JP2010170938A - Fuel cell - Google Patents

Abstract

Water leakage outside a casing of a fuel cell is prevented.
The fuel cell includes an anode, a cathode, a proton conductive electrolyte membrane sandwiched between the anode and the cathode, a fuel supply mechanism for supplying fuel to the anode, and transpiration of water generated at the cathode. The fuel cell is provided with a moisturizing layer that suppresses the above, and has a gas-liquid selective permeation layer outside the moisturizing layer. The fuel cell of another aspect has a water absorption layer on the outer side of a moisture retention layer.
[Selection] Figure 1

Description

  The present invention relates to a fuel cell, and more particularly, to a direct methanol fuel cell using a liquid fuel such as methanol.

  In recent years, electronic devices such as personal computers and mobile phones have been downsized with the development of semiconductor technology, and attempts have been made to use fuel cells as a power source for these electronic devices. A fuel cell is a system that can generate electricity simply by supplying fuel and an oxidant. In particular, direct methanol fuel cells (DMFCs) use methanol with high energy density as fuel, and can take out current directly from methanol on the electrode catalyst, eliminating the need for a reformer. It is regarded as a promising power source for small devices.

  As a fuel supply method in the DMFC, a gas supply type in which liquid fuel is vaporized and then sent into the fuel cell with a blower, etc., and a liquid supply type in which liquid fuel having a concentration of 50 mol% or less is directly sent into the fuel cell with a pump or the like, Furthermore, an internal vaporization type that vaporizes liquid fuel having a concentration of 50 mol% or more inside the fuel cell is known.

  The internal vaporization type DMFC was held by an anode (fuel electrode) and a cathode (air electrode), a proton conductive electrolyte membrane sandwiched between the anode and the cathode, and a fuel permeation layer holding liquid fuel. A gas-liquid separation membrane for diffusing the vaporized component of the liquid fuel is provided, and the vaporized fuel is configured to be supplied from the gas-liquid separation membrane to the anode (anode catalyst layer).

In the anode catalyst layer, as shown in Formula (1), vaporized methanol and water react to generate carbon dioxide and hydrogen ions (protons).
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)

In the cathode catalyst layer, as shown in Formula (2), a reaction accompanied by the generation of water proceeds.
(3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)
In the cathode catalyst layer, water is generated by directly oxidizing methanol diffused from the anode side to the cathode side. These waters are returned to the cathode again by the moisturizing layer provided between the cathode and the oxygen inlet, and are supplied to the anode side by self-diffusion. And it utilizes as water required for reaction of said Formula (1) in an anode catalyst layer.

  Thus, in DMFC, water is generated during power generation, and this water is used as water necessary for the anode reaction. A part of the water passes through the moisturizing layer disposed between the cathode and the oxygen inlet, and water vapor (gas ) Is diffused outside the housing. However, when the consumption (reaction) current increases and the amount of water generated increases, or in an environment where water vapor is likely to condense, such as low temperature or high humidity, it cannot be fully diffused into the atmosphere as water vapor (gas). There has been a problem that the water leaked out of the housing (see, for example, Patent Document 1).

JP 2003-331900 A

  The present invention has been made to solve such a problem, and an object thereof is to provide a fuel cell in which water leakage to the outside is prevented.

  A fuel cell according to a first aspect of the present invention includes an anode (fuel electrode), a cathode (air electrode), an electrolyte membrane having proton conductivity sandwiched between the anode and the cathode, and an anode. A fuel cell comprising a fuel supply mechanism for supplying fuel, and a moisturizing layer disposed outside the cathode to prevent transpiration of water generated at the cathode, and having a gas-liquid selective permeation layer outside the moisturizing layer It is characterized by that.

  A fuel cell according to a second aspect of the present invention includes an anode (fuel electrode), a cathode (air electrode), an electrolyte membrane having proton conductivity sandwiched between the anode and the cathode, and an anode. A fuel cell comprising a fuel supply mechanism for supplying fuel, and a moisture retention layer disposed outside the cathode to suppress transpiration of water generated at the cathode, and having a water absorption layer outside the moisture retention layer And

  According to the fuel cell of the first aspect of the present invention, since the gas-liquid selective permeation layer is disposed outside the moisture retention layer, when the consumption (reaction) current increases and the amount of water generated increases, or In an environment where water vapor is likely to condense, such as low temperature or high humidity, the condensed water is blocked and suppressed by the gas-liquid selective permeation layer, and does not leak to the outside as liquid water (leakage). Therefore, a stable and high output can be obtained over a long period of time. The water in the liquid state, the permeation of which is blocked by the gas / liquid selective permeation layer, is vaporized by the heat of the cathode, etc., and passes through the gas / liquid selective permeation layer as a gas (water vapor) and is released to the outside.

