WO2010013425A1

WO2010013425A1 - Fuel cell

Info

Publication number: WO2010013425A1
Application number: PCT/JP2009/003491
Authority: WO
Inventors: 矢嶋亨; 大道元太; 佐藤麻子; 古市満; 青木里紗; 吉田勇一
Original assignee: 株式会社東芝
Priority date: 2008-07-28
Filing date: 2009-07-24
Publication date: 2010-02-04
Also published as: JP2010033839A

Abstract

The fuel cell is equipped with an MEA (1), which comprises an anode (4), a cathode (7), an electrolyte membrane (8), and a seal member (11) disposed on the outside of the anode (4) and the cathode (7), and a fuel supply mechanism (14), which supplies liquid fuel (F) to the MEA (1). A space (S), the bottom surface area of which is 0.2 to 1.3 times the electrode surface area, is then provided between the seal member (11) and the electrode on at least one or the other of the anode (4) side or cathode (7) side of the MEA (1). The output of the fuel cell is increased by increasing the supply rate of fuel or air supplied to the MEA. The efficiency and stability over time of the power generating reaction of the fuel cell are thus improved.

Description

Fuel cell

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

In recent years, attempts have been made to use fuel cells as the power source of portable electronic devices in order to use electronic devices such as notebook computers and mobile phones without charging them for a long time. 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.

A direct methanol fuel cell (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 a fuel supply method in the DMFC, an active method such as a gas supply type or a liquid supply type, or 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 is known.

Among these, passive methods such as the internal vaporization type are particularly advantageous for downsizing the DMFC. In a passive type DMFC, a membrane electrode assembly (Mebrane Electrode Assembly: MEA) having a fuel electrode (anode), an electrolyte membrane, and an air electrode (cathode) is disposed on a fuel storage portion formed of a resin box-like container. A structure has been proposed (see, for example, Patent Document 1).

In such a passive method, methanol having a higher concentration than that of the active method is used in order to secure the amount of fuel supplied. As water (H ₂ O) necessary for the reaction at the anode, water produced at the cathode is supplied after being reverse-diffused 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. Therefore, conventionally, a gas vent is provided on the side surface of the container on the anode side so that the gas component is removed from the system. It was being considered for release. 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. The higher the temperature of the MEA and the higher the saturated vapor pressure of the fuel (methanol) and water present on the anode side, the more easily the methanol and water are discharged as vapor from the vent hole. Further, when the amount of water discharged from the anode side increases and the amount of water contained in the MEA decreases, the conductivity of protons (H ⁺ ) in the electrolyte membrane decreases, and the output of the fuel cell decreases. 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. It is another object of the present invention to provide a fuel cell in which the removability of gas components generated on the anode side of the MEA accompanying the power generation reaction is enhanced, and the efficiency of the power generation reaction and the stability over time are improved.

The fuel cell according to the first 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, the fuel electrode and the fuel electrode. A membrane electrode assembly (MEA) having a seal portion provided around each of the outer sides of the air electrode, a fuel storage portion for storing liquid fuel, and the liquid fuel stored in the fuel storage portion as the membrane electrode In the fuel cell comprising a fuel supply mechanism for supplying the fuel electrode of the assembly to the fuel electrode side and at least one of the air electrode side and the air electrode side of the membrane electrode assembly, the seal portion and the fuel electrode or the air A space portion having a bottom area of 0.2 to 1.3 times the area of the main surface of the fuel electrode or air electrode is provided between the electrode and the electrode.

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.

