JP2010086662A - Fuel cell - Google Patents

Abstract

A fuel cell in which output fluctuation is suppressed is provided.
A fuel cell comprising a cathode, an anode, and an electrolyte membrane disposed between the cathode and the anode, wherein the cathode is opposed to the electrolyte membrane. The cathode catalyst layer 5, the cathode gas diffusion layer 7, the hydrophobic porous layer 6 disposed between the cathode catalyst layer 5 and the cathode gas diffusion layer 7, and the cathode gas diffusion layer 7. The moisture permeability of the cathode gas diffusion layer 7 is greater than the moisture permeability of the hydrophobic porous layer 6 and the moisture vapor transmission suppressing layer 8.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell, and is particularly suitable for a small liquid fuel direct supply type fuel cell.

  In recent years, small fuel cells have attracted attention in place of lithium ion secondary batteries. In particular, a direct methanol fuel cell (DMFC) using methanol as a fuel is more difficult to handle hydrogen gas than a fuel cell using hydrogen gas, and the organic fuel is reformed to generate hydrogen. There is no need for a device to create, and it is excellent in miniaturization.

  In DMFC, methanol is oxidized and decomposed at an anode (for example, a fuel electrode) to generate carbon dioxide, protons, and electrons. On the other hand, in the cathode (for example, the air electrode), water is generated by oxygen obtained from air, protons supplied from the fuel electrode through the electrolyte membrane, and electrons supplied from the fuel electrode through an external circuit. In addition, power is supplied by electrons passing through the external circuit.

  Patent Document 1 discloses a polytetrafluoroethylene (PTFE) particle as a water repellent material as a diffusion electrode for introducing a reducing gas such as hydrogen or methanol or an oxidizing gas such as air or oxygen into an electrode catalyst layer. In addition, it is disclosed to use a material containing carbon black as an electron conductive material.

  Patent Document 2 discloses using a material containing conductive carbon and a hydrophobic polymer as a diffusion layer for introducing fuel or oxygen into the catalyst layer.

  Further, Patent Document 3 discloses that the MEA in the gas flow path is formed by forming a microporous layer composed of at least an electron conductive substance, a water repellent resin, and a pore former at the interface between the catalyst layer and the gas diffusion layer. It discloses dispersibility in the surface direction.

On the other hand, Patent Document 4 describes the use of carbon paper or carbon cloth as a gas diffusion layer.
JP 2004-214173 A JP 2005-1000074 A JP 2006-120508 A JP 2007-317391 A

  The present invention is intended to provide a fuel cell in which output fluctuation is suppressed.

A fuel cell according to the present invention is a fuel cell comprising a cathode, an anode, and an electrolyte membrane disposed between the cathode and the anode,
The cathode includes a cathode catalyst layer facing the electrolyte membrane, a cathode gas diffusion layer, a hydrophobic porous layer disposed between the cathode catalyst layer and the cathode gas diffusion layer, and a cathode gas diffusion layer. Including a water vapor permeation suppression layer disposed on the outside,
The cathode gas diffusion layer has a moisture permeability greater than that of the hydrophobic porous layer and the water vapor permeation suppression layer.

  ADVANTAGE OF THE INVENTION According to this invention, the fuel cell by which the output fluctuation was suppressed can be provided.

  A fuel cell according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view of a membrane electrode assembly used in a fuel cell according to an embodiment. As shown in FIG. 1, the membrane electrode assembly 1 includes a cathode (air electrode) 2, an anode (fuel electrode) 3, and a proton conductive electrolyte membrane 4 disposed between the cathode 2 and the anode 3. . The cathode 2 includes a cathode catalyst layer 5 laminated on one surface of the electrolyte membrane 4, a hydrophobic porous layer 6 laminated on the cathode catalyst layer 5, and a cathode gas diffusion laminated on the hydrophobic porous layer 6. A layer 7 and a water vapor permeation suppressing layer 8 laminated on the cathode gas diffusion layer 7. The moisture permeability of the cathode gas diffusion layer 7 is larger than the moisture permeability of the hydrophobic porous layer 6 and the water vapor permeation suppressing layer 8. On the other hand, the anode 3 includes an anode catalyst layer 9 laminated on the opposite surface of the electrolyte membrane 4 and an anode gas diffusion layer 10 laminated on the anode catalyst layer 9.

  In the membrane electrode assembly 1 shown in FIG. 1 described above, since the moisture permeability of the hydrophobic porous layer 6 is smaller than the moisture permeability of the cathode gas diffusion layer 7, the water generated in the cathode catalyst layer 5 by power generation is The permeation of the hydrophobic porous layer 6 is suppressed. As a result, water is retained between the cathode catalyst layer 5 and the hydrophobic porous layer 6, and water permeation to the anode 3 can be accelerated.