  Further, according to the fuel cell of the second aspect, since the water absorption layer is disposed outside the moisture retention layer, water condensed in the moisture retention layer or the like can be absorbed and retained by the water absorption layer and leaked to the outside. Absent. Therefore, a stable and high output can be obtained over a long period of time.

1 is a longitudinal sectional view showing a configuration of a first embodiment of a fuel cell according to the present invention. It is a schematic diagram of a Wangken type (back pressure type) air permeability resistance measuring machine. It is a figure which shows the flow path of the measuring machine shown in FIG. It is a figure which shows the flow path of a Gurley type measuring machine. It is a longitudinal cross-sectional view which shows the structure of 2nd Embodiment of the fuel cell which concerns on this invention.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration of a first embodiment of a fuel cell according to the present invention.

  As shown in FIG. 1, the fuel cell 20 of the first embodiment includes an anode 3 having an anode catalyst layer 1 and an anode gas diffusion layer 2, a cathode 6 having a cathode catalyst layer 4 and a cathode gas diffusion layer 5, and A membrane electrode assembly (MEA) 8 including a proton conductive electrolyte membrane 7 sandwiched between an anode catalyst layer 1 and a cathode catalyst layer 4 is provided. The MEA 8 has a cathode conductive layer 9, a moisture retention layer 10, and a surface cover layer 11 having a plurality of air inlets 11 a outside the cathode 6, and the moisture retention layer 10 and the surface cover layer 11 are interposed between the moisture retention layer 10 and the surface cover layer 11. The gas-liquid selective permeable layer 12 is disposed. Further, a fuel supply mechanism 30 that supplies liquid fuel F to the anode conductive layer 13, the gas-liquid separation membrane 14, and the anode 3 (anode catalyst layer 1) is provided outside the anode 3 of the MEA 8.

  Each of the anode catalyst layer 1 and the cathode catalyst layer 4 contains a catalyst and an electrolyte having proton conductivity. Examples of the anode catalyst contained in the anode catalyst layer 1 and the cathode catalyst contained in the cathode catalyst layer 4 include simple metals such as platinum group elements such as Pt, Ru, Rh, Ir, Os, and Pd. An alloy containing a platinum group element can be used. Specifically, alloys such as Pt—Ru and Pt—Mo having strong resistance to methanol and carbon monoxide are used as an anode catalyst, and alloys such as Pt, Pt—Ni, and Pt—Co are used as cathode catalysts. Although it is preferable to use such a metal catalyst, it is not limited to these. Further, a supported catalyst in which fine particles of these catalysts are supported on a conductive carrier may be used. As the conductive carrier, particulate carbon such as activated carbon or graphite or fibrous carbon is used.

  Examples of the proton conductive electrolyte contained in the anode catalyst layer 1 and the cathode catalyst layer 4 together with these catalysts include fluorine resins such as perfluorocarbon polymers having sulfonic acid groups, and sulfonic acid groups. Examples thereof include organic materials such as hydrocarbon resins, and inorganic materials such as tungstic acid and phosphotungstic acid. Specifically, Nafion (trade name; manufactured by DuPont), Flemion (trade name; manufactured by Asahi Glass Co., Ltd.), Aciplex (trade name; manufactured by Asahi Kasei Kogyo Co., Ltd.) and the like are exemplified. The electrolyte having proton conductivity is not limited to these. For example, a copolymer of a trifluorostyrene derivative, a polybenzimidazole membrane impregnated with phosphoric acid, an aromatic polyether ketone sulfonic acid, or a fatty acid. An electrolyte capable of transporting hydrogen ions (protons) and methanol, such as a group hydrocarbon-based resin, can be used.

  In the embodiment of the present invention, the anode gas diffusion layer 2 is laminated on the anode catalyst layer 1 configured as described above, and the cathode gas diffusion layer 5 is laminated on the cathode catalyst layer 4. The anode gas diffusion layer 2 serves to uniformly supply fuel to the anode catalyst layer 1 and also serves as a current collector for the anode catalyst layer 1. The cathode gas diffusion layer 5 serves to uniformly supply air as an oxidant to the cathode catalyst layer 4 and also serves as a current collector for the cathode catalyst layer 4. These anode gas diffusion layer 2 and cathode gas diffusion layer 5 are, for example, porous bodies made of a porous carbonaceous material such as carbon paper, carbon cloth, or carbon silk, or a metal material such as titanium, titanium alloy, stainless steel, or gold. Or it consists of meshes.

