JP2008071627A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize thinness and suppress methanol crossover of a fuel cell supplied with a liquid fuel. <P>SOLUTION: The fuel cell 10 has an anode 30 on one face of an electrolyte membrane 20 and a cathode 40 on the other face of the electrolyte membrane 20. An anode current collector 36 is installed between the anode 30 and the electrolyte membrane 20 and contacts the anode with at least a part embedded into the electrolyte membrane 20. Furthermore, a cathode current collector 46 is installed between the cathode 40 and the electrolyte membrane 20 and contacts the cathode 40 with at least a part embedded into the electrolyte membrane 20. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell in which liquid fuel is supplied directly to an anode.

  A fuel cell is a device that generates electrical energy from hydrogen and oxygen, and can achieve high power generation efficiency. The main features of the fuel cell are direct power generation that does not go through the process of thermal energy and kinetic energy as in the conventional power generation method, so that high power generation efficiency can be expected even on a small scale, and there is little emission of nitrogen compounds, Noise and vibration are also small, so the environmental performance is good. In this way, the fuel cell can effectively use the chemical energy of fuel and has environmentally friendly characteristics, so it is expected as an energy supply system for the 21st century, from space use to automobiles and portable devices. It is attracting attention as a promising new power generation system that can be used for various applications from large-scale power generation to small-scale power generation.

Among them, solid polymer fuel cells are characterized by low operating temperature and high output density compared to other types of fuel cells. In particular, as a form of solid polymer fuel cells, direct methanol A fuel cell (Direct Methanol Fuel Cell: DMFC) is attracting attention. In DMFC, an aqueous methanol solution as a fuel is directly supplied to the anode without modification, and electric power is obtained by an electrochemical reaction between the aqueous methanol solution and oxygen. By this electrochemical reaction, carbon dioxide is emitted from the anode to the cathode. The produced water is discharged as a reaction product (see Patent Document 1). Aqueous methanol solution has higher energy per unit volume than hydrogen, and is suitable for storage and has a low risk of explosion, so it can be used in automobiles and mobile devices (cell phones, notebook personal computers, PDAs, MP3 players, Use for power sources such as digital cameras or electronic dictionaries (books) is expected.
JP 2005-209584 A

  Conventionally, in DMFC, a phenomenon called methanol crossover is known in which methanol passes through an electrolyte membrane together with protons. When methanol crossover occurs, the methanol aqueous solution which is a liquid fuel is wasted, and the power generation efficiency is lowered. Methanol crossover is more likely to occur as the electrolyte membrane swells. Therefore, suppressing the swelling of the electrolyte membrane is a technical issue for preventing methanol crossover.

  On the other hand, as described above, the DMFC is required to be used as a power source for portable devices, and it is indispensable for practical use to make the DMFC smaller and thinner.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a technique for suppressing methanol crossover while reducing the thickness of a fuel cell to which liquid fuel is supplied.

  One embodiment of the present invention is a fuel cell. The fuel cell includes an electrolyte membrane, a first electrode joined to one surface of the electrolyte membrane, a second electrode joined to the other surface of the electrolyte membrane, and an electrolyte membrane and the first electrode. A first current collector that is in contact with the first electrode and a second current collector that is in contact with the second electrode with at least a portion embedded in the electrolyte membrane. It is characterized by.

  According to this aspect, when the liquid fuel is supplied, swelling of the electrolyte membrane on the first electrode side is suppressed by the current collector, thereby preventing methanol from entering the electrolyte membrane from the first electrode side. , Methanol crossover can be suppressed. Furthermore, since the fixing property of the first current collector is improved, a fastening tool for the first current collector is not necessary, and the fuel cell can be thinned.

  In the above aspect, the surface of the first current collector may be coated with a corrosion-resistant metal. According to this, corrosion of the first current collector can be suppressed and the life of the fuel cell can be extended.

