JP2009289620A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell improved in output performance. <P>SOLUTION: The fuel cell is provided with a cathode 6 which includes a cathode catalyst layer 10, a cathode diffusion layer 12, and a cathode porous layer 11 arranged between the cathode catalyst layer 10 and the cathode diffusion layer 12, an anode 5, and an electrolyte membrane 7 arranged between the cathode 6 and the anode 5. In the cathode porous layer 11, air permeability resistance in an Oken type air permeation resistance testing machine on a surface contacting the cathode catalyst layer 10 is larger than that in the Oken type air permeation resistance testing machine on the surface contacting the cathode diffusion layer 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

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.

  In the DMFC, in order to advance power generation with such a configuration, a pump for supplying methanol and a blower for feeding air are provided as auxiliary devices, and a DMFC having a complicated form as a system has been developed. Therefore, it is difficult to reduce the size of the DMFC having this structure.

  Therefore, instead of supplying methanol with a pump, a membrane through which methanol molecules pass is provided between the methanol storage chamber and the power generation element to allow methanol to permeate and reduce the size by bringing the methanol storage chamber close to the vicinity of the power generation element. Was advanced. For intake of air, a small DMFC was constructed by installing an intake port directly attached to the power generation element without using a blower (see, for example, Patent Document 1). However, it is difficult for such a small DMFC to send a certain amount of methanol to the power generation element when it is affected by external environmental factors such as temperature instead of the mechanism being simplified. For this reason, it has been difficult to generate power stably at a high output.

  Therefore, Patent Document 2 discloses a technique for reducing the methanol supply amount by installing a porous body between the fuel storage chamber portion and the negative electrode in order to control the supply amount of methanol.

Patent Document 3 discloses a catalyst layer in which a catalyst is infiltrated into a carbon substrate having pores, and a method of directly forming a catalyst on an electrolyte membrane.
JP 2007-157462 A JP 2004-171844 A US Patent Publication US6,221,523B1

  The present invention seeks to provide a fuel cell with improved output performance.

A fuel cell according to the present invention includes a cathode catalyst layer, a cathode diffusion layer, a cathode including the cathode catalyst layer and a cathode porous layer disposed between the cathode diffusion layer,
An anode,
An electrolyte membrane disposed between the cathode and the anode,
The cathode porous layer has an air resistance in a surface in contact with the cathode catalyst layer by an Oken type air resistance tester on a surface in contact with the cathode diffusion layer. It is characterized in that it is larger than the air resistance.

  According to the present invention, it is possible to provide a fuel cell with improved output performance.

(First embodiment)
The fuel cell according to the first embodiment includes a cathode including a cathode catalyst layer, a cathode diffusion layer, and a cathode porous layer disposed between the cathode catalyst layer and the cathode diffusion layer. The cathode porous layer has a surface (hereinafter, referred to as a first surface) in contact with the cathode catalyst layer having a surface resistance (hereinafter referred to as a first surface) in contact with the cathode diffusion layer. This is larger than the air resistance in the Oken air resistance tester.

  According to the fuel cell having such a configuration, water generated in the cathode catalyst layer by power generation cannot pass through the first surface of the cathode porous layer, and the space between the cathode catalyst layer and the cathode porous layer is not allowed. Therefore, the water can be returned quickly to the anode. Further, since the second surface of the cathode porous layer is superior in air diffusibility compared to the first surface, air can be taken into the cathode catalyst layer from the cathode diffusion layer faster.

  As a result, high output is obtained.

  It is desirable that the air permeability resistance of the second surface is 20 gale seconds or less and the air resistance of the first surface is larger than that of the second surface within the range of 20 to 500 gale seconds. By making the air permeability resistance of the second surface 20 galeseconds or less, the air can be taken into the cathode catalyst layer sufficiently quickly. Moreover, the amount of water that can be retained between the cathode catalyst layer and the cathode porous layer can be increased by setting the air resistance of the first surface within the range of 20 to 500 galeseconds. Therefore, the output of the fuel cell can be further improved. A more preferable range of the air resistance of the first surface is not less than 30 gale seconds and not more than 300 gale seconds. Further, a more preferable range of the air resistance of the second surface is 10 gale seconds or more and 100 gale seconds or less.

  The cathode porous layer is desirably hydrophobic. Thereby, the diffusibility of gas in the cathode porous layer can be improved, and the diffusion of water from the cathode catalyst layer can be further suppressed. In order for the cathode porous layer to be hydrophobic, it is desirable to contain a water repellent in the cathode porous layer. Examples of the water repellent include a fluorine resin such as polytetrafluoroethylene (PTFE).

  The cathode porous layer preferably contains a conductive material in order to reduce the electric resistance between the cathode catalyst layer and the cathode diffusion layer. 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 cathode porous layer is produced, for example, by the method described in (I) to (III) below.

  (I) A cathode porous layer is obtained by applying a slurry containing a carbon material and a water repellent to a carbon paper as a substrate by a spray coating method and drying or firing. The cathode porous layer can also be obtained by applying the slurry to only one side of the carbon paper and drying or firing. The carbon paper may or may not be subjected to water repellent treatment.

  (II) After applying the slurry to a substrate other than carbon paper by a spray coating method and drying or baking, the resulting porous layer can be peeled from the substrate to produce a cathode porous layer. Is possible.

  As shown in the above methods (I) and (II), the cathode porous layer may contain carbon paper or not.

  (III) Instead of adding a water repellent to the slurry, a cathode porous layer was prepared using a slurry not containing a water repellent, and the resulting cathode porous layer was immersed in a water repellent solution. You may do it.

  The air permeability resistance of the cathode porous layer can be adjusted by, for example, the following methods (1) to (7).

  (1) When the cathode porous layer includes a carbon material as a conductive substance, the air resistance can be adjusted by selecting the bulk density and shape of the carbon material.

