JP2006244949A - Electrode for fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for fuel cell superior in stability of output with the passage of time by progressing efficiently an oxidation reaction and a reduction reaction. <P>SOLUTION: The electrode for fuel cell contains an assembly of a hollow carbon fiber. The assembly of the hollow carbon fiber carries a catalyst inside the hole 10. At least one of the anode electrode and cathode electrode of the electrode for fuel cell uses the electrode having the assembly 11 of the hollow carbon fiber with the average diameter of the hole 100 nm or more and less than 1 mm, and the fuel cell is a direct methanol fuel cell. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrode for a fuel cell and a fuel cell.

  In recent years, with the rapid spread of portable electronic devices and wireless communication devices, fuel cells have attracted attention as portable power supply devices and energy sources for pollution-free automobiles, and their development has been focused on.

  A fuel cell is composed of an anode and a cathode, which are electrodes, and an electrolyte or the like provided between them. Hydrogen gas or methanol is used as a fuel, oxygen gas or air is used as an oxidant, and these are electrically connected. It is a power generation system that directly converts energy generated by chemical reaction into electrical energy. These include a molten carbonate electrolyte fuel cell that operates at a high temperature of 500 to 700 ° C., a phosphoric acid electrolyte fuel cell that operates near 200 ° C., an alkaline electrolyte fuel cell that operates from room temperature to 100 ° C. and a polymer electrolyte. Type fuel cells and the like.

  Hereinafter, a polymer electrolyte fuel cell will be described as an example.

  The polymer electrolyte fuel cell can be further subdivided into a hydrogen ion exchange membrane fuel cell that uses hydrogen gas as a fuel, and a direct use that supplies liquid methanol directly to the anode as fuel. There is a methanol fuel cell (Direct Methanol Fuel Cell).

  The polymer electrolyte fuel cell is a futuristic clean energy source that can replace fossil energy, has high power density and energy conversion efficiency, can be operated at room temperature, and can be downsized. It has the potential for a very wide range of applications in fields such as household power generation systems, portable power supplies for mobile communication equipment, medical equipment, and military equipment.

In such a polymer electrolyte fuel cell, a proton conductive solid polymer membrane is used as an electrolyte membrane, and carbon particles carrying a catalyst are applied to porous carbon paper as a diffusion layer through the electrolyte membrane. An anode electrode separator having a flow channel for supplying fuel is provided on the anode side, and air as an oxidant gas is supplied to the cathode side. It has a structure in which a cathode separator having a channel groove is provided. (See Patent Document 1)
The anode electrode and the cathode electrode are electrodes each having a diffusion layer for supplying and diffusing each reactant and a catalyst layer in which an oxidation / reduction reaction of the reactant occurs.

  The diffusion layer of the anode electrode serves as an electrode that supports the catalyst layer of the anode electrode and delivers electrons to the separator. The anode catalyst layer has an action of generating an electromotive force by causing an electrochemical reaction by the action of the catalyst.

  The electrolyte membrane has an effect of diffusing hydrogen ions generated in the catalyst layer of the anode electrode to the cathode side, while preventing the passage of electrons, and generates an electromotive force due to this effect.

  The cathode diffusion layer carries a cathode catalyst layer for the reduction reaction of the fuel cell and functions as an electrode for receiving electrons from the separator.

  The separator has a function of separating the flow and chemical reaction of fuel and oxidant generated at the cathode electrode and the anode electrode adjacent to each other when the fuel cell units are stacked. Moreover, it becomes a conductor which flows the generated electricity to an external circuit.

  In general, hydrogen ion exchange membrane fuel cells that use hydrogen as a fuel have the advantage of high energy density. However, care must be taken when handling hydrogen gas, and methane must be used to produce hydrogen as a fuel gas. In addition, there is a problem that ancillary facilities such as a fuel reformer for reforming methanol, natural gas, and the like are required.

  In contrast, a direct methanol fuel cell has a lower energy density than a gas fuel cell using hydrogen gas or the like, but it is easy to handle, has a low operating temperature, and does not require an additional fuel reformer. Based on these advantages, it is recognized as a system suitable for small and general-purpose mobile power supplies.

  Next, the chemical reaction contributing to the generation of electromotive force in the fuel cell and its problems will be described by taking a direct methanol fuel cell as an example. In the following description, the anode diffusion layer and the anode catalyst layer may be collectively referred to as an anode electrode, and the cathode diffusion layer and the cathode catalyst layer may be collectively referred to as a cathode electrode. In addition, as generally defined in a battery, also in a fuel cell, the anode electrode is an electrode having a negative potential with respect to the external circuit, and the cathode electrode functions as an electrode having a positive potential with respect to the external circuit.

