KR101000197B1 - Method of preparing electrode of membrane-electrode assembly for fuel cell, electrode and membrane-electrode assembly prepared by the same - Google Patents

Abstract

The present invention relates to a method for forming a catalyst layer of a membrane-electrode assembly for a fuel cell, and a catalyst layer and a membrane-electrode assembly manufactured by using the same. The method for forming a catalyst layer of the present invention comprises the steps of: dissolving a zirconium compound such as zirconium butoxide in a solvent (S1), adding a chelating agent and a catalyst, and drying the solution to prepare a zirconium precursor; (S2) preparing a catalyst ink by adding and mixing a catalyst, the zirconium precursor and a binder to a mixed solvent of water and alcohol; (S3) coating the catalyst ink on an electrolyte membrane or a gas diffusion layer and drying to form a catalyst layer; (S4) converting the zirconium precursor into zirconium phosphate or zirconium sulfate by introducing the catalyst layer into a phosphoric acid solution or a sulfuric acid solution and maintaining the temperature of the phosphoric acid solution or the sulfuric acid solution at 80 to 100 ° C; According to the method for forming a catalyst layer of a fuel cell membrane electrode assembly of the present invention, the zirconium compound is evenly dispersed in the catalyst layer to improve conductivity and moisture retention of the catalyst layer, and the zirconium compound is not dissolved by moisture generated during operation. The performance of the catalyst bed can be maintained continuously.

Fuel cell, membrane-electrode assembly, catalyst layer, zirconium compound, zirconium precursor

Description

TECHNICAL FIELD OF THE INVENTION A method for forming a catalyst layer of a membrane-electrode assembly for a fuel cell, and a catalyst layer and a membrane-electrode assembly prepared by using the same, the method of preparing electrode of membrane-electrode assembly for fuel cell, electrode and membrane-electrode assembly prepared by the same

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.

The present invention relates to a method for forming a catalyst layer of a fuel cell membrane-electrode assembly, and a catalyst layer and a membrane-electrode assembly manufactured using the same, to improve the moisture retention and conductivity of the catalyst layer and to maintain the performance of the catalyst layer even during operation of the fuel cell. The present invention relates to a method for forming a catalyst layer of a fuel cell membrane-electrode assembly, and a catalyst layer and a membrane-electrode assembly manufactured using the same.

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.

In order to solve this problem, inorganic nanoparticles, such as a zirconium compound, are used in the electrode layer, and they have moisturizing properties and hydrogen ion conductivity, contributing to the improvement of the performance of the membrane-electrode assembly. However, these inorganic nanoparticles do not disperse well in the electrode layer, and even dispersion of the inorganic nanoparticles is essential for improving moisture retention and conductivity through the inorganic nanoparticles. In addition, the inorganic nanoparticles may be humidified in a fuel cell after forming the electrode layer. Since there is a problem of dissolving by water generated during the condition or operation, in order to maintain performance, inorganic nanoparticles must be adjusted so that they do not dissolve in water and disappear from the electrode layer.

The present invention has been made to solve the above-described problems of the prior art, the technical problem to be achieved by the present invention is to evenly disperse the zirconium compound in the catalyst layer of the membrane-electrode assembly for fuel cells to improve the conductivity and moisture retention, zirconium compound The performance of the catalyst layer is continuously maintained by being dissolved by moisture generated during the operation, and an object of the present invention is to provide a method for forming a catalyst layer of a membrane-electrode assembly for fuel cells, which can achieve the technical problem, To provide a prepared catalyst layer and membrane-electrode assembly.

