JP2009135091A - Fuel cell, and method of manufacturing fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of enhancing output, and stably obtaining sufficient output for a long time; and to provide a method of manufacturing a fuel cell. <P>SOLUTION: The fuel cell includes an anode 13, a cathode 16 and a membrane electrode assembly 2 pinch-held between the anode 13 and the cathode 16, and the side surfaces of the anode 13 and the cathode 16 are covered with a coating body 50 having proton conductivity, and the coating body 50 comes in contact with the electrolyte membrane 17. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell using a liquid fuel and a method for manufacturing the fuel cell.

  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 type DMFC, for example, a structure in which a membrane electrode assembly (MEA) having a fuel electrode, an electrolyte membrane, and an air electrode is arranged on a fuel housing portion formed of a resin-made box-like container has been proposed. (For example, refer to Patent Document 1).

In a fuel cell using such a membrane electrode assembly, there is a problem in that the catalyst layer is peeled off or the electrolyte membrane is damaged due to swelling of the electrolyte membrane, and the power generation voltage of the fuel cell is reduced. For such a problem, for example, a configuration in which the periphery of the catalyst layer and the gas diffusion layer and the electrolyte membrane are bonded with a resin has been proposed (see, for example, Patent Document 2).
International Publication No. 2005/112172 Pamphlet JP 2006-032188 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to improve the output and to provide a fuel cell and a fuel capable of stably obtaining a sufficient output over a long period of time. It is in providing the manufacturing method of a battery.

The fuel cell according to the first aspect of the present invention comprises:
A membrane electrode assembly having an anode, a cathode, and an electrolyte membrane sandwiched between the anode and the cathode;
At least one side surface of the anode and the cathode is covered with a covering body having proton conductivity, and the electrolyte membrane and the covering body are in contact with each other.

A fuel cell manufacturing method according to a second aspect of the present invention comprises:
Preparing a membrane electrode assembly having an electrolyte membrane sandwiched between an anode and a cathode;
Covering at least one side surface of the anode and the cathode with a covering body having proton conductivity,
The electrolyte membrane and the covering are in contact with each other.

A fuel cell manufacturing method according to another aspect of the present invention includes:
Applying or spraying a proton conductive coating on at least one major plane of the electrolyte membrane;
Arranging the anode on one main plane of the electrolyte membrane and the cathode on the other main plane of the electrolyte membrane before the covering is cured,
The cured covering may cover at least one side surface of the anode and the cathode and may be in contact with the electrolyte membrane.

  According to this invention, the side surface of at least one of the anode and the cathode is covered with the covering body having proton conductivity, and the electrolyte membrane and the covering body are in contact with each other. As a result, proton conduction is possible even in the electrode portion that is separated from the electrolyte membrane (that is, not in contact with the electrolyte membrane), and contributes to the power generation reaction. Therefore, it is possible to provide a fuel cell and a method for manufacturing the fuel cell that can improve the output and stably obtain a sufficient output over a long period of time.

  The “side surface of the electrode” as used in the present invention refers to a surface in a direction substantially perpendicular to the direction of contact (stacking) with the electrolyte membrane not in contact with the electrolyte membrane.

  Hereinafter, a fuel cell and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing the structure of a fuel cell 1 according to this embodiment. In this embodiment, an internal vaporization type passive system will be described as the fuel cell 1, but the present invention is not limited to this system.

  The fuel cell 1 includes a membrane electrode assembly 2 constituting an electromotive unit. 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 serves to uniformly supply fuel to the anode catalyst layer 11 and also has a current collecting function of the anode catalyst layer 11. The cathode gas diffusion layer 15 laminated on the cathode catalyst layer 14 serves to uniformly supply the oxidant to the cathode catalyst layer 14 and also has a current collecting function of the cathode catalyst layer 14. Examples of the anode gas diffusion layer 12 and the cathode gas diffusion layer 15 include papers, nonwoven fabrics, woven fabrics, knitted fabrics, and conductive porous substrates made of fibers such as carbon and conductive polymers. It is preferably made of paper.