In the anode electrode of the direct methanol fuel cell, a methanol oxidation reaction occurs to generate hydrogen ions and electrons, and the generated hydrogen ions move to the cathode electrode through the electrolyte membrane. Hydrogen ions moved to the cathode electrode react with oxygen, that is, reduction occurs. An electromotive force based on electrons moving from the anode electrode to the cathode electrode via an external circuit becomes an energy generation source of the fuel cell. The following reaction formula shows the reaction that occurs at the anode and cathode and the total reaction that occurs at the fuel cell unit.
The reaction at the anode and the electromotive force on the anode side are
CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ Ea = 0.04V
The reaction at the cathode and the electromotive force on the cathode side are
3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O Ec = 1.23V
Therefore, the reaction and electromotive force of the entire fuel cell unit are
CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O Ecell = 1.19V
In the direct methanol fuel cell, battery characteristics are affected by the electrode. That is, the oxidation reaction at the anode electrode and the reduction reaction at the cathode electrode proceed mainly at the interface between the catalyst layer and the electrolyte membrane contained in the anode and cathode electrodes. Supply and discharge from the electrodes such as carbon dioxide and water produced are important factors in terms of reaction efficiency and output stability over time.

  In addition, the overall performance of the direct methanol fuel cell is greatly affected by the performance of the catalyst layer of the anode electrode because the reaction rate of the anode electrode is slow. Therefore, for practical use, it is very important to develop an excellent catalyst for the methanol oxidation reaction and to control the reaction.

A catalyst poison is known as a problem in the oxidation reaction on the anode electrode. That is, while methanol is electrically adsorbed on the platinum surface and oxidized to generate hydrogen ions and electrons, a catalytic poison that carbon dioxide binds linearly to platinum and diminishes its catalytic action. . It has been reported that the combination of ruthenium with platinum improves the platinum catalyst's resistance to the catalytic poisoning effect of carbon monoxide. In that report, the desirable atomic ratio was 50:50 (see, for example, Non-Patent Document 1). Such improved resistance to carbon monoxide is based on the ability of ruthenium to adsorb water molecules at the chemical potential of methanol adsorbing to platinum. Such a bifunctional mechanism explains the promotion of catalytic activity by the interaction of transition metals and is expressed as follows.
Pt—CO + Ru—OH → Pt + Ru + CO ₂ + H ⁺ + e ⁻
In the direct methanol fuel cell, the catalyst layer of the anode electrode has been mainly developed using a platinum-ruthenium (PtRu) binary alloy catalyst, and a part thereof has already been commercialized. Therefore, many studies have shown that platinum-based binary anode catalysts (Pt-Mo, Pt-W, Pt-Sn, Pt-Os, etc.) and platinum-ruthenium-based ternary catalysts ( The actual situation is concentrated on Pt-Ru-Os, Pt-Ru-Ni, and the like.
International Publication No. 2001/092151 Pamphlet D. Chu and S.H. Gillman, J, Electrochem. Soc. 1996, 143, 1685

  Patent Document 1 takes a process of forming an anode electrode and a cathode electrode by forming a catalyst layer by applying carbon particles carrying a catalyst on porous carbon paper as a diffusion layer.

  Therefore, the pore shape is not uniform in both the diffusion layer and the catalyst layer, and the pore diameter has a wide distribution. Therefore, in the portion where the pore diameter is small, a reaction product such as oxygen or methanol and a reaction such as water or carbon dioxide. The transfer / diffusion efficiency of the product was low, and output stability over time could not be obtained.

  Further, in the catalyst layer, the reactants pass through the catalyst layer in an unreacted state in a portion having a large pore diameter, and move to the electrolyte membrane, causing deterioration of the electrolyte membrane. It has been found that this is a factor that lowers the reaction efficiency and lowers the stability of the output of the fuel cell over time.

  In addition, even when the catalyst disclosed in Non-Patent Document 1 is used, it is difficult to control the oxidation reaction of methanol when the fuel cell is operated for a long time. It passed through and moved to the electrolyte membrane, causing deterioration of the electrolyte membrane.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode for a fuel cell and a fuel cell excellent in output aging stability by efficiently proceeding an oxidation reaction or a reduction reaction. It is in.

The object of the present invention can be achieved by the following constitution.
(Claim 1)
A fuel cell electrode comprising an assembly of hollow carbon fibers.
(Claim 2)
2. The fuel cell electrode according to claim 1, wherein the hollow carbon fiber aggregate has a catalyst supported inside its pores. 3.
(Claim 3)
3. The fuel cell electrode according to claim 2, wherein an average diameter of the pores in the hollow carbon fiber aggregate is 100 nm or more and less than 1 mm.
(Claim 4)
A fuel cell using the fuel cell electrode according to any one of claims 1 to 3 as at least one of an anode electrode and a cathode electrode.
(Claim 5)
The fuel cell according to claim 4, wherein the fuel cell is a direct methanol fuel cell.

  By using a fuel cell electrode characterized by containing an aggregate of hollow carbon fibers, the present inventors can align the shape and direction of the pores, and the pore diameter. The diffusibility of the reaction product of the fuel and oxidant is improved, the fuel and the oxidant are sufficiently supplied to the interface between the catalyst and the electrolyte membrane, and the reaction product of water and carbon dioxide generated by the electrode reaction is diffused. Thus, a fuel cell can be provided in which a sufficient output stability over time can be obtained by being discharged out of the reaction system promptly.

