JP2010103014A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of stabilizing output as well as elongating service life. <P>SOLUTION: The fuel cell is provided with a membrane electrode assembly 2 having an electrolyte membrane 17 pinched by an anode 13 and a cathode 16, and a fuel supply mechanism 3 for supplying fuel to the anode 13 of the membrane electrode assembly 2. The fuel supply mechanism 3 is provided with a fuel distribution plate 31 having a fuel exhaust port 33 opposed to the anode 13 of the membrane electrode assembly 2 and a surface 31S of the fuel distribution plate 31A opposed to the anode 13 has lyophilic property to liquid fuel. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technology of a fuel cell using a 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.

  For example, a direct methanol fuel cell (DMFC) using methanol as a fuel can be reduced in size and can be easily handled, and thus is regarded as a promising power source for portable electronic devices. Yes. 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 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 storage portion formed of a box-like container has been proposed (for example, , See Patent Document 1). In addition, it has been studied to connect a fuel cell of a DMFC and a fuel storage unit via a flow path (see, for example, Patent Documents 2 and 3).
International Publication No. 2005/112172 Pamphlet JP 2005-518646 A JP 2006-089552 A

  In the fuel cell, it is important to uniformly supply the fuel to the membrane electrode assembly in the plane thereof. That is, in the membrane electrode assembly, the output changes according to the fuel supply state. For example, an efficient power generation reaction cannot occur even if the amount of fuel supplied is excessive or insufficient. In addition, there may be a difference in the degree of deterioration between the portion where the fuel supply ratio is high and the portion where the fuel supply ratio is low. The local deterioration of the membrane / electrode assembly leads to a decrease in life.

  An object of the present invention is to provide a fuel cell capable of stably obtaining a high output and extending its life.

A fuel cell according to an aspect of the present invention includes:
A membrane electrode assembly having an electrolyte membrane sandwiched between an anode and a cathode;
A fuel supply mechanism for supplying fuel to the anode of the membrane electrode assembly,
The fuel supply mechanism includes a fuel distribution plate having a fuel discharge port facing the anode of the membrane electrode assembly,
The surface of the fuel distribution plate facing the anode is lyophilic with respect to liquid fuel.

  According to the present invention, it is possible to provide a fuel cell capable of stably obtaining a high output and extending its life.

  That is, according to the fuel cell of the present invention, the surface of the fuel distribution plate constituting the fuel supply mechanism that faces the anode of the membrane electrode assembly is lyophilic with respect to the liquid fuel. For this reason, even if the fuel discharged from the fuel discharge port of the fuel distribution plate toward the anode is liquid, the fuel can be diffused in a short time on the surface of the fuel distribution plate. For this reason, it becomes possible to supply a fuel uniformly to the whole surface of a membrane electrode assembly.

  Thereby, it is possible to efficiently generate a power generation reaction in the entire membrane electrode assembly and stably obtain a high output. In addition, local deterioration of the membrane electrode assembly is suppressed, and the life can be extended.

  A technique related to a fuel cell according to an embodiment of the present invention will be described below 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.

  The fuel cell 1 mainly includes a membrane electrode assembly (MEA) 2 that constitutes an electromotive unit, and a fuel supply mechanism 3 that supplies fuel to the membrane electrode assembly 2.

  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 (cathode catalyst layer 14 and 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 carrier 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 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 has a current collecting function of the cathode catalyst layer 14. The anode gas diffusion layer 12 and the cathode gas diffusion layer 15 are made of a conductive porous substrate such as carbon paper.

  In the example shown in FIGS. 2 and 3, the membrane electrode assembly 2 is composed of a plurality of anodes 13 arranged at intervals on one surface of a single electrolyte membrane 17. And a plurality of cathodes 16 arranged at intervals on the other surface of the electrolyte membrane 17 so as to face each of the anodes 13. Here, a case where there are four anodes 13 and four cathodes 16 is shown.

  Each combination of the anode 13 and the cathode 16 sandwiches the electrolyte membrane 17 to form a single cell C. 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 the plurality of single cells C as described above, the single cells C are electrically connected in series by the current collector 18.