  In the above aspect, the first current collector and the electrolyte membrane may be chemically bonded. According to this, it is possible to improve the adhesion between the first current collector and the electrolyte membrane, and to prevent the first current collector from peeling from the electrolyte membrane. Note that examples of the chemical bond include a covalent bond, a coordination bond, and an ionic bond.

  In the above aspect, the second current collector is provided between the electrolyte membrane and the second electrode, and at least a part of the second current collector is separated from the first current collector in a state of being in contact with the second electrode. It may be embedded in the electrolyte membrane. According to this, since the swelling of the electrolyte membrane is also suppressed from the second current collector side, methanol crossover can be further reduced and the fuel cell can be further reduced in thickness.

  In the above aspect, the surface of the second current collector may be coated with a corrosion-resistant metal. According to this, corrosion of the second current collector can be suppressed, and the life of the fuel cell can be extended.

    In the above aspect, the second current collector and the electrolyte membrane may be chemically bonded. According to this, it is possible to improve the adhesion between the second current collector and the electrolyte membrane, and to prevent the second current collector from being peeled off from the electrolyte membrane. Note that examples of the chemical bond include a covalent bond, a coordination bond, and an ionic bond.

  A combination of the above-described elements as appropriate can also be included in the scope of the invention for which patent protection is sought by this patent application.

  ADVANTAGE OF THE INVENTION According to this invention, methanol crossover can be suppressed, aiming at thickness reduction of the fuel cell supplied with liquid fuel.

  FIG. 1 is a schematic diagram showing a configuration of a fuel cell according to an embodiment. The fuel cell 10 includes a membrane electrode assembly (hereinafter referred to as MEA) including an electrolyte membrane 20, an anode 30 joined to one surface of the electrolyte membrane 20, and a cathode 40 joined to the other surface of the electrolyte membrane 20. ), And power is generated by an electrochemical reaction between an aqueous methanol solution as a liquid fuel and air.

  The electrolyte membrane 20 preferably exhibits good ion conductivity in a wet state, and functions as an ion exchange membrane that moves protons between the anode catalyst layer 32 constituting the anode 30 and the cathode catalyst layer 42. The electrolyte membrane 20 is formed of a solid polymer material such as a fluorine-containing polymer or a non-fluorine polymer. For example, a perfluorocarbon polymer having a sulfonic acid type perfluorocarbon polymer, a polysulfone resin, a phosphonic acid group, or a carboxylic acid group. Etc. can be used. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (manufactured by DuPont: registered trademark) 112. Examples of non-fluorine polymers include sulfonated aromatic polyetheretherketone and polysulfone.

  An anode catalyst layer 32 is bonded to one surface of the electrolyte membrane 20. The anode catalyst layer 32 is composed of an ion exchange resin and carbon particles carrying a catalyst, that is, catalyst-carrying carbon particles. The ion exchange resin connects the carbon particles carrying the catalyst and the electrolyte membrane 20, and has a role of transmitting protons between the two. The ion exchange resin may be formed of the same polymer material as the electrolyte membrane 20. Examples of the supported catalyst include those obtained by alloying one or two of platinum, ruthenium, rhodium and the like. Examples of the carbon particles supporting the catalyst include acetylene black, ketjen black, and carbon nanotube.

  An anode diffusion layer 34 constituting the anode 30 is further provided on one surface of the electrolyte membrane 20 via the anode catalyst layer 32. As the anode diffusion layer 34, for example, carbon paper, carbon woven fabric, or non-woven fabric can be used, and if necessary, gas diffusion including a water-repellent fluororesin such as tetrafluoroethylene resin (PTFE). A paste may be applied.

  The anode diffusion layer 34 faces the fuel storage portion 52 formed by the casing 50 so that the aqueous methanol solution stored in the fuel storage portion 52 is infiltrated.

  The casing 50 is provided with a gas-liquid separation filter 54 so that the generated gas accumulated in the fuel storage section 52 can be discharged to the outside.