In order to achieve the technical problem to be achieved by the present invention, the present invention, (S1) dissolving a zirconium compound selected from the group consisting of zirconium butoxide, zirconium chloride and zirconium ethoxide, chelating agent and nitric acid, sulfuric acid and Preparing a zirconium precursor by drying a solution prepared by adding and mixing a catalyst selected from the group consisting of hydrochloric acid; (S2) preparing a catalyst ink by adding and mixing a catalyst, the zirconium precursor and a binder to a mixed solvent of water and alcohol; (S3) coating the catalyst ink on an electrolyte membrane or a gas diffusion layer and drying to form a catalyst layer; (S4) converting the zirconium precursor into zirconium phosphate or zirconium sulfate by introducing the catalyst layer into a phosphoric acid solution or a sulfuric acid solution and maintaining the temperature of the phosphoric acid solution or a sulfuric acid solution at 80 to 100 ° C; Provided is a method for forming a catalyst layer of a fuel cell membrane-electrode assembly.

The solvent used in the step (S1) may be typically selected from isopropyl alcohol, ethanol and aromatic compounds such as benzene, toluene, xylene, and the chelating agent is typically acetyl acetone and EDTA (ethylenediaminetetraacetic Acid)). The amount of the chelating agent added to the solvent in the step (S1) is preferably 1 mol to 2 mol per mol of the zirconium compound, and the concentration of the zirconium compound in the solution prepared in the step (S1) is 20 to 40%. Preferably, the concentration of the catalyst in the solution prepared in the step (S1) is preferably 0.01 to 0.1%.

The alcohol used as the solvent in the step (S2) may be typically selected from the group consisting of isopropyl alcohol, ethanol, methanol and propanol, and the binder is typically a hydrogen ion conductive polymer or PTFE, PVdF, PEEK, PMMA And polymers selected from the group consisting of hydrogen ion conductive derivatives thereof. The amount of zirconium precursor in the catalyst ink is preferably 10 to 20 parts by weight based on 100 parts by weight of the catalyst, and the amount of the binder in the catalyst ink is preferably 0.1 to 1 parts by weight based on 100 parts by weight of the catalyst. Do.

In the step (S3), the electrolyte membrane is typically a perfluorosulfonic acid polymer, a hydrocarbon-based polymer, polyimide, polyvinylidene fluoride, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyphosphazine, polyethylenena Phthalates, polyesters, doped polybenzimidazoles, polyetherketones, polysulfones, and their acids and bases, the gas diffusion layer is typically in the group consisting of carbon paper, carbon cloth and carbon felt It can be made including a conductive substrate selected. The gas diffusion layer may further include a microporous layer formed on one surface of the conductive substrate, wherein the catalyst layer is formed on the microporous layer of the gas diffusion layer.

In the step (S4), the concentration of the phosphoric acid solution is preferably 1 to 2 M, the concentration of the sulfuric acid solution is preferably 1 to 2 M.

The present invention also provides a catalyst layer of a fuel cell membrane-electrode assembly manufactured by the method for forming a catalyst layer of the fuel cell membrane-electrode assembly according to the present invention.

The present invention also provides an electrolyte membrane; And an anode electrode and a cathode electrode formed with the electrolyte membrane interposed therebetween, each including a catalyst layer and a gas diffusion layer, wherein the anode electrode or the cathode electrode layer comprises a catalyst layer according to the present invention. Provided is a fuel cell membrane-electrode assembly, which is produced by a method for forming a catalyst layer of a fuel cell membrane-electrode assembly.

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

According to the method for forming a catalyst layer of a fuel cell membrane-electrode assembly of the present invention, a zirconium compound is first dissolved by dissolving a zirconium compound in a solvent, and a solution prepared by adding and mixing a chelating agent and a catalyst to prepare a zirconium precursor.

In the zirconium precursor manufacturing step, isopropyl alcohol, ethanol and an aromatic solvent may be used as a solvent, and aromatic solvents include benzene, toluene and xylene. Typical zirconium compounds include zirconium butoxide, zirconium chloride, zirconium ethoxide and the like, and chelating agents typically include acetyl acetone and EDTA (ethylenediaminetetraacetic acid) and nitric acid, sulfuric acid or hydrochloric acid as catalysts. have.