  Such a current collector 18 includes an anode current collector 18A and a cathode current collector 18C. In order to correspond to the membrane electrode assembly 2 shown in FIG. 2 and the like, the current collector 18 has four anode current collectors 18A and cathode current collectors 18C, respectively.

  Each of the anode current collectors 18A is laminated on the anode gas diffusion layer 12 in each single cell C. Each of the cathode current collectors 18C is stacked on the cathode gas diffusion layer 15 in each single cell C. As the anode current collector 18A and the cathode current collector 18C, 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 material such as stainless steel (SUS). A composite material obtained by coating a conductive metal material with a good conductive metal such as gold can be used.

  The membrane electrode assembly 2 is sealed by a seal member 19 such as a rubber O-ring disposed on the anode side and the cathode side of the electrolyte membrane 17, thereby preventing fuel leakage from the membrane electrode assembly 2. Oxidant leakage is prevented.

  A plate-like body 20 made of an insulating material is disposed on the cathode 16 side of the membrane electrode assembly 2. In the example shown in FIG. 1, the plate-like body 20 is disposed on the cathode current collector 18C.

  This plate-like body 20 mainly functions as a moisture retaining layer. That is, the plate-like body 20 is impregnated with a part of the water generated in the cathode catalyst layer 14 to suppress the transpiration of water, adjusts the amount of air taken into the cathode catalyst layer 14 and makes the air uniform. Promotes diffusion. The plate-like body 20 is constituted by, for example, a member having a porous structure, and specific constituent materials include polyethylene and polypropylene porous bodies.

  The membrane electrode assembly 2 described above is disposed between the fuel supply mechanism 3 and the cover plate 21. The cover plate 21 has a substantially rectangular appearance, and is made of, for example, stainless steel (SUS). The cover plate 21 has a plurality of openings (air introduction holes) 21A for taking in air as an oxidant.

  The fuel supply mechanism 3 is configured to supply fuel to the anode 13 of the membrane electrode assembly 2, and an example of the configuration will be described below.

  The fuel supply mechanism 3 includes a container 30 formed in a box shape, for example. The fuel supply mechanism 3 is connected to a fuel storage unit 4 that stores liquid fuel via a flow path 5. The container 30 has a fuel inlet 30A, and the fuel inlet 30A and the flow path 5 are connected. The container 30 is constituted by a resin container, for example. As a material for forming the container 30, a material having resistance to liquid fuel is selected.

  The fuel supply mechanism 3 includes a fuel supply unit 31 that supplies fuel while dispersing and diffusing fuel in the surface direction of the anode 13 of the membrane electrode assembly 2. In this embodiment, a configuration in which the fuel supply unit 31 includes a fuel distribution plate 31A will be described.

  That is, as shown in FIGS. 4 and 5, the fuel distribution plate 31 </ b> A has at least one fuel injection port 32 and a plurality of fuel discharge ports 33, via a fuel passage such as a narrow tube 34. The fuel injection port 32 and the fuel discharge port 33 are connected. This fuel passage may be constituted by a fuel flow groove or the like instead of the narrow tube 34 formed in the fuel distribution plate 31A. In this case, the fuel distribution plate 31A can also be configured by covering the flow path plate having the fuel flow grooves with a diffusion plate having a plurality of fuel discharge ports.

  In the example shown in FIGS. 4 and 5, the fuel inlet 32 is in one place and communicates with the fuel inlet 30 </ b> A of the container 30. As a result, the fuel inlet 32 of the fuel distribution plate 31 </ b> A is connected to the fuel storage portion 4 via the flow path 5. There are 128 fuel discharge ports 33 for discharging liquid fuel or vaporized components thereof.

  A fuel injection port 32 is provided at one end (starting end) of the thin tube 34. The narrow tube 34 is branched into a plurality of parts along the way, and a fuel discharge port 33 is provided at each terminal portion of the branched narrow tube 34. The thin tube 34 is preferably a through hole having an inner diameter of 0.05 to 5 mm, for example.

