JP2010033839A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the supply amount of fuel and air to be supplied to an MEA, increase output of a fuel cell, and improve efficiency of power generation reaction and stability with the passage of time of the fuel cell. <P>SOLUTION: The fuel cell is provided with the MEA 1 having an anode 4, a cathode 7, and an electrolyte membrane 8, and a seal material 11 arranged at the outside of the anode 4 and the cathode 7, and a fuel supply mechanism 14 to supply a liquid fuel to this MEA 1. Then, a space portion S having a bottom surface area of 0.2-1.3 times of the electrode area is installed between the seal material 11 and the electrode on at least one of the anode 4 side and the cathode 7 side of the MEA 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In recent years, in order to use electronic devices such as notebook computers and mobile phones without charging them for a long time, attempts have been made to use a fuel cell as a power source for these portable electronic devices. A fuel cell has a feature 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. Therefore, 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 particularly expected as a power source for portable electronic devices because it can be downsized and the fuel can be easily handled. As a fuel supply method in the DMFC, there are 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 storage portion is vaporized inside the cell and supplied to the fuel electrode (anode). Are known.

  Among these, a passive system such as an internal vaporization type is particularly advantageous for downsizing of the DMFC. In a passive type DMFC, a membrane electrode assembly (MEA) having a fuel electrode (anode), an electrolyte membrane, and an air electrode (cathode) is disposed on a fuel storage section made of a resin-made box-shaped container. A structure has been proposed (see, for example, Patent Document 1).

In such a passive method, methanol having a higher concentration than that in the active method is used in order to secure a supply amount of fuel, but water (H ₂ O) necessary for the reaction at the anode is generated at the cathode. Water is supplied by back diffusion to the anode.

  However, since the fuel introduced in the liquid state is once vaporized and then supplied to the MEA, the amount of fuel supplied is limited compared to the active method. In addition, in a passive type fuel cell, when fuel is supplied by an active method, the liquid supply pressure that is generated does not occur. Therefore, from the viewpoint of promoting the reaction, carbon dioxide generated by the anode reaction is quickly removed from the reaction system. It is important to escape. Furthermore, the supply of air (oxygen) to the cathode also depends on natural convection, so that it cannot be forced to supply air, so there is a risk that the reactivity may decrease due to the retention of air or heat on the cathode side. .

  In addition, in a passive fuel cell, it is necessary to release carbon dioxide generated by the electrode reaction on the anode side to the outside air. Conventionally, a gas vent is provided on the side surface of the container on the anode side to release gas components out of the system. To be considered. As another configuration, it has been studied to provide a gas vent hole in the electrolyte membrane so that carbon dioxide generated on the anode side is released to the cathode side.

However, in such a configuration, a part of the fuel gas supplied to the anode and a part of the water (H ₂ O) diffused from the cathode catalyst layer to the anode catalyst layer pass through the gas vent hole together with carbon dioxide. As a result, the reaction on the anode side is not sufficiently performed and the output is reduced. This problem is because the higher the temperature of the membrane electrode assembly (MEA) and the higher the saturated vapor pressure of the fuel (methanol) or water present on the anode side, the easier it is for methanol or water to be discharged as vapor from the vent hole. , Became prominent.

Furthermore, the more the amount of water discharged from the anode side, the MEA is the amount of water contained is reduced, a problem that conductivity of protons (H ⁺⁾ in the electrolyte membrane is lowered, the output of the fuel cell is lowered There was also.
International Publication No. 2005/112172 Pamphlet

  The present invention has been made in view of the above-described problems, and provides a high-power fuel cell by increasing the amount of fuel and air that are reactants supplied to the membrane electrode assembly (MEA). The purpose is to do. In addition, by improving the removability of the gas component generated on the anode side of the membrane electrode assembly (MEA) accompanying the power generation reaction, a fuel cell with improved power generation reaction efficiency and stability over time is provided. Objective.

  A fuel cell according to an aspect of the present invention includes a fuel electrode (anode) and an air electrode (cathode), a proton conductive electrolyte membrane sandwiched between the fuel electrode and the air electrode, and the fuel electrode and the air electrode. A membrane electrode assembly (MEA) having a seal portion provided around each of the outer sides, a fuel storage portion for storing liquid fuel, and the liquid fuel stored in the fuel storage portion of the membrane electrode assembly In the fuel cell comprising a fuel supply mechanism for supplying to the fuel electrode, at least one of the fuel electrode side and the air electrode side of the membrane electrode assembly, the seal portion and the fuel electrode or the air electrode A space portion having a bottom area of 0.2 to 1.3 times the area of the fuel electrode or air electrode is provided therebetween.

  According to the fuel cell according to the aspect of the present invention, the supply amount of fuel and air, which are reactants, supplied to the membrane electrode assembly (MEA) is increased, and a stable high output can be obtained.

  Hereinafter, a fuel cell according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the fuel cell according to the first embodiment of the present invention has a membrane electrode assembly (MEA) 1.

  The MEA 1 is sandwiched between the anode 4 having the anode catalyst layer 2 and the anode gas diffusion layer 3, the cathode 7 having the cathode catalyst layer 5 and the cathode gas diffusion layer 6, and the anode catalyst layer 2 and the cathode catalyst layer 5. The proton-conducting electrolyte membrane 8 is provided.

  The anode catalyst layer 2 and the cathode catalyst layer 5 are portions where a catalyst that mediates an electrode reaction is disposed, and contains a catalyst component. Examples of the catalyst component include single metals such as platinum group elements such as Pt, Ru, Rh, Ir, Os, and Pd, and alloys containing these platinum group elements. The catalyst components contained in the anode catalyst layer 2 and the cathode catalyst layer 5 may be the same or different, and the composition is not particularly limited. The anode catalyst layer 2 preferably contains a large amount of platinum, a platinum alloy, a palladium alloy, etc. from the viewpoint of catalytic activity, and preferably contains a large amount of a palladium alloy (for example, palladium-cobalt alloy) from the viewpoint of production cost. . The cathode catalyst layer 5 preferably contains a large amount of platinum or a platinum alloy (for example, a platinum-iridium alloy or a platinum-rhodium alloy) from the viewpoint of catalytic activity. A supported catalyst in which fine particles of these catalysts are supported on a conductive carrier may be used. As the conductive carrier, particulate carbon such as activated carbon or graphite, or fibrous carbon is used.