  In particular, when used in the catalyst layer, the diffusibility of the fuel and reaction gas can be controlled so that reactants such as oxygen and methanol do not pass through the catalyst layer in an unreacted state. It was considered that the time-dependent stability of the output of the fuel cell can be improved by efficiently advancing the reaction, and the present invention has been achieved.

  The fuel cell electrode according to the present invention can make the shape and direction of the pores and the pore diameter uniform, and is excellent in output stability over time when used in a fuel cell.

  Embodiments of the present invention will be described below.

  First, an embodiment of a fuel cell according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a basic configuration of a single cell I of a fuel cell according to the present invention. Reference numeral 1 is an electrolyte membrane, reference numeral 2 is an anode electrode catalyst layer, reference numeral 3 is a cathode electrode catalyst layer, reference numeral 4 is an anode electrode diffusion layer, reference numeral 5 is a cathode electrode diffusion layer, reference numeral 6 is an anode electrode side separator, and reference numeral 7 is a cathode. The pole separator, reference numeral 8 represents a fuel flow path, and reference numeral 9 represents an oxidant flow path.

  Here, for the sake of convenience, the diffusion layer 4 and the anode electrode side catalyst layer 2 provided thereon are referred to as an anode electrode, and the diffusion layer 5 and the cathode electrode side catalyst layer 3 provided thereon are referred to as a cathode electrode. Called.

  As shown in FIG. 1, an anode electrode side separator 6 and a cathode electrode side separator 7 are disposed outside a joined body in which the electrolyte membrane 1 is bonded by an anode electrode and a cathode electrode. By joining these, the single cell I is formed. A fuel cell is constructed by laminating a plurality of such single cells via a cooling plate (not shown).

  The present invention is characterized in that an electrode for a fuel cell containing an aggregate of hollow carbon fibers is used as at least one of an anode electrode and a cathode electrode of a fuel cell.

  In the present invention, the effect can be obtained by including the aggregate of the hollow carbon fibers of the present invention in at least one of the diffusion layer and the catalyst layer constituting the anode electrode, the cathode electrode.

  The diffusion layers 4 and 5 supply the reactants such as fuel and oxidant to the anode electrode side catalyst layer 2 and the cathode electrode side catalyst layer 3, discharge of reaction products such as water and carbon dioxide generated by the reaction, and This is a layer having a function of delivering generated electrons to a separator as a current collector. Although this diffusion layer is not necessarily required, if it is present, the function of supporting the catalyst layer can be ensured, and the supply of reactants and the transfer of electrons can be performed more effectively.

  Next, the aggregate of hollow carbon fibers according to the present invention will be described with reference to the drawings. FIG. 2 (a) is a perspective view of one hollow carbon fiber, FIG. 2 (b) is a perspective view schematically showing an assembly of hollow carbon fibers, and FIG. 2 (c) is a hollow carbon fiber. FIG. 2 is a perspective view showing a state in which an aggregate of hollow carbon fibers bundled in a shape as an electrode is cut into a predetermined thickness, with an arrow 1 in the figure as an electrolyte membrane side and an arrow 6 or 7 as a separator side, It can be used for the electrode of the fuel cell of FIG. 2 (a) to 2 (c), reference numeral 10 represents a hole, and reference numeral 11 represents an aggregate of carbon fibers.

  In the present invention, the aggregate of hollow carbon fibers refers to a bundle of hollow carbon fibers provided with pores extending long in the fiber axis direction of the carbon fibers.

  In order to produce this aggregate of hollow carbon fibers, the hollow carbon materials may be bundled and bonded and cut out into a flat plate. Alternatively, a hollow fiber made of an organic material that produces 30% or more of carbon when fired at a high temperature of 600 ° C. or higher in an inert atmosphere is bundled and fired in an inert atmosphere to form a carbide, and then cut into a flat plate. good. A particularly preferred production method is shown below.

  Using a non-cured novolac resin, a hollow continuous fiber is produced using a die having a doughnut-shaped discharge port that can produce a hollow fiber by extrusion. In this case, the inner diameter of the donut shape corresponds to the hollow diameter. Cured novolak resin fibers obtained by curing after spinning are bundled into 10 cm squares and carbonized in an inert gas at 500 ° C. or higher to produce a rod in which hollow carbon fibers having holes in the fiber axis direction are bundled. When the rod is cut perpendicularly to the fiber axis direction, the hollow carbon fiber assembly of the present invention can be produced.

  The uncured novolak resin used in the present invention is, for example, alkylphenols, other substituted phenols, polyhydric phenols and aldehydes such as formaldehyde and paraformaldehyde as raw materials in addition to phenol, and a generally known conventional method. It is obtained by reacting under an acidic catalyst.

  It is preferable to mix graphitizable carbon powder in the resin in that the conductivity of the carbide can be further increased. Moreover, the method of advancing carbonization while extending | stretching is also preferable. However, the firing temperature for carbonization is preferably 800 ° C. or higher, more preferably 1200 ° C. or higher.

