KR101008155B1 - Membrane-electrode assembly of fuel cell and fuel cell - Google Patents

Abstract

The present invention relates to a fuel cell membrane-electrode assembly and a fuel cell. The fuel cell membrane-electrode assembly of the present invention includes an electrolyte membrane; And an anode electrode and a cathode electrode positioned opposite to each other with the electrolyte membrane interposed therebetween, each including an catalyst layer and a gas diffusion layer, wherein the gas diffusion layer comprises: a substrate; And a microporous layer formed on a surface facing the catalyst layer of the substrate, wherein the microporous layer comprises a conductive powder, a hydrophobic additive and silica powder, calcium chloride (CaCl ₂ ), and soda lime (CaO + NaOH). Characterized in that it comprises an inorganic material selected from. According to the fuel cell membrane electrode assembly of the present invention, by forming a microporous layer on the surface facing the catalyst layer of the gas diffusion layer and by adding an inorganic material such as silica powder to the microporous layer, the amount of external water supply is reduced or eliminated Even if the water content of the electrolyte membrane is sufficiently maintained, the ion membrane conductivity of the electrolyte membrane can be improved, thereby improving the performance of the fuel cell and extending the lifespan.

Fuel cell, membrane-electrode assembly, electrolyte membrane, gas diffusion layer, catalyst layer, microporous layer

Description

Membrane-electrode assembly of fuel cell and fuel cell

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to.

1 is a view for explaining the principle of electricity generation of the fuel cell.

2 is a view schematically showing a fuel cell membrane electrode assembly according to an embodiment of the present invention.

3 is a view schematically showing a fuel cell according to an embodiment of the present invention.

The present invention relates to a membrane-electrode assembly and a fuel cell of a fuel cell, wherein in a fuel cell using a liquid fuel, a fuel cell is prevented or reduced by passing the electrolyte membrane along with water to the cathode electrode. The present invention relates to a fuel cell membrane-electrode assembly and a fuel cell capable of improving performance.

Recently, as the depletion of existing energy resources such as oil and coal is predicted, interest in energy that can replace them is increasing. As one of the alternative energy sources, the fuel cell is particularly attracting attention due to its advantages such as high efficiency, no pollutants such as NO _x and SO _x , and abundant fuel used.

A fuel cell is a power generation system that converts chemical reaction energy of a fuel and an oxidant into electrical energy. Hydrogen, a hydrocarbon such as methanol, butane, and the like are typically used as an oxidant.

In a fuel cell, the most basic unit for generating electricity is a membrane-electrode assembly (MEA), which consists of an electrolyte membrane and anode and cathode electrodes formed on both sides of the electrolyte membrane. Referring to FIG. 1 and Reaction Formula 1 (Reaction formula of a fuel cell when hydrogen is used as a fuel) showing the electricity generation principle of a fuel cell, an oxidation reaction of a fuel occurs at an anode electrode, and hydrogen ions and electrons are generated. The electrolyte moves through the electrolyte membrane to the cathode electrode, where water is generated by reaction between oxygen (oxidant) and hydrogen ions transferred through the electrolyte membrane and electrons. This reaction causes the movement of electrons in the external circuit.

The ^{_{anode: H 2 → 2H + + 2e}} -

^{_{Cathode: 1 / 2O 2 + 2H +}} + 2e - → H 2 O

Total Reaction Formula: H ₂ + 1 / 2O ₂ → H ₂ O

Fuel cells include polymer electrolyte fuel cells (PEMFC), direct methanol fuel cells (DMFC), phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), molten carbonate fuel cells (MCFC), solid oxide fuels Batteries (SOFC) and the like. Among them, polymer electrolyte fuel cells have been researched most actively because of their high energy density and high output.

