Method for making catalyst inks for fuel cells free of eluted transition metals

Abstract

The present invention relates to a method of making a catalyst ink for a fuel cell free of eluted transition metals, and in particular the method comprises removing eluted transition metals from a noble metal / transition metal alloy catalyst.

Description

Technical Field

[0001] The present invention relates to a method of making a catalyst ink for a fuel cell, and in particular, the method comprises removing eluted transition metals from a noble metal / transition metal alloy catalyst. Background Art

[0002] A fuel cell is a power generation device in which the chemical energy of a fuel is converted into electrical energy through an electrochemical reaction in a fuel cell stack, rather than being converted into heat through combustion. Fuel cells can be used not only to power industrial, household and vehicle applications, but also to power small electrical / electronic products (especially portable devices).

[0003] Currently, polymer electrolyte membrane fuel cells (PEMFC or proton exchange membrane fuel cells) having the highest power density among fuel cells used as power sources for vehicle applications have been studied, having a fast start-up time and a fast power conversion reaction time due to a low operating temperature.

[0004] Meanwhile, the electrode catalyst used in the fuel cell mainly includes platinum (Pt) noble metals, which is disadvantageous due to high manufacturing cost and increased economic burden. In polymer electrolyte membrane fuel cells, the overvoltage caused by the oxygen reduction reaction at the cathode is at least ten times the overvoltage caused by the hydrogen oxidation reaction at the anode. In addition, due to the limited supply and the use of very expensive platinum, its commercialization has been delayed. Therefore, the research and development of alloy catalyst materials using less platinum has been actively carried out.

[0005] Compared with pure platinum materials, alloy catalyst materials enable the use of small amounts of platinum to produce high-performance catalyst electrodes with increased catalytic activity, thereby commercializing them. Alloy catalyst materials may include two or more alloy phases, which is generally different from mixed catalyst materials in which two elements are mixed.

[0006] Meanwhile, binary and ternary alloy catalysts (e.g., PtCo, PtNi, PtY, PtNiCr, PtCoCr, etc.) used as fuel cell catalysts have problems because transition metals are eluted from the alloy catalysts during the production of catalyst inks. When electrodes are manufactured using inks containing eluted transition metals and applied to membrane electrode assemblies (MEAs), the eluted transition metals act as impurities in the electrodes, thereby reducing the performance of the catalyst, and the eluted transition metals can move to the electrolyte membrane to form free radicals, which undesirably causes degradation of the electrolyte membrane. Summary of the invention

[0007] In a preferred aspect, there is provided a method of manufacturing a catalyst ink including an alloy catalyst, which can prevent a decrease in catalyst performance or degradation of an electrolyte membrane which is conventionally caused by eluted transition metal.

[0008] The objects of the present invention are not limited to the aforementioned objects, which will be clearly understood from the following description, and are achieved by the means described in the claims and their combinations.

[0009] In a first preferred aspect, a method for making a catalyst ink for a fuel cell is provided, the method comprising: mixing 1) an alloy catalyst comprising a noble metal and a transition metal and 2) polymer particles, thereby forming aggregates comprising i) a transition metal and ii) polymer particles. In certain preferred aspects, a mixture comprising an alloy catalyst, an ionomer and a solvent is provided, the alloy catalyst comprising a noble metal and a transition metal; the mixture and the polymer particles form aggregates, the aggregates comprising 1) a transition metal associated with the alloy catalyst and 2) polymer particles. Aggregates are removed or combined by filtering or other procedures as needed. In a further preferred aspect, a method for making a catalyst ink for a fuel cell is provided. The method comprises preparing a mixture, such as a solution comprising an alloy catalyst, an ionomer and a solvent, the alloy catalyst comprising a noble metal and a transition metal, combining the solution and the polymer particles to form aggregates of transition metals and polymer particles eluted from the alloy catalyst, and then removing the aggregates by filtering the solution. For example, the solution can be added to the polymer particles.