The electrode of the present invention can be used for both the anode and the cathode, but is most effective when used for the anode. In addition, the aggregate of hollow carbon fibers contained in the electrode of the present invention is preferably formed with pores perpendicular to the plane of the electrolyte membrane, and the number of pores is stable over time with respect to the output of the fuel cell. From the viewpoint of further improving the properties, 10 pieces / cm ² or more is preferable. Further, from the viewpoint of further increasing the strength of the electrode, it is preferably less than 10 ¹⁰ / cm ² . A more preferable number of holes is 10 ² / cm ² or more and less than 10 ⁸ / cm ² .

  Moreover, the electrode in the present invention only needs to contain an aggregate of hollow carbon fibers. In the present invention, the hollow carbon of the present invention is included in at least one of the diffusion layer and the catalyst layer constituting the anode electrode, the cathode electrode. An effect is acquired by containing the aggregate of fibers.

  When the aggregate of hollow carbon fibers of the present invention is used for the diffusion layer, carbon particles carrying a platinum catalyst are formed on the flat portion of the portion in contact with the electrolyte membrane in the aggregate of hollow carbon fibers of the present invention that becomes the diffusion layer. Apply and heat-treat to form a catalyst layer to make an electrode, or apply the paste of the catalyst layer to the electrolyte membrane, and then hot press with the hollow carbon fiber assembly of the present invention to become the diffusion layer There is a way to make it.

  The catalyst ink for forming the catalyst layer is prepared by adding a solution containing catalyst metal or catalyst metal-supported carbon, proton conductive polymer electrolyte, and the like, and a mixed solvent of an organic solvent and water, and using an ultrasonic disperser. It is preferably supplied in the form of a uniformly dispersed dispersion. As the proton conductive polymer electrolyte, materials used for the proton conductive solid polymer membrane described later can be used.

  Organic solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, diethylene glycol, acetone, methyl ethyl ketone, dimethylformamide, dimethylimidazolidinone, dimethyl sulfoxide, dimethylacetamide, N-methylpyrrolidone, propylene Examples include carbonates, esters such as ethyl acetate and butyl acetate, and aromatic or halogen-based solvents, which can be used alone or as a mixture.

  The average diameter of the pores in the aggregate of hollow carbon fibers is preferably 100 nm or more from the viewpoint of further improving the diffusibility and mobility of the reactants and reaction products inside the pores. Moreover, in order to utilize a capillary phenomenon more effectively, less than 1 mm is preferable. More preferably, it is 0.1 mm or more and less than 1 mm.

Here, the hole diameter when the hole shape is not a circle refers to a diameter corresponding to a circle having an equivalent area. The average diameter is an average value of the pore diameters of a plurality of carbon fibers constituting the aggregate of hollow carbon fibers.
The average diameter of the pores can be measured, for example, by observing an aggregate of hollow carbon fibers with an electron microscope.

  As the carbon particles, activated carbon, carbon black, graphite and a mixture thereof can be preferably used.

  Examples of carbon black include acetylene black, ketjen black, furnace black, lamp black, and thermal black. Denka BLACK (manufactured by Denki Kagaku Kogyo Co., Ltd.), Valcan XC-72 (manufactured by Cabot Corporation), Black Pearl 2000 ( The same as before), commercially available products such as Ketjen Black EC300J (manufactured by Ketjenblack International Co., Ltd.) can be used.

  As the noble metal catalyst to be supported, platinum, ruthenium, rhodium, palladium, iridium, gold, silver, iron, cobalt, nickel, chromium, tungsten, magazine, vanadium, lanthanum, zirconium, titanium, magnesium or a multicomponent alloy thereof should be used. Preferably, it is at least one selected from platinum and platinum ruthenium alloys. The metal catalyst diameter is preferably 10 nm or less, and more preferably 5 nm or less.

  In order to support the noble metal catalyst on the carbon particles, for example, platinum or ruthenium salt is added to the carbon particle dispersion, reduced using hydrazine or the like, filtered, and dried. Further, heat treatment may be performed.

  Next, the case where the aggregate | assembly of the hollow carbon fiber of this invention is used for a catalyst layer is demonstrated.

  The average diameter of the pores in the aggregate of hollow carbon fibers is preferably 100 nm or more because of the ease of loading the catalyst inside the pores. Moreover, from the viewpoint of further enhancing the effect of suppressing the fuel and the oxidant from flowing into the electrolyte membrane without being reacted, the thickness is preferably less than 1 mm. More preferably, it is 0.1 mm or more and less than 1 mm. Here, the hole diameter when the hole shape is not a circle refers to a diameter corresponding to a circle having an equivalent area. The average diameter is an average value of the hole diameters of a plurality of holes constituting the electron conductor layer. The average diameter of the pores can be measured, for example, by observing an aggregate of hollow carbon fibers with an electron microscope and processing the image.

  When used in the catalyst layer, the noble metal catalyst supported inside the pores is platinum, ruthenium, rhodium, palladium, iridium, gold, silver, iron, cobalt, nickel, chromium, tungsten, magazine, vanadium, lanthanum, zirconium, Titanium, magnesium or a multicomponent alloy thereof can be used, and is preferably at least one selected from platinum and a platinum ruthenium alloy. The metal catalyst diameter is preferably 10 nm or less, and more preferably 5 nm or less.

