JP2009016312A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of stably acquiring a high output. <P>SOLUTION: The fuel cell comprises a membrane electrode assembly 2 having a fuel electrode, an air electrode, and an electrolyte membrane intervened between the fuel electrode and the air electrode, a current collector 20 sandwiching the membrane electrode assembly 2, and a cover member 18 arranged to face to the current collector 20 and having an air guide hole 18A in an air electrode side of the membrane electrode assembly 2. The cover member 18 has a first cover body 181 having a first air guide hole 181A arranged at a membrane electrode assembly side, and a second cover body 182 having a second air guide hole 182A laminated on the first cover body 181 and being in a shape different from the first air guide hole. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

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

  A direct methanol fuel cell (DMFC) is promising as a power source for portable electronic devices because it can be miniaturized and the fuel can be easily handled. As the liquid fuel supply method in the DMFC, there are known an active method such as a gas supply type and a liquid supply type, and a passive method such as an internal vaporization type in which the liquid fuel in the fuel container is vaporized inside the cell and supplied to the fuel electrode. It has been.

  Among these, a passive system such as an internal vaporization type is particularly advantageous for downsizing of the DMFC. In the passive DMFC, for example, a structure is proposed in which a membrane electrode assembly (fuel cell) having a fuel electrode, an electrolyte membrane, and an air electrode is disposed on a fuel containing portion made of a resin box-like container ( For example, see Patent Documents 1 and 2). When the fuel vaporized from the fuel container is directly supplied to the fuel cell, it is important to improve the output controllability of the fuel cell, but the current passive DMFC does not always have sufficient output controllability. .

  On the other hand, it has been studied to connect a fuel cell of DMFC and a fuel storage part via a flow path (see Patent Documents 3 to 5). By supplying the liquid fuel supplied from the fuel storage unit to the fuel cell via the flow path, the supply amount of the liquid fuel can be adjusted based on the shape and diameter of the flow path. However, depending on the supply structure of the liquid fuel from the flow path, the supply state of the fuel to the fuel cells may become uneven, and the output of the fuel cell may be reduced. For example, when the liquid fuel is caused to flow along the groove-like flow path, the fuel concentration is decreased on the flow path outlet side because the fuel is sequentially consumed as the liquid fuel flows through the flow path. For this reason, power generation reaction falls in the part near the channel outlet of a fuel cell, and as a result, the output falls.

Patent Document 3 discloses a configuration in which liquid fuel is supplied from a fuel storage portion by a pump provided in a flow path. Patent Document 4 discloses that an electric field forming means for forming an electroosmotic flow in a flow path is used instead of a pump. Patent Document 5 discloses supplying liquid fuel or the like using an electroosmotic flow pump. In a fuel cell to which a fuel circulation structure is applied, the pump is effective, but when the fuel is not circulated as in the case of a passive DMFC, even if the pump is applied, the fuel consumption will only increase and the fuel cell It is difficult to generate a uniform power generation reaction throughout.
International Publication No. 2005/112172 Pamphlet JP 2006-318712 A JP 2005-518646 A JP 2006-089552 A US Patent Publication No. 2006/0029851

  The fuel cell has a large internal resistance, and when a large current is taken out, the potential drops. For this reason, it is important to reduce internal resistance for practical use. The internal resistance mainly includes the reaction resistance at the anode and the cathode and the resistance generated at the electrolyte membrane, but the resistance of the current collector for extracting electricity from the electrode is also an important factor.

  In particular, in a small portable device application, in order to keep the thickness of the fuel cell thin, it is not possible to have a mechanism for closely contacting the electrode and the current collector with a strong force. For this reason, the current collector is made of a flexible and low contact resistance material such as a gold foil, and is brought into conduction by being brought into planar contact with each electrode. However, continuity by simple planar contact does not stabilize the contact resistance. For example, when the stress applied to the electrode changes due to gas generation accompanying the reaction, the contact resistance may be significantly increased.

  An object of the present invention is to provide a fuel cell capable of stably obtaining a high output, in view of the above-described problems.

A fuel cell according to an aspect of the present invention includes:
A membrane electrode assembly having a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode;
A current collector sandwiching the membrane electrode assembly;
A cover member disposed on the air electrode side of the membrane electrode assembly so as to face the current collector and having an air introduction hole;
The cover member is disposed on the membrane electrode assembly side and has a first cover body having a first air introduction hole, and a second air introduction layered on the first cover body and having a shape different from that of the first air introduction hole. And a second cover body having a hole.

