JP2008041401A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of suppressing the crossover causing the unreacted liquid fuel to permeate the membrane electrode assembly. <P>SOLUTION: The fuel cell has a hydrophilic film 41 covering a proton conductive film 11, and a film 42 which covers the hydrophilic film 41 and prevents a liquid fuel from permeating the electrode side of a cathode catalyst layer. Each of both films is provided at a gap between adjacent anode catalyst layer electrodes 12 and a gap between adjacent cathode catalyst layer electrodes 13, respectively. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell having a plurality of unit cells connected in series and connected in series, which is effective for the operation of a portable device, for example.

  In recent years, various electronic devices such as personal computers and mobile phones have been miniaturized with the development of semiconductor technology, and attempts have been made to use fuel cells as power sources for these small devices. Fuel cells have the advantage that they can generate electricity simply by supplying fuel and oxidant, and can continuously generate electricity if only the fuel is replenished / replaced. For this reason, if the size can be reduced, it can be said that the system is extremely advantageous for the operation of the portable electronic device. Direct methanol fuel cells (DMFCs), in particular, use methanol with high energy density as the fuel, and since current can be extracted directly from methanol on the electrode catalyst, it is possible to reduce the size and handle the fuel with hydrogen. Since it is easy compared to gas fuel, it is promising as a power supply for small devices, so it is expected to be put to practical use as an optimal power source for cordless portable devices such as notebook computers, mobile phones, portable audio devices, and portable game machines. .

For example, Patent Document 1 and Patent Document 2 include a proton conductive solid electrolyte membrane, an anode catalyst layer electrode, and an anode gas diffusion layer, an anode that generates charge and protons from fuel and water, a cathode catalyst layer electrode, and Membrane Electrode Assembly (MEA), which has a cathode gas diffusion layer and is formed by protons and cathodes that generate water from oxygen, is provided as a unit cell. A DMFC is disclosed in which a plurality are arranged and connected in series.
JP 2004-014148 A International Publication WO2005 / 112172A1

  However, in a conventional fuel cell, a so-called crossover occurs in which unreacted fuel permeates through the gap between the electrodes of adjacent unit cells to the cathode side. Produce.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a fuel cell capable of suppressing crossover in which unreacted fuel permeates through a membrane electrode assembly.

A fuel cell according to the present invention includes a proton conducting membrane, a plurality of anode catalyst layer electrodes that are arranged in a plane on one side of the proton conducting membrane and spaced apart from each other, and the other side of the proton conducting membrane. A plurality of cathode catalyst layer electrodes adjacent to each other with a gap between each other, and a liquid fuel disposed on the anode catalyst layer electrode. A fuel cell comprising: a liquid fuel supply means for supplying an oxidant; and an oxidant supply means for supplying an oxidant to the cathode catalyst layer electrode,
A hydrophilic membrane that is provided in a mutual gap between adjacent anode catalyst layer electrodes and a mutual gap between cathode catalyst layer electrodes and covers the proton conductive membrane, a mutual gap between adjacent anode catalyst layer electrodes, and the cathode catalyst And a hydrophobic membrane which is provided in the mutual gap between the layer electrodes, covers the hydrophilic membrane, and does not allow liquid fuel to permeate the cathode catalyst layer electrode side.

  In the fuel cell of the present invention, since the hydrophobic film covers the area between adjacent electrodes of each electrode, permeation of unreacted fuel from the anode side to the cathode side is blocked. This suppresses fuel crossover and improves power generation efficiency.

  Further, since the hydrophilic membrane covers the area between the adjacent electrodes of each electrode so as to be in contact with the proton conducting membrane, drying of the proton conducting membrane is effectively prevented, and a stable power generation operation is performed.

  The hydrophilic membrane and the hydrophobic membrane can each include a hydrophilic polymer and a hydrophobic polymer sequentially stacked on a common proton conducting membrane.

  As a material for the hydrophilic film, a hydrophilic polymer such as perfluorocarbon sulfonic acid (for example, Nafion (registered trademark), manufactured by DuPont), polyethylene glycol (PEG), polyvinyl alcohol (PVA), or the like can be used.