  In the example shown in FIGS. 2 and 3, the membrane electrode assembly 2 has a plurality of unit cells C, and each unit cell C is disposed separately in the plane of the electrolyte membrane 17. Yes. That is, the membrane electrode assembly 2 is opposed to each of the plurality of anodes 13 arranged at intervals on one surface of the single electrolyte membrane 17 and each of the anodes 13 on the other surface of the electrolyte membrane 17. And a plurality of cathodes 16 arranged at intervals. The combination of the anode 13 and the cathode 16 sandwiching the electrolyte membrane 17 forms a single cell C. Here, a case where there are four anodes 13 and four cathodes 16 is shown.

  In the example shown here, each of the single cells C are arranged side by side in the direction orthogonal to the longitudinal direction on the same plane. The structure of the membrane electrode assembly 2 is not limited to this example, and may be another structure.

  In the membrane electrode assembly 2 having a plurality of single cells C, each single cell C is electrically connected in series by a current collector. That is, the current collector has an anode current collector and a cathode current collector. In order to correspond to the membrane electrode assembly 2 shown in FIG. 2 and the like, each current collector has four anode current collectors and cathode current collectors.

  Each of the anode current collectors is stacked on the anode gas diffusion layer 12 in each single cell C. Each of the cathode current collectors is stacked on the cathode gas diffusion layer 15 in each single cell C. As the anode current collector and the cathode current collector, for example, a porous layer (for example, a mesh) or a foil body made of a metal material such as gold (Au) or nickel (Ni), or a conductive metal such as stainless steel (SUS). A composite material in which a material is coated with a highly conductive metal such as gold can be used.

  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 and oxidant leakage from the membrane electrode assembly 2.

  The fuel cell 1 further includes a fuel supply mechanism 3 that supplies the liquid fuel F 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, the liquid fuel F 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, a gas-liquid separation membrane 4 may be installed between the opening 30 </ b> A of the fuel storage unit 30 and the membrane electrode assembly 2. 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 but does not transmit the liquid fuel F. 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.

  The moisture retaining layer 20 is disposed on the cathode 16 of the membrane electrode assembly 2, but may be omitted. The moisturizing layer 20 is impregnated with a part of the water generated in the cathode catalyst layer 14 to suppress the transpiration of water and uniformly introduce an oxidant (air) into the cathode gas diffusion layer 15. It has a function of promoting uniform diffusion of the oxidizing agent to the cathode catalyst layer 14. The moisturizing layer 20 is composed of, for example, a porous member, and specific constituent materials include polyethylene and polypropylene porous bodies.

  In this embodiment, the fuel cell 1 further includes a cover member 18 disposed on the cathode (air electrode) 16 side of the membrane electrode assembly 2. The cover member 18 has a substantially box-like appearance and is made of, for example, stainless steel (SUS). The cover member 18 has a plurality of openings (air introduction holes) 18A for taking in air as an oxidant.

  Such a cover member 18 is fixed to the fuel storage unit 30 so as to cover the gas-liquid separation membrane 4, the membrane electrode assembly 2, and the moisture retention layer 20. That is, the membrane electrode assembly 2 is disposed between the fuel storage unit 30 and the cover member 18. The cover member 18 functions as a support that supports 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 the vaporized component passes through the gas-liquid separation membrane 4 and is supplied to the membrane electrode assembly 2. In the membrane electrode assembly 2, the vaporized component of the liquid fuel F diffuses in 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 opening 18 </ b> A provided in the cover member 18 passes through the moisture retention layer 20 and the cathode gas diffusion layer 15 and is supplied to the cathode catalyst layer 14. Electrons (e ⁻ ) and protons (H ⁺ ) that have reached the cathode 16 react with oxygen in the air in the cathode catalyst layer 14 according to the following formula (2), and water is generated with this reaction.

6e ⁻ + 6H ⁺ + (3/2) O ₂ → 3H ₂ O (2)
In the power generation reaction of the fuel cell 1 described above, in order to increase the power to be generated, 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, in the membrane electrode assembly 2 according to this embodiment, the side surface of at least one of the anode 13 and the cathode 16 is covered with a covering body having proton conductivity. In the example shown in FIGS. 2 to 4, the side surfaces 13 </ b> S and 16 </ b> S of all four sets of the anode 13 and the cathode 16 are covered with the covering 50. Here, in particular, the anode 13 and the cathode 16 are formed in a strip shape, and all four end surfaces thereof are covered with the covering 50. That is, the covering 50 is arranged in a frame shape along the outer periphery of the anode 13 and the cathode 16.

