JP2004235084A - Liquid fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid fuel cell that can stably generate electricity without the occurrence of leakage of liquid fuel even if the fuel cell is downsized. <P>SOLUTION: In the fuel cell comprising a positive electrode 4a to reduce oxygen, a negative electrode 4c to oxidize the liquid fuel, and a solid electrolyte layer 4b disposed between the positive electrode 4a and the negative electrode 4c, the electrolyte layer 4b has an area with a largeness of 150-250% of that of the negative electrode 4c, and a packing 8 for preventing leakage of the liquid fuel is disposed at a part where the electrolyte layer 4b is exposed when seen from a side of the negative electrode 4c. It is preferable that the positive and the negative electrodes 4a, 4c are disposed at the central section of the electrolyte layer 4b, and the positive and the negative electrodes 4a, 4b and the electrolyte layer 4b are formed in rectangular shape respectively. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a liquid fuel cell using a liquid as fuel.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the spread of cordless devices such as personal computers and mobile phones, there is a demand for smaller and higher capacity secondary batteries as power sources. At present, lithium ion secondary batteries have been put to practical use as secondary batteries having a high energy density and can be reduced in size and weight, and demand for portable power sources is increasing. However, depending on the type of cordless device used, this lithium secondary battery has not yet reached a level where sufficient continuous use time is guaranteed.
[0003]
Under such circumstances, a fuel cell can be cited as a cell that can meet the above demand.However, in the conventional fuel cell, since a single cell is formed by stacking cells, the cell becomes bulky, and also requires oxygen and fuel. It must be supplied to each of the positive electrode and the negative electrode by circulation, and an auxiliary device for fuel supply is required. As a result, the size of the battery is much larger than that of a small secondary battery such as a lithium ion battery, and there is a problem in using the battery as a small portable power supply.
[0004]
Here, although the output is reduced by removing the auxiliary device for forcibly flowing the oxygen and the fuel, the size of the fuel cell can be reduced. However, there is a limit to miniaturization in a fuel cell having a stacked structure in which the integrated electrodes and electrolytes are stacked. On the other hand, when a plurality of integrated electrodes and electrolytes are arranged such that the positive electrode (air electrode) and the negative electrode (fuel electrode) are respectively planar, the fuel tank can be shared, the contact with air is improved, and The battery can be reduced in size as compared with the structure (for example, see Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-56855
[Problems to be solved by the invention]
However, in such a case, if the electrode / electrolyte assemblies are electrically connected in series, there is a problem that leakage of liquid fuel occurs between the electrode / electrolyte assemblies particularly when a liquid fuel is used.
[0007]
The present invention provides a liquid fuel cell that can stably generate power without causing leakage of liquid fuel even when the size is reduced.
[0008]
[Means for Solving the Problems]
The present invention is a liquid fuel cell including a positive electrode for reducing oxygen, a negative electrode for oxidizing fuel, and a solid electrolyte disposed between the positive electrode and the negative electrode,
The area of the solid electrolyte is 150% or more and 250% or less with respect to the area of the negative electrode,
Provided is a liquid fuel cell in which a sealing material for preventing liquid fuel from leaking is disposed at a portion where the solid electrolyte is exposed when viewed from the negative electrode side.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0010]
One embodiment of the liquid fuel cell of the present invention is a liquid fuel cell including a positive electrode for reducing oxygen, a negative electrode for oxidizing fuel, and a solid electrolyte disposed between the positive electrode and the negative electrode. Is set to a size of 150% or more and 250% or less, more preferably 170% or more and 230% or less, more preferably 180% or more and 220% or less with respect to the area of the negative electrode, A seal member for preventing liquid fuel from leaking is disposed at a portion where the solid electrolyte is exposed when viewed from the negative electrode side.
[0011]
If the area of the solid electrolyte is less than 150% of the area of the negative electrode, the area for disposing the sealing material for preventing the liquid fuel from leaking cannot be sufficiently secured, and the liquid fuel may leak. On the other hand, if it exceeds 250%, the whole battery becomes large, and the battery cannot be downsized.