The amount of the chelating agent added to the solvent in the step (S1) is preferably 1 to 2 mol per mol of the zirconium compound, and the concentration of the zirconium compound in the solution prepared in the step (S1) is 20 to 40%. Preferably, the concentration of the catalyst in the solution prepared in the step (S1) is preferably 0.01 to 0.1%. When the amount of the chelating agent is less than the lower limit, there is a problem that a reaction does not occur and a zirconium precursor of a desired form is not produced. When the upper limit is exceeded, excessive by-products are generated in the solution due to the unreacted compound. There is a problem and is undesirable. In addition, when the concentration of the zirconium compound is less than the lower limit, there is a problem that the reaction rate is very low, and when the concentration exceeds the upper limit, there is a problem that the unreacted substance is not produced because a uniform reaction is not performed. In addition, if the concentration of the catalyst is less than the lower limit, there is a problem that the reaction between the compounds is slow, if the upper limit is exceeded, the reaction rate is too fast to uniformly react or the catalyst also remains a byproduct Not desirable

Since the zirconium precursor prepared as described above is well dispersed in a mixed solvent of water and alcohol for preparing a catalyst ink, the catalyst layer formed by using the zirconium compound is uniformly dispersed and has excellent conductivity and moisture retention. In addition, since the zirconium precursor is not dissolved in water, its performance is not degraded by moisture in the membrane-electrode assembly.

Next, the catalyst, the zirconium precursor and the binder are added to the mixed solvent of water and alcohol and mixed to prepare a catalyst ink.

In the catalyst ink manufacturing step, isopropyl alcohol, ethyl alcohol, methyl alcohol or normal propyl alcohol may be used as the alcohol constituting the mixed solvent, and the binder is typically a hydrogen ion conductive polymer or PTFE, PVdF, A polymer selected from the group consisting of PEEK, PMMA, and hydrogen ion conductive derivatives thereof may be used. As the catalyst, platinum, ruthenium, osmium, platinum-ruthenium alloy, platinum-osmium may be used for the anode electrode in which the oxidation reaction of the fuel occurs. A catalyst selected from the group consisting of an alloy, a platinum-palladium alloy and a platinum-transition metal alloy may be preferably used, and in the case of a cathode electrode in which a reduction reaction of an oxidant occurs, a platinum or platinum-transition metal alloy may be preferably used. The catalysts may be supported on a carbon-based carrier, and typical carriers include carbon-based carriers such as denca black, acetylene black, and graphite.

The amount of zirconium precursor in the catalyst ink is preferably 10 to 20 parts by weight based on 100 parts by weight of the catalyst, and the amount of the binder in the catalyst ink is preferably 0.1 to 1 parts by weight based on 100 parts by weight of the catalyst. Do. When the content ratio of the zirconium precursor is less than the lower limit, since a small amount of zirconium is dispersed in the electrode layer, it is difficult to expect a moisturizing effect, and when the upper limit is exceeded, the zirconium precursor nanoparticles rather than the catalyst It is not desirable to cover the active layer, which reduces the efficiency of the fuel cell. In addition, when the content ratio of the binder is less than the lower limit, there is a problem in that binding is not properly performed between the catalyst particles or between the catalyst particles and the zirconium precursor, and when the upper limit is exceeded, the binder covers the active layer of the catalyst to It is not preferable because there is a problem of lowering the efficiency.

In order to further improve the dispersion of the zirconium precursor, the catalyst ink manufacturing process is performed by dissolving the zirconium precursor in a mixed solvent of water and alcohol, adding the catalyst and binder to the same mixed solvent, mixing the mixture, and then mixing the two solutions. Can be done.

Next, the catalyst ink is coated on an electrolyte membrane (CCM method) or a gas diffusion layer (CCS method) and dried to form a catalyst layer.

The electrolyte membrane is typically a perfluorosulfonic acid polymer, a hydrocarbon-based polymer, polyimide, polyvinylidene fluoride, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyphosphazine, polyethylene naphthalate, polyester, Doped polybenzimidazole, polyetherketone, polysulfone, and a hydrogen ion conductive polymer selected from the group consisting of acids and bases thereof may be used, and the gas diffusion layer is typically in the group consisting of carbon paper, carbon cloth and carbon felt. It can be made including a conductive substrate selected. The gas diffusion layer may further include a microporous layer formed on one surface of the conductive substrate, wherein the catalyst layer is formed on the microporous layer of the gas diffusion layer.