[0010] As used herein, the term "ionomer" refers to a polymer material or resin that includes ionizable groups attached (e.g., covalently bonded) as pendant groups to a polymer backbone. Preferably, these ionizable groups may be functionalized to have ionic properties, such as cationic or anionic properties. The ionomer may suitably include one or more polymers selected from fluorine polymers, perfluorosulfone polymers, benzimidazole polymers, polyimide polymers, polyetherimide polymers, polyphenylene sulfide polymers, polysulfone polymers, polyethersulfone polymers, polyetherketone polymers, polyether-etherketone polymers, polyphenylquinoxaline polymers, and polystyrene polymers.

[0011] The noble metal may include one or more selected from platinum (Pt), iridium (Ir), palladium (Pd), ruthenium (Ru), rhodium (Rd), gold (Au), and silver (Ag).

[0012] The transition metal may include one or more selected from cobalt (Co), nickel (Ni), yttrium (Y), chromium (Cr), manganese (Mn), copper (Cu), lanthanum (La), and scandium (Sc).

[0013] The alloy catalyst may be supported on a carrier.

[0014] The polymer particles may include a chelating resin.

[0015] The polymer particles may include as side chains one or more chelate-forming groups selected from glutamine, amidoxime, thiol, iminodiacetic acid, aminophosphonic acid, phosphonic acid, sulfonic acid, polyamine, thiourea, aminomethylphosphonic acid, benzylamine, tertiary amines and derivatives thereof.

[0016] The polymer particles may include one or more selected from the group consisting of iminodiacetic acid-type chelating resins and aminophosphonic acid-type chelating resins.

[0017] The average diameter of the polymer particles may range from about 300 μm to about 800 μm.

[0018] The polymer particles are added to the solution and reacted at a temperature of about 25° C. to 60° C. for about 10 hours to 30 hours to provide aggregates of the transition metal and the polymer particles.

[0019] Aggregates can be removed by filtering the solution using a 32 to 400 mesh filter.

[0020] In one aspect, there is provided a method of manufacturing an electrode for a fuel cell, the method comprising: preparing a catalyst ink manufactured by the method described herein; and forming a catalyst layer by applying the catalyst ink on a substrate and drying it.

[0021] According to various exemplary embodiments of the present invention, transition metals eluted from an alloy catalyst during the manufacture of catalyst ink can be removed, thereby effectively preventing reduction in catalyst performance or degradation of an electrolyte membrane due to the transition metals.

[0022] The effects of the present invention are not limited to the aforementioned effects, and should be understood to include all effects that can be reasonably expected from the following description.

[0023] Other aspects of the invention are disclosed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Evaluation results of cell performances of membrane electrode assemblies of Examples and Comparative Examples in Test Examples according to exemplary embodiments of the present invention are shown. DETAILED DESCRIPTION

[0025] The above and other purposes, features and advantages of the present invention will be more clearly understood by the following preferred embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed herein and can be modified into different forms. These embodiments are provided to thoroughly explain the present invention and fully convey the spirit of the present invention to those skilled in the art.

[0026] Throughout the accompanying drawings, the same reference numerals will refer to the same or similar elements. For clarity of the present invention, the size of the structure is described as being larger than its actual size. It will be understood that, although various elements can be described herein using terms such as "first", "second", etc., these elements are not limited by these terms. These terms are only used to distinguish one element from another element. For example, without departing from the scope of the present invention, the "first" element discussed below may be referred to as the "second" element. Similarly, the "second" element may also be referred to as the "first" element. As used herein, the singular form is also intended to include the plural form, unless the context clearly indicates otherwise.

[0027] It will also be understood that when used in this specification, the terms "comprising", "including", "having", etc. specify the presence of the stated features, values, steps, operations, elements, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, or combinations thereof. Moreover, it will be understood that when an element such as a layer, film, region, or sheet is referred to as being "on" another element, it can be directly on the other element, or there can be intervening elements between them. Similarly, it will be understood that when an element such as a layer, film, region, or sheet is referred to as being "under" another element, it can be directly under the other element, or there can be intervening elements between them.