  Fluorine-containing resin and fluorine-containing rubber (for example, tetrafluoroethylene (TFE) -hexafluoropropylene (HFP) copolymer, tetrafluoroethylene (TFE) -hexafluoropropylene (HFP) -hexafluoroacetone ( HFA) copolymers, tetrafluoroethylene (TFE) -polypropylene (PP) copolymers, polyvinylidene fluoride, polyvinyl fluoride, etc.), silicone-containing resins and silicone-containing rubbers (eg, cyanosilicon rubber) are used. be able to.

  According to the present invention, since crossover of fuel can be suppressed, good battery performance can be stably obtained, and it can be used as a power source for cordless portable devices such as notebook computers, mobile phones, portable audio devices, and portable game machines. Crossover can be reduced and good output characteristics can be obtained.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  First, an overview of the entire fuel cell will be described with reference to FIGS. 1 and 2. The fuel cell 1 is used as a built-in power source of a portable electronic device, and includes a cell structure 10 and cell case covers 2 and 3. The cell case covers 2 and 3 correspond to an interior case that covers the entire cell structure 10. One cell case cover 2 has a plurality of vent holes 24 and a groove-shaped inflection portion 29 on the main surface, and covers the cathode side of the fuel cell. The other cell case cover 3 is a blind plate having no opening, and covers the anode side of the fuel cell. As shown in FIG. 1, the cell case cover 2 is put on the cell structure 10, the caulking portion 2a of the cover is caulked, the end 2b is bent as shown in FIG. By integrating, a cell assembly 20 shown in FIGS. 2A and 2B is obtained. When this cell assembly 20 is further covered with a housing cover (apparatus exterior case) (not shown) and connected with wiring, a portable electronic device is obtained.

  The cell structure 10 has a plurality of unit cells connected in a planar arrangement inside. As shown in FIG. 2, the unit cell includes a membrane electrode assembly in which a proton conductive solid electrolyte membrane 11, an anode catalyst layer electrode 12, and a cathode catalyst layer electrode 13 are integrated, and further includes an anode gas diffusion layer 14, A cathode gas diffusion layer 15, a positive electrode lead (cathode current collector) 16a, and a negative electrode lead (anode current collector) 16b are provided.

  Various spaces and gaps are formed in the fuel cell 1 by the seal members 17 and 18 and the spacer 25. Among these spaces and gaps, for example, the cathode side space is used as the air permeable layer 26, and the anode side space is used as the liquid fuel storage chamber 27 and the vaporization chamber (not shown). The air permeable layer 26 is defined at a constant interval by a plurality of spacers 25, and the periphery thereof is sealed by the seal member 18. The air permeable layer 26 is provided with a filter member so as not to obstruct the passage of outside air, and to prevent the entry of foreign dust and foreign matter, and contact from the outside. The filter member is preferably a porous film having a porosity of 20 to 60%, for example. In the liquid fuel storage chamber 27, a fuel supply passage 19 that communicates with the fuel supply port 21 is opened at an appropriate position. For example, a bayonet type coupler 23 is attached to the fuel supply port 21, and a nozzle of a fuel cartridge (not shown) is inserted into the coupler 23 so that liquid fuel is supplied to the liquid fuel storage chamber 27.

An exhaust channel (not shown) is provided on the anode side, and CO ₂ gas as a by-product is discharged out of the reaction system through the exhaust channel. Further, it is desirable that the negative electrode lead 16b has a large number of openings and gaps and does not obstruct the diffusion of fuel component gas and by-product gas (CO ₂ ).

  Liquid fuel includes methanol aqueous solution, pure methanol, ethanol aqueous solution, pure ethanol, propanol aqueous solution, formic acid aqueous solution, sodium formate aqueous solution, acetic acid aqueous solution, sodium borohydride aqueous solution, potassium borohydride aqueous solution, lithium hydride aqueous solution, ethylene An organic aqueous solution containing hydrogen such as an aqueous glycol solution or dimethyl ether is used. Among these, an aqueous methanol solution is preferable because it has carbon number of 1 and carbon dioxide gas generated during the reaction, and can generate a power generation reaction at a low temperature, and can be produced relatively easily from industrial waste. Further, fuels having various concentrations in a range from 100% to several percent can be used.

