JP2007026873A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell in which permeation of fuel to an oxidant electrode is suppressed. <P>SOLUTION: The fuel cell is equipped with a solid electrolyte membrane 3, a plurality of fuel electrode catalyst layers 6 formed on the solid electrolyte membrane 3, hydrophobic insulating layers 9 for fuel electrode formed on the solid electrolyte membrane 3 so as to surround the respective surroundings of the plurality of fuel electrode catalyst layers 6, a plurality of oxidant electrode catalyst layers 4 formed on a face on the opposite side of the solid electrolyte membrane 3 where the plurality of fuel electrode catalyst layers 6 are formed, and hydrophobic insulating layers 8 for oxidant electrode which are formed on the opposite face of the solid electrolyte membrane 3 so as to surround the respective surroundings of the plurality of oxidant electrode catalyst layers 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fuel cell having an assembled battery structure including a plurality of single cells.

  In recent years, various electronic devices such as personal computers and mobile phones have been miniaturized with the development of semiconductor technology, and attempts have been made to use fuel cells as power sources for these small devices. Fuel cells have the advantage that they can generate electricity simply by supplying fuel and oxidant, and can continuously generate electricity if only the fuel is replaced. This is a very advantageous system. In particular, direct methanol fuel cells (DMFCs) use methanol with high energy density as fuel and can directly extract current from methanol on the electrode catalyst, so a reformer is not required and the size can be reduced. It is possible and the fuel is easier to handle than hydrogen gas fuel, so it is promising as a power source for small equipment.

  DMFC fuel supply methods include gas supply type DMFC that vaporizes liquid fuel and then feeds it into the fuel cell with a blower, etc., liquid supply type DMFC that feeds liquid fuel directly into the fuel cell with a pump and the like, and fuel An internal vaporization type DMFC that vaporizes and uses liquid fuel in a battery is known. Of these, the internal vaporization type DMFC does not require large-scale equipment such as a pump or blower for fuel supply. Therefore, if the concentration of methanol in the fuel can be increased to reduce the size of the liquid fuel tank, high energy can be achieved. A small fuel cell with a high density can be realized.

  In these DMFCs, a plurality of single cells are used to obtain a high output. However, as the number of cells increases, methanol crossover due to fuel leaking from the periphery of the fuel electrode catalyst layer cannot be ignored. It has been demanded.

  By the way, Patent Document 1 discloses a rib member made of a carbon fiber body having a plurality of parallel ribs on one side or both sides of an impermeable plate made of an expanded graphite sheet, and dense charcoal at positions on both sides of the rib member. It discloses that gas leakage of a phosphoric acid fuel cell is suppressed by using a separator formed by joining a seal plate made of a material.

On the other hand, in Patent Document 2, by forming a conductive flexible portion made of expanded graphite material, carbon fiber material or conductive rubber in a separator, the electrical and thermal contact between the membrane electrode composite and the separator is good. Is disclosed.
Japanese Patent Laid-Open No. 3-138865 Japanese Patent Laid-Open No. 2003-243002

  An object of the present invention is to provide a fuel cell in which fuel permeation to the oxidant electrode is suppressed.

A fuel cell according to the present invention includes a solid electrolyte membrane,
A plurality of fuel electrode catalyst layers formed on the solid electrolyte membrane;
A hydrophobic insulating layer for a fuel electrode formed on the solid electrolyte membrane so as to surround each of the plurality of fuel electrode catalyst layers;
A plurality of oxidant electrode catalyst layers formed on a surface of the solid electrolyte membrane opposite to the plurality of fuel electrode catalyst layers formed;
An oxidant electrode hydrophobic insulating layer formed so as to surround each of the plurality of oxidant electrode catalyst layers is provided on the opposite surface of the solid electrolyte membrane.

Further, another fuel cell according to the present invention includes a solid electrolyte membrane, a fuel electrode catalyst layer formed on the solid electrolyte membrane, and a side opposite to the fuel electrode catalyst layer of the solid electrolyte membrane formed. A fuel cell comprising a plurality of membrane electrode assemblies provided with an oxidant electrode catalyst layer formed on a surface,
A hydrophobic insulating layer for a fuel electrode formed on the solid electrolyte membrane so as to surround the periphery of the fuel electrode catalyst layer;
And a hydrophobic insulating layer for an oxidant electrode formed so as to surround the periphery of the oxidant electrode catalyst layer on the opposite surface of the solid electrolyte membrane.

  According to the present invention, since the hydrophobic insulating layer for the fuel electrode is integrated on the surface of the solid electrolyte membrane so as to surround the periphery of the fuel electrode catalyst layer, the fuel leaked from the fuel electrode catalyst layer is solid electrolyte membrane. Can be suppressed. In addition, even if the fuel leaked from the fuel electrode catalyst layer passes through the solid electrolyte membrane, the surface of the solid electrolyte membrane surrounds the periphery of the oxidant electrode catalyst layer so that the hydrophobic insulating layer for the oxidant electrode Is integrated, it is possible to suppress fuel permeation to the oxidant electrode. From the above, since fuel permeation when using a plurality of single cells can be effectively suppressed, a high output fuel cell can be realized.

  Furthermore, since the hydrophobic insulating layer for the fuel electrode and the hydrophobic insulating layer for the oxidant electrode can reinforce the strength of the solid electrolyte membrane, the handling property of the solid electrolyte membrane can be improved, The reliability of the fuel cell can be increased. In addition, since both the hydrophobic insulating layer for the fuel electrode and the hydrophobic insulating layer for the oxidant electrode are insulating members, they can also serve as gaskets and improve the assemblability.