  An electrolyte membrane 7 having proton conductivity is sandwiched between the anode catalyst layer 1 and the cathode catalyst layer 4. Examples of the material constituting the electrolyte membrane 7 having proton conductivity include the same electrolytes contained in the anode catalyst layer 1 and the cathode catalyst layer 4, that is, having a sulfonic acid group such as Nafion or Flemion. Examples thereof include organic materials such as a fluorine-based resin (perfluorocarbon polymer) and a hydrocarbon-based resin having a sulfonic acid group, and inorganic materials such as tungstic acid and phosphotungstic acid. The proton conductive electrolyte membrane 7 is not limited to these.

  An anode conductive layer 13 is laminated outside the anode gas diffusion layer 2, and a cathode conductive layer 9 is laminated outside the cathode gas diffusion layer 5. The anode conductive layer 13 and the cathode conductive layer 9 are, for example, a porous layer (for example, a mesh) made of a conductive metal material having excellent electrical characteristics and chemical stability such as Au and Ni, or a foil, thin film, or stainless steel. It is composed of a composite material in which a conductive metal material such as steel (SUS) is coated with a good conductive metal such as gold. In particular, the anode conductive layer 13 is preferably composed of a thin film having a plurality of openings, and the fuel is guided to the MEA 8 through these openings. Although FIG. 1 shows a fuel cell including the cathode conductive layer 9, the cathode gas diffusion layer 5 may function as a conductive layer without providing the cathode conductive layer 9 separately.

  A seal between the proton conductive electrolyte membrane 7 and the anode conductive layer 13 and around the anode catalyst layer 1 and the anode gas diffusion layer 2 has, for example, an O-shaped cross section and a rectangular frame shape in plan view. A material 21 is provided. A sealing material 21 having the same shape is provided between the proton conductive electrolyte membrane 7 and the cathode conductive layer 9 and around the cathode catalyst layer 4 and the cathode gas diffusion layer 5. These sealing materials 21 prevent fuel leakage and oxidant leakage from the MEA 8, and are made of an elastic body such as rubber.

  A moisturizing layer 10 is laminated on the cathode conductive layer 9. The moisturizing layer 10 includes a part of the water generated in the cathode catalyst layer 4 and has a function of suppressing water evaporation. In addition, it also has a function of uniformly introducing air as an oxidant into the cathode gas diffusion layer 5 and promoting uniform diffusion of the oxidant (air) into the cathode catalyst layer 4. The moisturizing layer 10 can be composed of, for example, a porous polyethylene film.

  On the moisturizing layer 10, a gas-liquid selective transmission layer 12 made of a gas-liquid selective material is disposed. The gas-liquid selective permeable layer 12 is a sheet (film) that covers the entire surface of the moisturizing layer 10 with a material that has high gas permeability, low liquid permeability, and is inert and insoluble in methanol and water. However, the present invention is not limited to this.

The gas-liquid selective material constituting the gas-liquid selective permeation layer 12 has a gas permeability of 0.5 to 3.5 seconds / 100 cm ³ according to the measurement method defined in JIS P-8117-1998. It is preferable to use it. This air permeability measurement method will be described below.

First, the air permeability (air resistance) of the porous layer will be described. The air resistance is measured by a Oken type air permeability tester. The Gurley second, which is a unit of air resistance, conforms to the Gurley method (JIS P8117), and is a paper (sample) in which 100 cm ³ of air is 64.5 cm ² wide under a pressure difference of 0.0132 kgf / cm ^2. Means time (seconds) to pass through.

  The standard of the Oken air permeability tester is J. TAPPI NO5B (standard of paper pulp technology), and the model is EGO-2S. The diameter of the measurement end is φ30 mm and the nozzle type name is G, 100, or φ10 mm and the nozzle type name is 1 / 10G, 100. The measurement principle will be described below with reference to FIGS.

  FIG. 2 is a schematic view showing an Oken type (back pressure type) air permeability measuring machine. At the measurement end 101, a measurement sample 102 (for example, a gas-liquid selective transmission layer) is disposed. 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 Gurley air permeability _TG of the measurement sample 102 is obtained based on the principle described below.

  FIG. 3 shows a diagram relating to the flow path of the measuring machine of FIG. In FIG. 3, the same members as those in FIG. 2 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 looks like the measurement sample 102.

  With reference to FIG. 3, 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 at a pressure of constant pressure chamber (A chamber) 107 is kept at a constant pressure of 500mmH ₂ O. P is the pressure in the lateral pressure chamber (B chamber) 105, _{Q C} is the flow rate ^(cm 3 / sec) at the nozzle 106, the flow rate ^(cm 3 / sec) of Q is capillary 111, L is the length of the nozzle 106 (mm ), L is the length (mm) of the narrow tube 111, R is the inner diameter (mm) of the nozzle 106, r is the inner diameter (mm) of the narrow tube 111, and μ is the viscosity coefficient of air.