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 the structure of MEA of the fuel cell of 1st Embodiment. It is a cathode side top view which shows MEA of the fuel cell of 1st Embodiment. It is an anode side top view showing MEA of a fuel cell of a 1st embodiment. It is sectional drawing which shows the structure of MEA in the fuel cell of 2nd Embodiment. It is sectional drawing which shows the structure of MEA in the fuel cell of 3rd Embodiment. It is a cathode side top view of MEA in the fuel cell of a 3rd embodiment. 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 the structure of MEA in the fuel cell of 4th Embodiment. It is a top view which shows the structure of MEA in the fuel cell of 5th Embodiment. It is a top view which shows one shape of the electrode in the fuel cell of 6th Embodiment. It is a top view which shows another shape of the electrode in the fuel cell of 6th Embodiment. 6 is a plan view showing a configuration of an MEA in Example 3. FIG. FIG. 10 is a plan view showing a configuration of an MEA in Example 5.

Hereinafter, a fuel cell according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of the fuel cell according to the first embodiment. The fuel cell of 1st Embodiment has the membrane electrode assembly (MEA) 1 as shown in FIG.

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. Proton conductive 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 contain 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 contains a large amount of a palladium alloy (for example, a palladium-cobalt alloy) from the viewpoint of manufacturing cost. Is preferred. 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 improves the mobility of protons that move from the anode catalyst layer to the electrolyte membrane and from the electrolyte membrane to the cathode catalyst layer as power generation proceeds. 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.

There are no particular limitations on the blending ratios of the catalyst component in the anode catalyst layer 2 and the cathode catalyst layer 5, the carbon material that is the conductive carrier, and the proton conductive electrolyte. 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 which 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. 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. In order to efficiently transport the fuel gas and air to the catalyst, it is preferable to use a porous carbon woven fabric or carbon paper. 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.

The anode conductive layer 9 is laminated on the anode gas diffusion layer 3 of the MEA 1 configured as described above, and the cathode conductive layer 10 is laminated 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 catalyst layer 2 and the anode gas diffusion layer 3 constituting the anode 4, for example, the cross section is O-shaped and the planar shape is rectangular. A frame-shaped sealing material (O-ring) 11 is provided. Further, a sealing material (O-ring) having the same shape is disposed between the proton conductive electrolyte membrane 8 and the cathode conductive layer 10 and around the cathode catalyst layer 5 and the cathode gas diffusion layer 6 constituting the cathode 7. 11 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, 3A, and 3B, on the anode 4 side and the cathode 7 side of the MEA 1, the sealing material 11 and the peripheral end of the electrode (the anode 4 or the cathode 7) A space S having a bottom area of 0.2 to 1.3 times the area of the main surface of the electrode (anode 4 or cathode 7) is provided between them. The area of the electrode or the electrolyte membrane 8 indicates the area of the main surface, and the bottom area of the space S indicates the cross-sectional area in the plane direction parallel to the main surface of the electrode. Further, in the first embodiment, the structure 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.

Further, a fuel-resistant (for example, methanol-resistant) organic film (not shown) can be 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. The space S on the cathode 7 side is a space surrounded on three sides by the organic film, the sealing material 11 and the end face of the cathode 7.

In the first embodiment, the area of the proton conductive electrolyte membrane 8 is increased, and the peripheral end portion of the electrolyte membrane 8 reaches the seal 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. Moreover, since the catalyst layer is not laminated in the portion where the area of the electrolyte membrane 8 is increased, this 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 functions as an auxiliary diffusion layer that uniformly introduces air as an oxidant and promotes uniform diffusion of air into the cathode catalyst layer 5. As the moisture retaining layer 12, for example, a porous polyethylene film can be used.

On the moisturizing layer 12, a surface cover (cover plate) 13 having a plurality of air inlets 13a for taking in air as an oxidant is disposed. 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 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 heat dissipation body, metal is most desirable because it has high thermal conductivity and is thin but has high strength. 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 aluminum whose surface is black anodized in order to increase the heat emissivity to the outside air.