  The anode catalyst layer 2 and the cathode catalyst layer 5 can contain an electrolyte having proton conductivity together with the catalyst component. The proton-conductive electrolyte moves with the progress of power generation (anode catalyst layer → electrolyte membrane → cathode catalyst layer) and plays a role in improving the mobility of protons. As the proton conductive electrolyte contained in the catalyst layer, the same type as the polymer electrolyte constituting the electrolyte membrane 8 described later can be used.

  The blending ratio of the catalyst component in the anode catalyst layer 2 and the cathode catalyst layer 5, the carbon material as the conductive support, and the proton conductive electrolyte is not particularly limited. The anode catalyst layer 2 and the cathode catalyst layer 5 do not necessarily have to be one layer, and may have a multilayer structure in which two or more layers are laminated. At this time, for example, the catalyst content or the type of the carbon material may be changed between the layers.

  The anode gas diffusion layer 3 and the cathode gas diffusion layer 6 diffuse the gas supplied to the MEA 1 (a methanol-containing gas that is a fuel gas at the anode 4 and an oxygen-containing gas such as air at the cathode 7) to the catalyst layer. And has the function of supplying. That is, the anode gas diffusion layer 3 has a function of uniformly supplying the fuel gas to the anode catalyst layer 2. Further, the anode catalyst layer 2 also has a function as a current collector. The cathode gas diffusion layer 6 has a function of uniformly supplying air as an oxidant to the cathode catalyst layer 5, and also has a function as a current collector of the cathode catalyst layer 5.

  The anode gas diffusion layer 3 and the cathode gas diffusion layer 6 are each made of a conductive material. A known material can be used as the conductive material, but it is preferable to use a porous carbon woven fabric or carbon paper in order to efficiently transport the fuel gas and air to the catalyst. Specific forms of the anode gas diffusion layer 3 and the cathode gas diffusion layer 6 include carbon paper, carbon cloth, carbon non-woven fabric, carbon woven fabric, paper-like paper body, felt and the like.

  The proton conductive electrolyte membrane 8 is disposed between the anode catalyst layer 2 and the cathode catalyst layer 5. Examples of the proton conductive electrolyte membrane 8 include a fluorine-based resin having a sulfonic acid group such as a perfluorosulfonic acid polymer (trade name Nafion (manufactured by DuPont), trade name Flemion (manufactured by Asahi Glass Co., Ltd.)), Examples thereof include, but are not limited to, hydrocarbon resins having a sulfonic acid group.

  An anode conductive layer 9 is stacked on the anode gas diffusion layer 3 of the MEA 1 configured as described above, and a cathode conductive layer 10 is stacked on the cathode gas diffusion layer 6. The anode conductive layer 9 and the cathode conductive layer 10 have through holes through which fuel, oxidant (air), and the like circulate. Examples of the constituent material of the anode conductive layer 9 and the cathode conductive layer 10 include a porous film (for example, a mesh) or a foil body made of a conductive metal such as gold or nickel, or a conductive metal such as stainless steel (SUS). A composite material coated with a highly conductive metal such as gold can be used. Carbon materials such as graphite (graphite) can also be used.

  Between the proton conductive electrolyte membrane 8 and the anode conductive layer 9 and around the anode 4 (the anode catalyst layer 2 and the anode gas diffusion layer 3), for example, the cross section is O-shaped and the planar shape is a rectangular frame shape. The sealing material (O-ring) 11 is provided. A sealing material (O-ring) 11 having the same shape is also provided between the proton conductive electrolyte membrane 8 and the cathode conductive layer 10 and around the cathode 7 (cathode catalyst layer 5 and cathode gas diffusion layer 6). Is provided. These sealing materials 11 are for preventing fuel leakage and oxidant leakage from the MEA 1, and are made of an elastic body such as rubber.

  In the first embodiment, as shown in FIGS. 2 and 3A and 3B, the periphery of the sealing material 11 and the electrode (the anode 4 or the cathode 7) on the anode 4 side and the cathode 7 side of the MEA 1 is used. A space S having a bottom area 0.2 to 1.3 times the area of the electrode (the anode 4 or the cathode 7) is provided between the ends. In this embodiment, the configuration in which the space portion S is provided on both the anode 4 side and the cathode 7 side is shown, but the space portion S may be provided only on one side.

  A fuel-resistant (for example, methanol-resistant) organic film (not shown) is provided so as to separate the anode 4 side and the cathode 7 side of the space S. In such a structure, the space S on the anode 4 side is a space surrounded on three sides by the organic film, the sealing material 11 and the end face of the anode 4, and the space S on the cathode 7 side is sealed with the organic film and the seal. It is a space surrounded on three sides by the end surfaces of the material 11 and the cathode 7.

  It is also possible to increase the area of the proton conductive electrolyte membrane 8 so that the peripheral end of the electrolyte membrane 8 reaches the sealing material 11. In this configuration, it is not necessary to arrange the organic film that separates the anode 4 side and the cathode 7 side. And since the catalyst layer is not laminated | stacked in the part which enlarged the area of the electrolyte membrane 8, this area | region can participate in water retention. Therefore, the amount of water returning (diffusing) from the cathode 7 side to the anode 4 side can be increased, and a higher output can be obtained.

  Thus, by providing the space S on at least one of the anode 4 side and the cathode 7 side of the MEA 1, the intake port of the fuel to the anode 4 or the intake port of air as an oxidizer to the cathode 7 is expanded. And the supply amount of the reactant to the MEA 1 can be increased. As a result, the output per unit catalyst amount can be increased. When the bottom area of the space S is less than 0.2 times the area of the electrode (anode 4 or cathode 7), the amount of reactant supplied cannot be increased sufficiently. In addition, when the bottom area 11 of the space S exceeds 1.3 times the electrode area, the volume occupied by the electrode serving as the power generation unit with respect to the entire volume of the fuel cell becomes too small, so that the balance between fuel supply and heat generation is reduced. It is hard to take. In either case, it is difficult to obtain a high output.

