JP2006216449A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell of which fuel permeation to an oxidizer electrode has been suppressed. <P>SOLUTION: This is the fuel cell which is provided with a solid electrolyte membrane 8, with a fuel electrode catalyst layer 5 which is formed in the solid electrolyte membrane 8 and to which vaporized fuel is supplied, with a hydrophobic insulating layer 10 for the fuel electrode which has been formed in the solid electrolyte membrane 8 so as to surround the periphery of the fuel electrode catalyst layer 5, with the oxidizer electrode catalyst layer 2 which has been installed at the face on the opposite side to the face at which the fuel electrode catalyst layer 5 of the solid electrolyte membrane 8 has been formed, and with the hydrophobic insulating layer 9 for the oxidizer electrode which has been formed on the surface of the opposite side to the solid electrolyte membrane 8 so as to surround the periphery of the oxidizer electrode catalyst layer 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell including a fuel electrode catalyst layer to which vaporized fuel obtained by vaporizing liquid fuel is supplied.

  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 a gas supply type DMFC that vaporizes liquid fuel and then feeds it into the fuel cell with a blower, etc., a liquid supply type DMFC that feeds liquid fuel directly into the fuel cell with a pump or the like, and a 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.

  However, this internal vaporization type DMFC has a problem that the methanol crossover amount increases as the methanol concentration of the fuel increases.

  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.

In the above internal vaporization type DMFC, both methanol and water are vaporized and supplied to the fuel electrode. However, since water has a lower vapor pressure than methanol, if the liquid fuel is made highly concentrated, the amount of water supply will be significantly insufficient. The reaction resistance of the internal reforming reaction (CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ ) at the fuel electrode increases. Decreasing the thickness of the solid electrolyte membrane to reduce the reaction resistance can promote the diffusion of moisture generated at the oxidizer electrode to the fuel electrode, but increases the methanol permeability of the solid electrolyte membrane, The amount of methanol crossover increases.

  As a result of intensive studies to solve the above problems, the present inventors have formed a hydrophobic insulating layer on the solid electrolyte membrane so as to surround each of the fuel electrode catalyst layer and the oxidant electrode catalyst layer. In addition to suppressing the permeation of fuel to the oxidant electrode, it has been found that the reaction resistance of the internal reforming reaction can be improved because the water generated in the oxidant electrode catalyst layer returns to the fuel electrode catalyst layer better. It was.

That is, the present invention includes a solid electrolyte membrane,
A fuel electrode catalyst layer formed on the solid electrolyte membrane and supplied with vaporized fuel; and
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;
An oxidant electrode catalyst layer provided on the opposite surface of the solid electrolyte membrane from which the fuel electrode catalyst layer was formed;
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, evaporation of moisture from the catalyst layer and the solid electrolyte membrane can be suppressed by the hydrophobic insulating layer for the oxidant electrode and the hydrophobic insulating layer for the fuel electrode formed on both surfaces of the solid electrolyte membrane. Therefore, water diffusion from the oxidizer electrode to the fuel electrode can be promoted, and the reaction resistance of the internal reforming reaction can be kept low even when a high concentration liquid fuel is used. Moreover, according to these hydrophobic insulating layers, it is possible to suppress fuel permeation to the oxidizer electrode even when the concentration of liquid fuel is high.

  As a result, a high output characteristic can be obtained even when a high-concentration liquid fuel, particularly a rich fuel exceeding the stoichiometric ratio, is used, so that a small and high energy density fuel cell can be realized. .

  In addition, the water generated in the oxidant electrode catalyst layer can be used for the internal reforming reaction of the liquid fuel in the fuel electrode catalyst layer, so the treatment of the water generated in the oxidant electrode catalyst layer to the outside of the fuel cell is reduced. In addition, a special configuration for supplying water to the liquid fuel is not required, and a fuel cell having a simple configuration can be provided.

  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 the liquid 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, and inorganic substances such as tungstic acid and phosphotungstic acid. However, it is not limited to these.

  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.

(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.

  The thickness of the fuel electrode diffusion layer can be in the range of 380 to 430 μm, for example. The thickness of the oxidant electrode diffusion layer can be set in the range of 350 to 380 μm, for example.