  (2) When the cathode porous layer contains a carbon material and a water repellent, the air resistance can be adjusted by adjusting the ratio of the carbon material and the water repellent. When the amount of the carbon material is increased, the air resistance can be lowered, and when the amount of the water repellent is increased, the air resistance can be increased.

  (3) The air resistance can be adjusted by adjusting the amount of slurry applied to the substrate. Increasing the coating amount can increase the air resistance, and decreasing the coating amount can decrease the air resistance.

  (4) When a nozzle is used in the step of applying the slurry to the substrate in the above methods (I) to (III), the 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 air resistance can be adjusted. In general, the air resistance can be increased by increasing the smoothness of the surface of the film, and the air resistance can be decreased by increasing the surface roughness. Further, the air resistance can be reduced by reducing the density of the coating film.

  (5) When the film obtained by the above methods (I) to (III) is pressed, the film density is physically increased, so that the surface of the film becomes smooth and the air resistance is increased. be able to.

  (6) In the step of applying the slurry to the substrate in the above methods (I) to (III), when the application method is adopted from the spray method, the cast method, and the dip method, The air resistance can be adjusted.

  (7) After applying the slurry to the substrate in the above methods (I) to (III), the air resistance can be adjusted by adjusting the drying temperature of the applied slurry or the humidity of the drying atmosphere. .

  The thickness of the cathode porous layer is desirably in the range of 300 μm to 400 μm.

  The method for measuring the air resistance by the Oken type air resistance tester will be described.

  First, a membrane electrode assembly (MEA) is taken out from the fuel cell and used as a measurement sample. The sample is immersed in an epoxy resin base material (EPO-MIX EPOXIDE manufactured by BUEHLER) and left in this state at room temperature for 6 to 8 hours.

  Next, the sample is put on a polishing machine and an evaluation surface is taken out (the order in which the surface is put out is in order of increasing air resistance). The polishing conditions are sandpaper No. 2,400, and the disk rotation speed is 150 to 300 RPM.

  The air permeation resistance of the sample that has undergone the evaluation surface treatment is measured by the following method using the Oken air permeation resistance tester.

The Gurley second, which is the unit of air resistance, is based on the Gurley method (JIS P8117). A paper (sample) with 100 cm ³ of air and a width of 64.5 cm ² under a pressure difference of 0.0132 Kgf / cm ² is used. Means time (seconds) to pass.

  The standard of the Oken type air permeability resistance tester is J. TAPPI NO5B (Standard of Paper and Pulp Technology Association), and the model is EGO-2S. The diameter of the measurement end is φ30 mm, the nozzle type name is G, 100, or φ10 mm, and the nozzle type name is 1/10 G, 100.

  The measurement principle will be described below with reference to FIGS.

  FIG. 1 is a schematic view of a Wangken type (back pressure type) air resistance measuring machine. A measurement sample 102 (for example, an anode porous layer) is disposed at the measurement end 101. A water column pressure gauge 104 is connected to the measurement end 101 via a thin tube 103. The water column pressure gauge 104 has a side pressure chamber (B chamber) 105 connected to the narrow tube 103 and a constant pressure chamber (A chamber) 107 connected via a thin tube 106 called a nozzle. A constant pressure chamber (A chamber) 107 of the water column pressure gauge 104 is connected to an external compression source 109 via a thin tube 108. The thin tube 108 is provided with a pressure gauge 110.

  Air pressure supplied from the external compression source 109 through the pipe 108, the constant pressure chamber (A chamber) 107, the narrow tube 106, the side pressure chamber (B chamber) 105, and the narrow tube 103 is applied to the measurement sample 102. The air pressure when supplied from the external compression source 109 is measured by the pressure gauge 110. The pressure applied to the surface opposite to the side where the air pressure is applied is maintained at atmospheric pressure.

The air pressure that passes through the measurement sample 102 is measured by a water column pressure gauge 104. The air resistance _TG of the Gurley of the measurement sample 102 is obtained based on the principle described below.

  FIG. 2 shows a schematic diagram relating to the flow path of the measuring machine of FIG. In FIG. 2, the same members as those described in FIG. 1 are denoted by the same reference numerals, but the narrow tube 111 connected to the right side of the side pressure chamber (B chamber) 105 is an example of the measurement sample 102. It is.

  Regarding FIG. 2, when the flow in both capillaries is laminar, the relationship between the flow rate and the differential pressure follows Hagen-Poiseuille's law. Further, when the flow velocity is small, a continuous law can be applied to the flow path system.

Q _C = Q = π / 8 μ · (P _C −P) · R ⁴ / L (1)
Q = π / 8μ · P · r ⁴ / l (2)
P _C is the pressure in the constant pressure chamber (A chamber) 107 and is maintained at a constant pressure of 500 mmH ₂ O, P is the pressure in the side pressure chamber (B chamber) 105, and Q _C is the flow rate (cm ³ / sec), Q is the flow rate (cm ³ / sec) in the narrow tube 111, L is the length (mm) of the nozzle 106, l is the length (mm) of the narrow tube 111, and R is the inner diameter (mm) of the nozzle 106. ) Where r is the inner diameter (mm) of the narrow tube 111 and μ is the viscosity coefficient of air.

Figure 3 is a schematic diagram of the flow path of Gurley measuring instrument shows that the air in the G chamber 112 is maintained at a constant pressure P _G is released into the atmosphere through tubules 113. The thin tube 113 is an example of the measurement sample 102. The G chamber 112 and the narrow tube 113 in FIG. 3 follow the same rules as described in FIG.

Q _G = π / 8μ · P _G · r ⁴ / l (3)
T _G = 100 / Q _G (4)
P _G = 4 W / πD ² = 0.0132 (kgf / cm ² ) (5)
P _G is the inner cylinder of the measuring portion defined by JIS P8117 (W = 567g, D = 74mm) is calculated from. Q _G is the flow rate (cm ³ / sec) in the narrow tube 113, and _TG is the air resistance (sec).