[0012]
Further, it is preferable that the positive electrode and the negative electrode are arranged at the center of the solid electrolyte. This is because the arrangement of the sealing material for preventing liquid leakage becomes easy. Here, when the positive electrode and the negative electrode are arranged at the center of the solid electrolyte, the positive electrode and the negative electrode do not protrude from the solid electrolyte, and are formed by the outer periphery of the positive electrode and the negative electrode and the outer periphery of the solid electrolyte. It means that the annular portion is arranged so as to be symmetrical in front and rear, left and right.
[0013]
The shapes of the positive electrode, the negative electrode, and the solid electrolyte can be rectangular (rectangular), square, elliptical, and the like, but are preferably rectangular.
[0014]
Further, it is preferable that the positive electrode and the negative electrode are joined to each other via a solid electrolyte to form an integrated electrode-electrolyte product, and that the plurality of integrated electrode-electrolyte products are preferably arranged on the same plane. Thereby, the thickness of the battery can be further reduced.
[0015]
Further, it is preferable that the liquid fuel cell of the present embodiment further includes a liquid fuel storage unit that stores the liquid fuel. This eliminates the need for refueling for a certain period of time, so that the liquid fuel cell can be used as a power source for the portable electronic device.
[0016]
As the liquid fuel, an aqueous methanol solution, an aqueous ethanol solution, dimethyl ether, an aqueous sodium borohydride solution, an aqueous potassium borohydride solution, an aqueous lithium borohydride solution and the like can be used, and among them, an aqueous methanol solution is particularly preferable. This is because it is currently the best in terms of both discharge characteristics and price.
[0017]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
FIG. 1 is an exploded perspective view showing one example of the liquid fuel cell of the present invention. The electrode / electrolyte integrated body 4 includes a rectangular sheet-shaped positive electrode 4a, a rectangular sheet-shaped negative electrode (not shown), and a rectangular sheet-shaped solid electrolyte layer 4b provided between the positive electrode 4a and the negative electrode. Have been. FIG. 2 is a perspective view of an example of the electrode / electrolyte integrated body 4 viewed from the negative electrode 4c side. The area of the solid electrolyte layer 4b is set to be 150% or more and 250% or less with respect to the areas of the positive electrode 4a and the negative electrode 4c. At a portion of the solid electrolyte layer 4b protruding from the negative electrode 4c, a packing 8, which is a sealing material for preventing leakage of liquid fuel described later, is disposed.
[0019]
The positive electrode 4a is formed by stacking, for example, a diffusion layer made of a porous carbon material and a catalyst layer made of carbon powder supporting a catalyst. The positive electrode has a function of reducing oxygen, and for the catalyst, for example, platinum fine particles, alloy fine particles of platinum such as iron, nickel, cobalt, tin, ruthenium, or gold and the like are used. Further, the catalyst layer may contain polytetrafluoroethylene (PTFE) resin particles or proton exchange resin particles in some cases. As the proton exchange resin particles, for example, a polyperfluorosulfonic acid resin, a sulfonated polyethersulfonic acid resin, a sulfonated polyimide resin, or the like can be used. In some cases, a paste of carbon powder containing PTFE resin particles is applied on the catalyst layer side of the diffusion layer to improve water repellency.
[0020]
The solid electrolyte layer 4b is made of a material having no electron conductivity and capable of transporting protons. For example, a polyperfluorosulfonic acid resin membrane, specifically, "Nafion" (trade name) manufactured by DuPont, "Flemion" (trade name) manufactured by Asahi Glass Co., Ltd., "Aciplex" (trade name) manufactured by Asahi Kasei Corporation The solid electrolyte layer 4b can be formed by (name). In addition, it can be constituted by a sulfonated polyether sulfonic acid resin film, a sulfonated polyimide resin film, a sulfuric acid-doped polybenzimidazole film, or the like.
[0021]
The negative electrode 4c includes a diffusion layer and a catalyst layer, and has a function of generating protons from the fuel, that is, a function of oxidizing the fuel. For example, the negative electrode 4c can be configured similarly to the positive electrode.