In order to carry the noble metal catalyst inside the pores of the aggregate of hollow carbon fibers of the present invention, the aggregate of hollow carbon fibers subjected to oxidation treatment is placed in an electrolytic cell equipped with a relative electrode. Next, a platinum electrodeposition solution consisting of a 0.02M H ₂ PtCl ₆ solution to which about 1% by volume of 0.1M HCl and about 0.5% by volume of ethanol were added was added to the hollow carbon fiber assembly. It introduce | transduces into the said electrolytic cell so that a plane may be contacted. Next, by applying a square pulse potential to the electrolytic deposition solution in a potential region of -0.5 to 0.0 V relative to the reference electrode (SCE), a total charge of 0.1 to 10 C / cm ² is allowed to flow. A platinum catalyst is deposited on the aggregate of hollow carbon fibers. Next, the aggregate of the hollow carbon fibers is sufficiently washed with pure water and then heat-treated.

  The catalyst may be supported on the whole or a part of the pores of the aggregate of the hollow carbon fibers of the present invention, that is, in the vicinity in contact with the electrolyte membrane.

  Further, the catalyst layer in the pores may be impregnated with the proton conductive polymer electrolyte by impregnating the aggregate of hollow carbon fibers carrying the noble metal catalyst with a solution containing a proton conductive polymer electrolyte or the like. . As the proton conductive polymer electrolyte, materials used for the proton conductive solid polymer membrane described later can be used.

  Examples of the fuel that can be used in the fuel cell of the present invention include hydrogen gas, methanol, ethanol, 1-propanol, dimethyl ether, ammonia, and the like, and methanol is preferable.

  The direct methanol fuel cell has a feature that it can generate electric power by directly supplying a liquid as it is without taking out hydrogen gas by reforming an aqueous methanol solution as a fuel. Therefore, the fuel is gasified or reformed and supplied. Compared to conventional polymer electrolyte fuel cells, the structure as a power generation system can be simplified, and the size and weight can be easily reduced, and the use as a distributed power source and a portable power source has attracted attention.

In such a direct methanol fuel cell, for example, a proton conductive solid polymer membrane is used as an electrolyte membrane, and an anode electrode and a cathode electrode are joined via the electrolyte membrane, and a methanol aqueous solution as a fuel is provided on the anode electrode side. An anode electrode side separator having a channel groove for supplying gas is provided, and a cathode electrode side separator having a channel groove for supplying air as an oxidant gas is provided on the cathode electrode side. 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 -)}} , the cathode electrode is water produced by the reduction reaction between the hydrogen ions and the air having passed through the electrolyte membrane ( _{^{H + + (3/2) O 2}} + 6e - → 3H 2 O), it is possible to obtain electrical energy to an external circuit connecting the anode and cathode. 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.

  The electrolyte membrane 1 is a proton conductive solid polymer membrane, and a known proton conductive polymer can be used. Examples of the proton conductive polymer include ion exchange resins having an organic fluorine-containing polymer as a skeleton, such as perfluorocarbon sulfonic acid resins. It can be obtained as Nafion 112 (trade name, manufactured by DuPont), Nafion 117 (trade name, manufactured by DuPont) or DOW membrane (trade name, manufactured by Dow Chemical).

  In addition, sulfonated polyether ketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfone, sulfonated polysulfide, sulfonated polyphenylene and other sulfonated plastic electrolytes, sulfoalkylated polyetheretherketone, sulfoalkyl There are sulfoalkylated plastic electrolytes such as sulfonated polyethersulfone, sulfoalkylated polyetherethersulfone, sulfoalkylated polysulfone, sulfoalkylated polysulfide, and sulfoalkylated polyphenylene. The sulfonic acid equivalent of these electrolyte materials is about 0.5 to 2.0 meq / g dry resin, preferably 0.7 to 1.6 meq / g dry resin. When the sulfonic acid equivalent is less than 0.5 meq / g dry resin, the ionic conduction resistance is increased, and when it is greater than 2.0 meq / g dry resin, it is easily dissolved in water.

Moreover, as a fluorine-type electrolyte material, for example,
Formula _{CF 2 = CF- (OCF 2 CFX} ) m-Oq- (CF 2) n-A
(Wherein, m = 0 to 3, n = 0 to 12, q = 0 or 1, X = F or CF ₃ , A = sulfonic acid type functional group), tetrafluoroethylene, hexafluoro And copolymers with perfluoroolefins such as propylene, chlorotrifluoroethylene or perfluoroalkyl vinyl ether. Preferred examples of Furorobiniru compounds, for _{example, CF 2 = CFO (CF 2} ) aSO 2 F, CF 2 = CFOCF 2 CF (CF 3) O (CF 2) aSO 2 F, CF 2 = CF (CF 2) bSO ₂ F, CF ₂ = CF (OCF ₂ CF (CF ₃ )) cO (CF ₂ ) ₂ SO ₂ F (where a = 1 to 8, b = 0 to 8, c = 1 to 5) It can also be used.

