KR100696700B1 - Direct oxidation fuel cell system - Google Patents

Abstract

Provided is a direct oxidation fuel cell system to allow a suitable amount of carboxylic acid to be added simply to fuel to improve the output power of a system. The direct oxidation fuel cell system comprises at least one electricity generation part(3) which comprises a membrane electrode assembly(3c) and a separator(3a, 3b) and generates electricity; a fuel supply part(7) which comprises a pH sensitive polymer membrane(24), a first supply part(26) containing the fuel divided by the pH sensitive polymer membrane, and a second supply part(22) containing carboxylic acid and supplies fuel and carboxylic acid to the electricity generation part; an oxidant supply part(9) which supplies an oxidant to the electricity generation part; and a water separation part(17) which is supplied with the reaction product generated at the electricity generation part and separates water from the reaction product to circulate it to the fuel supply part.

Description

Direct Oxidation Fuel Cell System {DIRECT OXIDATION FUEL CELL SYSTEM}

1 is a schematic representation of a fuel cell system of the present invention;

[Industrial use]

The present invention relates to a direct oxidation fuel cell system, and more particularly to a direct oxidation fuel cell system capable of high output.

[Prior art]

A fuel cell is a power generation system that directly converts the chemical reaction energy of hydrogen and oxygen contained in hydrocarbon-based materials such as methanol, ethanol and natural gas into electrical energy. This fuel cell is a clean energy source that can replace fossil energy, and has the advantage of generating a wide range of outputs by stacking unit cells, and having an energy density of 4-10 times that of a small lithium battery. It is attracting attention as a compact and mobile portable power source.

Representative examples of the fuel cell include a polymer electrolyte fuel cell (PEMFC) and a direct oxidation fuel cell (Direct Oxidation Fuel Cell). When methanol is used as a fuel in the direct oxidation fuel cell, it is called a direct methanol fuel cell (DMFC).

The polymer electrolyte fuel cell has an advantage of having a high energy density and a high output, but requires attention to handling hydrogen gas and reforms fuel for reforming methane, methanol, natural gas, etc. to produce hydrogen as fuel gas. There is a problem that requires additional equipment such as a device.

On the other hand, the direct oxidation fuel cell has a slower reaction rate and has a lower energy density, a lower output, and a larger amount of electrode catalyst than the polymer electrolyte fuel cell. However, the liquid fuel is easy to handle and the operating temperature is high. Has the advantage of being low and in particular not requiring a fuel reformer.

It is an object of the present invention to provide a direct oxidation fuel cell system capable of producing high output.

In order to achieve the above object, the present invention provides a direct oxidation type fuel cell system including an electric generator including at least one membrane-electrode assembly and a separator, a fuel supply including a pH-sensitive polymer membrane, an oxidant supply and a water separator. do.

The fuel supply includes a first supply comprising a fuel partitioned with a pH sensitive polymer membrane and a second supply comprising a carboxylic acid.

The membrane-electrode assembly includes an anode electrode and a cathode electrode positioned opposite to each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode. In addition, the electricity generating unit serves to generate electricity through the electrochemical reaction of the fuel and the oxidant.

The oxidant supply unit serves to supply an oxidant to the electricity generation unit, and the water separation unit is supplied with a reaction product generated at the cathode electrode of the electricity generation unit, separates water from the reaction product, and separates the separated water again. It serves to feed the fuel supply, that is to circulate again.

The anode electrode may further comprise a carboxylic acid decomposition reforming catalyst.

Hereinafter, the present invention will be described in more detail.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct oxidation fuel cell, which generally supplies hydrocarbon fuel to an anode electrode to generate hydrogen ions by an oxidation reaction at the anode electrode, which reacts with the oxygen of the cathode to produce water. Generate electricity while generating Therefore, the overall reaction rate is low, the power output is low, there was a problem using an excess metal catalyst.

In the present invention, a carboxylic acid is used as a material for supplying hydrogen to the fuel supplied to the stack in order to increase the output of such a direct oxidation fuel cell, and a high output can be obtained by using only a small amount of such carboxylic acid. Therefore, the method of supplying an appropriate amount to fuel by the simple method was used.