  The liquid fuel injected from the fuel injection port 32 is guided to the plurality of fuel discharge ports 33 via the thin tubes 34 branched into a plurality. By using such a fuel distribution plate 31A, the liquid fuel injected from the fuel injection port 32 can be evenly distributed to the plurality of fuel discharge ports 33 regardless of the direction or position. Therefore, the uniformity of the power generation reaction in the surface of the membrane electrode assembly 2 can be further enhanced.

  Further, by connecting the fuel injection port 32 and the plurality of fuel discharge ports 33 with the thin tube 34, it is possible to design such that more fuel is supplied to a specific portion of the fuel cell. This contributes to improvement in the uniformity of the power generation degree of the membrane electrode assembly 2 and the like.

  The membrane electrode assembly 2 is arranged so that the anode 13 faces the fuel discharge port 33 of the fuel distribution plate 31A as described above. The cover plate 21 is fixed to the container 30 by a method such as caulking or screwing in a state where the membrane electrode assembly 2 is held between the cover plate 21 and the fuel supply mechanism 3. Thereby, the power generation unit of the fuel cell (DMFC) 1 is configured.

  The fuel supply unit 31 is preferably configured to form a space functioning as a fuel diffusion chamber 31B between the fuel distribution plate 31A and the membrane electrode assembly 2. The fuel diffusion chamber 31 </ b> B has a function of promoting vaporization and promoting diffusion in the surface direction even when liquid fuel is discharged from the fuel discharge port 33.

  A support member 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 particular, in the configuration as shown in FIG. 1, the following effects can be obtained by applying the support member. That is, by disposing the support member between the membrane electrode assembly 2 and the fuel supply unit 31, the distance from the fuel discharge 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 discharge 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.

  In addition, the membrane electrode assembly 2 is supported by the support member and the membrane electrode assembly 2 is held between the support member and the cover plate 21, so that deformation such as bending of the membrane electrode assembly 2 can be suppressed. It is possible to improve the adhesion between the membrane electrode assembly 2 and the current collector and suppress the decrease in output.

  At least one porous body may be disposed between the membrane electrode assembly 2 and the fuel supply unit 31. As a constituent material of the porous body, various resins are used, and a porous resin film or the like is used as the porous body. Such a porous body 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 applied in combination.

  In particular, in the configuration shown in FIG. 1, the following effects can be obtained by applying a porous body. That is, the fuel supply amount to the anode 13 can be further averaged by disposing the porous body. That is, the liquid fuel supplied from the fuel discharge port 33 of the fuel supply unit 31 is once absorbed by the porous body and diffuses in the in-plane direction inside the porous body. Thereafter, the fuel is supplied from the porous body to the anode 13, so that the fuel supply amount can be further averaged.

  Liquid fuel corresponding to the membrane electrode assembly 2 is stored in the fuel storage portion 4.

  Examples of the liquid fuel include methanol fuels such as aqueous methanol solutions of various concentrations and pure methanol. The liquid fuel is not necessarily limited to methanol fuel. The liquid fuel 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, liquid fuel corresponding to the membrane electrode assembly 2 is stored in the fuel storage portion 4.

  Further, a pump 6 may be interposed in the flow path 5. The pump 6 is not a circulation pump that circulates fuel, but is a fuel supply pump that sends liquid fuel from the fuel storage unit 4 to the fuel supply unit 31 to the last. The fuel supplied from the fuel supply unit 31 to the membrane electrode assembly 2 is used for a power generation reaction, and is not circulated thereafter and returned to the fuel storage unit 4.

  The fuel cell 1 of this embodiment is different from the conventional active method because it does not circulate the fuel, and does not impair the downsizing of the device. Further, the pump 6 is used to supply the liquid fuel, which is different from a pure passive system such as a conventional internal vaporization type. The fuel cell 1 shown in FIG. 1 employs a system called a semi-passive type, for example.

  The type of the pump 6 is not particularly limited, but a rotary vane pump, an electroosmotic pump, and a diaphragm pump can be used from the viewpoint that a small amount of liquid fuel can be fed with good controllability and can be reduced in size and weight. It is preferable to use a squeezing pump or the like.