[0022]
The positive electrode 4a, the solid electrolyte layer 4b, and the negative electrode 4c are joined by hot pressing or the like to form an electrode / electrolyte integrated body 4.
[0023]
A cover plate 1 serving as a lid is disposed on the side of the positive electrode 4a opposite to the solid electrolyte layer 4b. The cover plate 1 is made of, for example, PTFE, hard polyvinyl chloride, polypropylene, polyethylene, polyallylamide, polyallyl ether ketone, polyether ether ketone, polyether ketone ether ketone ketone, polyether ketone ketone, polyether imide, polyphthalate It can be formed of a synthetic resin such as an amide or a glass epoxy resin.
[0024]
Furthermore, when it is desired to further improve the strength of the cover plate 1, the cover plate 1 can be formed from a metal coated with an electrically insulating material. As the metal, for example, carbon steel, alloy steel, cemented carbide, aluminum alloy, magnesium alloy, titanium alloy, nickel alloy, or the like having a Young's modulus of 100000 MPa or more is used.
[0025]
In addition, as the electrically insulating substance, for example, high-molecular polyethylene, phenol resin, alkyd resin, vinyl resin, urethane resin, epoxy resin, acrylic resin, chlorinated rubber, and the like are used.
[0026]
Air holes 2 are provided in portions of the cover plate 1 that are in contact with the positive electrode 4a. This allows the positive electrode to come into contact with air, and oxygen is reduced at the positive electrode. A mesh-shaped positive electrode current collector 3 is arranged around a portion of the air hole 2 in contact with the positive electrode 4a. The positive electrode current collector 3 has, for example, fine particles of platinum, gold, stainless steel, nickel, or the like, or fine particles of an alloy of platinum and gold or the like adhered to the inner surface of the cover plate 1 using an epoxy resin, silicone, or the like in a thin film shape. Or a mixture of fine particles of these metals and an epoxy resin or silicone, etc. applied to the inner surface of the cover plate 1 as a thin film, or fine particles of these metals are subjected to sputtering, vacuum deposition, chemical plating, etc. For example, a thin film attached to the inner surface of the cover plate 1 is used. In addition, the positive electrode current collector 3 includes a plate-shaped rectangular portion 10.
[0027]
A fuel tank 5 for storing a liquid fuel is disposed on a side of the negative electrode 4c opposite to the solid electrolyte layer 4b. The fuel tank 5 can be formed of the same material as the cover plate 1. Examples of the liquid fuel include methanol aqueous solution, ethanol aqueous solution, dimethyl ether, sodium borohydride aqueous solution, potassium borohydride aqueous solution, and lithium borohydride aqueous solution.
[0028]
Further, fuel supply holes 7 are provided in portions of the fuel tank 5 which are in contact with the negative electrode 4c. This allows the liquid fuel to come into contact with the negative electrode, and the liquid fuel is oxidized at the negative electrode. A mesh-shaped negative electrode current collector 6 is arranged around a portion of the fuel supply hole 7 which is in contact with the negative electrode 4c. The negative electrode current collector 6 can be formed in the same manner as the positive electrode current collector 3. Note that the negative electrode current collector 6 includes a plate-shaped rectangular portion 11.
[0029]
Further, a rectangular annular packing 8 is provided around the fuel supply hole 7. The packing 8 is a sealing material for preventing liquid fuel from leaking, and is disposed between a portion of the solid electrolyte layer 4 b protruding from the negative electrode 4 c and a peripheral portion of the fuel supply hole 7. This makes it possible to more reliably prevent the liquid fuel from leaking from the gap between the fuel tank 5 and the electrode / electrolyte integrated body 4. As the material of the packing 8, for example, natural rubber, butadiene rubber, styrene rubber, butyl rubber, ethylene propylene rubber, nitrile rubber, rubber such as acrylic rubber, urethane rubber, silicone rubber, fluorine rubber, or PTFE resin is used. Can be.