Such a fuel cell system of the present invention includes at least one electricity generating portion, a fuel supply portion and an oxidant supply portion. In addition, in the case of the direct oxidation fuel cell, water is supplied together with the hydrocarbon fuel in order to increase the energy density by promoting the oxidation reaction of the hydrocarbon fuel at the anode, and water generated at the cathode electrode during the cell reaction is supplied to the fuel supply unit. It is desirable to mix it with fuel so that it is supplied to the anode electrode. Thus, the direct oxidation fuel cell system of the present invention includes a water separator.

Hereinafter, each component of the fuel cell system of the present invention will be described.

The fuel supply unit of the present invention serves to supply fuel to the electricity generation unit, and includes a pH sensitive polymer membrane, and the second supply unit includes a first supply unit including fuel and a carboxylic acid by the pH sensitive polymer membrane. It is divided into supply parts.

The pH-sensitive polymer membrane may be phase-transformed according to the pH of the first supply part. When the pH of the first supply part exceeds 7, the pH-sensitive polymer membrane may be broken and carboxylic acid may be supplied to the first supply part. Such pH-sensitive polymers include polyperfluorosulfonate, polyvinylacetate phthalate, methacrylic acid polymer, hydroxypropyl methylcellulose phthalate, cellulose propionate phthalate, Eudragit L, Eudragit S, and the like. Can be used.

Since the pH sensitive polymer membrane is located in the first supply portion, the pH of the first supply portion at the time of starting to supply fuel is present in the neutral state of the pH sensitive polymer membrane at about 7 so that the carboxylic acid is released from the second supply portion. Can be supplied to the supply section. As the supply of the carboxylic acid to the first supply portion proceeds, the pH of the first supply portion gradually decreases, and when the pH is less than 5, the supply of the carboxylic acid to the first supply portion is stopped because the pH-sensitive polymer membrane is phased into a solid. . In addition, when the mixture of the fuel and the additive is continuously supplied to the anode electrode of the electricity generating unit, and the water generated at the cathode electrode is supplied to the first supply unit due to the reaction of the fuel cell, the pH of the first supply unit gradually increases, and the neutral state is again increased. While maintaining the pH sensitive polymer membrane is decomposed, the carboxylic acid is fed back to the first supply.

As a result, the carboxylic acid can be continuously supplied to the fuel in a constant amount, and can be simply added while precisely controlling the addition amount.

The carboxylic acid used in the present invention is preferably represented by the following general formula (1) or (2).

[Formula 1]

C _e H _f (COOH) _g

(In Formula 1, e is 1 to 3, f is 1 to 7, g is an integer of 1 to 1)

[Formula 2]

C _a H _b XO ₂

(In Formula 2, a is an integer of 2 to 8, b is an integer of 3 to 17, X is a halogen)

As a more preferred example, formic acid, acetic acid, propanoic acid, butanoic acid and one or more halogenated alkyl carboxylic acids may be used, and formic acid is most preferred.

The electricity generation unit serves to generate electricity through an oxidation reaction of a fuel and a reduction reaction of an oxidant, and includes at least one membrane-electrode assembly and a separator. The membrane-electrode assembly includes an anode electrode and a cathode electrode positioned opposite each other, and includes a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode.

The oxidant supply unit serves to supply an oxidant to the electricity generation unit, and the water separation unit is supplied with a reaction product generated at the cathode electrode of the electricity generation unit, and separates water from the reaction product, thereby supplying the water to the fuel supply unit. It serves to circulate by feeding it back.

Next, each configuration will be described in more detail.

The fuel supply part serves to supply fuel and carboxylic acid to the anode electrode. In the present invention, the fuel refers to a hydrocarbon fuel generally used in a direct oxidation fuel cell such as methanol, ethanol, dimethoxyethane, etc., and these fuels may be used in a liquid state or a gaseous state. In the present invention, the fuel does not include carboxylic acid. In addition, in the case of using a liquid phase in general, water may be used in combination to increase the activity of the oxidation reaction of the liquid fuel.

The carboxylic acid is a substance capable of generating hydrogen through a reforming reaction, and the carboxylic acid is preferably represented by the following Chemical Formula 1 or Chemical Formula 2.

[Formula 1]

C _e H _f (COOH) _g

(In Formula 1, e is 1 to 3, f is 1 to 7, g is an integer of 1 to 1)

[Formula 2]

C _a H _b XO ₂

(In Formula 2, a is an integer of 2 to 8, b is an integer of 3 to 17, X is a halogen)

More preferred examples include formic acid, acetic acid, propanoic acid, butanoic acid, and halogenated alkyl carboxylic acid.