  That is, as shown in FIG. 4, the surface 11P of the anode catalyst layer 11 constituting the anode 13 and the surface 14P of the cathode catalyst layer 14 constituting the cathode 16 are joined to the main planes 17A and 17B of the electrolyte membrane 17, respectively. Yes. For this reason, these joint surfaces function as proton conduction paths and contribute to the above-described power generation reaction.

  On the other hand, the side surface 11S of the anode catalyst layer 11 and the side surface 14S of the cathode catalyst layer 14 are not in direct contact with the electrolyte membrane 17. For this reason, in the side part of each electrode, a proton conduction path is not formed and does not contribute to the power generation reaction.

  Therefore, in this embodiment, the side surfaces 13S and 16S of the electrodes of the anode 13 and the cathode 16 are covered with a covering 50 having proton conductivity. Thereby, the side surface 11S of the anode catalyst layer 11 and the side surface 14S of the cathode catalyst layer 14 are in contact with the electrolyte membrane 17 through the covering 50. That is, when the covering body 50 and the electrolyte membrane 17 are in contact with each other, proton conduction paths are formed on the portions that are not in direct contact with the electrolyte membrane 17, that is, on the side surface 11S of the anode catalyst layer 11 and the side surface 14S of the cathode catalyst layer 14. It becomes possible to form.

  As described above, in each electrode, the covering 50 is arranged so as to cover at least the side surface of the catalyst layer, whereby the electrode area contributing to the power generation reaction, that is, the proton conduction path can be increased. The anode catalyst layer 11 has a thickness of 100 μm to 130 μm, for example. The cathode catalyst layer 14 has a thickness of 60 μm to 80 μm, for example. For this reason, an area corresponding to the product of the thickness of the catalyst layer and the outer peripheral length of the catalyst layer is added as the electrode area.

  Of course, even if the covering 50 is arranged so as to cover not only the side surface of the catalyst layer but also the side surface of the gas diffusion layer, the electrode area contributing to the power generation reaction can be similarly increased. It becomes.

  Thereby, proton conduction is possible also on the side surface of each electrode that has not conventionally contributed to the power generation reaction, and contributes to the power generation reaction. That is, the electrode area contributing to the power generation reaction can be increased. Therefore, it is possible to improve the output, obtain a stable output over a long period of time, and improve the reliability.

  In the above-described embodiment, the electrolyte membrane 17 is formed with a size larger than that of the anode 13 and the cathode 16, and extends outward from the anode 13 and the cathode 16. For this reason, the covering 50 that covers the side surface 13 </ b> S of the anode 13 is in contact with the main plane 17 </ b> A of the electrolyte membrane 17. That is, a proton conduction path is formed between the side surface 13S and the main plane 17A by the covering body 50. The covering 50 that covers the side surface 16 </ b> S of the cathode 16 is in contact with the main plane 17 </ b> B of the electrolyte membrane 17. That is, a proton conduction path is formed between the side surface 16S and the main plane 17B by the covering 50.

  Further, as shown in FIGS. 5 and 6, not only the side surfaces of the electrodes of the anode 13 and the cathode 16 but also the electrolyte membrane 17 exposed from the anode 13 and the cathode 16 is covered with a covering 50 having proton conductivity. May be. At this time, the covering 50 may cover the entire surface of the electrolyte membrane 17 (except for the periphery of the electrolyte membrane 17 sealed by the sealing material 19), or may cover the electrolyte membrane 17 while the electrodes are adjacent to each other. Also good.

  In the case where the entire surface of the electrolyte membrane 17 is covered with the covering 50, there is also an effect of preventing a short circuit between adjacent single cells C, which leads to stabilization of quality in manufacturing. Further, covering the gaps between the electrodes with the covering 50 has the effect of eliminating the space, suppressing the permeation of fuel from the anode side to the cathode side, and giving the MEA as a whole a uniform temperature distribution. Is possible.