  A moisturizing layer 12 is laminated and disposed on the cathode conductive layer 10 of the MEA 1 configured as described above. The moisturizing layer 12 has a function of suppressing transpiration of water generated in the cathode catalyst layer 5 and diffusing part of the generated water to the anode 4 side in order to supply water necessary for the reaction at the anode 4. . The cathode gas diffusion layer 6 also has a function as an auxiliary diffusion layer that uniformly introduces air as an oxidant and promotes uniform diffusion of the oxidant into the cathode catalyst layer 5. As the moisture retaining layer 12, for example, a porous polyethylene film can be used.

  A surface cover (cover plate) 13 having a plurality of air inlets 13a for taking in air as an oxidant is disposed on the moisturizing layer 12. The front cover 13 also plays a role of increasing the adhesion by pressurizing the MEA 1 and the moisture retaining layer 12 and is made of a metal such as SUS304.

  A heat radiator (not shown) may be provided on the surface, side surface, or the vicinity thereof of the surface cover 13 in order to promote heat radiation from the surface cover 13 to the outside air. As a constituent material of the radiator, metals such as stainless steel, copper, aluminum, tungsten, and molybdenum, alloys of these metals, and ceramics such as alumina, 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.

  As a constituent material of the radiator, metal is most desirable because it has high thermal conductivity and high strength even when thin. In terms of high thermal conductivity, copper (thermal conductivity at 20 ° C. is 370 W / mK), aluminum (thermal conductivity at 20 ° C. is 204 W / mK), tungsten (thermal conductivity at 20 ° C. is 198 W / mK) Is particularly preferred. Furthermore, it is preferable to use aluminum whose surface is anodized (anodized), and in particular, it is preferable to use a material whose surface is black anodized in order to increase the heat emissivity to the outside air.

  The radiator may be manufactured from a material integral with the surface cover 13, and a separately manufactured member may be manufactured by means of welding, bolts, rivets, caulking, soldering, brazing, bonding, fitting, etc. You may fix to 13. Furthermore, the surface cover 13 and the heat radiating body do not necessarily have to be fixed, and may be simply in contact if heat conduction is sufficiently performed. A heat conductive grease can be applied between the surface cover 13 and the heat radiating body, or can be fixed with a heat conductive adhesive.

  A fuel supply mechanism 14 is disposed on the anode 4 side of the MEA 1. The fuel supply mechanism 14 includes a fuel storage unit 15, a fuel supply unit 16, a fuel distribution layer 17, and a flow path 18 such as a pipe.

  Liquid fuel F is stored in the fuel storage portion 15. As the liquid fuel F, a methanol aqueous solution or pure methanol is preferable. Moreover, although what has a density | concentration of 50 mol% or more is used suitably, it is not necessarily limited. 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. .

  The fuel supply unit 16 is connected to the fuel storage unit 15 via a flow path 18 constituted by piping or the like, and the liquid fuel F is introduced from the fuel storage unit 15 to the fuel supply unit 16 via the flow path 18. The The flow path 18 is not limited to piping independent from the fuel supply unit 16 and the fuel storage unit 15. For example, when the fuel supply unit 16 and the fuel storage unit 15 are stacked and integrated, a flow path of the liquid fuel F that connects them may be used.

  The fuel supply unit 16 has a fuel injection port 16a into which liquid fuel F flows, and a fuel distribution layer 17 having a plurality of fuel discharge ports 17a is disposed on the side in contact with the anode 4 (anode conductive layer 9). Has been.

  The liquid fuel F stored in the fuel storage unit 15 can be dropped and sent to the fuel supply unit 16 via the flow path 18 using gravity. Alternatively, the flow path 18 may be filled with a porous body or the like and fed to the fuel supply unit 16 by capillary action. Further, a pump may be interposed in a part of the flow path 18 to forcibly send the liquid fuel F stored in the fuel storage unit 15 to the fuel supply unit 16.

  The fuel distribution layer 17 is sandwiched between the anode conductive layer 9 and the fuel supply unit 16. The fuel distribution layer 17 is made of a material that does not allow the liquid fuel F and its vaporized components to permeate, such as polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, and polyimide resin, and has a plurality of openings. (Fuel discharge port 17a). Further, the fuel distribution layer 17 may be formed of a gas-liquid separation membrane having a function of separating the liquid fuel F and its vaporized component and allowing the vaporized component of the liquid fuel F to permeate to the MEA 1 side. Examples of gas-liquid separation membranes include silicone rubber thin films, low density polyethylene (LDPE) thin films, polyvinyl chloride (PVC) thin films, polyethylene terephthalate (PET) thin films, polytetrafluoroethylene (PTFE), tetrafluoroethylene perfluoro. A microporous film of a fluororesin such as an alkyl vinyl ether copolymer (PFA) is used.

  In the fuel cell of the first embodiment configured as described above, between at least one of the anode 4 side and the cathode 7 side of the MEA 1 and between the sealing material 11 and the peripheral end of the anode 4 or the cathode 7 as an electrode. Is provided with a space S having a bottom area 0.2 to 1.3 times the area of the anode 4 or the cathode 7 as an electrode, and the formation of the space S results in the cathode of air as an oxidant. Since the intake port to 7 or the fuel intake port to the anode 4 is widened, the supply amount of air or fuel as reactants to the MEA 1 can be increased. Therefore, the output of the fuel cell can be improved and a high output can be maintained over a long period of time.