  The cell case covers 2, 3 and the spacer 25 can be made of a metal material having excellent corrosion resistance such as stainless steel or nickel metal if a coating having excellent corrosion resistance is applied, for example. (PEEK: Trademark of Victorex PLC), polyphenylene sulfide (PPS), polytetrafluoroethylene (PTFE), and the like can be made of a hard plastic that hardly swells with liquid fuel. When the cell case covers 2 and 3 and the spacer 25 are made of a metal material, it is necessary to insert an insulating member (not shown) between the negative electrodes so that the negative electrodes arranged in the same battery container are not short-circuited.

  The unit cell of the fuel cell includes an electrolyte membrane 11, an anode, and a cathode. The anode and the cathode are arranged to face each other with the electrolyte membrane 11 therebetween. The anode has an anode catalyst layer electrode 12 and an anode gas diffusion layer 14. The anode catalyst layer electrode 12 oxidizes the fuel supplied through the gas diffusion layer 14 and extracts electrons and protons from the fuel. The anode catalyst layer electrode 12 and the gas diffusion layer 14 are stacked. It has a structure. The anode catalyst layer electrode 12 is made of, for example, carbon powder containing a catalyst. Examples of the catalyst include fine particles of platinum (Pt), transition metals such as iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru) and molybdenum (Mo), oxides thereof, and alloys thereof. Are used. However, it is preferable that the catalyst is made of an alloy of ruthenium and platinum, since inactivation of the catalyst due to adsorption of carbon monoxide (CO) can be prevented.

  The anode catalyst layer electrode 12 preferably includes fine particles of the resin used for the solid electrolyte membrane 11. This is to facilitate the movement of the generated protons. The anode gas diffusion layer 14 is made of a thin film made of, for example, a porous carbon material, and specifically made of carbon paper or carbon fiber. Note that a negative electrode lead 16 b that is electrically connected to an end of the anode gas diffusion layer 14 extends outward.

An exhaust channel (not shown) is provided on the anode side, and CO ₂ gas as a by-product is discharged out of the reaction system through the exhaust channel. Further, it is desirable that the negative electrode lead 16b has a large number of openings and gaps and does not obstruct the diffusion of fuel component gas and by-product gas (CO ₂ ).

  The cathode has a cathode catalyst layer electrode 13 and a cathode gas diffusion layer 15. The cathode catalyst layer electrode 13 reduces oxygen and reacts electrons with protons generated in the anode catalyst layer electrode 12 to generate water. For example, the anode catalyst layer electrode 12 and the gas diffusion layer 14 described above are used. It is configured in the same way. That is, the cathode has a laminated structure in which a cathode catalyst layer electrode 13 made of carbon powder containing a catalyst and a cathode gas diffusion layer 15 (gas permeable layer) made of a porous carbon material are stacked in this order from the solid electrolyte membrane 11 side. I am doing. The catalyst used for the cathode catalyst layer electrode 13 is the same as that of the anode catalyst layer electrode 12, and the anode catalyst layer electrode 12 may contain fine particles of resin used for the solid electrolyte membrane 11. It is the same. Note that a positive electrode lead 16 a that is electrically connected to the end of the cathode gas diffusion layer 15 extends outward.

  The proton conducting membrane 11 is for transporting protons generated in the anode catalyst layer electrode 12 to the cathode catalyst layer electrode 12 and is made of a material that does not have electron conductivity and can transport protons. Yes. For example, it is composed of a polyperfluorosulfonic acid resin film, specifically, a Nafion film manufactured by DuPont, a Flemion film manufactured by Asahi Glass, or an Aciplex film manufactured by Asahi Kasei Kogyo. In addition to polyperfluorosulfonic acid-based resin films, copolymer films of trifluorostyrene derivatives, polybenzimidazole films impregnated with phosphoric acid, aromatic polyether ketone sulfonic acid films, or aliphatic hydrocarbon-based films You may make it comprise the electrolyte membrane 11 which can transport protons, such as a resin container.

