JP2004185919A - Liquid fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to provide a compact liquid fuel cell capable of efficiently removing carbon dioxide generated by a cell reaction and with a large energy density. <P>SOLUTION: The cell includes a positive electrode 8 reducing oxygen, a negative electrode 9 oxidizing fuel, a solid electrolyte 10 fitted between the positive electrode 8 and the negative electrode 9, and a liquid fuel storage part 3 storing liquid fuel 4, with an absorbent 6 capable of absorbing the carbon dioxide arranged inside the liquid fuel storage part 3. As the absorbent 6, an OH type anion exchange resin is preferable. Further, the absorbent 6 is preferred to be in the form of a powder, granular, thin-film or fibrous state, or the like. Furthermore, the liquid fuel storage part 3 is preferred to be attachable and detachable. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell using a liquid as a 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 has been 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 ion secondary battery has not yet reached a level that guarantees sufficient continuous use time.
[0003]
In such a situation, a fuel cell using a solid polymer electrolyte is expected as a battery that can meet the above demand. Above all, direct methanol fuel cells, which directly use liquid fuel for the reaction of the cell, can be miniaturized because auxiliary equipment such as a fuel supply device can be eliminated by using capillary force or the like to supply liquid fuel. It is expected to be a promising portable power source in the future (for example, see Patent Document 1).
[0004]
[Patent Document 1]
JP 2000-268836 A
[Problems to be solved by the invention]
In the direct methanol fuel cell, upon discharge, oxygen is reduced at the positive electrode to generate water, and methanol is oxidized at the negative electrode to generate carbon dioxide. When the auxiliary device is not used, the liquid fuel does not flow automatically, so that the carbon dioxide generated by the cell reaction continues to stay inside the cell together with the liquid fuel. Therefore, when the fuel cell is continuously used, the internal pressure of the cell is increased, and the remaining carbon dioxide impedes the supply of the liquid fuel to the negative electrode.
[0006]
In order to solve this problem, a method has conventionally been adopted in which a gas-liquid separation hole provided with a gas-liquid separation membrane is provided in a battery to discharge generated carbon dioxide from the gas-liquid separation hole to the outside of the battery.
[0007]
However, in this method, when the concentration of methanol is increased in order to improve the energy density of the fuel cell, a new problem arises in that methanol leaks to the outside through the gas-liquid separation membrane.
[0008]
The present invention provides a small-sized liquid fuel cell capable of efficiently removing carbon dioxide generated by a cell reaction, having a high energy density, and a small size.
[0009]
[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, an electrolyte provided between the positive electrode and the negative electrode, and a liquid fuel storage unit,
An adsorbent capable of adsorbing carbon dioxide is disposed inside the liquid fuel storage unit.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0011]
One embodiment of the present invention is a liquid fuel cell including a positive electrode for reducing oxygen, a negative electrode for oxidizing fuel, an electrolyte provided between the positive electrode and the negative electrode, and a liquid fuel storage unit. An adsorbent capable of adsorbing carbon dioxide is disposed inside the fuel storage unit.
[0012]
This makes it possible to effectively remove carbon dioxide generated by the battery reaction of the negative electrode, suppress an increase in the internal pressure of the battery, and do not hinder the supply of the liquid fuel to the negative electrode. Further, since there is no need to provide a gas-liquid separation hole having a gas-liquid separation membrane, even when a high-concentration liquid fuel is used, the liquid fuel does not leak out of the battery, and the energy density of the battery can be improved.
[0013]
Examples of the adsorbent include OH-type anion exchange resin for chemically adsorbing, activated carbon, zeolite, hollow fiber membrane, silica gel, and cellulose, pulp, coconut, coal, phenol, and synthetic fibers for physically adsorbing. As a carbon fiber material as a raw material, hydroxides, oxides, carbonates and the like of alkali metals or alkaline earth metals can be used as those which undergo chemical adsorption and chemical reaction.