Figure 4 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 shown in FIG. 4 follow the same rules as described with reference to 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 ) = 1.29 (kPa) (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 permeability (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 device is determined, the air permeability _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.

Moreover, it is preferable that the gas-liquid selective material which comprises the gas-liquid selective permeation | transmission layer 12 has the moisture permeability of the range of 1000-40000g / (m < ² > * 24hr). Here, the moisture permeability indicates a value obtained by converting the mass (g) of water vapor that permeates the membrane in a predetermined temperature / humidity atmosphere per unit area (1 m ² ) and 24 hours of the membrane. Specifically, the value measured based on the A-1 method using calcium chloride as a hygroscopic agent by the moisture permeability test method specified in JIS L1099 is a value obtained by converting the film thickness per 10 μm.

When the gas-liquid selective material constituting the gas-liquid selective permeable layer 12 has a moisture permeability of less than 1000 g / (m ² · 24 hr), the moisture-permeable property of the gas-liquid selective permeable layer 12 becomes too low. An excessive amount of liquid such as water accumulates inside, causing a decrease in fuel cell performance due to flooding. Further, when the moisture permeability exceeds 40000 g / (m ² · 24 hr), water leakage to the outside cannot be sufficiently prevented.

  Specific examples of the gas-liquid selective material constituting the gas-liquid selective permeation layer 12 include silicone rubber, low density polyethylene (LDPE), polyvinyl chloride (PVC), polyethylene terephthalate (PET), fluororesin (for example, polytetra Examples thereof include microporous materials such as fluoroethylene (PTFE) and tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA). The gas-liquid selective permeation layer 12 is composed of a thin film of these materials, and is configured so that liquid or the like does not leak from the periphery.

  On the gas-liquid selective permeation layer 12, a surface cover layer 11 having a plurality of air inlets 11a for taking in air as an oxidant is disposed. The surface cover layer 11 also plays a role of increasing the adhesion by pressurizing the MEA 8 and the moisturizing layer 10. For example, it can be made of a metal such as SUS304, but is not limited thereto. Adjustment of the amount of air taken in the surface cover layer 11 is performed by changing the number and size of the air inlets 11a.

  A gas-liquid separation membrane 14 is disposed outside the anode conductive layer 13 (on the fuel supply mechanism 30 side). The gas-liquid separation membrane 14 separates the vaporized component and the liquid fuel of the liquid fuel F, and allows only the vaporized component to pass to the anode 3 side. The gas-liquid separation membrane 14 is made of a material that is inactive and does not dissolve in fuel (for example, methanol). Specifically, silicone rubber thin film, low density polyethylene (LDPE) thin film, polyvinyl chloride (PVC) thin film, polyethylene terephthalate (PET) thin film, fluororesin (for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene par Fluoroalkyl vinyl ether copolymer (PFA) and the like) and a microporous film. The gas-liquid separation membrane 14 is configured so that fuel or the like does not leak from the periphery.

  A resin frame (not shown) may be provided between the gas-liquid separation membrane 14 and the anode conductive layer 13. The space surrounded by the frame functions as a vaporized fuel storage chamber (so-called vapor pool) that temporarily stores the vaporized component of the fuel that has permeated and diffused through the gas-liquid separation membrane 14, and the MEA 8 and the anode conductive layer 13 are connected to each other. It also functions as a reinforcing plate that adheres closely. Due to the effect of suppressing the amount of methanol permeated through the vaporized fuel storage chamber and the gas-liquid separation membrane 14, a large amount of vaporized fuel is prevented from flowing into the MEA 8 (anode catalyst layer 1) at a time, and the occurrence of fuel crossover is suppressed. . The frame is made of engineering plastic having high chemical resistance such as polyether ether ketone (PEEK: trade name of Victorex).

  A fuel supply mechanism 30 is disposed outside the gas-liquid separation membrane 14. The fuel supply mechanism 30 includes a fuel distribution layer 31 having a plurality of openings 31 a provided to face the openings of the anode conductive layer 13, and a fuel supply unit main body 32 that supplies liquid fuel F to the fuel distribution layer 31. , A fuel storage unit 33, a flow path 34, and a pump 35 interposed in the flow path 34.