[0028] Unless otherwise indicated, all numbers, values ​​and / or expressions expressing quantities of components, reaction conditions, polymer compositions and mixtures used herein are to be construed as approximations including the various uncertainties in measurements that substantially occur in obtaining such values ​​and the like, and are therefore to be understood in all instances as being modified by the term "about".

[0029] Unless otherwise specified or apparent from the context, as used herein, the term "about" is understood to be within the normal tolerance range in the art, such as within 2 standard deviations of the mean. "About" may be understood to be within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless the context clearly indicates, all numerical values ​​provided herein are modified by the term "about".

[0030] In addition, when numerical ranges are disclosed in this specification, the range is continuous and includes all values ​​from the minimum value of the range to its maximum value, unless otherwise specified. In addition, when such a range belongs to an integer value, unless otherwise specified, all integers from the minimum value to the maximum value are included. In this specification, when describing the scope of a variable, it will be understood that the variable includes all values ​​of the endpoints described in the scope. For example, the scope of "5 to 10" will be understood to include any subranges, such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., and each value of 5, 6, 7, 8, 9 and 10, and will also be understood to include any value between the valid integers in the scope, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, etc. In addition, for example, a range of "10% to 30%" will be understood to include sub-ranges such as 10% to 15%, 12% to 18%, 20% to 30%, etc., and all integers including values ​​of 10%, 11%, 12%, 13%, etc. up to 30%, and will also be understood to include any values ​​between the valid integers in the stated range, for example 10.5%, 15.5%, 25.5%, etc.

[0031] In one aspect, a method of making a catalyst ink for a fuel cell is provided, the method comprising preparing a solution comprising an alloy catalyst, an ionomer, and a solvent, the alloy catalyst comprising a noble metal and a transition metal, combining the solution and polymer particles (e.g., by addition) to form aggregates of the transition metal and polymer particles that are eluted from the alloy catalyst, and then removing the aggregates by filtering the solution.

[0032] The noble metal / transition metal alloy catalyst may be at least a binary or ternary alloy catalyst of a noble metal and a transition metal.

[0033] The noble metal may include one or more selected from platinum (Pt), iridium (Ir), palladium (Pd), ruthenium (Ru), rhodium (Rd), gold (Au), and silver (Ag).

[0034] The transition metal may include one or more selected from cobalt (Co), nickel (Ni), yttrium (Y), chromium (Cr), manganese (Mn), copper (Cu), lanthanum (La), and scandium (Sc).

[0035] The alloy catalyst may be supported on a carrier.

[0036] The support is not particularly limited, and may include carbon black, carbon nanotubes, carbon nanofibers, metal oxides, noble metals, and the like.

[0037] The ionomer functions as a binder. Its type is not particularly limited, and a perfluorinated sulfonic acid-based polymer such as Nafion can be used.

[0038] The solvent may include one or more alcohol solvents selected from ethylene glycol, butanol, pentanol, dimethylacetamide, dimethyl sulfoxide, dimethylformamide, dipropylene glycol, isopropanol, n-propanol and ethanol, deionized water, or a mixture thereof.

[0039] The solution may include cations of the transition metal eluted from the alloy catalyst into the solvent, and thus, when the solution such as the catalyst ink is used to make an electrode, the cations of the transition metal may cause a decrease in catalyst performance or degradation of the electrolyte membrane. In particular, the method may include removing the cations of the transition metal.

[0040] The polymer particles may be added to the solution to form aggregates of the transition metal eluted from the alloy catalyst and the polymer particles, and then the solution may be filtered to easily remove the aggregates.

[0041] In particular, chelating resins (agents) can be used as polymer particles.

[0042] Preferably, the chelating resin that can form chemical bond (for example covalent bond, coordination bond etc.) with transition metal can be used as polymer particles, thus polymer particles are not bonded with the transition metal of precious metal alloying, but only bonded with free transition metal (cation of transition metal).Therefore, according to the present invention, can only selectively remove the transition metal of wash-out.