  According to the present invention, it is possible to provide a fuel cell in which fuel permeation to the oxidant electrode is suppressed.

  Solid electrolyte membrane, fuel electrode catalyst layer, fuel electrode diffusion layer, oxidant electrode catalyst layer, oxidant electrode diffusion layer, fuel electrode hydrophobic insulating layer, oxidant electrode hydrophobic insulation that can be used in the fuel cell of the present invention The layer and fuel will be described.

(1) Solid electrolyte membrane The solid electrolyte membrane preferably contains a proton conductive material as a main component. Examples of the proton conductive material include fluorine resins having a sulfonic acid group (for example, perfluorosulfonic acid polymer), hydrocarbon resins having a sulfonic acid group, inorganic substances such as tungstic acid and phosphotungstic acid, and the like. However, it is not limited to these.

(2) Fuel electrode catalyst layer and oxidant electrode catalyst layer Examples of the catalyst contained in the oxidant electrode catalyst layer and the fuel electrode catalyst layer include platinum group elemental metals (Pt, Ru, Rh, Ir, Os, Pd, etc.), alloys containing platinum group elements, and the like. Although it is desirable to use Pt-Ru, which is highly resistant to methanol and carbon monoxide, as the fuel electrode catalyst and platinum as the oxidant electrode catalyst, the present invention is not limited to this. Further, a supported catalyst using a conductive support such as a carbon material may be used, or an unsupported catalyst may be used.

(3) Fuel electrode diffusion layer and oxidant electrode diffusion layer The fuel electrode diffusion layer and the oxidant electrode diffusion layer can be formed from, for example, carbon paper.

(4) Hydrophobic insulating layer for fuel electrode and hydrophobic insulating layer for oxidant electrode Preferably, the hydrophobic insulating layer for fuel electrode and the hydrophobic insulating layer for oxidant electrode each contain a hydrophobic polymer material. . The hydrophobic polymer material desirably has adhesiveness when it is formed by a coating method or a thermocompression bonding method, which will be described later, from the viewpoint of securing the adhesive strength with the solid electrolyte membrane. Moreover, it is preferable that chemical stability like methanol resistance is high.

  Examples of hydrophobic polymer materials having adhesiveness and methanol resistance include fluorine-containing resins and fluorine-containing rubbers (for example, tetrafluoroethylene (TFE) -hexafluoropropylene (HFP) copolymer, tetrafluoroethylene (TFE)- Hexafluoropropylene (HFP) -hexafluoroacetone (HFA) copolymer, tetrafluoroethylene (TFE) -polypropylene (PP) copolymer, polyvinylidene fluoride, polyvinyl fluoride, etc.), silicon-containing resins and silicon-containing rubbers (eg, cyano) (Silicon rubber). Among these, a fluorine-containing resin or a fluorine-containing rubber is preferable because the adhesive strength with the solid electrolyte membrane is increased and the methanol permeation amount is also reduced.

  The hydrophobic insulating layer for the fuel electrode and the hydrophobic insulating layer for the oxidant electrode may be formed of the same type of material or different types of materials. By varying the hydrophobicity of the hydrophobic insulating layer, it is possible to realize a fuel cell with enhanced required characteristics. For example, by increasing the hydrophobicity of the hydrophobic insulating layer for the fuel electrode, it is possible to increase the methanol permeation suppressing effect. In the internal vaporization type fuel cell as shown in FIG. It is possible to promote water diffusion from the oxidant electrode to the fuel electrode by increasing the hydrophobicity of the hydrophobic insulating layer for use.

  As a method for forming the hydrophobic insulating layer, a coating method, a thermocompression bonding method, an adhesion method, or the like can be employed.

(A) Coating method This is a method obtained by dissolving a hydrophobic polymer resin in an appropriate solvent, coating it on a solid electrolyte membrane of a membrane electrode assembly formed in advance, and drying it. In order to apply uniformly on the surface of the solid electrolyte membrane, surface treatment such as plasma treatment, sandblast treatment, coupling treatment, acid treatment, alkali treatment, etc. may be performed on the solid electrolyte membrane before coating. Moreover, in order to make adhesive strength high, you may heat-press after apply | coating and drying.

(B) Thermocompression bonding method A hydrophobic polymer sheet (already in the form of a film) is formed on the surface of the solid electrolyte membrane of the membrane electrode assembly by thermocompression bonding. At this time, a dispersion in which components constituting the solid electrolyte membrane are dispersed in an appropriate solvent may be used as a binder for adhesion. If it is difficult to adhere depending on the type of hydrophobic polymer sheet, surface treatment such as plasma treatment, sandblast treatment, coupling treatment, acid treatment, or alkali treatment is applied to one or both of the hydrophobic polymer sheet and the solid electrolyte membrane. Also good.

(C) Adhesion method A hydrophobic polymer sheet is fixed to the surface of the solid electrolyte membrane of the membrane electrode assembly with an adhesive. As the adhesive, for example, a methanol-resistant adhesive can be used. In order to increase the adhesive strength, a hot press may be performed after the bonding.

(4) Fuel As the fuel, it is possible to use liquid fuel or vaporized fuel obtained by vaporizing liquid fuel. When liquid fuel is supplied as it is to the fuel electrode catalyst layer, it is desirable to use an aqueous methanol solution.