  The fuel storage unit 33 stores a liquid fuel F corresponding to the MEA 8. As the liquid fuel F, an aqueous solution or a non-aqueous solution of one or more substances selected from the group consisting of alcohol, carboxylic acid, and aldehyde can be used. Specifically, methanol fuel such as methanol aqueous solution and pure methanol, ethanol fuel such as ethanol aqueous solution and pure ethanol, propanol fuel such as propanol aqueous solution and pure propanol, glycol fuel such as glycol aqueous solution and pure glycol, dimethyl ether, formic acid, acetic acid It may be one or more substances selected from the group consisting of formaldehyde and acetaldehyde or other liquid fuels. In any case, liquid fuel corresponding to the fuel cell is accommodated. Among these, methanol has carbon number of 1 and is generated by carbon dioxide during the reaction, and can generate electricity at a low temperature, and can be relatively easily produced from industrial waste. Therefore, it is preferable to use a methanol aqueous solution or pure methanol as the liquid fuel F. Moreover, although what has a density | concentration of 50 mol% or more is used suitably, it is not necessarily limited.

  The fuel supply unit main body 32 includes a fuel supply unit 36 composed of recesses for dispersing the liquid fuel in order to uniformly supply the supplied liquid fuel F to the fuel distribution layer 31. The fuel supply unit 36 is connected to the fuel storage unit 33 via a flow path 34 constituted by piping or the like. Liquid fuel F is introduced into the fuel supply unit 36 from the fuel storage unit 33 via the flow path 34, and the introduced liquid fuel F and / or the vaporized component of the liquid fuel F is supplied via the fuel distribution layer 31. It is supplied to the gas-liquid separation membrane 14. Only the vaporized component is supplied from the gas-liquid separation membrane 14 to the MEA 8.

  The flow path 34 is not limited to piping independent of the fuel supply unit 36 and the fuel storage unit 33. For example, when the fuel supply unit 36 and the fuel storage unit 33 are stacked and integrated, a flow path of the liquid fuel F that connects them may be used. That is, the fuel supply unit 36 only needs to communicate with the fuel storage unit 33 via the flow path 34.

  A pump 35 is inserted in a part of the flow path 34, and the liquid fuel F stored in the fuel storage unit 33 is forcibly sent to the fuel supply unit 36. Instead of interposing the pump 35 in the flow path 34, the liquid fuel F stored in the fuel storage unit 33 may be dropped to the fuel supply unit 36 using gravity and fed. Alternatively, the flow path 34 may be filled with a porous body or the like, and the liquid fuel F may be sent to the fuel supply unit 36 by capillary action.

  The pump 35 functions as a supply pump that simply sends the liquid fuel F from the fuel storage unit 33 to the fuel supply unit 36, and functions as a circulation pump that circulates excess liquid fuel F supplied to the MEA 8. It does not provide. Since the fuel cell 20 including such a pump 35 does not circulate fuel, the configuration is different from that of the conventional active method. Further, the configuration is different from a pure passive method such as an internal vaporization type, and it corresponds to a so-called semi-passive type. The type of the pump 35 that functions as the fuel supply means is not particularly limited, but from the viewpoint that a small amount of liquid fuel F can be fed with good controllability, and that further reduction in size and weight is possible. It is preferable to use a rotary vane pump, an electroosmotic flow pump, a diaphragm pump, an iron pump or the like. The rotary vane pump feeds liquid by rotating wings with a motor. The electroosmotic flow pump uses a sintered porous body such as silica that causes an electroosmotic flow phenomenon. A diaphragm pump drives a diaphragm with an electromagnet or piezoelectric ceramics to send liquid. The squeezing pump presses a part of a flexible fuel flow path and squeezes the fuel. Among these, it is more preferable to use an electroosmotic pump or a diaphragm pump having piezoelectric ceramics from the viewpoint of driving power and size. The pump 35 is electrically connected to control means (not shown), and the supply amount of the liquid fuel F supplied to the fuel supply unit 36 is controlled by the control means.

  The fuel distribution layer 31 is a flat plate in which a plurality of openings 31a are formed, and is made of a material that does not allow the liquid fuel F and its vaporized components to pass therethrough. Specifically, the fuel distribution layer 31 is made of polyethylene terephthalate (PET) resin, polyethylene naphthalate (PEN) resin, polyimide resin, or the like, and is sandwiched between the gas-liquid separation membrane 14 and the fuel supply unit main body 32. Is done. The liquid fuel F introduced into the fuel supply unit main body 32 is supplied to the entire surface of the anode 3 from the plurality of openings 31 a of the fuel distribution layer 31. As described above, the fuel distribution layer 31 makes it possible to equalize the amount of fuel supplied to the anode 3.