  Next, second and third embodiments of the fuel cell of the present invention will be described. FIG. 4 shows the MEA 1 in the fuel cell of the second embodiment, and FIGS. 5 and 6 show the MEA 1 in the fuel cell of the third embodiment. In these drawings, the moisturizing layer, the surface cover, the fuel supply unit, the fuel storage unit, and the like are not shown, but the fuel cells of the second and third embodiments include these elements. The specific configuration of each element is the same as that of the fuel cell of the first embodiment described above.

  In the second embodiment, as shown in FIG. 4, an electrode (anode 4 or cathode 7) is laminated on at least one surface side of the proton conductive electrolyte membrane 8 on the anode 4 side and the cathode 7 side. An organic film 19 having no fuel permeability is affixed to a region corresponding to the space portion S between the peripheral end portion of the electrode and the sealing material 11. 4 shows a configuration in which the organic film 19 is attached only to the anode 4 side surface of the electrolyte membrane 8, it may be attached to the cathode 7 side surface or may be attached to both surfaces. . The organic film 19 having no fuel permeability is preferably an organic film having heat resistance and fuel resistance up to 100 ° C., specifically, a polyimide resin tape having an adhesive layer or Teflon ((registered trademark) polytetrafluoro). Ethylene) tape and the like are exemplified. Such an organic film 19 may be thermocompression bonded to the electrolyte membrane 8.

  In the fuel cell according to the second embodiment configured as described above, the crossover of fuel from the anode 4 side to the cathode 7 side is suppressed, so that the output voltage is improved. The size of the organic film 19 is preferably set to a size that covers the entire exposed region of the electrolyte membrane 8 up to the position where the sealing material 11 is disposed. If the organic film 19 laminated on the electrolyte membrane 8 is too small, the electrolyte membrane 8 in a region sandwiched between the peripheral portion of the organic film 19 and the sealing material 11 may be torn due to stress due to expansion / contraction. In particular, in the configuration in which the fuel is crossed over on the anode 4 side, the organic film 19 is not attached, but the catalyst is formed on the electrolyte membrane 8 between the peripheral edge of the electrode and the sealing material 11. The layer itself may be applied.

  In the third embodiment, as shown in FIGS. 5 and 6, the proton conductive electrolyte membrane 8 has a through hole (gas vent hole) 20. This through hole (gas vent hole) 20 is for releasing a gas component generated on the anode 4 side in response to the power generation reaction to the cathode 7 side, and is a region where the anode 4 or the cathode 7 of the electrolyte membrane 8 is laminated. One or a plurality of portions are provided in a region corresponding to the space portion S between the peripheral end portion of the electrode and the portion where the seal member 11 is disposed, that is, between the peripheral end portion of the electrode and the sealing material 11. Yes. The ratio of the saturated water vapor pressure at the position of the vent hole 20 to the saturated water vapor pressure at the position where the saturated water vapor pressure is highest (that is, the temperature is highest) on the cathode 7 side of the electrolyte membrane 8 is 0.8 or less. It has become. The ratio of the saturated fuel vapor pressure at the position of the vent hole 20 (for example, saturated methanol vapor pressure) to the saturated fuel vapor pressure at the position where the saturated fuel vapor pressure is highest on the cathode 7 side of the electrolyte membrane 8 is also 0. It is 8 or less. In the configuration in which the electrolyte membrane 8 does not have an area reaching the sealing material 11 and the fuel-resistant organic film is arranged so as to extend outward from the peripheral end portion of the electrolyte membrane 8, this fuel-resistant organic film. You may provide a through-hole (gas vent hole) in.

  In the third embodiment configured as described above, gas components such as carbon dioxide and water vapor generated on the anode 4 side by the power generation reaction through the gas vent hole 20 formed in the electrolyte membrane 8 are on the cathode 7 side. And then efficiently released out of the system. Accordingly, the electrode reaction can be promoted to improve the output, and the power generation efficiency and the stability over time can be improved. Further, since gas components such as carbon dioxide generated on the anode 4 side do not accumulate in the space S between the anode 4 and the sealing material 11, the electrolyte membrane 8 around the electrode is increased by increasing the pressure on the anode 4 side. It is possible to prevent the occurrence of problems such as tearing due to stress.

  The vent hole 20 of the electrolyte membrane 8 is desirably formed at a position where the distance from the peripheral end of the closest electrode (the anode 4 or the cathode 7) is 3 mm or more. As described above, by arranging the gas vent hole 20 apart from the electrode by a predetermined length or more, a gas component flow can be created in the space S between the anode 4 and the sealing material 11. Therefore, there is an advantage that diffusion of a substance used for an electrode reaction or a substance to be generated becomes easy.

  Further, as shown in FIG. 7, in order to prevent the gas component on the anode 4 side from being released outside the battery, as shown in FIG. The hole 13b can be formed. And the heat sink 21 made from aluminum can be arrange | positioned on the surface cover 15 so that it may adjoin to such an opening 13b for degassing. In such a configuration, a path with a large heat release property from the gas vent hole 20 of the electrolyte membrane 8 to the outside is formed, so that the heat release at the position of the gas vent hole 20 is effectively performed. Therefore, the saturated water vapor pressure at the position of the gas vent hole 20 is greatly reduced, and as a result, the ratio of the saturated water vapor pressure at the position where the saturated water vapor pressure is highest on the cathode 7 side can be adjusted to 0.8 or less. The same can be said for the saturated fuel vapor pressure.

  Next, fourth to seventh embodiments of the present invention will be described with reference to the drawings. 8 to 11 show the MEA 1 in the fourth to seventh embodiments of the present invention. In these drawings, the moisture retaining layer, the surface cover, the fuel supply unit, the fuel storage unit, and the like are not shown, but the fuel cells of the fourth to seventh embodiments include these elements. The specific configuration of each element is the same as that of the fuel cell of the first embodiment described above.