  Even in such a configuration, the side surface of the anode catalyst layer 11 and the side surface of the cathode catalyst layer 14 are in contact with the electrolyte membrane 17 through the covering 50, so that it is possible to increase the proton conduction path that contributes to the power generation reaction. Become. Therefore, it is possible to improve the output, obtain a stable output over a long period of time, and improve the reliability.

  The cross section as shown in FIG. 4 or the like can be confirmed when the membrane / electrode assembly is solidified with a resin, cut and then cut and observed with a scanning electron microscope (SEM).

  The covering body 50 described above can be formed of the same material as the proton conductive material constituting the electrolyte membrane 17.

  The covering 50 can also be formed of a hydrocarbon electrolyte.

  That is, as the hydrocarbon-based electrolyte, for example, (A) a polymer electrolyte in which a sulfonic acid group and / or a phosphonic acid group is introduced into a polymer in which the main chain is an aliphatic hydrocarbon, (B) the main chain has an aromatic ring. A polyelectrolyte in which a sulfonic acid group and / or a phosphonic acid group are introduced into the polymer having (C) the polymer before introduction of the sulfonic acid group and / or phosphonic acid group in (A) and (B) described above Examples thereof include a polymer electrolyte obtained by introducing a sulfonic acid group and / or a phosphonic acid group into a copolymer composed of any two or more kinds of repeating units selected from repeating units.

  Here, “the sulfonic acid group and / or phosphonic acid group is introduced into the polymer” means “the sulfonic acid group and / or phosphonic acid group is introduced into the polymer skeleton via a chemical bond”.

  Examples of the polymer electrolyte (A) described above include polyvinyl sulfonic acid, polystyrene sulfonic acid, poly (α-methylstyrene) sulfonic acid, and the like.

  The polymer electrolyte of (B) described above may be one in which the main chain is interrupted by a hetero atom such as an oxygen atom. For example, polyether ether ketone, polysulfone, polyether sulfone, poly (arylene. Ether), polyphosphazene, polyimide, poly (4-phenoxybenzoyl-1,4-phenylene), polyphenylene sulfide, polyphenylquinoxalen, and other homopolymers each having a sulfonic acid group introduced, arylsulfone Polybenzimidazole, alkylsulfonated polybenzimidazole, alkylphosphonated polybenzimidazole, phosphonated poly (phenylene ether), and the like.

  As the polymer electrolyte (C) described above, a sulfonic acid group and / or a phosphonic acid group is introduced into a random copolymer, but a sulfonic acid group and / or a phosphonic acid group is introduced into an alternating copolymer. Alternatively, a block copolymer having a sulfonic acid group and / or a phosphonic acid group introduced may be used. Examples of the sulfonic acid group introduced into the random copolymer include a sulfonated polyethersulfone-dihydroxybiphenyl copolymer. The block copolymer having a sulfonic acid group and / or a phosphonic acid group introduced is a block copolymer in which the main chain of all blocks is composed of aliphatic hydrocarbons, such as styrene- (ethylene-butylene). -A styrene triblock copolymer having a sulfonic acid group and / or a phosphonic acid group introduced may be used, but at least one block is a block copolymer having an aromatic ring in its main chain. High heat resistance is preferable. In addition, a block copolymer having at least one block having a sulfonic acid group and / or phosphonic acid group and one or more blocks having substantially no sulfonic acid group and / or phosphonic acid group is more preferable because of excellent conductivity.

  In particular, the hydrocarbon-based electrolyte is less swelled and contracted by water or fuel, and in addition, has high resistance to fuel (for example, methanol). For this reason, it becomes possible to form the tough covering 50 with the hydrocarbon electrolyte.

  As described above, the covering 50 formed of the hydrocarbon-based electrolyte can obtain a stable output over a long period of time as well as an improvement in output by improving the catalyst utilization efficiency, like the proton conductive material constituting the electrolyte membrane 17. become.

  Next, the manufacturing method of the membrane electrode assembly 2 having the above-described structure will be described. In addition, the manufacturing method demonstrated here is an example, Comprising: Another process may be added and the demonstrated process may be substituted by another process.