Next, the catalyst layer is introduced into a phosphoric acid solution or a sulfuric acid solution, and the temperature of the phosphoric acid solution or the sulfuric acid solution is maintained at 80 to 100 ° C.

This process converts the zirconium precursors dispersed in the catalyst layer into zirconium phosphate (if using phosphate solution) or zirconium sulfate (if using sulfuric acid). Therefore, it is preferable to carry out at least 60 minutes of treatment with the phosphoric acid solution or sulfuric acid solution for sufficient conversion. At this time, if the temperature of the phosphoric acid solution and sulfuric acid solution is less than the lower limit of the numerical range there is a problem that the zirconium precursor does not change to zirconium phosphate, if the upper limit exceeds the problem that the bond is broken or deformed in the membrane-electrode assembly It is not desirable to have.

The concentration of the phosphoric acid solution and the sulfuric acid solution is not particularly limited, but considering the efficiency, the concentration of the phosphoric acid solution is preferably 1 to 2 M, and the concentration of the sulfuric acid solution is preferably 1 to 2 M.

When zirconium phosphate or zirconium sulfate is formed through the above process, a washing process may be performed to remove impurities such as phosphoric acid or sulfuric acid solution remaining in the catalyst layer.

Hereinafter, an experimental example for evaluating the physical properties of the zirconium precursor used in the production of the catalyst layer of the membrane-electrode assembly for a fuel cell of the present invention will be described.

zirconium Precursor  Produce

After zirconium butoxide was dissolved in isopropyl alcohol, acetyl acetone was added to the prepared solution so that the ratio of zirconium butoxide to acetyl acetone was 0.1. The solution thus prepared was stirred at room temperature for 5 hours using 1 N nitric acid as a catalyst, filtered and dried at 90 ° C. for 12 hours to prepare a zirconium precursor.

zirconium Precursor  Solubility Assessment

0.3 g of the zirconium precursor prepared above was added to the solvent prepared in the amount of water and isopropyl alcohol described in Table 1 below, followed by stirring to prepare samples A to D. However, Sample D used a recrystallized zirconium precursor obtained by drying Sample A in a 90 ° C. oven for 12 hours. 2 is a photograph of a recrystallized zirconium precursor.

Water (g) Isopropyl Alcohol (g) Sample A 2 2 Sample B 4 0 Sample C 0 4 Sample D 4 0

3 is a photograph of Samples A to D prepared through the above process. The zirconium precursor was completely dissolved in a mixed solvent of water and isopropyl alcohol, but not in water or isopropyl alcohol, respectively. In addition, the recrystallized zirconium precursor exhibited the property of no longer being dissolved by the solvent (water).

Due to such physical properties of the zirconium precursor, the catalyst layer prepared through the catalyst layer forming method of the present invention is uniformly dispersed with zirconium phosphate or zirconium sulfate, and has excellent conductivity and moisture retention properties, and has excellent physical properties due to moisture in the membrane-electrode assembly. It does not deteriorate.

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 method for forming a catalyst layer of a fuel cell membrane electrode assembly of the present invention, the zirconium compound is evenly dispersed in the catalyst layer to improve conductivity and moisture retention of the catalyst layer, so that the zirconium compound is not dissolved by moisture generated during operation of the catalyst layer. Performance can be kept constant.