Next, the operation of the fuel cell 20 shown in the first embodiment will be described. The liquid fuel F supplied from the fuel storage unit 33 through the flow path 34 to the fuel supply unit 36 remains as a liquid fuel, or in a state where liquid fuel and vaporized fuel vaporized from the liquid fuel are mixed. After passing through the gas-liquid separation membrane 14, only the vaporized component is supplied to the anode gas diffusion layer 2. The fuel supplied to the anode gas diffusion layer 2 is diffused in the anode gas diffusion layer 2 and supplied to the anode catalyst layer 1. When methanol fuel is used as the liquid fuel F, an internal reforming reaction of methanol shown in the following formula (1) occurs in the anode catalyst layer 1.
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)

  When pure methanol is used as the methanol fuel, the methanol is reformed by performing the internal reforming reaction of the above formula (1) with the water generated in the cathode catalyst layer 4 and the water in the electrolyte membrane 7. Or modified by other reaction mechanisms that do not require water.

Electrons (e ⁻ ) generated by this reaction are led to the outside via a current collector, and are led to the cathode 6 after operating an electronic device or the like as so-called electricity. In addition, protons (H ⁺ ) generated by the internal reforming reaction of the formula (1) are guided to the cathode 6 through the electrolyte membrane 7. Air is supplied to the cathode 6 as an oxidant. The electrons (e ⁻ ) and protons (H ⁺ ) that have reached the cathode 6 cause a reaction represented by the following formula (2) with oxygen in the air in the cathode catalyst layer 4, and water is generated along with this reaction.
(3/2) O ₂ + 6e ⁻ + 6H ⁺ → 3H ₂ O (2)

  And the water produced | generated by the cathode catalyst layer 4 returns to the cathode 6 again by the moisture retention layer 10 provided between the surface cover layer 11 which has the air introduction port 11a, but the moisture retention layer 10 and the surface cover layer 11 are The gas-liquid selective permeable layer 12 made of a gas-liquid selective material having a high gas permeability and a low liquid permeability is disposed between them, so that the consumption (reaction) current increases and the amount of water generated increases. In an environment where water vapor is likely to condense, such as low temperature or high humidity, the water condensed in the moisture retaining layer 10 is blocked or suppressed by the gas-liquid selective permeation layer 12. Therefore, it does not leak out (leakage) as liquid water from the air inlet 11a of the surface cover layer 11. The water as the liquid whose permeation is blocked / suppressed by the gas-liquid selective permeable layer 12 is vaporized by heat on the cathode 6 side, etc., and permeates through the gas-liquid selective permeable layer 12 as a gas (water vapor) and is released to the outside. .

  Next, a second embodiment of the fuel cell of the present invention will be described. FIG. 5 is a cross-sectional view showing the configuration of the fuel cell 20 according to the second embodiment. In FIG. 5, the same components as those in FIG.

  In the second embodiment, the water absorption layer 15 is disposed between the surface cover layer 11 having the air introduction port 11 a and the moisturizing layer 10. As a material constituting the water absorbing layer 15, a highly water-absorbing polymer material can be used, and it is particularly preferable to use a highly water-absorbing resin. The superabsorbent resin is a resin having the ability to absorb and retain water several times to 1000 times its own weight without dissolving in water, and examples thereof include a crosslinked polyacrylate (sodium). Examples of commercially available high water-absorbing resins include Aquaric (trade name; manufactured by Nippon Shokubai Co., Ltd.), Aqua Keep (trade name; manufactured by Sumitomo Seika Co., Ltd.), and the like. A material that has been subjected to a highly water-absorbing process such as a porosification treatment or a hydrophilization treatment can be used, but the material is not limited to these as long as it has a high water-absorption property.

  Since such a highly water-absorbing polymer material does not have oxygen permeability, the water-absorbing layer 15 made of the highly water-absorbing polymer material preferably has an air introduction opening 15a. The air inlet opening 15 a of the water absorption layer 15 is preferably formed at a position corresponding to the air inlet 11 a of the surface cover layer 11.

  In the fuel cell 20 according to the second embodiment configured as described above, the water absorption layer 15 made of a highly water absorbent polymer material is disposed between the moisture retention layer 10 and the surface cover layer 11. Reaction) When the current increases and the amount of water generated increases, or in an environment where water vapor is likely to condense, such as at low temperature or high humidity, water condensed in the moisture retaining layer 10 is absorbed and retained by the water absorbing layer 15. Is done. Therefore, liquid water does not leak to the outside (water leakage) from the air inlet port 11a of the surface cover layer 11, and a stable and high output can be obtained over a long period of time.

  The fuel cell of the above-described embodiment is effective when various liquid fuels are used, and the type and concentration of the liquid fuel are not limited. Further, the above-described embodiment has been described by taking a semi-passive type using a pump for supplying fuel as an example of the configuration of the fuel cell main body, but for a purely passive type fuel cell such as an internal vaporization type However, the present invention can be applied.

  Next, the fact that the fuel cell according to the present invention has excellent water leakage prevention properties will be described based on Examples and Comparative Examples.