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

  A fuel cell according to an embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a passive type of internal vaporization method will be described as the fuel cell 1, but it is not limited to this method.

  As shown in FIG. 1, the fuel cell 1 includes a membrane electrode assembly (MEA) 2 that constitutes an electromotive part of the fuel cell 1. That is, in the fuel cell 1, the membrane electrode assembly 2 includes an anode (fuel electrode) 13 having an anode catalyst layer 11 and an anode gas diffusion layer 12, and a cathode having a cathode catalyst layer 14 and a cathode gas diffusion layer 15 ( (Air electrode / oxidant electrode) 16 and a proton (hydrogen ion) conductive electrolyte membrane 17 sandwiched between the anode catalyst layer 11 and the cathode catalyst layer 14.

  Examples of the catalyst contained in the anode catalyst layer 11 and the cathode catalyst layer 14 include platinum such as platinum (Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), osmium (Os), and palladium (Pd). Examples thereof include a group element simple substance and an alloy containing a platinum group element. For the anode catalyst layer 11, it is preferable to use Pt—Ru, Pt—Mo, or the like that has strong resistance to methanol, carbon monoxide, or the like. It is preferable to use Pt, Pt—Ni or the like for the cathode catalyst layer 14. However, the catalyst is not limited to these, and various substances having catalytic activity can be used. The catalyst may be either a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst.

  Examples of the proton conductive material constituting the electrolyte membrane 17 include fluorine-based resins (Nafion (trade name, manufactured by DuPont) and Flemion (trade name, manufactured by Asahi Glass Co., Ltd.) such as a perfluorosulfonic acid polymer having a sulfonic acid group. Etc.), organic materials such as hydrocarbon resins having sulfonic acid groups, or inorganic materials such as tungstic acid and phosphotungstic acid. However, the proton conductive electrolyte membrane 17 is not limited to these.

  The anode gas diffusion layer 12 laminated on the anode catalyst layer 11 plays a role of uniformly supplying fuel to the anode catalyst layer 11. The cathode gas diffusion layer 15 laminated on the cathode catalyst layer 14 serves to uniformly supply the oxidizing agent to the cathode catalyst layer 14. The anode gas diffusion layer 12 and the cathode gas diffusion layer 15 are made of a thin film material made of, for example, a porous carbon material, and specifically made of carbon paper or carbon fiber.

  A sealing material 19 such as a rubber O-ring is disposed on the anode side and the cathode side of the electrolyte membrane 17, respectively, thereby preventing fuel leakage from the membrane electrode assembly 2.

  In this embodiment, the membrane electrode assembly 2 includes a plurality of anodes 13 disposed on one surface 17A of the same electrolyte membrane 17 and a plurality of anodes 17 disposed on the other surface 17B of the electrolyte membrane 17. Each anode 13 and each cathode 16 are opposed to each other with the electrolyte membrane 17 interposed therebetween. That is, a plurality of sets of anodes 13 and cathodes 16 constituting a single MEA are arranged on the same plane.

  In the example shown in FIGS. 2 and 3, the membrane / electrode assembly 2 includes four anodes 131 to 134 disposed on one surface 17 </ b> A of the single electrolyte membrane 17 and the other surface of the electrolyte membrane 17. And four cathodes 161 to 164 arranged in 17B. The anode 131 and the cathode 161 are disposed so as to face each other, and constitute a set of MEAs. Similarly, the anode 132 and the cathode 162 are arranged so as to face each other, the anode 133 and the cathode 163 are arranged so as to face each other, and the anode 134 and the cathode 164 are arranged so as to face each other. Four sets of MEAs are arranged on the same plane.

  The fuel cell 1 includes a current collector 20 that electrically connects each set of the anode 13 and the cathode 16 in series.

  That is, as shown in FIGS. 4 and 5, the current collector 20 has an area approximately twice the outer dimension of the membrane electrode assembly 2, and the membrane electrode assembly 2 is bent by folding it into two. It is something to pinch. The current collector 20 has a plurality of first electrode portions 21 and a plurality of second electrode portions 22. The first electrode portion 21 and the second electrode portion 22 are disposed on the same surface of the support body 23. The support body 23 is made of a flexible insulating material.

  The first electrode portion 21 is provided corresponding to each of the anodes 13 and is provided in the same number as the anodes 13 included in the membrane electrode assembly 2. The second electrode portion 22 is provided corresponding to each of the cathodes 16 and is provided in the same number as the cathodes 16 included in the membrane electrode assembly 2.