  Inside the liquid fuel storage chamber 27, a liquid fuel impregnation layer (not shown) laminated on the liquid fuel storage chamber 27 side of a gas-liquid separation membrane (not shown) is provided. As the liquid fuel-impregnated layer, for example, multi-rigid fibers such as porous polyester fiber and porous olefin resin, and open-cell porous resin are preferable. In addition to the polyester fiber, it may be composed of various water-absorbing polymers such as acrylic resin, and is composed of a material that can hold the liquid by utilizing the permeability of the liquid, such as a sponge or an aggregate of fibers. . The liquid fuel-impregnated layer is effective for supplying an appropriate amount of fuel regardless of the posture of the main body.

  The liquid fuel storage chamber 27 is made up of a space of a predetermined capacity, the periphery of which is defined by the protective cover 3 and a frame (not shown), and a fuel supply port 21 is opened at an appropriate position in this space. For example, a bayonet type coupler 23 is attached to the fuel supply port 21, and the fuel supply port 21 is closed by the coupler 23 except when fuel is supplied. The coupler 23 on the fuel cell body side is formed in a shape such that a nozzle (not shown) on the external cartridge side can be liquid-tightly engaged. For example, when the nozzle is pushed into the coupler 23 while the outer peripheral groove of the cartridge nozzle is guided by engaging with the protrusion of the coupler 23 on the fuel cell body side, the nozzle and the built-in valve of the coupler 23 are opened, respectively. The path communicates with the flow path on the fuel cell main body side, and the liquid fuel flows into the liquid fuel storage chamber 27 from the fuel supply port 21 through the transport tube by the internal pressure of the cartridge.

  The periphery of the vaporizing chamber (not shown) is defined by a spacer and a gas-liquid separation film (not shown). In order to withstand the tightening of the caulking process and prevent deformation, the peripheral edge portion of the spacer is formed in a U-shaped cross section, and a space having a predetermined width as a vaporizing chamber is secured.

  A plurality of vaporized fuel supply ports 28 are opened on the upper surface of the spacer. These vaporized fuel supply ports 28 penetrate the negative electrode lead 16b and communicate with the anode gas diffusion layer 14 side. When a part of the liquid fuel in the liquid fuel storage chamber 27 is gasified, the fuel gas component enters the vaporization chamber through the gas-liquid separation membrane, and further passes through the vaporized fuel supply port 28 from the vaporization chamber to the anode gas diffusion layer. 14 is introduced to contribute to the power generation reaction.

  The unit cell of the fuel cell includes an electrolyte membrane 11, an anode, and a cathode. The anode and the cathode are opposed to each other with the electrolyte membrane 11 interposed therebetween. The cathode has a cathode catalyst layer electrode 13 and a cathode gas diffusion layer 15. The cathode catalyst layer electrode 13 reduces oxygen and reacts electrons with protons generated in the anode catalyst layer electrode 12 to generate water. For example, the anode catalyst layer electrode 12 and the gas diffusion layer 14 described above are used. It is configured in the same way. That is, the cathode has a laminated structure in which a cathode catalyst layer electrode 12 made of carbon powder containing a catalyst and a cathode gas diffusion layer 15 (gas permeable layer) made of a porous carbon material are stacked in this order from the solid electrolyte membrane 11 side. I am doing. The catalyst used for the cathode catalyst layer electrode 12 is the same as that of the anode catalyst layer electrode 13, and the anode catalyst layer electrode 12 may contain fine particles of resin used for the solid electrolyte membrane 11. It is the same. Note that a positive electrode lead 16 b that conducts to an end of the cathode gas diffusion layer 15 extends outward. A plurality of vent holes 24 are formed in the cathode-side protective cover 2, and communicate with the air permeable layer 26.