Example 1
Carbon black supporting anode catalyst particles (Pt: Ru = 1: 1), Nafion solution DE2020 (trade name; manufactured by DuPont) which is a proton conductive electrolyte (resin), water and methoxypropanol are mixed. An anode catalyst slurry was prepared. The obtained anode catalyst slurry was applied to one surface of a porous carbon paper (30 mm × 40 mm rectangle) serving as an anode gas diffusion layer and then dried to form an anode catalyst layer having a thickness of 100 μm.

  Further, carbon black carrying cathode catalyst particles (Pt), Nafion solution DE2020 (trade name; manufactured by DuPont), which is a proton-conductive electrolyte (resin), water and methoxypropanol are mixed, and cathode catalyst slurry Was prepared. The cathode catalyst slurry is applied to one surface of a porous carbon paper (same shape and size as the porous carbon paper that is the anode gas diffusion layer) that becomes the cathode gas diffusion layer, and then dried to form a cathode catalyst having a thickness of 100 μm. A layer was formed.

Next, Nafion 112 (manufactured by DuPont), which is a solid electrolyte membrane containing a perfluorosulfonic acid polymer having a thickness of 30 μm and a water content of 10 to 20% by weight, is used as a proton conductive electrolyte membrane. The membrane and the anode (anode gas diffusion layer and anode catalyst layer) and cathode (cathode gas diffusion layer and cathode catalyst layer) are superposed so that the anode catalyst layer and the cathode catalyst layer are on the electrolyte membrane side, respectively. An MEA was produced by applying a press. The electrode area was 14 cm ² for both the anode and the cathode.

  Next, the fuel cell shown in FIG. 1 was manufactured using the MEA thus manufactured. That is, the anode 3 side and the cathode 6 side of the MEA 8 were sandwiched between gold foils each having a plurality of openings, and the anode conductive layer 13 and the cathode conductive layer 9 were formed. Then, rubber O-rings were sandwiched between the electrolyte membrane 7 and the anode conductive layer 13 and between the electrolyte membrane 7 and the cathode conductive layer 9 to provide a seal. Further, a frame made of polyetheretherketone (PEEK) is disposed outside the anode conductive layer 13, and a gas-liquid separation membrane 14 made of a porous polyethylene film and a plurality of openings 31a are arranged on the outside (on the frame). A fuel distribution layer 31 and a fuel supply unit main body 32 are provided in this order.

Further, as the moisture retaining layer 10, the thickness is 500 μm, the air permeability is 2 seconds / 100 cm ³ (according to the measuring method of JIS P-8117), and the moisture permeability is 4000 g / (m ² · 24 hr) (JIS L1099 A-1). The porous polyethylene film (according to the measuring method) was used and placed on the cathode conductive layer 9. Further, on the entire surface of the moisture retaining layer 10, the air permeability is 4 seconds / 100 cm ³ (according to the measuring method of JIS P-8117) and the moisture permeability is 1000 g / (m ² · 24 hr) (the measuring method of JIS L1099 A-1). The gas-liquid permselective layer 12 was formed by placing a membrane (thickness: 100 μm) made of porous polyethylene. Further, a stainless steel plate (SUS304) having a thickness of 2 mm on which air inlets 11a (diameter 3 mm, number of ports 60) were formed was disposed on the gas-liquid selective permeation layer 12 to form the surface cover layer 11.

  A squeezing pump is used as the pump 35, and a part of the flow path 34 is squeezed in a certain direction to generate pressure, so that the liquid fuel F stored in the fuel storage unit 33 is sent to the fuel supply unit 32. did. Here, a control circuit that controls the rotation speed of the ironing pump by a current flowing through the fuel cell 20 is configured, and a fuel supply amount necessary for causing an electrochemical reaction in the fuel cell 20 (per 1 A of current per minute) The fuel was controlled so as to be always supplied at 1.2 times the methanol supply amount (3.3 mg).

  In this way, the fuel cell 20 shown in FIG. 1 was manufactured, and pure methanol was placed in the fuel storage chamber 33 to generate power. The output was measured in an environment with a temperature of 25 ° C. and a relative humidity of 50%. Further, the presence or absence of water leakage from the air inlet 11a of the surface cover layer 11 was examined. The set voltage was set to 0.2 V at which the generated water was likely to leak (water leakage).

  Even when measurement was performed at a voltage of 0.2 V for 100 hours, no water leakage was observed, and a stable output was obtained. Furthermore, no water leakage was observed even after 500 hours of power generation.