  Examples of the method for joining and manufacturing the electrolyte membrane and the electrode containing the hollow carbon fiber assembly of the present invention include the following methods.

  I. Whether carbon particles carrying a platinum catalyst are applied to the hollow carbon fiber assembly of the present invention as a diffusion layer, heat-treated to form a catalyst layer to form an electrode, and then hot-pressed with the electrolyte membrane for integration Alternatively, after the catalyst layer paste is applied to the electrolyte membrane, it is integrated by hot pressing with the aggregate of the hollow carbon fibers of the present invention to be the diffusion layer.

B. A method in which a catalyst is supported on the whole pore portion of the aggregate of hollow carbon fibers of the present invention or in the vicinity in contact with the electrolyte membrane, and then hot-pressed and integrated with the electrolyte membrane. This method is preferable because it is not necessary to separately provide a diffusion layer, and the number of parts can be reduced.

  A fuel distribution plate (anode electrode separator) in which grooves for forming a fuel flow path and an oxidant flow path are formed outside the assembly of the electrolyte membrane and the electrode produced as described above, and an oxidant flow distribution plate ( A fuel cell is formed by stacking a plurality of single cells via a cooling plate or the like.

  The fuel cell electrode and the fuel cell using the same according to the present invention will be described in more detail by way of examples. However, it goes without saying that the present invention is not limited to such examples.

(Preparation of hollow carbon fiber assembly 1)
After charging 1.2 kg of phenol, 0.6 kg of 50% formalin and 3.5 g of oxalic acid into a 3 liter flask and reacting for 4 hours at the reflux temperature, vacuum dehydration concentration was further performed under heating, and an uncured softening point of 110 ° C. 1 kg of novolak resin was obtained. On the other hand, 50 g of Ketjen Black EC600JD (Ketjen Black International Co., Ltd.) and 200 g of the uncured novolak resin were heated and melted, mixed and stirred to obtain an uncured novolak resin mixture. This uncured novolac resin mixture was melted at a speed of 260 m / min using a spinnerable die having a donut-shaped discharge port having 20 holes, an inner diameter (corresponding to a hole diameter) of 0.2 mmφ, and an outer diameter of 0.3 mmφ. Spinning was performed to obtain an uncured novolac resin mixture fiber. This novolak resin fiber was immersed in a hardening aqueous solution mainly composed of formaldehyde and hydrochloric acid, heated to 95 ° C. at a rate of 0.5 ° C./min, and held for 8 hours to obtain a hardening novolak resin fiber. A total of 400 fibers, 20 in length and 20 in width, were passed through a bag filled with a resol type phenol resin (PR-51107, Sumitomo Bakelite Co., Ltd.), and then a 1 cm square hole was formed in a 10 cm square iron piece. It passes through a jig heated to 200 ° C. at a speed of 1 m / min. After this treatment, a cured novolac resin fiber in which 400 fibers are hardened is formed, and is cut to a length of 30 cm. Further, 10 cuts of 10 by 10 are cut into 30 cm and fixed with carbon fiber. This sample was wrapped in carbon cloth, heated to 1300 ° C. at a rate of 5 ° C./min in a nitrogen stream, and held at 1300 ° C. for 30 minutes.

The finished carbide is cut to a thickness of 3 mm perpendicular to the fiber axis with a diamond cutter to produce a 10 cm square carbon electrode. When observed with an electron microscope, holes with an average diameter of 0.2 mmφ and an average number of holes of 1089 / cm ² penetrating from the front surface to the back surface were formed. There was almost no variation in hole diameter, and highly uniform holes were formed.

  Further, when the surface specific resistance was measured, it was found to be 0.1 Ωcm, and it was found to be optimal as a fuel cell electrode.

(Preparation of hollow carbon fiber assembly 2)
Phenol 1.2 kg, 50% formalin 0.6 kg, and oxalic acid 3.5 g were charged into a 3 liter flask and reacted at reflux temperature for 4 hours. Thereafter, vacuum dehydration and concentration are performed under heating until the internal temperature of the reaction product rises to 200 ° C., and then 50 g of Ketjen Black EC600JD (Ketjen Black International Co., Ltd.) is added to the flask, and the mixture is melt-mixed and stirred. A cured novolac resin was obtained. The uncured novolak resin weight in the flask before mixing was 1 kg. The obtained resin after mixing is discharged at a discharge rate of 0.3 g / min · Hole from a base having a donut-shaped discharge port having 20 holes, an inner diameter (corresponding to a hole diameter) of 0.4 mmφ, and an outer diameter of 0.6 mmφ. A heated air flow of 110 ° C. was passed through a slit having a width of 0.3 mm at a flow rate of 30 liters / minute · Hole and spun by a so-called melt blown method. The uncured novolac resin fiber was immersed in a cured aqueous solution mainly composed of formaldehyde and hydrochloric acid, heated to 95 ° C. at a rate of 0.5 ° C./min, and held for 8 hours to obtain a cured novolac resin fiber. . When this fiber was observed with an electron microscope, a continuous hollow fiber was formed. A total of 400 fibers, 20 in length and 20 in width, were passed through a bag filled with a resol type phenol resin (PR-51107, Sumitomo Bakelite Co., Ltd.), and then a 1 cm square hole was formed in a 10 cm square iron piece. It passes through a jig heated to 200 ° C. at a speed of 1 m / min. After this treatment, a cured novolac resin fiber in which 400 fibers are hardened is formed, and is cut to a length of 30 cm. Further, 10 cuts of 10 by 10 are cut into 30 cm and fixed with carbon fiber. This sample was wrapped in carbon cloth, heated to 1300 ° C. at a rate of 5 ° C./min in a nitrogen stream, and held at 1300 ° C. for 30 minutes.