(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.), fluorine-based surface treatment agent, silicon-containing resin and silicon Examples thereof include rubber containing (for example, cyanosilicon rubber). It is desirable that the type of hydrophobic polymer material to be used is one type or two or more types. For example, when a fluororesin membrane having a sulfonic acid group such as Nafion (registered trademark) membrane (Du Pont) is adopted as the solid electrolyte membrane, the adhesive strength with the solid electrolyte membrane is increased, and the methanol permeation amount Therefore, a fluorine-containing resin, a fluorine-containing rubber, or a fluorine-based surface treatment agent is preferable.

  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, the effect of suppressing methanol permeation can be increased, and by increasing the hydrophobicity of the hydrophobic insulating layer for the oxidant electrode, the oxidizing agent can be increased. It is possible to promote water diffusion from the electrode to the fuel electrode.

  The thickness of the hydrophobic insulating layer for the fuel electrode is preferably not less than the thickness of the fuel electrode catalyst layer and not more than the total thickness of the fuel electrode catalyst layer and the fuel electrode diffusion layer. This is due to the reason explained below. By making the thickness of the hydrophobic insulating layer for the fuel electrode equal to or greater than the thickness of the fuel electrode catalyst layer, fuel permeation and moisture evaporation can be further suppressed. The thicker the hydrophobic insulating layer for the fuel electrode, the more effective the suppression of fuel permeation and moisture evaporation is. However, if the total thickness of the fuel electrode catalyst layer and the fuel electrode diffusion layer is exceeded, the fuel electrode and the fuel electrode side collector The fuel cell output characteristics are likely to be deteriorated due to poor contact with the electric body, and the thickness of the entire fuel cell is increased, which may reduce the output per volume.

  The thickness of the hydrophobic insulating layer for the fuel electrode can be in the range of 400 to 450 μm, for example.

  The thickness of the hydrophobic insulating layer for the oxidant electrode is preferably not less than the thickness of the oxidant electrode catalyst layer and not more than the total thickness of the oxidant electrode catalyst layer and the oxidant electrode diffusion layer. This is due to the reason explained below. By making the thickness of the hydrophobic insulating layer for the oxidant electrode equal to or greater than the thickness of the oxidant electrode catalyst layer, fuel permeation and water evaporation can be further suppressed. The thicker the hydrophobic insulating layer for the oxidant electrode, the higher the effect of suppressing fuel permeation and moisture evaporation, but when the total thickness of the oxidant electrode catalyst layer and the oxidant electrode diffusion layer is exceeded, The fuel cell output characteristics are likely to deteriorate due to poor contact with the oxidant electrode side current collector. Flooding due to water generated on the oxidant electrode side is likely to occur, and there is also a possibility that the output is reduced due to insufficient supply of oxygen and the output per volume is reduced due to the increase in the thickness of the entire fuel cell.

  The thickness of the hydrophobic insulating layer for the oxidizer electrode can be set in the range of 350 to 400 μm, for example.

  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. The hot press temperature can be, for example, in the range of 80 to 150 ° C.

(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) Liquid fuel As the liquid fuel, an aqueous methanol solution, pure methanol, or the like can be used. 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 preferably 95% by weight or more and 100% by weight or less. Hereinafter, a direct methanol fuel cell which is an embodiment of a fuel cell according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a direct methanol fuel cell according to an embodiment of the present invention.

  As shown in FIG. 1, a membrane electrode assembly (MEA) 1 includes an oxidant electrode 4 comprising an oxidant electrode catalyst layer 2 and an oxidant electrode gas diffusion layer 3, a fuel electrode catalyst layer 5 and a fuel electrode gas diffusion layer. 6 and a proton conductive solid electrolyte membrane 8 disposed between the oxidant electrode catalyst layer 2 and the fuel electrode catalyst layer 5.