  In the fourth embodiment shown in FIG. 8, at least one surface side of the electrolyte membrane 8 on the anode 4 side and the cathode 7 side is between the peripheral end of the electrode (anode 4 or cathode 7) and the sealing material 11. A spacer 22 made of an insulating resin having a high fuel resistance is disposed so as to fill the space portion S. In particular, as illustrated, it is preferable to dispose the spacer 22 on the anode 4 side. As an insulating resin having high fuel resistance, a fluorine-based resin such as Teflon (registered trademark) can be given. The spacer 22 inserted and arranged in the space portion S does not need to fill the space portion S without gaps, and has a clearance of about 0.5 to 2.0 mm with respect to the space portion S in the planar shape, thickness, and the like. There may be.

  When the electrolyte membrane 8 to which the catalyst layer is not applied comes into contact with a high concentration fuel regardless of liquid or gas, the electrolyte membrane 8 may swell and the structure of the MEA 1 may be destroyed. In this embodiment, the insertion / arrangement of the spacer 22 in the space S prevents the electrolyte membrane 8 from being deformed due to a change in the internal pressure of the space S or the like and coming into contact with the fuel supply unit. Therefore, the output characteristics of the battery can be stabilized.

  In the fifth embodiment, as shown in FIG. 9, a gas vent hole is provided between a region where the electrode (anode 4 or cathode 7) of the electrolyte membrane 8 is laminated and a portion where the seal member 11 is disposed. As in the fourth embodiment, a spacer 22 is disposed on the surface of the electrolyte membrane 8 on the anode 4 side. A groove 22 a is formed in the spacer 22 so as to communicate the peripheral end of the anode 4 and the gas vent hole 20.

  In the fuel cell of the fifth embodiment configured as described above, gas components such as carbon dioxide and water vapor generated on the anode 4 side of the MEA 1 are guided to the groove 22a formed in the spacer 22 and are vented. 20 and further discharged through the vent hole 20 to the cathode 7 side. Accordingly, since the gas is rapidly released from the anode 4 side to the cathode 7 side, the electrode reaction is promoted and the output is improved.

  In the sixth embodiment, as shown in FIGS. 10A and 10B, the planar shape of the electrodes (the anode 4 and the cathode 7) is a polygon having a concave portion, and a square 1 having the same area is used. It is configured to have a perimeter length of 2 to 5 times. In addition, the numerical value in a figure has illustrated the length (cm) of each part of an electrode (anode 4 and cathode 7).

  In the fuel cell of the sixth embodiment configured as described above, since the electrodes (anode 4 and cathode 7) have a polygonal planar shape having a recess, the fuel having a rectangular electrode without a recess. Compared with the battery, the supply amount of the reactant MEA1 or air can be further increased, and the output can be further improved. That is, in the fuel cell according to the first embodiment, the supply amount of the reactant increases due to the space S around the electrode (the anode 4 or the cathode 7). However, the planar shape of the electrode is rectangular and the perimeter is long. Is 1.2 times or less of the square of the same area, the fuel diffused in the space S around the electrode may temporarily concentrate on the edge portion of the electrode and the concentration may become too high. Therefore, fuel cannot be consumed effectively, and the electrode structure may be damaged. In addition, even if the electrode has a polygonal planar shape with recesses, if the number of recesses is too large or the width is too narrow, the perimeter of the electrode is more than 5 times the square of the same area, A portion having an extremely narrow electrode width or a space portion S having a narrow width is present, and diffusion of reactants and reaction products is hindered. As a result, the output may be reduced.

  In the fuel cell of the seventh embodiment, the outer peripheral end surface (side peripheral surface) of the anode 4 and / or the cathode 7 is heat-treated at a temperature of 150 to 200 ° C.

  In the fuel cell of the seventh embodiment, the supply amount of air or fuel as reactants to the MEA 1 can be further increased, and the output can be further improved. That is, since the reactant diffused in the space S around the electrode (the anode 4 or the cathode 7) is supplied as fuel from the outer periphery of the electrode, the concentration of fuel such as methanol at the edge portion of the electrode increases. Therefore, there is a possibility that the organic polymer electrolyte contained as a proton path in the electrode is dissolved or the electrode structure is destroyed. By heating the outer peripheral end face of the anode 4 and / or the cathode 7 at a temperature of 150 to 200 ° C., the edge portion of the electrode is strengthened, and the organic polymer electrolyte is dissolved by the high-concentration fuel, or the electrode structure Can be prevented. When the temperature is lower than 150 ° C., the organic polymer electrolyte is not sufficiently strengthened. When the treatment is performed at a temperature of 200 ° C. or more, the structure may change due to the treatment and the function as a proton path may be reduced.

  The fuel cell of each embodiment described above is effective when various liquid fuels are used, and the type and concentration of the liquid fuel are not limited. Furthermore, although each embodiment mentioned above gave and demonstrated the passive type fuel cell as an example as a structure of a fuel cell main body, it is also applied to the semi-passive type fuel cell which used a pump etc. for some parts, such as fuel supply. The present invention can be applied. In the semi-passive type fuel cell, the fuel supplied from the fuel storage unit to the MEA is used for a power generation reaction and is not circulated thereafter and returned to the fuel storage unit. Since the semi-passive type fuel cell does not circulate the fuel, it is different from the conventional active method and does not impair the downsizing of the apparatus. In addition, since a pump is used for supplying fuel and it is different from a pure passive method such as a conventional internal vaporization type, it is called a semi-passive fuel cell.

  Next, specific examples of the fuel cell of the present invention and evaluation results thereof will be described. The technical scope of the present invention is not limited to the following examples.

Example 1
A fuel cell having the configuration shown in FIG. 1 was produced as follows. First, to a carbon black supporting anode catalyst particles (Pt: Ru = 1: 1), a solution of perfluorocarbon sulfonic acid as a proton conductive electrolyte, water and methoxypropanol as a dispersion medium are added, and an anode catalyst ( Pt-Ru) supported carbon was dispersed to prepare an anode catalyst slurry.

  Next, this anode catalyst slurry was uniformly applied onto porous carbon paper (30 mm × 20 mm rectangular shape) as the anode gas diffusion layer 3 and dried to form an anode catalyst layer 2 having a thickness of 100 μm.