From the above equations (1), (2), (3), (4), the relationship between _TG and P is given by the following equation (6). If the constant K of the measuring machine is determined, the air resistance _TG of the Gurley can be estimated directly on the water column pressure gauge of FIG.

T _G = 800 μ / πP _G · L / R ⁴ · P / (P _C -P)
= K · P / (P _C -P) (6)
Here, K is a measuring machine constant _{(K = 800μ / πP G ·} L / R 4), the length of capillary 106 L (mm) and an inside diameter R (mm) is defined on the design.

  Hereinafter, a first embodiment will be described with reference to FIGS.

  The fuel cell shown in FIG. 4 includes a membrane electrode assembly 1, a fuel distribution mechanism 2 that supplies fuel to the membrane electrode assembly 1, a fuel storage portion 3 that stores liquid fuel, and the fuel distribution mechanism 2 and the fuel. It is mainly composed of a flow path 4 that connects the accommodating portion 3.

  As shown in FIGS. 4 and 6, the membrane electrode assembly 1 includes an anode (fuel electrode) 5, a cathode (air electrode) 6, and protons (hydrogen ions) disposed between the fuel electrode 5 and the air electrode 6. And) a conductive electrolyte membrane 7. The fuel electrode 5 includes a fuel electrode catalyst layer 8 as an anode catalyst layer facing one surface of the electrolyte membrane 7, and a fuel electrode gas diffusion layer 9 as an anode diffusion layer laminated on the fuel electrode catalyst layer 8. Have

  The fuel electrode gas diffusion layer 9 serves to uniformly supply fuel to the fuel electrode catalyst layer 8 and also serves as a current collector for the fuel electrode catalyst layer 8. The fuel electrode gas diffusion layer 9 is made of, for example, carbon paper. The carbon paper may be imparted with water repellency or may not be imparted with water repellency. For the water repellent treatment, a fluorine resin such as polytetrafluoroethylene (PTFE) can be used.

  On the other hand, the air electrode 6 includes an air electrode catalyst layer 10 as a cathode catalyst layer facing the other surface of the electrolyte membrane 7, and an air electrode porous layer as a cathode porous layer laminated on the air electrode catalyst layer 10. A layer 11 and an air electrode gas diffusion layer 12 as a cathode diffusion layer laminated on the air electrode porous layer 11.

  For example, as shown in FIG. 6, the air electrode porous layer 11 is laminated on one surface of a conductive porous substrate 11a made of carbon paper and the conductive porous substrate 11a. Hydrophobic conductive porous portion 11b having a first surface in contact with the hydrophobic conductive material having a second surface stacked on the other surface of conductive porous substrate 11a and in contact with air electrode gas diffusion layer 12 It has a three-layer structure including a porous portion 11c.

  The air electrode gas diffusion layer 12 serves to uniformly supply the oxidant to the air electrode catalyst layer 10 and also serves as a current collector for the air electrode catalyst layer 10. For the air electrode gas diffusion layer 12, for example, carbon paper subjected to water repellent treatment can be used. For the water repellent treatment, a fluorine resin such as polytetrafluoroethylene (PTFE) can be used.

  Examples of the catalyst contained in the fuel electrode catalyst layer 8 and the air electrode catalyst layer 10 include, for example, platinum group elements such as Pt, Ru, Rh, Ir, Os, Pd, etc., and alloys containing platinum group elements. And so on. 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 the proton conductive material included in the fuel electrode catalyst layer 8, the air electrode catalyst layer 10, and the electrolyte membrane 7 include, for example, a fluorine-based resin having a sulfonic acid group (trade name Nafion (registered trademark) manufactured by DuPont) Asahi Glass Co., Ltd. trade name Flemion (registered trademark) perfluorosulfonic acid polymer, etc.), hydrocarbon resins having sulfonic acid groups, inorganic substances (eg, tungstic acid, phosphotungstic acid, lithium nitrate, etc.) Although it is mentioned, it is not limited to these.

  A conductive layer 13 is laminated on the fuel electrode gas diffusion layer 9 and the air electrode gas diffusion layer 12 as necessary. Examples of the conductive layer 13 include a porous layer (for example, a 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) with a highly conductive metal such as gold. A coated composite material or the like is used. Rubber O-rings 15 are interposed between the electrolyte membrane 7 and the fuel distribution mechanism 2 and the cover plate 14, respectively, thereby preventing fuel leakage and oxidant leakage from the membrane electrode assembly (MEA) 1. It is preventing.

Although not shown, the cover plate 14 has an opening for taking in air as an oxidant. A moisture retaining layer and a surface layer are disposed between the cover plate 14 and the cathode 6 as necessary. The moisturizing layer is impregnated with a part of the water produced in the air electrode catalyst layer 10 to suppress the transpiration of water and promote uniform diffusion of air into the air electrode catalyst layer 10. 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 14, the oxidant can be naturally supplied to the cathode 6 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.

  Liquid fuel corresponding to the membrane electrode assembly 1 is stored in the fuel storage portion 3. 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 3.

  The type and concentration of the liquid fuel are not limited. However, the characteristic of the fuel distribution mechanism 2 having a plurality of fuel discharge ports 22 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 2 is arranged on the anode (fuel electrode) 5 side of the membrane electrode assembly 1. The fuel distribution mechanism 2 is connected to the fuel storage portion 3 through a liquid fuel flow path 4 such as a pipe. Liquid fuel is introduced into the fuel distribution mechanism 2 from the fuel storage portion 3 through the flow path 4. The flow path 4 is not limited to piping independent of the fuel distribution mechanism 2 and the fuel storage unit 3. For example, when the fuel distribution mechanism 2 and the fuel storage unit 3 are stacked and integrated, a liquid fuel flow path connecting them may be used. The fuel distribution mechanism 2 only needs to be connected to the fuel storage unit 3 via the flow path 4.