  Further, since the moisture permeability of the water vapor permeation suppression layer 8 is smaller than the water permeability of the cathode gas diffusion layer 7, the water vapor permeation suppression layer 8 suppresses the diffusion of the generated water diffused from the hydrophobic porous layer 6, The water molecule concentration from the water vapor permeation suppression layer 8 to the cathode gas diffusion layer 7 can be stabilized. As a result, the water molecule concentration gradient between the hydrophobic porous layer 6 and the cathode gas diffusion layer 7 is reduced, and the permeation of generated water in the hydrophobic porous layer 6 can be further suppressed.

  Thereby, since the supply of water from the cathode 2 to the anode 3 is stably and promptly performed, the output fluctuation of the fuel cell can be reduced.

  When the moisture permeability of the cathode gas diffusion layer 7 is smaller than the moisture permeability of the hydrophobic porous layer 6 and / or the water vapor permeation suppression layer 8 or both, the water from the cathode catalyst layer 5 to the water vapor permeation suppression layer 8 is made of water. Clogging occurs and air diffusion is hindered.

  In the membrane electrode assembly 1 shown in FIG. 1 described above, it is desirable that the moisture permeability of the water vapor permeation suppressing layer 8 is equal to or higher than the moisture permeability of the hydrophobic porous layer 6. Thereby, since the diffusion of water from the cathode 2 to the anode 3 can be further promoted, the output fluctuation can be further reduced.

  Further, when the moisture permeability of the hydrophobic porous layer 6 is A and the moisture permeability of the cathode gas diffusion layer 7 is B, it is desirable that A: B = 1: 2 to 1: 3. When A: B is smaller than 1: 2, it is difficult to obtain the effect of suppressing diffusion to the produced water. On the other hand, when A: B exceeds 1: 3, the concentration of water molecules from the cathode catalyst layer to the water vapor permeation suppression layer increases, and air diffusion is inhibited.

  A fuel cell provided with the membrane electrode assembly shown in FIG. 1 will be described with reference to FIGS.

  The fuel cell shown in FIG. 2 includes a membrane electrode assembly 1 shown in FIG. 1, a fuel distribution mechanism 20 that supplies fuel to the membrane electrode assembly 1, a fuel storage unit 21 that stores liquid fuel, and these fuel distributions. It is mainly composed of a flow path 22 that connects the mechanism 20 and the fuel storage portion 21.

  Each member which comprises the membrane electrode assembly 1 is demonstrated.

  The hydrophobic porous layer 6 desirably has a microporous structure, and specifically, the pore diameter is preferably 50 nm or more and 100 μm or less.

  The hydrophobic porous layer 6 preferably contains a water repellent such as a fluororesin such as polytetrafluoroethylene (PTFE).

Moisture permeability of the hydrophobic porous layer 6 is preferably in the range of ^{30000~70000g / m 2 · 24hr · atm} (30~70kg / m 2 · 24hr · atm). When the moisture permeability is within this range, gaseous fuel can permeate and is sufficiently hydrophobic. A more preferable range of moisture permeability is 45000 to 65000 g / m ² · 24 hr · atm (45 to 65 kg / m ² · 24 hr · atm).

  The hydrophobic porous layer 6 preferably contains a conductive material in order to reduce the electrical resistance between the cathode catalyst layer 5 and the cathode gas diffusion layer 7. Examples of the conductive substance include a carbon material. Examples of the carbon material include ketjen black, print tex, and carbon nanotube, and the carbon material is not particularly limited as long as it is in the form of particles (for example, spherical particles, flat particles) or fibers. In particular, fine particles of carbon material or nanofibers of carbon material are suitable.

  The hydrophobic porous layer 6 is produced, for example, by the method described in the following (a) to (c).

  (A) A hydrophobic porous layer 6 is obtained by applying a slurry containing a carbon material, a water repellent and a solvent to a carbon paper as a substrate by a spray coating method and drying or baking. The hydrophobic porous layer 6 can also be obtained by applying the slurry to only one side of the carbon paper and drying or baking it. The carbon paper may or may not be subjected to water repellent treatment. For the water repellent treatment, a fluorine resin such as polytetrafluoroethylene (PTFE) can be used.

  (B) After applying the slurry to a substrate other than carbon paper by a spray coating method and drying or firing, the hydrophobic porous layer 6 is also produced by peeling the obtained layer from the substrate. It is possible.

  As shown in the above methods (a) and (b), the hydrophobic porous layer 6 can contain carbon paper or not.