The fuel supply portion of the present invention includes a pH sensitive polymer membrane, which is divided into a first supply portion containing fuel and a second supply portion containing carboxylic acid.

The pH-sensitive polymer membrane may be phase-transformed according to the pH of the first supply part. When the pH of the first supply part exceeds 7, the pH-sensitive polymer membrane may be broken and carboxylic acid may be supplied to the first supply part. Such pH-sensitive polymers include polyperfluorocarboxylic acid, polyvinylacetate phthalate, methacrylic acid polymer, hydroxypropyl methylcellulose phthalate, cellulose propionate phthalate, Eudragit L, Eudragit S, and the like. 1 or more types can be used.

Since the pH sensitive polymer membrane is located in the first supply portion, the pH of the first supply portion at the time of supplying fuel is present in the neutral state of the pH sensitive polymer membrane at about 7, so that the carboxylic acid is released from the second supply portion. Can be supplied to the supply section. As the supply of the carboxylic acid to the first supply portion proceeds, the pH of the first supply portion gradually decreases, and when the pH is less than 5, the supply of the carboxylic acid to the first supply portion is stopped because the pH-sensitive polymer membrane phase changes into a solid. . In addition, when the mixture of the fuel and the additive is continuously supplied to the anode electrode of the electricity generating unit, and the water generated at the cathode electrode is supplied to the first supply unit due to the reaction of the fuel cell, the pH of the first supply unit gradually increases, and the neutral state is again increased. While maintaining the pH sensitive polymer membrane is decomposed, the carboxylic acid is fed back to the first supply.

As a result, the carboxylic acid can be continuously supplied to the fuel in a constant amount, and can be simply added while precisely controlling the addition amount.

In the fuel cell system of the present invention, the electricity generating portion includes a membrane-electrode assembly and a separator (also called a bipolar plate). The membrane-electrode assembly includes an anode electrode and a cathode electrode positioned opposite each other, and includes a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode. The electricity generating unit generally includes at least one membrane-electrode assembly and a separator, and the at least one electricity generating unit is collectively referred to as a stack. The electricity generation unit serves to generate electricity through the oxidation reaction of the fuel and the reduction reaction of the oxidant.

The anode electrode includes an electrode substrate and a catalyst layer.

The catalyst layer includes a fuel oxidation catalyst, and representative examples thereof are platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-M alloy (M is Ga, Ti, V, Cr, Mn At least one catalyst selected from the group consisting of Fe, Co, Ni, Cu, Zn, Sn, Mo, W, and Rh). Representative examples include Pt, Pt / Ru, Pt / W, Pt / Ni, Pt / Sn, Pt / Mo, Pt / Pd, Pt / Fe, Pt / Cr, Pt / Co, Pt / Ru / W, Pt / And at least one selected from the group consisting of Ru / Mo, Pt / Ru / V, Pt / Fe / Co, Pt / Ru / Rh / Ni, and Pt / Ru / Sn / W.

The catalyst layer may further comprise a carboxylic acid oxidation catalyst. As the carboxylic acid oxidation catalyst, one or more metals selected from the group consisting of palladium, gold, copper, aluminum, iron, and alloys thereof may be used, and palladium is preferable.

The carboxylic acid oxidation catalyst serves to oxidize the carboxylic acid to generate hydrogen. Thus, since the anode electrode of the present invention further includes a carboxylic acid oxidation catalyst, the carboxylic acid together with the hydrocarbon fuel is used as a fuel cell. It is possible to provide to the system to provide a high output battery. That is, the carboxylic acid when provided in the fuel cell system, the carboxylic acid to produce a W H ₂ thing by acid oxidation catalyst of the anode electrode, and using the H ₂ is a fuel to increase the electrical output also produce hydrogen from a fuel Since the inner side functions as an accelerator to accelerate the reaction, the oxidation reaction of the fuel is fast and the conversion rate at which hydrogen ions are generated from the fuel is fast. ) Phenomenon can be drastically reduced, and a high output battery can be provided.

