JP2006213882A - Fuel composition for fuel cells - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel composition for a fuel cell capable of obtaining stable performance for a long time. <P>SOLUTION: This fuel composition for a fuel cell contains a fuel, and a fungicide or a bactericide. The fuel in the fuel composition for a fuel cell is preferably a 1-3C alcohol and water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel composition for a fuel cell, and more particularly to a fuel composition for a direct methanol fuel cell.

  There are several types of fuel cells, but direct methanol fuel cells have the feature that they can generate electricity by directly supplying liquid as it is without taking out hydrogen gas by reforming methanol aqueous solution as fuel. Yes. Therefore, compared with conventional polymer electrolyte fuel cells that supply fuel by gasification or reforming, the structure as a power generation system is simple, and it is easy to reduce the size and weight. Its use as a power source has attracted attention.

  Such a direct methanol fuel cell uses a proton conductive solid polymer membrane as an electrolyte membrane, and a cathode and an anode formed by applying a catalyst on porous carbon paper serving as a diffusion layer via the electrolyte membrane. The anode electrode side separator having a flow channel for supplying a methanol aqueous solution as a fuel is provided on the anode electrode side, and a flow for supplying air as an oxidant gas is provided on the cathode electrode side. It has a structure in which a cathode electrode side separator having a passage groove is provided.

When an aqueous methanol solution is supplied to the anode electrode and air is supplied to the cathode electrode, carbon dioxide gas is generated by the oxidation reaction of methanol and water at the anode electrode, and hydrogen ions and electrons are released (CH ₃ OH + H ₂ O → CO _2). + 6H ⁺ + 6e ⁻ ), and at the cathode electrode, water is generated by the reduction reaction between the hydrogen ions that have passed through the electrolyte membrane and air (6H ⁺ + (3/2) O ₂ + 6e ⁻ → 3H ₂ O). Electrical energy can be obtained in the external circuit by connecting the cathode and anode. Therefore, the total reaction of the direct methanol fuel cell is a reaction in which water and carbon dioxide are generated from methanol and oxygen.

  Various types of fuel cells are known, such as a fuel vaporization supply type and a type using capillary force, and a fuel prepared by mixing alcohol and water is used.

The fuel cell described in Patent Document 1 has a structure in which liquid fuel as fuel is introduced into each unit cell by capillary force, is vaporized in each unit cell, and the vaporized fuel is supplied to the fuel electrode (anode electrode). It is. For this reason, since high-concentration fuel can be used without using auxiliary equipment such as a fuel vaporizer, miniaturization is possible. The fuel composition for a fuel cell described in Patent Document 2 contains a fuel containing a C 1-3 alcohol and water and a surfactant. This fuel composition for a fuel cell not only can shorten the start-up time of the liquid fuel cell, but can also start the fuel cell described in Patent Document 1 from a low temperature.
JP 2000-353533 A JP 2001-93558 A

  Patent Document 2 focuses on problems such as shortening the startup time of the fuel cell and starting from a low temperature. On the other hand, long-term stability as an energy supply system is an important issue in putting fuel cells into practical use. The present invention focuses on long-term stability as an energy supply system, and an object of the present invention is to provide a fuel composition for a fuel cell that can provide stable performance over a long period of time.

  The above object can be achieved by the following means.

  The invention according to claim 1 is a fuel composition for a fuel cell containing a fuel and a fungicide or a bactericidal agent.

  The invention according to claim 2 is the fuel composition for a fuel cell according to claim 1, wherein the fuel is alcohol having 1 to 3 carbon atoms and water.

  The invention according to claim 3 is the fuel composition for a fuel cell according to claim 2, wherein the content of the alcohol is 10 to 40% by mass with respect to the fuel.

  The invention according to claim 4 is characterized in that the antifungal agent or fungicide is a 1,2-benzisothiazolin-3-one compound, an isothiazoline-3-one compound, a thiazolylbenzimidazole compound, or a 2-phenoxyethanol system. The fuel composition for a fuel cell according to any one of claims 1 to 3, wherein the fuel composition is a compound selected from a compound and a phenolic compound.