  In the example shown in FIGS. 4 and 5, the current collector 20 includes four first electrode portions 211 to 214 and four second electrode portions 221 to 224. The first electrode portion 211 corresponds to the anode 131, and similarly, the first electrode portion 212 corresponds to the anode 132, the first electrode portion 213 corresponds to the anode 133, and the first electrode portion 214 corresponds to the anode 134. . The second electrode portion 221 corresponds to the cathode 161, and similarly, the second electrode portion 222 corresponds to the cathode 162, the second electrode portion 223 corresponds to the cathode 163, and the second electrode portion 224 corresponds to the cathode 164. .

  In such a current collector 20, the first electrode portion 21 and the second electrode portion 22 may be formed in a frame shape so as to be in contact with the peripheral edges of the corresponding anode 13 and cathode 16, respectively (see FIG. 4). The example shown in FIG. 5 may be formed in an I-shape that linearly contacts the substantially center of the corresponding anode 13 and cathode 16 (example shown in FIG. 5). Alternatively, the first electrode portion 21 and the second electrode portion 22 may be formed in a ladder shape although not shown. In any of the examples, the first electrode portion 21 and the second electrode portion 22 expose portions of the anode 13 and the cathode 16 from the current collector 20, respectively, and supply fuel for supplying fuel to the anode catalyst layer 11. It has a hole and an air circulation hole for supplying air to the cathode catalyst layer 14.

  In the current collector 20, the first electrode portion 211 and the second electrode portion 224 disposed at positions farthest from each other have terminals 26 and 27 for taking out the collected electricity, respectively. The first electrode portion 21 and the second electrode portion 22 that do not have a terminal are electrically connected by a connecting portion 28. In the example shown in FIGS. 4 and 5, the first electrode part 212 and the second electrode part 221 are connected by the connecting part 281, and similarly, the first electrode part 213 and the second electrode part 222 are connected by the connecting part 282. The first electrode part 214 and the second electrode part 223 are connected by a connecting part 283.

  In the current collector 20 having the structure as described above, the membrane electrode assembly 2 is accommodated in the inner space folded in half. That is, each first electrode portion 21 is electrically connected to the corresponding anode 13, and each second electrode portion 22 is electrically connected to the corresponding cathode 16, so that the current collector is folded in half. The membrane electrode assembly 2 is sandwiched by 20.

  The fuel cell 1 further includes a fuel supply mechanism 3 that supplies fuel to the membrane electrode assembly 2. The fuel supply mechanism 3 includes a fuel storage unit 30 that stores the liquid fuel F. The fuel storage unit 30 is disposed on the anode 13 side of the membrane electrode assembly 2 and supplies fuel to the anode 13 of the membrane electrode assembly 2. The membrane electrode assembly 2 has, for example, a rectangular planar shape, and the fuel storage portion 30 also has the same rectangular planar shape. The fuel storage unit 30 has an opening 30 </ b> A provided on the surface of the membrane electrode assembly 2 facing the anode 13. That is, the fuel storage unit 30 is a box-shaped container having an entire upper surface opened. In such a fuel storage part 30, the liquid fuel F corresponding to the membrane electrode assembly 2 is stored.

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

  The fuel storage unit 30 is constituted by a resin container, for example. The fuel storage unit 30 is preferably formed of a transparent resin so that the remaining amount of the liquid fuel F can be visually observed from the outside. Moreover, it is preferable that such transparent resin has methanol resistance. The fuel storage unit 30 may be entirely formed of a transparent resin, or a part thereof may be formed of a transparent resin.

  Examples of the transparent resin described above include polyethylene naphthalate, polyethylene terephthalate, cyclic olefin copolymer, cycloolefin polymer, polymethylpentene, and polyphenylsulfone. However, this does not exclude the fuel storage unit 30 made of an olefin resin such as a general polyethylene resin or polypropylene resin.

  As shown in FIG. 1, the gas-liquid separation membrane 4 is installed between the opening 30 </ b> A of the fuel storage unit 30 and the membrane electrode assembly 2, but may be omitted. The gas-liquid separation membrane 4 is disposed so as to close the opening 30A of the fuel storage unit 30, and is formed of a membrane that transmits the vaporized component of the liquid fuel F and does not transmit the liquid fuel. Thereby, the vaporized component of the liquid fuel F vaporized in the fuel storage unit 30 is supplied to the anode 13 of the membrane electrode assembly 2 via the opening 30A of the fuel storage unit 30 and the gas-liquid separation membrane 4.