[0014]
Among these, an OH-type anion exchange resin is particularly preferred. This is because the OH-type anion exchange resin has a large carbon dioxide adsorbing power and can be disposed by coating in a battery container, so that its handling is easy. Furthermore, acidic compounds such as formic acid, which are intermediate products of the battery reaction of the negative electrode, can be removed by an acid-base reaction.
[0015]
As the OH-type anion exchange resin, a commercially available Cl-type anion exchange resin obtained by immersing a commercially available Cl-type anion exchange resin in a KOH aqueous solution or an NaOH aqueous solution and ion-exchanging from Cl-type to OH-type can be used. As a commercially available Cl-type anion exchange resin, for example, as a fluorine-based anion exchange resin membrane having ethylene tetrafluoride as a skeleton, “TOSFLEX” (trade name) manufactured by Tosoh Corp. As the hydrogen-based anion exchange resin membrane, "Selemion" (trade name) manufactured by Asahi Glass Co., Ltd. and "Neosepta" (trade name) manufactured by Tokuyama Corporation, and Rohm and Haas as powdered or granular hydrocarbon anion exchange resin "Amberlite" (trade name) manufactured by the company can be used. In addition, a quaternary ammonium salt type anion exchange resin having a polyepichlorohydrin skeleton described in JP-A-9-501722 can be used.
[0016]
As a form when the anion exchange resin is disposed inside the liquid fuel storage unit, a method in which an anion exchange resin previously formed into a thin film is attached to the inner wall portion of the liquid fuel storage unit, a powdery or granular anion exchange resin Is dispersed in a polymer binder solution such as polytetrafluoroethylene (PTFE), and then applied to the inner wall of the liquid fuel storage unit. The powder, granular, or fibrous anion exchange resin is directly stored in the liquid fuel storage For example, there is a method of arranging it inside the unit.
[0017]
Further, in the liquid fuel cell of the present embodiment, it is preferable that the liquid fuel storage unit is detachable. This is because the liquid fuel can be easily exchanged and replenished.
[0018]
Further, it is preferable that the positive electrode, the negative electrode, and the electrolyte of the liquid fuel cell of the present embodiment form an electrode-electrolyte integrated body, and that the plurality of electrode-electrolyte integrated bodies be arranged on the same plane. This is because the thickness of the battery can be reduced.
[0019]
The positive electrode is configured by, for example, stacking a diffusion layer containing a porous carbon material and a catalyst layer containing a carbon powder supporting a catalyst. The catalyst layer has a function of electrochemically reducing oxygen, and the catalyst includes, for example, platinum fine particles and alloy fine particles of platinum with iron, nickel, cobalt, tin, ruthenium, or gold. Used. The catalyst layer may include a PTFE resin or a proton exchange resin in some cases. As the proton exchange resin, for example, a polyperfluorosulfonic acid resin, a sulfonated polyethersulfonic acid resin, a sulfonated polyimide resin, or the like can be used.
[0020]
As the electrolyte, a solid electrolyte made of a material having no electron conductivity and capable of transporting protons can be used. 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 membrane can be formed by (name). Others include a sulfonated polyether sulfonic acid resin film, a sulfonated polyimide resin film, a sulfuric acid-doped polybenzimidazole film, a phosphoric acid-doped SiO ₂ film as a solid electrolyte, a hybrid film of a polymer and a solid electrolyte, or a polymer and an oxidized film. It can also be composed of a gel electrolyte impregnated with an acidic solution.
[0021]
The negative electrode is configured by, for example, laminating a diffusion layer containing a porous carbon material and a catalyst layer containing a carbon powder supporting a catalyst. This catalyst layer has a function of generating protons from the fuel, that is, a function of electrochemically oxidizing the fuel, and the catalyst includes, for example, platinum fine particles alone, ruthenium, indium, iridium, tin, and iron. Alloy fine particles of platinum with titanium, gold, silver, chromium, silicon, zinc, manganese, molybdenum, tungsten, rhenium, aluminum, lead, palladium, osmium and the like are used.
