plate member 22B. That is, each first heat radiating member 22 has a thickness of 0.5 mm as a first plate member 22A, a stainless steel (SUS304) plate having a length of 50 mm and a length of 10 mm, and a thickness of 0.5 mm as a second plate member 22B. There are 10 stainless steel plates with a height of 5 mm and a height of 10 mm. As shown in FIGS. 4 and 5, the first plate member 22A and the second plate member 22B are combined so as to be orthogonal to each other in the length direction and fixed by welding. As the second heat radiating member 21, four stainless steel (SUS304) plates having a thickness of 0.5 mm, a length of 50 mm, and a height of 10 mm are used.

  4 and 5, the thickness of the first plate member 22A and the second heat radiating member 21 of the first heat radiating member 22 is the length in the X direction, and the length is the length in the Y direction. The height is the length in the Z direction. The thickness of the second plate member 22B of the first heat radiating member 22 is the length in the Y direction, the width is the length in the X direction, and the height is the length in the Z direction.

  Therefore, the first heat radiating member 22 is configured to have a larger surface area in contact with the outside air than the second heat radiating member 21. Further, the first heat radiating member 22 is configured to have a larger area in contact with the moisture retaining layer 20 through the front cover 23 body than the second heat radiating member 21.

  The first heat radiating member 22 may be fixed so that the first plate member 22A and the second plate member 22B are not at the same height, as shown in FIG. As shown in FIG. 6, the second plate member 22B is fixed to the first plate member 22A so as not to contact the surface of the front cover 23 main body. The area in contact with can be increased. That is, in the fuel cell according to this example, the heat radiation area and the heat conduction area at the center in the planar direction (XY direction) of the membrane electrode assembly 10 are larger than those at the periphery.

  In the fuel cell according to the third embodiment, when the ratio (P1 / P0) of the output density P1 to the output density P0 is calculated in the same manner as in the fuel cell according to the first embodiment, 0.90 (90% )Met. Further, in the fuel cell according to this example, the value of the output density P0 when power generation was started was 100% with respect to the value of the output density P0 of the fuel cell according to the first example.

  Further, as in the case of the fuel cell according to the first example, the temperature of the surface of the cathode gas diffusion layer 14 when the fuel cell is generating power is measured. At 55 ° C., the temperature of the peripheral measurement portion A1 was 50 ° C.

(Fourth embodiment)
Next, a fuel cell according to a fourth embodiment of the present invention will be described below with reference to the drawings. In the fuel cell according to the present embodiment, as shown in FIG. 7, as the first heat radiating member 22, three stainless steel (SUS304) plates having a thickness of 2.0 mm, a length of 50 mm, and a height of 10 mm were used. This is the same as the fuel cell according to the first embodiment.

  In the case shown in FIG. 7, the thickness of the first heat radiating member 22 is the length in the X direction, the length is the length in the Y direction, and the height is the length in the Z direction. Therefore, the first heat radiating member 22 is configured to have a larger surface area in contact with the outside air than the second heat radiating member 21. Further, the first heat radiating member 22 is configured to have a larger area in contact with the moisture retaining layer 20 through the front cover 23 body than the second heat radiating member 21. That is, in the fuel cell according to this example, the heat radiation area and the heat conduction area at the center in the planar direction (XY direction) of the membrane electrode assembly 10 are larger than those at the periphery.

  In the fuel cell according to the fourth embodiment, when the ratio (P1 / P0) of the output density P1 to the output density P0 is calculated in the same manner as in the fuel cell according to the first embodiment, 0.90 (90 %)Met. Further, in the fuel cell according to this example, the value of the output density P0 when power generation was started was 97% with respect to the value of the output density P0 of the fuel cell according to the first example.

  Further, as in the case of the fuel cell according to the first example, as a result of measuring the temperature of the surface of the cathode gas diffusion layer 14 when the fuel cell according to this example is generating electric power, The temperature of A2 was 56 ° C., and the temperature of the peripheral measurement portion A1 was 51 ° C.

(5th Example)
Next, a fuel cell according to a fifth embodiment of the present invention will be described below with reference to the drawings. In the fuel cell according to the present example, the first heat radiating member 22 was formed by using three aluminum (heat conductivity 204 W / mK at 20 ° C.) plates having a thickness of 0.5 mm, a length of 50 mm, and a height of 10 mm. This is the same as the fuel cell according to the first embodiment.