  Examples of the constituent material of the gas-liquid separation membrane 4 include fluorine resins such as silicon and polytetrafluoroethylene. Here, the vaporized component of the liquid fuel F means, for example, when a methanol aqueous solution is applied as the liquid fuel F, it means an air-fuel mixture composed of a vaporized component of methanol and a vaporized component of water. Is applied, it means a vaporization component of methanol.

  Further, a support member disposed on the anode 13 side of the membrane electrode assembly 2 may be disposed. The support member to be arranged has a plurality of openings through which the vaporized component of the liquid fuel F can permeate, and has a function of supporting the membrane electrode assembly 2 with high rigidity.

  The moisturizing layer 5 is disposed on the cathode 16 of the membrane electrode assembly 2, but may be omitted. The moisturizing layer 5 impregnates a part of the water generated in the cathode catalyst layer 14 to suppress water evaporation and uniformly introduce an oxidant into the cathode gas diffusion layer 15. 14 has a function of promoting the uniform diffusion of the oxidant (air) to 14. The moisturizing layer 5 is composed of, for example, a porous member, and specific examples of the constituent material include polyethylene and polypropylene porous bodies.

  In this embodiment, the fuel cell 1 further includes a cover member 18 disposed so as to face the current collector 20 on the cathode (air electrode) 16 side of the membrane electrode assembly 2. In the example shown in FIG. 1, the cover member 18 is disposed on the moisture retention layer 5 disposed on the cathode 16 side of the membrane electrode assembly 2.

  The cover member 18 is formed of a material having high rigidity such as stainless steel (SUS). The cover member 18 has a plurality of openings, that is, air introduction holes 18A for taking in air as an oxidant. The air introduction holes 18A are formed, for example, at substantially equal intervals.

  Such a cover member 18 is fixed to the fuel accommodating portion 30 of the fuel supply mechanism 3 so as to cover the membrane electrode assembly 2 sandwiched between the current collectors 20. That is, the membrane electrode assembly 2 is disposed between the fuel storage unit 30 and the cover member 18. The first electrode portion 21 of the current collector 20 is sandwiched between the anode 13 of the membrane electrode assembly 2 and the fuel storage portion 30. Further, the second electrode portion 22 of the current collector 20 is sandwiched between the cathode 16 and the cover member 18 of the membrane electrode assembly 2.

  In the fuel cell 1 configured as described above, power is generated by the following process.

  That is, the liquid fuel F such as methanol fuel in the fuel storage unit 30 is vaporized, and this vaporized component is supplied to the membrane electrode assembly 2. In the membrane electrode assembly 2, the vaporized component of the liquid fuel F diffuses through the anode gas diffusion layer 12 and is supplied to the anode catalyst layer 11. When methanol fuel is used as the liquid fuel F, the vaporized component supplied to the anode catalyst layer 11 causes an internal reforming reaction of methanol shown in the following formula (1).

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
Note that when pure methanol is used as the methanol fuel, water vapor is not supplied from the fuel storage unit 30, so water generated in the cathode catalyst layer 14 or water in the electrolyte membrane 17 is reacted with methanol (1). Cause an internal reforming reaction. Alternatively, the internal reforming reaction is caused by another reaction mechanism that does not require water, regardless of the internal reforming reaction of the above formula (1).

Electrons (e ⁻ ) generated by this internal reforming reaction are led to the outside via a current collector, and are led to the cathode 16 after operating a portable electronic device or the like as so-called electricity. In addition, protons (H ⁺ ) generated by the internal reforming reaction of the formula (1) are guided to the cathode 16 through the electrolyte membrane 17.

On the other hand, air is supplied to the cathode 16 as an oxidant. That is, the air introduced from the air introduction hole 18 </ b> A provided in the cover member 18 passes through the cathode gas diffusion layer 15 and is supplied to the cathode catalyst layer 14. Electrons (e ⁻ ) and protons (H ⁺ ) reaching the cathode 16 react with oxygen in the air in the cathode catalyst layer 14 in accordance with the following equation (2), and water is generated along with this reaction.

6e ⁻ + 6H ⁺ + (3/2) O ₂ → 3H ₂ O (2)
In the power generation reaction of the fuel cell 1 described above, in order to increase the power to be generated, it is important to make the catalyst reaction smoothly and to make the entire electrode of the membrane electrode assembly 2 more effectively contribute to power generation.