The polymer electrolyte fuel cell differs from other fuel cells in that it uses a solid polymer electrolyte membrane instead of a liquid as an electrolyte. Since the polymer electrolyte membrane tends to have higher ion conductivity as the moisture content increases, the polymer electrolyte membrane should always maintain a certain level or more of moisture. Since the cathode generates water through the battery reaction, but this is not sufficient to maintain the ion conductivity of the electrolyte membrane, a method of humidifying the electrolyte membrane by supplying water together with the reaction gas to the membrane-electrode assembly is performed. However, if water is applied to the membrane-electrode assembly, the efficiency of the fuel cell is lowered. Therefore, it is desirable to reduce the amount of externally applied moisture as much as possible. Therefore, efforts to solve such problems have been made steadily in the related field, and the present invention has been devised under such technical background.

The present invention has been made to solve the above-mentioned problems of the prior art, the technical problem to be achieved by the present invention is to improve the ion conductivity of the electrolyte membrane by maintaining sufficient moisture in the electrolyte membrane even if the external water supply amount is reduced or eliminated In order to improve the performance of the fuel cell, it is an object of the present invention to provide a fuel cell membrane-electrode assembly and a fuel cell capable of achieving such a technical problem.

The present invention to achieve the technical problem to be achieved by the present invention, the electrolyte membrane; And an anode electrode and a cathode electrode positioned opposite to each other with the electrolyte membrane interposed therebetween, each including an catalyst layer and a gas diffusion layer, wherein the gas diffusion layer comprises: a substrate; And a microporous layer formed on a surface facing the catalyst layer of the substrate, wherein the microporous layer is formed of a conductive powder, a hydrophobic additive and silica powder, calcium chloride (CaCl ₂ ), and soda lime (CaO + NaOH). It provides a fuel cell membrane-electrode assembly comprising an inorganic material selected from.

In the membrane-electrode assembly, the conductive powder is typically graphite, acetylene black, carbon black, cathodic black, activated carbon, mesoporous carbon, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon nano rings, carbon One selected from the group consisting of nanowires and fullerenes (C60) may be used, and the hydrophobic additive may be one selected from the group consisting of PTFE (Polytetrafluoroethylene) and PVDF (Poly Vinyldene Fluoride).

The weight ratio of the inorganic material in the microporous layer is preferably 0.1 to 5% by weight, and the microporous layer typically includes screen printing, spray coating, doctor blade, roll coating or slit die coating. It can be formed through.

The polymer electrolyte membrane is a perfluorosulfonic acid polymer, a hydrocarbon-based polymer, polyimide, polyvinylidene fluoride, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyphosphazine, polyethylene naphthalate, polyester, doped poly It is preferable that it consists of a polymer selected from the group consisting of benzimidazole, polyether ketone, polysulfone, acids and bases thereof.

The anode catalyst layer may typically include a catalyst selected from the group consisting of platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-transition metal alloy, and the cathode electrode The catalyst layer of may typically be made of platinum. The catalysts can be used on their own as well as supported on the carrier. The catalyst layer may further comprise an ion conductive monomer or a hydrophobic binder.

The gas diffusion layer may typically comprise carbon paper, carbon cloth or carbon felt.

The membrane-electrode assembly can be effectively used in a polymer electrolyte fuel cell or a direct methanol fuel cell.

The invention also provides a stack comprising one or more membrane-electrode assemblies of the invention and a separator interposed between the membrane-electrode assemblies; A fuel supply unit supplying fuel to the stack; And an oxidant supply unit supplying an oxidant to the electricity generating unit.

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

2 is a view schematically showing a membrane-electrode assembly for a fuel cell according to an embodiment of the present invention. With reference to Figure 2 looks at with respect to the fuel cell membrane electrode assembly of the present invention.

The membrane-electrode assembly of the present invention includes an electrolyte membrane 201; And an anode electrode and a cathode electrode positioned opposite to each other with the electrolyte membrane 201 interposed therebetween, and including a catalyst layer 203 and 205 and a gas diffusion layer, respectively. The gas diffusion layer is a substrate (209a, 209b); And microporous layers 207a and 207b formed on surfaces facing the catalyst layers 203 and 205 of the substrates 209a and 209b, wherein the microporous layers 207a and 207b are conductive powders and hydrophobic additives. And inorganic materials.

