JP2008171612A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell which allows improved exhaust efficiency and facilitates an enhanced output. <P>SOLUTION: This fuel cell comprises fuel paths 10 opened in an anode 7 and exhausting paths 12 for exhausting gases to the outside through a gas-liquid separation membrane 4, wherein fuel paths 10c are opened toward the exhausting paths 12. In addition, the inner walls 10c of the fuel paths 10 consist of a material having a higher critical surface tension than that of liquid fuel, and the inner walls 12c of the exhausting paths 12 consist of a material having a lower critical surface tension than that of the liquid fuel. The path inner walls 10c of a liquid fuel path member 2 get wet with the liquid fuel, whereas the path inner walls 12c of a gas exhausting path member 3 does not get wet with the liquid fuel. Therefore, the exhausting paths 12 of the gas exhausting path member 3 can be prevented from being blocked with the liquid fuel. Therefore, gases generated by liquid fuel reaction in the anode 7 can easily flow into the exhausting paths 12 of the gas exhausting path member 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell using liquid as fuel.

  A fuel cell is an electrochemical device that continuously converts supplied fuel into electrical energy and heat. Since the fuel cell directly converts chemical energy into electric energy, it has higher theoretical energy conversion efficiency than a conventional internal combustion engine, and does not generate harmful nitrogen oxides and sulfides.

  In addition, hydrogen, which is the fuel of many fuel cells, can be reformed from various raw fuels such as city gas, liquefied petroleum gas (LPG), kerosene, methanol, naphtha, and biomass. Therefore, hydrogen, which is the fuel of the fuel cell, can be selected as a suitable raw fuel according to the application and conditions of the fuel cell, and it is advantageous from time to time in accordance with future technological innovations and changes in raw fuel supply conditions. It is possible to select a suitable raw fuel.

  A fuel cell having such advantages is expected to be put into practical use as a next-generation power source.

  Furthermore, since the fuel cell has a higher energy density per mass than an existing secondary battery and does not need to be charged, application to a power source for a small portable or portable electronic device is also attempted. .

  Instead of using hydrogen, which is difficult to store, as a fuel, a fuel cell that uses liquid fuel such as methanol or hydrazine directly without reforming or vaporizing has a simple structure and is advantageous in terms of size and weight. It is. In particular, direct methanol fuel cells (DMFC) that use methanol as a liquid fuel, which are easy to handle and can be expected to be produced from biomass, which is a sustainable energy source, are expected as an ideal compact power source. ing.

  In order to use a fuel cell using a liquid fuel such as the direct methanol fuel cell as a small power source of a portable device whose power consumption has been increasing in recent years, it is necessary to further increase the output density.

  For this reason, high performance catalysts and development of solid polymer membranes with low fuel methanol penetration into the cathode and high hydrogen ion conductivity are being carried out. Furthermore, a system that can efficiently supply fuel and efficiently discharge products without using auxiliary devices such as a fuel supply pump and an air supply blower as much as possible has been developed.

  For example, Patent Documents 1 and 2 disclose a fuel cell in which a gas-liquid separation tube or a gas-liquid separation membrane is disposed in a fuel chamber, and carbon dioxide generated at the anode is exhausted to the outside.

  By the way, in order to increase the output of the fuel cell, it is necessary to increase the reaction at the anode.

However, as the reaction at the anode increases, the carbon dioxide produced by the oxidation of the liquid fuel at the anode will increase. For this reason, bubbles of carbon dioxide adhere to the anode surface or block the fuel supply flow path, which obstructs the supply of liquid fuel to the anode, making it difficult to increase the output of the fuel cell. There is a problem of becoming.
JP 2006-24401 A JP 2006-24441 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell that can improve exhaust efficiency and easily achieve high output.

In order to solve the above problems, a fuel cell according to the present invention includes an anode having a catalyst unit that mediates a chemical reaction of supplied liquid fuel;
A liquid fuel flow path portion having a fuel flow path to which the liquid fuel is supplied and opened to the anode;
An exhaust stream that is stacked on the liquid fuel flow path and communicates with the anode via the fuel flow path and discharges gas generated by a chemical reaction of the liquid fuel at the anode. A gas discharge flow path portion having a path;
A gas-liquid separation membrane that is laminated on the gas discharge flow path and transmits the gas from the opening of the gas discharge flow path;
The fuel flow path of the liquid fuel flow path portion has a flow path inner wall having a critical surface tension larger than the surface tension of the liquid fuel,
The exhaust flow path of the gas discharge flow path section has a flow path inner wall having a critical surface tension smaller than the surface tension of the liquid fuel.

