KR20070023927A - Direct oxidation fuel cell system - Google Patents

Abstract

Provided is a direct oxidation fuel cell system, which includes a fuel supplying unit for feeding fuel to an anode together with a carboxylic acid, and thus shows a high output. The direct oxidation fuel cell system comprises: at least one electricity generating unit(5) having an membrane-electrode assembly having an anode and a cathode disposed opposite to each other and a polymer electrolyte membrane interposed between both electrodes, wherein the electricity generating unit generates electricity via oxidation of fuel and reduction of an oxidant; a fuel supplying unit(1) for feeding fuel and a carboxylic acid to the electricity generating unit; and an oxidant supplying unit for feeding an oxidant to the electricity generating unit.

Description

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

1 is a view showing a carboxylic acid addition method according to an embodiment of a fuel cell system of the present invention.

2 illustrates a method of adding a carboxylic acid according to another embodiment of a fuel cell system of the present invention.

3 illustrates a method of adding a carboxylic acid according to another embodiment of a fuel cell system of the present invention.

4 schematically shows the structure of a fuel cell system of the present invention;

Figure 5 is a graph showing the results of measuring the 0.4V output density of the fuel cell system of Example 1 of the present invention at various temperatures.

6 is a graph showing the results of measuring 0.4V output density of the fuel cell system of Comparative Example 1 at various temperatures.

7 is a graph showing the results of measuring 0.3V output density of the fuel cell systems of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention at a temperature of 30 ° C.

8 is a graph showing the results of measuring 0.3V output density of the fuel cell systems of Example 1, Comparative Example 1 and Comparative Example 2 of the present invention at a temperature of 50 ° C.

9 is a graph showing the results of measuring the 0.3V output density of the fuel cell systems of Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention at a temperature of 30 ° C.

10 is a graph showing the results of measuring the 0.3V output density of the fuel cell systems of Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention at a temperature of 50 ° C.

[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 includes at least one membrane-electrode assembly and a separator comprising an anode electrode and a cathode electrode positioned opposite each other and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, A fuel supply and an oxidant comprising at least one electricity generating unit for generating electricity through an electrochemical reaction of a fuel and an oxidant, and comprising a fuel and a carboxylic acid, and supplying fuel and carboxylic acid to the anode electrode. Provided is a direct oxidation fuel cell system including an oxidant supply unit for supplying an electricity generation unit.

The anode electrode may include a carboxylic acid decomposition reforming catalyst layer oxidation catalyst layer and an electrode substrate positioned between the carboxylic acid decomposition reforming catalyst layer and the oxidation catalyst layer.

The fuel supply unit may further include a carboxylic acid reformer that receives fuel and carboxylic acid from the fuel supply unit and reforms the carboxylic acid with hydrogen to supply fuel and hydrogen to the anode electrode.

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 liquid 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, carboxylic acid is used as a substance for supplying hydrogen to the fuel supplied to the stack in order to increase the output of such a direct oxidation fuel cell. The fuel cell system of the present invention includes at least one electricity generating portion, a fuel supply portion, and an oxidant supply portion. 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 fuel supply unit supplies fuel and carboxylic acid to the anode, and the oxidant supply unit serves to supply an oxidant to the electricity generator.

Next, each configuration will be described in more detail.

The fuel supply unit 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 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 formic acid, acetic acid or propanoic acid may be used as the carboxylic acid.

The carboxylic acid is preferably used at a concentration of 0.001 to 1M. When the carboxylic acid is less than 0.001M concentration, it is not meant to use carboxylic acid, and when the carboxylic acid is higher than 1M concentration, the energy density of the fuel cell is lowered, which is not preferable.

In the fuel cell system of the present invention, the anode electrode includes an electrode substrate having a carboxylic acid decomposition and reforming catalyst coating layer formed on one side and an oxidation catalyst layer located on the other side of the electrode substrate facing the reforming catalyst coating layer.