  (C) Instead of adding a water repellent to the slurry, the hydrophobic porous layer 6 was prepared using a slurry not containing a water repellent, and then the obtained hydrophobic porous layer 6 was replaced with a water repellent. You may immerse in a solution.

  The moisture permeability of the hydrophobic porous layer 6 can be adjusted by, for example, the following methods (1) to (5).

  (1) When the hydrophobic porous layer 6 contains a carbon material as a conductive substance, the moisture permeability can be set within a target range by selecting the bulk density and shape of the carbon material.

  (2) When the hydrophobic porous layer 6 contains a carbon material and a water repellent, the moisture permeability can be set within a target range by adjusting the ratio of the carbon material and the water repellent. it can. When the amount of the carbon material is increased, the moisture permeability can be increased, and when the amount of the water repellent is increased, the moisture permeability can be lowered.

  (3) The moisture permeability can be set within a target range by adjusting the amount of slurry applied to the substrate. Increasing the coating amount can lower the moisture permeability, and decreasing the coating amount can increase the moisture permeability.

  (4) When a nozzle is used in the step of applying slurry to the substrate in the methods (a) to (c) above, nozzle conditions, such as nozzle type, discharge pressure, discharge amount, discharge distance, discharge time, etc. Since the density of the film formed by applying the slurry and the surface state of the film change, the moisture permeability can be set within the target range. In general, the moisture permeability can be lowered by increasing the smoothness of the surface of the film, and the moisture permeability can be increased by increasing the surface roughness. Moreover, moisture permeability can be increased by reducing the density of the coating film.

  (5) When the film obtained by the above methods (a) to (c) is pressed, the density of the film is physically increased, so that the surface of the film becomes smooth and moisture permeability can be lowered. The moisture permeability can be set within a target range.

  The thickness of the hydrophobic porous layer 6 is desirably in the range of 300 μm to 360 μm.

  The cathode gas diffusion layer 7 serves to uniformly supply the oxidant to the cathode catalyst layer 5 and also serves as a current collector for the cathode catalyst layer 5. For the cathode gas diffusion layer 7, for example, carbon paper or carbon cloth subjected to water repellent treatment can be used. For the water repellent treatment, a fluorine resin such as polytetrafluoroethylene (PTFE) can be used. The cathode gas diffusion layer 7 preferably contains 60 to 90% by weight of a conductive material and 10 to 40% by weight of a fluorine resin. Examples of the conductive substance include carbon materials that are main raw materials for carbon paper and carbon cloth.

  The anode gas diffusion layer 10 serves to uniformly supply fuel to the anode catalyst layer 9 and also serves as a current collector for the anode catalyst layer 9. The anode gas diffusion layer 10 is formed from, for example, carbon paper or carbon cloth. Carbon paper and carbon cloth may or may not be imparted water repellency. For the water repellent treatment, a fluorine resin such as polytetrafluoroethylene (PTFE) can be used.

  Examples of the catalyst contained in the anode catalyst layer 9 and the cathode catalyst layer 5 include platinum group elements such as single metals such as Pt, Ru, Rh, Ir, Os, and Pd, alloys containing platinum group elements, and the like. Can be mentioned. Specifically, platinum, Pt—Ni, or the like is used as a catalyst on the air electrode side, such as Pt—Ru or Pt—Mo having strong resistance to methanol or carbon monoxide as the fuel electrode side catalyst. Although preferable, it is not limited to these. Further, a supported catalyst using a conductive support such as a carbon material or an unsupported catalyst may be used.

  Examples of proton conductive materials contained in the anode catalyst layer 9, the cathode catalyst layer 5, and the electrolyte membrane 4 include, for example, a fluorine-based resin having a sulfonic acid group (trade name Nafion (registered trademark) manufactured by DuPont, Asahi Glass Co., Ltd.). For example, a perfluorosulfonic acid polymer such as Flemion (registered trademark), a hydrocarbon resin having a sulfonic acid group, an inorganic substance (for example, tungstic acid, phosphotungstic acid, lithium nitrate, etc.). However, it is not limited to these.

  The water vapor permeation suppression layer 8 is impregnated with a part of the water generated in the cathode catalyst layer 5 to suppress water evaporation and promote uniform diffusion of air into the cathode catalyst layer 5. Examples of the water vapor permeation suppressing layer 8 include a polyethylene-based polymer, a polyolefin-based polymer, a polyurethane-based polymer, a polypropylene-based polymer, a polyester-based polymer, a fluorine-based polymer, or a polyimide-based porous film. Can do. Specific examples include water vapor permeation suppression layers such as Nitto Denko's trade name Sunmap and DuPont's trade name PTFE.