  Further, a cathode catalyst (Pt) -carrying carbon was dispersed by adding a perfluorocarbon sulfonic acid solution and water and methoxypropanol as dispersion media to carbon black carrying the cathode catalyst particles (Pt) to prepare a cathode catalyst slurry. .

  Next, this cathode catalyst slurry was uniformly applied onto porous carbon paper (30 mm × 20 mm rectangular shape) as the cathode gas diffusion layer 6 and dried to form a cathode catalyst layer 5 having a thickness of 100 μm. Note that the porous carbon paper as the anode gas diffusion layer 3 and the porous carbon paper as the cathode gas diffusion layer 6 have the same shape and the same thickness, and are formed on these gas diffusion layers. The formed anode catalyst layer 2 and cathode catalyst layer 5 have the same shape and the same size and the same thickness.

  Next, between the anode catalyst layer 2 and the cathode catalyst layer 5 thus formed, a Nafion membrane, which is a proton conductive electrolyte membrane 8 (manufactured by DuPont, 44 mm × 34 mm rectangular shape with a thickness of 30 μm, water content) 10-20 wt%) was sandwiched and hot pressing was performed to produce a membrane electrode assembly (MEA) 1.

  The MEA 1 thus obtained was sandwiched from both sides with gold foil (44 mm × 34 mm rectangular shape) having a plurality of apertures which are the anode conductive layer 9 and the cathode conductive layer 10, and then the electrolyte membrane 8 and the anode conductive layer 9. A rectangular frame-shaped rubber O-ring (2 mm wide and 44 mm × 34 mm in outer diameter) as a sealing material 11 is inserted between the electrolyte membrane 8 and the cathode conductive layer 10 as shown below. A seal was applied.

That is, as shown in FIGS. 2 and 3, the long side portion and the short side portion of the rectangular frame-shaped O-ring (seal material 11) are the anode 4 and cathode gas composed of the anode gas diffusion layer 3 and the anode catalyst layer 2. The long side and the short side of the cathode 7 composed of the diffusion layer 6 and the cathode catalyst layer 5 are parallel to each other, and the distances from the peripheral ends of the long side and the short side of the anode 4 and the cathode 7 are all equal to 5 mm. An O-ring (seal material 11) was arranged so that In this MEA 1, the areas of the cathode 7 and the anode 4 are each 6 cm ² , and the space S between the O-ring (seal material 11) and the electrodes (cathode 7 and anode 4) on the cathode 7 side and the anode 4 side is formed. The bottom area is 6 cm ² . That is, a space having a bottom area 1.0 times as large as the electrode area (6 cm ² ) between the O-ring (seal material 11) on the cathode 7 side and the anode 4 side and the electrode (cathode 7 and anode 4). Part S is provided.

Next, as the moisture retaining layer 12 on the cathode conductive layer 10, the thickness is 1.0 mm, the air permeability (according to the measurement method specified in JIS P-8117) is 2.0 seconds / 100 cm ³ , and the moisture permeability (JIS L A porous polyethylene film (44 mm × 34 mm rectangular shape) of 2000 g / m ² · 24 hr) is laminated as a surface cover 13 on the porous air film (according to the measurement method specified in -1099A-1). A stainless steel (SUS304) plate (rectangular shape with a thickness of 1 mm, 44 mm × 34 mm) provided with 48 introduction ports 13a evenly in the plane was laminated and fixed with bolts.

  A fuel supply mechanism 14 including a fuel distribution layer 17, a fuel supply unit 16, a fuel storage unit 15, and a flow path 18 is provided under the anode conductive layer 9, and the passive fuel cell shown in FIG. 1 was manufactured.

Example 2
As shown in FIG. 4, heat resistance and fuel resistance are provided on the surface of the proton conductive electrolyte membrane 8 extending outward from the peripheral ends of the electrodes (cathode 7 and anode 4) of the MEA 1 on the anode 4 side. A Kapton (registered trademark; polyimide resin) tape (thickness: 0.5 mm, width: 7 mm) was attached as the organic film 19 having the above. Otherwise, the MEA 1 was produced in the same manner as in Example 1, and a fuel cell was assembled.

Example 3
As shown in FIG. 11, two gas vent holes 20 having a diameter of 0.5 mm were provided in the following positions of the electrolyte membrane 8 of the MEA 1. The two gas vent holes 20 are 5 mm away from the peripheral end of the closest electrode (for example, the cathode 7), and are formed at positions facing the central portion of the short side of the O-ring (sealing material 11). did. Further, in the cathode conductive layer 10, a hole having a diameter of 0.5 mm is formed at a position corresponding to the gas vent hole 20 of the electrolyte membrane 8, and a position corresponding to the gas vent hole 20 also in the moisturizing layer 12 and the surface cover 13. A hole with a diameter of 1 mm was provided to prevent the outflow of the exhausted gas. Otherwise, a fuel cell was produced in the same manner as in Example 2.

Example 4
As shown in FIG. 6, in the electrolyte membrane 8 of the MEA 1, the distance from the peripheral end portion of the closest electrode (for example, the cathode 7) is 3 mm, and at the center of the short side of the O-ring (seal material 11). Gas vent holes 20 each having a diameter of 0.5 mm were provided at two positions facing each other. Otherwise, a fuel cell was produced in the same manner as in Example 3.

Example 5
As shown in FIG. 12, the short sides of the electrodes (cathode 7 and anode 4) of MEA 1 are parallel to the other layers including the electrolyte membrane 8 and the long sides of the O-ring (sealing material 11). 7 and the anode 4) were arranged so that the long sides of the electrolyte membrane 8 and the like and the short side of the O-ring (sealing material 11) were parallel to each other. And in the electrolyte membrane 8, the distance from the peripheral edge part of the nearest electrode (for example, the cathode 7) is 10 mm, and at two positions facing the central part of the short side of the O-ring (seal material 11), Gas vent holes 20 each having a diameter of 0.5 mm were provided. Otherwise, the fuel cell was fabricated in the same manner as in Example 2.