  In the present embodiment, the anode current collector 36 is provided between the electrolyte membrane 20 and the anode catalyst layer 32. The anode current collector 36 is in contact with the anode catalyst layer 32 and is electrically connected to the anode catalyst layer 32 while being embedded in the electrolyte membrane 20. The anode current collector 36 of the present embodiment is entirely buried in the electrolyte membrane 20, the contact surface between the anode current collector 36 and the anode catalyst layer 32, and the joint surface between the electrolyte membrane 20 and the anode catalyst layer 32. However, the anode current collector 36 may be partially embedded in the electrolyte membrane 20 and the remaining portion embedded in the anode catalyst layer 32.

  The anode current collector 36 is not particularly limited as long as it is a conductive material. Examples thereof include a metal, a conductive ceramic, a semiconductor such as Si, carbon, and an insulating member coated with a conductive material. It is done.

  The shape of the anode current collector 36 is not particularly limited as long as a through-hole through which protons can pass from the anode catalyst layer 32 to the electrolyte membrane 20 is provided. For example, the shape of the anode current collector 36 is shown in FIG. A honeycomb structure having a plurality of regular hexagonal through holes is exemplified. By making the anode current collector 36 into a honeycomb structure, the strength of the current collector can be improved. FIG. 3 is a view showing another shape of the anode current collector 36. In this example, a plurality of circular through holes are provided in the conductive sheet. In addition, the aperture ratio by a through-hole can be 10 to 90% with respect to the area of the whole contact surface with the anode catalyst layer 32. FIG. By setting the aperture ratio by the through hole within this range, both proton conductivity and current collection can be achieved.

  The anode current collector 36 is preferably coated with a protective layer made of a corrosion-resistant metal on the surface. Examples of the corrosion-resistant metal include Au and Pt. The thickness of the protective layer is preferably several nm to several tens of nm. The current collector can be coated with a corrosion-resistant metal by, for example, vapor deposition or plating. According to this, the anode current collector 36 is hardly corroded, and the life of the fuel cell 10 can be extended.

  Examples of the method for manufacturing the anode current collector 36 having the structure described above include wet etching, dry etching, and aluminum anodization.

  The outermost surface of the anode current collector 36 is desirably modified with a functional group such as an OH group or a COOH group that is highly reactive with the electrolyte membrane 20, and the functional group and the electrolyte membrane 20 are supplied and bonded. It is more preferable. The introduction of the functional group to the outermost surface of the anode current collector 36 can be realized by, for example, irradiating with plasma, ultraviolet light, electron beam or the like.

  According to this, the adhesion between the anode current collector 36 and the electrolyte membrane 20 can be improved, and the anode current collector 36 can be made difficult to peel from the electrolyte membrane 20.

  In addition, the outermost surface of the anode current collector 36 and the electrolyte membrane 20 are preferably chemically bonded. Although the kind of chemical bond is not specifically limited, For example, a covalent bond, a coordination bond, an ionic bond etc. are mentioned. According to this, the adhesion between the anode current collector 36 and the electrolyte membrane 20 can be improved, and the anode current collector 36 can be prevented from peeling off from the electrolyte membrane 20.

  On the other hand, a cathode catalyst layer 42 is bonded to the other surface of the electrolyte membrane 20, and a cathode diffusion layer 44 is provided in contact with the cathode catalyst layer 42. The materials that can be used for the cathode catalyst layer 42 and the cathode catalyst layer 42 are the same as those of the anode catalyst layer 32 and the anode catalyst layer 32 described above, respectively, and thus the description thereof is omitted. An air intake 56 is provided on the cathode side of the housing 50, and air necessary for an electrochemical reaction is supplied from the outside.