  The rotary vane pump feeds liquid by rotating wings with a motor. The electroosmotic flow pump uses a sintered porous body such as silica that causes an electroosmotic flow phenomenon. A diaphragm pump drives a diaphragm with an electromagnet or piezoelectric ceramics to send liquid. The squeezing pump presses a part of a flexible fuel flow path and squeezes the fuel. Among these, it is more preferable to use an electroosmotic pump or a diaphragm pump having piezoelectric ceramics from the viewpoint of driving power, size, and the like.

  A reservoir may be provided between the pump 6 and the fuel supply unit 31.

  Further, in order to improve the stability and reliability of the fuel cell 1, a fuel cutoff valve may be arranged in series with the pump 6. As the fuel cutoff valve, an electrically driven valve capable of controlling an opening / closing operation with an electric signal using an electromagnet, a motor, a shape memory alloy, piezoelectric ceramics, bimetal, or the like as an actuator is applied. The fuel cutoff valve is preferably a latch type valve having a state maintaining function.

  Further, a balance valve that balances the pressure in the fuel storage unit 4 with the outside air may be attached to the fuel storage unit 4 and the flow path 5. When fuel is supplied from the fuel storage unit 4 to the membrane electrode assembly 2 by the fuel supply mechanism 3, it is possible to adopt a configuration in which only the fuel cutoff valve is arranged instead of the pump 6. The fuel cutoff valve at this time is provided for controlling the supply of liquid fuel through the flow path 5.

  In the fuel cell 1 of this embodiment, liquid fuel is intermittently sent from the fuel storage unit 4 to the fuel supply unit 31 using the pump 6. The liquid fuel fed by the pump 6 is uniformly supplied to the entire surface of the anode 13 of the membrane electrode assembly 2 through the fuel supply unit 31.

  That is, the fuel is uniformly supplied to the planar direction of each anode 13 of the plurality of single cells C, thereby generating a power generation reaction. The operation of the fuel supply (liquid feeding) pump 6 is preferably controlled based on the output of the fuel cell 1, temperature information, operation information of an electronic device that is a power supply destination, and the like.

  As described above, the fuel released from the fuel supply unit 31 is supplied to the anode 13 of the membrane electrode assembly 2. In the membrane electrode assembly 2, the fuel 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, an internal reforming reaction of methanol shown in the following formula (1) occurs in the anode catalyst layer 11. When pure methanol is used as the methanol fuel, the water generated in the cathode catalyst layer 14 or the water in the electrolyte membrane 17 is reacted with methanol to cause the internal reforming reaction of the formula (1). Alternatively, the internal reforming reaction is caused by another reaction mechanism that does not require water.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
The electrons (e ⁻ ) generated by this reaction are guided to the outside via the current collector 18, and after operating a portable electronic device or the like as so-called electricity, the electrons (e ⁻ ) are passed to the cathode 16 via the current collector 18. Led. Proton (H ⁺ ) generated by the internal reforming reaction of the formula (1) is guided to the cathode 16 through the electrolyte membrane 17. Air is supplied to the cathode 16 as an oxidant. 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, the catalytic reaction is smoothly performed, and the fuel is uniformly supplied to the entire electrode of the membrane electrode assembly 2 so that the entire electrode becomes more effective. It is important to contribute to power generation.

  As described above, in this embodiment, the fuel distribution plate 31A constituting the fuel supply mechanism 3 has the fuel discharge port 33, and this fuel discharge port 33 is connected to the anode 13 of the membrane electrode assembly 2. It arrange | positions so that it may oppose. The surface 31S of the fuel distribution plate 31A facing the anode 13 is lyophilic with respect to the liquid fuel supplied by the fuel supply mechanism 3.

  For the anode 13 of the membrane electrode assembly 2, it is extremely important to supply the fuel uniformly over the entire surface. According to the configuration to which the fuel distribution plate 31A is applied, when the vaporized fuel is discharged from the fuel discharge port 33, it is diffused while reaching the anode 13, and the fuel supply amount can be made uniform. On the other hand, when liquid fuel is discharged from the fuel discharge port 33, in order to make the fuel supply amount uniform, one method is to increase the number of the fuel discharge ports 33 per unit area. However, it is difficult to further increase the number of fuel discharge ports 33 due to problems in manufacturing, mechanical strength, and the like.