[0022]
Examples of the liquid fuel include methanol aqueous solution, ethanol aqueous solution, 1-propanol aqueous solution, 2-propanol aqueous solution, dimethyl ether aqueous solution, sodium borohydride aqueous solution, potassium borohydride aqueous solution, and lithium borohydride aqueous solution.
[0023]
As the oxidizing agent for the liquid fuel, oxygen in the air taken in through an air hole provided in a portion in contact with the positive electrode is used.
[0024]
Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a liquid fuel cell according to one embodiment of the present invention. The positive electrode 8 is configured by, for example, laminating a diffusion layer 8a made of a porous carbon material and a catalyst layer 8b made of carbon powder supporting a catalyst. The solid electrolyte 10 is made of a material having no electron conductivity and capable of transporting protons. The negative electrode 9 includes a diffusion layer 9a and a catalyst layer 9b, and has a function of generating protons from fuel, that is, a function of oxidizing fuel. For example, the negative electrode 9 can be configured in the same manner as the positive electrode 8 described above.
[0025]
The positive electrode 8, the negative electrode 9, and the solid electrolyte 10 are stacked to form an electrode-electrolyte integrated body. In addition, a plurality of the electrode / electrolyte integrated materials are provided on the same plane in the same battery container.
[0026]
A liquid fuel storage unit 3 for storing the liquid fuel 4 is provided adjacent to the negative electrode 9 on the side opposite to the solid electrolyte 10. The liquid fuel storage unit 3 can be made detachable as described above. The liquid fuel storage unit 3 can be made of, for example, a synthetic resin such as PTFE, hard polyvinyl chloride, polypropylene, or polyethylene, or a corrosion-resistant metal such as stainless steel. However, when the liquid fuel storage unit 3 is made of a metal, the surface of the liquid fuel storage unit 3 is covered with an insulator so that the respective negative electrodes disposed in the same battery container are not electrically short-circuited. There is a need to. A fuel supply hole 3a is provided in a portion of the liquid fuel storage section 3 which is in contact with the negative electrode 9, and the liquid fuel 4 is supplied to the negative electrode 9 from this portion.
[0027]
In addition, a liquid fuel impregnating material 5 that impregnates and holds the liquid fuel and supplies the liquid fuel to the negative electrode is disposed in the fuel supply hole 3a and the liquid fuel storage unit 3. Thereby, even if the liquid fuel 4 is consumed, the liquid fuel 4 can be sucked up to the fuel supply hole 3a, and the liquid fuel 4 can be completely used up. As the liquid fuel impregnating material 5, for example, glass fiber or the like can be used, but other materials may be used as long as the material does not change much in size due to fuel impregnation and is chemically stable.
[0028]
An adsorbent 6 for adsorbing carbon dioxide generated by the negative electrode 9 is disposed in a thin film or a coating form, for example, on a bottom surface of the liquid fuel storage unit 3.
[0029]
A cover plate 2 is provided on a side of the positive electrode 8 opposite to the solid electrolyte 10, and an air hole 1 is provided in a portion of the cover plate 2 in contact with the positive electrode 8. As a result, oxygen in the atmosphere comes into contact with the positive electrode 8 through the air hole 1. In FIG. 1, the illustration of a filling port for replenishing the liquid fuel is omitted.
[0030]
A current collector 7 is provided between the adjacent positive electrode 8 and negative electrode 9, and both are electrically connected. The current collector 7 has a role of electrically connecting adjacent electrode / electrolyte integrated bodies in series, and all the electrode / electrolyte integrated bodies arranged in the same battery container are electrically connected in series by the current collector 7. It is connected. The current collector 7 can be made of, for example, a noble metal such as platinum or gold, a corrosion-resistant metal such as stainless steel, or carbon.