In addition, such a metal catalyst may be used as the metal catalyst (black) itself, or may be supported on a carrier. As the carrier, carbonaceous materials such as graphite, denka black, ketjen black, acetylene black, carbon nanotubes, carbon nanofibers, carbon nanowires, carbon nanoballs or activated carbon may be used, or alumina, silica, zirconia, Inorganic fine particles such as titania may be used, but carbon-based materials are generally used. In the case of using the noble metal supported on the carrier as a catalyst, a commercially available commercially available product may be used, or the noble metal supported on the carrier may be prepared and used. Since the process of supporting the precious metal on the carrier is well known in the art, detailed descriptions thereof will be readily understood by those skilled in the art even if the detailed description is omitted.

The catalyst layer also includes a binder. As the binder, a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups and derivatives thereof in the side chain can be used.

The polymer resin may be a fluoro-based polymer such as perfluorosulfonate, a polyamide-based polymer, a polyether-based polymer, a benzimidazole-based polymer, a polyimide-based polymer, a polyetherimide-based polymer, or a polyphenylene sulfide-based polymer. At least one hydrogen ion conductive polymer such as polysulfone polymer, polyether sulfone polymer, polyether ketone polymer, polyether ether ketone polymer or polyphenylquinoxaline polymer may be used. The hydrogen ion conductive polymer may replace H with Na, K, Li, Cs or tetrabutylammonium in an ion exchange group at the side chain end. In case of replacing H by Na in the ion-exchange group of the side chain terminal, NaOH is substituted when preparing the catalyst composition and tetrabutylammonium hydroxide when tetrabutylammonium is used. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The binder may be used in the form of a single substance or a mixture, and may also be optionally used with a nonionic conductive polymer for the purpose of further improving adhesion to the polymer electrolyte membrane. It is preferable to adjust the usage-amount so that it may be suitable for a purpose of use.

The nonionic conductive polymer may be polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer ethylene / tetrafluoroethylene, At least one selected from the group consisting of chlorotrifluoroethylene-ethylene copolymers, polyvinylidene fluorides, copolymers of polyvinylidene fluoride-hexafluoropropylene, dodecylbenzenesulfonic acid and sorbitol Can be used.

The electrode substrate plays a role of supporting the electrode and diffuses the fuel and the oxidant to the catalyst layer, thereby serving to easily access the fuel and the oxidant to the catalyst layer. A conductive substrate is used as the electrode substrate, and representative examples thereof include carbon paper, carbon cloth, carbon felt, or metal cloth (porous film or polymer composed of metal cloth in a fibrous state). The metal film formed on the surface of the fabric formed of fibers (referred to as metalized polymer fiber) may be used, but is not limited thereto.

In addition, it is preferable to use a water-repellent treatment with a fluorine-based resin as the electrode base material because it can prevent the reactant diffusion efficiency from being lowered by water generated when the fuel cell is driven. As the fluorine-based resin, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated ethylene propylene, polychlorotrifluoroethylene, fluoroethylene polymer, or the like may be used.

In addition, a microporous layer may be further included to enhance the reactant diffusion effect in the electrode substrate. These microporous layers are generally conductive powders having a small particle diameter, such as carbon powder, carbon black, acetylene black, activated carbon, carbon fiber, fullerene, carbon nanotubes, carbon nanowires, and carbon nanohorns. -horn or carbon nano ring.

The microporous layer is prepared by coating a composition comprising a conductive powder, a binder resin and a solvent on the electrode substrate. The binder resin may be polytetrafluoroethylene, polyvinylidene fluoride, polyhexafluoropropylene, polyperfluoroalkyl vinyl ether, polyperfluorosulfonyl fluoride, alkoxy vinyl ether, polyvinyl alcohol, cellulose acetate Or copolymers thereof and the like can be preferably used. As the solvent, alcohols such as ethanol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, water, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone and the like may be preferably used. The coating process may be screen printing, spray coating, or coating using a doctor blade according to the viscosity of the composition, but is not limited thereto.

The cathode electrode of the present invention has the same configuration as the anode electrode except that the carboxylic acid oxidation catalyst is not included in the above-described configuration of the anode electrode.

In addition, the polymer electrolyte membrane in the membrane-electrode assembly of the present invention is generally used as a polymer electrolyte membrane in a fuel cell, and any one made of a polymer resin having hydrogen ion conductivity may be used. Representative examples thereof include a polymer resin having a cation exchange group selected from the group consisting of sulfonic acid groups, carboxylic acid groups, phosphoric acid groups, phosphonic acid groups and derivatives thereof in the side chain.