  However, since it is difficult to weld the aluminum plate and the stainless steel plate, in the fuel cell according to the present embodiment, as shown in FIG. 8, the first heat radiating member 22 bends the position in contact with the front cover 23 main body, A cross section substantially orthogonal to the length direction is formed in a substantially L shape. That is, the cross section of the first heat radiating member 22 is substantially L-shaped to increase the area in contact with the front cover 23 body.

  A heat conductive adhesive (model number TA-01 manufactured by Arctic Silver, thermal conductivity 7.5 W / mK at 20 ° C.) is applied to the adhesive surface of the first heat radiating member 22 with the main body of the surface cover 23. It adhered to the surface of 23.

  In the fuel cell according to the fifth embodiment, when the ratio (P1 / P0) of the output density P1 to the output density P0 is calculated in the same manner as in the fuel cell according to the first embodiment, 0.90 (90 %)Met. Further, in the fuel cell according to the fifth example, the value of the output density P0 when power generation was started was 102% with respect to the value of the output density P0 of the fuel cell according to the first example.

  As in the case of the fuel cell according to the first embodiment, the temperature of the surface of the cathode gas diffusion layer 14 when the fuel cell is generating power is measured. The temperature was 53 ° C., and the temperature of the peripheral measurement part A1 was 49 ° C.

(First comparative example)
Next, the fuel cell according to the first comparative example will be described. In the fuel cell according to this comparative example, the first heat radiating member 22 and the second heat radiating member 21 are not provided, and only the front cover 23 main body is used as the heat radiating member. Except for the above points, the fuel cell is the same as the fuel cell according to the first embodiment.

  In the fuel cell of the first comparative example, when the ratio (P1 / P0) of the output density P1 to the output density P0 is calculated in the same manner as in the fuel cell according to the first embodiment, 0.90 (90% )Met. Further, in the fuel cell according to the first comparative example, the value of the output density P0 when power generation was started was 90% with respect to the value of the output density P0 of the fuel cell according to the first example.

  As in the case of the fuel cell according to the first embodiment, the temperature of the surface of the cathode gas diffusion layer 14 when the fuel cell is generating power is measured. The temperature was 57 ° C., and the temperature of the peripheral measurement part A1 was 52 ° C.

(Second comparative example)
Next, a fuel cell according to a second comparative example will be described. In the fuel cell according to this comparative example, a stainless steel (SUS304) plate having a thickness of 0.5 mm, a length of 50 mm, and a height of 20 mm, which is the same as the first heat dissipation member 22, is used for the second heat dissipation member 21. Except for the above points, the fuel cell is the same as that of the first embodiment. That is, in the fuel cell according to this comparative example, the area of the first heat radiating member 22 in contact with the outside air and the area of the second heat radiating member 21 in contact with the outside air are the same.

  In the fuel cell according to the second comparative example, when the ratio (P1 / P0) of the output density P1 to the output density P0 is calculated in the same manner as in the fuel cell according to the first embodiment, 0.85 (85 %)Met. Further, in the fuel cell according to the second comparative example, the value of the output density P0 when power generation was started was 94% with respect to the value of the output density P0 of the fuel cell according to the first example.

  Further, as in the case of the fuel cell according to the first example, the temperature of the surface of the cathode gas diffusion layer 14 when the fuel cell is generating power is measured. The temperature of the peripheral measurement part A1 was 47 ° C. at 52 ° C.

  An example of the evaluation results of the fuel cells according to the first to fifth examples and the fuel cells according to the first to second comparative examples is shown in FIG. As shown in FIG. 9, the fuel cell according to the first to third embodiments in which the heat radiation area in the central portion in the plane direction (XY direction) of the membrane electrode assembly 10 is larger than that in the peripheral portion, the heat in the central portion. In the fuel cell according to the fourth embodiment in which the conduction cross-sectional area is larger than the peripheral portion, and the fuel cell according to the fifth embodiment in which the thermal conductivity of the first heat radiating member 22 is larger than that of the second heat radiating member 21, In both cases, both the power density at the start of power generation and the power density after 1000 hours of power generation are equal to or higher than those of the fuel cells according to the first comparative example and the second comparative example. Yes.

  That is, it is shown that the fuel cells according to the first to fifth embodiments have a high output and can stably maintain the output over a long period of time.