[0031]
FIG. 2 is a sectional view of a liquid fuel cell according to another embodiment of the present invention. In the present embodiment, an adsorbent 6 for adsorbing carbon dioxide generated by the negative electrode 9 is provided on, for example, a bottom portion of the liquid fuel storage unit 3 such as a filter 6 a so that the adsorbent 6 does not scatter into the liquid fuel 4. The structure is the same as that of FIG. 1 except that the inside is filled and arranged in a powdery or granular state. The filter 6a can be formed from a microporous film or nonwoven fabric made of a polyolefin-based, polyester-based, PTFE-based, or cellulose-based material.
[0032]
FIG. 3 is a sectional view of a liquid fuel cell according to still another embodiment of the present invention. In this embodiment, for example, in the liquid fuel 4 of the liquid fuel storage unit 3, the adsorbent 6 for adsorbing the carbon dioxide generated at the negative electrode 9 is microcapsulated so that the adsorbent 6 does not scatter into the liquid fuel 4. The structure is the same as that shown in FIG. 1 except that the inside is filled and arranged in the form of powder or granules such as 6b. The microcapsules 6b can be formed from a polyvinyl alcohol (PVA) crosslinked film, a nylon film, a styrene-divinylbenzene copolymer film, a gelatin-arabic rubber film, a silica (TEOS) polymer film, or the like.
[0033]
【Example】
Hereinafter, the liquid fuel cell of the present invention will be specifically described based on examples. However, the present invention is not limited to the following examples.
[0034]
(Example 1)
A liquid fuel cell of Example 1 having a structure similar to that of FIG. 1 was manufactured as follows.
[0035]
First, a powdery Cl-type anion exchange resin “Amberlite IRA400” (trade name) manufactured by Rohm and Haas Co., Ltd. was prepared, and immersed in a 1 mol / dm ³ NaOH aqueous solution for 1 hour to form an OH-type. Was ion-exchanged. Further, a PTFE emulsion solution “D1” (trade name, emulsion concentration: 60% by mass) manufactured by Daikin was prepared as a binder.
[0036]
Next, 50 parts by mass of the OH-type ion exchange resin and 50 parts by mass of the PTFE emulsion solution were mixed, and the mixed solution was applied to the bottom surface of the liquid fuel storage unit at a thickness of 2 mm.
[0037]
The positive electrode was manufactured as follows. First, 50 parts by mass of "Ketjen Black EC" (trade name) manufactured by Lion Akzo, 10 parts by mass of platinum-supported carbon supporting 50 parts by mass of platinum fine particles having an average particle diameter of 3 nm, and 10 parts by mass of Electrochem. 75 parts by mass of the proton conductive substance "Nafion" (trade name, solid content concentration: 5% by mass), 10 parts by mass of the PTFE emulsion solution "D1" as a binder, and 5 parts by mass of water were prepared. These were mixed and dispersed with a homogenizer, applied to a carbon cloth as a diffusion layer so that the amount of platinum became 8 mg / cm ² , and dried. Next, hot pressing was performed at 120 ° C. and 10 MPa for 2 minutes to form an electrode, thereby obtaining a positive electrode.
[0038]
The negative electrode was manufactured as follows. First, 50 parts by mass of the above-mentioned "Ketjen Black EC", 10 parts by mass of platinum-supported carbon carrying 50 parts by mass of platinum-ruthenium alloy (alloy ratio 1: 1) fine particles having an average particle diameter of 3 nm, and 75 parts of the above-mentioned "Nafion" 10 parts by mass of the PTFE emulsion solution "D1" and 5 parts by mass of water were prepared as a mass part, a binder. These were uniformly mixed and dispersed with a homogenizer, applied to a carbon cloth as a diffusion layer so that the amount of platinum was 8 mg / cm ² , and dried. Next, hot pressing was performed for 2 minutes at 120 ° C. and 10 MPa to form an electrode to obtain a negative electrode.