  According to the first manufacturing method shown in FIG. 7A, first, a catalyst layer is applied on the gas diffusion layer. That is, a paste prepared by mixing a solvent, a catalyst, and the like is applied onto carbon paper that functions as a gas diffusion layer. Then, the applied paste is dried. Thereby, the anode 13 and the cathode 16 having a structure in which the catalyst layer is laminated on the gas diffusion layer are formed.

  The cathode 16 and the anode 13 thus formed are washed and then cut into a desired size (for example, a strip shape shown in FIG. 3). Then, the anode 13 and the cathode 16 are respectively arranged with the electrolyte membrane 17 interposed therebetween, and all are joined by heating and pressurizing, whereby the membrane electrode assembly 2 is manufactured.

  Subsequently, in the membrane / electrode assembly 2 manufactured as described above, the side surface of at least one of the anode 13 and the cathode 16 is covered with a covering 50 having the same proton conductivity as that of the electrolyte membrane 17. . That is, the liquid coating 50 is applied or sprayed along the side surface of the electrode, and then dried and cured. At this time, the covering 50 is disposed so as to cover at least the side surface of the catalyst layer. The covering 50 thus formed is in contact with the electrolyte membrane 17.

  According to the membrane electrode assembly 2 formed through such a manufacturing process, since at least one of the anode 13 and the cathode 16 is covered with a covering body having proton conductivity on the electrode side surface, Proton conduction is also possible on the side surface, contributing to power generation reactions. Therefore, the power generation efficiency can be improved and a fuel cell with a stable output can be supplied.

  According to the second manufacturing method shown in FIG. 7B, similarly to the first manufacturing method, first, the anode 13 and the cathode 16 having a structure in which a catalyst layer is laminated on a gas diffusion layer are prepared. Then, an electrolyte membrane 17 is prepared.

  Then, a liquid coating 50 having the same proton conductivity as that of the electrolyte membrane 17 is applied or sprayed on one main plane 17A of the electrolyte membrane 17. Then, before the covering 50 is cured, the anode 13 is disposed on the main plane 17A. At this time, by pressurizing the anode 13 toward the electrolyte membrane 17, the covering 50 between the anode 13 and the electrolyte membrane 17 escapes outward and is cured. For this reason, the hardened covering 50 covers the side surface 13 </ b> S of the anode 13 and contacts the electrolyte membrane 17.

  Similarly, on the other main plane 17B of the electrolyte membrane 17, after applying or spraying the liquid coating 50, the cathode 16 is disposed on the main plane 17B before the coating 50 is cured. Then, by pressing the cathode 16 toward the electrolyte membrane 17 and then drying, the cured covering 50 covers the side surface 16 </ b> S of the cathode 16 and contacts the electrolyte membrane 17.

  Also in the membrane electrode assembly 2 formed through such a manufacturing process, since the side surface of the electrode is covered with a covering body having proton conductivity, proton conduction is also possible on the side surface, contributing to the power generation reaction. . Therefore, the power generation efficiency can be improved and a fuel cell with a stable output can be supplied.

  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. 8, 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 part to the membrane electrode assembly 2 is used for a power generation reaction, and is not circulated and returned to the fuel storage part. The semi-passive type fuel cell is different from the conventional active type because it does not circulate the fuel, and does not impair the downsizing of the apparatus. Further, this semi-passive type fuel cell uses a pump for supplying fuel, and is different from a pure passive type such as a conventional internal vaporization type. In this semi-passive type fuel cell, a fuel cutoff valve may be arranged instead of the pump as long as the fuel is supplied from the fuel storage portion to the membrane electrode assembly 2. 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 may be disposed between the membrane electrode assembly 2 and the fuel supply unit 31.

  In such a semi-passive method, the following effects can be obtained by applying the support member 41. 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.

  At least one porous body 42 may be 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, a porous body mainly having high diffusibility in one direction and a porous body having high diffusivity in a direction intersecting (or orthogonal to) the main body may be used in combination.

  In such a semi-passive method, 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, so that the fuel supply amount can be further averaged.