  By the way, the cover member 18 applied to the fuel cell 1 according to the embodiment of the present invention includes a first cover body (reinforcing plate) 181 disposed on the membrane electrode assembly 2 side and a top of the first cover body 181. And a second cover body 182 stacked on each other. The first cover body 181 has a plurality of first air introduction holes 181A for taking in air as an oxidant. Similarly, the second cover body 182 has a plurality of second air introduction holes 182A for taking in air as an oxidant.

  Further, in this embodiment, the first air introduction hole 181A and the second air introduction hole 182A are formed to have different shapes. That is, the first air introduction hole 181A and the second air introduction hole 182A are not overlapped with each other when the first cover body 181 and the second cover body 182 are overlapped with each other. The portions overlap each other and communicate with each other so that the moisture retaining layer 5 can come into contact with the outside air.

  More specifically, one of the first cover body 181 and the second cover body 182 is configured as shown in FIG. 6 and has a relatively large opening size hole (coarse). The other of the first cover body 181 and the second cover body 182 is configured as shown in FIG. 7, and has a relatively small opening size (that is, an opening size smaller than the hole shown in FIG. 6) ( Fine). That is, when the first cover body 181 is configured as shown in FIG. 6, the second cover body 182 is configured as shown in FIG. 7, and the first air introduction hole 181A is the second air introduction hole. The opening size is larger than that of the hole 182A. When the first cover body 181 is configured as shown in FIG. 7, the second cover body 182 is configured as shown in FIG. 6, and the first air introduction hole 181A is the second air introduction hole. The opening size is smaller than the hole 182A.

  When the first cover body 181 and the second cover body 182 are laminated, one of the first air introduction hole 181A and the second air introduction hole 182A overlaps the other plurality of holes. . That is, when the first cover body 181 is configured as shown in FIG. 6 and the second cover body 182 is configured as shown in FIG. 7, the first cover body 181 and the second cover body 182 are connected. When stacked, when viewed from the second cover body 182 side, as shown in FIG. 8, a part of the single first air introduction hole 181A is overlapped so as to be exposed from the two second air introduction holes 182A. is doing. Further, when the first cover body 181 is configured as shown in FIG. 7 and the second cover body 182 is configured as shown in FIG. 6, the first cover body 181 and the second cover body 182 are connected. When stacked, when viewed from the second cover body 182 side, as shown in FIG. 9, the two first air introduction holes 181A overlap each other so as to be exposed from the single second air introduction hole 182A. Communicate.

  With such a configuration, it is possible to increase the holding strength of the first electrode portion 21 and the second electrode portion 22 of the current collector 20 on the membrane electrode assembly 2, and the membrane electrode assembly 2 and the current collector can be stably provided. Electrical contact with the body 20 can be maintained.

  Further, when the first cover body 181 and the second cover body 182 are laminated, the apparent air in the cover member 18 is compared with the case where the first air introduction hole and the second air introduction hole have the same shape. Since the area of the introduction hole 18A (the area where the first air introduction hole and the second air introduction hole overlap) is reduced, the diffusion of water generated by the power generation reaction on the cathode 16 side of the membrane electrode assembly 2 from the moisture retention layer 5 is reduced. It becomes possible to suppress. For this reason, water can be efficiently used in the power generation reaction on the anode 13 side.

  Further, when the first cover body 181 and the second cover body 182 are stacked, the first air introduction hole 181A and the second air introduction hole 182A are in communication with each other. Even when compared with the case where the introduction hole has the same shape, the substantial air intake amount is not reduced. For this reason, oxygen required for the power generation reaction on the cathode side can be efficiently used without being insufficient.

  Thereby, in the fuel cell 1 that collects electricity by bringing the current collector 20 into contact with the membrane electrode assembly 2, it is possible to stably obtain a high output with a low contact resistance.

  In the fuel cell 1 described above, when the current collector 20 having the I-shaped first electrode portion 21 and the second electrode portion 22 is applied as shown in FIG. One of the first cover body 181 and the second cover body 182 preferably has a pressing portion positioned on the first electrode portion 21 and the second electrode portion 22 of the current collector 20. .

  That is, in the example illustrated in FIG. 10, the current collector 20 that sandwiches the membrane electrode assembly 2 includes the I-shaped first electrode portion 21 and the second electrode portion 22. The first electrode portion 21 is in contact with the anode 13, and the second electrode portion 22 is in contact with the cathode 16. A support member 41 is disposed on the anode 13 side of the membrane electrode assembly 2. The support member 41 has a plurality of openings 41 </ b> A that allow the vaporized component of the liquid fuel F to pass therethrough. A cover member 18 is disposed on the cathode 16 side of the membrane electrode assembly 2. The cover member 18 has a first cover body 181 and a second cover body 182, which are laminated.