[0030]
Further, gas-liquid separation holes 9 are arranged around the fuel tank 5 and the cover plate 1. Each of the gas-liquid separation holes 9 of the fuel tank 5 is provided with a gas-liquid separation film 9a. The gas-liquid separation film 9a is formed of a PTFE thin film having pores, and can release carbon dioxide and the like generated by a discharge reaction to the outside without leaking liquid fuel.
[0031]
By laminating the cover plate 1, the electrode / electrolyte integrated material 4, and the fuel tank 5, the rectangular portion 10 of the positive electrode current collector 3 adjacent to the electrode / electrolyte integrated material 4 is arranged on the negative electrode current collector 6. An electrode / electrolyte integrated material 4 is disposed below the positive electrode current collector 3. That is, the positive electrode current collector 3 and the negative electrode current collector 6 are in contact with each other through the rectangular portions 10 and 11, and the adjacent electrode / electrolyte integrated products 4 are electrically connected in series. Although not shown, the cover plate 1 and the fuel tank 5 can be joined at an arbitrary pressure using bolts and nuts. As described above, an example of the liquid fuel cell of the present invention is configured.
[0032]
【Example】
Next, the present invention will be described more specifically with reference to examples.
[0033]
(Example 1)
A liquid fuel cell having the same configuration as that of FIG. 1 was manufactured as follows.
[0034]
The positive electrode was formed of a diffusion layer composed of carbon paper having a porosity of 78% and a thickness of 280 μm, and a catalyst layer having a thickness of 50 μm formed by supporting platinum particles having a particle diameter of 3 nm on carbon particles having a particle diameter of 30 nm. The negative electrode is composed of a diffusion layer composed of carbon paper having a porosity of 78% and a thickness of 280 μm, and a catalyst layer having a thickness of 50 μm formed by supporting platinum-ruthenium alloy particles having a particle diameter of 5 nm on carbon particles having a particle diameter of 30 nm. Formed. For the solid electrolyte layer, "Nafion" (trade name) manufactured by DuPont was used.
[0035]
The size of each of the positive electrode and the negative electrode was 40 mm in length, 10 mm in width, and 400 mm ² in area. The size of the solid electrolyte layer was 44 mm long, 14 mm wide, and 616 mm ² in area. Therefore, the ratio of the area of the solid electrolyte layer to the area of the negative electrode is 154%.
[0036]
A 3% by mass aqueous methanol solution was used as the liquid fuel, and a rectangular annular butadiene rubber packing having a diameter of 2 mm, a length of 42 mm and a width of 12 mm was used as the packing.
[0037]
The cover plate was formed from a plate-like PTEF having a length of 70 mm, a width of 100 mm, and a thickness of 1 mm. The fuel tank was formed from box-shaped PTFE (thickness: 2 mm) having a length of 70 mm, a width of 100 mm, and a depth of 7 mm. The cover plate and the fuel tank were joined at a pressure of 1 MPa. A 30 μm thick stainless steel was used for the positive electrode current collector. The negative electrode current collector used was stainless steel having a thickness of 30 μm. The overall size of the positive electrode current collector and the negative electrode current collector was 40 mm in length and 20 mm in width, and the size of the rectangular portion was 40 mm in length and 10 mm in width.
[0038]
FIG. 3 is a plan view showing a state where the cover plate is removed from the liquid fuel cell of the present embodiment. In FIG. 3, reference numeral 4 denotes an integrated electrode / electrolyte, 4a denotes a positive electrode, and 5 denotes a fuel tank. In FIG. 3, illustration of the gas-liquid separation membrane (9a) is omitted.
[0039]
(Example 2)
Except that the size of the solid electrolyte layer was 50 mm in length, 20 mm in width and 1000 mm ² in area, and the sizes of the positive electrode current collector and the negative electrode current collector were 40 mm in length and 18 mm in width, the same as in Example 1 A liquid fuel cell was manufactured. In this embodiment, the ratio of the area of the solid electrolyte layer to the area of the negative electrode is 250%.
[0040]
FIG. 4 is a plan view showing a state where the cover plate is removed from the liquid fuel cell of the present embodiment in the same manner as FIG.