  The oxidant electrode catalyst layer 2 is laminated on the oxidant electrode gas diffusion layer 3. The oxidant electrode gas diffusion layer 3 plays a role of supplying the oxidant uniformly to the oxidant electrode catalyst layer 2, but also serves as a current collector for the oxidant electrode catalyst layer 3. On the other hand, the fuel electrode catalyst layer 5 is laminated on the fuel electrode gas diffusion layer 6. The fuel electrode gas diffusion layer 6 serves to uniformly supply fuel to the fuel electrode catalyst layer 5 and also serves as a current collector for the fuel electrode catalyst layer 5. The oxidant electrode gas diffusion layer 3 and the fuel electrode gas diffusion layer 6 can be formed from, for example, carbon paper.

  The rectangular frame-shaped hydrophobic insulating layer 9 for the oxidant electrode surrounds the side surfaces of the oxidant electrode catalyst layer 2 and the oxidant electrode gas diffusion layer 3, that is, surrounds the periphery of the oxidant electrode 4. 8 is glued on top. Therefore, the thickness of the oxidant electrode hydrophobic insulating layer 9 is equal to the total thickness of the oxidant electrode catalyst layer 2 and the oxidant electrode gas diffusion layer 3. On the other hand, the rectangular electrode-shaped hydrophobic insulating layer 10 for the fuel electrode is formed on the surface of the solid electrolyte membrane 8 opposite to the side where the oxidant electrode 4 is formed, and the fuel electrode catalyst layer 5 and the fuel electrode gas are formed. It surrounds both sides of the diffusion layer 6, that is, the periphery of the fuel electrode 7. Therefore, the thickness of the fuel electrode hydrophobic insulating layer 10 is equal to the total thickness of the fuel electrode catalyst layer 5 and the fuel electrode gas diffusion layer 6.

  A fuel chamber 11 for supplying a vaporized component of the liquid fuel to the fuel electrode catalyst layer 5 is provided below the fuel electrode 7. The fuel chamber 11 is a liquid fuel tank (not shown) in which liquid methanol or an aqueous methanol solution is stored, and a fuel vaporization layer made of a gas-liquid separation membrane that allows only the vaporized component of the liquid fuel to permeate and cannot permeate the liquid fuel. (Not shown). Examples of the gas-liquid separation membrane include a silicone rubber sheet.

  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 13 in which the flow path 12 for taking in the air as the oxidant is formed covers the main surfaces of both the oxidant electrode gas diffusion layer 3 and the oxidant electrode hydrophobic insulating layer 9. Are stacked. The oxidant electrode side separator 13 can be formed from, for example, a carbon binder plate.

  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 11 to the fuel electrode catalyst layer 5 through the fuel electrode gas diffusion layer 6, the following The internal reforming reaction of methanol shown in the reaction 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 11, so water generated by the oxidation reaction of methanol mixed in the oxidant electrode catalyst layer 2 and the solid electrolyte membrane 8 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 8 and reach the oxidant electrode catalyst layer 2. On the other hand, the air taken in from the flow path 12 of the oxidant electrode side separator 13 diffuses through the oxidant electrode gas diffusion layer 3 and is supplied to the oxidant electrode catalyst layer 2. In the oxidant electrode catalyst layer 2, 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 2 by the reaction of the above-described formula (2). Since the hydrophobic insulating layers 9 and 10 integrated on both surfaces of the solid electrolyte membrane 8 can suppress the evaporation of water from the MEA 1, the water retention amount of the oxidant electrode catalyst layer 2 is the fuel electrode catalyst layer 5. It is possible to create a state in which the moisture retention amount is greater. As a result, water diffusion from the oxidant electrode catalyst layer 2 to the fuel electrode catalyst layer 5 is promoted by the osmotic pressure phenomenon, so that even if the methanol concentration in the liquid fuel is increased, the methanol shown in the above formula (1) The internal reforming reaction can be smoothly advanced.

  Further, unreacted methanol flows out from the fuel electrode catalyst layer 5 and the fuel electrode diffusion layer 6, but permeation of the unreacted methanol to the solid electrolyte membrane 8 can be suppressed by the fuel electrode hydrophobic insulating layer 10. Even if methanol permeates the solid electrolyte membrane 8, permeation to the oxidant electrode catalyst layer 2 can be prevented by the hydrophobic insulating layer 9 for oxidant electrode. Therefore, it is possible to reduce the methanol crossover phenomenon when the methanol concentration in the liquid fuel is increased.