  On the other hand, when the vaporized component of liquid fuel is supplied to the fuel electrode catalyst layer, an aqueous methanol solution, pure methanol, or the like can be used as the liquid fuel. The methanol concentration in the liquid fuel is desirably 50 mol% or more, and a more desirable range is a concentration exceeding 50 mol%. Thereby, the liquid fuel tank can be miniaturized and the energy density can be increased. The purity of pure methanol is desirably 95% by weight or more and 100% by weight or less.

  Hereinafter, an internal vaporization type direct methanol fuel cell according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional view showing an internal vaporization type direct methanol fuel cell according to a first embodiment of the present invention. FIG. 2 is a schematic plan view showing a hydrophobic insulating layer for an oxidant electrode used in the fuel cell of FIG.

  As shown in FIG. 1, this fuel cell is an assembled battery including a plurality of single cells. Each unit cell includes a membrane electrode assembly (MEA) having an oxidant electrode 1, a fuel electrode 2, and a proton conductive solid electrolyte membrane 3 disposed between the oxidant electrode 1 and the fuel electrode 2. Prepare. One solid electrolyte membrane 3 is shared by all membrane electrode assemblies (MEA). The single cells are connected in series or in parallel by leads (not shown). It is desirable that the outer area of each single cell is equal. Thereby, since the capacity variation between single cells can be reduced, the output and life of the fuel cell can be improved.

  Each oxidant electrode 1 includes an oxidant electrode catalyst layer 4 formed on one surface (the upper surface in FIG. 1) of the solid electrolyte membrane 3, and an oxidant electrode diffusion layer 5 laminated on the oxidant electrode catalyst layer 4. With. The oxidant electrode diffusion layer 5 plays a role of uniformly supplying the oxidant electrode catalyst layer 4 to the oxidant electrode catalyst layer 4, but also serves as a current collector for the oxidant electrode catalyst layer 4. On the other hand, each fuel electrode 2 includes a fuel electrode catalyst layer 6 formed on the opposite surface (the lower surface in FIG. 1) of the solid electrolyte membrane 3, and a fuel electrode diffusion layer 7 stacked on the fuel electrode catalyst layer 6. Is provided. The fuel electrode catalyst layer 6 is provided on the solid electrolyte membrane 3 so as to face the oxidant electrode catalyst layer 4 with the solid electrolyte membrane 3 interposed therebetween. The fuel electrode diffusion layer 7 serves to supply fuel uniformly to the fuel electrode catalyst layer 6 and also serves as a current collector for the fuel electrode catalyst layer 6. The oxidant electrode diffusion layer 5 and the fuel electrode diffusion layer 7 can be formed of carbon paper, for example. The thickness of the fuel electrode diffusion layer 7 is preferably in the range of 380 to 430 μm. On the other hand, the thickness of the oxidant electrode diffusion layer 5 is preferably in the range of 350 to 380 μm.

  As shown in FIG. 2, the oxidant electrode hydrophobic insulating layer 8 is a hydrophobic insulating plate having a plurality of rectangular through holes 8a into which the oxidant electrode 1 is inserted. The hydrophobic insulating layer 8 for the oxidant electrode is bonded onto the solid electrolyte membrane 3 so that the inner peripheral surface of the rectangular through hole 8a surrounds the periphery of the oxidant electrode catalyst layer 4 and the periphery of the oxidant electrode diffusion layer 5. Has been. Therefore, the thickness of the oxidant electrode hydrophobic insulating layer 8 is equal to the total thickness of the oxidant electrode catalyst layer 4 and the oxidant electrode diffusion layer 5. On the other hand, the hydrophobic insulating layer 9 for the fuel electrode is a hydrophobic insulating plate in which a plurality of rectangular through holes into which the fuel electrode 2 is inserted are opened. The hydrophobic insulating layer 9 for the fuel electrode is formed on the surface of the solid electrolyte membrane 3 opposite to the side where the oxidant electrode 1 is formed, and surrounds the fuel electrode catalyst layer 6 and the fuel electrode diffusion layer 7. Is enclosed. Therefore, the thickness of the fuel electrode hydrophobic insulating layer 9 is equal to the total thickness of the fuel electrode catalyst layer 6 and the fuel electrode diffusion layer 7. The thickness of the oxidant electrode hydrophobic insulating layer 8 is preferably in the range of 350 to 400 μm. On the other hand, the thickness of the hydrophobic insulating layer 9 for the fuel electrode is preferably in the range of 400 to 450 μm.

  A fuel chamber 10 for supplying a vaporized component of liquid fuel to the fuel electrode catalyst layer 6 is provided below the fuel electrode 2. The fuel chamber 10 includes a liquid fuel tank (not shown) and a fuel vaporization layer (not shown). The liquid fuel tank contains liquid methanol or an aqueous methanol solution as the liquid fuel. Further, the fuel vaporization layer includes a gas-liquid separation membrane that allows only the vaporized component of the liquid fuel to permeate and does not allow the liquid fuel to permeate. Examples of the gas-liquid separation membrane include a silicone rubber sheet. The vaporized component that has passed through the fuel vaporization layer is supplied to the fuel electrode catalyst layer 6 through the fuel electrode diffusion layer 7.