  According to this invention, the channel inner wall surface of the liquid fuel channel part gets wet with the liquid fuel, while the channel inner wall of the gas discharge channel part does not get wet with the liquid fuel. Therefore, it can prevent that the exhaust flow path of a gas exhaust flow path part is obstruct | occluded with liquid fuel. Therefore, the gas generated by the reaction of the liquid fuel at the anode can easily flow into the exhaust passage of the gas discharge passage section. Thereby, the discharge of the gas and the fuel supply to the anode can be efficiently performed, and a fuel cell having a large output can be obtained.

  Further, in the fuel cell according to an embodiment, the fuel flow path of the liquid fuel flow path portion is arranged in a width direction orthogonal to the stacking direction on a plane orthogonal to the direction in which the liquid fuel travels in the fuel flow path. The dimension in the stacking direction is smaller than the dimension.

  According to this embodiment, before the gas bubbles generated from the anode spread to the full width of the fuel flow path of the liquid fuel flow path portion and hinder the fuel supply to the anode, the bubbles are formed in the gas discharge flow path portion. Reach the exhaust passage. Since the critical surface tension of the inner wall surface of the gas discharge channel portion is smaller than the surface tension of the liquid fuel, the bubbles move to the channel side of the gas discharge channel portion. Therefore, the fuel supply is not hindered by the bubbles, and a fuel cell with high output can be obtained.

  Moreover, in the fuel cell of one Embodiment, the said gas discharge flow path part is produced with rubber | gum.

  According to this embodiment, since the gas discharge channel portion can be easily brought into close contact with the liquid fuel channel portion, a highly reliable fuel cell that is unlikely to cause fuel leakage or the like can be obtained.

  In one embodiment of the fuel cell, the rubber is silicon rubber. According to this embodiment, by using a silicone rubber having a large gas permeability coefficient as a material for producing the gas discharge flow path portion, the gas generated at the anode can be exhausted more quickly, and the fuel cell Output can be increased.

  According to the fuel cell of the present invention, the channel inner wall surface of the liquid fuel channel part gets wet with the liquid fuel, while the channel inner wall surface of the gas discharge channel part does not get wet with the liquid fuel. Therefore, the exhaust passage of the gas discharge passage portion can be prevented from being clogged with liquid fuel, the gas generated at the anode can be quickly exhausted from the fuel supply passage portion, the exhaust efficiency can be improved, and the fuel with high output A battery can be obtained.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  First, the basic operation of a direct methanol fuel cell as an embodiment of the fuel cell of the present invention will be described. The direct methanol fuel cell is a fuel cell using methanol as a fuel, which is the most common among fuel cells using liquid as fuel.

The overall reaction formula of this direct methanol fuel cell (DMFC) is represented by the following chemical formula (Formula 1). This direct methanol fuel cell generates electric power by taking out part of the difference in chemical energy between the left side and the right side of the chemical formula (Chemical Formula 1) as electric energy.
CH ₃ OH + (3/2) O ₂ → 2H ₂ O + CO ₂ (Chemical Formula 1)

A mixed liquid of methanol and water is supplied to the anode of the direct methanol fuel cell. As shown in the following chemical formula (Chemical Formula 2), the catalyst in the anode causes an oxidation reaction of methanol to generate carbon dioxide, hydrogen ions, and electrons.
CH ₃ OH + H ₂ O → 6H ⁺ + 6e ⁻ + CO ₂ (Chemical formula 2)

Hydrogen ions generated at the anode pass through the electrolyte membrane and reach the cathode from the anode. On the other hand, the electrons reach the cathode via an external circuit (a device that operates using a fuel cell as a power source). In this cathode, hydrogen ions, oxygen in the air and electrons react with each other as shown in the following chemical formula (Chemical Formula 3) to generate water.
6H ⁺ + (3/2) O ₂ + 6e ⁻ → 3H ₂ O (Chemical Formula 3)

  The voltage obtained from the direct methanol fuel cell without loss is 1.2 V corresponding to the difference in chemical energy between the left side and the right side of the above chemical formula (Chemical Formula 1), and the actually obtained voltage is 0.2-0. It is about .6V. Therefore, when this direct methanol fuel cell is used as a power source for an electronic device, a plurality of unit cells are connected in series to obtain a desired voltage.