The heat radiating body may be manufactured integrally with the surface cover 13, or a separately manufactured heat radiating member may be manufactured by means such as welding, bolts, rivets, caulking, soldering, brazing, bonding, and fitting. It may be fixed to. 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 unit 15. As the liquid fuel F, a methanol aqueous solution or pure methanol is preferable. A methanol concentration of 50 mol% or more is preferably used, but 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 composed of 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, in the configuration in which the fuel supply unit 16 and the fuel storage unit 15 are stacked and integrated, the flow path of the liquid fuel F that connects them may be used.

The fuel supply unit 16 has a fuel inlet 16a into which the liquid fuel F flows. A fuel distribution layer 17 having a plurality of fuel discharge ports 17 a is disposed on the side of the fuel supply unit 16 that contacts the anode conductive layer 9.

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. Furthermore, a pump may be inserted into 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 only 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. Further, a space S having a bottom area 0.2 to 1.3 times the area of the anode 4 or the cathode 7 which is an electrode is provided. The formation of the space S widens the intake of air, which is an oxidizer, into the cathode 7 or the intake of fuel, into the anode 4, so that the air and fuel as reactants into the MEA 1 are expanded. The supply amount is 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, the second and third embodiments of the fuel cell of the present invention will be described. FIG. 4 is a cross-sectional view showing the configuration of the MEA 1 in the fuel cell according to the second embodiment. FIG. 5 is a cross-sectional view showing the configuration of the MEA 1 in the fuel cell according to the third embodiment, and FIG. 6 is a plan view of the cathode side of the MEA 1. In addition to the MEA 1 shown in these drawings, the fuel cells of the second and third embodiments include elements such as an anode conductive layer and a cathode conductive layer, a moisture retention layer, a surface cover, a fuel supply unit, and a fuel storage unit. It has. 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 of the anode 4 side and the cathode 7 side of the proton conductive electrolyte membrane 8. A non-fuel permeable organic film 19 is affixed to a region not corresponding to the space portion S between the peripheral edge of the electrode and the sealing material 11. 4 shows a configuration in which the organic film 19 is attached only to the surface of the electrolyte membrane 8 on the anode 4 side, it may be attached to the surface on the cathode 7 side, or may be attached to both surfaces. . Examples of the organic film 19 having no fuel permeability include an organic film having heat resistance up to 100 ° C. and fuel resistance, and specifically, a polyimide resin tape or a Teflon (registered trademark) tape having an adhesive layer. Illustrated. Such an organic film 19 may be thermocompression bonded to the electrolyte membrane 8.

In the fuel cell of the second embodiment configured as described above, the fuel crossover 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. Further, in order to suppress the fuel crossover by laminating particularly on the anode 4 side, the organic film 19 is not attached, but on the electrolyte membrane 8 between the peripheral edge of the electrode and the sealing material 11, The catalyst layer itself may be applied.

In the third embodiment, as shown in FIGS. 5 and 6, a gas vent hole 20 through which the proton conductive electrolyte membrane 8 is penetrated is provided. The gas vent hole 20 is for releasing a gas component generated on the anode 4 side to the cathode 7 side in response to the power generation reaction, and is a peripheral end portion of a region where the anode 4 or the cathode 7 of the electrolyte membrane 8 is laminated. And a portion corresponding to the space portion S between the peripheral end portion of the electrode and the sealing material 11 are provided in one or a plurality. 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. A gas vent hole which is a through hole may be provided in the base plate.