  In addition, a vaporized fuel storage chamber for temporarily storing the vaporized fuel that has diffused through the fuel vaporized layer is provided between the fuel vaporized layer and the fuel electrode, or fuel penetration that temporarily holds liquid fuel. It is also possible to place the layer between the liquid fuel tank and the fuel vaporization layer.

  On the other hand, the oxidant electrode side separator 12 in which the flow path 11 for taking in the air as the oxidant is formed is laminated across both the oxidant electrode diffusion layer 5 and the hydrophobic insulating layer 8 for the oxidant electrode. Yes. The oxidant electrode side separator 12 can be formed from, for example, a carbon binder plate. Since the flow path 11 of the oxidant electrode side separator 12 is a through hole as shown in FIG. 1, it is possible to directly take outside air into the oxidant electrode diffusion layer 5 without using an auxiliary device such as a pump. is there. As a result, it is possible to reduce the size of the fuel cell and to reduce the power consumed by auxiliary equipment such as a pump.

  According to the direct methanol fuel cell having the above-described configuration, when a vaporized component of liquid fuel (for example, methanol aqueous solution) is supplied from the fuel chamber 10 to the fuel electrode catalyst layer 6 through the fuel electrode diffusion layer 7, the following reaction is performed. The internal reforming reaction of methanol shown in Formula (1) occurs.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
When pure methanol is used as the liquid fuel, there is no supply of water from the fuel chamber 10, so water generated by the oxidation reaction of methanol mixed in the oxidant electrode catalyst layer 4 and the solid electrolyte membrane 3 Moisture or the like reacts with methanol to cause the above-described internal reforming reaction of the formula (1), or an internal reforming reaction occurs in a water-free reaction mechanism not based on the above-described formula (1).

Protons (H ⁺ ) generated by these internal reforming reactions diffuse through the solid electrolyte membrane 3 and reach the oxidant electrode catalyst layer 4. On the other hand, the air taken in from the flow path 11 of the oxidant electrode side separator 12 diffuses through the oxidant electrode diffusion layer 5 and is supplied to the oxidant electrode catalyst layer 4. In the oxidant electrode catalyst layer 4, water is generated by the reaction shown in the following formula (2), that is, a power generation reaction occurs.

(3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)
When the power generation reaction proceeds, water is generated in the oxidant electrode catalyst layer 4 by the reaction of the above-described formula (2).

  In the fuel cell as described above, the inventors form hydrophobic insulating layers 8 and 9 on the solid electrolyte membrane 3 so as to surround the periphery of the fuel electrode catalyst layer 6 and the oxidant electrode catalyst layer 4, respectively. Further, not only the fuel permeation to the oxidant electrode 1 is suppressed, but also the reaction resistance of the internal reforming reaction is improved because the water generated in the oxidant electrode catalyst layer 4 returns to the fuel electrode catalyst layer 6 better. I found what I could do.

  That is, since the hydrophobic insulating layers 8 and 9 integrated on both surfaces of the solid electrolyte membrane 3 can suppress the evaporation of water from the MEA, the water retention amount of the oxidant electrode catalyst layer 4 is the fuel electrode catalyst. It is possible to create a state in which the moisture retention amount of the layer 6 is greater. As a result, water diffusion from the oxidant electrode catalyst layer 4 to the fuel electrode catalyst layer 6 is promoted by the osmotic pressure phenomenon, so that the concentration of methanol in the liquid fuel is increased to reduce the water supply from the liquid fuel, Or even if it does not exist at all, the internal reforming reaction of methanol shown in the above formula (1) can be smoothly advanced.

  Further, unreacted methanol flows out from the fuel electrode catalyst layer 6 and the fuel electrode diffusion layer 7, but permeation of the unreacted methanol to the solid electrolyte membrane 3 can be suppressed by the fuel electrode hydrophobic insulating layer 9. Even if methanol permeates through the solid electrolyte membrane 3, permeation to the oxidant electrode catalyst layer 4 can be prevented by the hydrophobic insulating layer 8 for oxidant electrode. Therefore, the methanol crossover phenomenon can be reduced even when the methanol concentration in the liquid fuel is increased.

  From the above, it is possible to obtain high output characteristics even when using liquid fuel with high methanol concentration, especially rich fuel exceeding the stoichiometric ratio, so that a small and high energy density fuel cell can be realized. Can do.

  Further, since the water generated in the oxidant electrode catalyst layer 4 can be used for the internal reforming reaction of the fuel in the fuel electrode catalyst layer 6, the treatment such as the discharge of the water generated in the oxidant electrode catalyst layer to the outside of the fuel cell can be performed. It is possible to provide a fuel cell with a simple configuration that can be reduced and does not require a special configuration for water supply.

  Furthermore, in the fuel cell having the above-described configuration, the MEA expands and contracts during power generation due to the intake of vaporized fuel and the intake of air, and both sides of the MEA are not tightened with separators or end plates. When the thickness is reduced (for example, 100 μm or less), the solid electrolyte membrane 3 is easily twisted. Since the hydrophobic insulating layers 8 and 9 integrated on both surfaces of the solid electrolyte membrane 3 can improve the tensile strength of the solid electrolyte membrane 3, the breakage when the thickness of the solid electrolyte membrane 3 is reduced is suppressed. can do.

  Further, since the hydrophobic insulating layers 8 and 9 can also serve as a gasket, it is possible to improve the handling property of the MEA when assembling the fuel cell.