[0043] Furthermore, the polymer particles form a coordination bond (eg, a covalent bond, a coordination bond, etc.) with the eluted transition metal, and therefore, even if a subsequent treatment such as filtration is performed, the bond with the transition metal is not broken.

[0044] The polymer particles may have any main chain selected from polystyrene, polyacryl and divinylbenzene. Specifically, the main chain of the polymer particles may be polystyrene-divinylbenzene copolymer, polyacrylonitrile, polyethylene, polymethacrylate, phenol resin, and the like.

[0045] The polymer particles may have as side chains one or more chelate-forming groups selected from glutamine, amidoxime, thiol, iminodiacetic acid, aminophosphonic acid, phosphonic acid, sulfonic acid, polyamine, thiourea, aminomethylphosphonic acid, benzylamine, tertiary amines and their derivatives.

[0046] Although not limited thereto, the polymer particles may be aminophosphonic acid-type chelating resins represented by the following structural formula 1 or iminodiacetic acid-type chelating resins represented by the following structural formula 2. Here, "-type chelating resins" means chelating resins having chelate-forming groups corresponding to "-".

[0047] [Structural Formula 1]

[0048]

[0049] Here, * specifies the point of attachment to the main chain.

[0050] [Structural Formula 2]

[0051]

[0052] Here, * specifies the point of attachment to the main chain.

[0053] The average diameter of the polymer particles may be about 300 μm to 800 μm. When the average diameter of the polymer particles is within the above numerical range, aggregates of the polymer particles and the eluted transition metal can be easily removed by filtration.

[0054] The polymer particles are added to the solution and reacted at a temperature of about 25° C. to 60° C. for about 10 to 30 hours to form aggregates of the polymer particles and the eluted transition metal. When the reaction time is less than about 10 hours, the amount of the eluted transition metal removed may be insufficient. From the viewpoint of shortening the reaction time, it may be desirable to keep the reaction temperature close to about 60° C.

[0055] A filter can be used to filter the solution including aggregates, thereby removing aggregates. The mesh size of the filter can be less than the average diameter of the aggregates and greater than the average diameter of the noble metal / transition metal alloy catalyst. Preferably, the filter can have a size of 32 meshes to 400 meshes. However, the present invention is not limited thereto, and the average diameter of the polymer particles used can be considered to appropriately change the filter size.

[0056] The solution can be filtered using a gravity filter or a vacuum filter at room temperature.

[0057] The catalyst ink thus prepared can be applied to a substrate and dried to form a catalyst layer. Any specific method and conditions thereof are not particularly limited, and any method can be applied as long as it is a method for manufacturing an electrode using the catalyst ink and the method is widely used in the technical field to which the present invention belongs.

[0058] The present invention will be better understood by the following examples. However, these examples are only provided for illustrating the present invention and are not intended to limit the scope of the present invention.

[0059] Example

[0060] The catalyst ink was prepared as follows.

[0061] As the noble metal / transition metal alloy catalyst, a Pt-Ni alloy catalyst was used. The alloy catalyst was supported on a carbon support. The noble metal / transition metal alloy catalyst was added to a solvent together with a Nafion ionomer to prepare a solution.

[0062] An aminophosphonic acid-type chelate resin represented by Structural Formula 1 is added to a solvent and reacted at a temperature of about 25° C. for about 20 hours, thereby forming an aggregate of the chelate resin and the eluted transition metal.

[0063] After the reaction was terminated, the solution was filtered to remove aggregates, thereby preparing a catalyst ink.

[0064] The catalyst ink was applied on a release sheet and dried at a temperature of about 80° C., thereby forming a catalyst layer. The catalyst layer was transferred to an electrode membrane, thereby manufacturing a membrane-electrode assembly.