Example 6
In the electrolyte membrane 8 of the MEA 1, at a position facing the center of the short side of the O-ring (sealing material 11), at two positions where the distance from the peripheral end of the nearest electrode (for example, the cathode 7) is 1 mm, Gas vent holes 20 each having a diameter of 0.5 mm were provided. Otherwise, a fuel cell was produced in the same manner as in Example 2.

Example 7
In the electrolyte membrane 8 of the MEA 1, at a position facing the central portion of the short side of the O-ring (sealing material 11), the distance from the nearest peripheral edge of the cathode is 5 mm, each having a diameter of 0.5 mm. As shown in FIG. 7, a gas vent hole 20 is provided on the front cover 13 with an aluminum plate (thickness 1 mm, 10 × 10 mm square) as a heat sink 21. It arrange | positioned so that it might adjoin to 13b, and was fixed with the volt | bolt. Otherwise, a fuel cell was produced in the same manner as in Example 2.

Example 8
As shown in FIG. 8, in the space S between the O-ring (seal material 11) on the anode 4 side of the MEA 1 and the electrode (anode 4), a Teflon ((registered trademark) having the same thickness as the anode 4 as a spacer 22 is formed. ) Tetrafluoroethylene) plate was placed and most of the space S was closed. Otherwise, a fuel cell was produced in the same manner as in Example 3.

Example 9
As shown in FIG. 9, the peripheral end of the anode 4 and the gas vent hole 20 of the electrolyte membrane 8 are communicated with a Teflon (registered trademark) plate, which is a spacer 22 disposed in the space S on the anode 4 side of the MEA 1. A groove 22a (width 1 mm) was formed. The depth of the groove 22a was made to coincide with the thickness of the anode 4. Otherwise, a fuel cell was fabricated in the same manner as in Example 8.

Example 10
As shown in FIG. 10B, electrodes (anode 4 and cathode 7) having a polygonal planar shape with concave portions were used. This electrode has a perimeter of 15 cm and has an outer circumference that is approximately 1.53 times the square perimeter (9.8 cm) of the same area. In the electrolyte membrane 8 of the MEA 1, the diameter 0 is provided at two positions where the distance from the peripheral end of the cathode 7 closest to the center of the short side of the O-ring (sealing material 11) is 7 mm. A 5 mm vent hole 20 was provided. Otherwise, a fuel cell was produced in the same manner as in Example 3.

Example 11
After hot pressing the anode 4 and the cathode 7 to the electrolyte membrane 8 by hot pressing, the MEA was re-used at 180 ° C. for 2 minutes using a copper frame having a width of 5 mm and the same outer shape as the anode 4 and the cathode 7. Pressed. Other than that was carried out similarly to Example 8, and produced the fuel cell.

Example 12
As the cathode gas diffusion layer 6 and the anode gas diffusion layer 3, porous carbon paper of 23.1 mm × 34.6 mm was used, and the area of the cathode 7 and the anode 4 was 8 cm ² . And between the O-ring (seal material 11) on the cathode 7 side and the anode 4 side and the electrodes (cathode 7 and anode 4), the bottom area of 0.5 times the area (8 cm ² ) of the cathode 7 and anode 4 A space S having (4 cm ² ) was provided. Further, in the electrolyte membrane 8 of the MEA 1, at two positions where the distance from the peripheral end portion of the cathode 7 closest to the central portion of the short side of the O-ring (seal material 11) is 2.5 mm, respectively. A vent hole 20 having a diameter of 0.5 mm was provided. Otherwise, a fuel cell was produced in the same manner as in Example 2.

Comparative Example 1
As the cathode gas diffusion layer 6 and the anode gas diffusion layer 3, porous carbon paper of 26.4 mm × 39.7 mm was used, and the area of the cathode 7 and the anode 4 was set to 10.5 cm ² . Between the O-ring (seal material 11) on the cathode 7 side and the anode 4 side and the electrode (cathode 7 and anode 4), 0.12 times the area (10.5 cm ² ) of the cathode 7 and anode 4 A space S having a cross-sectional area (1.26 cm ² ) was provided. Otherwise, a fuel cell was produced in the same manner as in Example 2.

Comparative Example 2
As the cathode gas diffusion layer 6 and the anode gas diffusion layer 3, 14.1 mm × 21.2 mm porous carbon paper was used, and the area of the cathode 7 and the anode 4 was 3 cm ² . And, between the cathode 7 side and anode 4 side O-ring (sealing material 11) and the electrodes (cathode 7 and anode 4), the cross-sectional area of 3.0 times the area (3 cm ² ) of the cathode 7 and anode 4 A space S having (9.0 cm ² ) was provided. Otherwise, a fuel cell was produced in the same manner as in Example 2.

Next, in the fuel cells obtained in Examples 1 to 12 and Comparative Examples 1 and 2, methanol having a purity of 99.99% was supplied to the fuel storage portion in an environment of a temperature of 25 ° C. and a humidity of 50% RH. In addition, a variable current power source was connected as an external load, and the current flowing through the fuel cell was controlled so as to gradually increase from zero. The current was controlled so that the current density (current value (mA / cm ² ) flowing per 1 cm ² area of the power generation unit) increased by 10 mA / cm ² per minute.

That is, the current density was controlled to be 150 mA / cm ² after 15 minutes from the start of current flow. The area of the power generation unit is the area of the portion where the anode catalyst layer and the cathode catalyst layer face each other. In the fuel cells of Examples 1 to 12 and Comparative Examples 1 and 2, the areas of the anode catalyst layer and the cathode catalyst layer were equal and opposed over the entire area. Equal to the area. Then, the output voltage of the fuel cell was measured, and when the measured value reached 0.2 V, the increase in current was terminated. Further, the output after 1000 hours was measured, and the ratio when the initial output was 100 was calculated. And this value was made into the output maintenance factor.