Representative examples of the polymer resin include a fluorine polymer, a benzimidazole polymer, a polyimide polymer, a polyetherimide polymer, a polyphenylene sulfide polymer, a polysulfone polymer, a polyether sulfone polymer and a polyether ketone It may include one or more selected from a polymer, a polyether-ether ketone-based polymer or a polyphenylquinoxaline-based polymer, more preferably poly (perfluorosulfonic acid) (generally marketed as Nafion), Poly (perfluorocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing sulfonic acid groups, defluorinated sulfide polyether ketones, aryl ketones, poly (2,2'-m-phenylene) Or at least one selected from -5,5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole) Can be.

In the hydrogen ion conductive group of the hydrogen ion conductive polymer, H may be substituted with Na, K, Li, Cs or tetrabutylammonium. In case of replacing H by Na in the ion-exchange group of the side chain terminal, NaOH is substituted when preparing the catalyst composition and tetrabutylammonium hydroxide when tetrabutylammonium is used. It can be substituted using. Since this substitution method is well known in the art, detailed description thereof will be omitted.

The separator is provided with a flow channel for supplying fuel to the anode and supplying an oxidant to the cathode, and formed of metal or graphite.

The oxidant supply unit serves to supply an oxidant to the electricity generator. As the oxidant, oxygen or air containing the same may be used.

In addition, the water separation unit is supplied with the reaction product generated from the cathode electrode of the electricity generation unit, and serves to separate the water of the reaction product, and to supply the separated water back to the first supply of the fuel supply unit.

The fuel cell system and its operating principle of the present invention will be described with reference to FIG. 1. The fuel cell system 1 of the present invention includes at least one electricity generation unit 3 for generating electrical energy through an oxidation reaction of a fuel and a reduction reaction of an oxidant, a fuel supply unit 5 for supplying the fuel, and an oxidant. It comprises a oxidant supply unit (9) for supplying to the electricity generating section (3).

In addition, the fuel supply unit 7 includes a pH sensitive polymer membrane 24, a first supply unit 26 for storing fuel partitioned by the pH sensitive polymer membrane 24, and a second supply unit for storing carboxylic acid ( 22).

The fuel supply unit 7 includes a fuel tank 15 and a fuel pump 13 connected to the fuel supply unit 7, and the fuel pump 15 is connected to the fuel tank 15 by a predetermined pumping force. The fuel stored in the discharged to the fuel supply unit 7 is to function. The operating conditions of the fuel pump 13 and the fuel supply 7 can be appropriately adjusted by the control board 30.

When fuel is injected into the first supply part 26 through the fuel pump 13, the carboxylic acid in the second supply part 22 is injected through the pH sensitive polymer membrane 24, so that the fuel and the carboxylic acid mixture are injected. Is formed.

The electricity generator 3 is a membrane-electrode assembly 3c for oxidizing and reducing a fuel and an oxidant, and separators 3a and 3b for supplying fuel and an oxidant to both sides of the membrane-electrode assembly 3c. It is configured, the electricity generating unit 3 is at least one gather to constitute a stack (20).

The fuel and carboxylic acid mixture is supplied to the anode electrode of the membrane-electrode assembly 3c. Subsequently, an oxygen-containing gas, which is an oxidant, is injected into the cathode of the membrane-electrode assembly 3c using the oxidant pump 7 of the oxidant supply unit 9.

At this time, the carboxylic acid is reformed into H ₂ gas by the carboxylic acid oxidation catalyst, and the H ₂ gas and the fuel generate H ⁺ and electrons (e ⁻ ) by the hydrocarbon oxidation catalyst. In this case, electrical energy is generated by the movement of generated electrons (e ⁻ ). The generated H ⁺ is moved to the cathode electrode through the polymer electrolyte membrane to react with the oxygen injected into the cathode to produce H ₂ O, H ₂ O and CO ₂ generated in the entire fuel cell reaction is a water separation unit ( Separated from 17), CO ₂ is discharged to the outside, and the generated H ₂ O is supplied to the first supply part 26 of the fuel supply part 7 and circulated again.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Example 1)

Anode using 88 wt% Pt-Ru black (Johnson Matthey) and Pt black (Johnson Matthey) catalyst and 12 wt% Nafion / H ₂ O / 2-propanol (Solution Technology Inc.) at 5 wt% concentration as binder Catalyst compositions for electrodes and catalyst compositions for cathode electrodes were prepared, respectively.