  Therefore, in this embodiment, the surface 31S of the fuel distribution plate 31A is lyophilic with respect to the liquid fuel. For this reason, it becomes possible to quickly diffuse the liquid fuel in the XY plane on the surface 31S of the fuel distribution plate 31A.

  As shown in the model of FIG. 6, when the surface 31S does not have lyophilicity, the liquid fuel discharged from the fuel discharge port 33 spreads in the vicinity of the fuel discharge port 33 as shown by A. Instead, it accumulates in a hemispherical shape. On the other hand, when the surface 31S has lyophilicity, as shown by B, the liquid fuel discharged from the fuel discharge port 33 travels along the surface 31S and diffuses in a short time.

  For this reason, even if liquid fuel is discharged from the fuel discharge port 33, it becomes possible to supply the fuel uniformly to the entire surface toward the anode 13 of the membrane electrode assembly 2. Further, even with a small amount of fuel, the fuel can be uniformly distributed over the entire surface, and the fuel can be stably and uniformly supplied to the anode 13 while promoting the vaporization of the fuel.

  Thereby, in the whole membrane electrode assembly 2, an appropriate amount of fuel can be supplied to efficiently generate a power generation reaction, and a high output can be stably obtained. In addition, local deterioration of the membrane electrode assembly 2 can be suppressed, and the life of the fuel cell can be extended. Further, a fuel diffusion sheet such as a porous body for accelerating the diffusion of fuel is not required between the membrane electrode assembly 2 and the fuel supply unit 31, and the fuel cell can be made thin.

  Here, the lyophilicity of the surface 31S will be described more specifically.

  The contact angle of the surface 31S with respect to the fuel is desirably 90 ° or less as a result of various studies by the inventors. Further, when verified from another viewpoint, the surface roughness of the surface 31S is desirably a center line average roughness (Ra) of 0.1 μm or more and 1.0 μm or less.

  Such a fuel distribution plate 31A includes, for example, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyethylene sulfide (PES), polyphenyl sulfide (PPS), and cyclic olefin copolymer. It is formed by one of polymers (COC).

  The surface 31S of the fuel distribution plate 31A is given lyophilicity by surface treatment (reforming treatment) by a method such as corona discharge treatment, plasma polymerization treatment, or electron beam treatment. For example, by performing corona discharge treatment on the fuel distribution plate 31A formed of polyethylene, the surface of polyethylene is activated and polar groups are generated, so that wettability is improved. In this way, lyophilicity is imparted to the surface 31S.

  Here, as shown in FIG. 9, the contact angle θ of the droplet DR made of water with respect to the fuel distribution plate 31A is tangent to the surface curve of the droplet DR at the point P where the droplet DR and the fuel distribution plate 31A contact each other. And the surface 31S of the fuel distribution plate 31A.

  This contact angle θ is measured as follows. As a measuring device, a contact angle meter (DropMaster 100), a solid-liquid interface analyzer (DropMaster 500), and a measurement / analysis integrated system software (FAMAS: 2004/7) manufactured by Kyowa Interface Science Co., Ltd. were used.

  First, as shown in FIG. 10, pure water droplets DR are formed with a microsyringe M (Teflon (registered trademark) coated needle 28G (φ0.1 mm)). In the case of the fuel cell according to the present embodiment, the droplet DR is about 0.5 microliter.

  Next, as shown in FIG. 11, the bottom of the droplet DR is brought into contact with the surface 31S of the fuel distribution plate 31A that is the measurement target. When the microsyringe M is separated from the fuel distribution plate 31A, a droplet DR as shown in FIG. 12 adheres to the surface 31S of the fuel distribution plate 31A. In this state, after 3000 ms, the height h of the droplet DR and the radius r of the droplet DR (or the distance between both ends of the droplet DR shown in FIG. 9 or the diameter 2r of the droplet DR) are measured.