  That is, the present inventors include a fume-proofing agent or a bactericidal agent in the fuel so that water remains in the fuel supply container, such as a fuel supply container and an introduction pipe connecting the fuel storage container and the fuel cell stack body. Or, it is possible to suppress the occurrence of fungi such as fungi in parts where water is present, such as a pipe for draining water generated on the cathode electrode or cathode electrode side of the fuel cell, and in the electrolyte membrane or electrode part. It was possible to obtain a stable output over a long period of time, and the present invention was achieved.

  A fuel composition for a fuel cell capable of obtaining stable performance over a long time could be obtained.

  In the fuel composition for a fuel cell of the present invention, examples of the fuel include alcohols, ethers, hydrazine and the like. Preferred are alcohols, specifically, alcohol having 1 to 3 carbon atoms and water. Examples of the alcohol having 1 to 3 carbon atoms include methanol, ethanol, isopropanol, and 1-propanol. The content of the alcohol is preferably 1 to 80% by mass, more preferably 10 to 40% by mass with respect to the entire fuel composed of alcohol and water. When the alcohol content is less than 1% by mass, the liquid fuel container becomes too large, and it is difficult to reduce the size. If it exceeds 80% by mass, the water component, which is the other component of the fuel, is reduced, which may make it difficult for the cell reaction to occur. The content of water which is the other component of the fuel can be appropriately determined according to the amount of such alcohol.

  Antifungal agents or fungicides blended in the fuel composition for fuel cells of the present invention include 1,2-benzisothiazolin-3-one compounds, isothiazoline-3-one compounds, thiazolylbenzimidazole compounds In addition to compounds, 2-phenoxyethanol compounds, and phenol compounds, phenethyl alcohol and the like can be given. Among these antifungal agents or fungicides, 1,2-benzisothiazolin-3-one compounds are preferable, and 1,2-benzisothiazolin-3-one is particularly preferable.

  The content of these fungicides or bactericides varies depending on the type of fungicides or bactericides, but the effect is sufficiently exerted if they are generally present in a proportion of 1% by mass or less in the fuel composition. However, it is preferably 0.005 to 0.5 mass%. Moreover, not only one type of antifungal agent or fungicide but also several types can be mixed and used. Specific examples of antifungal agents or fungicides are listed below, but are not limited thereto.

  (I) 1,2-benzisothiazolin-3-one compound;

(II) isothiazoline-3-one compounds;
II-1 2-Methyl-4-isothiazolin-3-one
II-2 5-chloro-2-methyl-4-isothiazolin-3-one
II-3 2-Methyl-5-phenyl-4-isothiazolin-3-one
II-4 2-hydroxymethyl-4-isothiazolin-3-one
II-5 5-chloro-2- (2-phenylethyl) -4-isothiazolin-3-one (III) thiazolylbenzimidazole compound;

  (IV) 2-phenoxyethanol compounds;

  (V) a phenolic compound;

  When the amount of alcohol contained in the fuel composition of the present invention exceeds 30% by mass of the whole fuel, it does not freeze even at a low temperature (below freezing point of 40 ° C.). When the amount is 30% by mass or less, it is preferable to add an antifreeze liquefying agent to make the fuel composition antifreeze.

  As the antifreezing agent, a polyhydric alcohol or a derivative thereof can be used. The addition amount of the antifreeze liquefying agent is preferably in the range of 0.1% by mass to 10% by mass with respect to the fuel.

  Examples of the polyhydric alcohol and derivatives thereof include ethylene glycol, diethylene glycol, glycerin, propylene glycol, ethylene glycol monomethyl ether, diglyme, polyoxyethylene oligomer, and polyoxypropylene oligomer.

  Next, a fuel cell to which the fuel composition for a fuel cell of the present invention is applied will be described with reference to the drawings.