  A conductive layer is laminated on the anode gas diffusion layer 10 and the cathode gas diffusion layer 7 as necessary. As these conductive layers, for example, a porous layer (for example, mesh) or a foil body made of a metal material such as gold or nickel, or a conductive metal material such as stainless steel (SUS) is coated with a highly conductive metal such as gold. Composite materials and the like are used. Rubber O-rings 24 are interposed between the electrolyte membrane 4 and the fuel distribution mechanism 20 and the cover plate 23, respectively, thereby preventing fuel leakage and oxidant leakage from the membrane electrode assembly (MEA) 1. It is preventing.

Although not shown, the cover plate 23 has an opening for taking in air as an oxidant. A surface layer is disposed between the cover plate 23 and the water vapor permeation suppression layer 8 as necessary. The surface layer adjusts the amount of air taken in, and has a plurality of air inlets whose number, size, etc. are adjusted according to the amount of air taken in. By providing such a cover plate 23, the oxidant can be naturally supplied to the cathode 2 without using a blower for supplying the oxidant. Note that the oxidizing agent is not limited to air, and a gas containing O ₂ can be used.

  The fuel storage unit 21 stores liquid fuel corresponding to the membrane electrode assembly 1. Examples of the liquid fuel include methanol fuels such as aqueous methanol solutions of various concentrations and pure methanol. The liquid fuel is not necessarily limited to methanol fuel. The liquid fuel may be, for example, an ethanol fuel such as an ethanol aqueous solution or pure ethanol, a propanol fuel such as a propanol aqueous solution or pure propanol, a glycol fuel such as a glycol aqueous solution or pure glycol, dimethyl ether, formic acid, or other liquid fuel. In any case, liquid fuel corresponding to the membrane electrode assembly 1 is stored in the fuel storage portion 21.

  The type and concentration of the liquid fuel are not limited. However, the characteristic of the fuel distribution mechanism 20 having the plurality of fuel discharge ports 25 becomes more apparent when the fuel concentration is high. For this reason, the fuel cell can particularly exhibit its performance and effects when a methanol aqueous solution or pure methanol having a concentration of 80% or more is used as the liquid fuel.

  A fuel distribution mechanism 20 is disposed on the anode (fuel electrode) 3 side of the membrane electrode assembly 1. The fuel distribution mechanism 20 is connected to a fuel storage portion 21 via a liquid fuel flow path 22 such as a pipe. Liquid fuel is introduced into the fuel distribution mechanism 20 from the fuel storage portion 21 through the flow path 22. The flow path 22 is not limited to piping independent of the fuel distribution mechanism 20 and the fuel storage unit 21. For example, when the fuel distribution mechanism 20 and the fuel storage unit 21 are stacked and integrated, a liquid fuel flow path connecting them may be used. The fuel distribution mechanism 20 only needs to be connected to the fuel storage portion 21 via the flow path 22.

  The mechanism for sending the liquid fuel from the fuel storage unit 21 to the fuel distribution mechanism 20 is not particularly limited. For example, when the installation location at the time of use is fixed, the liquid fuel can be dropped from the fuel storage unit 21 to the fuel distribution mechanism 20 and fed by using gravity. Further, by using the flow path 22 filled with a porous body or the like, the liquid can be fed from the fuel storage portion 21 to the fuel distribution mechanism 20 by a capillary phenomenon. Furthermore, liquid feeding from the fuel storage unit 21 to the fuel distribution mechanism 20 may be performed by a pump 26 as shown in FIG. Alternatively, as long as the fuel is supplied from the fuel distribution mechanism 20 to the membrane electrode assembly 1, a fuel cutoff valve may be arranged instead of the pump 26. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

  As shown in FIG. 3, the fuel distribution mechanism 20 includes at least one fuel inlet 27 through which liquid fuel flows through the flow path 22 and a plurality of fuel outlets 25 through which liquid fuel and its vaporized components are discharged. The fuel distribution plate 28 having As shown in FIG. 3, a gap 29 serving as a liquid fuel passage led from the fuel injection port 27 is provided inside the fuel distribution plate 28. The plurality of fuel discharge ports 25 are directly connected to gaps 29 that function as fuel passages.

  The liquid fuel introduced into the fuel distribution mechanism 20 from the fuel inlet 27 enters the gap portion 29 and is led to the plurality of fuel discharge ports 25 through the gap portion 29 functioning as the fuel passage. For example, a gas-liquid separator (not shown) that transmits only the vaporized component of the liquid fuel and does not transmit the liquid component may be disposed in the plurality of fuel discharge ports 25. As a result, the vaporized component of the liquid fuel is supplied to the anode 3 of the membrane electrode assembly 1. The gas-liquid separator may be installed as a gas-liquid separation membrane or the like between the fuel distribution mechanism 20 and the anode 3. The vaporized component of the liquid fuel is discharged from a plurality of fuel discharge ports 25 toward a plurality of locations on the anode 3.