  As shown in FIG. 7, the first cover body 181 has a first air introduction hole 181A having a relatively small opening size. As shown in FIG. 6, the second cover body 182 has a second air introduction hole 182 </ b> A having a relatively large opening size. In addition, in order to simplify description, the moisturizing layer was omitted.

  In addition, the first cover body 181 has a pressing portion 181B located on the first electrode portion 21 and the second electrode portion 22 of the current collector 20 between two adjacent second air introduction holes 181A. ing. That is, when the current collector 20 is pressed against the membrane electrode assembly 2 by the cover member 18, the pressing portion 181 </ b> B overlaps with the first electrode portion 21 and the second electrode 22 and faces the anode 13 and the cathode 16, respectively. It has a function of pressing the first electrode portion 21 and the second electrode 22.

  Thereby, the contact resistance between the current collector 20 and the membrane electrode assembly 2 can be further reduced, and a higher output can be stably obtained.

The first cover body 181 has a first air introduction hole 181A having a relatively large opening size as shown in FIG. 6, and the second cover body 182 has a relatively small opening as shown in FIG. In the case of having the second air introduction hole 182A of the size, the second cover body 182 has a pressing portion, and the same effect as that shown in FIG. It is done. When the performance of the fuel cell 1 was confirmed for such a configuration, the average output was 16.3 mW / cm ² , the efficiency was 1.10 Wh / g, and the resistance value Imp during operation was 550 mΩ. It was. In addition, when the first cover body 181 and the second cover body 182 both have air introduction holes having a relatively large opening size as shown in FIG. The average output was 15.8 mW / cm ² , the efficiency was 0.90 Wh / g, and the resistance value Imp during operation was 570 mΩ.

  In the above-described embodiment, a purely passive type fuel cell such as an internal vaporization type equipped with the fuel storage portion 30 on the anode side of the membrane electrode assembly 2 has been described. The same configuration is applied to a fuel cell of a semi-passive type that includes a fuel supply unit that supplies fuel to the fuel supply unit and a fuel storage unit that stores fuel supplied to the fuel supply unit. Needless to say, the same effect can be obtained.

  For example, in the example shown in FIG. 11, the fuel supply mechanism 3 includes a fuel supply unit 31 that is disposed on the anode 13 side of the membrane electrode assembly 2 and supplies fuel to the anode 13 of the membrane electrode assembly 2. Yes. The fuel supply mechanism 3 includes a fuel storage unit (not shown) that stores liquid fuel supplied to the fuel supply unit 31. The fuel storage unit stores liquid fuel corresponding to the membrane electrode assembly 2.

  The fuel supply unit 31 and the fuel storage unit are connected via a liquid fuel passage such as a pipe (not shown). That is, liquid fuel is introduced into the fuel supply unit 31 from the fuel storage unit via the flow path. The flow path is not limited to piping independent of the fuel supply unit 31 and the fuel storage unit. For example, when the fuel supply unit 31 and the fuel storage unit are stacked and integrated, a liquid fuel flow path connecting them may be used.

  In the semi-passive type fuel cell, the fuel supplied from the fuel storage unit 31 to the membrane electrode assembly 2 is used for a power generation reaction, and is not circulated and returned to the fuel storage unit 31 thereafter. The semi-passive type fuel cell is different from the conventional active method because it does not circulate the fuel, and does not impair the downsizing of the device. In addition, the fuel cell uses a pump for supplying fuel, and is different from a pure passive system such as a conventional internal vaporization type. For this reason, the fuel cell is referred to as a semi-passive method as described above. In this semi-passive type fuel cell, a fuel cutoff valve may be arranged in place of the pump as long as fuel is supplied from the fuel storage portion to the membrane electrode assembly. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

  The fuel supply unit 31 has a fuel inlet 32 through which liquid fuel is injected via a flow path at the bottom thereof, a fuel supply port 33 that supplies liquid fuel injected from the fuel inlet 32 and vaporized components thereof, And a thin tube 34 that connects the fuel inlet 32 and the fuel supply port 33. In the example of the fuel supply unit 31 shown here, the fuel injection port 32 and the fuel supply port 33 are each one place.

  A support member 41 that supports the membrane electrode assembly 2 from the anode 13 side is disposed between the membrane electrode assembly 2 and the fuel supply unit 31.