  As in the example shown in FIG. 1, at least one side surface of the anode 13 and the cathode 16 is covered with a covering 50 having proton conductivity, and a structure in which the electrolyte membrane 17 and the covering 50 are in contact is applied. is doing. Even with such a configuration, the same effect as the example shown in FIG. 1 can be obtained.

  In the example shown in FIG. 9, the fuel supply unit 31 constituting the fuel supply mechanism 3 is injected into the bottom thereof from the fuel injection port 32 through which liquid fuel is injected through the flow path and 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, at least one side surface of the anode 13 and the cathode 16 is covered with the covering body 50 having proton conductivity, as in the example shown in FIG. A structure in contact with the body 50 is applied. Even with such a configuration, the same effect as the example shown in FIG. 1 can be obtained.

  Furthermore, it goes without saying that the same effect can be obtained by applying the same configuration to the active fuel cell.

<< Example-Part 1 >>
Next, examples will be described.

  In the membrane electrode assembly 2 according to the example, the anode 13 and the cathode 16 are formed in a strip shape of 81.4 mm × 9.8 mm. In the anode 13, the anode catalyst layer 11 is formed to a thickness of 130 μm. In the cathode 16, the cathode catalyst layer 14 is formed with a thickness of 80 μm.

When the electrode outer periphery is not covered with the covering 50, the electrode area contributing to the power generation reaction is 81.4 × 9.8 = 797.7 mm ² .

On the other hand, when the entire outer periphery of the electrode is covered with the covering 50, in addition to the above electrode area, the electrode side surface (that is, the catalyst layer side surface) is further added as the electrode area. The addition amount, when a reference is thin cathode catalyst layer, the (81.4 + 9.8) × 2 × 0.08 = 14.59mm 2. That is, by covering the entire outer periphery of the electrode with the covering 50, the electrode area is increased by about 2% compared to the case where the covering is not performed. For this reason, the theoretical output also increases to the same extent as the increase in electrode area.

<< Example-Part 2 >>
Hereinafter, examples specifically showing the configuration of the present embodiment and the effects thereof will be described.

Example 1
The electrode 13 side surfaces of the anode 13 and the cathode 16 of the laminated and integrated membrane electrode assembly 2 were covered with a hydrocarbon electrolyte as a covering 50 and dried.

(Example 2)
The electrode body side surfaces of the anode 13 and the cathode 16 of the laminated membrane electrode assembly 2 and the entire surface of the electrolyte membrane 17 exposed from the electrodes were covered with a hydrocarbon electrolyte as a covering body 50 and dried.

(Example 3)
The electrode side surfaces of the anode 13 and the cathode 16 of the laminated membrane electrode assembly 2 were coated with Nafion manufactured by DuPont, which is a perfluorosulfonic acid polymer, and dried.

Example 4
A covering 50 is formed by Nafion manufactured by DuPont, which is a perfluorosulfonic acid polymer, on the side surfaces of the anode 13 and the cathode 16 of the laminated membrane electrode assembly 2 and the entire surface of the electrolyte membrane 17 exposed from the electrodes. Coated and dried.

(Comparative example)
A test fuel cell was assembled as it was without applying a covering to the laminated membrane electrode assembly 2.

In Examples 1 to 4 and the comparative example, the amount of noble metal contained in the anode catalyst layer was adjusted to 3.0 mg / cm ² , and the amount of noble metal contained in the cathode catalyst layer was adjusted to 2.5 mg / cm ² .

  About the fuel cell assembled using the membrane electrode assembly 2 produced in Examples 1 to 4 and the comparative example, each was assembled in a fuel cell evaluation device, methanol was directly supplied to the anode side, and 25 ° C. 50 to the cathode side. The power density was measured under the conditions of a cathode temperature of 55 ° C. and a voltage of 0.35 V while adjusting the air atmosphere to 50%.

  When the initial output density in the comparative example is 100%, the initial output density of Example 1 is 113%, the initial output density of Example 2 is 105%, and the initial output density of Example 3 is 116%. Thus, the initial output density of Example 4 was 103%, and it was confirmed that any of Examples 1 to 4 can obtain an initial output density higher than that of the comparative example. In particular, as in Examples 1 and 3, it was confirmed that a high power density tends to be obtained when the side surface of each electrode is covered with the covering 50.