  Since the contact angle θ is equal to twice θ1 (= arctan (r / h)) shown in FIG. 9, the following formula (A) is used from the measured height h and radius r of the droplet DR. Thus, the value of the contact angle θ is calculated.

θ = 2 arctan (r / h) Formula (A)
The contact angle θ calculated as described above indicates that the larger the value, the higher the hydrophobicity of the measurement object, and the smaller the value, the lower the hydrophobicity of the measurement object.

  In the example shown in FIG. 1, the fuel supply mechanism 3 has a gap between the membrane electrode assembly 2 and the fuel distribution plate 31 </ b> A, and forms a fuel diffusion chamber 31 </ b> B constituting the fuel supply unit 31. For this reason, even if liquid fuel is discharged from the fuel discharge port 33, it is possible to secure a path for promoting vaporization after being diffused on the surface of the fuel distribution plate 31A.

  The fuel cell 1 described above may further include a diffusion plate 40 disposed between the anode 13 of the membrane electrode assembly 2 and the fuel distribution plate 31A of the fuel supply mechanism 3.

  That is, as shown in FIG. 7, the diffusion plate 40 is overlapped with the fuel distribution plate 31A with a slight gap through which liquid fuel or gaseous fuel can pass. The diffusion plate 40 has a through hole 41 extending from the fuel distribution plate 31 </ b> A to the membrane electrode assembly 2. Thus, the fuel discharged from the fuel discharge port 33 is discharged from the through hole 41 toward the anode 13.

  Further, the diffusion plate 40 has at least a surface 42 facing the anode 13 having lyophilicity with respect to the liquid fuel. Such a diffusion plate 40 may be in the form of a film or a plate. The diffusion plate 40 may be formed of a lyophilic material, or may be surface-treated so that at least the surface 42 has lyophilic properties.

  By applying such a diffusion plate 40, even if the fuel discharged from the through hole 41 of the diffusion plate 40 toward the anode 13 is a liquid, the fuel is diffused in the surface 42 of the diffusion plate 40 in a short time. It becomes possible. For this reason, it becomes possible to supply fuel uniformly to the entire surface of the membrane electrode assembly 2.

  In addition, a path for promoting the vaporization of the liquid fuel can be secured between the fuel discharge port 33 and the anode 13.

  In particular, as shown in FIG. 7, it is more desirable that the through hole 41 of the diffusion plate 40 is disposed without overlapping the fuel discharge port 33 of the fuel distribution plate 31A. That is, the fuel discharge port 33 and the through hole 41 are not located on the same axis. Thereby, even if the liquid fuel is discharged from the fuel discharge port 33, a longer path for promoting the vaporization of the liquid fuel can be secured.

  In this case, it is desirable that the surface 43 of the diffusion plate 40 facing the fuel distribution plate 31A also has lyophilicity for the liquid fuel. That is, the gap between the fuel distribution plate 31A and the diffusion plate 40 is surrounded by a surface having lyophilicity. For this reason, it becomes possible to diffuse the liquid fuel discharged from the fuel discharge port 33 more rapidly.

  Further, it is desirable that the through holes 41 formed in the diffusion plate 40 are arranged more densely than the fuel discharge ports 33 formed in the fuel distribution plate 31A. That is, as shown in FIG. 8, the fuel discharge port 33 and the through hole 41 are not located on the same axis, and when the diffusion plate 40 is placed on the fuel distribution plate 31A, one fuel discharge port 33 is disposed. A plurality of through holes 41 are close to each other.

  That is, the fuel discharged from one fuel discharge port 33 is supplied toward the anode 13 through the plurality of through holes 41. For this reason, the diffusion of the liquid fuel is promoted and the vaporization is promoted, and the fuel can be uniformly supplied to the entire surface of the membrane electrode assembly 2.

  As described above, according to this embodiment, it is possible to provide a fuel cell capable of stably obtaining a high output and extending its life.

  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. However, the fuel supply unit 31 that supplies fuel while being dispersed in the plane direction is particularly effective when the fuel concentration is high. For this reason, the fuel cell 1 of each embodiment can exhibit its performance and effects particularly when methanol having a concentration of 80 wt% or more is used as the liquid fuel. Therefore, each embodiment is suitable for the fuel cell 1 using a methanol aqueous solution having a methanol concentration of 80 wt% or more or pure methanol as a liquid fuel.