  Although such a support member 41 may be omitted, the following effects can be obtained by applying the support member 41 in such a semi-passive system. That is, by disposing the support member 41 between the membrane electrode assembly 2 and the fuel supply unit 31, a distance from the fuel supply port 33 to the membrane electrode assembly 2 can be secured. For this reason, it is possible to secure a sufficient capacity to promote the vaporization of the liquid fuel supplied from the fuel supply port 33, and it is possible to diffuse the fuel in a gaseous state over a wide range. As a result, the fuel distribution in the plane of the anode 13 can be leveled, and the fuel required for the power generation reaction in the membrane electrode assembly 2 can be supplied as a whole without excess or deficiency. Therefore, it is possible to efficiently generate a power generation reaction in the membrane electrode assembly 2 without causing an increase in size or complexity of the fuel cell 1. As a result, the output of the fuel cell 1 can be improved. In other words, the output and its stability can be improved without impairing the advantages of the fuel cell 1 that does not circulate the fuel.

  Moreover, since the membrane electrode assembly 2 is supported by the support member 41 and the membrane electrode assembly 2 is held between the support member 41 and the cover member 18, deformation such as bending of the membrane electrode assembly 2 is suppressed. It is possible to increase the adhesion between the electromotive unit and the current collector and suppress the decrease in output.

  A porous body 42 is disposed between the membrane electrode assembly 2 and the fuel supply unit 31. As the constituent material of the porous body 42, various resins are used, and a porous resin film or the like is used as the porous body 42. Such a porous body 42 may be arranged by laminating a plurality of porous films. That is, you may apply combining the porous body 42 with high diffusivity mainly in one direction, and the porous body 42 with high diffusivity to the direction which cross | intersects this (or orthogonally crossing).

  Such a porous body 42 may be omitted, but in such a semi-passive system, the following effects can be obtained by applying the porous body 42. That is, by disposing the porous body 42, the amount of fuel supplied to the anode 13 can be further averaged. That is, the liquid fuel supplied from the fuel supply port 33 of the fuel supply unit 31 is once absorbed by the porous body 42 and diffuses in the in-plane direction inside the porous body 42. Thereafter, fuel is supplied from the porous body 42 to the anode 13 via the support member 41, so that the fuel supply amount can be further averaged.

  As in the example shown in FIG. 1, the cover member 18 is laminated on the first cover body 181 and the first cover body 181 disposed on the membrane electrode assembly 2 side and having the first air introduction hole 181A. By applying the configuration including the second cover body 182 having the second air introduction hole 182A having a shape different from that of the first air introduction hole 181A, the same effect as the example shown in FIG. 1 can be obtained.

  In the example shown in FIG. 12, the fuel supply unit 31 constituting the fuel supply mechanism 3 has a fuel injection port 32 into which liquid fuel is injected via a flow path and a fuel injection port 32 that is injected from the fuel injection port 32. A plurality of fuel supply ports 33 for supplying liquid fuel and vaporized components thereof, and a thin tube 34 connecting the fuel injection port 32 and each fuel supply port 33 are provided.

  In the fuel supply mechanism 3 having such a configuration, the liquid fuel injected from the fuel injection port 32 into the fuel supply unit 31 can be guided to the plurality of fuel supply ports 33 via the thin tubes 34 branched into a plurality of branches. Is possible. That is, by applying such a fuel supply mechanism 3, the liquid fuel injected from the fuel injection port 32 can be evenly distributed to the plurality of fuel supply ports 33 regardless of the direction or position. Therefore, the uniformity of the power generation reaction in the plane of the membrane electrode assembly 2 can be further enhanced.

  Further, by connecting the fuel injection port 32 and the plurality of fuel supply ports 33 with the thin tubes 34, it is possible to design to supply more fuel to a specific location of the fuel cell 1. For example, in the case where the heat dissipation by half of the fuel cell 1 is improved due to the convenience of mounting the device, a temperature distribution is conventionally generated, and a decrease in average output is inevitable. On the other hand, by adjusting the formation pattern of the thin tubes 34 and arranging the fuel supply ports 33 densely in a portion where heat dissipation is good in advance, it is possible to increase the heat generated by the power generation in that portion. Thereby, the in-plane power generation degree can be made uniform, and it is possible to suppress a decrease in output.