  The mechanism for feeding the liquid fuel from the fuel storage unit 3 to the fuel distribution mechanism 2 is not particularly limited. For example, when the installation location at the time of use is fixed, liquid fuel can be dropped from the fuel storage unit 3 to the fuel distribution mechanism 2 and fed using gravity. Further, by using the flow path 4 filled with a porous body or the like, the liquid can be fed from the fuel storage portion 3 to the fuel distribution mechanism 2 by a capillary phenomenon. Furthermore, liquid feeding from the fuel storage unit 3 to the fuel distribution mechanism 2 may be performed by a pump 16 as shown in FIG. Alternatively, as long as the fuel is supplied from the fuel distribution mechanism 2 to the membrane electrode assembly 1, a fuel cutoff valve may be arranged instead of the pump 16. In this case, the fuel cutoff valve is provided to control the supply of liquid fuel through the flow path.

  As shown in FIG. 5, the fuel distribution mechanism 2 includes at least one fuel inlet 21 through which liquid fuel flows through the flow path 4 and a plurality of fuel outlets 22 through which liquid fuel and its vaporized components are discharged. The fuel distribution plate 23 having As shown in FIG. 4, the fuel distribution plate 23 is provided with a gap 24 serving as a liquid fuel passage led from the fuel injection port 21. The plurality of fuel discharge ports 22 are directly connected to gaps 24 that function as fuel passages.

  The liquid fuel introduced into the fuel distribution mechanism 2 from the fuel inlet 21 enters the gap 24 and is guided to the plurality of fuel discharge ports 22 through the gap 24 functioning as a 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 22. As a result, the vaporized component of the liquid fuel is supplied to the fuel electrode 5 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 2 and the fuel electrode 5. The vaporized component of the liquid fuel is discharged from a plurality of fuel discharge ports 22 toward a plurality of locations on the fuel electrode 5.

A plurality of fuel discharge ports 22 are provided on the surface of the fuel distribution plate 23 facing the fuel electrode 5 so that fuel can be supplied to the entire membrane electrode assembly 1. The number of the fuel discharge ports 22 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 22 are provided. It is preferable to form it so that it exists. If the number of the fuel discharge ports 22 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 22 exceeds 10 / cm ² , no further effect can be obtained.

  The liquid fuel introduced into the fuel distribution mechanism 2 described above is guided to the plurality of fuel discharge ports 22 via the gaps 24. Since the gap 24 of the fuel distribution mechanism 2 functions as a buffer, fuel of a specified concentration is discharged from the plurality of fuel discharge ports 22. Since the plurality of fuel discharge ports 22 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 2 diffuses through the fuel electrode gas diffusion layer 9 and is supplied to the fuel electrode catalyst layer 8. When methanol fuel is used as the fuel, it is necessary to cause an internal reforming reaction of methanol represented by the following formula (A).

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 7 and reach the air electrode catalyst layer 10. The gaseous fuel (for example, air) supplied from the air electrode gas diffusion layer 12 diffuses through the air electrode gas diffusion layer 12 and the air electrode porous layer 11 and is supplied to the air electrode catalyst. The air supplied to the air electrode 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)
Water generated by the power generation reaction is supplied from the air electrode 6 to the fuel electrode catalyst layer 8 through the electrolyte membrane 7. In the present embodiment, the air electrode porous layer 11 is disposed between the air electrode catalyst layer 10 and the air electrode gas diffusion layer 12, and the Oken type on the surface (first surface) in contact with the air electrode catalyst layer 10. The air resistance in the air resistance tester is set to be larger than the air resistance in the surface (second surface) in contact with the air electrode gas diffusion layer 12 with the Oken air resistance tester.

  As a result, the water generated in the air electrode catalyst layer 10 by power generation does not pass through the first surface of the air electrode porous layer 11 and is retained between the air electrode catalyst layer 10 and the air electrode porous layer 11. Is done. Therefore, the water in the air electrode 6 can be quickly returned to the fuel electrode 5 through the electrolyte membrane 7, so that the internal reforming reaction shown in the above formula (A) in the fuel electrode 5 can be promoted.

  Moreover, since the air from the air electrode gas diffusion layer 12 quickly permeates through the second surface of the air electrode porous layer 11, the air can be taken into the air electrode catalyst layer 10 faster.

  As a result, high output is obtained.

(Second Embodiment)
The fuel cell according to the second embodiment includes a cathode used in the first embodiment and an anode described below. That is, the anode includes an anode catalyst layer, an anode diffusion layer, and an anode porous layer disposed between the anode catalyst layer and the anode diffusion layer.

  Any of the first to third anode porous layers can be used for the anode porous layer.

  The first anode porous layer has a surface that is in contact with the anode diffusion layer in terms of air resistance in a surface in contact with the anode catalyst layer (hereinafter referred to as a third surface) in the Oken type air resistance tester. Hereinafter, it is equal to the air resistance in the Oken air resistance tester in the fourth surface). Since the cathode porous layer is used as in the first embodiment, the air intake into the cathode catalyst layer is improved, and the water generated in the cathode by power generation permeates the electrolyte membrane to the anode catalyst layer. Promptly supplied. On the other hand, there is a possibility that water may permeate unnecessarily to the anode diffusion layer disposed on the side opposite to the electrolyte membrane side of the anode catalyst layer. Since the first anode porous layer can block water permeation, water is accumulated between the first anode porous layer and the anode catalyst layer, and clogging of the anode diffusion layer with water is suppressed. Can do. As a result, the fuel such as methanol is smoothly supplied to the anode catalyst layer. Further, when the fuel is pure methanol, the fuel efficiency is improved because water and fuel are mixed between the anode porous layer and the anode catalyst layer. These effects, improvement of the maximum output of the fuel cell, and suppression of output fluctuation can be achieved.