Claims (17)

(S1) A solution prepared by dissolving a zirconium compound selected from the group consisting of zirconium butoxide, zirconium chloride and zirconium ethoxide in a solvent, adding a chelating agent and a catalyst selected from the group consisting of nitric acid, sulfuric acid and hydrochloric acid and mixing Drying the prepared zirconium precursor; (S2) preparing a catalyst ink by adding and mixing a catalyst, the zirconium precursor and a binder to a mixed solvent of water and alcohol; (S3) coating the catalyst ink on an electrolyte membrane or a gas diffusion layer and drying to form a catalyst layer; And (S4) converting the zirconium precursor into zirconium phosphate or zirconium sulfate by adding the catalyst layer to a phosphoric acid solution or a sulfuric acid solution, and maintaining the temperature of the phosphoric acid solution or a sulfuric acid solution at 80 to 100 ° C. A method of forming a catalyst layer of a membrane-electrode assembly for a fuel cell. The method of claim 1, The solvent used in the step (S1) is isopropyl alcohol, ethanol, benzene, toluene and xylene catalyst layer forming method for a fuel cell membrane electrode assembly, characterized in that selected from the group consisting of. The method of claim 1, The chelating agent is a method for forming a catalyst layer of a membrane-electrode assembly for a fuel cell, characterized in that selected from the group consisting of acetyl acetone and EDTA. The method of claim 1, The amount of the chelating agent added to the solvent in the step (S1) is 1 to 2 mol per mol of the zirconium compound, the catalyst layer forming method for a fuel cell membrane electrode assembly. The method of claim 1, The method of forming a catalyst layer of a membrane-electrode assembly for a fuel cell, characterized in that the concentration of the zirconium compound in the solution prepared in the step (S1) is 20 to 40%. The method of claim 1, The catalyst layer forming method of the fuel cell membrane-electrode assembly, characterized in that the concentration of the catalyst in the solution prepared in the step (S1) is 0.01 to 0.1%. The method of claim 1, The alcohol used as the solvent in the step (S2) is a catalyst layer forming method of a fuel cell membrane-electrode assembly, characterized in that selected from the group consisting of isopropyl alcohol, ethyl alcohol, methyl alcohol and normal propyl alcohol. The method of claim 1, The binder is a hydrogen ion conductive polymer or a catalyst layer forming method for a fuel cell membrane-electrode assembly, characterized in that the polymer selected from the group consisting of PTFE, PVdF, PEEK, PMMA and hydrogen ion conductive derivatives thereof. The method of claim 1, The amount of the zirconium precursor in the catalyst ink is 10 to 20 parts by weight based on 100 parts by weight of the catalyst, the catalyst layer forming method of the fuel cell membrane electrode assembly. The method of claim 1, The amount of the binder in the catalyst ink is 0.1 to 1 part by weight based on 100 parts by weight of the catalyst, the catalyst layer forming method for a fuel cell membrane electrode assembly. The method of claim 1, The concentration of the phosphoric acid solution is 1 to 2 M, characterized in that the catalyst layer forming method for a fuel cell membrane electrode assembly. The method of claim 1, The catalyst layer forming method of the membrane-electrode assembly for fuel cell, characterized in that the concentration of the sulfuric acid solution is 1 to 2 M. The method of claim 1, The 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 polybenz A method for forming a catalyst layer of a membrane-electrode assembly for a fuel cell, characterized in that it is selected from the group consisting of imidazole, polyether ketone, polysulfone, and acids and bases thereof. The method of claim 1, The gas diffusion layer comprises a conductive substrate selected from the group consisting of carbon paper, carbon cloth and carbon felt, the catalyst layer forming method of a fuel cell membrane electrode assembly. The method of claim 14, The gas diffusion layer further includes a microporous layer formed on one surface of the conductive substrate, and the step (S3) includes forming a catalyst layer on the microporous layer of the gas diffusion layer. Formation method. The catalyst layer of the fuel cell membrane-electrode assembly manufactured by the method for forming a catalyst layer of the fuel cell membrane-electrode assembly according to any one of claims 1 to 15. Electrolyte membrane; And an anode electrode and a cathode electrode formed between the electrolyte membrane and having a catalyst layer and a gas diffusion layer, respectively. A catalyst layer of the anode electrode or the cathode electrode is a fuel cell membrane-electrode assembly, characterized in that produced by the catalyst layer forming method of the fuel cell membrane-electrode assembly according to any one of the preceding claims.

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