As the inorganic material, silica powder, calcium chloride (CaCl ₂ ) and soda lime (CaO + NaOH) are preferably used, and they have a hygroscopic effect to prevent moisture from escaping to the outside, thereby improving the water content of the electrolyte membrane 201. . This improves the ion conductivity of the electrolyte membrane 201. In addition, when the inorganic material is disposed between the catalyst layer and the membrane, the utilization rate and reaction efficiency of the catalyst layer can be greatly reduced, but in the present invention, this problem can be solved by including the inorganic material in the microporous layer.

Representative examples of the conductive powder include graphite, acetylene black, carbon black, cathodic black, activated carbon, mesoporous carbon, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon nanorings, carbon nanowires, and fullerenes (C60). The hydrophobic additive may be selected from the group consisting of, for example, a fluorine resin may be used. For example, PTFE and polyvinyldene fluoride (PVDF) may be used.

The weight ratio of the inorganic material in the microporous layers 207a and 207b is preferably 0.1 to 5% by weight. When the weight ratio of the inorganic material exceeds the upper limit, the electrical conductivity of the gas diffusion layer is lowered, and when the weight ratio is lower than the lower limit. Effective moisture retention due to reduced hygroscopic effect is difficult and undesirable.

The microporous layer 207a, 207b is typically a screen printing method, a spray coating method, a doctor blade method, a roll coating method using a composition for forming a microporous layer including the conductive powder, a hydrophobic additive, an inorganic material, and a solvent. Or through a slit die coating method. As the solvent, water, isopropyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol or a mixture of two or more thereof may be used.

The substrates 209a and 209b move and diffuse the reaction gas and water together with a role as a current conductor, and may typically include carbon paper, carbon cloth, or carbon felt.

The electrolyte membrane 201 serves as a transfer passage through which hydrogen ions generated from the anode electrode are transferred to the cathode electrode. Ethersulfones, polyphenylenesulfides, polyphenylene oxides, polyphosphazines, polyethylenenaphthalates, polyesters, doped polybenzimidazoles, polyetherketones, polysulfones, acids or bases thereof may be preferably used.

The anode electrode is where the oxidation of the fuel occurs, the catalyst layer 203 is selected from the group consisting of platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-transition metal alloy. The catalyst to be used may be preferably used, and the cathode electrode is where the reduction reaction of the oxidant occurs, and platinum may be used as the catalyst in the catalyst layer 205. The catalysts may be supported on a carbon-based carrier, and representative carriers include carbon-based carriers such as denca black, acetylene black, and graphite. The catalyst layer may further include an ion conductive monomer or a hydrophobic binder to improve the ion conductivity and reduce the flow of water.

The membrane-electrode assembly may be most effectively used in a polymer electrolyte fuel cell, and may also be effectively used in a direct methanol fuel cell using a polymer electrolyte membrane.

The present invention also provides a fuel cell comprising the membrane-electrode assembly of the present invention. 3 is a view schematically showing a fuel cell according to an embodiment of the present invention. Referring to FIG. 3, the fuel cell of the present invention includes a stack 200, a fuel supply unit 400, and an oxidant supply unit 300.

The stack 200 includes one or two or more membrane-electrode assemblies of the present invention, and in the case where two or more membrane-electrode assemblies are included, the stack 200 includes a separator interposed therebetween. It serves to transfer the fuel and oxidant supplied from the outside to the membrane-electrode assembly.

The fuel supply unit 400 serves to supply fuel to the stack, and includes a fuel tank 410 for storing fuel and a pump 420 for supplying fuel stored in the fuel tank 410 to the stack 200. Can be. The fuel may be a gas or liquid hydrogen or hydrocarbon fuel, examples of the hydrocarbon fuel may be methanol, ethanol, propanol, butanol or natural gas.

The oxidant supply unit 300 serves to supply an oxidant to the stack. Oxygen is typically used as the oxidant, and may be used by injecting oxygen or air into the pump 300.