The carboxylic acid decomposition and reforming catalyst coating layer includes a catalyst selected from the group consisting of Pt, Pd, Ru, Au, Rh, Fe, Cu and alloys thereof. As the catalyst, a black type catalyst not supported on the carrier may be used, or a catalyst type supported on the carrier may be used. As the carrier, carbon such as acetylene black, denka black, carbon black, ketjen black, activated carbon, and graphite may be used, or inorganic fine particles such as alumina, silica, titania, zirconia, etc. may be used. It is used.

The carboxylic acid decomposition and reforming catalyst coating layer is suitable for a thickness of about 5㎛ or less.

The carboxylic acid decomposition and reforming catalyst coating layer serves to oxidize the carboxylic acid to H ₂ gas as it passes through the coating layer when fuel and carboxylic acid are supplied to the anode electrode in the stack.

In addition, the fuel cell system of the present invention is a carboxylic which when supplied with fuel and carboxylic acid from the fuel supply unit, by modifying the carboxylic acid to produce the H ₂ gas supplied to the anode electrode of the stack with the H ₂ gas and the fuel It may further comprise an acid modifier. In this reformer, the catalyst used in the carboxylic acid decomposition and reforming coating layer may be used as it is.

In this way, the carboxylic acid is used in the fuel cell system so that the hydrogen gas generated from the carboxylic acid is injected into the anode electrode together with the fuel, so that the added hydrogen itself is used not only as a fuel for increasing the electric output but also to produce hydrogen in the fuel It functions as an accelerator to accelerate the reaction (homogeneous catalytic reaction). Therefore, the oxidation reaction of the fuel is fast and the conversion rate at which hydrogen ions are generated from the fuel is fast, so that the crossover phenomenon of the fuel in which the unreacted fuel is oxidized from the conventional anode electrode to the cathode electrode can be drastically reduced.

In addition, the pH of the fuel shows acidic (pH 5.6 or less) as hydrogen is added.

In the oxidation catalyst layer, a metal catalyst is used as the catalyst, and examples thereof include platinum or a binary to quaternary alloy containing platinum and a transition metal. Ruthenium, chromium, copper or nickel may be used as the transition metal. Among them, an alloy catalyst such as platinum-ruthenium is mainly used in the direct oxidation fuel cell in order to prevent catalyst poisoning caused by CO generated during the anode electrode reaction. 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, carbon such as acetylene black, denka black, activated carbon, ketjen black, graphite may be used, or inorganic fine particles such as alumina, silica, titania, zirconia may be used, but carbon is generally used.

A method of adding carboxylic acid in the present invention will be described with reference to FIGS. 1 to 3. An embodiment of adding carboxylic acid is shown in FIG. 1, and as shown in FIG. 1, fuel and carboxylic acid are mixed in one fuel supply 1 to the anode electrode 54 of the stack 5. The oxygen-containing gas 7, which is an oxidant, is injected into the cathode electrode 56 of the stack 5. At this time, the carboxylic acid is reformed with H ₂ gas while passing through the carboxylic acid decomposition and reforming coating layer 54c to pass the electrode substrate 54b together with the fuel to generate H ⁺ in the catalyst layer 54a. In this case, electrical energy is generated by the movement of generated electrons (e ⁻ ). The generated H ⁺ moves to the cathode electrode 56 through the polymer electrolyte membrane 58 and reacts with oxygen injected into the cathode electrode 56 to generate H ₂ O, and H generated in the fuel cell overall reaction. ₂ O and CO ₂ are emitted.

Another embodiment of adding carboxylic acid is shown in FIG. 2, and as shown in FIG. 2, fuel and carboxylic acid are passed through a carboxylic acid reformer 13 in one fuel supply 10 to stack 15. Is injected into the anode electrode, and the oxygen-containing gas 17 as the oxidant is injected into the cathode electrode of the stack 15. The carboxylic acid is modified with H ₂ gas while passing through the carboxylic acid reformer 13 and injected into the anode electrode of the stack 15 together with the fuel to produce H ₂ O, which is produced in the fuel cell overall reaction. H ₂ O and CO ₂ are emitted.

Another embodiment of the carboxylic acid addition method is shown in FIG. 3, and as shown in FIG. 3, fuel and carboxylic acid are injected into the anode electrode 356 of the stack 35 in one fuel supply 30. Then, the oxygen-containing gas 37 as an oxidant is injected into the cathode electrode 356 of the stack 35 to generate electricity, and the generated H ₂ O and CO ₂ are discharged.