  It is desirable that the air resistance of the third surface and the fourth surface is 20 gale seconds or more and 500 gale seconds or less. This is because a sufficient amount of water can be stored between the first anode porous layer and the anode catalyst layer. A more preferable range of the air resistance of the third surface and the fourth surface is 30 gale seconds or more and 300 gale seconds or less. A more preferable range is 10 gale seconds or more and 100 gale seconds or less.

  The second anode porous layer has a surface in contact with the anode diffusion layer (fourth surface) on the surface in contact with the anode catalyst layer (third surface). This is larger than the air resistance in the Oken type air resistance tester.

  According to such a configuration, water generated at the cathode by power generation is not only rapidly supplied to the anode catalyst layer through the electrolyte membrane, but also the third surface of the second anode porous layer blocks water permeation. Therefore, water can be stored between the second anode porous layer and the anode catalyst layer. As a result, clogging of the anode diffusion layer with water can be reduced, and fuel supply from the fuel chamber and the anode diffusion layer is not hindered.

  In addition, when the fuel is pure methanol, water and fuel are mixed between the second anode porous layer and the anode catalyst layer, so that fuel efficiency is improved.

  Further, since the fuel gas (for example, methanol) diffuses quickly on the fourth surface of the second anode porous layer, fuel supply is promoted more than in the case of the first anode porous layer.

  Moreover, since the cathode porous layer is used as in the case of the first embodiment, air can be taken into the cathode catalyst layer quickly.

  As a result, a high output fuel cell can be obtained.

  It is desirable that the air permeability resistance of the fourth surface is 20 gale seconds or less and the air resistance of the third surface is larger than that of the fourth surface within the range of 20 to 500 gale seconds. By setting the air permeability resistance of the fourth surface to 20 gale seconds or less, the diffusibility of the fuel gas can be made sufficient. In addition, by setting the air resistance of the third surface to a value larger than that of the fourth surface within a range of 20 to 500 galeseconds, it is sufficient between the second anode porous layer and the anode catalyst layer. A large amount of water can be stored. As a result, the output can be further improved. A more preferable range of the air resistance of the third surface is not less than 30 gale seconds and not more than 300 gale seconds. A more preferable range of the air resistance of the fourth surface is 10 gale seconds or more and 100 gale seconds or less.

  The third anode porous layer has a surface (fourth surface) in contact with the anode diffusion layer by the air resistance measured by the Oken air resistance tester on the surface (third surface) in contact with the anode catalyst layer. ) Is less than the air resistance in the Oken air resistance tester.

  Since the cathode porous layer is used as in the case of the first embodiment, air can be taken into the cathode catalyst layer faster. In addition, water generated at the cathode by power generation is not only rapidly supplied to the anode catalyst layer through the electrolyte membrane, but also the fourth surface of the third anode porous layer can prevent water from passing through, Water can be stored not only between the third anode porous layer and the anode catalyst layer but also in the third anode porous layer. As a result, clogging of the anode diffusion layer with water can be reduced, and fuel supply from the fuel chamber and the anode diffusion layer is not hindered.

  In addition, since the amount of water that can be held in the third anode porous layer and the anode catalyst layer has increased, when the fuel is pure methanol, compared to the case where the first or second anode porous layer is used. Since methanol is efficiently diluted and fuel efficiency is further improved, the output is improved and the stability of the output is also improved.

  The third anode porous layer has an air resistance of the fourth surface in the range of 20 to 500 galeseconds and the air resistance of the third surface of the fourth surface of 20 galeseconds or less. It is desirable to make the value smaller. By setting the air permeability resistance of the fourth surface within the range of 20 to 500 galeseconds, it is possible to suppress water supplied to the anode catalyst layer from permeating the third anode porous layer. The amount of water retained in the anode catalyst layer and the third anode porous layer can be increased. In addition, by setting the air resistance of the third surface to a value smaller than that of the fourth surface of 20 gale seconds or less, it is possible to promote the diffusion of fuel in the third anode porous layer. An amount of fuel can be supplied to the anode catalyst layer. As a result, the output and output stability can be further improved. A more preferable range of the air permeability resistance of the fourth surface is 30 gale seconds or more and 300 gale seconds or less, and a more preferable range of the air resistance resistance of the third surface is 10 gale seconds or 100 gale seconds or less. It is.

  It is desirable that the first to third anode porous layers have hydrophobicity. Thereby, the gas diffusibility in the anode porous layer can be improved, and the mixing of water into the anode diffusion layer can be further suppressed. In order for the anode porous layer to be hydrophobic, it is desirable to contain a water repellent in the anode porous layer. As the water repellent, the same one as in the case of the cathode porous layer can be used.

  The first to third anode porous layers preferably contain a conductive substance in order to improve the electrical connection between the anode catalyst layer and the anode diffusion layer. Examples of the conductive substance include a carbon material. Examples of the carbon material include those similar to those described in the first embodiment.

  The first to third anode porous layers are produced, for example, by the method described in the following (a) to (c).

  (A) An anode porous layer is obtained by applying a slurry containing a carbon material, a water repellent and a solvent to carbon paper as a substrate by a spray coating method and drying or firing. The anode porous layer can also be obtained by applying the slurry to only one side of the carbon paper and drying or firing. 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) The anode porous layer can also be produced by applying the slurry to a substrate other than carbon paper by a spray coating method, drying or firing, and then peeling the obtained layer from the substrate. Is possible.

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

  (C) Instead of adding a water repellent to the slurry, an anode porous layer was prepared using a slurry not containing a water repellent, and then the obtained anode porous layer was immersed in a water repellent solution. You may do it.

  The air resistance of the first to third anode porous layers can be adjusted by, for example, the methods (1) to (7) described above.