  Further, in the fuel cell according to the first comparative example in which the first heat radiating member 22 and the second heat radiating member 21 are not provided and only the front cover 23 main body is used as the heat radiating member, the output density when the power generation is started is first to first. It is lower than that of the fuel cell according to the fifth embodiment.

  This is because the first heat radiating member 22 and the second heat radiating member 21 are not provided, so that the amount of heat dissipated from the cathode to the outside air is small and the temperature of the cathode rises, so that the amount of water supplied from the cathode to the anode is sufficient. This is considered to be because the oxidation reaction of the liquid fuel in the anode catalyst layer 11 was not performed smoothly.

  Further, in the fuel cell according to the second comparative example using the same first heat radiating member 22 and second heat radiating member 21, the power density after 1000 hours of power generation relates to the first to fifth embodiments. Compared to fuel cells.

  This is because, in the planar direction (XY direction) of the membrane electrode assembly 10, although the temperature of the cathode of the membrane electrode assembly 10 is low in the peripheral part, the amount of heat released to the outside air is the same as that in the central part. If the water vapor generated at the cathode is condensed more than necessary and the amount of water retained in the cathode catalyst layer is larger than necessary, and the power generation time is prolonged, the pores of the cathode catalyst layer and the like are blocked with water. This is thought to be because the output decreased due to flooding.

  That is, from the above results, according to the fuel cell according to the present embodiment, the amount of water retained in the cathode constituting the membrane electrode assembly and the amount of water supplied from the cathode to the anode are A fuel cell that maintains a stable output over a long period of time can be provided by maintaining it in an appropriate range in all parts of the direction.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage.

  Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

1 is a diagram schematically showing a configuration example of a fuel cell according to a first embodiment of the present invention. The figure for demonstrating one structural example of the surface cover of the fuel cell which concerns on 1st Example of this invention. The figure for demonstrating one structural example of the surface cover of the fuel cell which concerns on 2nd Example of this invention. The figure which shows roughly the example of 1 structure of the fuel cell which concerns on 3rd Example of this invention. The figure for demonstrating one structural example of the surface cover of the fuel cell which concerns on 3rd Example of this invention. The figure for demonstrating the other structural example of the surface cover of the fuel cell which concerns on 3rd Example of this invention. The figure which shows roughly the example of 1 structure of the fuel cell which concerns on 4th Example of this invention. The figure which shows roughly the example of 1 structure of the fuel cell which concerns on 5th Example of this invention. The figure for demonstrating an example of the evaluation result of the fuel cell which concerns on the 1st thru | or 5th Example of this invention, and the 1st thru | or 2nd comparative example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Membrane electrode assembly, 11 ... Anode catalyst layer, 12 ... Anode gas diffusion layer, 13 ... Cathode catalyst layer, 14 ... Cathode gas diffusion layer, 15 ... Electrolyte membrane, 16 ... Anode conductive layer, 17 ... Cathode conductive layer, 21 ... 2nd heat radiating member, 22 ... 2nd heat radiating member, 23 ... Surface cover, 40 ... Fuel supply mechanism

Claims (5)

A membrane electrode assembly comprising a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode;
A fuel supply mechanism disposed on the fuel electrode side of the membrane electrode assembly for supplying fuel to the fuel electrode;
A moisture retention layer disposed on the air electrode side of the membrane electrode assembly and impregnated with water generated by the air electrode;
A heat radiating member in contact with the surface of the moisture retaining layer and dissipating heat to the outside air, and
The heat dissipating member is disposed corresponding to a region where the temperature of the air electrode is low and a first heat dissipating member disposed corresponding to a region where the temperature of the air electrode is high in the planar direction of the membrane electrode assembly. A second heat dissipating member,
A fuel cell configured such that a heat dissipation amount from the first heat dissipation member is larger than a heat dissipation amount from the second heat dissipation member during power generation.   The fuel cell according to claim 1, wherein the first heat radiating member has a larger surface area in contact with outside air than the second heat radiating member.   The fuel cell according to claim 1, wherein the first heat radiating member has a larger area in contact with the surface of the moisture retaining layer than the second heat radiating member.   4. The fuel cell according to claim 1, wherein the first heat radiating member has a higher thermal conductivity than the second heat radiating member. 5.   In the planar direction of the membrane electrode assembly, the first heat dissipating member is disposed so as to be in contact with a central portion of the air electrode, and the second heat dissipating member is disposed so as to be in contact with a peripheral portion of the air electrode. The fuel cell according to any one of claims 1 to 4.

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