  The thickness of the solid electrolyte membrane is desirably 100 μm or less. As a result, water diffusion from the oxidant electrode catalyst layer to the fuel electrode catalyst layer can be promoted, and the output characteristics can be further improved. However, if the thickness of the solid electrolyte membrane is less than 10 μm, the electrolyte membrane is likely to break even if the electrolyte membrane is reinforced with the hydrophobic insulating layer. Therefore, the thickness of the solid electrolyte membrane is in the range of 10 to 100 μm. More preferably. More preferably, it is the range of 10-80 micrometers.

  In FIG. 1 described above, an example in which the thickness of the hydrophobic insulating layer is made equal to the total thickness of the catalyst layer and the diffusion layer in both the oxidant electrode and the fuel electrode has been described. However, the thickness of the catalyst layer is not less than the thickness of the catalyst layer and not more than the total thickness of the catalyst layer and the diffusion layer.

  In each of the oxidant electrode and the fuel electrode, the permeation of the fuel and the evaporation of moisture can be further suppressed by making the thickness of the hydrophobic insulating layer equal to or greater than the thickness of the catalyst layer that surrounds it. A thicker hydrophobic insulating layer is more effective in suppressing fuel permeation and moisture evaporation, but if the thickness of the hydrophobic insulating layer exceeds the total thickness of the catalyst layer and diffusion layer that it surrounds, the fuel electrode The output per unit volume is reduced due to the deterioration of the fuel cell output characteristics due to poor contact with the fuel electrode side current collector and the oxidant electrode and the oxidant electrode side current collector, and the increase in the thickness of the entire fuel cell. May decrease.

  In FIG. 1 described above, each of the hydrophobic insulating layer 8 for the oxidant electrode and the hydrophobic insulating layer 9 for the fuel electrode is formed into one sheet, but the frame is formed on the surface of the solid electrolyte membrane on the oxidant electrode side or the fuel electrode side. It is also possible to form a plurality of shaped hydrophobic insulating layers, and individually seal the oxidant electrode 1 or the fuel electrode 2.

  Moreover, in FIG. 1 mentioned above, although the flat type solid electrolyte membrane was used, you may use a cylindrical solid electrolyte membrane.

  Next, a liquid supply type direct methanol fuel cell according to a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic cross-sectional view showing a liquid supply type direct methanol fuel cell according to a second embodiment of the present invention. The members of the same type as described in FIG. 1 are given the same reference numerals and description thereof is omitted.

  As shown in FIG. 3, this fuel cell is an assembled battery including a stack cell in which a plurality of single cells 20 are stacked with separators interposed therebetween. Each single cell 20 includes a membrane electrode assembly (MEA) having an oxidant electrode 1, a fuel electrode 2, and a proton conductive solid electrolyte membrane 3 disposed between the oxidant electrode 1 and the fuel electrode 2. Is provided.

  Each oxidant electrode 1 includes an oxidant electrode catalyst layer 4 formed on one surface of the solid electrolyte membrane 3 and an oxidant electrode diffusion layer 5 stacked on the oxidant electrode catalyst layer 4. On the other hand, each fuel electrode 2 includes a fuel electrode catalyst layer 6 formed on the opposite surface of the solid electrolyte membrane 3 and a fuel electrode diffusion layer 7 stacked on the fuel electrode catalyst layer 6. The fuel electrode catalyst layer 6 is provided at a position facing the oxidant electrode catalyst layer 4 with the solid electrolyte membrane 3 interposed therebetween. The thickness of the fuel electrode diffusion layer 7 is preferably in the range of 380 to 430 μm. On the other hand, the thickness of the oxidant electrode diffusion layer 5 is preferably in the range of 350 to 380 μm.

  The rectangular frame-shaped hydrophobic insulating layer 21 for the oxidant electrode is adhered on the solid electrolyte membrane 3 so that the inner peripheral surface surrounds the periphery of the oxidant electrode catalyst layer 4 and the periphery of the oxidant electrode diffusion layer 5. ing. For this reason, the thickness of the hydrophobic insulating layer 21 for the oxidant electrode is equal to the total thickness of the oxidant electrode catalyst layer 4 and the oxidant electrode diffusion layer 5. On the other hand, the hydrophobic insulating layer 22 for the fuel electrode is formed on the surface of the solid electrolyte membrane 3 opposite to the side where the oxidant electrode 1 is formed, and the periphery of the fuel electrode catalyst layer 6 and the fuel electrode diffusion layer 7. Surrounding. Therefore, the thickness of the fuel electrode hydrophobic insulating layer 22 is equal to the total thickness of the fuel electrode catalyst layer 6 and the fuel electrode diffusion layer 7. The thickness of the oxidant electrode hydrophobic insulating layer 21 and the fuel electrode hydrophobic insulating layer 22 is preferably in the range of 400 to 450 μm.

  The unit cell 20 having the above-described configuration is stacked via a separator 23 having flow paths formed on both sides. Since the separator 23 is made of, for example, a conductive material such as carbon, the single cells 20 are connected in series by stacking the single cells 20 via the separator 23. The groove-shaped channel 24 formed on the surface of the separator 23 facing the fuel electrode diffusion layer 7 is a fuel electrode channel. The groove-shaped channel 25 formed on the surface of the separator 23 facing the oxidant electrode diffusion layer 5 is an oxidant electrode channel.