  The anode has an anode catalyst layer electrode 12 and an anode gas diffusion layer 14. The anode catalyst layer electrode 12 oxidizes the fuel supplied through the gas diffusion layer 14 to extract electrons and protons from the fuel, and the laminated structure in which the catalyst layer electrode 12 and the gas diffusion layer 14 are stacked. I am doing. The anode catalyst layer electrode 12 is made of, for example, carbon powder containing a catalyst. Examples of the catalyst include fine particles of platinum (Pt), transition metals such as iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru) and molybdenum (Mo), oxides thereof, and alloys thereof. Are used. However, it is preferable that the catalyst is made of an alloy of ruthenium and platinum, since inactivation of the catalyst due to adsorption of carbon monoxide (CO) can be prevented.

  The anode catalyst layer electrode 12 preferably includes fine particles of resin used for the solid electrolyte membrane 11 described later. This is to facilitate the movement of the generated protons. The anode gas diffusion layer 14 is made of a thin film made of, for example, a porous carbon material, and specifically made of carbon paper or carbon fiber. Note that a negative electrode lead 16 a that is electrically connected to the end of the anode gas diffusion layer 14 extends outward.

  The anode gas diffusion layer 14 and the anode catalyst layer electrode 12 are substantially the same size, and both are overlapped and heat-press molded so as to be in close contact with each other, so that each fuel supply port 28 eventually becomes an anode catalyst layer electrode. In the vicinity of the 12 end portions (short sides) in the longitudinal direction, openings are made at positions corresponding to one-to-one. In the present embodiment, each anode catalyst layer electrode 12 has an elongated rectangular shape with an aspect ratio of 3 to 8.

  As shown in FIGS. 3A and 3B, in the present embodiment, catalyst layer electrodes E1 to E6 constituting six unit cells are arranged side by side on the same plane based on a common proton conducting membrane 11. . On the anode side, as shown in FIGS. 3A and 4, the gap between the six anode catalyst layer electrodes 12 (E1 to E6) is covered with two layers of a hydrophilic membrane 41 / hydrophobic membrane. . Also on the cathode side, the gap between the six cathode catalyst layer electrodes 13 (E1 to E6) is covered with two layers of hydrophilic membrane 41 / hydrophobic membrane 42 as shown in FIGS. It was. In addition, the mutual space | interval of the adjacent catalyst layer electrodes E1-E6 is about 1 mm. Each of the catalyst layer electrodes E1 to E6 has a length of 70 mm, a width of 9 mm, and a thickness of 0.8 mm. The film thickness of the hydrophilic film is 0.2 mm. The thickness of the hydrophobic film is 0.2 mm.

  In the present embodiment, a polymer material of perfluorocarbon sulfonic acid (Nafion (registered trademark), manufactured by DuPont) is used as a hydrophilic membrane material, and a fluorine-containing rubber (tetrafluoroethylene (TFE) is used as a hydrophobic membrane material. ) -Hexafluoropropylene (HFP) copolymer polymer material was used.

  A membrane / electrode assembly having a two-layer seal structure of a hydrophilic membrane 41 and a hydrophobic membrane 42 can be produced as follows.

  First, an anode catalyst layer electrode and a cathode catalyst layer electrode made of carbon paper or the like carrying a catalyst are disposed on both sides of a proton conducting membrane, and are integrated by hot pressing. Next, a hydrophilic polymer material is selectively applied or laminated on the area between the electrodes using a screen printing method or a photolithography method. Further, a hydrophobic polymer material is selectively applied or laminated on the interelectrode area by using a screen printing method or a photolithography method. These polymer films may be formed on each side or simultaneously on both sides. Further, these hydrophilic polymer materials or hydrophobic polymer materials can be applied by a method of sticking a film or tape.

  In the fuel cell of the present embodiment, the mutual gap between adjacent catalyst layer electrodes arranged in a plane is covered with a hydrophobic film, so that crossover of unreacted fuel from the anode side to the cathode side can be effectively suppressed. For this reason, stable power generation operation is performed while suppressing a decrease in power generation efficiency, and the reliability as a built-in power source of the portable electronic device is improved.

  The power generation efficiency of the cell of Example 1 and the cell of the comparative example was examined.