Example 2
Between the moisture retaining layer 10 and the surface cover layer 11, a sheet (100 μm in thickness) made of Aquakeep SA60S (manufactured by Sumitomo Seika Co., Ltd.), which is a highly water-absorbent resin, is disposed instead of the gas-liquid selective permeable layer 12. The water absorption layer 15 was formed. Other than that was carried out similarly to Example 1, and manufactured the fuel cell 20 shown in FIG. In the sheet made of the highly water-absorbent resin, an air introduction opening 15a having the same shape and the same size was formed by punching using a jig at a position corresponding to the air introduction port 11a of the surface cover layer 11.

  The fuel cell 20 of Example 2 manufactured in this way was subjected to power generation in the same manner as the fuel cell of Example 1 and examined for the presence or absence of water leakage from the surface cover layer 11 (air inlet 11a). Even if time measurement was performed, no water leakage was observed, and a stable output was obtained. Furthermore, when the measurement was continued, about 0.7 ml of water leakage was seen from the air inlet 11a of the surface cover layer 11 when 500 hours passed. This is presumably because water as a liquid was generated exceeding the limit of water absorption / retention of the superabsorbent resin, and as a result, water that could not be retained in the water absorption layer 15 leaked.

Comparative Example Neither the gas-liquid selective transmission layer 12 nor the water absorption layer 15 was disposed between the moisture retention layer 10 and the surface cover layer 11. Other than that was carried out similarly to Example 1, and manufactured the fuel cell. Then, the produced fuel cell was subjected to power generation in the same manner as the fuel cell of Example 1, and the presence or absence of water leakage from the surface cover layer 11 was examined. When 20 hours had passed since the start of power generation, water generated by the power generation reaction flowed out from the air inlet 11a of the surface cover layer 11 as liquid water, and a leaking state was observed. And the amount of water leakage at the time of 100-hour electric power generation was 2.7 ml.

  The present invention can be applied to various fuel cells using liquid fuel. Further, the specific configuration of the fuel cell, the supply state of the fuel, and the like are not particularly limited. In the implementation stage, the constituent elements can be modified and embodied without departing from the technical idea of the present invention. Furthermore, various modifications are possible, such as appropriately combining a plurality of components shown in the above embodiment, or deleting some components from all the components shown in the embodiment. Embodiments of the present invention can be expanded or modified within the scope of the technical idea of the present invention, and these expanded and modified embodiments are also included in the technical scope of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Anode catalyst layer, 2 ... Anode gas diffusion layer, 3 ... Anode, 4 ... Cathode catalyst layer, 5 ... Cathode gas diffusion layer, 6 ... Cathode, 7 ... Electrolyte membrane, 8 ... MEA, 9 ... Cathode conductive layer, 10 DESCRIPTION OF SYMBOLS ... Moisturizing layer, 11 ... Surface cover layer, 12 ... Gas-liquid selective permeation layer, 13 ... Anode conductive layer, 14 ... Gas-liquid separation membrane, 15 ... Water absorption layer, 30 ... Fuel supply mechanism, 31 ... Fuel distribution layer, 32 ... Fuel supply unit main body, 33... Fuel storage unit, 34... Flow path, 35.

Claims (7)

An anode (fuel electrode), a cathode (air electrode), an electrolyte membrane having proton conductivity sandwiched between the anode and the cathode, a fuel supply mechanism for supplying fuel to the anode, and a cathode A fuel cell comprising a moisturizing layer disposed on the outside to prevent transpiration of water generated at the cathode;
A fuel cell comprising a gas-liquid selective permeation layer outside the moisturizing layer. The gas-liquid selective permeable layer is made of a gas-liquid selective material having an air permeability of 0.5 to 3.5 seconds / 100 cm ³ according to a measuring method defined in JIS P-8117-1998. The fuel cell according to claim 1. The gas-liquid selective permeable layer is made of a gas-liquid selective material having a moisture permeability of 1000 to 40000 g / (m ² · 24 hr) according to a measurement method defined in JIS L1099-2006 A-1. Item 3. The fuel cell according to Item 1 or 2.   The outermost layer on the cathode side is provided with a surface layer having an air introduction port, and the gas-liquid selective permeation layer is provided between the surface layer and the moisturizing layer. The fuel cell according to claim 1. An anode (fuel electrode), a cathode (air electrode), an electrolyte membrane having proton conductivity sandwiched between the anode and the cathode, a fuel supply mechanism for supplying fuel to the anode, and a cathode A fuel cell comprising a moisturizing layer disposed on the outside to prevent transpiration of water generated at the cathode;
A fuel cell comprising a water absorption layer outside the moisture retention layer.   6. The fuel cell according to claim 5, wherein a surface layer having an air inlet is provided in the outermost layer on the cathode side, and the water absorbing layer is provided between the surface layer and the moisture retention layer.   The fuel cell according to claim 6, wherein the water absorption layer has an air introduction opening at a position corresponding to the air introduction port of the surface layer.

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