  Furthermore, although each embodiment mentioned above demonstrated the case where this invention was applied to the semi-passive type fuel cell 1, this invention is not limited to this, It is an internal vaporization type pure passive type fuel cell. It can also be applied to.

  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. FIG. 4 is a perspective view schematically showing the structure of the fuel distribution plate of the fuel supply unit in the fuel supply mechanism applicable to the fuel cell shown in FIG. FIG. 5 is a plan view of the fuel distribution plate shown in FIG. FIG. 6 is a diagram for explaining the effect when the surface of the fuel distribution plate has lyophilicity with respect to the liquid fuel. FIG. 7 is a cross-sectional view schematically showing another structure of a fuel supply mechanism applicable to the fuel cell shown in FIG. FIG. 8 is a view for explaining the positional relationship between the fuel discharge port of the fuel distribution plate and the through hole of the diffusion plate in the fuel supply mechanism shown in FIG. FIG. 9 is a diagram for explaining a method of measuring the contact angle of the surface of the fuel distribution plate. FIG. 10 is a diagram for explaining one process for measuring the contact angle of the surface of the fuel distribution plate. FIG. 11 is a diagram for explaining one process for measuring the contact angle of the surface of the fuel distribution plate. FIG. 12 is a diagram for explaining one process for measuring the contact angle of the surface of the fuel distribution plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Fuel cell 2 ... Membrane electrode assembly 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 18 ... Current collector 19 ... Seal Member 20 ... Plate-like body 21 ... Cover plate 3 ... Fuel supply mechanism 4 ... Fuel accommodating part 5 ... Flow path 6 ... Pump 31 ... Fuel supply part 31A ... Fuel distribution plate 31B ... Fuel diffusion chamber 31S ... Surface 32 ... Fuel inlet 33 ... Fuel outlet 40 ... Diffusion plate 41 ... Through hole

Claims (10)

A membrane electrode assembly having an electrolyte membrane sandwiched between an anode and a cathode;
A fuel supply mechanism for supplying fuel to the anode of the membrane electrode assembly,
The fuel supply mechanism includes a fuel distribution plate having a fuel discharge port facing the anode of the membrane electrode assembly,
The fuel cell according to claim 1, wherein a surface of the fuel distribution plate facing the anode is lyophilic with respect to a liquid fuel.   2. The fuel cell according to claim 1, wherein a contact angle of the surface of the fuel distribution plate with respect to the fuel is 90 ° or less.   2. The fuel cell according to claim 1, wherein the surface roughness of the surface of the fuel distribution plate is a center line average roughness (Ra) of 0.1 μm or more and 1.0 μm or less.   The fuel cell according to claim 1, wherein the fuel distribution plate includes a fuel inlet, a plurality of fuel outlets, and a fuel passage connecting the fuel inlet and the fuel outlet.   The fuel distribution plate includes polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyethylene sulfide (PES), polyphenyl sulfide (PPS), and cyclic olefin copolymer (COC). The fuel cell according to claim 1, wherein the fuel cell is formed of any one of the above.   The fuel cell according to claim 1, wherein the fuel supply mechanism includes a fuel diffusion chamber between the membrane electrode assembly and the fuel distribution plate.   Furthermore, it is disposed between the anode and the fuel distribution plate, and has a through hole for discharging the fuel discharged from the fuel discharge port toward the anode, and at least a surface facing the anode corresponds to the liquid fuel. 2. The fuel cell according to claim 1, further comprising a diffusive diffusion plate.   The fuel cell according to claim 7, wherein the through hole of the diffusion plate is disposed without overlapping the fuel discharge port of the fuel distribution plate.   The fuel cell according to claim 7, wherein the through hole is arranged more densely than the fuel discharge port.   2. The fuel cell according to claim 1, wherein the fuel supplied to the membrane electrode assembly is a methanol aqueous solution or pure methanol having a methanol concentration of 80 wt% or more.

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