  FIG. 1 is a schematic view of a fuel cell to which the fuel composition for a fuel cell of the present invention is applied. The fuel cell shown in FIG. 1 basically contains a liquid fuel containing a fuel composition 2 for the fuel cell (for example, methanol and water, a fungicide or a disinfectant, and an antifreeze liquefaction agent if necessary). The container 1 includes a fuel cell stack body 8, an introduction pipe 5 for introducing the fuel composition 2 from the fuel storage container 1 to the fuel cell stack body 8, and a fuel introduction path 6. Usually, an air supply / intake mechanism (not shown) such as a fan for supplying an oxidant gas is also provided. The illustrated fuel cell stack body 8 includes a plurality of unit cells 7 each having a fuel electrode (also referred to as an anode electrode), an oxidant electrode (also referred to as a cathode electrode), and an electromotive portion having an electrolyte membrane sandwiched between the two electrodes. It is a structure that includes a stacked. The unit cell 7 can also be used in a single layer without being stacked.

  In FIG. 1, the introduction tube 5 can be formed of a thin tube having a capillary action. Alternatively, the introduction pipe 5 may be filled with a porous material that allows the fuel composition 2 to permeate for the purpose of assisting the introduction of the fuel composition 2. As such a liquid osmotic material, for example, a porous material such as a sponge such as polyurethane, polyester, cellulose, or phenolic resin can be used.

  As shown in the drawing, the fuel container 1 is connected to the introduction pipe 5 at the connection portion 4, and the connection portion 4 is desirably sealed. This is because the fuel may be volatilized when the sealing of the connecting portion 4 is insufficient.

  The fuel composition 2 introduced into the fuel cell stack body 8 from the introduction pipe 5 passes through the molecular filtration membrane 3 and is referred to as a fuel introduction path 6 in order to stably and stably supply the unit cells 7 in the stack. Guided to holding material.

  FIG. 2 is a cross-sectional view showing the main configuration of the unit cell 7. As shown in the figure, an anode electrode 72, an electrolyte membrane 73, and a cathode electrode 74 are disposed between a fuel permeation layer 71 and a separator 75 to constitute a unit cell 7.

  Here, the anode electrode 72 and the cathode electrode 74 are formed of a conductive porous body so that the fuel composition 2 and the oxidant gas can be circulated and electrons can pass therethrough. Further, a fuel permeation layer 71 for introducing the fuel composition 2 into the battery by capillary force is provided. An oxidant gas supply groove 76 for flowing an oxidant gas is provided as a continuous groove on the surface of the separator 75 in contact with the cathode electrode 74. By having the separator 75 also have a function as a channel through which the oxidizing gas flows, the number of parts of the battery can be reduced.

  As a means for supplying the fuel composition 2 from the liquid fuel container 1 to the fuel permeation layer 71, for example, the fuel introduction path 6 is formed in the fuel cell stack body 8. The fuel composition 2 introduced into the fuel introduction path 6 is supplied to the fuel permeation layer 71 by capillary force. The form of the fuel permeation layer 71 is not particularly limited as long as it can permeate the fuel composition 2 by capillary force, and is a porous body composed of particles and fillers, a nonwoven fabric manufactured by a papermaking method, or the like. A woven fabric or the like woven can be used. The fuel permeation layer 71 is preferably closer to the electrolyte membrane 73 and is preferably set so that the capillary force is increased by reducing the capillary hole diameter.

  The separator 75 and the fuel permeation layer 71 are formed of a conductive material so as to function as a current collecting layer that conducts generated electrons. Further, a catalyst layer may be formed between the anode electrode 72 or the cathode electrode 74 and the electrolyte membrane 73, or the anode electrode 72 or the cathode electrode 74 itself may be used as a catalyst electrode. The catalyst electrode may be a catalyst layer alone or may have a multilayer structure in which a catalyst layer is formed on a support such as conductive paper or cloth.

  The electrolyte membrane 73 is preferably a solid polymer electrolyte membrane having proton conductivity, and known ones such as a sulfonated polyimide polymer electrolyte membrane, a fluorine polymer electrolyte membrane, a hydrocarbon polymer electrolyte membrane, and a composite material. Can be adopted. For example, as the hydrocarbon polymer electrolyte material, sulfonated engineering plastic electrolytes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfone, sulfonated polysulfide, and sulfonated polyphenylene, Examples include sulfoalkylated engineering plastic electrolytes such as sulfoalkylated polyetheretherketone, sulfoalkylated polyethersulfone, sulfoalkylated polyetherethersulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, and sulfoalkylated polyphenylene.