A plurality of fuel discharge ports 25 are provided on the surface of the fuel distribution plate 28 facing the anode 3 so that fuel can be supplied to the entire membrane electrode assembly 1. The number of the fuel discharge ports 25 may be two or more. However, in order to equalize the fuel supply amount in the surface of the membrane electrode assembly 1, 0.1 to 10 / cm ² fuel discharge ports 25 are provided. It is preferable to form it so that it exists. If the number of the fuel discharge ports 25 is less than 0.1 / cm ² , the amount of fuel supplied to the membrane electrode assembly 1 cannot be made sufficiently uniform. Even if the number of the fuel discharge ports 25 exceeds 10 / cm ² , no further effect can be obtained.

  The liquid fuel introduced into the fuel distribution mechanism 20 described above is guided to the plurality of fuel discharge ports 25 via the gaps 29. Since the gap portion 29 of the fuel distribution mechanism 20 functions as a buffer, fuel of a specified concentration is discharged from each of the plurality of fuel discharge ports 25. Since the plurality of fuel discharge ports 25 are arranged so that fuel is supplied to the entire surface of the membrane electrode assembly 1, the amount of fuel supplied to the membrane electrode assembly 1 can be made uniform.

  The fuel released uniformly from the fuel distribution mechanism 20 diffuses through the anode gas diffusion layer 10 and is supplied to the anode catalyst layer 9. When methanol fuel is used as the fuel, an internal reforming reaction of methanol shown in the following formula (A) is caused.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ Formula (A)
Protons (H ⁺ ) generated by the internal reforming reaction are conducted through the electrolyte membrane 4 and reach the cathode catalyst layer 5. The gaseous fuel (for example, air) supplied from the opening of the cover plate 23 to the cathode gas diffusion layer 7 through the water vapor permeation suppression layer 8 diffuses through the cathode gas diffusion layer 7 and is supplied to the cathode catalyst. The air supplied to the cathode catalyst causes the reaction shown in the following formula (B). By this reaction, water is generated and a power generation reaction occurs.

(3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O Formula (B)
The water generated in the cathode catalyst layer 5 by power generation attempts to diffuse outside through the hydrophobic porous layer 6, but the moisture permeability of the hydrophobic porous layer 6 is compared with the moisture permeability of the cathode gas diffusion layer 7. Therefore, the diffusion of water is suppressed by the hydrophobic porous layer 6. As a result, water is retained between the cathode catalyst layer 5 and the hydrophobic porous layer 6, and the diffusion of water to the anode 3 can be accelerated.

  Further, since the water vapor transmission rate of the water vapor permeation suppression layer 8 is smaller than the water vapor transmission rate of the cathode gas diffusion layer 7, the generated water permeates the hydrophobic porous layer 6 and diffuses outside. The suppression layer 8 is suppressed, and the water molecule concentration from the water vapor transmission suppression layer 8 to the cathode gas diffusion layer 7 can be stabilized. As a result, the water molecule concentration gradient between the hydrophobic porous layer 6 and the cathode gas diffusion layer 7 is reduced, and the permeation of generated water in the hydrophobic porous layer 6 can be further suppressed.

  As a result, the supply of water from the cathode 2 to the anode 3 is stably and promptly performed, so that the internal reforming reaction (A) described above occurs stably and the output fluctuation of the fuel cell is reduced. Can do.

  A method for measuring moisture permeability of the hydrophobic porous layer 6, the cathode gas diffusion layer 7, and the water vapor permeation suppression layer 8 will be described.

  First, a sample for evaluating each layer from the membrane electrode assembly (MEA) 1 is cut out as a square having a side of 5 mm. Specifically, the measurement sample of the cathode hydrophobic porous layer is the center position of the MEA (for example, in the case of a rectangular MEA, the vertical and horizontal center positions), and the measurement sample of the cathode gas diffusion layer is the cathode. The position adjacent to one side of the measurement sample of the hydrophobic porous layer and the measurement sample of the water vapor permeation suppression layer are relative to the side where the measurement sample of the cathode gas diffusion layer of the previous sample of the cathode hydrophobic porous layer is cut out. The position is adjacent to one side.

  About each obtained sample, in order to make grinding | polishing in a post process easy, it fixes with resin. Specifically, the sample (MEA) is immersed in a base material of epoxy resin (EPO-MIX EPOXIDE manufactured by BUEHLER). Next, the epoxy resin is cured by leaving it at room temperature for 6 to 8 hours. This completes the fixing of the sample.