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 preferably 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. 7, in the surface cover 13, an opening for degassing is provided at a position corresponding to the degassing hole 20 of the electrolyte membrane 8. The hole 13b can be formed. And the heat sink 21 made from aluminum can be arrange | positioned on the surface cover 13 so that it may adjoin to such an opening 13b for venting. In such a configuration, since a path with a large heat release property is formed from the gas vent hole 20 of the electrolyte membrane 8 to the outside, the heat release from 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 configuration of the MEA 1 in the fourth to seventh embodiments of the present invention. In addition to the MEA 1 shown in these drawings, the fuel cells of the fourth to seventh embodiments include elements such as an anode conductive layer and a cathode conductive layer, a moisture retention layer, a surface cover, a fuel supply unit, and a fuel storage unit. It has. 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, on the surface of at least one of the anode 4 side and the cathode 7 side of the electrolyte membrane 8, the peripheral end portion of the electrode (the anode 4 or the cathode 7) and the sealing material 11 are provided. A spacer 22 made of an insulating resin having high fuel resistance is disposed so as to fill the space S therebetween. 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 any gap, and has a clearance of about 0.5 to 2.0 mm with respect to the space portion S in the planar shape, thickness, etc. 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 the fourth embodiment, since the spacer 22 is inserted and arranged in the space portion S, the electrolyte membrane 8 is deformed due to a change in the internal pressure of the space portion S, etc., and contacts the fuel supply portion. No longer occurs. 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. 20 is formed. Similarly to the fourth embodiment, the 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 portion 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 (anode 4 and cathode 7) is a polygon having a recess, It is configured to have a perimeter of 5 times. In FIGS. 10A and 10B, the numerical values in parentheses indicate the length (cm) of each part of the electrodes (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. In particular, when the electrode has a planar shape having a perimeter that is 1.2 to 5 times the square of the same area, the electrode structure is not likely to be damaged and the diffusion of reactants and reaction products is enhanced. Output can be improved. In other words, in the fuel cell according to the first embodiment, the space S around the electrode (anode 4 or cathode 7) increases the amount of reactant supplied, but the electrode has a rectangular flat surface with no recess. If it has a shape and its perimeter is less than 1.2 times the square of the same area, the fuel diffused in the space S around the electrode will temporarily concentrate on the edge of the electrode and the concentration will increase It may be too much. 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.

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 the reactant air or fuel 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, a carbon black carrying anode catalyst particles (Pt: Ru = 1: 1) was added with a solution of perfluorocarbon sulfonic acid, which is a proton conductive electrolyte, and water and methoxypropanol, which are dispersion media, respectively. (Pt—Ru) -supported carbon was dispersed. Thus, an anode catalyst slurry was prepared.

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 then dried to form an anode catalyst layer 2 having a thickness of 100 μm.

Further, a solution of perfluorocarbon sulfonic acid and water and methoxypropanol as dispersion media were added to carbon black carrying cathode catalyst particles (Pt) to disperse the cathode catalyst (Pt) carrying carbon. Thus, a cathode catalyst slurry was prepared.

Next, the cathode catalyst slurry was uniformly applied onto porous carbon paper (30 mm × 20 mm rectangular shape) as the cathode gas diffusion layer 6 and then dried to form a cathode catalyst layer 5 having a thickness of 100 μm. 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 size and the same thickness. Also, the anode catalyst layer 2 and the cathode catalyst layer 5 formed on these gas diffusion layers 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) A membrane electrode assembly (MEA) 1 was produced by hot pressing with 10 to 20% by weight).

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. And sealed.

That is, as shown in FIGS. 2, 3 </ b> A, and 3 </ b> B, the long side and the short side of the rectangular frame-shaped O-ring (sealing material 11) are the anode 4 including the anode gas diffusion layer 3 and the anode catalyst layer 2. In addition, the long side and the short side of the cathode 7 composed of the cathode gas 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 both An O-ring (seal material 11) was arranged so as to be uniform at 5 mm. 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 retention 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 x 34 mm rectangular shape) of 2000 g / m ² · 24 hr (according to the measurement method specified in 1099A-1) is laminated, and then a circular air with a diameter of 3 mm is used as the surface cover 13 thereon. 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.

Further, 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 was provided under the anode conductive layer 9, and the passive fuel cell shown in FIG. 1 was produced.