  Next, the unit cell of the direct methanol fuel cell as the above embodiment will be described in detail.

  The exploded perspective view of FIG. 1 illustrates the structure of the unit cell of the fuel cell of this embodiment, and FIG. 2 illustrates the cross-sectional structure of the unit cell.

  This unit cell has a structure in which a thin film electrode assembly (MEA) 1, a liquid fuel channel member 2, and a gas exhaust channel member 3 are sandwiched between an anode support substrate 5 and a cathode support substrate 6. .

  As shown in FIG. 2, the thin film electrode assembly 1 has a structure in which an electrolyte membrane 9 is sandwiched between an anode 7 and a cathode 8. A liquid fuel flow path member 2 is disposed on the anode 7 side of the thin film electrode assembly 1, and a fuel flow path 10 is formed in the liquid fuel flow path member 2. This liquid fuel channel member 2 is made of a material having a critical surface tension that is larger than the surface tension of the liquid fuel (for example, a resin carrying a hydrophilic substance such as titanium oxide described later). Etc.).

  On the other hand, a gas exhaust passage member 3 is stacked on the liquid fuel passage member 2, and an exhaust passage 12 is formed in the gas exhaust passage member 3. The exhaust passage 12 passes through the gas exhaust passage member 3 in the stacking direction, and communicates with the anode 7 via the fuel passage 10. The inner wall 12c of the exhaust passage 12 is formed of a material (for example, rubber) whose critical surface tension is smaller than the surface tension of the liquid fuel. A gas-liquid separation film 4 is laminated on the gas exhaust flow path member 3, and an anode support substrate 5 is laminated on the gas-liquid separation film 4. The anode support substrate 5 is formed with an exhaust groove 11 for exhausting carbon dioxide generated at the anode 7 with power generation to the outside. The exhaust channel 12 is exhausted via the gas-liquid separation membrane 4. The groove 11 can be ventilated.

  On the other hand, a cathode support substrate 6 is disposed on the opposite side of the anode support substrate 5 with the electrolyte membrane 9 interposed therebetween, and a vent hole 13 extending in a direction orthogonal to the exhaust groove 11 is formed in the cathode support substrate 6. Through the vent hole 13, air containing oxygen as a reducing agent can be introduced into the cathode 8.

  As the material of the electrolyte membrane 9, it is desirable to use a material having good conductivity of hydrogen ions and low permeability of liquid fuel such as methanol. Examples of such materials include perfluorosulfonic acid polymer membranes and hydrocarbon polymer membranes.

  The anode 7 includes an anode current collector 7a, an anode diffusion layer 7b, and an anode catalyst (not shown) as a catalyst part. The anode current collector 7a is made of a material having high conductivity, being electrochemically inert in the use environment, and having corrosion resistance and durability. Further, the anode current collector 7a is preferably made of a material such as a metal mesh or sponge metal because it is necessary to transmit liquid dioxide or oxygen dioxide as a reaction product. As an example of such a metal material, gold (Au) or platinum (Pt) is desirable, but it is expensive. Therefore, stainless steel or titanium coated with gold or platinum is used as a material for the anode current collector 7a. Also good.

  The anode diffusion layer 7b is provided to uniformly distribute the liquid fuel to the anode current collector 7a and to quickly discharge the carbon dioxide generated by the reaction at the anode 7. Also, good conductivity is required to transmit electrons generated by the chemical reaction represented by the above chemical formula (Chemical Formula 1) from the anode catalyst (not shown) to the anode current collector 7a. As a material of the anode diffusion layer 7b, for example, a method of performing ultraviolet irradiation or plasma treatment on a woven or non-woven fabric of carbon fiber, a method of dispersing a resin having a large critical surface tension, or the like makes it easy to get wet with liquid fuel. Things can be used.