  The thickness of the first to third anode porous layers is preferably in the range of 300 μm to 400 μm.

  Hereinafter, a second embodiment will be described with reference to FIG. In FIG. 7, members similar to those described in FIGS. 4 to 6 are given the same reference numerals and description thereof is omitted.

  In the membrane electrode assembly 1 used in the second embodiment, as shown in FIG. 7, in the anode 5, an anode porous layer is provided between the anode electrode catalyst layer 8 and the anode gas diffusion layer 9. A fuel electrode porous layer 17 is disposed.

  The fuel electrode porous layer 17 is formed, for example, on a conductive porous substrate 17a made of carbon paper and a third surface in contact with the fuel electrode catalyst layer 8 on one surface of the conductive porous substrate 17a. A hydrophobic conductive porous portion 17b having a hydrophobic conductive porous portion 17c formed on the other surface of the conductive porous substrate 17a and having a fourth surface in contact with the fuel electrode gas diffusion layer 9. Have.

  The air resistance of the third surface of the hydrophobic conductive porous portion 17b is equal to the air resistance of the fourth surface of the hydrophobic conductive porous portion 17c, or the air resistance of the third surface is the same. The resistance can be increased or decreased as compared with the fourth surface.

  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, and a passive type (internal) that supplies vaporized components of liquid fuel to the anode. Vaporization type) fuel cell, and the semi-passive type fuel cell shown in FIGS. 4 to 7 described above. 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 fuel electrode gas diffusion layer>
First, carbon paper (TGP-H-120 manufactured by Toray Industries, Inc.) was compressed with a flat plate press in the thickness direction until the thickness became 1/2. In addition, the porosity before compression of this carbon paper was 75% when measured using the Archimedes method. Moreover, the porosity after compression of this carbon paper was 40.5% as a result of calculating by external dimension and weight measurement. This carbon paper was used as a fuel electrode gas diffusion layer.

<Preparation of fuel electrode catalyst layer>
Carbon particles carrying platinum ruthenium alloy fine particles, Nafion solution DE2020 (manufactured by DuPont) and a solvent are mixed with a homogenizer to prepare a slurry of about 15% solids, and this is applied to one side of the fuel electrode gas diffusion layer by Daiko. The coating was carried out using a catalyst. And this was dried at room temperature to form a fuel electrode catalyst layer.

<Preparation of air electrode porous layer>
One side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) was mixed with 53.0 wt% of graphite particles (VALCAN) and a 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. The other surface is mixed with 58.1 wt% of graphite particles (VALCAN) and a 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. After coating and natural drying at room temperature, it was fired at 340 ° C. for 1 hour to form a water-repellent ultra-microporous layer (hereinafter abbreviated as water-repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

<Production of air electrode>
Carbon particles carrying platinum fine particles, 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) was used. First, this electrolyte membrane and the air electrode catalyst layer were overlapped, and further, a water repellent MPL was applied to the air electrode catalyst layer, and a surface with high air resistance ( The first surface) is stacked so as to be in contact with the air electrode catalyst layer, and carbon paper (TGP-H-060 manufactured by Toray Industries, Inc.) having a porosity of 75% is stacked as the air electrode gas diffusion layer, and the temperature is Pressing was performed at a temperature of 40 ° C. and a pressure of 40 kgf / cm ² . Subsequently, the fuel electrode is overlaid on the opposite side of the air electrode of the electrolyte membrane so that the catalyst layer is on the electrolyte membrane side, and pressing is performed at a temperature of 135 ° C. and a pressure of 10 kgf / cm ^2. A membrane electrode assembly (MEA) was produced. The electrode area was 12 cm ² for both the air electrode and the fuel electrode. Moreover, when the air resistance of the fuel electrode gas diffusion layer and the air electrode gas diffusion layer was measured with a Oken type air resistance tester, it was 0.175 galeseconds, respectively.

<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, a porous plate having a porosity of 28% was disposed on the frame on the air electrode side to form a moisture retention layer. On this moisturizing 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 surface cover layer and screwed Fixed by.

  25 ml of pure methanol was injected into the liquid fuel storage chamber of the fuel cell formed as described above, and the maximum output value was measured from the current value and the voltage value in an environment of a temperature of 20 ° C. and a relative humidity of 50%. The above measurement is performed 150 times continuously, the average value of the maximum output for 141 to 150 times is calculated, and the result is shown in Table 1 below.

(Example 2)
<Fabrication of fuel electrode porous layer>
On one side of a carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) having a permeation resistance of 0.05 gale seconds, 52.3 wt% of graphite particles (VALCAN) and a PTFE solution of 60% were mixed. Then, a slurry with a solid content concentration of 10% was prepared and applied by spray coating. On the other side, 52.4 wt% of graphite particles (VALCAN) and a PTFE solution of 60% were mixed to obtain a solid content concentration. A 10% slurry was prepared, applied by a spray coating method, naturally dried at room temperature, and then fired at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

  The air resistance of the surface of the fuel electrode water-repellent MPL obtained in contact with the fuel electrode catalyst layer (third surface) and the surface in contact with the fuel electrode gas diffusion layer (fourth surface) is a value shown in Table 1 below. A fuel cell similar to that described in Example 1 was prepared except that the fuel cells were arranged so as to be. The output measurement results are shown in Table 1 below.

(Example 3)
<Fabrication of fuel electrode porous layer>
One side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) was mixed with 42.5 wt% of graphite particles (VALCAN) and a 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. The other surface is coated with 52.4 wt% of graphite particles (VALCAN) and a 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. After coating and natural drying at room temperature, it was baked at 340 ° C. for 1 hour to form a water-repellent ultra-microporous layer (hereinafter abbreviated as water-repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

  The air resistance of the surface of the fuel electrode water-repellent MPL obtained in contact with the fuel electrode catalyst layer (third surface) and the surface in contact with the fuel electrode gas diffusion layer (fourth surface) is a value shown in Table 1 below. A fuel cell similar to that described in Example 1 was prepared except that the fuel cells were arranged so as to be. The output measurement results are shown in Table 1 below.