  The sample subjected to the fixing treatment is polished by a polishing machine, and an evaluation surface (each layer) is provided for each sample. As the polishing conditions, No. 2,400 is used as sandpaper, and the disk rotation speed is set to 150 to 300 RPM.

  Next, the sample is adjusted. First, a hole with a diameter of 2 mm is formed in the center of an Al tape with a diameter of 20 mm to 35 mm. Adhere Al tape on both sides of the sample with the evaluation surface. At this time, the position is adjusted so that the center of the sample is at the same position as the center hole of the Al tape.

  For the sample after the above position adjustment, according to the standard of JIS K7126-2 (Establishment date is 2006/08/20), the moisture permeability is measured by the GTR Tech Co., Ltd. device name GTR-10XFTB. .

  In the measurement, moisture permeability is measured by flowing high-humidity nitrogen gas into one of the samples and flowing dry helium gas into the other, and checking the amount of water in the flowing-out helium gas. Therefore, nitrogen gas is measured under the conditions of a temperature of 40 ° C., a humidity of 90 RH%, and a flow rate of 200 ccm, and the helium gas is a temperature of 40 ° C., a humidity of 0 RH%, and a flow rate of 20 ccm.

  The fuel cell applicable to the present invention is an active type fuel cell in which liquid fuel and oxidant are supplied by using an auxiliary device such as a pump. (Vaporization type) fuel cell, semi-passive type fuel cell shown in FIGS. The active fuel cell employs a system in which a fuel made of an aqueous methanol solution is supplied to the anode of the MEA while being adjusted by a pump so that the amount thereof is constant, and air is also supplied to the cathode by a pump. In the passive type fuel cell, a system in which vaporized methanol is naturally supplied to the anode of the MEA and natural air is also supplied to the cathode and no extra equipment such as a pump is provided. In the semi-passive type fuel cell, the fuel supplied from the fuel storage part to the membrane electrode assembly is used for the power generation reaction, and is not circulated thereafter and returned to the fuel storage part. The semi-passive type fuel cell is different from the active method because it does not circulate the fuel, and does not impair the downsizing of the device. Further, the semi-passive type fuel cell uses a pump for supplying fuel, and is different from a pure passive type such as an internal vaporization type. In this semi-passive type fuel cell, a fuel cutoff valve may be arranged in place of the pump as long as fuel is supplied from the fuel storage portion to the membrane electrode assembly. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

[Example]
Embodiments of the present invention will be described below with reference to the drawings.

Example 1
<Preparation of hydrophobic porous layer>
Graphite particles (VALCAN) as a carbon material were mixed with a PTFE solution to prepare a slurry. The obtained slurry was applied to both sides of the carbon paper by a spray coating method, naturally dried at room temperature, and then fired to form a super microporous layer having hydrophobicity. In addition, the porosity, the hole diameter, the hole shape, the layer thickness, the material composition, the laminated structure, and the like were appropriately changed so that the moisture permeability measured by the above-described method becomes the value shown in Table 1.

<Preparation of fuel electrode gas diffusion layer>
Carbon paper (TGP-090 manufactured by Toray Industries, Inc.) having a porosity of 75% was prepared as the fuel electrode gas diffusion layer.

<Preparation of fuel electrode catalyst layer>
A carbon particle carrying platinum ruthenium alloy fine particles, a perfluorosulfonic acid polymer solution (Nafion solution DE2020 manufactured by DuPont) and a solvent are mixed with a homogenizer to prepare a slurry having a solid content of about 15%. The coating was applied to one surface using a die coater. And this was dried at normal temperature, it peeled from the base material, and the fuel electrode catalyst layer was formed.

<Production of air electrode gas diffusion layer>
Carbon paper was prepared as an air electrode gas diffusion layer. In addition, the porosity, the hole diameter, the hole shape, the layer thickness, the material composition, the laminated structure, and the like were appropriately changed so that the moisture permeability measured by the above-described method becomes the value shown in Table 1.

<Preparation of air electrode catalyst layer>
Carbon particles carrying platinum fine particles, a perfluorosulfonic acid polymer solution (Nafion solution DE2020 manufactured by DuPont) and a solvent were mixed with a homogenizer to prepare a slurry having a solid content of about 15%. The obtained slurry was applied to one surface of the substrate using a die coater. And this was dried at normal temperature, it peeled from the base material, and the air electrode catalyst layer was formed.