  An oxidant electrode end separator 26 is laminated on the outermost layer on the oxidant electrode 1 side of the stack cell. The oxidant electrode end separator 26 has a groove-shaped oxidant electrode channel 27 formed on the surface facing the oxidant electrode diffusion layer 5. A fuel electrode end separator 28 is stacked on the outermost layer of the stack cell on the fuel electrode 2 side. The fuel electrode end separator 28 has a groove-shaped fuel electrode channel 29 formed on the surface facing the fuel electrode diffusion layer 7.

  Air is supplied to the oxidant electrode flow paths 25 and 27 of the separator 23 and the oxidant electrode end separator 26 by, for example, an air pump. On the other hand, an aqueous methanol solution is supplied to the fuel electrode passages 24 and 29 of the separator 23 and the fuel electrode end separator 28 by, for example, a liquid pump.

  The stack cell is fastened by a bolt (not shown).

  According to the liquid supply type direct methanol fuel cell having the above-described configuration, unreacted methanol flows out from the fuel electrode catalyst layer 6 and the fuel electrode diffusion layer 7, but permeates into the solid electrolyte membrane 3. Can be suppressed by the hydrophobic insulating layer 22 for the fuel electrode. Even if methanol permeates through the solid electrolyte membrane 3, permeation to the oxidant electrode catalyst layer 4 can be prevented by the hydrophobic insulating layer 21 for oxidant electrode. Therefore, it is possible to reduce the methanol crossover phenomenon in a fuel cell having an assembled battery structure including a plurality of single cells.

  In FIG. 3 described above, an example in which the thickness of the hydrophobic insulating layer is made equal to the total thickness of the catalyst layer and the diffusion layer in both the oxidant electrode and the fuel electrode has been described. However, the thickness of the catalyst layer is not less than the thickness of the catalyst layer and not more than the total thickness of the catalyst layer and the diffusion layer.

  In each of the oxidant electrode and the fuel electrode, the permeation of the fuel can be further suppressed by making the thickness of the hydrophobic insulating layer equal to or greater than the thickness of the catalyst layer that surrounds it. The thicker the hydrophobic insulating layer, the higher the effect of suppressing fuel permeation. However, if the thickness of the hydrophobic insulating layer exceeds the total thickness of the catalyst layer and the diffusion layer that it surrounds, the fuel electrode and the fuel electrode The fuel cell output characteristics deteriorate due to poor contact with the side current collector and the oxidant electrode and the oxidant electrode side current collector, and the total fuel cell thickness increases, resulting in a decrease in output per volume. There is a fear.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

[Example]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Example 1
<Production of fuel electrode>
A perfluorocarbon sulfonic acid solution, water and methoxypropanol were added to a fuel electrode catalyst (Pt: Ru = 1: 1) supported carbon black, and the catalyst supported carbon black was dispersed to prepare a paste. The obtained paste was applied to porous carbon paper as a fuel electrode diffusion layer to obtain a fuel electrode catalyst layer having a thickness of 450 μm. Three such fuel electrode catalyst layers were produced.

<Preparation of oxidizer electrode>
A perfluorocarbon sulfonic acid solution, water and methoxypropanol were added to the oxidant electrode catalyst (Pt) -carrying carbon black, and the catalyst-carrying carbon black was dispersed to prepare a paste. The obtained paste was applied to porous carbon paper as an oxidant electrode diffusion layer to obtain an oxidant electrode catalyst layer having a thickness of 400 μm. Three such oxidant electrode catalyst layers were prepared.

  As a proton conductive electrolyte membrane, a perfluorocarbon sulfonic acid membrane (nafion membrane, manufactured by DuPont) having a thickness of 30 μm and a water content of 10 to 20% by weight was prepared, and a plurality of fuel electrode catalyst layers prepared earlier And an oxidant electrode catalyst layer, and hot-pressing them to obtain a membrane electrode assembly (MEA).

  A slurry was prepared by dissolving fluorine rubber as a hydrophobic polymer resin in methyl isobutyl ketone as a solvent. The obtained slurry was coated on the solid electrolyte membrane of the membrane electrode assembly so as to surround each of the oxidant electrodes and fill the gaps between the oxidant electrodes, dried, and then heated at 80 to 150 ° C. By pressing, a hydrophobic insulating layer for an oxidizer electrode having the structure shown in FIG. 2 was obtained.

  Further, the slurry described above is coated on the opposite surface of the solid electrolyte membrane of the membrane electrode assembly so as to surround each of the fuel electrodes and fill the gaps between the fuel electrodes, and after drying, 80 to 150 A hydrophobic insulating layer for a fuel electrode was obtained by hot pressing at ° C.

  An internal vaporization type direct methanol fuel cell having the structure shown in FIG. 1 was assembled using the obtained membrane electrode assembly, the oxidant electrode side separator, and the fuel chamber. At this time, 2 mL of pure methanol having a purity of 99.9% by weight was stored in the fuel tank.

(Example 2)
A direct methanol fuel cell was assembled in the same manner as described in Example 1 except that the type of the hydrophobic polymer resin was changed to a fluororesin.

(Example 3)
A direct methanol fuel cell was assembled in the same manner as described in Example 1 except that the type of the hydrophobic polymer resin was changed to hydrofluoroether.

(Comparative Example 1)
A direct methanol fuel cell was assembled in the same manner as described in Example 1 except that the hydrophobic insulating layer was not formed.