Next, a constant voltage power supply was connected instead of the variable current power supply, and power generation was performed while controlling the current so that the output voltage of the fuel cell was constant at 0.3 V, and the output density at that time was measured. Here, the output density (mW / cm ² ) of the fuel cell is obtained by multiplying the current density by the output voltage. This constant voltage power generation was continued for 24 hours, and the average value of the output density for 24 hours was taken as the value of the output density of the fuel cell. The measurement results are shown in Table 1 together with the value of the output maintenance rate described above. The output density of the fuel cell is shown as a relative value with the value of Comparative Example 1 being 100.

  Furthermore, in the fuel cells of Examples 3 to 7, during constant voltage power generation under the above conditions, the position of the center of the cathode gas diffusion layer (intersection of rectangular diagonal lines) and the vent holes provided in the electrolyte membrane A thermocouple was inserted at each position, and the temperature was measured. Then, from the measured temperature, using the graph of the saturated vapor pressure curve of water and methanol, the ratio of the saturated water vapor pressure P1 at the position of the gas vent hole to the saturated water vapor pressure P2 at the center of the cathode gas diffusion layer, and the gas The ratio between the saturated methanol vapor pressure P3 at the hole position and the saturated methanol vapor pressure P4 at the center of the cathode gas diffusion layer was determined. These results are also shown in Table 1.

  From Table 1, the fuel cells obtained in Examples 1 to 12 have a higher output density than the fuel cells of Comparative Examples 1 and 2, and the output maintenance rate is greatly improved. I understand.

  The present invention can be applied to various fuel cells using liquid fuel. In addition, the specific configuration of the fuel cell, the supply state of the fuel, and the like are not particularly limited, and all of the fuel supplied to the MEA is liquid fuel vapor, all is liquid fuel, or part is liquid state. The present invention can be applied to various forms such as a vapor of supplied liquid fuel. 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 embodiments, or deleting some constituent elements from all the constituent elements shown in the embodiments. 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.

It is sectional drawing which shows the structure of the fuel cell which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows typically the structure of MEA1 of the fuel cell shown in FIG. 1 shows the MEA 1 of the fuel cell shown in FIG. 1, FIG. 3 (a) is a plan view on the cathode 7 side, and FIG. 3 (b) is a plan view on the anode 4 side. It is sectional drawing which shows typically the structure of MEA1 in the fuel cell of 2nd Embodiment. It is sectional drawing which shows typically the structure of MEA1 in the fuel cell of 3rd Embodiment. FIG. 6 is a plan view of the MEA 1 shown in FIG. 5 on the cathode 7 side. In the fuel cell of 3rd Embodiment, it is a top view which shows the structure which has arrange | positioned the heat sink. It is sectional drawing which shows typically the structure of MEA1 in the fuel cell of 4th Embodiment. It is a top view which shows typically the structure of MEA1 in the fuel cell of 5th Embodiment. It is a top view which shows the example of the shape of the electrode in the fuel cell of 6th Embodiment. 7 is a plan view showing a configuration of MEA 1 in Embodiment 3. FIG. FIG. 10 is a plan view showing the configuration of MEA 1 in Example 5.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... MEA, 2 ... Anode catalyst layer, 3 ... Anode gas diffusion layer, 4 ... Anode, 5 ... Cathode catalyst layer, 6 ... Cathode gas diffusion layer, 7 ... Cathode, 8 ... Electrolyte membrane, 11 ... Sealing material (O-ring) ), 12 ... Moisturizing layer, 13 ... Surface cover, 15 ... Fuel storage part, 16 ... Fuel supply part, 17 ... Fuel distribution layer, S ... Space part, 19 ... Organic film, 20 ... Gas vent, 21 ... Heat sink 22 spacers.

Claims (11)

A fuel electrode (anode) and an air electrode (cathode), a proton-conducting electrolyte membrane sandwiched between the fuel electrode and the air electrode, and seals provided around the sides of the fuel electrode and the air electrode, respectively. A membrane electrode assembly (MEA) having a portion, a fuel storage portion that stores liquid fuel, and a fuel supply mechanism that supplies the liquid fuel stored in the fuel storage portion to the fuel electrode of the membrane electrode assembly; In a fuel cell comprising:
In at least one of the fuel electrode side and the air electrode side of the membrane electrode assembly, the area of the fuel electrode or the air electrode is 0.2 to 1 between the seal portion and the fuel electrode or the air electrode. A fuel cell having a space portion having a bottom area three times as large.   The fuel cell according to claim 1, wherein the electrolyte membrane has an area where a peripheral end reaches the seal portion.   At least one of the fuel electrode side and the air electrode side of the membrane electrode assembly is provided with a non-fuel permeable layer in a region not sandwiched by the fuel electrode or the air electrode of the electrolyte membrane. The fuel cell according to claim 2, wherein:   3. The electrolyte membrane according to claim 2, wherein the electrolyte membrane has a gas vent hole that allows a gas component generated on the fuel electrode side to escape to the air electrode side in a region not sandwiched by the fuel electrode or the air electrode. 3. The fuel cell according to 3.   The ratio of the saturated water vapor pressure at the position of the vent hole of the electrolyte membrane to the saturated water vapor pressure at the position where the saturated water vapor pressure is highest on the air electrode side is 0.8 or less. 4. The fuel cell according to 4.   6. The fuel cell according to claim 4, wherein a distance between the gas vent hole and a peripheral end portion of the fuel electrode or air electrode closest to the gas vent hole is 3 mm or more.   7. The fuel cell according to claim 4, wherein a heat release path to the outside is connected to the gas vent hole.   The spacer member made of an insulating resin having high fuel resistance is disposed in the space on the fuel electrode side of the membrane electrode assembly. Fuel cell.   The fuel cell according to claim 8, wherein the spacer member has a groove that communicates the peripheral end portion of the fuel electrode with the gas vent hole of the electrolyte membrane.   10. The fuel cell according to claim 1, wherein the planar shape of the fuel electrode and the air electrode is a shape having a perimeter that is 1.2 to 5 times the square of the same area. .   11. The fuel cell according to claim 1, wherein an outer peripheral end face of at least one of the fuel electrode and the air electrode is heat-treated at a temperature of 150 to 200 ° C. 11.

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