Applying the catalyst composition for the anode electrode on a carbon paper electrode substrate having a carbon content of 0.2mg / cm ² to produce an anode electrode, the catalyst composition for the cathode electrode on a carbon paper electrode substrate having a carbon content of 1.3mg / cm ² It was applied to prepare a cathode electrode. At this time, the catalyst loading in the anode electrode and cathode electrode was 8mg / cm ² .

A unit cell was prepared using the prepared anode and cathode electrodes and a commercial Nafion 115 (perfluorosulfonate) polymer electrolyte membrane.

The stack was prepared using the unit cell. Subsequently, a fuel cell system was manufactured by a conventional method using the stack and a fuel supply including a first supply for storing methanol partitioned with a polyperfluorosulfonate pH sensitive polymer membrane and a second supply for storing formic acid. It was.

As a result of driving the fuel cell system, formic acid stored in the second supply unit is initially supplied to the fuel of the first supply unit, and as time passes, the pH of the first supply unit is gradually lowered to form the pH-sensitive polymer membrane. The phase transition to a solid stopped the formic acid supply. Subsequently, when the fuel cell was further driven, the pH of the first supply portion was increased again, and the pH sensitive polymer membrane was broken to start formic acid supply.

The direct oxidation type fuel cell system of the present invention can simply add a carboxylic acid capable of improving the output to a fuel in an appropriate amount to provide a high output fuel cell.

Claims (11)

And at least one membrane-electrode assembly and a separator comprising an anode electrode and a cathode electrode positioned opposite to each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein the membrane comprises an electrode reaction and a reduction reaction of the oxidant. At least one electricity generating unit for generating electricity through; a fuel supply unit for supplying fuel and carboxylic acid to the electricity generation unit, the fuel supply unit including a pH sensitive polymer membrane, a first supply unit including a fuel divided by the pH sensitive polymer membrane, and a second supply unit including carboxylic acid; An oxidant supply unit for supplying an oxidant to the electricity generating unit; And The reaction product generated in the electricity generation unit is supplied, and the water separation unit for separating the water from the reaction product to circulate to the fuel supply unit Direct oxidation fuel cell system comprising a. The method of claim 1, The pH sensitive polymer membrane is polyperfluorocarboxylic acid, polyvinylacetate phthalate, methacrylic acid polymer, hydroxypropyl methylcellulose phthalate, cellulose propionate phthalate, Eudragit L, Eudragit S and combinations thereof Direct oxidation fuel cell system comprising a polymer selected from the group consisting of. The method of claim 1, The carboxylic acid is a direct oxidation fuel cell system that is represented by the following formula (1) or (2). [Formula 1] C _e H _f (COOH) _g (In Formula 1, e is 1 to 3, f is 1 to 7, g is an integer of 1 to 1) [Formula 2] C _a H _b XO ₂ (In Formula 2, a is an integer of 2 to 8, b is an integer of 3 to 17, X is a halogen) The method of claim 3, The carboxylic acid is a direct oxidation fuel selected from the group consisting of formic acid, acetic acid, propanoic acid, butanoic acid, halogenated alkyl carboxylic acid, and combinations thereof. Battery system. The method of claim 4, wherein Wherein said carboxylic acid is formic acid. The method of claim 1, The anode electrode is a direct oxidation fuel cell system comprising a fuel oxidation catalyst. The method of claim 6, And said anode electrode further comprises a carboxylic acid oxidation catalyst. The method of claim 7, wherein Wherein said carboxylic acid oxidation catalyst is selected from the group consisting of palladium, gold, copper, aluminum, iron, alloys thereof, and combinations thereof. The method of claim 8, Wherein said carboxylic acid oxidation catalyst comprises palladium. The method of claim 6, The fuel oxidation catalyst is platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-M alloy (M is Ga, Ti, V, Cr, Mn, Fe, Co, Ni, Cu And at least one transition metal selected from the group consisting of Zn, Sn, Mo, W, and Rh). The method of claim 1, Wherein said fuel is a hydrocarbon fuel.

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