  As the catalyst for the anode electrode 72 and the cathode electrode 74, known catalysts can be used, for example, noble metal catalysts such as platinum, palladium, ruthenium, iridium, gold, platinum-ruthenium, iron-nickel-cobalt-molybdenum-platinum. Alloys such as are used.

  The catalyst layers of the anode electrode 72 and the cathode electrode 74 preferably contain an electron conductor (conductive material) material for the purpose of improving conductivity. The electron conductor (conductive material) is not particularly limited, but an inorganic conductive material is preferably used from the viewpoints of electron conductivity and touch resistance. Among these, carbon black, graphite or carbonaceous carbon material, metal or metalloid can be mentioned. Here, as the carbon material, carbon black such as channel black, thermal black, furnace black, and acetylene black is preferably used from the viewpoint of electron conductivity and specific surface area. In particular, it is used as an electron conductor (conductive material) carrying a catalyst, such as platinum-carrying carbon. The catalyst layer preferably contains a proton conductive electrolyte material. The electrolyte is not particularly limited as long as it is an electrolyte having ion conductivity used for a solid polymer electrolyte membrane having proton conductivity, and examples thereof include a fluorine-based electrolyte material, a partial fluorine-based electrolyte material, and a hydrocarbon-based electrolyte material. The ratio of the noble metal catalyst-supported carbon and the polymer electrolyte in the catalyst layer should be appropriately determined according to the required electrode characteristics, and is not particularly limited. The mass ratio is preferably 5/95 to 95/5, and more preferably 40/60 to 85/15.

  The support that supports the catalyst layers of the anode electrode 72 and the cathode electrode 74, that is, the electrode substrate, can be used without particular limitation as long as it has a low electrical resistance and can collect current. . Examples of the constituent material of the electrode base material include those mainly composed of a conductive substance. Examples of the conductive substance include a fired body from polyacrylonitrile, a fired body from pitch, and carbon such as graphite and expanded graphite. Examples include raw materials, the aforementioned nanocarbon materials, stainless steel, molybdenum, and titanium. In addition, the catalyst layer and the support that supports the catalyst layer may contain a water repellency imparting agent for improving water repellency. Examples of water repellency-imparting agents include fluorine-containing resins such as polytetrafluoroethylene (PTFE) such as Teflon (registered trademark), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. Is mentioned. The catalyst layer of the cathode electrode 74 and the layer constituting the cathode electrode, such as a support for supporting the catalyst layer, can contain a compound having an antibacterial action such as titanium oxide.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to these.

[Production of catalyst-supported carbon]
(Platinum-supported carbon for cathode electrode)
9 g of acetylene black and 200 g of pure water are mixed. Subsequently, 1 g of chloroplatinic acid aqueous solution is added as platinum, and it heats up to 60 degreeC. After the temperature became constant, the pH was adjusted to 10 with a 2 mol / l sodium hydroxide solution, and a 3% by mass hydrazine solution was added dropwise to reduce chloroplatinic acid. After completion of the reduction, platinum-supported carbon was obtained by filtering and washing with a glass filter and drying. The amount of platinum supported on this carbon was 20% by mass.

(Platinum ruthenium-supporting carbon for anode electrode)
Platinum ruthenium-supporting carbon for anode electrode was prepared in the same manner as the preparation of platinum-supporting carbon for cathode electrode. However, in this case, platinum-ruthenium-supported carbon was obtained by using 1.2 g of chloroplatinic acid as platinum and 1 g of ruthenium chloride as ruthenium instead of 1 g of chloroplatinic acid as platinum. The amount of platinum supported on this carbon was 20% by mass.

[Preparation of electrode paste]
(Preparation of anode electrode paste)
Platinum: ruthenium-supporting carbon, Nafion 117 solution (manufactured by DuPont), and Teflon (registered trademark) dispersion PTFE31-J (manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) were each prepared as a 40: 55: 5 mixture in solid content mass ratio. Then, water and 2-propanol were added thereto, and the mixture was uniformly dispersed with ultrasonic waves to prepare an anode electrode paste.