[0039]
As the electrolyte, a solid polymer membrane “Nafion 117” (trade name) manufactured by DuPont was used. The solid electrolyte was sandwiched between the positive electrode and the negative electrode, and hot pressed at 120 ° C. and 10 MPa for 3 minutes. An integrated product was produced. The electrode area was 10 cm ² for both the positive electrode and the negative electrode.
[0040]
The cover plate and the liquid fuel storage unit were configured by applying a phenolic resin paint “Mycus A” (trade name) manufactured by Nippon Paint Co. as an insulating coating film to stainless steel (SUS316). The positive electrode current collector was made of a 10-μm-thick gold sheet, which was bonded to the positive electrode using an epoxy resin. As the liquid fuel, a 5% by mass aqueous methanol solution was used. The negative electrode current collector was composed of a mesh sheet made of the same material as the positive electrode current collector.
[0041]
Further, a liquid fuel impregnating material for impregnating and holding the liquid fuel and supplying the liquid fuel to the negative electrode was disposed in the fuel supply hole and on the side and top surfaces of the liquid fuel storage unit. The liquid fuel impregnated material was made of glass fiber.
[0042]
(Comparative Example 1)
A liquid fuel cell of Comparative Example 1 was produced in the same manner as in Example 1, except that no adsorbent capable of adsorbing carbon dioxide was used.
[0043]
The cell characteristics (polarization characteristics) of the liquid fuel cells of Example 1 and Comparative Example 1 at a temperature of 25 ° C. were measured. The battery characteristics were evaluated by measuring the current density when the battery voltage was set to 0.5 V, 0.4 V, and 0.3 V, respectively. The result is shown in FIG. As is clear from FIG. 4, in the comparative example 1, the polarization characteristics and the voltage stability are greatly reduced in the higher current density region, whereas in the example 1, both the polarization characteristics and the voltage stability are smaller than those in the comparative example 1. Is also good. This is thought to be because in Comparative Example 1, carbon dioxide generated at the negative electrode hindered the supply of methanol to the negative electrode. It is considered that the carbon dioxide generated in the step was adsorbed and removed.
[0044]
【The invention's effect】
As described above, the liquid fuel cell of the present invention can efficiently remove carbon dioxide generated by the cell reaction, provide a large energy density, and provide a small liquid fuel cell.
[Brief description of the drawings]
FIG. 1 is a sectional view of a liquid fuel cell according to an embodiment of the present invention.
FIG. 2 is a sectional view of a liquid fuel cell according to another embodiment of the present invention.
FIG. 3 is a sectional view of a liquid fuel cell according to still another embodiment of the present invention.
FIG. 4 is a diagram showing cell characteristics of liquid fuel cells in Example 1 and Comparative Example 1.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 air hole 2 cover plate 3 liquid fuel storage section 3a fuel supply hole 4 liquid fuel 5 liquid fuel impregnating material 6 adsorbent 6a filter 6b microcapsule 7 current collector 8 positive electrode 8a diffusion layer 8b catalyst layer 9 negative electrode 9a diffusion layer 9b catalyst Layer 10 Solid electrolyte

Claims (5)

A liquid fuel cell including a positive electrode for reducing oxygen, a negative electrode for oxidizing fuel, an electrolyte provided between the positive electrode and the negative electrode, and a liquid fuel storage unit,
A liquid fuel cell, wherein an adsorbent capable of adsorbing carbon dioxide is disposed inside the liquid fuel storage unit. The liquid fuel cell according to claim 1, wherein the adsorbent includes an OH-type anion exchange resin. 3. The liquid fuel cell according to claim 1, wherein the adsorbent has at least one form selected from powder, granule, thin film, and fibrous forms. The liquid fuel cell according to claim 1, wherein the liquid fuel storage unit is detachable. The positive electrode, the negative electrode, and the electrolyte form an electrode-electrolyte integrated body, and a plurality of the electrode-electrolyte integrated bodies are arranged on the same plane. Liquid fuel cell.

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