  In the present embodiment, the cathode current collector 46 is provided between the electrolyte membrane 20 and the anode catalyst layer 32. The cathode current collector 46 is in contact with the anode catalyst layer 32 and is electrically connected to the anode catalyst layer 32 while being embedded in the electrolyte membrane 20. The cathode current collector 46 of the present embodiment is entirely buried in the electrolyte membrane 20, the contact surface between the cathode current collector 46 and the anode catalyst layer 32, and the joint surface between the electrolyte membrane 20 and the anode catalyst layer 32. However, a part of the cathode current collector 46 may be embedded in the electrolyte membrane 20 and the remaining part may be embedded in the anode catalyst layer 32. Since the shape, material, and the like of the cathode current collector 46 are the same as those of the anode current collector 36 described above, description thereof is omitted.

  In the fuel cell 10 described above, the electrolyte membrane 20 is pressed down by the anode current collector 36 and the cathode current collector 46 at least partially embedded in the electrolyte membrane 20, so that the electrolyte membrane 20 is less likely to swell. As a result, methanol crossover is suppressed. Further, since at least a part of the anode current collector 36 and the cathode current collector 46 is embedded in the electrolyte membrane 20 and sandwiched between the electrolyte membrane 20 and the catalyst layer, the anode current collector is obtained. Since the fixing property of the body 36 and the cathode current collector 46 is improved, a fastening tool for fixing the anode current collector 36 and the cathode current collector 46 is not required, and thus the fuel cell can be thinned. Can do.

  Note that the depths of the anode current collector 36 and the cathode current collector 46 embedded in the electrolyte membrane 20 are close to half of the electrolyte membrane 20, respectively, and through holes provided in the anode current collector 36 and the cathode current collector 46 are also provided. Is as small as possible, for example, about 0.01 μm to 1000 μm, preferably about 0.1 μm to 10 μm. When the diameter of the through-hole is smaller than 0.01 μm, it becomes difficult for molecules constituting the electrolyte membrane 20 to enter the through-hole, and when the diameter of the through-hole is larger than 1000 μm, it is difficult to suppress the expansion of the electrolyte membrane 20. In addition, the current collection resistance increases. Furthermore, the expansion of the electrolyte membrane 20 can be more reliably suppressed by setting the diameter of the through hole to about 0.1 μm to 10 μm.

(Method of embedding current collector in electrolyte membrane)
Here, a method for embedding the current collector in the electrolyte membrane will be described. First, as shown in FIG. 4A, a plurality of through-holes 120 are formed in a Si sheet (film thickness of about 1 μm) 100 by dry etching using a predetermined pattern of photoresist 110 as a mask, thereby forming an anode collector. The electric body 36 is produced. Thereafter, Au is coated on the surface of the anode current collector 36 by sputtering, and plasma is irradiated onto the Au to introduce functional groups such as OH groups and COOH groups.

  Next, as shown in FIG. 4B, after the photoresist 110 is removed, an electrolyte solution 132 is applied in a state where the anode current collector 36 is placed on a substrate 130 having a flat surface. A film 20 is formed. Instead of applying the electrolyte solution, the electrolyte monomer may be applied and then polymerized. According to this, the production | generation of the covalent bond of the electrolyte membrane 20 and the said functional group can be promoted, and the adhesiveness of the anode electrical power collector 36 and the electrolyte membrane 20 can be improved more. The presence of a covalent bond between the electrolyte membrane 20 and the functional group can be confirmed by an analytical method such as XPS or IR. As shown in FIG. 4C, the anode current collector 36 is embedded in the electrolyte membrane 20 in a state where a part of the anode current collector 36 is exposed by peeling the anode current collector 36 from the base material 130. A member can be produced.