Example 4
<Fabrication of fuel electrode porous layer>
One side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) was mixed with 53.0 wt% of graphite particles (VALCAN) and 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 59.3 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to produce a slurry with a solid content concentration of 10% and applied by spray coating. The film was naturally dried at room temperature and then fired at 340 ° C. for 1 hour to form a water-repellent ultra-porous layer (hereinafter abbreviated as water-repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

  Except that the obtained fuel electrode water-repellent MPL is arranged so that the air resistance of the surface (third surface) in contact with the fuel electrode catalyst layer is increased, it is the same as described in the above-described first embodiment. A fuel cell was prepared. The output measurement results are shown in Table 1 below.

(Example 5)
<Fabrication of fuel electrode porous layer>
One side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) was mixed with 42.5 wt% of graphite particles (VALCAN) and a 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 49.5 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to prepare a slurry having a solid content concentration of 10%, and applied by spray coating. After natural drying at room temperature, the mixture was baked at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

  Except that the obtained fuel electrode water-repellent MPL is arranged so that the air resistance of the surface (third surface) in contact with the fuel electrode catalyst layer is increased, it is the same as described in the above-described first embodiment. A fuel cell was prepared. The output measurement results are shown in Table 1 below.

(Comparative Example 1)
A fuel cell similar to that described in Example 1 was prepared except that the water repellent MPL was not provided on both the fuel electrode and the air electrode. The output measurement results are shown in Table 1 below.

(Comparative Example 2)
<Preparation of air electrode porous layer>
One side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) was mixed with 53.0 wt% of graphite particles (VALCAN) and 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 53.0 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to prepare a slurry with a solid content concentration of 10%, and applied by spray coating. After natural drying at room temperature, the mixture was baked at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

The air resistance of the surface (first surface) in contact with the air electrode catalyst layer and the surface (second surface) in contact with the air electrode gas diffusion layer of the obtained air electrode water repellent MPL is a value shown in Table 1 below. A fuel cell similar to that described in Example 1 was prepared except that the fuel cells were arranged so as to be. The output measurement results are shown in Table 1 below.

  As is apparent from Table 1, the fuel cells of Examples 1 to 5 having the air electrode porous layer having the air permeability resistance of the first surface larger than that of the second surface are the air electrode porous layers. Compared to the fuel cell of Comparative Example 1 that does not have the air electrode porous layer having substantially the same air permeability resistance between the first surface and the second surface, the maximum output is large. . In particular, among Examples 1 to 5, the maximum output of Examples 2 to 5 including the fuel electrode porous layer was larger than that of Example 1. From the comparison between Example 2 and Example 3, it can be seen that the maximum output of Example 2 in which the air permeability resistance is in the range of 10 to 100 galeseconds is high. It can be seen from a comparison between Example 4 and Example 5 that there is a similar tendency.

(Example 6)
<Preparation of air electrode porous layer>
Graphite particles (VALCAN) 52.3 wt% and 60% PTFE solution were mixed on one side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 58.1 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to prepare a slurry with a solid content concentration of 10% and applied by spray coating. After natural drying at room temperature, the mixture was baked at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

Except that the obtained air electrode water repellent MPL is arranged so that the air permeation resistance of the surface (first surface) in contact with the air electrode catalyst layer is increased, it is the same as that described in the first embodiment. A fuel cell was prepared, and the maximum output value (maximum output) was measured from the current value and the voltage value in an environment where the pure methanol injection amount was 20 mL, the temperature was 25 ° C., and the relative humidity was 55%. The above measurement was continuously performed 150 times, and the average value of the maximum output for 10 times was calculated every 10 times. The average value of the maximum output for 1 to 10 times is A ₁ , the average value of the maximum output for 141 to 150 times is A _2, and the variation rate (%) of the average value is (A ₁ −A ₂ ) / A calculated from _1, and the results are shown in table 2 below.

(Example 7)
<Fabrication of fuel electrode porous layer>
One side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) was mixed with 53.0 wt% of graphite particles (VALCAN) and 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 53.0 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to prepare a slurry with a solid content concentration of 10%, and applied by spray coating. After natural drying at room temperature, the mixture was baked at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

  The air resistance of the obtained fuel electrode water repellent MPL on the surface (third surface) in contact with the fuel electrode catalyst layer and the surface (fourth surface) in contact with the fuel electrode gas diffusion layer is a value shown in Table 2 below. A fuel cell similar to that described in Example 6 was prepared except that the fuel cells were arranged so as to be. The output measurement results are shown in Table 2 below.

(Example 8)
<Fabrication of fuel electrode porous layer>
Graphite particles (VALCAN) 42.5 wt% and 60% PTFE solution were mixed on one side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 42.5 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to prepare a slurry with a solid content concentration of 10% and applied by spray coating. After natural drying at room temperature, the mixture was baked at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

  The air resistance of the obtained fuel electrode water repellent MPL on the surface (third surface) in contact with the fuel electrode catalyst layer and the surface (fourth surface) in contact with the fuel electrode gas diffusion layer is a value shown in Table 2 below. A fuel cell similar to that described in Example 6 was prepared except that the fuel cells were arranged so as to be. The output measurement results are shown in Table 2 below.

Example 9
<Fabrication of fuel electrode porous layer>
Graphite particles (VALCAN) 59.2 wt% and 60% PTFE solution were mixed on one side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 52.5 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to prepare a slurry with a solid content concentration of 10%, and applied by spray coating. After natural drying at room temperature, the mixture was baked at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

  The fuel electrode water-repellent MPL obtained is the same as that described in Example 6 except that the air permeability resistance of the surface (third surface) in contact with the fuel electrode catalyst layer is reduced. A fuel cell was prepared. The output measurement results are shown in Table 2 below.