The electricity generation unit serves to generate electricity through the oxidation reaction of the fuel and the reduction reaction of the oxidant. The electricity generating unit includes a membrane electrode assembly and a separator positioned at both sides of the membrane electrode assembly. 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 membrane-electrode assembly includes an anode electrode and a cathode electrode positioned opposite each other, and a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode. The anode electrode and the cathode electrode generally have a structure in which a catalyst layer is formed on an electrode backing layer. 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 carbon paper or carbon cloth may be used as a representative example, but is not limited thereto.

As the catalyst in the catalyst layer, a so-called metal catalyst which catalyzes the related reaction (oxidation of fuel and reduction of oxidant) is used. For example, platinum or a binary or quaternary alloy containing platinum and transition metal may be used. Can be. Examples of the transition metal include ruthenium, chromium, copper or nickel.

In the fuel cell, the same material may be used as the catalyst used for the anode electrode and the cathode electrode, but in the direct oxidation fuel cell, in order to prevent catalyst poisoning due to CO generated during the anode electrode reaction, The anode electrode mainly uses an alloy catalyst such as platinum-ruthenium.

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, carbon such as acetylene black and graphite may be used, or inorganic fine particles such as alumina and silica may be used. Generally, carbon is widely used.

As the polymer electrolyte membrane, a polymer having an ion exchange function of transferring hydrogen ions generated in the catalyst layer of the anode electrode to the catalyst layer of the cathode electrode and having excellent 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 at least one selected from a polymer, a polyether-etherketone-based polymer or a polyphenylquinoxaline-based polymer, more preferably poly (perfluorosulfonic acid), poly (perfluorocarboxylic acid), Copolymers of tetrafluoroethylene with fluorovinyl ethers containing sulfonic acid groups, defluorinated sulfided polyether ketones, aryl ketones, poly (2,2'-m-phenylene) -5,5'-bibenzimidazole (poly (2,2 '-(m-phenylene) -5,5'-bibenzimidazole) or poly (2,5-benzimidazole) may be used. To 200 μm Has a thickness.

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.

The structure of the fuel cell system of the present invention having such a configuration is schematically shown in FIG. 4, which will be described in more detail with reference to the following. Although the structure shown in FIG. 4 shows a system for supplying fuel and an oxidant to an electric generator using a pump, the fuel cell system of the present invention is not limited to such a structure, but a fuel cell of a type for supplying an oxidant in a diffusion manner. Of course, it can also be used for system architecture.

The fuel cell system 600 of the present invention includes at least one electricity generation unit 68 for generating electrical energy through an oxidation reaction of a fuel and a reduction reaction of an oxidant, a fuel supply source 60 for supplying the fuel, And an oxidant source 69 for supplying an oxidant to the electricity generator 68.

In addition, the fuel supply unit 60 for supplying the fuel includes a fuel tank 62 storing fuel and a fuel pump 64 connected to the fuel tank 62. The fuel pump 64 functions to discharge fuel stored in the fuel tank 62 by a predetermined pumping force.

The oxidant supply unit 69 for supplying an oxidant to the electricity generation unit 68 includes at least one oxidant pump 63 for sucking the oxidant at a predetermined pumping force, and the electricity generation unit 68 gathers at least one. The stack 67 is constituted.

The electricity generator 68 includes a membrane-electrode assembly 65 for oxidizing and reducing a fuel and an oxidant, and bipolar plates 64 and 66 for supplying fuel and an oxidant to both sides of the membrane-electrode assembly. It consists of unit cells 68.

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.

A stack was prepared using the unit cell, and 1M methanol and 1M formic acid were supplied to the stack to drive a fuel cell system having the structure shown in FIG.

(Example 2)

The same procedure as in Example 1 was carried out except that 0.1 M formic acid was used instead of 1 M formic acid.

(Comparative Example 1)

The same procedure as in Example 1 was conducted except that no formic acid was injected.

(Comparative Example 2)

The same procedure as in Example 1 was carried out except that only 1 M formic acid was injected without methanol injection.