The finished carbide is cut to a thickness of 3 mm perpendicular to the fiber axis with a diamond cutter to produce a 10 cm square carbon electrode. When observed with an electron microscope, holes having an average diameter of 0.4 mmφ penetrating from the front surface to the back surface and having an average number of holes of 256 holes / cm ² were found. There was almost no variation in hole diameter, and highly uniform holes were formed.

  Further, when the surface specific resistance was measured, it was found to be 0.15 Ωcm, which proved optimal as a fuel cell electrode.

[Production of electrode and solid electrolyte membrane assembly]
Example 1
I. Oxidation treatment Production of hollow carbon fiber assembly The hollow carbon fiber assembly obtained in 1 was placed in a 5M hydrogen peroxide solution and sonicated at about 80 ° C. for about 2 hours. Next, it is washed with pure water, and is again placed in a 0.1 M hydrogen peroxide solution and sonicated at about 40 ° C. for about 30 minutes. Further, after washing with pure water, ultrasonic washing is performed with pure water at about 30 ° C. for about 10 minutes. Repeat the ultrasonic cleaning until the pH is neutral.

B. Preparation of platinum electrode for cathode electrode An assembly of oxidized hollow carbon fibers is placed in an electrolytic cell provided with a relative electrode. Next, a platinum electrodeposition solution consisting of a 0.02M H ₂ PtCl ₆ solution to which about 1% by volume of 0.1M HCl and about 0.5% by volume of ethanol were added was added to the hollow carbon fiber assembly. It introduce | transduces into the said electrolytic vessel so that the surface by the side of an electrolyte membrane may be contacted. Next, by applying a square pulse potential to the electrolytic deposition solution in a potential region of -0.5 to 0.0 V relative to the reference electrode (SCE), a total charge of 0.1 to 10 C / cm ² is allowed to flow. A platinum catalyst is deposited inside the pores of the hollow carbon fiber. Next, the hollow carbon fiber is sufficiently washed with pure water and then heat-treated.

  Isopropanol is added to a DuPont Nafion solution to prepare a solution having a viscosity of 50 cp. An aggregate of hollow carbon fibers carrying a catalyst is immersed in this solution for 24 hours. Then, it was taken out and dried to produce a cathode electrode.

C. Production of platinum / ruthenium electrode for anode electrode An assembly of oxidized hollow carbon fibers is placed in an electrolytic cell equipped with a relative electrode. A platinum / ruthenium electrodeposition solution comprising 0.05M H ₂ PtCl ₆ solution and 0.05M RuCl ₃ solution is then added with about 5% by volume 0.1M HCl and about 2% by volume ethanol. It introduce | transduces into the said electrolytic vessel so that the surface by the side of the electrolyte membrane of the aggregate | assembly of the said hollow carbon fiber may be contacted.

Next, by applying a pulse potential to the electrolytic deposition solution in a potential region of −0.5 to 0.3 V relative to the reference electrode (SCE) and causing a total charge of 0.1 to 10 C / cm ² to flow, hollow carbon A platinum / ruthenium catalyst is deposited inside the pores of the fiber assembly. Next, after thoroughly washing with pure water, heat treatment was performed to produce an anode electrode.

  Isopropanol is added to a DuPont Nafion solution to prepare a solution having a viscosity of 50 cp. An aggregate of hollow carbon fibers carrying a catalyst is immersed in this solution for 24 hours. Then, it was taken out and dried to produce an anode electrode.

D. Assembling the electrode-solid electrolyte membrane assembly The electrodes prepared in (b) and (c) were hot-pressed on both surfaces of a DuPont solid electrolyte membrane Nafion 112 at a temperature of 130 ° C. and a pressure of 9.8 × 10 ⁵ (Pa). -A solid electrolyte membrane assembly was prepared.

(Example 2)
I. Oxidation treatment Production of hollow carbon fiber assembly The hollow carbon fiber assembly obtained in 1 was placed in a 5M hydrogen peroxide solution and sonicated at about 80 ° C. for about 2 hours. Next, it is washed with pure water, and is again placed in a 0.1 M hydrogen peroxide solution and sonicated at about 40 ° C. for about 30 minutes. Further, after washing with pure water, ultrasonic washing is performed with pure water at about 30 ° C. for about 10 minutes. Repeat the ultrasonic cleaning until the pH is neutral.

B. Preparation of platinum electrode for cathode electrode To a Nafion solution manufactured by DuPont, a catalyst-supported carbon (catalyst; Pt, carbon; Vulcan XC-72R manufactured by Cabot, platinum-supported amount: 50% by mass) and isopropanol are added, and the catalyst is stirred well. -A polymer composition was prepared.