  Also in the fuel cell 1 of such an example, similarly to the example shown in FIG. 1, as the cover member 18, the first cover body 181 disposed on the membrane electrode assembly 2 side and having the first air introduction hole 181A, FIG. 1 shows a configuration including a second cover body 182 that is stacked on the first cover body 181 and has a second air introduction hole 182A having a shape different from that of the first air introduction hole 181A. The same effect as the example can be obtained.

  The fuel cell 1 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. The fuel cell 1 of each embodiment can particularly exhibit its performance and effects when methanol having a concentration of 80 wt% or more is used as the liquid fuel. Therefore, each embodiment is preferably applied to the fuel cell 1 using a methanol aqueous solution or pure methanol having a concentration of 80 wt% or more as a liquid fuel.

  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 embodiment, or deleting some constituent elements from all the constituent elements shown in the embodiment. Embodiments of the present invention can be expanded or modified within the scope of the technical idea of the present invention, and these expanded and modified embodiments are also included in the technical scope of the present invention.

FIG. 1 is a cross-sectional view schematically showing a configuration of a fuel cell according to an embodiment of the present invention. FIG. 2 is a plan view schematically showing the appearance of the membrane electrode assembly in the fuel cell shown in FIG. FIG. 3 is a perspective view when the membrane electrode assembly shown in FIG. 2 is cut along the line III-III. FIG. 4 is a plan view schematically showing the structure of the current collector applicable to the fuel cell according to one embodiment of the present invention. FIG. 5 is a plan view schematically showing another structure of the current collector applicable to the fuel cell according to the embodiment of the present invention. FIG. 6 is a plan view schematically showing the structure of a cover body applicable to the fuel cell according to one embodiment of the present invention. FIG. 7 is a plan view schematically showing the structure of a cover body applicable to the fuel cell according to one embodiment of the present invention. FIG. 8 is a diagram illustrating a state when the second cover body illustrated in FIG. 7 is stacked on the first cover body illustrated in FIG. 6. FIG. 9 is a diagram illustrating a state when the second cover body illustrated in FIG. 6 is stacked on the first cover body illustrated in FIG. 7. FIG. 10 is a perspective view for explaining a laminated state of the membrane electrode assembly, the current collector, and the cover member. FIG. 11 is a cross-sectional view schematically showing another structure of the fuel cell according to the embodiment of the present invention. FIG. 12 is a sectional view schematically showing another structure of the fuel cell according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS F ... Liquid fuel 1 ... Fuel cell 2 ... Membrane electrode assembly 3 ... Fuel supply mechanism 4 ... Gas-liquid separation membrane 5 ... Moisturizing layer 11 ... Anode catalyst layer 12 ... Anode gas diffusion layer 13 ... Anode 14 ... Cathode catalyst layer 15 ... Cathode gas diffusion layer 16 ... cathode 17 ... electrolyte membrane 20 ... current collector 21 ... first electrode portion 22 ... second electrode portion 41 ... support member 42 ... porous body 18 ... cover member 18A ... air introduction hole 181 ... first cover Body 181A ... first air introduction hole 182 ... second cover body 182A ... second air introduction hole

Claims (7)

A membrane electrode assembly having a fuel electrode, an air electrode, and an electrolyte membrane sandwiched between the fuel electrode and the air electrode;
A current collector sandwiching the membrane electrode assembly;
A cover member disposed on the air electrode side of the membrane electrode assembly so as to face the current collector and having an air introduction hole;
The cover member is disposed on the membrane electrode assembly side and has a first cover body having a first air introduction hole, and a second air introduction layered on the first cover body and having a shape different from that of the first air introduction hole. A fuel cell comprising a second cover body having a hole.   2. The fuel cell according to claim 1, wherein an opening size of one of the first air introduction hole and the second air introduction hole is smaller than the other hole.   3. The fuel cell according to claim 2, wherein one of the first air introduction hole and the second air introduction hole overlaps the other plurality of holes. 4. The current collector has an I-shaped electrode portion that linearly contacts the substantially center of the air electrode and the fuel electrode in the membrane electrode assembly,
2. The fuel cell according to claim 1, wherein one cover body of the first cover body and the second cover body has a pressing portion positioned on the electrode portion of the current collector. .   The single hole of the other cover body of the first cover body and the second cover body overlaps two holes facing each other across the pressing portion of the one cover body. 5. The fuel cell according to 4.   The fuel cell according to claim 1, wherein the liquid fuel supplied to the membrane electrode assembly is methanol fuel.   The fuel cell according to claim 6, wherein the methanol fuel is a methanol aqueous solution or pure methanol having a methanol concentration of 80 wt% or more.

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