  First, the fuel cells of Examples 1 to 3 were subjected to a T-type peel test described in JIS K-6854 (Adhesive peel adhesion strength test method), and the adhesive strength between the hydrophobic insulating layer and the solid electrolyte membrane. As a result, it was confirmed that the hydrophobic insulating layers of Examples 1 to 3 were fixed to the solid electrolyte membrane with sufficient adhesive strength. Actually, when the fuel cells of Examples 1 to 3 were subjected to power generation at a constant load at room temperature, the hydrophobic insulating layer did not peel off during power generation.

Moreover, the result of a T-shaped peeling test is shown in FIG. In FIG. 4, the vertical axis represents the peeling load, and the horizontal axis represents G (dyn / cm ² ). As shown in FIG. 4, as a result of the T-type peel test, the peel strength varies depending on the type of hydrophobic polymer, and the hydrofluoroether used in Example 3 is desirable from the viewpoint of the adhesive strength with the solid electrolyte membrane. I understood.

  Moreover, about the fuel cell of Examples 1-3 and the comparative example 1, the methanol crossover amount was measured. A test cell was partitioned with a membrane to be tested, a predetermined amount of pure methanol was placed in one cell, and pure water was placed in the other cell. After a certain time at room temperature, the methanol concentration on the cell side containing pure water was measured by gas chromatography to determine the permeation amount of methanol, and the results are shown in FIG. The vertical axis in FIG. 5 represents the methanol permeation amount, and the horizontal axis represents the elapsed time.

  As for the membranes to be tested, for Examples 1 to 3, a solid electrolyte membrane in which the oxidant electrode and the fuel electrode are not formed is prepared, and both surfaces are hydrophobic in the same procedure as each example. A three-layer film having an insulating layer was used. Moreover, about the comparative example 1, although only the solid electrolyte membrane was used, the thickness of the solid electrolyte membrane was set to the same thickness as the three-layer membrane used in the case of Examples 1-3.

  As is clear from FIG. 5, in Examples 1 to 3 in which the hydrophobic insulating layers were formed on both surfaces of the solid electrolyte membrane, compared to the comparative example in which the solid electrolyte membrane was thickened without forming the hydrophobic insulating layer, It can be understood that the amount of methanol permeation is small and effective in suppressing methanol crossover. Among Examples 1 to 3, the hydrofluoroether used in Example 3 is desirable from the viewpoint of suppressing methanol crossover.

  As described above, according to the fuel cells of Examples 1 to 3, as confirmed in FIG. 4, the hydrophobic insulating layer for the oxidant electrode is integrated so as to surround the oxidant electrode on the solid electrolyte membrane. And the hydrophobic insulating layer for the fuel electrode is integrated so as to surround the periphery of the fuel electrode formed on the opposite surface of the solid electrolyte membrane, so that evaporation of moisture from the MEA can be suppressed. It is possible to improve water diffusion from the oxidizer electrode to the fuel electrode. At the same time, it is possible to suppress breakage of the solid electrolyte membrane during fuel cell assembly or power generation. Further, as confirmed in FIG. 5 described above, according to the fuel cells of Examples 1 to 3, methanol crossover can be suppressed.

  From the above, according to the fuel cells of Examples 1 to 3, it is possible to obtain high output characteristics even when the methanol concentration in the liquid fuel is increased from 50 mol%.

Example 4
<Production of fuel electrode>
A perfluorocarbon sulfonic acid solution, water and methoxypropanol were added to a fuel electrode catalyst (Pt: Ru = 1: 1) supported carbon black, and the catalyst supported carbon black was dispersed to prepare a paste. The obtained paste was applied to porous carbon paper as a fuel electrode diffusion layer to obtain a fuel electrode catalyst layer having a thickness of 450 μm.

<Preparation of oxidizer electrode>
A perfluorocarbon sulfonic acid solution, water and methoxypropanol were added to the oxidant electrode catalyst (Pt) -carrying carbon black, and the catalyst-carrying carbon black was dispersed to prepare a paste. The obtained paste was applied to porous carbon paper as an oxidant electrode diffusion layer to obtain an oxidant electrode catalyst layer having a thickness of 400 μm.

  A perfluorocarbon sulfonic acid membrane (nafion membrane, manufactured by DuPont) having a thickness of 180 μm and a water content of 10 to 20% by weight is prepared as a proton conductive electrolyte membrane, and these are prepared as a fuel electrode catalyst layer and an oxidant electrode catalyst layer. Membrane / electrode assembly (MEA) was obtained by sandwiching them with each other and subjecting them to hot pressing.

  A slurry was prepared by dissolving fluorine rubber as a hydrophobic polymer resin in methyl isobutyl ketone as a solvent. The obtained slurry was coated on the solid electrolyte membrane of the membrane electrode assembly in a frame shape so as to surround the periphery of the oxidant electrode, dried, and then hot-pressed at 80 to 150 ° C. to obtain an oxidant. An extreme hydrophobic insulating layer was obtained.

  In addition, the slurry described above is coated in a frame shape so as to surround the periphery of the fuel electrode on the surface opposite to the solid electrolyte membrane of the membrane electrode assembly, dried, and then hot-pressed at 80 to 150 ° C. Thus, a hydrophobic insulating layer for a fuel electrode was obtained.

  Three membrane electrode assemblies with such a hydrophobic insulating layer were produced.

  Using the obtained membrane electrode assembly, separator, and end separator, a liquid supply type direct methanol fuel cell having the structure shown in FIG. 3 was assembled. In this case, a methanol aqueous solution having a concentration of 3 mol% was used as the liquid fuel.