  An aggregate of hollow carbon fibers subjected to oxidation treatment was used as a diffusion layer, and the catalyst-polymer composition was applied as a catalyst layer on one side of this layer to produce a cathode electrode.

C. Preparation of platinum / ruthenium electrode for anode electrode Catalyst-supported carbon (catalyst; Pt and Ru, carbon; Vulcan XC-72R, platinum and ruthenium supported amount: 50% by mass) and isopropanol added to DuPont Nafion solution The catalyst-polymer composition was prepared by stirring well.

  A cathode electrode was produced by applying an aggregate of hollow carbon fibers subjected to oxidation treatment as a diffusion layer and applying the catalyst-polymer composition as a catalyst layer on one side of this layer.

D. Assembling the electrode-solid electrolyte membrane assembly The electrodes prepared in (b) and (c) were hot-pressed on both surfaces of a DuPont solid electrolyte membrane Nafion 112 at a temperature of 130 ° C. and a pressure of 9.8 × 10 ⁵ (Pa). -A solid electrolyte membrane assembly was prepared.

(Example 3)
Except for using the hollow carbon fiber aggregates produced in Hollow Carbon Fiber Aggregate Preparation 2 instead of using the hollow carbon fiber aggregates obtained in Hollow Carbon Fiber Aggregate Production 1 A cathode electrode and an anode electrode were produced in the same manner as in Example 1 to produce an electrode-solid electrolyte membrane assembly.

Example 4
Except for using the hollow carbon fiber aggregates produced in Hollow Carbon Fiber Aggregate Preparation 2 instead of using the hollow carbon fiber aggregates obtained in Hollow Carbon Fiber Aggregate Production 1 A cathode electrode and an anode electrode were prepared in the same manner as in Example 2 to prepare an electrode-solid electrolyte membrane assembly.

(Comparative Example 1)
Preparation of hollow carbon fiber assembly Cathode electrode and anode electrode as in Example 2 except that Toray carbon paper TGP-H-060 was used instead of using the hollow carbon fiber assembly obtained in 1 And an electrode-solid electrolyte membrane assembly was prepared.

[Battery evaluation and results]
The assembly of the electrolyte membrane and electrode of the example and the comparative example prepared above was sandwiched between a titanium anode electrode side separator in which a fuel channel was formed and a titanium cathode electrode side separator in which a gas channel was formed, A direct methanol fuel cell single cell was prepared and current-voltage characteristics were measured.

  In addition, an external output terminal was attached to the separator on the anode electrode side and cathode electrode side so that the output of the fuel cell could be taken out.

  Using the fuel cell prepared above, a 2 molar aqueous methanol solution at atmospheric pressure was caused to flow through the fuel flow path at a fuel flow rate of 30 ml / min, and 1 atm air as an oxidant gas was flowed through the gas flow path at 100 ml / min. Then, power generation was performed at 80 ° C., and current-voltage characteristics were measured. As a representative value, the output at the initial stage of operation, after 10 hours of operation, and after 1 week of operation was evaluated with a current value obtained by connecting resistors of 500Ω and 1 kΩ.

  The results are shown in Table 1.

  From this, when looking at the output after 10 hours and 1 week after operation, the current value in the case of using the assembly of the electrolyte membrane and the electrode of the present invention is better than that of the comparative example, and the stable high output It can be seen that is obtained for a long time.

  In particular, in Examples 1 and 3 using the aggregate of hollow carbon fibers of the present invention as a catalyst layer, no decrease in output was observed even after one week.

1 is a schematic view showing a single cell I of a fuel cell according to the present invention. (A) is a perspective view of one hollow carbon fiber, (b) is a perspective view schematically showing an assembly of hollow carbon fibers according to the present invention, and (c) is a hollow carbon fiber according to the present invention. It is a perspective view which shows the state which cut | disconnected the aggregate of the hollow carbon fiber bundled in the shape as an electrode to predetermined thickness.

Explanation of symbols

I Fuel cell single cell 1 Electrolyte membrane 2 Anode electrode side catalyst layer 3 Cathode electrode side catalyst layer 4 Anode electrode side diffusion layer 5 Cathode electrode side diffusion layer 6 Anode electrode side separator 7 Cathode electrode side separator 8 Fuel flow path 9 Oxidizing agent Channel 10 Hole 11 Aggregate of hollow carbon fibers

Claims (5)

A fuel cell electrode comprising an assembly of hollow carbon fibers. 2. The fuel cell electrode according to claim 1, wherein the hollow carbon fiber aggregate has a catalyst supported inside its pores. 3. 3. The fuel cell electrode according to claim 2, wherein an average diameter of the pores in the hollow carbon fiber aggregate is 100 nm or more and less than 1 mm. A fuel cell using the fuel cell electrode according to any one of claims 1 to 3 as at least one of an anode electrode and a cathode electrode. The fuel cell according to claim 4, wherein the fuel cell is a direct methanol fuel cell.

Images