  In the same manner as described above, a member in which the cathode current collector 46 is embedded in the electrolyte membrane 20 is manufactured, and the anode current collector 36 and the cathode current collector 46 are opposed to each other as shown in FIG. In this state, both members are bonded together via an electrolyte solution or an electrolyte membrane (film thickness of about 1 μm) 21. As a result, as shown in FIG. 4 (E), the anode current collector 36 and the cathode current collector 46 are respectively a fixed distance in a state where a part is exposed on one surface and the other surface of the electrolyte membrane 20. A member that is spaced apart and embedded in the electrolyte membrane 20 can be produced. By joining an electrode composed of a catalyst layer and a diffusion layer to this member, an MEA incorporating a current collector can be produced. As described above, in the MEA, a short circuit is prevented by bonding the anode current collector 36 and the cathode current collector 46 through the electrolyte membrane 20. Further, by making the anode current collector 36 and the cathode current collector 46 face each other, proton conduction in the film thickness direction of the electrolyte membrane 20 is not hindered, so that proton conductivity can be kept good.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The form can also be included in the scope of the present invention.

  For example, in the above-described embodiment, a current collector having a rectangular cross section is illustrated, but the cross sectional shape of the current collector is not limited thereto. For example, the current collector 36 may have a taper shape as shown in FIG. According to this, for example, when the current collector is embedded in the electrolyte membrane by hot pressing, the embedding can be more reliably and easily performed.

  In the above-described embodiment, at least a part of the anode current collector and the cathode current collector is embedded in the electrolyte membrane. However, any one of the anode current collector and the cathode current collector is replaced with a diffusion layer. It may be provided outside and fixed with a fastening tool or the like. However, since the swelling of the electrolyte membrane becomes significant on the anode side to which the fuel is supplied, it is more preferable to embed a part of the anode current collector in the electrolyte membrane.

  In the above-described embodiment, the current collector itself has conductivity. However, as a base material for the current collector, a porous polytetrafluoroethylene film (PTFE), a heat-resistant crosslinked polyethylene base material ( A porous insulating material such as CLPE) or porous polyimide may be used, and a metal may be coated.

  In the above-described embodiment, the structure in which the anode current collector and the cathode current collector face each other is illustrated, but the positions of the anode current collector and the cathode current collector may be shifted from each other. According to this, the strength of the electrolyte membrane can be increased.

  The fuel cell may be an active type that supplies and circulates the fuel to and from the fuel cell using an auxiliary device such as a pump, and without using the auxiliary device, the fuel and air are supplied using convection or a concentration gradient. A passive type supplying the fuel cell may be used.

It is a figure which shows the structure of the fuel cell which concerns on embodiment. It is a figure which shows an example of the shape of an anode electrical power collector. It is a figure which shows the other example of the shape of an anode electrical power collector. It is process drawing which shows the method of embedding a collector in an electrolyte membrane. It is a figure which shows the cross-sectional shape of a collector.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Fuel cell, 20 Electrolyte membrane, 30 Anode, 32 Anode catalyst layer, 34 Anode diffusion layer, 36 Anode collector, 40 Cathode, 42 Cathode catalyst layer, 44 Cathode diffusion layer, 46 Cathode collector, 50 Case, 52 Fuel storage part, 54 Gas-liquid separation filter, 56 Air intake.

Claims (6)

An electrolyte membrane;
A first electrode joined to one surface of the electrolyte membrane;
A second electrode joined to the other surface of the electrolyte membrane;
A first current collector provided between the electrolyte membrane and the first electrode and in contact with the first electrode with at least a portion embedded in the electrolyte membrane;
A second current collector in contact with the second electrode;
A fuel cell comprising:   2. The fuel cell according to claim 1, wherein the surface of the first current collector is coated with a corrosion-resistant metal.   The fuel cell according to claim 1 or 2, wherein the first current collector and the electrolyte membrane are chemically bonded.   The second current collector is provided between the electrolyte membrane and the second electrode, and at least a part of the second current collector is separated from the first current collector in contact with the second electrode. The fuel cell according to any one of claims 1 to 3, wherein the fuel cell is embedded in the electrolyte membrane.   The fuel cell according to claim 4, wherein the surface of the second current collector is coated with a corrosion-resistant metal.   6. The fuel cell according to claim 4, wherein the second current collector and the electrolyte membrane are chemically bonded.

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