(Example 5)
A direct methanol fuel cell was assembled in the same manner as described in Example 4 except that the type of the hydrophobic polymer resin was changed to a fluororesin.

(Example 6)
A direct methanol fuel cell was assembled in the same manner as described in Example 4 except that the type of the hydrophobic polymer resin was changed to hydrofluoroether.

(Comparative Example 2)
A direct methanol fuel cell was assembled in the same manner as described in Example 4 above, except that the hydrophobic insulating layer was not formed.

  First, for the fuel cells of Examples 4 to 6, a peel test was performed in the same manner as described in Example 1 above, and the adhesive strength between the hydrophobic insulating layer and the solid electrolyte membrane was determined. It was confirmed that the hydrophobic insulating layers 4 to 6 were fixed to the solid electrolyte membrane with sufficient adhesive strength. Actually, when the fuel cells of Examples 4 to 6 were subjected to power generation at a constant load at room temperature, the hydrophobic insulating layer did not peel off during power generation. As a result of the peel test, it was found that the peel strength differs depending on the type of the hydrophobic polymer, and that the hydrofluoroether used in Example 6 is desirable from the viewpoint of the adhesive strength with the solid electrolyte membrane.

  Further, for the fuel cells of Examples 4 to 6 and Comparative Example 2, when the methanol crossover amount was measured in the same manner as described in Example 1, the hydrophobic insulating layers were formed on both sides of the solid electrolyte membrane. In Examples 4 to 6 in which the thickness of the solid electrolyte membrane was formed without forming the hydrophobic insulating layer, the amount of methanol permeation was small, and it was confirmed that this was effective for suppressing methanol crossover. did it. Among Examples 4 to 6, the hydrofluoroether used in Example 6 is desirable from the viewpoint of suppressing methanol crossover.

  As described above, according to the fuel cells of Examples 4 to 6, the hydrophobic insulating layer for the oxidant electrode is integrated so as to surround the periphery of the oxidant electrode on the solid electrolyte membrane, and the solid electrolyte membrane Since the hydrophobic insulating layer for the fuel electrode is integrated so as to surround the periphery of the fuel electrode formed on the opposite surface, the tensile strength of the solid electrolyte membrane can be improved. Moreover, according to the fuel cells of Examples 4 to 6, methanol crossover can be suppressed.

  From the above, according to the fuel cells of Examples 4 to 6, high output characteristics can be obtained.

1 is a schematic cross-sectional view showing an internal vaporization type direct methanol fuel cell according to a first embodiment of the present invention. The typical top view which shows the hydrophobic insulating layer for oxidizer electrodes used for the fuel cell of FIG. The typical sectional view showing the liquid supply type direct methanol fuel cell concerning a 2nd embodiment of the present invention. The characteristic view which shows the result of the T-shaped peeling test about the direct methanol type fuel cell of Examples 1-3. The characteristic view which shows the result of the methanol crossover test about Examples 1-3 and the direct methanol type fuel cell of a comparative example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Oxidizer electrode, 2 ... Fuel electrode, 3 ... Solid electrolyte membrane, 4 ... Oxidant electrode catalyst layer, 5 ... Oxidant electrode diffusion layer, 6 ... Fuel electrode catalyst layer, 7 ... Fuel electrode diffusion layer, 8, 21 ... hydrophobic insulating layer for oxidant electrode, 8a ... rectangular hole, 9, 22 ... hydrophobic insulating layer for fuel electrode, 10 ... fuel chamber, 11 ... oxidant flow path, 12 ... oxidant electrode side separator, 20 ... single Cell, 23... Separator, 24, 29... Fuel electrode channel, 25, 27 .. Oxidant electrode channel, 26 .. Oxidant electrode end separator, 28.

Claims (4)

A solid electrolyte membrane;
A plurality of fuel electrode catalyst layers formed on the solid electrolyte membrane;
A hydrophobic insulating layer for a fuel electrode formed on the solid electrolyte membrane so as to surround each of the plurality of fuel electrode catalyst layers;
A plurality of oxidant electrode catalyst layers formed on a surface of the solid electrolyte membrane opposite to the plurality of fuel electrode catalyst layers formed;
A fuel cell comprising: a hydrophobic insulating layer for an oxidant electrode formed on the opposite surface of the solid electrolyte membrane so as to surround each of the plurality of oxidant electrode catalyst layers.   The container further comprising: a container for storing liquid fuel; and a fuel vaporization layer for separating a vaporized component from the liquid fuel in the container and supplying the vaporized component to the plurality of fuel electrode catalyst layers. 1. The fuel cell according to 1. A solid electrolyte membrane, a fuel electrode catalyst layer formed on the solid electrolyte membrane, and an oxidant electrode catalyst layer formed on the opposite surface of the solid electrolyte membrane from which the fuel electrode catalyst layer is formed. A fuel cell comprising a plurality of membrane electrode assemblies provided,
A hydrophobic insulating layer for a fuel electrode formed on the solid electrolyte membrane so as to surround the periphery of the fuel electrode catalyst layer;
A fuel cell comprising: a hydrophobic insulating layer for an oxidant electrode formed on the opposite surface of the solid electrolyte membrane so as to surround the periphery of the oxidant electrode catalyst layer.   The hydrophobic insulating layer for a fuel electrode and the hydrophobic insulating layer for an oxidant electrode each contain a polymer material having adhesiveness and hydrophobicity, respectively. Fuel cell.

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