The terms or words used in this specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors can appropriately define the concept of terms in order to best describe their invention. Based on the principle, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the exemplary embodiments described herein are only exemplary embodiments of the present invention and do not represent all of the technical ideas of the present invention, and various equivalents and modifications that may substitute them at the time of the present application may be used. It should be understood that there may be.

According to the fuel cell membrane electrode assembly of the present invention, by forming a microporous layer on the surface facing the catalyst layer of the gas diffusion layer and by adding an inorganic material such as silica powder to the microporous layer, the amount of external water supply is reduced or eliminated Even if the water content of the electrolyte membrane is sufficiently maintained, the ion conductivity of the electrolyte membrane can be improved, thereby improving the performance of the fuel cell and extending its life.

Claims (15)

Electrolyte membrane; And an anode electrode and a cathode electrode positioned opposite to each other with the electrolyte membrane interposed therebetween, each including an catalyst layer and a gas diffusion layer. The gas diffusion layer is a substrate; And a microporous layer formed on one surface of the substrate and in contact with the catalyst layer. The microporous layer is made of a conductive powder, a hydrophobic additive and an inorganic material, The inorganic material is a fuel cell membrane-electrode assembly, characterized in that selected from the group consisting of silica powder, calcium chloride (CaCl ₂ ) and soda lime (CaO + NaOH). The method of claim 1, The conductive powder is in the group consisting of graphite, acetylene black, carbon black, cathodic black, activated carbon, mesoporous carbon, carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon nano rings, carbon nanowires and fullerenes (C60) Membrane-electrode assembly for a fuel cell, characterized in that selected. The method of claim 1, The hydrophobic additive is a membrane-electrode assembly for a fuel cell, characterized in that selected from the group consisting of PTFE (Polytetrafluoroethylene) and PVDF (PolyVinyldeneFluoride). The method of claim 1, The weight ratio of the inorganic material in the microporous layer is a fuel cell membrane electrode assembly, characterized in that 0.1 to 5% by weight. The method of claim 1, The microporous layer is a fuel cell membrane-electrode assembly, characterized in that formed through the screen printing method, spray coating method, doctor blade method, roll coating or slit die coating method. The method of claim 1, The polymer electrolyte membrane is a perfluorosulfonic acid polymer, a hydrocarbon-based polymer, polyimide, polyvinylidene fluoride, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyphosphazine, polyethylene naphthalate, polyester, doped poly A membrane-electrode assembly for a fuel cell, comprising a polymer selected from the group consisting of benzimidazole, polyether ketone, polysulfone, and acids and bases thereof. The method of claim 1, The catalyst layer of the anode electrode is a fuel cell membrane, characterized in that it comprises a catalyst selected from the group consisting of platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium alloy, platinum-palladium alloy and platinum-transition metal alloy Electrode assembly. The method of claim 7, wherein The catalyst is a membrane-electrode assembly for a fuel cell, characterized in that supported on a carbon-based carrier. The method of claim 1, Membrane-electrode assembly for a fuel cell, characterized in that the catalyst layer of the cathode electrode comprises platinum. 10. The method of claim 9, Membrane electrode assembly for a fuel cell, characterized in that the platinum is supported on a carbon-based carrier. The method of claim 1, The catalyst layer is a fuel cell membrane-electrode assembly, characterized in that further comprises an ion conductive monomer. The method of claim 1, The catalyst layer further comprises a hydrophobic binder for fuel cell membrane electrode assembly. The method of claim 1, The gas diffusion layer is a fuel cell membrane-electrode assembly, characterized in that comprising a carbon paper, carbon cloth and carbon felt selected from the group consisting of. The method of claim 1, The membrane-electrode assembly is a fuel cell membrane-electrode assembly, characterized in that used in a polymer electrolyte fuel cell or direct methanol fuel cell. A stack comprising a membrane-electrode assembly according to any one of claims 1 to 14 and a separator interposed between the membrane-electrode assemblies; A fuel supply unit supplying fuel to the stack; And And an oxidant supply unit for supplying an oxidant to the electricity generating unit.

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