(Comparative Example 3)

The same procedure as in Comparative Example 2 was carried out except that 0.1 M formic acid was used.

* Temperature characteristic

The 0.4V output density of the fuel cell systems of Example 1 and Comparative Example 1 was measured at room temperature (25 ° C), 50 ° C, 60 ° C and 70 ° C, and the results are shown in Table 1 and FIGS. .

mW / cm ² , 0.4 V 25 ℃ 50 ℃ 60 ℃ 70 ℃ Comparative Example 1 19 37 41 45 Example 1 25 64 71 77 Increase 32% 73% 71% 77%

As shown in Table 1 and FIGS. 5 and 6, the fuel cell system of Example 1 in which formic acid is injected into the anode electrode together with methanol fuel improves the output density compared to the fuel cell system of Comparative Example 1 in which only methanol is injected. In particular, it can be seen that the power density improvement rate is particularly high at high temperatures.

* Use of formic acid

After measuring 0.3V and 0.4V output densities of the fuel cell systems prepared according to Example 1, Comparative Example 1 and Comparative Example 2 at 30 ° C and 50 ° C, respectively, the results are shown in Tables 2 and 3, respectively. It was. In addition, the result of measuring 0.3V power density at 30 degreeC is shown in FIG. 7, and the result of measuring at 50 degreeC is shown in FIG. In Tables 2 and 3 below, the rate of increase represents the rate of increase in power density of Example 1 relative to Comparative Example 1.

mV / cm ² Comparative Example 1 Comparative Example 2 Example 1 Increase 0.3 V 25 31 46 84% 0.4 V 19 33 25 32%

mV / cm ² Comparative Example 1 Comparative Example 2 Example 1 Increase 0.3 V 55 43 82 49% 0.4 V 37 45 57 82%

As shown in Table 2 and Table 3 and FIGS. 7 and 8, the fuel cell system of Comparative Example 2 using formic acid, compared to Comparative Example 1 using only methanol, has an output density at 30 ° C. and 50 ° C. and 0.3 V and 0.4 V. Although slightly increased, it can be seen that the fuel cell system of Example 1 using methanol and formic acid at the same time is significantly higher than that of Comparative Example 2.

* Formic acid concentration effect

The 0.3V and 0.4V output densities of the fuel cell systems prepared according to Examples 1 and 2 and Comparative Examples 1 to 3 were measured at 30 ° C. and 50 ° C., respectively, and the results are shown in Table 4 below. In addition, the results of measuring 0.3V output density at 30 ° C. are shown in FIG. 9 and the results of 0.3V output density at 50 ° C. are shown in FIG. 10, respectively.

mW / cm ² Comparative Example 1 Comparative Example 3 Comparative Example 2 Example 2 Example 1 Temperature 25 ℃ 50 ℃ 30 ℃ 50 ℃ 30 ℃ 50 ℃ 30 ℃ 50 ℃ 30 ℃ 50 ℃ 0.3 V 25 55 30 19 31 43 46 79 46 88 0.4 V 17 37 24 33 45 32 57 25 64

As shown in Table 4, the fuel cell systems of Comparative Example 1 using only formic acid and Comparative Examples 2 and 3 using only formic acid significantly reduced the output density at a high temperature of 50 ° C, while using methanol and formic acid together. In the batteries of Examples 1 and 2, it can be seen that the output density is improved even at a high temperature even at a low concentration.

In addition, it can be seen that Examples 1 to 2 are significantly higher than those of Comparative Examples 1 to 3 at 25 ° C, that is, at low temperatures. Based on these results, it can be predicted that the fuel and oxidant supply will be easy to apply to the diffusion type direct oxidation fuel cell without using a pump.

The direct oxidation fuel cell system of the present invention can exhibit high power by supplying carboxylic acid along with fuel to the anode electrode.