  Further, the output density after continuously generating power for 5000 hours was reduced by 68% from the initial output density in the comparative example, whereas it was reduced by 37% from the initial output density in the first example, and the initial density in the second example. It was confirmed that the output density decreased by 20%, that in Example 3, it decreased by 66% from the initial output density, and in Example 4, it decreased by 54% from the initial output density.

  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 the structure of a fuel cell according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing a cross section of a part of the structure of the membrane electrode assembly in the fuel cell shown in FIG. FIG. 3 is a plan view of the membrane electrode assembly shown in FIG. 4 is an enlarged view of a part of a cross section of a membrane electrode assembly applicable to the fuel cell shown in FIG. FIG. 5 is a perspective view schematically showing a cross section of a part of another structure of the membrane electrode assembly in the fuel cell shown in FIG. 6 is a plan view of the membrane electrode assembly shown in FIG. FIG. 7A is a flowchart for explaining a first method of manufacturing a membrane electrode assembly applicable to the fuel cell shown in FIG. FIG. 7B is a flowchart for explaining a second manufacturing method of the membrane electrode assembly applicable to the fuel cell shown in FIG. FIG. 8 is a cross-sectional view schematically showing another structure of the fuel cell according to the embodiment of the present invention. FIG. 9 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 1 ... Fuel cell 2 ... Membrane electrode assembly 3 ... Fuel supply mechanism 11 ... Anode catalyst layer 12 ... Anode gas diffusion layer 13 ... Anode 14 ... Cathode catalyst layer 15 ... Cathode gas diffusion layer 16 ... Cathode 50 ... Covering body 17 ... Electrolyte Membrane 18 ... Cover member 18A ... Opening 19 ... Sealing material 20 ... Moisturizing layer 3 ... Fuel supply mechanism 30 ... Fuel storage 30A ... Opening 31 ... Fuel supply

Claims (12)

A membrane electrode assembly having an anode, a cathode, and an electrolyte membrane sandwiched between the anode and the cathode;
At least one side surface of the anode and the cathode is covered with a covering body having proton conductivity, and the electrolyte membrane and the covering body are in contact with each other. The anode and the cathode have a gas diffusion layer, and a catalyst layer formed on the gas diffusion layer and facing the electrolyte membrane,
The fuel cell according to claim 1, wherein the covering covers at least a side surface of the catalyst layer. The electrolyte membrane extends outward from the anode and the cathode,
The fuel cell according to claim 1, wherein the covering is in contact with a main plane of the electrolyte membrane.   The membrane electrode assembly has a structure in which a single electrolyte membrane is sandwiched between a plurality of anodes and a plurality of cathodes, and a combination of the anodes and the cathodes is electrically connected. The fuel cell according to claim 1.   The fuel cell according to claim 1, wherein the liquid fuel supplied to the membrane electrode assembly is methanol fuel.   6. The fuel cell according to claim 5, wherein the methanol fuel is a methanol aqueous solution or pure methanol having a methanol concentration of 80 wt% or more.   The fuel cell according to claim 1, wherein the covering is made of the same material as the electrolyte membrane.   The fuel cell according to claim 1, wherein the covering is formed of a hydrocarbon-based electrolyte.   The fuel cell according to claim 1, wherein the covering covers the electrolyte membrane exposed from the plurality of anodes and the plurality of cathodes. Preparing a membrane electrode assembly having an electrolyte membrane sandwiched between an anode and a cathode;
Covering at least one side surface of the anode and the cathode with a covering body having proton conductivity,
A method of manufacturing a fuel cell, wherein the electrolyte membrane and the covering are in contact with each other.   The method of manufacturing a fuel cell according to claim 10, wherein the step of coating the covering includes a step of curing after applying or spraying a liquid coating. Applying or spraying a proton conductive coating on at least one major plane of the electrolyte membrane;
Arranging the anode on one main plane of the electrolyte membrane and the cathode on the other main plane of the electrolyte membrane before the covering is cured,
The cured covering body covers at least one side surface of the anode and the cathode and is in contact with the electrolyte membrane.

Images