[0065] Comparative Example

[0066] The solution containing the eluted transition metal that was not removed was used as catalyst ink. Its specific composition was the same as that of the above embodiment. The catalyst ink was applied to a release sheet and dried at a temperature of about 90° C., thereby forming a catalyst layer. The catalyst layer was transferred to an electrode membrane to manufacture a membrane-electrode assembly.

[0067] Test Example 1 - Amount of transition metal eluted in solution

[0068] The amount of eluted transition metal contained in the catalyst ink of each of Examples and Comparative Examples was measured. The results are shown in Table 1 below.

[0069] Table 1

[0070]

[0071] 1) Determine the amount of each component contained in a sample (a small amount extracted from a solution).

[0072] As shown in Table 1, by adding polymer particles to the solution and carrying out the reaction as in the Examples, the eluted transition metal can be significantly removed from the solution.

[0073] Test Example 2—Evaluation of Battery Performance

[0074] The performance of the membrane electrode assembly of each embodiment and comparative embodiment was evaluated. The current was maintained at 1 A / cm 2 The cell voltage was measured. The results are shown in Table 1. The cell voltage of the membrane-electrode assembly of the example was increased and thus the cell performance was improved.

[0075] As described above, the test embodiments and embodiments of the present invention have been described in detail, but the scope of the present invention is not limited to the above test embodiments and embodiments. According to the basic concept of the present invention defined in the attached claims, various modifications and improvements that are obvious to those skilled in the art are also included in the scope of the present invention.

Claims

1. A method for producing a catalyst ink for a fuel cell, the method include: preparing a solution comprising an alloy catalyst, an ionomer, and a solvent, wherein the alloy catalyst comprises a noble metal and a transition metal; The solution and polymer particles are combined to form aggregates of the transition metal and polymer particles eluted from the alloy catalyst; the aggregates are then removed by filtering the solution.

2. The method for producing a catalyst ink for a fuel cell according to claim 1, in, The noble metal includes one or more selected from platinum, iridium, palladium, ruthenium, rhodium, gold and silver.

3. The method for producing a catalyst ink for a fuel cell according to claim 1, in, The transition metal includes one or more selected from the group consisting of cobalt, nickel, yttrium, chromium, manganese, copper, lanthanum and scandium.

4. The method for producing a catalyst ink for a fuel cell according to claim 1, in, The alloy catalyst is supported on a carrier.

5. The method for producing a catalyst ink for a fuel cell according to claim 1, in, The polymer particles comprise a chelating resin.

6. The method for producing a catalyst ink for a fuel cell according to claim 1, in, The polymer particles contain as side chains one or more chelate-forming groups selected from glutamine, amidoxime, thiol, iminodiacetic acid, aminophosphonic acid, phosphonic acid, sulfonic acid, polyamine, thiourea, aminomethylphosphonic acid, benzylamine, tertiary amines and their derivatives.

7. The method for producing a catalyst ink for a fuel cell according to claim 1, in, The polymer particles include one or more selected from the group consisting of iminodiacetic acid-type chelating resins and aminophosphonic acid-type chelating resins.

8. The method for producing a catalyst ink for a fuel cell according to claim 1, in, The average diameter of the polymer particles ranges from 300 μm to 800 μm.

9. The method for producing a catalyst ink for a fuel cell according to claim 1, in, The polymer particles are added to the mixture and reacted at a temperature of 25° C. to 60° C. for 10 to 30 hours to provide aggregates of the transition metal and the polymer particles.

10. The method for producing a catalyst ink for a fuel cell according to claim 1, in, Aggregates were removed by filtering the mixture using a 32- to 400-mesh filter.

11. A method for manufacturing an electrode for a fuel cell, the method include: preparing a catalyst ink produced by the method of claim 1; as well as The catalyst layer is formed by applying the catalyst ink on the substrate and drying it.

12. A method for manufacturing an electrode for a fuel cell, the method include: preparing a catalyst ink made by the method of claim 1; as well as The catalyst layer is formed by applying the catalyst ink on the substrate and drying it.

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