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 central portion 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, an aluminum plate (a square shape having a thickness of 1 mm and 10 × 10 mm) is provided on the surface cover 13 as a heat sink 21 as shown in FIG. It arrange | positioned so that it might adjoin to the hole 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, Teflon (registered trademark) having the same thickness as the anode 4 as a spacer 22 in the space S between the O-ring (sealing material 11) on the anode 4 side of the MEA 1 and the electrode (anode 4). A plate was placed to block most of the space S. Otherwise, a fuel cell was produced in the same manner as in Example 3.

Example 9
As shown in FIG. 9, the peripheral end portion 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 portion 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, the electrodes (anode 4 and cathode 7) having a polygonal planar shape with concave portions were used. This electrode has a circumference of 15 cm, and has an outer circumference that is approximately 1.53 times the square circumference (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 portion of the cathode 7 closest to the center of the short side portion 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, using a copper frame having a width of 5 mm and the same outer shape as the anode 4 and the cathode 7, the MEA was re-applied at 180 ° C. for 2 minutes. 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 container 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. This value was used as the output maintenance rate.

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 retention 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 gas 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.

Note that 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.

Claims

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. Membrane electrode assembly (MEA) having a portion;
A fuel storage section for storing liquid fuel;
A fuel cell comprising 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 at least one of the fuel electrode side and the air electrode side of the membrane electrode assembly, the area of the main surface of the fuel electrode or air electrode is 0. 0 mm between the seal portion and the fuel electrode or air electrode. A fuel cell comprising a space portion having a bottom area of 2 to 1.3 times.
2. The fuel cell according to claim 1, wherein a fuel-resistant organic film is disposed in the space, and the space is divided into the fuel electrode side and the air electrode side by the organic film. .
2. The fuel cell according to claim 1, wherein the electrolyte membrane has an area where a peripheral end reaches the seal portion.
On at least one of the fuel electrode side and the air electrode side of the membrane electrode assembly, a layer having no fuel permeability is disposed in a region not sandwiched by the fuel electrode or the air electrode of the electrolyte membrane. The fuel cell according to claim 3, wherein
5. The fuel cell according to claim 4, wherein the non-fuel permeable layer covers the entire region of the electrolyte membrane that is not sandwiched between the fuel electrode or the air electrode.
4. The fuel cell according to claim 3, wherein a catalyst layer is formed on the electrolyte membrane between the seal portion and the fuel electrode on the fuel electrode side of the membrane electrode assembly.
4. The electrolyte membrane according to claim 3, wherein the electrolyte membrane has a vent hole for escaping a gas component generated on the fuel electrode side to the air electrode side in a region not sandwiched by the fuel electrode or the air electrode. 4. The fuel cell according to 4.
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. 7. The fuel cell according to 7.
The ratio between the saturated fuel vapor pressure at the position of the gas vent hole of the electrolyte membrane and the saturated fuel vapor pressure at the position where the saturated fuel vapor pressure is highest on the air electrode side is 0.8 or less, The fuel cell according to claim 7 or 8.
The fuel according to any one of claims 7 to 9, 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. battery.
11. The fuel cell according to claim 7, wherein a heat release path to the outside is connected to the gas vent hole.
The fuel cell according to claim 11, wherein a heat radiating plate is disposed in the vicinity of the outer end of the heat release path.
3. The fuel cell according to claim 2, wherein the fuel-resistant organic film has a gas vent for allowing a gas component generated on the fuel electrode side to escape to the air electrode side.
4. The fuel cell according to claim 3, wherein a 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.
The gas release hole is provided in a region of the electrolyte membrane that is not sandwiched between the fuel electrode or the air electrode, and the spacer member has a groove that allows the peripheral end of the fuel electrode to communicate with the gas release hole. The fuel cell according to claim 14.
16. The planar shape of the fuel electrode and / or the air electrode is a shape having a perimeter that is 1.2 to 5 times the square of the same area. Fuel cell.
The fuel cell according to claim 16, wherein the planar shape of the fuel electrode and / or the air electrode is a polygon having a recess.
The fuel cell according to any one of claims 1 to 17, 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.