<Production of membrane electrode assembly (MEA)>
As the electrolyte membrane, a solid electrolyte membrane Nafion 112 (manufactured by DuPont) containing a perfluorosulfonic acid polymer is used. First, the electrolyte membrane and the air electrode catalyst layer are overlapped, and a hydrophobic ultrafine particle is formed on the air electrode catalyst layer. The porous layer was overlaid, and further the air electrode gas diffusion layer was overlaid and pressed under conditions of a temperature of 135 ° C. and a pressure of 40 kgf / cm ² . Subsequently, a fuel electrode catalyst layer is stacked on the opposite side of the air electrode of the electrolyte membrane, and a fuel electrode gas diffusion layer is stacked on the fuel electrode catalyst layer. The temperature is 135 ° C. and the pressure is 10 kgf / cm. It pressed on conditions of ² and produced the membrane electrode assembly (MEA). The electrode area was 12 cm ² for both the air electrode and the fuel electrode.

<Assembly of fuel cell>
Subsequently, the membrane electrode assembly was sandwiched between gold foils having a plurality of holes for taking in air and vaporized methanol to form a fuel electrode conductive layer and an air electrode conductive layer.

  The laminate in which the membrane electrode assembly (MEA), the fuel electrode conductive layer, and the air electrode conductive layer were laminated was sandwiched between two resin-made frames. In addition, a rubber O-ring was sandwiched between the air electrode side of the membrane electrode assembly and one frame, and between the fuel electrode side of the membrane electrode assembly and the other frame, respectively. .

  The frame on the fuel electrode side was fixed to the liquid fuel storage chamber with screws via a gas-liquid separation membrane. A 0.2 mm thick silicone sheet was used for the gas-liquid separation membrane. On the other hand, on the frame on the air electrode side, the porosity, hole diameter, hole shape, layer thickness, material composition, laminated structure, etc. are appropriately set so that the moisture permeability measured by the above-mentioned method becomes the value shown in Table 1. The modified polymer porous plate was arranged to form a water vapor permeation suppression layer. On this water vapor permeation suppression layer, a stainless steel plate (SUS304) with a thickness of 2 mm formed with air inlets (4 mm diameter, 64 holes) for air intake is arranged to form a cover plate, and screws Fixed with a stop.

  10 ml of pure methanol is injected into the liquid fuel storage chamber of the fuel cell formed as described above, and the maximum output value (maximum output) is calculated from the current value and voltage value in an environment of temperature 20 ° C. and relative humidity 40%. It was measured. The above measurement was continuously performed 20 times, and the fluctuation rate (%) was calculated based on (maximum value−minimum value) / maximum value from the minimum value and the maximum value in the continuous measurement, and the results are shown in Table 1 below.

(Example 2)
Water vapor permeation suppression layer, air electrode gas diffusion, in which the porosity, pore diameter, pore shape, layer thickness, material composition, laminated structure, etc. are appropriately changed so that the moisture permeability measured by the above method becomes the value shown in Table 1. A fuel cell having the same configuration as that described in Example 1 was prepared except that a layer and a hydrophobic porous layer were used, and the output fluctuation rate (%) was the same as that described in Example 1. The results are shown in Table 1 below.

(Example 3)
Water vapor permeation suppression layer, air electrode gas diffusion, in which the porosity, pore diameter, pore shape, layer thickness, material composition, laminated structure, etc. are appropriately changed so that the moisture permeability measured by the above method becomes the value shown in Table 1. A fuel cell having the same configuration as that described in Example 1 was prepared except that a layer and a hydrophobic porous layer were used, and the output fluctuation rate (%) was the same as that described in Example 1. The results are shown in Table 1 below.

(Comparative Example 1)
The porosity, pore diameter, pore shape, layer thickness, material composition, so that the water vapor transmission suppression layer and the hydrophobic porous layer are not used, and the moisture permeability measured by the above-mentioned method is the value shown in Table 1. A fuel cell having the same configuration as that described in Example 1 described above was prepared except that an air electrode gas diffusion layer in which the laminated structure or the like was appropriately changed was used, and the output variation rate (%) was determined in Example 1. The measurement was performed under the same conditions as described, and the results are shown in Table 1 below.

(Comparative Example 2)
The porosity, pore diameter, pore shape, layer thickness, material composition, laminated structure, etc. are appropriately changed so that the moisture permeability measured by the above method is the value shown in Table 1 without using the hydrophobic porous layer. A fuel cell having the same configuration as described in Example 1 was prepared except that the water vapor permeation suppression layer and the air electrode gas diffusion layer were used, and the output fluctuation rate (%) was described in Example 1. The results are shown in Table 1 below.