  On the surface of the anode diffusion layer 7 b facing the electrolyte membrane 9, a mixture of the anode catalyst particles and a hydrogen ion conductor resin serving as an electrolyte material is applied. As the anode catalyst, for example, platinum and ruthenium (Ru) alloy particles or platinum and ruthenium mixed particles dispersed and supported on a supporting material such as carbon-based particles can be used.

  The cathode 8 includes a cathode current collector 8a, a cathode diffusion layer 8b, and a cathode catalyst (not shown). The cathode current collector 8a is made of a material having high conductivity, being electrochemically inactive under the use environment, and having corrosion resistance and durability. Further, as the cathode current collector 8a, it is necessary to permeate air or water as a reaction product, so that the cathode current collector 8a has the same configuration as the anode current collector 7a. The cathode diffusion layer 8b is provided in order to diffuse and discharge water vapor, which is a reaction product in the cathode 8, and prevent water from aggregating. The cathode diffusion layer 8b is required to have good conductivity in order to transmit electrons that have reached the cathode current collector 8a through an external load to the cathode catalyst (not shown). Therefore, as the cathode diffusion layer 8b, for example, a carbon fiber woven fabric or non-woven fabric immersed in an aqueous dispersion of polytetrafluorocarbon and then dried and baked to enhance water repellency can be used. Further, a mixture of the cathode catalyst particles forming the cathode catalyst (not shown) and the hydrogen ion conductor resin as the electrolyte material is applied to the surface of the cathode diffusion layer 8b facing the electrolyte membrane 9. As the cathode catalyst, platinum particles dispersed and supported on carbon-based fine particles can be used.

  As materials for the anode support substrate 5 and the cathode support substrate 6, resins such as polycarbonate, epoxy, polyimide, polyethylene, polypropylene, and vinyl chloride, and resins containing glass fibers or the like as a reinforcing material can be used. . In addition, a material obtained by applying a resin to the surface of a metal material such as carbon plate, magnesium, aluminum, nickel, and various metal alloys, and using it as a material for the anode support substrate 5 and the cathode support substrate 6 is used. Can do.

  In this embodiment, the liquid fuel is supplied to the anode 7 through the liquid fuel passage 10 formed in the liquid fuel passage member 2. In this embodiment, an exhaust passage 12 is formed between the gas-liquid separation membrane 4 and the fuel passage 10, and the inner wall 12c of the exhaust passage 12 has a critical surface tension smaller than the surface tension of the liquid fuel. The inner wall 12c of the exhaust passage 12 is made of a material and does not get wet with the liquid fuel. Therefore, the exhaust flow path 12 of the gas discharge flow path member 3 can be prevented from being blocked with the liquid fuel. Therefore, the gas generated by the reaction of the liquid fuel at the anode 7 can easily flow into the exhaust flow path 12 of the gas discharge flow path member 3.

  Thereby, even when the pressure in the fuel flow path 10 of the liquid fuel flow path member 2 is not so high that the carbon dioxide generated in the anode 7 can be discharged to the outside through the gas-liquid separation membrane 4, the carbon dioxide is removed from the exhaust flow path 12. Therefore, bubbles can be efficiently removed from the surface of the anode 7, and the output of the fuel cell can be stably maintained.

  Preferably, the height dimension (dimension in the stacking direction) D1 of the fuel flow path 10 is the width dimension of the fuel flow path 10 (X − perpendicular to the direction Z in which the liquid fuel travels in the fuel flow path 10). It is desirable that it is shorter than the dimension D2 in the width direction X perpendicular to the stacking direction Y on the Y plane. By adopting this structure, before the carbon dioxide bubbles expand to the full width of the fuel flow path 10, the carbon dioxide bubbles touch (reach) the exhaust flow path 12 and are destroyed. Therefore, bubbles can be efficiently removed from the surface of the anode 7 and the output of the fuel cell can be stably maintained. For the same reason, as shown in FIG. 1, the distance D3 between one exhaust flow path 12 and another exhaust flow path 12 adjacent in the direction Z is the width of the fuel flow path 10. Desirably shorter than dimension D2.