  Using Example 1 as a fuel cell evaluation cell having a two-layer seal structure in the inter-electrode area shown in FIGS. 3 and 4, one catalyst layer electrode E1 to E6 having an aspect ratio of 1: 5.8 is provided. 10 ml of methanol having a purity of 99.9 wt% was supplied to the liquid fuel storage chamber 27. Then, the voltage at the time of starting of each cell and the constant voltage measurement at the time of power generation were performed. In addition, as a comparative example, using a fuel cell evaluation cell having no seal structure in the area between the electrodes, voltage measurement was performed by performing a power generation operation under the same conditions as in Example 1.

The temperature of the battery surface (on the cell case cover) at a constant voltage was measured, and the temperature of the comparative example when the temperature of Example 1 was taken as 100 was calculated. In addition, the fuel utilization efficiency calculated from the amount of fuel used from the remaining fuel was compared with the amount of fuel input before the constant voltage measurement. The results are shown in Table 1.

  From the above results, it can be seen that by forming the layer of Example 1, crossover is reduced and the surface temperature of the battery is lowered. The two-layer seal structure of Example 1 also increases the utilization efficiency of the input fuel, and has the effect of suppressing wasteful consumption of fuel.

  Although various embodiments have been described above, the present invention is not limited to the above embodiments, and various modifications and combinations can be made.

The disassembled perspective view which shows the outline | summary of the fuel cell of this invention. The internal perspective sectional drawing of a fuel cell. (A) is a schematic plan view showing the membrane electrode assembly as seen from the anode side, and (b) is a schematic plan view showing the membrane electrode assembly as seen from the cathode side. The cross-sectional schematic diagram of a membrane electrode assembly.

Explanation of symbols

1 ... Fuel cell,
2, 3 ... Cell case cover,
2a ... crimping part,
2b ... the crimped bent part,
10 ... cell structure,
11 ... Solid electrolyte membrane (proton conductive membrane),
12 ... anode catalyst layer electrode,
13 ... Cathode catalyst layer electrode,
14 ... anode gas diffusion layer, 15 ... cathode gas diffusion layer,
16a: positive electrode lead, 16b: negative electrode lead,
17, 18 ... seal member,
20 ... Cell assembly,
21 ... refueling port,
24 ... vents,
25 ... spacer,
26 ... an air permeable layer,
27 ... Liquid fuel storage chamber,
28 ... Fuel supply port,
30 ... Case cover,
41 ... hydrophilic membrane,
42 ... hydrophobic membrane,
E1 to E6 ... catalyst layer electrodes.

Claims (3)

A proton conducting membrane;
A plurality of anode catalyst layer electrodes that are arranged in a plane on one side of the proton conducting membrane and are adjacent to each other with a space therebetween;
A plurality of cathode catalyst layer electrodes that are arranged in a plane on the other surface of the proton conductive membrane and are opposed to the anode catalyst layer electrode with the proton conductive membrane interposed therebetween;
Liquid fuel supply means for supplying liquid fuel to the anode catalyst layer electrode;
An oxidant supply means for supplying an oxidant to the cathode catalyst layer electrode;
A fuel cell comprising:
A hydrophilic membrane that is provided in an inter-gap between adjacent anode catalyst layer electrodes and an inter-gap between the cathode catalyst layer electrodes and covers the proton conducting membrane;
A hydrophobic membrane that is provided in a mutual gap between the adjacent anode catalyst layer electrodes and a mutual gap between the cathode catalyst layer electrodes, covers the hydrophilic membrane, and does not allow liquid fuel to permeate the cathode catalyst layer electrode side;
A fuel cell comprising: 2. The fuel cell according to claim 1, wherein the hydrophilic membrane and the hydrophobic membrane each include a hydrophilic polymer and a hydrophobic polymer sequentially laminated on a common proton conducting membrane. The cell structure including the proton conductive membrane, the anode catalyst layer electrode, and the cathode catalyst layer electrode is integrally formed by caulking and having a main surface with a vent hole for supplying air to the cathode catalyst layer electrode. The fuel cell according to claim 1, further comprising a protective cover having a caulking portion to be attached.

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