(Comparative Example 3)
The porosity, the pore diameter, the pore shape, the layer thickness, the material composition, the laminated structure, etc. were appropriately changed so that the water vapor transmission suppression layer was not used and the moisture permeability measured by the method described above was the value shown in Table 1. A fuel cell having the same configuration as that described in Example 1 was prepared except that the air electrode gas diffusion layer and the hydrophobic porous layer were used, and the output fluctuation rate (%) was described in Example 1. The results are shown in Table 1 below.

(Comparative Example 4)
Water vapor permeation suppression layer, air electrode gas diffusion, in which the porosity, pore diameter, pore shape, layer thickness, material composition, laminated structure, etc. are appropriately changed so that the moisture permeability measured by the above method becomes the value shown in Table 1. A fuel cell having the same configuration as that described in Example 1 was prepared except that a layer and a hydrophobic porous layer were used, and the output fluctuation rate (%) was the same as that described in Example 1. The results are shown in Table 1 below.

  As is clear from Table 1, the fuel cells of Examples 1 to 3 have smaller output fluctuations than the fuel cells of Comparative Examples 1 to 4. In each of Examples 1 to 3, when the moisture permeability of the hydrophobic porous layer is A and the moisture permeability of the air electrode gas diffusion layer is B, A: B is within a range of 1: 2 to 1: 3. Although the water vapor transmission rate of the water vapor permeation suppression layer was larger than the value of the water vapor transmission rate of the hydrophobic porous layer, the output fluctuation was smaller than that of Example 3.

  Further, as shown in Table 1, Comparative Examples 1 to 3, which do not include either the water vapor permeation suppression layer or the hydrophobic porous layer, the water vapor transmission rate of the water vapor permeation suppression layer and the hydrophobic porous layer is the air electrode. In Comparative Example 4, which is larger than the moisture permeability of the gas diffusion layer, the output fluctuation of the fuel cell was large.

  In the above embodiment, the passive DMFC has been described as an example. However, the fuel cell system is not limited to the passive type as long as the structure uses water generated by the reaction on the fuel electrode side. It is not something.

  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. Also, in the active type fuel cell and the semi-passive type fuel cell, the same effect as described above can be obtained. The liquid fuel vapor supplied to the MEA may be all supplied as a liquid fuel vapor, but the present invention can be applied even when a part of the liquid fuel vapor is supplied in a liquid state.

The expanded sectional view of the membrane electrode assembly used for the fuel cell concerning this embodiment. 1 is an internal perspective sectional view showing a fuel cell according to an embodiment of the present invention. The perspective view which shows the fuel distribution mechanism of the fuel cell of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Membrane electrode assembly (MEA), 2 ... Cathode (air electrode), 3 ... Anode (fuel electrode), 4 ... Electrolyte membrane, 5 ... Air electrode catalyst layer, 6 ... Hydrophobic porous layer, 7 ... Air electrode Gas diffusion layer, 8 ... Water vapor permeation suppression layer, 9 ... Fuel electrode catalyst layer, 10 ... Fuel electrode gas diffusion layer, 20 ... Fuel distribution mechanism, 21 ... Fuel container, 22 ... Flow path, 23 ... Cover plate, 24 ... O-ring, 25 ... fuel discharge port, 26 ... pump, 27 ... fuel injection port, 28 ... fuel distribution plate, 29 ... gap.

Claims (6)

A fuel cell comprising a cathode, an anode, and an electrolyte membrane disposed between the cathode and the anode,
The cathode includes a cathode catalyst layer facing the electrolyte membrane, a cathode gas diffusion layer, a hydrophobic porous layer disposed between the cathode catalyst layer and the cathode gas diffusion layer, and a cathode gas diffusion layer. Including a water vapor permeation suppression layer disposed on the outside,
The fuel cell, wherein the moisture permeability of the cathode gas diffusion layer is larger than the moisture permeability of the hydrophobic porous layer and the water vapor permeation suppression layer.   2. The fuel cell according to claim 1, wherein a moisture permeability of the water vapor permeation suppression layer is equal to or higher than a moisture permeability value of the hydrophobic porous layer.   3. A: B = 1: 2 to 1: 3, where A is a moisture permeability of the hydrophobic porous layer and B is a moisture permeability of the cathode gas diffusion layer. Fuel cell.   The fuel cell according to claim 1, wherein the hydrophobic porous layer contains a conductive substance.   The fuel cell according to any one of claims 1 to 4, wherein the cathode gas diffusion layer includes 60 to 90 wt% of a conductive material and 10 to 40 wt% of polytetrafluoroethylene.   The water vapor permeation suppressing layer is a porous film of polyethylene polymer, polyolefin polymer, polyurethane polymer, polypropylene polymer, polyester polymer, fluorine polymer or polyimide polymer. The fuel cell according to any one of claims 1 to 5.

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