Claims (19)

An anode electrode and a cathode electrode located opposite each other; And a membrane-electrode assembly and a separator comprising a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein at least one electricity generation generates electricity through an oxidation reaction of a fuel and a reduction reaction of an oxidant. part; A fuel supply unit including fuel and carboxylic acid, and supplying fuel and carboxylic acid to the electricity generator; And Oxidant supply unit for supplying an oxidant to the electricity generating unit Direct oxidation fuel cell system comprising a. The direct oxidation fuel cell system of claim 1, wherein the carboxylic acid is selected from the group consisting of formic acid, acetic acid, and propanoic acid. 3. The direct oxidation fuel cell system as recited in claim 2, wherein the carboxylic acid is formic acid. The direct oxidation fuel cell system of claim 1, wherein the concentration of the carboxylic acid is 0.001 to 1M. The method of claim 1, wherein the anode electrode Carboxylic acid cracking reforming catalyst layer; Oxidation catalyst layer; And An electrode substrate positioned between the carboxylic acid decomposition reforming catalyst layer and the oxidation catalyst layer Direct oxidation fuel cell system comprising a. The system of claim 5, wherein the carboxylic acid cracking reforming catalyst layer comprises a catalyst selected from the group consisting of Pt, Pd, Ru, Au, Rh, Fe, Cu, and alloys thereof. 7. The direct oxidation fuel cell system of claim 6, wherein the carboxylic acid cracking reforming catalyst layer comprises a Pd catalyst. The direct oxidation type according to claim 1, further comprising a carboxylic acid reformer for receiving fuel and carboxylic acid from the fuel supply unit and reforming the carboxylic acid with hydrogen to supply fuel and hydrogen to the anode electrode. Fuel cell system. The system of claim 8, wherein the carboxylic acid reformer comprises a catalyst selected from the group consisting of Pt, Pd, Ru, Au, Rh, Fe, Cu, and alloys thereof. 10. The direct oxidation fuel cell system of claim 9, wherein the carboxylic acid reformer comprises a Pd catalyst. An anode electrode and a cathode electrode located opposite each other; And a membrane-electrode assembly and a separator comprising a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein at least one electricity generation generates electricity through an oxidation reaction of a fuel and a reduction reaction of an oxidant. part; A fuel supply unit including fuel and carboxylic acid, and supplying fuel and carboxylic acid to the electricity generator; And Oxidant supply unit for supplying an oxidant to the electricity generating unit Including, The anode electrode Carboxylic acid cracking reforming catalyst layer; Oxidation catalyst layer; And And an electrode substrate positioned between the carboxylic acid decomposition reforming catalyst layer and the oxidation catalyst layer. 12. The direct oxidation fuel cell system as recited in claim 11, wherein the carboxylic acid is selected from the group consisting of formic acid, acetic acid and propanoic acid. 13. The direct oxidation fuel cell system as recited in claim 12, wherein the carboxylic acid is formic acid. 12. The direct oxidation fuel cell system as recited in claim 11, wherein the concentration of the carboxylic acid is 0.001 to 1M. The system of claim 11, wherein the carboxylic acid cracking reforming catalyst layer comprises a catalyst selected from the group consisting of Pt, Pd, Ru, Au, Rh, Fe, Cu, and alloys thereof. 16. The direct oxidation fuel cell system of claim 15, wherein the carboxylic acid cracking reforming catalyst layer comprises a Pd catalyst. An anode electrode and a cathode electrode located opposite each other; And a membrane-electrode assembly and a separator comprising a polymer electrolyte membrane positioned between the anode electrode and the cathode electrode, wherein at least one electricity generation generates electricity through an oxidation reaction of a fuel and a reduction reaction of an oxidant. part; Carboxylic acid modifiers that modify carboxylic acids to generate hydrogen; A fuel supply unit including a fuel and a carboxylic acid and supplying hydrogen generated from fuel and the carboxylic acid reformer to the electricity generator through the carboxylic acid reformer; And Oxidant supply unit for supplying an oxidant to the electricity generating unit Direct oxidation fuel cell system comprising a. 18. The direct oxidation fuel cell system of claim 17, wherein the carboxylic acid modifier comprises a catalyst selected from the group consisting of Pt, Pd, Ru, Au, Rh, Fe, Cu, and alloys thereof. 19. The direct oxidation fuel cell system of claim 18, wherein the carboxylic acid reformer comprises a Pd catalyst.

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