(Example 10)
<Fabrication of fuel electrode porous layer>
One side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) was mixed with 49.5 wt% of graphite particles (VALCAN) and a 60% PTFE solution to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 42.5 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to prepare a slurry with a solid content concentration of 10% and applied by spray coating. After natural drying at room temperature, the mixture was baked at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

  The fuel electrode water-repellent MPL obtained is the same as that described in Example 6 except that the air permeability resistance of the surface (third surface) in contact with the fuel electrode catalyst layer is reduced. A fuel cell was prepared. The output measurement results are shown in Table 2 below.

(Comparative Example 3)
A fuel cell similar to that described in Example 6 was prepared except that the water-repellent MPL was not provided on both the fuel electrode and the air electrode. The output measurement results are shown in Table 2 below.

(Comparative Example 4)
<Preparation of air electrode porous layer>
Graphite particles (VALCAN) 52.3 wt% and 60% PTFE solution were mixed on one side of carbon paper (TGP-H-030 manufactured by Toray Industries, Inc.) to prepare a slurry with a solid content concentration of 10%. It is applied by spray coating, and on the other side, 52.3 wt% of graphite particles (VALCAN) and 60% PTFE solution are mixed to prepare a slurry with a solid content concentration of 10% and applied by spray coating. After natural drying at room temperature, the mixture was baked at 340 ° C. for 1 hour to form a super microporous layer having water repellency (hereinafter abbreviated as water repellent MPL). At this time, the air resistance of each surface of the water-repellent MPL was measured with a Oken type air resistance tester.

The air resistance of the obtained air electrode water repellent MPL on the surface in contact with the air electrode catalyst layer (first surface) and the surface in contact with the air electrode gas diffusion layer (second surface) is a value shown in Table 2 below. A fuel cell similar to that described in Example 6 was prepared except that the fuel cells were arranged so as to be. The output measurement results are shown in Table 2 below.

  As is clear from Table 2, the fuel cells of Examples 6 to 10 having the air electrode porous layer having the air permeability resistance of the first surface larger than that of the second surface are the air electrode porous layers. Output fluctuation is small compared to the fuel cell of Comparative Example 3 that does not have an air electrode porous layer in which the air permeability resistance of the first surface and the second surface is substantially equal. . In particular, among Examples 6 to 10, the output fluctuation of Examples 7 to 10 including the fuel electrode porous layer is smaller than that of Example 6, and the permeability of the third surface of the fuel electrode porous layer is small. The output fluctuations of Examples 9 and 10 having a small air resistance compared to the fourth surface were the smallest. From the comparison between Example 7 and Example 8, it can be seen that the output fluctuation of Example 7 in which the air permeability resistance is in the range of 10 to 100 galeseconds is small. It can be seen from a comparison between Example 9 and Example 10 that there is a similar tendency.

  In the above embodiment, the passive DMFC has been described as an example. However, the fuel cell system is not limited as long as it has a structure that uses water generated by the reaction on the fuel electrode side without being limited to the passive type. 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.

Schematic diagram of Oken type (back pressure type) air permeability resistance measuring machine. The schematic diagram regarding the flow path of the measuring machine of FIG. The schematic diagram about the flow path of a Gurley type measuring machine. 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. The expanded sectional view of the membrane electrode assembly of the fuel cell of FIG. The expanded sectional view of the membrane electrode assembly used for the fuel cell concerning a 2nd embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Membrane electrode assembly (MEA), 2 ... Fuel distribution mechanism, 3 ... Fuel accommodating part, 4 ... Flow path, 5 ... Anode (fuel electrode), 6 ... Cathode (air electrode), 7 ... Electrolyte membrane, 8 ... Fuel electrode catalyst layer, 9 ... Fuel electrode gas diffusion layer, 10 ... Air electrode catalyst layer, 11 ... Air electrode porous layer, 11a ... Conductive porous substrate, 11b, 11c ... Water repellent conductive porous portion, 12 ... Air electrode gas diffusion layer, 13 ... conductive layer, 14 ... cover plate, 15 ... O-ring, 16 ... pump, 17 ... fuel electrode porous layer, 17a ... conductive porous substrate, 17b, 17c ... water repellent conductivity Porous part, 21 ... fuel inlet, 22 ... fuel outlet, 23 ... fuel distribution plate, 24 ... gap, 101 ... measuring end, 102 ... measurement sample, 103,108,111,113 ... capillary, 104 ... Water column pressure gauge, 105 ... side pressure chamber (B chamber), 106 ... nozzle, 107 Constant pressure chamber (A chamber), 109 ... external compression source, 110 ... pressure gauge, 112 ... chamber G.

Claims (3)

A cathode comprising a cathode catalyst layer, a cathode diffusion layer, and a cathode porous layer disposed between the cathode catalyst layer and the cathode diffusion layer;
An anode,
An electrolyte membrane disposed between the cathode and the anode,
The cathode porous layer has an air resistance in a surface in contact with the cathode catalyst layer by an Oken type air resistance tester on a surface in contact with the cathode diffusion layer. A fuel cell characterized by being larger than the air resistance of. The anode includes an anode catalyst layer, an anode diffusion layer, and an anode porous layer disposed between the anode catalyst layer and the anode diffusion layer,
The anode porous layer is an Oken type air resistance tester on the surface in contact with the anode catalyst layer, and the air resistance in the Oken type air resistance tester on the surface in contact with the anode catalyst layer. The fuel cell according to claim 1, wherein the air resistance is greater than the air resistance.   The fuel cell according to claim 2, wherein the cathode porous layer and the anode porous layer have a thickness of 300 to 400 μm.

Images