  From the above, it is possible to obtain high output characteristics even when liquid fuel having a high methanol concentration is used.

  Furthermore, in the fuel cell having the above-described configuration, the MEA 1 expands and contracts during power generation due to the intake of vaporized fuel and the intake of air, and both sides of the MEA 1 are not tightened with separators or end plates. When the thickness is reduced (for example, 100 μm or less), the solid electrolyte membrane 8 is easily twisted. Since the hydrophobic insulating layers 9 and 10 integrated on both surfaces of the solid electrolyte membrane 8 can improve the tensile strength of the solid electrolyte membrane 8, it is possible to suppress breakage when the thickness of the solid electrolyte membrane 8 is reduced. can do.

  Moreover, since the hydrophobic insulating layers 9 and 10 can also serve as a gasket, the handling property of the MEA 1 at the time of assembling the fuel cell can be improved.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements 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 components 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
<Fabrication 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 gas 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 gas diffusion layer to obtain an oxidant electrode catalyst layer having a thickness of 400 μm.

  Between the fuel electrode catalyst layer and the oxidant electrode catalyst layer, 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 is disposed as a proton conductive electrolyte membrane. And membrane electrode assembly (MEA) was obtained by performing hot press to these.

  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 composite so as to surround the oxidant electrode, dried, and then hot-pressed at 80 to 150 ° C. to thereby make the oxidant electrode hydrophobic. An insulating layer was obtained.

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

  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 hydrofluoroether was used as a solvent and a fluorinated surface treating agent was used as the main coating material.

(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.

The results of the T-type peel test are shown in FIG. The vertical axis in FIG. 2 represents the relative peeling load, and the horizontal axis represents the relative value of G (dyn / cm ² ). As shown in FIG. 2, as a result of the T-shaped peeling test, it was found that the peeling strength differs depending on the type of the hydrophobic polymer, and that Example 3 is desirable from the viewpoint of the adhesive strength with the solid electrolyte membrane.

  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 amount of methanol permeation, and the results are shown in FIG. The vertical axis in FIG. 3 represents the relative methanol permeation amount, and the horizontal axis represents the relative 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. 3, 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, Example 3 is desirable from the viewpoint of methanol crossover suppression.

  As described above, according to the fuel cells of Examples 1 to 3, as confirmed in FIG. 2, 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 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.

  Moreover, as confirmed in FIG. 3 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%.

1 is a schematic cross-sectional view showing a direct methanol fuel cell according to an 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 ... Membrane electrode assembly (MEA), 2 ... Oxidant electrode catalyst layer, 3 ... Oxidant electrode gas diffusion layer, 4 ... Oxidant electrode gas, 5 ... Fuel electrode catalyst layer, 6 ... Fuel electrode gas diffusion layer, 7 ... Fuel electrode, 8 ... Solid electrolyte membrane, 9 ... Hydrophobic insulating layer for oxidant electrode, 10 ... Hydrophobic insulating layer for fuel electrode, 11 ... Fuel chamber, 12 ... Oxidant channel, 13 ... Oxide electrode side separator.

Claims (3)

A solid electrolyte membrane;
A fuel electrode catalyst layer formed on the solid electrolyte membrane and supplied with vaporized fuel; and
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;
An oxidant electrode catalyst layer provided on the opposite surface of the solid electrolyte membrane from which the fuel electrode catalyst layer was 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 the periphery of the oxidant electrode catalyst layer.   A fuel electrode diffusion layer stacked on the fuel electrode catalyst layer; and an oxidant electrode diffusion layer stacked on the oxidant electrode catalyst layer; and the thickness of the hydrophobic insulating layer for the fuel electrode is The thickness of the electrode catalyst layer and the fuel electrode diffusion layer is less than the total thickness, and the thickness of the hydrophobic insulating layer for the oxidant electrode is less than the total thickness of the oxidant electrode catalyst layer and the oxidant electrode diffusion layer. The fuel cell according to claim 1, wherein the fuel cell is provided.   3. The fuel cell according to claim 1, wherein each of the hydrophobic insulating layer for a fuel electrode and the hydrophobic insulating layer for an oxidant electrode contains a polymer material having adhesiveness and hydrophobicity. 4.

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