  The material of the liquid fuel passage member 2 is a material that is electrochemically inert, corrosion resistant, and durable under the usage environment, and is not particularly limited as long as it is an insulated structure. For example, as the material of the liquid fuel flow path member 2, glass or the like can be used, and resins such as polycarbonate, epoxy, polyimide, polyethylene, polypropylene, and vinyl chloride, and glass fibers or the like are contained as a reinforcing material in these resins. Resin can be used.

  Further, the inner wall 10c of the fuel flow path 10 having a critical surface tension higher than the surface tension of the liquid fuel is coated with a resin having a critical surface tension larger than the surface tension of the liquid fuel, or hydrophilic such as titanium oxide. This can be realized by loading a substance. The material of the gas exhaust passage member 3 is not particularly limited as long as it is electrochemically inert under the use environment and has corrosion resistance and durability, but is preferably formed of rubber. It is desirable. When the gas exhaust flow path member 3 is made of rubber, the gas exhaust flow path member 3 is made to flow into the liquid fuel flow only by tightening the anode support substrate 5 and the liquid fuel flow path member 2 with screws or the like without using an adhesive. It becomes possible to make it close to the road member 2 easily.

  More preferably, the gas exhaust passage member 3 is formed of silicone rubber. When the material of the gas exhaust passage member 3 is a silicone rubber having a large gas permeability coefficient, the exhaust capacity of carbon dioxide is improved and the output of the fuel cell can be improved. As a material of the gas exhaust passage member 3, for example, vinyl methyl silicone rubber or fluorinated silicone rubber having a critical surface tension reduced by introducing a fluorinated alkyl group is suitable.

  Further, as the gas-liquid separation membrane 4, it is desirable to use a material that has high gas permeability, is electrochemically inactive, and has a critical surface tension smaller than the surface tension of the liquid fuel. As the gas-liquid separation membrane 4, for example, a porous membrane of polytetrafluoroethylene having a critical surface tension of 15 (mN / m) smaller than the surface tension of methanol (22.6 (mN / m)) is adopted. it can.

  In addition, it should be thought that embodiment mentioned above is an illustration and restrictive at no points. The scope of the present invention is defined not only by the above description but also by the scope of claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

It is a disassembled perspective view which shows the structure of the unit cell of embodiment of the fuel cell of this invention. It is sectional drawing which shows the cross-section of the fuel cell of the said embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thin film electrode assembly 2 Liquid fuel flow path member 3 Gas exhaust flow path member 4 Gas-liquid separation film 5 Anode support substrate 6 Cathode support substrate 7 Anode 8 Cathode 9 Electrolyte membrane 10 Fuel flow path 10c Inner wall 11 Exhaust groove 12 Exhaust flow path 12c Inner wall 13 Vent

Claims (4)

An anode having a catalyst part that mediates a chemical reaction of the supplied liquid fuel;
A liquid fuel flow path portion having a fuel flow path to which the liquid fuel is supplied and opened to the anode;
An exhaust stream that is stacked on the liquid fuel flow path and communicates with the anode via the fuel flow path and discharges gas generated by a chemical reaction of the liquid fuel at the anode. A gas discharge flow path portion having a path;
A gas-liquid separation membrane that is laminated on the gas discharge flow path and transmits the gas from the opening of the gas discharge flow path;
The fuel flow path of the liquid fuel flow path portion has a flow path inner wall having a critical surface tension larger than the surface tension of the liquid fuel,
The fuel cell according to claim 1, wherein the exhaust flow path of the gas discharge flow path section has a flow path inner wall having a critical surface tension smaller than a surface tension of the liquid fuel. The fuel cell according to claim 1, wherein
The fuel flow path of the liquid fuel flow path section is
A fuel cell characterized in that a dimension in the stacking direction is smaller than a dimension in a width direction orthogonal to the stacking direction on a plane orthogonal to the direction in which the liquid fuel travels in the fuel flow path. The fuel cell according to claim 1 or 2,
The fuel cell according to claim 1, wherein the gas discharge channel is made of rubber. The fuel cell according to claim 3, wherein
A fuel cell, wherein the rubber is a silicon rubber.

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