(Preparation of cathode electrode paste)
In the preparation of the anode electrode paste, a cathode electrode paste was prepared in the same manner as the anode electrode paste except that the platinum-ruthenium-supporting carbon was replaced with platinum-supporting carbon.

[Preparation of support for supporting catalyst layer]
(Production of water repellent carbon paper)
Carbon paper having a porosity of 75% and a thickness of 0.4 mm is immersed in Teflon (registered trademark) dispersion PTFE31-J (manufactured by Mitsui DuPont Fluorochemical Co., Ltd.), and 0.5 mg / cm ² of Teflon (registered trademark) is placed on the surface. A water-repellent carbon paper was prepared by applying.

[Production of electrodes]
(Preparation of anode electrode)
The anode electrode paste prepared above was uniformly applied to the surface of the water-repellent treated carbon paper prepared above so that the amount of platinum was 3.0 mg, and dried at 80 ° C. for 1 hour in a nitrogen atmosphere. Produced.

(Production of cathode electrode)
The cathode electrode paste prepared above is uniformly applied to the surface of the water-repellent treated carbon paper prepared above so that the amount of platinum is 3.0 mg, and dried at 80 ° C. for 1 hour in a nitrogen atmosphere to form the anode electrode. Produced.

[Preparation of electrolyte membrane-electrode assembly]
A Nafion 112 membrane (manufactured by DuPont) was sandwiched between the anode and cathode prepared above. These were hot-pressed and bonded at 140 ° C. for 5 minutes at a pressure of 100 kg / cm ² to prepare an electrolyte membrane-electrode assembly as an electromotive part.

[Fabrication of fuel cell stack body]
The electrolyte membrane-electrode assembly obtained above and a carbon porous plate (porosity 40%) as a fuel permeation layer are laminated, and a holder and an anode as a cathode electrode side separator provided with an oxidant gas supply groove A cell was prepared by placing it between the pole-side holders. Ten unit cells thus produced were stacked to produce a fuel cell stack body.

(Evaluation)
The fuel cell stack body produced above was set as shown in FIG. The fuel composition shown in Table 1 is supplied to the anode side and air is supplied to the cathode side under the conditions of a temperature of 60 ° C. and a fuel flow rate of 10 ml / min and an air flow rate of 50 ml / min at atmospheric pressure. The current-voltage characteristics were measured. In the measurement, the battery performance after 4 months was compared with the initial battery performance after repeating power generation for 2 hours and stopping for 2 days in a constant temperature room at 60 ° C. Table 1 shows the measurement results of current density at a voltage of 0.4 V at the initial stage and after 4 months.

  In the sample according to the present invention, deterioration in battery performance at the initial stage and after 4 months was not observed. On the other hand, deterioration of battery performance after 4 months was observed in the samples outside the present invention. Further, after 4 months, the battery was taken out and the inside of the battery was observed, but the sample according to the present invention was hardly changed. On the other hand, in the sample outside the present invention, the surface was slimy.

It is the schematic of the fuel cell to which the fuel composition for fuel cells of this invention is applied. It is sectional drawing which shows the principal part structure of a cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid fuel container 2 Fuel composition 3 Molecular filtration membrane 4 Connection part 5 Introducing pipe 6 Fuel introduction path 7 Single cell 71 Fuel penetration layer 72 Anode electrode 73 Electrolyte membrane 74 Cathode electrode 75 Separator 76 Oxidant gas supply groove 8 Fuel cell Stack body

Claims (4)

A fuel composition for a fuel cell comprising a fuel and a fungicide or a bactericidal agent. The fuel composition for a fuel cell according to claim 1, wherein the fuel is alcohol having 1 to 3 carbon atoms and water. The fuel composition for a fuel cell according to claim 2, wherein the alcohol content is 10 to 40% by mass with respect to the fuel. The antifungal agent or fungicide is selected from 1,2-benzisothiazolin-3-one compounds, isothiazoline-3-one compounds, thiazolylbenzimidazole compounds, 2-phenoxyethanol compounds, and phenol compounds. The fuel composition for a fuel cell according to any one of claims 1 to 3, which is a compound.

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