[0041]
(Comparative Example 1)
A liquid fuel cell was produced in the same manner as in Example 1, except that the size of the solid electrolyte layer was 42 mm long, 12 mm wide and 504 mm ² in area. In this comparative example, the ratio of the area of the solid electrolyte layer to the area of the negative electrode is 126%.
[0042]
FIG. 5 is a plan view showing a state where the cover plate is removed from the liquid fuel cell of this comparative example in the same manner as FIG.
[0043]
(Comparative Example 2)
The size of the solid electrolyte layer is 60 mm long, 30 mm wide, 1800 mm ² in area, the size of the cover plate is 80 mm long, 150 mm wide, 1 mm thick, and the size of the fuel tank is 80 mm long, 150 mm wide, A liquid fuel cell was manufactured in the same manner as in Example 1 except that the depth was 7 mm and the sizes of the positive electrode current collector and the negative electrode current collector were 40 mm in length and 24 mm in width. In this comparative example, the ratio of the area of the solid electrolyte layer to the area of the negative electrode is 450%.
[0044]
FIG. 6 is a plan view showing a state where the cover plate is removed from the liquid fuel cell of this comparative example in the same manner as FIG.
[0045]
When the liquid fuel cells of Examples 1 and 2 and Comparative Examples 1 and 2 fabricated as described above were oscillated with a sine wave of 100 Hz for 10 minutes, leakage of liquid fuel was observed in Comparative Example 1. Further, in Comparative Example 2, no leakage of the fuel cell was recognized, but the size of the cell was increased while the electrode area was the same as in Example 1 and Example 2. On the other hand, in Examples 1 and 2, no leakage of liquid fuel was observed at all, and the size of the battery could be kept small.
[0046]
【The invention's effect】
As described above, the present invention can provide a liquid fuel cell capable of stably generating power without causing leakage of liquid fuel even when the cell is downsized.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view showing an example of a liquid fuel cell of the present invention.
FIG. 2 is a perspective view of an example of an electrode / electrolyte integrated body of the present invention as viewed from a negative electrode side.
FIG. 3 is a plan view showing a state where a cover plate is removed from the liquid fuel cell according to the first embodiment.
FIG. 4 is a plan view showing a state in which a cover plate is removed from the liquid fuel cell according to the second embodiment.
FIG. 5 is a plan view of the liquid fuel cell of Comparative Example 1 with a cover plate removed.
FIG. 6 is a plan view showing a state where a cover plate is removed from the liquid fuel cell of Comparative Example 2.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 cover plate 2 air hole 3 positive electrode current collector 4 integrated electrode / electrolyte 4a positive electrode 4b solid electrolyte layer 4c negative electrode 5 fuel tank 6 negative electrode current collector 7 fuel supply hole 8 packing 9 gas-liquid separation hole 9a gas-liquid separation film 10 Rectangular part 11 of positive electrode current collector Rectangular part of negative electrode current collector

Claims (6)

A liquid fuel cell including a positive electrode for reducing oxygen, a negative electrode for oxidizing fuel, and a solid electrolyte disposed between the positive electrode and the negative electrode,
The area of the solid electrolyte is 150% or more and 250% or less with respect to the area of the negative electrode,
A liquid fuel cell, wherein a seal member for preventing liquid fuel from leaking is disposed at a portion where the solid electrolyte is exposed when viewed from the negative electrode side. The liquid fuel cell according to claim 1, wherein the positive electrode and the negative electrode are arranged at a center of the solid electrolyte. 3. The liquid fuel cell according to claim 1, wherein the positive electrode, the negative electrode, and the solid electrolyte are each formed in a rectangular shape. The said positive electrode, the said negative electrode, and the said solid electrolyte form an electrode / electrolyte integrated body, The several electrode / electrolyte integrated bodies are arrange | positioned on the same plane, The any one of Claims 1-3. Liquid fuel cell. The liquid fuel cell according to any one of claims 1 to 4, further comprising a liquid fuel storage unit that stores the liquid fuel. The liquid fuel cell according to claim 1, wherein the liquid fuel is an aqueous methanol solution.

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